Response Analysis Of Movable Offshore Platform In Process Of Diving Motion

Movable platform is a novel structure style,platform body has bilayer structure with an upper production module and lower reservoir tank module, production module and oil tank module are quadrilateral structures, upper production module is arranged corresponding processed oil and gas facilities, oil storage tank is connected to the lower module by four trussed leg. Platform enables self-installation,substantial savings in investment costs,it is the best choice for the development of marginal oil fields. But lower oil storage tanks in the decentralization process will be a sudden decrease waterline plane resulting in the case of platform instability, it is necessary to make the platform through the ballast has about 1.4° tilt angle of the bow, when the oil tank dive, production platform between the upper layer and the lower oil storage tank through the surface of the water, ensure waterplane of the platform has always existed,then diving operation,in order to solve the problem of instability leading to the platform. Therefore, the article will show the process of diving the moveable platform to model tests and numerical calculations, which is in the four kinds of typical conditions,analyzing oil storage tanks in the process of movement in response to dive. Details are as follows:Reduced scale tank tests carried out ratio of 1:36 for the movable platform model, first of all, It was rolling and pitching free decay test in calm water, getting key parameters of platforms and other natural period and damping without mooring system. Then, model test was carried out under the condition of white noise irregular waves to get six-degree-of-freedom response amplitude operator (RAO) in different incident angles.The numerical model of movable platform was established in four kinds of working conditions by the hydrodynamic software AQWA, calculating the platform's six-degree-of freedom RAO and natural period in different incident angles based on the damping coefficients obtained by model test. The numerical results were validated by comparing with the model test results.Motion response model test of the movable platform in irregular waves was carried out with horizontal mooring system, the environmental condition of which only considered about the wave condition including five kinds of wave conditions, time-domain simulation conducted in four kinds of working conditions, obtaining the roll, pitch and heave motions of the platform in 0° , 34° and 90° incident angle.AQWA software was applied to simulate the mooring system, calculating the motion responses of the platform , which was in four kinds of working conditions , with the incident angle of 0° , 34°and 90° in irregular wave condition. The working conditions of platform which drafting 11m passed through the waterplane was calculated in 0° , 34° , 90° , 146° and 180° incident angle. Then, when waterplane of platform restored, the time domain simulation was carried out, which verified the stability of the platform.The numerical results were compared with the experimental data, which indicated the accuracy of the choice of damping coefficients, for roll, pitch and heave motion. It verified the movable platform feasibility of decentralized operations with having 1.4° tilt bow , and giving the reasonable proposal.