Effect of wave spreading including multi-directional wave interaction on the responses of a spar platform
- 16 Downloads
This paper deals with the effect of directionality of waves on the responses of a spar-type floating offshore platform. Here, a spar-type offshore platform restrained by four catenary mooring cables is modelled as per the work done by Chen et al. (Ocean Eng 28:863–887, 2001). The numerical model and numerical simulation have been validated by comparing the results (natural periods, RAOs and statistics of response) available in the literature (Steen et al. in Offshore Technology Conference 2004; Wangz et al. in J Mar Sci Appl 8:168–174, 2010). The multi-directional sea spectrum is represented by the product of a cosine power spreading function and a uni-directional JONSWAP wave spectrum. The Quadratic Transfer Functions have been generated for the calculation of drift loads, taking into account the multi-directional wave interaction. The responses of the platform have been obtained under long-crested (uni-directional) and short-crested (multi-directional) sea states and the results thus obtained are compared. Further, the variations in responses due to change in power of spreading function and total spreading angle are also investigated. It is found that due to the multi-directional wave interaction, the second order drift loads assume higher values in all degrees of freedom. Subsequently, in short-crested seas, the structure exhibits higher responses in all degrees of freedom when multi-directional wave interaction is considered. This highlights the need for incorporation of the multi-directional wave interaction while modelling short-crested seas for a realistic assessment of response behaviour of the system.
KeywordsMulti-directional wave Spar platform Coupled dynamics Spreading function Drift force
This work is supported by National Institute of Technology, Durgapur [Grant Number NITD/Regis/OR/25].
- 2.ANSYS AQWA, AQWA User’s Manual Release 17.0 (ANSYS Inc., Canonsburg, 2016)Google Scholar
- 4.L.E. Borgman, Directional Spectra Models for Design Use. in Offshore Technology Conference. Houstan, TX, OTC 1069) (1969)Google Scholar
- 6.O.M. Faltinsen, Sea Loads on Ships and Offshore Structures (Cambridge University Press, Cambridge, 1990)Google Scholar
- 8.H. Gupta, L. Finn, T. Weaver, Effects of Spar Coupled Analysis. in Offshore Technology Conference. Houstan, TX, OTC 12082 (2000)Google Scholar
- 12.V.J. Kurian, C.Y. Ng, M.S. Liew, Effect of Short-Crested Waves on the Dynamic Responses of Truss Spar Platforms. 23rd edn. in Offshore and Polar Engineering Conference. (2013)Google Scholar
- 13.M.S. Longuet-Higgins, D.E. Cartwright, N.D. Smith, Observations of the directional spectrum of sea waves using the motions of a floating buoy. Ocean Wave Spectra. (Prentice Hall, 1963), pp. 111–136Google Scholar
- 18.A. Steen, M.H. Kim, M. Irani, Prediction of SPAR responses: model tests vs. analysis. in Offshore Technology Conference. Houston, OTC-16583, (2004)Google Scholar
- 19.O.J. Waals, The effect of wave directionality on low frequency motions and mooring forces. in Proceedings of the 28th International Conference on Ocean, Offshore and Arctic Engineering. Honolulu, Hawaii (2009)Google Scholar