Multi-Objective Optimization Of Semi-Submersible Platforms Based On Surrogate Models

In the initial design stage of semi-submersible platform,the main particulars of platform is the key factor affecting the hydrodynamic performance and construction cost.Therefore,multi-objective optimization of the main particulars of semi-submersible platform is of great engineering significance.The semi-submersible floating production unit(SEMI FPU),heave and vortex induced motion suppressed semisubmersible(HVS)and semi-submersible floating drilling unit(SEMI FDU)are selected as the case studies.Firstly,the design variables of each platform and sample database are determined by design of experiments(DOE).Secondly,the hydrodynamic performances of three types of semi-submersible platforms are analyzed by using panel method and Morison's equation.Through the response amplitude operator(RAO)and wave spectrum,the most probable maximum value(MPM)can be obtained.It can be used as an important measure of platform security.The distribution of probes for estimating the wave elevations on the calm water surface are arranged,and the airgap can be computed.Based on the database obtained by numerical simulation,surrogate models based on radial basis function(RBF)are established to improve the computing efficiency.Finally,multi-objective particle swarm optimization(MOPSO)is employed to search for the Pareto-optimal solutions.The safety and economy of offshore platforms are taken as two optimization objectives,and the platform stability,airgap and horizontal motion performance are taken as constraints.The optimization results of semi-submersible platforms can be obtained.Through the detailed analyses of optimization results,the most efficient design strategies for semi-submersible platforms are discussed and proposed.