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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Crowned spur gears - Methods for generation and Tooth Contact Analysis. II - Generation of the pinion tooth surface by a surface of revolution

A method for generation of crowned pinion tooth surfaces using a surface of revolution is developed. The crowned pinion meshes with a regular involute gear and has a prescribed parabolic type of transmission errors when the gears operate in the aligned mode. When the gears are misaligned the transmission error remains parabolic with the maximum level still remaining very small (less than 0.34 arc second for the numerical examples). Tooth Contact Analysis (TCA) is used to simulate the conditions of meshing, determine the transmission error, and the bearing contact.

Litvin, F. L.↗
NASA NTRS1990

Diffusive shock acceleration of energetic electrons and the method of generations

The diffusive shock acceleration of energetic electrons at a plane shock is studied by means of the method of generations developed by Petukhov et al. (1986), where the particles are binned according to the number of particle acceleration cycles. The method emphasizes the cyclic character of the shock acceleration process, and takes into account the particle energy increment per cycle, the energy loss per cycle, and the escape probability of particles downstream of the shock. In the limit of a small fractional momentum gain per cycle, the method reproduces the known steady-state semianalytic solution for constant diffusion coefficients on both sides of the shock. It is demonstrated that the method may also be applied to time-dependent shock-acceleration problems.

Webb, G. M.↗
NASA NTRS1995

Elliptic surface grid generation on minimal and parmetrized surfaces

An elliptic grid generation method is presented which generates excellent boundary conforming grids in domains in 2D physical space. The method is based on the composition of an algebraic and elliptic transformation. The composite mapping obeys the familiar Poisson grid generation system with control functions specified by the algebraic transformation. New expressions are given for the control functions. Grid orthogonality at the boundary is achieved by modification of the algebraic transformation. It is shown that grid generation on a minimal surface in 3D physical space is in fact equivalent to grid generation in a domain in 2D physical space. A second elliptic grid generation method is presented which generates excellent boundary conforming grids on smooth surfaces. It is assumed that the surfaces are parametrized and that the grid only depends on the shape of the surface and is independent of the parametrization. Concerning surface modeling, it is shown that bicubic Hermite interpolation is an excellent method to generate a smooth surface which is passing through a given discrete set of control points. In contrast to bicubic spline interpolation, there is extra freedom to model the tangent and twist vectors such that spurious oscillations are prevented.

Spekreijse, S. P.↗
NASA NTRS1988

Spur gears: Optimal geometry, methods for generation and Tooth Contact Analysis (TCA) program

The contents of this report include the following: (1) development of optimal geometry for crowned spur gears; (2) methods for their generation; and (3) tooth contact analysis (TCA) computer programs for the analysis of meshing and bearing contact on the crowned spur gears. The method developed for synthesis is used for the determination of the optimal geometry for crowned pinion surface and is directed to reduce the sensitivity of the gears to misalignment, localize the bearing contact, and guarantee the favorable shape and low level of the transmission errors. A new method for the generation of the crowned pinion surface has been proposed. This method is based on application of the tool with a surface of revolution that slightly deviates from a regular cone surface. The tool can be used as a grinding wheel or as a shaver. The crowned pinion surface can also be generated by a generating plane whose motion is provided by an automatic grinding machine controlled by a computer. The TCA program simulates the meshing and bearing contact of the misaligned gears. The transmission errors are also determined.

Litvin, Faydor L.↗
NASA NTRSDate not supplied

Copula-based Method to Generate Consistent Surface Pressures Under Uncertainty

This paper establishes a method to create surface pressure databases that allow for uncertainty quantification. Aerodynamic databases are critical products for launch vehicles and other aeronautical systems, and surface pressure databases are one such database that constains large quantities of data. The focus of this work is the relationship between the integrated force and moment data base and the surface pressure database. In particular, the work attempts to provide a method that maintains consistency between these two databases when accounting for uncertainty. The integrated force and moment database and surface pressure databases are constructed from CFD data which is high-density but low-trust. However, the force and moment database will often also include data from high-trust but low-density sources such as from wind tunnel experiments. This means that the quantified uncertainty of the force and moment database is higher quality as it includes this high fidelity wind tunnel data. This motivates the idea to use the force and moment database uncertainty when constructing the surface pressure database uncertainty. The method utilizes the statistical idea of a copula in order to generate surface pressures that match with uncertain integrated force and moment distributions as well as being consistent with known CFD data. This statistical consistency is quantified by using the Maximum Mean Discrepancy two-sample test. The predictive error of the method is also approximated using leave-one-out error estimation and the good overall performance of the method is presented using probability boxes in a simulated uncertainty scenario.

SLS↗
NASA NTRS1997

Fiber-optic delay-line stabilization of heterodyne optical signal generator and method using same

The present invention is a laser heterodyne frequency generator system with a stabilizer for use in the microwave and millimeter-wave frequency ranges utilizing a photonic mixer as a photonic phase detector in a stable optical fiber delay-line. Phase and frequency fluctuations of the heterodyne laser signal generators are stabilized at microwave and millimeter wave frequencies by a delay line system operating as a frequency discriminator. The present invention is free from amplifier and mixer 1/.function. noise at microwave and millimeter-wave frequencies that typically limit phase noise performance in electronic cavity stabilized electronic oscillators. Thus, 1/.function. noise due to conventional mixers is eliminated and stable optical heterodyne generation of electrical signals is achieved.

Logan, Ronald T.↗
NASA NTRS1989

An algebraic homotopy method for generating quasi-three-dimensional grids for high-speed configurations

A fast and versatile procedure for algebraically generating boundary conforming computational grids for use with finite-volume Euler flow solvers is presented. A semi-analytic homotopic procedure is used to generate the grids. Grids generated in two-dimensional planes are stacked to produce quasi-three-dimensional grid systems. The body surface and outer boundary are described in terms of surface parameters. An interpolation scheme is used to blend between the body surface and the outer boundary in order to determine the field points. The method, albeit developed for analytically generated body geometries is equally applicable to other classes of geometries. The method can be used for both internal and external flow configurations, the only constraint being that the body geometries be specified in two-dimensional cross-sections stationed along the longitudinal axis of the configuration. Techniques for controlling various grid parameters, e.g., clustering and orthogonality are described. Techniques for treating problems arising in algebraic grid generation for geometries with sharp corners are addressed. A set of representative grid systems generated by this method is included. Results of flow computations using these grids are presented for validation of the effectiveness of the method.

Moitra, Anutosh↗
NASA NTRS1990

Unstructured mesh methods for CFD

Mesh generation methods for Computational Fluid Dynamics (CFD) are outlined. Geometric modeling is discussed. An advancing front method is described. Flow past a two engine Falcon aeroplane is studied. An algorithm and associated data structure called the alternating digital tree, which efficiently solves the geometric searching problem is described. The computation of an initial approximation to the steady state solution of a given poblem is described. Mesh generation for transient flows is described.

Peraire, J.↗
NASA NTRS2011

High-velocity, multistage, nozzled, ion driven wind generator and method of operation of the same adaptable to mesoscale realization

Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, a methodology for increasing their flow velocities includes exploitation of the divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. The design becomes particularly advantageous when implemented in mesoscale domains.

Dunn-Rankin, Derek↗
NASA NTRS2015

Method to Generate Full-Span Ice Shape on Swept Wing Using Icing Tunnel Data

There is a collaborative research program by NASA, FAA, ONERA, and university partners to improve the fidelity of experimental and computational simulation methods for swept-wing ice accretion formulations and resultant aerodynamic effects on large transport aircraft. This research utilizes a 65 scale Common Research Model as the baseline configuration. In order to generate the ice shapes for the aerodynamic testing, ice-accretion testing will be conducted in the NASA Icing Research Tunnel utilizing hybrid model from the 20, 64, and 83 spanwise locations. The models will have full-scale leading edges with truncated chord in order to fit the IRT test section. The ice shapes from the IRT tests will be digitized using a commercially available articulated-arm 3D laser scanning system. The methodology to acquire 3D ice shapes using a laser scanner was developed and validated in a previous research effort. Each of these models will yield a 1.5ft span of ice than can be used. However, a full-span ice accretion will require 75 ft span of ice. This means there will be large gaps between these spanwise ice sections that must be filled, while maintaining all of the important aerodynamic features. A method was developed to generate a full-span ice shape from the three 1.5 ft span ice shapes from the three models.

swept↗
NASA NTRS1980

Application of the multigrid method to grid generation

The multigrid method (MGM), used to numerically solve the pair of nonlinear elliptic equations commonly used to generate two dimensional boundary-fitted coordinate systems is discussed. Two different geometries are considered: one involving a coordinate system fitted about a circle and the other selected for an impinging jet flow problem. Two different relaxation schemes are tried: one is successive point overrelaxation and the other is a four-color scheme vectorizeable to take advantage of a parallel processor computer for greater computational speed. Results using MGM are compared with those using SOR (doing successive overrelaxations with the corresponding relaxation scheme on the fine grid only). It is found that MGM becomes significantly more effective than SOR as more accuracy is demanded and as more corrective grids, or more grid points, are used. For the accuracy required, it is found that MGM is two to three times faster than SOR in computing time. With the four-color relaxation scheme as applied to the impinging jet problem, the advantage of MGM over SOR is not as great. This may be due to the effect of a poor initial guess on MGM for this problem.

Ohring, S.↗
NASA NTRS2009

Method of Generating X-Ray Diffraction Data for Integral Detection of Twin Defects in Super-Hetero-Epitaxial Materials

A method provides X-ray diffraction (XRD) data suitable for integral detection of a twin defect in a strained or lattice-matched epitaxial material made from components having crystal structures having symme try belonging to different space groups. The material is mounted in a n X-ray diffraction (XRD) system. In one embodiment, the XRD system's goniometer angle Omega is set equal to (Theta(sub B)-Beta) where The ta(sub B) is a Bragg angle for a designated crystal plane of the allo y that is disposed at a non-perpendicular orientation with respect to the {111) crystal plane, and Beta is the angle between the designate d crystal plane and a { 111 } crystal plane of one of the epitaxial components. The XRD system's detector angle is set equal to (Theta(su b B)+Beta). The material can be rotated through an angle of azimuthal rotation Phi about the axis aligned with the material. Using the det ector, the intensity of the X-ray diffraction is recorded at least at the angle at which the twin defect occurs.

Park, Yeonjoon↗
NASA NTRS2002

Computing Aerodynamic Performance of a 2D Iced Airfoil: Blocking Topology and Grid Generation

The ice accrued on airfoils can have enormously complicated shapes with multiple protruded horns and feathers. In this paper, several blocking topologies are proposed and evaluated on their ability to produce high-quality structured multi-block grid systems. A transition layer grid is introduced to ensure that jaggedness on the ice-surface geometry do not to propagate into the domain. This is important for grid-generation methods based on hyperbolic PDEs (Partial Differential Equations) and algebraic transfinite interpolation. A 'thick' wrap-around grid is introduced to ensure that grid lines clustered next to solid walls do not propagate as streaks of tightly packed grid lines into the interior of the domain along block boundaries. For ice shapes that are not too complicated, a method is presented for generating high-quality single-block grids. To demonstrate the usefulness of the methods developed, grids and CFD solutions were generated for two iced airfoils: the NLF0414 airfoil with and without the 623-ice shape and the B575/767 airfoil with and without the 145m-ice shape. To validate the computations, the computed lift coefficients as a function of angle of attack were compared with available experimental data. The ice shapes and the blocking topologies were prepared by NASA Glenn's SmaggIce software. The grid systems were generated by using a four-boundary method based on Hermite interpolation with controls on clustering, orthogonality next to walls, and C continuity across block boundaries. The flow was modeled by the ensemble-averaged compressible Navier-Stokes equations, closed by the shear-stress transport turbulence model in which the integration is to the wall. All solutions were generated by using the NPARC WIND code.

Chi, X.↗
NASA NTRS2012

Methods for generation of reporter phages and immobilization of active bacteriophages on a polymer surface

Novel reporter bacteriophages are provided. Provided are compositions and methods that allow bacteriophages that are used for specific detection or killing of E. coli 0157:H7 to be propagated in nonpathogenic E. coli, thereby eliminating the safety and security risks of propagation in E. coli 0157:H7. Provided are compositions and methods for attaching active bacteriophages to the surface of a polymer in order to kill target bacteria with which the phage comes into contact. Provided are modified bacteriophages immobilized to a surface, which capture E. coli 0157:H7 and cause the captured cells to emit light or fluorescence, allowing detection of the bacteria in a sample.

Applegate, Bruce Michael↗
NASA NTRS1993

Tsien's method for generating non-Keplerian trajectories. Part 2: The question of thrust to orbit a sphere and the restricted three-body problem

Tsien's method is extended to treat the orbital motion of a body undergoing accelerations and decelerations. A generalized solution is discussed for the generalized case where a body undergoes azimuthal and radial thrust and the problem is further simplified for azimuthal thrust alone. Judicious selection of thrust could generate either an elliptic or hyperbolic trajectory. This is unexpected especially when the body has only enough energy for a lower state trajectory. The methodology is extended treating the problem of vehicle thrust for orbiting a sphere and vehicle thrust within the classical restricted three-body problem. Results for the latter situation can produce hyperbolic trajectories through eigen value decomposition. Since eigen values for no-thrust can be imaginary, thrust can generate real eigen values to describe hyperbolic trajectories. Keplerian dynamics appears to represent but a small subset of a much larger non-Keplerian domain especially when thrust effects are considered. The need for high thrust long duration space-based propulsion systems for changing a trajectory's canonical form is clearly demonstrated.

Murad, P. A.↗
NASA NTRS2011

Power generation systems and methods

A power generation system includes a plurality of submerged mechanical devices. Each device includes a pump that can be powered, in operation, by mechanical energy to output a pressurized output liquid flow in a conduit. Main output conduits are connected with the device conduits to combine pressurized output flows output from the submerged mechanical devices into a lower number of pressurized flows. These flows are delivered to a location remote of the submerged mechanical devices for power generation.

Jones, Jack A.↗
NASA NTRS1991

Computation of three-dimensional flows using two stream functions

An approach to compute 3-D flows using two stream functions is presented. The method generates a boundary fitted grid as part of its solution. Commonly used two steps for computing the flow fields are combined into a single step in the present approach: (1) boundary fitted grid generation; and (2) solution of Navier-Stokes equations on the generated grid. The presented method can be used to directly compute 3-D viscous flows, or the potential flow approximation of this method can be used to generate grids for other algorithms to compute 3-D viscous flows. The independent variables used are chi, a spatial coordinate, and xi and eta, values of stream functions along two sets of suitably chosen intersecting stream surfaces. The dependent variables used are the streamwise velocity, and two functions that describe the stream surfaces. Since for a 3-D flow there is no unique way to define two sets of intersecting stream surfaces to cover the given flow, different types of two sets of intersecting stream surfaces are considered. First, the metric of the (chi, xi, eta) curvilinear coordinate system associated with each type is presented. Next, equations for the steady state transport of mass, momentum, and energy are presented in terms of the metric of the (chi, xi, eta) coordinate system. Also included are the inviscid and the parabolized approximations to the general transport equations.

Greywall, Mahesh S.↗