Waves, circulation and vertical dependence
Mellor, George
2013-04-01
Longuet-Higgins and Stewart (J Fluid Mech 13:481-504, 1962; Deep-Sea Res 11:529-562, 1964) and later Phillips (1977) introduced the problem of waves incident on a beach, from deep to shallow water. From the wave energy equation and the vertically integrated continuity equation, they inferred velocities to be Stokes drift plus a return current so that the vertical integral of the combined velocities was nil. As a consequence, it can be shown that velocities of the order of Stokes drift rendered the advective term in the momentum equation negligible resulting in a simple balance between the horizontal gradients of the vertically integrated elevation and wave radiation stress terms; the latter was first derived by Longuet-Higgins and Stewart. Mellor (J Phys Oceanogr 33:1978-1989, 2003a), noting that vertically integrated continuity and momentum equations were not able to deal with three-dimensional numerical or analytical ocean models, derived a vertically dependent theory of wave-circulation interaction. It has since been partially revised and the revisions are reviewed here. The theory is comprised of the conventional, three-dimensional, continuity and momentum equations plus a vertically distributed, wave radiation stress term. When applied to the problem of waves incident on a beach with essentially zero turbulence momentum mixing, velocities are very large and the simple balance between elevation and radiation stress gradients no longer prevails. However, when turbulence mixing is reinstated, the vertically dependent radiation stresses produce vertical velocity gradients which then produce turbulent mixing; as a consequence, velocities are reduced, but are still larger by an order of magnitude compared to Stokes drift. Nevertheless, the velocity reduction is sufficient so that elevation set-down obtained from a balance between elevation gradient and radiation stress gradients is nearly coincident with that obtained by the aforementioned papers. This paper
Wave Forces on a Vertical Smooth Cylinder in Directional Waves
DEFF Research Database (Denmark)
Høgedal, M.; Skourup, J.; Burcharth, H. F.
1994-01-01
In this paper the results from physical experiments with an instrumented cylinder conducted in laboratory environments are presented. The primary aim of the study has been to investigate the effect from wave directionality on the local and depth integrated maximum wave forces on a smooth vertical...
Parametric analysis of change in wave number of surface waves
Directory of Open Access Journals (Sweden)
Tadić Ljiljana
2015-01-01
Full Text Available The paper analyzes the dependence of the change wave number of materials soil constants, ie the frequency of the waves. The starting point in this analysis cosists of wave equation and dynamic stiffness matrix of soil.
Hostetler, Chris Alan
Gravity wave models for the horizontal wave number spectra of atmospheric velocity and density fluctuations are derived by assuming that both saturated and unsaturated waves obey the polarization and dispersion relations and that the joint (m,w) spectrum is separable. The models show that the joint (k,l,m) and (k,l,w) spectra are not separable. The one-dimensional horizontal wave number spectra models are consistent with existing observations of horizontal wave number spectra in the lower stratosphere and upper mesosphere. The gravity wave models are used to analyze the effects of Doppler shifting caused by the mean wind field on the separability of gravity wave spectra. If the intrinsic joint (m,w) spectrum is separable, Doppler effects associated with even small mean winds will destroy separability of the observed joint (m,w(sub o)) spectrum, particularly at high vertical wave numbers. Vertical and horizontal wave number spectra of density perturbations in the upper stratosphere (25-40 km) and the upper mesosphere (approximately 80-105 km) measured during the ALOHA-90 campaign are presented. The spectra were inferred from approximately 45 h of airborne Na/Rayleigh lidar observations in the vicinity of Hawaii. Density variances, vertical shear variances, Richardson's numbers, characteristic vertical and horizontal wave numbers, and power law slopes of the vertical and horizontal wave number spectra are computed and discussed. The observed m-spectra contradict the predictions of the linear instability theory of Dewan and Good, and the scale-dependent diffusive filtering theory of Gardner, and appear to be compatible with the Doppler spreading theory of Hines, the scale-dependent diffusion theory of Weinstock, the scale-independent diffusive filtering theory of Gardner, and the similitude model of Dewan. In the stratosphere, the m-spectra exhibit significant energy at low wave numbers less than the values expected for m(sub *). The source of this energy is believed
Selective excitation of tropical atmospheric waves in wave-CISK: The effect of vertical wind shear
Zhang, Minghua; Geller, Marvin A.
1994-01-01
The growth of waves and the generation of potential energy in wave-CISK require unstable waves to tilt with height oppositely to their direction of propagation. This makes the structures and instability properties of these waves very sensitive to the presence of vertical shear in the basic flow. Equatorial Kelvin and Rossby-gravity waves have opposite phase tilt with height to what they have in the stratosphere, and their growth is selectively favored by basic flows with westward vertical shear and eastward vertical shear, respectively. Similar calculations are also made for gravity waves and Rossby waves. It is shown that eastward vertical shear of the basic flow promotes CISK for westward propagating Rossby-gravity, Rossby, and gravity waves and suppresses CISK for eastward propagating Kelvin and gravity waves, while westward shear of the basic flow has the reverse effects.
Vertical Wave Impacts on Offshore Wind Turbine Inspection Platforms
DEFF Research Database (Denmark)
Bredmose, Henrik; Jacobsen, Niels Gjøl
2011-01-01
. The dependence of the vertical platform load to the platform level is discussed. Attention is given to the significant downward force that occur after the upward force associated with the vertical impact. The effect of the numerical resolution on the results is assessed. The position of wave overturning is found...
Vertical propagation of baroclinic Kelvin waves along the west coast ...
Indian Academy of Sciences (India)
A linear, continuously stratified ocean model is used to investigate vertical propagation of remotely forced, baroclinic Kelvin waves along the Indian west coast. The extent of vertical propagation over the length of the coast is found to be an increasing function of the forcing frequency. Simulations show that, over the length of ...
Vertical elliptic operator for efficient wave propagation in TTI media
Waheed, Umair bin
2015-08-19
Elliptic wave extrapolation operators require significantly less computational cost than the ones for transversely isotropic (TI) media. However, it does not provide accurate wavefield representation or imaging for the prevalent TI media. We propose a new vertical elliptically anisotropic (VEA) wave equation by decomposing the acoustic TI pseudo-differential wave equation. The decomposition results in a vertical elliptic differential equation and a scalar operator. The new VEA-like wave equation shares the same dispersion relation as that of the original acoustic TI wave equation. Therefore, the kinematic contents are correctly matched to the original equation. Moreover, the proposed decomposition yields better amplitude properties than the isotropic decomposition without increasing the computational load. Therefore, it exhibits better cost versus accuracy tradeoff compared to the isotropic or the tilted elliptic decompositions. We demonstrate with numerical examples that the proposed methodology is numerically stable for complex models and is free from shear-wave artifacts.
Vertical Transport of Momentum by the Inertial-Gravity Internal Waves in a Baroclinic Current
Directory of Open Access Journals (Sweden)
A. A. Slepyshev
2017-08-01
Full Text Available When the internal waves break, they are one of the sources of small-scale turbulence. Small-scale turbulence causes the vertical exchange in the ocean. However, internal waves with regard to the Earth rotation in the presence of vertically inhomogeneous two-dimensional current are able to contribute to the vertical transport. Free inertial-gravity internal waves in a baroclinic current in a boundless basin of a constant depth are considered in the Bussinesq approximation. Boundary value problem of linear approximation for the vertical velocity amplitude of internal waves has complex coefficients when current velocity component, which is transversal to the wave propagation direction, depends on the vertical coordinate (taking into account the rotation of the Earth. Eigenfunction and wave frequency are complex, and it is shown that a weak wave damping takes place. Dispersive relation and wave damping decrement are calculated in the linear approximation. At a fixed wave number damping decrement of the second mode is larger (in the absolute value than the one of the first mode. The equation for vertical velocity amplitude for real profiles of the Brunt – Vaisala frequency and current velocity are numerically solved according to implicit Adams scheme of the third order of accuracy. The dispersive curves of the first two modes do not reach inertial frequency in the low-frequency area due to the effect of critical layers in which wave frequency of the Doppler shift is equal to the inertial one. Termination of the second mode dispersive curves takes place at higher frequency than the one of the first mode. In the second order of the wave amplitude the Stokes drift speed is determined. It is shown that the Stokes drift speed, which is transversal to the wave propagation direction, differs from zero if the transversal component of current velocity depends on the vertical coordinate. In this case, the Stokes drift speed in the second mode is lower than
Characteristic wave diversity in Near Vertical Incidence Skywave propagation
Witvliet, Ben A.; van Maanen, Erik; Petersen, George J.; Westenberg, Albert J.; Bentum, Marinus Jan; Slump, Cornelis H.; Schiphorst, Roelof
2015-01-01
In Near Vertical Incidence Skywave (NVIS) propagation, effective diversity reception can be realized using a dual channel receiver and a dual polarization antenna with polarization matched to the (left hand and right hand) circular polarization of the characteristic waves propagating in the
Breaking Wave Impact Pressure on a Vertical Wall
Directory of Open Access Journals (Sweden)
C. Rajasekaran
2010-09-01
Full Text Available Offshore and coastal structures experience wave impact loads particularly due to breaking waves throughout its design period. In the present paper, an experimental program has been devised to improve our perceptive of the physics and the characteristics of impact pressures due to breaking waves on a vertical wall. The salient features of the study such as model details, breaking wave simulation, the impact and dynamic pressure variation along the depth of the wall are presented. The maximum impact pressure magnitude is found to be of the order of ten times that of the non-breaking dynamic pressure and it always occurred above the still water level for different intensities of breaking waves considered. The minimum pressure rise time is observed to be 0.235 ms.
Simulations of Extreme Wave Runup on a Vertical Wall by Analytic Boussinesq Model
Kurnia, Ruddy
2016-01-01
Wave runup on a vertical wall has both fundamental and practical interest. The wave impact on a structure is an important aspect that must be taken into account in the design of coastal structures. From linear wave theory, it is known that the wave amplitude on a vertical fully reflecting wall is
Energy Technology Data Exchange (ETDEWEB)
Salhi, A. [Departement de Physique, Faculte des Sciences de Tunis, 1060 Tunis (Tunisia); Lehner, T. [LUTH, UMR 8102 CNRS, Observatoire de Paris-Meudon, 5 place de Janssen, F-92195 Meudon (France); Godeferd, F.; Cambon, C. [Laboratoire de Mecanique des Fluides et d' Acoustique, Ecole Centrale de Lyon, Universite de Lyon, UMR 5509, CNRS, INSA, UCB, F-69134 Ecully Cedex (France)
2013-07-10
We examine accretion disk flow under combined radial and vertical stratification utilizing a local Cartesian (or ''shearing box'') approximation. We investigate both axisymmetric and nonaxisymmetric disturbances with the Boussinesq approximation. Under axisymmetric disturbances, a new dispersion relation is derived. It reduces to the Solberg-Hoieland criterion in the case without vertical stratification. It shows that, asymptotically, stable radial and vertical stratification cannot induce any linear instability; Keplerian flow is accordingly stable. Previous investigations strongly suggest that the so-called bypass concept of turbulence (i.e., that fine-tuned disturbances of any inviscid smooth shear flow can reach arbitrarily large transient growth) can also be applied to Keplerian disks. We present an analysis of this process for three-dimensional plane-wave disturbances comoving with the shear flow of a general rotating shear flow under combined stable radial and vertical rotation. We demonstrate that large transient growth occurs for K{sub 2}/k{sub 1} >> 1 and k{sub 3} = 0 or k{sub 1} {approx} k{sub 3}, where k{sub 1}, K{sub 2}, and k{sub 3} are the azimuthal, radial, and vertical components of the initial wave vector, respectively. By using a generalized ''wave-vortex'' decomposition of the disturbance, we show that the large transient energy growth in a Keplerian disk is mainly generated by the transient dynamics of the vortex mode. The analysis of the power spectrum of total (kinetic+potential) energy in the azimuthal or vertical directions shows that the contribution coming from the vortex mode is dominant at large scales, while the contribution coming from the wave mode is important at small scales. These findings may be confirmed by appropriate numerical simulations in the high Reynolds number regime.
Deep vertical propagation of mountain waves above Scandinavia
Dörnbrack, Andreas; Gisinger, Sonja; Rapp, Markus; Witschas, Benjamin; Ehard, Benedikt; Wagner, Johannes; Achtert, Peggy; Stober, Gunter; Kivi, Rigel; Gumbel, Jörg
2015-04-01
The project "Investigation of the life cycle of gravity waves (GW-LCYCLE) is part of the German research initiative ROMIC (Role of the Middle atmosphere In Climate) funded by the ministry of research. In close cooperation with Scandinavian partners as the Stockholm University and the Finnish Meteorological Institute a first field phase was conducted in November/December 2013. The field program combined ground-based observations of tropospheric and lower stratospheric flow and stratospheric and mesospheric temperature by lidars and radars at Alomar (N) and at Esrange (S) with airborne and balloonborne observations. Northern Scandinavia was chosen since the westerly flow across the mountains is often aligned with the polar night jet permitting gravity waves (GWs) to propagate into the middle atmosphere. From 2 until 14 December 2013, 24 hours of the DLR Falcon flown in four intensive observing periods (IOPs) provided in-situ and remote-sensing observations of atmospheric wind, temperature, water vapour and other trace gases (e.g. CO, N2O, O3) in the vicinity of the tropopause. During three IOPs, the airborne observations were supported by 3 hourly simultaneous radiosonde launches from Andøya (N), Esrange(S) and Sodankylä (FIN). Additionally, 1.5 hourly high-frequency radiosonde launches were conducted from the Arena Arctica at Kiruna airport with two systems (Väisälä and GRAW)and different balloon fillings to obtain different ascent rates. During GW-LCYCLE, the atmospheric flow above the Scandinavian mountains was observed under distinct meteorological conditions enabling or attenuating the deep vertical propagation of mountain-induced gravity waves. The presentation juxtaposes two different cases and analyses the associated meteorological conditions. The unique combination of airborne tropospheric wind lidar measurements, flight level data, high-frequency radiosonde profiles and the ground-based lidar observations allow a comprehensive study of deeply
Scour at Vertical Piles in Sand-Clay Mixtures under Waves
DEFF Research Database (Denmark)
Dey, Subhasish; Helkjær, Anders; Sumer, B. Mutlu
2011-01-01
Marine sediments often contain sand-clay mixtures in widely varying proportions. This study presents the results of equilibrium scour and time variation of scour depths at circular piles embedded vertically in clay alone and sand-clay mixed beds under waves. Experiments were conducted in a wave...... flume with different proportions of sand-clay mixtures as bed sediments. Test results for the cases of steady current and sand alone under waves are used as references. The equilibrium scour depth reduces with an increase in clay proportion n (by weight) in a sand-clay mixture. Interestingly, the scour...... depth reductions for n=0.3 and 1 are almost equal, suggesting that when the clay proportion in a sand-clay mixture becomes 0.3, the sand-clay mixture behaves as if it were a clay-alone mixture, in relation to scour depths. The dependency of equilibrium scour depth on the Keulegan-Carpenter number...
Hydrodynamic analysis and shape optimization for vertical axisymmetric wave energy converters
Zhang, Wan-chao; Liu, Heng-xu; Zhang, Liang; Zhang, Xue-wei
2016-12-01
The absorber is known to be vertical axisymmetric for a single-point wave energy converter (WEC). The shape of the wetted surface usually has a great influence on the absorber's hydrodynamic characteristics which are closely linked with the wave power conversion ability. For complex wetted surface, the hydrodynamic coefficients have been predicted traditionally by hydrodynamic software based on the BEM. However, for a systematic study of various parameters and geometries, they are too multifarious to generate so many models and data grids. This paper examines a semi-analytical method of decomposing the complex axisymmetric boundary into several ring-shaped and stepped surfaces based on the boundary discretization method (BDM) which overcomes the previous difficulties. In such case, by using the linear wave theory based on eigenfunction expansion matching method, the expressions of velocity potential in each domain, the added mass, radiation damping and wave excitation forces of the oscillating absorbers are obtained. The good astringency of the hydrodynamic coefficients and wave forces are obtained for various geometries when the discrete number reaches a certain value. The captured wave power for a same given draught and displacement for various geometries are calculated and compared. Numerical results show that the geometrical shape has great effect on the wave conversion performance of the absorber. For absorbers with the same outer radius and draught or displacement, the cylindrical type shows fantastic wave energy conversion ability at some given frequencies, while in the random sea wave, the parabolic and conical ones have better stabilization and applicability in wave power conversion.
Oblique wave motion over multiple submerged porous bars near a vertical wall
Zhao, Yang; Liu, Yong; Li, Huajun; Chang, Anteng
2017-08-01
This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall. Based on linear potential theory, an analytical solution for the present problem is developed using matched eigenfunction expansions. A complex dispersion relation is adopted to describe the wave elevation and energy dissipation over submerged porous bars. In the analytical solution, no limitations on the bar number, bar size, and spacing between adjacent bars are set. The convergence of the analytical solution is satisfactory, and the correctness of the analytical solution is confirmed by an independently developed multi-domain BEM (boundary element method) solution. Numerical examples are presented to examine the reflection and transmission coefficients of porous bars, C R and C T , respectively, for engineering applications. The calculation results show that when the sum of widths for all the porous bars is fixed, increasing the bar number can significantly improve the sheltering function of the bars. Increasing the bar height can cause more wave energy dissipation and lower C R and C T . The spacing between adjacent bars and the spacing between the last bar and the vertical wall are the key parameters affecting C R and C T . The proposed analytical method may be used to analyze the hydrodynamic performance of submerged porous bars in preliminary engineering designs.
Scattering of electromagnetic plane waves by a buried vertical dike
Directory of Open Access Journals (Sweden)
Batista Lurimar S.
2003-01-01
Full Text Available The complete and exact solution of the scattering of a TE mode frequency domain electromagnetic plane wave by a vertical dike under a conductive overburden has been established. An integral representation composed of one-sided Fourier transforms describes the scattered electric field components in each one of the five media: air, overburden, dike, and the country rocks on both sides of the dike. The determination of the terms of the series that represents the spectral components of the Fourier integrals requires the numerical inversion of a sparse matrix, and the method of successive approaches. The zero-order term of the series representation for the spectral components of the overburden, for given values of the electrical and geometrical parameters of the model, has been computed. This result allowed to determine an approximate value of the variation of the electric field on the top of the overburden in the direction perpendicular to the strike of the dike. The results demonstrate the efficiency of this forward electromagnetic modeling, and are fundamental for the interpretation of VLF and Magnetotelluric data.
Vertically propagating acoustic waves launched by seismic waves visualized in ionograms
Maruyama, Takashi; Shinagawa, Hiroyuki
2013-04-01
After the magnitude 9.0 earthquake off the Pacific coast of Tohoku (near the east coast of Honshu, Japan), which occurred on 11 March 2011, an unusual multiple-cusp signature (MCS) was observed in ionograms at three ionosonde stations across Japan. Similar MCSs in ionograms were identified in 8 of 43 earthquakes with a seismic magnitude of 8.0 or greater for the period from 1957 to 2011. The appearance of MCSs at different epicentral distances exhibited traveling characteristics at a velocity of ~4.0 km/s, which is in the range of Rayleigh waves. There was a ~7 min offset in delay time at each epicentral distance in the travel-time diagram. This offset is consistent with the propagation time of acoustic waves from the ground to the ionosphere. We analyzed vertical structure of electron density perturbation that caused MCSs. The ionosonde technique is essentially radar-based measurement of a reflection at a height where the plasma frequency is equal to the sounding radio frequency and it is possible to obtain an electron density profile by sweeping the frequency. However, this measured height is not a true height because radio waves do not propagate at the speed of light in the ionosphere. The group velocity of radio waves decreases just below the reflection height where the sounding frequency approaches the plasma frequency. The amount of delay is larger when this region is thicker. The vertically propagating acoustic waves modulate the electron density. The radio wave speed greatly delays and a cusp signature appears in the echo trace at a phase of the periodic perturbation of electron density where the density gradient is most gradual. Simulations were conducted how large amplitude of density perturbation produces cusp signatures as observed. First, the real height density profile was obtained by converting the ionogram trace just before the arrival of coseismic disturbances. The electron density profile was then modified by adding a periodic perturbation and the
Role of gravity waves in vertical coupling during sudden stratospheric warmings
Yiğit, Erdal
2016-01-01
Gravity waves are primarily generated in the lower atmosphere, and can reach thermospheric heights in the course of their propagation. This paper reviews the recent progress in understanding the role of gravity waves in vertical coupling during sudden stratospheric warmings. Modeling of gravity wave effects is briefly reviewed, and the recent developments in the field are presented. Then, the impact of these waves on the general circulation of the upper atmosphere is outlined. Finally, the role of gravity waves in vertical coupling between the lower and the upper atmosphere is discussed in the context of sudden stratospheric warmings.
Damage Accumulation in Vertical Breakwaters due to Combined Impact Loading and Pulsating Wave Loads
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Nielsen, Søren R. K.
1999-01-01
Vertical wall breakwaters used to protect for example an harbour from large waves usually consist of large concrete caissons placed on the seabed. The wave loads can be divided in two types, pulsating and impact loads. For some types of breakwaters especially the impact wave loads can be very large...
The effect of non-linear wave in front of vertical wall using bi ...
African Journals Online (AJOL)
of waves in front of a vertical wall are examined, using the new theoretical approach of a bi-parametric distribution, proposed by Ejinkonye [1] to investigate the effect of nonlinearity for the mechanics of the sea waves. The most probable value of the wave steepness is assumed to be = 0.055. From the subsequent calculation ...
Potential to kinetic energy conversion in wave number domain for the Southern Hemisphere
Huang, H.-J.; Vincent, D. G.
1984-01-01
Preliminary results of a wave number study conducted for the South Pacific Convergence Zone (SPCZ) using FGGE data for the period January 10-27, 1979 are reported. In particular, three variables (geomagnetic height, z, vertical p-velocity, omega, and temperature, T) and one energy conversion quantity, omega-alpha (where alpha is the specific volume), are shown. It is demonstrated that wave number 4 plays an important role in the conversion from available potential energy to kinetic energy in the Southern Hemisphere tropics, particularly in the vicinity of the SPCZ. It is therefore suggested that the development and movement of wave number 4 waves be carefully monitored in making forecasts for the South Pacific region.
Horizontal Coherence of Wave Forces on Vertical Wall Breakwaters
DEFF Research Database (Denmark)
Archetti, Renata; Lamberti, Alberto; Martinelli, Luca
2001-01-01
Evaluation of spatial coherence of breaking waves is of great importance and of recent interest.......Evaluation of spatial coherence of breaking waves is of great importance and of recent interest....
Graphs with fixed number of pendent vertices and minimal first Zagreb index
Directory of Open Access Journals (Sweden)
Ivan Gutman
2015-03-01
Full Text Available The first Zagreb index $M_1$ of a graph $G$ is equal to the sum of squares of degrees of the vertices of $G$. Goubko proved that for trees with $n_1$ pendent vertices, $M_1 geq 9,n_1-16$. We show how this result can be extended to hold for any connected graph with cyclomatic number $gamma geq 0$. In addition, graphs with $n$ vertices, $n_1$ pendent vertices, cyclomatic number $gamma$, and minimal $M_1$ are characterized. Explicit expressions for minimal $M_1$ are given for $gamma=0,1,2$, which directly can be extended for $gamma>2$.
Horizontal Coherence of Wave Forces on Vertical Wall Breakwaters
DEFF Research Database (Denmark)
Archetti, R.; Frigaard, Peter; Lamberti, A.
2001-01-01
of breaking waves for increasing wave height are estimated and compared with existing empirical formulae. The horizontal dimension of the breaker is investigated using two different methodologies: the first analyses the decreasing of the highest 1/250 force with increasing horizontal dimension of the caisson......, with special attention to the effects of wave spreading, and the second analyses the spatial correlation of impulsive force per unit length along the breakwater....
Directory of Open Access Journals (Sweden)
Sang Kil Park
2014-12-01
Full Text Available Rubble mound breakwaters protect the coastal line against severe erosion caused by wave action. This study examined the performance of different sizes and properties (i.e. height of vertical wall and tetrapod size of rubble mound breakwaters on reducing the overtopping discharge. The physical model used in this study was derived based on an actual rubble mound in Busan Yacht Harbor. This research attempts to fill the gap in practical knowledge on the combined effect of the armor roughness and vertical wall on wave overtopping in rubble mound breakwaters. The main governing parameters used in this study were the vertical wall height, variation of the tetrapod weights, initial water level elevation, and the volume of overtopping under constant wave properties. The experimental results showed that the roughness factor differed according to the tetrapod size. Furthermore, the overtopping discharge with no vertical wall was similar to that with relatively short vertical walls (γν = 1. Therefore, the experimental results highlight the importance of the height of the vertical wall in reducing overtopping discharge. Moreover, a large tetrapod size may allow coastal engineers to choose a shorter vertical wall to save cost, while obtaining better performance.
Directory of Open Access Journals (Sweden)
Park Sang Kil
2014-12-01
Full Text Available Rubble mound breakwaters protect the coastal line against severe erosion caused by wave action. This study examined the performance of different sizes and properties (i.e. height of vertical wall and tetrapod size of rubble mound breakwaters on reducing the overtopping discharge. The physical model used in this study was derived based on an actual rubble mound in Busan Yacht Harbor. This research attempts to fill the gap in practical knowledge on the combined effect of the armor roughness and vertical wall on wave overtopping in rubble mound breakwaters. The main governing parameters used in this study were the vertical wall height, variation of the tetrapod weights, initial water level elevation, and the volume of overtopping under constant wave properties. The experimental results showed that the roughness factor differed according to the tetrapod size. Furthermore, the overtopping discharge with no vertical wall was similar to that with relatively short vertical walls ( 1 γv = 1. Therefore, the experimental results highlight the importance of the height of the vertical wall in reducing overtopping discharge. Moreover, a large tetrapod size may allow coastal engineers to choose a shorter vertical wall to save cost, while obtaining better performance.
Rodda, Costanza; Borcia, Ion; Harlander, Uwe
2017-04-01
The differentially heated rotating annulus is a widely studied experimental apparatus for modelling large- scale features of the mid-latitude atmosphere. In the classic set-up, the instability is studied using a homogeneous fluid. In the present work, we study a modified version of the classical baroclinic experiment where the working fluid consists of sodium-chloride/de-ionized water solution. A continuously stratified salinity profile is initially prepared in the annular cavity with the standard double-bucket technique. The vertical salt stratification opposes the thermal convective motions until the ratio of the (horizontal) thermal density difference and the (vertical) salinity-induced density difference exceeds a certain critical threshold. Then double-diffusive convection rolls develop in thin layers located at top and bottom, where the salt stratification is weaker. This laboratory arrangement mimics the presence of a stratosphere above a baroclinic unstable troposphere. PIV velocity maps describe the wavy flow pattern at different altitudes. A baroclinic wave on top, and one at the bottom arise, but with different azimuthal wave numbers. These waves are decoupled by the presence of the motionless stratified layer between them. In some regimes, small scale wave trains have been detected along the baroclinic wave front. These waves might be traces of Internal Gravity Waves generated by the fluid motions in the baroclinic unstable layers.
Surface waves on currents with arbitrary vertical shear
Smeltzer, Benjamin K.; Ellingsen, Simen Å.
2017-04-01
We study dispersion properties of linear surface gravity waves propagating in an arbitrary direction atop a current profile of depth-varying magnitude using a piecewise linear approximation and develop a robust numerical framework for practical calculation. The method has been much used in the past for the case of waves propagating along the same axis as the background current, and we herein extend and apply it to problems with an arbitrary angle between the wave propagation and current directions. Being valid for all wavelengths without loss of accuracy, the scheme is particularly well suited to solve problems involving a broad range of wave vectors, such as ship waves and Cauchy-Poisson initial value problems. We examine the group and phase velocities over different wavelength regimes and current profiles, highlighting characteristics due to the depth-variable vorticity. We show an example application to ship waves on an arbitrary current profile and demonstrate qualitative differences in the wake patterns between concave down and concave up profiles when compared to a constant shear profile with equal depth-averaged vorticity. We also discuss the nature of additional solutions to the dispersion relation when using the piecewise-linear model. These are vorticity waves, drifting vortical structures which are artifacts of the piecewise model. They are absent for a smooth profile and are spurious in the present context.
Optimal number of waves for ribbon fin propulsion
Bale, Rahul; Bhalla, Amneet P. S.; Maciver, Malcolm A.; Patankar, Neelesh A.
2012-11-01
Many species of fish, such as rajiform, diodontiform, amiiform, gymnotiform and balistiformswimmers, use a ribbon fin as their primary mode of propulsion. It has been observed that each fish species, depending on its size, uses a specific number of waves on its ribbon fin. For example, the black ghost knifefish (10 ×1cm fin) typically uses 2-2.5 waves while a giant oarfish (3 ×0.1m fin) uses 6-8 waves. In this work we investigate whether this leads to optimal axial thrust. The axial thrust generated depends on the efficiency with which fin waves transport the fluid backward. We find that there are two competing mechanisms. On the one hand, an increase in wavelength (at fixed amplitude and frequency of the wave), and therefore the wave velocity, leads to an increased ability to transport the fluid backward. This leads to more thrust. On the other hand, longer wavelength leads to shallower waves. This reduces the efficacy to transport the fluid backward and reduces the thrust. The optimal wavelength, and therefore the optimal number of waves, is a result of a balance between the two competing mechanisms. We do our analysis in terms of specific wavelength, which is the wavelength non-dimensionalized by the wave amplitude. We find that the value of the specific wavelength at which the axial thrust is maximized is universal for ribbon fins and it is in agreement with biological data.
Tsunami Wave Run-up on a Vertical Wall in Tidal Environment
Didenkulova, Ira; Pelinovsky, Efim
2017-12-01
We solve analytically a nonlinear problem of shallow water theory for the tsunami wave run-up on a vertical wall in tidal environment. Shown that the tide can be considered static in the process of tsunami wave run-up. In this approximation, it is possible to obtain the exact solution for the run-up height as a function of the incident wave height. This allows us to investigate the tide influence on the run-up characteristics.
Drops and waves on a viscous film coating a vertical fiber
Duprat, Camille; Giorgiutti-Dauphine, Frederique
2009-11-01
We consider the nonlinear dynamics of a liquid viscous film flowing down a vertical fiber. The initially flat film spontaneously breaks up into a regular wavetrain due to the Rayleigh-Plateau instability. The characteristics of the fully developed structures then depend on the dominant mechanisms. When the advection of the waves by the flow dominates over the instability, we observe moderate amplitude waves that propagate without carrying mass. When surface tension is strong, the film breaks up into large amplitude drops exhibiting a recirculation region. The transition between drops and waves regimes and the corresponding structures have been characterized experimentally and numerically. When both surface tension and viscosity effects are strong, the system can be seen has a paradigm for active (unstable), dissipative and dispersive media. The particular shape of the resulting structures gives rise to complex interactions (attraction and repulsion) leading to the formation of bound states. The system then appears to select a finite number of preferred specific distances in agreement with a weak interaction theory developed by D. Tseluiko, S. Saprykin and S. Kalliadasis (Imperial College London).
Podglajen, Aurélien; Hertzog, Albert; Plougonven, Riwal; Legras, Bernard
2016-04-01
Wave-induced Lagrangian fluctuations of temperature and vertical velocity in the lower stratosphere are quantified using measurements from superpressure balloons (SPBs). Observations recorded every minute along SPB flights allow the whole gravity wave spectrum to be described and provide unprecedented information on both the intrinsic frequency spectrum and the probability distribution function of wave fluctuations. The data set has been collected during two campaigns coordinated by the French Space Agency in 2010, involving 19 balloons over Antarctica and 3 in the deep tropics. In both regions, the vertical velocity distributions depart significantly from a Gaussian behavior. Knowledge on such wave fluctuations is essential for modeling microphysical processes along Lagrangian trajectories. We propose a new simple parameterization that reproduces both the non-Gaussian distribution of vertical velocities (or heating/cooling rates) and their observed intrinsic frequency spectrum.
Internal wave-mediated shading causes frequent vertical migrations in fishes
Kaartvedt, Stein
2012-04-25
We provide evidence that internal waves cause frequent vertical migrations (FVM) in fishes. Acoustic data from the Benguela Current revealed that pelagic scattering layers of fish below ~140 m moved in opposite phases to internal waves, ascending ~20 m towards the wave trough and descending from the wave crest. At the trough, the downward displacement of upper waters and the upward migration of fish created an overlapping zone. Near-bottom fish correspondingly left the benthic boundary zone at the wave trough, ascending into an acoustic scattering layer likely consisting of zooplankton and then descending to the benthic boundary zone at the wave crest. We suggest that this vertical fish migration is a response to fluctuations in light intensity of 3 to 4 orders of magnitude caused by shading from a turbid surface layer that had chlorophyll a values of 3 to 4 mg m−3 and varied in thickness from ~15 to 50 m at a temporal scale corresponding to the internal wave period (30 min). This migration frequency thus is much higher than that of the common and widespread light-associated diel vertical migration. Vertical movements affect prey encounters, growth, and survival. We hypothesize that FVM increase the likelihood of prey encounters and the time for safe visual foraging among planktivorous fish, thereby contributing to efficient trophic transfer in major upwelling areas.
Testing strong gravity with gravitational waves and Love numbers
Franzin, E.; Cardoso, V.; Pani, P.; Raposo, G.
2017-05-01
The LIGO observation of GW150914 has inaugurated the gravitational-wave astronomy era and the possibility of testing gravity in extreme regimes. While distorted black holes are the most convincing sources of gravitational waves, similar signals might be produced also by other compact objects. In particular, we discuss what the gravitational-wave ringdown could tell us about the nature of the emitting object, and how measurements of the tidal Love numbers could help us in understanding the internal structure of compact dark objects.
Vertical pressure gradient and particle motions in wave boundary layers
DEFF Research Database (Denmark)
Jensen, Karsten Lindegård
and its role in the fully turbulent boundary layer. The pressure in the flow is obtained from the flow fields of the oscillatory boundary layer. What differs, the vertical pressure gradient, from other turbulent quantities, like e.g. velocity fluctuations is that it can detect newly generated turbulence....... The experiment is conducted in a oscillating water tunnel, for both smooth bed and rough bed. The particle motion is determined by utilizing particle tracking base on a video recording of the particle motion in the flow. In the oscillatory flow, in contrast to steady current, the particle motion is a function...
Determination of the number of Vertical Axis Wind Turbine blades based on power spectrum
Fedak, Waldemar; Anweiler, Stanisław; Gancarski, Wojciech; Ulbrich, Roman
2017-10-01
Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allows the reduction of costs. The maximum power of the rotor is selected as the performance target. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. The major result of this research is the Vertical Axis Wind Turbine power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.
DEFF Research Database (Denmark)
Martinelli, Luca; Lamberti, Alberto; Frigaard, Peter
2007-01-01
This paper addresses wave forces applied to vertical caisson breakwaters. Design diagrams are proposed to evaluate the reduction of the breaker wave force with increasing horizontal length of the units. A model in 1:100 scale of a typical Italian vertical breakwater was tested under multidirectio......This paper addresses wave forces applied to vertical caisson breakwaters. Design diagrams are proposed to evaluate the reduction of the breaker wave force with increasing horizontal length of the units. A model in 1:100 scale of a typical Italian vertical breakwater was tested under...
Wave Loading and Overtopping on Vertical Wall Breakwaters in Multidirectional Breaking Seas
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Grønbech, J.; Hald, Tue
1998-01-01
The present paper concerns the results and findings of a physical study on wave impacts on vertical caisson breakwaters situated in irregular, multidirectional breaking seas. The study has taken place as part of the framework programme "Dynamics of Structures" financially supported by the Danish...... Technical Research Council, during the period of January 97 to December 97. The test were carried out in the 3D wave basin at the Hydraulics and Coastal Engineering Laboratory, Aalborg University....
Analysis of vegetation effect on waves using a vertical 2-D RANS model
A vertical two-dimensional (2-D) model has been applied in the simulation of wave propagation through vegetated water bodies. The model is based on an existing model SOLA-VOF which solves the Reynolds-Averaged Navier-Stokes (RANS) equations with the finite difference method on a staggered rectangula...
Tailoring wave chaos in vertical-cavity surface-emitting lasers via polarization control.
Molitor, Andreas; Blazek, Martin; Elsässer, Wolfgang
2011-10-01
We demonstrate that polarization control in combination with the geometrical shape affects wave chaos phenomena in vertical-cavity surface-emitting lasers (VCSELs). In a grating-polarization-stabilized VCSEL, we demonstrate wave chaos in one polarization mode and a transition from wave chaos to regular behavior in the other orthogonal polarization mode. We quantify the amount of chaoticity via the Brody nearest-neighbor distribution. Comparing with a reference VCSEL without a surface-grating, we explain these results and their injection current dependence by the surface-grating-induced mode selection and a change in the effective resonator shape. © 2011 Optical Society of America
Configuration interaction wave functions: A seniority number approach
Energy Technology Data Exchange (ETDEWEB)
Alcoba, Diego R. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Física de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Universitaria, 1428 Buenos Aires (Argentina); Torre, Alicia; Lain, Luis, E-mail: qfplapel@lg.ehu.es [Departamento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apdo. 644, E-48080 Bilbao (Spain); Massaccesi, Gustavo E. [Departamento de Ciencias Exactas, Ciclo Básico Común, Universidad de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires (Argentina); Oña, Ofelia B. [Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Universidad Nacional de La Plata, CCT La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, Diag. 113 y 64 (S/N), Sucursal 4, CC 16, 1900 La Plata (Argentina)
2014-06-21
This work deals with the configuration interaction method when an N-electron Hamiltonian is projected on Slater determinants which are classified according to their seniority number values. We study the spin features of the wave functions and the size of the matrices required to formulate states of any spin symmetry within this treatment. Correlation energies associated with the wave functions arising from the seniority-based configuration interaction procedure are determined for three types of molecular orbital basis: canonical molecular orbitals, natural orbitals, and the orbitals resulting from minimizing the expectation value of the N-electron seniority number operator. The performance of these bases is analyzed by means of numerical results obtained from selected N-electron systems of several spin symmetries. The comparison of the results highlights the efficiency of the molecular orbital basis which minimizes the mean value of the seniority number for a state, yielding energy values closer to those provided by the full configuration interaction procedure.
Experimental and numerical study of the wave run-up along a vertical plate
DEFF Research Database (Denmark)
Molin, Bernard; Kimmoun, O.; Liu, Y.
2010-01-01
, strong deviations from the predictions of linear theory gradually take place as the reflected wave field develops in the basin. This phenomenon is attributed to third-order interactions between the incoming and reflected wave systems, on the weather side of the plate. The measured profiles along...... the plate are compared with the predictions of two numerical models: an approximate model based on the tertiary interaction theory of Longuet-Higgins & Phillips (J. Fluid Mech., vol. 12, 1962, p. 333) for plane waves, which provides a steady-state solution, and a fully nonlinear numerical wavetank based......Results from experiments on wave interaction with a rigid vertical plate are reported. The 5m long plate is set against the wall of a 30m wide basin, at 100m from the wavemaker. This set-up is equivalent to a 10m plate in the middle of a 60m wide basin. Regular waves are produced, with wavelengths...
The vertical gradient of gravity wave momentum flux in global observations and modeling
Preusse, Peter; Trinh, Thai; Chen, Dan; Ern, Manfred; Krisch, Isabell; Nogai, Karlheinz; Riese, Martin; Strube, Cornelia
2017-04-01
In their recent review paper Geller et al. (2013) compared climatologies of gravity wave momentum flux (GWMF) from various global models with GWMF inferred from different observation techniques. They find a generally good agreement in the global distributions in the lower stratosphere, but a strong difference in the vertical gradient of GWMF profiles: observations from various satellite data sets show a strong decrease of GWMF with a scale height of 9-12km while parametrized GWMF in ECHAM decreases only slowly with a scale height of 24km. The authors hint that this may be caused by the fact that observations see only part of the wave spectrum. In particular, gravity waves (GWs) with short horizontal scales are not seen by the infrared limb sounders. Is the horizontal scale the major reason? Are there other effects responsible for the different vertical gradients? We here consider this question using the GROGRAT ray-tracing model and GWs that are, in principle, visible to infrared limb sounding instruments. For this we analyze GWs in high resolution ECMWF analysis fields at 25km altitude and determine wave amplitudes and the 3D wave vector. The horizontal distribution of GWMF from these ECMWF-resolved waves matches observed distributions well. The inferred wave parameters are used as launch parameters and the GWs are propagated upward with GROGRAT up to 90km altitude. GROGRAT is here used as a 3D ray-tracer with wave action flux conservation and a Fritts and Rastogi saturation scheme, i.e. it is similar to a GW parametrization but can handle 3D propagation in addition. The GROGRAT results also display a very weak decrease of GWMF in the stratosphere and lower mesosphere, similar as the GW parametrization, and are thus an interesting test-bed for searching reasons for the difference between observed and modeled vertical gradients as they were seen in Geller et al. (2013). Using the GROGRAT simulations we investigate the following potential reasons for the difference
Total domination and matching numbers in graphs with all vertices in triangles
DEFF Research Database (Denmark)
Henning, Michael A.; Yeo, Anders
2013-01-01
A set M of edges of a graph G is a matching if no two edges in M are incident to the same vertex. The matching number of G is the maximum cardinality of a matching of G. A set S of vertices in G is a total dominating set if every vertex of G is adjacent to some vertex in S. The minimum cardinalit...... a Graffiti conjecture that relates the total domination and matching numbers in a graph....
Laughman, B.; Fritts, D. C.; Lund, T. S.
2017-05-01
Many characteristics of tsunami-driven gravity waves (TDGWs) enable them to easily propagate into the thermosphere and ionosphere with appreciable amplitudes capable of producing detectable perturbations in electron densities and total electron content. The impact of vertically varying background and tidal wind structures on TDGW propagation is investigated with a series of idealized background wind profiles to assess the relative importance of wave reflection, critical-level approach, and dissipation. These numerical simulations employ a 2-D nonlinear anelastic finite-volume neutral atmosphere model which accounts for effects accompanying vertical gravity wave (GW) propagation such as amplitude growth with altitude. The GWs are excited by an idealized tsunami forcing with a 50 cm sea surface displacement, a 400 km horizontal wavelength, and a phase speed of 200 ms-1 consistent with previous studies of the tsunami generated by the 26 December 2004 Sumatra earthquake. Results indicate that rather than partial reflection and trapping, the dominant process governing TDGW propagation to thermospheric altitudes is refraction to larger and smaller vertical scales, resulting in respectively larger and smaller vertical group velocities and respectively reduced and increased viscous dissipation. Under all considered background wind profiles, TDGWs were able to attain ionospheric altitudes with appreciable amplitudes. Finally, evidence of nonlinear effects is observed and the conditions leading to their formation is discussed.
EXPERIMENTAL STUDY OF WAVE FLOWS AROUND THE FINITE LENGTH VERTICAL WALL
Directory of Open Access Journals (Sweden)
Tran Long Giang
2012-10-01
Full Text Available Construction of breakwater structures of modern seaports requires computational models describing interaction of waves with structural elements of ports. The model should be based on numerical hydrodynamic models that contemplate all constituents of interaction between waves and structures, including those at various stages of construction. The above model makes it possible to have construction works performed in accordance with the pre-developed plan. Experimentalresearch of the behaviour of breakwater structures is to be conducted in laboratories. A scaled natural model is to be used for the above purpose to verify the model behaviour. The authors consider the methodology and results of experiments involving models of wave loads produced on vertical breakwater structures at various stages of their construction. On the basis of the experiments conducted by the authors, it is discovered that the value of the total wave force, that the vertical wall is exposed to, increases along with the wall length in the event of a constant wave mode, which is natural. However, the per-meter value of the wave force increases along with the increase in the length of the wall until it reaches the value of the length of a transverse obstacle divided by the length of waves equal to 0.28; thereafter, the wave force goes down. The authors assume that this phenomenon is caused by the change in the nature of interaction between waves and an obstacle and a transition from a diffraction-free flow to a diffraction flow. The authors believe that further researches are necessary to explore the phenomenon.
Bu, Q. T.; Hu, G. W.; Ye, Y. G.; Liu, C. L.; Li, C. F.; Best, A. I.; Wang, J. S.
2017-06-01
Knowledge of the elastic wave velocities of hydrate-bearing sediments is important for geophysical exploration and resource evaluation. Methane gas migration processes play an important role in geological hydrate accumulation systems, whether on the seafloor or in terrestrial permafrost regions, and their impact on elastic wave velocities in sediments needs further study. Hence, a high-pressure laboratory apparatus was developed to simulate natural continuous vertical migration of methane gas through sediments. Hydrate saturation (S h) and ultrasonic P- and S-wave velocities (V p and V s) were measured synchronously by time domain reflectometry (TDR) and by ultrasonic transmission methods respectively during gas hydrate formation in sediments. The results were compared to previously published laboratory data obtained in a static closed system. This indicated that the velocities of hydrate-bearing sediments in vertical gas migration systems are slightly lower than those in closed systems during hydrate formation. While velocities increase at a constant rate with hydrate saturation in the closed system, P-wave velocities show a fast-slow-fast variation with increasing hydrate saturation in the vertical gas migration system. The observed velocities are well described by an effective-medium velocity model, from which changing hydrate morphology was inferred to cause the fast-slow-fast velocity response in the gas migration system. Hydrate forms firstly at the grain contacts as cement, then grows within the pore space (floating), then finally grows into contact with the pore walls again. We conclude that hydrate morphology is the key factor that influences the elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems.
ANALYTICAL AND NUMERICAL RESEARCH OF WAVE LOADS ON A SHORT VERTICAL WALL
Directory of Open Access Journals (Sweden)
Kantarzhi Igor' Grigor'evich
2012-10-01
Full Text Available The problem of wave loads on a relatively short wall is related to the issue of the general design of the structure at the stage of its construction, particularly, if the structure is build offshore. The physical nature of interaction between waves and vertical walls that have different lengths is the subject matter of this paper. It is assumed that the wall is absolutely rigid. The comparison of numerical test results and an analytical calculation based on a short wall model is made. As a result, wave forces identified through the employment of the above two models demonstrate their satisfactory convergence. The difference is substantial for longer walls, and it increases along with the increase of the wall length. The conclusion is that a short wall is exposed to the wave load that is not accompanied by any diffraction, therefore, a related method of design may be recommended. Numerical models may be considered as the universal ones.
Directory of Open Access Journals (Sweden)
Liu Ming
2017-11-01
Full Text Available The wave energy, as a clean and non-pollution renewable energy sources, has become a hot research topic at home and abroad and is likely to become a new industry in the future. In this article, to effectively extract and maximize the energy from ocean waves, a vertical axisymmetric wave energy converter (WEC was presented according to investigating of the advantages and disadvantages of the current WEC. The linear and quadratic equations in frequency-domain for the reactive controlled single-point converter property under regular waves condition are proposed for an efficient power take-off (PTO. A method of damping coefficients, theoretical added mass and exciting force are calculated with the analytical method which is in use of the series expansion of eigen functions. The loads of optimal reactive and resistive, the amplitudes of corresponding oscillation, and the width ratios of energy capture are determined approximately and discussed in numerical results.
Pore-fluid effects on seismic waves in vertically fractured earth with orthotropic symmetry
Energy Technology Data Exchange (ETDEWEB)
Berryman, J.G.
2010-05-15
For elastically noninteracting vertical-fracture sets at arbitrary orientation angles to each other, a detailed model is presented in which the resulting anisotropic fractured medium generally has orthorhombic symmetry overall. Some of the analysis methods and ideas of Schoenberg are emphasized, together with their connections to other similarly motivated and conceptually related methods by Sayers and Kachanov, among others. Examples show how parallel vertical-fracture sets having HTI (horizontal transversely isotropic) symmetry transform into orthotropic fractured media if some subsets of the vertical fractures are misaligned with the others, and then the fractured system can have VTI (vertical transversely isotropic) symmetry if all of the fractures are aligned randomly or half parallel and half perpendicular to a given vertical plane. An orthotropic example having vertical fractures in an otherwise VTI earth system (studied previously by Schoenberg and Helbig) is compared with the other examples treated and it is finally shown how fluids in the fractures affect the orthotropic poroelastic system response to seismic waves. The key result is that fracture-influence parameters are multiplied by a factor of (1-B), where 0 {le} B < 1 is Skempton's second coefficient for poroelastic media. Skempton's B coefficient is itself a measurable characteristic of fluid-saturated porous rocks, depending on porosity, solid moduli, and the pore-fluid bulk modulus. For heterogeneous porous media, connections between the present work and earlier related results of Brown and Korringa are also established.
Wave-turbulence interaction-induced vertical mixing and its effects in ocean and climate models.
Qiao, Fangli; Yuan, Yeli; Deng, Jia; Dai, Dejun; Song, Zhenya
2016-04-13
Heated from above, the oceans are stably stratified. Therefore, the performance of general ocean circulation models and climate studies through coupled atmosphere-ocean models depends critically on vertical mixing of energy and momentum in the water column. Many of the traditional general circulation models are based on total kinetic energy (TKE), in which the roles of waves are averaged out. Although theoretical calculations suggest that waves could greatly enhance coexisting turbulence, no field measurements on turbulence have ever validated this mechanism directly. To address this problem, a specially designed field experiment has been conducted. The experimental results indicate that the wave-turbulence interaction-induced enhancement of the background turbulence is indeed the predominant mechanism for turbulence generation and enhancement. Based on this understanding, we propose a new parametrization for vertical mixing as an additive part to the traditional TKE approach. This new result reconfirmed the past theoretical model that had been tested and validated in numerical model experiments and field observations. It firmly establishes the critical role of wave-turbulence interaction effects in both general ocean circulation models and atmosphere-ocean coupled models, which could greatly improve the understanding of the sea surface temperature and water column properties distributions, and hence model-based climate forecasting capability. © 2016 The Authors.
On the vertical structure of wave forcing for the ocean circulation
Bennis, Anne-Claire
2010-01-01
The conservation of momentum, when averaged over the phase of surface gravity waves can take two forms, whether or not the momentum variable contains the wave pseudo-momentum. The vertical profiles of the resulting wave-induced forces are discussed, with application to realistic condition. It was already proved that forces for the total momentum that use analytical functions of the local wave properties are necessarily inconsistent, and thus inaccurate at the lowest order. The consequences of these inaccuracies are explored here. In inviscid conditions, it is shown that large spurious currents of the order of 10 times the Strokes drift are generated on a sloping bottom, however small that slope is. These spurious velocities are reduced but are still significant when a strong vertical mixing is applied. In contrast, forces for the quasi-Eulerian mean momentum do not suffer from this inconsistency, and accurate numerical models can be developed. Choosing to solve for the quasi-Eulerian mean flow is also intrins...
Harada, Y.; Hirooka, T.
2017-11-01
Observational features of the winter 2013/2014 are investigated using of the Japanese 55-year Reanalysis data. This winter can be characterized by the continuous predominance of planetary waves of zonal wave number two (WN2) that did not cause major sudden stratospheric warming (SSW) events. It is found that the vertical component of the Eliassen-Palm flux of WN2 for the winter 2013/2014 is almost equal to the highest value of the winter 2008/2009. The longitudinal distribution of vertical components of Plumb wave activity flux for this winter shows marked downward propagation around 100°W and upward propagation around 60°E, both of which are the strongest of their type among the 56 winters since 1958/1959. The convergence of wave packets propagating from around 60°E contributes to the development and continuance of the quasi-barotropic Aleutian High, which is associated with the extension of negative extended refractive index (Ks) region. The extension of negative Ks region is related to the convergence or reflection of the wave packets emanating from tropospheric blocking highs developing in the North Pacific Ocean; the development and continuance of the quasi-barotropic Aleutian High is considered to be one of plausible reasons for the lack of major SSWs in the winter 2013/2014. In addition to these results, we revealed the significant contribution of smaller scale waves (with a zonal wave number of three or more) to the structure of localized wave packet propagation in the stratosphere.
The Impact of a Deepwater Wave on a Wall with Finite Vertical Extent
Wang, An; Duncan, James H.
2016-11-01
The impact of a dispersively focused 2D plunging breaker (average wave frequency 1.15 Hz) on a 2D wall that is 45 cm high and 30 cm thick is studied experimentally. The temporal evolution of the water surface profile upstream of the wall is measured with a cinematic LIF technique using frame rates up to 4,500 Hz. Impact pressures on the wall are measured simultaneously at sample rates up to 900 kHz. The wall is located horizontally 6.41 m from the wave maker in all cases and the submergence of the bottom surface of the wall is varied. It is found that the impact behavior varies dramatically with the wall submergence. When the bottom is submerged by 13.3 cm, a flip-through impact occurs. In this case, the impact evolves without wave breaking and a vertical jet is formed. When the wall is submerged by less than 4.5 cm, small-amplitude components in the wave packet interact with the bottom of the wall before the main crest arrives. Ripples reflected during this interaction modify the behavior of the incoming breaker significantly. When the bottom of the wall is located sufficiently high above the mean water level, the first interaction occurs when the undisturbed wave crest collides with the wall. The highest pressures are observed in this case. The support of the Office of Naval Research is gratefully acknowledged.
New movable plate for efficient millimeter wave vertical on-chip antenna
Marnat, Loic
2013-04-01
A new movable plate concept is presented in this paper to realize mm-wave vertical on-chip antennas through MEMS based post-processing steps in a CMOS compatible process. By virtue of its vertical position, the antenna is isolated from the lossy Si substrate and hence performs with a better efficiency as compared to the horizontal position. In addition, the movable plate concept enables polarization diversity by providing both horizontal and vertical polarizations on the same chip. Through a first iteration fractal bowtie antenna design, dual band (60 and 77 GHz) operation is demonstrated in both horizontal and vertical positions without any change in dimensions or use of switches for two different mediums (Si and air). To support the movable plate concept, the transmission line and antenna are designed on a flexible polyamide, where the former has been optimized to operate in the bent position. The design is highly suitable for compact, low cost and efficient SoC solutions. © 1963-2012 IEEE.
Spanning Trees whose Stems have a Bounded Number of Branch Vertices
Directory of Open Access Journals (Sweden)
Yan Zheng
2016-08-01
Full Text Available Let T be a tree, a vertex of degree one and a vertex of degree at least three is called a leaf and a branch vertex, respectively. The set of leaves of T is denoted by Leaf(T. The subtree T − Leaf(T of T is called the stem of T and denoted by Stem(T. In this paper, we give two sufficient conditions for a connected graph to have a spanning tree whose stem has a bounded number of branch vertices, and these conditions are best possible.
Numerical and experimental study of disturbance wave development in vertical two-phase annular flow
Hewitt, Geoffrey; Yang, Junfeng; Zhao, Yujie; Markides, Christos; Matar, Omar
2013-11-01
The annular flow regime is characterized by the presence of a thin, wavy liquid film driven along the wall by the shear stress exerted by the gas phase. Under certain liquid film Reynolds numbers, large disturbance waves are observed to traverse the interface, whose length is typically on the order of 20 mm and whose height is typically on the order of 5 times the thickness of the thin (substrate) layer between the waves. Experimental wok has been conducted to study the disturbance wave onset by probing the local film thickness for different Reynolds numbers. It is observed the disturbance waves grow gradually from wavy initiation and form the ring-like structure. To predict the wavy flow field observed in the experiment, 3D CFD simulations are performed using different low Reynolds number turbulence models and Large Eddy Simulation. Modeling results confirm that there is recirculation within the waves, and that they as a packet of turbulence traveling over a laminar substrate film. We also predict the coalescence and the break-up of waves leading to liquid droplet entrainment into the gas core. Skolkovo Foundation, UNIHEAT project.
Prediction of Vertical-Plane Wave Loading and Ship Responses in High Seas
DEFF Research Database (Denmark)
Wang, Zhaohui; Xia, Jinzhu; Jensen, Jørgen Juncher
2000-01-01
The non-linearities in wave- and slamming-induced rigid-body motions and structural responses of ships such as heave, pitch and vertical bending moments are consistently investigated based on a rational time-domain strip method. A hydrodynamic model for predicting sectional green water force is a...... for a VLCC. The non-linearities in motions and structural loads of conventional monohull ships seem well predicted by the present non-linear strip theory.......The non-linearities in wave- and slamming-induced rigid-body motions and structural responses of ships such as heave, pitch and vertical bending moments are consistently investigated based on a rational time-domain strip method. A hydrodynamic model for predicting sectional green water force...... is also outlined for the investigation of the effect of green watrer oads on the globalhull girder bending moment. The computational results based on the non-linear time-domain strip theory are compared with those based on the fully non-linear 3-D panel method SWAN-DNW and other published results...
Effect of Vertically Propagating Shear Waves on Seismic Behavior of Circular Tunnels
Directory of Open Access Journals (Sweden)
Tohid Akhlaghi
2014-01-01
Full Text Available Seismic design loads for tunnels are characterized in terms of the deformations imposed on the structure by surrounding ground. The free-field ground deformations due to a seismic event are estimated, and the tunnel is designed to accommodate these deformations. Vertically propagating shear waves are the predominant form of earthquake loading that causes the ovaling deformations of circular tunnels to develop, resulting in a distortion of the cross sectional shape of the tunnel lining. In this paper, seismic behavior of circular tunnels has been investigated due to propagation of shear waves in the vertical direction using quasi-static analytical approaches as well as numerical methods. Analytical approaches are based on the closed-form solutions which compute the forces in the lining due to equivalent static ovaling deformations, while the numerical method carries out dynamic, nonlinear soil-structure interaction analysis. Based on comparisons made, the accuracy and reliability of the analytical solutions are evaluated and discussed. The results show that the axial forces determined using the analytical approaches are in acceptable agreement with numerical analysis results, while the computed bending moments are less comparable and show significant discrepancies. The differences between the analytical approaches are also investigated and addressed.
Effect of vertically propagating shear waves on seismic behavior of circular tunnels.
Akhlaghi, Tohid; Nikkar, Ali
2014-01-01
Seismic design loads for tunnels are characterized in terms of the deformations imposed on the structure by surrounding ground. The free-field ground deformations due to a seismic event are estimated, and the tunnel is designed to accommodate these deformations. Vertically propagating shear waves are the predominant form of earthquake loading that causes the ovaling deformations of circular tunnels to develop, resulting in a distortion of the cross sectional shape of the tunnel lining. In this paper, seismic behavior of circular tunnels has been investigated due to propagation of shear waves in the vertical direction using quasi-static analytical approaches as well as numerical methods. Analytical approaches are based on the closed-form solutions which compute the forces in the lining due to equivalent static ovaling deformations, while the numerical method carries out dynamic, nonlinear soil-structure interaction analysis. Based on comparisons made, the accuracy and reliability of the analytical solutions are evaluated and discussed. The results show that the axial forces determined using the analytical approaches are in acceptable agreement with numerical analysis results, while the computed bending moments are less comparable and show significant discrepancies. The differences between the analytical approaches are also investigated and addressed.
Shear-driven dynamo waves at high magnetic Reynolds number.
Tobias, S M; Cattaneo, F
2013-05-23
Astrophysical magnetic fields often display remarkable organization, despite being generated by dynamo action driven by turbulent flows at high conductivity. An example is the eleven-year solar cycle, which shows spatial coherence over the entire solar surface. The difficulty in understanding the emergence of this large-scale organization is that whereas at low conductivity (measured by the magnetic Reynolds number, Rm) dynamo fields are well organized, at high Rm their structure is dominated by rapidly varying small-scale fluctuations. This arises because the smallest scales have the highest rate of strain, and can amplify magnetic field most efficiently. Therefore most of the effort to find flows whose large-scale dynamo properties persist at high Rm has been frustrated. Here we report high-resolution simulations of a dynamo that can generate organized fields at high Rm; indeed, the generation mechanism, which involves the interaction between helical flows and shear, only becomes effective at large Rm. The shear does not enhance generation at large scales, as is commonly thought; instead it reduces generation at small scales. The solution consists of propagating dynamo waves, whose existence was postulated more than 60 years ago and which have since been used to model the solar cycle.
Li, Xiaochen; Liao, Shijun
2016-01-01
A system of two-dimensional, two coupled Faraday interfacial waves is experimentally observed at the two interfaces of the three layers of fluids (air, pure ethanol and silicon oil) in a sealed Hele-Shaw cell with periodic vertical vibration. The upper and lower Faraday waves coexist: the upper vibrates vertically, but the crests of the lower one oscillate horizontally with unchanged wave height and a frequency equal to the half of the forcing one of the vertically vibrating basin, while the troughs of the lower one always stay in the same place (relative to the basin). Besides, they are strongly coupled: the wave height of the lower Faraday wave is either a linear function (in the case of a fixed forcing frequency) or a parabolic function (in the case of a fixed acceleration amplitude) of that of the upper, with the same wave length. In addition, the upper Faraday wave temporarily loses its smoothness at around $t=T/4$ and $t=3T/4$, where $T$ denotes the wave period, and thus has fundamental difference from ...
A numerical study of nonlinear wave run-up on a vertical plate
DEFF Research Database (Denmark)
Jamois, Eric; Fuhrman, David R.; Bingham, Harry
2006-01-01
. This decreases the total number of unknowns in two horizontal dimensions from seven to five, simplifying the implementation, and leading to increased computational efficiency. Analysis of the embedded properties demonstrates that the resulting model has applications with errors of 2 to 3% for (wavenumber times...... demanding cases, where the local wave steepness can exceed (waveheight divided by wavelength) H / L = 0.20. The velocity potential model is additionally shown to have numerical advantages when dealing with wave-structure interactions, requiring less smoothing around exterior structural corners....
Continuous-wave optically pumped green perovskite vertical-cavity surface-emitter
Alias, Mohd Sharizal
2017-09-11
We report an optically pumped green perovskite vertical-cavity surface-emitter operating in continuous-wave (CW) with a power density threshold of ~89 kW/cm2. The device has an active region of CH3NH3PbBr3 embedded in a dielectric microcavity; this feat was achieved with a combination of optimal spectral alignment of the optical cavity modes with the perovskite optical gain, an adequate Q-factor of the microcavity, adequate thermal stability, and improved material quality with a smooth, passivated, and annealed thin active layer. Our results signify a way towards efficient CW perovskite emitter operation and electrical injection using low-cost fabrication methods for addressing monolithic optoelectronic integration and lasing in the green gap.
Directory of Open Access Journals (Sweden)
Nicole L. Jones
2008-06-01
Full Text Available A one-dimensional numerical model that simulates the effects of whitecapping waves was used to investigate the importance of whitecapping waves to vertical mixing at a 3-meter-deep site in Franks Tract in the Sacramento-San Joaquin Delta over an 11-day period. Locally-generated waves of mean period approximately 2 s were generated under strong wind conditions; significant wave heights ranged from 0 to 0.3 m. A surface turbulent kinetic energy flux was used to model whitecapping waves during periods when wind speeds > 5 m s-1 (62% of observations. The surface was modeled as a wind stress log-layer for the remaining 38% of the observations. The model results demonstrated that under moderate wind conditions (5–8 m s-1 at 10 m above water level, and hence moderate wave heights, whitecapping waves provided the dominant source of turbulent kinetic energy to only the top 10% of the water column. Under stronger wind (> 8 m s-1, and hence larger wave conditions, whitecapping waves provided the dominant source of turbulent kinetic energy over a larger portion of the water column; however, this region extended to the bottom half of the water column for only 7% of the observation period. The model results indicated that phytoplankton concentrations close to the bed were unlikely to be affected by the whitecapping of waves, and that the formation of concentration boundary layers due to benthic grazing was unlikely to be disrupted by whitecapping waves. Furthermore, vertical mixing of suspended sediment was unlikely to be affected by whitecapping waves under the conditions experienced during the 11-day experiment. Instead, the bed stress provided by tidal currents was the dominant source of turbulent kinetic energy over the bottom half of the water column for the majority of the 11-day period.
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J.C. Umavathi
2014-01-01
Full Text Available Fully developed laminar mixed convection in a corrugated vertical channel filled with two immiscible viscous fluids has been investigated. By using a perturbation technique, the coupled nonlinear equations governing the flow and heat transfer are solved. The fluids are assumed to have different viscosities and thermal conductivities. Separate solutions are matched at the interface using suitable matching conditions. The velocity, the temperature, the Nusselt number and the shear stress are analyzed for variations of the governing parameters such as Grashof number, viscosity ratio, width ratio, conductivity ratio, frequency parameter, traveling thermal temperature and are shown graphically. It is found that the Grashof number, viscosity ratio, width ratio and conductivity ratio enhance the velocity parallel to the flow direction and reduce the velocity perpendicular to the flow direction.
Sundkvist, David; Krasnoselskikh, V; Bale, S D; Schwartz, S J; Soucek, J; Mozer, F
2012-01-13
Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.
Energy Technology Data Exchange (ETDEWEB)
McKechnie, Scott [Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Booth, George H. [Theory and Simulation of Condensed Matter, King’s College London, The Strand, London WC2R 2LS (United Kingdom); Cohen, Aron J. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Cole, Jacqueline M., E-mail: jmc61@cam.ac.uk [Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Argonne National Laboratory, 9700 S Cass Avenue, Argonne, Illinois 60439 (United States)
2015-05-21
The best practice in computational methods for determining vertical ionization energies (VIEs) is assessed, via reference to experimentally determined VIEs that are corroborated by highly accurate coupled-cluster calculations. These reference values are used to benchmark the performance of density functional theory (DFT) and wave function methods: Hartree-Fock theory, second-order Møller-Plesset perturbation theory, and Electron Propagator Theory (EPT). The core test set consists of 147 small molecules. An extended set of six larger molecules, from benzene to hexacene, is also considered to investigate the dependence of the results on molecule size. The closest agreement with experiment is found for ionization energies obtained from total energy difference calculations. In particular, DFT calculations using exchange-correlation functionals with either a large amount of exact exchange or long-range correction perform best. The results from these functionals are also the least sensitive to an increase in molecule size. In general, ionization energies calculated directly from the orbital energies of the neutral species are less accurate and more sensitive to an increase in molecule size. For the single-calculation approach, the EPT calculations are in closest agreement for both sets of molecules. For the orbital energies from DFT functionals, only those with long-range correction give quantitative agreement with dramatic failing for all other functionals considered. The results offer a practical hierarchy of approximations for the calculation of vertical ionization energies. In addition, the experimental and computational reference values can be used as a standardized set of benchmarks, against which other approximate methods can be compared.
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Xu-Wei Bao
2012-02-01
Full Text Available Flow regimes of dry, stratified flow passing over an isolated two-dimensional (2-D orography mainly concentrate at two stagnation points. One occurs on the upslope of the orography owing to flow blocking; another is related to gravity wave breaking (GWB over the leeside. Smith (1979 put forward a hypothesis that the occurring of GWB is suppressed when the low-level vertical wind shear (VWS exceeds some value. In the present study, a theoretical solution in a two-layer linear model of orographic flow with a VWS over a bell-shaped 2-D orography is developed to investigate the effect of VWS on GWB's occurring over a range of surface Froude number Fr0=U0/Nh (U0 is surface wind speed, h is orography height and N is stability parameter, over which the GWB occurs first and the upstream flow blocking is excluded. Based on previous simulations and experiments, the range of surface Froude number selected is 0.6 ≤ Fr0≤2.0. Based on this solution, the conditions of surface wind speed (U0 and one-to-one matching critical VWS (Δuc for GWB's occurring are discussed. Over the selected range of Fr0, GWB's occurring will be suppressed if the VWS (Δu is larger than Δuc at given U0. Moreover, there is a maximum value of Δuc over the selected range of Fr0, which is labelled as Δumax, and its matching surface wind speed by U0m. Once the Δu is larger than Δumax, the flow will pass over the orography without GWB's occurring. That means, over the selected range of Fr0, the flow regime of 2-D orographic flow related to GWB occurring primarily will be absent when Δu > Δumax, regardless of the value for U0. In addition, the vertical profile of atmospheric stability and height of VWS could result in different features of mountain wave, which leads to different Δuc and Δumax for the GWB's occurring. The possible inaccuracy of estimated Δuc in the present linear model is also discussed.
Shock Tube Simulation of Low Mach Number Blast Waves
Morgan, R. G.; Gildfind, D. E.
The underground mining environment has always been high risk due to the presence of solid and gaseous flammables, and the potential for the creation of detonablemixtures. Following explosions in confined spaces, shock waves are generated and may propagate through the tunnel system, causing injuries and possibly initiating further combusting or detonating events. The ability to generate the conditions which exist post shock is a useful experimental tool for the study of such processes, and for the evaluation of techniques to control and limit propagation.
Hartmann, Matthias; Gashaj, Venera; Stahnke, Antje; Mast, Fred W
2014-08-01
Recent research in cognitive sciences shows a growing interest in spatial-numerical associations. The horizontal SNARC (spatial-numerical association of response codes) effect is defined by faster left-sided responses to small numbers and faster right-sided responses to large numbers in a parity judgment task. In this study we investigated whether there is also a SNARC effect for upper and lower responses. The grounded cognition approach suggests that the universal experience of "more is up" serves as a robust frame of reference for vertical number representation. In line with this view, lower hand responses to small numbers were faster than to large numbers (Experiment 1). Interestingly, the vertical SNARC effect reversed when the lower responses were given by foot instead of the hand (Experiments 2, 3, and 4). We found faster upper (hand) responses to small numbers and faster lower (foot) responses to large numbers. Additional experiments showed that spatial factors cannot account for the reversal of the vertical SNARC effect (Experiments 4 and 5). Our results question the view of "more is up" as a robust frame of reference for spatial-numerical associations. We discuss our results within a hierarchical framework of numerical cognition and point to a possible link between effectors and number representation.
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J. L. Innis
Full Text Available Zenith-directed Fabry-Perot Spectrometer (FPS and 3-Field Photometer (3FP observations of the λ630 nm emission (~240 km altitude were obtained at Davis station, Antarctica, during the austral winter of 1999. Eleven nights of suitable data were searched for significant periodicities common to vertical winds from the FPS and photo-metric variations from the 3FP. Three wave-like events were found, each of around one or more hours in duration, with periods around 15 minutes, vertical velocity amplitudes near 60 ms^{–1} , horizontal phase velocities around 300 ms^{–1} , and horizontal wavelengths from 240 to 400 km. These characteristics appear consistent with polar cap gravity waves seen by other workers, and we conclude this is a likely interpretation of our data. Assuming a source height near 125 km altitude, we determine the approximate source location by calculating back along the wave trajectory using the gravity wave property relating angle of ascent and frequency. The wave sources appear to be in the vicinity of the poleward border of the auroral oval, at magnetic local times up to 5 hours before local magnetic midnight.
Key words. Meteorology and atmospheric dynamics (thermospheric dynamics; waves and tides
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T. Maruyama
2016-02-01
Full Text Available The vertical ground motion of seismic surface waves launches acoustic waves into the atmosphere and induces ionospheric disturbances. Disturbances due to Rayleigh waves near the short-period Airy phase appear as wavy fluctuations in the virtual height of an ionogram and have a multiple-cusp signature (MCS when the fluctuation amplitude is increased. An extremely developed MCS was observed at Kazan, Russia, after the 2010 M 8.8 Chile earthquake. The ionogram exhibited steep satellite traces for which the virtual heights increased rapidly with frequency starting near the top of cusps and continuing for 0.1–0.2 MHz. This complicated ionogram was analyzed by applying a ray tracing technique to the radio wave propagation in the ionosphere that was perturbed by acoustic waves. Acoustic wavefronts were inclined by the effects of finite Rayleigh wave velocity and sound speed in the thermosphere. The satellite echo traces were reproduced by oblique returns from the inclined wavefronts, in addition to the nearly vertical returns that are responsible for the main trace.
Papoutsellis, Christos; Athanassoulis, Gerassimos; Charalampopoulos, Alexis-Tzianni
2017-04-01
In this work, we investigate the transformations that solitary surface waves undergo during their interaction with uneven seabed and/or fully reflective vertical boundaries. This is accomplished by performing simulations using a non-local Hamiltonian formulation, taking into account full nonlinearity and dispersion, in the presence of variable seabed [1]. This formulation is based on an exact coupled-mode representation of the velocity potential, leading to efficient and accurate computations of the Dirichlet to Neumann operator, required in Zakharov/Craig-Sulem formulation [2], [3]. In addition, it allows for the efficient computation of wave kinematics (velocity, acceleration) and the pressure field, in the time-dependent fluid domain, up to its physical boundaries. Such computations are performed for the case of high-amplitude solitary waves interacting with varying bathymetry and/or a vertical wall, shedding light to their kinematics and dynamics. More specifically, we first consider two benchmark cases, namely the transformation of solitary waves over a plane beach [4], and the reflection of solitary waves on a vertical wall [5]. As a further step, results on the scattering/reflection of a solitary wave due to an undulating seabed, and on the disintegration of a solitary wave travelling form shallow to deep water are also presented. References:[1] G.A. Athanassoulis. & Ch.E. Papoutsellis, in Volume 7: Ocean Engineering, ASME, OMAE2015-41452, p. V007T06A029 (2015)[2] W. Craig, C. Sulem, J. Comp. Phys. 108, 73-83 (1993) [3] V. Zakharov, J. Appl. Mech. Tech. Phys 9, 86-94 (1968)[4] S. Grilli, R. Subramanya, T. Svendsen. & J. Veeramony, J. Waterway, Port, Coastal, Ocean Eng. 120(6), 609-628. (1994)[5] Y.Y. Chen, C. Kharif , J.H. Yang, H.C. Hsu, J. Touboul & J. Chambarel, Eur. J. Mech B-Fluid 49, 20-28 (2015)
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C. Bossuet
Full Text Available Systematic westerly biases in the southern hemisphere wintertime flow and easterly equatorial biases are experienced in the Météo-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a significant deceleration of the mean flow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a significant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the Météo-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the first, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere, and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere; the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the finer tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the
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C. Bossuet
1998-02-01
Full Text Available Systematic westerly biases in the southern hemisphere wintertime flow and easterly equatorial biases are experienced in the Météo-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a significant deceleration of the mean flow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a significant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the Météo-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the first, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere, and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere; the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the finer tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the
Arshinov, Mikhail Yu.; Belan, Boris D.; Paris, Jean-Daniel; Machida, Toshinobu; Kozlov, Alexandr; Malyskin, Sergei; Simonenkov, Denis; Davydov, Denis; Fofonov, Alexandr
2016-04-01
Knowledge of the vertical distribution of aerosols particles is very important when estimating aerosol radiative effects. To date there are a lot of research programs aimed to study aerosol vertical distribution, but only a few ones exist in such insufficiently explored region as Siberia. Monthly research flights and several extensive airborne campaigns carried out in recent years in Siberian troposphere allowed the vertical distribution of aerosol number concentration to be summarized. In-situ aerosol measurements were performed in a wide range of particle sizes by means of improved version of the Novosibirsk-type diffusional particle sizer and GRIMM aerosol spectrometer Model 1.109. The data on aerosol vertical distribution enabled input parameters for the empirical equation of Jaenicke (1993) to be derived for Siberian troposphere up to 7 km. Vertical distributions of aerosol number concentration in different size ranges averaged for the main seasons of the year will be presented. This work was supported by Interdisciplinary integration projects of the Siberian Branch of the Russian Academy of Science No. 35, No. 70 and No. 131; the Branch of Geology, Geophysics and Mining Sciences of RAS (Program No. 5); and Russian Foundation for Basic Research (grant No. 14-05-00526). Jaenicke R. Tropospheric aerosols, in Aerosol-Cloud-Climate Interactions, edited by P.V. Hobs. -Academic Press, San Diego, CA, 1993.- P. 1-31.
Room temperature continuous wave InGaAsN quantum well vertical cavity lasers emitting at 1.3 um
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CHOQUETTE,KENT D.; KLEM,JOHN F.; FISCHER,ARTHUR J.; SPAHN,OLGA B.; ALLERMAN,ANDREW A.; FRITZ,IAN J.; KURTZ,STEVEN R.; BREILAND,WILLIAM G.; SIEG,ROBERT M.; GEIB,KENT M.; SCOTT,J.W.; NAONE,R.L.
2000-06-05
Selectively oxidized vertical cavity lasers emitting at 1294 nm using InGaAsN quantum wells are reported for the first time which operate continuous wave at and above room temperature. The lasers employ two n-type Al{sub 0.94}Ga{sub 0.06}As/GaAs distributed Bragg reflectors each with a selectively oxidized current aperture adjacent to the optical cavity, and the top output mirror contains a tunnel junction to inject holes into the active region. Continuous wave single mode lasing is observed up to 55 C. These lasers exhibit the longest wavelength reported to date for vertical cavity surface emitting lasers grown on GaAs substrates.
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Kesayoshi Hadano
2017-05-01
Full Text Available As a new technical approach, wave energy converter by using vertical motion of water in the multiple water chambers were developed to realize actual wave power generation as eco-environmental renewable energy. And practical use of wave energy converter was actually to require the following conditions: (1 setting up of the relevant device and its application to wave power generation in case that severe wave loading is avoided; (2 workability in installation and maintenance operations; (3 high energy conversion potential; and (4 low cost. In this system, neither the wall(s of the chambers nor the energy conversion device(s are exposed to the impulsive load due to water wave. Also since this system is profitable when set along the jetty or along a long floating body, installation and maintenance are done without difficulty and the cost is reduced. In this paper, we describe the system which consists of a float, a shaft connected with another shaft, a rack and pinion arrangement, a ratchet mechanism, and rotary type generator(s. Then, we present the dynamics model for evaluating the output electric power, and the results of numerical calculation including the effect of the phase shift of up/down motion of the water in the array of water chambers aligned along the direction of wave propagation.
Wave-Related Reynolds Number Parameterizations of CO2 and DMS Transfer Velocities
Brumer, Sophia E.; Zappa, Christopher J.; Blomquist, Byron W.; Fairall, Christopher W.; Cifuentes-Lorenzen, Alejandro; Edson, James B.; Brooks, Ian M.; Huebert, Barry J.
2017-10-01
Predicting future climate hinges on our understanding of and ability to quantify air-sea gas transfer. The latter relies on parameterizations of the gas transfer velocity k, which represents physical mass transfer mechanisms and is usually parameterized as a nonlinear function of wind forcing. In an attempt to reduce uncertainties in k, this study explores empirical parameterizations that incorporate both wind speed and sea state dependence via wave-wind and breaking Reynolds numbers, RH and RB. Analysis of concurrent eddy covariance gas transfer and measured wavefield statistics supplemented by wave model hindcasts shows for the first time that wave-related Reynolds numbers collapse four open ocean data sets that have a wind speed dependence of CO2 transfer velocity ranging from lower than quadratic to cubic. Wave-related Reynolds number and wind speed show comparable performance for parametrizing dimethyl sulfide (DMS) which, because of its higher solubility, is less affected by bubble-mediated exchange associated with wave breaking.
Liu, Wen-Jie; Hu, Xiao-Long; Ying, Lei-Ying; Zhang, Jiang-Yong; Zhang, Bao-Ping
2014-06-01
Continuous wave (CW) lasing of electrically injected GaN-based vertical cavity surface emitting lasers (VCSELs) was achieved at room temperature. First, a high quality factor (Q) VCSEL-structured device with very narrow linewidth of 0.12 nm, corresponding to a Q-value of 3570 was obtained through two-step substrate transfer technique. However, poor heat dissipation ability prevented the device from lasing. Based on the high-Q resonant cavity design, we further fabricated vertical-structured VCSELs through metal bonding technique on Si substrate. CW lasing from vertical-structured VCSELs was observed with threshold current of density of 1.2 kA/cm2 and lasing linewidth of about 0.20 nm.
Charland, Jenna; Touboul, Julien; Rey, Vincent
2013-04-01
Wave propagation against current : a study of the effects of vertical shears of the mean current on the geometrical focusing of water waves J. Charland * **, J. Touboul **, V. Rey ** jenna.charland@univ-tln.fr * Direction Générale de l'Armement, CNRS Délégation Normandie ** Université de Toulon, 83957 La Garde, France Mediterranean Institute of Oceanography (MIO) Aix Marseille Université, 13288 Marseille, France CNRS/INSU, IRD, MIO, UM 110 In the nearshore area, both wave propagation and currents are influenced by the bathymetry. For a better understanding of wave - current interactions in the presence of a 3D bathymetry, a large scale experiment was carried out in the Ocean Basin FIRST, Toulon, France. The 3D bathymetry consisted of two symmetric underwater mounds on both sides in the mean wave direction. The water depth at the top the mounds was hm=1,5m, the slopes of the mounds were of about 1:3, the water depth was h=3 m elsewhere. For opposite current conditions (U of order 0.30m/s), a huge focusing of the wave up to twice its incident amplitude was observed in the central part of the basin for T=1.4s. Since deep water conditions are verified, the wave amplification is ascribed to the current field. The mean velocity fields at a water depth hC=0.25m was measured by the use of an electromagnetic current meter. The results have been published in Rey et al [4]. The elliptic form of the "mild slope" equation including a uniform current on the water column (Chen et al [1]) was then used for the calculations. The calculated wave amplification of factor 1.2 is significantly smaller than observed experimentally (factor 2). So, the purpose of this study is to understand the physical processes which explain this gap. As demonstrated by Kharif & Pelinovsky [2], geometrical focusing of waves is able to modify significantly the local wave amplitude. We consider this process here. Since vertical velocity profiles measured at some locations have shown significant
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Hyuck-Min Kweon
2013-12-01
Full Text Available A steel-type breakwater that uses a submerged dual horizontal porous plate was originally proposed by Kweon et al. (2005, and its hydrodynamic characteristics and design methodology were investigated in a series of subsequent researches. In particular, Kweon et al. (2011 proposed a method of estimating the vertical uplift force that acts on the horizontal plate, applicable to the design of the pile uplift drag force. However, the difference between the method proposed by Kweon et al. (2011, and the wave force measured at a different time without a phase difference, have not yet been clearly analyzed. In this study, such difference according to the method of estimating the wave force was analyzed, by measuring the wave pressure acting on a breakwater model. The hydraulic model test was conducted in a two-dimensional wave flume of 60.0 m length, 1.5 m height and 1.0 m width. The steepness range of the selected waves is 0.01~0.03, with regular and random signals. 20 pressure gauges were used for the measurement. The analysis results showed that the wave force estimate in the method of Kweon et al. (2011 was smaller than the wave force calculated from the maximum pressure at individual points, under a random wave action. Meanwhile, the method of Goda (1974 that was applied to the horizontal plate produced a smaller wave force, than the method of Kweon et al. (2011. The method of Kweon (2011 was already verified in the real sea test of Kweon et al. (2012, where the safety factor of the pile uplift force was found to be greater than 2.0. Based on these results, it was concluded that the method of estimating the wave force by Kweon et al. (2011 can be satisfactorily used for estimating the uplift force of a pile.
National Aeronautics and Space Administration — Shock Wave / Turbulent Boundary Layer Flows at High Mach Numbers. This web page provides data from experiments that may be useful for the validation of turbulence...
Gigiyatullin, Ayrat; Kurkin, Andrey; Kurkina, Oxana; Rouvinskaya, Ekaterina; Rybin, Artem
2017-04-01
With the use of the Gardner equation, or its variable-coefficient forms, the velocity components of fluid particles in the vertical section induced by a passage of internal waves can be estimated in weakly nonlinear limit. The horizontal velocity gives the greatest contribution into the local current speed. This is a typical property of long waves. This feature of an internal wave field may greatly contribute to the local sediment transport and/or resuspension. The velocity field induced by mode I and II internal solitary waves are studied. The contribution from second-order terms in asymptotic expansion into the horizontal velocity is estimated for the models of two- and three-layer fluid density stratification for solitons of positive and negative polarity, as well as for breathers of different shapes and amplitudes. The influence of the nonlinear correction manifests itself firstly in the shape of the lines of zero horizontal velocity: they are curved and the shape depends on the soliton amplitude and polarity while for the leading-order wave field they are horizontal. Also the wavefield accounting for the nonlinear correction for mode I waves has smaller maximal absolute values of negative velocities (near-surface for the soliton of elevation, and near-bottom for the soliton of depression) and larger maximums of positive velocities. Thus for the solitary internal waves of positive polarity weakly nonlinear theory overestimates the near-bottom velocities and underestimates the near-surface current. For solitary waves of negative polarity, which are the most typical for hydrological conditions of low and middle latitudes, the situation is the opposite. Similar estimations are produced for mode II waves, which possess more complex structure. The presented results of research are obtained with the support of the Russian Foundation for Basic Research grant 16-35-00413.
Digital Repository Service at National Institute of Oceanography (India)
Horii, T.; Masumoto, Y.; Ueki, I.; PrasannaKumar, S.; Mizuno, K.
for African-Asian-Australian Monsoon Analysis and Prediction, in October-November 2006. Using an array of four subsurface moored acoustic Doppler current profilers, we estimated vertical velocity by applying the continuity equation. Results indicated...
Alexander, Pavelyev; Kefei, Zhang; Vladimir, Gubenko; Erjiang, Fu; Chuan-Sheng, Wang; Yuei-An, Liou; Yuriy, Kuleshov
2010-05-01
Identification and radio vision of the vertical structure of the layers and wave activity in the atmosphere Alexander Pavelyev, Vladimir Gubenko Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Fryazino, Russia Kefei Zhang, Erjiang Fu and Chuan-Sheng Wang School of Mathematical and Geospatial Sciences, RMIT University, Melbourne, Australia Yuei-An Liou Center for Space and Remote Sensing Research (CSRSR), National Central University, Jhongli, Taiwan Yuriy Kuleshov National Climate Centre, Bureau of Meteorology, Melbourne, Australia From an analysis of the CHAMP (Challenging Minisatellite Payload, Germany) and the FORMOSAT-3/COSMIC (FORMOSA Satellite Constellation Observing Systems for Meteorology, Ionosphere, and Climate mission, USA -Taiwan) satellite data it follows that the second-order time derivative of the eikonal (eikonal acceleration) and the Doppler frequency shift are two most important parameters indispensable for the radio vision of layers in the atmosphere and the ionosphere. Measurements of the temporal evolution of the Doppler shift permit one to study the vertical structure of the atmosphere under the condition of its spherical symmetry. Analysis of the amplitude and phase of interrelated variations in the eikonal acceleration and radio-wave intensity permits one to detect and identify the layers in the atmosphere and ionosphere. Therefore the eikonal acceleration/intensity technique can be applied to separate the influence of layered structures from contributions of irregularities and turbulence in the atmosphere. In many cases the layered structures in the atmosphere indicate quasi-periodical altitude dependence that reveals their wave origin. The altitude profile of the vertical gradient of refractivity in the layered structures can be used to find the main characteristics of the internal wave activity with a global coverage. When the type of internal waves are not known, the height dependence of the vertical gradient
DEFF Research Database (Denmark)
Cheng, Zhengshun; Aagaard Madsen, Helge; Gao, Zhen
2017-01-01
Floating vertical axis wind turbines (VAWTs) are promising solutions for exploiting the wind energy resource in deep waters due to their potential cost-of-energy reduction. The number of blades is one of the main concerns when designing a VAWT for offshore application. In this paper, the effect...... of blade number on the performance of VAWTs and dynamic behavior of floating VAWTs was comprehensively studied in a fully coupled aero-hydro-servo-elastic way. Three VAWTs with straight and parallel blades, with identical solidity and with a blade number varying from two to four, were designed using...... the actuator cylinder method and adapted to a semi-submersible platform. A generator torque controller was also designed based on a PI control algorithm. Time domain simulations demonstrated that the aerodynamic loads and structural responses are strongly dependent on the number of blades. In particular...
Model for modulated and chaotic waves in zero-Prandtl-number ...
Indian Academy of Sciences (India)
The effects of time-periodic forcing in a few-mode model for zero-Prandtl-number convection with rigid body rotation is investigated. The time-periodic modulation of the rotation rate about the vertical axis and gravity modulation are considered separately. In the presence of periodic variation of the rotation rate, the model ...
Wave Characteristics of Falling Film on Inclination Plate at Moderate Reynolds Number
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Chuan Lu
2016-01-01
Full Text Available Falling water film on an inclined plane is studied by shadowgraphy. The ranges of inclination angle and the film Reynolds number are, respectively, up to 21° and 60. Water is used as working fluid. The scenario of wave regime evolution is identified as three distinctive regimes, namely, initial quiescent smooth film flow, two-dimensional regular solitary wave pattern riding on film flow, and three-dimensional irregular wave pattern. Three characteristic parameters of two-dimensional solitary wave pattern, namely, inception length, primary pulse spacing, and propagation velocity, are examined, which are significant in engineering applications for estimation of heat and mass transfer on film flow. The present experimental data are well in agreement with the Koizumi correlations, the deviation from which is limited to 20% and 15%, respectively, for primary pulse spacing and propagation velocity. Through the scrutiny of the present experimental observation, it is concluded that wave evolution on film flow at the moderate Reynolds number is controlled by gravity and drag and the Rayleigh-Taylor instability that occurred on the steep front of primary pulse triggers the disintegration of continuous two-dimensional regular solitary wave pattern into three-dimensional irregular wave pattern.
Experimental Study of Wave Forces on Vertical Circular Cylinders in Long and Short Crested Sea
DEFF Research Database (Denmark)
Høgedal, Michael
The three-dimensional structure of ocean waves is generally ignored in favour of two-dimensional waves, which are easier to handle from a theoretical and computational point of view. For design fixed structures where horizontal in-line and resultant wave forces are important, this is normally...... cylinder in the near-surface-zone are investigated and suggestions for the force coefficients Cd, Cm and C1 in this region presented. The approximately 100 physical experiments have been condueted using a newly designed 2nd generation smooth circular cylinder with diameter, D = 0.0635 m and instrumented...... on the safe side, as the directional spreading of the wave field Ieads to reduced horizontal velocities and acceleration; in the fluid and hence a reduction of the resultant and in-line wave forces on the structure. The directional spreading of the horizontal velocity field generally causes an increase...
DEFF Research Database (Denmark)
Andersen, Ingrid Marie Vincent; Jensen, Jørgen Juncher
2012-01-01
for the 9,400 TEU container ship used as case-ship in the EU project TULCS (Tools for Ultra Large Container Ships). A non-linear time-domain strip theory is used for the hydrodynamic analysis of the vertical bending moment amidships in sagging and hogging conditions for a flexible and a rigid modelling...... of the ship. The theory takes into account non-linear radiation forces (memory effects) through the use of a set of higher order differential equations. The non-linear hydrostatic restoring forces and non-linear Froude-Krylov forces are determined accurately at the instantaneous position of the ship...... analysis is done using the First Order Reliability Method (FORM) supplemented with Monte Carlo simulations. Furthermore, strip-theory calculations are compared to model tests in regular waves of different wave lengths using a segmented, flexible model of the case-ship and good agreement is obtained...
Berngardt, O I; Podlesnyi, A V; Kurkin, V I; Zherebtsov, G A
2016-01-01
Based on the Irkutsk fast monostatic chirp ionosonde data we made a statistical analysis of ionospheric effects for 28 earthquakes which appeared in 2011-2016 years. These effects are related with surface (Rayleigh) seismic waves far from epicenter. The analysis has shown that nine of these earthquakes were accompanied by vertical midscale ionospheric irregularities (multicusp). To estimate the ionospheric efficiency of the seismic waves we proposed new index $K_{W}$. The index estimates the maximal amplitude of the acoustic shock wave generated by given spatial distribution of seismic vibrations and related with maximal spectral power of seismic oscillations. Based on the analysis of experimental data we have shown that earthquake-related multicusp is observed mostly at daytime [07:00-17:00]LST for $K_{W}\\ge4.7$. The observations of intrinsic gravity waves by GPS technique in the epicenter vicinity do not show such a daytime dependence. Based on 24/05/2013 Okhotsk Sea earthquake example, we demonstrated that...
Berngardt, O. I.; Perevalova, N. P.; Podlesnyi, A. V.; Kurkin, V. I.; Zherebtsov, G. A.
2017-04-01
Based on the Irkutsk fast monostatic chirp ionosonde data, we made a statistical analysis of ionospheric effects for 28 earthquakes which appeared in 2011-2016 years. These effects are related with surface (Rayleigh) seismic waves far from epicenter. The analysis has shown that nine of these earthquakes were accompanied by vertical midscale ionospheric irregularities (multicusp). To estimate the ionospheric efficiency of the seismic waves, we proposed new index KW. The index estimates the maximal amplitude of the acoustic shock wave generated by given spatial distribution of seismic vibrations and related with maximal spectral power of seismic oscillations. Based on the analysis of experimental data, we have shown that earthquake-related multicusp (5-25 s irregularities) is observed mostly at daytime [07:00-17:00] LST for KW≥4.7. The observations of acoustic waves by GPS technique in the epicenter vicinity (120-600 s irregularities) do not show such a daytime dependence. Based on 24 May 2013 Okhotsk Sea earthquake example, we demonstrated that deep-focus earthquakes can produce strong multicusp far from the epicenter, although do not produce significant GPS ionospheric response in the epicenter vicinity.
Liu, Zhongxian; Wang, Yirui; Liang, Jianwen
2016-06-01
The scattering of plane harmonic P and SV waves by a pair of vertically overlapping lined tunnels buried in an elastic half space is solved using a semi-analytic indirect boundary integration equation method. Then the effect of the distance between the two tunnels, the stiffness and density of the lining material, and the incident frequency on the seismic response of the tunnels is investigated. Numerical results demonstrate that the dynamic interaction between the twin tunnels cannot be ignored and the lower tunnel has a significant shielding effect on the upper tunnel for high-frequency incident waves, resulting in great decrease of the dynamic hoop stress in the upper tunnel; for the low-frequency incident waves, in contrast, the lower tunnel can lead to amplification effect on the upper tunnel. It also reveals that the frequency-spectrum characteristics of dynamic stress of the lower tunnel are significantly different from those of the upper tunnel. In addition, for incident P waves in low-frequency region, the soft lining tunnels have significant amplification effect on the surface displacement amplitude, which is slightly larger than that of the corresponding single tunnel.
Vertical motion of ionization induced by the linear interaction of tides with planetary waves
Directory of Open Access Journals (Sweden)
M. Voiculescu
2003-07-01
Full Text Available Experimental findings have shown that travelling planetary waves modulate the occurrence of mid-latitude sporadic-E-layers. Using a simple quantitative model, we analyse the effects of the linear interaction between tides and planetary waves on ion motion. Besides an expected variation of the dumping height, it is found that the boundaries of the oscillations induced by the descending semidiurnal tide are significantly modified by the presence of the planetary wave. The height variations of the ionisation cause planetary wave modulations of the metallic ion content in the background plasma density. This could explain the long-term variation found in the occurrence of strong Es layers. The fact that the dumping height variations are strongly influenced by the tidal phase velocity and amplitude, together with the variability of the metallic ion content, could contribute to the understanding of the sporadic nature of the E-layers.Key words. Ionosphere (Ionosphere-atmosphere interactions; Mid-latitude ionosphere
Lu, X.; Chen, C.; Chu, X.; Nguyen, V.; Smith, A. K.
2016-12-01
In the polar winter stratosphere, a group of eastward propagating planetary waves (relative to ground) are generated by the instability of the polar vortex and dominate the variability of chemistry and dynamics of the atmosphere. The strong polar vortex consisting of strong eastward winds support the propagation of these planetary waves until they reach the critical filtering level in the upper stratosphere. However, lidar measurements at McMurdo (78S), Antarctica illustrate the significant signatures of the planetary waves up to 110 km, making it intriguring to identify the wave source. The SD-WACCM well reproduces both local and global structure of these planeaty waves as compared with the ground-based lidar and satellite (MLS), which is thus used to derive the EP flux induced by these planetary waves. In addition to a region of positive EP flux divergence in the stratosphere where we expect to have the stratospheric planetary waves generated, a localized EP flux divergence is also found in the mesosphere and lower thermosphere (MLT) at high latitudes, which likely triggers the generation the waves locally or amplifies those waves that survive from the critical level filtering. By incorporating the background winds from SD-WACCM, a stand-alone mechanistic model with gravity wave effect parameterized is applied to investigate the relative importance of the vertical propagation and in-situ instability to the generation of the planetary waves in the mesosphere and lower thermosphere and whether and how there two processes are coupled together. The gravity wave effect on planetary waves is also addressed. This study provides insights on the vertical wave coupling via wave-wave and wave-mean interactions in the polar winter region.
Zhang, Kun; Wang, Dongfang; Bian, Qinggen; Duan, Yusen; Zhao, Mengfei; Fei, Dongnian; Xiu, Guangli; Fu, Qingyan
2017-04-01
A tethered balloon-based measurement campaign of particle number concentration (PNC) and particle number size distribution (PNSD) in the size range of 15.7-661.2 nm was conducted within the lower troposphere of 1000 m in Shanghai, a Chinese megacity, during December of 2015. The meteorological conditions, PNC, and PNSD were synchronously measured at the ground-based station as well as by the tethered balloon. On ground level, the 88.2 nm particles were found to have the highest PNC. The Pearson correlation analysis based on the ground level data showed NO2 had a strong correlation with PNC. The synchronous measurement of PNC and PNSD at the ground station and on the tethered balloon showed that the 15.7-200 nm particles had higher PNC on ground level, but the PNC of 200-661.2 nm particles was higher at 400 m. One haze event (Dec 22nd-Dec 23rd) was selected for detailed discussion on the variation of vertical profiles of PNSD and PNC. The vertical distribution of characteristics of PNC and PNSD were observed and compared. Results indicated that the highest MaxDm (the diameter with the highest PNC) during those three launches all appeared at a high altitude, usually above 300 m. Compared to the clean days, the relatively bigger MaxDm at each height in the haze days also indicated regional transport of pollutants might contribute to more to that haze event.
Effect of the number of blades and solidity on the performance of a vertical axis wind turbine
Delafin, PL; Nishino, T.; Wang, L.; Kolios, A.
2016-09-01
Two, three and four bladed ϕ-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.
DEFF Research Database (Denmark)
Gutin, Gregory; Yeo, Anders
2001-01-01
A digraph obtained by replacing each edge of a complete multipartite graph by an arc or a pair of mutually opposite arcs with the same end vertices is called a semicomplete multipartite digraph. L. Volkmann conjectured that l≤2c−1, where l (c, respectively) is the number of vertices in a longest ...
Model for modulated and chaotic waves in zero-Prandtl-number ...
Indian Academy of Sciences (India)
convective flow at the onset is quasiperiodic is not studied before. We present here the study of the role of external modulation on the quasiperiodic waves in the model of zero-Prandtl-number convection with rotation. We consider the effect of modulation of two parameters separately: first, the time-periodic rotation about a.
Extreme value prediction of the wave-induced vertical bending moment in large container ships
DEFF Research Database (Denmark)
Andersen, Ingrid Marie Vincent; Jensen, Jørgen Juncher
2015-01-01
Container ships of today are becoming increasingly larger. The increased ship size implies lower natural hull frequencies which influence the hull girder response in waves. The large bow and stern flare of container ships make them vulnerable to whipping-induced loads, and whipping loads may...
Vertical motion of ionization induced by the linear interaction of tides with planetary waves
Directory of Open Access Journals (Sweden)
M. Voiculescu
Full Text Available Experimental findings have shown that travelling planetary waves modulate the occurrence of mid-latitude sporadic-E-layers. Using a simple quantitative model, we analyse the effects of the linear interaction between tides and planetary waves on ion motion. Besides an expected variation of the dumping height, it is found that the boundaries of the oscillations induced by the descending semidiurnal tide are significantly modified by the presence of the planetary wave. The height variations of the ionisation cause planetary wave modulations of the metallic ion content in the background plasma density. This could explain the long-term variation found in the occurrence of strong E_{s} layers. The fact that the dumping height variations are strongly influenced by the tidal phase velocity and amplitude, together with the variability of the metallic ion content, could contribute to the understanding of the sporadic nature of the E-layers.
Key words. Ionosphere (Ionosphere-atmosphere interactions; Mid-latitude ionosphere
The effect of non-linear wave in front of vertical wall using bi ...
African Journals Online (AJOL)
From the subsequent calculation carried out, it was found that on deep water the parameter 2 tends to zero and 1 tends to , which is twice as much as the value of for the progressive waves on deep water. Moreover, for a fixed kd, this theory suggests that the non-linear effects increase while approaching the bottom, which is ...
Directory of Open Access Journals (Sweden)
Giancarlo Alfonsi
2015-08-01
Full Text Available A computational analysis is performed on the diffraction of water waves induced by large-diameter, surface-piercing, vertical circular cylinder. With reference to linear-wave cases, the phenomenon is preliminarly considered in terms of velocity potential, a simplified theoretical framework in which both hypotheses of inviscid fluid and irrotational flow are incorporated. Then, and as a first-approximation analysis, the Euler equations in primitive variables are considered (a framework in which the fluid is still handled as inviscid, but the field can be rotational. Finally, the real-fluid behavior is analyzed, by numerically integrating the full Navier-Stokes equations (viscous fluid and rotational field in their velocity-pressure formulation, by following the approach of the Direct Numerical Simulation (DNS, no models are used for the fluctuating portion of the velocity field. For further investigation of the flow fields, the swirling-strength criterion for flow-structure extraction, and the Karhunen-Loève (KL decomposition technique for the extraction of the most energetic flow modes respectively, are applied to the computed fields. It is found that remarkable differences exist between the wave-induced fields, as derived within the different computing frameworks tested.
Higher P-Wave Dispersion in Migraine Patients with Higher Number of Attacks
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A. Koçer
2012-01-01
Full Text Available Objective and Aim. An imbalance of the sympathetic system may explain many of the clinical manifestations of the migraine. We aimed to evaluate P-waves as a reveal of sympathetic system function in migraine patients and healthy controls. Materials and Methods. Thirty-five episodic type of migraine patients (complained of migraine during 5 years or more, BMI < 30 kg/m2 and 30 controls were included in our study. We measured P-wave durations (minimum, maximum, and dispersion from 12-lead ECG recording during pain-free periods. ECGs were transferred to a personal computer via a scanner and then used for magnification of x400 by Adobe Photoshop software. Results. P-wave durations were found to be similar between migraine patients and controls. Although P WD (P-wave dispersion was similar, the mean value was higher in migraine subjects. P WD was positively correlated with P max (P<0.01. Attacks number per month and male gender were the factors related to the P WD (P<0.01. Conclusions. Many previous studies suggested that increased sympathetic activity may cause an increase in P WD. We found that P WD of migraine patients was higher than controls, and P WD was related to attacks number per month and male gender. Further studies are needed to explain the chronic effects of migraine.
Real-Time Vertical Temperature, and Velocity Profiles from a Wave Glider
2012-09-30
Liquid Robotics navigated a Wave Glider from San Diego to Hawaii on a 82 day-long voyage that covered approximately 2500 nautical miles (http...Gawarkiewicz, G., et al. (2011), Circulation and Intrusions Northeast of Taiwan: Chasing and Predicting Uncertainty in the Cold Dome ., Oceanography, 24(4), 110...121. Lee, D.-K., and P. Niiler (2010), Influence of warm SST anomalies formed in the eastern Pacific subduction zone on recent El Nino events, J Mar Res, 68(3-4), 459-477.
Vertical slice modelling of nonlinear Eady waves using a compatible finite element method
Yamazaki, Hiroe; Shipton, Jemma; Cullen, Michael J. P.; Mitchell, Lawrence; Cotter, Colin J.
2017-08-01
A vertical slice model is developed for the Euler-Boussinesq equations with a constant temperature gradient in the direction normal to the slice (the Eady-Boussinesq model). The model is a solution of the full three-dimensional equations with no variation normal to the slice, which is an idealised problem used to study the formation and subsequent evolution of weather fronts. A compatible finite element method is used to discretise the governing equations. To extend the Charney-Phillips grid staggering in the compatible finite element framework, we use the same node locations for buoyancy as the vertical part of velocity and apply a transport scheme for a partially continuous finite element space. For the time discretisation, we solve the semi-implicit equations together with an explicit strong-stability-preserving Runge-Kutta scheme to all of the advection terms. The model reproduces several quasi-periodic lifecycles of fronts despite the presence of strong discontinuities. An asymptotic limit analysis based on the semi-geostrophic theory shows that the model solutions are converging to a solution in cross-front geostrophic balance. The results are consistent with the previous results using finite difference methods, indicating that the compatible finite element method is performing as well as finite difference methods for this test problem. We observe dissipation of kinetic energy of the cross-front velocity in the model due to the lack of resolution at the fronts, even though the energy loss is not likely to account for the large gap on the strength of the fronts between the model result and the semi-geostrophic limit solution.
Wave-number-frequency spectrum for turbulence from a random sweeping hypothesis with mean flow.
Wilczek, M; Narita, Y
2012-12-01
We derive the energy spectrum in wave-number-frequency space for turbulent flows based on Kraichnan's idealized random sweeping hypothesis with additional mean flow, which yields the instantaneous energy spectrum multiplied by a Gaussian frequency distribution. The model spectrum has two adjustable parameters, the mean flow velocity and the sweeping velocity, and has the property that the power-law index of the wave-number spectrum translates to the frequency spectrum, invariant for arbitrary choices of the mean velocity and sweeping velocity. The model spectrum incorporates both Taylor's frozen-in flow approximation and the random sweeping approximation in a natural way and can be used to distinguish between these two effects when applied to real time-resolved multipoint turbulence data. Evaluated in real space, its properties with respect to space-time velocity correlations are discussed, and a comparison to the recently introduced elliptic model is drawn.
A systematic approach for quantifying wave propagation in vertically inhomogeneous media
Foster, Douglas J.; Lane, F. D.; Zhao, Zeyu
2017-08-01
We examine wave propagation in transversely homogeneous media characterized by variations of properties with respect to depth. Our intent is to provide analytic formulae that quantify scattering effects from fine scale inhomogeneities typically observed on seismic field data. We employ a Born scattering series approach that systematically includes higher order phenomena (transmission losses, mode conversions and multiples). Although, the Born series is inexact, it provides useful approximations. Analytic examples show how various terms of the Born series include higher order scattering effects. We also document the inexact nature of the approximation. Numerical examples illustrate the magnitude of scattering induced time delays and attenuation. A generalized (complex) reflection coefficient is introduced to describe backscattered energy from a discrete interval instead of an isolated interface. The main goal of this paper is to quantify thin-bed scattering in order to provide a more complete representation of seismic reflections in realistic geological settings. It is our hope that this insight will lead to useful applications.
Louie, J. N.; Basler-Reeder, K.; Kent, G. M.; Pullammanappallil, S. K.
2015-12-01
Simultaneous joint seismic-gravity optimization improves P-wave velocity models in areas with sharp lateral velocity contrasts. Optimization is achieved using simulated annealing, a metaheuristic global optimization algorithm that does not require an accurate initial model. Balancing the seismic-gravity objective function is accomplished by a novel approach based on analysis of Pareto charts. Gravity modeling uses a newly developed convolution algorithm, while seismic modeling utilizes the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests show that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Detailed first arrival picking followed by trial velocity modeling remediates inconsistent data. We use a set of highly refined first arrival picks to compare results of a convergent joint seismic-gravity optimization to the Plotrefa™ and SeisOpt® Pro™ velocity modeling packages. Plotrefa™ uses a nonlinear least squares approach that is initial model dependent and produces shallow velocity artifacts. SeisOpt® Pro™ utilizes the simulated annealing algorithm and is limited to depths above the deepest raypath. Joint optimization increases the depth of constrained velocities, improving reflector coherency at depth. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts caused by limitations in refraction ray coverage. Seismic and gravity data from the San Emidio Geothermal field of the northwest Basin and Range province demonstrate that joint optimization changes interpretation outcomes. The prior shallow-valley interpretation gives way to a deep valley model, while shallow antiformal reflectors that could have been interpreted as antiformal folds are flattened. Furthermore, joint optimization provides a clearer image of the rangefront fault. This technique can readily be applied to existing datasets and could
Brodic, Bojan; Malehmir, Alireza; Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti
2017-04-01
Higher resolution of S-wave seismic data compared to the P-wave ones are attractive for the researches working with the seismic methods. This is particularly true for near-surface applications due to significantly lower shear-wave velocities of unconsolidated sediments. Shear-wave imaging, however, poses certain restrictions on both source and receiver selections and also processing strategies. With three component (3C) seismic receivers becoming more affordable and used, shear-wave imaging from vertical sources is attracting more attention for near-surface applications. Theoretically, a vertical impact source will always excite both P- and S-waves although the excited S-waves are radially polarized (SV). There is an exchange of seismic energy between the vertical and radial component of the seismic wavefield. Additionally, it is theoretically accepted that there is no energy conversion or exchange from vertical into the transverse (or SH) component of the seismic wavefield, and the SH-waves can only be generated using SH sources. With the objectives of imaging esker structure (glacial sediments), water table and depth to bedrock, we conducted a seismic survey in Virttaankangas, in southwestern Finland. A bobcat-mounted vertical drop hammer (500 kg) was used as the seismic source. To obtain better source coupling, a 75×75×1.5 cm steel plate was mounted at the bottom of the hammer casing and all the hits made on this plate after placing it firmly on the ground at every shot point. For the data recording, we used a state-of-the-art comprising of 100 units, 240 m-long, 3C MEMS (micro electro-mechanical system) based seismic landstreamer developed at Uppsala University. Although the focus of the study was on the vertical component data, careful inspection of the transverse (SH) component of the raw data revealed clear shear wave reflections (normal moveout velocities ranging from 280-350 m/s at 50 m depth) on several shot gathers. This indicated potential for their
Song, I.-S.; Lee, C.; Kim, J.-H.; Jee, G.; Kim, Y.-H.; Choi, H.-J.; Chun, H.-Y.; Kim, Y. H.
2017-04-01
Vertically propagating low-frequency inertia-gravity waves (IGWs) are retrieved from meteor radar winds observed at King Sejong Station (KSS: 62.22°S, 58.78°W), Antarctica. IGW horizontal winds extracted from temporal band-pass filtering in regular time-height bins show the frequent occurrence of IGWs with the downward phase progression and the counterclockwise rotation of their horizontal wind vectors with time (i.e., upward energy propagation) near the mesopause region throughout the whole year of 2014. The vertical wavelengths of the observed IGWs roughly range from 14 km to more than 20 km, which is consistent with previous observational studies on the mesospheric IGWs over Antarctica. Stokes parameters and rotary spectra computed from the hodographs of the IGW horizontal wind components reveal that the intrinsic frequencies of the upward propagating IGWs are |f|-3|f| with seasonal variations of the relative predominance between |f|-2|f| and 2|f|-3|f|, where f is the Coriolis parameter at KSS. The hodograph analysis also indicates that the N-S propagation is dominant in austral summer, while the NE-SW propagation is pronounced in austral winter. The propagation direction is discussed in relation to the generation of IGWs due to dynamical imbalances occurring in the tropospheric and stratospheric jet flow systems. Ray tracing results indicate that the N-S propagation in summer may be due to the jet flow systems roughly north of KSS and the NE-SW propagation in winter may be either the SW propagation from the jet flow systems northeast of KSS or the NE propagation (around the South Pole) from the south of Australia and Southern Indian and Pacific Oceans.
Directory of Open Access Journals (Sweden)
Syed Murtuza Mehdi
2016-01-01
Full Text Available Metallic tubes have been widely used as primary heat transfer elements in laminar convectors for domestic and aerospace heating purpose. This paper uses CFD tool to investigate the heat output and pressure drop of liquid sodium flowing inside a circular tube having a wavy profile throughout its length. The wavy tube can be utilized in laminar liquid metal convectors as basic heat transfer element. The effect of Reynolds number (500≤Re≤2000 wave pitch (25 mm≤λ≤100 mm and wave amplitude (2 mm≤a≤6 mm on the heat output and pressure drop has been numerically studied. Based on the CFD results important controlling parameters have been identified and it is concluded that the heat output from the wavy tube is affected by the wave pitch and the wave amplitude while the pressure drop is mostly affected by the Reynolds number and wave amplitude.
Perez, John Anthony
Averaged over appropriate space and time scales the dynamics of highly fluidized granular systems are often reminiscent of molecular fluid flows. As a result, theoretical efforts to describe these systems have borrowed heavily from continuum mechanics, particularly hydrodynamics. This has led to various proposed granular hydrodynamic theories which have been used to simulate granular materials in various states of confinement and excitation. These studies suggest that a continuum model for granular gasses can accurately reproduce the mean density, velocity and temperature profiles for an experimental granular gas. This thesis contributes to this body of work by presenting an experimental study of the hydrodynamic fields and velocity distributions within a vertically driven quasi-2D granular gas. We have taken pictures as fast as possible of a time-dependent granular gas using a high-speed CCD camera. We have extracted the positions and velocities of 57-564 particles per frame over 400 GB of raw images collected at 3700 fps. We used this data to compute the density, velocity and temperature fields as functions of time and space to a very high resolution. This approach led to the discovery of novel substructures within the hydrodynamic fields which would have been overlooked had we chosen to average over a drive cycle as earlier studies have done. In particular, the high spatial resolution available from our measurements reveals a serrated substructure in the shock waves which has not been reported before. This substructure is the result of collisional momentum transport . One of the current issues in formulating a granular continuum model is how to incorporate local and non-local dependencies between stress and strain correctly. In this thesis we demonstrate that the collisional transfer of momentum produces a non-local effect in the stress tensor which plays a major role in determining the mean flow. Current models have incorporated only the collisional or
Salissou, Yacoubou; Panneton, Raymond
2010-11-01
Several methods for measuring the complex wave number and the characteristic impedance of sound absorbers have been proposed in the literature. These methods can be classified into single frequency and wideband methods. In this paper, the main existing methods are revisited and discussed. An alternative method which is not well known or discussed in the literature while exhibiting great potential is also discussed. This method is essentially an improvement of the wideband method described by Iwase et al., rewritten so that the setup is more ISO 10534-2 standard-compliant. Glass wool, melamine foam and acoustical/thermal insulator wool are used to compare the main existing wideband non-iterative methods with this alternative method. It is found that, in the middle and high frequency ranges the alternative method yields results that are comparable in accuracy to the classical two-cavity method and the four-microphone transfer-matrix method. However, in the low frequency range, the alternative method appears to be more accurate than the other methods, especially when measuring the complex wave number.
Modification of AMD wave functions and application to the breaking of the N=20 magic number
Energy Technology Data Exchange (ETDEWEB)
Kimura, Masaaki; Horiuchi, Hisashi [Kyoto Univ. (Japan). Dept. of Physics
2001-09-01
By using the deformed Gaussian instead of the spherical one, we have modified the AMD (Antisymmetrized Molecular Dynamics) wave functions. The calculation results with this modified AMD shows the drastic improvement of the deformation properties of Mg isotopes. This improvement means that this new version of AMD can treat the deformation of mean field properly than before and the deformation of mean field is important in Mg isotopes. With this new version of AMD, we have also calculated 32Mg in which the breaking of magic number N=20 is experimentally known. In this nucleus, {beta}-energy surface is also drastically changed by the modification AMD wave function. Our results show that this nucleus is indeed deformed and neutron's 2p2h state is dominant in its ground state. This ground state reproduces the experimental data and shows the breaking of the magic number N=20 clearly. Additionally, near the ground state, there is also very interesting state which has neutron's 4p4h structure and shows parity violating density distribution and cluster-like nature. (author)
On the nonlinear shaping mechanism for gravity wave spectrum in the atmosphere
Directory of Open Access Journals (Sweden)
I. P. Chunchuzov
2009-11-01
Full Text Available The nonlinear mechanism of shaping of a high vertical wave number spectral tail in the field of a few discrete internal gravity waves in the atmosphere is studied in this paper. The effects of advection of fluid parcels by interacting gravity waves are taken strictly into account by calculating wave field in Lagrangian variables, and performing a variable transformation from Lagrangian to Eulerian frame. The vertical profiles and vertical wave number spectra of the Eulerian displacement field are obtained for both the case of resonant and non-resonant wave-wave interactions. The evolution of these spectra with growing parameter of nonlinearity of the internal wave field is studied and compared to that of a broad band spectrum of gravity waves with randomly independent amplitudes and phases. The calculated vertical wave number spectra of the vertical displacements or relative temperature fluctuations are found to be consistent with the observed spectra in the middle atmosphere.
Huo, Shao-yong; Chen, Jiu-jiu; Huang, Hong-bo; Huang, Guo-Liang
2017-01-01
The introduction of the concept of valley pseudospin to phononic crystals has made a remarkable topologically protected interface transport of sound, which opens a novel research area referred to as valley Hall topological insulators. Here, we demonstrate the simultaneous multi-band edge states of shear vertical waves in two-dimensional phononic crystals with veins. The multi-band edge states are topologically valley-protected and are obtained by simultaneously gapping multiple Dirac points a...
Nonlinear excitation of the ablative Rayleigh-Taylor instability for all wave numbers
Zhang, H.; Betti, R.; Gopalaswamy, V.; Yan, R.; Aluie, H.
2018-01-01
Small-scale perturbations in the ablative Rayleigh-Taylor instability (ARTI) are often neglected because they are linearly stable when their wavelength is shorter than a linear cutoff. Using two-dimensional (2D) and three-dimensional (3D) numerical simulations, it is shown that linearly stable modes of any wavelength can be destabilized. This instability regime requires finite amplitude initial perturbations and linearly stable ARTI modes to be more easily destabilized in 3D than in 2D. It is shown that for conditions found in laser fusion targets, short wavelength ARTI modes are more efficient at driving mixing of ablated material throughout the target since the nonlinear bubble density increases with the wave number and small-scale bubbles carry a larger mass flux of mixed material.
DEFF Research Database (Denmark)
Frigaard, Peter; Burcharth, Hans F.
1988-01-01
An experimental study is carried out to investigate the wave forces on a slender cylinder. Special attention is given to the wave forces in the surface zone and correlation of forces along the cylinder. The experiments consider the effects of both long and short-crested irregular waves.......An experimental study is carried out to investigate the wave forces on a slender cylinder. Special attention is given to the wave forces in the surface zone and correlation of forces along the cylinder. The experiments consider the effects of both long and short-crested irregular waves....
Budía Alba, A; López Acón, J D; Polo-Rodrigo, A; Bahílo-Mateu, P; Trassierra-Villa, M; Boronat-Tormo, F
2015-06-01
To assess the safety of increasing the number of waves per session in the treatment of urolithiasis using extracorporeal lithotripsy. Prospective, comparative, nonrandomized parallel study of patients with renoureteral lithiasis and an indication for extracorporeal lithotripsy who were consecutively enrolled between 2009 and 2010. We compared group I (160 patients) treated on schedule with a standard number of waves/session (mean 2858,3±302,8) using a Dornier lithotripter U/15/50 against group II (172 patients) treated with an expanded number of waves/session (mean, 6728,9±889,6) using a Siemens Modularis lithotripter. The study variables were age, sex, location, stone size, number of waves/session and total number of waves to resolution, stone-free rate (SFR) and rate of complications (Clavien-Dindo classification). Student's t-test and the chi-squared test were employed for the statistical analysis. The total rate of complications was 11.9% and 10.46% for groups I and II, respectively (P=.39). All complications were minor (Clavien-Dindo grade I). The most common complications were colic pain and hematuria in groups I and II, respectively, with a similar treatment intolerance rate (P>.05). The total number of waves necessary was lower in group II than in group I (P=.001), with SFRs of 96.5% and 71.5%, respectively (P=.001). Treatment with an expanded number of waves per session in extracorporeal lithotripsy does not increase the rate of complications or their severity. However, it could increase the overall effectiveness of the treatment. Copyright © 2014 AEU. Publicado por Elsevier España, S.L.U. All rights reserved.
Nonlinear Excitation of the Ablative Rayleigh-Taylor Instability for All Wave Numbers
Zhang, H.; Betti, R.; Gopalaswamy, V.; Aluie, H.; Yan, R.
2017-10-01
Small-scale modes of the ablative Rayleigh-Taylor instability (ARTI) are often neglected because they are linearly stable when their wavelength is shorter than a linear cutoff. Using 2-D and 3-D numerical simulations, it is shown that linearly stable modes of any wavelength can be destabilized. This instability regime requires finite amplitude initial perturbations. Compared to 2-D, linearly stable ARTI modes are more easily destabilized in 3-D and the penetrating bubbles have a higher density because of enhanced vorticity. It is shown that for conditions found in laser fusion targets, short-wavelength ARTI modes are more efficient at driving mixing of ablated material throughout the target since the nonlinear bubble density increases with the wave number and small-scale bubbles carry a larger mass flux of mixed material. This work was supported by the Office of Fusion Energy Sciences Nos. DE-FG02-04ER54789, DE-SC0014318, the Department of Energy National Nuclear Security Administration under Award No. DE-NA0001944, the Ministerio de Ciencia e Innovacion of Spain (Grant No. ENE2011-28489), and the NANL LDRD program through Project Number 20150568ER.
Allam, A. A.; Schulte-Pelkum, V.; Ben-Zion, Y.; Tape, C.; Ruppert, N.; Ross, Z. E.
2017-11-01
We examine the structure of the Denali fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of fault zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and fault zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovičić discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali fault in the imaged region, with the northern side having shallower Moho depths around 30 km. An automated phase picker algorithm is used to identify 1400 events that generate fault zone head waves only at near-fault stations. At shorter hypocentral distances head waves are observed at stations on the northern side of the fault, while longer propagation distances and deeper events produce head waves on the southern side. These results suggest a reversal of the velocity contrast polarity with depth, which we confirm by computing average 1D velocity models separately north and south of the fault. Using teleseismic events with M ≥ 5.1, we obtain 31,400 P receiver functions and apply common-conversion-point stacking. The results are migrated to depth using the derived 3D tomography model. The imaged interfaces agree with the tomography model, showing a Moho offset along the central Denali fault and also the sub-parallel Hines Creek fault, a suture zone boundary 30 km to the north. To the east, this offset follows the Totschunda fault, which ruptured during the M7.9 2002 earthquake, rather than the Denali fault itself. The combined results suggest that the Denali fault zone separates two distinct crustal blocks, and that the Totschunda and Hines Creeks segments are important components of the fault and Cretaceous-aged suture zone structure.
Kage, Azusa; Asato, Eriko; Chiba, Yoko; Wada, Yuuko; Katsu-Kimura, Yumiko; Kubota, Ayami; Sawai, Satoe; Niihori, Maki; Baba, Shoji A; Mogami, Yoshihiro
2011-03-01
Bioconvection emerges in a dense suspension of swimming protists as a consequence of their negative-gravitactic upward migration and later settling as a blob of density greater than that of water. Thus, gravity is an important parameter governing bioconvective pattern formation. However, inconsistencies are found in previous studies dealing with the response of bioconvection patterns to increased gravity acceleration (hypergravity); the wave number of the patterns has been reported to decrease during the hypergravity phases of parabolic aircraft flight, while it increases in centrifugal hypergravity. In this paper, we reassess the responses of bioconvection to altered gravity during parabolic flight on the basis of vertical and horizontal observations of the patterns formed by Tetrahymena thermophila and Chlamydomonas reinhardtii. Spatiotemporal analyses of the horizontal patterns revealed an increase in the pattern wave number in both pre- and post-parabola hypergravity. Vertical pattern analysis was generally in line with the horizontal pattern analysis, and further revealed that hypergravity-induced changes preceded at the top layer of the suspensions while microgravity-induced changes appeared to occur from the bottom part of the settling blobs. The responses to altered gravity were rather different between the two sample species: T. thermophila tended to drastically modify its bioconvection patterns in response to changes in gravity level, while the patterns of C. reinhardtii responded to a much lesser extent. This difference can be attributed to the distinct physical and physiological properties of the individual organisms, suggesting a significant contribution of the gyrotactic property to the swimming behavior of some protists.
Parolai, Stefano; Ansal, Atilla; Kurtulus, Asli; Strollo, Angelo; Wang, Rongjiang; Zschau, J.
2009-09-01
A vertical array of accelerometers was installed in Ataköy (western Istanbul) with the long-term aim of improving our understanding of in situ soil behaviour, to assess the modelling and parametric uncertainties associated with the employed methodologies for strong-motion site-response analysis, and for shallow geological investigations. Geotechnical and geophysical investigations were carried out to define the subsoil structure at the selected site. Data associated with 10 earthquakes (2.7 site amplification is mainly related to 1-D effects, the standard practice in engineering seismology of deconvolving the surface recording down to the bedrock using an approximate S-wave transfer function (generally valid for vertical incidence of SH waves) might lead to errors in the estimation of the input ground motion required in engineering calculations. Finally, downgoing waves with significant amplitudes were found down to 70 m and even to 140 m depth. This result provides a warning about the use of shallow borehole recordings as input for the numerical simulation of ground motion and for the derivation of ground motion prediction relationships.
DEFF Research Database (Denmark)
Xu, G. S.; Wan, B. N.; Wang, H. Q.
2016-01-01
A new model for the low-to-high (L-H) confinement transition has been developed based on a new paradigm for turbulence suppression by velocity shear [G. M. Staebler et al., Phys. Rev. Lett.110, 055003 (2013)]. The model indicates that the L-H transition can be mediated by a shift in the radial wave...... number spectrum of turbulence, as evidenced here, for the first time, by the direct observation of a turbulence radial wave number spectral shift and turbulence structure tilting prior to the L-H transition at tokamak edge by direct probing. This new mechanism does not require a pretransition overshoot...
Foda, Khaled; Abdeldaeim, Hussein; Youssif, Mohamed; Assem, Akram
2013-11-01
To define the parameters that accompanied a successful extracorporeal shock wave lithotripsy (ESWL), namely the number of shock waves (SWs), expulsion time (ET), mean stone density (MSD), and the skin-to-stone distance (SSD). A total of 368 patients diagnosed with renal calculi using noncontrast computerized tomography had their MSD, diameter, and SSD recorded. All patients were treated using a Siemens lithotripter. ESWL success meant a stone-free status or presence of residual fragments 934 HUs and SSD >99 mm. The required number of SWs and the expected ET can be anticipated. Copyright © 2013 Elsevier Inc. All rights reserved.
Barton, C.; Cai, M.; Shin, C.
2013-12-01
We have diagnosed phase speed, wave tilt, and form drag of atmospheric waves in the equatorial stratosphere using daily fields in the NCEP-NCAR II reanalysis dataset. The time series of phase speed, wave tilt, and form drag, or pressure torque, are studied with respect to the tropical stratospheric quasi-biennial oscillation (QBO) of mean zonal winds. Observed (ground-relative) phase speed values are found to oscillate quasi-biennially such that ground-relative phase speed increases during the local easterly QBO phase and decreases during the local westerly QBO phase. The wave is found to tilt westward during the local westerly phase and eastward during the local easterly phase. Such QBO oscillation of wave tilting is consistent with the well-known fact that Kelvin and mixed Rossby-gravity waves are dominant in the local easterly and westerly phase, respectively. The eastward tilting waves have positive pressure torque, acting to transfer easterly angular momentum downward, while westward tilting waves have negative pressure torque, transferring westerly angular momentum downward during the local westerly phase.
Energy Technology Data Exchange (ETDEWEB)
Yamamoto, H.; Yoshioka, M.; Saito, T. [Iwate University, Iwate (Japan). Faculty of Engineering
1996-05-01
Studies were conducted about the method of estimating the underground S-wave velocity structure by inversion making use of the horizontal/vertical motion spectral ratio of microtremors. For this purpose, a dynamo-electric velocity type seismograph was used, capable of processing the east-west, north-south, and vertical components integratedly. For the purpose of sampling the Rayleigh wave spectral ratio, one out of all the azimuths was chosen, whose horizontal motion had a high Fourier frequency component coherency with the vertical motions. For the estimation of the underground S-wave velocity structure, parameters (P-wave velocity, S-wave velocity, density, and layer thickness) were determined from the minimum residual sum of squares involving the observed microtremor spectral ratio and the theoretical value calculated by use of a model structure. The known boring data was utilized for the study of the S-wave velocity in the top layer, and it was determined using an S-wave velocity estimation formula for the Morioka area constructed using the N-value, depth, and geological classification. It was found that the optimum S-wave velocity structure even below the top layer well reflects the S-wave velocity obtained by the estimation formula. 5 refs., 6 figs.
Directory of Open Access Journals (Sweden)
Hafiz Abdul Wajid
2014-01-01
Full Text Available We construct modified forward, backward, and central finite difference schemes, specifically for the Helmholtz equation, by using the Bloch wave property. All of these modified finite difference approximations provide exact solutions at the nodes of the uniform grid for the second derivative present in the Helmholtz equation and the first derivative in the radiation boundary conditions for wave propagation. The most important feature of the modified schemes is that they work for large as well as low wave numbers, without the common requirement of a very fine mesh size. The superiority of the modified finite difference schemes is illustrated with the help of numerical examples by making a comparison with standard finite difference schemes.
Musielak, Z. E.; Rosner, R.
1987-01-01
The generation of MHD waves by turbulent motions in a stratified medium with an embedded uniform magnetic field, a topic which is relevant to the study of the solar atmosphere, is considered. Both compressible and incompressible MHD waves are treated in a one-dimensional approach; however, the direction of the background magnetic field is permitted to vary in an arbitrary direction. Theoretical expressions for MHD energy fluxes are obtained as a function of wave frequency and multipole coefficients. It is shown that monopole, dipole, and quadrupole emissions are responsible for the generation of the compressible components of the fast and slow modes. However, the incompressible components and the Alfven modes can be generated by the dipole emission only. Specific results obtained for special magnetic field geometries are discussed for the fast and slow modes.
Design Loads on Platforms on Offshore wind Turbine Foundations with Respect to Vertical Wave Run-up
DEFF Research Database (Denmark)
Damsgaard, Mathilde L.; Gravesen, Helge; Andersen, Thomas Lykke
2007-01-01
depending on the wave parameters in the area in question. This is approached by a three step calculation routine supported by model tests. Supplementary tests have been made to determine the reduction in loads, when grated platforms are used in preference to a closed surface. This leads to an appreciable...
Sukow, David W.; Gilfillan, Taylor; Pope, Brenton; Torre, Maria S.; Gavrielides, Athanasios; Masoller, Cristina
2012-09-01
We study experimentally the dynamics of vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated (PR) optical feedback, such that the natural lasing polarization of a VCSEL is rotated by 90 deg and then is reinjected into the laser. We observe noisy, square-wave-like polarization switchings with periodicity slightly longer than twice the delay time, which degrade to (or alternate with) bursts of irregular oscillations. We present results of simulations that are in good agreement with the observations. The simulations demonstrate that close to threshold the regular switching is very sensitive to noise, while well above threshold is less affected by the noise strength. The frequency splitting between the two polarizations plays a key role in the switching regularity, and we identify wide parameter regions where deterministic and robust switching can be observed.
Weng, Guoen; Mei, Yang; Liu, Jianping; Hofmann, Werner; Ying, Leiying; Zhang, Jiangyong; Bu, Yikun; Li, Zengcheng; Yang, Hui; Zhang, Baoping
2016-07-11
Low threshold continuous-wave (CW) lasing of current injected InGaN quantum dot (QD) vertical-cavity surface-emitting lasers (VCSELs) was achieved at room temperature. The VCSEL was fabricated by metal bonding technique on a copper substrate to improve the heat dissipation ability of the device. For the first time, lasing was obtained at yellow-green wavelength of 560.4 nm with a low threshold of 0.61 mA, corresponding to a current density of 0.78 kA/cm2. A high degree of polarization of 94% were measured. Despite the operation in the range of "green gap" of GaN-based devices, single longitudinal mode laser emission was clearly achieved due to the high quality of active region based on InGaN QDs and the excellent thermal design of the VCSELs.
Kawase, Hiroshi; Mori, Yuta; Nagashima, Fumiaki
2018-01-01
We have been discussing the validity of using the horizontal-to-vertical spectral ratios (HVRs) as a substitute for S-wave amplifications after Nakamura first proposed the idea in 1989. So far a formula for HVRs had not been derived that fully utilized their physical characteristics until a recent proposal based on the diffuse field concept. There is another source of confusion that comes from the mixed use of HVRs from earthquake and microtremors, although their wave fields are hardly the same. In this study, we compared HVRs from observed microtremors (MHVR) and those from observed earthquake motions (EHVR) at one hundred K-NET and KiK-net stations. We found that MHVR and EHVR share similarities, especially until their first peak frequency, but have significant differences in the higher frequency range. This is because microtremors mainly consist of surface waves so that peaks associated with higher modes would not be prominent, while seismic motions mainly consist of upwardly propagating plain body waves so that higher mode resonances can be seen in high frequency. We defined here the spectral amplitude ratio between them as EMR and calculated their average. We categorize all the sites into five bins by their fundamental peak frequencies in MHVR. Once we obtained EMRs for five categories, we back-calculated EHVRs from MHVRs, which we call pseudo-EHVRs (pEHVR). We found that pEHVR is much closer to EHVR than MHVR. Then we use our inversion code to invert the one-dimensional S-wave velocity structures from EHVRs based on the diffuse field concept. We also applied the same code to pEHVRs and MHVRs for comparison. We found that pEHVRs yield velocity structures much closer to those by EHVRs than those by MHVRs. This is natural since what we have done up to here is circular except for the average operation in EMRs. Finally, we showed independent examples of data not used in the EMR calculation, where better ground structures were successfully identified from p
From the CERN web: gravitational waves, magic numbers, innovation and more
2016-01-01
This section highlights articles, blog posts and press releases published in the CERN web environment over the past weeks. This way, you won’t miss a thing... Simulation of two massive black holes merging, based on data collected from the LIGO collaboration on 14 September 2015. (Image: LIGO Collaboration © 2016 SXS) The hills are alive, with the sound of gravitational waves 12 February – ATLAS Collaboration It’s 16:00 CET at CERN and I’m sitting in the CERN Main Auditorium. The room is buzzing with excitement, not unlike the day in 2012 when the Higgs discovery was announced in this very room. But today the announcement is not from CERN, but the LIGO experiment which is spread across two continents. Many expect the announcement to be about a discovery of gravitational waves, as predicted by Einstein in 1916, but which have remained elusive until today… Continue to read… The laser launch st...
Directory of Open Access Journals (Sweden)
Muthuraj R.
2012-01-01
Full Text Available A mathematical model is developed to examine the effect of chemical reaction on MHD mixed convective heat and mass transfer flow of a couple-stress fluid in vertical porous space in the presence of temperature dependent heat source with travelling thermal waves. The dimensionless governing equations are assumed to be made up of two parts: a mean part corresponding to the fully developed mean flow, and a small perturbed part, using amplitude as a small parameter. The analytical solution of perturbed part have been carried out by using the long-wave approximation. The expressions for the zeroth-order and the first order solutions are obtained and the results of the heat and mass transfer characteristics are presented graphically for various values of parameters entering into the problem. It is noted that velocity of the fluid increases with the increase of the couple stress parameter and increasing the chemical reaction parameter leads suppress the velocity of the fluid. Cross velocity decreases with an increase of the phase angle. The increase of the chemical reaction parameter and Schmidt number lead to decrease the fluid concentration. The hydrodynamic case for a non-porous space in the absence of the temperature dependent heat source for Newtonian fluid can be captured as a limiting case of our analysis by taking, and α1→0, Da→∞, a→∞.
Purdy, K. R.; Ventrice, M. B.; Fang, J.
1972-01-01
Analytical and experimental studies were initiated to determine if the response of a constant temperature hot wire anemometer to acoustic oscillations could serve as an analog to the response of the drop vaporization burning rate process to acoustic oscillations, and, perhaps, also as an analog to any Reynolds number dependent process. The motivation behind this study was a recent analytical study which showed that distorted acoustic oscillations could amplify the open-loop response of vaporization limited combustion. This type of amplification may be the cause of unstable combustion in liquid propellant rocket engines. The analytical results obtained for the constant temperature anemometer are similar in nature to those previously obtained for vaporization limited combustion and indicate that the response is dependent on the amount and type of distortion as well as other factors, such as sound pressure level, Mach number and hot wire temperature. Preliminary results indicate qualitative agreement between theory and experiment.
Reyt, Ida; Bailliet, Hélène; Valière, Jean-Christophe
2014-01-01
Measurements of streaming velocity are performed by means of Laser Doppler Velocimetry and Particle Image Velociimetry in an experimental apparatus consisting of a cylindrical waveguide having one loudspeaker at each end for high intensity sound levels. The case of high nonlinear Reynolds number ReNL is particularly investigated. The variation of axial streaming velocity with respect to the axial and to the transverse coordinates are compared to available Rayleigh streaming theory. As expected, the measured streaming velocity agrees well with the Rayleigh streaming theory for small ReNL but deviates significantly from such predictions for high ReNL. When the nonlinear Reynolds number is increased, the outer centerline axial streaming velocity gets distorted towards the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. This kind of behavior is followed by outer streaming cells only and measurements in the near wall region show that inner streaming vortices are less affected by this substantial evolution of fast streaming pattern. Measurements of the transient evolution of streaming velocity provide an additional insight into the evolution of fast streaming.
Directory of Open Access Journals (Sweden)
Z. Zhu
2017-06-01
Full Text Available Recent studies on the equatorial atmosphere–ionosphere coupling system have shown that planetary-wave-type oscillations, as an important seeding mechanism for equatorial spread F (ESF, play an important role in ESF irregularity development and its day-to-day variability in the equatorial latitudes. In this study, ionosonde virtual height and ESF measurements over Sanya (18.4° N, 109.6° E; 12.8° N dip latitude and meteor radar neutral-wind measurements over Fuke (19.5° N, 109.1° E; 14° N dip latitude during 2013 are used to investigate the features of planetary-wave-type oscillations in both the lower atmosphere and the ionosphere and their possible influences on ESF occurrence under the weak solar maximum year. The ∼ 3-day and ∼ 7-day planetary-wave-type oscillations have been observed in the neutral zonal winds and the time rate of change in F-layer virtual heights. According to the propagation characteristics, the 3-day and 7-day planetary-wave-type oscillations are basically recognized as ultrafast and fast Kelvin waves, respectively. With increasing heights, the 3-day wave oscillations are gradually amplified, while the 7-day wave oscillations are generally constant. By performing a cross-wavelet transform on the onsets of ESF and the vertical drifts of the F layer, we found that there are simultaneously occurring 7-day and 3-day common wave oscillations between them. The 7-day waves are mainly in the inversion phase, while the 3-day waves are mostly in an in-phase state, indicating that the 7-day waves may play a main role in ESF initiation. Approximate delays of 6 days for the 7-day waves and 5 days for the 3-day waves in their propagation upward from the lower atmosphere to the ionosphere are evaluated with wavelet power spectrum analysis. The estimated upward velocities from these time delays provide consistent evidence that the 7-day and 3-day waves propagate vertically upward with typical Kelvin wave
Zhao, J.; Chen, C.; Chu, X.; Lu, X.; Fong, W.; Yu, Z.; Roberts, B. R.; Dörnbrack, A.; Smith, J. A.
2016-12-01
Five years of atmospheric temperature data have been accumulated since the University of Colorado lidar group deployed an Fe Boltzmann lidar to Arrival Heights near McMurdo, Antarctica. Vertical wavelengths, periods, phase speeds, potential energy densities, and frequency spectra of gravity waves in the stratosphere (from 30 to 50 km) from 2011 to 2015 are investigated. Typical values for gravity wave vertical wavelength and period are 7.5 km and 5.5 h, respectively. However, they are all subjected to seasonal changes. Monthly means of vertical wavelength show a clear seasonal trend with considerably longer wavelengths in winter. Gravity wave potential energy densities (GWPEDs) obtained through temperature perturbations vary significantly from observation to observation; however, they do follow a seasonal trend with a winter maximum and a summer minimum. Efforts were made in order to reveal the mechanisms behind the observed signatures of stratospheric gravity waves. Background wind from European Centre for Medium-Range Weather Forecasts (ECMWF) model and polar vortex position information from Modern Era Retrospective-Analysis for Research and Applications (MERRA) are invoked. The increase in vertical wavelength in winter is linked to strong stratospheric westerlies due to the formation of polar vortex while the GWPED seasonal variations are connected to the changes of gravity wave sources and selective critical-level filtering. We did the first study of gravity wave frequency spectra in the Antarctica upper stratosphere. The slopes of power spectral density versus frequency range from 1.6 to 1.4 from 30 to 50 km, however, they change to 1.0 around 60 km.
DEFF Research Database (Denmark)
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many...... times smaller it remains very high. For example, whilst there is enough potential wave power off the UK to supply the electricity demands several times over, the economically recoverable resource for the UK is estimated at 25% of current demand; a lot less, but a very substantial amount nonetheless....
Gómez, Breogán; Miguez-Macho, Gonzalo
2017-04-01
Nudging techniques are commonly used to constrain the evolution of numerical models to a reference dataset that is typically of a lower resolution. The nudged model retains some of the features of the reference field while incorporating its own dynamics to the solution. These characteristics have made nudging very popular in dynamic downscaling applications that cover from shot range, single case studies, to multi-decadal regional climate simulations. Recently, a variation of this approach called Spectral Nudging, has gained popularity for its ability to maintain the higher temporal and spatial variability of the model results, while forcing the large scales in the solution with a coarser resolution field. In this work, we focus on a not much explored aspect of this technique: the impact of selecting different cut-off wave numbers and spin-up times. We perform four-day long simulations with the WRF model, daily for three different one-month periods that include a free run and several Spectral Nudging experiments with cut-off wave numbers ranging from the smallest to the largest possible (full Grid Nudging). Results show that Spectral Nudging is very effective at imposing the selected scales onto the solution, while allowing the limited area model to incorporate finer scale features. The model error diminishes rapidly as the nudging expands over broader parts of the spectrum, but this decreasing trend ceases sharply at cut-off wave numbers equivalent to a length scale of about 1000 km, and the error magnitude changes minimally thereafter. This scale corresponds to the Rossby Radius of deformation, separating synoptic from convective scales in the flow. When nudging above this value is applied, a shifting of the synoptic patterns can occur in the solution, yielding large model errors. However, when selecting smaller scales, the fine scale contribution of the model is damped, thus making 1000 km the appropriate scale threshold to nudge in order to balance both effects
Djebbi, Ramzi
2014-08-05
Multi-parameter inversion in anisotropic media suffers from the inherent trade-off between the anisotropic parameters, even under the acoustic assumption. Multi-component data, often acquired nowadays in ocean bottom acquisition and land data, provide additional information capable of resolving anisotropic parameters under the acoustic approximation assumption. Based on Born scattering approximation, we develop formulas capable of characterizing the radiation patterns for the acoustic pseudo-pure mode P-waves. Though commonly reserved for the elastic fields, we use displacement fields to constrain the acoustic vertical transverse isotropic (VTI) representation of the medium. Using the asymptotic Green\\'s functions and a horizontal reflector we derive the radiation patterns for perturbations in the anisotropic media. The radiation pattern for the anellipticity parameter η is identically zero for the horizontal displacement. This allows us to dedicate this component to invert for velocity and δ. Computing the traveltime sensitivity kernels based on the unwrapped phase confirms the radiation patterns observations, and provide the model wavenumber behavior of the update.
Sprengel, S.; Andrejew, A.; Federer, F.; Veerabathran, G. K.; Boehm, G.; Amann, M.-C.
2015-04-01
A concept for electrically pumped vertical cavity surface emitting lasers (VCSEL) for emission wavelength beyond 2 μm is presented. This concept integrates type-II quantum wells into InP-based VCSELs with a buried tunnel junction as current aperture. The W-shaped quantum wells are based on the type-II band alignment between GaInAs and GaAsSb. The structure includes an epitaxial GaInAs/InP and an amorphous AlF3/ZnS distributed Bragg reflector as bottom and top (outcoupling) mirror, respectively. Continuous-wave operation up to 10 °C at a wavelength of 2.49 μm and a peak output power of 400 μW at -18 °C has been achieved. Single-mode emission with a side-mode suppression ratio of 30 dB for mesa diameters up to 14 μm is presented. The long emission wavelength and current tunability over a wavelength range of more than 5 nm combined with its single-mode operation makes this device ideally suited for spectroscopy applications.
Analysis of P- and S-wave VSP (vertical seismic profile) data from the Salton Sea Geothermal Field
Energy Technology Data Exchange (ETDEWEB)
Daley, T.M.
1987-09-01
To understand any geophysical data, geologic information is necessary. This thesis will begin with a summary of the geology of the Salton Trough region and the Salton Sea Geothermal Field (SSGF). The information available from the SSSDP will also be summarized. After the geologic summary, the design of the VSP will be discussed, including acquisition equipment and procedures. The data processing procedures and software used will be discussed as a separate section. Processing procedures will also be described at various times in the thesis where more specialized procedures are used. Data analysis makes up the bulk of the thesis and it is divided into a number of sections detailing the basic VSP interpretation, the anisotropy analysis and the fracture detection and orientation analysis. A combined interpretation of the results, with probable geologic causes for observed events, is presented as a separate section from the data analysis. Finally, a summary of results for each of the goals stated above will be given. The reader should note that a large volume of data were collected and various display methods were used (from the standard wiggle-trace to three-component hodographs). Much of these data are left in the appendices with important or representative figures given in the body of the thesis. Also given in the appendices are listings of FORTRAN programs developed in conjunction with the thesis work. 46 refs., 63 figs., 12 tabs.
Giammarinaro, Bruno; Espíndola, David; Coulouvrat, François; Pinton, Gianmarco
2018-01-01
Focusing is a ubiquitous way to transform waves. Recently, a new type of shock wave has been observed experimentally with high-frame-rate ultrasound: shear shock waves in soft solids. These strongly nonlinear waves are characterized by a high Mach number, because the shear wave velocity is much slower, by 3 orders of magnitude, than the longitudinal wave velocity. Furthermore, these waves have a unique cubic nonlinearity which generates only odd harmonics. Unlike longitudinal waves for which only compressional shocks are possible, shear waves exhibit cubic nonlinearities which can generate positive and negative shocks. Here we present the experimental observation of shear shock wave focusing, generated by the vertical motion of a solid cylinder section embedded in a soft gelatin-graphite phantom to induce linearly vertically polarized motion. Raw ultrasound data from high-frame-rate (7692 images per second) acquisitions in combination with algorithms that are tuned to detect small displacements (approximately 1 μ m ) are used to generate quantitative movies of gel motion. The features of shear shock wave focusing are analyzed by comparing experimental observations with numerical simulations of a retarded-time elastodynamic equation with cubic nonlinearities and empirical attenuation laws for soft solids.
Valor, A; Bonche, P
2000-01-01
We present in this paper the general framework of a method which permits to restore the rotational and particle number symmetries of wave functions obtained in Skyrme HF + BCS calculations. This restoration is nothing but a projection of mean-field intrinsic wave functions onto good particle number and good angular momentum. The method allows us also to mix projected wave functions. Such a configuration mixing is discussed for sets of HF + BCS intrinsic states generated in constrained calculations with suitable collective variables. This procedure gives collective states which are eigenstates of the particle number and the angular momentum operators and between which transition probabilities are calculated. An application to sup 2 sup 4 Mg is presented, with mean-field wave functions generated by axial quadrupole constraints. Theoretical spectra and transition probabilities are compared to the experiment.
Short-crested waves in the surf zone
Wei, Zhangping; Dalrymple, Robert A.; Xu, Munan; Garnier, Roland; Derakhti, Morteza
2017-05-01
This study investigates short-crested waves in the surf zone by using the mesh-free Smoothed Particle Hydrodynamics model, GPUSPH. The short-crested waves are created by generating intersecting wave trains in a numerical wave basin with a beach. We first validate the numerical model for short-crested waves by comparison with large-scale laboratory measurements. Then short-crested wave breaking over a planar beach is studied comprehensively. We observe rip currents as discussed in Dalrymple (1975) and undertow created by synchronous intersecting waves. The wave breaking of the short-crested wavefield created by the nonlinear superposition of intersecting waves and wave-current interaction result in the formation of isolated breakers at the ends of breaking wave crests. Wave amplitude diffraction at these isolated breakers gives rise to an increase in the alongshore wave number in the inner surf zone. Moreover, 3-D vortices and multiple circulation cells with a rotation frequency much lower than the incident wave frequency are observed across the outer surf zone to the beach. Finally, we investigate vertical vorticity generation under short-crested wave breaking and find that breaking of short-crested waves generates vorticity as pointed out by Peregrine (1998). Vorticity generation is not only observed under short-crested waves with a limited number of wave components but also under directional wave spectra.
Martinez, Loïc; Morvan, Bruno; Izbicki, Jean Louis
2004-04-01
A new 4D space-time-wave number-frequency representation Z(x,t,k,f) is introduced. The Z(x,t,k,f) representation is used for processing 2D space-time signal collection issued from wave propagation along a 1D medium. This representation is an extension along the time dimension of the space-wave number-frequency representation. The Z(x,t,k,f) representation is obtained by short time-space 2D Fourier transforming the space-time collection. The Z(x,t,k,f) representation allows the characterization transient aspects of wave generation and propagation in both space and time dimensions. The Z(x,t,k,f) representation is used to experimentally investigate Lamb wave generation and propagation around a cylindrical shell (relative thickness is equal to 0.03) surrounded by water and excited by a pulse (0.1 micros duration with 1-5 MHz transducers). Three kinds of fluids have been used inside the shell: air, water, propanol. In all the cases, the Z(x,t,k,f) analysis clearly identify the reflected field on the insonified side of the shell and it allows the measurement of the local reflection coefficients R(x,t,k,f). The generation and the propagation of Lamb waves are also quantified. For the liquid filled shells, the multiple internal reflections are revealed by Z(x,t,k,f) analysis: the local transmission coefficients T(x,t,k,f) are also measured. When local matching conditions allows Lamb wave generation, the multiple regeneration of Lamb wave is observed. Based on these results, a link is establish toward the theoretical results obtained by steady state approach and Sommerfeld-Watson transform.
Directory of Open Access Journals (Sweden)
Y. Narita
2011-02-01
Full Text Available A new analysis method is presented that provides a high-resolution power spectrum in a broad wave number domain based on multi-point measurements. The analysis technique is referred to as the Multi-point Signal Resonator (MSR and it benefits from Capon's minimum variance method for obtaining the proper power spectral density of the signal as well as the MUSIC algorithm (Multiple Signal Classification for considerably reducing the noise part in the spectrum. The mathematical foundation of the analysis method is presented and it is applied to synthetic data as well as Cluster observations of the interplanetary magnetic field. Using the MSR technique for Cluster data we find a wave in the solar wind propagating parallel to the mean magnetic field with relatively small amplitude, which is not identified by the Capon spectrum. The Cluster data analysis shows the potential of the MSR technique for studying waves and turbulence using multi-point measurements.
Energy Technology Data Exchange (ETDEWEB)
Lee, Jae Ryong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Il Seouk [School of Mechanical Engineering, Kyungpook National University, Daegu (Korea, Republic of)
2012-04-15
The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of 103 to 106. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=106, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydro dynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.
DEFF Research Database (Denmark)
Jensen, Jørgen Juncher; Mansour, A. E.
2003-01-01
ABSTRACT: The effect of impulsive loads like slamming and green water on deck on the wave-induced bending mo-ment is estimated by a semi-analytical approach. The impulse loads leading to transient vibrations are described in terms of magnitude, phase lag relative to the wave-induced peak and decay...... rate. These loads can be due to bow flare slamming, bottom slamming or green water loads as they all can be characterised by a short duration relative to the wave cycle. The magnitude of the bow flare slamming loads is estimated using accurate results from wedge-shaped sections, Zhao and Faltinsen...... (1993) and for green water loads the results from Buchner (1995) and Wang et al .(1998) are applied. The phase lag relative to the wave-induced peak and the decay rate are derived mainly from published experimental results, Sikora, (1998). The results are given in closed-form expressions...
Holdaway, George H.; Mellenthin, Jack A.; Hatfield, Elaine W.
1959-01-01
A diamond wing and body combination was designed to have an area distribution which would result in near optimum zero-lift wave-drag coefficients at a Mach number of 1.00, and decreasing wave-drag coefficient with increasing Mach number up to near sonic leading-edge conditions for the wing. The airfoil section were computed by varying their shape along with the body radii (blending process) to match the selected area distribution and the given plan form. The exposed wing section had an average maximum thickness of about 3 percent of the local chords, and the maximum thickness of the center-line chord was 5.49 percent. The wing had an aspect ratio of 2 and a leading-edge sweep of 45 deg. Test data were obtained throughout the Mach number range from 0.20 to 3.50 at Reynolds numbers based on the mean aerodynamic chord of roughly 6,000,000 to 9,000,000. The zero-lift wave-drag coefficients of the diamond model satisfied the design objectives and were equal to the low values for the Mach number 1.00 equivalent body up to the limit of the transonic tests. From the peak drag coefficient near M = 1.00 there was a gradual decrease in wave-drag coefficient up to M = 1.20. Above sonic leading-edge conditions of the wing there was a rise in the wave-drag coefficient which was attributed in part to the body contouring as well as to the wing geometry. The diamond model had good lift characteristics, in spite of the prediction from low-aspect-ratio theory that the rear half of the diamond wing would carry little lift. The experimental lift-curve slope obtained at supersonic speeds were equal to or greater than the values predicted by linear theory. Similarly the other basic aerodynamic parameters, aerodynamic center position, and maximum lift-drag ratios were satisfactorily predicted at supersonic speeds.
Stability of an external gravity wave in a stratified basic flow with lateral shear
Tomizuka, Akira
2005-01-01
The author investigates the stability of an external gravity wave progressing horizontally in an inviscid and incompressible stratified basic flow with lateral shear. (1) In the model which basic flow has a Helmholtz velocity profile, there exist no neutral solutions contrary to internal gravity waves. Perturbations are always unstable independent of the coefficient of vertical wave mode m or the wave number k_y. (2) In the model which basic flow is composed of unbounded layers with the centr...
Directory of Open Access Journals (Sweden)
Glangeaud F.
2006-11-01
Full Text Available Most multichannel algorithms used for separation of upgoing and downgoing waves in VSPs assume depth-stationarity of the signal on all the traces used in the separation filter. However, if the depth-window of the filters becomes too large (100-200 m signal stationarity cannot be assumed. On the other hand, stationarity is a physically reasonable assumption for two neighbouring probe locations (5-20 m. A comparison is made of three algorithms used for the separation of upgoing and downgoing waves, that require only two adjacent traces and their first arrival times. They are independent of in-depth trace-spacing, provided there are no geological discontinuities between adjacent traces. The first approach (near-theoretical solution operates in the frequency domain. A system of two equations and two unknowns is solved for every frequency within the best coherencebandwidth. The second approach (simple solution is a delay-and-sum, and subtraction filter based on the semblance of the signals. The third approach (Wiener solution uses a Wiener filter to predict the strongest wave, which is generally the downgoing wave. The upgoing wave is then obtained by subtracting the estimated downgoing wave from the full wave record. A second application of the Wiener filter on the upgoing waves can enhance them. The near-theoretical solution and the simple solution are narrow-pass velocity filters and are applicable to zero-offset VSPs. The simple solution is suitable for noisy data. When the signal-to-noise ratio is high, the best results are obtained using the near-theoretical solution. The velocity-filter bandwidth can be increased in the Wiener solution, so that it can also be used in case of dipping reflectors or offset VSPs. The Wiener solution is suitable for noisy data, and its effectiveness can be increased by using a reference trace. The performance of these algorithms on synthetic and field data is evaluated in terms of signal-to-noise ratio, detection
Godin, Oleg A.
2015-04-01
Much like light and sound, acoustic-gravity waves in inhomogeneous atmosphere often have a caustic or caustics, where the ray theory predicts unphysical, divergent values of the wave amplitude and needs to be modified. Increase of the wave magnitude in the vicinity of a caustic makes such vicinities of primary interest in a number of problems, where a signal needs to be separated from a background noise. The value of wave focusing near caustics should be carefully quantified in order to evaluate possible nonlinearities promoted by the focusing. Physical understanding of the wave field in the vicinity of a caustic is also important for understanding of the wave reflection from and transmission (tunneling) through the caustic. To our knowledge, in contrast to caustics of acoustic, electromagnetic, and seismic waves as well as gravity waves in incompressible fluids, asymptotics of acoustic-gravity waves in the vicinity of a caustic have never been studied systematically. In this paper, we fill this gap. Atmospheric waves are considered as linear acoustic-gravity waves in a neutral, horizontally stratified, moving ideal gas of variable composition. Air temperature and wind velocity are assumed to be gradually varying functions of height, and slowness of these variations determines the large parameter of the problem. The scale height of the atmosphere can be large or small compared to the vertical wavelength. It is found that the uniform asymptotics of the wave field in the presence of a simple caustic can be expressed in terms of the Airy function and its derivative. As for the acoustic waves, the argument of the Airy function is expressed in terms of the eikonal calculated in the ray, or WKB, approximation. The geometrical, or Berry, phase, which arises in the consistent WKB approximation for acoustic-gravity waves, plays an important role in the caustic asymptotics. In the uniform asymptotics, the terms with the Airy function and its derivative are weighted by cosine
Directory of Open Access Journals (Sweden)
Peter Bachant
2016-01-01
Full Text Available Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially R e -independent at a Reynolds number based on the rotor diameter R e D ≈ 10 6 or an approximate average Reynolds number based on the blade chord length R e c ≈ 2 × 10 5 . A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of R e investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calculated, a similar R e threshold was revealed. These results imply that physical model studies of cross-flow turbines should achieve R e D ∼ 10 6 to properly approximate both the performance and wake dynamics of full-scale devices and arrays.
Raju, R. S.; Reddy, B. M.; Rashidi, M. M.; Gorla, R. S. R.
2017-08-01
In this investigation, the numerical results of a mixed convective MHD chemically reacting flow past a vertical plate embedded in a porous medium are presented in the presence of cross diffusion effects and convective boundary condition. Instead of the commonly used conditions of constant surface temperature or constant heat flux, a convective boundary condition is employed which makes this study unique and the results more realistic and practically useful. The momentum, energy, and concentration equations derived as coupled second-order, ordinary differential equations are solved numerically using a highly accurate and thoroughly tested element free Galerkin method (EFGM). The effects of the Soret number, Dufour number, Grashof number for heat and mass transfer, the viscous dissipation parameter, Schmidt number, chemical reaction parameter, permeability parameter and Biot number on the dimensionless velocity, temperature and concentration profiles are presented graphically. In addition, numerical results for the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are discussed through tabular forms. The discussion focuses on the physical interpretation of the results as well as their comparison with the results of previous studies.
Directory of Open Access Journals (Sweden)
Raju R.S.
2017-08-01
Full Text Available In this investigation, the numerical results of a mixed convective MHD chemically reacting flow past a vertical plate embedded in a porous medium are presented in the presence of cross diffusion effects and convective boundary condition. Instead of the commonly used conditions of constant surface temperature or constant heat flux, a convective boundary condition is employed which makes this study unique and the results more realistic and practically useful. The momentum, energy, and concentration equations derived as coupled second-order, ordinary differential equations are solved numerically using a highly accurate and thoroughly tested element free Galerkin method (EFGM. The effects of the Soret number, Dufour number, Grashof number for heat and mass transfer, the viscous dissipation parameter, Schmidt number, chemical reaction parameter, permeability parameter and Biot number on the dimensionless velocity, temperature and concentration profiles are presented graphically. In addition, numerical results for the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are discussed through tabular forms. The discussion focuses on the physical interpretation of the results as well as their comparison with the results of previous studies.
Nakamura, Hisashi; Miyasaka, Takafumi; Kosaka, Yu; Takaya, Koutarou; Honda, Meiji
Structure and dynamics of the Northern Hemisphere planetary waves, which cause geographically fixed longitudinal dependence to the climate, are examined through dynamical diagnoses applied to modern global data sets. Summertime planetary wave signature in the Western Hemisphere includes surface maritime subtropical anticyclones, for which pronounced land-sea thermal contrasts across the west coasts of subtropical continents are important as thermal forcing. Its Eastern Hemisphere counterpart is dominated by continental-scale cyclone and anticyclone in the lower and upper troposphere, respectively, associated with Asian monsoon. Wintertime planetary waves are forced orographically and thermally in middle/subpolar latitudes, with pronounced land-sea thermal contrasts, including a contribution from diabatic heating along oceanic "storm tracks." Wave activity thus generated propagates southeastward, maintaining an upper-level vorticity dipole over the Atlantic with an eddy-driven polar-front jet (PFJ) separated from a subtropical jet (STJ). Its Pacific counterpart is in the opposite sense with a predominant single jet with PFJ-STJ hybrid characteristics. Stationary circulation anomaly patterns that cause regional climate variability are strong in winter over the midlatitude ocean basins, extracting kinetic energy effectively from diffluent westerly jets and with feedback forcing by transient eddies along storm tracks. In the summertime Asian STJ exit, a stationary baroclinic anomaly pattern is dominant, maintaining itself by extracting potential energy from the jet and negating it by anomalous cumulus activity. Each of these patterns thus bears characteristics of a dynamical mode. Generation of shallow, cold surface anticyclones is discussed from a viewpoint of interaction of stationary Rossby waves with surface baroclinic zones.
Mixed convection flow and heat transfer in a vertical wavy channel ...
African Journals Online (AJOL)
Mixed convection flow and heat transfer in a vertical wavy channel containing porous and fluid layer with traveling thermal waves. ... Results for a wide range of governing parameters such as Grashof number, viscosity ratio, width ratio, conductivity ratio, and traveling thermal temperature are plotted for different values of ...
1993-02-01
The Ground Wave Emergency Network (GWEN) is a radio communication system designed to relay emergency messages between strategic military areas in the continental United States. The system is immune to the effects of high-altitude electromagnetic pulse (HEMP) energy surges caused by nuclear bursts in the ionosphere that would disrupt conventional communications equipment such as telephones and shortwave radios. A failure of such equipment would prevent timely communications among top military and civilian leaders and strategic Air Force locations and prevent U.S. assessment and retaliation during an attack. GWEN is an essential part of a defense modernization program to upgrade and improve our nation's communications system, thereby strengthening deterrence. The GWEN system consists of a network of relay nodes, receive-only stations, and input/output stations. Each relay node, such as the one proposed in southern Nevada consists of a guyed radio tower facility similar to those used by commercial AM broadcast transmitters.
Giuliani, C; Agostinelli, A; Di Nardo, F; Fioretti, S; Burattini, L
2016-01-01
Electrocardiographic (ECG) T-wave endpoint (Tend) identification suffers lack of reliability due to the presence of noise and variability among leads. Tend identification can be improved by using global repolarization waveforms obtained by combining several leads. The dominant T-wave (DTW) is a global repolarization waveform that proved to improve Tend identification when computed using the 15 (I to III, aVr, aVl, aVf, V1 to V6, X, Y, Z) leads usually available in clinics, of which only 8 (I, II, V1 to V6) are independent. The aim of the present study was to evaluate if the 8 independent leads are sufficient to obtain a DTW which allows a reliable Tend identification. To this aim Tend measures automatically identified from 15-dependent-lead DTWs of 46 control healthy subjects (CHS) and 103 acute myocardial infarction patients (AMIP) were compared with those obtained from 8-independent-lead DTWs. Results indicate that Tend distributions have not statistically different median values (CHS: 340 ms vs. 340 ms, respectively; AMIP: 325 ms vs. 320 ms, respectively), besides being strongly correlated (CHS: ρ=0.97, AMIP: 0.88; Plead DTWs is statistically equivalent to measuring Tend from the 8-independent-lead DTWs. In conclusion, for the clinical purpose of automatic Tend identification from DTW, the 8 independent leads can be used without a statistically significant loss of accuracy but with a significant decrement of computational effort. The lead dependence of 7 out of 15 leads does not introduce a significant bias in the Tend determination from 15 dependent lead DTWs.
A wave dynamical interpretation of Saturn's polar hexagon
Allison, M.; Godfrey, D. A.; Beebe, R. F.
1990-01-01
The hexagonal, pole-centered cloud feature in Saturn's northern atmosphere, as revealed in Voyager close-encounter imaging mosaics, may be interpreted as a stationary Rossby wave. The wave is embedded within a sharply peaked eastward jet (of 100 meters per second) and appears to be perturbed by at least one anticyclonic oval vortex immediately to the south. The effectively exact observational determination of the horizontal wave number and phase speed, applied to a simple model dispersion relation, suggests that the wave is vertically trapped and provides a diagnostic template for further modeling of the deep atmospheric stratification.
Scour at the head of a vertical-wall breakwater
DEFF Research Database (Denmark)
Sumer, B. Mutlu; Fredsøe, Jørgen
1997-01-01
This paper presents the results of an experimental investigation on the near-bed flow patterns, the bed shear stress amplification and scour around the head of a vertical-wall breakwater, using regular waves. The Keulegan-Carpenter number (KC), based on the diameter of the breakwater head, is found...... to be the major parameter that governs the flow and the equilibrium scour depth. Basic flow structures are identified as function of KC. The scour depth is found to increase with increasing the Keulegan-Carpenter number. The necessary extent of the conventional stone protection is studied. An empirical formula...
Identification of rocket-induced acoustic waves in the ionosphere
Mabie, Justin; Bullett, Terence; Moore, Prentiss; Vieira, Gerald
2016-10-01
Acoustic waves can create plasma disturbances in the ionosphere, but the number of observations is limited. Large-amplitude acoustic waves generated by energetic sources like large earthquakes and tsunamis are more readily observed than acoustic waves generated by weaker sources. New observations of plasma displacements caused by rocket-generated acoustic waves were made using the Vertically Incident Pulsed Ionospheric Radar (VIPIR), an advanced high-frequency radar. Rocket-induced acoustic waves which are characterized by low amplitudes relative to those induced by more energetic sources can be detected in the ionosphere using the phase data from fixed frequency radar observations of a plasma layer. This work is important for increasing the number and quality of observations of acoustic waves in the ionosphere and could help improve the understanding of energy transport from the lower atmosphere to the thermosphere.
Tidal and gravity waves study from the airglow measurements at ...
Indian Academy of Sciences (India)
The other waves may be the upward propagating gravity waves or waves resulting from the interaction of inter-mode tidal oscillations, interaction of tidal waves with planetary waves and gravity waves. Some times, the second harmonic wave has higher vertical velocity than the corresponding fundamental wave. Application ...
Coexistence of Strategic Vertical Separation and Integration
DEFF Research Database (Denmark)
Jansen, Jos
2003-01-01
This paper gives conditions under which vertical separation is chosen by some upstream firms, while vertical integration is chosen by others in the equilibrium of a symmetric model. A vertically separating firm trades off fixed contracting costs against the strategic benefit of writing a (two......-part tariff, exclusive dealing) contract with its retailer. Coexistence emerges when more than two vertical Cournot oligopolists supply close substitutes. When vertical integration and separation coexist, welfare could be improved by reducing the number of vertically separating firms. The scope...
Pritchard, Michael S.; Bretherton, Christopher S.; DeMott, Charlotte A.
2014-09-01
The effects of artificially restricting the 32-128 km horizontal scale regime on MJO dynamics in the Superparameterized Community Atmosphere Model v.3.0 have been explored through reducing the extent of its embedded cloud resolving model (CRM) arrays. Two and four-fold reductions in CRM extent (from 128 to 64 km and 32 km) produce statistical composite MJO signatures with spatial scale, zonal phase speed, and intrinsic wind-convection anomaly structure that are all remarkably similar to the standard SPCAM's MJO. This suggests that the physics of mesoscale convective organization on 32-128 km scales are not critical to MJO dynamics in SPCAM and that reducing CRM extent may be a viable strategy for 400% more computationally efficient analysis of superparameterized MJO dynamics. However several unexpected basic state responses caution that extreme CRM domain reduction can lead to systematic mean state issues in superparameterized models. We hypothesize that an artificial limit on the efficiency of vertical updraft mixing is set by the number of grid columns available for compensating subsidence in the embedded CRM arrays. This can lead to reduced moisture ventilation supporting too much liquid cloud and thus an overly strong cloud shortwave radiative forcing, particularly in regions of deep convection.
Ashby, G. C., Jr.
1974-01-01
Experimental data have been obtained for two series of bodies at Mach 6 and Reynolds numbers, based on model length, from 1.4 million to 9.5 million. One series consisted of axisymmetric power-law bodies geometrically constrained for constant length and base diameter with values of the exponent n of 0.25, 0.5, 0.6, 0.667, 0.75, and 1.0. The other series consisted of positively and negatively cambered bodies of polygonal cross section, each having a constant longitudinal area distribution conforming to that required for minimizing zero-lift wave drag at hypersonic speeds under the geometric constraints of given length and volume. At the highest Reynolds number, the power-law body for minimum drag is blunter (exponent n lower) than predicted by inviscid theory (n approximately 0.6 instead of n = 0.667); however, the peak value of lift-drag ratio occurs at n = 0.667. Viscous effects were present on the bodies of polygonal cross section but were less pronounced than those on the power-law bodies. The trapezoidal bodies with maximum width at the bottom were found to have the highest maximum lift-drag ratio and the lowest mimimum drag.
A tsunami wave recorded near a glacier front
Directory of Open Access Journals (Sweden)
A. V. Marchenko
2012-02-01
Full Text Available We observed a tsunami wave near the glacier front in the Temple Fjord (Spitsbergen. Two temperature and pressure recorders were deployed on a wire from the ice approximately 300 m from the glacier front. A pressure recorder was located under them on the bottom. The vertical displacement of the ice was approximately 30 cm and the period of the tsunami wave was 90 s. We attribute the generation of this wave to the displacement of the glacier similarly to the landslide tsunami generated by the motion of a block of rocks down the sloping bottom. The glacier motion also generated a short-period (12 s deformation wave in the ice cover. The measurements allowed us to estimate the wave number of these waves and the Young's modulus of the ice.
Huber, Grégory; Tanguy, Sébastien; Béra, Jean-Christophe; Gilles, Bruno
2015-10-01
This paper is focused on the numerical simulation of the interaction of an ultrasound wave and an air bubble surrounded by water. Our interest is to develop a fully compressible solver in the two phases and to account for surface tension effects. As the volume oscillation of the bubble occurs in a low Mach number regime, a specific attention must be paid to the effectiveness of the numerical method chosen to solve the compressible Euler equations. Several numerical methods are implemented and confronted on a benchmarck. This preliminary test highlights that the projection method is the most accurate one. Then a basic implementation of the surface tension leads to strong spurious currents and numerical instabilities. A specific velocity/pressure time splitting is thus proposed to overcome this issue. Numerical evidences of the efficiency of this new numerical scheme are provided with the numerical simulation of the interaction between a bubble and a wavefront. Indeed, both the accuracy and the stability of the overall algorithm are enhanced using this new numerical method.
Wave Transformation and Undertow Over a Barred Beach
Fujii, E.; Özkan-Haller, H.; Long, J.
2004-12-01
The mean cross-shore flow (undertow) over a barred beach is examined by calibrating an existing wave and circulation model which will provide predictions that will be compared to in-situ measurements. The wave model applied to the experiment is a linear shoaling model with wave breaking dissipation according to Dally, Dean, and Dalrymple (2002); following the calibration of the wave model the undertow model by Garcez Faria et al. (2000) is calibrated. The experiment was conducted in the long wave flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University (OSU). Regular waves with a wave height of 0.60 meters and a frequency of 0.25 Hz were generated and vertical velocity profiles were collected at seven different cross-shore locations each with eight to nine points per profile. Three Acoustic Doppler Velocimeters(ADV) were used to collect the cross-shore flow velocities and six fixed wave gauges were used to measure the water surface elevation. The data collected from the wave gauges were processed using a zero-upcrossing analysis followed by ensemble averaging the waves to determine the average wave height of each cross-shore gage. This approach was taken since regular waves are assumed to be similar to one another and would yield higher numbers of realizations, making it a more statistically reliable estimate. In total, 49 different time series were analyzed for each wave gage, yielding a reliable wave height estimate. The calibration of the wave model was accomplished by altering the three free parameters: higher breaking threshold γ , lower breaking threshold γ s, and an empirical constant κ , until the wave model best fit the data. Subsequently, the undertow model was calibrated by varying the eddy viscosity (μ ) for each profile. The presented work was performed as part of the Research Experience for Undergraduates (REU) program during the summer of 2004 at OSU.
Uplift Capacity of Inclined Underreamed Piles Subjected to Vertical Load
Rahman, Md. Akilur; Sengupta, Siddhartha
2017-12-01
Many offshore structures are subjected to overturning moments due to wind load, wave pressure, and ship impacts. Inclined (batter) piles are used to support such structures, and to carry the horizontal and vertical loads resulted from the overturning moments. Though studies have been done with inclined piles having no underream bulb, little information is available in the literature about estimating the uplift capacity of inclined underreamed piles. In the present study laboratory experiments have been done with vertically loaded model piles having no underream as well as with one and two underreams. The piles were positioned at angle of inclination of θ = 0°, 10°, 20°, 30° (with vertical); and placed in locally available sand under vertical uplift load. Three different pile stem diameters (D = 20, 25, and 35 mm) were used. The corresponding pile length to stem diameter (l/D) ratio were 18, 14, and 10 respectively. Experiments had been conducted with two relative different densities (45 and 70%) of sand. The failure uplift loads were obtained in each case. It had been found that for inclined piles increase in number of underream bulbs from 0 to 2 was quite effective in resisting uplift loads corresponding to piles having l/D equals to 10. The percentage decreases in uplift capacity corresponding to increase in inclination angle were more pronounced for piles with double underreams.
National Research Council Canada - National Science Library
Herrmann, Robert B; Julia, Jordi; Ammon, Charles J
2007-01-01
.... Receiver functions are primarily sensitive to shear-wave velocity contrast and vertical travel times and surface-wave dispersion measurements are sensitive to vertical shear-wave velocity averages...
National Research Council Canada - National Science Library
Julia, Jordi; Ammon, Charles J; Herrimann, Robert B
2006-01-01
.... Receiver functions are primarily sensitive to shear-wave velocity contrasts and vertical travel times and surface-wave dispersion measurements are sensitive to vertical shear-wave velocity averages...
Acquired vertical accommodative vergence.
Klein-Scharff, Ulrike; Kommerell, Guntram; Lagrèze, Wolf A
2008-03-08
Vertical accommodative vergence is an unusual synkinesis in which vertical vergence is modulated together with accommodation. It results from a supranuclear miswiring of the network normally conveying accommodative convergence. So far, it is unknown whether this condition is congenital or acquired. We identified an otherwise healthy girl who gradually developed vertical accommodative vergence between five to 13 years of age. Change of accommodation by 3 diopters induced a vertical vergence of 10 degrees. This observation proves that the miswiring responsible for vertical accommodative vergence must not necessarily be congenital, but can be acquired. The cause and the mechanism leading to vertical accommodative vergence are yet unknown.
Tezel, Okan; Karabulut, Savas; Imre, Nazire; Caglak, Faruk; Yeziz, Hatice; Ozcep, Ferhat
2013-04-01
Istanbul is a megacity with 17 million inhabitants. After the 17 August 1999 earthquake, many researchers have focused on the mitigation of earthquake hazards in the Sea of Marmara and its vicinity. If we want to lessen the effects of such an earthquake, we have to learn about three different types of problems which are properties of the earthquake's source, whether of site effect or properties of engineering structures. When İstanbul Metropolitian Municipilaty obtained a World Bank Credit 5 years ago, they had a microzonation report for only a limited area which finished at Har amidere in the western site of Istanbul. Because they will not have any new project, the western side of Haramidere hasn't been studied by any scientist. For this reason, we focused on the Gulf of Buyukcekmece which is located on the western part of Haramidere and suffered in the 1999 earthquake. There are five geological units in the study area such as Bakirkoy formation, Gurpinar formation, Çukurçeşme formation, Güngören formation and Alluvial deposit. We conducted some measurements which are multi-channel analysis of surface wave (MASW), microtremor array method (MAM) and vertical electrical sounding(VES). The aim of using VES data is to determine bedrock depth, learn whether there is a new fault and learn the electrical properties of each layer of bedrock. The MASW method is so attactive, cheap and fast. According to seismic refraction, it has some advantages that are determining the deeper part of sub-surface, lower velocity layers and velocity contrast. Especially, we use natural sources; MAM methods are more useful method in the city. For all of these purposes, we collected MASW and MAM measurements at 80 sites and VES measurements at 20 sites. As primary results for VES measurements, we determined the bedrock depth by evaluating the VES measurements for the central, eastern and western part of Buyukcekmece Gulf. Bedrock depth is 308 meters in the central and eastern part of
Numerical simulation of tsunami-scale wave boundary layers
DEFF Research Database (Denmark)
Williams, Isaac A.; Fuhrman, David R.
2016-01-01
This paper presents a numerical study of the boundary layer flow and properties induced by tsunami-scalewaves. For this purpose, an existing one-dimensional vertical (1DV) boundary layer model, based on the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equations...... demonstrating the ability to reproduce accurate velocity profiles, turbulence, and bed shear stresses on both smooth and rough beds.The validated model is then employed for the study of transient wave boundary layers at full tsunami scales,covering a wide and realistic geophysical range in terms of the flow...... duration, bottom roughness, and associated Reynolds numbers. For this purpose, three different “synthetic” (idealised) tsunami wave descriptions are considered i.e., invoking: (1) single wave (solitary-like, but with independent period and wave height),(2) sinusoidal, and (3) N-wave descriptions. The flow...
Diurnal variation of mountain waves
Directory of Open Access Journals (Sweden)
R. M. Worthington
2006-11-01
Full Text Available Mountain waves could be modified as the boundary layer varies between stable and convective. However case studies show mountain waves day and night, and above e.g. convective rolls with precipitation lines over mountains. VHF radar measurements of vertical wind (1990–2006 confirm a seasonal variation of mountain-wave amplitude, yet there is little diurnal variation of amplitude. Mountain-wave azimuth shows possible diurnal variation compared to wind rotation across the boundary layer.
Krivcov, Vladimir [Miass, RU; Krivospitski, Vladimir [Miass, RU; Maksimov, Vasili [Miass, RU; Halstead, Richard [Rohnert Park, CA; Grahov, Jurij [Miass, RU
2011-03-08
A vertical axis wind turbine is described. The wind turbine can include a top ring, a middle ring and a lower ring, wherein a plurality of vertical airfoils are disposed between the rings. For example, three vertical airfoils can be attached between the upper ring and the middle ring. In addition, three more vertical airfoils can be attached between the lower ring and the middle ring. When wind contacts the vertically arranged airfoils the rings begin to spin. By connecting the rings to a center pole which spins an alternator, electricity can be generated from wind.
Vertical and Interfacial Transport in Wetlands (Invited)
Variano, E. A.
2010-12-01
The objective of this work is to understand the fluxes connecting the water column, substrate, and atmosphere in wetland environments. To do this, analytical, numerical, and laboratory models have been used to quantify the hydrodynamic contributions to vertical fluxes. A key question is whether the hydrodynamic transport can be modeled as a diffusivity, and, if so, what the vertical structure of this diffusivity is. This question will be addressed in a number of flow types and for a number of fluxes. The fluxes of interest are heat, sediment, dissolved gases (such as methane and oxygen) and other dissolved solutes (such as nutrients and pollutants). The flows of interest include: unidirectional current, reversing flow (under waves, seiches, and tides), wind-sheared surface flows, and thermal convection. Rain and bioturbation can be important, but are not considered in the modeling work discussed herein. Specifically, we will present results on gas transport at wind-sheared free surface, sediment transport in unidirectional flow, and heat transfer in an oscillating flow cause by a seiche. All three of these will be used to consider the question of appropriate analytical models for vertical transport. The analytic models considered here are all 1D models that assume homogeneity in the horizontal plane. The numerical models use finite element methods and resolve the flow around individual vegetation stems in an idealized geometry. Laboratory models discussed herein also use an idealized geometry. Vegetation is represented by an array of cylinders, whose geometry is modeled after Scirpus spp. wetlands in Northern California. The laboratory model is constructed in a way that allows optical access to the flow, even in dense vegetation and far from boundaries. This is accomplished by using fluoropolymer plastics to construct vegetation models. The optical access allows us to employ particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) to measure
Energy Technology Data Exchange (ETDEWEB)
Hata, Koichi, E-mail: hata@iae.kyoto-u.ac.j [Institute of Advanced Energy, Kyoto Univ., Gokasho, Uji, Kyoto 611-0011 (Japan); Masuzaki, Suguru, E-mail: masuzaki@LHD.nifs.ac.j [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292 (Japan)
2009-12-15
The subcooled boiling heat transfer and the steady-state critical heat fluxes (CHFs) in a short vertical SUS304-tube for the flow velocities (u = 17.28-40.20 m/s), the inlet liquid temperatures (T{sub in} = 293.30-362.49 K), the inlet pressures (P{sub in} = 842.90-1467.93 kPa) and the exponentially increasing heat input (Q = Q{sub 0} exp(t/tau), tau = 8.5 s) are systematically measured by the experimental water loop comprised of a multistage canned-type circulation pump with high pump head. The SUS304 test tubes of inner diameters (d = 3 and 6 mm), heated lengths (L = 33 and 59.5 mm), effective lengths (L{sub eff} = 23.3 and 49.1 mm), L/d (=11 and 9.92), L{sub eff}/d (=7.77 and 8.18), and wall thickness (delta = 0.5 mm) with average surface roughness (Ra = 3.18 mum) are used in this work. The inner surface temperature and the heat flux from non-boiling to CHF are clarified. The subcooled boiling heat transfer for SUS304 test tube is compared with our Platinum test tube data and the values calculated by other workers' correlations for the subcooled boiling heat transfer. The influence of flow velocity on the subcooled boiling heat transfer and the CHF is investigated into details and the widely and precisely predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical SUS304-tube is given based on the experimental data. The correlation can describe the subcooled boiling heat transfer obtained in this work within 15% difference. Nucleate boiling surface superheats for the SUS304 test tube become very high. Those at the high flow velocity are close to the lower limit of Heterogeneous Spontaneous Nucleation Temperature. The dominant mechanisms of the flow boiling CHF in a short vertical SUS304-tube are discussed.
The instability of counter-propagating kernel gravity waves in a constant shear flow
Umurhan, O M; Harnik, N; Lott, F
2007-01-01
The mechanism describing the recently developed notion of kernel gravity waves (KGWs) is reviewed and such structures are employed to interpret the unstable dynamics of an example stratified plane parallel shear flow. This flow has constant vertical shear, is infinite in the vertical extent, and characterized by two density jumps of equal magnitude each decreasing successively with height, in which the jumps are located symmetrically away from the midplane of the system. We find that for a suitably defined bulk-Richardson number there exists a band of horizontal wavenumbers which exhibits normal-mode instability. The instability mechanism closely parallels the mechanism responsible for the instability seen in the problem of counter-propagating Rossby waves. In this problem the instability arises out of the interaction of counter-propagating gravity waves. We argue that the instability meets the Hayashi-Young criterion for wave instability. We also argue that the instability is the simplest one that can arise ...
Butt, A. R.; Abdullah, M.; Raza, N.; Imran, M. A.
2017-10-01
In this work, semi analytical solutions for the heat and mass transfer of a fractional MHD Jeffery fluid over an infinite oscillating vertical plate with exponentially heating and constant mass diffusion via the Caputo-Fabrizio fractional derivative are obtained. The governing equations are transformed into dimensionless form by introducing dimensionless variables. A modern definition of the Caputo-Fabrizio derivative has been used to develop the fractional model for a Jeffery fluid. The expressions for temperature, concentration and velocity fields are obtained in the Laplace transformed domain. We have used the Stehfest's and Tzou's algorithm for the inverse Laplace transform to obtain the semi analytical solutions for temperature, concentration and velocity fields. In the end, in order to check the physical impact of flow parameters on temperature, concentration and velocity fields, results are presented graphically and in tabular forms.
Earlie, C. S.; le Dantec, N.; Young, A.
2016-12-01
Coastal cliff erosion is a widespread problem that threatens property and infrastructure globally. The prediction of this risk calls for robust understanding of the processes and mechanisms involved in causing coastal cliff failure. Over the last decade, a number of geomorphological studies have highlighted the importance of the relationship between the offshore wave climate and cliff-toe water levels, and the resultant coastal response in terms of cliff-top ground motion and erosion. Field-based studies of instantaneous cliff response to direct wave impact have shown that wave-induced loading of the foreshore leads to cliff-top ground motions that may have the potential to weaken the integrity of the rocks and prepare them for failure. In order to understand wave-cliff interaction and how beach morphodynamics influences cliff-top ground motion and cliff erosion, two field experiments were carried out simultaneously at two locations in Northern Brittany (France). This three-month long winter field campaign (Jan-Mar 2016) included, for the first time, a comparison of cliff-top ground motion and cliff erosion at sites fronted by different beach morphologies (reflective/dissipative), along with monitoring of hydrodynamic forcing and beach topography. The magnitude of cliff-top displacements at both sites were dependent on tidal stage and free water surface elevation at the cliff toe, with the greatest contributions of cliff-top ground motions found at infragravity frequencies (0.05-0.005 Hz). Vertical displacements at infragravity and incident sea-swell (0.1-0.5 Hz) frequencies were greater at the dissipative site, apart from during spring high tide and energetic wave conditions, where displacements were two times that at the reflective site. Combining these wave-cliff interaction data with beach morphology and nearshore bathymetry will be key to understanding the spatial variability in cliff erosion under a variety of environmental settings and forcing conditions.
Near Vertical Incidence Skywave: Interaction of antenna and propagation mechanism
Witvliet, Ben A.
2015-01-01
In areas where no telecommunication infrastructure exists, or when that infrastructure is destroyed by a natural disaster, Near Vertical Incidence Skywave (NVIS) radio wave propagation may provide a lifeline to the outside world. To exploit NVIS propagation, radio waves are transmitted straight up,
Model for predicting mountain wave field uncertainties
Damiens, Florentin; Lott, François; Millet, Christophe; Plougonven, Riwal
2017-04-01
Studying the propagation of acoustic waves throughout troposphere requires knowledge of wind speed and temperature gradients from the ground up to about 10-20 km. Typical planetary boundary layers flows are known to present vertical low level shears that can interact with mountain waves, thereby triggering small-scale disturbances. Resolving these fluctuations for long-range propagation problems is, however, not feasible because of computer memory/time restrictions and thus, they need to be parameterized. When the disturbances are small enough, these fluctuations can be described by linear equations. Previous works by co-authors have shown that the critical layer dynamics that occur near the ground produces large horizontal flows and buoyancy disturbances that result in intense downslope winds and gravity wave breaking. While these phenomena manifest almost systematically for high Richardson numbers and when the boundary layer depth is relatively small compare to the mountain height, the process by which static stability affects downslope winds remains unclear. In the present work, new linear mountain gravity wave solutions are tested against numerical predictions obtained with the Weather Research and Forecasting (WRF) model. For Richardson numbers typically larger than unity, the mesoscale model is used to quantify the effect of neglected nonlinear terms on downslope winds and mountain wave patterns. At these regimes, the large downslope winds transport warm air, a so called "Foehn" effect than can impact sound propagation properties. The sensitivity of small-scale disturbances to Richardson number is quantified using two-dimensional spectral analysis. It is shown through a pilot study of subgrid scale fluctuations of boundary layer flows over realistic mountains that the cross-spectrum of mountain wave field is made up of the same components found in WRF simulations. The impact of each individual component on acoustic wave propagation is discussed in terms of
Jackson, F. C.
1980-01-01
Scanning beam microwave radars were used to measure ocean wave directional spectra from satellites. In principle, surface wave spectral resolution in wave number can be obtained using either short pulse (SP) or dual frequency (DF) techniques; in either case, directional resolution obtains naturally as a consequence of a Bragg-like wave front matching. A four frequency moment characterization of backscatter from the near vertical using physical optics in the high frequency limit was applied to an analysis of the SP and DF measurement techniques. The intrinsic electromagnetic modulation spectrum was to the first order in wave steepness proportional to the large wave directional slope spectrum. Harmonic distortion was small and was a minimum near 10 deg incidence. NonGaussian wave statistics can have an effect comparable to that in the second order of scattering from a normally distributed sea surface. The SP technique is superior to the DF technique in terms of measurement signal to noise ratio and contrast ratio.
Numerical modelling of wave current interactions at a local scale
Teles, Maria João; Pires-Silva, António A.; Benoit, Michel
2013-08-01
The present work is focused on the evaluation of wave-current interactions through numerical simulations of combined wave and current flows with the Code_Saturne (Archambeau et al., 2004), an advanced CFD solver based on the RANS (Reynolds Averaged Navier-Stokes) equations. The objectives of this paper are twofold. Firstly, changes in the mean horizontal velocity and the horizontal-velocity amplitude profiles are studied when waves are superposed on currents. The influence of various first and second order turbulence closure models is addressed. The results of the numerical simulations are compared to the experimental data of Klopman (1994) and Umeyama (2005). Secondly, a more detailed study of the shear stresses and the turbulence viscosity vertical profile changes is also pursued when waves and currents interact. This analysis is completed using the data from Umeyama (2005). A relationship between a non-dimensional parameter involving the turbulence viscosity and the Ursell number is subsequently proposed.
1993-02-01
The Ground Wave Emergency Network (GWEN) is a radio communication system designed to relay emergency messages between strategic military areas in the continental United States. The system is immune to the effects of high-altitude electromagnetic pulse (HEMP) energy surges caused by nuclear bursts in the ionosphere that would disrupt conventional communications equipment such as telephones and shortwave radios. A failure of such equipment would prevent timely communications among top military and civilian leaders and strategic Air Force locations and prevent U.S. assessment and retaliation during an attack. GWEN is an essential part of a defense modernization program to upgrade and improve our nation's communications system, thereby strengthening deterrence. The GWEN system consists of a network of relay nodes, receive-only stations, and input/output stations. Each relay node, such as the one proposed in northwestern Nebraska, consists of a guyed radio tower facility similar to those used by commercial AM broadcast transmitters.
1993-03-01
The Ground Wave Emergency Network (GWEN) is a radio communication system designed to relay emergency messages between strategic military areas in the continental United States. The system is immune to the effects of high-altitude electromagnetic pulse (HEMP) energy surges caused by nuclear bursts in the ionosphere that would disrupt conventional communications equipment such as telephones and shortwave radios. A failure of such equipment would prevent timely communications among top military and civilian leaders and strategic Air Force locations and prevent U.S. assessment and retaliation during an attack. GWEN is an essential part of a defense modernization program to upgrade and improve our nation's communications system, thereby strengthening deterrence. The GWEN system consists of a network of relay nodes, receive-only stations, and input/output stations. Each relay node, such as the one proposed in southern Nevada consists of a guyed radio tower facility similar to those used by commercial AM broadcast transmitters.
Nonlinear elastic waves in materials
Rushchitsky, Jeremiah J
2014-01-01
The main goal of the book is a coherent treatment of the theory of propagation in materials of nonlinearly elastic waves of displacements, which corresponds to one modern line of development of the nonlinear theory of elastic waves. The book is divided on five basic parts: the necessary information on waves and materials; the necessary information on nonlinear theory of elasticity and elastic materials; analysis of one-dimensional nonlinear elastic waves of displacement – longitudinal, vertically and horizontally polarized transverse plane nonlinear elastic waves of displacement; analysis of one-dimensional nonlinear elastic waves of displacement – cylindrical and torsional nonlinear elastic waves of displacement; analysis of two-dimensional nonlinear elastic waves of displacement – Rayleigh and Love nonlinear elastic surface waves. The book is addressed first of all to people working in solid mechanics – from the students at an advanced undergraduate and graduate level to the scientists, professional...
Propagation of gravity waves through non-uniform stratification
Pütz, Christopher; Klein, Rupert
2017-04-01
We present a method to compute the transmission of gravity waves through a finite region of a non-uniformly stratified atmosphere. It is based on an approximate solution of the Taylor-Goldstein equation. With the method, we are able to compute a transmission coefficient for gravity waves, which is defined as the ratio of the vertical wave energy fluxes below and above the region of non-uniform stratification. It makes use of the fact that plane wave solutions exist in uniform stratification and models the atmosphere as a multi-layer fluid where each layer is uniformly stratified. The solutions are matched at the interfaces in a way that the continuity of pressure and vertical wind is ensured, so that we are finally able to relate incident and transmitted wave amplitudes. Further, the limit of increasing number of layers is investigated and we obtain a reformulation of the Taylor-Goldstein equation. This equation can not be solved analytically, but numerically, giving a solution in which it is possible to distinguish between the two branches of the gravity wave dispersion relation, namely upward and downward travelling waves. Hence, we are also able to compute a transmission coefficient from this procedure. Moreover, it can be shown that the multi-layer solution converges to the limit solution quadratically with increasing number of layers. The results we obtain for some test cases are in accordance with several existing results, but provide more general insights into the interaction of gravity waves propagating through non-uniform stratification. Also, the multi-layer method can be extended to give an approximate solution to the Taylor-Goldstein equation without using any numerical integration.
Internal Solitary Wave Reflection Near Dongsha Atoll, the South China Sea
Bai, Xiaolin; Li, Xiaofeng; Lamb, Kevin G.; Hu, Jianyu
2017-10-01
Internal solitary wave (ISW) reflection is rarely observed in satellite images, even in the South China Sea (SCS), where the strongest and most energetic ISWs in the world have been observed. Compared to the large number of satellite images showing shoaling ISW in the SCS, fewer than 10 satellite images have been reported showing ISW reflection. In this study, we collect recent satellite images and implement a numerical model to analyze ISW reflection near Dongsha Atoll, in the SCS. Satellite observations show that the reflection appears to be associated with the large-amplitude ISWs generated by strong tidal currents in Luzon Strait. Numerical simulations show that ISWs break when reaching the sloping bottom. Part of ISW energy is reflected by mode-1 waves and their trailing mode-2 waves. The mode-1 waves have two types: long inertia-gravity waves and breaking ISW-induced short waves. They propagate quickly but induce weak vertical velocity and surface imprints. Mode-2 waves induce strong vertical velocity, showing visible signature in satellites. Horizontal distribution of the energy indicates that a maximum energy of about 2% of the incident energy is contained in a single reflected wave. This could explain why the reflected waves are rarely observed, because reflected waves must be sufficiently large to be detected in satellite images. Although individual wave's energy is small, in total up to 20% of the incident wave is reflected by the groups of mode-1 and mode-2 waves. This suggests that ISW reflection has a significant impact on energy distribution over the continental slopes.
Directory of Open Access Journals (Sweden)
Pensiri Sompong
2014-01-01
Full Text Available The effects of wavy geometry on natural convection in an enclosure with two wavy vertical walls and filled with fluid saturated porous media are investigated numerically by using finite element method. The wavy enclosure is transformed to a unit square in the computational domain and the finite element formulations are solved in terms of ξη-coordinate based on iterative method. In order to investigate the effects of interested parameters, the values of wave amplitude (λ = 0.05 and 0.1 and number of undulations (n = 1 and 2 are chosen with constants Ra = 105, Da = 10−3, and Pr = 0.71. It is found that the increase in number of undulations has small effect on natural convection inside the enclosure whereas the increase in wave amplitude reduces the strength of convection because higher wave volume plays a barricade role.
Research on Far-Field Wavelet's Extraction and Application of Vertical Cable System
Wang, Xiangchun; Xiao, Qingsong; Xia, Changliang; Wu, Zhongliang; Xie, Chengliang
2017-04-01
In marine seismic exploration, ghost wave and bubble effect reduce the vertical resolution and interpretation accuracy seriously. Here firstly the far-field wavelet including source wavelet, ghost wave and bubble effect recorded by the vertical cable system (VCS) is extracted. Then, filters are designed using the extracted far-field wavelet to eliminate ghost wave, bubble effect and source wavelet. At last, the designed filters are applied to the seismic data of VCS. The results show that this method can eliminate ghost wave, bubble effect and source wavelet effectively and the vertical resolution of the seismic data is improved obviously.
Hydrodynamic loads of sea waves on horizontal elements of berths with wave quenching chambers
Directory of Open Access Journals (Sweden)
Leshchenko Sergey Vladimirovich
2014-05-01
Full Text Available In the process of hydraulic structures design, in particular berths with wave cancelling structures, which serve to decrease the wave impact on structures, there appears a problem of vertical wave hydrodynamic loads calculation on floor slabs. In the existing normative documents there are no requirements on calculating vertical wave loads on the horizontal floor slabs of open-type structures (enveloping, mooring, approach trestles, etc. and stairs of sloping-staired open-type structures. A mathematical model is proposed for calculation of the vertical wave loads on the floor slab through moorings. The model is based on the theory of jet impact on a solid surface. The width of the wave crest, striking in the overlap of the pier, and its vertical velocity is determined by the linear wave theory. The coefficient of transmission of waves through wave quenching chambers is calculated according to the previously developed methods. Vertical wave loading is adjusted based on the ratio of the wave length and width of the overlay. Model validation is performed according to the hydraulic modelling interaction of waves with through berths in the port of Tuapse. 7 variants of their design were considered. Data mapping mathematical and hydraulic modeling showed them a close match.
Structure of the Mimas 5:3 Bending Wave in Saturn's Rings
Sega, Daniel D.; Colwell, Josh E.
2016-10-01
Saturn's moon Mimas is on an inclined orbit with several strong vertical orbital resonances in Saturn's rings. The 5:3 inner vertical resonance with Mimas lies in the outer A ring and produces a prominent spiral bending wave (BW) that propagates away from Mimas. While dozens of density waves in Saturn's rings have been analyzed to determine local surface mass densities and viscosities, the number of bending waves is limited by the requirement for a moon on an inclined orbit and because, unlike the Lindblad resonances that excite density waves, there can be no first order vertical resonances. The Mimas 5:3 BW is the most prominent in the ring system. Bending wave theory was initially developed by Shu et al. (1983, Icarus, 53, 185-206) following the Voyager encounters with Saturn. Later, Gresh et al. (1986, Icarus, 68, 481-502) modeled radio science occultation data of the Mimas 5:3 BW with an imperfect fit to the theory. The multitude of high resolution stellar occultations observed by Cassini UVIS provides an opportunity to reconstruct the full three-dimensional structure of this wave and learn more about local ring properties. Occultations at high elevation angles out of the ring plane are insensitive to the wave structure due to the small angles of the vertical warping of the rings in the wave. They thus reveal the underlying structure in the wave region. There is a symmetric increase in optical depth throughout the Mimas 5:3 BW region. This may be due to an increase in the abundance of small particles without a corresponding increase in surface mass density. We include this feature in a ray-tracing model of the vertical structure of the wave and fit it to multiple UVIS occultations. The observed amplitude of the wave and its damping behavior of are not well-described by the Shu et al. model, which assumes a fluid-like damping mechanism. A different damping behavior of the ring, perhaps radially varying across the wave region due to differences in the particle
Vertical atlantoaxial dislocation
Ramaré, S.; Lazennec, J. Y.; Camelot, C.; Saillant, G.; Hansen, S.; Trabelsi, R.
1999-01-01
An unusual case of vertical atlantoaxial dislocation without medulla oblongata or spinal cord injury is reported. The pathogenic process suggested occipito-axial dislocation. The case was treated surgically with excellent results on mobility and pain.
Coordination in vertical jumping
Bobbert, Maarten F.; van Ingen Schenau, Gerrit Jan
1988-01-01
The present study was designed to investigate for vertical jumping the relationships between muscle actions, movement pattern and jumping achievement. Ten skilled jumpers performed jumps with preparatory countermovement. Ground reaction forces and cinematographic data were recorded. In addition,
DEFF Research Database (Denmark)
Chung, Il-Sug; Mørk, Jesper
2010-01-01
A new hybrid vertical cavity laser structure for silicon photonics is suggested and numerically investigated. It incorporates a silicon subwavelength grating as a mirror and a lateral output coupler to a silicon ridge waveguide.......A new hybrid vertical cavity laser structure for silicon photonics is suggested and numerically investigated. It incorporates a silicon subwavelength grating as a mirror and a lateral output coupler to a silicon ridge waveguide....
Composition of vertical gardens
Sandeva, Vaska; Despot, Katerina
2013-01-01
Vertical gardens are fully functional gardens in areas where there is less oxygen and space, ideal for residential and urban cities where there is no vegetation; occupy a special place in interiors furniture. The gardens occupy an important aesthetic problem. Aesthetic task in vertical gardens can be achieved by forming sectors of identification in the urban landscape through the choice of a particular plant spatial composition and composition, to create comfort and representation in commu...
Hydrodynamic conditions in front of a vertical wall with an overhanging horizontal cantilever slab
Kisacik, Dogan; Ozyurt, Gulizar; Troch, Peter
2017-12-01
Transforming wave heights from offshore to the shoreline is the first step of any coastal engineering work. Wave breaking is analyzed to understand hydrodynamic conditions. For vertical breakwaters and sea walls, wave reflection is an important process that affects the determination of the wave height. Many of the design formulas presented in the literature depend on empirical studies based on the structures tested. In this study, the hydrodynamic conditions in front of a vertical wall with an overhanging horizontal cantilever slab with a foreshore slope of 1/20 are determined experimentally under regular wave conditions to assess the applicability of the formulas of Goda (2000) for predicting the nearshore wave height and breaker index equation (Goda, 2010). The selection of wave measurements used to determine the design wave height, the reflection coefficients, and wave breaking is also analyzed, and the reflection equations are derived from the dataset covering different breaker types. Small-scale tests show that the incident wave height is a good representative of the design wave height and that the values predicted by Goda are in good agreement with actual measurements. However, the predicted H max values are overestimated. In addition, the inception of the wave breaking point is postponed because of the reflection and/or turbulence left over from preceding waves, which is an effect of the vertical wall. At higher water levels, the effect of the vertical wall on the inception point becomes more significant.
THERMAL CONVECTION OF RIVLIN-ERICKSEN FLUID IN THE PRESENCE OF VERTICAL ROTATION
Directory of Open Access Journals (Sweden)
A.S. Banyal
2013-06-01
Full Text Available The thermal instability of a Rivlin-Ericksen viscoelastic fluid, acted upon by uniform vertical rotation and heated from below, is investigated. Following linearized stability theory and normal mode analysis, the mathematical analysis of the governing equations of Rivlin-Ericksen viscoelastic fluid convection with a uniform vertical rotation is performed. It is shown that for the cases of rigid boundaries the complex growth rate of oscillatory perturbations, neutral or unstable for all wave numbers, must lie inside a semi-circle, in the right-hand half of a complex -plane with the center at the origin. This prescribes the upper limits to the complex growth rate of arbitrary oscillatory motions of growing amplitude in a rotatory Rivlin-Ericksen viscoelastic fluid heated from below. Furthermore, the conditions necessary for the existence of oscillatory motions of growing amplitude in the present configuration and the sufficient condition for the validity of the Principle of Exchange of Stabilities are established.
Numerical simulation of scour and backfilling processes around a circular pile in waves
DEFF Research Database (Denmark)
Baykal, Cüneyt; Sumer, B. Mutlu; Fuhrman, David R.
2017-01-01
This study continues the investigation of flow and scour around a vertical pile, reported by Roulund et al.(2005). Flow and scour/backfilling around a vertical pile exposed to waves are investigated by using a threedimensionalnumerical model based on incompressible Reynolds averaged Navier......, 2013a), and the numerical results arecompared with those of the latter experiments. The simulations are carried out for two kinds of beds: rigid bed,and sediment bed. The rigid-bed simulations indicate that the vortex shedding for waves around the pile occursin a “one-cell” fashion with a uniform...... the areas under the horseshoe vortex and the lee wake region) is obtained for various values ofthe Keulegan-Carpenter number, the principal parameter governing the flow around the pile in waves. Thepresent model incorporated with the morphology component is applied to several scenarios of scour...
CFD Analysis of Water Solitary Wave Reflection
Directory of Open Access Journals (Sweden)
K. Smida
2011-12-01
Full Text Available A new numerical wave generation method is used to investigate the head-on collision of two solitary waves. The reflection at vertical wall of a solitary wave is also presented. The originality of this model, based on the Navier-Stokes equations, is the specification of an internal inlet velocity, defined as a source line within the computational domain for the generation of these non linear waves. This model was successfully implemented in the PHOENICS (Parabolic Hyperbolic Or Elliptic Numerical Integration Code Series code. The collision of two counter-propagating solitary waves is similar to the interaction of a soliton with a vertical wall. This wave generation method allows the saving of considerable time for this collision process since the counter-propagating wave is generated directly without reflection at vertical wall. For the collision of two solitary waves, numerical results show that the run-up phenomenon can be well explained, the solution of the maximum wave run-up is almost equal to experimental measurement. The simulated wave profiles during the collision are in good agreement with experimental results. For the reflection at vertical wall, the spatial profiles of the wave at fixed instants show that this problem is equivalent to the collision process.
Hypergraphs with large transversal number
DEFF Research Database (Denmark)
Henning, Michael A.; Yeo, Anders
2013-01-01
For κ ≥ 2, let H be a k-uniform hypergraph on n vertices and m edges. The transversal number τ (H) of H is the minimum number of vertices that intersect every edge. We consider the following question: Is τ (H) ≤ n/k + m/6? For κ ≥ 4, we show that the inequality in the question does not always hol...
Wave Height Distribution for Nonlinear Swell Waves in Deep an Depth Limited Wave Conditions
DEFF Research Database (Denmark)
Nørgaard, Jørgen Harck; Andersen, Thomas Lykke; Knudsen, Jannie Elkær
2017-01-01
This paper presents initial results from an on-going study on the influence from wave nonlinearity on the wave height distribution in deep- and depth-limited nonlinear wave conditions. A fully nonlinear VOF model, IH-2VOF, is applied to model the propagation of irregular waves on a sloping sea bed...... from deep to shallow water, including the effects of wave breaking. Different wave nonlinearities are evaluated in the model and the effects of the wave nonlinearity, described by the so-called Ursell-number, on the wave height distributions along the sloping sea bed are evaluated. The widely used...
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Osaland, E.
2005-01-01
The paper describes the optimization of the crest levels and geometrical layout of the SSG structure, focusing on maximizing the obtained potential energy in the overtopping water. During wave tank testing at AAU average overtopping rates into the individual reservoirs have been measured....... The initial tests led to an expression describing the derivative of the overtopping rate with respect to the vertical distance. Based on this, numerical optimizations of the crest levels, for a number of combinations of wave conditions, have been performed. The hereby found optimal crest levels have been...... tested in the wave tank and further optimizations of the geometry have been carried out....
DEFF Research Database (Denmark)
Frigaard, Peter; Kofoed, Jens Peter; Tedd, James William
2006-01-01
The Wave Dragon is a 4 to 11 MW offshore wave energy converter of the overtopping type. It basically consists of two wave reflectors focusing the waves towards a ramp, a reservoir for collecting the overtopping water and a number of hydro turbines for converting the pressure head into power......'s first offshore wave energy converter. During this period an extensive measuring program has established the background for optimal design of the structure and regulation of the power take off system. Planning for full scale deployment of a 7 MW unit within the next 2 years is in progress. The prototype...
Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk
Ferguson, Deborah; Gardner, Susan; Yanny, Brian
2017-07-01
We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.
Directory of Open Access Journals (Sweden)
Brett N Archer
Full Text Available Describing transmissibility parameters of past pandemics from diverse geographic sites remains critical to planning responses to future outbreaks. We characterize the transmissibility of influenza A(H1N1pdm09 (hereafter pH1N1 in South Africa during 2009 by estimating the serial interval (SI, the initial effective reproductive number (initial R(t and the temporal variation of R(t.We make use of data from a central registry of all pH1N1 laboratory-confirmed cases detected throughout South Africa. Whenever date of symptom onset is missing, we estimate it from the date of specimen collection using a multiple imputation approach repeated 100 times for each missing value. We apply a likelihood-based method (method 1 for simultaneous estimation of initial R(t and the SI; estimate initial R(t from SI distributions established from prior field studies (method 2; and the Wallinga and Teunis method (method 3 to model the temporal variation of R(t.12,360 confirmed pH1N1 cases were reported in the central registry. During the period of exponential growth of the epidemic (June 21 to August 3, 2009, we simultaneously estimate a mean R(t of 1.47 (95% CI: 1.30-1.72 and mean SI of 2.78 days (95% CI: 1.80-3.75 (method 1. Field studies found a mean SI of 2.3 days between primary cases and laboratory-confirmed secondary cases, and 2.7 days when considering both suspected and confirmed secondary cases. Incorporating the SI estimate from field studies using laboratory-confirmed cases, we found an initial R(t of 1.43 (95% CI: 1.38-1.49 (method 2. The mean R(t peaked at 2.91 (95% CI: 0.85-2.91 on June 21, as the epidemic commenced, and R(t>1 was sustained until August 22 (method 3.Transmissibility characteristics of pH1N1 in South Africa are similar to estimates reported by countries outside of Africa. Estimations using the likelihood-based method are in agreement with field findings.
Stochastic Procedures for Extreme Wave Load Predictions- Wave Bending Moment in Ships
DEFF Research Database (Denmark)
Jensen, Jørgen Juncher
2009-01-01
A discussion of useful stochastic procedures for stochastic wave load problems is given, covering the range from slightly linear to strongly non-linear (bifurcation) problems. The methods are: Hermite transformation, Critical wave episodes and the First Order Reliability Method (FORM). The proced......). The procedures will be illustrated by results for the extreme vertical wave bending moment in ships....
Suslov, Sergey A; Bozhko, Alexandra A; Sidorov, Alexander S; Putin, Gennady F
2012-07-01
Flow patterns arising in a vertical differentially heated layer of nonconducting ferromagnetic fluid placed in an external uniform transverse magnetic field are studied experimentally and discussed from the point of view of the perturbation energy balance. A quantitative criterion for detecting the parametric point where the dominant role in generating a flow instability is transferred between the thermogravitational and thermomagnetic mechanisms is suggested, based on the disturbance energy balance analysis. A comprehensive experimental study of various flow patterns is undertaken, and the existence is demonstrated of oblique thermomagnetic waves theoretically predicted by Suslov [Phys. Fluids 20, 084101 (2008)] and superposed onto the stationary magnetoconvective pattern known previously. It is found that the wave number of the detected convection patterns depends sensitively on the temperature difference across the layer and on the applied magnetic field. In unsteady regimes its value varies periodically by a factor of almost 2, indicating the appearance of two different competing wave modes. The wave numbers and spatial orientation of the observed dominant flow patterns are found to be in good agreement with theoretical predictions.
African Journals Online (AJOL)
2002-01-24
Jan 24, 2002 ... crustacean zooplankton but also in a Wide array of different marine zooplankton groups. (Russell 1927, McLaren 1963). Thus there is no doubt that ..... cooperation during ﬁeld work and for their fruitful discussion on the draft manuscript. REFERENCES. Bayly lAE 1986 Aspects of diel vertical migration in ...
DEFF Research Database (Denmark)
Schrader, Alexander; Martin, Stephen
1998-01-01
Firms that operate at both levels of vertically related Cournot oligopolies will purchase some input supplies from independent rivals, even though they can produce the good at a lower cost, driving up input price for nonintegrated firms at the final good level. Foreclosure, which avoids this stra...... this strategic behavior, yields better market performance than Cournot beliefs...
Ferrucci, V.; Overmars, Mark; Rao, A.; Vleugels, J.
1994-01-01
Given three objects in the plane, a Voronoi vertex is a point that is equidistant simultaneously from each. In this paper, we consider the problem of computing Voronoi vertices for planar objects of xed but possibly unknown shape; we only require the ability to query the closest point on an object
Grana, D. C.; Inge, S. V., Jr. (Inventor)
1983-01-01
A vertical shaft has several equally spaced blades mounted. Each blade consists of an inboard section and an outboard section skew hinged to the inboard section. The inboard sections automatically adjust their positions with respect to the fixed inboard sections with changes in velocity of the wind. This windmill design automatically governs the maximum rotational speed of shaft.
Numerical Modeling of the Vertical Heat Transport Through the Diffusive Layer of the Arctic Ocean
2013-03-01
transport through thermohaline staircases in the Arctic region. Results revealed that vertical fluxes exceeded those of extant “four-thirds flux...vertical heat flux, thermohaline staircase 15. NUMBER OF PAGES 73 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18...DNS) were conducted to assess the vertical heat transport through thermohaline staircases in the Arctic region. Results revealed that vertical
Vertical partitioning of relational OLTP databases using integer programming
DEFF Research Database (Denmark)
Amossen, Rasmus Resen
2010-01-01
for relational row- store OLTP databases with an H-store-like architecture, meaning that we would like to maximize the number of single-sited transactions. We present a model for the vertical partitioning problem that, given a schema together with a vertical partitioning and a workload, estimates the costs......A way to optimize performance of relational row store databases is to reduce the row widths by vertically partition- ing tables into table fractions in order to minimize the number of irrelevant columns/attributes read by each transaction. This pa- per considers vertical partitioning algorithms...
Vertical gastroplasty: evolution of vertical banded gastroplasty.
Mason, E E; Doherty, C; Cullen, J J; Scott, D; Rodriguez, E M; Maher, J W
1998-09-01
The objective of this paper is to summarize the goals, technical requirements, advantages, and potential risks of gastroplasty for treatment of severe obesity. Gastroplasty is preferred to more complex operations, as it preserves normal digestion and absorption and avoids complications that are peculiar to exclusion operations. The medical literature and a 30-year experience at the University of Iowa Hospitals and Clinics (UIHC) provides an overview of vertical banded gastroplasty (VBG) evolution. Preliminary 10-year results with the VBG technique currently used at UIHC are included. At UIHC the VBG is preferred to other gastroplasties because it provides weight control that extends for at least 10 years and the required objective, intraoperative quality control required for a low rate of reoperation. It is recommended that modifications of the operative technique not be attempted until a surgeon has had experience with the standardized operation--and then only under a carefully designed protocol. Realistic goals for surgery and criteria of success influence the choice of operation and the optimum, lifelong risk/benefit ratio. In conclusion, VBG is a safe, long-term effective operation for severe obesity with advantages over complex operations and more restrictive simple operations.
S wave propagation in acoustic anisotropic media
Stovas, Alexey
2017-04-01
The acoustic anisotropic medium can be defined in two ways. The first one is known as a pseudo-acoustic approximation (Alkhalifah, 1998) that is based on the fact that in TI media, P wave propagation is weakly dependent on parameter known as "vertical S-wave velocity" (Thomsen, 1986). The standard way to define the pseudo-acoustic approximation is to set this parameter to zero. However, as it was shown later (Grechka et al., 2004), there is "S wave artifact" in such a medium. Another way is to define the stack of horizontal solid-fluid layers and perform an upscaling based on the Backus (1962) averaging. The stiffness coefficient that responds to "vertical S wave velocity" turns to zero if any of layers has zero vertical S wave velocity. In this abstract, I analyze the S wave propagation is acoustic anisotropic medium and define important kinematic properties such as the group velocity surface and Dix-type equations. The kinematic properties can easily be defined from the slowness surface. In elastic transversely isotropic medium, the equations for P and SV wave slowness surfaces are coupled. Setting "vertical S wave velocity" to zero, results in decoupling of equations. I show that the S wave group velocity surface is given by quasi-astroidal form with the reference astroid defined by vertical and horizontal projections of group velocity. I show that there are cusps attached to both vertical and horizontal symmetry axes. The new S wave parameters include vertical, horizontal and normal moveout velocities. With the help of new parameterization, suitable for S wave, I also derived the Dix-type of equations to define the effective kinematical properties of S waves in multi-layered acoustic anisotropic medium. I have shown that effective media defined from P and S waves have different parameters. I also show that there are certain symmetries between P and S waves parameters and equations. The proposed method can be used for analysis of S waves in acoustic anisotropic
Finite Element Based Viscous Numerical Wave Flume
Directory of Open Access Journals (Sweden)
Jianmin Qin
2013-01-01
Full Text Available A two-dimensional numerical wave flume (NWF for viscous fluid flows with free surface is developed in this work. It is based on the upwind finite element solutions of Navier-Stokes equations, CLEAR-volume of fluid method for free surface capture, internal wave maker for wave generation, and sponge layer for wave absorbing. The wave generation and absorption by prescribing velocity boundary conditions along inlet and radiation boundary condition along outlet are also incorporated. The numerical model is validated against several benchmarks, including dam-breaking flow, liquid sloshing in baffled tank, linear water wave propagation and reflection from vertical wall, nonlinear solitary wave fission over sharp step, and wave-induced fluid resonance in narrow gap confined by floating structures. The comparisons with available experimental data, numerical results, and theoretical solutions confirm that the present numerical wave flume has good performance in dealing with complex interface flows and water wave interaction with structures.
minimal pairs of polytopes and their number of vertices
African Journals Online (AJOL)
Preferred Customer
Using this operation we give a new algorithm to reduce and find a minimal pair of polytopes from the given class of the ... statement does not hold true in general for higher dimensional spaces. Key words/phrases: Pairs of compact ..... rem gives us the necessary and sufficient condition for a pair of polytopes in the plane to ...
The Next Wave. Volume 19, Number 2
2012-01-01
Malware, short for "malicious software," includes computer viruses , worms, and Trojan horses , and can spread using various methods, including worms sent...through email and instant messages, Trojan horses dropped from websites, and virus -infected files downloaded from peer-to-peer connections.8 This...accidental bugs, faults, and leaks to maliciously induced Trojan horses . The problem is aggravated by growing system complexity and by increasingly
Optical anisotropy in vertically coupled quantum dots
DEFF Research Database (Denmark)
Yu, Ping; Langbein, Wolfgang Werner; Leosson, Kristjan
1999-01-01
We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single...
Vortical and internal wave shear and strain
Pinkel, R.
2014-01-01
Depth-time records of isopycnal vertical strain have been collected from intensive CTD profiling programs on the research platform (R/P) Floating Instrument Platform (FLIP). The associated vertical wavenumber frequency spectrum of strain, when viewed in an isopycnal-following frame, displays a clear spectral gap at low vertical wavenumber, separating the quasigeostrophic (vortical) strain field and the superinertial internal wave continuum. This gap enables both model and linear-filter-based ...
The domination number of a random graph
DEFF Research Database (Denmark)
Henning, Michael A.; Yeo, Anders
2014-01-01
The domination number γ(G) of a graph G is the minimum cardinality of a set S of vertices so that every vertex outside S is adjacent to a vertex in S, while its total domination number γt(G) is the minimum cardinality of a set S of vertices so that every vertex in the graph is adjacent to a vertex...
Snakes mimic earthworms: propulsion using rectilinear travelling waves
Marvi, Hamidreza; Bridges, Jacob; Hu, David L.
2013-01-01
In rectilinear locomotion, snakes propel themselves using unidirectional travelling waves of muscular contraction, in a style similar to earthworms. In this combined experimental and theoretical study, we film rectilinear locomotion of three species of snakes, including red-tailed boa constrictors, Dumeril's boas and Gaboon vipers. The kinematics of a snake's extension–contraction travelling wave are characterized by wave frequency, amplitude and speed. We find wave frequency increases with increasing body size, an opposite trend than that for legged animals. We predict body speed with 73–97% accuracy using a mathematical model of a one-dimensional n-linked crawler that uses friction as the dominant propulsive force. We apply our model to show snakes have optimal wave frequencies: higher values increase Froude number causing the snake to slip; smaller values decrease thrust and so body speed. Other choices of kinematic variables, such as wave amplitude, are suboptimal and appear to be limited by anatomical constraints. Our model also shows that local body lifting increases a snake's speed by 31 per cent, demonstrating that rectilinear locomotion benefits from vertical motion similar to walking. PMID:23635494
Energy Technology Data Exchange (ETDEWEB)
Schulz-Ruhtenberg, M [Institut fuer Angewandte Physik, Westfaelische Wilhelms-Universitaet Muenster, Corrensstrasse 2/4, 48149 Muenster (Germany); Tanguy, Y; Ackemann, T [SUPA and Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Huang, K F [Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan (China); Jaeger, R, E-mail: thorsten.ackemann@strath.ac.u [Philips Technologie GmbH, U-L-M Photonics, Lise-Meitner-Str. 13, 89081 Ulm (Germany)
2009-03-07
The wave number of transverse spatial structures in broad-area vertical-cavity surface-emitting lasers (VCSELs) is controlled via frequency-selective feedback from an external self-imaging cavity in a broad range of wave numbers and emission frequencies. The selected states follow the dispersion curves of the free-running laser. A control range of about 2.5 {mu}m{sup -1} in spatial frequency space and 2.5 nm in emission wavelength was obtained for square VCSELs and of about 3 {mu}m{sup -1} and 8 nm for circular VCSELs having a different dispersion curve. By spatial filtering in Fourier space, the shape of the structures can also be controlled to some extent. It is argued that the feedback techniques are useful to 'probe' emission states of the free-running laser.
DEFF Research Database (Denmark)
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis...
Vertically Polarized Omnidirectional Printed Slot Loop Antenna
DEFF Research Database (Denmark)
Kammersgaard, Nikolaj Peter Iversen; Kvist, Søren H.; Thaysen, Jesper
2015-01-01
A novel vertically polarized omnidirectional printed slot loop antenna has been designed, simulated, fabricated and measured. The slot loop works as a magnetic loop. The loop is loaded with inductors to insure uniform and in-phase fields in the slot in order to obtain an omnidirectional radiation...... pattern. The antenna is designed for the 2.45 GHz Industrial, Scientific and Medical band. Applications of the antenna are many. One is for on-body applications since it is ideal for launching a creeping waves due to the polarization....
Kallosh, Renata
1994-01-01
We study the gravitational waves in the 10-dimensional target space of the superstring theory. Some of these waves have unbroken supersymmetries. They consist of Brinkmann metric and of a 2-form field. Sigma-model duality is applied to such waves. The corresponding solutions we call dual partners of gravitational waves, or dual waves. Some of these dual waves upon Kaluza-Klein dimensional reduction to 4 dimensions become equivalent to the conformo-stationary solutions of axion-dilaton gravity...
Spectral Analysis of Surface Waves to Detect Buried Concrete Conduits
Hajiani, P.; Anderson, N.; Rogers, J. D.; Elkrry, A.
2016-12-01
The detection of underground cavities is of significant concern to geotechnical engineers working in karst terrain. In spite of the marked progress in nondestructive geophysical methods for detecting shallow underground voids, no unique methodology has emerged that can be applied globally. Various studies have been performed on the use of Rayleigh waves to detect shallow tunnels. In this study, we examined the potential of both Rayleigh and Love waves for detecting subsurface voids. Vertical geophones with Eigen-frequencies of 4.5 Hz, 14 Hz, and 100 Hz were utilized to evaluate Rayleigh waves to resolve near-surface tunnels. Seismic surveys were carried out using horizontal 14 Hz geophones to verify the feasibility of using Love waves to detect shallow tunnels. Two buried conduits of known size and embedment were chosen for the study. One conduit serves as a spillway outfall for an embankment dam, and the other as a low flow outlet for aa flood retention basin. Attenuation analyses of surface waves were performed on all of the data sets to identify locations of the buried concrete conduits. In order to minimize the far-field effects, such as body-wave domination, or low signal-to-noise ratio, it was suggested that we try muting the direct waves, refraction, reflection, air wave, and ambient noise. An amplification of energy on, or in front of the near boundary of the conduits was thereby observed. The muting process greatly reduced the number of false positives. The results of this study not only confirmed previous work, but also displayed the ability of Love waves in detecting the shallow subsurface tunnels or conduits.
Geophysical aspects of vertical streamer seismic data
Energy Technology Data Exchange (ETDEWEB)
Sognnes, Walter
1998-12-31
Vertical cable acquisition is performed by deploying a certain number of vertical hydrophone arrays in the water column, and subsequently shooting a source point on top of it. The advantage of this particular geometry is that gives a data set with all azimuths included. Therefore a more complete 3-D velocity model can be derived. In this paper there are presented some results from the Fuji survey in the Gulf of Mexico. Based on these results, improved geometries and review recommendations for future surveys are discussed. 7 figs.
Directory of Open Access Journals (Sweden)
Esteban Dörries
2016-03-01
Full Text Available La introducción de la metodología GPS en aplicaciones topográficas y geodésicas pone en notoria evidencia la clásica separación de sistemas de referencia en horizontal y vertical. Con GPS el posicionamiento es tridimensional, pero el concepto de altura difiere del clásico. Si se desea utilizar la información altimétrica debe contemplarse la ondulación del geoide.
Energy Technology Data Exchange (ETDEWEB)
Kramer, M.; Brorsen, M.; Frigaard, P.
2004-06-01
The wave energy converter Wave Star converts the waves' energy power content to electrical energy through a series of floats. For plants of this type it is outmost important that the vertical loads from the waves are maximized in order to reach optimal energy exploitation. At the same time the horizontal loads from the waves must be minimized in order to obtain the slightest and cheapest construction possible. A detailed analysis of the floats form will demand expense heavy CFD calculations. Therefore, the Wave Star project has decided to use potential theoretical calculations which will help formulate the problems. This report describes a preliminary study of the float geometry. (BA)
Prototype Testing of the Wave Energy Converter Wave Dragon
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Frigaard, Peter Bak; Friis-Madsen, Erik
2004-01-01
The Wave Dragon is an offshore wave energy converter of the overtopping type. It consists of two wave reflectors focusing the incoming waves towards a ramp, a reservoir for collecting the overtopping water and a number of hydro turbines for converting the pressure head into power. In the period...... from 1998 to 2001 extensive wave tank testing on a scale model was carried at Aalborg University. Then, a 57 x 27 m wide and 237 tonnes heavy (incl. ballast) prototype of the Wave Dragon, placed in Nissum Bredning, Denmark, was grid connected in May 2003 as the world's first offshore wave energy...... converter. The prototype is fully equipped with hydro turbines and automatic control systems, and is instrumented in order to monitor power production, wave climate, forces in mooring lines, stresses in the structure and movements of the Wave Dragon. During the last months, extensive testing has started...
Prototype Testing of the Wave Energy Converter Wave Dragon
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Frigaard, Peter; Friis-Madsen, Erik
2006-01-01
The Wave Dragon is an offshore wave energy converter of the overtopping type. It consists of two wave reflectors focusing the incoming waves towards a ramp, a reservoir for collecting the overtopping water and a number of hydro turbines for converting the pressure head into power. In the period...... from 1998 to 2001 extensive wave tank testing on a scale model was carried at Aalborg University. Then, a 57!27 m wide and 237 tonnes heavy (incl. ballast) prototype of the Wave Dragon, placed in Nissum Bredning, Denmark, was grid connected in May 2003 as the world’s first offshore wave energy...... converter. The prototype is fully equipped with hydro turbines and automatic control systems, and is instrumented in order to monitor power production, wave climate, forces in mooring lines, stresses in the structure and movements of the Wave Dragon. In the period May 2003 to January 2005 an extensive...
Approximation of wave action flux velocity in strongly sheared mean flows
Banihashemi, Saeideh; Kirby, James T.; Dong, Zhifei
2017-08-01
Spectral wave models based on the wave action equation typically use a theoretical framework based on depth uniform current to account for current effects on waves. In the real world, however, currents often have variations over depth. Several recent studies have made use of a depth-weighted current U˜ due to [Skop, R. A., 1987. Approximate dispersion relation for wave-current interactions. J. Waterway, Port, Coastal, and Ocean Eng. 113, 187-195.] or [Kirby, J. T., Chen, T., 1989. Surface waves on vertically sheared flows: approximate dispersion relations. J. Geophys. Res. 94, 1013-1027.] in order to account for the effect of vertical current shear. Use of the depth-weighted velocity, which is a function of wavenumber (or frequency and direction) has been further simplified in recent applications by only utilizing a weighted current based on the spectral peak wavenumber. These applications do not typically take into account the dependence of U˜ on wave number k, as well as erroneously identifying U˜ as the proper choice for current velocity in the wave action equation. Here, we derive a corrected expression for the current component of the group velocity. We demonstrate its consistency using analytic results for a current with constant vorticity, and numerical results for a measured, strongly-sheared current profile obtained in the Columbia River. The effect of choosing a single value for current velocity based on the peak wave frequency is examined, and we suggest an alternate strategy, involving a Taylor series expansion about the peak frequency, which should significantly extend the range of accuracy of current estimates available to the wave model with minimal additional programming and data transfer.
Yeh, P. S.; Chang, C.-C.; Chen, Y.-T.; Lin, D.-W.; Liou, J.-S.; Wu, C. C.; He, J. H.; Kuo, H.-C.
2016-12-01
A GaN-based vertical-cavity surface emitting laser (VCSEL) structure featuring a silicon-diffusion-defined current blocking layer for lateral confinement is described. Sub-milliamp threshold currents were achieved for both 3- and 5-μm-aperture VCSELs under continuous-wave operation at room temperature. The vertical cavity was defined by a top dielectric distributed Bragg reflector (DBR) and a bottom epitaxial DBR. The emission spectrum exhibited a single peak at 411.2 nm with a linewidth of 0.4 nm and a side mode suppression ratio of more than 10 dB before device packaging. The full-width-at-half-maximum divergence angle of the 3-μm-aperture VCSEL was as small as approximately 5° which is the lowest number reported. These results implied the 3-μm-aperture VCSEL was in near single-mode operation.
Large eddy simulation of breaking waves
DEFF Research Database (Denmark)
Christensen, Erik Damgaard; Deigaard, Rolf
2001-01-01
. The incoming waves are specified by a flux boundary condition. The waves are approaching in the shore-normal direction and are breaking on a plane, constant slope beach. The first few wave periods are simulated by a two-dimensional model in the vertical plane normal to the beach line. The model describes...... of the turbulence (the characteristic size of the eddies resolved by the model) is similar in the horizontal and the vertical direction. It is found to be of the order one half of the water depth....
Ocean floor mounting of wave energy converters
Siegel, Stefan G
2015-01-20
A system for mounting a set of wave energy converters in the ocean includes a pole attached to a floor of an ocean and a slider mounted on the pole in a manner that permits the slider to move vertically along the pole and rotate about the pole. The wave energy converters can then be mounted on the slider to allow adjustment of the depth and orientation of the wave energy converters.
Number names and number understanding
DEFF Research Database (Denmark)
Ejersbo, Lisser Rye; Misfeldt, Morten
2014-01-01
through using mathematical names for the numbers such as one-ten-one for 11 and five-ten-six for 56. The project combines the renaming of numbers with supporting the teaching with the new number names. Our hypothesis is that Danish children have more difficulties learning and working with numbers, because...
A vertical wall in the Whittard Canyon with a novel community assemblage
Johnson, Mark; White, Martin; Wilson, Annette; Wuerzberg, Laura; Schwabe, Enrico; Folch, Helka; Allcock, Louise
2013-04-01
We describe a hitherto unreported community from a vertical wall in the Whittard Canyon system on the Atlantic Margin. The wall extended vertically for about 100 m from approximately 750 m depth. We explored the wall with an ROV and discovered an assemblage cominated by large limid bivalves Acesta excavata and deep-water oysters Neopycnodonte zibrowii at very high densities, particularly at overhangs. The assemblage also contained deep-water corals (including solitary corals). It had high numbers of flytrap anemones and had many mobile species associated with it including crustaceans such as Paramola cuvieri and Bathynectes longispina, echinoderms and fishes. We took CTD transects in the area of the wall and beam attenuation indicated nepheloid layers present in the water column. The greatest densities of suspended material at the ROV dive site were at the depth of the wall. We hypothesise that internal waves concentrate suspended sediment at the foot of the vertical wall. This may provide the resources to support the high density of large filter feeders at these depths.
Going Wave as a Model of Particle
Goryunov, A V
2010-01-01
The concept of going wave is introduced from classical positions (including the special relativity theory). One- and three-dimensional going waves considered with their wave equations and dispersion equations. It is shown that wave characteristics (de Broglie's and Compton's wavelengths) and corpuscular characteristics (energy-momentum vector and the rest mass) of particle may be expressed through parameters of going wave. By that the new view on a number concepts of physic related with particle-wave dualism is suggested.
DEFF Research Database (Denmark)
Groß, Thomas; Mödersheim, Sebastian Alexander
2011-01-01
composition, and it is truly commonplace in today’s communication with the diversity of VPNs and secure browser sessions. In fact, it is normal that we have several layers of secure channels: For instance, on top of a VPN-connection, a browser may establish another secure channel (possibly with a different...... end point). Even using the same protocol several times in such a stack of channels is not unusual: An application may very well establish another TLS channel over an established one. We call this selfcomposition. In fact, there is nothing that tells us that all these compositions are sound, i.......e., that the combination cannot introduce attacks that the individual protocols in isolation do not have. In this work, we prove a composability result in the symbolic model that allows for arbitrary vertical composition (including self-composition). It holds for protocols from any suite of channel and application...
DEFF Research Database (Denmark)
2016-01-01
The present invention provides a vertical cavity laser comprising a grating layer comprising an in-plane grating, the grating layer having a first side and having a second side opposite the first side and comprising a contiguous core grating region having a grating structure, wherein an index......, an index of refraction of the second low-index layer or air being less than 2; and a thickness of the cap layer and a thickness of the grating layer, and a pitch and a duty cycle of the grating structure are selected to obtain a resonance having a free-space resonance wavelength in the interval 300 nm to 3...... microns, the cap layer comprises an active region configured to generate or absorb photons at the free-space resonance wavelength by stimulated emission or absorption when a sufficient forward or reverse bias voltage is applied across the active region, a thickness of the first low-index layer is less...
Directory of Open Access Journals (Sweden)
Schwarzweller Christoph
2015-02-01
Full Text Available In this article we introduce Proth numbers and prove two theorems on such numbers being prime [3]. We also give revised versions of Pocklington’s theorem and of the Legendre symbol. Finally, we prove Pepin’s theorem and that the fifth Fermat number is not prime.
Direct Observation of Ultralow Vertical Emittance using a Vertical Undulator
Energy Technology Data Exchange (ETDEWEB)
Wootton, Kent
2015-09-17
In recent work, the first quantitative measurements of electron beam vertical emittance using a vertical undulator were presented, with particular emphasis given to ultralow vertical emittances [K. P. Wootton, et al., Phys. Rev. ST Accel. Beams, 17, 112802 (2014)]. Using this apparatus, a geometric vertical emittance of 0.9 ± 0.3 pm rad has been observed. A critical analysis is given of measurement approaches that were attempted, with particular emphasis on systematic and statistical uncertainties. The method used is explained, compared to other techniques and the applicability of these results to other scenarios discussed.
Seismic Wave Propagation on the Tablet Computer
Emoto, K.
2015-12-01
Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the
Vorob'ev, Nikolai Nikolaevich
2011-01-01
Fibonacci numbers date back to an 800-year-old problem concerning the number of offspring born in a single year to a pair of rabbits. This book offers the solution and explores the occurrence of Fibonacci numbers in number theory, continued fractions, and geometry. A discussion of the ""golden section"" rectangle, in which the lengths of the sides can be expressed as a ration of two successive Fibonacci numbers, draws upon attempts by ancient and medieval thinkers to base aesthetic and philosophical principles on the beauty of these figures. Recreational readers as well as students and teacher
Mendonça, J. Ricardo G.
2012-01-01
We define a new class of numbers based on the first occurrence of certain patterns of zeros and ones in the expansion of irracional numbers in a given basis and call them Sagan numbers, since they were first mentioned, in a special case, by the North-american astronomer Carl E. Sagan in his science-fiction novel "Contact." Sagan numbers hold connections with a wealth of mathematical ideas. We describe some properties of the newly defined numbers and indicate directions for further amusement.
Directory of Open Access Journals (Sweden)
Watase Yasushige
2016-12-01
Full Text Available This article provides definitions and examples upon an integral element of unital commutative rings. An algebraic number is also treated as consequence of a concept of “integral”. Definitions for an integral closure, an algebraic integer and a transcendental numbers [14], [1], [10] and [7] are included as well. As an application of an algebraic number, this article includes a formal proof of a ring extension of rational number field ℚ induced by substitution of an algebraic number to the polynomial ring of ℚ[x] turns to be a field.
A Fresh Look at Longitudinal Standing Waves on a Spring
Rutherford, Casey
2013-01-01
Transverse standing waves produced on a string, as shown in Fig. 1, are a common demonstration of standing wave patterns that have nodes at both ends. Longitudinal standing waves can be produced on a helical spring that is mounted vertically and attached to a speaker, as shown in Fig. 2, and used to produce both node-node (NN) and node-antinode…
Petculescu, Andi; Achi, Peter
Measurements of thermodynamic quantities in Titan's atmosphere during the descent of Huygens in 2005 are used to predict the vertical profiles for the speed and intrinsic attenuation (or absorption) of sound. The calculations are done using one author's previous model modified to accommodate non-ideal equations of state. The vertical temperature profile places the tropopause about 40 km above the surface. In the model, a binary nitrogen-methane composition is assumed for Titan's atmosphere, quantified by the methane fraction measured by the gas chromatograph/mass spectrometer (GCMS) onboard Huygens. To more accurately constrain the acoustic wave number, the variation of thermophysical properties (specific heats,viscosity, and thermal conductivity) with altitude is included via data extracted from the NIST Chemistry WebBook [URL webbook.nist.gov, National Institute of Standards and Technology Chemistry WebBook (Last accessed 10/20/2011)]. The predicted speed of sound profile fits well inside the spread of the data recorded by Huygens' active acoustic sensor. In the N2-dominated atmosphere, the sound waves have negligible relaxational dispersion and mostly classical (thermo-viscous) absorption. The cold and dense environment of Titan can sustain acoustic waves over large distances with relatively small transmission losses, as evidenced by the small absorption. A ray-tracing program is used to assess the bounds imposed by the zonal wind-measured by the Doppler Wind Experiment on Huygens-on long-range propagation.
Petculescu, Andi; Achi, Peter
2012-05-01
Measurements of thermodynamic quantities in Titan's atmosphere during the descent of Huygens in 2005 are used to predict the vertical profiles for the speed and intrinsic attenuation (or absorption) of sound. The calculations are done using one author's previous model modified to accommodate non-ideal equations of state. The vertical temperature profile places the tropopause about 40 km above the surface. In the model, a binary nitrogen-methane composition is assumed for Titan's atmosphere, quantified by the methane fraction measured by the gas chromatograph/mass spectrometer (GCMS) onboard Huygens. To more accurately constrain the acoustic wave number, the variation of thermophysical properties (specific heats, viscosity, and thermal conductivity) with altitude is included via data extracted from the NIST Chemistry WebBook [URL webbook.nist.gov, National Institute of Standards and Technology Chemistry WebBook (Last accessed 10/20/2011)]. The predicted speed of sound profile fits well inside the spread of the data recorded by Huygens' active acoustic sensor. In the N(2)-dominated atmosphere, the sound waves have negligible relaxational dispersion and mostly classical (thermo-viscous) absorption. The cold and dense environment of Titan can sustain acoustic waves over large distances with relatively small transmission losses, as evidenced by the small absorption. A ray-tracing program is used to assess the bounds imposed by the zonal wind-measured by the Doppler Wind Experiment on Huygens-on long-range propagation.
Swanson, DG
1989-01-01
Plasma Waves discusses the basic development and equations for the many aspects of plasma waves. The book is organized into two major parts, examining both linear and nonlinear plasma waves in the eight chapters it encompasses. After briefly discussing the properties and applications of plasma wave, the book goes on examining the wave types in a cold, magnetized plasma and the general forms of the dispersion relation that characterize the waves and label the various types of solutions. Chapters 3 and 4 analyze the acoustic phenomena through the fluid model of plasma and the kinetic effects. Th
Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation
Directory of Open Access Journals (Sweden)
X. Liu
2009-07-01
Full Text Available The Kelvin-Helmholtz (KH billows which appear in the process of gravity wave (GW propagation are simulated directly by using a compressible nonlinear two-dimensional gravity wave model. The differences between our model and others include: the background field has no special initial configuration and there is no initial triggering mechanism needed in the mesosphere and lower thermosphere (MLT region to excite the KH billows. However, the initial triggering mechanism is performed in the lower atmosphere through GW, which then propagate into the MLT region and form billows. The braid structures and overturning of KH billows, caused by nonlinear interactions between GWs and mean flow, can be resolved precisely by the model. These results support the findings in airglow studies that GWs propagating from below into the MLT region are important sources of KH billows. The onset of small scale waves and the wave energy transfer induce the shallower vertical wave number power spectral densities (PSD. However, most of the slopes are steeper than the expected k_{z}^{−3} power law, which indicates that GWs with 10 km vertical wavelength are still a dominant mode. The results also show that the evolution of mean wind vary substantially between the different processes of GWs propagation. Before the KH billows evolve, the mean wind is accelerated greatly by GWs. By contrast, as the KH billows evolve and mix with mean flow, the mean wind and its peak value decrease.
Vertical allometry: fact or fiction?
Mahmood, Iftekhar; Boxenbaum, Harold
2014-04-01
In pharmacokinetics, vertical allometry is referred to the clearance of a drug when the predicted human clearance is substantially higher than the observed human clearance. Vertical allometry was initially reported for diazepam based on a 33-fold higher human predicted clearance than the observed human clearance. In recent years, it has been found that many other drugs besides diazepam, can be classified as drugs which exhibit vertical allometry. Over the years, many questions regarding vertical allometry have been raised. For example, (1) How to define and identify the vertical allometry? (2) How much difference should be between predicted and observed human clearance values before a drug could be declared 'a drug which follows vertical allometry'? (3) If somehow one can identify vertical allometry from animal data, how this information can be used for reasonably accurate prediction of clearance in humans? This report attempts to answer the aforementioned questions. The concept of vertical allometry at this time remains complex and obscure but with more extensive works one can have better understanding of 'vertical allometry'. Published by Elsevier Inc.
Wave-equation dispersion inversion
Li, Jing
2016-12-08
We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to wave-equation traveltime tomography, the complicated surface wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the phase-velocity and frequency domains. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2-D or 3-D S-wave velocity models. This procedure, denoted as wave-equation dispersion inversion (WD), does not require the assumption of a layered model and is significantly less prone to the cycle-skipping problems of full waveform inversion. The synthetic and field data examples demonstrate that WD can approximately reconstruct the S-wave velocity distributions in laterally heterogeneous media if the dispersion curves can be identified and picked. The WD method is easily extended to anisotropic data and the inversion of dispersion curves associated with Love waves.
Petersen, T Kyle
2015-01-01
This text presents the Eulerian numbers in the context of modern enumerative, algebraic, and geometric combinatorics. The book first studies Eulerian numbers from a purely combinatorial point of view, then embarks on a tour of how these numbers arise in the study of hyperplane arrangements, polytopes, and simplicial complexes. Some topics include a thorough discussion of gamma-nonnegativity and real-rootedness for Eulerian polynomials, as well as the weak order and the shard intersection order of the symmetric group. The book also includes a parallel story of Catalan combinatorics, wherein the Eulerian numbers are replaced with Narayana numbers. Again there is a progression from combinatorics to geometry, including discussion of the associahedron and the lattice of noncrossing partitions. The final chapters discuss how both the Eulerian and Narayana numbers have analogues in any finite Coxeter group, with many of the same enumerative and geometric properties. There are four supplemental chapters throughout, ...
Parsimonious Surface Wave Interferometry
Li, Jing
2017-10-24
To decrease the recording time of a 2D seismic survey from a few days to one hour or less, we present a parsimonious surface-wave interferometry method. Interferometry allows for the creation of a large number of virtual shot gathers from just two reciprocal shot gathers by crosscoherence of trace pairs, where the virtual surface waves can be inverted for the S-wave velocity model by wave-equation dispersion inversion (WD). Synthetic and field data tests suggest that parsimonious wave-equation dispersion inversion (PWD) gives S-velocity tomograms that are comparable to those obtained from a full survey with a shot at each receiver. The limitation of PWD is that the virtual data lose some information so that the resolution of the S-velocity tomogram can be modestly lower than that of the S-velocity tomogram inverted from a conventional survey.
On the vertical exchange of heat, mass and momentum over complex, mountainous terrain
Directory of Open Access Journals (Sweden)
Mathias Walter Rotach
2015-12-01
Full Text Available The role of the atmospheric boundary layer (ABL in the atmosphere-climate system is the exchange of heat, mass and momentum between ‘the earth’s surface’ and the atmosphere. Traditionally, it is understood that turbulent transport is responsible for this exchange and hence the understanding and physical description of the turbulence structure of the boundary layer is key to assess the effectiveness of earth-atmosphere exchange. This understanding is rooted in the (implicit assumption of a scale separation or spectral gap between turbulence and mean atmospheric motions, which in turn leads to the assumption of a horizontally homogeneous and flat (HHF surface as a reference, for which both physical understanding and model parameterizations have successfully been developed over the years. Over mountainous terrain, however, the ABL is generically inhomogeneous due to both thermal (radiative and dynamic forcing. This inhomogeneity leads to meso-scale and even sub-meso-scale flows such as slope and valley winds or wake effects. It is argued here that these (submeso-scale motions can significantly contribute to the vertical structure of the boundary layer and hence vertical exchange of heat and mass between the surface and the atmosphere. If model grid resolution is not high enough the latter will have to be parameterized (in a similar fashion as gravity wave drag parameterizations take into account the momentum transport due to gravity waves in large-scale models. In this contribution we summarize the available evidence of the contribution of (submeso-scale motions to vertical exchange in mountainous terrain from observational and numerical modeling studies. In particular, a number of recent simulation studies using idealized topography will be summarized and put into perspective – so as to identify possible limitations and areas of necessary future research.
DEFF Research Database (Denmark)
Kramer, Morten; Brorsen, Michael; Frigaard, Peter
Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....
Heat Waves Dangers we face during periods of very high temperatures include: Heat cramps: These are muscular pains and ... having trouble with the heat. If a heat wave is predicted or happening… - Slow down. Avoid strenuous ...
Reliability Analysis of Geotechnical Failure Modes for Vertical Wall Breakwaters
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Burcharth, H. F.
2000-01-01
Vertical wall breakwaters are usually designed as concrete caissons placed on the top of a rubble mound foundation or a rubble bedding layer. The purpose of the breakwater is usually to protect the area behind the breakwater from being flooded by large waves. The area protected can for example...... be a harbour of small or large importance, an important industrial area or a heavily populated coast line. This implies that vertical wall breakwaters are used under quite different conditions and therefore the consequences of a complete or partial failure also are very different. This implies...
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Frigaard, Peter; Sørensen, H. C.
1998-01-01
This paper concerns with the development of the wave energy converter (WEC) Wave Dragon. This WEC is based on the overtopping principle. An overview of the performed research done concerning the Wave Dragon over the past years is given, and the results of one of the more comprehensive studies......, concerning a hydraulic evaluation and optimisation of the geometry of the Wave Dragon, is presented. Furthermore, the plans for the future development projects are sketched....
Energy Technology Data Exchange (ETDEWEB)
Miller, Jonah Maxwell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-10-18
This report has slides on Gravitational Waves; Pound and Rebka: A Shocking Fact; Light is a Ruler; Gravity is the Curvature of Spacetime; Gravitational Waves Made Simple; How a Gravitational Wave Affects Stuff Here; LIGO; This Detection: Neutron Stars; What the Gravitational Wave Looks Like; The Sound of Merging Neutron Stars; Neutron Star Mergers: More than GWs; The Radioactive Cloud; The Kilonova; and finally Summary, Multimessenger Astronomy.
Wave propagation and impact in composite materials
Moon, F. C.
1975-01-01
Anisotropic waves in composites are considered, taking into account wave speeds, wave surfaces, flexural waves in orthotropic plates, surface waves, edge waves in plates, and waves in coupled composite plates. Aspects of dispersion in composites are discussed, giving attention to pulse propagation and dispersion, dispersion in rods and plates, dispersion in a layered composite, combined material and structural dispersion, continuum theories for composites, and variational methods for periodic composites. The characteristics of attenuation and scattering processes are examined and a description is given of shock waves and impact problems in composites. A number of experiments are also reported.
Blok, H.; van den Berg, P.M.
2011-01-01
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis, material characterization, electromagnetic properties of plasma, analysis and applications of periodic structures and waveguide components, etc.
DEFF Research Database (Denmark)
Tedd, James; Kofoed, Jens Peter; Knapp, W.
2006-01-01
Wave Dragon is a floating wave energy converter working by extracting energy principally by means of overtopping of waves into a reservoir. A 1:4.5 scale prototype has been sea tested for 20 months. This paper presents results from testing, experiences gained and developments made during...
Towne, Dudley H
1988-01-01
This excellent undergraduate-level text emphasizes optics and acoustics, covering inductive derivation of the equation for transverse waves on a string, acoustic plane waves, boundary-value problems, polarization, three-dimensional waves and more. With numerous problems (solutions for about half). ""The material is superbly chosen and brilliantly written"" - Physics Today. Problems. Appendices.
Vertical propagation of baroclinic Kelvin waves along the west coast ...
Indian Academy of Sciences (India)
Journal of Earth System Science. Current Issue : Vol. 126, Issue 8 · Current Issue Volume 126 | Issue 8. December 2017. Home · Volumes & Issues · Special Issues · Forthcoming Articles · Search · Editorial Board · Information for Authors · Subscription ...
Protected Vertices in Motzkin trees
Van Duzer, Anthony
2017-01-01
In this paper we find recurrence relations for the asymptotic probability a vertex is $k$ protected in all Motzkin trees. We use a similar technique to calculate the probabilities for balanced vertices of rank $k$. From this we calculate upper and lower bounds for the probability a vertex is balanced and upper and lower bounds for the expected rank of balanced vertices.
Multi-directional random wave interaction with an array of cylinders
DEFF Research Database (Denmark)
Ji, Xinran; Liu, Shuxue; Bingham, Harry B.
2015-01-01
Based on the linear theory of wave interaction with an array of circular bottom-mounted vertical cylinders, systematic calculations are made to investigate the effects of the wave directionality on wave loads in short-crested seas. The multi-directional waves are specified using a discrete form...... of the Mitsuyasu-type spreading function. The time series of multi-directional wave loads, including both the wave run-up and wave force, can be simulated. The effect of wave directionality on the wave run-up and wave loading on the cylinders is investigated. For multi-directional waves, as the distribution...... of wave spreading becomes wider, the wave run-up at some points around the cylinders is found to increase. This suggests that multi-directional wave run-up tends to be larger than unidirectional wave run-up. In addition, the wave directionality has a significant influence on the transverse force...
Andrews, George E
1994-01-01
Although mathematics majors are usually conversant with number theory by the time they have completed a course in abstract algebra, other undergraduates, especially those in education and the liberal arts, often need a more basic introduction to the topic.In this book the author solves the problem of maintaining the interest of students at both levels by offering a combinatorial approach to elementary number theory. In studying number theory from such a perspective, mathematics majors are spared repetition and provided with new insights, while other students benefit from the consequent simpl
Vertical Meandering Approach for Antenna Size Reduction
Directory of Open Access Journals (Sweden)
Li Deng
2012-01-01
Full Text Available A novel vertical meandering technique to reduce the lateral size of a planar printed antenna is presented. It is implemented by dividing a conventional spiral patch into a different number of segments and placing them on different sides of the microwave substrate with vias as the connections. To confirm the validity of this technique, measured electrical performance and radiation characteristics of five antennas with different numbers of segments are compared. The smallest antenna is reduced in size by 84% when compared with the conventional printed spiral antenna.
Nonlinear Hysteretic Torsional Waves.
Cabaret, J; Béquin, P; Theocharis, G; Andreev, V; Gusev, V E; Tournat, V
2015-07-31
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters.
Upper Mantle Shear Wave Structure Beneath North America From Multi-mode Surface Wave Tomography
Yoshizawa, K.; Ekström, G.
2008-12-01
The upper mantle structure beneath the North American continent has been investigated from measurements of multi-mode phase speeds of Love and Rayleigh waves. To estimate fundamental-mode and higher-mode phase speeds of surface waves from a single seismogram at regional distances, we have employed a method of nonlinear waveform fitting based on a direct model-parameter search using the neighbourhood algorithm (Yoshizawa & Kennett, 2002). The method of the waveform analysis has been fully automated by employing empirical quantitative measures for evaluating the accuracy/reliability of estimated multi-mode phase dispersion curves, and thus it is helpful in processing the dramatically increasing numbers of seismic data from the latest regional networks such as USArray. As a first step toward modeling the regional anisotropic shear-wave velocity structure of the North American upper mantle with extended vertical resolution, we have applied the method to long-period three-component records of seismic stations in North America, which mostly comprise the GSN and US regional networks as well as the permanent and transportable USArray stations distributed by the IRIS DMC. Preliminary multi-mode phase-speed models show large-scale patterns of isotropic heterogeneity, such as a strong velocity contrast between the western and central/eastern United States, which are consistent with the recent global and regional models (e.g., Marone, et al. 2007; Nettles & Dziewonski, 2008). We will also discuss radial anisotropy of shear wave speed beneath North America from multi-mode dispersion measurements of Love and Rayleigh waves.
Barnes, John
2016-01-01
In this intriguing book, John Barnes takes us on a journey through aspects of numbers much as he took us on a geometrical journey in Gems of Geometry. Similarly originating from a series of lectures for adult students at Reading and Oxford University, this book touches a variety of amusing and fascinating topics regarding numbers and their uses both ancient and modern. The author intrigues and challenges his audience with both fundamental number topics such as prime numbers and cryptography, and themes of daily needs and pleasures such as counting one's assets, keeping track of time, and enjoying music. Puzzles and exercises at the end of each lecture offer additional inspiration, and numerous illustrations accompany the reader. Furthermore, a number of appendices provides in-depth insights into diverse topics such as Pascal’s triangle, the Rubik cube, Mersenne’s curious keyboards, and many others. A theme running through is the thought of what is our favourite number. Written in an engaging and witty sty...
Time scale of scour around a pile in combined waves and current
DEFF Research Database (Denmark)
Petersen, Thor Ugelvig; Sumer, B. Mutlu; Fredsøe, Jørgen
The time scale of the scour process around a circular vertical pile is studied in combined waves and current. A series of tests were carried out in a flume with pile diameters 40 mm and 75 mm, in both steady current, waves and combined waves and current. In the combined wave and current flow regime...
Conversion of internal gravity waves into magnetic waves
Lecoanet, D.; Vasil, G. M.; Fuller, J.; Cantiello, M.; Burns, K. J.
2017-04-01
Asteroseismology probes the interiors of stars by studying oscillation modes at a star's surface. Although pulsation spectra are well understood for solar-like oscillators, a substantial fraction of red giant stars observed by Kepler exhibit abnormally low-amplitude dipole oscillation modes. Fuller et al. (2015) suggest this effect is produced by strong core magnetic fields that scatter dipole internal gravity waves (IGWs) into higher multipole IGWs or magnetic waves. In this paper, we study the interaction of IGWs with a magnetic field to test this mechanism. We consider two background stellar structures: one with a uniform magnetic field, and another with a magnetic field that varies both horizontally and vertically. We derive analytic solutions to the wave propagation problem and validate them with numerical simulations. In both cases, we find perfect conversion from IGWs into magnetic waves when the IGWs propagate into a region exceeding a critical magnetic field strength. Downward propagating IGWs cannot reflect into upward propagating IGWs because their vertical wavenumber never approaches zero. Instead, they are converted into upward propagating slow (Alfvénic) waves, and we show they will likely dissipate as they propagate back into weakly magnetized regions. Therefore, strong internal magnetic fields can produce dipole mode suppression in red giants, and gravity modes will likely be totally absent from the pulsation spectra of sufficiently magnetized stars.
Internal wave attractors examined using laboratory experiments and 3D numerical simulations
Brouzet, Christophe; Scolan, H; Ermanyuk, E V; Dauxois, Thierry
2016-01-01
In the present paper, we combine numerical and experimental approaches to study the dynamics of stable and unstable internal wave attractors. The problem is considered in a classic trapezoidal setup filled with a uniformly stratified fluid. Energy is injected into the system at global scale by the small-amplitude motion of a vertical wall. Wave motion in the test tank is measured with the help of conventional synthetic schlieren and PIV techniques. The numerical setup closely reproduces the experimental one in terms of geometry and the operational range of the Reynolds and Schmidt numbers. The spectral element method is used as a numerical tool to simulate the nonlinear dynamics of a viscous salt-stratified fluid. We show that the results of three-dimensional calculations are in excellent qualitative and quantitative agreement with the experimental data, including the spatial and temporal parameters of the secondary waves produced by triadic resonance instability. Further, we explore experimentally and numeri...
Vertically Integrated Multiple Nanowire Field Effect Transistor.
Lee, Byung-Hyun; Kang, Min-Ho; Ahn, Dae-Chul; Park, Jun-Young; Bang, Tewook; Jeon, Seung-Bae; Hur, Jae; Lee, Dongil; Choi, Yang-Kyu
2015-12-09
A vertically integrated multiple channel-based field-effect transistor (FET) with the highest number of nanowires reported ever is demonstrated on a bulk silicon substrate without use of wet etching. The driving current is increased by 5-fold due to the inherent vertically stacked five-level nanowires, thus showing good feasibility of three-dimensional integration-based high performance transistor. The developed fabrication process, which is simple and reproducible, is used to create multiple stiction-free and uniformly sized nanowires with the aid of the one-route all-dry etching process (ORADEP). Furthermore, the proposed FET is revamped to create nonvolatile memory with the adoption of a charge trapping layer for enhanced practicality. Thus, this research suggests an ultimate design for the end-of-the-roadmap devices to overcome the limits of scaling.
INTERFERENCE OF UNIDIRECTIONAL SHOCK WAVES
Directory of Open Access Journals (Sweden)
P. V. Bulat
2015-05-01
Full Text Available Subject of study.We consider interference of unidirectional shock waves or, as they are called, catching up shock waves. The scope of work is to give a classification of the shock-wave structures that arise in this type of interaction of shock waves, and the area of their existence. Intersection of unidirectional shock waves results in arising of a shock-wave structure at the intersection point, which contains the main shock wave, tangential discontinuity and one more reflected gas-dynamic discontinuity of unknown beforehand type. The problem of determining the type of reflected discontinuity is the main problem that one has to solve in the study of catching shock waves interference. Main results.The paper presents the pictures of shock-wave structures arising at the interaction of catching up shock waves. The areas with a regular and irregular unidirectional interaction of shocks are described. Characteristic shock-wave structures are of greatest interest, where reflected gas-dynamic discontinuity degenerates into discontinuous characteristics. Such structures have a number of extreme properties. We have found the areas of existence for such shock-wave structures. There are also areas in which the steady-state solution is not available. The latter has determined revival of interest for the theoretical study of the problem, because the facts of sudden shock-wave structure destruction inside the air intake of supersonic aircrafts at high Mach numbers have been discovered. Practical significance.The theory of interference for unidirectional shock waves and design procedure are usable in the design of supersonic air intakes. It is also relevant for application possibility investigation of catching up oblique shock waves to create overcompressed detonation in perspective detonation air-jet and rocket engines.
Directory of Open Access Journals (Sweden)
Theodore M. Porter
2012-12-01
Full Text Available The struggle over cure rate measures in nineteenth-century asylums provides an exemplary instance of how, when used for official assessments of institutions, these numbers become sites of contestation. The evasion of goals and corruption of measures tends to make these numbers “funny” in the sense of becoming dis-honest, while the mismatch between boring, technical appearances and cunning backstage manipulations supplies dark humor. The dangers are evident in recent efforts to decentralize the functions of governments and corporations using incen-tives based on quantified targets.
Influence of Whipping on Long term Vertical Bending Moment
DEFF Research Database (Denmark)
Baarholm, G. S.; Jensen, Jørgen Juncher
2004-01-01
approach. Effect of whipping is included by assuming that the whipping and wave induced response are independent, but the effect of correlation of the long term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by (Xia et al 1998......). Results are presented for the S-175 container ship, (15th & 16th ITTC Seakeeping Committee 1983). The analysis shoes that whipping increases the vertical bending moment and that the correlation is significant...
Understanding Vertical Jump Potentiation: A Deterministic Model.
Suchomel, Timothy J; Lamont, Hugh S; Moir, Gavin L
2016-06-01
This review article discusses previous postactivation potentiation (PAP) literature and provides a deterministic model for vertical jump (i.e., squat jump, countermovement jump, and drop/depth jump) potentiation. There are a number of factors that must be considered when designing an effective strength-power potentiation complex (SPPC) focused on vertical jump potentiation. Sport scientists and practitioners must consider the characteristics of the subject being tested and the design of the SPPC itself. Subject characteristics that must be considered when designing an SPPC focused on vertical jump potentiation include the individual's relative strength, sex, muscle characteristics, neuromuscular characteristics, current fatigue state, and training background. Aspects of the SPPC that must be considered for vertical jump potentiation include the potentiating exercise, level and rate of muscle activation, volume load completed, the ballistic or non-ballistic nature of the potentiating exercise, and the rest interval(s) used following the potentiating exercise. Sport scientists and practitioners should design and seek SPPCs that are practical in nature regarding the equipment needed and the rest interval required for a potentiated performance. If practitioners would like to incorporate PAP as a training tool, they must take the athlete training time restrictions into account as a number of previous SPPCs have been shown to require long rest periods before potentiation can be realized. Thus, practitioners should seek SPPCs that may be effectively implemented in training and that do not require excessive rest intervals that may take away from valuable training time. Practitioners may decrease the necessary time needed to realize potentiation by improving their subject's relative strength.
Indian Academy of Sciences (India)
How many points are there on a line? Which is more in number- points on a line or lines in a plane? These are some natural questions that have occurred to us sometime or the other. It is interesting to note the difference between the two questions. Do we have to know how many points and lines there are to answer.
Indian Academy of Sciences (India)
Admin
Left: Anuradha S Garge completed her PhD from. Pune University in 2008 under the supervision of Prof. S A Katre. Her research interests include K-theory and number theory. Besides mathematics, she is interested in (singing) indian classical music and yoga. Right: Shailesh Shirali is. Director of Sahyadri School.
Broadband Grounded Vertical Antennas for 30-180 MHZ (VHF)
2013-10-18
antennas are well known for their broadband gain (monocone, bicone ) but are never combined with a monopole. An eccentric combination of broadband...DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE Broadband Grounded Vertical Antennas For 30-180 MZH (VHF) 5a. CONTRACT NUMBER 5b...18 Attorney Docket No. 102536 1 of 17 BROADBAND GROUNDED VERTICAL ANTENNAS FOR 30-180 MHZ (VHF) STATEMENT OF GOVERNMENT INTEREST
CERN. Geneva
2005-01-01
We will present a brief introduction to the physics of gravitational waves and their properties. We will review potential astrophysical sources of gravitational waves, and the physics and astrophysics that can be learned from their study. We will survey the techniques and technologies for detecting gravitational waves for the first time, including bar detectors and broadband interferometers, and give a brief status report on the international search effort, with special emphasis on the LIGO detectors and search results.
Trade Liberalisation and Vertical Integration
DEFF Research Database (Denmark)
Bache, Peter Arendorf; Laugesen, Anders Rosenstand
producers face decisions on exporting, vertical integration of intermediate-input production, and whether the intermediate-input production should be offshored to a low-wage country. We find that the fractions of final-good producers that pursue either vertical integration, offshoring, or exporting are all......We build a three-country model of international trade in final goods and intermediate inputs and study the relation between four different types of trade liberalisation and vertical integration. Firms are heterogeneous with respect to both productivity and factor (headquarter) intensity. Final-good...... increasing when intermediate-input trade or final-goods trade is liberalised. Finally, we provide guidance for testing the open-economy property rights theory of the firm using firm-level data and surprisingly show that the relationship between factor (headquarter) intensity and the likelihood of vertical...
Horizontal and Vertical Line Designs.
Johns, Pat
2003-01-01
Presents an art lesson in which students learn about the artist Piet Mondrian and create their own abstract artworks. Focuses on geometric shapes using horizontal and vertical lines. Includes background information about the artist. (CMK)
Vertical axis wind turbine airfoil
Krivcov, Vladimir; Krivospitski, Vladimir; Maksimov, Vasili; Halstead, Richard; Grahov, Jurij Vasiljevich
2012-12-18
A vertical axis wind turbine airfoil is described. The wind turbine airfoil can include a leading edge, a trailing edge, an upper curved surface, a lower curved surface, and a centerline running between the upper surface and the lower surface and from the leading edge to the trailing edge. The airfoil can be configured so that the distance between the centerline and the upper surface is the same as the distance between the centerline and the lower surface at all points along the length of the airfoil. A plurality of such airfoils can be included in a vertical axis wind turbine. These airfoils can be vertically disposed and can rotate about a vertical axis.
Wave-particle interaction in the Faraday waves.
Francois, N; Xia, H; Punzmann, H; Shats, M
2015-10-01
Wave motion in disordered Faraday waves is analysed in terms of oscillons or quasi-particles. The motion of these oscillons is measured using particle tracking tools and it is compared with the motion of fluid particles on the water surface. Both the real floating particles and the oscillons, representing the collective fluid motion, show Brownian-type dispersion exhibiting ballistic and diffusive mean squared displacement at short and long times, respectively. While the floating particles motion has been previously explained in the context of two-dimensional turbulence driven by Faraday waves, no theoretical description exists for the random walk type motion of oscillons. It is found that the r.m.s velocity ⟨μ̃(osc)⟩(rms) of oscillons is directly related to the turbulent r.m.s. velocity ⟨μ̃⟩(rms) of the fluid particles in a broad range of vertical accelerations. The measured ⟨μ̃(osc)⟩(rms) accurately explains the broadening of the frequency spectra of the surface elevation observed in disordered Faraday waves. These results suggest that 2D turbulence is the driving force behind both the randomization of the oscillons motion and the resulting broadening of the wave frequency spectra. The coupling between wave motion and hydrodynamic turbulence demonstrated here offers new perspectives for predicting complex fluid transport from the knowledge of wave field spectra and vice versa.
Papazoglou, Dimitris G.; Fedorov, Vladimir Yu.; Tzortzakis, Stelios
2016-01-01
We show the existence of a family of waves that share a common interesting property affecting the way they propagate and focus. These waves are a superposition of twin waves, which are conjugate to each other under inversion of the propagation direction. In analogy to holography, these twin "real" and "virtual" waves are related respectively to the converging and the diverging part of the beam and can be clearly visualized in real space at two distinct foci under the action of a focusing lens...
Residual Liquefaction under Standing Waves
DEFF Research Database (Denmark)
Kirca, V.S. Ozgur; Sumer, B. Mutlu; Fredsøe, Jørgen
2012-01-01
This paper summarizes the results of an experimental study which deals with the residual liquefaction of seabed under standing waves. It is shown that the seabed liquefaction under standing waves, although qualitatively similar, exhibits features different from that caused by progressive waves....... The experimental results show that the buildup of pore-water pressure and the resulting liquefaction first starts at the nodal section and spreads towards the antinodal section. The number of waves to cause liquefaction at the nodal section appears to be equal to that experienced in progressive waves for the same...... wave height. Recommendations are made as to how to assess liquefaction potential in standing waves. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE)....
DEFF Research Database (Denmark)
Margheritini, Lucia; Vicinanza, Diego; Frigaard, Peter
2008-01-01
The SSG (Sea Slot-cone Generator) is a wave energy converter of the overtopping type. The structure consists of a number of reservoirs one on the top of each others above the mean water level, in which the water of incoming waves is stored temporary. In each reservoir, expressively designed low...... head hydroturbines are converting the potential energy of the stored water into power. A key to success for the SSG will be the low cost of the structure and its robustness. The construction of the pilot plant is scheduled and this paper aims to describe the concept of the SSG wave energy converter...... and the studies behind the process that leads to its construction. The pilot plant is an on-shore full scale module in 3 levels with an expected power production of 320 MWh/y in the North Sea. Location, wave climate and laboratory tests results will be used here to describe the pilot plant and its characteristics....
Unsteady MHD free convective flow past a vertical porous plate ...
African Journals Online (AJOL)
An attempt has been made to study the unsteady MHD free convective flow past a vertical porous plate immersed in a porous medium with Hall current, thermal diffusion and heat source. Analytical solution has been found depending on the physical parameters including the Hartmann number M, the Prandtl number Pr, the ...
Scales of Free Convection around a Vertical Cylinder
Lira, Ignacio
2008-01-01
The natural scales of the laminar steady-state free convection flow regime surrounding an isothermal vertical cylinder are established. It is shown that nondimensionalizing the momentum and energy equations in terms of the Rayleigh or Boussinesq numbers allows the use of the Prandtl number as a criterion to establish whether the motive buoyancy…
Backward integration, forward integration, and vertical foreclosure
Spiegel, Yossi
2013-01-01
I show that partial vertical integration may either alleviates or exacerbate the concern for vertical foreclosure relative to full vertical integration and I examine its implications for consumer welfare.
Number names and number understanding
DEFF Research Database (Denmark)
Ejersbo, Lisser Rye; Misfeldt, Morten
2014-01-01
This paper concerns the results from the first year of a three-year research project involving the relationship between Danish number names and their corresponding digits in the canonical base 10 system. The project aims to develop a system to help the students’ understanding of the base 10 syste...
Excitation of surface plasma waves over corrugated slow-wave ...
Indian Academy of Sciences (India)
A microwave propagating along vacuum–dielectric–plasma interface excites surface plasma wave (SPW). A periodic slow-wave structure placed over dielectric slows down the SPW. The phase velocity of slow SPW is sensitive to height, periodicity, number of periods, thickness and the separation between dielectric and ...
Excitation of surface plasma waves over corrugated slow-wave ...
Indian Academy of Sciences (India)
Abstract. A microwave propagating along vacuum–dielectric–plasma interface excites surface plasma wave (SPW). A periodic slow-wave structure placed over dielectric slows down the SPW. The phase velocity of slow SPW is sensitive to height, periodicity, number of periods, thickness and the separation between ...
2016-11-01
information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE 30...of acceleration application (i.e., jerk ), peak amplitude, and pulse duration, Eiband (1959). Consistent Wave Slam Type The time history responses of...systematic research for effects other than vertical, and there is a need for controlled studies to better describe and quantify the bounds of human
The physics of orographic gravity wave drag
Directory of Open Access Journals (Sweden)
Miguel A C Teixeira
2014-07-01
Full Text Available The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.
2005-01-01
tut quiz Tutorial Quiz Interactive Media Element This interactive tutorial reviews the mechanisms of Rossby waves. Rossby waves in both the northern and southern hemispheres are considered. The interactions involve answering simple fill-in-the-blank questions. Diagrams are used to illustrate some of the concepts reviewed. MR4322 Dynamic Meteorology
DEFF Research Database (Denmark)
Tedd, James; Kofoed, Jens Peter; Friis-Madsen, Erik
2008-01-01
Since March 2003 a prototype of Wave Dragon has been tested in an inland sea in Denmark. This has been a great success with all subsystems tested and improved through working in an offshore environment. The project has proved the Wave Dragon device and has enabled the next stage, a production sized...
DEFF Research Database (Denmark)
Kramer, Morten; Brorsen, Michael; Frigaard, Peter
Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....
Wave Characteristics in Breaststroke Technique with and Without Snorkel Use
Conceição, Ana; Silva, António J.; Boaventura, José; Marinho, Daniel A.; Louro, Hugo
2013-01-01
The purpose of this paper was to examine the characteristics of waves generated when swimming with and without the use of Aquatrainer® snorkels. Eight male swimmers performed two maximal bouts of 25 m breaststroke, first without the use of a snorkel (normal condition) and then using a snorkel (snorkel condition). The body landmarks, centre of the mass velocity, stroke rate, stroke length, stroke index, and Strouhal number (St) were quantified. Fourier analysis was conducted to determine the frequency, amplitude, and phase characteristics of the vertical undulations. We also determined the undulation period, the first and second harmonic wave percentage, and the contribution of these components to the power of each of the wave signals. The first wave harmonics had a frequency of 0.76 Hz (normal condition) and 0.78 Hz (snorkel condition), and the second wave harmonics had a frequency of 1.52 Hz (normal condition) and 1.56 Hz (snorkel condition). Under the normal conditions, the wave amplitude was higher on the vertex (0.72 m) and cervical (0.32 m) than that produced under snorkel conditions (0.71 m and 0.28 m, respectively). The lowest values were found in the hip (0.03 m in normal conditions, and 0.02 m in snorkel conditions) and in the trunk (0.06 m in normal conditions, and 0.04 m in snorkel conditions). It can be concluded that snorkel use seems to lead to slight changes in the biomechanical pattern in swimming velocity, as well as several stroke mechanical variables. PMID:24511354
Vertical profile of atmospheric conductivity that matches Schumann resonance observations.
Nickolaenko, Alexander P; Galuk, Yuri P; Hayakawa, Masashi
2016-01-01
We introduce the vertical profile of atmospheric conductivity in the range from 2 to 98 km. The propagation constant of extremely low frequency (ELF) radio waves was computed for this profile by using the full wave solution. A high correspondence is demonstrated of the data thus obtained to the conventional standard heuristic model of ELF propagation constant derived from the Schumann resonance records performed all over the world. We also suggest the conductivity profiles for the ambient day and ambient night conditions. The full wave solution technique was applied for obtaining the corresponding frequency dependence of propagation constant relevant to these profiles. By using these propagation constants, we computed the power spectra of Schumann resonance in the vertical electric field component for the uniform global distribution of thunderstorms and demonstrate their close similarity in all the models. We also demonstrate a strong correspondence between the wave attenuation rate obtained for these conductivity profiles and the measured ones by using the ELF radio transmissions.
High power 1060-nm super large vertical cavity semiconductor lasers
Tan, Shaoyang; Zhai, Teng; Wang, Wei; Zhang, Ruikang; Lu, Dan; Ji, Chen
2014-11-01
High power single-mode ridge waveguide 1060-nm semiconductor lasers are reported. The lasers consist of compressively strained double InGaAs/GaAs quantum wells and a GaAs/AlGaAs separate confinement vertical structure. A super large vertical optical cavity is employed to have a low internal loss, large optical spot size and low vertical optical divergence angle. The material composition and thickness of waveguide layers and claddings layer are optimized systematically. The active layer is detuned from center of the waveguide and thickness of cladding layers is optimized to guaranty single mode lasing of the large optical cavity. The large vertical cavity laser structure with thickness of 4 μm allows the lasers have a low internal loss of less than 0.6 /cm, a large optical spot size about 1μm and a vertical divergence angle about 20 degree. For lateral optical confinement, a double trench ridge waveguide is employed to maintain single-lateral-mode operation. Based on the optimization, 1.5 W continue wave optical power is achieved for broad area lasers with 1mm longitude cavity length. Narrow stripe ridge waveguide lasers of 1mm cavity length with single mode current and optical power of 700 mA and 340 mW is obtained. Suggestions for further improvements in terms of single mode power and applications of the high power semiconductors are discussed.
Christov, Ivan C
2012-01-01
In classical continuum physics, a wave is a mechanical disturbance. Whether the disturbance is stationary or traveling and whether it is caused by the motion of atoms and molecules or the vibration of a lattice structure, a wave can be understood as a specific type of solution of an appropriate mathematical equation modeling the underlying physics. Typical models consist of partial differential equations that exhibit certain general properties, e.g., hyperbolicity. This, in turn, leads to the possibility of wave solutions. Various analytical techniques (integral transforms, complex variables, reduction to ordinary differential equations, etc.) are available to find wave solutions of linear partial differential equations. Furthermore, linear hyperbolic equations with higher-order derivatives provide the mathematical underpinning of the phenomenon of dispersion, i.e., the dependence of a wave's phase speed on its wavenumber. For systems of nonlinear first-order hyperbolic equations, there also exists a general ...
Ando, Hiroki; Imamura, Takeshi; Sugimoto, Norihiko; Takagi, Masahiro; Kashimura, Hiroki; Tellmann, Silvia; Pätzold, Martin; Häusler, Bernd; Matsuda, Yoshihisa
2017-08-01
Vertical temperature profiles at 40-75 km around 80°N in the Venus polar vortex are retrieved over 13 Earth days almost continuously from radio occultation measurements (Venus Express radio occultation) in the Venus Express mission. They show periodical variations with a dominant period of ˜3.1 Earth days. These fluctuations are confined in an altitude range of 45-65 km with a local minimum at ˜58 km altitude, where the static stability abruptly increases with height. The phase of the temperature fluctuations is almost reversed at the 58 km level and varies little above and below this altitude. A numerical simulation of a Venusian atmospheric general circulation model (GCM) shows that the axi-asymmetric temperature disturbance with zonal wave number 1 is predominant at 50-75 km levels in the model atmosphere. The vertical structure of the reproduced disturbance agrees quite well with that retrieved by the radio occultation measurement: amplitude of the temperature fluctuation has a local minimum and its phase is reversed at the altitude (65 km in the model) where the static stability rapidly changes as in the observations. Above and below this altitude, the phase is almost constant in the vertical direction. The relationship among the temperature, horizontal winds, and geopotential height associated with the simulated disturbance suggests that the axi-asymmetric temperature disturbance observed in the Venus polar region can be interpreted as neutral barotropic Rossby waves related to barotropic instability in the polar region.
Fast magnetosonic wave excitation by an array of wires with time-modulated currents
Directory of Open Access Journals (Sweden)
G. Sanchez-Arriaga
2010-02-01
Full Text Available The excitation of Fast Magnetosonic (FMS waves by a cylindrical array of parallel tethers carrying time-modulated current is discussed. The tethers would fly vertical in the equatorial plane, which is perpendicular to the geomagnetic field when its tilt is ignored, and would be stabilized by the gravity gradient. The tether array would radiate a single FMS wave. In the time-dependent background made of geomagnetic field plus radiated wave, plasma FMS perturbations are excited in the array vicinity through a parametric instability. The growth rate is estimated by truncating the evolution equation for FMS perturbations to the two azimuthal modes of lowest order. Design parameters such as tether length and number, required power and mass are discussed for Low Earth Orbit conditions. The array-attached wave structure would have the radiated wave controlled by the intensity and modulation frequency of the currents, making an active experiment on non-linear low frequency waves possible in real space plasma conditions.
Directory of Open Access Journals (Sweden)
Eugênio F. Coelho
2003-08-01
feasibility of the use of wave guides of two and three rods with different spacings. Disturbed soil samples were packed in PVC tube segments of 0.075 m diameter. Two sets of 24 have guides were constructed. One of this sets had a capacitor. In each set one half of the wave guides had two rods and the other half contained three rods. The rod spacing varied from 0.009 to 0.022 m. Soil water content data from gravimetry and soil bulk dielectric constant values from Trase System analyzer were collected during drying process with water content values ranging from 0.31 to 0.13 m³ m-3. Five mathematical models were fitted to water content and bulk dielectric constant data. The Malicki's model was the most adequate for estimating soil water content as a function of bulk dielectric constant. The wave guides with three rods 0.017 m apart from each other showed the best performance. The three-rod wave-guides without capacitor performed better for water content determination than the two-rod wave-guides without capacitor. The three-rod wave-guides without capacitor performed better than three-rod wave-guides with capacitor.
Vertical saccades in dyslexic children.
Tiadi, Aimé; Seassau, Magali; Bui-Quoc, Emmanuel; Gerard, Christophe-Loïc; Bucci, Maria Pia
2014-11-01
Vertical saccades have never been studied in dyslexic children. We examined vertical visually guided saccades in fifty-six dyslexic children (mean age: 10.5±2.56 years old) and fifty-six age matched non dyslexic children (mean age: 10.3±1.74 years old). Binocular eye movements were recorded using an infrared video-oculography system (mobileEBT®, e(ye)BRAIN). Dyslexic children showed significantly longer latency than the non dyslexic group, also the occurrence of anticipatory and express saccades was more important in dyslexic than in non dyslexic children. The gain and the mean velocity values were significantly smaller in dyslexic than in non dyslexic children. Finally, the up-down asymmetry reported in normal population for the gain and the velocity of vertical saccades was observed in dyslexic children and interestingly, dyslexic children also reported an up-down asymmetry for the mean latency. Taken together all these findings suggested impairment in cortical areas responsible of vertical saccades performance and also at peripheral level of the extra-ocular oblique muscles; moreover, a visuo-attentionnal bias could explain the up-down asymmetry reported for the vertical saccade triggering. Copyright © 2014 Elsevier Ltd. All rights reserved.
Encounter Probability of Individual Wave Height
DEFF Research Database (Denmark)
Liu, Z.; Burcharth, H. F.
1998-01-01
wave height corresponding to a certain exceedence probability within a structure lifetime (encounter probability), based on the statistical analysis of long-term extreme significant wave height. Then the design individual wave height is calculated as the expected maximum individual wave height...... associated with the design significant wave height, with the assumption that the individual wave heights follow the Rayleigh distribution. However, the exceedence probability of such a design individual wave height within the structure lifetime is unknown. The paper presents a method for the determination...... of the design individual wave height corresponding to an exceedence probability within the structure lifetime, given the long-term extreme significant wave height. The method can also be applied for estimation of the number of relatively large waves for fatigue analysis of constructions....
Electromagnetic waves in stratified media
Wait, James R; Fock, V A; Wait, J R
2013-01-01
International Series of Monographs in Electromagnetic Waves, Volume 3: Electromagnetic Waves in Stratified Media provides information pertinent to the electromagnetic waves in media whose properties differ in one particular direction. This book discusses the important feature of the waves that enables communications at global distances. Organized into 13 chapters, this volume begins with an overview of the general analysis for the electromagnetic response of a plane stratified medium comprising of any number of parallel homogeneous layers. This text then explains the reflection of electromagne
Directory of Open Access Journals (Sweden)
V. Sivakumar
2006-05-01
Full Text Available The low-latitude middle atmospheric gravity wave characteristics are presented using 310 nights of Rayleigh lidar observations made at Gadanki (13.5° N, 79.2° E over the period from March 1998 to December 2002. The gravity wave characteristics are presented in terms of vertical wave number and frequency spectra, along with the estimated potential energy for the four seasons, namely, spring, summer, autumn and winter. The computed wave number spectra for both the stratosphere and the mesosphere are found to differ significantly from a saturated model predicted spectrum. The spectra were found to be shallower at lower wave numbers and steeper at higher wave numbers with transition at ~8.85×10-4 cy/m. The computed frequency spectra seem to follow the model plot with a power law index of -5/3 above a frequency of ~2×10-4 Hz. The estimated potential energy per unit mass increases gradually up to ~60 km and then rather rapidly above this height to reach values of the order of 200J/kg at ~70 km.
Soil-Pile Interaction in the Pile Vertical Vibration Based on Fictitious Soil-Pile Model
Deng, Guodong; Zhang, Jiasheng; Wu, Wenbing; Shi, Xiong; Meng, Fei
2014-01-01
By introducing the fictitious soil-pile model, the soil-pile interaction in the pile vertical vibration is investigated. Firstly, assuming the surrounding soil of pile to be viscoelastic material and considering its vertical wave effect, the governing equations of soil-pile system subjected to arbitrary harmonic dynamic force are founded based on the Euler-Bernoulli rod theory. Secondly, the analytical solution of velocity response in frequency domain and its corresponding semianalytical solu...
Plasma Waves as a Benchmark Problem
Kilian, Patrick; Schreiner, Cedric; Spanier, Felix
2016-01-01
A large number of wave modes exist in a magnetized plasma. Their properties are determined by the interaction of particles and waves. In a simulation code, the correct treatment of field quantities and particle behavior is essential to correctly reproduce the wave properties. Consequently, plasma waves provide test problems that cover a large fraction of the simulation code. The large number of possible wave modes and the freedom to choose parameters make the selection of test problems time consuming and comparison between different codes difficult. This paper therefore aims to provide a selection of test problems, based on different wave modes and with well defined parameter values, that is accessible to a large number of simulation codes to allow for easy benchmarking and cross validation. Example results are provided for a number of plasma models. For all plasma models and wave modes that are used in the test problems, a mathematical description is provided to clarify notation and avoid possible misunderst...
Soldatenko, Sergei; Tingwell, Chris
2013-01-01
The sensitivity of the main characteristics of baroclinically unstable waves with respect to fundamental parameters of the atmosphere (the static stability parameter σ0 and vertical shear of a zonal wind Λ) is theoretically explored. Two types of waves are considered: synoptic scale waves and planetary scale (ultralong) waves based on an Eady-type model and model with vertically averaged primitive equations. Sensitivity functions are obtained that estimate the impact of variations ...
Taylor, M. J.; Zhao, Y.; Pautet, P. D.; Carstens, J. N.; Pugmire, J. R.; Smith, S. M.; Liu, A. Z.; Vargas, F.; Swenson, G. R.; Randall, C. E.; Bailey, S. M.; Russell, J. M., III
2016-12-01
To date, the primary research goals of the Aeronomy of Ice in the Mesosphere (AIM) satellite have focussed on investigating the occurrence, properties and dynamics of high-latitude Polar Mesospheric Clouds (PMC). With the evolution of the AIM orbit beta angle the opportunity now exists to make measurements outside the PMC region covering mid-low and equatorial latitudes. As part of the extended AIM mission science program, the AIM platform in conjunction with auxiliary ground-based measurements will be used to better understand upper atmospheric dynamics and vertical coupling due to gravity waves. Over the next 2 years AIM will take advantage of a new imaging capability of the on-board large-field CIPS UV imager to capture new data on the characteristics and spatial extents of stratospheric gravity waves near the 50 km level and their variation with latitude and season. In this study we report on initial coordinated ground-based measurements with the Andes Lidar Observatory (ALO) at Cerro Pachon, Chile ( 30°S) and nearby El Leoncito Observatory, Argentina, high in the Andes Mountains, where regular remote-sensing measurements are made using meteor radar, mesospheric airglow imagers, temperature mappers and an Na wind-temperature lidar (on a campaign basis). First coordinated measurements were made during the winter period in June 2016. AIM daytime overpasses have been analysed to search for and characterize extensive stratospheric wave events, as well as long-lived "Mountain Waves" over South America. Subsequent night-time ground-based measurements have been used to quantify wave characteristics in the mesopause region ( 80-100 km) to investigate vertical coupling. These measurements are continuing and it is planned to extend the new AIM stratospheric gravity wave data set for similar studies from a number of well-instrumented ground sites around the world.
Modeling the QBO-Improvements resulting from higher-model vertical resolution.
Geller, Marvin A; Zhou, Tiehan; Shindell, D; Ruedy, R; Aleinov, I; Nazarenko, L; Tausnev, N L; Kelley, M; Sun, S; Cheng, Y; Field, R D; Faluvegi, G
2016-09-01
Using the NASA Goddard Institute for Space Studies (GISS) climate model, it is shown that with proper choice of the gravity wave momentum flux entering the stratosphere and relatively fine vertical layering of at least 500 m in the upper troposphere-lower stratosphere (UTLS), a realistic stratospheric quasi-biennial oscillation (QBO) is modeled with the proper period, amplitude, and structure down to tropopause levels. It is furthermore shown that the specified gravity wave momentum flux controls the QBO period whereas the width of the gravity wave momentum flux phase speed spectrum controls the QBO amplitude. Fine vertical layering is required for the proper downward extension to tropopause levels as this permits wave-mean flow interactions in the UTLS region to be resolved in the model. When vertical resolution is increased from 1000 to 500 m, the modeled QBO modulation of the tropical tropopause temperatures increasingly approach that from observations, and the "tape recorder" of stratospheric water vapor also approaches the observed. The transport characteristics of our GISS models are assessed using age-of-air and N2O diagnostics, and it is shown that some of the deficiencies in model transport that have been noted in previous GISS models are greatly improved for all of our tested model vertical resolutions. More realistic tropical-extratropical transport isolation, commonly referred to as the "tropical pipe," results from the finer vertical model layering required to generate a realistic QBO.
Berg, Ward; Smit, Han
2007-01-01
textabstractThis paper explains why consolidation acquisitions occur in waves and it predicts the differing role each firm is likely to play in the consolidation game. We propose that whether a firm assumes the role of rival consolidator, target, or passive observer depends on the position of the firm relative to the entity that merges first. Our model predicts that an initial acquisition triggers a wave of follow-on acquisitions, where the process of asset accumulation by the consolidator is...
DEFF Research Database (Denmark)
Kramer, Morten; Andersen, Thomas Lykke
Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....
DEFF Research Database (Denmark)
Kramer, Morten; Frigaard, Peter
Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....
Metamaterials and wave control
Lheurette, Eric
2013-01-01
Since the concept was first proposed at the end of the 20th Century, metamaterials have been the subject of much research and discussion throughout the wave community. More than 10 years later, the number of related published articles is increasing significantly. Onthe one hand, this success can be attributed to dreams of new physical objects which are the consequences of the singular properties of metamaterials. Among them, we can consider the examples of perfect lensing and invisibility cloaking. On other hand,metamaterials also provide new tools for the design of well-known wave functions s
Grid Representations and the Chromatic Number
Balko, Martin
2012-01-01
A grid drawing of a graph maps vertices to grid points and edges to line segments that avoid grid points representing other vertices. We show that there is a number of grid points that some line segment of an arbitrary grid drawing must intersect. This number is closely connected to the chromatic number. Second, we study how many columns we need to draw a graph in the grid, introducing some new $\\NP$-complete problems. Finally, we show that any planar graph has a planar grid drawing where eve...
Pegging Numbers For Various Tree Graphs
Levavi, Ariel
2011-01-01
In the game of pegging, each vertex of a graph is considered a hole into which a peg can be placed. A pegging move is performed by jumping one peg over another peg, and then removing the peg that has been jumped over from the graph. We define the pegging number as the smallest number of pegs needed to reach all the vertices in a graph no matter what the distribution. Similarly, the optimal-pegging number of a graph is defined as the smallest distribution of pegs for which all the vertices in ...
Equatorial wave activity during 2007 over Gadanki, a tropical station
Indian Academy of Sciences (India)
by equatorial Kelvin waves observed over the Galapagos;. Geophys. Res. Lett. 28 3143–3146. Holton J R and Lindzen R S 1972 An updated theory for the quasi-biennial oscillation; J. Atmos. Sci. 29 1076–. 1080. Holton J R, Alexander M J and Boehm M T 2001 Evi- dence for short vertical wavelength Kelvin waves in.
Needham, Charles E
2010-01-01
The primary purpose of this text is to document many of the lessons that have been learned during the author’s more than forty years in the field of blast and shock. The writing therefore takes on an historical perspective, in some sense, because it follows the author’s experience. The book deals with blast waves propagating in fluids or materials that can be treated as fluids. It begins by distinguishing between blast waves and the more general category of shock waves. It then examines several ways of generating blast waves, considering the propagation of blast waves in one, two and three dimensions as well as through the real atmosphere. One section treats the propagation of shocks in layered gases in a more detailed manner. The book also details the interaction of shock waves with structures in particular reflections, progressing from simple to complex geometries, including planar structures, two-dimensional structures such as ramps or wedges, reflections from heights of burst, and three-dimensional st...
Estimation of seabed shear-wave velocity profiles using shear-wave source data.
Dong, Hefeng; Nguyen, Thanh-Duong; Duffaut, Kenneth
2013-07-01
This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements.
Stochastic generation of continuous wave spectra
DEFF Research Database (Denmark)
Trulsen, J.; Dysthe, K. B.; Pécseli, Hans
1983-01-01
Wave packets of electromagnetic or Langmuir waves trapped in a well between oscillating reflectors are considered. An equation for the temporal evolution of the probability distribution for the carrier wave number is derived, and solved analytically in terms of moments in the limits of long...
Wave Dragon Buoyancy Regulation Study
DEFF Research Database (Denmark)
Jakobsen, Jens; Kofoed, Jens Peter
Wave Dragon is a wave energy converter, which was deployed offshore at Nissum Bredning in Denmark in 2003. The experience gained from operating Wave Dragon during 2003 and 2004 has shown that the buoyancy regulation system can be improved in a number of ways. This study describes the current...... situation, and proposes a number of activities in order to improve the buoyancy regulation system. This work was performed under EU ENERGIE contract no. ENK5-CT-2002-00603, and is a contribution to WP 2.3/2.4 and D40/D41....
DEFF Research Database (Denmark)
2010-01-01
The present invention provides a light source (2) for light circuits on a silicon platform (3). A vertical laser cavity is formed by a gain region (101) arranged between a top mirror (4) and a bottom grating-mirror (12) in a grating region (11) in a silicon layer (10) on a substrate. A waveguide...
Offenbacher, Elmer L.
1970-01-01
The physics of vertical jumping is described as an interesting illustration for motivating students in a general physics course to master the kinematics and dynamics of one dimensional motion. The author suggests that mastery of the physical principles of the jump may promote understanding of certain biological phenomena, aspects of physical…
Multiservice Vertical Handoff Decision Algorithms
Directory of Open Access Journals (Sweden)
Zhu Fang
2006-01-01
Full Text Available Future wireless networks must be able to coordinate services within a diverse-network environment. One of the challenging problems for coordination is vertical handoff, which is the decision for a mobile node to handoff between different types of networks. While traditional handoff is based on received signal strength comparisons, vertical handoff must evaluate additional factors, such as monetary cost, offered services, network conditions, and user preferences. In this paper, several optimizations are proposed for the execution of vertical handoff decision algorithms, with the goal of maximizing the quality of service experienced by each user. First, the concept of policy-based handoffs is discussed. Then, a multiservice vertical handoff decision algorithm (MUSE-VDA and cost function are introduced to judge target networks based on a variety of user- and network-valued metrics. Finally, a performance analysis demonstrates that significant gains in the ability to satisfy user requests for multiple simultaneous services and a more efficient use of resources can be achieved from the MUSE-VDA optimizations.
Development of Vertical Cable Seismic System
Asakawa, E.; Murakami, F.; Sekino, Y.; Okamoto, T.; Ishikawa, K.; Tsukahara, H.; Shimura, T.
2011-12-01
In 2009, Ministry of Education, Culture, Sports, Science and Technology(MEXT) started the survey system development for Hydrothermal deposit. We proposed the Vertical Cable Seismic (VCS), the reflection seismic survey with vertical cable above seabottom. VCS has the following advantages for hydrothermal deposit survey. (1) VCS is an efficient high-resolution 3D seismic survey in limited area. (2) It achieves high-resolution image because the sensors are closely located to the target. (3) It avoids the coupling problems between sensor and seabottom that cause serious damage of seismic data quality. (4) Because of autonomous recording system on sea floor, various types of marine source are applicable with VCS such as sea-surface source (GI gun etc.) , deep-towed or ocean bottom source. Our first experiment of 2D/3D VCS surveys has been carried out in Lake Biwa, JAPAN, in November 2009. The 2D VCS data processing follows the walk-away VSP, including wave field separation and depth migration. Seismic Interferometry technique is also applied. The results give much clearer image than the conventional surface seismic. Prestack depth migration is applied to 3D data to obtain good quality 3D depth volume. Seismic Interferometry technique is applied to obtain the high resolution image in the very shallow zone. Based on the feasibility study, we have developed the autonomous recording VCS system and carried out the trial experiment in actual ocean at the water depth of about 400m to establish the procedures of deployment/recovery and to examine the VC position or fluctuation at seabottom. The result shows that the VC position is estimated with sufficient accuracy and very little fluctuation is observed. Institute of Industrial Science, the University of Tokyo took the research cruise NT11-02 on JAMSTEC R/V Natsushima in February, 2011. In the cruise NT11-02, JGI carried out the second VCS survey using the autonomous VCS recording system with the deep towed source provided by
DEFF Research Database (Denmark)
Frigaard, Peter; Høgedal, Michael; Christensen, Morten
The intention of this manual is to provide some formulas and techniques which can be used for generating waves in hydraulic laboratories. Both long crested waves (2-D waves) and short crested waves (3-D waves) are considered....
Peralta, J.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.; López-Valverde, M. A.
2014-07-01
This paper is the first of a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases when the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this first part, only waves that are direct solutions of the generic dispersion relation are studied—acoustic and inertia-gravity waves. Concerning inertia-gravity waves, we found that in the cases of short horizontal wavelengths, null background wind, or propagation in the equatorial region, only pure gravity waves are possible, while for the limit of large horizontal wavelengths and/or null static stability, the waves are inertial. The correspondence between classical atmospheric approximations and wave filtering has been examined too, and we carried out a classification of the mesoscale waves found in the clouds of Venus at different vertical levels of its atmosphere. Finally, the classification of waves in exoplanets is discussed and we provide a list of possible candidates with cyclostrophic regimes.
Energy Technology Data Exchange (ETDEWEB)
Peralta, J.; López-Valverde, M. A. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, 18008 Granada (Spain); Imamura, T. [Institute of Space and Astronautical Science-Japan Aerospace Exploration Agency 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Read, P. L. [Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford (United Kingdom); Luz, D. [Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL), Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Piccialli, A., E-mail: peralta@iaa.es [LATMOS, UVSQ, 11 bd dAlembert, 78280 Guyancourt (France)
2014-07-01
This paper is the first of a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases when the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this first part, only waves that are direct solutions of the generic dispersion relation are studied—acoustic and inertia-gravity waves. Concerning inertia-gravity waves, we found that in the cases of short horizontal wavelengths, null background wind, or propagation in the equatorial region, only pure gravity waves are possible, while for the limit of large horizontal wavelengths and/or null static stability, the waves are inertial. The correspondence between classical atmospheric approximations and wave filtering has been examined too, and we carried out a classification of the mesoscale waves found in the clouds of Venus at different vertical levels of its atmosphere. Finally, the classification of waves in exoplanets is discussed and we provide a list of possible candidates with cyclostrophic regimes.
Characteristics of mid-latitude planetary waves in the lower atmosphere derived from radiosonde data
Directory of Open Access Journals (Sweden)
R. Wang
2012-10-01
Full Text Available The activities of mid-latitude planetary waves (PWs in the troposphere and lower stratosphere (TLS are presented by using the radiosonde data from 2000 to 2004 over four American stations (Miramar Nas, 32.9° N, 117.2° W; Santa Teresa, 31.9° N, 106.7° W; Fort Worth, 32.8° N, 97.3° W; and Birmingham, 33.1° N, 86.7° W and one Chinese station (Wuhan, 30.5° N, 114.4° E. Statistically, strong PWs mainly appear around subtropical jet stream in the troposphere and lower stratosphere. In the troposphere, the activities of the mid-latitude PWs are strong around the centre of the subtropical jet stream in winter and become small near the tropopause, which indicates that the subtropical jet stream may strengthen the propagation of PWs or even be one of the PW excitation sources. Among the three disturbance components of temperature, zonal and meridional winds, PWs at Wuhan are stronger in the temperature component, but weaker in the zonal wind component than at the other four American stations. While in the meridional wind component, the strengths of PW spectral amplitudes at the four American stations decrease from west to east, and their amplitudes are all larger than that of Wuhan. However, the PWs are much weaker in the stratosphere and only the lower frequency parts remain. The amplitudes of the PWs in the stratosphere increase with height and are strong in winter with the zonal wind component being the strongest. Using the refractive index, we found that whether the PWs could propagate upward to the stratosphere depends on the thickness of the tropopause reflection layer. In the case study of the 2000/2001 winter, it is observed that the quasi 16-day wave in the troposphere is a quasi standing wave in the vertical direction and propagates upward slowly with vertical wavelength greater than 24 km in the meridional component. It propagates eastward with the zonal numbers between 5 and 8, and the quasi 16-day wave at Wuhan is probably the same
Short Wave Multipolar Antenna for Propagation by NVIS Effect
Pereira, Igor; Martins, Maria João; Baptista, António; Gonçalves, Mariano
2017-01-01
The objectives of this papper is to design, build and test an antenna resonant at the frequencies of 4, 5, 6, and 7 MHz, in the high frequency band (HF). With this antenna we want to explore and use NVIS (Near Vertical Incidence Sky wave), which consists in using the ionosphere as a reflector layer of sky waves, that reach the ionosphere with angles near vertical incidence. When reflected, these waves achieve distances from dozens to hundreds of kilometers for the established communication. F...
Interference phenomena in the refraction of a surface polariton by vertical dielectric barriers
Shen, T. P.; Wallis, R. F.; Maradudin, A. A.; Stegeman, G. I.
1984-01-01
A normal mode analysis is used to calculate the transmission and reflection coefficients for a surface polariton propagating along the interface between a surface active medium and a dielectric and incident normally on a vertical dielectric barrier of finite thickness or a thin dielectric film of finite length. The efficiencies of conversion of the surface polariton into transmitted and reflected bulk waves are also determined. The radiation patterns associated with the latter waves are presented.
Comparing reading speed for horizontal and vertical English text.
Yu, Deyue; Park, Heejung; Gerold, David; Legge, Gordon E
2010-02-23
There are three formats for arranging English text for vertical reading-upright letters arranged vertically (marquee), and horizontal text rotated 90 degrees clockwise or counterclockwise. Previous research has shown that reading is slower for all three vertical formats than for horizontal text, with marquee being slowest (M. D. Byrne, 2002). It has been proposed that the size of the visual span-the number of letters recognized with high accuracy without moving the eyes-is a visual factor limiting reading speed. We predicted that reduced visual-span size would be correlated with the slower reading for the three vertical formats. We tested this prediction with uppercase and lowercase letters. Reading performance was measured using two presentation methods: RSVP (Rapid Serial Visual Presentation) and flashcard (a block of text on four lines). On average, reading speed for horizontal text was 139% faster than marquee text and 81% faster than the rotated texts. Size of the visual span was highly correlated with changes in reading speed for both lowercase and uppercase letters and for both RSVP and flashcard reading. Our results are consistent with the view that slower reading of vertical text is due to a decrease in the size of the visual span for vertical reading.
A snapshot of internal waves and hydrodynamic instabilities in the southern Bay of Bengal
Lozovatsky, Iossif; Wijesekera, Hemantha; Jarosz, Ewa; Lilover, Madis-Jaak; Pirro, Annunziata; Silver, Zachariah; Centurioni, Luca; Fernando, H. J. S.
2016-08-01
Measurements conducted in the southern Bay of Bengal (BoB) as a part of the ASIRI-EBoB Program portray the characteristics of high-frequency internal waves in the upper pycnocline as well as the velocity structure with episodic events of shear instability. A 20 h time series of CTD, ADCP, and acoustic backscatter profiles down to 150 m as well as temporal CTD measurements in the pycnocline at z = 54 m were taken to the east of Sri Lanka. Internal waves of periods ˜10-40 min were recorded at all depths below a shallow (˜20-30 m) surface mixed layer in the background of an 8 m amplitude internal tide. The absolute values of vertical displacements associated with high-frequency waves followed the Nakagami distribution with a median value of 2.1 m and a 95% quintile 6.5 m. The internal wave amplitudes are normally distributed. The tails of the distribution deviate from normality due to episodic high-amplitude displacements. The sporadic appearance of internal waves with amplitudes exceeding ˜5 m usually coincided with patches of low Richardson numbers, pointing to local shear instability as a possible mechanism of internal-wave-induced turbulence. The probability of shear instability in the summer BoB pycnocline based on an exponential distribution of the inverse Richardson number, however, appears to be relatively low, not exceeding 4% for Ri < 0.25 and about 10% for Ri < 0.36 (K-H billows). The probability of the generation of asymmetric breaking internal waves and Holmboe instabilities is above ˜25%.
Kinematic dynamo induced by helical waves
Wei, Xing
2014-01-01
We investigate numerically the kinematic dynamo induced by the superposition of two helical waves in a periodic box as a simplified model to understand the dynamo action in astronomical bodies. The effects of magnetic Reynolds number, wavenumber and wave frequency on the dynamo action are studied. It is found that this helical-wave dynamo is a slow dynamo. There exists an optimal wavenumber for the dynamo growth rate. A lower wave frequency facilitates the dynamo action and the oscillations o...
Directory of Open Access Journals (Sweden)
Xilian Han
2015-09-01
Full Text Available This study investigates natural convective heat transfer of copper–water nanofluids in a square enclosure with alternating temperature at one vertical wall, relatively low temperature at the opposite sidewall and adiabatic at the other walls. The transport equations are solved numerically with finite volume approach using SIMPLEC algorithm. Calculations are performed for nanoparticle volume fractions from 0 to 0.2 and dimensionless amplitude from 0 to 1.0 with consideration of three typical alternating waves (trapezoid wave, sine wave and triangle wave. Results show the utilization of nanoparticles enhances heat transfer and the percentage increase in the time-averaged Nusselt number is around 38% d from ϕ=0 to ϕ=0.2 under the certain conditions. The oscillating waveform has a degree effect on the heat transfer enhancement and the trapezoid wave is more conducive to the enhancement of heat transfer than sine and triangle waves. And the oscillating area is introduced to combine the oscillating waveform and its amplitude and the percentage increase in the time-averaged Nusselt number is around 14.5% from S=0 to S=0.075. In the end, the regression equation about the time-averaged Nusselt number is obtained as parameters of the solid volume fraction and the oscillating area.
Matthias, Vivien; Hoffmann, Peter; Rapp, Markus; Baumgarten, Gerd
2012-12-01
During winter the wind field in the mesosphere/lower thermosphere (MLT) at middle and polar latitudes is characterized by a strong variability due to enhanced planetary wave activity and related stratospheric sudden warming (SSW) events. Such events are considered as distinct vertical coupling processes influencing the atmosphere below and above the stratosphere. In the last 12 years, an enhanced number of SSW, compared to the period from 1989 to 1998, has been observed in the northern hemisphere. Every SSW is connected with different effects in the MLT (strength and temporal development of wind reversals, temperature changes, wave activity, longitudinal dependence). To characterize the average behavior of the mesospheric response to strong SSWs, we combine high-resolution wind measurements from MF- and meteor radar at Andenes (69°N, 16°E) with global temperature observations from MLS aboard the Aura satellite for SSW events with a return to the middle atmosphere normal winter condition afterwards. Our aim is to identify characteristic wave patterns which are common to the majority of these events and to define the average characteristics of the SSW-related wave activity in the MLT. These will be compared to the relatively quiet winter 2011 with only a short minor warming without a wind reversal and to the wave activity in 2009 and 2010. The results show clear signatures of enhanced mesospheric planetary wave activity before and during the SSW and an earlier onset of the short term wind reversal in the mesosphere compared to wind and temperature changes in the stratosphere. The strong eastward winds at altitudes below 80 km after SSW are connected with an enhanced gravity wave activity caused by changed filter conditions. This provides evidence for a strong modulation of semidiurnal tidal amplitudes before and during SSW by planetary waves. However, no clear relation has been found in the temporal development of tides relative to the onset of the selected SSW
Efficient Wave Energy Amplification with Wave Reflectors
Kramer, Morten Mejlhede; Frigaard, Peter Bak
2002-01-01
Wave Energy Converters (WEC's) extract wave energy from a limited area, often a single point or line even though the wave energy is generally spread out along the wave crest. By the use of wave reflectors (reflecting walls) the wave energy is effectively focused and increased to approximately 130-140%. In the paper a procedure for calculating the efficiency and optimizing the geometry of wave reflectors are described, this by use of a 3D boundary element method. The calculations are verified ...
Directory of Open Access Journals (Sweden)
Ahmed Elhanafi
2016-12-01
Full Text Available In this paper, hydrodynamic wave loads on an offshore stationary–floating oscillating water column (OWC are investigated via a 2D and 3D computational fluid dynamics (CFD modeling based on the RANS equations and the VOF surface capturing scheme. The CFD model is validated against previous experiments for nonlinear regular wave interactions with a surface-piercing stationary barge. Following the validation stage, the numerical model is modified to consider the pneumatic damping effect, and an extensive campaign of numerical tests is carried out to study the wave–OWC interactions for different wave periods, wave heights and pneumatic damping factors. It is found that the horizontal wave force is usually larger than the vertical one. Also, there a direct relationship between the pneumatic and hydrodynamic vertical forces with a maximum vertical force almost at the device natural frequency, whereas the pneumatic damping has a little effect on the horizontal force. Additionally, simulating the turbine damping with an orifice plate induces higher vertical loads than utilizing a slot opening. Furthermore, 3D modeling significantly escalates and declines the predicted hydrodynamic vertical and horizontal wave loads, respectively.
Estimation of Wave Disturbance in Harbours
DEFF Research Database (Denmark)
Helm-Petersen, Jacob
been presented for the analysis of reflected wave fields in 2D and 3D. The Bayesian Directional Wave Spectrum Estimation Method has been applied throughout the study. Reflection characteristics have been investigated by use of physical models for three types of coastal structures with vertical fronts......The motivation for the present study has been to improve the reliability in using numerical wave propagation models as a tool for estimating wave disturbance in harbours. Attention has been directed towards the importance of the modelling of reflection in the applied mild-slope model. Methods have....... The analyses include mainly directional waves. Analysis of field measurements has also taken place. Simulations with a mild-slope model have been carried out with individual structures and a complete harbour. The analyses clarify to a wide extent the behaviour of the sponge layers applied in the model...
Multiscale Simulation of Breaking Wave Impacts
DEFF Research Database (Denmark)
Lindberg, Ole
The purpose of this project is to make an accurate, robust, geometric flexible and efficient model for calculation of forces on structures from nonlinear ocean waves and breaking wave impacts. Accurate prediction of the extreme forces on wind turbine foundations, breakwaters and tidal or wave power...... devises are important for enhancement structural designs. The proposed model is based on an incompressible and inviscid flow approximation and the governing equations are applied in an arbitrary Lagrangian-Eulerian moving frame of reference (ALE). The Runge-Kutta method (RK) is used for time integration...... compare reasonably well. The incompressible and inviscid ALE-WLS model is coupled with the potential flow model of Engsig-Karup et al. [2009], to perform multiscale calculation of breaking wave impacts on a vertical breakwater. The potential flow model provides accurate calculation of the wave...
Segregation of helicity in inertial wave packets
Ranjan, A.
2017-03-01
Inertial waves are known to exist in the Earth's rapidly rotating outer core and could be important for the dynamo generation. It is well known that a monochromatic inertial plane wave traveling parallel to the rotation axis (along positive z ) has negative helicity while the wave traveling antiparallel (negative z ) has positive helicity. Such a helicity segregation, north and south of the equator, is necessary for the α2-dynamo model based on inertial waves [Davidson, Geophys. J. Int. 198, 1832 (2014), 10.1093/gji/ggu220] to work. The core is likely to contain a myriad of inertial waves of different wave numbers and frequencies. In this study, we investigate whether this characteristic of helicity segregation also holds for an inertial wave packet comprising waves with the same sign of Cg ,z, the z component of group velocity. We first derive the polarization relations for inertial waves and subsequently derive the resultant helicity in wave packets forming as a result of superposition of two or more waves. We find that the helicity segregation does hold for an inertial wave packet unless the wave numbers of the constituent waves are widely separated. In the latter case, regions of opposite color helicity do appear, but the mean helicity retains the expected sign. An illustration of this observation is provided by (a) calculating the resultant helicity for a wave packet formed by superposition of four upward-propagating inertial waves with different wave vectors and (b) conducting the direct numerical simulation of a Gaussian eddy under rapid rotation. Last, the possible effects of other forces such as the viscous dissipation, the Lorentz force, buoyancy stratification, and nonlinearity on helicity are investigated and discussed. The helical structure of the wave packet is likely to remain unaffected by dissipation or the magnetic field, but can be modified by the presence of linearly stable stratification and nonlinearity.
Similarity solution for rarefied flow over a vertical stretched surface
Al-Kouz, W.; Kiwan, S.; Sari, M.; Alkhalidi, A.
2017-07-01
Similarity technique is used to solve for the laminar natural convection heat transfer for rarefied flows over a linearly vertical stretched surface. Such flows have significant importance in many engineering and manufacturing applications. It is found that the flow is affected by flow parameters, namely, velocity slip (K1), temperature jump (K2), and the Prandtl number (Pr).
Vertical displacement of Ips Latidens and Ips Pini
Daniel R. Miller
2000-01-01
The effect of semiochemical interruptants was examined for Ips latidens (LeConte) and Ips pini (Say) using artificial trees (tall-traps) consisting of an array of seven Lindgren multiple-funnel traps suspended vertically on a rope ladder. S-(+)- Ipsdienol reduced the numbers of I. latidens captured in (Â±)-ipsenol...
Description of the IMR Standard Light Trap and the Vertical ...
African Journals Online (AJOL)
The construction of different versions of a cheap, robust, and easy to operate light trap for catching various aquatic organisms is shown. The trap can be used to > 300 m depth and meets a number of criteria. Small-scale vertical distribution of decapod larvae was investigated during trap trials. The traps (6-10) were set for 24 ...
Vertical datum unification for the International Height Reference System (IHRS)
Sánchez, Laura; Sideris, Michael G.
2017-05-01
The International Association of Geodesy released in July 2015 a resolution for the definition and realisation of an International Height Reference System (IHRS). According to this resolution, the IHRS coordinates are potential differences referring to the equipotential surface of the Earth's gravity field realised by the conventional value W0 = 62 636 853.4 m2s-2. A main component of the IHRS realisation is the integration of the existing height systems into the global one; that is existing vertical coordinates should be referred to one and the same reference level realised by the conventional W0. This procedure is known as vertical datum unification and its main result are the vertical datum parameters, that is the potential differences between the local and the global reference levels. In this paper, we rigorously derive the observation equations for the vertical datum unification in terms of potential quantities based on the geodetic boundary value problem (GBVP) approach. Those observation equations are then empirically evaluated for the vertical datum unification of the North American and South American height systems. In the first case, simulations performed in North America provide numerical estimates about the impact of omission errors and direct and indirect effects on the vertical datum parameters. In the second case, a combination of local geopotential numbers, ITRF coordinates, satellite altimetry observations, tide gauge registrations and high-resolution gravity field models is performed to estimate the level differences between the South American height systems and the global level W0. Results show that indirect effects vanish when a satellite-only gravity field model with a degree higher than n ≥ 180 is used for the solution of the GBVP. However, the component derived from satellite-only global gravity models has to be refined with terrestrial gravity data to minimise the omission error and its effect on the vertical datum parameter estimation
Waveform inversion for orthorhombic anisotropy with P-waves: feasibility & resolution
Kazei, Vladimir
2018-01-27
Various parameterizations have been suggested to simplify inversions of first arrivals, or P −waves, in orthorhombic anisotropic media, but the number and type of retrievable parameters have not been decisively determined. We show that only six parameters can be retrieved from the dynamic linearized inversion of P −waves. These parameters are different from the six parameters needed to describe the kinematics of P −waves. Reflection-based radiation patterns from the P − P scattered waves are remapped into the spectral domain to allow for our resolution analysis based on the effective angle of illumination concept. Singular value decomposition of the spectral sensitivities from various azimuths, offset coverage scenarios, and data bandwidths allows us to quantify the resolution of different parameterizations, taking into account the signal-to-noise ratio in a given experiment. According to our singular value analysis, when the primary goal of inversion is determining the velocity of the P −waves, gradually adding anisotropy of lower orders (isotropic, vertically transversally isotropic, orthorhombic) in hierarchical parameterization is the best choice. Hierarchical parametrization reduces the tradeoff between the parameters and makes gradual introduction of lower anisotropy orders straightforward. When all the anisotropic parameters affecting P −wave propagation need to be retrieved simultaneously, the classic parameterization of orthorhombic medium with elastic stiffness matrix coefficients and density is a better choice for inversion. We provide estimates of the number and set of parameters that can be retrieved from surface seismic data in different acquisition scenarios. To set up an inversion process, the singular values determine the number of parameters that can be inverted and the resolution matrices from the parameterizations can be used to ascertain the set of parameters that can be resolved.
Gravity Waves and Wind-Farm Efficiency in Neutral and Stable Conditions
Allaerts, Dries; Meyers, Johan
2017-10-01
We use large-eddy simulations (LES) to investigate the impact of stable stratification on gravity-wave excitation and energy extraction in a large wind farm. To this end, the development of an equilibrium conventionally neutral boundary layer into a stable boundary layer over a period of 8 h is considered, using two different cooling rates. We find that turbulence decay has considerable influence on the energy extraction at the beginning of the boundary-layer transition, but afterwards, energy extraction is dominated by geometrical and jet effects induced by an inertial oscillation. It is further shown that the inertial oscillation enhances gravity-wave excitation. By comparing LES results with a simple one-dimensional model, we show that this is related to an interplay between wind-farm drag, variations in the Froude number and the dispersive effects of vertically-propagating gravity waves. We further find that the pressure gradients induced by gravity waves lead to significant upstream flow deceleration, reducing the average turbine output compared to a turbine in isolated operation. This leads us to the definition of a non-local wind-farm efficiency, next to a more standard wind-farm wake efficiency, and we show that both can be of the same order of magnitude. Finally, an energy flux analysis is performed to further elucidate the effect of gravity waves on the flow in the wind farm.
Gravity Waves and Wind-Farm Efficiency in Neutral and Stable Conditions
Allaerts, Dries; Meyers, Johan
2018-02-01
We use large-eddy simulations (LES) to investigate the impact of stable stratification on gravity-wave excitation and energy extraction in a large wind farm. To this end, the development of an equilibrium conventionally neutral boundary layer into a stable boundary layer over a period of 8 h is considered, using two different cooling rates. We find that turbulence decay has considerable influence on the energy extraction at the beginning of the boundary-layer transition, but afterwards, energy extraction is dominated by geometrical and jet effects induced by an inertial oscillation. It is further shown that the inertial oscillation enhances gravity-wave excitation. By comparing LES results with a simple one-dimensional model, we show that this is related to an interplay between wind-farm drag, variations in the Froude number and the dispersive effects of vertically-propagating gravity waves. We further find that the pressure gradients induced by gravity waves lead to significant upstream flow deceleration, reducing the average turbine output compared to a turbine in isolated operation. This leads us to the definition of a non-local wind-farm efficiency, next to a more standard wind-farm wake efficiency, and we show that both can be of the same order of magnitude. Finally, an energy flux analysis is performed to further elucidate the effect of gravity waves on the flow in the wind farm.
Schneider, Andreas; Wagner, Johannes; Söder, Jens; Gerding, Michael; Lübken, Franz-Josef
2017-06-01
Measurements of turbulent energy dissipation rates obtained from wind fluctuations observed with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) are combined with simulations with the Weather Research and Forecasting (WRF) model to study the breakdown of waves into turbulence. One flight from Kiruna (68° N, 21° E) and two flights from Kühlungsborn (54° N, 12° E) are analysed. Dissipation rates are of the order of 0. 1 mW kg-1 (˜ 0.01 K d-1) in the troposphere and in the stratosphere below 15 km, increasing in distinct layers by about 2 orders of magnitude. For one flight covering the stratosphere up to ˜ 28 km, the measurement shows nearly no turbulence at all above 15 km. Another flight features a patch with highly increased dissipation directly below the tropopause, collocated with strong wind shear and wave filtering conditions. In general, small or even negative Richardson numbers are affirmed to be a sufficient condition for increased dissipation. Conversely, significant turbulence has also been observed in the lower stratosphere under stable conditions. Observed energy dissipation rates are related to wave patterns visible in the modelled vertical winds. In particular, the drop in turbulent fraction at 15 km mentioned above coincides with a drop in amplitude in the wave patterns visible in the WRF. This indicates wave saturation being visible in the LITOS turbulence data.
Kinematic Fitting of Detached Vertices
Energy Technology Data Exchange (ETDEWEB)
Mattione, Paul [Rice Univ., Houston, TX (United States)
2007-05-01
The eg3 experiment at the Jefferson Lab CLAS detector aims to determine the existence of the $\\Xi_{5}$ pentaquarks and investigate the excited $\\Xi$ states. Specifically, the exotic $\\Xi_{5}^{--}$ pentaquark will be sought by first reconstructing the $\\Xi^{-}$ particle through its weak decays, $\\Xi^{-}\\to\\pi^{-}\\Lambda$ and $\\Lambda\\to\\pi^{-}$. A kinematic fitting routine was developed to reconstruct the detached vertices of these decays, where confidence level cuts on the fits are used to remove background events. Prior to fitting these decays, the exclusive reaction $\\gamma D\\rightarrow pp\\pi^{-}$ was studied in order to correct the track measurements and covariance matrices of the charged particles. The $\\Lambda\\rightarrow p\\pi^{-}$ and $\\Xi^{-}\\to\\pi^{-}\\Lambda$ decays were then investigated to demonstrate that the kinematic fitting routine reconstructs the decaying particles and their detached vertices correctly.
Vertical distribution of Arctic methane
Tukiainen, Simo; Karppinen, Tomi; Hakkarainen, Janne; Kivi, Rigel; Heikkinen, Pauli; Tamminen, Johanna
2017-04-01
In this study we show the vertical distribution of atmospheric methane (CH4) measured in Sodankylä, Northern Finland. The CH4 profiles are retrieved from the direct Sun FTS measurements using the dimension reduction retrieval method. In the retrieval method, we have a few degrees of freedom about the profile shape. The data set covers years 2010-2016 (from February to November) and altitudes 0-40 km. The retrieved FTS profiles are validated against ACE satellite measurements and AirCore balloon measurements. The total columns derived from the FTS profiles are compared to the official TCCON XCH4 data. A vertically resolved methane data set can be used, e.g., to study stratospheric methane during the polar vortex.
INTERNATIONAL SPECIALIZATION AND VERTICAL DIFFERENTIATION
Directory of Open Access Journals (Sweden)
Furia Donatella
2010-07-01
Full Text Available During the last decades, market segmentation and intra-industry trade have become increasingly relevant. The underlying hypothesis of our work is that distinct articles have heterogeneous potential for vertical differentiation, implying that different patterns of international specialization should be identifiable. We carry out an analysis on revealed comparative advantage (through the Lafay Index in specific sectors of interest. Then we highlight the emergence of diverse degrees of product quality differentiation among sectors (through the Relative Quality Index. Results confirm our hypothesis. Indeed it appears that only certain goods, for which the pace of either creative or technological innovation (or both is particularly fast, present a high degree of vertical differentiation and market segmentation. This allows countries to specialize in a particular product variety and gain market power position for that variety. These findings should be taken in due consideration when designing trade policies.
Reflection of P and SV waves from free surface of an elastic solid ...
Indian Academy of Sciences (India)
The governing equations for generalized thermodiffusion in an elastic solid are solved. There exists three kinds of dilatational waves and a Shear Vertical (SV) wave in a two-dimensional model of the solid. The reflection phenomena of P and SV waves from free surface of an elastic solid with thermodiffusion is considered.
Tropical cyclogenesis in a tropical wave critical layer: easterly waves
Directory of Open Access Journals (Sweden)
T. J. Dunkerton
2009-08-01
cyclonic vorticity and weak deformation by the resolved flow, (ii containment of moisture entrained by the developing gyre and/or lofted by deep convection therein, (iii confinement of mesoscale vortex aggregation, (iv a predominantly convective type of heating profile, and (v maintenance or enhancement of the parent wave until the vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. The entire sequence is likened to the development of a marsupial infant in its mother's pouch. These ideas are formulated in three new hypotheses describing the flow kinematics and dynamics, moist thermodynamics and wave/vortex interactions comprising the "marsupial paradigm". A survey of 55 named tropical storms in 1998–2001 reveals that actual critical layers sometimes resemble the ideal east-west train of cat's eyes, but are usually less regular, with one or more recirculation regions in the co-moving frame. It is shown that the kinematics of isolated proto-vortices carried by the wave also can be visualized in a frame of reference translating at or near the phase speed of the parent wave. The proper translation speeds for wave and vortex may vary with height owing to vertical shear and wave-vortex interaction. Some implications for entrainment/containment of vorticity and moisture in the cat's eye are discussed from this perspective, based on the observational survey.
WAVE-E: The WAter Vapour European-Explorer Mission
Jimenez-LLuva, David; Deiml, Michael; Pavesi, Sara
2017-04-01
In the last decade, stratosphere-troposphere coupling processes in the Upper Troposphere Lower Stratosphere (UTLS) have been increasingly recognized to severely impact surface climate and high-impact weather phenomena. Weakened stratospheric circumpolar jets have been linked to worldwide extreme temperature and high-precipitation events, while anomalously strong stratospheric jets can lead to an increase in surface winds and tropical cyclone intensity. Moreover, stratospheric water vapor has been identified as an important forcing for global decadal surface climate change. In the past years, operational weather forecast and climate models have adapted a high vertical resolution in the UTLS region in order to capture the dynamical processes occurring in this highly stratified region. However, there is an evident lack of available measurements in the UTLS region to consistently support these models and further improve process understanding. Consequently, both the IPCC fifth assessment report and the ESA-GEWEX report 'Earth Observation and Water Cycle Science Priorities' have identified an urgent need for long-term observations and improved process understanding in the UTLS region. To close this gap, the authors propose the 'WAter Vapour European - Explorer' (WAVE-E) space mission, whose primary goal is to monitor water vapor in the UTLS at 1 km vertical, 25 km horizontal and sub-daily temporal resolution. WAVE-E consists of three quasi-identical small ( 500 kg) satellites (WAVE-E 1-3) in a constellation of Sun-Synchronous Low Earth Orbits, each carrying a limb sounding and cross-track scanning mid-infrared passive spectrometer (824 cm-1 to 829 cm-1). The core of the instruments builds a monolithic, field-widened type of Michelson interferometer without any moving parts, rendering it rigid and fault tolerant. Synergistic use of WAVE-E and MetOp-NG operational satellites is identified, such that a data fusion algorithm could provide water vapour profiles from the
Directory of Open Access Journals (Sweden)
Esteban Dörries
2016-03-01
Full Text Available La poligonación vertical es un método de medición de diferencias de altura que aprovecha las posibilidades de las estaciones totales. Se presta fundamentalmente para líneas de nivelación entre nodos formando red. El nombre se debe a que las visuales sucesivas se proyectan sobre aristas verticales en lugar de un plano horizontal, como ocurre en la poligonación convencional.
Vertical Launch System Loadout Planner
2015-03-01
United States Navy USS United States’ Ship VBA Visual Basic for Applications VLP VLS Loadout Planner VLS Vertical Launch System...mathematically complex and require training to operate the software. A Visual Basic for Applications ( VBA ) Excel (Microsoft Corporation, 2015...lockheed/data/ms2/documents/laun chers/MK41 VLS factsheet.pdf Microsoft Excel version 14.4.3, VBA computer software. (2011). Redmond, WA: Microsoft
Trade Liberalisation and Vertical Integration
DEFF Research Database (Denmark)
Bache, Peter Arendorf; Laugesen, Anders
We build a three-country model of international trade in final goods and intermediate inputs and study the relation between different types of trade liberalisation and vertical integration. Firms are heterogeneous with respect to both productivity and factor intensity as observed in data. Final......-economy property rights theory of the firm using firm-level data. Finally, we notice that our model's sorting pattern is in line with recent evidence when the wage difference across countries is not too big....
Number-unconstrained quantum sensing
Mitchell, Morgan W.
2017-12-01
Quantum sensing is commonly described as a constrained optimization problem: maximize the information gained about an unknown quantity using a limited number of particles. Important sensors including gravitational wave interferometers and some atomic sensors do not appear to fit this description, because there is no external constraint on particle number. Here, we develop the theory of particle-number-unconstrained quantum sensing, and describe how optimal particle numbers emerge from the competition of particle-environment and particle-particle interactions. We apply the theory to optical probing of an atomic medium modeled as a resonant, saturable absorber, and observe the emergence of well-defined finite optima without external constraints. The results contradict some expectations from number-constrained quantum sensing and show that probing with squeezed beams can give a large sensitivity advantage over classical strategies when each is optimized for particle number.
Vertical compact torus injection into the STOR-M tokamak
Liu, Dazhi
Central fuelling is a fundamental issue in the next generation tokamak-ITER (International Thermonuclear Experimental Reactor). It is essential for optimization of the bootstrap current which is proportional to the pressure gradient of trapped particles. The conventional fusion reactor fuelling techniques, such as gas puffing and cryogenic pellet injection, are considered inadequate to fulfill this goal due to premature ionization caused by high plasma temperature and density. Compact Torus (CT) injection is a promising fuelling technique for central fuelling a reactor-grade tokamak. An accelerated CT is expected to penetrate into the core region and deposit fuel there provided the CT kinetic energy density exceeds the magnetic energy density in a target plasma. This process is complicated and involves CT penetration into an external magnetic field, a CT stopping mechanism, magnetic reconnection, and excitation of plasma waves. CTs can be injected at different angles with respect to the tokamak toroidal magnetic field, either horizontally or vertically. Normally, CTs are injected radially in the mid-plane of a tokamak. In this configuration, CTs will undergo a decelerating force due to the gradient of the tokamak toroidal magnetic field. CTs will stop inside the tokamak chamber or bunce back depending on the relation between kinetic energy density of injected CTs and the tokamak toroidal magnetic field energy density. In the case of vertical injection, deeper penetration is expected due to the absence of the gradient of the tokamak toroidal field in that direction. Experimental investigations on vertical CT injection into a tokamak will be of great significance. The aim of this thesis is to experimentally investigate the feasibility of vertical CT injection into a tokamak and effects of CTs on tokamak plasma confinements. The Saskatchewan Torus-Modified (STOR-M) tokamak is currently the only tokamak equipped with a CT injector in the world. Vertical CT injection
Prophylaxis of vertical HBV infection.
Pawlowska, Malgorzata; Pniewska, Anna; Pilarczyk, Malgorzata; Kozielewicz, Dorota; Domagalski, Krzysztof
2016-10-01
An appropriate management of HBV infection is the best strategy to finally reduce the total burden of HBV infection. Mother-to-child transmission (MTCT) is responsible for more than one third of chronic HBV infections worldwide. Because HBV infection in infancy or early childhood often leads to chronic infection, appropriate prophylaxis and management of HBV in pregnancy is crucial to prevent MTCT. The prevention of HBV vertical transmission is a complex task and includes: universal HBV screening of pregnant women, administration of antivirals in the third trimester of pregnancy in women with high viral load and passive-active HBV immunoprophylaxis with hepatitis B vaccine and hepatitis B immune globulin in newborns of all HBV infected women. Universal screening of pregnant women for HBV infection, early identification of HBV DNA level in HBV-infected mothers, maternal treatment with class B according to FDA antivirals and passive/active anti-HBV immunoprophylaxis to newborns of HBV-positive mothers are crucial strategies for reducing vertical HBV transmission rates. Consideration of caesarean section in order to reduce the risk of vertical HBV transmission should be recommend in HBV infected pregnant women with high viral load despite antiviral therapy or when the therapy in the third trimester of pregnancy is not available.
Wave-to-wire Modelling of Wave Energy Converters
DEFF Research Database (Denmark)
Ferri, Francesco
and non-technical issues. These can be efficiently summarised in the cost of the energy produced by the various wave energy converters: If compared with other renewable energy technologies the cost of energy from the ocean waves is still significantly higher. Holding the comparison it also important...... to noticed that there is not a clear front runner in the wave energy sector, which fades effort and funding over a too broad frame. In order to assist efficient development and analysis of wave energy converters and therefore to accelerate the sector progression towards commercialisation, a generally......, but talking about renewable energy partially ravels the problem out. Wave energy is a large, mostly untapped, renewable energy resource. It has the potential to contribute significantly to the future energy mix, but the sector has not yet rolled off into the market in consequence of a number of technical...
Indian Academy of Sciences (India)
IAS Admin
(2). Hence, small amplitude waves are also called linear waves. Most of the aspects of the ocean waves can be explained by the small amplitude wave theory. Let us now see the water particle motion due to waves. While wave energy is carried by the wave as it progresses forward, the water particles oscillate up and down.
Peralta, J.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.; López-Valverde, M. A.
2014-07-01
This paper is the second in a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases where the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this second part, we study the waves' solutions when several atmospheric approximations are applied: Lamb, surface, and centrifugal waves. Lamb and surface waves are found to be quite similar to those in a geostrophic regime. By contrast, centrifugal waves turn out to be a special case of Rossby waves that arise in atmospheres in cyclostrophic balance. Finally, we use our results to identify the nature of the waves behind atmospheric periodicities found in polar and lower latitudes of Venus's atmosphere.
Energy Technology Data Exchange (ETDEWEB)
Peralta, J.; López-Valverde, M. A. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, 18008 Granada (Spain); Imamura, T. [Institute of Space and Astronautical Science-Japan Aerospace Exploration Agency 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Read, P. L. [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford (United Kingdom); Luz, D. [Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL), Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Piccialli, A., E-mail: peralta@iaa.es [LATMOS, UVSQ, 11 bd dAlembert, 78280 Guyancourt (France)
2014-07-01
This paper is the second in a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases where the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this second part, we study the waves' solutions when several atmospheric approximations are applied: Lamb, surface, and centrifugal waves. Lamb and surface waves are found to be quite similar to those in a geostrophic regime. By contrast, centrifugal waves turn out to be a special case of Rossby waves that arise in atmospheres in cyclostrophic balance. Finally, we use our results to identify the nature of the waves behind atmospheric periodicities found in polar and lower latitudes of Venus's atmosphere.
Frequency and wavelength prediction of ultrasonic induced liquid surface waves.
Mahravan, Ehsan; Naderan, Hamid; Damangir, Ebrahim
2016-12-01
A theoretical investigation of parametric excitation of liquid free surface by a high frequency sound wave is preformed, using potential flow theory. Pressure and velocity distributions, resembling the sound wave, are applied to the free surface of the liquid. It is found that for impinging wave two distinct capillary frequencies will be excited: One of them is the same as the frequency of the sound wave, and the other is equal to the natural frequency corresponding to a wavenumber equal to the horizontal wavenumber of the sound wave. When the wave propagates in vertical direction, mathematical formulation leads to an equation, which has resonance frequency equal to half of the excitation frequency. This can explain an important contradiction between the frequency and the wavelength of capillary waves in the two cases of normal and inclined interaction of the sound wave and the free surface of the liquid. Copyright © 2016 Elsevier B.V. All rights reserved.
Liu, Guiping; England, Scott L.; Immel, Thomas J.; Frey, Harald U.; Mannucci, Anthony J.; Mitchell, Nicholas J.
2015-04-01
This study reports a comprehensive survey of quasi 3 day (2.5-4.5 day period) planetary-scale waves in the low-latitude mesosphere and lower thermosphere using the temperature observations from Thermosphere Ionosphere and Mesosphere Electric Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry throughout 2002-2012. Occurrences and properties of the waves, including the eastward propagating zonal wave numbers of 1-3 (E1-E3) and vertical wavelengths, are determined for each case. The impacts of these waves on the equatorial ionosphere are investigated by searching for the corresponding variations with the same periods and wave numbers in total electron content (TEC) from the concurrent observations of the ground-based GPS network. For a threshold amplitude of 4 K in temperature, a total of 300 waves are identified, of which there are 186 E1, 63 E2, and 51 E3 events. The mean amplitudes and vertical wavelengths of these waves are calculated to be about 7.9 K and 34 km for the E1, 5.7 K and 29 km for the E2, and 5.1 K and 27 km for the E3, having the standard deviations of 1.5 K and 6.5 km, 0.6 K and 5.6 km, and 0.5 K and 6.7 km. Occurrences of the E1 cases are not observed to depend on season, but the large-amplitude (>8 K) cases occur more often during solstices than at equinoxes. Similarly, the E2 and E3 cases are observed to occur most often in January-February and May-August. Among these waves, 199 cases (66%) are found to have the corresponding variations in the equatorial ionosphere with amplitudes ≥4.2% relative to the mean TEC values (corresponding to 90th percentile). Most of these waves have long vertical wavelengths and large amplitudes (˜3 times more than short vertical wavelength and small-amplitude waves). Because no seasonal or solar cycle dependence on the frequency at which these waves have corresponding variations in the ionosphere at this TEC perturbation threshold is observed, we conclude that there is no seasonal and solar
Shallow Water Waves and Solitary Waves
Hereman, Willy
2013-01-01
Encyclopedic article covering shallow water wave models used in oceanography and atmospheric science. Sections: Definition of the Subject; Introduction and Historical Perspective; Completely Integrable Shallow Water Wave Equations; Shallow Water Wave Equations of Geophysical Fluid Dynamics; Computation of Solitary Wave Solutions; Numerical Methods; Water Wave Experiments and Observations; Future Directions, and Bibliography.
Wave groups in unidirectional surface wave models
van Groesen, Embrecht W.C.
1998-01-01
Uni-directional wave models are used to study wave groups that appear in wave tanks of hydrodynamic laboratories; characteristic for waves in such tanks is that the wave length is rather small, comparable to the depth of the layer. In second-order theory, the resulting Nonlinear Schrödinger (NLS)
Advanced composite vertical stabilizer for DC-10 transport aircraft
Stephens, C. O.
1979-01-01
Structural design, tooling, fabrication, and test activities are reported for a program to develop an advanced composite vertical stabilizer (CVS) for the DC 10 Commercial Transport Aircraft. Structural design details are described and the status of structural and weight analyses are reported. A structural weight reduction of 21.7% is currently predicted. Test results are discussed for sine wave stiffened shear webs containing representative of the CVS spar webs and for lightning current transfer and tests on a panel representative of the CVS skins.
Global estimates of gravity wave parameters from GPS radio occultation temperature data
Wang, L.; Alexander, M. J.
2010-11-01
Gravity waves (GWs) play critical roles in the global circulation and the temperature and constituent structures in the middle atmosphere. They also play significant roles in the dynamics and transport and mixing processes in the upper troposphere and lower stratosphere and can affect tropospheric weather. Despite significant advances in our understanding of GWS and their effects in different regions of the atmosphere in the past few decades, observational constraints on GW parameters including momentum flux and propagation direction are still sorely lacking. Global Positioning System (GPS) radio occultation (RO) technique provides global, all-weather, high vertical resolution temperature profiles in the stratosphere and troposphere. The unprecedentedly large number of combined temperature soundings from the Constellation Observing System for Meteorology, Ionosphere, and Climate and Challenging Minisatellite Payload GPS RO missions allows us to obtain GW perturbations by removing the gravest zonal modes using the wavelet method for each day. We extended the GW analysis method of Alexander et al. (2008) to three dimensions to estimate the complete set of GW parameters (including momentum flux and horizontal propagation direction) from the GW temperature perturbations thus derived. To demonstrate the effectiveness of the analysis, we showed global estimates of GW temperature amplitudes, vertical and horizontal wavelengths, intrinsic frequency, and vertical flux of horizontal momentum in the altitude range of 17.5-22.5 km during December 2006 to February 2007. Consistent with many previous studies, GW temperature amplitudes are a maximum in the tropics and are generally larger over land, likely reflecting convection and topography as main GW sources. GW vertical wavelengths are a minimum at equator, likely due to wave refraction, whereas GW horizontal wavelengths are generally longer in the tropics. Most of the waves captured in the analysis of the GPS data are low
DEFF Research Database (Denmark)
Kramer, Morten; Frigaard, Peter
På foranledning af Löwenmark F.R.I, er der udført numeriske beregninger af Wave Dragons (herefter WD) armes effektivitet for forskellige geometriske udformninger. 5 geometriske modeller, hvor WD's arme er forkortet/forlænget er undersøgt for 3 forskellige drejninger af armene. I alt er 15...
Interactions between waves, sediment, and turbulence on a shallow estuarine mudflat
MacVean, Lissa J.; Lacy, Jessica R.
2014-01-01
Measurements were collected on a shallow estuarine mudflat in northern San Francisco Bay to examine the physical processes controlling waves, turbulence, sediment resuspension, and their interactions. Tides alone forced weak to moderate currents of 10–30 cm s-1 in depths of 0–3 m, and maintained a background suspension of 30–50 mg L21 of fine sediment. In the presence of wind waves, bottom orbital velocities spanned 20–30 cm s-1, suspended-sediment concentrations (SSC) at 15 and 30 cm above the bed (cmab) increased by 1–2 orders of magnitude, and vertical gradients in SSC were strong enough to produce turbulence-limiting stratification, with gradient Richardson numbers exceeding 0.25. Simultaneously, turbulent
The lifecycle of axisymmetric internal solitary waves
Directory of Open Access Journals (Sweden)
J. M. McMillan
2010-09-01
Full Text Available The generation and evolution of solitary waves by intrusive gravity currents in an approximate two-layer fluid with equal upper- and lower-layer depths is examined in a cylindrical geometry by way of theory and numerical simulations. The study is limited to vertically symmetric cases in which the density of the intruding fluid is equal to the average density of the ambient. We show that even though the head height of the intrusion decreases, it propagates at a constant speed well beyond 3 lock radii. This is because the strong stratification at the interface supports the formation of a mode-2 solitary wave that surrounds the intrusion head and carries it outwards at a constant speed. The wave and intrusion propagate faster than a linear long wave; therefore, there is strong supporting evidence that the wave is indeed nonlinear. Rectilinear Korteweg-de Vries theory is extended to allow the wave amplitude to decay as r^{-p} with p=½ and the theory is compared to the observed waves to demonstrate that the width of the wave scales with its amplitude. After propagating beyond 7 lock radii the intrusion runs out of fluid. Thereafter, the wave continues to spread radially at a constant speed, however, the amplitude decreases sufficiently so that linear dispersion dominates and the amplitude decays with distance as r^{-1}.
[Vertical fractures: apropos of 2 clinical cases].
Félix Mañes Ferrer, J; Micò Muñoz, P; Sánchez Cortés, J L; Paricio Martín, J J; Miñana Laliga, R
1991-01-01
The aim of the study is to present a clinical review of the vertical root fractures. Two clinical cases are presented to demonstrates the criteria for obtaining a correct diagnosis of vertical root fractures.
On the g/2 Acceleration of a Pulse in a Vertical Chain
Foster, Theodore; van Wyngaarden, Willem; Cary, Arthur; Mottmann, John
2013-01-01
We have frequently enhanced our department's laboratory experiment involving standing transverse waves in a taut horizontal cord. In addition to the standard experiment, students in these labs investigate the surprising concept that the acceleration of a pulse in a chain hanging vertically is a constant and is equal to half the acceleration…
Crack-induced anisotropy and its effect on vertical seismic profiling
Douma, J.
1988-01-01
Media containing aligned rotationally symmetrical inclusions show transverse isotropy with respect to elastic wave propagation. The characteristics of this type of anisotropy have been investigated in the first part of this thesis (chapters 2, 3, and 4) while its implications on Vertical Seismic
Vertical and horizontal transport of mesospheric Na: Implications for the mass influx of cosmic dust
Gardner, Chester S.; Liu, Alan Z.; Guo, Yafang
2017-09-01
The mesospheric metal layers are formed by the vaporization of high-speed cosmic dust particles as they enter the Earth's upper atmosphere. We show that the downward fluxes of these metal atoms, induced locally by waves and turbulence, are related in a straightforward way to the meteoric influxes of the metals, their chemical losses and their advective transport by the large-scale vertical and horizontal motions associated with the meridional circulation system. Above the peak of the metal layers where chemical losses and large-scale vertical motions are small, the wave-induced flux is insensitive to changes in local wave activity. If the downward transport velocity increases, because wave activity increases, then in response, the metal densities will decrease to maintain a constant vertical flux. By fitting the theoretical Na flux profile to the annual mean vertical flux profile measured during the night at the Starfire Optical Range, NM, we derive improved estimates for the global influxes of both Na and cosmic dust. The mean Na influx is 22,500±1050 atoms/cm2/s, which equals 389±18 kg/d for the global input of Na vapor. If the Na composition of the dust particles is identical to CI chondritic meteorites (4990 ppm by mass), then the global influx of cosmic dust is 176±38 t/d. If the composition is identical to ordinary chondrites (7680 ppm), the global dust influx is 107±22 t/d.
Development of the Wave Energy Converter -Wave Dragon
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Frigaard, Peter; Sørensen, Hans Christian
2000-01-01
2Over the years wave energy has gradually been brought into focus, as it has become clear that the fossil energy resources are limited, and cause large environmental problems, e.g. CO2 pollution. On this background a number of different wave energy converters have been proposed. In Denmark...... the government have decided to appropriate 20 mill. DKK (approx. 2,7 mill. EUR) to the development of wave energy devices over two years, 1998-1999, and the European Community (EC) also supports the development through the JOULECRAFT program....
Energy Technology Data Exchange (ETDEWEB)
Hsiao, Y.K. [Shanxi Normal University, School of Physics and Information Engineering, Linfen (China); National Tsing Hua University, Department of Physics, Hsinchu (China); Geng, C.Q. [Shanxi Normal University, School of Physics and Information Engineering, Linfen (China); National Tsing Hua University, Department of Physics, Hsinchu (China); Hunan Normal University, Synergetic Innovation Center for Quantum Effects and Applications (SICQEA), Changsha (China)
2017-10-15
We present the first attempt to extract vertical stroke V{sub cb} vertical stroke from the Λ{sub b} → Λ{sub c}{sup +}l anti ν{sub l} decay without relying on vertical stroke V{sub ub} vertical stroke inputs from the B meson decays. Meanwhile, the hadronic Λ{sub b} → Λ{sub c}M{sub (c)} decays with M = (π{sup -},K{sup -}) and M{sub c} =(D{sup -},D{sup -}{sub s}) measured with high precisions are involved in the extraction. Explicitly, we find that vertical stroke V{sub cb} vertical stroke =(44.6 ± 3.2) x 10{sup -3}, agreeing with the value of (42.11 ± 0.74) x 10{sup -3} from the inclusive B → X{sub c}l anti ν{sub l} decays. Furthermore, based on the most recent ratio of vertical stroke V{sub ub} vertical stroke / vertical stroke V{sub cb} vertical stroke from the exclusive modes, we obtain vertical stroke V{sub ub} vertical stroke = (4.3 ± 0.4) x 10{sup -3}, which is close to the value of (4.49 ± 0.24) x 10{sup -3} from the inclusive B → X{sub u}l anti ν{sub l} decays. We conclude that our determinations of vertical stroke V{sub cb} vertical stroke and vertical stroke V{sub ub} vertical stroke favor the corresponding inclusive extractions in the B decays. (orig.)
Extreme waves impact on the ship mooring near berth
Leont'ev, Victor; Nudner, Igor; Semenov, Konstantin; Pelinovsky, Efim
2013-04-01
Ensuring safe ships berthing and loading-unloading operations at berths need reliable mooring systems. The choice of its parameters corresponds to calculating of the maximum displacements of the boat, which are caused by external impact of extreme waves, winds, and currents. Ship motions are described by system of differential equations, which contain disturbing, inertia, damping, and restoring forces, which magnitude strongly depends on the berth design and configuration of its elements. The major impact on the boat movements is caused by sea waves. In the given paper, an interaction between sea waves and ship located near the berth is studied. The cross-sectional shape of the boat is assumed to be rectangular and under-berth slope profile is approximated by finite number of steps. Different types of berth constructions are taken into account: containing impermeable or partially permeable front vertical wall, wave attenuation camera behind it with or without under-berth slope. The fluid is assumed ideal and incompressible, and its motion is potential. The stated problem is reduced to the determination of the velocity potential that satisfies the Laplace equation; the boundary condition on the free surface; the condition of non-flux through the impermeable bottom, the ship and berth elements; the condition on the surface of the permeable wall that is in proportionality between the wave flow velocity through the wall and pressure drop from its front to back faces. The problem is solved by dividing of the region into sub-domains with conditions of the hydrodynamic pressure and velocity continuity on its boundaries. In each sub-domain the solution is found using Fourier method in the form of functional series with unknown coefficients which are found from the system of linear algebraic equations. Calculated velocity potentials are used to determine different hydrodynamic characteristics of ship motions, such as horizontal and vertical components of disturbing force
Worlds Largest Wave Energy Project 2007 in Wales
DEFF Research Database (Denmark)
Christensen, Lars; Friis-Madsen, Erik; Kofoed, Jens Peter
2006-01-01
a large number of fundamentally different technologies are utilised to harvest wave energy. The Wave Dragon belongs to the wave overtopping class of converters and the paper describes the fundamentals and the technical solutions used in this wave energy converter. An offshore floating WEC like the Wave......This paper introduces world largest wave energy project being developed in Wales and based on one of the leading wave energy technologies. The background for the development of wave energy, the total resource ands its distribution around the world is described. In contrast to wind energy turbines...
The influence of wave action on coastal erosion along Monwabisi ...
African Journals Online (AJOL)
Microsoft account
through analysis of aerial photographs and wave data to establish whether there is a relationship between dynamic ... rate of coastline retreat and the wave data, the study has concluded that the extreme rates of coastline ... combination of influences including the number and height of big wave events, waves coming from.
Modeling the ascent of sounding balloons: derivation of the vertical air motion
Directory of Open Access Journals (Sweden)
A. Gallice
2011-10-01
Full Text Available A new model to describe the ascent of sounding balloons in the troposphere and lower stratosphere (up to ∼30–35 km altitude is presented. Contrary to previous models, detailed account is taken of both the variation of the drag coefficient with altitude and the heat imbalance between the balloon and the atmosphere. To compensate for the lack of data on the drag coefficient of sounding balloons, a reference curve for the relationship between drag coefficient and Reynolds number is derived from a dataset of flights launched during the Lindenberg Upper Air Methods Intercomparisons (LUAMI campaign. The transfer of heat from the surrounding air into the balloon is accounted for by solving the radial heat diffusion equation inside the balloon. In its present state, the model does not account for solar radiation, i.e. it is only able to describe the ascent of balloons during the night. It could however be adapted to also represent daytime soundings, with solar radiation modeled as a diffusive process. The potential applications of the model include the forecast of the trajectory of sounding balloons, which can be used to increase the accuracy of the match technique, and the derivation of the air vertical velocity. The latter is obtained by subtracting the ascent rate of the balloon in still air calculated by the model from the actual ascent rate. This technique is shown to provide an approximation for the vertical air motion with an uncertainty error of 0.5 m s^{−1} in the troposphere and 0.2 m s^{−1} in the stratosphere. An example of extraction of the air vertical velocity is provided in this paper. We show that the air vertical velocities derived from the balloon soundings in this paper are in general agreement with small-scale atmospheric velocity fluctuations related to gravity waves, mechanical turbulence, or other small-scale air motions measured during the SUCCESS campaign (Subsonic Aircraft: Contrail and Cloud Effects
A first course in vibrations and waves
Samiullah, Mohammad
2015-01-01
This book builds on introductory physics and emphasizes understanding of vibratory motion and waves based on first principles. The book is divided into three parts. Part I contains a preliminary chapter that serves as a review of relevant ideas of mechanics and complex numbers. Part II is devoted to a detailed discussion of vibrations of mechanical systems. This part covers a simple harmonic oscillator, coupled oscillators, normal coordinates, beaded string, continuous string, standing waves, and Fourier series. Part II ends with a presentation of stationary solutions of driven finite systems. Part III is concerned with waves. Here, the emphasis is on the discussion of common aspects of all types of waves. The applications to sound, electromagnetic, and matter waves are illustrated. The book also includes examples from water waves and electromagnetic waves on a transmission line. The emphasis of the book is to bring out the similarities among various types of waves. The book includes treatment of reflection a...
A comparison between vertical motions measured by ADCP and inferred from temperature data
Directory of Open Access Journals (Sweden)
H. van Haren
2008-09-01
Full Text Available Combined vertical current (w and thermistor string data demonstrate that high-, near-buoyancy frequency internal "wave" trains along a pycnocline in a flat-bottom shelf sea consist for 2 periods of a dominant mode-1 non-linear part, while thereafter mainly of linear [mode-2, quadrupled frequency] waves, to first order. In a simple [linear] heat budget the use of unfiltered temperature gradient or its time mean changes results by only 10%. The observations also demonstrate that temperature is not always adequate to estimate vertical motions using the linear 1-D heat equation. In shallow seas, tidal-w estimated from temperature data can be an order of magnitude weaker than directly observed w, and thus do not represent free internal waves. In the ocean, not too far from the main internal wave topography source, tidal motions represent linear waves and are well described by temperature-inferred w. There however, temperature-inferred w and directly observed w differ strongly near the buoyancy frequency, at which w is dominated by non-linear waves, and near [sub]inertial frequencies, at which w is dominated by eddies and gyroscopic waves.
DEFF Research Database (Denmark)
Rasmussen, Anders Rønne; Sørensen, Mads Peter; Gaididei, Yuri Borisovich
2011-01-01
the Hamiltonian structure, in contrast to the Kuznetsov equation, a model often used in nonlinear acoustics. An exact traveling wave front solution is derived from a generalized traveling wave assumption for the velocity potential. Numerical studies of the evolution of a number of arbitrary initial conditions...... as well as head-on colliding and confluent wave fronts exhibit several nonlinear interaction phenomena. These include wave fronts of changed velocity and amplitude along with the emergence of rarefaction waves. An analysis using the continuity of the solutions as well as the boundary conditions...
Brule, Stephane; Guenneau, Sebastien
2016-01-01
A prerequisite for achieving seismic invisibility is to demonstrate the ability of civil engineers to control seismic waves with artificially structured soils. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (< 10 Hz). This allows the identification of a distribution of energy inside the grid, which can be interpreted as the consequence of an effective negative refraction index. Such a flat lens reminiscent of what Veselago and Pendry envisioned for light opens avenues in seismic metamaterials to counteract the most devastating components of seismic signals.
?Vertical Sextants give Good Sights?
Richey, Michael
Mark Dixon suggests (Forum, Vol. 50, 137) that nobody thus far has attempted to quantify the errors from tilt that arise while observing with the marine sextant. The issue in fact, with the related problem of what exactly is the axis about which the sextant is rotated whilst being (to define the vertical), was the subject of a lively controversy in the first two volumes of this Journal some fifty years ago. Since the consensus of opinion seems to have been that the maximum error does not necessarily occur at 45 degrees, whereas Dixon's table suggests that it does, some reiteration of the arguments may be in order.
BATCH SETTLING IN VERTICAL SETTLERS
Lama Ramirez, R.; Universidad Nacional Mayor De San Marcos Facultad de Química e Ingeniería Química Departamento de Operaciones Unitarias Av. Venezuela cdra. 34 sin, Lima - Perú; Condorhuamán Ccorimanya, C.; Universidad Nacional Mayor De San Marcos Facultad de Química e Ingeniería Química Departamento de Operaciones Unitarias Av. Venezuela cdra. 34 sin, Lima - Perú
2014-01-01
lt has been studied the batch sedimentation of aqueous suspensions of precipitated calcium carbonate, barium sulphate and lead oxide , in vertical thickeners of rectangular and circular cross sectional area. Suspensions vary in concentration between 19.4 and 617.9 g/I and the rate of sedimentation obtained between 0.008 and 7.70 cm/min. The effect of the specific gravity of the solid on the rate of sedimentation is the same for all the suspensions, that is, the greater the value of the specif...
Binocular responses and vertical strabismus
Directory of Open Access Journals (Sweden)
Risović Dušica
2007-01-01
Full Text Available Background/Aim. Elevation in adduction is the most common pattern of vertical strabismus, and it is mostly treated with surgery. The results of weaking of inferior oblique muscle are very changeable. The aim of this study was to evaluate binocular vision using sensory tests before and one and six months after the surgery. Methods. A total of 79 children were divided in two groups: the first, with inferior oblique muscle of overaction (n = 52, and the second with dissociated vertical deviation (DVD, and primary inferior oblique muscle overaction (n = 27. We tested them by polaroid mirror test (PMT, Worth test at distance and near, fusion amplitudes on sinoptofore, Lang I stereo test and Wirt-Titmus stereo test. We examined our patients before and two times after the surgery for vertical strabismus. Results. Foveal suppression in the group I was found in 60.5% of the patients before, and in 56.4% after the surgery. In group II Foveal suppression was detected in 64.7% of the patients before, but in 55.6% 6 months after the surgery with PMT. Worth test revealed suppression in 23.5% of the patients before, and in 40.7% after the vertical muscle surgery. Parafoveal fussion persisted in about 1/3 of the patients before the surgery, and their amplitudes were a little larger after the surgery in the group I patients. Lang I stereo test was negative in 53.9% before and 51.9% after the surgery in the group I, and in 48.2% of the patients before and after the surgery in the group II patients. Wirt-Titmus stereo test was negative in 74.5% of the patients before and in 72.9% after the surgery in the group I, but in the group II it was negative in 70.8% before and in 68.0% of the patients 6 months after the surgery. Conclusion. Binocular responses were found after surgery in 65.7% of the patients the group I and in 55.6% patients the group II. There was no significant difference between these two groups, but binocular responses were more often in the patients
Ciufolini, I; Moschella, U; Fre, P
2001-01-01
Gravitational waves (GWs) are a hot topic and promise to play a central role in astrophysics, cosmology, and theoretical physics. Technological developments have led us to the brink of their direct observation, which could become a reality in the coming years. The direct observation of GWs will open an entirely new field: GW astronomy. This is expected to bring a revolution in our knowledge of the universe by allowing the observation of previously unseen phenomena, such as the coalescence of compact objects (neutron stars and black holes), the fall of stars into supermassive black holes, stellar core collapses, big-bang relics, and the new and unexpected.With a wide range of contributions by leading scientists in the field, Gravitational Waves covers topics such as the basics of GWs, various advanced topics, GW detectors, astrophysics of GW sources, numerical applications, and several recent theoretical developments. The material is written at a level suitable for postgraduate students entering the field.
DEFF Research Database (Denmark)
Kramer, Morten; Frigaard, Peter; Brorsen, Michael
Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....
Internal wave turbulence near a Texel beach.
Directory of Open Access Journals (Sweden)
Hans van Haren
Full Text Available A summer bather entering a calm sea from the beach may sense alternating warm and cold water. This can be felt when moving forward into the sea ('vertically homogeneous' and 'horizontally different', but also when standing still between one's feet and body ('vertically different'. On a calm summer-day, an array of high-precision sensors has measured fast temperature-changes up to 1 °C near a Texel-island (NL beach. The measurements show that sensed variations are in fact internal waves, fronts and turbulence, supported in part by vertical stable stratification in density (temperature. Such motions are common in the deep ocean, but generally not in shallow seas where turbulent mixing is expected strong enough to homogenize. The internal beach-waves have amplitudes ten-times larger than those of the small surface wind waves. Quantifying their turbulent mixing gives diffusivity estimates of 10(-4-10(-3 m(2 s(-1, which are larger than found in open-ocean but smaller than wave breaking above deep sloping topography.
Development of Vertical Cable Seismic System (3)
Asakawa, E.; Murakami, F.; Tsukahara, H.; Mizohata, S.; Ishikawa, K.
2013-12-01
The VCS (Vertical Cable Seismic) is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. Because VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed the method for the hydrothermal deposit survey tool development program that the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started in 2009. We are now developing a VCS system, including not only data acquisition hardware but data processing and analysis technique. We carried out several VCS surveys combining with surface towed source, deep towed source and ocean bottom source. The water depths of the survey are from 100m up to 2100m. The target of the survey includes not only hydrothermal deposit but oil and gas exploration. Through these experiments, our VCS data acquisition system has been completed. But the data processing techniques are still on the way. One of the most critical issues is the positioning in the water. The uncertainty in the positions of the source and of the hydrophones in water degraded the quality of subsurface image. GPS navigation system are available on sea surface, but in case of deep-towed source or ocean bottom source, the accuracy of shot position with SSBL/USBL is not sufficient for the very high-resolution imaging. We have developed another approach to determine the positions in water using the travel time data from the source to VCS hydrophones. In the data acquisition stage, we estimate the position of VCS location with slant ranging method from the sea surface. The deep-towed source or ocean bottom source is estimated by SSBL/USBL. The water velocity profile is measured by XCTD. After the data acquisition, we pick the first break times of the VCS recorded data. The estimated positions of
Wave-current interactions in megatidal environment
Bennis, A. C.; Pascal, B. D. B.; Feddy, A.; Garnier, V.; Accenti, M.; Dumas, F.; Ardhuin, F.
2016-12-01
The strongest tidal current in western Europe (up to 12 knots) occurs in Raz Blanchard (Normandy, France). High winds occur over six months which generate energetic wave conditions with breaking waves, hence the name of `Blanchard'. However, few studies have been conducted on the wave effects on the tidal current at this location because of the lack of measurements. Studies are now required to aid the creation of tidal farms. For this purpose, the 3D fully-coupled model MARS-WW3 is used with three nested ranks which are forced at boundaries by wave spectra from HOMERE database (Boudière et al., 2013) and by sea level from the French Navy (SHOM). The model is tested against ADCP data of IRSN at three locations near Raz Blanchard. Time series of current velocity and of mean sea level are consistent with ADCP data. A rephasing by waves of the tidal current is observed in comparison with simulations without waves, which fits the ADCP data. A strong dependence of the tidal current on bottom roughness is shown as well as the necessity to take into account its spatial heterogeneity. The simulated mean sea level is close to the measured one while it was underestimated for high tide in simulations without wave effects. The vertical shape of the tidal current is especially modified near the surface by waves as expected. Depending on the tidal cycle and wave direction, acceleration or deceleration of the surface current due to waves is observed. Lastly, several hydrodynamical scenarios for Raz Blanchard are carried out for different tidal and wave conditions pending the HYD2M'17 data (ADCP, ADV, drifting wave buoys, HF and VHF and X-Band radars). First results show the impacts of refractive, shoaling and blocking effects on the flood and ebb currents.
Ferrarese, Giorgio
2011-01-01
Lectures: A. Jeffrey: Lectures on nonlinear wave propagation.- Y. Choquet-Bruhat: Ondes asymptotiques.- G. Boillat: Urti.- Seminars: D. Graffi: Sulla teoria dell'ottica non-lineare.- G. Grioli: Sulla propagazione del calore nei mezzi continui.- T. Manacorda: Onde nei solidi con vincoli interni.- T. Ruggeri: "Entropy principle" and main field for a non linear covariant system.- B. Straughan: Singular surfaces in dipolar materials and possible consequences for continuum mechanics
Jiang, Z
2005-01-01
The International Symposium on Shock Waves (ISSW) is a well established series of conferences held every two years in a different location. A unique feature of the ISSW is the emphasis on bridging the gap between physicists and engineers working in fields as different as gas dynamics, fluid mechanics and materials sciences. The main results presented at these meetings constitute valuable proceedings that offer anyone working in this field an authoritative and comprehensive source of reference.
Natural convection heat transfer along vertical rectangular ducts
Energy Technology Data Exchange (ETDEWEB)
Ali, M. [King Saud University, Mechanical Engineering Department, Riyadh (Saudi Arabia)
2009-12-15
Experimental investigations have been reported on steady state natural convection from the outer surface of vertical rectangular and square ducts in air. Seven ducts have been used; three of them have a rectangular cross section and the rest have square cross section. The ducts are heated using internal constant heat flux heating elements. The temperatures along the vertical surface and the peripheral directions of the duct wall are measured. Axial (perimeter averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition to turbulent regimes of natural convection heat transfer. Axial (perimeter averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for laminar and transition regime using the vertical axial distance as a characteristic length. Critical values of the modified Rayleigh numbers are obtained for transition to turbulent. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers and the area ratio for the laminar regimes. The local axial (perimeter averaged) heat transfer coefficients are observed to decrease in the laminar region and increase in the transition region. Laminar regimes are obtained at the lower half of the ducts and its chance to appear decreases as the heat flux increases. (orig.)
Generation of internal solitary waves by frontally forced intrusions in geophysical flows.
Bourgault, Daniel; Galbraith, Peter S; Chavanne, Cédric
2016-12-06
Internal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada.
The Rossby wave instability in protoplanetary disks
Directory of Open Access Journals (Sweden)
Meheut H.
2013-04-01
Full Text Available The Rossby wave instability has been proposed as a mechanism to transport angular momentum in the dead zone of protoplanetary disks and to form vortices. These vortices are of particular interest to concentrate solids in their centres and eventually to form planetesimals. Here we summarize some recent results concerning the growth and structure of this instability in radially and vertically stratified disks, its saturation and non-linear evolution. We also discuss the concentration of solids in the Rossby vortices including vertical settling.
Vertically stacked nanocellulose tactile sensor.
Jung, Minhyun; Kim, Kyungkwan; Kim, Bumjin; Lee, Kwang-Jae; Kang, Jae-Wook; Jeon, Sanghun
2017-11-16
Paper-based electronic devices are attracting considerable attention, because the paper platform has unique attributes such as flexibility and eco-friendliness. Here we report on what is claimed to be the firstly fully integrated vertically-stacked nanocellulose-based tactile sensor, which is capable of simultaneously sensing temperature and pressure. The pressure and temperature sensors are operated using different principles and are stacked vertically, thereby minimizing the interference effect. For the pressure sensor, which utilizes the piezoresistance principle under pressure, the conducting electrode was inkjet printed on the TEMPO-oxidized-nanocellulose patterned with micro-sized pyramids, and the counter electrode was placed on the nanocellulose film. The pressure sensor has a high sensitivity over a wide range (500 Pa-3 kPa) and a high durability of 10(4) loading/unloading cycles. The temperature sensor combines various materials such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), silver nanoparticles (AgNPs) and carbon nanotubes (CNTs) to form a thermocouple on the upper nanocellulose layer. The thermoelectric-based temperature sensors generate a thermoelectric voltage output of 1.7 mV for a temperature difference of 125 K. Our 5 × 5 tactile sensor arrays show a fast response, negligible interference, and durable sensing performance.
Utilization of Double-Water-Chamber Seawall type for Wave Energy Extraction and Wave Dissipation
Husain, Firman
2016-01-01
Variation type and model of wave energy converter have been applied in many countries around the world in order to harvest the ocean wave power. A number of other devices were developing and testing by researchers in the experimental scale. In the present paper investigates double-water-chamber seawall performance for wave energy converter. The main body of water chamber seawall is like OWC structure. Savonius water turbine and guide vanes used to extract a wave power instead of air turbine a...
Energy Technology Data Exchange (ETDEWEB)
Thomas Cottman
2001-10-19
Pennsylvanian-age Morrow reservoirs are a key component of a large fluvial-deltaic system that extends across portions of Colorado, Kansas, Oklahoma, and Texas. A problem that operators have to solve in some Morrow plays in this multi-state area is that many of the fluvial channels within the Morrow interval are invisible to seismic compressional (P) waves. This P-wave imaging problem forces operators in such situations to site infill, field-extension, and exploration wells without the aid of 3-D seismic technology. The objective of this project was to develop and demonstrate seismic technology that can improve drilling success in Morrow plays. Current P-wave technology commonly results in 80-percent of Morrow exploration wells not penetrating economic reservoir facies. Studies at Colorado School of Mines have shown that some of the Morrow channels that are elusive as P-wave targets create robust shear (S) wave reflections (Rampton, 1995). These findings caused Visos Energy to conclude that exploration and field development of Morrow prospects should be done by a combination of P-wave and S-wave seismic imaging. To obtain expanded information about the P and S reflectivity of Morrow facies, 9-component vertical seismic profile (9-C VSP) data were recorded at three locations along the Morrow trend. These data were processed to create P and S images of Morrow stratigraphy. These images were then analyzed to determine if S waves offer an alternative to P waves, or perhaps even an advantage over P waves, in imaging Morrow reservoir targets. The study areas where these field demonstrations were done are defined in Figure 1. Well A was in Sherman County, Texas; well B in Clark County, Kansas; and well C in Cheyenne County, Colorado. Technology demonstrated at these sites can be applied over a wide geographical area and influence operators across the multi-state region spanned by Morrow channel plays. The scope of the investigation described here is significant on the
Wave-Turbulence Interactions: a DPIV Study
Lang, Amy; Lalinde, David
1999-11-01
Previous studies on wave-turbulence interactions, such as the one by Olmez & Milgram (JFM, 1992), supported the hypothesis that the dominant mechanism for the dissipation of non-breaking waves by turbulence is vertical mixing, rather than wave-to-turbulence energy transfer in the wave layer. In this study, Digital Particle Image Velocimetry (DPIV) was used to study the increase in turbulence levels due to the presence of surface waves. Two types of turbulent fields were studied. A grid of cylindrical rods was placed in a water tunnel with smaller scale turbulence resulting in the wake of the grid. The second case used a flat plate grid, with the plates aligned parallel to the free-stream flow. This allowed for a range of scales to be generated within the turbulent flow-field in the test section. Next, a wave-generator was placed in the tunnel allowing waves to propagate into the area studied and interact with the grid-generated turbulence. Variation in wavelength and frequency of the surface waves was performed. Results will be presented.
Slunyaev, Alexey; Klein, Marco; Clauss, Günther F.
2016-04-01
Envelope soliton solutions are key elements governing the nonlinear wave dynamics within a simplified theory for unidirectional weakly modulated weakly nonlinear wave groups on the water surface. Within integrable models the solitons preserve their structure in collisions with other waves; they do not disperse and can carry energy infinitively long. Steep and short soliton-like wave groups have been shown to exist in laboratory tests [1] and, even earlier, in numerical simulations [2, 3]. Thus, long-living wave groups may play important role in the dynamics of intense sea waves and wave-structure interactions. The solitary wave groups may change the wave statistics and can be taken into account when developing approaches for the deterministic forecasting of dangerous waves, including so-called rogue waves. An experimental campaign has been conducted in the wave basin of the Technical University of Berlin on simulations of intense solitary wave groups. The first successful experimental observation of intense envelope solitons took place in this facility [1]. The new experiments aimed at following main goals: 1) to reproduce intense envelope solitons with different carrier wave lengths; 2) to estimate the rate of envelope soliton dissipation; 3) to consider the reflection of envelope solitons on a vertical wall; 4) to consider head-on collisions of envelope solitons, and 5) to consider overtaking interactions of envelope solitons. Up to 9 wave gauges were used in each experimental run, which enabled registration of the surface movement at different distances from the wavemaker, at different locations across the wave flume and near the wall. Besides surface displacements, the group envelope shapes were directly recorded, with use of phase shifts applied to the modulated waves generated by the wavemaker. [1] A. Slunyaev, G.F. Clauss, M. Klein, M. Onorato, Simulations and experiments of short intense envelope solitons of surface water waves. Phys. Fluids 25, 067105
Coupling atmospheric and ocean wave models for storm simulation
DEFF Research Database (Denmark)
Du, Jianting
This thesis studies the wind-wave interactions through the coupling between the atmospheric model and ocean surface wave models. Special attention is put on storm simulations in the North Sea for wind energy applications in the coastal zones. The two aspects, namely storm conditions and coastal...... and coastal conditions, z0 parameterization method often fails in reproducing z0 because the complexity of the sea state cannot be represented by a few selected wave parameters. Different from the parameterization method, physics-based methods take the idea that the loss of momentum and kinetic energy from...... the above mentioned challenges, a wave boundary layer model (WBLM) is implemented in the wave model SWAN as a new Sin. The WBLM Sin is based on the momentum and kinetic energy conservation. The wave-induced mean wind profile changes at all vertical levels within the wave boundary layer, and the spectral...
Third-order theory for multi-directional irregular waves
DEFF Research Database (Denmark)
Madsen, Per A.; Fuhrman, David R.
2012-01-01
A new third-order solution for multi-directional irregular water waves in finite water depth is presented. The solution includes explicit expressions for the surface elevation, the amplitude dispersion and the vertical variation of the velocity potential. Expressions for the velocity potential...... breaks down due to singularities in the transfer functions. We analyse harmonic resonance for the case of a monochromatic short-crested wave interacting with a plane wave having a different frequency, and make long-term simulations with a high-order Boussinesq formulation in order to study the evolution...... of wave trains exposed to harmonic resonance....
REFLECTION OF ELECTROMAGNETIC WAVES FROM SOUND WAVES
The reflection of electromagnetic waves normally incident on the wavefronts of a semi-infinite standing sound wave is discussed. By analogy with the...with the sound frequency. An experiment is described in which the Bragg reflection of 3 cm electromagnetic waves from a standing sound wave beneath a water surface is observed.
Impact of Wave Dragon on Wave Climate
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Tedd, James; Kramer, Morten
This report is an advisory paper for use in determining the wave dragon effects on hydrography, by considering the effect on the wave climate in the region of a wave dragon. This is to be used in the impact assessment for the Wave Dragon pre-commercial demonstrator....
Erickson, Gary E.
2007-01-01
A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the effects of passive surface porosity and vertical tail placement on vortex flow development and interactions about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used that featured pressure sensitive paint (PSP), laser vapor screen (LVS), and schlieren, These techniques were combined with conventional electronically-scanned pressure (ESP) and six-component force and moment measurements to quantify and to visualize the effects of flow-through porosity applied to a wing leading edge extension (LEX) and the placement of centerline and twin vertical tails on the vortex-dominated flow field of a 65 cropped delta wing model. Test results were obtained at free-stream Mach numbers of 1.6, 1.8, and 2.1 and a Reynolds number per foot of 2.0 million. LEX porosity promoted a wing vortex-dominated flow field as a result of a diffusion and weakening of the LEX vortex. The redistribution of the vortex-induced suction pressures contributed to large nose-down pitching moment increments but did not significantly affect the vortex-induced lift. The trends associated with LEX porosity were unaffected by vertical tail placement. The centerline tail configuration generally provided more stable rolling moments and yawing moments compared to the twin wing-mounted vertical tails. The strength of a complex system of shock waves between the twin tails was reduced by LEX porosity.
Seasonal dynamics and vertical distribution of plant-feeding nematode communities in grasslands
Verschoor, B.C.; Goede, de R.G.M.; Hoop, de J.W.; Vries, de F.W.
2001-01-01
The vertical distribution and seasonal dynamics of plant- and fungal-feeding nematode taxa in permanent grasslands were investigated. Dolichodoridae, Paratylenchus, Pratylenchus, Tylenchidae and Aphelenchoides dominated the upper 10 cm soil and their numbers strongly decreased with depth. The
Some design aspects of high-speed vertical-axis wind turbines
National Research Council Canada - National Science Library
Templin, R. J; South, P
1977-01-01
... (rotor height to diameter ratio, solidity, number of blades, etc.) for high-speed vertical-axis wind turbines from kilowatt to megawatt sizes and shows that very large turbines are theoretically feasible...
Impact of the vertical dynamics on the thermosphere at low and middle latitudes: GITM simulations
Zhu, Qingyu; Deng, Yue; Maute, Astrid; Sheng, Cheng; Lin, Cissi Y.
2017-06-01
In this study, the influences of the electric fields at low and middle latitudes on the ionosphere and thermosphere are investigated by using the nonhydrostatic Global Ionosphere and Thermosphere Model (GITM). The equatorial ionization anomaly and the equatorial thermosphere anomaly (ETA) are well reproduced in the simulation when the electric fields are included. The term analysis of the continuity equation of the neutral mass density shows that the daytime upward vertical wind near the geomagnetic equator tends to increase the local neutral mass density at 400 km altitude, while the divergence in the meridional wind associated with the meridional ion-drag force tends to transport the neutral mass density away from the geomagnetic equator which might contribute to the formation of the ETA trough. The vertical dynamics is modulated by the vertical forces including ion-drag force and pressure gradient force acting on the neutrals, and the changing vertical dynamics can also feedback to vertical ion-drag and pressure gradient forces, particularly near the geomagnetic equator. The daytime vertical ion-drag force near the geomagnetic equator is generally upward, while the daytime vertical pressure gradient force near the geomagnetic equator is reduced at most times after adding in the electric fields at low and middle latitudes. Meanwhile, the sudden introduction of the electric fields at low and middle latitudes induces an acoustic wave.
Capillary holdup between vertical spheres
Directory of Open Access Journals (Sweden)
S. Zeinali Heris
2009-12-01
Full Text Available The maximum volume of liquid bridge left between two vertically mounted spherical particles has been theoretically determined and experimentally measured. As the gravitational effect has not been neglected in the theoretical model, the liquid interface profile is nonsymmetrical around the X-axis. Symmetry in the interface profile only occurs when either the particle size ratio or the gravitational force becomes zero. In this paper, some equations are derived as a function of the spheres' sizes, gap width, liquid density, surface tension and body force (gravity/centrifugal to estimate the maximum amount of liquid that can be held between the two solid spheres. Then a comparison is made between the result based on these equations and several experimental results.
Coherent electromagnetic waves in the presence of a half space of randomly distributed scatterers
Karam, M. A.; Fung, A. K.
1988-01-01
The present investigation of coherent field propagation notes, upon solving the Foldy-Twersky integral equation for a half-space of small spherical scatterers illuminated by a plane wave at oblique incidence, that the coherent field for a horizontally-polarized incident wave exhibits reflectivity and transmissivity consistent with the Fresnel formula for an equivalent continuous effective medium. In the case of a vertically polarized incident wave, both the vertical and longitudinal waves obtained for the coherent field have reflectivities and transmissivities that do not agree with the Fresnel formula.
Vertical jump coordination: fatigue effects.
Rodacki, André Luiz Felix; Fowler, Neil E; Bennett, Simon J
2002-01-01
The aim of this study was to investigate the segmental coordination of vertical jumps under fatigue of the knee extensor and flexor muscles. Eleven healthy and active subjects performed maximal vertical jumps with and without fatigue, which was imposed by requesting the subjects to extend/flex their knees continuously in a weight machine, until they could not lift a load corresponding to approximately 50% of their body weight. Knee extensor and flexor isokinetic peak torques were also measured before and after fatigue. Video, ground reaction forces, and electromyographic data were collected simultaneously and used to provide several variables of the jumps. Fatiguing the knee flexor muscles did not reduce the height of the jumps or induce changes in the kinematic, kinetic, and electromyographic profiles. Knee extensor fatigue caused the subjects to adjust several variables of the movement, in which the peak joint angular velocity, peak joint net moment, and power around the knee were reduced and occurred earlier in comparison with the nonfatigued jumps. The electromyographic data analyses indicated that the countermovement jumps were performed similarly, i.e., a single strategy was used, irrespective of which muscle group (extensor or flexors) or the changes imposed on the muscle force-generating characteristics (fatigue or nonfatigue). The subjects executed the movements as if they scaled a robust template motor program, which guided the movement execution in all jump conditions. It was speculated that training programs designed to improve jump height performance should avoid severe fatigue levels, which may cause the subjects to learn and adopt a nonoptimal and nonspecific coordination solution. It was suggested that the neural input used in the fatigued condition did not constitute an optimal solution and may have played a role in decreasing maximal jump height achievement.
Richardson Number, stability and turbulence- A coherent view
Digital Repository Service at National Institute of Oceanography (India)
Varkey, M.J.
As turbulence in water is governed by vertical mobility controlled by static stability and horizontal mobility controlled by currents, the Richardson Number should give a measure of turbulence also. It is argued in this note that inverse...
Bubble Number-density Data and Modeled Paleoclimates, Version 1
National Aeronautics and Space Administration — This data set includes bubble number-density measured at depths from 120 meters to 560 meters at 20-meter intervals in both horizontal and vertical samples. The data...
Ocean Wave Separation Using CEEMD-Wavelet in GPS Wave Measurement
Directory of Open Access Journals (Sweden)
Junjie Wang
2015-08-01
Full Text Available Monitoring ocean waves plays a crucial role in, for example, coastal environmental and protection studies. Traditional methods for measuring ocean waves are based on ultrasonic sensors and accelerometers. However, the Global Positioning System (GPS has been introduced recently and has the advantage of being smaller, less expensive, and not requiring calibration in comparison with the traditional methods. Therefore, for accurately measuring ocean waves using GPS, further research on the separation of the wave signals from the vertical GPS-mounted carrier displacements is still necessary. In order to contribute to this topic, we present a novel method that combines complementary ensemble empirical mode decomposition (CEEMD with a wavelet threshold denoising model (i.e., CEEMD-Wavelet. This method seeks to extract wave signals with less residual noise and without losing useful information. Compared with the wave parameters derived from the moving average skill, high pass filter and wave gauge, the results show that the accuracy of the wave parameters for the proposed method was improved with errors of about 2 cm and 0.2 s for mean wave height and mean period, respectively, verifying the validity of the proposed method.
Theoretical and Experimental Studies of Wave Impact underneath Decks of Offshore Platforms
Energy Technology Data Exchange (ETDEWEB)
Baarholm, Rolf Jarle
2001-07-01
structure experiences a positive slamming dominated force (upward directed) during the initial water entry phase, followed by a negative force during the water exit phase. The force in the latter phase is dominated by a negative added mass force due to negative vertical fluid particle accelerations in the wave crest. The positive force peak is highly dependent on the impact condition and is especially sensitive to the initial deck clearance. The magnitude of the negative force peak is less dependent on the impact condition. This peak occurs when the wetting of the deck is at its maximum and its magnitude may be larger than the positive force peak. Thus, the water exit phase is important for global effects. The initial impact yields the highest average pressures and is critical for local structural response in the deck. Comparisons between experiments and theory have been performed for a number of impact conditions. Second order Stokes' theory is used to describe the incident waves. The Wagner based method describes the water entry phase well. Both the magnitude and the duration of the positive force peak are well predicted. The computations for the water exit phase are less satisfactory. The WBM overestimates the magnitude of the negative force peak and it underestimates the duration of the water exit phase. In the nonlinear boundary element method, the impact induced vertical force on the deck is calculated by imposing conservation of fluid momentum and by using direct pressure integration. These two approaches yield similar force histories except during the final stage of water exit, where they tend to diverge. This is caused by inaccuracies in the numerical solution and in the formulation of the boundary value problem. The force at this stage is small. The BEM yields results that compare well with experiments for both the water entry and the water exit phase. Especially for the water exit phase the BEM is superior to the Wagner based method. (author)
The Unit Acquisition Number of a Graph
Johnson, Frederick; Raleigh, Anna; Wenger, Paul S.; West, Douglas B.
2017-01-01
Let $G$ be a graph with nonnegative integer weights. A {\\it unit acquisition move} transfers one unit of weight from a vertex to a neighbor that has at least as much weight. The {\\it unit acquisition number} of a graph $G$, denoted $a_u(G)$, is the minimum size that the set of vertices with positive weight can be reduced to via successive unit acquisition moves when starting from the configuration in which every vertex has weight $1$. For a graph $G$ with $n$ vertices and minimum degree $k$, ...
Instability of coupled gravity-inertial-Rossby waves on a β-plane in solar system atmospheres
Directory of Open Access Journals (Sweden)
J. F. McKenzie
2009-11-01
Full Text Available This paper provides an analysis of the combined theory of gravity-inertial-Rossby waves on a β-plane in the Boussinesq approximation. The wave equation for the system is fifth order in space and time and demonstrates how gravity-inertial waves on the one hand are coupled to Rossby waves on the other through the combined effects of β, the stratification characterized by the Väisälä-Brunt frequency N, the Coriolis frequency f at a given latitude, and vertical propagation which permits buoyancy modes to interact with westward propagating Rossby waves. The corresponding dispersion equation shows that the frequency of a westward propagating gravity-inertial wave is reduced by the coupling, whereas the frequency of a Rossby wave is increased. If the coupling is sufficiently strong these two modes coalesce giving rise to an instability. The instability condition translates into a curve of critical latitude Θ_{c} versus effective equatorial rotational Mach number M, with the region below this curve exhibiting instability. "Supersonic" fast rotators are unstable in a narrow band of latitudes around the equator. For example Θ_{c}~12° for Jupiter. On the other hand slow "subsonic" rotators (e.g. Mercury, Venus and the Sun's Corona are unstable at all latitudes except very close to the poles where the β effect vanishes. "Transonic" rotators, such as the Earth and Mars, exhibit instability within latitudes of 34° and 39°, respectively, around the Equator. Similar results pertain to Oceans. In the case of an Earth's Ocean of depth 4km say, purely westward propagating waves are unstable up to 26° about the Equator. The nonlinear evolution of this instability which feeds off rotational energy and gravitational buoyancy may play an important role in atmospheric dynamics.
Instability of coupled gravity-inertial-Rossby waves on a {beta}-plane in solar system atmospheres
Energy Technology Data Exchange (ETDEWEB)
McKenzie, J.F. [KwaZulu-Natal Univ., Durban (South Africa). Astrophysics and Cosmology Research Unit, School of Mathematical Sciences; Alabama Univ., AL (United States). Dept. of Physics, CSPAR; King' s College, Cambridge (United Kingdom)
2009-07-01
This paper provides an analysis of the combined theory of gravity-inertial-Rossby waves on a {beta}-plane in the Boussinesq approximation. The wave equation for the system is fifth order in space and time and demonstrates how gravity-inertial waves on the one hand are coupled to Rossby waves on the other through the combined effects of {beta}-, the stratification characterized by the Vaeisaelae-Brunt frequency N, the Coriolis frequency f at a given latitude, and vertical propagation which permits buoyancy modes to interact with westward propagating Rossby waves. The corresponding dispersion equation shows that the frequency of a westward propagating gravity-inertial wave is reduced by the coupling, whereas the frequency of a Rossby wave is increased. If the coupling is sufficiently strong these two modes coalesce giving rise to an instability. The instability condition translates into a curve of critical latitude {theta}{sub c} versus effective equatorial rotational Mach number M, with the region below this curve exhibiting instability. ''Supersonic'' fast rotators are unstable in a narrow band of latitudes around the equator. For example {theta}{sub c}{proportional_to}12 for Jupiter. On the other hand slow ''subsonic'' rotators (e.g. Mercury, Venus and the Sun's Corona) are unstable at all latitudes except very close to the poles where the {beta}- effect vanishes. ''Transonic'' rotators, such as the Earth and Mars, exhibit instability within latitudes of 34 and 39 , respectively, around the Equator. Similar results pertain to Oceans. In the case of an Earth's Ocean of depth 4km say, purely westward propagating waves are unstable up to 26 about the Equator. The nonlinear evolution of this instability which feeds off rotational energy and gravitational buoyancy may play an important role in atmospheric dynamics. (orig.)
Instability of coupled gravity-inertial-Rossby waves on a β-plane in solar system atmospheres
Directory of Open Access Journals (Sweden)
J. F. McKenzie
2009-11-01
Full Text Available This paper provides an analysis of the combined theory of gravity-inertial-Rossby waves on a β-plane in the Boussinesq approximation. The wave equation for the system is fifth order in space and time and demonstrates how gravity-inertial waves on the one hand are coupled to Rossby waves on the other through the combined effects of β, the stratification characterized by the Väisälä-Brunt frequency N, the Coriolis frequency f at a given latitude, and vertical propagation which permits buoyancy modes to interact with westward propagating Rossby waves. The corresponding dispersion equation shows that the frequency of a westward propagating gravity-inertial wave is reduced by the coupling, whereas the frequency of a Rossby wave is increased. If the coupling is sufficiently strong these two modes coalesce giving rise to an instability. The instability condition translates into a curve of critical latitude Θc versus effective equatorial rotational Mach number M, with the region below this curve exhibiting instability. "Supersonic" fast rotators are unstable in a narrow band of latitudes around the equator. For example Θc~12° for Jupiter. On the other hand slow "subsonic" rotators (e.g. Mercury, Venus and the Sun's Corona are unstable at all latitudes except very close to the poles where the β effect vanishes. "Transonic" rotators, such as the Earth and Mars, exhibit instability within latitudes of 34° and 39°, respectively, around the Equator. Similar results pertain to Oceans. In the case of an Earth's Ocean of depth 4km say, purely westward propagating waves are unstable up to 26° about the Equator. The nonlinear evolution of this instability which feeds off rotational energy and gravitational buoyancy may play an important role in atmospheric dynamics.
Autoresonant control of drift waves
DEFF Research Database (Denmark)
Shagalov, A.G.; Rasmussen, Jens Juul; Naulin, Volker
2017-01-01
The control of nonlinear drift waves in a magnetized plasmas column has been investigated. The studies are based on the Hasegawa–Mima model, which is solved on a disk domain with radial inhomogeneity of the plasma density. The system is forced by a rotating potential with varying frequency defined...... on the boundary. To excite and control the waves we apply the autoresonant effect, taking place when the amplitude of the forcing exceeds a threshold value and the waves are phase-locked with the forcing. We demonstrate that the autoresonant approach is applicable for excitation of a range of steady nonlinear...... waves of the lowest azimuthal mode numbers and for controlling their amplitudes and phases. We also demonstrate the excitation of zonal flows (m = 0 modes), which are controlled via the forced modes....
Assimilation of Wave Imaging Radar Observations for Real-time Wave-by-Wave Forecasting
Energy Technology Data Exchange (ETDEWEB)
Simpson, Alexandra [Oregon State Univ., Corvallis, OR (United States); Haller, Merrick [Oregon State Univ., Corvallis, OR (United States). School of Civil & Construction Engineering; Walker, David [SRI International, Menlo Park, CA (United States); Lynett, Pat [Univ. of Southern California, Los Angeles, CA (United States)
2017-08-29
This project addressed Topic 3: “Wave Measurement Instrumentation for Feed Forward Controls” under the FOA number DE-FOA-0000971. The overall goal of the program was to develop a phase-resolving wave forecasting technique for application to the active control of Wave Energy Conversion (WEC) devices. We have developed an approach that couples a wave imaging marine radar with a phase-resolving linear wave model for real-time wave field reconstruction and forward propagation of the wave field in space and time. The scope of the project was to develop and assess the performance of this novel forecasting system. Specific project goals were as follows: Develop and verify a fast, GPU-based (Graphical Processing Unit) wave propagation model suitable for phase-resolved computation of nearshore wave transformation over variable bathymetry; Compare the accuracy and speed of performance of the wave model against a deep water model in their ability to predict wave field transformation in the intermediate water depths (50 to 70 m) typical of planned WEC sites; Develop and implement a variational assimilation algorithm that can ingest wave imaging radar observations and estimate the time-varying wave conditions offshore of the domain of interest such that the observed wave field is best reconstructed throughout the domain and then use this to produce model forecasts for a given WEC location; Collect wave-resolving marine radar data, along with relevant in situ wave data, at a suitable wave energy test site, apply the algorithm to the field data, assess performance, and identify any necessary improvements; and Develop a production cost estimate that addresses the affordability of the wave forecasting technology and include in the Final Report. The developed forecasting algorithm (“Wavecast”) was evaluated for both speed and accuracy against a substantial synthetic dataset. Early in the project, performance tests definitively demonstrated that the system was capable of
Gravity Waves Near 300 km Over the Polar Caps
Johnson, F. S.; Hanson, W. B.; Hodges, R. R.; Coley, W. R.; Carignan, G. R.; Spencer, N. W.
1995-01-01
Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.
Heale, C. J.; Snively, J. B.
2014-12-01
Short-period (~5-15 minute), small-scale (10s of km) gravity waves propagating through the middle atmosphere will encounter and interact with other atmospheric waves and flows, which can vary horizontally, vertically, and temporally across a wide range of scales. Simulations of gravity wave impacts over global scales generally consider vertical propagation and atmospheric variations, and neglect small scale wave reflection and interactions between waves of different scales and the time dependent background atmosphere [e.g., Fritts and Alexander, Rev. Geo., 41, 1, 2003, and references cited therein]. Short period gravity waves , which are often subject to reflection, nevertheless carry significant momentum through the atmosphere [Hines, 1997, J. Atmos. Sol. Terr. Phys., 59]. Prior studies have investigated gravity wave propagation through horizontally sheared winds [e.g., Basovich and Tsimring, J. Fluid. Mech., 142, 1984], or in altitude and time varying backgrounds [e.g., Broutman and Young, J. Fluid. Mech., 166, 1986]. Senf and Achatz [JGR, 116, D24, 2011, and references cited therein] have also considered propagation through vertically, horizontally, and temporally varying background winds, finding significant reduction of dissipation by critical levels. We here use a combination of 2D numerical simulations and ray-tracing to study the effects of medium scale background wave wind fields on the upward propagation of small-scale, short-period waves. In particular, we consider cases where the short-period waves would be classically reflected or ducted in static realistic background temperature and wind structures. Results suggest an important role for medium-scale temporal and spatial atmospheric variability in reducing the strength of reflections and facilitating the upward propagation of small-scale waves.
Total dominator chromatic number of a graph
Directory of Open Access Journals (Sweden)
Adel P. Kazemi
2015-06-01
Full Text Available Given a graph $G$, the total dominator coloring problem seeks a proper coloring of $G$ with the additional property that every vertex in the graph is adjacent to all vertices of a color class. We seek to minimize the number of color classes. We initiate to study this problem on several classes of graphs, as well as finding general bounds and characterizations. We also compare the total dominator chromatic number of a graph with the chromatic number and the total domination number of it.
Convectively generated stratospheric gravity waves - The role of mean wind shear
Holton, J. R.; Durran, D.
1993-01-01
A two-dimensional numerical simulation of mid-latitude squall lines is used to study the properties of storm-induced stratospheric gravity waves. Owing to the tendency for convective cells to form at the forward edge of a squall line, and then propagate toward the rear, the simulated storms preferentially generate gravity waves that propagate toward the rear of the storm. This anisotropy in gravity wave generation leads to a net vertical transfer of momentum into the stratosphere. Cases with and without stratospheric mean wind shear are compared. In the latter case Doppler shifting of the waves to lower frequencies leads to wave breaking and enhanced wave - mean-flow interaction.
Radiative Fluid Flow Between Fixed Vertical Plates With Suction ...
African Journals Online (AJOL)
Radiating MHD free convective slip flow with mass transfer and chemical reaction is presented. The governing particles are solved by perturbation method. The temperature, velocity and concentration profiles are presented graphically. The effects of magnetic, Prandtl, Schmidt, radiation, chemical, wave numbers are ...
Efficient Wave Energy Amplification with Wave Reflectors
DEFF Research Database (Denmark)
Kramer, Morten Mejlhede; Frigaard, Peter Bak
2002-01-01
Wave Energy Converters (WEC's) extract wave energy from a limited area, often a single point or line even though the wave energy is generally spread out along the wave crest. By the use of wave reflectors (reflecting walls) the wave energy is effectively focused and increased to approximately 130......-140%. In the paper a procedure for calculating the efficiency and optimizing the geometry of wave reflectors are described, this by use of a 3D boundary element method. The calculations are verified by laboratory experiments and a very good agreement is found. The paper gives estimates of possible power benifit...... for different geometries of the wave reflectors and optimal geometrical design parameters are specified. On this basis inventors of WEC's can evaluate whether a specific WEC possible could benefit from wave reflectors....
[The hyoid bone and vertical dimension].
Doual, A; Léger, J L; Doual, J M; Hadjiat, F
2003-09-01
characteristics. Its maturation and its ossification occur slowly and late even though it migrates much more rapidly to a vertical position than does the bulk of the cervical complex. True articulations between the body and the horns of the hyoid bone persist for a very long time; and so the junction between the small horns doesn't fully calcify until about the age of 50; and, in spite of its appearance, the hyoid bone is extremely supple, a quality that allows it to make substantial contributions to functional activity. If the hyoid bone itself scarcely moves during normal respiration, modern research attributes an increasing role to it in the maintenance of the equilibrium of the pharyngeal column. It seems to be called upon to respond to a number of demands that it manages to satisfy as it helps to maintain the permeability of the pharyngeal column and thus make respiration possible. In so doing, the hyoid bone adjusts its positioning, and, perhaps most important, its orientation to the physiological requirements imposed by pharyngeal obstruction and mouth breathing. Intimately connected to the larynx, the hyoid bone plays a part in phonation that has long been recognized. Recent studies now also show that the contribution the hyoid bone makes to respiratory equilibrium is far more important than its small size would suggest.
Separate P‐ and SV‐wave equations for VTI media
Pestana, Reynam C.
2011-01-01
In isotropic media we use the scalar acoustic wave equation to perform reverse time migration RTM of the recorded pressure wavefleld data. In anisotropic media P- and SV-waves are coupled and the elastic wave equation should be used for RTM. However, an acoustic anisotropic wave equation is often used instead. This results in significant shear wave energy in both modeling and RTM. To avoid this undesired SV-wave energy, we propose a different approach to separate P- and SV-wave components for vertical transversely isotropic VTI media. We derive independent pseudo-differential wave equations for each mode. The derived equations for P- and SV-waves are stable and reduce to the isotropic case. The equations presented here can be effectively used to model and migrate seismic data in VTI media where ε - δ is small. The SV-wave equation we develop is now well-posed and triplications in the SV wavefront are removed resulting in stable wave propagation. We show modeling and RTM results using the derived pure P-wave mode in complex VTI media and use the rapid expansion method REM to propagate the waveflelds in time. © 2011 Society of Exploration Geophysicists.
Pulsejet engine dynamics in vertical motion using momentum conservation
Cheche, Tiberius O.
2017-01-01
The momentum conservation law is applied to analyse the dynamics of pulsejet engine in vertical motion in a uniform gravitational field in the absence of friction. The model predicts existence of a terminal speed given frequency of the short pulses. The conditions that the engine does not return to the starting position are identified. The number of short periodic pulses after which the engine returns to the starting position is found to be independent of the exhaust velocity and gravitationa...
The Titan -1:0 Nodal Bending Wave in Saturn's Ring C.
Rosen, P A; Lissauer, J J
1988-08-05
The most prominent oscillatory feature observed in the Voyager 1 radio occultation of Saturn's rings is identified as a one-armed spiral bending wave excited by Titan's -1:0 nodal inner vertical resonance. Ring partides in a bending wave move in coherently inclined orbits, warping the local mean plane of the rings. The Titan -1:0 wave is the only known bending wave that propagates outward, away from Saturn, and the only spiral wave yet observed in which the wave pattern rotates opposite to the orbital direction of the ring particles. It is also the first bending wave identified in ring C. Modeling the observed feature with existing bending wave theory gives a surface mass density of approximately 0.4 g/cm(2) outside the wave region and a local ring thickness of [unknown]5 meters, and suggests that surface mass density is not constant in the wave region.
Image processing to optimize wave energy converters
Bailey, Kyle Marc-Anthony
The world is turning to renewable energies as a means of ensuring the planet's future and well-being. There have been a few attempts in the past to utilize wave power as a means of generating electricity through the use of Wave Energy Converters (WEC), but only recently are they becoming a focal point in the renewable energy field. Over the past few years there has been a global drive to advance the efficiency of WEC. Placing a mechanical device either onshore or offshore that captures the energy within ocean surface waves to drive a mechanical device is how wave power is produced. This paper seeks to provide a novel and innovative way to estimate ocean wave frequency through the use of image processing. This will be achieved by applying a complex modulated lapped orthogonal transform filter bank to satellite images of ocean waves. The complex modulated lapped orthogonal transform filterbank provides an equal subband decomposition of the Nyquist bounded discrete time Fourier Transform spectrum. The maximum energy of the 2D complex modulated lapped transform subband is used to determine the horizontal and vertical frequency, which subsequently can be used to determine the wave frequency in the direction of the WEC by a simple trigonometric scaling. The robustness of the proposed method is provided by the applications to simulated and real satellite images where the frequency is known.
Laboratory modelling of resonant wave-current interaction in the vicinity wind farm masts
Gunnoo, Hans; Abcha, Nizar; Garcia-Hermosa, Maria-Isabel; Ezersky, Alexander
2015-04-01
In the nearest future, by 2020, about 4% of electricity in Europe will be supplied by sea stations operating from renewable sources: ocean thermal energy, wave and tidal energy, wind farms. By now the wind stations located in the coastal zone, provide the most part of electricity in different European countries. Meanwhile, effects of wind farms on the environment are not sufficiently studied. We report results of laboratory simulations aimed at investigation of hydrodynamic fields arising in the vicinity of wind farm masts under the action of currents and surface waves. The main attention is paid to modeling the resonance effects when the amplitude of velocity pulsations in the vicinity of the masts under the joint action of currents and harmonic waves demonstrate significant growth. This resonance can lead to an increase in Reynolds stress on the bottom, intensification of sediment transport and sound generation. The experiments are performed in the 17 meters hydrodynamical channel of laboratory Morphodynamique Continentale et Côtière UMR CNRS 6143. Mast are modeled by vertical cylinder placed in a steady flow. Behind the cylinder turbulent Karman vortex street occurs. Results are obtained in interval of Reynolds numbers Re=103 - 104(Re=Ud/v, where U is the velocity of the flow, d is diameter of the cylinder, ν is cinematic viscosity). Harmonic surface waves of small amplitude propagating upstream are excited by computer controlled wave maker. In the absence of surface waves, turbulent Karman street with averaged frequency f is observed. It is revealed experimentally that harmonic surface waves with a frequencies closed to 2f can synchronize vortex shedding and increase the amplitude of velocity fluctuations in the wake of the cylinder. Map of regimes is found on the parameter plane amplitude of the surface wave - wave frequency. In order to distinguish the synchronization regimes, we defined phase of oscillations using the Hilbert transform technique. We
Alvarez, G.; Estrada, C. A.
2000-12-01
A transient two-dimensional computational model of combined natural convection, conduction, and radiation in a cavity with an aspect ratio of one, containing air as a laminar and non-participating fluid, is presented. The cavity has two opaque adiabatic horizontal walls, one opaque isothermal vertical wall, and an opposite semitransparent wall, which consists of a 6-mm glass sheet with a solar control coating of SnS-CuxS facing the cavity. The semitransparent wall also exchanges heat by convection and radiation from its external surface to the surroundings and allows solar radiation pass through into the interior of the cavity. The momentum and energy equations in the transient state were solved by finite differences using the alternating direction implicit (ADI) technique. The transient conduction equation and the radiative energy flux boundary conditions are coupled to these equations. The results in this paper are limited to the following conditions: 104Gr106, an isothermal vertical cold wall of 21°C, outside air temperatures in the range 30°CT040°C and incident solar radiation of AM2 (750 W m-2) normal to the semitransparent wall. The model allows calculation of the redistribution of the absorbed component of solar radiation to the inside and outside of the cavity. The influences of the time step and mesh size were considered. Using arguments of energy balance in the cavity, it was found that the percentage difference was less than 4 per cent, showing a possible total numerical error less than this number. For Gr=106 a wave appeared in the upper side of the cavity, suggesting the influence of the boundary walls over the air flow inside the cavity. A Nusselt number correlation as a function of the Rayleigh number is presented. Copyright
Diagnosing ocean vertical velocities off New Caledonia from a SPRAY glider
Fuda, Jean-Luc; Marin, Frédéric; Durand, Fabien; Terre, Thierry
2013-04-01
A SPRAY glider has been operated in the Coral Sea (South-Western tropical Pacific ocean) since 2011, with the primary goal of monitoring the boundary currents and jets. In this presentation, we will describe how oceanic vertical velocities can be estimated from SPRAY glider measurements, with application to the observation of internal waves off New Caledonia in May-June 2012. Pressure measurements by the glider allow estimating the vertical velocities of the glider (relative to ocean bottom) at each time. These vertical velocities are the sum of the vertical velocities of the glider relative to the water body (governed by the laws of motion of the glider) and of the oceanic vertical velocities (due to ocean internal dynamics). If we solve the laws of motion of the glider (via an adequate flight model), we can thus retrieve oceanic vertical velocities. On account of their small magnitude, the retrieval of ocean vertical velocities would be tricky - if not impossible - through other conventional instruments such as ADCPs. Following a couple of similar previous studies on the SLOCUM and SEAGLIDER gliders, we describe a simplified flight model for the SPRAY glider. This model has three parameters that only depend on the characteristics of the glider: the compressibility and thermal expansion coefficients (that are constant) and the drag coefficient (that is allowed to change dive after dive, because of potential fouling of the hull). We estimate these parameters under the assumption that the absolute vertical water velocity average to zero over a long enough spatio-temporal window (typically: a profile or a group of profiles). Unlike previous studies, our flight model takes into account the vehicle roll to assess its impact on the flight model and oceanic vertical velocity retrieval. We apply this approach to a 40-day/250 dives/800km mission performed in May-June 2012 along 167°E south of New Caledonia. Dramatic water vertical velocities variations (up to 3-4 cm
Quasiperpendicular high Mach number Shocks
Sulaiman, A H; Dougherty, M K; Burgess, D; Fujimoto, M; Hospodarsky, G B
2015-01-01
Shock waves exist throughout the universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasi-perpendicular shocks across two orders of magnitude in Alfven Mach number (MA) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted timescale of ~0.3 {\\tau}c, where {\\tau}c is the ion gyroperio...
DEFF Research Database (Denmark)
Borg, Michael; Collu, M.
2015-01-01
The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency......-domain characteristics of floating vertical axis wind turbine aerodynamic loads. The impact of platform induced motion on aerodynamic loads is discussed in detail, with results indicating an increase in aerodynamic loads of several orders of magnitude over the range of frequencies usually containing significant wave...... energy. The subsequent impacts of these observations on system component design are elaborated. (C) 2015 Elsevier Ltd. All rights reserved....
Spin wave Feynman diagram vertex computation package
Price, Alexander; Javernick, Philip; Datta, Trinanjan
Spin wave theory is a well-established theoretical technique that can correctly predict the physical behavior of ordered magnetic states. However, computing the effects of an interacting spin wave theory incorporating magnons involve a laborious by hand derivation of Feynman diagram vertices. The process is tedious and time consuming. Hence, to improve productivity and have another means to check the analytical calculations, we have devised a Feynman Diagram Vertex Computation package. In this talk, we will describe our research group's effort to implement a Mathematica based symbolic Feynman diagram vertex computation package that computes spin wave vertices. Utilizing the non-commutative algebra package NCAlgebra as an add-on to Mathematica, symbolic expressions for the Feynman diagram vertices of a Heisenberg quantum antiferromagnet are obtained. Our existing code reproduces the well-known expressions of a nearest neighbor square lattice Heisenberg model. We also discuss the case of a triangular lattice Heisenberg model where non collinear terms contribute to the vertex interactions.
Wave Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flows
Zadrazil, Ivan; Hewitt, Geoff; Matar, Omar; Markides, Christos
2012-11-01
A downwards flow of gas in the core of a vertical pipe, and of liquid in the annulus between the pipe wall and the gas phase is referred to as a ``downwards annular flow'' (DAF). DAFs are conventionally described in terms of short-lived, small-amplitude ``ripples,'' and large-amplitude, high-speed ``disturbances.'' We use a combination of Laser Induced Fluorescence (LIF), Particle Image and Tracking Velocimetry (PIV, PTV) to study DAFs. We demonstrate through these techniques that the liquid films become progressively more complex with increasing liquid Reynolds number (ReL), while a similar increase of complexity is observed for increasing gas Reynolds number (ReG). Disturbance waves are observed for low and high ReL, and ripples for intermediate ReL. Additionally, a high degree of rolling breakdown of disturbance waves is observed in falling films at the highest ReL, which is a source of bubble entrainment into the film body. Our results will comprise: (i) statistical data on film thickness, and (ii) wave frequency, velocity, wavelength. In addition, a qualitative (e.g. re-circulation zones) and quantitative (e.g. mean/rms velocity profiles) velocity characterisation of the film flows will be presented.
Pochanin, Gennadiy P.; Poyedinchuk, Anatoliy Y.; Varianytsia-Roshchupkina, Liudmyla A.; Pochanina, Iryna Ye.
2016-04-01
Results of this research are intended to use at GPR investigations of layered media (for example, at roads' inspection) for the processing of collected data and reconstruction of dependence of permittivity on the depth. Recently, an antenna system with a vertical differential configuration of receiving module (Patent UA81652) for GPR was suggested and developed The main advantage of the differential antennas in comparison with bistatic antennas is a high electromagnetic decoupling between the transmitting and receiving modules. The new vertical differential configuration has an additional advantage because it allows collecting GPR data reflected by layered media without any losses of information about these layers [1] and, potentially, it is a more accurate instrument for the layers thickness measurements [2]. The developed antenna system is tested in practice with the GPR at asphalt thickness measurements [3] and shown an accuracy which is better than 0.5 cm. Since this antenna system is good for sounding from above the surface (air coupled technique), the mobile laboratory was equipped with the developed GPR [3]. In order to process big set of GPR data that collected during probing at long routes of the roads, for the data processing it was tested new algorithm of the inverse problem solution. It uses a fast algorithm for calculation of electromagnetic wave diffraction by non-uniform anisotropic layers [4]. The algorithm is based on constructing a special case solution to the Riccati equation for the Cauchy problem and enables a qualitative description of the wave diffraction by the electromagnetic structure of the type within a unitary framework. At this stage as initial data we used synthetic GPR data that were obtained as results of the FDTD simulation of the problem of UWB electromagnetic impulse diffraction on layered media. Differential and bistatic antenna configurations were tested at several different profiles of permittivity. Meanings of permittivity of
Simplified calculation methods for all-vertical-piled wharf in offshore deep water
Wang, Yuan-zhan; He, Lin-lin
2017-04-01
All-vertical-piled wharf is a kind of high-piled wharf, but it is extremely different from the traditional ones in some aspects, such as the structural property, bearing characteristics, failure mechanism, and static or dynamic calculation methods. In this paper, the finite element method (FEM) and theoretical analysis method are combined to analyze the structural property, bearing behavior and failure mode of the all-vertical-piled wharf in offshore deep water, and to establish simplified calculation methods determining the horizontal static ultimate bearing capacity and the dynamic response for the all-vertical-piled wharf. Firstly, the bearing capability and failure mechanism for all-vertical-piled wharf are studied by use of FEM, and the failure criterion is put forward for all-vertical-piled wharf based on the `plastic hinge'. According to the failure criterion and P-Y curve method, the simplified calculation method of the horizontal static ultimate bearing capacity for all-vertical-piled wharf is proposed, and it is verified that the simplified method is reasonable by comparison with the FEM. Secondly, the displacement dynamic magnification factor for the all-vertical-piled wharf under wave cyclic loads and ship impact loads is calculated by the FEM and the theory formula based on the single degree of freedom (SDOF) system. The results obtained by the two methods are in good agreement with each other, and the simplified calculation method of the displacement dynamic magnification factor for all-vertical-piled wharf under dynamic loads is proposed. Then the simplified calculation method determining the dynamic response for the all-vertical-piled wharf is proposed in combination with P-Y curve method. That is, the dynamic response of the structure can be obtained through the static calculation results of P-Y curve method multiplied by the displacement dynamic magnification factor. The feasibility of the simplified dynamic response method is verified by
Directory of Open Access Journals (Sweden)
Tatiana Yu. Tveretinova
2015-09-01
Full Text Available In the Earth's lithosphere, wavy alternation of positive and negative heterochronous structures is revealed; such structures are variable in ranks and separated by vergence zones of fractures and folds. In the vertical profile of the lithosphere, alternating are layers characterized by relatively plastic or fragile rheological properties and distinguished by different states of stress. During the Earth’s evolution, epochs of compression and extension are cyclically repeated, including planetary-scale phenomena which are manifested by fluctuating changes of the planet’s volume. Migration of geological and geophysical (geodynamic processes takes place at the Earth's surface and in its interior. The concept of the wave structure and evolution of the Earth's lithosphere provides explanations to the abovementioned regularities. Wavy nature of tectonic structures of the lithosphere, the cyclic recurrence of migration and geological processes in space and time can be described in terms of the multiple-order wave geodynamics of the Earth's lithosphere that refers to periodical variations of the state of stress. Effects of structure-forming tectonic forces are determined by «interference» of tangential and radial stresses of the Earth. The tangential stresses, which occur primarily due to the rotational regime of the planet, cause transformations of the Earth’s shape, redistributions of its substance in depths, the westward drift of the rock mass in its upper levels, and changes of structural deformation plans. The radial stresses, which are largely impacted by gravity, determine the gravitational differentiation of the substance, vertical flattening and sub-horizontal flow of the rock masses, and associated fold-rupture deformation. Under the uniform momentum geodynamic concept proposed by [Vikulin, Tveritinova, 2004, 2005, 2007, 2008], it is possible to provide consistent descriptions of seismic and volcanic, tectonic and geological processes
Directory of Open Access Journals (Sweden)
Tatiana Yu. Tveretinova
2010-01-01
Full Text Available In the Earth's lithosphere, wavy alternation of positive and negative heterochronous structures is revealed; such structures are variable in ranks and separated by vergence zones of fractures and folds. In the vertical profile of the lithosphere, alternating are layers characterized by relatively plastic or fragile rheological properties and distinguished by different states of stress. During the Earth’s evolution, epochs of compression and extension are cyclically repeated, including planetary-scale phenomena which are manifested by fluctuating changes of the planet’s volume. Migration of geological and geophysical (geodynamic processes takes place at the Earth's surface and in its interior. The concept of the wave structure and evolution of the Earth's lithosphere provides explanations to the abovementioned regularities. Wavy nature of tectonic structures of the lithosphere, the cyclic recurrence of migration and geological processes in space and time can be described in terms of the multiple-order wave geodynamics of the Earth's lithosphere that refers to periodical variations of the state of stress. Effects of structure-forming tectonic forces are determined by «interference» of tangential and radial stresses of the Earth. The tangential stresses, which occur primarily due to the rotational regime of the planet, cause transformations of the Earth’s shape, redistributions of its substance in depths, the westward drift of the rock mass in its upper levels, and changes of structural deformation plans. The radial stresses, which are largely impacted by gravity, determine the gravitational differentiation of the substance, vertical flattening and sub-horizontal flow of the rock masses, and associated fold-rupture deformation. Under the uniform momentum geodynamic concept proposed by [Vikulin, Tveritinova, 2004, 2005, 2007, 2008], it is possible to provide consistent descriptions of seismic and volcanic, tectonic and geological processes
Surface roughness and breaking wave properties retrieved from polarimetric microwave radar
Hwang, P.A.; Fois, F.
2015-01-01
Ocean surface roughness and wave breaking are the two main contributors of radar backscattering from the ocean surface. The relative weightings of the two contributions vary with the microwave polarization: the VV (vertical transmit vertical receive) is dominated by the Bragg resonance scattering
Molde, Trevor
1973-01-01
Outlines the discovery and nature of ultraviolet light, discusses some applications for these wavelengths, and describes a number of experiments with ultraviolet radiation suitable for secondary school science classes. (JR)
Vergence responses to vertical binocular disparity during lexical identification.
Nikolova, M; Jainta, S; Blythe, H I; Jones, M O; Liversedge, S P
2015-01-01
Humans typically make use of both eyes during reading, which necessitates precise binocular coordination in order to achieve a unified perceptual representation of written text. A number of studies have explored the magnitude and effects of naturally occurring and induced horizontal fixation disparity during reading and non-reading tasks. However, the literature concerning the processing of disparities in different dimensions, particularly in the context of reading, is considerably limited. We therefore investigated vertical vergence in response to stereoscopically presented linguistic stimuli with varying levels of vertical offset. A lexical decision task was used to explore the ability of participants to fuse binocular image disparity in the vertical direction during word identification. Additionally, a lexical frequency manipulation explored the potential interplay between visual fusion processes and linguistic processes. Results indicated that no significant motor fusional responses were made in the vertical dimension (all p-values>.11), though that did not hinder successful lexical identification. In contrast, horizontal vergence movements were consistently observed on all fixations in the absence of a horizontal disparity manipulation. These findings add to the growing understanding of binocularity and its role in written language processing, and fit neatly with previous literature regarding binocular coordination in non-reading tasks. Copyright © 2014 Elsevier Ltd. All rights reserved.
Measurements of fluid transport by controllable vertical migrations of plankton
Houghton, Isabel A.; Dabiri, John O.
2016-11-01
Diel vertical migration of zooplankton has been proposed to be a significant contributor to local and possibly large-scale fluid transport in the ocean. However, studies of this problem to date have been limited to order-of-magnitude estimates based on first principles and a small number of field observations. In this work, we leverage the phototactic behavior of zooplankton to stimulate controllable vertical migrations in the laboratory and to study the associated fluid transport and mixing. Building upon a previous prototype system, a laser guidance system induces vertical swimming of brine shrimp (Artemia salina) in a 2.1 meter tall, density-stratified water tank. The animal swimming speed and spacing during the controlled vertical migration is characterized with video analysis. A schlieren imaging system is utilized to visualize density perturbations to a stable stratification for quantification of fluid displacement length scales and restratification timescales. These experiments can add to our understanding of the dynamics of active particles in stratified flows. NSF and US-Israel Binational Science Foundation.
Ansari, Istafaul Haque; Rivas, Nicolas; Alam, Meheboob
2018-01-01
We report patterns consisting of coexistence of synchronous and asynchronous states [for example, a granular gas co-existing with (i) bouncing bed, (ii) undulatory subharmonic waves, and (iii) Leidenfrost-like states] in experiments on vertically vibrated binary granular mixtures in a Hele-Shaw cell. Most experiments have been carried out with equimolar binary mixtures of glass and steel balls of same diameter by varying the total layer height (F ) for a range of shaking acceleration (Γ ). All patterns as well as the related phase diagram in the (Γ ,F ) plane have been reproduced via molecular dynamics simulations of the same system. The segregation of heavier and lighter particles along the horizontal direction is shown to be the progenitor of such phase-coexisting patterns as confirmed in both experiment and simulation. At strong shaking we uncover a partial convection state in which a pair of convection rolls is found to coexist with a Leidenfrost-like state. The crucial role of the relative number density of two species on controlling the buoyancy-driven granular convection is demonstrated. The onset of horizontal segregation can be explained in terms of an anisotropic diffusion tensor.
A comparison between the dynamics of horizontal and vertical axis offshore floating wind turbines.
Borg, M; Collu, M
2015-02-28
The need to further exploit offshore wind resources in deeper waters has led to a re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications. However, there has been little effort to systematically compare VAWTs to the more conventional horizontal axis wind turbine (HAWT). This article initiates this comparison based on prime principles, focusing on the turbine aerodynamic forces and their impact on the floating wind turbine static and dynamic responses. VAWTs generate substantially different aerodynamic forces on the support structure, in particular, a potentially lower inclining moment and a substantially higher torque than HAWTs. Considering the static stability requirements, the advantages of a lower inclining moment, a lower wind turbine mass and a lower centre of gravity are illustrated, all of which are exploitable to have a less costly support structure. Floating VAWTs experience increased motion in the frequency range surrounding the turbine [number of blades]×[rotational speed] frequency. For very large VAWTs with slower rotational speeds, this frequency range may significantly overlap with the range of wave excitation forces. Quantitative considerations are undertaken comparing the reference NREL 5 MW HAWT with the NOVA 5 MW VAWT. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
Wave Energy Dissipation of Waves Breaking on a Reef with a Steep Front Slope
DEFF Research Database (Denmark)
Jensen, M.S.; Burcharth, Hans F.; Brorsen, Michael
2005-01-01
The Transformation of waves propagating over a steep bottom slope is of great importance regarding the coastal processes in the near-shore area.This study will contribute with tools to predict the dissipated wave energy for irregular waves passing a steep submerged slope. An extensive number...... of test with regular and irregular waves breaking over a steep bottom slope have been performed in the Hydraulics & Coastal Engineering Laboratory, Aalborg University. Based on these experimental data formulae have been developed capable of predicting he transmitted wave energy over steep slopes....
Directory of Open Access Journals (Sweden)
A. A. Bidokhti
2005-12-01
Full Text Available Layered structures in the oceans have always attracted the attention of oceanographers. The formation of these structures have been attributed to phenomena such as double – diffusive convection, internal waves and turbulent modulated mixing .In this paper, the vertical structures of temperature, salinity, density and the layered structure in the middle parts of Caspian Sea have been studied. Counters of iso-quantities of these physical properties, show the existence of regular structures, which indicate that internal waves which are produced by exchanging flow between two basins, as a result of horizontal density gradients (usually from north basin to south basin may generate these layers. Froude number of this flow is about one. The length of wave of the internal waves is found to be about 200 km and the flow velocity associated with this gravity drive flow is about 0.2 m/s, the frequency of these waves is of order of inertial frequency. The normal modes of these waves have a near steady structure and can fold the inflow front from the North Caspian sea to South Caspian Sea basins, then the layered structure are formed. The thickness of these layers so formed is found to be about 10-20 m. These are in agreement with the values predicted by the model of Wong et al, (2001. In these waters density ratio is negative. Thus, double – diffusive convection does not often happen and cannot produce these layered structures.
Anisotropic wave-equation traveltime and waveform inversion
Feng, Shihang
2016-09-06
The wave-equation traveltime and waveform inversion (WTW) methodology is developed to invert for anisotropic parameters in a vertical transverse isotropic (VTI) meidum. The simultaneous inversion of anisotropic parameters v0, ε and δ is initially performed using the wave-equation traveltime inversion (WT) method. The WT tomograms are then used as starting background models for VTI full waveform inversion. Preliminary numerical tests on synthetic data demonstrate the feasibility of this method for multi-parameter inversion.
Georgi, Howard
1993-01-01
The first complete introduction to waves and wave phenomena by a renowned theorist. Covers damping, forced oscillations and resonance; normal modes; symmetries; traveling waves; signals and Fourier analysis; polarization; diffraction.
Lidar measured vertical atmospheric scattering profiles
Kunz, G.J.
1985-01-01
The vertical structure of the atmosphere, which is of invaluable interest to meteorologists, geo-physicists and environmental researchers, can be measured with LIDAR. A method has been proposed and applied to invert lidar signals from vertical soundings to height resolved scattering coefficients. In
Vertical integration from the large Hilbert space
Erler, Theodore; Konopka, Sebastian
2017-12-01
We develop an alternative description of the procedure of vertical integration based on the observation that amplitudes can be written in BRST exact form in the large Hilbert space. We relate this approach to the description of vertical integration given by Sen and Witten.
Plasmon Modes of Vertically Aligned Superlattices
DEFF Research Database (Denmark)
Filonenko, Konstantin; Duggen, Lars; Willatzen, Morten
2017-01-01
By using the Finite Element Method we visualize the modes of vertically aligned superlattice composed of gold and dielectric nanocylinders and investigate the emitter-plasmon interaction in approximation of weak coupling. We find that truncated vertically aligned superlattice can function as plas...
A vertically resolved model for phytoplankton aggregation
Indian Academy of Sciences (India)
components undergo vertical mixing, and phytoplank- ton sink. Phytoplankton growth is limited by the product of nutrient and light terms. The equations for nitrate (NO3) and ... resolved model there is an extra complication: the largest particles that sink out of ...... and biogeochemistry with satellite ocean colour data. Vertically ...
Plasmon Modes of Vertically Aligned Superlattices
DEFF Research Database (Denmark)
Filonenko, Konstantin; Duggen, Lars; Willatzen, Morten
By using the Finite Element Method we visualize the modes of vertically aligned superlattice composed of gold and dielectric nanocylinders and investigate the emitter-plasmon interaction in approximation of weak coupling. We find that truncated vertically aligned superlattice can function as plas...
DESIGN, CONSTRUCTION AND EVALUATION OF A VERTICAL ...
African Journals Online (AJOL)
Vertical plate metering device is intended to minimize seed damage during planting while improving metering efficiency and field capacity. A vertical plate maize seed planter which is adapted for gardens and small holder farmers cultivating less than two hectares has been designed, constructed and tested. The major ...
The green building envelope : Vertical greening
Ottelé, M.
2011-01-01
Planting on roofs and façades is one of the most innovative and fastest developing fields of green technologies with respect to the built environment and horticulture. This thesis is focused on vertical greening of structures and to the multi-scale benefits of vegetation. Vertical green can improve
Vertical Integration, Monopoly, and the First Amendment.
Brennan, Timothy J.
This paper addresses the relationship between the First Amendment, monopoly of transmission media, and vertical integration of transmission and content provision. A survey of some of the incentives a profit-maximizing transmission monopolist may have with respect to content is followed by a discussion of how vertical integration affects those…
Removing Wave Artifacts from Eddy Correlation Data
Neumann, Andreas; Brand, Andreas
2017-04-01
The German Wadden Sea is an extensive system of back-barrier tidal basins along the margin of the southern North Sea. Due to their high productivity and the strong retention potential of labile organic carbon high mineralization rates are expected in this system. Since the sediment bed is sandy, the oxygen fluxes across the sediment-water interface (SWI) may be enhanced by strong tidal currents as well as by wind-induced surface waves. In order to measure oxygen fluxes in-situ without disturbance of the sediment, the Eddy Correlation method (ECM) was introduced to aquatic geoscience by Berg et al. (2003). The method is based on correlating turbulent fluctuations of oxygen concentration and vertical velocity measured at high frequency above the SWI. The method integrates over spatial heterogeneities and allows the observation of total benthic oxygen fluxes in complex systems where other methods like flux chamber deployments and oxygen profile measurements in the sediment fail. Therefore, the method should also reflect effects like the enhancement of oxygen fluxes by porewater advection driven by waves and currents over sandy sediments. Unfortunately the ECM suffers from wave contamination due to stirring sensitivity of the electrodes, spatial separation between the oxygen electrode and the location of velocity measurement as well as by a tilt of the measurement setup at the deployment side. In order to correct for this wave contamination we tested the method of spectral reconstruction initially introduced by Bricker and Monismith (2007) for the determination of Reynolds-stresses in wave-affected environments. In short, this method attempts to remove the wave signal from the Power spectral densities of oxygen concentration and vertical velocity fluctuations by cutting off the wave peak in these spectra. The wave contribution to the co-spectrum between both quantities is then reconstructed by assuming that the phasing in the wave band is dominated by the waves. Based
Directory of Open Access Journals (Sweden)
Jong-In Lee
2014-01-01
Full Text Available Fringing reefs play an important role in protecting the coastal area by inducing wave breaking and wave energy dissipation. However, modeling of wave transformation and energy dissipation on this topography is still difficult due to the unique structure. In the present study, two-dimensional laboratory experiments were conducted to investigate the cross-shore variations of wave transformation, setup, and breaking phenomena over an idealized fringing reef with the 1/40 reef slope and to verify the Boussinesq model under monochromatic wave conditions. One-layer and two-layer model configurations of the Boussinesq model were used to figure out the model capability. Both models predicted well (r2>0.8 the cross-shore variation of the wave heights, crests, troughs, and setups when the nonlinearity is not too high (A0/h0<0.07 in this study. However, as the wave nonlinearity and steepness increase, the one-layer model showed problems in prediction and stability due to the error on the vertical profile of fluid velocity. The results in this study revealed that one-layer model is not suitable in the highly nonlinear wave condition over a fringing reef bathymetry. This data set can contribute to the numerical model verification.
INTERFERENCE OF COUNTERPROPAGATING SHOCK WAVES
Directory of Open Access Journals (Sweden)
P. V. Bulat
2015-03-01
Full Text Available The subject of study. We examined the interaction of counterpropagating shock waves. The necessity of counterpropagating shock waves studying occurs at designing of high Mach number modern internal compression air intakes, Ramjets with subsonic and supersonic combustion, in asymmetrical supersonic nozzles and in some other cases. In a sense, this problem is a generalization of the case of an oblique shock reflection from the wall or from the plane of symmetry. With the renewed vigor, the interest to this problem emerged at the end of the 90s. This was due to the start of the programs for flight study at hypersonic speeds. The first experiments performed with air intakes, which realized the interaction of counterpropagating shock waves have shown that the change in flow velocity is accompanied by abrupt alteration of shock-wave structure, the occurrence of nonstationary and oscillatory phenomena. With an increase of flow velocity these phenomena undesirable for aircraft structure became more marked. The reason is that there are two fundamentally different modes of interaction of counterpropagating shock waves: a four-wave regular and a five-wave irregular. The transition from one mode to another can be nonstationary abrupt or gradual, it can also be accompanied by hysteresis. Main results. Criteria for the transition from regular reflection of counterpropagating shock waves to irregular are described: the criterion of von Neumann and the stationary Mach configuration criterion. We described areas in which the transition from one reflection type to another is possible only in abrupt way, as well as areas of possible gradual transition. Intensity dependences of the reflected shock waves from the intensity of interacting counterpropagating shocks were given. Qualitative pictures of shock-wave structures arising from the interaction of counterpropagating shock waves were shown. Calculation results of the intensity of outgoing gas
Learning styles in vertically integrated teaching.
Brumpton, Kay; Kitchener, Scott; Sweet, Linda
2013-10-01
With vertical integration, registrars and medical students attend the same educational workshops. It is not known whether these learners have similar or different learning styles related to their level of education within the medical training schema. This study aims to collect information about learning styles with a view to changing teaching strategies. If a significant difference is demonstrated this will impact on required approaches to teaching. The VARK learning inventory questionnaire was administered to 36 general practice registrars and 20 medical students. The learning styles were compared as individuals and then related to their level of education within the medical training schema. Students had a greater preference for multimodal learning compared with registrars (62.5 per cent versus 33.3 per cent, respectively). More than half of the registrars preferred uni or bimodal learning modalities, compared with one-third of the medical students. The present workshop format based on visual and aural material will not match the learning needs of most learners. This small study has shown that the majority of medical students and registrars could have their learning preferences better met by the addition of written material to the workshop series. Surprisingly, a significantly larger number of medical students than registrars appeared to be broadly multimodal in their learning style, and this warrants further research. © 2013 John Wiley & Sons Ltd.
The vertical oscillations of coupled magnets
Energy Technology Data Exchange (ETDEWEB)
Li Kewei; Lin Jiahuang; Kang Zi Yang [Raffles Institution, 1 Raffles Institution Lane, Singapore 575954 (Singapore); Liang, Samuel Yee Wei [Anglo-Chinese School Independent, 121 Dover Road, Singapore 139650 (Singapore); Juan, Jeremias Wong Say, E-mail: likewei92@gmail.com [NUS High School of Mathematics and Science, 20 Clementi Avenue 1, Singapore 129957 (Singapore)
2011-07-15
The International Young Physicists' Tournament (IYPT) is a worldwide, annual competition for high school students. This paper is adapted from the winning solution to Problem 14, Magnetic Spring, as presented in the final round of the 23rd IYPT in Vienna, Austria. Two magnets were arranged on top of each other on a common axis. One was fixed, while the other could move vertically. Various parameters of interest were investigated, including the effective gravitational acceleration, the strength, size, mass and geometry of the magnets, and damping of the oscillations. Despite its simplicity, this setup yielded a number of interesting and unexpected relations. The first stage of the investigation was concerned only with the undamped oscillations of small amplitudes, and the period of small amplitude oscillations was found to be dependent only on the eighth root of important magnet properties such as its strength and mass. The second stage sought to investigate more general oscillations. A numerical model which took into account magnet size, magnet geometry and damping effects was developed to model the general oscillations. Air resistance and friction were found to be significant sources of damping, while eddy currents were negligible.
Optimization of bottom-hinged flap-type wave energy converter for a specific wave rose
Behzad, Hamed; Panahi, Roozbeh
2017-06-01
In this paper, we conducted a numerical analysis on the bottom-hinged flap-type Wave Energy Convertor (WEC). The basic model, implemented through the study using ANSYS-AQWA, has been validated by a three-dimensional physical model of a pitching vertical cylinder. Then, a systematic parametric assessment has been performed on stiffness, damping, and WEC direction against an incoming wave rose, resulting in an optimized flap-type WEC for a specific spot in the Persian Gulf. Here, stiffness is tuned to have a near-resonance condition considering the wave rose, while damping is modified to capture the highest energy for each device direction. Moreover, such sets of specifications have been checked at different directions to present the best combination of stiffness, damping, and device heading. It has been shown that for a real condition, including different wave heights, periods, and directions, it is very important to implement the methodology introduced here to guarantee device performance.
Numerical simulation of floating bodies in extreme free surface waves
Directory of Open Access Journals (Sweden)
Z. Z. Hu
2011-02-01
Full Text Available In this paper, we use the in-house Computational Fluid Dynamics (CFD flow code AMAZON-SC as a numerical wave tank (NWT to study wave loading on a wave energy converter (WEC device in heave motion. This is a surface-capturing method for two fluid flows that treats the free surface as contact surface in the density field that is captured automatically without special provision. A time-accurate artificial compressibility method and high resolution Godunov-type scheme are employed in both fluid regions (air/water. The Cartesian cut cell method can provide a boundary-fitted mesh for a complex geometry with no requirement to re-mesh globally or even locally for moving geometry, requiring only changes to cut cell data at the body contour. Extreme wave boundary conditions are prescribed in an empty NWT and compared with physical experiments prior to calculations of extreme waves acting on a floating Bobber-type device. The validation work also includes the wave force on a fixed cylinder compared with theoretical and experimental data under regular waves. Results include free surface elevations, vertical displacement of the float, induced vertical velocity and heave force for a typical Bobber geometry with a hemispherical base under extreme wave conditions.
Numerical simulation of floating bodies in extreme free surface waves
Hu, Z. Z.; Causon, D. M.; Mingham, C. G.; Qian, L.
2011-02-01
In this paper, we use the in-house Computational Fluid Dynamics (CFD) flow code AMAZON-SC as a numerical wave tank (NWT) to study wave loading on a wave energy converter (WEC) device in heave motion. This is a surface-capturing method for two fluid flows that treats the free surface as contact surface in the density field that is captured automatically without special provision. A time-accurate artificial compressibility method and high resolution Godunov-type scheme are employed in both fluid regions (air/water). The Cartesian cut cell method can provide a boundary-fitted mesh for a complex geometry with no requirement to re-mesh globally or even locally for moving geometry, requiring only changes to cut cell data at the body contour. Extreme wave boundary conditions are prescribed in an empty NWT and compared with physical experiments prior to calculations of extreme waves acting on a floating Bobber-type device. The validation work also includes the wave force on a fixed cylinder compared with theoretical and experimental data under regular waves. Results include free surface elevations, vertical displacement of the float, induced vertical velocity and heave force for a typical Bobber geometry with a hemispherical base under extreme wave conditions.
Simple waves in Hertzian chains.
McDonald, B Edward; Calvo, David
2012-06-01
The discrete system of equations for a chain consisting of a large number of spheres interacting via the Hertz force of index 3/2 in strain is examined in the very long wavelength limit, yielding an effective medium description. The resulting continuum second-order equation of motion possesses a subset of simple waves obeying a first-order equation of reduced index 5/4. These simple waves appear not to have examined before. For a given initial strain, the simple wave solution prescribes initial sphere centroid velocities. Together the initial strain and velocities are used in the second-order discrete system. Results for shock wave development compare very well between the second-order discrete system (minus physically valid oscillations) and the reduced first-order equation. A second-order simulation of colliding waves examines the ability of waves to pass through each other, with a phase advance accruing during the collision process. An arbitrary initial condition is shown to evolve toward a universal similarity solution proportional to (x/t)(4). A closed-form solution is given including the complete history of the waveform, shock location, and amplitude.
Surface-wave potential for triggering tectonic (nonvolcanic) tremor
Hill, D.P.
2010-01-01
Source processes commonly posed to explain instances of remote dynamic triggering of tectonic (nonvolcanic) tremor by surface waves include frictional failure and various modes of fluid activation. The relative potential for Love- and Rayleigh-wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike-slip faults under the Coulomb-Griffith failure criteria as a function of incidence angle is anticorrelated over the 15- to 30-km-depth range that hosts tectonic tremor. Love-wave potential is high for strike-parallel incidence on low-angle reverse faults and null for strike-normal incidence; the opposite holds for Rayleigh waves. Love-wave potential is high for both strike-parallel and strike-normal incidence on vertical, strike-slip faults and minimal for ~45?? incidence angles. The opposite holds for Rayleigh waves. This pattern is consistent with documented instances of tremor triggered by Love waves incident on the Cascadia mega-thrust and the San Andreas fault (SAF) in central California resulting from shear failure on weak faults (apparent friction, ????? 0.2). However, documented instances of tremor triggered by surface waves with strike-parallel incidence along the Nankai megathrust beneath Shikoku, Japan, is associated primarily with Rayleigh waves. This is consistent with the tremor bursts resulting from mixed-mode failure (crack opening and shear failure) facilitated by near-lithostatic ambient pore pressure, low differential stress, with a moderate friction coefficient (?? ~ 0.6) on the Nankai subduction interface. Rayleigh-wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process, except perhaps for an indirect role on the SAF in sustaining tremor into the Rayleigh-wave coda that was initially triggered by Love waves.
Early electromagnetic waves from earthquake rupturing: I. theoretical formulations
Gao, Yongxin; Chen, Xiaofei; Hu, Hengshan; Zhang, Jie
2013-03-01
Earthquake taking place in a fluid-saturated porous medium can generate electromagnetic (EM) waves because of the electrokinetic effect. These generated EM waves arrive at a distant observatory much earlier than the seismic waves because their velocities are much faster than those of the seismic waves. They may explain the early EM signals which have been detected before the detection of the seismic waves after the occurrences of earthquakes. In this study, we attempt to analyse such a kind of early EM signals induced by an earthquake because of the electrokinetic effect. The earthquake is assumed to be a fault slip and is modelled by a moment tensor point source. With Pride's equations quantifying the coupling between seismic and EM waves, we first present a real-axis integration (RAI) algorithm to calculate the seismoelectric wavefields in a layered porous formation. Although full waveforms can be calculated by such a RAI technique, individual waves cannot be easily separated from the full waveforms. The need to compute the individual waves is eminent for the purpose of investigating the early EM waves, because these EM waves are usually several orders weaker than and are masked by the EM signals accompanying the seismic waves in the full waveforms. Therefore, we further develop a branch-cut integration (BCI) algorithm, by transforming the original wavenumber integral along the real axis in the complex wavenumber plane for the RAI technique to a sum of integrals along the vertical branch cuts and the residues of the poles. For performing the integrations along the vertical branch cuts, determination of the Riemann sheets are explained and displayed. Finally, the seismoelectric wavefields are represented in forms allowing calculating individual waves.