Research On Multi-body Coupling Motion Prediction And Control Method Of Semi-submersible Vehicle Towing System

The semi-submersible towing system can resist the sea state and the mutual coupling interference between system components through the fin rudder control of the semi-submersible and the towing body,so this type of towing system has high stability in towing navigation.Compared with the traditional naval towing system,the semi-submersible vessel has a large change in the draft during the switching process of diving or surfacing,and its hydrodynamic performance and rudder efficiency also change with the draft.Based on this,this paper constructs a multi-body coupled motion and control method of towing system integrating towing motion model and intelligent control algorithm,establishes a simplified motion model applicable to semi-submersible vehicles,proposes an expert control-improved S-surface algorithm applicable to nonlinear time-varying load disturbance,and improves the fast selection method of towing system parameters based on NSGA Ⅱ optimization algorithm.The research results and innovations are as follows:1)Since the existing motion model of the vehicle cannot accurately describe the phenomenon of large changes in the draught of the semi-submersible vehicle under the influence of waves and active diving and surfacing,a motion model simplification study was conducted to establish a simplified model for the motion of the semi-submersible vehicle with large changes in the navigation depth by sensitivity analysis and a free liquid correction was made to the model.The results show that the simplified model established in this paper can accurately describe the motion law of the semi-submersible vehicle,the accuracy of the proposed model is verified compared with the test,and the rapid prediction of the motion response of the semi-submersible vehicle is realized.2)To improve the motion stability of the semi-submersible navigator under nonlinear time-varying load disturbance,an improved S-plane control algorithm is proposed,which is combined with the expert intelligent control algorithm to establish a hybrid control algorithm of closed-loop expert control-improved S-plane algorithm,and the control effect of the hybrid algorithm under navigational depth,speed,heading and wave disturbance of the navigator is analyzed,and the prototype model is used to The effectiveness and robustness of the algorithm are verified by the self-sailing test of the prototype model.The results show that the expert control-improved S-surface algorithm can improve the rudder control efficiency,achieve fast convergence in still water,and reduce the mean amplitude of vertical oscillation by 10.4% and18.3%,and the mean amplitude of longitudinal rocking by 67.9% and 60.9% in level 3 and level4 regular waves.3)In order to balance the fixed depth performance and navigation safety of the towing system of the semi-submersible vehicle and realize the rapid design of the towing system,a multi-objective force model is established based on the NSGA Ⅱ algorithm,and the multi-objective optimization study of towing cable and towing body selection is carried out with the objectives of fixed depth,horizontal tension,and vertical tension,and the effects of towing cable density,towing cable diameter,cable length,navigation speed,towing body resistance and towing body lift on the performance of the towing system are analyzed.To study the reaction force range of the towing cable and towing body on the semi-submersible vehicle.The results show that the Pareto front of the towing system based on the NSGA Ⅱ algorithm model can determine the tension range on the semi-submersible vehicle,and realize the fast iteration of the towing body and towing cable selection.4)The multi-body coupled motion control model of a semi-submersible vehicle,towing body motion control model,and towing cable model are combined to construct a multi-body coupled motion control model of a semi-submersible vehicle towing system,and the accuracy of the model is verified by pool test and lake test.Based on the model,the simulation forecasts of towing deployment coupled motion,towing slewing coupled motion,and towing recovery coupled motion under static water and wave disturbance is completed,and the specific nonlinear behavior of the towing system in the rotation process,i.e.,the problem of dropping depth,is analyzed.The results show that the established multi-body coupled motion control model of the semi-submersible towing system has high prediction accuracy and can simulate and forecast the motion of the towing system under the disturbance of nonlinear time-varying loads such as sea state,etc.The proposed methods of increasing the slewing diameter,retracting and releasing the cable,and increasing the speed can effectively improve the problem of towing system slewing depth,and the maximum improvement of the depth can reach more than 70%.