Research On Modeling Of Ship Lifeboat Water Entry

Ship lifeboat is the main life-saving equipment used to escape from ship in distress and an important line of defense for human life safety at sea.The lifeboat should be drilled regularly on board.Whether ship in distress or life-saving drill,there are safety risks in the use of lifeboat.Therefore,it is necessary to strengthen the theoretical research on lifeboat motion and provide scientific guidance and suggestions for navigation practice.For the free-fall lifeboat and the totally enclosed lifeboat,this thesis has a research on model about lifeboats’ launch and the motion of lifeboats’ self-propulsion,towing life raft,and drifting after water entry.On this basis,the ship life-saving simulation training system is developed.The main work is as follows:For the launch of the free-fall lifeboat,it is divided into two phases: the motion on the skid and the water entry,which are modeled by using Kane’s method.The expressions of velocity,acceleration,generalized velocity,and partial velocity of rigid body and its any point in moving and fixed coordinate systems are given.During the motion on the skid,in order to consider the effect of ship motion on the boat,according to the actual structure of the boat and the skid,the edges of lifeboat are separated into panels,and the tangential and normal contact forces between the lifeboat and the skid are calculated according to the Coulomb friction model and the L-N model.Using the separate model theory,the mathematical model with the six-degree-of-freedom of the ship motion is established and written in the form of Kane’s equation.During the water entry,the fluid force is calculated according to the strip theory.Considering flow separation and asymmetric water entry,the slamming force of lifeboat is calculated by Wagner model and virtual object surface method.Through comparison with model experiments and numerical methods,the accuracy of the model in this thesis is verified.For the launch of the totally enclosed lifeboat,the Kane’s method is used to establish a multi-body dynamic model for the lifeboat system,accounting for the coupled motion among lifeboat slings,a cable-pulley system,the lifeboat,and the ship.Based on Kane’s method,the lumped mass method is adopted to model the slings,and the tension and damping are calculated based on the linear spring damping model.For the cable-pulley system,a dynamic model based on super element is proposed.The length of the rope passing through the pulleys and the displacement of the pulleys are taken as state variables.The linear spring model is used to calculate the tension of each section of the rope,and the tension of the rope is acted on the pulleys to consider the coupling between the rope and the pulleys.For the collision between the boat and the ship,the anti-collision device of the boat is divided into points,and the side of the ship is approximated to a plane.The Hertz contact theory and the contact force model with permanent indentation are separately used to calculate the contact force for the compression phase and restitution phase.Energy loss is characterized by permanent indentation.The accuracy of the model is verified by comparing with the model experiments.After the lifeboat is launched,dynamic models for the lifeboat self-propulsion and towing life raft are established based on the Kane’s method.The wave force on the lifeboat and life raft are calculated according to the Morison equation.The lumped mass method is used to model the towline.In order to consider the effect of the second-order wave on the towline,its inertia force is calculated according to the its added mass and the inertia of the fluid.For the lifeboat drift predicting,a differential equation for the drift of the lifeboat is constructed.The prediction-correction method is used to solve the differential equation,and the objective function is constructed.In order to consider the uncertainty of marine environment,the constraint condition is obtained by setting the range of environmental parameters.The nonlinear programming is used to solve the range of the lifeboat position.According to motion model of the lifeboat self-propulsion,the setback of the lifeboat at different initial positions on the wave surface is analyzed,and it is concluded that the best landing point of the totally enclosed is near the wave crest.For the model of lifeboat towing life raft,it improves the accuracy of the prediction of the peak tension of the towline by comparing with an existing method and the experimental data.The peak tension of the towline in heading wave is significantly smaller than that in the following wave through simulation analysis.When the difference between the towing line’s length and the wavelength is less than 15%,the peak tension is significantly reduced.For the drift predicting model,the predicted position area can cover the drift trajectory,which verifies the validity of the model.On the basis of the above research,for the actual needs of ship life-saving training,this thesis develops a simulation training system.In order to meet the requirements of actual operation,a collaborative training scheme is designed for team training,including: system network architecture,cooperative work mode,and interaction management.A matrix-based interaction management model is proposed to solve the problems among users,roles,and serial and parallel interactions.The geometric models of the life-saving equipment and the virtual sea scene are established by using three-dimensional modeling technology.The algorithms are integrated into the system to realize three-dimensional virtual interaction with good effect.