Nonlinear vibration reliability of hydraulic turbine-generator units with multiple failure modes

Taking the main shaft system of hydraulic turbine-generator unit as an object, the nonlinear dynamic equation is established by the finite element method. Based on the equation, the nonlinear vibration characteristics of the system are analyzed and the excitation frequencies of the system are obtained. Considering the randomness of the structure parameters, material parameters, hydraulic parameters and electromagnetic parameters of system, the gradients of natural frequencies to the random parameters are obtained. According to the criterion that the absolute values of difference between the natural frequencies and excitation frequencies of system should be less than specific values, the failure probability with one single failure mode and the combined failure probability with two failure modes are calculated by dividing the variable space into several simple areas. The nonlinear vibration reliability model of the main shaft system of hydraulic turbine-generator units with correlated failure modes is constructed and the method by which the nonlinear vibration reliability of system with multiple failure modes can be analyzed is proposed. An example is presented and the nonlinear vibration reliability model is proved by the Monte Carlo method. ©2013 Journal of Mechanical Engineering.