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  • Instrumentation and Photography  (5)
  • Astronomy  (4)
  • FLUID MECHANICS AND HEAT TRANSFER  (3)
  • 1
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    Petrov-Galerkin methods for natural convection in directional solidification of binary alloys (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A Petrov-Galerkin finite element method is presented for calculation of the steady, axisymmetric thermosolutal convection and interface morphology in a model for vertical Bridgman crystal growth of nondilute binary alloys. The Petrov-Galerkin method is based on the formulation for biquadratic elements developed by Heinrich and Zienkiewicz and is introduced into the calculation of the velocity, temperature and concentration fields. The algebraic system is solved simultaneously for the field variables and interface shape by Newton's method. The results of the Petrov-Galerkin method are compared critically with those of Galerkin's method using the same finite element grids. Significant improvements in accuracy are found with the Petrov-Galerkin method only when the mesh is refined and when the formulation of the residual equations is modified to account for the mixed boundary conditions that arise at the solidification interface. Calculations for alloys with stable and unstable solute gradients show the occurrence of classical flow transitions and morphological instabilities in the solidification system.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 7; 761-791
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  • 2
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    Third-order resonance effects and the nonlinear stability of drop oscillations (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The three-dimensional nonlinear oscillations of an isolated, inviscid drop with surface tension are studied by a multiple timescale analysis and pre-averaging applied to the variational principle for the appropriate Lagrangian. Amplitude equations are derived which describe the generic cubic resonance caused by the spatial degeneracy of the eigenfrequencies of the linear normal modes. This resonant coupling leads to the instability of the finite amplitude axisymmetric oscillations to small nonaxisymmetric perturbations, as is demonstrated here for the three- and four-lobed normal modes. Solutions to the interaction equations that describe finite amplitude, nonaxisymmetric traveling-wave solutions are also obtained and their stability is investigated. A nongeneric cubic resonance between the two-lobed and four-lobed oscillatory modes leads to quasi-periodic motions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 183; 95-121
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  • 3
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    Feasibility of Exoplanet Coronagraphy with the Hubble Space Telescope (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Herein we report on a preliminary study to assess the use of the Hubble Space Telescope (HST) for the direct detection and spectroscopic characterization of exoplanets and debris disks - an application for which HST was not originally designed. Coronagraphic advances may enable the design of a science instrument that could achieve limiting contrasts approx.10deg beyond 275 milli-arcseconds (4 lambda/D at 800 nm) inner working angle, thereby enabling detection and characterization of several known jovian planets and imaging of debris disks. Advantages of using HST are that it already exists in orbit, it's primary mirror is thermally stable and it is the most characterized space telescope yet flown. However there is drift of the HST telescope, likely due to thermal effects crossing the terminator. The drift, however, is well characterized and consists of a larger deterministic components and a smaller stochastic component. It is the effect of this drift versus the sensing and control bandwidth of the instrument that would likely limit HST coronagraphic performance. Herein we discuss the science case, quantifY the limiting factors and assess the feasibility of using HST for exoplanet discovery using a hypothetical new instrument. Keywords: Hubble Space Telescope, coronagraphy, exoplanets, telescopes
    Keywords: Astronomy
    Type: GSFC.CPR.4894.2011 , SPIE 7731, Astronomical Telescopes and Instrumentation, San Diego CA, June 2010; Jun 01, 2010; San Diego, CA; United States
    Format: application/pdf
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  • 4
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    Ball Aerospace AMSD Ambient and Cryogenic Test Plans (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The planned testing of the Advanced Mirror System Demonstrator program being performed by Ball Aerospace are presented.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 5
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    Ball Aerospace SBMD Coating Test Results (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The Sub-scale Beryllium Mirror Demonstrator that was successfully tested to demonstrate cryogenic figuring of a bare mirror has been coated with a protected gold reflective surface and retested at cryogenic temperatures. Results showing less than 9 nm rms surface distortion attributable to the added coating are presented.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 6
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    Ball Aerospace AMSD Progress Update (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The current status of the Advanced Mirror System Demonstrator program being performed by Ball Aerospace is presented. The hexagonal low-areal density Beryllium mirror blank has been fabricated and undergoing polishing at the time of this presentation.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 7
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    Spectroscopy of Kuiper Belt Objects and Centaurs (1998)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: Recent near-infrared spectroscopy of Kuiper Belt objects and Centaurs indicates considerable spectral diversity among them. Some have entirely bland spectra with no discernible spectral features (e.g., Chiron), while 5145 Pholus has a very active spectrum with absorption bands of H2O, CH3OH, and probably the mineral olivine present. In addition, the strong red color of Pholus indicates the presence of organic solids. Among the KBOs, 1993 SC has an active spectrum with the probably presence of hydrocarbons and possibly the ices of H2O and N2. The diversity among these spectra and the implications that such diversity has for models of the formation of the formation of the planets will be discussed.
    Keywords: Astronomy
    Type: Protostars and Planets IV Conference; Jul 06, 1998 - Jul 10, 1998; Santa Barbara, CA; United States
    Format: text
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  • 8
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    Optimized program completeness (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Overall program completeness is optimized by selecting the ordered set of observations and targets that maximizes the efficiency for the ensemble of stars. We describe the optimization approach and report on completeness sensitivity to instrument throughput, inner working angle, instrument sensitivity, observational overhead, exo-zodiacal brightness, and target revisit constraints.
    Keywords: Instrumentation and Photography
    Type: Terrestrial Planet Finder - Coronagraph STDT #5; Nov 30, 2005; Pasadena, CA; United States
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  • 9
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    Single visit completeness optimization (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Terrestrial Planet Finder Coronagraph (TPF-C) is a NASA pre-phase. A orbiting telescope with the goal of detecting and characterizing visible and near-IR light refelected from terrestrial planets. We use observational completeness, defined as the fraction of potentially observable planets that are detected, to determine how well the proposed telescope meets the mission goals. Single visit completeness is optimized by slecting the length of observation per target that maximizes the completeness for the ensemble of stars. In this memo we describe the integration time calculations and two approaches to single visit optimization.
    Keywords: Instrumentation and Photography
    Type: Terrestrial Planet Finder - Coronagraph STDT #5; Nov 30, 2005; Pasadena, CA; United States
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  • 10
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    Dynamic centering of liquid shells (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The moderate-amplitude axisymmetric oscillations of an inviscid liquid shell surrounding an incompressible gas bubble are calculated by a multiple-time-scale expansion for initial deformations composed of two-lobed perturbations of the shell and a displacement of the bubble from the center of mass of the liquid. Two types of small-amplitude motion are identified and lead to very different nonlinear dynamic interactions, as described by the results valid up to second order in the amplitude of the initial deformation. In the 'bubble mode', the oscillations of the captive bubble and the liquid shell are exactly in phase and the bubble vibrates about its initial eccentric location. The bubble moves toward the center of the drop when the shell is perturbed into a 'sloshing mode' of oscillation where both interfaces move out of phase. These results explain the centering of liquid shells observed in several experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 30; 27-35
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