Search for: wave-propagation
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    Guest editorial: Special issue on collective behavior of nonlinear dynamical networks

    , Article Scientia Iranica ; Volume 28, Issue 3 D , 2021 , Pages 1535-1538 ; 10263098 (ISSN) Jafari, S ; Perc, M ; Tavazoei, M. S ; Sharif University of Technology
    Sharif University of Technology  2021

    A ray tracing acceleration technique for wave propagation modeling

    , Article APMC 2009 - Asia Pacific Microwave Conference 2009, 7 December 2009 through 10 December 2009, Singapore ; 2009 , Pages 1100-1103 ; 9781424428021 (ISBN) Parsa, S ; Shishegar, A. A ; Sharif University of Technology
    IEEE  2009
    In this paper we deal with ray tracing acceleration problem in wave propagation simulation as a separate problem from its computer graphical counterpart and try to review accelerating techniques with this point of view. We build a classical kd-tree adapted to the special geometry of the problem. Then we mention the main differences between these two problems and devise algorithms that use these differences for accelerating intersection test in this problem even further  

    Far-field dynamic behavior of a half-space under an inertial strip foundation subjected to a time-harmonic force

    , Article Latin American Journal of Solids and Structures ; Volume 10, Issue 3 , 2013 , Pages 453-471 ; 16797817 (ISSN) Dehestani, M ; Malidarreh, N. R ; Choobbasti, A. J ; Vafai, A ; Sharif University of Technology
    Recent research works demonstrated that the interaction between the loads and the carrying structure's boundary which is related to the inertia of the load is an influential factor on the dynamic response of the structure. Although effects of the inertia in moving loads were considered in many works, very few papers can be found on the inertial effects of the stationary loads on structures. In this paper, an elastodynamic formulation was employed to investigate the dynamic response of a homogeneous isotropic elastic half-space under an inertial strip foundation subjected to a time-harmonic force. Fourier integral transformation was used to solve the system of Poisson-type partial... 

    Increasing the Accuracy of Vectorial Gaussian Beam Tracing in a Short Urban Link Using Hybrid Methods

    , M.Sc. Thesis Sharif University of Technology Alavi Rad, Mohammad (Author) ; Shishegar, Amir Ahmad (Supervisor)
    Recently, there has been a great interest toward site–specific modeling of outdoor radio wave propagation. Wave propagation in very large environments compared to a wavelength builds up an important category of electromagnetic wave propagation problems which occurs in
    versatile criteria from optical devices to long wireless microwave links. Well-known methods such as different ray tracing schemes used in these problems suffer from long execution time and great amount of needed memory. A new method has been proposed in this thesis to overcome such difficulties for high frequency wave propagation in large scale problems. The proposed method is based on tracing 3D vectorial Gaussian beam.... 

    Love waves propagation in functionally graded piezoelectric materials with quadratic variation

    , Article Journal of Sound and Vibration ; Volume 313, Issue 1-2 , 2008 , Pages 195-204 ; 0022460X (ISSN) Eskandari, M ; Shodja, H. M ; Sharif University of Technology
    The propagation behavior of Love waves in a semi-infinite functionally graded piezoelectric material (FGPM) with a quadratic variation is addressed. The coupled electromechanical field equations are solved, and the dispersion relations, displacement, electric potential, and stress fields are obtained analytically for both electrically open and short conditions. The effects of gradient coefficient on phase velocity, group velocity, and electromechanical coupling factor are plotted and discussed. It is shown that the phase velocity associated with the non-piezoelectric case coincides with that of the corresponding piezoelectric material under electrically open conditions. Because of gradual... 

    Wave propagation in a three-dimensional half-space with semi-infinite irregularities

    , Article Waves in Random and Complex Media ; 2021 ; 17455030 (ISSN) Daneshyar, A ; Sotoudeh, P ; Ghaemian, M ; Sharif University of Technology
    Taylor and Francis Ltd  2021
    Dynamic analysis of problems with complex geometries requires utilization of numerical methods. To completely capture the effects of seismic wave propagation in a system, one must consider the structure or irregularity within its encompassing half-space. Correct consideration of half-space in a numerical model is important specially when it comes to cases where the half-space contains semi-infinite irregularities. In this study, a generalized numerical methodology is presented for dynamic analysis of a half-space with semi-infinite irregularities. The methodology is first verified through comparison with analytical solution of known problems. Then the method is employed to solve the dynamic... 

    Inertial Effects of Moving Loads on the Dynamic Behavior of One and Two Dimensional Structures

    , Ph.D. Dissertation Sharif University of Technology Dehestani Kolagar, Mehdi (Author) ; Vafai, Abolhassan (Supervisor)
    In this study the dynamic responses of finite Euler-Bernoulli beams and homogeneous isotropic 2D half-spaces, as one and two dimensional structures, under a moving object are investigated. First, the dynamic responses of finite beams with various boundary conditions were investigated. The results illustrated that the speed of a moving mass has direct influence on the entire structural dynamic response, depending on its boundary conditions. Critical influential speeds in the moving mass problems were introduced and obtained in numerical examples for various BC’s. Dynamic response of a half-space under an inertial foundation subjected to a time-harmonic loading was investigated in the next... 

    Surface Waves Propagation in a Piezoelectric/Piezomagnetic Half Space Overlaid With a Finnite Layer

    , M.Sc. Thesis Sharif University of Technology Soltanian Fard, Mohammad Amin (Author) ; Skandari, Morteza (Supervisor)
    The propagation of the surface waves in the piezoelectric (PE) and piezomagnetic (PM) layered media are studied. The surface BG waves in the PE half-spaces overlaid by a layer are considered and the closed-form dispersion relations for the open and short electromechanical surface boundary conditions are obtained. The numerical results for the phase velocities and the electromechanical coupling factor for PZT-2 and PZT-8 media are presented. Furthermore, the propagation of the Rayleigh waves in the PE-PM layered media is considered. The effects of the imperfect bonding between the half-space and the layer are discussed. Later, we study the propagation of the Rayleigh waves in 4 different... 

    Three-dimensional scattering of plane harmonic SH, SV, and P waves in multilayered alluvial valleys

    , Article Asian Journal of Civil Engineering ; Volume 11, Issue 5 , 2010 , Pages 605-626 ; 15630854 (ISSN) Omidvar, B ; Rahimian, M ; Mohammadnejad, T ; Sanaeiha, A ; Sharif University of Technology
    In this paper, three-dimensional amplification of plane harmonic SH, SV, and P waves in multilayered alluvial valleys is investigated by using a boundary element method in frequency domain. It is shown that in order to achieve real responses, the problem must be analyzed and modeled three-dimensionally. Also, for exact evaluation of surface ground motions in alluvial valleys all key parameters such as layering, material and geometrical characteristics of each layer, stimulation frequency, wave type, plus angle and azimuth of incidence must be taken into account altogether. The accuracy and efficiency of the proposed formulations for the computation of the surface displacement field... 

    Asymmetric wave propagation in a transversely isotropic half-space in displacement potentials

    , Article International Journal of Engineering Science ; Volume 46, Issue 7 , 2008 , Pages 690-710 ; 00207225 (ISSN) Khojasteh, A ; Rahimian, M ; Eskandari, M ; Pak, R. Y. S ; Sharif University of Technology
    With the aid of a complete representation using two displacement potentials, an efficient and accurate analytical derivation of the fundamental Green's functions for a transversely isotropic elastic half-space subjected to an arbitrary, time-harmonic, finite, buried source is presented. The formulation includes a complete set of transformed stress-potential and displacement-potential relations that can be useful in a variety of elastodynamic as well as elastostatic problems. The present solutions are analytically in exact agreement with the existing solutions for a half-space with isotropic material properties. For the numerical evaluation of the inversion integrals, a quadrature scheme... 

    Reflection analysis of the end-facet dielectric slab waveguide by FDTD method

    , Article ICCEA 2004 - 2004 3rd International Conference on Computational Electromagnetics and its Applications, Beijing, 1 November 2004 through 4 November 2004 ; 2004 , Pages 453-456 ; 0780385624 (ISBN) Vahidpour, M ; Shishegar, A. A ; Sharif University of Technology
    The Finite Difference Time Domain (FDTD) method has been applied to the analysis of abruptly-ended dielectric waveguides. In these waveguides, incident propagating wave undergoes reflection in an interaction with the end-facet. As a result of the discontinuity, all possible propagating modes may be excited. The constituent propagating modes are extracted from the reflected wave by the least square method. Thus, we present a good estimation of the amplitudes of the reflected modes. This full wave analysis technique is also capable of analyzing any arbitrarily shaped facet. © 2004 IEEE  

    Theory of Nonlinear Lumped Element Transmission Lines

    , M.Sc. Thesis Sharif University of Technology Samizadeh Nikooytabalvandani, Mohammad (Author) ; Farzaneh, Forouhar (Supervisor) ; Hashemi, Morad Ali (Co-Advisor)
    With the rapid advances in microwave semiconductor devices and systems, the demand for implementation of nonlinear transmission lines (NLTLs) is rapidly increased. NLTLs support short pulses and wide band-widths. These networks provide cutoff frequencies over hundreds of GHz and picosecond rise times. Among all of the applications of NLTLs, the most attention has been paid to their application in the generation of high power RF pulses. In this application, a high power rectangular pulse is injected to the line, gradually evolved to an oscillatory pulse while propagating through the network, and finally, in the form of a high power RF pulse, is delivered to the load. NLTLs are the most... 

    Site-Specific Indoor Propagation Modeling Using Ray Tracing Method for 6g Wireless Communications

    , M.Sc. Thesis Sharif University of Technology Sheybani, Sina (Author) ; Shishegar, Amir Ahmad (Supervisor)
    This thesis explores the feasibility of implementing terahertz wireless communication in indoor environments (as suggested in 6G) by modeling the propagation of terahertz band waves. The roughness of indoor surfaces at the terahertz frequencies is investigated through the detailed examination of the electromagnetic fields scattered from these surfaces using the method of moments (MoM). To account for the random roughness of these surfaces, the Monte Carlo method is utilized, generating surfaces with Gaussian statistical distribution, and obtaining the scattered electromagnetic fields using MoM. The final results represent an average of all simulated scenarios. In addition, the study... 

    Interference analysis in an urban mesh network operating in the 60-GHz band

    , Article ETRI Journal ; Volume 35, Issue 5 , 2013 , Pages 775-785 ; 12256463 (ISSN) Rasekh, M. E ; Farzaneh, F ; Sharif University of Technology
    Because of their exclusive features, millimeter wave directive mesh networks can be considered for small cell backhaul support in urban environments. For this purpose, a network of closely spaced stations has been considered with very directive line-of-sight links operating in the 60-GHz band. An attempt is made to evaluate channel response and interference behavior in such a network, taking into account the effect of building blockage. A simple grid of building blocks is considered as the propagation environment, and wave propagation is simulated using 2.5-dimensional (2.5D) ray tracing (2D with ground effect) to calculate the received signal at different nodes in the network. The results... 

    Experimental study of continuous h2/air rotating detonations

    , Article Combustion Science and Technology ; 2020 Dehghan Nezhad, S ; Fahim, M ; Farshchi, M ; Sharif University of Technology
    Taylor and Francis Inc  2020
    An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in... 

    Wave propagation analysis of the laminated cylindrical nanoshell coupled with a piezoelectric actuator

    , Article Mechanics Based Design of Structures and Machines ; Volume 49, Issue 5 , 2021 , Pages 640-658 ; 15397734 (ISSN) Habibi, M ; Mohammadi, A ; Safarpour, H ; Shavalipour, A ; Ghadiri, M ; Sharif University of Technology
    Bellwether Publishing, Ltd  2021
    In this article, wave propagation characteristics of a size-dependent laminated composite nanostructure coupled with a piezoelectric actuator (PA) is investigated. In order to consider the effects of small scale, the governing equations of the laminated composite nanostructure coupled with PA are derived using Hamilton’s principle based on the nonlocal strain gradient theory (NSGT). The differential equations of motion are solved with the assistance of the analytical method. Afterward, a parametric study is carried out to investigate the effects of the PA thickness, wave number, angular velocity and the ply angle on the value of phase velocity. The results show that the ply angle plays an... 

    A Numerical Study of Train-induced Vibration and the Screening Effectiveness of Shredded-tire-Infilled Trenches

    , M.Sc. Thesis Sharif University of Technology Koocheki, Kianoosh (Author) ; Ahmadi, Mohammad Mahdi (Supervisor)
    Train-induced vibrations can disturb the residential areas close to the rail as well as making ground-borne noises that can create problems for sensitive apparatus and devices. To reduce these problems, there need to be an evaluation of the amplitude of the ground-borne vibrations. The goal in this study is creating a suitable finite difference model in order to predict the intensity of train induced vibrations propagating inside or on the surface of the soil using FLAC (Fast Lagrangian Analysis of Continua) software as well as assessing the effectiveness of recycled shredded tires in reducing the surface vibrations by using these material as the filler for vibration isolation trenches. The... 

    Indoor Wave Propagation Alanysis Using Modefied Wavefront Decomposition Method

    , M.Sc. Thesis Sharif University of Technology Babakhani, Behrouz (Author) ; Shishegar, Amir Ahmad (Supervisor)
    In recent years, there has been a great studying on site-specific indoor wave propagation mechanism. Conventional ray tracing method is the most common way to predict the profile of the signal in these environments. This method provides us with a deep understanding of signal propagation mechanism including reflection, refraction and diffraction. Knowing these characteristics, we can design a wireless system with optimal performance. Modified Wavefrond Decomposition Method is a ray tracing speed up technique. In this method, a bundle of rays will be traced instead of tracing single rays. If a ray bundle illuminates the receiver location, a ray that exactly crosses the receiver point would be... 

    Efficient enhancement of the accuracy of ray tracing

    , Article 2010 IEEE International Symposium on Antennas and Propagation and CNC-USNC/URSI Radio Science Meeting - Leading the Wave, AP-S/URSI 2010, 11 July 2010 through 17 July 2010 ; July , 2010 ; 9781424449682 (ISBN) Mohtashami, V ; Parsa, S ; Shishegar, A. A ; Sharif University of Technology
    Proper design of wireless personal and local area networks requires accurate characterization of radio wave propagation in indoor environments. The Shooting-and-Bouncing-Ray tracing (SBR) method, which uses Geometrical Optics (GO) approximation, has been widely used for indoor propagation modeling [1-2]  

    General solution to wave propagation in media undergoing arbitrary transient or periodic temporal variations of permittivity

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 35, Issue 11 , 2018 , Pages 29232932- ; 07403224 (ISSN) Chegnizadeh, M ; Mehrany, K ; Memarian, M ; Sharif University of Technology
    OSA - The Optical Society  2018
    A novel and general formulation for wave propagation in time-varying media is presented. Unlike previousreports, our formalism is able to solve propagation in media with arbitrary time variations of permittivity orpermeability, for both transient and steady-state periodic variations. The formulation is approximate yet strikingly accurate in most practical cases. The provided closed-form expressions show that the normalized averagepower after the transition of the permittivity does not depend on the details of the transition, while the energydensity does. Some important discussions are made about time-periodic media, and it is shown that there is anaccumulation of energy when the temporal...