Estimating the effect of wind loading on extremely large telescope performance using computational fluid dynamics

Vogiatzis, Konstantinos; Segurson, Anna; Angeli, George Z.

doi:10.1117/12.551477

Cited by 19 publications

(20 citation statements)

References 6 publications

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“…[3][4][5] More extensive data under more controlled conditions have been collected in an ϳ1% scale wind-tunnel experiment. 6 Finally, computational fluid dynamic (CFD) analyses 7 have been validated against these data sources and used primarily to understand differences between different sources of data.…”

Section: Introductionmentioning

confidence: 99%

Wind loads on ground-based telescopes

et al. 2006

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One of the factors that can influence the performance of large optical telescopes is the vibration of the telescope structure due to unsteady wind inside the telescope enclosure. Estimating the resulting degradation in image quality has been difficult because of the relatively poor understanding of the flow characteristics. Significant progress has recently been made, informed by measurements in existing observatories, wind-tunnel tests, and computational fluid dynamic analyses. We combine the information from these sources to summarize the relevant wind characteristics and enable a model of the dynamic wind loads on a telescope structure within an enclosure. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are defined as a function of relevant design parameters, providing a significant improvement in our understanding of an important design issue.

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Section: Introductionmentioning

confidence: 99%

Wind loads on ground-based telescopes

et al. 2006

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“…9,10 More extensive data under more controlled conditions has been collected in scaled wind-tunnel experiments; while this approach has been used for many years, 11 modern experimental techniques allow significantly more data to be collected. 12,13 Finally, computational fluid dynamics (CFD) [13][14][15] is an ideal design tool, and can take advantage of the experimental data for validation, so that CFD can be used with confidence in future design work. The parametric model of wind forces herein builds on earlier efforts 3,4 by incorporating new information from recent computational and wind tunnel studies.…”

Section: -8mentioning

confidence: 99%

“…The oscillation frequency of these modes scales with nσU ∞ /D s , where 0.5 < σ < 1 depends on the geometry. These tones occur in wind-tunnel tests at Caltech 12 and NRC, 13 and in CFD analyses of these geometries, 13,15 and for certain configurations are the dominant source of pressure variations within the telescope enclosure. The observed characteristics of these modes include a large oscillatory pressure throughout the entire telescope enclosure, and a large oscillatory vortex structure in the region of the enclosure near the secondary mirror and supporting structure.…”

Section: Mechanismsmentioning

confidence: 99%

“…Measurements of the mean and turbulent wind velocity inside an empty dome have been taken in a wind tunnel model at Caltech 12 and matching computations conducted at AURA. 15 The pressure force can be estimated from the velocity if one assumes that the structure would not have significantly altered the flow pattern. This would clearly be a poor assumption for computing the forces on the primary mirror, but the cross-sectional area of the secondary mirror is relatively small compared to the open area of the dome (roughly 1%).…”

Section: Parameter Estimatesmentioning

confidence: 99%

“…• a 3 (shear layer on M1): The peak-to-peak pressure amplitude for the shear layer mode on the primary can be estimated from theory 15 for deep cavities as no larger than p = (1/3)(…”

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Parametric modeling and control of telescope wind-induced vibration

et al. 2004

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A parametric model of the dynamic performance of an optical telescope due to wind-buffeting is presented. The model is being developed to support the design of next generation segmented-mirror optical telescopes through enabling rapid design iterations and allowing a more thorough exploration of the design space. A realistic performance assessment requires parametric descriptions of the wind, the structural dynamics, active control of the structure, and the optical response. The current model and its assumptions are presented, with the primary emphasis being on the parameterization of the wind forces. Understanding the temporal spectrum and spatial distribution of wind disturbances inside the telescope enclosure is one of the most challenging aspects in developing the overall parametric model. This involves integrating information from wind tunnel tests, computational fluid dynamics, and measurements at existing observatories. The potential and limitations of control to mitigate the response are also discussed, with realistic constraints on the control bandwidth obtained from the detailed structural model of a particular point design. Finally, initial results are presented on performance trends with a few key parameter variations.

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Servo-fluid-elastic modeling of contactless levitated adaptive secondary mirrors

2011

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The paper develops a comprehensive approach for the servo-fluid-elastic modeling of electromagnetically levitated secondary adaptive mirrors. The system modeling includes the mirror structural dynamics model, its interaction with the fluid film interposed between the mirror and its reference backplate and disturbances due to local air turbulence. The accuracy of the proposed fluid dynamic model is assessed by comparing it with a significant sample of high fidelity 3D Navier-Stokes analyses. The simulation tool is then used to demonstrate the effectiveness and robustness of a recently proposed control, based on a system dynamics cancellation and an iterated steady state feedforward contribution. The simulations clearly highlights the improvements achievable implementing the new control scheme.

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Estimating the effect of wind loading on extremely large telescope performance using computational fluid dynamics

Cited by 19 publications

References 6 publications

Wind loads on ground-based telescopes

Wind loads on ground-based telescopes

Parametric modeling and control of telescope wind-induced vibration

Servo-fluid-elastic modeling of contactless levitated adaptive secondary mirrors

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