Research On Flow-induced Vibration And Shape Optimization Of Trashracks Based On Test

With the development of modern electric network, how to solve the current peaking capability of electric network has become a urgent issue. One of the effective ways is to construct a good many large and medium-sized pumped storage power stations. However, the pumped-storage power station has two functions of power generation and pumping water. The trashracks or rack bars are prone to be destroyed because of vibration resulted from the impact of bidirectional turbulence to them. So it is of very realistic significance to study the dynamic characteristics and reaction of the trashracks subjected to turbulence, and take anti-vibration measures to guarantee normal function of the power station.Based on the trashracks project of Pu Shihe Pumped Storage Power Station, this paper carries on model test study and test-based finite element analysis on flow-induced vibration of trashracks. The purpose of this study is to identify measures to avoid vibration, providing the basis for the design. The main contents are organized as follows:(1) The hydroelastic model test is made for trashracks. Firstly, basic similitude theory of hydroelastic model test, model scale, test point arrangement, test equipment and test conditions are described. The model material according with the model scale is studied and determined. Secondly, The areas where the trashracks are easily destroyed are analyzed according to the test results, and fatigue lifetime of structure is estimated. The vibration dominant frequency of trashracks is studied and the vibration source is found.(2) The modal and the dynamic characteristics are analysed for trashracks. Firstly, theoretical solutions of natural frequency of the rack bars is solved by Levin formula, and a correction for Levin is carried out. The estimation method of maximum deflection is presented. Secondly, the inherent frequencies and vibration modes of the trashracks are calculated by means of the modal analysis function of the finite element analysis program of ANSYS. The hydraulic resonance of trashracks is studied with dominant frequency obtained from the hydroelastic model test. Thirdly, the approximate simulation of flow field is made by connecting among the pulsating force of current, dynamic strains at the position of measuring point and equivalent uniform load. The feasibility of numerical calculation is demonstrated by comparing the strain errors of test and numerical calculation. Finally, the reasonable design idea is carried out by researching the distribution law of maximum displacement, stress, strain and acceleration in the paper. (3) The shape optimization of trashracks is studied for trashracks. The natural frequency of trashracks is needed to increase in order to avoid resonance. Two strengthening methods are adopted and compared, i.e. weak stiffening project and strong stiffening project. It seems to be ineffective by comparing the two projects with the original one after the modal analysis of trashracks although the steel amount has been increased. The first-order natural frequency of strong stiffening project only rises 2.09% compared with the original project. And then, the shape optimization is studied by the subproblem approximation method of ANSYS. The results show that the shape optimization improves effectively the first-order natural frequency of the trashracks. The effect of weak stiffening project is very outstanding, and its first-order natural frequency rises 66.26% in comparison to the original project.