摘要
随着我国水电事业的蓬勃发展，水电站的规模越来越大，重要性越来越突出，其安全问题也越来越为人们所关注。水电站厂房，特别是大型水电站地下厂房，作为水电站的重要组成部分，它的振动会带来种种危害，甚至危及整个水电站的安全，这就使得水电站厂房的振动问题受到了普遍重视。
本文结合龙滩水电站实际工程，对大型水电站地下厂房结构的振动问题进行了计算研究。用有限元法计算分析了龙滩水电站地下厂房在各种不同情况下的动力特性；通过对比分析，深入研究了各个因素对水电站地下厂房动力特性的影响，为优化抗振设计提供了依据；对龙滩水电站地下厂房由水力、机械和电气三方面原因引起的18种振源进行了分析，根据分析结果进行了共振校核，并针对共振校核中出现的问题，提出了几点建议；通过分析和计算，确定了几种对水电站地下厂房振动产生重要影响的典型动荷载，并计算出了龙滩水电站地下厂房结构在这几种典型动荷载作用下的动力响应值。得出了如下主要结论：
（1）水电站地下厂房由于约束作用强，自振频率较高，第一阶自振频率属中频；厂房上下游边墙围岩对蜗壳层混凝土结构的水平链杆约束对结构动力特性影响较小；流固耦合作用对水电站地下厂房动力特性的影响甚微，可以不予考虑。
（2）水电站地下厂房动力特性的几个主要影响因素中，楼板的约束条件和二期混凝土弹模影响较大，在抗振设计中可以充分利用这一点来对地下厂房结构的整体动力特性进行有效优化；楼板间设柱也非常重要。
（3）水电站地下厂房容易与由推力瓦制造不良引起的激振力和由蜗壳不均匀流场引起的激振力发生共振，尤其是当机组出力需要经常大幅度变化时，更要引起注意。对此，需要从水轮发电机和蜗壳流道的设计、制造、安装等方面加以解决，同时，也应尽量避免在某些可能产生强烈振动的负荷区运行。
（4）拟静力法计算水电站地下厂房动力响应结果偏大，谐响应分析结果更接近实际情况；当地震作用力方向为横流向时，机墩处地震位移响应最大，是动力响应分析中的一个控制工况；龙滩水电站地下厂房动力响应分析结果显示其机墩处的最大振幅没有超过规范规定的值，从抗振的角度判断，设计刚度满足要求。
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.
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