船舶救助艇释放运动建模与仿真

Modeling and simulation of rescue boat's launching from a ship

采用Kane方法建立了救助艇释放运动模型,考虑了救助艇、柔性吊臂、吊索及船舶之间耦合运动;采用集中质量法建立了吊臂模型,根据弹性应变能函数及耗散函数计算了吊臂的内力;将救助艇和船舶之间的碰撞分为压缩和恢复2个阶段,分别根据赫兹接触理论和永久凹坑的接触力模型计算碰撞力;将吊臂模型与基于伯努利-欧拉梁理论的模型对比,稳定状态的吊臂形状基本一致;将救助艇释放运动模型与现有方法对比,进行了横浪条件下救助艇释放仿真试验与救助艇轨迹在水平和竖直方向的误差分析。分析结果表明:在波高为3m,波长为245m时,本文方法的平均绝对误差分别为0.11和0.12m,现有方法的平均绝对误差分别为0.54和0.34m;在波高为2m,波长为60m时,本文方法的平均绝对误差分别为0.09和0.14m,现有方法的平均绝对误差分别为1.72和0.31m;本文方法平均绝对误差均低于现有方法,可见本文方法提高了横浪条件下救助艇释放运动的计算精度;与碰撞试验对比,水平和竖直方向加速度峰值的相对误差分别约为0.5%和60.0%,水平方向加速度的峰值具有较高精确度,可见救助艇释放运动模型可用于辅助分析碰撞试验;根据救助艇释放运动模型,横浪条件下,为避免发生碰撞,4级海况时,救助艇与船舷初始距离最小为2.0倍艇宽,5级海况时,救助艇与船舷初始距离最小为2.5倍艇宽。

The model of rescue boat launching was built by using the Kane's method,and the coupled motion of the rescue boat,flexible boom,sling,and ship was considered.The boom model was constructed by using the lumped mass method,and the internal force of the boom was calculated by the elastic strain energy function and dissipation function.The collision between the rescue boat and the ship was divided into the phases of compression and restitution,and the collision force was calculated according to the Hertz contact theory and the contact force model of permanent indentations separately.The boom model was compared with the model based on the Bernoulli-Euler beam theory,and the boom's profiles were almost the same in a steady state.The model of rescue boat launching was compared with the existing method,and the simulation experiment of rescue boat launching and error analysis of rescue boat trajectories in horizontal and vertical directions were carried out under the cross wave.Analysis results show that at a wave height of 3mand a wavelength of 245m,the average absolute errors of the proposed method are 0.11and 0.12m,respectively,and 0.54and 0.34mwith the existing method.At a wave height of 2mand a wavelength of 60m,the average absolute errors of the proposed method are 0.09 and 0.14m,respectively,and 1.72and 0.31mwith the existing method.The average absolute errors of the proposed method are lower than those of existing method.Thus,the proposed method improves the calculation accuracy of the rescue boat's launching under the cross wave.Compared with the results of the collision experiment,the relative errors of horizontal and vertical acceleration peaks are about 0.5%and 60.0%,respectively,and as the horizontal acceleration peak is highly accurate,the model of rescue boat launching can assist the analysis of the collision experiment.On the basis of the model of rescue boat launching,the minimum initial distance between the rescue boat and the ship's side is 2.0times the width of the boat in sea state 4and 2.5times the width of the boat in sea state 5to avoid collision under the cross wave.4tabs,22figs,27refs.