Experimental Study Of The Structural Modal Parameter Identification Under Sound Excitation

In many fields, such as the fault diagnosing of the structure, health monitoring, vibration design, etc, it is very important to obtain the structural modal parameters. In routine modal test, the hammer or the vibration exciter is usually adopted for the excitation mode. But these methods may be not applicable to some precise equipment or structures, like the satellite or manned spacecraft structures, for they may destroy the instruments. However, using sound as a test method for non-contact excitation is a good choice, because it does not need to contact the structure. Furthermore, for a number of structures in some special circumstances, such as high temperature, it is also difficult to adopt the conventional excitation methods. Moreover, the spacecraft is usually under strong noise excitation during high-speed flight. Therefore, it is of great significance and value to study on the methods of the structural modal parameter identification under sound excitation.Compared with the conventional excitation methods, the input signals of acoustic excitation on the structure can not be accurately measured and precisely controlled. The signal-to-noise ratio of the structural vibration response is very poor under acoustic excitation, thus bringing many difficulties in modal parameters identification of the structural. Some research has done in this paper at the above-mentioned background.The main research work and conclusions are shown as follows:1. In this paper, the application background and significance of vibration modal analysis in the fields of engineering, the researches in the field at home and abroad were summed up. A variety of modal parameter identification methods were summarized and analysed in much detail.2. Experimental system of sound excitation which is based on hardware PXI and software LabVIEW was constructed.3. The model experiment of the airplane modal under sound excitation, and the finite element analysis of its structural was done.4. The random decrement technique and the natural excitation technique (NExT) were combined with eigensystem realization algorithm (ERA). The programs of the two kinds of modal parameter identification were edited by MATLAB language. Furthermore, the experimental data is collected to identify the modal parameters. Their results were compared with the modal parameter identification results by using the commercial software I-DEAS.In the paper, studies have shown that two kinds of modal parameter identification methods are effective. They can be used to identify modal parameters when the structure is excited by sound. It is feasible to identify structural modal parameter at low-frequency by using sound excitation.