With the rapid advances in high-performance computing technology in recent years, researchers at the University of Tennessee have initiated a collaborative project to address the theoretical, algorithmic, and numerica...
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There has been little research into the weak kinds of negating hypotheses. Hypotheses may be unfalsifiable. In this case it is impossible to find a contradiction in some area of the conceptual systems in which they ar...
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With the rapid advances in high-performance computing technology in recent years, researchers at the University of Tennessee have initiated a collaborative project to address the theoretical, algorithmic, and numerica...
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ISBN:
(纸本)0791816613
With the rapid advances in high-performance computing technology in recent years, researchers at the University of Tennessee have initiated a collaborative project to address the theoretical, algorithmic, and numerical implementation issues of computational mechanics simulations. To meet the challenge, a Parallel Interoperable computational Mechanics Simulator System (PICMSS) has been established. Such effort entails the development of a modular finite element platform capable of admitting diverse CFD formulations, as well as closure models for physics phenomena, as required/derived by the users operating on supercomputers and networks of PC clusters. Incompressible Navier Stokes Benchmark solutions via a velocity-vorticity formulation are proposed to examine the integrity and scalability of PICMSS.
The structure completion problem in fiber diffraction is addressed from a Bayesian perspective. The experimental data are sums of the squares of the amplitudes of particular sets of Fourier coefficients of the electro...
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The structure completion problem in fiber diffraction is addressed from a Bayesian perspective. The experimental data are sums of the squares of the amplitudes of particular sets of Fourier coefficients of the electron density. In addition, a part of the electron density is known. The image reconstruction problem is to estimate the missing part of the electron density. A Bayesian approach is taken in which the prior model for the image is based on the fact that it consists of atoms, i.e. the unknown electron density consists of separated sharp peaks. The conventional prior assumes that the positions of the unknown atoms are uniformly distributed. We improve this prior by treating the positions of the known atoms as containing normally distributed coordinate errors. Currently used heuristic methods are shown to correspond to certain maximum a posteriori estimates of the Fourier coefficients. An analytical solution for the Bayesian minimum mean-square-error estimate is derived. Simulations show that the minimum mean-square-error estimate gives better results when the new prior is used.
This paper develops and uses a computation model to explore the transient ignition dynamics of catalytic combustion in a stagnation-flow configuration. The analysis considers the elementary heterogeneous chemistry ass...
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This paper develops and uses a computation model to explore the transient ignition dynamics of catalytic combustion in a stagnation-flow configuration. The analysis considers the elementary heterogeneous chemistry associated with catalytic behavior at the surface. It also considers gas-dynamic effects in the boundary layer, including temporal and spatial pressure variations. The gas-dynamic effects are included through the axial momentum equation, which has been neglected in previous analyses of unsteady stagnation flows. In addition to the physical interpretation of ignition transients, the paper presents a mathematical and computational analysis and comparison of the constant-pressure and compressible stagnation-flow equations. The constant-pressure equations, as commonly formulated and used, are a system of differential-algebraic equations (DAE) that have an index greater than two. This high-index behavior is responsible for severe numerical difficulties in regions of fast transients or stringent numerical error control. This paper relaxes the constant-pressure assumption using a compressible-flow formulation, which extends the range of physical validity and reduces the index of the transient stagnation-flow problem while preserving stagnationflow "similarity.".
The restoration of an incomplete image from a known part and experimental data in the form of the Fourier amplitude squared sums is formulated as a Bayesian estimation problem. This problem is motivated by the structu...
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The restoration of an incomplete image from a known part and experimental data in the form of the Fourier amplitude squared sums is formulated as a Bayesian estimation problem. This problem is motivated by the structure completion problem in X-ray fiber diffraction analysis. An appropriate prior of uniformly distributed impulses is used. The Bayesian MMSE and MAP estimates are obtained. Simulations are used to compare the performance of the estimates. The results show that the MMSE estimate significantly outperforms the other estimates. The restored images exhibit some bias towards the known part of the image. This can be partly reduced by an unbiasing procedure.
A parallel method developed for reconstructing images from holograms obtained with optical scanning holography is presented. A standard portable message-passing library, MPI or message-passing interface, is used to pr...
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A parallel method developed for reconstructing images from holograms obtained with optical scanning holography is presented. A standard portable message-passing library, MPI or message-passing interface, is used to provide the environment of parallel programming. The parallel method is implemented using a network of workstations. The process of reconstructing images with twin-image removal from holograms is performed in parallel with respect to different reconstruction planes of interest. This process contributes to possible faster three-dimensional object identification to be investigated in future research.
Several recent studies have compared the relative efficiency of alternative flaw selection strategies for partial-order causal link (POCL) planning. We review this literature, and present new experimental results that...
Several recent studies have compared the relative efficiency of alternative flaw selection strategies for partial-order causal link (POCL) planning. We review this literature, and present new experimental results that generalize the earlier work and explain some of the discrepancies in it. In particular, we describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by Joslin and Pollack (1994), and compare it with other strategies, including Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very different, and apparently conflicting claims about the most effective way to reduce search-space size in POCL planning. We resolve this conflict, arguing that much of the benefit that Gerevini and Schubert ascribe to the LIFO component of their ZLIFO strategy is better attributed to other causes. We show that for many problems, a strategy that combines least-cost flaw selection with the delay of separable threats will be effective in reducing search-space size, and will do so without excessive computational overhead. Although such a strategy thus provides a good default, we also show that certain domain characteristics may reduce its effectiveness.
Despite the limits inherent within linearized frequency-domain ship motion and wave load computer codes, strip theory has been found to provide the design community with a fairly robust, practical design tool with rea...
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Despite the limits inherent within linearized frequency-domain ship motion and wave load computer codes, strip theory has been found to provide the design community with a fairly robust, practical design tool with reasonable accuracy for most conventional displacement monohulls. However, the advent of new design concepts including multi-hulls and application of new materials as well as the push to incorporate reliability methods within surface ship structural design criteria has highlighted the need for more rigorous methods of developing a lifetime load spectrum. In this paper, a multilevel computation system for predicting ship motions and wave loads, up through and including extreme sea conditions, is presented. This system includes a traditional strip theory approach and newly developed linear and nonlinear three-dimensional time-domain methods. The new nonlinear methods are currently in the process of being validated by the U.S. Navy. The status of the current development is presented. Sample numerical results from the new nonlinear methods are compared with both linear frequency domain predictions and model tests.
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