Study On Structural Vibration Back Analysis And Safety Evaluation Based On Flow-induced Vibration Respone

The scale of China’s dam-building is the biggest in the world, they have already kept ahead in the height of dam, discharge and spillway power. Because of the strong turbulence in the water tend to have a lot of momentum, so when catharsis flood discharge structure, they can easily lead to severe vibration sluice structure, even can cause structural damage. In recent years, it is common that high-speed discharge flood water induced structural vibration, and affects the safety of the project operation, and even cause serious damage. Through have a study on the reasons for discharge structural damage, people found that there are two reasons: structural dynamic vibration displacement exceeding safety standards; structural dynamic stress response is too large to vibration fatigue damage. Therefore, evaluation of discharge structure is based on dynamic displacement and dynamic stress discharge structure under flow-induced vibration. When carry out discharge structure prototype vibration testing, through the number of points measured dynamic response is limited, it is difficult to fully reflect the characteristics of the vibration response of the whole structure, and it is important to evaluate Discharge structure’s safety operational according to the limited measurement point to back-analysis the he dynamic response of the whole structure, especially for dynamic stress response of the structure under the water. Base on these main problem, this article describe three main areas:(1) Through the numerical simulation model of guide wall, verify the feasibility of back analysis method. Due to we didn’t know the hydrodynamic loads, which induce guide wall vibration response. So, first of all, this paper input a typical hydrodynamic load, and to establish ANSYS finite element model to transient analysis, we can extract point response of dynamic displacement measuring process, which can be known conditions to bace-analysis method; secondly, input the known dynamic displacement response spectra of these measurement points, and prepare back-analysis of the basic procedures to anti-vibration performance hydrodynamic loads which evoked guide wall response, we also achieve the recognition of the local oscillator. To prepare the movement of water load measured values and calculated values, verify the feasibility of back-analytical methods; finally, use the hydrodynamic loads calculate the overall dynamic displacement response of the entire guide wall structure, and were compared to verify. As well, based on modal superposition method, we inversion dynamic stress response of the whole structure. Prepare the inversion results with the transient response results shows that, error control in less than 5%, it is shows that based on back-analysis of discharge structure response is effective and feasible.(2) Inversion of ErTan dam prototype dynamic response field was studied based on limited measurement.Taking the prototype of ErTan arch dam as an example, response of vibration for dynamic displacement was tested aimed at six different drainage conditions of arch dam. According to the measured results of limited measurement for dynamic displacement, the displacement field and stress field of the entire dam were inversed. Through B1—B7 measurement’s dynamic displacement response time of ErTan arch dam under every conditions, there were three equivalent hydrodynamic load when the flow of arch dam was inversed. Genetic algorithm is introduced into the process and the results of recognition were optimized.The whole dynamic displacemen field get when the arch dam was discharging was calculated and validated with dynamic displacement of measuring points those had been known based on positive analysis of three equivalent load inversed.The whole dynamic stress field of prototype structure of the arch dam with six conditions were inversed based on modal superposition method.The dynamic stress was obtained and the dynamic stress of dam where the stress was the bigges. The results of the inversion showed that: ①the RMS value of displacement response in each points with same height on the arch dam showed that the values were big in the middle and delined on both sides; ② The change of tangential dynamic stress on the arch was similar with the dynamic displacement response. ③ The tangential dynamic stress root mean squarevalues of each node on the crown cantilever decreased with the elevation; The RMS value of vertical dynamic stresses increased gradually with the altitude.(3) According to the analysis and the investigation of the existing engineering structures vibration safety evaluation, and combine with the inversion of Ertan arch prototype dynamic displacement field and dynamic stress field, to evaluated if it is safe under the six conditions operation. The result show that under the six conditions, spillway vibration of Ertan arch dam is safe.