Model Updating with Closed-Loop Strain Mode Shapes

2007 ◽  
Vol 30 (4) ◽  
pp. 1206-1209 ◽  
Author(s):  
Jaehoon Ha ◽  
Youngjin Park ◽  
Younsik Park
Keyword(s):  
Closed Loop ◽  
Model Updating ◽  
Mode Shapes ◽  
Strain Mode ◽  
Strain Mode Shapes

Mode Decoupling Controller for Feedback Model Updating

2004 ◽  
Author(s):  
Hunsang Jung ◽  
Youngjin Park ◽  
K. C. Park
Keyword(s):  
Closed Loop ◽  
Model Updating ◽  
Control Method ◽  
Loop System ◽  
Mode Shapes ◽  
Closed Loop System ◽  
Sensitivity Matrix ◽  
Data Set ◽  
Conventional Methods ◽  
The Stability

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed-loop frequency information for parameter modifications to overcome the problems associated with the conventional methods employing the modal sensitivity matrix. To obtain new modal information from the closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of the closed-loop system. The present paper proposes a mode-decoupling controller that can alter a target mode while guaranteeing the stability of the closed-loop, and that can be constructed by using the measured open-loop, mode shapes. A simulation based on time domain input/output data is performed to evaluate the feasibility of the proposed control method, which is subsequently corroborated via experiments. Experimental data obtained on a beam via the proposed mode-decoupling controller have been applied to estimate thicknesses of a beam. The results show that the proposed approach outperforms conventional methods with a far less number of data set for the estimation of system parameters.

scholarly journals Damage identification using modal strains identified from operational fiber-optic Bragg grating data

2017 ◽  
Vol 17 (6) ◽  
pp. 1441-1459 ◽  
Author(s):  
Dimitrios Anastasopoulos ◽  
Maure De Smedt ◽  
Lucie Vandewalle ◽  
Guido De Roeck ◽  
Edwin P.B. Reynders
Keyword(s):  
Fiber Optic ◽  
Early Stage ◽  
Structural Characteristics ◽  
Mode Shapes ◽  
Dynamic Strain ◽  
Bragg Grating ◽  
Local Damage ◽  
Strain Mode ◽  
Displacement Mode ◽  
Strain Mode Shapes

Vibration-based structural health monitoring of civil structures relies on the repeated identification of dynamic structural characteristics of the structure from output-only vibration data. Natural frequencies and displacement mode shapes are the most commonly employed dynamic characteristics; yet their sensitivity to local damage of moderate severity is rather low with respect to their sensitivity to other factors such as temperature, necessitating data normalization. Strain mode shapes offer a higher sensitivity to local damage, but their accurate identification in a dense grid is challenging given the very small dynamic strain levels that are encountered under ambient excitation. In this article, a method is presented for tackling this challenge. It consists of three stages. First, fiber-optic Bragg grating strain sensors are attached to the structure and interrogated with a tunable laser performing a wavelength sweep. In this way, the measured strain amplitudes have the required accuracy but synchronization errors are introduced between the different Bragg sensors. Second, a modal analysis is performed on the dynamic strain data using an accurate parametric system identification technique. This is followed by a synchronization step which compensates for the delays introduced by the wavelength sweep. Finally, the synchronized strain mode shapes are employed as damage-sensitive features, either directly or via a newly proposed quantity, the top-to-bottom strain ratio. The method is validated by progressive damage testing of a complex, prestressed concrete “roof” beam, reinforced with steel fibers. It is observed that the proposed method can identify both the presence and the location of the damage in a relatively early stage.

Dual use of PZT patches as sensors in global dynamic and local electromechanical impedance techniques for structural health monitoring

2011 ◽  
Vol 22 (16) ◽  
pp. 1841-1856 ◽  
Author(s):  
Rama Shanker ◽  
Suresh Bhalla ◽  
Ashok Gupta ◽  
Matta Praveen Kumar
Keyword(s):  
Structural Damage ◽  
A Priori ◽  
Cost Effective ◽  
Integrated Approach ◽  
Mode Shapes ◽  
Strain Mode ◽  
Electromechanical Impedance ◽  
Global Dynamic ◽  
Dynamic Technique ◽  
Strain Mode Shapes

In this article, a new approach is proposed to effectively detect the initiation and progression of structural damage by combining the global dynamic and the local electromechanical impedance (EMI) techniques, using the same set of surface-bonded piezoelectric ceramic (PZT) patches as sensors. The PZT patches are used to determine the natural frequencies and the strain mode shapes of the structure (for use in the global dynamic technique) as well as to acquire the electromechanical admittance signature (for use in the EMI technique) to facilitate an improved damage assessment. Occurrence and location of the incipient damage are determined using the EMI technique, whereas for moderate to severe damages, the location and the severity are arrived at through the global dynamic technique. Finally, damage severity is determined in terms of the original stiffness of structure using the strain mode shapes directly determined using the PZT patches. The proposed technique is illustrated using two specimens—a 4-m long steel beam and a mild steel plate 1260 mm × 630 mm × 6.5 mm in size. The integrated approach provides greater information about damage, is simple to apply, does not involve any numerical/analytical modeling a priori, and is at the same time very cost effective.

scholarly journals Output-Only Damage Detection in Plate-Like Structures Based on Proportional Strain Flexibility Matrix

Sensors ◽  
2020 ◽  
Vol 20 (23) ◽  
pp. 6862
Author(s):  
Kang Yun ◽  
Mingyao Liu ◽  
Jiangtao Lv ◽  
Jingliang Wang ◽  
Zhao Li ◽  
...  
Keyword(s):  
Damage Detection ◽  
Damage Index ◽  
Identification Accuracy ◽  
Mode Shapes ◽  
Engineering Structures ◽  
Strain Mode ◽  
Flexibility Matrix ◽  
Construction Procedure ◽  
Output Only ◽  
Strain Mode Shapes

For engineering structures, strain flexibility-based approaches have been widely used for structural health monitoring purposes with prominent advantages. However, the applicability and robustness of the method need to be further improved. In this paper, a novel damage index based on differences in uniform load strain field (ULSF) is developed for plate-like structures. When estimating ULSF, the strain flexibility matrix (SFM) based on mass-normalized strain mode shapes (SMSs) is needed. However, the mass-normalized strain mode shapes (SMSs) are complicated and difficult to obtain when the input, i.e., the excitation, is unknown. To address this issue, the proportional strain flexibility matrix (PSFM) and its simplified construction procedure are proposed and integrated into the frames of ULSF, which can be easily obtained when the input is unknown. The identification accuracy of the method under the damage with different locations and degrees is validated by the numerical examples and experimental examples. Both the numerical and experimental results demonstrate that the proposed method provides a reliable tool for output-only damage detection of plate-like structures without estimating the mass-normalized strain mode shapes (SMSs).

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