RESEARCH PAPERS: Offshore Mechanics

Higher Order Wave Loading on Fixed, Slender, Surface-Piercing, Rigid Cylinders

[+] Author and Article Information
K. Thiagarajan

Department of Naval Architecture and Marine Engineering, The University of Michigan, Ann Arbor, MI 48109

R. E. Baddour

Memorial University of Newfoundland, St. John’s, Newfoundland, Canada

J. Offshore Mech. Arct. Eng 113(1), 23-29 (Feb 01, 1991) (7 pages) doi:10.1115/1.2919892 History: Received June 14, 1989; Revised May 04, 1990


The use of Morison’s equation together with the linear wave theory is considered a first approximation to evaluate the inline wave forces on a surface-piercing cylinder. Significant second-order forces are expected to arise from the waterline and dynamic pressure effects, even when a wave is described by the linear theory. Experiments have been carried out at the MUN (Memorial University of Newfoundland) wave tank facility to identify these second-order forces for various wave frequencies and for various cylinder diameters. A strain gage force transducer has been used for this purpose. First and second-order force components have been identified using a Fast Fourier Transform. Theoretical evaluation of wave forces involved computing components from Morison’s equation using second-order Stokes theory. The waterline forces and convective acceleration forces which contribute toward the total second-order force have also been evaluated. First-order results are in acceptance with previously established data. Theoretical considerations for second order are satisfactory. Scatter in second-order experimental results were observed. Different approaches to the second-order inertia force are compared. It is expected that the inclusion of second-order forces will lead to a better representation of wave loading on offshore structures.

Copyright © 1991 by The American Society of Mechanical Engineers
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