The method of large admissible perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures without trial and error or repetitive finite element analyses. When forced vibration constraints are incorporated into the redesign problem, damping and added mass due to the presence of fluid must be included into the model. The corresponding terms introduce theoretical and numerical difficulties, which are treated in this paper. The LEAP method has been implemented into a Fortran computer code RESTRUCT, developed at the University of Michigan. The redesign process is mathematically formulated as an optimization problem with nonlinear constraints, called general perturbation equations. First, a finite element analysis of the initial structure is executed. Then, the results are postprocessed by code RESTRUCT using an incremental scheme to find the optimum solution for the problem defined by the designer. Accurate determination of nonstructural terms, such as fluid added mass, is generally detrimental as far as forced response analysis is concerned. In redesign problems, however, simple but realistic models can be used. A simple transformation of the structural mass matrix is used to compute the added mass matrix and its dependency on the redesign variables. The presence of non-structural terms in the general perturbation equations requires the development of a new LEAP algorithm for solution of the optimization problem. A simple cantilever beam with 100 degrees of freedom is used to validate the fluid added mass model. The developed method and algorithm are then applied to a partially submerged 4,248 degree of freedom complex structure modeled with beam elements.
Redesign of Submerged Structures by Large Admissible Perturbations
Contributed by the Offshore Mechanics and Artic Engineering Division and presented at the ETCE/OMAE2000, New Orleans, Louisiana, February 14–17, 2000, of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received by the OMAE Division, March 2, 2000; revised manuscript received April 11, 2001. Associate Editor: R. Riggs.
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Blouin, V. Y., and Bernitsas, M. M. (April 11, 2001). "Redesign of Submerged Structures by Large Admissible Perturbations ." ASME. J. Offshore Mech. Arct. Eng. August 2001; 123(3): 103–111. https://doi.org/10.1115/1.1382594
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