Radio wave propagation and parabolic equation modeling
Apaydin, Gokhan
2018-01-01
A thorough understanding of electromagnetic wave propagation is fundamental to the development of sophisticated communication and detection technologies. The powerful numerical methods described in this book represent a major step forward in our ability to accurately model electromagnetic wave propagation in order to establish and maintain reliable communication links, to detect targets in radar systems, and to maintain robust mobile phone and broadcasting networks. The first new book on guided wave propagation modeling and simulation to appear in nearly two decades, Radio Wave Propagation and Parabolic Equation Modeling addresses the fundamentals of electromagnetic wave propagation generally, with a specific focus on radio wave propagation through various media. The authors explore an array of new applications, and detail various v rtual electromagnetic tools for solving several frequent electromagnetic propagation problems. All of the methods described are presented within the context of real-world scenari...
Modeling acoustic wave propagation in isotropic medium
Krasnoveikin, V. A.; Druzhinin, N. V.; Derusova, D. A.; Tarasov, S. Yu.
2017-12-01
The paper carries out the graphical analysis of acoustic wave propagation in plates of different thickness to reveal the surface wave patterns formed on the plate surfaces. The results of the analysis allowed explaining the non-uniform distribution of the surface wave pattern nodes formed on the PMMA plate by a point oscillator. The wave pattern reconstruction made it possible to reveal fundamental and reflected waves as well as their interference patterns with node distributions on the surfaces of the plate. These results may be useful for defect detection in composite materials such as delamination, impact damage, gaps, etc.
Modeling and Simulation of Ultrasound Wave Propagation
Isler, Sylvia Kay
The specific aim of this work is to model diagnostic ultrasound under strong acoustic scattering conditions. This work is divided into three main sub-topics. The first concerns the solution of the Helmholtz integral equation in three-dimensions. The Pade approximant method for accelerating the convergence of the Neumann series, first proposed by Chandra and Thompson for two-dimensional acoustic scattering problems, is extended to three-dimensions. Secondly, the propagation of acoustic pulses through a medium that is characterized by spatial variations in compressibility is considered. The medium is excited using an ideal, bandlimited acoustic transducer having a Gaussian radiation profile. The time response is determined by using a spatial Fourier wavenumber decomposition of the incident and scattered pressure fields. Using the Pade approximant method, the pressure is evaluated for each wavenumber at each spatial grid location. By taking the inverse Fourier transform of the result, the temporal and spatial evolution of the pressure field is obtained. The third part examines acoustic wave propagation in simulated soft tissue. Methods for generating spatially correlated random media are discussed and applied to simulating the structure of soft tissue. Simulated sonograms are constructed and the effects of strong scattering are considered.
Electromagnetic Wave Propagation Models for Multiple-Diffraction Scenarios
Directory of Open Access Journals (Sweden)
Mehmet Barış TABAKCIOĞLU
2014-04-01
Full Text Available Electromagnetic wave propagation models have been used for coverage estimation and field prediction at the receiver to make more reliable and efficient digital broadcasting systems. Propagation models can be classified into two groups as numerical and ray tracing based models. There is a tradeoff between computation time and accuracy of field prediction among electromagnetic wave propagation models. Although numerical models predict accurately, it requires more computation times. Ray tracing based models predicts the field strength less accurately with lower computation time. Many propagation models have been developed to provide optimum solution for accuracy and computation time
Models for seismic wave propagation in periodically layered porous media
Kudarova, A.; Van Dalen, K.N.; Drijkoningen, G.G.
2014-01-01
Several models are discussed for seismic wave propagation in periodically layered poroelastic media where layers represent mesoscopic-scale heterogeneities that are larger than the pore and grain sizes but smaller than the wavelength. The layers behave according to Biot’s theory. Wave propagation
Nijhof, M.J.J.
2010-01-01
In this work, the accuracy, efficiency and range of applicability of various (approximate) models for viscothermal wave propagation are investigated. Models for viscothermal wave propagation describe thewave behavior of fluids including viscous and thermal effects. Cases where viscothermal effects
Millimeter Wave Radio Frequency Propagation Model Development
2014-08-28
Anechoic Chamber .................................. 47 3.4.1 10 GHz Transmitting System...Propagation Losses ............................................................. 67 4.2 Experiment 2 - Quantifying Model Accuracy in an Anechoic Chamber ...44 Figure 20. Actual Footage of the Experiment at 10, 20, 30, and 40 GHz within the Anechoic Chamber
Modelling Acoustic Wave Propagation in Axisymmetric Varying-Radius Waveguides
DEFF Research Database (Denmark)
Bæk, David; Willatzen, Morten
2008-01-01
A computationally fast and accurate model (a set of coupled ordinary differential equations) for fluid sound-wave propagation in infinite axisymmetric waveguides of varying radius is proposed. The model accounts for fluid heat conduction and fluid irrotational viscosity. The model problem is solved...
Boussinesq Modeling of Wave Propagation and Runup over Fringing Coral Reefs, Model Evaluation Report
National Research Council Canada - National Science Library
Demirbilek, Zeki; Nwogu, Okey G
2007-01-01
..., for waves propagating over fringing reefs. The model evaluation had two goals: (a) investigate differences between laboratory and field characteristics of wave transformation processes over reefs, and (b...
A local-ether model of propagation of electromagnetic wave
Energy Technology Data Exchange (ETDEWEB)
Su, C.C. [Dept. of Electrical Engineering, National Tsinghua University, Hsinchu (Taiwan)
2001-07-01
It is pointed out that the classical propagation model can be in accord with the Sagnac effect due to earth's rotational and orbital motions in the high-precision GPS (global positioning system) and interplanetary radar, if the reference frame of the classical propagation medium is endowed with a switchability according to the location of the wave. Accordingly, it is postulated that, as in the obsolete theory, electromagnetic waves propagate via a medium like the ether. However, the ether is not universal. It is proposed that in the region under sufficient influence of the gravity due to the earth, the sun, or another celestial body, there forms a local ether, which in turn is stationary with respect to the gravitational potential of the respective body. For earthbound and interplanetary propagation, the medium is stationary in a geocentric and a heliocentric inertial frame, respectively. An electromagnetic wave propagates at a constant speed with respect to the associated local ether, independent of the motions of source and receiver. Based on this local-ether model of wave propagation, a wide variety of earthbound, interplanetary, and interstellar propagation phenomena are accounted for. Strong evidence of this new classical model is its consistent account of the Sagnac effect due to earth's motions among GPS, the intercontinental microwave link, and the interplanetary radar. Moreover, as examined within the present precision, this model is still in accord with the Michelson-Morley experiment. To test the local-ether propagation model, a one-way-link rotor experiment is proposed. (orig.)
Ferrarese, Giorgio
2011-01-01
Lectures: A. Jeffrey: Lectures on nonlinear wave propagation.- Y. Choquet-Bruhat: Ondes asymptotiques.- G. Boillat: Urti.- Seminars: D. Graffi: Sulla teoria dell'ottica non-lineare.- G. Grioli: Sulla propagazione del calore nei mezzi continui.- T. Manacorda: Onde nei solidi con vincoli interni.- T. Ruggeri: "Entropy principle" and main field for a non linear covariant system.- B. Straughan: Singular surfaces in dipolar materials and possible consequences for continuum mechanics
On modeling internal gravity wave dynamics from infrasound propagation
Ribstein, Bruno; Millet, Christophe; Lott, Francois
2017-04-01
Low frequency acoustic waves (infrasounds) are generally used to remotely detect strong explosions, using their possibility of long-distance and coherent propagation. Numerical prediction of infrasounds is a complex issue due to constantly changing atmospheric conditions and to the random nature of small-scale flows. Although it is well-known that part of the upward propagating wave is refracted at stratospheric levels, where gravity waves significantly affect both the temperature and the wind, yet the process by which the gravity wave field changes some infrasound arrivals remains not well understood. In the present work, we use a stochastic parameterization to model the subgrid scale gravity wave field from atmospheric states provided by ECMWF. Numerical evidence are presented showing that regardless of whether the superimposed gravity wave field possesses relatively small or large features the sensitivity of ground-based infrasound signals can be significantly different. A version of the gravity wave parameterization previously tuned by co-authors for climate modeling purpose is shown to not retrieve the duration of recorded acoustic signals. A new version of the wave-parameterization is here proposed which more accurately predict the small scale content of gravity wave fields, especially in the middle atmosphere. Compare to other semi-empirical approaches one value of this new parameterization is that the gravity wave drag obtained is in agreement with observations.
TWO-DIMENSIONAL MODELLING OF ACCIDENTAL FLOOD WAVES PROPAGATION
Directory of Open Access Journals (Sweden)
Lorand Catalin STOENESCU
2011-05-01
Full Text Available The study presented in this article describes a modern modeling methodology of the propagation of accidental flood waves in case a dam break; this methodology is applied in Romania for the first time for the pilot project „Breaking scenarios of Poiana Uzului dam”. The calculation programs used help us obtain a bidimensional calculation (2D of the propagation of flood waves, taking into consideration the diminishing of the flood wave on a normal direction to the main direction; this diminishing of the flood wave is important in the case of sinuous courses of water or with urban settlements very close to the minor river bed. In the case of Poiana Uzului dam, 2 scenarios were simulated with the help of Ph.D. Eng. Dan Stematiu, plausible scenarios but with very little chances of actually producing. The results were presented as animations with flooded surfaces at certain time steps successively.
Equivalent Continuum Modeling for Shock Wave Propagation in Jointed Media
Energy Technology Data Exchange (ETDEWEB)
Vorobiev, O; Antoun, T
2009-12-11
This study presents discrete and continuum simulations of shock wave propagating through jointed media. The simulations were performed using the Lagrangian hydrocode GEODYN-L with joints treated explicitly using an advanced contact algorithm. They studied both isotropic and anisotropic joint representations. For an isotropically jointed geologic medium, the results show that the properties of the joints can be combined with the properties of the intact rock to develop an equivalent continuum model suitable for analyzing wave propagation through the jointed medium. For an anisotropically jointed geologic medium, they found it difficult to develop an equivalent continuum (EC) model that matches the response derived from mesoscopic simulation. They also performed simulations of wave propagation through jointed media. Two appraoches are suggested for modeling the rock mass. In one approach, jointed are modeled explicitly in a Lagrangian framework with appropriate contact algorithms used to track motion along the interfaces. In the other approach, the effect of joints is taken into account using a constitutive model derived from mesoscopic simulations.
Modeling anomalous surface - wave propagation across the Southern Caspian basin
Energy Technology Data Exchange (ETDEWEB)
Priestly, K.F.; Patton, H.J.; Schultz, C.A.
1998-01-09
The crust of the south Caspian basin consists of 15-25 km of low velocity, highly attenuating sediment overlying high velocity crystalline crust. The Moho depth beneath the basin is about 30 km as compared to about 50 km in the surrounding region. Preliminary modeling of the phase velocity curves shows that this thick sediments of the south Caspian basin are also under-lain by a 30-35 km thick crystalline crust and not by typical oceanic crust. This analysis also suggest that if the effect of the over-pressuring of the sediments is to reduce Poissons` ratio, the over-pressured sediments observed to approximately 5 km do not persist to great depths. It has been shown since 1960`s that the south Caspian basin blocks the regional phase Lg. Intermediate frequency (0.02-0.04 Hz) fundamental mode Raleigh waves propagating across the basin are also severely attenuated, but the low frequency surface waves are largely unaffected. This attenuation is observed along the both east-to-west and west-to-east great circle paths across the basin, and therefore it cannot be related to a seismograph site effect. We have modeled the response of surface waves in an idealized rendition of the south Caspian basin model using a hybrid normal mode / 2-D finite difference approach. To gain insight into the features of the basin which cause the anomalous surface wave propagation, we have varied parameters of the basin model and computed synthetic record sections to compare with the observed seismograms. We varied the amount of mantel up-warp, the shape of the boundaries, the thickness and shear wave Q of the sediments and mantle, and the depth of the water layer. Of these parameters, the intermediate frequency surface waves are most severely affected by the sediments thickness and shear wave attenuation. fundamental mode Raleigh wave phase velocities measure for paths crossing the basin are extremely low.
Numerical modelling of nonlinear full-wave acoustic propagation
Energy Technology Data Exchange (ETDEWEB)
Velasco-Segura, Roberto, E-mail: roberto.velasco@ccadet.unam.mx; Rendón, Pablo L., E-mail: pablo.rendon@ccadet.unam.mx [Grupo de Acústica y Vibraciones, Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Ciudad Universitaria, Apartado Postal 70-186, C.P. 04510, México D.F., México (Mexico)
2015-10-28
The various model equations of nonlinear acoustics are arrived at by making assumptions which permit the observation of the interaction with propagation of either single or joint effects. We present here a form of the conservation equations of fluid dynamics which are deduced using slightly less restrictive hypothesis than those necessary to obtain the well known Westervelt equation. This formulation accounts for full wave diffraction, nonlinearity, and thermoviscous dissipative effects. A two-dimensional, finite-volume method using Roe’s linearisation has been implemented to obtain numerically the solution of the proposed equations. This code, which has been written for parallel execution on a GPU, can be used to describe moderate nonlinear phenomena, at low Mach numbers, in domains as large as 100 wave lengths. Applications range from models of diagnostic and therapeutic HIFU, to parametric acoustic arrays and nonlinear propagation in acoustic waveguides. Examples related to these applications are shown and discussed.
Evaluation of an energy-propagation wave refraction model
Vincent, C. E.; Carrie, A.
1988-03-01
over simple "control' bathymetries. These were (a) the irreversibility of the algorithm which results in different refraction rates over opposite sides of a linear bank, (b) edge influences which propagate into the middle of the domain and (c) the steady energy loss which occurs as energy leaks into directions beyond the range of the model. However, if the model is used with care, avoiding regions where diffraction and reflection may be important and selecting a friction factor appropriate to the area, it can be a useful tool for predicting wave heights and directions.
Modelling of wave propagation over a submerged sand bar using SWASH
Digital Repository Service at National Institute of Oceanography (India)
Jishad, M.; Vu, T.T.T.; JayaKumar, S.
A non-hydrostatic numerical model "SWASH" (Simulating WAves till SHore) is used to study the wave propagation over a submerged sand bar in a wave flume The SWASH model is calibrated and further used to validate the wave propagation for two different...
Modelling viscoacoustic wave propagation with the lattice Boltzmann method.
Xia, Muming; Wang, Shucheng; Zhou, Hui; Shan, Xiaowen; Chen, Hanming; Li, Qingqing; Zhang, Qingchen
2017-08-31
In this paper, the lattice Boltzmann method (LBM) is employed to simulate wave propagation in viscous media. LBM is a kind of microscopic method for modelling waves through tracking the evolution states of a large number of discrete particles. By choosing different relaxation times in LBM experiments and using spectrum ratio method, we can reveal the relationship between the quality factor Q and the parameter τ in LBM. A two-dimensional (2D) homogeneous model and a two-layered model are tested in the numerical experiments, and the LBM results are compared against the reference solution of the viscoacoustic equations based on the Kelvin-Voigt model calculated by finite difference method (FDM). The wavefields and amplitude spectra obtained by LBM coincide with those by FDM, which demonstrates the capability of the LBM with one relaxation time. The new scheme is relatively simple and efficient to implement compared with the traditional lattice methods. In addition, through a mass of experiments, we find that the relaxation time of LBM has a quantitative relationship with Q. Such a novel scheme offers an alternative forward modelling kernel for seismic inversion and a new model to describe the underground media.
Accelerating wave propagation modeling in the frequency domain using Python
Jo, Sang Hoon; Park, Min Jun; Ha, Wan Soo
2017-04-01
Python is a dynamic programming language adopted in many science and engineering areas. We used Python to simulate wave propagation in the frequency domain. We used the Pardiso matrix solver to solve the impedance matrix of the wave equation. Numerical examples shows that Python with numpy consumes longer time to construct the impedance matrix using the finite element method when compared with Fortran; however we could reduce the time significantly to be comparable to that of Fortran using a simple Numba decorator.
Directory of Open Access Journals (Sweden)
Feng Liu
2015-01-01
Full Text Available The signal fading in wireless underground sensor networks (WUSNs, which is caused by lossy media such as soil and sand, can be reduced by applying technology of magnetoinductive (MI propagation. This technology can effectively establish a communication at very low frequency (VLF. In contrast to the previous studies in the literature, which mostly focus on the propagation of plane waves, we propose a new approach based on the plane wave expansion (PWE to model the near field MI waves. The proposed approach is based on excitation of a point source, which is a common case in a practical WUSN. The frequent usage of square lattice MI structure is investigated. To verify the mathematical derivation, the simulation of time domain based on the fourth-order Runge-Kutta (RK method is carried out. Simulation results show that the new model can provide a precise prediction to the MI wave’s propagation, with the computation load being one-tenth of that of the time domain simulation. The characteristics of the propagation of the MI waves are presented and discussed. Finally, the reflection on the edge of the MI structure is reduced by analysing the terminal matching conditions and calculating a method for matching impedances.
Modeling paraxial wave propagation in free-electron laser oscillators
Karssenberg, J.G.; van der Slot, Petrus J.M.; Volokhine, I.; Verschuur, Jeroen W.J.; Boller, Klaus J.
2006-01-01
Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for
Energy Technology Data Exchange (ETDEWEB)
Puckett, Anthony D. [Colorado State Univ., Fort Collins, CO (United States)
2000-09-01
The ability to model wave propagation in circular cylindrical bars of finite length numerically or analytically has many applications. In this thesis the capability of an explicit finite element method to model longitudinal waves in cylindrical rods with circular cross-sections is explored. Dispersion curves for the first four modes are compared to the analytical solution to determine the accuracy of various element sizes and time steps. Values for the time step and element size are determined that retain accuracy while minimizing computational time. The modeling parameters are validated by calculating a signal propagated with a broadband input force. Limitations on the applicability are considered along with modeling parameters that should be applicable to more general geometries.
Wave propagation in fluids models and numerical techniques
Guinot, Vincent
2012-01-01
This second edition with four additional chapters presents the physical principles and solution techniques for transient propagation in fluid mechanics and hydraulics. The application domains vary including contaminant transport with or without sorption, the motion of immiscible hydrocarbons in aquifers, pipe transients, open channel and shallow water flow, and compressible gas dynamics. The mathematical formulation is covered from the angle of conservation laws, with an emphasis on multidimensional problems and discontinuous flows, such as steep fronts and shock waves. Finite
Passive models of viscothermal wave propagation in acoustic tubes.
Bilbao, Stefan; Harrison, Reginald; Kergomard, Jean; Lombard, Bruno; Vergez, Christophe
2015-08-01
A continued fraction expansion to the immittances defining viscothermal wave propagation in a cylindrical tube has been presented recently in this journal, intended as a starting point for time domain numerical method design. Though the approximation has the great benefit of passivity, or positive realness under truncation, its convergence is slow leading to approximations of high order in practice. Other passive structures, when combined with optimisation methods, can lead to good accuracy over a wide frequency range, and for relatively low order.
Theoretical Model of Acoustic Wave Propagation in Shallow Water
Directory of Open Access Journals (Sweden)
Kozaczka Eugeniusz
2017-06-01
Full Text Available The work is devoted to the propagation of low frequency waves in a shallow sea. As a source of acoustic waves, underwater disturbances generated by ships were adopted. A specific feature of the propagation of acoustic waves in shallow water is the proximity of boundaries of the limiting media characterised by different impedance properties, which affects the acoustic field coming from a source situated in the water layer “deformed” by different phenomena. The acoustic field distribution in the real shallow sea is affected not only by multiple reflections, but also by stochastic changes in the free surface shape, and statistical changes in the seabed shape and impedance. The paper discusses fundamental problems of modal sound propagation in the water layer over different types of bottom sediments. The basic task in this case was to determine the acoustic pressure level as a function of distance and depth. The results of the conducted investigation can be useful in indirect determination of the type of bottom.
Larmat, C. S.; Rougier, E.; Delorey, A.; Steedman, D. W.; Bradley, C. R.
2016-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. For this, the SPE program includes a strong modeling effort based on first principles calculations with the challenge to capture both the source and near-source processes and those taking place later in time as seismic waves propagate within complex 3D geologic environments. In this paper, we report on results of modeling that uses hydrodynamic simulation codes (Abaqus and CASH) coupled with a 3D full waveform propagation code, SPECFEM3D. For modeling the near source region, we employ a fully-coupled Euler-Lagrange (CEL) modeling capability with a new continuum-based visco-plastic fracture model for simulation of damage processes, called AZ_Frac. These capabilities produce high-fidelity models of various factors believed to be key in the generation of seismic waves: the explosion dynamics, a weak grout-filled borehole, the surrounding jointed rock, and damage creation and deformations happening around the source and the free surface. SPECFEM3D, based on the Spectral Element Method (SEM) is a direct numerical method for full wave modeling with mathematical accuracy. The coupling interface consists of a series of grid points of the SEM mesh situated inside of the hydrodynamic code's domain. Displacement time series at these points are computed using output data from CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests with the Sharpe's model and comparisons of waveforms modeled with Rg waves (2-8Hz) that were recorded up to 2 km for SPE. We especially show effects of the local topography, velocity structure and spallation. Our models predict smaller amplitudes of Rg waves for the first five SPE shots compared to pure elastic models such as Denny &Johnson (1991).
Rouze, Ned C; Wang, Michael H; Palmeri, Mark L; Nightingale, Kathy R
2013-11-15
Elastic properties of materials can be measured by observing shear wave propagation following localized, impulsive excitations and relating the propagation velocity to a model of the material. However, characterization of anisotropic materials is difficult because of the number of elasticity constants in the material model and the complex dependence of propagation velocity relative to the excitation axis, material symmetries, and propagation directions. In this study, we develop a model of wave propagation following impulsive excitation in an incompressible, transversely isotropic (TI) material such as muscle. Wave motion is described in terms of three propagation modes identified by their polarization relative to the material symmetry axis and propagation direction. Phase velocities for these propagation modes are expressed in terms of five elasticity constants needed to describe a general TI material, and also in terms of three constants after the application of two constraints that hold in the limit of an incompressible material. Group propagation velocities are derived from the phase velocities to describe the propagation of wave packets away from the excitation region following localized excitation. The theoretical model is compared to the results of finite element (FE) simulations performed using a nearly incompressible material model with the five elasticity constants chosen to preserve the essential properties of the material in the incompressible limit. Propagation velocities calculated from the FE displacement data show complex structure that agrees quantitatively with the theoretical model and demonstrates the possibility of measuring all three elasticity constants needed to characterize an incompressible, TI material. © 2013 Elsevier Ltd. All rights reserved.
Simplifications of a damping model for wave propagation in porous media
DEFF Research Database (Denmark)
Darula, Radoslav; Sorokin, Sergey V.
2015-01-01
The wave propagation through porous materials is in general modelled with a classical Biot’s approach. A drawback of this way of modeling is, that it is empirical and very specific experiments are necessary to determine the parameters required. Therefore we do present an alternative approach based...... of wave propagation are identified and the damping is assessed, where only the attenuation of the fluid originated waves was analyzed....
Coupling model for waves propagating over a porous seabed
Directory of Open Access Journals (Sweden)
C.C. Liao
2015-03-01
Full Text Available The wave–seabed interaction issue is of great importance for the design of foundation around marine infrastructures. Most previous investigations for such a problem have been limited to uncoupled or one-way coupled methods connecting two separated wave and seabed sub models with the continuity of pressures at the seabed surface. In this study, a strongly coupled model was proposed to realize both wave and seabed processes in a same program and to calculate the wave fields and seabed response simultaneously. The information between wave fields and seabed fields were strongly shared and thus results in a more profound investigation of the mechanism of the wave–seabed interaction. In this letter, the wave and seabed models were validated with previous experimental tests. Then, a set of application of present model were discussed in prediction of the wave-induced seabed response. Numerical results show the wave-induced liquefaction area of coupled model is smaller than that of uncoupled model.
Zhang, Benfeng; Han, Tao; Tang, Gongbin; Zhang, Qiaozhen; Omori, Tatsuya; Hashimoto, Ken-Ya
2017-09-01
This paper discusses lateral propagation of surface acoustic waves (SAWs) in periodic grating structures when two types of SAWs exist simultaneously and are coupled. The thin plate model proposed by the authors is extended to include the coupling between two different SAW modes. First, lateral SAW propagation in an infinitely long periodic grating is modeled and discussed. Then, the model is applied to the Al-grating/42° YX-LiTaO3 (42-LT) substrate structure, and it is shown that the slowness curve shape changes from concave to convex with the Al grating thickness. The transverse responses are also analyzed on an infinitely long interdigital transducer on the structure, and good agreement is achieved between the present and the finite-element method analyses. Finally, SAW resonators are fabricated on the Cu grating/42-LT substrate structure, and it is experimentally verified that the slowness curve shape of the shear horizontal SAW changes with the Cu thickness.
Unstructured Spectral Element Model for Dispersive and Nonlinear Wave Propagation
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter; Eskilsson, Claes; Bigoni, Daniele
2016-01-01
). In the present paper we use a single layer of quadratic (in 2D) and prismatic (in 3D) elements. The model has been stabilized through a combination of over-integration of the Galerkin projections and a mild modal filter. We present numerical tests of nonlinear waves serving as a proof-of-concept validation......We introduce a new stabilized high-order and unstructured numerical model for modeling fully nonlinear and dispersive water waves. The model is based on a nodal spectral element method of arbitrary order in space and a -transformed formulation due to Cai, Langtangen, Nielsen and Tveito (1998...
Directory of Open Access Journals (Sweden)
L. Sun
2007-10-01
Full Text Available In order to study the filter effect of the background winds on the propagation of gravity waves, a three-dimensional transfer function model is developed on the basis of the complex dispersion relation of internal gravity waves in a stratified dissipative atmosphere with background winds. Our model has successfully represented the main results of the ray tracing method, e.g. the trend of the gravity waves to travel in the anti-windward direction. Furthermore, some interesting characteristics are manifest as follows: (1 The method provides the distribution characteristic of whole wave fields which propagate in the way of the distorted concentric circles at the same altitude under the control of the winds. (2 Through analyzing the frequency and wave number response curve of the transfer function, we find that the gravity waves in a wave band of about 15–30 min periods and of about 200–400 km horizontal wave lengths are most likely to propagate to the 300-km ionospheric height. Furthermore, there is an obvious frequency deviation for gravity waves propagating with winds in the frequency domain. The maximum power of the transfer function with background winds is smaller than that without background winds. (3 The atmospheric winds may act as a directional filter that will permit gravity wave packets propagating against the winds to reach the ionospheric height with minimum energy loss.
Monitoring and modeling of ultrasonic wave propagation in crystallizing mixtures
Marshall, T.; Challis, R. E.; Tebbutt, J. S.
2002-05-01
The utility of ultrasonic compression wave techniques for monitoring crystallization processes is investigated in a study of the seeded crystallization of copper II sulfate pentahydrate from aqueous solution. Simple models are applied to predict crystal yield, crystal size distribution and the changing nature of the continuous phase. A scattering model is used to predict the ultrasonic attenuation as crystallization proceeds. Experiments confirm that modeled attenuation is in agreement with measured results.
Modeling Anisotropic Elastic Wave Propagation in Jointed Rock Masses
Hurley, R.; Vorobiev, O.; Ezzedine, S. M.; Antoun, T.
2016-12-01
We present a numerical approach for determining the anisotropic stiffness of materials with nonlinearly-compliant joints capable of sliding. The proposed method extends existing ones for upscaling the behavior of a medium with open cracks and inclusions to cases relevant to natural fractured and jointed rocks, where nonlinearly-compliant joints can undergo plastic slip. The method deviates from existing techniques by incorporating the friction and closure states of the joints, and recovers an anisotropic elastic form in the small-strain limit when joints are not sliding. We present the mathematical formulation of our method and use Representative Volume Element (RVE) simulations to evaluate its accuracy for joint sets with varying complexity. We then apply the formulation to determine anisotropic elastic constants of jointed granite found at the Nevada Nuclear Security Site (NNSS) where the Source Physics Experiments (SPE), a campaign of underground chemical explosions, are performed. Finally, we discuss the implementation of our numerical approach in a massively parallel Lagrangian code Geodyn-L and its use for studying wave propagation from underground explosions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
David, P
2013-01-01
Propagation of Waves focuses on the wave propagation around the earth, which is influenced by its curvature, surface irregularities, and by passage through atmospheric layers that may be refracting, absorbing, or ionized. This book begins by outlining the behavior of waves in the various media and at their interfaces, which simplifies the basic phenomena, such as absorption, refraction, reflection, and interference. Applications to the case of the terrestrial sphere are also discussed as a natural generalization. Following the deliberation on the diffraction of the "ground? wave around the ear
Packo, P.; Staszewski, W. J.; Uhl, T.
2016-01-01
Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress waves through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear wave propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear wave propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort. PMID:26884808
Directory of Open Access Journals (Sweden)
Z. Hashemiyan
2016-01-01
Full Text Available Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress waves through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear wave propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear wave propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort.
Enhanced micropolar model for wave propagation in granular materials
Merkel, Aurélien; Luding, Stefan
2016-04-01
well as a Cosserat model. The Cosserat model is derived from the discrete model through an expansion of the discrete displacement and particle rotation to continuum field variables. The long wavelength approximation of these two models are compared and, considering the discrete model as the reference, the Cosserat model shows inconsistent predictions of the bulk wave dispersion relations. The discrepancies between the two models are explained by an insufficient modeling of one of the particle interactions in the Cosserat model. A enhanced micropolar model is proposed to correctly describe all the particle interactions by including a new elastic tensor from the second order gradient micropolar theory. The enhanced micropolar model involve the minimum number of elastic constant to consistently predicts the bulk mode dispersion relations in the long wavelength limit.
Global sensitivity analysis of a wave propagation model for arm arteries
Leguy, C.A.D.; Bosboom, E.M.H.; Belloum, A.S.Z.; Hoeks, A.P.G.; van de Vosse, F.N.
2011-01-01
Wave propagation models of blood flow and blood pressure in arteries play an important role in cardiovascular research. For application of these models in patient-specific simulations a number of model parameters, that are inherently subject to uncertainties, are required. The goal of this study is
Stojadinović, Bojana; Nestorović, Zorica; Djurić, Biljana; Tenne, Tamar; Zikich, Dragoslav; Žikić, Dejan
2017-03-01
The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system. Here, we present a laboratory model of the cardiovascular system. We have designed an experimental setup which can help medical and nursing students to properly learn and understand basic fluid hemodynamic principles, pulse wave and the phenomenon of wave propagation in blood vessels. Demonstration of wave propagation allowed a real time observation of the formation of compression and expansion waves by students, thus enabling them to better understand the difference between the two waves, and also to measure the pulse wave velocity for different fluid viscosities. The laboratory model of the cardiovascular system could be useful as an active learning methodology and a complementary tool for understanding basic principles of hemodynamics.
Energy Technology Data Exchange (ETDEWEB)
Takashima, Keisuke; Adamovich, Igor V. [Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, Ohio 43210 (United States); Xiong Zhongmin; Kushner, Mark J. [Department of Electrical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Starikovskaia, Svetlana [Ecole Polytechnique, Paris (France); Czarnetzki, Uwe; Luggenhoelscher, Dirk [Department of Physics and Astronomy, Ruhr University Bochum, Bochum (Germany)
2011-08-15
Fast ionization wave (FIW), nanosecond pulse discharge propagation in nitrogen and helium in a rectangular geometry channel/waveguide is studied experimentally using calibrated capacitive probe measurements. The repetitive nanosecond pulse discharge in the channel was generated using a custom designed pulsed plasma generator (peak voltage 10-40 kV, pulse duration 30-100 ns, and voltage rise time {approx}1 kV/ns), generating a sequence of alternating polarity high-voltage pulses at a pulse repetition rate of 20 Hz. Both negative polarity and positive polarity ionization waves have been studied. Ionization wave speed, as well as time-resolved potential distributions and axial electric field distributions in the propagating discharge are inferred from the capacitive probe data. ICCD images show that at the present conditions the FIW discharge in helium is diffuse and volume-filling, while in nitrogen the discharge propagates along the walls of the channel. FIW discharge propagation has been analyzed numerically using quasi-one-dimensional and two-dimensional kinetic models in a hydrodynamic (drift-diffusion), local ionization approximation. The wave speed and the electric field distribution in the wave front predicted by the model are in good agreement with the experimental results. A self-similar analytic solution of the fast ionization wave propagation equations has also been obtained. The analytic model of the FIW discharge predicts key ionization wave parameters, such as wave speed, peak electric field in the front, potential difference across the wave, and electron density as functions of the waveform on the high voltage electrode, in good agreement with the numerical calculations and the experimental results.
Wave propagation in ballistic gelatine.
Naarayan, Srinivasan S; Subhash, Ghatu
2017-04-01
Wave propagation characteristics in long cylindrical specimens of ballistic gelatine have been investigated using a high speed digital camera and hyper elastic constitutive models. The induced transient deformation is modelled with strain rate dependent Mooney-Rivlin parameters which are determined by modelling the stress-strain response of gelatine at a range of strain rates. The varying velocity of wave propagation through the gelatine cylinder is derived as a function of prestress or stretch in the gelatine specimen. A finite element analysis is conducted using the above constitutive model by suitably defining the impulse imparted by the polymer bar into the gelatine specimen. The model results are found to capture the experimentally observed wave propagation characteristics in gelatine effectively. Copyright © 2017 Elsevier Ltd. All rights reserved.
Coupling hydrodynamic and wave propagation modeling for waveform modeling of SPE.
Larmat, C. S.; Steedman, D. W.; Rougier, E.; Delorey, A.; Bradley, C. R.
2015-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. This paper presents effort to improve knowledge of the processes that affect seismic wave propagation from the hydrodynamic/plastic source region to the elastic/anelastic far field thanks to numerical modeling. The challenge is to couple the prompt processes that take place in the near source region to the ones taking place later in time due to wave propagation in complex 3D geologic environments. In this paper, we report on results of first-principles simulations coupling hydrodynamic simulation codes (Abaqus and CASH), with a 3D full waveform propagation code, SPECFEM3D. Abaqus and CASH model the shocked, hydrodynamic region via equations of state for the explosive, borehole stemming and jointed/weathered granite. LANL has been recently employing a Coupled Euler-Lagrange (CEL) modeling capability. This has allowed the testing of a new phenomenological model for modeling stored shear energy in jointed material. This unique modeling capability has enabled highfidelity modeling of the explosive, the weak grout-filled borehole, as well as the surrounding jointed rock. SPECFEM3D is based on the Spectral Element Method, a direct numerical method for full waveform modeling with mathematical accuracy (e.g. Komatitsch, 1998, 2002) thanks to its use of the weak formulation of the wave equation and of high-order polynomial functions. The coupling interface is a series of grid points of the SEM mesh situated at the edge of the hydrodynamic code domain. Displacement time series at these points are computed from output of CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests and waveforms modeled for several SPE tests conducted so far, with a special focus on effect of the local topography.
Vector wave propagation method.
Fertig, M; Brenner, K-H
2010-04-01
In this paper, we extend the scalar wave propagation method (WPM) to vector fields. The WPM [Appl. Opt.32, 4984 (1993)] was introduced in order to overcome the major limitations of the beam propagation method (BPM). With the WPM, the range of application can be extended from the simulation of waveguides to simulation of other optical elements like lenses, prisms and gratings. In that reference it was demonstrated that the wave propagation scheme provides valid results for propagation angles up to 85 degrees and that it is not limited to small index variations in the axis of propagation. Here, we extend the WPM to three-dimensional vectorial fields (VWPMs) by considering the polarization dependent Fresnel coefficients for transmission in each propagation step. The continuity of the electric field is maintained in all three dimensions by an enhanced propagation vector and the transfer matrix. We verify the validity of the method by transmission through a prism and by comparison with the focal distribution from vectorial Debye theory. Furthermore, a two-dimensional grating is simulated and compared with the results from three-dimensional RCWA. Especially for 3D problems, the runtime of the VWPM exhibits special advantage over the RCWA.
Energy Technology Data Exchange (ETDEWEB)
Ernest Valeo, Jay R. Johnson, Eun-Hwa and Cynthia Phillips
2012-03-13
A wide variety of plasma waves play an important role in the energization and loss of particles in the inner magnetosphere. Our ability to understand and model wave-particle interactions in this region requires improved knowledge of the spatial distribution and properties of these waves as well as improved understanding of how the waves depend on changes in solar wind forcing and/or geomagnetic activity. To this end, we have developed a two-dimensional, finite element code that solves the full wave equations in global magnetospheric geometry. The code describes three-dimensional wave structure including mode conversion when ULF, EMIC, and whistler waves are launched in a two-dimensional axisymmetric background plasma with general magnetic field topology. We illustrate the capabilities of the code by examining the role of plasmaspheric plumes on magnetosonic wave propagation; mode conversion at the ion-ion and Alfven resonances resulting from external, solar wind compressions; and wave structure and mode conversion of electromagnetic ion cyclotron waves launched in the equatorial magnetosphere, which propagate along the magnetic field lines toward the ionosphere. We also discuss advantages of the finite element method for resolving resonant structures, and how the model may be adapted to include nonlocal kinetic effects.
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 5. Flood Wave Propagation-The Saint Venant Equations. P P Mujumdar. General Article Volume 6 Issue 5 May 2001 pp 66-73. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/006/05/0066-0073 ...
Directory of Open Access Journals (Sweden)
Julijana eGjorgjieva
2013-04-01
Full Text Available Drosophila larvae crawl by peristaltic waves of muscle contractions, which propagate along the animal body and involve the simultaneous contraction of the left and right side of each segment. Coordinated propagation of contraction does not require sensory input, suggesting that movement is generated by a central pattern generator (CPG. We characterized crawling behavior of newly hatched Drosophila larvae by quantifying timing and duration of segmental boundary contractions. We developed a CPG network model that recapitulates these patterns based on segmentally repeated units of excitatory and inhibitory neuronal populations coupled with immediate neighboring segments. A single network with symmetric coupling between neighboring segments succeeded in generating both forward and backward propagation of activity. The CPG network was robust to changes in amplitude and variability of connectivity strength. Introducing sensory feedback via `stretch-sensitive' neurons improved wave propagation properties such as speed of propagation and segmental contraction duration as observed experimentally. Sensory feedback also restored propagating activity patterns when an inappropriately tuned CPG network failed to generate waves. Finally, in a two-sided CPG model we demonstrated that two types of connectivity could synchronize the activity of two independent networks: connections from excitatory neurons on one side to excitatory contralateral neurons (E to E, and connections from inhibitory neurons on one side to excitatory contralateral neurons (I to E. To our knowledge, such I to E connectivity has not yet been found in any experimental system; however, it provides the most robust mechanism to synchronize activity between contralateral CPGs in our model. Our model provides a general framework for studying the conditions under which a single locally coupled network generates bilaterally synchronized and longitudinally propagating waves in either direction.
Yang Yang; Theodore A. Endreny; David J. Nowak
2016-01-01
Flood wave propagation modeling is of critical importance to advancing water resources management and protecting human life and property. In this study, we investigated how the advection-diffusion routing model performed in flood wave propagation on a 16 km long downstream section of the Big Piney River, MO. Model performance was based on gaging station data at the...
Nonlinear wave propagation studies, dispersion modeling, and signal parameters correction
Czech Academy of Sciences Publication Activity Database
Převorovský, Zdeněk
..: ..., 2004, 00. [European Workshop on FP6-AERONEWS /1./. Naples (IT), 13.09.2004-16.09.2004] EU Projects: European Commission(XE) 502927 - AERO-NEWS Institutional research plan: CEZ:AV0Z2076919 Keywords : nodestructive testing * nonlinear elastic wave spectroscopy Subject RIV: BI - Acoustics
DEFF Research Database (Denmark)
Bjelland, C; Bjarnø, Leif
1992-01-01
A model for wave propagation in a liquid-filled viscoelastic tube with arrays of receivers inside, is being used to analyze the influence of noise generated by in-line vibrational noise sources. In this model, distensibility is of greater importance than compressibility of the liquid...... accelerometers and arrays of hydrophones inside are compared to the theoretical model for wave propagation. A good agreement between experimental data and theoretical predictions is found........ The dispersion and attenuation is shown to be strongly dependent on the viscoelastic properties of the tube wall. The complex, frequency-dependent moduli of relevant tube materials have been measured in stress wave transfer function experiments. The moduli are used in the model to produce realistic dispersion...
A Temporal Millimeter Wave Propagation Model for Tunnels Using Ray Frustum Techniques and FFT
Directory of Open Access Journals (Sweden)
Choonghyen Kwon
2014-01-01
Full Text Available A temporal millimeter wave propagation model for tunnels is presented using ray frustum techniques and fast Fourier transform (FFT. To directly estimate or simulate effects of millimeter wave channel properties on the performance of communication services, time domain impulse responses of demodulated signals should be obtained, which needs rather large computation time. To mitigate the computational burden, ray frustum techniques are used to obtain frequency domain transfer function of millimeter wave propagation environment and FFT of equivalent low pass signals are used to retrieve demodulated waveforms. This approach is numerically efficient and helps to directly estimate impact of tunnel structures and surfaces roughness on the performance of millimeter wave communication services.
Modeling Seismic Wave Propagation Using Time-Dependent Cauchy-Navier Splines
Kammann, P.
2005-12-01
Our intention is the modeling of seismic wave propagation from displacement measurements by seismographs at the Earth's surface. The elastic behaviour of the Earth is usually described by the Cauchy-Navier equation. A system of fundamental solutions for the Fourier transformed Cauchy-Navier equation are the Hansen vectors L, M and N. We apply an inverse Fourier transform to obtain an orthonormal function system depending on time and space. By means of this system we construct certain splines, which are then used for interpolating the given data. Compared to polynomial interpolation, splines have the advantage that they minimize some curvature measure and are, therefore, smoother. First, we test this method on a synthetic wave function. Afterwards, we apply it to realistic earthquake data. (P. Kammann, Modelling Seismic Wave Propagation Using Time-Dependent Cauchy-Navier Splines, Diploma Thesis, Geomathematics Group, Department of Mathematics, University of Kaiserslautern, 2005)
An Improved Coupling of Numerical and Physical Models for Simulating Wave Propagation
DEFF Research Database (Denmark)
Yang, Zhiwen; Liu, Shu-xue; Li, Jin-xuan
2014-01-01
An improved coupling of numerical and physical models for simulating 2D wave propagation is developed in this paper. In the proposed model, an unstructured finite element model (FEM) based Boussinesq equations is applied for the numerical wave simulation, and a 2D piston-type wavemaker is used...... for the physical wave generation. An innovative scheme combining fourth-order Lagrange interpolation and Runge-Kutta scheme is described for solving the coupling equation. A Transfer function modulation method is presented to minimize the errors induced from the hydrodynamic invalidity of the coupling model and....../or the mechanical capability of the wavemaker in area where nonlinearities or dispersion predominate. The overall performance and applicability of the coupling model has been experimentally validated by accounting for both regular and irregular waves and varying bathymetry. Experimental results show...
Directory of Open Access Journals (Sweden)
Kumar Rajneesh
2012-01-01
Full Text Available The aim of the present paper is to study the wave propagation in anisotropic viscoelastic medium in the context of the theory threephase- lag model of thermoelasticity. It is found that there exist two quasi-longitudinal waves (qP1, qP2 and two transverse waves (qS1, qS2. The governing equations for homogeneous transversely isotropic thermoviscoelastic are reduced as a special case from the considered model. Different characteristics of waves like phase velocity, attenuation coefficient, specific loss and penetration depth are computed from the obtained results. Viscous effect is shown graphically on different resulting quantities for two-phase-lag model and three-phase-lag model of thermoelasticity. Some particular cases of interest are also deduced from the present investigation.
Near-surface attenuation estimation using wave-propagation modeling
El Yadari, N.; Ernst, F.; Mulder, W.
2008-01-01
The effect of the near surface on seismic land data can be so severe that static corrections are insufficient. Full-waveform inversion followed by redatuming may be an alternative, but inversion will work only if the starting model is sufficiently close to the true model. As a first step toward
Abortive and propagating intracellular calcium waves: analysis from a hybrid model.
Directory of Open Access Journals (Sweden)
Nara Guisoni
Full Text Available The functional properties of inositol(1,4,5-triphosphate (IP3 receptors allow a variety of intracellular Ca(2+ phenomena. In this way, global phenomena, such as propagating and abortive Ca(2+ waves, as well as local events such as puffs, have been observed. Several experimental studies suggest that many features of global phenomena (e.g., frequency, amplitude, speed wave depend on the interplay of biophysical processes such as diffusion, buffering, efflux and influx rates, which in turn depend on parameters such as buffer concentration, Ca(2+ pump density, cytosolic IP3 level, and intercluster distance. Besides, it is known that cells are able to modify some of these parameters in order to regulate the Ca(2+ signaling. By using a hybrid model, we analyzed different features of the hierarchy of calcium events as a function of two relevant parameters for the calcium signaling, the intercluster distance and the pump strength or intensity. In the space spanned by these two parameters, we found two modes of calcium dynamics, one dominated by abortive calcium waves and the other by propagating waves. Smaller distances between the release sites promote propagating calcium waves, while the increase of the efflux rate makes the transition from propagating to abortive waves occur at lower values of intercluster distance. We determined the frontier between these two modes, in the parameter space defined by the intercluster distance and the pump strength. Furthermore, we found that the velocity of simulated calcium waves accomplishes Luther's law, and that an effective rate constant for autocatalytic calcium production decays linearly with both the intercluster distance and the pump strength.
Lebedev, Sergey
In this research simple flood wave propagation model was based the Saint-Venant equations represented a good way to describe problems concerning with flood waves propagations in open channels. For solution of this task the Caspian Sea was approximated as channel with a rectangular section. Channel axis coincided with the sea longitudinal axis or location of descending pass 092 of satellites TOPEX/Poseidon and Jason-1/2. Altimetric measurements of this satellites permit to define more exactly empiric parameters of the flood wave (propagation speed amplitude et al.) which are solution of the model. Also it allows estimating of effective evaporation. In this approach it is possible to consider as an integrated difference between sea surface heights between previous and the subsequent cycles altimetric measurements. Results of calculations have confirmed well conformity given calculated by other researchers and the model. As is shown than interannual variability of flood wave speed in the North Caspian was well correlated with interannual the Caspian Sea level variability. This study was supported by the grant of the Russian Foundation for Basic Research.
Fazio, Claudio; Guastella, Ivan; Sperandeo-Mineo, Rosa Maria; Tarantino, Giovanni
2008-01-01
The present paper reports the design process and the experimentation of a teaching-learning sequence about the concept of mechanical wave propagation and the role played by media where waves are propagating. The sequence focuses on the central issue of the relationships between observable phenomena, like macroscopic behaviours of waves, and their…
THE BASIS OF MATHEMATICAL DESCRIPTION FOR WAVE MODEL OF STRESSES PROPAGATION IN RAILWAY TRACK
Directory of Open Access Journals (Sweden)
D. M. Kurhan
2016-10-01
Full Text Available Purpose. Modern scientific research has repeatedly cited practical examples of the dynamic effects of railway track operation that go beyond the static calculation schemes. For the track sections where the train speed is approaching to the velocity of wave propagation in the slab track layers such issues are of particular relevance. An adequate tool for the study of such issues can be the use of the wave theory of stress propagation. The purpose of the article is the creation of a mathematical description of the basic principles of the stress propagation wave model in the railway track, which can be used as a basis for the practical development of the relevant calculation system. Methodology. The model of stress-strain states of the railway track on the basis of the stress wave propagation theory is to bring together the equations of the geometry of the outline of the space systems that is involved in the interaction at a given time, and the dynamic equilibrium equations of deformation. The solution is based on the use of the laws of the theory of elasticity. The wave front is described by an ellipsoid equation. When determining the variation in time of the surface position of the ellipsoid a vector approach is used. Findings. The geometry equations of the wave motion determine the volumes of material layers of the slab track involved in the interaction at a given time. The dynamic equilibrium determination of the deformed condition of the space bounded by the wave front makes it possible to calculate both the stresses and strains, and their changes during the time of the load perception. Thus, mathematical descriptions of the processes that occur in the perception of the load by the elements of railway track at high speeds were obtained. Originality. The simulation tasks of the track and rolling stock interaction, in particular taking into account the dynamic deflection of slab track were further developed. For the first time the article
Wave propagation scattering theory
Birman, M Sh
1993-01-01
The papers in this collection were written primarily by members of the St. Petersburg seminar in mathematical physics. The seminar, now run by O. A. Ladyzhenskaya, was initiated in 1947 by V. I. Smirnov, to whose memory this volume is dedicated. The papers in the collection are devoted mainly to wave propagation processes, scattering theory, integrability of nonlinear equations, and related problems of spectral theory of differential and integral operators. The book is of interest to mathematicians working in mathematical physics and differential equations, as well as to physicists studying va
Wave propagation in relaxed micromorphic continua: modeling metamaterials with frequency band-gaps
Madeo, A.; Neff, P.; Ghiba, I. D.; Placidi, L.; Rosi, G.
2015-09-01
In this paper, the relaxed micromorphic model proposed in Ghiba et al. (Math Mech Solids, 2013), Neff et al. (Contin Mech Thermodyn, 2013) has been used to study wave propagation in unbounded continua with microstructure. By studying dispersion relations for the considered relaxed medium, we are able to disclose precise frequency ranges (band-gaps) for which propagation of waves cannot occur. These dispersion relations are strongly nonlinear so giving rise to a macroscopic dispersive behavior of the considered medium. We prove that the presence of band-gaps is related to a unique elastic coefficient, the so-called Cosserat couple modulus μ c , which is also responsible for the loss of symmetry of the Cauchy force stress tensor. This parameter can be seen as the trigger of a bifurcation phenomenon since the fact of slightly changing its value around a given threshold drastically changes the observed response of the material with respect to wave propagation. We finally show that band-gaps cannot be accounted for by classical micromorphic models as well as by Cosserat and second gradient ones. The potential fields of application of the proposed relaxed model are manifold, above all for what concerns the conception of new engineering materials to be used for vibration control and stealth technology.
Regulatory effects on the population dynamics and wave propagation in a cell lineage model.
Wang, Mao-Xiang; Ma, Yu-Qiang; Lai, Pik-Yin
2016-03-21
We consider the interplay of cell proliferation, cell differentiation (and de-differentiation), cell movement, and the effect of feedback regulations on the population and propagation dynamics of different cell types in a cell lineage model. Cells are assumed to secrete and respond to negative feedback molecules which act as a control on the cell lineage. The cell densities are described by coupled reaction-diffusion partial differential equations, and the propagating wave front solutions in one dimension are investigated analytically and by numerical solutions. In particular, wavefront propagation speeds are obtained analytically and verified by numerical solutions of the equations. The emphasis is on the effects of the feedback regulations on different stages in the cell lineage. It is found that when the progenitor cell is negatively regulated, the populations of the cell lineage are strongly down-regulated with the steady growth rate of the progenitor cell being driven to zero beyond a critical regulatory strength. An analytic expression for the critical regulation strength in terms of the model parameters is derived and verified by numerical solutions. On the other hand, if the inhibition is acting on the differentiated cells, the change in the population dynamics and wave propagation speed is small. In addition, it is found that only the propagating speed of the progenitor cells is affected by the regulation when the diffusion of the differentiated cells is large. In the presence of de-differentiation, the effect on down-regulating the progenitor population is weakened and there is no effect on the propagation speed due to regulation, suggesting that the effect of regulatory control is diminished by de-differentiation pathways. Copyright © 2016 Elsevier Ltd. All rights reserved.
Chen, Chin-Wu; Huang, Chen-Fen; Lin, Chien-Wen; Kuo, Ban-Yuan
2017-05-01
T waves are conventionally defined as seismically generated acoustic energy propagating horizontally over long distances within the minimum sound speed layer in the ocean (SOFAR axis minimum). However, T waves have also been observed by ocean-bottom seismometers in ocean basins at depths greater than the SOFAR axis minimum. Previously, nongeometrical processes, such as local scattering at rough seafloor and water-sediment interface coupling, have been proposed as possible mechanisms for deep seafloor detection of T waves. Here we employ a new T wave modeling approach based on hydroacoustic ray theory to demonstrate that seismoacoustic energy can propagate to reach deep seafloor, previously considered as shadow zone of acoustic propagation. Our new hydroacoustic simulations explain well the observations of T waves on ocean-bottom seismometers at deep ocean basins east of Taiwan and shed new light on the mechanism for deep ocean T wave propagation.
Wave propagation in elastic solids
Achenbach, Jan
1984-01-01
The propagation of mechanical disturbances in solids is of interest in many branches of the physical scienses and engineering. This book aims to present an account of the theory of wave propagation in elastic solids. The material is arranged to present an exposition of the basic concepts of mechanical wave propagation within a one-dimensional setting and a discussion of formal aspects of elastodynamic theory in three dimensions, followed by chapters expounding on typical wave propagation phenomena, such as radiation, reflection, refraction, propagation in waveguides, and diffraction. The treat
Wave propagation in electromagnetic media
Davis, Julian L
1990-01-01
This is the second work of a set of two volumes on the phenomena of wave propagation in nonreacting and reacting media. The first, entitled Wave Propagation in Solids and Fluids (published by Springer-Verlag in 1988), deals with wave phenomena in nonreacting media (solids and fluids). This book is concerned with wave propagation in reacting media-specifically, in electro magnetic materials. Since these volumes were designed to be relatively self contained, we have taken the liberty of adapting some of the pertinent material, especially in the theory of hyperbolic partial differential equations (concerned with electromagnetic wave propagation), variational methods, and Hamilton-Jacobi theory, to the phenomena of electromagnetic waves. The purpose of this volume is similar to that of the first, except that here we are dealing with electromagnetic waves. We attempt to present a clear and systematic account of the mathematical methods of wave phenomena in electromagnetic materials that will be readily accessi...
Wave Propagation in Bimodular Geomaterials
Kuznetsova, Maria; Pasternak, Elena; Dyskin, Arcady; Pelinovsky, Efim
2016-04-01
Observations and laboratory experiments show that fragmented or layered geomaterials have the mechanical response dependent on the sign of the load. The most adequate model accounting for this effect is the theory of bimodular (bilinear) elasticity - a hyperelastic model with different elastic moduli for tension and compression. For most of geo- and structural materials (cohesionless soils, rocks, concrete, etc.) the difference between elastic moduli is such that their modulus in compression is considerably higher than that in tension. This feature has a profound effect on oscillations [1]; however, its effect on wave propagation has not been comprehensively investigated. It is believed that incorporation of bilinear elastic constitutive equations within theory of wave dynamics will bring a deeper insight to the study of mechanical behaviour of many geomaterials. The aim of this paper is to construct a mathematical model and develop analytical methods and numerical algorithms for analysing wave propagation in bimodular materials. Geophysical and exploration applications and applications in structural engineering are envisaged. The FEM modelling of wave propagation in a 1D semi-infinite bimodular material has been performed with the use of Marlow potential [2]. In the case of the initial load expressed by a harmonic pulse loading strong dependence on the pulse sign is observed: when tension is applied before compression, the phenomenon of disappearance of negative (compressive) strains takes place. References 1. Dyskin, A., Pasternak, E., & Pelinovsky, E. (2012). Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration, 331(12), 2856-2873. 2. Marlow, R. S. (2008). A Second-Invariant Extension of the Marlow Model: Representing Tension and Compression Data Exactly. In ABAQUS Users' Conference.
Pulse Wave Propagation in the Arterial Tree
van de Vosse, Frans N.; Stergiopulos, Nikos
2011-01-01
The beating heart creates blood pressure and flow pulsations that propagate as waves through the arterial tree that are reflected at transitions in arterial geometry and elasticity. Waves carry information about the matter in which they propagate. Therefore, modeling of arterial wave propagation extends our knowledge about the functioning of the cardiovascular system and provides a means to diagnose disorders and predict the outcome of medical interventions. In this review we focus on the physical and mathematical modeling of pulse wave propagation, based on general fluid dynamical principles. In addition we present potential applications in cardiovascular research and clinical practice. Models of short- and long-term adaptation of the arterial system and methods that deal with uncertainties in personalized model parameters and boundary conditions are briefly discussed, as they are believed to be major topics for further study and will boost the significance of arterial pulse wave modeling even more.
Stojadinovic, Bojana; Nestorovic, Zorica; Djuric, Biljana; Tenne, Tamar; Zikich, Dragoslav; Žikic, Dejan
2017-01-01
The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system.…
Directory of Open Access Journals (Sweden)
Paul C. Rivera
2006-01-01
Full Text Available A common approach in modeling the generation and propagation of tsunami is based on the assumption of a kinematic vertical displacement of ocean water that is analogous to the ocean bottom displacement during a submarine earthquake and the use of a non-dispersive long-wave model to simulate its physical transformation as it radiates outward from the source region. In this study, a new generation mechanism and the use of a highly-dispersive wave model to simulate tsunami inception, propagation and transformation are proposed. The new generation model assumes that transient ground motion during the earthquake can accelerate horizontal currents with opposing directions near the fault line whose successive convergence and divergence generate a series of potentially destructive oceanic waves. The new dynamic model incorporates the effects of earthquake moment magnitude, ocean compressibility through the buoyancy frequency, the effects of focal and water depths, and the orientation of ruptured fault line in the tsunami magnitude and directivity.For tsunami wave simulation, the nonlinear momentum-based wave model includes important wave propagation and transformation mechanisms such as refraction, diffraction, shoaling, partial reflection and transmission, back-scattering, frequency dispersion, and resonant wave-wave interaction. Using this model and a coarse-resolution bathymetry, the new mechanism is tested for the Indian Ocean tsunami of December 26, 2004. A new flooding and drying algorithm that consider waves coming from every direction is also proposed for simulation of inundation of low-lying coastal regions.It is shown in the present study that with the proposed generation model, the observed features of the Asian tsunami such as the initial drying of areas east of the source region and the initial flooding of western coasts are correctly simulated. The formation of a series of tsunami waves with periods and lengths comparable to observations
Li, Zheng-Wei; Xi, Xiao-Li; Zhang, Jin-Sheng; Liu, Jiang-fan
2015-12-14
The unconditional stable finite-difference time-domain (FDTD) method based on field expansion with weighted Laguerre polynomials (WLPs) is applied to model electromagnetic wave propagation in gyrotropic materials. The conventional Yee cell is modified to have the tightly coupled current density components located at the same spatial position. The perfectly matched layer (PML) is formulated in a stretched-coordinate (SC) system with the complex-frequency-shifted (CFS) factor to achieve good absorption performance. Numerical examples are shown to validate the accuracy and efficiency of the proposed method.
Modeling and simulation of ocean wave propagation using lattice Boltzmann method
Nuraiman, Dian
2017-10-01
In this paper, we present on modeling and simulation of ocean wave propagation from the deep sea to the shoreline. This requires high computational cost for simulation with large domain. We propose to couple a 1D shallow water equations (SWE) model with a 2D incompressible Navier-Stokes equations (NSE) model in order to reduce the computational cost. The coupled model is solved using the lattice Boltzmann method (LBM) with the lattice Bhatnagar-Gross-Krook (BGK) scheme. Additionally, a special method is implemented to treat the complex behavior of free surface close to the shoreline. The result shows the coupled model can reduce computational cost significantly compared to the full NSE model.
Modeling of Beam Wave Pulse Propagation in Vegetation Using Transport Theory
National Research Council Canada - National Science Library
Whitman, Gerald M; Schwering, Felix K; Yu-Chi Wu, Michael
2005-01-01
The scalar time-dependent equation of radiative transfer in cylindrical coordinates was used to develop several new theories- both rigorous and approximate- for propagation and scattering of beam wave...
Ultrasonic wave propagation in trabecular bone predicted by the stratified model
Lin, W.; Qin, Y. X.; Rubin, C.
2001-01-01
The objective of this study was to investigate ultrasound propagation in trabecular bone by considering the wave reflection and transmission in a multilayered medium. The use of ultrasound to identify those at risk of osteoporosis is a promising diagnostic method providing a measure of bone mineral density (BMD). A stratified model was proposed to study the effect of transmission and reflection of ultrasound wave within the trabecular architecture on the relationship between ultrasound and BMD. The results demonstrated that ultrasound velocity in trabecular bone was highly correlated with the bone apparent density (r=0.97). Moreover, a consistent pattern of the frequency dependence of ultrasound attenuation coefficient has been observed between simulation using this model and experimental measurement of trabecular bone. The normalized broadband ultrasound attenuation (nBUA) derived from the simulation results revealed that nBUA was nonlinear with respect to trabecular porosity and BMD. The curve of the relationship between nBUA and BMD was parabolic in shape, and the peak magnitude of nBUA was observed at approximately 60% of bone porosity. These results agreed with the published experimental data and demonstrated that according to the stratified model, reflection and transmission were important factors in the ultrasonic propagation through the trabecular bone.
Watson, Willie R.; Jones, Michael G.; Tanner, Sharon E.; Parrott, Tony L.
1995-01-01
A propagation model method for extracting the normal incidence impedance of an acoustic material installed as a finite length segment in a wall of a duct carrying a nonprogressive wave field is presented. The method recasts the determination of the unknown impedance as the minimization of the normalized wall pressure error function. A finite element propagation model is combined with a coarse/fine grid impedance plane search technique to extract the impedance of the material. Results are presented for three different materials for which the impedance is known. For each material, the input data required for the prediction scheme was computed from modal theory and then contaminated by random error. The finite element method reproduces the known impedance of each material almost exactly for random errors typical of those found in many measurement environments. Thus, the method developed here provides a means for determining the impedance of materials in a nonprogressirve wave environment such as that usually encountered in a commercial aircraft engine and most laboratory settings.
Energy Technology Data Exchange (ETDEWEB)
Kim, Jung Yul; Hyun, Hye ja; Kim, Yoo Sung [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)
1997-12-01
In petroleum exploration seismic reflection method is by far the most widely used. The resulting seismogram or seismic trace consists of many wavelets with different strengths and arrival times, due to the wavefront that have traveled different source-to receiver paths. In this sense, the seismic trace may be represented as a convolution of a wavelet with an impulse response denoting the various wavelet amplitudes and arrival times present in the trace. However, the wavelet suffers different attenuations while traveling through the earth layers. For example, the weathered layer (near-surface structure : e.g. valley) affect the propagating seismic wave in ways that cannot be simply modeled, but rather described in terms of an overall time delay and significant distortion of the source wavelet as it travels downward. Of course, the weathered layer will also affect the upgoing wave. Thus, the reflection method does not always lead to a desirable resolution in reflection section, because some specific constraints on the illumination of the deeper reflectors can be often imposed by the near-surface effect. Among other things, the mechanism for attenuation in many types of rocks is not very well understood. The present work is then mostly focussed on studying problems of wave propagation especially dealing with the near-surface structure problem by using physical modeling. An attempt was made to compare the measured data in detail with those from numerical method (ray theory). Besides, various kinds of physical models were additionally built to simulate the complex geological structures comprising wavy layer, coal seam structure, absorbing inhomogeneities, gradient layer that are not simply amenable to theory. Hereby, an attention was given on the reflection and transmission responses. The results illustrated in this work will provide a basis for the future oil exploration in Korea and demonstrate the potential of physical modeling as well. (author). 7 refs., 4 tabs., 62
Acharyya, Muktish
2013-05-01
The dynamical steady state behaviour of the random field Ising ferromagnet swept by a propagating magnetic field wave is studied at zero temperature by Monte Carlo simulation in two dimensions. The distribution of the random field is bimodal type. For a fixed set of values of the frequency, wavelength and amplitude of propagating magnetic field wave and the strength of the random field, four distinct dynamical steady states or nonequilibrium phases were identified. These four nonequilibrium phases are characterised by different values of structure factors. State or phase of first kind, where all spins are parallel (up). This phase is a frozen or pinned where the propagating field has no effect. The second one is the propagating type, where the sharp strips formed by parallel spins are found to move coherently. The third one is also propagating type, where the boundary of the strips of spins is not very sharp. The fourth kind shows no propagation of strips of magnetic spins, forming a homogeneous distribution of up and down spins. This is disordered phase. The existence of these four dynamical phases or modes depends on the value of the amplitude of propagating magnetic field wave and the strength of random (static) field. A phase diagram has also been drawn, in the plane formed by the amplitude of propagating field and the strength of random field. It is also checked that the existence of these dynamical phases is neither a finite size effect nor a transient phenomenon.
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.
Modeling wave propagation in realistic heart geometries using the phase-field method
Fenton, Flavio H.; Cherry, Elizabeth M.; Karma, Alain; Rappel, Wouter-Jan
2005-03-01
We present a novel algorithm for modeling electrical wave propagation in anatomical models of the heart. The algorithm uses a phase-field approach that represents the boundaries between the heart muscle and the surrounding medium as a spatially diffuse interface of finite thickness. The chief advantage of this method is to automatically handle the boundary conditions of the voltage in complex geometries without the need to track the location of these boundaries explicitly. The algorithm is shown to converge accurately in nontrivial test geometries with no-flux (zero normal current) boundary conditions as the width of the diffuse interface becomes small compared to the width of the cardiac action potential wavefront. Moreover, the method is illustrated for anatomically realistic models of isolated rabbit and canine ventricles as well as human atria.
Vorontsov, Artem; Andreeva, Elena; Nesterov, Ivan; Padokhin, Artem; Kurbatov, Grigory
2016-04-01
The acoustic-gravity waves (AGW) in the upper atmosphere and ionosphere can be generated by a variety of the phenomena in the near-Earth environment and atmosphere as well as by some perturbations of the Earth's ground or ocean surface. For instance, the role of the AGW sources can be played by the earthquakes, explosions, thermal heating, seisches, tsunami waves. We present the examples of AGWs excited by the tsunami waves traveling in the ocean, by seisches, and by ionospheric heating by the high-power radio wave. In the last case, the gravity waves are caused by the pulsed modulation of the heating wave. The AGW propagation in the upper atmosphere induces the variations and irregularities in the electron density distribution of the ionosphere, whose structure can be efficiently reconstructed by the method of the ionospheric radio tomography (RT) based on the data from the global navigational satellite systems (GNSS). The input data for RT diagnostics are composed of the 150/400 MHz radio signals from the low-orbiting (LO) satellites and 1.2-1.5 GHz radio signals from the high-orbiting (HO) satellites with their orbits at ~1000 and ~20000 km above the ground, respectively. These data enable ionospheric imaging on different spatiotemporal scales with different spatiotemporal resolution and coverage, which is suitable, inter alia, for tracking the waves and wave-like features in the ionosphere. In particular, we demonstrate the maps of the ionospheric responses to the tornado at Moore (Oklahoma, USA) of May 20, 2013, which are reconstructed from the HO data. We present the examples of LORT images containing the waves and wavelike disturbances associated with various sources (e.g., auroral precipitation and high-power heating of the ionosphere). We also discuss the results of modeling the AGW generation by the surface and volumetric sources. The millihertz AGW from these sources initiate the ionospheric perturbation with a typical scale of a few hundred km at the
Mikhailov, Aleksandr A.; Martynov, Valery N.
2017-11-01
In this paper we consider the numerical solution to the problem of the infrasonic and seismic wave propagation for the spatial inhomogeneous model Atmosphere-Earth. The interface between the atmosphere and the elastic medium is assumed to be curvilinear. The efficient numerical algorithm for carrying out calculations on multi-processor computer systems is described. A specific feature of the algorithm proposed is a combination of integral transforms and the finite difference method. The propagation of infrasonic waves in the isothermal atmosphere is described by the linearized Navier-Stokes equations in the form of the hyperbolic first order system in the 3D Cartesian coordinate system. The propagation of seismic waves in the lithosphere is described by the hyperbolic first order system in terms of the displacement velocity vector and stress tensor according to elasticity theory. In this paper we present the results of numerical modeling of wave fields for the test models in the case when the interface between the atmosphere and elastic half-space is curvilinear.
Directory of Open Access Journals (Sweden)
Chun-Te Chen
2016-06-01
Full Text Available This study used the results from 45 microtremor array measurements to construct a shallow shear wave velocity structure in the western plain of Taiwan. We constructed a complete 3D velocity model based on shallow and tomography models for our numerical simulation. There are three major subsurfaces, engineering bedrock (VS = 600 m s-1, Pliocene formation and Miocene formation, constituted in the shallow model. The constant velocity is given in each subsurface. We employed a 3D-FD (finite-differences method to simulate seismic wave propagation in the western plain. The aim of this study was to perform a quantitative comparison of site amplifications and durations obtained from empirical data and numerical modelling in order to obtain the shallow substructure soil response. Modelling clearly revealed that the shallow substructure plays an important role in strong ground motion prediction using 3D simulation. The results show significant improvements in effective shaking duration and the peak ground velocity (PGV distribution in terms of the accuracy achieved by our developed model. We recommend a high-resolution shallow substructure as an essential component in future seismic hazard analyses.
Calculating Basin Response by Numerical Modeling of Wave Propagation - The Taipei Basin Example
Miksat, J.; Wen, K.-L.; Sokolov, V.; Chen, C.-T.; Wenzel, F.
2009-04-01
Calculating low frequency response of sedimentary basins and the understanding of the associated wave effects is an important issue because structures with large response periods such as bridges and tall buildings are sensitive to the low frequency range (f incident S-wave front on the basin for different azimuths and incidence angles corresponding to deep and shallow earthquakes. We perform the simulations for the 3D basin structure and a homogeneous model that reflects hard rock conditions. From the modeling results we calculate frequency dependent spectral amplification ratios. Because of the assumed planar wave front incidence source and path effects are excluded and the calculated amplification effects describe the relative influence of the basin structure only. These modeled amplification factors could be superimposed on existing standard hard rock attenuation relationship in order to calculate absolute ground motion parameters within the basin. Our modeling results reveal the generation of strong surface waves at the basin edges for shallow earthquakes. Consequently, shallow earthquakes produce larger spectral amplifications within the basin compared to deep earthquakes. The dominant frequencies of spectral amplifications vary between 0.3 Hz in the deepest part of the basin to 0.6 Hz in the eastern shallow part of the basin. This frequency behavior was also found from analysis of observed data. Furthermore, modeling results show, like the observations, strong earthquake azimuth dependence of spectral ratios. We compare also the modeled spectral amplification for 0.5 Hz with the results of a microtremor survey. Modeling and observations show the same areas of large amplifications and similar absolute maximum amplification factors of about 5 - 10. Our study showed that modeling explains the observed ground motion peculiarities. We found also a good quantitative agreement of the simulated and observed amplification factors at a frequency of 0.5 Hz. In the case
Shen, Yanfeng; Cesnik, Carlos E. S.
2015-03-01
This paper presents a hybrid modeling technique for the efficient simulation of guided wave propagation and interaction with damage in composite structures. This hybrid approach uses a local finite element model (FEM) to compute the excitability of guided waves generated by piezoelectric transducers, while the global domain wave propagation, wave-damage interaction, and boundary reflections are modeled with the local interaction simulation approach (LISA). A small-size multi-physics FEM with non-reflective boundaries (NRB) was built to obtain the excitability information of guided waves generated by the transmitter. Frequency-domain harmonic analysis was carried out to obtain the solution for all the frequencies of interest. Fourier and inverse Fourier transform and frequency domain convolution techniques are used to obtain the time domain 3-D displacement field underneath the transmitter under an arbitrary excitation. This 3-D displacement field is then fed into the highly efficient time domain LISA simulation module to compute guided wave propagation, interaction with damage, and reflections at structural boundaries. The damping effect of composite materials was considered in the modified LISA formulation. The grids for complex structures were generated using commercial FEM preprocessors and converted to LISA connectivity format. Parallelization of the global LISA solution was achieved through Compute Unified Design Architecture (CUDA) running on Graphical Processing Unit (GPU). The multi-physics local FEM can reliably capture the detailed dimensions and local dynamics of the piezoelectric transducers. The global domain LISA can accurately solve the 3-D elastodynamic wave equations in a highly efficient manner. By combining the local FEM with global LISA, the efficient and accurate simulation of guided wave structural health monitoring procedure is achieved. Two numerical case studies are presented: (1) wave propagation in a unidirectional CFRP composite plate
A 2D Time Domain DRBEM Computer Model for MagnetoThermoelastic Coupled Wave Propagation Problems
Directory of Open Access Journals (Sweden)
Mohamed Abdelsabour Fahmy
2014-07-01
Full Text Available A numerical computer model based on the dual reciprocity boundary element method (DRBEM is extended to study magneto-thermoelastic coupled wave propagation problems with relaxation times involving anisotropic functionally graded solids. The model formulation is tested through its application to the problem of a solid placed in a constant primary magnetic field acting in the direction of the z-axis and rotating about this axis with a constant angular velocity. In the case of two-dimensional deformation, an implicit-explicit time domain DRBEM was presented and implemented to obtain the solution for the displacement and temperature fields. A comparison of the results is presented graphically in the context of Lord and Shulman (LS and Green and Lindsay (GL theories. Numerical results that demonstrate the validity of the proposed method are also presented graphically.
Boussinesq Modeling of Wave Propagation and Runup over Fringing Coral Reefs, Model Evaluation Report
National Research Council Canada - National Science Library
Demirbilek, Zeki; Nwogu, Okey G
2007-01-01
This report describes evaluation of a two-dimensional Boussinesq-type wave model, BOUSS-2D, with data obtained from two laboratory experiments and two field studies at the islands of Guam and Hawaii...
Zelenyak, Andreea-Manuela; Schorer, Nora; Sause, Markus G R
2017-06-20
This paper presents a method for embedding realistic defect geometries of a fiber reinforced material in a finite element modeling environment in order to simulate active ultrasonic inspection. When ultrasonic inspection is used experimentally to investigate the presence of defects in composite materials, the microscopic defect geometry may cause signal characteristics that are difficult to interpret. Hence, modeling of this interaction is key to improve our understanding and way of interpreting the acquired ultrasonic signals. To model the true interaction of the ultrasonic wave field with such defect structures as pores, cracks or delamination, a realistic three dimensional geometry reconstruction is required. We present a 3D-image based reconstruction process which converts computed tomography data in adequate surface representations ready to be embedded for processing with finite element methods. Subsequent modeling using these geometries uses a multi-scale and multi-physics simulation approach which results in quantitative A-Scan ultrasonic signals which can be directly compared with experimental signals. Therefore, besides the properties of the composite material, a full transducer implementation, piezoelectric conversion and simultaneous modeling of the attached circuit is applied. Comparison between simulated and experimental signals provides very good agreement in electrical voltage amplitude and the signal arrival time and thus validates the proposed modeling approach. Simulating ultrasound wave propagation in a medium with a realistic shape of the geometry clearly shows a difference in how the disturbance of the waves takes place and finally allows more realistic modeling of A-scans. Copyright © 2017 Elsevier B.V. All rights reserved.
2D spectral element modeling of GPR wave propagation in inhomogeneous media
Zarei, Sajad; Oskooi, Behrooz; Amini, Navid; Dalkhani, Amin Rahimi
2016-10-01
We present a spectral element method, for simulation of ground-penetrating radar (GPR) in two dimensions. The technique is based upon a weak formulation of the equations of Maxwell and combines the flexibility of the elemental-based methods with the accuracy of the spectral based methods. The wave field on the elements is discretized using high-degree Lagrange interpolation and integration over an element is accomplished based upon the Gauss-Lobatto-Legendre integration rule. As a result, the mass matrix and the damping matrix are always diagonal, which drastically reduces the computational cost. We first develop the formulation of 2D spectral element method (SEM) in the time-domain based on Maxwell's equations. The presented formulation is with matrix notation that simplifies the implementation of the relations in computer programs, especially in MATLAB application. We discuss the differences between spectral element method and finite-element method in the time-domain. Also, we show that the SEM numerical dispersion is much lower than FEM. To absorb waves at the edges of the modeling domain, we implement first order Clayton and Engquist absorbing boundary conditions (CE-ABC) introduced in numerical finite-difference modeling of seismic wave propagation. We used the SEM to simulate a complex model to show its abilities and limitations. As well as, one distinct advantage of SEM is that we can easily define our model features in nodal points, because the integration points and the interpolation points are similar that makes it very flexible in simulation of complex models.
Controls on flood and sediment wave propagation
Bakker, Maarten; Lane, Stuart N.; Costa, Anna; Molnar, Peter
2015-04-01
The understanding of flood wave propagation - celerity and transformation - through a fluvial system is of generic importance for flood forecasting/mitigation. In association with flood wave propagation, sediment wave propagation may induce local erosion and sedimentation, which will affect infrastructure and riparian natural habitats. Through analysing flood and sediment wave propagation, we gain insight in temporal changes in transport capacity (the flood wave) and sediment availability and transport (the sediment wave) along the river channel. Heidel (1956) was amongst the first to discuss the progressive lag of sediment concentration behind the corresponding flood wave based on field measurements. Since then this type of hysteresis has been characterized in a number of studies, but these were often based on limited amount of floods and measurement sites, giving insufficient insight into associated forcing mechanisms. Here, as part of a project concerned with the hydrological and geomorphic forcing of sediment transfer processes in alpine environments, we model the downstream propagation of short duration, high frequency releases of water and sediment (purges) from a flow intake in the Borgne d'Arolla River in south-west Switzerland. A total of >50 events were measured at 1 minute time intervals using pressure transducers and turbidity probes at a number of sites along the river. We show that flood and sediment wave propagation can be well represented through simple convection diffusion models. The models are calibrated/validated to describe the set of measured waves and used to explain the observed variation in wave celerity and diffusion. In addition we explore the effects of controlling factors including initial flow depth, flood height, flood duration, bed roughness, bed slope and initial sediment concentration, on the wave propagation processes. We show that the effects of forcing mechanisms on flood and sediment wave propagation will lead to different
Modeling of ICRF wave propagation and heating in EAST with the full-wave code TORIC
Edlund, E. M.; Bonoli, P. T.; Porkolab, M.; Wukitch, S. J.
2015-11-01
Access to advanced tokamak (AT) scenarios in EAST depends on efficient coupling of the launched ion-cyclotron range of frequency (ICRF) power for heating and lower-hybrid waves to the plasma for steady-state current drive. This work builds on recent predictions from the full-wave code TORIC that have shown significant reductions in loading, resulting in improved heating efficiency, by operating with smaller phasing between antenna straps. The density regime of typical EAST experiments produces perpendicular wavelengths of the fast-wave that are comparable to the minor radius of the plasma, resulting in cavity-resonance effects and requiring full-spectrum analysis for accurate calculations of the antenna coupling. This study examines the effects of antenna phasing, as well as plasma density, temperature and current as control parameters for achieving good coupling of the ICRF power in the pursuit of the optimal conditions for AT plasmas. This work is funded by the US DOE under contract DoE Grant DE-SC0010492.
Directory of Open Access Journals (Sweden)
Xing Zheng
2017-06-01
Full Text Available The Smoothed Particle Hydrodynamics (SPH method has proven to have great potential in dealing with the wave–structure interactions since it can deal with the large amplitude and breaking waves and easily captures the free surface. The paper will adopt an incompressible SPH (ISPH approach to simulate the wave propagation and impact, in which the fluid pressure is solved using a pressure Poisson equation and thus more stable and accurate pressure fields can be obtained. The focus of the study is on comparing three different pressure gradient calculation models in SPH and proposing the most efficient first-order consistent kernel interpolation (C1_KI numerical scheme for modelling violent wave impact. The improvement of the model is validated by the benchmark dam break flows and laboratory wave propagation and impact experiments.
Turbofan Duct Propagation Model
Lan, Justin H.; Posey, Joe W. (Technical Monitor)
2001-01-01
The CDUCT code utilizes a parabolic approximation to the convected Helmholtz equation in order to efficiently model acoustic propagation in acoustically treated, complex shaped ducts. The parabolic approximation solves one-way wave propagation with a marching method which neglects backwards reflected waves. The derivation of the parabolic approximation is presented. Several code validation cases are given. An acoustic lining design process for an example aft fan duct is discussed. It is noted that the method can efficiently model realistic three-dimension effects, acoustic lining, and flow within the computational capabilities of a typical computer workstation.
Huberts, W; Donders, W P; Delhaas, T; van de Vosse, F N
2014-12-01
Patient-specific modeling requires model personalization, which can be achieved in an efficient manner by parameter fixing and parameter prioritization. An efficient variance-based method is using generalized polynomial chaos expansion (gPCE), but it has not been applied in the context of model personalization, nor has it ever been compared with standard variance-based methods for models with many parameters. In this work, we apply the gPCE method to a previously reported pulse wave propagation model and compare the conclusions for model personalization with that of a reference analysis performed with Saltelli's efficient Monte Carlo method. We furthermore differentiate two approaches for obtaining the expansion coefficients: one based on spectral projection (gPCE-P) and one based on least squares regression (gPCE-R). It was found that in general the gPCE yields similar conclusions as the reference analysis but at much lower cost, as long as the polynomial metamodel does not contain unnecessary high order terms. Furthermore, the gPCE-R approach generally yielded better results than gPCE-P. The weak performance of the gPCE-P can be attributed to the assessment of the expansion coefficients using the Smolyak algorithm, which might be hampered by the high number of model parameters and/or by possible non-smoothness in the output space. Copyright © 2014 John Wiley & Sons, Ltd.
Parametric uncertainty analysis of pulse wave propagation in a model of a human arterial network
Xiu, Dongbin; Sherwin, Spencer J.
2007-10-01
Reduced models of human arterial networks are an efficient approach to analyze quantitative macroscopic features of human arterial flows. The justification for such models typically arise due to the significantly long wavelength associated with the system in comparison to the lengths of arteries in the networks. Although these types of models have been employed extensively and many issues associated with their implementations have been widely researched, the issue of data uncertainty has received comparatively little attention. Similar to many biological systems, a large amount of uncertainty exists in the value of the parameters associated with the models. Clearly reliable assessment of the system behaviour cannot be made unless the effect of such data uncertainty is quantified. In this paper we present a study of parametric data uncertainty in reduced modelling of human arterial networks which is governed by a hyperbolic system. The uncertain parameters are modelled as random variables and the governing equations for the arterial network therefore become stochastic. This type stochastic hyperbolic systems have not been previously systematically studied due to the difficulties introduced by the uncertainty such as a potential change in the mathematical character of the system and imposing boundary conditions. We demonstrate how the application of a high-order stochastic collocation method based on the generalized polynomial chaos expansion, combined with a discontinuous Galerkin spectral/hp element discretization in physical space, can successfully simulate this type of hyperbolic system subject to uncertain inputs with bounds. Building upon a numerical study of propagation of uncertainty and sensitivity in a simplified model with a single bifurcation, a systematical parameter sensitivity analysis is conducted on the wave dynamics in a multiple bifurcating human arterial network. Using the physical understanding of the dynamics of pulse waves in these types of
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...
Modeling of thermal wave propagation in damaged composites with internal source
Ciampa, Francesco; Angioni, Stefano L.; Pinto, Fulvio; Scarselli, Gennaro; Almond, Darrel P.; Meo, Michele
2015-04-01
SMArt Thermography exploits the electrothermal properties of multifunctional smart structures, which are created by embedding shape memory alloy (SMA) wires in traditional carbon fibre reinforced composite laminates (known as SMArt composites), in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography techniques. However, a theoretical background of the thermal wave propagation behaviour, especially in the presence of internal structural defects, is needed to better interpret the observations/data acquired during the experiments and to optimise those critical parameters such as the mechanical and thermal properties of the composite laminate, the depth of the SMA wires and the intensity of the excitation energy. This information is essential to enhance the sensitivity of the system, thus to evaluate the integrity of the medium with different types of damage. For this purpose, this paper aims at developing an analytical model for SMArt composites, which is able to predict the temperature contrast on the surface of the laminate in the presence of in-plane internal damage (delamination-like) using pulsed thermography. Such a model, based on the Green's function formalism for one-dimensional heat equation, takes into account the thermal lateral diffusion around the defect and it can be used to compute the defect depth within the laminate. The results showed good agreement between the analytical model and the measured thermal waves using an infrared (IR) camera. Particularly, the contrast temperature curves were found to change significantly depending on the defect opening.
Wave propagation in thermoelastic saturated porous medium
Indian Academy of Sciences (India)
Biot 's theory for wave propagation in saturated porous solid is modiﬁed to study the propagation of thermoelastic waves in poroelastic medium. Propagation of plane harmonic waves is considered in isotropic poroelastic medium. Relations are derived among the wave-induced temperature in the medium and the ...
Energy Technology Data Exchange (ETDEWEB)
Kim, K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Petersson, N. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rodgers, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-10-25
Acoustic waveform modeling is a computationally intensive task and full three-dimensional simulations are often impractical for some geophysical applications such as long-range wave propagation and high-frequency sound simulation. In this study, we develop a two-dimensional high-order accurate finite-difference code for acoustic wave modeling. We solve the linearized Euler equations by discretizing them with the sixth order accurate finite difference stencils away from the boundary and the third order summation-by-parts (SBP) closure near the boundary. Non-planar topographic boundary is resolved by formulating the governing equation in curvilinear coordinates following the interface. We verify the implementation of the algorithm by numerical examples and demonstrate the capability of the proposed method for practical acoustic wave propagation problems in the atmosphere.
Khazanov, George V.
2006-01-01
The self-consistent treatment of the RC ion dynamics and EMIC waves, which are thought to exert important influences on the ion dynamical evolution, is an important missing element in our understanding of the storm-and recovery-time ring current evolution. Under certain conditions, relativistic electrons, with energies 21 MeV, can be removed from the outer radiation belt by EMIC wave scattering during a magnetic storm. That is why the modeling of EMIC waves is critical and timely issue in magnetospheric physics. To describe the RC evolution itself this study uses the ring current-atmosphere interaction model (RAM). RAM solves the gyration and bounce-averaged Boltzmann-Landau equation inside of geosynchronous orbit. Originally developed at the University of Michigan, there are now several branches of this model currently in use as describe by Liemohn namely those at NASA Goddard Space Flight Center This study will generalize the self-consistent theoretical description of RC ions and EMIC waves that has been developed by Khazanov and include the heavy ions and propagation effects of EMIC waves in the global dynamic of self-consistent RC - EMIC waves coupling. The results of our newly developed model that will be presented at GEM meeting, focusing mainly on the dynamic of EMIC waves and comparison of these results with the previous global RC modeling studies devoted to EMIC waves formation. We also discuss RC ion precipitations and wave induced thermal electron fluxes into the ionosphere.
Radio Wave Propagation in Tunnels
National Research Council Canada - National Science Library
Lee, Jeho
2000-01-01
This report examines the radio propagation model for narrow and long tunnels. Modal analysis is used to model the path gain in 2-D and 3-D rectangular tunnels and the coupling loss of L, T and cross tunnels...
Modeling Plankton Aggregation and Transport by Nonlinear Internal Waves Propagating Onshore.
Garwood, J. C.; Musgrave, R. C.; Franks, P. J. S.
2016-02-01
Many coastal benthic species have planktonic larval forms. These larvae must return to suitable adult habitat to allow recruitment to the breeding population. To a large extent these larvae are at the mercy of the ambient currents. However, simple vertical swimming behaviors may significantly enhance onshore or offshore transport of these organisms in certain coastal flows. Here we use models to investigate the interaction of nonlinear internal waves (NLIW) and swimming behaviors in determining plankton aggregation and cross-shelf transport. In a 2D, non-hydrostatic MITgcm with particle tracking, NLIW are generated and propagate onshore into a region of sloping bottom topography. Lagrangian and swimming particles representing plankton are introduced in the flow field to quantify transport and dispersion. Characteristics of the environment (bottom slope and stratification), as well as of the particles (source, depth, and swimming vs. passive) were varied to identify scenarios that would maximize transport or accumulation. Our results will be used to design experiments using swarms of autonomous buoyancy-controlled drifters to quantify transport and accumulation in the field.
A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function.
Keijsers, J M T; Leguy, C A D; Huberts, W; Narracott, A J; Rittweger, J; van de Vosse, F N
2015-07-01
The calf muscle pump is a mechanism which increases venous return and thereby compensates for the fluid shift towards the lower body during standing. During a muscle contraction, the embedded deep veins collapse and venous return increases. In the subsequent relaxation phase, muscle perfusion increases due to increased perfusion pressure, as the proximal venous valves temporarily reduce the distal venous pressure (shielding). The superficial and deep veins are connected via perforators, which contain valves allowing flow in the superficial-to-deep direction. The aim of this study is to investigate and quantify the physiological mechanisms of the calf muscle pump, including the effect of venous valves, hydrostatic pressure, and the superficial venous system. Using a one-dimensional pulse wave propagation model, a muscle contraction is simulated by increasing the extravascular pressure in the deep venous segments. The hemodynamics are studied in three different configurations: a single artery-vein configuration with and without valves and a more detailed configuration including a superficial vein. Proximal venous valves increase effective venous return by 53% by preventing reflux. Furthermore, the proximal valves shielding function increases perfusion following contraction. Finally, the superficial system aids in maintaining the perfusion during the contraction phase and reduces the refilling time by 37%. © 2015 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.
Investigation into stress wave propagation in metal foams
Directory of Open Access Journals (Sweden)
Li Lang
2015-01-01
Full Text Available The aim of this study is to investigate stress wave propagation in metal foams under high-speed impact loading. Three-dimensional Voronoi model is established to represent real closed-cell foam. Based on the one-dimensional stress wave theory and Voronoi model, a numerical model is developed to calculate the velocity of elastic wave and shock wave in metal foam. The effects of impact velocity and relative density of metal foam on the stress wave propagation in metal foams are explored respectively. The results show that both elastic wave and shock wave propagate faster in metal foams with larger relative density; with increasing the impact velocity, the shock wave propagation velocity increase, but the elastic wave propagation is not sensitive to the impact velocity.
Lebedev, S. A.
2010-12-01
In this research simple flood wave propagation model was based the Saint-Venant equations represented a good way to describe problems concerning with flood waves propagations in open channels. For solution of this task the Caspian Sea was approximated as channel with a rectangular cross-section. Channel axis coincided with the sea longitudinal axis or location of descending pass 092 of satellites TOPEX/Poseidon (T/P) and Jason- 1/2 (J1/2). Altimetric measurements of this satellites permit to define more exactly empiric parameters of the flood wave (propagation speed amplitude et al.) which are solution of the model. Also it allows estimating of effective evaporation. In this approach it is possible to consider as an integrated difference between sea surface heights between previous and the subsequent cycles altimetric measurements. Results of calculations have confirmed well conformity given calculated by other researchers and the model. As is shown than interannual variability of flood wave speed in the North Caspian was well correlated with interannual the Caspian Sea level variability.
Bilbao, Stefan; Harrison, Reginald
2016-07-01
Numerical modeling of wave propagation in acoustic tubes is a subject of longstanding interest, particularly for enclosures of varying cross section, and especially when viscothermal losses due to boundary layer effects are taken into consideration. Though steady-state, or frequency domain methods, are a common avenue of approach, recursive time domain methods are an alternative, allowing for the generation of wideband responses, and offer a point of departure for more general modeling of nonlinear wave propagation. The design of time-domain methods is complicated by numerical stability considerations, and to this end, a passive representation is a useful design principle leading to simple stable and explicit numerical schemes, particularly in the case of viscothermal loss modeling. Such schemes and the accompanying energy and stability analysis are presented here. Numerical examples are presented for a variety of duct profiles, illustrating strict energy dissipation, and for comparison of computed input impedances against frequency-domain results.
Rup, K.; Dróżdż, A.
2014-08-01
The purpose of this article is to develop a non-linear, one-dimensional model of pulse wave propagation in the arterial cardiovascular system. The model includes partial differential equations resulting from the balance of mass and momentum for the fluid-filled area and the balance equation for the area of the wall and vessels. The considered mathematical model of pulse wave propagation in the thoracic aorta section takes into account the viscous dissipation of fluid energy, realistic values of parameters describing the physicochemical properties of blood and vessel wall. Boundary and initial conditions contain the appropriate information obtained from in vivo measurements. As a result of the numerical solution of the mass and momentum balance equations for the blood and the equilibrium equation for the arterial wall area, time- dependent deformation, respective velocity profiles and blood pressure were determined.
Yu, Ting; Chaix, Jean-François; Komatitsch, Dimitri; Garnier, Vincent; Audibert, Lorenzo; Henault, Jean-Marie
2017-02-01
Multiple scattering is important when ultrasounds propagate in a heterogeneous medium such as concrete, the scatterer size of which is in the order of the wavelength. The aim of this work is to build a 2D numerical model of ultrasonic wave propagation integrating the multiple scattering phenomena in SPECFEM software. The coherent field of multiple scattering could be obtained by averaging numerical wave fields, and it is used to determine the effective phase velocity and attenuation corresponding to an equivalent homogeneous medium. After the creation of numerical model under several assumptions, its validation is completed in a case of scattering by one cylinder through the comparison with analytical solution. Two cases of multiple scattering by a set of cylinders at different concentrations are simulated to perform a parametric study (of frequency, scatterer concentration, scatterer size). The effective properties are compared with the predictions of Waterman-Truell model as well, to verify its validity.
Wave propagation and group velocity
Brillouin, Léon
1960-01-01
Wave Propagation and Group Velocity contains papers on group velocity which were published during the First World War and are missing in many libraries. It introduces three different definitions of velocities: the group velocity of Lord Rayleigh, the signal velocity of Sommerfeld, and the velocity of energy transfer, which yields the rate of energy flow through a continuous wave and is strongly related to the characteristic impedance. These three velocities are identical for nonabsorbing media, but they differ considerably in an absorption band. Some examples are discussed in the last chapter
Morelli, Andrea; Danecek, Peter; Molinari, Irene; Postpischl, Luca; Schivardi, Renata; Serretti, Paola; Tondi, Maria Rosaria
2010-05-01
Together with the building and maintenance of observational and data banking infrastructures - i.e. an integrated organization of coordinated sensor networks, in conjunction with connected data banks and efficient data retrieval tools - a strategic vision for bolstering the future development of geophysics in Europe should also address the essential issue of improving our current ability to model coherently the propagation of seismic waves across the European plate. This impacts on fundamental matters, such as correctly locating earthquakes, imaging detailed earthquake source properties, modeling ground shaking, inferring geodynamic processes. To this extent, we both need detailed imaging of shallow and deep earth structure, and accurate modeling of seismic waves by numerical methods. Our current abilities appear somewhat limited, but emerging technologies may enable soon a significant leap towards better accuracy and reliability. To contribute to this debate, we present here the state-of-the-art of knowledge of earth structure and numerical wave modeling in the European plate, as the result of a comprehensive study towards the definition of a continental-scale reference model. Our model includes a description of crustal structure (EPcrust) merging information deriving from previous studies - large-scale compilations, seismic prospection, receiver functions, inversion of surface wave dispersion measurements and Green functions from noise correlation. We use a simple description of crustal structure, with laterally-varying sediment and cristalline layers thickness, density, and seismic parameters. This a priori crustal model improves the overall fit to observed Bouguer anomaly maps over CRUST2.0. The new crustal model is then used as a constraint in the inversion for mantle shear wave speed, based on fitting Love and Rayleigh surface wave dispersion. The new mantle model sensibly improves over global S models in the imaging of shallow asthenospheric (slow) anomalies
Wave equations for pulse propagation
Energy Technology Data Exchange (ETDEWEB)
Shore, B.W.
1987-06-24
Theoretical discussions of the propagation of pulses of laser radiation through atomic or molecular vapor rely on a number of traditional approximations for idealizing the radiation and the molecules, and for quantifying their mutual interaction by various equations of propagation (for the radiation) and excitation (for the molecules). In treating short-pulse phenomena it is essential to consider coherent excitation phenomena of the sort that is manifest in Rabi oscillations of atomic or molecular populations. Such processes are not adequately treated by rate equations for excitation nor by rate equations for radiation. As part of a more comprehensive treatment of the coupled equations that describe propagation of short pulses, this memo presents background discussion of the equations that describe the field. This memo discusses the origin, in Maxwell's equations, of the wave equation used in the description of pulse propagation. It notes the separation into lamellar and solenoidal (or longitudinal and transverse) and positive and negative frequency parts. It mentions the possibility of separating the polarization field into linear and nonlinear parts, in order to define a susceptibility or index of refraction and, from these, a phase and group velocity. The memo discusses various ways of characterizing the polarization characteristics of plane waves, that is, of parameterizing a transverse unit vector, such as the Jones vector, the Stokes vector, and the Poincare sphere. It discusses the connection between macroscopically defined quantities, such as the intensity or, more generally, the Stokes parameters, and microscopic field amplitudes. The material presented here is a portion of a more extensive treatment of propagation to be presented separately. The equations presented here have been described in various books and articles. They are collected here as a summary and review of theory needed when treating pulse propagation.
Wave propagation in axially moving periodic strings
DEFF Research Database (Denmark)
Sorokin, Vladislav S.; Thomsen, Jon Juel
2017-01-01
The paper deals with analytically studying transverse waves propagation in an axially moving string with periodically modulated cross section. The structure effectively models various relevant technological systems, e.g. belts, thread lines, band saws, etc., and, in particular, roller chain drive...
Shallow water sound propagation with surface waves.
Tindle, Chris T; Deane, Grant B
2005-05-01
The theory of wavefront modeling in underwater acoustics is extended to allow rapid range dependence of the boundaries such as occurs in shallow water with surface waves. The theory allows for multiple reflections at surface and bottom as well as focusing and defocusing due to reflection from surface waves. The phase and amplitude of the field are calculated directly and used to model pulse propagation in the time domain. Pulse waveforms are obtained directly for all wavefront arrivals including both insonified and shadow regions near caustics. Calculated waveforms agree well with a reference solution and data obtained in a near-shore shallow water experiment with surface waves over a sloping bottom.
Modeling Radar Wave Propagation Through Comet 67P / Churyumov-Gerasimenko
Scabbia, G.; Heggy, E.; Lasue, J.; Kofman, W. W.; Palmer, E. M.
2014-12-01
The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) onboard the Rosetta mission, as well as future cometary mission concepts, are planned to explore the inner structure of comets to complement our knowledge on the evolution of these small bodies that is currently only driven by surficial remote sensing measurements. An essential step in understanding the performance and the science return of current and future sounding experiments is an accurate understanding of the dielectric properties of comets and how they translate to the different physical, chemical and structural hypotheses of these bodies. To help constrain the ambiguities associated with this wide parametric space, we build eight parametric 3D dielectric models of the comet nucleus representing different structural and physical formation hypotheses, and we simulated the propagation of radar waves through each nucleus model using the finite difference time domain (FDTD) method. We extrapolated the shape model from the first Rosetta Navigation Camera images, while the different internal structures of each model are representative of existing theories of comet nuclei structures. The complex dielectric constants used in our models have been generated using mixing laws for a porous mixture of ice and meteoritic dust. Our simulations were performed at a lower frequency with respect to the central frequency of the CONSERT instrument due to computational memory limitations. The lower resolution obtained will still provide a sufficient and close approximation of the final experiment, given that the dielectric properties of the nucleus' materials are non-dispersive. Our results suggest that each model of the comet nucleus' interior structure produces a different radar signature in both the transmitted and reflected signals. In particular we note that scattering from inner-structure complexity compromises the visibility of the comet backside. Our simulation suggests that we can discern the
Optimized Variational 1D Boussinesq modelling of coastal waves propagating over a slope
Adytia, D.; van Groesen, Embrecht W.C.
2012-01-01
The Variational Boussinesq Model (VBM) for waves is based on the essential property that wave phenomena can be exactly described as a Hamiltonian system. In the VBM, the fluid potential in the expression of the kinetic energy is approximated by its value at the free surface plus a linear combination
Lee, Shiann-Jong; Huang, Hsin-Hua; Shyu, J. Bruce H.; Yeh, Te-Yang; Lin, Tzu-Chi
2014-12-01
We build a numerical earthquake model, including numerical source and wave propagation models, to understand the rupture process and the ground motion time history of the 2013 ML 6.4 Ruisui earthquake in Taiwan. This moderately large event was located in the Longitudinal Valley, a suture zone of the Philippine Sea Plate and the Eurasia Plate. A joint source inversion analysis by using teleseismic body wave, GPS coseismic displacement and near field ground motion data was performed first. The inversion results derived from a western dipping fault plane indicate that the slip occurred in depths between 10 and 20 km. The rupture propagated from south to north and two asperities were resolved. The largest one was located approximately 15 km north of the epicenter with a maximum slip about 1 m. A 3D seismic wave propagation simulation based on the spectral-element method was then carried out by using the inverted source model. A strong rupture directivity effect in the northern area of the Longitudinal Valley was found, which was due to the northward rupture process. Forward synthetic waveforms could explain most of the near-field ground motion data for frequencies between 0.05 and 0.2 Hz. This numerical earthquake model not only helps us confirm the detailed rupture processes on the Central Range Fault but also gives contribution to regional seismic hazard mitigation for future large earthquakes.
Numerical Modelling of Rayleigh Wave Propagation in Course of Rapid Impulse Compaction
Herbut, Aneta; Rybak, Jarosław
2017-10-01
As the soil improvement technologies are the area of a rapid development, they require designing and implementing novel methods of control and calibration in order to ensure the safety of geotechnical works. At Wroclaw University of Science and Technology (Poland), these new methods are continually developed with the aim to provide the appropriate tools for the preliminary design of work process, as well as for the further ongoing on-site control of geotechnical works (steel sheet piling, pile driving or soil improvement technologies). The studies include preliminary numerical simulations and field tests concerning measurements and continuous histogram recording of shocks and vibrations and its ground-born dynamic impact on engineering structures. The impact of vibrations on reinforced concrete and masonry structures in the close proximity of the construction site may be destroying in both architectural and structural meaning. Those limits are juxtaposed in codes of practice, but always need an individual judgment. The results and observations make it possible to delineate specific modifications to the parameters of technology applied (e.g. hammer drop height). On the basis of numerous case studies of practical applications, already summarized and published, we were able to formulate the guidelines for work on the aforementioned sites. This work presents specific aspects of the active design (calibration of building site numerical model) by means of technology calibration, using the investigation of the impact of vibrations that occur during the Impulse Compaction on adjacent structures. A case study entails the impact of construction works on Rayleigh wave propagation in the zone of 100 m (radius) around the Compactor.
Stochastic model in microwave propagation
Energy Technology Data Exchange (ETDEWEB)
Ranfagni, A. [“Nello Carrara” Institute of Applied Physics, CNR Florence Research Area, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy); Mugnai, D., E-mail: d.mugnai@ifac.cnr.it [“Nello Carrara” Institute of Applied Physics, CNR Florence Research Area, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy)
2011-11-28
Further experimental results of delay time in microwave propagation are reported in the presence of a lossy medium (wood). The measurements show that the presence of a lossy medium makes the propagation slightly superluminal. The results are interpreted on the basis of a stochastic (or path integral) model, showing how this model is able to describe each kind of physical system in which multi-path trajectories are present. -- Highlights: ► We present new experimental results on electromagnetic “anomalous” propagation. ► We apply a path integral theoretical model to wave propagation. ► Stochastic processes and multi-path trajectories in propagation are considered.
Wave propagation simulation in normal and infarcted myocardium: computational and modelling issues
Maglaveras, N.; van Capelle, F. J.; de Bakker, J. M.
1998-01-01
Simulation of propagating action potentials (PAP) in normal and abnormal myocardium is used for the understanding of mechanisms responsible for eliciting dangerous arrhythmias. One- and two-dimensional models dealing with PAP properties are reviewed in this paper viewed both from the computational
Wave equations for pulse propagation
Shore, B. W.
1987-06-01
Theoretical discussions of the propagation of pulses of laser radiation through atomic or molecular vapor rely on a number of traditional approximations for idealizing the radiation and the molecules, and for quantifying their mutual interaction by various equations of propagation (for the radiation) and excitation (for the molecules). In treating short-pulse phenomena it is essential to consider coherent excitation phenomena of the sort that is manifest in Rabi oscillations of atomic or molecular populations. Such processes are not adequately treated by rate equations for excitation nor by rate equations for radiation. As part of a more comprehensive treatment of the coupled equations that describe propagation of short pulses, this memo presents background discussion of the equations that describe the field. This memo discusses the origin, in Maxwell's equations, of the wave equation used in the description of pulse propagation. It notes the separation into lamellar and solenoidal (or longitudinal and transverse) and positive and negative frequency parts. It mentions the possibility of separating the polarization field into linear and nonlinear parts, in order to define a susceptibility or index of refraction and, from these, a phase and group velocity.
Propagation of sound waves in ducts
DEFF Research Database (Denmark)
Jacobsen, Finn
2000-01-01
Plane wave propagation in ducts with rigid walls, radiation from ducts, classical four-pole theory for composite duct systems, and three-dimentional waves in wave guides of various cross-sectional shape are described.......Plane wave propagation in ducts with rigid walls, radiation from ducts, classical four-pole theory for composite duct systems, and three-dimentional waves in wave guides of various cross-sectional shape are described....
A hybrid scheme for absorbing edge reflections in numerical modeling of wave propagation
Liu, Yang
2010-03-01
We propose an efficient scheme to absorb reflections from the model boundaries in numerical solutions of wave equations. This scheme divides the computational domain into boundary, transition, and inner areas. The wavefields within the inner and boundary areas are computed by the wave equation and the one-way wave equation, respectively. The wavefields within the transition area are determined by a weighted combination of the wavefields computed by the wave equation and the one-way wave equation to obtain a smooth variation from the inner area to the boundary via the transition zone. The results from our finite-difference numerical modeling tests of the 2D acoustic wave equation show that the absorption enforced by this scheme gradually increases with increasing width of the transition area. We obtain equally good performance using pseudospectral and finite-element modeling with the same scheme. Our numerical experiments demonstrate that use of 10 grid points for absorbing edge reflections attains nearly perfect absorption. © 2010 Society of Exploration Geophysicists.
Simulation of wave propagation inside a human eye: acoustic eye model (AEM)
Požar, T.; Halilovič, M.; Horvat, D.; Petkovšek, R.
2018-02-01
The design and development of the acoustic eye model (AEM) is reported. The model consists of a computer-based simulation that describes the propagation of mechanical disturbance inside a simplified model of a human eye. The capabilities of the model are illustrated with examples, using different laser-induced initial loading conditions in different geometrical configurations typically occurring in ophthalmic medical procedures. The potential of the AEM is to predict the mechanical response of the treated eye tissue in advance, thus complementing other preliminary procedures preceding medical treatments.
Wave equations and computational models for sonic boom propagation through a turbulent atmosphere
Pierce, Allan D.
1992-01-01
The improved simulation of sonic boom propagation through the real atmosphere requires greater understanding of how the transient acoustic pulses popularly termed sonic booms are affected by atmospheric turbulence. A nonlinear partial differential equation that can be used to simulate the effects of smaller-scale atmospheric turbulence on sonic boom waveforms is described. The equation is first order in the time derivative and involves an extension of geometrical acoustics to include diffraction phenomena. Various terms in the equation are explained in physical terms. Such terms include those representing convection at the wave speed, diffraction, molecular relaxation, classical dissipation, and nonlinear steepening. The atmospheric turbulence enters through an effective sound speed, which varies with all three spatial coordinates, and which is the sum of the local sound speed and the component of the turbulent flow velocity projected along a central ray that connects the aircraft trajectory with the listener.
Wave propagation in sandwich panels with a poroelastic core.
Liu, Hao; Finnveden, Svante; Barbagallo, Mathias; Arteaga, Ines Lopez
2014-05-01
Wave propagation in sandwich panels with a poroelastic core, which is modeled by Biot's theory, is investigated using the waveguide finite element method. A waveguide poroelastic element is developed based on a displacement-pressure weak form. The dispersion curves of the sandwich panel are first identified as propagating or evanescent waves by varying the damping in the panel, and wave characteristics are analyzed by examining their motions. The energy distributions are calculated to identify the dominant motions. Simplified analytical models are also devised to show the main physics of the corresponding waves. This wave propagation analysis provides insight into the vibro-acoustic behavior of sandwich panels lined with elastic porous materials.
Garcia, Raphael F.; Brissaud, Quentin; Rolland, Lucie; Martin, Roland; Komatitsch, Dimitri; Spiga, Aymeric; Lognonné, Philippe; Banerdt, Bruce
2017-10-01
The propagation of acoustic and gravity waves in planetary atmospheres is strongly dependent on both wind conditions and attenuation properties. This study presents a finite-difference modeling tool tailored for acoustic-gravity wave applications that takes into account the effect of background winds, attenuation phenomena (including relaxation effects specific to carbon dioxide atmospheres) and wave amplification by exponential density decrease with height. The simulation tool is implemented in 2D Cartesian coordinates and first validated by comparison with analytical solutions for benchmark problems. It is then applied to surface explosions simulating meteor impacts on Mars in various Martian atmospheric conditions inferred from global climate models. The acoustic wave travel times are validated by comparison with 2D ray tracing in a windy atmosphere. Our simulations predict that acoustic waves generated by impacts can refract back to the surface on wind ducts at high altitude. In addition, due to the strong nighttime near-surface temperature gradient on Mars, the acoustic waves are trapped in a waveguide close to the surface, which allows a night-side detection of impacts at large distances in Mars plains. Such theoretical predictions are directly applicable to future measurements by the INSIGHT NASA Discovery mission.
Directory of Open Access Journals (Sweden)
Sergey F Pravdin
Full Text Available We develop a numerical approach based on our recent analytical model of fiber structure in the left ventricle of the human heart. A special curvilinear coordinate system is proposed to analytically include realistic ventricular shape and myofiber directions. With this anatomical model, electrophysiological simulations can be performed on a rectangular coordinate grid. We apply our method to study the effect of fiber rotation and electrical anisotropy of cardiac tissue (i.e., the ratio of the conductivity coefficients along and across the myocardial fibers on wave propagation using the ten Tusscher-Panfilov (2006 ionic model for human ventricular cells. We show that fiber rotation increases the speed of cardiac activation and attenuates the effects of anisotropy. Our results show that the fiber rotation in the heart is an important factor underlying cardiac excitation. We also study scroll wave dynamics in our model and show the drift of a scroll wave filament whose velocity depends non-monotonically on the fiber rotation angle; the period of scroll wave rotation decreases with an increase of the fiber rotation angle; an increase in anisotropy may cause the breakup of a scroll wave, similar to the mother rotor mechanism of ventricular fibrillation.
Pravdin, Sergey F; Dierckx, Hans; Katsnelson, Leonid B; Solovyova, Olga; Markhasin, Vladimir S; Panfilov, Alexander V
2014-01-01
We develop a numerical approach based on our recent analytical model of fiber structure in the left ventricle of the human heart. A special curvilinear coordinate system is proposed to analytically include realistic ventricular shape and myofiber directions. With this anatomical model, electrophysiological simulations can be performed on a rectangular coordinate grid. We apply our method to study the effect of fiber rotation and electrical anisotropy of cardiac tissue (i.e., the ratio of the conductivity coefficients along and across the myocardial fibers) on wave propagation using the ten Tusscher-Panfilov (2006) ionic model for human ventricular cells. We show that fiber rotation increases the speed of cardiac activation and attenuates the effects of anisotropy. Our results show that the fiber rotation in the heart is an important factor underlying cardiac excitation. We also study scroll wave dynamics in our model and show the drift of a scroll wave filament whose velocity depends non-monotonically on the fiber rotation angle; the period of scroll wave rotation decreases with an increase of the fiber rotation angle; an increase in anisotropy may cause the breakup of a scroll wave, similar to the mother rotor mechanism of ventricular fibrillation.
Wave propagation simulation in normal and infarcted myocardium: computational and modelling issues.
Maglaveras, N; Van Capelle, F J; De Bakker, J M
1998-01-01
Simulation of propagating action potentials (PAP) in normal and abnormal myocardium is used for the understanding of mechanisms responsible for eliciting dangerous arrhythmias. One- and two-dimensional models dealing with PAP properties are reviewed in this paper viewed both from the computational and mathematical aspects. These models are used for linking theoretical and experimental results. The discontinuous nature of the PAP is demonstrated through the combination of experimental and theoretically derived results. In particular it can be shown that for increased intracellular coupling resistance the PAP upstroke phase properties (Vmax, dV/dtmax and tau foot) change considerably, and in some cases non-monotonically with increased coupling resistance. It is shown that tau foot) is a parameter that is very sensitive to the cell's distance to the stimulus site, the stimulus strength and the coupling resistance. In particular it can be shown that in a one-dimensional structure the tau foot value can increase dramatically for lower coupling resistance values near the stimulus site and subsequently can be reduced as we move to distances larger than five resting length constants from the stimulus site. The tau foot variability is reduced with increased coupling resistance, rendering the lower coupling resistance structures, under abnormal excitation sequences, more vulnerable to conduction block and arrhythmias. Using the theory of discontinuous propagation of the PAP in the myocardium it is demonstrated that for specific abnormal situations in the myocardium, such as infarcted tissue, one- and two-dimensional models can reliably simulate propagation characteristics and explain complex phenomena such as propagation at bifurcation sites and mechanisms of block and re-entry. In conclusion it is shown that applied mathematics and informatics can help in elucidating electrophysiologically complex mechanisms such as arrhythmias and conduction disturbances in the myocardium.
Rigorous 2D Model for Study of Pulsed and Monochromatic Waves Propagation Near the Earth’s Surface
Directory of Open Access Journals (Sweden)
Seil S. Sautbekov
2014-01-01
Full Text Available A model problem considered in the paper allows solving rather complex 2D problems of the electromagnetic wave propagation with a required accuracy using conventional personal computers. The problems are of great importance for the theory and practical applications. The association of FDTD schemes with exact absorbing conditions makes up the basis for constructing models of the kind. This approach reduces the original open initial boundary value problems to the equivalent closed problems which can be solved numerically using the standard grid methods.
Large-scale Globally Propagating Coronal Waves
Directory of Open Access Journals (Sweden)
Alexander Warmuth
2015-09-01
Full Text Available Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the “classical” interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which “pseudo waves” are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.
Delrue, Steven; Aleshin, Vladislav; Truyaert, Kevin; Bou Matar, Olivier; Van Den Abeele, Koen
2018-01-01
Our study aims at the creation of a numerical toolbox that describes wave propagation in samples containing internal contacts (e.g. cracks, delaminations, debondings, imperfect intergranular joints) of known geometry with postulated contact interaction laws including friction. The code consists of two entities: the contact model and the solid mechanics module. Part I of the paper concerns an in-depth description of a constitutive model for realistic contacts or cracks that takes into account the roughness of the contact faces and the associated effects of friction and hysteresis. In the crack model, three different contact states can be recognized: contact loss, total sliding and partial slip. Normal (clapping) interactions between the crack faces are implemented using a quadratic stress-displacement relation, whereas tangential (friction) interactions were introduced using the Coulomb friction law for the total sliding case, and the Method of Memory Diagrams (MMD) in case of partial slip. In the present part of the paper, we integrate the developed crack model into finite element software in order to simulate elastic wave propagation in a solid material containing internal contacts or cracks. We therefore implemented the comprehensive crack model in MATLAB® and introduced it in the Structural Mechanics Module of COMSOL Multiphysics®. The potential of the approach for ultrasound based inspection of solids with cracks showing acoustic nonlinearity is demonstrated by means of an example of shear wave propagation in an aluminum sample containing a single crack with rough surfaces and friction. Copyright © 2017 Elsevier B.V. All rights reserved.
Modeling of high‐frequency seismic‐wave scattering and propagation using radiative transfer theory
Zeng, Yuehua
2017-01-01
This is a study of the nonisotropic scattering process based on radiative transfer theory and its application to the observation of the M 4.3 aftershock recording of the 2008 Wells earthquake sequence in Nevada. Given a wide range of recording distances from 29 to 320 km, the data provide a unique opportunity to discriminate scattering models based on their distance‐dependent behaviors. First, we develop a stable numerical procedure to simulate nonisotropic scattering waves based on the 3D nonisotropic scattering theory proposed by Sato (1995). By applying the simulation method to the inversion of M 4.3 Wells aftershock recordings, we find that a nonisotropic scattering model, dominated by forward scattering, provides the best fit to the observed high‐frequency direct S waves and S‐wave coda velocity envelopes. The scattering process is governed by a Gaussian autocorrelation function, suggesting a Gaussian random heterogeneous structure for the Nevada crust. The model successfully explains the common decay of seismic coda independent of source–station locations as a result of energy leaking from multiple strong forward scattering, instead of backscattering governed by the diffusion solution at large lapse times. The model also explains the pulse‐broadening effect in the high‐frequency direct and early arriving S waves, as other studies have found, and could be very important to applications of high‐frequency wave simulation in which scattering has a strong effect. We also find that regardless of its physical implications, the isotropic scattering model provides the same effective scattering coefficient and intrinsic attenuation estimates as the forward scattering model, suggesting that the isotropic scattering model is still a viable tool for the study of seismic scattering and intrinsic attenuation coefficients in the Earth.
Directory of Open Access Journals (Sweden)
Richard A. Hazelwood
2016-08-01
Full Text Available Seismic interface waves generated by seabed impacts are believed to have biological importance. Various wave types are of interest to seismologists, who can minimize the unwanted, but often dominant, ground roll waves with suitable instrumentation. Waves made by dredging and piling have been measured using geophones and found to be of this interface type, which propagate much more slowly than the pressure waves in the water column above. Short interface wavelets of a few cycles were modeled using transient finite element analysis (FEA. Wavelets with low losses have been modeled using graded sediment data from the literature. They do not radiate energy away from the interface because the evanescent acoustic pressures they generate decay rapidly with distance from the seabed. Associated water particle velocities are much greater than would be expected from similar acoustic pressure measurements in a free field. This motion is significant to aquatic life which is dependent on inertial sensors (otoliths, etc. to respond to the environment. Additional amplification of the horizontal seabed motion of the adjacent water is predicted for a short seismic wavelet modeled in a graded solid seabed. Further recent analysis studied the distribution of the energy flux within the sediment layers.
Simulations of Seismic Wave Propagation on Mars
Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; Khan, Amir; Leng, Kuangdai; van Driel, Martin; Wieczorek, Mark; Rivoldini, Attilio; Larmat, Carène S.; Giardini, Domenico; Tromp, Jeroen; Lognonné, Philippe; Banerdt, Bruce W.
2017-10-01
We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust (Sohl and Spohn in J. Geophys. Res., Planets 102(E1):1613-1635, 1997). For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp in Geophys. J. Int. 149(2):390-412, 2002a; 150(1):303-318, 2002b) against the 2D axisymmetric wave propagation solver AxiSEM (Nissen-Meyer et al. in Solid Earth 5(1):425-445, 2014) at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars' northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D (Fichtner et al. Geophys. J. Int. 179:1703-1725, 2009) based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. We conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.
Topology Optimization in wave-propagation and flow problems
DEFF Research Database (Denmark)
Sigmund, Ole; Jensen, Jakob Søndergaard; Gersborg-Hansen, A.
2004-01-01
We discuss recent extensions of the topology optimization method to wave-propagation and flow problems. More specifically, we optimize material distribution in scalar wave propagation problems modelled by Helmholtz equation. Moreover, we investigate the influence of the inertia term on the optimal...
Wave propagation in the magnetosphere of Jupiter
Liemohn, H. B.
1972-01-01
A systematic procedure is developed for identifying the spatial regimes of various modes of wave propagation in the Jupiter magnetosphere that may be encountered by flyby missions. The Clemmow-Mullaly-Allis (CMA) diagram of plasma physics is utilized to identify the frequency regimes in which different modes of propagation occur in the magnetoplasma. The Gledhill model and the Ioannidis and Brice model of the magnetoplasma are summarized, and configuration-space CMA diagrams are constructed for each model for frequencies from 10 Hz to 1 MHz. The distinctive propagation features, the radio noise regimes, and the wave-particle interactions are discussed. It is concluded that the concentration of plasma in the equatorial plane makes this region of vital importance for radio observations with flyby missions. Local radio noise around the electron cyclotron frequency will probably differ appreciably from its terrestrial counterpart due to the lack of field-line guidance. Hydromagnetic wave properties at frequencies near the ion cyclotron frequency and below will probably be similar to the terrestrial case.
Sixty gigahertz indoor radio wave propagation prediction method based on full scattering model
Järveläinen, J.; Haneda, K.
2014-04-01
In radio system deployment, the main focus is on assuring sufficient coverage, which can be estimated with path loss models for specific scenarios. When more detailed performance metrics such as peak throughput are studied, the environment has to be modeled accurately in order to estimate multipath behavior. By means of laser scanning we can acquire very accurate data of indoor environments, but the format of the scanning data, a point cloud, cannot be used directly in available deterministic propagation prediction tools. Therefore, we propose to use a single-lobe directive model, which calculates the electromagnetic field scattering from a small surface and is applicable to the point cloud, and describe the overall field as fully diffuse backscattering from the point cloud. The focus of this paper is to validate the point cloud-based full diffuse propagation prediction method at 60 GHz. The performance is evaluated by comparing characteristics of measured and predicted power delay profiles in a small office room and an ultrasonic inspection room in a hospital. Also directional characteristics are investigated. It is shown that by considering single-bounce scattering only, the mean delay can be estimated with an average error of 2.6% and the RMS delay spread with an average error of 8.2%. The errors when calculating the azimuth and elevation spreads are 2.6° and 0.6°, respectively. Furthermore, the results demonstrate the applicability of a single parameter set to characterize the propagation channel in all transmit and receive antenna locations in the tested scenarios.
A new global model for the ionospheric F2 peak height for radio wave propagation
Directory of Open Access Journals (Sweden)
M. M. Hoque
2012-05-01
Full Text Available The F2-layer peak density height hmF2 is one of the most important ionospheric parameters characterizing HF propagation conditions. Therefore, the ability to model and predict the spatial and temporal variations of the peak electron density height is of great use for both ionospheric research and radio frequency planning and operation. For global hmF2 modelling we present a nonlinear model approach with 13 model coefficients and a few empirically fixed parameters. The model approach describes the temporal and spatial dependencies of hmF2 on global scale. For determining the 13 model coefficients, we apply this model approach to a large quantity of global hmF2 observational data obtained from GNSS radio occultation measurements onboard CHAMP, GRACE and COSMIC satellites and data from 69 worldwide ionosonde stations. We have found that the model fits to these input data with the same root mean squared (RMS and standard deviations of 10%. In comparison with the electron density NeQuick model, the proposed Neustrelitz global hmF2 model (Neustrelitz Peak Height Model – NPHM shows percentage RMS deviations of about 13% and 12% from the observational data during high and low solar activity conditions, respectively, whereas the corresponding deviations for the NeQuick model are found 18% and 16%, respectively.
A new global model for the ionospheric F2 peak height for radio wave propagation
Directory of Open Access Journals (Sweden)
M. M. Hoque
2012-05-01
Full Text Available The F2-layer peak density height hmF2 is one of the most important ionospheric parameters characterizing HF propagation conditions. Therefore, the ability to model and predict the spatial and temporal variations of the peak electron density height is of great use for both ionospheric research and radio frequency planning and operation. For global hmF2 modelling we present a nonlinear model approach with 13 model coefficients and a few empirically fixed parameters. The model approach describes the temporal and spatial dependencies of hmF2 on global scale. For determining the 13 model coefficients, we apply this model approach to a large quantity of global hmF2 observational data obtained from GNSS radio occultation measurements onboard CHAMP, GRACE and COSMIC satellites and data from 69 worldwide ionosonde stations. We have found that the model fits to these input data with the same root mean squared (RMS and standard deviations of 10%. In comparison with the electron density NeQuick model, the proposed Neustrelitz global hmF2 model (Neustrelitz Peak Height Model – NPHM shows percentage RMS deviations of about 13% and 12% from the observational data during high and low solar activity conditions, respectively, whereas the corresponding deviations for the NeQuick model are found 18% and 16%, respectively.
Observations of Obliquely Propagating Electron Bernstein Waves
DEFF Research Database (Denmark)
Armstrong, R. J.; Juul Rasmussen, Jens; Stenzel, R. L.
1981-01-01
Plane electron Bernstein waves propagating obliquely to the magnetic field are investigated. The waves are excited by a plane grid antenna in a large volume magnetoplasma. The observations compare favorably with the predictions of the linear dispersion relation.......Plane electron Bernstein waves propagating obliquely to the magnetic field are investigated. The waves are excited by a plane grid antenna in a large volume magnetoplasma. The observations compare favorably with the predictions of the linear dispersion relation....
Wave Propagation Across Muddy Seafloors
2007-01-01
cm thick layer of yogurt -like mud (density about 1.6 g/l [G. Kineke and S. Bentley]) that caused significant dissipation of the wave field, as shown...time series and processed data products for their studies. For example, NCEX observations are being used in collaboration with modeling studies and as
Topology optimization of wave-propagation problems
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard; Sigmund, Ole
2006-01-01
Topology optimization is demonstrated as a useful tool for systematic design of wave-propagation problems. We illustrate the applicability of the method for optical, acoustic and elastic devices and structures.......Topology optimization is demonstrated as a useful tool for systematic design of wave-propagation problems. We illustrate the applicability of the method for optical, acoustic and elastic devices and structures....
Petrov, P.; Newman, G. A.
2010-12-01
Quantitative imaging of the subsurface objects is essential part of modern geophysical technology important in oil and gas exploration and wide-range engineering applications. A significant advancement in developing a robust, high resolution imaging technology is concerned with using the different geophysical measurements (gravity, EM and seismic) sense the subsurface structure. A joint image of the subsurface geophysical attributes (velocity, electrical conductivity and density) requires the consistent treatment of the different geophysical data (electromagnetic and seismic) due to their differing physical nature - diffusive and attenuated propagation of electromagnetic energy and nonlinear, multiple scattering wave propagation of seismic energy. Recent progress has been reported in the solution of this problem by reducing the complexity of seismic wave field. Works formed by Shin and Cha (2009 and 2008) suggests that low-pass filtering the seismic trace via Laplace-Fourier transformation can be an effective approach for obtaining seismic data that has similar spatial resolution to EM data. The effect of Laplace- Fourier transformation on the low-pass filtered trace changes the modeling of the seismic wave field from multi-wave propagation to diffusion. The key benefit of transformation is that diffusive wave-field inversion works well for both data sets seismic (Shin and Cha, 2008) and electromagnetic (Commer and Newman 2008, Newman et al., 2010). Moreover the different data sets can also be matched for similar and consistent resolution. Finally, the low pass seismic image is also an excellent choice for a starting model when analyzing the entire seismic waveform to recover the high spatial frequency components of the seismic image; its reflectivity (Shin and Cha, 2009). Without a good starting model full waveform seismic imaging and migration can encounter serious difficulties. To produce seismic wave fields consistent for joint imaging in the Laplace
Chen, Wen; Fang, Jun; Pang, Guofei; Holm, Sverre
2017-01-01
This paper proposes a fractional biharmonic operator equation model in the time-space domain to describe scattering attenuation of acoustic waves in heterogeneous media. Compared with the existing models, the proposed fractional model is able to describe arbitrary frequency-dependent scattering attenuation, which typically obeys an empirical power law with an exponent ranging from 0 to 4. In stark contrast to an extensive and rapidly increasing application of the fractional derivative models for wave absorption attenuation in the literature, little has been reported on frequency-dependent scattering attenuation. This is largely because the order of the fractional Laplacian is from 0 to 2 and is infeasible for scattering attenuation. In this study, the definition of the fractional biharmonic operator in space with an order varying from 0 to 4 is proposed, as well as a fractional biharmonic operator equation model of scattering attenuation which is consistent with arbitrary frequency power-law dependency and obeys the causal relation under the smallness approximation. Finally, the correlation between the fractional order and the ratio of wavelength to the diameter of the scattering heterogeneity is investigated and an expression on exponential form is also provided.
Terrestrial propagation of long electromagnetic waves
Galejs, Janis; Fock, V A
2013-01-01
Terrestrial Propagation of Long Electromagnetic Waves deals with the propagation of long electromagnetic waves confined principally to the shell between the earth and the ionosphere, known as the terrestrial waveguide. The discussion is limited to steady-state solutions in a waveguide that is uniform in the direction of propagation. Wave propagation is characterized almost exclusively by mode theory. The mathematics are developed only for sources at the ground surface or within the waveguide, including artificial sources as well as lightning discharges. This volume is comprised of nine chapte
Wave propagation in nanostructures nonlocal continuum mechanics formulations
Gopalakrishnan, Srinivasan
2013-01-01
Wave Propagation in Nanostructures describes the fundamental and advanced concepts of waves propagating in structures that have dimensions of the order of nanometers. The book is fundamentally based on non-local elasticity theory, which includes scale effects in the continuum model. The book predominantly addresses wave behavior in carbon nanotubes and graphene structures, although the methods of analysis provided in this text are equally applicable to other nanostructures. The book takes the reader from the fundamentals of wave propagation in nanotubes to more advanced topics such as rotating nanotubes, coupled nanotubes, and nanotubes with magnetic field and surface effects. The first few chapters cover the basics of wave propagation, different modeling schemes for nanostructures and introduce non-local elasticity theories, which form the building blocks for understanding the material provided in later chapters. A number of interesting examples are provided to illustrate the important features of wave behav...
Costantino, Lorenzo; Heinrich, Philippe
2014-05-01
Small scale atmospheric waves, usually referred as internal of Gravity Waves (GW), represent an efficient transport mechanism of energy and momentum through the atmosphere. They propagate upward from their sources in the lower atmosphere (flow over topography, convection and jet adjustment) to the middle and upper atmosphere. Depending on the horizontal wind shear, they can dissipate at different altitudes and force the atmospheric circulation of the stratosphere and mesosphere. The deposition of momentum associated with the dissipation, or wave breaking, exerts an acceleration to the mean flow, that can significantly alter the thermal and dynamical structure of the atmosphere. GW may have spatial scales that range from few to hundreds of kilometers and range from minutes to hours. For that reason, General Circulation Model (GCM) used in climate studies have generally a coarse resolution, of approximately 2-5° horizontally and 3 km vertically, in the stratosphere. This resolution is fine enough to resolve Rossby-waves but not the small-scale GW activity. Hence, to calculate the momentum-forcing generated by the unresolved waves, they use a drag parametrization which mainly consists in some tuning parameters, constrained by observations of wind circulation and temperature in the upper troposphere and middle atmosphere (Alexander et al., 2010). Traditionally, the GW Drag (GWD) parametrization is used in climate and forecasting models to adjust the structure of winter jets and the horizontal temperature gradient. It was firstly based on the parametrization of orographic waves, which represent zero-phase-speed waves generated by sub-grid topography. Regional models, with horizontal resolutions that can reach few tens or hundreds of meters, are able to directly resolve small-scale GW and may represent a valuable addition to direct observations. In the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project, this study tests the
Kotova, D. S.; Klimenko, M. V.; Klimenko, V. V.; Zakharov, V. E.; Ratovsky, K. G.; Nosikov, I. A.; Zhao, B.
2015-11-01
This paper analyses the geomagnetic storm on September 26-29, 2011. We compare the calculation results obtained using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) and IRI-2012 (Bilitza et al., 2014) model with ground-based ionosonde data of stations at different latitudes and longitudes. We examined physical mechanisms responsible for the formation of ionospheric effects during the main phase of geomagnetic storm that occurred at the rising phase of the 24th solar cycle. We used numerical results obtained from IRI-2012 and GSM TIP models as propagation environment for HF signals from an equatorial transmitter during quiet and disturbed conditions. We used the model of HF radio wave propagation developed in I. Kant Baltic Federal University (BFU) that is based on the geometrical optics approximation. We compared the obtained radio paths in quiet conditions and during the main and recovery storm phases and evaluated radio wave attenuation in different media models.
Lallouette, Jules; De Pittà, Maurizio; Ben-Jacob, Eshel; Berry, Hugues
2014-01-01
Traditionally, astrocytes have been considered to couple via gap-junctions into a syncytium with only rudimentary spatial organization. However, this view is challenged by growing experimental evidence that astrocytes organize as a proper gap-junction mediated network with more complex region-dependent properties. On the other hand, the propagation range of intercellular calcium waves (ICW) within astrocyte populations is as well highly variable, depending on the brain region considered. This suggests that the variability of the topology of gap-junction couplings could play a role in the variability of the ICW propagation range. Since this hypothesis is very difficult to investigate with current experimental approaches, we explore it here using a biophysically realistic model of three-dimensional astrocyte networks in which we varied the topology of the astrocyte network, while keeping intracellular properties and spatial cell distribution and density constant. Computer simulations of the model suggest that changing the topology of the network is indeed sufficient to reproduce the distinct ranges of ICW propagation reported experimentally. Unexpectedly, our simulations also predict that sparse connectivity and restriction of gap-junction couplings to short distances should favor propagation while long–distance or dense connectivity should impair it. Altogether, our results provide support to recent experimental findings that point toward a significant functional role of the organization of gap-junction couplings into proper astroglial networks. Dynamic control of this topology by neurons and signaling molecules could thus constitute a new type of regulation of neuron-glia and glia-glia interactions. PMID:24795613
Asano, K.; Sekiguchi, H.; Iwata, T.; Yoshimi, M.; Hayashida, T.; Saomoto, H.; Horikawa, H.
2013-12-01
The three-dimensional velocity structure model for the Osaka sedimentary basin, southwest Japan is developed and improved based on many kinds of geophysical explorations for decades (e.g., Kagawa et al., 1993; Horikawa et al., 2003; Iwata et al., 2008). Recently, our project (Sekiguchi et al., 2013) developed a new three-dimensional velocity model for strong motion prediction of the Uemachi fault earthquake in the Osaka basin considering both geophysical and geological information by adding newly obtained exploration data such as reflection surveys, microtremor surveys, and receiver function analysis (hereafter we call UMC2013 model) . On April 13, 2013, an inland earthquake of Mw5.8 occurred in Awaji Island, which is close to the southwestern boundary of the aftershock area of the 1995 Kobe earthquake. The strong ground motions are densely observed at more than 100 stations in the basin. The ground motion lasted longer than four minutes in the Osaka urban area where its bedrock depth is about 1-2 km. This long-duration ground motions are mainly due to the surface waves excited in this sedimentary basin whereas the magnitude of this earthquake is moderate and the rupture duration is expected to be less than 5 s. In this study, we modeled long-period (more than 2s) ground motions during this earthquake to check the performance of the present UMC2013 model and to obtain a better constraint on the attenuation factor of sedimentary part of the basin. The seismic wave propagation in the region including the source and the Osaka basin is modeled by the finite difference method using the staggered grid solving the elasto-dynamic equations. The domain of 90km×85km×25.5km is modeled and discretized with a grid spacing of 50 m. Since the minimum S-wave velocity of the UMC2013 model is about 250 m/s, this calculation is valid up to the period of about 1 s. The effect of attenuation is included in the form of Q(f)=Q0(T0/T) proposed by Graves (1996). A PML is implemented in
Wave propagation and impact in composite materials
Moon, F. C.
1975-01-01
Anisotropic waves in composites are considered, taking into account wave speeds, wave surfaces, flexural waves in orthotropic plates, surface waves, edge waves in plates, and waves in coupled composite plates. Aspects of dispersion in composites are discussed, giving attention to pulse propagation and dispersion, dispersion in rods and plates, dispersion in a layered composite, combined material and structural dispersion, continuum theories for composites, and variational methods for periodic composites. The characteristics of attenuation and scattering processes are examined and a description is given of shock waves and impact problems in composites. A number of experiments are also reported.
Multilayered tissues model for wave propagation loss assessment in cochlear implants
Paun, Maria-Alexandra; Dehollain, Catherine
2017-05-01
In this paper, a study of the power loss attenuation of the plane wave travelling through the tissue layers, from the outside to the inside of the skull within a cochlear implant, is performed. Different implantation depths of the internal antenna from 10 to 30 mm are considered. To this purpose, the gain and attenuation in dB are studied. A multilayer tissue model is developed, consisting of mainly skin, mastoid bone and brain. An s-parameter analysis is also carried out, using loop antennas and simulated head tissue. Ansoft Ansys® HFSS software is used for electro-magnetic simulations of the antennas, placed in different types of human tissues. Smith charts for antenna placed in both skin and multi-tissue model are included.
A Model for the Propagation of Nonlinear Surface Waves over Viscous Muds
2007-07-05
here that the linear long wave theory ( Dean and Dalrymple , 1991) the length of the domain, the water depth and the extent of the mud expected...herein. From Similar to the previous test, our next test involves the linear long wave theory ( Dean and Dalrymple , 1991) the transformation of waves of...diffraction on the dissertation, Delft University of Technology. lee side. Further downwave, the discontinuity in the wave crest Dean , R.G., Dalrymple , R.A
Efficient Rasterization for Outdoor Radio Wave Propagation.
Schmitz, A; Rick, T; Karolski, T; Kuhlen, T; Kobbelt, L
2011-02-01
Conventional beam tracing can be used for solving global illumination problems. It is an efficient algorithm and performs very well when implemented on the GPU. This allows us to apply the algorithm in a novel way to the problem of radio wave propagation. The simulation of radio waves is conceptually analogous to the problem of light transport. We use a custom, parallel rasterization pipeline for creation and evaluation of the beams. We implement a subset of a standard 3D rasterization pipeline entirely on the GPU, supporting 2D and 3D frame buffers for output. Our algorithm can provide a detailed description of complex radio channel characteristics like propagation losses and the spread of arriving signals over time (delay spread). Those are essential for the planning of communication systems required by mobile network operators. For validation, we compare our simulation results with measurements from a real-world network. Furthermore, we account for characteristics of different propagation environments and estimate the influence of unknown components like traffic or vegetation by adapting model parameters to measurements.
A Two-Dimensional Transverse Magnetic Propagation Model of a Sine Wave Using Mur Boundary Conditions
National Research Council Canada - National Science Library
Korjack, T
1997-01-01
.... The nonreflecting boundary conditions due to Mur were used at the boundary surfaces. Electric field intensity distributions resulted over a progressive time expansion to illustrate the propagation effect over the entire 2-D mesh...
Wave Propagation inside Random Media
Cheng, Xiaojun
=-x/l where l is the transport mean free path. The result does not depend on the sample length, which is counterintuitive yet remarkably simple. More supprisingly, the linear fall-off of energy profile holds for totally disordered random 1D layered samples in simulations where the LDOS is uniform as well as for single mode random waveguide experiments and 1D nearly periodic samples where the LDOS is suppressed in the middle of the sample. The generalization of the transmission matrix to the interior of quasi-1D random samples, which is defined as the field matrix, and its eigenvalues statistics are also discussed. The maximum energy deposition at a location is not the intensity of the first transmission eigenchannel but the eigenvalue of the first energy density eigenchannels at that cross section, which can be much greater than the average value. The contrast, which is the ratio of the intensity at the focused point to the background intensity, in optimal focusing is determined by the participation number of the energy density eigenvalues and its inverse gives the variance of the energy density at that cross section in a single configuration. We have also studied topological states in photonic structures. We have demonstrated robust propagation of electromagnetic waves along reconfigurable pathways within a topological photonic metacrystal. Since the wave is confined within the domain wall, which is the boundary between two distinct topological insulating systems, we can freely steer the wave by reconstructing the photonic structure. Other topics, such as speckle pattern evolutions and the effects of boundary conditions on the statistics of transmission eigenvalues and energy profiles are also discussed.
Theoretical Studies of Stress Wave Propagation in Laterally Confined Soils
National Research Council Canada - National Science Library
Rohani, Behzad
1999-01-01
.... A considerable body of scientific literature on one-dimensional stress wave propagation for such models has been published in recent years by various researchers, both in the United States and abroad...
Electromagnetic Wave Propagation in Random Media
DEFF Research Database (Denmark)
Pécseli, Hans
1984-01-01
The propagation of a narrow frequency band beam of electromagnetic waves in a medium with randomly varying index of refraction is considered. A novel formulation of the governing equation is proposed. An equation for the average Green function (or transition probability) can then be derived....... A Fokker-Planck type equation is contained as a limiting case. The results are readily generalized to include the features of the random coupling model and it is argued that the present problem is particularly suited for an analysis of this type....
On all-FLR order numerical modelling of RF wave propagation and damping
Directory of Open Access Journals (Sweden)
Van Eester Dirk
2017-01-01
Full Text Available Determining the fate of waves in hot magnetized plasmas in magnetic confinement fusion machines close to arbitrary cyclotron harmonics retaining finite Larmor radius effects requires solving the relevant integro-differential wave equation for waves of arbitrary wavelength. Anticipating exploitation in as realistic geometry as possible this requires massive computer resources. Work is ongoing to attempt reducing the required CPU memory and time. As Morlet wavelets are localised in x-space as well as k-space, they potentially offer a means to solve the relevant wave equation at reduced CPU requirement cost. Encouraging first results are obtained.
On all-FLR order numerical modelling of RF wave propagation and damping
Van Eester, Dirk; Lerche, Ernesto
2017-10-01
Determining the fate of waves in hot magnetized plasmas in magnetic confinement fusion machines close to arbitrary cyclotron harmonics retaining finite Larmor radius effects requires solving the relevant integro-differential wave equation for waves of arbitrary wavelength. Anticipating exploitation in as realistic geometry as possible this requires massive computer resources. Work is ongoing to attempt reducing the required CPU memory and time. As Morlet wavelets are localised in x-space as well as k-space, they potentially offer a means to solve the relevant wave equation at reduced CPU requirement cost. Encouraging first results are obtained.
Torsional wave propagation in solar tornadoes
Vasheghani Farahani, S.; Ghanbari, E.; Ghaffari, G.; Safari, H.
2017-03-01
Aims: We investigate the propagation of torsional waves in coronal structures together with their collimation effects in the context of magnetohydrodynamic (MHD) theory. The interplay of the equilibrium twist and rotation of the structure, e.g. jet or tornado, together with the density contrast of its internal and external media is studied to shed light on the nature of torsional waves. Methods: We consider a rotating magnetic cylinder embedded in a plasma with a straight magnetic field. This resembles a solar tornado. In order to express the dispersion relations and phase speeds of the axisymmetric magnetohydrodynamic waves, the second-order thin flux tube approximation is implemented for the internal medium and the ideal MHD equations are implemented for the external medium. Results: The explicit expressions for the phase speed of the torsional wave show the modification of the torsional wave speed due to the equilibrium twist, rotation, and density contrast of the tornado. The speeds could be either sub-Alfvénic or ultra-Alfvénic depending on whether the equilibrium twist or rotation is dominant. The equilibrium twist increases the phase speed while the equilibrium rotation decreases it. The good agreement between the explicit versions for the phase speed and that obtained numerically proves adequate for the robustness of the model and method. The density ratio of the internal and external media also play a significant role in the speed and dispersion. Conclusions: The dispersion of the torsional wave is an indication of the compressibility of the oscillations. When the cylinder is rotating or twisted, in contrast to when it only possesses a straight magnetic field, the torsional wave is a collective mode. In this case its phase speed is determined by the Alfvén waves inside and outside the tornado.
Tunik, Yu. V.
In the present paper the direct initiation of a self supporting detonation and propagation of a low-speed combustion in methane-air-coal particles mixtures are solved. For particles, a heterogeneous regime of combustion is used, for methane one overall chemical reaction is taken into account: CH 4 + 2O 2 = CO 2 + 2H 2O. The heat release rate is assumed to be defined as a delay time based on the well-known thermal theory of Frank-Kamenetsky (1967). The proposed model allows one to investigate the influence inert particles or coal dust on the explosion limits of methane-air mixtures. It is shown that the addition of a limited quantity of particles leads to detonation stability. In low speed combustion problems this method allows one to get a good correlation between theoretical and experimental velocities of steady flame propagation in carbon-hydrogen gaseous mixtures. Coal dust influence on gasdynamics of a methane-air mixture combustion is investigated in an unsteady problem by using of the global modelling. It is shown that limited coal dust concentration increases the flame wave intensity in lean methane-air mixtures in contrast to inert particles. In stoichiometric gas mixtures, sand and coal dusts decrease a flame velocity. Far from the ignition point flame, the velocity is largely defined by the dust mass concentration and not by the size of particles.
Propagation of SLF/ELF electromagnetic waves
Pan, Weiyan
2014-01-01
This book deals with the SLF/ELF wave propagation, an important branch of electromagnetic theory. The SLF/ELF wave propagation theory is well applied in earthquake electromagnetic radiation, submarine communication, thunderstorm detection, and geophysical prospecting and diagnostics. The propagation of SLF/ELF electromagnetic waves is introduced in various media like the earth-ionospheric waveguide, ionospheric plasma, sea water, earth, and the boundary between two different media or the stratified media. Applications in the earthquake electromagnetic radiation and the submarine communications are also addressed. This book is intended for scientists and engineers in the fields of radio propagation and EM theory and applications. Prof. Pan is a professor at China Research Institute of Radiowave Propagation in Qingdao (China). Dr. Li is a professor at Zhejiang University in Hangzhou (China).
Wave propagation and scattering in random media
Ishimaru, Akira
1978-01-01
Wave Propagation and Scattering in Random Media, Volume 2, presents the fundamental formulations of wave propagation and scattering in random media in a unified and systematic manner. The topics covered in this book may be grouped into three categories: waves in random scatterers, waves in random continua, and rough surface scattering. Random scatterers are random distributions of many particles. Examples are rain, fog, smog, hail, ocean particles, red blood cells, polymers, and other particles in a state of Brownian motion. Random continua are the media whose characteristics vary randomly an
Coupled seismic and electromagnetic wave propagation
Schakel, M.D.
2011-01-01
Coupled seismic and electromagnetic wave propagation is studied theoretically and experimentally. This coupling arises because of the electrochemical double layer, which exists along the solid-grain/fluid-electrolyte boundaries of porous media. Within the double layer, charge is redistributed,
PROPAGATION OF CYLINDRICAL WAVES IN POROELASTIC MEDIA
Directory of Open Access Journals (Sweden)
Vorona Yu.V.
2014-12-01
Full Text Available The paper investigates the harmonic axisymmetric wave propagation in poroelastic media. The computational formulas for the study of displacements and stresses that occur during vibrations in a wide frequency range are proposed.
Wave Beam Propagation Through Density Fluctuations
Balakin, A. A.; Bertelli, N.; Westerhof, E.
2011-01-01
Perturbations induced by edge density fluctuations on electron cyclotron wave beams propagating in fusion plasmas are studied by means of a quasi-optical code. The effects of such fluctuations are illustrated here by showing the beam propagation in the case of single harmonic perturbations to the
Wave propagation in thermoelastic saturated porous medium
Indian Academy of Sciences (India)
playing a crucial role in non-destructive evaluation. (NDE) of composite materials and structures. The studies of ... diffusion type heat equation used in this study predicted infinite speed for propagation of ther- mal signals. ..... the NDE problems involving wave propagation in thermoelastic porous solids. When supported with.
Directory of Open Access Journals (Sweden)
L. Costantino
2015-09-01
Full Text Available In this work we perform numerical simulations of convective gravity waves (GWs, using the WRF (Weather Research and Forecasting model. We first run an idealized, simplified and highly resolved simulation with model top at 80 km. Below 60 km of altitude, a vertical grid spacing smaller than 1 km is supposed to reliably resolve the effects of GW breaking. An eastward linear wind shear interacts with the GW field generated by a single convective thunderstorm. After 70 min of integration time, averaging within a radius of 300 km from the storm centre, results show that wave breaking in the upper stratosphere is largely dominated by saturation effects, driving an average drag force up to −41 m s−1 day−1. In the lower stratosphere, mean wave drag is positive and equal to 4.4 m s−1 day−1. In a second step, realistic WRF simulations are compared with lidar measurements from the NDACC network (Network for the Detection of Atmospheric Composition Changes of gravity wave potential energy (Ep over OHP (Haute-Provence Observatory, southern France. Using a vertical grid spacing smaller than 1 km below 50 km of altitude, WRF seems to reliably reproduce the effect of GW dynamics and capture qualitative aspects of wave momentum and energy propagation and transfer to background mean flow. Averaging within a radius of 120 km from the storm centre, the resulting drag force for the study case (2 h storm is negative in the higher (−1 m s−1 day−1 and positive in the lower stratosphere (0.23 m s−1 day−1. Vertical structures of simulated potential energy profiles are found to be in good agreement with those measured by lidar. Ep is mostly conserved with altitude in August while, in October, Ep decreases in the upper stratosphere to grow again in the lower mesosphere. On the other hand, the magnitude of simulated wave energy is clearly underestimated with respect to lidar data by about 3–4 times.
Vertical propagation of baroclinic Kelvin waves along the west coast ...
Indian Academy of Sciences (India)
A linear, continuously stratified ocean model is used to investigate vertical propagation of remotely forced, baroclinic Kelvin waves along the Indian west coast. The extent of vertical propagation over the length of the coast is found to be an increasing function of the forcing frequency. Simulations show that, over the length of ...
AVELLA CASTIBLANCO, Jorge; Seetharamdoo, Divitha; Berbineau, Marion; Ney, Michel; GALLEE, François
2013-01-01
This chapter is organized as follows : Section II introduces the modal approach for guiding structures. It is based on a full-wave method, namely the Transmission Line Matrix (TLM) method. These methods has been hampered by their large computational time when compared to asymptotic methods when large size environments are considered. Thus, a suitable 2.5 D TLM implementation to reduce the computational time and to include lossy dielectric walls of tunnels is briefly presented [2]. The computa...
DEFF Research Database (Denmark)
Guo, Kai; Friis, Søren Michael Mørk; Christensen, Jesper Bjerge
2017-01-01
We derive from Maxwell's equations full-vectorial nonlinear propagation equations of four-wave mixing valid in straight semiconductor-on-insulator waveguides. Special attention is given to the resulting effective mode area, which takes a convenient form known from studies in photonic crystal fibers...
Whistler Wave Propagation Through the Ionosphere of Venus
Pérez-Invernón, F. J.; Lehtinen, N. G.; Gordillo-Vázquez, F. J.; Luque, A.
2017-11-01
We investigate the attenuation of whistler waves generated by hypotetical Venusian lightning occurring at the altitude of the cloud layer under different ionospheric conditions. We use the Stanford full-wave method for stratified media of Lehtinen and Inan (2008) to model wave propagation through the ionosphere of Venus. This method calculates the electromagnetic field created by an arbitrary source in a plane-stratified medium (i.e., uniform in the horizontal direction). We see that the existence of holes in electronic densities and the magnetic field configuration caused by solar wind play an important role in the propagation of electromagnetic waves through the Venusian ionosphere.
Evaluation of approaches for modeling temperature wave propagation in district heating pipelines
DEFF Research Database (Denmark)
Gabrielaitiene, I.; Bøhm, Benny; Sunden, B.
2008-01-01
code ANSYS and a node method, was examined for a low turbulent Reynolds number regime and small velocity fluctuations. Both approaches are found to have limitations in predicting the temperature response time and predicting the peak values of the temperature wave, which is further hampered by the fact...
Sound wave propagation in weakly polydisperse granular materials.
Mouraille, O; Luding, S
2008-11-01
Dynamic simulations of wave propagation are performed in dense granular media with a narrow polydisperse size-distribution and a linear contact-force law. A small perturbation is created on one side of a static packing and its propagation, for both P- and S-waves, is examined. A size variation comparable to the typical contact deformation already changes sound propagation considerably. The transmission spectrum becomes discontinuous, i.e., a lower frequency band is transmitted well, while higher frequencies are not, possibly due to attenuation and scattering. This behaviour is qualitatively reproduced for (i) Hertz non-linear contacts, for (ii) frictional contacts, (iii) for a range of smaller amplitudes, or (iv) for larger systems. This proves that the observed wave propagation and dispersion behaviour is intrinsic and not just an artifact of (i) a linear model, (ii) a frictionless packing, (iii) a large amplitude non-linear wave, or (iv) a finite size effect.
Unidirectional propagation of designer surface acoustic waves
Lu, Jiuyang; Ke, Manzhu; Liu, Zhengyou
2014-01-01
We propose an efficient design route to generate unidirectional propagation of the designer surface acoustic waves. The whole system consists of a periodically corrugated rigid plate combining with a pair of asymmetric narrow slits. The directionality of the structure-induced surface waves stems from the destructive interference between the evanescent waves emitted from the double slits. The theoretical prediction is validated well by simulations and experiments. Promising applications can be anticipated, such as in designing compact acoustic circuits.
Radiation and propagation of electromagnetic waves
Tyras, George; Declaris, Nicholas
1969-01-01
Radiation and Propagation of Electromagnetic Waves serves as a text in electrical engineering or electrophysics. The book discusses the electromagnetic theory; plane electromagnetic waves in homogenous isotropic and anisotropic media; and plane electromagnetic waves in inhomogenous stratified media. The text also describes the spectral representation of elementary electromagnetic sources; the field of a dipole in a stratified medium; and radiation in anisotropic plasma. The properties and the procedures of Green's function method of solution, axial currents, as well as cylindrical boundaries a
Hamiltonian models for the propagation of irrotational surface gravity waves over a variable bottom.
Compelli, A; Ivanov, R; Todorov, M
2018-01-28
A single incompressible, inviscid, irrotational fluid medium bounded by a free surface and varying bottom is considered. The Hamiltonian of the system is expressed in terms of the so-called Dirichlet-Neumann operators. The equations for the surface waves are presented in Hamiltonian form. Specific scaling of the variables is selected which leads to approximations of Boussinesq and Korteweg-de Vries (KdV) types, taking into account the effect of the slowly varying bottom. The arising KdV equation with variable coefficients is studied numerically when the initial condition is in the form of the one-soliton solution for the initial depth.This article is part of the theme issue 'Nonlinear water waves'. © 2017 The Author(s).
Characteristics of worst hour rainfall rate for radio wave propagation modelling in Nigeria
Osita, Ibe; Nymphas, E. F.
2017-10-01
Radio waves especially at the millimeter-wave band are known to be attenuated by rain. Radio engineers and designers need to be able to predict the time of the day when radio signal will be attenuated so as to provide measures to mitigate this effect. This is achieved by characterizing the rainfall intensity for a particular region of interest into worst month and worst hour of the day. This paper characterized rainfall in Nigeria into worst year, worst month, and worst hour. It is shown that for the period of study, 2008 and 2009 are the worst years, while September is the most frequent worst month in most of the stations. The evening time (LT) is the worst hours of the day in virtually all the stations.
Stress Wave Propagation in Larch Plantation Trees-Numerical Simulation
Fenglu Liu; Fang Jiang; Xiping Wang; Houjiang Zhang; Wenhua Yu
2015-01-01
In this paper, we attempted to simulate stress wave propagation in virtual tree trunks and construct two dimensional (2D) wave-front maps in the longitudinal-radial section of the trunk. A tree trunk was modeled as an orthotropic cylinder in which wood properties along the fiber and in each of the two perpendicular directions were different. We used the COMSOL...
1990-01-01
ELF Communcations ," NRL Rept. 7269, 1974 Ferguson, J.A., "Ionospheric Profiles for Predicting Nighttime VLF/LF Propagation," Naval Ocean Systems...waves in wireless telegraphy," Ann. Physik, Vol. 28, pp 665-736, 1909 Stewart, F.G., L.A. Berry, C.M. Rush and V. Agy, "An air-to-ground HY...How Many MU.F~s?" Wireless World. Vol. 65, pp 537-538. Dec. 1959 Bradley, P.A., *Propagation at medium and high frequencies,2: Long and short term
All electrical propagating spin wave spectroscopy with broadband wavevector capability
Energy Technology Data Exchange (ETDEWEB)
Ciubotaru, F., E-mail: Florin.Ciubotaru@imec.be [imec, Kapeldreef 75, B-3001 Leuven (Belgium); KU Leuven, Departement Electrotechniek (ESAT), Kasteelpark Arenberg 10, B-3001 Leuven (Belgium); Devolder, T. [Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); Manfrini, M.; Adelmann, C.; Radu, I. P. [imec, Kapeldreef 75, B-3001 Leuven (Belgium)
2016-07-04
We developed an all electrical experiment to perform the broadband phase-resolved spectroscopy of propagating spin waves in micrometer sized thin magnetic stripes. The magnetostatic surface spin waves are excited and detected by scaled down to 125 nm wide inductive antennas, which award ultra broadband wavevector capability. The wavevector selection can be done by applying an excitation frequency above the ferromagnetic resonance. Wavevector demultiplexing is done at the spin wave detector thanks to the rotation of the spin wave phase upon propagation. A simple model accounts for the main features of the apparatus transfer functions. Our approach opens an avenue for the all electrical study of wavevector-dependent spin wave properties including dispersion spectra or non-reciprocal propagation.
Wave propagation of spectral energy content in a granular chain
Directory of Open Access Journals (Sweden)
Shrivastava Rohit Kumar
2017-01-01
Full Text Available A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting or non-destructive testing of the internal structure of solids. The focus is on the total energy content of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain, which allows understanding the energy attenuation due to disorder since it isolates the longitudinal P-wave from shear or rotational modes. It is observed from the signal that stronger disorder leads to faster attenuation of the signal. An ordered granular chain exhibits ballistic propagation of energy whereas, a disordered granular chain exhibits more diffusive like propagation, which eventually becomes localized at long time periods. For obtaining mean-field macroscopic/continuum properties, ensemble averaging has been used, however, such an ensemble averaged spectral energy response does not resolve multiple scattering, leading to loss of information, indicating the need for a different framework for micro-macro averaging.
Acoustical Wave Propagation in Sonic Composites
Directory of Open Access Journals (Sweden)
Iulian Girip
2015-09-01
Full Text Available The goal of this paper is to discuss the technique of controlling the mechanical properties of sonic composites. The idea is to architecture the scatterers and material from which they are made, their number and geometry in order to obtain special features in their response to external waves. We refer to perfectly reflecting of acoustical waves over a desired range of frequencies or to prohibit their propagation in certain directions, or confining the waves within specified volumes. The internal structure of the material has to be chosen in such a way that to avoid the scattering of acoustical waves inside the material. This is possible if certain band-gaps of frequencies can be generated for which the waves are forbidden to propagate in certain directions. These bandgaps can be extended to cover all possible directions of propagation by resulting a full band-gap. If the band-gaps are not wide enough, their frequency ranges do not overlap. These band-gaps can overlap due to reflections on the surface of thick scatterers, as well as due to wave propagation inside them. growth.
Radio Channel Modelling Using Stochastic Propagation Graphs
DEFF Research Database (Denmark)
Pedersen, Troels; Fleury, Bernard Henri
2007-01-01
In this contribution the radio channel model proposed in [1] is extended to include multiple transmitters and receivers. The propagation environment is modelled using random graphs where vertices of a graph represent scatterers and edges model the wave propagation between scatterers. Furthermore...
Wave Propagation in Smart Materials
DEFF Research Database (Denmark)
Pedersen, Michael
1999-01-01
In this paper we deal with the behavior of solutions to hyperbolic equations such as the wave equation: \\begin{equation}\\label{waveeq1} \\frac{\\partial^2}{\\partial t^2}u-\\Delta u=f, \\end{equation} or the equations of linear elasticity for an isotropic medium: \\begin{equation}\\label{elasteq1} \\frac...
Wave Propagation in Smart Materials
DEFF Research Database (Denmark)
Pedersen, Michael
1999-01-01
In this paper we deal with the behavior of solutions to hyperbolicequations such as the wave equation:\\begin{equation}\\label{waveeq1}\\frac{\\partial^2}{\\partial t^2}u-\\Delta u=f,\\end{equation}or the equations of linear elasticity for an isotropic medium:\\begin{equation}\\label{elasteq1}\\frac...
Snow Slab Failure Due to Biot-Type Acoustic Wave Propagation
Sidler Rolf
2014-01-01
Even though seismic methods are among the most used geophysical methods today their application in snow has been sparse. This might be related to the fact that commonly observed wave velocity attenuation and reflection coefficients can not be well explained by the widely used elastic or visco elastic models for wave propagation. Biot's well established model of wave propagation in porous media instead is much better suited to describe acoustic wave propagation in snow. This model predicts als...
Stress wave propagation in rock
Energy Technology Data Exchange (ETDEWEB)
Grady, D.E
1977-01-01
Earth penetration, design and hardening of structures to explosive or earthquake-induced ground shock effects, rapid excavation, and in situ preparation of coal, shale, or geothermal deposits are representative problems in which accurate constitutive descriptions of the geological medium are required to provide meaningful predictions. The rock or rock masses involved undergo complex, finite amplitude deformation during the process of transient dynamic loading, and quasi-static experimental compression techniques are normally used to provide much of the necessary data base. Strain rates typically range between 10/sup 1//s and 10/sup 5//s in the problems of interest, however, and further studies are required to determine the importance of rate dependence in the mechanical constitutive behavior of rock. Material response at the higher strain rates can be investigated with impact generated stress waves where controlled strain rates between about 10/sup 4//s to 10/sup 7//s can be achieved. Experimental methods have been developed to conduct and analyze impact-induced shock wave, ramp wave, and tensile fracture studies. Experimental results on some select crustal silicate and carbonate rocks show that strain rate dependence and the processes of phase transformation, compressive yielding, and fracture are important features in the dynamic constitutive response.
Effect of Resolution on Propagating Detonation Wave
Energy Technology Data Exchange (ETDEWEB)
Menikoff, Ralph [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2014-07-10
Simulations of the cylinder test are used to illustrate the effect of mesh resolution on a propagating detonation wave. For this study we use the xRage code with the SURF burn model for PBX 9501. The adaptive mesh capability of xRage is used to vary the resolution of the reaction zone. We focus on two key properties: the detonation speed and the cylinder wall velocity. The latter is related to the release isentrope behind the detonation wave. As the reaction zone is refined (2 to 15 cells for cell size of 62 to 8μm), both the detonation speed and final wall velocity change by a small amount; less than 1 per cent. The detonation speed decreases with coarser resolution. Even when the reaction zone is grossly under-resolved (cell size twice the reaction-zone width of the burn model) the wall velocity is within a per cent and the detonation speed is low by only 2 per cent.
Mechanical Wave Propagation within Nanogold Granular Crystals
Zheng, Bowen; Xu, Jun
2017-01-01
We computationally investigate the wave propagation characteristics of nanoscopic granular crystals composed of one-dimensionally arrayed gold nanoparticles using molecular dynamics simulation. We examine two basic configurations, i.e. homogeneous lattices and diatomic lattices with mass-mismatch. We discover that homogeneous lattices of gold nanospheres support weakly dissipative and highly localized solitary wave at 300 K, while diatomic lattices have a good tuning ability of transmittance ...
Waichman, Karol; Barmashenko, Boris D.; Rosenwaks, Salman
2017-10-01
Analysis of beam propagation, kinetic and fluid dynamic processes in Cs diode pumped alkali lasers (DPALs), using wave optics model and gasdynamic code, is reported. The analysis is based on a three-dimensional, time-dependent computational fluid dynamics (3D CFD) model. The Navier-Stokes equations for momentum, heat and mass transfer are solved by a commercial Ansys FLUENT solver based on the finite volume discretization technique. The CFD code which solves the gas conservation equations includes effects of natural convection and temperature diffusion of the species in the DPAL mixture. The DPAL kinetic processes in the Cs/He/C2H6 gas mixture dealt with in this paper involve the three lowest energy levels of Cs, (1) 62S1/2, (2) 62P1/2 and (3) 62P3/2. The kinetic processes include absorption due to the 1->3 D2 transition followed by relaxation the 3 to 2 fine structure levels and stimulated emission due to the 2->1 D1 transition. Collisional quenching of levels 2 and 3 and spontaneous emission from these levels are also considered. The gas flow conservation equations are coupled to fast-Fourier-transform algorithm for transverse mode propagation to obtain a solution of the scalar paraxial propagation equation for the laser beam. The wave propagation equation is solved by the split-step beam propagation method where the gain and refractive index in the DPAL medium affect the wave amplitude and phase. Using the CFD and beam propagation models, the gas flow pattern and spatial distributions of the pump and laser intensities in the resonator were calculated for end-pumped Cs DPAL. The laser power, DPAL medium temperature and the laser beam quality were calculated as a function of pump power. The results of the theoretical model for laser power were compared to experimental results of Cs DPAL.
Propagation of polarized millimeter waves through falling snow.
Brien, S G; Goedecke, G H
1988-06-15
Propagation of coherent linearly polarized waves through falling snow is calculated for two monodisperse and one polydisperse model snowstorms for fixed orientation and for random orientation of the snow crystals, at a 10-mm wavelength, utilizing a theoretical model based on the Foldy-Lax model. Results for linearly polarized waves incident on oriented monodispersions and polydispersions exhibit a marked damped oscillatory behavior as a function of propagation distance for the copolarized and cross-polarized intensities. For the polydispersion, a simple approximation for the dependence of the forward scattering matrix elements on snow crystal size is also obtained.
A new numerical model for simulating the propagation of and inundation by tsunami waves
Cui, H.
2013-01-01
This thesis has involved the development of an unstructured grid ocean model, H2Ocean, with accurate flooding and drying algorithms for tsunami studies. The research is co-funded by the Alfred Wegener Institute (AWI) in Bremerhaven, Germany, as part of their contribution to the German-Indonesian
Functional reentrant waves propagate outwardly in cardiac tissue
Energy Technology Data Exchange (ETDEWEB)
Gong Yunfan [Department of Medicine, Division of Cardiology, Weill Medical College of Cornell University, New York, NY 10021 (United States)]. E-mail: yug2002@med.cornell.edu; Christini, David J. [Department of Medicine, Division of Cardiology, Weill Medical College of Cornell University, New York, NY 10021 (United States) and Department of Physiology and Biophysics, Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021 (United States)]. E-mail: dchristi@med.cornell.edu
2004-10-18
The dynamical nature of cardiac arrhythmias has been investigated for decades by researchers from a wide range of disciplines. One long-standing unsettled issue involves whether the mechanism of functional reentry should be described by the 'leading-circle' hypothesis or the 'spiral-wave' hypothesis, which rely on inward and outward wave propagation, respectively. To address this issue, we investigated two-dimensional FitzHugh-Nagumo type models and found that inwardly propagating waves could occur in the spontaneous oscillatory mode, but not the excitable mode. However, such spontaneous oscillatory behavior is characterized by small-amplitude, sinusoidal oscillations that are fundamentally different from the stimulus-driven, excitable behavior of cardiac myocytes. This finding suggests that inward wave propagation, which is posited by the leading-circle hypothesis for the purpose of maintaining functional reentry, is unlikely to occur in cardiac tissue.
Domain Wall Propagation through Spin Wave Emission
Wang, X.S.; Yan, P.; Shen, Y.H.; Bauer, G.E.W.; Wang, X.R.
2012-01-01
We theoretically study field-induced domain wall motion in an electrically insulating ferromagnet with hard- and easy-axis anisotropies. Domain walls can propagate along a dissipationless wire through spin wave emission locked into the known soliton velocity at low fields. In the presence of
Electromagnetic wave propagations in conjugate metamaterials.
Xu, Yadong; Fu, Yangyang; Chen, Huanyang
2017-03-06
In this work, by employing field transformation optics, we deduce a special kind of materials called conjugate metamaterials, which can support intriguing electromagnetic wave propagations, such as negative refractions and lasing phenomena. These materials could also serve as substrates for making a subwavelength-resolution lens, and the so-called "perfect lens" is demonstrated to be a limiting case.
Apparent superluminal behavior in wave propagation
Jackson, AD; Lande, A; Lautrup, B
2001-01-01
The apparent superluminal propagation of electromagnetic signals seen in recent experiments is shown to be the result of simple and robust properties of relativistic field equations. Although the wave front of a signal passing through a classically forbidden region can never move faster than light,
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...
Topology Optimization for Transient Wave Propagation Problems
DEFF Research Database (Denmark)
Matzen, René
as for vectorial elastic wave propagation problems using finite element analysis [P2], [P4]. The concept is implemented in a parallel computing code that includes efficient techniques for performing gradient based topology optimization. Using the developed computational framework the thesis considers four...
Antenna Construction and Propagation of Radio Waves.
Marine Corps Inst., Washington, DC.
Developed as part of the Marine Corps Institute (MCI) correspondence training program, this course on antenna construction and propagation of radio waves is designed to provide communicators with instructions in the selection and/or construction of the proper antenna(s) for use with current field radio equipment. Introductory materials include…
Study on the electromagnetic waves propagation characteristics in partially ionized plasma slabs
Directory of Open Access Journals (Sweden)
Zhi-Bin Wang
2016-05-01
Full Text Available Propagation characteristics of electromagnetic (EM waves in partially ionized plasma slabs are studied in this paper. Such features are significant to applications in plasma antennas, blackout of re-entry flying vehicles, wave energy injection to plasmas, and etc. We in this paper developed a theoretical model of EM wave propagation perpendicular to a plasma slab with a one-dimensional density inhomogeneity along propagation direction to investigate essential characteristics of EM wave propagation in nonuniform plasmas. Particularly, the EM wave propagation in sub-wavelength plasma slabs, where the geometric optics approximation fails, is studied and in comparison with thicker slabs where the geometric optics approximation applies. The influences of both plasma and collisional frequencies, as well as the width of the plasma slab, on the EM wave propagation characteristics are discussed. The results can help the further understanding of propagation behaviours of EM waves in nonuniform plasma, and applications of the interactions between EM waves and plasmas.
S wave propagation in acoustic anisotropic media
Stovas, Alexey
2017-04-01
The acoustic anisotropic medium can be defined in two ways. The first one is known as a pseudo-acoustic approximation (Alkhalifah, 1998) that is based on the fact that in TI media, P wave propagation is weakly dependent on parameter known as "vertical S-wave velocity" (Thomsen, 1986). The standard way to define the pseudo-acoustic approximation is to set this parameter to zero. However, as it was shown later (Grechka et al., 2004), there is "S wave artifact" in such a medium. Another way is to define the stack of horizontal solid-fluid layers and perform an upscaling based on the Backus (1962) averaging. The stiffness coefficient that responds to "vertical S wave velocity" turns to zero if any of layers has zero vertical S wave velocity. In this abstract, I analyze the S wave propagation is acoustic anisotropic medium and define important kinematic properties such as the group velocity surface and Dix-type equations. The kinematic properties can easily be defined from the slowness surface. In elastic transversely isotropic medium, the equations for P and SV wave slowness surfaces are coupled. Setting "vertical S wave velocity" to zero, results in decoupling of equations. I show that the S wave group velocity surface is given by quasi-astroidal form with the reference astroid defined by vertical and horizontal projections of group velocity. I show that there are cusps attached to both vertical and horizontal symmetry axes. The new S wave parameters include vertical, horizontal and normal moveout velocities. With the help of new parameterization, suitable for S wave, I also derived the Dix-type of equations to define the effective kinematical properties of S waves in multi-layered acoustic anisotropic medium. I have shown that effective media defined from P and S waves have different parameters. I also show that there are certain symmetries between P and S waves parameters and equations. The proposed method can be used for analysis of S waves in acoustic anisotropic
Wave propagation in transversely impacted composite laminates
Daniel, I. M.; Liber, T.; Labedz, R. H.
1979-01-01
An experimental study was conducted to determine the wave-propagation characteristics, transient strains and residual properties of unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 m/sec. Results include the following: (1) the predominant wave is the flexural wave propagating at different velocities in different directions; (2) peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers; (3) strain rates up to 640/sec were measured; and (4) unidirectional laminates under impact showed appreciable modulus and strength degradation in the direction transverse to fibers.
Wave propagation in transversely impacted composite laminates
Energy Technology Data Exchange (ETDEWEB)
Daniel, I.M.; Liber, T.; Labedz, R.H.
1979-01-01
An experimental study was conducted to determine the wave-propagation characteristics, transient strains and residual properties of unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 m/sec. Results include the following: (1) the predominant wave is the flexural wave propagating at different velocities in different directions (2) peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers (3) strain rates up to 640/sec were measured and (4) unidirectional laminates under impact showed appreciable modulus and strength degradation in the direction transverse to fibers.
Radio Channel Modelling Using Stochastic Propagation Graphs
Pedersen, Troels; Fleury, Bernard Henri
2007-01-01
In this contribution the radio channel model proposedin [1] is extended to include multiple transmitters and receivers.The propagation environment is modelled using randomgraphs where vertices of a graph represent scatterers and edgesmodel the wave propagation between scatterers. Furthermore,we develop a closed form analytical expression for the transfermatrix of the propagation graph. It is shown by simulation thatimpulse response and the delay-power spectrum of the graphexhibit exponentiall...
Seismic wave propagation in fractured media: A discontinuous Galerkin approach
De Basabe, Jonás D.
2011-01-01
We formulate and implement a discontinuous Galekin method for elastic wave propagation that allows for discontinuities in the displacement field to simulate fractures or faults using the linear- slip model. We show numerical results using a 2D model with one linear- slip discontinuity and different frequencies. The results show a good agreement with analytic solutions. © 2011 Society of Exploration Geophysicists.
Surface-plasmon-assisted electromagnetic wave propagation.
Yang, Wenbo; Reed, Jennifer M; Wang, Haining; Zou, Shengli
2010-10-21
Using electrodynamics tools, we investigated the effect of surface plasmons on the propagation direction of electromagnetic waves around a spherical silver nanoparticle and nano-structured silver film. The studies showed that the calculated effective index of refraction of a spherical silver nanoparticle from the Kramers-Kronig transformation method may not represent the index of refraction of the system but is consistent with the Poynting vector (the energy flow) direction at the microscopic scale. Using a silver film composed of periodic triangular prisms, we numerically demonstrated that electromagnetic waves may propagate along different directions depending on the incident polarization direction. When the incident polarization is in the plane of incidence and the surface plasmons are excited, the refracted light ray propagates along the same side of the surface normal as the incident wave. When the incident polarization is perpendicular to the plane of incidence, the refracted light ray always propagates on the opposite side of the surface normal. The results show that a silver film composed of periodic nano-sized triangular prisms may be used as a filter to simultaneously generate two polarized light rays of orthogonal polarizations from one light source.
Surface acoustic wave propagation in graphene film
Energy Technology Data Exchange (ETDEWEB)
Roshchupkin, Dmitry, E-mail: rochtch@iptm.ru; Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Irzhak, Dmitry [Institute of Microelectronics Technology and High-Purity Materials Russian Academy of Sciences, Chernogolovka 142432 (Russian Federation); Ortega, Luc [Laboratoire de Physique des Solides, Univ. Paris-Sud, CNRS, UMR 8502, 91405 Orsay Cedex (France); Zizak, Ivo; Erko, Alexei [Institute for Nanometre Optics and Technology, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein Strasse 15, 12489 Berlin (Germany); Tynyshtykbayev, Kurbangali; Insepov, Zinetula [Nazarbayev University Research and Innovation System, 53 Kabanbay Batyr St., Astana 010000 (Kazakhstan)
2015-09-14
Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.
Transient Aspects of Wave Propagation Connected with Spatial Coherence
Directory of Open Access Journals (Sweden)
Ezzat G. Bakhoum
2013-01-01
Full Text Available This study presents transient aspects of light wave propagation connected with spatial coherence. It is shown that reflection and refraction phenomena involve spatial patterns which are created within a certain transient time interval. After this transient time interval, these patterns act like a memory, determining the wave vector for subsequent sets of reflected/refracted waves. The validity of this model is based on intuitive aspects regarding phase conservation of energy for waves reflected/refracted by multiple centers in a certain material medium.
Spatial damping of propagating sausage waves in coronal cylinders
Guo, Ming-Zhe; Chen, Shao-Xia; Li, Bo; Xia, Li-Dong; Yu, Hui
2015-09-01
Context. Sausage modes are important in coronal seismology. Spatially damped propagating sausage waves were recently observed in the solar atmosphere. Aims: We examine how wave leakage influences the spatial damping of sausage waves propagating along coronal structures modeled by a cylindrical density enhancement embedded in a uniform magnetic field. Methods: Working in the framework of cold magnetohydrodynamics, we solve the dispersion relation (DR) governing sausage waves for complex-valued, longitudinal wavenumber k at given real angular frequencies ω. For validation purposes, we also provide analytical approximations to the DR in the low-frequency limit and in the vicinity of ωc, the critical angular frequency separating trapped from leaky waves. Results: In contrast to the standing case, propagating sausage waves are allowed for ω much lower than ωc. However, while able to direct their energy upward, these low-frequency waves are subject to substantial spatial attenuation. The spatial damping length shows little dependence on the density contrast between the cylinder and its surroundings, and depends only weakly on frequency. This spatial damping length is of the order of the cylinder radius for ω ≲ 1.5vAi/a, where a and vAi are the cylinder radius and the Alfvén speed in the cylinder, respectively. Conclusions: If a coronal cylinder is perturbed by symmetric boundary drivers (e.g., granular motions) with a broadband spectrum, wave leakage efficiently filters out the low-frequency components.
Radio Wave Propagation Scene Partitioning for High-Speed Rails
Directory of Open Access Journals (Sweden)
Bo Ai
2012-01-01
Full Text Available Radio wave propagation scene partitioning is necessary for wireless channel modeling. As far as we know, there are no standards of scene partitioning for high-speed rail (HSR scenarios, and therefore we propose the radio wave propagation scene partitioning scheme for HSR scenarios in this paper. Based on our measurements along the Wuhan-Guangzhou HSR, Zhengzhou-Xian passenger-dedicated line, Shijiazhuang-Taiyuan passenger-dedicated line, and Beijing-Tianjin intercity line in China, whose operation speeds are above 300 km/h, and based on the investigations on Beijing South Railway Station, Zhengzhou Railway Station, Wuhan Railway Station, Changsha Railway Station, Xian North Railway Station, Shijiazhuang North Railway Station, Taiyuan Railway Station, and Tianjin Railway Station, we obtain an overview of HSR propagation channels and record many valuable measurement data for HSR scenarios. On the basis of these measurements and investigations, we partitioned the HSR scene into twelve scenarios. Further work on theoretical analysis based on radio wave propagation mechanisms, such as reflection and diffraction, may lead us to develop the standard of radio wave propagation scene partitioning for HSR. Our work can also be used as a basis for the wireless channel modeling and the selection of some key techniques for HSR systems.
Hussain, Muzamal; Naeem, M. Nawaz; Shahzad, Aamir; He, Maogang
2017-04-01
The vibration analysis, based on the Donnell thin shell theory, of single-walled carbon nanotubes (SWCNTs) has been investigated. The wave propagation approach in standard eigenvalue form has been employed in order to derive the characteristic frequency equation describing the natural frequencies of vibration in SWCNTs. The complex exponential functions, with the axial modal numbers that depend on the boundary conditions stated at edges of a carbon nanotube, have been used to compute the axial modal dependence. In our new investigations, the vibration frequency spectra are obtained and calculated for various physical parameters like length-to-diameter ratios for armchair and zigzag SWCNTs for different modes and in-plane rigidity and mass density per unit lateral area for armchair and zigzag SWCNTs on the vibration frequencies. The computer software MATLAB is used in order to compute these frequencies of the SWCNTs. The results obtained from wave propagation method are found to be in satisfactory agreement with that obtained through the previously known numerical molecular dynamics simulations.
Propagation of sound waves in tubes of noncircular cross section
Richards, W. B.
1986-01-01
Plane-acoustic-wave propagation in small tubes with a cross section in the shape of a flattened oval is described. Theoretical descriptions of a plane wave propagating in a tube with circular cross section and between a pair of infinite parallel plates, including viscous and thermal damping, are expressed in similar form. For a wide range of useful duct sizes, the propagation constant (whose real and imaginary parts are the amplitude attenuation rate and the wave number, respectively) is very nearly the same function of frequency for both cases if the radius of the circular tube is the same as the distance between the parallel plates. This suggests that either a circular-cross-section model or a flat-plate model can be used to calculate wave propagation in flat-oval tubing, or any other shape tubing, if its size is expressed in terms of an equivalent radius, given by g = 2 x (cross-sectional area)/(length of perimeter). Measurements of the frequency response of two sections of flat-oval tubing agree with calculations based on this idea. Flat-plate formulas are derived, the use of transmission-line matrices for calculations of plane waves in compound systems of ducts is described, and examples of computer programs written to carry out the calculations are shown.
COMSTAR Millimeter-Wave Propagation Measurements,
1980-04-01
downlink frequency. 2,3 In addition, NASA collected some simultan- eous 15- and 32-GHz attenuation data at the Rosman , North Carolina site. ATS-6...moving in azimuth and elevation when using suntrackers. Two NASA research satellites, ATS-5 and ATS-6, offered the first opportunity to utilize...communications, Proceedings of IEEE 63:1308-1331. 2. Ippolito, L.J. (1970) Millimeter-Wave Propagation Experiments Utilizing the ATS-5 Satellite, NASA
Takemura, Shunsuke; Kobayashi, Manabu; Yoshimoto, Kazuo
2017-09-01
For practical modelling of high-frequency (>1 Hz) seismic wave propagation, we analysed the apparent radiation patterns and attenuations of P and S waves using observed Hi-net velocity seismograms for small-to-moderate crustal earthquakes in the Chugoku region, southwestern Japan. By comparing observed and simulated seismograms, we estimated practical parameter sets of crustal small-scale velocity heterogeneity and intrinsic attenuations of P and S waves (QP.int-1 and QS.int-1). Numerical simulations of seismic wave propagation were conducted via the finite-difference method using a 1-D crustal velocity structure model with additional 3-D small-scale velocity heterogeneity and intrinsic attenuation. The estimated crustal small-scale velocity heterogeneity is stochastically characterized by an exponential-type power spectral density function with correlation length of 1 km and root-mean-square value of 0.03. Estimated QP.int-1 and QS.int-1 values range from 10-2.6 to 10-2.0 and 10-2.8 to 10-2.4, respectively, indicating QP.int-1 > QS.int-1 for high frequencies (>1 Hz). Intrinsic attenuation dominates over scattering attenuation, which is caused by small-scale velocity heterogeneity. The crustal parameters obtained in this study are useful for evaluating peak ground velocities and coda envelopes for moderate crustal earthquakes via physical-based simulations using a 3-D heterogeneous structure model.
Directory of Open Access Journals (Sweden)
S. Popinet
2012-04-01
Full Text Available The 11 March 2011 Tohoku tsunami is simulated using the quadtree-adaptive Saint-Venant solver implemented within the Gerris Flow Solver. The spatial resolution is adapted dynamically from 250 m in flooded areas up to 250 km for the areas at rest. Wave fronts are tracked at a resolution of 1.8 km in deep water. The simulation domain extends over 73° of both latitude and longitude and covers a significant part of the north-west Pacific. The initial wave elevation is obtained from a source model derived using seismic data only. Accurate long-distance wave prediction is demonstrated through comparison with DART buoys timeseries and GLOSS tide gauges records. The model also accurately predicts fine-scale flooding compared to both satellite and survey data. Adaptive mesh refinement leads to orders-of-magnitude gains in computational efficiency compared to non-adaptive methods. The study confirms that consistent source models for tsunami initiation can be obtained from seismic data only. However, while the observed extreme wave elevations are reproduced by the model, they are located further south than in the surveyed data. Comparisons with inshore wave buoys data indicate that this may be due to an incomplete understanding of the local wave generation mechanisms.
Directional bending wave propagation in periodically perforated plates
DEFF Research Database (Denmark)
Andreassen, Erik; Manktelow, Kevin; Ruzzene, Massimo
2015-01-01
We report on the investigation of wave propagation in a periodically perforated plate. A unit cell with double-C perforations is selected as a test article suitable to investigate two-dimensional dispersion characteristics, group velocities, and internal resonances. A numerical model, formulated ...
Observations of apparent superslow wave propagation in solar prominences
Raes, J. O.; Van Doorsselaere, T.; Baes, M.; Wright, A. N.
2017-06-01
Context. Phase mixing of standing continuum Alfvén waves and/or continuum slow waves in atmospheric magnetic structures such as coronal arcades can create the apparent effect of a wave propagating across the magnetic field. Aims: We observe a prominence with SDO/AIA on 2015 March 15 and find the presence of oscillatory motion. We aim to demonstrate that interpreting this motion as a magneto hydrodynamic (MHD) wave is faulty. We also connect the decrease of the apparent velocity over time with the phase mixing process, which depends on the curvature of the magnetic field lines. Methods: By measuring the displacement of the prominence at different heights to calculate the apparent velocity, we show that the propagation slows down over time, in accordance with the theoretical work of Kaneko et al. We also show that this propagation speed drops below what is to be expected for even slow MHD waves for those circumstances. We use a modified Kippenhahn-Schlüter prominence model to calculate the curvature of the magnetic field and fit our observations accordingly. Results: Measuring three of the apparent waves, we get apparent velocities of 14, 8, and 4 km s-1. Fitting a simple model for the magnetic field configuration, we obtain that the filament is located 103 Mm below the magnetic centre. We also obtain that the scale of the magnetic field strength in the vertical direction plays no role in the concept of apparent superslow waves and that the moment of excitation of the waves happened roughly one oscillation period before the end of the eruption that excited the oscillation. Conclusions: Some of the observed phase velocities are lower than expected for slow modes for the circumstances, showing that they rather fit with the concept of apparent superslow propagation. A fit with our magnetic field model allows for inferring the magnetic geometry of the prominence. The movie attached to Fig. 1 is available at http://www.aanda.org
Wave propagation in a strongly coupled magnetized plasma
Reynolds, Alexi; Kählert, Hanno; Bonitz, Michael
2011-10-01
Strongly coupled plasmas play a growing role in many fields of physics--from dusty plasmas to compact stars and the quark-gluon plasma, e.g.. In many cases these plasmas are subject to a strong magnetic field. The one-component plasma (OCP) model is often used to theoretically analyze strong plasma correlations. Here the wave propagation in a strongly coupled OCP subject to an external magnetic field is investigated by means of the quasi- localized charge approximation. The dispersion relation and the wave polarization are studied for wave propagation across and along the magnetic field as well as for arbitrary directions of the wave vector. Support by the Deutsche Forschungsgemeinschaft via SFB-TR 24 and DAAD via the RISE program is acknowledged.
d'Avila, Maria Paola Santisi
2016-01-01
In this paper, a model of one-directional propagation of three-component seismic waves in a nonlinear multilayered soil profile is coupled with a multi-story multi-span frame model to consider, in a simple way, the soil-structure interaction modelled in a finite element scheme. Modeling the three-component wave propagation enables the effects of a soil multiaxial stress state to be taken into account. These reduce soil strength and increase nonlinear effects, compared with the axial stress state. The simultaneous propagation of three components allows the prediction of the incident direction of seismic loading at the ground surface and the analysis of the behavior of a frame structure shaken by a three-component earthquake. A parametric study is carried out to characterize the changes in the ground motion due to dynamic features of the structure, for different incident wavefield properties and soil nonlinear effects. A seismic response depending on parameters such as the frequency content of soil and structur...
Maeda, Takuto; Takemura, Shunsuke; Furumura, Takashi
2017-07-01
We have developed an open-source software package, Open-source Seismic Wave Propagation Code (OpenSWPC), for parallel numerical simulations of seismic wave propagation in 3D and 2D (P-SV and SH) viscoelastic media based on the finite difference method in local-to-regional scales. This code is equipped with a frequency-independent attenuation model based on the generalized Zener body and an efficient perfectly matched layer for absorbing boundary condition. A hybrid-style programming using OpenMP and the Message Passing Interface (MPI) is adopted for efficient parallel computation. OpenSWPC has wide applicability for seismological studies and great portability to allowing excellent performance from PC clusters to supercomputers. Without modifying the code, users can conduct seismic wave propagation simulations using their own velocity structure models and the necessary source representations by specifying them in an input parameter file. The code has various modes for different types of velocity structure model input and different source representations such as single force, moment tensor and plane-wave incidence, which can easily be selected via the input parameters. Widely used binary data formats, the Network Common Data Form (NetCDF) and the Seismic Analysis Code (SAC) are adopted for the input of the heterogeneous structure model and the outputs of the simulation results, so users can easily handle the input/output datasets. All codes are written in Fortran 2003 and are available with detailed documents in a public repository.[Figure not available: see fulltext.
Seismic Wave Propagation on the Tablet Computer
Emoto, K.
2015-12-01
Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the
Karpoukhin, Mikhii G.; Kogan, Boris Y.; Karplus, Walter J.
1995-01-01
The simulation of heart arrhythmia and fibrillation are very important and challenging tasks. The solution of these problems using sophisticated mathematical models is beyond the capabilities of modern super computers. To overcome these difficulties it is proposed to break the whole simulation problem into two tightly coupled stages: generation of the action potential using sophisticated models. and propagation of the action potential using simplified models. The well known simplified models are compared and modified to bring the rate of depolarization and action potential duration restitution closer to reality. The modified method of lines is used to parallelize the computational process. The conditions for the appearance of 2D spiral waves after the application of a premature beat and the subsequent traveling of the spiral wave inside the simulated tissue are studied.
Wave propagation simulation of radio occultations based on ECMWF refractivity profiles
DEFF Research Database (Denmark)
von Benzon, Hans-Henrik; Høeg, Per
2015-01-01
of radio occultations. The output from the wave propagator simulator is used as input to a Full Spectrum Inversion retrieval module which calculates geophysical parameters. These parameters can be compared to the ECMWF atmospheric profiles. The comparison can be used to reveal system errors and get......This paper describes a complete radio occultation simulation environment, including realistic refractivity profiles, wave propagation modeling, instrument modeling, and bending angle retrieval. The wave propagator is used to simulate radio occultation measurements. The radio waves are propagated...... a better understanding of the physics. The wave propagation simulations will in this paper also be compared to real measurements. These radio occultations have been exposed to the same atmospheric conditions as the radio occultations simulated by the wave propagator. This comparison reveals that precise...
Enhancing propagation characteristics of truncated localized waves in silica
Salem, Mohamed
2011-07-01
The spectral characteristics of truncated Localized Waves propagating in dispersive silica are analyzed. Numerical experiments show that the immunity of the truncated Localized Waves propagating in dispersive silica to decay and distortion is enhanced as the non-linearity of the relation between the transverse spatial spectral components and the wave vector gets stronger, in contrast to free-space propagating waves, which suffer from early decay and distortion. © 2011 IEEE.
Ye, W; Bel-Brunon, A; Catheline, S; Combescure, A; Rochette, M
2018-01-01
In this study, visco-hyperelastic Landau's model, which is widely used in acoustical physic field, is introduced into a finite element formulation. It is designed to model the nonlinear behaviour of finite amplitude shear waves in soft solids, typically, in biological tissues. This law is used in finite element models based on elastography, experiments reported in Jacob et al, the simulations results show a good agreement with the experimental study: It is observed in both that a plane shear wave generates only odd harmonics and a nonplane wave generates both odd and even harmonics in the spectral domain. In the second part, a parametric study is performed to analyse the influence of different factors on the generation of odd harmonics of plane wave. A quantitative relation is fitted between the odd harmonic amplitudes and the non-linear elastic parameter of Landau's model, which provides a practical guideline to identify the non-linearity of homogeneous tissues using elastography experiment. Copyright © 2017 John Wiley & Sons, Ltd.
Al-Jabr, Ahmad Ali
2013-01-01
This paper presents methods of simulating gain media in the finite difference time-domain (FDTD) algorithm utilizing a generalized polarization formulation. The gain can be static or dynamic. For static gain, Lorentzian and non-Lorentzian models are presented and tested. For the dynamic gain, rate equations for two-level and four-level models are incorporated in the FDTD scheme. The simulation results conform with the expected behavior of wave amplification and dynamic population inversion.
Wave propagation through an electron cyclotron resonance layer
Westerhof, E.
1997-01-01
The propagation of a wave beam through an electron cyclotron resonance layer is analysed in two-dimensional slab geometry in order to assess the deviation from cold plasma propagation due to resonant, warm plasma changes in wave dispersion. For quasi-perpendicular propagation, N-parallel to x
Wave energy converter effects on wave propagation: A sensitivity study in Monterey Bay, CA
Chang, G.; Jones, C. A.; Roberts, J.; Magalen, J.; Ruehl, K.; Chartrand, C.
2014-12-01
The development of renewable offshore energy in the United States is growing rapidly and wave energy is one of the largest resources currently being evaluated. The deployment of wave energy converter (WEC) arrays required to harness this resource could feasibly number in the hundreds of individual devices. The WEC arrays have the potential to alter nearshore wave propagation and circulation patterns and ecosystem processes. As the industry progresses from pilot- to commercial-scale it is important to understand and quantify the effects of WECs on the natural nearshore processes that support a local, healthy ecosystem. To help accelerate the realization of commercial-scale wave power, predictive modeling tools have been developed and utilized to evaluate the likelihood of environmental impact. At present, direct measurements of the effects of different types of WEC arrays on nearshore wave propagation are not available; therefore wave model simulations provide the groundwork for investigations of the sensitivity of model results to prescribed WEC characteristics over a range of anticipated wave conditions. The present study incorporates a modified version of an industry standard wave modeling tool, SWAN (Simulating WAves Nearshore), to simulate wave propagation through a hypothetical WEC array deployment site on the California coast. The modified SWAN, referred to as SNL-SWAN, incorporates device-specific WEC power take-off characteristics to more accurately evaluate a WEC device's effects on wave propagation. The primary objectives were to investigate the effects of a range of WEC devices and device and array characteristics (e.g., device spacing, number of WECs in an array) on nearshore wave propagation using SNL-SWAN model simulations. Results showed that significant wave height was most sensitive to variations in WEC device type and size and the number of WEC devices in an array. Locations in the lee centerline of the arrays in each modeled scenario showed the
A Database for Propagation Models
Kantak, Anil V.; Rucker, James
1997-01-01
The Propagation Models Database is designed to allow the scientists and experimenters in the propagation field to process their data through many known and accepted propagation models. The database is an Excel 5.0 based software that houses user-callable propagation models of propagation phenomena. It does not contain a database of propagation data generated out of the experiments. The database not only provides a powerful software tool to process the data generated by the experiments, but is also a time- and energy-saving tool for plotting results, generating tables and producing impressive and crisp hard copy for presentation and filing.
Energy Technology Data Exchange (ETDEWEB)
LU, B.
2011-11-07
This study takes place in the framework of tools development for the telemetry simulation. Telemetry is a possible technology applied to monitoring the sodium-cooled fast reactors (SFR) and consists in positioning in the reactor core a transducer to generate an ultrasonic beam. This beam propagates through an inhomogeneous random medium since temperature fluctuations occur in the liquid sodium and consequently the sound velocity fluctuates as well, which modifies the bream propagation. Then the beam interacts with a reactor structure immersed in sodium. By measuring the time of flight of the backscattered echo received by the same transducer, one can determine the precise location of the structure. The telemetry simulation therefore requires modeling of both the acoustic wave propagation in an inhomogeneous random medium and the interaction of this wave with structures of various shapes; this is the objective of this work. A stochastic model based on a Monte Carlo algorithm is developed in order to take into account the random fluctuations of the acoustic field. The acoustic field through an inhomogeneous random medium is finally modeled from the field calculated in a mean homogeneous medium by modifying the travel times of rays in the homogeneous medium, using a correction provided by the stochastic model. This stochastic propagation model has been validated by comparison with a deterministic model and is much simpler to integrate in the CIVA software platform for non destructive evaluation simulation and less time consuming than the deterministic model. In order to model the interaction between the acoustic wave and the immersed structures, classical diffraction models have been evaluated for rigid structures, including the geometrical theory of diffraction (GTD) and the Kirchhoff approximation (KA). These two approaches appear to be complementary. Combining them so as to retain only their advantages, we have developed a hybrid model (the so-called refined KA
Propagation of waves in a gravitating and rotating anisotropic heat ...
African Journals Online (AJOL)
Bheema
propagations become anti-symmetric. It is illustrated that the phase speed of the forward propagating mode increases with increasing drift and the backward propagating mode decreases with increasing drift. In this particular direction of propagation and axis of rotation, this wave mode is also independent of rotation ...
WAVE: Interactive Wave-based Sound Propagation for Virtual Environments.
Mehra, Ravish; Rungta, Atul; Golas, Abhinav; Ming Lin; Manocha, Dinesh
2015-04-01
We present an interactive wave-based sound propagation system that generates accurate, realistic sound in virtual environments for dynamic (moving) sources and listeners. We propose a novel algorithm to accurately solve the wave equation for dynamic sources and listeners using a combination of precomputation techniques and GPU-based runtime evaluation. Our system can handle large environments typically used in VR applications, compute spatial sound corresponding to listener's motion (including head tracking) and handle both omnidirectional and directional sources, all at interactive rates. As compared to prior wave-based techniques applied to large scenes with moving sources, we observe significant improvement in runtime memory. The overall sound-propagation and rendering system has been integrated with the Half-Life 2 game engine, Oculus-Rift head-mounted display, and the Xbox game controller to enable users to experience high-quality acoustic effects (e.g., amplification, diffraction low-passing, high-order scattering) and spatial audio, based on their interactions in the VR application. We provide the results of preliminary user evaluations, conducted to study the impact of wave-based acoustic effects and spatial audio on users' navigation performance in virtual environments.
Viscothermal wave propagation including acousto-elastic interaction
Beltman, W.M.
1998-01-01
This research deals with pressure waves in a gas trapped in thin layers or narrow tubes. In these cases viscous and thermal effects can have a significant effect on the propagation of waves. This so-called viscothermal wave propagation is governed by a number of dimensionless parameters. The two
Moskalenko, I. V.
2004-01-01
Astrophysics of cosmic rays and gamma rays depends very much on the quality of the data, which become increasingly accurate each year and therefore more constraining. While direct measurements of cosmic rays are possible in only one location on the outskirts of the Milky Way, the Galactic diffuse gamma-ray emission provides insights into the spectra of cosmic rays in distant locations, therefore complementing the local cosmic-ray studies. This connection, however, requires extensive modeling and is yet to be explored in detail. The GUST mission, which is scheduled for launch in 2007 and is capable of measuring gamma-rays in the range 20 MeV - 300 GeV, will change the status quo dramatically. Galactic diffuse gamma-ray emission gathered by GUST will require adequate theoretical models. The efforts will be rewarded by the wealth of information on cosmic ray spectra and fluxes in remote locations. In its turn, a detailed cosmic ray propagation model will provide a reliable basis for other studies such as search for dark matter signals in cosmic rays and diffuse gamma rays, spectrum and origin of the extragalactic gamma-ray emission, theories of nucleosynthesis and evolution of elements etc. In this talk, I will discuss what we can learn studying the cosmic ray propagation and diffuse gamma-ray emission.
VLF Radio Wave Propagation Across the Day/Night Terminator
Burch, H.; Moore, R. C.
2016-12-01
In May 2016, a new array of VLF radio receivers was deployed spanning the East Coast of the United States. We present preliminary observations from the array, which was designed in part to track the propagation of the narrowband VLF transmitter signal, NAA (24.0 kHz), down the coast from Cutler, Maine. Amplitude, phase, and polarization observations are compared over multiple days and at different times of year to investigate the dependence of VLF propagation characteristics on solar zenith angle. Measurements are compared to simulations using the Long Wave Propagation Capability code (LWPC) in order to evaluate the accuracy of LWPC's built-in ionosphere model. Efforts to improve the ionosphere model based on observations are discussed.
Directory of Open Access Journals (Sweden)
H. Ekhlas
2014-05-01
.Conclusion: The presented model is easy and practical and allows managers to model scenarios of noise pollution reduction in indoor environments, before huge expenses of actual control measures. This method is faster comparing to numerical modeling methods. Furthermore, its accuracy is also acceptable.
Radio propagation measurement and channel modelling
Salous, Sana
2013-01-01
While there are numerous books describing modern wireless communication systems that contain overviews of radio propagation and radio channel modelling, there are none that contain detailed information on the design, implementation and calibration of radio channel measurement equipment, the planning of experiments and the in depth analysis of measured data. The book would begin with an explanation of the fundamentals of radio wave propagation and progress through a series of topics, including the measurement of radio channel characteristics, radio channel sounders, measurement strategies
The physical theory and propagation model of THz atmospheric propagation
Wang, R.; Yao, J. Q.; Xu, D. G.; Wang, J. L.; Wang, P.
2011-02-01
Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.
Wave propagation in layered anisotropic media with application to composites
Nayfeh, AH
1995-01-01
Recent advances in the study of the dynamic behavior of layered materials in general, and laminated fibrous composites in particular, are presented in this book. The need to understand the microstructural behavior of such classes of materials has brought a new challenge to existing analytical tools. This book explores the fundamental question of how mechanical waves propagate and interact with layered anisotropic media. The chapters are organized in a logical sequence depending upon the complexity of the physical model and its mathematical treatment.
Propagation of radio frequency waves through density fluctuations
Valvis, S. I.; Papagiannis, P.; Papadopoulos, A.; Hizanidis, K.; Glytsis, E.; Bairaktaris, F.; Zisis, A.; Tigelis, I.; Ram, A. K.
2017-10-01
On their way to the core of a tokamak plasma, radio frequency (RF) waves, excited in the vacuum region, have to propagate through a variety of density fluctuations in the edge region. These fluctuations include coherent structures, like blobs that can be field aligned or not, as well as turbulent and filamentary structures. We have been studying the effect of fluctuations on RF propagation using both theoretical (analytical) and computational models. The theoretical results are being compared with those obtained by two different numerical codes ``a Finite Difference Frequency Domain code and the commercial COMSOL package. For plasmas with arbitrary distribution of coherent and turbulent fluctuations, we have formulated an effective dielectric permittivity of the edge plasma. This permittivity tensor is then used in numerical simulations to study the effect of multi-scale turbulence on RF waves. We not only consider plane waves but also Gaussian beams in the electron cyclotron and lower hybrid range of frequencies. The analytical theory and results from simulations on the propagation of RF waves will be presented. Supported in part by the Hellenic National Programme on Controlled Thermonuclear Fusion associated with the EUROfusion Consortium and by DoE Grant DE-FG02-91ER-54109.
Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation
Jing, Yun; Tao, Molei; Clement, Greg T.
2011-01-01
A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green’s function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed. PMID:21302985
Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation.
Jing, Yun; Tao, Molei; Clement, Greg T
2011-01-01
A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green's function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed.
Acoustic precursor wave propagation in viscoelastic media.
Zhu, Guangran Kevin; Mojahedi, Mohammad; Sarris, Costas D
2014-03-01
Precursor field theory has been developed to describe the dynamics of electromagnetic field evolution in causally attenuative and dispersive media. In Debye dielectrics, the so-called Brillouin precursor exhibits an algebraic attenuation rate that makes it an ideal pulse waveform for communication, sensing, and imaging applications. Inspired by these studies in the electromagnetic domain, the present paper explores the propagation of acoustic precursors in dispersive media, with emphasis on biological media. To this end, a recently proposed causal dispersive model is employed, based on its interpretation as the acoustic counterpart of the Cole¿Cole model for dielectrics. The model stems from the fractional stress¿strain relation, which is consistent with the empirically known frequency power-law attenuation in viscoelastic media. It is shown that viscoelastic media described by this model, including human blood, support the formation and propagation of Brillouin precursors. The amplitude of these precursors exhibits a sub-exponential attenuation rate as a function of distance, actually being proportional to z(-p), where z is the distance traveled within the medium and 0.5
propagation in complex media, creating new possibilities for acoustic-pulse-based communication and imaging systems.
Wave Propagation Characteristics in Functionally Graded Double-Beams
Directory of Open Access Journals (Sweden)
Fatih Karacam
2017-09-01
Full Text Available The wave propagation characteristics of functionally graded (FG double-beams are investigated by use of Euler-Bernoulli beam theory. Two beams are connected by a Winkler foundation. The wave propagation characteristics like frequency, phase and group velocities are obtained for different wave numbers and material properties. Four frequencies are obtained for functionally graded double-beam system. It is obtained that flexural and axial waves are coupled for FG double-beams.
Source Modeling Sleep Slow Waves
National Research Council Canada - National Science Library
Michael Murphy; Brady A. Riedner; Reto Huber; Marcello Massimini; Fabio Ferrarelli; Giulio Tononi; Marcus E. Raichle
2009-01-01
.... Here we use high-density EEG (hd-EEG) source modeling to show that individual spontaneous slow waves have distinct cortical origins, propagate uniquely across the cortex, and involve unique subsets of cortical structures...
Mathematical problems in wave propagation theory
1970-01-01
The papers comprising this collection are directly or indirectly related to an important branch of mathematical physics - the mathematical theory of wave propagation and diffraction. The paper by V. M. Babich is concerned with the application of the parabolic-equation method (of Academician V. A. Fok and M. A, Leontovich) to the problem of the asymptotic behavior of eigenfunc tions concentrated in a neighborhood of a closed geodesie in a Riemannian space. The techniques used in this paper have been föund useful in solving certain problems in the theory of open resonators. The topic of G. P. Astrakhantsev's paper is similar to that of the paper by V. M. Babich. Here also the parabolic-equation method is used to find the asymptotic solution of the elasticity equations which describes Love waves concentrated in a neighborhood of some surface ray. The paper of T. F. Pankratova is concerned with finding the asymptotic behavior of th~ eigenfunc tions of the Laplace operator from the exact solution for the surf...
DEFF Research Database (Denmark)
Benzon, Hans-Henrik; Bovith, Thomas
2008-01-01
Weather radars are essential sensors for observation of precipitation in the troposphere and play a major part in weather forecasting and hydrological modelling. Clutter caused by non-standard wave propagation is a common problem in weather radar applications, and in this paper a method...... for prediction of this type of weather radar clutter is presented. The method uses a wave propagator to identify areas of potential non-standard propagation. The wave propagator uses a three dimensional refractivity field derived from the geophysical parameters: temperature, humidity, and pressure obtained from...... a high-resolution Numerical Weather Prediction (NWP) model. The wave propagator is based on the parabolic equation approximation to the electromagnetic wave equation. The parabolic equation is solved using the well-known Fourier split-step method. Finally, the radar clutter prediction technique is used...
Energy Technology Data Exchange (ETDEWEB)
Nishizawa, O.; Sato, T. [Geological Survey of Japan, Tsukuba (Japan); Lei, X. [Dia Consultants Company, Tokyo (Japan)
1996-05-01
In the study of seismic wave propagation, a model experimenting technique has been developed using a laser Doppler velocimeter (LDV) as the sensor. This technique, not dependent on conventional piezoelectric devices, only irradiates the specimen with laser to measure the velocity amplitude on the target surface, eliminating the need for close contact between the specimen and sensor. In the experiment, elastic penetration waves with their noise levels approximately 0.05mm/s were observed upon application of vibration of 10{sup 6}-10{sup 5}Hz. The specimen was stainless steel or rock, and waveforms caught by the LDV and piezoelectric device were compared. As the result, it was found that the LDV is a powerful tool for effectively explaining elastic wave propagation in inhomogeneous media. The piezoelectric device fails to reproduce accurately the waves to follow the initial one while the LDV detect the velocity amplitude on the specimen surface in a wide frequency range encouraging the discussion over the quantification of observed waveforms. 10 refs., 7 figs.
Wave propagation in elastic layers with damping
DEFF Research Database (Denmark)
Sorokin, Sergey; Darula, Radoslav
2016-01-01
The conventional concepts of a loss factor and complex-valued elastic moduli are used to study wave attenuation in a visco-elastic layer. The hierarchy of reduced-order models is employed to assess attenuation levels in various situations. For the forcing problem, the attenuation levels are found...
Radio Wave Propagation Handbook for Communication on and Around Mars
Ho, Christian; Golshan, Nasser; Kliore, Arvydas
2002-01-01
This handbook examines the effects of the Martian environment on radio wave propagation on Mars and in the space near the planet. The environmental effects include these from the Martian atmosphere, ionosphere, global dust storms, aerosols, clouds, and geomorphologic features. Relevant Martian environmental parameters were extracted from the measurements of Mars missions during the past 30 years, especially from Mars Pathfinder and Mars Global Surveyor. The results derived from measurements and analyses have been reviewed through an extensive literature search. The updated parameters have been theoretically analyzed to study their effects on radio propagation. This handbook also provides basic information about the entire telecommunications environment on and around Mars for propagation researchers, system engineers, and link analysts. Based on these original analyses, some important recommendations have been made, including the use of the Martian ionosphere as a reflector for Mars global or trans-horizon communication between future Martian colonies, reducing dust storm scattering effects, etc. These results have extended our wave propagation knowledge to a planet other than Earth; and the tables, models, and graphics included in this handbook will benefit telecommunication system engineers and scientific researchers.
Wave Packet Propagation and Electric Conductivity of Nanowires
Maeda, Munehiko; Saito, Keiji; Miyashita, Seiji; Raedt, Hans De
2004-01-01
We compute the electric conductivity of nanowires in the presence of magnetic domain walls by the method of wave packet propagation. We demonstrate that the propagation through the wire depends on the initial state used in the wave packet simulation. We propose a procedure, based on the Landauer
Sound wave propagation in weakly polydisperse granular materials
Mouraille, O.J.P.; Luding, Stefan
2008-01-01
Dynamic simulations of wave propagation are performed in dense granular media with a narrow polydisperse size-distribution and a linear contact-force law. A small perturbation is created on one side of a static packing and its propagation, for both P- and S-waves, is examined. A size variation
Propagation of waves in a multicomponent plasma having charged ...
Indian Academy of Sciences (India)
Abstract. Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed and the dispersion relation deduced is a generalization of ...
Topology optimization for transient wave propagation problems in one dimension
DEFF Research Database (Denmark)
Dahl, Jonas; Jensen, Jakob Søndergaard; Sigmund, Ole
2008-01-01
Structures exhibiting band gap properties, i.e., having frequency ranges for which the structure attenuates propagating waves, have applications in damping of acoustic and elastic wave propagation and in optical communication. A topology optimization method for synthesis of such structures......, employing a time domain formulation, is developed. The method is extended to synthesis of pulse converting structures with possible applications in optical communication....
Nonlinear wave propagation through a ferromagnet with damping in ...
Indian Academy of Sciences (India)
We investigate how dissipation and nonlinearity can affect the electromagnetic wave propagating through a saturated ferromagnet in the presence of an external magnetic ﬁeld in (2+1) dimensions. The propagation of electromagnetic waves through a ferromagnet under an external magnetic ﬁeld in the presence of ...
Analysis of flexural wave propagation in poroelastic composite ...
African Journals Online (AJOL)
Wave propagation in an infinitely long poroelastic composite hollow cylinder in is examined by employing Biot's theory of wave propagation in poroelastic media. A poroelastic composite hollow cylinder consists of two concentric poroelastic cylindrical layers both of which are made of different poroelastic materials with each ...
Zhang, Jichun; Coffey, Victoria N.; Chandler, Michael O.; Boardsen, Scott A.; Saikin, Anthony A.; Mello, Emily M.; Russell, Christopher T.; Torbert, Roy B.; Fuselier, Stephen A.; Giles, Barbara L.;
2017-01-01
Electromagnetic ion cyclotron (EMIC) waves (0.1-5 Hz) play an important role in particle dynamics in the Earth's magnetosphere. EMIC waves are preferentially excited in regions where hot anisotropic ions and cold dense plasma populations spatially overlap. While the generation region of EMIC waves is usually on or near the magnetic equatorial plane in the inner magnetosphere, EMIC waves have both equatorial and off-equator source regions on the dayside in the compressed outer magnetosphere. Using field and plasma measurements from the Magnetospheric Multiscale (MMS) mission, we perform a case study of EMIC waves and associated local plasma conditions observed on 19 October 2015. From 0315 to 0810 UT, before crossing the magnetopause into the magnetosheath, all four MMS spacecraft detected long-lasting He(exp +)-band EMIC wave emissions around local noon (MLT = 12.7 - 14.0) at high L-shells (L = 8.8 - 15.2) and low magnetic latitudes (MLAT = -21.8deg - -30.3deg). Energetic (greater than 1 keV) and anisotropic ions were present throughout this event that was in the recovery phase of a weak geomagnetic storm (min. Dst = -48 nT at 1000 UT on 18 October 2015). The testing of linear theory suggests that the EMIC waves were excited locally. Although the wave event is dominated by small normal angles, its polarization is mixed with right- and left-handedness and its propagation is bi-directional with regard to the background magnetic field. The short inter-spacecraft distances (as low as 15 km) of the MMS mission make it possible to accurately determine the k vector of the waves using the phase difference technique. Preliminary analysis finds that the k vector magnitude, phase speed, and wavelength of the 0.3-Hz wave packet at 0453:55 UT are 0.005 km(exp -1), 372.9 km/s, and 1242.9 km, respectively.
Electromagnetic wave propagation and wave-vector diagram in space-time periodic media.
Elachi, C.
1972-01-01
Analysis of TE and TM wave propagation in space-time periodic media such as dielectrics, isotropic plasmas and uniaxial plasmas. A numerical solution is obtained for media with sinusoidal periodicity. Wave-vector diagrams are plotted to facilitate studies of dipole radiation, wave propagation in waveguides and wave interactions with a half-space.
Propagation of ionization waves during ignition of fluorescent lamps
Langer, R.; Garner, R.; Hilscher, A.; Tidecks, R.; Horn, S.
2008-07-01
The propagation of the first ionization wave in a compact fluorescent lamp (T4 tube with standard electrodes) during ignition was investigated for various initial dc-voltages (both polarities measured against ground) and gas compositions (with and without mercury). In addition the effect of the presence of a fluorescent powder coating was studied. The propagation velocity of the initial wave was measured by an assembly of photomultipliers installed along the tube, which detected the light emitted by the wave head. The propagation was found to be faster for positive than for negative polarity. This effect is explained involving processes in the electrode region as well as in the wave head. Waves propagate faster in the presence of a fluorescent powder coating than without it and gases of lighter mass show a faster propagation than gases with higher mass.
Propagation of ionization waves during ignition of fluorescent lamps
Energy Technology Data Exchange (ETDEWEB)
Langer, R; Tidecks, R; Horn, S [Institute of Physics, Chair for Experimental Physics II, University of Augsburg, Universitaetsstrasse 1, D-86159 Augsburg (Germany); Garner, R [Central Research and Services Laboratory, OSRAM SYLVANIA Inc., 71 Cherry Hill Drive, Beverly, MA 01915 (United States); Hilscher, A [OSRAM GmbH, Berliner Allee 65, D-86136 Augsburg (Germany)], E-mail: Reinhard.Langer@physik.uni-augsburg.de
2008-07-21
The propagation of the first ionization wave in a compact fluorescent lamp (T4 tube with standard electrodes) during ignition was investigated for various initial dc-voltages (both polarities measured against ground) and gas compositions (with and without mercury). In addition the effect of the presence of a fluorescent powder coating was studied. The propagation velocity of the initial wave was measured by an assembly of photomultipliers installed along the tube, which detected the light emitted by the wave head. The propagation was found to be faster for positive than for negative polarity. This effect is explained involving processes in the electrode region as well as in the wave head. Waves propagate faster in the presence of a fluorescent powder coating than without it and gases of lighter mass show a faster propagation than gases with higher mass.
Pilotti, Marco
2016-01-01
Shallow Water Equations (SWE) provide a fundamental component for the quantification and mapping of hydraulic hazard. In steep mountain valleys, the use of one-dimensional SWE (also known as St. Venant Equations, SVE) is often legitimate and computationally competitive against two-dimensional solvers. However, in the same environment, the solution of SVE is hindered by the need of an accurate bathymetric reconstruction, which implies a number of cross sections which cannot be readily acquired by conventional field surveys. On the other hand, Digital Elevation Models (DEM) with resolution adequate for studies of flood propagation are available in many areas of the world. In this paper, I propose to compute cross sections automatically by operating along the channel network derived from a valley's raster DEM, on the basis of algorithms that hitherto have been used for geomorphological and hydrological purposes. The extraction process can be refined by varying cross section inter-distance and width, in order to prevent superimpositions that might occur due to the sinuosity of the thalweg and to better capture the valley's local topography. At the end of this process, the geometric functions needed by SVE solvers can be computed for each cross section. A software tool that implements the described algorithm is provided to the scientific community.
Energy Technology Data Exchange (ETDEWEB)
Wirdelius, Haakan; Persson, Gert; Hamberg, Kenneth (SCeNDT, Chalmers Univ. Of Tech., SE-412 96 Goeteborg (SE)); Hoegberg, Kjell (SQC Kvalificeringscentrum AB, SE-183 25 Taeby (SE))
2008-07-01
New and stronger demands on reliability of used NDE/NDT procedures and methods have evolved in Europe during the last decade. In order to elaborate these procedures, efforts have to be taken towards the development of mathematical models of applied NDT methods. Modelling of ultrasonic non-destructive testing is useful for a number of reasons, e.g. physical understanding, parametric studies, and the qualification of procedures and personnel. An important issue regarding all models is the validation, i.e. securing that the results of the model and the corresponding computer programs are correct. This can be accomplished by comparisons with other models, but ultimately by comparisons with experiments. In this study a numerical model and experimental results are compared and the work has been performed in collaboration with SQC Kvalificeringscentrum AB. Four different welds have been investigated to give basic data to a mathematical model that describes the ultra sonic wave paths through the welds in these materials. The welds are made in austenitic stainless steel (type 18-8) and in Inconel 182. Two cuts outs are made in each weld, one longitudinal and one transversal cut across the welds, in order to determine the material orientation. In the numerical model the incident field, described by rays, is given by a P wave probe model. The ray tracing technique is based on geometrical optics and a 2D algorithm has been developed. The model of the weld is based on a relatively primitive assumption of the grain structure for a V-butt weld. The columnar structure of austenitic welds is here modelled as a weld where each sub region corresponds to a grain group. The response of the receiver is calculated according to Auld's reciprocity principle. UT data collection was performed by SQC according to guidelines given from Chalmers. The purpose to collect data from real inspection objects with known material structure is to compare experimental data with theoretically
ENERGY CONTENT AND PROPAGATION IN TRANSVERSE SOLAR ATMOSPHERIC WAVES
Energy Technology Data Exchange (ETDEWEB)
Goossens, M.; Van Doorsselaere, T. [Centre for mathematical Plasma Astrophysics, Mathematics Department, Celestijnenlaan 200B bus 2400, B-3001 Heverlee (Belgium); Soler, R. [Solar Physics Group, Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Verth, G., E-mail: tom.vandoorsselaere@wis.kuleuven.be [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hounsfield Road, Hicks Building, Sheffield S3 7RH (United Kingdom)
2013-05-10
Recently, a significant amount of transverse wave energy has been estimated propagating along solar atmospheric magnetic fields. However, these estimates have been made with the classic bulk Alfven wave model which assumes a homogeneous plasma. In this paper, the kinetic, magnetic, and total energy densities and the flux of energy are computed for transverse MHD waves in one-dimensional cylindrical flux tube models with a piecewise constant or continuous radial density profile. There are fundamental deviations from the properties for classic bulk Alfven waves. (1) There is no local equipartition between kinetic and magnetic energy. (2) The flux of energy and the velocity of energy transfer have, in addition to a component parallel to the magnetic field, components in the planes normal to the magnetic field. (3) The energy densities and the flux of energy vary spatially, contrary to the case of classic bulk Alfven waves. This last property has the important consequence that the energy flux computed with the well known expression for bulk Alfven waves could overestimate the real flux by a factor in the range 10-50, depending on the flux tube equilibrium properties.
The Green-function transform and wave propagation
Directory of Open Access Journals (Sweden)
Colin eSheppard
2014-11-01
Full Text Available Fourier methods well known in signal processing are applied to three-dimensional wave propagation problems. The Fourier transform of the Green function, when written explicitly in terms of a real-valued spatial frequency, consists of homogeneous and inhomogeneous components. Both parts are necessary to result in a pure out-going wave that satisfies causality. The homogeneous component consists only of propagating waves, but the inhomogeneous component contains both evanescent and propagating terms. Thus we make a distinction between inhomogeneous waves and evanescent waves. The evanescent component is completely contained in the region of the inhomogeneous component outside the k-space sphere. Further, propagating waves in the Weyl expansion contain both homogeneous and inhomogeneous components. The connection between the Whittaker and Weyl expansions is discussed. A list of relevant spherically symmetric Fourier transforms is given.
Instabilities and propagation of neutrino magnetohydrodynamic waves in arbitrary direction
Haas, Fernando; Pascoal, Kellen Alves
2017-09-01
In a previous work [Haas et al., Phys. Plasmas 23, 012104 (2016)], a new model was introduced, taking into account the role of the Fermi weak force due to neutrinos coupled to magnetohydrodynamic plasmas. The resulting neutrino-magnetohydrodynamics was investigated in a particular geometry associated with the magnetosonic wave, where the ambient magnetic field and the wavevector are perpendicular. The corresponding fast, short wavelength neutrino beam instability was then obtained in the context of supernova parameters. The present communication generalizes these results, allowing for arbitrary direction of wave propagation, including fast and slow magnetohydrodynamic waves and the intermediate cases of oblique angles. The numerical estimates of the neutrino-plasma instabilities are derived in extreme astrophysical environments where dense neutrino beams exist.
Model development for wireless propagation in forested environments
Zegarra, Jesus
2015-01-01
Approved for public release; distribution is unlimited Wireless propagation modeling is a necessary task in the design of countless applications. Wireless signals attenuate at different rates according to the propagation environment. Given that vegetation is an unavoidable feature for most outdoor wireless channels, propagation models in forested environments are in high demand. The characterization of radio waves propagating through foliage is particularly complex due to the random charac...
Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan
2017-03-01
This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.
Superluminal propagation of solitary kinklike waves in amplifying media.
Janowicz, Maciej; Mostowski, Jan
2006-04-01
It is shown that solitary-wave, kinklike structures can propagate superluminally in two- and four-level amplifying media with strongly damped oscillations of coherences. This is done by solving analytically the Maxwell-Bloch equations in the kinetic limit. It is also shown that the true wave fronts--unlike the pseudo wave fronts of the kinks--must propagate with velocity c, so that no violation of special relativity is possible. The conditions of experimental verification are discussed.
Shock wave propagation along constant sloped ocean bottoms.
Maestas, Joseph T; Taylor, Larissa F; Collis, Jon M
2014-12-01
The nonlinear progressive wave equation (NPE) is a time-domain model used to calculate long-range shock propagation using a wave-following computational domain. Current models are capable of treating smoothly spatially varying medium properties, and fluid-fluid interfaces that align horizontally with a computational grid that can be handled by enforcing appropriate interface conditions. However, sloping interfaces that do not align with a horizontal grid present a computational challenge as application of interface conditions to vertical contacts is non-trivial. In this work, range-dependent environments, characterized by sloping bathymetry, are treated using a rotated coordinate system approach where the irregular interface is aligned with the coordinate axes. The coordinate rotation does not change the governing equation due to the narrow-angle assumption adopted in its derivation, but care is taken with applying initial, interface, and boundary conditions. Additionally, sound pressure level influences on nonlinear steepening for range-independent and range-dependent domains are used to quantify the pressures for which linear acoustic models suffice. A study is also performed to investigate the effects of thin sediment layers on the propagation of blast waves generated by explosives buried beneath mud line.
Effect of near-surface topography on high-frequency Rayleigh-wave propagation
Wang, Limin; Xu, Yixian; Xia, Jianghai; Luo, Yinhe
2015-05-01
Rayleigh waves, which are formed due to interference of P- and Sv-waves near the free surface, propagate along the free surface and vanish exponentially in the vertical direction. Their propagation is strongly influenced by surface topography. Due to the high resolution and precision requirements of near-surface investigations, the high-frequency Rayleigh waves are usually used for near-surface structural detecting. Although there are some numerical studies on high-frequency Rayleigh-wave propagation on topographic free surface, detailed analysis of characters of high-frequency Rayleigh-wave propagation on topographic free surface remains untouched. Hence, research of propagation of Rayleigh waves on complex topographic surface becomes critical for Rayleigh-wave methods in near-surface applications. To study the propagation of high-frequency Rayleigh waves on topographic free surface, two main topographic models are designed in this study. One of the models contains a depressed topographic surface, and another contains an uplifted topographic surface. We numerically simulate the propagation of high-frequency Rayleigh waves on these two topographic surfaces by finite-difference method. Soon afterwards, we analyze the propagation character of high-frequency Rayleigh waves on such topographic models, and compare the variations on its energy and frequency before and after passing the topographic region. At last, we discuss the relationship between the variations and topographical steepness of each model. Our numerical results indicate that influence of depressed topography for high-frequency Rayleigh waves is more distinct than influence of uplifted topography. Rayleigh waves produce new scattering body waves during passing the depressed topography with reduction of amplitude and loss of high-frequency components. Moreover, the steeper the depressed topography is, the more energy of Rayleigh waves is lost. The uplifted topography with gentle slope produces similar
Wave Propagation in Pipe-like Structures
DEFF Research Database (Denmark)
Morsbøl, Jonas
. In the curved beam regime the waveguide properties of the pipe can be approximated by classical curved beam theory while in the cylinder regime they can be approximated by cylindrical shell theory. In the torus regime none of the two other regimes apply, and a full-blown shell model is needed. For the straight...... pipe with changing radius, which is known as the shell of revolution, it is found that classical rod and beam theory, to some extent, can be used to approximate the fundamental modes of the torsional, axial, and breathing wave. However, by means of the shell model some remarkable effects are predicted...
A database for propagation models
Kantak, Anil V.; Suwitra, Krisjani; Le, Choung
1993-01-01
The NASA Propagation Program supports academic research that models various propagation phenomena in the space research frequency bands. NASA supports such research via school and institutions prominent in the field. The products of such efforts are particularly useful for researchers in the field of propagation phenomena and telecommunications systems engineers. The systems engineer usually needs a few propagation parameter values for a system design. Published literature on the subject, such as the Cunsultative Committee for International Radio (CCIR) publications, may help somewhat, but often times, the parameter values given in such publications use a particular set of conditions which may not quite include the requirements of the system design. The systems engineer must resort to programming the propagation phenomena model of interest and to obtain the parameter values to be used in the project. Furthermore, the researcher in the propagation field must then program the propagation models either to substantiate the model or to generate a new model. The researcher or the systems engineer must either be a skillful computer programmer or hire a programmer, which of course increases the cost of the effort. An increase in cost due to the inevitable programming effort may seem particularly inappropriate if the data generated by the experiment is to be used to substantiate the already well-established models, or a slight variation thereof. To help researchers and the systems engineers, it was recommended by the participants of NASA Propagation Experimenters (NAPEX) 15 held in London, Ontario, Canada on 28-29 June 1991, that propagation software should be constructed which will contain models and prediction methods of most propagation phenomenon. Moreover, the software should be flexible enough for the user to make slight changes to the models without expending a substantial effort in programming.
On the propagation of truncated localized waves in dispersive silica
Salem, Mohamed
2010-01-01
Propagation characteristics of truncated Localized Waves propagating in dispersive silica and free space are numerically analyzed. It is shown that those characteristics are affected by the changes in the relation between the transverse spatial spectral components and the wave vector. Numerical experiments demonstrate that as the non-linearity of this relation gets stronger, the pulses propagating in silica become more immune to decay and distortion whereas the pulses propagating in free-space suffer from early decay and distortion. © 2010 Optical Society of America.
Peculiarities of sea wave propagation in the Klaipėda Strait, Lithuania
Kriaučiūnienė, Jūratė; Gailiušis, Brunonas; Kovalenkovienė, Milda
2006-01-01
During rough weather, navigation in Klaipėda port is risky because of the high wave penetration into the Klaipėda Strait from the Baltic Sea. Objectives of the present paper are to study wind and wave regimes in Klaipėda port water area and to develop the short wave propagation model at wind speeds of 15, 20 and 25 m/s and varying directions. The modelled wave parameters are significant wave height and wave disturbance coefficient. The software MIKE 21 BW (Boussinesq Wave Module) is used for ...
A critical survey of wave propagation and impact in composite materials
Moon, F. C.
1973-01-01
A review of the field of stress waves in composite materials is presented covering the period up to December 1972. The major properties of waves in composites are discussed and a summary is made of the major experimental results in this field. Various theoretical models for analysis of wave propagation in laminated, fiber and particle reinforced composites are surveyed. The anisotropic, dispersive and dissipative properties of stress pulses and shock waves in such materials are reviewed. A review of the behavior of composites under impact loading is presented along with the application of wave propagation concepts to the determination of impact stresses in composite plates.
Ionization wave propagation on a micro cavity plasma array
Energy Technology Data Exchange (ETDEWEB)
Wollny, Alexander; Hemke, Torben; Gebhardt, Markus; Peter Brinkmann, Ralf; Mussenbrock, Thomas [Institute of Theoretical Electrical Engineering, Ruhr University Bochum, D-44780 Bochum (Germany); Boettner, Henrik; Winter, Joerg; Schulz-von der Gathen, Volker [Institute for Experimental Physics II, Ruhr University Bochum, D-44780 Bochum (Germany); Xiong, Zhongmin; Kushner, Mark J. [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)
2011-10-03
Microcavity plasma arrays of inverse pyramidal cavities fabricated on p-Si wafers act as localized dielectric barrier discharges. When operated at atmospheric pressure in argon and excited with high voltage at 10 kHz, a strong interaction between individual cavities is observed leading to wave-like optical emission propagating along the surface of the array. This phenomenon is numerically investigated. The computed ionization wave propagates with a speed of 5 km/s, which agrees well with experiments. The wave propagation is due to the sequential drift of electrons followed by drift of ions between cavities seeded by photoemission of electrons by the plasma in adjacent cavities.
CASTIBLANCO, J; SEETHARAMDOO, D; Berbineau, M.; Ney, M.; GALLEE, F
2010-01-01
Entirely automated and driverless metros are becoming more and more popular and the demand for more reliable, higher performance wireless systems is growing. Proper deployment and enhancement of these wireless systems is thus becoming an important issue to guarantee the quality of service and reliability required. Realistic prediction of radio propagation is required during deployment even in very specific environments such as tunnels and whatever the electromagnetic characteristics of the in...
Propagation and dispersion of shock waves in magnetoelastic materials
Crum, R. S.; Domann, J. P.; Carman, G. P.; Gupta, V.
2017-12-01
Previous studies examining the response of magnetoelastic materials to shock waves have predominantly focused on applications involving pulsed power generation, with limited attention given to the actual wave propagation characteristics. This study provides detailed magnetic and mechanical measurements of magnetoelastic shock wave propagation and dispersion. Laser generated rarefacted shock waves exceeding 3 GPa with rise times of 10 ns were introduced to samples of the magnetoelastic material Galfenol. The resulting mechanical measurements reveal the evolution of the shock into a compressive acoustic front with lateral release waves. Importantly, the wave continues to disperse even after it has decayed into an acoustic wave, due in large part to magnetoelastic coupling. The magnetic data reveal predominantly shear wave mediated magnetoelastic coupling, and were also used to noninvasively measure the wave speed. The external magnetic field controlled a 30% increase in wave propagation speed, attributed to a 70% increase in average stiffness. Finally, magnetic signals propagating along the sample over 20× faster than the mechanical wave were measured, indicating these materials can act as passive antennas that transmit information in response to mechanical stimuli.
Nonlinear propagation of lower hybrid waves in a plasma
Energy Technology Data Exchange (ETDEWEB)
Kaw, P.K.; Cheng, C.Z.; Chen, L.
1976-11-01
A model equation was used to investigate the competition between the electron E x B/sub o/ nonlinearities (which lead to parametric instabilities and anomalous absorption) and the electron polarization drift and ion nonlinearities (which induce filamentation and self-focusing effects) in the propagation of a large amplitude lower hybrid wave in a plasma. The conclusion is that the former dominates for plasma regions with ..omega../sup 2//sub pi/ > ..omega../sup 2//sub ci/ (i.e., everywhere except in a thin skin region).
Wave propagation, scattering and emission in complex media
Jin, Ya-Qiu
I. Polarimetric scattering and SAR imagery. EM wave propagation and scattering in polarimetric SAR interferometry / S. R. Cloude. Terrain topographic inversion from single-pass polarimetric SAR image data by using polarimetric stokes parameters and morphological algorithm / Y. Q. Jin, L. Luo. Road detection in forested area using polarimetric SAR / G. W. Dong ... [et al.]. Research on some problems about SAR radiometric resolution / G. Dong ... [et al.]. A fast image matching algorithm for remote sensing applications / Z. Q. Hou ... [et al.]. A new algorithm of noised remote sensing image fusion based on steerable filters / X. Kang ... [et al.]. Adaptive noise reduction of InSAR data based on anisotropic diffusion models and their applications to phase unwrapping / C. Wang, X. Gao, H. Zhang -- II. Scattering from randomly rough surfaces. Modeling tools for backscattering from rough surfaces / A. K. Fung, K. S. Chen. Pseudo-nondiffracting beams from rough surface scattering / E. R. Méndez, T. A. Leskova, A. A. Maradudin. Surface roughness clutter effects in GPR modeling and detection / C. Rappaport. Scattering from rough surfaces with small slopes / M. Saillard, G. Soriano. Polarization and spectral characteristics of radar signals reflected by sea-surface / V. A. Butko, V. A. Khlusov, L. I. Sharygina. Simulation of microwave scattering from wind-driven ocean surfaces / M. Y. Xia ... [et al.]. HF surface wave radar tests at the Eastern China Sea / X. B. Wu ... [et al.] -- III. Electromagnetics of complex materials. Wave propagation in plane-parallel metamaterial and constitutive relations / A. Ishimaru ... [et al.]. Two dimensional periodic approach for the study of left-handed metamaterials / T. M. Grzegorczyk ... [et al.]. Numerical analysis of the effective constitutive parameters of a random medium containing small chiral spheres / Y. Nanbu, T. Matsuoka, M. Tateiba. Wave propagation in inhomogeneous media: from the Helmholtz to the Ginzburg -Landau equation / M
Harfi, Thura T; Seo, Jung-Hee; Yasir, Hayder S; Welsh, Nathaniel; Mayer, Susan A; Abraham, Theodore P; George, Richard T; Mittal, Rajat
2017-01-15
To describe the derivation and validation of a novel echocardiographic metric for prediction of left ventricle thrombus (LVT). Computational fluid dynamic modeling using cardiac CT images was used to derive a novel echocardiography-based metric to predict the presence of LVT. We retrospectively reviewed 25 transthoracic echocardiograms showing definite LVT (LVT group). We then randomly selected 25 patients with LVEF ≥55% (Normal EF group) and 25 patients with severe cardiomyopathy (CMP) with LVEF ≤40% without evidence of LVT (CMP group). The E-wave Propagation Index (EPI) was measured as the E-wave velocity time-integral divided by the LV length. An EPI>1 indicates penetration of the mitral jet into the apex whereas an EPIEPI was compared between the three groups. Crude and adjusted odd ratios of EPI and LVT association were also measured. Mean EPI was highest for the normal EF group and lowest in the LVT group (1.7 vs. 0.8; pEPI also differed significantly between LVT and CMP groups (0.8 vs. 1.2; pEPI EPI EPI of less than 1 is an independent predictor of LVT formation. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.
Propagation of gravity waves through non-uniform stratification
Pütz, Christopher; Klein, Rupert
2017-04-01
We present a method to compute the transmission of gravity waves through a finite region of a non-uniformly stratified atmosphere. It is based on an approximate solution of the Taylor-Goldstein equation. With the method, we are able to compute a transmission coefficient for gravity waves, which is defined as the ratio of the vertical wave energy fluxes below and above the region of non-uniform stratification. It makes use of the fact that plane wave solutions exist in uniform stratification and models the atmosphere as a multi-layer fluid where each layer is uniformly stratified. The solutions are matched at the interfaces in a way that the continuity of pressure and vertical wind is ensured, so that we are finally able to relate incident and transmitted wave amplitudes. Further, the limit of increasing number of layers is investigated and we obtain a reformulation of the Taylor-Goldstein equation. This equation can not be solved analytically, but numerically, giving a solution in which it is possible to distinguish between the two branches of the gravity wave dispersion relation, namely upward and downward travelling waves. Hence, we are also able to compute a transmission coefficient from this procedure. Moreover, it can be shown that the multi-layer solution converges to the limit solution quadratically with increasing number of layers. The results we obtain for some test cases are in accordance with several existing results, but provide more general insights into the interaction of gravity waves propagating through non-uniform stratification. Also, the multi-layer method can be extended to give an approximate solution to the Taylor-Goldstein equation without using any numerical integration.
Leng, K.; Nissen-Meyer, T.; van Driel, M.; Al-Attar, D.
2016-12-01
We present a new, computationally efficient numerical method to simulate global seismic wave propagation in realistic 3-D Earth models with laterally heterogeneous media and finite boundary perturbations. Our method is a hybrid of pseudo-spectral and spectral element methods (SEM). We characterize the azimuthal dependence of 3-D wavefields in terms of Fourier series, such that the 3-D equations of motion reduce to an algebraic system of coupled 2-D meridional equations, which can be solved by a 2-D spectral element method (based on www.axisem.info). Computational efficiency of our method stems from lateral smoothness of global Earth models (with respect to wavelength) as well as axial singularity of seismic point sources, which jointly confine the Fourier modes of wavefields to a few lower orders. All boundary perturbations that violate geometric spherical symmetry, including Earth's ellipticity, topography and bathymetry, undulations of internal discontinuities such as Moho and CMB, are uniformly considered by means of a Particle Relabeling Transformation.The MPI-based high performance C++ code AxiSEM3D, is now available for forward simulations upon 3-D Earth models with fluid outer core, ellipticity, and both mantle and crustal structures. We show novel benchmarks for global wave solutions in 3-D mantle structures between our method and an independent, fully discretized 3-D SEM with remarkable agreement. Performance comparisons are carried out on three state-of-the-art tomography models, with seismic period going down to 5s. It is shown that our method runs up to two orders of magnitude faster than the 3-D SEM for such settings, and such computational advantage scales favourably with seismic frequency. By examining wavefields passing through hypothetical Gaussian plumes of varying sharpness, we identify in model-wavelength space the limits where our method may lose its advantage.
Zhao, L.; Wen, L.
2009-12-01
The shear wave splitting measurements provide important information on mantle flow, deformation and mineralogy. They are now routinely made using the method developed by Silver and Chan (1994). More and more dense regional observations also begin to reveal sharp spatial variations of seismic anisotropy which could not be explained by simplified horizontal homogeneous anisotropic structures. To better constrain the mantle anisotropy beneath those regions, we developed a two-dimensional hybrid method for simulating seismic wave propagation in laterally-varying anisotropic media [Zhao et al., 2008]. In this presentation, we apply the method to study anisotropic structures beneath central Tibet by waveform modeling the teleseismic SKS phases recorded in the International Deep Profiling of Tibet and the Himalayas project (INDEPTH) III. Using data from two events that were selected such that the stations and sources can be approximated as a two-dimensional profile, we derived an optimal model for the anisotropic structures of the upper mantle beneath the study region: a 50-70 km thick anisotropic layer with a fast direction trending N95°E beneath the Qiangtang block, a 150 km thick and 60 km wide anisotropic segment with an axis trending N95°E beneath the northernmost Lhasa block, and a ~30 km wide transition zone in between within which the fast direction trends N45°E and the depth extent of anisotropy decreases northward sharply. Synthetic waveform modeling further suggests that an anisotropic model with a horizontal symmetry axis can explain the observations better than that with a dipping symmetry, and a low velocity zone possibly underlies or mixes with the anisotropic structures in the northern portion of the region. The optimal model yields synthetic seismograms that are in good agreement with the observations in both amplitudes and relative arrival times of SKS phases. Synthetic tests also indicate that different elastic constants, source parameters and depth
Local principles of wave propagation in inhomogeneous media
Gingold, Harry; She, Jianming; Zorumski, William E.
1993-01-01
Four local principles are proven for waves propagating in a layered medium with a variable wave speed. These principles are (1) that inhomogeneities increase the amplitude of waves generated by a source of fixed strength, (2) that inhomogeneities reduce spatial oscillation, or increase the wavelength, (3) that inhomogeneities decrease transmission, or increase reflection, and (4) that transmission increases monotonically with frequency. Definitions of inhomogeneity, local wave function, and local reflection and transmission coefficients are made as a basis for stating these principles.
Energy Technology Data Exchange (ETDEWEB)
Melchor Garcia, Nicolas Ageo
2005-02-15
This work presents the state of art of the behavior of buried pipelines facing the effect of the propagation of seismic waves. Special attention has been given to the modeling of the soil-piping system. Some analytical models are presented and discussed in great detail. The purpose of this is to contribute, in particular, to the following aspects: First, it attempts to be a reference work for the geotechnical engineers facing problems related to the seismic wave propagation phenomenon in buried structures, since within the consulted literature there are many of the principles presented in here, that are related with the seismic engineering, the reaction module, as well as expressions or investigations performed in piles. Second, a cuasi-static numerical model is presented that analyzes the continuous piping through a stress vector of sinusoidal type. The analysis of the stresses and deformations that the ground transmits to the pipe is made using a ground-to-pipe interaction model. For a low level of deformations an elastic behavior of transference in the interface is considered in the inter-phase ground-piping. In the case of greater deformations it is assumed that sliding is presented because the surrounding ground presents fault by shearing stress in the surrounding ground. The analysis covers solely the case with axial deformations in straight sections. Finally, it intends to give a series of recommendations for future research works on the modeling of buried pipelines. In this work, the influence of several aspects on the response of the pipelines to the propagation of seismic waves is analyzed and discussed; such as the conditions of topography, geology, ground stratigraphy and the rigidity changes in the surrounding ground of the pipe. [Spanish] Este trabajo presenta el estado del arte sobre el comportamiento de tuberias enterradas ante efecto de programacion de ondas sismicas. Una especial atencion ha sido dada a la modelacion del sistema suelo
Wave propagation in reconfigurable broadband gain metamaterials at microwave frequencies
Fan, Yifeng; Nagarkoti, Deepak S.; Rajab, Khalid Z.; Hao, Yang; Zhang, Hao Chi; Cui, Tie Jun
2016-05-01
The wave dispersion characteristics for loop array-based metamaterials were analyzed, based on the general transmission line model of a one-dimensional host medium interacting with a chain of coupled loops. By relating the wave propagation constant and the effective parameters of the coupled host medium, we showed that an active medium embedded with non-Foster loaded loop array can be designed to exhibit broadband negative material parameters with positive gain. Accounting for all interactions, the stability of the active medium was investigated, further yielding necessary design specifications for the non-Foster loads. Subsequently, an experimental demonstration was provided to verify the theoretical analysis, showing that stable reconfigurable broadband gain metamaterials at microwave frequencies can be obtained with proper negative impedance converter design.
Wave propagation in channels and cracks with elastic walls
Sukhinin, S. V.; Yurkovskiy, V. S.; Konstantinov, A. P.; Trilis, A. V.
2017-10-01
In this paper wave propagation in the uniform and nonuniform elastic channels filled with fluid or gas is investigated. The weak discontinuities theory approach is proposed to determine the criteria of gradient catastrophe phenomena to occur for the cases of uniform and nonuniform channels. The results of the paper can be applied to studying of the nonlinear wave propagation phenomena in elastic pores, cracks and channels filled with fluid or gas.
Topology optimization of vibration and wave propagation problems
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard
2007-01-01
The method of topology optimization is a versatile method to determine optimal material layouts in mechanical structures. The method relies on, in principle, unlimited design freedom that can be used to design materials, structures and devices with significantly improved performance and sometimes...... novel functionality. This paper addresses basic issues in simulation and topology design of vibration and wave propagation problems. Steady-state and transient wave propagation problems are addressed and application examples for both cases are presented....
Wave propagation in a general anisotropic poroelastic medium ...
Indian Academy of Sciences (India)
The medium considered is a general anisotropic poroelastic (APE) solid with a viscous fluid saturating its pores of anisotropic permeability. The wave propagation phenomenon in a saturated porous medium is explained through two relations. One defines modified Christoffel equations for the propagation of plane harmonic ...
Wave Propagation: Odd is Better, but Three is Best
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 9; Issue 7. Wave Propagation: Odd is Better, but Three is Best - Propagation in Spaces of Different Dimensions. V Balakrishnan. General Article Volume 9 Issue 7 July 2004 pp 8-17 ...
Characteristic wave diversity in Near Vertical Incidence Skywave propagation
Witvliet, Ben A.; van Maanen, Erik; Petersen, George J.; Westenberg, Albert J.; Bentum, Marinus Jan; Slump, Cornelis H.; Schiphorst, Roelof
2015-01-01
In Near Vertical Incidence Skywave (NVIS) propagation, effective diversity reception can be realized using a dual channel receiver and a dual polarization antenna with polarization matched to the (left hand and right hand) circular polarization of the characteristic waves propagating in the
Directory of Open Access Journals (Sweden)
M. Caputo
1998-06-01
Full Text Available Since the dispersion and attenuation properties of dielectric and anelastic media, in the frequency domain, are expressed by similar formulae, as shown experimentally by Cole and Cole (1941 and Bagley and Torvik (1983, 1986 respectively, we note that the same properties may be represented in the time domain by means of an equation of the same form; this is obtained by introducing derivatives of fractional order into the system functions of the media. The Laplace Transforms (LT of such system functions contain fractional powers of the imaginary frequency and are, therefore, multivalued functions defined in the Riemann Sheets (RS of the function. We determine the response of the medium (dielectric o anelastic to a generic signal summing the time domain representation due to the branches of the solutions in the RSs of the LT. It is found that, if the initial conditions are equal in all the RSs, the solution is a sum of two exponentials with complex exponents, if the initial conditions are different in some of the RSs, then a transient for each of those RSs is added to the exponentials. In all cases a monochromatic wave is split into a set of waves with the same frequency and slightly different wavelengths which interfere and disperse. As a consequence a monochromatic electromagnetic wave with frequency around 1 MHz in water has a relevant dispersion and beats generating a tunnel effect. In the atmosphere of the Earth the dispersion of a monochromatic wave with frequency around 1 GHz, like those used in tracking artificial satellites, has a negligible effect on the accuracy of the determination of the position of the satellites and the positioning of the bench marks on the Earth. We also find the split eigenfunctions of the free modes of infinite plates and shells made of dielectric and anelastic media.
Plasma and radio waves from Neptune: Source mechanisms and propagation
Wong, H. K.
1994-01-01
This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.
Fully resolved simulations of expansion waves propagating into particle beds
Marjanovic, Goran; Hackl, Jason; Annamalai, Subramanian; Jackson, Thomas; Balachandar, S.
2017-11-01
There is a tremendous amount of research that has been done on compression waves and shock waves moving over particles but very little concerning expansion waves. Using 3-D direct numerical simulations, this study will explore expansion waves propagating into fully resolved particle beds of varying volume fractions and geometric arrangements. The objectives of these simulations are as follows: 1) To fully resolve all (1-way coupled) forces on the particles in a time varying flow and 2) to verify state-of-the-art drag models for such complex flows. We will explore a range of volume fractions, from very low ones that are similar to single particle flows, to higher ones where nozzling effects are observed between neighboring particles. Further, we will explore two geometric arrangements: body centered cubic and face centered cubic. We will quantify the effects that volume fraction and geometric arrangement plays on the drag forces and flow fields experienced by the particles. These results will then be compared to theoretical predictions from a model based on the generalized Faxen's theorem. This work was supported in part by the U.S. Department of Energy under the Predictive Science Academic Alliance Program, under Contract No. DE-NA0002378.
Time dependent wave envelope finite difference analysis of sound propagation
Baumeister, K. J.
1984-01-01
A transient finite difference wave envelope formulation is presented for sound propagation, without steady flow. Before the finite difference equations are formulated, the governing wave equation is first transformed to a form whose solution tends not to oscillate along the propagation direction. This transformation reduces the required number of grid points by an order of magnitude. Physically, the transformed pressure represents the amplitude of the conventional sound wave. The derivation for the wave envelope transient wave equation and appropriate boundary conditions are presented as well as the difference equations and stability requirements. To illustrate the method, example solutions are presented for sound propagation in a straight hard wall duct and in a two dimensional straight soft wall duct. The numerical results are in good agreement with exact analytical results.
Self-propagating waves of crystallization in metallic glasses
Rogachev, A. S.; Vadchenko, S. G.; Aronin, A. S.; Rouvimov, S.; Nepapushev, A. A.; Kovalev, I. D.; Baras, F.; Politano, O.; Rogachev, S. A.; Mukasyan, A. S.
2017-08-01
Self-propagating thermal waves of the amorphous-crystalline transformation in Fe-based metallic glasses, obtained by melt spinning, were observed using a high-speed infrared camera and reported here. Some experimental results are also reported concerning oscillating waves in the CuTi glassy foils. The thermal characteristics and wave propagating velocities, as well as the microstructure and atomic structure transformations, were studied. A comparison of the results with exothermic reaction waves and explosive crystallization shows that the self-propagating waves in metallic glasses are slower and less violent than classical explosive crystallization in deposited films; thus, we suggest naming this phenomenon "soft explosive crystallization." The experimental data were confirmed by molecular dynamics simulation of the crystallization phenomenon.
Dynamics in Layer Models of Solid Flame Propagation
Aldushin, A. P.; Bayliss, A.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)
2000-01-01
Self-propagating high-temperature synthesis (SHS) is a process in which combustion waves, e.g., "solid flames", which are considered here, are employed to synthesize desired materials. Like many other systems, SHS is a pattern forming system. The problem of describing experimentally observed patterns and of predicting new, as yet unobserved, patterns continues to attract the attention of scientists and mathematicians due to the fundamental significance of the phenomena in combustion in particular, and in nonlinear science in general. Here, we analyze the dynamics of solid flame propagation in a 2D region by considering the region to be composed of parallel, identical layers aligned along the direction of propagation and having thermal contact. Each layer is then described by wave propagation in 1D, with the transverse Laplacian replaced by a term describing heat exchange between neighboring layers. This configuration is the simplest model of a 2D system because it accounts, in a simple way, for the principal feature of the problem, i.e., heat exchange between neighbors in the transverse direction. For simplicity, we describe the situation for two layers. Because the layers are identical, uniformly propagating waves in each layer must be identical, independent of the heat exchange rate alpha. When the Zeldovich number Z exceeds a critical value Z(sub c), which depends on alpha, uniformly propagating waves become unstable. The stability diagram for the two coupled layers reproduces that for the full 2D problem after appropriate identification of parameters in the two problems. Depending on parameter values, we determine three different steady-state dynamical behaviors (though additional behaviors are also expected to occur). The three behaviors are: (i) waves in each layer which pulsate in phase as they propagate, so that together they form a single pulsating propagating wave; (ii) the waves in each layer are no longer identical, and antiphase pulsations occur, with
Propagation of gravitational waves in the nonperturbative spinor vacuum
Energy Technology Data Exchange (ETDEWEB)
Dzhunushaliev, Vladimir [Al-Farabi Kazakh National University, Department of Theoretical and Nuclear Physics, Almaty (Kazakhstan); Al-Farabi Kazakh National University, Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Eurasian National University, Institute for Basic Research, Astana (Kazakhstan); Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, Bishkek (Kyrgyzstan); Folomeev, Vladimir [Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, Bishkek (Kyrgyzstan)
2014-09-15
The propagation of gravitational waves on the background of a nonperturbative vacuum of a spinor field is considered. It is shown that there are several distinctive features in comparison with the propagation of plane gravitational waves through empty space: there exists a fixed phase difference between the h{sub yy,zz} and h{sub yz} components of the wave; the phase and group velocities of gravitational waves are not equal to the velocity of light; the group velocity is always less than the velocity of light; under some conditions the gravitational waves are either damped or absent; for given frequency, there exist two waves with different wave vectors. We also discuss the possibility of an experimental verification of the obtained effects as a tool to investigate nonperturbative quantum field theories. (orig.)
Beam propagation of tidal internal waves over a submarine slope of the Mascarene Ridge
Morozov, E. G.; Nechvolodov, L. V.; Sabinin, K. D.
2009-12-01
The generation of internal tides over the Mascarene Ridge is studied on the basis of moored measurements and numerical modeling. The beam structure of the internal wave propagation over a submarine ridge is analyzed. The dependence of the beam propagation of the perturbations on the steepness of the slope, the depth of the ridge crest, and the stratification is studied.
Chu, Chunlei
2009-01-01
We analyze the dispersion properties and stability conditions of the high‐order convolutional finite difference operators and compare them with the conventional finite difference schemes. We observe that the convolutional finite difference method has better dispersion properties and becomes more efficient than the conventional finite difference method with the increasing order of accuracy. This makes the high‐order convolutional operator a good choice for anisotropic elastic wave simulations on rotated staggered grids since its enhanced dispersion properties can help to suppress the numerical dispersion error that is inherent in the rotated staggered grid structure and its efficiency can help us tackle 3D problems cost‐effectively.
Nguyen-Dinh, Maxime; Gainville, Olaf; Lardjane, Nicolas
2015-10-01
We present new results for the blast wave propagation from strong shock regime to the weak shock limit. For this purpose, we analyse the blast wave propagation using both Direct Numerical Simulation and an acoustic asymptotic model. This approach allows a full numerical study of a realistic pyrotechnic site taking into account for the main physical effects. We also compare simulation results with first measurements. This study is a part of the french ANR-Prolonge project (ANR-12-ASTR-0026).
Simulation of non-hydrostatic gravity wave propagation in the upper atmosphere
Directory of Open Access Journals (Sweden)
Y. Deng
2014-04-01
Full Text Available The high-frequency and small horizontal scale gravity waves may be reflected and ducted in non-hydrostatic simulations, but usually propagate vertically in hydrostatic models. To examine gravity wave propagation, a preliminary study has been conducted with a global ionosphere–thermosphere model (GITM, which is a non-hydrostatic general circulation model for the upper atmosphere. GITM has been run regionally with a horizontal resolution of 0.2° long × 0.2° lat to resolve the gravity wave with wavelength of 250 km. A cosine wave oscillation with amplitude of 30 m s−1 has been applied to the zonal wind at the low boundary, and both high-frequency and low-frequency waves have been tested. In the high-frequency case, the gravity wave stays below 200 km, which indicates that the wave is reflected or ducted in propagation. The results are consistent with the theoretical analysis from the dispersion relationship when the wavelength is larger than the cutoff wavelength for the non-hydrostatic situation. However, the low-frequency wave propagates to the high altitudes during the whole simulation period, and the amplitude increases with height. This study shows that the non-hydrostatic model successfully reproduces the high-frequency gravity wave dissipation.
Directory of Open Access Journals (Sweden)
Vojkan M. Radonjić
2011-01-01
Full Text Available Quality transmission of digital signals from a transmitting radio-relay device to a receiving one depends on the impact of environmental effects on the propagation of electromagnetic waves. In this paper some of the most important effects are explained and modeled, especially those characteristic for the frequency range within which the GRC 408E operates. The modeling resulted in the conclusions about the quality of transmission of digital signals in the GRC 408E radio-relay equipment. Propagation of electromagnetic waves A radio-relay link is achieved by direct electromagnetic waves, provided there is a line of sight between the transmitting and receiving antenna of a radio-relay device. Electromagnetic waves on the road are exposed to various environmental influences causing phenomena such as bending, reflection, refraction, absorption and multiple propagation. Due to these environmental effects, the quality of information transmission is not satisfactory and a radio-relay link is not reliable. The approach to the analysis of the quality of links in digital radiorelay devices is different from the one in analog radio-relay devices. Therefore, the quality is seen through errors in the received bit ( BER , the propagation conditions are taken into account, a reservation for the fading is determined by other means, etc.. Phenomena which accompany the propagation of electromagnetic waves in digital radio-relay links The propagation of direct EM waves is followed by the following phenomena: - attenuation due to propagation, - diffraction (changing table, - refraction (refraction, - reflection (refusing, - absorption (absorption and - multiple wave propagation. Each of these has a negative effect on the quality of the received signal at the receiving antenna of the radio-relay device. Attenuation due to propagation of electromagnetic waves The main parameter for evaluating the quality of radio-relay links is the level of the field at the reception
Propagation characteristics of ultrasonic guided waves in continuously welded rail
Yao, Wenqing; Sheng, Fuwei; Wei, Xiaoyuan; Zhang, Lei; Yang, Yuan
2017-07-01
Rail defects cause numerous railway accidents. Trains are derailed and serious consequences often occur. Compared to traditional bulk wave testing, ultrasonic guided waves (UGWs) can provide larger monitoring ranges and complete coverage of the waveguide cross-section. These advantages are of significant importance for the non-destructive testing (NDT) of the continuously welded rail, and the technique is therefore widely used in high-speed railways. UGWs in continuous welded rail (CWR) and their propagation characteristics have been discussed in this paper. Finite element methods (FEMs) were used to accomplish a vibration modal analysis, which is extended by a subsequent dispersion analysis. Wave structure features were illustrated by displacement profiles. It was concluded that guided waves have the ability to detect defects in the rail via choice of proper mode and frequency. Additionally, thermal conduction that is caused by temperature variation in the rail is added into modeling and simulation. The results indicated that unbalanced thermal distribution may lead to the attenuation of UGWs in the rail.
Wave Propagation: Odd is Better, but Three is Best
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 9; Issue 6. Wave Propagation: Odd is Better, but Three is Best - The Formal Solution of the Wave Equation. V Balakrishnan. General Article Volume 9 Issue 6 June 2004 pp 30-38 ...
Surface wave propagation in a fluid-saturated incompressible ...
Indian Academy of Sciences (India)
Keywords. Incompressible porous medium; volume fractions; frequency equation; phase velocity; wave number; attenuation coefﬁcient. ... and discussed. As a particular case, the propagation of Rayleigh type surface waves at the free surface of an incompressible porous half-space is also deduced and discussed.
Nonlinear propagation of short wavelength drift-Alfven waves
DEFF Research Database (Denmark)
Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens
1986-01-01
Making use of a kinetic ion and a hydrodynamic electron description together with the Maxwell equation, the authors derive a set of nonlinear equations which governs the dynamics of short wavelength ion drift-Alfven waves. It is shown that the nonlinear drift-Alfven waves can propagate as two...
Statistical Characterization of Electromagnetic Wave Propagation in Mine Environments
Yucel, Abdulkadir C.
2013-01-01
A computational framework for statistically characterizing electromagnetic (EM) wave propagation through mine tunnels and galleries is presented. The framework combines a multi-element probabilistic collocation method with a full-wave fast Fourier transform and fast multipole method accelerated surface integral equation-based EM simulator to statistically characterize fields from wireless transmitters in complex mine environments. 1536-1225 © 2013 IEEE.
Propagation of Rayleigh surface waves with small wavelengths in ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
MS received 23 November 2001. Abstract. This paper investigates Rayleigh waves, propagating on the surface of a visco-elastic solid under the linear theory of nonlocal elasticity. Dispersion relations are obtained. It is observed that the waves are dispersive in nature for small wavelengths. Numerical calculations and ...
Stress Wave Propagation Through Heterogeneous Media
National Research Council Canada - National Science Library
2002-01-01
.... In this work the influence of interface scattering on finite-amplitude shock waves was experimentally investigated by impacting flyer plates onto periodically layered polycarbonate/6061 aluminum...
Numerical Homogenization of Jointed Rock Masses Using Wave Propagation Simulation
Gasmi, Hatem; Hamdi, Essaïeb; Bouden Romdhane, Nejla
2014-07-01
Homogenization in fractured rock analyses is essentially based on the calculation of equivalent elastic parameters. In this paper, a new numerical homogenization method that was programmed by means of a MATLAB code, called HLA-Dissim, is presented. The developed approach simulates a discontinuity network of real rock masses based on the International Society of Rock Mechanics (ISRM) scanline field mapping methodology. Then, it evaluates a series of classic joint parameters to characterize density (RQD, specific length of discontinuities). A pulse wave, characterized by its amplitude, central frequency, and duration, is propagated from a source point to a receiver point of the simulated jointed rock mass using a complex recursive method for evaluating the transmission and reflection coefficient for each simulated discontinuity. The seismic parameters, such as delay, velocity, and attenuation, are then calculated. Finally, the equivalent medium model parameters of the rock mass are computed numerically while taking into account the natural discontinuity distribution. This methodology was applied to 17 bench fronts from six aggregate quarries located in Tunisia, Spain, Austria, and Sweden. It allowed characterizing the rock mass discontinuity network, the resulting seismic performance, and the equivalent medium stiffness. The relationship between the equivalent Young's modulus and rock discontinuity parameters was also analyzed. For these different bench fronts, the proposed numerical approach was also compared to several empirical formulas, based on RQD and fracture density values, published in previous research studies, showing its usefulness and efficiency in estimating rapidly the Young's modulus of equivalent medium for wave propagation analysis.
Lipkens, Bart
2002-01-01
In previous papers, we have shown that model experiments are successful in simulating the propagation of sonic booms through the atmospheric turbulent boundary layer. The results from the model experiment, pressure wave forms of spark-produced N waves and turbulence characteristics of the plane jet, are used to test various sonic boom models for propagation through turbulence. Both wave form distortion models and rise time prediction models are tested. Pierce's model [A. D. Pierce, "Statistical theory of atmospheric turbulence effects on sonic boom rise times," J. Acoust. Soc. Am. 49, 906-924 (1971)] based on the wave front folding mechanism at a caustic yields an accurate prediction for the rise time of the mean wave form after propagation through the turbulence.
Propagation of Electromagnetic Waves in Extremely Dense Media
Masood, Samina
2016-01-01
We study the propagation of electromagnetic (EM) waves in extremely dense exotic systems with very unique properties. These EM waves develop a longitudinal component due to its interaction with the medium. Renormalization scheme of QED is used to understand the propagation of EM waves in both longitudinal and transverse directions. The propagation of EM waves in a quantum statistically treatable medium affects the properties of the medium itself. The electric permittivity and the magnetic permeability of the medium are modified and influence the related behavior of the medium. All the electromagnetic properties of a medium become a function of temperature and chemical potential of the medium. We study in detail the modifications of electric permittivity and magnetic permeability and other related properties of a medium in the superdense stellar objects.
Wakefield and wave propagation at non-linear dispersion
Smirnov, A V
2002-01-01
Synchronous wakefield excitation and wave propagation along a dispersive slow-wave structure is considered. An explicit form for wakefields is obtained for a single bunch in the second and third approximations of dispersion while taking into account the effect of substantial group velocity with respect to charge velocity. Generalized differential equations describing diffused fields induced by a beam current or generated by an external source are derived. Field excitation and propagation near the cut-off is considered including trapped modes in the stopband. This theory can be applied to the fields induced by single bunch and bunch train in Standing Wave and Traveling Wave devices operating near pi-mode, self-consistent beam break-up simulations, RF-generation, pulse propagation, and breakdown study in waveguides as well as some of new methods of acceleration in a dispersive medium.
Plasma wave propagation with a plasma density gradient
Cho, Guangsup; Choi, Eun-Ha; Uhm, Han Sup
2011-03-01
Plasma waves with the plasma diffusion velocity un due to a plasma density gradient are described in a positive column plasma. The ion wave is generated by the perturbation of the operating frequency 106 s-1 and it propagates with the group velocity ug˜cs2/un˜(105-106) m/s, where cs is the acoustic velocity in a fine tube fluorescent lamp, while the electron wave cannot be generated with a turbulence of low frequency less than the electron oscillation frequency ωpe. The propagation of the lighting signal observed in long tube fluorescent lamps is well understood with the propagation of ion waves occurring along the plasma density gradient.
Zhebel, E.; Minisini, S.; Kononov, A.; Mulder, W.A.
2013-01-01
With the rapid developments in parallel compute architectures, algorithms for seismic modeling and imaging need to be reconsidered in terms of parallelization. The aim of this paper is to compare scalability of seismic modeling algorithms: finite differences, continuous mass-lumped finite elements
ICRF antenna coupling and wave propagation in a tokamak plasma
Energy Technology Data Exchange (ETDEWEB)
Greene, G.J.
1984-01-01
A variety of experiments are reported pertaining to the excitation, propagation, and damping of waves in the ion cyclotron range of frequencies (ICRF) in the Caltech Research Tokamak. Complex impedance studies on five different RF antennas addressed the nature of the anomalous density-dependent background loading observed previously in several laboratories. A model proposed successfully explained many of the observed impedance characteristics solely in terms of particle collection and rectification through the plasma sheath surrounding the antenna electrode. The toroidal eigenmodes were studied in detail with magnetic field probes. A surprising result was that all of the antennas, both magnetic and electric in nature, coupled to the eigenmodes with comparable efficiency with respect to the antenna excitation current. Wave damping was investigated and found to be considerably higher than predicted by a variety of physical mechanisms. A numerical model of the wave equations permitting an arbitrary radial density profile was developed, and a possible mechanism for enhanced cyclotron damping due to density perturbations was proposed.
Real solution of monochromatic wave propagation in ...
Indian Academy of Sciences (India)
concept of the signal structure propagating in inhomogeneous media and the method of inhomogeneous basic modes ... agating in an isotropic, inhomogeneous, linear media parallel to the gradient of the one- dimensional ..... neous half-spaces and in every place where Z¼ has local extremum the derivatives. dZ¼/dx = 0.
Propagation of waves in shear flows
Fabrikant, A L
1998-01-01
The state of the art in a theory of oscillatory and wave phenomena in hydrodynamical flows is presented in this book. A unified approach is used for waves of different physical origins. A characteristic feature of this approach is that hydrodynamical phenomena are considered in terms of physics; that is, the complement of the conventionally employed formal mathematical approach. Some physical concepts such as wave energy and momentum in a moving fluid are analysed, taking into account induced mean flow. The physical mechanisms responsible for hydrodynamic instability of shear flows are conside
Surface wave propagation effects on buried segmented pipelines
Directory of Open Access Journals (Sweden)
Peixin Shi
2015-08-01
Full Text Available This paper deals with surface wave propagation (WP effects on buried segmented pipelines. Both simplified analytical model and finite element (FE model are developed for estimating the axial joint pullout movement of jointed concrete cylinder pipelines (JCCPs of which the joints have a brittle tensile failure mode under the surface WP effects. The models account for the effects of peak ground velocity (PGV, WP velocity, predominant period of seismic excitation, shear transfer between soil and pipelines, axial stiffness of pipelines, joint characteristics, and cracking strain of concrete mortar. FE simulation of the JCCP interaction with surface waves recorded during the 1985 Michoacan earthquake results in joint pullout movement, which is consistent with the field observations. The models are expanded to estimate the joint axial pullout movement of cast iron (CI pipelines of which the joints have a ductile tensile failure mode. Simplified analytical equation and FE model are developed for estimating the joint pullout movement of CI pipelines. The joint pullout movement of the CI pipelines is mainly affected by the variability of the joint tensile capacity and accumulates at local weak joints in the pipeline.
Nonlinear multi-frequency electromagnetic wave propagation phenomena
Valovik, Dmitry V.
2017-11-01
A generalisation of the concept of monochromatic electromagnetic waves guided by layered waveguide structures filled with non-linear medium is introduced. This generalisation leads to guided waves of a novel type: a non-linear multi-frequency guided wave. The existence of such waves, in particular guide structures, is proven using the perturbation method. Numerical experiments are presented for non-linear 1- and 2-frequency guided waves in plane and cylindrical (with a circular cross-section) waveguides. Numerically, a novel non-linear effect is found for particular cases of non-linear multi-frequency guided waves. The suggested generalisation gives not only a unified approach to treat various electromagnetic wave propagation problems but also paves the way to study non-linear interactions of guided waves.
On Boussinesq's paradigm in nonlinear wave propagation
Christov, Christo I.; Maugin, Gérard A.; Porubov, Alexey V.
2007-09-01
Boussinesq's original derivation of his celebrated equation for surface waves on a fluid layer opened up new horizons that were to yield the concept of the soliton. The present contribution concerns the set of Boussinesq-like equations under the general title of 'Boussinesq's paradigm'. These are true bi-directional wave equations occurring in many physical instances and sharing analogous properties. The emphasis is placed: (i) on generalized Boussinesq systems that involve higher-order linear dispersion through either additional space derivatives or additional wave operators (so-called double-dispersion equations); and (ii) on the 'mechanics' of the most representative localized nonlinear wave solutions. Dissipative cases and two-dimensional generalizations are also considered. To cite this article: C.I. Christov et al., C. R. Mecanique 335 (2007).
Nonlinear ultrasound wave propagation in thermoviscous fluids
DEFF Research Database (Denmark)
Sørensen, Mads Peter
Traditional ultrasound theory is based on linear theory, however, for strongly focused sound beams, the pressure levels are sufficiently high to generate nonlinear waves. In thermoviscous fluids nonlinearity arises as a result of a nonlinear equation of state together with nonlinear advection...... is interpreted as a shock wave formation, similar in nature to those of the simple Burgers equation. The results are relevant for medical ultrasound imaging....
Valier-Brasier, Tony; Conoir, Jean-Marc
2017-08-01
The propagation of coherent transverse waves through a homogeneous elastic medium containing a set of spherical dense inclusions is an interesting topic. In such a material, in addition to the coherent longitudinal wave, two coherent transverse waves can propagate. The modeling used is based on the multiple scattering theory, which requires the scattering coefficients of the single scattering problem. These coefficients are calculated for moving rigid particles, leading to approximations of the two subwavelength dipolar resonances, one associated to a translational motion and the other to a rotational motion. Numerical simulations are carried out in order to compare the effective wavenumbers of the coherent elastic waves through the analysis of their phase velocity and attenuation. This comparison is performed for elastic and moving rigid spheres. It is shown that both dipolar resonances may have a great influence on the propagation of coherent transverse waves.
Wave propagation in fiber composite laminates, part 2
Daniel, I. M.; Liber, T.
1976-01-01
An experimental investigation was conducted to determine the wave propagation characteristics, transient strains and residual properties in unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicone rubber projectiles at velocities up to 250 MS-1. The predominant wave is flexural, propagating at different velocities in different directions. In general, measured wave velocities were higher than theoretically predicted values. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. The dynamics of impact were also studied with high speed photography.
Wave propagation in metamaterials and effective parameters retrieving
DEFF Research Database (Denmark)
Andryieuski, Andrei; Ha, S.; Sukhorukov, A.
2011-01-01
as handsome for implementation. We set a goal to develop a method which is unambiguous but at the same time simple and straightforward. We assume that this can be done by observing the wave propagation inside a metamaterial slab thick enough to avoid transient effects. First, we formulated a retrieval method...... with a plane wave incident from vacuum. Then we determine the effective refractive index from the propagation constant of the dominating (fundamental) Bloch mode. The Bloch and wave impedances are determined by definition as the proportionality coefficient between the electric and magnetic fields...... complex wave effective parameters. Extending the method further we developed the approach to determine both wave and material effective parameters through the Bloch-mode analysis [3]. The idea is to perform the Bloch mode expansion [4] of the field inside the metamaterial slab when it is illuminated...
Discrete Element Simulation of Elastoplastic Shock Wave Propagation in Spherical Particles
Directory of Open Access Journals (Sweden)
M. Shoaib
2011-01-01
Full Text Available Elastoplastic shock wave propagation in a one-dimensional assembly of spherical metal particles is presented by extending well-established quasistatic compaction models. The compaction process is modeled by a discrete element method while using elastic and plastic loading, elastic unloading, and adhesion at contacts with typical dynamic loading parameters. Of particular interest is to study the development of the elastoplastic shock wave, its propagation, and reflection during entire loading process. Simulation results yield information on contact behavior, velocity, and deformation of particles during dynamic loading. Effects of shock wave propagation on loading parameters are also discussed. The elastoplastic shock propagation in granular material has many practical applications including the high-velocity compaction of particulate material.
Carcione, José M
2014-01-01
Authored by the internationally renowned José M. Carcione, Wave Fields in Real Media: Wave Propagation in Anisotropic, Anelastic, Porous and Electromagnetic Media examines the differences between an ideal and a real description of wave propagation, starting with the introduction of relevant stress-strain relations. The combination of this relation and the equations of momentum conservation lead to the equation of motion. The differential formulation is written in terms of memory variables, and Biot's theory is used to describe wave propagation in porous media. For each rheology, a plane-wave analysis is performed in order to understand the physics of wave propagation. This book contains a review of the main direct numerical methods for solving the equation of motion in the time and space domains. The emphasis is on geophysical applications for seismic exploration, but researchers in the fields of earthquake seismology, rock acoustics, and material science - including many branches of acoustics of fluids and ...
Special Course on Acoustic Wave Propagation
1979-08-01
silence a cotia- tique at balistique. DepuiS la econde guerre mondiale de tres nombreux travaux Sur la propagation acoustique dans les fluides et das...sous-marins [83, -le second , li4 Z l’acoustiqua des canons et des projectiles [9]. Ce dernier ouvrage (rdfdrence [9]) nous intdreaaa au plus haut chef...anplitude motion of a Stokesian fluid about an equilibrium rest state. Second , ,he fiuid motion, through the coefficients involving the velocity vi
Achieving directional propagation of elastic waves via topology optimization.
He, Jingjie; Kang, Zhan
2018-01-01
This paper presents a study on topology optimization of novel material microstructural configurations to achieve directional elastic wave propagation through maximization of partial band gaps. A waveguide incorporating a periodic-microstructure material may exhibit different propagation properties for the plane elastic waves incident from different inlets. A topology optimization problem is formulated to enhance such a property with a gradient-based mathematical programming algorithm. For alleviating the issue of local optimum traps, the random morphology description functions (RMDFs) are introduced to generate random initial designs for the optimization process. The optimized designs finally converge to the orderly material distribution and numerical validation shows improved directional propagation property as expected. The utilization of linear two-dimension phononic crystal with efficient partial band gap is suitable for directional propagation with a broad frequency range. Copyright © 2017 Elsevier B.V. All rights reserved.
Detecting electromagnetic cloaks using backward-propagating waves
Salem, Mohamed
2011-08-01
A novel approach for detecting transformation-optics invisibility cloaks is proposed. The detection method takes advantage of the unusual backward-propagation characteristics of recently reported beams and pulses to induce electromagnetic scattering from the cloak. Even though waves with backward-propagating energy flux cannot penetrate the cloaking shell and interact with the cloaked objects (i.e., they do not make the cloaked object visible), they provide a mechanism for detecting the presence of cloaks. © 2011 IEEE.
Prediction of propagated wave profiles based on point measurement
Directory of Open Access Journals (Sweden)
Sang-Beom Lee
2014-03-01
Full Text Available This study presents the prediction of propagated wave profiles using the wave information at a fixed point. The fixed points can be fixed in either space or time. Wave information based on the linear wave theory can be expressed by Fredholm integral equation of the first kinds. The discretized matrix equation is usually an ill-conditioned system. Tikhonov regularization was applied to the ill-conditioned system to overcome instability of the system. The regularization parameter is calculated by using the L-curve method. The numerical results are compared with the experimental results. The analysis of the numerical computation shows that the Tikhonov regularization method is useful.
Topology Optimization for Wave Propagation Problems with Experimental Validation
DEFF Research Database (Denmark)
Christiansen, Rasmus Ellebæk
from acoustics, however problems for TE or TM polarized electromagnetic waves and shear waves in solids in two dimensions may be treated using the proposed methods with minor modifications. A brief introduction to wave problems and to density-based topology optimizationis included, as is a brief......This Thesis treats the development and experimental validation of density-based topology optimization methods for wave propagation problems. Problems in the frequency regime where design dimensions are between approximately one fourth and ten wavelengths are considered. All examples treat problems...
Sjoberg, Daniel
2008-01-01
This paper presents an overview of how circuit models can be used for analysing wave propagation in stratified structures. Relatively complex structures can be analysed using models which are accessible to undergraduate students. Homogeneous slabs are modelled as transmission lines, and thin sheets between the slabs are modelled as lumped…
Huba, J. D.; Rowland, H. L.
1993-01-01
The propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere is presented in a theoretical and numerical analysis. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as that produced by lightning. Specifically addressed is wave propagation in the altitude range z = 130-160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector: 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. Parameterizations of the wave intensities, peak electron density, and Poynting flux as a function of magnetic field are presented. The waves are found to propagate most easily in conditions of low electron density and high magnetic field. The results of the model are consistent with observational data.
Electromagnetic wave propagation through a slab of a dispersive medium
Ismail, Mohamed
2016-01-01
A method is proposed for the analysis of the propagation of electromagnetic waves through a homogeneous slab of a medium with Drude-Lorentz dispersion behavior, and excited by a causal sinusoidal source. An expression of the time dependent field, free from branch-cuts in the plane of complex frequencies, is established. This method provides the complete temporal response in both the steady-state and transient regimes in terms of discrete poles contributions. The Sommerfeld and Brillouin precursors are retrieved and the corresponding set of poles are identified. In addition, the contribution in the transient field of the resonance frequency in the Drude-Lorentz model is exhybited, and the effect of reflections resulting from the refractive index mismatch at the interfaces of the slab are analyzed.
Vibration and wave propagation characteristics of multisegmented elastic beams
Nayfeh, Adnan H.; Hawwa, Muhammad A.
1990-01-01
Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.
A functional renormalization method for wave propagation in random media
Lamagna, Federico; Calzetta, Esteban
2017-08-01
We develop the exact renormalization group approach as a way to evaluate the effective speed of the propagation of a scalar wave in a medium with random inhomogeneities. We use the Martin-Siggia-Rose formalism to translate the problem into a non equilibrium field theory one, and then consider a sequence of models with a progressively lower infrared cutoff; in the limit where the cutoff is removed we recover the problem of interest. As a test of the formalism, we compute the effective dielectric constant of an homogeneous medium interspersed with randomly located, interpenetrating bubbles. A simple approximation to the renormalization group equations turns out to be equivalent to a self-consistent two-loops evaluation of the effective dielectric constant.
Ansari, M. H.; Attarzadeh, M. A.; Nouh, M.; Karami, M. Amin
2018-01-01
In this paper, a physical platform is proposed to change the properties of phononic crystals in space and time in order to achieve nonreciprocal wave transmission. The utilization of magnetoelastic materials in elastic phononic systems is studied. Material properties of magnetoelastic materials change significantly with an external magnetic field. This property is used to design systems with a desired wave propagation pattern. The properties of the magnetoelastic medium are changed in a traveling wave pattern, which changes in both space and time. A phononic crystal with such a modulation exhibits one-way wave propagation behavior. An extended transfer matrix method (TMM) is developed to model a system with time varying properties. The stop band and the pass band of a reciprocal and a nonreciprocal bar are found using this method. The TMM is used to find the transfer function of a magnetoelastic bar. The obtained results match those obtained via the theoretical Floquet–Bloch approach and numerical simulations. It is shown that the stop band in the transfer function of a system with temporal varying property for the forward wave propagation is different from the same in the backward wave propagation. The proposed configuration enables the physical realization of a class of smart structures that incorporates nonreciprocal wave propagation.
Mézière, Fabien; Muller, Marie; Dobigny, Blandine; Bossy, Emmanuel; Derode, Arnaud
2013-02-01
Ultrasound propagation in clusters of elliptic (two-dimensional) or ellipsoidal (three-dimensional) scatterers randomly distributed in a fluid is investigated numerically. The essential motivation for the present work is to gain a better understanding of ultrasound propagation in trabecular bone. Bone microstructure exhibits structural anisotropy and multiple wave scattering. Some phenomena remain partially unexplained, such as the propagation of two longitudinal waves. The objective of this study was to shed more light on the occurrence of these two waves, using finite-difference simulations on a model medium simpler than bone. Slabs of anisotropic, scattering media were randomly generated. The coherent wave was obtained through spatial and ensemble-averaging of the transmitted wavefields. When varying relevant medium parameters, four of them appeared to play a significant role for the observation of two waves: (i) the solid fraction, (ii) the direction of propagation relatively to the scatterers orientation, (iii) the ability of scatterers to support shear waves, and (iv) a continuity of the solid matrix along the propagation. These observations are consistent with the hypothesis that fast waves are guided by the locally plate/bar-like solid matrix. If confirmed, this interpretation could significantly help developing approaches for a better understanding of trabecular bone micro-architecture using ultrasound.
APPARENT CROSS-FIELD SUPERSLOW PROPAGATION OF MAGNETOHYDRODYNAMIC WAVES IN SOLAR PLASMAS
Energy Technology Data Exchange (ETDEWEB)
Kaneko, T.; Yokoyama, T. [Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan); Goossens, M.; Doorsselaere, T. Van [Centre for Mathematical Plasma Astrophysics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, Bus 2400, B-3001 Herverlee (Belgium); Soler, R.; Terradas, J. [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Wright, A. N., E-mail: kaneko@eps.s.u-tokyo.ac.jp [School of Mathematics and Statistics, University of St Andrews, St Andrews, KY16 9SS (United Kingdom)
2015-10-20
In this paper we show that the phase-mixing of continuum Alfvén waves and/or continuum slow waves in the magnetic structures of the solar atmosphere as, e.g., coronal arcades, can create the illusion of wave propagation across the magnetic field. This phenomenon could be erroneously interpreted as fast magnetosonic waves. The cross-field propagation due to the phase-mixing of continuum waves is apparent because there is no real propagation of energy across the magnetic surfaces. We investigate the continuous Alfvén and slow spectra in two-dimensional (2D) Cartesian equilibrium models with a purely poloidal magnetic field. We show that apparent superslow propagation across the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén waves and continuum slow waves that naturally live on those structures and phase-mix as time evolves. The apparent cross-field phase velocity is related to the spatial variation of the local Alfvén/slow frequency across the magnetic surfaces and is slower than the Alfvén/sound velocities for typical coronal conditions. Understanding the nature of the apparent cross-field propagation is important for the correct analysis of numerical simulations and the correct interpretation of observations.
In Situ Observations of Seismic Wave Propagation
Hudson, Kenneth Stewart
Instrumented geotechnical field sites are designed to capture the infrequent but critically important in situ case histories of ground response, deformation, and liquefaction during significant earthquakes that generate high intensity ground shaking and large strains. The University of California at Santa Barbara has been monitoring densely instrumented geotechnical array field sites for almost three decades, with continuous recording now for more than a decade. When seismic waves travel into soil with sufficiently large ground motions, the soil behaves nonlinearly meaning the shear modulus of the material decreases from the linear value observed during weak ground motions. The degraded shear modulus can continue to affect a site for a period of time by changing the soil response during smaller ground motions after the large event. Decreased shear modulus is inferred when a decrease of shear wave velocity between two sensors in a vertical downhole array is observed. This velocity is calculated by measuring the difference in shear wave arrival times between the sensors using normalized cross correlation. The trend of decreasing shear wave velocity with increasing peak ground acceleration is observed at multiple geotechnical array field sites. The length of time the decreased velocity remains following stronger shaking is analyzed using more than 450 events over more than a decade at the Wildlife Liquefaction Array (WLA). Using both monthly and yearly velocity averages between sensors, there is evidence that suggests the shear wave velocity remains low over a period of months following larger significant shaking events at the site. In addition, at WLA there is evidence that the decrease in shear wave velocity can be detected at ground motion levels as low as 20 cm/s2. Additionally at the Garner Valley Downhole Array, a permanent cross-hole experiment is used to measure velocity changes in the soil with changing water table height. An underground hammer source swings
Analytical Time-Domain Solution of Plane Wave Propagation Across a Viscoelastic Rock Joint
Zou, Yang; Li, Jianchun; Laloui, Lyesse; Zhao, Jian
2017-10-01
The effects of viscoelastic filled rock joints on wave propagation are of great significance in rock engineering. The solutions in time domain for plane longitudinal ( P-) and transverse ( S-) waves propagation across a viscoelastic rock joint are derived based on Maxwell and Kelvin models which are, respectively, applied to describe the viscoelastic deformational behaviour of the rock joint and incorporated into the displacement discontinuity model (DDM). The proposed solutions are verified by comparing with the previous studies on harmonic waves, which are simulated by sinusoidal incident P- and S-waves. Comparison between the predicted transmitted waves and the experimental data for P-wave propagation across a joint filled with clay is conducted. The Maxwell is found to be more appropriate to describe the filled joint. The parametric studies show that wave propagation is affected by many factors, such as the stiffness and the viscosity of joints, the incident angle and the duration of incident waves. Furthermore, the dependences of the transmission and reflection coefficients on the specific joint stiffness and viscosity are different for the joints with Maxwell and Kelvin behaviours. The alternation of the reflected and transmitted waveforms is discussed, and the application scope of this study is demonstrated by an illustration of the effects of the joint thickness. The solutions are also extended for multiple parallel joints with the virtual wave source method and the time-domain recursive method. For an incident wave with arbitrary waveform, it is convenient to adopt the present approach to directly calculate wave propagation across a viscoelastic rock joint without additional mathematical methods such as the Fourier and inverse Fourier transforms.
High frequency guided wave propagation in monocrystalline silicon wafers
Pizzolato, Marco; Masserey, Bernard; Robyr, Jean-Luc; Fromme, Paul
2017-04-01
Monocrystalline silicon wafers are widely used in the photovoltaic industry for solar panels with high conversion efficiency. The cutting process can introduce micro-cracks in the thin wafers and lead to varying thickness. High frequency guided ultrasonic waves are considered for the structural monitoring of the wafers. The anisotropy of the monocrystalline silicon leads to variations of the wave characteristics, depending on the propagation direction relative to the crystal orientation. Full three-dimensional Finite Element simulations of the guided wave propagation were conducted to visualize and quantify these effects for a line source. The phase velocity (slowness) and skew angle of the two fundamental Lamb wave modes (first anti-symmetric mode A0 and first symmetric mode S0) for varying propagation directions relative to the crystal orientation were measured experimentally. Selective mode excitation was achieved using a contact piezoelectric transducer with a custom-made wedge and holder to achieve a controlled contact pressure. The out-of-plane component of the guided wave propagation was measured using a noncontact laser interferometer. Good agreement was found with the simulation results and theoretical predictions based on nominal material properties of the silicon wafer.
Wave propagation in photonic crystals and metamaterials: Surface waves, nonlinearity and chirality
Energy Technology Data Exchange (ETDEWEB)
Wang, Bingnan [Iowa State Univ., Ames, IA (United States)
2009-01-01
Photonic crystals and metamaterials, both composed of artificial structures, are two interesting areas in electromagnetism and optics. New phenomena in photonic crystals and metamaterials are being discovered, including some not found in natural materials. This thesis presents my research work in the two areas. Photonic crystals are periodically arranged artificial structures, mostly made from dielectric materials, with period on the same order of the wavelength of the working electromagnetic wave. The wave propagation in photonic crystals is determined by the Bragg scattering of the periodic structure. Photonic band-gaps can be present for a properly designed photonic crystal. Electromagnetic waves with frequency within the range of the band-gap are suppressed from propagating in the photonic crystal. With surface defects, a photonic crystal could support surface modes that are localized on the surface of the crystal, with mode frequencies within the band-gap. With line defects, a photonic crystal could allow the propagation of electromagnetic waves along the channels. The study of surface modes and waveguiding properties of a 2D photonic crystal will be presented in Chapter 1. Metamaterials are generally composed of artificial structures with sizes one order smaller than the wavelength and can be approximated as effective media. Effective macroscopic parameters such as electric permittivity ϵ, magnetic permeability μ are used to characterize the wave propagation in metamaterials. The fundamental structures of the metamaterials affect strongly their macroscopic properties. By designing the fundamental structures of the metamaterials, the effective parameters can be tuned and different electromagnetic properties can be achieved. One important aspect of metamaterial research is to get artificial magnetism. Metallic split-ring resonators (SRRs) and variants are widely used to build magnetic metamaterials with effective μ < 1 or even μ < 0. Varactor based
Estimation of surface wave propagation in mouse cornea
Manapuram, Ravi Kiran; Menodiado, Floredes M.; Truong, Phiet; Aglyamov, Salavat; Emelianov, Stanislav; Twa, Michael; Larin, Kirill V.
2012-03-01
In this paper, we report the use of phase stabilized swept source optical coherence tomography (PhSSSOCT) for the measurement of surface mechanical wave propagation in ocular tissue in-situ. Mechanical wave propagation was measured in the mouse cornea for both young and older mice to assess tissue properties as a function of age. The measurements were performed by inducing low amplitude (cornea and 0.37 μm/mm for 9 month old mice (and presumably of different stiffness for 1 month and 9 months old). Results also suggest that PhS-SSOCT is capable of measuring the changes in the wave amplitude as small as 0.03 μm (limited by the phase stability of the system) that allowed the measurements with a very low amplitude excitation wave, thus making the method minimally invasive. Therefore, this method could potentially be used to assess tissue biomechanical properties and to reconstruct stiffness maps of the cornea.
Parallel Irregular Software for Wave Propagation Simulation
Guidec, Frédéric; Calégari, Patrice; Kuonen, Pierre
1998-01-01
Extended version of a paper presented at the High Performance Computing and Networking Europe conference (HPCN, Vienna, Austria, April 1997); International audience; The objective of the European project STORMS (Software Tools for the Optimization of Resources in Mobile Systems) is to develop a software tool to be used for the design and the planning of the future Universal Mobile Telecommunication System (UMTS). In this context the ParFlow method permits the simulation of outdoor radio wave ...
Electromagnetic wave propagation in alternating material-metamaterial layered structures
Carrera-Escobedo, V H
2016-01-01
Using the transfer matrix method, we examine the parametric behavior of the transmittance of an electromagnetic plane wave propagating in the lossless regime through a periodic multilayered system as a function of the frequency and angle of incidence of the electromagnetic wave for the case in which the periodic structure comprises alternating material-metamaterial layers. A specific example of high transmittance at any angle of incidence in the visible region of the spectrum is identified
Unified interpretation of superluminal behaviors in wave propagation
Energy Technology Data Exchange (ETDEWEB)
Ranfagni, A. [Istituto di Fisica Applicata ' Nello Carrara' , Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze (Italy); Viliani, G. [Dipartimento di Fisica, Universita di Trento, 38050 Povo, Trento (Italy); Ranfagni, C. [Facolta di Scienze Matematiche Fisiche e Naturali, Corso di Laurea in Fisica dell' Universita di Firenze, Firenze (Italy); Mignani, R. [Dipartimento di Fisica ' Edoardo Amaldi' , Universita degli Studi di Roma ' Roma Tre' , Via della Vasca Navale 84, 00146 Roma (Italy); Ruggeri, R. [Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Sezione di Firenze, Firenze (Italy)], E-mail: rocco.ruggeri@isc.cnr.it; Ricci, A.M. [Istituto per le Telecomunicazioni e l' Elettronica della Marina Militare ' Giancarlo Vallauri' (Mariteleradar), Viale Italia 72, 57100 Livorno (Italy)
2007-10-29
By using two approaches, we demonstrate that superluminal behaviors in wave propagation can be attributed to mechanisms acting in the near-field limit. One approach is based on complex waves, while the other relies on a path-integral treatment of stochastic motion. The results of the two approaches are comparable, and suitable for interpreting the data obtained in microwave experiments; these experiments, over a wide range of distances, show a time advance which, in any case, is limited to nanoseconds.
Transient Topology Optimization of Two-Dimensional Elastic Wave Propagation
DEFF Research Database (Denmark)
Matzen, René; Jensen, Jakob Søndergaard; Sigmund, Ole
2008-01-01
A tapering device coupling two monomodal waveguides is designed with the topology optimization method based on transient wave propagation. The gradient-based optimization technique is applied to predict the material distribution in the tapering area such that the squared output displacement (a...... measure for transmission) in the taper is maximized. High transmission in a large frequency range is gained by use of incident wave packets. To avoid nondiscrete properties in the design domain a density ﬁltering technique is employed....
Solitary wave propagation in surface stabilized ferroelectric liquid crystal cells
VIJ, JAGDISH; SONG, JANG-KUN
2008-01-01
PUBLISHED Solitary wave propagation in surface stabilized ferroelectric liquid crystal cells controlled by surface anchoring of the alignment layers is investigated for different conditions of alignment on the two opposite surfaces. We show that the critical field Ec, where the speed of the solitary wave becomes zero, is finite for asymmetric alignment on two surfaces. We also show that the polar anchoring energy difference (Deltawp) between the alignment layers can be calculated by measur...
Radio-wave propagation for space communications systems
Ippolito, L. J.
1981-01-01
The most recent information on the effects of Earth's atmosphere on space communications systems is reviewed. The design and reliable operation of satellite systems that provide the many applications in space which rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence causes uncontrolled variations in the signal characteristics. These variations can result in a reduction of the quality and reliability of the transmitted information. Models and other techniques are used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz have been reviewed. Particular emphasis has been placed on the effects of precipitation on the Earth/space path, including rain attenuation, and ice particle depolarization. Other factors are sky noise, antenna gain degradation, scintillations, and bandwidth coherence. Each of the various propagation factors has an effect on design criteria for communications systems. These criteria include link reliability, power margins, noise contribution, modulation and polarization factors, channel cross talk, error rate, and bandwidth limitations.
Gusev, Vitalyi; Aleshin, Vladislav
2002-12-01
Nonlinear wave propagation in materials, where distribution function of mesoscopic mechanical elements has very different scales of variation along and normally to diagonal of Preisach-Mayergoyz space, is analyzed. An evolution equation for strain wave, which takes into account localization of element distribution near the diagonal and its slow variation along the diagonal, is proposed. The evolution equation provides opportunity to model propagation of elastic waves with strain amplitudes comparable to and even higher than characteristic scale of element localization near Preisach-Mayergoyz space diagonal. Analytical solutions of evolution equation predict nonmonotonous dependence of wave absorption on its amplitude in a particular regime. The regime of self-induced absorption for small-amplitude nonlinear waves is followed by the regime of self-induced transparency for high-amplitude waves. The developed theory might be useful in seismology, in high-pressure nonlinear acoustics, and in nonlinear acoustic diagnostics of damaged and fatigued materials.
Mathematical Modelling of Tsunami Propagation | Eze | Journal of ...
African Journals Online (AJOL)
The generation of tsunamis with the help of a simple dislocation model of an earthquake and their propagation in the basin are discussed. In this study, we examined the formation of a tsunami wave from an initial sea surface displacement similar to those obtained from earthquakes that have generated tsunami waves and ...
Propagation Characteristics of Oblique Incident Terahertz Wave in Nonuniform Dusty Plasma
Directory of Open Access Journals (Sweden)
Yunhua Cao
2016-01-01
Full Text Available Propagation characteristics of oblique incident terahertz wave from the nonuniform dusty plasma are studied using the propagation matrix method. Assuming that the electron density distribution of dusty plasma is parabolic model, variations of power reflection, transmission, and absorption coefficients with frequencies of the incident wave are calculated as the wave illuminates the nonuniform dusty plasma from different angles. The effects of incident angles, number density, and radius of the dust particles on propagation characteristics are discussed in detail. Numerical results show that the number density and radius of the dust particles have very little influences on reflection and transmission coefficients and have obvious effects on absorption coefficients. The terahertz wave has good penetrability in dusty plasma.
Effect of fracture compliance on wave propagation within a fluid-filled fracture.
Nakagawa, Seiji; Korneev, Valeri A
2014-06-01
Open and partially closed fractures can trap seismic waves. Waves propagating primarily within fluid in a fracture are sometimes called Krauklis waves, which are strongly dispersive at low frequencies. The behavior of Krauklis waves has previously been examined for an open, fluid-filled channel (fracture), but the impact of finite fracture compliance resulting from contacting asperities and porous fillings in the fracture (e.g., debris, proppants) has not been fully investigated. In this paper, a dispersion equation is derived for Krauklis wave propagation in a fracture with finite fracture compliance, using a modified linear-slip-interface model (seismic displacement-discontinuity model). The resulting equation is formally identical to the dispersion equation for the symmetric fracture interface wave, another type of guided wave along a fracture. The low-frequency solutions of the newly derived dispersion equations are in good agreement with the exact solutions available for an open fracture. The primary effect of finite fracture compliance on Krauklis wave propagation is to increase wave velocity and attenuation at low frequencies. These effects can be used to monitor changes in the mechanical properties of a fracture.
Plane-Wave Propagation in Extreme Magnetoelectric (EME) Media
Lindell, I V; Favaro, A
2016-01-01
The extreme magnetoelectric medium (EME medium) is defined in terms of two medium dyadics, $\\alpha$, producing electric polarization by the magnetic field and $\\beta$, producing magnetic polarization by the electric field. Plane-wave propagation of time-harmonic fields of fixed finite frequency in the EME medium is studied. It is shown that (if $\\omega\
Shock wave propagation in soda lime glass using optical ...
Indian Academy of Sciences (India)
Propagation of shock waves in soda lime glass, which is a transparent material, has been studied using the optical shadowgraphy technique. The time-resolved shock velocity information has been obtained (1) in single shot, using the chirped pulse shadowgraphy technique, with a temporal resolution of tens of picoseconds ...
Shock wave propagation in soda lime glass using optical ...
Indian Academy of Sciences (India)
2016-06-16
Jun 16, 2016 ... ties, they create a near discontinuity in material prop- erties like pressure, temperature, and density across the shock front. These material properties, before and after the shock wave propagation, are related to each other through the well-known Rankine–Hugoniot equations. [10]. ρ0Us = ρ1(Us − Up),. (1).
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...
Analysis of flexural wave propagation in poroelastic composite ...
African Journals Online (AJOL)
DR OKE
and Tajuddin (2010) studied axially symmetric vibrations of composite poroelastic cylinders. Sharma and Sharma (2010) analyzed free vibration in a homogeneous transradially isotropic thermoelastic sphere. Flexural wave propagation in coated poroelastic cylinders is presented by Ahmed shah (2011). Tajuddin (2011) et ...
Electromagnetic wave propagation in rain and polarization effects
OKAMURA, Sogo; OGUCHI, Tomohiro
2010-01-01
This paper summarizes our study on microwave and millimeter-wave propagation in rain with special emphasis on the effects of polarization. Starting from a recount of our past findings, we will discuss developments with these and how they are connected with subsequent research. PMID:20551593
Oblique Propagation and Dissipation of Alfven Waves in Coronal ...
Indian Academy of Sciences (India)
Home; Journals; Journal of Astrophysics and Astronomy; Volume 28; Issue 1 ... Sun: Alfvén waves; coronal holes; solar wind. ... For any propagation angle, the energy flux density and damping length scale also show a decrement in the source region of the solar wind (< 1.05 R⊙) where these may be one of the primary ...
Statistical characterization of wave propagation in mine environments
Bakir, Onur
2012-07-01
A computational framework for statistically characterizing electromagnetic (EM) wave propagation through mine tunnels and galleries is presented. The framework combines a multi-element probabilistic collocation (ME-PC) method with a novel domain-decomposition (DD) integral equation-based EM simulator to obtain statistics of electric fields due to wireless transmitters in realistic mine environments. © 2012 IEEE.
Wave propagation in a general anisotropic poroelastic medium ...
Indian Academy of Sciences (India)
Anisotropic wave propagation is studied in a fluid-saturated porous medium, using two differ- ent approaches. One is the dynamic approach of Biot's theories. The other approach known as homogenisation theory, is based on the averaging process to derive macroscopic equations from the microscopic equations of motion.
Solitary waves in dimer binary collision model
Ahsan, Zaid; Jayaprakash, K. R.
2017-01-01
Solitary wave propagation in nonlinear diatomic (dimer) chains is a very interesting topic of research in the study of nonlinear lattices. Such waves were recently found to be supported by the essentially nonlinear granular lattice and Toda lattice. An interesting aspect of this discovery is attributed to the realization of a spectrum of the mass ratio (the only system parameter governing the dynamics) that supports the propagation of such waves corresponding to the considered interaction potential. The objective of this exposition is to explore solitary wave propagation in the dimer binary collision (BC) model. Interestingly, the dimer BC model supports solitary wave propagation at a discrete spectrum of mass ratios similar to those observed in granular and Toda dimers. Further, we report a qualitative and one-to-one correspondence between the spectrum of the mass ratio corresponding to the dimer BC model and those corresponding to granular and Toda dimer chains.
Wave propagation in a strongly nonlinear locally resonant granular crystal
Vorotnikov, K.; Starosvetsky, Y.; Theocharis, G.; Kevrekidis, P. G.
2018-02-01
In this work, we study the wave propagation in a recently proposed acoustic structure, the locally resonant granular crystal. This structure is composed of a one-dimensional granular crystal of hollow spherical particles in contact, containing linear resonators. The relevant model is presented and examined through a combination of analytical approximations (based on ODE and nonlinear map analysis) and of numerical results. The generic dynamics of the system involves a degradation of the well-known traveling pulse of the standard Hertzian chain of elastic beads. Nevertheless, the present system is richer, in that as the primary pulse decays, secondary ones emerge and eventually interfere with it creating modulated wavetrains. Remarkably, upon suitable choices of parameters, this interference "distills" a weakly nonlocal solitary wave (a "nanopteron"). This motivates the consideration of such nonlinear structures through a separate Fourier space technique, whose results suggest the existence of such entities not only with a single-side tail, but also with periodic tails on both ends. These tails are found to oscillate with the intrinsic oscillation frequency of the out-of-phase motion between the outer hollow bead and its internal linear attachment.
Skewon field and cosmic wave propagation
Ni, Wei-Tou
2013-01-01
For the study of the gravitational coupling of electromagnetism and the equivalence principle, we have used the spacetime constitutive tensor density {chi}ijkl, and discovered the nonmetric (axion) part (A){chi}ijkl (equal to {phi}eijkl) of {chi}ijkl worthy investigation. Since we have used Lagrangian formalism, {chi}ijkl is effectively symmetric under the interchange of index pairs, ij and kl, and has 21 independent degrees of freedom. Hehl, Obukhov and Rubilar have started from charge-flux formalism to study electromagnetism, discovered the antisymmetric part (Sk){chi}ijkl (15 degrees of freedom) of {chi}ijkl under the interchange of index pairs ij and kl worthy investigation, and called it skewon field. In this paper, we study the propagation of the Hehl-Obukhov-Rubilar skewon field in weak gravity field/dilute matter or with weak violation of the Einstein Equivalence Principle (EEP), and further classify it into Type I and Type II skewons. From the dispersion relation we show that no dissipation/no amplif...
Acoustic wave propagation in an axisymmetric swirling jet.
Yu, J. C.; Mungur, P.
1973-01-01
An analysis has been developed to study the acoustic wave propagation in an axisymmetric swirling subsonic jet flow. The governing convected wave equation derived in the spherical coordinates includes mean shears, shear gradients and pressure gradients. The directivity patterns for various spinning and non-spinning modes due to the influence of the mean jet swirl were obtained by numerically integrating the governing wave equation. The mean flow field used in the computation was that obtained semiempirically for subsonic swirling turbulent jet and is completely specified once the degree of swirl is known. The dependence of sound directivity on jet Mach number, swirl ratio and frequency are discussed.
Modulation instability of wave packets propagating in inhomogeneous nonlinear fiber
Lapin, V. A.; Fotiadi, A. A.
2017-05-01
The formation conditions and the effective gain of frequency-modulated soliton wave packets in a non-uniform along the length of active optical fibers were investigated. For packets modulated wave propagating in the nonlinear dependence of the fibers with the dispersion of the fiber length, the power of the generated pulses can be considerably increased in comparison with the homogeneous fibers. Due to the constant growth of the spectral width of the generated pulse sequence can no longer return to the state of the modulated continuous wave. As a result, the pulse duration with some fluctuations steadily declining. The amplitude and period of these oscillations are also reduced.
Nagatani, Yoshiki; Mizuno, Katsunori; Saeki, Takashi; Matsukawa, Mami; Sakaguchi, Takefumi; Hosoi, Hiroshi
2008-11-01
In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae in the propagation path. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. Since the fast wave mainly propagates in trabeculae, this wave is considered to reflect the structure of trabeculae. For a new diagnosis method using the information of this fast wave, therefore, it is necessary to understand the generation mechanism and propagation behavior precisely. In this study, the generation process of fast wave was examined by numerical simulations using elastic finite-difference time-domain (FDTD) method and experimental measurements. As simulation models, three-dimensional X-ray computer tomography (CT) data of actual bone samples were used. Simulation and experimental results showed that the attenuation of fast wave was always higher in the early state of propagation, and they gradually decreased as the wave propagated in bone. This phenomenon is supposed to come from the complicated propagating paths of fast waves in cancellous bone.
Propagation of Tsunami-like Surface Long Waves in the Bays of a Variable Depth
Directory of Open Access Journals (Sweden)
A.Yu. Bazykina
2016-08-01
Full Text Available Within the framework of the nonlinear long wave theory the regularities of solitary long wave propagation in the semi-closed bays of model and real geometry are numerically studied. In the present article the zones of wave amplification in the bay are found. The first one is located near the wave running-up on the beach (in front of the bay entrance and the other one – in the middle part of the sea basin. Wave propagation in these zones is accompanied both by significant rise and considerable fall of the sea level. Narrowing of the bay entrance and increase of the entering wave length result in decrease of the sea level maximum rises and falls. The Feodosiya Gulf in the Black Sea is considered as a real basin. In general the dynamics of the waves in the gulf is similar to wave dynamics in the model bay. Four zones of the strongest wave amplification in the Feodosiya Gulf are revealed in the article. The sea level maximum rises and extreme falls which tend to grow with decrease of the entering wave length are observed in these zones. The distance traveled by the wave before the collapse (due to non-linear effects, was found to reduce with decreasing wavelength of the entrance to the bay (gulf.
Propagation Characteristics of Electromagnetic Waves in Concrete
1989-03-01
from the preceding stage. This removes the limitation of the equivalent media theory (Feng, 1985). The model proposed by Feng and Sen (1985) assumes a...a continuous size distribution of spherical grains. On the other hand, a model proposed by Madden and Williams (1989) using the equivalent media ... theory considers a discrete particle size distribution of spherical grains, which is thus a more realistic model for concrete. This model is also built in
Characterization of wedge waves propagating along wedge tips with defects.
Chen, Ming-I; Tesng, Seng-Po; Lo, Pei-Yuan; Yang, Che-Hua
2018-01-01
Wedge waves are guided acoustic waves propagating along the tip of a wedge with the energy tightly confined near the wedge. Anti-symmetric flexural (ASF) modes are wedge waves with their particle motion anti-symmetric with the apex mid-plane. This study investigates the behaviors of ASF modes propagation along wedge tips with perfect and imperfect rectangular defects. Numerical finite element simulations and experimental measurements using a laser ultrasound technique are employed to explore the behaviors of ASF modes interacting with defects. Complex reflections and transmissions involved with direct reflections and transmissions as well as the newly discovered mode conversions will be explored and quantified in numerical as well as experimental ways. Copyright © 2017 Elsevier B.V. All rights reserved.
Superluminal X-wave propagation: energy localization and velocity.
Mugnai, D; Mochi, I
2006-01-01
The electromagnetic propagation of a Bessel-X wave is analyzed on the basis of a vectorial treatment in order to obtain information about the propagation of energy flux and the velocity of the energy. Knowledge of these quantities is of great interest since they are connected to the production of localized electromagnetic energy and to the topic of superluminality, respectively. The electric and magnetic fields are obtained in the far-field approximation by considering a realistic situation able to generate a Bessel-X wave. The vectorial treatment confirms the capability of this kind of wave to localize energy, while, quite surprisingly, even if the group velocity is superluminal, the energy velocity is equal to the light speed.
Torsional wave propagation in multiwalled carbon nanotubes using nonlocal elasticity
Arda, Mustafa; Aydogdu, Metin
2016-03-01
Torsional wave propagation in multiwalled carbon nanotubes is studied in the present work. Governing equation of motion of multiwalled carbon nanotube is obtained using Eringen's nonlocal elasticity theory. The effect of van der Waals interaction coefficient is considered between inner and outer nanotubes. Dispersion relations are obtained and discussed in detail. Effect of nonlocal parameter and van der Waals interaction to the torsional wave propagation behavior of multiwalled carbon nanotubes is investigated. It is obtained that torsional van der Waals interaction between adjacent tubes can change the rotational direction of multiwalled carbon nanotube as in-phase or anti-phase. The group and escape velocity of the waves converge to a limit value in the nonlocal elasticity approach.
Obliquely propagating magnetosonic waves in multicomponent quantum magnetoplasma
Energy Technology Data Exchange (ETDEWEB)
Masood, W. [Theoretical Plasma Physics Division, PO Nilore, Islamabad (Pakistan)], E-mail: waqasmas@gmail.com; Mushtaq, A. [Theoretical Plasma Physics Division, PO Nilore, Islamabad (Pakistan)
2008-06-02
Linear properties of obliquely propagating magnetosonic waves (both fast and slow) in multicomponent (electron-positron-ion (e-p-i) and dust-electron-ion (d-e-i)) quantum magnetoplasma are studied. It is found that the quantum Bohm potential term significantly changes the propagation of fast and slow magnetosonic waves in both e-p-i and d-e-i quantum plasmas. The variation of the dispersion characteristics with the increase/decrease of positron concentration in e-p-i and dust concentration in d-e-i quantum magnetoplasma is explored. Finally, the effect of angle {theta} (that the ambient magnetic field makes with the x-axis) on the dispersion properties of magnetosonic waves in multicomponent quantum magnetoplasma is investigated. The relevance of the present investigation to the dense astrophysical environments and microelectronic devices is also pointed out.
Experimental study of Lamb wave propagation in composite laminates
Wang, Lei; Yuan, F. G.
2006-03-01
This paper focuses on the existence of higher-order Lamb wave modes that can be observed from piezoelectric sensors by the excitation of ultrasonic frequencies from piezoelectric actuators. Using three-dimensional (3-D) elasticity theory, the exact dispersion relations governed by transcendental equations are numerically solved for an infinite number of possible wave modes. For symmetric laminates, a robust method by imposing boundary conditions on mid-plane and top surface is developed to separate wave modes. Then both phase and group velocity dispersions of Lamb waves in composites are obtained. Meanwhile three characteristic wave curves including velocity, slowness, and wave curves are introduced to analyze the angular dependency of Lamb wave propagation at a given frequency. In the experiments, two surface-mounted piezoelectric actuators are operated corporately to excite either symmetric or anti-symmetric wave modes with narrow banded excitation signals, and a Gabor wavelet transform is used to extract group velocities from arrival times of Lamb wave received by a piezoelectric sensor. In comparison with the results from the theory and experiment, it is confirmed that the higher-order Lamb waves can be excited from piezoelectric actuators and the measured group velocities agree well with those from 3-D elasticity theory.
Licer, Matjaz; Mourre, Baptiste; Troupin, Charles; Krietemeyer, Andreas; Tintoré, Joaquín
2017-04-01
A high resolution nested ocean modelling system forced by synthetic atmospheric gravity waves is used to investigate meteotsunami generation, amplification and propagation properties over the Mallorca-Menorca shelf (Balearic Islands, Western Mediterranean Sea). We determine how meteotsunami amplitude outside and inside of the Balearic port of Ciutadella depends on forcing gravity wave direction, speed and trajectory. Contributions of Mallorca shelves and Menorca Channel are quantified for different gravity wave forcing angles and speeds. Results indicate that the Channel is the key build-up region and that Northern and Southern Mallorca shelves do not significantly contribute to the amplitude of substantial harbour oscillations in Ciutadella. This fact seriously reduces early-warning alert times in cases of locally generated pressure perturbations. Tracking meteotsunami propagation paths in the Menorca Channel for several forcing velocities, we show that the Channel bathymetry serves as a focusing lens for meteotsunami waves whose paths are constrained by the forcing direction. Faster meteotsunamis are shown to propagate over deeper ocean regions, as required by the Proudman resonance. Meteotsunami speed under sub- and supercritical forcing is estimated and a first order estimate of its magnitude is derived. Meteotsunamis generated by the supercritical gravity waves are found to propagate with a velocity which is equal to an arithmetic mean of the gravity wave speed and local ocean barotropic wave speed.
Obliquely Propagating Electromagnetic Waves in Magnetized Kappa Plasmas
Gaelzer, R.
2015-12-01
The effects of velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subjectof intense research by the space plasma community. Such functions, known as kappa or superthermal distributions, have beenfound to provide a better fitting to the VDF measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. An anisotropic kappa VDF contains a large amount of free energy that can excite waves in the solar wind. Conversely, the wave-particle interaction is important to determine the shape of theobserved particle distributions.In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, either isotropic or anisotropic, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation. Contributions for the general case of obliquely-propagating electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities, such as the firehose, can operate simultaneously both in the parallel and oblique directions.In a recent work [1], we have obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfvén waves resulting from a kappa VDF. In the present work, we generalize the formalism introduced by [1] for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles.We employ an isotropic distribution, but the methods used here can be easily applied to more general anisotropic distributions,such as the bi-kappa or product-bi-kappa. [1] R. Gaelzer and L. F. Ziebell, Journal of Geophysical Research 119, 9334
Low-frequency pressure wave propagation in liquid-filled, flexible tubes. (A)
DEFF Research Database (Denmark)
Bjørnø, Leif; Bjelland, C.
1992-01-01
A model has been developed for propagation of low-frequency pressure waves in viscoelastic tubes with distensibility of greater importance than compressibility of the liquid. The dispersion and attenuation are shown to be strongly dependent on the viscoelastic properties of the tube wall...... the model and are compared with results of experimental pressure wave propagation in the liquid-filled, flexible tube. A good agreement between experimental data and theoretical predictions is found........ The complex, frequency-dependent moduli of relevant tube materials have been measured in a series of experiments using three different experimental procedures, and the data obtained are compared. The three procedures were: (1) ultrasonic wave propagation, (2) transversal resonance in bar samples, and (3...
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.
Modal analysis of wave propagation in dispersive media
Abdelrahman, M. Ismail; Gralak, B.
2018-01-01
Surveys on wave propagation in dispersive media have been limited since the pioneering work of Sommerfeld [Ann. Phys. 349, 177 (1914), 10.1002/andp.19143491002] by the presence of branches in the integral expression of the wave function. In this article a method is proposed to eliminate these critical branches and hence to establish a modal expansion of the time-dependent wave function. The different components of the transient waves are physically interpreted as the contributions of distinct sets of modes and characterized accordingly. Then, the modal expansion is used to derive a modified analytical expression of the Sommerfeld precursor improving significantly the description of the amplitude and the oscillating period up to the arrival of the Brillouin precursor. The proposed method and results apply to all waves governed by the Helmholtz equations.
Kampinga, W.R.; Wijnant, Ysbrand H.; de Boer, Andries; Sas, P.; De Munck, M.
2006-01-01
The so called low reduced frequency model has been shown to be both an accurate and a relatively simple description of wave propagation in narrow tubes or layers, under small signal conditions. In this paper, the low reduced frequency model will be applied on a circular layer between a fixed surface
Electromagnetic induction and radiation-induced abnormality of wave propagation in excitable media
Ma, Jun; Wu, Fuqiang; Hayat, Tasawar; Zhou, Ping; Tang, Jun
2017-11-01
Continuous wave emitting from sinus node of the heart plays an important role in wave propagating among cardiac tissue, while the heart beating can be terminated when the target wave is broken into turbulent states by electromagnetic radiation. In this investigation, local periodical forcing is applied on the media to induce continuous target wave in the improved cardiac model, which the effect of electromagnetic induction is considered by using magnetic flux, then external electromagnetic radiation is imposed on the media. It is found that target wave propagation can be blocked to stand in a local area and the excitability of media is suppressed to approach quiescent but homogeneous state when electromagnetic radiation is imposed on the media. The sampled time series for membrane potentials decrease to quiescent state due to the electromagnetic radiation. It could accounts for the mechanism of abnormality in heart failure exposed to continuous electromagnetic field.
Energy Content & Spectral Energy Representation of Wave Propagation in a Granular Chain
Shrivastava, Rohit; Luding, Stefan
2017-04-01
A mechanical wave is propagation of vibration with transfer of energy and momentum. Studying the energy as well as spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting) or non-destructive testing for the study of internal structure of solids. Wave propagation through granular materials is often accompanied by energy attenuation which is quantified by Quality factor and this parameter has often been used to characterize material properties, hence, determining the Quality factor (energy attenuation parameter) can also help in determining the properties of the material [3], studied experimentally in [2]. The study of Energy content (Kinetic, Potential and Total Energy) of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain can assist in understanding the energy attenuation due to disorder as a function of propagation distance. The spectral analysis of the energy signal can assist in understanding dispersion as well as attenuation due to scattering in different frequencies (scattering attenuation). The selection of one-dimensional granular chain also helps in studying only the P-wave attributes of the wave and removing the influence of shear or rotational waves. Granular chains with different mass distributions have been studied, by randomly selecting masses from normal, binary and uniform distributions and the standard deviation of the distribution is considered as the disorder parameter, higher standard deviation means higher disorder and lower standard deviation means lower disorder [1]. For obtaining macroscopic/continuum properties, ensemble averaging has been invoked. Instead of analyzing deformation-, velocity- or stress
Investigation on the propagation process of rotating detonation wave
Deng, Li; Ma, Hu; Xu, Can; Zhou, Changsheng; Liu, Xiao
2017-10-01
Effects of mass flow rate and equivalence ratio on the wave speed performance and instantaneous pressure characteristics of rotating detonation wave are investigated using hydrogen and air mixtures. The interaction between air and fuel manifolds and combustion chamber is also identified. The results show that the rotating detonation waves are able to adapt themselves to the changes of equivalence ratio during the run, the rotating detonation waves decayed gradually and then quenched after the shutdown of reactants supply. The wave speed performance is closely related to the mass flow rate and the pressure ratio of the fuel to air manifolds at different equivalence ratios. The blockage ratio of the air manifold increases with the increasing of the wave speed due to high-pressure detonation products, while increasing of the equivalence ratios will reduce the blockage ratio of the hydrogen manifold. Higher equivalence ratio can enhance the stabilization of the rotating detonation wave and lower equivalence ratio will lead to the large fluctuations of the lap time and instantaneous pressure magnitude. The overpressure of rotating detonation wave is determined by the combination of mass flow rate and equivalence ratio, which increases with the increasing of mass flow rate in the equivalence ratio ranges that the rotating detonation wave propagates stably. The secondary spike in the instantaneous pressure and ionization signals indicates that a shocked mixing zone exists near the fuel injection holes and the reflection of shock in the mixing zone induces the reaction.
A model for wideband HF propagation channels
Vogler, L. E.; Hoffmeyer, J. A.
1993-11-01
Expressions to model the sky wave propagation conditions that occur in a HF communication link are presented. The model is intended not only for narrowband applications but also for wideband systems such as those using spread spectrum techniques. A discussion of the background leading to the present development effort is followed by a description of the method used to derive the model transfer function. Analytic expressions for the impulse response and the scattering function are given, and the introduction of random processes into the model is described. Comparisons of scattering functions from the model and from measurements are shown for spread-F conditions ranging from mild to intense and for both an auroral path and a midlatitude path.
Zdeslav Hrepic; Zollman, Dean A; N. Sanjay Rebello
2010-01-01
We investigated introductory physics students’ mental models of sound propagation. We used a phenomenographic method to analyze the data in the study. In addition to the scientifically accepted Wave model, students used the “Entity” model to describe the propagation of sound. In this latter model sound is a self-standing entity, different from the medium through which it propagates. All other observed alternative models contain elements of both Entity and Wave models, but at the same time are...
Analysis of 38 GHz mmWave Propagation Characteristics of Urban Scenarios
DEFF Research Database (Denmark)
Rodriguez Larrad, Ignacio; Nguyen, Huan Cong; Sørensen, Troels Bundgaard
2015-01-01
The 38 GHz mm-wave frequency band is a strong candidate for the future deployment of wireless systems. Compared to lower frequency bands, propagation in the 38 GHz band is relatively unexplored for access networks in urban scenarios. This paper presents a detailed measurement-based analysis......, diffraction, transmission, as well as polarization effects. The measurement results confirm that, at this particular frequency, propagation in urban scenarios is mainly driven by line-of-sight and reflection. The proposed models are practical for implementation in system level simulators or ray-tracing tools...... of urban outdoor and outdoor-to-indoor propagation characteristics at 38 GHz. Different sets of measurements were performed in order to understand, quantify and model the behavior of the different underlying propagation mechanisms. The study considers line-of-sight propagation, reflection, scattering...
Electron plasma wave propagation in external-electrode fluorescent lamps
Cho, Guangsup; Kim, Jung-Hyun; Jeong, Jong-Mun; Hong, Byoung-Hee; Koo, Je-Huan; Choi, Eun-Ha; Verboncoeur, John P.; Uhm, Han Sup
2008-01-01
The optical propagation observed along the positive column of external electrode fluorescent lamps is shown to be an electron plasma wave propagating with the electron thermal speed of (kTe/m)1/2. When the luminance of the lamp is 10000-20000cd/m2, the electron plasma temperature and the plasma density in the positive column are determined to be kTe˜1.26-2.12eV and no˜(1.28-1.69)×1017m-3, respectively.
Propagation models for non line-of-sight scenarios
Tasu, A. S.; Anchidin, L.; Tamas, R.; Petrescu, T.
2016-12-01
The log-normal propagation model is usually applied for scenarios including a line-of-sight path. However, there are many cases that do not include such a propagation path, e.g. indoor transmission and disaster situations, when radio waves have to penetrate trough ruins. In this paper, we show that the log-normal model can also be applied for non line-of-sight transmission. Both indoor scenario and trough-ruins scenario, are investigated.
Spectral-element seismic wave propagation on emerging HPC architectures
Peter, Daniel; Liu, Qiancheng; Komatitsch, Dimitri
2017-04-01
Seismic tomography is the most prominent approach to infer physical properties of Earth's internal structures such as compressional- and shear-wave speeds, anisotropy and attenuation. Using seismic signals from ground-motion records, recent advances in full-waveform inversions require increasingly accurate simulations of seismic wave propagation in complex 3D media to provide access to the complete 3D seismic wavefield. However, such numerical simulations are computationally expensive and need high-performance computing (HPC) facilities for further improving the current state of knowledge. During recent years, new multi- and many-core architectures such as graphics processing units (GPUs) have been added to available large HPC systems. GPU-accelerated computing together with advances in multi-core central processing units (CPUs) can greatly accelerate scientific applications. To employ a wide variety of hardware accelerators for seismic wave propagation simulations, we incorporated a code generation tool BOAST into an existing spectral-element code package SPECFEM3D_GLOBE. This allows us to use meta-programming of computational kernels and generate optimized source code for both CUDA and OpenCL languages, running simulations on either CUDA or OpenCL hardware accelerators. We show here benchmark applications of seismic wave propagation on GPUs and CPUs, comparing performances on emerging hardware architectures.
Propagation of Love waves in an elastic layer with void pores
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
of longitudinal and shear waves in void media and came to the conclusion that there may be two wave fronts for longitudinal waves. Deyet al(1993) discussed the propagation of torsional surface waves in an elastic medium with void pores. The influence of local irregularities on propagation of Love waves has been studied ...
Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation
Directory of Open Access Journals (Sweden)
X. Liu
2009-07-01
Full Text Available The Kelvin-Helmholtz (KH billows which appear in the process of gravity wave (GW propagation are simulated directly by using a compressible nonlinear two-dimensional gravity wave model. The differences between our model and others include: the background field has no special initial configuration and there is no initial triggering mechanism needed in the mesosphere and lower thermosphere (MLT region to excite the KH billows. However, the initial triggering mechanism is performed in the lower atmosphere through GW, which then propagate into the MLT region and form billows. The braid structures and overturning of KH billows, caused by nonlinear interactions between GWs and mean flow, can be resolved precisely by the model. These results support the findings in airglow studies that GWs propagating from below into the MLT region are important sources of KH billows. The onset of small scale waves and the wave energy transfer induce the shallower vertical wave number power spectral densities (PSD. However, most of the slopes are steeper than the expected k_{z}^{−3} power law, which indicates that GWs with 10 km vertical wavelength are still a dominant mode. The results also show that the evolution of mean wind vary substantially between the different processes of GWs propagation. Before the KH billows evolve, the mean wind is accelerated greatly by GWs. By contrast, as the KH billows evolve and mix with mean flow, the mean wind and its peak value decrease.
Tango waves in a bidomain model of fertilization calcium waves
Li, Yue-Xian
2003-12-01
Fertilization of an egg cell is marked by one or several Ca 2+ waves that travel across the intra-cellular space, called fertilization Ca 2+ waves. Patterns of Ca 2+ waves observed in mature or immature oocytes include traveling fronts and pulses as well as concentric and spiral waves. These patterns have been studied in other excitable media in physical, chemical, and biological systems. Here, we report the discovery of a new wave phenomenon in the numerical study of a bidomain model of fertilization Ca 2+ waves. This wave is a front that propagates in a back-and-forth manner that resembles the movement of tango dancers, thus is called a tango wave. When the medium is excitable, a forward-moving tango wave can generate traveling pulses that propagate down the space without reversal. The study shows that the occurrence of tango waves is related to spatial inhomogeneity in the local dynamics. This is tested and confirmed by simulating similar waves in a medium with stationary spatial inhomogeneity. Similar waves are also obtained in a FitzHugh-Nagumo system with a linear spatial ramp. In both the bidomain model of Ca 2+ waves and the FitzHugh-Nagumo system, the front is stable when the slope of a linear ramp is large. As the slope decreases beyond a critical value, front oscillations occur. The study shows that tango waves facilitate the dispersion of localized Ca 2+. Key features of the bidomain model underlying the occurrence of tango waves are revealed. These features are commonly found in egg cells of a variety of species. Thus, we predict that tango waves can occur in real egg cells provided that a slowly varying inhomogeneity does occur following the sperm entry. The observation of tango wave-like waves in nemertean worm and ascidian eggs seems to support such a prediction.
The energy transport by the propagation of sound waves in wave guides with a moving medium
le Grand, P.
1977-01-01
The problem of the propagation of sound waves radiated by a source in a fluid moving with subsonic velocity between two parallel walls or inside a cylindrical tube is considered in [2], The most interesting thing of this problem is that waves may occur with constant amplitude coming from infinity.
Nonlinearities of waves propagating over a mild-slope beach: laboratory and numerical results
Rocha, Mariana V. L.; Michallet, Hervé; Silva, Paulo A.; Cienfuegos, Rodrigo
2014-05-01
As surface gravity waves propagate from deeper waters to the shore, their shape changes, primarily due to nonlinear wave interactions and further on due to breaking. The nonlinear effects amplify the higher harmonics and cause the oscillatory flow to transform from nearly sinusoidal in deep water, through velocity-skewed in the shoaling zone, to velocity asymmetric in the inner-surf and swash zones. In addition to short-wave nonlinearities, the presence of long waves and wave groups also results in a supplementary wave-induced velocity and influences the short-waves. Further, long waves can themselves contribute to velocity skewness and asymmetry at low frequencies, particularly for very dissipative mild-slope beach profiles, where long wave shoaling and breaking can also occur. The Hydralab-IV GLOBEX experiments were performed in a 110-m-long flume, with a 1/80 rigid-bottom slope and allowed the acquisition of high-resolution free-surface elevation and velocity data, obtained during 90-min long simulations of random and bichromatic wave conditions, and also of a monochromatic long wave (Ruessink et al., Proc. Coastal Dynamics, 2013). The measurements are compared to numerical results obtained with the SERR-1D Boussinesq-type model, which is designed to reproduce the complex dynamics of high-frequency wave propagation, including the energy transfer mechanisms that enhance infragravity-wave generation. The evolution of skewness and asymmetry along the beach profile until the swash zone is analyzed, relatively to that of the wave groupiness and long wave propagation. Some particularities of bichromatic wave groups are further investigated, such as partially-standing long-wave patterns and short-wave reformation after the first breakpoint, which is seen to influence particularly the skewness trends. Decreased spectral width (for random waves) and increased modulation (for bichromatic wave groups) are shown to enhance energy transfers between super- and sub
Wave Propagation From Electrons to Photonic Crystals and Left-Handed Materials
Markos, Peter
2010-01-01
This textbook offers the first unified treatment of wave propagation in electronic and electromagnetic systems and introduces readers to the essentials of the transfer matrix method, a powerful analytical tool that can be used to model and study an array of problems pertaining to wave propagation in electrons and photons. It is aimed at graduate and advanced undergraduate students in physics, materials science, electrical and computer engineering, and mathematics, and is ideal for researchers in photonic crystals, negative index materials, left-handed materials, plasmonics, nonlinear effects,
Shock Wave Propagation in Functionally Graded Mineralized Tissue
Nelms, Matthew; Hodo, Wayne; Livi, Ken; Browning, Alyssa; Crawford, Bryan; Rajendran, A. M.
2017-06-01
In this investigation, the effects of shock wave propagation in bone-like biomineralized tissue was investigated. The Alligator gar (Atractosteus spatula) exoskeleton is comprised of many disparate scales that provide a biological analog for potential design of flexible protective material systems. The gar scale is identified as a two-phase, (1) hydroxyapatite mineral and (2) collagen protein, biological composite with two distinct layers where a stiff, ceramic-like ganoine overlays a soft, highly ductile ganoid bone. Previous experimentations has shown significant softening under compressive loading and an asymmetrical stress-strain response for analogous mineralized tissues. The structural features, porosity, and elastic modulus were determined from high-resolution scanning electron microscopy, 3D micro-tomography, and dynamic nanoindentation experiments to develop an idealized computational model for FE simulations. The numerical analysis employed Gurson's yield criterion to determine the influence of porosity and pressure on material strength. Functional gradation of elastic moduli and certain structural features, such as the sawtooth interface, are explicitly modeled to study the plate impact shock profile for a full 3-D analysis using ABAQUS finite element software.
Wound-induced Ca2+wave propagates through a simple release and diffusion mechanism.
Handly, L Naomi; Wollman, Roy
2017-06-01
Damage-associated molecular patterns (DAMPs) are critical mediators of information concerning tissue damage from damaged cells to neighboring healthy cells. ATP acts as an effective DAMP when released into extracellular space from damaged cells. Extracellular ATP receptors monitor tissue damage and activate a Ca 2+ wave in the surrounding healthy cells. How the Ca 2+ wave propagates through cells after a wound is unclear. Ca 2+ wave activation can occur extracellularly via external receptors or intracellularly through GAP junctions. Three potential mechanisms to propagate the Ca 2+ wave are source and sink, amplifying wave, and release and diffusion. Both source and sink and amplifying wave regulate ATP levels using hydrolysis or secretion, respectively, whereas release and diffusion relies on dilution. Here we systematically test these hypotheses using a microfluidics assay to mechanically wound an epithelial monolayer in combination with direct manipulation of ATP hydrolysis and release. We show that a release and diffusion model sufficiently explains Ca 2+ -wave propagation after an epithelial wound. A release and diffusion model combines the benefits of fast activation at short length scales with a self-limiting response to prevent unnecessary inflammatory responses harmful to the organism. © 2017 Handly et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).
Prediction of propagated wave profiles based on point measurement
Directory of Open Access Journals (Sweden)
Lee Sang-Beom
2014-03-01
Full Text Available This study presents the prediction of propagated wave profiles using the wave information at a fixed point. The fixed points can be fixed in either space or time. Wave information based on the linear wave theory can be expressed by Fredholm integral equation of the first kinds. The discretized matrix equation is usually an ill-conditioned system. Tikhonov regularization was applied to the ill-conditioned system to overcome instability of the system. The regularization parameter is calculated by using the L-curve method. The numerical results are compared with the expe¬rimental results. The analysis of the numerical computation shows that the Tikhonov regularization method is useful.
Wave propagation in one-dimensional nonlinear acoustic metamaterials
Fang, Xin; Wen, Jihong; Bonello, Bernard; Yin, Jianfei; Yu, Dianlong
2017-05-01
The propagation of waves in nonlinear acoustic metamaterial (NAM) is fundamentally different from that in conventional linear ones. In this article we consider two one-dimensional (1D) NAM systems featuring respectively a diatomic and a tetratomic meta unit-cell. We investigate the attenuation of waves, band structures, and bifurcations to demonstrate novel nonlinear effects, which can significantly expand the bandwidth for elastic wave suppression and cause nonlinear wave phenomena. The harmonic averaging approach, continuation algorithm, and Lyapunov exponents (LEs) are combined to study the frequency responses, nonlinear modes, bifurcations of periodic solutions, and chaos. The nonlinear resonances are studied, and the influence of damping on hyperchaotic attractors is evaluated. Moreover, a ‘quantum’ behavior is found between the low-energy and high-energy orbits. This work provides a theoretical base for furthering understandings and applications of NAMs.
Carcione, José M
2007-01-01
This book examines the differences between an ideal and a real description of wave propagation, where ideal means an elastic (lossless), isotropic and single-phase medium, and real means an anelastic, anisotropic and multi-phase medium. The analysis starts by introducing the relevant stress-strain relation. This relation and the equations of momentum conservation are combined to give the equation of motion. The differential formulation is written in terms of memory variables, and Biot's theory is used to describe wave propagation in porous media. For each rheology, a plane-wave analysis is performed in order to understand the physics of wave propagation. The book contains a review of the main direct numerical methods for solving the equation of motion in the time and space domains. The emphasis is on geophysical applications for seismic exploration, but researchers in the fields of earthquake seismology, rock acoustics, and material science - including many branches of acoustics of fluids and solids - may als...
Propagation of Gaussian wave packets in complex media and application to fracture characterization
Ding, Yinshuai; Zheng, Yingcai; Zhou, Hua-Wei; Howell, Michael; Hu, Hao; Zhang, Yu
2017-08-01
Knowledge of the subsurface fracture networks is critical in probing the tectonic stress states and flow of fluids in reservoirs containing fractures. We propose to characterize fractures using scattered seismic data, based on the theory of local plane-wave multiple scattering in a fractured medium. We construct a localized directional wave packet using point sources on the surface and propagate it toward the targeted subsurface fractures. The wave packet behaves as a local plane wave when interacting with the fractures. The interaction produces multiple scattering of the wave packet that eventually travels up to the surface receivers. The propagation direction and amplitude of the multiply scattered wave can be used to characterize fracture density, orientation and compliance. Two key aspects in this characterization process are the spatial localization and directionality of the wave packet. Here we first show the physical behaviour of a new localized wave, known as the Gaussian Wave Packet (GWP), by examining its analytical solution originally formulated for a homogenous medium. We then use a numerical finite-difference time-domain (FDTD) method to study its propagation behaviour in heterogeneous media. We find that a GWP can still be localized and directional in space even over a large propagation distance in heterogeneous media. We then propose a method to decompose the recorded seismic wavefield into GWPs based on the reverse-time concept. This method enables us to create a virtually recorded seismic data using field shot gathers, as if the source were an incident GWP. Finally, we demonstrate the feasibility of using GWPs for fracture characterization using three numerical examples. For a medium containing fractures, we can reliably invert for the local parameters of multiple fracture sets. Differing from conventional seismic imaging such as migration methods, our fracture characterization method is less sensitive to errors in the background velocity model
Monograph on propagation of sound waves in curved ducts
Rostafinski, Wojciech
1991-01-01
After reviewing and evaluating the existing material on sound propagation in curved ducts without flow, it seems strange that, except for Lord Rayleigh in 1878, no book on acoustics has treated the case of wave motion in bends. This monograph reviews the available analytical and experimental material, nearly 30 papers published on this subject so far, and concisely summarizes what has been learned about the motion of sound in hard-wall and acoustically lined cylindrical bends.
24 GHz cmWave Radio Propagation Through Vegetation
DEFF Research Database (Denmark)
Rodriguez, Ignacio; Abreu, Renato Barbosa; Portela Lopes de Almeida, Erika
2016-01-01
This paper presents a measurement-based analysis of cm-wave radio propagation through vegetation at 24 GHz. A set of dedicated directional measurements were performed with horn antennas located close to street level inside a densely-vegetated area illuminated from above. The full azimuth...... along the paper are useful for simulation and radio network planning of future wireless systems operating at 24 GHz in presence of vegetation....
Elastic Wave Propagation Mechanisms in Underwater Acoustic Environments
2015-09-30
Collis, and Robert I. Odom. Elastic parabolic equation solutions for oceanic T -wave generation and propagation from deep seismic sources. J. Acoust...navigation under Arctic ice. In Oceans , 2012, pages 1–8. IEEE, October 2012. 10.1109/ OCEANS .2012.6405005. PUBLICATIONS • Published in refereed journal...or elastic ice cover. OBJECTIVES To apply EPE solutions to scenarios that include fluid-elastic boundaries, either at the ocean floor, or at the
Nonlinear physics of electrical wave propagation in the heart: a review
Alonso, Sergio; Bär, Markus; Echebarria, Blas
2016-09-01
The beating of the heart is a synchronized contraction of muscle cells (myocytes) that is triggered by a periodic sequence of electrical waves (action potentials) originating in the sino-atrial node and propagating over the atria and the ventricles. Cardiac arrhythmias like atrial and ventricular fibrillation (AF,VF) or ventricular tachycardia (VT) are caused by disruptions and instabilities of these electrical excitations, that lead to the emergence of rotating waves (VT) and turbulent wave patterns (AF,VF). Numerous simulation and experimental studies during the last 20 years have addressed these topics. In this review we focus on the nonlinear dynamics of wave propagation in the heart with an emphasis on the theory of pulses, spirals and scroll waves and their instabilities in excitable media with applications to cardiac modeling. After an introduction into electrophysiological models for action potential propagation, the modeling and analysis of spatiotemporal alternans, spiral and scroll meandering, spiral breakup and scroll wave instabilities like negative line tension and sproing are reviewed in depth and discussed with emphasis on their impact for cardiac arrhythmias.
Propagation characteristics of acoustic emission wave in reinforced concrete
Directory of Open Access Journals (Sweden)
Haoxiong Feng
Full Text Available Due to the complexity of components and damage mechanism of reinforced concrete, the wave propagation characteristics in reinforced concrete are always complicated and difficult to determine. The objective of this article is to study the failure process of reinforced concrete structure under the damage caused by pencil-broken. A new method on the basis of the acoustic emission technique and the Hilbert-Huang transform theory is proposed in this work. By using acoustic emission technique, the acoustic emission wave signal is generating while the real-time damage information and the strain field of the reinforced concrete structure is receiving simultaneously. Based on the Hilbert-Huang transform (HHT theory, the peak frequency characteristics of the acoustic emission signals were extracted to identify the damage modes of the reinforced concrete structure. The results demonstrate that this method can quantitatively investigate the acoustic emission wave propagation characteristic in reinforced concrete structures and might also be promising in other civil constructions. Keywords: Acoustic emission, Reinforced concrete structure, Hilbert-Huang transform (HHT, Propagation characteristics
Wijnant, Ysbrand H.; Spiering, R.M.E.J.; Blijderveen, M.; de Boer, Andries
2006-01-01
Previous research has shown that viscothermal wave propagation in narrow gaps can efficiently be described by means of the low reduced frequency model. For simple geometries and boundary conditions, analytical solutions are available. For example, Beltman [4] gives the acoustic pressure in the gap
Directory of Open Access Journals (Sweden)
Apisit Tongchai
2011-07-01
Full Text Available We recently developed a multiple-choice conceptual survey in mechanical waves. The development, evaluation, and demonstration of the use of the survey were reported elsewhere [A. Tongchai et al., Developing, evaluating and demonstrating the use of a conceptual survey in mechanical waves, Int. J. Sci. Educ. 31, 2437 (2009ISEDEB0950-069310.1080/09500690802389605]. We administered the survey to 902 students from seven different groups ranging from high school to second year university. As an outcome of that analysis we were able to identify several conceptual models which the students seemed to be using when answering the questions in the survey. In this paper we attempt to investigate the strength with which the students were committed to these conceptual models, as evidenced by the consistency with which they answered the questions. For this purpose we focus on the patterns of student responses to questions in one particular subtopic, wave propagation. This study has three main purposes: (1 to investigate the consistency of student conceptions, (2 to explore the relative usefulness of different analysis techniques, and (3 to determine what extra information a study of consistency can give about student understanding of basic concepts. We used two techniques: first, categorizing and counting, which is widely used in the science education community, and second, model analysis, recently introduced into physics education research. The manner in which categorizing and counting is used is very diverse while model analysis has been employed only in prescriptive ways. Research studies have reported that students often use their conceptual models inconsistently when solving a series of questions that test the same idea. Our results support their conclusions. Moreover, our findings suggest that students who have had more experiences in physics learning seem to use the scientifically accepted models more consistently. Further, the two analysis techniques
Source and listener directivity for interactive wave-based sound propagation.
Mehra, Ravish; Antani, Lakulish; Kim, Sujeong; Manocha, Dinesh
2014-04-01
We present an approach to model dynamic, data-driven source and listener directivity for interactive wave-based sound propagation in virtual environments and computer games. Our directional source representation is expressed as a linear combination of elementary spherical harmonic (SH) sources. In the preprocessing stage, we precompute and encode the propagated sound fields due to each SH source. At runtime, we perform the SH decomposition of the varying source directivity interactively and compute the total sound field at the listener position as a weighted sum of precomputed SH sound fields. We propose a novel plane-wave decomposition approach based on higher-order derivatives of the sound field that enables dynamic HRTF-based listener directivity at runtime. We provide a generic framework to incorporate our source and listener directivity in any offline or online frequency-domain wave-based sound propagation algorithm. We have integrated our sound propagation system in Valve's Source game engine and use it to demonstrate realistic acoustic effects such as sound amplification, diffraction low-passing, scattering, localization, externalization, and spatial sound, generated by wave-based propagation of directional sources and listener in complex scenarios. We also present results from our preliminary user study.
Propagation of electromagnetic waves in stochastic helical media.
Mendez, David; Reyes, J Adrian
2012-09-01
We have developed a model for studying the axial propagation of elliptically polarized electromagnetic waves in a spatially random helical media. We start by writing Maxwell equations for a structurally chiral medium whose dielectric permittivities, polar, and helical angles contain both a stochastic contribution and a deterministic one. We write the electromagnetic equations into a Marcuvitz-Schwigner representation to transform them afterward in a simpler expression by using the Oseen transformation. We exhibit that in the Oseen frame the Marcuvitz-Schwigner equations turns out to be a linear vector stochastic system of differential equations with multiplicative noise. Applying to the resulting equation a formalism for treating stochastic differential equations, we find the governing equations for the first moments of the electromagnetic field amplitudes for a general autocorrelation function for the system diffractive indexes, and calculate their corresponding band structure for a particular spectral noise density. We have shown that the average resulting electromagnetic fields exhibit a decaying exponential dependence which stems from by dissipation and the presence of qualitative modifications in the band structure including a considerable widening of the band gap and the existence of new local maxima for the modes without a band gap.
Nonlocal wave propagation in an embedded DWBNNT conveying fluid via strain gradient theory
Energy Technology Data Exchange (ETDEWEB)
Ghorbanpour Arani, A., E-mail: aghorban@kashanu.ac.ir [Faculty of Mechanical Engineering, University of Kashan, Kashan (Iran, Islamic Republic of); Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan (Iran, Islamic Republic of); Kolahchi, R.; Vossough, H. [Faculty of Mechanical Engineering, University of Kashan, Kashan (Iran, Islamic Republic of)
2012-11-01
Based on the strain gradient and Eringen's piezoelasticity theories, wave propagation of an embedded double-walled boron nitride nanotube (DWBNNT) conveying fluid is investigated using Euler-Bernoulli beam model. The elastic medium is simulated by the Pasternak foundation. The van der Waals (vdW) forces between the inner and outer nanotubes are taken into account. Since, considering electro-mechanical coupling made the nonlinear motion equations, a numerical procedure is proposed to evaluate the upstream and downstream phase velocities. The results indicate that the effect of nonlinear terms in motion equations on the phase velocity cannot be neglected at lower wave numbers. Furthermore, the effect of fluid-conveying on wave propagation of the DWBNNT is significant at lower wave numbers.
Atoms in the counter-propagating frequency-modulated waves: splitting, cooling, confinement
Romanenko, Victor I.; Kornilovska, Nataliya V.
2017-09-01
We show that the counter-propagating frequency-modulated (FM) waves of the same intensity can split an orthogonal atomic beam into two beams. We calculate the temperature of the atomic ensemble for the case when the atoms are grouped around zero velocity in the direction of the waves propagation. The high-intensity laser radiation with a properly chosen carrier frequency can form a one-dimensional trap for atoms. We carry out the numerical simulation of the atomic motion (two-level model of the atom-field interaction) using parameters appropriate for sodium atoms and show that sub-Doppler cooling can be reached. We suppose that such a cooling is partly based on the cooling without spontaneous emission in polychromatic waves [H. Metcalf, Phys. Rev. A 77, 061401 (2008)]. We calculate the state of the atom in the field by the Monte Carlo wave-function method and describe its mechanical motion by the classical mechanics.
Selective spatial damping of propagating kink waves due to resonant absorption
Terradas, J.; Goossens, M.; Verth, G.
2010-12-01
Context. There is observational evidence of propagating kink waves driven by photospheric motions. These disturbances, interpreted as kink magnetohydrodynamic (MHD) waves are attenuated as they propagate upwards in the solar corona. Aims: We show that resonant absorption provides a simple explanation to the spatial damping of these waves. Methods: Kink MHD waves are studied using a cylindrical model of solar magnetic flux tubes, which includes a non-uniform layer at the tube boundary. Assuming that the frequency is real and the longitudinal wavenumber complex, the damping length and damping per wavelength produced by resonant absorption are analytically calculated in the thin tube (TT) approximation, valid for coronal waves. This assumption is relaxed in the case of chromospheric tube waves and filament thread waves. Results: The damping length of propagating kink waves due to resonant absorption is a monotonically decreasing function of frequency. For kink waves with low frequencies, the damping length is exactly inversely proportional to frequency, and we denote this as the TGV relation. When moving to high frequencies, the TGV relation continues to be an exceptionally good approximation of the actual dependency of the damping length on frequency. This dependency means that resonant absorption is selective as it favours low-frequency waves and can efficiently remove high-frequency waves from a broad band spectrum of kink waves. The efficiency of the damping due to resonant absorption depends on the properties of the equilibrium model, in particular on the width of the non-uniform layer and the steepness of the variation in the local Alfvén speed. Conclusions: Resonant absorption is an effective mechanism for the spatial damping of propagating kink waves. It is selective because the damping length is inversely proportional to frequency so that the damping becomes more severe with increasing frequency. This means that radial inhomogeneity can cause solar
Modeling fluctuations in scattered waves
Jakeman, E
2006-01-01
Fluctuations in scattered waves limit the performance of imaging and remote sensing systems that operate on all wavelengths of the electromagnetic spectrum. To better understand these fluctuations, Modeling Fluctuations in Scattered Waves provides a practical guide to the phenomenology, mathematics, and simulation of non-Gaussian noise models and discusses how they can be used to characterize the statistics of scattered waves.Through their discussion of mathematical models, the authors demonstrate the development of new sensing techniques as well as offer intelligent choices that can be made for system analysis. Using experimental results and numerical simulation, the book illustrates the properties and applications of these models. The first two chapters introduce statistical tools and the properties of Gaussian noise, including results on phase statistics. The following chapters describe Gaussian processes and the random walk model, address multiple scattering effects and propagation through an extended med...
Mapping of spin wave propagation in a one-dimensional magnonic crystal
Energy Technology Data Exchange (ETDEWEB)
Ordóñez-Romero, César L., E-mail: cloro@fisica.unam.mx; Lazcano-Ortiz, Zorayda; Aguilar-Huerta, Melisa; Monsivais, Guillermo [Instituto de Física, Universidad Nacional Autónoma de México, CU, México D.F. 04510 (Mexico); Drozdovskii, Andrey; Kalinikos, Boris [St. Petersburg Electrotechnical University, 197376 St. Petersburg (Russian Federation); International laboratory “MultiferrLab,” ITMO University, 197101 St. Petersburg (Russian Federation); Domínguez-Juárez, J. L. [Cátedras CONACyT, CFATA, Universidad Nacional Autónoma de México, Juriquilla, Querétaro 76230 (Mexico); Lopez-Maldonado, Guillermo [Universidad Autónoma Metropolitana, Lerma de Villada, 52006 Estado de México (Mexico); Qureshi, Naser; Kolokoltsev, Oleg [CCADET, Universidad Nacional Autónoma de México, CU, México D.F. 04510 (Mexico)
2016-07-28
The formation and evolution of spin wave band gaps in the transmission spectrum of a magnonic crystal have been studied. A time and space resolved magneto inductive probing system has been used to map the spin wave propagation and evolution in a geometrically structured yttrium iron garnet film. Experiments have been carried out using (1) a chemically etched magnonic crystal supporting the propagation of magnetostatic surface spin waves, (2) a short microwave pulsed excitation of the spin waves, and (3) direct spin wave detection using a movable magneto inductive probe connected to a synchronized fast oscilloscope. The results show that the periodic structure not only modifies the spectra of the transmitted spin waves but also influences the distribution of the spin wave energy inside the magnonic crystal as a function of the position and the transmitted frequency. These results comprise an experimental confirmation of Bloch′s theorem in a spin wave system and demonstrate good agreement with theoretical observations in analogue phononic and photonic systems. Theoretical prediction of the structured transmission spectra is achieved using a simple model based on microwave transmission lines theory. Here, a spin wave system illustrates in detail the evolution of a much more general physical concept: the band gap.
Guided wave propagation in porous unidirectional carbon fiber reinforced plastic
Dobmann, Nicolas; Bach, Martin
2017-02-01
Networks of piezoelectric transducers mounted on aircraft structures for Acousto Ultrasonics (AU) purposes are designed to be applied during the service life of the aircraft. The approach to integrate these sensor networks already during the manufacture of carbon fiber reinforced plastic (CFRP) host structures prompts ideas to achieve an additional benefit by their application for cure monitoring, thus extending their use to the manufacturing chain. This benefit could be extended even further if guided waves generated by AU sensor networks could be used for porosity testing extensively applied for CFRP aircraft structures. In light of this, an experimental study was conducted to investigate effects of porosity on the propagation of guided waves in a basic configuration of unidirectional CFRP. Several samples were manufactured at different porosity levels by variation of the processing pressure. Wave fields were acquired using an ultrasonic scanning device. In the present work, phase velocities are chosen as best measurable and quantifiable propagation feature and the approach for the analysis of phase velocities in porosity samples is outlined. First results are presented and discussed regarding the influence of porosity on guided wave phase velocity and basic applicability for porosity testing of aircraft structures.
Low frequency piezoresonance defined dynamic control of terahertz wave propagation.
Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G; Bhalla, Amar S; Guo, Ruyan
2016-11-30
Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.
Indoor propagation and assessment of blast waves from weapons using the alternative image theory
Kong, B.; Lee, K.; Lee, S.; Jung, S.; Song, K. H.
2016-03-01
Blast waves generated from the muzzles of various weapons might have significant effects on the human body, and these effects are recognized as being more severe when weapons are fired indoors. The risk can be assessed by various criteria, such as waveform, exposed energy, and model-based types. This study introduces a prediction model of blast wave propagation for estimating waveform parameters related to damage risk assessment. To simulate indoor multiple reflections in a simple way, the model is based on the alternative image theory and discrete wavefront method. The alternative theory is a kind of modified image theory, but it uses the image space concept from a receiver's perspective, so that it shows improved efficiency for indoor problems. Further, the discrete wavefront method interprets wave propagation as the forward movement of a finite number of wavefronts. Even though the predicted results show slight differences from the measured data, the locations of significant shock waves indicate a high degree of correlation between them. Since the disagreement results not from the proposed techniques but from the assumptions used, it is concluded that the model is appropriate for analysis of blast wave propagation in interior spaces.
Wave propagation phenomena in metamaterials for retrieving of effective parameters
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Ha, S.
2011-01-01
into account propagation of eigen-waves in multilayered structures (thicknesses 10-100 unit cells). Thus, the question of pa-rameters convergence is naturally resolved in our approach. The method has been tested on complex three-dimensional structures like a split-cube-in-carcass and with circular polarized...... waves on chiral MMs [1, 2]. Elaborating our approach the new method has been established, where the unit-cell volume and face field averaging procedures define wave and input (Bloch) impedances correspond-ingly. The first part of the method involves the extraction of the dominating (fundamental) Bloch...... between constitutive elements, multipoles resonances, multimode or photonic crystal (diffraction type) regimes. There are also technical limitations of the retrieval methods connected with very strong losses, branching ambiguity, convergence to bulk parameters, etc. Moreover, most of the simple methods...
Propagation models for computing biochemical reaction networks
Henzinger, Thomas A; Mateescu, Maria
2011-01-01
We introduce propagation models, a formalism designed to support general and efficient data structures for the transient analysis of biochemical reaction networks. We give two use cases for propagation abstract data types: the uniformization method and numerical integration. We also sketch an implementation of a propagation abstract data type, which uses abstraction to approximate states.
Deep vertical propagation of mountain waves above Scandinavia
Dörnbrack, Andreas; Gisinger, Sonja; Rapp, Markus; Witschas, Benjamin; Ehard, Benedikt; Wagner, Johannes; Achtert, Peggy; Stober, Gunter; Kivi, Rigel; Gumbel, Jörg
2015-04-01
The project "Investigation of the life cycle of gravity waves (GW-LCYCLE) is part of the German research initiative ROMIC (Role of the Middle atmosphere In Climate) funded by the ministry of research. In close cooperation with Scandinavian partners as the Stockholm University and the Finnish Meteorological Institute a first field phase was conducted in November/December 2013. The field program combined ground-based observations of tropospheric and lower stratospheric flow and stratospheric and mesospheric temperature by lidars and radars at Alomar (N) and at Esrange (S) with airborne and balloonborne observations. Northern Scandinavia was chosen since the westerly flow across the mountains is often aligned with the polar night jet permitting gravity waves (GWs) to propagate into the middle atmosphere. From 2 until 14 December 2013, 24 hours of the DLR Falcon flown in four intensive observing periods (IOPs) provided in-situ and remote-sensing observations of atmospheric wind, temperature, water vapour and other trace gases (e.g. CO, N2O, O3) in the vicinity of the tropopause. During three IOPs, the airborne observations were supported by 3 hourly simultaneous radiosonde launches from Andøya (N), Esrange(S) and Sodankylä (FIN). Additionally, 1.5 hourly high-frequency radiosonde launches were conducted from the Arena Arctica at Kiruna airport with two systems (Väisälä and GRAW)and different balloon fillings to obtain different ascent rates. During GW-LCYCLE, the atmospheric flow above the Scandinavian mountains was observed under distinct meteorological conditions enabling or attenuating the deep vertical propagation of mountain-induced gravity waves. The presentation juxtaposes two different cases and analyses the associated meteorological conditions. The unique combination of airborne tropospheric wind lidar measurements, flight level data, high-frequency radiosonde profiles and the ground-based lidar observations allow a comprehensive study of deeply
Directory of Open Access Journals (Sweden)
Chernchok Soankwan
2011-07-01
Full Text Available We recently developed a multiple-choice conceptual survey in mechanical waves. The development, evaluation, and demonstration of the use of the survey were reported elsewhere [ A. Tongchai et al. Int. J. Sci. Educ. 31 2437 (2009]. We administered the survey to 902 students from seven different groups ranging from high school to second year university. As an outcome of that analysis we were able to identify several conceptual models which the students seemed to be using when answering the questions in the survey. In this paper we attempt to investigate the strength with which the students were committed to these conceptual models, as evidenced by the consistency with which they answered the questions. For this purpose we focus on the patterns of student responses to questions in one particular subtopic, wave propagation. This study has three main purposes: (1 to investigate the consistency of student conceptions, (2 to explore the relative usefulness of different analysis techniques, and (3 to determine what extra information a study of consistency can give about student understanding of basic concepts. We used two techniques: first, categorizing and counting, which is widely used in the science education community, and second, model analysis, recently introduced into physics education research. The manner in which categorizing and counting is used is very diverse while model analysis has been employed only in prescriptive ways. Research studies have reported that students often use their conceptual models inconsistently when solving a series of questions that test the same idea. Our results support their conclusions. Moreover, our findings suggest that students who have had more experiences in physics learning seem to use the scientifically accepted models more consistently. Further, the two analysis techniques have different advantages and disadvantages. Our findings show that model analysis can be used in more diverse ways, provides
Energy Technology Data Exchange (ETDEWEB)
Lo, W.-C.; Sposito, G.; Majer, E.
2007-02-01
An analytical theory is presented for the low-frequency behavior of dilatational waves propagating through a homogeneous elastic porous medium containing two immiscible fluids. The theory is based on the Berryman-Thigpen-Chin (BTC) model, in which capillary pressure effects are neglected. We show that the BTC model equations in the frequency domain can be transformed, at sufficiently low frequencies, into a dissipative wave equation (telegraph equation) and a propagating wave equation in the time domain. These partial differential equations describe two independent modes of dilatational wave motion that are analogous to the Biot fast and slow compressional waves in a single-fluid system. The equations can be solved analytically under a variety of initial and boundary conditions. The stipulation of 'low frequency' underlying the derivation of our equations in the time domain is shown to require that the excitation frequency of wave motions be much smaller than a critical frequency. This frequency is shown to be the inverse of an intrinsic time scale that depends on an effective kinematic shear viscosity of the interstitial fluids and the intrinsic permeability of the porous medium. Numerical calculations indicate that the critical frequency in both unconsolidated and consolidated materials containing water and a nonaqueous phase liquid ranges typically from kHz to MHz. Thus engineering problems involving the dynamic response of an unsaturated porous medium to low excitation frequencies (e.g. seismic wave stimulation) should be accurately modeled by our equations after suitable initial and boundary conditions are imposed.
Finite element analysis of electromagnetic propagation in an absorbing wave guide
Baumeister, Kenneth J.
1986-01-01
Wave guides play a significant role in microwave space communication systems. The attenuation per unit length of the guide depends on its construction and design frequency range. A finite element Galerkin formulation has been developed to study TM electromagnetic propagation in complex two-dimensional absorbing wave guides. The analysis models the electromagnetic absorptive characteristics of a general wave guide which could be used to determine wall losses or simulate resistive terminations fitted into the ends of a guide. It is believed that the general conclusions drawn by using this simpler two-dimensional geometry will be fundamentally the same for other geometries.
Electromagnetic wave propagation in a random distribution of C{sub 60} molecules
Energy Technology Data Exchange (ETDEWEB)
Moradi, Afshin, E-mail: a.moradi@kut.ac.ir [Department of Engineering Physics, Kermanshah University of Technology, Kermanshah, Iran and Department of Nano Sciences, Institute for Studies in Theoretical Physics and Mathematics (IPM), Tehran (Iran, Islamic Republic of)
2014-10-15
Propagation of electromagnetic waves in a random distribution of C{sub 60} molecules are investigated, within the framework of the classical electrodynamics. Electronic excitations over the each C{sub 60} molecule surface are modeled by a spherical layer of electron gas represented by two interacting fluids, which takes into account the different nature of the π and σ electrons. It is found that the present medium supports four modes of electromagnetic waves, where they can be divided into two groups: one group with shorter wavelength than the light waves of the same frequency and the other with longer wavelength than the free-space radiation.
FDTD simulation of EM wave propagation in 3-D media
Energy Technology Data Exchange (ETDEWEB)
Wang, T.; Tripp, A.C. [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Geology and Geophysics
1996-01-01
A finite-difference, time-domain solution to Maxwell`s equations has been developed for simulating electromagnetic wave propagation in 3-D media. The algorithm allows arbitrary electrical conductivity and permittivity variations within a model. The staggered grid technique of Yee is used to sample the fields. A new optimized second-order difference scheme is designed to approximate the spatial derivatives. Like the conventional fourth-order difference scheme, the optimized second-order scheme needs four discrete values to calculate a single derivative. However, the optimized scheme is accurate over a wider wavenumber range. Compared to the fourth-order scheme, the optimized scheme imposes stricter limitations on the time step sizes but allows coarser grids. The net effect is that the optimized scheme is more efficient in terms of computation time and memory requirement than the fourth-order scheme. The temporal derivatives are approximated by second-order central differences throughout. The Liao transmitting boundary conditions are used to truncate an open problem. A reflection coefficient analysis shows that this transmitting boundary condition works very well. However, it is subject to instability. A method that can be easily implemented is proposed to stabilize the boundary condition. The finite-difference solution is compared to closed-form solutions for conducting and nonconducting whole spaces and to an integral-equation solution for a 3-D body in a homogeneous half-space. In all cases, the finite-difference solutions are in good agreement with the other solutions. Finally, the use of the algorithm is demonstrated with a 3-D model. Numerical results show that both the magnetic field response and electric field response can be useful for shallow-depth and small-scale investigations.
Effects of internal waves on sound propagation in the shallow waters of the continental shelves
Ong, Ming Yi
2016-01-01
Approved for public release; distribution is unlimited Sound waves propagating through the oceans are refracted by internal waves. In the shallow waters of the continental shelves, an additional downward refraction of sound waves due to internal waves can cause them to interact more often with the seabed, resulting in additional energy from the sound waves being dissipated into the seabed. This study investigates how internal waves affect sound propagation on the continental shelves. It fi...
Wave groups in unidirectional surface wave models
van Groesen, Embrecht W.C.
1998-01-01
Uni-directional wave models are used to study wave groups that appear in wave tanks of hydrodynamic laboratories; characteristic for waves in such tanks is that the wave length is rather small, comparable to the depth of the layer. In second-order theory, the resulting Nonlinear Schrödinger (NLS)
Directory of Open Access Journals (Sweden)
Ibrahim K. Abu Seif
2015-01-01
Full Text Available In this paper a fast numerical algorithm to solve an integral equation model for wave propagation along a perfectly conducting two-dimensional terrain is suggested. It is applied to different actual terrain profiles and the results indicate very good agreement with published work. In addition, the proposed algorithm has achieved considerable saving in processing time. The formulation is extended to solve the propagation over lossy dielectric surfaces. A combined field integral equation (CFIE for wave propagation over dielectric terrain is solved efficiently by utilizing the method of moments with complex basis functions. The numerical results for different cases of dielectric surfaces are compared with the results of perfectly conducting surface evaluated by the IE conventional algorithm.
PROPAGATION AND STABILITY OF SUPERLUMINAL WAVES IN PULSAR WINDS
Energy Technology Data Exchange (ETDEWEB)
Mochol, Iwona; Kirk, John G., E-mail: iwona.mochol@mpi-hd.mpg.de, E-mail: john.kirk@mpi-hd.mpg.de [Max-Planck-Institut fuer Kernphysik, Postfach 10 39 80, D-69029 Heidelberg (Germany)
2013-07-01
Nonlinear electromagnetic waves with superluminal phase velocity can propagate in the winds around isolated pulsars, and around some pulsars in binary systems. Using a short-wavelength approximation, we find and analyze an integrable system of equations that govern their evolution in spherical geometry. A confined mode is identified that stagnates to finite pressure at large radius and can form a precursor to the termination shock. Using a simplified criterion, we find this mode is stable for most isolated pulsars, but may be unstable if the external pressure is high, such as in the pulsar wind nebulae in starburst galaxies and in W44. Pulsar winds in eccentric binary systems, such as PSR 1259-63, may go through phases with stable and unstable electromagnetic precursors, as well as phases in which the density is too high for these modes to propagate.
Electromagnetic waves propagation through a stochastic anisotropic medium
Energy Technology Data Exchange (ETDEWEB)
Ledinegg, E.
1985-01-01
Electromagnetic waves propagating through a stochastic medium are disturbed by field fluctuations. These can be treated by use of multiple scattering theories in order to get realistic results. In this paper, the multiple scattering theory developed by B.J. Uscinski is employed for anisotropic media and first and second-order field moments are calculated. Extending an earlier paper, the author considers primary fields with an arbitrary angle of incidence in order to investigate problems of practical interest (i.e.: radio propagation through the ionosphere between satellite and ground stations). As a result, it is shown that the attenuation factor of the first order field moment depends strongly on the angle of incidence due to media fluctuations.
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.
Energy Technology Data Exchange (ETDEWEB)
Romeo, Francesco [Dipartimento di Ingegneria Strutturale e Geotecnica, Universita di Roma ' La Sapienza' , Via Gramsci 53, 00197 Rome (Italy)] e-mail: francesco.romeo@uniromal.it; Rega, Giuseppe [Dipartimento di Ingegneria Strutturale e Geotecnica, Universita di Roma ' La Sapienza' , Via Gramsci 53, 00197 Rome (Italy)] e-mail: giuseppe.rega@uniromal.it
2006-02-01
Free wave propagation properties in one-dimensional chains of nonlinear oscillators are investigated by means of nonlinear maps. In this realm, the governing difference equations are regarded as symplectic nonlinear transformations relating the amplitudes in adjacent chain sites (n, n + 1) thereby considering a dynamical system where the location index n plays the role of the discrete time. Thus, wave propagation becomes synonymous of stability: finding regions of propagating wave solutions is equivalent to finding regions of linearly stable map solutions. Mechanical models of chains of linearly coupled nonlinear oscillators are investigated. Pass- and stop-band regions of the mono-coupled periodic system are analytically determined for period-q orbits as they are governed by the eigenvalues of the linearized 2D map arising from linear stability analysis of periodic orbits. Then, equivalent chains of nonlinear oscillators in complex domain are tackled. Also in this case, where a 4D real map governs the wave transmission, the nonlinear pass- and stop-bands for periodic orbits are analytically determined by extending the 2D map analysis. The analytical findings concerning the propagation properties are then compared with numerical results obtained through nonlinear map iteration.
Anisotropic stress as a signature of nonstandard propagation of gravitational waves.
Saltas, Ippocratis D; Sawicki, Ignacy; Amendola, Luca; Kunz, Martin
2014-11-07
We make precise the heretofore ambiguous statement that anisotropic stress is a sign of a modification of gravity. We show that in cosmological solutions of very general classes of models extending gravity-all scalar-tensor theories (Horndeski), Einstein-aether models, and bimetric massive gravity-a direct correspondence exists between perfect fluids apparently carrying anisotropic stress and a modification in the propagation of gravitational waves. Since the anisotropic stress can be measured in a model-independent manner, a comparison of the behavior of gravitational waves from cosmological sources with large-scale-structure formation could, in principle, lead to new constraints on the theory of gravity.
Vertical elliptic operator for efficient wave propagation in TTI media
Waheed, Umair bin
2015-08-19
Elliptic wave extrapolation operators require significantly less computational cost than the ones for transversely isotropic (TI) media. However, it does not provide accurate wavefield representation or imaging for the prevalent TI media. We propose a new vertical elliptically anisotropic (VEA) wave equation by decomposing the acoustic TI pseudo-differential wave equation. The decomposition results in a vertical elliptic differential equation and a scalar operator. The new VEA-like wave equation shares the same dispersion relation as that of the original acoustic TI wave equation. Therefore, the kinematic contents are correctly matched to the original equation. Moreover, the proposed decomposition yields better amplitude properties than the isotropic decomposition without increasing the computational load. Therefore, it exhibits better cost versus accuracy tradeoff compared to the isotropic or the tilted elliptic decompositions. We demonstrate with numerical examples that the proposed methodology is numerically stable for complex models and is free from shear-wave artifacts.
Radio Wave Propagation Simulation on the Cray T3D
Guidec, Frédéric; Kuonen, Pierre; Calégari, Patrice
1997-01-01
International audience; The ParFlow method permits the simulation of outdoor wave propagation in urban environment, describing the physical system in terms of the motion of fictitious particles over a lattice. This paper begins with a brief introduction to the ParFlow method. It then reports the design, the implementation in C++, and the experimentation on a Cray T3D of ParFlow++, an object-oriented parallel irregular implementation of the ParFlow method, primarily targeted at MIMD-DM platforms.
Efficient techniques for wave-based sound propagation in interactive applications
Mehra, Ravish
Sound propagation techniques model the effect of the environment on sound waves and predict their behavior from point of emission at the source to the final point of arrival at the listener. Sound is a pressure wave produced by mechanical vibration of a surface that propagates through a medium such as air or water, and the problem of sound propagation can be formulated mathematically as a second-order partial differential equation called the wave equation. Accurate techniques based on solving the wave equation, also called the wave-based techniques, are too expensive computationally and memory-wise. Therefore, these techniques face many challenges in terms of their applicability in interactive applications including sound propagation in large environments, time-varying source and listener directivity, and high simulation cost for mid-frequencies. In this dissertation, we propose a set of efficient wave-based sound propagation techniques that solve these three challenges and enable the use of wave-based sound propagation in interactive applications. Firstly, we propose a novel equivalent source technique for interactive wave-based sound propagation in large scenes spanning hundreds of meters. It is based on the equivalent source theory used for solving radiation and scattering problems in acoustics and electromagnetics. Instead of using a volumetric or surface-based approach, this technique takes an object-centric approach to sound propagation. The proposed equivalent source technique generates realistic acoustic effects and takes orders of magnitude less runtime memory compared to prior wave-based techniques. Secondly, we present an efficient framework for handling time-varying source and listener directivity for interactive wave-based sound propagation. The source directivity is represented as a linear combination of elementary spherical harmonic sources. This spherical harmonic-based representation of source directivity can support analytical, data
Hu, Dingzhu; Tian, Wenshou; Xie, Fei; Wang, Chunxiao; Zhang, Jiankai
2015-08-01
This paper uses a state-of-the-art general circulation model to study the impacts of the stratospheric ozone depletion from 1980 to 2000 and the expected partial ozone recovery from 2000 to 2020 on the propagation of planetary waves in December, January, and February. In the Southern Hemisphere (SH), the stratospheric ozone depletion leads to a cooler and stronger Antarctic stratosphere, while the stratospheric ozone recovery has the opposite effects. In the Northern Hemisphere (NH), the impacts of the stratospheric ozone depletion on polar stratospheric temperature are not opposite to that of the stratospheric ozone recovery; i.e., the stratospheric ozone depletion causes a weak cooling and the stratospheric ozone recovery causes a statistically significant cooling. The stratospheric ozone depletion leads to a weakening of the Arctic polar vortex, while the stratospheric ozone recovery leads to a strengthening of the Arctic polar vortex. The cooling of the Arctic polar vortex is found to be dynamically induced via modulating the planetary wave activity by stratospheric ozone increases. Particularly interesting is that stratospheric ozone changes have opposite effects on the stationary and transient wave fluxes in the NH stratosphere. The analysis of the wave refractive index and Eliassen-Palm flux in the NH indicates (1) that the wave refraction in the stratosphere cannot fully explain wave flux changes in the Arctic stratosphere and (2) that stratospheric ozone changes can cause changes in wave propagation in the northern midlatitude troposphere which in turn affect wave fluxes in the NH stratosphere. In the SH, the radiative cooling (warming) caused by stratospheric ozone depletion (recovery) produces a larger (smaller) meridional temperature gradient in the midlatitude upper troposphere, accompanied by larger (smaller) zonal wind vertical shear and larger (smaller) vertical gradients of buoyancy frequency. Hence, there are more (fewer) transient waves
Cui, Linyan
2014-09-01
Current theoretical temporal power spectra models of an optical wave have been developed for terrestrial environments. The interactions between humidity and temperature fluctuations in the marine atmospheric environments make the marine atmospheric turbulence particularly challenging, and the optical waves' propagation through marine turbulence exhibits a different behavior with respect to terrestrial propagation. In this paper, the temporal power spectra of irradiance scintillation under weak marine atmospheric turbulence, which is one of the key temporal statistics to describe the correlation of irradiance fluctuations at different time instances, is investigated in detail both analytically and numerically. Closed-form expressions for the temporal power spectra of irradiance scintillation are derived for infrared plane and spherical waves under weak marine atmospheric turbulence, and they consider physically the influences of finite turbulence inner and outer scales. The final results indicate that the marine atmospheric turbulence brings more effects on the irradiance scintillation than the terrestrial atmospheric turbulence.
Lieske, Mike; Schlurmann, Torsten
2016-04-01
INTRODUCTION & MOTIVATION The design of structures in coastal and offshore areas and their maintenance are key components of coastal protection. Usually, assessments of processes and loads on coastal structures are derived from experiments with flow and wave parameters in separate physical models. However, Peregrin (1976) already points out that processes in natural shallow coastal waters flow and sea state processes do not occur separately, but influence each other nonlinearly. Kemp & Simons (1982) perform 2D laboratory tests and study the interactions between a turbulent flow and following waves. They highlight the significance of wave-induced changes in the current properties, especially in the mean flow profiles, and draw attention to turbulent fluctuations and bottom shear stresses. Kemp & Simons (1983) also study these processes and features with opposing waves. Studies on the wave-current interaction in three-dimensional space for a certain wave height, wave period and water depth were conducted by MacIver et al. (2006). The research focus is set on the investigation of long-crested waves on obliquely opposing and following currents in the new 3D wave-current basin. METHODOLOGY In a first step the flow analysis without waves is carried out and includes measurements of flow profiles in the sweet spot of the basin at predefined measurement positions. Five measuring points in the water column have been delineated in different water depths in order to obtain vertical flow profiles. For the characterization of the undisturbed flow properties in the basin, an uniformly distributed flow was generated in the wave basin. In the second step wave analysis without current, the unidirectional wave propagation and wave height were investigated for long-crested waves in intermediate wave conditions. In the sweet spot of the wave basin waves with three different wave directions, three wave periods and uniform wave steepness were examined. For evaluation, we applied a common
Full wave simulations of fast wave mode conversion and lower hybrid wave propagation in tokamaks
DEFF Research Database (Denmark)
Wright, J.C.; Bonoli, P.T.; Brambilla, M.
2004-01-01
). Two full wave codes, a massively-parallel-processor (MPP) version of the TORIC-2D finite Larmor radius code [M. Brambilla, Plasma Phys. Controlled Fusion 41, 1 (1999)] and also an all orders spectral code AORSA2D [E. F. Jaeger , Phys. Plasmas 9, 1873 (2002)], have been developed which for the first......Fast wave (FW) studies of mode conversion (MC) processes at the ion-ion hybrid layer in toroidal plasmas must capture the disparate scales of the FW and mode converted ion Bernstein and ion cyclotron waves. Correct modeling of the MC layer requires resolving wavelengths on the order of k...... time are capable of achieving the resolution and speed necessary to address mode conversion phenomena in full two-dimensional (2-D) toroidal geometry. These codes have been used in conjunction with theory and experimental data from the Alcator C-Mod [I. H. Hutchinson , Phys. Plasmas 1, 1511 (1994...
Off-great-circle propagation of teleseismic surface waves across AlpArray
Kolínský, Petr; Fuchs, Florian; Bokelmann, Götz; AlpArray Working Group
2017-04-01
Distributed across the greater Alpine region in Europe, the AlpArray seismic network stretches hundreds of kilometers in width and more than thousand kilometers in length, with interstation distances around 40 km. AlpArray can thus be used to study heterogeneities in crust and mantle by their influence on long-period surface waves propagating from distant earthquakes to the array. The heterogeneous structure of the orogenic belt may produce characteristic effects on the propagation pattern of surface waves as they pass through the region. We present a mapping of true propagation paths of 20 - 150 s surface waves that deviate from the great-circles as they propagate from the source to the receiver. We utilize array beamforming techniques to investigate (deterministic) surface waves from regional and teleseismic earthquakes. The signal is well-recognized and the fundamental mode for both Love and Rayleigh waves is separated before the beamforming. Instead of searching for energy of all possible signals as used in traditional beamforming, we identify the frequency-dependence of surface wave phase velocity and the true backazimuths of propagation. We consider each AlpArray station as a centre of a subarray of neighboring (6 - 15) stations. This allows us to calculate the local phase velocity dispersion curves for individual subarrays with a diameter of approximately 80 - 100 km. We repeat the procedure for more than 450 stations included in the AlpArray project. By the beamforming, phase velocities are corrected for the true propagation backazimuth, which is slightly frequency-dependent for each event. The local phase velocity dispersion curves for each subarray are inverted for the local 1D velocity model. In addition, the true backazimuths determined for each subarray and plotted for all the subarrays together show the frequency-dependent propagation paths through the whole Alpine region. To benchmark the backazimuths from the array measurement of phase velocities
Fan, Z; Lowe, M J S; Castaings, M; Bacon, C
2008-10-01
Guided torsional waves in a bar with a noncircular cross section have been exploited by previous researchers to measure the density of fluids. However, due to the complexity of the wave behavior in the noncircular cross-sectional shape, the previous theory can only provide an approximate prediction; thus the accuracy of the measurement has been compromised. In this paper, a semianalytical finite element method is developed to model accurately the propagation velocity and leakage of guided waves along an immersed waveguide with arbitrary noncircular cross section. An accurate inverse model is then provided to measure the density of the fluid by measuring the change of the torsional wave speed. Experimental results obtained with a rectangular bar in a range of fluids show very good agreement with the theoretical predictions. Finally, the potentials to use the model for sensor optimization are discussed.
Fourier Transform Ultrasound Spectroscopy for the determination of wave propagation parameters.
Pal, Barnana
2017-01-01
The reported results for ultrasonic wave attenuation constant (α) in pure water show noticeable inconsistency in magnitude. A "Propagating-Wave" model analysis of the most popular pulse-echo technique indicates that this is a consequence of the inherent wave propagation characteristics in a bounded medium. In the present work Fourier Transform Ultrasound Spectroscopy (FTUS) is adopted to determine ultrasonic wave propagation parameters, the wave number (k) and attenuation constant (α) at 1MHz frequency in tri-distilled water at room temperature (25°C). Pulse-echo signals obtained under same experimental conditions regarding the exciting input signal and reflecting boundary wall of the water container for various lengths of water columns are captured. The Fast Fourier Transform (FFT) components of the echo signals are taken to compute k, α and r, the reflection constant at the boundary, using Oak Ridge and Oxford method. The results are compared with existing literature values. Copyright © 2016 Elsevier B.V. All rights reserved.
PROPAGATION AND DISPERSION OF SAUSAGE WAVE TRAINS IN MAGNETIC FLUX TUBES
Energy Technology Data Exchange (ETDEWEB)
Oliver, R.; Terradas, J. [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Ruderman, M. S., E-mail: ramon.oliver@uib.es [School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)
2015-06-10
A localized perturbation of a magnetic flux tube produces wave trains that disperse as they propagate along the tube, where the extent of dispersion depends on the physical properties of the magnetic structure, on the length of the initial excitation, and on its nature (e.g., transverse or axisymmetric). In Oliver et al. we considered a transverse initial perturbation, whereas the temporal evolution of an axisymmetric one is examined here. In both papers we use a method based on Fourier integrals to solve the initial value problem. We find that the propagating wave train undergoes stronger attenuation for longer axisymmetric (or shorter transverse) perturbations, while the internal to external density ratio has a smaller effect on the attenuation. Moreover, for parameter values typical of coronal loops axisymmetric (transverse) wave trains travel at a speed 0.75–1 (1.2) times the Alfvén speed of the magnetic tube. In both cases, the wave train passage at a fixed position of the magnetic tube gives rise to oscillations with periods of the order of seconds, with axisymmetric disturbances causing more oscillations than transverse ones. To test the detectability of propagating transverse or axisymmetric wave packets in magnetic tubes of the solar atmosphere (e.g., coronal loops, spicules, or prominence threads) a forward modeling of the perturbations must be carried out.
Travelling waves in the lattice epidemic model
Directory of Open Access Journals (Sweden)
Zhixian Yu
2010-07-01
Full Text Available In this article, we establish the existence and nonexistence of travelling waves for a lattice non-monotone integral equation which is an epidemic model. Moreover, the wave is either convergent to the positive equilibrium or oscillating on the positive equilibrium at positive infinity, and has the exponential asymptotic behavior at negative infinity. For the non-monotone case, the asymptotic speed of propagation also coincides with the minimal wave speed.
Obliquely propagating large amplitude solitary waves in charge neutral plasmas
Directory of Open Access Journals (Sweden)
F. Verheest
2007-01-01
Full Text Available This paper deals in a consistent way with the implications, for the existence of large amplitude stationary structures in general plasmas, of assuming strict charge neutrality between electrons and ions. With the limit of pair plasmas in mind, electron inertia is retained. Combining in a fluid dynamic treatment the conservation of mass, momentum and energy with strict charge neutrality has indicated that nonlinear solitary waves (as e.g. oscillitons cannot exist in electron-ion plasmas, at no angle of propagation with respect to the static magnetic field. Specifically for oblique propagation, the proof has turned out to be more involved than for parallel or perpendicular modes. The only exception is pair plasmas that are able to support large charge neutral solitons, owing to the high degree of symmetry naturally inherent in such plasmas. The nonexistence, in particular, of oscillitons is attributed to the breakdown of the plasma approximation in dealing with Poisson's law, rather than to relativistic effects. It is hoped that future space observations will allow to discriminate between oscillitons and large wave packets, by focusing on the time variability (or not of the phase, since the amplitude or envelope graphs look very similar.
Wave Propagation in Lossy and Superconducting Circular Waveguides
Directory of Open Access Journals (Sweden)
K. H. Yeap
2010-06-01
Full Text Available We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly.
Surface Waves Propagating on Grounded Anisotropic Dielectric Slab
Directory of Open Access Journals (Sweden)
Zhuozhu Chen
2018-01-01
Full Text Available This paper investigates the characteristics of surface waves propagating on a grounded anisotropic dielectric slab. Distinct from the existing analyses that generally assume that the fields of surface wave uniformly distribute along the transverse direction of the infinitely large grounded slab, our method takes into account the field variations along the transverse direction of a finite-width slab. By solving Maxwell’s equations in closed-form, it is revealed that no pure transverse magnetic (TM or transverse electric (TE mode exists if the fields are non-uniformly distributed along the transverse direction of the grounded slab. Instead, two hybrid modes, namely quasi-TM and quasi-TE modes, are supported. In addition, the propagation characteristics of two hybrid modes supported by the grounded anisotropic slab are analyzed in terms of the slab thickness, slab width, as well as the relative permittivity tensor of the anisotropic slab. Furthermore, different methods are employed to compare the analyses, as well as to validate our derivations. The proposed method is very suitable for practical engineering applications.
DEFF Research Database (Denmark)
Burcharth, H. F.; Larsen, Brian Juul
The investigation concerns the design of a new internal breakwater in the main port of Ibiza. The objective of the model tests was in the first hand to optimize the cross section to make the wave reflection low enough to ensure that unacceptable wave agitation will not occur in the port. Secondly...... wave overtopping was studied as well....
Herbold, G.; Ulmschneider, P.; Spruit, H. C.; Rosner, R.
1985-01-01
For solar magnetic flux tubes three types of waves are compared: longitudinal MHD tube waves, acoustic tube waves propagating in the same tube geometry but with rigid walls and ordinary acoustic waves in plane geometry. It is found that the effect of the distensibility of the tube is small and that longitudinal waves are essentially acoustic tube waves. Due to the tube geometry there is considerable difference between longitudinal waves or acoustic tube waves and ordinary acoustic waves. Longitudinal waves as well as acoustic tube waves show a smaller amplitude growth, larger shock formation heights, smaller mean chromospheric temperature but a steeper dependence of the temperature gradient on wave period.
Viscothermal wave propagation including acousto-elastic interaction, part I: theory
Beltman, W.M.
1999-01-01
This research deals with pressure waves in a gas trapped in thin layers or narrow tubes. In these cases viscous and thermal effects can have a significant effect on the propagation of waves. This so-called viscothermal wave propagation is governed by a number of dimensionless parameters. The two
Fuh, Andy Ying-Guey; Li, Ming Shian; Wu, Shing Trong
2011-07-04
This study investigates the transversely propagating waves in a body-centered tetragonal photonic crystal based on a holographic polymer-dispersed liquid crystal film. Rotating the film reveals three different transverse propagating waves. Degeneracy of optical Bloch waves from reciprocal lattice vectors explains their symmetrical distribution.
Working towards a numerical solver for seismic wave propagation in unsaturated porous media
Boxberg, Marc S.; Friederich, Wolfgang
2017-04-01
Modeling the propagation of seismic waves in porous media gets more and more popular in the seismological community. However, it is still a challenging task in the field of computational seismology. Nevertheless, it is important to account for the fluid content of, e.g., reservoir rocks or soils, and the interaction between the fluid and the rock or between different immiscible fluids to accurately describe seismic wave propagation through such porous media. Often, numerical models are based on the elastic wave equation and some might include artificially introduced attenuation. This simplifies the computation, because it only approximates the physics behind that problem. However, the results are also simplified and could miss phenomena and lack accuracy in some applications. We present a numerical solver for wave propagation in porous media saturated by two immiscible fluids. It is based on Biot's theory of poroelasticity and accounts for macroscopic flow that occurs on the same scale as the wavelength of the seismic waves. Fluid flow is described by a Darcy type flow law and interactions between the fluids by means of capillary pressure curve models. In addition, consistent boundary conditions on interfaces between poroelastic media and elastic or acoustic media are derived from this poroelastic theory itself. The poroelastic solver is integrated into the larger software package NEXD that uses the nodal discontinuous Galerkin method to solve wave equations in 1D, 2D, and 3D on a mesh of linear (1D), triangular (2D), or tetrahedral (3D) elements. Triangular and tetrahedral elements have great advantages as soon as the model has a complex structure, like it is often the case for geologic models. We illustrate the capabilities of the codes by numerical examples. This work can be applied to various scientific questions in, e.g., exploration and monitoring of hydrocarbon or geothermal reservoirs as well as CO2 storage sites.
A vector model for error propagation
Energy Technology Data Exchange (ETDEWEB)
Smith, D.L.; Geraldo, L.P.
1989-03-01
A simple vector model for error propagation, which is entirely equivalent to the conventional statistical approach, is discussed. It offers considerable insight into the nature of error propagation while, at the same time, readily demonstrating the significance of uncertainty correlations. This model is well suited to the analysis of error for sets of neutron-induced reaction cross sections. 7 refs., 1 fig.
Directory of Open Access Journals (Sweden)
Mahmood Falah
2015-01-01
Full Text Available In this paper, we implement real irregular terrain model in computer program by using image processing. We show how this approach can be used in simulation of E.M. wave propagation on irregular earth’s surface in a realistic manner. Some simulations are performed for implementation of longitudinal height differences over the propagation path as PEC surface .We also describe that how this approach can be used for any boundary condition in computational space. The results observed in Snapshots of the field profiles taken at different simulation times, validates capability of this method.
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.
Assessment of the hybrid propagation model, Volume 1: Analysis of noise propagation effects
2012-08-31
This is the first of two volumes of a report on the Hybrid Propagation Model (HPM), an advanced prediction model for aviation noise propagation. This volume presents the noise level predictions for eleven different sets of propagation conditions, run...
Propagation of Nonlinear Surface Waves over Viscoelastic Mud
Sharifi-Neyestani, E.; Tahvildari, N.
2016-12-01
Mud is ubiquitous in coastal waters, and it is well known that surface waves dissipate strongly over a muddy seabed. An accurate model for wave evolution requires an accurate characterization of mud rheology. There has been several assumptions for mud rheology. In this study, we incorporate a mud-induced damping mechanism in a frequency-domain phase-resolving nonlinear wave model. The mud layer is assumed to be thin and behave as a viscoelastic medium. First, model results for monochromatic surface waves are compared with laboratory experiments and a good comparison is obtained. It is shown that increasing the mud elasticity results in a decrease in damping and an increase in phase-shift from the case with a purely viscous mud. The validated model is then employed to examine the combined effect of mud viscosity and elasticity on evolution of surface wave spectrum. Two-dimensional simulations demonstrate strong wave dissipation over a mud patch resulting in a significant diffraction in the lee side.
Energy Technology Data Exchange (ETDEWEB)
Goldstein, P; Ryall, F D; Pasyanos, M E; Schultz, C A; Walter, W R
2000-07-18
An important challenge for seismic monitoring of nuclear explosions at low magnitude to verify a nuclear-test-ban treaty is the development of techniques that use regional phases for detection, location, and identification. In order to use such phases, region-specific earth models and tools are needed that accurately predict features such as travel times, amplitudes, and spectral characteristics. In this paper, we present our efforts to use two-dimensional finite-difference modeling to help develop and validate regional earth models for the Middle East and North Africa and to develop predictive algorithms for identifying anomalous regional phases. To help develop and validate a model for the Middle East and North Africa, we compare data and finite-difference simulations for selected regions. We show that the proposed three-dimensional regional model is a significant improvement over standard one-dimensional models by comparing features of broadband data and simulations and differences between observed and predicted features such as narrow-band group velocities. We show how a potential trade-off between source and structure can be avoided by constraining source parameters such as depth, mechanism, and moment/source-time function with independent data. We also present numerous observations of anomalous timing and amplitude of regional phases and show how incorporation of two-dimensional structure can explain many of these observations. Based on these observations, and the predictive capability of our simulations, we develop a simple model that can accurately predict the timing of such phases.
Propagating semantic information in biochemical network models
Directory of Open Access Journals (Sweden)
Schulz Marvin
2012-01-01
Full Text Available Abstract Background To enable automatic searches, alignments, and model combination, the elements of systems biology models need to be compared and matched across models. Elements can be identified by machine-readable biological annotations, but assigning such annotations and matching non-annotated elements is tedious work and calls for automation. Results A new method called "semantic propagation" allows the comparison of model elements based not only on their own annotations, but also on annotations of surrounding elements in the network. One may either propagate feature vectors, describing the annotations of individual elements, or quantitative similarities between elements from different models. Based on semantic propagation, we align partially annotated models and find annotations for non-annotated model elements. Conclusions Semantic propagation and model alignment are included in the open-source library semanticSBML, available on sourceforge. Online services for model alignment and for annotation prediction can be used at http://www.semanticsbml.org.
Observations of up- and downward propagating gravity waves in the strato- and mesosphere.
Strelnikova, Irina; Baumgarten, Gerd; Lübken, Franz-Josef; Hildebrand, Jens; Höffner, Josef; Stober, Gunter
2017-04-01
Experimental and modeling efforts show that small-scale gravity waves (GW) essentially affect large-scale circulations, thermal states, and dynamics from the surface to the middle atmosphere. In climate modeling and weather-forecasting applications the gravity-wave drag and its interaction with large-scale dynamics are referred to as sub-gridscale, i.e. unresolved processes and are the most uncertain aspect of these models. Advances in lidar measurement techniques allow for experimental studies of GWs at very small spatial and temporal scales, which are not accessible by other means. The state of the art Doppler lidars and radars at the ALOMAR research station located in Northern Norway (69°N, 16°E) provide an observational database of GWs at the edge of the polar vortex connected to global dynamics of the Earth atmosphere. Doppler Rayleigh Iodine System (DoRIS) provides horizontal wind measurements in addition to the temperature observation. The altitude coverage is extended from 30 to 110 km by using the temperature observed by mobile Fe lidar with wind observations taken from meteor radar system. This give us unique possibility to obtain wave propagation direction, intrinsic frequency and horizontal wavelength from the single station. Making use of the advantage of this system, we derive wave parameters more precisely, and under some conditions we observe waves with downward propagating energy. In this paper we will present results of analyses of the GW observations by lidars and radars and discuss implications on atmospheric dynamics.
Hrepic, Zdeslav; Zollman, Dean A.; Rebello, N. Sanjay
2010-01-01
We investigated introductory physics students' mental models of sound propagation. We used a phenomenographic method to analyze the data in the study. In addition to the scientifically accepted Wave model, students used the "Entity" model to describe the propagation of sound. In this latter model sound is a self-standing entity,…
Energy Technology Data Exchange (ETDEWEB)
Vinas, A.F.; Goldstein, M.L. (National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center)
1991-08-01
The parametric decay and modulational instabilities of a large-amplitude circularly polarized dispersive Alfven wave are investigated. The treatment is more general than that of previous derivations based on the two-fluid equations in that allowance is made for propagation of the unstable daughter waves at arbitrary angles to the background magnetic field, although the main concern is the exploration of new aspects of propagation parallel to the DC magnetic field. In addition to the well-known coupling of pump waves to electrostatic daughter waves, a new parametric channel is found where the pump wave couples directly to electromagnetic daughter waves. The growth rate of the electromagnetic instability increases monotonically with increasing pump wave amplitude. Analysis confirms that, for decay, the dominant process is coupling to electrostatic daughter waves, at least for parallel propagation. For modulation, the coupling to electromagnetic daughter waves usually dominates, suggesting that the parametric modulational instability is really an electromagnetic phenomena. (author).
Experimental research on dust lifting by propagating shock wave
Żydak, P.; Oleszczak, P.; Klemens, R.
2017-03-01
The aim of the presented work was to study the dust lifting process from a layer of dust behind a propagating shock wave. The experiments were conducted with the use of a shock tube and a specially constructed, five-channel laser optical device enabling measurements at five positions located in one vertical plane along the height of the tube. The system enabled measurements of the delay in lifting up of the dust from the layer, and the vertical velocity of the dust cloud was calculated from the dust concentration measurements. The research was carried out for various initial conditions and for three fractions of black coal dust. In the presented tests, three shock wave velocities: 450, 490 and 518 m/s and three dust layer thicknesses, equal to 1.0, 1.5 and 2.0 mm, were taken into consideration. On the grounds of the obtained experimental results, it was assumed that the vertical component of the lifted dust velocity is a function of the dust particle diameter, the velocity of the air flow in the channel, the layer thickness and the dust bulk density. It appeared, however, that lifting up of the dust from the thick layers, thicker than 1 mm, is a more complex process than that from thin layers and still requires further research. A possible explanation is that the shock wave action upon the thick layer results in its aggregation in the first stage of the dispersing process, which suppresses the dust lifting process.
Laser Beam Propagation Through Inhomogeneous Media with Shock-Like Profiles: Modeling and Computing
Adamovsky, Grigory; Ida, Nathan
1997-01-01
Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in wave propagation through shocks in supersonic flows. Results of experiments conducted in the past few years has shown such interesting phenomena as a laser beam splitting and spreading. The paper describes a model constructed to propagate a laser beam through shock-like inhomogeneous media. Numerical techniques are presented to compute the beam through such media. The results of computation are presented, discussed, and compared with experimental data.
Modeling broadband poroelastic propagation using an asymptotic approach
Energy Technology Data Exchange (ETDEWEB)
Vasco, Donald W.
2009-05-01
An asymptotic method, valid in the presence of smoothly-varying heterogeneity, is used to derive a semi-analytic solution to the equations for fluid and solid displacements in a poroelastic medium. The solution is defined along trajectories through the porous medium model, in the manner of ray theory. The lowest order expression in the asymptotic expansion provides an eikonal equation for the phase. There are three modes of propagation, two modes of longitudinal displacement and a single mode of transverse displacement. The two longitudinal modes define the Biot fast and slow waves which have very different propagation characteristics. In the limit of low frequency, the Biot slow wave propagates as a diffusive disturbance, in essence a transient pressure pulse. Conversely, at low frequencies the Biot fast wave and the transverse mode are modified elastic waves. At intermediate frequencies the wave characteristics of the longitudinal modes are mixed. A comparison of the asymptotic solution with analytic and numerical solutions shows reasonably good agreement for both homogeneous and heterogeneous Earth models.
On the propagation of elasto-thermodiffusive surface waves in heat-conducting materials
Sharma, J. N.; Sharma, Y. D.; Sharma, P. K.
2008-09-01
The present paper deals with the study of the propagation of Rayleigh surface waves in homogeneous isotropic, thermodiffusive elastic half-space. After developing the formal solution of the model, the secular equations for stress free, thermally insulated or isothermal, and isoconcentrated boundary conditions of the half-space have been obtained. The secular equations have been solved by using irreducible Cardano's method with the help of DeMoivre's theorem in order to obtain phase velocity and attenuation coefficient of waves under consideration. The motion of the surface particles during the Rayleigh surface wave propagation is also discussed and found to be elliptical in general. The inclinations of wave normal with the major axis of the elliptical path of a typical particle have also been computed. Finally, the numerically simulated results regarding phase velocity, attenuation coefficient, specific loss and thermo-mechanical coupling factors of thermoelastic diffusive waves have been obtained and presented graphically. Some very interesting and useful characteristics of surface acoustic waves have been obtained, which may help in improving the fabrication quality of optical and electronic devices in addition to construction and design of materials such as semiconductors and composite structures. Therefore, this work finds applications in the geophysics and electronics industry.
Observational indications of downward-propagating gravity waves in middle atmosphere lidar data
Kaifler, N.; Kaifler, B.; Ehard, B.; Gisinger, S.; Dörnbrack, A.; Rapp, M.; Kivi, R.; Kozlovsky, A.; Lester, M.; Liley, B.
2017-09-01
Two Rayleigh lidars were employed at a southern-hemisphere mid-latitude site in New Zealand (45°S) and a northern-hemisphere high-latitude site in Finland (67°N) in order to observe gravity waves between 30 and 85 km altitude under wintertime conditions. Two-dimensional wavelet analysis is used to analyze temperature perturbations caused by gravity waves and to determine their vertical wavelengths and phase progression. In both datasets, upward phase progression waves occur frequently between 30 and 85 km altitude. Six cases of large-amplitude wave packets are selected which exhibit upward phase progression in the stratosphere and/or mesosphere. We argue that these wave packets propagate downward and we discuss possible wave generation mechanisms. Spectral analysis reveals that superpositions of two or three wave packets are common. Furthermore, their characteristics often match those of upward-propagating waves which are observed at the same time or earlier. In the dataset means, the contribution of upward phase progression waves to the potential energy density Ep is largest in the lower stratosphere above Finland. There, Ep of upward and downward phase progression waves is comparable. At 85 km one third of the potential energy carried by propagating waves is attributed to upward phase progression waves. In some cases Ep of upward phase progression waves far exceeds Ep of downward phase progression waves. The downward-propagating waves might be generated in situ in the middle atmosphere or arise from reflection of upward-propagating waves.
DEFF Research Database (Denmark)
Bertelli, N.; Balakin, A.A.; Westerhof, E.
2010-01-01
A numerical analysis of the electron cyclotron (EC) wave beam propagation in the presence of edge density fluctuations by means of a quasi-optical code [Balakin A. A. et al, Nucl. Fusion 48 (2008) 065003] is presented. The effects of the density fluctuations on the wave beam propagation are estim......A numerical analysis of the electron cyclotron (EC) wave beam propagation in the presence of edge density fluctuations by means of a quasi-optical code [Balakin A. A. et al, Nucl. Fusion 48 (2008) 065003] is presented. The effects of the density fluctuations on the wave beam propagation...
Energy Technology Data Exchange (ETDEWEB)
Zhang, Sun, E-mail: szhang@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210008 (China); Joint Center for Particle, Nuclear Physics and Cosmology (J-CPNPC), PMO-NJU, Nanjing 210008 (China)
2014-02-05
In this Letter, we have studied the shock wave and discontinuity propagation for relativistic superfluid with spontaneous U(1) symmetry breaking in the framework of hydrodynamics. General features of shock waves are provided, the propagation of discontinuity and the sound modes of shock waves are also presented. The first sound and the second sound are identified as the propagation of discontinuity, and the results are in agreement with earlier theoretical studies. Moreover, a differential equation, called the growth equation, is obtained to describe the decay and growth of the discontinuity propagating along its normal trajectory. The solution is in an integral form and special cases of diverging waves are also discussed.
Object-oriented parallel software for radio wave propagation simulation in urban environment
F. Guidec; P. Calégari; P. Kuonen; M. Pahud
2012-01-01
The objective of the European project STORMS (Software Tools for the Optimization of Resources in Mobile Systems) is to develop a software tool to be used for design and planning of the future Universal Mobile Telecommunication System (UMTS). In this context the ParFlow method permits the simulation of outdoor radio wave propagation in urban environment, modeling the physical system in terms of the motion of fictitious microscopic particles over a lattice. This paper gives an overview of the ...
Guidec, Frédéric; Calégari, Patrice; Kuonen, Pierre; Pahud, Michel
1999-01-01
International audience; The objective of the European project STORMS (Software Tools for the Optimization of Resources in Mobile Systems) is to develop a software tool to be used for the design and the planning of the future Universal Mobile Telecommunication System (UMTS). In this context the ParFlow method permits the simulation of outdoor radio wave propagation in urban environment, modeling the physical system in terms of the motion of fictitious microscopic particles over a lattice. This...
Miller, Nathaniel; Lizarralde, Daniel
2016-01-01
Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, with slowest speeds in the fault-normal direction. Propagation is fastest along faults, but, for fault widths on the order of the seismic wavelength, apparent wave speeds in this direction depend on frequency. For the 5–12 Hz Pn arrivals used in tomographic studies, joint-parallel wavefronts are slowed by joints. This delay can account for the slowing seen in tomographic images of the outer rise upper mantle. At the Middle America Trench, confining serpentine to fault zones, as opposed to a uniform distribution, reduces estimates of bulk upper mantle hydration from ~3.5 wt % to as low as 0.33 wt % H2O.
Li, Jiasong; Wang, Shang; Manapuram, Ravi Kiran; Singh, Manmohan; Menodiado, Floredes M.; Aglyamov, Salavat; Emelianov, Stanislav; Twa, Michael D.; Larin, Kirill V.
2013-12-01
We demonstrate the use of phase-stabilized swept-source optical coherence tomography to assess the propagation of low-amplitude (micron-level) waves induced by a focused air-pulse system in tissue-mimicking phantoms, a contact lens, a silicone eye model, and the mouse cornea in vivo. The results show that the wave velocity can be quantified from the analysis of wave propagation, thereby enabling the estimation of the sample elasticity using the model of surface wave propagation for the tissue-mimicking phantoms. This noninvasive, noncontact measurement technique involves low-force methods of tissue excitation that can be potentially used to assess the biomechanical properties of ocular and other delicate tissues in vivo.
Error Propagation in a System Model
Schloegel, Kirk (Inventor); Bhatt, Devesh (Inventor); Oglesby, David V. (Inventor); Madl, Gabor (Inventor)
2015-01-01
Embodiments of the present subject matter can enable the analysis of signal value errors for system models. In an example, signal value errors can be propagated through the functional blocks of a system model to analyze possible effects as the signal value errors impact incident functional blocks. This propagation of the errors can be applicable to many models of computation including avionics models, synchronous data flow, and Kahn process networks.
Studying propagation of seismic waves across the Valley of Mexico from correlations of seismic noise
Rivet, D. N.; Campillo, M.; Shapiro, N. M.; Singh, S.; Cruz Atienza, V. M.; Quintanar, L.; Valdés, C.
2009-12-01
We reconstruct Rayleigh and Love waves from cross-correlations of ambient seismic noise recorded at 22 broad-band stations of the MesoAmerica Seismic Experiment (MASE) and Valley of Mexico Experiment (VMEX). The cross-correlations are computed over 2 years of noise data for the 9 MASE stations and over 1 year for the 13 VMEX stations. Surface waves with sufficient signal-to-noise ratio are then used in the group velocity dispersion analysis. We use the reconstructed waveforms to measure group velocity dispersion curves at period of 0.5 to 5 seconds. For traveling path inside the lake-bed zone, the maximum energy is observed at velocity higher than expected for the fundamental mode. This indicates that the propagation within the Mexico basin is dominated by higher modes of surface waves that propagate deeper in the basin. We identify the propagation modes by comparing observations with theoretical dispersion curves and eigenfunctions calculated for Rayleigh and Loves waves associated with a given model of the upper crust. The fundamental mode shows a very low group velocity, determining factor in the long duration of the seismic signal. A better velocity constraint on the deeper structure of the basin is thus needed to fully understand this phenomenon.
Simulation analysis of effects of single fragment size on air-blast wave and fragment propagation
Directory of Open Access Journals (Sweden)
ZHENG Hongwei
2017-12-01
Full Text Available [Objectives] This paper involves the propagation and attenuation of the velocity and energy of air-blast waves and high-velocity fragments while taking their combined effects into account.[Methods] With ANSYS/LS-DYNA software, a simulation model of a columnar TNT air blast is built with prefabricated fragments affixed to its end. When the total quality of fragments is constant, the effects of a single fragment's size on the propagation of the air-blast wave and fragments are studied by changing the size of the single fragment.[Results] The results show that fragments greatly reduce the intensity and velocity of a shockwave, and block the air-blast waves behind them. When the total quality of the fragments remains constant, the effects of single fragment size on blast shockwave propagation characteristics show little difference. The smaller the single fragment, the more kinetic energy the fragments will have and the faster that energy will dissipate.[Conclusions] As a result, more attention should be paid to the combined effects of air-blast waves and high-velocity fragments. Such research can provide reference points for the deeper study of blast loads and their interaction.
Do calcium buffers always slow down the propagation of calcium waves?
Tsai, Je-Chiang
2013-12-01
Calcium buffers are large proteins that act as binding sites for free cytosolic calcium. Since a large fraction of cytosolic calcium is bound to calcium buffers, calcium waves are widely observed under the condition that free cytosolic calcium is heavily buffered. In addition, all physiological buffered excitable systems contain multiple buffers with different affinities. It is thus important to understand the properties of waves in excitable systems with the inclusion of buffers. There is an ongoing controversy about whether or not the addition of calcium buffers into the system always slows down the propagation of calcium waves. To solve this controversy, we incorporate the buffering effect into the generic excitable system, the FitzHugh-Nagumo model, to get the buffered FitzHugh-Nagumo model, and then to study the effect of the added buffer with large diffusivity on traveling waves of such a model in one spatial dimension. We can find a critical dissociation constant (K = K(a)) characterized by system excitability parameter a such that calcium buffers can be classified into two types: weak buffers (K ∈ (K(a), ∞)) and strong buffers (K ∈ (0, K(a))). We analytically show that the addition of weak buffers or strong buffers but with its total concentration b(0)(1) below some critical total concentration b(0,c)(1) into the system can generate a traveling wave of the resulting system which propagates faster than that of the origin system, provided that the diffusivity D1 of the added buffers is sufficiently large. Further, the magnitude of the wave speed of traveling waves of the resulting system is proportional to √D1 as D1 --> ∞. In contrast, the addition of strong buffers with the total concentration b(0)(1) > b(0,c)(1) into the system may not be able to support the formation of a biologically acceptable wave provided that the diffusivity D1 of the added buffers is sufficiently large.
Li, Peng; Cheng, Li
2018-03-01
The high-order waveguide modal theory, usually used in electromagnetics and acoustics, is adopted to investigate the propagation properties of shear horizontal waves in a periodic stubbed plate. Beyond the sub-wavelength regime, higher-order modes are included to calculate the exact band structures caused by the stubs. Theoretical solutions are obtained in a closed form, in which both the dynamic governing equations and the boundary conditions are strictly satisfied. It is shown that the proposed modelling approach exhibits good convergence and accuracy, in agreement with results obtained from the finite element method. After a systematic investigation on the influence of the stub on the evolution of the band structures, the so-called rainbow trapping phenomenon of SH waves is revealed and explored in a graded stubbed plate with monotonously increasing height or width of the stubs, featuring an obvious reduction of the group velocity and blocking of the wave propagation at different locations for SH waves of different frequencies. The proposed model is expected to provide a useful theoretical tool for the physical mechanism exploration, structural design and eventually system optimization to guide various engineering applications of SH waves. Copyright © 2017 Elsevier B.V. All rights reserved.
Propagation speed of a starting wave in a queue of pedestrians.
Tomoeda, Akiyasu; Yanagisawa, Daichi; Imamura, Takashi; Nishinari, Katsuhiro
2012-09-01
The propagation speed of a starting wave, which is a wave of people's successive reactions in the relaxation process of a queue, has an essential role for pedestrians and vehicles to achieve smooth movement. For example, a queue of vehicles with appropriate headway (or density) alleviates traffic jams since the delay of reaction to start is minimized. In this paper, we have investigated the fundamental relation between the propagation speed of a starting wave and the initial density by both our mathematical model built on the stochastic cellular automata and experimental measurements. Analysis of our mathematical model implies that the relation is characterized by the power law αρ-β (β≠1), and the experimental results verify this feature. Moreover, when the starting wave is characterized by the power law (β>1), we have revealed the existence of optimal density, where the required time, i.e., the sum of the waiting time until the starting wave reaches the last pedestrian in a queue and his/her travel time to pass the head position of the initial queue, is minimized. This optimal density inevitably plays a significant role in achieving a smooth movement of crowds and vehicles in a queue.
Two-dimensional wave propagation in layered periodic media
Quezada de Luna, Manuel
2014-09-16
We study two-dimensional wave propagation in materials whose properties vary periodically in one direction only. High order homogenization is carried out to derive a dispersive effective medium approximation. One-dimensional materials with constant impedance exhibit no effective dispersion. We show that a new kind of effective dispersion may arise in two dimensions, even in materials with constant impedance. This dispersion is a macroscopic effect of microscopic diffraction caused by spatial variation in the sound speed. We analyze this dispersive effect by using highorder homogenization to derive an anisotropic, dispersive effective medium. We generalize to two dimensions a homogenization approach that has been used previously for one-dimensional problems. Pseudospectral solutions of the effective medium equations agree to high accuracy with finite volume direct numerical simulations of the variable-coeffi cient equations.
Energy Technology Data Exchange (ETDEWEB)
Mirzade, Fikret Kh. [Institute on Laser and Information Technology, Russian Academy of Sciences, Svyatizerskaya Ul. 1, Shatura 140700, Moscow Region (Russian Federation)]. E-mail: fmirzade@rambler.ru
2005-11-01
The propagation of longitudinal strain wave in a plate with quadratic nonlinearity of elastic continuum was studied in the context of a model that takes into account the joint dynamics of elastic displacements in the medium and the concentration of the nonequilibrium laser-induced point defects. The input equations of the problem are reformulated in terms of only the total displacements of the medium points. In this case, the presence of structural defects manifests itself in the emergence of a delayed response of the system to the propagation of the strain-related perturbations, which is characteristic of media with relaxation or memory. The model equations describing the nonlinear displacement wave were derived with allowance made for the values of the relaxation parameter. The influence of the generation and relaxation of lattice defects on the propagation of this wave was analyzed. It is shown that, for short relaxation times of defects, the strain can propagate in the form of shock fronts. In the case of longer relaxation times, shock waves do not form and the strain wave propagates only in the form of solitary waves or a train of solitons. The contributions of the finiteness of the defect-recombination rate to linear and nonlinear elastic modulus, and spatial dispersion are determined.
Shahmirzadi, Danial; Li, Ronny X; Konofagou, Elisa E
2012-11-01
Pulse wave imaging (PWI) is an ultrasound-based method for noninvasive characterization of arterial stiffness based on pulse wave propagation. Reliable numerical models of pulse wave propagation in normal and pathological aortas could serve as powerful tools for local pulse wave analysis and a guideline for PWI measurements in vivo. The objectives of this paper are to (1) apply a fluid-structure interaction (FSI) simulation of a straight-geometry aorta to confirm the Moens-Korteweg relationship between the pulse wave velocity (PWV) and the wall modulus, and (2) validate the simulation findings against phantom and in vitro results. PWI depicted and tracked the pulse wave propagation along the abdominal wall of canine aorta in vitro in sequential Radio-Frequency (RF) ultrasound frames and estimates the PWV in the imaged wall. The same system was also used to image multiple polyacrylamide phantoms, mimicking the canine measurements as well as modeling softer and stiffer walls. Finally, the model parameters from the canine and phantom studies were used to perform 3D two-way coupled FSI simulations of pulse wave propagation and estimate the PWV. The simulation results were found to correlate well with the corresponding Moens-Korteweg equation. A high linear correlation was also established between PWV² and E measurements using the combined simulation and experimental findings (R² = 0.98) confirming the relationship established by the aforementioned equation.
Gherm, Vadim E.; Zernov, Nikolay N.
2017-07-01
The detailed effects of the high-frequency radio wave propagation in a stochastic transionospheric propagation channel are discussed. This is a special case of propagation along or almost along the lines of the Earth's magnetic field. In this case, the ionospheric random irregularities of the electron density of the ionosphere may have very high values of the aspect ratio, which stands beyond the range of validity of the traditional analytical approaches utilized to treat the appropriate transionospheric propagation problems. In the consideration presented here, new analytical results are obtained for treating the problem under consideration. Based on the analytical results obtained, the previously developed Hybrid Scintillation Propagation Model is further extended, which also includes the software simulator of the signals propagating on the transionospheric paths with the random electron density irregularities highly elongated in the direction of the Earth's magnetic field.
The analysis of optical wave beams propagation in lens systems
Kazakov, I.; Mosentsov, S.; Moskaletz, O.
2016-08-01
In this paper some aspects of the formation and propagation of optical wave beams in lens systems were considered. As an example, the two-lens optical information processing system was considered. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters
Lateral variation of Lg wave propagation in southern Mexico
Ottemöller, Lars; Shapiro, Nikolai M.; Krishna Singh, Shri; Pacheco, Javier F.
2002-01-01
In this study we investigated lateral variation of Lg wave propagation in southern Mexico from recordings of 92 crustal earthquakes along 591 travel paths. The efficiency of Lg propagation was measured in terms of Lgto Pn spectral ratio. It was found that Lgpropagation is inefficient for travel paths through the Gulf of Mexico coastal plains and the Gulf of Tehuantepec, areas with thick layers of sediments. An average Lg quality factor, QLg, as a function of frequency for southern Mexico was estimated for the efficient Lg travel paths. The relation obtained for QLg in the frequency range 1.6-8 Hz is QLg(f) = 204 f0.85. The lateral variation of QLg-1was solved as a mixed-determined inverse tomography problem, separately for each frequency, in which a spatial smoothness constraint was imposed and a priori information was added in poorly covered regions. The spatial resolution obtained was about 200 km. It was found that the Trans-Mexican Volcanic Belt, the Gulf of Mexico coastal plains, and the area east of 94°W are characterized by lower than average QLgvalues, i.e., higher attenuation. High QLg values were obtained for the Mixteco-Oaxaca terranes, while for the Guerrero terrane, values similar to the average were obtained. The results show a correlation between QLg and crustal structure and provide valuable information on lateral variation of QLg, which is needed for reliable prediction of ground motion during future earthquakes.
Directory of Open Access Journals (Sweden)
Bin Xu
2015-01-01
Full Text Available Wave propagation along a closely spaced folded cylindrical helix (FCH array is investigated for the purpose of designing compact array for energy transport and antenna radiation. It is found that the height of this surface wave guiding structure can be decreased from 0.24λ0 to 0.06λ0 by replacing the monopole element with the FCH. Both the propagation constant and the mode distribution of the dominant wave mechanism are extracted by ESPRIT algorithm, which indicates that a backward propagating surface wave is supported by the array structure. A compact backfire FCH antenna array is designed and measured based on the identified dominant wave mechanism.
Rumor Propagation Model: An Equilibrium Study
Piqueira, José Roberto C.
2010-01-01
Compartmental epidemiological models have been developed since the 1920s and successfully applied to study the propagation of infectious diseases. Besides, due to their structure, in the 1960s an interesting version of these models was developed to clarify some aspects of rumor propagation, considering that spreading an infectious disease or disseminating information is analogous phenomena. Here, in an analogy with the SIR (Susceptible-Infected-Removed) epidemiological model, the ISS (Ignoran...
A STUDY OF NONLINEAR PHENOMENA IN THE PROPAGATION OF ELECTROMAGNETIC WAVES IN A WEAKLY IONIZED GAS.
This paper is a study of nonlinear phenomena in the propagation of electromagnetic waves in a weakly ionized gas externally biased with a magneto...static field. The present study is restricted to the nonlinear phenomena arising from the interaction of electromagnetic waves in the ionized gas. The...the propagation of electromagnetic waves in the ionized gas, and also on the reflection of waves from an ionized gas semi-infinite extent. (Author)
Frequency-domain bridging multiscale method for wave propagation simulations in damaged structures
Casadei, F.; Ruzzene, M.
2010-03-01
Efficient numerical models are essential for the simulation of the interaction of propagating waves with localized defects. Classical finite elements may be computationally time consuming, especially when detailed discretizations are needed around damage regions. A multi-scale approach is here propose to bridge a fine-scale mesh defined on a limited region around the defect and a coarse-scale discretization of the entire domain. This "bridging" method is formulated in the frequency domain in order to further reduce the computational cost and provide a general framework valid for different types of structures. Numerical results presented for propagating elastic waves in 1D and 2D damaged waveguides illustrate the proposed technique and its advantages.
Propagation of optical spatial solitary waves in bias-free nematic-liquid-crystal cells
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Minzoni, Antonmaria A. [Fenomenos Nonlineales y Mecanica (FENOMEC), Department of Mathematics and Mechanics, Instituto de Investigacion en Matematicas Aplicadas y Sistemas, Universidad Nacional Autonoma de Mexico, 01000 Mexico D.F. (Mexico); Sciberras, Luke W.; Worthy, Annette L. [School of Mathematics and Applied Statistics, University of Wollongong, Northfields Avenue, Wollongong, New South Wales 2522 (Australia); Smyth, Noel F. [School of Mathematics and Maxwell Institute for Mathematical Sciences, University of Edinburgh, Edinburgh EH9 3JZ, Scotland (United Kingdom)
2011-10-15
The propagation of a bulk optical solitary wave in a rectangular cell filled with a nematic liquid crystal--a nematicon--is mathematically modelled. In order to overcome the Freedricksz threshold the cell walls are rubbed to pretilt the nematic. A modulation theory, based on a Lagrangian formulation, is developed for the (2+1)-dimensional propagation of the solitary wave beam down the cell. This modulation theory is based on two different formulations of the director distribution. The relative advantages and disadvantages of these two methods are discussed. A previously unexplored method based on images is found to possess significant advantages. Excellent agreement with full numerical solutions of the nematicon equations is found for both methods. Finally, the implications of the results obtained for some widely used approximations to the nematicon equations are discussed, particularly their use in comparisons with experimental results.
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Tetsuya Hiraiwa
2017-07-01
Full Text Available During animal development, epithelial cells forming a monolayer sheet move collectively to achieve the morphogenesis of epithelial tissues. One driving mechanism of such collective cell movement is junctional remodeling, which is found in the process of clockwise rotation of Drosophila male terminalia during metamorphosis. However, it still remains unknown how the motions of cells are spatiotemporally organized for collective movement by this mechanism. Since these moving cells undergo elastic deformations, the influence of junctional remodeling may mechanically propagate among them, leading to spatiotemporal pattern formations. Here, using a numerical cellular vertex model, we found that the junctional remodeling in collective cell movement exhibits spatiotemporal self-organization without requiring spatial patterns of molecular signaling activity. The junctional remodeling propagates as a wave in a specific direction with a much faster speed than that of cell movement. Such propagation occurs in both the absence and presence of fluctuations in the contraction of cell boundaries.