Modeling and analysis of complex structural -acoustic systems.

Techniques are developed for modeling and analyzing the vibration response of complex structural-acoustic systems. A novel application of Lagrange multipliers to couple domains modeled independently with linear elasto-dynamic and reduced-order theories is presented. This method is developed from a variational formulation of the continuous problem and is easily implemented within a finite element code. Applications include modeling of cracks, holes, and junctions within a frame-like structure. Simulations using this method compare well with a full elasto-dynamic discretizations and existing methods for modeling such problems. In an experimental context, it is desirable to have a robust, flexible method for analyzing wave phenomena along a structure and in the surrounding fluid. A general framework is developed for determining the underlying parameters of general signal models through the application of maximum likelihood estimation theory for functions whose variables separate. This method extends previous work in sinusoidal and exponential estimation to include models with other functional bases, such as exponential functions with non-constant amplitudes and Bessel functions. Non-uniform spatial sampling is also possible with this technique. The maximum likelihood method is applied to the identification of wave components along one-dimensional structural elements. Results are given which demonstrate the viability and accuracy of the technique estimating exponential and Bessel function model parameters from noisy simulation data. Algorithms for determining material properties and power flow in vibrating structures are presented. New techniques are achieved by synthesizing wave component identification methods with new methods targeted towards material property and structural intensity estimation. The effectiveness of this nonlinear least-squares approach is investigated through laboratory and numerical experiments on a non-uniform structure, yielding guidelines for spatial sampling and the effects of noise. The study of harmonically driven in vacuo and fluid-loaded T-beams with various joint configurations is presented to demonstrate the ability of these modeling and analysis techniques to investigate complex structures. Numerical experiments are performed which investigate wave propagation in multiply connected beams, transmission of energy through a complex joint, power dissipation in a structure, and the effect of fluid loading on both wave propagation and energy dissipation.PhDApplied SciencesMechanical engineeringMechanicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132583/2/9977169.pd