121016085
A Pseudospectral method for solution of the three-dimensional incompressible Navier-Stokes equations
Abstract A new Chebyshev pseudospectral technique (based on the projection method that was previously applied by the authors to the solution of two-dimensional incompressible Navier-Stokes equations in primitive variables for nonperiodic boundary conditions) is extended to solve the three-dimensional Navier-Stokes equations. The crucial point of the method is the requirement that the continuity equation be satisfied everywhere in the domain, on the boundaries as well as in the interior. The key feature of the work presented in this paper is that the computer storage requirements of the full matrix inversion resulting from direct solution of the pressure Poisson equation in three dimensions is greatly reduced by considering an eigenfunction decomposition. The method was tested on a two-dimensional driven cavity flow and the results were compared with those of the most accurate finite-difference calculation. The three-dimensional driven cavity flow was then calculated at the same Reynolds numbers as the two-dimensional cases, i.e., Re = 100, 400, and 1000. In the calculated results, three-dimensional boundary effects were observed in all cases and became more apparent with increasing Reynolds number.
119776755
Pseudospectral methods for solution of the incompressible Navier-Stokes equations
Abstract Four numerical schemes for solving the incompressible Navier-Stokes equations in primitive variables are discussed and compared. All use the Chebyshev pseudospectral matrix (CPSM) approach for evaluating spatial derivatives. Two of the methods are new and two are previously reported methods that have been recast in CPSM form in order to compare results. The methods are (1) time-splitting of velocity and pressure (the projection method) with prescribed boundary conditions on the velocity only and satisfaction of the continuity equation at boundaries to close the system (no pressure boundary conditions required), (2) a quasi-velocity potential formulation with either continuity or Neumann boundary conditions, (3) direct solution of velocity and pressure with prescribed boundary conditions on velocity and either Neumann or continuity conditions for the pressure, and (4) the influence matrix technique with prescribed velocity and pressure boundary conditions specified to satisfy continuity. All the methods share one characteristic: a Poisson equation must be solved for either the pressure or quasi-potential field. When applied to the test problem of a thermally driven cavity flow, it was found that the best accuracy was obtained by all methods that employed satisfaction of continuity as the boundary condition for solution of the Poisson equation.
9237533
Development and application of NASA's first standard spacecraft computer
To provide the autonomy needed by low, earth-orbiting satellites, NASA's first standard on-board processor requires changing only interfacing hardware from mission to mission.
195870288
Advanced simulation, battle managers, and visualization
Advanced modeling, visualization, and simulation is of growing utility for the military, e.g., the Navy and Marine Corps. Potential uses are for situational awareness displays, analysis, assessment, doctrine, mission support, rehearsal and replay, tactics, and training. Advanced technology platforms can be assessed using simulation. New sensors and systems can be evaluated. A battle or simulation manager (BM or SM) is a flexible piece of software that commands, controls, and displays the simulation of a group of objects. It is an environment or toolkit for analysis, assessment, training, and wargaming. Current doctrine and tactics can be tested and missions planned with this type of software. The objects (military platforms) propagate and interact in space over the course of time through well-defined object-oriented processes. Features of a good BM include graphical two and three dimensional displays, database access, sensor and weapon models, and networking (via DIS or Distributed Interactive Simulation). A BM should be easy to use, fast, useful to the user, readily available, and widely used. It should be portable cross computer platforms. Today, there is a wide assortment of BMs, none of which satisfies these criteria.