导轴承刚度对水轮机轴系自振特性的影响

Influence of bearing rigidity on characterisitics of natural vibration of shaft system in hydro-turbine generating unit

为研究水轮发电机组轴系横向自振特性,采用有限元方法对轴系进行离散,利用能量法获得运动方程,根据简化的实际机组轴系参数,采用Matlab软件计算机组轴系各阶的固有频率、主振型以及临界转速,分析导轴承刚度系数的变化对机组轴系临界转速和主振型的影响.计算结果表明:当仅改变其中1个导轴承刚度时,上导轴承对机组临界转速几乎没有影响,下导和水导轴承对临界转速的影响较大.当导轴承刚度达到一定值时,临界转速不再随其增大而增大,出现"饱和"现象;而同时增加3个导轴承的刚度,机组轴系的临界转速有较大的增大.上导轴承的改变对前三阶振型几乎没有影响,下导和水导轴承的改变会导致某一阶的振型与原振型相反.工程中估算机组临界转速时需充分考虑导轴承刚度对机组的影响.

To study the characteristics of the lateral natural vibration of the main shaft system in hydro-turbine generating unit,with the finite element method the main shaft system was discretized;and with energy method the dynamic equation was obtained.Based on simplified actual parameters,with MATLAB software,fixed frequencies,mode shapes and critical speed of rotation of the shaft system were calculated and influences on critical speed caused by changes in the guide bearing rigidity were analyzed.The results show that when only one guide-bearing rigidity is changed,up guide-bearing has little influence on critical speed;however,the down bearing and the water guide-bearing greatly affect the critical speed.There occurs a ＂saturated＂ phenomenon,that is to say,the critical speed remains unchanged when the rigidity reaches or exceeds a certain value.If the rigidity of the three guide-bearings is increasing simultaneously,the critical speed can be increased significantly.Change in the up guide-bearing has little effect on the modes in the first three orders;Change in the down guide-bearing and water guide-bearing will result in an opposite mode in a certain mode.It can be concluded that it is necessary to fully consider the effect caused by the guide-bearing rigidity in evaluating the critical speed of the shaft system.