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Strength Analysis for a Spar in the Load-Out Operation Process

[+] Author Affiliations
Yue Yang, Jianmin Yang, Zhiqiang Hu

Shanghai Jiao Tong University, Shanghai, China

Zhixia Fan, Weiying Sun

China Offshore Oil Engineering Co., Ltd., Tianjin, China

Paper No. OMAE2011-49653, pp. 475-486; 12 pages
doi:10.1115/OMAE2011-49653
From:
  • ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 2: Structures, Safety and Reliability
  • Rotterdam, The Netherlands, June 19–24, 2011
  • ISBN: 978-0-7918-4434-2
  • Copyright © 2011 by ASME

abstract

Load-out operation is one of the important processes for Spar construction and transportation. The Spar is towed onto the deck of a semi-barge, supported by special cradles during the whole process. Variation in weight distribution of the Spar, tidal changes, the barge draft level and positioning are main factors that affect the consistence of the barge deck and the dock surface, which will induce the Spar to sustain vertical bending moments and shear force. Transverse wind acting on the Spar also forms a slight transverse shift of the barge deck, which will induce the Spar to suffer horizontal bending moments. Nevertheless, structural components of the Spar are not allowed to endure any plastic deformations or buckling. So, the ultimate loading condition should be determined and the weakest structural components during the load-out process should also be ascertained. A truss Spar is chosen as the objective, and twenty steps are defined for the load-out process. The code SESAM is used to do the analysis. A finite element model is made, consists of the whole Spar and the cradle frames, which also take part in the load-out process. Two groups of load cases are defined. The initial forced displacement is applied on the cradle, simulating the difference between the deck and the dock surface. The initial forced displacement can be modified to the state when the Spar structural components endure ultimate elastic load. On the transverse wind condition, the initial forced displacement is modified in the same way introduced above. By the analysis results, two envelope curves for the vertical force applying on the barge are obtained, to provide guidance for the operation. The stresses and the internal forces of the Spar structural components are summarized, on purpose of giving the flexural performance and the shearing stress condition of the Spar during the load-out process. The ultimate elastic loads can be obtained for each of the twenty steps, and the characteristic of every ultimate elastic load cases is concluded. According to elastic-plastic theory, affordable displacement between barge deck and dock surface is obtained.

Copyright © 2011 by ASME

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