海上吊物六自由度系统动力学特性分析

以海上吊物系统为研究对象,考虑长方体吊物模型六自由度的运动和风载荷,建立广义坐标的第二类拉格朗日方程,并利用高阶的龙格-库塔方法求解该方程。根据牛顿第二定律,推导出吊绳动张力计算公式,对不同吊绳长度、不同起吊速度、不同激励频率时的吊绳摆角、吊物转动角度和动张力进行分析。结果表明,吊绳长度,起吊速度和激励频率的变化均对吊物的摆角和吊绳动张力产生很大影响,吊物的升降对吊绳摆动、吊物转动和吊绳中的动张力有抑制作用,且起升速度越大,对吊物系统的抑制效果越明显,可以通过控制起吊速度和时间来减小吊重的摆动。当激励频率接近于吊物系统特征频率时,会出现共振现象,因此起吊作业中需要选择合适的吊索长度以避开共振区。

Dynamic Analysis of Six-degree-of-freedom Marine Load-lifting System

For the marine load-lifting system, considering six-degree-of-freedom motions and the wind load of the cuboid lifted-load model, the Lagrange equation of the second kind based on generalized coordinates is established. High-order Runge-Kutta method is used to solve the equation. The dynamic tension calculation formula of the lifting wire is deduced based on Newton"s second law. The motion responses and dynamic tensions under different wire lengths, different lifting speeds and different excitation frequencies are analyzed. Results show that all those three factors have great effect on the pendulum angle of the lifted load and on the dynamic tension of the lifting wire. The lifting of the load has an inhibiting effect on the swing of the wire, rotating of the load and dynamic tension of the lifting wire. The higher the lifting speed is, the greater the inhibition effect on the system is. Therefore, the swing of the load can be reduced by controlling the lifting speed and lifting time. When the excitation frequency is close to the characteristic frequency of the lifting system, there will be a resonance phenomenon. That makes it necessary to choose the appropriate length of the lifting wire to avoid the resonance region in the lifting operation.