Mapping Conjugate Gradient Algorithms for Neutron Diffusion Applications onto SIMD, MIMD, and Mixed-Mode Machines

The performance of conjugate gradient (CG) algorithms for the solution of the system of linear equations that results from the finite-differencing of the neutron diffusion equation was analyzed on SIMD, MIMD, and mixed-mode parallel machines. A block preconditioner based on the incomplete Cholesky factorization was used to accelerate the conjugate gradient search. The issues involved in mapping both the unpreconditioned and preconditioned conjugate gradient algorithms onto the mixed-mode PASM prototype, the SIMD MasPar MP-1, and the MIMD Intel Paragon XP/S are discussed. On PASM , the mixed-mode implementation outperformed either SIMD or MIMD alone. Theoretical performance predictions were analyzed and compared with the experimental results on the MasPar MP-1 and the Paragon XP/S. Other issues addressed include the impact on execution time of the number of processors used, the effect of the interprocessor communication network on performance, and the relationship of the number of processors to the quality of the preconditioning. Applications studies such as this are necessary in the development of software tools for mapping algorithms onto either a single parallel machine or a heterogeneous suite of parallel machines.     

Estimation of Weibull parameters with linear regression method

Abstract

Based on minimum mean square error, a modified probability estimator is proposed by a Monte Carlo simulation for estimating the Weibull parameters with the linear regression method. It is shown that compared with the commonly used estimators, the modified probability estimator gives a more accurate estimation of the Weibull modulus and the same estimation precision of the scale parameter. Furthermore, it is more conservative than the commonly used estimator recommended by previous authors and hence results in a higher safety in reliability predictions.     

Design of a low-cost,highly mobile urban search and rescue robot

In this paper, we discuss the design of a novel robotic platform for urban search and rescue. The system developed possesses unique mobility capabilities based on a new adjustable compliance mechanism and overall locomotive morphology. The main facets of this work involve the morphological concepts, initial design and construction of a prototype vehicle, and a physical simulation to be used for developing controllers for semi-autonomous (supervisory) operation.     

Dynamic simulation of cooling stack and cooling circuit for converter gas cooling

Abstract

A dynamic simulation programme for the recooling circuit of converter gas cooling systems has been developed to assist in the design of new plant and efforts to increase the production capacity of existing plant. A suitable choice of independent variables (enthalpy h and pressure p) allows clear mathematical modelling and enhances the numeric performance of the model. The results have been verified by comparison with the operational data from existing steel plants. This simulation programme offers steelmakers the following advantages when seeking an increase in production: recalibration of existing systems and determination of maximum allowable heat input to the cooling circuit; proposals for modification of existing systems to increase the allowable heat input under constraints for optimal investment cost and installation downtime; design of new, low investment cost cooling systems tailored for existing plant infrastructure and local market conditions.     

Dynamic strain aging effects in niobium microalloyed steel

Abstract

The dynamic strain aging behaviour of a niobium microalloyed steel has been examined. Hot tensile testing was carried out on heat treated and as received specimens. Heat treated specimens were austenitised at 1000°C for 1 h, and then cooled in air or in a stainless steel cylinder to obtain various amounts of free or uncombined interstitial solutes in solid solution, to examine the effect on the dynamic strain aging behaviour of the steel. It was found that dynamic strain aging takes place in niobium microalloyed steel during tensile testing at temperatures ranging from ambient temperature to 450°C at a crosshead displacement rate of 2 mm min^-1. As a result, the ultimate tensile strength and initial work hardening rate exhibit maximum values at temperatures between 200 and 350°C. Also, load-extension graphs for tested specimens show serrated behaviour and yield points at 200, 250, and 300°C. It is believed that dynamic strain aging in niobium steel is caused by interaction between dislocations and interstitial solutes (nitrogen and carbon) or solute pairs consisting of one interstitial and one substitutional solute atom (for example Mn-C and Mn-N).     

Modeling and simulation study of an insect-like flapping-wing micro aerial vehicle

The goal of this paper is to show some of the most important features of flying insects from a control point of view, describe in details the kinematics of insects during flapping flight, establish the corresponding kinematics equations of flying insects, analyze the force and moment acting on the flying insects, and establish the corresponding aerodynamic equations. Through the kinematics equations and aerodynamic equations of flying insects, the trajectory equations and attitude equations have also been established. A detailed mathematical model of flying insects is presented in this paper, which including 3 d.o.f. of wings kinematics, i.e., flapping, lagging and feathering, and 6 d.o.f. of insects body, i.e., yaw, roll, up–down flight, left–right flight and fore–back flight. All these motions of flying insects are interrelated by the kinematics equations, attitude equations, aerodynamics model and dynamics equations of the insects' centroid. In the findal part of this paper, the mathematical simulation model of flapping-wing insects is set up and the corresponding simulation curve created.     

Influence of clamping support distance on distortion of welded T joints

Abstract

A study is presented on the influence of the clamping support distance on welding distortion of 6 mm thick gas metal arc welded structural steel T joints. Experiments were performed for two clamping conditions and are compared to simulations based on a previously presented model. It was found that clamping closer to the weld seam reduces angular as well as bending distortion. In order to assess the accuracy of the results, sensitivity analyses were performed on the influence of predeformation and material parameters. It is shown that an initial predeformation has an influence on the final welding distortion. Additionally, it has been found that selection of material properties within the range of variations permitted by the material norms has a strong influence on the predicted distortion. Results were improved using material specific data rather than generic data for the relevant material class. Also the assumed phase volume change plays an important role.     

A multi-phase micro-segregation model

Abstract

A multi-component multi-phase micro-segregation model was developed to cope with eutectic transformations of ductile iron, assuming mixed dendritic–globular solidification morphology. Solute partitioning is calculated by an equilibrium assumption at the interfaces using commercial CALPHAD software. Time-sensitive micro-segregation patterns and phase fractions are solved by the micro-segregation model. The development of fraction liquid over temperature with time was compared to Gulliver–Scheil simulations for a model with and without cross-diffusion. The micro-segregation model was coupled to a commercial process simulations tool to deal with interaction effects between material and process scale during solidification of a benchmark test casting made of EN-GJSA-X NiCr 20–2. The precipitation kinetics of phases, especially of graphite, is of particular interest during solidification of ductile iron, due to feeding effects. The coupling procedure as well as important aspects during solidification of ductile iron will be explained.     

Simulating diffraction limiting in a pinhole camera

Abstract

Images synthesized by the simulation of light transport are typically generated with the premiss of rays passing through a theoretical or ideal pinhole, the implication being that an infinitely small hole will produce a perfectly sharp image. However, this is not the case. Ray and particle based models of light transport cannot reproduce the effect of diffraction limiting found of small aperture systems.

Here we consider a more appropriate wave based model. While computationally expensive, and practical for only very small apertures, it is capable of reproducing the results of a real pinhole camera. In simulating such a system, we observe that superposition of waves from multiple photons is unlikely to occur in real systems, and that Nyquist theory can be used to explain diffraction limiting as a sampling artefact.