Static/Dynamic Redesign of Marine Structures.

A finite element analysis can accurately predict the static and dynamic response of a large marine structure. In many instances the response characteristics are undesirable and structural redesign is required. Current methods to solve the redesign problem are based on trial and error approaches which are expensive in terms of computer and manpower resources. A method is developed to solve the static redesign problem to achieve large displacement and stress changes. Perturbation of the static equilibrium equation is used to develop an equation governing the static redesign. This equation is solved using an iterative technique which is efficient since the inverse (or Cholesky decomposition) of the stiffness matrix is not required. Two methods are developed to solve the dynamic redesign problem to meet natural frequency and normal mode objectives. By perturbing the dynamic energy equations, a governing perturbation equation is developed. The equation is solved by a predictor-corrector scheme. In the predictor phase, a linear approximation to the solution is obtained. The corrector phase uses the approximate solution along with the governing perturbation equation to obtain the final solution. A predictor-alternate corrector method is also developed where the necessary and sufficient conditions for the orthogonality of the perturbed eigenvector are included in the corrector phase. The static and dynamic redesign methods are illustrated on several examples. Large response changes which resulted in large structural changes are specified in order to illustrate the usefulness and accuracy of the methods.PhDOcean engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160534/1/8512429.pd