This paper addresses the problem of estimating the air gap for a large semisubmersible production platform. Although it has a great impact on the design of the floating unit, many times the minimum deck height is still defined from simplified methods that incorporate relatively large safety margins. The reason for this is the intrinsic complexity of the associated hydrodynamic problem. Nonlinear effects on the incoming and scattered waves are usually relevant and sometimes nonlinear effects on the motions of the floating hull may also play an important role. This discussion is illustrated by means of wave basin tests performed with the model of a large semisubmersible designed to operate in Campos Basin. Significant run-up effects on its squared-section columns were observed for the steepest waves in several design conditions. Also, the unit presented relatively large low-frequency motions in heave, roll and pitch, which also affected the dynamic air gap measurements. In order to evaluate the difficulties involved in modeling such phenomena, simplified tests were also performed with the model fixed and moored in regular waves of varying steepness. Wave elevation in different points was measured in these tests and compared to the predictions obtained from two different numerical methods: a BEM code that incorporates second order diffraction effects (WAMIT) and a VOF CFD code (ComFLOW), the latter employed for fixed model tests only. Results show that a standard linear analysis may lead to significant errors concerning the air gap evaluation. Extending the BEM model to second order clearly improve the results as the wave-steepness increases. Although the VOF analysis is considerably time-consuming, simulations presented very good agreement to the experimental results, even for the steepest waves tested.
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February 2013
Research-Article
Wave Run-Up and Air Gap Prediction for a Large-Volume Semi-Submersible Platform
Fabio T. Matsumoto,
Rafael A. Watai,
Alexandre N. Simos,
Alexandre N. Simos
e-mail: alesimos@usp.br
TPN (Numerical Offshore Tank),
Department of Naval Architecture and Ocean Engineering,
Av. Prof. Mello Moraes, 2231,
Cidade Universitária,
São Paulo, SP, 05508-900,
TPN (Numerical Offshore Tank),
Department of Naval Architecture and Ocean Engineering,
Escola Politécnica
,University of São Paulo
,Av. Prof. Mello Moraes, 2231,
Cidade Universitária,
São Paulo, SP, 05508-900,
Brazil
Search for other works by this author on:
Marcos D. A. S. Ferreira
Marcos D. A. S. Ferreira
Research and Development Center (CENPES),
Petróleo Brasileiro S.A. (Petrobras),
Rio de Janeiro, RJ,
e-mail: marcos.donato@petrobras.com.br
Petróleo Brasileiro S.A. (Petrobras),
Rio de Janeiro, RJ,
Brazil
e-mail: marcos.donato@petrobras.com.br
Search for other works by this author on:
Fabio T. Matsumoto
e-mail: fabio_matsumoto@tpn.usp.br
Rafael A. Watai
e-mail: rafael.watai@tpn.usp.br
Alexandre N. Simos
e-mail: alesimos@usp.br
TPN (Numerical Offshore Tank),
Department of Naval Architecture and Ocean Engineering,
Av. Prof. Mello Moraes, 2231,
Cidade Universitária,
São Paulo, SP, 05508-900,
TPN (Numerical Offshore Tank),
Department of Naval Architecture and Ocean Engineering,
Escola Politécnica
,University of São Paulo
,Av. Prof. Mello Moraes, 2231,
Cidade Universitária,
São Paulo, SP, 05508-900,
Brazil
Marcos D. A. S. Ferreira
Research and Development Center (CENPES),
Petróleo Brasileiro S.A. (Petrobras),
Rio de Janeiro, RJ,
e-mail: marcos.donato@petrobras.com.br
Petróleo Brasileiro S.A. (Petrobras),
Rio de Janeiro, RJ,
Brazil
e-mail: marcos.donato@petrobras.com.br
Contributed by the Ocean Offshore and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received July 26, 2010; final manuscript received May 11, 2012; published online February 22, 2013. Assoc. Editor: M. H. (Moo-Hyun) Kim. Paper presented at the 29th International Conference on Ocean, Offshore and Arctic Engineering, Shanghai, China, 2010.
J. Offshore Mech. Arct. Eng. Feb 2013, 135(1): 011302 (9 pages)
Published Online: February 22, 2013
Article history
Received:
July 26, 2010
Revision Received:
May 11, 2012
Citation
Matsumoto, F. T., Watai, R. A., Simos, A. N., and Ferreira, M. D. A. S. (February 22, 2013). "Wave Run-Up and Air Gap Prediction for a Large-Volume Semi-Submersible Platform." ASME. J. Offshore Mech. Arct. Eng. February 2013; 135(1): 011302. https://doi.org/10.1115/1.4007380
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