A semi-direct procedure using a local relaxation factor and its application to an internal flow problem

Generally, fast direct solvers are not directly applicable to a nonseparable elliptic partial differential equation. This limitation, however, is circumvented by a semi-direct procedure, i.e., an iterative procedure using fast direct solvers. An efficient semi-direct procedure which is easy to implement and applicable to a variety of boundary conditions is presented. The current procedure also possesses other highly desirable properties, i.e.: (1) the convergence rate does not decrease with an increase of grid cell aspect ratio, and (2) the convergence rate is estimated using the coefficients of the partial differential equation being solved

Inversion of the fermionic matrix and multigrid

Numerical simulations indicate that the multigrid method has some natural limitations when applied to the calculation of the quark propagator in the Lattice QCD

Discussion of the potential and limitations of direct and large-eddy simulations

The full text of the discussion paper presented at the Whither Turbulence Workshop on the potential and limitations of direct and large-eddy simulations is provided. Particular emphasis is placed on discussing the role of numerics and mathematical theory in direct simulations of both compressible and incompressible flows. A variety of unresolved issues with large-eddy simulations such as their implementation in high-order finite difference codes, problems with defiltering, and modifications to accommodate integrations to solid boundaries are elaborated on. These as well as other points are discussed in detail along with the authors' views concerning the prospects for future research

Solution of elliptic partial differential equations by fast Poisson solvers using a local relaxation factor. 1: One-step method

An algorithm for solving a large class of two- and three-dimensional nonseparable elliptic partial differential equations (PDE's) is developed and tested. It uses a modified D'Yakanov-Gunn iterative procedure in which the relaxation factor is grid-point dependent. It is easy to implement and applicable to a variety of boundary conditions. It is also computationally efficient, as indicated by the results of numerical comparisons with other established methods. Furthermore, the current algorithm has the advantage of possessing two important properties which the traditional iterative methods lack; that is: (1) the convergence rate is relatively insensitive to grid-cell size and aspect ratio, and (2) the convergence rate can be easily estimated by using the coefficient of the PDE being solved

Particle-in-cell plasma simulation with OmpSs-2

Develop a plasma simulator based on iPic3D, used to simulate the interaction of the solar wind with the magnetosphere of planets, by using different parallelization techniques provided by the OmpSs-2 programming model

2D3V Particle-in-cell simulations of Electron Cyclotron Drift Instability and anomalous electron transport in ExB plasmas

This thesis is devoted to nonlinear physics of plasmas investigated with kinetic modeling. The emphasis is on the characterization of waves, instabilities, and anomalous electron transport. The main topic is related to partially magnetized plasmas immersed in crossed ExB fields with magnetized electrons and unmagnetized ions. Such plasmas are abundant in many applications such as Hall thrusters devices for space propulsion and material processing. The nonlinear evolution of the Electron Cyclotron Drift Instability (ECDI) driven by the electron ExB drift in partially magnetized plasmas and anomalous electron transport in two dimensions are studied using particle-in-cell (PIC) simulations. PIC simulations were performed for the parameters typical of the Hall-effect thruster in two-dimensional azimuthal-radial geometry to investigate the role of the boundaries conditions, electric and magnetic field magnitudes, sheath losses and finite-length on the mode development and anomalous electron current. The turbulence and the induced anomalous electron current are studied. Nature of the anomalous current and contribution of different wavelength are investigated. It is shown that the magnitude of the anomalous current can be explained as a ExB drift of magnetized electrons in fluctuating fields. The same PIC code was used for a benchmark project in simulations of a similar radial-azimuthal configuration of a Hall thruster. Seven different groups using independently developed codes were able to capture the same physics, both for ECDI and Modified Two-Stream Instability (MTSI) modes. An additional study related to the role of noise in kinetic plasma simulations is presented. It confirmed that statistical particle noise could distort some Buneman-type instabilities to be identified in the linear regime

Numerical techniques for predicting aerodynamic characteristics of bodies

Two methods are presented characteristics of bodies SUMMARY for predicting the aerodynamic in inviscid and irrotational flow. The first method is limited to incompressible flow and makes use of panels of ring sources to approximate the body surface. The technique is dedicated to single, axisymmetric body configurations in either uniform longitudinal or rectilinear motion. The versatility of the method is due to the use of sources as singularities placed on the body surface, allowing discontinuous body profiles to be analysed. The method has been compared for accuracy and efficiency with experimental and theoretical results. Further investigation showed that at present there existed no numerical technique which could predict the aerodynamic behaviour of multiple bodies in compressible flow. Hence, a fully three-dimensional method was developed which made use of the Full Potential Equation (F.P.E.) in conservative form. A computational mesh is placed around the body configuration and at each mesh node the F.P.E. is satisfied ~n finite difference form. The method is able to give a complete description of the flow around the bodies at transonic mach numbers. Comparisons to test the accuracy and efficiency of the method are limited to either, purely subsonic flow for two body configurations or zero incidence for transonic flow around a single body.Ph

Aeronautical engineering: A continuing bibliography with indexes, supplement 146, March 1982

This bibliography lists 442 reports, articles, and other documents introduced into the NASA scientific and technical system in February 1982