Search for: wave-equations
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    An interruption in the highway: New approach to modeling the car-traffic

    , Article Electronic Journal of Theoretical Physics ; Volume 6, Issue 23 , 2009 , Pages 123-136 ; 17295254 (ISSN) Rezaeezadeh, A ; Sharif University of Technology
    A very common phenomena in car-traffic system is investigated in this article. The problem is one-dimensional. We try to find the wave equation of the traffic and then, we'll talk more about the simulation of the system using Matlab7.6  

    Explicit analytic solution for the nonlinear ion sound waves equation

    , Article Applied Mathematical Sciences ; Volume 4, Issue 21-24 , 2010 , Pages 1183-1195 ; 1312885X (ISSN) Doosthoseini, A ; Sharifi, A ; Jafari, A. J ; Oskoui, R. N ; Sharif University of Technology
    In this article, we use an efficient analytical method called homotopy analysis method (HAM) to derive an approximate solution of nonlinear ion sound waves equation. Actually, we solved Korteweg-de Vries equation arises in a one-dimensional macroscopic plasma model describing the weakly nonlinear evolution of ion sound speed by the HAM. Unlike the perturbation method, the HAM does not require the addition of a small physically parameter to the differential equation. It is applica-ble to strongly and weakly nonlinear problems. Moreover, the HAM involves an auxiliary parameter, which renders the convergence param-eter of series solutions controllable, and increases the convergence, and... 

    Extended energy approach to propagation problems in general anisotropic media

    , Article Scientia Iranica ; Volume 11, Issue 3 , 2004 , Pages 255-264 ; 10263098 (ISSN) Khorasani, S ; Rashidian, B ; Sharif University of Technology
    Sharif University of Technology  2004
    In this article, a new general approach has been presented for exact and efficient extraction of eigenpolarizations in anisotropic electromagnetic media with arbitrary constitutive relations. It is shown that the plane wave propagation eigenpolarizations in a linear homogeneous time-independent anisotropic media without free sources, can be obtained through extremizing the difference between stored electric and magnetic energies as a variational functional. It is demonstrated that at these stationary points the wave equation is satisfied by showing that each of the Maxwell curl equations may be obtained by using the other equation as a constraint. Furthermore, it is proven that the theorem... 

    Mode identification of high-amplitude pressure waves in liquid rocket engines

    , Article Journal of Sound and Vibration ; Volume 229, Issue 4 , 2000 , Pages 973-991 ; 0022460X (ISSN) Ebrahimi, R ; Mazaheri, K ; Ghafourian, A ; Sharif University of Technology
    Identification of existing instability modes from experimental pressure measurements of rocket engines is difficult, specially when steep waves are present. Actual pressure waves are often non-linear and include steep shocks followed by gradual expansions. It is generally believed that interaction of these non-linear waves is difficult to analyze. A method of mode identification is introduced. After presumption of constituent modes, they are superposed by using a standard finite difference scheme for solution of the classical wave equation. Waves are numerically produced at each end of the combustion tube with different wavelengths, amplitudes, and phases with respect to each other. Pressure... 

    A steady-state saturation model to determine the subsurface travel time (STT) in complex hillslopes

    , Article Hydrology and Earth System Sciences ; Volume 14, Issue 6 , Jun , 2010 , Pages 891-900 ; 10275606 (ISSN) Sabzevari, T ; Talebi, A ; Ardakanian, R ; Shamsai, A ; Sharif University of Technology
    The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The saturation capacity of hillslopes affect the travel time of subsurface flow. The saturation capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater... 

    Analytical solution for penetration of deformable blunt projectiles into the metallic targets

    , Article Mechanika ; Volume 82, Issue 2 , 2010 , Pages 5-13 ; 13921207 (ISSN) Radmehr, D ; Liaghat, G. H ; Felli, S ; Naderi, D ; Sharif University of Technology
    At the present research, a new analytical model is developed for the impact of a deformable blunt projectile to metallic targets using the plastic stress wave propagation theory and the momentum equations. At this model, the deformation of the projectile is considered, too. Also, the effects of dishing and plugging phenomena on failure of the target are investigated. All of the obtained results are compared with the experimental and other available analytical results where good agreement has been observed. The other outcome of this research is a new definition for the penetration stages which includes 9 ones. Motion equations are derived for each of these stages, accordingly  

    A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

    , Article Optics Communications ; Volume 265, Issue 1 , 2006 , Pages 283-300 ; 00304018 (ISSN) Bahrampour, A. R ; Mahjoei, M ; Rasouli, A ; Sharif University of Technology
    In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop... 

    Optimization analysis of alternate tube section for pulse tube refrigerators

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Jafarian, A ; Saidi, M. H ; Hannani, S. K ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    In spite of numerous attempts which have been made during the last decade to optimize pulse tube refrigerators, still theoretical and analytical realization of this device needs to be thoroughly explained. In this paper, in addition to the oscillatory flow analysis in the pulse tube refrigerator through a simple analytical model, the performance of the alternate tube section of this device is analyzed using a generalized efficiency, based on the entropy generation rate. In this model, in order to extract the entropy generation rate and the dissipative terms caused by fluid friction and heat flow in alternate tube, simplified momentum and energy equations are solved analytically and velocity... 

    General solution of linear differential equations by using differential transfer matrix method

    , Article 2005 European Conference on Circuit Theory and Design, Cork, 28 August 2005 through 2 September 2005 ; Volume 3 , 2005 , Pages 113-116 ; 0780390660 (ISBN); 9780780390669 (ISBN) Eghlidi, M. H ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    A new analytical method for finding the general solution of the nth-order linear differential equation with variable coefficients is given based on generalizing the idea of differential transfer matrix method already proposed for solving the second order Helmholtz equation. Our generalization has two aspects. First, the given formulation copes with the nth-order linear differential equations, rather than the special case of second order wave equations. Second, the proposed approach is generalized in several different ways each yielding different types of differential transfer matrices with correspondingly different numerical accuracies. The presented methods can be applied to problems such... 

    Basis functions for solution of non-homogeneous wave equation

    , Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 8619 , February , 2013 ; 0277786X (ISSN); 9780819493880 (ISBN) Khorasani, S ; Karimi, F ; Sharif University of Technology
    In this note we extend the Differential Transfer Matrix Method (DTMM) for a second-order linear ordinary differential equation to the complex plane. This is achieved by separation of real and imaginary parts, and then forming a system of equations having a rank twice the size of the real-valued problem. The method discussed in this paper also successfully removes the problem of dealing with essential singularities, which was present in the earlier formulations. Then we simplify the result for real-valued problems and obtain a new set of basis functions, which may be used instead of the WKB solutions. These basis functions not only satisfy the initial conditions perfectly, but also, may... 

    A novel numerical solution to the diffraction term in the KZK nonlinear wave equation

    , Article Proceedings of the 38th Annual Symposium of Ultrasonic Industry Association, UIA 2009, 23 March 2009 through 25 March 2009, Vancouver, BC ; 2009 ; 9781424464296 (ISBN) Hajihasani, M ; Farjami, Y ; Gharibzadeh, S ; Tavakkoli, J ; Sharif University of Technology
    Nonlinear ultrasound modeling is finding an increasing number of applications in both medical and industrial areas where due to high pressure amplitudes the effects of nonlinear propagation are no longer negligible. Taking nonlinear effects into account makes the ultrasound beam analysis more accurate in these applications. One of the most widely used nonlinear models for propagation of 3D diffractive sound beams in dissipative media is the KZK (Khokhlov, Kuznetsov, Zabolotskaya) parabolic nonlinear wave equation. Various numerical algorithms have been developed to solve the KZK equation. Generally, these algorithms fall into one of three main categories: frequency domain, time domain and... 

    Frequency Comb Generation Using Time-Varying Electromagnetic Structures

    , M.Sc. Thesis Sharif University of Technology Hakimi, Amin (Author) ; Mehrany, Khashayar (Supervisor) ; Memarian, Mohammad (Co-Supervisor)
    This thesis presents a resonant time-periodic structure based on the Fabry-Perot resonator for frequency comb generation. Time-periodic structures cannot generate a frequency comb by themselves because side-harmonic amplitudes are really weak. However, due to resonant structure, it is expected that the side-harmonics, which are generated because of the time-periodic part of the structure, are increased if they are close to the main modes of the structure. But the results show that, generally, the amplitude of side harmonics, which are close to the main mode, is increased and far side-harmonics don't have remarkable amplitudes. However, we will show that if the modulation frequency of the... 

    The effect of higher order harmonics on second order nonlinear phenomena

    , Article Optics Communications ; Volume 343 , May , 2015 , Pages 124-130 ; 00304018 (ISSN) Shahverdi, A ; Borji, A ; Sharif University of Technology
    Elsevier  2015
    A new method which is a combination of the harmonic balance and finite difference techniques (HBFD) is proposed for complete time-harmonic solution of the nonlinear wave equation. All interactions between different harmonics up to an arbitrary order can be incorporated. The effect of higher order harmonics on two important nonlinear optical phenomena, namely, the second harmonic generation (SHG) and frequency mixing is investigated by this method and the results are compared with well-known analytical solutions. The method is quite general and can be used to study wave propagation in all nonlinear media  

    Develop of a fully nonlinear and highly dispersive water wave equation set; analysis of wave interacting with varying bathymetry

    , Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009, Kyoto ; 2009 , Pages 213-218 ; 9780415804820 (ISBN) Najafi Jilani, A ; Ataie Ashtiani, B ; Sharif University of Technology
    Extended Boussinesq-type water wave equations are derived in two horizontal dimensions to capture the nonlinearity effects and frequency dispersion of wave in a high accuracy order. A multi-parameter perturbation analysis is applied in several steps to extend the previous second order Boussinesq-type equations in to 6th order for frequency dispersion and consequential order for nonlinearity terms. The presented high-order Boussinesq-type equation is applied in a numerical model to simulate the wave field transformation due to physical processes such as shoaling, refraction and diffraction. The models results are compared with available experimental data which obtained in a laboratory wave... 

    Laboratory investigations on impulsive waves caused by underwater landslide

    , Article Coastal Engineering ; Volume 55, Issue 12 , December , 2008 , Pages 989-1004 ; 03783839 (ISSN) Ataie Ashtiani, B ; Najafi Jilani, A ; Sharif University of Technology
    Laboratory investigations have been performed on the submarine landslide generated waves by performing 120 laboratory tests. Both rigid and deforming-slide masses are considered. The effects of bed slope angle, initial submergence, slide geometry, shape and deformation on impulse wave characteristics have been inspected. Impulse wave amplitude, period, energy and nonlinearity are studied in this work. The effects of bed slope angle on energy conversion from slide into wave are also investigated. Laboratory-based prediction equations are presented for impulse wave amplitude and period in near and far-field and are successfully verified using the available data in previous laboratory and... 

    An analytical method in computational aeroelasticity based on Wagner function

    , Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1808-1814 Shams, Sh ; Haddadpour, H ; Sadr Lahidjani, M. H ; Kheiri, M ; Sharif University of Technology
    Curran Associates Inc  2006
    This paper presents an analytical method in computational aeroelasticity for an airfoil considering two degrees of freedom (heaving and pitching) based on the Wagner integral function. In the obtained aeroelastic equations of motion, there are some integral parts that give an integro-differential system of equations. Using appropriate approximation for the Wagner function, a new form of equations can be obtained by derivation from mentioned equations. These equations are in the form of ordinary differential equations. Using the obtained equations, the flutter speed is predicted for a given airfoil and the results are compared with the results of other investigators. Also, the dynamic... 

    Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 16 April 2010 ; Volume 7721 , April , 2010 ; 0277786X (ISSN) ; 9780819481948 (ISBN) Sadighi Bonabi, R ; Dehghani, Z ; Irani, E ; The Society of Photo-Optical Instrumentation Engineers (SPIE); Brussels Photonics Team (B-PHOT); Brussels-Capital Region; Fonds Wetenschappelijk Onderzoek (FWO); International Commission for Optics (ICO) ; Sharif University of Technology
    Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4 + molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4 + molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and... 

    Numerical modeling of turbulent surface wave motion using a coupled boundary element-finite difference technique

    , Article 2008 ASME Fluids Engineering Division Summer Conference, FEDSM 2008, Jacksonville, FL, 10 August 2008 through 14 August 2008 ; Volume 1, Issue PART B , 2009 , Pages 1025-1029 ; 9780791848418 (ISBN) Jamali, M ; Fluids Engineering Division, ASME ; Sharif University of Technology
    In this paper an effective numerical technique is presented to model turbulent motion of a standing surface wave in a tank. The equations of motion for turbulent boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to obtain the wave and boundary layer characteristics. A mixing-length theory is used for turbulence modeling. The results are compared with previous experimental data. Although the technique is presented for a standing surface wave, it can be easily applied to other free surface problems. Copyright © 2008 by ASME  

    Axial-torsional vibrations of rotating pretwisted thin walled composite beams

    , Article International Journal of Mechanical Sciences ; Vol. 80 , 2014 , pp. 93-101 ; ISSN: 00207403 Sina, S. A ; Haddadpour, H ; Sharif University of Technology
    Axial-torsional vibrations of rotating pretwisted thin-walled composite box beams exhibiting primary and secondary warping are investigated. Considering the nonlinear strain-displacement relations, the coupled nonlinear axial-torsional equations of motion are derived using Hamilton's principle. Ignoring the axial inertia term leads to differential equation of motion in terms of elastic torsion in the case of axially immovable beams. Centrifugal load in the presence of material anisotropy and pretwist angle leads to an induced static torque. The nonlinear equation should be linearized about the corresponding equilibrium state to obtain the linear differential equation of motion. Extended... 

    Nonlinear normal modes of axial-torsional vibrations of rotating thin walled composite beam

    , Article International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012: International Conference on Uncertainty in Structure Dynamics, 17 September 2012 through 19 September 2012 ; Volume 4 , September , 2012 , Pages 2547-2556 ; 9781622768257 (ISBN) Sina, S ; Kerschen, G ; Haddadpour, H ; Katholieke Universiteit Leuven ; Sharif University of Technology
    Katholieke Universiteit Leuven  2012
    The aim of this study is to carry out the numerical computation of nonlinear normal modes for rotating pretwisted composite thin-walled beam in axial-torsional vibrations. The structural model considered here, incorporates a number of non-classical effects such as primary and secondary warping, non-uniform torsional model, rotary inertia and pretwist angle. Ignoring the axial inertia term leads to differential equation of motion in terms of angle of twist in the case of axially immovable beam ends. The governing differential equations of motion are derived using Hamilton's principle and the reduced model around the static equilibrium position is obtained using 2-mode Galerkin discretization...