Dynamics Characterisrtic Combined Analysis And Engineering Application For Mechanical Systems

Significant changes have been taken place in mechanical and electrical products as the information technology, which is represented by computer technology, network technology and communication technology, is widely used in various fields of mechanical engineering. Of course, these changes also include the development of the theory of mechanical disciplines which provide support for the product design and application of technology. In recent years, the above studies have made a series of important achievements. These achievements play an important role in innovation and design of the mechanical and electrical products. Based on the academic principles of the system identification, structural dynamics and the corresponding test techniques, the Experimental Modal Analysis (EMA) and Operational Modal Analysis (OMA) technology have made considerable development, which helps the designers to get more insight of object mechanisms from the identified models and apply the mechanisms to the design of products, to promote originality exploitation and design of the products effectively and to expand its application areas continuously.In recent years, the Operational Modal Analysis is widely used in the dynamic analysis and the design of mechanical system and structure, as well as in monitoring and fault diagnosis. The existing problems and disadvantages of these methods are also exposed in applications. In order to make these methods be effective in industrial applications, these problems must be resolved. The research in this paper is suitable for the Operational Modal Analysis of large-scale machinery equipments and structures, as well as suitable for eliminating some shortcomings of modal analysis. The purpose of this study is to reduce the test time, to allow to exploit maximal test data, to decrease the complexity of the analysis, to allow to process the data easily, to apply in modal test of large mechanical structure which existing the problems of a large number of sensors, high damping, noise data, short data records etc, to increase the accuracy of the estimate of mode. In order to achieve the above purpose, starting from modal testing and modal parameter estimation, some problems of operational modal analysis have been solved, some important achievements have been made and applied to large industrial equipments successfully.In this paper the basic theories and methods of modal analysis are reviewed, which includes Experimental Modal Analysis (EMA), Operational Modal Analysis (OMA) and an Operational Modal Analysis with eXogenous inputs (OMAX). The frequency response function estimation of deterministic contribution and the positive power spectrum estimation of random contribution are discussed in the frame of OMAX. On this basis, the limitations and shortcomings of these methods are pointed, which is used as the background of this paper.Operation modal analysis based on cyclic cepstrum is proposed. This method relieves the assumption that the input signal of OMA is white noise and improves the accuracy of the identification of modal parameters. The portion of the responses caused by the cyclostationary input is separated by the technique of cyclostationary signal processing. The MIMO system is effectively reduced to an SIMO system. In the cepstrum domain the SIMO responses are curve-fitted, the input and transfer function then can be separated, and the system resonances and anti-resonances are identified. The transfer functions of system can be regenerated. Through the steel beam test the method is verified and is compared with the EMA analysis results. In this trial, the resonance frequencies and mode shapes are estimated accurately and the estimated imprecision is reduced by increasing the average number of times.In order to solve the problems of scale lost when the input stimulus is not white noise, a simple method is proposed to recover the relative proportion (scale) between mode shapes and global proportions (scale) of all mode shapes. This method is based on cyclic cepstrum. The method includes the recognition of resonance and anti-resonance by response spectrum and using them to correct the finite element model. Then, the equivalent curve is acquired by the finite element model, and then the scale of.the frequency response function is recovered.Qusical OMA is put forward against the problem of modals lost and problem of low speed of Calculation in the process of OMA of large mechanical structures because of narrow band of the operation or ambient excitation. In part of the area of the large structure is combined with measured excitation force (similar to the experimental modal analysis), and part auxiliary excitation input is used in Operational Modal Analysis method. Suitable modal identification algorithm for Quasi OMA based on the mixed reference deterministic stochastic subspace is also proposed, the accuracy and speed of the modal identification is improved.In order to verify Quasi OMA, it is applied to modal analysis of industrial screen; the modal parameters of the screen are accurately identified and achieved very good results. This method is proved be robust and reliable.