Uncertainty of transmission loss due to small scale fluctuations of sound speed in two environments

2013 ◽  
Vol 133 (5) ◽  
pp. 3312-3312
Author(s):  
Josette P. Fabre ◽  
Warren Wood
Keyword(s):  
Sound Speed ◽  
Transmission Loss ◽  
Small Scale

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

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.

scholarly journals Symmetrical and Asymmetrical Rectifications Employed for Deeper Ocean Extrapolations of In Situ CTD Data and Subsequent Sound Speed Profiles

Symmetry ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1455
Author(s):  
Kashif Iqbal ◽  
Minghui Zhang ◽  
Shengchun Piao
Keyword(s):  
Ocean Circulation ◽  
Sound Speed ◽  
Transmission Loss ◽  
Spatial Scales ◽  
Deep Ocean ◽  
The United States ◽  
Critical Parameters ◽  
Argo Data ◽  
Argo Floats

The multinational Argo program, which was initiated in 1999, has completed its global requirement of 3000 floats deployed by 2007. This program has revolutionized ocean observations with the provision of varying data in the upper half of the ocean. However, various studies have reiterated the requirement for deep ocean coverage, since the ocean below 2000 meters (m) is warming. In this regard, full-depth studies are mandatory in order to estimate the rising sea level due to thermal expansion and analyze critical parameters of deep ocean circulation sub 2000 m; further, data below 2000 m are mandatory for multifarious model simulations. As a landmark initiative, in mid-2015, the “Deep Argo Implementation Workshop” was held in Hobart. An array comprising 1228 floats was suggested by G. C. Johnson, rendering coverage of 5° latitude × 5° longitude × 15-day cycles. This was conclusively agreed to be an affordable solution for varying scientific needs for assessing data in abyssal oceans. Thence, Deep New profilINg float of JApan (NINJA) and Deep Arvor floats were developed by Japan and France, respectively, to cover depths of 0–4000 m. Similarly, Deep Autonomous Profiling Explorer (APEX) and Deep Sounding Oceanographic Lagrangian Observer (SOLO) by the United States were designed to cover 0–6000 m. The data offered by this underdeveloped deep pilot array are scarce on both temporal and spatial scales. This particular study offers an ingenious and novel approach to extrapolating conductivity–temperature–depth (CTD) profiles, as well as sound speed profiles (SSPs), in abyssal oceans below 2000 m. The primitive results of this method exhibited certain discrepancies which were subsequently rectified by modifying the aforementioned method both symmetrically and asymmetrically in an innovative way. The final outcomes of this method are almost identical to the in situ values obtained from Deep Argo floats, and in this way, offer a way to compute deep ocean calculations both spatially and temporally since Deep Argo floats are aimed at relatively sparse deployments and require a longer duration to provide data (5° latitude × 5° longitude × 15-day cycles) as compared to Core Argo data (3° latitude × 3° longitude × 10-day cycles). The SSP computations were conducted by employing multiple equations such as Chen and Millero, Del Grosso, and UNESCO (United Nations Educational, Scientific, and Cultural Organization) algorithms. The study concludes by offering transmission loss rectifications by employing the aforementioned method as a future course of action.

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

2001 ◽  
Vol 09 (01) ◽  
pp. 205-225
Author(s):  
PETER L. NIELSEN ◽  
FINN B. JENSEN
Keyword(s):  
Normal Mode ◽  
Sound Speed ◽  
Transmission Loss ◽  
Equation Model ◽  
Test Cases ◽  
Homogeneous Fluid ◽  
Flat Bottom ◽  
Propagation Models ◽  
Propagation Analysis ◽  
Model C

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.

scholarly journals Towards a Wave Theory Interpretation of Time-Distance Helioseismology Data

2001 ◽  
Vol 203 ◽  
pp. 180-182
Author(s):  
A. C. Birch ◽  
A. G. Kosovichev
Keyword(s):  
Spatial Scale ◽  
Born Approximation ◽  
Acoustic Waves ◽  
Sound Speed ◽  
Large Scale ◽  
Small Scale ◽  
Ray Theory ◽  
Travel Times ◽  
Large Spatial Scale ◽  
Time Distance

Time-distance helioseismology, which measures the time for acoustic waves to travel between points on the solar surface, has been used to study small-scale three-dimensional features in the sun, for example active regions, as well as large-scale features, such as meridional flow, that are not accessible by standard global helioseismology. Traditionally, travel times have been interpreted using geometrical ray theory, which is not always a good approximation. In order to develop a wave interpretation of time-distance data we employ the first Born approximation, which takes into account finite-wavelength effects and is expected to provide more accurate inversion results. In the Born approximation, in contrast with ray theory, travel times are sensitive to perturbations to sound speed which are located off the ray path. In an example calculation of travel time perturbations due to sound speed perturbations that are functions only of depth, we see that that the Born and ray approximations agree when applied to perturbations with large spatial scale and that the ray approximation fails when applied to perturbations with small spatial scale.

A time-domain finite volume approach for prediction of muffler transmission loss including thermal effects

2013 ◽  
Vol 228 (1) ◽  
pp. 108-118 ◽  
Author(s):  
Ling-Kuan Xuan ◽  
Jing-Feng Gong ◽  
Ping-Jian Ming ◽  
Guo-Yong Jin ◽  
Wen-Ping Zhang
Keyword(s):  
Temperature Field ◽  
Finite Volume ◽  
Time Domain ◽  
Thermal Effects ◽  
Sound Speed ◽  
Heterogeneous Media ◽  
Transmission Loss ◽  
Expansion Chamber ◽  
Commercial Code ◽  
Finite Volume Approach

A time-domain finite volume approach is presented for predicting the transmission loss of muffler including thermal effects with non-uniform sound speed field and density field, in which the acoustic wave equation in heterogeneous media is solved by using unstructured finite volume method with the temperature field specified or solved by some commercial code. An improved time-domain impulse method based on the absorbing boundary condition is applied to predict the acoustic attenuation characteristics of mufflers. The approach is validated by numerical simulations of a simple expansion chamber muffler and a complex muffler with five chambers. The predicted results agree well with the corresponding experimental ones and numerical ones obtained by finite element method with commercial code SYSNOISE. The results of both mufflers under different thermal conditions indicate that the temperature distribution has a significant influence on transmission loss. According to the analysis of a complex muffler with ideal medium, it is shown that the variation of working conditions can obviously affect density and sound speed distributions but have little influence on transmission loss. On the other hand, the obtained transmission loss with the solved temperature field deviates much from the one with specified uniform temperature field.

scholarly journals Reconstruction of Ocean Front Model Based on Sound Speed Clustering and Its Effectiveness in Ocean Acoustic Forecasting

2021 ◽  
Vol 11 (18) ◽  
pp. 8461
Author(s):  
Yuyao Liu ◽  
Wei Chen ◽  
Wen Chen ◽  
Yu Chen ◽  
Lina Ma ◽  
...  
Keyword(s):  
Sound Speed ◽  
Frontal Zone ◽  
Transmission Loss ◽  
Structural Characteristics ◽  
Kuroshio Extension ◽  
Reanalysis Data ◽  
Reconstruction Method ◽  
Ocean Front ◽  
Sea Area ◽  
The Kuroshio

As a mesoscale phenomenon of the ocean, the ocean front can directly affect the structural characteristics of sound speed profiles and further affect the acoustic propagation characteristics of the sea area. In this paper, we use the fuzzy C-means (FCM) algorithm to cluster the surface sound speed in the sea area of the Kuroshio Extension (KE) and detect the frontal zone of Kuroshio Extension (KEF). At the same time, the sound speed profile (SSP) is used instead of the temperature profile to establish the model of the sound speed field in the front area of the Kuroshio Extension and to improve the theoretical model of the ocean front. Compared with the actual ocean front calculated by reanalysis data, the root means square error (RSME) of the transmission loss (TL) calculated by the model is controlled below 6 dB, which proves the validity of the model. Finally, we propose the melt function in the model to forecast the depth change of the acoustic convergence area. Compared with the actual calculation result based on reanalysis data, the root means square error (RSME) of the depth forecasting after the frontal zone is 43.3 m. This reconstruction method does not rely on the high spatial resolution data of the whole sea depth and can be of referential significance to acoustic detection in the ocean front environment.

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