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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

e+/- Pair Loading and the Origin of the Upstream Field in GRB Shocks

We investigate here the effects of plasma instabilities driven by rapid e(sup plus or minus) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of their original spectrum. The injection of e(sup plus or minus) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup plus or minus) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup plus or minus) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

Ramirez-Ruiz, Enrico↗
NASA NTRS2007

Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability

We have investigated the effects of plasma instabilities driven by rapid e(sup plus or minus) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of the original spectrum. The injection of e(sup plus or minus) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup plus or minus) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup plus or minus) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

Nishikawa, K.-I.↗
NASA NTRS2006

e(sup +/-) Pair Loading and the Origin of the Upstream Magnetic Field in GRB Shocks

We investigate here the effects of plasma instabilities driven by rapid e(sup +/-) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of their original spectrum. The injection of e(sup +/-) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup +/-) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup +/-) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

Ramirez-Ruiz, Enrico↗
NASA NTRS2017

The Three-Dimensional Expansion of the Ejecta from Tycho's Supernova Remnant

We present the first 3D measurements of the velocity of various ejecta knots in Tycho's supernova remnant, known to result from a Type Ia explosion. Chandra X-ray observations over a 12 yr baseline from 2003 to 2015 allow us to measure the proper motion of nearly 60 tufts of Si-rich ejecta, giving us the velocity in the plane of the sky. For the line-of-sight velocity, we use two different methods: a nonequilibrium ionization model fit to the strong Si and S lines in the 1.22.8 keV regime, and a fit consisting of a series of Gaussian lines. These methods give consistent results, allowing us to determine the redshift or blueshift of each of the knots. Assuming a distance of 3.5 kpc, we find total velocities that range from 2400 to 6600 km/s, with a mean of 4430 km/s. We find several regions where the ejecta knots have overtaken the forward shock. These regions have proper motions in excess of 6000 km/s. Some SN Ia explosion models predict a velocity asymmetry in the ejecta. We find no such velocity asymmetries in Tycho, and we discuss our findings in light of various explosion models, favoring those delayed-detonation models with relatively vigorous and symmetrical deflagrations. Finally, we compare measurements with models of the remnant's evolution that include both smooth and clumpy ejecta profiles, finding that both ejecta profiles can be accommodated by the observations.

ISM: individual objects (Tycho’s SNR) – ISM: s↗
NASA NTRS1994

Qualitative study of the behavior of minor species during a stratospheric warming with a 3-D model

It is well-known that the behavior of the ozone layer depends upon the coupling between several processes in the atmosphere. Natural or anthropogenic pollutants emitted from the surface or injected directly at high altitude may affect this layer. Assessment studies for long-term changes of the ozone layer are conducted with the aid of various two-dimensional models. These models describe the long-term and seasonal evolution of minor constituents and take into account the interaction between all processes. However, many limitations affect the self-consistency of these models e.g., the circulation in these models is only meridional and vertical and is not able to represent all types of motion in the atmosphere. During a perturbed winter in the north polar regions, the vortex is displaced from the pole to lower latitude so that wind may be reversed at a given location. Perturbed air masses are transported outside the darkened regions and may mix with local air masses. Three-dimensional models are the only tools which can describe correctly these sporadic phenomena.

Ramaroson, R.↗
NASA NTRS1993

On nonlinear Tollmien-Schlichting/vortex interaction in three-dimensional boundary layers

The instability of an incompressible three-dimensional boundary layer (that is, one with cross-flow) is considered theoretically and computationally in the context of vortex/wave interactions. Specifically the work centers on two low amplitude, lower-branch Tollmien-Schlichting waves which mutually interact to induce a weak longitudinal vortex flow; the vortex motion, in turn, gives rise to significant wave-modulation via wall-shear forcing. The characteristic Reynolds number is taken as a large parameter and, as a consequence, the waves' and the vortex motion are governed primarily by triple-deck theory. The nonlinear interaction is captured by a viscous partial-differential system for the vortex coupled with a pair of amplitude equations for each wave pressure. Three distinct possibilities were found to emerge for the nonlinear behavior of the flow solution downstream - an algebraic finite-distance singularity, far downstream saturation or far-downstream wave-decay (leaving pure vortex flow) - depending on the input conditions, the wave angles, and the size of the cross-flow.

Davis, Dominic A. R.↗
NASA NTRS1981

Subcritical transition to turbulence in planar shear flows

The two-dimensional steady and time dependent properties of plane Poiseuille and plane Couette flows are analyzed using iterative techniques and full numerical simulation of the Navier-Stokes equations. It is shown that the finite-amplitude two-dimensional states investigated are strongly unstable to very small three-dimensional perturbations. It is also shown, through full numerical simulation, that this explosive secondary instability can explain the subcritical transitions that occur in real flows. Finally, it is shown that the three-dimensional instability can be analyzed by a linear stability analysis of a two-dimensional flow consisting of the basic parallel flow and a steady (or quasi-steady) finite-amplitude two-dimensional cellular motion.

Orszag, S. A.↗
NASA NTRS1987

Turbulence structure at high shear rate

The structure of homogeneous turbulence in the presence of a high shear rate is studied using results obtained from three-dimensional time-dependent numerical simulations of the Navier-Stokes equations on a grid of 512 x 128 x 128 node points. It is shown that high shear rate enhances the streamwise fluctuating motion to such an extent that a highly anisotropic turbulence state with a one-dimensional velocity field and two-dimensional small-scale turbulence develops asymptotically as total shear increases. Instantaneous velocity fields show that high shear rate in homogeneous turbulent shear flow produces structures which are similar to the streaks present in the viscous sublayer of turbulent boundary layers.

Lee, Moon Joo↗
NASA NTRS1988

The recovery and utilization of space suit range-of-motion data

A technique for recovering data for the range of motion of a subject wearing a space suit is described along with the validation of this technique on an EVA space suit. Digitized data are automatically acquired from video images of the subject; three-dimensional trajectories are recovered from these data, and can be displayed using three-dimensional computer graphics. Target locations are recovered using a unique video processor and close-range photogrammetry. It is concluded that such data can be used in such applications as the animation of anthropometric computer models.

Reinhardt, AL↗
NASA NTRS1991

US automated rendezvous and capture capabilities review. Remote umbilical system abstract

This document will describe the technology developed at Kennedy Space Center (KSC) to demonstrate automatic tracking, docking, and mating of umbilical systems. Specifically the use of a real time six degree of freedom (6DOF) target tracking vision system, (developed by Adaptive Automation, Inc. under contract to KSC), is discussed in detail. The paper describes the use of mechanical compliance in the docking, mating, and tracking-after-mating operations. The vision system computes six coordinates that define the position and orientation of a three dimensional target using data from a single CCD camera. The camera is mounted on a 6DOF robot arm. After target coordinates are computed, they are transmitted to a supervisory computer which controls the robot motion in real time. Details of the image processing algorithms, image processing hardware, and target configuration used in the vision system are discussed in the paper. The motion of the space vehicle relative to the service structure after mating led us to the development of a compliant system that allows enough displacement of the target relative to the camera so that tracking after mating may continue. This reduces internal stresses between flight and ground hardware.

Delcastillo, Eduardo Lopez↗
NASA NTRS2002

Design and Analysis of Turbomachinery for Space Applications

This presentation provides an overview of CORSAIR, a three dimensional computational fluid dynamics software code for the analysis of turbomachinery components available from NASA, and discusses its potential use in the design of these parts. Topics covered include: time-dependent equations of motion, grid topology, turbulence models, boundary conditions, parallel simulations and miscellaneous capabilities.

Dorney, D.↗
NASA NTRS2011

A Flight Dynamics Model for a Multi-Actuated Flexible Rocket Vehicle

A comprehensive set of motion equations for a multi-actuated flight vehicle is presented. The dynamics are derived from a vector approach that generalizes the classical linear perturbation equations for flexible launch vehicles into a coupled three-dimensional model. The effects of nozzle and aerosurface inertial coupling, sloshing propellant, and elasticity are incorporated without restrictions on the position, orientation, or number of model elements. The present formulation is well suited to matrix implementation for large-scale linear stability and sensitivity analysis and is also shown to be extensible to nonlinear time-domain simulation through the application of a special form of Lagrange s equations in quasi-coordinates. The model is validated through frequency-domain response comparison with a high-fidelity planar implementation.

Orr, Jeb S.↗
NASA NTRSDate not supplied

Mission Design & Operations Approach for the HelioSwarm Mission

HelioSwarm: The Nature of Turbulence in Space Plasmas is a transformational mission to explore the dynamic three-dimensional mechanisms controlling the physics of plasma turbulence, a ubiquitous process occurring in the heliosphere and plasmas throughout the universe. Turbulence is the process by which energy contained in fluctuating magnetic fields and plasma motion cascades from large to smaller spatial scales. HelioSwarm achieves its science goals by making simultaneous measurements across a wide range of measurement baselines, spanning magnetohydrodynamic scales (1000’s of km) to sub-ion heating scales (10’s of km), using a novel nine-spacecraft swarm. The swarm operates in a high-altitude lunar resonant Earth orbit (two-week period, ~63 RE apogee, ~13 RE perigee), giving it access to both the pristine solar wind and regions of strongly driven turbulence (specifically the magnetosphere and foreshock), and utilizes customized relative orbital motion of the swarm members to produce the range of measurement baselines and configurations. The swarm comprises eight “node” spacecraft, manufactured by Blue Canyon Technologies, and a “hub” spacecraft produced by Northrop Grumman Corp. The hub serves as a communications relay, with all communications between the ground and the nodes flowing through it. Mission operations are conducted within the Multi-Mission Operations Center at the NASA Ames Research Center and science operations at the University of New Hampshire, Durham. HelioSwarm was selected in 2022 as one of NASA’s newest Heliophysics Explorer missions to proceed from mission concept into mission implementation, with a target launch in 2029. This paper provides an overview of the mission’s science goals and objectives, the mission design, and the concept of operations, with an emphasis on how the swarm aspects of the mission both enable the science measurements and present unique operational challenges. The paper then describes the proposed development approach for the mission operations system and ground data system which relies on a selective combination of scaling strategies to meet the challenges.

HelioSwarm↗
NASA NTRS2002

Three-Dimensional Stress Fields and Slip Systems for Single Crystal Superalloy Notched Specimens

Single crystal superalloys have become increasingly popular for turbine blade and vane applications due to their high strength, and creep and fatigue resistance at elevated temperatures. The crystallographic orientation of a single crystal material greatly affects its material properties, including elastic modulus, shear modulus, and ductility. These directional properties, along with the type of loading and temperature, dictate an anisotropic response in the yield strength, creep resistance, creep rupture ductility, fatigue resistance, etc. A significant amount of research has been conducted to determine the material properties in the <001> orientation, yet the material properties deviating from the <001> orientation have not been assessed for all cases. Based on the desired application and design criteria, a crystal orientation is selected to yield the maximum properties. Currently, single crystal manufacturing is able to control the primary crystallographic orientation within 15 of the target orientation, which is an acceptable deviation to meet both performance and cost guidelines; the secondary orientation is rarely specified. A common experiment is the standard load-controlled tensile test, in which specimens with different orientations can be loaded to observe the material response. The deformation behavior of single-crystal materials under tension and compression is known to be a function of not only material orientation, but also of varying microdeformation (i.e. dislocation) mechanisms. The underlying dislocation motion causes deformation via slip, and affects the activation of specific slip systems based on load and orientation. The slip can be analyzed by observing the visible traces left on the surface of the specimen from the slip activity within the single crystal material. The goal of this thesis was to predict the slip systems activated in three-dimensional stress fields of a notched tensile specimen, as a function of crystal orientation, using finite element analysis without addressing microstructural deformation mechanisms that govern their activation. Out of three orientations tested, the specimen with a [110] load orientation and a [001] growth direction had the lowest maximum resolved shear stress; this specimen orientation appears to be the best design candidate for a tensile application.

Magnan, Shannon M.↗
NASA NTRS1985

Unsteady transonic flow calculations for two-dimensional canard-wing configurations with aeroelastic applications

Unsteady transonic flow calculations for aerodynamically interfering airfoil configurations are performed as a first-step toward solving the three-dimensional canard-wing interaction problem. These calculations are performed by extending the XTRAN2L two-dimensional unsteady transonic small-disturbance code to include an additional airfoil. Unsteady transonic forces due to plunge and pitch motions of a two-dimensional canard and wing are presented. Results for a variety of canard-wing separation distances reveal the effects of aerodynamic interference on unsteady transonic airloads. Aeroelastic analyses employing these unsteady airloads demonstrate the effects of aerodynamic interference on aeroelastic stability and flutter. For the configurations studied, increases in wing flutter speed result with the inclusion of the aerodynamically interfering canard.

Batina, J. T.↗
NASA NTRS1989

Results and applications of a space suit range-of-motion study

The range of motion of space suits has traditionally been described using limited 2-D mapping of limb, torso, or arm movements performed in front of an orthogonal grid. A new technique for recovering extra-vehicular (EVA) space suit range-of-motion data during underwater testing was described in a paper presented by the author at the 1988 conference. The new technique uses digitized data which is automatically acquired from video images of the subject. Three-dimensional trajectories are recovered from these data, and can be displayed using 2-D computer graphics. Results of using this technique for the current shuttle EVA suit during underwater simulated weightlessness testing are discussed. Application of the data for use in animating anthropometric computer models is highlighted.

Reinhardt, AL↗
NASA NTRS1989

Results and applications of a space suit range-of-motion study

The range of motion of space suits has traditionally been described using limited 2-D mapping of limb, torso, or arm movements performed in front of an orthogonal grid. A new technique for recovering extra-vehicular (EVA) space suit range-of-motion data during underwater testing was described in a paper presented by the author at the 1988 conference. The new technique uses digitized data which is automatically acquired from video images of the subject. Three-dimensional trajectories are recovered from these data, and can be displayed using 2-D computer graphics. Results of using this technique for the current shuttle EVA suit during underwater simulated weightlessness testing are discussed. Application of the data for use in animating anthropometric computer models is highlighted.

Reinhardt, AL↗
NASA NTRS1990

Simple model of plasma acceleration in a magnetic nozzle

A collisionless, steady-state, cold-plasma model is used to calculate the three-dimensional trajectory of a plasma as it is accelerated through a diverging magnetic field. The magnetic field is assumed to be axisymmetric with nonzero radial and axial components and zero azimuthal component. Although random thermal motion of plasma species is neglected in the cold plasma approximation, an important effect of plasma thermal energy is accounted for in the model as the kinetic energy of electrons in their Larmor motion about magnetic field lines. Calculations based on this model confirm previous studies which suggested that plasma separation from the field of a magnetic nozzle can take place even in the absence of collisional diffusion. It is shown that plasma divergence in a magnetic nozzle can be controlled by tailoring the field geometry.

Sercel, Joel C.↗