13 research outputs found
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A Component Architecture for High-Performance Scientific Computing
The Common Component Architecture (CCA) provides a means for software developers to manage the complexity of large-scale scientific simulations and to move toward a plug-and-play environment for high-performance computing. In the scientific computing context, component models also promote collaboration using independently developed software, thereby allowing particular individuals or groups to focus on the aspects of greatest interest to them. The CCA supports parallel and distributed computing as well as local high-performance connections between components in a language-independent manner. The design places minimal requirements on components and thus facilitates the integration of existing code into the CCA environment. The CCA model imposes minimal overhead to minimize the impact on application performance. The focus on high performance distinguishes the CCA from most other component models. The CCA is being applied within an increasing range of disciplines, including combustion research, global climate simulation, and computational chemistry
A CSP and tabulation based adaptive chemistry model
We demonstrate the feasibility of a new strategy for the construction of an adaptive chemistry model that is based on an explicit integrator stabilized by an approximation of the Computational Singular Perturbation (CSP)-slow-manifold projector. We examine the effectiveness and accuracy of this technique first using a model problem with variable stiffness. We assess the effect of using an approximation of the CSP-slow-manifold by either reusing the CSP vectors calculated in previous steps or from a pre-built tabulation. We find that while accuracy is preserved, the associated CPU cost was reduced substantially by this method. We used two ignition simulations – hydrogen–air and heptane–air mixtures – to demonstrate the feasibility of using the new method to handle realistic kinetic mechanisms. We test the effect of utilizing an approximation of the CSP-slow-manifold and find that its use preserves the order of the explicit integrator, produces no degradation in accuracy, and results in a scheme that is competitive with traditional implicit integration. Further analysis on the performance data demonstrates that the tabulation of the CSP-slow-manifold provides an increasing level of efficiency as the size of the mechanism increases. From the software engineering perspective, all the machinery developed is Common Component Architecture compliant, giving the software a distinct advantage in the ease of maintainability and flexibility in its utilization. Extension of this algorithm is underway to implement an automated tabulation of the CSP-slow-manifold for a detailed chemical kinetic system either off-line, or on-line with a reactive flow simulation code
A sparse reconstruction method for the estimation of multi-resolution emission fields via atmospheric inversion
Atmospheric inversions are frequently used to estimate fluxes of atmospheric
greenhouse gases (e.g., biospheric CO<sub>2</sub> flux fields) at Earth's surface.
These inversions typically assume that flux departures from a prior model are
spatially smoothly varying, which are then modeled using a multi-variate
Gaussian. When the field being estimated is spatially rough, multi-variate
Gaussian models are difficult to construct and a wavelet-based field model
may be more suitable. Unfortunately, such models are very high dimensional
and are most conveniently used when the estimation method can simultaneously
perform data-driven model simplification (removal of model parameters that
cannot be reliably estimated) and fitting. Such sparse reconstruction methods
are typically not used in atmospheric inversions. In this work, we devise a sparse reconstruction method, and illustrate it in an idealized atmospheric inversion problem for the
estimation of fossil fuel CO<sub>2</sub> (ffCO<sub>2</sub>) emissions in the lower 48 states
of the USA.
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Our new method is based on stagewise orthogonal matching pursuit (StOMP), a
method used to reconstruct compressively sensed images. Our adaptations
bestow three properties to the sparse reconstruction procedure which are
useful in atmospheric inversions. We have modified StOMP to incorporate prior
information on the emission field being estimated and to enforce
non-negativity on the estimated field. Finally, though based on wavelets, our
method allows for the estimation of fields in non-rectangular geometries, e.g.,
emission fields inside geographical and political boundaries.
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Our idealized inversions use a recently developed multi-resolution (i.e.,
wavelet-based) random field model developed for ffCO<sub>2</sub> emissions and
synthetic observations of ffCO<sub>2</sub> concentrations from a limited set of
measurement sites. We find that our method for limiting the estimated field
within an irregularly shaped region is about a factor of 10 faster than
conventional approaches. It also reduces the overall computational cost by
a factor of 2. Further, the sparse reconstruction scheme imposes
non-negativity without introducing strong nonlinearities, such as those
introduced by employing log-transformed fields, and thus reaps the benefits
of simplicity and computational speed that are characteristic of linear
inverse problems
On chain branching and its role in homogeneous ignition and premixed flame propagation
The role of chain branching in a chemical kinetic system was investigated by analyzing the eigenvalues of the system. We found that in the homogeneous ignition of the hydrogen/air and methane/air mixtures, the branching mechanism gives rise to explosive modes (eigenvalues with positive real parts) in the induction period as expected; however, in their respective premixed flames, we found none. Thus, their existence is not a necessary condition for the propagation of a premixed flame. © 2005 Elsevier Ltd