RESEARCH PAPERS: Offshore Mechanics

Computation of Wave-Induced Drift Forces Introduced by Displaced Position of Compliant Offshore Platforms

[+] Author and Article Information
Y. Li

Shell Development Company, Bellaire Research Center, Houston, TX 77001-0481

A. Kareem

Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556-0767

J. Offshore Mech. Arct. Eng 114(3), 175-184 (Aug 01, 1992) (10 pages) doi:10.1115/1.2919969 History: Received December 21, 1990; Revised April 22, 1992; Online June 12, 2008


The wave forces computed at the displaced position of offshore structures may introduce additional drift forces. This contribution is particularly significant for compliant offshore structures that are configured by design to experience large excursions under the environmental load effects, e.g., tension leg platform. In a random sea environment, this feature can be included in the time domain analysis by synthesizing drag and diffraction forces through a summation of a large number of harmonics with an appropriate phase relationship that reflects the platform displaced position. This approach is not only limited to the time domain analysis, but the superposition of a large number of trigonometric terms in such an analysis requires a considerable computational effort. This paper presents a computationally efficient procedure in both the time and frequency domains that permits inclusion of the time-dependent drift forces, introduced by the platform displacement, in terms of linear and nonlinear feedback contributions. These time-dependent feedback forces are expressed in terms of the applied wave loads by linear and quadratic transformations. It is demonstrated that the results obtained by this approach exhibit good agreement with the procedure based on the summation of trigonometric functions.

Copyright © 1992 by The American Society of Mechanical Engineers
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