Study On Operational Modal Identification And Structural Dynamic Model Updating Of Large-scale Mine Gearbox

Large-scale, low-speed, heavy-duty gear transmission system is widely used in key equipment of mining, metallurgical industry production. The Gears have a tendency to fail in the severe working conditions. As the accident or catastrophic accident occurred, the entire assembly line production is probablely knocked out. Most structural dynamic models are deterministic models built according to the design for the mining machinery at present. The modal identification result of the model is very different from real structure, owing to a variety of assumptions and simplifications in the model. Therefore, it has important theoretical significance and practical value to carry out study on large-scale mine gearbox running modal identification methods and structural dynamic model updating method. In this paper, a operational modal identification method is proposed for mine hoister gearbox under multi-excitation; a structural dynamic model updating method is also proposed based on stochastic combining stiffness for large-scale and heavy-duty transmission equipment, by combining stochastic dynamics theory and operational modal identification theory, and the application analysis of gearbox dynamic reliability is based on the updated structural dynamic model. The main works and results are as follows:(1) First proposed the concept of relative frequency response functions and virtual frequency response function. The three properties of relative frequency response function are proposed by theory deducing, namely:As there is only single exciting force in the structure system, the zero points of relative frequency response function is the system poles; As there is only single exciting force in the structure system, at the system poles, relative frequency response function between any given two points on the system structure converges to a certain value, which has nothing to do with the amplitude and direction of the exciting force; As there are multi-exciting force in the structure system, at the system poles, relative frequency response function between any given two points on the system structure also converges to a certain value, which has nothing to do with the amplitude and direction of the multi-exciting forces.(2) A operational modal identification method are proposed under unknown multi-exciting forces, by applying three properties of relative frequency response function. That is, as there are multi-exciting forces in the structure system, at system poles, relative frequency response function between any given two points on the system structure also converges to a certain value, which has nothing to do with the amplitude and direction of each of multi-exciting forces, but at the non-system poles, relative frequency response function value between the given two points is changing with the exciting force changes. And unknown multi-exciting forces include white noise, harmonics, variable frequency excitation, and any other way of excitations.(3) A de-noising method based on wavelet entropy modulus maxima is proposed by combining with the wavelet maximum modulus singularity theory and wavelet energy entropy theory. Using the characteristics that information entropy can be quantitatively described as energy probability distribution in time-frequency domain, the method of adaptively fixing the noise threshold based on wavelet entropy, can effectively remove the continuously decreasing wavelet maximum modulus with the wavelet decomposition scale increasing, can reserve the continuously increasing wavelet maximum modulus with the wavelet decomposition scale increasing, and reconstruct the remaining wavelet maximum modulus after the effectively filtering. The method effectively separated the real signal from the strong background noise.(4)The actual dynamic characteristics of large-scale mine gearbox is identified by using harmonic wavelet packet transform and harmonic wavelet packet demodulated resonance.The modulated informations are separated from the vibration signal after transformation and the information are applied in analysis of work status, the type of injury and extent of injury for the gearbox. By extracting coefficient of the real and the imaginary in harmonic wavelet packet transform, the relative vibration directions of the input shaft and the output shaft is obtained, which is one of the model updating target parameters.(5) A mechanical joint modeling method is proposed. The method used beam element and shell element in the gearbox main body, and used equivalent spring and equivalent damper instead of gear engagement, and the inner ring and outer ring connection of the mechanical junction surface.(6) A mechanical model based on the combining stiffness is applied in modal frequency sensitivity analysis. Stochastic dynamics theory is introduced into the sensitivity analysis model updating method, and a modal frequency dynamic model updating method based on the stochastic combining stiffness is proposed. Obtained modal frequency sensitivity based on the combining stiffness, by analyzing the statistics of the sample response value,and updated corresponding combining stiffness, according to the comparison of mode shapes. It indicates that modal frequency model updating method based on stochastic combining stiffness is effective by experimental verification of the gearbox element model.(7) Structural dynamic model updating method is applied to the gearbox dynamic reliability analysis, and based on the model updated a gearbox dynamic reliability research methods is proposed. By using of gearbox structural dynamic model updated, to predict the vibration response of the real unmeasured point, based on stress strength interference theory; and by analyzing dangerous position of the gearbox, the reliability sensitivity and dynamic reliability analysis is carried out based on the theory of First Passage Failure mechanism. According to solved results, obtained the most important three factors for gearbox dynamic reliability, namely:the stochastic stiffness of gear pairs, the stochastic stiffness of input bearing in horizontal direction and the load of output shaft.