Study On Some Techniques In Mechanical Testing And Computation

Modeling, computation and testing are the three important parts as well as the foundation of computer assisted engineering (CAE). For large-scale computation, and broad-band and non-stationary excitation, many problems still remain unsolved on computation and integration measurement technique. This dissertation discusses in details some important problems in digit signal processing technique, such as mesh-free technique in FE analysis, response computation technique under broad-band excitation and the integration measurement technique based on digit processing technique. In part I, the mesh-free technique is discussed. Two types of quadrilateral element for mesh-free method, outer-quadrilateral FMM (OQFFM) and inner-quadrilateral FMM (IQFFM), are proposed to achieve high accurate solutions. The OQFFM assembles matrices node by node, which is suitable for parallel computation. The numerical examples show that it remarkably improves the accuracy compared with that of the original mesh-free method. In order to combine the mesh-free technique with the general finite element method, a new approach for assembling stiffness matrix is developed based on the NBN technique, which is suitable for parallel computation. In part II, a strange phenomenon is reported, which cab be found in a specially designed simple example where the response of a broad-band loading system is computed. Using the existing conventional computing technique in general finite element method, the obtained result is incorrect. In order to gain insight into the problem, the form of the general response computation methods with digit signal processing technique is analyzed. The cause of the phenomenon is found, and developing a synthesis response computation method based on signal time-frequency analysis technique therefore, solves the problem. In part III, a de-noising method based on the translation invariant is proposed, for processing the broad-band loading signal. The method performs the cycle-spinning for the signal to be analyzed. The soft (hard) threshold is then used to shrink the wavelet coefficient of the signal and reconstruct the signal. Finally, the decomposition and the reconstruction technique for broad-band loading signal with signal time-frequency analysis technique are discussed. In part IV, a new technique based on FFT is proposed. Using this technique, digit weight and digit system error modification for noise octave analyzer can be realized with software. The technique makes a full use of the advantage of virtual instrument technique, and can realize synchronously analyses for all kinds of weight noise sound level measurement and real-time noise octave. Using digit weight and digit system error modification, precision and stability of the instrument can be greatly improved. As an application, combined with the method of digit weight, the technique of digit system error modification and the method of Parallel Varied-Time-Based Sample, a low cost and high precision virtual real-time noise octave analyzer is developed, and a new method to develop virtual axis locus analyzer is suggested. The method can process the spectrum of two vibration signals that are vertical to each other by using FFT and realize decomposing axis locus, compounding axis locus and analyzing axis position. Finally, as an application, a low cost virtual axis locus analyzer is developed.