156 research outputs found
Indirect addressing and load balancing for faster solution to Mandelbrot Set on SIMD architectures
SIMD computers with local indirect addressing allow programs to have queues and buffers, making certain kinds of problems much more efficient. Examined here are a class of problems characterized by computations on data points where the computation is identical, but the convergence rate is data dependent. Normally, in this situation, the algorithm time is governed by the maximum number of iterations required by each point. Using indirect addressing allows a processor to proceed to the next data point when it is done, reducing the overall number of iterations required to approach the mean convergence rate when a sufficiently large problem set is solved. Load balancing techniques can be applied for additional performance improvement. Simulations of this technique applied to solving Mandelbrot Sets indicate significant performance gains
Introduction to a system for implementing neural net connections on SIMD architectures
Neural networks have attracted much interest recently, and using parallel architectures to simulate neural networks is a natural and necessary application. The SIMD model of parallel computation is chosen, because systems of this type can be built with large numbers of processing elements. However, such systems are not naturally suited to generalized communication. A method is proposed that allows an implementation of neural network connections on massively parallel SIMD architectures. The key to this system is an algorithm permitting the formation of arbitrary connections between the neurons. A feature is the ability to add new connections quickly. It also has error recovery ability and is robust over a variety of network topologies. Simulations of the general connection system, and its implementation on the Connection Machine, indicate that the time and space requirements are proportional to the product of the average number of connections per neuron and the diameter of the interconnection network
Description and capabilities of a traveling wave sonic boom simulator
Description and capabilities of traveling wave sonic boom simulator
A system for routing arbitrary directed graphs on SIMD architectures
There are many problems which can be described in terms of directed graphs that contain a large number of vertices where simple computations occur using data from connecting vertices. A method is given for parallelizing such problems on an SIMD machine model that is bit-serial and uses only nearest neighbor connections for communication. Each vertex of the graph will be assigned to a processor in the machine. Algorithms are given that will be used to implement movement of data along the arcs of the graph. This architecture and algorithms define a system that is relatively simple to build and can do graph processing. All arcs can be transversed in parallel in time O(T), where T is empirically proportional to the diameter of the interconnection network times the average degree of the graph. Modifying or adding a new arc takes the same time as parallel traversal
Evaluating local indirect addressing in SIMD proc essors
In the design of parallel computers, there exists a tradeoff between the number and power of individual processors. The single instruction stream, multiple data stream (SIMD) model of parallel computers lies at one extreme of the resulting spectrum. The available hardware resources are devoted to creating the largest possible number of processors, and consequently each individual processor must use the fewest possible resources. Disagreement exists as to whether SIMD processors should be able to generate addresses individually into their local data memory, or all processors should access the same address. The tradeoff is examined between the increased capability and the reduced number of processors that occurs in this single instruction stream, multiple, locally addressed, data (SIMLAD) model. Factors are assembled that affect this design choice, and the SIMLAD model is compared with the bare SIMD and the MIMD models
Spectral solution of the incompressible Navier-Stokes equations on the Connection Machine 2
The issue of solving the time-dependent incompressible Navier-Stokes equations on the Connection Machine 2 is addressed, for the problem of transition to turbulence of the steady flow in a channel. The spectral algorithm used serially requires O(N(4)) operations when solving the equations on an N x N x N grid; using the massive parallelism of the CM, it becomes an O(N(2)) problem. Preliminary timings of the code, written in LISP, are included and compared with a corresponding code optimized for the Cray-2 for a 128 x 128 x 101 grid
Research and development of a sonic boom simulation device
Design and performance of sonic boom simulato
Programming the Navier-Stokes computer: An abstract machine model and a visual editor
The Navier-Stokes computer is a parallel computer designed to solve Computational Fluid Dynamics problems. Each processor contains several floating point units which can be configured under program control to implement a vector pipeline with several inputs and outputs. Since the development of an effective compiler for this computer appears to be very difficult, machine level programming seems necessary and support tools for this process have been studied. These support tools are organized into a graphical program editor. A programming process is described by which appropriate computations may be efficiently implemented on the Navier-Stokes computer. The graphical editor would support this programming process, verifying various programmer choices for correctness and deducing values such as pipeline delays and network configurations. Step by step details are provided and demonstrated with two example programs
A visual programming environment for the Navier-Stokes computer
The Navier-Stokes computer is a high-performance, reconfigurable, pipelined machine designed to solve large computational fluid dynamics problems. Due to the complexity of the architecture, development of effective, high-level language compilers for the system appears to be a very difficult task. Consequently, a visual programming methodology has been developed which allows users to program the system at an architectural level by constructing diagrams of the pipeline configuration. These schematic program representations can then be checked for validity and automatically translated into machine code. The visual environment is illustrated by using a prototype graphical editor to program an example problem
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Lightweight, High-Temperature Radiator for In-Space Nuclear-Electric Power and Propulsion
The desire to explore deep space destinations with high-power and high-speed spacecraft inspired this work. Nuclear Electric Propulsion (NEP), shown to provide orders of magnitude higher specific impulse and propulsion efficiency over traditional chemical rockets, has been identified as an enabling technology for this goal. One of large obstacle to launching an NEP vehicle is total mass. Increasing the specific power (kW/kg) of the heat radiator component is necessary to meet NASA’s mass targets.
This work evaluated a novel lightweight, high-temperature carbon fiber radiator designed to meet the mass requirements of future NEP missions. The research is grouped into three major sections: 1) a micro-scale radiation study, 2) bench-scale experimental and analytical investigations, and 3) large-scale radiator system modeling.
In the first section, a Monte Carlo ray tracing model built to predict the effective emissivity of a carbon fiber fin by modeling the radiation scattering among fibers showed that the added surface area of the fibers over a flat fin surface increases the effective emissivity of the radiator area by up to 20%. The effective emissivity increases as the fiber volume fraction decreases from 1 to about 0.16 due to increased scattering among the fibers. For fiber volume fractions lower than 0.10, the effective emissivity decreases rapidly as the effect of radiation transmission becomes significant.
In the second section, thermal analyses of the carbon fiber radiator fin predicted that these radiators could meet NASA’s performance targets by reducing the areal density to 2.2 kg/m2 or below. These models were validated through experimental tests conducted on sub-scale radiator test articles. This work elevated the technology readiness level (TRL) of the carbon fiber radiator fin from level 2 to 4.
In the last section, a radiator system model for an NEP vehicle was built to analyze the dependence of radiator mass on selected system parameters. The model was used to minimize the radiator mass for test cases. The results predicted that carbon fiber fins operated near 600°C reduced the radiator mass by a factor of 7 as compared with traditional radiators operating near 100°C. This significant mass-reduction could enable future NEP systems
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