Investigation On The Structural Vibration In A Large-scale Underground Powerhouse

With the development of the hydro-electrical enterprise in China, the scale of the hydropower station is increasing and its importance is also becoming more and more significant. In the meantime, the safety issue of the hydropower station has also been drawn more attention. As an important constituent part of the power station, the powerhouse, especially the underground powerhouse of the large-scaled station, induces serious vibration problem, which brings various impairs, even causes danger of the whole station. Therefore, the vibration of the powerhouse has been given a common emphasis.In this study, the vibration of the underground powerhouse of the large-scaled hydropower station was investigated. Taking the Longtan hydropower station as an example, the finite element method was applied to analyze the dynamic characteristics of the powerhouse under different conditions. Based on the comparison and analysis of the studying results, the influencing factors were explored, which provided the gist for the optimization of the vibration design of the underground powerhouse. In addition, eighteen kinds of vibration source from the hydraulic, mechanic and electrical factors were analyzed. According to the analytical results, the resonance was calibrated and a few pieces of suggestion were put forward in the light of the problems occurred during the resonance calibration. Furthermore, by analyzing and computing, several kinds of typical dynamic loads, which were supposed to introduce the cardinal influence on the vibration of the underground powerhouse structure, were determined. The response of the underground powerhouse structure of the Longtan hydropower station was calculated under these typical loading conditions. The main conclusions were drawn as follows:Due to the strong constraints, the natural frequency of the underground powerhouse structure is high and the first s natural frequency is on the middle level. The parallel chain constraint, which is imposed by the sidewall on the concrete structure of the volute layer, plays a relatively small role on the dynamic characteristics of the structure. And the effect of the fluid-solid coupling on the dynamic characteristics of the underground powerhouse structure can be neglected.Among the main factors, which affect the dynamic characteristics of the underground powerhouse of the hydropower station, the constraint of the slab and the Young's modulus of the second-term concrete are most significant. This could be made full use of to optimize the overall dynamic characteristics of the underground powerhouse structure. Additionally, the design of the columns between the slabs is also important.The resonance between the underground powerhouse structure and the centrifugal force which is induced by the poor manufacture of the thrust bushing and the non-uniform potential field in the scroll case should be paid attention, especially when the output of the power station needs to be changed frequently and greatly. Improving the design, manufacture and installation of the power generator and the flow path of scroll case could solve this problem. At the same time, it is better to avoid the operation in the region where strong vibrations are possible to happen. Compared with the dynamic responses computed from the method of simulation static state, the results of the harmonic response analysis is more close to the real condition. When the earthquake force is in the cross-flow horizontal direction, the displacement response of supporting structure is the largest, which is a controlling condition in the analysis of dynamic responses. It was found that the maximum amplitude of supporting structure did not exceed the standard value defined by the norm. It indicates that the stiffness designed satisfies the requirements from the vibration resistance point of view.