Acceleration Techniques for Discrete-Ordinates Transport Methods with Highly Forward-Peaked Scattering

In this dissertation, advanced numerical methods for highly forward peaked scattering deterministic calculations are devised, implemented, and assessed. Since electrons interact with the surrounding environment through Coulomb interactions, the scattering kernel is highly forward-peaked. This bears the consequence that, with standard preconditioning, the standard Legendre expansion of the scattering kernel requires too many terms for the discretized equation to be solved efficiently using a deterministic method. The Diffusion Synthetic Acceleration (DSA), usually used to speed up the calculation when the scattering is weakly anisotropic, is inefficient for electron transport. This led Morel and Manteuffel to develop a one-dimensional angular multigrid (ANMG) which has proved to be very effective when the scattering is highly anisotropic. Later, Pautz et al. generalized this scheme to multidimensional geometries, but this method had to be stabilized by a diffusive filter that degrades the overall convergence of the iterative scheme. In this dissertation, we recast the multidimensional angular multigrid method without the filter as a preconditioner for a Krylov solver. This new method is stable independently of the anisotropy of the scattering and is increasingly more effective and efficient as the anisotropy increases compared to DSA preconditioning wrapped inside a Krylov solver. At the coarsest level of ANMG, a DSA step is needed. In this research, we use the Modified Interior Penalty (MIP) DSA. This DSA was shown to be always stable on triangular cells with isotropic scattering. Because this DSA discretization leads to symmetric definite-positive matrices, it is usually solved using a conjugate gradient preconditioned (CG) by SSOR but here, we show that algebraic multigrid methods are vastly superior than more common CG preconditioners such as SSOR. Another important part of this dissertation is dedicated to transport equation and diffusion solves on arbitrary polygonal meshes. The advantages of polygonal cells are that the number of unknowns needed to mesh a domain can be decreased and that adaptive mesh refinement implementation is simplified: rather than handling hanging nodes, the adapted computational mesh includes different types of polygons. Numerical examples are presented for arbitrary quadrilateral and polygonal grids

ArborX: A Performance Portable Geometric Search Library

Searching for geometric objects that are close in space is a fundamental component of many applications. The performance of search algorithms comes to the forefront as the size of a problem increases both in terms of total object count as well as in the total number of search queries performed. Scientific applications requiring modern leadership-class supercomputers also pose an additional requirement of performance portability, i.e. being able to efficiently utilize a variety of hardware architectures. In this paper, we introduce a new open-source C++ search library, ArborX, which we have designed for modern supercomputing architectures. We examine scalable search algorithms with a focus on performance, including a highly efficient parallel bounding volume hierarchy implementation, and propose a flexible interface making it easy to integrate with existing applications. We demonstrate the performance portability of ArborX on multi-core CPUs and GPUs, and compare it to the state-of-the-art libraries such as Boost.Geometry.Index and nanoflann

Private household demand for vehicles on alternative fuels and drive trains: a review

ny attempt of the government to encourage the purchase of vehicles on alternative fuels and drive trains will depend on the acceptance of the end-users on the demand side. This paper offers an in-depth understanding of the consumers’ attitudes and preferences towards AFVs which can guide the government to establish effective policy measures. A comprehensive review of research is performed under different conceptual frameworks and research methodologies: attitudinal, experimental, preference valuation studies and others. Research findings are reported with the general objective to (1) uncover the attitudes and preferences towards AFVs and (2) examine whether the environmental benefits of AFVs play a role in the car purchase decision. Overall, there exists a strong environmental concern, and positive attitudes towards AFVs. However, environmental benefits are of little importance in the car purchase decision, which is principally driven by price characteristics, performance and convenience attributes. Limited knowledge levels also seem to prevent building up awareness of AFVs, which is the key to their adoption. The adoption of AFVs is likely to be limited without significant governmental incentives and regulations. Based on the key findings, it can be recommended that a combination of educational campaigns (e.g., information tools), pricing measures (e.g., differentiated vehicle taxation), supply-sided measures and large-scale demonstrations is required to support the adoption of AFVs. Document type: Articl

The deal.II Library, Version 8.3

deal.II version 8.3 was released August 1, 2015. This paper provides an overview of the new features of this release and serves as a citable reference for the deal.II software library version 8.3. deal.II is an object-oriented finite element library used around the world in the development of finite element solvers. It is available for free under the GNU Lesser General Public License (LGPL) from the deal.II homepage at http://www.dealii.org/

The deal.II Library, Version 8.5

This paper provides an overview of the new features of the finite element library deal.II version 8.5

The deal.II Library, Version 9.0

This paper provides an overview of the new features of the finite element library deal.II version 9.0

The deal.II Library, Version 9.1

This paper provides an overview of the new features of the finite element library deal.II, version 9.1