Study On The Resonance Of The Platform With Moonpool Under The Combined Action Of Wave And Current

Due to the depletion of oil and gas resources on land,people cast light on the ocean.However,the environment of oil and gas development in the ocean is worse than that in the land,and the marine environment is more complex.The oil and gas development platform has to consider more.Under the joint action of ocean wind,wave and current,the risk of the development platform is more dangerous.Therefore,how to build a safe and efficient development platform has become everyone Problems to be solved.With the continuous improvement of operation efficiency and safety requirements of offshore platform with moonpool,the problems of movement of platform with moonpool structure and resonance of fluid movement in the moonpool become more and more serious under the combined action of wave and current.In order to solve this problem effectively,this paper develops a program based on the constant boundary element method of potential flow theory to calculate the interaction between wave current and three-dimensional object,selects an FPSO ship form,and carries out frequency-domain numerical calculation for its motion.The results of wave condition calculation are compared with those of Aqwa calculation to verify the reliability of the program.The results of wave current condition calculation are compared with those of experiment to verify the accuracy of the numerical method.In this paper,it is found that the ship with the moonpool will have resonance phenomenon in the heave and sway motion,especially in the heave motion resonance under different conditions such as the length width ratio of the moonpool,the draft of the moonpool,the incident angle of the wave and the current.With or without the current,the increase of draft will intensify the resonance of heave motion caused by the existence of moonpool and restrain the resonance of shaking motion.The increase of the current also affects the resonance of heave motion,which is related to the angle between the current and wave incidence.Whether there is the current or not,the resonance of heave and sloshing motion is also related to the aspect ratio of the moonpool,which depends on the effective length of the moonpool in the direction of wave current.It is found that the incidence angle of wave has a great influence on the heave motion,and the resonance amplitude of the wave is small.Considering the current situation,the existence of the current will aggravate the resonance of the ship and the moonpool,and modulate the resonance frequency of the moonpool.The resonance amplitude of the first-order and second-order heave motion of the ship caused by the movement of the liquid piston in the moonpool is generally increased(only in the case of shallow draft,the resonance frequency of the ship itself will absorb the first-order resonance energy caused by the moonpool and highlight);at the same time,the longitudinal resonance amplitude of the ship caused by the sloshing motion of the liquid in the moonpool is increased.