WorldWideScience

Sample records for surface wind forcing

  1. Ocean surface wind stress

    Science.gov (United States)

    Harrison, D. E.

    1984-01-01

    The need for improved surface wind and wind stress data is discussed. The collection of wind data using ship reports, research buoys, and cloud motion vectors is examined. The need for data on surface-wind stress fields is emphasized. Accurate stress data are required for studying: (1) the normal seasonal cycle and the intraannual events; (2) wind stress curls and the forcing of ocean circulation; (3) El Nino events; and (4) the low response of the midlatitude ocean circulation.

  2. NUMERICAL SIMULATION OF SEA SURFACE DIRECTIONAL WAVE SPECTRA UNDER TYPHOON WIND FORCING

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Numercial simulation of sea surface directional wave spectra under typhoon wind forcing in the South China Sea (SCS) was carreid out using the WAVEWATCH-III wave model. The simulation was run for 210 h until the Typhoon Damrey (2005) approached Vietnam. The simulated data were compared with buoy observations, which were obtained in the northwest sea area of Hainan Island. The results show that the significant wave height, wave direction, wave length and frequency spetra agree well with buoy observations. The spatial characteristics of the signifciant wave height, mean wave period, mean wave length, wave age and directional spectra depend on the relative position from the typhoon center. Also, the misalignment between local wind and wave directions were investigated.

  3. Energy transfer of surface wind-induced currents to the deep ocean via resonance with the Coriolis force

    Science.gov (United States)

    Ashkenazy, Yosef

    2017-03-01

    There are two main comparable sources of energy to the deep ocean-winds and tides. However, the identity of the most efficient mechanism that transfers wind energy to the deep ocean is still debated. Here we study, using oceanic general circulation model simulations and analytic derivations, the way that the wind directly supplies energy down to the bottom of the ocean when it is stochastic and temporally correlated or when it is periodic with a frequency that matches the Coriolis frequency. Basically, under these, commonly observed, conditions, one of the wind components resonates with the Coriolis frequency. Using reanalysis surface wind data and our simple model, we show that about one-third of the kinetic energy that is associated with wind-induced currents resides in the abyssal ocean, highlighting the importance of the resonance of the wind with the Coriolis force.

  4. Surface river plume in a large lake under wind forcing: Observations and laboratory experiments

    Science.gov (United States)

    Demchenko, Natalia; He, Cheng; Rao, Yerubandi R.; Valipour, Reza

    2017-10-01

    Observations of a small riverine plume (Grand River, ON) in the nearshore zones of Lake Erie were analyzed to describe its spatial variability and its thickness under different wind forcing conditions during late spring of 2012. Observational results reveal a well-marked frontal region in the vicinity of the river mouth, causing the plume to discharge into the lake in the surface layers (positive buoyant). Wind driven alongshore currents at the mid-depth had speeds of 2-9 cm/s, in comparison to those in the cross-shore 3-6 cm/s, which transported the plume along the shore during the measurement period. Series of laboratory experiments were conducted to obtain the propagation speed (U) of the buoyant plume in terms of buoyancy anomaly (Ba), Richardson number (Ri), dimensionless time (t‧), and aspect ratio (A). Based on our experiments, we developed two non-dimensional relationships describing the speed of propagation (U) as U/Ba1/2 = 8 Ri-1/2t‧1/3A and the plume thickness (h) as h/H = 0.8 Ri-1/4t‧1/2A in the water depth (H), which are in agreement with field observations.

  5. Effects of sea surface winds on marine aerosols characteristics and impacts on longwave radiative forcing over the Arabian Sea

    Directory of Open Access Journals (Sweden)

    Vijayakumar S. Nair

    2008-08-01

    Full Text Available Collocated measurements of spectral aerosol optical depths (AODs, total and BC mass concentrations, and number size distributions of near surface aerosols, along with sea surface winds, made onboard a scientific cruise over southeastern Arabian Sea, are used to delineate the effects of changes in the wind speed on aerosol properties and its implication on the shortwave and longwave radiative forcing. The results indicated that an increase in the sea-surface wind speed from calm to moderate (<1 to 8 m s−1 values results in a selective increase of the particle concentrations in the size range 0.5 to 5 μm, leading to significant changes in the size distribution, increase in the mass concentration, decrease in the BC mass fraction, a remarkable increase in AODs in the near infrared and a flattening of the AOD spectrum. The consequent increase in the longwave direct radiative forcing almost entirely offsets the corresponding increase in the short wave direct radiative forcing (or even overcompensates at the top of the atmosphere; while the surface forcing is offset by about 50%.

  6. Wind Forces on Container Ships

    DEFF Research Database (Denmark)

    Andersen, Ingrid Marie Vincent

    2012-01-01

    An investigation of the wind forces acting on a 9,000+ TEU container ship has been carried out through a series of wind tunnel tests. It was investigated how the wind forces depend on the container configuration on the deck using a 1:450 scale model and a series of appropriate container...... are presented as nondimensional coefficients. It is concluded, that the measured forces and moment depend on the container configuration on deck, and the results may provide a general idea of how the magnitude of the wind forces is affected by a given container stacking configuration on a similar container ship....

  7. Sensitivity of simulated circulation dynamics to the choice of surface wind forcing in the Japan/East Sea

    Science.gov (United States)

    Hogan, Patrick J.; Hurlburt, Harley E.

    2005-06-01

    The circulation sensitivity to the choice of wind-forcing product is investigated with the NRL Layered Ocean Model (NLOM) configured for the Japan/East Sea. Monthly climatologies from seven different wind-stress data sets (and wind-stress curl) are formed from observed and model-derived atmospheric data sets. The resulting maps of wind-stress curl reveal significantly different spatial patterns and magnitudes, even two with largely opposite large-scale patterns of wind-stress curl. These wind sets were used in forcing three sets of simulations, 1/8° linear and 1/8° and 1/32° nonlinear. In addition, seasonally varying straits forcing (inflow through Tsushima balanced by outflow through Tsugaru and Soya) was included in all the simulations, and simulations with straits forcing only were performed. The 1.5-layer linear reduced-gravity simulations include only the lowest order dynamics, mainly Munk β 1/3 western boundary layers (due to both wind and straits forcing) and a Sverdrup interior. The nonlinear simulations add bottom topography, multiple internal modes, diapycnal mixing, and ventilation of layer interfaces. At 1/8° resolution, only weak barotropic/baroclinic instabilities occur, but at 1/32° resolution these are much stronger, allowing vigorous transfer of energy from the upper ocean to the abyssal layer via baroclinic instability. This drives much stronger mean abyssal currents that more strongly steer upper-ocean current pathways than at 1/8°, i.e. there is much stronger upper ocean-topographical coupling. The linear model simulates most of the basic features, e.g., the subpolar gyre with all but the straits forcing only, the East Korean Warm Current (EKWC) and its connection to the subpolar front with all but one wind-forcing set, but the remaining wind set gives a continuous Nearshore Branch (NB) of the Tsushima Warm Current along the coast of Honshu. In all of the linear simulations with an EKWC, the separation latitude from the coast of Korea is

  8. Zonal surface wind jets across the Red Sea due to mountain gap forcing along both sides of the Red Sea

    KAUST Repository

    Jiang, Houshuo

    2009-01-01

    [1] Mesoscale atmospheric modeling over the Red Sea, validated by in-situ meteorological buoy data, identifies two types of coastal mountain gap wind jets that frequently blow across the longitudinal axis of the Red Sea: (1) an eastward-blowing summer daily wind jet originating from the Tokar Gap on the Sudanese Red Sea coast, and (2) wintertime westward-blowing wind-jet bands along the northwestern Saudi Arabian coast, which occur every 10-20 days and can last for several days when occurring. Both wind jets can attain wind speeds over 15 m s-1 and contribute significantly to monthly mean surface wind stress, especially in the cross-axis components, which could be of importance to ocean eddy formation in the Red Sea. The wintertime wind jets can cause significant evaporation and ocean heat loss along the northeastern Red Sea coast and may potentially drive deep convection in that region. An initial characterization of these wind jets is presented. Copyright 2009 by the American Geophysical Union.

  9. 49 CFR 193.2067 - Wind forces.

    Science.gov (United States)

    2010-10-01

    ... fluids with a capacity of not more than 70,000 gallons, applicable wind load data in ASCE/SEI 7-05... 49 Transportation 3 2010-10-01 2010-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be...

  10. Nanofluids mediating surface forces.

    Science.gov (United States)

    Pilkington, Georgia A; Briscoe, Wuge H

    2012-11-01

    Fluids containing nanostructures, known as nanofluids, are increasingly found in a wide array of applications due to their unique physical properties as compared with their base fluids and larger colloidal suspensions. With several tuneable parameters such as the size, shape and surface chemistry of nanostructures, as well as numerous base fluids available, nanofluids also offer a new paradigm for mediating surface forces. Other properties such as local surface plasmon resonance and size dependent magnetism of nanostructures also present novel mechanisms for imparting tuneable surface interactions. However, our fundamental understanding, experimentally and theoretically, of how these parameters might affect surface forces remains incomplete. Here we review recent results on equilibrium and dynamic surface forces between macroscopic surfaces in nanofluids, highlighting the overriding trends in the correlation between the physical parameters that characterise nanofluids and the surface forces they mediate. We also discuss the challenges that confront existing surface force knowledge as a result of this new paradigm.

  11. Wind-Forced Baroclinic Beta-Plumes

    Science.gov (United States)

    Belmadani, A.; Maximenko, N. A.; Melnichenko, O.; Schneider, N.; Di Lorenzo, E.

    2011-12-01

    A planetary beta-plume is a classical example of oceanic circulation induced by a localized vorticity source or sink that allows an analytical description in simplistic cases. Its barotropic structure is a zonally-elongated, gyre-like cell governed by the Sverdrup circulation on the beta-plane. The dominant zonal currents, found west of the source/sink, are often referred to as zonal jets. This simple picture describes the depth-integrated flow. Previous studies have investigated beta-plumes in a reduced-gravity framework or using other simple models with a small number of vertical layers, thereby lacking representation of the vertical structure. In addition, most previous studies use a purely linear regime without considering the role of eddies. However, these jets are often associated with strong lateral shear that makes them unstable under increased forcing. The circulation in such a nonlinear regime may involve eddy-mean flow interactions, which modify the time-averaged circulation. Here, the baroclinic structures of linear and nonlinear wind-forced beta-plumes are studied using a continuously-stratified, primitive equation, eddy-permitting ocean model (ROMS). The model is configured in an idealized rectangular domain for the subtropical ocean with a flat bottom. The surface wind forcing is a steady anticyclonic Gaussian wind vortex, which provides a localized vorticity source in the center of the domain. The associated wind stress curl and Ekman pumping comprise downwelling in the vortex center surrounded by a ring of weaker upwelling. Under weak forcing, the simulated steady-state circulation corresponds well with a theoretical linear beta-plume. While its depth-integrated transport exhibits a set of zonal jets, consistent with Sverdrup theory, the baroclinic structure of the plume is remarkably complex. Relatively fast westward decay of the surface currents occurs simultaneously with the deepening of the lower boundary of the plume. This deepening suggests

  12. Solar wind ion impacts into ice surfaces: A molecular-dynamics study using the REAX force field

    Science.gov (United States)

    Anders, Christian; Urbassek, Herbert M.

    2017-01-01

    Molecular dynamics simulation is used to study the effects of solar-wind ion irradiation on an ice target, focusing on the effects of nuclear energy deposition. A reactive force field (REAX) interatomic interaction potential is employed that allows us to model the breaking and formation of molecular bonds and hence to follow the chemistry occurring in the target. As ions we study H and He ions as typical constituents of the solar wind, and Ne as an example of a heavier ion; they impact at the speed of maximum flux in the solar wind, 400 km/s. The ice consists of a mixture of H2O, CO2, CH3OH and NH3. We find that molecular dissociations occur within 0.2 ps after ion impact and new products are formed up to a time of 1 ps; only water has a slower dynamics, due to highly mobile H atoms allowing for late recombinations. The number of dissociations, and hence also of product molecules increases from H over He to Ne ion projectiles and can be quantified by the amount of energy deposited in the target by these ions. The most abundant products formed include CO, OH and NH2. Reaction products are most complex for Ne impact, and include H3O, formaldehyde (H2CO), HO2, and NO. Formaldehyde is important as it is formed relatively frequently and is known as a precursor in the formation of sugars. In addition, molecules containing all CHON elements are formed, among which are CH2NO, CONH, methanolamine (CH5NO), and ethyne (C2H2). Repeated impacts generate novel, and more complex product species; we found CN, CH4, CH3NO, methylamine (CH3NH2), and acetamide (CH3CONH2), among others; the complex species are formed less frequently than the simple fragments. Sputtering occurs for all projectiles, even H. The ejecta are either original molecules - in particular CO2 - or simple fragments; only few product molecules are emitted.

  13. OW CCMP ocean surface wind

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Cross-Calibrated Multi-Platform (CCMP) Ocean Surface Wind Vector Analyses (Atlas et al., 2011) provide a consistent, gap-free long-term time-series of ocean...

  14. Modulational instability in wind-forced waves

    CERN Document Server

    Brunetti, Maura

    2014-01-01

    We consider the wind-forced nonlinear Schroedinger (NLS) equation obtained in the potential flow framework when the Miles growth rate is of the order of the wave steepness. In this case, the form of the wind-forcing terms gives rise to the enhancement of the modulational instability and to a band of positive gain with infinite width. This regime is characterised by the fact that the ratio between wave momentum and norm is not a constant of motion, in contrast to what happens in the standard case where the Miles growth rate is of the order of the steepness squared.

  15. Surface winds over West Antarctica

    Science.gov (United States)

    Bromwich, David

    1993-01-01

    Five winter months (April-August 1988) of thermal infrared satellite images were examined to investigate the occurrence of dark (warm) signatures across the Ross Ice Shelf in the Antarctic continent. These features are inferred to be generated by katabatic winds that descend from southern Marie Byrd Land and then blow horizontally across the ice shelf. Significant mass is added to this airstream by katabatic winds blowing from the major glaciers that flow through the Transantarctic Mountains from East Antarctica. These negatively buoyant katabatic winds can reach the northwestern edge of the shelf - a horizontal propagation distance of up to 1,000 km - 14 percent of the time. Where the airstream crosses from the ice shelf to the ice-covered Ross Sea, a prominent coastal polynya is formed. Because the downslope buoyancy force is near zero over the Ross Ice Shelf, the northwestward propagation of the katabatic air mass requires pressure gradient support. The study shows that the extended horizontal propagation of this atmospheric density current occurred in conjunction with the passage of synoptic cyclones over the southern Amundsen Sea. These cyclones can strengthen the pressure gradient in the interior of West Antarctica and make the pressure field favorable for northwestward movement of the katabatic winds from West Antarctica across the ice shelf in a geostrophic direction. The glacier winds from East Antarctica are further accelerated by the synoptic pressure gradient, usually undergo abrupt adjustment beyond the exit to the glacier valley, and merge into the mountain-parallel katabatic air mass.

  16. Intermolecular and surface forces

    CERN Document Server

    Israelachvili, Jacob N

    2011-01-01

    This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.· starts fr

  17. The near-surface wind field over the Antarctic continent

    Science.gov (United States)

    van Lipzig, N. P. M.; Turner, J.; Colwell, S. R.; van den Broeke, M. R.

    2004-12-01

    A 14 year integration with a regional atmospheric model has been used to determine the near-surface climatological wind field over the Antarctic ice sheet at a horizontal grid spacing of 55 km. Previous maps of the near-surface wind field were generally based on models ignoring the large-scale pressure-gradient forcing term in the momentum equation. Presently, state-of-the-art atmospheric models include all pressure-gradient forcing terms. Evaluation of our model output against in situ data shows that the model is able to represent realistically the observed increase in wind speed going from the interior to the coast, as well as the observed wind direction at South Pole and Dumont d'Urville and the bimodal wind distribution at Halley.

  18. Distributed Surface Force

    Science.gov (United States)

    2014-06-01

    proposed SSC. 1. Definition and Planning The definition and planning phase is appropriate when utilizing any problem- solving algorithm . Before any... MONKEY 149 AGENDA · Background · Scenario · Assumptions · Mission, Commander’s Intent, and Org. Chart · Naval and Air forces . Concept of...forces provide support to Coal ition partners during the execution of Operation Mute Monkey in the South China Sea. · End-state: Deter Chinese

  19. Wind Stress Forcing of the North Sea "Pole Tide"

    Science.gov (United States)

    OConnor, William P.; Chao, Benjamin Fong; Zheng, Dawei; Au, Andrew Y.

    1998-01-01

    We conducted numerical simulations of the wind-forcing of the sea level variations in the North Sea using a barotropic ocean model with realistic geography, bathymetry, and boundary conditions, to examine the forcing of the 14-month "pole tide" which is known to be strong along the Denmark- Netherlands coast. The simulation input is the monthly-mean surface wind stress field from the National Centers for Environmental Prediction (NCEP) reanalysis for the 40-year period 1958-1997. The output sea level response was then compared with 10 coastal tide gauge records from the Permanent Service for Mean Sea Level (PSMSL). Besides the strong seasonal variations, several prominent quasi-periodicities exist at around 7 years, 3 years, 14 months, 9 months, and 6.5 months. Correlation and spectral analyses show remarkable agreement between the model output and the observations, particularly in the 14-month, or Chandler period band. The latter indicates that the enhanced pole tide found in the North Sea along the Denmark-Netherlands coast is actually the coastal setup response to wind stress forcing with a periodicity of 14 months. We find no need to invoke a geophysical explanation involving resonance-enhancement of pole tide in the North Sea to explain the observations.

  20. Drag force in wind tunnels: A new method

    Science.gov (United States)

    Souza, P. V. S.; Girardi, D.; de Oliveira, P. M. C.

    2017-02-01

    A rigid object of general shape is fixed inside a wind tunnel. The drag force exerted on it by the wind is determined by a new method based on simple basic Physics concepts, provided one has a solver, any solver, for the corresponding dynamic Navier-Stokes equation which determines the wind velocity field around the object. The method is completely general, but here we apply it to the traditional problem of a long cylinder perpendicular to the wind.

  1. Mapping surface disturbance from wind farms

    Science.gov (United States)

    Diffendorfer, James E.

    2013-04-01

    Wind energy is one of the fastest growing segments of the electricity market and this trend will likely continue as countries strive to reduce CO2 production while meeting growing energy demands. One impact of wind facilities is surface disturbance, including roads, that lead to habitat loss and fragmentation. Numerous studies of wind power utilize estimates of surface disturbance for GIS-based modeling or basic calculations of the land area required to generate energy using wind. However published estimates of the land use required for a MW of electricity from wind facilities vary by more than 10 times (0.83 to 250 MW/Km2). We report results from a geospatial analysis of 39 wind facilities in the United States that we fully digitized using high resolution photo-imagery. The selected sites and analyses were designed to elucidate the effects of turbine size, topography, and land use on the area requirements of wind facilities. The results indicate point estimates of average surface disturbance/MW have wide levels of variation, explained primarily by Landcover and Topography. Wind facilities in agricultural landscapes had smaller surface disturbance/ha than facilities in forests and shrublands, and facilities in relatively flat topography had smaller surface disturbance/ha than facilities on hills, ridges, or mesas. Land use, topography, and turbine size all influenced turbine spacing. The statistical models suggest we can predict geographic locations where new wind facilities could be placed with minimized surface disturbance.

  2. Synoptic forcing of wind relaxations at Pt. Conception, California

    Science.gov (United States)

    Fewings, Melanie R.; Washburn, Libe; Dorman, Clive E.; Gotschalk, Christopher; Lombardo, Kelly

    2016-08-01

    Over the California Current upwelling system in summer, the prevailing upwelling-favorable winds episodically weaken (relax) or reverse direction for a few days. Near Pt. Conception, California, the wind usually does not reverse, but wind relaxation allows poleward oceanic coastal flow with ecological consequences. To determine the offshore extent and synoptic forcing of these wind relaxations, we formed composite averages of wind stress from the QuikSCAT satellite and atmospheric pressure from the North American Regional Reanalysis (NARR) using 67 wind relaxations during summer 2000-2009. Wind relaxations at Pt. Conception are the third stage of an event sequence that repeatedly affects the west coast of North America in summer. First, 5-7 days before the wind weakens near Pt. Conception, the wind weakens or reverses off Oregon and northern California. Second, the upwelling-favorable wind intensifies along central California. Third, the wind relaxes at Pt. Conception, and the area of weakened winds extends poleward to northern California over 3-5 days. The NARR underestimates the wind stress within ˜200 km of coastal capes by a factor of 2. Wind relaxations at Pt. Conception are caused by offshore extension of the desert heat low. This synoptic forcing is related to event cycles that cause wind reversal as in Halliwell and Allen (1987) and Mass and Bond (1996), but includes weaker events. The wind relaxations extend ˜600 km offshore, similarly to the California-scale hydraulic expansion fan shaping the prevailing winds, and ˜1000 km alongshore, limited by an opposing pressure gradient force at Cape Mendocino.

  3. Estimating Wind and Wave Induced Forces On a Floating Wind Turbine

    DEFF Research Database (Denmark)

    Henriksen, Lars Christian; Natarajan, Anand; Kim, Taeseong

    -principles derived state space model of the floating wind turbine. The ability to estimate aero- and hydrodynamic states could prove crucial for the performance of model-based control methods applied on floating wind turbines. Furthermore, two types of water kinematics have been compared two determine whether......In this work, the basic model for a spar buoy floating wind turbine [1], used by an extended Kalman filter, is presented and results concerning wind speed and wave force estimations are shown. The wind speed and aerodynamic forces are estimated using an extended Kalman filter based on a first...... or not linear and nonlinear water kinematics lead to significantly different loads....

  4. Estimating Wind and Wave Induced Forces On a Floating Wind Turbine

    DEFF Research Database (Denmark)

    Henriksen, Lars Christian; Natarajan, Anand; Kim, Taeseong

    2013-01-01

    -principles derived state space model of the floating wind turbine. The ability to estimate aero- and hydrodynamic states could prove crucial for the performance of model-based control methods applied on floating wind turbines. Furthermore, two types of water kinematics have been compared two determine whether......In this work, the basic model for a spar buoy floating wind turbine [1], used by an extended Kalman filter, is presented and results concerning wind speed and wave force estimations are shown. The wind speed and aerodynamic forces are estimated using an extended Kalman filter based on a first...... or not linear and nonlinear water kinematics lead to significantly different loads....

  5. Predicting wind farm wake interaction with RANS: an investigation of the Coriolis force

    DEFF Research Database (Denmark)

    van der Laan, Paul; Hansen, Kurt Schaldemose; Sørensen, Niels N.;

    2015-01-01

    A Reynolds-averaged Navier-Stokes code is used to simulate the interaction of two neighboring wind farms. The influence of the Coriolis force is investigated by modeling the atmospheric surface/boundary layer with three different methodologies. The results show that the Coriolis force is negligible...

  6. Surface wind energy trends near Taiwan in winter since 1871

    Directory of Open Access Journals (Sweden)

    Lei Zhang

    2017-01-01

    Full Text Available The tropical surface wind speed in boreal winter reaches a maximum near Taiwan. This stable wind resource may be used for future clean energy development. How this surface wind energy source has changed in past 141 years is investigated using the 20th century reanalysis dataset and CMIP5 models. Our observational analysis shows that the surface wind speed experienced a weakening trend in the past 141 years (1871 - 2010. The average decreasing rate is around -1.4 m s-1 per century. The decrease is primarily attributed to the relative sea surface temperature (SST cooling in the subtropical North Pacific, which forces a large-scale low-level anti-cyclonic circulation anomaly in situ and is thus responsible for the southerly trend near Taiwan. The relative SST trend pattern is attributed mainly to the greenhouse gas effect associated with anthropogenic activities. The southerly trend near Taiwan is more pronounced in the boreal winter than in summer. Such seasonal difference is attributed to the reversed seasonal mean wind, which promotes more efficient positive feedback in the boreal winter. The CMIP5 historical run analysis reveals that climate models capture less SST warming and large-scale anti-cyclonic circulation in the subtropical North Pacific, but the simulated weakening trend of the surface wind speed near Taiwan is too small.

  7. Wind forces and related saltation transport

    NARCIS (Netherlands)

    Leenders, J.K.; Boxel, van J.H.; Sterk, G.

    2005-01-01

    The effect of several wind characteristics on sand transport was studied in three experiments in north Burkina Faso, West Africa. The first experiment is used to analyse the relation between wind speed and shear stress fluctuations across height. The second experiment is used to study the relation

  8. Modeling wind adjustment factor and midflame wind speed for Rothermel's surface fire spread model

    Science.gov (United States)

    Patricia L. Andrews

    2012-01-01

    Rothermel's surface fire spread model was developed to use a value for the wind speed that affects surface fire, called midflame wind speed. Models have been developed to adjust 20-ft wind speed to midflame wind speed for sheltered and unsheltered surface fuel. In this report, Wind Adjustment Factor (WAF) model equations are given, and the BehavePlus fire modeling...

  9. Global analysis of ocean surface wind and wind stress using a general circulation model and Seasat scatterometer winds

    Science.gov (United States)

    Kalnay, E.; Atlas, R.

    1986-01-01

    Instantaneous and 15-day time-averaged fields of surface wind, wind stress, curl of the wind stress, and wind divergence are presented. These fields are derived from the Goddard Laboratory for Atmospheres four-dimensional analysis/forecast cycle, for the period September 6-30, 1978, using conventional data, satellite temperature soundings, cloud-track winds, and subjectively dealiased Seasat scatterometer winds.

  10. Steady State Ocean Response to Wind Forcing in Extratropical Frontal Regions.

    Science.gov (United States)

    Cronin, Meghan F; Tozuka, Tomoki

    2016-06-29

    In regions of strong sea surface temperature (SST) gradients, the surface "geostrophic" currents have a vertical shear aligned with the surface density front defined by the temperature. This surface geostrophic ("thermal wind") shear can balance a portion of the surface wind stress, altering the classic Ekman response to wind forcing. Here we show that these frontal effects cannot be ignored in the Tropics or in strong frontal regions in the extratropics, such as found in coastal regions and in western boundary currents of all basins. Frontal effects also dominate the classic Ekman response in the regions of both hemispheres where Trade winds change to westerlies. Implications for vertical motion and global heat transport are discussed.

  11. Analysis and control of the compaction force in the composite prepreg tape winding process for rocket motor nozzles

    Directory of Open Access Journals (Sweden)

    Xiaodong He

    2017-04-01

    Full Text Available In the process of composite prepreg tape winding, the compaction force could influence the quality of winding products. According to the analysis and experiments, during the winding process of a rocket motor nozzle aft exit cone with a winding angle, there would be an error between the deposition speed of tape layers and the feeding speed of the compaction roller, which could influence the compaction force. Both a lack of compaction and overcompaction related to the feeding of the compaction roller could result in defects of winding nozzles. Thus, a flexible winding system has been developed for rocket motor nozzle winding. In the system, feeding of the compaction roller could be adjusted in real time to achieve an invariable compaction force. According to experiments, the force deformation model of the winding tape is a time-varying system. Thus, a forgetting factor recursive least square based parameter estimation proportional-integral-differential (PID controller has been developed, which could estimate the time-varying parameter and control the compaction force by adjusting the feeding of the compaction roller during the winding process. According to the experimental results, a winding nozzle with fewer voids and a smooth surface could be wounded by the invariable compaction force in the flexible winding system.

  12. Added damping of a wind turbine rotor: Two-dimensional discretization expressing the nonlinear wind-force dependency

    NARCIS (Netherlands)

    Van der Male, P.; Van Dalen, K.N.; Metrikine, A.

    2014-01-01

    In determining wind forces on wind turbine blades, and subsequently on the tower and the foundation, the blade response velocity cannot be neglected. This velocity alters the wind force, which depends on the wind velocity relative to that of the blades This blade response velocity component of the w

  13. Added damping of a wind turbine rotor: Two-dimensional discretization expressing the nonlinear wind-force dependency

    NARCIS (Netherlands)

    Van der Male, P.; Van Dalen, K.N.; Metrikine, A.

    2014-01-01

    In determining wind forces on wind turbine blades, and subsequently on the tower and the foundation, the blade response velocity cannot be neglected. This velocity alters the wind force, which depends on the wind velocity relative to that of the blades This blade response velocity component of the

  14. Response of large-scale coastal basins to wind forcing: influence of topography

    Science.gov (United States)

    Chen, Wen L.; Roos, Pieter C.; Schuttelaars, Henk M.; Kumar, Mohit; Zitman, Tjerk J.; M. H. Hulscher, Suzanne J.

    2016-04-01

    Because wind is one of the main forcings in storm surge, we present an idealised process-based model to study the influence of topographic variations on the frequency response of large-scale coastal basins subject to time-periodic wind forcing. Coastal basins are represented by a semi-enclosed rectangular inner region forced by wind. It is connected to an outer region (represented as an infinitely long channel) without wind forcing, which allows waves to freely propagate outward. The model solves the three-dimensional linearised shallow water equations on the f plane, forced by a spatially uniform wind field that has an arbitrary angle with respect to the along-basin direction. Turbulence is represented using a spatially uniform vertical eddy viscosity, combined with a partial slip condition at the bed. The surface elevation amplitudes, and hence the vertical profiles of the velocity, are obtained using the finite element method (FEM), extended to account for the connection to the outer region. The results are then evaluated in terms of the elevation amplitude averaged over the basin's landward end, as a function of the wind forcing frequency. In general, the results point out that adding topographic elements in the inner region (such as a topographic step, a linearly sloping bed or a parabolic cross-basin profile), causes the resonance peaks to shift in the frequency domain, through their effect on local wave speed. The Coriolis effect causes the resonance peaks associated with cross-basin modes (which without rotation only appear in the response to cross-basin wind) to emerge also in the response to along-basin wind and vice versa.

  15. Experimental modeling of the effect of hurricane wind forces on driving behavior and vehicle performance.

    Science.gov (United States)

    Rodriguez, Jose M; Codjoe, Julius; Osman, Osama; Ishak, Sherif; Wolshon, Brian

    2015-01-01

    While traffic planning is important for developing a hurricane evacuation plan, vehicle performance on the roads during extreme weather conditions is critical to the success of the planning process. This novel study investigates the effect of gusty hurricane wind forces on the driving behavior and vehicle performance. The study explores how the parameters of a driving simulator could be modified to reproduce wind loadings experienced by three vehicle types (passenger car, ambulance, and bus) during gusty hurricane winds, through manipulation of appropriate software. Thirty participants were then tested on the modified driving simulator under five wind conditions (ranging from normal to hurricane category 4). The driving performance measures used were heading error and lateral displacement. The results showed that higher wind forces resulted in more varied and greater heading error and lateral displacement. The ambulance had the greatest heading errors and lateral displacements, which were attributed to its large lateral surface area and light weight. Two mathematical models were developed to estimate the heading error and lateral displacements for each of the vehicle types for a given change in lateral wind force. Through a questionnaire, participants felt the different characteristics while driving each vehicle type. The findings of this study demonstrate the valuable use of a driving simulator to model the behavior of different vehicle types and to develop mathematical models to estimate and quantify driving behavior and vehicle performance under hurricane wind conditions.

  16. Wave slamming forces on truss support structures for wind turbines

    OpenAIRE

    Aashamar, Miriam Zakri

    2012-01-01

    This thesis is a study of the slamming forces from plunging breaking waves on truss support structures in shallow water. The main parts have been model testing and analysis on an existing 1:50 scale model of a truss support structure for wind turbines at NTNU.An expanding building of offshore structures has led to increased focus on wave forces. Large slamming forces from breaking waves can occur in shallow water. These forces will impact the structure in a much bigger way than non-breaking w...

  17. Bearingless motor's radial suspension force control based on flux equivalent with virtual winding current analysis method

    Institute of Scientific and Technical Information of China (English)

    ZHU HuangQiu; CHENG OiuLiang

    2009-01-01

    A bearingless motor has two sets of intercoupling stator windings, namely torque windings and sus-pension force windings. The decoupling control of the two sets is difficult and a key technology to stable operation for a bearingless motor. In this paper, a simple, reliable and accurate analysis method is put forward using the concept of flux equivalent with virtual winding currents. By this method, the suspension operation condition PB=PM±1 for bearingless motors is testified, and under the rotation condition of the motor, it is also proved that currents in suspension force windings must have the same phase sequence and frequency as torque windings to generate a stable single direction radial force in the rotor's whole circumference. On this basis, the control strategy of realizing the suspension opera-tion of the bearingless motor is presented, and a prototype of the bearingless surface-mounted per-manent magnet synchronous motor is tested. The research results have indicated that the experimen-tal results correspond with theoretical analysis adopting this method, a stable and reliable radial sus-pension force can be generated, and the validity and feasibility of this control strategy are confirmed.

  18. Steady State Ocean Response to Wind Forcing in Extratropical Frontal Regions

    Science.gov (United States)

    Cronin, Meghan F.; Tozuka, Tomoki

    2016-01-01

    In regions of strong sea surface temperature (SST) gradients, the surface “geostrophic” currents have a vertical shear aligned with the surface density front defined by the temperature. This surface geostrophic (“thermal wind”) shear can balance a portion of the surface wind stress, altering the classic Ekman response to wind forcing. Here we show that these frontal effects cannot be ignored in the Tropics or in strong frontal regions in the extratropics, such as found in coastal regions and in western boundary currents of all basins. Frontal effects also dominate the classic Ekman response in the regions of both hemispheres where Trade winds change to westerlies. Implications for vertical motion and global heat transport are discussed. PMID:27354231

  19. Steady State Ocean Response to Wind Forcing in Extratropical Frontal Regions

    Science.gov (United States)

    Cronin, Meghan F.; Tozuka, Tomoki

    2016-06-01

    In regions of strong sea surface temperature (SST) gradients, the surface “geostrophic” currents have a vertical shear aligned with the surface density front defined by the temperature. This surface geostrophic (“thermal wind”) shear can balance a portion of the surface wind stress, altering the classic Ekman response to wind forcing. Here we show that these frontal effects cannot be ignored in the Tropics or in strong frontal regions in the extratropics, such as found in coastal regions and in western boundary currents of all basins. Frontal effects also dominate the classic Ekman response in the regions of both hemispheres where Trade winds change to westerlies. Implications for vertical motion and global heat transport are discussed.

  20. How predictable are equatorial Atlantic surface winds?

    Science.gov (United States)

    Richter, Ingo; Doi, Takeshi; Behera, Swadhin

    2017-04-01

    Sensitivity tests with the SINTEX-F general circulation model (GCM) as well as experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to examine the extent to which sea-surface temperature (SST) anomalies contribute to the variability and predictability of monthly mean surface winds in the equatorial Atlantic. In the SINTEX-F experiments, a control experiment with prescribed observed SST for the period 1982-2014 is modified by inserting climatological values in certain regions, thereby eliminating SST anomalies. When SSTs are set to climatology in the tropical Atlantic only (30S to 30N), surface wind variability over the equatorial Atlantic (5S-5N) decreases by about 40% in April-May-June (AMJ). This suggests that about 60% of surface wind variability is due to either internal atmospheric variability or SSTs anomalies outside the tropical Atlantic. A further experiment with climatological SSTs in the equatorial Pacific indicates that another 10% of variability in AMJ may be due to remote influences from that basin. Experiments from the CMIP5 archive, in which climatological SSTs are prescribed globally, tend to confirm the results from SINTEX-F but show a wide spread. In some models, the equatorial Atlantic surface wind variability decreases by more than 90%, while in others it even increases. Overall, the results suggest that about 50-60% of surface wind variance in AMJ is predictable, while the rest is due to internal atmospheric variability. Other months show significantly lower predictability. The relatively strong internal variability as well as the influence of remote SSTs suggest a limited role for coupled ocean-atmosphere feedbacks in equatorial Atlantic variability.

  1. WIND STRESS AND SURFACE ROUGHNESS AT AIR-SEA INTERFACE

    Science.gov (United States)

    Based on the compiled data of thirty independent observations, the report presents the wind - stress coefficient, the surface roughness and the...boundary layer flow regime at the air-sea interface under various wind conditions. Both the wind - stress coefficient and the surface roughness are found to...data and Charnock’s proportionality constant is determined. Finally, two approximate formulae for the wind - stress coefficient, one for light wind and the other for strong wind are suggested.

  2. Dynamic Stability of Euler Beams under Axial Unsteady Wind Force

    Directory of Open Access Journals (Sweden)

    You-Qin Huang

    2014-01-01

    Full Text Available Dynamic instability of beams in complex structures caused by unsteady wind load has occurred more frequently. However, studies on the parametric resonance of beams are generally limited to harmonic loads, while arbitrary dynamic load is rarely involved. The critical frequency equation for simply supported Euler beams with uniform section under arbitrary axial dynamic forces is firstly derived in this paper based on the Mathieu-Hill equation. Dynamic instability regions with high precision are then calculated by a presented eigenvalue method. Further, the dynamically unstable state of beams under the wind force with any mean or fluctuating component is determined by load normalization, and the wind-induced parametric resonant response is computed by the Runge-Kutta approach. Finally, a measured wind load time-history is input into the dynamic system to indicate that the proposed methods are effective. This study presents a new method to determine the wind-induced dynamic stability of Euler beams. The beam would become dynamically unstable provided that the parametric point, denoting the relation between load properties and structural frequency, is located in the instability region, no matter whether the wind load component is large or not.

  3. Measuring Forces between Oxide Surfaces Using the Atomic Force Microscope

    DEFF Research Database (Denmark)

    Pedersen, Henrik Guldberg; Høj, Jakob Weiland

    1996-01-01

    The interactions between colloidal particles play a major role in processing of ceramics, especially in casting processes. With the Atomic Force Microscope (AFM) it is possible to measure the inter-action force between a small oxide particle (a few micron) and a surface as function of surface sep...

  4. Measuring Forces between Oxide Surfaces Using the Atomic Force Microscope

    DEFF Research Database (Denmark)

    Pedersen, Henrik Guldberg; Høj, Jakob Weiland

    1996-01-01

    The interactions between colloidal particles play a major role in processing of ceramics, especially in casting processes. With the Atomic Force Microscope (AFM) it is possible to measure the inter-action force between a small oxide particle (a few micron) and a surface as function of surface...

  5. Evidence for water structuring forces between surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, Christopher B [ORNL; Rau, Dr. Donald [National Institutes of Health

    2011-01-01

    Structured water on apposing surfaces can generate significant energies due to reorganization and displacement as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water.

  6. Soil erosion rates from mixed soil and gravel surfaces in a wind tunnel: A preliminary report

    Energy Technology Data Exchange (ETDEWEB)

    Ligotke, M.W.

    1988-12-01

    Tests of wind erosion were performed in a controlled-environment wind tunnel to support the development of natural-material protective barriers for long-term isolation of radioactive waste. Barrier performance standards currently being developed for internal and external barrier performance are expected to mandate a surface layer that is resistant to wind erosion. The purpose of this study was to initiate a series of tests to determine suitable soil and gravel mixtures for such a barrier and to test worst-case surface layer conditions under the influence of high wind speeds. Six mixed soil and gravel surfaces were prepared, weathered to represent natural wind-blown desert areas, and subjected to controlled wind erosion forces in a wind tunnel. The applied erosive forces, including surface shear forces, were characterized to provide a means of relating wind tunnel results with actual field conditions. Soil particle losses from the surfaces caused by suspension, saltation, and surface creep were monitored by aerosol sample probes and mass balance measurements. 23 refs., 22 figs., 3 tabs.

  7. The magnetosphere under weak solar wind forcing

    Directory of Open Access Journals (Sweden)

    C. J. Farrugia

    2007-02-01

    Full Text Available The Earth's magnetosphere was very strongly disturbed during the passage of the strong shock and the following interacting ejecta on 21–25 October 2001. These disturbances included two intense storms (Dst*≈−250 and −180 nT, respectively. The cessation of this activity at the start of 24 October ushered in a peculiar state of the magnetosphere which lasted for about 28 h and which we discuss in this paper. The interplanetary field was dominated by the sunward component [B=(4.29±0.77, −0.30±0.71, 0.49±0.45 nT]. We analyze global indicators of geomagnetic disturbances, polar cap precipitation, ground magnetometer records, and ionospheric convection as obtained from SuperDARN radars. The state of the magnetosphere is characterized by the following features: (i generally weak and patchy (in time low-latitude dayside reconnection or reconnection poleward of the cusps; (ii absence of substorms; (iii a monotonic recovery from the previous storm activity (Dst corrected for magnetopause currents decreasing from ~−65 to ~−35 nT, giving an unforced decreased of ~1.1 nT/h; (iv the probable absence of viscous-type interaction originating from the Kelvin-Helmholtz (KH instability; (v a cross-polar cap potential of just 20–30 kV; (vi a persistent, polar cap region containing (vii very weak, and sometimes absent, electron precipitation and no systematic inter-hemisphere asymmetry. Whereas we therefore infer the presence of a moderate amount of open flux, the convection is generally weak and patchy, which we ascribe to the lack of solar wind driver. This magnetospheric state approaches that predicted by Cowley and Lockwood (1992 but has never yet been observed.

  8. Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow

    CERN Document Server

    Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias

    2015-01-01

    The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.

  9. An overview on SAR measurements of sea surface wind

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Studies show that synthetic aperture radar (SAR) has the capability of providing high-resolution (sub-kilometer) sea surface wind fields. This is very useful for applications where knowledge of the sea surface wind at fine scales is crucial. This paper aims to review the latest work on sea surface wind field retrieval using SAR images. As shown, many different approaches have been developed for retrieving wind speed and wind direction. However, much more work will be required to fully exploit the SAR data for improving the retrieval accuracy of high-resolution winds and for producing wind products in an operational sense.

  10. Changes in Surface Wind Speed over North America from CMIP5 Model Projections and Implications for Wind Energy

    Directory of Open Access Journals (Sweden)

    Sujay Kulkarni

    2014-01-01

    Full Text Available The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5 archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models projected decreases in the wind speed ranging from 5 to 10 percent per century over the same coastal regions. These projected changes in the surface wind speed are moderate and imply that the current estimate of wind power potential for North America based on present-day climatology will not be significantly changed by the greenhouse gas forcing in the coming decades.

  11. Energetic dynamics of a rotating horizontal convection model of an ocean basin with wind forcing

    Science.gov (United States)

    Zemskova, Varvara; White, Brian; Scotti, Alberto

    2016-11-01

    We analyze the energetic dynamics in a rotating horizontal convection model, where flow is driven by a differential buoyancy forcing along a horizontal surface. This model is used to quantify the influence of surface heating and cooling and surface wind stress on the Meridional Overturning Circulation. We study a model of the Southern Ocean in a rectangular basin with surface cooling on one end (the South pole) and surface warming on the other end (mid-latitudes). Free-slip boundary conditions are imposed in the closed box, while zonally periodic boundary conditions are enforced in the reentrant channel. Wind stress and differential buoyancy forcing are applied at the top boundary. The problem is solved numerically using a 3D DNS model based on a finite-volume AMR solver for the Boussinesq Navier-Stokes equations with rotation. The overall dynamics, including large-scale overturning, baroclinic eddying, turbulent mixing, and resulting energy cascades are investigated using the local Available Potential Energy framework introduced in. We study the relative contributions of surface buoyancy and wind forcing along with the effects of bottom topography to the energetic balance of this dynamic model. This research is part of the Blue Waters sustained-petascale computing project, supported by the NSF (awards OCI-0725070, ACI-1238993 and ACI-14-44747) and the state of Illinois.

  12. Statistical Short-Range Guidance for Peak Wind Speed Forecasts at Edwards Air Force Base, CA

    Science.gov (United States)

    Dreher, Joseph G.; Crawford, Winifred; Lafosse, Richard; Hoeth, Brian; Burns, Kerry

    2009-01-01

    The peak winds near the surface are an important forecast element for space shuttle landings. As defined in the Flight Rules (FR), there are peak wind thresholds that cannot be exceeded in order to ensure the safety of the shuttle during landing operations. The National Weather Service Spaceflight Meteorology Group (SMG) is responsible for weather forecasts for all shuttle landings, and is required to issue surface average and 10-minute peak wind speed forecasts. They indicate peak winds are a challenging parameter to forecast. To alleviate the difficulty in making such wind forecasts, the Applied Meteorology Unit (AMU) developed a PC-based graphical user interface (GUI) for displaying peak wind climatology and probabilities of exceeding peak wind thresholds for the Shuttle Landing Facility (SLF) at Kennedy Space Center (KSC; Lambert 2003). However, the shuttle occasionally may land at Edwards Air Force Base (EAFB) in southern California when weather conditions at KSC in Florida are not acceptable, so SMG forecasters requested a similar tool be developed for EAFB.

  13. Spatial development of the wind-driven water surface flow

    Science.gov (United States)

    Chemin, Rémi; Caulliez, Guillemette

    2015-04-01

    The water velocity field induced by wind and waves beneath an air-water interface is investigated experimentally versus fetch in the large Marseille-Luminy wind wave tank. Measurements of the vertical velocity profiles inside the subsurface shear layer were performed by a three-component Nortek acoustic Doppler velocimeter. The surface drift current was also derived from visualizations of small floating drifters recorded by a video camera looking vertically from above the water surface. Surface wave height and slopes were determined simultaneously by means of capacitance gauges and a single-point laser slope system located in the immediate vicinity of the profiler. Observations were made at steady low to moderate wind speeds and various fetches ranging between 1 and 15 meters. This study first corroborates that the thin subsurface water boundary layer forced by wind at the leading edge of the water sheet is laminar. The surface drift current velocity indeed increases gradually with fetch, following a 1/3 power law characteristic of an accelerated flat-plate laminar boundary layer. The laminar-turbulent transition manifests itself by a sudden decrease in the water surface flow velocity and a rapid deepening of the boundary layer due to the development of large-scale longitudinal vortices. Further downstream, when characteristic capillary-gravity wind waves develop at the surface, the water flow velocity increases again rapidly within a sublayer of typically 4 mm depth. This phenomenon is explained by the occurrence of an intense momentum flux from waves to the mean flow due to the dissipation of parasitic capillaries generated ahead of the dominant wave crests. This phenomenon also sustains significant small-scale turbulent motions within the whole boundary layer. However, when gravity-capillary waves of length longer than 10 cm then grow at the water surface, the mean flow velocity field decreases drastically over the whole boundary layer thickness. At the same

  14. Interfacial forces between silica surfaces measured by atomic force microscopy

    Institute of Scientific and Technical Information of China (English)

    DUAN Jinming

    2009-01-01

    Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy (AFM) colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the 'constant charge' and 'constant potential' models of DLVO theory. The difference between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.

  15. Interfacial forces between silica surfaces measured by atomic force microscopy.

    Science.gov (United States)

    Duan, Jinming

    2009-01-01

    Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy (AFM) colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the 'constant charge' and 'constant potential' models of DLVO theory. The difference between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.

  16. Breaking wave impact forces on truss support structures for offshore wind turbines

    Science.gov (United States)

    Cieślikiewicz, Witold; Gudmestad, Ove T.; Podrażka, Olga

    2014-05-01

    Due to depletion of the conventional energy sources, wind energy is becoming more popular these days. Wind energy is being produced mostly from onshore farms, but there is a clear tendency to transfer wind farms to the sea. The foundations of offshore wind turbines may be truss structures and might be located in shallow water, where are subjected to highly varying hydrodynamic loads, particularly from plunging breaking waves. There are models for impact forces prediction on monopiles. Typically the total wave force on slender pile from breaking waves is a superposition of slowly varying quasi-static force, calculated from the Morison equation and additional dynamical, short duration force due to the impact of the breaker front or breaker tongue. There is not much research done on the truss structures of wind turbines and there are still uncertainties on slamming wave forces, due to plunging breaking waves on those structures. Within the WaveSlam (Wave slamming forces on truss structures in shallow water) project the large scale tests were carried out in 2013 at the Large Wave Flume in Forschungszentrum Küste (FZK) in Hannover, Germany. The following institutions participated in this initiative: the University of Stavanger and the Norwegian University of Science and Technology (project management), University of Gdańsk, Poland, Hamburg University of Technology and the University of Rostock, Germany and Reinertsen AS, Norway. This work was supported by the EU 7th Framework Programme through the grant to the budget of the Integrating Activity HYDRALAB IV. The main aim of the experiment was to investigate the wave slamming forces on truss structures, development of new and improvement of existing methods to calculate forces from the plunging breakers. The majority of the measurements were carried out for regular waves with specified frequencies and wave heights as well as for the irregular waves based on JONSWAP spectrum. The truss structure was equipped with both

  17. QuikSCAT and SSM/I ocean surface winds for wind energy

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Astrup, Poul; Nielsen, Per

    2007-01-01

    Ocean surface winds observed by satellite scatterometer (QuikSCAT) and passive microwave (SMM/I) provide valuable information for wind energy applications. In wind energy two long-term aspects on the offshore wind climate is of concern. One is the 20-year average necessary for the estimation...

  18. Soil erosion rates from mixed soil and gravel surfaces in a wind tunnel

    Energy Technology Data Exchange (ETDEWEB)

    Ligotke, M.W.; Klopfer, D.C.

    1990-08-01

    Protective barriers have been identified as integral components of plans to isolate defense waste on the Hanford Site. The use of natural materials to construct protective barriers over waste site is being considered. Design requirements for protective barriers include preventing exposure of buried waste, and restricting penetration or percolation of surface waters through the waste zone. Studies were initiated to evaluate the effects of wind erosion on candidate protective barrier surfaces. A wind tunnel was used to provide controlled erosive stresses and to investigate the erosive effects of wind forces on proposed surface layers for protective barriers. Mixed soil and gravel surfaces were prepared and tested for resistance to wind erosion at the Pacific Northwest Laboratory Aerosol Wind Tunnel Research Facility. These tests were performed to investigate surface deflation caused by suspension of soil from various surface layer configurations and to provide a comparison of the relative resistance of the different surfaces to wind erosion. Planning, testing, and analyzing phases of this wind erosion project were coordinated with other tasks supporting the development of protective barriers. These tasks include climate-change predictions, field studies and modeling efforts. This report provides results of measurements of deflation caused by wind forces over level surfaces. Section 2.0 reviews surface layer characteristics and previous relevant studies on wind erosion, describes effects of erosion, and discusses wind tunnel modeling. Materials and methods of the wind tunnel tests are discussed in Section 3.0. Results and discussion are presented in Section 4.0, and conclusions and recommendations Section 5.0. 53 refs., 29 figs., 7 tabs.

  19. Weather Research and Forecasting Model Wind Sensitivity Study at Edwards Air Force Base, CA

    Science.gov (United States)

    Watson, Leela R.; Bauman, William H., III

    2008-01-01

    NASA prefers to land the space shuttle at Kennedy Space Center (KSC). When weather conditions violate Flight Rules at KSC, NASA will usually divert the shuttle landing to Edwards Air Force Base (EAFB) in Southern California. But forecasting surface winds at EAFB is a challenge for the Spaceflight Meteorology Group (SMG) forecasters due to the complex terrain that surrounds EAFB, One particular phenomena identified by SMG is that makes it difficult to forecast the EAFB surface winds is called "wind cycling". This occurs when wind speeds and directions oscillate among towers near the EAFB runway leading to a challenging deorbit bum forecast for shuttle landings. The large-scale numerical weather prediction models cannot properly resolve the wind field due to their coarse horizontal resolutions, so a properly tuned high-resolution mesoscale model is needed. The Weather Research and Forecasting (WRF) model meets this requirement. The AMU assessed the different WRF model options to determine which configuration best predicted surface wind speed and direction at EAFB, To do so, the AMU compared the WRF model performance using two hot start initializations with the Advanced Research WRF and Non-hydrostatic Mesoscale Model dynamical cores and compared model performance while varying the physics options.

  20. Wind Resource Estimation using QuikSCAT Ocean Surface Winds

    DEFF Research Database (Denmark)

    Xu, Qing; Zhang, Guosheng; Cheng, Yongcun

    2011-01-01

    and the complexity of air-sea interaction processes, an empirical relationship that adjusts QuikSCAT winds in coastal waters was first proposed based on vessel measurements. Then the shape and scale parameters of Weibull function are determined for wind resource estimation. The wind roses are also plotted. Results...

  1. Surface forces studied with colloidal probe atomic force microscopy

    NARCIS (Netherlands)

    Giesbers, M.

    2001-01-01

    Forces between surfaces are a determining factor for the performance of natural as well as synthetic colloidal systems, and play a crucial role in industrial production processes. Measuring these forces is a scientific and experimental challenge and over the years several techniques have been develo

  2. Surface forces studied with colloidal probe atomic force microscopy

    NARCIS (Netherlands)

    Giesbers, M.

    2001-01-01

    Forces between surfaces are a determining factor for the performance of natural as well as synthetic colloidal systems, and play a crucial role in industrial production processes. Measuring these forces is a scientific and experimental challenge and over the years several techniques have

  3. Deterministic prediction of surface wind speed variations

    OpenAIRE

    Drisya, G. V.; Kiplangat, D. C.; Asokan, K; K. Satheesh Kumar

    2014-01-01

    Accurate prediction of wind speed is an important aspect of various tasks related to wind energy management such as wind turbine predictive control and wind power scheduling. The most typical characteristic of wind speed data is its persistent temporal variations. Most of the techniques reported in the literature for prediction of wind speed and power are based on statistical methods or probabilistic distribution of wind speed data. In this paper we demonstrate that determin...

  4. Surface forces: Surface roughness in theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, Drew F., E-mail: Drew.Parsons@anu.edu.au; Walsh, Rick B.; Craig, Vincent S. J. [Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia)

    2014-04-28

    A method of incorporating surface roughness into theoretical calculations of surface forces is presented. The model contains two chief elements. First, surface roughness is represented as a probability distribution of surface heights around an average surface height. A roughness-averaged force is determined by taking an average of the classic flat-surface force, weighing all possible separation distances against the probability distributions of surface heights. Second the model adds a repulsive contact force due to the elastic contact of asperities. We derive a simple analytic expression for the contact force. The general impact of roughness is to amplify the long range behaviour of noncontact (DLVO) forces. The impact of the elastic contact force is to provide a repulsive wall which is felt at a separation between surfaces that scales with the root-mean-square (RMS) roughness of the surfaces. The model therefore provides a means of distinguishing between “true zero,” where the separation between the average centres of each surface is zero, and “apparent zero,” defined by the onset of the repulsive contact wall. A normal distribution may be assumed for the surface probability distribution, characterised by the RMS roughness measured by atomic force microscopy (AFM). Alternatively the probability distribution may be defined by the histogram of heights measured by AFM. Both methods of treating surface roughness are compared against the classic smooth surface calculation and experimental AFM measurement.

  5. Study of Practicability of Improved Irwin's Surface Wind Sensor

    National Research Council Canada - National Science Library

    Junji KATAGIRI; Toshio TSURUMI; Takeshi OHKUMA; Hisao MARUKAWA

    2009-01-01

      The practicability of a surface wind sensor (SWS) is examined by comparing the mean and fluctuating wind velocities obtained from this instrument with those measured by an omni-directional multi-channel anemometer (OMA...

  6. On the Effect of Extratropical Wind Stress Forcing on Pacific Subtropical Cells and Tropical Climate

    Science.gov (United States)

    Graffino, Giorgio; Farneti, Riccardo; Kucharski, Fred

    2017-04-01

    The influence of extratropical atmospheric dynamics on the tropical ocean state is a classical example of ocean-atmosphere teleconnection. One way to influence tropical climate is through oceanic SubTropical Cells (STCs), shallow overturning circulation structures connecting the Equatorial Ocean with the subtropical regions. STC are responsible for large mass and energy transports, and their influence on tropical climate, and consequently on the global climate, is fundamental both on the mean and its variability. These circulation structures are present in all basins across the Tropics (Pacific, Atlantic, and Indian Ocean), with different properties and strengths due to the features of each basin. We focus here on the effect of off-equatorial winds on the Pacific STCs, which are the largest and have been previously studied for their potential role in driving low-frequency Pacific variability. Using the Modular Ocean Model version 5 (MOM5), we force the ocean surface with idealized wind stress and wind stress curl anomaly patterns, in order to highlight the influence of subtropical and extratropical forcing on STCs dynamics, and, eventually, on some aspects of Pacific tropical climate. Results have been compared with a control simulation, in which a climatological forcing has been applied at the ocean surface. Our simulations show an increased (reduced) meridional water transport for positive (negative) wind stress anomalies in the Subtropics; the structure of the thermocline at the Equator is modified as well, where cold (warm) anomalies appear. Those signatures result from anomalous values of Equatorial UnderCurrent (EUC), which is partly fed by the STCs. Meridional ocean heat transport is influenced too, showing larger (weaker) values for stronger (weaker) subtropical wind stress. Anomalous circulations are further analyzed for the interior and western boundary transports, and scalings are derived linking subtropical wind stress, STC transports and tropical

  7. Vandenberg Air Force Base Upper Level Wind Launch Weather Constraints

    Science.gov (United States)

    Shafer, Jaclyn A.; Wheeler, Mark M.

    2012-01-01

    The 30th Operational Support Squadron Weather Flight (30 OSSWF) provides comprehensive weather services to the space program at Vandenberg Air Force Base (VAFB) in California. One of their responsibilities is to monitor upper-level winds to ensure safe launch operations of the Minuteman III ballistic missile. The 30 OSSWF tasked the Applied Meteorology Unit (AMU) to analyze VAFB sounding data with the goal of determining the probability of violating (PoV) their upper-level thresholds for wind speed and shear constraints specific to this launch vehicle, and to develop a tool that will calculate the PoV of each constraint on the day of launch. In order to calculate the probability of exceeding each constraint, the AMU collected and analyzed historical data from VAFB. The historical sounding data were retrieved from the National Oceanic and Atmospheric Administration Earth System Research Laboratory archive for the years 1994-2011 and then stratified into four sub-seasons: January-March, April-June, July-September, and October-December. The maximum wind speed and 1000-ft shear values for each sounding in each subseason were determined. To accurately calculate the PoV, the AMU determined the theoretical distributions that best fit the maximum wind speed and maximum shear datasets. Ultimately it was discovered that the maximum wind speeds follow a Gaussian distribution while the maximum shear values follow a lognormal distribution. These results were applied when calculating the averages and standard deviations needed for the historical and real-time PoV calculations. In addition to the requirements outlined in the original task plan, the AMU also included forecast sounding data from the Rapid Refresh model. This information provides further insight for the launch weather officers (LWOs) when determining if a wind constraint violation will occur over the next few hours on day of launch. The interactive graphical user interface (GUI) for this project was developed in

  8. Surface plasmon polariton assisted optical pulling force

    CERN Document Server

    Petrov, M I; Bogdanov, A A; Shalin, A S; Dogariu, A

    2016-01-01

    We demonstrate both analytically and numerically the existence of optical pulling forces acting on particles located near plasmonic interfaces. Two main factors contribute to the appearance of this negative reaction force. The interference between the incident and reflected waves induces a rotating dipole with an asymmetric scattering pattern while the directional excitation of surface plasmon polaritons (SPP) enhances the linear momentum of scattered light. The strongly asymmetric SPP excitation is determined by spin-orbit coupling of the rotating dipole and surface plasmon polariton. As a result of the total momentum conservation, the force acting on the particle points in a direction opposite to the incident wave propagation. We derive analytical expressions for the force acting on a dipolar particles placed in the proximity of plasmonic surfaces. Analytical expressions for this pulling force are derived within the dipole approximation and are in excellent agreement with results of electromagnetic numerica...

  9. Identifying Stratospheric Air Intrusions and Associated Hurricane-Force Wind Events over the North Pacific Ocean

    Science.gov (United States)

    Malloy, Kelsey; Folmer, Michael J.; Phillips, Joseph; Sienkiewicz, Joseph M.; Berndt, Emily

    2017-01-01

    Motivation: Ocean data is sparse: reliance on satellite imagery for marine forecasting; Ocean Prediction Center (OPC) –“mariner’s weather lifeline”. Responsible for: Pacific, Atlantic, Pacific Alaska surface analyses –24, 48, 96 hrs.; Wind & wave analyses –24, 48, 96 hrs.; Issue warnings, make decisions, Geostationary Operational Environmental Satellite –R Series (now GOES-16), Compared to the old GOES: 3 times spectral resolution, 4 times spatial resolution, 5 times faster coverage; Comparable to Japanese Meteorological Agency’s Himawari-8, used a lot throughout this research. Research Question: How can integrating satellite data imagery and derived products help forecasters improve prognosis of rapid cyclogenesis and hurricane-force wind events? Phase I –Identifying stratospheric air intrusions: Water Vapor –6.2, 6.9, 7.3 micron channels; Airmass RGB Product; AIRS, IASI, NUCAPS total column ozone and ozone anomaly; ASCAT (A/B) and AMSR-2 wind data.

  10. Casimir force measurements from silicon carbide surfaces

    NARCIS (Netherlands)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-01-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold-coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was mea

  11. Effectiveness of WRF wind direction for retrieving coastal sea surface wind from synthetic aperture radar

    DEFF Research Database (Denmark)

    Takeyama, Yuko; Ohsawa, Teruo; Kozai, Katsutoshi;

    2013-01-01

    Wind direction is required as input to the geophysical model function (GMF) for the retrieval of sea surface wind speed from a synthetic aperture radar (SAR) images. The present study verifies the effectiveness of using the wind direction obtained from the weather research and forecasting model...

  12. Offshore Wind Energy: Wind and Sea Surface Temperature from Satellite Observations

    DEFF Research Database (Denmark)

    Karagali, Ioanna

    and the Baltic Sea. The aim is to evaluate their potential use and demonstrate their applicability within the context of offshore wind energy; for the quantication of the wind resources and for the identication of diurnal warming of the sea surface temperature. Space-borne observations of wind are obtained from...

  13. Simulation of the surface wind field and wind waves over the Oman Sea

    Science.gov (United States)

    Hamzeloo, Sima; Hadi Moeini, Mohammad; Jandaghi Alaee, Majid

    2016-04-01

    Surface wind field is one of the most important factors in the generation of the marine hydrodynamic phenomena such as wind waves that highly affected by the surface winds. Therefore, accessibility to the correct wind field is of great importance for accurate prediction and simulation of the hydrodynamic variables. Nowadays numerical mesoscale weather prediction models are widely applied as powerful tools to simulate wind and other atmospheric variables with predefined temporal and spatial resolution in desired areas. Despite appropriate results of the numerical models in many regions, there are still some complications in the simulation of the surface wind field in areas with complex orography since the surface wind field is highly affected by the local topography, land-sea discontinuity, temperature gradient etc. Nowadays, with the development of high-speed processors the third generation spectral models are generally used for simulation of wind waves. Wind data are the main input parameters of the numerical spectral wave model. Therefore, the quality of the input wind data can be assessed by comparison of the wave model outputs with measured values. The main goal of the current study is to simulate surface wind field over the Oman Sea using WRF modeling system. To verify the model results, the simulated wind speeds were compared with synoptic and buoy measurements and satellite observations. Wind-wave parameters simulated by the spectral model were also compared with wave measurements to verify simulated surface wind field as the input of the wave model. The Comparison simulated wind speed and directions in coastal synoptic stations and QuikSCAT satellite shows sufficient results for both offshore and coastal areas.

  14. On the dependence of sea surface roughness on wind waves

    DEFF Research Database (Denmark)

    Johnson, H.K.; Højstrup, J.; Vested, H.J.;

    1998-01-01

    The influence of wind waves on the momentum transfer (wind stress) between the atmosphere and sea surface was studied using new measured data from the RASEX experiment and other datasets compiled by Donelan et al. Results of the data analysis indicate that errors in wind friction velocity u...

  15. Responses of the Tropical Pacific to Wind Forcing as Observed by Spaceborne Sensors and Simulated by an Ocean General Circulation Model

    Science.gov (United States)

    Liu, W. Timothy; Tang, Qenqing; Atlas, Robert

    1996-01-01

    In this study, satellite observations, in situ measurements, and model simulations are combined to assess the oceanic response to surface wind forcing in the equatorial Pacific. The surface wind fields derived from observations by the spaceborne special sensor microwave imager (SSM/I) and from the operational products of the European Centre for Medium-Range Weather Forecasts (ECMWF) are compared. When SSM/I winds are used to force a primitive-equation ocean general circulation model (OGCM), they produce 3 C more surface cooling than ECMWF winds for the eastern equatorial Pacific during the cool phase of an El Nino-Southern Oscillation event. The stronger cooling by SSM/I winds is in good agreement with measurements at the moored buoys and observations by the advanced very high resolution radiometer, indicating that SSM/I winds are superior to ECMWF winds in forcing the tropical ocean. In comparison with measurements from buoys, tide gauges, and the Geosat altimeter, the OGCM simulates the temporal variations of temperature, steric, and sea level changes with reasonable realism when forced with the satellite winds. There are discrepancies between model simulations and observations that are common to both wind forcing fields, one of which is the simulation of zonal currents; they could be attributed to model deficiencies. By examining model simulations under two winds, vertical heat advection and uplifting of the thermocline are found to be the dominant factors in the anomalous cooling of the ocean mixed layer.

  16. Statistical Short-Range Guidance for Peak Wind Speed Forecasts at Edwards Air Force Base, CA

    Science.gov (United States)

    Dreher, Joseph; Crawford, Winifred; Lafosse, Richard; Hoeth, Brian; Burns, Kerry

    2008-01-01

    The peak winds near the surface are an important forecast element for Space Shuttle landings. As defined in the Shuttle Flight Rules (FRs), there are peak wind thresholds that cannot be exceeded in order to ensure the safety of the shuttle during landing operations. The National Weather Service Spaceflight Meteorology Group (SMG) is responsible for weather forecasts for all shuttle landings. They indicate peak winds are a challenging parameter to forecast. To alleviate the difficulty in making such wind forecasts, the Applied Meteorology Unit (AMTJ) developed a personal computer based graphical user interface (GUI) for displaying peak wind climatology and probabilities of exceeding peak-wind thresholds for the Shuttle Landing Facility (SLF) at Kennedy Space Center. However, the shuttle must land at Edwards Air Force Base (EAFB) in southern California when weather conditions at Kennedy Space Center in Florida are not acceptable, so SMG forecasters requested that a similar tool be developed for EAFB. Marshall Space Flight Center (MSFC) personnel archived and performed quality control of 2-minute average and 10-minute peak wind speeds at each tower adjacent to the main runway at EAFB from 1997- 2004. They calculated wind climatologies and probabilities of average peak wind occurrence based on the average speed. The climatologies were calculated for each tower and month, and were stratified by hour, direction, and direction/hour. For the probabilities of peak wind occurrence, MSFC calculated empirical and modeled probabilities of meeting or exceeding specific 10-minute peak wind speeds using probability density functions. The AMU obtained and reformatted the data into Microsoft Excel PivotTables, which allows users to display different values with point-click-drag techniques. The GUT was then created from the PivotTables using Visual Basic for Applications code. The GUI is run through a macro within Microsoft Excel and allows forecasters to quickly display and

  17. 2D study of wind forces around multiple cooling towers using ...

    African Journals Online (AJOL)

    user

    2D study of wind forces around multiple cooling towers using computational ... Due to the complexity of wind turbulence near ground (Atmospheric Boundary. Layer), the .... In the past, before the computer revolution, the analysis used to be.

  18. Strongly-sheared wind-forced currents in the nearshore regions of the central Southern California Bight

    Science.gov (United States)

    Noble, Marlene A.; Rosenberger, Kurt; Robertson, George L.

    2015-01-01

    Contrary to many previous reports, winds do drive currents along the shelf in the central portion of the Southern California Bight (SCB). Winds off Huntington Beach CA are the dominant forcing for currents over the nearshore region of the shelf (water depths less than 20 m). Winds control about 50–70% of the energy in nearshore alongshelf surface currents. The wind-driven current amplitudes are also anomalously high. For a relatively weak 1 dyne/cm2 wind stress, the alongshelf surface current amplitudes in this region can reach 80 cm/s or more. Mid-depth current amplitudes for the same wind stress are around 30–40 cm/s. These wind-driven surface current amplitudes are much larger than previously measured over other nearshore shelf regions, perhaps because this program is one of the few that measured currents within a meter of the surface. The near-bed cross-shelf currents over the nearshore region of the Huntington Beach shelf have an Ekman response to winds in that they upwell (downwell) for down (up) coast winds. This response disappears further offshore. Hence, there is upwelling in the SCB, but it does not occur across the entire shelf. Subthermocline water in the nearshore region that may contain nutrients and plankton move onshore when winds are southeastward, but subthermocline water over the shelf break is not transported to the beach. The currents over the outer shelf are not predominately controlled by winds, consistent with previous reports. Instead, they are mainly driven by cross-shelf pressure gradients that are independent of local wind stress.

  19. Force-Control Algorithm for Surface Sampling

    Science.gov (United States)

    Acikmese, Behcet; Quadrelli, Marco B.; Phan, Linh

    2008-01-01

    A G-FCON algorithm is designed for small-body surface sampling. It has a linearization component and a feedback component to enhance performance. The algorithm regulates the contact force between the tip of a robotic arm attached to a spacecraft and a surface during sampling.

  20. Calculating the sensitivity of wind turbine loads to wind inputs using response surfaces

    DEFF Research Database (Denmark)

    Rinker, Jennifer M.

    2016-01-01

    This paper presents a methodology to calculate wind turbine load sensitivities to turbulence parameters through the use of response surfaces. A response surface is a high-dimensional polynomial surface that can be calibrated to any set of input/output data and then used to generate synthetic data...... parameters examined in this paper, the variance caused by the Kaimal length scale and nonstationarity parameter are negligible. Thus, the findings in this paper represent the first systematic evidence that stochastic wind turbine load response statistics can be modeled purely by mean wind wind speed...

  1. Will surface winds weaken in response to global warming?

    Science.gov (United States)

    Ma, Jian; Foltz, Gregory R.; Soden, Brian J.; Huang, Gang; He, Jie; Dong, Changming

    2016-12-01

    The surface Walker and tropical tropospheric circulations have been inferred to slow down from historical observations and model projections, yet analysis of large-scale surface wind predictions is lacking. Satellite measurements of surface wind speed indicate strengthening trends averaged over the global and tropical oceans that are supported by precipitation and evaporation changes. Here we use corrected anemometer-based observations to show that the surface wind speed has not decreased in the averaged tropical oceans, despite its reduction in the region of the Walker circulation. Historical simulations and future projections for climate change also suggest a near-zero wind speed trend averaged in space, regardless of the Walker cell change. In the tropics, the sea surface temperature pattern effect acts against the large-scale circulation slow-down. For higher latitudes, the surface winds shift poleward along with the eddy-driven mid-latitude westerlies, resulting in a very small contribution to the global change in surface wind speed. Despite its importance for surface wind speed change, the influence of the SST pattern change on global-mean rainfall is insignificant since it cannot substantially alter the global energy balance. As a result, the precipitation response to global warming remains ‘muted’ relative to atmospheric moisture increase. Our results therefore show consistency between projections and observations of surface winds and precipitation.

  2. Deterministic prediction of surface wind speed variations

    Science.gov (United States)

    Drisya, G. V.; Kiplangat, D. C.; Asokan, K.; Satheesh Kumar, K.

    2014-11-01

    Accurate prediction of wind speed is an important aspect of various tasks related to wind energy management such as wind turbine predictive control and wind power scheduling. The most typical characteristic of wind speed data is its persistent temporal variations. Most of the techniques reported in the literature for prediction of wind speed and power are based on statistical methods or probabilistic distribution of wind speed data. In this paper we demonstrate that deterministic forecasting methods can make accurate short-term predictions of wind speed using past data, at locations where the wind dynamics exhibit chaotic behaviour. The predictions are remarkably accurate up to 1 h with a normalised RMSE (root mean square error) of less than 0.02 and reasonably accurate up to 3 h with an error of less than 0.06. Repeated application of these methods at 234 different geographical locations for predicting wind speeds at 30-day intervals for 3 years reveals that the accuracy of prediction is more or less the same across all locations and time periods. Comparison of the results with f-ARIMA model predictions shows that the deterministic models with suitable parameters are capable of returning improved prediction accuracy and capturing the dynamical variations of the actual time series more faithfully. These methods are simple and computationally efficient and require only records of past data for making short-term wind speed forecasts within practically tolerable margin of errors.

  3. Effects of winds, tides and storm surges on ocean surface waves in the Sea of Japan

    Institute of Scientific and Technical Information of China (English)

    ZHAO Wei; TIAN Jiwei; LI Peiliang; HOU Yijun

    2007-01-01

    Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyō, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions.

  4. Offshore Wind Energy: Wind and Sea Surface Temperature from Satellite Observations

    DEFF Research Database (Denmark)

    Karagali, Ioanna

    as the entire atmosphere above. Under conditions of light winds and strong solar insolation, warming of the upper oceanic layer may occur. In this PhD study, remote sensing from satellites is used to obtain information for the near-surface ocean wind and the sea surface temperature over the North Sea...

  5. Altimeter Estimation of Sea Surface Wind Stress for Light to Moderate Winds

    Science.gov (United States)

    Vandemark, Douglas; Edson, James B.; Chapron, Bertrand

    1997-01-01

    Aircraft altimeter and in situ measurements are used to examine relationships between altimeter backscatter and the magnitude of near-surface wind and friction velocities. Comparison of altimeter radar cross section with wind speed is made through the modified Chelton-Wentz algorithm. Improved agreement is found after correcting 10-m winds for both surface current and atmospheric stability. An altimeter friction velocity algorithm is derived based on the wind speed model and an open-ocean drag coefficient. Close agreement between altimeter- and in situ-derived friction velocities is found. For this dataset, quality of the altimeter inversion to surface friction velocity is comparable to that for adjusted winds and clearly better than the inversion to true 10-m wind speed.

  6. Monitoring dynamic loads on wind tunnel force balances

    Science.gov (United States)

    Ferris, Alice T.; White, William C.

    1989-01-01

    Two devices have been developed at NASA Langley to monitor the dynamic loads incurred during wind-tunnel testing. The Balance Dynamic Display Unit (BDDU), displays and monitors the combined static and dynamic forces and moments in the orthogonal axes. The Balance Critical Point Analyzer scales and sums each normalized signal from the BDDU to obtain combined dynamic and static signals that represent the dynamic loads at predefined high-stress points. The display of each instrument is a multiplex of six analog signals in a way that each channel is displayed sequentially as one-sixth of the horizontal axis on a single oscilloscope trace. Thus this display format permits the operator to quickly and easily monitor the combined static and dynamic level of up to six channels at the same time.

  7. WIND TUNNEL RESEARCH ON THE INFLUENCE OF ACTIVE AIRFLOW ON THE LIFT FORCE GENERATED BY THE AIRFOIL

    Directory of Open Access Journals (Sweden)

    Paweł Magryta

    2013-09-01

    Full Text Available The paper discusses the results of wind tunnel tests of airfoils with additional active airflow applied to their upper surfaces. These studies were carried out for a range of velocities up to 28 m/s in an open wind tunnel. Several types of airfoils selected for the examination feature different geometries and are widely applied in today’s aviation industry. The changes in the lift and drag force generated by these airfoils were recorded during the study. The test bench for the tests was equipped with a compressor and a vacuum pump to enable airflow through some holes on the airfoil upper surface. A rapid prototyping method and a 3D printer based on a powder printing technique were applied to print the airfoils. All of their surfaces were subject to surface grinding to smooth their external surfaces. The wind tunnel tests with and without active airflow applied to airfoils are summarised in the paper.

  8. Using Potential Vorticity to Characterize the Forcing of a Coastally Trapped Wind Reversal Along the California Coast

    Science.gov (United States)

    2015-03-01

    creates cooler temperatures at the surface as the northerly winds enable coastal upwelling through Ekman processes. Thus, the West Coast of the United...of the ocean, balance between the stress and the Coriolis force enables strong upwelling due to Ekman transport. This upwelling brings colder waters

  9. Applications of SMAP data to retrieval of ocean surface wind and salinity

    Science.gov (United States)

    Yueh, Simon; Fore, Alexander; Tang, Wenqing; Hayashi, Akiko; Stiles, Bryan; Zhang, Fuqing; Weng, Yonghui; Real, Nicolas

    2016-10-01

    We have examined the L-band radiometer and radar data from NASA's Soil Moisture Active Passive (SMAP) mission for ocean research and applications. We find that the SMAP data are in excellent agreement with the geophysical model function (GMF) derived from the Aquarius data up to a wind speed of 20 ms-1. For severe wind conditions, the higher resolution data from SMAP allowed us to assess the sensitivity of L-band radiometer signals to hurricane force winds. We applied the L-band GMF to the retrieval of ocean surface wind and SSS from the SMAP data. Comparison with the European Center for Medium-Range Weather Forecasting, WindSat and RapidSCAT wind speeds suggests that SMAP's radiometer wind speed reaches an excellent accuracy of about 1.1-1.7 ms-1 below a wind speed of 20 ms-1. We have also found that the maximum wind speed derived from the SMAP radiometer data can reach 140 knots for severe storms and are generally in good agreement with the hurricane track analysis and operational aircraft Stepped Frequency Microwave Radiometer wind speeds. The spatial patterns of the SMAP SSS agree well with climatological distributions, but exhibit several unique spatial and temporal features.

  10. Comparison of Force and Moment Coefficients for the Same Test Article in Multiple Wind Tunnels

    Science.gov (United States)

    Deloach, Richard

    2013-01-01

    This paper compares the results of force and moment measurements made on the same test article and with the same balance in three transonic wind tunnels. Comparisons are made for the same combination of Reynolds number, Mach number, sideslip angle, control surface configuration, and angle of attack range. Between-tunnel force and moment differences are quantified. An analysis of variance was performed at four unique sites in the design space to assess the statistical significance of between-tunnel variation and any interaction with angle of attack. Tunnel to tunnel differences too large to attribute to random error were detected were observed for all forces and moments. In some cases these differences were independent of angle of attack and in other cases they changed with angle of attack.

  11. The role of external forcing and Pacific trade winds in recent changes of the global climate system

    Science.gov (United States)

    Friedman, Andrew; Gastineau, Guillaume; Khodri, Myriam

    2017-04-01

    The Pacific trade winds experienced an unprecedented strengthening since the mid 1990s. Several studies have proposed that the increased Pacific trade winds were associated with the reduced rate of global mean surface temperature warming in the first decade of the 21st century, as well as far-reaching atmospheric teleconnections. We designed a set of ensemble partial coupling experiments using the IPSL-CM5A-LR coupled model that allow us to cleanly distinguish the influence of Pacific trade wind variability from that of external forcing over the past few decades. In this study, we quantify the respective impacts of these processes on surface temperature, ocean heat content, and atmospheric teleconnections. We designed two ensembles of coupled simulations using partial coupling with the IPSL-CM5A-LR model to separate the Pacific internal variability and that of external radiative forcing. We prescribe surface wind stress in the tropical Pacific (20°S to 20°N) from 1979-2014 in two ensembles of 30 members each: (1) Prescribed climatological model wind stress, which allows us to estimate the influence of external radiative forcing in the absence of variability within the Pacific Ocean. (2) Wind stress anomalies from ERA-Interim reanalysis added to the model wind stress climatology, which accounts for the effects of both external radiative forcing and the wind stress variability. We find that the observed wind stress anomalies account for the pattern of eastern tropical Pacific cooling when compared to the climatology experiment, so that it resembles the observed trends from 1992-2011. The tropical Pacific shows dominant heat uptake in the western Pacific above the 20°C isotherm, which contributed to slow the warming of tropical SST during the 2000s. The trade wind increase is associated with a strengthening of the Pacific Walker circulation, and zonal shifts in tropical rainfall. Despite tropical SST biases which affect the response of tropical rainfall and the

  12. Wind flow and wind loads on the surface of a tower- shaped building: Numerical simulations and wind tunnel experiment

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Flow structure and wind pressure distribution caused by obtuse obstacles are usually the focuses in Computational Wind Engineer researches (CWE). By solving the non- hydrostatical dynamic equations, PUMA model (Peking University Model of Atmospheric Environment) was developed and applied to simulating the flow structure and wind pressure distribution around a tower-shaped building. Evaluation about the wind environment and wind loads around the building was obtained through the analysis of the numerical simulation results and wind tunnel data. Comparisons between the simulation and wind tunnel study indicate that numerical simulation results agree well in the flow field and wind pressure distribution around the tower-shaped building. On the other hand, the horizontal grid interval of 2 m and the vertical grid of 3 m were still too crude to simulate the flow structure and wind pressure distribution on the building surface more exactly in detail; and the absence of suitable pressure perturbation parameterization scheme between the solid and the adjacent space also limits the accuracy of the numerical simulation. The numerical simulation model can be used to evaluate the wind environment and wind load around high buildings.

  13. Impacts of wind farms on surface air temperatures

    Science.gov (United States)

    Baidya Roy, Somnath; Traiteur, Justin J.

    2010-01-01

    Utility-scale large wind farms are rapidly growing in size and numbers all over the world. Data from a meteorological field campaign show that such wind farms can significantly affect near-surface air temperatures. These effects result from enhanced vertical mixing due to turbulence generated by wind turbine rotors. The impacts of wind farms on local weather can be minimized by changing rotor design or by siting wind farms in regions with high natural turbulence. Using a 25-y-long climate dataset, we identified such regions in the world. Many of these regions, such as the Midwest and Great Plains in the United States, are also rich in wind resources, making them ideal candidates for low-impact wind farms. PMID:20921371

  14. A modeling approach to identify the effective forcing exerted by wind on a prealpine lake surrounded by a complex topography

    Science.gov (United States)

    Valerio, G.; Cantelli, A.; Monti, P.; Leuzzi, G.

    2017-05-01

    The representation of spatial wind distribution is recognized as a serious difficulty when modeling the hydrodynamics of lakes surrounded by a complex topography. To address this issue, we propose to force a 3-D lake model with the wind field simulated by a high-resolution atmospheric model, considering as a case study a 61 km2 prealpine lake surrounded by mountain ranges that reach 1800 m above the lake's surface, where a comprehensive data set was available in the stratified season. The improved distributed description of the wind stress over the lake surface led to a significant enhancement in the representation of the main basin-scale internal wave motions, and hence provided a reference solution to test the use of simplified approaches. Moreover, the analysis of the power exerted by the computed wind field enabled us to identify measuring stations that provide suitable wind data to be applied uniformly on the lake surface in long-term simulations. Accordingly, the proposed methodology can contribute to reducing the uncertainties associated with the definition of wind forcing for modeling purposes and can provide a rational criterion for installing representative measurement locations in prealpine lakes.

  15. Casimir force measurements from silicon carbide surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-02-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.

  16. Response of large-scale coastal basins to wind forcing: influence of topography

    NARCIS (Netherlands)

    Chen, WenLong; Roos, P.C.; Schuttelaars, H.M.; Kumar, M.; Zitman, T.J.; Hulscher, S.J.M.H.

    2016-01-01

    Because wind is one of the main forcings in storm surge, we present an idealised process-based model to study the influence of topographic variations on the frequency response of large-scale coastal basins subject to time-periodic wind forcing. Coastal basins are represented by a semi-enclosed recta

  17. Interpretation of nonlinearity in wind generated ocean surface waves

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    This study attempts to resolve a mix-up between a physical process and its mathematical interpretation in the context of wind waves on ocean surface. Wind generated wave systems, are conventionally interpreted as a result of interaction of a number...

  18. Widespread land surface wind decline in the Northern Hemisphere

    Science.gov (United States)

    Vautard, R.; Cattiaux, J.; Yiou, P.; Thépaut, J.-N.; Ciais, P.

    2010-09-01

    The decline of surface wind observed in many regions of the world is a potential source of concern for wind power electricity generation. It is also suggested as the main cause of decreasing pan evaporation. In China, a persistent and significant decrease of monsoon winds was observed in all seasons. Surface wind declines were also evidenced in several regions of the world (U.S., Australia, several European countries). Except over China, no clear explanation was given for the wind decrease in the regions studied. Whether surface winds decrease is due to changes in the global atmospheric circulation or its variability, in surface processes or to observational trends has therefore not been elucidated. The identification of the drivers of such a decline requires a global investigation of available surface and upper-air wind data, which has not been conducted so far. Here we use global datasets of in-situ wind measurements that contain surface weather stations wind data (hourly or three-hourly data acquisition time step) and rawinsonde vertical wind data profiles (monthly time step) prepared by the NCAR. A set of 822 worldwide surface stations with continuous wind records was selected after a careful elimination of stations with obvious breaks and large gaps. This dataset mostly covers the Northern mid latitudes over the period 1979-2008. Using this data set, we found that annual mean wind speeds have declined at 73% of the surface stations over the past 30 years. In the Northern Hemisphere, positive wind trends are found only in a few places. In Europe, Central Asia, Eastern Asia and in North America the annual mean surface wind speed has decreased on average at a rate of -2.9, -5.9, -4.2, and -1.8 %/decade respectively, i.e. a decrease of about 10% in 30 years and up to about 20% in Central Asia. These results are robust to changes in the station selection method and parameters. By contrast, upper-air winds observed from rawinsondes, geostrophic winds deduced from

  19. Wind influence on surface current variability in the Ibiza Channel from HF Radar

    Science.gov (United States)

    Lana, Arancha; Marmain, Julien; Fernández, Vicente; Tintoré, Joaquin; Orfila, Alejandro

    2016-04-01

    Surface current variability is investigated using 2.5 years of continuous velocity measurements from an high frequency radar (HFR) located in the Ibiza Channel (Western Mediterranean Sea). The Ibiza Channel is identified as a key geographical feature for the exchange of water masses but still poorly documented. Operational, quality controlled, HFR derived velocities are provided by the Balearic Islands Coastal Observing and Forecasting System (SOCIB). They are assessed by performing statistical comparisons with current-meter, ADCP, and surface lagrangian drifters. HFR system does not show significant bias, and its accuracy is in accordance with previous studies performed in other areas. The main surface circulation patterns are deduced from an EOF analysis. The first three modes represent almost 70 % of the total variability. A cross-correlation analysis between zonal and meridional wind components and the temporal amplitudes of the first three modes reveal that the first two modes are mainly driven by local winds, with immediate effects of wind forcing and veering following Ekman effect. The first mode (37 % of total variability) is the response of meridional wind while the second mode (24 % of total variability) is linked primarily with zonal winds. The third and higher order modes are related to mesoscale circulation features. HFR derived surface transport presents a markedly seasonal variability being mostly southwards. Its comparison with Ekman-induced transport shows that wind contribution to the total surface transport is on average around 65 %.

  20. A discrete force allocation algorithm for modelling wind turbines in computational fluid dynamics

    DEFF Research Database (Denmark)

    Réthoré, Pierre-Elouan; Sørensen, Niels N.

    2012-01-01

    This paper describes an algorithm for allocating discrete forces in computational fluid dynamics (CFD). Discrete forces are useful in wind energy CFD. They are used as an approximation of the wind turbine blades’ action on the wind (actuator disc/line), to model forests and to model turbulent......, this algorithm does not address the specific cases where discrete forces are present. The velocities and pressure exhibit some significant numerical fluctuations at the position where the body forces are applied. While this issue is limited in space, it is usually critical to accurately estimate the velocity...

  1. Global ocean wind power sensitivity to surface layer stability

    Science.gov (United States)

    Capps, Scott B.; Zender, Charles S.

    2009-05-01

    Global ocean wind power has recently been assessed (W. T. Liu et al., 2008) using scatterometry-based 10 m winds. We characterize, for the first time, wind power at 80 m (typical wind turbine hub height) above the global ocean surface, and account for the effects of surface layer stability. Accounting for realistic turbine height and atmospheric stability increases mean global ocean wind power by +58% and -4%, respectively. Our best estimate of mean global ocean wind power is 731 W m-2, about 50% greater than the 487 W m-2 based on previous methods. 80 m wind power is 1.2-1.5 times 10 m power equatorward of 30° latitude, between 1.4 and 1.7 times 10 m power in wintertime storm track regions and >6 times 10 m power in stable regimes east of continents. These results are relatively insensitive to methodology as wind power calculated using a fitted Weibull probability density function is within 10% of power calculated from discrete wind speed measurements over most of the global oceans.

  2. Altering Kinetic Energy Entrainment in Large Eddy Simulations of Large Wind Farms Using Unconventional Wind Turbine Actuator Forcing

    Directory of Open Access Journals (Sweden)

    Claire VerHulst

    2015-01-01

    Full Text Available In this study, horizontally periodic large eddy simulations (LES are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt to increase power generation by enhancing the mean kinetic energy (MKE entrainment to the wind turbines, hypothetical synthetic forcing is applied to the flow at the turbine rotor locations. The synthetic forcing is not meant to represent any existing devices or control schemes, but rather acts as a proof of concept to inform future designs. The turbines are modeled using traditional actuator disks, and the unconventional synthetic forcing is applied in the vertical direction with the magnitude and direction dependent on the instantaneous velocity fluctuation at the rotor disk; in one set of LES meant to enhance the vertical entrainment of MKE, a downward force is prescribed in conjunction with a positive axial velocity fluctuation, whereas a negative axial velocity fluctuation results in an upward force. The magnitude of the forcing is proportional to the instantaneous thrust force with prefactors ranging from 0.1 to 1. The synthetic vertical forcing is found to have a significant effect on the power generated by the wind farm. Consistent with previous findings, the MKE flux to the level of the turbines is found to vary along with the total power produced by the wind turbine array. The reverse strategy of downward forcing of slow axial velocity flow is found to have almost no effect on the power output or entrainment. Several of the scenarios tested, e.g., where the vertical force is of similar magnitude to the horizontal thrust, would be very difficult to implement in practice, but the simulations serve the purpose of identifying trends and bounds on possible power increases from flow modifications through action at the turbine rotor.

  3. OW ASCAT Ocean Surface Winds - 2-Day Composites

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Advanced Scatterometer (ASCAT) sensor onboard the EUMETSAT MetOp polar-orbiting satellite provides ocean surface wind observations by means of radar...

  4. Effect of film slicks on near-surface wind

    Science.gov (United States)

    Charnotskii, Mikhail; Ermakov, Stanislav; Ostrovsky, Lev; Shomina, Olga

    2016-09-01

    The transient effects of horizontal variation of sea-surface wave roughness due to surfactant films on near-surface turbulent wind are studied theoretically and experimentally. Here we suggest two practical schemes for calculating variations of wind velocity profiles near the water surface, the average short-wave roughness of which is varying in space and time when a film slick is present. The schemes are based on a generalized two-layer model of turbulent air flow over a rough surface and on the solution of the continuous model involving the equation for turbulent kinetic energy of the air flow. Wave tank studies of wind flow over wind waves in the presence of film slicks are described and compared with theory.

  5. Wind Forcing Experiments in the California Current System.

    Science.gov (United States)

    boundary on which either free-slip or zero-slip boundary conditions are imposed. Time-invariant winds, either with or without a component of wind stress curl...deeper and wider than the observed jet. Finally, the inclusion of wind stress curl and the zero-slip boundary condition are demonstrated to be important elements in model simulations of the coastal jet.

  6. Wind Characteristics of Coastal and Inland Surface Flows

    Science.gov (United States)

    Subramanian, Chelakara; Lazarus, Steven; Jin, Tetsuya

    2015-11-01

    Lidar measurements of the winds in the surface layer (up to 80 m) inland and near the beach are studied to better characterize the velocity profile and the effect of roughness. Mean and root-mean-squared profiles of horizontal and vertical wind components are analyzed. The effects of variable time (18, 60 and 600 seconds) averaging on the above profiles are discussed. The validity of common surface layer wind profile models to estimate skin friction drag is assessed in light of these measurements. Other turbulence statistics such as auto- and cross- correlations in spatial and temporal domains are also presented. The help of FIT DMES field measurement crew is acknowledged.

  7. Response of an ocean general circulation model to wind and thermodynamic forcings

    Indian Academy of Sciences (India)

    A Chakraborty; H C Upadhyaya; O P Sharma

    2000-09-01

    The stretched-coordinate ocean general circulation model has been designed to study the observed variability due to wind and thermodynamic forcings. The model domain extends from 60°N to 60°S and cyclically continuous in the longitudinal direction. The horizontal resolution is 5° × 5° and 9 discrete vertical levels. First a spin-up experiment has been done with ECMWF-AMIP 1979 January mean fields. The wind stress, ambient atmospheric temperature, evaporation and precipitation have been used in order to derive mechanical and thermodynamical surface forcings. Next, the experiment has been extended for another 30 years (3 cycles each of 10 year period) with varying surface boundary conditions (from January 1979 to December 1988 of ECMWF-AMIP monthly fields for each cycle) along with 120 years extended spin-up control run's results as initial conditions. The results presented here are for the last 10 years simulations. The preliminary results of this experiment show that the model is capable of simulating some of the general features and the pattern of interannual variability of the ocean.

  8. Characterizing Tropospheric Winds by Combining MISR Cloud-Track and QuikSCAT Surface Wind Vectors

    Science.gov (United States)

    Davies, R.; Garay, M. J.; Moroney, C. M.; Liu, W. T.

    2007-12-01

    Numerous studies have found that the inclusion of wind observations results in a significantly greater improvement in operational weather forecasts compared to the addition of temperature or pressure observations alone. However, global tropospheric wind measurements are only available from 12-hourly rawinsonde launches from selected locations, primarily over land. For years the world's oceans were "data voids" in terms of wind measurements. Only recently have satellites begun to fill this gap. The SeaWinds scatterometer on the QuikSCAT satellite obtains winds referenced to 10 meters above the surface over the global oceans under nearly all weather conditions. The wind speed and direction data from QuikSCAT have been extensively tested against surface observations and are of such quality that these data are routinely assimilated into numerical weather prediction models run by both the National Center for Environmental Prediction (NCEP) and the European Centre for Medium Range Weather Forecasting (ECMWF). However, scatterometer data only provide wind information near the ocean surface. This information can be complemented with satellite cloud-track winds that provide information about winds in the free troposphere over the ocean, as well as over land, where scatterometer data are not available. In particular, the height resolved cloud motion vectors from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on the NASA EOS Terra satellite yield wind speeds for clouds at altitudes less than approximately 2.5 km that are shown to compare favorably with the QuikSCAT winds globally. In addition, the direction of the MISR winds is similar to the QuikSCAT wind vectors when compared on the same basis. The synergistic use of these two sets of wind observations has the potential to make possible a variety of new studies: from improved forecast and climate model validation; to increased understanding of tropospheric water vapor transport; to observations of the coupling

  9. Ocean Surface Wind Speed of Hurricane Helene Observed by SAR

    DEFF Research Database (Denmark)

    Xu, Qing; Cheng, Yongcun; Li, Xiaofeng

    2011-01-01

    The hurricanes can be detected by many remote sensors, but synthetic aperture radar (SAR) can yield high-resolution (sub-kilometer) and low-level wind information that cannot be seen below the cloud by other sensors. In this paper, an assessment of SAR capability of monitoring high-resolution hur......The hurricanes can be detected by many remote sensors, but synthetic aperture radar (SAR) can yield high-resolution (sub-kilometer) and low-level wind information that cannot be seen below the cloud by other sensors. In this paper, an assessment of SAR capability of monitoring high......-resolution hurricane was conducted. A case study was carried out to retrieve ocean surface wind field from C-band RADARSAT-1 SAR image which captured the structure of hurricane Helene over the Atlantic Ocean on 20 September, 2006. With wind direction from the outputs of U.S. Navy Operational Global Atmospheric...... CIWRAP models have been tested to extract wind speed from SAR data. The SAR retrieved ocean surface winds were compared to the aircraft wind speed observations from stepped frequency microwave radiometer (SFMR). The results show the capability of hurricane wind monitoring by SAR....

  10. Influence of the Coriolis force on the structure and evolution of wind turbine wakes

    Science.gov (United States)

    Abkar, Mahdi; Porté-Agel, Fernando

    2016-10-01

    In this study, large-eddy simulation combined with a turbine model is used to investigate the effect of vertical wind veer associated with the Coriolis force on the structure and evolution of wind turbine wakes. In order to isolate the Coriolis effect on the wake, two cases are considered. In the first case, atmospheric boundary-layer flow is driven by a geostrophic wind, including the effect of Earth's rotation and the Coriolis force. In the second case, the boundary-layer flow is unidirectional and is forced by an imposed pressure gradient. Both cases have the same mean horizontal velocity and turbulence intensity at the hub height. The simulation results show that the Coriolis force significantly affects the aerodynamics of the wake including the mean velocity deficit, turbulence statistics, and wake-meandering characteristics downwind of the turbine. In particular, when the flow is forced by a geostrophic wind, vertical wind veer causes a skewed spatial structure in the wake. Moreover, the presence of lateral wind shear, in addition to the vertical one, enhances the shear production of turbulent kinetic energy and the turbulent momentum flux. This leads to a larger flow entrainment and, thus, a faster wake recovery compared to the case forced by unidirectional pressure gradient. Consistent with this result, wake meandering is also stronger in both lateral and vertical directions in the case of geostrophic forcing compared to the case with pressure-gradient forcing.

  11. Casimir forces from conductive silicon carbide surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-05-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.

  12. Surface impedance and the Casimir force

    CERN Document Server

    Bezerra, V B; Romero, C

    2002-01-01

    The impedance boundary condition is used to calculate the Casimir force in configurations of two parallel plates and a shpere (spherical lens) above a plate at both zero and nonzero temperature. The impedance approach allows one to find the Casimir force between the realistic test bodies regardless of the electromagnetic fluctuations inside the media. Although this approach is an approximate one, it has wider areas of application than the Lifshitz theory of the Casimir force. The general formulas of the impedance approach to the theory of the Casimir force are given and the formal substitution is found for connecting it with the Lifshitz formula. The range of micrometer separations between the test bodies which is interesting from the experimental point of view is investigated in detail. It is shown that at zero temperature the results obtained on the basis of the surface impedance method are in agreement with those obtained in framework of the Lifshitz theory within a fraction of a percent. The temperature c...

  13. Weather Research and Forecasting Model Wind Sensitivity Study at Edwards Air Force Base, CA

    Science.gov (United States)

    Watson, Leela R.; Bauman, William H., III; Hoeth, Brian

    2009-01-01

    This abstract describes work that will be done by the Applied Meteorology Unit (AMU) in assessing the success of different model configurations in predicting "wind cycling" cases at Edwards Air Force Base, CA (EAFB), in which the wind speeds and directions oscillate among towers near the EAFB runway. The Weather Research and Forecasting (WRF) model allows users to choose among two dynamical cores - the Advanced Research WRF (ARW) and the Non-hydrostatic Mesoscale Model (NMM). There are also data assimilation analysis packages available for the initialization of the WRF model - the Local Analysis and Prediction System (LAPS) and the Advanced Regional Prediction System (ARPS) Data Analysis System (ADAS). Having a series of initialization options and WRF cores, as well as many options within each core, creates challenges for local forecasters, such as determining which configuration options are best to address specific forecast concerns. The goal of this project is to assess the different configurations available and determine which configuration will best predict surface wind speed and direction at EAFB.

  14. Preparation of stable silica surfaces for surface forces measurement

    Science.gov (United States)

    Ren, Huai-Yin; Mizukami, Masashi; Kurihara, Kazue

    2017-09-01

    A surface forces apparatus (SFA) measures the forces between two surfaces as a function of the surface separation distance. It is regarded as an essential tool for studying the interactions between two surfaces. However, sample surfaces used for the conventional SFA measurements have been mostly limited to thin (ca. 2-3 μm) micas, which are coated with silver layers (ca. 50 nm) on their back, due to the requirement of the distance determination by transmission mode optical interferometry called FECO (fringes of equal chromatic order). The FECO method has the advantage of determining the absolute distance, so it should be important to increase the availability of samples other than mica, which is chemically nonreactive and also requires significant efforts for cleaving. Recently, silica sheets have been occasionally used in place of mica, which increases the possibility of surface modification. However, in this case, the silver layer side of the sheet is glued on a cylindrical quartz disc using epoxy resin, which is not stable in organic solvents and can be easily swollen or dissolved. The preparation of substrates more stable under severe conditions, such as in organic solvents, is necessary for extending application of the measurement. In this study, we report an easy method for preparing stable silica layers of ca. 2 μm in thickness deposited on gold layers (41 nm)/silica discs by sputtering, then annealed to enhance the stability. The obtained silica layers were stable and showed no swelling in organic solvents such as ethanol and toluene.

  15. Forced wetting of a reactive surface.

    Science.gov (United States)

    Blake, T D

    2012-11-01

    The dynamic wetting of water on gelatin-coated poly(ethylene terephthalate) (GC-PET) has been investigated by forced wetting over a wide speed range and compared with earlier data obtained with unmodified PET. The results were analysed according to the molecular-kinetic theory of dynamic wetting (MKT). Both substrates show complex behaviour, with separate low- and high-speed modes. For the GC-PET, this is attributed to a rapid change in the wettability of the substrate on contact with water, specifically a surface molecular transformation from hydrophobic to hydrophilic. This results in a smooth wetting transition from one mode to the other. For the PET, the bimodal behaviour is attributed to surface heterogeneity, with the low-speed dynamics dominated by interactions with polar sites on the substrate that become masked at higher speeds. In this case, the transition is discontinuous. The study has general ramifications for the investigation of any wetting processes in which a physicochemical transformation takes place at the solid surface on contact with the liquid. In particular, it shows how forced wetting, combined with the MKT, can reveal subtle details of the processes involved. It is unlikely that similar insight could be gained from spontaneous wetting studies, such as spreading drops.

  16. The Character of the Solar Wind, Surface Interactions, and Water

    Science.gov (United States)

    Farrell, William M.

    2011-01-01

    We discuss the key characteristics of the proton-rich solar wind and describe how it may interact with the lunar surface. We suggest that solar wind can be both a source and loss of water/OH related volatiles, and review models showing both possibilities. Energy from the Sun in the form of radiation and solar wind plasma are in constant interaction with the lunar surface. As such, there is a solar-lunar energy connection, where solar energy and matter are continually bombarding the lunar surface, acting at the largest scale to erode the surface at 0.2 Angstroms per year via ion sputtering [1]. Figure 1 illustrates this dynamically Sun-Moon system.

  17. Surface Currents and Winds at the Delaware Bay Mouth

    Energy Technology Data Exchange (ETDEWEB)

    Muscarella, P A; Barton, N P; Lipphardt, B L; Veron, D E; Wong, K C; Kirwan, A D

    2011-04-06

    Knowledge of the circulation of estuaries and adjacent shelf waters has relied on hydrographic measurements, moorings, and local wind observations usually removed from the region of interest. Although these observations are certainly sufficient to identify major characteristics, they lack both spatial resolution and temporal coverage. High resolution synoptic observations are required to identify important coastal processes at smaller scales. Long observation periods are needed to properly sample low-frequency processes that may also be important. The introduction of high-frequency (HF) radar measurements and regional wind models for coastal studies is changing this situation. Here we analyze synoptic, high-resolution surface winds and currents in the Delaware Bay mouth over an eight-month period (October 2007 through May 2008). The surface currents were measured by two high-frequency radars while the surface winds were extracted from a data-assimilating regional wind model. To illustrate the utility of these monitoring tools we focus on two 45-day periods which previously were shown to present contrasting pictures of the circulation. One, the low-outflow period is from 1 October through 14 November 2007; the other is the high-outflow period from 3 March through 16 April 2008. The large-scale characteristics noted by previous workers are clearly corroborated. Specifically the M2 tide dominates the surface currents, and the Delaware Bay outflow plume is clearly evident in the low frequency currents. Several new aspects of the surface circulation were also identified. These include a map of the spatial variability of the M2 tide (validating an earlier model study), persistent low-frequency cross-mouth flow, and a rapid response of the surface currents to a changing wind field. However, strong wind episodes did not persist long enough to set up a sustained Ekman response.

  18. Assessment of Wind Turbine Structural Integrity using Response Surface Methodology

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Svenningsen, Lasse; Moser, Wolfgang

    2016-01-01

    Highlights •A new approach to assessment of site specific wind turbine loads is proposed. •The approach can be applied in both fatigue and ultimate limit state. •Two different response surface methodologies have been investigated. •The model uncertainty introduced by the response surfaces is dete...

  19. Dominant patterns of winter Arctic surface wind variability

    Institute of Scientific and Technical Information of China (English)

    WU Bingyi; John Walsh; LIU Jiping; ZHANG Xiangdong

    2014-01-01

    Dominant statistical patterns of winter Arctic surface wind (WASW) variability and their impacts on Arctic sea ice motion are investigated using the complex vector empirical orthogonal function (CVEOF) method. The results indicate that the leading CVEOF of Arctic surface wind variability, which accounts for 33% of the covariance, is characterized by two different and alternating spatial patterns (WASWP1 and WASWP2). Both WASWP1 and WASWP2 show strong interannual and decadal variations, superposed on their declining trends over past decades. Atmospheric circulation anomalies associated with WASWP1 and WASWP2 exhibit, respectively, equivalent barotropic and some baroclinic characteristics, differing from the Arctic dipole anomaly and the seesaw structure anomaly between the Barents Sea and the Beaufort Sea. On decadal time scales, the decline trend of WASWP2 can be attributed to persistent warming of sea surface temperature in the Greenland—Barents—Kara seas from autumn to winter, relfecting the effect of the Arctic warming. The second CVEOF, which accounts for 18% of the covariance, also contains two different spatial patterns (WASWP3 and WASWP4). Their time evolutions are signiifcantly correlated with the North Atlantic Oscillation (NAO) index and the central Arctic Pattern, respectively, measured by the leading EOF of winter sea level pressure (SLP) north of 70°N. Thus, winter anomalous surface wind pattern associated with the NAO is not the most important surface wind pattern. WASWP3 and WASWP4 primarily relfect natural variability of winter surface wind and neither exhibits an apparent trend that differs from WASWP1 or WASWP2. These dominant surface wind patterns strongly inlfuence Arctic sea ice motion and sea ice exchange between the western and eastern Arctic. Furthermore, the Fram Strait sea ice volume lfux is only signiifcantly correlated with WASWP3. The results demonstrate that surface and geostrophic winds are not interchangeable in terms of

  20. Self-Similar Force-Free Wind From an Accretion Disk

    CERN Document Server

    Narayan, R; Farmer, A J; Narayan, Ramesh; Kinney, Jonathan C. Mc; Farmer, Alison J.

    2006-01-01

    We consider a self-similar force-free wind flowing out of an infinitely thin disk located in the equatorial plane. On the disk plane, we assume that the magnetic stream function $P$ scales as $P\\propto R^\

  1. United States Air Force Academy (USAFA) Vertical Axis Wind Turbine.

    Science.gov (United States)

    1980-09-01

    Laboratories (Reference 9) resulted in the conclusion that a two-bucket Savonius -type arrangement with gaps at the rotating shaft was most efficient...and at some orientations of the Savonius buckets, the actual static torque produced may be as much as 35 percent less than above. Thus, a wind gust to...from the Savonius starting turbine alone. -63- SECTION VII CONCLUSIONS AND RECOMIENDATIONS 1. CONCLUSIONS One objective of the USAF Academy Wind

  2. The Dynamic Stiffness of Surface Footings for Offshore Wind Turbines

    DEFF Research Database (Denmark)

    Vahdatirad, Mohammadjavad; Andersen, Lars; Clausen, Johan;

    2011-01-01

    This study concerns the dynamic stiffness of foundations for large offshore wind turbines. Especially, the purpose of the analysis is to quantify the uncertainties related to the first natural frequency of a turbine supported by a surface footing on layered soil. The dynamic properties...... due to sediment transportation. Further, the stiffness and density of the materials within a single layer is subject to uncertainties. This leads to uncertainties of the dynamic stiffness of the foundation and therefore the natural frequencies. The aim of the study is to quantify the level...... of uncertainties and discuss the utilization of reliability-based design of surface footings for wind turbines....

  3. THE IMPACT OF INITIAL FORCED WIND ON THE PREDICTABILITY OF THE ZEBIAK-CANE COUPLED OCEAN-ATMOSPHERE MODEL

    Institute of Scientific and Technical Information of China (English)

    YUE Cai-jun; LU Wei-song; LI Qing-quan

    2006-01-01

    With simultaneous observed sea surface temperature anomaly (SSTA), the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly (NCEPWSA) and FSU wind stress anomaly (FSUWSA) is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model (ZC coupled model) with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows.The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA.Particularly, it succeeded in predicting 1997/1998 El Ni(n)o 6 to 8 months ahead; further analysis shows that on the antecedent and onset stages of the 1997/1998 El Ni(n)o event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.

  4. An assessment of wind forcing impact on a spectral wave model for the Indian Ocean

    Indian Academy of Sciences (India)

    P G Remya; Raj Kumar; Sujit Basu

    2014-07-01

    The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with in-situ observations and satellite altimeter data. This study also evaluated the performance of the wind products during local phenomenon like sea breeze, since it has a significant impact on the wave prediction in the Indian coastal region. Hence we explored the possibility of studying the impact of diurnal variation of winds on coastal waves using different wind fields. An analysis of the model performance has also been made during high wind conditions with the inference that blended winds generate more realistic wave fields in the high wind conditions and are able to produce the growth and decay of waves more realistically.

  5. Effects of surface wind speed decline on hydrology in China

    Science.gov (United States)

    Liu, X.; Zhang, X.; Tang, Q.; Zhang, X.

    2013-12-01

    Surface wind speed decline in China has been widely reported, but its effects on hydrology have not been fully evaluated to date. In this study, we evaluate the effects of wind speed decline on hydrology in China during 1966-2011 by using the Variable Infiltration Capacity (VIC) hydrological model. Two model experiments, i.e. VIC simulations with the observed (EXP1) and detrended wind speed (EXP2), are performed in the major river basins in China. The differences between the two experiments are analyzed to assess the effects of wind speed decline on hydrology. Results show that wind speed has decreased by 29% of its mean in China, even by 80% for some areas in the northern China. The wind speed decline have resulted in a decrease of evapotranspiration by 1-3% of mean annual evapotranspiration and an increase of runoff by 1-6% of mean annual runoff at most basins in China. The effect of wind speed on runoff and soil moisture is large in the northern basins where small change in hydrological conditions would have significant implications for water management. In addition, Wind speed decline has offset the expansion of the drought area in China. It has contributed to a reduction of drought areas by 21%, 17%, 15% and 12% for the mean drought area in the Songhuajiang River, Hai River, Liao River and Yellow River basins, respectively, and by 8.8% of the mean drought area over China. The effect of wind speed decline on soil moisture drought is large in most basins in China expect for the Southwest and Pearl River basins.

  6. Observation and numerical experiments for drag coefficient under typhoon wind forcing

    Science.gov (United States)

    Cao, Huiqiu; Zhou, Liangming; Li, Shuiqing; Wang, Zhifeng

    2017-02-01

    This paper presents a study on drag coefficients under typhoon wind forcing based on observations and numerical experiments. The friction velocity and wind speed are measured at a marine observation platform in the South China Sea. Three typhoons: SOULIK (2013), TRAMI (2013) and FITOW (2013) are observed at a buoy station in the northeast sea area of Pingtan Island. A new parameterization is formulated for the wind drag coefficient as a function of wind speed. It is found that the drag coefficient ( C d ) increases linearly with the slope of 0.083×10-3 for wind speed less than 24 m s-1. To investigate the drag coefficient under higher wind conditions, three numerical experiments are implemented for these three typhoons using SWAN wave model. The wind input data are objective reanalysis datasets, which are assimilated with many sources and provided every six hours with the resolution of 0.125°×0.125°. The numerical simulation results show a good agreement with wave observation data under typhoon wind forcing. The results indicate that the drag coefficient levels off with the linear slope of 0.012×10-3 for higher wind speeds (less than 34 m s-1) and the new parameterization improvese the simulation accuracy compared with the Wu (1982) default used in SWAN.

  7. Optimal smoothing length scale for actuator line models of wind turbine blades based on Gaussian body force distribution: Wind energy, actuator line model

    Energy Technology Data Exchange (ETDEWEB)

    Martínez-Tossas, L. A. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore 21218 MD USA; Churchfield, M. J. [National Renewable Energy Laboratory, Golden 80401 CO USA; Meneveau, C. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore 21218 MD USA

    2017-01-20

    The actuator line model (ALM) is a commonly used method to represent lifting surfaces such as wind turbine blades within large-eddy simulations (LES). In the ALM, the lift and drag forces are replaced by an imposed body force that is typically smoothed over several grid points using a Gaussian kernel with some prescribed smoothing width e. To date, the choice of e has most often been based on numerical considerations related to the grid spacing used in LES. However, especially for finely resolved LES with grid spacings on the order of or smaller than the chord length of the blade, the best choice of e is not known. In this work, a theoretical approach is followed to determine the most suitable value of e, based on an analytical solution to the linearized inviscid flow response to a Gaussian force. We find that the optimal smoothing width eopt is on the order of 14%-25% of the chord length of the blade, and the center of force is located at about 13%-26% downstream of the leading edge of the blade for the cases considered. These optimal values do not depend on angle of attack and depend only weakly on the type of lifting surface. It is then shown that an even more realistic velocity field can be induced by a 2-D elliptical Gaussian lift-force kernel. Some results are also provided regarding drag force representation.

  8. Low-Frequency Rotation of Surface Winds over Canada

    Directory of Open Access Journals (Sweden)

    Richard B. Richardson

    2012-10-01

    Full Text Available Hourly surface observations from the Canadian Weather Energy and Engineering Dataset were analyzed with respect to long-term wind direction drift or rotation. Most of the Canadian landmass, including the High Arctic, exhibits a spatially consistent and remarkably steady anticyclonic rotation of wind direction. The period of anticyclonic rotation recorded at 144 out of 149 Canadian meteostations directly correlated with latitude and ranged from 7 days at Medicine Hat (50°N, 110°W to 25 days at Resolute (75°N, 95°W. Only five locations in the vicinity of the Rocky Mountains and Pacific Coast were found to obey a “negative” (i.e., cyclonic rotation. The observed anticyclonic rotation appears to be a deterministic, virtually ubiquitous, and highly persistent feature of continental surface wind. These findings are directly applicable to probabilistic assessments of airborne pollutants.

  9. Analysis of Disturbance Source Inducing by The Variable Speed Wind Turbine System Forced Power Oscillations

    DEFF Research Database (Denmark)

    Tan, Jin; Hu, Weihao; Wang, Xiaoru

    2015-01-01

    The main focus of forced low frequency oscillations is to analyze the disturbance source and the origin of forced oscillations. In this paper, the origin of low-frequency periodical oscillations induced by wind turbines’ mechanical power is investigated and the mechanism is studied of fluctuating...

  10. Determining Land-Surface Parameters from the ERS Wind Scatterometer

    NARCIS (Netherlands)

    Woodhouse, I.H.; Hoekman, D.H.

    2000-01-01

    The ERS-1 wind scatterometer (WSC) has a resolution cell of about 50 km but provides a high repetition rate (less than four days) and makes measurements at multiple incidence angles. In order to retrieve quantitative geophysical parameters over land surfaces using this instrument, a method is presen

  11. The Influence of Wind on HF Radar Surface Current Forecasts

    Science.gov (United States)

    2008-12-01

    9 1. Ekman , 1905 .........................................................................................9 2. McNally, Luther and...x THIS PAGE INTENTIONALLY LEFT BLANK xi LIST OF FIGURES Figure 1. Ekman Spiral. – The angle between the wind and the surface current is 45º... Paul Jessen Terry Rago Superv. Gen. Eng. Robert Wyland I also appreciate the Oceanography and Meteorology/Oceanography students

  12. Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces

    DEFF Research Database (Denmark)

    Hansson, Petra M; Claesson, Per M.; Swerin, Agne;

    2013-01-01

    by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All...... the particle coated surfaces exhibited similar friction coefficients, from which it may be concluded that the surface geometry, and not the roughness amplitude per se, influenced the measured friction. During measurements with hydrophobic surfaces, strong adhesive forces related to the formation of a bridging...... air cavity were evident from both normal force and friction force measurements. In contrast to the frictional forces between the hydrophilic surfaces, the friction coefficient for hydrophobic surfaces was found to depend on the surface structure and we believe that this dependence is related...

  13. Wind enhances differential air advection in surface snow at sub-meter scales

    Science.gov (United States)

    Drake, Stephen A.; Selker, John S.; Higgins, Chad W.

    2017-09-01

    Atmospheric pressure gradients and pressure fluctuations drive within-snow air movement that enhances gas mobility through interstitial pore space. The magnitude of this enhancement in relation to snow microstructure properties cannot be well predicted with current methods. In a set of field experiments, we injected a dilute mixture of 1 % carbon monoxide (CO) and nitrogen gas (N2) of known volume into the topmost layer of a snowpack and, using a distributed array of thin film sensors, measured plume evolution as a function of wind forcing. We found enhanced dispersion in the streamwise direction and also along low-resistance pathways in the presence of wind. These results suggest that atmospheric constituents contained in snow can be anisotropically mixed depending on the wind environment and snow structure, having implications for surface snow reaction rates and interpretation of firn and ice cores.

  14. Widespread land surface wind decline in the Northern Hemisphere partly attributed to land surface changes

    Science.gov (United States)

    Thepaut, J.; Vautard, R.; Cattiaux, J.; Yiou, P.; Ciais, P.

    2010-12-01

    The decline of surface wind observed in many regions of the world is a potential source of concern for wind power electricity generation. It is also suggested as the main cause of decreasing pan evaporation. In China, a persistent and significant decrease of monsoon winds was observed in all seasons. Surface wind declines were also evidenced in several regions of the world (U.S., Australia, several European countries). Except over China, no clear explanation was given for the wind decrease in the regions studied. Whether surface winds decrease is due to changes in the global atmospheric circulation or its variability, in surface processes or to observational trends has therefore not been elucidated. The identification of the drivers of such a decline requires a global investigation of available surface and upper-air wind data, which has not been conducted so far. Here we use global datasets of in-situ wind measurements that contain surface weather stations wind data (hourly or three-hourly data acquisition time step) and rawinsonde vertical wind data profiles (monthly time step) prepared by the NCAR. A set of 822 worldwide surface stations with continuous wind records was selected after a careful elimination of stations with obvious breaks and large gaps. This dataset mostly covers the Northern mid latitudes over the period 1979-2008. Using this data set, we found that annual mean wind speeds have declined at 73% of the surface stations over the past 30 years. In the Northern Hemisphere, positive wind trends are found only in a few places. In Europe, Central Asia, Eastern Asia and in North America the annual mean surface wind speed has decreased on average at a rate of -2.9, -5.9, -4.2, and -1.8 %/decade respectively, i.e. a decrease of about 10% in 30 years and up to about 20% in Central Asia. These results are robust to changes in the station selection method and parameters. By contrast, upper-air winds observed from rawinsondes, geostrophic winds deduced from

  15. Wind-Speed—Surface-Heat-Flux Feedback in Dust Devils

    Science.gov (United States)

    Ito, Junshi; Niino, Hiroshi

    2016-06-01

    Strong winds associated with dust devils can induce locally large heat fluxes from the surface, and resulting enhanced buoyancy may further intensify the dust devils. This positive wind—surface-heat-flux feedback is studied using a large-eddy simulation of a convective boundary layer. A comparison of the results with and without the feedback process for the same environment demonstrates the significance of the feedback process for simulated dust devils.

  16. Hydrodynamic Boundary Conditions and Dynamic Forces between Bubbles and Surfaces

    Science.gov (United States)

    Manor, Ofer; Vakarelski, Ivan U.; Tang, Xiaosong; O'Shea, Sean J.; Stevens, Geoffrey W.; Grieser, Franz; Dagastine, Raymond R.; Chan, Derek Y. C.

    2008-07-01

    Dynamic forces between a 50μm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  17. Influence of roughness on capillary forces between hydrophilic surfaces

    NARCIS (Netherlands)

    van Zwol, P. J.; Palasantzas, G.; De Hosson, J. Th. M.

    2008-01-01

    Capillary forces have been measured by atomic force microscopy in the plate-sphere setup between gold, borosilicate glass, GeSbTe, titanium, and UV-irradiated amorphous titanium-dioxide surfaces. The force measurements were performed as a function contact time and surface roughness in the range 0.2-

  18. Electrostatic forces in wind-pollination—Part 1: Measurement of the electrostatic charge on pollen

    Science.gov (United States)

    Bowker, George E.; Crenshaw, Hugh C.

    Under fair weather conditions, a weak electric field exists between negative charge induced on the surface of plants and positive charge in the air. This field is magnified around points (e.g. stigmas) and can reach values up to 3×10 6 V m -1. If wind-dispersed pollen grains are electrically charged, the electrostatic force (which is the product of the pollen's charge and the electric field at the pollen's location) could influence pollen capture. In this article, we report measurements of the electrostatic charge carried by wind-dispersed pollen grains. Pollen charge was measured using an adaptation of the Millikan oil-drop experiment for seven anemophilous plants: Acer rubrum, Cedrus atlantica, Cedrus deodara, Juniperus virginiana, Pinus taeda, Plantago lanceolata and Ulmus alata. All species had charged pollen, some were positive others negative. The distributions (number of pollen grains as a function of charge) were bipolar and roughly centered about zero although some distributions were skewed towards positive charges. Most pollen carried small amounts of charge, 0.8 fC in magnitude, on average. A few carried charges up to 40 fC. For Juniperus, pollen charges were also measured in nature and these results concurred with those found in the laboratory. For nearly all charged pollen grains, the likelihood that electrostatics influence pollen capture is evident.

  19. Blended 6-Hourly Sea Surface Wind Vectors and Wind Stress on a Global 0.25 Degree Grid (1987-2011)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Blended Global Sea Surface Winds products contain ocean surface wind vectors and wind stress on a global 0.25 degree grid, in multiple time resolutions of...

  20. Near-nadir microwave specular returns from the sea surface - Altimeter algorithms for wind and wind stress

    Science.gov (United States)

    Wu, Jin

    1992-01-01

    Two approaches have been adopted to construct altimeter wind algorithms: one is based on the mean-square sea surface slope, and the other is based on the Seasat scatterometer wind. Both types of algorithms are critically reviewed with respect to the mechanism governing near-nadir sea returns and the comparison between altimeter and buoy winds. A new algorithm is proposed; it is deduced on the basis of microwave specular reflection and is finely tuned with buoy-measured winds. On the basis of this algorithm and the formula of the wind-stress coefficient, a simple wind-stress algorithm is also proposed.

  1. Barotropic response in a lake to wind-forcing

    Directory of Open Access Journals (Sweden)

    Y. Wang

    Full Text Available We report results gained with a three-dimensional, semi-implicit, semi-spectral model of the shallow water equations on the rotating Earth that allowed one to compute the wind-induced motion in lakes. The barotropic response to unidirectional, uniform winds, Heaviside in time, is determined in a rectangular basin with constant depth, and in Lake Constance, for different values and vertical distributions of the vertical eddy viscosities. It is computationally demonstrated that both the transitory oscillating, as well as the steady state current distribution, depends strongly upon the absolute value and vertical shape of the vertical eddy viscosity. In particular, the excitation and attenuation in time of the inertial waves, the structure of the Ekman spiral, the thickness of the Ekman layer, and the exact distribution and magnitude of the upwelling and downwelling zones are all significantly affected by the eddy viscosities. Observations indicate that the eddy viscosities must be sufficiently small so that the oscillatory behaviour can be adequately modelled. Comparison of the measured current-time series at depth in one position of Lake Constance with those computed on the basis of the measured wind demonstrates fair agreement, including the rotation-induced inertial oscillation.

    Key words. Oceanography: general (limnology – Oceanography: physical (Coriolis effects; general circulation

  2. Intercomparison of Several Ocean Surface Wind Products over the Nordic Seas

    Science.gov (United States)

    Dukhovskoy, Dmitry; Bourassa, Mark

    2014-05-01

    Surface winds are one of the key parameters that control the exchange of energy between the atmosphere and oceans. Being the major source of momentum for the upper ocean, winds mainly control ocean processes and air-sea interaction especially in synoptically active regions such as the Nordic Seas (Greenland, Norwegian, Iceland, and Barents Seas). Intense formation of water masses takes place in the Nordic Seas through cooling, brine rejection, and mixing of Arctic Ocean and North Atlantic waters. Deep water produced in this region by deep convection participates in the Atlantic Meridional Overturning Circulation. Water masses formed in the Nordic Seas are also important for the maintenance of thermohaline structure of the Arctic Ocean. The Nordic Seas has always been a challenging region for Arctic Ocean modeling due to complex ocean circulation, water mass transformation, intense air-sea interaction, deep vertical convection, etc. The lack of reliable high-resolution wind products over the Polar region is another factor that has been impacting modeling of the Arctic Ocean in general and the Nordic Seas in particular. Coarse resolution atmospheric fields are often used to force the Arctic Ocean models. The major drawback of the coarse resolution wind products is their inability to resolve small- and meso-scale cyclones frequently impacting the Nordic Seas. Several gridded surface wind products derived from scatterometer wind observations have reasonably high spatial resolution to represent most of the small scale cyclones in the region. In the present model study, Cross-Calibrated Multi-Platform surface wind data (CCMP) are compared against the wind fields from traditional the NCEP/NCAR Reanalysis 2 (NCEPR), from NCEP Climate Forecast System Reanalysis (CFSR), and from the interium version (30km) of the Arctic System Reanalysis (ASR). The NCEPR is a coarse resolution product (1.9°) and still is the primary source of forcing fields for the Arctic Ocean models. The

  3. Drag Forces, Neutral Wind and Electric Conductivity Changes in the Ionospheric E Region

    CERN Document Server

    Nenovski, Petko

    2014-01-01

    The neutrals in the Earth environment are in fact free and subjected to drag forces (by ions). In this study we show that drag or friction forces in the ionosphere-thermosphere system initiate changes in the plasma flow, neutral wind, and the conductivity, as well. Ions and electrons embedded in neutral wind field of velocity u acquire drifts perpendicular both to the initial neutral wind velocity and to the ambient magnetic field producing a perpendicular electric current. This perpendicular electric current is defined by a conductivity derived previously and the polarization electric field u x B. Self-consistently, the free neutrals acquires an additional neutral velocity component perpendicular to the initial neutral wind velocity u. The Pedersen and Hall currents wane within a specific time inversely proportional to neutral-ion collision frequency. These findings are relevant to a better understanding of electric current generation, distribution and closure in weakly ionized plasmas where charged particle...

  4. Influence of surface stressing on stellar coronae and winds

    CERN Document Server

    Jardine, M; van Ballegooijen, A; Donati, J -F; Morin, J; Fares, R; Gombosi, T I

    2013-01-01

    The large-scale field of the Sun is well represented by its lowest energy (or potential) state. Recent observations, by comparison, reveal that many solar-type stars show large-scale surface magnetic fields that are highly non-potential - that is, they have been stressed above their lowest-energy state. This non-potential component of the surface field is neglected by current stellar wind models. The aim of this paper is to determine its effect on the coronal structure and wind. We use Zeeman-Doppler surface magnetograms of two stars - one with an almost potential, one with a non-potential surface field - to extrapolate a static model of the coronal structure for each star. We find that the stresses are carried almost exclusively in a band of uni-directional azimuthal field that is confined to mid-latitudes. Using this static solution as an initial state for an MHD wind model, we then find that the final state is determined primarily by the potential component of the surface magnetic field. The band of azimut...

  5. Wind tunnel experiment of drag of isolated tree models in surface boundary layer

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    For very sparse tree land individual tree was the basic element of interaction between atmosphere and the surface. Drag of isolated tree was preliminary aerodynamic index for analyzing the atmospheric boundary layer of this kind of surface. A simple pendulum method was designed and carried out in wind tunnel to measure drag of isolated tree models according to balance law of moment of force. The method was easy to conduct and with small error. The results showed that the drag and drag coefficient of isolated tree increased with decreasing of its permeability or porosity. Relationship between drag coefficient and permeability of isolated tree empirically was expressed by quadric curve.

  6. A Peak Wind Probability Forecast Tool for Kennedy Space Center and Cape Canaveral Air Force Station

    Science.gov (United States)

    Crawford, Winifred; Roeder, William

    2008-01-01

    This conference abstract describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) in east-central Florida. The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violatioas.The tool will include climatologies of the 5-minute mean end peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

  7. Fine-measuring technique and application for sea surface wind by mobile Doppler wind lidar

    Science.gov (United States)

    Liu, Zhishen; Wang, Zhangjun; Wu, Songhua; Liu, Bingyi; Li, Zhigang; Zhang, Xin; Bi, Decang; Chen, Yubao; Li, Rongzhong; Yang, Yuqiang

    2009-06-01

    The Key Laboratory of Ocean Remote Sensing of the Ministry of Education of China, Ocean University of China, has developed the first mobile Doppler wind lidar in China. As an important component of meteorological services for the Good Luck Beijing 2007 Qingdao International Regatta, the mobile Doppler wind lidar was used to measure the sea surface wind (SSW) with 100 m*100 m spatial and 10-min temporal resolution in Qingdao from 15 to 23 August 2007. We present the results from two aspects of this campaign. First, the lidar was operated in the fixed-direction mode and compared to SSW simultaneously measured by a collocated buoy. Second, we present lidar wind measurements throughout the regatta and show good agreement with the match situation of the International Regatta. In addition, we present a case study, accounting for the observation of sailboats stopped by the headwind. With considerable data accumulated, we have shown that the mobile Doppler wind lidar can indeed provide near real-time SSW in support of the sailing games. The lidar has also provided meteorological services for the 2008 Olympic sailing games from 8 to 22 August and Paralympics Sailing Games from 8 to 13 September 2008 in Qingdao.

  8. Deterministic nature of the underlying dynamics of surface wind fluctuations

    Directory of Open Access Journals (Sweden)

    R. C. Sreelekshmi

    2012-10-01

    Full Text Available Modelling the fluctuations of the Earth's surface wind has a significant role in understanding the dynamics of atmosphere besides its impact on various fields ranging from agriculture to structural engineering. Most of the studies on the modelling and prediction of wind speed and power reported in the literature are based on statistical methods or the probabilistic distribution of the wind speed data. In this paper we investigate the suitability of a deterministic model to represent the wind speed fluctuations by employing tools of nonlinear dynamics. We have carried out a detailed nonlinear time series analysis of the daily mean wind speed data measured at Thiruvananthapuram (8.483° N,76.950° E from 2000 to 2010. The results of the analysis strongly suggest that the underlying dynamics is deterministic, low-dimensional and chaotic suggesting the possibility of accurate short-term prediction. As most of the chaotic systems are confined to laboratories, this is another example of a naturally occurring time series showing chaotic behaviour.

  9. Deterministic nature of the underlying dynamics of surface wind fluctuations

    Science.gov (United States)

    Sreelekshmi, R. C.; Asokan, K.; Satheesh Kumar, K.

    2012-10-01

    Modelling the fluctuations of the Earth's surface wind has a significant role in understanding the dynamics of atmosphere besides its impact on various fields ranging from agriculture to structural engineering. Most of the studies on the modelling and prediction of wind speed and power reported in the literature are based on statistical methods or the probabilistic distribution of the wind speed data. In this paper we investigate the suitability of a deterministic model to represent the wind speed fluctuations by employing tools of nonlinear dynamics. We have carried out a detailed nonlinear time series analysis of the daily mean wind speed data measured at Thiruvananthapuram (8.483° N,76.950° E) from 2000 to 2010. The results of the analysis strongly suggest that the underlying dynamics is deterministic, low-dimensional and chaotic suggesting the possibility of accurate short-term prediction. As most of the chaotic systems are confined to laboratories, this is another example of a naturally occurring time series showing chaotic behaviour.

  10. Retrieval algorithm of sea surface wind vectors for WindSat based on a simple forward model

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yili

    2013-01-01

    WindSat/Coriolis is the first satellite-borne polarimetric microwave radiometer,which aims to improve the potential of polarimetric microwave radiometry for measuring sea surface wind vectors from space.In this paper,a wind vector retrieval algorithm based on a novel and simple forward model was developed for WindSat.The retrieval algorithm of sea surface wind speed was developed using multiple linear regression based on the simulation dataset of the novel forward model.Sea surface wind directions that minimize the difference between simulated and measured values of the third and fourth Stokes parameters were found using maximum likelihood estimation,by which a group of ambiguous wind directions was obtained.A median filter was then used to remove ambiguity of wind direction.Evaluated with sea surface wind speed and direction data from the U.S.National Data Buoy Center (NDBC),root mean square errors are 1.2 m/s and 30° for retrieved wind speed and wind direction,respectively.The evaluation results suggest that the simple forward model and the retrieval algorithm are practicable for near-real time applications,without reducing accuracy.

  11. Surface Forces on a Deforming Ellipsoid in Shear Flow

    CERN Document Server

    Kightley, E P; Evans, J A; Bortz, D M

    2016-01-01

    We present a model for computing the surface force density on a fluid ellipsoid in simple shear flow, which we derive by coupling existing models for the shape of a fluid droplet and the surface force density on a solid ellipsoid. The primary contribution of this coupling is to develop a method to compute the force acting against a plane intersecting the ellipsoid, which we call the fragmentation force. The model can be used to simulate the motion, shape, surface force density, and breakage of fluid droplets and colloidal aggregates in shear flow.

  12. Effect of thermal diffusion and electrostatic force on evolution of wind-blown sand flow

    Institute of Scientific and Technical Information of China (English)

    YUE Gao-wei; ZHENG Xiao-jing

    2007-01-01

    A theoretical model is suggested to mathematically describe the effect of thermal diffusion from a sand-bed on evolution of a wind-blown sand flow. An upward wind field is engendered by the thermal diffusion and the coupling interaction among the horizontal and upward wind flow, saltating grains, and a kind of electrostatic force exerted on the grains are considered in this theoretical model. The numerical results show that the effect of the thermal diffusion on the evolution process of wind-blown grain flow is quite obvious and very similar to the effect of the electrostatic force on the evolution. Not only the time for the entire system to reach a steady state (called the duration time), the transport rate of grains, the mass-flux profiles and the trajectory of saltating grains are affected by the thermal diffusion and the electrostatic force exerted on saltating grains,but also the wind profiles and the temperature profiles at the steady state are affected by the wind-blown sand flow.

  13. High resolution observations of the near-surface wind field over an isolated mountain and in a steep river canyon

    Directory of Open Access Journals (Sweden)

    B. W. Butler

    2014-06-01

    Full Text Available A number of numerical wind flow models have been developed for simulating wind flow at relatively fine spatial resolutions (e.g., ∼100 m; however, there are very limited observational data available for evaluating these high resolution models. This study presents high-resolution surface wind datasets collected from an isolated mountain and a steep river canyon. The wind data are presented in terms of four flow regimes: upslope, afternoon, downslope, and a synoptically-driven regime. There were notable differences in the data collected from the two terrain types. For example, wind speeds collected on the isolated mountain increased with distance upslope during upslope flow, but generally decreased with distance upslope at the river canyon site during upslope flow. Wind speed did not have a simple, consistent trend with position on the slope during the downslope regime on the isolated mountain, but generally increased with distance upslope at the river canyon site. The highest measured speeds occurred during the passage of frontal systems on the isolated mountain. Mountaintop winds were often twice as high as wind speeds measured on the surrounding plain. The highest speeds measured in the river canyon occurred during late morning hours and were from easterly downcanyon flows, presumably associated with surface pressure gradients induced by formation of a regional thermal trough to the west and high pressure to the east. Under periods of weak synoptic forcing, surface winds tended to be decoupled from large-scale flows, and under periods of strong synoptic forcing, variability in surface winds was sufficiently large due to terrain-induced mechanical effects (speed-up over ridges and decreased speeds on leeward sides of terrain obstacles that a large-scale mean flow would not be representative of surface winds at most locations on or within the terrain feature. These findings suggest that traditional operational weather model (i.e., with

  14. Experiments on waves under impulsive wind forcing in view of the Phillips (1957) theory

    Science.gov (United States)

    Shemer, Lev; Zavadsky, Andrey

    2016-11-01

    Only limited information is currently available on the initial stages of wind-waves growth from rest under sudden wind forcing; the mechanisms leading to the appearance of waves are still not well understood. In the present work, waves emerging in a small-scale laboratory facility under the action of step-like turbulent wind forcing are studied using capacitance and laser slope gauges. Measurements are performed at a number of fetches and for a range of wind velocities. Taking advantage of the fully automated experimental procedure, at least 100 independent realizations are recorded for each wind velocity at every fetch. The accumulated data sets allow calculating ensemble-averaged values of the measured parameters as a function of time elapsed from the blower activation. The accumulated results on the temporal variation of wind-wave field initially at rest allow quantitative comparison with the theory of Phillips (1957). Following Phillips, appearance of the initial detectable ripples was considered first, while the growth of short gravity waves at later times was analyzed separately. Good qualitative and partial quantitative agreement between the Phillips predictions and the measurements was obtained for both those stages of the initial wind-wave field evolution.

  15. Auto-correlation analysis of ocean surface wind vectors

    Indian Academy of Sciences (India)

    Abhijit Sarkar; Sujit Basu; A K Varma; Jignesh Kshatriya

    2002-09-01

    The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measured in situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the auto- correlation in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived products and in situ data, satellite data acquired at different time intervals should be used with appropriate `weights', rather than treating the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These temporal `weights' can potentially improve the root mean square (rms) deviation between satellite and in situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement of about 10%.

  16. Surface force measurement of ultraviolet nanoimprint lithography materials

    Science.gov (United States)

    Taniguchi, Jun; Hasegawa, Masayuki; Amemiya, Hironao; Kobayashi, Hayato

    2016-02-01

    Ultraviolet nanoimprint lithography (UV-NIL) has advantages such as room-temperature operation, high through-put, and high resolution. In the UV-NIL process, the mold needs a release coating material to prevent adhesion of the transfer resin. Usually, fluorinated silane coupling agents are used as release coating materials. To evaluate the release property, surface force analyzer equipment was used. This equipment can measure the surface forces between release-coated or noncoated mold material surfaces and UV-cured resin surfaces in the solid state. Lower surface forces were measured when a release coating was used on the mold material surface.

  17. Modeling the Circulation of Manila Bay: Assessing the Relative Magnitudes of Wind and Tide Forcing

    Directory of Open Access Journals (Sweden)

    Cesar Villanoy

    1997-12-01

    Full Text Available A two-dimensional circulation model of Manila Bay was used to determine the relative importance of wind and tide forcing. Tidal forcing was prescribed using tidal curves based on two diurnal (O1 and K1 and two semidiurnal (M2 and S2 components on both sides of the bay mouth. A slight amplitude increase towards the head of the bay was obtained, presumably due to shoaling effects. The high correlation between sea level variations at selected coastal tide stations and model results suggests the dependence on tidal forcing at the mouth. Strongest tidal velocities were found at the mouth and decreased towards the head of the bay. The wind-driven component of the flow using mean September 1995 wind forcing shows the presence of two asymmetrical, counter-rotating gyres. Comparison of wind and tidal kinetic energies indicates the dominance of the wind-driven component of the flow only in selected shallow areas adjacent to the coast.

  18. Influence of Model Simplifications Excitation Force in Surge for a Floating Foundation for Offshore Wind Turbines

    DEFF Research Database (Denmark)

    Andersen, Morten Thøtt; Hindhede, Dennis; Lauridsen, Jimmy

    2015-01-01

    , thereby, increases the difficulty in wave force determination due to limitations of the commonly used simplified methods. This paper deals with a physical model test of the hydrodynamic excitation force in surge on a fixed three-columned structure intended as a floating foundation for offshore wind......As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and...

  19. Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Osvaldo N. Oliveira

    2012-10-01

    Full Text Available The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS, it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of afs, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.

  20. Theoretical models for surface forces and adhesion and their measurement using atomic force microscopy.

    Science.gov (United States)

    Leite, Fabio L; Bueno, Carolina C; Da Róz, Alessandra L; Ziemath, Ervino C; Oliveira, Osvaldo N

    2012-10-08

    The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of afs, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.

  1. Superhydrophobic wind turbine blade surfaces obtained by a simple deposition of silica nanoparticles embedded in epoxy

    Science.gov (United States)

    Karmouch, Rachid; Ross, Guy G.

    2010-11-01

    Samples of wind turbine blade surface have been covered with a superhydrophobic coating made of silica nanoparticles embedded in commercial epoxy paint. The superhydrophobic surfaces have a water contact angle around 152°, a hysteresis less than 2° and a water drop sliding angle around 0.5°. These surfaces are water repellent so that water drops cannot remain motionless on the surface. Examination of coated and uncoated surfaces with scanning electron microscopy and atomic force microscopy, together with measurements of water contact angles, indicates that the air trapped in the cavity enhances the water repellency similarly to the lotus leaf effect. Moreover, this new coating is stable under UVC irradiation and water pouring. The production of this nanoscale coating film being simple and low cost, it can be considered as a suitable candidate for water protection of different outdoor structures.

  2. Superhydrophobic wind turbine blade surfaces obtained by a simple deposition of silica nanoparticles embedded in epoxy

    Energy Technology Data Exchange (ETDEWEB)

    Karmouch, Rachid, E-mail: karmouch@emt.inrs.ca [INRS-Centre Energie Materiaux Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada); Ross, Guy G. [INRS-Centre Energie Materiaux Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada)

    2010-11-15

    Samples of wind turbine blade surface have been covered with a superhydrophobic coating made of silica nanoparticles embedded in commercial epoxy paint. The superhydrophobic surfaces have a water contact angle around 152{sup o}, a hysteresis less than 2{sup o} and a water drop sliding angle around 0.5{sup o}. These surfaces are water repellent so that water drops cannot remain motionless on the surface. Examination of coated and uncoated surfaces with scanning electron microscopy and atomic force microscopy, together with measurements of water contact angles, indicates that the air trapped in the cavity enhances the water repellency similarly to the lotus leaf effect. Moreover, this new coating is stable under UVC irradiation and water pouring. The production of this nanoscale coating film being simple and low cost, it can be considered as a suitable candidate for water protection of different outdoor structures.

  3. On the onset of surface wind drift at short fetches as observed in a wind wave flume

    Science.gov (United States)

    Ocampo-Torres, Francisco J.; Branger, Hubert; Osuna, Pedro; Robles, Lucia

    2014-05-01

    Ocean surface drift is of great relevance to properly model wind waves and specially the early stages of surface waves development and ocean-atmosphere fluxes during incipient wind events and storms. In particular, wave models are not so accurate predicting wave behaviour at short fetches, where wind drift onset might be very important. The onset of surface drift induced by wind and waves is being studied through detailed laboratory measurements in a large wind-wave flume. Wind stress over the water surface, waves and surface drift are measured in the 40m long wind-wave tank at IRPHE, Marseille. While momentum fluxes are estimated directly through the eddy correlation method in a station about the middle of the tank, they provide reference information to the corresponding surface drift onset recorded at rather short non-dimensional fetches. At each experimental run very low wind was on (about 1m/s) for a certain period and suddenly it was constantly accelerated to reach about 13 m/s (as well as 8 and 5 m/s during different runs) in about 15 sec to as long as 600 sec. The wind was kept constant at that high speed for 2 to 10 min, and then suddenly and constantly decelerate to 0. Surface drift values were up to 0.5 cm/s for the highest wind while very distinctive shear was detected in the upper 1.5 cm. Rather linear variation of surface drift was observed with depth. Evolution of the surface drift velocity is analysed and onset behaviour is addressed with particular emphasis in accelerated winds. This work represents a RugDiSMar Project (CONACYT 155793) contribution. The support from ANUIES-ECOS M09-U01 project, CONACYT-187112 Estancia Sabática, and Institute Carnot, is greatly acknowledged.

  4. Tool for Forecasting Cool-Season Peak Winds Across Kennedy Space Center and Cape Canaveral Air Force Station

    Science.gov (United States)

    Barrett, Joe H., III; Roeder, William P.

    2010-01-01

    The expected peak wind speed for the day is an important element in the daily morning forecast for ground and space launch operations at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The 45th Weather Squadron (45 WS) must issue forecast advisories for KSC/CCAFS when they expect peak gusts for >= 25, >= 35, and >= 50 kt thresholds at any level from the surface to 300 ft. In Phase I of this task, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a cool-season (October - April) tool to help forecast the non-convective peak wind from the surface to 300 ft at KSC/CCAFS. During the warm season, these wind speeds are rarely exceeded except during convective winds or under the influence of tropical cyclones, for which other techniques are already in use. The tool used single and multiple linear regression equations to predict the peak wind from the morning sounding. The forecaster manually entered several observed sounding parameters into a Microsoft Excel graphical user interface (GUI), and then the tool displayed the forecast peak wind speed, average wind speed at the time of the peak wind, the timing of the peak wind and the probability the peak wind will meet or exceed 35, 50 and 60 kt. The 45 WS customers later dropped the requirement for >= 60 kt wind warnings. During Phase II of this task, the AMU expanded the period of record (POR) by six years to increase the number of observations used to create the forecast equations. A large number of possible predictors were evaluated from archived soundings, including inversion depth and strength, low-level wind shear, mixing height, temperature lapse rate and winds from the surface to 3000 ft. Each day in the POR was stratified in a number of ways, such as by low-level wind direction, synoptic weather pattern, precipitation and Bulk Richardson number. The most accurate Phase II equations were then selected for an independent verification. The Phase I and II forecast methods were

  5. Premier`s Task Force on NAFTA wind turbine manufacturing facility and windpower plants : final report

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-01

    The proposal for a 700 MW wind farm and associated manufacturing facility at Pincher Creek, Alberta was discussed. York WindPower and ENERCON submitted the joint proposal in the spring of 1996 and requested a financial arrangement to guarantee a sale price of 5.4 cents per kWh (escalated) over 25 years. This was later revised in February, 1997 to 350 MW, 4.9 cents per kWh (escalated) over 15 years. A Task Force was established to assess this proposal and any other prospects for development of renewables in general. The two inseparable elements of the proposed project would be a manufacturing facility which would produce approximately 400 wind turbines a year, and a 700 MW wind farm, phased in over 10 years. The size of the wind farm would be based on a calculation of the minimal annual production required for the manufacturing facility to be viable. Pincher Creek residents are supportive of renewable energy and have been promoting wind energy long before the York/ENERCON proposal. They view this project as a support for regional economic development. The Task Force was pleased that York/ENERCON is pursuing the Alberta Advantage and is considering setting up a manufacturing facility. The Task Force did not seek to make a finding with respect to the business viability of the project, instead, the Task Force concluded that the commercial test for the project should be provided by competition in the marketplace. Nevertheless, the Task Force is supportive of the project, provided it proceeds on a voluntary, market-driven basis, and there are no conflicts with the existing government policy framework. 4 tabs., 2 appendices.

  6. Impact of surface wind biases on the Antarctic sea ice concentration budget in climate models

    Science.gov (United States)

    Lecomte, O.; Goosse, H.; Fichefet, T.; Holland, P. R.; Uotila, P.; Zunz, V.; Kimura, N.

    2016-09-01

    We derive the terms in the Antarctic sea ice concentration budget from the output of three models, and compare them to observations of the same terms. Those models include two climate models from the 5th Coupled Model Intercomparison Project (CMIP5) and one ocean-sea ice coupled model with prescribed atmospheric forcing. Sea ice drift and wind fields from those models, in average over April-October 1992-2005, all exhibit large differences with the available observational or reanalysis datasets. However, the discrepancies between the two distinct ice drift products or the two wind reanalyses used here are sometimes even greater than those differences. Two major findings stand out from the analysis. Firstly, large biases in sea ice drift speed and direction in exterior sectors of the sea ice covered region tend to be systematic and consistent with those in winds. This suggests that sea ice errors in these areas are most likely wind-driven, so as errors in the simulated ice motion vectors. The systematic nature of these biases is less prominent in interior sectors, nearer the coast, where sea ice is mechanically constrained and its motion in response to the wind forcing more depending on the model rheology. Second, the intimate relationship between winds, sea ice drift and the sea ice concentration budget gives insight on ways to categorize models with regard to errors in their ice dynamics. In exterior regions, models with seemingly too weak winds and slow ice drift consistently yield a lack of ice velocity divergence and hence a wrong wintertime sea ice growth rate. In interior sectors, too slow ice drift, presumably originating from issues in the physical representation of sea ice dynamics as much as from errors in surface winds, leads to wrong timing of the late winter ice retreat. Those results illustrate that the applied methodology provides a valuable tool for prioritizing model improvements based on the ice concentration budget-ice drift biases-wind biases

  7. Capillary-force measurement on SiC surfaces

    NARCIS (Netherlands)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-01-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness similar to 4-14 nm mainly

  8. Indian Ocean surface winds from NCMRWF analysis as compared to QuikSCAT and moored buoy winds

    Indian Academy of Sciences (India)

    B N Goswami; E N Rajagopal

    2003-03-01

    The quality of the surface wind analysis at the National Centre for Medium Range Weather Forecasts (NCMRWF), New Delhi over the tropical Indian Ocean and its improvement in 2001 are examined by comparing it with in situ buoy measurements and satellite derived surface winds from NASA QuikSCAT satellite (QSCT) during 1999, 2000 and 2001. The NCMRWF surface winds su ered from easterly bias of 1.0-1.5 ms-1 in the equatorial Indian Ocean (IO) and northerly bias of 2.0-3.0 ms-1 in the south equatorial IO during 1999 and 2000 compared to QSCT winds. The amplitude of daily variability was also underestimated compared to that in QSCT. In particular, the amplitude of daily variability of NCMRWF winds in the eastern equatorial IO was only about 60% of that of QSCT during 1999 and 2000. The NCMRWF surface winds during 2001 have significantly improved with the bias of the mean analyzed winds considerably reduced everywhere bringing it to within 0.5 ms-1 of QSCT winds in the equatorial IO. The amplitude and phase of daily and intraseasonal variability are very close to that in QSCT almost everywhere during 2001. It is shown that the weakness in the surface wind analysis during 1999 and 2000 and its improvement in 2001 are related to the weakness in simulation of precipitation by the forecast model in the equatorial IO and its improvement in 2001.

  9. The effects of the accuracy of the atmospheric forcings on the prediction of the sea surface transport in coastal areas.

    Science.gov (United States)

    Cucco, Andrea; Quattrocchi, Giovanni; Satta, Andrea; Antognarelli, Fabio; della Valle, Antonio; De Biasio, Francesco; Cadau, Enrico; Zecchetto, Stefano; Umgiesser, Georg

    2015-04-01

    In the framework of the Italian flagship project RITMARE (http://www.ritmare.it/en/) an Operational Oceanography Systems (OOS hereafter) based on high resolution 3D hydrodynamic model has been developed for the Oristano Gulf (Sardinia, Italy), with the aim of making short term predictions of water currents and pollutant transport. Atmospheric data provided by the SKIRON meteorological model system (http://forecast.uoa.gr/) were used to make the predictions. In order to asses the quality of the wind field adopted to force the hydrodynamic model, a coastal wind measuring system (WMS hereafter) was developed. The WMS is composed by five three-components anemometers located along the Gulf coasts, which provide hourly and operationally wind measurements. These data are then used operationally to derive high resolution wind fields over the entire Gulf and surrounding coastal areas. The modelled wind data have been compared with the measured ones and the meteorological model accuracy estimated. A set of lagrangian buoys were deployed within the Gulf to measure the sea surface transport due to the main local wind regimes. The OOS were used to reproduce the paths followed by each lagrangian buoy using as forcing conditions both the wind fields measured by the local WMS and the predicted ones. Therefore the effects of the atmospheric forcing quality on predicting the surface hydrodynamics at coastal scale were determined.

  10. Estimation of the CO2 fluxes between the ocean and atmosphere for the hurricane wind forces using remote sensing data.

    Science.gov (United States)

    Sergeev, Daniil; Soustova, Irina; Balandina, Galina

    2017-04-01

    CO2 transfer between the hydrosphere and atmosphere in the boundary layer is an important part of the global cycle of the main greenhouse gas. Gas flux is determined by the difference of the partial pressures of the gas between the atmosphere and hydrosphere, near the border, as well as to a large extent processes involving turbulent boundary layer. The last is usually characterized by power dependence on the equivalent wind speed (10-m height). Hurricane-force winds lead to intensive wave breaking, with formation of spray in the air, and bubbles in the water. Such multiphase turbulent processes at the interface strongly intensify gas transfer. Currently, data characterizing the dependence of the gas exchange of the wind speed for the hurricane conditions demonstrate a strong variation. On the other hand there is an obvious problem of obtaining reliable data on the wind speed. Widely used reanalysis data typically underestimate wind speed, due to the low spatial and temporal resolution One of the most promising ways to measure near water wind speed is the use of the data of remote sensing. The present study used technique to obtain near water wind speed based on the processing of remote sensing of the ocean surface data obtained with C-band scattermeter of RADARSAT using geophysical model function, developed in a laboratory conditions for a wide range of wind speeds, including hurricanes (see [1]). This function binds wind speed with effective radar cross-section in cross-polarized mode. We used two different parameterizations of gas transfer velocity of the wind speed. Widely used in [2], and obtained by processing results of recent experiment in modeling winds up to hurricane on wind-wave facility [3]. The new method of calculating was tested by the example of hurricane Earl image (09.2010). Estimates showed 13-18 times excess CO2 fluxes rates in comparison with monitoring data NOAA (see. [4]). 1. Troitskaya Yu., Abramov V., Ermoshkin A., Zuikova E., Kazakov V

  11. Impact of Air Pollution on Summer Surface Winds in Xi'an

    Institute of Scientific and Technical Information of China (English)

    杨新; 董文杰; 刘芳霞

    2011-01-01

    By analysis of observation data,this paper demonstrates that pollution particles could reduce surface wind speed through blocking solar radiation to the ground.The comparation between temperature at the lowland meteorological station Xi'an and that over the nearby highland station Mt.Hun suggests that surface solar radiation at Xi'an is reduced due to the increasing anthropogenic aerosols.The reduced surface energy suppresses the atmospheric instability and convective flows,and thus the downward transfer of faster winds aloft is reduced.Consequently,wind speeds near surface are weakened.This reduction of surface winds is shown by the significant reverse trends of wind speeds over the two stations at different elevations.The aerosols' effects on winds are also manifested in the trends of radionsonde wind speed.The decreased surface winds in Xi'an have also reduced local pan evaporation.

  12. Immunogold labels: cell-surface markers in atomic force microscopy

    NARCIS (Netherlands)

    Putman, Constant A.J.; Grooth, de Bart G.; Hansma, Paul K.; Hulst, van Niek F.; Greve, Jan

    1993-01-01

    The feasibility of using immunogold labels as cell-surface markers in atomic force microscopy is shown in this paper. The atomic force microscope (AFM) was used to image the surface of immunogold-labeled human lymphocytes. The lymphocytes were isolated from whole blood and labeled by an indirect imm

  13. Surface Stability of Epitaxial Elastic Films by the Casimir Force

    Science.gov (United States)

    Zhao, Ya-Pu; Li, Wen J.

    2002-08-01

    We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical wavelength of the surface perturbation.

  14. Surface Stability of Epitaxial Elastic Films by the Casimir Force

    Institute of Scientific and Technical Information of China (English)

    赵亚溥; 李文荣

    2002-01-01

    We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical vavelength of the surface perturbation.

  15. Development of a Wind Directly Forced Heat Pump and Its Efficiency Analysis

    Directory of Open Access Journals (Sweden)

    Ching-Song Jwo

    2013-01-01

    Full Text Available The requirements of providing electric energy through the wind-forced generator to the heat pump for water cooling and hot water heating grow significantly by now. This study proposes a new technique to directly adopt the wind force to drive heat pump systems, which can effectively reduce the energy conversion losses during the processes of wind force energy converting to electric energy and electric energy converting to kinetic energy. The operation of heat pump system transfers between chiller and heat that are controlled by a four-way valve. The theoretical efficiency of the traditional method, whose heat pump is directly forced by wind, is 42.19%. The experimental results indicated average value for cool water producing efficiency of 54.38% in the outdoor temperature of 35°C and the indoor temperature of 25°C and the hot water producing efficiency of 52.25% in the outdoor temperature and the indoor temperature both of 10°C. We proposed a method which can improve the efficiency over 10% in both cooling and heating.

  16. Evanescent pressure gradient response in the upper ocean to subinertial wind stress forcing of finite wavelength

    Science.gov (United States)

    White, Warren B.; Mcnally, Gerard

    1987-01-01

    A schematic model is used to interpret field observations related to the mixed layer response to wind stress at subinertial frequencies. It is shown that subinertial density and pressure fluctuations can arise locally from the finite wavelength character of the wind stress forcing as a fundamental part of the upper ocean transient, wind-driven response on time scales of 2-10 pendulum days. Evanescent vertical motions arise which alter the density field of the pycnocline, and hence the pressure field over the entire upper ocean. It is thus found that in the real ocean driven by wind stress, a transient geostrophic response exists which can be as large or larger than the transient Eckman response.

  17. Hydrodynamic force between a sphere and a soft, elastic surface.

    Science.gov (United States)

    Kaveh, Farzaneh; Ally, Javed; Kappl, Michael; Butt, Hans-Jürgen

    2014-10-07

    The hydrodynamic drainage force between a spherical silica particle and a soft, elastic polydimethylsiloxane surface was measured using the colloidal probe technique. The experimental force curves were compared to finite element simulations and an analytical model. The hydrodynamic repulsion decreased when the particle approached the soft surface as compared to a hard substrate. In contrast, when the particle was pulled away from the surface again, the attractive hydrodynamic force was increased. The hydrodynamic attraction increased because the effective area of the narrow gap between sphere and the plane on soft surfaces is larger than on rigid ones.

  18. Wind forcing of salinity anomalies in the Denmark Strait overflow

    Directory of Open Access Journals (Sweden)

    S. Hall

    2011-06-01

    Full Text Available The overflow of dense water from the Nordic Seas to the North Atlantic through Denmark Strait is an important part of the global thermohaline circulation. The salinity of the overflow plume has been measured by an array of current meters across the continental slope off the coast of Angmagssalik, southeast Greenland since September 1998. During 2004 the salinity of the overflow plume changed dramatically, with the entire width of the array (70 km freshening between January 2004 and July 2004, with a significant negative salinity anomaly of about 0.06 in May. The event in May represents a fresh anomaly of over 3 standard deviations from the mean since recording began in 1998. We show that the OCCAM 1/12° Ocean General Circulation Model not only reproduces the 2004 freshening event (r=0.96, p<0.01, but also correlates well with salinity observations over a previous 6 year period (r=0.54, p<0.01. Consequently the physical processes causing the 2004 anomaly and prior variability in salinity are investigated using the model output. Our results reject the hypotheses that the anomaly is caused by processes occurring between the overflow sill and the moorings, or by an increase in upstream net freshwater input. Instead, we show that the 2004 salinity anomaly is caused by an increase in volume flux of low salinity water, with a potential density greater than 27.60 kg m−3, flowing towards the Denmark Strait sill in the East Greenland Current. This is caused by an increase of southward wind stress upstream of the sill at around 75° N 20° W four and a half months earlier, and an associated spin-up of the Greenland Sea Gyre.

  19. Mapping the surface adsorption forces of nanomaterials in biological systems.

    Science.gov (United States)

    Xia, Xin R; Monteiro-Riviere, Nancy A; Mathur, Sanjay; Song, Xuefeng; Xiao, Lisong; Oldenberg, Steven J; Fadeel, Bengt; Riviere, Jim E

    2011-11-22

    The biological surface adsorption index (BSAI) is a novel approach to characterize surface adsorption energy of nanomaterials that is the primary force behind nanoparticle aggregation, protein corona formation, and other complex interactions of nanomaterials within biological systems. Five quantitative nanodescriptors were obtained to represent the surface adsorption forces (hydrophobicity, hydrogen bond, polarity/polarizability, and lone-pair electrons) of the nanomaterial interaction with biological components. We have mapped the surface adsorption forces over 16 different nanomaterials. When the five-dimensional information of the nanodescriptors was reduced to two dimensions, the 16 nanomaterials were classified into distinct clusters according their surface adsorption properties. BSAI nanodescriptors are intrinsic properties of nanomaterials useful for quantitative structure-activity relationship (QSAR) model development. This is the first success in quantitative characterization of the surface adsorption forces of nanomaterials in biological conditions, which could open a quantitative avenue in predictive nanomedicine development, risk assessment, and safety evaluation of nanomaterials. © 2011 American Chemical Society

  20. Effect of Surface waves On air-sea momentum flux in high wind conditions for typhoons in the South China Sea

    Institute of Scientific and Technical Information of China (English)

    Liangming Zhou; Aifang Wang; Peifang Guo; Zhifeng Wang

    2008-01-01

    The WAVEWATCH-Ⅲ wave model is implemented in the South China Sea to investigate the air-sea momentum flux in high wind conditions during 23 passages of typhoon occurred in 2005.The wave model is driven by the reanalyzed surface winds assimilated by sevcral meteorologic data sources.The friction velocity was calculated and the relationships between different air-sea momentum param. eters were studied.The results show that the drag coefficient decreases with the wave age generally and levels off for wind speeds higher than 35 m/s under typhoon wind forcing.The spatial variations of air-sea momentum flux parameters in high wind conditions forced by typhoons are completely different from those at weak wind speeds and significantly depend on the relative position from the typhoon center.

  1. Seasonal Spatial Patterns of Surface Water Temperature, Surface Heat Fluxes and Meteorological Forcing Over Lake Geneva

    Science.gov (United States)

    Irani Rahaghi, A.; Lemmin, U.; Bouffard, D.; Riffler, M.; Wunderle, S.; Barry, D. A.

    2015-12-01

    In many lakes, surface heat flux (SHF) is the most important component controlling the lake's energy content. Accurate methods for the determination of SHF are valuable for water management, and for use in hydrological and meteorological models. Large lakes, not surprisingly, are subject to spatially and temporally varying meteorological conditions, and hence SHF. Here, we report on an investigation for estimating the SHF of a large European lake, Lake Geneva. We evaluated several bulk formulas to estimate Lake Geneva's SHF based on different data sources. A total of 64 different surface heat flux models were realized using existing representations for different heat flux components. Data sources to run the models included meteorological data (from an operational numerical weather prediction model, COSMO-2) and lake surface water temperature (LSWT, from satellite imagery). Models were calibrated at two points in the lake for which regular depth profiles of temperature are available, and which enabled computation of the total heat content variation. The latter, computed for 03.2008-12.2012, was the metric used to rank the different models. The best calibrated model was then selected to calculate the spatial distribution of SHF. Analysis of the model results shows that evaporative and convective heat fluxes are the dominant terms controlling the spatial pattern of SHF. The former is significant in all seasons while the latter plays a role only in fall and winter. Meteorological observations illustrate that wind-sheltering, and to some extent relative humidity variability, are the main reasons for the observed large-scale spatial variability. In addition, both modeling and satellite observations indicate that, on average, the eastern part of the lake is warmer than the western part, with a greater temperature contrast in spring and summer than in fall and winter whereas the SHF spatial splitting is stronger in fall and winter. This is mainly due to negative heat flux

  2. Influence of roughness on capillary forces between hydrophilic surfaces

    Science.gov (United States)

    van Zwol, P. J.; Palasantzas, G.; de Hosson, J. Th. M.

    2008-09-01

    Capillary forces have been measured by atomic force microscopy in the plate-sphere setup between gold, borosilicate glass, GeSbTe, titanium, and UV-irradiated amorphous titanium-dioxide surfaces. The force measurements were performed as a function contact time and surface roughness in the range 0.2-15nm rms and relative humidity ranging between 2% and 40%. It is found that even for the lowest attainable relative humidity (˜2%±1%) very large capillary forces are still present. The latter suggests the persistence of a nanometers-thick adsorbed water layer that acts as a capillary bridge between contacting surfaces. Moreover, we found a significantly different scaling behavior of the force with rms roughness for materials with different hydrophilicity as compared to gold-gold surfaces.

  3. Casimir forces from conductive silicon carbide surfaces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-01-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of fr

  4. Mid-latitude wind forced ocean circulation studies

    Science.gov (United States)

    Harrison, D. E.

    1981-01-01

    A simple barotropic vorticity equation model was developed to study some of the various modeling factors that affect the characteristics of strong western boundary currents like the Gulf Stream and Kuroshio. Successful prediction of sea surface temperature, both in the climatological mean and over periods as short as 1 month requires that the heating tendency, due to horizontal advection of heat by these currents, be accurately modeled. Conventional, coarse resolution ocean models do not satisfactorily reproduce the dominant features of these currents. It is concluded that it is important to understand why they do not and what must be done to do so in the future.

  5. Sea ice dynamics and the role of wind forcing over the Beaufort Sea

    Science.gov (United States)

    Petty, A.; Hutchings, J. K.; Farrell, S. L.; Richter-Menge, J.; Tschudi, M. A.

    2014-12-01

    Both the ocean circulation and overlying sea ice cover of the Beaufort and Chukchi seas have experienced significant change in recent decades. We use sea ice drift estimates from satellite feature tracking (NSIDC/CERSAT), wind forcing from atmospheric reanalysis products (NCEP-R2/ERA-I/JRA-55), and ice type information from satellite and direct ship-based observations (obtained during the Beaufort Gyre Exploration Project), to investigate the role of wind forcing and ice mechanics in driving these changes. An assessment of ice drift shows reasonable agreement across the different products, revealing interannual variability in the ice flux around the Beaufort Sea. However, clear uncertainties remain in determining the magnitude of these fluxes, especially in regions of low ice concentration. We find an increase in ice export out of the southern Beaufort Sea (into the Chukchi Sea) across all seasons. We find slight differences in the strength of the decadal (1980-2013) trends in the mean seasonal wind curl over the Beaufort Sea, although all reanalysis products indicate a strong and significant increase in anti-cyclonic winds in summer. Analysis of ice drift curl suggests increasing anti-cyclonic drift across all seasons, despite the wind curl showing a similar trend in summer only. The strongest trend in ice drift curl appears to be in autumn, however recent years have seen a strong reduction in this anti-cyclonic drift, likely due to a combination of changes in the wind forcing and sea ice state. The implication of this finding is an enhanced response of the ocean circulation to shifts in atmospheric circulation compared to that experienced prior to 2000.

  6. Features of wind field over the sea surface in the coastal area

    Science.gov (United States)

    Monzikova, A. K.; Kudryavtsev, V. N.; Myasoedov, A. G.; Chapron, B.; Zilitinkevich, S. S.

    2017-01-01

    In this paper we analyze SAR wind field features, in particular the effects of wind shadowing. These effects represent the dynamics of the internal atmospheric boundary layer, which is formed due to the transition of the air flow arriving from the rough land surface to the "smooth" water surface. In the wind-shadowed area, the flow accelerates, and a surface wind stress increases with fetch. The width of the shadow depends not only on the wind speed and atmospheric boundary layer stratification, but also on geographic features such as windflow multiple transformations over the complex surface land-Lake Chudskoe-land-Gulf of Finland. Measurements showed that, in the area of wind acceleration, the surface stress normalized by an equilibrium value (far from the coast) is a universal function of dimensionless fetch Xf/G. Surface wind stress reaches an equilibrium value at Xf/G ≈ 0.4, which is the scale of the planetary-boundary-layer relaxation.

  7. Space Weathering of the Lunar Surface by Solar Wind Particles

    Science.gov (United States)

    Kim, Sungsoo S.; Sim, Chaekyung

    2017-08-01

    The lunar regolith is space-weathered to a different degree in response to the different fluxes of incident solar wind particles and micrometeoroids. Crater walls, among other slating surfaces, are good tracers of the space-weathering process because they mature differently depending on the varying incident angles of weathering agents. We divide a crater wall into four quadrants (north, south, east, and west) and analyze the distribution of 950-nm/750-nm reflectance-ratio and 750-nm reflectance values in each wall quadrant, using the topography-corrected images by Multispectral Imager (MI) onboard SELENE (Kaguya). For thousands of impact craters across the Moon, we interpret the spectral distributions in the four wall quadrants in terms of the space weathering by solar wind particles and micrometeoroids and of gardening by meteroids. We take into account the solar-wind shielding by the Earth’s magnetotail to correctly assess the different spectral behaviors between east- and west-facing walls of the craters in the near-side of the Moon.

  8. Identification of aeroelastic forces on twin bridge cables from full-scale measurements in skew winds

    DEFF Research Database (Denmark)

    Acampora, Antonio; Macdonald, J.H.G.; Georgakis, Christos T.;

    2012-01-01

    Despite much research in recent years, large amplitude vibrations of inclined bridge cables continue to be of concern. Various mechanisms for the excitation have been suggested, including rain-wind excitation, dry inclined cable galloping, high reduced-velocity vortex shedding and excitation from...... of this paper is to identify the aeroelastic forces for in-plane and out-of-plane vibrations of bridge cables in dry conditions as in [2], but now for skewed winds. To achieve this, an output-only system identification employing the Eigenvalue Realisation Algorithm (ERA) [3] has been applied to selected...

  9. HVAC cable systems with forced water cooling for wind energy transmission

    Energy Technology Data Exchange (ETDEWEB)

    Brakelmann, Heinrich; Zhang, Dongping [Duisburg-Essen Univ., Duisburg (DE). Dept. Energy Transport and Storage (ETS)

    2008-07-01

    This paper presents a solution for an efficient wind energy transmission onshore: HVAC cable system with forced water cooling, which provides a substantial increase of the cable ampacity without any modification of the cable construction and design. This work shows the projecting and planning of such HVAC cable systems in combination with a cooling system, especially considering the faulty (n-1)-case. The efficiency utilizing the short-term load capacity of the cable systems transmitting wind energy is shown by computations provided by specialized and adapted FEM (Finite Element Method) software. (orig.)

  10. Measurements of wind friction speeds over lava surfaces and assessment of sediment transport

    Science.gov (United States)

    Greeley, Ronald; Iversen, James D.

    1987-01-01

    Wind velocity profiles were obtained over alluvial plains, lava flows, and a cinder cone in the Mojave Desert to determine the wind shear and the potential for particle transport. It was found that aerodynamic roughness for winds increases nearly a factor of 5 as flow crosses from the alluvium to the lava surface, resulting in wind shear that is 21 percent greater. Thus, wind erosion and sand flux may be substantially enhanced over the lava field. Moreover, wind flow turbulence is enhanced in the wake of the cinder cone, which also increases erosion and sediment transportation by the wind.

  11. Forced synchronization of large-scale circulation to increase predictability of surface states

    Science.gov (United States)

    Shen, Mao-Lin; Keenlyside, Noel; Selten, Frank; Wiegerinck, Wim; Duane, Gregory

    2016-04-01

    Numerical models are key tools in the projection of the future climate change. The lack of perfect initial condition and perfect knowledge of the laws of physics, as well as inherent chaotic behavior limit predictions. Conceptually, the atmospheric variables can be decomposed into a predictable component (signal) and an unpredictable component (noise). In ensemble prediction the anomaly of ensemble mean is regarded as the signal and the ensemble spread the noise. Naturally the prediction skill will be higher if the signal-to-noise ratio (SNR) is larger in the initial conditions. We run two ensemble experiments in order to explore a way to reduce the SNR of surface winds and temperature. One ensemble experiment is AGCM with prescribing sea surface temperature (SST); the other is AGCM with both prescribing SST and nudging the high-level temperature and winds to ERA-Interim. Each ensemble has 30 members. Larger SNR is expected and found over the tropical ocean in the first experiment because the tropical circulation is associated with the convection and the associated surface wind convergence as these are to a large extent driven by the SST. However, small SNR is found over high latitude ocean and land surface due to the chaotic and non-synchronized atmosphere states. In the second experiment the higher level temperature and winds are forced to be synchronized (nudged to reanalysis) and hence a larger SNR of surface winds and temperature is expected. Furthermore, different nudging coefficients are also tested in order to understand the limitation of both synchronization of large-scale circulation and the surface states. These experiments will be useful for the developing strategies to synchronize the 3-D states of atmospheric models that can be later used to build a super model.

  12. Correlation of nanoscale behaviour of forces and macroscale surface wettability.

    Science.gov (United States)

    Rana, Abhimanyu; Patra, Abhijeet; Annamalai, Meenakshi; Srivastava, Amar; Ghosh, Siddhartha; Stoerzinger, Kelsey; Lee, Yueh-Lin; Prakash, Saurav; Jueyuan, Reuben Yeo; Goohpattader, Partho S; Satyanarayana, Nalam; Gopinadhan, Kalon; Dykas, Michal M; Poddar, Kingshuk; Saha, Surajit; Sarkar, Tarapada; Kumar, Brijesh; Bhatia, Charanjit S; Giordano, Livia; Shao-Horn, Yang; Venkatesan, T

    2016-08-25

    In this manuscript, we demonstrate a method based on atomic force microscopy which enables local probing of surface wettability. The maximum pull-off force, obtained from force spectroscopy shows a remarkable correlation with the macroscopically observed water contact angle, measured over a wide variety of surfaces starting from hydrophilic, all the way through to hydrophobic ones. This relationship, consequently, facilitates the establishment of a universal behaviour. The adhesion forces scale with the polar component of surface energy. However, no such relation could be established with the dispersive component. Hence, we postulate that the force(s) which enable us to correlate the force spectroscopy data measured on the nanoscale to the macroscopic contact angle are primarily arising from electrostatic-dipole-dipole interactions at the solid-liquid interface. London forces play less of a role. This effect in is line with density functional theory (DFT) calculations suggesting a higher degree of hydroxylation of hydrophilic surfaces. This result shows that molecular simulations and measurements on an atomic scale can be extrapolated to macroscopic surface wetting problems.

  13. DISTRIBUTED EXTERNAL SURFACE HARDENING OF CAR DESIGN BY WINDING

    Directory of Open Access Journals (Sweden)

    O. V. Fomin

    2017-04-01

    Full Text Available Purpose. The paper involves coverage of features and results of the research conducted by the authors to determine the feasibility and establishment of pre-stressed-strained state of freight cars by winding in order to improve their strength characteristics. It is also necessary to present the theoretical justification for the effectiveness of the application of this method for car designs and an appropriate example for the tank-car. Methodology. The conducted study is based on an analysis of known works on the subject, mathematical justification and computer modeling. At the calculations of rolling stock components contemporary conventional techniques were used. Findings. Authors found that the winding method for pre-stressed-strained state is effective and appropriate for use in the construction of railway rolling stock and, in particular freight cars. Freight car designs with the pre-stressed-strained state are characterized by a number of strength advantages, among which there is an improvement of the work on the perception of operational loads and resource conservation. Originality. For the first time it is proposed the improvement of bearing capacity of freight car constructions through the creation of its component in the directed stress-strained state. It is also for the first time proposed the use of distributed external surface hardening by the method of winding to create a pre-stress-strained state of structural components of freight cars. The methods for winding designs of freight cars and their implementation were considered. Practical value. The studies developed a number of technical solutions for improving the design of freight cars and tank-container, which has been patented. Corresponding solutions for the tank-car are partially presented. Practical implementation of such solutions will significantly improve the technical, economic and operational performances of car designs.

  14. Some results from 50 years' research on surface forces

    Science.gov (United States)

    Derjaguin, B. V.

    1992-05-01

    A review is presented about research on surface forces and surface interactions conducted over the past half-century, with some emphasis on the pioneering contributions of the Department of Surface Phenomena at the Institute of Physical Chemistry of the USSR Academy of Sciences.

  15. Observing seasonal variations of sea surface wind speed and significant wave height using TOPEX altimetry

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    One year of ocean topography experiment (TOPEX) altimeter data are used to study the seasonal variations of global sea surface wind speed and significant wave height. The major wind and wave zones of the world oceans are precisely identified, their seasonal variability and characteristics are quantitatively analyzed, and the diversity of global wind speed seasonality and the variability of significant wave height in response to sea surface wind speed are also revealed.

  16. Retrieval of ocean surface wind stress and drag coefficient from spaceborne SAR

    Institute of Scientific and Technical Information of China (English)

    杨劲松; 黄韦艮; 周长宝

    2001-01-01

    A model for retrieval of wind stress and drag coefficient on the sea surface with the data measured by spacebome synthetic aperture radar (SAR) has been developed based on the SAR imaging mechanisms of ocean surface capillary waves and short gravity waves. This model consists of radiometric calibration, wind speed retrieval and wind stress and drag coefficient calculation. A Radarsat SAR image has been used to calculate wind stress and drag coeffi cient. Good results have been achieved.

  17. Competition between ocean carbon pumps in simulations with varying Southern Hemisphere westerly wind forcing

    Science.gov (United States)

    Huiskamp, W. N.; Meissner, K. J.; d'Orgeville, M.

    2016-06-01

    We analyse the impact of migration and strength of Southern Hemisphere westerly winds on the ocean carbon cycle in a systematic sensitivity study with the University of Victoria Earth System Climate Model. We find that changes in the biological pump are mainly driven by changes in ocean residence times while changes in export production are negligible. Changes in the biological and physical pumps are always of opposite sign; with the physical pump being dominant for southward shifts and the biological pump being dominant for northward shifts. Furthermore, changes in the Pacific Ocean carbon budget dictate the overall changes in global marine and atmospheric carbon. Overall, atmospheric hbox {CO}_2 increases (and Δ ^{14}hbox {C} decreases) for northward shifts or a strengthening in wind forcing. The opposite is true for a southward shift or a weakening in wind forcing. Combining forcings (shift and intensity change) results in a combination of their impacts with the direction of the shift being the first order forcing. The terrestrial carbon reservoir absorbs (releases) 50-70 % of the net oceanic carbon loss (increase), counterbalancing the effect on atmospheric hbox {CO}_2.

  18. Wind flow and wind loads on the surface of a tower-shaped building:Numerical simulations and wind tunnel experiment

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Flow structure and wind pressure distribution caused by obtuse obstacles are usually the focuses in Computational Wind Engineer researches (CWE). By solving the non-hydrostatical dynamic equations, PUMA model (Peking University Model of Atmospheric Environment) was developed and applied to simulating the flow structure and wind pressure distribution around a tower-shaped building. Evaluation about the wind environment and wind loads around the building was obtained through the analysis of the numerical simulation results and wind tunnel data. Comparisons between the simulation and wind tunnel study indicate that numerical simulation results agree well in the flow field and wind pressure distribution around the tower-shaped building. On the other hand, the horizontal grid interval of 2 m and the vertical grid of 3 m were still too crude to simulate the flow structure and wind pressure distribution on the building surface more exactly in detail; and the absence of suitable pressure perturbation parameterization scheme between the solid and the adjacent space also limits the accuracy of the numerical simulation. The numerical simulation model can be used to evaluate the wind environment and wind load around high buildings.

  19. Relative Contributions of Heating and Momentum Forcing to High-Latitude Lower Thermospheric Winds

    Science.gov (United States)

    Kwak, Y. S.; Richmond, A. D.

    2015-12-01

    At high latitudes the thermospheric dynamics are gov­erned by various heat and momentum sources. Recently several modeling studies have been attempt­ed to understand the physical process that control the high-latitude lower thermospheric dynamics. Kwak and Richmond [2007] and Kwak et al. [2007] studied the momentum forcing bal­ance that are mainly responsible for maintaining the high-latitude lower thermospheric wind system by using the National Center for Atmospheric Research Thermo­sphere Ionosphere Electrodynamics General Circulation Model (NCAR TIE-GCM). Kwak and Richmond [2014] analyzed the divergence and vorticity of the high-latitude neutral wind field in the lower thermosphere during the south­ern summertime. In this study, we extend previous works by Kwak and Rich­mond [2007, 2014] and Kwak et al. [2007], which helped to better understand the physical processes maintaining thermospheric dynamics at high latitudes, and here perform a "term analysis of the potential vorticity equation" for the high-latitude neu­tral wind field in the lower thermosphere, on the basis of numerical simulations using the NCAR TIE-GCM. These analyses can provide insight into the relative strength of the heating and the momentum forcing responsible for driving rotational winds at the high-latitude lower thermosphere. The heating is the net heat including the heat transfer by downward molecular and eddy heat conduction, the absorption of solar ultraviolet (UV) and extreme ultraviolet (EUV) ra­diation, auroral heating by particles, Joule dissipation of ionospheric currents, release of chemical energy by the atomic oxygen recombination, and radiative CO2, NO and O infrared emissions. The momentum forcing is associated with the viscous force and the frictional drag force from convecting ions.

  20. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    Science.gov (United States)

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  1. Exact results for Casimir forces using Surface Impedance: Nonlocal Media

    CERN Document Server

    Esquivel-Sirvent, R; Mochán, W L

    2003-01-01

    We show that exact results are obtained for the calculation of Casimir forces between arbitrary materials using the concept of surface impedances, obtaining in a trivial way the force in the limit of perfect conductors and also Lifshitz formula in the limit of semi-infinite media. As an example we present a full and rigorous calculation of the Casimir force between two metallic half-spaces described by a hydrodynamic nonlocal dielectric response.

  2. Surface forces between rough and topographically structured interfaces

    DEFF Research Database (Denmark)

    Thormann, Esben

    2017-01-01

    Within colloidal science, direct or indirect measurements of surface forces represent an important tool for developing a fundamental understanding of colloidal systems, as well as for predictions of the stability of colloidal suspensions. While the general understanding of colloidal interactions ...

  3. Scaling forces to asteroid surfaces: The role of cohesion

    CERN Document Server

    Scheeres, D J; Sanchez, P; Swift, M

    2010-01-01

    The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together b...

  4. Estimation of Near Surface Wind Speeds in Strongly Rotating Flows

    CERN Document Server

    Crowell, Sean; Wicker, Louis

    2013-01-01

    Modeling studies consistently demonstrate that the most violent winds in tornadic vortices occur in the lowest tens of meters above the surface. These velocities are unobservable by radar platforms due to line of sight consider- ations. In this work, a methodology is developed which utilizes parametric tangential velocity models derived from Doppler radar measurements, to- gether with a tangential momentum and mass continuity constraint, to esti- mate the radial and vertical velocities in a steady axisymmetric frame. The main result is that information from observations aloft can be extrapolated into the surface layer of the vortex. The impact of the amount of information available to the retrieval is demonstrated through some numerical tests with pseudo-data.

  5. Trends in significant wave height and surface wind speed in the China Seas between 1988 and 2011

    Science.gov (United States)

    Zheng, Chongwei; Zhang, Ren; Shi, Weilai; Li, Xin; Chen, Xuan

    2017-10-01

    Wind and waves are key components of the climate system as they drive air-sea interactions and influence weather systems and atmospheric circulation. In marine environments, understanding surface wind and wave fields and their evolution over time is important for conducting safe and efficient human activities, such as navigation and engineering. This study considers long-term trends in the sea surface wind speed (WS) and significant wave height (SWH) in the China Seas over the period 1988-2011 using the Cross-Calibrated Multi-Platform (CCMP) ocean surface wind product and a 24-year hindcast wave dataset obtained from the WAVEWATCH-III (WW3) wave model forced with CCMP winds. The long-term trends in WS and SWH in the China Seas are analyzed over the past 24 years to provide a reference point from which to assess future climate change and offshore wind and wave energy resource development in the region. Results demonstrate that over the period 1988-2011 in the China Seas: 1) WS and SWH showed a significant increasing trend of 3.38 cm s-1 yr-1 and 1.52 cm yr-1, respectively; 2) there were notable regional differences in the long-term trends of WS and SWH; 3) areas with strong increasing trends were located mainly in the middle of the Tsushima Strait, the northern and southern areas of the Taiwan Strait, and in nearshore regions of the northern South China Sea; and 4) the long-term trend in WS was closely associated with El Niño and a significant increase in the occurrence of gale force winds in the region.

  6. Influence of surface roughness on dispersion forces

    NARCIS (Netherlands)

    Svetovoy, V. B.; Palasantzas, G.

    Surface roughness occurs in a wide variety of processes where it is both difficult to avoid and control. When two bodies are separated by a small distance the roughness starts to play an important role in the interaction between the bodies, their adhesion, and friction. Control of this

  7. Wettability and surface forces measured by atomic force microscopy: the role of roughness

    Science.gov (United States)

    Gavoille, J.; Takadoum, J.; Martin, N.; Durand, D.

    2009-10-01

    Thin films of titanium, copper and silver with various roughnesses were prepared by physical vapour deposition technique: dc magnetron sputtering. By varying the deposition time from few minutes to one hour it was possible to obtain metallic films with surface roughness average ranging from 1 to 20 nm. The wettability of these films was studied by measuring the contact angle using the sessile drop method and surface forces were investigated using the atomic force microscopy (AFM) by measuring the pull-off force between the AFM tip and the surfaces. Experimental results have been mainly discussed in terms of metal surface reactivity, Young modulus of the materials and real surface of contact between the AFM tip and the film surfaces.

  8. Effects from fully nonlinear irregular wave forcing on the fatigue life of an offshore wind turbine and its monopile foundation

    DEFF Research Database (Denmark)

    Schløer, Signe; Bredmose, Henrik; Bingham, Harry B.;

    2013-01-01

    The effect from fully nonlinear irregular wave forcing on the fatigue life of the foundation and tower of an offshore wind turbine is investigated through aeroelastic calculations. Five representative sea states with increasing significant wave height are considered in a water depth of 40 m....... The waves are both linear and fully nonlinear irregular 2D waves. The wind turbine is the NREL 5-MW reference wind turbine. Fatigue analysis is performed in relation to analysis of the sectional forces in the tower and monopile. Impulsive excitation of the sectional force at the bottom of the tower is seen...

  9. Influence of Model Simplifications Excitation Force in Surge for a Floating Foundation for Offshore Wind Turbines

    Directory of Open Access Journals (Sweden)

    Morten Thøtt Andersen

    2015-04-01

    Full Text Available As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and, thereby, increases the difficulty in wave force determination due to limitations of the commonly used simplified methods. This paper deals with a physical model test of the hydrodynamic excitation force in surge on a fixed three-columned structure intended as a floating foundation for offshore wind turbines. The experiments were conducted in a wave basin at Aalborg University. The test results are compared with a Boundary Element Method code based on linear diffraction theory for different wave force regimes defined by the column diameter, wave heights and lengths. Furthermore, the study investigates the influence of incident wave direction and stabilizing heave-plates. The structure can be divided into primary, secondary and tertiary parts, defined by the columns, heave-plates and braces to determine the excitation force in surge. The test results are in good agreement with the numerical computation for the primary parts only, which leads to simplified determination of peak frequencies and corresponding dominant force regime.

  10. Circuit Design of Surface Acoustic Wave Based Micro Force Sensor

    Directory of Open Access Journals (Sweden)

    Yuanyuan Li

    2014-01-01

    Full Text Available Pressure sensors are commonly used in industrial production and mechanical system. However, resistance strain, piezoresistive sensor, and ceramic capacitive pressure sensors possess limitations, especially in micro force measurement. A surface acoustic wave (SAW based micro force sensor is designed in this paper, which is based on the theories of wavelet transform, SAW detection, and pierce oscillator circuits. Using lithium niobate as the basal material, a mathematical model is established to analyze the frequency, and a peripheral circuit is designed to measure the micro force. The SAW based micro force sensor is tested to show the reasonable design of detection circuit and the stability of frequency and amplitude.

  11. A constant compliance force modulation technique for scanning force microscopy (SFM) imaging of polymer surface elasticity

    Science.gov (United States)

    Stroup, E.W.; Pungor, A/

    2012-01-01

    A new method of force modulation scanning force microscopy (SFM) imaging based on a constant compliance feedback loop is presented. The feedback adjusts the loading force applied by the SFM tip to the surface in order to maintain a constant compliance beneath the tip. The new method, constant compliance force modulation (CCFM), has the advantage of being able to quantify the loading force exerted by the tip onto the sample surface and thus to estimate the elastic modulus of the material probed by the SFM tip. Once the elastic modulus of one region is known, the elastic moduli of other surface regions can be estimated from the spatial map of loading forces using the Hertz model of deformation. Force vs. displacement measurements made on one surface locality could also be used to estimate the local modulus. Several model surfaces, including a rubber-toughened epoxy polymer blend which showed clearly resolved compliant rubber phases within the harder epoxy matrix, were analyzed with the CCFM technique to illustrate the method’s application. PMID:9195751

  12. Force control is related to low-frequency oscillations in force and surface EMG.

    Directory of Open Access Journals (Sweden)

    Hwasil Moon

    Full Text Available Force variability during constant force tasks is directly related to oscillations below 0.5 Hz in force. However, it is unknown whether such oscillations exist in muscle activity. The purpose of this paper, therefore, was to determine whether oscillations below 0.5 Hz in force are evident in the activation of muscle. Fourteen young adults (21.07 ± 2.76 years, 7 women performed constant isometric force tasks at 5% and 30% MVC by abducting the left index finger. We recorded the force output from the index finger and surface EMG from the first dorsal interosseous (FDI muscle and quantified the following outcomes: 1 variability of force using the SD of force; 2 power spectrum of force below 2 Hz; 3 EMG bursts; 4 power spectrum of EMG bursts below 2 Hz; and 5 power spectrum of the interference EMG from 10-300 Hz. The SD of force increased significantly from 5 to 30% MVC and this increase was significantly related to the increase in force oscillations below 0.5 Hz (R(2 = 0.82. For both force levels, the power spectrum for force and EMG burst was similar and contained most of the power from 0-0.5 Hz. Force and EMG burst oscillations below 0.5 Hz were highly coherent (coherence = 0.68. The increase in force oscillations below 0.5 Hz from 5 to 30% MVC was related to an increase in EMG burst oscillations below 0.5 Hz (R(2 = 0.51. Finally, there was a strong association between the increase in EMG burst oscillations below 0.5 Hz and the interference EMG from 35-60 Hz (R(2 = 0.95. In conclusion, this finding demonstrates that bursting of the EMG signal contains low-frequency oscillations below 0.5 Hz, which are associated with oscillations in force below 0.5 Hz.

  13. ELECTROSTATIC FORCES IN WIND-POLLINATION: PART 1: MEASUREMENT OF THE ELECTROSTATIC CHARGE ON POLLEN

    Science.gov (United States)

    Under fair weather conditions, a weak electric field exists between negative charge induced on the surface of plants and positive charge in the air. This field is magnified around points (e.g. stigmas) and can reach values up to 3x106 V m-1. If wind-disperse...

  14. ELECTROSTATIC FORCES IN WIND-POLLINATION: PART 1: MEASUREMENT OF THE ELECTROSTATIC CHARGE ON POLLEN

    Science.gov (United States)

    Under fair weather conditions, a weak electric field exists between negative charge induced on the surface of plants and positive charge in the air. This field is magnified around points (e.g. stigmas) and can reach values up to 3x106 V m-1. If wind-disperse...

  15. Transverse Chiral Optical Forces by Locally Excited Surface Plasmon Polaritons

    CERN Document Server

    Alizadeh, M H

    2015-01-01

    Recently the new concepts of transverse spin angular momentum and Belinfante spin momentum of evanescent waves have drawn considerable attention. Here, we investigate these novel physical properties of electromagnetic fields in the context of locally excited surface plasmon polaritons. We demonstrate, both analytically and numerically, that locally excited surface plasmon polaritons possess transverse spin angular momentum and Belinfante momentum with rich and non-trivial characteristics. We also show that the transverse spin angular momentum of locally excited surface plasmon polaritons leads to the emergence of transverse chiral forces in opposite directions for chiral objects of different handedness. The magnitude of such a transverse force is comparable to the optical gradient force and scattering forces. This finding may pave the way for realization of optical separation of chiral biomolecules.

  16. Capillary-force measurement on SiC surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ˜4-14 nm mainly due to sphere morphology, the relative humidity (RH) ˜0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH˜40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.

  17. Pacific trade winds accelerated by aerosol forcing over the past two decades

    Science.gov (United States)

    Takahashi, Chiharu; Watanabe, Masahiro

    2016-08-01

    The Pacific trade winds, coupled with the zonal sea surface temperature gradient in the equatorial Pacific Ocean, control regional sea levels, and therefore their trend is a great concern in the Pacific Rim. Over the past two decades, easterly winds have been accelerated in association with eastern tropical Pacific cooling. They may represent natural interdecadal variability in the Pacific and possibly explain the recent global warming hiatus. However, the intensification of the winds has been the strongest ever observed in the past century, the reason for which is still unclear. Here we show, using multiple climate simulations for 1921-2014 by a global climate model, that approximately one-third of the trade-wind intensification for 1991-2010 can be attributed to changes in sulfate aerosols. The multidecadal sea surface temperature anomaly induced mostly by volcanic aerosols dominates in the western North Pacific, and its sign changed rapidly from negative to positive in the 1990s, coherently with Atlantic multidecadal variability. The western North Pacific warming resulted in intensification of trade winds to the west of the dateline. These trends have not contributed much to the global warming hiatus, but have greatly impacted rainfall over the western Pacific islands.

  18. Atomic force microscopy of lead iodide crystal surfaces

    Science.gov (United States)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Biao, Y.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-03-01

    Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

  19. Comparison of surface wind stress measurements - Airborne radar scatterometer versus sonic anemometer

    Science.gov (United States)

    Brucks, J. T.; Leming, T. D.; Jones, W. L.

    1980-01-01

    Sea surface wind stress measurements recorded by a sonic anemometer are correlated with airborne scatterometer measurements of ocean roughness (cross section of radar backscatter) to establish the accuracy of remotely sensed data and assist in the definition of geophysical algorithms for the scatterometer sensor aboard Seasat A. Results of this investigation are as follows: Comparison of scatterometer and sonic anemometer wind stress measurements are good for the majority of cases; however, a tendency exists for scatterometer wind stress to be somewhat high for higher wind conditions experienced in this experiment (6-9 m/s). The scatterometer wind speed algorithm tends to overcompute the higher wind speeds by approximately 0.5 m/s. This is a direct result of the scatterometer overestimate of wind stress from which wind speeds are derived. Algorithmic derivations of wind speed and direction are, in most comparisons, within accuracies defined by Seasat A scatterometer sensor specifications.

  20. Influence of Coriolis forces on the structure and evolution of wind-turbine wakes

    Science.gov (United States)

    Abkar, Mahdi; Porté-Agel, Fernando

    2015-11-01

    In this study, large-eddy simulation (LES) is combined with a turbine model to investigate the effect of Coriolis forces on the structure and evolution of wind-turbine wakes. In order to isolate the Coriolis effect on the turbulent wake flow, two set of simulations are performed. In the first set of simulations, atmospheric boundary layer (ABL) flow is driven by the geostrophic forces including the effect of Earth's rotation, while in the second case, the ABL flow is driven by a unidirectional pressure gradient forcing. Both cases have the same mean horizontal velocity and turbulence intensity at the hub height. The simulation results show that the Coriolis forces significantly affect the spatial distribution of the mean velocity deficit and turbulence statistics in the wake region. In particular, it is found that the Coriolis effect, responsible for vertical wind veer, has important lateral wake stretching effects, which in turn significantly impacts the wake recovery and wake meandering characteristics downwind of the turbines. We also apply the proper orthogonal decomposition (POD) to LES data of the wake. The results indicate a very high correlation between the most energetic modes and both maximum velocity deficit and wake meandering characteristics.

  1. Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations Part I: Surface fluxes

    Directory of Open Access Journals (Sweden)

    H. Giordani

    Full Text Available A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer

  2. Modeling noncontact atomic force microscopy resolution on corrugated surfaces

    Directory of Open Access Journals (Sweden)

    Kristen M. Burson

    2012-03-01

    Full Text Available Key developments in NC-AFM have generally involved atomically flat crystalline surfaces. However, many surfaces of technological interest are not atomically flat. We discuss the experimental difficulties in obtaining high-resolution images of rough surfaces, with amorphous SiO2 as a specific case. We develop a quasi-1-D minimal model for noncontact atomic force microscopy, based on van der Waals interactions between a spherical tip and the surface, explicitly accounting for the corrugated substrate (modeled as a sinusoid. The model results show an attenuation of the topographic contours by ~30% for tip distances within 5 Å of the surface. Results also indicate a deviation from the Hamaker force law for a sphere interacting with a flat surface.

  3. Inter-annual variability of sea surface temperature, wind speed and sea surface height anomaly over the tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Muraleedharan, P.M.; Pankajakshan, T.; Sathe, P.V.

    have made an attempt to study the annual and inter-annual variability of certain prominent processes occurring over the tropical Indian Ocean. The monthly mean values of Wind Speed (FSU), Sea Surface Temperature (REYNOLDS) and Sea Surface Height Anomaly...

  4. Dynamics of the east India coastal current. 1. Analytic solutions forced by interior Ekman pumping and local alongshore winds

    Digital Repository Service at National Institute of Oceanography (India)

    Shankar, D.; McCreary, J.P.; Han, W.; Shetye, S.R.

    OF GEOPHYSICAL RESEARCH, VOL. 101, NO. C6, PAGES 13,975-13,991, JUNE 15, 1996 Dynamics of the East India Coastal Current 1. Analytic solutions forced by interior Ekman pumping and local alongshore winds D. Snankar Centre for Mathematical Modelling... linear, continuously stratified model is used to investigate how forcing by interior Ekman pumping and local alongshore winds affects the East India Coastal Current (EICC). Solutions are found analytically to an approximate version of the equations...

  5. Sea surface wind speed estimation from space-based lidar measurements

    Directory of Open Access Journals (Sweden)

    Y. Hu

    2008-02-01

    Full Text Available Global satellite observations of lidar backscatter measurements acquired by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO mission and collocated sea surface wind speed data from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E, are used to investigate the relation between wind driven wave slope variance and sea surface wind speed. The new slope variance – wind speed relation established from this study is similar to the linear relation from Cox-Munk (1954 and the log-linear relation from Wu (1972, 1990 for wind speed larger than 7 m/s and 13.3 m/s, respectively. For wind speed less than 7 m/s, the slope variance is proportional to the square root of the wind speed, assuming a two dimensional isotropic Gaussian wave slope distribution. This slope variance – wind speed relation becomes linear if a one dimensional Gaussian wave slope distribution is assumed. Contributions from whitecaps and subsurface backscattering are effectively removed by using 532 nm lidar depolarization measurements. This new slope variance – wind speed relation is used to derive sea surface wind speed from CALIPSO single shot lidar measurements (70 m spot size, after correcting for atmospheric attenuation. The CALIPSO wind speed result agrees with the collocated AMSR-E wind speed, with 1.2 m/s rms error.

  6. Addressing Spatial Variability of Surface-Layer Wind with Long-Range WindScanners

    DEFF Research Database (Denmark)

    Berg, Jacob; Vasiljevic, Nikola; Kelly, Mark C.;

    2015-01-01

    This paper presents an analysis of mean wind measurements from a coordinated system of long-range WindScanners. From individual scan patterns the mean wind field was reconstructed over a large area, and hence it highlights the spatial variability. From comparison with sonic anemometers, the quality...

  7. Anomalous Arctic surface wind patterns and their impacts on September sea ice minima and trend

    Directory of Open Access Journals (Sweden)

    Bingyi Wu

    2012-05-01

    Full Text Available We used monthly mean surface wind data from the National Centers for Environmental Prediction/National Centers for Atmospheric Research (NCEP/NCAR reanalysis dataset during the period 1979–2010 to describe the first two patterns of Arctic surface wind variability by means of the complex vector empirical orthogonal function (CVEOF analysis. The first two patterns respectively account for 31 and 16% of its total anomalous kinetic energy. The leading pattern consists of the two subpatterns: the northern Laptev Sea (NLS pattern and the Arctic dipole (AD pattern. The second pattern contains the northern Kara Sea (NKS pattern and the central Arctic (CA pattern. Over the past two decades, the combined dynamical forcing of the first two patterns has contributed to Arctic September sea ice extent (SIE minima and its declining trend. September SIE minima are mainly associated with the negative phase of the AD pattern and the positive phase of the CA pattern during the summer (July to September season, and both phases coherently show an anomalous anticyclone over the Arctic Ocean. Wind patterns affect September SIE through their frequency and intensity. The negative trend in September SIE over the past two decades is associated with increased frequency and enhanced intensity of the CA pattern during the melting season from April to September. Thus, it cannot be simply attributed to the AD anomaly characterised by the second empirical orthogonal function mode of sea level pressure north of 70°N. The CA pattern exhibited interdecadal variability in the late 1990s, and an anomalous cyclone prevailed before 1997 and was then replaced by an anomalous anticyclone over the Arctic Ocean that is consistent with the rapid decline trend in September SIE. This paper provides an alternative way to identify the dominant patterns of climate variability and investigate their associated Arctic sea ice variability from a dynamical perspective. Indeed, this study

  8. Peak Wind Forecasts for the Launch-Critical Wind Towers on Kennedy Space Center/Cape Canaveral Air Force Station, Phase IV

    Science.gov (United States)

    Crawford, Winifred

    2011-01-01

    This final report describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The peak winds arc an important forecast clement for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to update the statistics in the current peak-wind forecast tool to assist in forecasting LCC violations. The tool includes onshore and offshore flow climatologies of the 5-minute mean and peak winds and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

  9. Fundamental Distinctions in Physics underlying Nonsteady Forcings of Wind Turbine Power vs. Drivetrain by Atmospheric Turbulence

    Science.gov (United States)

    Brasseur, James; Lavely, Adam; Nandi, Tarak

    2016-11-01

    Whereas the primary function of a wind turbine (WT) is the generation of electricity, wind farm profitability is decreased both by integrated losses in power and increases in premature failures of drivetrain components resulting from energetic nonsteady aerodynamic forcings of WT rotors by atmospheric and wake turbulence. Here we contrast the physics underlying dominant nonsteady atmospheric turbulence forcings of the bending moments in the WT rotor plane (torque/power) vs. the out-of-plane bending moments (OPBM) that underlie premature drivetrain component failure. Using an advanced actuator line model of the 5 MW NREL and the 1.5 MW GE wind turbine rotors embedded within a high-fidelity spectral LES of a typical daytime convective atmospheric boundary layer, we show that (1) the physics underlying large torque vs. OBPM fluctuations are associated with fundamentally different turbulence eddy characteristics and (2) nonsteady response centers on 4 characteristic time scales associated advection of eddies and load response of blades cutting through internal turbulence eddy structure. Supported by DOE. Computer resources by NSF/XSEDE.

  10. Pre-Test Assessment of the Use Envelope of the Normal Force of a Wind Tunnel Strain-Gage Balance

    Science.gov (United States)

    Ulbrich, N.

    2016-01-01

    The relationship between the aerodynamic lift force generated by a wind tunnel model, the model weight, and the measured normal force of a strain-gage balance is investigated to better understand the expected use envelope of the normal force during a wind tunnel test. First, the fundamental relationship between normal force, model weight, lift curve slope, model reference area, dynamic pressure, and angle of attack is derived. Then, based on this fundamental relationship, the use envelope of a balance is examined for four typical wind tunnel test cases. The first case looks at the use envelope of the normal force during the test of a light wind tunnel model at high subsonic Mach numbers. The second case examines the use envelope of the normal force during the test of a heavy wind tunnel model in an atmospheric low-speed facility. The third case reviews the use envelope of the normal force during the test of a floor-mounted semi-span model. The fourth case discusses the normal force characteristics during the test of a rotated full-span model. The wind tunnel model's lift-to-weight ratio is introduced as a new parameter that may be used for a quick pre-test assessment of the use envelope of the normal force of a balance. The parameter is derived as a function of the lift coefficient, the dimensionless dynamic pressure, and the dimensionless model weight. Lower and upper bounds of the use envelope of a balance are defined using the model's lift-to-weight ratio. Finally, data from a pressurized wind tunnel is used to illustrate both application and interpretation of the model's lift-to-weight ratio.

  11. Surface deformations and wave generation by wind blowing over a viscous liquid

    CERN Document Server

    Paquier, Anna; Rabaud, Marc

    2015-01-01

    We investigate experimentally the early stage of the generation of waves by a turbulent wind at the surface of a viscous liquid. The spatio-temporal structure of the surface deformation is analyzed by the optical method Free Surface Synthetic Schlieren, which allows for time-resolved measurements with a micrometric accuracy. Because of the high viscosity of the liquid, the flow induced by the turbulent wind in the liquid remains laminar, with weak surface drift velocity. Two regimes of deformation of the liquid-air interface are identified. In the first regime, at low wind speed, the surface is dominated by rapidly propagating disorganized wrinkles, elongated in the streamwise direction, which can be interpreted as the surface response to the pressure fluctuations advected by the turbulent airflow. The amplitude of these deformations increases approximately linearly with wind velocity and are essentially independent of the fetch (distance along the channel). Above a threshold in wind speed, the perturbations ...

  12. Dynamic forces between bubbles and surfaces and hydrodynamic boundary conditions.

    Science.gov (United States)

    Manor, Ofer; Vakarelski, Ivan U; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R; Chan, Derek Y C

    2008-10-21

    A bubble attached to the end of an atomic force microscope cantilever and driven toward or away from a flat mica surface across an aqueous film is used to characterize the dynamic force that arises from hydrodynamic drainage and electrical double layer interactions across the nanometer thick intervening aqueous film. The hydrodynamic response of the air/water interface can range from a classical fully immobile, no-slip surface in the presence of added surfactants to a partially mobile interface in an electrolyte solution without added surfactants. A model that includes the convection and diffusion of trace surface contaminants can account for the observed behavior presented. This model predicts quantitatively different interfacial dynamics to the Navier slip model that can also be used to fit dynamic force data with a post hoc choice of a slip length.

  13. Scattering by Artificial Wind and Rain Roughened Water Surfaces at Oblique Incidences

    Science.gov (United States)

    Craeye, C.; Sobieski, P. W.; Bliven, L. F.

    1997-01-01

    Rain affects wind retrievals from scatterometric measurements of the sea surface. To depict the additional roughness caused by rain on a wind driven surface, we use a ring-wave spectral model. This enables us to analyse the rain effect on K(u) band scatterometric observations from two laboratory experiments. Calculations based on the small perturbation method provide good simulation of scattering measurements for the rain-only case, whereas for combined wind and rain cases, the boundary perturbation method is appropriate.

  14. Force Measurement on Aircraft Model with and without Winglet using Low Speed Wind Tunnel

    Directory of Open Access Journals (Sweden)

    N.Muthusamy

    2014-12-01

    Full Text Available The objective of the research is to conduct experiment by fabricating a standard aircraft model and retrofit winglets with cant angles 0 degree (vertical,30 degree and 60 degree. The experiments were conducted in a subsonic wind tunnel of size (feet 3x4x6.The experiment was conducted both for basic model and the model modified with winglets. The model with winglet has exhibited substantial reduction of coefficient of drag. The stall characteristics of the winglet were analyzed by plotting suitable graph. A calibrated three component balance was used for measuring the forces. Automated turntable mounted in the test section of the wind tunnel and therecording systems were used efficiently. The results were compared and discussed.

  15. Drag force and surface roughness measurements on freshwater biofouled surfaces.

    Science.gov (United States)

    Andrewartha, J; Perkins, K; Sargison, J; Osborn, J; Walker, G; Henderson, A; Hallegraeff, G

    2010-05-01

    The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m x 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.

  16. Sea Surface Wakes Observed by Spaceborne SAR in the Offshore Wind Farms

    Science.gov (United States)

    Li, Xiaoming; Lehner, Susanne; Jacobsen, Sven

    2014-11-01

    In the paper, we present some X-band spaceborne synthetic aperture radar (SAR) TerraSAR-X (TS-X) images acquired at the offshore wind farms in the North Sea and the East China Sea. The high spatial resolution SAR images show different sea surface wake patterns downstream of the offshore wind turbines. The analysis suggests that there are major two types of wakes among the observed cases. The wind turbine wakes generated by movement of wind around wind turbines are the most often observed cases. In contrast, due to the strong local tidal currents in the near shore wind farm sites, the tidal current wakes induced by tidal current impinging on the wind turbine piles are also observed in the high spatial resolution TS-X images. The discrimination of the two types of wakes observed in the offshore wind farms is also described in the paper.

  17. A preliminary assessment of the sea surface wind speed production of HY-2 scanning microwave radiometer

    Institute of Scientific and Technical Information of China (English)

    HUANG Xiaoqi; ZHU Jianhua; LIN Mingsen; ZHAO Yili; WANG He; CHEN Chuntao; PENG Hailong; ZHANG Youguang

    2014-01-01

    A scanning microwave radiometer (RM) was launched on August 16, 2011, on board HY-2 satellite. The six-month long global sea surface wind speeds observed by the HY-2 scanning microwave radiometer are preliminarily validated using in-situ measurements and WindSat observations, respectively, from January to June 2012. The wind speed root-mean-square (RMS) difference of the comparisons with in-situ data is 1.89 m/s for the measurements of NDBC and 1.72 m/s for the recent four-month data measured by PY30-1 oil platform, respectively. On a global scale, the wind speeds of HY-2 RM are compared with the sea surface wind speeds derived from WindSat, the RMS difference of 1.85 m/s for HY-2 RM collocated observations data set is calculated in the same period as above. With analyzing the global map of a mean difference between HY-2 RM and WindSat, it appears that the bias of the sea surface wind speed is obviously higher in the inshore regions. In the open sea, there is a relatively higher positive bias in the mid-latitude regions due to the overestimation of wind speed observations, while the wind speeds are underestimated in the Southern Ocean by HY-2 RM relative to WindSat observations.

  18. A Statistical Model for the Prediction of Wind-Speed Probabilities in the Atmospheric Surface Layer

    Science.gov (United States)

    Efthimiou, G. C.; Hertwig, D.; Andronopoulos, S.; Bartzis, J. G.; Coceal, O.

    2016-11-01

    Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behaviour of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The model's basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds shows a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on knowledge of only a few simple flow statistics (mean wind speed, wind-speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence.

  19. Two decades [1992-2012] of surface wind analyses based on satellite scatterometer observations

    Science.gov (United States)

    Desbiolles, Fabien; Bentamy, Abderrahim; Blanke, Bruno; Roy, Claude; Mestas-Nuñez, Alberto M.; Grodsky, Semyon A.; Herbette, Steven; Cambon, Gildas; Maes, Christophe

    2017-04-01

    Surface winds (equivalent neutral wind velocities at 10 m) from scatterometer missions since 1992 have been used to build up a 20-year climate series. Optimal interpolation and kriging methods have been applied to continuously provide surface wind speed and direction estimates over the global ocean on a regular grid in space and time. The use of other data sources such as radiometer data (SSM/I) and atmospheric wind reanalyses (ERA-Interim) has allowed building a blended product available at 1/4° spatial resolution and every 6 h from 1992 to 2012. Sampling issues throughout the different missions (ERS-1, ERS-2, QuikSCAT, and ASCAT) and their possible impact on the homogeneity of the gridded product are discussed. In addition, we assess carefully the quality of the blended product in the absence of scatterometer data (1992 to 1999). Data selection experiments show that the description of the surface wind is significantly improved by including the scatterometer winds. The blended winds compare well with buoy winds (1992-2012) and they resolve finer spatial scales than atmospheric reanalyses, which make them suitable for studying air-sea interactions at mesoscale. The seasonal cycle and interannual variability of the product compare well with other long-term wind analyses. The product is used to calculate 20-year trends in wind speed, as well as in zonal and meridional wind components. These trends show an important asymmetry between the southern and northern hemispheres, which may be an important issue for climate studies.

  20. Analysis of the forces acting on the saltating particles in the coupled wind-sand-electricity fields

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Based on the theoretical model describing the saltation of sand particles in the coupled wind-sand- electricity fields, the numerical simulations of the forces acting on saltating particles, such as the aerodynamic drag force, Magnus effect, Saffman force and electrostatic force, are analyzed in com- parison to the gravity force of the particles in the steady windblown sand movement. Furthermore, the laws of the above forces vary with the friction velocity, the diameter of the sand particle, the initial an- gular velocity and the lift-off velocity are discussed.

  1. Analysis of the forces acting on the saltating particles in the coupled wind-sand-electricity fields

    Institute of Scientific and Technical Information of China (English)

    WU JianJun; YAN GuangHu

    2009-01-01

    Based on the theoretical model describing the saltation of sand particles in the coupled wind-sand-electricity fields, the numerical simulations of the forces acting on saltating particles, such as the aerodynamic drag force, Magnus effect, Saffman force and electrostatic force, are analyzed in com-parison to the gravity force of the particles in the steady windblown sand movement. Furthermore, the laws of the above forces vary with the friction velocity, the diameter of the sand particle, the initial an-gular velocity and the lift-off velocity are discussed.

  2. Variation in wind speed and surface shear stress from open floor to porous parallel windbreaks: A wind tunnel study

    Science.gov (United States)

    Guan, De-Xin; Zhong, Ye; Jin, Chang-Jie; Wang, An-Zhi; Wu, Jia-Bing; Shi, Ting-Ting; Zhu, Ting-Yao

    2009-08-01

    As vegetative windbreaks become established on a large scale in agricultural ecosystems, understanding the influence of windbreak networks on the momentum budget of the atmospheric boundary layer becomes important. The authors conducted a wind tunnel experiment to study the variation of wind speed profile and surface shear stress of wind flow passing from an open surface to another with parallel windbreaks. Five spacing (L = 5, 10, 15, 20, 30 h, wherein h is the windbreak height) windbreak arrays with moderate porosity (aerodynamic porosity α = 0.501) were used in the experiments. Both near-floor and over-array wind speed measurements showed that airflow will approach equilibrium state behind a special windbreak of the array, varying from 4th to 9th windbreak when the spacing change from 30 to 5 h. Within the range of L/h values investigated, arrays with narrower spacing cause higher friction velocity and roughness length, which were up to 2.26 and nearly 100 times those observed over open floor, respectively. A semiempirical momentum budget model is developed on the arrayed surface to estimate windbreak drag and shear stress on the protected floor. Windbreak drag accounts for more than 80% of shear stress on the arrayed surface, and the shear stress on protected floor is less than 20% when L/h < 40 based on the model estimation. The sum of the two estimated components agrees well with the estimates obtained from over-array wind profiles.

  3. (abstract) Using TOPEX/Poseidon Sea Level Observations to Test the Sensitivity of an Ocean Model to Wind Forcing

    Science.gov (United States)

    Fu, Lee-Lueng; Chao, Yi

    1996-01-01

    It has been demonstrated that current-generation global ocean general circulation models (OGCM) are able to simulate large-scale sea level variations fairly well. In this study, a GFDL/MOM-based OGCM was used to investigate its sensitivity to different wind forcing. Simulations of global sea level using wind forcing from the ERS-1 Scatterometer and the NMC operational analysis were compared to the observations made by the TOPEX/Poseidon (T/P) radar altimeter for a two-year period. The result of the study has demonstrated the sensitivity of the OGCM to the quality of wind forcing, as well as the synergistic use of two spaceborne sensors in advancing the study of wind-driven ocean dynamics.

  4. Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades

    Directory of Open Access Journals (Sweden)

    Xavier Ortiz

    2015-03-01

    Full Text Available To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 104 to 2 × 105. Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases.

  5. Anisotropic Solar Wind Sputtering of the Lunar Surface Induced by Crustal Magnetic Anomalies

    Science.gov (United States)

    Poppe, A. R.; Sarantos, M.; Halekas, J. S.; Delory, G. T.; Saito, Y.; Nishino, M.

    2014-01-01

    The lunar exosphere is generated by several processes each of which generates neutral distributions with different spatial and temporal variability. Solar wind sputtering of the lunar surface is a major process for many regolith-derived species and typically generates neutral distributions with a cosine dependence on solar zenith angle. Complicating this picture are remanent crustal magnetic anomalies on the lunar surface, which decelerate and partially reflect the solar wind before it strikes the surface. We use Kaguya maps of solar wind reflection efficiencies, Lunar Prospector maps of crustal field strengths, and published neutral sputtering yields to calculate anisotropic solar wind sputtering maps. We feed these maps to a Monte Carlo neutral exospheric model to explore three-dimensional exospheric anisotropies and find that significant anisotropies should be present in the neutral exosphere depending on selenographic location and solar wind conditions. Better understanding of solar wind/crustal anomaly interactions could potentially improve our results.

  6. Wave glider observations of surface winds and currents in the core of Typhoon Danas

    Science.gov (United States)

    Mitarai, S.; McWilliams, J. C.

    2016-11-01

    Simultaneous monitoring of surface winds and currents is essential to understand oceanic responses to tropical cyclones. We used a new platform, a Wave Glider (Liquid Robotics) to observe air-sea processes during a typhoon, equivalent to a category 4-hurricane, at peak strength, near Okinawa, Japan. Surface winds showed strong asymmetry in both speed and direction, faster fore than aft. Rotations of surface winds and currents were not coupled; currents rotated clockwise in the wake of the typhoon eye after passage of rapid wind rotations. Wind work was mostly done ahead of the eye, amplifying prior inertial motions with a phase shift. Wind-induced energy was nearly balanced with an increase in estimated kinetic energy of the upper ocean current, relative to prior inertial oscillations. This study provides a newer, more complete view of actual atmosphere-ocean interactions in a typhoon.

  7. Analysis of intraocular lens surface adhesiveness by atomic force microscopy.

    Science.gov (United States)

    Lombardo, Marco; Carbone, Giovanni; Lombardo, Giuseppe; De Santo, Maria P; Barberi, Riccardo

    2009-07-01

    To analyze intraocular lens (IOL) optic surface adhesiveness using atomic force microscopy (AFM). LiCryL Laboratory, University of Calabria, Rende, Italy. The surface adhesive properties of poly(methyl methacrylate) (PMMA), silicone, hydrophilic acrylic, and hydrophobic acrylic IOLs were evaluated by AFM. Analysis was performed at room temperature (21 degrees C) in a liquid environment using the force-versus-distance mode of a commercial instrument (NanoScope III). Measurements were acquired with rectangular silicon cantilevers of a nominal elastic constant of 10 Newton/m. The nominal value of the tip's radius of curvature was 1 mum, and the scanning speed during the acquisitions ranged from 10 to 400 nm/s. The adhesion force measurements showed different characteristics for the various types of IOLs (Pdevelopment and the interface interactions between the IOL and capsule, the results in this study may bolster the theory of manufacturing more-adhesive materials to prevent PCO.

  8. Computation of a Single-phase Shell-Type Transformer Windings Forces Caused by Inrush and Short-circuit Currents

    Directory of Open Access Journals (Sweden)

    M. B.B. Sharifian

    2008-01-01

    Full Text Available This research studies the forces on the windings of transformer due to inrush current. These forces are compared with the corresponding forces due to short-circuit of the windings. Two-dimensional finite element computation of a single-phase shell-type transformer is carried out based on the maximum permissible inrush current value where its amplitude is the same as the rated short-circuit current. To verify the computation results, they are compared with those recently obtained using Artificial Neural Network (ANN.

  9. "Magic" surface clustering of borazines driven by repulsive intermolecular forces.

    Science.gov (United States)

    Kervyn, Simon; Kalashnyk, Nataliya; Riello, Massimo; Moreton, Ben; Tasseroul, Jonathan; Wouters, Johan; Jones, Tim S; De Vita, Alessandro; Costantini, Giovanni; Bonifazi, Davide

    2013-07-15

    It's a kind of magic: Hydroxy pentaaryl borazine molecules self-assemble into small clusters (see structure) on Cu(111) surfaces, whereas with symmetric hexaaryl borazine molecules large islands are obtained. Simulations indicate that the observed "magic" cluster sizes result from long-range repulsive Coulomb forces arising from the deprotonation of the B-OH groups of the hydroxy pentaaryl borazine.

  10. High-resolution satellite-derived ocean surface winds in the Nordic-Barents seas region: Implications for ocean modeling (Invited)

    Science.gov (United States)

    Dukhovskoy, D. S.; Bourassa, M. A.; Hughes, P. J.

    2010-12-01

    High-resolution (0.25°) ocean surface wind velocity data derived from satellite observations are used to analyze winds in the Nordic-Barents seas during 2007-2008. For the analysis, a Cross-Calibrated, Multi-Platform (CCMP), multi-instrument ocean surface wind velocity data set is utilized. The product has been developed by National Aeronautics and Space Administration (NASA) within Making Earth Science data records for Use in Research Environments (MEaSUREs) Program. A variational method was used to combine wind measurements derived from satellite-born active and passive remote sensing instruments. In the objective procedure, winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) Operational Analysis (DS111.1) were used as the background fields. The ocean surface wind fields are compared with those derived from the National Centers for Environmental Protection/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The NCEP/NCAR fields are commonly used to provide atmospheric forcing for Arctic Ocean models. The utility of using high-resolution winds in the ocean modeling is discussed. In particular, air-sea heat fluxes estimated from the two wind data sets are compared. It is anticipated that wind fields with higher spatial and temporal resolution will better resolve small-scale, short-lived atmospheric systems. As an example, the ice free region in the Nordic and Barents seas is frequently impacted by very intense cyclones known as “polar lows” with wind speeds near to or above gale force. A polar low forms over the sea and predominantly during the winter months. The size of these cyclones varies greatly from 100 to 1000 km. Presumably small-scale cyclones are misrepresented or not resolved in the NCAR fields leading to biases in the air-sea flux calculations in the ocean models. Inaccurate estimates of the air-sea fluxes eventually lead to biases in the Arctic Ocean model solutions.

  11. Effect of Suspension Winding Pole Pair and Permanent Magnet Thickness on Magnetic Levitation Force in Bearingless {PMSM

    Directory of Open Access Journals (Sweden)

    H. Ebrahimpoor Hendoo

    2014-11-01

    Full Text Available One maintenance task that still exist with conventional motors, are bearing lubrication and renewal. Bearingless motors are replaced with conventional motor that uses a magnetic levitation force to suspend a rotor without any mechanical contact. In bearingless motors, additional windings are wound together with motor windings in stator slots. In this paper, a bearingless permanent magnet-type synchronous motor (BPMSM Has been studied. First, the generation of radial levitation forces is discussed and then the optimum permanent magnet thickness is determined to produce maximum levitation force. After that the effect of additional winding pole-pair in the amount of levitation force is investigated. The simulation is done in Maxwell software

  12. Interannual variations of surface winds over China marginal seas

    Institute of Scientific and Technical Information of China (English)

    SUN Che; YAN Xiaomei

    2012-01-01

    In a study of surface monsoon winds over the China marginal seas,Sun et al.(2012) use singular value decomposition method to identify regional dominant modes and analyze their interdecadal variability.This paper continues to evaluate the interannual variability of each dominant mode and its relation to various atmospheric,oceanic and land factors.The findings include:1) The intensity of the winter monsoon over the East China Sea is highly correlated with the Siberian High intensity and anti-correlated with the latitudinal position of the Aleutian Low as well as the rainfall in eastem China,Korean Peninsula and Japan; 2) The western Pacific subtropical high is significantly correlated with the summer monsoon intensity over the East China Sea and anti-correlated with the summer monsoon over the South China Sea; 3) The winter monsoon in a broad zonal belt through the Luzon Strait is dominated by the ENSO signal,strengthening in the La Ni(n)a phase and weakening in the El Ni(n)o phase.This inverse relation exhibits interdecadal shift with a period of weak correlation in the 1980s; 4) Analysis of tidal records validates the interdecadal weakening of the East Asian summer monsoon and reveals an atmospheric bridge that conveys the ENSO signal into the South China Sea via the winter monsoon.

  13. Effect of wind forcing on the meridional heat transport in a coupled climate model: equilibrium response

    Science.gov (United States)

    Yang, Haijun; Dai, Haijin

    2015-09-01

    The effect of the ocean surface winds on the meridional heat transports is studied in a coupled model. Shutting down the global surface winds causes significant reductions in both wind-driven and thermohaline ocean circulations, resulting in a remarkable decrease in the poleward oceanic heat transport (OHT). The sea surface temperature responds with significant warming in the equator and cooling off the equator, causing an enhancement and equatorward shift in the Hadley cell. This increases the poleward atmospheric heat transport (AHT), which in turn compensates the decrease in the OHT. This compensation implies a fundamental constraint in changes of ocean-atmosphere energy transports. Several other compensation changes are also identified. For the OHT components, the changes in the Eulerian mean and bolus OHT are compensated with each other in the Southern Ocean, since a stronger wind driven Ekman transport is associated with a stronger meridional density gradient (stronger bolus circulation) and vice versa. For the AHT components, the changes in the dry static energy (DSE) and latent energy transports are compensated within the tropics (30°N/S), because a stronger Hadley cell causes a stronger equatorward convergence of moisture. In the extratropics, the changes in the mean and eddy DSE transports show perfect compensation, as a result of the equatorward shift of the Ferrell Cell and enhancement of atmospheric baroclinicity in mid-high latitudes, particularly over the North Atlantic. This work also shows how the Earth's climate is trying to maintain the balance between two hemispheres: the ocean in the Northern Hemisphere is colder than that in the Southern Hemisphere due to much reduced northward heat transports cross the Equator in the Atlantic, therefore, the atmosphere responds to the ocean with temperature colder in the Southern Hemisphere than in the Northern Hemisphere by transporting more heat northward cross the equator over the Pacific, in association

  14. Surface energy budget responses to radiative forcing at Summit, Greenland

    Science.gov (United States)

    Miller, Nathaniel B.; Shupe, Matthew D.; Cox, Christopher J.; Noone, David; Persson, P. Ola G.; Steffen, Konrad

    2017-02-01

    Greenland Ice Sheet surface temperatures are controlled by an exchange of energy at the surface, which includes radiative, turbulent, and ground heat fluxes. Data collected by multiple projects are leveraged to calculate all surface energy budget (SEB) terms at Summit, Greenland, for the full annual cycle from July 2013 to June 2014 and extend to longer periods for the radiative and turbulent SEB terms. Radiative fluxes are measured directly by a suite of broadband radiometers. Turbulent sensible heat flux is estimated via the bulk aerodynamic and eddy correlation methods, and the turbulent latent heat flux is calculated via a two-level approach using measurements at 10 and 2 m. The subsurface heat flux is calculated using a string of thermistors buried in the snow pack. Extensive quality-control data processing produced a data set in which all terms of the SEB are present 75 % of the full annual cycle, despite the harsh conditions. By including a storage term for a near-surface layer, the SEB is balanced in this data set to within the aggregated uncertainties for the individual terms. November and August case studies illustrate that surface radiative forcing is driven by synoptically forced cloud characteristics, especially by low-level, liquid-bearing clouds. The annual cycle and seasonal diurnal cycles of all SEB components indicate that the non-radiative terms are anticorrelated to changes in the total radiative flux and are hence responding to cloud radiative forcing. Generally, the non-radiative SEB terms and the upwelling longwave radiation component compensate for changes in downwelling radiation, although exact partitioning of energy in the response terms varies with season and near-surface characteristics such as stability and moisture availability. Substantial surface warming from low-level clouds typically leads to a change from a very stable to a weakly stable near-surface regime with no solar radiation or from a weakly stable to neutral

  15. Survey on effect of surface winds on aircraft design and operation and recommendations for needed wind research

    Science.gov (United States)

    Houbolt, J. C.

    1973-01-01

    A survey of the effect of environmental surface winds and gusts on aircraft design and operation is presented. A listing of the very large number of problems that are encountered is given. Attention is called to the many studies that have been made on surface winds and gusts, but development in the engineering application of these results to aeronautical problems is pointed out to be still in the embryonic stage. Control of the aircraft is of paramount concern. Mathematical models and their application in simulation studies of airplane operation and control are discussed, and an attempt is made to identify their main gaps or deficiencies. Key reference material is cited. The need for better exchange between the meteorologist and the aeronautical engineer is discussed. Suggestions for improvements in the wind and gust models are made.

  16. Requirements for large-eddy simulation of surface wind gusts in a mountain valley

    Science.gov (United States)

    Revell, Michael J.; Purnell, Don; Lauren, Michael K.

    1996-09-01

    During the passage of a front, data from a light-weight cup anemometer and wind vane, sited in a steep-walled glacial valley of the Mt Cook region of the Southern Alps of New Zealand, were analysed to derive a power spectrum of the wind velocity for periods between 0.5 and 16 min. The energy spectrum roughly followed a -5/3 power law over the range of periods from 0.5 4 min — as might be expected in the case of an inertial subrange of eddies. However, any inertial subrange clearly does not extend to periods longer than this. We suggest that the observed eddies were generated in a turbulent wake associated with flow separation at the ridge crests, and large eddies are shed at periods of 4 8 min or more. A compressible fluid-dynamic model, with a Smagorinsky turbulence closure scheme and a “law of the wall” at the surface, was used to calculate flow over a cross section through this area in neutrally stratified conditions. A range of parameters was explored to assess some of the requirements for simulating surface wind gusts in mountainous terrain in New Zealand. In order to approximate the observed wind spectrum at Tasman aerodrome, Mount Cook, we found the model must be three-dimensional, with a horizontal resolution better than 250 m and with a Reynolds-stress eddy viscosity of less than 5 m2 s-1. In two-dimensional simulations, the eddies were too big in size and in amplitude and at the surface this was associated with reversed flow extending too far downstream. In contrast the three-dimensional simulations gave a realistic gusting effect associated with large scale “cat's paws” (a bigger variety of those commonly seen over water downstream of moderate hills), with reversed flow only at the steep part of the lee slope. The simulations were uniformly improved by better resolution, at all tested resolutions down to 250 m mesh size. The spectra of large eddies simulated in steep terrain were not very sensitive to the details of the eddy stress formulation

  17. Coalescence and noncoalescence of sessile drops: impact of surface forces.

    Science.gov (United States)

    Karpitschka, Stefan; Hanske, Christoph; Fery, Andreas; Riegler, Hans

    2014-06-17

    Due to capillarity, sessile droplets of identical liquids will instantaneously fuse when they come in contact at their three-phase lines. However, with drops of different, completely miscible liquids, instantaneous coalescence can be suppressed. Instead, the drops remain in a state of noncoalescence for some time, with the two drop bodies connected only by a thin neck. The reason for this noncoalescence is the surface tension difference, Δγ, between the liquids. If Δγ is sufficiently large, then it induces a sufficiently strong Marangoni flow, which keeps the main drop bodies temporarily separated. Studies with spreading drops have revealed that the boundary between instantaneous coalescence and noncoalescence is sharp (Karpitschka, S.; Riegler, H. J. Fluid. Mech. 2014, 743, R1). The boundary is a function of two parameters only: Δγ and Θ(a), the arithmetic mean of the contact angles in the moment of drop-drop contact. It appears plausible that surface forces (the disjoining pressure) could also influence the coalescence behavior. However, in experiments with spreading drops, surface forces always promote coalescence and their influence might be obscured. Therefore, we present here coalescence experiments with partially wetting liquids and compare the results to the spreading case. We adjust different equilibrium contact angles (i.e., different surface forces) with different substrate surface coatings. As for spreading drops, we observe a sharp boundary between regimes of coalescence and noncoalescence. The boundary follows the same power law relation for both partially and completely wetting cases. Therefore, we conclude that surface forces have no significant, explicit influence on the coalescence behavior of sessile drops from different miscible liquids.

  18. Pulsatory characteristics of wind velocity in sand flow over typical underlying surfaces

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Pulsatory characteristics of wind velocity in sand flow over Gobi and mobile sand surface have been investigated experimentally in the wind tunnel. The primary goal of this paper is to reveal the relation- ship between pulsatory characteristics of instantaneous wind speed in sand flow and the motion state of sand grains. For a given underlying surface, pulsation of wind velocities in sand flow on different heights has a good correlation. As the space distance among different heights increases, fluctuation of instantaneous wind speed presents a decreasing trend and its amplitude is closely related to the mo- tion state of sand grains and their transport. Pulsatory intensity increases with the indicated wind speed, but its relative value does not depend on it, only agrees with height.

  19. Atomically resolved graphitic surfaces in air by atomic force microscopy.

    Science.gov (United States)

    Wastl, Daniel S; Weymouth, Alfred J; Giessibl, Franz J

    2014-05-27

    Imaging at the atomic scale using atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomic resolution of graphite and hydrogen-intercalated graphene on SiC in air. The main challenges arise from the overall surface cleanliness and the water layers which form on almost all surfaces. To further investigate the influence of the water layers, we compare data taken with a hydrophilic bulk-silicon tip to a hydrophobic bulk-sapphire tip. While atomic resolution can be achieved with both tip materials at moderate interaction forces, there are strong differences in force versus distance spectra which relate to the water layers on the tips and samples. Imaging at very low tip-sample interaction forces results in the observation of large terraces of a naturally occurring stripe structure on the hydrogen-intercalated graphene. This structure has been previously reported on graphitic surfaces that are not covered with disordered adsorbates in ambient conditions (i.e., on graphite and bilayer graphene on SiC, but not on monolayer graphene on SiC). Both these observations indicate that hydrogen-intercalated graphene is close to an ideal graphene sample in ambient environments.

  20. Understanding nanorheology and surface forces of confined thin films

    Science.gov (United States)

    Huang, Jun; Yan, Bin; Faghihnejad, Ali; Xu, Haolan; Zeng, Hongbo

    2014-02-01

    Understanding the nanorheology and associated intermolecular/surface forces of fluids in confined geometries or porous media is of both fundamental and practical importance, providing significant insights into various applications such as lubrication and micro/nanoelectromechanical systems. In this work, we briefly reviewed the fundamentals of nanoreheolgy, advances in experimental techniques and theoretical simulation methods, as well as important progress in the nanorheology of confined thin films. The advent of advanced experimental techniques such as surface forces apparatus (SFA), X-ray surface forces apparatus (XSFA) and atomic force microscope (AFM) and computational methods such as molecular dynamics simulations provides powerful tools to study a wide range of rheological phenomena at molecular level and nano scale. One of the most challenging issues unresolved is to elucidate the relationship between the rheological properties and structural evolution of the confined fluid films and particles suspensions. Some of the emerging research areas in the nanorheology field include, but are not limited to, the development of more advanced characterization techniques, design of multifunctional rheological fluids, bio-related nanorheology, and polymer brushes.

  1. Complex Wind-Induced Variations of Surface Snow Accumulation Rates over East Antarctica

    Science.gov (United States)

    Das, I.; Scambos, T. A.; Koenig, L.; van den Broeke, M.; Lenaerts, J.

    2015-12-01

    Accurate quantification of surface snow-accumulation over Antarctica is important for mass balance estimates and climate studies based on ice core records. Using airborne radar, lidar and thresholds of surface slope, modeled surface mass balance (SMB) and wind fields, we have predicted continent-wide distribution of wind-scour zones over Antarctica. These zones are located over relatively steep ice surfaces formed by ice flow over bedrock topography. Near-surface winds accelerate over these steeper slopes and erode and sublimate the snow. This results in numerous localized regions (typically ≤ 200 km2) with reduced or negative surface accumulation. Although small zones of re-deposition occur at the base of the steeper slope areas, the redeposited mass is small relative to the ablation loss. Total losses from wind-scour and wind-glaze areas amounts to tens of gigatons annually. Near the coast, winds often blow significant amounts of surface snow from these zones into the ocean. Large uncertainties remain in SMB estimates over East Antarctica as climate models do not adequately represent the small-scale physical processes that lead to mass loss or redistribution over the wind-scour zones. In this study, we also use Operation IceBridge's snow radar data to provide evidence for a gradual ablation of ~16-18 m of firn (~200 years of accumulation) from wind-scour zones over the upper Recovery Ice Stream catchment. The maximum ablation rates observed in this region are ~ -54 kg m-2 a-1 (-54 mm water equivalent a-1). Our airborne radio echo-sounding analysis show snow redeposition downslope of the wind-scour zones is <10% of the cumulative mass loss. Our study shows that the local mass loss is dominated by sublimation to water vapor rather than wind-transport of snow.

  2. A Numerical Study of Time-Dependent Wind Forcing Off the West Coast of Portugal, 1987 - 1988

    Science.gov (United States)

    1991-06-01

    and the Icelandic Low controls the seasonal variation in wind stress. Seasonal variations in the wind stress dominate the general ocean surface...correntes, temperaturas e salinidades na vertente continental Portuguesa a 40 N. Relatorio tecnico, 1185, Grupo de Oceanografia, Universidade de Lisboa

  3. ForceFit: a code to fit classical force fields to quantum mechanical potential energy surfaces.

    Science.gov (United States)

    Waldher, Benjamin; Kuta, Jadwiga; Chen, Samuel; Henson, Neil; Clark, Aurora E

    2010-09-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under UNIX and is written in C++, is an easy-to-use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field, and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program. Copyright 2010 Wiley Periodicals, Inc.

  4. A Method for Sea Surface Wind Field Retrieval from SAR Image Mode Data

    Institute of Scientific and Technical Information of China (English)

    SHAO Weizeng; SUN Jian; GUAN Changlong; SUN Zhanfeng

    2014-01-01

    To retrieve wind field from SAR images, the development for surface wind field retrieval from SAR images based on the improvement of new inversion model is present. Geophysical Model Functions (GMFs) have been widely applied for wind field retrieval from SAR images. Among them CMOD4 has a good performance under low and moderate wind conditions. Although CMOD5 is developed recently with a more fundamental basis, it has ambiguity of wind speed and a shape gradient of normalized radar cross section under low wind speed condition. This study proposes a method of wind field retrieval from SAR image by com-bining CMOD5 and CMOD4 Five VV-polarisation RADARSAT2 SAR images are implemented for validation and the retrieval re-sults by a combination method (CMOD5 and CMOD4) together with CMOD4 GMF are compared with QuikSCAT wind data. The root-mean-square error (RMSE) of wind speed is 0.75 m s-1 with correlation coefficient 0.84 using the combination method and the RMSE of wind speed is 1.01 m s-1 with correlation coefficient 0.72 using CMOD4 GMF alone for those cases. The proposed method can be applied to SAR image for avoiding the internal defect in CMOD5 under low wind speed condition.

  5. Observations of wind and waves in the central Bay of Bengal during BOBMEX-99 and their effect on mixed layer depth variability due to forced mixing

    Indian Academy of Sciences (India)

    J Swain; R K Shukla; A Raghunadha Rao; J K Panigrahi; N R Venkitachalam

    2003-06-01

    Time-series wind and wave measurements were carried out onboard INS Sagardhwani in the central Bay of Bengal during BOBMEX-99. Various other marine meteorological and oceanographic measurements relevant to monsoon studies were also collected simultaneously. The observed variations of wind and waves and the associated mixed layer depth (MLD) variability based on both temperature and density criteria at 3 hourly intervals are presented in this paper as a case study. At the time-series location (13°N, 87°E) wind varied between 6 and 16 m/s and the predominant direction was southwesterly. The significant wave height and period varied from 1.9 to 3.7m and 8 to 13 s respectively. Some of the available statistical predictive methods for the determination of MLD by forced mixing are utilized to test the extent of mechanical mixing within the top layer of water by the local wind and wave activity. The same is extended to formulate a new empirical relation for gross estimation of effective depth within which the sound energy is generally trapped during its transmission in the surface duct. The present analysis aiming for estimation of observed MLD variability (35 to 75 m) using the suggested simple empirical relation reveals that, the mixed layer variability observed during the experiment depends on both local ocean variability as well as remote forcing as reported earlier.

  6. Developing a Peak Wind Probability Forecast Tool for Kennedy Space Center and Cape Canaveral Air Force Station

    Science.gov (United States)

    Lambert, WInifred; Roeder, William

    2007-01-01

    This conference presentation describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) in east-central Florida. The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violations. The tool will include climatologies of the 5-minute mean and peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

  7. Removing the impact of wind direction on remote sensing of sea surface salinity

    Institute of Scientific and Technical Information of China (English)

    YIN Xiaobin; LIU Yuguang; ZHANG Hande

    2006-01-01

    Using the small-slope approximation model of microwave emission of rough sea surface, the impacts of sea surface wind on brightness temperature variations generated by the surface roughness, i.e. △Th,v, are investigated. Here △T denotes the brightness temperature variation, and "h" and "v" denote the horizontal and vertical polarizations respectively. △Th,v has a linear relation with wind speed, sea surface temperature (SST) and sea surface salinity (SSS) respectively. Further more, the impact of wind direction on SSS retrieval, under small incidence angles, can be removed by calculating (△Th+△Tv). These characteristics provide simple new ways to develop an SSS retrieval algorithm without wind direction factor.

  8. Influence of Persistent Wind Scour on the Surface Mass Balance of Antarctica

    Science.gov (United States)

    Das, Indrani; Bell, Robin E.; Scambos, Ted A.; Wolovick, Michael; Creyts, Timothy T.; Studinger, Michael; Fearson, Nicholas; Nicolas, Julien P.; Lenaerts, Jan T. M.; vandenBroeke, Michiel R.

    2013-01-01

    Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that approx. 2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt /yr in present surface-mass-balance calculations.

  9. Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

    Energy Technology Data Exchange (ETDEWEB)

    Kweon, Hyojin [Georgia Institute of Technology; Yiacoumi, Sotira [Georgia Institute of Technology; Tsouris, Costas [ORNL

    2011-01-01

    The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. The poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

  10. Wind fields of storms from surface isobars for wave hindcasting

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.; Vaithiyanathan, R.; Santanam, K.

    Marine operations of various types are critically linked to mean and extreme wave statistics. In the Indian seas extreme wave conditions are caused by cyclones and steady strong monsoon winds. Wave data from cyclone areas are not directly available...

  11. Surface deformations and wave generation by wind blowing over a viscous liquid

    Science.gov (United States)

    Paquier, A.; Moisy, F.; Rabaud, M.

    2015-12-01

    We investigate experimentally the early stage of the generation of waves by a turbulent wind at the surface of a viscous liquid. The spatio-temporal structure of the surface deformation is analyzed by the optical method Free Surface Synthetic Schlieren, which allows for time-resolved measurements with a micrometric accuracy. Because of the high viscosity of the liquid, the flow induced by the turbulent wind in the liquid remains laminar, with weak surface drift velocity. Two regimes of deformation of the liquid-air interface are identified. In the first regime, at low wind speed, the surface is dominated by rapidly propagating disorganized wrinkles, elongated in the streamwise direction, which correspond to the surface response to the pressure fluctuations advected by the turbulent airflow. The amplitude of these deformations increases approximately linearly with wind velocity and are essentially independent of the fetch (distance along the channel). Above a threshold in wind speed, we observe the growth of well defined gravity-capillary waves with crests nearly perpendicular to the wind direction. In this second regime, the wave amplitude increases with wind speed but far more quickly than in the first regime.

  12. Surface Fluxes and Wind-Wave Interactions in Weak Wind Conditions

    Science.gov (United States)

    2016-06-07

    science /abl/cblast LONG-TERM GOALS We will investigate air-sea transfer of momentum, heat, and moisture under weak wind conditions. We will...over the ASIT tower and the wind direction was good for the tower sonic performance (6 days in total). As we found last year that although the momentum...flux derived from the aircraft is flight- direction dependent, which was recently found to be a common problem for all aircraft flux measurements

  13. Changes in Surface Wind Speed over North America from CMIP5 Model Projections and Implications for Wind Energy

    OpenAIRE

    Sujay Kulkarni; Huei-Ping Huang

    2014-01-01

    The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5) archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models proje...

  14. Large surface radiative forcing from surface-based ice crystal events measured in the High Arctic at Eureka

    Directory of Open Access Journals (Sweden)

    G. Lesins

    2008-09-01

    Full Text Available Ice crystals, also known as diamond dust, are suspended in the boundary layer air under clear sky conditions during most of the Arctic winter in Northern Canada. Occasionally ice crystal events can produce significantly thick layers with optical depths in excess of 2.0 even in the absence of liquid water clouds. Four case studies of high optical depth ice crystal events at Eureka in the Nunavut Territory of Canada during the winter of 2006–2007 are presented. They show that the measured ice crystal surface infrared downward radiative forcing ranged from 8 to 36 W m−2 in the wavelength band from 5.6 to 20 μm for visible optical depths ranging from 0.2 to 1.7. MODIS infrared and visible images and the operational radiosonde wind profile were used to show that these high optical depth events were caused by surface snow being blown off 600 to 800 m high mountain ridges about 20 to 30 km North-West of Eureka and advected by the winds towards Eureka as they settled towards the ground within the highly stable boundary layer. This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events and points to a new source of boundary layer ice crystal events distinct from the classical diamond dust phenomenon.

  15. Annual and interannual variability of scatterometer ocean surface wind over the South China Sea

    DEFF Research Database (Denmark)

    Zhang, GS; Xu, Q.; Gong, Z.

    2014-01-01

    To investigate the annual and interannual variability of ocean surface wind over the South China Sea (SCS), the vector empirical orthogonal function (VEOF) method and the Hilbert-Huang transform (HHT) method were employed to analyze a set of combined satellite scatterometer wind data during...

  16. Atomic force microscopic observation of surface-supported human erythrocytes

    Science.gov (United States)

    Ho, Mon-Shu; Kuo, Feng-Jia; Lee, Yu-Siang; Cheng, Chao-Min

    2007-07-01

    The nanomechanical characteristics of the membrane cytoskeleton of human erythrocytes were studied using atomic force microscopy (AFM). The self-assembly, fine structure, cell diameter, thickness, and reticulate cytoskeleton of erythrocytes on the mica surface were investigated. The adhesive forces that correspond to the membrane elasticity of various parts of the erythrocyte membrane surface were measured directly by AFM to be 0.64±0.14nN for cell indentation, 4.2±0.7nN for cell hump, and 11.5nN for side waist, respectively. The deformation of erythrocytes was discussed. Standing waves on the membrane that were set up by increased AFM amplitude were observed. The propagating velocity on the erythrocyte membrane was estimated to be ˜2.02×10-2m/s. Liquid physiological conditions were considered throughout.

  17. Probability distribution of surface wind speed induced by convective adjustment on Venus

    Science.gov (United States)

    Yamamoto, Masaru

    2017-03-01

    The influence of convective adjustment on the spatial structure of Venusian surface wind and probability distribution of its wind speed is investigated using an idealized weather research and forecasting model. When the initially uniform wind is much weaker than the convective wind, patches of both prograde and retrograde winds with scales of a few kilometers are formed during active convective adjustment. After the active convective adjustment, because the small-scale convective cells and their related vertical momentum fluxes dissipate quickly, the large-scale (>4 km) prograde and retrograde wind patches remain on the surface and in the longitude-height cross-section. This suggests the coexistence of local prograde and retrograde flows, which may correspond to those observed by Pioneer Venus below 10 km altitude. The probability distributions of surface wind speed V during the convective adjustment have a similar form in different simulations, with a sharp peak around ∼0.1 m s-1 and a bulge developing on the flank of the probability distribution. This flank bulge is associated with the most active convection, which has a probability distribution with a peak at the wind speed 1.5-times greater than the Weibull fitting parameter c during the convective adjustment. The Weibull distribution P(> V) (= exp[-(V/c)k]) with best-estimate coefficients of Lorenz (2016) is reproduced during convective adjustments induced by a potential energy of ∼7 × 107 J m-2, which is calculated from the difference in total potential energy between initially unstable and neutral states. The maximum vertical convective heat flux magnitude is proportional to the potential energy of the convective adjustment in the experiments with the initial unstable-layer thickness altered. The present work suggests that convective adjustment is a promising process for producing the wind structure with occasionally generating surface winds of ∼1 m s-1 and retrograde wind patches.

  18. General Forced Oscillations in a Real Power Grid Integrated with Large Scale Wind Power

    Directory of Open Access Journals (Sweden)

    Ping Ju

    2016-07-01

    Full Text Available According to the monitoring of the wide area measurement system, inter-area oscillations happen more and more frequently in a real power grid of China, which are close to the forced oscillation. Applying the conventional forced oscillation theory, the mechanism of these oscillations cannot be explained well, because the oscillations vary with random amplitude and a narrow frequency band. To explain the mechanism of such oscillations, the general forced oscillation (GFO mechanism is taken into consideration. The GFO is the power system oscillation excited by the random excitations, such as power fluctuations from renewable power generation. Firstly, properties of the oscillations observed in the real power grid are analyzed. Using the GFO mechanism, the observed oscillations seem to be the GFO caused by some random excitation. Then the variation of the wind power measured in this power gird is found to be the random excitation which may cause the GFO phenomenon. Finally, simulations are carried out and the power spectral density of the simulated oscillation is compared to that of the observed oscillation, and they are similar with each other. The observed oscillation is thus explained well using the GFO mechanism and the GFO phenomenon has now been observed for the first time in real power grids.

  19. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces.

    Science.gov (United States)

    Boks, Niels P; Norde, Willem; van der Mei, Henny C; Busscher, Henk J

    2008-10-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the following three hypotheses. 1. A strong hydrodynamic shear force to prevent adhesion relates to a strong hydrodynamic shear force to detach an adhering organism. 2. A weak hydrodynamic shear force to detach adhering bacteria implies that more bacteria will be stimulated to detach by passing an air-liquid interface (an air bubble) through the flow chamber. 3. DLVO (Derjaguin, Landau, Verwey, Overbeek) interactions determine the characteristic hydrodynamic shear forces to prevent adhesion and to detach adhering micro-organisms as well as the detachment induced by a passing air-liquid interface. F(prev) varied from 0.03 to 0.70 pN, while F(det) varied from 0.31 to over 19.64 pN, suggesting that after initial contact, strengthening of the bond occurs. Generally, it was more difficult to detach bacteria from DDS-coated glass than from hydrophilic glass, which was confirmed by air bubble detachment studies. Calculated attractive forces based on the DLVO theory (F(DLVO)) towards the secondary interaction minimum were higher on glass than on DDS-coated glass. In general, all three hypotheses had to be rejected, showing that it is important to distinguish between forces acting parallel (hydrodynamic shear) and perpendicular (DLVO, air-liquid interface passages) to the substratum surface.

  20. Cauchy-Matern Model of Sea Surface Wind Speed at the Lake Worth, Florida

    Directory of Open Access Journals (Sweden)

    Ming Li

    2012-01-01

    Full Text Available We study the Cauchy-Matern (CM process with long-range dependence (LRD. The closed form of its power spectrum density (PSD function is given. We apply it to model the autocovariance function (ACF and the PSD of the sea surface wind speed (wind speed for short observed in the Lake Worth, Florida, over the 1984–2006 period. The present results exhibit that the wind speed at the Lake Worth over 1984–2006 is of LRD. The present results exhibit that the CM process may yet be a novel model to fit the wind speed there.

  1. Some issues on atomic force microscopy based surface characterization

    Institute of Scientific and Technical Information of China (English)

    CHEN Yu-hang; HUANG Wen-hao

    2007-01-01

    Influences of tip radius and sampling interval on applying atomic force microscopy(AFM)in quantitative surface evaluations are investigated by numerical simulations and experiments. Several evaluation parameters of surfaces ranging from amplitude to functional parameters are studied. Numerical and experimental results are in good agreements. The accuracy of estimating tip radius on random rough surface with Gaussian distribution of heights using a blind reconstruction method is also discussed theoretically. It is found that the accuracy is greatly depending on the ratio of actual tip radius to rootmean-square (rms) radius of curvature. To obtain an accurate estimation of tip radius under Gaussian rough surface, the ratio has to be larger than 3/2.

  2. Atomic force microscopy of polymer and oligomer surfaces

    CERN Document Server

    Winkel, A K

    2001-01-01

    The surface of ultra-thin films of polyethylene, isotactic polypropylene, polybutene, isotactic polystyrene and polytetrafluoroethylene was studied using an atomic force microscope and resolution of individual molecules was achieved. Comparison of the images with Connolly surfaces enabled identification of which plane was observed in the AFM images, with greater accuracy than conclusions drawn on the basis of surface feature measurement alone. In particular, the results from the experiments with polybutene show that for samples aged sufficiently so that the stable phase is expected in the bulk, this phase is also stable on the surface. The samples were aged sufficiently to ensure that the bulk would be in the stable phase. It is found that this phase is also stable on the surface. Additionally, the annealing behaviour of once folded crystals of the long-chain alkane, C sub 1 sub 6 sub 2 H sub 3 sub 2 sub 6 , is examined in situ, in real time, by atomic force microscopy. Regions of thickening material can be c...

  3. Surface waves propagation on a turbulent flow forced electromagnetically

    CERN Document Server

    Gutiérrez, Pablo

    2015-01-01

    We study the propagation of monochromatic surface waves on a turbulent flow. The flow is generated in a layer of liquid metal by an electromagnetic forcing. This forcing creates a quasi two-dimensional (2D) turbulence with strong vertical vorticity. The turbulent flow contains much more energy than the surface waves. In order to focus on the surface wave, the deformations induced by the turbulent flow are removed. This is done by performing a coherent phase averaging. For wavelengths smaller than the forcing lengthscale, we observe a significant increase of the wavelength of the propagating wave that has not been reported before. We suggest that it can be explained by the random deflection of the wave induced by the velocity gradient of the turbulent flow. Under this assumption, the wavelength shift is an estimate of the fluctuations of deflection angle. The local measurements of the wave frequency far from the wavemaker do not reveal such systematic behavior, although a small shift is measured. Finally we qu...

  4. Spectral Properties of ENVISAT ASAR and QuikSCAT Surface Winds in the North Sea

    DEFF Research Database (Denmark)

    Karagali, Ioanna; Larsén, Xiaoli Guo; Badger, Merete

    2013-01-01

    Spectra derived from ENVISAT Advanced Synthetic Aperture Radar (ASAR) and QuikSCAT near-surface ocean winds are investigated over the North Sea. The two sensors offer a wide range of spatial resolutions, from 600 m to 25 km, with different spatial coverage over the area of interest. This provides...... a unique opportunity to study the impact of the spatial resolution on the spectral properties of the wind over a wide range of length scales. Initially, a sub-domain in the North Sea is chosen, due to the overlap of 87 wind scenes from both sensors. The impact of the spatial resolution is manifested...... or lower. The lower power levels of coarser resolution wind products, particularly when comparing QuikSCAT to ENVISAT ASAR, strongly suggest that the effective resolution of the wind products should be high enough to resolve the spectral properties. Spectra computed from 87 wind maps are consistent...

  5. nowCOAST's Map Service for NOAA NWS NDFD Gridded Forecasts of Surface Wind Gust (knots)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Map Information: This nowCOAST time-offsets map service provides maps depicting the NWS surface wind gust forecasts from the National Digital Forecast Database...

  6. Effect of phase coupling on surface amplitude distribution of wind waves

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    Nonlinear features of wind generated surface waves are considered here to be caused by nonrandomness (non-Uniform) in the phase spectrum. Nonrandomness in recorded waves, if present, would be generally obscured within the error level of observations...

  7. Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

    Science.gov (United States)

    Bathomarco, Ti R. V.; Solorzano, G.; Elias, C. N.; Prioli, R.

    2004-06-01

    The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 μm, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 μm. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

  8. Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Bathomarco, R.V.; Solorzano, G.; Elias, C.N.; Prioli, R

    2004-06-30

    The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 {mu}m, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 {mu}m. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

  9. Tropical Pacific Sea Surface Temperature Anomalies, El Niño, and Equatorial Westerly Wind Events*.

    Science.gov (United States)

    Vecchi, Gabriel A.; Harrison, D. E.

    2000-06-01

    The authors examine global statistical relationships between westerly wind events (WWEs) and sea surface temperature anomaly (SSTA) variability, using a compositing technique for the period 1986-98. The authors describe the extent to which equatorial WWEs are associated with central and eastern equatorial Pacific waveguide warming and with local SSTA changes under the WWE. Their goal is to quantify the extent to which equatorial WWEs are fundamental to the onset and maintenance of warm El Niño-Southern Oscillation conditions. In order to understand the effect of WWEs on SSTA evolution, they begin by examining how SSTA changes in the absence of equatorial WWEs. They find that SSTA tends toward mean climate values in the absence of equatorial WWEs, whether the eastern equatorial Pacific has close to normal SSTA or warmer than normal SSTA.The two equatorial WWE types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling. The equatorial WWE type that has equatorial westerly wind anomalies east of the date line is associated with weak warming under those anomalies, when the eastern equatorial Pacific SSTA is close to normal.When the tropical Pacific has near-normal eastern equatorial Pacific SST, each of the equatorial WWE types is followed by substantial equatorial waveguide warming in the central and eastern Pacific (composite warming as large as 1.0°C); also more than 50% of the large-amplitude WWEs were followed by Niño-3 SSTA warming in excess of 0.5°C. These changes are of similar amplitude and spatial structure as those seen in the onset of El Niño and are consistent with the predicted oceanic response to WWE forcing. When the eastern equatorial Pacific is initially warmer than usual, the two westernmost equatorial WWE types are associated with the maintenance of warm El Niño eastern and central Pacific SSTA; these warm anomalies tend to disappear in the absence of those WWE types. WWEs, or some mechanism

  10. Doppler lidar investigation of wind turbine wake characteristics and atmospheric turbulence under different surface roughness.

    Science.gov (United States)

    Zhai, Xiaochun; Wu, Songhua; Liu, Bingyi

    2017-06-12

    Four field experiments based on Pulsed Coherent Doppler Lidar with different surface roughness have been carried out in 2013-2015 to study the turbulent wind field in the vicinity of operating wind turbine in the onshore and offshore wind parks. The turbulence characteristics in ambient atmosphere and wake area was analyzed using transverse structure function based on Plane Position Indicator scanning mode. An automatic wake processing procedure was developed to determine the wake velocity deficit by considering the effect of ambient velocity disturbance and wake meandering with the mean wind direction. It is found that the turbine wake obviously enhances the atmospheric turbulence mixing, and the difference in the correlation of turbulence parameters under different surface roughness is significant. The dependence of wake parameters including the wake velocity deficit and wake length on wind velocity and turbulence intensity are analyzed and compared with other studies, which validates the empirical model and simulation of a turbine wake for various atmosphere conditions.

  11. Comparison among four kinds of data of sea surface wind stress in the South China Sea

    Institute of Scientific and Technical Information of China (English)

    谢强; 王卫强; 毛庆文

    2002-01-01

    By using remote sensing (ERS) data, FSU data, GOADS data and Hellerman & Rcsenstein objective analysis data to analyze the sea surface wind stress in the South China Sea, it is found that the remote sensing data have higher resolution and more reasonable values. Therefore we suggest that remote sensing data be chosen in the study of climatological features of sea surface wind stress and its seasonal variability in the South China Sea, especially in the study of small and middle scale eddies.

  12. Effect of humidity on the sur-face adhesion force of inor-ganic crystals by the force spectrum method

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Effect of relative humidity on the surface adhesion force of several inorganic crystals of mica, CaF2 and KCl was studied by atomic force microscopy (AFM). The results showed that the magnitude of surface adhesion force is mainly dependent on the surface free energy of the adsorbed liquid film, but almost independent of the thickness of the film. Furthermore, the deliquescence on the crystal surface was investigated, which demonstrated the capability of the force spectrum method to monitor changes in ionic concentrations of adsorbed liquid film in real-time.

  13. Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings

    Directory of Open Access Journals (Sweden)

    Qian Wang

    2016-11-01

    Full Text Available Permanent magnet linear motors (PMLMs with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes.

  14. Influence of persistent wind scour on the surface mass balance of Antarctica

    NARCIS (Netherlands)

    Das, I.; Bell, R.E.; Lenaerts, J.T.M.; Broeke, M.R. van den

    2013-01-01

    Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records1,2. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimati

  15. La force de Casimir et les plasmons de surface

    Science.gov (United States)

    Intravaia, F.; Lambrecht, A.; Reynaud, S.

    2004-11-01

    La présence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreux effets bien connus, dont l'archétype est la force de Casimir apparaîssant entre deux miroirs placés dans le vide par suite de la pression de radiation du vide. Elle a été récemment mesurée avec une précision de l'ordre du %. De nombreux travaux sont consacrés à l'évaluation théorique de cette force en visant une précision du même ordre. Ici nous étudions la force de Casimir dans la configuration de deux miroirs métalliques plans parallèles à température nulle. En supposant les miroirs décrits par un modèle plasma nous interprétons la force de Casimir comme le résultat de l'interaction entre les plasmons de surface des deux miroirs.

  16. A Numerical Study of Wind- and Thermal-Forcing Effects on the Ocean Circulation off Western Australia

    OpenAIRE

    Batteen, Mary L.; Rutherford, Martin J.; Bayler, Eric J.

    1992-01-01

    A high-resolution, multilevel, primitive equation model is initialized with climatological data to investigate the combined effects of wind and thermal forcing on the ocean circulation off Western Australia during the austral fall and winter, corresponding to the period of strongest flow for the anomalous Leeuwin Current. This process-oriented study builds on previous modeling studies, which have elucidated the role of thermal forcing in the generation of the Leeuwin Current and e...

  17. Large surface radiative forcing from topographic blowing snow residuals measured in the High Arctic at Eureka

    Directory of Open Access Journals (Sweden)

    G. Lesins

    2009-03-01

    Full Text Available Ice crystals, also known as diamond dust, are suspended in the boundary layer air under clear sky conditions during most of the Arctic winter in Northern Canada. Occasionally ice crystal events can produce significantly thick layers with optical depths in excess of 2.0 even in the absence of liquid water clouds. Four case studies of high optical depth ice crystal events at Eureka in the Nunavut Territory of Canada during the winter of 2006/07 are presented. They show that the measured ice crystal surface infrared downward radiative forcing ranged from 8 to 36 W m−2 in the wavelength band from 5.6 to 20 μm for 532 nm optical depths ranging from 0.2 to 1.7. MODIS infrared and visible images and the operational radiosonde wind profile were used to show that these high optical depth events were caused by surface snow being blown off 600 to 800 m high mountain ridges about 20 to 30 km North-West of Eureka and advected by the winds towards Eureka as they settled towards the ground within the highly stable boundary layer. This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events from residual blowing snow that becomes a source of boundary layer ice crystals distinct from the classical diamond dust phenomenon.

  18. Multisensor satellite data integration for sea surface wind speed and direction determination

    Science.gov (United States)

    Glackin, D. L.; Pihos, G. G.; Wheelock, S. L.

    1984-01-01

    Techniques to integrate meteorological data from various satellite sensors to yield a global measure of sea surface wind speed and direction for input to the Navy's operational weather forecast models were investigated. The sensors were launched or will be launched, specifically the GOES visible and infrared imaging sensor, the Nimbus-7 SMMR, and the DMSP SSM/I instrument. An algorithm for the extrapolation to the sea surface of wind directions as derived from successive GOES cloud images was developed. This wind veering algorithm is relatively simple, accounts for the major physical variables, and seems to represent the best solution that can be found with existing data. An algorithm for the interpolation of the scattered observed data to a common geographical grid was implemented. The algorithm is based on a combination of inverse distance weighting and trend surface fitting, and is suited to combing wind data from disparate sources.

  19. Characteristics of surface wind structure of tropical cyclones over the north Indian Ocean

    Indian Academy of Sciences (India)

    M Mohapatra; Monica Sharma

    2015-10-01

    Tropical cyclone (TC) wind field monitoring and forecast are important for mariners, ships on sea and modelling group for creation of synthetic vortex, and storm surge and coastal inundation forecasting. Among others, a multi-platform satellite surface wind analysis developed by Co-operative Institute for Research in the Atmosphere (CIRA), USA for the TCs are referred by India Meteorological Department for surface wind field monitoring of TC. Hence, a study has been undertaken to analyze the characteristics of surface wind distribution and hence the structure of TC based on the real time data available from CIRA during 2007–2013. The study includes 19 TCs over the Bay of Bengal (BOB) and six over Arabian Sea (AS). The maximum radial extent of winds reaching threshold values of 34(17), 50(26) and 64(33) knot (ms−1) in each of the four geographical quadrants has been segregated with respect to season of formation, basin of formation and intensity of TC for analysis. The objective is to develop a reference surface wind structure of TC and examine its validity with respect to physical processes. The size of outer core (34(17) knot (ms−1) wind radial extension) as well as inner core (50(26) and 64(33) knot (ms−1) wind radial extension) increases significantly with increase in intensification of TC over BOB during both pre-monsoon and post-monsoon seasons and over AS during pre-monsoon season. The outer core of winds in TCs over the BOB is asymmetric in both pre-monsoon and post-monsoon seasons and for all categories of intensity of TCs. On the other hand, the asymmetry in inner core winds is significantly less. There is also no asymmetry in radial wind extension over the AS during both the seasons, except in case of outer core wind radial extension of VSCS during pre-monsoon season. The low level environment like enhanced cross equatorial flow, lower/middle level relative humidity, vertical wind shear and proximity of TC to the land surface are the determining

  20. The impact of weak synoptic forcing on the valley-wind circulation in the Alpine Inn Valley

    Science.gov (United States)

    Zängl, Günther

    2009-09-01

    This paper investigates the impact of weak synoptic-scale forcing on the thermally induced valley-wind circulation in the Alpine Inn Valley and one of its largest tributaries, the Wipp Valley. To this end, high-resolution numerical simulations with realistic topography but idealized large-scale atmospheric conditions are performed. The large-scale flow has a speed increasing linearly from 5 m s-1 at sea level to 12.5 m s-1 at tropopause level, but its direction is varied between each experiment. For reference, an experiment without large-scale winds is conducted as well. The results indicate that the sensitivity to ambient flow forcing differs substantially between the Inn Valley and the Wipp Valley. The valley-wind circulation of the Inn Valley is found to be fairly robust against weak ambient forcing, changing by a much smaller amount than the along-valley component of the imposed large-scale flow. The valley wind tends to be intensified (weakened) when the ambient flow is aligned with (opposite to) the local valley orientation. However, the flow response is complicated by larger-scale interactions of the ambient flow with the Alpine massif. Most notably, northerly and northwesterly flow is deflected around the Alps, leading to the formation of a low-level jet along the northern edge of the Alps which in turn affects the valley-wind circulation in the lower Inn Valley. For the Wipp Valley, which is oriented approximately normal to the Alpine crest line and constitutes a deep gap in the Alpine crest, two distinctly different flow regimes are found depending on whether the large-scale flow has a significant southerly component or not. In the absence of a southerly flow component, the valley-wind circulation is similarly robust against ambient forcing as in the Inn Valley, with a fairly weak response of the local wind speeds. However, southerly ambient flow tends to force continuous downvalley (southerly) wind in the Wipp Valley. The flow dynamics can then be

  1. Satellite-derived sea surface height and sea surface wind data fusion for spilled oil tracking

    Science.gov (United States)

    Kozai, Katsutoshi

    2003-12-01

    An attempt is made to estimate the trajectory of the spilled oil from the sunken tanker Nakhodka occurred on January 2, 1997 in the Japan Sea by fusing two microwave sensor data, namely ERS-2 altimeter and ADEOS/NSCAT scatterometer data. In this study 'fusion' is defined as the method of more reliable prediction for the trajectory of spilled oil than before. Geostrophic current vectors are derived from ERS-2 altimeter and wind-induced drift vectors are derived from ADEOS/NSCAT scatterometer data These two different satellite-derived vectors are 'fused' together in the surface current model to estimate and evaluate the trajectory of spilled oil from the sunken tanker Nakhodka. The distribution of component of spill vector is mostly accounted for by the distribution of geostrophic velocity component during the study period with some discrepancies during March, 1997.

  2. Simultaneous measurements of air-sea gas transfer velocity and near surface turbulence at low to moderate winds (Invited)

    Science.gov (United States)

    Wang, B.; Liao, Q.; Fillingham, J. H.; Bootsma, H. A.

    2013-12-01

    Parameterization of air-sea gas transfer velocity was routinely made with wind speed. Near surface turbulent dissipation rate has been shown to have better correlation with the gas transfer velocity in a variety of aquatic environments (i.e., the small eddy model) while wind speed is low to moderate. Wind speed model may underestimate gas transfer velocity at low to moderate winds when the near surface turbulence is produced by other environmental forcing. We performed a series of field experiments to measure the CO2 transfer velocity, and the statistics of turbulence immediately below the air-water interface using a novel floating PIV and chamber system. The small eddy model was evaluated and the model coefficient was found to be a non-constant, and it varies with the local turbulent level (figure 1). Measure results also suggested an appropriate scaling of the vertical dissipation profile immediately below the interface under non-breaking conditions, which can be parameterized by the wind shear, wave height and wave age (figure 2). Figure 1. Relation between the coefficient of the small eddy model and dissipation rate. The data also include Chu & Jirka (2003) and Vachon et al. (2010). The solid regression line: α = 0.188log(ɛ)+1.158 Figure 2. Non-dimensional dissipation profiles. Symbols: measured data with the floating PIV. Solid line: regression of measured data with a -0.79 decaying rate. Dash line with -2 slope: Terray et al. (1996) relation. Dash line with two layer structure: Siddiqui & Loewen (2007) relation.

  3. Probing anisotropic surface properties and interaction forces of chrysotile rods by atomic force microscopy and rheology.

    Science.gov (United States)

    Yang, Dingzheng; Xie, Lei; Bobicki, Erin; Xu, Zhenghe; Liu, Qingxia; Zeng, Hongbo

    2014-09-16

    Understanding the surface properties and interactions of nonspherical particles is of both fundamental and practical importance in the rheology of complex fluids in various engineering applications. In this work, natural chrysotile, a phyllosilicate composed of 1:1 stacked silica and brucite layers which coil into cylindrical structure, was chosen as a model rod-shaped particle. The interactions of chrysotile brucite-like basal or bilayered edge planes and a silicon nitride tip were measured using an atomic force microscope (AFM). The force-distance profiles were fitted using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which demonstrates anisotropic and pH-dependent surface charge properties of brucite-like basal plane and bilayered edge surface. The points of zero charge (PZC) of the basal and edge planes were estimated to be around pH 10-11 and 6-7, respectively. Rheology measurements of 7 vol % chrysotile (with an aspect ratio of 14.5) in 10 mM NaCl solution showed pH-dependent yield stress with a local maximum around pH 7-9, which falls between the two PZC values of the edge and basal planes of the rod particles. On the basis of the surface potentials of the edge and basal planes obtained from AFM measurements, theoretical analysis of the surface interactions of edge-edge, basal-edge, and basal-basal planes of the chrysotile rods suggests the yield stress maximum observed could be mainly attributed to the basal-edge attractions. Our results indicate that the anisotropic surface properties (e.g., charges) of chrysotile rods play an important role in the particle-particle interaction and rheological behavior, which also provides insight into the basic understanding of the colloidal interactions and rheology of nonspherical particles.

  4. Understanding the Role of Wind in Reducing the Surface Mass Balance Estimates over East Antarctica

    Science.gov (United States)

    Das, I.; Scambos, T. A.; Koenig, L.; Creyts, T. T.; Bell, R. E.; van den Broeke, M. R.; Lenaerts, J.; Paden, J. D.

    2014-12-01

    Accurate quantification of surface snow-accumulation over Antarctica is important for mass balance estimates and climate studies based on ice core records. An improved estimate of surface mass balance must include the significant role near-surface wind plays in the sublimation and redistribution of snow across Antarctica. We have developed an empirical model based on airborne radar and lidar observations, and modeled surface mass balance and wind fields to produce a continent-wide prediction of wind-scour zones over Antarctica. These zones have zero to negative surface mass balance, are located over locally steep ice sheet areas (>0.002) and controlled by bedrock topography. The near-surface winds accelerate over these zones, eroding and sublimating the surface snow. This scouring results in numerous localized regions (≤ 200 km2) with reduced surface accumulation. Each year, tens of gigatons of snow on the Antarctic ice sheet are ablated by persistent near-surface katabatic winds over these wind-scour zones. Large uncertainties remain in the surface mass balance estimates over East Antarctica as climate models do not adequately represent the small-scale physical processes that lead to mass loss through sublimation or redistribution over the wind-scour zones. In this study, we integrate Operation IceBridge's snow radar over the Recovery Ice Stream with a series of ice core dielectric and depth-density profiles for improved surface mass balance estimates that reflect the mass loss over the wind-scour zones. Accurate surface mass balance estimates from snow radars require spatially variable depth-density profiles. Using an ensemble of firn cores, MODIS-derived surface snow grain size, modeled accumulation rates and surface temperatures from RACMO2, we assemble spatially variable depth-density profiles and use our mapping of snow density variations to estimate layer mass and net accumulation rates from snow radar layer data. Our study improves the quantification of

  5. Satellite SAR observation of the sea surface wind field caused by rain cells

    Institute of Scientific and Technical Information of China (English)

    YE Xiaomin; LIN Mingsen; YUAN Xinzhe; DING Jing; XIE Xuetong; ZHANG Yi; XU Ying

    2016-01-01

    Rain cells or convective rain, the dominant form of rain in the tropics and subtropics, can be easy detected by satellite Synthetic Aperture Radar (SAR) images with high horizontal resolution. The footprints of rain cells on SAR images are caused by the scattering and attenuation of the rain drops, as well as the downward airflow. In this study, we extract sea surface wind field and its structure caused by rain cells by using a RADARSAT-2 SAR image with a spatial resolution of 100 m for case study. We extract the sea surface wind speeds from SAR image by using CMOD4 geophysical model function with outside wind directions of NCEP final operational global analysis data, Advance Scatterometer (ASCAT) onboard European MetOp-A satellite and microwave scatterometer onboard Chinese HY-2 satellite, respectively. The root-mean-square errors (RMSE) of these SAR wind speeds, validated against NCEP, ASCAT and HY-2, are 1.48 m/s, 1.64 m/s and 2.14 m/s, respectively. Circular signature patterns with brighter on one side and darker on the opposite side on SAR image are interpreted as the sea surface wind speed (or sea surface roughness) variety caused by downdraft associated with rain cells. The wind speeds taken from the transect profile which superposes to the wind ambient vectors and goes through the center of the circular footprint of rain cell can be fitted as a cosine or sine curve in high linear correlation with the values of no less than 0.80. The background wind speed, the wind speed caused by rain cell and the diameter of footprint of the rain cell with kilometers or tens of kilometers can be acquired by fitting curve. Eight cases interpreted and analyzed in this study all show the same conclusion.

  6. Wind flow modulation due to variations of the water surface roughness

    Science.gov (United States)

    Shomina, Olga; Ermakov, Stanislav; Kapustin, Ivan; Lazareva, Tatiana

    2016-04-01

    Air-ocean interaction is a classical problem in atmosphere and ocean physics, which has important geophysical applications related to calculation of vertical and horizontal humidity, aerosol and gas fluxes, development of global climate models and weather forecasts. The structure of wind flow over fixed underlying surfaces, such as forestry, buildings, mountains, is well described, while the interaction between a rough water surface and turbulent wind is far more complicated because of the presence of wind waves with different wavelength and amplitudes and propagating with different velocities and directions. The aim of this study was to investigate experimentally the variability of the wind profile structure due to variations of wave characteristics. The surface roughness variations were produced using a) surfactant films (oleic acid) spread on the water surface and b) mechanically generated waves superimposed on wind waves. The first case is related to oil slicks on sea surface, the second one - to the sea swell, which propagates into zones with lower wind velocities and interacts with wind flow. Laboratory experiments were conducted in the Oval Wind Wave Tank (OWWT) at the Institute of Applied Physics, cross-section of the wind channel is 30 cm x30 cm. Wave amplitude and the spectrum of surface waves were measured by a wire wave gauge, the wind speed was measured using a hot-wire anemometer DISA and a Pitot tube. In the experiments with surfactants, two frequencies of dripping of the oleic acid were studied, so that low concentration films with the elasticity parameters of about 19 mN/m and the high concentration ("thick") films with the elasticity of 34 mN/m were formed. In the experiments with mechanically generated waves (MGW) different regimes were studied with MGW amplitude of 3.4 mm and of 4.4 mm, and with MGW frequencies of 3.3 Hz and 3.7 Hz. It was shown, that: a) the mean velocity of the wind flow in the presence of surfactant and MGW can be described

  7. Heat Transfer in a Forced Wall Jet on a heated Rough Surface

    Institute of Scientific and Technical Information of China (English)

    Marie-FrancoiseScibilia

    2000-01-01

    In this paper,an experimental investigation of a laminar wall jet in the presence of a heated wall with stationary particles on its surface,is reproted.The wall jet was submitted to external acoustic vibration amplifying the coherent structures appearing in the laminar region.A wind tunnel was used at very low Reynolds number,Mean velocity and turbulence intensity were measured by a constant temperature anemometer .Measurements were taken in the transition and turbulent regions.Embedded particles were outside the vissous sublayer and it was observed that their presence modifies significantly the flow characteristics in particular the boundary layer is thickened.This study can bring a better understanding of the structure of a flow when it is heated and forced on a rough wall.

  8. Using Surface Pressure to Improve Tropical Cyclone Surface Wind Retrievals from Synthetic Aperture Radar Imagery

    Science.gov (United States)

    2012-09-30

    Jochen Horstmann of NATO Undersea Research Centre ( NURC ). GD and NURC have developed separate methods for estimating wind directions. In addition, NURC ...has been developing “cross-pol” GMFs, which have a lot of promise in the high wind regime. The GD and NURC wind directions are merged into a single

  9. Research on Robot Surface Tracking Motion Based on Force Control of Six-Axis Wrist Force Sensor

    Directory of Open Access Journals (Sweden)

    Zhijun Wang

    2015-01-01

    Full Text Available In order to reduce the environmental contact force and make the operation task completed successfully, the robot is frequently required with force perception and active compliance control. Based on the six-axis wrist force sensor measuring, a robot model of surface tracking motion is proposed, and its force control algorithm and experiment are studied. The measurement principle of the six-axis wrist force sensor and the inadequacy of the sensor measuring the six-dimensional force online are introduced firstly. The surface tracking motion model and its coordinate system are established. On this basis, the relationship between the pose adjustment of surface tracking motion and the measuring results of the six-axis wrist force sensor is deduced. At last, the experimental study of the surface tracking robot system that applied the force control algorithm is conducted. The experiment shows that the robot can adjust the current position and orientation in real time according to the six-axis wrist force sensor measuring, which demonstrates the feasibility of the surface tracking motion model and the correctness of the force control algorithm.

  10. DIRECT MEASUREMENT OF WEAK DEPLETION FORCE BETWEEN TWO SURFACES*

    Institute of Scientific and Technical Information of China (English)

    Xiang-jun Gong; Xiao-chen Xing; Xiao-ling Wei; To Ngai

    2011-01-01

    In a mixture of colloidal particles and polymer molecules, the particles may experience an attractive “depletion force” if the size of the polymer molecule is larger than the interparticle separation. This is because individual polymer molecules experience less conformational entropy if they stay between the particles than they escape the inter-particle space,which results in an osmotic pressure imbalance inside and outside the gap and leads to interparticle attraction. This depletion force has been the subject of several studies since the 1980s, but the direct measurement of this force is still experimentally challenging as it requires the detection of energy variations of the order of kBT and beyond. We present here our results for applying total internal reflection microscopy (TIRM) to directly measure the interaction between a free-moving particle and a flat surface in solutions consisting of small water-soluble organic molecules or polymeric surfactants. Our results indicate that stable nanobubbles (ca. 150 nm) exist free in the above aqueous solutions. More importantly, the existence of such nanobubbles induces an attraction between the spherical particle and flat surface. Using TIRM, we are able to directly measure such weak interaction with a range up to 100 nm. Furthermore, we demonstrate that by employing thermo-sensitive microgel particles as a depleting agent, we are able to quantitatively measure and reversibly control kBT-scale depletion attraction as function of solution pH.

  11. High wind speeds prevent formation of a distinct bacterioneuston community in the sea-surface microlayer.

    Science.gov (United States)

    Rahlff, Janina; Stolle, Christian; Giebel, Helge-Ansgar; Brinkhoff, Thorsten; Ribas-Ribas, Mariana; Hodapp, Dorothee; Wurl, Oliver

    2017-05-01

    The sea-surface microlayer (SML) at the boundary between atmosphere and hydrosphere represents a demanding habitat for bacteria. Wind speed is a crucial but poorly studied factor for its physical integrity. Increasing atmospheric burden of CO2, as suggested for future climate scenarios, may particularly act on this habitat at the air-sea interface. We investigated the effect of increasing wind speeds and different pCO2 levels on SML microbial communities in a wind-wave tunnel, which offered the advantage of low spatial and temporal variability. We found that enrichment of bacteria in the SML occurred solely at a U10 wind speed of ≤5.6 m s-1 in the tunnel and ≤4.1 m s-1 in the Baltic Sea. High pCO2 levels further intensified the bacterial enrichment in the SML during low wind speed. In addition, low wind speed and pCO2 induced the formation of a distinctive bacterial community as revealed by 16S rRNA gene fingerprints and influenced the presence or absence of individual taxonomic units within the SML. We conclude that physical stability of the SML below a system-specific wind speed threshold induces specific bacterial communities in the SML entailing strong implications for ecosystem functioning by wind-driven impacts on habitat properties, gas exchange and matter cycling processes. © FEMS 2017.

  12. Modeling Solar-Wind Heavy-Ions' Potential Sputtering of Lunar KREEP Surface

    Science.gov (United States)

    Barghouty, A. F.; Meyer, F. W.; Harris, R. P.; Adams, J. H., Jr.

    2012-01-01

    Recent laboratory data suggest that potential sputtering may be an important weathering mechanism that can affect the composition of both the lunar surface and its tenuous exosphere; its role and implications, however, remain unclear. Using a relatively simple kinetic model, we will demonstrate that solar-wind heavy ions induced sputtering of KREEP surfaces is critical in establishing the timescale of the overall solar-wind sputtering process of the lunar surface. We will also also show that potential sputtering leads to a more pronounced and significant differentiation between depleted and enriched surface elements. We briefly discuss the impacts of enhanced sputtering on the composition of the regolith and the exosphere, as well as of solar-wind sputtering as a source of hydrogen and water on the moon.

  13. Doppler Navigation System with a Non-Stabilized Antenna as a Sea-Surface Wind Sensor.

    Science.gov (United States)

    Nekrasov, Alexey; Khachaturian, Alena; Veremyev, Vladimir; Bogachev, Mikhail

    2017-06-09

    We propose a concept of the utilization of an aircraft Doppler Navigation System (DNS) as a sea-surface wind sensor complementary to its normal functionality. The DNS with an antenna, which is non-stabilized physically to the local horizontal with x-configured beams, is considered. We consider the wind measurements by the DNS configured in the multi-beam scatterometer mode for a rectilinear flight scenario. The system feasibility and the efficiency of the proposed wind algorithm retrieval are supported by computer simulations. Finally, the associated limitations of the proposed approach are considered.

  14. Short term forecasting of surface layer wind speed using a continuous cascade model

    CERN Document Server

    Baile, Rachel; Poggi, Philippe

    2010-01-01

    This paper describes a statistical method for short-term forecasting of surface layer wind velocity amplitude relying on the notion of continuous cascades. Inspired by recent empirical findings that suggest the existence of some cascading process in the mesoscale range, we consider that wind speed can be described by a seasonal component and a fluctuating part represented by a "multifractal noise" associated with a random cascade. Performances of our model are tested on hourly wind speed series gathered at various locations in Corsica (France) and Netherlands. The obtained results show a systematic improvement of the prediction as compared to reference models like persistence or Artificial Neural Networks.

  15. Validation of sea surface temperature, wind speed and integrated water vapour from MSMR measurements. Project report

    Digital Repository Service at National Institute of Oceanography (India)

    Muraleedharan, P.M.

    and autonomous weather station) were utilized for measuring sea truth parameters such as sea surface temperature (SST), Sea Surface Wind Speed (WS) and Columnar Water Vapor (WV). Total match-ups for SST and WS measured from various platforms exceeded 1400 (2 hrs...

  16. A fast model for mean and turbulent wind characteristics over terrain with mixed surface roughness

    DEFF Research Database (Denmark)

    Astrup, P.; Mikkelsen, T.; Jensen, N.O.

    1997-01-01

    The real-time near-range atmospheric model chain in RODOS already includes the fast spectral LINCOM code, which was originally developed by Rise for modelling the mean wind fields over hilly, but otherwise homogeneous, terrain. Its output is used as a wind field driver for the dispersion model...... of arrival of radioactive clouds traversing, for instance, a land/water/land surface, and (2) for calculation of the turbulent shear stress, and thereby the scaling parameters, over mixed terrain....

  17. Remote Sensing of Sea Surface Wind of Hurricane Michael by GPS Reflected Signals

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, the propagating geometry and the waveform of the GPS reflected signals are expatiated in detail. Furthermore, the principle and the method of retrieving sea surface wind are presented. In order to test the feasibility of retrieval, the experiment data obtained by NASA in Hurricane Michael are used. The result shows that the retrieval accuracy of wind speed is about 2 m/s.

  18. Airborne Wind Energy: Implementation and Design for the U.S. Air Force

    Science.gov (United States)

    2011-03-01

    Excitement among researchers about Airborne Wind Energy (AWE) technology matches DoD aims to advance and employ renewable energy. AWE seeks to cost...effectively tap the vast supply of wind energy available at altitudes high above the reach of conventional, ground-based wind turbines (e.g. 500

  19. Comments on Evanescent Pressure Gradient Response in the Upper Ocean to Subinertial Wind Stress Forcing of Finite Wavelength

    Science.gov (United States)

    1988-07-01

    IIl/r’ (b). The dashed curve is the solution presented by response in the upper ocean to subinertial wind stress forcing Codes WM and the solid curve...especially as c hand side of Eq. (3). approaches the inertial frequency f,. h nd s re is 0 With pressure terms included, the expression for The wind ... stress is mixed layer velocities are [Eq. (3.1) in WM], in the 7 = [0, r’ Re(e""’ C)] (6) usual fluid mechanical notation. and following WM. we are

  20. Statistical downscaling of IPCC sea surface wind and wind energy predictions for U.S. east coastal ocean, Gulf of Mexico and Caribbean Sea

    Science.gov (United States)

    Yao, Zhigang; Xue, Zuo; He, Ruoying; Bao, Xianwen; Song, Jun

    2016-08-01

    A multivariate statistical downscaling method is developed to produce regional, high-resolution, coastal surface wind fields based on the IPCC global model predictions for the U.S. east coastal ocean, the Gulf of Mexico (GOM), and the Caribbean Sea. The statistical relationship is built upon linear regressions between the empirical orthogonal function (EOF) spaces of a cross- calibrated, multi-platform, multi-instrument ocean surface wind velocity dataset (predictand) and the global NCEP wind reanalysis (predictor) over a 10 year period from 2000 to 2009. The statistical relationship is validated before applications and its effectiveness is confirmed by the good agreement between downscaled wind fields based on the NCEP reanalysis and in-situ surface wind measured at 16 National Data Buoy Center (NDBC) buoys in the U.S. east coastal ocean and the GOM during 1992-1999. The predictand-predictor relationship is applied to IPCC GFDL model output (2.0°×2.5°) of downscaled coastal wind at 0.25°×0.25° resolution. The temporal and spatial variability of future predicted wind speeds and wind energy potential over the study region are further quantified. It is shown that wind speed and power would significantly be reduced in the high CO2 climate scenario offshore of the mid-Atlantic and northeast U.S., with the speed falling to one quarter of its original value.

  1. Tool for Forecasting Cool-Season Peak Winds Across Kennedy Space Center and Cape Canaveral Air Force Station (CCAFS)

    Science.gov (United States)

    Barrett, Joe H., III; Roeder, William P.

    2010-01-01

    Peak wind speed is important element in 24-Hour and Weekly Planning Forecasts issued by 45th Weather Squadron (45 WS). Forecasts issued for planning operations at KSC/CCAFS. 45 WS wind advisories issued for wind gusts greater than or equal to 25 kt. 35 kt and 50 kt from surface to 300 ft. AMU developed cool-season (Oct - Apr) tool to help 45 WS forecast: daily peak wind speed, 5-minute average speed at time of peak wind, and probability peak speed greater than or equal to 25 kt, 35 kt, 50 kt. AMU tool also forecasts daily average wind speed from 30 ft to 60 ft. Phase I and II tools delivered as a Microsoft Excel graphical user interface (GUI). Phase II tool also delivered as Meteorological Interactive Data Display System (MIDDS) GUI. Phase I and II forecast methods were compared to climatology, 45 WS wind advisories and North American Mesoscale model (MesoNAM) forecasts in a verification data set.

  2. Surface Wind Vector and Rain Rate Observation Capability of Future Hurricane Imaging Radiometer (HIRAD)

    Science.gov (United States)

    Miller, Timothy; Atlas, Robert; Bailey, M. C.; Black, Peter; El-Nimri, Salem; Hood, Robbie; James, Mark; Johnson, James; Jones, Linwood; Ruf, Christopher; Uhlhorn, Eric

    2009-01-01

    The Hurricane Imaging Radiometer (HIRAD) is the next-generation Stepped Frequency Microwave Radiometer (SFMR), and it will offer the capability of simultaneous wide-swath observations of both extreme ocean surface wind vector and strong precipitation from either aircraft (including UAS) or satellite platforms. HIRAD will be a compact, lightweight, low-power instrument with no moving parts that will produce valid wind observations under hurricane conditions when existing microwave sensors (radiometers or scatterometers) are hindered by precipitation. The SFMR i s a proven aircraft remote sensing system for simultaneously observing extreme ocean surface wind speeds and rain rates, including those of major hurricane intensity. The proposed HIRAD instrument advances beyond the current nadir viewing SFMR to an equivalent wide-swath SFMR imager using passive microwave synthetic thinned aperture radiometer technology. The first version of the instrument will be a single polarization system for wind speed and rain rate, with a dual-polarization system to follow for wind vector capability. This sensor will operate over 4-7 GHz (C-band frequencies) where the required tropical cyclone remote sensing physics has been validated by both SFMR and WindSat radiometers. HIRAD incorporates a unique, technologically advanced array antenna and several other technologies successfully demonstrated by NASA s Instrument Incubator Program. A brassboard (laboratory) version of the instrument has been completed and successfully tested in a test chamber. Development of the aircraft instrument is underway, with flight testing planned for the fall of 2009. Preliminary Observing System Simulation Experiments (OSSEs) show that HIRAD will have a significant positive impact on surface wind analyses as either a new aircraft or satellite sensor. New off-nadir data collected in 2008 by SFMR that affirms the ability of this measurement technique to obtain wind speed data at non-zero incidence angle will

  3. Role of Surface Energy Exchange for Simulating Wind Turbine Inflow: A Case Study in the Southern Great Plains, USA

    OpenAIRE

    Sonia Wharton; Matthew Simpson; Jessica L. Osuna; Jennifer F. Newman; Biraud, Sebastien C.

    2014-01-01

    The Weather Research and Forecasting (WRF) model is used to investigate choice of land surface model (LSM) on the near surface wind profile, including heights reached by multi-megawatt (MW) wind turbines. Simulations of wind profiles and surface energy fluxes were made using five LSMs of varying degrees of sophistication in dealing with soil–plant–atmosphere feedbacks for the Department of Energy (DOE) Southern Great Plains (SGP) Atmospheric Radiation Measurement Program (ARM) Central Facili...

  4. CYGNSS Observations of Surface Wind Speeds in Oceanic Tropical and Extratropical Cyclones

    Science.gov (United States)

    Posselt, D. J.; Crespo, J.; Naud, C. M.

    2016-12-01

    The Cyclone Global Navigation Satellite System (CYGNSS) mission is the first of the new generation of NASA Earth Venture missions, and consists of a constellation of eight small satellites scheduled for launch in November 2016. The mission utilizes GPS signals reflected from the Earth's surface to infer near-surface wind speeds over the global tropical oceans. The eight-satellite constellation will observe ocean-surface wind speeds in all weather conditions (including in heavy precipitation) with a median revisit time of approximately 3 hours. While CYGNSS is designed to measure wind speeds in the inner core of tropical cyclones, it will observe near-surface winds over all oceanic regions within the span of its orbit. The orbit inclination is 35 degrees, which means that the satellite will observe primarily the tropics and sub-tropics; however, because the antennae are angled 28 degrees off-nadir, the effective range of latitudes spans -40 to 40 degrees. As such, CYGNSS will observe regions known to be characterized by rapid extratropical cyclone development (e.g., the southern portion of the Gulf Stream off the U.S. East Coast). In this presentation, we discuss CYGNSS sampling characteristics, with an eye toward its potential to observe winds not only in tropical cyclones, but in extratropical cyclones as well. We simulate orbits over a historical extratropical storm, and also utilize a multi-year database of cyclone centers to determine CYGNSS sampling characteristics integrated over many storms.

  5. A Study of DC Surface Plasma Discharge in Absence of Free Airflow: Ionic Wind Velocity Profile

    Directory of Open Access Journals (Sweden)

    M. Rafika

    2009-01-01

    Full Text Available In our study we are interested with the DC (Direct Current electric corona discharge created between two wire electrodes. We present experimental results related to some electroaerodynamic actuators based on the DC corona discharge at the surface of a dielectric material. We used different geometrical forms of dielectric surface such as a plate, a cylinder and a wing of aircraft of type NACA 0015. We present the current density-electric filed characteristics for different cases in order to determine the discharge regimes. The corona discharge produces non-thermal plasma so that it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. We have measured the ionic wind induced by the corona discharge in absence of free external airflow, we give the ionic wind velocity profiles for different surface forms and we compare the actuators effect based on the span of the ionic wind velocity values. We notice that the maximum ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

  6. Micro-swimmer dynamics in free-surface turbulence subject to wind stress

    Science.gov (United States)

    Marchioli, Cristian; Lovecchio, Salvatore; Soldati, Alfredo

    2016-11-01

    We examine the effect of wind-induced shear on the orientation and distribution of motile micro-swimmers in free-surface turbulence. Winds blowing above the air-water interface can influence the distribution and productivity of motile organisms via the shear generated just below the surface. Swimmer dynamics depend not only by the advection of the fluid but also by external stimuli like nutrient concentration, light, gravity. Here we focus on gyrotaxis, resulting from the gravitational torque generated by an asymmetric mass distribution within the organism. The combination of such torque with the viscous torque due to shear can re-orient swimmers, reducing their vertical migration and causing entrapment in horizontal fluid layers. Through DNS-based Euler-Lagrangian simulations we investigate the effect of wind-induced shear on the motion of gyrotactic swimmers in turbulent open channel flow. We consider different wind directions and swimmers with different reo-rientation time (reflecting the ability to react to turbulent fluctuations). We show that only stable (high-gyrotaxis) swimmers may reach the surface and form densely concentrated filaments, the topology of which depends on the wind direction. Otherwise swimmers exhibit weaker vertical fluxes and segregation at the surface.

  7. Flight paths of seabirds soaring over the ocean surface enable measurement of fine-scale wind speed and direction.

    Science.gov (United States)

    Yonehara, Yoshinari; Goto, Yusuke; Yoda, Ken; Watanuki, Yutaka; Young, Lindsay C; Weimerskirch, Henri; Bost, Charles-André; Sato, Katsufumi

    2016-08-09

    Ocean surface winds are an essential factor in understanding the physical interactions between the atmosphere and the ocean. Surface winds measured by satellite scatterometers and buoys cover most of the global ocean; however, there are still spatial and temporal gaps and finer-scale variations of wind that may be overlooked, particularly in coastal areas. Here, we show that flight paths of soaring seabirds can be used to estimate fine-scale (every 5 min, ∼5 km) ocean surface winds. Fine-scale global positioning system (GPS) positional data revealed that soaring seabirds flew tortuously and ground speed fluctuated presumably due to tail winds and head winds. Taking advantage of the ground speed difference in relation to flight direction, we reliably estimated wind speed and direction experienced by the birds. These bird-based wind velocities were significantly correlated with wind velocities estimated by satellite-borne scatterometers. Furthermore, extensive travel distances and flight duration of the seabirds enabled a wide range of high-resolution wind observations, especially in coastal areas. Our study suggests that seabirds provide a platform from which to measure ocean surface winds, potentially complementing conventional wind measurements by covering spatial and temporal measurement gaps.

  8. Impact of climate change on surface wind regime over the Peru-Chile upwelling region

    Science.gov (United States)

    Goubanova, K.; Echevin, V.; Dewitte, B.; Garreaud, R.; Terray, P.; Vrac, M.

    2009-04-01

    The ocean region off the Chile-Peru coast is characterized by upwelling of cold, nutrient-rich waters, which drives an exceptionally high biological productivity. This upwelling is induced by the persistent southerly winds along the coast that exhibit a coastal jet structure at intraseasonal scales. Recent climate change studies based on the coupled atmosphere-ocean general circulation models (AOGCM) show a strengthening of the large-scale southerlies along the subtropical coast that could lead to an increase in coastal upwelling. However the coastal jet events which represent a considerable source of the synoptic variability of the alongshore winds are characterized by horizontal scale comparable to a AOGCM grid cell size, and cannot be therefore explicitly resolved by the AOGCMs. In order to provide a regional estimate of the winds as predicted by the coarse-resolution AOGCMs, a statistical downscaling method based on multiple linear regression is proposed. Large-scale wind at 10 m and sea level pressure are chosen as the predictor variables for regional 10 m wind. The validation is performed in two steps. First, QuikSCAT and ERS satellite products and NCEP reanalysis for the period 1992-2006 are used to build and validate the statistical model for the present climate. Second, the model is validated under a warmer climate: it is applied to large-scale predictors extracted from HadCM3 AOGCM simulations for the A2 and B2 SRES scenarios (2071-2100); the downscaled wind is then compared with outputs of the PRECIS regional climate model, forced at its boundaries by the same HadCM3 scenarios. To assess climate change impact on the along-shore wind, the statistical downscaling is applied to two contrasted SRES scenarios, namely the so-called preindustrial and CO2 quadrupling. The outputs of the IPSL-CM4 AOGCM are used as predictors. Evolution of the along-shore wind regime with a focus on the change of the coastal jet characteristics is discussed. For this particular

  9. The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

    Science.gov (United States)

    Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

    1994-01-01

    The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat

  10. The k-ε-fP model applied to double wind turbine wakes using different actuator disk force methods

    DEFF Research Database (Denmark)

    Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan

    2015-01-01

    The newly developed k-ε-fP  eddy viscosity model is applied to double wind turbine wake configurations in a neutral atmospheric boundary layer, using a Reynolds-Averaged Navier–Stokes solver. The wind turbines are represented by actuator disks. A proposed variable actuator disk force method...... is employed to estimate the power production of the interacting wind turbines, and the results are compared with two existing methods: a method based on tabulated airfoil data and a method based on the axial induction from 1D momentum theory. The proposed method calculates the correct power, while the other...... two methods overpredict it. The results of the k-ε-fP  eddy viscosity model are also compared with the original k-ε eddy viscosity model and large-eddy simulations. Compared to the large-eddy simulations-predicted velocity and power deficits, the k-ε-fP  is superior to the original k-ε model...

  11. Coastal Boundary Layer Characteristics of Wind, Turbulence, and Surface Roughness Parameter over the Thumba Equatorial Rocket Launching Station, India

    Directory of Open Access Journals (Sweden)

    K. V. S. Namboodiri

    2014-01-01

    Full Text Available The study discusses the features of wind, turbulence, and surface roughness parameter over the coastal boundary layer of the Peninsular Indian Station, Thumba Equatorial Rocket Launching Station (TERLS. Every 5 min measurements from an ultrasonic anemometer at 3.3 m agl from May 2007 to December 2012 are used for this work. Symmetries in mesoscale turbulence, stress off-wind angle computations, structure of scalar wind, resultant wind direction, momentum flux (M, Obukhov length (L, frictional velocity (u*, w-component, turbulent heat flux (H, drag coefficient (CD, turbulent intensities, standard deviation of wind directions (σθ, wind steadiness factor-σθ relationship, bivariate normal distribution (BND wind model, surface roughness parameter (z0, z0 and wind direction (θ relationship, and variation of z0 with the Indian South West monsoon activity are discussed.

  12. Entrainment of radio frequency chaff by wind as a function of surface aerodynamic roughness.

    Science.gov (United States)

    Gillies, John A; Nickling, William G

    2003-02-01

    Radio frequency (RF) chaff (approximately 2-cm x 25-microm diameter aluminum-coated glass silicate cylinders) released by military aircraft during testing and training activities has the potential to become entrained by wind upon settling to the Earth's surface. Once entrained from the surface there is the potential for RF chaff to be abraded and produce PM10 and PM2.5, which are regulated pollutants and pose health concerns. A series of portable wind tunnel tests were carried out to examine the propensity of RF chaff to become entrained by wind by defining the relationship between the threshold friction velocity of RF chaff (u(*t RF chaff)) and aerodynamic roughness (z(o)) of surfaces onto which it may deposit. The test surfaces were of varying roughness including types near the Naval Air Station (NAS), Fallon, NV, where RF chaff is released. The u(*t) of this fibrous material ranged from 0.14 m/sec for a smooth playa to 0.82 m/sec for a rough crusted playa surface with larger cobble-sized (approximately 6-26-cm diameter) rocks rising above the surface. The u(*t RF chaff) is dependent on the z(o) of the surface onto which it falls as well as the physical characteristics of the roughness. The wind regime of Fallon would allow for chaff suspension events to occur should it settle on typical surfaces in the area. However, the wind climatology of this area makes the probability of such events relatively low.

  13. Optimized Model Surfaces for Advanced Atomic Force Microscopy Studies of Surface Nanobubbles.

    Science.gov (United States)

    Song, Bo; Zhou, Yi; Schönherr, Holger

    2016-11-01

    The formation of self-assembled monolayers (SAMs) of binary mixtures of 16-mercaptohexadecanoic acid (MHDA) and 1-octadecanethiol (ODT) on ultraflat template-stripped gold (TSG) surfaces was systematically investigated to clarify the assembly behavior, composition, and degree of possible phase segregation in light of atomic force microscopy (AFM) studies of surface nanobubbles on these substrates. The data for SAMs on TSG were compared to those obtained by adsorption on rough evaporated gold, as reported in a previous study. Quartz crystal microbalance and surface plasmon resonance data acquired in situ on TSG indicate that similar to SAM formation on conventional evaporated gold substrates ODT and MHDA form monolayers and bilayers, respectively. The second layer on MHDA, whose formation is attributed to hydrogen bonding, can be easily removed by adequate rinsing with water. The favorable agreement of the grazing incidence reflection Fourier transform infrared (GIR FTIR) spectroscopy and contact angle data analyzed with the Israelachvili-Gee model suggests that the binary SAMs do not segregate laterally. This conclusion is fully validated by high-resolution friction force AFM observations down to a length scale of 8-10 nm, which is much smaller than the typical observed surface nanobubble radii. Finally, correspondingly functionalized TSG substrates are shown to be valuable supports for studying surface nanobubbles by AFM in water and for addressing the relation between surface functionality and nanobubble formation and properties.

  14. Numerical and Observational Investigations of Long-Lived Mcs-Induced Severe Surface Wind Events: the Derecho

    Science.gov (United States)

    Schmidt, Jerome Michael

    This study addresses the production of sustained, straight-line, severe surface winds associated with mesoscale convective systems (MCSs) of extratropical origin otherwise known as derechos. The physical processes which govern the observed derecho characteristics are identified and their possible forcing mechanisms are determined. Detailed observations of two derechos are presented along with simulations using the Colorado State University Regional Atmospheric Modeling System (CSU-RAMS). The observations revealed a derecho environment characterized by strong vertical wind shear through the depth of the troposphere and large values of convective available potential energy (CAPE). The thermodynamic environment of the troposphere in each case had a distinct three-layer structure consisting of: (i) a surface-based stable layer of 1-to-2 km in depth, (ii) an elevated well -mixed layer of 2-4 km in depth, and (iii) an upper tropospheric layer of intermediate stability that extended to the tropopause. Two primary sets of simulations were performed to assess the impact of the observed environmental profiles on the derecho structure, propagation, and longevity. The first set consisted of nested-grid regional-scale simulations initialized from the standard NMC analyses on a domain having relatively coarse horizontal resolution (75 km). The second set of simulations consisted of two and three-dimensional experiments initialized in a horizontally homogeneous environment having a relatively fine horizontal resolution (2 km) and explicit microphysics. The results from these experiments indicate the importance of convectively -induced gravity waves on the MCS structure, propagation, longevity, and severe surface wind development. The sensitivity of the simulated convection and gravity waves to variations in the vertical wind shear and moisture profiles are described. Detailed Doppler radar analyses and 3-D simulations of a severe, bow echo squall line are presented which reveal

  15. Surface microstructure of bitumen characterized by atomic force microscopy.

    Science.gov (United States)

    Yu, Xiaokong; Burnham, Nancy A; Tao, Mingjiang

    2015-04-01

    Bitumen, also called asphalt binder, plays important roles in many industrial applications. It is used as the primary binding agent in asphalt concrete, as a key component in damping systems such as rubber, and as an indispensable additive in paint and ink. Consisting of a large number of hydrocarbons of different sizes and polarities, together with heteroatoms and traces of metals, bitumen displays rich surface microstructures that affect its rheological properties. This paper reviews the current understanding of bitumen's surface microstructures characterized by Atomic Force Microscopy (AFM). Microstructures of bitumen develop to different forms depending on crude oil source, thermal history, and sample preparation method. While some bitumens display surface microstructures with fine domains, flake-like domains, and dendrite structuring, 'bee-structures' with wavy patterns several micrometers in diameter and tens of nanometers in height are commonly seen in other binders. Controversy exists regarding the chemical origin of the 'bee-structures', which has been related to the asphaltene fraction, the metal content, or the crystallizing waxes in bitumen. The rich chemistry of bitumen can result in complicated intermolecular associations such as coprecipitation of wax and metalloporphyrins in asphaltenes. Therefore, it is the molecular interactions among the different chemical components in bitumen, rather than a single chemical fraction, that are responsible for the evolution of bitumen's diverse microstructures, including the 'bee-structures'. Mechanisms such as curvature elasticity and surface wrinkling that explain the rippled structures observed in polymer crystals might be responsible for the formation of 'bee-structures' in bitumen. Despite the progress made on morphological characterization of bitumen using AFM, the fundamental question whether the microstructures observed on bitumen surfaces represent its bulk structure remains to be addressed. In addition

  16. Quality Control Methodology Of A Surface Wind Observational Database In North Eastern North America

    Science.gov (United States)

    Lucio-Eceiza, Etor E.; Fidel González-Rouco, J.; Navarro, Jorge; Conte, Jorge; Beltrami, Hugo

    2016-04-01

    This work summarizes the design and application of a Quality Control (QC) procedure for an observational surface wind database located in North Eastern North America. The database consists of 526 sites (486 land stations and 40 buoys) with varying resolutions of hourly, 3 hourly and 6 hourly data, compiled from three different source institutions with uneven measurement units and changing measuring procedures, instrumentation and heights. The records span from 1953 to 2010. The QC process is composed of different phases focused either on problems related with the providing source institutions or measurement errors. The first phases deal with problems often related with data recording and management: (1) compilation stage dealing with the detection of typographical errors, decoding problems, site displacements and unification of institutional practices; (2) detection of erroneous data sequence duplications within a station or among different ones; (3) detection of errors related with physically unrealistic data measurements. The last phases are focused on instrumental errors: (4) problems related with low variability, placing particular emphasis on the detection of unrealistic low wind speed records with the help of regional references; (5) high variability related erroneous records; (6) standardization of wind speed record biases due to changing measurement heights, detection of wind speed biases on week to monthly timescales, and homogenization of wind direction records. As a result, around 1.7% of wind speed records and 0.4% of wind direction records have been deleted, making a combined total of 1.9% of removed records. Additionally, around 15.9% wind speed records and 2.4% of wind direction data have been also corrected.

  17. Super-Eddington stellar winds driven by near-surface energy deposition

    Science.gov (United States)

    Quataert, Eliot; Fernández, Rodrigo; Kasen, Daniel; Klion, Hannah; Paxton, Bill

    2016-05-01

    We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g. unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in the giant eruptions of luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem v_crit˜ (dot{E} G)^{1/5} (where dot{E} is the heating rate) to the stellar escape speed near the heating region vesc(rh). For vcrit ≳ vesc(rh), the wind kinetic power at large radii dot{E}_w ˜ dot{E}. For vcrit ≲ vesc(rh), most of the energy is used to unbind the wind material and thus dot{E}_w ≲ dot{E}. Multidimensional hydrodynamic simulations without radiation diffusion using FLASH and one-dimensional hydrodynamic simulations with radiation diffusion using MESA are in good agreement with the analytic predictions. The photon luminosity from the wind is itself super-Eddington but in many cases the photon luminosity is likely dominated by `internal shocks' in the wind. We discuss the application of our models to eruptive mass-loss from massive stars and argue that the wind models described here can account for the broad properties of LBV outflows and the enhanced mass-loss in the years prior to Type IIn core-collapse supernovae.

  18. A contoured continuum surface force model for particle methods

    Science.gov (United States)

    Duan, Guangtao; Koshizuka, Seiichi; Chen, Bin

    2015-10-01

    A surface tension model is essential to simulate multiphase flows with deformed interfaces. This study develops a contoured continuum surface force (CCSF) model for particle methods. A color function that varies sharply across the interface to mark different fluid phases is smoothed in the transition region, where the local contour curvature can be regarded as the interface curvature. The local contour passing through each reference particle in the transition region is extracted from the local profile of the smoothed color function. The local contour curvature is calculated based on the Taylor series expansion of the smoothed color function, whose derivatives are calculated accurately according to the definition of the smoothed color function. Two schemes are proposed to specify the smooth radius: fixed scheme, where 2 ×re (re = particle interaction radius) is assigned to all particles in the transition region; and varied scheme, where re and 2 ×re are assigned to the central and edged particles in the transition region respectively. Numerical examples, including curvature calculation for static circle and ellipse interfaces, deformation of square droplet to a circle (2D and 3D), droplet deformation in shear flow, and droplet coalescence, are simulated to verify the CCSF model and compare its performance with those of other methods. The CCSF model with the fixed scheme is proven to produce the most accurate curvature and lowest parasitic currents among the tested methods.

  19. Eddy heat flux in the Southern Ocean: response to variable wind forcing

    OpenAIRE

    Hogg, Andrew Mcc.; Meredith, Michael P.; Blundell, Jeffrey R.; Wilson, Christopher

    2008-01-01

    We assess the role of time-dependent eddy variability in the Antarctic Circumpolar Current (ACC) in influencing warming of the Southern Ocean. For this, we use an eddy-resolving quasigeostrophic model of the wind-driven circulation, and quantify the response of circumpolar transport, eddy kinetic energy and eddy heat transport to changes in winds. On interannual timescales, the model exhibits the behaviour of an "eddy saturated" ocean state, where increases in wind stress do not signicantly ...

  20. [Influence of surface roughness on oral streptococcal adhesion forces to dental filling materials].

    Science.gov (United States)

    Sainan, Zheng; Li, Jiang; Lei, Zhang; Liying, Hao; Lu, Ye; Wei, Li

    2016-10-01

    This study is to determine the common oral streptococcal adhesion forces by using composite resin and glass ionomer cement (GIC) with different degrees of surface roughness via atomic force microscopy (AFM) analysis. The influence of surface roughness on bacterial adhesion force is also discussed. Polishing and grinding were applied to obtain 300, 200, 100, and 10 nm surfaces of light-cured composite resin and GIC samples. Surface topography was assessed by AFM analysis. Initial colonizers (Streptococcus sanguinis and Streptococcus mitis) and cariogenic bacterial strains (Streptococcus mutans and Streptococcus sobrinus) were used to obtain bacteria-modified AFM probes. The force-distance curves were also measured by AFM analysis to determine the adhesion forces of bacteria on the surfaces of the composite resin and GIC. Material surface roughness was analyzed using ANOVA, and adhesion forces were subjected to nonparametric analysis (Kruskal-Wallis test). Comparison among groups was performed by Dunn's test. Material surface roughness and bacterial adhesion forces were subjected to correlation analysis. Bacterial adhesion forces increased with increasing material roughness. The adhesion forces of the four bacterial species reached the maximum on the material surface of 300 nm. The adhesion force of Streptococcus mutans increased from 0.578 nN to 2.876 nN on GIC surfaces with 10 and 300 nm roughness. The adhesion forces of the four species on the surface of the composite resin were stronger than that of GIC. The initial colonizers exhibited stronger adhesion forces to different materials than the cariogenic strains. Intergroup differences were evident on the 200 and 300 nm material surfaces. The surface roughness of the material significantly affected the bacterial adhesion forces, and a significant linear correlation existed between both factors. The bacterial adhesion forces of the GIC were lower than that of the composite resin. Furthermore, surface roughness

  1. Effects of bridge cable surface roughness and cross-sectional distortion on aerodynamic force coefficients

    DEFF Research Database (Denmark)

    Matteoni, G.; Georgakis, C.T.

    2012-01-01

    Theoretical and experimental investigations to date have assumed that bridge cables can be modeled as ideal circular cylinders and the associated aerodynamic coefficients are invariant with the wind angle-of-attack. On the other hand, bridge cables are normally characterized by local alterations...... of their inherent surface roughness and shape, which might present a significant disturbance for the surrounding wind flow. The present study focuses on the experimental determination, based on static wind tunnel tests, of the aerodynamic coefficients of full-scale bridge cable section models both perpendicular...... and inclined to the flow, for varying wind angles-of-attack. The wind tunnel test results demonstrate that the aerodynamic coefficients of bridge cables can be significantly affected by the wind angle-of-attack....

  2. Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

    Science.gov (United States)

    Allaerts, Dries; Meyers, Johan

    2015-11-01

    In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.

  3. Retrieval of sea surface winds under hurricane conditions from GNSS-R observations

    Institute of Scientific and Technical Information of China (English)

    JING Cheng; YANG Xiaofeng; MA Wentao; YU Yang; DONG Di; LI Ziwei; XU Cong

    2016-01-01

    Reflected signals from global navigation satellite systems (GNSSs) have been widely acknowledged as an important remote sensing tool for retrieving sea surface wind speeds. The power of GNSS reflectometry (GNSS-R) signals can be mapped in delay chips and Doppler frequency space to generate delay Doppler power maps (DDMs), whose characteristics are related to sea surface roughness and can be used to retrieve wind speeds. However, the bistatic radar cross section (BRCS), which is strongly related to the sea surface roughness, is extensively used in radar. Therefore, a bistatic radar cross section (BRCS) map with a modified BRCS equation in a GNSS-R application is introduced. On the BRCS map, three observables are proposed to represent the sea surface roughness to establish a relationship with the sea surface wind speed. Airborne Hurricane Dennis (2005) GNSS-R data are then used. More than 16 000 BRCS maps are generated to establish GMFs of the three observables. Finally, the proposed model and classic one-dimensional delay waveform (DW) matching methods are compared, and the proposed model demonstrates a better performance for the high wind speed retrievals.

  4. Mesoscale Near-Surface Wind Speed Variability Mapping with Synthetic Aperture Radar.

    Science.gov (United States)

    Young, George; Sikora, Todd; Winstead, Nathaniel

    2008-11-05

    Operationally-significant wind speed variability is often observed within synthetic aperture radar-derived wind speed (SDWS) images of the sea surface. This paper is meant as a first step towards automated distinguishing of meteorological phenomena responsible for such variability. In doing so, the research presented in this paper tests feature extraction and pixel aggregation techniques focused on mesoscale variability of SDWS. A sample of twenty eight SDWS images possessing varying degrees of near-surface wind speed variability were selected to serve as case studies. Gaussian high- and low-pass, local entropy, and local standard deviation filters performed well for the feature extraction portion of the research while principle component analysis of the filtered data performed well for the pixel aggregation. The findings suggest recommendations for future research.

  5. Completion of the Edward Air Force Base Statistical Guidance Wind Tool

    Science.gov (United States)

    Dreher, Joseph G.

    2008-01-01

    The goal of this task was to develop a GUI using EAFB wind tower data similar to the KSC SLF peak wind tool that is already in operations at SMG. In 2004, MSFC personnel began work to replicate the KSC SLF tool using several wind towers at EAFB. They completed the analysis and QC of the data, but due to higher priority work did not start development of the GUI. MSFC personnel calculated wind climatologies and probabilities of 10-minute peak wind occurrence based on the 2-minute average wind speed for several EAFB wind towers. Once the data were QC'ed and analyzed the climatologies were calculated following the methodology outlined in Lambert (2003). The climatologies were calculated for each tower and month, and then were stratified by hour, direction (10" sectors), and direction (45" sectors)/hour. For all climatologies, MSFC calculated the mean, standard deviation and observation counts of the Zminute average and 10-minute peak wind speeds. MSFC personnel also calculated empirical and modeled probabilities of meeting or exceeding specific 10- minute peak wind speeds using PDFs. The empirical PDFs were asymmetrical and bounded on the left by the 2- minute average wind speed. They calculated the parametric PDFs by fitting the GEV distribution to the empirical distributions. Parametric PDFs were calculated in order to smooth and interpolate over variations in the observed values due to possible under-sampling of certain peak winds and to estimate probabilities associated with average winds outside the observed range. MSFC calculated the individual probabilities of meeting or exceeding specific 10- minute peak wind speeds by integrating the area under each curve. The probabilities assist SMG forecasters in assessing the shuttle FR for various Zminute average wind speeds. The A M ' obtained the processed EAFB data from Dr. Lee Bums of MSFC and reformatted them for input to Excel PivotTables, which allow users to display different values with point

  6. Estimating Sea Surface Salinity and Wind Using Combined Passive and Active L-Band Microwave Observations

    Science.gov (United States)

    Yueh, Simon H.; Chaubell, Mario J.

    2012-01-01

    Several L-band microwave radiometer and radar missions have been, or will be, operating in space for land and ocean observations. These include the NASA Aquarius mission and the Soil Moisture Active Passive (SMAP) mission, both of which use combined passive/ active L-band instruments. Aquarius s passive/active L-band microwave sensor has been designed to map the salinity field at the surface of the ocean from space. SMAP s primary objectives are for soil moisture and freeze/thaw detection, but it will operate continuously over the ocean, and hence will have significant potential for ocean surface research. In this innovation, an algorithm has been developed to retrieve simultaneously ocean surface salinity and wind from combined passive/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction, thus minimizing the least squares error (LSE) measure, which signifies the difference between measurements and model functions of brightness temperatures and radar backscatter. The algorithm uses the conjugate gradient method to search for the local minima of the LSE. Three LSE measures with different measurement combinations have been tested. The first LSE measure uses passive microwave data only with retrieval errors reaching 1 to 2 psu (practical salinity units) for salinity, and 1 to 2 m/s for wind speed. The second LSE measure uses both passive and active microwave data for vertical and horizontal polarizations. The addition of active microwave data significantly improves the retrieval accuracy by about a factor of five. To mitigate the impact of Faraday rotation on satellite observations, the third LSE measure uses measurement combinations invariant under the Faraday rotation. For Aquarius, the expected RMS SSS (sea surface salinity) error will be less than about 0.2 psu for low winds, and increases to 0.3 psu at 25 m/s wind speed

  7. Field and numerical study of wind and surface waves at short fetches

    Science.gov (United States)

    Baydakov, Georgy; Kuznetsova, Alexandra; Sergeev, Daniil; Papko, Vladislav; Kandaurov, Alexander; Vdovin, Maxim; Troitskaya, Yuliya

    2016-04-01

    Measurements were carried out in 2012-2015 from May to October in the waters of Gorky Reservoir belonging to the Volga Cascade. The methods of the experiment focus on the study of airflow in the close proximity to the water surface. The sensors were positioned at the oceanographic Froude buoy including five two-component ultrasonic sensors WindSonic by Gill Instruments at different levels (0.1, 0.85, 1.3, 2.27, 5.26 meters above the mean water surface level), one water and three air temperature sensors, and three-channel wire wave gauge. One of wind sensors (0.1 m) was located on the float tracking the waveform for measuring the wind speed in the close proximity to the water surface. Basic parameters of the atmospheric boundary layer (the friction velocity u∗, the wind speed U10 and the drag coefficient CD) were calculated from the measured profiles of wind speed. Parameters were obtained in the range of wind speeds of 1-12 m/s. For wind speeds stronger than 4 m/s CD values were lower than those obtained before (see eg. [1,2]) and those predicted by the bulk parameterization. However, for weak winds (less than 3 m/s) CD values considerably higher than expected ones. The new parameterization of surface drag coefficient was proposed on the basis of the obtained data. The suggested parameterization of drag coefficient CD(U10) was implemented within wind input source terms in WAVEWATCH III [3]. The results of the numerical experiments were compared with the results obtained in the field experiments on the Gorky Reservoir. The use of the new drag coefficient improves the agreement in significant wave heights HS [4]. At the same time, the predicted mean wave periods are overestimated using both built-in source terms and adjusted source terms. We associate it with the necessity of the adjusting of the DIA nonlinearity model in WAVEWATCH III to the conditions of the middle-sized reservoir. Test experiments on the adjusting were carried out. The work was supported by the

  8. Projected changes to surface wind characteristics and extremes over North America in CRCM5

    Science.gov (United States)

    Jeong, Dae Il; Sushama, Laxmi

    2017-04-01

    Changes in the tendency of wind speed and direction have significant implications for long-term water cycle, air pollution, arid and semiarid environments, fire activity, and wind energy production. Furthermore, changes in wind extremes have direct impacts on buildings, infrastructures, agriculture, power lines, and trees. This study evaluates projected changes to wind speed characteristics (i.e., seasonal and annual mean, seasonal and diurnal cycles, directional distribution, and extreme events) for the future 2071-2100 period, with respect to the current 1981-2010 period over North America, using four different simulations from the fifth-generation Canadian Regional Climate Model (CRCM5) with two driving GCMs under RCP (Representative Concentration Pathways) 4.5 and 8.5 scenarios. The CRCM5 simulates the climatology of mean sea level pressure gradient and associated wind direction over North America well when compared to ERA-Interim reanalysis dataset. The CRCM5 also reproduces properly the spatial distributions of observed seasonal and annual mean wind speeds obtained from 611 meteorological stations across North America. The CRCM5 simulations generally suggest an increase in future mean wind speed for northern and eastern parts of Canada, due to a decrease of future mean sea level pressure and more intense low pressure air circulation systems already situated in those regions such as Aleutian and Icelandic Lows. Projected changes to annual maximum wind speed show more spatial variability compared to seasonal and annual mean wind speed as extreme wind speed is influenced more by regional-scale features associated with instantaneous surface temperature and air pressure gradients. The CRCM5 simulations suggest some increases in the future 50-year return levels of wind speed, mainly due to changes in the inter-annual variability of annual maximum wind speed. However, the projected changes vary in spatial pattern with the driving GCM fields and emission scenarios

  9. Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

    Directory of Open Access Journals (Sweden)

    F. C. Bassinot

    2011-07-01

    Full Text Available The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G. bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present.

    Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer.

  10. Elephant overflows: Multi-annual variability in Weddell Sea Deep Water driven by surface forcing

    Science.gov (United States)

    Meijers, Andrew; Meredith, Michael; Abrahamsen, Povl; Naviera-Garabato, Alberto; Ángel Morales Maqueda, Miguel; Polzin, Kurt

    2015-04-01

    The volume of the deepest and densest water mass in Drake Passage, Lower Weddell Sea Deep Water (LWSDW), is shown to have been decreasing over the last 20 years of observations, with an associated reduction in density driven by freshening. Superimposed on this long term trend is a multi-annual oscillation with a period of 3-5 years. This variability only appears in Drake Passage; observations in the east of the Scotia Sea show a similar long term trend, but with no apparent multi-annual variability. Clues as to the source of this variability may be found on the continental slope at approximately 1000 m immediately north of Elephant Island on the northern tip of the Antarctic Peninsula. Here there is an intermittent westward flowing cold/fresh slope current whose volume and properties are strongly correlated with the LWSDW multi-annual variability, although leading the LWSDW by around one year. As the slope current and LWSDW are separated from each other both geographically and in water mass characteristics, their co-variability implies that they are responding to a common forcing, while the lag between deep LWSDW and shallow slope current provides information on the timescale of this response. A newly available high resolution temperature and salinity multi-year time series from the Elephant Island slope at 1000 m is compared with reanalysis and model derived surface fluxes, sea ice extent and wind stress. We find that there are strong positive relationships between the surface wind stress and heat flux over the shelf at the tip of the Antarctic Peninsula and the properties of the slope current at 1000 m on seasonal to annual timescales. We use tracer release experiments in the Southern Ocean State Estimate (SOSE) model to investigate the lag between the slope current and LWSDW timeseries and hypothesise that the observed multi-annual variability in both water masses is driven by surface forcing over the shelf and the overflow of modified water from the slope in

  11. A wind loading correlation for an isolated square heliostat, part 1: lift and drag forces

    CSIR Research Space (South Africa)

    Roos, TH

    2012-05-01

    Full Text Available A design requirement of a heliostat is the ability to withstand storm loads in the stow position and operational wind loads in any position. To design a heliostat, therefore, one must be able to predict the wind loading on the heliostat for all...

  12. Development of a six-axis force/moment sensor for wind tunnel model test

    Science.gov (United States)

    Wang, Wenjun

    2013-11-01

    A novel structure for a six-axis force/moment sensor is proposed in this paper. Parallel plate structures are combined in the one-block structure of the sensor. A method for estimating the sensitivity and stiffness is developed by comparing the results of numeric estimations with those of finite element method (FEM) analyses. A detailed FEM model was used to analyse the surface strain in the area where the strain gauge was attached. Tests carried out on the characteristics revealed a sensitivity design error of less than 8.5%, a relative measurement error of less than 2.13%, and an interference error of less than 9.51%. A performance enhancement method is also proposed.

  13. Super-Eddington Stellar Winds Driven by Near-Surface Energy Deposition

    CERN Document Server

    Quataert, Eliot; Kasen, Daniel; Klion, Hannah; Paxton, Bill

    2015-01-01

    We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g., unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem vc ~ (Edot G)^{1/5} (where Edot is the heating rate) to the stellar escape speed near the heating region vesc(r_h). For vc > vesc(r_h) the wind kinetic power at large radii Edot_w ~ Edot. For vc < vesc(r_h), most of the energy is used to unbind the wind material and thus Edot_w < Edot. Multidimensional hydrodynamic simulations without radiation di...

  14. Correlation between dust events in Mongolia and surface wind and precipitation

    Directory of Open Access Journals (Sweden)

    Ganbat Amgalan

    2017-01-01

    Full Text Available This study presents dust event spatiotemporal distribution and regional trends, and the impact of surface wind and precipitation on dust occurrences in Mongolia. We used data collected between 2000 and 2013 from 113 meteorological stations in natural forest steppe, steppe, Gobi Desert, and mountain zones. We analyzed the relationship between dusty days, derived using the sum of days with dust storms and/or drifting dust, and days with strong winds (at a threshold wind speed of a constant 6.5 m s-1, hereafter, strong wind days and precipitation by comparing the dusty days in dust-frequent years, dust-less years, and dust-mean years. Dusty days in dust-frequent years were associated with strong wind days when the precipitation is about 10 mm and dust occurrences were suppressed by large amounts of precipitation (approximately 22 mm in dust-less years over the southeastern part of the Gobi Desert in May. We propose a potential dust index (PDI based on the correlations among dusty days, strong winds and precipitation. The PDI performed as predicted in most areas of the country in the spring season.

  15. Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5

    OpenAIRE

    Zhang, Kai; Zhao, Chun; Wan, Hui; Qian, Yun; Easter, Richard C.; Ghan, Steven J; Sakaguchi, Koichi; LIU, Xiaohong

    2016-01-01

    This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities. In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into ac...

  16. Conceptions of Tornado Wind Speed and Land Surface Interactions among Undergraduate Students in Nebraska

    Science.gov (United States)

    Van Den Broeke, Matthew S.; Arthurs, Leilani

    2015-01-01

    To ascertain novice conceptions of tornado wind speed and the influence of surface characteristics on tornado occurrence, 613 undergraduate students enrolled in introductory science courses at a large state university in Nebraska were surveyed. Our findings show that students lack understanding of the fundamental concepts that (1) tornadoes are…

  17. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Ainslie, M.A.; Colin, M.E.G.D.; Janmaat, J.

    2012-01-01

    Sea surface scattering by wind-generated waves and bubbles is regarded to be the main nonplatform-related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modelling

  18. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Colin, M.E.G.D.; Ainslie, M.A.; Walree, P.A. van; Janmaat, J.

    2013-01-01

    Abstract—Sea-surface scattering by wind-generated waves and bubbles is regarded to be the main nonplatform related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate m

  19. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Colin, M.E.G.D.; Ainslie, M.A.; Walree, P.A. van; Janmaat, J.

    2012-01-01

    Sea surface scattering by wind-generated waves and bubbles is regarded to be the main non-platform related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modeling

  20. Optimizing Surface Winds using QuikSCAT Measurements in the Mediterranean Sea During 2000-2006

    Science.gov (United States)

    2009-02-28

    r.com/ locate / jmarsysOptimizing surface winds using QuikSCAT measurements in the Mediterranean Sea during 2000–2006 A. Birol Kara a,⁎, Alan J...flux algorithms. J. Geophys. Res. 113, C04009. doi:10.1029/2007JC004324. Large, W.G., Danabasoglu, G., Doney, S.C., McWilliams , J.C., 1997

  1. Lightning attachment to wind turbine surfaces affected by internal blade conditions

    DEFF Research Database (Denmark)

    Garolera, Anna Candela; Holboell, Joachim; Madsen, Soren Find

    2012-01-01

    on the blade surface instead of the receptor is also possible, with the risk of damages in the composite structure as a consequence. The present paper focuses on electrical fields and streamer activity in connection to conductive components inside a wind turbine blade when a downward leader is approaching...

  2. Evaporation of HD Droplets From Nonporous, Inert Surfaces in TGA Microbalance Wind Tunnels

    Science.gov (United States)

    2008-09-01

    2007 4. TITLE AND SUBTITLE Evaporation of HD Droplets from Nonporous, Inert Surfaces in TGA Microbalancc Wind Tunnels 5a. CONTRACT NUMBER DAAD13...hr (lightly swirled on a rotating plateau). Then, the glass was rinsed with dematerialized water and dried (using appropriate fat-free non-felting

  3. Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel

    Institute of Scientific and Technical Information of China (English)

    Tian Li-mei; Ren Lu-quan; Han Zhi-wu; Zhang Shi-cun

    2005-01-01

    The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship be tween drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of 1 mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13 % to 22.30%.

  4. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Ainslie, M.A.; Colin, M.E.G.D.; Janmaat, J.

    2012-01-01

    Sea surface scattering by wind-generated waves and bubbles is regarded to be the main nonplatform-related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modelling

  5. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Colin, M.E.G.D.; Ainslie, M.A.; Walree, P.A. van; Janmaat, J.

    2013-01-01

    Abstract—Sea-surface scattering by wind-generated waves and bubbles is regarded to be the main nonplatform related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate m

  6. Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    NARCIS (Netherlands)

    Dol, H.S.; Colin, M.E.G.D.; Ainslie, M.A.; Walree, P.A. van; Janmaat, J.

    2012-01-01

    Sea surface scattering by wind-generated waves and bubbles is regarded to be the main non-platform related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modeling

  7. The Impact of Sea-Surface Winds on Meteorological Conditions in Israel: An Initial Study

    Science.gov (United States)

    Otterman, J.; Saaroni, H.; Atlas, R.; Ardizzone, J.; Ben-Dor, E.; Druyan, L.; Jusem, C. J.; Karnieli, A.; Terry, J.

    2000-01-01

    The SSM/I (Spectral Sensor Microwave Imager) dataset is used to monitor surface wind speed and direction at four locations over the Eastern Mediterranean during December 1998 - January 1999. Time series of these data are compared to concurrent series of precipitation, surface temperature, humidity and winds at selected Israeli stations: Sde Dov (coastal), Bet Dagan (5 km. inland), Jerusalem (Judean Hills), Hafetz Haim (3 km. inland) and Sde Boker (central Negev). December 1998 and the beginning of January 1999 were dry in Israel, but significant precipitation was recorded at many stations during the second half of January (1999). SSM/I data show a surge in westerly surface winds west of Israel (32 N, 32.5 E) on 15 January, coinciding with the renewal of precipitation. We discuss the relevant circulation and pressure patterns during this transition in the context of the evolving meteorological conditions at the selected Israeli locations. The SSM/I dataset of near ocean surface winds, available for the last 12 years, is described. We analyze lagged correlation between these data and the Israeli station data and investigate possibility of predictive skill. Application of such relationships to short-term weather prediction would require real-time access to the SSM/I observations.

  8. Surface Roughness and Material Optical Properties Influence on Casimir/van der Waals and Capillary Surface Forces

    NARCIS (Netherlands)

    Zwol, P.J. van; Palasantzas, G.

    2010-01-01

    Theory calculations using the Lifshitz theory and atomic force microscopy force measurements show that Casimir/van der Weals dispersive forces have a strong dependence on material optical properties and surface roughness. At separations below 100 nm the roughness effect is manifested through a

  9. Impact of non-uniform surface magnetic fields on stellar winds

    CERN Document Server

    Holzwarth, V R

    2005-01-01

    Observations of active stars reveal highly non-uniform surface distributions of magnetic flux. Theoretical models considering magnetised stellar winds however often presume uniform surface magnetic fields, characterised by a single magnetic field strength. The present work investigates the impact of non-uniform surface magnetic field distributions on the stellar mass and angular momentum loss rates. The approach of Weber & Davis (1967) is extended to non-equatorial latitudes to quantify the impact of latitude-dependent magnetic field distributions over a large range of stellar rotation rates and thermal wind properties. The analytically prescribed field patterns are dominated by magnetic flux concentrations at intermediate and high latitudes. The global stellar mass loss rates are found to be rather insensitive to non-uniformities of the surface magnetic field. Depending on the non-uniformity of the field distribution, the angular momentum loss rates deviate in contrast at all rotation rates between -60% ...

  10. ForceFit: a code to fit classical force fields to ab-initio potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henson, Neil Jon [Los Alamos National Laboratory; Waldher, Benjamin [WSU; Kuta, Jadwiga [WSU; Clark, Aurora [WSU; Clark, Aurora E [NON LANL

    2009-01-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under Unix and is written in C++, is an easy to use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  11. ForceFit: a code to fit classical force fields to ab-initio potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henson, Neil Jon [Los Alamos National Laboratory; Waldher, Benjamin [WSU; Kuta, Jadwiga [WSU; Clark, Aurora [WSU; Clark, Aurora E [NON LANL

    2009-01-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under Unix and is written in C++, is an easy to use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  12. Temporal step fluctuations on a conductor surface: electromigration force, surface resistivity and low-frequency noise

    Science.gov (United States)

    Williams, E. D.; Bondarchuk, O.; Tao, C. G.; Yan, W.; Cullen, W. G.; Rous, P. J.; Bole, T.

    2007-10-01

    Scattering of charge carriers from surface structures will become an increasing factor in the resistivity as the structure decreases in size to the nanoscale. The effects of scattering at the most basic surface defect, a kink in a step edge, are here analyzed using the continuum step model. Using a Langevin analysis, it has been shown that the electromigration force on the atoms at the step edge causes changes in the temporal evolution of the step-edge. For an electromigration force acting perpendicular to the average step edge and mass-transport dominated by step-edge diffusion, significant deviations from the usual t1/4 scaling of the displacement correlation function occur dependent on a critical time τ and the direction of the force relative to the step edge (i.e. uphill or downhill). Experimental observations of step fluctuations on Ag(111) show the predicted changes among step fluctuations without current, and with current in the up- and down-hill directions for a current density of order 105 A cm-2. The results yield the magnitude of the electromigration force acting on kinked sites at the step-edge. This in turn yields the contribution of the fluctuating steps to the surface resistivity, which exceeds 1% of the bulk resistivity as wire diameters decrease below 10s of nanometres. The temporal fluctuations of kink density can thus also be related to resistivity noise. Relating the known fluctuation spectrum of the step displacements to fluctuations in their lengths, the corresponding resistivity noise is predicted to show spectral signatures of ~f-1/2 for step fluctuations governed by random attachment/detachment, and ~f-3/4 for step fluctuations governed by step-edge diffusion.

  13. Using Surface Pressure To Improve Tropical Cyclone /Surface Wind Retrievals From SAR

    Science.gov (United States)

    2012-03-19

    Jochen Horstmann of NATO Undersea Research Centre ( NURC ). GD and NURC have developed separate methods for estimating wind directions. The GD and NURC ...Working version of SLP retrieval code, including necessary PBL model developments, that is compatible with GD, NURC and WiSAR file formats (as well as for...installed at NURC and we have been experimenting with Horstmann to determine if it can (or should) be included as an integrated part of the NURC SAR wind

  14. Evaluation of ENVISAT ASAR data for sea surface wind retrieval in Hong Kong coastal waters of China

    Institute of Scientific and Technical Information of China (English)

    XU Qing; LIN Hui; ZHENG Quanan; XIU Peng; CHENG Yongcun; LIU Yuguang

    2008-01-01

    The C-band wind speed retrieval models,CMOD4,CMOD-IFR2,and CMODS were applied to retrieval of sea surface wind speeds from ENVISAT(European environmental satellite)ASAR(advanced synthetic aperture radar)data in the coastal waters near Hang Kong during a period from October 2005 to July 2007.The retrieved wind speeds are evaluated by comparing with buoy measurements and the QuikSCAT(quick scatterometer)wind products.The results show that the CMOD4 model gives the best performance at wind speeds lower than 15 m/s.The correlation coefficients with buoy and QuikSCAT winds are 0.781 and 0.896,respectively.The root mean square errors are the same 1.74m/s.Namely,the CMOD4 model is the best one for sea surface wind speed retrieval from ASAR data in the COastal waters near Hong Kong.

  15. Transient stability and control of wind turbine generation based on Hamiltonian surface shaping and power flow control

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, David G.; Robinett, Rush D. III [Sandia National Laboratories, Albuquerque, NM (United States). Energy, Resources and Systems Analysis Center

    2010-07-01

    The swing equations for renewable generators connected to the grid are developed and a simple wind turbine with UPFC is used as an example. The swing equations for renewable generator are formulated as a natural Hamiltonian system with externally applied non-conservative forces. A two-step process referred to as Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) is used to analyze and design feedback controllers for the renewable generators system. This formulation extends previous results on the analytical verification of the Potential Energy Boundary Surface (PEBS) method to nonlinear control analysis and design and justifies the decomposition of the system into conservative and nonconservative systems to enable a two-step, serial analysis and design procedure. This paper presents the analysis and numerical simulation results for a nonlinear control design example that includes the One-Machine Infinite Bus (OMIB) system with a Unified Power Flow Control (UPEC) and applied to a simplified wind turbine generator. The needed power and energy storage/charging responses are also determined. (orig.)

  16. CYGNSS Spaceborne Constellation for Ocean Surface Winds: Mission Design and Sampling Properties

    Science.gov (United States)

    Ruf, Chris; Ridley, Aaron; Clarizia, Maria Paola; Gleason, Scott; Rose, Randall; Scherrer, John

    2014-05-01

    The NASA Earth Venture Cyclone Global Navigation Satellite System (CYGNSS) is a spaceborne mission scheduled to launch in October 2016 that is focused on tropical cyclone (TC) inner core process studies. CYGNSS is specifically designed to address the inadequacy in observations of the inner core that result from two causes: 1) much of the inner core ocean surface is obscured from conventional remote sensing instruments by intense precipitation in the eye wall and inner rain bands; and 2) the rapidly evolving (genesis and intensification) stages of the TC life cycle are poorly sampled in time by conventional polar-orbiting, wide-swath surface wind imagers. CYGNSS measurements of bistatic radar cross section of the ocean can be directly related to the near surface wind speed, in a manner roughly analogous to that of conventional ocean wind scatterometers. The technique has been demonstrated previously from space by the UK-DMC mission in 2005-6. CYGNSS will advance the wind measuring capability demonstrated by the experimental payload on UK-DMC to a more mature ocean science mission. The CYGNSS constellation is comprised of 8 observatories in 500 km circular orbits at a common inclination angle of 35°. Each observatory contains a Delay Doppler Mapping Instrument (DDMI) which consists of a multi-channel GPS receiver, a low gain zenith antenna and two high gain nadir antennas. Each DDMI measures simultaneous specular scattered signals from the 4 GPS transmitters with the highest probable signal-to-noise ratio. The receivers coherently integrate the received signals for 1 ms, then incoherently integrate on board for an additional one second. This results in 32 wind measurements per second. CYGNSS has spatial and temporal sampling properties that are distinctly different from conventional wide-swath polar imagers. Spatial sampling is marked by 32 simultaneous single pixel "swaths" that are 25 km wide and, typically, 100s of km long. They can be considered roughly

  17. Bond-Strengthening in Staphylococcal Adhesion to Hydrophilic and Hydrophobic Surfaces Using Atomic Force Microscopy

    NARCIS (Netherlands)

    Boks, N.P.; Busscher, H.J.; Mei, van der H.C.; Norde, W.

    2008-01-01

    Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface

  18. Bond-Strengthening in Staphylococcal Adhesion to Hydrophilic and Hydrophobic Surfaces Using Atomic Force Microscopy

    NARCIS (Netherlands)

    Boks, Niels P.; Busscher, Henk J.; van der Mei, Henny C.; Norde, Willem

    2008-01-01

    Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface hydrophobi

  19. Short-term variation in the body weight of Oystercatchers Haematopus ostralegus : Effect of available feeding time by day and night, temperature and wind force

    NARCIS (Netherlands)

    Zwarts, L; Hulscher, JB; Koopman, K; Zegers, PM

    1996-01-01

    The available feeding time of coastal Oystercatchers varies from day to day due to the effect of wind direction and wind force on the water level. If the birds are not able to feed at all during a day, they lose 30 g, or 6% of their body weight. The body weight increases with the duration of the ava

  20. Short-term variation in the body weight of Oystercatchers Haematopus ostralegus : Effect of available feeding time by day and night, temperature and wind force

    NARCIS (Netherlands)

    Zwarts, L; Hulscher, JB; Koopman, K; Zegers, PM

    1996-01-01

    The available feeding time of coastal Oystercatchers varies from day to day due to the effect of wind direction and wind force on the water level. If the birds are not able to feed at all during a day, they lose 30 g, or 6% of their body weight. The body weight increases with the duration of the

  1. Wind Pressure Characteristics at Windward Side of Long-Span Cantilevered Roof by Wind Tunnel Test

    Institute of Scientific and Technical Information of China (English)

    XIAN Rong; LIAO Hai-li; LI Ming-shui

    2009-01-01

    A rigid mode of long-span cantilevered roof was tested in wind tunnel.By analyzing the relation between wind angle and wind pressure coefficient and the relation between wind angle and wind shape factor,we found that 90° is the most disadvantageous wind angle.Furthermore,the fluctuation of wind pressure at the windward edge was reflected by power spectrum density (PSD) and coherence function.The correlation coefficients of measuring points on outer and inner surfaces verifys that the largest lift force was produced at 90°.

  2. Measuring and modelling of the wind on the scale of tall wind turbines

    DEFF Research Database (Denmark)

    Floors, Rogier Ralph

    and the negative wind speed bias at larger heights were not improved when a different synoptic forcing and a different vertical resolution were used in the model. The effect of baroclinity was explored for the two sites. The surface geostrophic wind, the gradient wind and the thermal wind were derived from...... simulations with a mesoscale model. In both locations the thermal wind up to 970 m was approximately Gaussianly distributed with a standard deviation of three m s−1 and the thermal wind vector varied seasonally due to temperature differences between sea and land. The wind veer was particularly sensitive...

  3. The role of free stream turbulence and blade surface conditions on the aerodynamic performance of wind turbine blades

    Science.gov (United States)

    Maldonado, Victor Hugo

    Wind turbines operate within the atmospheric boundary layer (ABL) which gives rise to turbulence among other flow phenomena. There are several factors that contribute to turbulent flow: The operation of wind turbines in two layers of the atmosphere, the surface layer and the mixed layer. These layers often have unstable wind conditions due to the daily heating and cooling of the atmosphere which creates turbulent thermals. In addition, wind turbines often operate in the wake of upstream turbines such as in wind farms; where turbulence generated by the rotor can be compounded if the turbines are not sited properly. Although turbulent flow conditions are known to affect performance, i.e. power output and lifespan of the turbine, the flow mechanisms by which atmospheric turbulence and other external conditions (such as blade debris contamination) adversely impact wind turbines are not known in enough detail to address these issues. The main objectives of the current investigation are thus two-fold: (i) to understand the interaction of the turbulent integral length scales and surface roughness on the blade and its effect on aerodynamic performance, and (ii) to develop and apply flow control (both passive and active) techniques to alleviate some of the adverse fluid dynamics phenomena caused by the atmosphere (i.e. blade contamination) and restore some of the aerodynamic performance loss. In order to satisfy the objectives of the investigation, a 2-D blade model based on the S809 airfoil for horizontal axis wind turbine (HAWT) applications was manufactured and tested at the Johns Hopkins University Corrsin Stanley Wind Tunnel facility. Additional levels of free stream turbulence with an intensity of 6.14% and integral length scale of about 0.321 m was introduced into the flow via an active grid. The free stream velocity was 10 m/s resulting in a Reynolds number based on blade chord of Rec ≃ 2.08x105. Debris contamination on the blade was modeled as surface roughness

  4. Intensification of aerosol pollution associated with its feedback with surface solar radiation and winds in Beijing

    Science.gov (United States)

    Yang, Xin; Zhao, Chuanfeng; Guo, Jianping; Wang, Yang

    2016-04-01

    Beijing has been experiencing serious air pollution in recent years, resulting in serious impacts on the local environment and climate and on human health. In addition to individual pollution sources and weather systems, feedback between aerosols and downwelling solar radiation (DSR) and between aerosols and winds also contribute to heavy aerosol pollution. By using atmospheric visibility (VIS) to represent the relative amount of aerosol pollution during a 5 week observation around the Asia-Pacific Economic Cooperation (APEC) period (22 October to 25 November 2014) over a site in south Beijing, China, we show clear positive relationships between DSR and VIS and between winds and VIS. The sensitivities of daily DSR and surface winds to VIS are approximately 15.42 W/m2/km and 0.068 m/s/km, respectively. The strengthening contributions to atmospheric visibility by surface DSR-VIS interactions and between surface wind-aerosol interactions are estimated at approximately 15% and 12%, respectively, in south Beijing around the APEC period.

  5. Solar Wind Sputtering of Lunar Surface Materials: Role and Some Possible Implications of Potential Sputtering

    Science.gov (United States)

    Barghouty, A. F.; Adams, J. H., Jr.; Meyer, F.; Reinhold, c.

    2010-01-01

    Solar-wind induced sputtering of the lunar surface includes, in principle, both kinetic and potential sputtering. The role of the latter mechanism, however, in many focused studies has not been properly ascertained due partly to lack of data but can also be attributed to the assertion that the contribution of solar-wind heavy ions to the total sputtering is quite low due to their low number density compared to solar-wind protons. Limited laboratory measurements show marked enhancements in the sputter yields of slow-moving, highly-charged ions impacting oxides. Lunar surface sputtering yields are important as they affect, e.g., estimates of the compositional changes in the lunar surface, its erosion rate, as well as its contribution to the exosphere as well as estimates of hydrogen and water contents. Since the typical range of solar-wind ions at 1 keV/amu is comparable to the thickness of the amorphous rim found on lunar soil grains, i.e. few 10s nm, lunar simulant samples JSC-1A AGGL are specifically enhanced to have such rims in addition to the other known characteristics of the actual lunar soil particles. However, most, if not all laboratory studies of potential sputtering were carried out in single crystal targets, quite different from the rim s amorphous structure. The effect of this structural difference on the extent of potential sputtering has not, to our knowledge, been investigated to date.

  6. Error estimates for ocean surface winds: Applying Desroziers diagnostics to the Cross-Calibrated, Multi-Platform analysis of wind speed

    Science.gov (United States)

    Hoffman, Ross N.; Ardizzone, Joseph V.; Leidner, S. Mark; Smith, Deborah K.; Atlas, Robert M.

    2013-04-01

    The cross-calibrated, multi-platform (CCMP) ocean surface wind project [Atlas et al., 2011] generates high-quality, high-resolution, vector winds over the world's oceans beginning with the 1987 launch of the SSM/I F08, using Remote Sensing Systems (RSS) microwave satellite wind retrievals, as well as in situ observations from ships and buoys. The variational analysis method [VAM, Hoffman et al., 2003] is at the center of the CCMP project's analysis procedures for combining observations of the wind. The VAM was developed as a smoothing spline and so implicitly defines the background error covariance by means of several constraints with adjustable weights, and does not provide an explicit estimate of the analysis error. Here we report on our research to develop uncertainty estimates for wind speed for the VAM inputs and outputs, i.e., for the background (B), the observations (O) and the analysis (A) wind speed, based on the Desroziers et al. [2005] diagnostics (DD hereafter). The DD are applied to the CCMP ocean surface wind data sets to estimate wind speed errors of the ECMWF background, the microwave satellite observations and the resulting CCMP analysis. The DD confirm that the ECMWF operational surface wind speed error standard deviations vary with latitude in the range 0.7-1.5 m/s and that the cross-calibrated Remote Sensing Systems (RSS) wind speed retrievals standard deviations are in the range 0.5-0.8 m/s. Further the estimated CCMP analysis wind speed standard deviations are in the range 0.2-0.4 m/s. The results suggests the need to revise the parameterization of the errors due to the FGAT (first guess at the appropriate time) procedure. Errors for wind speeds S. M. Leidner, J. C. Jusem, D. K. Smith, and D. Gombos, A cross-calibrated, multi-platform ocean surface wind velocity product for meteorological and oceanographic applications, Bull. Am. Meteorol. Soc., 92, 157-174, 2011, doi:10.1175/2010BAMS2946.1. Desroziers, G., L. Berre, B. Chapnik, and P. Poli

  7. Effects of surface design on aerodynamic forces of iced bridge cables

    DEFF Research Database (Denmark)

    Koss, Holger

    2014-01-01

    In recent years the relevance of ice accretion for wind-induced vibration of structural bridge cables has been recognised and became a subject of research in bridge engineering. Full-scale monitoring and observation indicate that light precipitation at moderate low temperatures between zero and -5......°C may lead to large amplitude vibrations of bridge cables under wind action. For the prediction of aerodynamic instability quasi-steady models have been developed estimating the cable response magnitude based on structural properties and aerodynamic force coefficients for drag, lift and torsion...... influences the accretion of ice to an extent that the aerodynamic forces differ significantly amongst the designs. The experiments were conducted in a wind tunnel facility capable amongst others to simulate in-cloud icing conditions....

  8. A Large Eddy Simulation to determine the effect of trees on wind and turbulence over a suburban surface

    Science.gov (United States)

    Egli, P. E.; Giometto, M. G.; Tooke, T. R.; Krayenhoff, S.; Christen, A.; Parlange, M. B.

    2014-12-01

    Robust modeling of flow and turbulence within and over urban canopies is required to properly predict air pollution and dispersion in cities. Trees are an integral part of the urban landscape. In many suburban neighbourhoods, tree cover is 10 to 30% and trees are often taller than buildings. Effects of trees on drag, mean wind and turbulence in cities are not accounted for in current weather, air pollution and dispersion models. Our goal is to use high-resolution Large Eddy Simulations (LES) over a realistic urban canopy to determine the effects of trees on drag, mean wind and turbulence in the urban roughness sublayer (RSL). The simulated area is part of the Sunset-Neighbourhood in Vancouver, Canada. In this area, long-term wind and turbulence measurements are available from instruments on a 28m-tall tower. Further, a three-dimensional point cloud was captured from high precision airborne Light Detection and Ranging (LiDAR), and analyzed to represent the structural characteristics of both buildings and trees at high spatial resolution. Trees are described by location-specific leaf area density (LAD) profiles. LES simulations are performed over a 512 x 512m characteristic subset of the city that contains the tower location and predominant source area. In the LES, buildings are accounted for with an immersed boundary method, adopting a zero level-set distance function to localize the surface, whereas drag forces from trees are parametrized as a function of the height-dependent LAD. Spectra of streamwise and vertical velocity components compare well between tower data and the model data, confirming the good performance of LES in simulations of flow over fully rough surfaces. We show how the presence of trees impacts mean velocity and computed momentum flux profiles; they significantly decrease dispersive terms in the bulk of the flow. The impact of trees on integral length scales in the flow is discussed.

  9. Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements

    Science.gov (United States)

    Behunin, R. O.; Dalvit, D. A. R.; Decca, R. S.; Genet, C.; Jung, I. W.; Lambrecht, A.; Liscio, A.; López, D.; Reynaud, S.; Schnoering, G.; Voisin, G.; Zeng, Y.

    2014-12-01

    Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D ) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D ) does not explain the magnitude or the separation dependence of the difference Δ P (D ) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.

  10. The Response of North Pacific Sea Surface Temperature, Wind Speed and Ocean Circulation to the Freshwater Forcing in Boreal Winter%北太平洋冬季SST、风场及环流对淡水强迫的响应

    Institute of Scientific and Technical Information of China (English)

    周舒岚; 林霄沛; 张进乐

    2012-01-01

    通过海气耦合模式CCSM3( The Community Climate System Model version 3),研究在北大西洋高纬度淡水强迫下,北太平洋冬季的海表温度SST、风场及流场的响应及其区域性差异.结果表明:淡水的注入使北太平洋整体变冷,但有部分区域异常增暖;在太平洋东部赤道两侧,SST的变化出现北负南正的偶极子型分布.阿留申低压北移的同时中纬度西风减弱,热带附近东北信风增强.黑潮和南赤道流减弱,北太平洋副热带逆流和北赤道流增强,日本海被南向流控制.风场及流场的改变共同导致了北太平洋SST异常出现复杂的空间差异:北太平洋中高纬度SST的降温主要由大气过程决定,海洋动力过程主要影响黑潮、日本海及副热带逆流区域的SST,太平洋热带地区SST异常由大气与海洋共同主导.%The changes and its regional differences of sea surface temperature, wind speed and ocean circulation in North Pacific Ocean induced by freshwater input in North Atlantic Ocean are investigated using The Community Climate System Model version 3 (CCSM 3). The analyses are based on boreal winter responses. The results demonstrate as follow: warming in particular areas on North Pacific Ocean although cooling is dominated; SST increases on south of the equator in the eastern tropical Pacific and causes tropical SST dipole. Aleutian low is shifted northward while midlatitude westerlies are weakened; the northeast trades are intensified in tropical Pacific. Kurshio and south equatorial current are weakened while subtropical countercurrent and north equatorial current are intensified. The southward currents play a crucial role in Japan Sea. The changing of wind and ocean current together cause SST in north Pacific. a-nomaly distributes in a complex space variability. The cooling in North Pacific mid and high latitudes are dominated by atmospheric processes. Ocean dynamic process mainly affects the area of Kuroshio, Japan Sea and

  11. Solar wind interaction with the Reiner Gamma crustal magnetic anomaly: Connecting source magnetization to surface weathering

    Science.gov (United States)

    Poppe, Andrew R.; Fatemi, Shahab; Garrick-Bethell, Ian; Hemingway, Doug; Holmström, Mats

    2016-03-01

    Remanent magnetization has long been known to exist in the lunar crust, yet both the detailed topology and ultimate origin(s) of these fields remains uncertain. Some crustal magnetic fields coincide with surface albedo anomalies, known as lunar swirls, which are thought to be formed by differential surface weathering of the regolith underlying crustal fields due to deflection of incident solar wind protons. Here, we present results from a three-dimensional, self-consistent, plasma hybrid model of the solar wind interaction with two different possible source magnetizations for the Reiner Gamma anomaly. We characterize the plasma interaction with these fields and the resulting spatial distribution of charged-particle weathering of the surface and compare these results to optical albedo measurements of Reiner Gamma. The model results constrain the proposed source magnetizations for Reiner Gamma and suggest that vertical crustal magnetic fields are required to produce the observed "dark lanes."

  12. Simulation of rotor aerodynamics : use of the actuator surface method to model the MEXICO wind turbine

    Energy Technology Data Exchange (ETDEWEB)

    Breton, S.P.; Watters, C.S.; Masson, C. [Ecole de Technologie Superieure, Montreal, PQ (Canada)

    2010-07-01

    This presentation discussed the model rotor experiments under controlled conditions (MEXICO) project. The experiments are being conducted in the largest wind tunnel in Europe in order to determine optimal yaw and pitch angles for wind turbines as well as to test the performance of blade aerodynamic profiles and rotor instrumentation. Data obtained during the experiments are used to determine velocity component points in order to develop a greater understanding of wind turbine aerodynamics and improve calculation methods. Blade element momentum (BEM) computational fluid dynamics (CFD) and vortex wake codes are used in the program, which includes an actuator surface method embedded in a customized CFD finite element method. To date, the project has validated various models with experimental data, and mapped the induced velocities upwind and downwind from rotors. Further research is being conducted to compare experimental results with other results in the literature related to blade loading, root bending moments, and detailed flow characteristics. Charts of experimental results were included. tabs., figs.

  13. Effects of Second-Order Hydrodynamic Forces on Floating Offshore Wind Turbines

    Energy Technology Data Exchange (ETDEWEB)

    Duarte, T.; Sarmento, A. J. N. A.; Jonkman, J.

    2014-04-01

    Relative to first-order, second-order wave-excitation loads are known to cause significant motions and additional loads in offshore oil and gas platforms. The design of floating offshore wind turbines was partially inherited from the offshore oil and gas industry. Floating offshore wind concepts have been studied with powerful aero-hydro-servo-elastic tools; however, most of the existing work on floating offshore wind turbines has neglected the contribution of second-order wave-excitation loads. As a result, this paper presents a computationally efficient methodology to consider these loads within FAST, a wind turbine computer-aided engineering tool developed by the National Renewable Energy Laboratory. The method implemented was verified against the commercial OrcaFlex tool, with good agreement, and low computational time. A reference floating offshore wind turbine was studied under several wind and wave load conditions, including the effects of second-order slow-drift and sum-frequency loads. Preliminary results revealed that these loads excite the turbine's natural frequencies, namely the surge and pitch natural frequencies.

  14. Effect of wind turbine wakes on cropland surface fluxes in the US Great Plains during a Nocturnal Low Level Jet

    Science.gov (United States)

    Rhodes, M. E.; Aitken, M.; Lundquist, J. K.; Takle, E. S.; Prueger, J. H.

    2010-12-01

    Installation of large scale wind farms is becoming a common operation in the Midwest, and wind farms frequently are situated among fields of agricultural crops. Each wind turbine is known to alter the behavior of the air mass downwind of the rotor; consequently, the rotor wakes alter the local microclimate. Quantification of the effects of wind turbine wakes on local microclimate is required to understand how large-scale wind deployment affects large-scale agriculture. This study examines the potential effect of wind turbine wakes on a corn crop in central Iowa during summer 2010. The field site consisted of one surface flux tower upwind of a row of five modern wind turbine generators, an identical surface flux station downwind of the turbine row, and a ground based LIDAR system downwind of the wind turbines. Each flux tower was instrumented with an array consisting of radiometers, a three-dimensional sonic anemometer, an open cell CO2 analyzer, a cup anemometer and wind vane, temperature and relative humidity sensors, and a tipping bucket. The LIDAR system reliably obtained readings up to 200 m above ground level (AGL), spanning the entire rotor disk (~40 m to 120 m AGL). This presentation examines wake-surface interaction on one particular night, during which the prevailing winds situated the LIDAR directly behind a wind turbine approximately 2 rotor diameters downwind of the turbine tower. As expected preliminary LIDAR results indicate that in the turbine rotor shadow there is a strong deficit of horizontal momentum. Additionally, a strong nocturnal low-level jet occurred above the turbine rotor disk. Wavelet spectral analysis indicates that oscillatory behavior, with frequencies characteristic of wind turbine wakes, is observed in the LIDAR horizontal and vertical winds and in the downwind flux station datastreams. The characterization of wake effects provided by this unique dataset will allow for better parameterization and modeling of wind turbine wake

  15. Metric of the 2–6 day sea-surface temperature response to wind stress in the Tropical Pacific and its sensitivity to the K-Profile Parameterization of vertical mixing

    KAUST Repository

    Wagman, Benjamin M.

    2014-05-04

    Uncertainty in wind forcing has long hampered direct tests of ocean model output against observations for the purpose of refining the boundary layer K-Profile Parameterization (KPP) of oceanic vertical mixing. Considered here is a short-term metric that could be sensitive to the ways in which the KPP directly affects the adjustment of sea surface temperatures for a given change in wind stress. In particular a metric is developed based on the lagged correlation between the 2–6 day filtered wind stress and sea surface temperature. The metric is normalized by estimated observational and model uncertainties such that the significance of differences may be assessed. For this purpose multiple wind reanalysis products and their blended combinations were used to represent the range of forcing uncertainty, while perturbed KPP parameter model runs explore the sensitivity of the metric to the parameterization of vertical mixing. The correlation metric is sensitive to perturbations to most KPP parameters, in ways that accord with expectations, although only a few parameters show a sensitivity on the same order as the sensitivity to switching between wind products. This suggests that uncertainties in wind forcing continue to be a significant limitation for applying direct observational tests of KPP physics. Moreover, model correlations are biased high, suggesting that the model lacks or does not resolve sources of variability on the 2–6 day time scale.

  16. Stability of sliding frictional surfaces with varying normal force

    Energy Technology Data Exchange (ETDEWEB)

    Dupont, P.E.; Bapna, D. (Boston Univ., MA (United States))

    1994-04-01

    This paper presents the stability analysis of a single degree-of-freedom elastic system following a rate- and state-dependent friction law. Normal force is assumed to depend on the displacement, velocity, and acceleration of the sliding interface. The history dependence of friction on normal force is included in the analysis. It is shown that to achieve steady sliding, system stiffness must exceed a critical value which depends on the expression for normal force. A system in which normal force depends on spring displacement is analyzed in detail. These results indicate that the functional dependence of normal force on system state can have a significant effect on the stability of low-velocity motion. 15 refs.

  17. Role of surface states in the Casimir force between semiconducting films

    CERN Document Server

    Govoni, Marco; Benassi, Andrea

    2010-01-01

    We present results of first principle calculations of the Casimir force between Si films of nanometric size, which show that it depends significantly upon the configuration of the surface atoms, and give evidence of the importance of surface states.

  18. Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

    Directory of Open Access Journals (Sweden)

    M. Ern

    2009-03-01

    Full Text Available The quasi-biennial oscillation (QBO of the zonal mean zonal wind is one of the most important processes in the dynamics of the middle atmosphere in the tropics. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossby-gravity, or inertia-gravity waves, as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Global distributions are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the later parts of the periods of westerly wind shear at the equator between 20 and 35 km altitude. During other phases of the westerly wind shear periods, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed to mesoscale gravity waves or intermediate scale waves, can be the by far dominant contribution of

  19. Large-eddy simulation of the atmospheric boundary layer: Influence of unsteady forcing, baroclinicity, inversion strength and stability on the wind profile

    DEFF Research Database (Denmark)

    Pedersen, Jesper Grønnegaard

    of the large-scale pressure forcing, when using LES for prediction of real-world wind profiles. In the Høvsøre case study, simulated wind speeds agree well with measurements throughout the ABL, but only when the applied forcing follows a height- and time-dependent pressure gradient estimated from continuous...... facilitate the formation of a super-geostrophic jet near the top of the ABL. It is considered to be a rare phenomena in the real-world ABL, and is not accounted for by the analytical models of the wind shear included in this study. It is furthermore shown that the considered wind profile model can...... the site in Hamburg are insufficient for accurate estimation of the driving pressure gradient, and that phenomena such as large-scale subsidence and advection also should be included in the LES for accurate wind profile prediction. A range of simulations of more idealized conditions are performed to study...

  20. Importance of thermal effects and sea surface roughness for offshore wind resource assessment

    DEFF Research Database (Denmark)

    Lange, B.; Larsen, Søren Ejling; Højstrup, Jørgen;

    2004-01-01

    in the Danish Baltic Sea. Monin-Obukhov theory is often used for the description of the wind speed profile. From a given wind speed at one height, the profile is predicted using two parameters, Obukhov length and sea surface roughness. Different methods to estimate these parameters are discussed and compared......-Obukhov theory, a simple correction method to account for this effect has been developed and is tested in the same way. The models for the estimation of the sea surface roughness were found to lead only to small differences. For the purpose of wind resource assessment, even the assumption of a constant roughness......). The power output estimation has also been compared with the method of the resource estimation program WAsP. For the Rodsand data set the prediction error of WAsP is about 4%. For the extrapolation with Monin-Obukhov theory with different L and z(0) estimations, it is 5-9%. The simple wind profile correction...

  1. Sea surface wind perturbations over the Kashevarov Bank of the Okhotsk Sea: a satellite study

    Directory of Open Access Journals (Sweden)

    T. I. Tarkhova

    2011-02-01

    Full Text Available Sea surface wind perturbations over sea surface temperature (SST cold anomalies over the Kashevarov Bank (KB of the Okhotsk Sea are analyzed using satellite (AMSR-E and QuikSCAT data during the summer-autumn period of 2006–2009. It is shown, that frequency of cases of wind speed decreasing over a cold spot in August–September reaches up to 67%. In the cold spot center SST cold anomalies reached 10.5 °C and wind speed lowered down to ~7 m s−1 relative its value on the periphery. The wind difference between a periphery and a centre of the cold spot is proportional to SST difference with the correlations 0.5 for daily satellite passes data, 0.66 for 3-day mean data and 0.9 for monthly ones. For all types of data the coefficient of proportionality consists of ~0.3 m s−1 on 1 °C.

  2. L band radar backscatter dependence upon surface wind stress - A summary of new Seasat-1 and aircraft observations

    Science.gov (United States)

    Thompson, T. W.; Weissman, D. E.; Gonzalez, F. I.

    1983-01-01

    The wind-scale relationships for L band radar wavelengths near 25 cm and 20 deg angle of incidence and HH polarization are reviewed using a number of aircraft and Seasat-1 SAR observations. The dependence of the L band backscatter coefficient from the ocean upon surface wind speed and direction is stated. The wind speed coefficient is 0.5 + or - 0.1 for a wide range of wind speeds. The wind direction coefficient is near zero for lower winds and stable marine boundary layers, but may be 0.20 + or - 0.05 for moderate wind speeds and an unstable marine boundary layer. These results are interpreted in terms of existing theoretical models for radar scattering from the ocean.

  3. Using Image Pro Plus Software to Develop Particle Mapping on Genesis Solar Wind Collector Surfaces

    Science.gov (United States)

    Rodriquez, Melissa C.; Allton, J. H.; Burkett, P. J.

    2012-01-01

    The continued success of the Genesis mission science team in analyzing solar wind collector array samples is partially based on close collaboration of the JSC curation team with science team members who develop cleaning techniques and those who assess elemental cleanliness at the levels of detection. The goal of this collaboration is to develop a reservoir of solar wind collectors of known cleanliness to be available to investigators. The heart and driving force behind this effort is Genesis mission PI Don Burnett. While JSC contributes characterization, safe clean storage, and benign collector cleaning with ultrapure water (UPW) and UV ozone, Burnett has coordinated more exotic and rigorous cleaning which is contributed by science team members. He also coordinates cleanliness assessment requiring expertise and instruments not available in curation, such as XPS, TRXRF [1,2] and synchrotron TRXRF. JSC participates by optically documenting the particle distributions as cleaning steps progress. Thus, optical document supplements SEM imaging and analysis, and elemental assessment by TRXRF.

  4. Discussion on wind factor influencing the distribution of biological soil crusts on surface of sand dunes

    Institute of Scientific and Technical Information of China (English)

    YongSheng Wu; Hasi Erdun; RuiPing Yin; Xin Zhang; Jie Ren; Jian Wang; XiuMin Tian; ZeKun Li; HengLu Miao

    2013-01-01

    Biological soil crusts are widely distributed in arid and semi-arid regions, whose formation and development have an important impact on the restoration process of the desert ecosystem. In order to explore the relationship between surface airflow and development characteristics of biological soil crusts, we studied surface airflow pattern and development characteristics of biological soil crusts on the fixed dune profile through field observation. Results indicate that the speed of near-surface airflow is the lowest at the foot of windward slope and the highest at the crest, showing an increasing trend from the foot to the crest. At the leeward side, although near-surface airflow increases slightly at the lower part of the slope after an initial sudden decrease at upper part of the slope, its overall trend decreases from the crest. Wind velocity variation coefficient varied at different heights over each observation site. The thickness, shear strength of biological soil crusts and percentage of fine particles at crusts layer decreased from the slope foot to the upper part, showing that biological soil crusts are less developed in high wind speed areas and well developed in low wind speed areas. It can be seen that there is a close relationship between the distribution of biological soil crusts in different parts of the dunes and changes in airflow due to geomorphologic variation.

  5. Surface phonon-polariton enhanced optical forces in silicon carbide nanostructures.

    Science.gov (United States)

    Li, Dongfang; Lawandy, Nabil M; Zia, Rashid

    2013-09-09

    The enhanced optical forces induced by surface phonon-polariton (SPhP) modes are investigated in different silicon carbide (SiC) nanostructures. Specifically, we calculate optical forces using the Maxwell stress tensor for three different geometries: spherical particles, slab waveguides, and rectangular waveguides. We show that SPhP modes in SiC can produce very large forces, more than one order of magnitude larger than the surface plasmon-polariton (SPP) forces in analogous metal nanostructures. The material and geometric basis for these large optical forces are examined in terms of dispersive permittivity, separation distance, and operating wavelength.

  6. Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces.

    Science.gov (United States)

    Levine, Zachary A; Rapp, Michael V; Wei, Wei; Mullen, Ryan Gotchy; Wu, Chun; Zerze, Gül H; Mittal, Jeetain; Waite, J Herbert; Israelachvili, Jacob N; Shea, Joan-Emma

    2016-04-19

    Translating sticky biological molecules-such as mussel foot proteins (MFPs)-into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue's molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces.

  7. NUMERICAL STUDY OF WAVE EFFECTS ON SURFACE WIND STRESS AND SURFACE MIXING LENGTH BY THREE-DIMENSIONAL CIRCULATION MODELING

    Institute of Scientific and Technical Information of China (English)

    LIANG Bing-chen; LI Hua-jun; LEE Dong-yong

    2006-01-01

    The effects of waves on Surface Drag Coefficient (SDC) and surface mixing length were analyzed and discussed by carrying out three-dimensional current modeling for the Bohai Sea in the present work. A three- dimensional coupled hydrodynamical-ecological model for regional and shelf seas (COHERENS) incorporating the influences of wave-current interactions was coupled with the third-generation wave model swan taking into account time-varying currents. The effects of waves on currents were included in the SDC, surface mixing length and bottom drag coefficient. Firstly, the formulations in Donelan were incorporated into the COHERENS to account for wave-dependent SDC. In order to compare simulation results for the wave-dependent SDC, the simulation for wind-dependent SDC was also carried out. Second, Wave-Induced Surface Mixing Length (described as WISML sometimes in this paper) was incorporated into the COHERENS. Four numerical experiments were conducted to discuss the effects of two kinds of wave processes. Generally, the values of time series of current velocity and water surface elevation given by the simulation with all of the three wave processes have a good agreement with observed data. The existence of WISML changes obviously current vertical profiles and the existence of the wave dependent SDC modifies the current field of both top and bottom layers with the wind-dependent SDC.

  8. The Casimir force on a surface with shallow nanoscale corrugations: Geometry and finite conductivity effects

    CERN Document Server

    Bao, Y; Lussange, J; Lambrecht, A; Cirelli, R A; Klemens, F; Mansfield, W M; Pai, C S; Chan, H B

    2010-01-01

    We measure the Casimir force between a gold sphere and a silicon plate with nanoscale, rectangular corrugations with depth comparable to the separation between the surfaces. In the proximity force approximation (PFA), both the top and bottom surfaces of the corrugations contribute to the force, leading to a distance dependence that is distinct from a flat surface. The measured Casimir force is found to deviate from the PFA by up to 15%, in good agreement with calculations based on scattering theory that includes both geometry effects and the optical properties of the material.

  9. Surface chlorophyll, westerly winds, and El Nino in the western Pacific warm pool

    Science.gov (United States)

    Radenac, Marie-Hélène; Messié, Monique; Bosc, Christelle

    The western equatorial Pacific warm pool is characterized by sea surface temperature (SST) higher than 29° C and sea surface salinity (SSS) lower than 35. It is usually considered as a broad oligotrophic region with a nitrate exhausted and low chlorophyll (lower than 0.1 mg m-3 ) surface layer. Nevertheless, ocean colour imagery shows that surface chlorophyll concentrations vary at the interannual, seasonal, and intraseasonal time-scales. In this study, we use the 2000-2007 SeaWiFS data together with QuikScat wind, TMI SST, altimetric sea level, and OSCAR satellite-derived surface currents to describe and understand the variability of the surface chlorophyll in the region. In particular, nutrient and phytoplankton-rich waters upwelled near the country-regionplaceNew Guinea coast influence the distribution of surface chlorophyll in the equatorial warm pool from intra-seasonal to interannual time-scales. We show that the eastern part of the region is occupied by a quasi-persistent strip of very oligotrophic waters with chlorophyll concentrations close to those observed in the subtropical gyres (0.07 mg m-3 ). It extends over about 20 degrees of longitude and its width varies seasonally and with the El Niño/La Niña phases. Overall, this very oligotrophic zone matches n n the well-documented region with the warmest SST (over 30° C), thickest barrier layer (more than 20 m), and highest sea level (more than 220 cm) of the equatorial Pacific. Its eastern limit matches the eastern edge of the warm pool and moves zonally at seasonal and interannual time-scales. While the eastern edge has been described in previous studies, the western edge is poorly known. It is marked by the 0.1 mg m-3 chlorophyll isoline and its zonal motions occur at seasonal, interannual, and intraseasonal time-scales, as well. We investigate the late-2001 to late-2002 time period to assess the intra-seasonal variability of the surface chlorophyll in relation with the wind intra-seasonal variability

  10. High resolution modelling and observation of wind-driven surface currents in a semi-enclosed estuary

    Science.gov (United States)

    Nash, S.; Hartnett, M.; McKinstry, A.; Ragnoli, E.; Nagle, D.

    2012-04-01

    Hydrodynamic circulation in estuaries is primarily driven by tides, river inflows and surface winds. While tidal and river data can be quite easily obtained for input to hydrodynamic models, sourcing accurate surface wind data is problematic. Firstly, the wind data used in hydrodynamic models is usually measured on land and can be quite different in magnitude and direction from offshore winds. Secondly, surface winds are spatially-varying but due to a lack of data it is common practice to specify a non-varying wind speed and direction across the full extents of a model domain. These problems can lead to inaccuracies in the surface currents computed by three-dimensional hydrodynamic models. In the present research, a wind forecast model is coupled with a three-dimensional numerical model of Galway Bay, a semi-enclosed estuary on the west coast of Ireland, to investigate the effect of surface wind data resolution on model accuracy. High resolution and low resolution wind fields are specified to the model and the computed surface currents are compared with high resolution surface current measurements obtained from two high frequency SeaSonde-type Coastal Ocean Dynamics Applications Radars (CODAR). The wind forecast models used for the research are Harmonie cy361.3, running on 2.5 and 0.5km spatial grids for the low resolution and high resolution models respectively. The low-resolution model runs over an Irish domain on 540x500 grid points with 60 vertical levels and a 60s timestep and is driven by ECMWF boundary conditions. The nested high-resolution model uses 300x300 grid points on 60 vertical levels and a 12s timestep. EFDC (Environmental Fluid Dynamics Code) is used for the hydrodynamic model. The Galway Bay model has ten vertical layers and is resolved spatially and temporally at 150m and 4 sec respectively. The hydrodynamic model is run for selected hindcast dates when wind fields were highly energetic. Spatially- and temporally-varying wind data is provided by

  11. Comparison of the lateral retention forces on sessile and pendant water drops on a solid surface

    Science.gov (United States)

    de la Madrid, Rafael; Whitehead, Taylor; Irwin, George M.

    2015-06-01

    We present a simple experiment that demonstrates how a water drop hanging from a Plexiglas surface (pendant drop) experiences a lateral retention force that is comparable to, and in some cases larger than, the lateral retention force on a drop resting on top of the surface (sessile drop). The experiment also affords a simple demonstration of the Coriolis effect in two dimensions.

  12. Comparison of the lateral retention forces on sessile and pendant water drops on a solid surface

    OpenAIRE

    de la Madrid, Rafael; Whitehead, Taylor; Irwin, George

    2015-01-01

    We present a simple experiment that demonstrates how a water drop hanging from a Plexiglas surface (pendant drop) experiences a lateral retention force that is comparable to, and in some cases larger than, the lateral retention force on a drop resting on top of the surface (sessile drop). The experiment also affords a simple demonstration of the Coriolis effect in two dimensions.

  13. A 15-year climatology of wind pattern impacts on surface ozone in Houston, Texas

    Science.gov (United States)

    Souri, Amir Hossein; Choi, Yunsoo; Li, Xiangshang; Kotsakis, Alexander; Jiang, Xun

    2016-06-01

    Houston is recognized for its large petrochemical industrial facilities providing abundant radicals for tropospheric ozone formation. Fortunately, maximum daily 8-h average (MDA8) surface ozone concentrations have declined in Houston (- 0.6 ± 0.3 ppbv yr- 1) during the summers (i.e., May to September) of 2000 to 2014, possibly due to the reductions in precursor emissions by effective control policies. However, it is also possible that changes in meteorological variables have affected ozone concentrations. This study focused on the impact of long-term wind patterns which have the highest impact on ozone in Houston. The analysis of long-term wind patterns can benefit surface ozone studies by 1) providing wind patterns that distinctly changed ozone levels, 2) investigating the frequency of patterns and the respective changes and 3) estimating ozone trends in specific wind patterns that local emissions are mostly involved, thus separating emissions impacts from meteorology to some extent. To this end, the 900-hPa flow patterns in summers of 2000 to 2014 were clustered in seven classes (C1-C7) by deploying an unsupervised partitioning method. We confirm the characteristics of the clusters from a backward trajectory analysis, monitoring networks, and a regional chemical transport model simulation. The results indicate that Houston has experienced a statistically significant downward trend (- 0.6 ± 0.4 day yr- 1) of the cluster of weak easterly and northeasterly days (C4), when the highest fraction of ozone exceedances (MDA8 > 70 ppbv) occurred. This suggests that the reduction in ozone precursors was not the sole reason for the decrease in ozone exceedance days (- 1.5 ± 0.6 day yr- 1). Further, to examine the efficiency of control policies intended to reduce the amount of ozone, we estimated the trend of MDA8 ozone in C4 and C5 (weak winds) days when local emissions are primarily responsible for high ambient ozone levels. Both C4 and C5 show a large reduction in the

  14. Quantitative evaluation of interaction force between functional groups in protein and polymer brush surfaces.

    Science.gov (United States)

    Sakata, Sho; Inoue, Yuuki; Ishihara, Kazuhiko

    2014-03-18

    To understand interactions between polymer surfaces and different functional groups in proteins, interaction forces were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Various polymer brush surfaces were systematically prepared by surface-initiated atom transfer radical polymerization as well-defined model surfaces to understand protein adsorption behavior. The polymer brush layers consisted of phosphorylcholine groups (zwitterionic/hydrophilic), trimethylammonium groups (cationic/hydrophilic), sulfonate groups (anionic/hydrophilic), hydroxyl groups (nonionic/hydrophilic), and n-butyl groups (nonionic/hydrophobic) in their side chains. The interaction forces between these polymer brush surfaces and different functional groups (carboxyl groups, amino groups, and methyl groups, which are typical functional groups existing in proteins) were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Furthermore, the amount of adsorbed protein on the polymer brush surfaces was quantified by surface plasmon resonance using albumin with a negative net charge and lysozyme with a positive net charge under physiological conditions. The amount of proteins adsorbed on the polymer brush surfaces corresponded to the interaction forces generated between the functional groups on the cantilever and the polymer brush surfaces. The weakest interaction force and least amount of protein adsorbed were observed in the case of the polymer brush surface with phosphorylcholine groups in the side chain. On the other hand, positive and negative surfaces generated strong forces against the oppositely charged functional groups. In addition, they showed significant adsorption with albumin and lysozyme, respectively. These results indicated that the interaction force at the functional group level might be

  15. Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM) phase images

    OpenAIRE

    Andreae, M. O.; G. Helas

    2008-01-01

    We show that atomic force microscopy (AFM) phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly...

  16. Observation and simulation of near-surface wind and its variation with topography in Urumqi, West China

    Science.gov (United States)

    Jin, Lili; Li, Zhenjie; He, Qing; Miao, Qilong; Zhang, Huqiang; Yang, Xinghua

    2016-12-01

    Near-surface wind measurements obtained with five 100-m meteorology towers, 39 regional automatic stations, and simulations by the Weather Research and Forecasting (WRF) model were used to investigate the spatial structure of topography-driven flows in the complex urban terrain of Urumqi, China. The results showed that the wind directions were mainly northerly and southerly within the reach of 100 m above ground in the southern suburbs, urban area, and northern suburbs, which were consistent with the form of the Urumqi gorge. Strong winds were observed in southern suburbs, whereas the winds in the urban, northern suburbs, and northern rural areas were weak. Static wind occurred more frequently in the urban and northern rural areas than in the southern suburbs. In the southern suburbs, wind speed was relatively high throughout the year and did not show significant seasonal variations. The average annual wind speed in this region varied among 1.9-5.5, 1.1-3.6, 1.2-4.3, 1.2-4.3, and 1.1-3.5 m s -1 within the reach of 100 m above ground at Yannanlijiao, Shuitashan, Liyushan, Hongguangshan, and Midong, respectively. The flow characteristics comprised more airflows around the mountain, where the convergence and divergence were dominated by the terrain in eastern and southwestern Urumqi. Further analysis showed that there was a significant mountain-valley wind in spring, summer, and autumn, which occurred more frequently in spring and summer for 10-11 h in urban and northern suburbs. During daytime, there was a northerly valley wind, whereas at night there was a southerly mountain wind. The conversion time from the mountain wind to the valley wind was during 0800-1000 LST (Local Standard Time), while the conversion from the valley wind to the mountain wind was during 1900-2100 LST. The influence of the mountain-valley wind in Urumqi City was most obvious at 850 hPa, according to the WRF model.

  17. Considerations on the effect of wind-tunnel walls on oscillating air forces for two-dimensional subsonic compressible flow

    Science.gov (United States)

    Runyan, Harry L; Watkins, Charles E

    1953-01-01

    This report treats the effect of wind-tunnel walls on the oscillating two-dimensional air forces in a compressible medium. The walls are simulated by the usual method of placing images at appropriate distances above and below the wing. An important result shown is that, for certain conditions of wing frequency, tunnel height, and Mach number, the tunnel and wing may form a resonant system so that the forces on the wing are greatly changed from the condition of no tunnel walls. It is pointed out that similar conditions exist for three-dimensional flow in circular and rectangular tunnels and apparently, within certain Mach number ranges, in tunnels of nonuniform cross section or even in open tunnels or jets.

  18. The seasonal variations in the significant wave height and sea surface wind speed of the China’s seas

    Institute of Scientific and Technical Information of China (English)

    ZHENG Chongwei; PAN Jing; TAN Yanke; GAO Zhansheng; RUI Zhenfeng; CHEN Chaohui

    2015-01-01

    Long-term variations in a sea surface wind speed (WS) and a significant wave height (SWH) are associated with the global climate change, the prevention and mitigation of natural disasters, and an ocean resource exploitation, and other activities. The seasonal characteristics of the long-term trends in China’s seas WS and SWH are determined based on 24 a (1988–2011) cross-calibrated, multi-platform (CCMP) wind data and 24 a hindcast wave data obtained with the WAVEWATCH-III (WW3) wave model forced by CCMP wind data. The results show the following. (1) For the past 24 a, the China’s WS and SWH exhibit a significant increasing trend as a whole, of 3.38 cm/(s·a) in the WS, 1.3 cm/a in the SWH. (2) As a whole, the increasing trend of the China’s seas WS and SWH is strongest in March-April-May (MAM) and December-January-February (DJF), followed by June-July-August (JJA), and smallest in September-October-November (SON). (3) The areal extent of significant increases in the WS was largest in MAM, while the area decreased in JJA and DJF;the smallest area was apparent in SON. In contrast to the WS, almost all of China’s seas exhibited a significant increase in SWH in MAM and DJF;the range was slightly smaller in JJA and SON. The WS and SWH in the Bohai Sea, the Yellow Sea, East China Sea, the Tsushima Strait, the Taiwan Strait, the northern South China Sea, the Beibu Gulf, and the Gulf of Thailand exhibited a significant increase in all seasons. (4) The variations in China’s seas SWH and WS depended on the season. The areas with a strong increase usually appeared in DJF.

  19. Training the People’s Liberation Army Air Force Surface-to-Air Missile (SAM) Forces

    Science.gov (United States)

    2016-01-01

    Bao MR Military Region MRAF Beijing Military Region Air Force MUCD Military Unit Cover Designator NASIC National Air and Space Intelligence Center...为荣], ed., 2006, p. 253. 49 Air Force Engineering University [空军工程大学], undated. 50 An Hongqiang [安红强] and Yang Tao [杨涛], “Quenching the Blade Before...115 These are designated as third-generation aircraft in Chinese. 116 Yuan Hai [袁海] and Zhou Tengjiao [周腾蛟], 2013, p. 3. 117 One air force

  20. Strong winter monsoon wind causes surface cooling over India and China in the Late Miocene

    Directory of Open Access Journals (Sweden)

    H. Tang

    2015-01-01

    Full Text Available Modern Asian winter monsoon characterised by the strong northwesterly wind in East Asia and northeasterly wind in South Asia, has a great impact on the surface temperature of the Asian continent. Its outbreak can result in significant cooling of the monsoon region. However, it is still unclear whether such an impact existed and is detectable in the deep past. In this study, we use temperature reconstructions from plant and mammal fossil data together with climate model results to examine the co-evolution of surface temperature and winter monsoon in the Late Miocene (11–5 Ma, when a significant change of the Asian monsoon system occurred. We find that a stronger-than-present winter monsoon wind might have existed in the Late Miocene due to the lower Asian orography, particularly the northern Tibetan Plateau and the mountains north of it. This can lead to a pronounced cooling in southern China and northern India, which counteracts the generally warmer conditions in the Late Miocene compared to present. The Late Miocene strong winter monsoon was characterised by a marked westerly component and primarily caused by a pressure anomaly between the Tibetan Plateau and Northern Eurasia, rather than by the gradient between the Siberian High and the Aleutian Low. As a result, the close association of surface temperature with winter monsoon strength on inter-annual scale as observed at present may not have established in the Late Miocene.

  1. Errors of five-day mean surface wind and temperature conditions due to inadequate sampling

    Science.gov (United States)

    Legler, David M.

    1991-01-01

    Surface meteorological reports of wind components, wind speed, air temperature, and sea-surface temperature from buoys located in equatorial and midlatitude regions are used in a simulation of random sampling to determine errors of the calculated means due to inadequate sampling. Subsampling the data with several different sample sizes leads to estimates of the accuracy of the subsampled means. The number N of random observations needed to compute mean winds with chosen accuracies of 0.5 (N sub 0.5) and 1.0 (N sub 1,0) m/s and mean air and sea surface temperatures with chosen accuracies of 0.1 (N sub 0.1) and 0.2 (N sub 0.2) C were calculated for each 5-day and 30-day period in the buoy datasets. Mean values of N for the various accuracies and datasets are given. A second-order polynomial relation is established between N and the variability of the data record. This relationship demonstrates that for the same accuracy, N increases as the variability of the data record increases. The relationship is also independent of the data source. Volunteer-observing ship data do not satisfy the recommended minimum number of observations for obtaining 0.5 m/s and 0.2 C accuracy for most locations. The effect of having remotely sensed data is discussed.

  2. Effects of surface current-wind interaction in an eddy-rich general ocean circulation simulation of the Baltic Sea

    Science.gov (United States)

    Dietze, Heiner; Löptien, Ulrike

    2016-08-01

    Deoxygenation in the Baltic Sea endangers fish yields and favours noxious algal blooms. Yet, vertical transport processes ventilating the oxygen-deprived waters at depth and replenishing nutrient-deprived surface waters (thereby fuelling export of organic matter to depth) are not comprehensively understood. Here, we investigate the effects of the interaction between surface currents and winds on upwelling in an eddy-rich general ocean circulation model of the Baltic Sea. Contrary to expectations we find that accounting for current-wind effects inhibits the overall vertical exchange between oxygenated surface waters and oxygen-deprived water at depth. At major upwelling sites, however (e.g. off the southern coast of Sweden and Finland) the reverse holds: the interaction between topographically steered surface currents with winds blowing over the sea results in a climatological sea surface temperature cooling of 0.5 K. This implies that current-wind effects drive substantial local upwelling of cold and nutrient-replete waters.

  3. A wind loading correlation for an isolated square heliostat part 2: Moments and side forces

    CSIR Research Space (South Africa)

    Roos, TH

    2012-05-01

    Full Text Available on the heliostat for all elevation angles of the heliostat and all wind directions relative to the heliostat coordinate system. A companion paper has described a technique for using of Fourier analysis to fit a small number of correlations to a large experimental...

  4. Solar Wind Access to Lunar Polar Craters: Feedback Between Surface Charging and Plasma Expansion

    Science.gov (United States)

    Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.; Halekas, J. S.; Jackson, T. L.

    2011-01-01

    Determining the plasma environment within permanently shadowed lunar craters is critical to understanding local processes such as surface charging, electrostatic dust transport, volatile sequestration, and space weathering. In order to investigate the nature of this plasma environment, the first two-dimensional kinetic simulations of solar wind expansion into a lunar crater with a self-consistent plasma-surface interaction have been undertaken. The present results reveal how the plasma expansion into a crater couples with the electrically-charged lunar surface to produce a quasi-steady wake structure. In particular, there is a negative feedback between surface charging and ambipolar wake potential that allows an equilibrium to be achieved, with secondary electron emission strongly moderating the process. A range of secondary electron yields is explored, and two distinct limits are highlighted in which either surface charging or ambipoiar expansion is responsible for determining the overall wake structure.

  5. Toward an Engineering Model for the Aerodynamic Forces Acting on Wind Turbine Blades in Quasisteady Standstill and Blade Installation Situations

    Science.gov (United States)

    Gaunaa, Mac; Heinz, Joachim; Skrzypiński, Witold

    2016-09-01

    The crossflow principle is one of the key elements used in engineering models for prediction of the aerodynamic loads on wind turbine blades in standstill or blade installation situations, where the flow direction relative to the wind turbine blade has a component in the direction of the blade span direction. In the present work, the performance of the crossflow principle is assessed on the DTU 10MW reference blade using extensive 3D CFD calculations. Analysis of the computational results shows that there is only a relatively narrow region in which the crossflow principle describes the aerodynamic loading well. In some conditions the deviation of the predicted loadings can be quite significant, having a large influence on for instance the integral aerodynamic moments around the blade centre of mass; which is very important for single blade installation applications. The main features of these deviations, however, have a systematic behaviour on all force components, which in this paper is employed to formulate the first version of an engineering correction method to the crossflow principle applicable for wind turbine blades. The new correction model improves the agreement with CFD results for the key aerodynamic loads in crossflow situations. The general validity of this model for other blade shapes should be investigated in subsequent works.

  6. The Effect of Non-Lambertian Surface Reflectance on Aerosol Radiative Forcing

    Energy Technology Data Exchange (ETDEWEB)

    Ricchiazzi, P.; O' Hirok, W.; Gautier, C.

    2005-03-18

    Surface reflectance is an important factor in determining the strength of aerosol radiative forcing. Previous studies of radiative forcing assumed that the reflected surface radiance is isotropic and does not depend on incident illumination angle. This Lambertian reflection model is not a very good descriptor of reflectance from real land and ocean surfaces. In this study we present computational results for the seasonal average of short and long wave aerosol radiative forcing at the top of the atmosphere and at the surface. The effect of the Lambertian assumption is found through comparison with calculations using a more detailed bi-direction reflectance distribution function (BRDF).

  7. Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM) phase images

    Science.gov (United States)

    Helas, G.; Andreae, M. O.

    2008-10-01

    We show that atomic force microscopy (AFM) phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly shows deposits of distinguishable material on the surface. We apply this technique to dust aerosol particles from the Sahara collected over the Atlantic Ocean and describe micro-features on the surfaces of such particles.

  8. A Ka-Band Backscatter Model Function and an Algorithm for Measurement of the Wind Vector Over the Sea Surface

    NARCIS (Netherlands)

    Nekrasov, A.; Hoogeboom, P.

    2005-01-01

    A Ka-band backscatter model and an algorithm for measurement of the wind speed and direction over the sea surface by a frequency-modulated continous-wave radar demonstrator system operated in scatterometer mode have been developed. To evaluate the proposed algorithm, a simulation of the wind vector

  9. Surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea

    Science.gov (United States)

    Lincoln, B. J.; Rippeth, T. P.; Simpson, J. H.

    2016-08-01

    Inertial oscillations are a ubiquitous feature of the surface ocean. Here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea. Observations of temperature and current structure, from a mooring in the Western Irish Sea, reveal episodes of strong currents (>0.3 m s-1) lasting several days, resulting in enhanced shear across the thermocline. While the episodes of strong currents are coincident with windy periods, the variance in the shear is not directly related to the wind stress. The shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14.85 h. These shear maxima coincide with the orientation of the surface current being at an angle of approximately 90° to the right of the wind direction. Observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear. During the periods of enhanced shear gradient, Richardson number estimates indicate Ri-1 ≥ 4 at the base of the surface mixed layer, implying the deepening as a result of shear instability. A one-dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step-like deepening. The observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow, seasonally stratified sea.

  10. Variation of Surface Charge along the Surface of Wool Fibers Assessed by High-Resolution Force Spectroscopy

    Science.gov (United States)

    Zimmerman, Bonnie; Chow, James; Abbott, Albert G.; Ellison, Michael S.; Kennedy, Marian S.; Dean, Delphine

    2011-01-01

    In this study, we have mapped the surface charge of wool fibers using chemically specific high-resolution force spectroscopy in order to better understand the dispersion of amino acids in relation to fiber morphology. The inter-surface forces between standard atomic force microscopy (AFM) probe tips (tip radius ~ 50 nm) functionalized with COOH and NH3 terminated alkanethiol self assembling monolayers and the wool surface were used to estimate the surface charge per unit area using linear Poisson-Boltzmann-based electrostatic double layer theory. The positional measurement of nano-scale surface charge showed a correlation between the surface charge and fiber morphology, indicated that basic amino acids are located near the scale edges. PMID:21866220

  11. A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

    Science.gov (United States)

    Ho, Yat-Kiu; Liu, Chun-Ho

    2016-08-01

    Dynamics in the roughness (RSLs) and inertial (ISLs) sublayers in the turbulent boundary layers (TBLs) over idealised urban surfaces are investigated analytically and experimentally. In this paper, we derive an analytical solution to the mean velocity profile, which is a continuous function applicable to both RSL and ISL, over rough surfaces in isothermal conditions. Afterwards, a modified mixing-length model for RSL/ISL transport is developed that elucidates how surface roughness affects the turbulence motions. A series of wind tunnel experiments are conducted to measure the vertical profiles of mean and fluctuating velocities, together with momentum flux over various configurations of surface-mounted ribs in cross flows using hot-wire anemometry (HWA). The analytical solution agrees well with the wind tunnel result that improves the estimate to mean velocity profile over urban surfaces and TBL dynamics as well. The thicknesses of RSL and ISL are calculated by monitoring the convergence/divergence between the temporally averaged and spatio-temporally averaged profiles of momentum flux. It is found that the height of RSL/ISL interface is a function of surface roughness. Examining the direct, physical influence of roughness elements on near-surface RSL flows reveals that the TBL flows over rough surfaces exhibit turbulence motions of two different length scales which are functions of the RSL and ISL structure. Conclusively, given a TBL, the rougher the surface, the higher is the RSL intruding upward that would thinner the ISL up to 50 %. Therefore, the conventional ISL log-law approximation to TBL flows over urban surfaces should be applied with caution.

  12. Aerosol Direct Radiative Forcing and Forcing Efficiencies at Surface from the shortwave Irradiance Measurements in Abu Dhabi, UAE

    Science.gov (United States)

    Beegum S, N.; Ben Romdhane, H.; Ghedira, H.

    2013-12-01

    Atmospheric aerosols are known to affect the radiation balance of the Earth-Atmospheric system directly by scattering and absorbing the solar and terrestrial radiation, and indirectly by affecting the lifetime and albedo of the clouds. Continuous and simultaneous measurements of short wave global irradiance in combination with synchronous spectral aerosol optical depth (AOD) measurements (from 340 nm to 1640 nm in 8 channels), for a period of 1 year from June 2012 to May 2013, were used for the determination of the surface direct aerosol radiative forcing and forcing efficiencies under cloud free conditions in Abu Dhabi (24.42°N, 54.61o E, 7m MSL), a coastal location in United Arab Emirates (UAE) in the Arabian Peninsula. The Rotating Shadow band Pyranometer (RSP, LI-COR) was used for the irradiance measurements (in the spectral region 400-1100 nm), whereas the AOD measurements were carried out using CIMEL Sunphotometer (CE 318-2, under AERONET program). The differential method, which is neither sensitive to calibration uncertainties nor model assumptions, has been employed for estimating forcing efficiencies from the changes in the measured fluxes. The forcing efficiency, which quantifies the net change in irradiance per unit change in AOD, is an appropriate parameter for the characterization of the aerosol radiative effects even if the microphysical and optical properties of the aerosols are not completely understood. The corresponding forcing values were estimated from the forcing efficiencies. The estimated radiative forcing and forcing efficiencies exhibited strong monthly variations. The forcing efficiencies (absolute magnitudes) were highest during March, and showed continuous decrease thereafter to reach the lowest value during September. In contrast, the forcing followed a slightly different pattern of variability, with the highest solar dimming during April ( -60 W m-2) and the minimum during February ( -20 W m-2). The results indicate that the aerosol

  13. Connecting the surface of the Sun to the Heliosphere : wind speed and magnetic field geometry

    Science.gov (United States)

    Pinto, Rui

    2016-07-01

    The large-scale solar wind speed distribution varies in time in response to the cyclic variations of the strength and geometry of the magnetic field of the corona. Based on this idea, semi-empirical predictive laws for the solar wind speed (such as in the widely-used WSA law) use simple parameters describing the geometry of the coronal magnetic field. In practice, such scaling laws require ad-hoc corrections and empirical fits to in-situ spacecraft data, and a predictive law based solely on physical principles is still missing. I will discuss improvements to this kind of laws based on the analysis of very large samples of wind acceleration profiles in open flux-tubes (both from MHD simulations and potential-field extrapolations), and possible strategies for corona and heliosphere model coupling. I will, furthermore present an ongoing modelling effort to determine the magnetic connectivity, paths and propagation delays of any type of disturbance (slow/fast solar wind, waves, energetic particles, ballistic propagation) between the solar surface and any point in the interplanetary space at any time. This is a key point for the exploitation of data from Solar Orbiter and Solar Probe Plus, and more generally for establishing connections between remote and in-situ spacecraft data. This is work is supported by the FP7 project #606692 (HELCATS).

  14. Near surface spatially averaged air temperature and wind speed determined by acoustic travel time tomography

    Directory of Open Access Journals (Sweden)

    Armin Raabe

    2001-03-01

    Full Text Available Acoustic travel time tomography is presented as a possibility for remote monitoring of near surface airtemperature and wind fields. This technique provides line-averaged effective sound speeds changing with temporally and spatially variable air temperature and wind vector. The effective sound speed is derived from the travel times of sound signals which propagate at defined paths between different acoustic sources and receivers. Starting with the travel time data a tomographic algorithm (Simultaneous Iterative Reconstruction Technique, SIRT is used to calculate area-averaged air temperature and wind speed. The accuracy of the experimental method and the tomographic inversion algorithm is exemplarily demonstrated for one day without remarkable differences in the horizontal temperature field, determined by independent in situ measurements at different points within the measuring field. The differences between the conventionally determined air temperature (point measurement and the air temperature determined by tomography (area-averaged measurement representative for the area of the measuring field 200m x 260m were below 0.5 K for an average of 10 minutes. The differences obtained between the wind speed measured at a meteorological mast and calculated from acoustic measurements are not higher than 0.5 ms-1 for the same averaging time. The tomographically determined area-averaged distribution of air temperature (resolution 50 m x 50 m can be used to estimate the horizontal gradient of air temperature as a pre-condition to detect horizontal turbulent fluxes of sensible heat.

  15. Statistical parameters of the spatiotemporal variability of the wind direction in the surface layer

    Science.gov (United States)

    Shishov, E. A.; Koprov, B. M.; Koprov, V. M.

    2017-01-01

    Multipoint measurements of wind direction were carried out during the expedition of the Institute of Atmospheric Physics, Russian Academy of Sciences (IPA RAS), in Tsimlyansk in 2012. Spatial correlation functions for the transverse direction and temporal correlation functions for the longitudinal direction are plotted under stable and unstable stratification of the atmosphere. The longitudinal correlation radius is much higher than the transverse one, and radii in daytime realizations are larger than in nighttime. To determine the stratification conditions, an ultrasonic anemometer-thermometer was used. Autospectra of wind direction fluctuations were plotted. They include long segments of power dependence on the frequency. The spectral correlation coefficients of variations in the wind direction versus intersensor distance in the transverse direction are also calculated. A set of fast-response thermometers was used in the experiment. They allowed temperature mapping, i.e., plotting the time variations in the isothermal surface altitude. That analysis was also applied to visualization of the spatiotemporal variability of wind direction. The resulting data were used for planning the helicity measurements in the Tsimlyansk expedition in 2014.

  16. Variability in the coupling between sea surface temperature and wind stress in the global coastal ocean

    Science.gov (United States)

    Wang, Yuntao; Castelao, Renato M.

    2016-08-01

    Mesoscale ocean-atmosphere interaction between sea surface temperature (SST) and wind stress throughout the global coastal ocean was investigated using 7 years of satellite observations. Coupling coefficients between crosswind SST gradients and wind stress curl and between downwind SST gradients and wind stress divergence were used to quantify spatial and temporal variability in the strength of the interaction. The use of a consistent data set and standardized methods allow for direct comparisons between coupling coefficients in the different coastal regions. The analysis reveals that strong coupling is observed in many mid-latitude regions throughout the world, especially in regions with strong fronts like Eastern and Western Boundary Currents. Most upwelling regions in Eastern Boundary Currents are characterized by strong seasonal variability in the strength of the coupling, which generally peaks during summer in mid latitudes and during winter at low latitudes. Seasonal variability in coastal regions along Western Boundary Currents is comparatively smaller. Intraseasonal variability is especially important in regions of strong eddy activity (e.g., Western Boundary Currents), being particularly relevant for the coupling between crosswind SST gradients and wind stress curl. Results from the analysis can be used to guide modeling studies, since it allows for the a priori identification of regions in which regional models need to properly represent the ocean-atmosphere interaction to accurately represent local variability.

  17. On the "force-free surface " of the magnetized celestial bodies

    CERN Document Server

    Epp, V

    2015-01-01

    The field of a uniformly magnetized rotating sphere is studied with special attention to the surface where the electric and magnetic fields are orthogonal to each other. The equation of this surface, valid at arbitrary distances from the rotating magnetized sphere, is obtained. Inside the light cylinder this surface can be considered as a force-free surface, i.e. as a place where the particles with strong radiation damping can be trapped due to their energy loss. Outside the light cylinder this surface makes just a geometric locus which moves with a superlight velocity around the axis of rotation. The 2- and 3-dimensional plots of the force-free surface are constructed. Estimation of influence of the centrifugal force on the particle dynamics is made. It is shown, that in case of strong magnetic field the centrifugal force is negligible small everywhere except a narrow neighbourhood of the light cylinder.

  18. On alpha stable distribution of wind driven water surface wave slope

    CERN Document Server

    Joelson, Maminirina

    2008-01-01

    We propose a new formulation of the probability distribution function of wind driven water surface slope with an $\\alpha$-stable distribution probability. The mathematical formulation of the probability distribution function is given under an integral formulation. Application to represent the probability of time slope data from laboratory experiments is carried out with satisfactory results. We compare also the $\\alpha$-stable model of the water surface slopes with the Gram-Charlier development and the non-Gaussian model of Liu et al\\cite{Liu}. Discussions and conclusions are conducted on the basis of the data fit results and the model analysis comparison.

  19. Specific features of heat transfer on the external surface of smoke stacks blown by wind

    Science.gov (United States)

    Maneev, A. P.; Terekhov, V. I.

    2015-03-01

    Results of a full-scale experiment on studying heat transfer on the surface of a reinforced-concrete smoke stack blown by wind at the value of Reynolds number Re = 1.05 × 107 are presented. Comparison of the experimental results with the experimental data obtained previously by other researchers under laboratory conditions at Re cylinder in a transcritical streamlining mode. The data obtained in the present study open the possibility to estimate the average values of heat transfer coefficient on the surface of smoke stacks in a flow of atmospheric air at 4 × 106 < Re < 107.

  20. Application of the FlexiForce contact surface force sensor to continuous extraocular compression monitoring during craniotomy for cerebral aneurysms.

    Science.gov (United States)

    Mutoh, Tatsushi; Ishikawa, Tatsuya; Nishimura, Hiromi; Yasui, Nobuyuki

    2010-01-01

    The aims of this study were to introduce our newly developed device equipped with a contact surface force sensor (FlexiForce) for monitoring extraocular compression continuously, and to illustrate its potential clinical application using this device in patients undergoing uncomplicated frontotemporal or bifrontal craniotomy for surgical clipping of unruptured anterior circulation aneurysms. In a pilot study with volunteers, we determined the critical force of 100 gf to cause painful ocular sensation. Then we performed the bilateral extraocular force measurements in 15 patients undergoing uncomplicated frontotemporal or bifrontal craniotomy for surgical clipping of unruptured anterior circulation aneurysms. Extraocular force increased immediately after retraction of the flap, increased to 144+/-26 gf (mean+/-SD) during lower craniotomy close to the orbit, was maintained at 91+/-18 gf during microsurgery, and returned close to baseline at 24+/-14 gf after restoration of skin flap retraction. Such changes were observed only on the surgical side in frontotemporal craniotomy. Abnormal increase in extraocular force was effectively reduced by placing a real-time digital panel meter to warn surgeons to avoid excessive skin flap retraction during the surgical procedure. In conclusion, this new tool may allow us to monitor the external forces that can be applied intraoperatively to the ocular globe in the supine position.

  1. Surface Polarity Of Beta-hmx Crystal And The Related Adhesive Forces With Estane Binder

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Lu [Los Alamos National Laboratory; Hanson, David E [Los Alamos National Laboratory

    2008-01-01

    Here we present the results on the study of surface properties of {beta}-HMX crystal utilizing molecular simulations. The surface polarity of three principal crystal surfaces are investigated by measuring the water contact angles. The calculated contact angles agree excellently with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain with and without nitroplasticizer from the three principal crystal surfaces were calculated using umbrella sampling technique. We find that the detaching free energy/force increases with the increasing HMX surface polarity. In addition, our results also show that nitroplasticizer plays an important role in the adhesion forces between Estane and HMX surfaces.

  2. Hurricane Force Winds in Explosive Maritime Extratropical Cyclones: A Modeling and Observational Study of Their Evolution and Dynamics

    Science.gov (United States)

    Albright, Benjamin Scott

    Extratropical cyclones can be as powerful as tropical cyclones with winds reaching 33 m s-1 or even stronger. They can also be very large in scale, and impact life and property on the oceans as well as over the land if the storms make a landfall. Two conceptual models exist that attempt to explain how the extreme winds in the bent-back frontal zone of these cyclones occur. The first is a jet associated with the cold conveyor belt and the second is through a phenomenon known as a sting jet. Some of the objectives this thesis will address are: (1) The role of gradient wind is during the life-cycle of the cyclone, (2) how model results compare to actual observations, and (3) if the sting jet or cold conveyor belt jet are the only causes for high winds within the bent-back frontal zone, among others. This thesis will examine two case studies of extreme, extratropical cyclones that occurred over the North Atlantic Ocean. Extensive observations including dropsondes, Stepped Frequency Microwave Radiometer (SFMR) measurements from a NOAA WP-3D aircraft and satellite scatterometer measurements are used to compare with modeled results of the two case studies. The Weather Research and Forecasting (WRF) Model Version 3.4.1 and the NOAA Environmental Modeling System (NEMS) NMM-B Launcher are used to model the two case studies and for high resolution and sensitivity testing. Trajectories calculated by the Read/Interpolate/Plot program and cross sections are additional tools used in the study. Some of the major conclusions included identifying sting jets in each storm but they were found not to be the major cause of the highest winds within the bent-back frontal zone. A secondary stream of air that accelerates from the west of the rapidly intensifying cyclone into a low-level jet located within a larger pressure gradient force and thermal gradient was found to be the major source of the high winds. It is suggested that the findings and conclusions based on the results of this

  3. Wind load modeling for topology optimization of continuum structures

    NARCIS (Netherlands)

    Zakhama, R.; Abdalla, M.M.; Gürdal, Z.; Smaoui, H.

    2010-01-01

    Topology optimization of two and three dimensional structures subject to dead and wind loading is considered. The wind loading is introduced into the formulation by using standard expressions for the drag force, and a strategy is devised so that wind pressure is ignored where there is no surface obs

  4. Atomic force microscopy study of cellulose surface interaction controlled by cellulose binding domains

    OpenAIRE

    Nigmatullin, R.; Lovitt, R.; Wright, C; Linder, M.; Nakari-Setälä, T; Gama, F. M.

    2004-01-01

    Colloidal probe microscopy has been used to study the interaction between model cellulose surfaces and the role of cellulose binding domain (CBD), peptides specifically binding to cellulose, in interfacial interaction of cellulose surfaces modified with CBDs. The interaction between pure cellulose surfaces in aqueous electrolyte solution is dominated by double layer repulsive forces with the range and magnitude of the net force dependent on electrolyte concentration. AFM imaging reve...

  5. The climate influence of anthropogenic land-use changes on near-surface wind energy potential in China

    Institute of Scientific and Technical Information of China (English)

    LI Yan; WANG Yuan; CHU HuiYun; TANG JianPing

    2008-01-01

    There is considerable interest in the potential impact of climate change on wind energy in China. The climate change of near-surface wind energy potential in China under the background of global warming and its association with anthropogenic land-use changes are investigated by calculating the difference in surface wind speeds between the NCEP/NCAR reanalysis data and the observations since the re-analysis dataset contains the influence of large-scale climate changes due to greenhouse gases, it is less sensitive to regional surface processes associated with land types. The surface wind data in this study consist of long-tarm observations from 604 Chinese Roution Meteorological Stations and theNCEP/NCAR reanalysis data from 1960-1999. The results suggest that the observed mean wind speeds significantly weakened and the near-surface wind power trended downward due to urbanization and other land-use changes in the last 40 years. The mean wind energy weakened by -3.84 W·m-2 per decade due to the influence of anthropogenic land-use change, which is close to the observed climate change (-4.51 W·m-2/10 a).

  6. Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

    Directory of Open Access Journals (Sweden)

    F. C. Bassinot

    2011-02-01

    Full Text Available The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes at ODP Site 723 (19°03' N, 57°37' E; Oman Margin and core MD77-191 (07°30' N, 76°43' E; Southern tip of India. Today, the primary productivity at both sites peaks during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G.~bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum and decreased since then, suggesting a direct response to insolation forcing. On the opposite, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present.

    Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites have been directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian sea during boreal summer.

  7. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces

    NARCIS (Netherlands)

    Boks, N.P.; Norde, W.; Meil, H.C.; Busscher, H.J.

    2008-01-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F-prev) and to detach adhering bacteria (F-det) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the

  8. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces

    NARCIS (Netherlands)

    Boks, Niels P.; Norde, Willem; van der Mei, Henny C.; Busscher, Henk J.

    2008-01-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the

  9. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces

    NARCIS (Netherlands)

    Boks, N.P.; Norde, W.; Meil, H.C.; Busscher, H.J.

    2008-01-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F-prev) and to detach adhering bacteria (F-det) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the fol

  10. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces

    NARCIS (Netherlands)

    Boks, Niels P.; Norde, Willem; van der Mei, Henny C.; Busscher, Henk J.

    2008-01-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the f

  11. A Numerical Study of Wind Forcing Effects on the California Current System

    Science.gov (United States)

    1994-09-01

    INSTABILITIES FOR EXPERIMENT 1 ( CLIMO ) . . 149 APPENDIX B. INSTABILITIES FOR EXPERIMENT 2 (1981) . . 157 APPENDIX C. INSTABILITIES FOR EXPERIMENT 3...1983) . 167 APPENDIX D. INSTABILITIES FOR EXPERIMENT 4 ( CLIMO II) 183 APPENDIX E. INSTABILITIES FOR EXPERIMENT 5 (1982) . . 193 APPENDIX F. INSTABILITIES...Total kinetic energy per unit mass time series for Climo II over the entire domain ............ ................. 105 xiii 4.49 Kid-monthly IOU? winds

  12. nowCOAST's Map Service for NOAA NWS NDFD Gridded Forecasts of Surface Wind Velocity Barb (knots) (Time Offsets)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Map Information: This nowCOAST time-offsets map service provides maps depicting the NWS surface wind velocity forecasts from the National Digital Forecast Database...

  13. nowCOAST's Map Service for NOAA NWS NDFD Gridded Forecasts of Surface Wind Speed (knots) (Time Offsets)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Map Information: This nowCOAST time-offsets map service provides maps depicting the NWS surface wind speed forecasts from the National Digital Forecast Database...

  14. On stochastic stability of regional ocean models with uncertainty in wind forcing

    Directory of Open Access Journals (Sweden)

    L. M. Ivanov

    2007-10-01

    Full Text Available A shallow-water model was used to understand model error induced by non-Gaussian wind uncertainty. Although the model was simple, it described a generic system with many degrees of freedom randomized by external noise. The study focused on the nontrivial collective behavior of finite-amplitude perturbations on different scales and their influence on model predictability. The error growth strongly depended on the intensity and degree of spatial inhomogeneity of wind perturbations. For moderate but highly inhomogeneous winds, the error grew as a power law. This behavior was a consequence of varying local characteristic exponents and nonlinear interactions between different scales. Coherent growth of perturbations was obtained for different scales at various stages of error evolution. For the nonlinear stage, statistics of prediction error could be approximated by a Weibull distribution. An approach based on the Kullback-Leibler distance (the relative entropy and probability-weighted moments was developed for identification of Weibull statistics. Bifurcations of the variance, skewness and kurtosis of the irreversible predictability time (a measure of model prediction skill were detected when the accepted prediction accuracy (tolerance exceeded some threshold.

  15. Muscle force estimation with surface EMG during dynamic muscle contractions: a wavelet and ANN based approach.

    Science.gov (United States)

    Bai, Fengjun; Chew, Chee-Meng

    2013-01-01

    Human muscle force estimation is important in biomechanics studies, sports and assistive devices fields. Therefore, it is essential to develop an efficient algorithm to estimate force exerted by muscles. The purpose of this study is to predict force/torque exerted by muscles under dynamic muscle contractions based on continuous wavelet transform (CWT) and artificial neural networks (ANN) approaches. Mean frequency (MF) of the surface electromyography (EMG) signals power spectrum was calculated from CWT. ANN models were trained to derive the MF-force relationships from the subset of EMG signals and the measured forces. Then we use the networks to predict the individual muscle forces for different muscle groups. Fourteen healthy subjects (10 males and 4 females) were voluntarily recruited in this study. EMG signals were collected from the biceps brachii, triceps, hamstring and quadriceps femoris muscles to evaluate the proposed method. Root mean square errors (RMSE) and correlation coefficients between the predicted forces and measured actual forces were calculated.

  16. Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

    Directory of Open Access Journals (Sweden)

    M. Ern

    2009-06-01

    Full Text Available The quasi-biennial oscillation (QBO of the zonal mean zonal wind is a dynamical phenomenon of the tropical middle atmosphere. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossby-gravity, or inertia-gravity waves, as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Altitude-time cross sections are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the periods of strong westerly wind shear when the zonal wind is between −20 and 10 m/s at the equator in the altitude range 20 to 35 km. During other parts of the phases of strong westerly wind shear, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed to mesoscale gravity waves or intermediate scale waves, can be the by far

  17. Comments on Navy/NRL requirements for sea surface temperature and surface wind measurements on Seasat-A

    Science.gov (United States)

    Ruskin, R. E.; Jeck, R. K., Jr.

    1974-01-01

    SEASAT instrumentation payload requirements to provide satellite data for the Navy fleet operational fog prediction program include: (1) some form of C-band microwave radiometer capability; (2) a scanning antenna with a 40-km Instanteneous Field of View (IFOV) for the C-band channel; (3) a narrow band and high resolution IR scanning radiometer for cloud free areas; and (4) a capability for measuring surface winds of 3 to 50 m/sec at + or - 10% accuracy and 50 to 100 km spatial resolution.

  18. Why is surface tension a force parallel to the interface?

    NARCIS (Netherlands)

    Marchand, Antonin; Weijs, Joost H.; Weijs, Joost; Snoeijer, Jacobus Hendrikus; Andreotti, Bruno

    2011-01-01

    A paperclip can float on water. Drops of mercury do not spread on a surface. These capillary phenomena are macroscopic manifestations of molecular interactions and can be explained in terms of surface tension. We address several conceptual questions that are often encountered when teaching

  19. Statistical Short-Range Guidance for Peak Wind Forecasts on Kennedy Space Center/Cape Canaveral Air Force Station, Phase III

    Science.gov (United States)

    Crawford, Winifred

    2010-01-01

    This final report describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violations.The tool includes climatologies of the 5-minute mean and peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

  20. Atomic force microscopy imaging and single molecule recognition force spectroscopy of coat proteins on the surface of Bacillus subtilis spore.

    Science.gov (United States)

    Tang, Jilin; Krajcikova, Daniela; Zhu, Rong; Ebner, Andreas; Cutting, Simon; Gruber, Hermann J; Barak, Imrich; Hinterdorfer, Peter

    2007-01-01

    Coat assembly in Bacillus subtilis serves as a tractable model for the study of the self-assembly process of biological structures and has a significant potential for use in nano-biotechnological applications. In the present study, the morphology of B. subtilis spores was investigated by magnetically driven dynamic force microscopy (MAC mode atomic force microscopy) under physiological conditions. B. subtilis spores appeared as prolate structures, with a length of 0.6-3 microm and a width of about 0.5-2 microm. The spore surface was mainly covered with bump-like structures with diameters ranging from 8 to 70 nm. Besides topographical explorations, single molecule recognition force spectroscopy (SMRFS) was used to characterize the spore coat protein CotA. This protein was specifically recognized by a polyclonal antibody directed against CotA (anti-CotA), the antibody being covalently tethered to the AFM tip via a polyethylene glycol linker. The unbinding force between CotA and anti-CotA was determined as 55 +/- 2 pN. From the high-binding probability of more than 20% in force-distance cycles it is concluded that CotA locates in the outer surface of B. subtilis spores.

  1. Measuring adhesion on rough surfaces using atomic force microscopy with a liquid probe

    Directory of Open Access Journals (Sweden)

    Juan V. Escobar

    2017-04-01

    Full Text Available We present a procedure to perform and interpret pull-off force measurements during the jump-off-contact process between a liquid drop and rough surfaces using a conventional atomic force microscope. In this method, a micrometric liquid mercury drop is attached to an AFM tipless cantilever to measure the force required to pull this drop off a rough surface. We test the method with two surfaces: a square array of nanometer-sized peaks commonly used for the determination of AFM tip sharpness and a multi-scaled rough diamond surface containing sub-micrometer protrusions. Measurements are carried out in a nitrogen atmosphere to avoid water capillary interactions. We obtain information about the average force of adhesion between a single peak or protrusion and the liquid drop. This procedure could provide useful microscopic information to improve our understanding of wetting phenomena on rough surfaces.

  2. Atomic force microscopy characterization of the surface wettability of natural fibres

    Science.gov (United States)

    Pietak, Alexis; Korte, Sandra; Tan, Emelyn; Downard, Alison; Staiger, Mark P.

    2007-01-01

    Natural fibres represent a readily available source of ecologically friendly and inexpensive reinforcement in composites with degradable thermoplastics, however chemical treatments of fibres are required to prepare feasible composites. It is desirable to characterize the surface wettability of fibres after chemical treatment as the polarity of cellulose-based fibres influences compatibility with a polymer matrix. Assessment of the surface wettability of natural fibres using conventional methods presents a challenge as the surfaces are morphologically and chemically heterogeneous, rough, and can be strongly wicking. In this work it is shown that under atmospheric conditions the adhesion force between an atomic force microscopy (AFM) tip and the fibre surface can estimate the water contact angle and surface wettability of the fibre. AFM adhesion force measurements are suitable for the more difficult surfaces of natural fibres and in addition allow for correlations between microstructural features and surface wettability characteristics.

  3. Closed-Form Equations for Contact Force and Moment in Elastic Contact of Rough Surfaces

    Directory of Open Access Journals (Sweden)

    Ali Sepehri

    2011-01-01

    Full Text Available It is reasonable to expect that, when two nominally flat rough surfaces are brought into contact by an applied resultant force, they must support, in addition to the compressive load, an induced moment. The existence of a net applied moment would imply noneven distribution of contact force so that there are more asperities in contact over one region of the nominal area. In this paper, we consider the contact between two rectangular rough surfaces that provide normal and tangential contact force as well as contact moment to counteract the net moment imposed by the applied forces. The surfaces are permitted to develop slight angular misalignment, and thereby contact moment is derived. Through this scheme, it is possible to also define elastic contribution to friction since the half-plane tangential contact force on one side of an asperity is no longer balanced by the half-plane tangential force component on the opposite side. The elastic friction force, however, is shown to be of a much smaller order than the contact normal force. Approximate closed-form equations are found for contact force and moment for the contact of rough surfaces.

  4. Forces Acting on Sessile Droplet on Inclined Surfaces

    OpenAIRE

    Annapragada, S. Ravi; Murthy, Jayathi Y.; Garimella, Suresh V.

    2009-01-01

    Although many analytical, experimental and numerical studies have focused on droplet motion, the mechanics of the droplet while still in its static state, and just before motion starts, are not well understood. A study of static droplets would shed light on the threshold voltage (or critical inclination) for initiating electrically (or gravitationally) induced droplet motion. Before the droplet starts to move, the droplet shape changes such that the forces acting at the triple contact line ba...

  5. Effect of Surface Forces on the Gas Flow in Nanosize Capillaries

    Science.gov (United States)

    Roldughin, V. I.; Zhdanov, V. M.

    2005-05-01

    The flow of gas in ultrafine capillary under the action of temperature gradient is considered with allowance for the action of surface forces. It is shown that the presence of surface forces considerably increases the effect of thermal transpiration compared to the classical value determined in a free molecular regime of gas flow. The coefficient responsible for the mechanocaloric effect for the case of gas flow under the pressure gradient was also determined using Onsager relation for the kinetic coefficients calculated with accownt of the effect of surface forces.

  6. Thermal and Pressure Characterization of a Wind Tunnel Force Balance Using the Single Vector System. Experimental Design and Analysis Approach to Model Pressure and Temperature Effects in Hypersonic Wind Tunnel Research

    Science.gov (United States)

    Lynn, Keith C.; Commo, Sean A.; Johnson, Thomas H.; Parker, Peter A,

    2011-01-01

    Wind tunnel research at NASA Langley Research Center s 31-inch Mach 10 hypersonic facility utilized a 5-component force balance, which provided a pressurized flow-thru capability to the test article. The goal of the research was to determine the interaction effects between the free-stream flow and the exit flow from the reaction control system on the Mars Science Laboratory aeroshell during planetary entry. In the wind tunnel, the balance was exposed to aerodynamic forces and moments, steady-state and transient thermal gradients, and various internal balance cavity pressures. Historically, these effects on force measurement accuracy have not been fully characterized due to limitations in the calibration apparatus. A statistically designed experiment was developed to adequately characterize the behavior of the balance over the expected wind tunnel operating ranges (forces/moments, temperatures, and pressures). The experimental design was based on a Taylor-series expansion in the seven factors for the mathematical models. Model inversion was required to calculate the aerodynamic forces and moments as a function of the strain-gage readings. Details regarding transducer on-board compensation techniques, experimental design development, mathematical modeling, and wind tunnel data reduction are included in this paper.

  7. Surface-charge differentiation of streptavidin and avidin by atomic force microscopy-force spectroscopy.

    Science.gov (United States)

    Almonte, Lisa; Lopez-Elvira, Elena; Baró, Arturo M

    2014-09-15

    Chemical information can be obtained by using atomic force microscopy (AFM) and force spectroscopy (FS) with atomic or molecular resolution, even in liquid media. The aim of this paper is to demonstrate that single molecules of avidin and streptavidin anchored to a biotinylated bilayer can be differentiated by using AFM, even though AFM topographical images of the two proteins are remarkably alike. At physiological pH, the basic glycoprotein avidin is positively charged, whereas streptavidin is a neutral protein. This charge difference can be determined with AFM, which can probe electrostatic double-layer forces by using FS. The force curves, owing to the electrostatic interaction, show major differences when measured on top of each protein as well as on the lipid substrate. FS data show that the two proteins are negatively charged. Nevertheless, avidin and streptavidin can be clearly distinguished, thus demonstrating the sensitivity of AFM to detect small changes in the charge state of macromolecules. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Role of Surface Energy Exchange for Simulating Wind Turbine Inflow: A Case Study in the Southern Great Plains, USA

    Directory of Open Access Journals (Sweden)

    Sonia Wharton

    2014-12-01

    Full Text Available The Weather Research and Forecasting (WRF model is used to investigate choice of land surface model (LSM on the near surface wind profile, including heights reached by multi-megawatt (MW wind turbines. Simulations of wind profiles and surface energy fluxes were made using five LSMs of varying degrees of sophistication in dealing with soil–plant–atmosphere feedbacks for the Department of Energy (DOE Southern Great Plains (SGP Atmospheric Radiation Measurement Program (ARM Central Facility in Oklahoma, USA. Surface flux and wind profile measurements were available for validation. WRF was run for three, two-week periods covering varying canopy and meteorological conditions. The LSMs predicted a wide range of energy flux and wind shear magnitudes even during the cool autumn period when we expected less variability. Simulations of energy fluxes varied in accuracy by model sophistication, whereby LSMs with very simple or no soil–plant–atmosphere feedbacks were the least accurate; however, the most complex models did not consistently produce more accurate results. Errors in wind shear were also sensitive to LSM choice and were partially related to energy flux accuracy. The variability of LSM performance was relatively high suggesting that LSM representation of energy fluxes in WRF remains a large source of model uncertainty for simulating wind turbine inflow conditions.

  9. Effect of Difference-frequency Forces on the Dynamics of a Semi-submersible Type FVAWT in Misaligned Wave-wind Condition

    DEFF Research Database (Denmark)

    Wang, Kai; Cheng, Zhengshun; Moan, Torgeir;

    2015-01-01

    With increasing interests in the development of offshore floating vertical axis wind turbines (FVAWTs), a large amount of studies on the FVAWTs have been conducted. This paper focuses on evaluating the effect of second-order difference-frequency force on the dynamics of a 5 MW FVAWT in misaligned...... wave-wind condition. The studied FVAWT is composed of a 5 MW Darrieus rotor, a semi-submersible floater and a catenary mooring system. Fully coupled nonlinear time domain simulations were conducted using the state-of-art code Simo- Riflex-DMS. Several misaligned wave-wind conditions were selected...... to investigate the global dynamic responses of the FVAWT, such as the platform motions, structural responses and mooring line tensions. It has been found that the wave-wind misalignment does not significantly affect the mean values of the global responses since the global responses are primarily wind...

  10. Stochastic Modeling of Lift and Drag Dynamics to Obtain Aerodynamic Forces with Local Dynamics on Rotor Blade under Unsteady Wind Inflow

    Directory of Open Access Journals (Sweden)

    Muhammad Ramzan Luhur

    2014-01-01

    Full Text Available This contribution provides the development of a stochastic lift and drag model for an airfoil FX 79-W-151A under unsteady wind inflow based on wind tunnel measurements. Here we present the integration of the stochastic model into a well-known standard BEM (Blade Element Momentum model to obtain the corresponding aerodynamic forces on a rotating blade element. The stochastic model is integrated as an alternative to static tabulated data used by classical BEM. The results show that in comparison to classical BEM, the BEM with stochastic approach additionally reflects the local force dynamics and therefore provides more information on aerodynamic forces that can be used by wind turbine simulation codes

  11. Why is surface tension a force parallel to the interface?

    CERN Document Server

    Marchand, Antonin; Snoeijer, Jacco H; Andreotti, Bruno

    2012-01-01

    A paperclip can float on water. Drops of mercury refuse to spread on a surface. These capillary phenomena are macroscopic manifestations of molecular interactions, and can be explained in terms of surface tension. For students, the concept of surface tension is quite challenging since the microscopic intuition is often in conflict with the common macroscopic interpretations. In this paper we address a number of conceptual questions that are often encountered when teaching capillarity. By answering these questions we provide a perspective that reconciles the macroscopic viewpoints, from thermodynamics or fluid mechanics, and the microscopic perspective from statistical physics.

  12. The Role of Surface Energy Exchange for Simulating Wind Inflow: An Evaluation of Multiple Land Surface Models in WRF for the Southern Great Plains Site Field Campaign Report

    Energy Technology Data Exchange (ETDEWEB)

    Wharton, Sonia [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Simpson, Matthew [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Osuna, Jessica [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Newman, Jennifer [National Renewable Energy Lab. (NREL), Golden, CO (United States); Biraud, Sebastien [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2016-05-01

    The Weather Research and Forecasting (WRF) model is used to investigate choice of land surface model (LSM) on the near-surface wind profile, including heights reached by multi-megawatt wind turbines. Simulations of wind profiles and surface energy fluxes were made using five LSMs of varying degrees of sophistication in dealing with soil-plant-atmosphere feedbacks for the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Southern Great Plains (SGP) Central Facility in Oklahoma. Surface-flux and wind-profile measurements were available for validation. The WRF model was run for three two-week periods during which varying canopy and meteorological conditions existed. The LSMs predicted a wide range of energy-flux and wind-shear magnitudes even during the cool autumn period when we expected less variability. Simulations of energy fluxes varied in accuracy by model sophistication, whereby LSMs with very simple or no soil-plant-atmosphere feedbacks were the least accurate; however, the most complex models did not consistently produce more accurate results. Errors in wind shear also were sensitive to LSM choice and were partially related to the accuracy of energy flux data. The variability of LSM performance was relatively high, suggesting that LSM representation of energy fluxes in the WRF model remains a significant source of uncertainty for simulating wind turbine inflow conditions.

  13. Importance of Second-Order Difference-Frequency Wave-Diffraction Forces in the Validation of a Fast Semi-Submersible Floating Wind Turbine Model: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Couling, A. J.; Goupee, A. J.; Robertson, A. N.; Jonkman, J. M.

    2013-06-01

    To better access the abundant offshore wind resource, efforts across the world are being undertaken to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools that can be relied upon in the design process. The National Renewable Energy Laboratory (NREL) has created a comprehensive, coupled analysis CAE tool for floating wind turbines, FAST, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are currently underway that leverage the extensive 1/50th-scale DeepCwind wind/wave basin model test dataset, obtained at the Maritime Research Institute Netherlands (MARIN) in 2011, to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. In this paper, further work is undertaken to continue this validation. In particular, the ability of FAST to replicate global response behaviors associated with dynamic wind forces, second-order difference-frequency wave-diffraction forces and their interaction with one another are investigated.

  14. Initial bioadhesion on surfaces in the oral cavity investigated by scanning force microscopy

    Science.gov (United States)

    Schwender, N.; Huber, K.; Marrawi, F. Al; Hannig, M.; Ziegler, Ch.

    2005-09-01

    Scanning force microscopy (SFM) was used to measure the adhesion forces between BSA, a saliva protein, and two dental surfaces, natural enamel and a filling material (Dyract AP™). Measurements were taken in phosphate buffered aqueous solutions (PBS). Forces were resolved down to the piconewton regime. The dependency of the adhesion force on the interaction time, pH-value and substrate surface was monitored. In a further step, surface samples were fixed on an enamel brace and carried for a defined time in the oral cavity. The formed biofilm, called pellicle, shows a different morphology on the different substrates. This can be explained by the above-mentioned substrate dependence of the adhesion force.

  15. Final Environmental Assessment: F. E. Warren Air Force Base Wind Farm Project Cheyenne, Wyoming

    Science.gov (United States)

    2004-04-14

    those in a library ( Tipler 1991). The nearest residential developments are located 5,000 feet from the Proposed Action and 4,300 feet from the...and molt patterns of red bats. Bulletin of the Chicago Academy of Sciences 14: 1−7. Tipler , P.A. 1991. Physics for Scientists and Engineers...3rd Edition. Published by P.A. Tipler , 1,167 pp. Usgaard, R.E., D.E. Naugle, R.G. Osborn, and K.F. Higgins. 1997. Effects of wind turbines on

  16. An Evaluation of Wind Turbine Technology at Peterson Air Force Base

    Science.gov (United States)

    2005-03-01

    the Savonius model, which originated in Finland in the 1920’s, is an S-shaped blade, which rotates and turns a vertical shaft. The benefit of the... Savonius turbine is that it has a high starting torque and thus needs no starting motor and can operate in low winds (Johnson, 1985:16). On the...down side, the Savonius turbine operates at a slow rotational speed which is not as good for generating electricity but is better for grinding grain or

  17. An Anisotropic Ocean Surface Emissivity Model Based on WindSat Polarimetric Brightness Observations

    Science.gov (United States)

    Smith, D. F.; Gasiewski, A. J.; Sandeep, S.; Weber, B. L.

    2012-12-01

    The goal of this research has been to develop a standardized fast full-Stokes ocean surface emissivity model with Jacobian for a wind-driven ocean surface applicable at arbitrary microwave frequencies, polarizations, and incidence angles. The model is based on the Ohio State University (OSU) two-scale code for surface emission developed by Johnson (2006, IEEE TGRS, 44, 560) but modified as follows: (1) the Meissner-Wentz dielectric permittivity (2012, IEEE TGRS, 50, 3004) replaces the original permittivity, (2) the Elfouhaily sea surface spectrum (1997, JGR, 102, C7,15781) replaces the Durden-Vesecky spectrum (1985, IEEE TGRS, OE-10, 445), but the Durden-Vesecky angular spreading function is retained, (3) the high-frequency portion of the Elfouhaily spectrum is multiplied by the Pierson-Moskowitz shape spectrum to correct an error in the original paper, (4) the generalized Phillips-Kitaigorodskii equilibrium range parameter for short waves is modeled as a continuous function of the friction velocity at the water surface to eliminate a discontinuous jump in the original paper. A total of five physical tuning parameters were identified, including the spectral strength and the hydrodynamic modulation factor. The short wave part of the spectrum is also allowed to have an arbitrary ratio relative to the long wave part. The foam fraction is multiplied by a variable correction factor, and also modulated to allow an anisotropic foam fraction with more foam on the leeward side of a wave. The model is being tuned against multi-year sequences of WindSat and Special Sensor Microwave/Imager (SSMI) data as analyzed by Meissner and Wentz (2012, IEEE TGRS, 50, 3004) for up to four Stokes brightnesses and in all angular harmonics up to two in twenty five wind bins from 0.5-25.5 m/s and of 1 m/s width. As a result there are 40 brightnesses per wind bin, for a total of 1000 brightnesses used to constrain the modified model. A chi-squared tuning criterion based on error standard

  18. Response of Mercury's Magnetosphere to Solar Wind Forcing: Results of Global MHD Simulations with Coupled Planetary Interior

    Science.gov (United States)

    Jia, Xianzhe; Slavin, James; Poh, Gangkai; Toth, Gabor; Gombosi, Tamas

    2016-04-01

    are spatially non-uniform in nature, and consequently they result in an induced magnetic field at the core that contains significant power in not only the dipole but also high order moments. Based on the simulation results, we determine how the induced magnetic field varies with the external solar wind conditions, and provide quantitative constraints on the ability of Mercury's core to shield the planetary surface from direct solar wind impact.

  19. Tracking Traction Force Changes of Single Cells on the Liquid Crystal Surface

    OpenAIRE

    Chin Fhong Soon; Kian Sek Tee; Mansour Youseffi; Denyer, Morgan C. T.

    2015-01-01

    Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT) system can be used in conjunction with a bespoke cell traction force mapping (CTFM) software to monitor cell/surface traction forces from quiescent state in real time. In this study, time-lapse photo microscopy allowed cell induced deformations in liquid crystal coated substrates to be monitored and analyzed. The results indicated th...

  20. The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

    Indian Academy of Sciences (India)

    M N Patil; R T Waghmare; T Dharmaraj; G R Chinthalu; Devendraa Siingh; G S Meena

    2016-10-01

    Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurementsof wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16◦44'N, 77◦59'E) in the south-west monsoon season. Using these observations, an attempt was made to investigatethe behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds greater than 4 m s−1; under stable regime for wind speeds less than 2 m s−1 and under neutral regime for wind speeds in the range of 2–3 m s$^{−1}$. All the three stability regimes were mixed for wind speeds 3–4 m s$^{−1}$. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.

  1. Spatio-temporal variability in sea surface wind stress near and off the east coast of Korea

    Institute of Scientific and Technical Information of China (English)

    NAM SungHyun; KIM Young Ho; PARK Kyung-Ae; KIM Kuh

    2005-01-01

    Sea surface wind stress variabilities near and off the east coast of Korea, are examined using 7 kinds of wind datasets from measurements at 2 coastal (land) stations and 2 ocean buoys,satellite scatterometer (QuikSCAT), and global reanalyzed products (ECMWF,NOGAPS,and NCEP/NCAR). Temporal variabilities are analyzed at 3 frequency bands; synoptic (2~20 d), intra-seasonal (20~90 d),and seasonal (>90 d).Synoptic and intra-seasonal variations are predominant near and off the Donghae City due to the passage of the mesoscale weather system. Seasonal variation is caused by southeastward wind stress during Asian winter monsoon. The sea surface wind stress from reanalyzed datasets,QuikSCAT and KMA-B measurements off the coast show good agreement in the magnitude and direction,which are strongly aligned with the alongshore direction. At the land-based sites,wind stresses are much weaker by factors of 3~10 due to the mountainous landmass on the east parts of Korea Peninsula. The first EOF modes(67 % ~70%) of wind stresses from reanalyzed and QuikSCAT data have similar structures of the strong southeastward wind stress in winter along the coast but show different curl structures at scales less than 200 kn due to the orographic effects. The second EOF modes (23 % ~25%)show southwestward wind stress in every September along the east coast of the North Korea

  2. The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

    Science.gov (United States)

    Patil, M. N.; Waghmare, R. T.; Dharmaraj, T.; Chinthalu, G. R.; Siingh, Devendraa; Meena, G. S.

    2016-09-01

    Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16∘44'N, 77∘59'E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin-Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s-1; under stable regime for wind speeds <2 m s-1 and under neutral regime for wind speeds in the range of 2-3 m s-1. All the three stability regimes were mixed for wind speeds 3-4 m s-1. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.

  3. Wind Structure and Wind Loading

    DEFF Research Database (Denmark)

    Brorsen, Michael

    The purpose of this note is to provide a short description of wind, i.e. of the flow in the atmosphere of the Earth and the loading caused by wind on structures. The description comprises: causes to the generation of windhe interaction between wind and the surface of the Earthhe stochastic nature...... of windhe interaction between wind and structures, where it is shown that wind loading depends strongly on this interaction...

  4. Determination of aerodynamic damping and force coefficients of filleted twin cables in dry conditions through passive-dynamic wind tunnel tests

    DEFF Research Database (Denmark)

    Mattiello, E.; Eriksen, M. B.; Georgakis, Christos T.

    Moderate amplitude vibrations continue to be reported on the Øresund Bridge cables, although fitted with fillets and dampers. To further investigate the aerodynamics of the bridge’s twin-cable arrangement, 1:2.3 scale passive-dynamic wind tunnel tests of the cables were performed at the DTU....../FORCE Technology Climatic Wind Tunnel facility. The measured aerodynamic damping of the twin-cable arrangement in dry conditions was compared to the values obtained from full-scale monitoring and from an analytical model using static force coefficients. The comparison revealed broad agreement in the investigated...

  5. Determination of aerodynamic damping and force coefficients of filleted twin cables in dry conditions through passive-dynamic wind tunnel tests

    DEFF Research Database (Denmark)

    Mattiello, E.; Eriksen, M. B.; Georgakis, Christos T.

    /FORCE Technology Climatic Wind Tunnel facility. The measured aerodynamic damping of the twin-cable arrangement in dry conditions was compared to the values obtained from full-scale monitoring and from an analytical model using static force coefficients. The comparison revealed broad agreement in the investigated......Moderate amplitude vibrations continue to be reported on the Øresund Bridge cables, although fitted with fillets and dampers. To further investigate the aerodynamics of the bridge’s twin-cable arrangement, 1:2.3 scale passive-dynamic wind tunnel tests of the cables were performed at the DTU...

  6. Force

    CERN Document Server

    Graybill, George

    2007-01-01

    Forces are at work all around us. Discover what a force is, and different kinds of forces that work on contact and at a distance. We use simple language and vocabulary to make this invisible world easy for students to ""see"" and understand. Examine how forces ""add up"" to create the total force on an object, and reinforce concepts and extend learning with sample problems.

  7. The Wind, Temperature, and Surface Pressure on Pluto from a Pluto General Circulation Model

    Science.gov (United States)

    Zalucha, A. M.; Gulbis, A.

    2011-12-01

    A variety of methods have been used to derive Pluto's atmospheric temperature, composition, and surface pressure from spectra and stellar occultation data, while wind is less easily determined. Gravity wave dissipation has been investigated [1] in the 18 March 2007 stellar occultation dataset [2], demonstrating that wind is occurring in the form of perturbations about a mean. Rossby waves have also been proposed [2] as an explanation to the 2007 dataset; however the method was used incorrectly. General circulation models (GCMs) are a ubiquitous tool in the field of planetary atmospheres to solve for the global state of the atmosphere in a physically consistent manner, but only recently have they began to be developed for Pluto. We use a Pluto version of the Massachusetts Institute of Technology (MIT) GCM to solve for the first time for wind, temperature, and surface pressure globally in Pluto's atmosphere. The Pluto version of the MIT GCM (PGCM) uses the MIT GCM dynamical core [3] with a radiative-conductive model [4]. It includes vertical thermal conduction and non-local thermodynamic equilibrium heating and cooling by methane at 3.3 um and 7.6 um, respectively. We perform a parameter sweep with methane volume mixing ratios of 0.2, 0.6, and 1% and initial global mean surface pressures of 6-26 ubar. We ran the model from rest starting in the model year 1973. We compared the PGCM results with occultation data from the years 1988, 2002, 2006, and 2007. Model light curves were calculated from the PGCM temperature output (averaged at 90 day intervals) at the corresponding date and Pluto latitudes of each occultation. The match between data and PGCM is better than between data and the radiative-conductive equilibrium solution (i.e. no wind), but the PGCM light curves contain wave-like features while the data do not. We do not believe that this feature represents an atmospheric wave; rather, it is numerical noise known to occur in 2D GCMs. The PGCM-predicted zonal

  8. Dynamic Image Forces Near a Metal Surface and the Point-Charge Motion

    Science.gov (United States)

    Gabovich, A. M.; Voitenko, A. I.

    2012-01-01

    The problem of charge motion governed by image force attraction near a plane metal surface is considered and solved self-consistently. The temporal dispersion of metal dielectric permittivity makes the image forces dynamic and, hence, finite, contrary to the results of the conventional approach. Therefore, the maximal attainable velocity turns out…

  9. Statistical Analysis of Long- and Short-Range Forces Involved in Bacterial Adhesion to Substratum Surfaces as Measured Using Atomic Force Microscopy

    NARCIS (Netherlands)

    Chen, Yun; Busscher, Henk J.; van der Mei, Henny C.; Norde, Willem

    Surface thermodynamic analyses of microbial adhesion using measured contact angles on solid substrata and microbial cell surfaces are widely employed to determine the nature of the adhesion forces, i.e., the interplay between Lifshitz-van der Waals and acid-base forces. While surface thermodynamic

  10. Surface roughness and cutting force estimation in the CNC turning using artificial neural networks

    Directory of Open Access Journals (Sweden)

    Mohammad Ramezani

    2015-04-01

    Full Text Available Surface roughness and cutting forces are considered as important factors to determine machinability rate and the quality of product. A number of factors like cutting speed, feed rate, depth of cutting and tool noise radius influence the surface roughness and cutting forces in turning process. In this paper, an Artificial Neural Network (ANN model was used to forecast surface roughness and cutting forces with related inputs, including cutting speed, feed rate, depth of cut and tool noise radius. The machined surface roughness and cutting force parameters related to input parameters are the outputs of the ANN model. In this work, 24 samples of experimental data were used to train the network. Moreover, eight other experimental tests were implemented to test the network. The study concludes that ANN was a reliable and accurate method for predicting machining parameters in CNC turning operation.

  11. Impact of upper-level jet-generated inertia-gravity waves on surface wind and precipitation

    Directory of Open Access Journals (Sweden)

    C. Zülicke

    2007-11-01

    Full Text Available A meteorological case study for the impact of inertia-gravity waves on surface meteorology is presented. The large-scale environment from 17 to 19 December 1999 was dominated by a poleward breaking Rossby wave transporting subtropical air over the North Atlantic Ocean upward and north-eastward. The synoptic situation was characterized with an upper tropospheric jet streak passing Northern Europe. The unbalanced jet spontaneously radiated inertia-gravity waves from its exit region. Near-inertial waves appeared with a horizontal wavelength of about 200 km and an apparent period of about 12 h. These waves transported energy downwards and interacted with large-scale convection.

    This configuration is simulated with the nonhydrostatic Fifth-Generation Mesoscale Model. Together with simplified runs without orography and moisture it is demonstrated that the imbalance of the jet (detected with the cross-stream ageostrophic wind and the deep convection (quantified with the latent heat release are forcing inertia-gravity waves. This interaction is especially pronounced when the upper tropospheric jet is located above a cold front at the surface and supports deep frontal convection. Weak indication was found for triggering post-frontal convection by inertia-gravity waves.

    The realism of model simulations was studied in an extended validation study for the Baltic Sea region. It included observations from radar (DWDPI, BALTRAD, satellite (GFZGPS, weather stations (DWDMI and assimilated products (ELDAS, MESAN. The detected spatio-temporal patterns show wind pulsations and precipitation events at scales corresponding to those of inertia-gravity waves. In particular, the robust features of strong wind and enhanced precipitation near the front appeared with nearly the same amplitudes as in the model. In some datasets we found indication for periodic variations in the post-frontal region.

    These findings demonstrate the impact of upper

  12. Interannual increase of regional haze-fog in North China Plain in summer by intensified easterly winds and orographic forcing

    Science.gov (United States)

    Cao, Ziqi; Sheng, Lifang; Liu, Qian; Yao, Xiaohong; Wang, Wencai

    2015-12-01

    Regional haze-fog events over the North China Plain (NCP) have attracted much attention in recent years. Their increase has been attributed to anthropogenic emissions of air pollutants and synoptic weather conditions. We investigated the influence of local meteorological conditions and large-scale circulation on the haze-fog events over the NCP during 2001-2012, and found a significant interannual increase in the number of summer regional haze-fog days. Analysis indicated that local meteorological conditions could partly explain the increase but failed to explain the spatial variation; meanwhile, regional circulation change induced by large-scale circulation and orographic forcing unveiled a possible spatiotemporal variation mechanism. In summer, the prevalent southerly winds over the NCP were obstructed by the Taihang and Yanshan mountains, steadying the outflow direction to the southeast, while different inflow direction controlled by large-scale circulation had different effects on regional circulation. In weak (strong) East Asian summer monsoon years, an intensified eastward (westward) zonal inflow wind component reinforced (weakened) the negative vorticity and formed an anomalous anticyclone (cyclone), which strengthened (weakened) the downward motion, so the dissipation capability was weakened (strengthened) and the wind speed decreased (increased), ultimately resulting in the increased (decreased) occurrence of haze-fog. We also found that the circulation anomaly had a good relationship with strong El Niño and La Niña events. There was more haze-fog over the NCP in the summers that followed a La Niña event, and less in summers that followed an El Niño event. This suggested the possibility that summer haze-fog phenomena could be predicted based on the phase of ENSO.

  13. Satellite Observations of Wind Farm Impacts on Nocturnal Land Surface Temperature in Iowa

    Directory of Open Access Journals (Sweden)

    Ronald A. Harris

    2014-12-01

    Full Text Available Wind farms (WFs are believed to have an impact on lower boundary layer meteorology. A recent study examined satellite-measured land surface temperature data (LST and found a local nighttime warming effect attributable to a group of four large WFs in Texas. This study furthers their work by investigating the impacts of five individual WFs in Iowa, where the land surface properties and climate conditions are different from those in Texas. Two methods are used to assess WF impacts: first, compare the spatial coupling between the LST changes (after turbine construction versus before and the geographic layouts of the WFs; second, quantify the LST difference between the WFs and their immediate surroundings (non-WF areas. Each WF shows an irrefutable nighttime warming signal relative to the surrounding areas after their turbines were installed, and these warming signals are generally coupled with the geographic layouts of the wind turbines, especially in summer. This study provides further observational evidence that WFs can cause surface warming at nighttime, and that such a signal can be detected by satellite-based sensors.

  14. Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Ingo [Research Institute for Global Change, JAMSTEC, Yokohama (Japan); University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Xie, Shang-Ping [University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); University of Hawaii at Manoa, Department of Meteorology, Honolulu, HI (United States); Wittenberg, Andrew T. [NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ (United States); Masumoto, Yukio [Research Institute for Global Change, JAMSTEC, Yokohama (Japan)

    2012-03-15

    Most coupled general circulation models (GCMs) perform poorly in the tropical Atlantic in terms of climatological seasonal cycle and interannual variability. The reasons for this poor performance are investigated in a suite of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled GCM. The experiments show that a significant portion of the equatorial SST biases in the model is due to weaker than observed equatorial easterlies during boreal spring. Due to these weak easterlies, the tilt of the equatorial thermocline is reduced, with shoaling in the west and deepening in the east. The erroneously deep thermocline in the east prevents cold tongue formation in the following season despite vigorous upwelling, thus inhibiting the Bjerknes feedback. It is further shown that the surface wind errors are due, in part, to deficient precipitation over equatorial South America and excessive precipitation over equatorial Africa, which already exist in the uncoupled atmospheric GCM. Additional tests indicate that the precipitation biases are highly sensitive to land surface conditions such as albedo and soil moisture. This suggests that improving the representation of land surface processes in GCMs offers a way of improving their performance in the tropical Atlantic. The weaker than observed equatorial easterlies also contribute remotely, via equatorial and coastal Kelvin waves, to the severe warm SST biases along the southwest African coast. However, the strength of the subtropical anticyclone and along-shore winds also play an important role. (orig.)

  15. The effect of interplanetary magnetic field orientation on the solar wind flux impacting Mercury's surface

    CERN Document Server

    Varela, J; Moncuquet, M

    2016-01-01

    The aim of this paper is to study the plasma flows on the Mercury surface for different interplanetary magnetic field orientations on the day side of the planet. We use a single fluid MHD model in spherical coordinates to simulate the interaction of the solar wind with the Hermean magnetosphere for six solar wind realistic configurations with different magnetic field orientations: Mercury-Sun, Sun-Mercury, aligned with the magnetic axis of Mercury (Northward and Southward) and with the orbital plane perpendicular to the previous cases. In the Mercury-Sun (Sun-Mercury) simulation the Hermean magnetic field is weakened in the South-East (North-East) of the magnetosphere leading to an enhancement of the flows on the South (North) hemisphere. For a Northward (Southward) orientation there is an enhancement (weakening) of the Hermean magnetic field in the nose of the bow shock so the fluxes are reduced and drifted to the poles (enhanced and drifted to the equator). If the solar wind magnetic field is in the orbital...

  16. Dependence of Lunar Surface Charging on Solar Wind Plasma Conditions and Solar Irradiation

    Science.gov (United States)

    Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.; Burchill, J. K.; Collier, M. R.; Zimmerman, M. I.; Vondrak, R. R.; Delory, G. T.; Pfaff, R. F.

    2014-01-01

    The surface of the Moon is electrically charged by exposure to solar radiation on its dayside, as well as by the continuous flux of charged particles from the various plasma environments that surround it. An electric potential develops between the lunar surface and ambient plasma, which manifests itself in a near-surface plasma sheath with a scale height of order the Debye length. This study investigates surface charging on the lunar dayside and near-terminator regions in the solar wind, for which the dominant current sources are usually from the pohotoemission of electrons, J(sub p), and the collection of plasma electrons J(sub e) and ions J(sub i). These currents are dependent on the following six parameters: plasma concentration n(sub 0), electron temperature T(sub e), ion temperature T(sub i), bulk flow velocity V, photoemission current at normal incidence J(sub P0), and photo electron temperature T(sub p). Using a numerical model, derived from a set of eleven basic assumptions, the influence of these six parameters on surface charging - characterized by the equilibrium surface potential, Debye length, and surface electric field - is investigated as a function of solar zenith angle. Overall, T(sub e) is the most important parameter, especially near the terminator, while J(sub P0) and T(sub p) dominate over most of the dayside.

  17. Hall-magnetohydrodynamic surface waves in solar wind flow-structures

    Science.gov (United States)

    Miteva, Rossitsa; Zhelyazkov, Ivan; Erdélyi, Robert

    2004-02-01

    This paper investigates the parallel propagation of agnetohydrodynamic (MHD) surface waves travelling along an ideal steady plasma slab surrounded by a steady plasma environment in the framework of Hall magnetohydrodynamics. The magnitudes of the ambient magnetic field, plasma density and flow velocity inside and outside the slab are different. Two possible directions of the relative flow velocity (in a frame of reference co-moving with the ambient flow) have been studied. In contrast to the conventional MHD surface waves which are usually assumed to be pure surface or pseudo-surface waves, the Hall-MHD approach makes it necessary to treat the normal MHD slab's modes as generalized surface waves. The latter have to be considered as a superposition of two partial waves, one of which is a pure/pseudo-surface-wave whereas the other constitutive wave is a leaky one. From the two kinds of surface-wave modes that can propagate, notably sausage and kink ones, the dispersion behaviour of the kink mode turns out to be more complicated than that of the sausage mode. In general, the flow increases the waves' phase velocities comparing with their magnitudes in a static Hall-MHD plasma slab. The applicability of the results to real solar wind flow-structures is briefly discussed. EHPRG Award Lecture.

  18. Two dimensional unsteady aerodynamic force measurement by combination of complex model information under wind action; Sofuji no shindo modo joho wo riyoshita hiteijo kukiryoku suiteiho no kaihatsu

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, H.; Miyata, T. [Yokohama National Univ. (Japan). Faculty of Engineering; Nakajima, S. [Yokohama National Univ., Yokohama (Japan). Graduate School

    1996-04-21

    In wind resistance design of long span bridge, as the vibration found in long span bridges is very complicated, the estimation with high precision of the unsteady aerodynamic force acting on structures in complicated motion becomes more and more important. In this paper, as a problem to directly identify the parameter by using the observation hysteresis response obtained from wind tunnel test, the problems existing in combining the system identification into unsteady aerodynamic force estimation were indicated. Then, newly developed flexible method in extension relating to two dimensional aerodynamic force measurement concerning composite flutter was proposed. Using the wind tunnel test response observation data obtained from two dimensional rigid model, and from the estimated results of unsteady aerodynamic force, it is possible to obtain stable results in the relationship among the plural eigenvalues displaying identified vibration frequency and attenuation rate with the reduced wind velocity. As a new unsteady aerodynamic force measuring method, the method proposed by this study is considered to be very useful. 6 refs., 5 figs., 1 tab.

  19. Sliding mode control of wind-induced vibrations using fuzzy sliding surface and gain adaptation

    Science.gov (United States)

    Thenozhi, Suresh; Yu, Wen

    2016-04-01

    Although fuzzy/adaptive sliding mode control can reduce the chattering problem in structural vibration control applications, they require the equivalent control and the upper bounds of the system uncertainties. In this paper, we used fuzzy logic to approximate the standard sliding surface and designed a dead-zone adaptive law for tuning the switching gain of the sliding mode control. The stability of the proposed controller is established using Lyapunov stability theory. A six-storey building prototype equipped with an active mass damper has been used to demonstrate the effectiveness of the proposed controller towards the wind-induced vibrations.

  20. Thermal sensing of cryogenic wind tunnel model surfaces Evaluation of silicon diodes

    Science.gov (United States)

    Daryabeigi, K.; Ash, R. L.; Dillon-Townes, L. A.

    1986-01-01

    Different sensors and installation techniques for surface temperature measurement of cryogenic wind tunnel models were investigated. Silicon diodes were selected for further consideration because of their good inherent accuracy. Their average absolute temperature deviation in comparison tests with standard platinum resistance thermometers was found to be 0.2 K in the range from 125 to 273 K. Subsurface temperature measurement was selected as the installation technique in order to minimize aerodynamic interference. Temperature distortion caused by an embedded silicon diode was studied numerically.