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

Off-line programming industrial robots based in the information extracted from neutral files generated by the commercial CAD tools

In order for a robotic manipulator to perform useful work, it must be programmed to accomplish the desired task or motion cycle. Nowadays industrial robots generally require a tremendous amount of programming to make them useful. Their controllers are very sophisticated, the commercial robot programming environments are typically closed systems and the programming languages varies from manufacturer to manufacturer. Despite the great evolution of the industrial robots controllers, in the majority of the industrial applications, the robot programming is made, using one of the following ways: • Manual on-line programming; • Off-line programming; Manual on-line programming refers to physically teaching a robot the required trajectory, through interaction with teach pendant or other similar device (Lee & ElMaraghy, 1990). This programming kind presents the following disadvantages: very slow, it needs that the robot is available, difficulty in the handling of equipments, need some practice in the language used by the robot, and technical knowledge to understand the operation of the equipment. These disadvantages are very expensive in the industry because the productive process needs to stop for a long time. One simple approach to solve some disadvantages described above is the Off-line programming environments. These environments are based in graphical simulation platforms, in which the programming and execution process are shown using models of the real objects. Consequently, the robot programmer has to learn only the simulation language and not any of the robot programming languages. Other benefits in off-line programming environments include libraries of pre-defined high-level commands for certain types of applications, such as painting or welding, and the possibility to assess the kinematics feasibility of a move, thus enabling the user to plan collision-free paths. The simulation may also be used to determine the cycle time for a sequence of movements. These environments usually provide a set of primitives commonly used by various robots, and produce a sequence of robot manipulator language primitives such as ”move” or ”open gripper” that are then downloaded in the respective robot controllers. However, the off-line programming tools based in graphically 3D representation presents several problems in many industry applications, particularly, when the robot task or the robot trajectory needs frequent changes, for example: in welding applications where the configuration of the pieces to weld change frequently (the size, the shape, etc.); the robot painting and gluing applications can have similar problems. Nowadays, the CAD tools are often used in the industry to develop and to document the products and its manufacture. There are a lot of commercial CAD tools, like, AutoCAD, SolidWorks, Ideas and Cimatron, having each tool its own file format. However, it is possible to export the information of these pieces, in a neutral file format, namely: STL, IGES, STEP and SET formats. This work presents one solution for programming different robots based in the relevant information extracted from neutral files. The solution implemented was tested in the industrial robots Mitsubishi (Mitsubishi Move Master Industrial Robot) and ABB (model IRB 140 with IRC5 controller). This chapter is organized as follows: section 2 presents an overview about the format of neutral files (STL, IGS, STEP and SET); in the section 3, the algorithms for extraction of the relevant information from the neutral files are described; in the section 4, the developed tool for code generation for different industrial robots is presented; section 5 and 6 present the results and conclusions; section 7 presents future work.European Union Programme of High Level Scholarships for Latin America, Scholarship no. E04M033540BR - Programme ALBAN

A heuristic-based approach to code-smell detection

Encapsulation and data hiding are central tenets of the object oriented paradigm. Deciding what data and behaviour to form into a class and where to draw the line between its public and private details can make the difference between a class that is an understandable, flexible and reusable abstraction and one which is not. This decision is a difficult one and may easily result in poor encapsulation which can then have serious implications for a number of system qualities. It is often hard to identify such encapsulation problems within large software systems until they cause a maintenance problem (which is usually too late) and attempting to perform such analysis manually can also be tedious and error prone. Two of the common encapsulation problems that can arise as a consequence of this decomposition process are data classes and god classes. Typically, these two problems occur together – data classes are lacking in functionality that has typically been sucked into an over-complicated and domineering god class. This paper describes the architecture of a tool which automatically detects data and god classes that has been developed as a plug-in for the Eclipse IDE. The technique has been evaluated in a controlled study on two large open source systems which compare the tool results to similar work by Marinescu, who employs a metrics-based approach to detecting such features. The study provides some valuable insights into the strengths and weaknesses of the two approache

Digital sculpture : conceptually motivated sculptural models through the application of three-dimensional computer-aided design and additive fabrication technologies

Thesis (D. Tech.) - Central University of Technology, Free State, 200

Extracting, managing, and exploiting the semantics of mechanical CAD models in assembly tasks

The manufacturing of mechanical products is increasingly assisted by technologies that exploit the CAD model of the final assembly to address complex tasks in an automated and simplified way, to reduce development time and costs. However, it is proven that industrial CAD models are heterogeneous objects, involving different design conventions, providing geometric data on parts but often lacking explicit semantic information on their functionalities. As a consequence, existing approaches are mainly mathematics-based or need expert intervention to interpret assembly components, and this is limiting. The work presented in the thesis is placed in this context and aims at automatically extracting and leveraging in industrial applications high-level semantic information from B-rep models of mechanical products in standard format (e.g. STEP). This makes possible the development of promising knowledge intensive processes that take into account the engineering meaning of the parts and their relationships. The guiding idea is to define a rule-based approach that matches the shape features, the dimensional relations, and the mounting schemes strictly governing real mechanical assemblies with the geometric and topological properties that can be retrieved in CAD models of assemblies. More in practice, a standalone system is implemented which carries out two distinct operations, namely the data extraction and the data exploitation. The first involves all the steps necessary to process and analyze the geometric objects representing the parts of the assembly to infer their engineering meaning. It returns an enriched product model representation based on a new data structure, denoted as liaison, containing all the extracted information. The new product model representation, then, stands at the basis of the data exploitation phase, where assembly tasks, such as subassembly identification, assembly planning, and design for assembly, are addressed in a more effective way

Real-time simulation and visualisation of cloth using edge-based adaptive meshes

Real-time rendering and the animation of realistic virtual environments and characters has progressed at a great pace, following advances in computer graphics hardware in the last decade. The role of cloth simulation is becoming ever more important in the quest to improve the realism of virtual environments. The real-time simulation of cloth and clothing is important for many applications such as virtual reality, crowd simulation, games and software for online clothes shopping. A large number of polygons are necessary to depict the highly exible nature of cloth with wrinkling and frequent changes in its curvature. In combination with the physical calculations which model the deformations, the effort required to simulate cloth in detail is very computationally expensive resulting in much diffculty for its realistic simulation at interactive frame rates. Real-time cloth simulations can lack quality and realism compared to their offline counterparts, since coarse meshes must often be employed for performance reasons. The focus of this thesis is to develop techniques to allow the real-time simulation of realistic cloth and clothing. Adaptive meshes have previously been developed to act as a bridge between low and high polygon meshes, aiming to adaptively exploit variations in the shape of the cloth. The mesh complexity is dynamically increased or refined to balance quality against computational cost during a simulation. A limitation of many approaches is they do not often consider the decimation or coarsening of previously refined areas, or otherwise are not fast enough for real-time applications. A novel edge-based adaptive mesh is developed for the fast incremental refinement and coarsening of a triangular mesh. A mass-spring network is integrated into the mesh permitting the real-time adaptive simulation of cloth, and techniques are developed for the simulation of clothing on an animated character

MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology

renewable; green; energy; environment; law; polic

Functional requirements for the man-vehicle systems research facility

The NASA Ames Research Center proposed a man-vehicle systems research facility to support flight simulation studies which are needed for identifying and correcting the sources of human error associated with current and future air carrier operations. The organization of research facility is reviewed and functional requirements and related priorities for the facility are recommended based on a review of potentially critical operational scenarios. Requirements are included for the experimenter's simulation control and data acquisition functions, as well as for the visual field, motion, sound, computation, crew station, and intercommunications subsystems. The related issues of functional fidelity and level of simulation are addressed, and specific criteria for quantitative assessment of various aspects of fidelity are offered. Recommendations for facility integration, checkout, and staffing are included