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  • Other Sources  (27)
  • Astronomy  (19)
  • FLUID MECHANICS AND HEAT TRANSFER  (5)
  • Numerical Analysis
  • 2005-2009  (20)
  • 1995-1999  (3)
  • 1970-1974  (4)
  • 1
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    Prospects and expectations for unstructured methods (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The last decade has witnessed a vigorous and sustained research effort on unstructured methods for computational fluid dynamics. Unstructured mesh generators and flow solvers have evolved to the point where they are now in use for design purposes throughout the aerospace industry. In this paper we survey the various mesh types, structured as well as unstructured, and examine their relative strengths and weaknesses. We argue that unstructured methodology does offer the best prospect for the next generation of computational fluid dynamics algorithms.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Surface Modeling, Grid Generation, and Related Issues in Computational Fluid Dynamic (CFD) Solutions; p 273-287
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  • 2
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    Gauge Conditions for Moving Black Holes Without Excision (2006)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Recent demonstrations of unexcised, puncture black holes traversing freely across computational grids represent a significant advance in numerical relativity. Stable an$ accurate simulations of multiple orbits, and their radiated waves, result. This capability is critically undergirded by a careful choice of gauge. Here we present analytic considerations which suggest certain gauge choices, and numerically demonstrate their efficacy in evolving a single moving puncture.
    Keywords: Astronomy
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  • 3
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    Mergers of Non-spinning Black-hole Binaries: Gravitational Radiation Characteristics (2008)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: We present a detailed descriptive analysis of the gravitational radiation from black-hole binary mergers of non-spinning black holes, based on numerical simulations of systems varying from equal-mass to a 6:1 mass ratio. Our primary goal is to present relatively complete information about the waveforms, including all the leading multipolar components, to interested researchers. In our analysis, we pursue the simplest physical description of the dominant features in the radiation, providing an interpretation of the waveforms in terms of an implicit rotating source. This interpretation applies uniformly to the full wavetrain, from inspiral through ringdown. We emphasize strong relationships among the l = m modes that persist through the full wavetrain. Exploring the structure of the waveforms in more detail, we conduct detailed analytic fitting of the late-time frequency evolution, identifying a key quantitative feature shared by the l = m modes among all mass-ratios. We identify relationships, with a simple interpretation in terms of the implicit rotating source, among the evolution of frequency and amplitude, which hold for the late-time radiation. These detailed relationships provide sufficient information about the late-time radiation to yield a predictive model for the late-time waveforms, an alternative to the common practice of modeling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model.
    Keywords: Astronomy
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  • 4
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    The High Energy Telescope for STEREO (2008)
    In:  CASI
    Details
    Publication Date: 2018-08-10
    Description: The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to approx. 13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to approx. 100 MeV/n, as are penetrating He. For stopping He, the individual isotopes He-3 and He-4 can be distinguished. Stopping electrons are measured in the energy range approx. 0.7 - 6 MeV.
    Keywords: Astronomy
    Type: To appear in Space Science Reviews
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  • 5
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    COMOC: Three dimensional boundary region variant, theoretical manual and user's guide (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The theoretical and mechanical structure of the computer program is presented along with guidance on adaptation of the code to solution of a particular problem. Sample solutions are discussed for several problems, especially with respect to solution accuracy and speed as a function of parameters under control of the user. Construction of input data decks for sample problems is discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-132450 , D9192-950002
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  • 6
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    COMOC: Three dimensional boundary region variant, programmer's manual (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The three-dimensional boundary region variant of the COMOC computer program system solves the partial differential equation system governing certain three-dimensional flows of a viscous, heat conducting, multiple-species, compressible fluid including combustion. The solution is established in physical variables, using a finite element algorithm for the boundary value portion of the problem description in combination with an explicit marching technique for the initial value character. The computational lattice may be arbitrarily nonregular, and boundary condition constraints are readily applied. The theoretical foundation of the algorithm, a detailed description on the construction and operation of the program, and instructions on utilization of the many features of the code are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-132449 , D9192-954001
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  • 7
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    Finite element solution theory for three-dimensional boundary flows (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A finite element algorithm is derived for the numerical solution of a three-dimensional flow field described by a system of initial-valued, elliptic boundary value partial differential equations. The familiar three-dimensional boundary layer equations belong to this description when diffusional processes in only one coordinate direction are important. The finite element algorithm transforms the original description into large order systems of ordinary differential equations written for the dependent variables discretized at node points of an arbitrarily irregular computational lattice. The generalized elliptic boundary conditions is piecewise valid for each dependent variable on boundaries that need not explicitly coincide with coordinate surfaces. Solutions for sample problems in laminar and turbulent boundary flows illustrate favorable solution accuracy, convergence, and versatility.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computer Methods in Applied Mechanics and Engineering; 4; Nov. 197
    Format: text
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  • 8
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    Observing Merging Massive Black Hole Binaries with LISA (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: The Laser Interferometer Space Antenna (LISA) is expected to detect gravitational radiation from the inspiral and merger of massive black hole binaries at high redshifts with large signal-to-noise ratios (SNRs). These high-SNR observations will make it possible to extract physical parameters such as hole masses and spins, luminosity distance, and sky position from the observed waveforms. LISA'S effectiveness as a tool for astrophysics will be influenced by the precision with which these parameters can be measured. In addition, the practicality of coordinated observations with other instruments will be affected by the temporal evolution of parameter errors such as sky position. We present estimates of parameter errors for the special case of non-spinning black holes. Our focus is on the contribution of the late inspiral and merger portions of the waveform, a regime which typically dominates the SNR but has not been extensively studied due to the historic lack of a precise description of the waveform. Advances in numerical relativity have recently made such studies possible. Initial results suggest that the portion of the waveform beyond the Schwarzchild inner-most stable circular orbit can reduce parameter uncertainties by up to a factor of two.
    Keywords: Astronomy
    Type: 2009 Meeting of the American Physical Society; May 02, 2009 - May 05, 2009; Colorado; United States
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  • 9
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    Nonlinear initial-boundary value solutions by the finite element method (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The finite-element method is used to establish a numerical solution algorithm for the Navier-Stokes equations for two-dimensional flows of a viscous compressible fluid. Numerical experiments confirm the advection property for the finite-element equivalent of the nonlinear convection term for both unidirectional and recirculating flowfields. For linear functionals, the algorithm demonstrates good accuracy using coarse discretizations and h squared convergence with discretization refinement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computational methods in nonlinear mechanics; International Conference; Sep 23, 1974 - Sep 25, 1974; Austin, TX
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  • 10
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    The Design and Performance of the Astro-E/XRS Signal Processing System (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We describe the signal processing system of the Astro-E XRS instrument. The Calorimeter Analog Processor (CAP) provides bias and power for the detectors and amplifies the detector signals by a factor of 20,000. The Calorimeter Digital Processor (CDP) performs the digital processing of the calorimeter signals, detecting X-ray pulses and analyzing them by optimal filtering. We describe the operation of pulse detection, pulse height analysis, and risetime determination. We also discuss performance, including the three event grades (hi-res, mid-res, and low-res), anticoincidence detection, counting rate dependence, and noise rejection.
    Keywords: Astronomy
    Type: Jul 18, 1999 - Jul 23, 1999; Denver, CO; United States
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