Research On Automatic Identification Method Of Structural Experimental Modal Parameters And Software Development

Modal is the inherent property of the structure,which can reflect the dynamic performance of the structure,in civil engineering,modal parameters are often used as indicators to evaluate the dynamic characteristics of the structure.Modal parameters are divided into operational modals and experimental modals according to whether input（stimulus）information is required,operational modal analysis only obtains modal parameters through output（response）data;experimental modal analysis requires that the input（excitation）data and output（response）data are known before the modal information of the structure can be obtained.Since the excitation is known,the frequency response function of the structure can be obtained through the structural response,compared with operational modal analysis,the amplitude of the frequency response function is clear,which can be used to determine the contribution of each order mode and accurately obtain modal parameters such as damping ratio.However,most of the experimental modal softwares at home and abroad have problems such as insufficient modal recognition process,which requires professionals to manually set a large number of parameters,and the accuracy of false modal rejection requires professionals to control and other issues,therefore,it is particularly important to automate the process of structural modal recognition under the conditions of known incentives,streamline parameter settings,and make the software easy for engineers to use.In this paper,the least squares complex frequency domain method is selected as the main algorithm for modal parameter identification,and on this basis,an engineering software integrating visual modeling,signal data acquisition and automatic identification of modal parameters has been developed,and further connecting with the acquisition equipment to realize the integration of experimental modal analysis software and hardware.This topic starts with the research status of experimental modal field and modal automation,summarizes the experimental modal recognition methods,selects the least squares complex frequency domain method as the modal recognition algorithm,and conducts detailed theoretical derivation and MATLAB program implementation.The basic modal information is obtained by combining the stability diagram,and the correctness of the program is verified by a four-degree-of-freedom centralized mass model calculation example.At the same time,corresponding optimizations are made for the problem of insufficient automation in the process of experimental modal parameter identification,the main improvements include five aspects: automatic judgment of combos;automatically generate the number of spectral lines;automatic division of analysis frequency bands;automatic determination of the calculation range of the stability map;automatic elimination of the false modal points,and prove the feasibility of the improved content through the cantilever beam model experiment.Relying on the App Designer in the MATLAB software to develop the modal automatic identification software,the interface layout and functional modules of the modal automatic identification software are designed mainly from the two aspects of human-computer interaction and functional programming of the software interface.The main function layout of the software is in the form of a menu bar.Since the excitation information is known,data collection and data analysis including excitation and response information are required.Therefore,the overall function of the software is composed of five parts,including of the file module,the geometric modeling module,the data preparation module,the modal analysis module,and the help module.This software mainly focuses on the development of the coordinate generation model sub-module in the geometric modeling module,the data acquisition sub-module in the data preparation module,and the modal analysis module.The coordinate generation model function is used for the construction of the structural geometric model;the data acquisition function is used to control the NI c DAQ-9171 data acquisition card for real-time signal collection and synchronously display the signal image during the signal acquisition process;the modal analysis module automatically analyzes and calculates the modal parameters based on the collected data.Using this software to analyze and calculate the modal information of the cantilever,and compare the analysis results of LMS Test.Lab,it proves that the analysis results and accuracy of this software are basically consistent with the analysis results of LMS Test.Lab,and verify the effectiveness of the software to automatically identify modal parameters,the software is convenient for engineers to use.