Ultra-Deepwater Model Testing of a Semisubmersible and Hybrid Verification

Abstract

Model test verification of floater systems in ultra-deep water meets limitations when it comes to available laboratory sizes. Systems in depths beyond 1000–1500 m cannot be tested at reasonable scales without the truncation of the mooring and riser system. The development of methods and procedures to overcome this problem has been addressed through extensive research programs at MARINTEK (VERIDEEP, VERIDEEP Extension, NDP, DEMO2000). This led to a hybrid verification procedure which combines reasonable truncation principles, model tests of the truncated system, and numerical simulations, to estimate the system’s response at full depth. There is, however, still a need to address the actual influence from the truncation procedure, and from the integration with simulations, on the final extrapolated full depth results. This paper presents a case study for the validation of the procedure, that compares full depth model test results of a semisubmersible in water depth 1250m against the extrapolated full depth results obtained from a truncated system of 500m. Results are presented for line tension and vessel responses in 3 seastates. In general the extrapolated full depth results were found to be in good agreement with the full depth model tests. However, the results confirmed expectation that the low frequency response has the greater uncertainties and presents the greatest challenge for the procedure.

Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches

“…SIMO [39] models the rigid body hydrodynamics of the hull while RIFLEX [40] includes the finite element solver, and flexible elements for the mooring lines or tendons, tower, shaft, and blades. The SIMO-RIFLEX simulation tool has been used and validated for various offshore structures [41,42,43,44].…”

Mooring truncation design of a deepwater SPAR

“…But for model tests of deepwater mooring systems, the worldwide ocean basins are not large enough to simulate the whole system in reasonable model scales, and equivalent water depth truncation to mooring lines and risers and the model-the-model method is recognized to be an effective method in this field. Research on truncation design and optimization methods of different platforms has been carried out in recent years, such as Luo and Baudic (2003), Ward (2004), Stansberg (2004), Waals (2004), Baarholm (2006), Kendon (2008), Zhang et al (2006) and Su (2007Su ( , 2008Su ( , 2009. "Trial and error" method, experiential formula and optimization design are common used at present.…”