FULLY NONLINEAR WAVE COMPUTATIONS FOR ARBITRARY FLOATING BODIES USING THE DELTA METHOD
Institute of Scientific and Technical Information of China (English)
Lee Tzung-hang
2003-01-01
Fully nonlinear water wave problems are solved using Eulerian-Lagrangian time stepping methods in conjunction with a desingularized approach to solve the mixed boundary value problem that arises at each time step. In the desingularized approach, the singularities generating the flow field are outside the fluid domain. This allows the singularity distribution to be replaced by isolated Rankine sources with the corresponding reduction in computational complexity and computer time. A moving boundary technique is applied to eliminate the reflection waves from limited computational boundaries. Examples of the use of the method in three-dimensions are given for the exciting forces acting on a modified wigley hull and Series 60 are presented. The numerical results show good agreements with those of experiments.
Tao, Xin; Zonca, Fulvio; Chen, Liu
2017-09-01
The evolution of the electron phase space structures during excitation of a triggered emission is investigated using the nonlinear δ f method. Previous studies suggested that the dynamics of phase space structures due to nonlinear wave particle interactions is critical to the excitation of triggered emissions with frequency chirping. We introduce the use of the nonlinear δ f method to simulate triggered emissions. Compared with full-f particle-in-cell method, the nonlinear δ f method significantly reduces numerical noise, therefore making the phase space structures more identifiable. Specific to the simulation of triggered emissions, the nonlinear δ f method also does not show numerical distortion of the distribution function due to reflecting particle boundary conditions. Using the nonlinear δ f method, we show that during the main portion of the chirping element, the phase space structure roughly maintains a shape so that the resonant island moves a distance in phase space that is on the same order as its width during one phase space bounce period of deeply trapped particles, supporting that the interaction is non-adiabatic. We also demonstrate the disappearance of the phase space structure near the end of the chirping. Our work suggests that the nonlinear δ f method could be very useful for the study of excitation of triggered emissions and to understand the mechanism of frequency chirping.
Electromagnetic form factors of the Delta with D-waves
Ramalho, G; Gross, Franz
2010-01-01
The electromagnetic form factors of the Delta baryon are evaluated within the framework of a covariant spectator quark model, where S and D-states are included in the $\\Delta$ wave function. We predict all the four Delta multipole form factors: the electric charge GE0, the magnetic dipole GM1, the electric quadrupole GE2 and the magnetic octupole GM3. We compare our predictions with other theoretical calculations. Our results are compatible with the available experimental data and recent lattice QCD data.
A NOTE ON DELTA-PERTURBATION EXPANSION METHOD
Institute of Scientific and Technical Information of China (English)
何吉欢
2002-01-01
The Delta-perturbation expansion method, a kind of new perturbation technique depending upon an artificial parameter Delta was studied. The study reveals that the method exits some advantages, but also exits some limitations. To overcome the limitations, the socalled linearized perturbation method proposed by HE Ji-huan can be powerfully applied.
Vetoshkin, Evgeny; Babikov, Dmitri
2007-09-28
For the first time Feshbach-type resonances important in recombination reactions are characterized using the semiclassical wave packet method. This approximation allows us to determine the energies, lifetimes, and wave functions of the resonances and also to observe a very interesting correlation between them. Most important is that this approach permits description of a quantum delta-zero-point energy effect in recombination reactions and reproduces the anomalous rates of ozone formation.
Transformation method and wave control
Chang, Zheng; Hu, Jin; Hu, Geng-Kai
2010-12-01
Transformation method provides an efficient way to control wave propagation by materials. The transformed relations for field and material during a transformation are essential to fulfill this method. We propose a systematic method to derive the transformed relations for a general physic process, the constraint conditions are obtained by considering geometrical and physical constraint during a mapping. The proposed method is applied to Navier's equation for elastodynamics, Helmholtz's equation for acoustic wave and Maxwell's equation for electromagnetic wave, the corresponding transformed relations are derived, which can be used in the framework of transformation method for wave control. We show that contrary to electromagnetic wave, the transformed relations are not uniquely determined for elastic wave and acoustic wave, so we have a freedom to choose them differently. Using the obtained transformed relations, we also provide some examples for device design, a concentrator for elastic wave, devices for illusion acoustic and illusion optics are conceived and validated by numerical simulations.
Deltas, freshwater discharge, and waves along the Young Sound, NE Greenland.
Kroon, Aart; Abermann, Jakob; Bendixen, Mette; Lund, Magnus; Sigsgaard, Charlotte; Skov, Kirstine; Hansen, Birger Ulf
2017-02-01
A wide range of delta morphologies occurs along the fringes of the Young Sound in Northeast Greenland due to spatial heterogeneity of delta regimes. In general, the delta regime is related to catchment and basin characteristics (geology, topography, drainage pattern, sediment availability, and bathymetry), fluvial discharges and associated sediment load, and processes by waves and currents. Main factors steering the Arctic fluvial discharges into the Young Sound are the snow and ice melt and precipitation in the catchment, and extreme events like glacier lake outburst floods (GLOFs). Waves are subordinate and only rework fringes of the delta plain forming sandy bars if the exposure and fetch are optimal. Spatial gradients and variability in driving forces (snow and precipitation) and catchment characteristics (amount of glacier coverage, sediment characteristics) as well as the strong and local influence of GLOFs in a specific catchment impede a simple upscaling of sediment fluxes from individual catchments toward a total sediment flux into the Young Sound.
Quantifying the Effects of Combined Waves and Tides on Deltas: An Experimental Study
Paola, C.; Baumgardner, S. E.
2015-12-01
The classical Galloway diagram captures qualitatively the dramatic effect waves and tides have on reshaping river deltas. Here we investigate these controls in a series of laboratory experiments in which the relative energetics of river, wave, and tidal forcing could be controlled and systematically varied. The delta is fed from a single source of water and low-density, sand-size sediment in one corner of a 5m x 5m basin. Experimental tides are produced by transferring water back and forth between the main experimental basin and an auxiliary holding basin. The tidal period is 60 s and a typical tidal range is 30 mm. Waves are produced using a floating, oscillating paddle placed opposite the sediment feed location. They typically have a period of 1 s and an amplitude of 10 mm. The total energy flux associated with waves and tides is controlled by varying the temporal intermittency of each process, while river energy and sediment fluxes are held steady. The experiments show a variation in delta morphology as a function of wave and tidal forcing that parallels that observed in the field: increasing wave strength redistributes sediment and flattens the shoreline; increasing tidal strength creates well defined tidal channels as well as inlets through the wave-worked shoreline. Both waves and tides reduce the mobility of the main fluvial channel. Quantitative morphologic measures of these effects vary systematically as a function of dimensionless relative wave and tidal strength. The image below shows typical experimental delta morphology associated with mixed wave-tide forcing.
Delta Shock Wave for the Suliciu Relaxation System
Directory of Open Access Journals (Sweden)
Richard De la cruz
2014-01-01
Full Text Available We study the one-dimensional Riemann problem for a hyperbolic system of three conservation laws of Temple class. This system is a simplification of a recently proposed system of five conservations laws by Bouchut and Boyaval that model viscoelastic fluids. An important issue is that the considered 3×3 system is such that every characteristic field is linearly degenerate. We show an explicit solution for the Cauchy problem with initial data in L∞. We also study the Riemann problem for this system. Under suitable generalized Rankine-Hugoniot relation and entropy condition, both existence and uniqueness of particular delta-shock type solutions are established.
Electromagnetic form factors of the Delta in a S-wave approach
Ramalho, G
2008-01-01
Without any further adjusting of parameters, a relativistic constituent quark model, successful in the description of the data for the nucleon elastic form factors and the dominant contribution to the nucleon to $\\Delta$ electromagnetic transition, is used here to predict the dominant electromagnetic form factors of the $\\Delta$ baryon. The model considered is based on a simple $\\Delta$ wave function corresponding to a quark-diquark system in an S-state. The results for E0 and M1 are consistent both with experimental results and lattice calculations. The remaining form factors M1 and E2 are negligible for small $Q^2$, as expected, given the symmetric structure considered for the $\\Delta$.
METHOD OF MAKING DELTA ZIRCONIUM HYDRIDE MONOLITHIC MODERATOR PIECES
Vetrano, J.B.
1962-01-23
A method is given for preparing large, sound bodies of delta zirconium hydride. The method includes the steps of heating a zirconium body to a temperature of not less than l000 deg C, providing a hydrogen atmosphere for the zirconium body at a pressure not greater than one atmosphere, reducing the temperature slowly to 800 deg C at such a rate that cracks do not form while maintaining the hydrogen pressure substantially constant, and cooling in an atmosphere of hydrogen. (AEC)
Near Surface Shear Wave Velocity Model of the Sacramento-San Joaquin Delta
Shuler, S.; Craig, M. S.; Hayashi, K.; Galvin, J. L.; Deqiang, C.; Jones, M. G.
2015-12-01
Multichannel analysis of surface wave measurements (MASW) and microtremor array measurements (MAM) were performed at twelve sites across the Sacramento-San Joaquin Delta to obtain high resolution shear wave velocity (VS) models. Deeper surveys were performed at four of the sites using the two station spatial autocorrelation (SPAC) method. For the MASW and MAM surveys, a 48-channel seismic system with 4.5 Hz geophones was used with a 10-lb sledgehammer and a metal plate as a source. Surveys were conducted at various locations on the crest of levees, the toe of the levees, and off of the levees. For MASW surveys, we used a record length of 2.048 s, a sample interval of 1 ms, and 1 m geophone spacing. For MAM, ambient noise was recorded for 65.536 s with a sampling interval of 4 ms and 1 m geophone spacing. VS was determined to depths of ~ 20 m using the MASW method and ~ 40 m using the MAM method. Maximum separation between stations in the two-station SPAC surveys was typically 1600 m to 1800 m, providing coherent signal with wavelengths in excess of 5 km and depth penetration of as much as 2000 m. Measured values of VS30 in the study area ranged from 97 m/s to 257 m/s, corresponding to NEHRP site classifications D and E. Comparison of our measured velocity profiles with available geotechnical logs, including soil type, SPT, and CPT, reveals the existence of a small number of characteristic horizons within the upper 40m in the Delta: levee fill material, peat, transitional silty sand, and eolian sand at depth. Sites with a peat layer at the surface exhibited extremely low values of VS. Based on soil borings, the thickness of peat layers were approximately 0 m to 8 m. The VS for the peat layers ranged from 42 m/s to 150 m/s while the eolian sand layer exhibited VS ranging from of 220 m/s to 370 m/s. Soft near surface soils present in the region pose an increased earthquake hazard risk due to the potential for high ground accelerations.
A new identification method for energetic ion {delta}E-E telescopes
Energy Technology Data Exchange (ETDEWEB)
Martin, Cesar [Departamento de Fisica, Universidad de Alcala, 28871 Alcala de Henares, Madrid (Spain); Institut fuer Experimentelle und Angewandte Physik, Christian-Albrechts, Universitaet zu Kiel, 24118 Kiel (Germany); Bronchalo, Enrique [Departamento de Fisica, Universidad de Alcala, 28871 Alcala de Henares, Madrid (Spain); Departamento de Fisica y Arquitectura de Computadores, Universidad Miguel Hernandez, Avda. Universidad s/n, 03202 Elche, Alicante (Spain)], E-mail: ebronchalo@umh.es; Medina, Jose [Departamento de Fisica, Universidad de Alcala, 28871 Alcala de Henares, Madrid (Spain)
2007-11-21
A new ion identification method for {delta}E-E telescopes is presented. The method works by counting data points under {delta}E(E) curves on {delta}E-E diagrams. These curves are obtained by simulating the telescope response to a flux of energetic ions. The method is checked against three published methods applied to several experimental data sets.
Interactions of Delta Shock Waves for Zero-Pressure Gas Dynamics with Energy Conservation Law
Directory of Open Access Journals (Sweden)
Wei Cai
2016-01-01
Full Text Available We study the interactions of delta shock waves and vacuum states for the system of conservation laws of mass, momentum, and energy in zero-pressure gas dynamics. The Riemann problems with initial data of three piecewise constant states are solved case by case, and four different configurations of Riemann solutions are constructed. Furthermore, the numerical simulations completely coinciding with theoretical analysis are shown.
An accurate {delta}f method for neoclassical transport calculation
Energy Technology Data Exchange (ETDEWEB)
Wang, W.X.; Nakajima, N.; Murakami, S.; Okamoto, M. [National Inst. for Fusion Science, Toki, Gifu (Japan)
1999-03-01
A {delta}f method, solving drift kinetic equation, for neoclassical transport calculation is presented in detail. It is demonstrated that valid results essentially rely on the correct evaluation of marker density g in weight calculation. A general and accurate weighting scheme is developed without using some assumed g in weight equation for advancing particle weights, unlike the previous schemes. This scheme employs an additional weight function to directly solve g from its kinetic equation using the idea of {delta}f method. Therefore the severe constraint that the real marker distribution must be consistent with the initially assumed g during a simulation is relaxed. An improved like-particle collision scheme is presented. By performing compensation for momentum, energy and particle losses arising from numerical errors, the conservations of all the three quantities are greatly improved during collisions. Ion neoclassical transport due to self-collisions is examined under finite banana case as well as zero banana limit. A solution with zero particle and zero energy flux (in case of no temperature gradient) over whole poloidal section is obtained. With the improvement in both like-particle collision scheme and weighting scheme, the {delta}f simulation shows a significantly upgraded performance for neoclassical transport study. (author)
Fletcher, Jon B.; Erdem, Jemile
2017-06-01
Rayleigh wave group velocities obtained from ambient noise tomography are inverted for an upper crustal model of the Central Valley, California, centered on the Sacramento/San Joaquin Delta. Two methods were tried; the first uses SURF96, a least squares routine. It provides a good fit to the data, but convergence is dependent on the starting model. The second uses a genetic algorithm, whose starting model is random. This method was tried at several nodes in the model and compared to the output from SURF96. The genetic code is run five times and the variance of the output of all five models can be used to obtain an estimate of error. SURF96 produces a more regular solution mostly because it is typically run with a smoothing constraint. Models from the genetic code are generally consistent with the SURF96 code sometimes producing lower velocities at depth. The full model, calculated using SURF96, employed a 2-pass strategy, which used a variable damping scheme in the first pass. The resulting model shows low velocities near the surface in the Central Valley with a broad asymmetrical sedimentary basin located close to the western edge of the Central Valley near 122°W longitude. At shallow depths, the Rio Vista Basin is found nestled between the Pittsburgh/Kirby Hills and Midland faults, but a significant basin also seems to exist to the west of the Kirby Hills fault. There are other possible correlations between fast and slow velocities in the Central Valley and geologic features such as the Stockton Arch, oil or gas producing regions and the fault-controlled western boundary of the Central Valley.
Separation of Waves by Interpolation Method
Institute of Scientific and Technical Information of China (English)
孙鹤泉; 王永学
2003-01-01
The separation of waves by an interpolation method is presented in detail. The composite wave sequences measured with two wave gauges in the wave flume are separated very quickly into two series of incident and reflected waves in time domain via the simple interpolation and difference operations. Then, the reflection coefficient can be estimated easily and accurately without calculation of wave heights and phases. The intial phase of reflection can also be detected easily for improvement of the accuracy of calculation. The present method is applicable to both regular and irregular trains of waves based on the linear wave theory which are proved to be accurate through numerical sample tests. Physical experiments are conducted and compared with Goda′s method and analytical method with satisfactory results. Furthermore, the present method can be used for the absorbing wave-maker to extract reflected waves in real time.
Schönherr, Margit; Stefan, Hermann; Hamer, Hajo M; Rössler, Karl; Buchfelder, Michael; Rampp, Stefan
2017-01-01
In this study, we use a novel automated method for localization and quantitative comparison of magnetoencephalographic (MEG) delta activity in patients with and without recurrent seizures after epilepsy surgery as well as healthy controls. We identified the generators of delta activity by source location in frequency domain between 1 and 4 Hz in spontaneous MEG data. Comparison with healthy control subjects by z-transform emphasized relative changes of activation in patients. The individual results were compared to spike localizations and statistical group analysis was performed. Additionally, MEG results were compared to 1-4 Hz activity in invasive EEG (iEEG) in two patients, in whom this data was available. Patients with recurrent seizures exhibited significantly increased focal MEG delta activity both in comparison to healthy controls and seizure free patients. This slow activity showed a correlation to interictal epileptic activity and was not explained by consequences of the resection alone. In two patients with iEEG, iEEG analysis was concordant with the MEG findings. The quantity of delta activity could be used as a diagnostic marker for recurrent seizures. The close relation to epileptic spike localizations and the resection volume of patients with successful second surgery imply involvement in seizure recurrence. This initial evidence suggests a potential application in the planning of second epilepsy surgery.
Development of fluoroimmunoassay methods for delta-9-tetrahydrocannabinol
Energy Technology Data Exchange (ETDEWEB)
Mason, A.P.
1986-01-01
Heterogeneous, competitive, labelled-ligand solid-phase primary antibody fluoroimmunoassay methods for the detection of THC in blood and plasma were proposed, and the required assay components were produced and characterized. These components included polyclonal rabbit antisera and monoclonal antibodies reactive with tetrahydrocannabinols, solid-phase immunoglobin reagents, a fluoroligand, and protein conjugates of THC for immunization and immunoassay response amplification. The stereoselective rabbit anti-THC antiserum F-444-12 was found to have a high binding titer, a high affinity (K/sub D/ = 3.4 x 10/sup -/exclamation/sup 1/ M for 5'-iodo/sup -125/I-..delta../sup 2/-THC), and high specificity versus a large number of cannabinoid compounds. Immobilization of the immunoglobulin fraction of the antiserum on hydrophilic polyacrylamide microspheres resulted in only a four fold increase in K/sub D/, and a two fold increase in the concentration of binding sites required for the production of equivalent binding titers. Specificity for small ligands was not affected, but the binding of THC-protein conjugates was reduced in potency. Two monoclonal hybridoma cell lines were produced that secrete monoclonal antibodies which bind the radioligand. The fluoroligand was synthesized from 5'-carboxy-..delta../sup 2/-THC and FITC using a diamimoethane linkage structure. While the compound had the fluorescence properties of FTIC, it was bound to the antiserum F-144-12 with a cross-reactive potency 1.4x greater than the radioligand, and 10x greater than THC.
Delta-f and hydrodynamic methods for semiconductor transport
Energy Technology Data Exchange (ETDEWEB)
Thode, L.E.; Hotchkiss, R.; Gray, M.; Snell, C.; Barnes, D.
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory. The authors have developed a prototype plug-and-play (PCUBED) environment based upon a C++ class called a fragment. A fragment is a universal object that can represent any data type. Fragments provide an excellent intuitive approach to the development of an efficient architecture, as well as providing a common data implementation within and between codes. As a result, the PCUBED environment allows for the generation of many different codes within a common framework. At this time, there are seven major codes implemented within the PCUBED environment. Input, output, restart, setup, and graphics are programmed using a high-level approach to insure human efficiency. In contrast, computationally intensive algorithms are programmed using a low-level approach to insure computational efficiency. Fragments provide a straightforward approach to switch between high-level and low-level programming. PCUBED has been tested on a Macintosh PowerPC; on IBM, SUN, HP, and SGI workstations; and on the CRAY YMP and Cray T3D. Using this environment, the authors have incorporated a drift diffusion, energy balance, hydrodynamic, and Monte Carlo model for metal-oxide semiconductor field-effect transistors (MOSFETs) into a single architecture. With all the models in a common framework, they have investigated the noise characteristics of hybrid and delta-f models. Although hybrid and delta-f models appear viable in one dimension, the noise level of higher order transport coefficients in two and three dimensions makes the utility of such combined methods questionable.
Dada, Olusegun A.; Li, Guangxue; Qiao, Lulu; Ma, Yanyan; Ding, Dong; Xu, Jishang; Li, Pin; Yang, Jichao
2016-08-01
River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosystems as well as high concentrations of human population, are highly vulnerable to the effects of global climate change. In order to understand the wave climate, their potential changes and implication on coastline evolution for environment monitoring and sustainable management of the Niger Delta in the Gulf of Guinea, an investigation was carried out based on offshore wave statistics of an 110-year time series (1900-2010) dataset obtained from the ECMWF ERA-20C atmospheric reanalysis. Results of multivariate regression analyses indicate that interannual mean values of Hs and Tm trends tended to increase over time, especially in the western part of the delta coast, so that they are presently (1980 and 2010) up to 264 mm (300%) and 0.32 s (22%), respectively, higher than 80 years (1900-1930) ago. The maximum directions of the wave have become more westerly (southward) than southerly (westward) by up to 2° (33%) and the mean longshore sediment transport rate has increased by more than 8% over the last 80 years. The linear regression analysis for shoreline changes from 1987 to 2013 shows an erosional trend at the western part of the delta and accretional trends towards eastern part. The relationship between wave climate of the study area and atmospheric circulation using Pearson's correlation shows that the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), East Atlantic pattern (EA) and El-Nino/Southern Oscillation (ENSO) Index explain significant proportion of the seasonal and annual wave variabilities compared to other indices. But it is most likely that the combination of these climatic indices acting together or separately constitutes a powerful and effective mechanism responsible for much of the variability of the offshore Niger Delta wave climate. The study concludes that changing wave climate off the Niger Delta has strong implications on the
A NUMERICAL METHOD FOR NONLINEAR WATER WAVES
Institute of Scientific and Technical Information of China (English)
ZHAO Xi-zeng; SUN Zhao-chen; LIANG Shu-xiu; HU Chang-hong
2009-01-01
This article presents a numerical method for modeling nonlinear water waves based on the High Order Spectral (HOS) method proposed by Dommermuth and Yue and West et al., involving Taylor expansion of the Dirichlet problem and the Fast Fourier Transform (FFT) algorithm. The validation and efficiency of the numerical scheme is illustrated by a number of case studies on wave and wave train configuration including the evolution of fifth-order Stokes waves, wave dispersive focusing and the instability of Stokes wave with finite slope. The results agree well with those obtained by other studies.
Exact solutions of a particle in a box with a delta function potential: The factorization method
Pedram, Pouria
2010-01-01
We find the exact eigenvalues and eigenfunctions for the problem of a particle in a box with a delta function potential $V(x)=\\lambda\\delta(x-x_{0})$ using the factorization method. We show that the presence of the delta function potential results in the discontinuity of the corresponding ladder operators. More importantly, the presence of the delta function potential allows us to obtain the full spectrum of the problem in the first step of the factorization procedure even for the weak coupling limit ($\\lambda\\to 0$).
DEFF Research Database (Denmark)
Gavnholt, Jeppe; Olsen, Thomas; Engelund, Mads;
2008-01-01
We present a modification of the Delta self-consistent field (Delta SCF) method of calculating energies of excited states in order to make it applicable to resonance calculations of molecules adsorbed on metal surfaces, where the molecular orbitals are highly hybridized. The Delta SCF approximation...... is a density-functional method closely resembling standard density-functional theory (DFT), the only difference being that in Delta SCF one or more electrons are placed in higher lying Kohn-Sham orbitals instead of placing all electrons in the lowest possible orbitals as one does when calculating the ground......-state energy within standard DFT. We extend the Delta SCF method by allowing excited electrons to occupy orbitals which are linear combinations of Kohn-Sham orbitals. With this extra freedom it is possible to place charge locally on adsorbed molecules in the calculations, such that resonance energies can...
Review: Advances in delta-subsidence research using satellite methods
Higgins, Stephanie A.
2016-05-01
Most of the world's major river deltas are sinking relative to local sea level. The effects of subsidence can include aquifer salinization, infrastructure damage, increased vulnerability to flooding and storm surges, and permanent inundation of low-lying land. Consequently, determining the relative importance of natural vs. anthropogenic pressures in driving delta subsidence is a topic of ongoing research. This article presents a review of knowledge with respect to delta surface-elevation loss. The field is rapidly advancing due to applications of space-based techniques: InSAR (interferometric synthetic aperture radar), GPS (global positioning system), and satellite ocean altimetry. These techniques have shed new light on a variety of subsidence processes, including tectonics, isostatic adjustment, and the spatial and temporal variability of sediment compaction. They also confirm that subsidence associated with fluid extraction can outpace sea-level rise by up to two orders of magnitude, resulting in effective sea-level rise that is one-hundred times faster than the global average rate. In coming years, space-based and airborne instruments will be critical in providing near-real-time monitoring to facilitate management decisions in sinking deltas. However, ground-based observations continue to be necessary for generating complete measurements of surface-elevation change. Numerical modeling should seek to simulate couplings between subsidence processes for greater predictive power.
Conservative numerical methods for solitary wave interactions
Energy Technology Data Exchange (ETDEWEB)
Duran, A; Lopez-Marcos, M A [Departamento de Matematica Aplicada y Computacion, Facultad de Ciencias, Universidad de Valladolid, Paseo del Prado de la Magdalena s/n, 47005 Valladolid (Spain)
2003-07-18
The purpose of this paper is to show the advantages that represent the use of numerical methods that preserve invariant quantities in the study of solitary wave interactions for the regularized long wave equation. It is shown that the so-called conservative methods are more appropriate to study the phenomenon and provide a dynamic point of view that allows us to estimate the changes in the parameters of the solitary waves after the collision.
A scalable method for computing quadruplet wave-wave interactions
Van Vledder, Gerbrant
2017-04-01
Non-linear four-wave interactions are a key physical process in the evolution of wind generated ocean waves. The present generation operational wave models use the Discrete Interaction Approximation (DIA), but it accuracy is poor. It is now generally acknowledged that the DIA should be replaced with a more accurate method to improve predicted spectral shapes and derived parameters. The search for such a method is challenging as one should find a balance between accuracy and computational requirements. Such a method is presented here in the form of a scalable and adaptive method that can mimic both the time consuming exact Snl4 approach and the fast but inaccurate DIA, and everything in between. The method provides an elegant approach to improve the DIA, not by including more arbitrarily shaped wave number configurations, but by a mathematically consistent reduction of an exact method, viz. the WRT method. The adaptiveness is to adapt the abscissa of the locus integrand in relation to the magnitude of the known terms. The adaptiveness is extended to the highest level of the WRT method to select interacting wavenumber configurations in a hierarchical way in relation to their importance. This adaptiveness results in a speed-up of one to three orders of magnitude depending on the measure of accuracy. This definition of accuracy should not be expressed in terms of the quality of the transfer integral for academic spectra but rather in terms of wave model performance in a dynamic run. This has consequences for the balance between the required accuracy and the computational workload for evaluating these interactions. The performance of the scalable method on different scales is illustrated with results from academic spectra, simple growth curves to more complicated field cases using a 3G-wave model.
Experimental methods of shock wave research
Seiler, Friedrich
2016-01-01
This comprehensive and carefully edited volume presents a variety of experimental methods used in Shock Waves research. In 14 self contained chapters this 9th volume of the “Shock Wave Science and Technology Reference Library” presents the experimental methods used in Shock Tubes, Shock Tunnels and Expansion Tubes facilities. Also described is their set-up and operation. The uses of an arc heated wind tunnel and a gun tunnel are also contained in this volume. Whenever possible, in addition to the technical description some typical scientific results obtained using such facilities are described. Additionally, this authoritative book includes techniques for measuring physical properties of blast waves and laser generated shock waves. Information about active shock wave laboratories at different locations around the world that are not described in the chapters herein is given in the Appendix, making this book useful for every researcher involved in shock/blast wave phenomena.
High-Frequency Rayleigh-Wave Method
Institute of Scientific and Technical Information of China (English)
Jianghai Xia; Richard D Millerg; Xu Yixian; Luo Yinhe; Chen Chao; Liu Jiangping; Julian Ivanov; Chong Zeng
2009-01-01
High-frequency (≥2 Hz) Rayleigh-wave data acquired with a multichannei recording sys-tem have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave tech-niques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a nou-iuvasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution.
Bonanni, Enrica; Di Coscio, Elisa; Maestri, Michelangelo; Carnicelli, Luca; Tsekou, Hara; Economou, Nicholas Tiberio; Paparrigopoulos, Thomas; Bonakis, Anastasios; Papageorgiou, Sokratis G; Vassilopoulos, Dimitris; Soldatos, Constantin R; Murri, Luigi; Ktonas, Periklis Y
2012-02-01
To evaluate the modifications of EEG activity during slow-wave sleep in patients with dementia compared with healthy elderly subjects, using spectral analysis and period-amplitude analysis. Five patients with dementia and 5 elderly control subjects underwent night polysomnographic recordings. For each of the first three nonrapid eye movement-rapid eye movement sleep cycles, a well-defined slow-wave sleep portion was chosen. The delta frequency band (0.4-3.6 Hz) in these portions was analyzed with both spectral analysis and period-amplitude analysis. Spectral analysis showed an increase in the delta band power in the dementia group, with a decrease across the night observed only in the control group. For the dementia group, period-amplitude analysis showed a decrease in well-defined delta waves of frequency lower than 1.6 Hz and an increase in such waves of frequency higher than 2 Hz, in incidence and amplitude. Our study showed (1) a loss of the dynamics of delta band power across the night sleep, in dementia, and (2) a different distribution of delta waves during slow-wave sleep in dementia compared with control subjects. This kind of computer-based analysis can highlight the presence of a pathologic delta activity during slow-wave sleep in dementia and may support the hypothesis of a dynamic interaction between sleep alteration and cognitive decline.
High Frequency Tan Delta Measurement Method for 132kV Transmission Underground Cables
Directory of Open Access Journals (Sweden)
A.R. Avinash
2015-07-01
Full Text Available Tangent Delta is a measurement technique to investigate cables insulation strength. Current techniques utilize Very Low Frequency (VLF at 0.1 Hz and power frequency at 50 Hz. However, high voltages are required, thus requiring larger space and cost. Proposed method of tangent delta testing utilizes High frequency Low voltage diagnoses. The phase between the current and the voltage is utilized to determine the tangent delta (tan δ. The aim of this study is to develop a low voltage high frequency tangent delta measurement method and test if it can discriminate manufactured 132 kV good conditioned cable sample from defect induced cables with void, scotched and contamination in its insulation. Impurities are clearly discriminated using this method. Comparison of Tangent Delta of cables manufactured simultaneously in good condition and defect induced is performed using High Frequency Tangent Delta method and in 50 Hz conventional method to validate the effectiveness of the measurement technique. The High Frequency AC setup utilizes a small testing environment which can sample small lengths with minimum 1 m length of cable. The small lengths will result in the reduction of total capacitance of the cable but using High Frequency induces high electric stress on XLPE layer thus resulting in measureable dielectric current.
Wave envelopes method for description of nonlinear acoustic wave propagation.
Wójcik, J; Nowicki, A; Lewin, P A; Bloomfield, P E; Kujawska, T; Filipczyński, L
2006-07-01
A novel, free from paraxial approximation and computationally efficient numerical algorithm capable of predicting 4D acoustic fields in lossy and nonlinear media from arbitrary shaped sources (relevant to probes used in medical ultrasonic imaging and therapeutic systems) is described. The new WE (wave envelopes) approach to nonlinear propagation modeling is based on the solution of the second order nonlinear differential wave equation reported in [J. Wójcik, J. Acoust. Soc. Am. 104 (1998) 2654-2663; V.P. Kuznetsov, Akust. Zh. 16 (1970) 548-553]. An incremental stepping scheme allows for forward wave propagation. The operator-splitting method accounts independently for the effects of full diffraction, absorption and nonlinear interactions of harmonics. The WE method represents the propagating pulsed acoustic wave as a superposition of wavelet-like sinusoidal pulses with carrier frequencies being the harmonics of the boundary tone burst disturbance. The model is valid for lossy media, arbitrarily shaped plane and focused sources, accounts for the effects of diffraction and can be applied to continuous as well as to pulsed waves. Depending on the source geometry, level of nonlinearity and frequency bandwidth, in comparison with the conventional approach the Time-Averaged Wave Envelopes (TAWE) method shortens computational time of the full 4D nonlinear field calculation by at least an order of magnitude; thus, predictions of nonlinear beam propagation from complex sources (such as phased arrays) can be available within 30-60 min using only a standard PC. The approximate ratio between the computational time costs obtained by using the TAWE method and the conventional approach in calculations of the nonlinear interactions is proportional to 1/N2, and in memory consumption to 1/N where N is the average bandwidth of the individual wavelets. Numerical computations comparing the spatial field distributions obtained by using both the TAWE method and the conventional approach
Feinberg, I; Thode, H C; Chugani, H T; March, J D
1990-01-23
We analyzed the available ontogenetic data (birth to 30 years of age) for: amplitude of delta EEG (DA) waves during sleep; cortical metabolic rate (CMR) measured with positron emission tomography; and synaptic density (SD) in frontal cortex. Each is at the adult level at birth, increases to about twice this level by 3 years of age, and then gradually falls back to the adult level over the next two decades. Statistical analyses revealed that individual gamma distribution models fit each data set as well as did the best ad hoc polynomial. A test of whether a single gamma distribution model could describe all three data sets gave good results for DA and CMR but the fit was unsatisfactory for SD. However, because so few data were available for SD, this test was not conclusive. We proposed the following model to account for these changes. First, cortical neurons are stimulated by birth to enter a proliferative state (PS) that creates many connections. Next, as a result of interactions in the PS, neurons are triggered into a transient organizational state (OS) in which they make enduring connections. The OS has a finite duration (minutes to years), and is characterized by high rates of information-processing and metabolism. Levels of CMR, SD and DA, therefore, are proportional to the number of neurons in the OS at any time. Thus, the cortex after birth duplicates, over a vastly greater time scale, the overproduction and regression of neural elements that occurs repeatedly in embryonic development. Finally, we discussed the implications of post-natal brain changes for normal and abnormal brain function. Mental disorders that have their onset after puberty (notably schizophrenia and manic-depressive psychoses) might be caused by errors in these late maturational processes. In addition to age of onset, this neurodevelopmental hypothesis might explain several other puzzling features of these subtle disorders.
Coastal erosion in response to wave dynamics operative in Sagar Island, Sundarban delta, India
Institute of Scientific and Technical Information of China (English)
Barendra PURKAIT
2009-01-01
Coastal erosion at Sagar Island of Sunderban delta, India, has been critically studied. The area is in the subtropical humid region. There are mainly three seasons viz: winter, summer and the monsoon. Different wave dynamic parameters were measured from theodolite observations with leveling staff and measuring gauges during lunar days at two sections of the western and eastern parts of the coastal zone during post-and pre-monsoons. A comparative study was made on the erosion/depositional pattern between the two sections in relation to different hydrodynamic parameters prevailing in these two sections. Plane table mapping was carried out to demarcate the different geomorphic units. The marine coastal landforms show dune ridges with intervening flats bordered by gently sloping beach on one side and a flat beach on the other side. The western part of the beach is mainly sandy; whereas the eastern part is silty and clayey with mud bank remnants. Actual field measurements indicate that the coastal dune belt has retreated to the order by about 20 m since 1985. The eastern part of the beach has lowered by about 2 m since 1985 and the western part was raised almost to the same tune. It is observed that accretion in the western and central parts of the beach took place; whereas severe erosion in the eastern part made the beach very narrow with remnants of mud banks and tree roots. Frequent embankment failures, submergence and flooding, beach erosion and siltation at jetties and navigational channels, cyclones and storm surges made this area increasingly vulnerable.
Adaptive Management Methods to Protect the California Sacramento-San Joaquin Delta Water Resource
Bubenheim, David
2016-01-01
The California Sacramento-San Joaquin River Delta is the hub for California's water supply, conveying water from Northern to Southern California agriculture and communities while supporting important ecosystem services, agriculture, and communities in the Delta. Changes in climate, long-term drought, water quality changes, and expansion of invasive aquatic plants threatens ecosystems, impedes ecosystem restoration, and is economically, environmentally, and sociologically detrimental to the San Francisco Bay/California Delta complex. NASA Ames Research Center and the USDA-ARS partnered with the State of California and local governments to develop science-based, adaptive-management strategies for the Sacramento-San Joaquin Delta. The project combines science, operations, and economics related to integrated management scenarios for aquatic weeds to help land and waterway managers make science-informed decisions regarding management and outcomes. The team provides a comprehensive understanding of agricultural and urban land use in the Delta and the major water sheds (San Joaquin/Sacramento) supplying the Delta and interaction with drought and climate impacts on the environment, water quality, and weed growth. The team recommends conservation and modified land-use practices and aids local Delta stakeholders in developing management strategies. New remote sensing tools have been developed to enhance ability to assess conditions, inform decision support tools, and monitor management practices. Science gaps in understanding how native and invasive plants respond to altered environmental conditions are being filled and provide critical biological response parameters for Delta-SWAT simulation modeling. Operational agencies such as the California Department of Boating and Waterways provide testing and act as initial adopter of decision support tools. Methods developed by the project can become routine land and water management tools in complex river delta systems.
Control methods for localization of nonlinear waves
Porubov, Alexey; Andrievsky, Boris
2017-03-01
A general form of a distributed feedback control algorithm based on the speed-gradient method is developed. The goal of the control is to achieve nonlinear wave localization. It is shown by example of the sine-Gordon equation that the generation and further stable propagation of a localized wave solution of a single nonlinear partial differential equation may be obtained independently of the initial conditions. The developed algorithm is extended to coupled nonlinear partial differential equations to obtain consistent localized wave solutions at rather arbitrary initial conditions. This article is part of the themed issue 'Horizons of cybernetical physics'.
Digital Repository Service at National Institute of Oceanography (India)
Sastry, J.S.; Vethamony, P.; Swamy, G.N.
the speed of 200 cm/sec. The morphological changes due to the effect of river discharge during various seasons and the development of Godavari sand spit off Kakinada and its influence to delta modification are detailed....
Radio identification of decameter-wave sources. II: The 30deg<delta<40deg declination interval
Verkhodanov, O V; Andernach, H; 10.1134/S1990341309010052
2009-01-01
This paper is dedicated to the identification of decameter-wave sources of the UTR catalog within declination interval 30deg<delta<40deg. UTR sources are cross-identified with CATS database catalogs within 40'x40' error boxes. The sources are deblended using the data on the coordinates of the objects and the behavior of their continuum radio spectra. The spectra of 876 sources are derived and fitted by standard analytical functions. Of these sources, 221 objects have straight-line spectra with spectral indices alpha<-1.0. All objects are catalogued and stored in the CATS database.
Wave propagation retrieval method for chiral metamaterials
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
2010-01-01
In this paper we present the wave propagation method for the retrieving of effective properties of media with circularly polarized eigenwaves, in particularly for chiral metamaterials. The method is applied for thick slabs and provides bulk effective parameters. Its strong sides are the absence...... of artificial branches of the refractive index and simplicity in implementation. We prove the validity of the method on three case studies of homogeneous magnetized plasma, bi-cross and U-shaped metamaterials....
Directory of Open Access Journals (Sweden)
Lucia Švábová
2015-09-01
Full Text Available Financial derivatives are a widely used tool for investors to hedge against the risk caused by changes in asset prices in the financial markets. A usual type of hedging derivative is an asset option. In case of unexpected changes in asset prices, in the investment portfolio, the investor will exercise the option to eliminate losses resulting from these changes. Therefore, it is necessary to include the options in the investor´s portfolio in such a ratio that the losses caused by decreasing of assets prices will be covered by profits from those options. Futures option is a type of call or put option to buy or to sell an option contract at a designated strike price. The change in price of the underlying assets or underlying futures contract causes a change in the prices of options themselves. For investor exercising option as a tool for risk insurance, it is important to quantify these changes. The dependence of option price changes, on the underlying asset or futures option price changes, can be expressed by the parameter delta. The value of delta determines the composition of the portfolio to be risk-neutral. The parameter delta is calculated as a derivation of the option price with respect to the price of the underlying asset, if the option price formula exists. But for some types of more complex options, the analytical formula does not exist, so calculation of delta by derivation is not possible. However, it is possible to estimate the value of delta numerically using the principles of the numerical method called “Finite Difference Method.” In the paper the parameter delta for a Futures call option calculated from the analytical formula and estimated from the Finite difference method are compared.
Systems and methods for wave energy conversion
Energy Technology Data Exchange (ETDEWEB)
MacDonald, Daniel G.; Cantara, Justin; Nathan, Craig; Lopes, Amy M.; Green, Brandon E.
2017-02-28
Systems for wave energy conversion that have components that can survive the harsh marine environment and that can be attached to fixed structures, such as a pier, and having the ability to naturally adjust for tidal height and methods for their use are presented.
Calibration methods in millimeter-wave Radioastronomy
Energy Technology Data Exchange (ETDEWEB)
Abraham, Z.; Botti, L.C.L.; del Ciampo, L.F.
1986-02-01
The authors discuss a calibration method for millimeter wave observations that automatically compensates the atmospheric attenuation, even in the presence of a radome, or when the mean kinetic temperature of the sky is smaller than the ambient temperature. 2 references, 1 figure, 1 table.
Park, Sang Hyuk; Kim, So-Young; Lee, Woochang; Chun, Sail; Min, Won-Ki
2012-09-01
Many laboratories use 4 delta check methods: delta difference, delta percent change, rate difference, and rate percent change. However, guidelines regarding decision criteria for selecting delta check methods have not yet been provided. We present new decision criteria for selecting delta check methods for each clinical chemistry test item. We collected 811,920 and 669,750 paired (present and previous) test results for 27 clinical chemistry test items from inpatients and outpatients, respectively. We devised new decision criteria for the selection of delta check methods based on the ratio of the delta difference to the width of the reference range (DD/RR). Delta check methods based on these criteria were compared with those based on the CV% of the absolute delta difference (ADD) as well as those reported in 2 previous studies. The delta check methods suggested by new decision criteria based on the DD/RR ratio corresponded well with those based on the CV% of the ADD except for only 2 items each in inpatients and outpatients. Delta check methods based on the DD/RR ratio also corresponded with those suggested in the 2 previous studies, except for 1 and 7 items in inpatients and outpatients, respectively. The DD/RR method appears to yield more feasible and intuitive selection criteria and can easily explain changes in the results by reflecting both the biological variation of the test item and the clinical characteristics of patients in each laboratory. We suggest this as a measure to determine delta check methods.
Directory of Open Access Journals (Sweden)
Margit Schönherr
2017-01-01
Significance: The quantity of delta activity could be used as a diagnostic marker for recurrent seizures. The close relation to epileptic spike localizations and the resection volume of patients with successful second surgery imply involvement in seizure recurrence. This initial evidence suggests a potential application in the planning of second epilepsy surgery.
Projector augmented wave method: ab initio molecular dynamics with full wave functions
Indian Academy of Sciences (India)
Peter E Blöchl; Clemens J Först; Johannes Schimpl
2003-01-01
A brief introduction to the projector augmented wave method is given and recent developments are reviewed. The projector augmented wave method is an all-electron method for efficient ab initio molecular dynamics simulations with full wave functions. It extends and combines the traditions of existing augmented wave methods and the pseudopotential approach. Without sacrificing efficiency, the PAW method avoids transferability problems of the pseudopotential approach and it has been valuable to predict properties that depend on the full wave functions.
Approximation of acoustic waves by explicit Newmark's schemes and spectral element methods
Zampieri, Elena; Pavarino, Luca F.
2006-01-01
A numerical approximation of the acoustic wave equation is presented. The spatial discretization is based on conforming spectral elements, whereas we use finite difference Newmark's explicit integration schemes for the temporal discretization. A rigorous stability analysis is developed for the discretized problem providing an upper bound for the time step [Delta]t. We present several numerical results concerning stability and convergence properties of the proposed numerical methods.
An analytical filter design method for guided wave phased arrays
Kwon, Hyu-Sang; Kim, Jin-Yeon
2016-12-01
This paper presents an analytical method for designing a spatial filter that processes the data from an array of two-dimensional guided wave transducers. An inverse problem is defined where the spatial filter coefficients are determined in such a way that a prescribed beam shape, i.e., a desired array output is best approximated in the least-squares sense. Taking advantage of the 2π-periodicity of the generated wave field, Fourier-series representation is used to derive closed-form expressions for the constituting matrix elements. Special cases in which the desired array output is an ideal delta function and a gate function are considered in a more explicit way. Numerical simulations are performed to examine the performance of the filters designed by the proposed method. It is shown that the proposed filters can significantly improve the beam quality in general. Most notable is that the proposed method does not compromise between the main lobe width and the sidelobe levels; i.e. a narrow main lobe and low sidelobes are simultaneously achieved. It is also shown that the proposed filter can compensate the effects of nonuniform directivity and sensitivity of array elements by explicitly taking these into account in the formulation. From an example of detecting two separate targets, how much the angular resolution can be improved as compared to the conventional delay-and-sum filter is quantitatively illustrated. Lamb wave based imaging of localized defects in an elastic plate using a circular array is also presented as an example of practical applications.
Fletcher, Jon Peter B.; Erdem, Jemile; Seats, Kevin; Lawrence, Jesse
2016-01-01
If shaking from a local or regional earthquake in the San Francisco Bay region were to rupture levees in the Sacramento/San Joaquin Delta then brackish water from San Francisco Bay would contaminate the water in the Delta: the source of fresh water for about half of California. As a prelude to a full shear-wave velocity model that can be used in computer simulations and further seismic hazard analysis, we report on the use of ambient noise tomography to build a fundamental-mode, Rayleigh-wave group velocity model for the region around the Sacramento/San Joaquin Delta in the western Central Valley, California. Recordings from the vertical component of about 31 stations were processed to compute the spatial distribution of Rayleigh wave group velocities. Complex coherency between pairs of stations were stacked over 8 months to more than a year. Dispersion curves were determined from 4 to about 18 seconds. We calculated average group velocities for each period and inverted for deviations from the average for a matrix of cells that covered the study area. Smoothing using the first difference is applied. Cells of the model were about 5.6 km in either dimension. Checkerboard tests of resolution, which is dependent on station density, suggest that the resolving ability of the array is reasonably good within the middle of the array with resolution between 0.2 and 0.4 degrees. Overall, low velocities in the middle of each image reflect the deeper sedimentary syncline in the Central Valley. In detail, the model shows several centers of low velocity that may be associated with gross geologic features such as faulting along the western margin of the Central Valley, oil and gas reservoirs, and large cross cutting features like the Stockton arch. At shorter periods around 5.5s, the model’s western boundary between low and high velocities closely follows regional fault geometry and the edge of a residual isostatic gravity low. In the eastern part of the valley, the boundaries
METHOD TO ASSESS THE EXTREME HYDROLOGICAL EVENTS IN DANUBE FLUVIAL DELTA
Directory of Open Access Journals (Sweden)
MARIAN MIERLĂ
2012-03-01
Full Text Available Method to assess the extreme hydrological events in Danube fluvial Delta. In this paper the subject is about of testing a method for Romania to assess the extreme hydrological events. In this paper through hydrological extreme events it should be understood as the extreme droughts and the extreme flooding. The place to be tested this method for Romania is the Danube Delta, fluvial delta to be more precisely. The importance of the area consists in the fact that is the third Delta of the Europe (after the Volga’s and Kuban’s. The method that is supposed to be tested on a specific part of the delta is aiming to rise the knowledge about the extreme hydrological events (drought and flooding and to be able to respond in an appropriate way to these. For this paper it will be taken into account the hydrological events occurred in 2003 (the exceptional drought and in 2006 (the exceptional flood. To do the analysis there were used satellite images (LANDSAT from the period that was taken into account and additional there were used the hypsometrical model of the Danube Delta for the specific area. The first two datasets (2003 and 2006 satellite images give information about were the border of the water (in drought period and respective in flooding one reached. The second dataset (the delta’s hypsometry give information about the altitude of the terrain in order to establish which areas, at a certain water level, are flooded. The result of these datasets combination is the calibration of the hypsometrical model of the Danube Delta, in that region, regarding the hydrological events in the sense of building-up the hydrograds as isolines. The new approach of this matter can be more concrete and makes easier to see on the cartographic support the hydrologic events. The information obtained from these datasets makes the awareness regarding the extreme hydrological events to be higher and respective the measures taken to mitigate these will be more efficient.
Deltas, freshwater discharge, and waves along the Young Sound, NE Greenland
DEFF Research Database (Denmark)
Kroon, Aart; Abermann, Jakob; Bendixen, Mette
2017-01-01
, and bathymetry), fluvial discharges and associated sediment load, and processes by waves and currents. Main factors steering the Arctic fluvial discharges into the Young Sound are the snow and ice melt and precipitation in the catchment, and extreme events like glacier lake outburst floods (GLOFs). Waves...
Structure analysis of interstellar clouds: I. Improving the Delta-variance method
Ossenkopf, V; Stutzki, J
2008-01-01
The Delta-variance analysis, has proven to be an efficient and accurate method of characterising the power spectrum of interstellar turbulence. The implementation presently in use, however, has several shortcomings. We propose and test an improved Delta-variance algorithm for two-dimensional data sets, which is applicable to maps with variable error bars and which can be quickly computed in Fourier space. We calibrate the spatial resolution of the Delta-variance spectra. The new Delta-variance algorithm is based on an appropriate filtering of the data in Fourier space. It allows us to distinguish the influence of variable noise from the actual small-scale structure in the maps and it helps for dealing with the boundary problem in non-periodic and/or irregularly bounded maps. We try several wavelets and test their spatial sensitivity using artificial maps with well known structure sizes. It turns out that different wavelets show different strengths with respect to detecting characteristic structures and spectr...
A Pseudospectral Method for Gravitational Wave Collapse
Hilditch, David; Bruegmann, Bernd
2015-01-01
We present a new pseudospectral code, bamps, for numerical relativity written with the evolution of collapsing gravitational waves in mind. We employ the first order generalized harmonic gauge formulation. The relevant theory is reviewed and the numerical method is critically examined and specialized for the task at hand. In particular we investigate formulation parameters, gauge and constraint preserving boundary conditions well-suited to non-vanishing gauge source functions. Different types of axisymmetric twist-free moment of time symmetry gravitational wave initial data are discussed. A treatment of the axisymmetric apparent horizon condition is presented with careful attention to regularity on axis. Our apparent horizon finder is then evaluated in a number of test cases. Moving on to evolutions, we investigate modifications to the generalized harmonic gauge constraint damping scheme to improve conservation in the strong field regime. We demonstrate strong-scaling of our pseudospectral penalty code. We em...
Runge-Kutta methods and viscous wave equations
J.G. Verwer (Jan)
2008-01-01
htmlabstractWe study the numerical time integration of a class of viscous wave equations by means of Runge-Kutta methods. The viscous wave equation is an extension of the standard second-order wave equation including advection-diffusion terms differentiated in time. The viscous wave equation can be
Runge–Kutta methods and viscous wave equations
J.G. Verwer (Jan)
2009-01-01
htmlabstractWe study the numerical time integration of a class of viscous wave equations by means of Runge–Kutta methods. The viscous wave equation is an extension of the standard second-order wave equation including advection–diffusion terms differentiated in time. The viscous wave equation can be
Numerical method of studying nonlinear interactions between long waves and multiple short waves
Institute of Scientific and Technical Information of China (English)
Xie Tao; Kuang Hai-Lan; William Perrie; Zou Guang-Hui; Nan Cheng-Feng; He Chao; Shen Tao; Chen Wei
2009-01-01
Although the nonlinear interactions between a single short gravity wave and a long wave can be solved analytically,the solution is less tractable in more general cases involving multiple short waves.In this work we present a numerical method of studying nonlinear interactions between a long wave and multiple short harmonic waves in infinitely deep water.Specifically,this method is applied to the calculation of the temporal and spatial evolutions of the surface elevations in which a given long wave interacts with several short harmonic waves.Another important application of our method is to quantitatively analyse the nonlinear interactions between an arbitrary short wave train and another short wave train.From simulation results,we obtain that the mechanism for the nonlinear interactions between one short wave train and another short wave train(expressed as wave train 2)leads to the energy focusing of the other short wave train(expressed as wave train 31.This mechanism Occurs on wave components with a narrow frequency bandwidth,whose frequencies are near that of wave train 3.
An Irregular Wave Maker of Active Absorption with VOF Method
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid (VOF) method. An active absorbing wave-maker based on linear wave-theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen (1995) is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.
A method for generating highly nonlinear periodic waves in physical wave basins
DEFF Research Database (Denmark)
Zhang, Haiwen; Schäffer, Hemming A.; Bingham, Harry B.
2006-01-01
This abstract describes a new method for generating nonlinear waves of constant form in physical wave basins. The idea is to combine fully dispersive linear wavemaker theory with nonlinear shallow water wave generation theory; and use an exact nonlinear theory as the target. We refer to the metho...... as an ad-hoc unified wave generation theory, since there is no rigorous analysis behind the idea which is simply justified by the improved results obtained for the practical generation of steady nonlinear waves....
Liu, Guanqun; Wang, Juan; Yuan, Ruiqiang; Sun, Beibei; Zhu, Liangchao; Wang, Yansi
2010-01-01
In this paper, cross-section method was used to estimate the groundwater and nutrients discharge fluxing to the Bohai Sea from the Yellow River Delta. The flux of shallow phreatic groundwater (within 10 m) in the Yellow River Farm discharging into sea was 2.9x10(-5) m3/m d in 2004 and 3.1x10(-5) m3/m d in 2005. Time distribution monthly mean flux is consistent with the Yellow River's runoff but taking on lag effect. And the volume of the phreatic water discharging from the whole delta is 3.71-3.77x10(3) m3, which is 2x10(-5)% of the Yellow River's annual runoff. The transport amount of shallow confined water (buried depth 15-20 m) from 2004 to 2005 was 5.7-6.2x10(-3) m3/m d in the Yellow River delta, 0.0037-0.004% of the runoff of Yellow River. There is low concentration of NO3-, NH4+ and PO4(3-) but high dissolved SiO2 in the shallow confined aquifer. Despite the high concentration of phreatic nitrate, it weakly influences the seawater because of the little flux of discharge into sea.
Krebs, H; Meissner, U G; Epelbaum, Evgeny; Krebs, Hermann; Mei{\\ss}ner, Ulf-G.
2007-01-01
We study the two-nucleon force at next-to-next-to-leading order in a chiral effective field theory with explicit Delta degrees of freedom. Fixing the appearing low-energy constants from a next-to-leading order calculation of pion-nucleon threshold parameters, we find an improved convergence of most peripheral nucleon-nucleon phases compared to the theory with pions and nucleons only. In the delta-full theory, the next-to-leading order corrections are dominant in most partial waves considered.
Bifurcation methods of dynamical systems for handling nonlinear wave equations
Indian Academy of Sciences (India)
Dahe Feng; Jibin Li
2007-05-01
By using the bifurcation theory and methods of dynamical systems to construct the exact travelling wave solutions for nonlinear wave equations, some new soliton solutions, kink (anti-kink) solutions and periodic solutions with double period are obtained.
Energy Technology Data Exchange (ETDEWEB)
Hartmann, H.; Rossmann, P. [Technologie- und Foerderzentrum (TFZ), Straubing (Germany); Ester, S. [Woehler MGKG GmbH, Bad Wuennenberg (Germany); Wazula, H. [Landesinnungsverband fuer das Bayerische Kaminkehrerhandwerk, Muenchen (Germany); Schmoeckel, G. [Bayerisches Landesamt fuer Umweltschutz LfU, Augsburg (Germany)
2004-07-01
Recurrent dust emission measurements from domestic wood boilers are laborious and time consuming as they require an additional laboratory determination by reweighing the filters after the flue gas sampling on the site. Therefore the conventional determination method for dust emissions was combined with an additional rapid testing feature which promises an immediate identification of any dust emission boundary exceedance. In this method the accumulating filter pollution during a 15 minute flue gas sampling period is reflected by an increase of the pressure drop over the filter while the volume flow is kept constant (Delta-p-method). In a series of 137 trials on a test stand this correlation between pressure drop and dust emissions was proved. From subsequent field trials with 363 measurements an optimum threshold value for the pressure drop was identified: At a pressure drop of 24 hPa only 47% of all measurements would still require a subsequent gravimetric evaluation of the loaded filter. This means that under realistic conditions an immediate reporting of the measuring result on the site would be possible in the majority of all cases (53%), identifying the furnace as 'dust proof'. In only 3.7% of all such reports this would prove false. (orig.)
Traveling wave tube and method of manufacture
Vancil, Bernard K. (Inventor)
2004-01-01
A traveling wave tube includes a glass or other insulating envelope having a plurality of substantially parallel glass rods supported therewithin which in turn support an electron gun, a collector and an intermediate slow wave structure. The slow wave structure itself provides electrostatic focussing of a central electron beam thereby eliminating the need for focussing magnetics and materially decreasing the cost of construction as well as enabling miniaturization. The slow wave structure advantageously includes cavities along the electron beam through which the r.f. energy is propagated, or a double, interleaved ring loop structure supported by dielectric fins within a ground plane cylinder disposed coaxially within the glass envelope.
Lacy, Jessica R.; Carlson, Emily
2016-01-01
Data were collected by the U.S. Geological Survey (USGS) Pacific Coastal and Marine Science Center to investigate the influence of wind waves on sediment dynamics in two flooded agricultural tracts in the northern Sacramento-San Joaquin Delta: Little Holland Tract and Liberty Island. This effort is part of a large interdisciplinary study led by the USGS California Water Science Center and funded by the U.S. Bureau of Reclamation to investigate how shallow-water habitats in the Sacramento-San Joaquin Delta function and whether they provide good habitat for native fish species, including the Delta smelt. Elevated turbidity is a requirement for Delta smelt habitat, and turbidity is largely comprised of suspended sediment. Wind waves develop in large open-water regions with large fetch, and can increase turbidity by mobilizing bottom sediments.Data were collected at two stations each in Little Holland Tract (LHT) and Liberty Island (LI) beginning in August 2015. In table 1 (below), station names starting with ‘H’ are in LHT and station names starting with ‘L’ are in LI. At two stations (indicated by ‘W’ in the second character of the station name) we collected time series of water surface elevation, wave height and period, and turbidity. At the other two stations (indicated by ‘V’ in the second character of the station name) we collected these same data types as well as time series of current velocity and wave velocity. Throughout the experiment, some of the instrumentation was moved to alternate locations in the tracts. The turbidity sensors were calibrated to suspended-sediment concentration measured in water samples collected on site (table 2a and b). Details on instrumentation and sampling are included on the individual pages for each station (see links below). Data are sequentially added to this data release as they are retrieved and post-processed.
Approximate k-NN delta test minimization method using genetic algorithms: Application to time series
Mateo, F; Gadea, Rafael; Sovilj, Dusan
2010-01-01
In many real world problems, the existence of irrelevant input variables (features) hinders the predictive quality of the models used to estimate the output variables. In particular, time series prediction often involves building large regressors of artificial variables that can contain irrelevant or misleading information. Many techniques have arisen to confront the problem of accurate variable selection, including both local and global search strategies. This paper presents a method based on genetic algorithms that intends to find a global optimum set of input variables that minimize the Delta Test criterion. The execution speed has been enhanced by substituting the exact nearest neighbor computation by its approximate version. The problems of scaling and projection of variables have been addressed. The developed method works in conjunction with MATLAB's Genetic Algorithm and Direct Search Toolbox. The goodness of the proposed methodology has been evaluated on several popular time series examples, and also ...
Efficient computation method for two-dimensional nonlinear waves
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The theory and simulation of fully-nonlinear waves in a truncated two-dimensional wave tank in time domain are presented. A piston-type wave-maker is used to generate gravity waves into the tank field in finite water depth. A damping zone is added in front of the wave-maker which makes it become one kind of absorbing wave-maker and ensures the prescribed Neumann condition. The efficiency of nmerical tank is further enhanced by installation of a sponge layer beach (SLB) in front of downtank to absorb longer weak waves that leak through the entire wave train front. Assume potential flow, the space- periodic irrotational surface waves can be represented by mixed Euler- Lagrange particles. Solving the integral equation at each time step for new normal velocities, the instantaneous free surface is integrated following time history by use of fourth-order Runge- Kutta method. The double node technique is used to deal with geometric discontinuity at the wave- body intersections. Several precise smoothing methods have been introduced to treat surface point with high curvature. No saw-tooth like instability is observed during the total simulation.The advantage of proposed wave tank has been verified by comparing with linear theoretical solution and other nonlinear results, excellent agreement in the whole range of frequencies of interest has been obtained.
The method of successive decrease and the harmonic wave filter for wave control in structures
Institute of Scientific and Technical Information of China (English)
王泉; 王大钧; A. Y. T. Leung
1996-01-01
Attempt is made to solve some of the existing problems due to the application of themodal control method. A wave control method--the method of successive decrease is set up at first, which isaimed at one harmonic wave. Then, a new design method in wave control is proposed based on the above method. The problem of control spillover is analyzed and the concept of harmonic wave filter is introduced.As an example, the problem of the control of structures with closely spaced natural frequencies is treated by both the method of modal control and the method of successive decrease. The numerical results show that the method of successive decrease is more effective than the method of modal control for this problem.
A spectroscopic method for determining thickness of quartz wave plate
Institute of Scientific and Technical Information of China (English)
Weiwei Feng; Lihuang Lin; Ligang Chen; Huafeng Zhu; Ruxin Li; Zhizhan Xu
2006-01-01
A spectroscopic method to determine thickness of quartz wave plate is presented. The method is based on chromatic polarization interferometry. With the polarization-resolved transmission spectrum (PRTS)curve, the phase retardation of quartz wave plate can be determined at a wide spectral range from 200 to2000 nm obviously. Through accurate judgment of extreme points of PRTS curve at long-wave band, the physical thickness of quartz wave plates can be obtained exactly. We give a measuring example and the error analysis. It is found that the measuring precision of thickness is mainly determined by the spectral resolution of spectrometer.
Plane wave method for elastic wave scattering by a heterogeneous fracture
Energy Technology Data Exchange (ETDEWEB)
Nakagawa, Seiji; Nihei, Kurt T.; Myer, Larry R.
2003-02-21
A plane-wave method for computing the three-dimensional scattering of propagating elastic waves by a planar fracture with heterogeneous fracture compliance distribution is presented. This method is based upon the spatial Fourier transform of the seismic displacement-discontinuity (SDD) boundary conditions (also called linear slip interface conditions), and therefore, called the wave-number-domain SDD method (wd-SDD method). The resulting boundary conditions explicitly show the coupling between plane waves with an incident wave number component (specular component) and scattered waves which do not follow Snell's law (nonspecular components) if the fracture is viewed as a planar boundary. For a spatially periodic fracture compliance distribution, these boundary conditions can be cast into a linear system of equations that can be solved for the amplitudes of individual wave modes and wave numbers. We demonstrate the developed technique for a simulated fracture with a stochastic (correlated) surface compliance distribution. Low- and high-frequency solutions of the method are also compared to the predictions by low-order Born series in the weak and strong scattering limit.
Practical methods for a direct calculation of Delta I=1/2 K to pipi Decay
Liu, Q.
A direct calculation of the complex $\\Delta I=1/2$ kaon decay amplitude is notoriously difficult because of the presence of disconnected graphs. Here we describe and demonstrate two practical methods to defeat this problem: the EigCG algorithm and the use of time-separated $\\pi-\\pi$ sources. With a fine tuned EigCG implementation for domain wall fermions, the calculation of light quark propagators is accelerated by a factor of 5-10 on a variety of lattices from small ($16^3\\times32\\times16$) to large ($32^3\\times64\\times32$). In addition, a substantial reduction in noise is achieved by separating each of the sources for the two pions in the time direction by 2-5 lattice spacings. These methods are combined in a calculation of $K$ to $\\pi\\pi$ threshold decay using a $24^3\\times64\\times16$ volume and 329 MeV pions. These methods result in non-zero signals for both Re($A_0$) and Im($A_0$) from 138 gauge configurations.
Yong, Peng; Huang, Jianping; Li, Zhenchun; Liao, Wenyuan; Qu, Luping; Li, Qingyang; Liu, Peijun
2017-02-01
In finite-difference (FD) method, numerical dispersion is the dominant factor influencing the accuracy of seismic modelling. Various optimized FD schemes for scalar wave modelling have been proposed to reduce grid dispersion, while the optimized time-space domain FD schemes for elastic wave modelling have not been fully investigated yet. In this paper, an optimized FD scheme with Equivalent Staggered Grid (ESG) for elastic modelling has been developed. We start from the constant P- and S-wave speed elastic wave equations and then deduce analytical plane wave solutions in the wavenumber domain with eigenvalue decomposition method. Based on the elastic plane wave solutions, three new time-space domain dispersion relations of ESG elastic modelling are obtained, which are represented by three equations corresponding to P-, S- and converted-wave terms in the elastic equations, respectively. By using these new relations, we can study the dispersion errors of different spatial FD terms independently. The dispersion analysis showed that different spatial FD terms have different errors. It is therefore suggested that different FD coefficients to be used to approximate the three spatial derivative terms. In addition, the relative dispersion error in L2-norm is minimized through optimizing FD coefficients using Newton's method. Synthetic examples have demonstrated that this new optimal FD schemes have superior accuracy for elastic wave modelling compared to Taylor-series expansion and optimized space domain FD schemes.
Thakadu, Olekae T.; Irani, Tracy; Telg, Ricky
2011-01-01
The present study examined the relative effectiveness of 2 public instructional communication methods in improving selected predictors of knowledge-sharing behaviors among communities in the Okavango Delta, Botswana. A total of 120 subjects took part in a quasiexperimental study, with 2 experimental treatments: (a) visualized PowerPoint…
Total-variation-based methods for gravitational wave denoising
Torres, Alejandro; Font, José A; Ibáñez, José M
2014-01-01
We describe new methods for denoising and detection of gravitational waves embedded in additive Gaussian noise. The methods are based on Total Variation denoising algorithms. These algorithms, which do not need any a priori information about the signals, have been originally developed and fully tested in the context of image processing. To illustrate the capabilities of our methods we apply them to two different types of numerically-simulated gravitational wave signals, namely bursts produced from the core collapse of rotating stars and waveforms from binary black hole mergers. We explore the parameter space of the methods to find the set of values best suited for denoising gravitational wave signals under different conditions such as waveform type and signal-to-noise ratio. Our results show that noise from gravitational wave signals can be successfully removed with our techniques, irrespective of the signal morphology or astrophysical origin. We also combine our methods with spectrograms and show how those c...
Numerical Method for Wave Forces Acting on Partially Perforated Caisson
Institute of Scientific and Technical Information of China (English)
姜峰; 唐晓成; 金钊; 张莉; 陈洪洲
2015-01-01
The perforated caisson is widely applied to practical engineering because of its great advantages in effectively wave energy consumption and cost reduction. The attentions of many scientists were paid to the fluid–structure interaction between wave and perforated caisson studies, but until now, most concerns have been put on theoretical analysis and experimental model set up. In this paper, interaction between the wave and the partial perforated caisson in a 2D numerical wave flume is investigated by means of the renewed SPH algorithm, and the mathematical equations are in the form of SPH numerical approximation based on Navier–Stokes equations. The validity of the SPH mathematical method is examined and the simulated results are compared with the results of theoretical models, meanwhile the complex hydrodynamic characteristics when the water particles flow in or out of a wave absorbing chamber are analyzed and the wave pressure distribution of the perforated caisson is also addressed here. The relationship between the ratio of total horizontal force acting on caisson under regular waves and its influence factors is examined. The data show that the numerical calculation of the ratio of total horizontal force meets the empirical regression equation very well. The simulations of SPH about the wave nonlinearity and breaking are briefly depicted in the paper, suggesting that the advantages and great potentiality of the SPH method is significant compared with traditional methods.
Numerical method for wave forces acting on partially perforated caisson
Jiang, Feng; Tang, Xiao-cheng; Jin, Zhao; Zhang, Li; Chen, Hong-zhou
2015-04-01
The perforated caisson is widely applied to practical engineering because of its great advantages in effectively wave energy consumption and cost reduction. The attentions of many scientists were paid to the fluid-structure interaction between wave and perforated caisson studies, but until now, most concerns have been put on theoretical analysis and experimental model set up. In this paper, interaction between the wave and the partial perforated caisson in a 2D numerical wave flume is investigated by means of the renewed SPH algorithm, and the mathematical equations are in the form of SPH numerical approximation based on Navier-Stokes equations. The validity of the SPH mathematical method is examined and the simulated results are compared with the results of theoretical models, meanwhile the complex hydrodynamic characteristics when the water particles flow in or out of a wave absorbing chamber are analyzed and the wave pressure distribution of the perforated caisson is also addressed here. The relationship between the ratio of total horizontal force acting on caisson under regular waves and its influence factors is examined. The data show that the numerical calculation of the ratio of total horizontal force meets the empirical regression equation very well. The simulations of SPH about the wave nonlinearity and breaking are briefly depicted in the paper, suggesting that the advantages and great potentiality of the SPH method is significant compared with traditional methods.
Gao, Shanghua; Xue, Bing
2017-04-01
The dynamic range of the currently most widely used 24-bit seismic data acquisition devices is 10-20 dB lower than that of broadband seismometers, and this can affect the completeness of seismic waveform recordings under certain conditions. However, this problem is not easy to solve because of the lack of analog to digital converter (ADC) chips with more than 24 bits in the market. So the key difficulties for higher-resolution data acquisition devices lie in achieving more than 24-bit ADC circuit. In the paper, we propose a method in which an adder, an integrator, a digital to analog converter chip, a field-programmable gate array, and an existing low-resolution ADC chip are used to build a third-order 16-bit oversampling delta-sigma modulator. This modulator is equipped with a digital decimation filter, thus forming a complete analog to digital converting circuit. Experimental results show that, within the 0.1-40 Hz frequency range, the circuit board's dynamic range reaches 158.2 dB, its resolution reaches 25.99 dB, and its linearity error is below 2.5 ppm, which is better than what is achieved by the commercial 24-bit ADC chips ADS1281 and CS5371. This demonstrates that the proposed method may alleviate or even solve the amplitude-limitation problem that broadband observation systems so commonly have to face during strong earthquakes.
Analysis shear wave velocity structure obtained from surface wave methods in Bornova, Izmir
Energy Technology Data Exchange (ETDEWEB)
Pamuk, Eren, E-mail: eren.pamuk@deu.edu.tr; Akgün, Mustafa, E-mail: mustafa.akgun@deu.edu.tr [Department of Geophysical Engineering, Dokuz Eylul University, Izmir (Turkey); Özdağ, Özkan Cevdet, E-mail: cevdet.ozdag@deu.edu.tr [Dokuz Eylul University Rectorate, Izmir (Turkey)
2016-04-18
Properties of the soil from the bedrock is necessary to describe accurately and reliably for the reduction of earthquake damage. Because seismic waves change their amplitude and frequency content owing to acoustic impedance difference between soil and bedrock. Firstly, shear wave velocity and depth information of layers on bedrock is needed to detect this changing. Shear wave velocity can be obtained using inversion of Rayleigh wave dispersion curves obtained from surface wave methods (MASW- the Multichannel Analysis of Surface Waves, ReMi-Refraction Microtremor, SPAC-Spatial Autocorrelation). While research depth is limeted in active source study, a passive source methods are utilized for deep depth which is not reached using active source methods. ReMi method is used to determine layer thickness and velocity up to 100 m using seismic refraction measurement systems.The research carried out up to desired depth depending on radius using SPAC which is utilized easily in conditions that district using of seismic studies in the city. Vs profiles which are required to calculate deformations in under static and dynamic loads can be obtained with high resolution using combining rayleigh wave dispersion curve obtained from active and passive source methods. In the this study, Surface waves data were collected using the measurements of MASW, ReMi and SPAC at the İzmir Bornova region. Dispersion curves obtained from surface wave methods were combined in wide frequency band and Vs-depth profiles were obtained using inversion. Reliability of the resulting soil profiles were provided by comparison with theoretical transfer function obtained from soil paremeters and observed soil transfer function from Nakamura technique and by examination of fitting between these functions. Vs values are changed between 200-830 m/s and engineering bedrock (Vs>760 m/s) depth is approximately 150 m.
Mathematical Methods in Wave Propagation: Part 2--Non-Linear Wave Front Analysis
Jeffrey, Alan
1971-01-01
The paper presents applications and methods of analysis for non-linear hyperbolic partial differential equations. The paper is concluded by an account of wave front analysis as applied to the piston problem of gas dynamics. (JG)
Ossenkopf, V; Stutzki, J
2008-01-01
The Delta-variance analysis is an efficient tool for measuring the structural scaling behaviour of interstellar turbulence in astronomical maps. In paper I we proposed essential improvements to the Delta-variance analysis. In this paper we apply the improved Delta-variance analysis to i) a hydrodynamic turbulence simulation with prominent density and velocity structures, ii) an observed intensity map of rho Oph with irregular boundaries and variable uncertainties of the different data points, and iii) a map of the turbulent velocity structure in the Polaris Flare affected by the intensity dependence on the centroid velocity determination. The tests confirm the extended capabilities of the improved Delta-variance analysis. Prominent spatial scales were accurately identified and artifacts from a variable reliability of the data were removed. The analysis of the hydrodynamic simulations showed that the injection of a turbulent velocity structure creates the most prominent density structures are produced on a sca...
Delta-Sigma Modulated Photodetection Method to Reduce Laser Power Project
National Aeronautics and Space Administration — This delta-sigma technique may be thought of as a form of analog-to-digital converter (ADC). The proposed network offers a means of processing electronic signals...
A COMPARATIVE STUDY OF SPECTRAL METHODS WITH SEA WAVE DATA
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Two spectral methods are used to study sea wave data.Firstly, the estimated results calculated by the sequency spectrum method and frequency spectrum method are compared, and then the differences between the two methods are discussed.Furthermore, compared with frequency spectral analysis, sequency spectral analysis has many advantages: faster calculating speed, convenient use and high distinguishability.
Isentropic compressive wave generator and method of making same
Barker, L.M.
An isentropic compressive wave generator and method of making same are disclosed. The wave generator comprises a disk or flat pillow member having component materials of different shock impedances formed in a configuration resulting in a smooth shock impedance gradient over the thickness thereof for interpositioning between an impactor member and a target specimen for producing a shock wave of a smooth predictable rise time. The method of making the pillow member comprises the reduction of the component materials to a powder form and forming the pillow member by sedimentation and compressive techniques.
Investigation of lagoon lakes in Kocacay delta by using remote sensing method.
Irtem, Emel; Sacin, Yener
2012-04-01
Coasts are areas that are under the influence of the interaction of the air, water and land and attract attention with the abundance of their natural resources and therefore are subjected to excessive usage. This excessive usage may disturb the sensitive balance of the coast ecosystem. In this study, the changes in Arapçiftligi, Poyraz, Dalyan lakes area found in Kocacay delta located in the south coast of Marmara sea was evaluated between the periods of 2000 to 2007 with remote sensing method. These lakes, located on the shores, have a very sensitive naturally dynamic balance and very importance in terms of natural surroundings and the coastal zones management plan. It must be known the change of the lakes mentioned above area according to years. Research and applications have demonstrated the advantages of remote sensing and geographic information system techiques on river,delta, lake, lagoon lake, sensitivite areas in a lakeshore, coastal erosion etc. monitoring and management. In the study, we benefited from Erdas and Intergraph-Geomedia 6.1 image processing and GIS, and also from AutoCAD 2007 and NetCAD 4.0 computer-aided design (CAD) software. For 2000, 2001, 2005 and 2007 years (4 number) Landsat-5 TM satellite images belonging to the region were used. As a result of the study, Arapçiftligi, Dalyan and Poyraz lake areas, number of islets that are seen in the lakes were given in respect to years. Arapçiftligi lake shrank 29.5% in size in the years 2000 and 2007. The fact that the lake continued to get smaller in size even in periods of high precipitation may be due to the sediment flowing from the agricultural fields established close to the lake area. Dalyan and Poyraz lakes lost 60% in terms of their surface area in the years 2000 and 2007. In 2000-2001 periods, Dalyan and Poyraz lakes increased in size by 3.2%. The reason for this could be the excessive precipitation and the fact that the seawater from Marmara sea seeps into the lake. Protection of the
Directory of Open Access Journals (Sweden)
Ochuko Anomohanran
2013-01-01
Full Text Available This study was carried out to evaluate the aquifer characteristics of groundwater at Echi, Delta State, Nigeria. This was carried out by conducting electrical resistivity and spontaneous potential loggings in a drilled well at the study location. Pumping test using a one kilowatt pumping machine was carried out in the well. The logs were interpreted while the record of the pumping test was analysed using the Jacob straight line method. The result showed that five lithologic formations which are lateritic sand, clay, fine sand, medium grain sand and coarse sand exist in the area and that groundwater exist in the third, fourth and fifth formations. The analysis of the log record showed that the water quality increased with respect to the depth of the well. The value of the conductivity of the aquifer obtained from the analysis of the log record was 5.8Ã10-3 mS/m while the transmissivity was obtained as 86.0 m2/day. The specific capacity of the aquifer was obtained as 0.258. These values obtained from the test well revealed that the aquifer contained good quality water suitable for drinking and other purposes.
A Spectral Element Method for Nonlinear and Dispersive Water Waves
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter; Bigoni, Daniele; Eskilsson, Claes
The use of flexible mesh discretisation methods are important for simulation of nonlinear wave-structure interactions in offshore and marine settings such as harbour and coastal areas. For real applications, development of efficient models for wave propagation based on unstructured discretisation...... methods is of key interest. We present a high-order general-purpose three-dimensional numerical model solving fully nonlinear and dispersive potential flow equations with a free surface.......The use of flexible mesh discretisation methods are important for simulation of nonlinear wave-structure interactions in offshore and marine settings such as harbour and coastal areas. For real applications, development of efficient models for wave propagation based on unstructured discretisation...
Tang, Chen; Zhang, Fang; Li, Botao; Yan, Haiqing
2006-10-01
The ordinary differential equation (ODE) and partial differential equation (PDE) image- processing methods have been applied to reduce noise and enhance the contrast of electronic speckle pattern interferometry fringe patterns. We evaluate the performance of a few representative PDE denoising models quantitatively with two parameters called image fidelity and speckle index, and then we choose a good denoising model. Combining this denoising model with the ODE enhancement method, we make it possible to perform contrast enhancement and denoising simultaneously. Second, we introduce the delta-mollification method to smooth the unwrapped phase map. Finally, based on PDE image processing, delta mollification and some traditional techniques, an approach of phase extraction from a single fringe pattern is tested for computer-simulated and experimentally obtained fringe patterns. The method works well under a high noise level and limited visibility and can extract accurate phase values.
A three-dimensional boundary-layer method for flow over delta wings with leading-edge separation
Woodson, S. H.; Dejarnette, F. R.
1985-01-01
A three-dimensional, laminar boundary-layer method is applied to the incompressible flow over a slender delta wing at incidence. The predictor-corrector finite-difference scheme of Matsuno is used to difference the governing equations. The method has the advantages that no iterations are required to advance the solution and the cross-flow derivatives are formed independent of the cross-field direction. The difference scheme is demonstrated to yield accurate numerical results when compared to the exact solution of the three-dimensional boundary-layer equations for parabolic flow over a moving flat plate. The method is applied to delta wings of various sweep angles at angles of attack up to 20 deg., with the inviscid solution determined using a higher-order, three-dimensional panel method.
Numerical method for solving fuzzy wave equation
Kermani, M. Afshar
2013-10-01
In this study a numerical method for solving "fuzzy partial differential equation" (FPDE) is considered. We present difference method to solve the FPDEs such as fuzzy hyperbolic equation, then see if stability of this method exist, and conditions for stability are given.
Improved HPC method for nonlinear wave tank
DEFF Research Database (Denmark)
Zhu, Wenbo; Greco, Marilena; Shao, Yanlin
2017-01-01
The recently developed Harmonic Polynomial Cell (HPC) method has been proved to be a promising choice for solving potential-flow Boundary Value Problem (BVP). In this paper, a flux method is proposed to consistently deal with the Neumann boundary condition of the original HPC method and enhance...
Evaluation of bias correction methods for wave modeling output
Parker, K.; Hill, D. F.
2017-02-01
Models that seek to predict environmental variables invariably demonstrate bias when compared to observations. Bias correction (BC) techniques are common in the climate and hydrological modeling communities, but have seen fewer applications to the field of wave modeling. In particular there has been no investigation as to which BC methodology performs best for wave modeling. This paper introduces and compares a subset of BC methods with the goal of clarifying a "best practice" methodology for application of BC in studies of wave-related processes. Specific focus is paid to comparing parametric vs. empirical methods as well as univariate vs. bivariate methods. The techniques are tested on global WAVEWATCH III historic and future period datasets with comparison to buoy observations at multiple locations. Both wave height and period are considered in order to investigate BC effects on inter-variable correlation. Results show that all methods perform uniformly in terms of correcting statistical moments for individual variables with the exception of a copula based method underperforming for wave period. When comparing parametric and empirical methods, no difference is found. Between bivariate and univariate methods, results show that bivariate methods greatly improve inter-variable correlations. Of the bivariate methods tested the copula based method is found to be not as effective at correcting correlation while a "shuffling" method is unable to handle changes in correlation from historic to future periods. In summary, this study demonstrates that BC methods are effective when applied to wave model data and that it is essential to employ methods that consider dependence between variables.
Electronic standing waves on the surface of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}
Energy Technology Data Exchange (ETDEWEB)
Vershinin, M.; Misra, S.; Abe, Y.; Ono, S.; Ando, Y.; Yazdani, A
2004-08-01
Scanning tunneling microscopy (STM) measurements have shown that electronic states at the surface of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals form standing wave patterns at temperatures far below the superconducting transition. It has been shown that these patterns are consistent with those expected from the interference of well-defined quasi-particles around the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} Fermi surface. We have extended STM measurements of these standing wave patterns to higher temperatures and have found that four unit-cell periodicity patterns observed in the superconducting state persist well above T{sub C}, in the pseudogap state. In this regime, many different experimental studies of the cuprates have long claimed the absence of well-defined quasi-particles. If the pseudogap regime is indeed devoid of any coherent quasi-particles then our results suggest that other phenomena, such as stripe formation, must play a role in formation of these patterns.
Institute of Scientific and Technical Information of China (English)
Liu Xiqiang; Zhou Huilan; Li Hong; Gai Dianguang
2000-01-01
Based on the propagation characteristics of shear wave in the anisotropic layers, thecorrelation among several splitting shear-wave identification methods hasbeen studied. Thispaper puts forward the method estimating splitting shear-wave phases and its reliability byusing of the assumption that variance of noise and useful signal data obey normaldistribution. To check the validity of new method, the identification results and errorestimation corresponding to 95% confidence level by analyzing simulation signals have beengiven.
Efficient rendering of breaking waves using MPS method
Institute of Scientific and Technical Information of China (English)
WANG Qiang; ZHENG Yao; CHEN Chun; FUJIMOTO Tadahiro; CHIBA Norishige
2006-01-01
This paper proposes an approach for rendering breaking waves out of large-scale ofparticle-based simulation. Moving particle semi-implicit (MPS) is used to solve the governing equation, and 2D simulation is expanded to 3D representation by giving motion variation using fractional Brownian motion (fBm). The waterbody surface is reconstructed from the outlines of 2D simulation. The splashing effect is computed according to the properties of the particles. Realistic features of the wave are rendered on GPU, including the reflective and refractive effect and the effect of splash. Experiments showed that the proposed method can simulate large scale breaking waves efficiently.
Optical method for inspecting LSI patterns using reflected diffraction waves.
Kimura, S; Suda, K; Hase, S; Munakata, C
1988-03-15
An optical inspection method has been developed for finding defects in LSI lithographic patterns. A focused He-Ne laser beam scans the patterns on a wafer. The reflected diffraction waves around the wafer are observed. These diffraction waves indicate whether the patterns contain defects. To implement this judgment rapidly, signals of the waves characterizing the patterns are input directly into the address lines of random access memories. The system can detect a defect of ~0.8-microm diameter and inspect a 1-cm(2) chip in 9 s.
Saisho, S; Shimozawa, K; Yata, J
1986-12-20
Taking an advantage of the property of delta 4-steroid that have a maximum absorbance around 250 nm wave-length of ultraviolet, we devised an assay method for the determination of serum delta 4-steroids concentration using a reverse phase high performance liquid chromatography (HPLC)-UV spectrometry. The assay procedure was as follows: A mixed solvent containing methanol, acetonitrile and water in 55/3/42 by volume was used as a mobile phase, and which was pumped at a constant flow rate of 1.5 ml/min. The main column and precolumn used were ERC-ODS-1161 (phi 6 mm X 10 cm) and ERC-ODS-1652 (phi 6mm X 3 cm), respectively. Two liquid-liquid extraction methods were used. One was a conventional method using dichloromethane for an extraction solvent, and the other was a simplified method using Extrelut column and ethyl acetate. Before a practical assay we examined the retention time of each steroid determined and its ratio of peak height to that of the internal standard (dexamethasone). We found good correlations between the concentrations of cortisol (F), 17 alpha-hydroxyprogesterone (17-OHP) and 21-deoxycortisol (21-DOF) estimated by this HPLC method and those by highly specific radioimmunoassay method. The concentrations of cortisone (E) and F of eight umbilical venous blood specimens were 159.7 +/- 26.3 (Mean +/- SD) ng/ml and 93.3 +/- 58.9 ng/ml, respectively, and 17-OHP was detected 7 of them and its concentration was 17.4 +/- 12.4 ng/ml. On the other hand, 17-OHP and 21-DOF peaks could not be detected in 1 month old normal infants.(ABSTRACT TRUNCATED AT 250 WORDS)
VARIATION METHOD FOR ACOUSTIC WAVE IMAGING OF TWO DIMENSIONAL TARGETS
Institute of Scientific and Technical Information of China (English)
冯文杰; 邹振祝
2003-01-01
A new way of acoustic wave imaging was investigated. By using the Green function theory a system of integral equations, which linked wave number perturbation function with wave field, was firstly deduced. By taking variation on these integral equations an inversion equation, which reflected the relation between the little variation of wave number perturbation function and that of scattering field, was further obtained. Finally, the perturbation functions of some identical targets were reconstructed, and some properties of the novel method including converging speed, inversion accuracy and the abilities to resist random noise and identify complex targets were discussed. Results of numerical simulation show that the method based on the variation principle has great theoretical and applicable value to quantitative nondestructive evaluation.
Multi-Center Vector Field Methods for Wave Equations
Soffer, Avy; Xiao, Jianguo
2016-12-01
We develop the method of vector-fields to further study Dispersive Wave Equations. Radial vector fields are used to get a-priori estimates such as the Morawetz estimate on solutions of Dispersive Wave Equations. A key to such estimates is the repulsiveness or nontrapping conditions on the flow corresponding to the wave equation. Thus this method is limited to potential perturbations which are repulsive, that is the radial derivative pointing away from the origin. In this work, we generalize this method to include potentials which are repulsive relative to a line in space (in three or higher dimensions), among other cases. This method is based on constructing multi-centered vector fields as multipliers, cancellation lemmas and energy localization.
Finite element and discontinuous Galerkin methods for transient wave equations
Cohen, Gary
2017-01-01
This monograph presents numerical methods for solving transient wave equations (i.e. in time domain). More precisely, it provides an overview of continuous and discontinuous finite element methods for these equations, including their implementation in physical models, an extensive description of 2D and 3D elements with different shapes, such as prisms or pyramids, an analysis of the accuracy of the methods and the study of the Maxwell’s system and the important problem of its spurious free approximations. After recalling the classical models, i.e. acoustics, linear elastodynamics and electromagnetism and their variational formulations, the authors present a wide variety of finite elements of different shapes useful for the numerical resolution of wave equations. Then, they focus on the construction of efficient continuous and discontinuous Galerkin methods and study their accuracy by plane wave techniques and a priori error estimates. A chapter is devoted to the Maxwell’s system and the important problem ...
Institute of Scientific and Technical Information of China (English)
BI Chuanxing; CHEN Xinzhao; ZHOU Rong; CHEN Jian
2005-01-01
In the light of the concept of spherical wave source, the theoretical model of nearfield acoustic holography (NAH) based on the spherical wave superposition method (SWSM), including reconstruction of expansion coefficients, prediction of acoustic field, error sensitivity analysis, regularization method and a searching method with dual measurement surfaces for determining the optimal number of expansion terms, is established. Subsequently, the spherical wave source boundary point method (SWSBPM) and its application in the NAH are introduced briefly. Considering the similarity of the SWSM and the SWSBPM for realizing the NAH, they are compared. The similarities and differences of the two methods are illuminated by a rigorous mathematical justification and two experiments on a single source and two coherent sources in the semi-free acoustic field. And, the superiority of the NAH based on the SWSBPM is demonstrated.
Chiral metamaterials characterisation using the wave propagation retrieval method
DEFF Research Database (Denmark)
Andryieuski, Andrei; Lavrinenko, Andrei; Malureanu, Radu
2010-01-01
In this presentation we extend the wave propagation method for the retrieval of the effective properties to the case of chiral metamaterials with circularly polarised eigenwaves. The method is unambiguous, simple and provides bulk effective parameters. Advantages and constraints are discussed...
Chiral metamaterials characterisation using the wave propagation retrieval method
DEFF Research Database (Denmark)
Andryieuski, Andrei; Lavrinenko, Andrei; Malureanu, Radu
2010-01-01
In this presentation we extend the wave propagation method for the retrieval of the effective properties to the case of chiral metamaterials with circularly polarised eigenwaves. The method is unambiguous, simple and provides bulk effective parameters. Advantages and constraints are discussed...
A Wave Expansion Method for Aeroacoustic Propagation
Hammar, Johan
2016-01-01
Although it is possible to directly solve an entire flow-acoustics problem in one computation, this approach remains prohibitively large in terms of the computational resource required for most practical applications. Aeroacoustic problems are therefore usually split into two parts; one consisting of the source computation and one of the source propagation. Although both these parts entail great challenges on the computational method, in terms of accuracy and efficiency, it is still better th...
The Mississippi Delta Cardiovascular Health Examination Survey: Study Design and Methods
Directory of Open Access Journals (Sweden)
Vanessa L. Short
2014-01-01
Full Text Available Assessment of cardiovascular disease (CVD morbidity and mortality in subnational areas is limited. A model for regional CVD surveillance is needed, particularly among vulnerable populations underrepresented in current monitoring systems. The Mississippi Delta Cardiovascular Health Examination Survey (CHES is a population-based, cross-sectional study on a representative sample of adults living in the 18-county Mississippi Delta region, a rural, impoverished area with high rates of poor health outcomes and marked health disparities. The primary objectives of Delta CHES are to (1 determine the prevalence and distribution of CVD and CVD risk factors using self-reported and directly measured health metrics and (2 to assess environmental perceptions and existing policies that support or deter healthy choices. An address-based sampling frame is used for household enumeration and participant recruitment and an in-home data collection model is used to collect survey data, anthropometric measures, and blood samples from participants. Data from all sources will be merged into one analytic dataset and sample weights developed to ensure data are representative of the Mississippi Delta region adult population. Information gathered will be used to assess the burden of CVD and guide the development, implementation, and evaluation of cardiovascular health promotion and risk factor control strategies.
Method of folding a piecewise polynomial function in the delta function integral representation
Energy Technology Data Exchange (ETDEWEB)
Lee, D.K.
1978-12-01
A simple procedure is presented for determining the folded form of a piecewise polynomial function in the delta function integral representation. The procedure is useful in evaluating the autocorrelation function by means of the algebraic convolution technique developed by Polge and Hasy (IEEE Trans. Comput. pp. 970-975, Nov 1973).
Methods for wave equation prestack depth migration and numerical experiments
Institute of Scientific and Technical Information of China (English)
ZHANG Guanquan; ZHANG Wensheng
2004-01-01
In this paper the methods of wave theory based prestack depth migration and their implementation are studied. Using the splitting of wave operator, the wavefield extrapolation equations are deduced and the numerical schemes are presented. The numerical tests for SEG/EAEG model with MPI are performed on the PC-cluster. The numerical results show that the methods of single-shot (common-shot) migration and synthesized-shot migration are of practical values and can be applied to field data processing of 3D prestack depth migration.
An Unconditionally Stable Method for Solving the Acoustic Wave Equation
Directory of Open Access Journals (Sweden)
Zhi-Kai Fu
2015-01-01
Full Text Available An unconditionally stable method for solving the time-domain acoustic wave equation using Associated Hermit orthogonal functions is proposed. The second-order time derivatives in acoustic wave equation are expanded by these orthogonal basis functions. By applying Galerkin temporal testing procedure, the time variable can be eliminated from the calculations. The restriction of Courant-Friedrichs-Levy (CFL condition in selecting time step for analyzing thin layer can be avoided. Numerical results show the accuracy and the efficiency of the proposed method.
Multichannel analysis of surface wave method with the autojuggie
Tian, G.; Steeples, D.W.; Xia, J.; Miller, R.D.; Spikes, K.T.; Ralston, M.D.
2003-01-01
The shear (S)-wave velocity of near-surface materials and its effect on seismic-wave propagation are of fundamental interest in many engineering, environmental, and groundwater studies. The multichannel analysis of surface wave (MASW) method provides a robust, efficient, and accurate tool to observe near-surface S-wave velocity. A recently developed device used to place large numbers of closely spaced geophones simultaneously and automatically (the 'autojuggie') is shown here to be applicable to the collection of MASW data. In order to demonstrate the use of the autojuggie in the MASW method, we compared high-frequency surface-wave data acquired from conventionally planted geophones (control line) to data collected in parallel with the automatically planted geophones attached to steel bars (test line). The results demonstrate that the autojuggie can be applied in the MASW method. Implementation of the autojuggie in very shallow MASW surveys could drastically reduce the time required and costs incurred in such surveys. ?? 2003 Elsevier Science Ltd. All rights reserved.
A numerical method for determining the radial wave motion correction in plane wave couplers
DEFF Research Database (Denmark)
Cutanda Henriquez, Vicente; Barrera Figueroa, Salvador; Torras Rosell, Antoni
2016-01-01
solution is an analytical expression that estimates the difference between the ideal plane wave sound field and a more complex lossless sound field created by a non-planar movement of the microphone’s membranes. Alternatively, a correction may be calculated numerically by introducing a full model......Microphones are used for realising the unit of sound pressure level, the pascal (Pa). Electro-acoustic reciprocity is the preferred method for the absolute determination of the sensitivity. This method can be applied in different sound fields: uniform pressure, free field or diffuse field. Pressure...... calibration, carried out in plane wave couplers, is the most extended. Here plane wave propagation is assumed. While this assumption is valid at low and mid frequencies, it fails at higher frequencies because the membrane of the microphones is not moving uniformly, and there are viscous losses. An existing...
Signal processing method for shear wave velocity measurement
Institute of Scientific and Technical Information of China (English)
Hou Xingmin; Qu Shuying; Shi Xiangdong
2007-01-01
Soil shear wave velocity (SWV) is an important parameter in geotechnical engineering. To measure the soil SWV, three methods are generally used in China, including the single-hole method, cross-hole method and the surface-wave technique. An optimized approach based on a correlation function for single-hole SWV measurement is presented in this paper. In this approach, inherent inconsistencies of the artificial methods such as negative velocities, and too-large and too-small velocities, are eliminated from the single-hole method, and the efficiency of data processing is improved. In addition, verification using the cross-hole method of upper measuring points shows that the proposed optimized approach yields high precision in signal processing.
Galerkin ﬁnite element methods for wave problems
Indian Academy of Sciences (India)
T K Sengupta; S B Talla; S C Pradhan
2005-10-01
We compare here the accuracy, stability and wave propagation properties of a few Galerkin methods. The basic Galerkin methods with piecewise linear basis functions (called G1FEM here) and quadratic basis functions (called G2FEM) have been compared with the streamwise-upwind Petrov Galerkin (SUPG) method for their ability to solve wave problems. It is shown here that when the piecewise linear basis functions are replaced by quadratic polynomials, the stencils become much larger (involving ﬁve overlapping elements), with only a very small increase in spectral accuracy. It is also shown that all the three Galerkin methods have restricted ranges of wave numbers and circular frequencies over which the numerical dispersion relation matches with the physical dispersion relation - a central requirement for wave problems. The model one-dimensional convection equation is solved with a very ﬁne uniform grid to show the above properties. With the help of discontinuous initial condition, we also investigate the Gibbs’ phenomenon for these methods.
Robust Admissible Analyse of Uncertain Singular Systems via Delta Operator Method
Institute of Scientific and Technical Information of China (English)
WANG Wen; WANG Hui
2016-01-01
This paper investigates the problem of robust admissible analysis for uncertain singular delta operator systems(SDOSs). Firstly, we introduce the definition of generalized quadratic admissibility to ensure robust admissibility. Then, by means of LMI, a necessary and sufficient condition is given to prove a uncertain SDOS is generalized quadratic admissible. Finally, a numerical example is provided to demonstrate the effectiveness of the results in this paper.
Compressive spectral method for the simulation of the water waves
Bayindir, Cihan
2015-01-01
In this paper an approach for decreasing the computational effort required for the spectral simulations of the water waves is introduced. Signals with majority of the components zero, are known as the sparse signals. Like majority of the signals in the nature it can be realized that water waves are sparse either in time or in the frequency domain. Using the sparsity property of the water waves in the time or in the frequency domain, the compressive sampling algorithm can be used as a tool for improving the performance of the spectral simulation of the water waves. The methodology offered in this paper depends on the idea of using a smaller number of spectral components compared to the classical spectral method with a high number of components. After performing the time integration with a smaller number of spectral components and using the compressive sampling technique, it is shown that the water wave field can be reconstructed with a significantly better efficiency compared to the classical spectral method w...
Wave propagation in turbulent media: use of convergence acceleration methods.
Baram, A; Tsadka, S; Azar, Z; Tur, M
1988-06-01
We propose the use of convergence acceleration methods for the evaluation of integral expressions of an oscillatory nature, often encountered in the study of optical wave propagation in the turbulent atmosphere. These techniques offer substantial savings in computation time with appreciable gain in accuracy. As an example, we apply the Levin u acceleration scheme to the problem of remote sensing of transversal wind profiles.
Experimental Study for the Different Methods of Generating Millimeter Waves
Directory of Open Access Journals (Sweden)
Aamer Jamal Albaghdadi
2014-08-01
Full Text Available In this paper a analytical comparison and experimental implementation of different methods used in generating a low phase noise millimeter wave signals is presented. Four techniques were experimented and compared, Multiplication, phase lock loop (PLL, Injection locking (IL, and Injection locking with phase lock loop (ILPLL. The comparison and experimental results of a laboratory discussed.
Short-time Chebyshev wave packet method for molecular photoionization
Sun, Zhaopeng; Zheng, Yujun
2016-08-01
In this letter we present the extended usage of short-time Chebyshev wave packet method in the laser induced molecular photoionization dynamics. In our extension, the polynomial expansion of the exponential in the time evolution operator, the Hamiltonian operator can act on the wave packet directly which neatly avoids the matrix diagonalization. This propagation scheme is of obvious advantages when the dynamical system has large Hamiltonian matrix. Computational simulations are performed for the calculation of photoelectronic distributions from intense short pulse ionization of K2 and NaI which represent the Born-Oppenheimer (BO) model and Non-BO one, respectively.
An improved wave-vector frequency-domain method for nonlinear wave modeling.
Jing, Yun; Tao, Molei; Cannata, Jonathan
2014-03-01
In this paper, a recently developed wave-vector frequency-domain method for nonlinear wave modeling is improved and verified by numerical simulations and underwater experiments. Higher order numeric schemes are proposed that significantly increase the modeling accuracy, thereby allowing for a larger step size and shorter computation time. The improved algorithms replace the left-point Riemann sum in the original algorithm by the trapezoidal or Simpson's integration. Plane waves and a phased array were first studied to numerically validate the model. It is shown that the left-point Riemann sum, trapezoidal, and Simpson's integration have first-, second-, and third-order global accuracy, respectively. A highly focused therapeutic transducer was then used for experimental verifications. Short high-intensity pulses were generated. 2-D scans were conducted at a prefocal plane, which were later used as the input to the numerical model to predict the acoustic field at other planes. Good agreement is observed between simulations and experiments.
Miniature traveling wave tube and method of making
Kosmahl, Henry G. (Inventor)
1989-01-01
It is an object of the invention to provide a miniature traveling wave tube which will have most of the advantages of solid state circuitry but with higher efficiency and without being highly sensitive to temperature and various types of electromagnetic radiation and subatomic particles as are solid state devices. The traveling wave tube which is about 2.5 cm in length includes a slow wave circuit (SWS) comprising apertured fins with a top cover which is insulated from the fins by strips or rungs of electrically insulating, dielectric material. Another object of the invention is to construct a SWS of extremely small size by employing various grooving or etching methods and by providing insulating strips or rungs by various deposition and masking techniques.
Artificial Boundary Method for Calculating Ship Wave Resistance
Institute of Scientific and Technical Information of China (English)
文新; 韩厚德
2003-01-01
The calculation of wave resistance for a ship moving at constant speed near a free surface is considered. This wave resistance is calculated with a linearized steady potential model. To deal with the unboundedness of the physical domain in the potential flow problem, we introduce one vertical side as an artificial upstream boundary and two vertical sides as the artificial downstream boundaries. On the artificial boundaries, a sequence of high-order global artificial boundary conditions are given. Then the potential flow problem is reduced to a problem defined on a finite computational domain, which is equivalent to a variational problem. The solution of the variational problem by the finite element method gives the numerical approximation of the potential flow around the ship, which was used to calculate the wave resistance. The numerical examples show the accuracy and efficiency of the proposed numerical scheme.
Application of singular perturbation method in analyzing traffic density waves
Institute of Scientific and Technical Information of China (English)
SHEN Fei-ying; GE Hong-xia; LEI Li
2009-01-01
Car following model is one of microscopic models for describing traffic flow. Through linear stability analysis, the neutral stability lines and the critical points are obtained for the different types of car following models and two modified models. The singular perturbation method has been used to derive various nonlinear wave equations, such as the Korteweg-de-Vries (KdV) equation and the modified Korteweg-de-Vries (mKdV) equation, which could describe different density waves occurring in traffic flows under certain conditions. These density waves are mainly employed to depict the formation of traffic jams in the congested traffic flow. The general soliton solutions are given for the different types of car following models, and the results have been used to the modified models efficiently.
Laser ablation method for production of surface acoustic wave sensors
Lukyanov, Dmitry; Shevchenko, Sergey; Kukaev, Alexander; Safronov, Daniil
2016-10-01
Nowadays surface acoustic wave (SAW) sensors are produced using a photolithography method. In case of inertial sensors it suffers several disadvantages, such as difficulty in matching topologies produced on opposite sides of the wafer, expensive in small series production, not allowing further topology correction. In this case a laser ablation method seems promising. Details of a proposed technique are described in the paper along with results of its experimental test and discussion.
Self-adaptive method for high frequency multi-channel analysis of surface wave method
When the high frequency multi-channel analysis of surface waves (MASW) method is conducted to explore soil properties in the vadose zone, existing rules for selecting the near offset and spread lengths cannot satisfy the requirements of planar dominant Rayleigh waves for all frequencies of interest ...
Multi-stage temperature compensation method for Lamb wave measurements
Dworakowski, Ziemowit; Ambrozinski, Lukasz; Stepinski, Tadeusz
2016-11-01
One of the important issues related to the applications of Lamb waves for structural health monitoring is their undesired sensitivity to variation of environmental conditions. Temperature is the main factor that can affect wave propagation and hence significantly reduce performance of a SHM system. Therefore, there is a need for development of robust monitoring methods with low sensitivity to temperature variations. This paper is aimed at verification of efficiency of four methods designed for damage detection using Lamb wave measurements performed in variable environmental conditions. The methods investigated in the comparison are the following: optimal baseline selection approach, the damage index based on a signal alignment with respect to instantaneous phase, and a group measurement approach capable of distinguishing local damage-related changes from temperature-induced global ones. The fourth method relies on fusion all these solutions simultaneously. The methods' ability to damage detection is compared using a specimen that is subjected to large temperature changes. It is found that although all the methods have their strengths and weaknesses, a cooperation of all solutions allows for significant increase of the damage detection efficiency.
A Three-Point Method for Separating Incident and Reflected Waves over A Sloping Bed
Institute of Scientific and Technical Information of China (English)
CHANG Hsien-Kuo
2002-01-01
This study presents a three-point method for separating incident and reflected waves to explain normally incident waves' propagating over a sloping bed. Linear wave shoaling is used to determine changes in wave amplitude and phase in response to variations of bathymetry. The wave reflection coefficient and incident amplitude are estimated from wave heights measured at three fixed wave gauges with unequal spacing. Sensitivity analysis demonstrates that the proposed method can predict the reflection and amplitude of waves over a sloping bed more accurately than the two-point method.
Dinis, Pedro A.; Pereira, Alcides C.; Quinzeca, Domingos; Jombi, Domingos
2017-10-01
A strandplain at the downdrift side of the wave-dominated Catumbela delta (Angola) includes distinguishable deposits with very high natural radioactivity (up to 0.44 microSv/hour). In order to establish the geometry of these sedimentary units and understand their genetic processes, dose rate surveys were performed with the portable equipment Rados RDS-40WE. In addition, grain-size distribution, heavy-mineral composition and gamma-ray mass spectra of the high dose rate deposits were analysed. High dose rate values are found in ribbon units aligned parallel to the shoreline, which are a few tens of meters wide and up to approximately 3 km long. These units reflect the concentration of Th-bearing grains in coastal deposits enriched in heavy minerals. An integrated analysis of the high dose rate ribbons in GIS environment with aerial photography and topographic maps suggests that parts of the high dose rate units formed during the last two centuries may be related with the erosion of older shoreline deposits, due to updrift displacements of the Catumbela river outlet and recycling of shoreline accumulations with downdrift deposition. Simple gamma-ray surveys carried out with a portable detector can unravel depositional units characterised by significant enrichment in heavy-mineral grains that are likely to correspond to key events in the evolution of wave-dominated accumulations. The location of such deposits should be taken into account when planning future work using more expensive or time-consuming techniques.
Dinis, Pedro A.; Pereira, Alcides C.; Quinzeca, Domingos; Jombi, Domingos
2017-02-01
A strandplain at the downdrift side of the wave-dominated Catumbela delta (Angola) includes distinguishable deposits with very high natural radioactivity (up to 0.44 microSv/hour). In order to establish the geometry of these sedimentary units and understand their genetic processes, dose rate surveys were performed with the portable equipment Rados RDS-40WE. In addition, grain-size distribution, heavy-mineral composition and gamma-ray mass spectra of the high dose rate deposits were analysed. High dose rate values are found in ribbon units aligned parallel to the shoreline, which are a few tens of meters wide and up to approximately 3 km long. These units reflect the concentration of Th-bearing grains in coastal deposits enriched in heavy minerals. An integrated analysis of the high dose rate ribbons in GIS environment with aerial photography and topographic maps suggests that parts of the high dose rate units formed during the last two centuries may be related with the erosion of older shoreline deposits, due to updrift displacements of the Catumbela river outlet and recycling of shoreline accumulations with downdrift deposition. Simple gamma-ray surveys carried out with a portable detector can unravel depositional units characterised by significant enrichment in heavy-mineral grains that are likely to correspond to key events in the evolution of wave-dominated accumulations. The location of such deposits should be taken into account when planning future work using more expensive or time-consuming techniques.
Wave packet propagation across barriers by semiclassical initial value methods
Petersen, Jakob; Kay, Kenneth G.
2015-07-01
Semiclassical initial value representation (IVR) formulas for the propagator have difficulty describing tunneling through barriers. A key reason is that these formulas do not automatically reduce, in the classical limit, to the version of the Van Vleck-Gutzwiller (VVG) propagator required to treat barrier tunneling, which involves trajectories that have complex initial conditions and that follow paths in complex time. In this work, a simple IVR expression, that has the correct tunneling form in the classical limit, is derived for the propagator in the case of one-dimensional barrier transmission. Similarly, an IVR formula, that reduces to the Generalized Gaussian Wave Packet Dynamics (GGWPD) expression [D. Huber, E. J. Heller, and R. Littlejohn, J. Chem. Phys. 89, 2003 (1988)] in the classical limit, is derived for the transmitted wave packet. Uniform semiclassical versions of the IVR formulas are presented and simplified expressions in terms of real trajectories and WKB penetration factors are described. Numerical tests show that the uniform IVR treatment gives good results for wave packet transmission through the Eckart and Gaussian barriers in all cases examined. In contrast, even when applied with the proper complex trajectories, the VVG and GGWPD treatments are inaccurate when the mean energy of the wave packet is near the classical transmission threshold. The IVR expressions for the propagator and wave packet are cast as contour integrals in the complex space of initial conditions and these are generalized to potentially allow treatment of a larger variety of systems. A steepest descent analysis of the contour integral formula for the wave packet in the present cases confirms its relationship to the GGWPD method, verifies its semiclassical validity, and explains results of numerical calculations.
Forecasting ocean wave energy: A Comparison of the ECMWF wave model with time series methods
DEFF Research Database (Denmark)
Reikard, Gordon; Pinson, Pierre; Bidlot, Jean
2011-01-01
days. In selecting a method, the forecaster has a choice between physics-based models and statistical techniques. A further idea is to combine both types of models. This paper analyzes the forecasting properties of a well-known physics-based model, the European Center for Medium-Range Weather Forecasts......Recently, the technology has been developed to make wave farms commercially viable. Since electricity is perishable, utilities will be interested in forecasting ocean wave energy. The horizons involved in short-term management of power grids range from as little as a few hours to as long as several...... energy flux. In the initial tests, the ECMWF model and the statistical models are compared directly. The statistical models do better at short horizons, producing more accurate forecasts in the 1–5 h range. The ECMWF model is superior at longer horizons. The convergence point, at which the two methods...
The treatment of radioactive wastewater by ultrasonic standing wave method
Energy Technology Data Exchange (ETDEWEB)
Su-xia, Hou, E-mail: hsxljj@sina.com; Ji-jun, Luo; Bin, He; Ru-song, Li; Tao, Shen
2014-06-01
Highlights: • USWM can be considered as the green cleaning separation techniques. • A physical model of suspended radioactive particle is established. • A computer program is developed to achieve numerical calculation and analysis. • The experimental device for low-level radioactive wastes treatment is designed. • Lots of experimental data are used to analysis the influence of the parameters. - Abstract: The radiation hazards of radionuclide arising from the storage of nuclear weapons cannot be ignored to the operators. Ultrasonic standing wave methods can be considered as the green cleaning separation techniques with high efficiency. The application of ultrasonic standing wave methods for liquid radioactive wastes treatment requires solving many problems connected with the proper selection of the frequency and power of ultrasonic transducers, and the processing time, etc. Based on the model of one single suspended radioactive particle subjected to in the field of ultrasonic standing wave, the principle of the treatment of low-level radioactive wastewater by ultrasound was analyzed. The theoretical and simulation results show that under the action of ultrasonic standing wave, the particle will move toward the wave node plane, and the time of particle reaching the plane become shorter when the radius of particle and the frequency and power of ultrasound was enlarged. The experimental results show that the radioactive concentration of wastewater could be reduced from 400 Bq L{sup −1} to 9.3 Bq L{sup −1} and the decontamination efficiency was 97.68%. The decontamination efficiency could not be obviously improved by further increasing the treating time.
Full wave simulation of waves in ECRIS plasmas based on the finite element method
Energy Technology Data Exchange (ETDEWEB)
Torrisi, G. [INFN - Laboratori Nazionali del Sud, via S. Sofia 62, 95123, Catania, Italy and Università Mediterranea di Reggio Calabria, Dipartimento di Ingegneria dell' Informazione, delle Infrastrutture e dell' Energia Sostenibile (DIIES), Via Graziella, I (Italy); Mascali, D.; Neri, L.; Castro, G.; Patti, G.; Celona, L.; Gammino, S.; Ciavola, G. [INFN - Laboratori Nazionali del Sud, via S. Sofia 62, 95123, Catania (Italy); Di Donato, L. [Università degli Studi di Catania, Dipartimento di Ingegneria Elettrica Elettronica ed Informatica (DIEEI), Viale Andrea Doria 6, 95125 Catania (Italy); Sorbello, G. [INFN - Laboratori Nazionali del Sud, via S. Sofia 62, 95123, Catania, Italy and Università degli Studi di Catania, Dipartimento di Ingegneria Elettrica Elettronica ed Informatica (DIEEI), Viale Andrea Doria 6, 95125 Catania (Italy); Isernia, T. [Università Mediterranea di Reggio Calabria, Dipartimento di Ingegneria dell' Informazione, delle Infrastrutture e dell' Energia Sostenibile (DIIES), Via Graziella, I-89100 Reggio Calabria (Italy)
2014-02-12
This paper describes the modeling and the full wave numerical simulation of electromagnetic waves propagation and absorption in an anisotropic magnetized plasma filling the resonant cavity of an electron cyclotron resonance ion source (ECRIS). The model assumes inhomogeneous, dispersive and tensorial constitutive relations. Maxwell's equations are solved by the finite element method (FEM), using the COMSOL Multiphysics{sup ®} suite. All the relevant details have been considered in the model, including the non uniform external magnetostatic field used for plasma confinement, the local electron density profile resulting in the full-3D non uniform magnetized plasma complex dielectric tensor. The more accurate plasma simulations clearly show the importance of cavity effect on wave propagation and the effects of a resonant surface. These studies are the pillars for an improved ECRIS plasma modeling, that is mandatory to optimize the ion source output (beam intensity distribution and charge state, especially). Any new project concerning the advanced ECRIS design will take benefit by an adequate modeling of self-consistent wave absorption simulations.
Nonlinear instability and chaos in plasma wave-wave interactions. II. Numerical methods and results
Energy Technology Data Exchange (ETDEWEB)
Kueny, C.S.; Morrison, P.J.
1995-05-01
In Part I of this work and Physics of Plasmas, June 1995, the behavior of linearly stable, integrable systems of waves in a simple plasma model was described using a Hamiltonian formulation. It was shown that explosive instability arises from nonlinear coupling between modes of positive and negative energy, with well-defined threshold amplitudes depending on the physical parameters. In this concluding paper, the nonintegrable case is treated numerically. Several sets of waves are considered, comprising systems of two and three degrees of freedom. The time evolution is modelled with an explicit symplectic integration algorithm derived using Lie algebraic methods. When initial wave amplitudes are large enough to support two-wave decay interactions, strongly chaotic motion destroys the separatrix bounding the stable region for explosive triplets. Phase space orbits then experience diffusive growth to amplitudes that are sufficient for explosive instability, thus effectively reducing the threshold amplitude. For initial amplitudes too small to drive decay instability, small perturbations might still grow to arbitrary size via Arnold diffusion. Numerical experiments do not show diffusion in this case, although the actual diffusion rate is probably underestimated due to the simplicity of the model.
Integral Equation Methods for Electromagnetic and Elastic Waves
Chew, Weng; Hu, Bin
2008-01-01
Integral Equation Methods for Electromagnetic and Elastic Waves is an outgrowth of several years of work. There have been no recent books on integral equation methods. There are books written on integral equations, but either they have been around for a while, or they were written by mathematicians. Much of the knowledge in integral equation methods still resides in journal papers. With this book, important relevant knowledge for integral equations are consolidated in one place and researchers need only read the pertinent chapters in this book to gain important knowledge needed for integral eq
Gravitational gradients in gravitational wave detectors: data analysis methods
Garrison, David; Gonzalez, Gabriela; Khanna, Gaurav
2000-04-01
We present a method of analyzing seismic data at the sites of gravitational wave detectors to determine the possible influence of gravitational gradients as a noise source in the detectors. We use statistical methods to distinguish between local and gobal noise sources, as well as compare our findings to models of gravitational gradients (S. A. Hughes and K. S. Thorne, Physical Review D, Volume 58, 122002). We apply these methods to data taken at the Hanford LIGO site, and present preliminary results. This work was supported by Pennsylvannia State University and the National Science Foundation. We acknowledge the collaboration of the LIGO project while taking the data presented.
Accurate finite difference methods for time-harmonic wave propagation
Harari, Isaac; Turkel, Eli
1994-01-01
Finite difference methods for solving problems of time-harmonic acoustics are developed and analyzed. Multidimensional inhomogeneous problems with variable, possibly discontinuous, coefficients are considered, accounting for the effects of employing nonuniform grids. A weighted-average representation is less sensitive to transition in wave resolution (due to variable wave numbers or nonuniform grids) than the standard pointwise representation. Further enhancement in method performance is obtained by basing the stencils on generalizations of Pade approximation, or generalized definitions of the derivative, reducing spurious dispersion, anisotropy and reflection, and by improving the representation of source terms. The resulting schemes have fourth-order accurate local truncation error on uniform grids and third order in the nonuniform case. Guidelines for discretization pertaining to grid orientation and resolution are presented.
Wave properties in poroelastic media using a Wave Finite Element Method
Serra, Q.; Ichchou, M. N.; Deü, J.-F.
2015-01-01
The application of the bidirectional Wave Finite Element Method (WFE) to Biot-Allard's theory of poroelasticity is investigated. This method has been successfully used in previous elastodynamics studies. In the case of porous media, the rigidity of the layer is very low, leading to very small wavelengths, and a high dissipation rate occurs within the pores. These differences with the elastic case justify a study of their consequences on numerical results. In this paper, it is shown that despite these difficulties, the WFE provides an efficient tool to compute the waves propagating through poroelastic media. The influence of boundary conditions on wave propagation is discussed, as well as the convergence of the numerical results, depending on the spatial discretization, the order of shape functions, and the choice of the formulation. Finally, the wavenumbers predicted with this method are compared with some simplified models such as equivalent fluid models or equivalent plate models. It is shown that the WFE can be used to validate the assumptions made by the simplified models.
Wave Scattering in Heterogeneous Media using the Finite Element Method
2016-10-21
impose absorbing boundary conditions. A Rayleigh-Ritz approximation has been developed to obtain the depth eigensolution. The depth modes have a...several absorbing or nonreflecting boundary condition have been developed . In the present study, following Fix and Marin (1978) and Vendhan et. al...propagation. The two well-known methods that have been developed to study acoustic waves in depth dependent waveguides are the fast-field technique and the
Variational space–time (dis)continuous Galerkin method for nonlinear free surface water waves
Gagarina, E.; Ambati, V.R.; Vegt, van der J.J.W.; Bokhove, O.
2014-01-01
A new variational finite element method is developed for nonlinear free surface gravity water waves using the potential flow approximation. This method also handles waves generated by a wave maker. Its formulation stems from Miles’ variational principle for water waves together with a finite element
Variational space-time (dis)continuous Galerkin method for nonlinear free surface waves
Gagarina, E.; Vegt, van der J.J.W.; Ambati, V.R.; Bokhove, O.
2013-01-01
A new variational finite element method is developed for nonlinear free surface gravity water waves. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a space-time finite element discretization that is cont
Directory of Open Access Journals (Sweden)
H. Apel
2015-08-01
Full Text Available Many urban areas experience both fluvial and pluvial floods, because locations next to rivers are preferred settlement areas, and the predominantly sealed urban surface prevents infiltration and facilitates surface inundation. The latter problem is enhanced in cities with insufficient or non-existent sewer systems. While there are a number of approaches to analyse either fluvial or pluvial flood hazard, studies of combined fluvial and pluvial flood hazard are hardly available. Thus this study aims at the analysis of fluvial and pluvial flood hazard individually, but also at developing a method for the analysis of combined pluvial and fluvial flood hazard. This combined fluvial-pluvial flood hazard analysis is performed taking Can Tho city, the largest city in the Vietnamese part of the Mekong Delta, as example. In this tropical environment the annual monsoon triggered floods of the Mekong River can coincide with heavy local convective precipitation events causing both fluvial and pluvial flooding at the same time. Fluvial flood hazard was estimated with a copula based bivariate extreme value statistic for the gauge Kratie at the upper boundary of the Mekong Delta and a large-scale hydrodynamic model of the Mekong Delta. This provided the boundaries for 2-dimensional hydrodynamic inundation simulation for Can Tho city. Pluvial hazard was estimated by a peak-over-threshold frequency estimation based on local rain gauge data, and a stochastic rain storm generator. Inundation was simulated by a 2-dimensional hydrodynamic model implemented on a Graphical Processor Unit (GPU for time-efficient flood propagation modelling. All hazards – fluvial, pluvial and combined – were accompanied by an uncertainty estimation considering the natural variability of the flood events. This resulted in probabilistic flood hazard maps showing the maximum inundation depths for a selected set of probabilities of occurrence, with maps showing the expectation (median
Kesireddy, K.; Mareddy, A.
2007-05-01
Coastal populations are critically dependent upon the coastal aquifers for their freshwater requirements. Excessive withdrawal of groundwater leads to saline incursion and the consequent degradation of quality and quantity of freshwater. The paper describes a multiple parametric method of assessment of vulnerability of the coastal aquifer in Pennar delta, south India, in the context of the hydrogeological, biophysical, geochemical and socioeconomic environments of the delta. Seven parameters, forming the acronym LASTRIG viz. landuse, aquifer type, soil depth, groundwater table, rainfall, soil infiltration and geomorphology are made use in the assessment, and involve the use of remote sensing, GIS and modeling tools. The parameters are weighted, and a suitable ranking system has been designed to quantify the degree of vulnerability of the aquifer for salinization. It has been found that zones with high vulnerability index correlate well with zones of high TDS and chloride contents of groundwater. This observation thus validates the geochemical basis of the proposed LASTRIG system. The new system has been found useful in the management of the groundwater resources of the delta region. It has been made use of identify the aquifer segments which are in danger of being degraded, to enable the decision- makers to design counter measures to avoid further deterioration in water quality. Where the groundwater has already been rendered non-potable because of saline incursion, the LASTRIG index could be made use to identify possible use of that water for drinking by cattle, and for growing of salt-tolerant vegetables (e.g. beetroot and lettuce), and trees (e.g. casuarinas obese, Prosopis juliflora)
Ito, Yuji; Doki, Shinji; Okuma, Sigeru
1-bit signal processing based on delta-sigma modulation has been studied for hardware implementation of signal processng systems. In the 1-bit signal processing, finite word-length problems such as overflow and coefficent quantization error occur. To solve the problems, new design method with state space is proposed in this paper. Digital filters are designed to show the feasibility of the method. Firstly, L1/L2-sensitivity is shown to evaluate coefficient quantization error and L2 scaling constraints to prevent overflow. Secondly, state space equation is shown and L1/L2-sensitivity and L2-scaling constraints are extended to take filter structure and oversampling effects into account. Finally, the proposed method is shown to attain higher SNR than conventional ones.
Time reversal method for guided wave inspection in pipes
Institute of Scientific and Technical Information of China (English)
Fei DENG; Bin WU; Cunfu HE
2008-01-01
The application of the time reversal method in pipe-like structures based on finite element method (FEM) is investigated. A steel pipe model measuring 70 mm × 3.5 mm is used to analyze the reflection coef-ficient of the L(0,2) mode with the time reversal process. Simulation results show that the time reversal array method is beneficial to the improvement of the signal-to-noise ratio of a guided wave inspection system. As the intercepting window is widened, more energy is included in re-emitted signals, which leads to a large reflection coefficient of the L(0,2) mode. In parallel, a circumferential locating method based on the time reversal method is described. The time reversal process used for guided wave inspection leads to the temporal and spatial focusing. When the time reversal signals are re-emitted, the angular profile obtained at the axial loca-tion of the defect can be used to determine the circumfer-ential location of the defect. Except for a pipe with one defect, the circumferential locating method has been veri-fied on another pipe model with two defects. Meanwhile, the elements number of the time reversal array has been discussed for enhancing the discrimination of the defect circumferential location.
Material measurement method based on femtosecond laser plasma shock wave
Zhong, Dong; Li, Zhongming
2017-03-01
The acoustic emission signal of laser plasma shock wave, which comes into being when femtosecond laser ablates pure Cu, Fe, and Al target material, has been detected by using the fiber Fabry-Perot (F-P) acoustic emission sensing probe. The spectrum characters of the acoustic emission signals for three kinds of materials have been analyzed and studied by using Fourier transform. The results show that the frequencies of the acoustic emission signals detected from the three kinds of materials are different. Meanwhile, the frequencies are almost identical for the same materials under different ablation energies and detection ranges. Certainly, the amplitudes of the spectral character of the three materials show a fixed pattern. The experimental results and methods suggest a potential application of the plasma shock wave on-line measurement based on the femtosecond laser ablating target by using the fiber F-P acoustic emission sensor probe.
Linear density response function in the projector augmented wave method
DEFF Research Database (Denmark)
Yan, Jun; Mortensen, Jens Jørgen; Jacobsen, Karsten Wedel;
2011-01-01
We present an implementation of the linear density response function within the projector-augmented wave method with applications to the linear optical and dielectric properties of both solids, surfaces, and interfaces. The response function is represented in plane waves while the single......-particle eigenstates can be expanded on a real space grid or in atomic-orbital basis for increased efficiency. The exchange-correlation kernel is treated at the level of the adiabatic local density approximation (ALDA) and crystal local field effects are included. The calculated static and dynamical dielectric...... functions of Si, C, SiC, AlP, and GaAs compare well with previous calculations. While optical properties of semiconductors, in particular excitonic effects, are generally not well described by ALDA, we obtain excellent agreement with experiments for the surface loss function of graphene and the Mg(0001...
S. Baker(Department of Physics and Astronomy, University College London, London, United Kingdom); Bedard, R.; Patton, M.; Wilson, O.
1990-01-01
A method is described by which the free-field, open-circuit voltage sensitivity of a reversible underwater acoustic transducer may be obtained from measurements of its input electrical impedance in water and in air. This method, which we have termed the Delta-Z reciprocity calibration method, is being developed for the in-service calibration of sonar transducers installed in domes which can be flooded and purged. The application of the Delta-Z method to the calibration of a single tonpilz-typ...
Regional wave propagation using the discontinuous Galerkin method
Directory of Open Access Journals (Sweden)
S. Wenk
2013-01-01
Full Text Available We present an application of the discontinuous Galerkin (DG method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER Riemann problem. This ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy. We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.
Regional wave propagation using the discontinuous Galerkin method
Directory of Open Access Journals (Sweden)
S. Wenk
2012-08-01
Full Text Available We present an application of the discontinuous Galerkin (DG method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy. We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper-mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.
Shaaban, H.; El-Qady, G.; Al-Sayed, E.; Ghazala, H.; Taha, A. I.
2016-12-01
The Nile Delta is one of the oldest known ancient delta, largest and most important depositional complex in the Mediterranean sedimentary basin. Furthermore, it is a unique site in Egypt that is suitable for accumulation and preservation of the Quaternary sediments. In this work we applied time-domain electromagnetic (TEM) method to investigate the Quaternary sediments sequence as well as detecting the groundwater aquifer in the area of study. A suite of 232 TEM sounding at 43 stations were carried out using a "SIROTEM MK-3" time-domain electromagnetic system. A simple coincident loop configuration, in which the same loop transmits and receives signals, was employed with loop side length of 25 m. The 1-D modeling technique was applied to estimate the depth and the apparent resistivity of the interpreted geoelectrical data. Based on the interpretation of the acquired geophysical data, four geoelectric cross-sections were constructed. These sections show that the Upper Quaternary sequence consists of three geoelectric layers. The Holocene Nile mud is separated into two layers: the agricultural root zone (Layer 1) and thick water saturated mud (Layer 2). The Upper Pleistocene sandy aquifer (Layer 3) is very complicated non-linear boundary. This aquifer is the most important unit since it is considered as the main water bearing unit in the study area.
An Approximate Method for Analysis of Solitary Waves in Nonlinear Elastic Materials
Rushchitsky, J. J.; Yurchuk, V. N.
2016-05-01
Two types of solitary elastic waves are considered: a longitudinal plane displacement wave (longitudinal displacements along the abscissa axis of a Cartesian coordinate system) and a radial cylindrical displacement wave (displacements in the radial direction of a cylindrical coordinate system). The basic innovation is the use of nonlinear wave equations similar in form to describe these waves and the use of the same approximate method to analyze these equations. The distortion of the wave profile described by Whittaker (plane wave) or Macdonald (cylindrical wave) functions is described theoretically
Fault detection for T-S fuzzy time-delay systems: delta operator and input-output methods.
Li, Hongyi; Gao, Yabin; Wu, Ligang; Lam, H K
2015-02-01
This paper focuses on the problem of fault detection for Takagi-Sugeno fuzzy systems with time-varying delays via delta operator approach. By designing a filter to generate a residual signal, the fault detection problem addressed in this paper can be converted into a filtering problem. The time-varying delay is approximated by the two-term approximation method. Fuzzy augmented fault detection system is constructed in δ -domain, and a threshold function is given. By applying the scaled small gain theorem and choosing a Lyapunov-Krasovskii functional in δ -domain, a sufficient condition of asymptotic stability with a prescribed H∞ disturbance attenuation level is derived for the proposed fault detection system. Then, a solvability condition for the designed fault detection filter is established, with which the desired filter can be obtained by solving a convex optimization problem. Finally, an example is given to demonstrate the feasibility and effectiveness of the proposed method.
DSMC calculations for the delta wing. [Direct Simulation Monte Carlo method
Celenligil, M. Cevdet; Moss, James N.
1990-01-01
Results are reported from three-dimensional direct simulation Monte Carlo (DSMC) computations, using a variable-hard-sphere molecular model, of hypersonic flow on a delta wing. The body-fitted grid is made up of deformed hexahedral cells divided into six tetrahedral subcells with well defined triangular faces; the simulation is carried out for 9000 time steps using 150,000 molecules. The uniform freestream conditions include M = 20.2, T = 13.32 K, rho = 0.00001729 kg/cu m, and T(wall) = 620 K, corresponding to lambda = 0.00153 m and Re = 14,000. The results are presented in graphs and briefly discussed. It is found that, as the flow expands supersonically around the leading edge, an attached leeside flow develops around the wing, and the near-surface density distribution has a maximum downstream from the stagnation point. Coefficients calculated include C(H) = 0.067, C(DP) = 0.178, C(DF) = 0.110, C(L) = 0.714, and C(D) = 1.089. The calculations required 56 h of CPU time on the NASA Langley Voyager CRAY-2 supercomputer.
Dispersive photonic crystals from the plane wave method
Energy Technology Data Exchange (ETDEWEB)
Guevara-Cabrera, E.; Palomino-Ovando, M.A. [Facultad de Ciencias Físico Matemáticas, Benemérita Universidad Autónoma de Puebla, Apdo. Post. 165, Puebla, Pue. 72000, México (Mexico); Flores-Desirena, B., E-mail: bflores@fcfm.buap.mx [Facultad de Ciencias Físico Matemáticas, Benemérita Universidad Autónoma de Puebla, Apdo. Post. 165, Puebla, Pue. 72000, México (Mexico); Gaspar-Armenta, J.A. [Departamento de Investigación en Física de la Universidad de Sonora Apdo, Post 5-088, Hermosillo Sonora 83190, México (Mexico)
2016-03-01
Nowadays photonic crystals are widely used in many different applications. One of the most used methods to compute their band structure is the plane wave method (PWM). However, it can only be applied directly to non-dispersive media and be extended to systems with a few model dielectric functions. We explore an extension of the PWM to photonic crystals containing dispersive materials, that solves an eigenvalue equation for the Bloch wave vectors. First we compare our calculation with analytical results for one dimensional photonic crystals containing Si using experimental values of its optical parameters, and obtainig very well agreement, even for the spectrum region with strong absorption. Then, using the same method, we computed the band structure for a two dimensional photonic crystal without absorption, formed by an square array of MgO cylinders in air. The optical parameters for MgO were modeled with the Lorentz dielectric function. Finally, we studied an array of MgO cylinders in a metal, using Drude model without absorption, for the metal dielectric function. For this last case, we study the gap–midgap ratio as a function of the filling fraction for both the square and triangular lattice. The gap–midgap ratio is larger for the triangular lattice, with a maximum value of 10% for a filling fraction of 0.6. Our results show that the method can be applied to dispersive materials, and then to a wide range of applications where photonic crystals can be used.
An Analytical Method of Auxiliary Sources Solution for Plane Wave Scattering by Impedance Cylinders
DEFF Research Database (Denmark)
Larsen, Niels Vesterdal; Breinbjerg, Olav
2004-01-01
Analytical Method of Auxiliary Sources solutions for plane wave scattering by circular impedance cylinders are derived by transformation of the exact eigenfunction series solutions employing the Hankel function wave transformation. The analytical Method of Auxiliary Sources solution thus obtained...
An ultrasonic guided wave method to estimate applied biaxial loads
Shi, Fan; Michaels, Jennifer E.; Lee, Sang Jun
2012-05-01
Guided waves propagating in a homogeneous plate are known to be sensitive to both temperature changes and applied stress variations. Here we consider the inverse problem of recovering homogeneous biaxial stresses from measured changes in phase velocity at multiple propagation directions using a single mode at a specific frequency. Although there is no closed form solution relating phase velocity changes to applied stresses, prior results indicate that phase velocity changes can be closely approximated by a sinusoidal function with respect to angle of propagation. Here it is shown that all sinusoidal coefficients can be estimated from a single uniaxial loading experiment. The general biaxial inverse problem can thus be solved by fitting an appropriate sinusoid to measured phase velocity changes versus propagation angle, and relating the coefficients to the unknown stresses. The phase velocity data are obtained from direct arrivals between guided wave transducers whose direct paths of propagation are oriented at different angles. This method is applied and verified using sparse array data recorded during a fatigue test. The additional complication of the resulting fatigue cracks interfering with some of the direct arrivals is addressed via proper selection of transducer pairs. Results show that applied stresses can be successfully recovered from the measured changes in guided wave signals.
Quantum properties of d-wave YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} Josephson junction
Energy Technology Data Exchange (ETDEWEB)
Lombardi, Floriana [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)]. E-mail: Floriana.Lombardi@mc2.chalmers.se; Bauch, Thilo [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Johansson, Jesper [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Cedergren, Karin [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Lindstroem, Tobias [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Tafuri, Francesco [INFM-Dipartimento Ingegneria dell' Informazione, Seconda Universita di Napoli, Aversa (CE) (Italy); Stepantsov, Evgueni [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Institute of Crystallography, Russian Academy of Sciences, Moscow, RU 117333 (Russian Federation)
2006-03-15
We have measured the transport properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) dc SQUIDs with Josephson junctions characterized by a combination of 45 deg. [0 0 1] tilt and {alpha} [1 0 0] tilt grain boundary with {alpha} 0{sup o}, {+-}10{sup o} and 45{sup o}. By increasing the component of transport in the YBCO c-axis direction (increasing values of {alpha}), the SQUIDs showed an enhanced quality factor. At the same time, for all the devices the response under an external magnetic field presented the main features of an unconventional Josephson current phase relation with a pronounced sin 2{phi} component. Switching current measurements at low temperature (10th of mK) also revealed that the dynamics of grain boundary junction resulting from a combination of 45 deg. [0 0 1] and 45 deg. [1 0 0] tilt is dominated by macroscopic quantum tunnelling of the superconductive phase. The features are quite encouraging for applications of d-wave junctions in quantum circuitry.
Effective wave identification and interference analysis of the seismic reflection method in mines
Institute of Scientific and Technical Information of China (English)
HU Yun-bing; WU Yan-qing; KANG Hou-qing
2009-01-01
Through discussion of the time-distance curve characteristics of the direct wave and from the front, side and rear of the reflection waves of the seismic reflection method for advanced exploration in mines, and analysis of several major interference waves in mines, the differences in time-distance curve, frequency, apparent velocity between the effective wave and interference wave in the seismic reflection method for advanced ex-ploration are obtained. According to the differences, the effective wave is extracted and the interference wave is filtered and the system's precision and accuracy is improved.
A Time-Domain Method for Separating Incident and Reflected Irregular Waves
DEFF Research Database (Denmark)
Frigaard, Peter; Brorsen, Michael
In the hydraulic laboratory environment a seperation of an irregular wave field into incident waves propagating towards a structure, and reflected waves propagating away from the structure is often wanted. This is due to the fact that the response of the structure to the incident waves is target...... of the model test. Goda and Suzuki (1976) presented a frequency method for estimation of irregular incident and reflected waves in random waves. Mansard and Funke (1980) improved this method uaing a least squares technique. In the following, a time-domain method for seperating the incident waves...... and the reflected waves (SIRW-method), is presented. the method is based on the use of digital filters and can seperate the waves fields in real time....
Hernández, P; Peña, C; Torro, E; Wennekers, J; Wittig, H
2008-01-01
A new method to determine the low-energy couplings of the $\\Delta S=1$ weak Hamiltonian is presented. It relies on a matching of the topological poles in $1/m^2$ of three-point correlators of two pseudoscalar densities and a four-fermion operator, measured in lattice QCD, to the same observables computed in the $\\epsilon$-regime of chiral perturbation theory. We test this method in a theory with a light charm quark, i.e. with an SU(4) flavour symmetry. Quenched numerical measurements are performed in a 2 fm box, and chiral perturbation theory predictions are worked out up to next-to-leading order. The matching of the two sides allows to determine the weak low-energy couplings in the SU(4) limit. We compare the results with a previous determination, based on three-point correlators containing two left-handed currents, and discuss the merits and drawbacks of the two procedures.
Semiclassical methods for high frequency wave propagation in periodic media
Delgadillo, Ricardo A.
We will study high-frequency wave propagation in periodic media. A typical example is given by the Schrodinger equation in the semiclassical regime with a highly oscillatory periodic potential and external smooth potential. This problem presents a numerical challenge when in the semiclassical regime. For example, conventional methods such as finite differences and spectral methods leads to high numerical cost, especially in higher dimensions. For this reason, asymptotic methods like the frozen Gaussian approximation (FGA) was developed to provide an efficient computational tool. Prior to the development of the FGA, the geometric optics and Gaussian beam methods provided an alternative asymptotic approach to solving the Schrodinger equation efficiently. Unlike the geometric optics and Gaussian beam methods, the FGA does not lose accuracy due to caustics or beam spreading. In this thesis, we will briefly review the geometric optics, Gaussian beam, and FGA methods. The mathematical techniques used by these methods will aid us in formulating the Bloch-decomposition based FGA. The Bloch-decomposition FGA generalizes the FGA to wave propagation in periodic media. We will establish the convergence of the Bloch-decomposition based FGA to the true solution for Schrodinger equation and develop a gauge-invariant algorithm for the Bloch-decomposition based FGA. This algorithm will avoid the numerical difficulty of computing the gauge-dependent Berry phase. We will show the numerical performance of our algorithm by several one-dimensional examples. Lastly, we will propose a time-splitting FGA-based artificial boundary conditions for solving the one-dimensional nonlinear Schrodinger equation (NLS) on an unbounded domain. The NLS will be split into two parts, the linear and nonlinear parts. For the linear part we will use the following absorbing boundary strategy: eliminate Gaussian functions whose centers are too distant to a fixed domain.
Gravitational waves: Classification, Methods of detection, Sensitivities, and Sources
Kuroda, Kazuaki; Pan, Wei-Ping
2015-01-01
After giving a brief introduction and presenting a complete classification of gravitational waves (GWs) according to their frequencies, we review and summarize the detection methods, the sensitivities, and the sources. We notice that real-time detections are possible above 300 pHz. Below 300 pHz, the detections are possible on GW imprints or indirectly. We are on the verge of detection. The progress in this field will be promising and thriving. We will see improvement of a few orders to several orders of magnitude in the GW detection sensitivities over all frequency bands in the next hundred years.
A trigonometric method for the linear stochastic wave equation
Cohen, D; Sigg, M
2012-01-01
A fully discrete approximation of the linear stochastic wave equation driven by additive noise is presented. A standard finite element method is used for the spatial discretisation and a stochastic trigonometric scheme for the temporal approximation. This explicit time integrator allows for error bounds independent of the space discretisation and thus do not have a step size restriction as in the often used St\\"ormer-Verlet-leap-frog scheme. Moreover it enjoys a trace formula as does the exact solution of our problem. These favourable properties are demonstrated with numerical experiments.
Full Wave Simulation of Integrated Circuits Using Hybrid Numerical Methods
Tan, Jilin
Transmission lines play an important role in digital electronics, and in microwave and millimeter-wave circuits. Analysis, modeling, and design of transmission lines are critical to the development of the circuitry in the chip, subsystem, and system levels. In the past several decays, at the EM modeling level, the quasi-static approximation has been widely used due to its great simplicity. As the clock rates increase, the inter-connect effects such as signal delay, distortion, dispersion, reflection, and crosstalk, limit the performance of microwave systems. Meanwhile, the quasi-static approach loses its validity for some complex system structures. Since the successful system design of the PCB, MCM, and the chip packaging, rely very much on the computer aided EM level modeling and simulation, many new methods have been developed, such as the full wave approach, to guarantee the successful design. Many difficulties exist in the rigorous EM level analysis. Some of these include the difficulties in describing the behavior of the conductors with finite thickness and finite conductivity, the field singularity, and the arbitrary multilayered multi-transmission lines structures. This dissertation concentrates on the full wave study of the multi-conductor transmission lines with finite conductivity and finite thickness buried in an arbitrary lossy multilayered environment. Two general approaches have been developed. The first one is the integral equation method in which the dyadic Green's function for arbitrary layered media has been correctly formulated and has been tested both analytically and numerically. By applying this method, the double layered high dielectric permitivitty problem and the heavy dielectrical lossy problem in multilayered media in the CMOS circuit design have been solved. The second approach is the edge element method. In this study, the correct functional for the two dimensional propagation problem has been successfully constructed in a rigorous way
On the local plane wave methods for in situ measurement of acoustic absorption
Wijnant, Y.H.
2015-01-01
In this paper we address a series of so-called local plane wave methods (LPW) to measure acoustic absorption. As opposed to other methods, these methods do not rely on assumptions of the global sound field, like e.g. a plane wave or diffuse field, but are based on a local plane wave assumption. Ther
Focused Wave Properties Based on A High Order Spectral Method with A Non-Periodic Boundary
Institute of Scientific and Technical Information of China (English)
李金宣; 柳淑学
2015-01-01
In this paper, a numerical model is developed based on the High Order Spectral (HOS) method with a non-periodic boundary. A wave maker boundary condition is introduced to simulate wave generation at the incident boundary in the HOS method. Based on the numerical model, the effects of wave parameters, such as the assumed focused amplitude, the central frequency, the frequency bandwidth, the wave amplitude distribution and the directional spreading on the surface elevation of the focused wave, the maximum generated wave crest, and the shifting of the focusing point, are numerically investigated. Especially, the effects of the wave directionality on the focused wave properties are emphasized. The numerical results show that the shifting of the focusing point and the maximum crest of the wave group are dependent on the amplitude of the focused wave, the central frequency, and the wave amplitude distribution type. The wave directionality has a definite effect on multidirectional focused waves. Generally, it can even out the difference between the simulated wave amplitude and the amplitude expected from theory and reduce the shifting of the focusing points, implying that the higher order interaction has an influence on wave focusing, especially for 2D wave. In 3D wave groups, a broader directional spreading weakens the higher nonlinear interactions.
Method of synthesizing silica nanofibers using sound waves
Energy Technology Data Exchange (ETDEWEB)
Sharma, Jaswinder K.; Datskos, Panos G.
2015-09-15
A method for synthesizing silica nanofibers using sound waves is provided. The method includes providing a solution of polyvinyl pyrrolidone, adding sodium citrate and ammonium hydroxide to form a first mixture, adding a silica-based compound to the solution to form a second mixture, and sonicating the second mixture to synthesize a plurality of silica nanofibers having an average cross-sectional diameter of less than 70 nm and having a length on the order of at least several hundred microns. The method can be performed without heating or electrospinning, and instead includes less energy intensive strategies that can be scaled up to an industrial scale. The resulting nanofibers can achieve a decreased mean diameter over conventional fibers. The decreased diameter generally increases the tensile strength of the silica nanofibers, as defects and contaminations decrease with the decreasing diameter.
Method of synthesizing silica nanofibers using sound waves
Energy Technology Data Exchange (ETDEWEB)
Sharma, Jaswinder K.; Datskos, Panos G.
2017-08-08
A method for synthesizing silica nanofibers using sound waves is provided. The method includes providing a solution of polyvinyl pyrrolidone, adding sodium citrate and ammonium hydroxide to form a first mixture, adding a silica-based compound to the solution to form a second mixture, and sonicating the second mixture to synthesize a plurality of silica nanofibers having an average cross-sectional diameter of less than 70 nm and having a length on the order of at least several hundred microns. The method can be performed without heating or electrospinning, and instead includes less energy intensive strategies that can be scaled up to an industrial scale. The resulting nanofibers can achieve a decreased mean diameter over conventional fibers. The decreased diameter generally increases the tensile strength of the silica nanofibers, as defects and contaminations decrease with the decreasing diameter.
Method of synthesizing silica nanofibers using sound waves
Sharma, Jaswinder K.; Datskos, Panos G.
2015-09-15
A method for synthesizing silica nanofibers using sound waves is provided. The method includes providing a solution of polyvinyl pyrrolidone, adding sodium citrate and ammonium hydroxide to form a first mixture, adding a silica-based compound to the solution to form a second mixture, and sonicating the second mixture to synthesize a plurality of silica nanofibers having an average cross-sectional diameter of less than 70 nm and having a length on the order of at least several hundred microns. The method can be performed without heating or electrospinning, and instead includes less energy intensive strategies that can be scaled up to an industrial scale. The resulting nanofibers can achieve a decreased mean diameter over conventional fibers. The decreased diameter generally increases the tensile strength of the silica nanofibers, as defects and contaminations decrease with the decreasing diameter.
The N/D method with non-perturbative left-hand-cut discontinuity and the $^1S_0$ $NN$ partial wave
Entem, D R
2016-01-01
In this letter we deduce an integral equation that allows to calculate the exact left-hand-cut discontinuity for an uncoupled $S$-wave partial-wave amplitude in potential scattering for a given finite-range potential. The results obtained from the $N/D$ method for the partial-wave amplitude are rigorous, since now the discontinuities along the left-hand cut and right-hand cut are exactly known. This solves the open question with respect to the $N/D$ method and the effect on the final result of the non-perturbative iterative diagrams in the evaluation of $\\Delta(A)$. A big advantage of the method is that short-range physics (corresponding to integrated out degrees of freedom within low-energy Effective Field Theory) does not contribute to $\\Delta(A)$ and it manifests through the extra subtractions that are implemented within the method. We show the equivalence of the $N/D$ method and the Lippmann-Schwinger (LS) equation for a nonsingular $^1S_0$ $NN$ potential (Yukawa potential). The equivalence between the $N...
Hijaz, Faraj; Killiny, Nabil
2016-05-20
Delta-aminolevulinic (δ-ALA) acid is an important intermediate for tetrapyrroles biosynthesis and it has recently received great attention in plant physiology and human toxicology. However, the colorimetric method which is the most common method for determination of δ-ALA is time consuming and is not specific. In this study, a method for determination of δ-ALA in plant tissues was developed based on the trimethylsilyl (TMS) derivative of the pyrrole formed from the reaction of δ-ALA with ethyl acetoacetate via Knorr condensation. The δ-ALA in the HCl extract was reacted with ethyl acetoacetate to form a pyrrole. Then, the pyrrole compound was extracted using ethyl acetate and the solvent was evaporated to dryness. The dried sample was derivatized to its TMS ester and analyzed using GC-MS. The concentration of δ-ALA in citrus leaves incubated with levulinic acid was also determined by the conventional colorimetric method. The linear range was 10-200ppm in the full scan mode and 0.1-20ppm in the selected ion monitoring (SIM). The limit of detection was 6ppm in the full scan and 0.05ppm in SIM mode, representing a four-fold increase in sensitivity compared to the colorimetric method. The GC-MS method developed in this study is simple, accurate, sensitive, and could also be used to measure δ-ALA in other biological samples.
A method for separating O-wave and X-wave and its application in digital ionosonde
Directory of Open Access Journals (Sweden)
Wang Shun
2014-01-01
Full Text Available Separation for O wave and X wave is a very important job in interpretation of ionograms, which is premise for automatic scaling. In this paper, a new digital method for separating O wave and X wave is presented, based on a numerical synthesizing technique, which is different from using image recognition to separate trace O and trace X in the ionograms, and from using the electrical method to synthesize and detect circularly polarized waves. By replacing analog phase shifters and switches in existing ionosonde with digital phase shifters with different initial phase, 0°, +90°, −90°, circularly polarized waves are synthesized digitally within the range of 1-30 MHz, which eliminates the nonlinearity and expands the bandwidth of the ionosonde, and there is no need to switch the analog switches continuously. The new method has been successfully applied to CAS-DIS ionosonde and testing results show that the new digital method is capable of separating O wave and X wave well.
Method of Calculation of Crown Wall Stability in Oblique Waves
DEFF Research Database (Denmark)
Burcharth, Hans F.
2007-01-01
The wave loading along a structure exposed to oblique waves varies in time and space. Despite of this, the wave generated pressures are usually recorded by gauges only in one position of the wall (more gauges densily spaced is regarded as one position).......The wave loading along a structure exposed to oblique waves varies in time and space. Despite of this, the wave generated pressures are usually recorded by gauges only in one position of the wall (more gauges densily spaced is regarded as one position)....
Time evolution of the wave equation using rapid expansion method
Pestana, Reynam C.
2010-07-01
Forward modeling of seismic data and reverse time migration are based on the time evolution of wavefields. For the case of spatially varying velocity, we have worked on two approaches to evaluate the time evolution of seismic wavefields. An exact solution for the constant-velocity acoustic wave equation can be used to simulate the pressure response at any time. For a spatially varying velocity, a one-step method can be developed where no intermediate time responses are required. Using this approach, we have solved for the pressure response at intermediate times and have developed a recursive solution. The solution has a very high degree of accuracy and can be reduced to various finite-difference time-derivative methods, depending on the approximations used. Although the two approaches are closely related, each has advantages, depending on the problem being solved. © 2010 Society of Exploration Geophysicists.
Dominant partition method. [based on a wave function formalism
Dixon, R. M.; Redish, E. F.
1979-01-01
By use of the L'Huillier, Redish, and Tandy (LRT) wave function formalism, a partially connected method, the dominant partition method (DPM) is developed for obtaining few body reductions of the many body problem in the LRT and Bencze, Redish, and Sloan (BRS) formalisms. The DPM maps the many body problem to a fewer body one by using the criterion that the truncated formalism must be such that consistency with the full Schroedinger equation is preserved. The DPM is based on a class of new forms for the irreducible cluster potential, which is introduced in the LRT formalism. Connectivity is maintained with respect to all partitions containing a given partition, which is referred to as the dominant partition. Degrees of freedom corresponding to the breakup of one or more of the clusters of the dominant partition are treated in a disconnected manner. This approach for simplifying the complicated BRS equations is appropriate for physical problems where a few body reaction mechanism prevails.
Hernández, Antonio García; Monteiro, Mário J P F G; Suárez, Juan Carlos; Reese, Daniel R; Pascual-Granado, Javier; Garrido, Rafael
2015-01-01
Delta Scuti ($\\delta$ Sct) stars are intermediate-mass pulsators, whose intrinsic oscillations have been studied for decades. However, modelling their pulsations remains a real theoretical challenge, thereby even hampering the precise determination of global stellar parameters. In this work, we used space photometry observations of eclipsing binaries with a $\\delta$ Sct component to obtain reliable physical parameters and oscillation frequencies. Using that information, we derived an observational scaling relation between the stellar mean density and a frequency pattern in the oscillation spectrum. This pattern is analogous to the solar-like large separation but in the low order regime. We also show that this relation is independent of the rotation rate. These findings open the possibility of accurately characterizing this type of pulsator and validate the frequency pattern as a new observable for $\\delta$ Sct stars.
Tupu methods of spatial-temporal pattern on land use change：a case study in the Yellow River Delta
Institute of Scientific and Technical Information of China (English)
YEQinghua; TIANGuoliang; LIUGaohuan; YEJingmin; YAOXin; LIUQingsheng; LOUWeiguo; WUShuguang
2004-01-01
Comprehensive study on land-use change of spatial pattern and temporal process is the key component in LUCC study nowadays. Based on the theories and methods of Geo-information Tupu(Carto-methodology in Geo-information, CMGI), integration of spatial pattern and temporal processes of land-use change in the Yellow River Delta (YRD) are studied in the paper, which is supported by ERDAS and ARC/INFO software. The main contents include: (1) concept models of Tupu by spatial-temporal integration on land-use change, whose Tupu unit is synthesized by "Spatial·Attribute·Process" features and composed of relatively homogeneous geographical unit and temporal unit; (2)data sources and handling process, where four stages of spatial features in 1956, 1984, 1991, and 1996are acquired; (3) integration of series of temporal-spatial Tupu, reconstruction series of "Arising" Tupu,spatial-temporal Process Tupu and the spatial temporal Pattern Tupu on land-use change by remap tables; (4) Pattern Tupu analysis on land-use change in YRD during 1956-1996; and (5) spatial difference of the Pattem Tupu analysis by dynamic Tupu units. The various landform units and seven sub-deltas generated by the Yellow River since 1855 are different. The Tupu analysis on land-use in the paper is a promising try on the comprehensive research of "spatial pattern of dynamic process" and "temporal process of spatial pattern" in LUCC research. The Tupu methodology would be a powerful and efficient tool on integrated studies of spatial pattern and temporal process in Geo-science.
Schulze, Brigit; Wirth, Christian; Linke, Petra; Brand, Willi A; Kuhlmann, Iris; Horna, Viviana; Schulze, Ernst-Detlef
2004-11-01
We present a new, rapid method for high-resolution online determination of delta13C in tree rings, combining laser ablation (LA), combustion (C), gas chromatography (GC) and isotope ratio mass spectrometry (IRMS) (LA-C-GC-IRMS). Sample material was extracted every 6 min with a UV-laser from a tree core, leaving 40-microm-wide holes. Ablated wood dust was combusted to CO2 at 700 degrees C, separated from other gases on a GC column and injected into an isotope ratio mass spectrometer after removal of water vapor. The measurements were calibrated against an internal and an external standard. The tree core remained intact and could be used for subsequent dendrochronological and dendrochemical analyses. Cores from two Scots pine trees (Pinus sylvestris spp. sibirica Lebed.) from central Siberia were sampled. Inter- and intra-annual patterns of delta13C in whole-wood and lignin-extracted cores were indistinguishable apart from a constant offset, suggesting that lignin extraction is unnecessary for our method. Comparison with the conventional method (microtome slicing, elemental analysis and IRMS) indicated high accuracy of the LA-C-GC-IRMS measurements. Patterns of delta13C along three parallel ablation lines on the same core showed high congruence. A conservative estimate of the precision was +/- 0.24 per thousand. Isotopic patterns of the two Scots pine trees were broadly similar, indicating a signal related to the forest stand's climate history. The maximum variation in delta13C over 22 years was about 5 per thousand, ranging from -27 to -22.3 per thousand. The most obvious pattern was a sharp decline in delta13C during latewood formation and a rapid increase with spring early growth. We conclude that the LA-C-GC-IRMS method will be useful in elucidating short-term climate effects on the delta13C signal in tree rings.
Cubic Trigonometric B-spline Galerkin Methods for the Regularized Long Wave Equation
Irk, Dursun; Keskin, Pinar
2016-10-01
A numerical solution of the Regularized Long Wave (RLW) equation is obtained using Galerkin finite element method, based on Crank Nicolson method for the time integration and cubic trigonometric B-spline functions for the space integration. After two different linearization techniques are applied, the proposed algorithms are tested on the problems of propagation of a solitary wave and interaction of two solitary waves.
Jiang, Jia-Jia; Duan, Fa-Jie; Li, Yan-Chao; Hua, Xiang-Ning
2014-03-01
Synchronization sampling is very important in underwater towed array system where every acquisition node (AN) samples analog signals by its own analog-digital converter (ADC). In this paper, a simple and effective synchronization sampling method is proposed to ensure synchronized operation among different ANs of the underwater towed array system. We first present a master-slave synchronization sampling model, and then design a high accuracy phase-locked loop to synchronize all delta-sigma ADCs to a reference clock. However, when the master-slave synchronization sampling model is used, both the time-delay (TD) of messages traveling along the wired transmission medium and the jitter of the clocks will bring out synchronization sampling error (SSE). Therefore, a simple method is proposed to estimate and compensate the TD of the messages transmission, and then another effective method is presented to overcome the SSE caused by the jitter of the clocks. An experimental system with three ANs is set up, and the related experimental results verify the validity of the synchronization sampling method proposed in this paper.
Werners, Saskia Elisabeth; van Loon-Steensma, Jantsje Mintsje; Oost, Albert Peter
2016-01-01
Many methods are available to support adaptation planning. Yet there is little guidance on their selection. A recently developed diagnostic framework offers a structured set of criteria to choose research methods for specific adaptation questions. It has been derived from science-driven cases mostly
Revised single-spacecraft method for determining wave vector k and resolving space-time ambiguity
Bellan, P. M.
2016-09-01
A practical method is proposed for determining the wave vector of waves from single-spacecraft measurements. This wave vector knowledge can then be used to remove the space-time ambiguity produced by frequency Doppler shift associated with spacecraft motion. The method involves applying the Wiener-Khinchin theorem to cross correlations of the current and magnetic field oscillations and to autocorrelations of the magnetic field oscillations. The method requires that each wave frequency component map to a unique wave vector, a condition presumed true in many spacecraft measurement situations. Examples validating the method are presented.
Integrability: mathematical methods for studying solitary waves theory
Wazwaz, Abdul-Majid
2014-03-01
In recent decades, substantial experimental research efforts have been devoted to linear and nonlinear physical phenomena. In particular, studies of integrable nonlinear equations in solitary waves theory have attracted intensive interest from mathematicians, with the principal goal of fostering the development of new methods, and physicists, who are seeking solutions that represent physical phenomena and to form a bridge between mathematical results and scientific structures. The aim for both groups is to build up our current understanding and facilitate future developments, develop more creative results and create new trends in the rapidly developing field of solitary waves. The notion of the integrability of certain partial differential equations occupies an important role in current and future trends, but a unified rigorous definition of the integrability of differential equations still does not exist. For example, an integrable model in the Painlevé sense may not be integrable in the Lax sense. The Painlevé sense indicates that the solution can be represented as a Laurent series in powers of some function that vanishes on an arbitrary surface with the possibility of truncating the Laurent series at finite powers of this function. The concept of Lax pairs introduces another meaning of the notion of integrability. The Lax pair formulates the integrability of nonlinear equation as the compatibility condition of two linear equations. However, it was shown by many researchers that the necessary integrability conditions are the existence of an infinite series of generalized symmetries or conservation laws for the given equation. The existence of multiple soliton solutions often indicates the integrability of the equation but other tests, such as the Painlevé test or the Lax pair, are necessary to confirm the integrability for any equation. In the context of completely integrable equations, studies are flourishing because these equations are able to describe the
Variational space-time (dis)continuous Galerkin method for nonlinear free surface waves
Gagarina, E; Vegt, van der, N.F.A.; Ambati, V.R.; Bokhove, O.
2013-01-01
A new variational finite element method is developed for nonlinear free surface gravity water waves. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a space-time finite element discretization that is continuous in space and discontinuous in time. The key features of this formulation are: (i) a discrete variational approach that gives rise to conservation of discrete energy and phase space and prese...
Comparison between wave generation methods for numerical simulation of bimodal seas
Directory of Open Access Journals (Sweden)
Daniel A. Thompson
2016-01-01
Full Text Available This paper describes an investigation of the generation of desired sea states in a numerical wave model. Bimodal sea states containing energetic swell components can be coastal hazards along coastlines exposed to large oceanic fetches. Investigating the effects of long-period bimodal seas requires large computational domains and increased running time to ensure the development of the desired sea state. Long computational runs can cause mass stability issues due to the Stokes drift and wave reflection, which in turn affect results through the variation of the water level. A numerical wave flume, NEWRANS, was used to investigate two wave generation methods: the wave paddle method, allowing for a smaller domain; and the internal mass source function method, providing an open boundary allowing reflected waves to leave the domain. The two wave generation methods were validated against experimental data by comparing the wave generation accuracy and the variance of mass in the model during simulations. Results show that the wave paddle method not only accurately generates the desired sea state but also provides a more stable simulation, in which mass fluctuation has less of an effect on the water depth during the long-duration simulations. As a result, it is suggested that the wave paddle method with active wave absorption is preferable to the internal wave maker option when investigating intermediate-depth long-period bimodal seas for long-duration simulations.
Directory of Open Access Journals (Sweden)
Hamed Faghanpour Ganji
2016-09-01
Full Text Available The present study further examines two recent semi-analytic methods, a reduced order of nonlinear differential transformation method (also called RDTM and differential transformation method along with Pade approximation to discuss Jaulent–Miodek and coupled Whitham–Broer–Kaup equations. The basic ideas of these methods are briefly introduced and performance of the proposed methods for above mentioned equations is evaluated via comparing with exact solution. The results illustrate that the so-called DTM method, unlike RDTM, due to the presence of secular terms (similar to perturbation method, cannot be found practical for nonlinear partial differential equations (particularly in Acoustic and Wave propagation problems even through utilizing Pade approximation; meanwhile, RDTM method, despite its simplicity and rapid convergence, assured a significant accuracy and great agreement, and thus it is fair to say that nonlinear problems together with Acoustic application which cannot be solved via Analytical methods, can be studied with reduced order of nonlinear differential transformation method.
Wu, Kun; Zhang, Feng; Min, Jinzhong; Yu, Qiu-Run; Wang, Xin-Yue; Ma, Leiming
2016-09-01
The adding method, which could calculate the infrared radiative transfer (IRT) in inhomogeneous atmosphere with multiple layers, has been applied to δ -four-stream discrete ordinate method (DOM). This scheme is referred as δ -4DDA. However, there is a lack of application for adding method of δ -four-stream spherical harmonic expansion approximation (SHM) to solve infrared radiative transfer through multiple layers. In this paper, the adding method for δ -four-stream SHM (δ -4SDA) will be obtained and the accuracy of it will be evaluated as well. The result of δ -4SDA in an idealized medium with homogeneous optical property is significantly more accurate than that of the adding method for δ -two-stream DOM (δ -2DDA). The relative errors of δ -2DDA can be over 15% in thin optical depths for downward emissivity, while errors of δ -4SDA are bounded by 2%. However, the result of δ -4SDA is slightly less accurate than that of δ -4DDA. In a radiation model with realistic atmospheric profile considering gaseous transmission, the accuracy for heating rate of δ -4SDA is significantly superior than that of δ -2DDA, especially for the cloudy sky. The accuracy for heating rate of δ -4SDA is slightly less accurate than that of δ -4DDA under water cloud conditions, while it is superior than that of δ -4DDA in ice cloud cases. Beside, the computational efficiency of δ -4SDA is higher than that of δ -4DDA.
Experimental methods of molecular matter-wave optics.
Juffmann, Thomas; Ulbricht, Hendrik; Arndt, Markus
2013-08-01
We describe the state of the art in preparing, manipulating and detecting coherent molecular matter. We focus on experimental methods for handling the quantum motion of compound systems from diatomic molecules to clusters or biomolecules.Molecular quantum optics offers many challenges and innovative prospects: already the combination of two atoms into one molecule takes several well-established methods from atomic physics, such as for instance laser cooling, to their limits. The enormous internal complexity that arises when hundreds or thousands of atoms are bound in a single organic molecule, cluster or nanocrystal provides a richness that can only be tackled by combining methods from atomic physics, chemistry, cluster physics, nanotechnology and the life sciences.We review various molecular beam sources and their suitability for matter-wave experiments. We discuss numerous molecular detection schemes and give an overview over diffraction and interference experiments that have already been performed with molecules or clusters.Applications of de Broglie studies with composite systems range from fundamental tests of physics up to quantum-enhanced metrology in physical chemistry, biophysics and the surface sciences.Nanoparticle quantum optics is a growing field, which will intrigue researchers still for many years to come. This review can, therefore, only be a snapshot of a very dynamical process.
Characterization and diagnostic methods for geomagnetic auroral infrasound waves
Oldham, Justin J.
Infrasonic perturbations resulting from auroral activity have been observed since the 1950's. In the last decade advances in infrasonic microphone sensitivity, high latitude sensor coverage, time series analysis methods and computational efficiency have elucidated new types of auroral infrasound. Persistent periods of infrasonic activity associated with geomagnetic sub-storms have been termed geomagnetic auroral infrasound waves [GAIW]. We consider 63 GAIW events recorded by the Fairbanks, AK infrasonic array I53US ranging from 2003 to 2014 and encompassing a complete solar cycle. We make observations of the acoustic features of these events alongside magnetometer, riometer, and all-sky camera data in an effort to quantify the ionospheric conditions suitable for infrasound generation. We find that, on average, the generation mechanism for GAIW is confined to a region centered about ~60 0 longitude east of the anti-Sun-Earth line and at ~770 North latitude. We note furthermore that in all cases considered wherein imaging riometer data are available, that dynamic regions of heightened ionospheric conductivity periodically cross the overhead zenith. Consistent features in concurrent magnetometer conditions are also noted, with irregular oscillations in the horizontal component of the field ubiquitous in all cases. In an effort to produce ionosphere based infrasound free from the clutter and unknowns typical of geophysical observations, an experiment was undertaken at the High Frequency Active Auroral Research Program [HAARP] facility in 2012. Infrasonic signals appearing to originate from a source region overhead were observed briefly on 9 August 2012. The signals were observed during a period when an electrojet current was presumed to have passed overhead and while the facilities radio transmitter was periodically heating the lower ionosphere. Our results suggest dynamic auroral electrojet currents as primary sources of much of the observed infrasound, with
An improved method for delta 15N measurements in ice cores
Directory of Open Access Journals (Sweden)
M. Leuenberger
2008-02-01
Full Text Available The use of isotopic ratios of nitrogen gas (δ15N trapped in ice cores as a paleothermometer to characterise abrupt climate changes is becoming a widespread technique. The versatility of the technique could be enhanced, for instance in quantifying small temperature changes during the last glacial period in Antarctic ice cores, by using high precision methods. In this paper, we outline a method for measuring δ15N to a precision of 0.006permil (1σ, n=9 from replicate ice core samples. The high precision results from removing oxygen, carbon dioxide and water vapour from the air extracted from ice cores. The advantage of the technique is that it does not involve correction for isobaric interference due to CO+ ions. We also highlight the importance of oxygen removal from the sample, and how it influences δ15N measurements. The results show that a small amount of oxygen in the sample can be detrimental to achieving an optimum precision in δ15N measurements of atmospheric nitrogen trapped ice core samples.
Directory of Open Access Journals (Sweden)
S. Lecacheux
2012-07-01
Full Text Available This paper outlines a new approach devoted to the analysis of extreme waves in presence of several wave regimes. It entails discriminating the different wave regimes from offshore wave data using classification algorithms, before conducting the extreme wave analysis for each regime separately. The concept is applied to the pilot site of Reunion Island which is affected by three main wave regimes: southern waves, trade-wind waves and cyclonic waves. Several extreme wave scenarios are determined for each regime, based on real historical cases (for cyclonic waves and extreme value analysis (for non-cyclonic waves. For each scenario, the nearshore wave characteristics are modelled all around Reunion Island and the linear theory equations are used to back calculate the equivalent deep-water wave characteristics for each portion of the coast. The relative exposure of the coastline to the extreme waves of each regime is determined by comparing the equivalent deep-water wave characteristics.
This method provides a practical framework to perform an analysis of extremes within a complex environment presenting several sources of extreme waves. First, at a particular coastal location, it allows for inter-comparison between various kinds of extreme waves that are generated by different processes and that may occur at different periods of the year. Then, it enables us to analyse the alongshore variability in wave exposition, which is a good indicator of potential runup extreme values. For the case of Reunion Island, cyclonic waves are dominant offshore around the island, with equivalent deep-water wave heights up to 18 m for the northern part. Nevertheless, due to nearshore wave refraction, southern waves may become as energetic as cyclonic waves on the western part of the island and induce similar impacts in terms of runup and submersion. This method can be easily transposed to other case studies and can be adapted, depending on the data
Waveform synthesis of surface waves in a laterally heterogeneous earth by the Gaussian beam method
Yomogida, K.; Aki, K.
1985-01-01
The present investigation is concerned with an application of the Gaussian beam method to surface waves in the laterally heterogeneous earth. The employed method has been developed for ray tracing and synthesizing seismograms of surface waves in cases involving the laterally heterogeneous earth. The procedure is based on formulations derived by Yomogida (1985). Vertical structure of the wave field is represented by the eigenfunctions of normal mode theory, while lateral variation is expressed by the parabolic equation as in two-dimensional acoustic waves or elastic body waves. It is demonstrated that a large-amplitude change can result from a slight perturbation in the phase velocity model.
A probabilistic method for constructing wave time-series at inshore locations using model scenarios
Long, Joseph W.; Plant, Nathaniel G.; Dalyander, P. Soupy; Thompson, David M.
2014-01-01
Continuous time-series of wave characteristics (height, period, and direction) are constructed using a base set of model scenarios and simple probabilistic methods. This approach utilizes an archive of computationally intensive, highly spatially resolved numerical wave model output to develop time-series of historical or future wave conditions without performing additional, continuous numerical simulations. The archive of model output contains wave simulations from a set of model scenarios derived from an offshore wave climatology. Time-series of wave height, period, direction, and associated uncertainties are constructed at locations included in the numerical model domain. The confidence limits are derived using statistical variability of oceanographic parameters contained in the wave model scenarios. The method was applied to a region in the northern Gulf of Mexico and assessed using wave observations at 12 m and 30 m water depths. Prediction skill for significant wave height is 0.58 and 0.67 at the 12 m and 30 m locations, respectively, with similar performance for wave period and direction. The skill of this simplified, probabilistic time-series construction method is comparable to existing large-scale, high-fidelity operational wave models but provides higher spatial resolution output at low computational expense. The constructed time-series can be developed to support a variety of applications including climate studies and other situations where a comprehensive survey of wave impacts on the coastal area is of interest.
Institute of Scientific and Technical Information of China (English)
H.SAGHI; M.J.KETABDARI; S.BOOSHI
2012-01-01
A two-dimensional (2D) numerical model is developed for the wave simulation and propagation in a wave flume.The fluid flow is assumed to be viscous and incompressible,and the Navier-Stokes and continuity equations are used as the governing equations.The standard κ-ε model is used to model the turbulent flow.The NavierStokes equations are discretized using the staggered grid finite difference method and solved by the simplified marker and cell (SMAC) method. Waves are generated and propagated using a piston type wave maker. An open boundary condition is used at the end of the numerical flume.Some standard tests,such as the lid-driven cavity,the constant unidirectional velocity field,the shearing flow,and the dam-break on the dry bed,are performed to valid the model.To demonstrate the capability and accuracy of the present method,the results of generated waves are compared with available wave theories.Finally,the clustering technique (CT) is used for the mesh generation,and the best condition is suggested.
The (′/-Expansion Method for Abundant Traveling Wave Solutions of Caudrey-Dodd-Gibbon Equation
Directory of Open Access Journals (Sweden)
Hasibun Naher
2011-01-01
Full Text Available We construct the traveling wave solutions of the fifth-order Caudrey-Dodd-Gibbon (CDG equation by the (/-expansion method. Abundant traveling wave solutions with arbitrary parameters are successfully obtained by this method and the wave solutions are expressed in terms of the hyperbolic, the trigonometric, and the rational functions. It is shown that the (/-expansion method is a powerful and concise mathematical tool for solving nonlinear partial differential equations.
A New General Algebraic Method and Its Application to Shallow Long Wave Approximate Equations
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A new general algebraic method is presented to uniformly construct a series of exact solutions for nonlinear evolution equations (NLEEs). For illustration, we apply the new method to shallow long wave approximate equations and successfully obtain abundant new exact solutions, which include rational solitary wave solutions and rational triangular periodic wave solutions. The method is straightforward and concise, and it can also be applied to other nonlinear evolution equations in mathematical physics.
Herder, J.L.; Van der Wijk, V.
2010-01-01
The invention relates to a delta robot comprising a stationary base (2) and a movable platform (3) that is connected to the base with three chains of links (4,5,6), and comprising a balancing system incorporating at least one pantograph (7) for balancing the robot's center of mass, wherein the at le
Herder, J.L.; Van der Wijk, V.
2010-01-01
The invention relates to a delta robot comprising a stationary base (2) and a movable platform (3) that is connected to the base with three chains of links (4,5,6), and comprising a balancing system incorporating at least one pantograph (7) for balancing the robot's center of mass, wherein the at le
Finite volume methods for submarine debris flows and generated waves
Kim, Jihwan; Løvholt, Finn; Issler, Dieter
2016-04-01
Submarine landslides can impose great danger to the underwater structures and generate destructive tsunamis. Submarine debris flows often behave like visco-plastic materials, and the Herschel-Bulkley rheological model is known to be appropriate for describing the motion. In this work, we develop numerical schemes for the visco-plastic debris flows using finite volume methods in Eulerian coordinates with two horizontal dimensions. We provide parameter sensitivity analysis and demonstrate how common ad-hoc assumptions such as including a minimum shear layer depth influence the modeling of the landslide dynamics. Hydrodynamic resistance forces, hydroplaning, and remolding are all crucial terms for underwater landslides, and are hence added into the numerical formulation. The landslide deformation is coupled to the water column and simulated in the Clawpack framework. For the propagation of the tsunamis, the shallow water equations and the Boussinesq-type equations are employed to observe how important the wave dispersion is. Finally, two cases in central Norway, i.e. the subaerial quick clay landslide at Byneset in 2012, and the submerged tsunamigenic Statland landslide in 2014, are both presented for validation. The research leading to these results has received funding from the Research Council of Norway under grant number 231252 (Project TsunamiLand) and the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement 603839 (Project ASTARTE).
Levshin, Anatoli L.; Barmin, Mikhail P.; Moschetti, Morgan P.; Mendoza, Carlos; Ritzwoller, Michael H.
2012-01-01
The purpose of this study is to develop and test a modiﬁcation to a previous method of regional seismic event location based on Empirical Green’s Functions (EGFs) produced from ambient seismic noise. Elastic EGFs between pairs of seismic stations are determined by cross-correlating long ambient noise time-series recorded at the two stations. The EGFs principally contain Rayleigh- and Love-wave energy on the vertical and transverse components, respectively, and we utilize these signals between about 5 and 12 s period. The previous method, based exclusively on Rayleigh waves, may yield biased epicentral locations for certain event types with hypocentral depths between 2 and 5 km. Here we present theoretical arguments that show how Love waves can be introduced to reduce or potentially eliminate the bias. We also present applications of Rayleigh- and Love-wave EGFs to locate 10 reference events in the western United States. The separate Rayleigh and Love epicentral locations and the joint locations using a combination of the two waves agree to within 1 km distance, on average, but conﬁdence ellipses are smallest when both types of waves are used.
Kaneko, Nobu-hisa; Maruyama, Michitaka; Urano, Chiharu; Kiryu, Shogo
2012-01-01
A method of AC waveform synthesis with quantum-mechanical accuracy has been developed on the basis of the Josephson effect in national metrology institutes, not only for its scientific interest but its potential benefit to industries. In this paper, we review the development of Josephson arbitrary waveform synthesizers based on the two types of Josephson junction array and their distinctive driving methods. We also discuss a new operation technique with multibit delta-sigma modulation and a thermometer code, which possibly enables the generation of glitch-free waveforms with high voltage levels. A Josephson junction array for this method has equally weighted branches that are operated by thermometer-coded bias current sources with multibit delta-sigma conversion.
A Method and an Apparatus for Generating a Phase-Modulated Wave Front of Electromagnetic Radiation
DEFF Research Database (Denmark)
2002-01-01
The present invention provides a method and a system for generating a phase-modulated wave front. According to the present invention, the spatial phase-modulation is not performed on the different parts of the wave front individually as in known POSLMs. Rather, the spatial phase-modulation of the......The present invention provides a method and a system for generating a phase-modulated wave front. According to the present invention, the spatial phase-modulation is not performed on the different parts of the wave front individually as in known POSLMs. Rather, the spatial phase......-modulation of the present invention is performed by generating an amplitude modulation in the wave front, Fourier or Fresnel transforming the amplitude modulated wave front, filtering Fourier or Fresnel components of the Fourier or Fresnel distribution with a spatial filter such as a phase contrast filter, and regenerating...... the wave front whereby the initial amplitude modulation has transformed into a phase-modulation....
Wave Number Method for Three-Dimensional Steady-State Acoustic Problems
Institute of Scientific and Technical Information of China (English)
HUANG Fei; HE Zeng; WEI Jun-hong; PENG Wei-cai
2007-01-01
Based on the indirect Trefftz approach, a wave number method (WNM) is proposed to deal with three-dimensional steady-state acoustic problems. In the WNM, the dynamic pressure response variable is approximated by a set of wave functions, which exactly satisfy the Helmholtz equation. The set of wave functions comprise the exact solutions of the homogeneous part of the governing equations and some particular solution functions. The unknown coefficients of the wave functions can be obtained by enforcing the pressure approximation to satisfy the boundary conditions. Compared with the boundary element method (BEM), the WNM have a smaller system matrix, and is applicable to the radiation problems since the wave functions are independent of the domain size. A 3D acoustic cavity is exemplified to show the properties of the method. The results show that the wave number method is more efficient than the BEM, and it is fairly accurate.
A NUMERICAL CALCULATION METHOD FOR EIGENVALUE PROBLEMS OF NONLINEAR INTERNAL WAVES
Institute of Scientific and Technical Information of China (English)
SHI Xin-gang; FAN Zhi-song; LIU Hai-long
2009-01-01
Generally speaking, the background shear current U(z)must be taken into account in eigenvalue problems of nonlinear internal waves in ocean, as is different from those of linear internal waves. A numerical calculation method for eigenvalue problems of nonlinear internal waves is presented in this paper on the basis of the Thompson-Haskell's calculation method. As an application of this method, at a station (21°N, 117°15′E) in the South China Sea, a modal structure and parameters of nonlinear internal waves are calculated, and the results closely agree with the calculated results based on observation by Yang et al..
Modeling seismic wave propagation in heterogeneous medium using overlap domain pseudospectral method
Institute of Scientific and Technical Information of China (English)
YAN Jiu-peng; WANG Yan-bin
2008-01-01
Pseudospectral method is an efficient and high accuracy numerical method for simulating seismic wave propagation in heterogeneous earth medium. Since its derivative operator is global, this method is commonly considered not suitable for parallel computation. In this paper, we introduce the parallel overlap domain decomposition scheme and give a parallel pseudospectral method implemented on distributed memory PC cluster system for modeling seismic wave propagation in heterogeneous medium. In this parallel method, the medium is decomposed into several subdomains and the wave equations are solved in each subdomain simultaneously. The solutions in each subdomain are connected through the transferring at the overlapped region. Using 2D models, we compared the parallel and traditional pseudospectral method, analyzed the accuracy of the parallel method. The results show that the parallel method can efficiently reduce computation time for the same accuracy as the traditional method. This method could be applied to large scale modeling of seismic wave propagation in 3D heterogeneous medium.
Talebian-Ashkezari, Alireza; Abolhasani, Ali Akbar
2016-01-01
We study the evolution of the "non-perturbative" metric perturbations in a Bianchi background in the long-wavelength limit. By applying the gradient expansion to the equations of motion we exhibit a generalized "Separate Universe" approach to the cosmological perturbation theory. Having found this consistent separate universe picture, we introduce the "{\\delta}M formalism" for calculating the evolution of the tensor perturbations in anisotropic inflation models in almost similar way as the so-called {\\delta}N formula for the super-horizon dynamics of the curvature perturbations. Likewise its ancestor, {\\delta}N formalism, this new method can substantially reduce the amount of calculations related to the evolution of the tensor modes.
Characteristics and method of synthesis seismic wave based on wavelet reconstruction
Institute of Scientific and Technical Information of China (English)
ZOU Li-hua; LIU Ai-ping; YANG Hong; CHAI Xin-jian; SHANG Xin; DAI Su-liang; DONG Bo
2007-01-01
A novel method of synthesizing seismic wave using wavelet reconstruction is proposed and compared with the traditional method of using theory of Fourier transform. By adjusting the frequency band energy and taking it as criterion, the formula of synthesizing seismic wave is deduced. Using the design parameters specified in Chinese Seismic Design Code for buildings, seismic waves are synthesized. Moreover, the method of selecting wavelet bases in synthesizing seismic wave and the influence of the damping ratio on synthesizing results are analyzed.The results show that the synthesis seismic waves using wavelet bases can represent the characteristics of the seismic wave as well as the ground characteristic period, and have good time-frequency non-stationary.
DEFF Research Database (Denmark)
Alvarez, Yuri; Cappellin, Cecilia; Las-Heras, Fernando
2008-01-01
A comparison between two recently developed methods for antenna diagnostics is presented. On one hand, the Spherical Wave Expansion-to-Plane Wave Expansion (SWE-PWE), based on the relationship between spherical and planar wave modes. On the other hand, the Sources Reconstruction Method (SRM), based...
Teixeira, Helena; Verstraete, Alain; Proença, Paula; Corte-Real, Francisco; Monsanto, Paula; Vieira, Duarte Nuno
2007-08-01
A fully validated, sensitive and specific method for the extraction and quantification of Delta(9)-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-Delta(9)-THC (THC-COOH) and for the detection of 11-hydroxy-Delta(9)-THC (11-OH THC) in oral fluid, urine and whole blood is presented. Solid-phase extraction and liquid chromatography-mass spectrometry (LC-MS) technique were used, with electrospray ionization. Three ions were monitored for THC and THC-COOH and two for 11-OH THC. The compounds were quantified by selected ion recording of m/z 315.31, 329.18 and 343.16 for THC, 11-OH THC and THC-COOH, respectively, and m/z 318.27 and 346.26 for the deuterated internal standards, THC-d(3) and THC-COOH-d(3), respectively. The method proved to be precise for THC and THC-COOH both in terms of intra-day and inter-day analysis, with intra-day coefficients of variation (CV) less than 6.3, 6.6 and 6.5% for THC in saliva, urine and blood, respectively, and 6.8 and 7.7% for THC-COOH in urine and blood, respectively. Day-to-day CVs were less than 3.5, 4.9 and 11.3% for THC in saliva, urine and blood, respectively, and 6.2 and 6.4% for THC-COOH in urine and blood, respectively. Limits of detection (LOD) were 2 ng/mL for THC in oral fluid and 0.5 ng/mL for THC and THC-COOH and 20 ng/mL for 11-OH THC, in urine and blood. Calibration curves showed a linear relationship for THC and THC-COOH in all samples (r(2)>0.999) within the range investigated. The procedure presented here has high specificity, selectivity and sensitivity. It can be regarded as an alternative method to GC-MS for the confirmation of positive immunoassay test results, and can be used as a suitable analytical tool for the quantification of THC and THC-COOH in oral fluid, urine and/or blood samples.
A Method for EIA Scoping of Wave Energy Converters
DEFF Research Database (Denmark)
Margheritini, Lucia; Hansen, Anne Merrild; Frigaard, Peter
2012-01-01
During the first decade of the 21st Century the World faces spread concern for global warming caused by rise of green house gasses produced mainly by combustion of fossil fuels. Under this latest spin all renewable energies run parallel in order to achieve sustainable development. Among them wave...... energy has an unequivocal potential and technology is ready to enter the market and contribute to the renewable energy sector. Yet, frameworks and regulations for wave energy development are not fully ready, experiencing a setback caused by lack of understanding of the interaction of the technologies....... This paper presents the development of a classification of wave energy converters that is based on the different impact the technologies are expected to have on the environment. This innovative classification can be used in order to simplify the scoping process for developers and authorities....
Synthesized Multi-Method to Detect and Classify Epileptic Waves in EEG
Institute of Scientific and Technical Information of China (English)
万柏坤; 毕卡诗; 綦宏志; 赵丽
2004-01-01
In order to sufficiently exploit the advantages of different signal processing methods, such as wavelet transformation (WT), artificial neural networks (ANN) and expert rules (ER),a synthesized multi-method was introduced to detect and classify the epileptic waves in the EEG data. Using this method, at first, the epileptic waves were detected from pre-processed EEG data at different scales by WT, then the characteristic parameters of the chosen candidates of epileptic waves were extracted and sent into the well-trained ANN to identify and classify the true epileptic waves,and at last, the detected epileptic waves were certificated by ER. The statistic results of detection and classification show that, the synthesized multi-method has a good capacity to extract signal features and to shield the signals from the random noise. This method is especially fit for the analysis of the biomedical signals in biomedical engineering which are usually non-placid and nonlinear.
Second-Order Wave Diffraction Around 3-D Bodies by A Time-Domain Method
Institute of Scientific and Technical Information of China (English)
柏威; 滕斌
2001-01-01
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable.
A NEW NUMERICAL WAVE FLUME COMBINING THE 0-1 TYPE BEM AND THE VOF METHOD
Institute of Scientific and Technical Information of China (English)
GUO Li-dong; SUN Da-peng; WU Hao
2012-01-01
A new coupling numerical wave model,based on both the Boundary Element Method (BEM) and the Volume Of Fluid (VOF) method,is established by taking advantages of the both methods to solve the wave-structure interaction problems.In this model,the wave transformation in front of structures is calculated by the 0-1 type BEM,and the intense wave motions near the structures are calculated by the VOF method.In this paper,the characteristics of the BEM and the VOF method are discussed first,and then the coupling treatments are describcd in detail.In the end,the accuracy and the validity of the coupling model are examined by comparing the numerical results with experiment results and other numerical results available for the interactions between regular waves with a monolayer horizontal plate.
Fast calculation of spherical computer generated hologram using spherical wave spectrum method.
Jackin, Boaz Jessie; Yatagai, Toyohiko
2013-01-14
A fast calculation method for computer generation of spherical holograms in proposed. This method is based on wave propagation defined in spectral domain and in spherical coordinates. The spherical wave spectrum and transfer function were derived from boundary value solutions to the scalar wave equation. It is a spectral propagation formula analogous to angular spectrum formula in cartesian coordinates. A numerical method to evaluate the derived formula is suggested, which uses only N(logN)2 operations for calculations on N sampling points. Simulation results are presented to verify the correctness of the proposed method. A spherical hologram for a spherical object was generated and reconstructed successfully using the proposed method.
Tidal river dynamics: Implications for deltas
Hoitink, A. J. F.; Jay, D. A.
2016-03-01
Tidal rivers are a vital and little studied nexus between physical oceanography and hydrology. It is only in the last few decades that substantial research efforts have been focused on the interactions of river discharge with tidal waves and storm surges into regions beyond the limit of salinity intrusion, a realm that can extend inland hundreds of kilometers. One key phenomenon resulting from this interaction is the emergence of large fortnightly tides, which are forced long waves with amplitudes that may increase beyond the point where astronomical tides have become extinct. These can be larger than the linear tide itself at more landward locations, and they greatly influence tidal river water levels and wetland inundation. Exploration of the spectral redistribution and attenuation of tidal energy in rivers has led to new appreciation of a wide range of consequences for fluvial and coastal sedimentology, delta evolution, wetland conservation, and salinity intrusion under the influence of sea level rise and delta subsidence. Modern research aims at unifying traditional harmonic tidal analysis, nonparametric regression techniques, and the existing understanding of tidal hydrodynamics to better predict and model tidal river dynamics both in single-thread channels and in branching channel networks. In this context, this review summarizes results from field observations and modeling studies set in tidal river environments as diverse as the Amazon in Brazil, the Columbia, Fraser and Saint Lawrence in North America, the Yangtze and Pearl in China, and the Berau and Mahakam in Indonesia. A description of state-of-the-art methods for a comprehensive analysis of water levels, wave propagation, discharges, and inundation extent in tidal rivers is provided. Implications for lowland river deltas are also discussed in terms of sedimentary deposits, channel bifurcation, avulsion, and salinity intrusion, addressing contemporary research challenges.
A numerical method for determining the radial wave motion correction in plane wave couplers
DEFF Research Database (Denmark)
Cutanda Henriquez, Vicente; Barrera Figueroa, Salvador; Torras Rosell, Antoni
2016-01-01
solution is an analytical expression that estimates the difference between the ideal plane wave sound field and a more complex lossless sound field created by a non-planar movement of the microphone’s membranes. Alternatively, a correction may be calculated numerically by introducing a full model...
Ja, Y. H.
1984-12-01
Using a new seventh-order numerical method [the O(h 7) method] for solving two-point boundary value problems, numerical solutions of the first-order nonlinear coupledwave equations for degenerate two-wave and four-wave mixing in a reflection geometry have been obtained. A computer program employing the Gauss-Jordan elimination technique has also been adopted to effectively solve the resultant large, sparse and unsymmetric matrix, obtained from the O(h 7) method and the Newton-Raphson iteration method. Numerical results from the computer calculations are presented graphically. A comparison between this O(h 7) method and the shooting method, mainly from the viewpoint of computational efficiency, is also made.
Amador Carrascal, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F; Urban, Matthew
2017-01-11
Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver shear wave velocities values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue shear wave velocity values, such as food intake, body mass index (BMI), ultrasound scanners, scanning protocols, ultrasound image quality, etc. Time-to-peak (TTP) methods have been routinely used to measure the shear wave velocity. However, there is still a need for methods that can provide robust shear wave velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this study, two modified shear wave speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time (spatiotemporal peak, STP); the second method applies an amplitude filter (spatiotemporal thresholding, STTH) to select points with motion amplitude higher than a threshold for shear wave group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in shear wave velocity estimates compared to TTP in phantom. Moreover, in a cohort of 14 healthy subjects STP and STTH methods improved both the shear wave velocity measurement precision and the.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method (PFSM), was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.
Institute of Scientific and Technical Information of China (English)
FAN Hong-Yi; ZHU Jia-Min; WANG Tong-Tong; LU Zhi-Ming; LIU Yu-Lu
2008-01-01
One of the advantages of the variational iteration method is the free choice of initial guess. In this paper we use the basic idea of the Jacobian-function method to construct a generalized trial function with some unknown parameters. The Jaulent-Miodek equations are used to illustrate effectiveness and convenience of this method, some new explicit exact travelling wave solutions have been obtained, which include bell-type soliton solution, kink-type soliton solutions, solitary wave solutions, and doubly periodic wave solutions.
A Green's function method for surface acoustic waves in functionally graded materials.
Matsuda, Osamu; Glorieux, Christ
2007-06-01
Acoustic wave propagation in anisotropic media with one-dimensional inhomogeneity is discussed. Using a Green's function approach, the wave equation with inhomogeneous variation of elastic property and mass density is transformed into an integral equation, which is then solved numerically. The method is applied to find the dispersion relation of surface acoustic waves for a medium with continuously or discontinuously varying elastic property and mass density profiles.
A method for finding the optimal predictor indices for local wave climate conditions
Camus, Paula; Méndez, Fernando J.; Losada, Inigo J.; Menéndez, Melisa; Espejo, Antonio; Pérez, Jorge; Rueda, Ana; Guanche, Yanira
2014-07-01
In this study, a method to obtain local wave predictor indices that take into account the wave generation process is described and applied to several locations. The method is based on a statistical model that relates significant wave height with an atmospheric predictor, defined by sea level pressure fields. The predictor is composed of a local and a regional part, representing the sea and the swell wave components, respectively. The spatial domain of the predictor is determined using the Evaluation of Source and Travel-time of wave Energy reaching a Local Area (ESTELA) method. The regional component of the predictor includes the recent historical atmospheric conditions responsible for the swell wave component at the target point. The regional predictor component has a historical temporal coverage ( n-days) different to the local predictor component (daily coverage). Principal component analysis is applied to the daily predictor in order to detect the dominant variability patterns and their temporal coefficients. Multivariate regression model, fitted at daily scale for different n-days of the regional predictor, determines the optimum historical coverage. The monthly wave predictor indices are selected applying a regression model using the monthly values of the principal components of the daily predictor, with the optimum temporal coverage for the regional predictor. The daily predictor can be used in wave climate projections, while the monthly predictor can help to understand wave climate variability or long-term coastal morphodynamic anomalies.
Directory of Open Access Journals (Sweden)
Zhong-ye Tian
2014-01-01
Full Text Available The seismic responses of a long-span cable-stayed bridge under uniform excitation and traveling wave excitation in the longitudinal direction are, respectively, computed. The numerical results show that the bridge’s peak seismic responses vary significantly as the apparent wave velocity decreases. Therefore, the traveling wave effect must be considered in the seismic design of long-span bridges. The bridge’s peak seismic responses do not vary monotonously with the apparent wave velocity due to the traveling wave resonance. A new traveling wave excitation method that can simplify the multisupport excitation process into a two-support excitation process is developed.
New method for gravitational wave detection with atomic sensors.
Graham, Peter W; Hogan, Jason M; Kasevich, Mark A; Rajendran, Surjeet
2013-04-26
Laser frequency noise is a dominant noise background for the detection of gravitational waves using long-baseline optical interferometry. Amelioration of this noise requires near simultaneous strain measurements on more than one interferometer baseline, necessitating, for example, more than two satellites for a space-based detector or two interferometer arms for a ground-based detector. We describe a new detection strategy based on recent advances in optical atomic clocks and atom interferometry which can operate at long baselines and which is immune to laser frequency noise. Laser frequency noise is suppressed because the signal arises strictly from the light propagation time between two ensembles of atoms. This new class of sensor allows sensitive gravitational wave detection with only a single baseline. This approach also has practical applications in, for example, the development of ultrasensitive gravimeters and gravity gradiometers.
Fault location method for transmission line based on traveling waves
Institute of Scientific and Technical Information of China (English)
ZHENG Na; ZHAO Yulin
2007-01-01
The single phase grounding fault location is the focus which researchers pay attention to and study in power system. The accurate fault location can lighten the patrolling burden, and enhance the reliability of the power network. It adopts A/D which has high speed, and uses TMS320VC5402 DSP chip as the system core. This paper presented theory of operation based on traveling waves and achieved software and hardware in detail.
An efficient wave extrapolation method for anisotropic media with tilt
Waheed, Umair bin
2015-03-23
Wavefield extrapolation operators for elliptically anisotropic media offer significant cost reduction compared with that for the transversely isotropic case, particularly when the axis of symmetry exhibits tilt (from the vertical). However, elliptical anisotropy does not provide accurate wavefield representation or imaging for transversely isotropic media. Therefore, we propose effective elliptically anisotropic models that correctly capture the kinematic behaviour of wavefields for transversely isotropic media. Specifically, we compute source-dependent effective velocities for the elliptic medium using kinematic high-frequency representation of the transversely isotropic wavefield. The effective model allows us to use cheaper elliptic wave extrapolation operators. Despite the fact that the effective models are obtained by matching kinematics using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy trade-off for wavefield computations in transversely isotropic media, particularly for media of low to moderate complexity. In addition, the wavefield solution is free from shear-wave artefacts as opposed to the conventional finite-difference-based transversely isotropic wave extrapolation scheme. We demonstrate these assertions through numerical tests on synthetic tilted transversely isotropic models.
Institute of Scientific and Technical Information of China (English)
LI Xu-Dong; LIU Kai-Xin; ZHANG Guang-Sheng; WEN Shang-Gang; TAN Fu-Li
2008-01-01
@@ Interaction of shock waves in cement mortar plate is studied by digital speckle correlation method and digital high-speed photography technique. When the plates were destroyed by two detonators exploding at the same time, variation of shock wave field is obtained. Experimental results show that the interaction of shock waves will result in a nonlinear huge increase of local normal strain, leading to large deformation and serious destruction. However, the occurrence of this strongly nonlinear phenomenon sensitively depends on the interval between detonators, and it will only appear when the interval is smaller than the diameter of the region where shock waves exist.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Using direct algebraic method,exact solitary wave solutions are performed for a class of third order nonlinear dispersive disipative partial differential equations. These solutions are obtained under certain conditions for the relationship between the coefficients of the equation. The exact solitary waves of this class are rational functions of real exponentials of kink-type solutions.
Clapp, Ned E.; Hively, Lee M.
1997-01-01
Methods and apparatus automatically detect alertness in humans by monitoring and analyzing brain wave signals. Steps include: acquiring the brain wave (EEG or MEG) data from the subject, digitizing the data, separating artifact data from raw data, and comparing trends in f-data to alertness indicators, providing notification of inadequate alertness.
Numerical simulation of hydrodynamic wave loading by a compressible two-phase flow method
Wemmenhove, Rik; Luppes, Roelf; Veldman, Arthur; Bunnik, Tim
2015-01-01
Hydrodynamic wave loading on and in offshore structures is studied by carrying out numerical simulations. Particular attention is paid to complex hydrodynamic phenomena such as wave breaking and air entrapment. The applied CFD method, ComFLOW, solves the Navier–Stokes equations with an improved Volu
Real-space grid implementation of the projector augmented wave method
DEFF Research Database (Denmark)
Mortensen, Jens Jørgen; Hansen, Lars Bruno; Jacobsen, Karsten Wedel
2005-01-01
A grid-based real-space implementation of the projector augmented wave sPAWd method of Blöchl fPhys. Rev. B 50, 17953 s1994dg for density functional theory sDFTd calculations is presented. The use of uniform three-dimensional s3Dd real-space grids for representing wave functions, densities...
Manning, Robert M.
2004-01-01
The extended wide-angle parabolic wave equation applied to electromagnetic wave propagation in random media is considered. A general operator equation is derived which gives the statistical moments of an electric field of a propagating wave. This expression is used to obtain the first and second order moments of the wave field and solutions are found that transcend those which incorporate the full paraxial approximation at the outset. Although these equations can be applied to any propagation scenario that satisfies the conditions of application of the extended parabolic wave equation, the example of propagation through atmospheric turbulence is used. It is shown that in the case of atmospheric wave propagation and under the Markov approximation (i.e., the delta-correlation of the fluctuations in the direction of propagation), the usual parabolic equation in the paraxial approximation is accurate even at millimeter wavelengths. The comprehensive operator solution also allows one to obtain expressions for the longitudinal (generalized) second order moment. This is also considered and the solution for the atmospheric case is obtained and discussed. The methodology developed here can be applied to any qualifying situation involving random propagation through turbid or plasma environments that can be represented by a spectral density of permittivity fluctuations.
Calculation of leaky Lamb waves with a semi-analytical finite element method.
Hayashi, Takahiro; Inoue, Daisuke
2014-08-01
A semi-analytical finite element method (SAFE) has been widely used for calculating dispersion curves and mode shapes of guided waves as well as transient waves in a bar like structures. Although guided wave inspection is often conducted for water-loaded plates and pipes, most of the SAFE techniques have not been extended to a plate with leaky media. This study describes leaky Lamb wave calculation with the SAFE. We formulated a new solution using a feature that a single Lamb wave mode generates a harmonic plane wave in leaky media. Dispersion curves obtained with the SAFE agreed well with the previous theoretical studies, which represents that the SAFE calculation was conducted with sufficient accuracy. Moreover, we discussed dispersion curves, attenuation curves, and displacement distributions for total transmission modes and leaky plate modes in a single side and both two side water-loaded plate.
Humberston, J. L.; McNinch, J.; Lippmann, T. C.
2016-12-01
The morphology of tidal inlet ebb-shoals varies dynamically over time, particularly in response to large wave events. Understanding which wave qualities most influence shoals' evolution would support advancements in sediment bypassing models as well as targeted maintenance dredging for hydrographic purposes. Unfortunately, shallow and rapidly changing bathymetry, turbid waters and ambiguous wave speeds resulting from multiple shoaling and de-shoaling areas limits many traditional surveying techniques from obtaining the spatial and temporal resolution necessary to effectively characterize shoal development. The Radar Inlet Observing System (RIOS) is a uniquely designed mobile X-band radar system that can be deployed to inlet environments and, using roof-mounted solar panels and an automatically triggered highly efficient diesel generator, run automated hourly collections and wirelessly stream data for up to several months at a time in nearly all weather and water conditions. During 2015 and early 2016, RIOS was deployed to St. Augustine Inlet, FL., New River Inlet, N.C., and Oregon Inlet, N.C. for periods of one to six months to allow for measureable shoal evolution. During deployments, ten minute collections (at 1 Hz) were conducted every hour and the data gridded to a 5m alongshore/cross-shore grid. Raw intensity returns were time-averaged and analyzed to define three metrics of shoal evolution: movement direction, movement velocity and inferred bathymetry. For each location and time period, wave frequencies, wave directions and significant wave heights were collected from the nearest wave-buoy. Time lapse videos of shoal positions were inspected and used in concert with cross-correlations values from each pair of shoal and wave parameters to determine the incident wave qualities most strongly relating to shoal evolution. Preliminary results suggest wave height, more than frequency, controls shoal movement. Wave direction and size collaboratively appear to direct
2003-01-01
An efficient numerical method is developed for the numerical solution of non-linear wave equations typified by the regularized long wave equation (RLW) and its generalization (GRLW). The method developed uses a pseudo-spectral (Fourier transform) treatment of the space dependence together with a linearized implicit scheme in time. An important advantage to be gained from the use of this method, is the ability to vary the mesh length, thereby reducing the computational time. Using a linearized...
Energy Technology Data Exchange (ETDEWEB)
Enkovaara, J [CSC-IT Center for Science Ltd, PO Box 405 FI-02101 Espoo (Finland); Rostgaard, C; Mortensen, J J; Chen, J; Dulak, M; Glinsvad, C; Hansen, H A; Larsen, A H; Moses, P G; Petzold, V [Center for Atomic-scale Materials Design, Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Ferrighi, L; Kristoffersen, H H [Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Gavnholt, J; Olsen, T [Danish National Research Foundation' s Center for Individual Nanoparticle Functionality (CINF), Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Haikola, V; Lehtovaara, L [Department of Applied Physics, Aalto University School of Science and Technology, PO Box 11000, FIN-00076 Aalto, Espoo (Finland); Kuisma, M; Ojanen, J [Department of Physics, Tampere University of Technology, PO Box 692, FI-33101 Tampere (Finland); Ljungberg, M [FYSIKUM, Stockholm University, Albanova University Center, SE-10691 Stockholm (Sweden); Lopez-Acevedo, O [Departments of Physics and Chemistry, Nanoscience Center, University of Jyvaeskylae, PO Box 35 (YFL), FI-40014 (Finland)
2010-06-30
Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, {Delta}SCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals. (topical review)
A coupled DEM-CFD method for impulse wave modelling
Zhao, Tao; Utili, Stefano; Crosta, GiovanBattista
2015-04-01
Rockslides can be characterized by a rapid evolution, up to a possible transition into a rock avalanche, which can be associated with an almost instantaneous collapse and spreading. Different examples are available in the literature, but the Vajont rockslide is quite unique for its morphological and geological characteristics, as well as for the type of evolution and the availability of long term monitoring data. This study advocates the use of a DEM-CFD framework for the modelling of the generation of hydrodynamic waves due to the impact of a rapid moving rockslide or rock-debris avalanche. 3D DEM analyses in plane strain by a coupled DEM-CFD code were performed to simulate the rockslide from its onset to the impact with still water and the subsequent wave generation (Zhao et al., 2014). The physical response predicted is in broad agreement with the available observations. The numerical results are compared to those published in the literature and especially to Crosta et al. (2014). According to our results, the maximum computed run up amounts to ca. 120 m and 170 m for the eastern and western lobe cross sections, respectively. These values are reasonably similar to those recorded during the event (i.e. ca. 130 m and 190 m respectively). In these simulations, the slope mass is considered permeable, such that the toe region of the slope can move submerged in the reservoir and the impulse water wave can also flow back into the slope mass. However, the upscaling of the grains size in the DEM model leads to an unrealistically high hydraulic conductivity of the model, such that only a small amount of water is splashed onto the northern bank of the Vajont valley. The use of high fluid viscosity and coarse grain model has shown the possibility to model more realistically both the slope and wave motions. However, more detailed slope and fluid properties, and the need for computational efficiency should be considered in future research work. This aspect has also been
Analysis of efficient preconditioned defect correction methods for nonlinear water waves
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter
2014-01-01
prediction of free-surface wave transformation and accurate wave kinematics in both deep and shallow waters in large marine areas or for predicting the outcome of experiments in large numerical wave tanks. We revisit the classical governing equations are fully nonlinear and dispersive potential flow......Robust computational procedures for the solution of non-hydrostatic, free surface, irrotational and inviscid free-surface water waves in three space dimensions can be based on iterative preconditioned defect correction (PDC) methods. Such methods can be made efficient and scalable to enable...... models. Our study is particularly relevant for fast and efficient simulation of non-breaking fully nonlinear water waves over varying bottom topography that may be limited by computational resources or requirements. To gain insight into algorithmic properties and proper choices of discretization...
Institute of Scientific and Technical Information of China (English)
Yin Hai-Rong; Gong Yu-Bin; Wei Yan-Yu; Gong Hua-Rong; Yue Ling-Na; Lu Zhi-Gang; Huang Min-Zhi; Wang Wen-Xiang
2007-01-01
A method of designing a photonic crystal grating slow-wave circuit in which the cylinders of the 2D photonic crystals dot on a cross-sectional plane is established by calculating the band structures of the 2D photonic crystals, and the eigenfrequency of the equivalent waveguide grating. For calculating the band structures, the eigenvalue equations of the photonic crystals in the system of photonic crystal grating slow-wave circuit are derived in a special polarization mode. Two examples are taken to show the method. The design result is validated by the scattering parameters of the same circuit. The result indicates that there exists no photonic band gap if the metal gratings do not extend into the photonic crystals; the design of the circuit without the metal gratings extending into the photonic crystals is less flexible than that with the metal gratings extending into the photonic crystals.
Institute of Scientific and Technical Information of China (English)
XU Fu-min; XUE Hong-chao
2004-01-01
The Maximum Entropy Principle (MEP) method is elaborated, and the corresponding probability density evaluation method for the random fluctuation system is introduced, the goal of the article is to find the best fitting method for the wave climate statistical distribution. For the first time, a kind of new maximum entropy probability distribution (MEP distribution) expression is deduced in accordance with the second order moment of a random process. Different from all the fitting methods in the past, the MEP distribution can describe the probability distribution of any random fluctuation system conveniently and reasonably. If the moments of the random signal is limited to the second order, that is, the ratio of the root-mean-square value to the mean value of the random variable is obtained from the random sample, the corresponding MEP distribution can be computed according to the deduced expression in this essay. The concept of the wave climate is introduced here, and the MEP distribution is applied to fit the probability density distributions of the significant wave height and spectral peak period. Take the Mexico Gulf as an example, three stations at different locations, depths and wind wave strengths are chosen in the half-closed gulf, the significant wave height and spectral peak period distributions at each station are fitted with the MEP distribution, the Weibull distribution and the Log-normal distribution respectively, the fitted results are compared with the field observations, the results show that the MEP distribution is the best fitting method, and the Weibull distribution is the worst one when applied to the significant wave height and spectral peak period distributions at different locations, water depths and wind wave strengths in the Gulf. The conclusion shows the feasibility and reasonability of fitting wave climate statistical distributions with the deduced MEP distributions in this essay, and furthermore proves the great potential of MEP method to
Photonic methods of millimeter-wave generation based on Brillouin fiber laser
Al-Dabbagh, R. K.; Al-Raweshidy, H. S.
2016-05-01
In optical communication link, generation and delivering millimeter-wave (mm-waves) in radio over fiber (RoF) systems has limitation due to fiber non-linearity effects. To solve this problem, photonic methods of mm-wave generation based on characterizations of Brillouin fiber laser are proposed in this work for the first time. Three novel photonic approaches for mm-wave generation methods based on Brillouin fiber laser and phase modulator are proposed and demonstrated by simulation. According to our theoretical analysis and simulation, mm-waves with frequency up to 80 GHz and good signal to noise ratio (SNR) up to 90 dB are generated by new and cost effective methods of generation that make them suitable for applications of the fifth generation (5G) networks. The proposed configurations increase the stability and the quality of the mm-wave generation system by using a single laser source as a pump wave and the fiber non-linearity effects are reduced. A key advantage of this research is that proposed a number of very simple generation methods and cost effective which only use standard components of optical telecommunications. Stimulated Brillouin Scattering (SBS) effect that exists in the optical fiber is studied with the characterization of phase modulator. An all optically stable mm-wave carriers are achieved successfully in the three different methods with different frequencies from 20 GHz up to 80 GHz. Simulation results show that all these carriers have low phase noise, good SNR ranging between 60 and 90 dB and tuning capability in comparison with previous methods reported. This makes them suitable for mm-wave transmission in RoF systems to transmit data in the next generation networks.
Institute of Scientific and Technical Information of China (English)
2008-01-01
Two residual-based a posteriori error estimators of the nonconforming Crouzeix-Raviart element are derived for elliptic problems with Dirac delta source terms.One estimator is shown to be reliable and efficient,which yields global upper and lower bounds for the error in piecewise W1,p seminorm.The other one is proved to give a global upper bound of the error in Lp-norm.By taking the two estimators as refinement indicators,adaptive algorithms are suggested,which are experimentally shown to attain optimal convergence orders.
Traveling Wave Solutions of ZK-BBM Equation Sine-Cosine Method
Directory of Open Access Journals (Sweden)
Sadaf Bibi
2014-03-01
Full Text Available Travelling wave solutions are obtained by using a relatively new technique which is called sine-cosine method for ZK-BBM equations. Solution procedure and obtained results re-confirm the efficiency of the proposed scheme.
Directional spectrum of ocean waves from array measurements using phase/time/path difference methods
Digital Repository Service at National Institute of Oceanography (India)
Fernandes, A.A.; Sarma, Y.V.B.; Menon, H.B.
Wave direction has for the first time been consistently, accurately and unambiguously evaluated from array measurements using the phase/time/path difference (PTPD) methods of Esteva in case of polygonal arrays and Borgman in case of linear arrays...
A penalization method for calculating the flow beneath travelling water waves of large amplitude
Constantin, Adrian; Scherzer, Otmar
2014-01-01
A penalization method for a suitable reformulation of the governing equations as a constrained optimization problem provides accurate numerical simulations for large-amplitude travelling water waves in irrotational flows and in flows with constant vorticity.
A Refined Method for Estimating the Annual Extreme Wave Heights at A Project Site
Institute of Scientific and Technical Information of China (English)
徐德伦; 范海梅; 张军
2003-01-01
This paper presents a refined method for estimating the annual extreme wave heights at a coastal or offshore project site on the basis of the data acquired at some nearby routine hydrographic stations. This method is based on the orthogonality principle in linear mean square estimation of stochastic processes. The error of the method is analyzed and compared with that of the conventional method. It is found that the method is able to effectively reduce the error so long as some feasible measures are adopted. A simulated test of the method has been conducted in a large-scale wind-wave flume. The test results are in good agreement with those given by theoretical error analysis. A scheme to implement the method is proposed on the basis of error analysis. The scheme is so designed as to reduce the estimation error as far as possible. This method is also suitable to utilizing satellite wave data for the estimation.
Yelve, Nitesh P; Mitra, Mira; Mujumdar, P M; Ramadas, C
2016-08-01
A new hybrid method based upon nonlinear Lamb wave response in time and frequency domains is introduced to locate a delamination in composite laminates. In Lamb wave based nonlinear method, the presence of damage is shown by the appearance of higher harmonics in the Lamb wave response. The proposed method not only uses this spectral information but also the corresponding temporal response data, for locating the delamination. Thus, the method is termed as a hybrid method. The paper includes formulation of the method and its application to locate a Barely Visible Impact Damage (BVID) induced delamination in a Carbon Fiber Reinforced Polymer (CFRP) laminate. The method gives the damage location fairly well. It is a baseline free method, as it does not need data from the pristine specimen.
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 t...
Application of the wave finite element method to reinforced concrete structures with damage
El Masri, Evelyne; Ferguson, Neil; Waters, Timothy
2016-09-01
Vibration based methods are commonly deployed to detect structural damage using sensors placed remotely from potential damage sites. Whilst many such techniques are modal based there are advantages to adopting a wave approach, in which case it is essential to characterise wave propagation in the structure. The Wave Finite Element method (WFE) is an efficient approach to predicting the response of a composite waveguide using a conventional FE model of a just a short segment. The method has previously been applied to different structures such as laminated plates, thinwalled structures and fluid-filled pipes. In this paper, the WFE method is applied to a steel reinforced concrete beam. Dispersion curves and wave mode shapes are first presented from free wave solutions, and these are found to be insensitive to loss of thickness in a single reinforcing bar. A reinforced beam with localised damage is then considered by coupling an FE model of a short damaged segment into the WFE model of the undamaged beam. The fundamental bending, torsion and axial waves are unaffected by the damage but some higher order waves of the cross section are significantly reflected close to their cut-on frequencies. The potential of this approach for detecting corrosion and delamination in reinforced concrete beams will be investigated in future work.
Institute of Scientific and Technical Information of China (English)
FENG Bo; ZHENG Yong-hong; YOU Ya-ge; HE Zai-ming
2007-01-01
The two-dimensional problems concerning the interaction of linear water waves with cylinders of arbitrary shape in two-layer deep water are investigated by use of the Boundary Integral Equation Method (BIEM). Simpler new expressions for the Green functions are derived, and verified by comparison of results obtained by BIEM with those by an analytical method. Examined are the radiation and scattering of linear waves by two typical configurations of cylinders in two-layer deep water. Hydrodynamic behaviors including hydrodynamic coefficients, wave forces, reflection and transmission coefficients and energies are analyzed in detail, and some interesting physical phenomena are observed.
Structural Design and Protective Methods for the 100 kW Shoreline Wave Power Station
Institute of Scientific and Technical Information of China (English)
游亚戈; 郑永红; 马玉久; 余志; 蒋念东
2003-01-01
The structural design and protective methods for the 100 kW shoreline wave power station in China are described in detail. The proper structural type is designed for effective minimization of wave loads and bending stress. Various protective devices are adopted to protect the station in the extreme conditions against excessive power of airflow, excessive torsion of the shaft, over-pressure of the chamber, over-speed of rotation, power failure, and so on. It turns out that the structural design and protective methods for the 100 kW shoreline wave power station are successful.
Generation and detection of thermoelastic waves in metals by a photothermal mirror method
Capeloto, O. A.; Zanuto, V. S.; Lukasievicz, G. V. B.; Malacarne, L. C.; Bialkowski, S. E.; Požar, T.; Astrath, N. G. C.
2016-11-01
We investigate the thermoelastic waves launched by a localized heat deposition. Pulsed laser excitation is used to generate mechanical perturbations in metals that are detected using the photothermal mirror method. This method detects the wavefront distortion of the probe beam reflected from the perturbed sample surface. Nanometer scale expansion of the material is induced just under the irradiated surface releasing transient thermoelastic waves of much smaller amplitudes on the surface. Numerical predictions and the experimental results are in a good agreement and represent both the thermal diffusion of the large amplitude, long-lasting outward bulge, and the released elastic waves.
Fictitious domain method for acoustic waves through a granular suspension of movable rigid spheres
Imbert, David; McNamara, Sean; Le Gonidec, Yves
2015-01-01
International audience; We develop a model to couple acoustic waves and the motion of rigid movable grains in a submerged suspension. To do so, we use the fictitious domain method based on distributed Lagrange multipliers to enforce the natural jump condition of the wave equation and a rigidity constraint. One can then model the granular medium with “Molecular Dynamics” or related methods. Both dynamic and acoustic numerical results are compared with analytic solutions of acoustics and an est...
The superposition method in seeking the solitary wave solutions to the KdV-Burgers equation
Indian Academy of Sciences (India)
Yuanxi Xie; Jilashi Tang
2006-03-01
In this paper, starting from the careful analysis on the characteristics of the Burgers equation and the KdV equation as well as the KdV-Burgers equation, the superposition method is put forward for constructing the solitary wave solutions of the KdV-Burgers equation from those of the Burgers equation and the KdV equation. The solitary wave solutions for the KdV-Burgers equation are presented successfully by means of this method.
Zhang Hong Lin
2002-01-01
Relativistic distorted-wave collision strengths have been calculated for the 45 DELTA n=0 transitions with n=2 in the 79 O-like ions with nuclear charge number Z in the range 14<=Z<=92. The calculations were made for the six final, or scattered, electron energies E'=0.03, 0.08, 0.20, 0.42, 0.80, and 1.40, where E' is in units of Z sup 2 sub e sub f sub f Ry with Z sub e sub f sub f =Z-5.83. In addition, the transition energies and electric dipole oscillator strengths are given. To our knowledge the present work is the first comprehensive publication of the results of fully relativistic calculations of the collision strengths for excitation of highly charged O-like ions.
Continuous-wave organic dye lasers and methods
Shapira, Ofer; Chua, Song-Liang; Zhen, Bo; Lee, Jeongwon; Soljacic, Marin
2014-09-16
An organic dye laser produces a continuous-wave (cw) output without any moving parts (e.g., without using flowing dye streams or spinning discs of solid-state dye media to prevent photobleaching) and with a pump beam that is stationary with respect to the organic dye medium. The laser's resonant cavity, organic dye medium, and pump beam are configured to excite a lasing transition over a time scale longer than the associated decay lifetimes in the organic dye medium without photobleaching the organic dye medium. Because the organic dye medium does not photobleach when operating in this manner, it may be pumped continuously so as to emit a cw output beam. In some examples, operation in this manner lowers the lasing threshold (e.g., to only a few Watts per square centimeter), thereby facilitating electrical pumping for cw operation.
Chen, Zhongxian; Yu, Haitao; Wen, Cheng
2014-01-01
The goal of direct drive ocean wave energy extraction system is to convert ocean wave energy into electricity. The problem explored in this paper is the design and optimal control for the direct drive ocean wave energy extraction system. An optimal control method based on internal model proportion integration differentiation (IM-PID) is proposed in this paper though most of ocean wave energy extraction systems are optimized by the structure, weight, and material. With this control method, the heavy speed of outer heavy buoy of the energy extraction system is in resonance with incident wave, and the system efficiency is largely improved. Validity of the proposed optimal control method is verified in both regular and irregular ocean waves, and it is shown that IM-PID control method is optimal in that it maximizes the energy conversion efficiency. In addition, the anti-interference ability of IM-PID control method has been assessed, and the results show that the IM-PID control method has good robustness, high precision, and strong anti-interference ability.
Perfectly-matched-layer boundary integral equation method for wave scattering in a layered medium
Lu, Wangtao; Qian, Jianliang
2016-01-01
For scattering problems of time-harmonic waves, the boundary integral equation (BIE) methods are highly competitive, since they are formulated on lower-dimension boundaries or interfaces, and can automatically satisfy outgoing radiation conditions. For scattering problems in a layered medium, standard BIE methods based on the Green's function of the background medium must evaluate the expensive Sommefeld integrals. Alternative BIE methods based on the free-space Green's function give rise to integral equations on unbounded interfaces which are not easy to truncate, since the wave fields on these interfaces decay very slowly. We develop a BIE method based on the perfectly matched layer (PML) technique. The PMLs are widely used to suppress outgoing waves in numerical methods that directly discretize the physical space. Our PML-based BIE method uses the Green's function of the PML-transformed free space to define the boundary integral operators. The method is efficient, since the Green's function of the PML-tran...
Synthesis of Numerical Methods for Modeling Wave Energy Converter-Point Absorbers: Preprint
Energy Technology Data Exchange (ETDEWEB)
Li, Y.; Yu, Y. H.
2012-05-01
During the past few decades, wave energy has received significant attention among all ocean energy formats. Industry has proposed hundreds of prototypes such as an oscillating water column, a point absorber, an overtopping system, and a bottom-hinged system. In particular, many researchers have focused on modeling the floating-point absorber as the technology to extract wave energy. Several modeling methods have been used such as the analytical method, the boundary-integral equation method, the Navier-Stokes equations method, and the empirical method. However, no standardized method has been decided. To assist the development of wave energy conversion technologies, this report reviews the methods for modeling the floating-point absorber.
A probabilistic crack size quantification method using in-situ Lamb wave test and Bayesian updating
Yang, Jinsong; He, Jingjing; Guan, Xuefei; Wang, Dengjiang; Chen, Huipeng; Zhang, Weifang; Liu, Yongming
2016-10-01
This paper presents a new crack size quantification method based on in-situ Lamb wave testing and Bayesian method. The proposed method uses coupon test to develop a baseline quantification model between the crack size and damage sensitive features. In-situ Lamb wave testing data on actual structures are used to update the baseline model parameters using Bayesian method to achieve more accurate crack size predictions. To demonstrate the proposed method, Lamb wave testing on simple plates with artificial cracks of different sizes is performed using surface-bonded piezoelectric wafers, and the data are used to obtain the baseline model. Two damage sensitive features, namely, the phase change and normalized amplitude are identified using signal processing techniques and used in the model. To validate the effectiveness of the method, the damage data from an in-situ fatigue testing on a realistic lap-joint component are used to update the baseline model using Bayesian method.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
When there exists anisotropy in underground media, elastic parameters of the observed coordinate possibly do not coincide with that of the natural coordinate. According to the theory that the density of potential energy, dissipating energy is independent of the coordinate, the relationship of elastic parameters between two coordinates is derived for two-phase anisotropic media. Then, pseudospectral method to solve wave equations of two-phase anisotropic media is derived. At last, we use this method to simulate wave propagation in two-phase anisotropic media, four types of waves are observed in the snapshots, i.e., fast P wave and slow P wave, fast S wave and slow S wave. Shear wave splitting, SV wave cusps and elastic wave reflection and transmission are also observed.
Variational space-time (dis)continuous Galerkin method for nonlinear free surface water waves
Gagarina, E.; Ambati, V. R.; van der Vegt, J. J. W.; Bokhove, O.
2014-10-01
A new variational finite element method is developed for nonlinear free surface gravity water waves using the potential flow approximation. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a finite element discretization that is continuous in space and discontinuous in time. One novel feature of this variational finite element approach is that the free surface evolution is variationally dependent on the mesh deformation vis-à-vis the mesh deformation being geometrically dependent on free surface evolution. Another key feature is the use of a variational (dis)continuous Galerkin finite element discretization in time. Moreover, in the absence of a wave maker, it is shown to be equivalent to the second order symplectic Störmer-Verlet time stepping scheme for the free-surface degrees of freedom. These key features add to the stability of the numerical method. Finally, the resulting numerical scheme is verified against nonlinear analytical solutions with long time simulations and validated against experimental measurements of driven wave solutions in a wave basin of the Maritime Research Institute Netherlands.
Numerical Simulation of Water Mitigation Effects on Shock Wave with SPH Method
Institute of Scientific and Technical Information of China (English)
MAO Yiming; FANG Qin; ZHANG Yadong; GAO Zhenru
2008-01-01
The water mitigation effect on the propagation of shock wave was investigated numerically.The traditionaf smoothed particle hydrodynamics(SPH)method was modified based on Riemann solution.The comparison of numerical results with the analytical solution indicated that the modified SPH method has more advantages than the traditional SPH method.Using the modified SPH algorithm.a series of one-dimensional planar wave propagation problems were investigated,focusing on the influence of the air-gap between the high-pressure air and water and the thickness of water.The humerical results showed that water mitigation effect is significant.Up to 60%shock wave pressure reduction could be achieved with the existence of water.and the shape of shock wave was also changed greatly.It is seemly that fhe small air-gap between the high-pressure air and water has more influence on water mitigation effect.
New Exact Solutions of Ion-Acoustic Wave Equations by (G′/G-Expansion Method
Directory of Open Access Journals (Sweden)
Wafaa M. Taha
2013-01-01
Full Text Available The (G′/G-expansion method is used to study ion-acoustic waves equations in plasma physic for the first time. Many new exact traveling wave solutions of the Schamel equation, Schamel-KdV (S-KdV, and the two-dimensional modified KP (Kadomtsev-Petviashvili equation with square root nonlinearity are constructed. The traveling wave solutions obtained via this method are expressed by hyperbolic functions, the trigonometric functions, and the rational functions. In addition to solitary waves solutions, a variety of special solutions like kink shaped, antikink shaped, and bell type solitary solutions are obtained when the choice of parameters is taken at special values. Two- and three-dimensional plots are drawn to illustrate the nature of solutions. Moreover, the solution obtained via this method is in good agreement with previously obtained solutions of other researchers.
Jiang, Lijian
2010-08-01
In this paper, we discuss a numerical multiscale approach for solving wave equations with heterogeneous coefficients. Our interest comes from geophysics applications and we assume that there is no scale separation with respect to spatial variables. To obtain the solution of these multiscale problems on a coarse grid, we compute global fields such that the solution smoothly depends on these fields. We present a Galerkin multiscale finite element method using the global information and provide a convergence analysis when applied to solve the wave equations. We investigate the relation between the smoothness of the global fields and convergence rates of the global Galerkin multiscale finite element method for the wave equations. Numerical examples demonstrate that the use of global information renders better accuracy for wave equations with heterogeneous coefficients than the local multiscale finite element method. © 2010 IMACS.
Reconstruction of Dispersive Lamb Waves in Time Plates Using a Time Reversal Method
Energy Technology Data Exchange (ETDEWEB)
Jeong, Hyun Jo [Wonkwang University, Iksan (Korea, Republic of)
2008-02-15
Time reversal (TR) of nondispersive body waves has been used in many applications including ultrasonic NDE. However, the study of the TR method for Lamb waves on thin structures is not well established. In this paper, the full reconstruction of the input signal is investigated for dispersive Lamb waves by introducing a time reversal operator based on the Mindlin plate theory. A broadband and a narrowband input waveform are employed to reconstruct the A{sub 0} mode of Lamb wave propagations. Due to the frequency dependence of the TR process of Lamb waves, different frequency components of the broadband excitation are scaled differently during the time reversal process and the original input signal cannot be fully restored. This is the primary reason for using a narrowband excitation to enhance the flaw detectability
Application of the Most Likely Extreme Response Method for Wave Energy Converters: Preprint
Energy Technology Data Exchange (ETDEWEB)
Quon, Eliot; Platt, Andrew; Yu, Yi-Hsiang; Lawson, Michael
2016-07-01
Extreme loads are often a key cost driver for wave energy converters (WECs). As an alternative to exhaustive Monte Carlo or long-term simulations, the most likely extreme response (MLER) method allows mid- and high-fidelity simulations to be used more efficiently in evaluating WEC response to events at the edges of the design envelope, and is therefore applicable to system design analysis. The study discussed in this paper applies the MLER method to investigate the maximum heave, pitch, and surge force of a point absorber WEC. Most likely extreme waves were obtained from a set of wave statistics data based on spectral analysis and the response amplitude operators (RAOs) of the floating body; the RAOs were computed from a simple radiation-and-diffraction-theory-based numerical model. A weakly nonlinear numerical method and a computational fluid dynamics (CFD) method were then applied to compute the short-term response to the MLER wave. Effects of nonlinear wave and floating body interaction on the WEC under the anticipated 100-year waves were examined by comparing the results from the linearly superimposed RAOs, the weakly nonlinear model, and CFD simulations. Overall, the MLER method was successfully applied. In particular, when coupled to a high-fidelity CFD analysis, the nonlinear fluid dynamics can be readily captured.
Application of the Most Likely Extreme Response Method for Wave Energy Converters
Energy Technology Data Exchange (ETDEWEB)
Quon, Eliot; Platt, Andrew; Yu, Yi-Hsiang; Lawson, Michael
2016-06-24
Extreme loads are often a key cost driver for wave energy converters (WECs). As an alternative to exhaustive Monte Carlo or long-term simulations, the most likely extreme response (MLER) method allows mid- and high-fidelity simulations to be used more efficiently in evaluating WEC response to events at the edges of the design envelope, and is therefore applicable to system design analysis. The study discussed in this paper applies the MLER method to investigate the maximum heave, pitch, and surge force of a point absorber WEC. Most likely extreme waves were obtained from a set of wave statistics data based on spectral analysis and the response amplitude operators (RAOs) of the floating body; the RAOs were computed from a simple radiation-and-diffraction-theory-based numerical model. A weakly nonlinear numerical method and a computational fluid dynamics (CFD) method were then applied to compute the short-term response to the MLER wave. Effects of nonlinear wave and floating body interaction on the WEC under the anticipated 100-year waves were examined by comparing the results from the linearly superimposed RAOs, the weakly nonlinear model, and CFD simulations. Overall, the MLER method was successfully applied. In particular, when coupled to a high-fidelity CFD analysis, the nonlinear fluid dynamics can be readily captured.
Study on estimate method of wave velocity and quality factor to fault seals
Institute of Scientific and Technical Information of China (English)
LI Zhensheng; LIU Deliang; LIU Bo; YANG Qiang; LI Jingming
2005-01-01
Based on ultrasonic test of fault rocks, the responses for wave velocity and quality factor (Q value) to lithology, porosity and permeability of fault rocks and mechanical property of faults are studied. In this paper, a new quantitative estimate method of fault seals is originally offered. The conclusions are as follows: (1) Wave velocity and Q value increase and porosity decreases with the increase in stress perpendicular to joint; (2) In compressive and compresso-shear fault rocks that are obviously anisotropic compared with their original rocks, the wave velocity and Q value are greater in the direction parallel with foliation, and usually less perpendicular to it. In tensile and tenso-shear fault rocks that are not obviously anisotropic, the wave velocity and Q value are under that of original rocks; (3) In foliated fault rocks, the direction with minimal wave velocity and Q value is the best direction for sealing; on the contrary it is the best for flowing; (4) Structural factures develop mainly along foliation, the minimal wave velocity and Q value reflect the flowing capacity in parallel direction to foliation, and the maximal wave velocity as well as Q value reflect the sealing capacity in normal direction to foliation. The new estimate method is based upon contrast of wave velocity and Q value between fault rocks and their original rocks, and is divided into three parts that are respectively to identify rock's lithology, to judge mechanic property of faults and to Judge sealing capacity of faults. Although there is vast scale effect between ultrasonic wave and seismic wave, they have similar regularity of response to fabric and porosity of faults. This research offers new application for seismic data and petrophysical basis for seismological estimation of fault seals. The estimate precision will be improved with the enhancement of three-dimensional seismic prospecting work.
Compositeness of the Delta(1232) resonance in pi N scattering
Sekihara, Takayasu; Yamagata-Sekihara, Junko; Yasui, Shigehiro
2015-01-01
We evaluate the $\\pi N$ compositeness of the $\\Delta (1232)$ resonance so as to clarify the internal structure of $\\Delta (1232)$ in terms of the $\\pi N$ component. Here the compositeness is defined as contributions from two-body wave functions to the normalization of the total wave function and is extracted from the $\\pi N$ scattering amplitude. In this study we employ the chiral unitary approach with the interaction up to the next-to-leading order plus a bare $\\Delta$ term in chiral perturbation theory and describe $\\Delta (1232)$ in an elastic $\\pi N$ scattering. Fitting the $\\pi N$ scattering amplitude to the solution of the partial wave analysis, we obtain a large real part of the $\\pi N$ compositeness for $\\Delta (1232)$ comparable to unity and non-negligible imaginary part as well, with which we reconfirm the result in the previous study on the $\\pi N$ compositeness for $\\Delta (1232)$.
Research on model testing of a new ultrasonic multi-wave detecting method
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
@@ The traditional crack exploring method with echo (reflected wave) in metals is called the "single-wave detecting method" that uses a probe of single weight. This method is not able to detect directly the size and shape of the crack and the result can only be obtained by relative comparison, that is to compare the echo amplitudes of the unknown quantity (crack) with the known quantity (regular artificial crack) to determine the equivalent size and shape of a certain crack. In this way, the site of a crack can be basically determined, but it is not the size, scale and site of the actual crack. So the traditional method is incapable to satisfy the demands in real applications, and there was not any big improvement in the past several decades. Therefore, we introduce a new method called the "multi-wave detecting method" in the paper, which is capable to detect directly the size, scale and site of a crack.
Hametner, Bernhard; Wassertheurer, Siegfried; Kropf, Johannes; Mayer, Christopher; Holzinger, Andreas; Eber, Bernd; Weber, Thomas
2013-03-01
Within the last decade the quantification of pulse wave reflections mainly focused on measures of central aortic systolic pressure and its augmentation through reflections based on pulse wave analysis (PWA). A complementary approach is the wave separation analysis (WSA), which quantifies the total amount of arterial wave reflection considering both aortic pulse and flow waves. The aim of this work is the introduction and comparison of aortic blood flow models for WSA assessment. To evaluate the performance of the proposed modeling approaches (Windkessel, triangular and averaged flow), comparisons against Doppler measurements are made for 148 patients with preserved ejection fraction. Stepwise regression analysis between WSA and PWA parameters are performed to provide determinants of methodological differences. Against Doppler measurement mean difference and standard deviation of the amplitudes of the decomposed forward and backward pressure waves are comparable for Windkessel and averaged flow models. Stepwise regression analysis shows similar determinants between Doppler and Windkessel model only. The results indicate that the Windkessel method provides accurate estimates of wave reflection in subjects with preserved ejection fraction. The comparison with waveforms derived from Doppler ultrasound as well as recently proposed simple triangular and averaged flow waves showed that this approach may reduce variability and provide realistic results.
Delta III—an evolutionary delta growth
Arvesen, R. J.; Simpson, J. S.
1996-03-01
In order to remain competitive in the future and expand the McDonnell Douglas Aerospace market share, MDA has developed an expendable launch system strategy that devices cost-effective launch systems from the Delta II with a growth vehicle configuration called Delta III. The Delta III evolves from the Delta II launch system through development of a larger payload fairing (4-meter diameter), new cryogenically propelled upper stage, new first stage fuel tank, and larger strap-on solid rocket motors. We are developing the Delta III using Integrated Product Development Teams that capitalize on the experience base that has led us to a world record breaking mission success of 49 consecutive Delta II missions. The Delta III first-launch capability is currently planned for the spring of 1998 in support of our first spacecraft customer, Hughes Space and Communications International.
Heinen, Vernon O.; Miranda, Felix A.; Bhasin, Kul B.
1992-01-01
A power transmission measurement technique was used to determine the magnetic penetration depth (lambda) of YBa2Cu3O(7-delta) superconducting thin films on LaAlO3 within the 26.5 to 40.0 GHz frequency range, and at temperatures from 20 to 300 K. Values of lambda ranging from 1100 to 2500 A were obtained at low temperatures. The anisotropy of lambda was determined from measurements of c-axis and a-axis oriented films. An estimate of the intrinsic value of lambda of 90 +/- 30 nm was obtained from the dependence of lambda on film thickness. The advantage of this technique is that it allows lambda to be determined nondestructively.
Modal Ring Method for the Scattering of Electromagnetic Waves
Baumeister, Kenneth J.; Kreider, Kevin L.
1993-01-01
The modal ring method for electromagnetic scattering from perfectly electric conducting (PEC) symmetrical bodies is presented. The scattering body is represented by a line of finite elements (triangular) on its outer surface. The infinite computational region surrounding the body is represented analytically by an eigenfunction expansion. The modal ring method effectively reduces the two dimensional scattering problem to a one-dimensional problem similar to the method of moments. The modal element method is capable of handling very high frequency scattering because it has a highly banded solution matrix.
Surface and downhole shear wave seismic methods for thick soil site investigations
Hunter, J.A.; Benjumea, B.; Harris, J.B.; Miller, R.D.; Pullan, S.E.; Burns, R.A.; Good, R.L.
2002-01-01
Shear wave velocity-depth information is required for predicting the ground motion response to earthquakes in areas where significant soil cover exists over firm bedrock. Rather than estimating this critical parameter, it can be reliably measured using a suite of surface (non-invasive) and downhole (invasive) seismic methods. Shear wave velocities from surface measurements can be obtained using SH refraction techniques. Array lengths as large as 1000 m and depth of penetration to 250 m have been achieved in some areas. High resolution shear wave reflection techniques utilizing the common midpoint method can delineate the overburden-bedrock surface as well as reflecting boundaries within the overburden. Reflection data can also be used to obtain direct estimates of fundamental site periods from shear wave reflections without the requirement of measuring average shear wave velocity and total thickness of unconsolidated overburden above the bedrock surface. Accurate measurements of vertical shear wave velocities can be obtained using a seismic cone penetrometer in soft sediments, or with a well-locked geophone array in a borehole. Examples from thick soil sites in Canada demonstrate the type of shear wave velocity information that can be obtained with these geophysical techniques, and show how these data can be used to provide a first look at predicted ground motion response for thick soil sites. ?? 2002 Published by Elsevier Science Ltd.
Few, Roger; Lake, Iain; Hunter, Paul R; Tran, Pham Gia
2013-03-01
Any analysis of how changing environmental hazards impact on public health is fundamentally constrained unless it recognizes the centrality of the social and behavioral dimensions of risk. This paper reports on a research project conducted among low-income peri-urban households in the Mekong Delta of Vietnam. The research was based on cross-disciplinary inputs to develop a multi-layered understanding of the implications of a dynamic seasonal environment for diarrheal disease risk. It is a widely held assumption that the major changes in the abundance of surface water between the flood and dry seasons in the Mekong Delta are likely to be reflected in the changing patterns of disease risk, especially for poorer households that tend to rely heavily on river water for domestic water use. Therefore, this study investigated seasonal patterns in the contamination of environmental water, incidences of diarrheal illnesses, water use and hygiene behavior, together with perceptions of health risks and seasonality. During the period of October 2007 to October 2008, the UK and Vietnamese research team worked with a total of 120 households in four low-income sites around the city of Long Xuyen to conduct water testing; administer questionnaires on self-reported health, risk perceptions and behavior; and conduct semi-structured interviews. The research team found no overall evidence of a systematic seasonal risk pattern. At the population level, marginal temporal variations in water quality in the environment failed to translate into health outcomes. A complex risk narrative emerged from the interweaving data elements, demonstrating major inter- and intra-household variations in risk perceptions, hygiene behavior, seasonal behavior and other risk factors. It is suggested that these complexities of human behavior and transmission routes challenge simplistic assumptions about change in health outcomes as a result of seasonal environmental changes. These findings demonstrate the key
Application of the SPH method to solitary wave impact on an offshore platform
Pan, K.; IJzermans, R. H. A.; Jones, B. D.; Thyagarajan, A.; van Beest, B. W. H.; Williams, J. R.
2016-04-01
This paper investigates the interaction between large waves and floating offshore structures. Here, the fluid-structure interaction is considered using the weakly compressible smoothed particle hydrodynamics (SPH) method. To ensure the applicability of this method, we validate its prediction for fluid forces and rigid-body motion against two sets of experimental data. These are impact due to dam break, and wave induced motion of a floating cube. For the dam break problem, the SPH method is used to predict impact forces on a rectangular column located downstream. In the second case of a floating cube, the SPH method simulates the motion of a buoyant cube under the action of induced waves, where a wall placed upstream of the cube is displaced sinusoidally to induce waves. In both cases, the SPH framework implemented is able to accurately reproduce the experimental results. Following validation, we apply this framework to simulation of a toy model of a tension-leg platform upon impact of a large solitary wave. This analysis shows that the platform may be pulled into the water by stretched tension legs, where the extension of the tension legs also governs the rotational behavior of the platform. The result also indicates that a tension-leg platform is very unlikely to topple over during the arrival of an extreme wave.
Calculation Method for the Prediction of the Performance of a Traveling-Wave Thermoacoustic Cooler
Ueda, Yuki
When a traveling acoustic wave propagates through a regenerator, the gas in the regenerator undergoes the Stirling thermodynamic cycle, and thus, the energy conversion between heat flux and acoustic power takes place. A cooler that utilizes this energy conversion is called as a traveling-wave thermoacoustic cooler. Swift et al. [The Journal of the Acoustical Society of America, 105, 711 (1998)] have proposed a new traveling wave thermoacoustic cooler that is equipped with a looped tube. This paper describes a numerical method to estimate the performance of this thermoacoustic cooler and shows a comparison between the estimated and experimentally obtained performances.
Systematic Analysis Method of Shear-Wave Splitting:SAM Software System
Institute of Scientific and Technical Information of China (English)
Gao Yuan; Liu Xiqiang; Liang Wei; Hao Ping
2004-01-01
In order to make a more effective use of the data from regional digital seismograph networks and to promote the study on shear wave splitting and its application to earthquake stressforecasting, SAM software system, i.e., the software on systematic analysis method of shear wave splitting has been developed. This paper introduces the design aims, system structure,function and characteristics about the SAM software system and shows some graphical interfaces of data input and result output. Lastly, it discusses preliminarily the study of shear wave splitting and its application to earthquake forecasting.
Singular boundary method using time-dependent fundamental solution for scalar wave equations
Chen, Wen; Li, Junpu; Fu, Zhuojia
2016-11-01
This study makes the first attempt to extend the meshless boundary-discretization singular boundary method (SBM) with time-dependent fundamental solution to two-dimensional and three-dimensional scalar wave equation upon Dirichlet boundary condition. The two empirical formulas are also proposed to determine the source intensity factors. In 2D problems, the fundamental solution integrating along with time is applied. In 3D problems, a time-successive evaluation approach without complicated mathematical transform is proposed. Numerical investigations show that the present SBM methodology produces the accurate results for 2D and 3D time-dependent wave problems with varied velocities c and wave numbers k.
Tao, Zhi-Fu; Han, Zhong-Ling; Yao, Meng
2011-01-01
Using the difference of dielectric constant between malignant tumor tissue and normal breast tissue, breast tumor microwave sensor system (BRATUMASS) determines the detected target of imaging electromagnetic trait by analyzing the properties of target tissue back wave obtained after near-field microwave radicalization (conelrad). The key of obtained target properties relationship and reconstructed detected space is to analyze the characteristics of the whole process from microwave transmission to back wave reception. Using traveling wave method, we derive spatial transmission properties and the relationship of the relation detected points distances, and valuate the properties of each unit by statistical valuation theory. This chapter gives the experimental data analysis results.
Advances in surface wave methods: Cascaded MASW-SASW
Westerhoff, R.S.; Brouwer, J.H.; Meekes, J.A.C.
2005-01-01
The application of the MASW method in areas that show strong lateral variations in subsurface properties is limited. Traditional SASW may yield a better lateral resolution but the dispersion curves (and thus the subsurface models) obtained with the method may be poor. The joint application of MASW a
Lattice Boltzmann method for multimode wave propagation in viscoelastic media and in elastic solids.
Frantziskonis, George N
2011-06-01
This paper reports the lattice Boltzmann method (LBM) based formulation for viscoelastic fluids with both volumetric and shear viscoelasticity. The relaxation limit of the viscoelastic fluid formulation yields the LBM for elastic solids with both volumetric or pressure (p) and shear (s) wave propagation modes. The reflection of a two-dimensional p wave from an obstacle (wedge) inclined to the propagation direction of the p wave is studied together with the convergence and stability behavior of the LBM as the lattice size and lattice time step decrease. The model is capable of accurately predicting the mode change (p to s) due to the reflection. The model provides a unique unified approach capable of simulating fluids, viscoelastic fluids, and solids within a single LBM framework, thus avoiding interface problems between different simulation methods. The paper concentrates on the wave propagation part of the model, in the quasielastic regime.
Partial-wave Coulomb transition matrices for attractive interaction by Fock's method
Kharchenko, V F
2016-01-01
Leaning upon the Fock method of the stereographic projection of the three-dimensional momentum space onto the four-dimensional unit sphere the possibility of the analytical solving of the Lippmann-Schwinger integral equation for the partial wave two-body Coulomb transition matrix at the ground bound state energy has been studied. In this case new expressions for the partial p-, d- and f-wave two-body Coulomb transition matrices have been obtained in the simple analytical form. The developed approach can also be extended to determine analytically the partial wave Coulomb transition matrices at the energies of excited bound states. Keywords: Partial wave Coulomb transition matrix; Lippmann-Schwinger equation; Fock method; Analytical solution PACS Nos. 03.65.-w; 03.65.Nk; 34.20.Cf
Use of Finite Point Method for Wave Propagation in Nonhomogeneous Unbounded Domains
Directory of Open Access Journals (Sweden)
S. Moazam
2015-01-01
Full Text Available Wave propagation in an unbounded domain surrounding the stimulation resource is one of the important issues for engineers. Past literature is mainly concentrated on the modelling and estimation of the wave propagation in partially layered, homogeneous, and unbounded domains with harmonic properties. In this study, a new approach based on the Finite Point Method (FPM has been introduced to analyze and solve the problems of wave propagation in any nonhomogeneous unbounded domain. The proposed method has the ability to use the domain properties by coordinate as an input. Therefore, there is no restriction in the form of the domain properties, such as being periodical as in the case of existing similar numerical methods. The proposed method can model the boundary points between phases with trace of errors and the results of this method satisfy both conditions of decay and radiation.
Extended F-Expansion Method and Periodic Wave Solutions for Klein-Gordon-Schr(o)dinger Equations
Institute of Scientific and Technical Information of China (English)
LI Xiao-Yan; LI Xiang-Zheng; WANG Ming-Liang
2006-01-01
We present an extended F-expansion method for finding periodic wave solutions of nonlinear evolution equations in mathematical physics. By using extended F-expansion method, many periodic wave solutions expressed by various Jacobi elliptic functions for the Klein-Gordon-Schrodinger equations are obtained. In the limit cases, the solitary wave solutions and trigonometric function solutions for the equations are also obtained.
Indian Academy of Sciences (India)
Jalil Manafian; Mehrdad Lakestani
2015-07-01
An application of the (′/)-expansion method to search for exact solutions of nonlinear partial differential equations is analysed. This method is used for Burgers, Fisher, Huxley equations and combined forms of these equations. The (′/)-expansion method was used to construct periodic wave and solitary wave solutions of nonlinear evolution equations. This method is developed for searching exact travelling wave solutions of nonlinear partial differential equations. It is shown that the (′/)-expansion method, with the help of symbolic computation, provides a straightforward and powerful mathematical tool for solving nonlinear partial differential equations.
Kinetic Flux Vector Splitting Method for the Shallow Water Wave Equations
Institute of Scientific and Technical Information of China (English)
施卫平; WeiShyy
2003-01-01
Based on the analogy to gas dynamics,the kinetic flux flux vector splitting (KFVS) method is used to stimulate the shallow water wave equations,The flus vectors of the equations are split on the basis of the local equilibrium Maxwell-Boltzmann distribution One dimensional examples including a dam breaking wave and flows over a ridge are calcualted.The solutions exhibit second-order accuracy with no spurious oscillation.
A comparison of high-order polynomial and wave-based methods for Helmholtz problems
Lieu, Alice; Gabard, Gwénaël; Bériot, Hadrien
2016-09-01
The application of computational modelling to wave propagation problems is hindered by the dispersion error introduced by the discretisation. Two common strategies to address this issue are to use high-order polynomial shape functions (e.g. hp-FEM), or to use physics-based, or Trefftz, methods where the shape functions are local solutions of the problem (typically plane waves). Both strategies have been actively developed over the past decades and both have demonstrated their benefits compared to conventional finite-element methods, but they have yet to be compared. In this paper a high-order polynomial method (p-FEM with Lobatto polynomials) and the wave-based discontinuous Galerkin method are compared for two-dimensional Helmholtz problems. A number of different benchmark problems are used to perform a detailed and systematic assessment of the relative merits of these two methods in terms of interpolation properties, performance and conditioning. It is generally assumed that a wave-based method naturally provides better accuracy compared to polynomial methods since the plane waves or Bessel functions used in these methods are exact solutions of the Helmholtz equation. Results indicate that this expectation does not necessarily translate into a clear benefit, and that the differences in performance, accuracy and conditioning are more nuanced than generally assumed. The high-order polynomial method can in fact deliver comparable, and in some cases superior, performance compared to the wave-based DGM. In addition to benchmarking the intrinsic computational performance of these methods, a number of practical issues associated with realistic applications are also discussed.
Ousley, Gilbert W., Sr.
1991-12-01
The utilization of the Delta 2 as the vehicle for launching Aristoteles into its near Sun synchronous orbit is addressed. Delta is NASA's most reliable launch vehicle and is well suited for placing the present Aristoteles spacecraft into a 400 m circular orbit. A summary of some of the Delta 2 flight parameters is presented. Diagrams of a typical Delta 2 two stage separation are included along with statistics on delta reliability and launch plans.
Feenstra, BJ; Klaassen, FC; vanderMarel, D; Barber, ZH; Pinaya, RP; Decroux, M
1997-01-01
Using mm-wave transmission, information about both the real and imaginary part of the dielectric function of superconducting thin films is obtained. This is done by fitting the Fabry-Perot resonance spectrum for the film plus substrate over a broad frequency range (110-180 GHz) using the full Fresne
DELTA机器人传送带与视觉的综合标定方法%Method of Integrated Calibration on DELTA Robot Conveyor and Vision
Institute of Scientific and Technical Information of China (English)
杨强; 刘冠峰
2015-01-01
In this paper we propose an method of integrated calibration on DELTA robot conveyor and vision. We first use the end of DELTA robot arm to touch the same point on the conveyor when the conveyor moves some distance,which allows us to obtain the value of the point’s location in the robot coordinate system and the corresponding value of the encoder.,then we get the scale factor of the robot and conveyor,determine the transformation matrix between the robot coordinate system and the conveyor coordinate system, then we can know the pose of the conveyor coordinate system relative to the coordinate system of the robot,which is the conveyor calibration. By using the camera to posit in contact with the robot at the same point, we obtain the intrinsic matrix and the external parameters matrix of the camera, which can know the transformation matrix between the robot coordinate system and the camera coordinate system, which is the robot vision calibration. DELTA robot conveyor and vision calibration will make the foundation of achieving DELTA robot high-precision control.%提出一种关于DELTA机器人传送带与视觉的综合标定方法。通过DELTA机器人臂末端在传送带移动一段距离接触传送带始末同一点，得到该点在机器人坐标系的位置和编码器上对应的读数，得到传送带与机器人的比例因子，确定机器人坐标系与传送带坐标系的转化矩阵，从而得到传动带相对于机器人坐标系的位姿，即传送带的标定。通过相机定位与机器人接触同一点，从而确定相机的内参矩阵与外参矩阵，从而得到机器人与相机坐标系的转换关系，即机器人视觉的标定。DELTA机器人传送带与视觉的标定，为DELTA机器人高精度控制的实现打下基础。
de Vries, Sandra; Rutten, Martine; de Vries, Liselotte; Anema, Kim; Klop, Tanja; Kaspersma, Judith
2017-04-01
In highly populated deltas, much work is to be done. Complex problems ask for new and knowledge driven solutions. Innovations in delta technology and water can bring relief to managing the water rich urban areas. Testing fields form a fundamental part of the knowledge valorisation for such innovations. In such testing fields, product development by start-ups is coupled with researchers, thus supplying new scientific insights. With the help of tests, demonstrations and large-scale applications by the end-users, these innovations find their way to the daily practices of delta management. More and more cities embrace the concept of Smart Cities to tackle the ongoing complexity of urban problems and to manage the city's assets - such as its water supply networks and other water management infrastructure. Through the use of new technologies and innovative systems, data are collected from and with citizens and devices - then processed and analysed. The information and knowledge gathered are keys to enabling a better quality of life. By testing water innovations together with citizens in order to find solutions for water management problems, not only highly spatial amounts of data are provided by and/or about these innovations, they are also improved and demonstrated to the public. A consortium consisting of a water authority, a science centre, a valorisation program and two universities have joined forces to create a testing field for delta technology and water innovations using citizen science methods. In this testing field, the use of citizen science for water technologies is researched and validated by facilitating pilot projects. In these projects, researchers, start-ups and citizens work together to find the answer to present-day water management problems. The above mentioned testing field tests the use of crowd-sourcing data as for example hydrological model inputs, or to validate remote sensing applications, or improve water management decisions. Currently the
A Spectral Multiscale Method for Wave Propagation Analysis: Atomistic-Continuum Coupled Simulation
Patra, Amit K; Ganguli, Ranjan
2014-01-01
In this paper, we present a new multiscale method which is capable of coupling atomistic and continuum domains for high frequency wave propagation analysis. The problem of non-physical wave reflection, which occurs due to the change in system description across the interface between two scales, can be satisfactorily overcome by the proposed method. We propose an efficient spectral domain decomposition of the total fine scale displacement along with a potent macroscale equation in the Laplace domain to eliminate the spurious interfacial reflection. We use Laplace transform based spectral finite element method to model the macroscale, which provides the optimum approximations for required dynamic responses of the outer atoms of the simulated microscale region very accurately. This new method shows excellent agreement between the proposed multiscale model and the full molecular dynamics (MD) results. Numerical experiments of wave propagation in a 1D harmonic lattice, a 1D lattice with Lennard-Jones potential, a ...
An Improved Split-Step Wavelet Transform Method for Anomalous Radio Wave Propagation Modelling
Directory of Open Access Journals (Sweden)
A. Iqbal
2014-12-01
Full Text Available Anomalous tropospheric propagation caused by ducting phenomenon is a major problem in wireless communication. Thus, it is important to study the behavior of radio wave propagation in tropospheric ducts. The Parabolic Wave Equation (PWE method is considered most reliable to model anomalous radio wave propagation. In this work, an improved Split Step Wavelet transform Method (SSWM is presented to solve PWE for the modeling of tropospheric propagation over finite and infinite conductive surfaces. A large number of numerical experiments are carried out to validate the performance of the proposed algorithm. Developed algorithm is compared with previously published techniques; Wavelet Galerkin Method (WGM and Split-Step Fourier transform Method (SSFM. A very good agreement is found between SSWM and published techniques. It is also observed that the proposed algorithm is about 18 times faster than WGM and provide more details of propagation effects as compared to SSFM.
Simulation of Lamb wave reflections at plate edges using the semi-analytical finite element method.
Ahmad, Z A B; Gabbert, U
2012-09-01
In typical Lamb wave simulation practices, effects of plate edge reflections are often not considered in order to simplify the wave signal interpretations. Methods that are based on infinite plates such as the semi-analytical finite element method is effective in simulating Lamb waves as it excludes the effect of plate edges. However, the inclusion of plate edges in a finite plate could render this method inapplicable, especially for transient response simulations. Here, by applying the ratio of Lamb mode reflections at plate edges, and representing the reflection at plate edges using infinite plate solutions, the semi-analytical finite element method can be applied for transient response simulation, even when the plate is no longer infinite.
New ultrasonic Bleustein-Gulyaev wave method for measuring the viscosity of liquids at high pressure
Kiełczyński, P.; Szalewski, M.; Siegoczyński, R. M.; Rostocki, A. J.
2008-02-01
In this paper, a new method for measuring the viscosity of liquids at high pressure is presented. To this end the authors have applied an ultrasonic method using the Bleustein-Gulyaev (BG) surface acoustic wave. By applying the perturbation method, we can prove that the change in the complex propagation constant of the BG wave produced by the layer of liquid loading the waveguide surface is proportional to the shear mechanical impedance of the liquid. In the article, a measuring setup employing the BG wave for the purpose of measuring the viscosity of liquids at high pressure (up to 1GPa) is presented. The results of high-pressure viscosity measurements of triolein and castor oil are also presented. In this paper the model of a Newtonian liquid was applied. Using this new method it is also possible to measure the viscosity of liquids during the phase transition and during the decompression process (hysteresis of the dependence of viscosity on pressure).
Incorporation of an Adaptive Real Space Grid in the Projector Augmented Wave Method
Tackett, A. R.; Dunning, R. B.; Matthews, G. Eric; Holzwarth, N. A. W.
1997-03-01
We report initial efforts to incorporate a real space adaptive grid into the projector augmented wave (PAW) method developed by Blöchl(P. Blöchl, Phys. Rev. B50,17953 (1994).). The PAW method allows straightforward treatment of valence electrons while offering computational efficiency similar to pseudopotential methods. Real space adaptive grid methods have been shown to improve speed and decrease storage requirements. The adaptive grid also allows an effective increased plane wave energy cutoff in the vicinity of the ions. In this work, we use a real space adapative grid to solve for the potential, while using a transformed plane wave basis for the wavefunctions, as described by Gygi(F. Gygi, Europhysics Letters 19, 617 (1992).).
Overdetermined Shooting Methods for Computing Standing Water Waves with Spectral Accuracy
Wilkening, Jon
2012-01-01
A high-performance shooting algorithm is developed to compute time-periodic solutions of the free-surface Euler equations with spectral accuracy in double and quadruple precision. The method is used to study resonance and its effect on standing water waves. We identify new nucleation mechanisms in which isolated large-amplitude solutions, and closed loops of such solutions, suddenly exist for depths below a critical threshold. We also study degenerate and secondary bifurcations related to Wilton's ripples in the traveling case, and explore the breakdown of self-similarity at the crests of extreme standing waves. In shallow water, we find that standing waves take the form of counter-propagating solitary waves that repeatedly collide quasi-elastically. In deep water with surface tension, we find that standing waves resemble counter-propagating depression waves. We also discuss existence and non-uniqueness of solutions, and smooth versus erratic dependence of Fourier modes on wave amplitude and fluid depth. In t...
Institute of Scientific and Technical Information of China (English)
XiangYu; HuangYuying; MaXiaoqiang
2004-01-01
By virtue of the comparability between the wave superposition method and the dynamic analysis of structures, a general format for overcoming the non-uniqueness of solution induced by the wave superposition method at the eigenfrequencies of the corresponding interior problems is proposed. By adding appropriate damp to the virtual source system of the wave superposition method, the unique solutions for all wave numbers can be ensured. Based on this thought, a novel method-wave superposition method with complex radius vector is constructed.Not only is the computational time of this method approximately equal to that of the standard wave superposition method, but also the accuracy is much higher compared with other correlative methods. Finally, by taking the pulsating sphere and oscillating sphere as examples, the results of calculation show that the present method can effectively overcome the non-uniqueness problem.
Traveling wave solutions of nonlinear evolution equations via the enhanced (G′/G-expansion method
Directory of Open Access Journals (Sweden)
Kamruzzaman Khan
2014-07-01
Full Text Available In this article, an enhanced (G′/G-expansion method is suggested to find the traveling wave solutions for the modified Korteweg de-Vries (mKDV equation. Abundant traveling wave solutions are derived, which are expressed by the hyperbolic and trigonometric functions involving several parameters. The efficiency of this method for finding these exact solutions has been demonstrated. It is shown that the proposed method is effective and can be used for many other nonlinear evolution equations (NLEEs in mathematical physics.
A new variable coefficient algebraic method and non-traveling wave solutions of nonlinear equations
Institute of Scientific and Technical Information of China (English)
Lu Bin; Zhang Hong-Qing
2008-01-01
In this paper,a new auxiliary equation method is presented of constructing more new non-travelling wave solutions of nonlinear differential equations in mathematical physics,which is direct and more powerful than projective Riccati equation method.In order to illustrate the validity and the advantages of the method,(2+1)-dimensional asymmetric Nizhnik-Novikov-Vesselov equation is employed and many new double periodic non-travelling wave solutions are obtained.This algorithm can also be applied to other nonlinear differential equations.
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
In this paper, an extended method is proposed for constructing new forms ofexact travelling wave solutions to nonlinear partial differential equations by making a more general transformation. For illustration, we apply the method to the asymmetric Nizhnik-Novikov-Vesselov equation and the coupled Drinfel'd-Sokolov-Wilson equation and successfully cover the previously known travelling wave solutions found by Chen's method [Y. Chen, et al. Chaos, Solitons and Fractals 22 (2004) 675; Y. Chen, et al. Int. J. Mod. Phys. C 4 (2004) 595].
Grosse, Ralf
1990-01-01
Propagation of sound through the turbulent atmosphere is a statistical problem. The randomness of the refractive index field causes sound pressure fluctuations. Although no general theory to predict sound pressure statistics from given refractive index statistics exists, there are several approximate solutions to the problem. The most common approximation is the parabolic equation method. Results obtained by this method are restricted to small refractive index fluctuations and to small wave lengths. While the first condition is generally met in the atmosphere, it is desirable to overcome the second. A generalization of the parabolic equation method with respect to the small wave length restriction is presented.
Institute of Scientific and Technical Information of China (English)
Houde Han; Zhongyi Huang
2008-01-01
In this paper, we propose a tailored-finite-point method for the numerical simulation of the Helmholtz equation with high wave numbers in heterogeneous medium. Our finite point method has been tailored to some particular properties of the problem, which allows us to obtain approximate solutions with the same behaviors as that of the exact solution very naturally. Especially, when the coefficients are piecewise constant, we can get the exact solution with only one point in each subdomain. Our finite-point method has uniformly convergent rate with respect to wave number k in L2-norm.
Ultrasonic guided wave based damage imaging by time-reversal method in frequency-wavenumber domain
Xu, C. G.; Xu, B. Q.; Luo, Y.; Xu, G. D.; Lu, L. Z.
2017-05-01
More attention has been drawn to ultrasonic guided waves (UGW) based damage detection method for its advantages of wide range inspection of large scale structures. However, complex propagation characteristics of guided waves as well as traditional contact ultrasonic transducers limit its application for the practical damage detection. By combining Scanning Laser Doppler vibrometer (SLDV) technology, Time-Reversal method in frequency-wavenumber domain (f-k RTM) can compensate for the dispersive nature of Lamb waves, localize multiple damage sites and identify their sizes without time consuming numerical calculation. In this work, we adopt f-k RTM for damage detection in plate-like structure. Instead of SLDV in experiment, 3D finite element numerical method is adopted to obtain scattered ultrasonic guided wavefield data with high spatial resolution. The direct path waves were extracted to obtain the incident wavefield while the scattered signals were used to calculate the scattering wave field. Damage imaging can also be achieved by introducing crosscorrelation imaging condition. Imaging results show that the method is very effective for crack localization and boundary shape-recognition. Numerical simulation results and imaging algorithm laid the foundation for the method applied in experiment and practice.
Holmqvist, Fredrik; Platonov, Pyotr G; Havmöller, Rasmus; Carlson, Jonas
2007-10-09
The study was designed to investigate the effect of different measuring methodologies on the estimation of P wave duration. The recording length required to ensure reproducibility in unfiltered, signal-averaged P wave analysis was also investigated. An algorithm for automated classification was designed and its reproducibility of manual P wave morphology classification investigated. Twelve-lead ECG recordings (1 kHz sampling frequency, 0.625 microV resolution) from 131 healthy subjects were used. Orthogonal leads were derived using the inverse Dower transform. Magnification (100 times), baseline filtering (0.5 Hz high-pass and 50 Hz bandstop filters), signal averaging (10 seconds) and bandpass filtering (40-250 Hz) were used to investigate the effect of methodology on the estimated P wave duration. Unfiltered, signal averaged P wave analysis was performed to determine the required recording length (6 minutes to 10 s) and the reproducibility of the P wave morphology classification procedure. Manual classification was carried out by two experts on two separate occasions each. The performance of the automated classification algorithm was evaluated using the joint decision of the two experts (i.e., the consensus of the two experts). The estimate of the P wave duration increased in each step as a result of magnification, baseline filtering and averaging (100 +/- 18 vs. 131 +/- 12 ms; P manual classification in 90% of the cases. The methodology used has profound effects on the estimation of P wave duration, and the method used must therefore be validated before any inferences can be made about P wave duration. This has implications in the interpretation of multiple studies where P wave duration is assessed, and conclusions with respect to normal values are drawn.P wave morphology and duration assessed using unfiltered, signal-averaged P wave analysis have high reproducibility, which is unaffected by the length of the recording. In the present study, the performance of
A new method to record subglottal pressure waves : potential applications
Neumann, K; Gall, [No Value; Schutte, HK; Miller, DG
Rapid subglottal pressure changes related to the glottal cycles influence the aerodynamics of phonation. Various methods to measure these have been developed, but are not practical for routine phoniatric use. For that reason, a noninvasive measurement tool is necessary. This article presents a
Verweij, M.D.; Huijssen, J.
2009-01-01
The full-wave computation of transient acoustic fields with sizes in the order of 100x100x100 wavelengths by 100 periods requires a numerical method that is extremely efficient in terms of storage and computation. Iterative integral equation methods offer a good performance on these points, provided
Time-dependent density-functional theory in the projector augmented-wave method
DEFF Research Database (Denmark)
Walter, Michael; Häkkinen, Hannu; Lehtovaara, Lauri
2008-01-01
We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we...
Wave propagation method as an accurate technique for effective refractive index retrieving
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
2009-01-01
An effective parameters retrieval method based on the wave propagation simulation is proposed and compared with the standard S-parameter procedure. The method is free from possible mistakes originated by the multiple branching of solutions in the S-parameter procedure and shows high accuracy. The...
Che, Cheng-Xuan; Wang, Xiu-Ming; Lin, Wei-Jun
2010-06-01
Based on strong and weak forms of elastic wave equations, a Chebyshev spectral element method (SEM) using the Galerkin variational principle is developed by discretizing the wave equation in the spatial and time domains and introducing the preconditioned conjugate gradient (PCG)-element by element (EBE) method in the spatial domain and the staggered predictor/corrector method in the time domain. The accuracy of our proposed method is verified by comparing it with a finite-difference method (FDM) for a homogeneous solid medium and a double layered solid medium with an inclined interface. The modeling results using the two methods are in good agreement with each other. Meanwhile, to show the algorithm capability, the suggested method is used to simulate the wave propagation in a layered medium with a topographic traction free surface. By introducing the EBE algorithm with an optimized tensor product technique, the proposed SEM is especially suitable for numerical simulation of wave propagations in complex models with irregularly free surfaces at a fast convergence rate, while keeping the advantage of the finite element method.
Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.
2014-12-01
Low-frequency events such as tsunamis generate acoustic and gravity waves which quickly propagate in the atmosphere. Since the atmospheric density decreases exponentially as the altitude increases and from the conservation of the kinetic energy, those waves see their amplitude raise (to the order of 105 at 200km of altitude), allowing their detection in the upper atmosphere. Various tools have been developed through years to model this propagation, such as normal modes modeling or to a greater extent time-reversal techniques, but none offer a low-frequency multi-dimensional atmospheric wave modelling.A modeling tool is worthy interest since there are many different phenomena, from quakes to atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool.Starting from the SPECFEM program that already propagate waves in solid, porous or fluid media using a spectral element method, this work offers a tool with the ability to model acoustic and gravity waves propagation in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source.Atmospheric attenuation is required in a proper modeling framework since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals. The bottom forcing feature has been implemented due to its ability to easily model the coupling with the Earth's or ocean's surface (that vibrates when a surface wave go through it) but also huge atmospheric events.
Jung, Ju-Hyun
2016-01-01
We present a microscopic description of the strong $\\pi NN$, $\\pi N\\Delta$ and $\\pi\\Delta\\Delta$ vertices. Our starting point is a constituent-quark model supplemented by an additional $3q\\pi$ non-valence component. In the spirit of chiral constituent-quark models, quarks are allowed to emit and reabsorb a pion. This multichannel system is treated in a relativistically invariant way within the framework of point-form quantum mechanics. Starting with a common $SU(6)$ spin-flavor-symmetric wave function for $N$ and $\\Delta$, we calculate the strength of the $\\pi NN$, $\\pi N\\Delta$ and $\\pi\\Delta\\Delta$ couplings and the corresponding vertex form factors. Our results are in accordance with phenomenological fits of these quantities that have been obtained within purely hadronic multichannel models for baryon resonances.
Tubman, Norm; Hammes-Schiffer, Sharon; Ceperley, David
2016-01-01
Simulating nonadiabatic effects with many-body wave function approaches is an open field with many challenges. Recent interest has been driven by new algorithmic developments and improved theoretical understanding of properties unique to electron-ion wave functions. Fixed-node diffusion Monte Caro is one technique that has shown promising results for simulating electron-ion systems. In particular, we focus on the CH molecule for which previous results suggested a relatively significant contribution to the energy from nonadiabatic effects. We propose a new wave function ansatz for diatomic systems which involves interpolating the determinant coefficients calculated from configuration interaction methods. We find this to be an improvement beyond previous wave function forms that have been considered. The calculated nonadiabatic contribution to the energy in the CH molecule is reduced compared to our previous results, but still remains the largest among the molecules under consideration.
New imaging method for seismic reflection wave and its theoretical basis
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Some new imaging formulas for seismic reflection wave and theirtheoretical basis are given. Phenomena of wave propagation should be characterized by instantaneous spectrum and expressed by complex function of three variables (time, space and frequency) in mathematics. Various physical parameters of medium are also complex functions of two variables (space and frequency). The relationship between reflection coefficient of medium and spectrum of reflected wave is given. Multi-reflection and filter of formations are considered in inversion formulas. Prob-lems in classical convolution model and wave equation are illustrated. All these inversion formulas can be used to image underground medium by wavelet transform and method of "3-basic colors". Different colors mean different media.
A Finite Difference-Augmented Peridynamics Method for Wave Dispersion
2014-10-21
model using a blending function in 1D, though again, the focus is on preset, unchang- ing local/ nonlocal regions. In contrast, this work will focus on...Fracture. 2014; 190:39-52. 14. ABSTRACT A method is presented for the modeling of brittle elastic fracture which combines peridynamics and a finite...propagation modeling , while peridynamics is automatically inserted in high strain areas to model crack initiation and growth. The dispersion
Composite Materials NDE Using Enhanced Leaky Lamb Wave Dispersion Data Acquisition Method
Bar-Cohen, Yoseph; Mal, Ajit; Lih, Shyh-Shiuh; Chang, Zensheu
1999-01-01
The leaky Lamb wave (LLW) technique is approaching a maturity level that is making it an attractive quantitative NDE tool for composites and bonded joints. Since it was first observed in 1982, the phenomenon has been studied extensively, particularly in composite materials. The wave is induced by oblique insonification using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates has been well documented and corroborated experimentally with high accuracy. The sensitivity of the wave to the elastic constants of the material and to the boundary conditions led to the capability to measure the elastic properties of bonded joints. Recently, the authors significantly enhanced the LLW method's capability by increasing the speed of the data acquisition, the number of modes that can be identified and the accuracy of the data inversion. In spite of the theoretical and experimental progress, methods that employ oblique insonification of composites are still not being applied as standard industrial NDE methods. The authors investigated the issues that are hampering the transition of the LLW to industrial applications and identified 4 key issues. The current capability of the method and the nature of these issues are described in this paper.
Algebraic method for constructing singular steady solitary waves: A case study
Clamond, Didier; Galligo, André
2016-01-01
This article describes the use of algebraic methods in a phase plane analysis of ordinary differential equations. The method is illustrated by the study of capillary-gravity steady surface waves propagating in shallow water. We consider the (fully nonlinear, weakly dispersive) Serre-Green-Naghdi equations with surface tension, because it provides a tractable model that, in the same time, is not too simple so the interest of the method can be emphasised. In particular, we analyse a special class of solutions, the solitary waves, which play an important role in many fields of Physics. In capillary-gravity regime, there are two kinds of localised infinitely smooth travelling wave solutions -- solitary waves of elevation and of depression. However, if we allow the solitary waves to have an angular point, the "zoology" of solutions becomes much richer and the main goal of this study is to provide a complete classification of such singular localised solutions using the methods of the effective Algebraic Geometry.
Algebraic method for constructing singular steady solitary waves: a case study
Clamond, Didier; Dutykh, Denys; Galligo, André
2016-07-01
This article describes the use of algebraic methods in a phase plane analysis of ordinary differential equations. The method is illustrated by the study of capillary-gravity steady surface waves propagating in shallow water. We consider the (fully nonlinear, weakly dispersive) Serre-Green-Naghdi equation with surface tension, because it provides a tractable model that, at the same time, is not too simple, so interest in the method can be emphasized. In particular, we analyse a special class of solutions, the solitary waves, which play an important role in many fields of physics. In capillary-gravity regime, there are two kinds of localized infinitely smooth travelling wave solutions-solitary waves of elevation and of depression. However, if we allow the solitary waves to have an angular point, then the `zoology' of solutions becomes much richer, and the main goal of this study is to provide a complete classification of such singular localized solutions using the methods of the effective algebraic geometry.
Energy Technology Data Exchange (ETDEWEB)
Han Jinduo [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 DingXi Road, Shanghai 200050 (China); Wen Zhaoyin, E-mail: zywen@mail.sic.ac.c [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 DingXi Road, Shanghai 200050 (China); Zhang Jingchao; Xu Xiaohe; Gu Zhonghua; Liu Yu [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 DingXi Road, Shanghai 200050 (China)
2010-12-15
A citric acid complexation method is applied to synthesize CaZr{sub 0.90}In{sub 0.10}O{sub 3-{delta}}. TG-DSC, XRD, SEM, linear shrinkage and the complex impedance method are conducted to investigate the physical and protonic conduction properties of CaZr{sub 0.90}In{sub 0.10}O{sub 3-{delta}}. The results show that the citrate method is a favorable way to produce high purity nano-CaZr{sub 0.90}In{sub 0.10}O{sub 3-{delta}} powders suitable for fabricating dense ceramics at lower temperature. In addition, the protonic conduction tests indicate that the total, bulk and grain boundary conductivities of the ceramics are much higher than those of the ceramics fabricated from the powders synthesized by the conventional solid-state reaction method.
Indirect (source-free) integration method. I. Wave-forms from geodesic generic orbits of EMRIs
Ritter, Patxi; Aoudia, Sofiane; Spallicci, Alessandro D. A. M.; Cordier, Stéphane
2016-12-01
The Regge-Wheeler-Zerilli (RWZ) wave-equation describes Schwarzschild-Droste black hole perturbations. The source term contains a Dirac distribution and its derivative. We have previously designed a method of integration in time domain. It consists of a finite difference scheme where analytic expressions, dealing with the wave-function discontinuity through the jump conditions, replace the direct integration of the source and the potential. Herein, we successfully apply the same method to the geodesic generic orbits of EMRI (Extreme Mass Ratio Inspiral) sources, at second order. An EMRI is a Compact Star (CS) captured by a Super-Massive Black Hole (SMBH). These are considered the best probes for testing gravitation in strong regime. The gravitational wave-forms, the radiated energy and angular momentum at infinity are computed and extensively compared with other methods, for different orbits (circular, elliptic, parabolic, including zoom-whirl).
Scattering cluster wave functions on the lattice using the adiabatic projection method
Rokash, Alexander; Elhatisari, Serdar; Lee, Dean; Epelbaum, Evgeny; Krebs, Hermann
2015-01-01
The adiabatic projection method is a general framework for studying scattering and reactions on the lattice. It provides a low-energy effective theory for clusters which becomes exact in the limit of large Euclidean projection time. Previous studies have used the adiabatic projection method to extract scattering phase shifts from finite periodic-box energy levels using L\\"uschers method. In this paper we demonstrate that scattering observables can be computed directly from asymptotic cluster wave functions. For a variety of examples in one and three spatial dimensions, we extract elastic phase shifts from asymptotic cluster standing waves corresponding to spherical wall boundary conditions. We find that this approach of extracting scattering wave functions from the adiabatic Hamiltonian to be less sensitive to small stochastic and systematic errors as compared with using periodic-box energy levels.
Indirect (source-free) integration method. I. Wave-forms from geodesic generic orbits of EMRIs
Ritter, P; Spallicci, A; Cordier, S
2015-01-01
The Regge-Wheeler-Zerilli (RWZ) wave-equation describes Schwarzschild-Droste black hole perturbations. The source term contains a Dirac distribution and its derivative. We have previously designed a method of integration in time domain. It consists of a finite difference scheme where analytic expressions, dealing with the wave-function discontinuity through the jump conditions, replace the direct integration of the source and the potential. Herein, we successfully apply the same method to the geodesic generic orbits of EMRI (Extreme Mass Ratio Inspiral) sources, at second order. An EMRI is a Compact Star (CS) captured by a Super Massive Black Hole (SMBH). These are considered the best probes for testing gravitation in strong regime. The gravitational wave-forms, the radiated energy and angular momentum at infinity are computed and extensively compared with other methods, for different orbits (circular, elliptic, parabolic, including zoom-whirl).
Institute of Scientific and Technical Information of China (English)
WANG Sheng'an; LONG Xiaomin; ZHANG Keben; CHEN Junchang; ZHANG Wenjing; CAI Shuqun
2007-01-01
Multi-parameter hydrological gauge is an instrument developed by the South China Sea Institute of Oceanology,the Chinese Academy of Sciences to make simultaneous observation of current, wave, tide, water temperature and conductivity.By using the well-known "PUV method", the directional wave spectrum can be calculated and the dominant wave direction is then obtained.The comparison of the dominant wave directions derived from the measurements using both the multi-parameter hydrological gauge and the MARK Ⅱ "Wave-Rider" directional buoy shows that the dominant wave directions derived from the two kinds of measurements are in good agreement.
The Numerical Simulation of Ship Waves using Cartesian Grid Methods
Sussman, Mark
2014-01-01
Two different cartesian-grid methods are used to simulate the flow around the DDG 5415. The first technique uses a "coupled level-set and volume-of-fluid" (CLS) technique to model the free-surface interface. The no-flux boundary condition on the hull is imposed using a finite-volume technique. The second technique uses a level-set technique (LS) to model the free-surface interface. A body-force technique is used to impose the hull boundary condition. The predictions of both numerical techniques are compared to whisker-probe measurements of the DDG 5415. The level-set technique is also used to investigate the breakup of a two-dimensional spray sheet.
Seismic wave generation systems and methods for cased wells
Minto, James; Sorrells, Martin H; Owen, Thomas E.; Schroeder, Edgar C.
2011-03-29
A vibration source (10) includes an armature bar (12) having a major length dimension, and a driver (20A) positioned about the armature bar. The driver (20A) is movably coupled to the armature bar (12), and includes an electromagnet (40). During operation the electromagnet (40) is activated such that the driver (20A) moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar. A described method for generating a vibratory signal in an object includes positioning the vibration source (10) in an opening of the object, coupling the armature bar (12) to a surface of the object within the opening, and activating the electromagnet (40) of the driver (20A) such that the driver moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar and the object.
Migration in Deltas: An Integrated Analysis
Nicholls, Robert J.; Hutton, Craig W.; Lazar, Attila; Adger, W. Neil; Allan, Andrew; Arto, Inaki; Vincent, Katharine; Rahman, Munsur; Salehin, Mashfiqus; Sugata, Hazra; Ghosh, Tuhin; Codjoe, Sam; Appeaning-Addo, Kwasi
2017-04-01
Deltas and low-lying coastal regions have long been perceived as vulnerable to global sea-level rise, with the potential for mass displacement of exposed populations. The assumption of mass displacement of populations in deltas requires a comprehensive reassessment in the light of present and future migration in deltas, including the potential role of adaptation to influence these decisions. At present, deltas are subject to multiple drivers of environmental change and often have high population densities as they are accessible and productive ecosystems. Climate change, catchment management, subsidence and land cover change drive environmental change across all deltas. Populations in deltas are also highly mobile, with significant urbanization trends and the growth of large cities and mega-cities within or adjacent to deltas across Asia and Africa. Such migration is driven primarily by economic opportunity, yet environmental change in general, and climate change in particular, are likely to play an increasing direct and indirect role in future migration trends. The policy challenges centre on the role of migration within regional adaptation strategies to climate change; the protection of vulnerable populations; and the future of urban settlements within deltas. This paper reviews current knowledge on migration and adaptation to environmental change to discern specific issues pertinent to delta regions. It develops a new integrated methodology to assess present and future migration in deltas using the Volta delta in Ghana, Mahanadi delta in India and Ganges-Brahmaputra-Meghna delta across India and Bangladesh. The integrated method focuses on: biophysical changes and spatial distribution of vulnerability; demographic changes and migration decision-making using multiple methods and data; macro-economic trends and scenarios in the deltas; and the policies and governance structures that constrain and enable adaptation. The analysis is facilitated by a range of
Applications of a simplified bilinear method to ion-acoustic solitary waves in plasma
Awawdeh, Fadi; Jaradat, H. M.; Al-Shara', S.
2012-02-01
In this paper, we propose a computational method for nonlinear partial differential equations modeling ion-acoustic waves as well as dusty plasmas in laboratory and space sciences. Many types of solitary waves including soliton solutions, N-soliton solutions and singular N-soliton solutions are derived. The characteristic line method and graphical analysis are applied to discuss the solitonic propagation and collision, including the bidirectional solitons and elastic interactions. Furthermore, the effects of inhomogeneities of media and nonuniformities of boundaries, depicted by the variable coefficients, on the soliton behavior are discussed.
Methods to increase the depth and precision of transient Rayleigh wave exploration
Institute of Scientific and Technical Information of China (English)
ZHANG Jian-jun(张建军); WEI Xiu-cheng(魏修成); LIU Yang(刘洋)
2004-01-01
In order to increase the exploration depth of Rayleigh wave, new idea that different from the former principles in data acquisition was applied. Suitable data acquisition parameter was given out on the basis of large amount of experiments. By reducing the group interval, the low frequency signal are enhanced instead of been attenuated. Furthermore, to solve the problem that the precision of Rayleigh wave exploration method count much to the signal-to-noise ratio, some preprocessing methods were put forward. By using zero shift rectifying, digital F-K filtering and cutting, noises can be effectively eliminated.
Energy Technology Data Exchange (ETDEWEB)
Nenadic, Ivan Z; Urban, Matthew W; Mitchell, Scott A; Greenleaf, James F [Basic Ultrasound Research Laboratory, Department of Physiology and Biophysics, Mayo Clinic, Rochester, MN 55905 (United States)
2011-04-07
Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of shear wave dispersion ultrasound vibrometry (SDUV), a noninvasive ultrasound-based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave dispersion ultrasound vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify the mechanical properties of soft tissues with a plate-like geometry.
Nenadic, Ivan Z; Urban, Matthew W; Mitchell, Scott A; Greenleaf, James F
2011-04-07
Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of shear wave dispersion ultrasound vibrometry (SDUV), a noninvasive ultrasound-based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave dispersion ultrasound vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify the mechanical properties of soft tissues with a plate-like geometry.
Haney, Matthew M.; Mikesell, T. Dylan; van Wijk, Kasper; Nakahara, Hisashi
2012-01-01
Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations were not considered in the development of the SPAC method. The method originally addressed the vertical–vertical (ZZ), RR and TT correlations, hence the name spatial autocorrelation. The theoretical expressions we derive for the ZR and RZ correlations offer additional ways to measure Rayleigh wave dispersion within the SPAC framework. Expanding on the results for isotropic incidence, we derive the complete correlation matrix in the case of generally anisotropic incidence. We show that the ZR and RZ correlations have advantageous properties in the presence of an out-of-plane directional wavefield compared to ZZ and RR correlations. We apply the results for mixed-component correlations to a data set from Akutan Volcano, Alaska and find consistent estimates of Rayleigh wave phase velocity from ZR compared to ZZ correlations. This work together with the recently discovered connections between the SPAC method and time-domain correlations of ambient noise provide further insights into the retrieval of surface wave Green’s functions from seismic noise.
The Detection of Vertical Cracks in Asphalt Using Seismic Surface Wave Methods
Iodice, M.; Muggleton, J.; Rustighi, E.
2016-09-01
Assessment of the location and of the extension of cracking in road surfaces is important for determining the potential level of deterioration in the road overall and the infrastructure buried beneath it. Damage in a pavement structure is usually initiated in the tarmac layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. This paper presents an investigation of two surface wave methods to detect and locate top-down cracks in asphalt layers. The aim of the study is to compare the results from the well- established Multichannel Analysis of Surface Waves (MASW) and the more recent Multiple Impact of Surface Waves (MISW) in the presence of a discontinuity and to suggest the best surface wave technique for evaluating the presence and the extension of vertical cracks in roads. The study is conducted through numerical simulations alongside experimental investigations and it considers the cases for which the cracking is internal and external to the deployment of sensors. MISW is found to enhance the visibility of the reflected waves in the frequency wavenumber (f-k) spectrum, helping with the detection of the discontinuity. In some cases, by looking at the f-k spectrum obtained with MISW it is possible to extract information regarding the location and the depth of the cracking.
Martin, Roland; Brissaud, Quentin; Garcia, Raphael; Komatitsch, Dimitri
2015-04-01
During low-frequency events such as tsunamis, acoustic and gravity waves are generated and quickly propagate in the atmosphere. Due to the exponential decrease of the atmospheric density with the altitude, the conservation of the kinetic energy imposes that the amplitude of those waves increases (to the order of 105 at 200km of altitude), which allows their detection in the upper atmosphere. This propagation bas been modelled for years with different tools, such as normal modes modeling or to a greater extent time-reversal techniques, but a low-frequency multi-dimensional atmospheric wave modelling is still crucially needed. A modeling tool is worth of interest since there are many different sources, as earthquakes or atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool. By adding some developments to the SPECFEM package that already models wave propagation in solid, porous or fluid media using a spectral element method, we show here that acoustic and gravity waves propagation can now be modelled in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source. The bottom forcing feature has been implemented to easily model the coupling with the Earth's or ocean's vibrating surfaces but also huge atmospheric events. Atmospheric attenuation is also introduced since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals.
An element by element spectral element method for elastic wave modeling
Institute of Scientific and Technical Information of China (English)
LIN Weijun; WANG Xiuming; ZHANG Hailan
2006-01-01
The spectral element method which combines the advantages of spectral method with those of finite element method,provides an efficient tool in simulating elastic wave equation in complex medium. Based on weak form of elastodynamic equations, mathematical formulations for Legendre spectral element method are presented. The wave field on an element is discretized using high-order Lagrange interpolation, and integration over the element is accomplished based upon the Gauss-Lobatto-Legendre integration rule. This results in a diagonal mass matrix which leads to a greatly simplified algorithm. In addition, the element by element technique is introduced in our method to reduce the memory sizes and improve the computation efficiency. Finally, some numerical examples are presented to demonstrate the spectral accuracy and the efficiency. Because of combinations of the finite element scheme and spectral algorithms, this method can be used for complex models, including free surface boundaries and strong heterogeneity.
Arbitrary Difference Precise Integration Method for Solving the Seismic Wave Equation
Institute of Scientific and Technical Information of China (English)
Jia Xiaofeng; Wang Runqiu; Hu Tianyue
2004-01-01
Wave equation migration is often applied to solve seismic imaging problems. Usually, the finite difference method is used to obtain the numerical solution of the wave equation. In this paper,the arbitrary difference precise integration (ADPI) method is discussed and applied in seismic migration. The ADPI method has its own distinctive idea. When dispersing coordinates in the space domain, it employs a relatively unrestrained form instead of the one used by the conventional finite difference method. Moreover, in the time domain it adopts the sub-domain precise integration method. As a result, it not only takes the merits of high precision and narrow bandwidth, but also can process various boundary conditions and describe the feature of an inhomogeneous medium better. Numerical results show the benefit of the presented algorithm using the ADPI method.
Rouden, Jacques; Seitz, Thomas; Lemoucheux, Laurent; Lasne, Marie-Claire
2004-05-28
With the aim of the radiolabeling of cytisine, a potent agonist of nicotinic receptors, with [(11)C]phosgene, the rapid synthesis of a lactam model of our target has been studied. The key step of the delta-lactam formation is a new chemoselective lithiation-annulation method, under high dilution, of a suitable piperidinylcarbamoyl chloride. This precursor was obtained from (2-hydroxyethyl)piperidine in a linear synthetic sequence involving a Corey-Fuchs olefination of the corresponding aldehyde, followed by a selective reduction, using a diimide equivalent, of an iodoalkyne into a (Z)-iodopropene piperidine. This alkene served as main precursor to study the cyclization according to several procedures using phosgene as the required carbonylating reagent.
Delta Plaza kohvik = Delta Plaza cafe
2010-01-01
Tallinnas Pärnu mnt 141 asuva kohviku Delta Plaza sisekujundusest. Sisearhitektid Tiiu Truus ja Marja Viltrop (Stuudio Truus OÜ). Tiiu Truusi tähtsamate tööde loetelu. Büroohoone Delta Plaza arhitektid Marika Lõoke ja Jüri Okas (AB J. Okas & M. Lõoke)
Delta Plaza kohvik = Delta Plaza cafe
2010-01-01
Tallinnas Pärnu mnt 141 asuva kohviku Delta Plaza sisekujundusest. Sisearhitektid Tiiu Truus ja Marja Viltrop (Stuudio Truus OÜ). Tiiu Truusi tähtsamate tööde loetelu. Büroohoone Delta Plaza arhitektid Marika Lõoke ja Jüri Okas (AB J. Okas & M. Lõoke)
Laugel, Amélie; Menendez, Melisa; Benoit, Michel; Mattarolo, Giovanni; Mendez, Fernando
2013-04-01
Wave climate forecasting is a major issue for numerous marine and coastal related activities, such as offshore industries, flooding risks assessment and wave energy resource evaluation, among others. Generally, there are two main ways to predict the impacts of the climate change on the wave climate at regional scale: the dynamical and the statistical downscaling of GCM (Global Climate Model). In this study, both methods have been applied on the French coast (Atlantic , English Channel and North Sea shoreline) under three climate change scenarios (A1B, A2, B1) simulated with the GCM ARPEGE-CLIMAT, from Météo-France (AR4, IPCC). The aim of the work is to characterise the wave climatology of the 21st century and compare the statistical and dynamical methods pointing out advantages and disadvantages of each approach. The statistical downscaling method proposed by the Environmental Hydraulics Institute of Cantabria (Spain) has been applied (Menendez et al., 2011). At a particular location, the sea-state climate (Predictand Y) is defined as a function, Y=f(X), of several atmospheric circulation patterns (Predictor X). Assuming these climate associations between predictor and predictand are stationary, the statistical approach has been used to project the future wave conditions with reference to the GCM. The statistical relations between predictor and predictand have been established over 31 years, from 1979 to 2009. The predictor is built as the 3-days-averaged squared sea level pressure gradient from the hourly CFSR database (Climate Forecast System Reanalysis, http://cfs.ncep.noaa.gov/cfsr/). The predictand has been extracted from the 31-years hindcast sea-state database ANEMOC-2 performed with the 3G spectral wave model TOMAWAC (Benoit et al., 1996), developed at EDF R&D LNHE and Saint-Venant Laboratory for Hydraulics and forced by the CFSR 10m wind field. Significant wave height, peak period and mean wave direction have been extracted with an hourly-resolution at
Chen, Zaigao; Wang, Jianguo; Wang, Yue; Qiao, Hailiang; Zhang, Dianhui; Guo, Weijie
2013-11-01
Optimal design method of high-power microwave source using particle simulation and parallel genetic algorithms is presented in this paper. The output power, simulated by the fully electromagnetic particle simulation code UNIPIC, of the high-power microwave device is given as the fitness function, and the float-encoding genetic algorithms are used to optimize the high-power microwave devices. Using this method, we encode the heights of non-uniform slow wave structure in the relativistic backward wave oscillators (RBWO), and optimize the parameters on massively parallel processors. Simulation results demonstrate that we can obtain the optimal parameters of non-uniform slow wave structure in the RBWO, and the output microwave power enhances 52.6% after the device is optimized.
Denoising of gravitational-wave signal GW150914 via total-variation methods
Torres-Forné, Alejandro; Font, José A; Ibáñez, José M
2016-01-01
We apply a regularized Rudin-Osher-Fatemi total variation (TV) method to denoise the transient gravitational wave signal GW150914. We have previously applied TV techniques to denoise numerically generated grav- itational waves embedded in additive Gaussian noise, obtaining satisfactory results irrespective of the signal morphology or astrophysical origin. We find that the non-Gaussian, non-stationary noise from the gravitational wave event GW150914 can also be successfully removed with TV-denoising methods. The quality of the de- noised waveform is comparable to that obtained with the Bayesian approach used in the discovery paper [1]. TV-denoising techniques may thus offer an additional viable approach for waveform reconstruction.
An operator expansion method for computing nonlinear surface waves on a ferrofluid jet
Guyenne, Philippe; Părău, Emilian I.
2016-09-01
We present a new numerical method to simulate the time evolution of axisymmetric nonlinear waves on the surface of a ferrofluid jet. It is based on the reduction of this problem to a lower-dimensional computation involving surface variables alone. To do so, we describe the associated Dirichlet-Neumann operator in terms of a Taylor series expansion where each term can be efficiently computed by a pseudo-spectral scheme using the fast Fourier transform. We show detailed numerical tests on the convergence of this operator and, to illustrate the performance of our method, we simulate the long-time propagation and pairwise collisions of axisymmetric solitary waves. Both depression and elevation waves are examined by varying the magnetic field. Comparisons with weakly nonlinear predictions are also provided.
Wave system fitting: A new method for force measurements in shock tunnels with long test duration
Luo, Changtong; Wang, Yunpeng; Wang, Chun; Jiang, Zonglin
2015-10-01
Force measurements in shock tunnels are difficult due to the existence of vibrations excited by a sudden aerodynamic loading. Accelerometer inertia compensation could reduce its negative effect to some extent, but has inherent problems. A new signal decomposition method, wave system fitting (WSF), is proposed to remove vibration waves of low frequency. The WSF is accelerometer-free. It decomposes the balance signal and can separate vibration waves without the influence on the DC component, and it does work no matter the cycle of the sample signal is complete or not. As a standard signal post-processing tool in JF-12, the application results show that it works reliably with high accuracy, and it can also explain puzzling signals encountered in JF-12. WSF method is especially useful and irreplaceable whenever only a few cycles of a periodic signal could be obtained, as is usual for shock tunnels.
Methods and applications of 3-D wave equation common-azimuth prestack migration
Institute of Scientific and Technical Information of China (English)
CHENG Jiubing; WANG Huazhong; GENG Jianhua; MA Zaitian
2007-01-01
To tackle the difficulties of a 3-D full volum eprestack migration based on the double-square-root (DSR) one-way wave equation in practical applications, the common-azimuth migration approach is first discussed using dual-domain wave propagators under the theoretical frame of crossline common-offset migration. Through coor-dinate transforming, a common-azimuth prestack tau migra-tion technology that recursively continues the source and receiver wavefields and picks up the migrated results in the two-way vertical traveltime (tau) direction is developed.The migrations of synthetic data sets of SEG/EAGE salt model prove that our common-azimuth migration approaches are effective in both depth and tau domains. Two real data examples show the advantages of wave-theory based prestack migration methods in accuracy and imaging resolution over the conventional Kirchhoff integral methods.
Paraxial Wentzel-Kramers-Brillouin method applied to the lower hybrid wave propagation
Energy Technology Data Exchange (ETDEWEB)
Bertelli, N.; Phillips, C. K.; Valeo, E.; Wilson, J. R. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Maj, O.; Poli, E. [Max Planck Institute for Plasma Physics, EURATOM Association, Boltzmannstr. 2, 85748, Garching (Germany); Harvey, R. [CompX, Del Mar, California 92014 (United States); Wright, J. C.; Bonoli, P. T. [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States); Smirnov, A. P. [Lomonosov Moscow State University, Moscow (Russian Federation)
2012-08-15
The paraxial Wentzel-Kramers-Brillouin (pWKB) approximation, also called beam tracing method, has been employed in order to study the propagation of lower hybrid waves in a tokamak plasma. Analogous to the well-know ray tracing method, this approach reduces Maxwell's equations to a set of ordinary differential equations, while, in addition, retains the effects of the finite beam cross-section, and, thus, the effects of diffraction. A new code, LHBEAM (lower hybrid BEAM tracing), is presented, which solves the pWKB equations in tokamak geometry for arbitrary launching conditions and for analytic and experimental plasma equilibria. In addition, LHBEAM includes linear electron Landau damping for the evaluation of the absorbed power density and the reconstruction of the wave electric field in both the physical and Fourier space. Illustrative LHBEAM calculations are presented along with a comparison with the ray tracing code GENRAY and the full wave solver TORIC-LH.
Institute of Scientific and Technical Information of China (English)
WANG Jun-Mao; ZHANG Miao; ZHANG Wen-Liang; ZHANG Rui; HAN Jia-Hua
2008-01-01
We present a new method to find the exact travelling wave solutions of nonlinear evolution equations, with the aid of the symbolic computation. Based on this method, we successfully solve the modified Benjamin-Bona-Mahoney equation, and obtain some new solutions which can be expressed by trigonometric functions and hyperbolic functions. It is shown that the proposed method is direct, effective and can be used for many other nonlinear evolution equations in mathematical physics.
Institute of Scientific and Technical Information of China (English)
ZHANGJin-Liang; WANGMing-Liang
2004-01-01
The complex tanh-function expansion method was presented recently, and it can be applied to derive exact solutions to the Schroedinger-type nonlinear evolution equations directly without transformation. In this paper,the complex tanh-function expansion method is applied to derive the exact solutions to the general coupled nonlinear evolution equations. Zakharov system and a long-short-wave interaction system are considered as examples, and the new applications of the complex tanh-function expansion method are shown.
Institute of Scientific and Technical Information of China (English)
ZHANG Jin-Liang; WANG Ming-Liang
2004-01-01
The complex tanh-function expansion method was presented recently, and it can be applied to derive exact solutions to the Schrodinger-type nonlinear evolution equations directly without transformation. In this paper,the complex tanh-function expansion method is applied to derive the exact solutions to the general coupled nonlinear evolution equations. Zakharov system and a long-short-wave interaction system are considered as examples, and the new applications of the complex tanh-function expansion method are shown.
Energy Technology Data Exchange (ETDEWEB)
Kim, S. [Purdue Univ., West Lafayette, IN (United States)
1994-12-31
Parallel iterative procedures based on domain decomposition techniques are defined and analyzed for the numerical solution of wave propagation by finite element and finite difference methods. For finite element methods, in a Lagrangian framework, an efficient way for choosing the algorithm parameter as well as the algorithm convergence are indicated. Some heuristic arguments for finding the algorithm parameter for finite difference schemes are addressed. Numerical results are presented to indicate the effectiveness of the methods.
Fourier Deconvolution Methods for Resolution Enhancement in Continuous-Wave EPR Spectroscopy.
Reed, George H; Poyner, Russell R
2015-01-01
An overview of resolution enhancement of conventional, field-swept, continuous-wave electron paramagnetic resonance spectra using Fourier transform-based deconvolution methods is presented. Basic steps that are involved in resolution enhancement of calculated spectra using an implementation based on complex discrete Fourier transform algorithms are illustrated. Advantages and limitations of the method are discussed. An application to an experimentally obtained spectrum is provided to illustrate the power of the method for resolving overlapped transitions.
Institute of Scientific and Technical Information of China (English)
WAN Yong; ZHANG Jie; MENG Junmin; WANG Jing; DAI Yongshou
2016-01-01
Wave energy resource is a very important ocean renewable energy. A reliable assessment of wave energy resources must be performed before they can be exploited. Compared with wave model, altimeter can provide more accuratein situ observations for ocean wave which can be as a novel method for wave energy assessment. The advantage of altimeter data is to provide accurate significant wave height observations for wave. In order to develop characteristic and advantage of altimeter data and apply altimeter data to wave energy assessment, in this study, we established an assessing method for wave energy in local sea area which is dedicated to altimeter data. This method includes three parts including data selection and processing, establishment of evaluation indexes system and criterion of regional division. Then a case study of Northwest Pacific was performed to discuss specific application for this method. The results show that assessing method in this paper can assess reserves and temporal and spatial distribution effectively and provide scientific references for the siting of wave power plants and the design of wave energy convertors.
Yamashita, Teppei; Ichihara, Kiyoshi; Miyamoto, Ayaho
2013-04-01
We sought to detect specimen mix-up by developing a new cumulative delta-check method applicable to a mixture of test items with heterogeneous units and distribution patterns. The distributions of all test results were successfully made Gaussian using power transformation. Values were then standardized into z-score (zx) based on reference interval (RI) so that limits of RI take zx=±1.96. To find a weight for summing absolute value of delta between current and previous zx (Dz), we evaluated the distribution of Dz. Its central portion was always regarded as Gaussian despite the presence of symmetrical long tails. Thus, an adjusted SD (aSD) representing the center was estimated with an iterative method. By setting 1/aSD2 as a weight factor, we computed a weighted mean of Dz as an index for specimen mix-up (wCDI). The performance of wCDI was evaluated, using a model laboratory database consisting of 32 basic test items, by a simulation study generating artificial cases of mix-up. When wCDI was computed from three commonly ordered test sets consisting of 6-9 items each, its diagnostic efficiency in detecting the artificial cases was 0.937-0.967 expressed as area under ROC curves (AUC). When the performance of wCDI was evaluated simply by the number of test items (p) included in the computation, AUC gradually increased from 0.944 (p=5) to 0.976 (p=8). However, when p≥10, AUC stayed at approximately 0.98. wCDI was proven to be highly effective in uncovering cases of specimen mix-up. The diagnostic efficiency of wCDI depends only on the number of test items included in the computation.
Efficient methods to model the scattering of ultrasonic guided waves in 3D
Moreau, L.; Velichko, A.; Wilcox, P. D.
2010-03-01
The propagation of ultrasonic guided waves and their interaction with a defect is of interest to the nondestructive testing community. There is no general solution to the scattering problem and it is still an ongoing research topic. Due to the complexity of guided wave scattering problems, most existing models are related to the 2D case. However, thanks to the increase in computer calculation power, specific 3D problems can also be studied, with the help of numerical or semi-analytical methods. This paper describes two efficient methods aimed at modeling 3D scattering problems. The first method is the use of the Huygens' principle to reduce the size of finite element models. This principle allows the area of interest to be restricted to the very near field of the defect, for both the generation of the incident field and the modal decomposition of the scattered field. The second method consists of separating the 3D problem into two 2D problems for which the solutions are calculated and used to approximate the 3D solution. This can be used at low frequency-thickness products, where Lamb waves have a similar behavior to bulk waves. These two methods are presented briefly and compared on simple scattering cases.
Directed electromagnetic wave propagation in 1D metamaterial: Projecting operators method
Energy Technology Data Exchange (ETDEWEB)
Ampilogov, Dmitrii, E-mail: DVAmpilogov@kantiana.ru; Leble, Sergey, E-mail: sleble@kantiana.ru
2016-07-01
We consider a boundary problem for 1D electrodynamics modeling of a pulse propagation in a metamaterial medium. We build and apply projecting operators to a Maxwell system in time domain that allows to split the linear propagation problem to directed waves for a material relations with general dispersion. Matrix elements of the projectors act as convolution integral operators. For a weak nonlinearity we generalize the linear results still for arbitrary dispersion and derive the system of interacting right/left waves with combined (hybrid) amplitudes. The result is specified for the popular metamaterial model with Drude formula for both permittivity and permeability coefficients. We also discuss and investigate stationary solutions of the system related to some boundary regimes. - Highlights: • The problem of boundary regime propagation is solved by a systematic dynamic projecting method. • By this method a hybrid amplitude is introduced and used for derivation of nonlinear equation of opposite directed waves. • The equations are specified for Drude metamaterial dispersion and Kerr nonlinearity. • It is shown that one of unidirection waves in the metamaterial is specified as Shafer–Wayn integrable equation. • A stationary wave solution is approximately expressed in terms of elliptic functions.
A time reversal damage imaging method for structure health monitoring using Lamb waves
Institute of Scientific and Technical Information of China (English)
Zhang Hai-Yan; Cao Ya-Ping; Sun Xiu-Li; Chen Xian-Hua; Yu Jian-Bo
2010-01-01
This paper investigates the Lamb wave imaging method combining time reversal for health monitoring of a metal-lic plate structure.The temporal focusing effect of the time reversal Lamb waves is investigated theoretically.It demonstrates that the focusing effect is related to the frequency dependency of the time reversal operation.Numerical simulations are conducted to study the time reversal behaviour of Lamb wave modes under broadband and narrowband excitations.The results show that the reconstructed time reversed wave exhibits close similarity to the reversed nar-rowband tone burst signal validating the theoretical model.To enhance the similarity,the cycle number of the excited signal should be increased.Experiments combining finite element model are then conducted to study the imaging method in the presence of damage like hole in the plate structure.In this work,the time reversal technique is used for the recompression of Lamb wave signals.Damage imaging results with time reversal using broadband and narrowhand excitations are compared to those without time reversal.It suggests that the narrowband excitation combined time reversal can locate and determine the size of structural damage more precisely,but the cycle number of the excited signal should be chosen reasonably.
Luo, Zhi; Zeng, Liang; Lin, Jing; Hua, Jiadong
2017-02-01
Dispersion effect of Lamb wave will cause wave-packets to spread out in space and time, making received signals hard to be interpreted. Though the conventional dispersion compensation method can restrain dispersion effect, waveform deformation still remains in the compensated results. To eliminate dispersion effect completely, a reshaped excitation dispersion compensation method is proposed in this paper. The method compensates the dispersed signal to the same shape as the original excitation by generating a reshaped excitation and then mapping the received signal from time domain to distance domain. Simulations and experiments are conducted for the validation of the waveform correction of the reshaped excitation dispersion compensation method. Applied in the traditional delay-and-sum algorithm, the new dispersion compensation method can effectively enhance the resolution of the damage imaging.
Directory of Open Access Journals (Sweden)
Koichi Narahara
2012-01-01
Full Text Available Nonlinear transmission lines, which define transmission lines periodically loaded with nonlinear devices such as varactors, diodes, and transistors, are modeled in the framework of finite-difference time-domain (FDTD method. Originally, some root-finding routine is needed to evaluate the contributions of nonlinear device currents appropriately to the temporally advanced electrical fields. Arbitrary nonlinear transmission lines contain large amount of nonlinear devices; therefore, it costs too much time to complete calculations. To reduce the calculation time, we recently developed a simple model of diodes to eliminate root-finding routines in an FDTD solver. Approximating the diode current-voltage relation by a piecewise-linear function, an extended Ampere's law is solved in a closed form for the time-advanced electrical fields. In this paper, we newly develop an FDTD model of field-effect transistors (FETs, together with several numerical examples that demonstrate pulse-shortening phenomena in a traveling-wave FET.
Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Lambert, J. J.; Little, C.; Paw U, K. T.; Snyder, R. L.
2016-12-01
Eddy covariance and surface renewal measurements were used to estimate evapotranspiration (ET) over a variety of crop fields in the Sacramento-San Joaquin River Delta during the 2016 growing season. However, comparing and evaluating multiple measurement systems and methods for determining ET was focused upon at a single alfalfa site. The eddy covariance systems included two systems for direct measurement of latent heat flux: one using a separate sonic anemometer and an open path infrared gas analyzer and another using a combined system (Campbell Scientific IRGASON). For these methods, eddy covariance was used with measurements from the Campbell Scientific CSAT3, the LI-COR 7500a, the Campbell Scientific IRGASON, and an additional R.M. Young sonic anemometer. In addition to those direct measures, the surface renewal approach included several energy balance residual methods in which net radiation, ground heat flux, and sensible heat flux (H) were measured. H was measured using several systems and different methods, including using multiple fast-response thermocouple measurements and using the temperatures measured by the sonic anemometers. The energy available for ET was then calculated as the residual of the surface energy balance equation. Differences in ET values were analyzed between the eddy covariance and surface renewal methods, using the IRGASON-derived values of ET as the standard for accuracy.
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...
Positron-impact ionization of helium in the distorted-wave polarized-orbital method
Energy Technology Data Exchange (ETDEWEB)
Mukherjee, K.K.; Mazumdar, P.S.; Brajamani, S.
1989-02-15
The total cross sections for positron-impact ionization of helium are evaluated by using the distorted-wave polarized-orbital method taking into account the effects of screening and final-channel distortion. The present results are in fair agreement with other elaborate theoretical calculations and experimental results.
Band structure of thin films by the linear augmented-plane-wave method
DEFF Research Database (Denmark)
Jepsen, O.; Madsen, J.; Andersen, Ole Krogh
1978-01-01
We present a linear augmented-plane-wave method for solving the band-structure problem in thin crystalline films. The potential is separated into a muffin-tin potential inside the film, a potential depending exclusively on the normal coordinate outside the film, and corrections in both regions...
Generalized Variational Principle for Long Water-Wave Equation by He's Semi-Inverse Method
Directory of Open Access Journals (Sweden)
Weimin Zhang
2009-01-01
Full Text Available Variational principles for nonlinear partial differential equations have come to play an important role in mathematics and physics. However, it is well known that not every nonlinear partial differential equation admits a variational formula. In this paper, He's semi-inverse method is used to construct a family of variational principles for the long water-wave problem.
Travelling wave solutions to nonlinear physical models by means of the ﬁrst integral method
Indian Academy of Sciences (India)
İsmail Aslan Aslan
2011-04-01
This paper presents the ﬁrst integral method to carry out the integration of nonlinear partial differential equations in terms of travelling wave solutions. For illustration, three important equations of mathematical physics are analytically investigated. Through the established ﬁrst integrals, exact solutions are successfully constructed for the equations considered.
Review of shock wave detection method in CFD post-processing
Institute of Scientific and Technical Information of China (English)
Wu Ziniu; Xu Yizhe; Wang Wenbin; Hu Ruifeng
2013-01-01
In the present computational fluid dynamics (CFD) community,post-processing is regarded as a procedure to view parameter distribution,detect characteristic structure and reveal physical mechanism of fluid flow based on computational or experimental results.Field plots by contours,iso-surfaces,streamlines,vectors and others are traditional post-processing techniques.While the shock wave,as one important and critical flow structure in many aerodynamic problems,can hardly be detected or distinguished in a direct way using these traditional methods,due to possible confusions with other similar discontinuous flow structures like slip line,contact discontinuity,etc.Therefore,method for automatic detection of shock wave in post-processing is of great importance for both academic research and engineering applications.In this paper,the current status of methodologies developed for shock wave detection and implementations in post-processing platform are reviewed,as well as discussions on advantages and limitations of the existing methods and proposals for further studies of shock wave detection method.We also develop an advanced post-processing software,with improved shock detection.
Stress Wave Propagation in Soils Modelled by the Boundary Element Method
DEFF Research Database (Denmark)
Rasmussen, K. M.
This thesis deals with different aspects of the boundary element method (BEM) applied to stress wave propagation problems in soils. Among other things BEM formulations for coupled FEM and BEM, moving loads, direct BEM and indirect BEM are presented. For all the formulations both analytical expres...
Variational space-time (dis)continuous Galerkin method for linear free surface waves
Ambati, V.R.; Vegt, van der J.J.W.; Bokhove, O.
2008-01-01
A new variational (dis)continuous Galerkin finite element method is presented for the linear free surface gravity water wave equations. We formulate the space-time finite element discretization based on a variational formulation analogous to Luke's variational principle. The linear algebraic system
Love waves in functionally graded piezoelectric materials by stiffness matrix method.
Ben Salah, Issam; Wali, Yassine; Ben Ghozlen, Mohamed Hédi
2011-04-01
A numerical matrix method relative to the propagation of ultrasonic guided waves in functionally graded piezoelectric heterostructure is given in order to make a comparative study with the respective performances of analytical methods proposed in literature. The preliminary obtained results show a good agreement, however numerical approach has the advantage of conceptual simplicity and flexibility brought about by the stiffness matrix method. The propagation behaviour of Love waves in a functionally graded piezoelectric material (FGPM) is investigated in this article. It involves a thin FGPM layer bonded perfectly to an elastic substrate. The inhomogeneous FGPM heterostructure has been stratified along the depth direction, hence each state can be considered as homogeneous and the ordinary differential equation method is applied. The obtained solutions are used to study the effect of an exponential gradient applied to physical properties. Such numerical approach allows applying different gradient variation for mechanical and electrical properties. For this case, the obtained results reveal opposite effects. The dispersive curves and phase velocities of the Love wave propagation in the layered piezoelectric film are obtained for electrical open and short cases on the free surface, respectively. The effect of gradient coefficients on coupled electromechanical factor, on the stress fields, the electrical potential and the mechanical displacement are discussed, respectively. Illustration is achieved on the well known heterostructure PZT-5H/SiO(2), the obtained results are especially useful in the design of high-performance acoustic surface devices and accurately prediction of the Love wave propagation behaviour.
A Fatigue Crack Size Evaluation Method Based on Lamb Wave Simulation and Limited Experimental Data
Directory of Open Access Journals (Sweden)
Jingjing He
2017-09-01
Full Text Available This paper presents a systematic and general method for Lamb wave-based crack size quantification using finite element simulations and Bayesian updating. The method consists of construction of a baseline quantification model using finite element simulation data and Bayesian updating with limited Lamb wave data from target structure. The baseline model correlates two proposed damage sensitive features, namely the normalized amplitude and phase change, with the crack length through a response surface model. The two damage sensitive features are extracted from the first received S0 mode wave package. The model parameters of the baseline model are estimated using finite element simulation data. To account for uncertainties from numerical modeling, geometry, material and manufacturing between the baseline model and the target model, Bayesian method is employed to update the baseline model with a few measurements acquired from the actual target structure. A rigorous validation is made using in-situ fatigue testing and Lamb wave data from coupon specimens and realistic lap-joint components. The effectiveness and accuracy of the proposed method is demonstrated under different loading and damage conditions.
DETERMINATION OF COORDINATES OF SEISMIC WAVE SOURCE BY AMPLITUDE METHOD OF PASSIVE LOCATION
Directory of Open Access Journals (Sweden)
Vasily D. Syten’ky
2015-10-01
Full Text Available The paper presents results of the mathematical synthesis of the method of passive location of a seismic wave source. The method employs measurements of regular attenuation of seismic oscillation amplitudes. If it is impossible to determine the location of a seismic event by means of direct measurements, indirect measurements are needed. A priori information for the mathematical synthesis was obtained from functional equations showing inverse proportions of measured amplitudes, arbitrary effective attenuation coefficients and corresponding coordinates. An original method was applied to process the data. The method providing for passive location of seismic waves sources has been developed; it is called the radial basic method. In the one-dimensional case, a distance is determined on the basis of seismic oscillation amplitudes measured by two seismographs that are located at a known base distance coinciding with the direction to the source of seismic waves. The distance is calculated from the receiver that is nearest to the source. If the base distance and the direct line between the seismograph and the seismic wave source do not coincide, a projection of the distance between the receivers to the given straight line is taken into account.Three seismographs were placed at mutually perpendicular base distances in a plane (i.e. the two-dimensional space. This allowed us to obtain an analytical equation for determining the direction to the seismic wave source using measured amplitudes. The value of the angle is taken into account when calculating the distance.For the seismic wave source located in the three-dimensional space, transition equations for combined coordinate systems (i.e. the Descartes (Cartesian, at the axes of which the seismographs were placed, and the spherical coordinate systems were applied, and analytical equations were obtained for determination of coordinates, such as distance/polar radius, elevation
Our purpose was to describe community workshops on the CPPE process to identify the top three nutrition- and health-related issues that could be addressed by nutrition and physical activity intervention research. The Lower Mississippi Delta Nutrition Intervention Research Initiative (Delta NIRI) is ...
Karataylı, Ersin; Altunoğlu, Yasemin Çelik; Karataylı, Senem Ceren; Alagöz, S Gökçe K; Cınar, Kubilay; Yalçın, Kendal; Idilman, Ramazan; Yurdaydın, Cihan; Bozdayı, A Mithat
2014-05-01
Hepatitis delta virus (HDV) RNA viral load measurement is critical in diagnosis and monitoring the response to antiviral treatment. Our aim is to design a real time PCR method for accurate quantitation of HDV RNA in clinical specimens using an armored RNA as external standard, and an intrinsic internal control. A plasmid bearing delta antigen region of genotype I HDV genome was used to develop an armored RNA. Serial dilutions of the armored HDV RNA standard with 10(12)copy/mL were used as standards for quantitation. A primer-probe set derived from HDAg region was used in one step EZ RT PCR kit chemistry which uses rTth enzyme allowing reverse transcription and polymerization in the same tube. The kit also uses the advantage of uracil-N-glycosylase (UNG) enzyme treatment to prevent PCR contamination. The established assay has a dynamic range of 10(2)-10(11)copy/mL with a PCR efficiency of 96.9%. Detection limit was 858±32copy/mL with 95% confidence interval. Intra- and inter-assay variabilities were low for high, medium and low levels of viremia. Incorporation of freely circulating GAPDH in serum into the assay as an intrinsic internal control prevented false negative results and failures in PCR amplifications due to inhibitors, inefficient extraction procedures or enzymatic reactions. In conclusion, this study defines a novel assay for sensitive and reliable quantification of HDV RNA using an armored HDV RNA as a standard and GAPDH in plasma or serum as an intrinsic internal control in a single tube. Copyright © 2014 Elsevier B.V. All rights reserved.
DUAL RECIPROCITY BOUNDARY ELEMENT METHOD FOR FLEXURAL WAVES IN THIN PLATE WITH CUTOUT
Institute of Scientific and Technical Information of China (English)
GAO Suo-wen; WANG Yue-sheng; ZHANG Zi-mao; MA Xing-rui
2005-01-01
The theoretical analysis and numerical calculation of scattering of elastic waves and dynamic stress concentrations in the thin plate with the cutout was studied using dual reciprocity boundary element method (DRM). Based on the work equivalent law, the dual reciprocity boundary integral equations for flexural waves in the thin plate were established using static fundamental solution. As illustration, numerical results for the dynamic stress concentration factors in the thin plate with a circular hole are given.The results obtained demonstrate good agreement with other reported results and show high accuracy.
PARTITION OF UNITY FINITE ELEMENT METHOD FOR SHORT WAVE PROPAGATION IN SOLIDS
Institute of Scientific and Technical Information of China (English)
LI Xi-kui; ZHOU Hao-yang
2005-01-01
A partition of unity finite element method for numerical simulation of short wave propagation in solids is presented. The finite element spaces were constructed by multiplying the standard isoparametric finite element shape functions, which form a partition of unity, with the local subspaces defined on the corresponding shape functions, which include a priori knowledge about the wave motion equation in trial spaces and approximately reproduce the highly oscillatory properties within a single element. Numerical examples demonstrate the performance of the proposed partition of unity finite element in both computational accuracy and efficiency.
Applied Analytical Methods for Solving Some Problems of Wave Propagation in the Coastal Areas
Gagoshidze, Shalva; Kodua, Manoni
2016-04-01
Analytical methods, easy for application, are proposed for the solution of the following four classical problems of coastline hydro mechanics: 1. Refraction of waves on coast slopes of arbitrary steepness; 2. Wave propagation in tapering water areas; 3. Longitudinal waves in open channels; 4. Long waves on uniform and non-uniform flows of water. The first three of these problems are solved by the direct Galerkin-Kantorovich method with a choice , of basic functions which completely satisfy all boundary conditions. This approach leads to obtaining new evolutionary equations which can be asymptotically solved by the WKB method. The WKB solution of the first problem enables us to easily determine the three-dimensional field of velocities and to construct the refraction picture of the wave surface near the coast having an arbitrary angle of slope to the horizon varying from 0° to 180°. This solution, in particular for a vertical cliff, fully agrees with Stoker's particular but difficult solution. Moreover, it is shown for the first time that our Schrödinger type evolutionary equation leads to the formation of the so-called "potential wells" if the angle of coast slope to the horizon exceeds 45°, while the angle given at infinity (i.e. at a large distance from the shore) between the wave crests and the coastline exceeds 75°. This theoretical result expressed in terms of elementary functions is well consistent with the experimental observations and with lot of aerial photographs of waves in the coastal zones of the oceans [1,2]. For the second problem we introduce the notions of "wide" and "narrow" water areas. It is shown that Green's law on the wave height growth holds only for the narrow part of the water area, whereas in the wide part the tapering of the water area leads to an insignificant decrease of the wave height. For the third problem, the bank slopes of trapezoidal channels are assumed to have an arbitrary angle of steepness. So far we have known the
Nenadic, Ivan Z.; Urban, Matthew W.; Mitchell, Scott A.; Greenleaf, James F.
2011-01-01
Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of Shearwave Dispersion Ultrasound Vibrometry (SDUV), a noninvasive ultrasound based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave Dispersion Ultrasound Vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify mechanical properties of soft tissues with a plate-like geometry. PMID:21403186
Study Notes on Numerical Solutions of the Wave Equation with the Finite Difference Method
Adib, A B
2000-01-01
In this introductory work I will present the Finite Difference method for hyperbolic equations, focusing on a method which has second order precision both in time and space (the so-called leap-frog method) and applying it to the case of the 1d and 2d wave equation. A brief derivation of the energy and equation of motion of a wave is done before the numerical part in order to make the transition from the continuum to the lattice clearer. To illustrate the extension of the method to more complex equations, I also add dissipative terms of the kind $-\\eta \\dot{u}$ into the equations. The von Neumann numerical stability analysis and the Courant criterion, two of the most popular in the literature, are briefly discussed. In the end I present some numerical results obtained with the leap-frog algorithm, illustrating the importance of the lattice resolution through energy plots.
Limited-view ultrasonic guided wave tomography using an adaptive regularization method
Rao, Jing; Ratassepp, Madis; Fan, Zheng
2016-11-01
Ultrasonic guided waves are useful to assess the integrity of a structure from a remote location. Recently, tomography techniques have been developed to quantitatively estimate the thickness map of plate-like structures based on the dispersion characteristics of guided waves. In many applications only limited locations are available to place transducers. The missing viewing angles lead to artifacts which can degrade the image quality. To address this problem, this paper applies the regularization method to synthesize the missing components. The regularization technique is performed by an adaptive threshold approach to the limited view reconstruction. The effectiveness of this method combined with the full waveform inversion method is demonstrated by using numerical simulations as well as experiments on an irregularly shaped defect and two flat-bottom defects. The results indicate that the additional components obtained from the regularization method can significantly reduce the artifacts, leading to better reconstruction accuracy.
A comparison of methods for the detection of gravitational waves from unknown neutron stars
Walsh, Sinead; D'Antonio, Sabrina; Dergachev, Vladimir; Krolak, Andrzej; Oliver, Miquel; Astone, Pia; Bejger, Michal; Di Giovanni, Matteo; Dorosh, Orest; Frasca, Sergio; Leaci, Paola; Mastrogiovanni, Simone; Miller, Andrew; Palomba, Cristiano; Papa, Maria Alessandra; Piccinni, Ornella J; Riles, Keith; Sauter, Orion; Sintes, Alicia M
2016-01-01
Rapidly rotating neutron stars are promising sources of continuous gravitational wave radiation for the LIGO and Virgo interferometers. The majority of neutron stars in our galaxy have not been identified with electromagnetic observations. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from these unidentified sources. The parameter space of these blind all-sky searches, which also cover a large range of frequencies and frequency derivatives, presents a significant computational challenge. Different methods have been designed to perform these searches within acceptable computational limits. Here we describe the first benchmark in a project to compare the search methods currently available for the detection of unknown isolated neutron stars. We employ a mock data challenge to compare the ability of each search method to recover signals simulated assuming a standard signal model. We find similar performance among the short duration search methods, while the long dur...
A Stabilised Nodal Spectral Element Method for Fully Nonlinear Water Waves
Engsig-Karup, Allan Peter; Bigoni, Daniele
2015-01-01
We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al (1998) \\cite{CaiEtAl1998}, although the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global $L^2$ projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions can cause severe aliasing problems and consequently numerical instability for marginally resolved or very steep waves. We show how the scheme can be stabilised through a combination of over-integration of the Galerkin projections and a mild spectral filtering on a per element basis. This effectively removes any aliasing driven instabilities while retaining the high-order accuracy of the numerical...
Estimation of SH-Wave Amplification in the Bandung Basin Using Haskell’s Method
Directory of Open Access Journals (Sweden)
Afnimar
2014-04-01
Full Text Available The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell’s method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks.
An iterative Rankine boundary element method for wave diffraction of a ship with forward speed
Institute of Scientific and Technical Information of China (English)
何广华
2014-01-01
A 3-D time-domain seakeeping analysis tool has been newly developed by using a higher-order boundary element method with the Rankine source as the kernel function. An iterative time-marching scheme for updating both kinematic and dynamic free-surface boundary conditions is adopted for achieving numerical accuracy and stability. A rectangular computational domain moving with the mean speed of ship is introduced. A damping beach at the outer portion of the truncated free surface is installed for satisfying the radiation condition. After numerical convergence checked, the diffraction unsteady problem of a Wigley hull traveling with a constant forward speed in waves is studied. Extensive results including wave exciting forces, wave patterns and pressure distributions on the hull are presented to validate the efficiency and accuracy of the proposed 3-D time-domain iterative Rankine BEM approach. Computed results are compared to be in good agreement with the corresponding experimental data and other published numerical solutions.
Nonlinear evolution of cylindrical gravitational waves: Numerical method and physical aspects
Celestino, Juliana; de Oliveira, H. P.; Rodrigues, E. L.
2016-05-01
General cylindrical waves are the simplest axisymmetrical gravitational waves that contain both + and × modes of polarization. In this paper, we have studied the evolution of general cylindrical gravitational waves in the realm of the characteristic scheme with a numerical code based on the Galerkin-Collocation method. The investigation consists of the numerical realization of concepts such as Bondi mass and the news functions adapted to cylindrical symmetry. The Bondi mass decays due to the presence of the news functions associated with both polarization modes. We have interpreted each polarization mode as channels from which mass is extracted. Under this perspective, we have presented the enhancement effect of the polarization mode + due to the nonlinear interaction with the mode ×. After discussing the role of matter in cylindrical symmetry, we have extended the numerical code to include electromagnetic fields.
Nonlinear evolution of cylindrical gravitational waves: numerical method and physical aspects
Celestino, Juliana; Rodrigues, E L
2015-01-01
General cylindrical waves are the simplest axisymmetrical gravitational waves that contain both $+$ and $\\times$ modes of polarization. In this paper, we have studied the evolution of general cylindrical gravitational waves in the realm of the characteristic scheme with a numerical code based on the Galerkin-Collocation method. The investigation consists of the numerical realization of concepts such as Bondi mass and the news functions adapted to cylindrical symmetry. The Bondi mass decays due to the presence of the news functions associated with both polarization modes. We have interpreted that each polarization mode as channels from which mass is extracted. Under this perspective, we have presented the enhancement effect of the polarization mode $+$ due to the nonlinear interaction with the mode $\\times$. After discussing the role of matter in cylindrical symmetry, we have extended the numerical code to include electromagnetic fields.
RESEARCH ON THE METHOD AND CALCULATION OF THE NEW SLENDER-SHIP WAVE RESISTANCE THEORY
Institute of Scientific and Technical Information of China (English)
Han Duan-feng
2003-01-01
Analyses of the new slender-ship theory of wave resistance were made and corresponding calculation methods were proposed. Based on these theoretical methods, the calculations of wave resistance of near surface submersible, Wigley hull and vertical/canted strut SWATHs were conducted.In the single and double integral parts of Green's function, the method of special function expansion and Chebyshev polynomial approach were adopted respectively. The formulas for zeroth-first-and second-order wave-making resistance were derived. In a towing tank, the calm water resistance experiment of SWATH model ASW-2 with canted strut was conducted and researched.The influences of waterline integral term, the surface mesh number, element node number, range of the integration and truncation of special function expansions on velocity potential and numerical results of resistance were investigated, and the difference between the zeroth-order and first-order wave resistance was analyzed. The theoretical calculation results agree well with the well-found model experimental results.
Mode perturbation method for optimal guided wave mode and frequency selection.
Philtron, J H; Rose, J L
2014-09-01
With a thorough understanding of guided wave mechanics, researchers can predict which guided wave modes will have a high probability of success in a particular nondestructive evaluation application. However, work continues to find optimal mode and frequency selection for a given application. This "optimal" mode could give the highest sensitivity to defects or the greatest penetration power, increasing inspection efficiency. Since material properties used for modeling work may be estimates, in many cases guided wave mode and frequency selection can be adjusted for increased inspection efficiency in the field. In this paper, a novel mode and frequency perturbation method is described and used to identify optimal mode points based on quantifiable wave characteristics. The technique uses an ultrasonic phased array comb transducer to sweep in phase velocity and frequency space. It is demonstrated using guided interface waves for bond evaluation. After searching nearby mode points, an optimal mode and frequency can be selected which has the highest sensitivity to a defect, or gives the greatest penetration power. The optimal mode choice for a given application depends on the requirements of the inspection.
Senveli, Sukru U.; Tigli, Onur
2013-12-01
This paper introduces the use of finite element method analysis tools to investigate the use of a Rayleigh type surface acoustic wave (SAW) sensor to interrogate minute amounts of liquids trapped in microcavities placed on the delay line. Launched surface waves in the ST-X quartz substrate couple to the liquid and emit compressional waves. These waves form a resonant cavity condition and interfere with the surface waves in the substrate. Simulations show that the platform operates in a different mechanism than the conventional mass loading of SAW devices. Based on the proposed detection mechanism, it is able to distinguish between variations of 40% and 90% glycerin based on phase relations while using liquid volumes smaller than 10 pl. Results from shallow microcavities show high correlation with sound velocity parameter of the liquid whereas deeper microcavities display high sensitivities with respect to glycerin concentration. Simulated devices yield a maximum sensitivity of -0.77°/(% glycerin) for 16 μm wavelength operation with 8 μm deep, 24 μm wide, and 24 μm long microcavities.
The finite product method in the theory of linear wave propagation
DEFF Research Database (Denmark)
Sorokin, Sergey; Chapman, John
2012-01-01
This paper presents a method of analysing the dispersion relation and field shape of any type of linear wave field for which the dispersion relation is transcendental. The method involves replacing each transcendental term in the dispersion relation by a finite-product polynomial. Details....... These polynomial approximations, which are unrelated to Taylor series, introduce no spurious branches into the dispersion relation, and are perfectly suited for computations....
Institute of Scientific and Technical Information of China (English)
XIE; Hongsen(谢鸿森); ZHOU; Wenge; 周文戈); LIU; Yonggang; (刘永刚); GUO; Jie; (郭捷); HOU; Wei; (侯渭); ZHAO; Zhidan(赵志丹)
2002-01-01
To measure elastic wave velocities in rocks at high temperature and high pressure is an important way to acquire the mechanics and thermodynamics data of rocks in the earth's interior and also a substantial approach to studying the structure and composition of materials there. In recent years, a rapid progress has been made in methodology pertaining to the measurements of elastic wave velocities in rocks at high temperature and high pressure with solids as the pressure-transfer media. However, no strict comparisons have been made of the elastic wave velocity data of rocks measured at high temperature and high pressure by various laboratories. In order to compare the experimental results from various laboratories, we have conducted a comparative experimental study on three measuring methods and made a strict comparison with the results obtained by using the transmission method with fluid as the pressure-transfer medium. Our experimental results have shown that the measurements obtained by the three methods are comparable in the pressure ranges of their application. The cubic sample pulse transmission method used by Kern is applicable to measuring elastic wave velocities in crustal rocks at lower temperature and lower pressure. The prism sample pulse reflection-transmission method has some advantages in pressure range, heating temperature and measuring precision. Although the measurements obtained under relatively low pressure conditions by the prism sample pulse transmission method are relatively low in precision, the samples are large in length and their assemblage is simple. So this method is suitable to the experiments that require large quantities of samples and higher pressures. Therefore, in practical application the latter two methods are usually recommended because their measurements can be mutually corrected and supplemented.
A fault location method using Lamb waves and discrete wavelet transform
Souza, Pablo Rodrigo de; Nobrega, Eurípedes Guilherme de Oliveira
2012-01-01
Non-destructive evaluation methods and signal process techniques are important steps in structural health monitoring systems to assess the structure integrity. This paper presents a method for fault location in aluminum beams based on time of flight of Lamb waves. The dynamic response signal captured from the structure was processed using the discrete wavelet transform. The information accuracy obtained from the processed signal depends on the correct choice of the mother wavelet. The best mo...
An H1-Galerkin Expanded Mixed Element Method for Semi-linear Hyperbolic Wave Equation
Institute of Scientific and Technical Information of China (English)
WANG Jin-feng; LIU Yang; LI Hong; HE Siriguleng
2013-01-01
An H1-Galerkin expanded mixed finite element method is discussed for a class of second order semi-linear hyperbolic wave equations.By using the mixed formulation,we can get the optimal approximation for three variables:the scalar unknown,its gradient and its flux(coefficient times the gradient),simultaneously.We also prove the existence and uniqueness of semi-discrete solution.Finally,we obtain some numerical results to illustrate the efficiency of the method.
First Integral Method for Systems of (1+1-Dimensional Dispersive Long Wave
Directory of Open Access Journals (Sweden)
Jafar BIAZAR
2014-05-01
Full Text Available The First Integral method (FIM is applied to solve a dispersive long wave system. In this method the division theorem, as a statement in commutative Algebra has an important role. To show the ability and the efficiency of this approach an example is provided. Application of FIM to the illustrative example leads to six exact solutions, which it is shown that these six solutions are independent to each other. So there are six different exact solutions.
Muller, Aurelia; Robertson-Welsh, Bradley; Gaydecki, Patrick; Gresil, Matthieu; Soutis, Constantinos
2017-04-01
This investigation aimed to adapt the total focusing method (TFM) algorithm (originated from the synthetic aperture focusing technique in digital signal processing) to accommodate a circular array of piezoelectric sensors (PZT) and characterise defects using guided wave signals for the development of a structural health monitoring system. This research presents the initial results of a broader study focusing on the development of a structural health monitoring (SHM) guided wave system for advance carbon fibre reinforced plastic (CFRP) composite materials. The current material investigated was an isotropic (aluminium) square plate with 16 transducers operating successively as emitter or sensor in pitch and catch configuration enabling the collection of 240 signals per assessment. The Lamb wave signals collected were tuned on the symmetric fundamental mode with a wavelength of 17 mm, by setting the excitation frequency to 300 kHz. The initial condition for the imaging system, such as wave speed and transducer position, were determined with post processing of the baseline signals through a method involving the identification of the waves reflected from the free edge of the plate. The imaging algorithm was adapted to accommodate multiple transmitting transducers in random positions. A circular defect of 10 mm in diameter was drilled in the plate, which is similar to the delamination size introduced by a low velocity impact event in a composite plate. Images were obtained by applying the TFM to the baseline signals, Test 1 data (corresponding to the signals obtained after introduction of the defect) and to the data derived from the subtraction of the baseline to the Test 1 signals. The result shows that despite the damage diameter being 40 % smaller than the wavelength, the image (of the subtracted baseline data) demonstrated that the system can locate where the waves were reflected from the defect boundary. In other words, the contour of the damaged area was
Muller, Aurelia; Robertson-Welsh, Bradley; Gaydecki, Patrick; Gresil, Matthieu; Soutis, Constantinos
2016-11-01
This investigation aimed to adapt the total focusing method (TFM) algorithm (originated from the synthetic aperture focusing technique in digital signal processing) to accommodate a circular array of piezoelectric sensors (PZT) and characterise defects using guided wave signals for the development of a structural health monitoring system. This research presents the initial results of a broader study focusing on the development of a structural health monitoring (SHM) guided wave system for advance carbon fibre reinforced plastic (CFRP) composite materials. The current material investigated was an isotropic (aluminium) square plate with 16 transducers operating successively as emitter or sensor in pitch and catch configuration enabling the collection of 240 signals per assessment. The Lamb wave signals collected were tuned on the symmetric fundamental mode with a wavelength of 17 mm, by setting the excitation frequency to 300 kHz. The initial condition for the imaging system, such as wave speed and transducer position, were determined with post processing of the baseline signals through a method involving the identification of the waves reflected from the free edge of the plate. The imaging algorithm was adapted to accommodate multiple transmitting transducers in random positions. A circular defect of 10 mm in diameter was drilled in the plate, which is similar to the delamination size introduced by a low velocity impact event in a composite plate. Images were obtained by applying the TFM to the baseline signals, Test 1 data (corresponding to the signals obtained after introduction of the defect) and to the data derived from the subtraction of the baseline to the Test 1 signals. The result shows that despite the damage diameter being 40 % smaller than the wavelength, the image (of the subtracted baseline data) demonstrated that the system can locate where the waves were reflected from the defect boundary. In other words, the contour of the damaged area was
Hu, Wenjing
2017-08-01
This paper uses Fourier’s triple integral transform method to simplify the calculation of the non-homogeneous wave equations of the time-varying electromagnetic field. By adding several special definite conditions to the wave equation, it becomes a mathematical problem of definite condition. Then by using Fourier’s triple integral transform method, this three-dimension non-homogeneous partial differential wave equation is changed into an ordinary differential equation. Through the solution to this ordinary differential equation, the expression of the relationship between the time-varying scalar potential and electromagnetic wave excitation source is developed precisely. This method simplifies the solving process effectively.
Modeling of wave propagation in drill strings using vibration transfer matrix methods.
Han, Je-Heon; Kim, Yong-Joe; Karkoub, Mansour
2013-09-01
In order to understand critical vibration of a drill bit such as stick-slip and bit-bounce and their wave propagation characteristics through a drill string system, it is critical to model the torsional, longitudinal, and flexural waves generated by the drill bit vibration. Here, a modeling method based on a vibration transfer matrix between two sets of structural wave variables at the ends of a constant cross-sectional, hollow, circular pipe is proposed. For a drill string system with multiple pipe sections, the total vibration transfer matrix is calculated by multiplying all individual matrices, each is obtained for an individual pipe section. Since drill string systems are typically extremely long, conventional numerical analysis methods such as a finite element method (FEM) require a large number of meshes, which makes it computationally inefficient to analyze these drill string systems numerically. The proposed "analytical" vibration transfer matrix method requires significantly low computational resources. For the validation of the proposed method, experimental and numerical data are obtained from laboratory experiments and FEM analyses conducted by using a commercial FEM package, ANSYS. It is shown that the modeling results obtained by using the proposed method are well matched with the experimental and numerical results.
K2_SPH Method and its Application for 2-D Water Wave Simulation
Institute of Scientific and Technical Information of China (English)
Zhenhong Hu; Xing Zheng; Wenyang Duan; Qingwei Ma
2011-01-01
Smoothed Particle Hydrodynamics(SPH)is a Lagrangian meshless particle method.However,its low accuracy of kernel approximation when particles are distributed disorderly or located near the boundary is an obstacle standing in the way of its wide application.Adopting the Taylor series expansion method and solving the integral equation matrix,the second order kernel approximation method can be obtained,namely K2_SPH,which is discussed in this paper.This method is similar to the Finite Particle Method.With the improvement of kernel approximation,some numerical techniques should be adopted for different types of boundaries,such as a free surface boundary and solid boundary,which are two key numerical techniques of K2_SPH for water wave simulation.This paper gives some numerical results of two dimensional water wave simulations involving standing wave and sloshing tank problems by using K2_SPH.From the comparison of simulation results,the K2 SPH method is more reliable than standard SPH.
Vibro-acoustic design sensitivity analysis using the wave-based method
Koo, Kunmo; Pluymers, Bert; Desmet, Wim; Wang, Semyung
2011-08-01
Conventional element-based methods, such as the finite element method (FEM) and boundary element method (BEM), require mesh refinements at higher frequencies in order to converge. Therefore, their applications are limited to low frequencies. Compared to element-based methods, the wave-based method (WBM) adopts exact solutions of the governing differential equation instead of simple polynomials to describe the dynamic response variables within the subdomains. As such, the WBM does not require a finer division of subdomains as the frequency increases in order to exhibit high computational efficiency. In this paper, the design sensitivity formulation of a semi-coupled structural-acoustic problem is implemented using the WBM. Here, the results of structural harmonic analyses are imported as the boundary conditions for the acoustic domain, which consists of multiple wave-based subdomains. The cross-sectional area of each beam element is considered as a sizing design variable. Then, the adjoint variable method (AVM) is used to efficiently compute the sensitivity. The adjoint variable is obtained from structural reanalysis using an adjoint load composed of the system matrix and an evaluation of the wave functions of each boundary. The proposed sensitivity formulation is subsequently applied to a two-dimensional (2D) vehicle model. Finally, the sensitivity results are compared to the finite difference sensitivity results, which show good agreement.
Demi, L; van Dongen, K W A; Verweij, M D
2011-03-01
Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation.
WaveSeq: a novel data-driven method of detecting histone modification enrichments using wavelets.
Directory of Open Access Journals (Sweden)
Apratim Mitra
Full Text Available BACKGROUND: Chromatin immunoprecipitation followed by next-generation sequencing is a genome-wide analysis technique that can be used to detect various epigenetic phenomena such as, transcription factor binding sites and histone modifications. Histone modification profiles can be either punctate or diffuse which makes it difficult to distinguish regions of enrichment from background noise. With the discovery of histone marks having a wide variety of enrichment patterns, there is an urgent need for analysis methods that are robust to various data characteristics and capable of detecting a broad range of enrichment patterns. RESULTS: To address these challenges we propose WaveSeq, a novel data-driven method of detecting regions of significant enrichment in ChIP-Seq data. Our approach utilizes the wavelet transform, is free of distributional assumptions and is robust to diverse data characteristics such as low signal-to-noise ratios and broad enrichment patterns. Using publicly available datasets we showed that WaveSeq compares favorably with other published methods, exhibiting high sensitivity and precision for both punctate and diffuse enrichment regions even in the absence of a control data set. The application of our algorithm to a complex histone modification data set helped make novel functional discoveries which further underlined its utility in such an experimental setup. CONCLUSIONS: WaveSeq is a highly sensitive method capable of accurate identification of enriched regions in a broad range of data sets. WaveSeq can detect both narrow and broad peaks with a high degree of accuracy even in low signal-to-noise ratio data sets. WaveSeq is also suited for application in complex experimental scenarios, helping make biologically relevant functional discoveries.
A stabilised nodal spectral element method for fully nonlinear water waves
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter; Eskilsson, C.; Bigoni, Daniele
2016-01-01
We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al. (1998) [5], although...... the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global L2 projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions...
Zhao, Yu; Piao, Mei-lan; Li, Gang; Kim, Nam
2015-07-01
Fast calculation method for a computer-generated cylindrical hologram (CGCH) is proposed. The method consists of two steps: the first step is a calculation of a virtual wave-front recording surface (WRS), which is located between the 3D object and CGCH. In the second step, in order to obtain a CGCH, we execute the diffraction calculation based on the fast Fourier transform (FFT) from the WRS to the CGCH, which are in the same concentric arrangement. The computational complexity is dramatically reduced in comparison with direct integration method. The simulation results confirm that our proposed method is able to improve the computational speed of CGCH.
Novel Method for Optimal Synthesis of 5G Millimeter Wave Linear Antenna Array
Directory of Open Access Journals (Sweden)
Zarko Rosic
2017-01-01
Full Text Available We will propose a useful method for 5G mm wave antenna array synthesis, based on Genetic Algorithm for the synthesis of linear array with nonuniform interelement spacing. Our design method was used to obtain the optimal position of the elements in order to get the minimum side lobe level and nulls in desired directions. The simulation results verify that proposed method outperforms the previously published methods in terms of suppression side lobe level while maintaining nulls in specified directions. The flexibility of proposed algorithm shows good potential for the antenna array synthesis.
A numerical method for imaging of biological microstructures by VHF waves
Ala, Guido; Francomano, Elisa; Ganci, Salvatore
2013-01-01
Imaging techniques give a fundamental support to medical diagnostics during the pathology discovery as well as for the characterization of biological structures. The imaging methods involve electromagnetic waves in a frequency range that spans from some Hz to GHz and over. Most of these methods involve scanning of wide human body areas even if only small areas need to be analyzed. In this paper, a numerical method to evaluate the shape of micro-structures for application in the medical ?field, with a very low invasiveness for the human body, is proposed. A flexible thin-wire antenna radiates the VHF waves and then, by measuring the spatial magnetic ?field distribution it is possible to reconstruct the micro-structures image by estimating the location of the antenna against a sensors panel. The typical inverse problem described above is solved numerically, and ?first simulation results are presented in order to show the validity and the robustness of the proposed approach.
Rahman, S; Barnes, C H W
2005-01-01
We describe and evaluate a numerical solution strategy for simulating surface acoustic waves through semiconductor devices with complex geometries. This multi-physics problem is of particular relevance to the design of quantum electronic devices. The mathematical model consists of two coupled partial differential equations for the elastic wave propagation and the electric field, respectively, in anisotropic piezoelectric media. These equations are discretized by the finite element method in space and by a finite difference method in time. The latter method yields a convenient numerical decoupling of the governing equations. We describe how a computer implementation can utilize the decoupling and via object-oriented programming techniques reuse independent codes for the Poisson equation and the linear time-dependent elasticity equation. First we apply the simulator to a simplified model problem for verifying the implementation, and thereafter we show that the methodology is capable of simulating a real-world c...
Linear-scaling density functional theory using the projector augmented wave method
Hine, Nicholas D. M.
2017-01-01
Quantum mechanical simulation of realistic models of nanostructured systems, such as nanocrystals and crystalline interfaces, demands computational methods combining high-accuracy with low-order scaling with system size. Blöchl’s projector augmented wave (PAW) approach enables all-electron (AE) calculations with the efficiency and systematic accuracy of plane-wave pseudopotential calculations. Meanwhile, linear-scaling (LS) approaches to density functional theory (DFT) allow for simulation of thousands of atoms in feasible computational effort. This article describes an adaptation of PAW for use in the LS-DFT framework provided by the ONETEP LS-DFT package. ONETEP uses optimisation of the density matrix through in situ-optimised local orbitals rather than the direct calculation of eigenstates as in traditional PAW approaches. The method is shown to be comparably accurate to both PAW and AE approaches and to exhibit improved convergence properties compared to norm-conserving pseudopotential methods.
An improved method of evaluating liquefaction potential with the velocity of shear-waves
Institute of Scientific and Technical Information of China (English)
KE Han; CHEN Yun-min
2000-01-01
According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (s d/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (emin). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests,.
Explicit local time-stepping methods for time-dependent wave propagation
Grote, Marcus
2012-01-01
Semi-discrete Galerkin formulations of transient wave equations, either with conforming or discontinuous Galerkin finite element discretizations, typically lead to large systems of ordinary differential equations. When explicit time integration is used, the time-step is constrained by the smallest elements in the mesh for numerical stability, possibly a high price to pay. To overcome that overly restrictive stability constraint on the time-step, yet without resorting to implicit methods, explicit local time-stepping schemes (LTS) are presented here for transient wave equations either with or without damping. In the undamped case, leap-frog based LTS methods lead to high-order explicit LTS schemes, which conserve the energy. In the damped case, when energy is no longer conserved, Adams-Bashforth based LTS methods also lead to explicit LTS schemes of arbitrarily high accuracy. When combined with a finite element discretization in space with an essentially diagonal mass matrix, the resulting time-marching scheme...
LOCAL DISCONTINUOUS GALERKIN METHODS FOR THREE CLASSES OF NONLINEAR WAVE EQUATIONS
Institute of Scientific and Technical Information of China (English)
Yan Xu; Chi-wang Shu
2004-01-01
In this paper, we further develop the local discontinuous Galerkin method to solve three classes of nonlinear wave equations formulated by the general KdV-Burgers type equations, the general fifth-order KdV type equations and the fully nonlinear K(n, n, n)equations, and prove their stability for these general classes of nonlinear equations. The schemes we present extend the previous work of Yan and Shu [30, 31] and of Levy, Shu and Yan [24] on local discontinuous Galerkin method solving partial differential equations with higher spatial derivatives. Numerical examples for nonlinear problems are shown to illustrate the accuracy and capability of the methods. The numerical experiments include stationary solitons, soliton interactions and oscillatory solitary wave solutions.The numerical experiments also include the compacton solutions of a generalized fifthorder KdV equation in which the highest order derivative term is nonlinear and the fully nonlinear K(n, n, n) equations.
Chubar, O.
2006-09-01
The paper describes methods of efficient calculation of spontaneous synchrotron radiation (SR) by relativistic electrons in storage rings, and propagation of this radiation through optical elements and drift spaces of beamlines, using the principles of wave optics. In addition to the SR from one electron, incoherent and coherent synchrotron radiation (CSR) emitted by electron bunches is treated. CPU-efficient CSR calculation method taking into account 6D phase space distribution of electrons in a bunch is proposed. The properties of CSR emitted by electron bunches with small longitudinal and large transverse size are studied numerically (such situation can be realized in storage rings e.g. by transverse deflection of the electron bunches in special RF cavities). It is shown that if the transverse size of a bunch is much larger than the diffraction limit for single-electron SR at a given wavelength - it affects the angular distribution of the CSR at this wavelength and reduces the coherent flux. Nevertheless, for transverse bunch dimensions up to several millimeters and the longitudinal bunch size smaller than hundred micrometers, the resulting CSR flux in the far infrared spectral range is still many orders of magnitude higher than the flux of incoherent SR.
Multiphase flow modeling of landslide induced impulse wave by VOF method
Paik, J.; Shin, C.
2015-12-01
Numerical simulations of impulse waves induced by landslides are carried out using a multiphase modeling approach. The three-dimensional filtered Navier-Stokes equations are used for reproduces the propagation and interaction of Newtonian water wave and non-Newtonian debris flow along the bottom. A multiphase volume of fluid (VOF) method is employed for tracking of fluid interfaces. The governing equations are solved by a second-order-accurate in space and time, finite volume methods and the no-slip conditions are applied for all solid wall. The turbulent shear stress is calculated the Smagorinsky model and the non-Newtonian behavior of debris flow is computed by the Hershel-Bulkley fluid model. The multiphase flow model is applied to reproduce the laboratory measurements of Fritz (Pure Appl. Geophys., 166, 153, 2009) who experimentally investigated the propagation of impulse wave induced by the 1958 Lituya Bay Landslide. The numerical results shows that the proper treatment of the non-Newtonian behavior of debris flow is essential to reproduce its head speed and shape which control the deformation and propagation of the resulting impulse wave.
Ebrahimian, Mahdi; Todorovska, Maria I.
2014-03-01
A layered Timoshenko beam (TB) model of a high-rise building is presented and applied to system identification of a full-scale building from recorded seismic response. This model is a new development in a wave method for earthquake damage detection and structural health monitoring being developed by the authors' research group. The method is based on monitoring changes in the wave properties of the structure, such as the velocity of wave propagation vertically through the structure. This model is an improvement over the previously used layered shear beam (SB) model because it accounts for wave dispersion caused by flexural deformation present in addition to shear. It also accounts for the rotatory inertia and the variation of the building properties with height. The case study is a 54-story steel frame building located in downtown Los Angeles. Recorded accelerations during the Northridge earthquake of 1994 are used for system identification of the NS response. The model parameters are identified by matching, in the least squares sense, the model and observed impulse response functions at all levels where motion was recorded. The model is then used to compute the building vertical phase and group velocities. Impulse responses computed by deconvolution of the recorded motions with the roof response are used, which represent the building response to a virtual source at the roof. The better match of transfer-function amplitudes of the fitted TB model than of previously fitted SB model indicates that the layered TB model is a better physical model for this building.
Moore, David G.; Stair, Sarah L.; Jack, David A.
2017-02-01
Ultrasonic stress wave amplitude and time-of-flight values may change as a media is heated. The measurement of relatively small variations in velocity and material attenuation can detect and quantify significant variations within a material's microstructure, such as a change in phase from solid to liquid. This paper discusses the experimental setup, ultrasonic wave speed tracking methods and signal analysis algorithms that are used in this study to document the changes within highly attenuative wax material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The ultrasonic waveforms are recorded and analyzed during long duration thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) was also created, which uses unstructured meshes to determine how waves travel in this media and how the sound interacts with the prescribed boundary conditions. This numerical method solves particle motion travel using partial differential equations and outputs a wave trace per unit time. Both experimental and analytical data are presented and compared. The experimental and analytical data share some similarities; however, the differences between the two, including a high frequency component present in the analytical data that is not observed in the experimental data, are continuing to be studied and addressed in the model.
Directory of Open Access Journals (Sweden)
Esteban Flores-Mendez
2012-01-01
Full Text Available This work is focused on studying interface waves for three canonical models, that is, interfaces formed by vacuum-solid, solid-solid, and liquid-solid. These interfaces excited by dynamic loads cause the emergence of Rayleigh's, Stoneley's, and Scholte's waves, respectively. To perform the study, the indirect boundary element method is used, which has proved to be a powerful tool for numerical modeling of problems in elastodynamics. In essence, the method expresses the diffracted wave field of stresses, pressures, and displacements by a boundary integral, also known as single-layer representation, whose shape can be regarded as a Fredholm's integral representation of second kind and zero order. This representation can be considered as an exemplification of Huygens' principle, which is equivalent to Somigliana's representation theorem. Results in frequency domain for the three types of interfaces are presented; then, using the fourier discrete transform, we derive the results in time domain, where the emergence of interface waves is highlighted.
Directory of Open Access Journals (Sweden)
Antonis Kordas
2016-12-01
Full Text Available Salmonella enterica serovar Typhimurium is a major foodborne pathogen that causes Salmonellosis, posing a serious threat for public health and economy; thus, the development of fast and sensitive methods is of paramount importance for food quality control and safety management. In the current work, we are presenting a new approach where an isothermal amplification method is combined with an acoustic wave device for the development of a label free assay for bacteria detection. Specifically, our method utilizes a Love wave biosensor based on a Surface Acoustic Wave (SAW device combined with the isothermal Rolling Circle Amplification (RCA method; various protocols were tested regarding the DNA amplification and detection, including off-chip amplification at two different temperatures (30 °C and room temperature followed by acoustic detection and on-chip amplification and detection at room temperature, with the current detection limit being as little as 100 Bacteria Cell Equivalents (BCE/sample. Our acoustic results showed that the acoustic ratio, i.e., the amplitude over phase change observed during DNA binding, provided the only sensitive means for product detection while the measurement of amplitude or phase alone could not discriminate positive from negative samples. The method's fast analysis time together with other inherent advantages i.e., portability, potential for multi-analysis, lower sample volumes and reduced power consumption, hold great promise for employing the developed assay in a Lab on Chip (LoC platform for the integrated analysis of Salmonella in food samples.
A stochastic collocation method for the second order wave equation with a discontinuous random speed
Motamed, Mohammad
2012-08-31
In this paper we propose and analyze a stochastic collocation method for solving the second order wave equation with a random wave speed and subjected to deterministic boundary and initial conditions. The speed is piecewise smooth in the physical space and depends on a finite number of random variables. The numerical scheme consists of a finite difference or finite element method in the physical space and a collocation in the zeros of suitable tensor product orthogonal polynomials (Gauss points) in the probability space. This approach leads to the solution of uncoupled deterministic problems as in the Monte Carlo method. We consider both full and sparse tensor product spaces of orthogonal polynomials. We provide a rigorous convergence analysis and demonstrate different types of convergence of the probability error with respect to the number of collocation points for full and sparse tensor product spaces and under some regularity assumptions on the data. In particular, we show that, unlike in elliptic and parabolic problems, the solution to hyperbolic problems is not in general analytic with respect to the random variables. Therefore, the rate of convergence may only be algebraic. An exponential/fast rate of convergence is still possible for some quantities of interest and for the wave solution with particular types of data. We present numerical examples, which confirm the analysis and show that the collocation method is a valid alternative to the more traditional Monte Carlo method for this class of problems. © 2012 Springer-Verlag.
Cheng, Feng; Xia, Jianghai; Xu, Yixian; Xu, Zongbo; Pan, Yudi
2015-06-01
We proposed a new passive seismic method (PSM) based on seismic interferometry and multichannel analysis of surface waves (MASW) to meet the demand for increasing investigation depth by acquiring surface-wave data at a low-frequency range (1 Hz ≤ f ≤ 10 Hz). We utilize seismic interferometry to sort common virtual source gathers (CVSGs) from ambient noise and analyze obtained CVSGs to construct 2D shear-wave velocity (Vs) map using the MASW. Standard ambient noise processing procedures were applied to the computation of cross-correlations. To enhance signal to noise ratio (SNR) of the empirical Green's functions, a new weighted stacking method was implemented. In addition, we proposed a bidirectional shot mode based on the virtual source method to sort CVSGs repeatedly. The PSM was applied to two field data examples. For the test along Han River levee, the results of PSM were compared with the improved roadside passive MASW and spatial autocorrelation method (SPAC). For test in the Western Junggar Basin, PSM was applied to a 70 km long linear survey array with a prominent directional urban noise source and a 60 km-long Vs profile with 1.5 km in depth was mapped. Further, a comparison about the dispersion measurements was made between PSM and frequency-time analysis (FTAN) technique to assess the accuracy of PSM. These examples and comparisons demonstrated that this new method is efficient, flexible, and capable to study near-surface velocity structures based on seismic ambient noise.
An effective method based on dynamic sampling for data assimilation in a global wave model
Sun, Meng; Yin, Xunqiang; Yang, Yongzeng; Wu, Kejian
2017-01-01
The ensemble Kalman filter (EnKF) performs well because that the covariance of background error is varying along time. It provides a dynamic estimate of background error and represents the reasonable statistic characters of background error. However, high computational cost due to model ensemble in EnKF is employed. In this study, two methods referred as static and dynamic sampling methods are proposed to obtain a good performance and reduce the computation cost. Ensemble adjustment Kalman filter (EAKF) method is used in a global surface wave model to examine the performance of EnKF. The 24-h interval difference of simulated significant wave height (SWH) within 1 year is used to compose the static samples for ensemble errors, and these errors are used to construct the ensemble states at each time the observations are available. And then, the same method of updating the model states in the EAKF is applied for the ensemble states constructed by a static sampling method. The dynamic sampling method employs a similar method to construct the ensemble states, but the period of the simulated SWH is changing with time. Here, 7 days before and after the observation time is used as this period. To examine the performance of three schemes, EAKF, static, or dynamic sampling method, observations from satellite Jason-2 in 2014 are assimilated into a global wave model, and observations from satellite Saral are used for validation. The results indicate that the EAKF performs best, while the static sampling method is relatively worse. The dynamic sampling method improves an assimilation effect dramatically compared to the static sampling method, and its overall performance is closed to the EAKF. In low latitudes, the dynamic sampling method has a slight advantage over the EAKF. In the dynamic or static sampling methods, only one wave model is required to run and their computational cost is reduced sharply. According to the performance of these three methods, the dynamic sampling
Frehner, Marcel; Schmalholz, Stefan M.; Saenger, Erik H.; Steeb, Holger
2008-01-01
Two-dimensional scattering of elastic waves in a medium containing a circular heterogeneity is investigated with an analytical solution and numerical wave propagation simulations. Different combinations of finite difference methods (FDM) and finite element methods (FEM) are used to numerically solve
Frehner, Marcel; Schmalholz, Stefan M.; Saenger, Erik H.; Steeb, Holger Karl
2008-01-01
Two-dimensional scattering of elastic waves in a medium containing a circular heterogeneity is investigated with an analytical solution and numerical wave propagation simulations. Different combinations of finite difference methods (FDM) and finite element methods (FEM) are used to numerically solve
Serpentine: Finite Difference Methods for Wave Propagation in Second Order Formulation
Energy Technology Data Exchange (ETDEWEB)
Petersson, N A; Sjogreen, B
2012-03-26
Wave propagation phenomena are important in many DOE applications such as nuclear explosion monitoring, geophysical exploration, estimating ground motion hazards and damage due to earthquakes, non-destructive testing, underground facilities detection, and acoustic noise propagation. There are also future applications that would benefit from simulating wave propagation, such as geothermal energy applications and monitoring sites for carbon storage via seismic reflection techniques. In acoustics and seismology, it is of great interest to increase the frequency bandwidth in simulations. In seismic exploration, greater frequency resolution enables shorter wave lengths to be included in the simulations, allowing for better resolution in the seismic imaging. In nuclear explosion monitoring, higher frequency seismic waves are essential for accurate discrimination between explosions and earthquakes. When simulating earthquake induced motion of large structures, such as nuclear power plants or dams, increased frequency resolution is essential for realistic damage predictions. Another example is simulations of micro-seismic activity near geothermal energy plants. Here, hydro-fracturing induces many small earthquakes and the time scale of each event is proportional to the square root of the moment magnitude. As a result, the motion is dominated by higher frequencies for smaller seismic events. The above wave propagation problems are all governed by systems of hyperbolic partial differential equations in second order differential form, i.e., they contain second order partial derivatives of the dependent variables. Our general research theme in this project has been to develop numerical methods that directly discretize the wave equations in second order differential form. The obvious advantage of working with hyperbolic systems in second order differential form, as opposed to rewriting them as first order hyperbolic systems, is that the number of differential equations in the
Energy Technology Data Exchange (ETDEWEB)
Appelo, D; Petersson, N A
2007-12-17
The isotropic elastic wave equation governs the propagation of seismic waves caused by earthquakes and other seismic events. It also governs the propagation of waves in solid material structures and devices, such as gas pipes, wave guides, railroad rails and disc brakes. In the vast majority of wave propagation problems arising in seismology and solid mechanics there are free surfaces. These free surfaces have, in general, complicated shapes and are rarely flat. Another feature, characterizing problems arising in these areas, is the strong heterogeneity of the media, in which the problems are posed. For example, on the characteristic length scales of seismological problems, the geological structures of the earth can be considered piecewise constant, leading to models where the values of the elastic properties are also piecewise constant. Large spatial contrasts are also found in solid mechanics devices composed of different materials welded together. The presence of curved free surfaces, together with the typical strong material heterogeneity, makes the design of stable, efficient and accurate numerical methods for the elastic wave equation challenging. Today, many different classes of numerical methods are used for the simulation of elastic waves. Early on, most of the methods were based on finite difference approximations of space and time derivatives of the equations in second order differential form (displacement formulation), see for example [1, 2]. The main problem with these early discretizations were their inability to approximate free surface boundary conditions in a stable and fully explicit manner, see e.g. [10, 11, 18, 20]. The instabilities of these early methods were especially bad for problems with materials with high ratios between the P-wave (C{sub p}) and S-wave (C{sub s}) velocities. For rectangular domains, a stable and explicit discretization of the free surface boundary conditions is presented in the paper [17] by Nilsson et al. In summary
von Larcher, Thomas; Harlander, Uwe; Alexandrov, Kiril; Wang, Yongtai
2010-05-01
Experiments on baroclinic wave instabilities in a rotating cylindrical gap have been long performed, e.g., to unhide regular waves of different zonal wave number, to better understand the transition to the quasi-chaotic regime, and to reveal the underlying dynamical processes of complex wave flows. We present the application of appropriate multivariate data analysis methods on time series data sets acquired by the use of non-intrusive measurement techniques of a quite different nature. While the high accurate Laser-Doppler-Velocimetry (LDV ) is used for measurements of the radial velocity component at equidistant azimuthal positions, a high sensitive thermographic camera measures the surface temperature field. The measurements are performed at particular parameter points, where our former studies show that kinds of complex wave patterns occur [1, 2]. Obviously, the temperature data set has much more information content as the velocity data set due to the particular measurement techniques. Both sets of time series data are analyzed by using multivariate statistical techniques. While the LDV data sets are studied by applying the Multi-Channel Singular Spectrum Analysis (M - SSA), the temperature data sets are analyzed by applying the Empirical Orthogonal Functions (EOF ). Our goal is (a) to verify the results yielded with the analysis of the velocity data and (b) to compare the data analysis methods. Therefor, the temperature data are processed in a way to become comparable to the LDV data, i.e. reducing the size of the data set in such a manner that the temperature measurements would imaginary be performed at equidistant azimuthal positions only. This approach initially results in a great loss of information. But applying the M - SSA to the reduced temperature data sets enable us to compare the methods. [1] Th. von Larcher and C. Egbers, Experiments on transitions of baroclinic waves in a differentially heated rotating annulus, Nonlinear Processes in Geophysics
Nagatani, Yoshiki; Imaizumi, Hirotaka; Fukuda, Takashi; Matsukawa, Mami; Watanabe, Yoshiaki; Otani, Takahiko
2006-09-01
In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. We have, therefore, simulated wave propagation in such a complex medium by the finite-difference time-domain (FDTD) method, using a three-dimensional X-ray computer tomography (CT) model of an actual cancellous bone. In this simulation, experimentally observed acoustic constants of the cortical bone were adopted. As a result, the generation of fast and slow waves was confirmed. The speed of fast waves and the amplitude of slow waves showed good correlations with the bone volume fraction. The simulated results were also compared with the experimental results obtained from the identical cancellous bone.
Wang, Yan; Li, Qilu; Xu, Yue; Luo, Chunling; Liu, Xiang; Li, Jun; Zhang, Gan
2012-07-01
An improved correction method was established using passive air samplers to assess the distributions of polychlorinated naphthalenes (PCNs) in the eastern Pearl River Delta, South China. This method was based on a joint correction that used the active air sampling rate and the addition of depuration compounds. As a correction factor, the depuration compounds' properties do not need to be similar to the target compounds. The total PCN air concentrations ranged from 6.4 to 832, with an average of 148 ± 201 pg m-3 in the study area, while the TEQ of the PCNs ranged from 1.2 × 10-4 to 2.6 × 10-2 pg m-3. High concentrations of PCNs were mostly observed in the highly industrialized areas. The PCN air levels were remarkably increased in winter compared with summer. Tri-CNs was the most dominant homologue group, while CN 24 was the most dominant congener. The high proportion of combustion-related PCNs suggests that the contribution of combustion sources to the PCN air burden has been significant recently in comparison with historical emissions.
Energy Technology Data Exchange (ETDEWEB)
Mahmed, N; Soederberg, O; Hannula, S-P [Aalto University School of Science and Technology, Department of Materials Science and Engineering, PO Box 16200, FI-00076 Aalto (Finland); Heczko, O, E-mail: norsuria@cc.hut.f [Institute of Physics, Academy of Sciences, Czech Republic Na Slovance 2, CZ-182 21 Praha 8 (Czech Republic)
2011-10-29
Magnetite (Fe{sub 3-{delta}O4}) nanoparticles with the size less than 30 nm have been synthesized by using a simple reverse co-precipitation method at room temperature. During the process, ferrous sulfate (FeSO{sub 4{center_dot}}7H{sub 2}O) powder was used as an iron precursor, and ammonium hydroxide (NH{sub 4}OH) as a precipitating agent. The experiment was carried out in ambient atmosphere without any surfactant added. In this method, the base solution for the precipitation process was adjusted to have a pH value suitable for the formation of the magnetite phase. The iron salt precursor was added into the solution during the synthesis by two different synthesis protocols. The phase, morphology and magnetic characteristic of differently synthesized magnetite particles were characterized by using an X-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The morphologies of the particles were spherical or irregular in shape depending on the synthesis protocol used. Magnetic measurement shows that the particles are ferromagnetic at room temperature with relatively high saturation magnetization and low hysteresis. The saturation magnetization and magnetic hysteresis of the particles varied with preparation reaction conditions and the resulting oxidation state of the particles.
A reflected wave superposition method for vibration and energy of a travelling string
Chen, E. W.; Luo, Q.; Ferguson, N. S.; Lu, Y. M.
2017-07-01
This paper considers the analytical free time domain response and energy in an axially translating and laterally vibrating string. The domain of the string is either a constant or variable length, dependent upon the general initial conditions. The translating tensioned strings possess either fixed-fixed or fixed-free boundaries. An alternative analytical solution using a reflected wave superposition method is presented for a finite translating string. Firstly, the cycles of vibration for both constant and variable length strings are provided, which for the latter are dependent upon the variable string length. Each cycle is divided into three time intervals according to the magnitude and the direction of the translating string velocity. Applying d'Alembert's method combined with the reflection properties, expressions for the reflected waves at the two boundaries are obtained. Subsequently, superposition of all of the incident and reflected waves provides results for the free vibration of the string over the three time intervals. The variation in the total mechanical energy of the string system is also shown. The accuracy and efficiency of the proposed method are confirmed numerically by comparison to simulations produced using a Newmark-Beta method solution and an existing state space function representation of the string dynamics.
Imaging shear wave propagation for elastic measurement using OCT Doppler variance method
Zhu, Jiang; Miao, Yusi; Qu, Yueqiao; Ma, Teng; Li, Rui; Du, Yongzhao; Huang, Shenghai; Shung, K. Kirk; Zhou, Qifa; Chen, Zhongping
2016-03-01
In this study, we have developed an acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE) method for the visualization of the shear wave and the calculation of the shear modulus based on the OCT Doppler variance method. The vibration perpendicular to the OCT detection direction is induced by the remote acoustic radiation force (ARF) and the shear wave propagating along the OCT beam is visualized by the OCT M-scan. The homogeneous agar phantom and two-layer agar phantom are measured using the ARFOE-OCE system. The results show that the ARFOE-OCE system has the ability to measure the shear modulus beyond the OCT imaging depth. The OCT Doppler variance method, instead of the OCT Doppler phase method, is used for vibration detection without the need of high phase stability and phase wrapping correction. An M-scan instead of the B-scan for the visualization of the shear wave also simplifies the data processing.
Exact traveling wave solutions to the Klein-Gordon equation using the novel (G‧/G)-expansion method
Hafez, M. G.; Alam, Md. Nur; Akbar, M. Ali
The novel (G‧/G)-expansion method is one of the powerful methods that appeared in recent times for establishing exact traveling wave solutions of nonlinear partial differential equations. Exact traveling wave solutions in terms of hyperbolic, trigonometric and rational functions to the cubic nonlinear Klein-Gordon equation via this method are obtained in this article. The efficiency of this method for finding exact solutions and traveling wave solutions has been demonstrated. It is shown that the novel (G‧/G)-expansion method is a simple and valuable mathematical tool for solving nonlinear evolution equations (NLEEs) in applied mathematics, mathematical physics and engineering.
Exact traveling wave solutions to the Klein–Gordon equation using the novel (G′/G-expansion method
Directory of Open Access Journals (Sweden)
M.G. Hafez
2014-01-01
Full Text Available The novel (G′/G-expansion method is one of the powerful methods that appeared in recent times for establishing exact traveling wave solutions of nonlinear partial differential equations. Exact traveling wave solutions in terms of hyperbolic, trigonometric and rational functions to the cubic nonlinear Klein–Gordon equation via this method are obtained in this article. The efficiency of this method for finding exact solutions and traveling wave solutions has been demonstrated. It is shown that the novel (G′/G-expansion method is a simple and valuable mathematical tool for solving nonlinear evolution equations (NLEEs in applied mathematics, mathematical physics and engineering.
Tripathi, B. B.; Espíndola, D.; Pinton, G. F.
2017-06-01
The recent discovery of shear shock wave generation and propagation in the porcine brain suggests that this new shock phenomenology may be responsible for a broad range of traumatic injuries. Blast-induced head movement can indirectly lead to shear wave generation in the brain, which could be a primary mechanism for injury. Shear shock waves amplify the local acceleration deep in the brain by up to a factor of 8.5, which may tear and damage neurons. Currently, there are numerical methods that can model compressional shock waves, such as comparatively well-studied blast waves, but there are no numerical full-wave solvers that can simulate nonlinear shear shock waves in soft solids. Unlike simplified representations, e.g., retarded time, full-wave representations describe fundamental physical behavior such as reflection and heterogeneities. Here we present a piecewise parabolic method-based solver for one-dimensional linearly polarized nonlinear shear wave in a homogeneous medium and with empirical frequency-dependent attenuation. This method has the advantage of being higher order and more directly extendable to multiple dimensions and heterogeneous media. The proposed numerical scheme is validated analytically and experimentally and compared to other shock capturing methods. A Riemann step-shock problem is used to characterize the numerical dissipation. This dissipation is then tuned to be negligible with respect to the physical attenuation by choosing an appropriate grid spacing. The numerical results are compared to ultrasound-based experiments that measure planar polarized shear shock wave propagation in a tissue-mimicking gelatin phantom. Good agreement is found between numerical results and experiment across a 40 mm propagation distance. We anticipate that the proposed method will be a starting point for the development of a two- and three-dimensional full-wave code for the propagation of nonlinear shear waves in heterogeneous media.
A fast fault location method using modal decomposition technique of traveling wave
Energy Technology Data Exchange (ETDEWEB)
Cho, Kyung Rae; Kim, Sung Soo; Kang, Yong Cheol; Park, Jong Keun [Seoul National University, Seoul (Korea, Republic of); Hong, Jun Hee [Kyungwon University, Songnam (Korea, Republic of)
1996-02-01
In this paper, a fault location algorithm is presented, which uses novel signal processing techniques and takes a new paradigm to overcome some drawbacks of the conventional methods. This new method for fault location on electric power transmission lines uses only one-terminal fault signals. The main feature of the method is hat it uses the high frequency components in fault signal and considers the influence of the source network by using a traveling wave propagation characteristics. As a result, we can develop a high speed, good accuracy fault locator. (author). 15 refs., 15 figs., 1 tab.
Inversion method for defects in depth evaluation and thermal wave imaging
Institute of Scientific and Technical Information of China (English)
吕跃凯; 张淑仪; 周庆标
2001-01-01
A hybrid Newton-like iterative method and a regularization method are employed to perform the numerical simulations of the defects in depth evaluation and the thermal wave imaging for defects-included solid sample by analysis of the surface photo-thermal signals. A simple and effective data processing method is suggested to improve the reconstructed data. The results of the numerical calculation demonstrate that the algorithm presented in this paper is very effective, and can be used for qualitative and quantitative analyses of homogeneous materials with defects in depth included. It is also proved that the algorithm is stable even with noise disturbance.
Soft Computing Methods for Microwave and Millimeter-Wave Design Problems
Chauhan, Narendra; Mittal, Ankush
2012-01-01
The growing commercial market of Microwave/ Millimeter wave industry over the past decade has led to the explosion of interests and opportunities for the design and development of microwave components.The design of most microwave components requires the use of commercially available electromagnetic (EM) simulation tools for their analysis. In the design process, the simulations are carried out by varying the design parameters until the desired response is obtained. The optimization of design parameters by manual searching is a cumbersome and time consuming process. Soft computing methods such as Genetic Algorithm (GA), Artificial Neural Network (ANN) and Fuzzy Logic (FL) have been widely used by EM researchers for microwave design since last decade. The aim of these methods is to tolerate imprecision, uncertainty, and approximation to achieve robust and low cost solution in a small time frame. Modeling and optimization are essential parts and powerful tools for the microwave/millimeter wave design. This boo...
Multiple scattering of elastic waves: a numerical method for computing the effective wavenumbers
Chekroun, Mathieu; Lombard, Bruno; Piraux, Joël
2012-01-01
Elastic wave propagation is studied in a heterogeneous 2-D medium consisting of an elastic matrix containing randomly distributed circular elastic inclusions. The aim of this study is to determine the effective wavenumbers when the incident wavelength is similar to the radius of the inclusions. A purely numerical methodology is presented, with which the limitations usually associated with low scatterer concentrations can be avoided. The elastodynamic equations are integrated by a fourth-order time-domain numerical scheme. An immersed interface method is used to accurately discretize the interfaces on a Cartesian grid. The effective field is extracted from the simulated data, and signal-processing tools are used to obtain the complex effective wavenumbers. The numerical reference solution thus-obtained can be used to check the validity of multiple scattering analytical models. The method is applied to the case of concrete. A parametric study is performed on longitudinal and transverse incident plane waves at v...
Directory of Open Access Journals (Sweden)
Bashar Zogheib
2017-01-01
Full Text Available A numerical approach is proposed for solving multidimensional parabolic diffusion and hyperbolic wave equations subject to the appropriate initial and boundary conditions. The considered numerical solutions of the these equations are considered as linear combinations of the shifted Bernoulli polynomials with unknown coefficients. By collocating the main equations together with the initial and boundary conditions at some special points (i.e., CGL collocation points, equations will be transformed into the associated systems of linear algebraic equations which can be solved by robust Krylov subspace iterative methods such as GMRES. Operational matrices of differentiation are implemented for speeding up the operations. In both of the one-dimensional and two-dimensional diffusion and wave equations, the geometrical distributions of the collocation points are depicted for clarity of presentation. Several numerical examples are provided to show the efficiency and spectral (exponential accuracy of the proposed method.
A Square Wave Based Electrical Method for Human Skin Moisture Assessment
Institute of Scientific and Technical Information of China (English)
Guolin Zhou; Yonggui Dong
2006-01-01
The moisture content measurement of human skin is a significant way to assess skin conditions and diagnose diseases that influence skin function. The necessity of evaluating the efficacy of a cosmetic product makes it important to improve the accuracy and reproducibility of the measurement. A pair of interdigitated gold electrodes was fabricated on the printed circuit board (PCB) substrate and utilized directly in contact with the measured skin. A square-wave voltage at a single frequency was applied to the electrodes and the corresponding response current was measured to get the equivalent impedance of human skin. Since it's easy to generate and control a square-wave signal by digital electric circuits, this method is suitable to be used in the portable application. The experimental results indicate that good repeatability and satisfied accuracy can be obtained by this method.
Time-domain hybrid method for simulating large amplitude motions of ships advancing in waves
Directory of Open Access Journals (Sweden)
Shukui Liu
2011-03-01
Full Text Available Typical results obtained by a newly developed, nonlinear time domain hybrid method for simulating large amplitude motions of ships advancing with constant forward speed in waves are presented. The method is hybrid in the way of combining a time-domain transient Green function method and a Rankine source method. The present approach employs a simple double integration algorithm with respect to time to simulate the free-surface boundary condition. During the simulation, the diffraction and radiation forces are computed by pressure integration over the mean wetted surface, whereas the incident wave and hydrostatic restoring forces/moments are calculated on the instantaneously wetted surface of the hull. Typical numerical results of application of the method to the seakeeping performance of a standard containership, namely the ITTC S175, are herein presented. Comparisons have been made between the results from the present method, the frequency domain 3D panel method (NEWDRIFT of NTUA-SDL and available experimental data and good agreement has been observed for all studied cases between the results of the present method and comparable other data.
Comparison of methods for the detection of gravitational waves from unknown neutron stars
Walsh, S.; Pitkin, M.; Oliver, M.; D'Antonio, S.; Dergachev, V.; Królak, A.; Astone, P.; Bejger, M.; Di Giovanni, M.; Dorosh, O.; Frasca, S.; Leaci, P.; Mastrogiovanni, S.; Miller, A.; Palomba, C.; Papa, M. A.; Piccinni, O. J.; Riles, K.; Sauter, O.; Sintes, A. M.
2016-12-01
Rapidly rotating neutron stars are promising sources of continuous gravitational wave radiation for the LIGO and Virgo interferometers. The majority of neutron stars in our galaxy have not been identified with electromagnetic observations. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from these unidentified sources. The parameter space of these blind all-sky searches, which also cover a large range of frequencies and frequency derivatives, presents a significant computational challenge. Different methods have been designed to perform these searches within acceptable computational limits. Here we describe the first benchmark in a project to compare the search methods currently available for the detection of unknown isolated neutron stars. The five methods compared here are individually referred to as the PowerFlux, sky Hough, frequency Hough, Einstein@Home, and time domain F -statistic methods. We employ a mock data challenge to compare the ability of each search method to recover signals simulated assuming a standard signal model. We find similar performance among the four quick-look search methods, while the more computationally intensive search method, Einstein@Home, achieves up to a factor of two higher sensitivity. We find that the absence of a second derivative frequency in the search parameter space does not degrade search sensitivity for signals with physically plausible second derivative frequencies. We also report on the parameter estimation accuracy of each search method, and the stability of the sensitivity in frequency and frequency derivative and in the presence of detector noise.
Mapping crustal S-wave velocity structure with SV-component receiver function method
Institute of Scientific and Technical Information of China (English)
邹最红; 陈晓非
2003-01-01
In this article, we analyze the characters of SV-component receiver function of teleseismic body waves and its advantages in mapping the S-wave velocity structure of crust in detail. Similar to radial receiver function, SV-component receiver function can be obtained by directly deconvolving the P-component from the SV-component of teleseismic recordings. Our analyses indicate that the change of amplitude of SV-component receiver function against the change of epicentral distance is less than that of radial receiver function. Moreover, the waveform of SV-component receiver function is simpler than the radial receiver function and gives prominence to the PS converted phases that are the most sensitive to the shear wave velocity structure in the inversion. The synthetic tests show that the convergence of SV-component receiver function inversion is faster than that of the radial receiver function inversion. As an example, we investigate the S-wave velocity structure beneath HIA station by using the SV-component receiver function inversion method.
In vivo noninvasive method for measuring local wave velocity in femoral arteries of pig
Zhang, Xiaoming; Kinnick, Randall; Pislaru, Cristina; Fatemi, Mostafa; Greenleaf, James
2005-09-01
We have proposed generating a bending wave in the arterial wall using ultrasound radiation force and measuring the wave velocity along the arterial wall [Zhang et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Control 52, 642-652 (2005)]. Here, we report the results of in vivo studies on pigs. The pig was anesthetized, and a micromanometer tip catheter was inserted into the femoral artery to measure luminal pressure. A water bath was created on the animal's groin to allow unimpeded access of the ultrasound beams to the femoral artery. The femoral artery was first located using a 13-MHz linear-array transducer. Then, a vibro-acoustography image was obtained to ensure precise positioning of the excitation force relative to the artery. The artery was excited by the force transducer and the resulting vibration of the arterial wall was measured by a sensing Doppler transceiver. Measured wave velocity was 3.1 m/s at 300 Hz. With this new method wave velocity over a distance of 5 mm, and therefore stiffness of arteries, can be measured locally and non-invasively. Measurement time is short in a few tens of milliseconds, which allows pressure dependence and pharmacological effect on the wall properties to be measured at different cardiac times.
Re-study on Recurrence Period of Stokes Wave Train with High Order Spectral Method
Institute of Scientific and Technical Information of China (English)
TAO Ai-feng; ZHENG Jin-hai; MEE Mee Soe; CHEN Bo-tao
2011-01-01
Owing to the Benjamin-Feir instability,the Stokes wave train experiences a modulation-demodulation process,and presents a recurrence characteristics.Stiassnie and Shemer researched the unstable evolution process and provided a theoretical formulation for the recurrence period in 1985 on the basis of the nonlinear cubic Schr(o)dinger equation (NLS).However,NLS has limitations on the narrow band and the weak nonlinearity.The recurrence period is re-investigated in this paper by using a highly efficient High Order Spectral (HOS) method,which can be applied for the direct phaseresolved simulation of the nonlinear wave train evolution.It is found that the Stiassnie and Shemer's formula should be modified in the cases with most unstable initial conditions,which is important for such topics as the generation mechanisms of freak waves.A new recurrence period formula is presented and some new evolution characteristics of the Stokes wave train are also discussed in details.
A stabilised nodal spectral element method for fully nonlinear water waves
Engsig-Karup, A. P.; Eskilsson, C.; Bigoni, D.
2016-08-01
We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al. (1998) [5], although the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global L2 projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions can cause severe aliasing problems and consequently numerical instability for marginally resolved or very steep waves. We show how the scheme can be stabilised through a combination of over-integration of the Galerkin projections and a mild spectral filtering on a per element basis. This effectively removes any aliasing driven instabilities while retaining the high-order accuracy of the numerical scheme. The additional computational cost of the over-integration is found insignificant compared to the cost of solving the Laplace problem. The model is applied to several benchmark cases in two dimensions. The results confirm the high order accuracy of the model (exponential convergence), and demonstrate the potential for accuracy and speedup. The results of numerical experiments are in excellent agreement with both analytical and experimental results for strongly nonlinear and irregular dispersive wave propagation. The benefit of using a high-order - possibly adapted - spatial discretisation for accurate water wave propagation over long times and distances is particularly attractive for marine hydrodynamics applications.
Importance of a 3D forward modeling tool for surface wave analysis methods
Pageot, Damien; Le Feuvre, Mathieu; Donatienne, Leparoux; Philippe, Côte; Yann, Capdeville
2016-04-01
Since a few years, seismic surface waves analysis methods (SWM) have been widely developed and tested in the context of subsurface characterization and have demonstrated their effectiveness for sounding and monitoring purposes, e.g., high-resolution tomography of the principal geological units of California or real time monitoring of the Piton de la Fournaise volcano. Historically, these methods are mostly developed under the assumption of semi-infinite 1D layered medium without topography. The forward modeling is generally based on Thomson-Haskell matrix based modeling algorithm and the inversion is driven by Monte-Carlo sampling. Given their efficiency, SWM have been transfered to several scale of which civil engineering structures in order to, e.g., determine the so-called V s30 parameter or assess other critical constructional parameters in pavement engineering. However, at this scale, many structures may often exhibit 3D surface variations which drastically limit the efficiency of SWM application. Indeed, even in the case of an homogeneous structure, 3D geometry can bias the dispersion diagram of Rayleigh waves up to obtain discontinuous phase velocity curves which drastically impact the 1D mean velocity model obtained from dispersion inversion. Taking advantages of high-performance computing center accessibility and wave propagation modeling algorithm development, it is now possible to consider the use of a 3D elastic forward modeling algorithm instead of Thomson-Haskell method in the SWM inversion process. We use a parallelized 3D elastic modeling code based on the spectral element method which allows to obtain accurate synthetic data with very low numerical dispersion and a reasonable numerical cost. In this study, we choose dike embankments as an illustrative example. We first show that their longitudinal geometry may have a significant effect on dispersion diagrams of Rayleigh waves. Then, we demonstrate the necessity of 3D elastic modeling as a forward
2.5-D frequency-domain viscoelastic wave modelling using finite-element method
Zhao, Jian-guo; Huang, Xing-xing; Liu, Wei-fang; Zhao, Wei-jun; Song, Jian-yong; Xiong, Bin; Wang, Shang-xu
2017-10-01
2-D seismic modelling has notable dynamic information discrepancies with field data because of the implicit line-source assumption, whereas 3-D modelling suffers from a huge computational burden. The 2.5-D approach is able to overcome both of the aforementioned limitations. In general, the earth model is treated as an elastic material, but the real media is viscous. In this study, we develop an accurate and efficient frequency-domain finite-element method (FEM) for modelling 2.5-D viscoelastic wave propagation. To perform the 2.5-D approach, we assume that the 2-D viscoelastic media are based on the Kelvin-Voigt rheological model and a 3-D point source. The viscoelastic wave equation is temporally and spatially Fourier transformed into the frequency-wavenumber domain. Then, we systematically derive the weak form and its spatial discretization of 2.5-D viscoelastic wave equations in the frequency-wavenumber domain through the Galerkin weighted residual method for FEM. Fixing a frequency, the 2-D problem for each wavenumber is solved by FEM. Subsequently, a composite Simpson formula is adopted to estimate the inverse Fourier integration to obtain the 3-D wavefield. We implement the stiffness reduction method (SRM) to suppress artificial boundary reflections. The results show that this absorbing boundary condition is valid and efficient in the frequency-wavenumber domain. Finally, three numerical models, an unbounded homogeneous medium, a half-space layered medium and an undulating topography medium, are established. Numerical results validate the accuracy and stability of 2.5-D solutions and present the adaptability of finite-element method to complicated geographic conditions. The proposed 2.5-D modelling strategy has the potential to address modelling studies on wave propagation in real earth media in an accurate and efficient way.
Wave propagation in one-dimension: Methods and applications to complex and fractal structures
Akkermans, Eric; Levy, Eli
2012-01-01
This chapter is a pedagogical review of methods and results for studying wave propagation in one-dimensional complex structures. We describe and compare the tight-binding, scattering matrix, transfer matrix and Riccati formalisms. We present examples for transport through finite-sized layered dielectric systems with periodic, quasi-periodic, fractal, disordered, and random structure, illustrating how can spatial structure affect the spectrum of modes as well as the local mode intensity.
Numerical methods for wave propagation in solids containing faults and fluid-filled fractures
2016-01-01
This thesis develops numerical methods for the simulation of wave propagation in solids containing faults and fluid-filled fractures. These techniques have applications in earthquake hazard analysis, seismic imaging of reservoirs, and volcano seismology. A central component of this work is the coupling of mechanical systems. This aspect involves the coupling of both ordinary differential equations (ODE)(s) and partial differential equations (PDE)(s) along curved interfaces. All of these prob...
Variational space-time (dis)continuous Galerkin method for linear free surface waves
Ambati, V.R.; Vegt, van der, N.F.A.; Bokhove, O.
2008-01-01
A new variational (dis)continuous Galerkin finite element method is presented for the linear free surface gravity water wave equations. We formulate the space-time finite element discretization based on a variational formulation analogous to Luke's variational principle. The linear algebraic system of equations resulting from the finite element discretization is symmetric with a very compact stencil. To build and solve these equations, we have employed PETSc package in which a block sparse ma...
Finite volume evolution Galerkin (FVEG) methods for three-dimensional wave equation system
Lukácová-Medvid'ová, Maria; Warnecke, Gerald; Zahaykah, Yousef
2004-01-01
The subject of the paper is the derivation of finite volume evolution Galerkin schemes for three-dimensional wave equation system. The aim is to construct methods which take into account all of the infinitely many directions of propagation of bicharacteristics. The idea is to evolve the initial function using the characteristic cone and then to project onto a finite element space. Numerical experiments are presented to demonstrate the accuracy and the multidimensional behaviour of the solutio...
Low-Frequency Gravitational Wave Searches Using Spacecraft Doppler Tracking
Directory of Open Access Journals (Sweden)
Armstrong J. W.
2006-01-01
Full Text Available This paper discusses spacecraft Doppler tracking, the current-generation detector technology used in the low-frequency (~millihertz gravitational wave band. In the Doppler method the earth and a distant spacecraft act as free test masses with a ground-based precision Doppler tracking system continuously monitoring the earth-spacecraft relative dimensionless velocity $2 Delta v/c = Delta u/ u_0$, where $Delta u$ is the Doppler shift and $ u_0$ is the radio link carrier frequency. A gravitational wave having strain amplitude $h$ incident on the earth-spacecraft system causes perturbations of order $h$ in the time series of $Delta u/ u_0$. Unlike other detectors, the ~1-10 AU earth-spacecraft separation makes the detector large compared with millihertz-band gravitational wavelengths, and thus times-of-flight of signals and radio waves through the apparatus are important. A burst signal, for example, is time-resolved into a characteristic signature: three discrete events in the Doppler time series. I discuss here the principles of operation of this detector (emphasizing transfer functions of gravitational wave signals and the principal noises to the Doppler time series, some data analysis techniques, experiments to date, and illustrations of sensitivity and current detector performance. I conclude with a discussion of how gravitational wave sensitivity can be improved in the low-frequency band.
Shigehara, T; Mishima, T; Cheon, T; Cheon, Taksu
1999-01-01
We propose a new method to construct a four parameter family of quantum-mechanical point interactions in one dimension, which is known as all possible self-adjoint extensions of the symmetric operator $T=-\\Delta \\lceil C^{\\infty}_{0}({\\bf R} \\backslash\\{0\\})$. It is achieved in the small distance limit of equally spaced three neighboring Dirac's $\\delta$ potentials. The strength for each $\\delta$ is appropriately renormalized according to the distance and it diverges, in general, in the small distance limit. The validity of our method is ensured by numerical calculations. In general cases except for usual $\\delta$, the wave function discontinuity appears around the interaction and one can observe such a tendency even at a finite distance level.
Energy Technology Data Exchange (ETDEWEB)
Zheng Xuedong; Chen Yong; Zhang Hongqing
2003-05-12
Making use of a new generalized ansatzes, we present the generalized extended tanh-function method for constructing the exact solutions of nonlinear partial differential equations (NPDEs) in a unified way. Applying the generalized method, with the aid of MAPLE, we consider the Wu-Zhang equation (which describes (1+1)-dimensional dispersive long wave). As a result, we can successfully obtain the solitary wave solutions that can be found by the extended tanh-function method and the modified extended tanh-function method. More importantly, for the equation, we also obtain other new and more general solutions at the same time. The results include kink-profile solitary wave solutions, bell-profile solitary wave solutions, periodic wave solutions, rational solutions, singular solutions and other new formal solutions. As an illustrative sample, the properties of some soliton solutions for Wu-Zhang equation are shown by some figures.
Directory of Open Access Journals (Sweden)
Fucai Li
2012-01-01
Full Text Available A three-dimensional spectral element method (SEM was developed for analysis of Lamb wave propagation in composite laminates containing a delamination. SEM is more efficient in simulating wave propagation in structures than conventional finite element method (FEM because of its unique diagonal form of the mass matrix. Three types of composite laminates, namely, unidirectional-ply laminates, cross-ply laminates, and angle-ply laminates are modeled using three-dimensional spectral finite elements. Wave propagation characteristics in intact composite laminates are investigated, and the effectiveness of the method is validated by comparison of the simulation results with analytical solutions based on transfer matrix method. Different Lamb wave mode interactions with delamination are evaluated, and it is demonstrated that symmetric Lamb wave mode may be insensitive to delamination at certain interfaces of laminates while the antisymmetric mode is more suited for identification of delamination in composite structures.
Carretero, Luis; Acebal, Pablo; Blaya, Salvador
2013-04-01
We present a complete electromagnetic study, which includes electric, magnetic, and Poynting vector fields of diffracted convergent spherical waves under all possible polarization states compatible with Maxwell's equations. Exit pupil boundary conditions for these polarizations were obtained by means of Hertz potentials. Using these boundary conditions, two-dimensional Luneburg diffraction integrals for the three components of electric and magnetic fields were formulated, and after some approximations, we showed that the complete electromagnetic description of the inhomogeneous polarization states of spherical waves is reduced to the knowledge of seven one-dimensional integrals. The consistency of the method was tested by comparison with other previously reported methods for linearly polarized (LP), TE, and TM polarizations, while the versatility of the method was showed with the study of nonstandard polarization states, for example, that resulting from the superposition of TE and TM dephased spherical waves, which shows a helicoidal behavior of the Poynting vector at the focalization region, or the inhomogeneous LP state that exhibits a ring structure for the Poynting vector at the focal plane.
3-D computational method of wave loads on turret moored FPSO tankers
Institute of Scientific and Technical Information of China (English)
REN Hui-long; ZHANG Hai-bin; DAI Yu-zhi; SONG Jing-zheng
2003-01-01
A three-dimensional method of calculating wave loads of turret moored FPSO (Floating Production Storage and Offloading) tankers is presented. The linearized restoring forces acting on the ship hull by the mooring system are calculated according to the catenary theory, which are expressed as the function of linear stiffness coefficients and the displacements of the upper ends of mooring chains. The hydrodynamic coefficients of the ship are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for ships with a low forward speed. The equations of ship motions are established with the effect of the restoring forces from the mooring system included as linear stiffness coefficients. The equations of motions are solved in frequency domain, and the responses of wave-induced motions and loads on the ship can be obtained. A computer program based on this method has been developed,and some calculation examples are illustrated. Analysis results show that the method can give satisfying prediction of wave loads.
Systematic examination of 'precursor waves' of strong earthquakes by using the wavelet method
Institute of Scientific and Technical Information of China (English)
Longshou Zhou; Zehua Qiu; Lei Tang; Baoxiang Kan
2009-01-01
Based on the borehole strainmeter recordings immediately before the strong earthquakes (MS≥7.5) during the period from 2001 to 2005 observed at the Taian observation station, Shandong Province, the authors make a systematic and objective examination of the precursor waves of the quakes. The effects of Earth tides with periods larger than 128 min are eliminated through high-pass filtering; and atmospheric-pressure inferences are removed by linear regression. The 2-128 min signals ate then separated into six frequency bands by employing the wavelet method. Results indicate that the wavelet method is capable of picking out information of weak variations in the signals. According to the characteristics of the 'pre-euraor waves' obtained from wavelet transformation, the method of overrun ratio analysis is put forward for examination. All the detailed components of the wavelets have been analyzed. For the time series of the overrun rate in all these components, statisitical calculation has been made for the slopes of fit curves, and mean values and standard deviations were obtained and positive-negative slope ratios were analyzed. The three statistical data show that 'precursor waves' are not widely recorded by borehole strainmeter within 15 days before remote strong earthquakes.
Ishikawa, Tomonari; Matsumoto, Yoshitaka; Hozumi, Naohiro
2017-07-01
Measuring the quality and thickness of bottom sediment that it causes some environmental problem, the shortage of water storage volume and anaerobic zone in the bottom of reservoirs, takes huge costs and long time. The purpose of our research is to develop a new method to measure the thickness and size characteristics of bottom sediment using ultrasonic waves that allow obtaining the quality of it indirectly. This new method applies the echo characteristic of bottom sediment in each particle size using the higher frequency than another method, which uses for measuring geological layer at seabed survey. In this research, we attempted to estimate the particle size of bottom sediment by ultrasonic waves irradiating from two different directions such as horizontal and vertical direction, and compare these experiments. We use sediment that we sampled from the lake bottom classified by particle size. At first, we acquired the results that show a relation between particle size and intensity; the obtained echo intensities, which were observed with oscilloscope, were changed depending on the particle sizes. In addition, peaks, which were obtained by power spectrum analysis, appeared on the same frequency band even though the different particle size. However the relation between the experiments of horizontal and vertical direction is not clear. This research indicated the possibility of estimating the characteristics of each particle size in bottom sediment by ultrasonic waves.
Ultrasonic Guided Wave Method For Crack Detection In Buried Plastic Pipe
Directory of Open Access Journals (Sweden)
Wan Hamat Wan Sofian
2016-01-01
Full Text Available Plastic pipe are widely used in many fields for the fluid or gaseous product conveyance but basic components of a plastic material made it very sensitive to damage, which requires techniques for detecting damage reliable and efficient. Ultrasonic guided wave is a sensitive method based on propagation of low-frequency excitation in solid structures for damage detection. Ultrasonic guided wave method are performed to investigate the effect of crack to the frequency signal using Fast Fourier Transform (FFT analysis. This paper researched to determine performance of ultrasonic guided wave method in order to detect crack in buried pipeline. It was found that for an uncrack pipe, FFT analysis shows one peak which is the operating frequency by the piezoelectric actuator itself while the FFT analysis for single cracked pipe shows two peak which is the operating frequency by the piezoelectric actuator itself and the resultant frequency from the crack. For multi cracked pipe, the frequency signal shows more than two peak depend the number of crack. The results presented here may facilitate improvements in the accuracy and precision of pipeline crack detection.
Huntington, K W; Eiler, J M; Affek, H P; Guo, W; Bonifacie, M; Yeung, L Y; Thiagarajan, N; Passey, B; Tripati, A; Daëron, M; Came, R
2009-09-01
The geochemistry of multiply substituted isotopologues ('clumped-isotope' geochemistry) examines the abundances in natural materials of molecules, formula units or moieties that contain more than one rare isotope (e.g. (13)C(18)O(16)O, (18)O(18)O, (15)N(2), (13)C(18)O(16)O(2) (2-)). Such species form the basis of carbonate clumped-isotope thermometry and undergo distinctive fractionations during a variety of natural processes, but initial reports have provided few details of their analysis. In this study, we present detailed data and arguments regarding the theoretical and practical limits of precision, methods of standardization, instrument linearity and related issues for clumped-isotope analysis by dual-inlet gas-source isotope ratio mass spectrometry (IRMS). We demonstrate long-term stability and subtenth per mil precision in 47/44 ratios for counting systems consisting of a Faraday cup registered through a 10(12) ohm resistor on three Thermo-Finnigan 253 IRMS systems. Based on the analyses of heated CO(2) gases, which have a stochastic distribution of isotopes among possible isotopologues, we document and correct for (1) isotopic exchange among analyte CO(2) molecules and (2) subtle nonlinearity in the relationship between actual and measured 47/44 ratios. External precisions of approximately 0.01 per thousand are routinely achieved for measurements of the mass-47 anomaly (a measure mostly of the abundance anomaly of (13)C-(18)O bonds) and follow counting statistics. The present technical limit to precision intrinsic to our methods and instrumentation is approximately 5 parts per million (ppm), whereas precisions of measurements of heterogeneous natural materials are more typically approximately 10 ppm (both 1 s.e.). These correspond to errors in carbonate clumped-isotope thermometry of +/-1.2 degrees C and +/-2.4 degrees C, respectively.
Millimeter wave dosimetry of human skin.
Alekseev, S I; Radzievsky, A A; Logani, M K; Ziskin, M C
2008-01-01
To identify the mechanisms of biological effects of mm waves it is important to develop accurate methods for evaluating absorption and penetration depth of mm waves in the epidermis and dermis. The main characteristics of mm wave skin dosimetry were calculated using a homogeneous unilayer model and two multilayer models of skin. These characteristics included reflection, power density (PD), penetration depth (delta), and specific absorption rate (SAR). The parameters of the models were found from fitting the models to the experimental data obtained from measurements of mm wave reflection from human skin. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. The thin SC produced little influence on the interaction of mm waves with skin. On the contrary, the thick SC in the palm played the role of a matching layer and significantly reduced reflection. In addition, the palmar skin manifested a broad peak in reflection within the 83-277 GHz range. The viable epidermis plus dermis, containing a large amount of free water, greatly attenuated mm wave energy. Therefore, the deeper fat layer had little effect on the PD and SAR profiles. We observed the appearance of a moderate SAR peak in the therapeutic frequency range (42-62 GHz) within the skin at a depth of 0.3-0.4 mm. Millimeter waves penetrate into the human skin deep enough (delta = 0.65 mm at 42 GHz) to affect most skin structures located in the epidermis and dermis.
Hsu, Jin-Chen; Wu, Tsung-Tsong
2008-02-01
Based on Mindlin's piezoelectric plate theory and the plane wave expansion method, a formulation is proposed to study the frequency band gaps and dispersion relations of the lower-order Lamb waves in two-dimensional piezoelectric phononic plates. The method is applied to analyze the phononic plates composed of solid-solid and airsolid constituents with square and triangular lattices, respectively. Factors that influence the opening and width of the complete Lamb wave gaps are identified and discussed. For solid/solid phononic plates, it is suggested that the filling material be chosen with larger mass density, proper stiffness, and weak anisotropic factor embedded in a soft matrix in order to obtain wider complete band gaps of the lower-order Lamb waves. By comparing to the calculated results without considering the piezoelectricity, the influences of piezoelectric effect on Lamb waves are analyzed as well. On the other hand, for air/solid phononic plates, a background material itself with proper anisotropy and a high filling fraction of air may favor the opening of the complete Lamb wave gaps.
Vibration band gaps for elastic metamaterial rods using wave finite element method
Nobrega, E. D.; Gautier, F.; Pelat, A.; Dos Santos, J. M. C.
2016-10-01
Band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators are investigated. New techniques to analyze metamaterial systems are using a combination of analytical or numerical method with wave propagation. One of them, called here wave spectral element method (WSEM), consists of combining the spectral element method (SEM) with Floquet-Bloch's theorem. A modern methodology called wave finite element method (WFEM), developed to calculate dynamic behavior in periodic acoustic and structural systems, utilizes a similar approach where SEM is substituted by the conventional finite element method (FEM). In this paper, it is proposed to use WFEM to calculate band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators of multi-degree-of-freedom (M-DOF). Simulated examples with band gaps generated by Bragg scattering and local resonators are calculated by WFEM and verified with WSEM, which is used as a reference method. Results are presented in the form of attenuation constant, vibration transmittance and frequency response function (FRF). For all cases, WFEM and WSEM results are in agreement, provided that the number of elements used in WFEM is sufficient to convergence. An experimental test was conducted with a real elastic metamaterial rod, manufactured with plastic in a 3D printer, without local resonance-type effect. The experimental results for the metamaterial rod with band gaps generated by Bragg scattering are compared with the simulated ones. Both numerical methods (WSEM and WFEM) can localize the band gap position and width very close to the experimental results. A hybrid approach combining WFEM with the commercial finite element software ANSYS is proposed to model complex metamaterial systems. Two examples illustrating its efficiency and accuracy to model an elastic metamaterial rod unit-cell using 1D simple rod element and 3D solid element are
Liu, Cai; Song, Chao; Lu, Qi
2017-09-01
In this paper, we present a method using singular value decomposition (SVD) which aims at eliminating the random noise and direct wave from ground penetrating radar (GPR) signals. To demonstrate the validity and high efficiency of the SVD method in eliminating random noise, we compare the SVD de-noising method with wavelet threshold de-noising method and bandpass filtering method on both noisy synthetic data and field data. After that, we compare the SVD method with the mean trace deleting in eliminating direct wave on synthetic data and field data. We set general and quantitative criteria on choosing singular values to carry out the random noise de-noising and direct wave eliminating process. We find that by choosing appropriate singular values, SVD method can eliminate the random noise and direct wave in the GPR data validly and efficiently to improve the signal-to-noise ratio (SNR) of the GPR profiles and make effective reflection signals clearer.
Application of Wavelet Packet De-noising in Time-Frequency Analysis of the Local Wave Method
Institute of Scientific and Technical Information of China (English)
LI Hong-kun; MA Xiao-jiang; WANG Zhen; ZHU Hong
2003-01-01
The local wave method is a very good time-frequency method for nonstationary vibration signal analysis. But the interfering noise has a big influence on the accuracy of time-frequency analysis. The wavelet packet de-noising method can eliminate the interference of noise and improve the signal-noise-ratio. This paper uses the local wave method to decompose the de-noising signal and perform a time-frequency analysis. We can get better characteristics. Finally, an example of wavelet packet de-noising and a local wave time-frequency spectrum application of diesel engine surface vibration signal is put forward.
Directory of Open Access Journals (Sweden)
ȘOVĂILĂ Florin
2016-07-01
Full Text Available 3D printing is a very used process in industry, the generic name being “rapid prototyping”. The essential advantage of a 3D printer is that it allows the designers to produce a prototype in a very short time, which is tested and quickly remodeled, considerably reducing the required time to get from the prototype phase to the final product. At the same time, through this technique we can achieve components with very precise forms, complex pieces that, through classical methods, could have been accomplished only in a large amount of time. In this paper, there are presented the stages of a 3D model execution, also the physical achievement after of a Delta 3D printer after the model.
Institute of Scientific and Technical Information of China (English)
王凯; 冯晅; 刘财
2012-01-01
横波分裂是各向异性介质的重要特征,当横波或转换波穿过各向异性介质到达地面时,地面三分量检波器的x分量和y分量接收到的地震记录中都会同时存在快横波和慢横波.将快横波和慢横波进行分离,进而计算介质的各向异性参数是多分量数据处理中重要的一步.将数学中的Pearson相关系数引入到多分量地震勘探中,提出了Pearson相关系数法进行旋转角度识别,进而分离快、慢横波波场.相比于传统的互相关法,Pearson相关系数法从精度、抗噪性能和计算效率上都有提高.%Shear-wave splitting is an important characteristic of anisotropic media. Generally, when S or P-SV waves reach to the ground through anisotropic media, the seismic record received by x component and y component of three-component detector contains fast wave and slow wave simultaneously- Separating fast wave and slow wave and then calculating the anisotropic parameters of media are an important step in multi-component data processing. The authors introduce the Pearson correlation coefficients into multi-component seismic exploration and propose the Pearson correlation coefficients to detect the rotation angle and then separate the fast wave and slow wave. Compared with the traditional cross-correlation method, the Pearson correlation coefficient method is better in accuracy, noise immunity and computational efficiency.
On the use of the Muskingum method for the simulation of flood wave movements
Baláž, M.; Danáčová, M.; Szolgay, J.
2010-09-01
The Muskingum method is a hydrological flow routing model with lumped parameters, which describes the transformation of discharge waves in a river bed using two equations. The first one is the continuity equation (conservation of mass) and the second equation is the relationship between the storage, inflow, and outflow of the reach (the discharge storage equation). These equations are applied within a river reach between two cross sections of a river. The parameters of the model can be estimated by several methods. Here the classical graphic method is compared with two new methods where a genetic algorithm and harmony search was used for optimization. The discrete state space formulation of the Muskingum method was applied on the lower Morava reach between Moravský Svätý Ján and Záhorská Ves. The results showed a good degree of accuracy of all three methods, which were assessed by the Nash-Sutcliffe efficiency coefficient.
Topology optimization of bounded acoustic problems using the hybrid finite element-wave based method
DEFF Research Database (Denmark)
Goo, Seongyeol; Wang, Semyung; Kook, Junghwan
2017-01-01
This paper presents an alternative topology optimization method for bounded acoustic problems that uses the hybrid finite element-wave based method (FE-WBM). The conventional method for the topology optimization of bounded acoustic problems is based on the finite element method (FEM), which...... is limited to low frequency applications due to considerable computational efforts. To this end, we propose a gradient-based topology optimization method that uses the hybrid FE-WBM whereby the entire domain of a problem is partitioned into design and non-design domains. In this respect, the FEM is used...... as a design domain of topology optimization, and the WBM is used as a non-design domain to increase computational efficiency. The adjoint variable method based on the hybrid FE-WBM is also proposed as a means of computing design sensitivities. Numerical examples are presented to demonstrate the effectiveness...
Energy Technology Data Exchange (ETDEWEB)
Hou Zhilin [Laboratoire de Physique des Milieux Ionises et Applications (LPMIA), Nancy University, CNRS Boulevard des Aiguillettes, BP 239 F-54506, Vandoeuvre-les-Nancy (France)], E-mail: zhilin.hou@lpmi.uhp-nancy.fr; Assouar, Badreddine M. [Laboratoire de Physique des Milieux Ionises et Applications (LPMIA), Nancy University, CNRS Boulevard des Aiguillettes, BP 239 F-54506, Vandoeuvre-les-Nancy (France)
2008-03-17
We show that the conversional three-dimensional plane wave expansion method can be revised to investigate the lamb wave propagation in the plate with two-dimensional phononic crystal layer coated on uniform substrate. We find that an imaginary three-dimensional periodic system can be constructed by stacking the studied plates and vacuum layers alternately, and then the Fourier series expansion can be performed. The difference between our imaginary periodic system and the true three-dimensional one is that, in our system, the Bloch feature of the wave along the thickness direction is broken. Three different systems are investigated by the proposed method as examples. The principle and reliability of the method are also discussed.
Institute of Scientific and Technical Information of China (English)
叶宝娟; 温忠麟
2012-01-01
Reliability is very important in evaluating the quality of a test. Based on the confirmatory factor analysis, composite reliabili- ty is a good index to estimate the test reliability for general applications. As is well known, point estimate contains limited information a- bout a population parameter and cannot indicate how far it can be from the population parameter. The confidence interval of the parame- ter can provide more information. In evaluating the quality of a test, the confidence interval of composite reliability has received atten- tion in recent years. There are three approaches to estimating the confidence interval of composite reliability of an unidimensional test: the Bootstrap method, the Delta method, and the direct use of the standard error of a software output (e. g. , LISREL). The Bootstrap method pro- vides empirical results of the standard error, and is the most credible method. But it needs data simulation techniques, and its computa- tion process is rather complex. The Delta method computes the standard error of composite reliability by approximate calculation. It is simpler than the Bootstrap method. The LISREL software can directly prompt the standard error, and it is the easiest among the three methods. By simulation study, it had been found that the interval estimates obtained by the Delta method and the Bootstrap method were almost identical, whereas the results obtained by LISREL and by the Bootstrap method were substantially different ( Ye & Wen, 2011 ). The Delta method is recommended when the confidence interval of composite reliability of a unidimensional test is estimated, because the Delta method is simpler than the Bootstrap method. There was little research about how to compute the confidence interval of composite reliability of a multidimensional test. We de- duced a formula by using the Delta method for computing the standard error of composite reliability of a multidimensional test. Based on the standard error, the
Methods for processing experimental data in microwave diagnostics of shock waves and detonation
Sedov, Alexander; Rodionov, Alexey; Kanakov, Vladimir
2013-06-01
Microwave interferometry is a promising method of unperturbing diagnostics of short-time processes. It is a bit less effective than the optical methods in accuracy, but it provides a researcher with more capabilities, in particular, for measurements in optically opaque media. The classic methods for processing experimental interferograms using extremums allow to obtain data on motion of investigated objects with the resolution of a quarter of wavelength of probing radiation. It is insufficient for majority of practical applications. Use of the mathematical methods for processing output signals of the receiver allows to improve the method resolution significantly and to obtain motion measurement errors of 0.05...0.1 of wavelength or even less. This paper presents schemes of conduction and brief description of the methods for processing a series of tests, which were performed in RFNC-VNIIEF with use of radio interferometer having length of wave of probing radiation λ = 3.2 mm, namely: to measure velocity of stationary detonation; to measure depth of detonation initiation by shock wave; to investigate shock compressibility of dielectric materials; to investigate dynamics of constructions.
An efficient higher-order PML in WLP-FDTD method for time reversed wave simulation
Wei, Xiao-Kun; Shao, Wei; Ou, Haiyan; Wang, Bing-Zhong
2016-09-01
Derived from a stretched coordinate formulation, a higher-order complex frequency shifted (CFS) perfectly matched layer (PML) is proposed for the unconditionally stable finite-difference time-domain (FDTD) method based on weighted Laguerre polynomials (WLPs). The higher-order PML is implemented with an auxiliary differential equation (ADE) approach. In order to further improve absorbing performance, the parameter values of stretching functions in the higher-order PML are optimized by the multi-objective genetic algorithm (MOGA). The optimal solutions can be chosen from the Pareto front for trading-off between two independent objectives. It is shown in a numerical test that the higher-order PML is efficient in terms of attenuating propagating waves and reducing late time reflections. Moreover, the higher-order PML can be placed very close to the wall when analyzing the channel characteristics of time reversal (TR) waves in a multipath indoor environment. Numerical examples of TR wave propagation demonstrate the availability of the proposed method.
Goncharsky, Alexander V.; Romanov, Sergey Y.
2017-02-01
We develop efficient iterative methods for solving inverse problems of wave tomography in models incorporating both diffraction effects and attenuation. In the inverse problem the aim is to reconstruct the velocity structure and the function that characterizes the distribution of attenuation properties in the object studied. We prove mathematically and rigorously the differentiability of the residual functional in normed spaces, and derive the corresponding formula for the Fréchet derivative. The computation of the Fréchet derivative includes solving both the direct problem with the Neumann boundary condition and the reversed-time conjugate problem. We develop efficient methods for numerical computations where the approximate solution is found using the detector measurements of the wave field and its normal derivative. The wave field derivative values at detector locations are found by solving the exterior boundary value problem with the Dirichlet boundary conditions. We illustrate the efficiency of this approach by applying it to model problems. The algorithms developed are highly parallelizable and designed to be run on supercomputers. Among the most promising medical applications of our results is the development of ultrasonic tomographs for differential diagnosis of breast cancer.
Sugimoto, Tsuneyoshi; Sugimoto, Kazuko; Kosuge, Nobuaki; Utagawa, Noriyuki; Katakura, Kageyoshi
2017-07-01
The noncontact acoustic inspection method focuses on the resonance phenomenon, and the target surface is measured by being vibrated with an airborne sound. It is possible to detect internal defects near the surface layer of a concrete structure from a long distance. However, it requires a fairly long measurement time to achieve the signal-to-noise (S/N) ratio just to find some resonance frequencies. In our method using the conventional waveform “single-tone burst wave”, only one frequency was used for one-sound-wave emission to achieve a high S/N ratio using a laser Doppler vibrometer (LDV) at a safe low power (e.g., He-Ne 1 mW). On the other hand, in terms of the difference in propagation velocity between laser light and sound waves, the waveform that can be used for high-speed measurement was devised using plural frequencies for one-sound-wave emission (“multitone burst wave”). The measurement time at 35 measurement points has been dramatically decreased from 210 to 28 s when using this waveform. Accordingly, 7.5-fold high-speed measurement became possible. By some demonstration experiments, we confirmed the effectiveness of our measurement technique.
Radiation from a D-dimensional collision of shock waves: numerical methods
Sampaio, Marco O P
2013-01-01
We present a pedagogical introduction to the problem of evolving a head on collision of two Aichelburg-Sexl gravitational shock waves in D-dimensions, using perturbative techniques. We follow a constructive approach with examples, going in some detail through: the set up of the exact initial conditions and their properties; perturbative methods in flat space-time with Green function solutions; and numerical strategies to evaluate the integral solutions. We also discuss, briefly, radiation extraction methods adapted to this problem, together with some of the results for this system.
Extension of standard transfer-matrix method for three-wave mixing for plasmonic structures
Loot, A.; Hizhnyakov, V.
2017-03-01
Fast and accurate modeling of three-wave mixing processes in arbitrary stratified medium has significant practical and scientific importance. Several attempts to generalize transfer-matrix method (TMM) for nonlinear interactions have been made; however, none suits for easy-to-use modeling of plasmonic structures which requires oblique angle of incidence, p-polarization and minimal approximations. In this work, an easy-to-use extension to standard TMM is proposed. The proposed method is used to study the strength of unconventional plasmonic enhancement of second harmonic generation.
Griffiths, Graham
2010-01-01
Although the Partial Differential Equations (PDE) models that are now studied are usually beyond traditional mathematical analysis, the numerical methods that are being developed and used require testing and validation. This is often done with PDEs that have known, exact, analytical solutions. The development of analytical solutions is also an active area of research, with many advances being reported recently, particularly traveling wave solutions for nonlinear evolutionary PDEs. Thus, the current development of analytical solutions directly supports the development of numerical methods by p
Liu, Yu; Yu, Xiping
2016-09-01
A coupled phase-field and volume-of-fluid method is developed to study the sensitive behavior of water waves during breaking. The THINC model is employed to solve the volume-of-fluid function over the entire domain covered by a relatively coarse grid while the phase-field model based on Allen-Cahn equation is applied over the fine grid. A special algorithm that takes into account the sharpness of the diffuse-interface is introduced to correlate the order parameter obtained on the fine grid and the volume-of-fluid function obtained on the coarse grid. The coupled model is then applied to the study of water waves generated by moving pressures on the free surface. The deformation process of the wave crest during the initial stage of breaking is discussed in details. It is shown that there is a significant variation of the free nappe developed at the front side of the wave crest as the wave steepness differs. It is of a plunging type at large wave steepness while of a spilling type at small wave steepness. The numerical results also indicate that breaking occurs later and the duration of breaking is shorter for waves of smaller steepness and vice versa. Neglecting the capillary effect leads to wave breaking with a sharper nappe and a more dynamic plunging process. The surface tension also has an effect to prevent the formation of a free nappe at the front side of the wave crest in some cases.
Kishoni, Doron; Taasan, Shlomo
1994-01-01
Solution of the wave equation using techniques such as finite difference or finite element methods can model elastic wave propagation in solids. This requires mapping the physical geometry into a computational domain whose size is governed by the size of the physical domain of interest and by the required resolution. This computational domain, in turn, dictates the computer memory requirements as well as the calculation time. Quite often, the physical region of interest is only a part of the whole physical body, and does not necessarily include all the physical boundaries. Reduction of the calculation domain requires positioning an artificial boundary or region where a physical boundary does not exist. It is important however that such a boundary, or region, will not affect the internal domain, i.e., it should not cause reflections that propagate back into the material. This paper concentrates on the issue of constructing such a boundary region.
Low-dispersion finite difference methods for acoustic waves in a pipe
Davis, Sanford
1991-01-01
A new algorithm for computing one-dimensional acoustic waves in a pipe is demonstrated by solving the acoustic equations as an initial-boundary-value problem. Conventional dissipation-free second-order finite difference methods suffer severe phase distortion for grids with less that about ten mesh points per wavelength. Using the signal generation by a piston in a duct as an example, transient acoustic computations are presented using a new compact three-point algorithm which allows about 60 percent fewer mesh points per wavelength. Both pulse and harmonic excitation are considered. Coupling of the acoustic signal with the pipe resonant modes is shown to generate a complex transient wave with rich harmonic content.
A goal-oriented reduced basis method for the wave equation in inverse analysis
Hoang, Khac Chi; Bordas, Stephane P A
2013-01-01
In this paper, we extend the reduced-basis methods developed earlier for wave equations to goal-oriented wave equations with affine parameter dependence. The essential new ingredient is the dual (or adjoint) problem and the use of its solution in a sampling procedure to pick up "goal-orientedly" parameter samples. First, we introduce the reduced-basis recipe --- Galerkin projection onto a space $Y_N$ spanned by the reduced basis functions which are constructed from the solutions of the governing partial differential equation at several selected points in parameter space. Second, we propose a new "goal-oriented" Proper Orthogonal Decomposition (POD)--Greedy sampling procedure to construct these associated basis functions. Third, based on the assumption of affine parameter dependence, we use the offline-online computational procedures developed earlier to split the computational procedure into offline and online stages. We verify the proposed computational procedure by applying it to a three-dimensional simulat...
Exact solution to the Coulomb wave using the linearized phase-amplitude method
Directory of Open Access Journals (Sweden)
Shuji Kiyokawa
2015-08-01
Full Text Available The author shows that the amplitude equation from the phase-amplitude method of calculating continuum wave functions can be linearized into a 3rd-order differential equation. Using this linearized equation, in the case of the Coulomb potential, the author also shows that the amplitude function has an analytically exact solution represented by means of an irregular confluent hypergeometric function. Furthermore, it is shown that the exact solution for the Coulomb potential reproduces the wave function for free space expressed by the spherical Bessel function. The amplitude equation for the large component of the Dirac spinor is also shown to be the linearized 3rd-order differential equation.
An efficient algorithm for time propagation as applied to linearized augmented plane wave method
Dewhurst, J. K.; Krieger, K.; Sharma, S.; Gross, E. K. U.
2016-12-01
An algorithm for time propagation of the time-dependent Kohn-Sham equations is presented. The algorithm is based on dividing the Hamiltonian into small time steps and assuming that it is constant over these steps. This allows for the time-propagating Kohn-Sham wave function to be expanded in the instantaneous eigenstates of the Hamiltonian. The method is particularly efficient for basis sets which allow for a full diagonalization of the Hamiltonian matrix. One such basis is the linearized augmented plane waves. In this case we find it is sufficient to perform the evolution as a second-variational step alone, so long as sufficient number of first variational states are used. The algorithm is tested not just for non-magnetic but also for fully non-collinear magnetic systems. We show that even for delicate properties, like the magnetization density, fairly large time-step sizes can be used demonstrating the stability and efficiency of the algorithm.
Partially implicit Runge-Kutta methods for wave-like equations in spherical-type coordinates
Cordero-Carrión, Isabel
2012-01-01
Partially implicit Runge-Kutta methods are presented in this work in order to numerically evolve in time a set of partial differential equations. These methods are designed to overcome numerical instabilities appearing during the evolution of a system of equations due to potential numerical unstable terms in the sources, such as stiff terms or the presence of factors as a result of a particular chosen system of coordinates. In this article, partially implicit Runge-Kutta methods for several convergence orders have been derived and stability properties have been analyzed. These methods are shown to be appropriated to avoid the development of numerical instabilities in the evolution in time of wave-like equations in spherical-type coordinates, in contrast to the explicit Runge-Kutta methods.
A new numerical method for shock wave propagation based on geometrical shock dynamics
Schwendeman, D. W.
1993-05-01
In this paper, a new numerical method for calculating the motion of shock waves in two and three dimensions is presented. The numerical method is based on Whitham's theory of geometrical shock dynamics, which is an approximate theory that determines the motion of the leading shockfront explicitly. The numerical method uses a conservative finite difference discretization of the equations of geometrical shock dynamics. These equations are similar to those for steady supersonic potential flow, and thus the numerical method developed here is similar to ones developed for that context. Numerical results are presented for shock propagation in channels and for converging cylindrical and spherical shocks. The channel problem is used in part to compare this new numerical method with ones developed earlier. Converging cylindrical and spherical shocks arc calculated to analyze their stability.
Institute of Scientific and Technical Information of China (English)
SONG Li-Na; ZHANG Hong-Qing
2007-01-01
In this work, by means of a generalized method and symbolic computation, we extend the Jacobi elliptic function rational expansion method to uniformly construct a series of stochastic wave solutions for stochastic evolution equations. To illustrate the effectiveness of our method, we take the (2+1)-dimensional stochastic dispersive long wave system as an example. We not only have obtained some known solutions, but also have constructed some new rational formal stochastic Jacobi elliptic function solutions.
Spectral element method for elastic and acoustic waves in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Shi, Linlin; Zhou, Yuanguo; Wang, Jia-Min; Zhuang, Mingwei [Institute of Electromagnetics and Acoustics, and Department of Electronic Science, Xiamen, 361005 (China); Liu, Na, E-mail: liuna@xmu.edu.cn [Institute of Electromagnetics and Acoustics, and Department of Electronic Science, Xiamen, 361005 (China); Liu, Qing Huo, E-mail: qhliu@duke.edu [Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708 (United States)
2016-12-15
Numerical techniques in time domain are widespread in seismic and acoustic modeling. In some applications, however, frequency-domain techniques can be advantageous over the time-domain approach when narrow band results are desired, especially if multiple sources can be handled more conveniently in the frequency domain. Moreover, the medium attenuation effects can be more accurately and conveniently modeled in the frequency domain. In this paper, we present a spectral-element method (SEM) in frequency domain to simulate elastic and acoustic waves in anisotropic, heterogeneous, and lossy media. The SEM is based upon the finite-element framework and has exponential convergence because of the use of GLL basis functions. The anisotropic perfectly matched layer is employed to truncate the boundary for unbounded problems. Compared with the conventional finite-element method, the number of unknowns in the SEM is significantly reduced, and higher order accuracy is obtained due to its spectral accuracy. To account for the acoustic-solid interaction, the domain decomposition method (DDM) based upon the discontinuous Galerkin spectral-element method is proposed. Numerical experiments show the proposed method can be an efficient alternative for accurate calculation of elastic and acoustic waves in frequency domain.
Spectral element method for elastic and acoustic waves in frequency domain
Shi, Linlin; Zhou, Yuanguo; Wang, Jia-Min; Zhuang, Mingwei; Liu, Na; Liu, Qing Huo
2016-12-01
Numerical techniques in time domain are widespread in seismic and acoustic modeling. In some applications, however, frequency-domain techniques can be advantageous over the time-domain approach when narrow band results are desired, especially if multiple sources can be handled more conveniently in the frequency domain. Moreover, the medium attenuation effects can be more accurately and conveniently modeled in the frequency domain. In this paper, we present a spectral-element method (SEM) in frequency domain to simulate elastic and acoustic waves in anisotropic, heterogeneous, and lossy media. The SEM is based upon the finite-element framework and has exponential convergence because of the use of GLL basis functions. The anisotropic perfectly matched layer is employed to truncate the boundary for unbounded problems. Compared with the conventional finite-element method, the number of unknowns in the SEM is significantly reduced, and higher order accuracy is obtained due to its spectral accuracy. To account for the acoustic-solid interaction, the domain decomposition method (DDM) based upon the discontinuous Galerkin spectral-element method is proposed. Numerical experiments show the proposed method can be an efficient alternative for accurate calculation of elastic and acoustic waves in frequency domain.
Rawles, Christopher; Thurber, Clifford
2015-08-01
We present a simple, fast, and robust method for automatic detection of P- and S-wave arrivals using a nearest neighbours-based approach. The nearest neighbour algorithm is one of the most popular time-series classification methods in the data mining community and has been applied to time-series problems in many different domains. Specifically, our method is based on the non-parametric time-series classification method developed by Nikolov. Instead of building a model by estimating parameters from the data, the method uses the data itself to define the model. Potential phase arrivals are identified based on their similarity to a set of reference data consisting of positive and negative sets, where the positive set contains examples of analyst identified P- or S-wave onsets and the negative set contains examples that do not contain P waves or S waves. Similarity is defined as the square of the Euclidean distance between vectors representing the scaled absolute values of the amplitudes of the observed signal and a given reference example in time windows of the same length. For both P waves and S waves, a single pass is done through the bandpassed data, producing a score function defined as the ratio of the sum of similarity to positive examples over the sum of similarity to negative examples for each window. A phase arrival is chosen as the centre position of the window that maximizes the score function. The method is tested on two local earthquake data sets, consisting of 98 known events from the Parkfield region in central California and 32 known events from the Alpine Fault region on the South Island of New Zealand. For P-wave picks, using a reference set containing two picks from the Parkfield data set, 98 per cent of Parkfield and 94 per cent of Alpine Fault picks are determined within 0.1 s of the analyst pick. For S-wave picks, 94 per cent and 91 per cent of picks are determined within 0.2 s of the analyst picks for the Parkfield and Alpine Fault data set
Institute of Scientific and Technical Information of China (English)
HE Ying; HAN Bo
2008-01-01
In this paper,we consider numerical simulation of wave propagation in fluidsaturated porous media.A wavelet finite-difference method is proposed to solve the 2-D elastic wave equation.The algorithm combines flexibility and computational efficiency of wavelet multi-resolution method with easy implementation of the finite-difference method.The orthogonal wavelet basis provides a natural framework,which adapt spatial grids to local wavefield properties.Numerical results show usefulness of the approach as an accurate and stable tool for simulation of wave propagation in fluid-saturated porous media.
Delta hedging strategies comparison
DEFF Research Database (Denmark)
De Giovanni, Domenico; Ortobelli, S.; Rachev, S.T.
2008-01-01
In this paper we implement dynamic delta hedging strategies based on several option pricing models. We analyze different subordinated option pricing models and we examine delta hedging costs using ex-post daily prices of S&P 500. Furthermore, we compare the performance of each subordinated model ...
Yin, Yixing; Chen, Haishan; Xu, Chong-Yu; Xu, Wucheng; Chen, Changchun; Sun, Shanlei
2016-05-01
The regionalization methods, which "trade space for time" by pooling information from different locations in the frequency analysis, are efficient tools to enhance the reliability of extreme quantile estimates. This paper aims at improving the understanding of the regional frequency of extreme precipitation by using regionalization methods, and providing scientific background and practical assistance in formulating the regional development strategies for water resources management in one of the most developed and flood-prone regions in China, the Yangtze River Delta (YRD) region. To achieve the main goals, L-moment-based index-flood (LMIF) method, one of the most popular regionalization methods, is used in the regional frequency analysis of extreme precipitation with special attention paid to inter-site dependence and its influence on the accuracy of quantile estimates, which has not been considered by most of the studies using LMIF method. Extensive data screening of stationarity, serial dependence, and inter-site dependence was carried out first. The entire YRD region was then categorized into four homogeneous regions through cluster analysis and homogenous analysis. Based on goodness-of-fit statistic and L-moment ratio diagrams, generalized extreme-value (GEV) and generalized normal (GNO) distributions were identified as the best fitted distributions for most of the sub-regions, and estimated quantiles for each region were obtained. Monte Carlo simulation was used to evaluate the accuracy of the quantile estimates taking inter-site dependence into consideration. The results showed that the root-mean-square errors (RMSEs) were bigger and the 90 % error bounds were wider with inter-site dependence than those without inter-site dependence for both the regional growth curve and quantile curve. The spatial patterns of extreme precipitation with a return period of 100 years were finally obtained which indicated that there are two regions with highest precipitation
A Novel Complementary Method for the Point-Scan Nondestructive Tests Based on Lamb Waves
Directory of Open Access Journals (Sweden)
Rahim Gorgin
2014-01-01
Full Text Available This study presents a novel area-scan damage identification method based on Lamb waves which can be used as a complementary method for point-scan nondestructive techniques. The proposed technique is able to identify the most probable locations of damages prior to point-scan test which lead to decreasing the time and cost of inspection. The test-piece surface was partitioned with some smaller areas and the damage probability presence of each area was evaluated. A0 mode of Lamb wave was generated and collected using a mobile handmade transducer set at each area. Subsequently, a damage presence probability index (DPPI based on the energy of captured responses was defined for each area. The area with the highest DPPI value highlights the most probable locations of damages in test-piece. Point-scan nondestructive methods can then be used once these areas are found to identify the damage in detail. The approach was validated by predicting the most probable locations of representative damages including through-thickness hole and crack in aluminum plates. The obtained experimental results demonstrated the high potential of developed method in defining the most probable locations of damages in structures.
FGG-NUFFT-Based Method for Near-Field 3-D Imaging Using Millimeter Waves.
Kan, Yingzhi; Zhu, Yongfeng; Tang, Liang; Fu, Qiang; Pei, Hucheng
2016-09-19
In this paper, to deal with the concealed target detection problem, an accurate and efficient algorithm for near-field millimeter wave three-dimensional (3-D) imaging is proposed that uses a two-dimensional (2-D) plane antenna array. First, a two-dimensional fast Fourier transform (FFT) is performed on the scattered data along the antenna array plane. Then, a phase shift is performed to compensate for the spherical wave effect. Finally, fast Gaussian gridding based nonuniform FFT (FGG-NUFFT) combined with 2-D inverse FFT (IFFT) is performed on the nonuniform 3-D spatial spectrum in the frequency wavenumber domain to achieve 3-D imaging. The conventional method for near-field 3-D imaging uses Stolt interpolation to obtain uniform spatial spectrum samples and performs 3-D IFFT to reconstruct a 3-D image. Compared with the conventional method, our FGG-NUFFT based method is comparable in both efficiency and accuracy in the full sampled case and can obtain more accurate images with less clutter and fewer noisy artifacts in the down-sampled case, which are good properties for practical applications. Both simulation and experimental results demonstrate that the FGG-NUFFT-based near-field 3-D imaging algorithm can have better imaging performance than the conventional method for down-sampled measurements.
FGG-NUFFT-Based Method for Near-Field 3-D Imaging Using Millimeter Waves
Directory of Open Access Journals (Sweden)
Yingzhi Kan
2016-09-01
Full Text Available In this paper, to deal with the concealed target detection problem, an accurate and efficient algorithm for near-field millimeter wave three-dimensional (3-D imaging is proposed that uses a two-dimensional (2-D plane antenna array. First, a two-dimensional fast Fourier transform (FFT is performed on the scattered data along the antenna array plane. Then, a phase shift is performed to compensate for the spherical wave effect. Finally, fast Gaussian gridding based nonuniform FFT (FGG-NUFFT combined with 2-D inverse FFT (IFFT is performed on the nonuniform 3-D spatial spectrum in the frequency wavenumber domain to achieve 3-D imaging. The conventional method for near-field 3-D imaging uses Stolt interpolation to obtain uniform spatial spectrum samples and performs 3-D IFFT to reconstruct a 3-D image. Compared with the conventional method, our FGG-NUFFT based method is comparable in both efficiency and accuracy in the full sampled case and can obtain more accurate images with less clutter and fewer noisy artifacts in the down-sampled case, which are good properties for practical applications. Both simulation and experimental results demonstrate that the FGG-NUFFT-based near-field 3-D imaging algorithm can have better imaging performance than the conventional method for down-sampled measurements.
A generalized multiscale finite element method for elastic wave propagation in fractured media
Chung, Eric T.
2016-02-26
In this paper, we consider elastic wave propagation in fractured media applying a linear-slip model to represent the effects of fractures on the wavefield. Fractured media, typically, are highly heterogeneous due to multiple length scales. Direct numerical simulations for wave propagation in highly heterogeneous fractured media can be computationally expensive and require some type of model reduction. We develop a multiscale model reduction technique that captures the complex nature of the media (heterogeneities and fractures) in the coarse scale system. The proposed method is based on the generalized multiscale finite element method, where the multiscale basis functions are constructed to capture the fine-scale information of the heterogeneous, fractured media and effectively reduce the degrees of freedom. These multiscale basis functions are coupled via the interior penalty discontinuous Galerkin method, which provides a block-diagonal mass matrix. The latter is needed for fast computation in an explicit time discretization, which is used in our simulations. Numerical results are presented to show the performance of the presented multiscale method for fractured media. We consider several cases where fractured media contain fractures of multiple lengths. Our numerical results show that the proposed reduced-order models can provide accurate approximations for the fine-scale solution.
Kingan, Michael J.; Yang, Yi; Mace, Brian R.
2016-09-01
This paper concerns the prediction of sound transmission through a cylindrical structure. The problem considered is that of sound generated by a line source located exterior to a two-dimensional circular cylinder which produces sound waves which transmit through the cylinder to an internal medium. An analytical solution is presented for the case of sound transmission through a thin cylindrical shell, by modelling the shell response using the Flugge- Byrne-Lur'ye equations. This solution is then compared to calculations where the response of the cylinder is calculated using the Wave and Finite Element (WFE) method. The WFE method involves modelling a small segment of a structure using traditional finite element (FE) methods. The mass and stiffness matrices of the segment are then used to calculate the response of the structure to excitation by an acoustic field. The WFE approach for calculating sound transmission is validated by comparison with the analytic solution. Formulating analytic solutions for more complicated structures can be cumbersome whereas using a numerical technique, such as the WFE method, is relatively straightforward.
Newmark-Beta-FDTD method for super-resolution analysis of time reversal waves
Shi, Sheng-Bing; Shao, Wei; Ma, Jing; Jin, Congjun; Wang, Xiao-Hua
2017-09-01
In this work, a new unconditionally stable finite-difference time-domain (FDTD) method with the split-field perfectly matched layer (PML) is proposed for the analysis of time reversal (TR) waves. The proposed method is very suitable for multiscale problems involving microstructures. The spatial and temporal derivatives in this method are discretized by the central difference technique and Newmark-Beta algorithm, respectively, and the derivation results in the calculation of a banded-sparse matrix equation. Since the coefficient matrix keeps unchanged during the whole simulation process, the lower-upper (LU) decomposition of the matrix needs to be performed only once at the beginning of the calculation. Moreover, the reverse Cuthill-Mckee (RCM) technique, an effective preprocessing technique in bandwidth compression of sparse matrices, is used to improve computational efficiency. The super-resolution focusing of TR wave propagation in two- and three-dimensional spaces is included to validate the accuracy and efficiency of the proposed method.
Three-Dimensional Transient Electromagnetic Modeling Based on Fictitious Wave Domain Methods
Ji, Yanju; Hu, Yanpu; Imamura, Naoto
2017-05-01
Finite-difference time domain (FDTD) methods, which have been widely employed in three-dimensional transient electromagnetic (TEM) modeling, require very small time steps to simulate the electromagnetic fields and this will be time consuming. We present an efficient numerical method for three-dimensional TEM forward modeling. Its key features are based on a correspondence principle between the diffusive and fictitious wave fields. The diffusive Maxwell's equations are transformed and solved in a so-called fictitious wave domain. This scheme allows larger time steps than conventional FDTD methods, allows including air layers, and allows simulating topography. The need for initial field calculations is avoided by including an electric current source in the governing equations. This also avoids a traditional assumption of a flat earth surface in TEM modeling. We test the accuracy of the electromagnetic fields' responses using our method with the spectral differential difference (SLDM) solutions. The results show good agreement even under the existence of air layers and topography in the model.
Novel method for incorporating model uncertainties into gravitational wave parameter estimates.
Moore, Christopher J; Gair, Jonathan R
2014-12-19
Posterior distributions on parameters computed from experimental data using Bayesian techniques are only as accurate as the models used to construct them. In many applications, these models are incomplete, which both reduces the prospects of detection and leads to a systematic error in the parameter estimates. In the analysis of data from gravitational wave detectors, for example, accurate waveform templates can be computed using numerical methods, but the prohibitive cost of these simulations means this can only be done for a small handful of parameters. In this Letter, a novel method to fold model uncertainties into data analysis is proposed; the waveform uncertainty is analytically marginalized over using with a prior distribution constructed by using Gaussian process regression to interpolate the waveform difference from a small training set of accurate templates. The method is well motivated, easy to implement, and no more computationally expensive than standard techniques. The new method is shown to perform extremely well when applied to a toy problem. While we use the application to gravitational wave data analysis to motivate and illustrate the technique, it can be applied in any context where model uncertainties exist.
Institute of Scientific and Technical Information of China (English)
Chang-Jun Zheng; Hai-Bo Chen; Lei-Lei Chen
2013-01-01
This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/planesymmetric acoustic wave problems.The half-space fundamental solution is employed in the boundary integral equations so that the tree structure required in the fast multipole algorithm is constructed for the boundary elements in the real domain only.Moreover,a set of symmetric relations between the multipole expansion coefficients of the real and image domains are derived,and the half-space fundamental solution is modified for the purpose of applying such relations to avoid calculating,translating and saving the multipole/local expansion coefficients of the image domain.The wideband adaptive multilevel fast multipole algorithm associated with the iterative solver GMRES is employed so that the present method is accurate and efficient for both lowand high-frequency acoustic wave problems.As for exterior acoustic problems,the Burton-Miller method is adopted to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method.Details on the implementation of the present method are described,and numerical examples are given to demonstrate its accuracy and efficiency.
Abboud, Toufic; Joly, Patrick; Rodríguez, Jerónimo; Terrasse, Isabelle
2011-07-01
This work deals with the numerical simulation of wave propagation on unbounded domains with localized heterogeneities. To do so, we propose to combine a discretization based on a discontinuous Galerkin method in space and explicit finite differences in time on the regions containing heterogeneities with the retarded potential method to account the unbounded nature of the computational domain. The coupling formula enforces a discrete energy identity ensuring the stability under the usual CFL condition in the interior. Moreover, the scheme allows to use a smaller time step in the interior domain yielding to quasi-optimal discretization parameters for both methods. The aliasing phenomena introduced by the local time stepping are reduced by a post-processing by averaging in time obtaining a stable and second order consistent (in time) coupling algorithm. We compute the numerical rate of convergence of the method for an academic problem. The numerical results show the feasibility of the whole discretization procedure.