MODE AND PE PREDICTIONS OF PROPAGATION IN RANGE-DEPENDENT ENVIRONMENTS: SWAM'99 WORKSHOP RESULTS

Three numerical acoustic models, a coupled normal-mode model (C-SNAP), an adiabatic normal-mode model (PROSIM), and a parabolic equation model (RAM), are applied to test cases defined for the SWAM'99 workshop. The test cases consist of three shallow water (flat bottom) scenarios with range-dependent sound-speed profiles imitating internal wave fields and a shelf-break case, with range-dependent sound-speed profiles and bathymetry. The bottom properties in all the cases are range-independent and modeled as a homogeneous fluid half-space. The results from the modeling are presented as transmission loss for selected acoustic frequencies and source-receiver geometries, and as received time series. The results are compared in order to evaluate the effect of applying different propagation models to the same range-dependent underwater environment. It should be emphasized that the propagation analysis is not an attempt to benchmark the selected propagation models, but to demonstrate the performance of practical, range-dependent models based on different approximations in particular underwater scenarios.

Download Full-text

WHAT ABOUT ADIABATIC NORMAL MODES?

Journal of Computational Acoustics ◽

10.1142/s0218396x01000474 ◽

2001 ◽

Vol 09 (01) ◽

pp. 287-309 ◽

Cited By ~ 3

Author(s):

A. TOLSTOY

Keyword(s):

Normal Mode ◽

Normal Modes ◽

Single Frequency ◽

Test Case ◽

Test Cases ◽

Flat Bottom ◽

Energy Conserving ◽

Water Test ◽

Independent Behavior ◽

Benchmark Solutions

In this paper we closely examine the performance of several propagation models, i.e., KRAKEN (coupled and adiabatic) and PE (energy-conserving), applied to a number of the SWAM'99 range-dependent shallow water test cases (FLAT, DOWN, and UP). We begin by considering range-independent behavior (including the ORCA model) in: the CAL case of Workshop'97 (Vancouver, '97),9 the first segment of FLATa, and the Benchmark Wedge test case3 but with a flat bottom of 200 m depth. We next examine the proper Benchmark Wedge behavior for the sloping bottom for our PE (conserving and nonconserving) and for our normal mode model (KRAKEN, adiabatic and coupled). These preliminary tests confirm that the models are behaving properly under known conditions and that the input parameters have been appropriately set. Thus, when we study the models' behavior on the new SWAM'99 cases we will have some confidence that they are being applied properly. It is nontrivial to run these models even when one is familiar with them. The SWAM'99 test cases which are examined here are run only to 10 km range (five-step segments) and at a single frequency of 25 Hz. No elasticity is considered. We find that all the models generally agree, but there are quantitive differences. Since there are no proper benchmark solutions for these SWAM'99 test cases, it is difficult to determine to what extent any of them are in error. However, for the purposes of Matched Field Processing, particularly the tomographic geoacoustic inversion using adibatic normal modes (KRAKEN), it is likely that the simple adiabatic normal mode KRAKEN model is sufficiently accurate under most circumstances, i.e., unless there is a loss or gain of a critical mode.

Download Full-text

A Two-Phase Fluid Model for Simulation of Cavitation Phenomena in Pipe-Line Hydraulic Systems

Recent Advances in Mechanics of Solids and Structures ◽

10.1115/imece2003-43187 ◽

2003 ◽

Author(s):

Claudio Negri

Keyword(s):

Sound Speed ◽

Fluid Model ◽

Test Cases ◽

Hydraulic Systems ◽

Homogeneous Fluid ◽

Two Phase ◽

Pipe Line ◽

Line Test ◽

Phase Fluid ◽

Energy Conservation Law

This paper presents the details of a new fluid mathematical model developed for the numerical simulation of hydraulic systems that can work in cavitating conditions. The proposed fluid model allows you to obtain physical properties, i.e. density, bulk modulus, enthalpy, entropy, void fraction and sound speed, of a liquid-vapor-gas mixture so that the mixture itself can be treated as a homogeneous fluid (homogeneous two-phase fluid model). The model was applied in the numerical analysis of pipe-line test cases. in particular, both travelling cavitation, followed by a shock-wave, and fixed cavitation due to the superposition of depression waves, are examined and numerically simulated. Besides, relevant results are shown about sound speed variations in the zones of cavitation. The author is then interested in evaluating the approximation affecting the results obtainable by using an isothermal approach, by comparing them to the results obtainable by solving the full set of conservation equations (including the energy conservation law). An analysis on the entropy production due to the propagation of shock waves is proposed, along with an estimation of the inaccuracies occurring if an isentropic or isothermal evolution is assumed.

Download Full-text

ACOUSTIC SCATTERING FROM AN ELASTIC SPHERICAL SHELL IN AN OCEANIC WAVEGUIDE WITH A PENETRABLE BOTTOM

Journal of Computational Acoustics ◽

10.1142/s0218396x13500094 ◽

2013 ◽

Vol 21 (03) ◽

pp. 1350009 ◽

Cited By ~ 3

Author(s):

NATALIE S. GRIGORIEVA ◽

GREGORY M. FRIDMAN

Keyword(s):

Normal Mode ◽

Critical Frequency ◽

Transmission Loss ◽

Elastic Shell ◽

Acoustic Scattering ◽

Oceanic Waveguide ◽

Homogeneous Fluid ◽

Scattering Coefficients ◽

Spherical Elastic Shell ◽

Probability Integral

The paper describes the theory and implementation issues of modeling of the acoustic field scattered by an air-filled spherical elastic shell immersed in a shallow-water waveguide over a homogeneous, fluid half-space. The normal mode evaluation is applied to the source contribution and to the scattering coefficients. The arising branch cut integrals are simplified and expressed via the probability integral. Two cases are analyzed: when a source frequency differs from the critical frequency of a normal mode and when they coincide. The formalism is applied to evaluate the effect of coupling between propagation and scattering on transmission loss.

Download Full-text

Heat Transfer at the Boundary Between a Porous Medium and a Homogeneous Fluid: The One-Equation Model

Journal of Porous Media ◽

10.1615/jpormedia.v1.i1.30 ◽

1998 ◽

Vol 1 (1) ◽

pp. 31-46 ◽

Cited By ~ 27

Author(s):

Stephen Whitaker ◽

J Alberto Ochoa-Tapia

Keyword(s):

Heat Transfer ◽

Porous Medium ◽

Equation Model ◽

Homogeneous Fluid ◽

The One

Download Full-text

A Computationally Efficient Rayleigh–Ritz Model for Heterogeneous Oceanic Waveguides Using Fourier Series of Sound Speed Profile

Journal of Theoretical and Computational Acoustics ◽

10.1142/s2591728521500158 ◽

2021 ◽

pp. 2150015

Author(s):

A. D. Chowdhury ◽

S. K. Bhattacharyya ◽

C. P. Vendhan

Keyword(s):

Fourier Series ◽

Sound Speed ◽

Transmission Loss ◽

Ritz Method ◽

Computational Cost ◽

Least Square ◽

Speed Profile ◽

Matrix Elements ◽

Sound Speed Profile ◽

The Matrix

The normal mode method is widely used in ocean acoustic propagation. Usually, finite difference and finite element methods are used in its solution. Recently, a method has been proposed for heterogeneous layered waveguides where the depth eigenproblem is solved using the classical Rayleigh–Ritz approximation. The method has high accuracy for low to high frequency problems. However, the matrices that appear in the eigenvalue problem for radial wavenumbers require numerical integration of the matrix elements since the sound speed and density profiles are numerically defined. In this paper, a technique is proposed to reduce the computational cost of the Rayleigh–Ritz method by expanding the sound speed profile in a Fourier series using nonlinear least square fit so that the integrals of the matrix elements can be computed in closed form. This technique is tested in a variety of problems and found to be sufficiently accurate in obtaining the radial wavenumbers as well as the transmission loss in a waveguide. The computational savings obtained by this approach is remarkable, the improvements being one or two orders of magnitude.

Download Full-text