Research On Normal Mode Testing By Laser Scanning Vibrometer

Modal analysis is a kind of testing method to obtain the vibration characteristics of structures. Modal parameters are the basis for the verifying or updating of theoretical or numerical models. modal testing methods can be categorized as normal mode measuring method (phase resonance method) and phase separation method. The normal mode measuring method is mainly used under the occasions when the tested structures are in large scale and the required testing precision is high while the phase separation method is often used in the modal analysis of little or middle scale articles. In the traditional normal mode measuring process, the appropriate excitation forces are always adjusted manually by the operators based on their techniques and experience and there are also some drawbacks such as redundant consume of testing time, very difficult operating process, mass additional effect of transducers etc. Focus on these problems four aspects of work have been finished in the thesis.(1) A method based on phase resonance and laser scanning vibrometer is presented for the normal mode measuring. When a testing structure is vibrating in a normal mode, the responses are scanned by a laster vibrameter. Thus, the mode is obtained directly.(2) Multiple exciters are used for the structure excitation and the appropriate forces are adjusted automatically by a computer.(3) A Personal computer,VXI and a vibrometer are integrated into a measuring system. A control software with the functions of multiple- channel signals sampling, generating,processing, viewing and storing is completed.(4) A great deal of normal tests are tried on a aircrafter model in order to verify the above system and the results show that it is effective in normal modes measuring.In summary, the normal mode mesuring method presented in the thesis is effective and it is important for the advance of normal mode measuring in the maneuverability,dependability and accuracy.