Second-order dynamic response of a large spar platform: Numerical predictions versus experimental results

Book · Tue Dec 31 04:00:00 EST 1996

OSTI ID:449695

Weggel, D C; Roesset, J M ^[1]

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1. Univ. of Texas, Austin, TX (United States). Offshore Technology Research Center

The dynamic response of a large spar platform was investigated. A 1:55 scale model of the platform was tested at the wave basin of the Center at Texas A and M University. It was subjected to unidirectional monochromatic, bichromatic, and irregular waves in deep water. The prototype spar with a diameter of D = 40.5 m and a draft of h = 198.2 m would be moored to the sea floor in a water depth of 922 meters. Numerical predictions using second-order diffraction/radiation theory are compared in this paper to the experimental results to assess the degree of appropriateness provided by this theory alone. The first- and second-order diffraction forces and radiation coefficients were computed with WAMIT5.1s, a widely-used radiation/diffraction panel program for bodies of arbitrary geometry. The forces and radiation coefficients obtained for a truncated cylinder with the spar`s dimensions were then input into a program that calculates responses using the hydrodynamic equations of motion of a rigid body with three degrees of freedom. The response program interpolates between actual hydrodynamic force values computed by WAMIT so that high resolution spectral outputs can be obtained. Mooring lines were modeled by linear springs although their behavior was nonlinear for large displacements. The numerical and experimental responses for surge and pitch are compared in the form of time histories and spectral densities. The heave motion was not considered because it should be more strongly affected by viscous damping which was not included in the model.

• OSTI ID: 449695
• Report Number(s): CONF-9606279--; ISBN 0-7918-1490-4
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
COMPUTERIZED SIMULATION
EXPERIMENTAL DATA
FLUID-STRUCTURE INTERACTIONS
MATHEMATICAL MODELS
MOORINGS
OFFSHORE PLATFORMS
PETROLEUM INDUSTRY
RESPONSE FUNCTIONS
SCALE MODELS
THEORETICAL DATA
WAVE FORCES