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RESEARCH PAPERS: Offshore Mechanics

Nonlinear Inverse Perturbation in Structural Dynamics Redesign of Risers

[+] Author and Article Information
M. M. Bernitsas, C. J. Hoff, J. E. Kokarakis

Department of Naval Architecture and Marine Engineering, The University of Michigan, North Campus, Ann Arbor, Mich. 48109

J. Energy Resour. Technol 107(2), 256-263 (Jun 01, 1985) (8 pages) doi:10.1115/1.3231186 History: Received August 16, 1983; Revised October 23, 1984; Online October 22, 2009

Abstract

Marine risers, and offshore structures in general, may have undesirable natural frequencies and/or mode shapes. Structural redesign is mandatory in such cases. An Inverse Perturbation Redesign (IPR) method, which uses only the finite element analysis of the baseline system and was developed in previous work for general structures, is extended in this work to handle systems with geometric stiffness matrices like marine risers. The IPR method is currently applicable to undamped structural systems or systems with Rayleigh damping and is valid for large or small changes which are frequently required to change modal characteristics of offshore structures. The vibratory characteristics of risers can be altered by modifying among others, the riser top tension, the drilling mud density and the geometry of the riser tubes. The effects of their change on the riser frequencies and modes are derived and applied to two typical riser redesign problems using the IPR method.

Copyright © 1985 by ASME
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