Peter G. Eltgroth

Spatially Homogeneous Anisotropic Cosmological Models Containing Relativistic Fluid and Magnetic Field

We review spatially homogeneous, axially symmetric universes containing either an ideal fluid (with a γ‐law equation of state) or a uniform magnetic field parallel to the symmetry axis or both. In many cases, the field equations may be solved by the technique (described in detail) of replacing the cosmic time by a suitably chosen timelike parameter. We systematically derive all known exact solutions for such universes.

Performance of a distributed memory finite difference atmospheric general circulation model

Abstract A new version of the UCLA atmospheric general circulation model suitable for massively parallel computer architectures has been developed. This paper presents the principles for the codes design and examines performance on a variety of distributed memory computers. A two dimensional domain decomposition strategy is used to achieve parallelism and is implemented by message passing. This parallel algorithm is shown to scale favorably as the number of processors is increased. In the fastest configuration, performance roughly equivalent to that of multitasking vector supercomputers is achieved.

A simulator for MIMD performance prediction: application to the S-1 MkIIa multiprocessor

We describe a MIMD multiprocessor simulator and application of that simulator to a multiprocessor of current interest, the S-1 MkIIa. The simulator runs on the CRAY-1 and is designed so that computational physics benchmarks are actually run and produce results. Simulator output from this run is fed into a second level (hardware) simulator which calculates the behavior of the multiprocessor. The simulator can simulate multiprocessors whose basic architecture is that of a few, large processors with or without data caches, sharing global memory through an interconnection switch. The simulator is applied to the investigation of the behavior of four problems on the S-1: The benchmark physics code SIMPLE, a conjugate gradient linear algebra problem, a simple Monte-Carlo problem, and a new method for neutron transport calculations.

Comparison of plasma focus calculations

A simple model for the current history of plasma focus experiments is presented. The presence of a leak current which does not pass through the plasma sheath is allowed. Results are found to compare quite well with those of much more sophisticated two‐dimensional magnetohydrodynamic calculations. For the Frascati experiment, which has detailed current measurements, computed results do not agree with experimentally derived values. A reasonable match for the total current in the Frascati experiment can be found by lowering the leak current. Both total and leak current can be matched if a mass loss from the run‐down region is allowed.

Similarity Analysis for Relativistic Flow in One Dimension

Transformations and restrictions are applied to the equations of relativistic flow in one space dimension which reduce the problem to a consideration of simpler differential equations. The results are closely related to those of characteristic analysis. It is found that for cases in which one similarity variable describes the system, the fluid has constant velocity along straight lines in the x, ct system. Two special equations of state, p = 13E and p = 13(E−nmc2) are considered in detail. Analytic results are obtained and are applied to the problem of shock propagation into a region of decreasing density.

Toward a high performance distributed memory climate model

As part of a long range plan to develop a comprehensive climate systems modeling capability, the authors have taken the atmospheric general circulation model originally developed by Arakawa and collaborators at UCLA and have recast it in a portable, parallel form. The code uses an explicit time-advance procedure on a staggered three-dimensional Eulerian mesh. They have implemented a two-dimensional latitude/longitude domain decomposition message passing strategy. Both dynamic memory management and interprocess communication are handled with macro constructs that are preprocessed prior to compilation. The code can be moved about a variety of platforms, including massively parallel processors, workstation clusters, and vector processors, with a mere change of three parameters. Performance on the various platforms as well as issues associated with coupling different models for major components of the climate system are discussed.<<ETX>>

CLIMATE SYSTEM MODELING USING A DOMAIN AND TASK DECOMPOSITION MESSAGE-PASSING APPROACH

Abstract We have developed a Climate System Modeling Framework (CSMF) for high-performance computing systems, designed to schedule and couple multiple physics simulation packages in a flexible and transportable manner. Some of the major packages in the CSMF include models of atmospheric and oceanic circulation and chemistry, land surface and sea ice processes, and trace gas biogeochemistry. Parallelism is achieved through both domain decomposition and process-level concurrency, with data transfer and synchronization accomplished through message-passing. Both machine transportability and architecture-dependent optimization are handled through libraries and conditional compile directives. Preliminary experiments with the CSMF have been executed on a number of high-performance platforms, including the Intel Paragon, the TMC CM-5 and the Meiko CS-2, and we are in the very early stages of optimization. Progress to date is presented.

Nonplanar Relativistic Flow

The equations for nonplanar relativistic flow are solved by similarity analysis for a restricted set of problems. The relativistic equation of state p = 13 E is used. The solutions obtained are for flow resulting from a point source of energy at the origin, having a power law time dependence. The results are applied to the problem of spherical shock propagation into a medium and to the problem of cosmic ray generation from supernovae. It is found that the predicted spectrum of cosmic rays is somewhat steeper than is actually observed.

Distributing a climate model across gigabit networks

The authors investigate the distribution of a climate model across homogeneous and heterogeneous computer environments with nodes that can reside at geographically different locations. The application consists of an atmospheric general circulation model (AGCM) coupled to an oceanic general circulation model (OGCM). Three levels of code decomposition are considered to achieve a high degree of parallelism and to mask communication with computation. First, the domains of both the grid-point AGCM and OGCM are divided into sub-domains for which calculations are carried out concurrently (domain decomposition). Second, the model is decomposed based on the diversity of tasks performed by its major components (task decomposition). Last, computation and communication are organized in such a way that the exchange of data between different tasks is carried out in subdomains of the model domain (I/O decomposition). In a dedicated computer/network environment, the wall-clock time required by the resulting distributed application is reduced to that for the AGCM/Physics, with the other two model components and interprocessor communications running in parallel.<<ETX>>

Plasma heating calculations using a transform method

The problem of a strongly driven one‐dimensional electrostatic plasma is treated by the method of expansion of the distribution function in terms of Hermite polynomials in velocity space. Numerical results for hydrodynamic variables are similar to those found in simulation calculations. The shapes of the ion and electron distribution functions are significantly altered from Maxwellian form during heating.