Estimation method and goodness of fit analysison natural frequencies of large cooling towers

The natural frequency is the key factor that determines the dynamic deformation and stress of structure.The natural frequencies of the existing cooling towers are mainly obtained by finite element analysis, and there is no simple and effective formula for estimating the natural frequencies of the cooling towers.To resolve this problem,a large cooling tower was takenas the reference tower. Firstly, 38 models were obtained by changing the typical parameters of the reference tower, and the dynamic characteristics were analyzed.The law of fundamental frequency changing with the structure parameters was also extracted.Then, the sensitivity of the structural natural frequency parameters was analyzed by Latin hypercube sampling method, and the sensitive factors of various structural parameters under different orders were obtained.On this basis, the practical estimation formula of multi-parameter fundamental frequency considering sensitivity factor weight was innovatively fitted. Finally, eight cooling towersof typical height and typein China were selected for the field measurements, and the first 10-order self-oscillation frequencies of cooling tower were obtained by different mode identification methods.Further, the goodness of fit was analyzed using eight seat structure parameters of cooling tower. The results show thatthe natural frequencies are most sensitive to the height of cooling towers, and the sensitive factors are significantly higher than those of other parameters.By using 8 measured towers, the formula for estimating fundamental frequency isverified. The maximum value of self-vibration frequency fitting is 0.996, in which the mean value and mean variance of each target tower are 0.948 and 0.047, respectively. The estimation formula ofthe natural frequencies is of high accuracy and stability. © 2018, Editorial Board of Journal of Harbin Institute of Technology. All right reserved.