Updating Turbine Blade FE Model Considering the Modal Parameters Scatter

The paper considers an issue of updating a turbine blade finite element model. The turbine blade is fixed in the special rig and the unknown contact conditions strongly influences on the blade dynamics. Hence, there is a difference between the real blade dynamic characteristics and the results of the finite element simulation. The task is to update the blade FE model on the basis of the modal test data to obtain fine dynamic model of the structure. The experimental modal parameters are known with some scatter, which is the result of measurement errors, and some differences from blade to blade within the kit of parts.The proposed algorithm is capable to update the turbine blade finite element model by variation of elasticity modulus in contact areas taking into account the experimental modal parameters scatter. It is worth noting that elasticity modulus of finite elements near the contact area should be considered as unknown contact stiffness parameters.The stochastic updating algorithm based on the sensitivity analysis is proposed. The paper presents equations to define sensitivity coefficients and provides the special recurrence relations, on which the proposed algorithm is based. The eigenvalue problem is resolved repeatedly with system parameters changing during the algorithm implementation. The system parameters (elasticity modulus in the contact areas) are recalculated according to the recurrence relations, mentioned above. To implement the proposed algorithm, a special software in C++ language has been developed.The proposed algorithm has demonstrated its efficiency for updating the finite element model of the complex structure. Thus, the differences between the calculated eigenfrequencies and those of identified from modal testing have been reduced from 13% to 3%. The updated model of the turbine blade could be used for accurate simulation of the blade dynamic behavior under different operating conditions.