Dynamic Responses of Classic Spar Platform: Short Crested Waves vs. Long Crested Waves

Abstract:

The long-crested wave properties have been widely implemented in the design of offshore structures. However, long-crested waves are seldom found in the real sea condition. Many research papers have also stated that wave forces obtained by the waves would be overestimated. Indeed, the real sea conditions are better represented by the short-crested waves. Hence, in order to obtain an optimum design for the offshore structures with cost and time effective, consideration of the short-crested nature of waves is necessary. In this paper, a study comparing the responses of the classic spar due to short-crested waves and long-crested waves obtained experimentally has been performed. The model tests have been carried out in the wave tank of Offshore Laboratory for Universiti Teknologi PETRONAS. In the model tests, short-crested waves and long-crested waves were generated. Responses of the classic spar model were recorded by the Optical Tracking System (OptiTrack). The responses of the classic spar due to short-crested waves and long-crested waves were compared among. From the comparisons, the responses for short-crested waves in all the three degree of freedom (DOF) were found to be about 35% less than the responses for long-crested waves. Thus, it could be concluded that optimized and economical designs can be arrived at by considering the short-crestedness of the waves for classic spar structures.

• Periodical: Applied Mechanics and Materials (Volume 567)
• Pages: 235-240
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.567.235
• Online since: June 2014
• Authors: Cheng Yee Ng, V. John Kurian, Mohd Shahir Liew
• Keywords: Classic Spar, Long-Crested Waves, RAO, Short-Crested Waves, Wave Tank Test

References

[1] H. Mitwally and M. Novak, Wave forces on fixed offshore structures in short-crested seas, J. Eng. Mech, 115, (1989) 636-655.

DOI: 10.1061/(asce)0733-9399(1989)115:3(636)

[2] S.K. Chakrabarti, Hydrodynamic of Offshore Structures., WIT Press, (2001).

[3] C. Colby, N. Sodahl, E. Katla and S. Okkenhaug, Coupling effects for a deepwater spar, OTC, (2000) 1-7.

DOI: 10.4043/12083-ms

[4] Z. Ran, M.H. Kim, J.M. Niedzwecki, R.P. Johnson, Responses of a Spar Platform In Random Waves And Currents (Experiment Vs. Theory), International Journal of Offshore and Polar Engineering, 6, 1, (1996) 27-34.

[5] Z.H. Ran, Coupled dynamic analysis of floating platforms in waves and currents, PhD Dissertation, Texas A&M University, (2000).

[6] J.C. Young, Reliability assessment of foundations for offshore mooring systems under extreme environments, PhD Dissertation, The University of Texas at Austin, (2007).

[7] F.Z. Sun, Analysis of motions of semi-submersible in sea waves, Offshore Technology Conference, (1980) 429-442.

[8] C.J. Garrison, A. Torum, C. Iversen, S. Leivseth and C.C. Ebbesmeyer, Wave forces on large volume platforms - A comparison between theory and model tests, Offshore Technology Conference, (1974) 1061-1070.

DOI: 10.4043/2137-ms

[9] J.G.L. Pijfers and A.W. Brink, Calculate drift forces of two semi-submersible platform types in regular and irregular waves, Offshore Technology Conference, (1977) 155-165.

DOI: 10.4043/2977-ms

[10] S. Zhu, Diffraction of short-crested waves around a circular cylinder, Ocean Engineering, Vol. 20. No. 4, (1993) 389-407.

DOI: 10.1016/0029-8018(93)90003-z

[11] S. Zhu and P. Satravaha, Second-order wave diffraction forces on a vertical circular cylinder due to short-crested waves, Ocean engineering, Vol. 22, No. 2, (1995) 135-189.

DOI: 10.1016/0029-8018(94)00002-6

[12] Y.J. Jian, J.M. Zhan and Q.Y. Zhu, Short-crested wave-current forces around a large vertical circular cylinder, European Journal of Mechanics B/Fluids, Vol 27, (2008) 346-360.

DOI: 10.1016/j.euromechflu.2007.08.001

[13] S. Zhu and G. Moule, Numerical calculation of forces induced by short crested waves on a vertical cylinder with arbitrary cross section, Ocean Engineering, Vol. 21, No. 7, (1994) 645-662.

DOI: 10.1016/0029-8018(94)90043-4

[14] L. Tao, H. Song and S. Chakrabarti, Scaled boundary FEM solution of short-crested wave diffraction by a vertical cylinder, in Computer Methods in Applied Mechanics and Engineering, Vol. 197, Issues 1–4, Pages 232–242, 1 December (2007).

DOI: 10.1016/j.cma.2007.07.025

[15] H. Song and L. Tao, Short-crested wave interaction with a concentric porous cylindrical platform, Applied Ocean Research, Vol. 29, No. 4, p.199–209, November (2007).

DOI: 10.1016/j.apor.2008.01.001

[16] J. Liu and G. Lin, Scaled boundary FEM solution of short-crested wave interaction with a concentric platform with double-layer arc-shaped perforated cylinders , Computers &Fluids, Vol. 79, (2013). 82–104.

DOI: 10.1016/j.compfluid.2013.03.013

[17] J. Liu and G. Lin, Numerical modeling of wave interaction with a concentric cylindrical system with an arc-shaped porous outer cylinder, European Journal of Mechanics / B Fluids, Vol. 37, (2013) 59-71.

DOI: 10.1016/j.euromechflu.2012.07.005