International Journal of Naval Architecture and Ocean Engineering

The Society of Naval Architects of Korea (대한조선학회)
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Effects of nonlinear FK (Froude- Krylov) and hydrostatic restoring forces on arctic-spar motions in waves

  • Jang, HaKun (LSU Center for Computation and Technology) ;
  • Kim, MooHyun (Dept. of Ocean Engineering, Texas A&M University)
  • Received : 2019.06.03
  • Accepted : 2020.01.30
  • Published : 2020.12.31
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Abstract

An Arctic Spar is characterized by its conical shape near the waterline. In this case, the nonlinear effects from its irregular hull shape would be significant if there is either a large amplitude floater motion or steep wave conditions. Therefore, in this paper, the nonlinear effects of an Arctic Spar are numerically investigated by introducing a weakly nonlinear time-domain model that considers the time dependent hydrostatic restoring stiffness and Froude-Krylov forces. Through numerical simulations under multiple regular and irregular wave conditions, the nonlinear behavior of the Arctic Spar is clearly observed, but it is not shown in the linear analysis. In particular, it is found that the nonlinear Froude-Krylov force plays an important role when the wave frequency is close to the heave natural frequency. In addition, the nonlinear hydrostatic restoring stiffness causes the structure's unstable motion at a half of heave natural period.

Keywords

Acknowledgement

This work was partly supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2017R1A5A1014883).

References

  1. Bruun, P.K., et al., 2009. Ice model test of an Arctic SPAR. In: Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions.
  2. Bruun, P.K., et al., 2011. Ice model testing of structures with a downward breaking cone at the waterline JIP: presentation, set-up and objectives. In: ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers.
  3. Cao, Y., et al., 2010. Effects of hydrostatic nonlinearity on motions of floating structures. surge 3 (2), 1.
  4. Chernetsov, V., Karlinsky, S., 2006. Ice-resistant spar-type platform for middle sea depth. In: The Sixteenth International Offshore and Polar Engineering Conference. International Society of Offshore and Polar Engineers.
  5. Dalane, O., et al., 2012. Nonlinear coupled hydrostatics of arctic conical platforms. J. Offshore Mech. Arctic Eng. 134 (2), 021602. https://doi.org/10.1115/1.4004633
  6. Guerinel, M., et al., 2011. Nonlinear Modelling of the Dynamics of a Free Floating Body. EWTEC, Southampton.
  7. Haslum, H., Faltinsen, O., 1999. Alternative shape of spar platforms for use in hostile areas. In: Offshore Technology Conference, Offshore Technology Conference.
  8. Haslum, H.A., 2000. Simplified Methods Applied to Nonlinear Motion of Spar Platforms. NTNU, Doctoral thesis.
  9. He, H., 2004. Hydrodynamics of Thin Plates.
  10. Jang, H., Kim, M., 2019. Mathieu instability of Arctic Spar by nonlinear time-domain simulations. Ocean. Eng. 176, 31-45. https://doi.org/10.1016/j.oceaneng.2019.02.029
  11. Jochmann, P., Evers, K., 2014. Best practice in ice model testing on moored floaters. In: OTC Arctic Technology Conference, Offshore Technology Conference.
  12. Kang, H., Kim, M., 2014. Safety assessment of Caisson transport on a floating dock by frequency-and time-domain calculations. Ocean Systems Engineering 4 (2), 99-115. https://doi.org/10.12989/ose.2014.4.2.099
  13. Kim, M., 2006. CHARM3D User's Manual." Ocean Engineering Program. Civil Engineering Department, Texas A&M University, College Station, TX.
  14. Kim, M., et al., 2005. Vessel/mooring/riser coupled dynamic analysis of a turretmoored FPSO compared with OTRC experiment. Ocean. Eng. 32 (14-15), 1780-1802. https://doi.org/10.1016/j.oceaneng.2004.12.013
  15. Kim, M., et al., 2001. Hull/mooring coupled dynamic analysis of a truss spar in time domain. Int. J. Offshore Polar Eng. 11 (1).
  16. Kumar, N.S., Nallayarasu, S., 2016. Experimental and Numerical Investigation on the Effect of Varying Hull Shape Near the Water Plane on the Mathieu-type Instability of Spar. ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers.
  17. Liapis, S., et al., 2015. "Bigfoot" DVA semi-submersible model tests and comparison with numerical predictions. In: ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers.
  18. Mulk, M.T.U., Falzarano, J., 1994. Complete six-degrees-of-freedom nonlinear ship rolling motion. J. Offshore Mech. Arctic Eng. 116 (4), 191-201. https://doi.org/10.1115/1.2920150
  19. Murray, J., et al., 2009. Model tests on a spar in level ice and ice ridge conditions. In: ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers.
  20. Murray, J., Yang, C., 2009. A comparison of Spar and single column floater in an Arctic environment. In: Offshore Technology Conference (OTC 10953). Houston, TX.
  21. Nallayarasu, S., Kumar, N.S., 2017. Experimental and numerical investigation on hydrodynamic response of buoy form spar under regular waves. Ships Offshore Struct. 12 (1), 19-31. https://doi.org/10.1080/17445302.2015.1099227
  22. Sablok, A., et al., 2011. Disconnectable arctic spar. In: OTC Arctic Technology Conference, Offshore Technology Conference.
  23. Yang, C.K., Kim, M., 2011. The structural safety assessment of a tie-down system on a tension leg platform during hurricane events. Ocean Systems Engineering 1 (4), 263-283. https://doi.org/10.12989/ose.2011.1.4.263

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