Study On Experimental Modal Analysis And Laser Measurement Technology

With the aid of the non-contact laser measurement technology, the experiment of a cubic modal and a car body modal is completed. In order to constitute the 3-dimension modal shapes of a structure by using the test data, the methods of determining the phase relationship and the ratios of amplitude of vibration mode in different planes are discussed. The main contributions of this thesis are as follows:Review the basic principles of laser measurement technology, such as the holographic interferometry, the electronic speckle pattern interferometry, optical triangulation and laser Doppler technology, the advantages and disadvantages between them are also compared.The modal experiment of a cubic model is done by using the scanning laser vibrometer. The natural frequencies and corresponding modes are obtained. The signals of vibration in different planes are collected by sensor and dynamical data acquisition system. The experimental data is studied by the correlative analysis method which is based on LABVIEW. The phase relationship and the amplitude ratio of vibration modes are determined. The whole modal shapes of the model are drawn out by MATLAB and compared with the results of FEM, which show that the errors of the natural frequencies and corresponding whole modes between experiment and FEM are in the allowable range. This experiment method has some reference value on testing the 3-dimension modal shapes of a structure by using a single scanning laser vibrometer.The natural frequencies and corresponding modes of a car body are obtained by mode test. The phase relationship and the amplitude ratio of vibration mode in different planes of the car body is determined and the 3-dimension modal shape of a structure is constituted by the method mentioned above. Also, the natural frequencies and corresponding modes of PANEL ASSY-DASH.LWR are obtained by the test. This is a good application of laser measurement technology in the test of a car body mode, which overcomes the limitation of a single scanning laser vibrometer in the test of 3-dimension modal shape of a structure. The use range of the single scanning laser vibrometer is also expanded.