Numerical Simulation of Pollutant Transport in a Shallow-Water System on the Cell Heterogeneous Processor

[Abstract] This paper presents an implementation, optimized for the Cell processor, of a finite volume numerical scheme for 2D shallow-water systems with pollutant transport. A description of the special architecture and programming required by the Cell processor motivates the methodology to develop optimized implementations for this platform. This process involves parallelization, data structure reorganization, explicit transfers of data and computation vectorization. Our implementation, tested using a realistic problem, achieves very good speedups with respect to the sequential execution on a standard CPU.This work was partially supported by the Science and Innovation Ministry of Spain (Projects TIN2010-16735, MTM2010-21135-C02-01 and MTM2009-11923), Xunta de Galicia CN2012/211 (partially supported by FEDER funds), and the FPU program of the Spanish Government (ref AP2009-4752)Xunta de Galicia; CN 2012/21

Lattice Boltzmann Flachwassergleichungen für großskalige hydraulische Analyse

This thesis presents a new lattice Boltzmann model for both steady and unsteady two-dimensional shallow water equations. Throughout this work, the usage of different collision operators (CO) for the lattice Boltzmann solution of shallow water equations is proposed and investigated: BGK linear CO based on a single relaxation time (SRT), cascaded and cumulant CO with a multiple relaxation times approach (MRT). The motivation in using a MRT collision operator instead of the standard BGK, was to introduce the maximum number of adjustable parameters, which leads to an improvement of both stability and accuracy. The thesis focuses on the development, validation and applications of the aforementioned CO for shallow water flows. The cascaded LBM is based on the use of central moments as basis; it overcomes the defects in Galilean invariance of the original MRT method and it has been shown to further improve stability. An adaptation of the original formulation proposed for a single-phase fluid is therefore proposed and developed to reproduce shallow free surface flow. Furthermore, an alternative and more concise approach is based on the use of a cumulant collision operator, which relaxes, in the collision step, quantities (i.e. cumulants) that are Galilean invariant by construction. In the first part of the thesis, a convergence study of the different approaches, based on the use of the Taylor Green Vortex as test case, is performed, to compare conventional and innovative solution methods from stability and accuracy point of view. Then, the second part is devoted to analyzing different strategies to introduce, in the innovative models, the treatment of external forces term and various kinds of boundary conditions, that maintain the accuracy characteristics of the model. Special attention is due to the wet-dry front in shallow flows; in fact, a correct simulation of such processes plays a crucial role in practical engineering studies. The proposed methodologies are tested and validated through the use of analytical solutions and experimental solutions, taken as benchmarks throughout the thesis. Finally, the suitability of the proposed mathematical model for hydraulic engineering applications is discussed through the modelling of a real flood event.Diese Arbeit präsentiert ein neues Gitter-Boltzmann-Modell für stationäre und instationäre zweidimensionale Flachwassergleichungen. In dieser Arbeit wird die Verwendung verschiedener Kollisionsoperatoren (CO) für die Gitter-Boltzmann-Lösung von Flachwassergleichungen vorgeschlagen und untersucht: der lineare BGK CO basierend auf einer einzelnen Relaxationszeit (SRT), der kaskadierte und der Kumulanten CO mit multiplen Relaxationszeitansatz (MRT). Die Motivation bei der Verwendung eines MRT-Kollisionsoperators anstelle des standardmäßigen BGK bestand darin, die maximale Anzahl an einstellbaren Parametern einzuführen, was zu einer Verbesserung sowohl der Stabilität als auch der Genauigkeit führt. Die Arbeit konzentriert sich auf die Entwicklung, Validierung und Anwendung des oben genannten CO für die Flachwassergleichung. Die kaskadierte LBM basiert auf der Verwendung zentraler Momente als Basis. Sie überwindet die Verletzung der Galilei-Invarianz der ursprünglichen MRT-Methode und verbessert nachweislich die Stabilität. Eine Anpassung der ursprünglichen Formulierungfür die Flachwassergleichung wird daher vorgeschlagen und entwickelt. Darüber hinaus basiert ein alternativer Ansatz auf der Verwendung eines Kumulantenkollisionsoperators, der in dem Kollisionsschritt Größen (d. H. Kumulanten) relaxiert, die per Konstruktion Galilei-Invarianten sind. Basierend auf der Verwendung des Taylor Green Vortex als Testfall wird im ersten Teil der Arbeit eine Konvergenzstudie der verschiedenen Ansätze durchgeführt. Damit werden die konventionellen und innovativen Lösungsmethoden aus Sicht der Stabilitäts-und Genauigkeit verglichen. Der zweite Teil widmet sich der Analyse verschiedener Strategien, um in den innovativen Modellen die Behandlung von äußeren Kräften und verschiedene Arten von Randbedingungen einzuführen, die die Genauigkeitseigenschaften des Modells beibehalten. Besonderes Augenmerk liegt auf der Nass-Trocken-Front in flachen Strömungen. Eine korrekte Simulation solcher Prozesse spielt eine entscheidende Rolle in praktischen Ingenieurstudien. Die vorgeschlagenen Methoden werden durch die Verwendung von analytischen Lösungen und experimentellen Lösungen in Form von Benchmarks in der Arbeit getestet und validiert. Abschließend wird die Eignung des vorgeschlagenen mathematischen Modells für wasserbauliche Anwendungen durch die Modellierung eines realen Hochwasserereignisses diskutiert

PHYSICS-AWARE MODEL SIMPLIFICATION FOR INTERACTIVE VIRTUAL ENVIRONMENTS

Rigid body simulation is an integral part of Virtual Environments (VE) for autonomous planning, training, and design tasks. The underlying physics-based simulation of VE must be accurate and computationally fast enough for the intended application, which unfortunately are conflicting requirements. Two ways to perform fast and high fidelity physics-based simulation are: (1) model simplification, and (2) parallel computation. Model simplification can be used to allow simulation at an interactive rate while introducing an acceptable level of error. Currently, manual model simplification is the most common way of performing simulation speedup but it is time consuming. Hence, in order to reduce the development time of VEs, automated model simplification is needed. The dissertation presents an automated model simplification approach based on geometric reasoning, spatial decomposition, and temporal coherence. Geometric reasoning is used to develop an accessibility based algorithm for removing portions of geometric models that do not play any role in rigid body to rigid body interaction simulation. Removing such inaccessible portions of the interacting rigid body models has no influence on the simulation accuracy but reduces computation time significantly. Spatial decomposition is used to develop a clustering algorithm that reduces the number of fluid pressure computations resulting in significant speedup of rigid body and fluid interaction simulation. Temporal coherence algorithm reuses the computed force values from rigid body to fluid interaction based on the coherence of fluid surrounding the rigid body. The simulations are further sped up by performing computing on graphics processing unit (GPU). The dissertation also presents the issues pertaining to the development of parallel algorithms for rigid body simulations both on multi-core processors and GPU. The developed algorithms have enabled real-time, high fidelity, six degrees of freedom, and time domain simulation of unmanned sea surface vehicles (USSV) and can be used for autonomous motion planning, tele-operation, and learning from demonstration applications

Heterogeneous multicore systems for signal processing

This thesis explores the capabilities of heterogeneous multi-core systems, based on multiple Graphics Processing Units (GPUs) in a standard desktop framework. Multi-GPU accelerated desk side computers are an appealing alternative to other high performance computing (HPC) systems: being composed of commodity hardware components fabricated in large quantities, their price-performance ratio is unparalleled in the world of high performance computing. Essentially bringing “supercomputing to the masses”, this opens up new possibilities for application fields where investing in HPC resources had been considered unfeasible before. One of these is the field of bioelectrical imaging, a class of medical imaging technologies that occupy a low-cost niche next to million-dollar systems like functional Magnetic Resonance Imaging (fMRI). In the scope of this work, several computational challenges encountered in bioelectrical imaging are tackled with this new kind of computing resource, striving to help these methods approach their true potential. Specifically, the following main contributions were made: Firstly, a novel dual-GPU implementation of parallel triangular matrix inversion (TMI) is presented, addressing an crucial kernel in computation of multi-mesh head models of encephalographic (EEG) source localization. This includes not only a highly efficient implementation of the routine itself achieving excellent speedups versus an optimized CPU implementation, but also a novel GPU-friendly compressed storage scheme for triangular matrices. Secondly, a scalable multi-GPU solver for non-hermitian linear systems was implemented. It is integrated into a simulation environment for electrical impedance tomography (EIT) that requires frequent solution of complex systems with millions of unknowns, a task that this solution can perform within seconds. In terms of computational throughput, it outperforms not only an highly optimized multi-CPU reference, but related GPU-based work as well. Finally, a GPU-accelerated graphical EEG real-time source localization software was implemented. Thanks to acceleration, it can meet real-time requirements in unpreceeded anatomical detail running more complex localization algorithms. Additionally, a novel implementation to extract anatomical priors from static Magnetic Resonance (MR) scansions has been included