Continuous Scanning Laser Doppler Vibration Measurement Technology And Its Application In Modal Testing Of Cylindrical Structures

The working performance and operating life of an aero-engine are closely related to its dynamic characteristics.The thin-walled axisymmetric circular structures such as the casing and the combustion chamber are the main components of the aero-engine except for the rotor,and their dynamic characteristics have long attracted the attention of researchers.Modal testing is one of the effective means to study the dynamic characteristics of structures and achieve structural design optimization.In general,the process of testing a thin-wall axisymmetric circular modal with a conventional acceleration sensor such as a casing is cumbersome.In order to obtain the modal shape,more measurement points need to be arranged,and the test and data processing time is long.Continuous Scanning Laser Doppler Vibrometry(CSLDV)has the advantages of no additional quality,high accuracy,short test time,and high spatial resolution,and has been widely used.In this paper,a virtual test method of CSLDV technology is proposed and applied to the measurement of the operational deflection shape(ODS)of the outer surface of a thin-walled cylindrical structure.The main research contents of the paper are as follows:(1)Propose and study the CSLDV virtual test method based on scan path and mode node;reveal the influence of laser scan frequency and test time on laser sinusoidal velocity surface scan vibration test,including the impact of laser X and Y scan frequency on the sideband spectrum of CSLDV signal,the impact of test time on the laser scanning path,and the impact of the laser X and Y scanning frequencies on the denseness of the scanning path.(2)A Cylinder-Continuous Scanning Laser Doppler Vibrometry(C-CSLDV)test method for the outer surface of a thin-walled cylindrical structure is proposed;the mode conversion and radial vibration component decomposition methods are studied,and a C-CSLDV virtual test is performed to verify the feasibility of this method.(3)Design and build C-CSLDV system,write C-CSLDV test software based on Lab View,select servo motors,assemble and debug C-CSLDV test platform.Based on C-CSLDV technology and servo motor control method,a sinusoidal speed rotation control algorithm was developed.The C-CSLDV test results were compared with SLDV test results and finite element simulation calculation results,which proved that the effectiveness and accuracy of CSLDV technology,and analyzed the advantages and disadvantages of speed control and position control,and the impact of different rotation frequencies on the test results.This thesis is an extended research on CSLDV technology.The effects of CSLDV virtual test and scanning frequency on CSLDV test greatly help the actual test.The realization of C-CSLDV technology is further applied to the thin-walled axisymmetric of actual cases and other cases.The vibration test of circular structure has guiding significance and practical value.