Modal testing

About: Modal testing is a research topic. Over the lifetime, 4047 publications have been published within this topic receiving 64772 citations.

Structural modal analysis using collocated piezoelectric actuator/sensors: an electromechanical approach

Abstract: This paper presents a modal analysis technique based on the measurement of electric admittance of collocated actuator/sensors. The technique utilizes thin piezoelectric patches bonded on structures as both sensor and actuator. A commercial electrical impedance analyzer is used to measure the electrical admittance of the PZT patch. An SDOF model governing the electromechanical interaction is derived and then used to extract the mechanical impedance of the structures from the measured electrical admittance. Two corresponding algorithms, revised inverse Nyquist plane curve fitting and admittance matching-half power bandwidth approaches are presented for the extraction of modal parameters. Both approaches exclude the stiffening effect of PZT on structure yielding better estimations of extracted structure natural frequencies. The placement of PZT on structure is also studied. An experimental example is given on a small flexible beam. The results show the advantages of this technique in modal test of lightweight and flexible structures whose modal parameters are extremely sensitive to the stiffening of the transducers and shaker.

A synthesis of peak picking method and wavelet packet transform for structural modal identification

Abstract: Damage identification problem involves detection, localization and assessment of the extent of damage in a structure so that the remaining life could be predicted. Visual or nondestructive experimental damage detection methods such as ultrasonic and acoustic emission ones are based on a local evaluation in easily accessible areas, and therefore, they require a certain prior knowledge of the damage distribution. With the purpose of providing global damage detection methods applicable to complex structures, techniques based on modal testing and signal processing constitute a promising approach for damage identification. These methods examine changes in the dynamic characteristics of structure, such as natural frequencies and mode shapes to detect the structural damage. Modal parameters including natural frequencies, mode shapes and damping ratios are known as essential parameters for analyzing the dynamic behavior of a structure. This paper deals with identification of modal parameters of structures using a two-step algorithm. In the proposed method, free vibration response of structure is decomposed using wavelet packet transform. Then, decomposed signal, which has the same energy with the main signal, is used for modal parameter identification using peak picking method. The performance of the proposed method is verified against the results of an experimental benchmark problem.

Operational modal analysis of Canton Tower by a fast frequency domain Bayesian method

Abstract: The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.