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Unsteady wind loads for TMT: Replacing parametric models with CFD

MacMartin, Douglas G. and Vogiatzis, Konstantinos (2014) Unsteady wind loads for TMT: Replacing parametric models with CFD. In: Systems Engineering, and Project Management for Astronomy VI. Proceedings of SPIE. No.9150. Society of Photo-Optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 91500Q. ISBN 978-0-8194-9618-8. http://resolver.caltech.edu/CaltechAUTHORS:20141114-131928001

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Abstract

Unsteady wind loads due to turbulence inside the telescope enclosure result in image jitter and higher-order image degradation due to M1 segment motion. Advances in computational fluid dynamics (CFD) allow unsteady simulations of the flow around realistic telescope geometry, in order to compute the unsteady forces due to wind turbulence. These simulations can then be used to understand the characteristics of the wind loads. Previous estimates used a parametric model based on a number of assumptions about the wind characteristics, such as a von Karman spectrum and frozen-flow turbulence across M1, and relied on CFD only to estimate parameters such as mean wind speed and turbulent kinetic energy. Using the CFD-computed forces avoids the need for assumptions regarding the flow. We discuss here both the loads on the telescope that lead to image jitter, and the spatially-varying force distribution across the primary mirror, using simulations with the Thirty Meter Telescope (TMT) geometry. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are all estimated; these are then used to compute the resulting image motion and degradation. There are several key differences relative to our earlier parametric model. First, the TMT enclosure provides sufficient wind reduction at the top end (near M2) to render the larger cross-sectional structural areas further inside the enclosure (including M1) significant in determining the overall image jitter. Second, the temporal spectrum is not von Karman as the turbulence is not fully developed; this applies both in predicting image jitter and M1 segment motion. And third, for loads on M1, the spatial characteristics are not consistent with propagating a frozen-flow turbulence screen across the mirror: Frozen flow would result in a relationship between temporal frequency content and spatial frequency content that does not hold in the CFD predictions. Incorporating the new estimates of wind load characteristics into TMT response predictions leads to revised estimates of the response of TMT to wind turbulence, and validates the aerodynamic design of the enclosure.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1117/12.2057295DOIArticle
http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1895355PublisherArticle
ORCID:
AuthorORCID
MacMartin, Douglas G.0000-0003-1987-9417
Additional Information:© 2014 SPIE. The TMT Project gratefully acknowledges the support of the TMT collaborating institutions. They are the Association of Canadian Universities for Research in Astronomy (ACURA), the California Institute of Technology, the University of California, the National Astronomical Observatory of Japan, the National Astronomical Observatories of China and their consortium partners, and the Department of Science and Technology of India and their supported institutes. This work was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the Ontario Ministry of Research and Innovation, the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the British Columbia Knowledge Development Fund, the Association of Universities for Research in Astronomy (AURA), the U.S. National Science Foundation and the National Institutes of Natural Sciences of Japan.
Group:Thirty Meter Telescope
Funders:
Funding AgencyGrant Number
Association of Canadian Universities for Research in Astronomy (ACURA)UNSPECIFIED
CaltechUNSPECIFIED
University of CaliforniaUNSPECIFIED
National Astronomical Observatory of JapanUNSPECIFIED
National Astronomical Observatories of ChinaUNSPECIFIED
Department of Science and Technology of IndiaUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Ontario Ministry of Research and InnovationUNSPECIFIED
National Research Council of CanadaUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
British Columbia Knowledge Development FundUNSPECIFIED
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
NSFUNSPECIFIED
National Institutes of Natural Sciences of JapanUNSPECIFIED
Subject Keywords:Computational Fluid Dynamics (CFD), Wind Loading, Ground Based Telescopes
Record Number:CaltechAUTHORS:20141114-131928001
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141114-131928001
Official Citation:Douglas G. MacMartin and Konstantinos Vogiatzis " Unsteady wind loads for TMT: replacing parametric models with CFD ", Proc. SPIE 9150, Modeling, Systems Engineering, and Project Management for Astronomy VI, 91500Q (August 4, 2014); doi:10.1117/12.2057295; http://dx.doi.org/10.1117/12.2057295
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51784
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:14 Nov 2014 22:16
Last Modified:17 Jul 2018 23:55

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