Simulation Of Acoustic Wave Propagation Research Articles

Acoustic wave propagation in atmospheric boundary layer above a rough terrain

In this paper we will present the latest development in the numerical simulation of acoustic wave propagation in the lowest atmospheric boundary layer above a rough terrain with a finite difference time domain (FDTD) algorithm. It is of great interest to investigate the effect of dynamic turbulent boundary layer meteorology coupled with surface terrain on acoustic wave propagation in frequency bands relevant to battlefield sensor systems. Turbulent mixing in the vicinity of the earth–air boundary layer is the key factor contributing to acoustic signal fluctuations such as upward refraction, scattering, high attenuation, and coherence degradations. Using first principles acoustic wave equation expressions for a moving fluid will allow us to couple acoustic models with time varying, 3-D large eddy simulation (LES) results. The specific meteorological parameters are vector wind velocity, temperature, pressure, and density as a function of space and time. Our acoustic simulation uses a coupled system of first-order temporal and spatial differential equations relating wind velocity, pressure, and density variations. This system of equations was evaluated with an explicitly time-stepping finite difference numerical approach. The coupling of LES and acoustic FDTD simulation will allow us to directly identify spectral portions of turbulent boundary layer meteorology contributing to short- and long-term acoustic signal variations.

SIMULATION OF ACOUSTIC WAVE PROPAGATION IN COMPLEX MEDIA USING MRFD METHOD

This paper is devoted to the simulation of acoustic wave propagation in complex media, applying the finite difference scheme and the orthonormal compactly supported wavelet transform approximation,to the time and the space dimension of the wave equation, respectively. A new method, which is a fast adaptive arithmetic, named Multiresolution Finite Difference (MRFD) is first proposed to solve the problem of the wave propagation in multi-layered medium with nonperiodic boundary condition. Thus the problem is solved in the wavelet domain rather than in the traditional Euclidian space. Due to adaptive and vanishing-moment property of the wavelet basis, the difference operator and solution vector have sparseness in the wavelet domain. MRFD is a promising method because of some advantages such as lighter computational burden, efficiency of convergence and robustness. Numerical results in geophysics exploration show the effectiveness and potential of the method.

Simulation of acoustic wave propagation in dispersive media with relaxation losses by using FDTD method with PML absorbing boundary condition

We present a method to incorporate the relaxation dominated attenuation into the finite-difference time-domain (FDTD) simulation of acoustic wave propagation in complex media. A dispersive perfectly matched layer (DPML) boundary condition, which is suitable for boundary matching to such a dispersive media whole space, is also proposed to truncate the FDTD simulation domain. The numerical simulation of a Ricker wavelet propagating in a dispersive medium, described by second-order Debye model, shows that the Ricker wavelet is attenuated in amplitude and expanded in time in its course of propagation, as required by Kramers-Kronig relations. The numerical results also are compared to exact solution showing that the dispersive FDTD method is accurate and that the DPML boundary condition effectively dampens reflective waves. The method presented here is applicable to the simulation of ultrasonic instrumentation for medical imaging and other nondestructive testing problems with frequency dependent, attenuating media.

2.5-D Numerical Simulation of Acoustic Wave Propagation

—Endeavors to simulate the 3-D seismic wave propagation effects in the 2-D environment have stimulated the development of 2.5-D simulation techniques. Liner (1991) has developed a damped 2.5-D acoustic wave equation using the 3-D Green's function for a constant density medium. This paper presents the finite-difference simulation and study of various numerical artifacts, using Liner's acoustic wave equation. Comparisons of second-order as well as fourth-order accurate 2.5-D and 2-D acoustic wave simulation results have been given. The snapshots at different times and zero off-set response of a salt dome model have been computed and strong reflections and diffraction phases have been reported. Also, the analysis of amplitude behaviors and computational time for Liner's (1991) and Williamson and Pratt's (1995) 2.5-D wave equations, with and without the last term (1/t 2),reveals that this last term is superfluous as suggested by Stockwell (1995). The effectiveness of Sponge transmissive as well as Clayton and Engquist (1980) absorbing boundary conditions has been studied. A modified Ricker wavelet, the second derivative of the convolution of Gaussian function and a polynomial window, has been used as a source. It has been found that the stability condition and the requirement of the number of grid points per wavelength to avoid grid dispersion are the same as for the 2-D acoustic cases.

Formulation and validation of Berenger's PML absorbing boundary for the FDTD simulation of acoustic scattering

Berenger's perfectly matched layer (PML) absorbing boundary condition for electromagnetic (EM) waves is derived to absorb 2-D and 3-D acoustic waves in finite difference time domain (FDTD) simulation of acoustic wave propagation and scattering. A PML medium suitable for acoustic waves is constructed. Plane wave propagation in the PML medium is solved for both 2-D and 3-D cases and explicit FDTD boundary conditions are derived. The equations show that a matched PML medium is a perfect simulation of free space in that a plane wave does not change its direction of propagation or its speed when it propagates from free space into a matched PML medium. FDTD simulation of a pulsed point source propagating in two dimensions is carried out to test the performance of the PML boundary for acoustic waves. Results show that an eight layer PML boundary condition reduces the reflected error 40 dB over Mur's second order boundary condition.

Computer Simulation of Acoustic Waves Propagation in Elastically Anisotropic Materials

Computer Simulation of Acoustic Waves Propagation in Elastically Anisotropic Materials