Steven P. Hamilton

Development of an American Sign Language game for deaf children

We present a design for an interactive American Sign Language game geared for language development for deaf children. In addition to work on game design, we show how Wizard of Oz techniques can be used to facilitate our work on ASL recognition. We report on two Wizard of Oz studies which demonstrate our technique and maximize our iterative design process. We also detail specific implications to the design raised from working with deaf children and possible solutions.

A gesture-based american sign language game for deaf children

We present a system designed to facilitate language development in deaf children. The children interact with a computer game using American Sign Language (ASL). The system consists of three parts: an ASL (gesture) recognition engine; an interactive, game-based interface; and an evaluation system. Using interactive, user-centered design and the results of two Wizard-of-Oz studies at Atlanta Area School for the Deaf, we present some unique insights into the spatial organization of interfaces for deaf children.

Massively Parallel, Three-Dimensional Transport Solutions for the k-Eigenvalue Problem

Abstract We have implemented a new multilevel parallel decomposition in the Denovo discrete ordinates radiation transport code. In concert with Krylov subspace iterative solvers, the multilevel decomposition allows concurrency over energy in addition to space-angle, enabling scalability beyond the limits imposed by the traditional Koch-Baker-Alcouffe (KBA) space-angle partitioning. Furthermore, a new Arnoldi-based k-eigenvalue solver has been implemented. The added phase-space concurrency combined with the high-performance Krylov and Arnoldi solvers has enabled weak scaling to O(105) cores on the Titan XK7 supercomputer. The multilevel decomposition provides a mechanism for scaling to exascale computing and beyond.

New multigrid smoothers for the Oseen problem

We investigate the performance of smoothers based on the Hermitian/skew-Hermitian (HSS) and augmented Lagrangian (AL) splittings applied to the Marker-and-Cell (MAC) discretization of the Oseen problem. Both steady and unsteady flows are considered. Local Fourier analysis and numerical experiments on a two-dimensional lid-driven cavity problem indicate that the proposed smoothers result in h-independent convergence and are fairly robust with respect to the Reynolds number. A direct comparison shows that the new smoothers compare favorably to coupled smoothers of Braess–Sarazin type, especially in terms of scaling for increasing Reynolds number. Copyright

High performance radiation transport simulations: preparing for Titan

In this paper we describe the Denovo code system. Denovo solves the six-dimensional, steady-state, linear Boltzmann transport equation, of central importance to nuclear technology applications such as reactor core analysis (neutronics), radiation shielding, nuclear forensics and radiation detection. The code features multiple spatial differencing schemes, state-of-the-art linear solvers, the Koch-Baker-Alcouffe (KBA) parallel-wavefront sweep algorithm for inverting the transport operator, a new multilevel energy decomposition method scaling to hundreds of thousands of processing cores, and a modern, novel code architecture that supports straightforward integration of new features. In this paper we discuss the performance of Denovo on the 20+ petaflop ORNL GPU-based system, Titan. We describe algorithms and techniques used to exploit the capabilities of Titans heterogeneous compute node architecture and the challenges of obtaining good parallel performance for this sparse hyperbolic PDE solver containing inherently sequential computations. Numerical results demonstrating Denovo performance on early Titan hardware are presented.

Advances in the Subcritical, Gas-Cooled, Fast Transmutation Reactor Concept

The design concept for a subcritical, He-cooled, fast reactor, fueled with transuranics (TRUs) from spent nuclear fuel in coated TRISO particles and driven by a tokamak D-T fusion neutron source, is being developed at Georgia Institute of Technology. The basic concept has been developed in two previous papers. This paper reports (a) advances in the design concept intended to enable achievement of “deep-burn” of the TRUs and passive safety, (b) investigations of the possibility of reprocessing the TRISO TRU fuel and of extending the strength of the fusion neutron source, (c) more extensive analyses to confirm and improve the design with respect to the adequacy of the fuel and nuclear performance, heat removal, tritium self-sufficiency and shielding, (d) more extensive analyses to confirm that the International Tokamak Experimental Reactor divertor, magnet and heating/current drive systems can be adapted, and (e) fuel cycle analyses to further investigate the contribution that such a reactor could make to closing the nuclear fuel cycle.

An assessment of coupling algorithms for nuclear reactor core physics simulations

This paper evaluates the performance of multiphysics coupling algorithms applied to a light water nuclear reactor core simulation. The simulation couples the k-eigenvalue form of the neutron transport equation with heat conduction and subchannel flow equations. We compare Picard iteration (block Gauss-Seidel) to Anderson acceleration and multiple variants of preconditioned Jacobian-free Newton-Krylov (JFNK). The performance of the methods are evaluated over a range of energy group structures and core power levels. A novel physics-based approximation to a Jacobian-vector product has been developed to mitigate the impact of expensive on-line cross section processing steps. Numerical simulations demonstrating the efficiency of JFNK and Anderson acceleration relative to standard Picard iteration are performed on a 3D model of a nuclear fuel assembly. Both criticality (k-eigenvalue) and critical boron search problems are considered.

Efficient solution of the simplified P N equations

In this paper we show new solver strategies for the multigroup SP N equations for nuclear reactor analysis. By forming the complete matrix over space, moments, and energy, a robust set of solution strategies may be applied. Power iteration, shifted power iteration, Rayleigh quotient iteration, Arnoldis method, and a generalized Davidson method, each using algebraic and physics-based multigrid preconditioners, have been compared on the C5G7 MOX test problem as well as an operational pressurized water reactor model. Our results show that the most efficient approach is the generalized Davidson method, which is 30-40 times faster than traditional power iteration and 6-10 times faster than Arnoldis method.

A parallel multi-domain solution methodology applied to nonlinear thermal transport problems in nuclear fuel pins

This paper describes an efficient and nonlinearly consistent parallel solution methodology for solving coupled nonlinear thermal transport problems that occur in nuclear reactor applications over hundreds of individual 3D physical subdomains. Efficiency is obtained by leveraging knowledge of the physical domains, the physics on individual domains, and the couplings between them for preconditioning within a Jacobian Free Newton Krylov method. Details of the computational infrastructure that enabled this work, namely the open source Advanced Multi-Physics (AMP) package developed by the authors is described. Details of verification and validation experiments, and parallel performance analysis in weak and strong scaling studies demonstrating the achieved efficiency of the algorithm are presented. Furthermore, numerical experiments demonstrate that the preconditioner developed is independent of the number of fuel subdomains in a fuel rod, which is particularly important when simulating different types of fuel rods. Finally, we demonstrate the power of the coupling methodology by considering problems with couplings between surface and volume physics and coupling of nonlinear thermal transport in fuel rods to an external radiation transport code.

Hot zero power reactor calculations using the Insilico code

In this paper we describe the reactor physics simulation capabilities of the Insilico code. A description of the various capabilities of the code is provided, including detailed discussion of the geometry, meshing, cross section processing, and neutron transport options. Numerical results demonstrate that Insilico using an SPN solver with pin-homogenized cross section generation is capable of delivering highly accurate full-core simulation of various pressurized water reactor problems. Comparison to both Monte Carlo calculations and measured plant data is provided.