On Prism-based Motion Blur and Locking-proof Tetrahedra

Motion blur is an important visual effect in computer graphics for both real-time, interactive, and offline applications. Current methods offer either slow and accurate solutions for offline ray tracing applications, or fast and inaccurate solutions for real-time applications. This thesis is a collection of three papers, two of which address the need for motion blur solutions that cater to applications that need to be accurate and as well as interactive, and a third that addresses the problem of locking in standard FEM simulations. In short, this thesis deals with the problem of representing continuous motion in a discrete setting.In Paper I, we implement a GPU based fast analytical motion blur renderer. Using ray/triangular prism intersections to determine triangle visibility and shading, we achieve interactive frame rates.In Paper II, we show and address the limitations of using prisms as approximations of the triangle swept volume. A hybrid method of prism intersections and time-dependent edge equations is used to overcome the limitations of Paper I.In Paper III, we provide a solution that alleviates volumetric locking in standard Neo-Hookean FEM simulations without resorting to higher order interpolation

Describing and Simulating Dynamic Reconfiguration in SystemC Exemplified by a Dedicated 3D Collision Detection Hardware

The ongoing trend towards development of parallel software and the increased flexibility of state-of-the-art programmable logic devices are currently converging in the field of reconfigurable hardware. On the other hand there is the traditional hardware market, with its increasingly short development cycles, which is mainly driven by high-level prototyping of products. To enable the design community to conveniently develop reconfigurable architectures in a short time-to-market, this thesis introduces the library ReChannel, which extends SystemC with advanced language constructs for high level reconfiguration modelling. It combines IP reuse and high-level modelling with reconfiguration. The proposed methodology was tested on a hierarchical FPGA-based 3D collision detection accelerator, is also presented. To enable implementation of such a complex algorithm in FPGA logic it had to be implemented using fixed-point arithmetic. Therefore a special method was derived that enables rounding of the used bounding-volumes without incurring the correctness of the non-intersection reports. This guarantees a correct overall result. A bound on the rounding error was derived that gives a measure of the number of false intersection reports, and thus on the run-time. A triangle and a quadrangle intersection test were implemented as the second</p

Real-Time Collision Detection for Deformable Characters with Radial Fields

Many techniques facilitate real-time collision detection against complex models. These typically work by pre-computing information about the spatial distribution of geometry into a form that can be quickly queried. When models deform though, expensive pre-computations are impractical. We present radial fields: a variant of distance fields parameterised in cylindrical space, rather than Cartesian space. This 2D parameterisation significantly reduces the memory and computation requirements of the field, while introducing minimal overhead in collision detection tests. The interior of the mesh is defined implicitly for the entire domain. Importantly, it maps well to the hardware rasteriser of the GPU. Radial fields are much more application-specific than traditional distance fields. For these applications - such as collision detection with articulated characters - however, the benefits are substantial

WebGL-Based Simulation of Bone Removal in Surgical Orthopeadic Procedures

The effective role of virtual reality simulators in surgical operations has been demonstrated during the last decades. The proposed work has been done to give a perspective of the actual orthopeadic surgeries such as a total shoulder arthroplasty with low incidence and visibility of the operation to the surgeon. The research in this thesis is focused on the design and implementation of a web-based graphical feedback for a total shoulder arthroplasty (TSA) surgery. For portability of the simulation and powerful 3D programming features, WebGL is being applied. To simulate the reaming process of the shoulder bone, multiple steps has been passed to be able to remove the volumetric amount of bone which was touched by the reamer tool. A fast and accurate collision detection algorithm utilizing Möller –Trumbore ray-triangle method was implemented to detect the first collision of the bone and the tool in order to accelerate the computations for the bone removal process. Once the collision detected, a mesh Boolean operation using CSG method is being invoked to calculate the volumetric amount of bone which is intersected with the tool and should be removed. This work involves the user interaction to transform the tool in a Three.js scene for the simulated operation

Automated CNC Tool Path Planning and Machining Simulation on Highly Parallel Computing Architectures

This work has created a completely new geometry representation for the CAD/CAM area that was initially designed for highly parallel scalable environment. A methodology was also created for designing highly parallel and scalable algorithms that can use the developed geometry representation. The approach used in this work is to move parallel algorithm design complexity from an algorithm level to a data representation level. As a result the developed methodology allows an easy algorithm design without worrying too much about the underlying hardware. However, the developed algorithms are still highly parallel because the underlying geometry model is highly parallel. For validation purposes, the developed methodology and geometry representation were used for designing CNC machine simulation and tool path planning algorithms. Then these algorithms were implemented and tested on a multi-GPU system. Performance evaluation of developed algorithms has shown great parallelizability and scalability; and that main algorithm properties are required for modern highly parallel environment. It was also proved that GPUs are capable of performing work an order of magnitude faster than traditional central processors. The last part of the work demonstrates how high performance that comes with highly parallel hardware can be used for development of a next level of automated CNC tool path planning systems. As a proof of concept, a fully automated tool path planning system capable of generating valid G-code programs for 5-axis CNC milling machines was developed. For validation purposes, the developed system was used for generating tool paths for some parts and results were used for machining simulation and experimental machining. Experimental results have proved from one side that the developed system works. And from another side, that highly parallel hardware brings computational resources for algorithms that were not even considered before due to computational requirements, but can provide the next level of automation for modern manufacturing systems

Intelligent Computational Transportation

Transportation is commonplace around our world. Numerous researchers dedicate great efforts to vast transportation research topics. The purpose of this dissertation is to investigate and address a couple of transportation problems with respect to geographic discretization, pavement surface automatic examination, and traffic ow simulation, using advanced computational technologies. Many applications require a discretized 2D geographic map such that local information can be accessed efficiently. For example, map matching, which aligns a sequence of observed positions to a real-world road network, needs to find all the nearby road segments to the individual positions. To this end, the map is discretized by cells and each cell retains a list of road segments coincident with this cell. An efficient method is proposed to form such lists for the cells without costly overlapping tests. Furthermore, the method can be easily extended to 3D scenarios for fast triangle mesh voxelization. Pavement surface distress conditions are critical inputs for quantifying roadway infrastructure serviceability. Existing computer-aided automatic examination techniques are mainly based on 2D image analysis or 3D georeferenced data set. The disadvantage of information losses or extremely high costs impedes their effectiveness iv and applicability. In this study, a cost-effective Kinect-based approach is proposed for 3D pavement surface reconstruction and cracking recognition. Various cracking measurements such as alligator cracking, traverse cracking, longitudinal cracking, etc., are identified and recognized for their severity examinations based on associated geometrical features. Smart transportation is one of the core components in modern urbanization processes. Under this context, the Connected Autonomous Vehicle (CAV) system presents a promising solution towards the enhanced traffic safety and mobility through state-of-the-art wireless communications and autonomous driving techniques. Due to the different nature between the CAVs and the conventional Human- Driven-Vehicles (HDVs), it is believed that CAV-enabled transportation systems will revolutionize the existing understanding of network-wide traffic operations and re-establish traffic ow theory. This study presents a new continuum dynamics model for the future CAV-enabled traffic system, realized by encapsulating mutually-coupled vehicle interactions using virtual internal and external forces. A Smoothed Particle Hydrodynamics (SPH)-based numerical simulation and an interactive traffic visualization framework are also developed

Interactive ray tracing of massive and deformable models

Ray tracing is a fundamental algorithm used for many applications such as computer graphics, geometric simulation, collision detection and line-of-sight computation. Even though the performance of ray tracing algorithms scales with the model complexity, the high memory requirements and the use of static hierarchical structures pose problems with massive models and dynamic data-sets. We present several approaches to address these problems based on new acceleration structures and traversal algorithms. We introduce a compact representation for storing the model and hierarchy while ray tracing triangle meshes that can reduce the memory footprint by up to 80%, while maintaining high performance. As a result, can ray trace massive models with hundreds of millions of triangles on workstations with a few gigabytes of memory. We also show how to use bounding volume hierarchies for ray tracing complex models with interactive performance. In order to handle dynamic scenes, we use refitting algorithms and also present highly-parallel GPU-based algorithms to reconstruct the hierarchies. In practice, our method can construct hierarchies for models with hundreds of thousands of triangles at interactive speeds. Finally, we demonstrate several applications that are enabled by these algorithms. Using deformable BVH and fast data parallel techniques, we introduce a geometric sound propagation algorithm that can run on complex deformable scenes interactively and orders of magnitude faster than comparable previous approaches. In addition, we also use these hierarchical algorithms for fast collision detection between deformable models and GPU rendering of shadows on massive models by employing our compact representations for hybrid ray tracing and rasterization

Automatic calculation and evaluation of flow in complex geometries using finite volume and lattice boltzmann methods

Trotz großen Fortschritts kann die numerische Strömungsmechanik (englisch Computational Fluid Dynamics, CFD) nicht als Blackbox-Verfahren verwendet werden, da Schritte wie die Gittergenerierung oder die Wahl numerischer Parameter vertiefte Kenntnisse der Theorie von CFD erfordert. Eine Verbesserung von CFD in Richtung einer Blackbox-Lösung würde nicht nur die Anwendungsbarriere verringern, weil weniger spezielles Wissen notwendig ist, sondern auch wissenschaftliche Erkenntnisse ermöglichen. Beispielsweise können viel mehr Datenpunkte erzeugt werden, die für die Entwicklung genauer Modelle für manche Fragestellungen notwendig sind. Diese Arbeit veranschaulicht die Vorteile einer automatisierten Berechnung anhand dreier beispielhafter Anwendungen: • Die genaue Vorhersage des Druckverlusts einer Kugelschüttung ist von großer Bedeutung in der Verfahrenstechnik. Für Schüttungen, bei denen die Kugeln relativ groß verglichen mit den Abmessungen des Behälters sind, spielt zudem der Wandeffekt eine wichtige Rolle. Viele Korrelationen, die üblicherweise auf experimentellen Messungen basieren, wurden in der Literatur vorgestellt, zeigen aber Abweichungen von ca. 20 % voneinander. Die Kombination von simulierter Generierung von Kugelschüttung und CFD wird hier verwendet, um den Druckverlust einer großen Anzahl von Kugelpackungen mit unterschiedlichen Kugeldurchmessern und für unterschiedliche Abmessungen des Behälters zu berechnen. Es wird gezeigt, dass der Druckverlust eine nicht-monotone Funktion für kleine Verhältnisse von Kugeldurchmesser zu hydraulischem Durchmesser des Reaktors ist, was die Abweichungen in den experimentellen Ergebnissen erklären kann. • Die Fischer-Tropsch-Synthese ist wieder von wachsendem Interesse, da sie die Herstellung von CO2 neutralen Treibstoffen erlaubt. Transportporen können genutzt werden, um den Stofftransport im benötigten Katalysator zu beschleunigen und somit auch die Ausbeute zu erhöhen. Ein eindimensionales Modell aus der Literatur wird in dieser Arbeit auf drei Dimensionen erweitert. Die Berechnung wird automatisiert wodurch die Katalysatorschichten algorithmisch optimiert werden können. Die Ergebnisse zeigen, dass für Transportporen mit einem Durchmesser größer als 50 µm eine drei-dimensionale Betrachtung nötig ist. Größere Transportporen mit einem Durchmesser von bis zu 250 µm können ebenfalls verwendet werden, um die Ausbeute pro Zeit und Fläche zu erhöhen, erfordern aber dickere Katalysatorschichten und eine größere Transportporenporosität um die Nachteile der größeren Poren zu kompensieren. • Nasenscheidewandverkrümmungen sind sehr verbreitet in der Bevölkerung, aber es ist unklar, warum einige Betroffene Beschwerden entwickeln während andere hingegen keine Einschränkungen haben. Bisherige Arbeiten setzten den Schwerpunkt auf die Analyse einiger ausgewählter Fälle, was aufgrund der hohen natürlichen Variationen der Nasenscheidewand zu keinen klaren Ergebnissen führte. In dieser Arbeit wird ein vollautomatischer Ansatz zur Berechnung integraler Beiwerte wie Druckverlust und der Strömungsverteilung zwischen den beiden Atemwegen ausgehend von Computertomographie-Aufnahmen vorgestellt. Zusätzlich wird eine Methode zur Verringerung des Rechenaufwandes durch das Entfernen der Nasennebenhöhlen in den CT-Bildern basierend auf maschinellem Lernen vorgeschlagen. Für diesen Anwendungsfall kann die automatische Berechnung und Auswertung verwendet werden, um eine ganze Datenbank von CT-Aufnahmen in strömungsmechanische Kennziffern umzuwandeln, die für eine statistische Analyse verwendet werden können. Weiterhin könnte sie die Anwendung von CFD in der klinischen Praxis ermöglichen. Das Lattice-Boltzmann Verfahren (LBM) ist eine alternative Methode zu „klassischen“, Finite-Volumen basierten Lösern der Navier-Stokes-Gleichungen. Da es eine einfache Generierung von Gittern erlaubt, wird hier eine neue LBM-Implementierung verwendet um die Strömung durch die Kugelschüttung und Nasenhöhle zu berechnen. Die Implementierung bietet gute Portabilität zu unterschiedlichen Systemen und zu unterschiedlicher Hardware wie Grafikkarten (GPUs), die aufgrund ihrer Kosteneffektivität die Anwendbarkeit von CFD erhöhen. Sie kann außerdem Gitterverfeinerung verwenden und es wird ein Algorithmus zur Gittergenerierung, der auch für Grafikkarten geeignet ist, vorgestellt. Um den Flaschenhals langsamer Datenspeicher zu umgehen und die Auswertung zu vereinfachen, wird eine GPU basierte in-situ Verarbeitung implementiert. Der Anwendungsfall der Fischer-Tropsch-Synthese zeigt dennoch, dass „klassische“, Finite-Volumen basierte Löser wie OpenFOAM eine ebenso valide Wahl für automatische Berechnungen sind, wenn strukturierte Gitter verwendet werden. Außerdem ist es für einige Anwendungen einfacher, die Fragestellung mittels partieller Differenzialgleichungen zu modellieren, die mittels Finite-Volumen-Verfahren direkt gelöst werden können.Despite significant progress, computational fluid dynamics (CFD) can still not be used as a “black box approach” as meshing often requires manual intervention and the choosing of numerical parameters deep knowledge of the methods behind CFD. Improving CFD towards such a black box solution not only reduces the barrier of application as less specialized knowledge is required, but also allows for scientific insight. For example, much more data can be generated that is needed to develop accurate models for some problems. This thesis illustrates these benefits with three exemplary applications: • The accurate prediction of the pressure drop of a sphere packed bed is of great importance in engineering. For geometries where the spheres are relatively large compared to the confinement, the wall effect plays another important role. Many correlations have been presented, usually based on experimental measurements that differ in a range of approx. 20 %. Here, the combination of simulated packing generation and CFD is used to evaluate the pressure drop for a very large number of packings with different sphere diameters and different geometries of the confining walls. It is shown that for small ratios of sphere diameter to hydraulic diameter of the reactor the pressure drop is a non-monotonic function which can explain the differences in experimental findings. • The Fischer-Tropsch synthesis is again of increasing interest as it allows the production of carbon-neutral fuel. Transport pores can be added to the catalyst needed for the reaction to enhance transport and consequently the yield. A three-dimensional extension of a one-dimensional model from literature for transport and reaction is presented here. The automation of the calculation is used to enable the algorithmic optimization of the catalyst layers. The results show that for transport pores larger than 50 µm the problem must be treated as three-dimensional. Larger transport pores up to a diameter of 250 µm can also be used to achieve a gain in area-time yield, but thicker catalyst layers and a higher transport pore porosity are needed to overcome the drawbacks of larger pores. • Nasal septum deviation is very common in general population but it is unclear why it causes symptoms for certain patients while others report no discomfort. Previous studies focused on the analysis of few selected cases which did not lead to clear results as the human nose shows high natural variations in geometry. Here, a fully automatic approach for calculating critical parameters like the pressure drop and the flow distribution between the two airways from computed tomography (CT) scans is presented. Furthermore, a method to reduce the computational time by removing paranasal sinuses from the scan incorporating machine learning algorithms is proposed. For this case, fully automatic processing can be used to convert a whole database of CT scans to fluid dynamic parameters that can be used for statistical analysis. Furthermore, it could allow the introduction of CFD analysis to clinical practice. The lattice Boltzmann method (LBM) is an alternative method to “classical” finite-volume based solvers of the Navier-Stokes equations. Since it offers easy generation of grids, a novel LBM implementation is used here to calculate the flow through the sphere packings and the nasal cavity. The implementation features good portability to various systems and hardware like GPUs which due to their cost-effectiveness broaden the applicability of CFD. It can utilize grid refinement and a meshing algorithm suitable for GPUs is presented. To overcome slow IO and to simplify automatic evaluation, GPU assisted co-processing is implemented. Nevertheless, the application case of Fischer-Tropsch synthesis shows that “classical”, finite volume based solvers like OpenFOAM are also valid choice for automatic processing if structured meshes can be used. Furthermore, for some applications, it is easier to model the problem using partial differential equations which can be directly solved using FVM