JournalTOCs

Journal of Computational Acoustics
Journal Prestige (SJR): 0.388

Citation Impact (citeScore): 1
Number of Followers: 5

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0218-396X - ISSN (Online) 1793-6489
Published by World Scientific

[119 journals]

Nonlinear Distortion Characteristic Analysis for the Finite Amplitude
Sound Pressures in the Pistonphone
- Authors: Fan Zhang, Wen He, Junjie Zhong
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  The wide concern on absolute calibration of microphones at high pressure levels prompts the development of the pistonphone technique. However, as the sound pressure level goes higher, the linear hypothesis, which is applicable for the small amplitude sound wave, will no longer be valid. The nonlinear characteristics of the finite amplitude sound wave will produce high order harmonic components and also some other complex frequency components, which eventually result in the distortion of the sound pressure in the pistonphone, and should be quantitatively calculated to assess the accuracy of absolute sound pressure calibration of microphones at high sound pressure levels using pistonphones. In this paper, the linearized wave equations were built based on the perturbation method and the Euler system. Then, the distributed parameter expressions for the finite amplitude sound pressure both neglecting and considering the intermodulation characteristic have been explicitly derived. Nonlinear distortion characteristics of the sound pressure in the pistonphone have been studied, and the effects of the intermodulation on the sound pressure distortion have been evaluated. Computations reveal that the nonlinear distortion characteristics of the sound pressure produced by pistonphones should be quantitatively considered when the sound pressure level reaches 148[math]dB, and the intermodulation characteristic can be neglected when the sound pressure level is lower than 174[math]dB.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:59Z
  DOI: 10.1142/S0218396X1850008X
  Issue No: Vol. 25, No. 04 (2017)
Diffusion Equation-Based Finite Element Modeling of a Monumental Worship
Space
- Authors: Zühre Sü Gül, Ning Xiang, Mehmet Çalışkan
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  In this work, a diffusion equation model (DEM) is applied to a room acoustics case for in-depth sound field analysis. Background of the theory, the governing and boundary equations specifically applicable to this study are presented. A three-dimensional geometric model of a monumental worship space is composed. The DEM is solved over this model in a finite element framework to obtain sound energy densities. The sound field within the monument is numerically assessed; spatial sound energy distributions and flow vector analysis are conducted through the time-dependent DEM solutions.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:56Z
  DOI: 10.1142/S0218396X17500291
  Issue No: Vol. 25, No. 04 (2017)
Author Index Volume 25 (2017)
- Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:55Z
  DOI: 10.1142/S0218396X17990016
  Issue No: Vol. 25, No. 04 (2017)
Infinite Elements and Their Influence on Normal and Radiation Modes in
Exterior Acoustics
- Authors: Lennart Moheit, Steffen Marburg
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  Acoustic radiation modes (ARMs) and normal modes (NMs) are calculated at the surface of a fluid-filled domain around a solid structure and inside the domain, respectively. In order to compute the exterior acoustic problem and modes, both the finite element method (FEM) and the infinite element method (IFEM) are applied. More accurate results can be obtained by using finer meshes in the FEM or higher-order radial interpolation polynomials in the IFEM, which causes additional degrees of freedom (DOF). As such, more computational cost is required. For this reason, knowledge about convergence behavior of the modes for different mesh cases is desirable, and is the aim of this paper. It is shown that the acoustic impedance matrix for the calculation of the radiation modes can be also constructed from the system matrices of finite and infinite elements instead of boundary element matrices, as is usually done. Grouping behavior of the eigenvalues of the radiation modes can be observed. Finally, both kinds of modes in exterior acoustics are compared in the example of the cross-section of a recorder in air. When the number of DOF is increased by using higher-order radial interpolation polynomials, different eigenvalue convergences can be observed for interpolation polynomials of even and odd order.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:53Z
  DOI: 10.1142/S0218396X1650020X
  Issue No: Vol. 25, No. 04 (2017)
Acoustical Green’s Function and Boundary Element Techniques for 3D
Half-Space Problems
- Authors: Rafael Piscoya, Martin Ochmann
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  This paper presents a review of basic concepts of the boundary element method (BEM) for solving 3D half-space problems in a homogeneous medium and in frequency domain. The usual BEM for exterior problems can be extended easily for half-space problems only if the infinite plane is either rigid or soft, since the necessary tailored Green’s function is available. The difficulties arise when the infinite plane has finite impedance. Numerous expressions for the Green’s function have been found which need to be computed numerically. The practical implementation of some of these formulas shows that their application depends on the type of impedance of the plane. In this work, several formulas in frequency domain are discussed. Some of them have been implemented in a BEM formulation and results of their application in specific numerical examples are summarized. As a complement, two formulas of the Green’s function in time domain are presented. These formulas have been computed numerically and after the application of the Fourier Transformation compared with the frequency domain formulas and with a FEM calculation.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:52Z
  DOI: 10.1142/S0218396X17300018
  Issue No: Vol. 25, No. 04 (2017)
More Than Six Elements Per Wavelength: The Practical Use of Structural
Finite Element Models and Their Accuracy in Comparison with Experimental
Results
- Authors: P. Langer, M. Maeder, C. Guist, M. Krause, S. Marburg
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  Choosing the right number and type of elements in modern commercial finite element tools is a challenging task. It requires a broad knowledge about the theory behind or much experience by the user. Benchmark tests are a common method to prove the element performance against analytical solutions. However, these tests often analyze the performance only for single elements. When investigating the complete mesh of an arbitrary structure, the comparison of the element’s performance is quite challenging due to the lack of closed or fully converged solutions. The purpose of this paper is to show a high-precision comparison of eigenfrequencies of a real structure between experimental and numerical results in the context of an element performance check with respect to a converged solution. Additionally, the authors identify the practically relevant accuracy of simulation and experiment. Finally, the influence of accuracy with respect to the number of elements per standing structural bending wave is shown.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:48Z
  DOI: 10.1142/S0218396X17500254
  Issue No: Vol. 25, No. 04 (2017)
A Fourier Collocation Approach for Transit-Time Ultrasonic Flowmeter Under
Multi-Phase Flow Conditions
- Authors: Matej Simurda, Benny Lassen, Lars Duggen, Nils T. Basse
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  A numerical model for a clamp-on transit-time ultrasonic flowmeter (TTUF) under multi-phase flow conditions is presented. The method solves equations of linear elasticity for isotropic heterogeneous materials with background flow where acoustic media are modeled by setting shear modulus to zero. Spatial derivatives are calculated by a Fourier collocation method allowing the use of the fast Fourier transform (FFT) and time derivatives are approximated by a finite difference (FD) scheme. This approach is sometimes referred to as a pseudospectral time-domain method. Perfectly matched layers (PML) are used to avoid wave-wrapping and staggered grids are implemented to improve stability and efficiency. The method is verified against exact analytical solutions and the effect of the time-staggering and associated lowest number of points per minimum wavelengths value is discussed. The method is then employed to model a complete TTUF measurement setup to simulate the effect of a flow profile on the flowmeter accuracy and a study of an impact of inclusions in flowing media on received signals is carried out.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:47Z
  DOI: 10.1142/S0218396X17500059
  Issue No: Vol. 25, No. 04 (2017)
Acoustic Imaging with Compressed Sensing and Microphone Arrays
- Authors: Fangli Ning, Yong Liu, Chao Zhang, Jingang Wei, Xudong Shi, Juan Wei
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  This work studies the acoustic imaging problem with compressed sensing (CS) and microphone arrays. The CS algorithm with Basis Pursuit (BP) algorithm has shown satisfying results in acoustic imaging, the maps of which are characterized by super-resolution. However, the performance of the CS algorithm with the BP algorithm is limited to Restricted Isometry Property (RIP), and the algorithm has a long CPU-time. We propose a new CS algorithm with Orthogonal Matching Pursuit (OMP) algorithm for acoustic imaging. The performance of the OMP algorithm with regard to RIP is examined through numerical simulation in this work. The simulation results and CPU-time for OMP algorithm are compared with those of the BP algorithm and the conventional beamformer (CBF). When the RIP does not hold, satisfying results can still be obtained by the OMP algorithm, and the CPU-time for OMP algorithm is far less than BP algorithm. In order to validate the feasibility of the OMP algorithm in acoustic imaging, an experiment is also conducted in a semi-anechoic room. Two mobile phones are served as sound sources. We investigate the mobile phones sources and compare the experimental results with those of BP algorithm and CBF method. The OMP algorithm can locate the main sources at low frequencies, while the CBF method can just give a rough indication and fails for low frequencies due to the width of its main lobe. Due to many reconstructed sources outside of the expected source positions existing on the map, the BP algorithm fails to locate the main sources at low frequencies.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:45Z
  DOI: 10.1142/S0218396X17500278
  Issue No: Vol. 25, No. 04 (2017)
A Numerical Model of an Acoustic Metamaterial Using the Boundary Element
Method Including Viscous and Thermal Losses
- Authors: V. Cutanda Henríquez, P. Risby Andersen, J. Søndergaard Jensen, P. Møller Juhl, J. Sánchez-Dehesa
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  In recent years, boundary element method (BEM) and finite element method (FEM) implementations of acoustics in fluids with viscous and thermal losses have been developed. They are based on the linearized Navier–Stokes equations with no flow. In this paper, such models with acoustic losses are applied to an acoustic metamaterial. Metamaterials are structures formed by smaller, usually periodic, units showing remarkable physical properties when observed as a whole. Acoustic losses are relevant in metamaterials in the millimeter scale. In addition, their geometry is intricate and challenging for numerical implementation. The results are compared with existing measurements.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:42Z
  DOI: 10.1142/S0218396X17500060
  Issue No: Vol. 25, No. 04 (2017)
Editorial
- Authors: Steffen Marburg, Martin Ochmann
  Abstract: Journal of Computational Acoustics, Volume 25, Issue 04, December 2017.
  
  Citation: Journal of Computational Acoustics
  PubDate: 2017-11-22T04:18:41Z
  DOI: 10.1142/S0218396X17020015
  Issue No: Vol. 25, No. 04 (2017)
Parallel Ellipsoidal Perfectly Matched Layers for Acoustic Helmholtz
Problems on Exterior Domains
- Authors: Gregory Bunting, Arun Prakash, Timothy Walsh, Clark Dohrmann
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Exterior acoustic problems occur in a wide range of applications, making the finite element analysis of such problems a common practice in the engineering community. Various methods for truncating infinite exterior domains have been developed, including absorbing boundary conditions, infinite elements, and more recently, perfectly matched layers (PML). PML are gaining popularity due to their generality, ease of implementation, and effectiveness as an absorbing boundary condition. PML formulations have been developed in Cartesian, cylindrical, and spherical geometries, but not ellipsoidal. In addition, the parallel solution of PML formulations with iterative solvers for the solution of the Helmholtz equation, and how this compares with more traditional strategies such as infinite elements, has not been adequately investigated. In this paper, we present a parallel, ellipsoidal PML formulation for acoustic Helmholtz problems. To faciliate the meshing process, the ellipsoidal PML layer is generated with an on-the-fly mesh extrusion. Though the complex stretching is defined along ellipsoidal contours, we modify the Jacobian to include an additional mapping back to Cartesian coordinates in the weak formulation of the finite element equations. This allows the equations to be solved in Cartesian coordinates, which is more compatible with existing finite element software, but without the necessity of dealing with corners in the PML formulation. Herein we also compare the conditioning and performance of the PML Helmholtz problem with infinite element approach that is based on high order basis functions. On a set of representative exterior acoustic examples, we show that high order infinite element basis functions lead to an increasing number of Helmholtz solver iterations, whereas for PML the number of iterations remains constant for the same level of accuracy. This provides an additional advantage of PML over the infinite element approach.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-12-18T06:43:30Z
  DOI: 10.1142/S0218396X18500157
A Pollution Effect in the Boundary Element Method for Acoustic Problems
- Authors: Steffen Marburg
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  The pollution effect is a well-known and well-investigated phenomenon of the finite element method for wave problems in general and for acoustic problems in particular. It is understood as the problem that a local mesh refinement cannot compensate the numerical error which is generated and accumulated in other regions of the model. This is the case for the phase error of the finite element method which leads to dispersion resulting in very large numerical errors for domains with many waves in them and is of particular importance for low order elements. Former investigations have shown that a pollution effect resulting from dispersion is unlikely for the boundary element method. However, numerical damping in the boundary element method can account for a pollution effect. A further investigation of numerical damping reveals that it has similar consequences as the phase error of the finite element method. One of these consequences is that the number of waves within the domain may be controlling the discretization error in addition to the size and the order of the boundary elements. This will be demonstrated in computational examples discussing traveling waves in rectangular ducts. Different lengths, element types and mesh sizes are tested for the boundary element collocation method. In addition to the amplitude error which is due to numerical damping, a rather small phase error is observed. This may indicate numerical dispersion.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-12-18T06:43:30Z
  DOI: 10.1142/S0218396X18500182
Range-Dependent Seismo-Acoustic Propagation in the Marginal Ice Zone
- Authors: Joseph M. Fialkowski, Michael D. Collins, David C. Calvo, Altan Turgut
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Single-scattering operators are used to extend the seismo-acoustic parabolic equation to problems involving transitions between areas with and without ice cover, which are common in the marginal ice zone. Gradual transitions are handled with single-scattering operators for sloping fluid–solid interfaces. Sudden transitions, which may occur when the ice fractures and drifts, are handled with a single-scattering operator that conserves normal displacement and tangential stress across the vertical interfaces between the range-independent regions that are used to approximate a range-dependent environment. The approach is tested by making comparisons with a finite-element model for problems involving range-dependent features in the ice cover and in a sediment that supports shear waves.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:30Z
  DOI: 10.1142/S0218396X18500133
Influence of Relaxation Frequency on Acoustic Wave in Unconsolidated Sands
and Acoustic Logging Simulation
- Authors: Chongwang Yue, Xiaopeng Yue
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Apart from consolidated rocks, the effect of relaxation on acoustic propagation in unconsolidated sands cannot be neglected. In this paper, we study the influence of relaxation frequency on the propagation of acoustic waves. We compute the frequency-dependent velocities and attenuation of P1-wave, P2-wave, and S-wave at different bulk or shear relaxation frequency for plane wave. In addition, we derive the integral solutions of acoustic field equations in cylindrical coordinate system to simulate acoustic logging. The reflected acoustic waveforms in a borehole are calculated at different bulk or shear relaxation frequency. Calculation results show that the increase of bulk relaxation frequency will cause the velocity of P1-wave to decrease slightly, and the velocity of P2-wave to decrease substantially. The change of bulk relaxation frequency has no effect on the velocity of S-wave. The increase of bulk relaxation frequency will cause the attenuation of P1-wave or P2-wave to decrease or increase in different wave frequency range. The change of bulk relaxation frequency has no effect on the attenuation of S-wave. The increase of shear relaxation frequency will cause the velocity of P1-wave to increase slightly, and the velocity of P2-wave or S-wave to decrease substantially. The increase of the shear relaxation frequency will cause the attenuation of P1-wave, P2-wave or S-wave to decrease. For acoustic field in a borehole surrounded by unconsolidated sands, the effect of bulk or shear relaxation frequency on the velocity of reflected waves in a borehole is negligible at the dimension of the distance from a logging source. The increase of bulk or shear relaxation frequency will cause the amplitude of the reflected waveforms from the borehole wall to increase.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:30Z
  DOI: 10.1142/S0218396X18500145
Optimization of Sound Transmission Loss Characteristics of Orthogonally
Stiffened Plate
- Authors: Tao Fu, Zhaobo Chen, Hongyin Yu, Chengfei Li, Xiaoxiang Liu
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  An analytical model is developed to investigate the sound transmission loss from orthogonally rib-stiffened plate structure under diffuse acoustic field excitation. The validity and feasibility of the model are verified by comparing the present theoretical predictions with the numerical results published previously. The influences of structure geometrical parameters on sound transmission loss are subsequently presented. The optimization algorithm is used to search for the optimal structural parameters with the objective to maximize the sound transmission loss over a frequency band. Furthermore, the sensitivity of structural parameters on the overall vibration and acoustic performance of the stiffened plates structure is also analyzed.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:29Z
  DOI: 10.1142/S0218396X18500108
Directivity-Based Passive Barrier for Local Control of Low-Frequency Noise
- Authors: Gyani Shankar Sharma, Abhijit Sarkar
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  This work concerns with improving the transmission loss offered by a noise barrier separating two acoustic spaces in the low-frequency range. A novel concept of local mitigation of the transmitted noise at a target receiver location is presented by controlling the directivity of the transmitted noise through a point mass attachment on the barrier surface. Mass attachment at an arbitrary location is shown to increase the noise transmission. Optimal locations of the mass to minimize the sound transmission in the normal, oblique and tangential directions to the barrier are obtained. Optimal placement of the mass results in a major transmission reduction around the target location, much more than achievable by a uniform distribution of the mass over the barrier. Total transmitted pressure is also reduced; however, local reduction around the target location is much higher. The effects of variation in the excitation frequency and magnitude of the attached mass are investigated.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:29Z
  DOI: 10.1142/S0218396X18500121
A Numerical Evidence of Biosonar Beam Formation of a Neonate Yangtze
Finless Porpoise (Neophocaena asiaeorientalis)
- Authors: Chong Wei, Zhongchang Song, Whitlow W. L. Au, Yu Zhang, Ding Wang
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Yangtze finless porpoises (Neophocaena asiaeorientalis) are known to use the narrowband signals for echolocation. In this study, a finite-element model was configured based on computed tomography imaging technique and tissue physical properties measurement to simulate biosonar signal emission and transmission processes through animal’s head. The roles of the main structures in the head such as the air sacs, melon, bony structures, connective tissue, blubber, mandibular fat on the biosonar beam formation were investigated, and the relative importance of these structures was compared. The biosonar beam properties of this neonate porpoise were compared with those of adult ones. The method in this paper suggested an effective way for investigating the acoustic processes in the heads of the neonate odontocetes.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:28Z
  DOI: 10.1142/S0218396X18500091
An Absorbing Boundary Condition Based on Perfectly Matched Layer Technique
Combined with Discontinuous Galerkin Boltzmann Method for Low Mach Number
Flow Noise
- Authors: Weidong Shao, Jun Li
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  For flow noise simulations, the nonreflecting boundary condition (NRBC) is significant to confine the computational domain to a small domain. Lattice Boltzmann method (LBM) has advantages for noise because of its low dissipation, but is limited to the uniform grid. In this paper, an absorbing boundary condition (ABC) based on perfectly matched layer (PML) technique is introduced to LBM. Then PML stability is analyzed and a new strategy is developed to achieve robustness. Invoking the decoupling time integration, the underlying equation for streaming is solved with the nodal discontinuous Galerkin method. Benchmark acoustic problems were used to demonstrate the PML absorption. Moreover, PML parameters, long time behavior and inhomogeneous pseudo mean flow are discussed. The methodology appears to work very well and would be hoped for practical flow noise computation.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-10-19T09:14:28Z
  DOI: 10.1142/S0218396X1850011X
GPU Elastic Modeling Using an Optimal Staggered-Grid Finite-Difference
Operator
- Authors: Wang Jian, Meng Xiaohong, Liu Hong, Zheng Wanqiu, Liu Zhiwei
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Staggered-grid finite-difference forward modeling in the time domain has been widely used in reverse time migration and full waveform inversion because of its low memory cost and ease to implementation on GPU, however, high dominant frequency of wavelet and big grid interval could result in significant numerical dispersion. To suppress numerical dispersion, in this paper, we first derive a new weighted binomial window function (WBWF) for staggered-grid finite-difference, and two new parameters are included in this new window function. Then we analyze different characteristics of the main and side lobes of the amplitude response under different parameters and accuracy of the numerical solution between the WBWF method and some other optimum methods which denotes our new method can drive a better finite difference operator. Finally, we perform elastic wave numerical forward modeling which denotes that our method is more efficient than other optimum methods without extra computing costs.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-09-05T01:14:20Z
  DOI: 10.1142/S0218396X18500054
A Method for Noise Source Levels Inversion with Underwater Ambient Noise
Generated by Typhoon in Deep Ocean
- Authors: Qiulong Yang, Kunde Yang, Shunli Duan
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Sea-surface wind agitation can be considered the dominant noise sources whose intensity relies on local wind speed during typhoon period. Noise source levels in previous researches may be unappreciated for all oceanic regions and should be corrected for modeling typhoon-generated ambient noise fields in deep ocean. This work describes the inversion of wind-driven noise source level based on a noise field model and experimental measurements, and the verification of the inverted noise source levels with experimental results during typhoon period. A method based on ray approach is presented for modeling underwater ambient noise fields generated by typhoons in deep ocean. Besides, acoustic field reciprocity is utilized to decrease the calculation amount in modeling ambient noise field. What is more, the depth dependence and the vertical directionality of noise field based on the modeling method and the Holland typhoon model are evaluated and analyzed in deep ocean. Furthermore, typhoons named “Soulik” in 2013 and “Nida” in 2016 passed by the receivers deployed in the western Pacific (WP) and the South China Sea (SCS). Variations in sound speed profile, bathymetry, and the related oceanic meteorological parameters are analyzed and taken into consideration for modeling noise field. Boundary constraint simulated annealing (SA) method is utilized to invert the three parameters of noise source levels and to minimize the objective function value. The prediction results with the inverted noise source levels exhibit good agreement with the measured experiment data and are compared with predicted results with other noise sources levels derived in previous researches.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-09-05T01:14:20Z
  DOI: 10.1142/S0218396X18500078
Analysis on the Synthetic Seismograms of Seismic Wave Caused by Low
Frequency Sound Source in Shallow Sea with Porous Seabed
- Authors: Zai-Hua Lu, Zhi-Hong Zhang, Jian-Nong Gu
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Elastic wave in the seabed caused by low frequency noise radiated from ship is called ship seismic wave and can be used to identify ship target. In order to obtain the propagation features of ship seismic wave in shallow sea with thick sediment, this paper introduces an algorithm for synthetic seismogram aroused by low frequency point sound source in shallow sea based on Biot’s wave theory for saturated porous media. Numerical calculation of synthetic seismogram at seafloor was carried out at a typical shallow sea environment with thick sediment. According to the results of numerical examples, the time series of seismic wave at seafloor is mostly composed of interface wave and leaky modes. The interface wave can propagate to far distance with small attenuation when the source frequency is very low. When the source frequency increases, the interface wave can no longer propagate to far distance like the leaky modes because the attenuation of sediment increases rapidly with frequency. The porosity and permeability of sediment in shallow sea have some influence on the dispersion characteristic of seismic wave at seafloor.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-09-05T01:14:19Z
  DOI: 10.1142/S0218396X18500017
Computing Where Perturbations Affect the Acoustic Impulse Response in the
Ocean
- Authors: John L. Spiesberger, Dmitry Yu Mikhin
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  We compute accurate maps of oceanic perturbations affecting transient acoustic signals propagating from source to receiver. The technological advance involves coupling the one-way wave equation (OWWE) propagation model with the theory for the Differential Measure of Influence (DMI) yielding the map. The DMI requires two finite-frequency solutions of the acoustic wave equation obeying reciprocity: from source to receiver and vice versa. OWWE satisfies reciprocity at basin-scales with sound speed varying horizontally and vertically. At infinite frequency, maps of the DMI collapse into rays. Mapping the DMI is useful for understanding measurements of acoustic perturbations at finite frequencies.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-09-05T01:14:19Z
  DOI: 10.1142/S0218396X18500042
Sensitivity Analysis of Hybrid Split-Step Fourier/Finite Difference
Parabolic Equation Models
- Authors: Mustafa Aslan, Kevin B. Smith, Geoffrey Moss
  Abstract: Journal of Computational Acoustics, Ahead of Print.
  Traditionally, ocean acoustic propagation models assume the sea surface can be treated as an idealized pressure release boundary. For flat surfaces, this can easily be accomplished through a variety of modeling techniques. Rough surfaces, however, introduce additional complexities in numerical models which assume a pressure release condition. An alternative approach is to model the physical water/air interface in a manner analogous to the water/sediment interface of the bottom. However, the ocean surface boundary introduces a much larger interface discontinuity than the bottom interface. In this work, a previously developed hybrid split-step Fourier/finite-difference approach is implemented at the water/air interface. Results are compared with standard SSF smoothing approaches. Normal mode and finite element models are utilized to provide benchmark solutions. Tradeoffs between accuracy and stability are discussed, as well as the model’s ability to accurately compute transmission across the water/air interface.
  Citation: Journal of Computational Acoustics
  PubDate: 2017-09-05T01:14:18Z
  DOI: 10.1142/S0218396X18500066