An optical-based technique to obtain operating deflection shapes of structures with complex geometries

Srivastava, Vanshaj; Baqersad, Javad

doi:10.1016/j.ymssp.2019.03.021

Cited by 44 publications

(17 citation statements)

References 20 publications

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“…For a utility‐scale WTB within a test facility, the use of a standard stereo‐photogrammetry to measure the entire blade may be limited by the camera separation or the required working distance to capture the area of interest. Therefore, larger FOVs can be obtained by stitching together in a global coordinate system the images recorded using the two adjacent sets of cameras as demonstrated in several prior studies 39,40,58,59 . Thus, to perform a 3D‐DIC measurement, it is desirable to couple several pairs of cameras to simultaneously monitor the distributed strain, deflections, and deformations within the line of sight of each stereo‐vision system.…”

Section: Edgewise Fatigue Testmentioning

confidence: 99%

“…In this research, a multicamera measurement system, employing a stereo‐photogrammetry technique in conjunction with dynamic spatial data stitching, is used to evaluate the static and dynamic characteristics of a utility‐scale WTB subjected to static and dynamic loadings. Alternative approaches include image stitching operations performed in the frequency domain 39 and a single moving camera for multiview 3D reconstruction 40 . Figure 1 shows the conceptual setup of a multicamera system made of five synchronized stereo‐vision systems recording adjacent views of the low pressure side of a WTB.…”

Section: Introductionmentioning

confidence: 99%

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Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

et al. 2020

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Wind turbine blade certification requires static and fatigue testing at a large-scale facility similar to the Wind Technology Testing Center (WTTC) located in Charlestown, Massachusetts. Usually, these tests are conducted by using wire-based sensors such as strain gages, accelerometers, and string potentiometers. These systems are expensive, require a time-consuming installation (e.g., up to 3 weeks and $35 k-$50 k for a strain gage system on a 55-m-long blade), are difficult to deploy on large-sized structures, require additional instrumentations (e.g., power amplifiers and data acquisition systems), and produce results only at a handful of a discrete number of measurement points. In this study, a multicamera measurement system is implemented and experimentally evaluated to obtain full-field displacement and strain over a~12-m-long portion of a~60-m utility-scale wind turbine blade. The proposed system has the potential to streamline the certification process by reducing the blade's preparation and sensor installation cost and time to a few hundreds of dollars (for painting equipment) and a few days for preparing the surface of the blade for the test. Furthermore, operational modal analysis was used in conjunction with the multicamera system to estimate the natural frequencies and mode shapes of the wind turbine blade. The obtained results have shown that the proposed approach can detect in-plane displacement as low as 0.2 mm, mechanical strain with an error below 3% when compared with measurement performed using strain gages, and the first five natural frequencies with an error below 2% when compared with data recorded using traditional wire-based accelerometers. This paper presents these results and provides a summary of the strengths and weaknesses of the proposed optical measurement approach in the context of streamlining the blade certification/testing process and performing vision-based structural dynamic measurements on large-scale structures. K E Y W O R D Sdigital image correlation, fatigue tests, operational modal analysis, stitched field of view, structural health monitoring, wind turbine blades

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Section: Edgewise Fatigue Testmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

et al. 2020

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“…Considering the advantages and limitations, mode shapes or operational deflection shapes take the greatest advantage among the modal parameters owing to high spatial density. Hence, many studies have employed this technique for simply obtaining shapes [ 9 , 10 , 11 , 12 , 13 ], even with low-speed equipment [ 14 , 15 ]. Full modal characterization has been also performed in different studies for experimental modal analysis [ 16 , 17 , 18 ], showing different capabilities and applications such as the combination of measurements with a multiview system [ 19 ], the evaluation of a single-camera alternative to DIC for 3D measurements [ 20 ] or measuring in rotating disks [ 21 ] and in artificial beetle’s wings [ 22 ].…”

Section: Introductionmentioning

confidence: 99%

Full-Field Operational Modal Analysis of an Aircraft Composite Panel from the Dynamic Response in Multi-Impact Test

Molina-Viedma

López‐Alba

Felipe-Sesé

et al. 2021

Sensors

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Experimental characterization and validation of skin components in aircraft entails multiple evaluations (structural, aerodynamic, acoustic, etc.) and expensive campaigns. They require different rigs and equipment to perform the necessary tests. Two of the main dynamic characterizations include the energy absorption under impact forcing and the identification of modal parameters through the vibration response under any broadband excitation, which also includes impacts. This work exploits the response of a stiffened aircraft composite panel submitted to a multi-impact excitation, which is intended for impact and energy absorption analysis. Based on the high stiffness of composite materials, the study worked under the assumption that the global response to the multi-impact excitation is linear with small strains, neglecting the nonlinear behavior produced by local damage generation. Then, modal identification could be performed. The vibration after the impact was measured by high-speed 3D digital image correlation and employed for full-field operational modal analysis. Multiple modes were characterized in a wide spectrum, exploiting the advantages of the full-field noninvasive techniques. These results described a consistent modal behavior of the panel along with good indicators of mode separation given by the auto modal assurance criterion (Auto-MAC). Hence, it illustrates the possibility of performing these dynamic characterizations in a single test, offering additional information while reducing time and investment during the validation of these structures.

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“…The digital image correlation (DIC) method is a kind of photogrammetry method that measures the full-field deformation of structure in various fields of research, such as for vibration [ 44 ], crack monitoring [ 45 , 46 , 47 ], high-temperature structures [ 48 , 49 , 50 ], electronic packaging [ 51 , 52 , 53 ], and small structures [ 54 , 55 ]. The identification of a whole area displacement field or operating deflection shape (ODS) is one of the most interesting features using the DIC method [ 56 ]. Thus, the use of the DIC method in vibration and modal analysis has become common [ 57 ].…”

Section: Introductionmentioning

confidence: 99%

Dynamic Characteristics and Damage Detection of a Metallic Thermal Protection System Panel Using a Three-Dimensional Point Tracking Method and a Modal Assurance Criterion

Goo

2020

Sensors

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A thermal protection system (TPS) is designed and fabricated to protect a hypersonic vehicle from extreme conditions. Good condition of the TPS panels is necessary for the next flight mission. A loose bolted joint is a crucial defect in a metallic TPS panel. This study introduces an experimental method to investigate the dynamic characteristics and state of health of a metallic TPS panel through an operational modal analysis (OMA). Experimental investigations were implemented under free-free supports to account for a healthy state, the insulation effect, and fastener failures. The dynamic deformations resulted from an impulse force were measured using a non-contact three-dimensional point tracking (3DPT) method. Using changes in natural frequencies, the damping ratio, and operational deflection shapes (ODSs) due to the TPS failure, we were able to detect loose bolted joints. Moreover, we also developed an in-house program based on a modal assurance criterion (MAC) to detect the state of damage of test structures. In a damage state, such as a loose bolted joint, the stiffness of the TPS panel was reduced, which resulted in changes in the natural frequency and the damping ratio. The calculated MAC values were less than one, which pointed out possible damage in the test TPS panels. Our results also demonstrated that a combination of the 3DPT-based OMA method and the MAC achieved good robustness and sufficient accuracy in damage identification for complex aerospace structures such as TPS structures.

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An optical-based technique to obtain operating deflection shapes of structures with complex geometries

Cited by 44 publications

References 20 publications

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

Full-Field Operational Modal Analysis of an Aircraft Composite Panel from the Dynamic Response in Multi-Impact Test

Dynamic Characteristics and Damage Detection of a Metallic Thermal Protection System Panel Using a Three-Dimensional Point Tracking Method and a Modal Assurance Criterion

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