Array processing and forward modeling methods for the analysis of stiffened, fluid-loaded cylindrical shells
Bondaryk, Joseph E.
MetadataShow full item record
This thesis investigates array processing and forward modeling methods for the analysis of experimental, structural acoustic data to understand wave propagation on fluid-loaded, elastic, cylindrical shells in the mid-frequency range, 2 < ka < 12. The transient, acoustic, in-plane, bistatic scattering response to wideband, plane waves at various angles of incidence was collected by a synthetic array for three shells, a finite, air-filled, empty thin shell, a duplicate shell stiffened with four unequally spaced ring-stiffeners and a duplicate ribbed shell augmented by resiliently-mounted, wave-bearing, internal structural elements. Array and signal processing techniques, including source deconvolution, array weighting, conventional focusing and the removal of the geometrically scattered contribution, are used to transform the collected data to a more easily interpreted representation. The resulting waveforms show that part of the transient, dynamic, structural response of the shell surface which is capable of radiating to the far field. Compressional membrane waves are directly observable in this representation and evidence of flexural membrane waves is present. Comparisons between the shells show energy compartmentalized by the ring stiffeners and coupled into the wave-bearing internals. Energy calculations show a decay rate of 30dB/msec due to radiation for the Empty shell but only 10dB/msec for the other shells at bow incidence. The Radon Transform is used to estimate the reflection coefficient of compressional waves at the shell endcap as 0.2. The measurement array does not provide enough resolution to allow use of this technique to determine the reflection, transmission and coupling coefficients at the ring stiffeners. Therefore, a forward modeling technique is used to further analyze the 0° incidence case. This modeling couples a Transmission Line model of the shell with a Simulated Annealing approach to multi-dimensional, parameter estimation. This procedure estimates the compressional wavespeed at 5284m/sec and a compressional decay rate of 49dB/msec. Small cross-coupling coefficients between flexural and compressional wavetypes at the slope discontinuities on the Empty shell are found to be responsible for most of the radiation later in time. High reflection coefficients at the ring stiffeners on the Ribbed shell are shown to cause energy compartmentalization in the bays between ribs and pressure doubling of incident structural waves at the ribs.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution March 1994
Showing items related by title, author, creator and subject.
Li, Lin (Woods Hole Oceanographic Institution, 1995-02)The response of vertical arrays at single frequencies (CW) and for homogeneous media is well known. This paper addresses the issues of frequency dependence and sound velocity gradients for the vertical array response in ...
The horizontal mooring : a two-dimensional array, description of the array, components, instrumentation, deployment and recovery operations Trask, Richard P.; Anderson, Steven P.; Way, Bryan S.; Ostrom, William M.; Paul, Walter; Grosenbaugh, Mark A.; Gobat, Jason I.; Weller, Robert A. (Woods Hole Oceanographic Institution, 1999-09)A moored two-dimensional array with instrumentation distributed both horizontally and vertically was deployed for 27 days in August 1998 at an 85 meter deep site in Massachusetts Bay near Stellwagon basin. The horizontal ...
Modeling acoustic propagation of airgun array pulses recorded on tagged sperm whales (Physeter macrocephalus) DeRuiter, Stacy L.; Tyack, Peter L.; Lin, Ying-Tsong; Newhall, Arthur E.; Lynch, James F.; Miller, Patrick J. O. (Acoustical Society of America, 2006-12)In 2002 and 2003, tagged sperm whales (Physeter macrocephalus) were experimentally exposed to airgun pulses in the Gulf of Mexico, with the tags providing acoustic recordings at measured ranges and depths. Ray trace and ...