Offshore Technology Research Center


OTRC Project Summary

Project Title:

Evaluation of the Dynamic Response of Spar Platforms

Prinicipal Investigators:

Jose Roesset


National Science Foundation

Completion Date:

February, 2000

Final Report ID#

A105(Click to view final report abstract)

Despite the considerable amount of analytical work done on the spar, there is a need to compare and correlate the results obtained by various approaches.  The literature has shown the possibility of getting relatively accurate results irrespective of the type of wave input (time-series or idealized spectrum), method of analysis time domain or frequency domain, coupled or uncoupled analysis), calculation of forces (Morison’s equation or diffraction theory), nonlinear effects (i.e. their inclusion or omission) or damping considered (drag, wave-drift damping, structural and mooring-line damping),  and wave kinematics (Extrapolation, Stretching or HWM).  But a rational comparison aimed at a clearer understanding of the differences between the various approaches remains to be achieved.  Therefore, the main objective of this work is to investigate these differences and to try to suggest a workable approach for the dynamic analysis of spars.  This includes comparison between the time domain and frequency domain approaches, coupled and uncoupled analyses, diffraction theory and Morison’s equation, different wave kinematics approximations and individual nonlinear interaction forces.  These are to be compared to experimental results for bichromatic and irregular waves for spars with and with risers.

Some recent field data collected on existing spars in real sea environment will also be compared with numerical predictions.  In order to do that, the effects of wave-directionally, wind current and VIV will be studied.  Statistical studies in time frequency domains will be presented, and the accuracy of a stochastic model in the frequency domain will be investigated by comparing with corresponding results from simulations and in time domain and frequency domain.

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