Most modern engines utilise pistons with an offset gudgeon pin. In internal combustion engines, the offset is to the major thrust side of the piston. The piston thrust side is the part of the piston perpendicular to the gudgeon pin that carries the majority of side loading during the power stroke. Primary reason for having the gudgeon pin positioned eccentrically is to prevent the piston from slamming into the cylinder bore after the connecting rod journal passes the top dead centre. This phenomenon is referred to as piston slap, and is more pronounced in compression ignition and high performance engines due to higher combustion pressure than that of commercial spark ignition engines. The coming together of the piston and the bore results in scuffing, at best, or, catastrophic failure at worst. Clearance space between bore and piston is filled by a lubricant film. The main role of the lubricant is to separate the piston and bore by reacting to the applied load. Investigating the above problem requires a holistic approach, whereby a dynamic three degree-of-freedom piston model is coupled with a lubrication model to represent the actual system. The dynamic model determines the motion of the piston in combined axial, lateral and rotation about the gudgeon pin. The reactive forces due to lubricant films on the major and minor thrust sides of the piston play significant roles in piston dynamics and are evaluated by either quasi-static or transient solution of the lubricant contact conjunctions. The novel quasi-static analysis is carried out in the sense of its detailed approach, including many key practical features. not incorporated in other analyses, hitherto reported in literature. These features include first and foremost the development of a specific contact mechanics model for evaluation of conforming contacts for piston skirt against liner or bore. The quasi-static analysis includes many practical feature not encountered in other literature on the subject, such as detailed surface irregularities and modification features, and with thermal distortion. The analysis has been extended to thermohydrodynamics, as well as micro-hydrodynamics, all with high computational mesh densities, and robust methods of solution in space and time domains, including effective influence Newton-Raphson method and linear acceleration integration scheme. The transient tribo-elasto-multi-body dynamics problem includes physics of motion study from film thickness prediction and secondary motion evaluation of the order of micrometers and minutes of arc to large rigid body dynamics, including simultaneous solution of the contact problem at both major and minor thrust sides. Such a comprehensive solution has not hitherto been reported in literature. The thesis discusses many aspects of piston dynamics problem, through the broad spectrum of vehicle manufacture, with many pertinent practical engineering issues. In particular, it provides solutions for high performance Formula 1 racing engines. This is the first ever comprehensive analysis of piston tribodynamics for this range of engines at very high combustion pressures. This study has shown the paramount influence of profile of piston in promoting lubrication between the contiguous bodies, as evident from the pattern of lubricant flow through the contact. Deformation of the bodies increases the volume of lubricant in the contact. During the reversal in direction of piston motion, when the entraining velocity momentarily cases and reversal takes place, the load is held by an elastic squeeze.

Atherosclerosis is often diagnosed using an ultrasound (US) examination in the carotid and femoral arteries and the abdominal aorta. A decision to operate requires two measures of disease severity: the degree of stenosis measured using B-mode US; and the blood flow patterns in the artery measured using spectral Doppler US. However other biomechanical factors such as wall shear stress (WSS) and areas of flow recirculation are also important in disease development and rupture. These are estimated using an image-guided modelling approach, where a three-dimensional computational mesh of the artery is simulated. To generate a patient-specific arterial 3D computational mesh, a 3D ultrasound (3DUS) system was developed. This system uses a standard clinical US scanner with an optical position sensor to measure the position of the transducer; a video capture card to record video images from the scanner; and a PC running Stradwin software to reconstruct 3DUS data. The system was characterised using an industry-standard set of calibration phantoms, giving a reconstruction accuracy of ± 0.17 mm with a 12MHz linear array transducer. Artery movements from pulsatile flow were reduced using a retrospective gating technique. The effect of pressure applied to the transducer moving and deforming the artery was reduced using an image-based rigid registration technique. The artery lumen found on each 3DUS image was segmented using a semi-automatic segmentation technique known as ShIRT (the Sheffield Image Registration Toolkit). Arterial scans from healthy volunteers and patients with diagnosed arterial disease were segmented using the technique. The accuracy of the semi-automatic technique was assessed by comparing it to manual segmentation of each artery using a set of segmentation metrics. The mean accuracy of the semi-automatic technique ranged from 85% to 99% and depended on the quality of the images and the complexity of the shape of the lumen. Patient-specific 3D computational artery meshes were created using ShIRT. An idealised mesh was created using key features of the segmented 3DUS scan. This was registered and deformed to the rest of the segmented dataset, producing a mesh that represents the shape of the artery. Meshes created using ShIRT were compared to meshes created using the Rhino solid modelling package. ShIRT produced smoother meshes; Rhino reproduced the shape of arterial disease more accurately. The use of 3DUS with image-guided modelling has the potential to be an effective tool in the diagnosis of atherosclerosis. Simulations using these data reflect in vivo studies of wall shear stress and recirculation in diseased arteries and are comparable with results in the literature created using MRI and other 3DUS systems.

En géométrie discrète, les objets euclidiens sont représentés par leurs approximations discrètes, telles que des sous-ensembles du réseau des points à coordonnées entières. Les déplacements de ces ensembles doivent être définis comme des applications depuis et sur un espace discret donné. Une façon de concevoir de telles transformations est de combiner des déplacements continus définis sur un espace euclidien avec un opérateur de discrétisation. Cependant, les déplacements discrétisés ne satisfont souvent plus les propriétés de leurs équivalents continus. En effet, en raison de la discrétisation, de telles transformations ne préservent pas les distances, et la bijectivité et la connexité entre les points sont généralement perdues. Dans le contexte des espaces discrets 2D, nous étudions des déplacements discrétisés sur les réseaux d'entiers de Gauss et d'Eisenstein. Nous caractérisons les déplacements discrétisés bijectifs sur le réseau carré, et les rotations bijectives discrétisées sur le réseau hexagonal régulier. En outre, nous comparons les pertes d'information induites par des déplacements discrétisés non bijectifs définis sur ces deux réseaux. Toutefois, pour des applications pratiques, l'information pertinente n'est pas la bijectivité globale, mais celle d'un déplacement discrétisé restreint à un sous-ensemble fini donné d'un réseau. Nous proposons deux algorithmes testant cette condition pour les sous-ensembles du réseau entier, ainsi qu'un troisième algorithme fournissant des intervalles d'angles optimaux qui préservent cette bijectivité restreinte. Nous nous concentrons ensuite sur les déplacements discrétisés sur le réseau cubique 3D. Tout d'abord, nous étudions à l'échelle locale des défauts géométriques et topologiques induits par des déplacements discrétisés. Une telle analyse consiste à générer toutes les images d'un ensemble du réseau fini sous des déplacements discrétisés. Un tel problème revient à calculer un arrangement d'hypersurfaces dans un espace de paramètres de dimension six. La dimensionnalité et les cas dégénérés rendent le problème insoluble, en pratique, par les techniques usuelles. Nous proposons une solution ad hoc reposant sur un découplage des paramètres, et un algorithme pour calculer des points d'échantillonnage de composantes connexes 3D dans un arrangement de polynômes du second degré. Enfin, nous nous concentrons sur le problème ouvert de déterminer si une rotation discrétisée 3D est bijective ou non. Dans notre approche, nous explorons les propriétés arithmétiques des quaternions de Lipschitz. Ceci conduit à un algorithme qui détermine si une rotation discrétisée donnée, associée à un quaternion de Lipschitz, est bijective ou non / In digital geometry, Euclidean objects are represented by their discrete approximations, e.g. subsets of the lattice of integers. Rigid motions of such sets have to be defined as maps from and onto a given discrete space. One way to design such motions is to combine continuous rigid motions defined on Euclidean space with a digitization operator. However, digitized rigid motions often no longer satisfy properties of their continuous siblings. Indeed, due to digitization, such transformations do not preserve distances, while bijectivity and point connectivity are generally lost. In the context of 2D discrete spaces, we study digitized rigid motions on the lattices of Gaussian and Eisenstein integers. We characterize bijective digitized rigid motions on the integer lattice, and bijective digitized rotations on the regular hexagonal lattice. Also, we compare the information loss induced by non-bijective digitized rigid motions defined on both lattices. Yet, for practical applications, the relevant information is not global bijectivity, but bijectivity of a digitized rigid motion restricted to a given finite subset of a lattice. We propose two algorithms testing that condition for subsets of the integer lattice, and a third algorithm providing optimal angle intervals that preserve this restricted bijectivity. We then focus on digitized rigid motions on 3D integer lattice. First, we study at a local scale geometric and topological defects induced by digitized rigid motions. Such an analysis consists of generating all the images of a finite digital set under digitized rigid motions. This problem amounts to computing an arrangement of hypersurfaces in a 6D parameter space. The dimensionality and degenerate cases make the problem practically unsolvable for state-of-the-art techniques. We propose an ad hoc solution, which mainly relies on parameter uncoupling, and an algorithm for computing sample points of 3D connected components in an arrangement of second degree polynomials. Finally, we focus on the open problem of determining whether a 3D digitized rotation is bijective or not. In our approach, we explore arithmetic properties of Lipschitz quaternions. This leads to an algorithm which answers whether a given digitized rotation—related to a Lipschitz quaternion—is bijective or not

Nosso grupo tem dedicado atenção especial em manter o Novo Catálogo de Aglomerados Abertos e Candidatos Opticamente Visíveis (Dias et.al. [1] denominado comumente DAML02), que vem sendo continuamente atualizado com novos resultados vindos da literatura. Além de manter o catálogo, nosso grupo está constantemente produzindo novos resultados como movimentos próprios médios e determinação de probabilidades de pertinência de estrelas aos aglomerados estudados (Dias et. al. [2] [3] [4]), também descobrindo novos aglomerados abertos (Alessi et. al. [5]) contribuindo para o conhecimento da amostra de aglomerados abertos conhecida na nossa Galáxia. Neste trabalho nós apresentamos os primeiros resultados de um estudo cinemático e fotométrico de uma amostra de aglomerados abertos com distância e idade desconhecidas. Trata-se de uma amostra de 850 aglomerados originalmente listados na versão 2.3 do catálogo DAML02. As probabilidades de pertinência das estrelas na região de cada aglomerado foram determinadas através de métodos estatísticos conhecidamente eficazes como (Vasilevskis e Rach [6], Sanders [7] e Zhao e He [8] aplicados aos movimentos próprios individuais UCAC2 (Zacharias et.al.[9]). Conseqüentemente, os movimentos próprios médios dos aglomerados também foram estimados. Utilizando apenas as estrelas membro e dados fotométricos 2MASS (Skrutskie et.al.[10]) construímos os diagramas cor-magnitude para cada aglomerado que nos permitiram estimar parâmetros fundamentais dos aglomerados como distâncias, excessos de cor nas bandas do infravermelho e idades. A determinação desses parâmetros envolve o ajuste de isócronas a seqüência principal do aglomerado e a partir de valores iniciais ajustamos essas curvas para a obtenção dos valores de distâncias, excessos de cor e idades. Desenvolvemos com o objetivo de fornecer esses valores preliminares, um programa que usa apenas as estrelas com Tipo Espectral identificado no SIMBAD. Portanto, neste trabalho determinamos movimentos próprios e probabilidades de pertinência para 319 aglomerados. Desses, 32 apresentaram solução para os parâmetros fundamentais (distância, excesso de cor e idade) e segundo nossas análises para os casos inéditos, 11 aglomerados encontram-se na vizinhança solar. Os erros envolvidos estimados são totalmente coerentes com os erros do catálogo DAML02. / Our group has dedicate a special attention to maintain the New Catalogue of Optically Visible Open Clusters and Candidates (Dias et al.[1] hereinafter DAML02) that is being continuously updated with new results from the literature. Besides maintaining the catalogue, our group is actively producing new results such as the mean absolute proper motion and membership determination (Dias et. al. [2] [3] [4]) and discovering new open clusters (Alessi et al.[5]) contributing to complete the knowledge of the hole sample of open clusters in the Galaxy. In this work we present the first results of the kinematic and photometric study of the open clusters with unknown distance and age in DAML02. The membership probabilities of the stars in the region of each cluster were determined applying the statistical method of Zhao e He [8] using the individual stellar UCAC2 (Zacharias et.al.[9]) proper motions. Consequently, the mean absolute proper motion of the clusters were also estimated. Using the investigated stars we were able to construct the colourmagnitude diagrams that allowed us to derive preliminary estimates of the fundamental parameters of the clusters such as reddening, distance and ages where the 2MASS (Strutskie et.al.[10]) photometric data were considered.

Este trabalho apresenta o desenvolvimento de uma metodologia para a estimativa de funções de resposta em freqüência angulares (FRFAs). Trata-se de uma técnica que utiliza transdutores piezelétricos (PZT) do tipo bimorph para a medição da curvatura local da estrutura através do potencial elétrico induzido pela extensão e compressão do sensor. A partir da estimativa da curvatura, a rotação pode ser obtida diretamente através de várias técnicas de interpolação (polinomial, formas modais, etc). Apresenta-se a modelagem téorica da qual se deriva as equações que governam a dinâmica de estruturas uni-dimensionais, do tipo viga, e estruturas bidimensionais, do tipo placa, ambas isotrópicas, onde se incorpora o sensor bimorph. Modelos em elementos finitos foram propostos no intuito de avaliar a utilização destes sensores (bimorphs) aplicados à estimativa das FRFAs. Apresentam-se também resultados numéricos e experimentais considerando-se uma viga engastada-livre (cantilever) e resultados numéricos considerando-se uma placa simplesmente apoiada. Um algoritmo genético foi ainda desenvolvido no intuito de determinar a posição e dimensão ótimas dos bimorphs em estruturas do tipo viga. / The present work aims to perform the development of an attractive approach for accurate measurement of angular frequency response functions (AFRFs). It uses bimorph piezoceramic patches to measure the structure\'s local curvature through the measurement of the electric potential induced by the extension and compression of the patch\'s top and bottom stripes, respectively. From this curvature, rotation can be obtained directly by several interpolation techniques (single polynomial, modes basis). Theoretical modeling of the vibration incorporating piezoelectric bimorph sensor is presented and equations governing the dynamics for one-dimensional structures, like a beam, and for two-dimensional structures, like a plate, are derived for isotropic structures. Finite element model for the dynamic analysis were proposed to evaluate bimorphs patches applied to the measurement of angular FRFs. Numerical and experimental results are presented considering a cantilever beam and numerical results for a simply supported plate as tested structured. Also, in this work, a genetic algorithm was used as an adaptive heuristic search algorithm for optimal placement and sizing of the bimorph sensor into beam like structures.

This thesis focuses on the effects of wave-induced motions on the airwake of a ship and on the operation of a helicopter in the airwake. While the topic is broad, efforts are concentrated on understanding fundamentals of the ship’s airwake structure at varying Reynolds (Re) numbers without motions, using available experimental data for validation of the computational fluid dynamics (CFD) methodology used, and on studying the effects of waves and motions on the airwake of a ship and a helicopter operating above a ship’s flight deck in full-scale. The static ONR Tumblehome (ONRT) ship geometry with a solid boundary representative of the free surface is simulated at three different Re numbers, 3.2x104, 1x106, and 1.3x108. Validation is performed against experimental measurements at model-scale Re=1x106. Full-scale simulations of the ONRT are carried out in head winds and regular waves approximately equivalent to conditions seen at sea states 3 and 6. Effects of waves and motions are isolated for both sea states using simulations with combinations of waves and motions, waves and no motions, no waves with motions, and no motions or waves. A triple velocity decomposition is conducted in order to quantify changes in the airwake due to motions and waves. The operation of rotorcraft in the ONRT airwake is analyzed using one-way and two-way coupling approaches. The one-way coupling approach uses the velocity field data from the full-scale ONRT simulations and disk actuator theory to calculate thrust fluctuations for three different rotor sizes. The results of the one-way coupling approach show that the smallest rotor is much more affected by small scale turbulence, while small scale fluctuations are filtered out by larger rotor diameters. In the two-way coupling approach, a helicopter based on the Sikorsky SH-60 hovering above the flight deck is simulated, including explicitly moving grids to discretize the main rotor, tail rotor, and fuselage. This method captures the effects of the interaction between the rotor downwash and the ONRT airwake. The study shows that for the mild conditions of sea state 3 the motions have little effect on the airwake behavior. At sea state 6 the airwake behavior is significantly altered, which is reflected in the resulting forces on the helicopter body operating in this condition.

Barrier options have become increasingly popular financial instruments due to the lower costs and the ability to more closely match speculating or hedging needs. In addition, barrier options play a significant role in modeling and managing risks in insurance and finance as well as in refining insurance products such as variable annuities and equity-indexed annuities. Motivated by these immediate applications arising from actuarial and financial contexts, the thesis studies the pricing of barrier options and some exotic variations, assuming that the underlying asset price follows the Black-Scholes model or jump-diffusion processes. Barrier options have already been well treated in the classical Black-Scholes framework. The first part of the thesis aims to develop a new valuation approach based on the technique of exponential stopping and/or path counting of Brownian motions. We allow the option's boundaries to vary exponentially in time with different rates, and manage to express our pricing formulas properly as combinations of the prices of certain binary options. These expressions are shown to be extremely convenient in further pricing some exotic variations including sequential barrier options, immediate rebate options, multi-asset barrier options and window barrier options. Many known results will be reproduced and new explicit formulas will also be derived, from which we can better understand the impact on option values of various sophisticated barrier structures. We also consider jump-diffusion models, where it becomes difficult, if not impossible, to obtain the barrier option value in analytical form for exponentially curved boundaries. Our model assumes that the logarithm of the underlying asset price is a Brownian motion plus an independent compound Poisson process. It is quite common to assign a particular distribution (such as normal or double exponential distribution) for the jump size if one wants to pursue closed-form solutions, whereas our method permits any distributions for the jump size as long as they belong to the exponential family. The formulas derived in the thesis are explicit in the sense that they can be efficiently implemented through Monte Carlo simulations, from which we achieve a good balance between solution tractability and model complexity.

The spatial structure and temporal evolution of sea breeze and the latitudinal distribution of propagation and mixing of sea breeze driven near-inertial ocean response in the Gulf of Mexico are investigated using comprehensive data sets and a non-linear numerical model. Near 30�N, inertial oceanic response is significantly enhanced by a near-resonant condition between inertial and diurnal forcing frequencies. Observational results indicate that sea breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation. The maximum near-inertial oceanic response occurs in June when there is a shallow mixed layer, strong stratification, and an approximately 10-day period of continuous sea breeze forcing. Near-inertial current variance decreases in July and August due to the deepening of the mixed layer and a more variable phase relationship between the wind and current. River discharge varies interannually and can significantly alter the oceanic response during summer. During 1993, the ?great flood? of the Mississippi River deepens the summer mixed layer and reduces the sea breeze response. The near-inertial currents can provide considerable vertical mixing on the shelf in summer, as seen by the suppression of bulk Richardson number during strong near-inertial events. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30� latitude, however, it can propagate offshore as Poincare waves equatorward of 30� latitude. Near 30� latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased vertical mixing. This local dissipation is greatly reduced at other latitudes. Simulations with realistic bathymetry of the Gulf of Mexico confirm that a basin-wide ocean response to coastal sea breeze forcing is established in the form of Poincare waves. This enhanced vertical mixing is consistent with observations on the Texas-Louisiana Shelf. Comparison of the three-dimensional and one-dimensional models shows some significant limitations of one-dimensional simplified models for sea breeze simulations near the critical latitude.

In the video database, each video contains temporal and spatial relationships between content objects. The temporal relationships can be specified between frame sequences and the spatial relationships can be specified by the relationships between objects in a single frame. Moreover, the information related to locations and motions of objects is included in video database. Many video indexing strategies have been proposed, which include the above information to speed up the query processing time. For example, the 3D C-string strategy, it uses the projections of objects to represent spatial and temporal relations between objects in a video. Moreover, the 3D C-string strategy can keep track of the motions and size changes of the objects in a video. However, there are three problems caused by the 3D C-string strategy. The first one is that it cannot index some kinds of videos in which an object appears and then disappears for more than one time. The second one is that the representation of the 3D C-string is too complex for deriving spatial relationships. The last one is that the 3D C-string cannot derive the absolute locations of objects, since it records the relative locations of objects. In this thesis, in order to solve the problems of the 3D C-string strategy, we propose three new spatial relationships. By making use of the three spatial relationships, we can express the condition that objects disappear and appear. Moreover, based on the sequence of spatial relationships, we can derive the temporal relationships. Based on this technique, we propose three index processing strategies for video database. The first strategy is the Temporal UID Matrix (TUID) strategy. We use those 13 unique numbers used in the UID strategy and our 3 new added unique numbers to represent spatial relationships. Then, we store the sequence of spatial relationships in the TUID matrix. In this way, we can efficiently support query types of spatial, temporal, and spatio-temporal relationships. However, since the TUID strategy does not record the information of objects, it cannot support the query type by the information of objects. Therefore, we propose the second strategy, the 2D Video String strategy, to keep track of the motions, locations, and size changes associated with the video objects. Although the 2D Video String strategy can support all types of queries, it is less efficient than the TUID strategy. By making use of the advantages of both strategies, we propose another video indexing strategy, the Hybrid strategy. We record the information of objects in the diagonal part of the TUID matrix. From our simulation study, we show that our proposed strategies can provide a shorter search time for video data than Lee et al.'s 3D C-string strategy, except the 2D Video String strategy for the temporal query.

The frequent use of two or more closely positioned vessels during offshore operations makes the study of multi-body hydrodynamics an important topic, especially for the design of deepwater offshore systems. This research investigation studies the response behavior of a coupled mini-TLP / barge system in both head and beam sea conditions. The design sea conditions were selected to represent the combined wind, wave and current conditions for a target location off the coast of West Africa. Both the mini-TLP and the barge were designed to have independent mooring systems. Coupling between the two vessels is introduced through a connection consisting of two breast lines and a fender system. This connection is designed to restrain the horizontal movements of the two vessels while keeping a constant distance between them and avoiding collisions. The main focus of this study is to analyze the experimental data obtained during the model testing, especially the motions of the two bodies and the values related to the fender system, in order to characterize the behavior of the uncoupled and coupled system configurations. A statistical approach is used for the data analysis and interpretation. Statistical parameters are used to provide an overall characterization of system behavior, and Gaussian and Weibull distribution functions are utilized to detect the importance of non-linearity in the data with particular attention to extreme values. Correlations between the two vessels in time domain and frequency domain are investigated. In addition, auto and cross spectrum analyses of the data are used to contrast the motion behavior of the uncoupled and coupled configurations. It is shown that the connection system reduces the horizontal vessel motions; however the forces exerted on the fender system show significant variation depending on sea heading conditions.