| A wind turbine is a device that generates electricity by wind energy.Its principle is to apply wind energy to the impeller to make it rotate,and then the turbine is powered by a speed-increasing instrument.As a large thin-walled structure,the tower is a key component of the fan.With the enlargement of the fan,the height of tower has reached nearly 100 meters,and the influence of external load on the vibration characteristics of the tower is significantly increased.At home and abroad,the damage of the tower structure is the reason that the fan can not operate normally,and the analysis shows that the rotation of the blades is the main reason that cause the vibration of the tower.If the 3 time frequency of the fan blade is consistent with the natural frequency of the tower,the tower will be resonance and suffer serious damage,which will cause the collapse of the whole fan and affect the economic benefits.Therefore,in order to solve the problem of tower resonance,this paper establishes a theoretical model for solving the natural frequency of large fan towers by theoretical methods,hoping to provide reference for future design work.In this paper,a theoretical model of predicting the natural frequency of large-scale fan tower was established by means of Rayleigh Ritz method and receptance method.In order to verify the accuracy of the model,an acceleration test of fan was performed during normal operation,and the acceleration vibration characteristics and natural frequency were obtained from the time domain and the spectrum signals.The three-dimensional software Solidworks was used to build the fan model,and its modal was analyzed by ANSYS software.The main work and conclusions of this paper are as follows:(1)In the theoretical analysis,the tower was simplified as a uniform cantilever beam structure.the wind turbine was studied as a whole structure in the Rayleigh-Ritz method,the tower and the concentrated mass were studied separately in the Receptance method,and the theoretical model for predicting the natural frequency was established,the results show that the error is 0.43%.(2)the dynamic signal analyzer was used to measure the acceleration signal of the tower,and its principle,equipment model and test plan were briefly introduced.And finally the results were analyzed.The natural frequency of the tower is between 0.72 Hz and 0.76 Hz,by comparing the date,it is found that when the rotation speed is 14.87rpm,the peak vibration of the tower in the X axis and Y axis reaches the maximum.(3)During the modal analysis,two types of fan models were established by Solidworks and added to ANSYS for modal analysis.The result shows that the difference is about 0.44%,which shows that the simplified model is correct.After verification,the natural frequency of the tower differs from the blade rotation frequency and passing frequency by 40.9%and 33.3%,and the tower will not resonate with the blade coupling.(4)The numerical results of theoretical model,field test and finite element analysis were compared with each other,the results show that the first-order natural frequency obtained by the three methods are very close,which indicates that the theoretical model has good reliability.The theoretical model established in this paper,the tower vibration characteristics and conclusions obtained from the analysis can provide a reference for the design and prediction of the natural frequency of tower. |
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