5 research outputs found
Array processing and forward modeling methods for the analysis of stiffened, fluid-loaded cylindrical shells
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 1994This 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.Support for this thesis was provided by Office of Naval Research, Structural Mechanics
and Advanced Vehicle Technology Divisions, it is most gratefully acknowledged
Array processing and forward modeling methods for the analysis of stiffened, fluid-loaded cylindrical shells
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994.Includes bibliographical references (leaves 154-157).by Joseph E. Bondaryk.Ph.D
Digital Signal Processing
Contains table of contents for Part III, table of contents for Section 1, an introduction and reports on seventeen research projects.National Science Foundation FellowshipNational Science Foundation (Grant ECS 84-07285)National Science Foundation (Grant MIP 87-14969)U.S. Navy - Office of Naval Research (Contract N00014-81-K-0742)Scholarship from the Federative Republic of BrazilU.S. Air Force - Electronic Systems Division (Contract F19628-85-K-0028)AT&T Bell Laboratories Doctoral Support ProgramCanada, Bell Northern Research ScholarshipCanada, Fonds pour la Formation de Chercheurs et I'Aide a la Recherche Postgraduate FellowshipSanders Associates, Inc.OKI Semiconductor, Inc.Tel Aviv University, Department of Electronic SystemsU.S. Navy - Office of Naval Research (Contract N00014-85-K-0272)Natural Sciences and Engineering Research Council of Canada, Science and Engineering Scholarshi
Digital Signal Processing
Contains an introduction and reports on fifteen research projects.National Science Foundation FellowshipU.S. Navy - Office of Naval Research (Contract N00014-81-K-0742)National Science Foundation (Grant ECS 84-07285)Sanders Associates, Inc.U.S. Air Force - Office of Scientific Research (Contract F19628-85-K-0028)AT&T Bell Laboratories Doctoral Support ProgramCanada, Bell Northern Research ScholarshipCanada, Fonds pour la Formation de Chercheurs et /'Aide a la Recherche Postgraduate FellowshipCanada, Natural Science and Engineering Research Council Postgraduate FellowshipAmoco Foundation FellowshipFannie and John Hertz Foundation Fellowshi
Digital Signal Processing
Contains an introduction and reports on twenty research projects.National Science Foundation (Grant ECS 84-07285)U.S. Navy - Office of Naval Research (Contract N00014-81-K-0742)National Science Foundation FellowshipSanders Associates, Inc.U.S. Air Force - Office of Scientific Research (Contract F19628-85-K-0028)Canada, Bell Northern Research ScholarshipCanada, Fonds pour la Formation de Chercheurs et l'Aide a la Recherche Postgraduate FellowshipCanada, Natural Science and Engineering Research Council Postgraduate FellowshipU.S. Navy - Office of Naval Research (Contract N00014-81-K-0472)Fanny and John Hertz Foundation FellowshipCenter for Advanced Television StudiesAmoco Foundation FellowshipU.S. Air Force - Office of Scientific Research (Contract F19628-85-K-0028