Efficient upwind algorithms for solution of the Euler and Navier-stokes equations

An efficient three-dimensionasl tructured solver for the Euler and Navier-Stokese quations is developed based on a finite volume upwind algorithm using Roe fluxes. Multigrid and optimal smoothing multi-stage time stepping accelerate convergence. The accuracy of the new solver is demonstrated for inviscid flows in the range 0.675 :5M :5 25. A comparative grid convergence study for transonic turbulent flow about a wing is conducted with the present solver and a scalar dissipation central difference industrial design solver. The upwind solver demonstrates faster grid convergence than the central scheme, producing more consistent estimates of lift, drag and boundary layer parameters. In transonic viscous computations, the upwind scheme with convergence acceleration is over 20 times more efficient than without it. The ability of the upwind solver to compute viscous flows of comparable accuracy to scalar dissipation central schemes on grids of one-quarter the density make it a more accurate, cost effective alternative. In addition, an original convergencea cceleration method termed shock acceleration is proposed. The method is designed to reduce the errors caused by the shock wave singularity M -+ 1, based on a localized treatment of discontinuities. Acceleration models are formulated for an inhomogeneous PDE in one variable. Results for the Roe and Engquist-Osher schemes demonstrate an order of magnitude improvement in the rate of convergence. One of the acceleration models is extended to the quasi one-dimensiona Euler equations for duct flow. Results for this case d monstrate a marked increase in convergence with negligible loss in accuracy when the acceleration procedure is applied after the shock has settled in its final cell. Typically, the method saves up to 60% in computational expense. Significantly, the performance gain is entirely at the expense of the error modes associated with discrete shock structure. In view of the success achieved, further development of the method is proposed

Development of a computational model for predicting solar wind flows past nonmagnetic terrestrial planets

A computational model for the determination of the detailed plasma and magnetic field properties of the global interaction of the solar wind with nonmagnetic terrestrial planetary obstacles is described. The theoretical method is based on an established single fluid, steady, dissipationless, magnetohydrodynamic continuum model, and is appropriate for the calculation of supersonic, super-Alfvenic solar wind flow past terrestrial ionospheres

Algorithms for the reconstruction, analysis, repairing and enhancement of 3D urban models from multiple data sources

Over the last few years, there has been a notorious growth in the field of digitization of 3D buildings and urban environments. The substantial improvement of both scanning hardware and reconstruction algorithms has led to the development of representations of buildings and cities that can be remotely transmitted and inspected in real-time. Among the applications that implement these technologies are several GPS navigators and virtual globes such as Google Earth or the tools provided by the Institut Cartogràfic i Geològic de Catalunya. In particular, in this thesis, we conceptualize cities as a collection of individual buildings. Hence, we focus on the individual processing of one structure at a time, rather than on the larger-scale processing of urban environments. Nowadays, there is a wide diversity of digitization technologies, and the choice of the appropriate one is key for each particular application. Roughly, these techniques can be grouped around three main families: - Time-of-flight (terrestrial and aerial LiDAR). - Photogrammetry (street-level, satellite, and aerial imagery). - Human-edited vector data (cadastre and other map sources). Each of these has its advantages in terms of covered area, data quality, economic cost, and processing effort. Plane and car-mounted LiDAR devices are optimal for sweeping huge areas, but acquiring and calibrating such devices is not a trivial task. Moreover, the capturing process is done by scan lines, which need to be registered using GPS and inertial data. As an alternative, terrestrial LiDAR devices are more accessible but cover smaller areas, and their sampling strategy usually produces massive point clouds with over-represented plain regions. A more inexpensive option is street-level imagery. A dense set of images captured with a commodity camera can be fed to state-of-the-art multi-view stereo algorithms to produce realistic-enough reconstructions. One other advantage of this approach is capturing high-quality color data, whereas the geometric information is usually lacking. In this thesis, we analyze in-depth some of the shortcomings of these data-acquisition methods and propose new ways to overcome them. Mainly, we focus on the technologies that allow high-quality digitization of individual buildings. These are terrestrial LiDAR for geometric information and street-level imagery for color information. Our main goal is the processing and completion of detailed 3D urban representations. For this, we will work with multiple data sources and combine them when possible to produce models that can be inspected in real-time. Our research has focused on the following contributions: - Effective and feature-preserving simplification of massive point clouds. - Developing normal estimation algorithms explicitly designed for LiDAR data. - Low-stretch panoramic representation for point clouds. - Semantic analysis of street-level imagery for improved multi-view stereo reconstruction. - Color improvement through heuristic techniques and the registration of LiDAR and imagery data. - Efficient and faithful visualization of massive point clouds using image-based techniques.Durant els darrers anys, hi ha hagut un creixement notori en el camp de la digitalització d'edificis en 3D i entorns urbans. La millora substancial tant del maquinari d'escaneig com dels algorismes de reconstrucció ha portat al desenvolupament de representacions d'edificis i ciutats que es poden transmetre i inspeccionar remotament en temps real. Entre les aplicacions que implementen aquestes tecnologies hi ha diversos navegadors GPS i globus virtuals com Google Earth o les eines proporcionades per l'Institut Cartogràfic i Geològic de Catalunya. En particular, en aquesta tesi, conceptualitzem les ciutats com una col·lecció d'edificis individuals. Per tant, ens centrem en el processament individual d'una estructura a la vegada, en lloc del processament a gran escala d'entorns urbans. Avui en dia, hi ha una àmplia diversitat de tecnologies de digitalització i la selecció de l'adequada és clau per a cada aplicació particular. Aproximadament, aquestes tècniques es poden agrupar en tres famílies principals: - Temps de vol (LiDAR terrestre i aeri). - Fotogrametria (imatges a escala de carrer, de satèl·lit i aèries). - Dades vectorials editades per humans (cadastre i altres fonts de mapes). Cadascun d'ells presenta els seus avantatges en termes d'àrea coberta, qualitat de les dades, cost econòmic i esforç de processament. Els dispositius LiDAR muntats en avió i en cotxe són òptims per escombrar àrees enormes, però adquirir i calibrar aquests dispositius no és una tasca trivial. A més, el procés de captura es realitza mitjançant línies d'escaneig, que cal registrar mitjançant GPS i dades inercials. Com a alternativa, els dispositius terrestres de LiDAR són més accessibles, però cobreixen àrees més petites, i la seva estratègia de mostreig sol produir núvols de punts massius amb regions planes sobrerepresentades. Una opció més barata són les imatges a escala de carrer. Es pot fer servir un conjunt dens d'imatges capturades amb una càmera de qualitat mitjana per obtenir reconstruccions prou realistes mitjançant algorismes estèreo d'última generació per produir. Un altre avantatge d'aquest mètode és la captura de dades de color d'alta qualitat. Tanmateix, la informació geomètrica resultant sol ser de baixa qualitat. En aquesta tesi, analitzem en profunditat algunes de les mancances d'aquests mètodes d'adquisició de dades i proposem noves maneres de superar-les. Principalment, ens centrem en les tecnologies que permeten una digitalització d'alta qualitat d'edificis individuals. Es tracta de LiDAR terrestre per obtenir informació geomètrica i imatges a escala de carrer per obtenir informació sobre colors. El nostre objectiu principal és el processament i la millora de representacions urbanes 3D amb molt detall. Per a això, treballarem amb diverses fonts de dades i les combinarem quan sigui possible per produir models que es puguin inspeccionar en temps real. La nostra investigació s'ha centrat en les següents contribucions: - Simplificació eficaç de núvols de punts massius, preservant detalls d'alta resolució. - Desenvolupament d'algoritmes d'estimació normal dissenyats explícitament per a dades LiDAR. - Representació panoràmica de baixa distorsió per a núvols de punts. - Anàlisi semàntica d'imatges a escala de carrer per millorar la reconstrucció estèreo de façanes. - Millora del color mitjançant tècniques heurístiques i el registre de dades LiDAR i imatge. - Visualització eficient i fidel de núvols de punts massius mitjançant tècniques basades en imatges

Real-time hybrid cutting with dynamic fluid visualization for virtual surgery

It is widely accepted that a reform in medical teaching must be made to meet today's high volume training requirements. Virtual simulation offers a potential method of providing such trainings and some current medical training simulations integrate haptic and visual feedback to enhance procedure learning. The purpose of this project is to explore the capability of Virtual Reality (VR) technology to develop a training simulator for surgical cutting and bleeding in a general surgery

Characterising pattern asymmetry in pigmented skin lesions

Abstract. In clinical diagnosis of pigmented skin lesions asymmetric pigmentation is often indicative of melanoma. This paper describes a method and measures for characterizing lesion symmetry. The estimate of mirror symmetry is computed first for a number of axes at different degrees of rotation with respect to the lesion centre. The statistics of these estimates are the used to assess the overall symmetry. The method is applied to three different lesion representations showing the overall pigmentation, the pigmentation pattern, and the pattern of dermal melanin. The best measure is a 100% sensitive and 96% specific indicator of melanoma on a test set of 33 lesions, with a separate training set consisting of 66 lesions

Shape Modelling of Bones: Application to the Primate Shoulder

The aims of this work were to develop techniques for describing morphological variations of shoulder bones and to test these on real datasets. The robust measurement and description of anatomical geometry can provide accu- rate estimation and better understanding of bone morphology. Feature lines were detected automatically using crest line techniques and shape information from shoulder bones was extracted based on the extracted feature lines. Redefinition of local coordinate systems was proposed utilising the crest line technique. Three dimensional statistical shape models (SSM) were built for a set of primate humeri and scapulae. Two types of models were constructed: one incorporated the main- tained original scale whilst the other used scaled bones. Variations were captured and quantified by Principal Component Analysis (PCA). The application can be extended generally to long bones and other complex bones and was also tested on human femora. Techniques to predict the shape of one bone from its neighbour at a joint were presented. PCA was used to reduce data dimensionality to a few principal components. Canonical Correlation Analysis (CCA) and Partial Least Square (PLS) Regression were applied to explore the linear morphological correlations between the two shoulder bones and to predict the shape of one segment given the shape of the adjoining segment

Computer-based simulation of the effects of instrumental delivery on the fetal head

Fetal head moulding is a phenomenon that happens during the process of human childbirth. Due to the highly deformable fetal scalp being in contact with the maternal anatomy, the shape of the fetal head changes. This can be benefi�cial when the fetal head dimensions are very similar to the dimensions of the female pelvis hence allowing the baby to progress safely through the birth canal. Conversely, excessive head moulding may have serious eff�ects on the baby's wellbeing. The fi�rst part of this thesis presents a computer-based �finite element model of fetal head moulding as an improvement on previously developed models. The second part of the research focuses on another cause of potentially excessive fetal head moulding, i.e. the incorrect use of obstetric instruments including the obstetric forceps and the ventouse (vacuum extractor). The degree of damage that may be caused by incorrectly placing a forceps (i.e. asymmetric placement of the blades) or a ventouse (i.e. placement on top of soft parts of the skull such as the fontanelles) was assessed by means of fi�nite element analysis after developing a set of software tools to facilitate these experiments. The fi�nal results of this research included: an improved and more realistic model of fetal head moulding under conditions of normal delivery, and results that reveal the great potential of severe damage that obstetric forceps and/or the ventouse may cause to the baby's head when applied incorrectly

Modelling the effect of step and roughness features on swept wing boundary layer instabilities

Destabilisation effects of forward facing steps, backward facing steps and bumps on stationary and travelling crossflow disturbances are investigated computationally for a 40 degree infinitely swept wing. Step and bump heights range from 18% to 82% of the boundary layer thickness and are located at 3%, 10% and 20% chord. The spectral/hp element solver, Nektar++, is used to compute base flow profiles with an embedded swept wing geometry. Parabolised Stability Equations (PSE) and Linearised Harmonic Navier-Stokes (LHNS) models are used to evaluate growth of convecting instabilities. The presence of surface step features impose an extremely rapidly varying flow field locally, which requires accurate resolution of the perturbed flow field. Derivations of these PSE and LHNS models incorporating the excrescence (PSEh, LHNSh) are elucidated. Unlike the PSE, which suffer from a stream-wise numerical step size restriction, the LHNS are a fully elliptic set of equations which may use an arbitrarily fine grid resolution. Unsurprisingly, the PSE codes fail to capture the effect of abrupt changes in surface geometry introduced by the step features. Results for the LHNS and roughness incorporating LHNSh are given for the varying vertical step and ramped type steps. Comparisons are made between the LHNSh model and direct numerical simulations involving the time-stepping linearised Navier-Stokes solver (NekLNS) in the Nektar++ software framework. Most previous work in the topic area has focused on Tollmien-Schlichting perturbations over two-dimensional flat plate flows or aerofoils, the novelty of this work lies with analysing crossflow instability over a swept wing boundary-layer flow with step features. PSEh and LHNSh models are tested with convecting Tollmien Schlichting instability over a dimple and randomly distributed roughness on an overall flat plate flow. The dimple case performs very well whereas it is more difficult to obtain converged results with the random roughness case, likely due to large stream-wise velocity gradient changes. A 45degree ramped shape roughness is investigated and remarkably good agreement between the LHNSh solution and NekLNS solution is found. Forward facing ramps and steps are found to act as greater amplifiers with increased height, whilst backward facing ramps and steps predict very weak changes in the disturbance development. This is contrary to the wider literature and an argument is made that backward facing steps and ramps initiate an immediate non-linear interaction which cannot be captured with linear theory. Vertical forward facing step cases also predict greater amplification with increased step height, which is not observed in the backward facing step cases. Again, this is believed to be due to non-linear mode interaction that is immediately triggered by the step. Bump roughness cases agree well qualitatively with experimental work on a 40 degree swept wing, the AERAST geometry. Good agreement locally to the roughness could not be drawn with the NekLNS solutions, likely due to the presence of strong stream-wise gradients and mesh limitations.Open Acces