Theoretical and computational acoustics 2001 li qihu shang e c gao t f
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Twenty pages are devoted to references. The situation is further complicated by the nonorthogonality of the coordinate system and by the common practice of using highly nonuniform stretching for the vertical grids, which, unless special precautions are taken, causes both a loss of discretization accuracy overall and an increase in interference of the component errors. Description: xiii, 676 pages : illustrations ; 26 cm Contents: Efficient broadband signal simulation in shallow water - a modal approach, F. The effects of nonlinear waves were not well modeled, consistent with their known three-dimensional effects but also with the lack of measurements to initialize and constrain them. An approach of extracting the modal back-scattering matrix from the reverberation data in shallow-water is proposed recently Shang, Gao and Tang, 2002. The method that we used for singularity analysis is to calculate the maximum value of the determinant of this kernel matrix. A simple acoustic model of El Nino based on the 1982—1983 event Georges et al.

This calls for the use of fast acoustic propagation models. The modeled uncertainties in the transmission loss estimate and their relations to the error statistics in the ocean estimate are discussed. In both cases, strong mode coupling takes place for the used frequency and mode number. Technical aspects of using information from internal tide generation models such as this to initialize coastal internal wave models for use with acoustic propagation models are discussed. These synoptic features are then melded with available climatology of the region for initialization and assimilation. Owing to the weak damping process, βm , the modal attenuation coefficient can be obtained by using a modified Prony's method. The region of study is focused on the ocean waters surrounding Taiwan in the East China Sea.

The retrieved El Nino profile is very promising. Two examples of the nongradual ocean structures are discussed: 1 polar frontal zone with a width of about 2 km, and 2 internal solitons in shallow water with a width about 0. It is known that the waveguide invariant β is affected by the shallow-water environment. Under typical ocean conditions, low wind speeds, and the available bubble population data, the calculated noise level agrees well with experimental results, both in magnitude and in the shape of the spectrum. The physical reason behind this is most likely that the mode coupling impact can be canceled at the sound signal propagation along the two very close paths. The results show that the new model can explain the shallow water reverberation in most cases. The interesting result is that even in a strong mode coupling environment the numerically obtained phase difference is quite close to its value as calculated by adiabatic approximation.

We found that there is an optimum source depth distribution corresponding to the maximum value of the determinant of the kernel matrix. Numerical examples are conducted to show this complexity. In practice, it is always impossible to pre-know the layout of the real sediment, so a supposed model is used. Approaches of inversion of the matrix from reverberation data are proposed. The major multiscale synoptic circulation features include the mean flow and southeastward meandering jet s of the California Current, the poleward flowing California Undercurrent, and six upwelling regions along the western coast of the U. In order to achieve these objectives, the report collects, generates and analyzes empirical evidence on patterns of equity, examines the underlying causes of inequity, and evaluates government policies for addressing inequity. They consists of defining trends in the signal arrival pattern caused by the temperature changes, and computing average parameters of the arriving signal ensemble.

The mode filtering processor was used to process the field data of a vertical array to obtain individual modes. About this Item: World Bank Publications, United States, 2017. By using the approximate modal eigenvalue solution, the analytic expressions for describing the impacts of water-depth mismatch in a Pekeris waveguide and sediment-type mismatch have been derived. The quantified uncertainty can then be used to provide enhanced sonar performance predictions for tactical decision aides. About this Item: Tianjin People's Fine Arts Publishing House. Refereed invited Manuscript, Proceedings of the 5th International conference on theoretical and computational acoustics, May 21-25, 2001. In this paper, matched field processing is performed after quick inversion.

When the isosurfaces of the vertical coordinate are not aligned with either geopotential surfaces or isopycnals, the horizontal pressure gradient consists of two large terms that tend to cancel; the associated pressure-gradient error stems from interference of the discretization errors of these terms. Using a modal decomposition of the parabolic-equation field, we find that mode coupling at the circumpolar. The title page there is a little stain. The conclusion is that, under a quite tolerant condition, the matrix is not singular, and the backscattering matrix can be inverted. It is shown that the value of β related to different high-speed sediments including layered sediment is ranged in 1.

A shallow-water reverberation model is developed based on Bass perturbation theory. With a vertical receiving array, the modal features of each individual mode can be measured by mode filtering, or on the other hand, to measure the total field at each hydrophone for the matched? The normal mode model of reverberation in shallow-water waveguides has been presented based on Born approximation. About this Item: World Bank Publications, United States, 2017. Time-evolving three-dimensional four-dimensional numerical modeling of sound is performed for ocean environmental conditions calculated using regional ocean flow models. This volume represents the latest advances in the field of theoretical and computational acoustics.

In this paper, an inversion scheme is presented that accounts for the acoustic mode interaction. To detect the El Nino onset and estimate its intensity as early as possible are a challenge for global climate forecasting and modeling. That means that by choosing the optimum source depth distribution we can get the most stable inversion. It has clear physical picture and it is satisfied the waveguide constraint without any adjustable parameters. An end-to-end system, which couples meteorology-physical oceanography-geoacoustics-ocean acoustics-bottom-noise-target-sonar data and models, is used to estimate uncertainties and their transfers and feedbacks. As the source changed range at constant bearing end fire , the apparent direction changed by as much as 25°.

Efficient broadband signal simulation in shallow water - a modal approach, F. The characteristics of scattering due to interface roughness are usually described by the backscattering matrix for reverberation modeling. For most of the practical interesting cases, this condition can be satisfied quite easy. It has been found that this thin layer can significantly affect the acoustic field in water column. The different forecast realizations of the sound speed field are then fed into a Naval Postgraduate School coupled-mode sound propagation model to produce realizations of the predicted acoustic wavefield in a vertical plane across the shelfbreak frontal zone. Du et al; theoretical simulation of the behaviour of micromachined electrostatic ultrasonic transducers, L. .