Operational modal analysis on a VAWT in a large wind tunnel using stereo vision technique

Najafi, Nadia; Paulsen, Uwe Schmidt

doi:10.1016/j.energy.2017.02.133

Cited by 14 publications

(12 citation statements)

References 11 publications

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“…However, it does provide mode shapes of the VAWT. A stereo vision technique was used to measure a Φ-type VAWT vibration in Reference [11], and the mode shapes of the Φ-type VAWT shaft were also cantilevers. However, the mode shapes of the H-type VAWT shaft in our study are not completely cantilever shapes since the shaft was connected with two bearings, which cannot be simplified as totally rigid boundary conditions.…”

Section: Mode Identificationmentioning

confidence: 99%

“…However, studies on VAWTs are limited when compared to those on horizontal wind turbines. Although several laboratory vibration tests were performed to study the dynamic behavior of VAWTs [8][9][10][11], only a limited number of field vibration measurements were conducted. Some studies showed that the vibration of the VAWT support structure may be influenced by the wind turbine's operation [9].…”

Section: Introductionmentioning

confidence: 99%

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Dynamic Study of a Rooftop Vertical Axis Wind Turbine Tower Based on an Automated Vibration Data Processing Algorithm

et al. 2018

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When constructed on tall building rooftops, the vertical axis wind turbine (VAWT) has the potential of power generation in highly urbanized areas. In this paper, the ambient dynamic responses of a rooftop VAWT were investigated. The dynamic analysis was based on ambient measurements of the structural vibration of the VAWT (including the supporting structure), which resides on the top of a 24-story building. To help process the ambient vibration data, an automated algorithm based on stochastic subspace identification (SSI) with a fast clustering procedure was developed. The algorithm was applied to the vibration data for mode identification, and the results indicate interesting modal responses that may be affected by the building vibration, which have significant implications for the condition monitoring strategy for the VAWT. The environmental effects on the ambient vibration data were also investigated. It was found that the blade rotation speed contributes the most to the vibration responses.

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Section: Mode Identificationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamic Study of a Rooftop Vertical Axis Wind Turbine Tower Based on an Automated Vibration Data Processing Algorithm

et al. 2018

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“…Traditional contact transducers such as strain gauges and accelerometers have been used for vibration analysis, health monitoring, damage detection and structural displacement of wind turbines (Weijtjens et al, 2017;Yang et al, 2014;Osgood et al, 2010;Lorenzo et al, 2016; and other large structures like bridges (Hoffmann, 1989;Fukuda et al, 2013;Park et al, 2005;Ye et al, 2012;Xia et al, 2014, andSiriwardane, 2015), but they have difficulties measuring on a large scale; the installation process, which often includes wiring, is costly and time consuming. The measured signal from conventional sensors such as accelerometers is not very accurate in measuring low frequencies of the structure (for instance frequencies between 0.2 and 0.5 Hz in horizontal-axis wind turbines) and includes the centrifugal components (Najafi and Paulsen, 2017). In addition, contact transducers can only measure the structure at a few points and increasing the measurement points creates additional cost and complication (Hunt, 1998).…”

Section: Introductionmentioning

confidence: 99%

Point to point response to reviewers 3

Anonymous

2018

Preprint

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Health monitoring by conventional sensors like accelerometers or strain gauges becomes challenging for large rotating structures due to the issues with feasibility, sensing and data transmission. In addition, acceleration measurements have low capability of presenting very small frequencies, which happen very often for large structures (for instance, frequencies between 0.2 and 0.5 Hz in horizontal-axis wind turbines). By contrast, displacement measurement using stereo vision is rapid, non-contacting and distributed over the structure. The sensors are cheaper and more easily applied to many places on the object to be measured. Horizontal-axis wind turbines are one of the most important large rotating structures and need to be measured and monitored in time to prevent damage and failure, and the blade tip position is one of the key parameters to measure in order to prevent the blade hitting the turbine tower.This paper presents a clearly described and easily applicable procedure for measuring the displacement on the components of a rotating horizontal-axis wind turbine with stereophotogrammetry. Paper markers have been applied on the rotor and tower of a scaled-down horizontal-axis wind turbine model in the workshop and the displacement measurement method has been demonstrated by measuring displacement during operation. The method is mainly developed in two parts: (1) camera calibration and (2) tracking algorithm. We introduce an efficient camera calibration method for measurement in large fields of view, which has always been a challenge. This method is easy and practical and offers better accuracy compared with 2-D traditional camera calibration. The tracking algorithm also works successfully and is able to track the points during rotation within the measurement time. Finally, the accuracy analysis has been conducted and has shown better accuracy of the new calibration method compared with 2-D traditional camera calibration.Published by Copernicus Publications on behalf of the European Academy of Wind Energy e.V.

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“…The measured signal from conventional sensors such as accelerometers is not very accurate in measuring low frequencies of the structure to be studied (For instance frequencies between 0.2 and 0.5 Hz in horizontal axis wind turbines) and is including the centrifugal components (Najafi and Paulsen, 2017). In addition the contact transducers can only measure the structure in a few numbers of points and increasing the measurement points creates additional cost and complication (Hunt, 1998).…”

Section: Introductionmentioning

confidence: 99%

“…In, Najafi and Paulsen, 2017, 3DPT has been used to study structural vibrations of a model scale vertical axis wind turbine. Najafi and Paulsen, 2017, have investigated the challenges of using stereo vision for vibration analysis of complex geometries with sharp curvatures and out of plane components. In (Prowell, et al, 2011;Prowell, et al, 2012 andPaulsen, et al, 2012) the displacement measurements by point tracking stereo 30 photometry is used for structural response and modal properties of utility-scale horizontal axis wind turbines.…”

Section: Introductionmentioning

confidence: 99%

Establishing a robust testing approach for displacement measurement on a rotating horizontal axis wind turbine

Najafi¹,

Vesth²

2017

Preprint

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Abstract. Health monitoring by conventional sensors like accelerometers or strain gauges becomes challenging for large rotating structures due to the feasibility, sensing and data transmission. In addition acceleration measurements have low capability in presenting very small frequencies which happen so often for large structures (For instance frequencies between 0.2 and 0.5 Hz in horizontal axis wind turbines). By contrast the displacement measurement using stereo vision is rapid, noncontacting and also distributed over the structure. The sensors are cheaper and easier to be applied in many places on the 10 object to be measured. Horizontal axis wind turbines are one of the important large rotating structures which need to be measured and monitored in time to prevent damage and failure and the blade tip position is one of the key parameters to measure to prevent blade hitting the turbine tower. This paper presents a well-defined procedure for measuring the displacement on the components of a rotating horizontal axis wind turbine (HAWT) with stereo photometry. Paper markers have been applied on the rotor and tower of a scaled down 15 HAWT model in the workshop and the displacement measurement method has been demonstrated by measuring displacement during operation. The method is mainly developed in two parts: 1) the camera calibration and 2) tracking algorithm. We introduce an efficient camera calibration method for measurement in the large field of views that has always been a challenge. This method is easy and practical and offers better accuracy compared with 2D traditional camera calibration. The tracking algorithm also worked quite successfully and kept tracking the points during rotation within the 20 measurement time.Finally the accuracy analysis has been conducted and has shown the better accuracy of the new calibration method compared with 2D traditional camera calibration.

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Operational modal analysis on a VAWT in a large wind tunnel using stereo vision technique

Cited by 14 publications

References 11 publications

Dynamic Study of a Rooftop Vertical Axis Wind Turbine Tower Based on an Automated Vibration Data Processing Algorithm

Dynamic Study of a Rooftop Vertical Axis Wind Turbine Tower Based on an Automated Vibration Data Processing Algorithm

Point to point response to reviewers 3

Establishing a robust testing approach for displacement measurement on a rotating horizontal axis wind turbine

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