SEARCH · Search NASA

Results for “Particle simulations”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Electromagnetic particle simulation codes

Electromagnetic particle simulations solve the full set of Maxwell's equations. They thus include the effects of self-consistent electric and magnetic fields, magnetic induction, and electromagnetic radiation. The algorithms for an electromagnetic code which works directly with the electric and magnetic fields are described. The fields and current are separated into transverse and longitudinal components. The transverse E and B fields are integrated in time using a leapfrog scheme applied to the Fourier components. The particle pushing is performed via the relativistic Lorentz force equation for the particle momentum. As an example, simulation results are presented for the electron cyclotron maser instability which illustrate the importance of relativistic effects on the wave-particle resonance condition and on wave dispersion.

Pritchett, P. L.↗

NASA NTRS1992

Statistical discrete particle simulation studies

A particle simulation code was developed that is suited to Multiple Instruction Multiple Data multiprocessor computers. The resulting code is designed to be portable between a large class of multiprocessor computer architectures, including hypercubes (e.g., Intel iPSC/860), shared memory machines (e.g., Cray, SGI, DASH), and simple uniprocessors (e.g., SUN, VAX, IBM PC). This code provides a powerful general framework that can be adapted to specific applications, such as thermomechanical modeling, general 3-D geometry support, or visualization support via a codeveloped CPlot data reduction and visualization system. Chemistry models were implemented and validated with comparison to continuum solutions of thermochemically relaxing gas mixtures and with experimental results from the high speed flow about a circular cylinder. Furthermore, the exchange of energy between translational and internal modes was modeled. New models were developed, combining greater efficiency than earlier phenomenological models. They offer greater physical detail by addressing vibrational energy as a discretely distributed quantity.

Mcdonald, Jeffrey D.↗

NASA NTRS1992

Decoupled predictions of radiative heating in air using a particle simulation method

A particle simulation technique with decoupled radiation is used to estimate the radiative emission along the stagnation streamline and the radiative heating at the stagnation point of a blunt-nosed vehicle entering the earth's atmosphere at hypersonic speed. The direct simulation Monte Carlo (DSMC) method is used to compute the fluid mechanics of the weakly ionized flow. The radiative emission is computed using the NEQAIR computer code with the radiation decoupled from the flowfield solution. It is concluded that the new models make it possible to decrease the predicted total radiative heating at the stagnation point of the vehicle by a factor of 15. A comparison of the DSMC approach with a continuum flow model shows that the total predicted radiative heating estimates agree within a factor of 2.

Boyd, Iain D.↗

NASA NTRS1993

Energy storage and dissipation in the magnetotail during substorms. I - Particle simulations. II - MHD simulations

2D electromagnetic particle simulations are used to investigate the dynamics of the tail during development of substorms under the influence of the pressure in the magnetospheric boundary layer and the dawn-to-dusk electric field. It is shown that pressure pulses result in thinning of the tail current sheet as the magnetic field becomes pinched near the region where the pressure pulse is applied. The pinching leads to the tailward flow of the current sheet plasma and the eventual formation and injection of a plasmoid. Surges in the dawn-to-dusk electric field cause plasma on the flanks to convect into the center of the current sheet, thereby thinning the current sheet. The pressure in the magnetospheric boundary laser is coupled to the dawn-to-dusk electric field through the conductivity of the tail. Changes in the predicted evolution of the magnetosphere during substorms due to changes in the resistivity are investigated under the assumption that MHD theory provides a suitable representation of the global or large-scale evolution of the magnetotail to changes in the solar wind and to reconnection at the dayside magnetopause. It is shown that the overall evolution of the magnetosphere is about the same for three different resistivity distributions with plasmoid formation and ejection in each case.

Winglee, R. M.↗

NASA NTRS1999

Particle Simulations of Plasma Detachment in VASIMR

The particle simulations in a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) currently include self-consistent calculation of. 1) stationary magnetic field in plasma, 2) ion density and velocity, 3) ion-cyclotron radio-frequency heating, 4) ambipolar electric field. The assumptions of quasineutral and collissionless plasma are based on the range of operating VASIMR parameters. The main motivation for the particle simulation in VASIMR is plasma detachment from the magnetic field in the exhaust area. The plasma detachment is caused mainly by the Larmor radius increase. The plasma beta effect on detachment is observed and investigated as well. The results of particle simulations are compared with those from MHD simulations.

Ilin, A. V.↗

NASA NTRS1989

Application of a vectorized particle simulation in high-speed near-continuum flow

An efficient particle simulation technique, developed for use on vector architecture based supercomputers for studying hypersonic rarefied gas flows is employed to simulate the complex wake generated by Mach six flow over a 10 deg half-angle wedge for freestream Reynolds numbers of 1780 and 3560. Data obtained are compared against higher Reynolds number experimental results. Simulations utilized as many as 10 to the 5th computational cells and 10 to the 7th simulated particles having power-law interaction potentials. A code performance of 1.8-2.4 microsec of Cray-2 CPU time to process a single particle per timestep is achieved. Diffuse adiabatic and isothermal wedge surface models are used in this investigation. Although the wedge geometry is two-dimensional, the simulation incorporates a width-wise direction, resulting in a three-dimensional computation.

Woronowicz, Michael S.↗

NASA NTRS1990

On the suitability of the connection machine for direct particle simulation

The algorithmic structure was examined of the vectorizable Stanford particle simulation (SPS) method and the structure is reformulated in data parallel form. Some of the SPS algorithms can be directly translated to data parallel, but several of the vectorizable algorithms have no direct data parallel equivalent. This requires the development of new, strictly data parallel algorithms. In particular, a new sorting algorithm is developed to identify collision candidates in the simulation and a master/slave algorithm is developed to minimize communication cost in large table look up. Validation of the method is undertaken through test calculations for thermal relaxation of a gas, shock wave profiles, and shock reflection from a stationary wall. A qualitative measure is provided of the performance of the Connection Machine for direct particle simulation. The massively parallel architecture of the Connection Machine is found quite suitable for this type of calculation. However, there are difficulties in taking full advantage of this architecture because of lack of a broad based tradition of data parallel programming. An important outcome of this work has been new data parallel algorithms specifically of use for direct particle simulation but which also expand the data parallel diction.

Dagum, Leonard↗

NASA NTRS1992

Direct particle simulation on the Connection Machine CM-2

Particle simulation is a useful technique for analyzing low density flows. The Connection Machine CM-2 is a useful test bed for studying the fine-grain data objects decomposition and the coarse-grain domain decomposition single instruction multiple datastream (SIMD) approaches to particle simulation. Both approaches are investigated for the model problem of uniform flow through a channel and the algorithms required for the SIMD domain decomposition approach are presented. An unresolved issue with the domain decomposition approach is the effect of a poor partitioning on flows with real geometries. Initial results with the channel flow problem indicate that a poor partitioning has only a small detrimental effect on the overall performance.

Dagum, L.↗

NASA NTRS1991

Three-dimensional direct particle simulation on the Connection Machine

This paper presents the algorithms necessary for an efficient data parallel implementation of a 3D particle simulation. In particular, a general master/slave algorithm and a fast sorting algorithm are described and the use of these algorithms in a particle simulation is outlined. A particle simulation using these algorithms has been implemented on a 32768 processor Connection Machine that is capable of simulating over 30 million particles at an average rate of 2.4-microsec/particle/step. Results are presented from the simulation of flow over an Aeroassisted Flight Experiment geometry at 100 km altitude.

Dagum, Leonardo↗

NASA NTRS1992

Data parallel sorting for particle simulation

Sorting on a parallel architecture is a communications intensive event which can incur a high penalty in applications where it is required. In the case of particle simulation, only integer sorting is necessary, and sequential implementations easily attain the minimum performance bound of O (N) for N particles. Parallel implementations, however, have to cope with the parallel sorting problem which, in addition to incurring a heavy communications cost, can make the minimun performance bound difficult to attain. This paper demonstrates how the sorting problem in a particle simulation can be reduced to a merging problem, and describes an efficient data parallel algorithm to solve this merging problem in a particle simulation. The new algorithm is shown to be optimal under conditions usual for particle simulation, and its fieldwise implementation on the Connection Machine is analyzed in detail. The new algorithm is about four times faster than a fieldwise implementation of radix sort on the Connection Machine.

Dagum, Leonardo↗

DOE OSTI2020

Gyrokinetic particle simulations of interactions between energetic particles and magnetic islands induced by neoclassical tearing modes

Interactions between energetic particles (EPs) and neoclassical tearing mode (NTM) islands in the DIII-D tokamak are studied using the global gyrokinetic toroidal code (GTC). GTC simulations find that the EP radial profile is partially flattened within the magnetic island regions and that there are stochastic regions in the particle phase space. Radial particle flux is induced mainly around the magnetic island regions and decreases with time to almost zero when the initial EP distribution achieves a new steady-state in the absence of EP sources. Stochastic regions of magnetic field lines induced by the superposition of multiple islands have weak effects on the particle flux when the width of stochastic regions is smaller than the EP drift orbit width. In conclusion, the perturbed parallel EP current induced by the magnetic islands has weak stabilizing effects on the linear growth rate of the NTM instability in this DIII-D experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1989

Three dimensional discrete particle simulation of an AOTV

A discrete Particle Simulation method, recently formulated by Baganoff, is discussed in the context of its application to the simulation of the flow field about the Aeroassisted Flight Experiment (AFE). As a basis for discussion the current algorithm is first described. Because of the use of a cubic Cartesian mesh, the representation of the geometry is different than that of other particle methods and an algorithm for its generation is discussed. The method is applied to test problems and then to the AFE calculation with the use of 9.52 million particles and 432,000 cells.

Feiereisen, William J.↗

NASA NTRS1993

Comparison of continuum and particle simulations of expanding rarefied flows

Comparisons of Navier-Stokes solutions and particle simulations for a simple two-dimensional model problem at a succession of altitudes are performed in order to assess the importance of rarefaction effects on the base flow region. In addition, an attempt is made to include 'Burnett-type' extensions to the Navier-Stokes constitutive relations. The model geometry consists of a simple blunted wedge with a 0.425 meter nose radius, a 70 deg cone half angle, a 1.7 meter base length, and a rounded shoulder. The working gas is monatomic with a molecular weight and viscosity similar to air and was chosen to focus the study on the continuum and particle methodologies rather than the implementation of thermo-chemical modeling. Three cases are investigated, all at Mach 29, with densities corresponding to altitudes of 92 km, 99 km, and 105 km. At the lowest altitude, Navier-Stokes solutions agree well with particle simulations. At the higher altitudes, the Navier-Stokes equations become less accurate. In particular, the Navier-Stokes equations and particle method predict substantially different flow turning angle in the wake near the after body. Attempts to achieve steady continuum solutions including 'Burnett-type' terms failed. Further research is required to determine whether the boundary conditions, the equations themselves, or other unknown causes led to this failure.

Lumpkin, Forrest E., III↗

NASA NTRS1994

A Coulomb collision algorithm for weighted particle simulations

A binary Coulomb collision algorithm is developed for weighted particle simulations employing Monte Carlo techniques. Charged particles within a given spatial grid cell are pair-wise scattered, explicitly conserving momentum and implicitly conserving energy. A similar algorithm developed by Takizuka and Abe (1977) conserves momentum and energy provided the particles are unweighted (each particle representing equal fractions of the total particle density). If applied as is to simulations incorporating weighted particles, the plasma temperatures equilibrate to an incorrect temperature, as compared to theory. Using the appropriate pairing statistics, a Coulomb collision algorithm is developed for weighted particles. The algorithm conserves energy and momentum and produces the appropriate relaxation time scales as compared to theoretical predictions. Such an algorithm is necessary for future work studying self-consistent multi-species kinetic transport.

Miller, Ronald H.↗

NASA NTRS1987

Particle simulation of plasmas on the massively parallel processor

Particle simulations, in which collective phenomena in plasmas are studied by following the self consistent motions of many discrete particles, involve several highly repetitive sets of calculations that are readily adaptable to SIMD parallel processing. A fully electromagnetic, relativistic plasma simulation for the massively parallel processor is described. The particle motions are followed in 2 1/2 dimensions on a 128 x 128 grid, with periodic boundary conditions. The two dimensional simulation space is mapped directly onto the processor network; a Fast Fourier Transform is used to solve the field equations. Particle data are stored according to an Eulerian scheme, i.e., the information associated with each particle is moved from one local memory to another as the particle moves across the spatial grid. The method is applied to the study of the nonlinear development of the whistler instability in a magnetospheric plasma model, with an anisotropic electron temperature. The wave distribution function is included as a new diagnostic to allow simulation results to be compared with satellite observations.

Gledhill, I. M. A.↗

NASA NTRS1988

Vectorization of a particle simulation method for hypersonic rarefied flow

An efficient particle simulation technique for hypersonic rarefied flows is presented at an algorithmic and implementation level. The implementation is for a vector computer architecture, specifically the Cray-2. The method models an ideal diatomic Maxwell molecule with three translational and two rotational degrees of freedom. Algorithms are designed specifically for compatibility with fine grain parallelism by reducing the number of data dependencies in the computation. By insisting on this compatibility, the method is capable of performing simulation on a much larger scale than previously possible. A two-dimensional simulation of supersonic flow over a wedge is carried out for the near-continuum limit where the gas is in equilibrium and the ideal solution can be used as a check on the accuracy of the gas model employed in the method. Also, a three-dimensional, Mach 8, rarefied flow about a finite-span flat plate at a 45 degree angle of attack was simulated. It utilized over 10 to the 7th particles carried through 400 discrete time steps in less than one hour of Cray-2 CPU time. This problem was chosen to exhibit the capability of the method in handling a large number of particles and a true three-dimensional geometry.

Mcdonald, Jeffrey D.↗

NASA NTRS1990

Three dimensional Discrete Particle Simulation about the AFE geometry

The Discrete Particle Simulation method, due to Baganoff, has recently been extended to allow representation of gases composed of multiple species, to general power-law molecular interactions and to permit flows in thermal non-equilibrium. Particular attention has been paid to the implementation of this physics while retaining the efficiency of the original algorithm. Here, the enhanced algorithm is applied to the simulation of the flow field about the Aeroassisted Flight Experiment (AFE) vehicle with the same flight parameters as in a previous paper. The enhancements to the algorithm are introduced and comparisons are made to the previous calculation.

Feiereisen, William J.↗

DOE OSTI2022

Sensitivity Analyses for Monte Carlo Sampling-Based Particle Simulations

Computational design-based optimization is a well-used tool in science and engineering. Our report documents the successful use of a particle sensitivity analysis for design-based optimization within Monte Carlo sampling-based particle simulation—a currently unavailable capability. Such a capability enables the particle simulation communities to go beyond forward simulation and promises to reduce the burden on overworked analysts by getting more done with less computation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗