發(fā)布時間：2018-10-31 08:24

【摘要】：阻尼作為重要的動力學特性參數(shù),表征振動系統(tǒng)能量耗散的快慢。能否準確識別出阻尼值,直接影響阻尼在結構損傷診斷、減震降噪等領域的應用。改進阻尼識別方法,提高阻尼識別精度,一直是國內外學者所關注的重要課題。各種阻尼識別方法中,學者們對采樣時間長度研究分析不足。本文針對采樣時間長度對阻尼識別影響,展開了研究工作。本文首先分析無噪聲干擾情況下,采樣時間長度對阻尼識別精度的影響。以半功率帶寬法與內積法為例展開研究,給出阻尼比為0.006、0.03、0.1時,500采樣點、5000采樣點、40000采樣點的仿真算例。仿真結果表明無噪聲干擾時,兩種阻尼識別方法均存在采樣時間越長阻尼識別精度越高的現(xiàn)象。實際工程不可避免地存在噪聲干擾,研究存在噪聲干擾時,采樣時間長度對阻尼識別精度的影響。分別推導響應信號頻譜幅值和噪聲信號頻譜幅值與采樣點數(shù)的關系式。理論分析指出采樣時間長度不宜過長,否則會出現(xiàn)響應信號被噪聲信號掩蓋,阻尼識別誤差增大的現(xiàn)象。本文將響應信號與噪聲信號頻譜相等時,所對應的采樣時間長度定義為臨界采樣長度,通過理論推導得到臨界采樣長度表達式,為選取合理采樣時間長度提供參考。針對有噪聲干擾時采用過長采樣時間會帶來阻尼識別誤差的問題,研究采用聯(lián)立方程法使用較短數(shù)據(jù)識別信號阻尼。運用傅里葉變換初估信號固有頻率,以此固有頻率構造傅里葉變換基函數(shù),通過對信號與構造函數(shù)作兩次時間不同的積分運算構造方程組,求解得到固有頻率誤差及衰減系數(shù),進而得到信號阻尼比。對方程組積分時間,討論任意積分時間與特定積分時間T(28)k??(k為正整數(shù))兩種方案,分析指出選用特定積分時間能降低負頻率干擾,提高阻尼識別精度。聯(lián)立方程法核心運算選取積分時間較短,使噪聲干擾影響不突出,具有運算量少、識別速度快、抗噪能力強的特點。研究聯(lián)立方程法對多自由度響應信號阻尼識別的適用性。對非密集模態(tài)信號,將識別出的各階次模態(tài)依次從原信號中減去,多自由度響應信號阻尼識別簡化為多個單自由度響應信號阻尼識別。對密集模態(tài)信號引入迭代算法,消除各階次模態(tài)的相互干擾,準確識別各階次模態(tài)阻尼。將聯(lián)立方程法運用于齒輪箱蓋阻尼識別試驗,識別出齒輪箱蓋響應信號在208.824 Hz、363.913 Hz、636.561 Hz、940.817 Hz處具有四階模態(tài),對應的四階模態(tài)阻尼比分別為0.004798、0.004509、0.001933和0.001674。將識別出四階模態(tài)信號從原信號中減去,剩余信號頻域圖中觀測不到明顯峰值,證明聯(lián)立方程法準確有效,具有工程實用性。
[Abstract]:As an important dynamic characteristic parameter, damping represents the speed of energy dissipation of vibration system. Whether the damping value can be accurately identified will directly affect the application of damping in the fields of structural damage diagnosis, vibration absorption and noise reduction, etc. Improving the damping identification method and improving the accuracy of damping identification has always been an important subject that scholars at home and abroad pay close attention to. Among all kinds of damping identification methods, the research and analysis of sampling time length is insufficient. In this paper, the influence of sampling time length on damping identification is studied. In this paper, the influence of sampling time length on the accuracy of damping identification is analyzed. Taking the half-power bandwidth method and inner product method as an example, a simulation example of the damping ratio of 0.006 ~ 0.03,0.1, 500 sampling points, 5000 sampling points and 40000 sampling points is given. The simulation results show that the longer the sampling time, the higher the accuracy of damping identification for both damping identification methods without noise interference. The influence of sampling time length on the accuracy of damping identification is studied. The relationship between the spectrum amplitude of response signal and the amplitude of noise signal and the number of sampling points are derived respectively. The theoretical analysis indicates that the sampling time should not be too long, otherwise the response signal will be masked by the noise signal and the damping identification error will increase. In this paper, when the spectrum of response signal and noise signal is equal, the corresponding sampling time length is defined as critical sampling length, and the expression of critical sampling length is obtained by theoretical derivation, which provides a reference for selecting reasonable sampling time length. In order to solve the problem of damping identification error caused by long sampling time when there is noise interference, the simultaneous equation method is used to identify the damping of the signal with short data. Using the Fourier transform to estimate the natural frequency of the signal, the Fourier transform basis function is constructed, and the equations are constructed by integrating the signal and the construction function at different times, and the natural frequency error and attenuation coefficient are obtained. Then the signal damping ratio is obtained. For the integral time of equations, two schemes of arbitrary integral time and special integral time T _ (28) K ~? (k is a positive integer) are discussed. It is pointed out that the selection of specific integral time can reduce the negative frequency disturbance and improve the damping identification accuracy. The integration time of the core operation of simultaneous equation method is short, which makes the influence of noise interference not prominent, and has the characteristics of less computation, faster recognition speed and stronger anti-noise ability. The applicability of simultaneous equation method to the identification of damping of response signals with multiple degrees of freedom is studied. For the non-dense modal signal, the identified modes are subtracted from the original signal in turn, and the damping identification of the multi-degree-of-freedom response signal is simplified to that of multiple single-degree-of-freedom response signals. The iterative algorithm is introduced to the dense modal signal to eliminate the interference of each order mode and to identify the damping of each order mode accurately. The simultaneous equation method is applied to the gear box cover damping identification test. It is found that the response signal of the gear box cap has the fourth order mode at 208.824 Hz,363.913 Hz,636.561 Hz,940.817 Hz. The corresponding fourth-order mode damping ratios are 0.004798 / 0.004509N 0.001933 and 0.001674 respectively. The fourth order modal signal is subtracted from the original signal and no obvious peak value can be observed in the frequency domain diagram of the remaining signal. It is proved that the simultaneous equation method is accurate and effective and has engineering practicability.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TB53

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