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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Computational challenge - Euler solution for ellipses

The present treatment of the inviscid flow past an ellipse via the numerical solution of the Euler equations yields a lifting solution for any combination of grid and/or angle of attack which is nonsymmetric, in order to illustrate the CFD challenge posed by this unusual flow behavior. The results obtained call into question the general capability and validity of numerical Euler results in the realm of conventional difference methods; specifically, the mechanism generating lifting results is not understood, and the problem's resolution is not yet in sight.

Pulliam, Thomas H.↗
NASA NTRS1990

DSMC calculations for the double ellipse

The direct simulation Monte Carlo (DSMC) method involves the simultaneous computation of the trajectories of thousands of simulated molecules in simulated physical space. Rarefied flow about the double ellipse for test case 6.4.1 has been calculated with the DSMC method of Bird. The gas is assumed to be nonreacting nitrogen flowing at a 30 degree incidence with respect to the body axis, and for the surface boundary conditions, the wall is assumed to be diffuse with full thermal accommodation and at a constant wall temperature of 620 K. A parametric study is presented that considers the effect of variations of computational domain, gas model, cell size, and freestream density on surface quantities.

Moss, James N.↗
NASA NTRS1989

Optimal Chebyshev polynomials on ellipses in the complex plane

The design of iterative schemes for sparse matrix computations often leads to constrained polynomial approximation problems on sets in the complex plane. For the case of ellipses, we introduce a new class of complex polynomials which are in general very good approximations to the best polynomials and even optimal in most cases.

Fischer, Bernd↗
NASA NTRS1991

Computation of thermochemical nonequilibrium flows around a simple and a double ellipse

The nonequilibrium viscous reactive flows over a simple and a double ellipse at a 30 degree angle of attack were computed. The geometry and the free stream conditions are given by INRIA/GAMNI/SMAI workshop test cases 6.2-2 and 6.2-4. The governing Navier-Stokes equations coupled with thermochemical nonequilibrium processes are solved numerically using a fully coupled, implicit, finite volume technique with a dynamically adaptive grid. The nonequilibrium gas model and the numerical method used in the calculations are briefly described.

Gokcen, Tahir↗
NASA NTRS1991

The hypersonic double ellipse in rarefied flow

The problem of the hypersonic double ellipse in rarefied flow is treated by a particle method using the collision model first described by McDonald (1988). In the approach used here, the computational overhead is reduced by using simple cubic cells. The problem of the definition of complex geometries is addressed by developing an algorithm to define the relation of a body surface to the network of cells.

Feiereisen, William J.↗
NASA NTRS1999

Determination of Principal Curvatures and Contact Ellipse for Profile Crowned Helical Gears

Helical gears with localized bearing contact of tooth surfaces achieved by profile crowning of tooth surfaces are considered. Profile crowning is provided by application of two imaginary rack-cutters with mismatched surfaces. The goal is to determine the dimensions and orientation of the instantaneous contact ellipse that requires the determination of principle curvatures of pinion-gear tooth surfaces. A simplified solution to this problem is proposed based on the approach development for correlation of principal curvatures and directions of generating and generated tooth surfaces. The obtained equations are applied for profile crowning where the normal profiles of the rack-cutters are either a circular arc or a straight line.

Feng, P.-H.↗
NASA NTRS2002

Strategy for the In Situ Search of Evaporite and Carbonate Deposits in Gusev Crater Within the 2003 MER A Landing Ellipse

Topographic profiles and MOC images suggest that the flat floor of Gusev results from sediment deposition in the absence of strong sublacustrine currents. This setting is favorable to preserve undisturbed sedimentary sequences and identify carbonates and evaporites in the landing ellipse. Additional information is contained in the original extended abstract.

Grin, E. A.↗
NASA NTRS2005

Safety Ellipse Motion with Coarse Sun Angle Optimization

The Hubble Space Telescope Robotic Servicing and De-orbit Mission (HRSDM) was t o be performed by the unmanned Hubble Robotic Vehicle (HRV) consisting of a Deorbit Module (DM), responsible for the ultimate disposal of Hubble Space Telescope (HST) at the end of science operations, and an Ejection Module (EM), responsible for robotically servicing the HST to extend its useful operational lifetime. HRSDM consisted of eight distinct phases, including: launch, pursuit, proximity operations, capture, servicing, EM jettison and disposal, science operations, and deorbit. The scope of this paper is limited to the Proximity Operations phase of HRSDM. It introduces a relative motion strategy useful for Autonomous Rendezvous and Docking (AR&D) or Formation Flying missions where safe circumnavigation trajectories, or close proximity operations (tens or hundreds of meters) are required for extended periods of time. Parameters and algorithms used to model the relative motion of HRV with respect to HST during the Proximity Operations phase of the HRSDM are described. Specifically, the Safety Ellipse (SE) concept, convenient parameters for describing SE motion, and a concept for initializing SE motion around a target vehicle to coarsely optimize sun and relative navigation sensor angles are presented. The effects of solar incidence angle variations on sun angle optimization, and the effects of orbital perturbations and navigation uncertainty on long term SE motion are discussed.

Naasz, Bo↗
NASA NTRS2015

Crater Morphology in the Phoenix Landing Ellipse: Insights Into Net Erosion and Ice Table Depth

Icebreaker [1] is a Discovery class mission being developed for future flight opportunities. Under this mission concept, the Icebreaker payload is carried on a stationary lander, and lands in the same landing ellipse as Phoenix. Samples are acquired from the subsurface using a drilling system that penetrates into materials which may include loose or cemented soil, icy soil, pure ice, rocks, or mixtures of these. To avoid the complexity of mating additional strings, the drill is single-string, limiting it to a total length of 1 m.

Icebreaker mission↗
NASA NTRSDate not supplied

Spacecraft Passive Safety Assessment Using Ellipse Constraints and Relative Orbital Elements

This paper presents necessary and sufficient conditions for validating spacecraft passive safety using relative orbital elements (ROE) centered around the far-field to near-field trajectory design of a hypothetical autonomous rendezvous and docking (AR&D) mission. The specific formulation of the ROEs used in this study are of quasi-nonsingular form based on elative eccentricity/inclination vectors. Current methodologies for ensuring passive safety apply keep-out volumes (KOV) to maintain appropriate separation between the Servicer and Client. Widely used techniques to assess the integrity of the KOV involve forward propagation of the relative Cartesian state to check for a potential KOV breach. In this study, an alternative approach to the propagation-based method is proposed using ROEs due to their valuable geometric insights of spacecraft relative motion. Modeling the relative trajectory and KOV ellipsoids as ellipses into the 2-D ROE sub-space simplifies the passive safety validation to a root-finding problem within the unit disk with high computational efficiency. Other approaches to intersection detection of the KOV are also evaluated in accuracy and run-time. Furthermore, a Monte Carlo simulation was employed to compare the ROE-based and relative Cartesian approaches in terms of maneuver error.

Bruce Barbour↗
DOE OSTI2022

Mid-infrared chiral metasurface absorbers with split-ellipse structures

Natural chiral materials usually have very weak circular dichroism (CD) responses. Here, in this study, we design and demonstrate one type of mid-infrared chiral metasurface absorber with strong chiroptical effects, which can achieve high CD in absorption above 0.57 over the wavelength range of 5 to 5.9 μm. The maximum absorption of the chiral metasurface absorber under circularly polarized light can reach 0.90 and the maximum CD in absorption is 0.63. Meanwhile, the chiral resonance wavelength and the CD value can be tuned by varying the geometric parameters of the metasurface. A thermal analysis of the metasurface absorber further shows the strong connection between CD in absorption and temperature difference. The demonstrated chiral metasurface absorbers can be used in many promising applications such as molecular sensing, thermophotovoltaics and chiral spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Longitudinal Twiss parameters for tilted phase space ellipses

The longitudinal emittance ϵ s is usually defined under the implicit assumption that the longitudinal phase space distribution is erect, an assumption that is significantly incorrect near transition. This note generalizes the definition of e, to include tilted distributions, by introducing longitudinal Twiss functions β a , α s and γ s that are analogous to transverse Twiss functions. The evolution of these longitudinal parameters through RHIC transition is presented, for a typical set of simulation data.

43 PARTICLE ACCELERATORS↗