A Moving Zonal Method in the Time-Domain Simulation for Acoustic Propagation

2010 ◽  
Author(s):  
Z. Charlie Zheng ◽  
Guoyi Ke
Keyword(s):  
Long Range ◽  
Time Domain ◽  
Region Of Interest ◽  
Acoustic Propagation ◽  
Coordinate Frame ◽  
Computational Domain ◽  
Perfectly Matched Layers ◽  
Zonal Method ◽  
Moving Domain ◽  
The Time Domain

Conventional time-domain schemes have limited capability in modeling long-range acoustic propagation because of the vast computer resources needed to cover the entire region of interest with a computational domain. Many of the long-range acoustic propagation problems need to consider propagation distances of hundreds or thousands of meters. It is thus very difficult to maintain adequate grid resolution for such a large computational domain, even with the state-of-the-art capacity in computer memory and computing speed. In order to overcome this barrier, a moving zonal-domain approach is developed. This concept uses a moving computational domain that follows an acoustic wave. The size and interval of motion of the domain are problem dependent. In this paper, an Euler-type moving domain in a stationary coordinate frame is first tested. Size effects and boundary conditions for the moving domain are considered. The results are compared and verified with both analytical solutions and results from the non-zonal domain. Issues of using the moving zonal-domain with perfectly-matched layers for the free-space boundary are also discussed.

EXACT WAVE‐SHAPING WITH A TIME‐DOMAIN DIGITAL FILTER OF FINITE LENGTH

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 659-672 ◽  
Author(s):  
R. F. Mereu
Keyword(s):  
Time Series ◽  
Time Domain ◽  
Symmetric Functions ◽  
Wiener Filter ◽  
Region Of Interest ◽  
Number Of Zeros ◽  
Series Of Experiments ◽  
Optimum Filter ◽  
The Time Domain ◽  
Spike Sequence

When the signs of alternate terms of a symmetric discrete time series are reversed and the newly created series is then convolved with the original series, the resultant time‐series will have alternate values equal to zero. This property of symmetric functions may be exploited to design a new deconvolution and wave‐shaping time‐domain filter which is capable of transforming a given wavelet into an output made up of a sequence of spikes separated by zeros, or a sequence of wavelets, whose shapes are identical to that of any desired wavelet. In its design, no Z-transform polynomials are factored or divided and no equations are solved. The weights are derived entirely in the time domain from a series of successively derived subfilters ([Formula: see text], [Formula: see text], [Formula: see text] ⋯ [Formula: see text]) which, when convolved with the original wavelet, creates the spike sequence output. These subfilters may be conveniently grouped into a symmetric component which is derived from the autocorrelation function, a component which depends upon the characteristics of the original wavelet and a component which depends upon the desired wavelet. The number of zeros separating the spike outputs may be controlled by increasing the number of sub‐filters N according to the formula [Formula: see text]. The Wiener filter is an optimum filter in the least‐squares sense but its errors occur across the output. The new filter is an optimum filter in an “error‐distribution” sense. Its errors are in reality the noncentral spikes of the spike sequence. By choosing the length properly, the errors may be moved away from the region of interest leaving that region effectively “error‐free”. A limitation to this procedure is the computational round‐off error which increases as the filter length is increased. In a series of experiments with various types of wavelets it was found that the spike position always occurs at the center of the filter, with the anticipation and memory components automatically falling into place. A very important property of the filter is the fact that the input parameters required for its design are identical to those needed for the normal equations of the Wiener filter. Initial tests with a noisy time‐series showed that the new filter could be effectively employed using the statistical properties of the noise in the same manner that the Wiener filter is applied.

Numerical Analysis of Hydrodynamic Performance of Backward Bent Duct Buoy (BBDB)

2012 ◽  
Author(s):  
W. C. Koo ◽  
S. J. Kim ◽  
M. H. Kim
Keyword(s):  
Time Domain ◽  
Hydrodynamic Performance ◽  
Damping Coefficient ◽  
Surface Boundary ◽  
Viscous Damping ◽  
Computational Domain ◽  
Time Domain Simulation ◽  
Free Surface Boundary Condition ◽  
Floating Type ◽  
The Time Domain

The hydrodynamic performance of Backward Bent Duct Buoy (BBDB), a floating-type wave energy converter, was evaluated in the time-domain simulation by using a two-dimensional fully-nonlinear numerical wave tank (NWT) technique. The developed NWT was based on potential theory, boundary element method with constant panels, and the mixed Eulerian-Lagrangian (MEL) approach to capture the nonlinear free-surfaces. The viscous damping at the chamber entrance due to oscillating water column and the shape of body causing generation of vortex shedding were modeled and applied to the free surface boundary condition inside the chamber. The calculated surface elevations inside the chamber with open chamber condition were compared with experimental data to select a proper viscous damping coefficient. Then, the surface elevations with a tuned viscous damping coefficient were calculated for various wave conditions. The results of linear and nonlinear time-domain simulation with two different corner-shaped BBDBs were compared to investigate the mean drift force of BBDB. Energy conservation in the computational domain was checked for all cases.

Study on electromagnetic characteristics of plasma model-based on the symplectic multiresolution time-domain scheme

2020 ◽  
Vol 34 (06) ◽  
pp. 2050046
Author(s):  
Zhu Ma ◽  
Min Wei ◽  
Meng Li ◽  
Wenbin Xu
Keyword(s):  
Time Domain ◽  
Numerical Solutions ◽  
Numerical Dispersion ◽  
Computational Domain ◽  
Plasma Model ◽  
Perfectly Matched Layers ◽  
Factors Affecting ◽  
Transmission Coefficients ◽  
Plasma Slab ◽  
Dispersive Model

A novel numerical computation scheme, which is symplectic multiresolution time-domain (S-MRTD) scheme, for modeling plasma model is proposed. The loss plasma dispersive model is taken into account in S-MRTD scheme, and the detailed formulations of the proposed S-MRTD scheme are also provided. A one-dimensional perfectly matched layers (PML) are used to terminate the computational domain. The analyses of stability and numerical dispersion demonstrate that S-MRTD scheme is more efficient than traditional finite-different time-domain (FDTD) and MRTD methods. The energy conservation characteristics of S-MRTD scheme in electromagnetic simulation are proved by the propagation of pulse in free space for long-term simulation. In the end, the S-MRTD formulations are confirmed by computing the electric field intensity, reflection and the transmission coefficients for the pulse wave through an unmagnetized plasma slab. A favorable agreement between the numerical solutions is demonstrated, and the efficiency of the proposed scheme is verified. Meanwhile, numerical results show that plasma frequency, collision frequency and thickness are important factors affecting reflection and transmission coefficients.

scholarly journals Exact nonreflecting boundary conditions for exterior wave equation problems

2014 ◽  
Vol 96 (110) ◽  
pp. 103-123 ◽  
Author(s):  
Silvia Falletta ◽  
Giovanni Monegato
Keyword(s):  
Boundary Condition ◽  
Wave Equation ◽  
Time Domain ◽  
Region Of Interest ◽  
Boundary Integral ◽  
Implicit Time ◽  
Artificial Boundary ◽  
Equation Problem ◽  
Classical Wave Equation ◽  
The Time Domain

We consider the classical wave equation problem defined on the exterior of a bounded 2D space domain, possibly having far field sources. We consider this problem in the time domain, but also in the frequency domain. For its solution we propose to associate with it a boundary integral equation (BIE) defined on an artificial boundary surrounding the region of interest. This boundary condition is nonreflecting (or transparent) for both outgoing and incoming waves and it does not have to include necessarily the problem datum supports. The problem physical domain can even be a multi-domain, defined by the union of several disjoint domains. These domains can be convex or nonconvex. This transparent boundary condition is imposed pointwise on the chosen artificial boundary; therefore, its (space collocation) discretization can be coupled with a (space) finite difference or finite element method for the associated PDE problem. In the time-domain case, a classical (explicit or implicit) time integrator is also used. We present a consistency result for the BIE discretization and a sample of the intensive numerical testing we have performed.

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