A Nodal Computational Scheme for the 2-D Burger's Equation
R. Uddin,* B. L. Westcott
DOE Center for Simulation of Advanced Rockets

To demonstrate its feasibility in solving the Navier-Stokes equations, the modified nodal integral method has been applied to solve the 2-D Burger's equation at high Reynolds numbers. Performance of the nodal method is being compared with other competing methods. The method is being extended to single-phase and multiphase fluid equations.

Development of Advanced Computational Methods for Navier-Stokes Equations
R. Uddin,* F. Wang
DOE Center for Simulation of Advanced Rockets

An advanced coarse-mesh nodal scheme is being developed to solve the incompressible, time-dependent Navier-Stokes equations. Local solutions for transverse-integrated velocities have a (linear and exponential) variation in each spatial direction, and linear variation in time. Local pressure has a quadratic variation. The set of equations is being implemented in a computer code.

Energy Gain Calculations in Spherical, Virtual Cathode IEC Devices Using a Bounce-averaged Fokker-Planck Model
G. H. Miley,* L. Chacon, D. Barnes
Daimler-Chrysler Aerospace AG; Los Alamos National Laboratory

A bounce-averaged Fokker-Planck code (BAFP) has been developed to model the ion physics in virtual-cathode IEC fusion devices in the ion-ion collision time scale and to calculate fusion energy gains in a variety of operating regimes. A single ion species is considered. Electrons in the system are assumed to distribute uniformly in configuration space. Collisional ion-electron interactions are neglected in this time scale, although space charge interactions are taken into account self-consistently via the determination of the electrostatic potential. Results indicate that operating regimes that result in quasi-thermal ion populations-confined by the electrostatic well-are most efficient. Operating regimes with fusion power to ion input power ratios > 100 have been identified.

Improved Particle Tracking in Monte Carlo Simulations
M. Hardwidge,* M. Ragheb*
University of Illinois

We are exploring the use of the inverse problem of analytical geometry to generate exact analytical expressions for complex geometrical objects. These could be used in the geometry packages of existing Monte Carlo particle transport codes. Currently, simple geometrical objects such as spheres and cylinders are combined through the OR and AND logical operations to construct equivalent more complex objets. Writing exact analytical expressions for complex objects is expected to enhance significantly the particle tracks process in complex geometries analyzed by existing Monte Carlo simulation codes.

Numerical Simulation of Neutron Transport in Spallation Source Target/Moderator Systems
B. Heuser,* T. Li
U.S. Department of Energy, ANL 970392401/LM ORNL 19X-SX702V

The design of the Spallation Neutron Source (SNS) is currently underway. Line-item construction funding for this 1-MW neutron source was passed by Congress in the fall of 1998. The primary purpose of the SNS is to provide intense neutron beams for a variety of scattering techniques. Our involvement in this project centers on the optimized coupling of long-wavelength, elastic scattering instruments (small-angle and reflectometry instruments) to the target/moderator system. We are simulating neutron moderation and transport within the complex spatial geometry of the target/moderator system using MCNP.

Parallel Monte Carlo Particle Transport Algorithm with Neuro-Fuzzy Optimal Tracks Scaling
M. Ragheb,* H. Wang
University of Illinois

We are exploring the application of a sequential formulation of a Monte Carlo particle track scaling algorithm to parallel computer architectures. In this case, each processing element will be devoted to exploring a subset of the problem's parameter space. The results obtained by the parallel processes will be combined to generate a second moment surface which will then be searched for local or global minima to identify the location(s) corresponding to minimum or near-optimal variance. Resources of the parallel processors will be reallocated by a neuro-fuzzy search engine as the simulation progresses to explore the minimum variance location. Incorporation of the developed methodology will be attempted in an existing Monte Carlo particle transport code.