Zhou et al. [J. Acoust. Soc. Am. 90, 2042–2054 (1987)] have hypothesized that mode conversion due to large-amplitude shallow-water internal waves (solitons) could explain the anomalous transmission loss observed in acoustic data taken in the Yellow Sea. Numerical experiments had been performed that substantiated their hypothesis [Chin-Bing et al., Math. Model. Sci. Comput. 4 (1994); King et al., Theor. Comput. Acoust. 2, 793–807 (1994)]. It is also found that the effect is most prominent when there is strong coupling between the lower-order propagation modes and the very lossy, higher-order modes. In reaching these conclusions, both groups assumed an idealized sinusoidal soliton structure. The analysis has recently been repeated using a soliton sound-speed structure more characteristic of what is found in straits. Results will be presented that show the similarities and differences in anomalous transmission loss for the realistic and the idealized sinusoidal soliton. [Work supported by ONR/NRL and by a Federal High Performance Computing DoD grant.]
A search algorithm for resonance anomalies (SARA) has been developed to predict possible resonance frequencies of shallow-water soliton packets as they travel through straits. The algorithm relies on characteristics that accompany large losses due to acoustic wave-soliton interactions: (a) acoustic mode conversions; (b) large signal losses within a narrow band of acoustic frequencies; and, (c) large transmission losses due to strong couplings between lower-order propagation modes and higher-order, bottom-interacting modes. The SARA algorithm has been verified using oceanographic data from the Strait of Messina. As a remote acoustic sensor, the SARA algorithm could be used in an ‘‘inverse mode’’ to predict key oceanographic parameters (e.g., predominant horizontal spatial wave numbers and travel speeds) of those soliton packets that produce large acoustic losses. The parameters would initialize a primitive shallow-water soliton model that generates soliton simulations. The SARA algorithm could be used in a forward fashion to validate the soliton simulations. The concept exploits the unique sloping bathymetry of straits, where natural mode stripping can occur around the sills that generate the solitons. Details will be discussed and computer simulations will be presented that illustrate the feasibility of the approach. [Work supported by ONR/NRL and by a High Performance Computing DoD grant.]
Recently a number of researchers have performed acoustic simulations of shallow-water regions that contain large amplitude internal waves (solitons). Their results have confirmed earlier findings: (a) mode conversions, due to acoustic interactions with soliton packets, can produce a large loss in acoustic transmission; (b) this loss occurs within a narrow band of acoustic frequencies (about the resonance frequency); and, (c) the transmission loss is most prominent when there is strong coupling between the lower-order (water-borne) propagation modes and the higher-order, very lossy (bottom interacting) modes. Using this knowledge, development of a search algorithm has begun to predict the resonance frequency of a shallow-water soliton packet. In this proof-of-concept work, a shallow-water soliton model was used to generate replicas of the soliton fields in the Strait of Messina. The allowable acoustic mode conversions were calculated and correlated with the dominate spatial wave numbers of the soliton packet. This was used to predict the resonance frequency. The resonance frequency was later confirmed by making hundreds of acoustic runs. The search algorithm will be discussed and examples shown. [Work supported by ONR/NRL and by a Federal High Performance Computing DoD grant.]
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