New Simplified Algorithm for the Multiple Rotating Frame Approach in Computational Fluid Dynamics

This paper deals with rotating effects simulation of steady flows in turbomachinery. To take into account the rotating nature of the flow, the frozen rotor approach is one of the widely used approaches. This technique, known in a more general context as a multiple rotating frame (MRF), consists on building axisymmetric interfaces around the rotating parts and solves for the flow in different frames (static and rotating). This paper aimed to revisit this technique and propose a new algorithm referred to it by a virtual multiple rotating frame (VMRF). The goal is to replace the geometrical interfaces (part of the computer-aided design (CAD)) that separate the rotating parts replaced by the virtual ones created at the solver level by a simple user input of few point locations and/or parameters of basic shapes. The new algorithm renders the MRF method easy to implement, especially for edge-based numerical schemes, and very simple to use. Moreover, it allows avoiding any remeshing (required by the MRF approach) when one needs to change the interface position, shape, or simply remove or add a new one, which frequently happened in practice. Consequently, the new algorithm sensibly reduces the overall computations cost of a simulation. This work is an extension of a first version published in an ASME conference, and the main new contributions are the detailed description of the new algorithm in the context of cell-vertex finite volume method and the validation of the method for viscous flows and the three-dimensional (3D) case which is of significant importance to the method to be attractive for real and industrial applications.BCAM-BALTOGAR CFD Platform for Turbomachinery Simulation and Design (BFA/DFB - 6/12/TK/2012/00020

Proceedings of the Eighth Annual Thermal and Fluids Analysis Workshop: Spacecraft Analysis and Design

This document contains papers presented at the Eighth Annual Thermal and Fluids Analysis Workshop (TFAWS) on Spacecraft Analysis and Design hosted by the NASA/Johnson Space Center (JSC) on September 8-11, 1997, and held at the University of Houston - Clear Lake (UHCL) in the Bayou Building. The Workshop was sponsored by NASA/JSC. Seminars were hosted and technical papers were provided in fluid and thermal dynamics. Seminars were given in GASP, SINDA, SINAPS Plus, TSS, and PHOENICS. Seventeen papers were presented

Integrated tactile-optical coordinate measurement for the reverse engineering of complex geometry

Complex design specifications and tighter tolerances are increasingly required in modern engineering applications, either for functional or aesthetic demands. Multiple sensors are therefore exploited to achieve both holistic measurement information and improved reliability or reduced uncertainty of measurement data. Multi-sensor integration systems can combine data from several information sources (sensors) into a common representational format in order that the measurement evaluation can benefit from all available sensor information and data. This means a multi-sensor system is able to provide more efficient solutions and better performances than a single sensor based system. This thesis develops a compensation approach for reverse engineering applications based on the hybrid tactile-optical multi-sensor system. In the multi-sensor integration system, each individual sensor should be configured to its optimum for satisfactory measurement results. All the data measured from different equipment have to be precisely integrated into a common coordinate system. To solve this problem, this thesis proposes an accurate and flexible method to unify the coordinates of optical and tactile sensors for reverse engineering. A sphere-plate artefact with nine spheres is created and a set of routines are developed for data integration of a multi-sensor system. Experimental results prove that this novel centroid approach is more accurate than the traditional method. Thus, data sampled by different measuring devices, irrespective of their location can be accurately unified. This thesis describes a competitive integration for reverse engineering applications where the point cloud data scanned by the fast optical sensor is compensated and corrected by the slower, but more accurate tactile probe measurement to improve its overall accuracy. A new competitive approach for rapid and accurate reverse engineering of geometric features from multi-sensor systems based on a geometric algebra approach is proposed and a set of programs based on the MATLAB platform has been generated for the verification of the proposed method. After data fusion, the measurement efficiency is improved 90% in comparison to the tactile method and the accuracy of the reconstructed geometric model is improved from 45 micrometres to 7 micrometres in comparison to the optical method, which are validated by case study

Strukture polja v aktivnih in pasivnih tekočih kristalih

Field structures are developed in passive and active nematic fluids. These are field profiles that are determined by confinement, particles, flow and external fields. Our central methodological approach is numerical modeling based on free energy minimization with finite difference method and flow modeling with hybrid lattice Boltzmann method. We develop structures by combining concepts of topological defects, external confinement and colloidal particles. Ordering properties of horseshoe nematic colloidal particles with planar degenerate anchoring are investigated with numerical modeling, where we optimize their geometrical parameters such that the particle exhibit attractive interactions and can self assemble into 2D and even 3D colloidal crystals. The metamaterial response of horseshoe colloids that perform as split ring resonators is studied. Optical cloaking is achieved by generating polymer microstructures embedded directly within a electric field switchable liquid crystal device. Using numerical modelling we explore the director field structures forming in the vicinity of composite colloidal particles with specially designed conic anchoring, which are assumed to induce high multipoles. Simple rule that allow predictions of multipolar moment from defect configuration is extracted. Starting with a gyroid structure, which is a photonic crystal by itself, we introduce an achiral and chiral nematic into one labyrinth of channels with homeotropic anchoring. Complexly shaped channels induce both ordered and disordered structures of defects. Simulating the passive nematic flow in porous microchannels we study the formation of individual umbilic defects of various strength and umbilic defect lattices that arise as the consequence of complex velocity field containing both multiple peaks and saddles. We investigate the 3D active turbulence in droplets of active nematic with homeotropic and non slip boundary condition. The transition from the point defect to the active turbulence is studied by analysing both the topological defects and corresponding events as well as flow. More generally, this work is aimed at the development of novel functional soft matter, which can exhibit exciting and unusual material characteristics, including light guiding, topological defect states, photonic bandgaps, metamaterials and optical cloaking.V doktorskem delu smo razvili strukture polja v pasivnih in aktivnih nematskih tekočinah. Ti profili v polju so določeni z ograditvijo, delci, tokom in zunanjimi polji. Osrednji raziskovalni pristop je numerično modeliranje, ki temelji na minimizaciji proste energije z metodo končnih diferenc, in modeliranje toka s hibridno mrežno Boltzmannovo metodo. Ustvarjene strukture so rezultat kombinacije topoloških defektov, zunanje ograditve in koloidnih delcev. Preučevali smo urejanje podkvastih koloidnih delcev s planarnim sidranjem. Geometrijske parametre koloidnega delca smo optimizirali tako, da so delci medsebojno interagirali privlačno in so se lahko sestavili v 2D in tudi 3D koloidne kristale. Študirali smo tudi metamaterialni odziv tovrstnih podkvastih koloidov, ki se obnašajo kot resonatorji. Pokazali smo optično zakrivanje z ustvarjanjem polimernih struktur direktno v tekočekristalni celici, nastavljivi z električnim poljem. S pomočjo numeričnega modeliranja smo raziskali strukture v nematskem polju, ki se formirajo v okolici kompozitnih koloidnih delcev s posebnim koničnim sidranjem in ustvarjajo višje multipolne momente. Predstavimo tudi preprosto pravilo, s katerim lahko napovemo multipolni moment samo z opazovanjem defektnih struktur. V enega od obeh prepletov kanalov, v giroidni strukturi, uvedemo kiralni in nekiralni nematski tekoči kristal. Kompleksna oblika kanalov povzroči nastanek tako urejenih, kot tudi neurejenih defektnih struktur. Simuliramo pasivni nematski tok v poroznih mikrokanalih in študiramo nastanek umbiličnih defektov različnih moči ter regularnih mrež umbiličnih defektov, ki nastanejo zaradi sedelnih in ekstremalnih točk v toku. Preučimo 3D aktivno turbulenco v kapljicah aktivnega nematika s homeotropnimi robnimi pogoji. Študiramo prehod iz točkastega defekta v topološko turbulenco z analizo topoloških defektov in topoloških dogodkov, kot tudi z analizo samega toka. To delo je torej namenjeno razvoju nove funkcionalne mehke snovi, ki ima zanimive lastnosti, kot so na primer vodenje svetlobe, topološka defektna stanja, fotonske reže, metamateriali in optično zakrivanje

Numerical solutions of the general relativistic equations for black hole fluid dynamics

Related data - see record for Numerical Solutions of the General Relativistic Equations for Black Hole Fluid Dynamics at http://www.dspace.cam.ac.uk/handle/1810/226117 containing the data from the DVD referred to in the main text.The aims of this thesis are to develop and validate a robust and efficient algorithm for the numerical solution of the equations of General Relativistic Hydrodynamics, to implement the algorithm in a computationally efficient manner, and to apply the resulting computer code to the problem of perturbed Bondi-Hoyle-Lyttleton accretion onto a Kerr black hole. The algorithm will also be designed to evolve the space-time metric, and standardised tests will be applied to this aspect of the algorithm. The algorithm will use up-to-date High-Resolution Shock-Capturing numerical schemes that have been developed for the stable and accurate solution of complex systems of equations. It will be built around the Adaptive Mesh Refinement and overlapping, curvilinear grid methodologies in order to extend these schemes to the efficient solution of two and three-dimensional problems. When implementing the algorithm, we will use previously written code libraries, where appropriate, to avoid excessive software development. We will validate the algorithm against standard test-cases for Special and General Relativistic Hydrodynamics, and for Einstein's equations for the evolution of the space-time metric. The methodologies we use will be tested to ensure that they lead to the stable and accurate numerical solution of these problems. Finally, the implemented algorithm will be applied to the problem of Bondi-Hoyle-Lyttleton flow onto a Kerr black hole in three dimensions. It will be validated against existing exact and numerical solutions of the problem, and then be used to perform an extensive parametric study of the problem, varying the spin of the black hole and the incident wind direction, and allowing for the perturbation of the fluid density upstream of the black hole. We will then analyze the results of the study, and present the complete set of results on a DVD accompanying this thesis.This work was supported by an EPSRC Doctoral Training Grant. Some simulations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England

Computer-Aided Geometry Modeling

Techniques in computer-aided geometry modeling and their application are addressed. Mathematical modeling, solid geometry models, management of geometric data, development of geometry standards, and interactive and graphic procedures are discussed. The applications include aeronautical and aerospace structures design, fluid flow modeling, and gas turbine design

Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

Investigation of the use of meshfree methods for haptic thermal management of design and simulation of MEMS

This thesis presents a novel approach of using haptic sensing technology combined with virtual environment (VE) for the thermal management of Micro-Electro-Mechanical-Systems (MEMS) design. The goal is to reduce the development cycle by avoiding the costly iterative prototyping procedure. In this regard, we use haptic feedback with virtua lprototyping along with an immersing environment. We also aim to improve the productivity and capability of the designer to better grasp the phenomena operating at the micro-scale level, as well as to augment computational steering through haptic channels. To validate the concept of haptic thermal management, we have implemented a demonstrator with a user friendly interface which allows to intuitively "feel" the temperature field through our concept of haptic texturing. The temperature field in a simple MEMS component is modeled using finite element methods (FEM) or finite difference method (FDM) and the user is able to feel thermal expansion using a combination of different haptic feedback. In haptic application, the force rendering loop needs to be updated at a frequency of 1Khz in order to maintain continuity in the user perception. When using FEM or FDM for our three-dimensional model, the computational cost increases rapidly as the mesh size is reduced to ensure accuracy. Hence, it constrains the complexity of the physical model to approximate temperature or stress field solution. It would also be difficult to generate or refine the mesh in real time for CAD process. In order to circumvent the limitations due to the use of conventional mesh-based techniques and to avoid the bothersome task of generating and refining the mesh, we investigate the potential of meshfree methods in the context of our haptic application. We review and compare the different meshfree formulations against FEM mesh based technique. We have implemented the different methods for benchmarking thermal conduction and elastic problems. The main work of this thesis is to determine the relevance of the meshfree option in terms of flexibility of design and computational charge for haptic physical model