Dynamic analysis of jack-up rigs using advanced foundation models
- Exxon Production Research Co., Houston, TX (United States). Offshore Division
The dynamic response of an independent leg jack-up is greatly affected by the rotational fixity of the spud can foundations. A simplified, planar, numerical model was developed to study fixity effects. Two elastic-plastic, associated flow, work-hardening models for simulating spud can/soil interaction in sand and clay are presented. These foundation models utilize a ``macro``-yield surface in load space for each footing rather than a detailed continuum model of the foundation. These surfaces are characterized by using experimental data directly. The main features of the iterative solution procedure necessary for implementing the plasticity models include an implicit integration scheme with subincrementation, a yield surface drift control procedure and a convergence criterion. Based on a limited sensitivity study, the amount of computational effort was found to decrease with increasing time increment size and convergence tolerance and to be relatively independent of the number of subincrements. A time increment size equal to 5% of the natural period of the jack-up (based on the initial elastic stiffness), a convergence tolerance of 0.01 (1%) and a minimum value of 5 subincrements were found to be optimum. Reasonably good agreements were obtained between centrifuge model measurements and predictions from the numerical model. However, the comparison indicated further improvements could be achieved by incorporating a non-associated flow rule and sub-yield plasticity.
- OSTI ID:
- 55780
- Report Number(s):
- CONF-940230--; ISBN 0-7918-1265-0
- Country of Publication:
- United States
- Language:
- English
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