Nonlinear internal wave parameter influences on energy propagation using radiative transport theory.

McMahon, Kara G.; Lynch, James F.; Lin, Ying‐Tsong; Xiang, Ning; Siegmann, William L.

doi:10.1121/1.3588080

Cited by 3 publications

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“…Based on recent studies by McMahon [73], a diffusion type equation can be applied for studying the acoustic propagation problem statistically in presence of such waves. This is an alternative method of obtaining the statistics of the modal amplitude scintillations due to three-dimensional effects.…”

Section: Analysis and Modelingmentioning

confidence: 99%

Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Shmelev¹

2011

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This thesis describes the physics of fully three-dimensional low frequency acoustic interaction with internal waves, bottom sediment waves and surface swell waves that are often observed in shallow waters and on continental slopes. A simple idealized model of the ocean waveguide is used to analytically study the properties of acoustic normal modes and their perturbations due to waves of each type. The combined approach of a semi-quantitative study based on the geometrical acoustics approximation and on fully three-dimensional coupled mode numerical modeling is used to examine the azimuthal dependence of sound wave horizontal reflection from, transmission through and ducting between straight parallel waves of each type. The impact of the natural crossings of nonlinear internal waves on horizontally ducted sound energy is studied theoretically and modeled numerically using a three-dimensional parabolic equation acoustic propagation code. A realistic sea surface elevation is synthesized from the directional spectrum of long swells and used for three-dimensional numerical modeling of acoustic propagation. As a result, considerable normal mode amplitude scintillations were observed and shown to be strongly dependent on horizontal azimuth, range and mode number. Full field numerical modeling of low frequency sound propagation through large sand waves located on a sloped bottom was performed using the high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic ducting is shown to steer acoustic energy beams along the sand wave's curved crests.

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Section: Analysis and Modelingmentioning

confidence: 99%

Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Shmelev¹

2011

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“…James Lynch and Timothy Duda and their colleagues [8]- [11] of propagation effects from waveguides of variable structure generated by nonlinear internal waves, a related project characterizes whispering gallery and other modes [21].…”

Section: Related Projectsmentioning

confidence: 99%

“…• Calculations from the modal transport theory are used to determine the influence of NIW parameter variations, background environmental conditions, and acoustic parameters on averaged intensity [11], and results are compared and benchmarked with propagation computations.…”

Section: Work Completedmentioning

confidence: 99%

Shallow Water Propagation

Siegmann¹,

Metzler²,

McMahon³

2011

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LONG-TERM GOALSDevelop methods for deterministic and stochastic acoustic calculations in complex shallow water environments, specify their capabilities and accuracy, and apply them to explain experimental data and understand physical mechanisms of propagation. OBJECTIVES(A) Treat propagation from narrowband and broadband sources over elastic and poro-elastic sediments, and incorporate realistic bathymetric, topographic, and geoacoustic variations. (B) Construct representations for ocean environmental and geoacoustic variability using data and parametric models. Determine acoustic fields with PE, normal mode, and other approximation methods. Use experimental data and computational results to assess propagation mechanisms.

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Shallow Water Propagation

Siegmann¹

2010

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During the performance period, six students received their PhD degrees from Rensselaer Polytechnic Institute with ONR support, and their initial and current positions are provided in Section IV. Twenty-one papers were published, including ten in the Journal of the Acoustical Society of America and six in IEEE publications, and their references are listed in Section V. Thirty-six professional presentations were made, including thirty-two at national or international meetings, and their titles and venues are given in Section VI. Some research results and figures from the performance period are highlighted in Sections II and III. II. RESEARCH HIGHLIGHTS A. Propagation Model Development and Applications• Layered elastic sediments are important in shallow water and must be accurately handled as the basis for extensions to more complicated bottoms that include range dependence, poro-elasticity, and other physical mechanisms. Our parabolic equation formulation [1] resolved this task by using new choices of dependent variables, along with the same efficient and reliable numerical schemes as for fluid bottom models. The formulation accommodates all physical conditions at layer interfaces and avoids stability difficulties that arise in other approaches. Figure 1 illustrates results from our implementation. Comparing the upper and middle contour plots, we conclude that significant transmission level differences can occur in the ocean as a result of the elastic bottom waveguide. The lower contour plot demonstrates that this method, unlike other parabolic equations, can treat seismic sources. 20100308162

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Nonlinear internal wave parameter influences on energy propagation using radiative transport theory.

Cited by 3 publications

References 0 publications

Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Shallow Water Propagation

Shallow Water Propagation

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