| China has abundant water resource,water resource has broad prospects for development because of its zero pollution and renewable characteristic,while Hydropower Station takes many tasks such as power generation,flood control,irrigation,shipping.With the crew manufacturing technology skilled,the installed capacity of the unit turns towards the development of high-capacity high-parameter,structural size and running head of hydropower station also increases,accordingly,the vibration of the unit and induced vibration of hydropower station are inevitable.The pier as a support structure of hydropower house must meet requirements of the safety and stability.Taking a practical engineering as a example,in order to study that the simplified method of the dynamic calculation of the cylinder pier has effect on the dynamic characteristics of the pier in the design code of the hydropower house,then the finite element model and method are compared.The specific contents and results of this paper are as follows:1.Firstly,based on structural dynamic theory,the dynamic formula of the cylindrical pier is deduced,the basic assumptions and model simplification are summarized.The results demonstrate that,the dynamic calculation formula of the pier does not take into account the characteristics of the pier’ mass with height distribution;the spatial effect of the structure and local structures around the pier are not considered while the pier is simplified into a single degree of freedom;the range of model is only from the installation elevation to the top of the pier,without considering the elastic effect of the lower structure and the foundation;loads are applied in accordance with the central concentrated force,without considering the directionality and nonuniformity of the load distribution;the amplitude of the normative method represents only the overall displacement of the center,without considering spatial characteristics of deformation and nonuniformity of the deformation,and so on.2.Finite element method is used to analyze the influence of each factor on the dynamic characteristics of the pier from aspects of spatial characteristic,the range of model.The results show that: the spatial characteristics of structure have great influence on the dynamic characteristics of the pier,compared with the pier,the spatial characteristic of the volute roof has a greater effect on the vertical natural frequency.The local structures around the pier have an effect on the natural frequency of the structure,however,the degree of influence is quite different;the ventilation barrel of generator,the floor and the side wall have no influence on the amplitude of the pier,volute and tail pipe have a great influence on the amplitude of the pier.The increase of surrounding rock simulation range has no influence on natural frequency and horizontal amplitude of the pier,the vertical amplitude of the pier increase slightly.In general,when the range of surrounding rock is taken to 3L,it can meet the calculation accuracy requirement.3.The influence of factors on the dynamic characteristics of the pier is analyzed from three aspects of load frequency,application methods of load,selection methods of displacement.The results show that,the amplitude of the pier varies under different excitation frequency,the middle frequency is the key point in the research of the dynamic analysis of the pier.The application methods of radial dynamic load have different influence on the horizontal amplitude of the pier,the basic order of amplitude: uniform application,rod unit arm,beam unit arm,own characteristics,according to actual situation,it is more reasonable to simulate the frame arm in order to transfer forces.The selection methods of displacement have a great influence on the amplitude of the pier,the trend of displacement is basically same by choosing the maximum of base plate and node as amplitude,considering the deformation characteristics of structure,it is relatively reasonable to use the average value of the pier foundation as representative value of the amplitude. |
