A comparison between measured and predicted hydrodynamic damping for a jack-up rig model

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:449669

Laursen, T; Rohbock, L; Jensen, J J; Baatrup, J ^[1]; Gruendlehner, G J ^[2]

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1. Technical Univ. of Denmark, Lyngby (Denmark). Dept. of Naval Architecture and Offshore Engineering
2. Marine Structure Consultants, Schiedam (Netherlands)

An extensive set of measurements funded by the EU project Large Scale Facilities Program has been carried out on a model of a jack-up rig at the Danish Hydraulic Institute. The test series were conducted by MSC and included determination of base shears and overturning moments in both regular and irregular waves. These results have been compared in a recent paper by one of the authors (G.J. Gruendlehner) with theoretical predictions based on a time simulation procedure using various stretching methods for the wave kinematics above the still water level and applying both the relative and the absolute velocity assumption in Morison`s equation for the wave load. In the present paper another procedure is used. It is a non-linear, single degree-of-freedom method making use of the theory of diffusion processes. This procedure is also able to account for the spectral content in the random waves and requires much lesser computational effort than the time simulation methods. In the comparison between the model test results and the theoretical predictions, the hydrodynamic damping proves to be the most important uncertain parameter. In accordance with the previous analysis of the test results, it is shown that a hydrodynamic damping larger than normally assumed in engineering practice must be assumed in the theoretical calculations in order to predict the measured results.

• OSTI ID: 449669
• Report Number(s): CONF-9606279--; ISBN 0-7918-1490-4
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
DAMPING
FLUID-STRUCTURE INTERACTIONS
HYDRODYNAMICS
MATHEMATICAL MODELS
OFFSHORE PLATFORMS
RESPONSE FUNCTIONS
SCALE MODELS
TEST FACILITIES
WAVE FORCES