基于复合建模方法的轴系扭转振动特性及仿真

为了提高主机轴系计算准确度，本文提出了一种新型的主机轴系建模方法，该方法将主机轴系分为连续子系统和离散子系统。推进轴段如螺旋桨轴、中间轴、螺旋桨及法兰划分为连续子系统，柴油机曲轴端划分为离散子系统。分别应用波分析法和多自由度动力特性分析，得到连续子系统和离散子系统的控制方程，同时通过边界条件将两个子系统动态刚度矩阵连接，推导出全局控制方程。对某型主机轴系扭转振动计算进行了仿真分析，并与传统建模方法比较。从计算结果可知，在高阶模态上，新型建模方法计算更精确，更接近真实振动状态，同时在保证相同计算精度的情况下，新型建模计算方法计算时间和计算资源占用较少，相对更为简便。同时，新型建模方法克服了当模态节点集中于轴段时，传统建模方法由于将轴系等效为一至两个质量单元而引起的节点偏移所带来的误差，这在实际主机轴系计算特别是长推进轴和刚度较低的轴系中具有重要意义。

Torsional Vibration Calculation Based on a Combined Modelling Method

In order to improve torsional vibration calculation (TVC), a combined modelling method is put out in this paper, which separates the ship propulsion system into discrete and continuous subsystem. The discrete subsystem refers to the diesel engine part of the actual ship, while the continuous one represents the shafts, propeller and flanges. Wave analysis and Multi-DOF dynamic analysis approach are used respectively in continuous and discrete subsystem to deduce the dynamic equation, and a global governing equation is obtained by combining the two subsystems through boundary conditions. To validate the effectiveness of the combined modelling method, numerical computations with different modelling methods are carried out on a propulsion shafting system of an engineering ship. It can be seen from the comparison of results that the combined method is more accurate to the modal vibration, with less time and computation resources especially in high frequencies. Moreover, the method put out in this paper can largely reduce the error caused by the node offset when dispersing the shaft into only one or two mass elements by using traditional method. This is helpful for accurate vibration calculation of propulsion shafting system with large length and low stiffness.