Finite element model updating of liquid rocket engine nozzle based on modal test results obtained from 3-D SLDV technique

In order to update the finite element model, the modal test results must be highly accurate since they are used as the basis. The major problems with traditional modal test method are limited measurement points and poor mode shape precision. In this paper, modal test based on 3-D Scanning Laser Doppler Vibrometry (SLDV) technique was carried out. High spatial resolution and accurate mode shapes were obtained, which is beneficial to subsequent correlation analysis and updating process. High order modal parameters were identified and more information can be added in the objective function. Due to the consistent coordinate system in modal test and finite element model, the measurement points and corresponding finite element nodes were easily matched in order to compare mode shapes. By means of a real liquid rocket engine nozzle, an integrated model updating process is presented from proper initial model, accurate modal test results, test/analysis correlation to automatic model updating. The single steps of detailed updating process are highlighted. The discrepancy between the finite element model predicted and the experiment measured modal parameters are minimized and satisfactory results were obtained.