| The vibration generated during the operation of the hydropower house is a key factor affecting its safety,and the relative position of the structural stiffness center and the mass center is the decisive condition that affects the intensity of the torsional effect during the vibration process.In order to study the influence of the eccentric distance between the structural stiffness center and the mass center(rigid-mass eccentricity)on the vibration of the hydropower plant during flood discharge,this paper takes the typical dam section of a bulb tubular overflow hydropower plant as the research object.The calculation formula of the structural stiffness center is expanded and the stiffness center of the hydropower plant is solved.By changing the mass distribution at the top of the plant,four rigid-mass eccentricity schemes are set up in the cross-river direction and along-river direction.The finite element analysis software ANSYS Workbench is used to simulate the transient flow field under the check condition.The influence of the rigid-mass eccentricity on the natural vibration characteristics of the structure is analyzed,and the flow field calculation results are loaded onto the structure for fluid-solid coupling analysis.The influence of the rigid-mass eccentricity on the dynamic response of the hydropower plant during flood discharge is studied.The research in this paper shows that the water pressure pulsation characteristics of the flow field are obvious during the flood discharge of the hydropower station under the check flood level condition.The vibration generated by the structure will gradually change to torsional vibration with the increase of the rigid-mass eccentricity.The main research contents and conclusions are as follows :(1)Several sections are selected in the direction of the flow field along the river to analyze the velocity distribution characteristics of the flow field,and the pressure time history curve of each point is drawn by selecting the feature points on each section,so as to study the pressure distribution characteristics of the flow field.The results show that the velocity distribution of the flow field is greatly affected by the change of the external geometric size,and the velocity distribution in the flow channel of the unit is more complex than that in the surface hole flow channel.The water pressure fluctuation characteristics of the flow field mainly appear in the surface hole flow channel and the middle and rear parts of the unit flow channel,and the fluctuation water pressure disorder of the unit flow channel is stronger than that of the surface hole flow channel.The time-averaged pressure and maximum pressure of the flow field are compared with the measured data,and the error of the flow field simulation results is within the acceptable range.(2)The natural vibration characteristics of the hydropower house of each scheme are analyzed,and the first 30 modes and corresponding natural frequencies of the structure are solved.The influence of the change of eccentricity on the inherent properties of the structure is studied,and the resonance between the structure and the main vibration source is checked.The results show that the increase of eccentricity increases the torsional component in the basic vibration mode of the structure,and changes the natural frequency of each order of the structure,thus changing the torsion-flat period ratio of the structure.The torsion period ratio of each scheme structure is within the threshold,and the structure will not be seriously damaged due to the torsion effect.The structure may resonate with some vibration sources.The change of eccentricity will change the stagger degree between the natural frequency of the structure and the frequency of the vibration source in the resonance check,but the influence is limited and will not have much influence on the conclusion of the resonance check.(3)The transient dynamic analysis based on fluid-solid coupling is carried out for the powerhouse of each scheme.The amplitude,vibration root mean square velocity and vibration root mean square acceleration of the structure during flood discharge are solved,and the influence of eccentricity on the dynamic response of the structure is studied.The results show that the stiffness distribution characteristics of the structure and the action form of the external load are the main factors affecting the location of the maximum displacement.The amplitude,vibration root mean square velocity and vibration root mean square acceleration of the structure are affected by the change of eccentricity,which makes the vibration form of the structure gradually change to torsional vibration under the action of water pressure pulsation.Due to the direct contact and impact between the water surface of the structure and the water flow,and the torsion effect of the area is relatively large,it should be paid more attention in practical engineering. |
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