Research Papers

Structural Dynamics Testing and Analysis for Design Evaluation and Monitoring of Heliostats

[+] Author and Article Information
D. Todd Griffith

Engineering Sciences Center,
Sandia National Laboratories,
P.O. Box 5800,
Albuquerque, NM 87185-1124
e-mail: dgriffi@sandia.gov

Adam C. Moya, Clifford K. Ho

Concentrating Solar Technologies Department,
P.O. Box 5800,
Albuquerque, NM 87185-1127

Patrick S. Hunter

Engineering Sciences Center,
Sandia National Laboratories,
P.O. Box 5800,
Albuquerque, NM 87185-0557

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received June 19, 2012; final manuscript received September 2, 2014; published online October 23, 2014. Assoc. Editor: Markus Eck.

The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

J. Sol. Energy Eng 137(2), 021010 (Oct 23, 2014) (10 pages) Paper No: SOL-12-1160; doi: 10.1115/1.4028561 History: Received June 19, 2012; Revised September 02, 2014

Heliostat vibrations due to wind loading can degrade optical pointing accuracy while fatiguing the structural components. This paper reports the use of structural dynamic measurements for design evaluation and monitoring of heliostat vibrations. A heliostat located at the national solar thermal testing facility (NSTTF) at Sandia National Laboratories in Albuquerque, New Mexico, has been instrumented to measure its modes of vibration, strain and displacements under wind loading. The information gained from these tests will be used to evaluate and improve structural models that predict the motions/deformations of the heliostat due to gravitational and dynamic wind loadings. These deformations can cause optical errors and motions that degrade the performance of the heliostat. The main contributions of this work include: (1) demonstration of the role of structural dynamic tests (also known as modal tests) to provide a characterization of the important dynamics of the heliostat structure as they relate to durability and optical accuracy, (2) the use of structural dynamic tests to provide data to evaluate and improve the accuracy of computer-based design models, and (3) the selection of sensors and data-processing techniques that are appropriate for long-term monitoring of heliostat motions. This work also demonstrates the first measurements of rigid body modes of vibration associated with heliostat drive (azimuth and elevation) mechanisms, which are important structural dynamic response characteristics in dynamic design of heliostats.

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Fig. 1

Aerial view of Sandia 5-MWt central receiver test facility

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Fig. 2

A heliostat located at the Sandia CRTF

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Fig. 3

Description of heliostat major structural elements

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Fig. 4

Eight lowest frequency pretest analysis mode shapes for vertical configuration: (a) yoke bending in-plane, (b) yoke bending out-of-plane, (c) first torque tube bending, (d) second torque tube bending, (e) yoke bending (out-of-plane, out-of-phase), (f) in-plane bending (1), (g) in-plane bending (2), and (h) in-plane bending (3)

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Fig. 5

Test configurations: 0 deg, 45 deg, and 90 deg (from left to right)

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Fig. 6

Instrumentation layout for preliminary modal test

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Fig. 7

Accelerometer mountings with cable: (a) truss mounted accelerometer and (b) yoke mounted accelerometer

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Fig. 9

Instrumented impact hammers

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Fig. 10

Hammer excitation during testing: (a) truss excitation and (b) yoke excitation

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Fig. 11

Wind speed measurement near site

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Fig. 12

Comparison of numerical and experimental mode shapes for first torque tube bending mode 4 in Table 3)




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