Ocean Systems Engineering

Techno-Press (테크노프레스)
권호 표지
DOI QR코드

DOI QR Code

Nonlinear response of stiffened triceratops under impact and non-impact waves

  • Received : 2017.05.28
  • Accepted : 2017.08.26
  • Published : 2017.09.25
⟨ Previous Next ⟩

Abstract

Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.

Keywords

References

  1. Capanoglu, C.C., Shaver, C.B, Hirayama, H. and Sao, K. (2002), "Comparison of model test results and analytical motion analyses for a buoyant leg structure", Proceedings of the 12th Int. Offshore and Polar Eng. Conf., May 25-31, Kitakyushu, Japan.
  2. Chandrasekaran, S., Bhaskar, K. and Hashim, M. (2010a), "Experimental study on dynamic response behavior of multi-legged articulated tower", Proceedings of the 29th Int. Conf. on Ocean, Offshore and Arctic Engg, 6-11th June, Shanghai, China.
  3. Chandrasekaran, S., Chandak, N.R. and Gupta, A. (2006), "Stability analysis of TLP tethers", Ocean Eng., 33(3), 471-482. https://doi.org/10.1016/j.oceaneng.2005.04.015
  4. Chandrasekaran, S., Gaurav, G., Giorgio, S. and Salvatore, M. (2011), "Springing and ringing response of Triangular TLPs", Int. Shipbuild. Progress, 58(2-3), 141-163.
  5. Chandrasekaran, S., Gaurav and Jain, A.K. (2010b), "Ringing response of offshore compliant structures", Int. J. Ocean Climate Syst., 1(3-4), 133-144. https://doi.org/10.1260/1759-3131.1.3-4.133
  6. Chandrasekaran, S., Jain, A.K. and Madhuri, S. (2013), "Aerodynamic response of offshore triceratops", Ships Offshore Struct., 8(2), 123-140. https://doi.org/10.1080/17445302.2012.691271
  7. Chandrasekaran, S. and Jain, A.K. (2016), Ocean structures: Construction, Materials and Operations, CRC Press, Florida, ISBN: 978-14-987-9742-9.
  8. Chandrasekaran, S and Nannaware, M. (2013), "Response analyses of offshore triceratops to seismic activities", Ships Offshore Struct., 9(6), 633-642. https://doi.org/10.1080/17445302.2013.843816
  9. Chandrasekaran, S., Madhuri, S., Jain, A.K. and Gaurav. (2010c), "Dynamic response of offshore triceratops under environmental loads", Proceedings of the Int. Conf. of Marine Tech., 11-12 Dec, Dhaka, Bangladesh.
  10. Chandrasekaran, S. and Madhuri, S. (2012a), "Free vibration response of offshore triceratops: Experimental and analytical investigations", Proceedings of the 3rd Asian Conf. on Mech. of Functional Materials and Structures (ACFMS), 8-9 Dec, Delhi.
  11. Chandrasekaran, S. and Madhuri, S. (2012b), "Stability studies on offshore triceratops", Proc. Int. Conf. Tech. of Sea, Indian Maritime University, Vishakapatnam, 1(10), 398-404.
  12. Chandrasekaran, S. and Madhuri, S. (2015), "Dynamic response of offshore triceratops: Numerical and Experimental investigations", Ocean Eng., 109(15), 401-409. https://doi.org/10.1016/j.oceaneng.2015.09.042
  13. Chandrasekaran, S. and Madhuri, S. (2012), "Stability studies on offshore triceratops", Int. J. Res. Development, 1(10), 398-404.
  14. Chandrasekaran, S. and Mayank, S. (2017), "Dynamic analyses of stiffened triceratops under regular waves: experimental investigations", Ships Offshore Struct., 12(5), 697-705. https://doi.org/10.1080/17445302.2016.1200957
  15. Chandrasekaran, S. (2016), Offshore structural engineering: Reliability and Risk Assessment, CRC Press, Florida, ISBN: 978-14-987-6519-0.
  16. Chandrasekaran, S. (2015a), Advanced Marine structures, CRC Press, Florida, ISBN 9781498739689.
  17. Chandrasekaran, S. (2014), Advanced Theory on Offshore Plant FEED Engineering, Changwon National University Press, Republic of South Korea, pp. 237, ISBN:978-89-969792-8-9.
  18. Chandrasekaran, S. (2015b), Dynamic analysis and design of ocean structures, Springer, INDIA, ISBN: 978-81-322-2276-7.
  19. Halkyard, J.E., Paulling, J.R., Davies, R.L. and Glanville, R.S. (1991), "Tension buoyant tower: A design for deep water", Proceedings of the Offshore Tech. Conf., May 6-9, Houston, TX.
  20. Isherwood, R.M. (1987), "A revised parameterization of the JONSWAP spectrum", Tech. Note, Appl. Ocean Res., 9(1), 47-50. https://doi.org/10.1016/0141-1187(87)90030-7
  21. Jeffreys, E.R. and Rainey, R.C. (1994), "Slender body models of TLP and GBS ringing", Proceedings of the Int. Conf. on Behaviour of Offshore Struc., Massachusetts, USA.
  22. Kim, C.H., Randall, R.E., Boo, S.Y. and Krafft, M.J. (1992), "Kinematics of 2-D transient water waves using laser Doppler anemometry", J. Waterw. Port, C -ASCE., 118(2), 147-165. https://doi.org/10.1061/(ASCE)0733-950X(1992)118:2(147)
  23. Kim, C.H., Xu, Y. and Zou, J. (1998), "Impact and nonimpact on vertical truncated cylinder due to strong and weak asymmetric wave", Oceanographic Lit. Rev., 1(45), 174.
  24. Kim, C.H., Xu, Y. and Zou, J. (1997), "Impact and nonimpact on vertical truncated cylinder due to strong and weak asymmetric waves", Int. J. Offshore Polar., 7(3).
  25. Kim, C.H. (2009), "Nonlinear response of offshore structures to high seas", Int. J. Offshore Polar., 19(1), 1-7.
  26. Longuet-Higgins, M.S. and Cokelet, E.D. (1976), "The deformation of steep surface waves on water: Numerical method of computation", P. Roy. Soc. London A: Math. Phy., The Royal Society, 1-26.
  27. Murert, J., Flugstad, P., Greiner, B., D'Souza, R. and Solber, I.C. (1996), "The three-column TLP: A cost efficient deepwater production and drilling platform", Proceedings of the Offshore Tech. Conf., 6-9 May, Houston, Texas.
  28. Myrhaug, D. and Kjeldsen, S.P. (1984), "Parametric modelling of joint probability density distributions for steepness and asymmetry in deep water waves", App. Ocean Res., 6(4), 207-220. https://doi.org/10.1016/0141-1187(84)90059-2
  29. Price, W.G. and Bishop, R.E.D. (1974), "Probabilistic theory of ship dynamics", Halsted Press.
  30. Shaver, C.B., Capanoglu, C.C. and Serrahn, C.S. (2001), "Buoyant leg structure: Preliminary design, constructed cost and model test results", Proceedings of the 11th Int. Offshore and Polar Engg. Conf., 17-22 June, Stavenger, Norway.
  31. Tromans, P., Swan, C. and Masterton, S. (2006), "Nonlinear potential flow forcing ringing of concrete gravity based structures", Health and Safety Executive, United Kingdom, HSE Report, pp. 468.
  32. Tucker, M.J., Challenor, P.G. and Carter, D.J.T. (1984), "Numerical simulation of a random sea: a common error and its effect upon wave group statistics", App. Ocean Res., 6(2), 118-122. https://doi.org/10.1016/0141-1187(84)90050-6
  33. White, C.N., Copple, R.W. and Capanoglu, C. (2005), "Triceratops: An effective platform for developing oil and gas fields in deep and ultra deep water", Proceedings of the 15th Int. Offshore and Polar Engg. Conf., June 19-24, Busan, South Korea.
  34. Zou, J. and Kim, C.H. (2000), "Generation of strongly asymmetric wave in random seaway", Proceedings of the 10th Int. Offshore and Polar Engg. Conf., May 28 - June 2, Seattle, USA.

Cited by

  1. Aerodynamic behaviour of double hinged articulated loading platforms vol.11, pp.1, 2021, https://doi.org/10.12989/ose.2021.11.1.017
  2. Aerodynamic and hydrodynamic force simulation for the dynamics of double-pendulum articulated offshore tower vol.32, pp.4, 2021, https://doi.org/10.12989/was.2021.32.4.341
  3. Aerodynamic and hydrodynamic force simulation for the dynamics of double-hinged articulated offshore tower vol.33, pp.2, 2017, https://doi.org/10.12989/was.2021.33.2.141