| The effect of interaction between the unit and the plant structure on hydropower station is complex,and the vibration source is related to many factors,such as hydraulic,mechanical and electromagnetic,etc.The dynamic system formed has the characteristics of randomness,complexity and nonlinear correlation.Based on the prototype observation and numerical simulation method,this paper studies the vibration source characteristics and response characteristics of hydropower plant under multi-source excitation,and puts forward a vibration response prediction method of hydropower plant.The main research contents are as follows:(1)Based on the study of the vibration source characteristics of the plant structure and the calculation of the theoretical vibration sources,the measured vibration sources are classified.The main vibration source of the unit and plant structure of the hydropower station is studied by statistical analysis of the frequency of the main frequency of vibration and the analysis of the energy ratio of different vibration components.The results show that the main vibration sources include unit frequency conversion,low frequency tailwater vortex belt,unit frequency conversion 5 times frequency and volute uneven current.The vibration RMS of the vertical measuring point with large vibration amplitude increases with the increase of unit load and gate opening,especially when the gate opening is adjusted from 2 m to 4.7 m,the vibration RMS increases suddenly.As the opening of the gate is 2 m,the low frequency tailwater vortex belt component is not decomposed,while the opening of the gate is more than4.7 m,the low frequency tailwater vortex belt can be decomposed.The results indicate that when the gate opening reaches 4.7 m,the discharge has a great influence on the structure of the plant.(2)Study on response characteristics of unit and plant structure.The resonance check analysis of the factory building structure shows that the main excitation frequency is quite different from the natural vibration frequency of the structure,and the possibility of resonance is low by the numerical simulation method.The mechanical load provided by the manufacturer is applied to the model in a simple harmonic way.The actual working conditions can well be simulated combined with the measured pulse pressure signal multiplied by the point surface conversion coefficient applied to the model.Meanwhile,the structural response under limit condition is analyzed by numerical model.The mechanical load,volute pulse pressure load and tailwater tube pulse pressure load are applied to the model respectively.It is found that the mechanical load has a great influence on the structure and is consistent with the actual working conditions.The vibration superposition enhancement phenomenon is found in the elbow position of the elbow tube and the measuring point of the tail water cone tube.Through the analysis of its causes,it can be found that the correlation between pulse pressure load signals is good,and the phenomenon of modal aliasing is the main cause of vibration superposition enhancement.(3)Study on structural response prediction of unit and plant.Three prediction models namely KELM、AVMD-KELM and AVMD-BSA-KELM are established,the prediction R2 of the three models is above 0.45.The prediction accuracy of the model can be improved by preprocessing the vibration signal based on AVMD decomposition method and optimizing the parameters by BSA optimization algorithm.Especially,as the frequency component is more complex and the signal is predicted,the preprocessing of vibration signal by AVMD decomposition method can improve the prediction accuracy.Since the frequency components in the vibration signal of hydropower plant structure are more complex,the prediction accuracy of the vibration signal prediction model is low.However,this problem can solved well by using AVMD decomposition method,because the vibration signal can be decomposed into multiple IMF components. |
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