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Nonlinear Wave Loads on Deep-Water Semisubmersibles

Lookup NU author(s): Dr Arun DevORCiD, Dr Xin WangORCiD


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Among various types of offshore drilling rigs, the semisubmersible platform is the most popular one for the mid and deep-water exploration activities thanks to its good motion characteristics. With the oil exploration activities moving into deeper water and variable deck load capacity growing, the size of semisubmersible units has increased significantly. Because of the increased usage of these large units in harsh environments, the prediction of the extreme wave loads has become more important. The critical responses of the large semisubmersibles include the longitudinal shear force between pontoons, the split forces between pontoons, and torsional moment. For these giant deep-water units, the traditional linear analysis overestimates the wave loads, which leads to a substantial increase of the lightship weight and hence the cost of the rig. In this paper, we compare the experimental and linear numerical results of the wave loads of a 7th generation deep-water semisubmersible drilling unit. The linear numerical calculation uses a three-dimensional panel method in the frequency domain. The important findings in this paper are 1. The wave loads measured in the model tests were 10 to 15% less than the linear analysis, and the torsional moment showed a maximum difference as about 30%. This result indicates potentials of a substantial reduction of the lightship weight by using nonlinear analysis. 2. The linear and nonlinear results also showed different characteristics to different wave directions in some cases. This difference will affect the selection of the critical design wave and thus influence the global structural analysis and the design of the platform.

Publication metadata

Author(s): Dev AK, Rahul M, Wang X, Velizar P

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: 14th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2019)

Year of Conference: 2019

Online publication date: 22/09/2019

Acceptance date: 31/08/2019