1 / 25

What Do We Need to Know about Wind for GSMT?

What Do We Need to Know about Wind for GSMT?. George Angeli 26 November, 2001. Introduction. GSMT modeling environment. Wind information needed. Known (perceived) inconsistencies between models and experiments. What to expect from wind simulations?. Design process.

dominy
Télécharger la présentation

What Do We Need to Know about Wind for GSMT?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What Do We Need to Know about Wind for GSMT? George Angeli 26 November, 2001

  2. Introduction • GSMT modeling environment • Wind information needed • Known (perceived) inconsistencies between models and experiments • What to expect from wind simulations?

  3. Design process • Concurrent engineering (structural, optical and control) • Design verification through simulation • Feedback to reiterate and improve the design

  4. Our approach

  5. Our approach • Advantages • Highly improved simulation speed • Significantly reduced computer requirements • Potential for more complex model • Each discipline (mechanical, optical, control) keeps its preferred “native” tools and environment (unlike IMOS but like IODA) • Affordable price

  6. Our approach • Potential drawbacks • Difficult to handle nonlinear effects in structure or optics • Limits of the linear optical approach should be explored and established

  7. Structural model Modal description: State-Space description:

  8. Optical model Modal description: Small deformations! P - optical sensitivity Zernike expansion: Ray tracing

  9. Integrated model

  10. What to expect? • Improve the design of the structure to make it less sensitive to wind load by • Optimizing the shape and surface of structural elements to minimize the wind-to-force efficiency • Optimizing the geometry of structure to minimize the coupling of wind power into higher order modes • Recognize the need and location of additional damping and stiffening

  11. What to expect? • Aid the enclosure design to optimize its effect on the wind by • Optimizing the shape and surface of the dome • Optimizing the vents and opening on the dome to achieve the required filtering effect

  12. What to expect? • Verify the control architecture by • Estimating the amplitude and bandwidth for wind induced deformation of telescope structure and primary mirror • Recognizing the need and location of actuators and sensors • Determining the necessary range and speed of actuators and sensors

  13. What to expect? • Aid the design of the various feedback loops by • Providing well defined disturbance signals to reject • Help to estimate the optical performance of the telescope

  14. Need to know… • Time evolution of wind forces on structural nodes • Wind characteristics • Velocity distribution in the vicinity of the structure with spatial sampling rate of node distances • Pressure distribution on the primary mirror with at least 3 samples per segments (to resolve torque)

  15. Need to know… • Drag and lift: • Wind-to-force conversion • Vortex shedding (buffeting with Strouhal frequency at low Reynolds number) • Aerodynamic attenuation of large structures • Effect of enclosure generated turbulence • Validity of first order approximation

  16. Experimental wind data

  17. Use of experimental wind data • Current approach • Using Gemini South wind measurements • Problems • Real amplitude and direction time functions, no “assumptions” • Limited relevance (different place, different size) • No simulation flexibility (given sampling rate, sample length, amplitude, etc.) • Limited environment control (vent gates, direction, elevation, etc.) • Limited feedback to design (no understanding of process)

  18. Use of simulated wind data • CFD output • Amplitude and direction time functions • Flexible environmental and simulation parameters • Problems • Limited understanding of the process • Time and resource consuming • Off-line calculations and data transfer

  19. Use of calculated wind data • Wind generated in Matlab • Calculation based on mathematical wind model (mean velocity and direction, velocity, pressure and direction PSDs, cross-correlations) – filtered random variable • Process understanding applicable to design optimization • Flexible environmental and simulation parameters • On-line data generation • Problems • Significant research effort • Probably: simplifying assumptions

  20. Atmospheric model • Kolmogorov’s isotropic turbulence theory • Energy cascade: large eddies ⇒ small eddies • Outer scale L0: turbulence not isotropic • Inner scale l0: turbulence disappears, energy dissipated through viscosity • Inertial subrange • Spatial PSD

  21. Atmospheric model • Taylor’s frozen flow hypothesis • Atmospheric “dispersion” • Temporal PSD

  22. Atmospheric model • Infinite energy @ κ=0 (outside of outer scale) • Problem • Solution • Von Karman spectrum • Davenport spectrum • HOWEVER, inside the enclosure and around the structure the turbulence is NOT isotropic and homogenous

  23. Basic questions • How are the statistics of the random process of wind changing due to: • the mountain top environment; • the enclosure; • the telescope itself • How is the interaction between the wind and telescope structure changing due to: • the enclosure; • the telescope itself

  24. Basic questions • How to scale our existing measurements to the GSMT? • What kind of additional measurements we need (if any)?

  25. Pressure/Force PSD on primary mirror

More Related