4岛式半潜船的振动特性分析

Analysis of Vibration Characteristics of 4-Island Semi-Submersible Vessel

4岛式半潜船的上层建筑处于边岛位置,结构瘦长且重心较高,虽提高了主甲板载货的空间利用率,但同时降低了上层建筑横向的刚度,在风浪及船上大型机械设备的激励下,易发生较大的横向振动,振动耦合性较强,影响上层建筑生活区的安全性和舒适性。对此,需在早期设计阶段对4岛式半潜船进行有限元分析。利用有限元方法,建立4岛式半潜船的三维数值模型,分析其振动的固有频率及模态,计算航行工况及定位工况下整船的速度响应,并优化上层建筑底部的强肘板。结果显示:4岛式半潜船振动的前6阶固有频率均可避开螺旋桨激励正常工况下的风险频率范围;在航行工况和定位工况下,上层建筑各甲板的速度加权值均符合船舶舒适性相关要求的标准限值;当加强上层建筑底部的肘板后,上层建筑各甲板横向的速度响应峰值可显著下降50%~60%,减振效果良好。为准确预报、优化4岛式半潜船的振动特性提供借鉴。

The superstructure of 4-island semi-submersible vessel is at the side of the island with slender structure and high center of gravity which improves the space utilization of main deck,but also reduces the lateral stiffness of the superstructure.Under the excitation of wind and waves and large mechanical equipment on board,large transverse vibration is easy to occur,and the vibration coupling is strong which will affect the safety and comfort of the living area of superstructure.Aiming at it,it is necessary to carry out the finite element analysis of the 4-island semi-submersible vessel in the early design stage.The three-dimensional numerical model of the 4-island semi-submersible vessel is established by using the finite element method,and the natural frequencies and modes of its vibration are analyzed.The velocity response of the whole vessel under sailing and DP conditions are calculated.The strong bracket at the bottom of the superstructure is optimized.The results show that the first six natural frequencies of the 4-island semi-submersible vessel can avoid the risk frequency range of propeller excitation under normal operating conditions.Under the sailing condition and the DP condition,the speed weighted values of each deck of the superstructure are all in line with the standard limit of ship comfort.When the bracket are strengthened,the velocity response of each deck of the superstructure can be significantly reduced by 50%~60%which indicates that the vibration reduction effect is good. It provides reference for the accurate prediction and optimization of the vibration characteristics of the 4-island semisubmersible vessel 。