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Research Papers

A Noncontacting Approach for Full-Field Strain Monitoring of Rotating Structures

[+] Author and Article Information
Javad Baqersad

Mechanical Engineering Department,
Kettering University,
1700 University Avenue,
Flint, MI 48504
e-mail: Jbaqersad@kettering.edu

Peyman Poozesh

Mechanical Engineering Department,
University of Massachusetts Lowell,
1 University Avenue,
Lowell, MA 01854
e-mail: Peyman_Poozesh@student.uml.edu

Christopher Niezrecki

Mechanical Engineering Department,
University of Massachusetts Lowell,
1 University Avenue,
Lowell, MA 01854
e-mail: Christopher_Niezrecki@uml.edu

Peter Avitabile

Mechanical Engineering Department,
University of Massachusetts Lowell,
1 University Avenue,
Lowell, MA 01854
e-mail: Peter_Avitabile@uml.edu

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received April 12, 2015; final manuscript received October 31, 2015; published online April 7, 2016. Assoc. Editor: John Yu.

J. Vib. Acoust 138(3), 031008 (Apr 07, 2016) (9 pages) Paper No: VIB-15-1123; doi: 10.1115/1.4032721 History: Received April 12, 2015; Revised October 31, 2015

The three-dimensional point-tracking (3DPT) measurement approach is used in conjunction with finite element (FE) method and modal expansion technique to predict full-field dynamic response on a rotating structure. A rotating three-bladed wind turbine rotor was subjected to different loading scenarios, and the displacement of optical targets located on the blades was measured using 3DPT. The out-of-plane measured displacement of the targets was expanded and applied to the FE model of the turbine to extract full-field strain on the turbine. The sensitivity of the proposed approach to the number of optical targets was also studied in this paper. The results show that the dynamic strain on a structure can be extracted with a very limited set of measurement points (optical targets) placed on appropriate locations on the blades. It was shown that the proposed technique is able to extract dynamic strain all over the entire structure, even inside the structure beyond the line of sight of the measurement system. Because the method is based on a noncontacting measurement approach, it can be readily applied to a variety of structures having different boundary conditions.

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References

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Figures

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Fig. 1

A schematic of the setup of the cameras and turbine (left) and a photo (right) of the actual test setup

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Fig. 2

A schematic of the physical strain gage locations and orientations along the blades; gage S12 was installed on the lower surface of the blade

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Fig. 3

FE mode shapes and natural frequencies of the turbine placed in a semi-built-in boundary condition (shown with solid blades) compared with experimental mode shapes measured using experimental modal analysis (shown with lines and points)

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Fig. 4

A flowchart of the expansion method and 3DPT to predict full-field dynamic strain using modes shapes of the turbine and optically measured displacement data

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Fig. 5

Displacement vectors showing the 3D displacement (out-of-plane and in-plane) of optical targets during rotation

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Fig. 6

A sectional view of the turbine at one instant of time showing the strain distribution at outer surface and inner parts of the turbine blades during rotation and when it is vibrating due to initial deflections

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Fig. 7

Comparison of the strain (measured with mounted strain gages) and the predicted strain on a rotating turbine for the first test case when the initial rotational force was applied to one blade and initial out-of-plane deflections were applied to the two other blades; the photo shows the location of the strain gages where the comparison is performed; and S12 is located on the low-pressure side of the turbine. TRAC refers to the time-response assurance criterion.

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Fig. 8

FFT for the in-plane (X and Z) and out-of-plane (Y) measured displacement of a point near the tip of the blade (left) and near the center of a blade (right)

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Fig. 9

Comparison of the strain (measured with mounted strain gages) and the predicted strain on a rotating turbine for the first test case when the initial rotation was applied to one blade and initial deflections were applied to the two other blades; the photo shows the location of the strain gages where the comparison is performed; and S12 is located on the low-pressure side of the turbine. TRAC refers to the time-response assurance criterion.

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Fig. 10

A photo of the test setup showing the spinning turbine, an air blower located underneath the turbine, and the associated displacement vectors of the optical targets

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Fig. 11

Comparison of the strain (measured with mounted strain gages) and the predicted strain on a rotating turbine for test case 3 when then turbine was excited using a blower; the photo shows the location of the strain gages where the comparison is performed; and S12 is located on the low-pressure side of the turbine

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Fig. 12

A schematic showing the locations of different sets of targets on a blade for each set; the locations of optical targets on the two other blades were similar to this blade

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Fig. 13

Comparison of the strain predicted using all the optical targets and strain predicted using reduced sets of optical targets (set 1, set 2, and set 3) for test case 2 (i.e., small impacts were made to the blades during turbine rotation); the photo shows the location of the strain gages where the comparison is performed

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