Wind loads on ground-based telescopes

MacMynowski, Douglas G.; Vogiatzis, Konstantinos; Angeli, George Z.; Fitzsimmons, Joeleff; Nelson, Jerry

doi:10.1364/ao.45.007912

Cited by 33 publications

(37 citation statements)

References 27 publications

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“…This model is based on work from reference [13], and is detailed in reference [14]. The temporal power spectrum of the tilt error due to windshake has the same structure as that of the atmospheric tilt, with a plateau at low frequencies and the same −17/3 ≈ −6…”

Section: E Gemini Planet Imager Tilt Simulationmentioning

confidence: 99%

Kalman filtering to suppress spurious signals in adaptive optics control

Poyneer

Véran

2010

J. Opt. Soc. Am. A

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1In many scenarios, an Adaptive Optics (AO) control system operates in the presence of temporally non-white noise. We use a Kalman filter with a state space formulation that allows suppression of this colored noise, hence improving residual error over the case where the noise is assumed to be white. We demonstrate the effectiveness of this new filter in the case of the estimated Gemini Planet Imager tip-tilt environment, where there are both common-path and non-common path vibrations. We discuss how this same framework can also be used to suppress spatial aliasing during predictive wavefront control assuming frozen flow in a low-order AO system without a spatially filtered wavefront sensor, and present experimental measurements from Altair that clearly reveal these aliased components.

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Section: E Gemini Planet Imager Tilt Simulationmentioning

confidence: 99%

Kalman filtering to suppress spurious signals in adaptive optics control

Poyneer

Véran

2010

J. Opt. Soc. Am. A

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“…Drilling some vents around the enclosure structure, appeared to weaken the shear layer and the amplitudes of the oscillatory modes were dampened. MacMynowski et al (2006) documented the effect of wind load and buffeting on groundbased telescopes and identified the sources that lead to better understanding the wind flow characteristics inside the telescope enclosure and past its aperture. One of the sources relies on CFD analyses using current state-of-the-art numerical techniques and advanced turbulence models.…”

Section: Review Of Flow Simulations On Large Telescopesmentioning

confidence: 99%

Unsteady Computational and Experimental Fluid Dynamics Investigations of Aerodynamic Loads of Large Optical Telescopes

Mamou¹,

Mébarki²,

Tahi³

2010

Computational Fluid Dynamics

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“…3,4 Previous models of wind loading on the telescope structure for TMT have been based on a parametric model [4][5][6] informed by a combination of Gemini data, 7,8 wind tunnel testing 9 and CFD. Advances in CFD now allow the unsteady forces on the structure and optics to be computed directly, as a function of external wind speed, orientation of the telescope with respect to the wind, and with enclosure vents either open or closed.…”

Section: Introductionmentioning

confidence: 99%

Unsteady wind loads for TMT: replacing parametric models with CFD

MacMartin

Vogiatzis

2014

SPIE Proceedings

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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.

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Wind loads on ground-based telescopes

Cited by 33 publications

References 27 publications

Kalman filtering to suppress spurious signals in adaptive optics control

Kalman filtering to suppress spurious signals in adaptive optics control

Unsteady Computational and Experimental Fluid Dynamics Investigations of Aerodynamic Loads of Large Optical Telescopes

Unsteady wind loads for TMT: replacing parametric models with CFD

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