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 Propagation of Shock Waves in Metals
Howard, W. M.; Molitoris, J. D.
2006-07-01
We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P ˜ 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C-J pressure (P ˜ 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.
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
Computer modeling of inelastic wave propagation in porous rock
International Nuclear Information System (INIS)
Cheney, J.A.; Schatz, J.F.; Snell, C.
1979-01-01
Computer modeling of wave propagation in porous rock has several important applications. Among them are prediction of fragmentation and permeability changes to be caused by chemical explosions used for in situ resource recovery, and the understanding of nuclear explosion effects such as seismic wave generation, containment, and site hardness. Of interest in all these applications are the distance from the source to which inelastic effects persist and the amount of porosity change within the inelastic region. In order to study phenomena related to these applications, the Cam Clay family of models developed at Cambridge University was used to develop a similar model that is applicable to wave propagation in porous rock. That model was incorporated into a finite-difference wave propagation computer code SOC. 10 figures, 1 table
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...
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
Modeling ocean wave propagation under sea ice covers
Zhao, Xin; Shen, Hayley H.; Cheng, Sukun
2015-02-01
Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice-covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as: landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ice cover. Being closest to open water, wave propagation in the marginal ice zone is the most complex to model. The physical appearance of sea ice in the marginal ice zone varies. Grease ice, pancake ice, brash ice, floe aggregates, and continuous ice sheet may be found in this zone at different times and locations. These types of ice are formed under different thermal-mechanical forcing. There are three classic models that describe wave propagation through an idealized ice cover: mass loading, thin elastic plate, and viscous layer models. From physical arguments we may conjecture that mass loading model is suitable for disjoint aggregates of ice floes much smaller than the wavelength, thin elastic plate model is suitable for a continuous ice sheet, and the viscous layer model is suitable for grease ice. For different sea ice types we may need different wave ice interaction models. A recently proposed viscoelastic model is able to synthesize all three classic models into one. Under suitable limiting conditions it converges to the three previous models. The complete theoretical framework for evaluating wave propagation through various ice covers need to be implemented in the operational ocean wave models. In this review, we introduce the sea ice types, previous wave ice interaction models, wave attenuation mechanisms, the methods to calculate wave reflection and transmission between different ice covers, and the effect of ice floe breaking on shaping the sea ice morphology
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.
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...... by expanding solutions in terms of cross-sectional eigenfunctions following Stevenson’s method. A transfer matrix can be easily constructed from simple model responses of a given waveguide and later used in computing the response to any complex wave input. Energy losses due to heat conduction and viscous...
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.
Modeling of Electromagnetic Wave Propagation with Tapered Transmission Line
Lee, Kun-A.; Ko, Kwang-Cheol
2012-09-01
Tapered transmission line was used for impedance matching, for high voltage pulse, and atmospheric medium is applied to characteristic equation of tapered transmission line and reflection coefficient so that nonlinear load and circuit modeling of atmospheric medium was simulated by electromagnetic transient program (EMTP). A characteristic of atmospheric medium and Time delay are decided by inductance and capacitance of tapered transmission line. For electromagnetic wave propagation modeling, in this paper, tapered transmission line is implemented. It is difficult to model tapered transmission line directly. Other transmission line that can be expressed by the circuit is used. So object of this paper is efficient modeling of tapered transmission line.
Modeling the Propagation of Shock Waves in Metals
Howard, W. Michael
2005-07-01
We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P ˜300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and bulk modulus depends on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and bulk modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that gives the correct detonation velocity and C-J pressure (P ˜ 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov. We also discuss the dependence of our results upon our material model for aluminum.
Topics in Computational Modeling of Shock and Wave Propagation
National Research Council Canada - National Science Library
Gazonas, George A; Main, Joseph A; Laverty, Rich; Su, Dan; Santare, Michael H; Raghupathy, R; Molinari, J. F; Zhou, F
2006-01-01
This report contains reprints of four papers that focus on various aspects of shock and wave propagation in cellular, viscoelastic, microcracked, and fragmented media that appear in the Proceedings...
Mathematical modelling of generation and forward propagation of dispersive waves
Lie She Liam, L.S.L.
2013-01-01
This dissertation concerns the mathematical theory of forward propagation and generation of dispersive waves. We derive the AB2-equation which describes forward traveling waves in two horizontal dimension. It is the generalization of the Kadomtsev-Petviashvilli (KP) equation. The derivation is based
Seismoelectric wave propagation numerical modelling in partially saturated materials
Warden, S.; Garambois, S.; Jouniaux, L.; Brito, D.; Sailhac, P.; Bordes, C.
2013-09-01
To better understand and interpret seismoelectric measurements acquired over vadose environments, both the existing theory and the wave propagation modelling programmes, available for saturated materials, should be extended to partial saturation conditions. We propose here an extension of Pride's equations aiming to take into account partially saturated materials, in the case of a water-air mixture. This new set of equations was incorporated into an existing seismoelectric wave propagation modelling code, originally designed for stratified saturated media. This extension concerns both the mechanical part, using a generalization of the Biot-Gassmann theory, and the electromagnetic part, for which dielectric permittivity and electrical conductivity were expressed against water saturation. The dynamic seismoelectric coupling was written as a function of the streaming potential coefficient, which depends on saturation, using four different relations derived from recent laboratory or theoretical studies. In a second part, this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half-space. Subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response (IR) may be best recovered when the shallow layer exhibits low saturation. We also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half-space. Our first modelling results suggest that the study of the seismoelectric IR may help to detect a sharp saturation contrast better than a smooth saturation transition. In our example, a saturation contrast of 50 per cent between a fully saturated sand half-space and a partially saturated shallow sand layer yields a stronger IR than a stepwise decrease in saturation.
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
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.
Nurhandoko, Bagus Endar B.; Wardaya, Pongga Dikdya; Adler, John; Siahaan, Kisko R.
2012-06-01
Seismic wave parameter plays very important role to characterize reservoir properties whereas pore parameter is one of the most important parameter of reservoir. Therefore, wave propagation phenomena in pore media is important to be studied. By referring this study, in-direct pore measurement method based on seismic wave propagation can be developed. Porosity play important role in reservoir, because the porosity can be as compartment of fluid. Many type of porosity like primary as well as secondary porosity. Carbonate rock consist many type of porosity, i.e.: inter granular porosity, moldic porosity and also fracture porosity. The complexity of pore type in carbonate rocks make the wave propagation in these rocks is more complex than sand reservoir. We have studied numerically wave propagation in carbonate rock by finite difference modeling in time-space domain. The medium of wave propagation was modeled by base on the result of pattern recognition using artificial neural network. The image of thin slice of carbonate rock is then translated into the velocity matrix. Each mineral contents including pore of thin slice image are translated to velocity since mineral has unique velocity. After matrix velocity model has been developed, the seismic wave is propagated numerically in this model. The phenomena diffraction is clearly shown while wave propagates in this complex carbonate medium. The seismic wave is modeled in various frequencies. The result shows dispersive phenomena where high frequency wave tends to propagate in matrix instead pores. In the other hand, the low frequency waves tend to propagate through pore space even though the velocity of pore is very low. Therefore, this dispersive phenomena of seismic wave propagation can be the future indirect measurement technology for predicting the existence or intensity of pore space in reservoir rock. It will be very useful for the future reservoir characterization.
Preliminary Modeling of Global Seismic Wave Propagation in the Whole Mars
Toyokuni, G.; Ishihara, Y.; Takenaka, H.
2011-03-01
Global seismic wave propagation in the whole Mars is simulated by an accurate and efficient numerical scheme which has been developed for the Earth. Simple Mars models are used to obtain preliminary results of martian seismic waveform modeling.
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
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). In...
Non-homogeneous polymer model for wave propagation and its ...
African Journals Online (AJOL)
This article concerns certain aspects of four parameter polymer models to study harmonic waves in the non-homogeneous polymer rods of varying density. There are two sections of this paper, in first section, the rheological behaviour of the model is discussed numerically and then it is solved analytically with the help of ...
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.
International Nuclear Information System (INIS)
Paćko, P; Bielak, T; Staszewski, W J; Uhl, T; Spencer, A B; Worden, K
2012-01-01
This paper demonstrates new parallel computation technology and an implementation for Lamb wave propagation modelling in complex structures. A graphical processing unit (GPU) and computer unified device architecture (CUDA), available in low-cost graphical cards in standard PCs, are used for Lamb wave propagation numerical simulations. The local interaction simulation approach (LISA) wave propagation algorithm has been implemented as an example. Other algorithms suitable for parallel discretization can also be used in practice. The method is illustrated using examples related to damage detection. The results demonstrate good accuracy and effective computational performance of very large models. The wave propagation modelling presented in the paper can be used in many practical applications of science and engineering. (paper)
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
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.
Model for small arms fire muzzle blast wave propagation in air
Aguilar, Juan R.; Desai, Sachi V.
2011-11-01
Accurate modeling of small firearms muzzle blast wave propagation in the far field is critical to predict sound pressure levels, impulse durations and rise times, as functions of propagation distance. Such a task being relevant to a number of military applications including the determination of human response to blast noise, gunfire detection and localization, and gun suppressor design. Herein, a time domain model to predict small arms fire muzzle blast wave propagation is introduced. The model implements a Friedlander wave with finite rise time which diverges spherically from the gun muzzle. Additionally, the effects in blast wave form of thermoviscous and molecular relaxational processes, which are associated with atmospheric absorption of sound were also incorporated in the model. Atmospheric absorption of blast waves is implemented using a time domain recursive formula obtained from numerical integration of corresponding differential equations using a Crank-Nicholson finite difference scheme. Theoretical predictions from our model were compared to previously recorded real world data of muzzle blast wave signatures obtained by shooting a set different sniper weapons of varying calibers. Recordings containing gunfire acoustical signatures were taken at distances between 100 and 600 meters from the gun muzzle. Results shows that predicted blast wave slope and exponential decay agrees well with measured data. Analysis also reveals the persistency of an oscillatory phenomenon after blast overpressure in the recorded wave forms.
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
Modeling of high-frequency wave propagation in the heterogenous Earth using screen method
Ding, Y.; Zheng, Y.
2017-12-01
High-frequency (1Hz) wave propagation modeling in the heterogenous Earth is difficult due to computation cost. We have developed one alternative method to do high-frequency wave propagation locally in the Earth. First, we divide the heterogeneous Earth model into two parts: the background gradient velocity model, and the velocity perturbation. Then we trace rays from the source to the Earth surface and make screens perpendicular to the rays. We propagate the wavefield in each screen by Kirchhoff surface integral and account for the velocity perturbations with a phase shift. Recursively, the algorithm will propagate the wavefield locally from the source to the surface. The result is compared with that from the finite difference method.
Wu, S. T.
1974-01-01
The responses of the solar atmosphere due to an outward propagation shock are examined by employing the Lax-Wendroff method to solve the set of nonlinear partial differential equations in the model of the solar atmosphere. It is found that this theoretical model can be used to explain the solar phenomena of surge and spray. A criterion to discriminate the surge and spray is established and detailed information concerning the density, velocity, and temperature distribution with respect to the height and time is presented. The complete computer program is also included.
International Nuclear Information System (INIS)
Valeo, Ernest; Johnson, Jay R.; Kim, Eun-Hwa; Phillips, Cynthia
2012-01-01
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.
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 ...
Indian Academy of Sciences (India)
I available for forecasting the propagation of the flood wave. Introduction. Among all natural disasters, floods are the most frequently occurring phenomena that affect a large section of population all over the world, every year. Throughout the last century, flood- ing has been one of the most devastating disasters both in terms.
Directory of Open Access Journals (Sweden)
Juexuan Long
Full Text Available In this paper, we present a combined theoretical and experimental study of the propagation of calcium signals in multicellular structures composed of human endothelial cells. We consider multicellular structures composed of a single chain of cells as well as a chain of cells with a side branch, namely a "T" structure. In the experiments, we investigate the result of applying mechano-stimulation to induce signaling in the form of calcium waves along the chain and the effect of single and dual stimulation of the multicellular structure. The experimental results provide evidence of an effect of architecture on the propagation of calcium waves. Simulations based on a model of calcium-induced calcium release and cell-to-cell diffusion through gap junctions shows that the propagation of calcium waves is dependent upon the competition between intracellular calcium regulation and architecture-dependent intercellular diffusion.
Wave propagation in magneto-electro-elastic nanobeams via two nonlocal beam models
Ma, Li-Hong; Ke, Liao-Liang; Wang, Yi-Ze; Wang, Yue-Sheng
2017-02-01
This paper makes the first attempt to investigate the dispersion behavior of waves in magneto-electro-elastic (MEE) nanobeams. The Euler nanobeam model and Timoshenko nanobeam model are developed in the formulation based on the nonlocal theory. By using the Hamilton's principle, we derive the governing equations which are then solved analytically to obtain the dispersion relations of MEE nanobeams. Results are presented to highlight the influences of the thermo-electro-magnetic loadings and nonlocal parameter on the wave propagation characteristics of MEE nanobeams. It is found that the thermo-electro-magnetic loadings can lead to the occurrence of the cut-off wave number below which the wave can't propagate in MEE nanobeams.
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
Hedayatrasa, Saeid; Bui, Tinh Quoc; Zhang, Chuanzeng; Lim, Chee Wah
2014-02-01
Numerical modeling of the Lamb wave propagation in functionally graded materials (FGMs) by a two-dimensional time-domain spectral finite element method (SpFEM) is presented. The high-order Chebyshev polynomials as approximation functions are used in the present formulation, which provides the capability to take into account the through thickness variation of the material properties. The efficiency and accuracy of the present model with one and two layers of 5th order spectral elements in modeling wave propagation in FGM plates are analyzed. Different excitation frequencies in a wide range of 28-350 kHz are investigated, and the dispersion properties obtained by the present model are verified by reference results. The through thickness wave structure of two principal Lamb modes are extracted and analyzed by the symmetry and relative amplitude of the vertical and horizontal oscillations. The differences with respect to Lamb modes generated in homogeneous plates are explained. Zero-crossing and wavelet signal processing-spectrum decomposition procedures are implemented to obtain phase and group velocities and their dispersion properties. So it is attested how this approach can be practically employed for simulation, calibration and optimization of Lamb wave based nondestructive evaluation techniques for the FGMs. The capability of modeling stress wave propagation through the thickness of an FGM specimen subjected to impact load is also investigated, which shows that the present method is highly accurate as compared with other existing reference data.
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.
Wave propagation modeling in composites reinforced by randomly oriented fibers
Kudela, Pawel; Radzienski, Maciej; Ostachowicz, Wieslaw
2018-02-01
A new method for prediction of elastic constants in randomly oriented fiber composites is proposed. It is based on mechanics of composites, the rule of mixtures and total mass balance tailored to the spectral element mesh composed of 3D brick elements. Selected elastic properties predicted by the proposed method are compared with values obtained by another theoretical method. The proposed method is applied for simulation of Lamb waves in glass-epoxy composite plate reinforced by randomly oriented fibers. Full wavefield measurements conducted by the scanning laser Doppler vibrometer are in good agreement with simulations performed by using the time domain spectral element method.
Acoustic Wave Propagation in Snow Based on a Biot-Type Porous Model
Sidler, R.
2014-12-01
Despite the fact that acoustic methods are inexpensive, robust and simple, the application of seismic waves to snow has been sparse. This might be due to the strong attenuation inherent to snow that prevents large scale seismic applications or due to the somewhat counterintuitive acoustic behavior of snow as a porous material. Such materials support a second kind of compressional wave that can be measured in fresh snow and which has a decreasing wave velocity with increasing density of snow. To investigate wave propagation in snow we construct a Biot-type porous model of snow as a function of porosity based on the assumptions that the solid frame is build of ice, the pore space is filled with a mix of air, or air and water, and empirical relationships for the tortuosity, the permeability, the bulk, and the shear modulus.We use this reduced model to investigate compressional and shear wave velocities of snow as a function of porosity and to asses the consequences of liquid water in the snowpack on acoustic wave propagation by solving Biot's differential equations with plain wave solutions. We find that the fast compressional wave velocity increases significantly with increasing density, but also that the fast compressional wave velocity might be even lower than the slow compressional wave velocity for very light snow. By using compressional and shear strength criteria and solving Biot's differential equations with a pseudo-spectral approach we evaluate snow failure due to acoustic waves in a heterogeneous snowpack, which we think is an important mechanism in triggering avalanches by explosives as well as by skiers. Finally, we developed a low cost seismic acquisition device to assess the theoretically obtained wave velocities in the field and to explore the possibility of an inexpensive tool to remotely gather snow water equivalent.
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.
The finite-difference and finite-element modeling of seismic wave propagation and earthquake motion
International Nuclear Information System (INIS)
Moszo, P.; Kristek, J.; Galis, M.; Pazak, P.; Balazovijech, M.
2006-01-01
Numerical modeling of seismic wave propagation and earthquake motion is an irreplaceable tool in investigation of the Earth's structure, processes in the Earth, and particularly earthquake phenomena. Among various numerical methods, the finite-difference method is the dominant method in the modeling of earthquake motion. Moreover, it is becoming more important in the seismic exploration and structural modeling. At the same time we are convinced that the best time of the finite-difference method in seismology is in the future. This monograph provides tutorial and detailed introduction to the application of the finite-difference, finite-element, and hybrid finite-difference-finite-element methods to the modeling of seismic wave propagation and earthquake motion. The text does not cover all topics and aspects of the methods. We focus on those to which we have contributed. (Author)
Abortive and propagating intracellular calcium waves: analysis from a hybrid model.
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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.
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
The limitations of a pseudo-transient approach for modeling temperature wave propagation in district heating pipes were investigated by comparing numerical predictions with experimental data. The performance of two approaches, namely a pseudo-transient approach implemented in the finite element...... 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...... that the fluid is represented as an ideal fluid. The approaches failed to adequately predict the temperature wave propagation in the case of rapid inlet temperature changes. The overall conclusion from this case study was that in order to improve the prediction of the transient temperature, attention has...
THE BASIS OF MATHEMATICAL DESCRIPTION FOR WAVE MODEL OF STRESSES PROPAGATION IN RAILWAY TRACK
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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
Emulation of a Kalman Filter algorithm on a diffusive flood wave propagation model
Pannekoucke, O.; Ricci, S. M.; Ninove, F.; Thual, O.
2011-12-01
River stream flow forecasting is a critical issue for the security of people and infrastructures, the function of power plants, and water resources management. The benefit of data assimilation for free-surface flow simulation and flood forecasting has already been demonstrated as it is applied to optimize model parameters and to improve simulated water level and discharge state [1]. The correction of the hydraulic state with a Kalman Filter algorithm implies the propagation of the background error covariance matrix B by the dynamics of the model. This step requires the formulation and the integration in time of the tangent linear approximation of the model, which is generally fastidious and costly. The aim of this study is to describe the evolution of the background error covariance function with the Kalman Filter algorithm applied to a 1D diffuse flood wave propagation model. For this simplified model, the formulation of the tangent linear model as well as the propagation of B is affordable as opposed as for an operational hydraulics model solving the shallow water equations. Starting from Gaussian background covariance functions, it was first shown that the diffusive flood wave propagation model increases the correlation length and that the propagated covariance function can be approximated by a Gaussian. Working with a steady observation network, it was then demonstrated that the analysis and propagation steps of the Kalman Filter modify the covariance function at the observation point. The resulting covariance function at the observation point is inhomogeneous, with a shorter correlation length downstream of the observation point than upstream. The diagnosed correlation lengths [2] were used to build a parametrized covariance matrix using a diffusion operator with an inhomogenous diffusion coefficient [3]. This approach led to the formulation of a parametrized background error covariance matrix where the evolution of the covariance function with the Kalman
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
Eckermann, S. D.; Broutman, D.; Ma, J.; Doyle, J. D.; Pautet, P. D.; Taylor, M. J.; Bossert, K.; Williams, B. P.; Fritts, D. C.; Smith, R. B.; Kuhl, D.; Hoppel, K.; McCormack, J. P.; Ruston, B. C.; Baker, N. L.; Viner, K.; Whitcomb, T.; Hogan, T. F.; Peng, M.
2016-12-01
The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was an international aircraft-based field program to observe and study the end-to-end dynamics of atmospheric gravity waves from 0-100 km altitude and the effects on atmospheric circulations. On 14 July 2014, aircraft remote-sensing instruments detected large-amplitude gravity-wave oscillations within mesospheric airglow and sodium layers downstream of the Auckland Islands, located 1000 km south of Christchurch, New Zealand. A high-altitude reanalysis and a three-dimensional Fourier gravity wave model are used to investigate the dynamics of this event from the surface to the mesosphere. At 0700 UTC when first observations were made, surface flow across the islands' terrain generated linear three-dimensional wavefields that propagated rapidly to ˜78 km altitude, where intense breaking occurred in a narrow layer beneath a zero-wind region at ˜83 km altitude. In the following hours, the altitude of weak winds descended under the influence of a large-amplitude migrating semidiurnal tide, leading to intense breaking of these wavefields in subsequent observations starting at 1000 UTC. The linear Fourier model constrained by upstream reanalysis reproduces the salient aspects of observed wavefields, including horizontal wavelengths, phase orientations, temperature and vertical displacement amplitudes, heights and locations of incipient wave breaking, and momentum fluxes. Wave breaking has huge effects on local circulations, with inferred layer-averaged westward mean-flow accelerations of ˜350 m s-1 hour-1 and dynamical heating rates of ˜8 K hour-1, supporting recent speculation of important impacts of orographic gravity waves from subantarctic islands on the mean circulation and climate of the middle atmosphere during austral winter. We also study deep orographic gravity waves from islands during DEEPWAVE more widely using observations from the Atmospheric Infrared Sounder (AIRS) and high-resolution high
Directory of Open Access Journals (Sweden)
Hussein Rappel
2014-01-01
integration technique (EFIT as well as its validation with analytical results. Lamb wave method is a long range inspection technique which is considered to have unique future in the field of structural health monitoring. One of the main problems facing the lamb wave method is how to choose the most appropriate frequency to generate the waves for adequate transmission capable of properly propagating in the material, interfering with defects/damages, and being received in good conditions. Modern simulation tools based on numerical methods such as finite integration technique (FIT, finite element method (FEM, and boundary element method (BEM may be used for modeling. In this paper, two sets of simulation are performed. In the first set, group velocities of lamb wave in a steel plate are obtained numerically. Results are then compared with analytical results to validate the simulation. In the second set, EFIT is employed to study fundamental symmetric mode interaction with a surface braking defect.
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....... 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...... relations and frequency-dependent attenuation. A 12-m-long, liquid-filled tube with interior stress members and connectors in each end is hanging vertically from an upper fixture. The lower end connector is excited by a power vibrator to generate the relevant wave modes. Measurements with reference...
Directory of Open Access Journals (Sweden)
Hosein Ghaffarzadeh
Full Text Available Abstract This paper investigates the numerical modeling of the flexural wave propagation in Euler-Bernoulli beams using the Hermite-type radial point interpolation method (HRPIM under the damage quantification approach. HRPIM employs radial basis functions (RBFs and their derivatives for shape function construction as a meshfree technique. The performance of Multiquadric(MQ RBF to the assessment of the reflection ratio was evaluated. HRPIM signals were compared with the theoretical and finite element responses. Results represent that MQ is a suitable RBF for HRPIM and wave propagation. However, the range of the proper shape parameters is notable. The number of field nodes is the main parameter for accurate wave propagation modeling using HRPIM. The size of support domain should be less thanan upper bound in order to prevent high error. With regard to the number of quadrature points, providing the minimum numbers of points are adequate for the stable solution, but the existence of more points in damage region does not leads to necessarily the accurate responses. It is concluded that the pure HRPIM, without any polynomial terms, is acceptable but considering a few terms will improve the accuracy; even though more terms make the problem unstable and inaccurate.
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.
Modeling of acoustic wave propagation and scattering for telemetry of complex structures
International Nuclear Information System (INIS)
LU, B.
2011-01-01
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
A two-dimensional analytical model for tidal wave propagation in convergent estuaries
Cai, Huayang; Toffolon, Marco; Savenije, Hubert H. G.; Chua, Vivien P.
2015-04-01
A knowledge of tidal dynamics in large-scale semi-closed estuaries, such as the Bay of Fundy, the Gulf of California, the Adriatic Sea, is very important since it affects the estuarine environment and its potential use of water resource in many ways (e.g., navigation, coastal safety, ecology). To obtain insight into physical mechanisms on tidal wave propagation in such systems, analytical models are invaluable tools. It is well known that the analytical solutions for tidal dynamics in semi-closed estuaries can be obtained by Taylor's method, where a cooscillating tide can be described as a superposition of an incident Kelvin wave, a reflected Kelvin wave, and Poincare waves. However, the method is usually limited to special conditions, e.g., prismatic channel with uniform depth, negligible friction etc. In this study, we extend the one-dimensional linear solution for tidal wave propagation in convergent estuaries to the two-dimensional case, explicitly accounting for both the channel convergence (width and depth convergence) and friction.
Mesoscale Modeling of Shock Wave Propagation and Dynamic Failure in Metallic Systems
Dongare, Avinash
2013-03-01
The response of materials under conditions of thermomechanical extremes is very complex and involves damage creation and propagation, phase transformation, heat generation and transfer, etc. A principal challenge in predictive modeling of failure behavior is presented by the gap between the atomistic description of micromechanisms of the relevant processes and the macoscale response in continuum simulations/experiments. This difficulty can be approached through the development of a robust mesoscopic computational model that retains the relevant physics and is capable of representing the material behavior at time- and length-scales intermediate between the atomistic or continuum levels. Mesoscale models typically reduce a group of atoms by a mesoparticle system with much smaller number of collective degrees of freedom, and hence are often difficult to apply for problems such as heat transfer, phase transformation, and dissipation of mechanical energy during wave propagation. To achieve this goal, a novel mesoscopic model is being developed based on the idea of coarse-graining with the energetics defined for the particles based on interatomic potentials used in molecular dynamics (MD) simulations. The coarse-grained molecular dynamics simulations (CGMD) allows larger size systems and improved time-steps for simulations and thus able to extend the capabilities of MD simulations to model materials behavior at mesoscales. The successful application of the CGMD method is demonstrated by prediction of the phase-transformation, heat generation and wave-propagation behavior under the conditions of shock loading, as would be predicted using MD simulations.
Homogeneous microwave field emitted propagating spin waves: Direct imaging and modeling
Lohman, Mathis; Mozooni, Babak; McCord, Jeffrey
2018-03-01
We explore the generation of propagating dipolar spin waves by homogeneous magnetic field excitation in the proximity of the boundaries of magnetic microstructures. Domain wall motion, precessional dynamics, and propagating spin waves are directly imaged by time-resolved wide-field magneto-optical Kerr effect microscopy. The aspects of spin wave generation are clarified by micromagnetic calculations matching the experimental results. The region of dipolar spin wave formation is confined to the local resonant excitation due to non-uniform internal demagnetization fields at the edges of the patterned sample. Magnetic domain walls act as a border for the propagation of plane and low damped spin waves, thus restraining the spin waves within the individual magnetic domains. The findings are of significance for the general understanding of structural and configurational magnetic boundaries for the creation, the propagation, and elimination of spin waves.
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...
Pelat, Adrien; Felix, Simon; Pagneux, Vincent
2011-03-01
In modeling the wave propagation within a street canyon, particular attention must be paid to the description of both the multiple reflections of the wave on the building facades and the radiation in the free space above the street. The street canyon being considered as an open waveguide with a discontinuously varying cross-section, a coupled modal-finite element formulation is proposed to solve the three-dimensional wave equation within. The originally open configuration-the street canyon open in the sky above-is artificially turned into a close waveguiding structure by using perfectly matched layers that truncate the infinite sky without introducing numerical reflection. Then the eigenmodes of the resulting waveguide are determined by a finite element method computation in the cross-section. The eigensolutions can finally be used in a multimodal formulation of the wave propagation along the canyon, given its geometry and the end conditions at its extremities: initial field condition at the entrance and radiation condition at the output. © 2011 Acoustical Society of America
Zvietcovich, Fernando; Rolland, Jannick P.; Grygotis, Emma; Wayson, Sarah; Helguera, Maria; Dalecki, Diane; Parker, Kevin J.
2018-02-01
Determining the mechanical properties of tissue such as elasticity and viscosity is fundamental for better understanding and assessment of pathological and physiological processes. Dynamic optical coherence elastography uses shear/surface wave propagation to estimate frequency-dependent wave speed and Young's modulus. However, for dispersive tissues, the displacement pulse is highly damped and distorted during propagation, diminishing the effectiveness of peak tracking approaches. The majority of methods used to determine mechanical properties assume a rheological model of tissue for the calculation of viscoelastic parameters. Further, plane wave propagation is sometimes assumed which contributes to estimation errors. To overcome these limitations, we invert a general wave propagation model which incorporates (1) the initial force shape of the excitation pulse in the space-time field, (2) wave speed dispersion, (3) wave attenuation caused by the material properties of the sample, (4) wave spreading caused by the outward cylindrical propagation of the wavefronts, and (5) the rheological-independent estimation of the dispersive medium. Experiments were conducted in elastic and viscous tissue-mimicking phantoms by producing a Gaussian push using acoustic radiation force excitation, and measuring the wave propagation using a swept-source frequency domain optical coherence tomography system. Results confirm the effectiveness of the inversion method in estimating viscoelasticity in both the viscous and elastic phantoms when compared to mechanical measurements. Finally, the viscoelastic characterization of collagen hydrogels was conducted. Preliminary results indicate a relationship between collagen concentration and viscoelastic parameters which is important for tissue engineering applications.
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.
Numerical simulation of wave propagation in a realistic model of the human external ear.
Fadaei, Mohaddeseh; Abouali, Omid; Emdad, Homayoun; Faramarzi, Mohammad; Ahmadi, Goodarz
2015-01-01
In this study, a numerical investigation is performed to evaluate the effects of high-pressure sinusoidal and blast wave's propagation around and inside of a human external ear. A series of computed tomography images are used to reconstruct a realistic three-dimensional (3D) model of a human ear canal and the auricle. The airflow field is then computed by solving the governing differential equations in the time domain using a computational fluid dynamics software. An unsteady algorithm is used to obtain the high-pressure wave propagation throughout the ear canal which is validated against the available analytical and numerical data in literature. The effects of frequency, wave shape, and the auricle on pressure distribution are then evaluated and discussed. The results clearly indicate that the frequency plays a key role on pressure distribution within the ear canal. At 4 kHz frequency, the pressure magnitude is much more amplified within the ear canal than the frequencies of 2 and 6 kHz, for the incident wave angle of 90° investigated in this study, attributable to the '4-kHz notch' in patients with noise-induced hearing loss. According to the results, the pressure distribution patterns at the ear canal are very similar for both sinusoidal pressure waveform with the frequency of 2 kHz and blast wave. The ratio of the peak pressure value at the eardrum to that at the canal entrance increases from about 8% to 30% as the peak pressure value of the blast wave increases from 5 to 100 kPa for the incident wave angle of 90° investigated in this study. Furthermore, incorporation of the auricle to the ear canal model is associated with centerline pressure magnitudes of about 50% and 7% more than those of the ear canal model without the auricle throughout the ear canal for sinusoidal and blast waves, respectively, without any significant effect on pressure distribution pattern along the ear canal for the incident wave angle of 90° investigated in this study.
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.…
Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP
Energy Technology Data Exchange (ETDEWEB)
McCandless, K P; Petersson, N A; Nilsson, S; Rodgers, A; Sjogreen, B; Blair, S C
2006-05-09
We are developing a new parallel 3D wave propagation code at LLNL called WPP (Wave Propagation Program). WPP is being designed to incorporate the latest developments in embedded boundary and mesh refinement technology for finite difference methods, as well as having an efficient portable implementation to run on the latest supercomputers at LLNL. We are currently exploring seismic wave applications, including a recent effort to compute ground motions for the 1906 Great San Francisco Earthquake. This paper will briefly describe the wave propagation problem, features of our numerical method to model it, implementation of the wave propagation code, and results from the 1906 Great San Francisco Earthquake simulation.
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
Rappaport, Theodore S.; Xing, Yunchou; MacCartney, George R.; Molisch, Andreas F.; Mellios, Evangelos; Zhang, Jianhua
2017-12-01
This paper provides an overview of the features of fifth generation (5G) wireless communication systems now being developed for use in the millimeter wave (mmWave) frequency bands. Early results and key concepts of 5G networks are presented, and the channel modeling efforts of many international groups for both licensed and unlicensed applications are described here. Propagation parameters and channel models for understanding mmWave propagation, such as line-of-sight (LOS) probabilities, large-scale path loss, and building penetration loss, as modeled by various standardization bodies, are compared over the 0.5-100 GHz range.
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
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.
cases The wave heights and wave induced velocities obtained from the model and the laboratory experimental resultsare compared The model without the morphology feedback provided good correlation with the measurements for case of low wave energy, whereas...
Comparison of geometrical shock dynamics and kinematic models for shock-wave propagation
Ridoux, J.; Lardjane, N.; Monasse, L.; Coulouvrat, F.
2018-03-01
Geometrical shock dynamics (GSD) is a simplified model for nonlinear shock-wave propagation, based on the decomposition of the shock front into elementary ray tubes. Assuming small changes in the ray tube area, and neglecting the effect of the post-shock flow, a simple relation linking the local curvature and velocity of the front, known as the A{-}M rule, is obtained. More recently, a new simplified model, referred to as the kinematic model, was proposed. This model is obtained by combining the three-dimensional Euler equations and the Rankine-Hugoniot relations at the front, which leads to an equation for the normal variation of the shock Mach number at the wave front. In the same way as GSD, the kinematic model is closed by neglecting the post-shock flow effects. Although each model's approach is different, we prove their structural equivalence: the kinematic model can be rewritten under the form of GSD with a specific A{-}M relation. Both models are then compared through a wide variety of examples including experimental data or Eulerian simulation results when available. Attention is drawn to the simple cases of compression ramps and diffraction over convex corners. The analysis is completed by the more complex cases of the diffraction over a cylinder, a sphere, a mound, and a trough.
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
Wave propagation in electromagnetic media
International Nuclear Information System (INIS)
Davis, J.L.
1990-01-01
This book is concerned with wave propagation in reacting media, specifically in electromagnetic materials. An account is presented of the mathematical methods of wave phenomena in electromagnetic materials. The author presents the theory of time-varying electromagnetic fields, which involves a discussion of Faraday's laws, Maxwell's equations and their application to electromagnetic wave propagation under a variety of conditions. The author gives a discussion of magnetohydrodynamics and plasma physics. Chapters are included on quantum mechanics and the theory of relativity. The mathematical foundation of electromagnetic waves vis a vis partial differential equations is discussed
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...
The finite-difference and finite-element modeling of seismic wave propagation and earthquake motion
International Nuclear Information System (INIS)
Moczo, P.; Kristek, J.; Pazak, P.; Balazovjech, M.; Moczo, P.; Kristek, J.; Galis, M.
2007-01-01
Numerical modeling of seismic wave propagation and earthquake motion is an irreplaceable tool in investigation of the Earth's structure, processes in the Earth, and particularly earthquake phenomena. Among various numerical methods, the finite-difference method is the dominant method in the modeling of earthquake motion. Moreover, it is becoming more important in the seismic exploration and structural modeling. At the same time we are convinced that the best time of the finite-difference method in seismology is in the future. This monograph provides tutorial and detailed introduction to the application of the finite difference (FD), finite-element (FE), and hybrid FD-FE methods to the modeling of seismic wave propagation and earthquake motion. The text does not cover all topics and aspects of the methods. We focus on those to which we have contributed. We present alternative formulations of equation of motion for a smooth elastic continuum. We then develop alternative formulations for a canonical problem with a welded material interface and free surface. We continue with a model of an earthquake source. We complete the general theoretical introduction by a chapter on the constitutive laws for elastic and viscoelastic media, and brief review of strong formulations of the equation of motion. What follows is a block of chapters on the finite-difference and finite-element methods. We develop FD targets for the free surface and welded material interface. We then present various FD schemes for a smooth continuum, free surface, and welded interface. We focus on the staggered-grid and mainly optimally-accurate FD schemes. We also present alternative formulations of the FE method. We include the FD and FE implementations of the traction-at-split-nodes method for simulation of dynamic rupture propagation. The FD modeling is applied to the model of the deep sedimentary Grenoble basin, France. The FD and FE methods are combined in the hybrid FD-FE method. The hybrid
Protopappas, Vasilios C; Kourtis, Iraklis C; Kourtis, Lampros C; Malizos, Konstantinos N; Massalas, Christos V; Fotiadis, Dimitrios I
2007-06-01
The use of guided waves has recently drawn significant interest in the ultrasonic characterization of bone aiming at supplementing the information provided by traditional velocity measurements. This work presents a three-dimensional finite element study of guided wave propagation in intact and healing bones. A model of the fracture callus was constructed and the healing course was simulated as a three-stage process. The dispersion of guided modes generated by a broadband 1-MHz excitation was represented in the time-frequency domain. Wave propagation in the intact bone model was first investigated and comparisons were then made with a simplified geometry using analytical dispersion curves of the tube modes. Then, the effect of callus consolidation on the propagation characteristics was examined. It was shown that the dispersion of guided waves was significantly influenced by the irregularity and anisotropy of the bone. Also, guided waves were sensitive to material and geometrical changes that take place during healing. Conversely, when the first-arriving signal at the receiver corresponded to a nondispersive lateral wave, its propagation velocity was almost unaffected by the elastic symmetry and geometry of the bone and also could not characterize the callus tissue throughout its thickness. In conclusion, guided waves can enhance the capabilities of ultrasonic evaluation.
Wave propagation in mechanical metamaterials
Zhou, Y.
2017-01-01
In mechanical metamaterials, large deformations can occur in systems which are topological from the point of view of linear waves. The interplay between such nonlinearities and topology affects wave propagation. Beyond perfectly periodic systems, defects provide a way to modify and control
Calculation models of pressure wave propagation within the WWER-440 primary circulating loop
International Nuclear Information System (INIS)
Adamik, V.; Tkach, A.
1982-01-01
Computer codes SHOCK, LOVE, BAREL are described that can be used for the study of pressure wave propagation within the reactor and pipeline system during a LOCA as well as for mechanical loads identification in various parts of the system. SHOCK code is applicable to one-dimensional pressure wave propagation analysis in any hydraulic network containing a compressible nonviscous liquid with a constant (within the considered transient process period) density. LOVE code allows to calculate non-symmetrical mechanical loads on the WWER shaft in case of the main circulation pipeline cold branch rupture. BAREL code is an advanced modification of SHOCK code. It is fitted for two-dimensional pressure wave propagation analysing in the downstream section of a pressurised water reactor in case of the main circulation pipeline cold branch rupture. The calculation results for B-213 type WWER-440 reactor are presented that have been obtained under the assumption of perfect structure rigidity [ru
Liu, Antony K.; Holt, Benjamin; Vachon, Paris W.
1991-01-01
Ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The Labrador ice margin experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada in March 1987, provided aircraft SAR imagery, ice property and wave buoy data. Wave energy attenuation rates are estimated from SAR data and the ice motion package data that were deployed at the ice edge and into the ice pack, and compared with a model. It is shown that the model data comparisons are quite good for the ice conditions observed during LIMEX 1987.
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.
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
Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.
2017-12-01
Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments
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...
International Nuclear Information System (INIS)
Kijanka, P; Radecki, R; Packo, P; Staszewski, W J; Uhl, T
2013-01-01
Temperature has a significant effect on Lamb wave propagation. It is important to compensate for this effect when the method is considered for structural damage detection. The paper explores a newly proposed, very efficient numerical simulation tool for Lamb wave propagation modelling in aluminum plates exposed to temperature changes. A local interaction approach implemented with a parallel computing architecture and graphics cards is used for these numerical simulations. The numerical results are compared with the experimental data. The results demonstrate that the proposed approach could be used efficiently to produce a large database required for the development of various temperature compensation procedures in structural health monitoring applications. (paper)
Emulation of an ensemble Kalman filter algorithm on a flood wave propagation model
Barthélémy, S.; Ricci, S.; Pannekoucke, O.; Thual, O.; Malaterre, P. O.
2013-06-01
This study describes the emulation of an Ensemble Kalman Filter (EnKF) algorithm on a 1-D flood wave propagation model. This model is forced at the upstream boundary with a random variable with gaussian statistics and a correlation function in time with gaussian shape. This allows for, in the case without assimilation, the analytical study of the covariance functions of the propagated signal anomaly. This study is validated numerically with an ensemble method. In the case with assimilation with one observation point, where synthetical observations are generated by adding an error to a true state, the dynamic of the background error covariance functions is not straightforward and a numerical approach using an EnKF algorithm is prefered. First, those numerical experiments show that both background error variance and correlation length scale are reduced at the observation point. This reduction of variance and correlation length scale is propagated downstream by the dynamics of the model. Then, it is shown that the application of a Best Linear Unbiased Estimator (BLUE) algorithm using the background error covariance matrix converged from the EnKF algorithm, provides the same results as the EnKF but with a cheaper computational cost, thus allowing for the use of data assimilation in the context of real time flood forecasting. Moreover it was demonstrated that the reduction of background error correlation length scale and variance at the observation point depends on the error observation statistics. This feature is quantified by abacus built from linear regressions over a limited set of EnKF experiments. These abacus that describe the background error variance and the correlation length scale in the neighboring of the observation point combined with analytical expressions that describe the background error variance and the correlation length scale away from the observation point provide parametrized models for the variance and the correlation length scale. Using this
Smith, J. A.; Peter, D. B.; Tromp, J.; Komatitsch, D.; Lefebvre, M. P.
2015-12-01
We present both SPECFEM3D_Cartesian and SPECFEM3D_GLOBE open-source codes, representing high-performance numerical wave solvers simulating seismic wave propagation for local-, regional-, and global-scale application. These codes are suitable for both forward propagation in complex media and tomographic imaging. Both solvers compute highly accurate seismic wave fields using the continuous Galerkin spectral-element method on unstructured meshes. Lateral variations in compressional- and shear-wave speeds, density, as well as 3D attenuation Q models, topography and fluid-solid coupling are all readily included in both codes. For global simulations, effects due to rotation, ellipticity, the oceans, 3D crustal models, and self-gravitation are additionally included. Both packages provide forward and adjoint functionality suitable for adjoint tomography on high-performance computing architectures. We highlight the most recent release of the global version which includes improved performance, simultaneous MPI runs, OpenCL and CUDA support via an automatic source-to-source transformation library (BOAST), parallel I/O readers and writers for databases using ADIOS and seismograms using the recently developed Adaptable Seismic Data Format (ASDF) with built-in provenance. This makes our spectral-element solvers current state-of-the-art, open-source community codes for high-performance seismic wave propagation on arbitrarily complex 3D models. Together with these solvers, we provide full-waveform inversion tools to image the Earth's interior at unprecedented resolution.
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.
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.
International Nuclear Information System (INIS)
Ishida, Hitoshi; Meshii, Toshiyuki
2010-01-01
This study proposes an element size selection method named the 'Impact-Meshing (IM) method' for a finite element waves propagation analysis model, which is characterized by (1) determination of element division of the model with strain energy in the whole model, (2) static analysis (dynamic analysis in a single time step) with boundary conditions which gives a maximum change of displacement in the time increment and inertial (impact) force caused by the displacement change. In this paper, an example of application of the IM method to 3D ultrasonic wave propagation problem in an elastic solid is described. These examples showed an analysis result with a model determined by the IM method was convergence and calculation time for determination of element subdivision was reduced to about 1/6 by the IM Method which did not need determination of element subdivision by a dynamic transient analysis with 100 time steps. (author)
Solitary wave propagation in solar flux tubes
International Nuclear Information System (INIS)
Erdelyi, Robert; Fedun, Viktor
2006-01-01
The aim of the present work is to investigate the excitation, time-dependent dynamic evolution, and interaction of nonlinear propagating (i.e., solitary) waves on vertical cylindrical magnetic flux tubes in compressible solar atmospheric plasma. The axisymmetric flux tube has a field strength of 1000 G at its footpoint, which is typical for photospheric regions. Nonlinear waves that develop into solitary waves are excited by a footpoint driver. The propagation of the nonlinear signal is investigated by solving numerically a set of fully nonlinear 2.0D magnetohydrodynamic (MHD) equations in cylindrical coordinates. For the initial conditions, axisymmetric solutions of the linear dispersion relation for wave modes in a magnetic flux tube are applied. In the present case, we focus on the sausage mode only. The dispersion relation is solved numerically for a range of plasma parameters. The equilibrium state is perturbed by a Gaussian at the flux tube footpoint. Two solitary solutions are found by solving the full nonlinear MHD equations. First, the nonlinear wave propagation with external sound speed is investigated. Next, the solitary wave propagating close to the tube speed, also found in the numerical solution, is studied. In contrast to previous analytical and numerical works, here no approximations were made to find the solitary solutions. A natural application of the present study may be spicule formation in the low chromosphere. Future possible improvements in modeling and the relevance of the photospheric chromospheric transition region coupling by spicules is suggested
Directory of Open Access Journals (Sweden)
Yang Yu
2017-10-01
Full Text Available Recently, guided wave (GW-based non-destructive evaluation (NDE techniques have been developed and considered as a potential candidate for integrity assessment of wood structures, such as wood utility poles. However, due to the lack of understanding on wave propagation in such structures, especially under the effect of surroundings such as soil, current GW-based NDE methods fail to properly account for the propagation of GWs and to contribute reliable and correct results. To solve this critical issue, this work investigates the behaviour of wave propagation in the wood utility pole with the consideration of the influence of soil. The commercial finite element (FE analysis software ANSYS is used to simulate GW propagation in a wood utility pole. In order to verify the numerical findings, the laboratory testing is also conducted in parallel with the numerical results to experimentally verify the effectiveness of developed FE models. Finally, sensitivity analysis is also carried out based on FE models of wood pole under different material properties, boundary conditions and excitation types.
Radio wave propagation in the Martian polar deposits: models and implications for radar sounding.
Ilyushin, Ya. A.
In the present study the propagation of electromagnetic waves in the northern polar ice sheet of Mars is considered Several different scenarios of the structure of the polar deposits and composition of the ice compatible with previously published observational data are proposed Both analytical and numerical simulations of ultra wide band chirp radar pulse propagating through the cap are performed Approximate approach based on the non-coherent theory of the radiative transfer in layered media has been applied to the problem of the propagation of radar pulses in the polar caps Both 1D and 2D and 3D geometry applicable to the orbital and landed radar instruments are studied The side clutter and phase distortions of the signal are also addressed analyzed The possibilities of retrieval of the geological information depending on transparency of the polar cap for radio waves are discussed If the polar cap is relatively transparent the echo from the base of the sheet should be clearly distinctive and interpretable in terms of basal topography of the cap In the case of moderate optical thickness coherent basal echo is corrupted by strong multiple scattering in the layered structure However some conclusions about basal conditions could be made from the signals for example the subglacial lakes may be detected Finally optically thick polar caps prevent any sounding of the base so only the medium itself can be characterized by GPR measurements e g the impurity content in the ice can be found Ilyushin Y A R Seu
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
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.
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.
The variational 2D Boussinesq model for wave propagation over a shoal
Adytia, D.; van Groesen, Embrecht W.C.
2011-01-01
The Variational Boussinesq Model (VBM) for waves (Klopman et al. 2010) is based on the Hamiltonian structure of gravity surface waves. In its approximation, the fluid potential in the kinetic energy is approximated by the sum of its value at the free surface and a linear combination of vertical
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
International Nuclear Information System (INIS)
Ranfagni, A.; Mugnai, D.
2011-01-01
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
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....
Persinger, R. R.; Stutzman, W. L.
1978-01-01
A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations.
Miyoshi, Y.; Jin, H.; Fujiwara, H.; Shinagawa, H.
2017-12-01
It has been recognized that gravity waves (GWs) play an important role on the momentum and energy budget in the thermosphere/ionosphere. In this study, using a whole atmosphere-ionosphere coupled model (GAIA), behaviors of Traveling Ionospheric Disturbances (TIDs) generated by upward propagating GWs in the thermosphere are investigated. The horizontal resolution of GAIA is 1 degree longitude by 1 degree latitude, which is adequate to simulate large-scale GWs. The GAIA contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of gravity waves in the lower atmosphere, their upward propagation to the mesosphere and thermosphere, and their impacts on the thermosphere/ionosphere system. The GAIA can simulate TIDs because interaction processes between the ionosphere and neutral atmosphere are included. We focus on seasonal and longitudinal variations of TIDs and their relation to GW activity in the thermosphere. Our results indicate that many TIDs are generated by upward propagating GWs in the thermosphere, and these TIDs propagate equatorward. TIDs are much stronger in winter than in summer. Moreover, day-to-day variability of GW activity in the stratosphere and mesosphere are examined, and their impacts on temporal variability of TIDs are discussed.
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.
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...... are derived by use of the adjoint variable method. Many wave propagation problems are open-region problems, i.e. the outer boundaries of the modeling domain must be re ection-less. The thesis contains new and independent developments within perfectly matched layer techniques for scalar as well......The study of elastic and optical waves together with intensive material research has revolutionized everyday as well as cutting edge technology in very tangible ways within the last century. Therefore it is important to continue the investigative work towards improving existing as well as innovate...
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.
Gravitational wave propagation in isotropic cosmologies
International Nuclear Information System (INIS)
Hogan, P.A.; O'Shea, E.M.
2002-01-01
We study the propagation of gravitational waves carrying arbitrary information through isotropic cosmologies. The waves are modeled as small perturbations of the background Robertson-Walker geometry. The perfect fluid matter distribution of the isotropic background is, in general, modified by small anisotropic stresses. For pure gravity waves, in which the perturbed Weyl tensor is radiative (i.e. type N in the Petrov classification), we construct explicit examples for which the presence of the anisotropic stress is shown to be essential and the histories of the wave fronts in the background Robertson-Walker geometry are shear-free null hypersurfaces. The examples derived in this case are analogous to the Bateman waves of electromagnetic theory
Modeling seismic wave propagation using staggered-grid mimetic finite differences
Directory of Open Access Journals (Sweden)
Freysimar Solano-Feo
2017-04-01
Full Text Available Mimetic finite difference (MFD approximations of continuous gradient and divergence operators satisfy a discrete version of the Gauss-Divergence theorem on staggered grids. On the mimetic approximation of this integral conservation principle, an unique boundary flux operator is introduced that also intervenes on the discretization of a given boundary value problem (BVP. In this work, we present a second-order MFD scheme for seismic wave propagation on staggered grids that discretized free surface and absorbing boundary conditions (ABC with same accuracy order. This scheme is time explicit after coupling a central three-level finite difference (FD stencil for numerical integration. Here, we briefly discuss the convergence properties of this scheme and show its higher accuracy on a challenging test when compared to a traditional FD method. Preliminary applications to 2-D seismic scenarios are also presented and show the potential of the mimetic finite difference method.
Leclerc, Gwladys E; Charleux, Fabrice; Ho Ba Tho, Marie-Christine; Bensamoun, Sabine F
2015-01-01
Magnetic resonance elastography (MRE), based on shear wave propagation generated by a specific driver, is a non-invasive exam performed in clinical practice to improve the liver diagnosis. The purpose was to develop a finite element (FE) identification method for the mechanical characterisation of phantom mimicking soft tissues investigated with MRE technique. Thus, a 3D FE phantom model, composed of the realistic MRE liver boundary conditions, was developed to simulate the shear wave propagation with the software ABAQUS. The assumptions of homogeneity and elasticity were applied to the FE phantom model. Different ranges of mesh size, density and Poisson's ratio were tested in order to develop the most representative FE phantom model. The simulated wave displacement was visualised with a dynamic implicit analysis. Subsequently, an identification process was performed with a cost function and an optimisation loop provided the optimal elastic properties of the phantom. The present identification process was validated on a phantom model, and the perspective will be to apply this method on abdominal tissues for the set-up of new clinical MRE protocols that could be applied for the follow-up of the effects of treatments.
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.
Two-dimensional modelling of thermonuclear combustion wave propagation in a z-pinch
International Nuclear Information System (INIS)
Vikhrev, V.V.; Rozanova, G.A.
1993-01-01
The development of sausage-type instabilities in initially homogeneous z-pinch plasma column lead to the appearance of dense plasma which temperature is substantially higher than the average plasma temperature in the column. This fact leads to the idea of using this high temperature areas for thermonuclear combustion wave initiation along a z-pinch axis. Calculate solution of MHD-equations was made for the case of large radiative energy losses and thermonuclear heat release. The influence of thermonuclear heat emission on the dynamics of sausage instability growth is seen most obviously in the slowing-down of α-particles in the plasma. In the calculations we assumed local emission of energy by the α-particles in the plasma. To fulfill the condition for thermonuclear combustion wave propagation in the axial direction, it is essential to have ρr>A in the pinch, where ρ is the density of the material compressed by the magnetic field and r is the characteristic transverse dimension of the region occupied by that material (for example the radius), and A is a constant determined by the type of thermonuclear fuel and the compression conditions. (author) 5 refs., 3 figs
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.
Propagating wave correlations in complex systems
International Nuclear Information System (INIS)
Creagh, Stephen C; Gradoni, Gabriele; Hartmann, Timo; Tanner, Gregor
2017-01-01
We describe a novel approach for computing wave correlation functions inside finite spatial domains driven by complex and statistical sources. By exploiting semiclassical approximations, we provide explicit algorithms to calculate the local mean of these correlation functions in terms of the underlying classical dynamics. By defining appropriate ensemble averages, we show that fluctuations about the mean can be characterised in terms of classical correlations. We give in particular an explicit expression relating fluctuations of diagonal contributions to those of the full wave correlation function. The methods have a wide range of applications both in quantum mechanics and for classical wave problems such as in vibro-acoustics and electromagnetism. We apply the methods here to simple quantum systems, so-called quantum maps, which model the behaviour of generic problems on Poincaré sections. Although low-dimensional, these models exhibit a chaotic classical limit and share common characteristics with wave propagation in complex structures. (paper)
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.
Wave Propagation in Jointed Geologic Media
Energy Technology Data Exchange (ETDEWEB)
Antoun, T
2009-12-17
Predictive modeling capabilities for wave propagation in a jointed geologic media remain a modern day scientific frontier. In part this is due to a lack of comprehensive understanding of the complex physical processes associated with the transient response of geologic material, and in part it is due to numerical challenges that prohibit accurate representation of the heterogeneities that influence the material response. Constitutive models whose properties are determined from laboratory experiments on intact samples have been shown to over-predict the free field environment in large scale field experiments. Current methodologies for deriving in situ properties from laboratory measured properties are based on empirical equations derived for static geomechanical applications involving loads of lower intensity and much longer durations than those encountered in applications of interest involving wave propagation. These methodologies are not validated for dynamic applications, and they do not account for anisotropic behavior stemming from direcitonal effects associated with the orientation of joint sets in realistic geologies. Recent advances in modeling capabilities coupled with modern high performance computing platforms enable physics-based simulations of jointed geologic media with unprecedented details, offering a prospect for significant advances in the state of the art. This report provides a brief overview of these modern computational approaches, discusses their advantages and limitations, and attempts to formulate an integrated framework leading to the development of predictive modeling capabilities for wave propagation in jointed and fractured geologic materials.
International Nuclear Information System (INIS)
Dupuy, B.
2011-11-01
Seismic wave propagation in multiphasic porous media have various environmental (natural risks, geotechnics, groundwater pollutions...) and resources (aquifers, oil and gas, CO 2 storage...) issues. When seismic waves are crossing a given material, they are distorted and thus contain information on fluid and solid phases. This work focuses on the characteristics of seismic waves propagating in multiphasic media, from the physical complex description to the parameter characterisation by inversion, including 2D numerical modelling of the wave propagation. The first part consists in the description of the physics of multiphasic media (each phase and their interactions), using several up-scaling methods, in order to obtain an equivalent mesoscale medium defined by seven parameters. Thus, in simple porosity saturated media and in complex media (double porosity, patchy saturation, visco-poro-elasticity), I can compute seismic wave propagation without any approximation. Indeed, I use a frequency-space domain for the numerical method, which allows to consider all the frequency dependent terms. The spatial discretization employs a discontinuous finite elements method (discontinuous Galerkin), which allows to take into account complex interfaces.The computation of the seismic attributes (velocities and attenuations) of complex porous media shows strong variations in respect with the frequency. Waveforms, computed without approximation, are strongly different if we take into account the full description of the medium or an homogenisation by averages. The last part of this work deals with the poro-elastic parameters characterisation by inversion. For this, I develop a two-steps method: the first one consists in a classical inversion (tomography, full waveform inversion) of seismograms data to obtain macro-scale parameters (seismic attributes). The second step allows to recover, from the macro-scale parameters, the poro-elastic micro-scale properties. This down-scaling step
Pressure wave propagation in sodium loop
International Nuclear Information System (INIS)
Botelho, D.A.
1989-01-01
A study was done on the pressure wave propagation within the pipes and mixture vessel of a termohydraulic loop for thermal shock with sodium. It was used the characteristic method to solve the one-dimensional continuity and momentum equations. The numerical model includes the pipes and the effects of valves and other accidents on pressure losses. The study was based on designer informations and engineering tables. It was evaluated the pressure wave sizes, parametrically as a function of the draining valve closure times. (author) [pt
Simioni, Stephan; Sidler, Rolf; Dual, Jürg; Schweizer, Jürg
2015-04-01
Avalanche control by explosives is among the key temporary preventive measures. Yet, little is known about the mechanism involved in releasing avalanches by the effect of an explosion. Here, we test the hypothesis that the stress induced by acoustic waves exceeds the strength of weak snow layers. Consequently the snow fails and the onset of rapid crack propagation might finally lead to the release of a snow slab avalanche. We performed experiments with explosive charges over a snowpack. We installed microphones above the snowpack to measure near-surface air pressure and accelerometers within three snow pits. We also recorded pit walls of each pit with high speed cameras to detect weak layer failure. Empirical relationships and a priori information from ice and air were used to characterize a porous layered model from density measurements of snow profiles in the snow pits. This model was used to perform two-dimensional numerical simulations of wave propagation in Biot-type porous material. Locations of snow failure were identified in the simulation by comparing the axial and deviatoric stress field of the simulation to the corresponding snow strength. The identified snow failure locations corresponded well with the observed failure locations in the experiment. The acceleration measured in the snowpack best correlated with the modeled acceleration of the fluid relative to the ice frame. Even though the near field of the explosion is expected to be governed by non-linear effects as for example the observed supersonic wave propagation in the air above the snow surface, the results of the linear poroelastic simulation fit well with the measured air pressure and snowpack accelerations. The results of this comparison are an important step towards quantifying the effectiveness of avalanche control by explosives.
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.
Larmat, C. S.; Delorey, A.; Rougier, E.; Knight, E. E.; Steedman, D. W.; Bradley, C. R.
2017-12-01
This presentation reports numerical modeling efforts to improve knowledge of the processes that affect seismic wave generation and propagation from underground explosions, with a focus on Rg waves. The numerical model is based on the coupling of hydrodynamic simulation codes (Abaqus, CASH and HOSS), with a 3D full waveform propagation code, SPECFEM3D. Validation datasets are provided by the Source Physics Experiment (SPE) which is a series of highly instrumented chemical explosions at the Nevada National Security Site with yields from 100kg to 5000kg. A first series of explosions in a granite emplacement has just been completed and a second series in alluvium emplacement is planned for 2018. The long-term goal of this research is to review and improve current existing seismic sources models (e.g. Mueller & Murphy, 1971; Denny & Johnson, 1991) by providing first principles calculations provided by the coupled codes capability. The hydrodynamic codes, Abaqus, CASH and HOSS, model the shocked, hydrodynamic region via equations of state for the explosive, borehole stemming and jointed/weathered granite. A new material model for unconsolidated alluvium materials has been developed and validated with past nuclear explosions, including the 10 kT 1965 Merlin event (Perret, 1971) ; Perret and Bass, 1975). We use the efficient Spectral Element Method code, SPECFEM3D (e.g. Komatitsch, 1998; 2002), and Geologic Framework Models to model the evolution of wavefield as it propagates across 3D complex structures. The coupling interface is a series of grid points of the SEM mesh situated at the edge of the hydrodynamic code domain. We will present validation tests and waveforms modeled for several SPE tests which provide evidence that the damage processes happening in the vicinity of the explosions create secondary seismic sources. These sources interfere with the original explosion moment and reduces the apparent seismic moment at the origin of Rg waves up to 20%.
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 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 drives...... for diesel engines by capturing both their spatial periodicity and axial motion. The Method of Varying Amplitudes is employed in the analysis. It is shown that the compound wave traveling in the axially moving periodic string comprises many components with different frequencies and wavenumbers....... This is in contrast to non-moving periodic structures, for which all components of the corresponding compound wave feature the same frequency. Due to this "multi-frequency" character of the wave motion, the conventional notion of frequency band-gaps appears to be not applicable for the moving periodic strings. Thus...
Seismic Wave Propagation in Layered Viscoelastic Media
Borcherdt, R. D.
2008-12-01
Advances in the general theory of wave propagation in layered viscoelastic media reveal new insights regarding seismic waves in the Earth. For example, the theory predicts: 1) P and S waves are predominantly inhomogeneous in a layered anelastic Earth with seismic travel times, particle-motion orbits, energy speeds, Q, and amplitude characteristics that vary with angle of incidence and hence, travel path through the layers, 2) two types of shear waves exist, one with linear and the other with elliptical particle motions each with different absorption coefficients, and 3) surface waves with amplitude and particle motion characteristics not predicted by elasticity, such as Rayleigh-Type waves with tilted elliptical particle motion orbits and Love-Type waves with superimposed sinusoidal amplitude dependencies that decay exponentially with depth. The general theory provides closed-form analytic solutions for body waves, reflection-refraction problems, response of multiple layers, and surface wave problems valid for any material with a viscoelastic response, including the infinite number of models, derivable from various configurations of springs and dashpots, such as elastic, Voight, Maxwell, and Standard Linear. The theory provides solutions independent of the amount of intrinsic absorption and explicit analytic expressions for physical characteristics of body waves in low-loss media such as the deep Earth. The results explain laboratory and seismic observations, such as travel-time and wide-angle reflection amplitude anomalies, not explained by elasticity or one dimensional Q models. They have important implications for some forward modeling and inverse problems. Theoretical advances and corresponding numerical results as recently compiled (Borcherdt, 2008, Viscoelastic Waves in Layered Media, Cambridge University Press) will be reviewed.
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....
Huberts, W; de Jonge, C; van der Linden, W P M; Inda, M A; Passera, K; Tordoir, J H M; van de Vosse, F N; Bosboom, E M H
2013-06-01
Decision-making in vascular access surgery for hemodialysis can be supported by a pulse wave propagation model that is able to simulate pressure and flow changes induced by the creation of a vascular access. To personalize such a model, patient-specific input parameters should be chosen. However, the number of input parameters that can be measured in clinical routine is limited. Besides, patient data are compromised with uncertainty. Incomplete and uncertain input data will result in uncertainties in model predictions. In part A, we analyzed how the measurement uncertainty in the input propagates to the model output by means of a sensitivity analysis. Of all 73 input parameters, 16 parameters were identified to be worthwhile to measure more accurately and 51 could be fixed within their measurement uncertainty range, but these latter parameters still needed to be measured. Here, we present a methodology for assessing the model input parameters that can be taken constant and therefore do not need to be measured. In addition, a method to determine the value of this parameter is presented. For the pulse wave propagation model applied to vascular access surgery, six patient-specific datasets were analyzed and it was found that 47 out of 73 parameters can be fixed on a generic value. These model parameters are not important for personalization of the wave propagation model. Furthermore, we were able to determine a generic value for 37 of the 47 fixable model parameters. Copyright © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.
Oral, Elif; Gélis, Céline; Bonilla, Luis Fabián; Delavaud, Elise
2017-12-01
Numerical modelling of seismic wave propagation, considering soil nonlinearity, has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions. Indeed, when strong ground motion propagates in saturated soils, pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected. Here, we model 1-D seismic wave propagation in linear and nonlinear media using the spectral element numerical method. The study uses a three-component (3C) nonlinear rheology and includes pore-pressure excess. The 1-D-3C model is used to study the 1987 Superstition Hills earthquake (ML 6.6), which was recorded at the Wildlife Refuge Liquefaction Array, USA. The data of this event present strong soil nonlinearity involving pore-pressure effects. The ground motion is numerically modelled for different assumptions on soil rheology and input motion (1C versus 3C), using the recorded borehole signals as input motion. The computed acceleration-time histories show low-frequency amplification and strong high-frequency damping due to the development of pore pressure in one of the soil layers. Furthermore, the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1C analysis, and significant differences in surface displacements are observed between the 1C and 3C approaches. This study contributes to identify and understand the dominant phenomena occurring in superficial layers, depending on local soil properties and input motions, conditions relevant for site-specific studies.
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....
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
Distributed parameter and finite element models for wave propagation in railway contact lines
Sorrentino, S.; Anastasio, D.; Fasana, A.; Marchesiello, S.
2017-12-01
A distributed parameter model of a railway two-level catenary system is presented for the analysis of the coupled wave dynamics. The wires are modelled as two straight axis parallel beams, with linear equilibrium equations, and the moving load applied by the pantograph is modelled as a constant concentrated travelling force. The general solution is sought by an application of the Ritz-Galerkin method, and then compared with direct time integrations of a finite element model (FEM), achieved by two different integration schemes. The proposed model provides a valid reference for appropriately selecting the FEM parameters, in order to reduce the errors due to spurious modes, affecting the numerical integrations especially at high speeds of the moving pantograph.
Wave propagation in damage assessment of ground anchors
Zima, B.; Rucka, M.
2015-07-01
The inspection possibilities of ground anchors are limited to destructive test such as pull-out test. Guided wave propagation gives an opportunity to develop an inspection system dedicated to determine the condition of inspected element without violation of their integrity. In this paper the experimental study on wave propagation in laboratory models of ground anchors are presented. Experiments were conducted for different bonding lengths and different frequencies of excitation. Waves were generated by a piezoelectric actuator and the laser vibrometry technique was used to register velocity signals. For all tested anchors it was possible to identify the boundary between steel and concrete based on the registered reflections in wave propagation signals.
Directory of Open Access Journals (Sweden)
M. E. Gorbunov
2018-01-01
Full Text Available A new reference occultation processing system (rOPS will include a Global Navigation Satellite System (GNSS radio occultation (RO retrieval chain with integrated uncertainty propagation. In this paper, we focus on wave-optics bending angle (BA retrieval in the lower troposphere and introduce (1 an empirically estimated boundary layer bias (BLB model then employed to reduce the systematic uncertainty of excess phases and bending angles in about the lowest 2 km of the troposphere and (2 the estimation of (residual systematic uncertainties and their propagation together with random uncertainties from excess phase to bending angle profiles. Our BLB model describes the estimated bias of the excess phase transferred from the estimated bias of the bending angle, for which the model is built, informed by analyzing refractivity fluctuation statistics shown to induce such biases. The model is derived from regression analysis using a large ensemble of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC RO observations and concurrent European Centre for Medium-Range Weather Forecasts (ECMWF analysis fields. It is formulated in terms of predictors and adaptive functions (powers and cross products of predictors, where we use six main predictors derived from observations: impact altitude, latitude, bending angle and its standard deviation, canonical transform (CT amplitude, and its fluctuation index. Based on an ensemble of test days, independent of the days of data used for the regression analysis to establish the BLB model, we find the model very effective for bias reduction and capable of reducing bending angle and corresponding refractivity biases by about a factor of 5. The estimated residual systematic uncertainty, after the BLB profile subtraction, is lower bounded by the uncertainty from the (indirect use of ECMWF analysis fields but is significantly lower than the systematic uncertainty without BLB correction. The
Gorbunov, Michael E.; Kirchengast, Gottfried
2018-01-01
A new reference occultation processing system (rOPS) will include a Global Navigation Satellite System (GNSS) radio occultation (RO) retrieval chain with integrated uncertainty propagation. In this paper, we focus on wave-optics bending angle (BA) retrieval in the lower troposphere and introduce (1) an empirically estimated boundary layer bias (BLB) model then employed to reduce the systematic uncertainty of excess phases and bending angles in about the lowest 2 km of the troposphere and (2) the estimation of (residual) systematic uncertainties and their propagation together with random uncertainties from excess phase to bending angle profiles. Our BLB model describes the estimated bias of the excess phase transferred from the estimated bias of the bending angle, for which the model is built, informed by analyzing refractivity fluctuation statistics shown to induce such biases. The model is derived from regression analysis using a large ensemble of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO observations and concurrent European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields. It is formulated in terms of predictors and adaptive functions (powers and cross products of predictors), where we use six main predictors derived from observations: impact altitude, latitude, bending angle and its standard deviation, canonical transform (CT) amplitude, and its fluctuation index. Based on an ensemble of test days, independent of the days of data used for the regression analysis to establish the BLB model, we find the model very effective for bias reduction and capable of reducing bending angle and corresponding refractivity biases by about a factor of 5. The estimated residual systematic uncertainty, after the BLB profile subtraction, is lower bounded by the uncertainty from the (indirect) use of ECMWF analysis fields but is significantly lower than the systematic uncertainty without BLB correction. The systematic and
International Nuclear Information System (INIS)
Suarez Antola, R.
2006-11-01
After a brief historical survey of some work done on the linear theory of longitudinal vibrations and wave propagation in rods and tubes of uniform cross-section, a simple mathematical model for rods and tubes of linear elastic materials is proposed. Three suitably selected propagation modes (one extensional and two shear modes) with dispersion relations corresponding to mixed boundary conditions are coupled in order to approximately comply with zero-stress boundary conditions. The coupling gives a set of partial differential equations in the mode amplitudes, with time and a single space coordinate (along the axis of symmetry of the rod or tube) as independent variables. Then, the model is generalized to a set of partial integral-differential equations in order to be able to describe vibrations and wave propagation in rods and tubes made of linear hereditary-elastic solids. In this first part of the work, the focus is in either very low frequency or very high frequency phenomena using a simple model with only two coupled modes. The model allows a fairly elegant and comparatively powerful analytical approach to longitudinal vibrations and to longitudinal pulse propagation in solid waveguides. Analytical formulae for group velocities are derived, as well as asymptotic expressions for the propagation of mode amplitudes. The limitations and pitfalls of the model are assessed, and new experiments and digital simulations are suggested to test some of its predictions, wave propagation; elastic and hereditary-elastic materials; propagation modes in rods and tubes
Petrov, P.; Newman, G. A.
2011-12-01
Recent developments in high resolution imaging technology of subsurface objects involves a combination of different geophysical measurements (gravity, EM and seismic). A joint image of the subsurface geophysical attributes (velocity, electrical conductivity and density) requires the consistent treatment of the different geophysical data due to their differing physical nature. For example, in conducting media, which is typical of the Earth's interior, EM energy propagation is defined by a diffusive mechanism and may be characterized by two specific length scales: wavelength and skin depth. However, the propagation of seismic signals is a multiwave process and is characterized by a set of wavelengths. Thus, to consistently treat seismic and electromagnetic data an additional length scale is needed for seismic data that does not directly depend on a wavelength and describes a diffusive process, similar to EM wave propagation in the subsurface. Works by Brown et al.(2005), Shin and Cha(2008), and Shin and Ha(2008) suggest that an artificial damping of seismic wave fields via Laplace-Fourier transformation can be an effective approach to obtain a seismic data that have similar spatial resolution to EM data. The key benefit of such transformation is that diffusive wave-field inversion works well for both data sets: seismic (Brown et al.,2005; Shin and Cha,2008) and electromagnetic (Commer and Newman,2008; Newman et al.,2010). With the recent interest in the Laplace-Fourier domain full waveform inversion, 3D fourth and second-order finite-difference schemes for modeling of seismic wave propagation have been developed (Petrov and Newman, 2010). Incorporation of attenuation and anisotropy into a velocity model is a necessary step for a more realistic description of subsurface media. Here we consider the extension of our method which includes attenuation and VTI anisotropy. Our approach is based on the integro-interpolation technique for velocity-stress formulation. Seven
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.
Full wave simulations of lower hybrid wave propagation in tokamaks
Wright, J. C.; Bonoli, P. T.; Phillips, C. K.; Valeo, E.; Harvey, R. W.
2009-11-01
Lower hybrid (LH) waves have the attractive property of damping strongly via electron Landau resonance on relatively fast tail electrons at (2.5-3)×vte, where vte ≡ (2Te/me)1/2 is the electron thermal speed. Consequently these waves are well-suited to driving current in the plasma periphery where the electron temperature is lower, making LH current drive (LHCD) a promising technique for off-axis (r/a⩾0.60) current profile control in reactor grade plasmas. Established techniques for computing wave propagation and absorption use WKB expansions with non-Maxwellian self-consistent distributions. In typical plasma conditions with electron densities of several 1019 m-3 and toroidal magnetic fields strengths of 4 Telsa, the perpendicular wavelength is of the order of 1 mm and the parallel wavelength is of the order of 1 cm. Even in a relatively small device such as Alcator C-Mod with a minor radius of 22 cm, the number of wavelengths that must be resolved requires large amounts of computational resources for the full wave treatment. These requirements are met with a massively parallel version of the TORIC full wave code that has been adapted specifically for the simulation of LH waves [J. C. Wright, et al., Commun. Comput. Phys., 4, 545 (2008), J. C. Wright, et al., Phys. Plasmas 16 July (2009)]. This model accurately represents the effects of focusing and diffraction that occur in LH propagation. It is also coupled with a Fokker-Planck solver, CQL3D, to provide self-consistent distribution functions for the plasma dielectric as well as a synthetic hard X-ray (HXR) diagnostic for direct comparisons with experimental measurements of LH waves. The wave solutions from the TORIC-LH zero FLR model will be compared to the results from ray tracing from the GENRAY/CQL3D code via the synthetic HXR diagnostic and power deposition.
Full wave simulations of lower hybrid wave propagation in tokamaks
International Nuclear Information System (INIS)
Wright, J. C.; Bonoli, P. T.; Phillips, C. K.; Valeo, E.; Harvey, R. W.
2009-01-01
Lower hybrid (LH) waves have the attractive property of damping strongly via electron Landau resonance on relatively fast tail electrons at (2.5-3)xv te , where v te ≡ (2T e /m e ) 1/2 is the electron thermal speed. Consequently these waves are well-suited to driving current in the plasma periphery where the electron temperature is lower, making LH current drive (LHCD) a promising technique for off-axis (r/a≥0.60) current profile control in reactor grade plasmas. Established techniques for computing wave propagation and absorption use WKB expansions with non-Maxwellian self-consistent distributions.In typical plasma conditions with electron densities of several 10 19 m -3 and toroidal magnetic fields strengths of 4 Telsa, the perpendicular wavelength is of the order of 1 mm and the parallel wavelength is of the order of 1 cm. Even in a relatively small device such as Alcator C-Mod with a minor radius of 22 cm, the number of wavelengths that must be resolved requires large amounts of computational resources for the full wave treatment. These requirements are met with a massively parallel version of the TORIC full wave code that has been adapted specifically for the simulation of LH waves [J. C. Wright, et al., Commun. Comput. Phys., 4, 545 (2008), J. C. Wright, et al., Phys. Plasmas 16 July (2009)]. This model accurately represents the effects of focusing and diffraction that occur in LH propagation. It is also coupled with a Fokker-Planck solver, CQL3D, to provide self-consistent distribution functions for the plasma dielectric as well as a synthetic hard X-ray (HXR) diagnostic for direct comparisons with experimental measurements of LH waves.The wave solutions from the TORIC-LH zero FLR model will be compared to the results from ray tracing from the GENRAY/CQL3D code via the synthetic HXR diagnostic and power deposition.
Some considerations of wave propagation
Verdonk, P. L. F. M.
The meaning of group velocity and its relation to conserved quantities are demonstrated. The origin of wave dispersion in terms of nonlocal and relaxation phenomena are clarified. The character of a wave described by an equation with a general type of nonlinearity and general dispersion terms is explained. The steepening of a wave flank and the occurrence of stationary waves are 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...
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.
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,
Propagating waves in human motor cortex
Directory of Open Access Journals (Sweden)
Kazutaka eTakahashi
2011-04-01
Full Text Available Previous studies in non-human primates have shown that beta oscillations (15-30Hz of local field potentials (LFPs in the arm/hand areas of primary motor cortex (MI propagate as traveling waves across the cortex. These waves exhibited two stereotypical features across animals and tasks: 1 The waves propagated in two dominant modal directions roughly 180 degrees apart, and 2 their propagation speed ranged from 10 ~ 35 cm/s. It is, however, unknown if such cortical waves occur in the human motor cortex. This study shows that the two properties of propagating beta waves are present in MI of a tetraplegic human patient while he was instructed to perform an instruction delay center out task using a cursor controlled by the chin. Moreover, we show that beta waves are sustained and have similar properties whether the subject was engaged in the task or at rest. The directions of the successive sustained waves both in the human subject and a nonhuman primate (NHP subject tended to switch from one dominant mode to the other, and at least in the NHP subject the estimated distance travelled between successive waves traveling into and out of the central sulcus is consistent with the hypothesis of wave reflection between the border of motor and somatosensory cortices. Further, we show that the occurrence of the beta waves is not uniquely tied to periods of increased power in the beta frequency band. These results demonstrate that traveling beta waves in MI are a general phenomenon occurring in human as well as non-human primates. Consistent with the non-human primate data, the dominant directions of the beta LFP waves in human aligned to the proximal to distal gradient of joint representations in MI somatotopy. This consistent finding of wave propagation may imply the existence of a hardwired organization of motor cortex that mediates this spatio-temporal pattern.
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.
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.
Variation principle for nonlinear wave propagation
International Nuclear Information System (INIS)
Watanabe, T.; Lee, Y.C.; Nishikawa, Kyoji; Hojo, H.; Yoshida, Y.
1976-01-01
Variation principle is derived which determines stationary nonlinear propagation of electrostatic waves in the self-consistent density profile. Example is given for lower-hybrid waves and the relation to the variation principle for the Lagrangian density of electromagnetic fluids is discussed
Wave propagation in thermoelastic saturated porous medium
Indian Academy of Sciences (India)
tural engineering or to hydrocarbon/geothermal processes. References. Bear J, Sorek S, Ben-Dor G and Mazor G 1992 Displacement waves in saturated thermoelastic porous media, I. Basic equations; Fluid Dyn. Res. 9 155–164. Biot M A 1956a The theory of propagation of elastic waves in a fluid-saturated porous solid, ...
Froger, A.
2004-07-01
The standard models in use to simulate the reactive detonation wave propagation are not accurate in computing the transient evolutions because they focus on the shock front, not on the reaction zone where the coupling of thermodynamic and mechanic effects occurs. The model we propose is based on a new thermodynamic description of the constituents in the reaction zone, and on the use of the enthalpy balance of the chemical reaction as the energetic parameter instead of the heat of reaction. The enthalpy balance of the reaction results from the enthalpies of formation of all the chemical species involved in the reaction and is, therefore, a physical constant. The model is based on four basic assumptions: -1) the reaction zone is anevolving intimate mixture of non-reacted material and detonation products, -2) the energy released by thereaction is inherent to the detonation products alone, -3) the two constituents have the same pressure but different temperatures, -4) the specific energy released is not a constant but is related to the enthalpy balance and depends on the thermodynamic state. The model only needs the physical properties of the materials (equations of state of the constituents, chemical reaction and initiation delay), not the CJ state nor any other sub-model. When coupled with the Euler equations this thermodynamic description of the reaction zone permits us to simulate the transient evolution of an emerging detonation for any geometry (2D or 3D) or confinement structure.
Martin, Roland; Komatitsch, Dimitri; Bruthiaux, Emilien; Gedney, Stephen D.
2010-05-01
by 40% in 2D comparing to the GFPML split formulation of [4]. Examples of waves propagating in heterogeneous thin slices in presence of free surface are shown. We also applied this CPML technique to more complex models like poroelastic [5] or viscoelastic [6] media based on a fourth-order staggered finite-difference method. For the two-dimensional Biot poroelastic equations we show its efficiency for both non dissipative and dissipative Biot porous models. For the three-dimensional viscoelastic seismic wave equation, the time marching equations of the standard linear solid mechanisms used do not need to be split and only the memory variables associated with velocity derivatives are stored at each time step. In the case of more than one damping mechanism, we are able to reduce memory storage by more than 70% in the PML regions in 3D simulations compared to split PMLs optimized at grazing incidence. Benchmarks of the CPML technique have been validated in poroelastic or viscoelastic thin mesh slices. These unsplit CPMLs are usually computed based on a second-order finite-difference time scheme. However, in many situations like very long time simulations, it is of interest to increase the accuracy of the method by increasing the order of the time marching and spatial discretizations. The CPML is not able to be increased at high orders because of its convolution formulation. In [7] we study then how to build a new unsplit PML (ADE-PML/Auxiliary Differential Equations PML) that remains optimized at grazing incidence based on a high-order time scheme like the fourth-order Runge-Kutta scheme. At second order in time we demonstrate that CPML and ADE-PML are equivalent. At second or high order discretization in time, explicit and semi-implicit solutions can be obtained with very good accuracy. References [1]Dimitri Komatitsch and Roland Martin. An unsplit convolutional Perfectly Matched Layer improved at grazing incidence for the differential anisotropic elastic wave equation
International Nuclear Information System (INIS)
Iooss, B.
2009-01-01
The present document constitutes my Habilitation thesis report. It recalls my scientific activity of the twelve last years, since my PhD thesis until the works completed as a research engineer at CEA Cadarache. The two main chapters of this document correspond to two different research fields both referring to the uncertainty treatment in engineering problems. The first chapter establishes a synthesis of my work on high frequency wave propagation in random medium. It more specifically relates to the study of the statistical fluctuations of acoustic wave travel-times in random and/or turbulent media. The new results mainly concern the introduction of the velocity field statistical anisotropy in the analytical expressions of the travel-time statistical moments according to those of the velocity field. This work was primarily carried by requirements in geophysics (oil exploration and seismology). The second chapter is concerned by the probabilistic techniques to study the effect of input variables uncertainties in numerical models. My main applications in this chapter relate to the nuclear engineering domain which offers a large variety of uncertainty problems to be treated. First of all, a complete synthesis is carried out on the statistical methods of sensitivity analysis and global exploration of numerical models. The construction and the use of a meta-model (inexpensive mathematical function replacing an expensive computer code) are then illustrated by my work on the Gaussian process model (kriging). Two additional topics are finally approached: the high quantile estimation of a computer code output and the analysis of stochastic computer codes. We conclude this memory with some perspectives about the numerical simulation and the use of predictive models in industry. This context is extremely positive for future researches and application developments. (author)
Huberts, W; de Jonge, C; van der Linden, W P M; Inda, M A; Tordoir, J H M; van de Vosse, F N; Bosboom, E M H
2013-06-01
Previously, a pulse wave propagation model was developed that has potential in supporting decision-making in arteriovenous fistula (AVF) surgery for hemodialysis. To adapt the wave propagation model to personalized conditions, patient-specific input parameters should be available. In clinics, the number of measurable input parameters is limited which results in sparse datasets. In addition, patient data are compromised with uncertainty. These uncertain and incomplete input datasets will result in model output uncertainties. By means of a sensitivity analysis the propagation of input uncertainties into output uncertainty can be studied which can give directions for input measurement improvement. In this study, a computational framework has been developed to perform such a sensitivity analysis with a variance-based method and Monte Carlo simulations. The framework was used to determine the influential parameters of our pulse wave propagation model applied to AVF surgery, with respect to parameter prioritization and parameter fixing. With this we were able to determine the model parameters that have the largest influence on the predicted mean brachial flow and systolic radial artery pressure after AVF surgery. Of all 73 parameters 51 could be fixed within their measurement uncertainty interval without significantly influencing the output, while 16 parameters importantly influence the output uncertainty. Measurement accuracy improvement should thus focus on these 16 influential parameters. The most rewarding are measurement improvements of the following parameters: the mean aortic flow, the aortic windkessel resistance, the parameters associated with the smallest arterial or venous diameters of the AVF in- and outflow tract and the radial artery windkessel compliance. Copyright © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.
Bou Matar, Olivier; Gasmi, Noura; Zhou, Huan; Goueygou, Marc; Talbi, Abdelkrim
2013-03-01
A numerical method to compute propagation constants and mode shapes of elastic waves in layered piezoelectric-piezomagnetic composites, potentially deposited on a substrate, is described. The basic feature of the method is the expansion of particle displacement, stress fields, electric and magnetic potentials in each layer on different polynomial bases: Legendre for a layer of finite thickness and Laguerre for the semi-infinite substrate. The exponential convergence rate of the method for propagation of Love waves is numerically verified. The main advantage of the method is to directly determine complex wave numbers for a given frequency via a matricial eigenvalue problem, in a way that no transcendental equation has to be solved. Results are presented and the method is discussed.
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
Lamb wave propagation in monocrystalline silicon wafers.
Fromme, Paul; Pizzolato, Marco; Robyr, Jean-Luc; Masserey, Bernard
2018-01-01
Monocrystalline silicon wafers are widely used in the photovoltaic industry for solar panels with high conversion efficiency. Guided ultrasonic waves offer the potential to efficiently detect micro-cracks in the thin wafers. Previous studies of ultrasonic wave propagation in silicon focused on effects of material anisotropy on bulk ultrasonic waves, but the dependence of the wave propagation characteristics on the material anisotropy is not well understood for Lamb waves. The phase slowness and beam skewing of the two fundamental Lamb wave modes A 0 and S 0 were investigated. Experimental measurements using contact wedge transducer excitation and laser measurement were conducted. Good agreement was found between the theoretically calculated angular dependency of the phase slowness and measurements for different propagation directions relative to the crystal orientation. Significant wave skew and beam widening was observed experimentally due to the anisotropy, especially for the S 0 mode. Explicit finite element simulations were conducted to visualize and quantify the guided wave beam skew. Good agreement was found for the A 0 mode, but a systematic discrepancy was observed for the S 0 mode. These effects need to be considered for the non-destructive testing of wafers using guided waves.
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...
Wang, Aichen; Lu, Renfu; Xie, Lijuan
2016-01-01
Spatially resolved spectroscopy provides a means for measuring the optical properties of biological tissues, based on analytical solutions to diffusion approximation for semi-infinite media under the normal illumination of an infinitely small light beam. The method is, however, prone to error in measurement because the actual boundary condition and light beam often deviate from that used in deriving the analytical solutions. It is therefore important to quantify the effect of different boundary conditions and light beams on spatially resolved diffuse reflectance in order to improve the measurement accuracy of the technique. This research was aimed at using finite element method (FEM) to model light propagation in turbid media, subjected to normal illumination by a continuous-wave beam of infinitely small or finite size. Three types of boundary conditions [i.e., partial current (PCBC), extrapolated (EBC), and zero (ZBC)] were evaluated and compared against Monte Carlo (MC) simulations, since MC could provide accurate fluence rate and diffuse reflectance. The effect of beam size was also investigated. Overall results showed that FEM provided results as accurate as those of the analytical method when an appropriate boundary condition was applied. ZBC did not give satisfactory results in most cases. FEM-PCBC yielded a better fluence rate at the boundary than did FEM-EBC, while they were almost identical in predicting diffuse reflectance. Results further showed that FEM coupled with EBC effectively simulated spatially resolved diffuse reflectance under the illumination of a finite size beam. A large beam introduced more error, especially within the region of illumination. Research also confirmed an earlier finding that a light beam of less than 1 mm diameter should be used for estimation of optical parameters. FEM is effective for modeling light propagation in biological tissues and can be used for improving the optical property measurement by the spatially resolved
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.
Lloyd, Stephen F.
The purpose of this research is to test the effectiveness of forward and inverse modeling approaches in wave propagation analysis problems with complex settings and scenarios that include fluid-solid interfaces, non-stationary sources, and non-point sources not previously investigated. The research is made up of three components. First, finite element method modeling and a genetic algorithm are employed to assess the feasibility of using inverse modeling to determine the thickness of the surface ice on Europa, one of Jupiter's moons, and the depth of a possible subsurface ocean. The feasibility study presented in this dissertation considers the specific case in which inverse modeling might be used to determine the depths of ice and ocean layers on Europa for a possible space mission in which the effects of a spacecraft-released impactor on Europa's surface are measured. Second, reconstructing dynamic distributed loads, such as truck loads on highways, require inverting for large numbers of parameters. To address solving for the large number of unknowns in such problems, an adjoint-method-based acoustic-source inversion procedure for reconstructing multiple moving, non-point acoustic sources is developed and tested with numerical experiments. Third, forward modeling of moving sources in three-dimensional (3D) settings is tested with numerical experiments using SPECFEM3D, an open source spectral element method program. Researching forward modeling for complicated scenarios such as moving acoustic sources in fluid-solid coupled systems in 3D is an important step toward using SPECFEM3D for moving-source inversion problems in 3D. The conclusions of the research presented are as follows: It is feasible to estimate the thickness of the ice layer on the surface of Europa and the depth of a subsurface ocean with inverse modeling based on measured wave motions in the ice caused by a planned impact. The adjoint method is effective in reconstructing large numbers of acoustic
Wave propagation in heterogeneous excitable media
Schebesch, I.; Engel, H.
1998-04-01
Heterogeneities deeply affect pulse dynamics in excitable media. In one dimension, spatially periodic variation of the excitation threshold leads to a characteristic dependence of the propagation speed on the modulation period d with a maximum at a certain optimal value dopt. The maximum speed may be larger than the pulse velocity in an effective homogeneous medium. In two dimensions, the geometry and size of heterogeneities determine the wave dynamics. For example, an excitability distribution made of oblique stripes with different angles of inclination can result in a speedup or a slowdown of the pulse. The calculations are carried out with a modified Oregonator model for light-sensitive Belouzov-Zhabotinskii media where a heterogeneous distribution of excitability can be achieved by inhomogeneous illumination. Nevertheless, the results do not depend on the details of the local kinetics, but apply to the general case of excitable media.
Wave Propagation in Finite Element and Mass-Spring-Dashpot Lattice Models
National Research Council Canada - National Science Library
Holt-Phoenix, Marianne S
2006-01-01
...), and a mass-spring-dashpot lattice model (MSDLM) are investigated. Specifically, the error in the ultrasonic phase speed with variations in Poisson's ratio and angle of incidence is evaluated in each model of an isotropic elastic solid...
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...
Submillimeter wave propagation in tokamak plasmas
International Nuclear Information System (INIS)
Ma, C.H.; Hutchinson, D.P.; Staats, P.A.; Vander Sluis, K.L.; Mansfield, D.K.; Park, H.; Johnson, L.C.
1986-01-01
Propagation of submillimeter waves (smm) in tokamak plasma was investigated both theoretically and experimentally to ensure successful measurements of electron density and plasma current distributions in tokamak devices. Theoretical analyses were carried out to study the polarization of the smm waves in TFTR and ISX-B tokamaks. A multichord smm wave interferometer/polarimeter system was employed to simultaneously measure the line electron density and poloidal field-induced Faraday rotation in the ISX-B tokamak. The experimental study on TFTR is under way. Computer codes were developed and have been used to study the wave propagation and to reconstruct the distributions of plasma current and density from the measured data. The results are compared with other measurements. 5 references, 2 figures
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.
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......{\\partial^2}{\\partial t^2}u -(\\lambda+\\mu){\\text{\\rm grad div}} u -\\mu\\Deltau=0,\\end{equation}where $u=u(t,x)$ denotes a 3-vector field on $\\Bbb R\\times\\Bbb R^3$,and $\\lambda$ and $\\mu$ are the Lame-constants....
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......{\\partial^2}{\\partial t^2}u -(\\lambda+\\mu){\\text{\\rm grad div}} u -\\mu\\Delta u=0, \\end{equation} where $u=u(t,x)$ denotes a 3-vector field on $\\Bbb R\\times\\Bbb R^3$, and $\\lambda$ and $\\mu$ are the Lame-constants....
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.
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
Uniform and Multi-Grid Modeling of Acoustic Wave Propagation With Cellular Automaton Techniques
2013-03-01
reflecting boundary conditions, as the interpolation mechanism between the local and global domain, produce the best modeling results. A devised...Beijing, China , 2012. [19] A. D. White, SONAR for Practising Engineers, England: John Wiley & Sons, 2002. [20] F. Sturm and J. A. Fawcett, “On the
Time-domain modeling of high-frequency electromagnetic wave propagation, overhead wires, and earth
Stenvig, Nils Markus
2011-12-01
Prediction of radiated fields from transmission lines has not previously been studied from a panoptical power system perspective. The application of BPL technologies to overhead transmission lines would benefit greatly from an ability to simulate real power system environments, not limited to the transmission lines themselves. Presently circuit-based transmission line models used by EMTP-type programs utilize Carson's formula for a waveguide parallel to an interface. This formula is not valid for calculations at high frequencies, considering effects of earth return currents. This thesis explains the challenges of developing such improved models, explores an approach to combining circuit-based and electromagnetics modeling to predict radiated fields from transmission lines, exposes inadequacies of simulation tools, and suggests methods of extending the validity of transmission line models into very high frequency ranges. Electromagnetics programs are commonly used to study radiated fields from transmission lines. However, an approach is proposed here which is also able to incorporate the components of a power system through the combined use of EMTP-type models. Carson's formulas address the series impedance of electrical conductors above and parallel to the earth. These equations have been analyzed to show their inherent assumptions and what the implications are. Additionally, the lack of validity into higher frequencies has been demonstrated, showing the need to replace Carson's formulas for these types of studies. This body of work leads to several conclusions about the relatively new study of BPL. Foremost, there is a gap in modeling capabilities which has been bridged through integration of circuit-based and electromagnetics modeling, allowing more realistic prediction of BPL performance and radiated fields. The proposed approach is limited in its scope of validity due to the formulas used by EMTP-type software. To extend the range of validity, a new set of
Controlling wave propagation through nonlinear engineered granular systems
Leonard, Andrea
We study the fundamental dynamic behavior of a special class of ordered granular systems in order to design new, structured materials with unique physical properties. The dynamic properties of granular systems are dictated by the nonlinear, Hertzian, potential in compression and zero tensile strength resulting from the discrete material structure. Engineering the underlying particle arrangement of granular systems allows for unique dynamic properties, not observed in natural, disordered granular media. While extensive studies on 1D granular crystals have suggested their usefulness for a variety of engineering applications, considerably less attention has been given to higher-dimensional systems. The extension of these studies in higher dimensions could enable the discovery of richer physical phenomena not possible in 1D, such as spatial redirection and anisotropic energy trapping. We present experiments, numerical simulation (based on a discrete particle model), and in some cases theoretical predictions for several engineered granular systems, studying the effects of particle arrangement on the highly nonlinear transient wave propagation to develop means for controlling the wave propagation pathways. The first component of this thesis studies the stress wave propagation resulting from a localized impulsive loading for three different 2D particle lattice structures: square, centered square, and hexagonal granular crystals. By varying the lattice structure, we observe a wide range of properties for the propagating stress waves: quasi-1D solitary wave propagation, fully 2D wave propagation with tunable wave front shapes, and 2D pulsed wave propagation. Additionally the effects of weak disorder, inevitably present in real granular systems, are investigated. The second half of this thesis studies the solitary wave propagation through 2D and 3D ordered networks of granular chains, reducing the effective density compared to granular crystals by selectively placing wave
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…
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...
An optimal design problem in wave propagation
DEFF Research Database (Denmark)
Bellido, J.C.; Donoso, Alberto
2007-01-01
We consider an optimal design problem in wave propagation proposed in Sigmund and Jensen (Roy. Soc. Lond. Philos. Trans. Ser. A 361:1001-1019, 2003) in the one-dimensional situation: Given two materials at our disposal with different elastic Young modulus and different density, the problem consists...
Ionospheric Plasma Heating During Powerful Wave Propagation ...
African Journals Online (AJOL)
Ionospheric Plasma Heating During Powerful Wave Propagation. S Ram. Full Text: EMAIL FULL TEXT EMAIL FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · http://dx.doi.org/10.4314/dai.v12i1.15563 · AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's ...
International Nuclear Information System (INIS)
Ben-Khalifa, Warida
2013-01-01
AE Non-destructive testing is used in many fields such as nuclear energy, oil and gas, civil engineering or mechanical engineering to check the integrity of structures under stress. Depending on the ratio of structure thickness to wavelength, the energy released by a crack under stress can propagate either as guided waves (in thin structures) or as Rayleigh wave (in thick structures). The analysis of signals resulting from this ultrasonic 'passive' method is particularly difficult due to the complexity of typically measured signals. The objective of this thesis is to develop models to enable the simulation of AE testing experiments in the case of thick or thin structure. The developed models rely on the coupling between an AE source model, wave propagation models and an AE Sensor model. In the case of thick structures two 2D models (for plane and cylindrical surfaces) and a 3D model (for plane surface) have been developed to predict the signal corresponding to the Rayleigh wave emitted by a crack under stress. In the case of thin structures, a 2D model has been developed to predict the signal corresponding to the guided modes emitted by a crack under stress. Several parametric studies have been conducted to determine the influence of the different model input data on the AE signals and thus help to interpret AE testing results. (author) [fr
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.
Propagation of an ionizing surface electromagnetic wave
Energy Technology Data Exchange (ETDEWEB)
Boev, A.G.; Prokopov, A.V.
1976-11-01
The propagation of an rf surface wave in a plasma which is ionized by the wave itself is analyzed. The exact solution of the nonlinear Maxwell equations is discussed for the case in which the density of plasma electrons is an exponential function of the square of the electric field. The range over which the surface wave exists and the frequency dependence of the phase velocity are found. A detailed analysis is given for the case of a plasma whose initial density exceeds the critical density at the wave frequency. An increase in the wave amplitude is shown to expand the frequency range over which the plasma is transparent; The energy flux in the plasma tends toward a certain finite value which is governed by the effective ionization field.
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.
Detection of Electromechanical Wave Propagation Using Synchronized Phasor Measurements
Suryawanshi, Prakash; Dambhare, Sanjay; Pramanik, Ashutosh
2014-01-01
Considering electrical network as a continuum has become popular for electromechanical wave analysis. This paper reviews the concept of electromechanical wave propagation. Analysis of large number of generator ring system will be an easy way to illustrate wave propagation. The property of traveling waves is that the maximum and minimum values do not occur at the same time instants and hence the difference between these time delays can be easily calculated. The homogeneous, isotropic 10 generator ring system is modeled using electromagnetic transient simulation programs. The purpose of this study is to investigate the time delays and wave velocities using Power System Computer Aided Design (PSCAD)/Electromagnetic Transient Program (EMTP). The disturbances considered here are generator disconnections and line trips.
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......, but has not been introduced in the context of integrated waveguides. We show that the difference between our full-vectorial effective mode area and the scalar equivalent often referred to in the literature may lead to mistakes when evaluating the nonlinear refractive index and optimizing designs of new...
The effect of lower-hybrid waves on the propagation of hydromagnetic waves
International Nuclear Information System (INIS)
Hamabata, Hiromitsu; Namikawa, Tomikazu; Mori, Kazuhiro
1988-01-01
Propagation characteristics of hydromagnetic waves in a magnetic plasma are investigated using the two-plasma fluid equations including the effect of lower-hybrid waves propagating perpendicularly to the magnetic field. The effect of lower-hybrid waves on the propagation of hydromagnetic waves is analysed in terms of phase speed, growth rate, refractive index, polarization and the amplitude relation between the density perturbation and the magnetic-field perturbation for the cases when hydromagnetic waves propagate in the plane whose normal is perpendicular to both the magnetic field and the propagation direction of lower-hybrid waves and in the plane perpendicular to the propagation direction of lower-hybrid waves. It is shown that hydromagnetic waves propagating at small angles to the propagation direction of lower-hybrid waves can be excited by the effect of lower-hybrid waves and the energy of excited waves propagates nearly parallel to the propagation direction of lower-hybrid waves. (author)
Jefrey, A
1964-01-01
In this book, we study theoretical and practical aspects of computing methods for mathematical modelling of nonlinear systems. A number of computing techniques are considered, such as methods of operator approximation with any given accuracy; operator interpolation techniques including a non-Lagrange interpolation; methods of system representation subject to constraints associated with concepts of causality, memory and stationarity; methods of system representation with an accuracy that is the best within a given class of models; methods of covariance matrix estimation;methods for low-rank mat
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.
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 EPIwave propagation index is a novel, easily-obtainable, echocardiographic metric to evaluate apical LV flow. An EPI of less than 1 is an independent predictor of LVT formation. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.
Nonlinear transient wave propagation in homgeneous plasmas
International Nuclear Information System (INIS)
Thomsen, K.
1983-01-01
The transient phenomena associated with the propagation of nonlinear high frequency waves in homogeneous and isotropic or anisotropic plasma are considered. The basic equation for the different wave types included in this analysis are derived by using a two-fluid description of the plasma. Before discussing the importance of different nonlinearities the main results from a linear treatment are given. Generation of harmonic and local changes in the plasma frequency caused by ponderomotive forces are the nonlinear phenomena which are included in the nonlinear treatment. Generation of harmonics is only important for extraordinary waves and this case is discussed in detail. The density perturbations are described either as forced non-dispersive or as forced dispersive low frequency electrostatic waves. The differences between these two descriptions are first considered analytically then by a numerical analysis of the problem with the influence of the density variations on the propagation of the high frequency wave included. A one-dimensional description is used in all cases. (Auth.)
International Nuclear Information System (INIS)
Boaratti, Mario Francisco Guerra
2006-01-01
Leaks in pressurized tubes generate acoustic waves that propagate through the walls of these tubes, which can be captured by accelerometers or by acoustic emission sensors. The knowledge of how these walls can vibrate, or in another way, how these acoustic waves propagate in this material is fundamental in the detection and localization process of the leak source. In this work an analytic model was implemented, through the motion equations of a cylindrical shell, with the objective to understand the behavior of the tube surface excited by a point source. Since the cylindrical surface has a closed pattern in the circumferential direction, waves that are beginning their trajectory will meet with another that has already completed the turn over the cylindrical shell, in the clockwise direction as well as in the counter clockwise direction, generating constructive and destructive interferences. After enough time of propagation, peaks and valleys in the shell surface are formed, which can be visualized through a graphic representation of the analytic solution created. The theoretical results were proven through measures accomplished in an experimental setup composed of a steel tube finished in sand box, simulating the condition of infinite tube. To determine the location of the point source on the surface, the process of inverse solution was adopted, that is to say, known the signals of the sensor disposed in the tube surface , it is determined through the theoretical model where the source that generated these signals can be. (author)
Wave propagation retrieval method for chiral metamaterials
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
2010-01-01
In this paper we present the wave propagation method for the retrieving of effective properties of media with circularly polarized eigenwaves, in particularly for chiral metamaterials. The method is applied for thick slabs and provides bulk effective parameters. Its strong sides are the absence...... of artificial branches of the refractive index and simplicity in implementation. We prove the validity of the method on three case studies of homogeneous magnetized plasma, bi-cross and U-shaped metamaterials....
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.
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...... using Mindlin plate elements, is developed to predict relevant wave characteristics such as dispersion, and group velocity variation as a function of frequency and direction of propagation. Experimental tests are conducted through a scanning laser vibrometer, which provides full wave field information....... The analysis of time domain wave field images allows the assessment of plate dispersion, and the comparison with numerical predictions. The obtained results show the predictive ability of the considered numerical approach and illustrate how the considered plate configuration could be used as the basis...
Ultrasonic guided wave propagation in pipes with elbows
Breon, Luke J.
Guided wave inspection of pipelines is an important and growing area of Non-Destructive Evaluation (NDE). This technique can be used for remote inspection or monitoring of buried pipelines, or pipelines with insulation. Guided waves are sensitive to flaws such as corrosion pits and cracks. They can be used to locate flaws existing on either the outer or the inner surface of a pipe. Guided wave energy focusing can be performed to concentrate guided wave energy at particular combinations of circumferential and axial locations in straight pipes. When it can be used, this practice enhances the circumferential resolution of defects. Elbows in a piping system are sufficiently disruptive to guided wave energy that the focusing methods used in practical inspections of straight pipe have not been extended to the region beyond an elbow. Counter-intuitively, elbows with a 45 degree bend are more harmful to guided waves than those with a 90 degree bend. A simple and elegant explanation for this phenomenon is provided in this dissertation. Theoretical advancements to guided wave physics propagating around an elbow have tended to be few and slow. This is at least partly due to the complexity of the mathematics involved in the conventional description of guided wave mechanics. Parametric focusing for pipes with bends has not been previously possible as it is for straight sections of pipes. While some techniques such as time-reversal mirrors and blind finite-element-method modeling have existed for focusing beyond elbows, these techniques have been limited and largely of academic value. Also, the understanding of wave behavior in a pipe elbow has in the past been generally unclear. Consequently, signal interpretation has also been very limited for guided waves initiating in, or returning from, the far side of an elbow. A new approach to understanding guided wave propagation is developed in this work. This understanding consists of the idea that the pathway a guided wave will take
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
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.
Guo, Kai; Friis, Søren M M; Christensen, Jesper B; Christensen, Erik N; Shi, Xiaodong; Ding, Yunhong; Ou, Haiyan; Rottwitt, Karsten
2017-09-15
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, but has not been introduced in the context of integrated waveguides. We show that the difference between our full-vectorial effective mode area and the scalar equivalent often referred to in the literature may lead to mistakes when evaluating the nonlinear refractive index and optimizing designs of new waveguides. We verify the results of our derivation by comparing it to experimental measurements in a silicon-on-insulator waveguide, taking tolerances on fabrication parameters into account.
Soloviev, O.
2003-03-01
The problem of radio wave propagation allowing for 3D localized lower ionosphere irregularity appears in accordance with the necessity of the theoretical interpretation of VLF remote sensing data. The various processes in the Earth's crust and in space (earthquakes, magnetic storms, sporadic E-layers, lightning induced electron precipitations, rocket launches, artificial ionosphere heating, nuclear explosions, etc.) may cause different power and size ionospheric disturbances. This paper presents a further development of the numerical-analytical method for 3D problem solving. We consider a vector problem of VLF vertical electric dipole field in a plane Earth-ionosphere waveguide with a localized anisotropic ionosphere irregularity. The possibility of lowering (elevating) of the local region of the upper waveguide wall is taken into account. The field components on the boundary surfaces obey the Leontovich impedance conditions. The problem is reduced to a system of 2D integral equations taking into account the depolarization of the field scattered by the irregularity. Using asymptotic /(kr>>1) integration along the direction perpendicular to the propagation path, we transform this system to a system of 1D integral equations. The system is solved in the diagonal approximation, combining direct inversion of the Volterra integral operator and the subsequent iterations. The proposed method is useful for study of both small-scale and large-scale irregularities. We obtained estimates of the TE field components that originate entirely from field scattering by a 3D irregularity.
Wave propagation simulation of radio occultations based on ECMWF refractivity profiles
DEFF Research Database (Denmark)
von Benzon, Hans-Henrik; Høeg, Per
2015-01-01
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...... 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...... 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.
Spiral Calcium Wave Propagation and Annihilation in Xenopus laevis Oocytes
Lechleiter, James; Girard, Steven; Peralta, Ernest; Clapham, David
1991-04-01
Intracellular calcium (Ca2+) is a ubiquitous second messenger. Information is encoded in the magnitude, frequency, and spatial organization of changes in the concentration of cytosolic free Ca2+. Regenerative spiral waves of release of free Ca2+ were observed by confocal microscopy in Xenopus laevis oocytes expressing muscarinic acetylcholine receptor subtypes. This pattern of Ca2+ activity is characteristic of an intracellular milieu that behaves as a regenerative excitable medium. The minimal critical radius for propagation of focal Ca2+ waves (10.4 micrometers) and the effective diffusion constant for the excitation signal (2.3 x 10-6 square centimeters per second) were estimated from measurements of velocity and curvature of circular wavefronts expanding from foci. By modeling Ca2+ release with cellular automata, the absolute refractory period for Ca2+ stores (4.7 seconds) was determined. Other phenomena expected of an excitable medium, such as wave propagation of undiminished amplitude and annihilation of colliding wavefronts, were observed.
Nonlinear internal wave effects on acoustic propagation and scattering
McMahon, Kara Grace
Experimental observations and theoretical studies show that nonlinear internal waves occur widely in shallow water and cause acoustic propagation effects including ducting and mode coupling. Horizontal ducting results when acoustic modes travel between internal wave fronts that form waveguide boundaries. For small grazing angles between a mode trajectory and a front, an interference pattern may arise that is a horizontal Lloyd mirror pattern. An analytic description for this feature is provided, along with comparisons between results from the formulated model predicting a horizontal Lloyd mirror pattern and an adiabatic mode parabolic equation. Different waveguide models are considered, including boxcar and jump sound speed profiles where change in sound speed is assumed 12 m/s. Modifications to the model are made to include multiple and moving fronts. The focus of this analysis is on different front locations relative to the source, as well as on the number of fronts and their curvatures and speeds. Curvature influences mode incidence angles and thereby changes the interference patterns. For sources oriented so that the front appears concave, the areas with interference patterns shrink as curvature increases, while convexly oriented fronts cause patterns to expand. Curvature also influence how energy is distributed in the internal wave duct. For certain curvatures and duct widths energy forms a whispering gallery or becomes fully ducted. Angular constraints which indicate when to expect these phenomena are presented. Results are compared to propagation calculations and were found to agree in most examples. In some cases trailing internal waves are present in the duct and disturb horizontal propagation. This type of propagation is characterized as a scattering process as a result of broken internal wave fronts between the lead waves. Traditionally this is handled in regimes where adiabatic normal modes are valid using sound speed perturbations to describe energy
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
Ten Tusscher, K. H. W. J.; Panfilov, A. V.
2006-12-01
In this paper, we formulate a model for human ventricular cells that is efficient enough for whole organ arrhythmia simulations yet detailed enough to capture the effects of cell level processes such as current blocks and channelopathies. The model is obtained from our detailed human ventricular cell model by using mathematical techniques to reduce the number of variables from 19 to nine. We carefully compare our full and reduced model at the single cell, cable and 2D tissue level and show that the reduced model has a very similar behaviour. Importantly, the new model correctly produces the effects of current blocks and channelopathies on AP and spiral wave behaviour, processes at the core of current day arrhythmia research. The new model is well over four times more efficient than the full model. We conclude that the new model can be used for efficient simulations of the effects of current changes on arrhythmias in the human heart.
Energy Technology Data Exchange (ETDEWEB)
Tusscher, K H W J Ten; Panfilov, A V [Department of Theoretical Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands)
2006-12-07
In this paper, we formulate a model for human ventricular cells that is efficient enough for whole organ arrhythmia simulations yet detailed enough to capture the effects of cell level processes such as current blocks and channelopathies. The model is obtained from our detailed human ventricular cell model by using mathematical techniques to reduce the number of variables from 19 to nine. We carefully compare our full and reduced model at the single cell, cable and 2D tissue level and show that the reduced model has a very similar behaviour. Importantly, the new model correctly produces the effects of current blocks and channelopathies on AP and spiral wave behaviour, processes at the core of current day arrhythmia research. The new model is well over four times more efficient than the full model. We conclude that the new model can be used for efficient simulations of the effects of current changes on arrhythmias in the human heart.
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
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.
Gao, Liming; Ji, Wang; Zheng, Zhong; Jianke, Du
2008-02-01
In a homogeneous plate, Rayleigh waves will have a symmetric and anti-symmetric mode regarding to the mid-plane with different phase velocities. If plate properties vary along the thickness, or the plate is of functionally graded material (FGM), the symmetry of modes and frequency behavior will be modified, thus producing different features for engineering applications such as amplifying or reducing the velocity and deformation. This kind of effect can also be easily realized by utilizing a layered structure with desired material properties that can produce these effects in terms of velocity and displacements, since Rayleigh waves in a solid with general material property grading schemes are difficult to analyze with known methods. Solutions from layered structures with exponential and polynomial property grading schemes are obtained from the layered model and comparisons with known analytical results are made to validate the method and examine possible applications of such structures in engineering.
Lipatov, A. S.; Sibeck, D. G.
2016-01-01
We use a new hybrid kinetic model to simulate the response of ring current, outer radiation belt, and plasmaspheric particle populations to impulsive interplanetary shocks. Since particle distributions attending the interplanetary shock waves and in the ring current and radiation belts are non-Maxwellian, waveparticle interactions play a crucial role in energy transport within the inner magnetosphere. Finite gyroradius effects become important in mass loading the shock waves with the background plasma in the presence of higher energy ring current and radiation belt ions and electrons. Initial results show that shocks cause strong deformations in the global structure of the ring current, radiation belt, and plasmasphere. The ion velocity distribution functions at the shock front, in the ring current, and in the radiation belt help us determine energy transport through the Earth's inner magnetosphere.
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.
Wave propagation in a magnetically structured atmosphere. Pt. 2
International Nuclear Information System (INIS)
Roberts, B.
1981-01-01
Magnetic fields may introduce structure (inhomogeneity) into an otherwise uniform medium and thus change the nature of wave propagation in that medium. As an example of such structuring, wave propagation in an isolated magnetic slab is considered. It is supposed that disturbances outside the slab are laterally non-propagating. The effect of gravity is ignored. The field can support the propagation of both body and surface waves. The existence and nature of these waves depends upon the relative magnitudes of the sound speed c 0 and Alfven speed upsilonsub(A) inside the slab, and the sound speed csub(e) in the field-free environment. (orig./WL)
Influence of Sea Surface Roughness on the Electromagnetic Wave Propagation in the Duct Environment
Zhao, X.; Huang, S.
2010-01-01
This paper deals with a study of the influence of sea surface roughness on the electromagnetic wave propagation in the duct environment. The problem of electromagnetic wave propagation is modeled by using the parabolic equation method. The roughness of the sea surface is computed by modifying the smooth surface Fresnel reflection coefficient to account for the reduction in the specular reflection due to the roughness resulting from sea wind speed. The propagation model is solved by the mixed ...
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.
Simulation of the acoustic wave propagation using a meshless method
Directory of Open Access Journals (Sweden)
Bajko J.
2017-01-01
Full Text Available This paper presents numerical simulations of the acoustic wave propagation phenomenon modelled via Linearized Euler equations. A meshless method based on collocation of the strong form of the equation system is adopted. Moreover, the Weighted least squares method is used for local approximation of derivatives as well as stabilization technique in a form of spatial ltering. The accuracy and robustness of the method is examined on several benchmark problems.
On the Relation Between Complex Modes and Wave Propagation Phenomena
Ahmida, K. M.; Arruda, J. R. F.
2002-08-01
This paper discusses the well-known, but often misunderstood, concept of complex modes of dynamic structures. It shows how complex modes can be interpreted in terms of wave propagation phenomena caused by either localized damping or propagation to the surrounding media. Numerical simulation results are presented for different kinds of structures exhibiting modal and wave propagation characteristics: straight beams, an L-shaped beam, and a three-dimensional frame structure. The input/output transfer relations of these structures are obtained using a spectral formulation known as the spectral element method (SEM). With this method, it is straightforward to use infinite elements, usually known as throw-off elements, to represent the propagation to infinity, which is a possible cause of modal complexity. With the SEM model, the exact dynamic behavior of structures can be investigated. The mode complexity of these structures is investigated. It is shown that mode complexity characterizes a behavior that is half-way between purely modal and purely propagative. A coefficient for quantifying mode complexity is introduced. The mode complexity coefficient consists of the correlation coefficient between the real and imaginary parts of the eigenvector, or of the operational deflection shape (ODS). It is shown that, far from discontinuities, this coefficient is zero in the case of pure wave propagation in which case the plot of the ODS in the complex plane is a perfect circle. In the other extreme situation, a finite structure without damping (or with proportional damping), where the mode shape (or the ODS) is a straight line on the complex plane, has a unitary complexity coefficient. For simple beam structures, it is shown that the mode complexity factor can also be calculated by curve-fitting the mode to an ellipse and computing the ratio of its radii.
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
Propagation of bottom-trapped waves over variable topography
Digital Repository Service at National Institute of Oceanography (India)
Shetye, S.R.
on a topographic slope, as they propagate towards a deeper region of constant depth, is examined using a quasi-geostrophic model. It is seen that there can be no free transmitted wave to the region of constant depth. The bottom-trapped energy is thus... currents farther away. 1. INTRODUCTION Rhines (1970) showed that a stratified rotating fluid over sloping bottom topography can support free waves that are bottom-intensified. The in- crease in the kinetic energy of the currents with depth...
Electromagnetic wave propagation in relativistic magnetized plasmas
International Nuclear Information System (INIS)
Weiss, I.
1985-01-01
An improved mathematical technique and a new code for deriving the conductivity tensor for collisionless plasmas have been developed. The method is applicable to a very general case, including both hot (relativistic) and cold magnetized plasmas, with only isotropic equilibrium distributions being considered here. The usual derivation starts from the relativistic Vlasov equation and leads to an integration over an infinite sum of Bessel functions which has to be done numerically. In the new solution the integration is carried out over a product of two Bessel functions only. This reduces the computing time very significantly. An added advantage over existing codes is our capability to perform the computations for waves propagating obliquely to the magnetic field. Both improvements greatly facilitate investigations of properties of the plasma under conditions hitherto unexplored
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...
Induced wave propagation from a vibrating containment envelope
International Nuclear Information System (INIS)
Stout, R.B.; Thigpen, L.; Rambo, J.T.
1985-09-01
Low frequency wave forms are observed in the particle velocity measurements around the cavity and containment envelope formed by an underground nuclear test. The vibration solution for a spherical shell is used to formulate a model for the low frequency wave that propagates outward from this region. In this model the containment envelope is the zone of material that is crushed by the compressive shock wave of the nuclear explosion. The containment envelope is approximated by a spherical shell of material. The material in the spherical shell is densified and is given a relatively high kinetic energy density because of the high compressive stress and particle velocity of the shock wave. After the shock wave has propagated through the spherical shell, the spherical shell vibrates in order to dissipate the kinetic energy acquired from the shock wave. Based on the model, the frequency of vibration depends on the dimensions and material properties of the spherical shell. The model can also be applied in an inverse mode to obtain global estimates of averaged materials properties. This requires using experimental data and semi-empirical relationships involving the material properties. A particular case of estimating a value for shear strength is described. Finally, the oscillation time period of the lowest frequency from five nuclear tests is correlated with the energy of the explosion. The correlation provides another diagnostic to estimate the energy of a nuclear explosion. Also, the longest oscillation time period measurement provides additional experimental data that can be used to assess and validate various computer models. 11 refs., 2 figs
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...
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...
Surface wave propagation characteristics in atmospheric pressure plasma column
International Nuclear Information System (INIS)
Pencheva, M; Benova, E; Zhelyazkov, I
2007-01-01
In the typical experiments of surface wave sustained plasma columns at atmospheric pressure the ratio of collision to wave frequency (ν/ω) is much greater than unity. Therefore, one might expect that the usual analysis of the wave dispersion relation, performed under the assumption ν/ω = 0, cannot give adequate description of the wave propagation characteristics. In order to study these characteristics we have analyzed the wave dispersion relationship for arbitrary ν/ω. Our analysis includes phase and wave dispersion curves, attenuation coefficient, and wave phase and group velocities. The numerical results show that a turning back point appears in the phase diagram, after which a region of backward wave propagation exists. The experimentally observed plasma column is only in a region where wave propagation coefficient is higher than the attenuation coefficient. At the plasma column end the electron density is much higher than that corresponding to the turning back point and the resonance
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 Pipe-like Structures
DEFF Research Database (Denmark)
Morsbøl, Jonas
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...... when even these very fundamental waves are travelling along a shell of revolution. The effects cover modal changes and excitation of localised resonances. For modes of higher order similar excitations of localised resonances are also predicted....
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.
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 ...
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
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
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 ...
Modelling the gluon propagator
Energy Technology Data Exchange (ETDEWEB)
Leinweber, D.B.; Parrinello, C.; Skullerud, J.I.; Williams, A.G
1999-03-01
Scaling of the Landau gauge gluon propagator calculated at {beta} = 6.0 and at {beta} = 6.2 is demonstrated. A variety of functional forms for the gluon propagator calculated on a large (32{sup 3} x 64) lattice at {beta} = 6.0 are investigated.
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
Numerical simulation of ultrasonic wave propagation in elastically anisotropic media
International Nuclear Information System (INIS)
Jacob, Victoria Cristina Cheade; Jospin, Reinaldo Jacques; Bittencourt, Marcelo de Siqueira Queiroz
2013-01-01
The ultrasonic non-destructive testing of components may encounter considerable difficulties to interpret some inspections results mainly in anisotropic crystalline structures. A numerical method for the simulation of elastic wave propagation in homogeneous elastically anisotropic media, based on the general finite element approach, is used to help this interpretation. The successful modeling of elastic field associated with NDE is based on the generation of a realistic pulsed ultrasonic wave, which is launched from a piezoelectric transducer into the material under inspection. The values of elastic constants are great interest information that provide the application of equations analytical models, until small and medium complexity problems through programs of numerical analysis as finite elements and/or boundary elements. The aim of this work is the comparison between the results of numerical solution of an ultrasonic wave, which is obtained from transient excitation pulse that can be specified by either force or displacement variation across the aperture of the transducer, and the results obtained from a experiment that was realized in an aluminum block in the IEN Ultrasonic Laboratory. The wave propagation can be simulated using all the characteristics of the material used in the experiment valuation associated to boundary conditions and from these results, the comparison can be made. (author)
Wave propagation in plasma-filled wave-guide
International Nuclear Information System (INIS)
Leprince, Philippe
1966-01-01
This research thesis reports the study of wave propagation along a plasma column without external magnetic field. The author first present and comment various theoretical results, and dispersion curves plotted for the main modes (particularly, the bipolar mode). He tries to define fundamental magnitudes which characterise a plasma-filled wave-guide. He reports the comparison of some experimental results with the previous theoretical results. Based on the study of the bipolar mode, the author develops a method of measurement of plasma column density. In the last part, the author reports the study of the resonance of a plasma-containing cavity. Several resonances are highlighted and new dispersion curves are plotted by using a varying length cavity. He also addresses the coupling of plasma modes with guide modes, and thus indicates the shape of Brillouin diagrams for a plasma-filled wave-guide. Moreover, some phenomena highlighted during plasma column density measurements by using the cavity method could then be explained [fr
International Nuclear Information System (INIS)
Wirdelius, Haakan; Persson, Gert; Hamberg, Kenneth; Hoegberg, Kjell
2008-01-01
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 calculated
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.
A wave propagation matrix method in semiclassical theory
International Nuclear Information System (INIS)
Lee, S.Y.; Takigawa, N.
1977-05-01
A wave propagation matrix method is used to derive the semiclassical formulae of the multiturning point problem. A phase shift matrix and a barrier transformation matrix are introduced to describe the processes of a particle travelling through a potential well and crossing a potential barrier respectively. The wave propagation matrix is given by the products of phase shift matrices and barrier transformation matrices. The method to study scattering by surface transparent potentials and the Bloch wave in solids is then applied
Development of an analysis code for pressure wave propagation, (1)
International Nuclear Information System (INIS)
Tanaka, Yoshihisa; Sakano, Kosuke; Shindo, Yoshihisa
1974-11-01
We analyzed the propagation of the pressure-wave in the piping system of SWAT-1B rig by using SWAC-5 Code. We carried out analyses on the following parts. 1) A straight pipe 2) Branches 3) A piping system The results obtained in these analyses are as follows. 1) The present our model simulates well the straight pipe and the branch with the same diameters. 2) The present our model simulates approximately the branch with the different diameters and the piping system. (auth.)
Linear wave propagation in a hot axisymmetric toroidal plasma
Energy Technology Data Exchange (ETDEWEB)
Jaun, A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)
1995-03-01
Kinetic effects on the propagation of the Alfven wave are studied for the first time in a toroidal plasma relevant for experiments. This requires the resolution of a set of coupled partial differential equations whose coefficients depend locally on the plasma parameters. For this purpose, a numerical wave propagation code called PENN has been developed using either a bilinear or a bicubic Hermite finite element discretization. It solves Maxwell`s equations in toroidal geometry, with a dielectric tensor operator that takes into account the linear response of the plasma. Two different models have been implemented and can be used comparatively to describe the same physical case: the first treats the plasma as resistive fluids and gives results which are in good agreement with toroidal fluid codes. The second is a kinetic model and takes into account the finite size of the Larmor radii; it has successfully been tested against a kinetic plasma model in cylindrical geometry. New results have been obtained when studying kinetic effects in toroidal geometry. Two different conversion mechanisms to the kinetic Alfven wave have been described: one occurs at toroidally coupled resonant surfaces and is the kinetic counterpart of the fluid models` resonance absorption. The other has no such correspondence and results directly from the toroidal coupling between the kinetic Alfven wave and the global wavefield. An analysis of a heating scenario suggests that it might be difficult to heat a plasma with Alfven waves up to temperatures that are relevant for a tokamak reactor. Kinetic effects are studied for three types of global Alfven modes (GAE, TAE, BAE) and a new class of kinetic eigenmodes is described which appear inside the fluid gap: it could be related to recent observations in the JET (Joint European Torus) tokamak. (author) 56 figs., 6 tabs., 58 refs.
Study of acoustic wave propagation through the cross section of green wood
Dikrallah, Adil; Kabouchi, Bousselham; Hakam, Abdelillah; Brancheriau, Loïc; Bailleres, Henri; Famiri, Abderrahim; Ziani, Mohsine
2010-02-01
An experimental approach was used to model stress wave propagation in green wood (Douglas fir). Based on the assumption that wood is an orthotropic material, the stress wave velocity through the cross section was calculated using plane strain motion equations. The experiments were carried out in two steps under axial restraint, while the wave propagation time was measured on discs and bars sliced from the discs. Mechanical and physical properties were determined in free vibration. The results showed a significant difference in propagation velocity between waves propagating throughout the whole disc volume and guided waves in bars. The acoustic anisotropy of green wood is discussed and the stress wave form simulation is presented. Good agreement between the simulation and experimental results was obtained.
Propagation of photosensitive chemical waves on the circular routes.
Kitahata, Hiroyuki; Yamada, Akiko; Nakata, Satoshi; Ichino, Takatoshi
2005-06-09
The propagation of chemical waves in the photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated using an excitable field in the shape of a circular ring or figure "8" that was drawn by computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. For a chemical wave in a circular reaction field, the shape of the chemical wave was investigated depending on the ratio of the inner and outer radii. When two chemical waves were generated on a field shaped like a figure "8" (one chemical wave in each circle) as the initial condition, the location of the collision of the waves either was constant or alternated depending on the degree of overlap of the two circular rings. These experimental results were analyzed on the basis of a geometrical discussion and theoretically reproduced on the basis of a reaction-diffusion system using a modified Oregonator model. These results suggest that the photosensitive BZ reaction may be useful for creating spatio-temporal patterns depending on the geometric arrangement of excitable fields.
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
Propagation law of impact elastic wave based on specific materials
Directory of Open Access Journals (Sweden)
Chunmin CHEN
2017-02-01
Full Text Available In order to explore the propagation law of the impact elastic wave on the platform, the experimental platform is built by using the specific isotropic materials and anisotropic materials. The glass cloth epoxy laminated plate is used for anisotropic material, and an organic glass plate is used for isotropic material. The PVDF sensors adhered on the specific materials are utilized to collect data, and the elastic wave propagation law of different thick plates and laminated plates under impact conditions is analyzed. The Experimental results show that in anisotropic material, transverse wave propagation speed along the fiber arrangement direction is the fastest, while longitudinal wave propagation speed is the slowest. The longitudinal wave propagation speed in anisotropic laminates is much slower than that in the laminated thick plates. In the test channel arranged along a particular angle away from the central region of the material, transverse wave propagation speed is larger. Based on the experimental results, this paper proposes a material combination mode which is advantageous to elastic wave propagation and diffusion in shock-isolating materials. It is proposed to design a composite material with high acoustic velocity by adding regularly arranged fibrous materials. The overall design of the barrier material is a layered structure and a certain number of 90°zigzag structure.
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.
Acoustic wave propagation in bubbly flow with gas, vapor or their mixtures.
Zhang, Yuning; Guo, Zhongyu; Gao, Yuhang; Du, Xiaoze
2018-01-01
Presence of bubbles in liquids could significantly alter the acoustic waves in terms of wave speed and attenuation. In the present paper, acoustic wave propagation in bubbly flows with gas, vapor and gas/vapor mixtures is theoretically investigated in a wide range of parameters (including frequency, bubble radius, void fraction, and vapor mass fraction). Our finding reveals two types of wave propagation behavior depending on the vapor mass fraction. Furthermore, the minimum wave speed (required for the closure of cavitation modelling in the sonochemical reactor design) is analyzed and the influences of paramount parameters on it are quantitatively discussed. Copyright © 2017 Elsevier B.V. All rights reserved.
Vertical propagation of baroclinic Kelvin waves along the west coast of India
Digital Repository Service at National Institute of Oceanography (India)
Nethery, D.; Shankar, D.
, this paper is intended to provide the motivation for studying the vertical propagation of coastal Kelvin waves with a general circulation model, allowing the influence of density variations, basin geometry, and mixing processes to be examined...
Propagation of shear wave in nonlinear and dissipative medium
International Nuclear Information System (INIS)
Jeambrun, D.
1995-01-01
The civil engineering projects, like nuclear installations, submitted to vibrations or seismic motions, require the study of the soil behaviour underlying the site under intensive dynamic loading. In order to understand in depth the soil damping phenomenon, a propagation of a shear seismic wave in a dissipative medium has been numerically simulated. The computer code, based on a nonlinear hysteretic model using Newmark-Wilson and Newton-Raphson algorithms and variable spatial steps, passes through the difficulties related to acceleration discontinuities. The simulation should allow the identification of the soil parameters by comparison with in situ measures. (author)
International Nuclear Information System (INIS)
Schulte, R T; Fritzen, C-P; Moll, J
2010-01-01
During the last decades, guided waves have shown great potential for Structural Health Monitoring (SHM) applications. These waves can be excited and sensed by piezoelectric elements that can be permanently attached onto a structure offering online monitoring capability. However, the setup of wave based SHM systems for complex structures may be very difficult and time consuming. For that reason there is a growing demand for efficient simulation tools providing the opportunity to design wave based SHM systems in a virtual environment. As usually high frequency waves are used, the associated short wavelength leads to the necessity of a very dense mesh, which makes conventional finite elements not well suited for this purpose. Therefore in this contribution a flat shell spectral element approach is presented. By including electromechanical coupling a SHM system can be simulated entirely from actuator voltage to sensor voltage. Besides a comparison to measured data for anisotropic materials including delamination, a numerical example of a more complex, stiffened shell structure with debonding is presented.
Aeroacoustics: Acoustic wave propagation; Aircraft noise prediction; Aeroacoustic instrumentation
Schwartz, I. R.
1976-01-01
The papers in this volume deal with recent research into acoustic-wave propagation through the atmosphere and progress in aeroacoustic instrumentation, facilities, and test techniques. Topics include the propagation of aircraft noise over long distances in the lower atmosphere, measured effects of turbulence on the rise time of a weak shock, sound scattering from atmospheric turbulence, saturation effects associated with sound propagation in a turbulent medium, and a computer model of the lightning-thunder process. Other papers discuss the development of a computer system for aircraft noise prediction; aircraft flyover noise measurements; and theories and methods for the prediction of ground effects on aircraft noise propagation, for the prediction of airframe aerodynamic noise, for turbine noise prediction, and for combustion noise prediction. Attention is also given to the use of Hartmann generators as sources of high-intensity sound in a large absorption flow-duct facility, an outdoor jet noise facility, factors in the design and performance of free-jet acoustic wind tunnels, and the use of a laser shadowgraph for jet noise diagnosis.
Propagation of Elastic Waves in Prestressed Media
Directory of Open Access Journals (Sweden)
Inder Singh
2010-01-01
Full Text Available 3D solutions of the dynamical equations in the presence of external forces are derived for a homogeneous, prestressed medium. 2D plane waves solutions are obtained from general solutions and show that there exist two types of plane waves, namely, quasi-P waves and quasi-SV waves. Expressions for slowness surfaces and apparent velocities for these waves are derived analytically as well as numerically and represented graphically.
Sources and propagation of atmospherical acoustic shock waves
Coulouvrat, François
2012-09-01
Sources of aerial shock waves are numerous and produce acoustical signals that propagate in the atmosphere over long ranges, with a wide frequency spectrum ranging from infrasonic to audible, and with a complex human response. They can be of natural origin, like meteors, lightning or volcanoes, or human-made as for explosions, so-called "buzz-saw noise" (BSN) from aircraft engines or sonic booms. Their description, modeling and data analysis within the viewpoint of nonlinear acoustics will be the topic of the present lecture, with focus on two main points: the challenges of the source description, and the main features of nonlinear atmospheric propagation. Inter-disciplinary aspects, with links to atmospheric and geo-sciences will be outlined. Detailed description of the source is very dependent on its nature. Mobile supersonic sources can be rotating (fan blades of aircraft engines) or in translation (meteors, sonic boom). Mach numbers range from transonic to hypersonic. Detailed knowledge of geometry is critical for the processes of boom minimization and audible frequency spectrum of BSN. Sources of geophysical nature are poorly known, and various mechanisms for explaining infrasound recorded from meteors or thunderstorms have been proposed. Comparison between recorded data and modeling may be one way to discriminate between them. Moreover, the nearfield of these sources is frequently beyond the limits of acoustical approximation, or too complex for simple modeling. A proper numerical description hence requires specific matching procedures between nearfield behavior and farfield propagation. Nonlinear propagation in the atmosphere is dominated by temperature and wind stratification. Ray theory is an efficient way to analyze observations, but is invalid in various situations. Nonlinear effects are enhanced locally at caustics, or in case of grazing propagation over a rigid surface. Absorption, which controls mostly the high frequency part of the spectrum contained
Seismic Wave Propagation in Icy Ocean Worlds
Stähler, Simon C.; Panning, Mark P.; Vance, Steven D.; Lorenz, Ralph D.; vanÂ Driel, Martin; Nissen-Meyer, Tarje; Kedar, Sharon
2018-01-01
Seismology was developed on Earth and shaped our model of the Earth's interior over the twentieth century. With the exception of the Philae lander, all in situ extraterrestrial seismological effort to date was limited to other terrestrial planets. All have in common a rigid crust above a solid mantle. The coming years may see the installation of seismometers on Europa, Titan, and Enceladus, so it is necessary to adapt seismological concepts to the setting of worlds with global oceans covered in ice. Here we use waveform analyses to identify and classify wave types, developing a lexicon for icy ocean world seismology intended to be useful to both seismologists and planetary scientists. We use results from spectral-element simulations of broadband seismic wavefields to adapt seismological concepts to icy ocean worlds. We present a concise naming scheme for seismic waves and an overview of the features of the seismic wavefield on Europa, Titan, Ganymede, and Enceladus. In close connection with geophysical interior models, we analyze simulated seismic measurements of Europa and Titan that might be used to constrain geochemical parameters governing the habitability of a sub-ice ocean.
Investigation of guided waves propagation in pipe buried in sand
International Nuclear Information System (INIS)
Leinov, Eli; Cawley, Peter; Lowe, Michael J.S.
2014-01-01
The inspection of pipelines by guided wave testing is a well-established method for the detection of corrosion defects in pipelines, and is currently used routinely in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipes buried in soil, test ranges tend to be significantly compromised because of attenuation of the waves caused by energy radiating into the soil. Moreover, the variability of soil conditions dictates different attenuation characteristics, which in-turn results in different, unpredictable, test ranges. We investigate experimentally the propagation and attenuation characteristics of guided waves in pipes buried in fine sand using a well characterized full scale experimental apparatus. The apparatus consists of an 8 inch-diameter, 5.6-meters long steel pipe embedded over 3 meters of its length in a rectangular container filled with fine sand, and an air-bladder for the application of overburden pressure. Longitudinal and torsional guided waves are excited in the pipe and recorded using a transducer ring (Guided Ultrasonics Ltd). Acoustic properties of the sand are measured independently in-situ and used to make model predictions of wave behavior in the buried pipe. We present the methodology and the systematic measurements of the guided waves under a range of conditions, including loose and compacted sand. It is found that the application of overburden pressure modifies the compaction of the sand and increases the attenuation, and that the measurement of the acoustic properties of sand allows model prediction of the attenuation of guided waves in buried pipes with a high level of confidence
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.
Surface wave propagation in a fluid-saturated incompressible ...
Indian Academy of Sciences (India)
saturated incompressible porous media. Many studies have discussed the surface wave propagation in elastic media and a com- prehensive review is available in the standard texts, e.g., Ewing et al (1957) and Achenbach. (1976). The surface ...
Regional wave propagation using the discontinuous Galerkin method
Directory of Open Access Journals (Sweden)
S. Wenk
2013-01-01
Full Text Available We present an application of the discontinuous Galerkin (DG method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER Riemann problem. This ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy. We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.
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
A comparative study on propagation of elastic waves in random particulate composites
Directory of Open Access Journals (Sweden)
Mohammad Rahimzadeh
Full Text Available This paper aims to conduct a comparative study on four different models of effective field and effective medium for modeling propagation of plane elastic waves through the composites containing spherical particles with random distribution. Effective elastic properties along with the normalized phase velocity and attenuation of the average wave was numerically evaluated by the models. The plane incident wave was considered longitudinal to get the results. The numerical analyses were performed on four types of composites in the range of low to intermediate frequency and different volume fractions. Judgment about this comparative study is done based on physical and theoretical concepts in the wave propagation phenomenon. The obtained results provide a good viewpoint in using different models for studying propagation of the plane elastic waves in various particulate composites.
Propagation of pulsed waves in a magnetized chiroplasma
International Nuclear Information System (INIS)
Torres S, H.
1998-01-01
When subject to a constant magnetic field, chiroplasmas exhibit anisotropic constitutive parameters. For electronic chiroplasmas, the focus of this paper, this anisotropy must be described by using a permittivity tensor instead of the usual scalar permittivity. Each member of this tensor is also highly frequency dependent. This paper describes a finite difference time-domain formulation which incorporates both anisotropy and frequency dispersion at the same time , enabling the wide-band transient analysis of magnetoactive chiroplasma. Results are shown for the reflection and transmission through a magnetized chiroplasma layer which show the growing modes in the RCP chiro transverse wave. This stratified model can be scaled to solar photonic frequencies and plasma density to study the wave propagation in the ionosphere contaminated by aerosols and Cfc molecules. (Author)
On wave propagation in a random micropolar generalized thermoelastic medium
Mitra Manindra; Bhattacharyya Rabindra Kumar
2017-01-01
This paper endeavours to study aspects of wave propagation in a random generalized-thermal micropolar elastic medium. The smooth perturbation technique conformable to stochastic differential equations has been employed. Six different types of waves propagate in the random medium. The dispersion equations have been derived. The effects due to random variations of micropolar elastic and generalized thermal parameters have been computed. Randomness causes change of phase speed and attenuation of...
Energy Technology Data Exchange (ETDEWEB)
Lonne, S.
2003-11-01
The Resin Transfer Molding process for manufacturing composite materials is used to produce parts of complex shape. During the ultrasonic examination of such parts, attenuation is measured to characterize possible porosity content (a potential defect in this material). However, strong variation of attenuation is observed including on sound plates. The present study aims at explaining this by developing a model for ultrasonic propagation and attenuation in such parts which complex microstructure exhibits a multiple-scale aspect. An original model has been developed to predict attenuation at the elementary scale of an unidirectional layer of carbon fibers in an epoxy matrix. It couples multiple scattering by fibers and viscoelastic losses phenomena. It has been experimentally validated and applies to arbitrary two-phase fiber reinforced composites whatever the fiber volume fraction. At the upper scale of a ply made of several elementary layers of various orientations, the anisotropic behavior of ultrasonic waves and their attenuation are obtained by a homogenization procedure. An actual plate is made of several plies separated by pure resin layers. Plies and layers thicknesses are highly variable. A statistical study has been conducted to evaluate the influence of these geometrical variations on the ultrasonic transmission predicted by a model derived from Thomson-Haskell formalism. Ultrasonic attenuation variability practically observed is quantitatively reproduced and explained as resulting from the geometrical irregularity of the microstructure. (author)
Free wave propagation in continuous pipes carrying a flowing fluid
International Nuclear Information System (INIS)
Espindola, J.J. de; Silva, J.B. da
1982-01-01
The propagation constants of a periodically supported pipe are computed. Use is made of a general free wave-propagation theory, based on transfer matrices. Comparison is made with previously published results, computed through a simpler, limited scope theory. (Author) [pt
Numerical simulation of stress wave propagation from underground nuclear explosions
International Nuclear Information System (INIS)
Cherry, J.T.; Petersen, F.L.
1970-01-01
This paper presents a numerical model of stress wave propagation (SOC) which uses material properties data from a preshot testing program to predict the stress-induced effects on the rock mass involved in a Plowshare application. SOC calculates stress and particle velocity history, cavity radius, extent of brittle failure, and the rock's efficiency for transmitting stress. The calculations are based on an equation of state for the rock, which is developed from preshot field and laboratory measurements of the rock properties. The field measurements, made by hole logging, determine in situ values of the rock's density, water content, and propagation velocity for elastic waves. These logs also are useful in judging the layering of the rock and in choosing which core samples to test in the laboratory. The laboratory analysis of rock cores includes determination of hydrostatic compressibility to 40 kb, triaxial strength data, tensile strength, Hugoniot elastic limit, and, for the rock near the point of detonation, high-pressure Hugoniot data. Equation-of-state data are presented for rock from three sites subjected to high explosive or underground nuclear shots, including the Hardhat and Gasbuggy sites. SOC calculations of the effects of these two shots on the surrounding rock are compared with the observed effects. In both cases SOC predicts the size of the cavity quite closely. Results of the Gasbuggy calculations indicate that useful predictions of cavity size and chimney height can be made when an adequate preshot testing program is run to determine the rock's equation of state. Seismic coupling is very sensitive to the low-pressure part of the equation of state, and its successful prediction depends on agreement between the logging data and the static compressibility data. In general, it appears that enough progress has been made in calculating stress wave propagation to begin looking at derived numbers, such as number of cracks per zone, for some insight into the
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.
Bulk elastic wave propagation in partially saturated porous solids
International Nuclear Information System (INIS)
Berryman, J.G.; Thigpen, L.; Chin, R.C.Y.
1988-01-01
The linear equations of motion that describe the behavior of small disturbances in a porous solid containing both liquid and gas are solved for bulk wave propagation. The equations have been simplified by neglecting effects due to changes in capillary pressure. With this simplifying assumption, the equations reduce to two coupled (vector) equations of the form found in Biot's equations (for full saturation) but with more complicated coefficients. As in fully saturated solids, two shear waves with the same speed but different polarizations exist as do two compressional waves with distinct speeds. Attenuation effects can be enhanced in the partially saturated solid, depending on the distribution of gas in the pore space. Two models of the liquid/gas spatial distribution are considered: a segregated-fluids model and a mixed-fluids model. The two models predict comparable attentuation when the gas saturation is low, but the segregated-fluids model predicts a more rapid roll-off of attenuation as the gas saturation increases
On wave propagation in a random micropolar generalized thermoelastic medium
Directory of Open Access Journals (Sweden)
Mitra Manindra
2017-06-01
Full Text Available This paper endeavours to study aspects of wave propagation in a random generalized-thermal micropolar elastic medium. The smooth perturbation technique conformable to stochastic differential equations has been employed. Six different types of waves propagate in the random medium. The dispersion equations have been derived. The effects due to random variations of micropolar elastic and generalized thermal parameters have been computed. Randomness causes change of phase speed and attenuation of waves. Attenuation coefficients for high frequency waves have been computed. Second moment properties have been briefly discussed with application to wave propagation in the random micropolar elastic medium. Integrals involving correlation functions have been transformed to radial forms. A special type of generalized thermo-mechanical auto-correlation functions has been used to approximately compute effects of random variations of parameters. Uncoupled problem has been briefly outlined.
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.)
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.
Propagation of solar disturbances - Theories and models
Wu, S. T.
1983-01-01
Recent theoretical developments and construction of several models for the propagation of solar disturbances from the sun and their continuation throughout heliospheric space are discussed. Emphasis centers on physical mechanisms as well as mathematical techniques (i.e., analytical and numerical methods). This outline will lead to a discussion of the state-of-the-art of theoretically based modeling efforts in this area. It is shown that the fundamental theory for the study of propagation of disturbances in heliospheric space is centered around the self-consistent analysis of wave and mass motion within the context of magnetohydrodynamics in which the small scale structures will be modified by kinetic effects. Finally, brief mention is made of some interesting problems for which attention is needed for advancement of the understanding of the physics of large scale propagation of solar disturbances in heliospheric space.
Effects of pore fluids in the subsurface on ultrasonic wave propagation
Energy Technology Data Exchange (ETDEWEB)
Seifert, Patricia Katharina [Univ. of California, Berkeley, CA (United States)
1998-05-01
This thesis investigates ultrasonic wave propagation in unconsolidated sands in the presence of different pore fluids. Laboratory experiments have been conducted in the sub-MHz range using quartz sand fully saturated with one or two liquids. Elastic wave propagation in unconsolidated granular material is computed with different numerical models: in one-dimension a scattering model based on an analytical propagator solution, in two dimensions a numerical approach using the boundary integral equation method, in three dimensions the local flow model (LFM), the combined Biot and squirt flow theory (BISQ) and the dynamic composite elastic medium theory (DYCEM). The combination of theoretical and experimental analysis yields a better understanding of how wave propagation in unconsolidated sand is affected by (a) homogeneous phase distribution; (b) inhomogeneous phase distribution, (fingering, gas inclusions); (c) pore fluids of different viscosity; (d) wettabilities of a porous medium. The first study reveals that the main ultrasonic P-wave signatures, as a function of the fraction on nonaqueous-phase liquids in initially water-saturated sand samples, can be explained by a 1-D scattering model. The next study investigates effects of pore fluid viscosity on elastic wave propagation, in laboratory experiments conducted with sand samples saturated with fluids of different viscosities. The last study concentrates on the wettability of the grains and its effect on elastic wave propagation and electrical resistivity.
Propagation-invariant waves in acoustic, optical, and radio-wave fields
Salo, Janne
2003-01-01
The physical phenomena considered in this thesis are associated with electromagnetic and acoustic waves that propagate in free space or in homogeneous media without diffraction. The concept of rotationally periodic wave propagation is introduced in the first journal article included in the thesis and it is subsequently used to analyse waves that avoid diffractive deterioration by repeatedly returning to their initial shape, possibly rotated around the optical axis. Such waves constitute an es...
Belhadj, H; Taik, A; Ouazar, D
2006-01-01
International audience; This study is devoted to the flood wave propagation modelling corresponding to a realistic situation. The equations that governs the propagation of a flood wave, in natural rivers, corresponds to the free surface flow equations in the Shallow Water case. The obtained two dimensional system, known as Saint Venant's system, is derived from the three-dimensional incompressible Navier Stokes equations by depth-averaging of the state variables. This system is written in a c...
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.
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.
Nonlinear wave propagation through a ferromagnet with damping in ...
Indian Academy of Sciences (India)
magnetic waves in a ferromagnet can be reduced to an integro-differential equation. Keywords. Solitons; integro-differential equations; reductive perturbation method. PACS Nos 41.20 Jb; 05.45 Yv; 03.50 De; 78.20 Ls. 1. Introduction. The phenomenon of propagation of electromagnetic waves in ferromagnets are not only.
Nonlinear wave propagation through a ferromagnet with damping in ...
Indian Academy of Sciences (India)
wavelength in (2+1) dimensions. The purpose of the present work is to study the property of electromagnetic waves of long wavelength propagating through an isotropic ferromagnet in the classical continuum limit in (2+1) dimensions taking into account the dissipative effect. By using the long wave approximation of the ...
Mathematical Modelling of Tsunami Propagation 1EZE, C. L.; 2UKO ...
African Journals Online (AJOL)
MICHAEL
propagation of waves in the open ocean; (c) propagation of waves in shallow water and on the shore. The development of numerical models to describe tsunami wave generation, propagation and interaction with complicated topography such as bays or harbours and the resulting flooding has advanced to the stage where ...
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.
A theory of coherent propagation of light wave in semiconductors
International Nuclear Information System (INIS)
Zi-zhao, G.; Guo-zhen, Y.
1980-05-01
In this paper, we suggest a theory to describe the pheonmena of coherent propagation of light wave in semiconductors. Basing on two band system and considering the interband and intraband transitions induced by light wave and the interaction between electrons, we obtain the nonlinear equations for the description of interaction between carriers and coherent light wave. We have made use of the equations to analyse the phenomena which arise from the interaction between semiconductors and coherent light, for example, the multiphoton transitions, the saturation of light absorption of exciton, the shift of exciton line in intense light field, and the coherent propagation phenomena such as self-induced transparency, etc. (author)
Spetzler, J.
2001-01-01
Small-scale heterogeneity alters the arrival time of waves in a way that cannot be explained by ray theory. It is because ray theory is a high-frequency approximation that does not take the finite-frequency of wavefields into account. A theory based on the first Rytov approximation is
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 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
Itzá Balam, Reymundo; Iturrarán-Viveros, Ursula; Parra, Jorge O.
2018-03-01
Two main stages of seismic modeling are geological model building and numerical computation of seismic response for the model. The quality of the computed seismic response is partly related to the type of model that is built. Therefore, the model building approaches become as important as seismic forward numerical methods. For this purpose, three petrophysical facies (sands, shales and limestones) are extracted from reflection seismic data and some seismic attributes via the clustering method called Self-Organizing Maps (SOM), which, in this context, serves as a geological model building tool. This model with all its properties is the input to the Optimal Implicit Staggered Finite Difference (OISFD) algorithm to create synthetic seismograms for poroelastic, poroacoustic and elastic media. The results show a good agreement between observed and 2-D synthetic seismograms. This demonstrates that the SOM classification method enables us to extract facies from seismic data and allows us to integrate the lithology at the borehole scale with the 2-D seismic data.
International Nuclear Information System (INIS)
Macia, R.; Correig, A.M.
1987-01-01
Seismic wave propagation is described by a second order differential equation for medium displacement. By Fourier transforming with respect to time and space, wave equation transforms into a system of first order linear differential equations for the Fourier transform of displacement and stress. This system of differential equations is solved by means of Matrix Propagator and applied to the propagation of body waves in stratified media. The matrix propagators corresponding to P-SV and SH waves in homogeneous medium are found as an intermediate step to obtain the spectral response of body waves propagating through a stratified medium with homogeneous layers. (author) 14 refs
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.
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.
Propagation of shear waves in viscoelastic medium at irregular boundaries
Chattopadhyay, Amares; Gupta, Shishir; Sharma, Vikash; Kumari, Pato
2010-04-01
The aim of the paper is to study the shear wave propagation in a viscoelastic layer over a semi-infinite viscoelastic half space due to irregularity in the viscoelastic layer. It is of great interest to study the propaga-tion of shear waves in the assumed medium having a non planar boundary due to its similarity to most of the real situations. The perturbation method is applied to find the displacement field. The effect of complex wave number on dissipation factor is analysed. Finally, as an application, the result obtained has been used to get the reflected field in viscoelastic layer when the shear wave is incident on an irregular boundary in the shape of parabolic irregularity as well as triangular notch. It is observed that the amplitude of this reflected wave decreases with increasing length of the notch, and increases with increasing depth of the irregularity.
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 ...
Influence of Sea Surface Roughness on the Electromagnetic Wave Propagation in the Duct Environment
Directory of Open Access Journals (Sweden)
X. Zhao
2010-12-01
Full Text Available This paper deals with a study of the influence of sea surface roughness on the electromagnetic wave propagation in the duct environment. The problem of electromagnetic wave propagation is modeled by using the parabolic equation method. The roughness of the sea surface is computed by modifying the smooth surface Fresnel reflection coefficient to account for the reduction in the specular reflection due to the roughness resulting from sea wind speed. The propagation model is solved by the mixed Fourier split-step algorithm. Numerical experiments indicate that wind-driven roughened sea surface has an impact on the electromagnetic wave propagation in the duct environment, and the strength is intensified along with the increment of sea wind speeds and/or the operating frequencies. In a fixed duct environment, however, proper disposition of the transmitter could reduce these impacts.
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.
Unidirectional wave propagation in media with complex principal axes
Horsley, S. A. R.
2018-02-01
In an anisotropic medium, the refractive index depends on the direction of propagation. Zero index in a fixed direction implies a stretching of the wave to uniformity along that axis, reducing the effective number of dimensions by 1. Here we investigate two-dimensional gyrotropic media where the refractive index is 0 in a complex valued direction, finding that the wave becomes an analytic function of a single complex variable z . For simply connected media this analyticity implies unidirectional propagation of electromagnetic waves, similar to the edge states that occur in photonic "topological insulators." For a medium containing holes the propagation is no longer unidirectional. We illustrate the sensitivity of the field to the topology of the space using an exactly solvable example. To conclude we provide a generalization of transformation optics where a complex coordinate transformation can be used to relate ordinary anisotropic media to the recently highlighted gyrotropic ones supporting one-way edge states.
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.
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
Guided wave propagation in an elastic hollow cylinder coated with a viscoelastic material.
Barshinger, James N; Rose, Joseph L
2004-11-01
The propagation of ultrasonic guided waves in an elastic hollow cylinder with a viscoelastic coating is studied. The principle motivation is to provide tools for performing a guided wave, nondestructive inspection of piping and tubing with viscoelastic coatings. The theoretical boundary value problem is solved that describes the guided wave propagation in these structures for the purpose of finding the guided wave modes that propagate with little or no attenuation. The model uses the global matrix technique to generate the dispersion equation for the longitudinal modes of a system of an arbitrary number of perfectly bonded hollow cylinders with traction-free outer surfaces. A numerical solution of the dispersion equation produces the phase velocity and attenuation dispersion curves that describe the nature of the guided wave propagation. The attenuation dispersion curves show some guided wave modes that propagate with little or no attenuation in the coated structures of interest. The wave structure is examined for two of the modes to verify that the boundary conditions are satisfied and to explain their attenuation behavior. Experimental results are produced using an array of transducers positioned circumferentially around the pipe to evaluate the accuracy of the numerical solution.
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.
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.
Dautov, O. Sh.
2017-01-01
As one means to solving propagation problems are considered modeling of electromagnetic wave in inhomogeneous layered media. There are exact relations for the field exciting by the plane monochromatic electromagnetic wave in flat-layered one-dimensional inhomogeneous isotropic media is used in this paper for analysis field structure in media with linear dependence characteristic impedance along propagation directions.
Wave propagation phenomena in metamaterials for retrieving of effective parameters
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Ha, S.
2011-01-01
reveal so-called wave effective parameters, assigned for particular ligh propagation direction in numerical or real experiments. Therefore, finding the EP is a tricky problem, which still requires a lot of contribution to get deeper insight in it. We report on our advances in restoration MMs EP taking...... 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...
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
Estimating propagation velocity through a surface acoustic wave sensor
Xu, Wenyuan; Huizinga, John S.
2010-03-16
Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.
Love wave propagation in piezoelectric layered structure with dissipation.
Du, Jianke; Xian, Kai; Wang, Ji; Yong, Yook-Kong
2009-02-01
We investigate analytically the effect of the viscous dissipation of piezoelectric material on the dispersive and attenuated characteristics of Love wave propagation in a layered structure, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of the viscous coefficient on the phase velocity of Love waves and attenuation are presented and discussed in detail. The analytical method and the results can be useful for the design of the resonators and sensors.
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.
Millimetre Wave Propagation Over the Sea
1990-10-29
gases in the atmospherei (in particular oxygen and water vapour) causes part of the energy transmitted in millimetre waves to be absorbed. In order to...respectively to water vapour and oxygen reach 0.5 dB/km and 0.03 dB/km. Mlecular attenuation may vary substantially according to the meteorological conditions...significatifs de houle et d’un capteur embarcable utdl- sant cer algorithmex, Th~se de doctorat de 3tme cycle, Universiti Pierre et Marie Curie, Paris VI
Mishra, Rinku; Dey, M.
2018-04-01
An analytical model is developed that explains the propagation of a high frequency electrostatic surface wave along the interface of a plasma system where semi-infinite electron-ion plasma is interfaced with semi-infinite dusty plasma. The model emphasizes that the source of such high frequency waves is inherent in the presence of ion acoustic and dust ion acoustic/dust acoustic volume waves in electron-ion plasma and dusty plasma region. Wave dispersion relation is obtained for two distinct cases and the role of plasma parameters on wave dispersion is analyzed in short and long wavelength limits. The normalized surface wave frequency is seen to grow linearly for lower wave number but becomes constant for higher wave numbers in both the cases. It is observed that the normalized frequency depends on ion plasma frequencies when dust oscillation frequency is neglected.
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 ...
Seismic wave propagation on heterogeneous systems with CHAPEL
Gokhberg, Alexey; Fichtner, Andreas
2014-05-01
Simulations of seismic wave propagation play a key role in the exploration of the Earth's internal structure, the prediction of earthquake-induced ground motion, and numerous other applications. In order to harness modern heterogeneous HPC systems, we implement a spectral-element discretization of the seismic wave equation using the emerging parallel programming language Chapel. High-performance massively parallel computing systems are widely used for solving seismological problems. A recent trend in the evolution of such systems is a transition from homogeneous architectures based on the conventional CPU to faster and more energy-efficient heterogeneous architectures that combine CPU with the special purpose GPU accelerators. These new heterogeneous architectures have much higher hardware complexity and are thus more difficult to program. Therefore transition to heterogeneous computing systems widens the well known gap between the performance of the new hardware and the programmers' productivity. In particular, programming heterogeneous systems typically involves a mix of various programming technologies like MPI, CUDA, or OpenACC. This conventional approach increases complexity of application code, limits its portability and reduces the programmers' productivity. We are approaching this problem by introducing a unified high-level programming model suitable for both conventional and hybrid architectures. Our model is based on the Partitioned Global Address Space (PGAS) paradigm used by several modern parallel programming languages. We implemented this model by extending Chapel, the emerging parallel programming language created at Cray Inc. In particular, we introduced the language abstractions for GPU-based domain mapping and extended the open source Chapel compiler (version 1.8.0) with facilities designed to translate Chapel high-level parallel programming constructs into CUDA kernels. We used this extended Chapel implementation to re-program the package for the
Oblique Propagation and Dissipation of Alfven Waves in Coronal ...
Indian Academy of Sciences (India)
2016-01-27
Jan 27, 2016 ... We investigate the effect of viscosity and magnetic diffusivity on the oblique propagation and dissipation of Alfvén waves with respect to the normal outward direction, making use of MHD equations, density, temperature and magnetic field structure in coronal holes and underlying magnetic funnels. We find ...
Propagation of waves in a gravitating and rotating anisotropic heat ...
African Journals Online (AJOL)
Bheema
(1956) equations neglecting the heat flux vector. Gravitational instability on propagation of magnetohydrodynamic (MHD) waves in astrophysical plasma is investigated by Alemayehu and Tessema (2013a) by considering the effect of gravitational instability and viscosity with anisotropic pressure tensor and heat conducting.
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...
Propagation of waves in a multicomponent plasma having charged ...
Indian Academy of Sciences (India)
Propagation of waves in a multicomponent plasma having charged dust particles has been investigated by various authors in recent times as the presence of charged dust grains give rise to a new kind of modes called dust modes and it has wide applications in magneto- sphere and space plasma [1–3]. In fact, Rao et al [4] ...
Wave propagation in coated cylinders with reference to fretting fatigue
Indian Academy of Sciences (India)
The frequency of vibration or contact loading is an important parameter. The general frequency regime ... dicting initiation and propagation of micro cracks during fretting demands a proper study of stress wave .... The following expressions give the stresses and displacements in terms of potential func- tions. 2μur = ∂. ∂r. +.
Nonlinear propagation of weakly relativistic ion-acoustic waves in ...
Indian Academy of Sciences (India)
2016-10-06
Oct 6, 2016 ... Abstract. This work presents theoretical and numerical discussion on the dynamics of ion-acoustic solitary wave for weakly relativistic regime in unmagnetized plasma comprising non-extensive electrons, Boltzmann positrons and relativistic ions. In order to analyse the nonlinear propagation phenomena, ...
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)
Home; Journals; Journal of Earth System Science; Volume 116; Issue 4. Wave propagation in a general anisotropic poroelastic medium: Biot's theories and homogenisation theory. M D Sharma. Volume 116 Issue 4 August ... Keywords. Anisotropic poroelastic (APE) solid; Biot's theory; homogenisation theory; phase velocity.
Analysis of flexural wave propagation in poroelastic composite ...
African Journals Online (AJOL)
DR OKE
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 poroelastic material as homogeneous and isotropic. The inner and outer boundaries of composite hollow poroelastic ...
Influence of support viscoelastic properties on the structural wave propagation
International Nuclear Information System (INIS)
Park, Jun Hong
2007-01-01
The dissipation of the structural vibration energy at viscoelastic supports is an efficient method of reducing modal resonances and consequent noise and fatigue related problems. The support stiffness has significant impact on the modal characteristics. The dissipation capabilities of the viscoelastic support depend on its stiffness. Methods to optimally tune this support stiffness are proposed in this study. The characteristic mechanical impedance for structural vibration is obtained from wave propagation analysis and non-reflecting boundary conditions. The wave propagation is analyzed near the supports installed at edges, middle of a structure, and for the tuned vibration absorber. The dependence of the optimal stiffness on the location and mass of the supports is identified. A simple analytical solution for optimal support stiffness for maximum dissipation of propagating vibration energy at supports is presented
The impact of crustal density variations on seismic wave propagation
Plonka, A.; Fichtner, A.
2014-12-01
Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct.We propose to develop a seismic tomography technique that directly inverts for density, using complete seismograms rather than arrival times of certain waves only. The first task in this challenge is to systematically study the imprints of density on synthetic seismograms.To compute the full seismic wavefield in a 3D heterogeneous medium without making significant approximations, we usenumerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the 1D Earth model PREM (with 40 km crust thickness) as a background. Onto this (in the uppermost 40 km) we superimpose 3D randomly generated velocity and density heterogeneities of various magnitudes and correlation lenghts. We use different random realizations of heterogeneity distribution.We compare the synthetic seismograms for 3D velocity and density structure with 3D velocity structure and with the 1D background, calculating relative amplitude differences and timeshifts as functions of time and frequency.Our analyses indicate that reasonably sized density variations within the crust can leave a strong imprint on both traveltimes and amplitudes. This suggests (1) that crustal tomography can be significantly biased when density heterogeneities are not properly accounted for, and (2) that the solution of the seismic inverse problem for density may become feasible.
Effective constants for wave propagation through partially saturated porous media
International Nuclear Information System (INIS)
Berryman, J.G.; Thigpen, L.
1985-01-01
The multipole scattering coefficients for elastic wave scattering from a spherical inhomogeneity in a fluid-saturated porous medium have been calculated. These coefficients may be used to obtain estimates of the effective macroscopic constants for long-wavelength propagation of elastic waves through partially saturated media. If the volume average of the single scattering from spherical bubbles of gas and liquid is required to vanish, the resulting equations determine the effective bulk modulus, density, and viscosity of the multiphase fluid filling the pores. The formula for the effective viscosity during compressional wave excitation is apparently new
Spin wave propagation in a uniformly biased curved magnonic waveguide
Sadovnikov, A. V.; Davies, C. S.; Kruglyak, V. V.; Romanenko, D. V.; Grishin, S. V.; Beginin, E. N.; Sharaevskii, Y. P.; Nikitov, S. A.
2017-08-01
Using Brillouin light scattering microscopy and micromagnetic simulations, we study the propagation and transformation of magnetostatic spin waves across uniformly biased curved magnonic waveguides. Our results demonstrate that the spin wave transmission through the bend can be enhanced or weakened by modifying the distribution of the inhomogeneous internal magnetic field spanning the structure. Our results open up the possibility of optimally molding the flow of spin waves across networks of magnonic waveguides, thereby representing a step forward in the design and construction of the more complex magnonic circuitry.
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 at the human muscle-compact bone interface
Directory of Open Access Journals (Sweden)
Hsia Shao-Yi
2006-01-01
Full Text Available Due to the improvement of the signal processing and image technology, the clinical ultrasound system becomes an important tool to assist doctors in detecting diseases. Hence, it is necessary to know the biological effects of ultrasound in human tissue. In ultrasonic waves, the discrepancy between classic elasticity and experimental elasticity becomes a particularly important problem, especially when there are higher frequencies and smaller wavelengths, i.e., in the case of wave propagation in human muscle and compact bone. Consequently, the influence of the microstructure is important and this fact leads to the generation of new types of waves unknown in classic elasticity. General continuum theories, such as couple stress theory and micropolar theory, have degrees of freedom in addition to those of classic elasticity. Such theories are thought to be applicable to composites with granular or porous structure, effective chiral composite, and human compact bone. In this work, a theoretical analysis concerning the reflected and transmitted fields of an incident plane wave P propagating at the human muscle-compact bone interface has been investigated. The results show that the wave fields are affected by microstructures of the human bone. Knowledge of this occurrence may offer some contribution to the understanding of the ultrasound propagation in the biological effects of human tissue.
Propagation and application of waves in the ionosphere.
Yeh, K. C.; Liu, C. H.
1972-01-01
This review deals with the propagation of waves, especially radio waves in the ionosphere. In the macroscopic electromagnetic theory, the mathematical structure of wave propagation problems depends entirely on the properties of the dielectric operator in a magnetically nonpermeable medium. These properties can be deduced from general discussions of symmetry and considerations of physical principles. When the medium is specifically the ionosphere, various physical phenomena may occur. Because of a large number of parameters, it is desirable to define a parameter space. A point in the parameter space corresponds to a specific plasma. The parameter space is subdivided into regions whose boundaries correspond to conditions of resonance and cutoff. As the point crosses these boundaries, the refractive index surface transforms continuously.
Excitation of coherent propagating spin waves by pure spin currents.
Demidov, Vladislav E; Urazhdin, Sergei; Liu, Ronghua; Divinskiy, Boris; Telegin, Andrey; Demokritov, Sergej O
2016-01-28
Utilization of pure spin currents not accompanied by the flow of electrical charge provides unprecedented opportunities for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. It was recently shown that pure spin currents can be used to excite coherent magnetization dynamics in magnetic nanostructures. However, because of the intrinsic nonlinear self-localization effects, magnetic auto-oscillations in the demonstrated devices were spatially confined, preventing their applications as sources of propagating spin waves in magnonic circuits using these waves as signal carriers. Here, we experimentally demonstrate efficient excitation and directional propagation of coherent spin waves generated by pure spin current. We show that this can be achieved by using the nonlocal spin injection mechanism, which enables flexible design of magnetic nanosystems and allows one to efficiently control their dynamic characteristics.
Stress Wave Propagation due to a Moving Force
DEFF Research Database (Denmark)
Rasmussen, K. M.; Nielsen, Søren R. K.; Kirkegaard, Poul Henning
1999-01-01
In this paper the performance of two numerical methods of solving the problem of a time dependent moving force on the surface of an elastic continuum will be evaluated. One method is the finite element method (FEM) formulated in convected coordinates coupled with an absorbing boundary condition...... of the impedance type. The other method to be considered is the boundary element method (BEM), where a new formulation using Green's functions transformed to a moving coordinate system is introduced. The methods are tested by the classic wave propagation problem of a Ricker Pulse propagating from the surface...... of an elastic halfspace. The time integral net impulse of the considered loading must be null for the considered FEM to work. Further, the FEM is unable to absorb Rayleigh waves, since the considered impedance condition has been tuned P- and S-waves. By contrast the BEM is able to handle also these cases...
Quasinormal modes and classical wave propagation in analogue black holes
International Nuclear Information System (INIS)
Berti, Emanuele; Cardoso, Vitor; Lemos, Jose P.S.
2004-01-01
Many properties of black holes can be studied using acoustic analogues in the laboratory through the propagation of sound waves. We investigate in detail sound wave propagation in a rotating acoustic (2+1)-dimensional black hole, which corresponds to the 'draining bathtub' fluid flow. We compute the quasinormal mode frequencies of this system and discuss late-time power-law tails. Because of the presence of an ergoregion, waves in a rotating acoustic black hole can be superradiantly amplified. We also compute superradiant reflection coefficients and instability time scales for the acoustic black hole bomb, the equivalent of the Press-Teukolsky black hole bomb. Finally we discuss quasinormal modes and late-time tails in a nonrotating canonical acoustic black hole, corresponding to an incompressible, spherically symmetric (3+1)-dimensional fluid flow
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.
Topology Optimization for Wave Propagation Problems with Experimental Validation
DEFF Research Database (Denmark)
Christiansen, Rasmus Ellebæk
discussion of the finite element method and a hybrid ofa wave based method and the finite element method, used to discretize the modelproblems under consideration. A short discussion of the benefits and drawbacks of applying the hybrid method compared to the finite element method, used in conjunction......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...... 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...
Near-perfect conversion of a propagating plane wave into a surface wave using metasurfaces
Tcvetkova, S. N.; Kwon, D.-H.; Díaz-Rubio, A.; Tretyakov, S. A.
2018-03-01
In this paper theoretical and numerical studies of perfect/nearly perfect conversion of a plane wave into a surface wave are presented. The problem of determining the electromagnetic properties of an inhomogeneous lossless boundary which would fully transform an incident plane wave into a surface wave propagating along the boundary is considered. An approximate field solution which produces a slowly growing surface wave and satisfies the energy conservation law is discussed and numerically demonstrated. The results of the study are of great importance for the future development of such devices as perfect leaky-wave antennas and can potentially lead to many novel applications.
Topics in the Analysis of Shear-Wave Propagation in Oblique-Plate Impact Tests
National Research Council Canada - National Science Library
Scheidler, Mike
2007-01-01
This report addresses several topics in the theoretical analysis of shock waves, acceleration waves, and centered simple waves, with emphasis on the propagation of shear waves generated in oblique-plate impact tests...
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
SPATIAL DAMPING OF PROPAGATING KINK WAVES IN PROMINENCE THREADS
International Nuclear Information System (INIS)
Soler, R.; Oliver, R.; Ballester, J. L.
2011-01-01
Transverse oscillations and propagating waves are frequently observed in threads of solar prominences/filaments and have been interpreted as kink magnetohydrodynamic (MHD) modes. We investigate the spatial damping of propagating kink MHD waves in transversely nonuniform and partially ionized prominence threads. Resonant absorption and ion-neutral collisions (Cowling's diffusion) are the damping mechanisms taken into account. The dispersion relation of resonant kink waves in a partially ionized magnetic flux tube is numerically solved by considering prominence conditions. Analytical expressions of the wavelength and damping length as functions of the kink mode frequency are obtained in the thin tube and thin boundary approximations. For typically reported periods of thread oscillations, resonant absorption is an efficient mechanism for the kink mode spatial damping, while ion-neutral collisions have a minor role. Cowling's diffusion dominates both the propagation and damping for periods much shorter than those observed. Resonant absorption may explain the observed spatial damping of kink waves in prominence threads. The transverse inhomogeneity length scale of the threads can be estimated by comparing the observed wavelengths and damping lengths with the theoretically predicted values. However, the ignorance of the form of the density profile in the transversely nonuniform layer introduces inaccuracies in the determination of the inhomogeneity length scale.
Wave propagation in thermoelastic saturated porous medium
Indian Academy of Sciences (India)
computed for a numerical model of liquid-saturated sandstone. Their variations with thermal as well as poroelastic ... hyperbolic equation of heat conduction with a relaxation time ensured the finite speed for ther- ... Consider a thermally conducting isotropic porous solid saturated with a non-viscous fluid. The stresses (τij) in ...
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 estimated in a vacuum beam propagation between the edge density layer and the EC resonance absorption layer. Consequences on the EC beam propagation are investigated by using a simplified model in which the density fluctuations are described by a single harmonic oscillation. In addition, quasi......-optical calculations are shown by using edge density fluctuations as calculated by two-dimensional interchange turbulence simulations and validated with the experimental data [O. E. Garcia et al, Nucl. Fusion 47 (2007) 667]...
Bertoldi, Katia; Boyce, M.C.
2008-01-01
Wave propagation in elastomeric materials undergoing large deformations is relevant in numerous application areas, including nondestructive testing of materials and ultrasound techniques, where finite deformations and corresponding stress states can influence wave propagation and hence
Ferroics and Multiferroics for Dynamically Controlled Terahertz Wave Propagation
Dutta, Moumita
The terahertz (THz) region of electromagnetic spectra, referred roughly to the frequency range of 100 GHz (0.1 THz) to 10 THz, is the bridging gap between the microwave and infrared spectral bands. Previously confined only to astronomy and analytical sciences due to the unavailability of technology, with the recent advancements in non-linear optics, this novel field has now started emerging as a promising area of research and study. Considerable efforts are underway to fill this 'THz gap' by developing efficient THz sources, detectors, switches, modulators etc. Be it any field, to realize this regime as one of the active frontiers, it is essential to have an efficient control over the wave propagation. In this research, functional materials (ferroics/multiferroics) have been explored to attain dynamic control over the THz beam propagation. The objective is to expand the horizon by enabling different family of materials to be incorporated in the design of THz modulators, exploiting the novel properties they exhibit. To reach that goal, following a comprehensive but selective (to dielectrics) review on the current-status of this research field, some preliminary studies on ferroic materials have been performed to understand the crux of ferroism and the novel functionalities they have to offer. An analytical study on microstructural and nanoscale properties of solid-solution ferroelectric Pb(Zr0.52Ti 0.48)O3 (PZT) and composite bio-ferroic seashells have been performed to elucidate the significance of structure-property relationship in intrinsic ferroelectrics. Moving forward, engineered ferroelectricity has been demonstrated. A precise control over fabrication parameters has been exploited to introduce oxygen-vacancy defined nanoscale polar-domains in centrosymmetric BaZrO3. Realizing that structure-property relationship can significantly influence the material properties and therefore the device performance, models for figure of merit analysis have been developed for
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.
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 kz−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.
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.
Directory of Open Access Journals (Sweden)
Mati Goldberg
Full Text Available A new paradigm has recently emerged in brain science whereby communications between glial cells and neuron-glia interactions should be considered together with neurons and their networks to understand higher brain functions. In particular, astrocytes, the main type of glial cells in the cortex, have been shown to communicate with neurons and with each other. They are thought to form a gap-junction-coupled syncytium supporting cell-cell communication via propagating Ca(2+ waves. An identified mode of propagation is based on cytoplasm-to-cytoplasm transport of inositol trisphosphate (IP(3 through gap junctions that locally trigger Ca(2+ pulses via IP(3-dependent Ca(2+-induced Ca(2+ release. It is, however, currently unknown whether this intracellular route is able to support the propagation of long-distance regenerative Ca(2+ waves or is restricted to short-distance signaling. Furthermore, the influence of the intracellular signaling dynamics on intercellular propagation remains to be understood. In this work, we propose a model of the gap-junctional route for intercellular Ca(2+ wave propagation in astrocytes. Our model yields two major predictions. First, we show that long-distance regenerative signaling requires nonlinear coupling in the gap junctions. Second, we show that even with nonlinear gap junctions, long-distance regenerative signaling is favored when the internal Ca(2+ dynamics implements frequency modulation-encoding oscillations with pulsating dynamics, while amplitude modulation-encoding dynamics tends to restrict the propagation range. As a result, spatially heterogeneous molecular properties and/or weak couplings are shown to give rise to rich spatiotemporal dynamics that support complex propagation behaviors. These results shed new light on the mechanisms implicated in the propagation of Ca(2+ waves across astrocytes and the precise conditions under which glial cells may participate in information processing in the brain.
Book Review: Wave propagation in materials and structures
Ferguson, Neil
2018-02-01
This book's remit is to provide a very extensive and detailed coverage of many one and two dimensional wave propagating behaviours primarily in structures such as rods, beams and plates of complexity covering laminated, sandwich plates, smart configurations and complex material compositions. This is potentially where the detailed presentation, including the derivation of the governing equations of motion from first principles, i.e. Hamilton's method, for example, distracts slightly from the subsequent wave solutions, the numerical simulations showing time responses, the wave speeds and importantly the dispersion characteristics. The author introduces a number of known analytical methodologies and means to obtain wave solutions, including the spectral finite element approach and also provides numerical examples showing the approach being applied to joints and framed structures.
Perfectly Matched Layer (PML) for Transient Wave Propagation in a Moving Frame of Reference
DEFF Research Database (Denmark)
Madsen, Stine Skov; Krenk, Steen; Hededal, Ole
2013-01-01
In relation to the development of a Rolling Wheel Deflectometer (RWD), which is a non-destructive testing device for measuring pavement deflections, a finite element model for obtaining the soil/pavement response is developed. Absorbing boundary conditions are necessary in order to prevent...... reflections of the waves propagating through the soil due to the dynamic loading. The Perfectly Matched Layer (PML) has proven to be highly efficient when solving transient wave propagation problems in a fixed mesh. However, since the RWD is operating at traffic speeds, the load is moving with high speed...
Gravity Wave Variances and Propagation Derived from AIRS Radiances
2011-04-15
even if the waves are initially conservative there. The zonal mean values of N2 at January, 2005 are shown in Fig. 1. The input 2-D wave amplitude A is...Sigmond, M., Vin - cent, R., and Watanabe, S.: Recent developments in gravity-wave effects in climate models and the global distribution of gravity
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).
Wave propagation in a quasi-chemical equilibrium plasma
Fang, T.-M.; Baum, H. R.
1975-01-01
Wave propagation in a quasi-chemical equilibrium plasma is studied. The plasma is infinite and without external fields. The chemical reactions are assumed to result from the ionization and recombination processes. When the gas is near equilibrium, the dominant role describing the evolution of a reacting plasma is played by the global conservation equations. These equations are first derived and then used to study the small amplitude wave motion for a near-equilibrium situation. Nontrivial damping effects have been obtained by including the conduction current terms.
On the lamb wave propagation in anisotropic laminated composite plates
International Nuclear Information System (INIS)
Park, Soo Keun; Jeong, Hyun Jo; Kim, Moon Saeng
1998-01-01
This paper examines the propagation of Lamb (or plate) waves in anisotropic laminated composite plates. The dispersion relations are explicitly derived using the classical plate theory (CLT), the first-order shear deformation theory (FSDT) and the exact solution (ES), Attention is paid to the lowest antisymmetric (flexural) and lowest symmetric(extensional) modes in the low frequency, long wavelength limit. Different values of shear correction factor were tested in FSDT and comparisons between flexural wave dispersion curves were made with exact results to asses the range of validity of approximate plate theories in the frequency domain.
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...
Ultrasonic Guided Wave Propagation through Welded Lap Joints
Directory of Open Access Journals (Sweden)
Audrius Jankauskas
2016-12-01
Full Text Available The objective of the research presented here is the investigation of ultrasonic guided wave (UGW propagation through the lap joint welded plates used in the construction of a storage tank floors. The investigations have been performed using numerical simulation by finite element method (FEM and tested by measurement of the transmission losses of the guided waves transmitted through the welded lap joints. Propagation of the symmetric S0 mode in the welded stainless steel plates in the cases of different lap joint overlap width, operation frequency, and additional plate bonding caused by corrosion were investigated. It was shown that the transmission losses of the S0 mode can vary in the range of 2 dB to 8 dB depending on the ratio between lap joint width and wavelength. It was also demonstrated that additional bonding in the overlap zone caused by corrosion can essentially reduce transmission losses.
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....
Singular value decomposition methods for wave propagation analysis
Czech Academy of Sciences Publication Activity Database
Santolík, Ondřej; Parrot, M.; Lefeuvre, F.
2003-01-01
Roč. 38, č. 1 (2003), s. 10-1-10-13 ISSN 0048-6604 R&D Projects: GA ČR GA205/01/1064 Grant - others:Barrande(CZ) 98039/98055 Institutional research plan: CEZ:AV0Z3042911; CEZ:MSM 113200004 Keywords : wave propagation * singular value decomposition Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 0.832, year: 2003
Flat lens effect on seismic waves propagation in the subsoil.
Brûlé, Stéphane; Javelaud, Emmanuel H; Enoch, Stefan; Guenneau, Sébastien
2017-12-22
We show that seismic energy simulated by an artificial source that mainly propagates Rayleigh surface waves, is focused in structured soil made of a grid of holes distributed in the ground. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (seismic metamaterials to counteract partially or totally the most devastating components of seismic signals.
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.
Surface wave propagation in a fluid-saturated incompressible ...
Indian Academy of Sciences (India)
Surface wave propagation in a fluid-saturated incompressible porous medium157 where ˙xi˙xi˙xi and ¨xi¨xi¨xi(i = F,S) denote the velocities and accelerations of solid and fluid phases respectively and p is the effective pore pressure of the incompressible pore fluid. ρS and ρF are the densities of the solid and fluid phases ...
Highly Nonlinear Wave Propagation in Elastic Woodpile Periodic Structures
2016-08-03
Highly Nonlinear Wave Propagation in Elastic Woodpile Periodic Structures E. Kim,1 F. Li,1 C. Chong,2 G. Theocharis ,3 J. Yang,1 and P.G. Kevrekidis2...Kevrekidis, IMA J. Appl. Math. 76, 389 (2011). [4] G. Theocharis , N. Boechler, and C. Daraio, in Phononic Crystals and Metamaterials, Ch. 6, Springer...9] N. Boechler, G. Theocharis , and C. Daraio, Nature Ma- terials 10, 665 (2011). [10] F. Li, P. Anzel, J. Yang, P.G. Kevrekidis, and C. Daraio, Nat
Lamb waves propagation in layered piezoelectric/piezomagnetic plates.
Ezzin, Hamdi; Ben Amor, Morched; Ben Ghozlen, Mohamed Hédi
2017-04-01
A dynamic solution is presented for the propagation of harmonic waves in magneto-electro-elastic plates composed of piezoelectric BaTiO 3 (B) and magnetostrictive CoFe 2 O 4 (F) material. The state-vector approach is employed to derive the propagator matrix which connects the field variables at the upper interface to those at the lower interface of each layer. The ordinary differential approach is employed to determine the wave propagating characteristics in the plate by imposing the traction-free boundary condition on the top and bottom surfaces of the layered plate. The dispersion curves of the piezoelectric-piezomagnetic plate are shown for different thickness ratios. The numerical results show clearly the influence of different stacking sequences as well as thickness ratio on dispersion curves and on magneto-electromechanical coupling factor. These findings could be relevant to the analysis and design of high-performance surface acoustic wave (SAW) devices constructed from piezoelectric and piezomagnetic materials. Copyright Â© 2016 Elsevier B.V. All rights reserved.
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
International Nuclear Information System (INIS)
Braginsky, V.B.; Kardashev, N.S.; Polnarev, A.G.; Novikov, I.D.
1989-12-01
Propagation of an electromagnetic wave in the field of gravitational waves is considered. Attention is given to the principal difference between the electromagnetic wave propagation in the field of random gravitational waves and the electromagnetic wave propagation in a medium with a randomly-inhomogeneous refraction index. It is shown that in the case of the gravitation wave field the phase shift of an electromagnetic wave does not increase with distance. The capability of space radio interferometry to detect relic gravitational waves as well as gravitational wave bursts of non cosmological origin are analyzed. (author). 64 refs, 2 figs
Propagation of extensional waves in a piezoelectric semiconductor rod
Directory of Open Access Journals (Sweden)
C.L. Zhang
2016-04-01
Full Text Available We studied the propagation of extensional waves in a thin piezoelectric semiconductor rod of ZnO whose c-axis is along the axis of the rod. The macroscopic theory of piezoelectric semiconductors was used which consists of the coupled equations of piezoelectricity and the conservation of charge. The problem is nonlinear because the drift current is the product of the unknown electric field and the unknown carrier density. A perturbation procedure was used which resulted in two one-way coupled linear problems of piezoelectricity and the conservation of charge, respectively. The acoustic wave and the accompanying electric field were obtained from the equations of piezoelectricity. The motion of carriers was then determined from the conservation of charge using a trigonometric series. It was found that while the acoustic wave was approximated by a sinusoidal wave, the motion of carriers deviates from a sinusoidal wave qualitatively because of the contributions of higher harmonics arising from the originally nonlinear terms. The wave crests become higher and sharper while the troughs are shallower and wider. This deviation is more pronounced for acoustic waves with larger amplitudes.
Kinematics of waves propagating and breaking on a barred beach
Michallet, H.; Cienfuegos, R.; Barthélemy, E.; Grasso, F.R.
2011-01-01
Laboratory experiments are conducted in a wave facility with a loose sediment beach in order to estimate the wave characteristics needed for sediment transport modeling. A roller model and a Boussinesq-type model are used for comparing and discussing the experimental results. It is shown that the
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.
Van Allen Probe observations of EMIC wave propagation in the inner magnetosphere
Saikin, A.; Zhang, J.; Smith, C. W.; Spence, H. E.; Torbert, R. B.; Kletzing, C.; Wygant, J. R.
2017-12-01
This study examines the propagation of inner magnetosphere (L vector, , analysis on all observed EMIC wave events to determine the direction of propagation, with bi-directionally propagating EMIC waves indicating the presence of the EMIC wave source region. EMIC waves were considered bi-directional (i.e., in the source region) if at least two wave packets exhibited opposing flux components, and (W/km2), consistently for 60 seconds. Events not observed to have opposing flux components are considered unidirectional. EMIC wave events observed at relatively high magnetic latitudes, generally, are found to propagate away from the magnetic equator (i.e., unidirectional). Bi-directionally propagating EMIC waves are preferably observed at lower magnetic latitudes. The occurrence rate, spatial distribution, and the energy propagation angle of both unidirectionally and bi-directionally propagating EMIC waves are examined with respect to L, MLT, and MLAT.
Badiey, M.; Lynch, J. F.
2012-11-01
In the past half-century numerous scientific research programs have been conducted which have advanced our understanding of shallow water acoustics far beyond the original and pioneering work by Ewing, Worzel, and Pekeris (1948). In particular, during the last three decades several major initiatives have focused on both observation and modeling of acoustic waves in shallow water region with extremely variable environmental properties. We now realize that the shallow water acoustic wave propagation problem is a complicated study of wave propagation in a 4D partially random media with anisotropic, time and space dependent physical properties. The nonlinear internal wave field, the shelf break front, and coastal eddies are good examples of oceanographic processes that cause this type of variability. A review of our progress, which focuses on the effects of the water column, is presented, as well as an assessment of what future questions will be of interest and importance.
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.
Liu, Xu; Chen, Lunjin; Yang, Lixia; Xia, Zhiyang; Malaspina, David M.
2018-01-01
The effect of the plasmapause on equatorially radially propagating fast magnetosonic (MS) waves in the Earth's dipole magnetic field is studied by using finite difference time domain method. We run 1-D simulation for three different density profiles: (1) no plasmapause, (2) with a plasmapause, and (3) with a plasmapause accompanied with fine-scale density irregularity. We find that (1) without plasmapause the radially inward propagating MS wave can reach ionosphere and continuously propagate to lower altitude if no damping mechanism is considered. The wave properties follow the cold plasma dispersion relation locally along its trajectory. (2) For simulation with a plasmapause with a scale length of 0.006 RE compared to wavelength, only a small fraction of the MS wave power is reflected by the plasmapause. WKB approximation is generally valid for such plasmapause. (3) The multiple fine-scale density irregularities near the outer edge of plasmapause can effectively block the MS wave propagation, resulting in a terminating boundary for MS waves near the plasmapause.
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...
Wave propagation in metamaterials and effective parameters retrieving
DEFF Research Database (Denmark)
Andryieuski, Andrei; Ha, S.; Sukhorukov, A.
2011-01-01
of the determined effective parameters and applicability to thin slabs only. The other methods based, for example, on the eigenfunctions calculations [Menzel], or analytical calculations [Simovski] require advanced skills either in numerical methods and programming or in analytical derivations and maybe considered...... 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...... 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...
Theory of electromagnetic wave propagation in ferromagnetic Rashba conductor
Shibata, Junya; Takeuchi, Akihito; Kohno, Hiroshi; Tatara, Gen
2018-02-01
We present a comprehensive study of various electromagnetic wave propagation phenomena in a ferromagnetic bulk Rashba conductor from the perspective of quantum mechanical transport. In this system, both the space inversion and time reversal symmetries are broken, as characterized by the Rashba field α and magnetization M, respectively. First, we present a general phenomenological analysis of electromagnetic wave propagation in media with broken space inversion and time reversal symmetries based on the dielectric tensor. The dependence of the dielectric tensor on the wave vector q and M is retained to first order. Then, we calculate the microscopic electromagnetic response of the current and spin of conduction electrons subjected to α and M, based on linear response theory and the Green's function method; the results are used to study the system optical properties. First, it is found that a large α enhances the anisotropic properties of the system and enlarges the frequency range in which the electromagnetic waves have hyperbolic dispersion surfaces and exhibit unusual propagations known as negative refraction and backward waves. Second, we consider the electromagnetic cross-correlation effects (direct and inverse Edelstein effects) on the wave propagation. These effects stem from the lack of space inversion symmetry and yield q-linear off-diagonal components in the dielectric tensor. This induces a Rashba-induced birefringence, in which the polarization vector rotates around the vector (α ×q ) . In the presence of M, which breaks time reversal symmetry, there arises an anomalous Hall effect and the dielectric tensor acquires off-diagonal components linear in M. For α ∥M , these components yield the Faraday effect for the Faraday configuration q ∥M and the Cotton-Mouton effect for the Voigt configuration ( q ⊥M ). When α and M are noncollinear, M- and q-induced optical phenomena are possible, which include nonreciprocal directional dichroism in the
Aquatic manoeuvering with counter-propagating waves: a novel locomotive strategy.
Curet, Oscar M; Patankar, Neelesh A; Lauder, George V; Maciver, Malcolm A
2011-07-06
Many aquatic organisms swim by means of an undulating fin. These undulations often form a single wave travelling from one end of the fin to the other. However, when these aquatic animals are holding station or hovering, there is often a travelling wave from the head to the tail, and another moving from the tail to the head, meeting in the middle of the fin. Our study uses a biomimetic fish robot and computational fluid dynamics on a model of a real fish to uncover the mechanics of these inward counter-propagating waves. In addition, we compare the flow structure and upward force generated by inward counter-propagating waves to standing waves, unidirectional waves, and outward counter-propagating waves (i.e. one wave travelling from the middle of the fin to the head, and another wave travelling from the middle of the fin to the tail). Using digital particle image velocimetry to capture the flow structure around the fish robot, and computational fluid dynamics, we show that inward counter-propagating waves generate a clear mushroom-cloud-like flow structure with an inverted jet. The two streams of fluid set up by the two travelling waves 'collide' together (forming the mushroom cap) and collect into a narrow jet away from the cap (the mushroom stem). The reaction force from this jet acts to push the body in the opposite direction to the jet, perpendicular to the direction of movement provided by a single travelling wave. This downward jet provides a substantial increase in the perpendicular force when compared with the other types of fin actuation. Animals can thereby move upward if the fin is along the bottom midline of the body (or downward if on top); or left-right if the fins are along the lateral margins. In addition to illuminating how a large number of undulatory swimmers can use elongated fins to move in unexpected directions, the phenomenon of counter-propagating waves provides novel motion capabilities for systems using robotic undulators, an emerging
Near-Field Ground Motion Modal versus Wave Propagation Analysis
Directory of Open Access Journals (Sweden)
Artur Cichowicz
2010-01-01
Full Text Available The response spectrum generally provides a good estimate of the global displacement and acceleration demand of far-field ground motion on a structure. However, it does not provide accurate information on the local shape or internal deformation of the response of the structure. Near-field pulse-like ground motion will propagate through the structure as waves, causing large, localized deformation. Therefore, the response spectrum alone is not a sufficient representation of near-field ground motion features. Results show that the drift-response technique based on a continuous shear-beam model has to be employed here to estimate structure-demand parameters when structure is exposed to the pulse like ground motion. Conduced modeling shows limited applicability of the drift spectrum based on the SDOF approximation. The SDOF drift spectrum approximation can only be applied to structures with smaller natural periods than the dominant period of the ground motion. For periods larger than the dominant period of ground motion the SDOF drift spectra model significantly underestimates maximum deformation. Strong pulse-type motions are observed in the near-source region of large earthquakes; however, there is a lack of waveforms collected from small earthquakes at very close distances that were recorded underground in mines. The results presented in this paper are relevant for structures with a height of a few meters, placed in an underground excavation. The strong ground motion sensors recorded mine-induced earthquakes in a deep gold mine, South Africa. The strongest monitored horizontal ground motion was caused by an event of magnitude 2 at a distance of 90 m with PGA 123 m/s2, causing drifts of 0.25%–0.35%. The weak underground motion has spectral characteristics similar to the strong ground motion observed on the earth's surface; the drift spectrum has a maximum value less than 0.02%.
Modeling UHF Radio Propagation in Buildings.
Honcharenko, Walter
The potential implementation of wireless Radio Local Area Networks and Personal Communication Services inside buildings requires a thorough understanding of signal propagation within buildings. This work describes a study leading to a theoretical understanding of wave propagation phenomenon inside buildings. Covered first is propagation in the clear space between the floor and ceiling, which is modeled using Kirchoff -Huygens diffraction theory. This along with ray tracing techniques are used to develop a model to predict signal coverage inside buildings. Simulations were conducted on a hotel building, two office buildings, and a university building to which measurements of CW signals were compared, with good agreement. Propagation to other floors was studied to determine the signal strength as a function of the number of floors separating transmitter and receiver. Diffraction paths and through the floor paths which carry significant power to the receivers were examined. Comparisons were made to measurements in a hotel building and an office building, in which agreements were excellent. As originally developed for Cellular Mobile Radio (CMR) systems, the sector average is obtained from the spatial average of the received signal as the mobile traverses a path of 20 or so wavelengths. This approach has also been applied indoors with the assumption that a unique average could be obtained by moving either end of the radio link. However, unlike in the CMR environment, inside buildings both ends of the radio link are in a rich multipath environment. It is shown both theoretically and experimentally that moving both ends of the link is required to achieve a unique average. Accurate modeling of the short pulse response of a signal within a building will provide insight for determining the hardware necessary for high speed data transmission and recovery, and a model for determining the impulse response is developed in detail. Lastly, the propagation characteristics of
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
Propagation and attenuation of Rayleigh waves in a semi-infinite unsaturated poroelastic medium
Lo, Wei-Cheng
2008-10-01
An analytical model for describing the propagation and attenuation of Rayleigh waves along the free surface of an elastic porous medium containing two immiscible, viscous, compressible fluids is developed in the present study based on the poroelastic equations formulated by Lo et al. [Lo WC, Sposito G, Majer E. Wave propagation through elastic porous media containing two immiscible fluids. Water Resour Res 2005;41:W02025]. The dispersion equation obtained is complex-valued due to viscous dissipation resulting from the relative motion of the solid to the pore fluids. As an excitation frequency is stipulated, the dispersion equation that is a cubic polynomial is numerically solved to determine the phase speed and attenuation coefficient of Rayleigh waves in Columbia fine sandy loam permeated by an air-water mixture. Our numerical results show that, corresponding to three dilatational waves, there is also the existence of three different modes of Rayleigh wave in an unsaturated porous medium, which are designated as the R1, R2, and R3 waves in descending order of phase speed, respectively. The phase speed of the R1 wave is non-dispersive (frequency-independent) in the frequency range we examined (10 Hz-10 kHz) and decreases as water saturation increases, whose magnitude ranges from 20% to 49% of that of the first dilatational wave with respect to water content. However, it is revealed numerically that the R2 and R3 waves are functions of excitation frequency. Given the same water saturation and excitation frequency, the phase speeds of the R2 and R3 waves are found to be approximately 90% of those of the second and third dilatational waves, respectively. The R1 wave has the lowest attenuation coefficient whereas the R3 wave attenuates highest.
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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.
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.
An investigation of long-distance propagation of gravity waves under CAWSES India Phase II Programme
Directory of Open Access Journals (Sweden)
N. Parihar
2015-05-01
Full Text Available Coordinated measurements of airglow features from the mesosphere–lower thermosphere (MLT region were performed at Allahabad (25.5° N, 81.9° E and Gadanki (13.5° N, 79.2° E, India to study the propagation of gravity waves in 13–27° N latitude range during the period June 2009 to May 2010 under CAWSES (Climate And Weather of Sun Earth System India Phase II Programme. At Allahabad, imaging observations of OH broadband emissions and OI 557.7 nm emission were made using an all-sky imager, while at Gadanki photometric measurements of OH (6, 2 Meinel band and O2 (0, 1 Atmospheric band emissions were carried out. On many occasions, the nightly observations reveal the presence of similar waves at both locations. Typically, the period of observed similar waves lay in the 2.2–4.5 h range, had large phase speeds (~ 77–331 m s−1 and large wavelengths (~ 1194–2746 km. The images of outgoing long-wave radiation activity of the National Oceanic and Atmospheric Administration (NOAA and the high-resolution infrared images of KALPANA-1 satellite suggest that such waves possibly originated from some nearby convective sources. An analysis of their propagation characteristics in conjunction with SABER/TIMED temperature profiles and Horizontal Wind Model (HWM 2007 wind estimates suggest that the waves propagated over long distances (~ 1200–2000 km in atmospheric ducts.
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...
Propagation of three-dimensional electron-acoustic solitary waves
Shalaby, M.; El-Labany, S. K.; Sabry, R.; El-Sherif, L. S.
2011-06-01
Theoretical investigation is carried out for understanding the properties of three-dimensional electron-acoustic waves propagating in magnetized plasma whose constituents are cold magnetized electron fluid, hot electrons obeying nonthermal distribution, and stationary ions. For this purpose, the hydrodynamic equations for the cold magnetized electron fluid, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation, Zkharov-Kuznetsov (ZK) equation, in the small- but finite- amplitude regime. The ZK equation is solved analytically and it is found that it supports both solitary and blow-up solutions. It is found that rarefactive electron-acoustic solitary waves strongly depend on the density and temperature ratios of the hot-to-cold electron species as well as the nonthermal electron parameter. Furthermore, there is a critical value for the nonthermal electron parameter, which decides whether the electron-acoustic solitary wave's amplitude is decreased or increased by changing various plasma parameters. Importantly, the change of the propagation angles leads to miss the balance between the nonlinearity and dispersion; hence, the localized pulses convert to explosive/blow-up pulses. The relevance of this study to the nonlinear electron-acoustic structures in the dayside auroral zone in the light of Viking satellite observations is discussed.
Propagation of three-dimensional electron-acoustic solitary waves
International Nuclear Information System (INIS)
Shalaby, M.; El-Sherif, L. S.; El-Labany, S. K.; Sabry, R.
2011-01-01
Theoretical investigation is carried out for understanding the properties of three-dimensional electron-acoustic waves propagating in magnetized plasma whose constituents are cold magnetized electron fluid, hot electrons obeying nonthermal distribution, and stationary ions. For this purpose, the hydrodynamic equations for the cold magnetized electron fluid, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation, Zkharov-Kuznetsov (ZK) equation, in the small- but finite- amplitude regime. The ZK equation is solved analytically and it is found that it supports both solitary and blow-up solutions. It is found that rarefactive electron-acoustic solitary waves strongly depend on the density and temperature ratios of the hot-to-cold electron species as well as the nonthermal electron parameter. Furthermore, there is a critical value for the nonthermal electron parameter, which decides whether the electron-acoustic solitary wave's amplitude is decreased or increased by changing various plasma parameters. Importantly, the change of the propagation angles leads to miss the balance between the nonlinearity and dispersion; hence, the localized pulses convert to explosive/blow-up pulses. The relevance of this study to the nonlinear electron-acoustic structures in the dayside auroral zone in the light of Viking satellite observations is discussed.
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.
Evaluation of arterial propagation velocity based on the automated analysis of the Pulse Wave Shape
International Nuclear Information System (INIS)
Clara, F M; Scandurra, A G; Meschino, G J; Passoni, L I
2011-01-01
This paper proposes the automatic estimation of the arterial propagation velocity from the pulse wave raw records measured in the region of the radial artery. A fully automatic process is proposed to select and analyze typical pulse cycles from the raw data. An adaptive neuro-fuzzy inference system, together with a heuristic search is used to find a functional approximation of the pulse wave. The estimation of the propagation velocity is carried out via the analysis of the functional approximation obtained with the fuzzy model. The analysis of the pulse wave records with the proposed methodology showed small differences compared with the method used so far, based on a strong interaction with the user. To evaluate the proposed methodology, we estimated the propagation velocity in a population of healthy men from a wide range of ages. It has been found in these studies that propagation velocity increases linearly with age and it presents a considerable dispersion of values in healthy individuals. We conclude that this process could be used to evaluate indirectly the propagation velocity of the aorta, which is related to physiological age in healthy individuals and with the expectation of life in cardiovascular patients.
Wave propagation downstream of a high power helicon in a dipolelike magnetic field
International Nuclear Information System (INIS)
Prager, James; Winglee, Robert; Roberson, B. Race; Ziemba, Timothy
2010-01-01
The wave propagating downstream of a high power helicon source in a diverging magnetic field was investigated experimentally. The magnetic field of the wave has been measured both axially and radially. The three-dimensional structure of the propagating wave is observed and its wavelength and phase velocity are determined. The measurements are compared to predictions from helicon theory and that of a freely propagating whistler wave. The implications of this work on the helicon as a thruster are also discussed.
On guided wave propagation in fully clamped porous functionally graded nanoplates
Karami, Behrouz; Janghorban, Maziar; Li, Li
2018-02-01
The study on bulk waves in nanoplates has been done for several times in recent years, but guided waves have not been investigated yet. This paper is focused on the size-dependent guided wave propagation in mounted nanoplates made of porous functionally graded materials. To capture the size-dependent and shear effects, the first-order shear deformation theory and nonlocal elasticity theory are used to model the nanoplate. Porosity-dependent material properties of functionally graded nanoplate are defined via a modified power-law function. Governing equations were derived by using Hamilton's principle and are solved analytically to obtain wave frequencies and phase velocities. It is the first time that the presented model is used for studying guided wave propagation in fully clamped functionally graded nanoplates with porosities. In this research, wave frequencies as well as phase velocities of a fully clamped porous functionally graded nanoplate incorporating the effects of length-to-thickness ratio, aspect ratio, porosities, material gradation, nonlocal parameter, elastic foundation parameters and wave number are studied in detail.
Effect of the Blood Vessel Viscoelasticity on Periodic Blood Pressure Wave Propagation
Kitawaki, Tomoki; Shimizu, Masashi
Clinical arterial stiffness indexes such as PWV (pulse wave velocity) or PP (pulse pressure), which are obtained by analyzing blood pressure pulse waveforms in vivo, are used in the prognosis of cardiovascular diseases and thus analyses of pulse waveform are clinically important. The pulse wave in vivo, however, is complicated because of the complex viscoelastic property of the blood vessel wall. In addition, numerical flow simulations are useful for understanding pulse wave propagation in circulatory systems. Our proposed nonlinear one-dimensional numerical simulation model can accurately simulate the measurements of pressure waves in a silicone rubber tube and indicate that the viscoelasticity of the tube wall was significantly influenced by a single pulse waveform; however, the influence of viscoelasticity change on periodic pulsatile wave propagation has not yet been studied. The purpose of this study was therefore to investigate the effect of viscoelasticity change on the periodic pulsatile wave. For this purpose, we examined the effect of the viscoelasticity of a single silicone tube on periodic pulse wave propagation by comparing the calculated results using a one-dimensional model. As a result, the one-dimensional model could accurately express the experimental results with periodic pulsatile waves. In addition, both PWV and PP increase when the viscoelastic value of the dynamic modulus elasticity ratio increases, because increasing the elastic modulus is more effective than the energy dissipation effect by viscoelasticity change. Consequently, it is necessary to measure the viscoelastic property of the vessel wall accurately in order to estimate the arterial stiffness index (PWV and PP) accurately.
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.
Introduction to Wave Propagation in Nonlinear Fluids and Solids
Drumheller, Douglas S.
1998-02-01
Waves occur widely in nature and have innumerable commercial uses. Waves are responsible for the sound of speech, meteors igniting the atmosphere, radio and television broadcasting, medical diagnosis using ultrasound. This book provides a thorough, modern introduction to the study of linear and nonlinear waves. Beginning with fundamental concepts of motion, the book goes on to discuss linear and nonlinear mechanical waves, thermodynamics, and constitutive models for a variety of gases, liquids, and solids. Among the important areas of research and application are impact analysis, shock wave research, explosive detonation, nonlinear acoustics, and hypersonic aerodynamics. Students at an advanced undergraduate/graduate level will find this text a clear and comprehensive introduction to the study of nonlinear wave phenomena, and it will also be valuable as a professional reference in engineering and applied physics.
Gas explosion characterization, wave propagation (small scale experiments)
International Nuclear Information System (INIS)
Larsen, G.C.
1985-08-01
A number of experiments have been performed with blast waves arising from the ignition of homogeneous and well defined mixtures of methane, oxygen and nitrogen, contained within spherical balloons with controlled initial dimensions. The pressure characteristics has been studied for blast waves with and without influence from reflected waves. The influence of obstacles in the flow field has also been treated. Both configuration with one box and two closely spaced boxes have been considered, and a wave-wave interaction phenomenon was observed in the case of closely spaced obstacles. Moreover reflection coefficients have been established and some pressure variations over the surfaces have been observed. An acoustic appriximation has been used to model the blast wave originating from an expanding sphere. It has been demonstrated, that the generated pressure pulse is very sensitive to the expansion rate. Calculated and measured data have been compared, and a reasonable agreement has been found. (author)
International Nuclear Information System (INIS)
Romeo, Francesco; Rega, Giuseppe
2006-01-01
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
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.
Wave propagation in tyres and the resultant noise radiation
Gi-Jeon, Kim
Tyre noise has become an increasingly important road traffic noise source. This is because other sources on the vehicle, such as the air intake system, the exhaust system and the engine, have tended to become relatively quieter. This situation forces the tyre noise component to be reduced in order to achieve a reduction in the overall traffic noise level. In the research reported here, vibration, sound radiation and sound transmission of a passenger car radial tyre were investigated. The first half of this thesis discusses the vibration characteristics using two methods; (1)FEM to analysis modal behaviour in detail, (2)Analytical models to interpret the FEM results. These methods have both advantages and disadvantages in investigating tyre vibration. Combining the two methods is necessary in order to a fully understand the vibration behaviour of a tyre. Dispersion relationships and the related frequency of tyre modes is analysed by FEM and the flexural wave propagation in the tyre shell and the sound radiation of the tyre wall by flexural modes is analyzed using plate and shell theory. The second part of this thesis discusses the radiation and transmission of tyre noise. To predict the radiation of sound with only a knowledge of the surface vibration velocity, the experimental Green's functions were estimated by using the acoustic reciprocity principle. This technique was also applied to separate airborne structure borne noise for identification of the transmission path of tyre noise into a vehicle cabin and quantification of the relative contribution of various regions of the vibrating tyre surface to vehicle interior noise. The application of acoustic reciprocity for the tyre noise problem was verified and compared with BEM analysis.
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.
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
Measurements on wave propagation characteristics of spiraling electron beams
Singh, A.; Getty, W. D.
1976-01-01
Dispersion characteristics of cyclotron-harmonic waves propagating on a neutralized spiraling electron beam immersed in a uniform axial magnetic field are studied experimentally. The experimental setup consisted of a vacuum system, an electron-gun corkscrew assembly which produces a 110-eV beam with the desired delta-function velocity distribution, a measurement region where a microwave signal is injected onto the beam to measure wavelengths, and a velocity analyzer for measuring the axial electron velocity. Results of wavelength measurements made at beam currents of 0.15, 1.0, and 2.0 mA are compared with calculated values, and undesirable effects produced by increasing the beam current are discussed. It is concluded that a suitable electron beam for studies of cyclotron-harmonic waves can be generated by the corkscrew device.
Elastic Wave Propagation in Concrete and Continuous Wavelet Transform
Chiang, Chih-Hung; Gi, Yu-Fung; Pan, Chi-Ling; Cheng, Chia-Chi
2005-04-01
Elastic wave methods, such as the ultrasonic pulse velocity and the impact echo, are often subject to multiple reflections at the boundaries of various constituents of concrete. Current study aims to improve the feature identification of elastic wave propagation due to buried objects in concrete slabs and cylinders. Embedded steel reinforcement, steel and PVC tubes, wooden disks, and rubber spheres are tested. The received signals are analyzed using continuous wavelet transform. As a result, signals are decomposed into distinctive frequency bands with transient information preserved. The interpretation of multiple reflections at different boundary conditions thus becomes more straightforward. Features related to reflections from steel bar, PVC tube, and steel tube can be readily identified in the magnitude plot of wavelet coefficients. Vibration modes of the concrete slab corresponding to different buried objects can also be separated based on corresponding time duration.
Directory of Open Access Journals (Sweden)
Wenwan Ding
2016-01-01
Full Text Available An improved fractal sea surface model, which can describe the capillary waves very well, is introduced to simulate the one-dimension rough sea surface. In this model, the propagation of electromagnetic waves (EWs is computed by the parabolic equation (PE method using the finite-difference (FD algorithm. The numerical simulation results of the introduced model are compared with those of the Miller-Brown model and the Elfouhaily spectrum inversion model. It has been shown that the effects of the fine structure of the sea surface on the EWs propagation in the introduced model are more apparent than those in the other two models.
International Nuclear Information System (INIS)
Rohatgi, R.; Chen, K.; Bekefi, G.; Bonoli, P.; Luckhardt, S.C.; Mayberry, M.; Porkolab, M.; Villasenor, J.
1991-01-01
A series of 139 GHz microwave scattering experiments has been performed on the Versator II tokamak (B. Richards, Ph.D. thesis, Massachusetts Institute of Technology, 1981) to study the propagation of externally launched 0.8 GHz lower-hybrid waves. During lower-hybrid current drive, the launched waves are found to follow a highly directional resonance cone in the outer portion of the plasma. Wave power is also detected near the center of the plasma, and evidence of wave absorption is seen. Scattering of lower-hybrid waves in k space by density fluctuations appears to be a weak effect, although measurable frequency broadening by density fluctuations is found, Δω/ω=3x10 -4 . In the detectable range (2.5 parallel parallel spectra inferred from the scattering measurements are quite similar above and below the current drive density limit. Numerical modeling of these experiments using ray tracing is also presented
Anisotropic capillary wave propagation in a ripple tank
Velazquez, Daniel; Crowder, Daniel; Linville, Jon; Wilson, Thomas
2007-10-01
A preliminary study has been undertaken to demonstrate the anisotropic wave propagation of capillary waves in a water ripple tank. We have fabricated, using a computer-controlled milling machine, a contoured surface upon a 12'' square, .5ex1-.1em/ -.15em.25ex2 '' thick Plexiglas plate with gradually deepened (˜4 mm) angular channels emanating from the center of the plate and spaced every ninety degrees, with an additional cylindrical well in the plate's center, to accept the vibrating ball of the wave generator. The plate is submerged in the ripple tank, with the cylindrical well aligned with the point source (ball), and the water level adjusted such that the minimum and maximum water depths are 2 and 6 mm respectively and resulting wavefronts have been photographed. Provided the difference between the minimum and maximum of the phase velocities (˜17, 23 cm/s) for the corresponding depths (2 and 6 mm) of the capillary waves, can be made appropriately large (˜25%) at a fixed frequency (˜5 Hz), then one would expect to observe interesting folds (`caustics') in the wavefront in the directions of largest phase velocity (along the channels), corresponding to zero-curvature inflection points in the slowness surface. (See J.P. Wolfe ``Phonon Imaging'' (Cambridge University Press, 1998)). We have observed anisotropic wavefronts but as yet, no evidence for the expected folds.
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
Oliver, R.; Ruderman, M. S.; Terradas, J.
2015-06-01
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.
PROPAGATION AND DISPERSION OF SAUSAGE WAVE TRAINS IN MAGNETIC FLUX TUBES
International Nuclear Information System (INIS)
Oliver, R.; Terradas, J.; Ruderman, M. S.
2015-01-01
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
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.
A combined model for tsunami generation and propagation
Lima, Vania; Baptista, Maria Ana; Avilez-Valente, Paulo; Miranda, Miguel
2016-04-01
Several tsunami models apply different wave models and numerical schemes with the aim of modelling the wide variety of wave phenomena, as its generation, propagation, transformation and run-up. However, models are limited by mathematical and numerical formulations which constrain their scope of applications. Combined models are an interesting option as they allow merging the advantages of different existent models into a single one. In this work a tsunami combined model which couples the GeoClaw code, an extension of the Clawpack software for geophysical flows using adaptive finite volume methods, with the fully non-linear, phase-resolving, time-stepping Boussinesq wave model FUNWAVE-TVD for near-shore water wave propagation is presented. GeoClaw is used for the seismic tsunami generation of the 1969 Portugal tsunami and with FUNWAVE-TVD we study the propagation of the tsunami and near-shore surface elevations. Both codes have been individually benchmarked with some mandatory established benchmark problems. The results obtained from the numerical simulation are compared with existent observational data along the Portuguese coast for this historical event. This work received funding from FCT (SFRH/BD/96725/2013) and project ASTARTE - Assessment Strategy and risk Reduction For Tsunamis in Europe - Grant 603839 - FP7.
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
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(perpendi......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......(perpendicular to)rho(i)similar to1 which leads to a scaling of the maximum poloidal mode number, M-max, proportional to 1/rho(*) (rho(*)equivalent torho(i)/L). The computational resources needed scale with the number of radial (N-r), poloidal (N-theta), and toroidal (N-phi) elements as N-r * N-phi * N-theta(3...... 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...
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.
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.
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.
Nikitin, A. N.; Vasin, R. N.; Ivankina, T. I.; Kruglov, A. A.; Lokajicek, T.; Phan, L. T. N.
2012-07-01
The peculiarities of elastic wave propagation in a bilayer medium are studied theoretically and experimentally. One (isotropic) layer was an acrylic glass plate, and the other (anisotropic) was a quartz single-crystal. In experiments, the elastic waves were generated by a piezoelectric transmitter and received by a piezoelectric transducer contacting the surface of the model medium. The propagation time of a quasi-longitudinal wave was determined using high-order statistics. In the general case, the incident elastic waves are split at the interface between the layers: beams undergo double reflection and triple refraction. The measured dependences of the propagation times of quasi-longitudinal split waves on the angles of refraction are in satisfactory agreement with the calculated ones. The calculation was performed by solving the Christoffel equation with allowance for the boundary conditions.
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...
Ram Reddy, M. K.; Dahlem, M.; Zykov, V. S.; Müller, S. C.
1995-04-01
The influence of visible light on the trigger wave propagation in a thin layer of the Ru(bpy) 32+-catalyzed Belousov-Zhabotinsky reaction is investigated. The velocity evolution of a wave propagating in the dark was followed after switching on the light. The velocity starts to decrease immediately, but a new stationary value is attained only after about 10 s. The inhibitory effect on the propagation velocity was more pronounced in thin reactive layers than in thick ones. The experimental data were compared with computational results obtained with a modified Oregonator model.
Love wave propagation in functionally graded piezoelectric material layer.
Du, Jianke; Jin, Xiaoying; Wang, Ji; Xian, Kai
2007-03-01
An exact approach is used to investigate Love waves in functionally graded piezoelectric material (FGPM) layer bonded to a semi-infinite homogeneous solid. The piezoelectric material is polarized in z-axis direction and the material properties change gradually with the thickness of the layer. We here assume that all material properties of the piezoelectric layer have the same exponential function distribution along the x-axis direction. The analytical solutions of dispersion relations are obtained for electrically open or short circuit conditions. The effects of the gradient variation of material constants on the phase velocity, the group velocity, and the coupled electromechanical factor are discussed in detail. The displacement, electric potential, and stress distributions along thickness of the graded layer are calculated and plotted. Numerical examples indicate that appropriate gradient distributing of the material properties make Love waves to propagate along the surface of the piezoelectric layer, or a bigger electromechanical coupling factor can be obtained, which is in favor of acquiring a better performance in surface acoustic wave (SAW) devices.
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.
Ciliary metachronal wave propagation on the compliant surface of Paramecium cells.
Narematsu, Naoki; Quek, Raymond; Chiam, Keng-Hwee; Iwadate, Yoshiaki
2015-12-01
Ciliary movements in protozoa exhibit metachronal wave-like coordination, in which a constant phase difference is maintained between adjacent cilia. It is at present generally thought that metachronal waves require hydrodynamic coupling between adjacent cilia and the extracellular fluid. To test this hypothesis, we aspirated a Paramecium cell using a micropipette which completely sealed the surface of the cell such that no fluid could pass through the micropipette. Thus, the anterior and the posterior regions of the cell were hydrodynamically decoupled. Nevertheless, we still observed that metachronal waves continued to propagate from the anterior to the posterior ends of the cell, suggesting that in addition to hydrodynamic coupling, there are other mechanisms that can also transmit the metachronal waves. Such transmission was also observed in computational modeling where the fluid was fully decoupled between two partitions of a beating ciliary array. We also imposed cyclic stretching on the surface of live Paramecium cells and found that metachronal waves persisted in the presence of cyclic stretching. This demonstrated that, in addition to hydrodynamic coupling, a compliant substrate can also play a critical role in mediating the propagation of metachronal waves. © 2015 Wiley Periodicals, Inc.
Impact of internal waves on sound propagation off Bhimilipatnam, east coast of India
Digital Repository Service at National Institute of Oceanography (India)
Sridevi, B.; Murty, T.V.R.; Sadhuram, Y.; Rao, M.M.M.; Maneesha, K.; SujithKumar, S.; Prasanna, P.L.
-259 Impact of internal waves on sound propagation off Bhimilipatnam, East coast of India B.Sridevi, T.V. Ramana Murty, Y. Sadhuram, M.M.M. Rao, K. Maneesha, S. Sujith Kumar and P.L. Prasanna National Institute of Oceanography, Regional center, 176... the variability of ocean environment rather than it’s mean. Oceanic changes relevant to underwater acoustics are classified into mean and fluctuating components (De Santo 1979) with the following general model of the sound velocity equation...
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.
Low-frequency wave propagation in an elastic plate loaded by a two-layer fluid
DEFF Research Database (Denmark)
Indeitsev, Dmitrij; Sorokin, Sergey
2012-01-01
concern is propagation of low-frequency waves in such a coupled waveguide. In the present paper, we assume that an inhomogeneous fluid may be modelled as two homogeneous, inviscid and incompressible layers with slightly different densities. The lighter layer of fresh water lies on top of the heavier layer...... of salty water. The former one produces fluid loading at the plate, whereas the latter one is bounded by the sea bottom. We employ classical asymptotic methods to identify significant regimes of wave motion in the compound three-component waveguide. The roles of parameters involved in the problem...
On the propagation of transient waves in a viscoelastic Bessel medium
Colombaro, Ivano; Giusti, Andrea; Mainardi, Francesco
2017-06-01
In this paper, we discuss the uniaxial propagation of transient waves within a semi-infinite viscoelastic Bessel medium. First, we provide the analytic expression for the response function of the material as we approach the wave front. To do so, we take profit of a revisited version of the so called Buchen-Mainardi algorithm. Secondly, we provide an analytic expression for the long-time behavior of the response function of the material. This result is obtained by means of the Tauberian theorems for the Laplace transform. Finally, we relate the obtained results to a peculiar model for fluid-filled elastic tubes.
Numerical simulation of seismic wave propagation from land-excited large volume air-gun source
Cao, W.; Zhang, W.
2017-12-01
The land-excited large volume air-gun source can be used to study regional underground structures and to detect temporal velocity changes. The air-gun source is characterized by rich low frequency energy (from bubble oscillation, 2-8Hz) and high repeatability. It can be excited in rivers, reservoirs or man-made pool. Numerical simulation of the seismic wave propagation from the air-gun source helps to understand the energy partitioning and characteristics of the waveform records at stations. However, the effective energy recorded at a distance station is from the process of bubble oscillation, which can not be approximated by a single point source. We propose a method to simulate the seismic wave propagation from the land-excited large volume air-gun source by finite difference method. The process can be divided into three parts: bubble oscillation and source coupling, solid-fluid coupling and the propagation in the solid medium. For the first part, the wavelet of the bubble oscillation can be simulated by bubble model. We use wave injection method combining the bubble wavelet with elastic wave equation to achieve the source coupling. Then, the solid-fluid boundary condition is implemented along the water bottom. And the last part is the seismic wave propagation in the solid medium, which can be readily implemented by the finite difference method. Our method can get accuracy waveform of land-excited large volume air-gun source. Based on the above forward modeling technology, we analysis the effect of the excited P wave and the energy of converted S wave due to different water shapes. We study two land-excited large volume air-gun fields, one is Binchuan in Yunnan, and the other is Hutubi in Xinjiang. The station in Binchuan, Yunnan is located in a large irregular reservoir, the waveform records have a clear S wave. Nevertheless, the station in Hutubi, Xinjiang is located in a small man-made pool, the waveform records have very weak S wave. Better understanding of
Variational structure of inverse problems in wave propagation and vibration
Energy Technology Data Exchange (ETDEWEB)
Berryman, J.G.
1995-03-01
Practical algorithms for solving realistic inverse problems may often be viewed as problems in nonlinear programming with the data serving as constraints. Such problems are most easily analyzed when it is possible to segment the solution space into regions that are feasible (satisfying all the known constraints) and infeasible (violating some of the constraints). Then, if the feasible set is convex or at least compact, the solution to the problem will normally lie on the boundary of the feasible set. A nonlinear program may seek the solution by systematically exploring the boundary while satisfying progressively more constraints. Examples of inverse problems in wave propagation (traveltime tomography) and vibration (modal analysis) will be presented to illustrate how the variational structure of these problems may be used to create nonlinear programs using implicit variational constraints.
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.
Torsional Wave Propagation in a Pre-Stressed Structure with Corrugated and Loosely Bonded Surfaces
Directory of Open Access Journals (Sweden)
Singh Manoj K.
2017-12-01
Full Text Available An analytical model is presented to study the behaviour of propagation of torsional surface waves in initially stressed porous layer, sandwiched between an orthotropic half-space with initial stress and pre-stressed inhomogeneous anisotropic half-space. The boundary surfaces of the layer and halfspaces are taken as corrugated, as well as loosely bonded. The heterogeneity of the lower half-space is due to trigonometric variation in elastic parameters of the pre-stressed inhomogeneous anisotropic medium. Expression for dispersion relation has been obtained in closed form for the present analytical model to observe the effect of undulation parameter, flatness parameter and porosity on the propagation of torsional surface waves. The obtained dispersion relation is found to be in well agreement with classical Love wave equation for a particular case. The cases of ideally smooth interface and welded interface have also been analysed. Numerical example and graphical illustrations are made to demonstrate notable effect of initial stress, wave number, heterogeneity parameter and initial stress on the phase velocity of torsional surface waves.
Modes in light wave propagating in semiconductor laser
Manko, Margarita A.
1994-01-01
The study of semiconductor laser based on an analogy of the Schrodinger equation and an equation describing light wave propagation in nonhomogeneous medium is developed. The active region of semiconductor laser is considered as optical waveguide confining the electromagnetic field in the cross-section (x,y) and allowing waveguide propagation along the laser resonator (z). The mode structure is investigated taking into account the transversal and what is the important part of the suggested consideration longitudinal nonhomogeneity of the optical waveguide. It is shown that the Gaussian modes in the case correspond to spatial squeezing and correlation. Spatially squeezed two-mode structure of nonhomogeneous optical waveguide is given explicitly. Distribution of light among the laser discrete modes is presented. Properties of the spatially squeezed two-mode field are described. The analog of Franck-Condon principle for finding the maxima of the distribution function and the analog of Ramsauer effect for control of spatial distribution of laser emission are discussed.
Chaos and Intermittency in the DNLS Equation Describing the Parallel Alfvén Wave Propagation
Directory of Open Access Journals (Sweden)
Gustavo Krause
2014-01-01
Full Text Available When the Hall effect is included in the magnetohydrodynamics equations (Hall-MHD model the wave propagation modes become coupled, but for propagation parallel to the ambient magnetic field the Alfvén mode decouples from the magnetosonic ones, resulting in circularly polarized waves that are described by the derivative nonlinear Schrödinger (DNLS equation. In this paper, the DNLS equation is numerically solved using spectral methods for the spatial derivatives and a fourth order Runge-Kutta scheme for time integration. Firstly, the nondiffusive DNLS equation is considered to test the validity of the method by verifying the analytical condition of modulational stability. Later, diffusive and excitatory effects are incorporated to compare the numerical results with those obtained by a three-wave truncation model. The results show that different types of attractors can exist depending on the diffusion level: for relatively large damping, there are fixed points for which the truncation model is a good approximation; for low damping, chaotic solutions appear and the three-wave truncation model fails due to the emergence of new nonnegligible modes.
Solitary-wave propagation and interactions for a sixth-order generalized Boussinesq equation
Directory of Open Access Journals (Sweden)
Bao-Feng Feng
2005-01-01
based on the phase plane analysis around the equilibrium point, is used to construct the solitary-wave solutions for this nonintegrable equation. A symmetric three-level implicit finite difference scheme with a free parameter θ is proposed to study the propagation and interactions of solitary waves. Numerical simulations show the propagation of a single solitary wave of SGBE, and two solitary waves pass by each other without changing their shapes in the head-on collisions.
A Large Scale Simulation of Ultrasonic Wave Propagation in Concrete Using Parallelized EFIT
Nakahata, Kazuyuki; Tokunaga, Jyunichi; Kimoto, Kazushi; Hirose, Sohichi
A time domain simulation tool for the ultrasonic propagation in concrete is developed using the elastodynamic finite integration technique (EFIT) and the image-based modeling. The EFIT is a grid-based time domain differential technique and easily treats the different boundary conditions in the inhomogeneous material such as concrete. Here, the geometry of concrete is determined by a scanned image of concrete and the processed color bitmap image is fed into the EFIT. Although the ultrasonic wave simulation in such a complex material requires much time to calculate, we here execute the EFIT by a parallel computing technique using a shared memory computer system. In this study, formulations of the EFIT and treatment of the different boundary conditions are briefly described and examples of shear horizontal wave propagations in reinforced concrete are demonstrated. The methodology and performance of parallelization for the EFIT are also discussed.
Asymmetric wave propagation through nonlinear PT-symmetric oligomers
D'Ambroise, J.; Kevrekidis, P. G.; Lepri, S.
2012-11-01
In the present paper, we consider nonlinear PT-symmetric dimers and trimers (more generally, oligomers) embedded within a linear Schrödinger lattice. We examine the stationary states of such chains in the form of plane waves, and analytically compute their reflection and transmission coefficients through the nonlinear PT symmetric oligomer, as well as the corresponding rectification factors which clearly illustrate the asymmetry between left and right propagation in such systems. We examine not only the existence but also the dynamical stability of the plane wave states and interestingly find them to be unstable except in the vicinity of the linear limit. Lastly, we generalize our numerical considerations to the more physically relevant case of Gaussian initial wavepackets and confirm that the asymmetry in the transmission properties persists in the case of such wavepackets, as well. The role of potential asymmetries in the nonlinearity or in the gain/loss pattern is also considered. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.
Excitation of Structures Near Railway Tracks-Analysis of the Wave Propagation Path
DEFF Research Database (Denmark)
Bucinskas, Paulius; Andersen, Lars Vabbersgaard
2017-01-01
High-speed rails are an attractive alternative to other forms of intercity transportation. It is a fast, cost-efficient and environmentally friendly solution, which is being developed in various countries across the world. However, in order to be successful, high-speed rails need to transport....... This work aims to analyse how different features in the wave propagation path affect the excitation of a structure. A numerical model is constructed to account for the track structure and the underlying soil. The model utilizes a finite-element model for the structures together with a semi-analytical model...
Modeling and Inversion of Scattered Surface waves
Riyanti, C.D.
2005-01-01
In this thesis, we present a modeling method based on a domain-type integral representation for waves propagating along the surface of the Earth which have been scattered in the vicinity of the source or the receivers. Using this model as starting point, we formulate an inversion scheme to estimate
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 ... The present paper attempts to examine Love waves in elastic media containing voids. The mechanical ..... References. Achenbach J D 1973 Wave propagation in elastic solids (New York: North Holland).
Micromechanics of seismic wave propagation in granular materials
O’Donovan, J.; Ibraim, E.; O’Sullivan, C.; Hamlin, S.; Muir Wood, D.; Marketos, G.
2016-01-01
In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from
Modeling Propagation of Gas Path Damage
National Aeronautics and Space Administration — This paper describes how damage propagation can be tracked and modeled for a range of fault modes in some modules of commercial high bypass aircraft engines. To that...
Energy Technology Data Exchange (ETDEWEB)
Light, Max Eugene [Los Alamos National Laboratory
2017-04-13
This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density n_{e}(r), which will modify the wave propagation in the direction of the gradient rn_{e}(r).
Effect of fluid viscosity on wave propagation in a cylindrical bore in ...
Indian Academy of Sciences (India)
Wave propagation in a cylindrical bore filled with viscous liquid and situated in a micropolar elastic medium of infinite extent is studied. Frequency equation for surface wave propagation near the surface of the cylindrical bore is obtained and the effect of viscosity and micropolarity on dispersion curves is observed.
Propagation of nonlinear waves in bi-inductance nonlinear transmission lines
Kengne, Emmanuel; Lakhssassi, Ahmed
2014-10-01
We consider a one-dimensional modified complex Ginzburg-Landau equation, which governs the dynamics of matter waves propagating in a discrete bi-inductance nonlinear transmission line containing a finite number of cells. Employing an extended Jacobi elliptic functions expansion method, we present new exact analytical solutions which describe the propagation of periodic and solitary waves in the considered network.
Wavelet Spectral Finite Elements for Wave Propagation in Composite Plates with Damages - Years 3-4
2014-05-23
2012.01.001. Ichchou, M.N., Berthaut, J., Collet , M., 2008a. Multi-mode wave propagation ribbed plates: part I, wavenumber-space characteristics. Int. J...Solids Struct. 45 (5), 1179- 1195. Ichchou, M.N., Berthaut, J., Collet , M., 2008b. Multi-mode wave propagation ribbed plates: part II, predictions
Surface wave propagation in a double liquid layer over a liquid ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
So, some parts or the whole may be considered inhomogeneous. Propagation of plane waves in inhomogeneous media was discussed by. Pekeris (1935, 1946), Scholte (1961, 1962), Eason (1967) and Scott (1970) among many others. Wave propagation in inhomogeneous liquid media was discussed by Gupta (1965),.
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...
Linear and nonlinear wave propagation in rarefied plasmas
International Nuclear Information System (INIS)
Ballai, I.; Erdelyi, R.; Voitenko, Y.; Goossens, M.
2002-01-01
Small-amplitude magnetohydrodynamic waves are studied in a dilute collisionless plasma with an anisotropic plasma pressure. The parallel and perpendicular pressure components are defined by two polytropic pressure laws. Previous results obtained within the framework of the Chew-Goldberger-Low double-adiabatic and double-isothermal models are recovered for specific values of the polytropic indices. The double-polytropic model can be considered as an extension of its single-polytropic counterpart model. Dispersion relations for the linear waves are derived and analyzed in the presence of pressure anisotropy. Particular cases of linear and nonlinear waves in a magnetic slab with double-polytropic plasma are investigated. The presence of the effective parallel and perpendicular sound speeds in the slab gives rise to a complicated interplay between kink and sausage modes supported by the slab. The behavior of weakly nonlinear waves in the slab are governed by the Benjamin-Ono equation. The soliton-like solution of this equation may be accelerated or retarded depending on the values of parallel and perpendicular sound speeds. The solitons are always accelerated in the magnetically dominated slab
Acoustic field distribution of sawtooth wave with nonlinear SBE model
Energy Technology Data Exchange (ETDEWEB)
Liu, Xiaozhou, E-mail: xzliu@nju.edu.cn; Zhang, Lue; Wang, Xiangda; Gong, Xiufen [Key Laboratory of Modern Acoustics, Ministry of Education, Institute of Acoustics, Nanjing University, Nanjing 210093 (China)
2015-10-28
For precise prediction of the acoustic field distribution of extracorporeal shock wave lithotripsy with an ellipsoid transducer, the nonlinear spheroidal beam equations (SBE) are employed to model acoustic wave propagation in medium. To solve the SBE model with frequency domain algorithm, boundary conditions are obtained for monochromatic and sawtooth waves based on the phase compensation. In numerical analysis, the influence of sinusoidal wave and sawtooth wave on axial pressure distributions are investigated.
Source mechanisms and near-source wave propagation from broadband seismograms
Directory of Open Access Journals (Sweden)
J. Perrot
1994-06-01
Full Text Available Recording seismic events at teleseismic distances with broadband and high dynamic range instruments provides new high-quality data that allow us to interpret in more detail the complexity of seismic rupture as well as the heterogeneous structure of the medium surrounding the source where waves are initially propagating. Wave propagation analysis is performed by ray tracing in a local cartesian coordinate system near the source and in a global spherical coordinate system when waves enter the mantle. Seismograms are constructed at each station for a propagation in a 2.5-D medium. Many phases can be included and separately analyzed; this is one of the major advantages of ray tracing compared to other wave propagation techniques. We have studied four earthquakes, the 1988 Spitak Armenia Earthquake (Ms = 6.9, the 1990 Iran earthquake (Ms = 7.7, the 1990 romanian earthquake (Ms = 5.8 and the 1992 Erzincan, Turkey earthquake (Ms = 6.8. These earthquakes exhibit in different ways the complexity of the rupture and the signature of the medium surrounding the source. The use of velocity seismograms, the time derivative of displacement, increases the difficulty of the fit between synthetic seismograms and real seismograms but provides clear evidence for a need of careful time delay estimations of the different converted phases. We find that understanding of the seismic rupture as well as the influence of the medium surrounding the source for teleseismically recorded earthquakes requires a multi-stop procedure: starting with ground displacement seismograms, one is able to give a first description of the rupture as well as of the first-order influence of the medium. Then, considering the ground velocity seismograms makes the fit more difficult to obtain but increases our sensitivity to the rupture process and early converted phases. With increasing number of worldwide broadband stations, a complex rupture description is possible independently of field
Features of propagation and recordingof the stress waves in plates of finite thickness
Directory of Open Access Journals (Sweden)
Cherednichenko Rostislav Andreevich
2014-02-01
Full Text Available This work was carried out to study at the same time the dynamics of wave propagation in plane and axisymmetric plates by finite-difference numerical calculation and by the method of dynamic photoelasticity.In many cases it is possible to carry out the investigation of the dynamic stressed state of solid structures under the impact of seismic waves in plane statement, observing the foundation and the building itself in the conditions of plane deformation. Such problems in structural mechanics are usually investigated on plates providing the conditions of generalized plane stressed condition and accounting for the necessity of the known substitution of elastic constants. In case of applying the model of generalized plane stressed state for investigating two-dimensional waves’ propagation in three-dimensional elastic medium it may be necessary to observe certain additional conditions, which for example limit the class of external impacts of high frequencies (short waves. The use of candling for wave recording in plane models explored with the method of dynamic photoelasticity in the observed cases of impulse loading of the plates with finite thickness gives satisfactory results.
Lebiedzik, Catherine
1995-01-01
Development of design tools to furnish optimal acoustic environments for lightweight aircraft demands the ability to simulate the acoustic system on a workstation. In order to form an effective mathematical model of the phenomena at hand, we have begun by studying the propagation of acoustic waves inside closed spherical shells. Using a fully-coupled fluid-structure interaction model based upon variational principles, we have written a finite element analysis program and are in the process of examining several test cases. Future investigations are planned to increase model accuracy by incorporating non-linear and viscous effects.
Spatial and Temporal Characterization of Indoor Millimeter Wave Propagation at 24 GHz
Seok-hwan Min; Hayeon Kim; Haengseon Lee; Woo Jin Byun; Minsoo Kang; Kwangseon Kim; Bong-su Kim; Myung-sun Song
2016-01-01
Indoor millimeter wave propagation at the frequency of 24 GHz is studied by experimental methods. Measurements are performed to obtain temporal and spatial channel model using a channel sounder and rotating antennas in a corridor. The measured impulse responses are processed to obtain compact channel model following Saleh-Valenzuela’s model. The responses are compared with those of 5.3 GHz for the same test sites. Angular spread of 24 GHz is found to be smaller than that of 5.3 GHz, while ech...
On the propagation of sound waves in a stellar wind traversed by periodic strong shocks
Pijpers, F. P.
1994-01-01
It has been claimed that in stellar winds traversed by strong shocks the mechanism for driving the wind by sound wave pressure cannot operate because sound waves cannot propagate past the shocks. It is shown here that sound waves can propagate through shocks in one direction and that this is a sufficient condition for the sound wave pressure mechanism to work. A strong shock amplifies a sound wave passing through it and can drag the sound wave away from the star. It is immaterial for the soun...
Model Investigations of Lithospheric Propagation
1988-05-01
22iwJuo ky2+kzy J,( ApA 2 dA. (30) 8477 J Appl Phvs Vol 53.No 12.December 1982 Ronold W P King 8477 - - ., . . . -- -43- E,.4o,z) = eP ede’ Jo(Ap)22d...p. zI p,(p . .) The plane wave reflection coefficient R for norma ! o,,non, ....... 14,) Z •(.0) incidence, as seen from region i (where the dipole is
Su, Junjing; Logan, Charmilie C; Hughes, Alun D; Parker, Kim H; Dhutia, Niti M; Danielsen, Carl Christian; Simonsen, Ulf
2018-03-16
Arterial stiffness and wave reflection are important components of the ventricular afterload. Therefore, we aimed to assess the arterial wave characteristics and mechanical properties of the proximal pulmonary arteries (PAs) in the hypoxic pulmonary hypertensive rat model. After 21 days in normoxic or hypoxic chambers (24 animals in each group), the animals underwent transthoracic echocardiography and pulmonary artery catheterization with a dual-tipped pressure and Doppler flow sensor wire. Wave intensity analysis (WIA) was performed. Artery rings obtained from the pulmonary trunk, right and left PAs and the aorta were subjected to a tensile test to rupture. Collagen and elastin content was determined. In hypoxic rats, proximal PA wall thickness, collagen content, tensile strength per unit collagen, maximal elastic modulus and wall viscosity increased; while the elastin:collagen ratio and arterial distensibility decreased. Arterial pulse wave velocity was also increased and the increase was more prominent in vivo than ex vivo. Wave intensity was similar in the hypoxic and normoxic animals with negligible wave reflection. In contrast, aortic maximal elastic modulus remained unchanged, while the wall viscosity decreased. There was no evidence of altered arterial wave propagation in the proximal PAs of hypoxic rats, while the extracellular matrix protein composition altered and the collagen tensile strength increased. This was accompanied by altered mechanical properties in vivo and ex vivo.
Model for Atmospheric Propagation of Spatially Combined Laser Beams
2016-09-01
pp. 432–445, Aug. 2002. [10] D. R. Williams. (2016, May.). Earth fact sheet. NASA Goddard Space Flight Center . [Online]. Available: http...propagation model by generating WaveTrain results for all my test cases. I would also like to thank my wife, Amy, for supporting me throughout this journey ...The LaWS project started in 2010 [4] and was awarded to Kratos Defense and Security solutions by the Naval Surface Warfare Center . LaWS was designed
Sound Propagation in a Duct with Wall Corrugations Having Square-Wave Profiles
Directory of Open Access Journals (Sweden)
Muhammad A. Hawwa
2015-01-01
Full Text Available Acoustic wave propagation in ducts with rigid walls having square-wave wall corrugations is considered in the context of a perturbation formulation. Using the ratio of wall corrugation amplitude to the mean duct half width, a small parameter is defined and a two levels of approximations are obtained. The first-order solution produces an analytical description of the pressure field inside the duct. The second-order solution yields an analytical estimate of the phase speed of waves transmitting through the duct. The effect of wall corrugation density on acoustic impedance and wave speeds is highlighted. The analysis reveals that waves propagating in a duct with square-wave wall corrugation are slower than waves propagating in a duct with sinusoidal wave corrugation having the same corrugation wavelength.
Propagation of Ultrasonic Guided Waves in Composite Multi-Wire Ropes
Directory of Open Access Journals (Sweden)
Renaldas Raisutis
2016-06-01
Full Text Available Multi-wire ropes are widely used as load-carrying constructional elements in bridges, cranes, elevators, etc. Structural integrity of such ropes can be inspected by using non-destructive ultrasonic techniques. The objective of this work was to investigate propagation of ultrasonic guided waves (UGW along composite multi-wire ropes in the cases of various types of acoustic contacts between neighboring wires and the plastic core. The modes of UGW propagating along the multi-wire ropes were identified using modelling, the dispersion curves were calculated using analytical and semi-analytical finite element (SAFE techniques. In order to investigate the effects of UGW propagation, the two types of the acoustic contact between neighboring wires were simulated using the 3D finite element method (FE as well. The key question of investigation was estimation of the actual boundary conditions between neighboring wires (solid or slip and the real depth of penetration of UGW into the overall cross-section of the rope. Therefore, in order to verify the results of FE modelling, the guided wave penetration into strands of multi-wire rope was investigated experimentally. The performed modelling and experimental investigation enabled us to select optimal parameters of UGW to be used for non-destructive testing.
Effect of soil texture on the propagation and attenuation of acoustic wave at unsaturated conditions
Lo, Wei-Cheng; Yeh, Chao-Lung; Tsai, Chang-Tai
2007-05-01
SummaryA central issue in the successful application of acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil texture on the propagation and attenuation of acoustic wave as moisture content is varied, which was numerically investigated in the present study. Our earlier studies have demonstrated the existence of three different modes of acoustic wave in an elastic porous medium containing two immiscible, viscous, compressible fluids. Based on the dispersion equation obtained in the Lo-Sposito-Majer (LSM) model, the phase velocity and attenuation coefficient of the P1 and P2 waves which respectively propagate the fastest and second fastest were determined as a function of water saturation for 11 soil texture classes. The slowest wave (P3) was not characterized in this study since it does not travel far, due to very high attenuation. To provide a more general result, the calculated phase velocity and attenuation coefficient for different soil textures were normalized by those computed for sand. The normalization leads the resulting dimensionless parameters to be frequency independent throughout the whole range (up to 500 Hz) with Darcy's law remaining valid for the description of each fluid flow under wave excitation. The normalized phase velocity of the P1 wave was shown to have a substantially constant value at higher water saturations, but in the lower saturation range it first increases to reach a certain maximum value for different soil types and then decreases. The physical parameter controlling this phenomenon is the ratio of two effective non-wetting fluid storativity factors. Numerical results reveal that the normalized attenuation coefficient of the P1 wave is sensitive to soil texture and water saturation. Sand and loamy sand have the highest and second highest attenuation coefficients for the P1 wave, respectively. The magnitude of the normalized phase velocity of the P2 wave is found to be
DEFF Research Database (Denmark)
Rasmussen, Anders Rønne; Sørensen, Mads Peter; Gaididei, Yuri Borisovich
2008-01-01
, the model equation considered here is capable to describe waves propagating in opposite directions. Owing to the Hamiltonian structure of the proposed model equation, the front solution is in agreement with the classical Rankine Hugoniot relations. The exact front solution propagates at supersonic speed...
Research on Band-limited Local Plane Wave Propagator and Imaging Method in TI Medium
Han, B.; Gu, H.; Liu, S.
2017-12-01
Traditional ray-based seismic wave propagators, under the infinite frequency assumption, are widely used in seismic wave propagation and imaging due to its efficiency and flexibility. Seismic wave is a typical band-limited signal; consequently, the high-frequency ray theory is difficult to accurately describe the propagation characteristics of the band-limited signals, and it cannot avoid ray shading zones and caustics. As for wave equation based operators, even though they can propagate band-limited waves accurately, they are computationally demanding. In this study, under the framework of traditional ray theory, a seismic wave propagator applicable to transverse anisotropic medium is proposed, which is based on the local plane wave assumption. The proposed band-limited local plane wave propagator not only preserves the advantages of conventional ray-based propagators but also propagates band-limited waves accurately. To be detailed, a band-limited Snell's Law is constructed by solving the Kirchhoff boundary integral in a local plane, which is perpendicular to the central ray. Then band-limited rays are traced following the band-limited Snell's Law, and equivalent ray parameters are calculated by averaging local plane wave parameters. Physically, band-limited Snell's Law depicts that the directions of band-limited wavefields with maximum energy rays in the first Fresnel zone. Finally, the band-limited beam migration method in TI medium is developed by combining the paraxial beams with the band-limited central rays. Numerical experiments show that the local plane wave propagator can enhance the illumination in shadow zone and the imaging qualities of complex structures, such as rugose salt boundaries. Compared to conventional beam migration, our method generates better angle domain common imaging gathers (ADCIGs).
Fast acceleration of 2D wave propagation simulations using modern computational accelerators.
Wang, Wei; Xu, Lifan; Cavazos, John; Huang, Howie H; Kay, Matthew
2014-01-01
Recent developments in modern computational accelerators like Graphics Processing Units (GPUs) and coprocessors provide great opportunities for making scientific applications run faster than ever before. However, efficient parallelization of scientific code using new programming tools like CUDA requires a high level of expertise that is not available to many scientists. This, plus the fact that parallelized code is usually not portable to different architectures, creates major challenges for exploiting the full capabilities of modern computational accelerators. In this work, we sought to overcome these challenges by studying how to achieve both automated parallelization using OpenACC and enhanced portability using OpenCL. We applied our parallelization schemes using GPUs as well as Intel Many Integrated Core (MIC) coprocessor to reduce the run time of wave propagation simulations. We used a well-established 2D cardiac action potential model as a specific case-study. To the best of our knowledge, we are the first to study auto-parallelization of 2D cardiac wave propagation simulations using OpenACC. Our results identify several approaches that provide substantial speedups. The OpenACC-generated GPU code achieved more than 150x speedup above the sequential implementation and required the addition of only a few OpenACC pragmas to the code. An OpenCL implementation provided speedups on GPUs of at least 200x faster than the sequential implementation and 30x faster than a parallelized OpenMP implementation. An implementation of OpenMP on Intel MIC coprocessor provided speedups of 120x with only a few code changes to the sequential implementation. We highlight that OpenACC provides an automatic, efficient, and portable approach to achieve parallelization of 2D cardiac wave simulations on GPUs. Our approach of using OpenACC, OpenCL, and OpenMP to parallelize this particular model on modern computational accelerators should be applicable to other computational models of
Fast acceleration of 2D wave propagation simulations using modern computational accelerators.
Directory of Open Access Journals (Sweden)
Wei Wang
Full Text Available Recent developments in modern computational accelerators like Graphics Processing Units (GPUs and coprocessors provide great opportunities for making scientific applications run faster than ever before. However, efficient parallelization of scientific code using new programming tools like CUDA requires a high level of expertise that is not available to many scientists. This, plus the fact that parallelized code is usually not portable to different architectures, creates major challenges for exploiting the full capabilities of modern computational accelerators. In this work, we sought to overcome these challenges by studying how to achieve both automated parallelization using OpenACC and enhanced portability using OpenCL. We applied our parallelization schemes using GPUs as well as Intel Many Integrated Core (MIC coprocessor to reduce the run time of wave propagation simulations. We used a well-established 2D cardiac action potential model as a specific case-study. To the best of our knowledge, we are the first to study auto-parallelization of 2D cardiac wave propagation simulations using OpenACC. Our results identify several approaches that provide substantial speedups. The OpenACC-generated GPU code achieved more than 150x speedup above the sequential implementation and required the addition of only a few OpenACC pragmas to the code. An OpenCL implementation provided speedups on GPUs of at least 200x faster than the sequential implementation and 30x faster than a parallelized OpenMP implementation. An implementation of OpenMP on Intel MIC coprocessor provided speedups of 120x with only a few code changes to the sequential implementation. We highlight that OpenACC provides an automatic, efficient, and portable approach to achieve parallelization of 2D cardiac wave simulations on GPUs. Our approach of using OpenACC, OpenCL, and OpenMP to parallelize this particular model on modern computational accelerators should be applicable to other
An accurate, fast, and scalable solver for high-frequency wave propagation
Zepeda-Núñez, L.; Taus, M.; Hewett, R.; Demanet, L.
2017-12-01
In many science and engineering applications, solving time-harmonic high-frequency wave propagation problems quickly and accurately is of paramount importance. For example, in geophysics, particularly in oil exploration, such problems can be the forward problem in an iterative process for solving the inverse problem of subsurface inversion. It is important to solve these wave propagation problems accurately in order to efficiently obtain meaningful solutions of the inverse problems: low order forward modeling can hinder convergence. Additionally, due to the volume of data and the iterative nature of most optimization algorithms, the forward problem must be solved many times. Therefore, a fast solver is necessary to make solving the inverse problem feasible. For time-harmonic high-frequency wave propagation, obtaining both speed and accuracy is historically challenging. Recently, there have been many advances in the development of fast solvers for such problems, including methods which have linear complexity with respect to the number of degrees of freedom. While most methods scale optimally only in the context of low-order discretizations and smooth wave speed distributions, the method of polarized traces has been shown to retain optimal scaling for high-order discretizations, such as hybridizable discontinuous Galerkin methods and for highly heterogeneous (and even discontinuous) wave speeds. The resulting fast and accurate solver is consequently highly attractive for geophysical applications. To date, this method relies on a layered domain decomposition together with a preconditioner applied in a sweeping fashion, which has limited straight-forward parallelization. In this work, we introduce a new version of the method of polarized traces which reveals more parallel structure than previous versions while preserving all of its other advantages. We achieve this by further decomposing each layer and applying the preconditioner to these new components separately and
In-situ Measurements of the Direction of Propagation of Pump Waves
James, H. G.; Bernhardt, P. A.; Leyser, T.; Siefring, C. L.
2017-12-01
In the course of an experiment to modify the ionosphere, the direction of pump wave propagation is affected by density gradients in the horizontal and vertical directions, fundamentally affecting wave-energy transport. Horizontal gradients on various scales may await a modification attempt as a preexisting state of the ionosphere and/or be changed by the deposition of heater radio-frequency energy. In the results from the Radio Receiver Instrument (RRI) in the enhanced Polar Outflow Probe (e-POP), we have recorded on the order of 100 flights over ionospheric heaters revealing a variety of processes that high-frequency pump waves experience in the ionosphere. E-POP flies on the Canadian satellite CASSIOPE in an elliptic (320 x 1400 km), highly-inclined (81°) orbit. High frequency measurements have been/are being made near SPEAR, HAARP, Sura, EISCAT Heating and Arecibo. Electromagnetic waves from ground-based heaters are detected by the two, orthogonal, 6-m dipoles on the RRI. The high input impedance of the RRI means that the dipoles act as voltage probes, from which the electric field of incoming waves can be simply computed. When combined with cold-magnetoplasma electric-field theory, the relationship of voltages on the two orthogonal dipoles is used to deduce the direction of arrival of an incoming wave in three dimensions. We illustrate the technique by its application to analysis of signals from different transmitters. These results show a variety of pump-wave propagation directions, indicating the complexity of density structure within which modification might take place. Such complexity illustrates the importance of three-dimensional models of density in the vicinity of modification.
Wave propagation in bubble, two-component, two-phase flows. Theoretical and experimental study
International Nuclear Information System (INIS)
Micaelli, Jean-Claude
1982-01-01
This research thesis first reports the theoretical study of pressure and vacuum rate waves (of low amplitude) propagating through two-phase flows. This study is performed by using hybrid models. These models, based on assessment equations averaged for each phase, are developed by using a stochastic processing of the gas phase behaviour. This stochastic processing allows the model closure. The author highlights, in the case of vacuum rate waves, the importance of mass effects, interface friction and interface heat transfer. An experimental study is performed by using a vertical test section equipped with resistive probes and pressure sensors, and a signal processing unit (Fourier transform, inter-spectrum). Experimental results are confirmed by theoretical results, and leads to quantitative information on laws governing the interaction between phases which are necessary for model closure [fr
Directory of Open Access Journals (Sweden)
Rajneesh Kumar
2014-01-01
Full Text Available The present investigation deals with the propagation of Rayleigh type surface waves in an isotropic microstretch thermoelastic diffusion solid half space under a layer of inviscid liquid. The secular equation for surface waves in compact form is derived after developing the mathematical model. The dispersion curves giving the phase velocity and attenuation coefficients with wave number are plotted graphically to depict the effect of an imperfect boundary alongwith the relaxation times in a microstretch thermoelastic diffusion solid half space under a homogeneous inviscid liquid layer for thermally insulated, impermeable boundaries and isothermal, isoconcentrated boundaries, respectively. In addition, normal velocity component is also plotted in the liquid layer. Several cases of interest under different conditions are also deduced and discussed.
Study of ICRF wave propagation and plasma coupling efficiency in a linear magnetic mirror device
Energy Technology Data Exchange (ETDEWEB)
Peng, S.Y.
1991-07-01
Ion Cyclotron Range of Frequency (ICRF) wave propagation in an inhomogeneous axial magnetic field in a cylindrical plasma-vacuum system has historically been inadequately modelled. Previous works either sacrifice the cylindrical geometry in favor of a simpler slab geometry, concentrate on the resonance region, use a single mode to represent the entire field structure, or examine only radial propagation. This thesis performs both analytical and computational studies to model the ICRF wave-plasma coupling and propagation problem. Experimental analysis is also conducted to compare experimental results with theoretical predictions. Both theoretical as well as experimental analysis are undertaken as part of the thesis. The theoretical studies simulate the propagation of ICRF waves in an axially inhomogeneous magnetic field and in cylindrical geometry. Two theoretical analysis are undertaken - an analytical study and a computational study. The analytical study treats the inhomogeneous magnetic field by transforming the (r,z) coordinate into another coordinate system ({rho},{xi}) that allows the solution of the fields with much simpler boundaries. The plasma fields are then Fourier transformed into two coupled convolution-integral equations which are then differenced and solved for both the perpendicular mode number {alpha} as well as the complete EM fields. The computational study involves a multiple eigenmode computational analysis of the fields that exist within the plasma-vacuum system. The inhomogeneous axial field is treated by dividing the geometry into a series of transverse axial slices and using a constant dielectric tensor in each individual slice. The slices are then connected by longitudinal boundary conditions.
Study of ICRF wave propagation and plasma coupling efficiency in a linear magnetic mirror device
International Nuclear Information System (INIS)
Peng, S.Y.
1991-07-01
Ion Cyclotron Range of Frequency (ICRF) wave propagation in an inhomogeneous axial magnetic field in a cylindrical plasma-vacuum system has historically been inadequately modelled. Previous works either sacrifice the cylindrical geometry in favor of a simpler slab geometry, concentrate on the resonance region, use a single mode to represent the entire field structure, or examine only radial propagation. This thesis performs both analytical and computational studies to model the ICRF wave-plasma coupling and propagation problem. Experimental analysis is also conducted to compare experimental results with theoretical predictions. Both theoretical as well as experimental analysis are undertaken as part of the thesis. The theoretical studies simulate the propagation of ICRF waves in an axially inhomogeneous magnetic field and in cylindrical geometry. Two theoretical analysis are undertaken - an analytical study and a computational study. The analytical study treats the inhomogeneous magnetic field by transforming the (r,z) coordinate into another coordinate system (ρ,ξ) that allows the solution of the fields with much simpler boundaries. The plasma fields are then Fourier transformed into two coupled convolution-integral equations which are then differenced and solved for both the perpendicular mode number α as well as the complete EM fields. The computational study involves a multiple eigenmode computational analysis of the fields that exist within the plasma-vacuum system. The inhomogeneous axial field is treated by dividing the geometry into a series of transverse axial slices and using a constant dielectric tensor in each individual slice. The slices are then connected by longitudinal boundary conditions
On the propagation of low-hybrid waves of finite amplitude
International Nuclear Information System (INIS)
Kozyrev, A.N.; Piliya, A.D.; Fedorov, V.I.
1979-01-01
Propagation of low-hybrid waves of a finite amplitude with allowance for variation in plasma density caused by HF field pressure is studied. Considered is wave ''overturning'' which takes place in the absence of space dispersion. With taking account of dispersion the wave propagation is described by the third-order nonlinear equation which differs in shape from the complex modified Korteweg-de-Vries (Hirota) equation. Solutions of this equation of the space solution type are found
Stress Wave Propagation in Viscoelastic-Plastic Rock-Like Materials
Directory of Open Access Journals (Sweden)
Liu Lang
2016-05-01
Full Text Available Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic rock-like materials under a high-strain-rate loading and verifies the solution through an experimental test. A constitutive equation of viscoelastic-plastic rock-like materials was first established, and then kinematic and kinetic equations were then solved to derive the analytic solution for stress wave propagation in viscoelastic-plastic rock-like materials. An experimental test using the SHPB (Split Hopkinson Pressure Bar for a concrete specimen was conducted to obtain a stress-strain curve under a high-strain-rate loading. Inverse analysis based on differential evolution was conducted to estimate undetermined variables for constitutive equations. Finally, the relationship between the attenuation factor and the strain rate in viscoelastic-plastic rock-like materials was investigated. According to the results, the frequency of the stress wave, viscosity coefficient, modulus of elasticity, and density play dominant roles in the attenuation of the stress wave. The attenuation decreases with increasing strain rate, demonstrating strongly strain-dependent attenuation in viscoelastic-plastic rock-like materials.
Molecular hydrodynamics: Vortex formation and sound wave propagation
Han, Kyeong Hwan; Kim, Changho; Talkner, Peter; Karniadakis, George Em; Lee, Eok Kyun
2018-01-01
In the present study, quantitative feasibility tests of the hydrodynamic description of a two-dimensional fluid at the molecular level are performed, both with respect to length and time scales. Using high-resolution fluid velocity data obtained from extensive molecular dynamics simulations, we computed the transverse and longitudinal components of the velocity field by the Helmholtz decomposition and compared them with those obtained from the linearized Navier-Stokes (LNS) equations with time-dependent transport coefficients. By investigating the vortex dynamics and the sound wave propagation in terms of these field components, we confirm the validity of the LNS description for times comparable to or larger than several mean collision times. The LNS description still reproduces the transverse velocity field accurately at smaller times, but it fails to predict characteristic patterns of molecular origin visible in the longitudinal velocity field. Based on these observations, we validate the main assumptions of the mode-coupling approach. The assumption that the velocity autocorrelation function can be expressed in terms of the fluid velocity field and the tagged particle distribution is found to be remarkably accurate even for times comparable to or smaller than the mean collision time. This suggests that the hydrodynamic-mode description remains valid down to the molecular scale.
Acoustic wave propagation in fluids with coupled chemical reactions
International Nuclear Information System (INIS)
Margulies, T.S.; Schwarz, W.H.
1984-08-01
This investigation presents a hydroacoustic theory which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids (assuming a set of first-order acoustic equations without diffusion) such that several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff-Langevin equation) for the complex propagation variable chi = - (α + iω/c) in which α is the attenuation coefficient, c is the phase speed of the progressive wave and ω is the angular frequency. Computer simulations of sound absorption spectra have been made for three different chemical systems, each comprised of two-step chemical reactions using physico-chemical data available in the literature. The chemical systems studied include: (1) water-dioxane, (2) aqueous solutions of glycine and (3) cobalt polyphosphate mixtures. Explicit comparisons are made between the exact biquadratic characteristic solution and the approximate equation (sometimes referred to as a Debye equation) previously applied to interpret the experimental data for the chemical reaction contribution to the absorption versus frequency. The relative chemical reaction and classical viscothermal contributions to the sound absorption are also presented. Several discrepancies that can arise when estimating thermodynamic data (chemical reaction heats or volume changes) for multistep chemical reaction systems when making dilute solution or constant density assumptions are discussed
Rumor Propagation Model: An Equilibrium Study
Directory of Open Access Journals (Sweden)
José Roberto C. Piqueira
2010-01-01
information is analogous phenomena. Here, in an analogy with the SIR (Susceptible-Infected-Removed epidemiological model, the ISS (Ignorant-Spreader-Stifler rumor spreading model is studied. By using concepts from the Dynamical Systems Theory, stability of equilibrium points is established, according to propagation parameters and initial conditions. Some numerical experiments are conducted in order to validate the model.
Blanco, Joaquín. E.; Nolan, David S.; Tulich, Stefan N.
2016-10-01
Convectively coupled Kelvin waves (CCKWs) represent a significant contribution to the total variability of the Intertropical Convergence Zone (ITCZ). This study analyzes the structure and propagation of CCKWs simulated by the Weather Research and Forecasting (WRF) model using two types of idealized domains. These are the "aquachannel," a flat rectangle on a beta plane with zonally periodic boundary conditions and length equal to the Earth's circumference at the equator, and the "aquapatch," a square domain with zonal extent equal to one third of the aquachannel's length. A series of simulations are performed, including a doubly nested aquapatch, in which convection is solved explicitly along the equator. The model intercomparison is carried out throughout the use of several techniques such as power spectra, filtering, wave tracking, and compositing, and it is extended to some simulations from the Aquaplanet Experiment (APE). Results show that despite the equatorial superrotation bias produced by the WRF simulations, the CCKWs simulated with this model propagate with similar phase speeds (relative to the low-level mean flow) as the corresponding waves from the APE simulations. Horizontal and vertical structures of the CCKWs simulated with aquachannels are also in overall good agreement with those from aquaplanet simulations and observations, although there is a distortion of the zonal extent of anomalies when the shorter aquapatch is used.
Directory of Open Access Journals (Sweden)
A. Laribi
2017-09-01
Full Text Available This paper introduces a novel target height estimation approach using a Frequency Modulation Continuous Wave (FMCW automotive radar. The presented algorithm takes advantage of radar wave multipath propagation to measure the height of objects in the vehicle surroundings. A multipath propagation model is presented first, then a target height is formulated using geometry, based on the presented propagation model. It is then shown from Sensor-Target geometry that height estimation of targets is highly dependent on the radar range resolution, target range and target height. The high resolution algorithm RELAX is discussed and applied to collected raw data to enhance the radar range resolution capability. This enables a more accurate height estimation especially for low targets. Finally, the results of a measurement campaign using corner reflectors at different heights are discussed to show that target heights can be very accurately resolved by the proposed algorithm and that for low targets an average mean height estimation error of 0.03 m has been achieved by the proposed height finding algorithm.
Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals
Energy Technology Data Exchange (ETDEWEB)
Foteinopoulou, Stavroula [Iowa State Univ., Ames, IA (United States)
2003-01-01
In this dissertation, they have undertaken the challenge to understand the unusual propagation properties of the photonic crystal (PC). The photonic crystal is a medium where the dielectric function is periodically modulated. These types of structures are characterized by bands and gaps. In other words, they are characterized by frequency regions where propagation is prohibited (gaps) and regions where propagation is allowed (bands). In this study they focus on two-dimensional photonic crystals, i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction. They start by studying a two-dimensional photonic crystal system for frequencies inside the band gap. The inclusion of a line defect introduces allowed states in the otherwise prohibited frequency spectrum. The dependence of the defect resonance state on different parameters such as size of the structure, profile of incoming source, etc., is investigated in detail. For this study, they used two popular computational methods in photonic crystal research, the Finite Difference Time Domain method (FDTD) and the Transfer Matrix Method (TMM). The results for the one-dimensional defect system are analyzed, and the two methods, FDTD and TMM, are compared. Then, they shift their attention only to periodic two-dimensional crystals, concentrate on their band properties, and study their unusual refractive behavior. Anomalous refractive phenomena in photonic crystals included cases where the beam refracts on the ''wrong'' side of the surface normal. The latter phenomenon, is known as negative refraction and was previously observed in materials where the wave vector, the electric field, and the magnetic field form a left-handed set of vectors. These materials are generally called left-handed materials (LHM) or negative index materials (NIM). They investigated the possibility that the photonic crystal behaves as a LHM, and how this behavior relates
SDEM modelling of fault-propagation folding
DEFF Research Database (Denmark)
Clausen, O.R.; Egholm, D.L.; Poulsen, Jane Bang
2009-01-01
Understanding the dynamics and kinematics of fault-propagation-folding is important for evaluating the associated hydrocarbon play, for accomplishing reliable section balancing (structural reconstruction), and for assessing seismic hazards. Accordingly, the deformation style of fault-propagation-......Understanding the dynamics and kinematics of fault-propagation-folding is important for evaluating the associated hydrocarbon play, for accomplishing reliable section balancing (structural reconstruction), and for assessing seismic hazards. Accordingly, the deformation style of fault......-propagation-folding has already been the topic of a large number of empirical studies as well as physical and computational model experiments. However, with the newly developed Stress-based Discrete Element Method (SDEM), we have, for the first time, explored computationally the link between self-emerging fault patterns...
Directory of Open Access Journals (Sweden)
Tanigaki Kenichi
2015-01-01
Full Text Available Finite element models of closed-cell foam structures were created using the three-dimensional Voronoi tessellation method coupled with the random sequential addition algorithm. The dynamic compressive deformation behaviors of the models were numerically studied using LS-DYNA code. The deformation mode of the models changed gradually as the deformation rate increases. Also, the generation and the propagation of plastic wave was clearly observed with the rate of 100 m/s. The longitudinal elastic wave velocity showed a weak negative dependency on the deformation rate although the strain rate dependence of material properties was not considered. Furthermore, a prediction method for the dynamic stress state on the impact side based on the static stress-strain relationship was presented.
Adaptive numerical modeling of dynamic crack propagation
International Nuclear Information System (INIS)
Adouani, H.; Tie, B.; Berdin, C.; Aubry, D.
2006-01-01
We propose an adaptive numerical strategy that aims at developing reliable and efficient numerical tools to model dynamic crack propagation and crack arrest. We use the cohesive zone theory as behavior of interface-type elements to model crack. Since the crack path is generally unknown beforehand, adaptive meshing is proposed to model the dynamic crack propagation. The dynamic study requires the development of specific solvers for time integration. As both geometry and finite element mesh of the studied structure evolve in time during transient analysis, the stability behavior of dynamic solver becomes a major concern. For this purpose, we use the space-time discontinuous Galerkin finite element method, well-known to provide a natural framework to manage meshes that evolve in time. As an important result, we prove that the space-time discontinuous Galerkin solver is unconditionally stable, when the dynamic crack propagation is modeled by the cohesive zone theory, which is highly non-linear. (authors)
Directory of Open Access Journals (Sweden)
Q. Li
2007-01-01
Full Text Available The probability density on a height-meridional plane of negative refractive index squared f(nk2<0 is introduced as a new analysis tool to investigate the climatology of the propagation conditions of stationary planetary waves based on NCEP/NCAR reanalysis data for 44 Northern Hemisphere boreal winters (1958–2002. This analysis addresses the control of the atmospheric state on planetary wave propagation. It is found that not only the variability of atmospheric stability with altitudes, but also the variability with latitudes has significant influence on planetary wave propagation. Eliassen-Palm flux and divergence are also analyzed to investigate the eddy activities and forcing on zonal mean flow. Only the ultra-long planetary waves with zonal wave number 1, 2 and 3 are investigated. In Northern Hemisphere winter the atmosphere shows a large possibility for stationary planetary waves to propagate from the troposphere to the stratosphere. On the other hand, waves induce eddy momentum flux in the subtropical troposphere and eddy heat flux in the subpolar stratosphere. Waves also exert eddy momentum forcing on the mean flow in the troposphere and stratosphere at middle and high latitudes. A similar analysis is also performed for stratospheric strong and weak polar vortex regimes, respectively. Anomalies of stratospheric circulation affect planetary wave propagation and waves also play an important role in constructing and maintaining of interannual variations of stratospheric circulation.
Heale, C. J.; Snively, J. B.
2014-12-01
Short-period (~5-15 minute), small-scale (10s of km) gravity waves propagating through the middle atmosphere will encounter and interact with other atmospheric waves and flows, which can vary horizontally, vertically, and temporally across a wide range of scales. Simulations of gravity wave impacts over global scales generally consider vertical propagation and atmospheric variations, and neglect small scale wave reflection and interactions between waves of different scales and the time dependent background atmosphere [e.g., Fritts and Alexander, Rev. Geo., 41, 1, 2003, and references cited therein]. Short period gravity waves , which are often subject to reflection, nevertheless carry significant momentum through the atmosphere [Hines, 1997, J. Atmos. Sol. Terr. Phys., 59]. Prior studies have investigated gravity wave propagation through horizontally sheared winds [e.g., Basovich and Tsimring, J. Fluid. Mech., 142, 1984], or in altitude and time varying backgrounds [e.g., Broutman and Young, J. Fluid. Mech., 166, 1986]. Senf and Achatz [JGR, 116, D24, 2011, and references cited therein] have also considered propagation through vertically, horizontally, and temporally varying background winds, finding significant reduction of dissipation by critical levels. We here use a combination of 2D numerical simulations and ray-tracing to study the effects of medium scale background wave wind fields on the upward propagation of small-scale, short-period waves. In particular, we consider cases where the short-period waves would be classically reflected or ducted in static realistic background temperature and wind structures. Results suggest an important role for medium-scale temporal and spatial atmospheric variability in reducing the strength of reflections and facilitating the upward propagation of small-scale waves.
International Nuclear Information System (INIS)
Guo Bin
2009-01-01
Based on the electromagnetic theory and by using an analytical technique-the transfer matrix method, the obliquely incident electromagnetic waves propagating in one-dimension plasma photonic crystals is studied. The dispersion relations for both the P-polarization waves and S-polarization waves, depending on the plasma density, plasma thickness and period, are discussed. (basic plasma phenomena)
International Nuclear Information System (INIS)
Benoit, M.; Marcos, F.; Teisson, Ch.
1999-01-01
Nuclear power stations located on the coast take the water they use to cool their circuits from the sea. The water intake and discharge devices must be able to operate in all weathers, notably during extreme storms, with waves 10 m high and over. To predict the impact of the waves on the equipment, they are modeled digitally from the moment they form in the middle of the ocean right up to the moment they break on the shore. (authors)
Wu, Z.; Zheng, Y.; Wang, K. W.
2018-02-01
We present an approach to achieve adaptable band structures and nonreciprocal wave propagation by exploring and exploiting the concept of metastable modular metastructures. Through studying the dynamics of wave propagation in a chain composed of finite metastable modules, we provide experimental and analytical results on nonreciprocal wave propagation and unveil the underlying mechanisms that facilitate such unidirectional energy transmission. In addition, we demonstrate that via transitioning among the numerous metastable states, the proposed metastructure is endowed with a large number of bandgap reconfiguration possibilities. As a result, we illustrate that unprecedented adaptable nonreciprocal wave propagation can be realized using the metastable modular metastructure. Overall, this research elucidates the rich dynamics attainable through the combinations of periodicity, nonlinearity, spatial asymmetry, and metastability and creates a class of adaptive structural and material systems capable of realizing tunable bandgaps and nonreciprocal wave transmissions.
Ebrahimi, Farzad; Dabbagh, Ali
2018-03-01
In this paper, a three-variable plate model is utilized to explore the wave propagation problem of smart sandwich nanoplates made of a magnetostrictive core and ceramic face sheets while subjected to thermo-magnetic loading. Herein, the magnetostriction effect is considered and controlled via a feedback control system. The nanoplate is supposed to be embedded on a visco-Pasternak elastic substrate. The kinematic relations are derived based on the Kirchhoff plate theory; also, combining these obtained equations with Hamilton's principle, the local equations of motion are achieved. According to a nonlocal strain gradient theory (NSGT), the small-scale influences are covered precisely by introducing two scale coefficients. Afterwards, the nonlocal governing equations are derived coupling the local equations with those of the NSGT. Applying an analytical solution, the wave frequency and phase velocity of the propagated waves can be gathered solving an eigenvalue problem. On the other hand, accuracy and efficiency of the presented model are verified by setting a comparison between the obtained results with those of previous published researches. Effects of different variants are plotted in some figures and the highlights are discussed in detail.
Nakata, Satoshi; Ezaki, Takato; Ikura, Yumihiko S; Kitahata, Hiroyuki
2013-10-17
The propagation of a chemical wave on an inhibitory field, which was wedged between two excitable fields, was investigated for the photosensitive Belousov-Zhabotinsky (BZ) reaction. With an increase in the width of the inhibitory field between the excitable fields (W), the chemical wave divided into two waves at W = Wα. The divided chemical waves then coalesced at W = Wβ with a decrease in W. Wα was larger than Wβ, i.e., hysteresis on the width of the inhibitory field was observed between the division and coalescence of the chemical wave. The experimental results were qualitatively reproduced by a numerical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that the chemical wave may be preserved on the inhibitory field due to an activator supplied from a chemical wave on the excitable field.
International Nuclear Information System (INIS)
Parchevsky, K. V.; Kosovichev, A. G.
2009-01-01
Investigation of propagation, conversion, and scattering of MHD waves in the Sun is very important for understanding the mechanisms of observed oscillations and waves in sunspots and active regions. We have developed a three-dimensional linear MHD numerical model to investigate the influence of the magnetic field on excitation and properties of the MHD waves. The results show that surface gravity waves (f-modes) are affected by the background magnetic field more than acoustic-type waves (p-modes). Comparison of our simulations with the time-distance helioseismology results from Solar and Heliospheric Observatory/MDI shows that the amplitude of travel time variations with azimuth around sunspots caused by the inclined magnetic field does not exceed 25% of the observed amplitude even for strong fields of 1400-1900 G. This can be an indication that other effects (e.g., background flows and nonuniform distribution of the magnetic field) can contribute to the observed azimuthal travel time variations. The azimuthal travel time variations caused by the wave interaction with the magnetic field are similar for simulated and observed travel times for strong fields of 1400-1900 G if Doppler velocities are taken at the height of 300 km above the photosphere where the plasma parameter β << 1. For the photospheric level the travel times are systematically smaller by approximately 0.12 minutes than for the height of 300 km above the photosphere for all studied ranges of the magnetic field strength and inclination angles. Numerical MHD wave modeling and new data from the HMI instrument of the Solar Dynamics Observatory will substantially advance our knowledge of the wave interaction with strong magnetic fields on the Sun and improve the local helioseismology diagnostics.
Ho, Christian; Golshan, Nasser
1999-01-01
We recommend to use the dayside Martian ionosphere as a reflector for global communication, because the dayside ionosphere has stable density peak and usable critic frequency. This is very crucial for the future Mars ground to around communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest to perform the Martian nightside ionospheric modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosond instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity has small value, it still can cause the ray bending and multipath effects. We recommend to perform an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. are also needed to be estimated. Ice depolarization effects due to Martian clouds on radio waves is unknown yet, which is expected to be small, because lower optical depth and thinner layer of cloud: Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves band, because the Martian atmosphere has very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available yet. Under the normal condition, CO2 and N2 gases do not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is most dominant factor to the radio wave attenuation. Large Martian dust storm can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The
Modeling of Shock Propagation and Attenuation in Viscoelastic Components
Directory of Open Access Journals (Sweden)
R. Rusovici
2001-01-01
Full Text Available Protection from the potentially damaging effects of shock loading is a common design requirement for diverse mechanical structures ranging from shock accelerometers to spacecraft. High damping viscoelastic materials are employed in the design of geometrically complex, impact-absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material behavior over a wide frequency range. The Anelastic Displacement Fields (ADF method is employed herein to model frequency-dependence within a time-domain finite element framework. Axisymmetric, ADF finite elements are developed and then used to model shock propagation and absorption through viscoelastic structures. The model predictions are verified against longitudinal wave propagation experimental data and theory.
Energy Technology Data Exchange (ETDEWEB)
Damiano, P. A. [Princeton Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton University, Princeton New Jersey USA; Johnson, J. R. [Princeton Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton University, Princeton New Jersey USA; Chaston, C. C. [Space Sciences Laboratory, University of California, Berkeley California USA; School of Physics, University of Sydney, Sydney New South Wales Australia
2015-07-01
A new 2-D self-consistent hybrid gyrofluid-kinetic electron model in dipolar coordinates is presented and used to simulate dispersive-scale Alfvén wave pulse propagation from the equator to the ionosphere along an L = 10 magnetic field line. The model is an extension of the hybrid MHD-kinetic electron model that incorporates ion Larmor radius corrections via the kinetic fluid model of Cheng and Johnson (1999). It is found that consideration of a realistic ion to electron temperature ratio decreases the propagation time of the wave from the plasma sheet to the ionosphere by several seconds relative to a ρi=0 case (which also implies shorter timing for a substorm onset signal) and leads to significant dispersion of wave energy perpendicular to the ambient magnetic field. Additionally, ion temperature effects reduce the parallel current and electron energization all along the field line for the same magnitude perpendicular electric field perturbation.
The role of a metal screen on the coaxial discharge wave propagation characteristics
International Nuclear Information System (INIS)
Bogdanov, T; Benova, E
2010-01-01
The purpose of this work is to investigate theoretically the propagation characteristics of the electromagnetic wave that can produce and sustain plasma in a coaxial structure, as well as the wave field components. We have investigated the coaxial structure which consists of a metal rod in the centre, a dielectric tube, plasma outside the tube and with or without a metal screen. The plasma is both radially and axially inhomogeneous but we consider a radially averaged electron density in describing the plasma and we are presenting here one-dimensional axial model. The basic relation in our model is the local dispersion relation obtained from Maxwell's equations. Since the plasma is axially inhomogeneous the local dispersion relation gives the dependence between the normalized plasma density and the dimensionless wave number, so called phase diagrams. The radial variations of the normalized wave field components are calculated. The behavior of the phase diagrams and the wave field components is compared in four configurations: metal-vacuum-plasma; metal-vacuum-dielectric-plasma; metal-vacuum-plasma-metal; metal-vacuum-dielectric-plasma-metal.
International Nuclear Information System (INIS)
Johnson, R.S.
1984-01-01
The propagation of surface waves - that is 'third' sound -on superfluid helium is considered. The fluid is treated as a continuum, using the two-fluid model of Landau, and incorporating the effects of healing, relaxation, thermal conductivity and Newtonian viscosity. A linear theory is developed which includes some discussion of the matching to the outer regions of the vapour. This results in a comprehensive propagation speed for linear waves, although a few properties of the flow are left undetermined at this order. A nonlinear theory is then outlined which leads to the Burgers equation in an appropriate far field, and enables the leading-order theory to be concluded. Some numerical results, for two temperatures, are presented by first recording the Helmholtz free energy as a polynomial in densities, but only the equilibrium state can be satisfactorily reproduced. The propagation speed, as a function of film thickness, is roughly estimated. The looked-for reduction in the predicted speeds is evident, but the magnitude of this reduction is too large for very thin films. However, these analytical results should prove more effective when a complete and accurate description of the Helmholtz free energy is available. (author)
International Nuclear Information System (INIS)
Bakkali, M El; Lhémery, A; Baronian, V; Chapuis, B
2015-01-01
Elastic guided waves (GW) are used to inspect pipeworks in various industries. Modelling tools for simulating GW inspection are necessary to understand complex scattering phenomena occurring at specific features (welds, elbows, junctions...). In pipeworks, straight pipes coexist with elbows. GW propagation in the former cases is well-known, but is less documented in the latter. Their scattering at junction of straight and curved pipes constitutes a complex phenomenon. When a curved part is joined to two straight parts, these phenomena couple and give rise to even more complex wave structures. In a previous work, the SemiAnalytic Finite Element method extended to curvilinear coordinates was used to handle GW propagation in elbows, combined with a mode matching method to predict their scattering at the junction with a straight pipe. Here, a pipework comprising an arbitrary number of elbows of finite length and of different curvature linking straight pipes is considered. A modal scattering matrix is built by cascading local scattering and propagation matrices. The overall formulation only requires meshing the pipe section to compute both the modal solutions and the integrals resulting from the mode-matching method for computing local scattering matrices. Numerical predictions using this approach are studied and compared to experiments
Nonlinear Wave Propagation and Solitary Wave Formation in Two-Dimensional Heterogeneous Media
Luna, Manuel
2011-05-01
Solitary wave formation is a well studied nonlinear phenomenon arising in propagation of dispersive nonlinear waves under suitable conditions. In non-homogeneous materials, dispersion may happen due to effective reflections between the material interfaces. This dispersion has been used along with nonlinearities to find solitary wave formation using the one-dimensional p-system. These solitary waves are called stegotons. The main goal in this work is to find two-dimensional stegoton formation. To do so we consider the nonlinear two-dimensional p-system with variable coefficients and solve it using finite volume methods. The second goal is to obtain effective equations that describe the macroscopic behavior of the variable coefficient system by a constant coefficient one. This is done through a homogenization process based on multiple-scale asymptotic expansions. We compare the solution of the effective equations with the finite volume results and find a good agreement. Finally, we study some stability properties of the homogenized equations and find they and one-dimensional versions of them are unstable in general.
International Nuclear Information System (INIS)
Wen Jihong; Yu, Dianlong; Wang Gang; Zhao Honggang; Liu Yaozong; Wen Xisen
2007-01-01
The directional propagation characteristics of elastic wave during pass bands in two-dimensional thin plate phononic crystals are analyzed by using the lumped-mass method to yield the phase constant surface. The directions and regions of wave propagation in phononic crystals for certain frequencies during pass bands are predicted with the iso-frequency contour lines of the phase constant surface, which are then validated with the harmonic responses of a finite two-dimensional thin plate phononic crystals with 16x16 unit cells. These results are useful for controlling the wave propagation in the pass bands of phononic crystals