The recognition of 3-D objects from their silhouettes demands a shape representation which is invariant to minor changes in viewpoint and articulation. This invariance can be achieved by parsing a silhouette into parts and relationships that are stable across similar object views. Medial descriptions, such as skeletons and shock graphs, attempt to decompose a shape into parts, but suffer from instabilities that lead to similar shapes being represented by dissimilar part sets. We propose a novel shape parsing approach based on identifying and regularizing the ligature structure of a given medial axis. The result of this process is a bone graph, a new medial shape abstraction that captures a more intuitive notion of an object’s parts than a skeleton or a shock graph, and offers improved stability and within-class deformation invariance over the shock graph. The bone graph, unlike the shock graph, has attributed edges that specify how and where two medial parts meet. We propose a novel shape matching framework that exploits this relational information by formulating the problem as an inexact directed acyclic graph matching, and extending a leading bipartite graph-based matching framework introduced for matching shock graphs. In addition to accommodating the relational information, our new framework is better able to enforce hierarchical and sibling constraints between nodes, resulting in a more general and more powerful matching framework. We evaluate our matching framework with respect to a competing shock graph matching framework, and show that for the task of view-based object categorization, our matching framework applied to bone graphs outperforms the competing framework. Moreover, our matching framework applied to shock graphs also outperforms the competing shock graph matching algorithm, demonstrating the generality and improved performance of our matching algorithm.

The predominant model of the human hip is a mechanical ball-and-socket joint. This description has two key implications: that the motion of the hip is purely rotational, and that the rigid articulating geometry of the hip is a sphere-on-sphere contact. Since the widespread adoption of this model, in the late 1960s, there has however been a persistent thread of literature suggesting that the articulating geometry of the hip is aspherical. The recent widespread availability of three-dimensional medical imaging now makes it possible to empirically assess the applicability of the predominant model. For this research dissertation, two arthritic groups were examined: patients either had primary early-life osteoarthritis of the hip, or hip dysplasia with secondary osteoarthritis. Computed tomography scans, taken as part of routine preoperative preparation, served as the source data for this work. The scans were manually segmented to produce 3D models of the bones of the hip, which were further refined to isolate the bony articular surfaces. These surfaces were fit to general ellipsoids and to spheres, the latter being the ball-and-socket model. The arthritic hips examined had comparable fitting accuracy for both ellipsoids and spheres; however, sixteen of nineteen hips formed geometrically incompatible ball-and-socket joints. The dysplastic hips examined had a notable difference in fitting accuracy, with ellipsoids being a statistically significantly better fit to the hip geometry. The ellipsoid shapes in all cases were aspherical, and in each population formed a statistically significantly aspherical group. There were no trends relating the ellipsoid shapes of bones of an individual joint, nor were there practical differences between the ellipsoid shapes between the two populations. Despite patient groups not being controlled for age, sex, or race, and accounting for typical manual segmentation errors, these results suggest that the hip is aspherically shaped. Thus, the geometric foundation of the ball-and-socket motion may be unsupported, and the conventional kinematic description of the hip may be called into question. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-09-28 09:41:29.114

No description available.

Non-Uniform Rational B-Splines (NURBS) curve has acquired great significance in the field of Computer Aided Design and Machining due to their ability to draw a large variety of shapes in an interactive computer graphics environment. A biarc curve is a composition of two circular arcs such that they are tangent continuous at the point of join. Biarcs have replaced traditionally used line segments in approximating curves and surfaces for generating tool paths of Computerised cutting machines called CNC (Computerised Numerical Controlled) machines. This is due to their ability to be at a greater proximity to the original curve with fewer number of segments. Since most of the machining tools can move only in straight lines and circular arcs, it is desirable that the tool paths be composed of biarcs and/or straight line segments. Shape preserving interpolation is a technique of drawing a curve through a set of points such that the shape represented by the data points are preserved. Both NURBS and biarc curves are not essentially shape preserving curves; however, if certain constraints are imposed on them, they are able to preserve the shape represented by the data points. This work proposes a technique that incorporates both NURBS and biarcs to perform the interpolation. The advantages are twofold; it acts as a common platform for the two techniques to operate together, which is novel, and the fitted NURBS curve can be approximated by biarcs, which has applications in the machining industry.

The recognition of 3-D objects from their silhouettes demands a shape representation which is invariant to minor changes in viewpoint and articulation. This invariance can be achieved by parsing a silhouette into parts and relationships that are stable across similar object views. Medial descriptions, such as skeletons and shock graphs, attempt to decompose a shape into parts, but suffer from instabilities that lead to similar shapes being represented by dissimilar part sets. We propose a novel shape parsing approach based on identifying and regularizing the ligature structure of a given medial axis. The result of this process is a bone graph, a new medial shape abstraction that captures a more intuitive notion of an object’s parts than a skeleton or a shock graph, and offers improved stability and within-class deformation invariance over the shock graph. The bone graph, unlike the shock graph, has attributed edges that specify how and where two medial parts meet. We propose a novel shape matching framework that exploits this relational information by formulating the problem as an inexact directed acyclic graph matching, and extending a leading bipartite graph-based matching framework introduced for matching shock graphs. In addition to accommodating the relational information, our new framework is better able to enforce hierarchical and sibling constraints between nodes, resulting in a more general and more powerful matching framework. We evaluate our matching framework with respect to a competing shock graph matching framework, and show that for the task of view-based object categorization, our matching framework applied to bone graphs outperforms the competing framework. Moreover, our matching framework applied to shock graphs also outperforms the competing shock graph matching algorithm, demonstrating the generality and improved performance of our matching algorithm.

No description available.

Shape memory alloy (SMA) wires are becoming increasingly popular as actuators in automotive applications due to properties such as large recovery strain, low weight, and silent actuation. The length change and thus actuation in SMA wires occur when the wire is heated, usually by passing a direct current through them. One of the difficulties in controlling electrically-heated SMAs occurs in monitoring their temperature, which is done to control the transformation and hence, actuation and avoid possibly permanent damage due to overheating. The temperature of a SMA wire is usually calculated theoretically based on the wire???s natural convection heat transfer coefficient(h).First-order convective heating models are typically used to calculate the natural convection heat transfer coefficient for SMA wires, but there is often significant uncertainty in these calculations due to a lack of existing correlations for thin cylinders, where curvature effects are significant. The purpose of this investigation is to develop models for SMA wires that may be used to predict the temperature of a current-carrying SMA wire without using direct temperature measurement methods. The models were developed based on experimental results for 0.5 mm diameter NiTi SMA wire. First the effect of various parameters such as wire inclination angle, wire length, ambient pressure, phase transformation time rate and applied external stress were investigated on the SMA wire???s electrical resistance. The electrical resistance of the SMA wire was monitored during one complete heating and cooling cycle. Later, based on the experimental results, a resistance model was developed for the current-carrying SMA wires that can be used to predict the wires??? temperature based on electrical resistance. Second, a natural convection heat transfer correlation was developed for NiTi SMA wire, in the range 2.6E-8??? RaD ??? 6E-1, which is appropriate for modeling natural convection in most practical applications at ambient conditions. A pressure variation method was used to obtain a range of Rayleigh number for a heated SMA wire. The ambient pressure was controlled within a vacuum chamber, from 1 atm to 2E-4 atm (0.1 MPa to 2E-5 MPa). Data were collected for the wire at various angles under both 100 MPa and stress-free conditions between horizontal to vertical at each set pressure. The new correlation can be used to determine the convective heat transfer coefficient of an SMA wire of known diameter and inclination angle. The convection coefficient (h) is determined using the correlation along with the Prandtl number (Pr), air dynamic viscosity (??), air compressibility factor (Z), air thermal conductivity (k), and gas constant (Rc). The wire temperature can then be determined by substituting this coefficient into the convective heat transfer equation.

Non-Uniform Rational B-Splines (NURBS) curve has acquired great significance in the field of Computer Aided Design and Machining due to their ability to draw a large variety of shapes in an interactive computer graphics environment. A biarc curve is a composition of two circular arcs such that they are tangent continuous at the point of join. Biarcs have replaced traditionally used line segments in approximating curves and surfaces for generating tool paths of Computerised cutting machines called CNC (Computerised Numerical Controlled) machines. This is due to their ability to be at a greater proximity to the original curve with fewer number of segments. Since most of the machining tools can move only in straight lines and circular arcs, it is desirable that the tool paths be composed of biarcs and/or straight line segments. Shape preserving interpolation is a technique of drawing a curve through a set of points such that the shape represented by the data points are preserved. Both NURBS and biarc curves are not essentially shape preserving curves; however, if certain constraints are imposed on them, they are able to preserve the shape represented by the data points. This work proposes a technique that incorporates both NURBS and biarcs to perform the interpolation. The advantages are twofold; it acts as a common platform for the two techniques to operate together, which is novel, and the fitted NURBS curve can be approximated by biarcs, which has applications in the machining industry.

No description available.

Topology optimisation techniques help designers to nd the best layout of structural members. When followed by shape and sizing optimisation, these techniques result in far greater savings than shape and sizing optimisation alone. During the last three decades extensive research has been carried out in the topology optimisation area. Consequently topology optimisation techniques have been considerably improved and successfully applied to a range of physical problems. These techniques are now regarded as invaluable tools in mechanical, aerostructural and structural design. In spite of great potential in geomechanical problems, however, the application of topology optimisation techniques in this eld has not been studied thoroughly. This thesis explores the state-of-the-art topology and shape optimisation methods in excavation design. The main problems of concern in this thesis are to nd the optimum shape of an underground opening and to optimise the reinforcement distribution around it. To tackle these problems, new formulations for some topology optimisation techniques are proposed in this thesis to match the requirements in excavation problems. Although linear elastic material models have limited applications in excavation design, these models are used in the rst part of this thesis to introduce the proposed optimisation technique and to verify it. Simultaneous shape and reinforcement optimisation is considered as well. Using the proposed optimisation techniques, it is shown that the computational effort needed for this mixed optimisation problem is almost the same as the effort required to solve each of shape or reinforcement optimisation problems alone. In the next part of this thesis, reinforcement optimisation of tunnels in massive rocks is addressed where the behaviour of the rock mass is in uenced by few major discontinuities. Although discontinuities exist in the majority of rock masses, due to its complexities, optimising the excavations in these types of rocks has not been considered by any other researcher before. A method for reinforcement optimisation of tunnels in such rock masses is proposed in this thesis and its capability is demonstrated by means of numerical examples. Lastly, shape optimisation of excavations in elasto-plastic soil is addressed. In this problem the excavation sequence is also taken into account. A stressbased parameter is dened to evaluate the efficiency of the soil elements assuming Mohr-Coulomb material model. Some examples are solved to illustrate and verify the application of the proposed technique. Being one of the rst theses on the topic, this work concentrates on the theoretical background and the possibility of applying topology optimisation techniques in excavation designs. It has been demonstrated that a properly tailored topology optimisation technique can be applied to nd both the optimum shape and the optimum reinforcement design of openings. Optimising the excavations in various types of grounds including elastic homogeneous rock masses, massive rocks, and elasto-plastic soil and rock media have been considered. Different objective functions, namely, mean compliance, oor heave, and tunnel convergence have been selected and successfully minimised using the proposed techniques. The results obtained in this thesis illustrate that the proposed topology optimisation techniques are very useful for improving excavation designs.