Merged with duplicate record 10026.1/2055 on 12.04.2017 by CS (TIS)In this thesis we consider the problem of the dynamic fluid-structure interaction
between a finite elastic structure and the acoustic field in an unbounded fluid-filled
exterior domain.
We formulate the exterior acoustic problem as an integral equation over the
structure surface. However, the classical boundary integral equation formulations
of this problem do not have unique solutions at certain characteristic frequencies
(which depend on the surface) and it is necessary to employ modified boundary
integral equation formulations which are valid for all frequencies. The modified
integral equation formulation used here involves certain arbitrary parameters and
we shall study the effect of these parameters on the stability and accuracy of the
numerical methods used to solve the integral equation.
We then couple the boundary element analysis of the exterior acoustic problem
with a finite element analysis of the elastic structure to investigate the interaction
between the structure and the acoustic field. Recently there has been some controversy
over whether or not the coupled problem suffers from the non-uniqueness
problems associated with the classical integral equation formulations of the exterior
acoustic problem. We resolve this question by demonstrating that the solution to
the coupled problem is not unique at the characteristic frequencies and that we
need to employ an integral equation formulation valid for all frequencies.
We discuss the accuracy of our numerical results for both the acoustic problem
and the coupled problem, for a number of axisymmetric and fully three-dimensional
problems. Finally, we apply our method to the problem of a piezoelectric sonar
transducer transmitting an acoustic signal in water, and observe reasonable agreement
between our theoretical predictions and some experimental results.Admiralty Research Establishment, Portlan
