Hydrodynamic Study and Performance Analysis of the OC4-DeepCWind Platform by CFD Method

Abstract

(1) The RAOs of OC4-DeepCWind platform motions are more sensitive to the low-frequency wave than the high-frequency wave. The nonlinear motion responses for platform heave and pitch motions are comparatively remarkable. (2) The pitch motion of OC4-DeepCWind platform is much more apparently influenced by the height of center of gravity (COG) than surge and heave motions. The lower COG height within a suitable range leads to a smaller fluctuation amplitude of platform pitch motion in waves. (3) A large horizontal displacement abruptly occurs to the OC4-DeepCWind platform when one mooring line is failure. The risk of failure for the other mooring lines significantly increases. To better understand the hydrodynamic performance of a floating support platform in various wave environments, a two-phase CFD solver naoe-FOAM-SJTU based on the open source CFD toolbox OpenFOAM is applied to investigate the hydrodynamic characteristics and motion performance of the OC4-DeepCWind platform. Moreover, the restoring force and moment of mooring lines are simulated using the solver in time domain. The studies of grid sensitivity and time step refinement are first conducted to determine an appropriate time step and mesh size. Then hydrodynamic responses of the floater in free-decay tests are analyzed and compared with experimental data, and the motion performance of the platform in regular waves with different parameters is also investigated. In addition, the platform motion responses with one mooring line broken and different heights of center of gravity are explored. It is shown that simulation results have good agreement with published data, and several conclusions can be drawn through the study. The RAOs of platform motions are found to be more sensitive to the low-frequency wave than the high-frequency wave. Nonlinear motion responses are comparatively remarkable in platform heave and pitch motions. Besides, the lower height of center of gravity within a suitable range is benefit to the stability of floating platform. Survival condition with broken mooring line should be paid enough attention to avoid the failure of other mooring lines.