Research on Reliability Probability of SRSS Method for Multi-Point Displacement of Foundation of H-Class Gas Turbine in High Position

[Introduction] The foundation of a large H-class gas turbine usually has multiple disturbing forces, and the vibration displacement of the mass points is obtained by the square root of the sum of the squares (SRSS) method, but the vibration displacement obtained by the SRSS method is not the maximum possible displacement. The research aims to analyze all possible vibration displacements and study the reliability probability of the SRSS method. [Method] A three-dimensional finite element model was established for the foundation of a H-class gas turbine in high position, the unidirectional disturbing forces separately applied on mass points were analyzed, and the vibration displacement of the mass points was calculated by the SRSS method. It was proposed to apply the bidirectional disturbing forces on the mass points separately. Considering the uncertainty of angle between the disturbing forces at the mass points, the linear superposition method was used to calculate all possible vibration displacements and analyze their statistical probability distribution. [Result] The combined value of the lateral vibration displacement of mass point 10 of the H-class gas turbine at 40.75 Hz by the SRSS method is 16.40 μm, and the maximum possible lateral vibration displacement value is 24.18 μm. The reliability probability of the SRSS method is about 50%. [Conclusion] The multi-point vibration displacement value obtained based on the SRSS method is not the maximum value, and the method has a certain reliability probability. For particularly sensitive or important dynamic foundation analysis, the reliability probability of the method should be controlled, and it can be improved by increasing the margin.