Doctor of Philosophy

dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest

Transform domain texture synthesis on surfaces

In the recent past application areas such as virtual reality experiences, digital cinema and computer gamings have resulted in a renewed interest in advanced research topics in computer graphics. Although many research challenges in computer graphics have been met due to worldwide efforts, many more are yet to be met. Two key challenges which still remain open research problems are, the lack of perfect realism in animated/virtually-created objects when represented in graphical format and the need for the transmissiim/storage/exchange of a massive amount of information in between remote locations, when 3D computer generated objects are used in remote visualisations. These challenges call for further research to be focused in the above directions. Though a significant amount of ideas have been proposed by the international research community in their effort to meet the above challenges, the ideas still suffer from excessive complexity related issues resulting in high processing times and their practical inapplicability when bandwidth constraint transmission mediums are used or when the storage space or computational power of the display device is limited. In the proposed work we investigate the appropriate use of geometric representations of 3D structure (e.g. Bezier surface, NURBS, polygons) and multi-resolution, progressive representation of texture on such surfaces. This joint approach to texture synthesis has not been considered before and has significant potential in resolving current challenges in virtual realism, digital cinema and computer gaming industry. The main focus of the novel approaches that are proposed in this thesis is performing photo-realistic texture synthesis on surfaces. We have provided experimental results and detailed analysis to prove that the proposed algorithms allow fast, progressive building of texture on arbitrarily shaped 3D surfaces. In particular we investigate the above ideas in association with Bezier patch representation of 3D objects, an approach which has not been considered so far by any published world wide research effort, yet has flexibility of utmost practical importance. Further we have discussed the novel application domains that can be served by the inclusion of additional functionality within the proposed algorithms.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Structural-Electromagnetic Simulation Coupling and Conformal Antenna Design Tool

Airborne and spaceborne radar has long been an effective tool for remote sensing, surveillance, and reconnaissance. Most airborne systems utilize antenna arrays that are installed inside the moldline of the aircraft or in radomes that protect the array from in-flight loads. While externally-mounted arrays can offer the advantage of larger apertures, sensor-vehicle interactions often result in performance degradation of both systems. The presence of an externally-mounted array will increase the vehicle’s drag and potentially affect the dynamics and control of the vehicle. In addition, in-flight structural loads will deform the array, thus resulting in relative phase errors. While there exist a multitude of physics-based simulation tools to determine the effects of the array on the aircraft performance, existing tools are not sufficient for generating deformed arrays necessary for determining in-flight array performance. In response to this need, a computer tool for analyzing antennas undergoing structural loads is developed. The Antenna Deformation Tool (ADT) has two primary uses: generating deformed geometry from the output of a structural Finite Element Model (FEM) for use in an Electromagnetic (EM) simulation, and designing conformal antenna arrays. The two commercial software packages ADT is optimized for are MSC NASTRAN and ANSYS HFSS. Specifically, ADT is designed to generate a deformed 3D Computer Aided Design (CAD) model from a NASTRAN structural mesh. The resulting CAD model is compatible with HFSS electromagnetic simulation software for the assessment of the effects of loads on performance. The main purpose for the development of ADT is to facilitate studies of how structural deformations affect airborne antenna arrays performance and to provide the capability to perform studies easily and quickly using different antennas on the same structural model. ADT capabilities are demonstrated using several representative airborne antenna array structures. ADT is also demonstrated in the design of conformal antenna arrays. ADT can import CAD geometry and deform it according to a prescribed deformation field. The deformation field can either be determined from structural simulations or be provided by the user. This functionality allows the user to take an existing planar antenna design and conform it to a desired shape. Within the scope of airborne antenna arrays, this would allow an engineer to conform the antenna to the moldline of the aircraft or other support structure. Currently, ADT can interpret only quad and triangular 2D elements from NASTRAN. In addition, its ability to interpret a surface from a point cloud is limited to surface meshes in which there are exactly four explicit vertices, or surfaces which have a fairly even boundary with no major discontinuities and can be divided into four even segments. ADT is tested on NASTRAN structural models of small to medium complexity, and the geometry generated from simple models is used in HFSS simulations with success (with occasional post processing required). The antenna deformation submodule shows favorable performance with sheet and solid CAD geometry, though post-processing is required in the case of the latter. Results of some deformed antennas simulated with HFSS in the 200 MHz range are presented. The surface error of the geometry produced by ADT varies with the type of input mesh, with curved meshes and surfaces having higher errors. In terms of average element edge length, the maximum surface error is up to 1% for surfaces with no to small curvatures, and up to 3.6% for highly curved surfaces. This translates to about 0.17% of the mesh diagonal. ADT contains a set of classes and functions which provide ample capabilities for surface generation from meshes, and the process implemented is mostly automatic, requiring minimal user intervention. Due to ADT defining deformed geometry purely on separate meshes, adjacent surfaces are not associative and continuity between them is not guaranteed, which inherently can result in small intersections. These intersections can cause meshing problems with HFSS; however, these issues can be mitigated by adding a small offset. While demonstrated applications are still limited, ADT promises to substantially contribute to the design of aircraft-integrated antennas and multifunctional structures. With very limited capabilities for generating and assessing deformed antenna geometry currently existing, ADT represents a unique tool. ADT could be used not only in developing the next-generation of airborne remote sensing technologies, but to characterize in-flight performance of existing systems as well

Functional representation and manipulation of shapes with applications in surface and solid modeling

Real-valued functions have wide applications in various areas within computer graphics. In this work, we examine three representation of shapes using functions. In particular, we study the classical B-spline representation of piece-wise polynomials in the univariate domain. We provide a generalization of B-spline to the bivariate domain using intuition gained from the univariate construction. We also study the popular scheme of representing 3D density distribution using a uniform, rectilinear grid, where we provide a novel contouring scheme that culls occluded inner geometries. Lastly, we examine a ray-based representation for 3D indicator functions called ray-rep, for which we present a novel meshing scheme with multi-material extensions

Frequency Response Based Repetitive Control for Periodic Coefficient Systems Motivated by Cam Followers

Cam follower systems are generally designed to operate at a fixed speed or a range of fixed speeds. However manufacturing defects, wear, or a change of design goals may require altering the camshaft speed to produce a follower trajectory which is not possible using a fixed speed. The follower trajectory may also be optimized for some performance criteria such as minimizing vibration and wear. Like most real world systems, the differential equations governing a cam follower system are nonlinear. A common approach for controlling a nonlinear system is to first linearize the system about a nominal operating point, then apply linear control laws. In many cases, such as the cam follower system, one can create a trajectory and numerically solve the nonlinear system for the inputs required to follow it. Linearizing about this solution creates a linear time varying system whose states are deviations from the desired solution. The speed trajectory in the cam follower system is periodic, which results in a linear system with periodic coefficients. Repetitive control creates control systems that aim to converge to zero tracking error following a periodic command, or aim to completely cancel the effects of a periodic disturbance. Using the inverse of the steady state frequency response as a compensator has been shown to be very effective for linear time invariant systems. That idea is applied here to linear time periodic systems. The periodic state matrices lend themselves well to frequency domain representations, which can be used to construct a matrix form of the steady state frequency response. The first law studied in this work analyzes a moving window implementation which monitors the output errors and previous commands to create an update to the change in the command for the current time step using the inverse of the steady state frequency response matrix. Asymptotic convergence conditions for zero tracking error are derived. When the number of samples in one period is not an integer number, the moving window method is not feasible without interpolation. Therefore a second method based on the projection algorithm from adaptive control is developed and analyzed. In linear constant coefficient systems, one generally needs to incorporate a frequency cutoff filter to robustify to high frequency model error. The additional intricacies of designing a cutoff filter for periodic systems is considered, aiming to handle the fact that for periodic coefficient systems, addressing error components below the intended cutoff can excite harmonics above the cutoff. The control laws developed in this work are applicable to any nonlinear system which may be linearized about a periodic trajectory. Development of these control laws is motivated by improving the performance of a cam follower system. Additional improvements in cam follower behavior can be done through parameter optimization. This includes optimizing a nonlinear follower spring such that it provides just sufficient force to maintain contact while reducing the load on the cam

An Adaptive Parameterisation Method for Shape Optimisation Using Adjoint Sensitivities.

PhD Theses.Adjoint methods are the most e cient approach to compute the design sensitivities as the entire gradient vector of a single objective function is obtained in a single adjoint system solve. This in turn opens up a wide range of possibilities to parameterise the shape. Most shape parameterisation methods require manual set-up which typically results in a restricted design space. In this work, two parameterisation methods that can be derived automatically from existing information are extended to include adaptive design space in shape optimisation. The node-based method derives parameterisation directly from the computational mesh employed for simulation and normal displacements of the surface grid nodes are taken as design variables. This method o ers the richest design space for shape optimisation. However, this method requires an additional surface regularization method to annihilate high-frequency shape modes. Hence the best achievable design depends on the amount of smoothing applied on the design surface. An improved adaptive explicit surface regularization method is proposed in this thesis to capture superior shape modes in the design process. The NSPCC approach takes CAD descriptions as input and perturbs the control points of the NURBS boundary representation to modify the shape. The adaptive NSPCC method is proposed where the optimisation begins with a coarser design space and adapts to ner parameterisation during the design process. Driven by adjoint sensitivity information the control points on the design surfaces are adaptively enriched using knot insertion algorithm without modifying the shape. Both parameterisation methods are coupled in the adjoint-based shape optimisation process to reduce the total pressure loss of a turbine blade internal cooling channel. Based on analyses regarding the quality of the optima and the rate of convergence of the design process the adaptive NSPCC method outperforms both adaptive node-based and the static NSPCC approach

Towards a Phenomenological Theory of the Visceral in the Interactive Arts

This is a digitised version of a thesis that was deposited in the University Library. If you are the author and you have a query about this item please contact PEARL Admin ([email protected])Metadata merged with duplicate record (http://hdl.handle.net/10026.1/2319) on 20.12.2016 by CS (TIS).This thesis explores the ways in which certain forms of interactive art may and do elicit visceral responses. The term "visceral" refers to the cardiovascular, respiratory, uro-genital and especially excretory systems that affect mind and body on a continuum of awareness. The "visceral" is mentioned in the field of interactive arts, but it remains systematically unexplored and undefined. Further, interactive artworks predominantly focus on the exteroceptive (stimuli from outside) rather than the interoceptive (stimuli arising within the body, especially the viscera) senses. The existentialist phenomenology of Maurice Merleau-Ponty forms the basis for explorations of the visceral dimension of mind/body. New approaches to understanding interactive art, design and the mind/body include: attunements to the world; intertwinings of mind/body, technology and world; and of being in the world. Each artwork within utilizes a variation of the phenomenological methods derived from Merl eau-Ponty's; these are discussed primarily in Chapters One and Three. Because subjective, first-person, experiences are a major aspect of a phenomenological approach, the academic writing is interspersed with subjective experiences of the author and others. This thesis balances facets of knowledge from diverse disciplines that account for visceral phenomena and subjective experience. Along with the textual exegesis, one major work of design and two major works of art were created. These are documented on the compact disc (CDROM) bound within. As an essential component of each artwork, new technological systems were created or co-created by the author. User surveys comprise Appendices Two, Three and Four, and are also online at: www. sfu. ca/-dgromala/thesis. To access the URL: login as , and use the password . Numerous talks, exhibitions and publications that directly relate to the thesis work is in Appendix One. This work begins with an introduction to Merleau-Ponty's ideas of flesh and reversibility. Chapter Two is the review of the literature, while Chapter Three is an explication of the hypothesis, an overview of the field, and a framing of the problem. Discussions of each artwork are in Chapter Four (The Meditation Chamber), Chapter Five (BioMorphic Typography) and Chapter Six (The MeatBook). Chapter Seven forms the conclusion. References to the documentation on the CD are found throughout the thesis, and italicized paragraphs provide an artistic context for each chapter

Virtual sculpting : an investigation of directly manipulated free-form deformation in a virtual environment

This thesis presents a Virtual Sculpting system, which addresses the problem of Free-Form Solid Modelling. The disparate elements of a Polygon-Mesh representation, a Directly Manipulated Free-Form Deformation sculpting tool, and a Virtual Environment are drawn into a cohesive whole under the mantle of a clay-sculpting metaphor. This enables a user to mould and manipulate a synthetic solid interactively as if it were composed of malleable clay. The focus of this study is on the interactivity, intuitivity and versatility of such a system. To this end, a range of improvements is investigated which significantly enhances the efficiency and correctness of Directly Manipulated Free-Form Deformation, both separately and as a seamless component of the Virtual Sculpting system

FITTING A PARAMETRIC MODEL TO A CLOUD OF POINTS VIA OPTIMIZATION METHODS

Computer Aided Design (CAD) is a powerful tool for designing parametric geometry. However, many CAD models of current configurations are constructed in previous generations of CAD systems, which represent the configuration simply as a collection of surfaces instead of as a parametrized solid model. But since many modern analysis techniques take advantage of a parametrization, one often has to re-engineer the configuration into a parametric model. The objective here is to generate an efficient, robust, and accurate method for fitting parametric models to a cloud of points. The process uses a gradient-based optimization technique, which is applied to the whole cloud, without the need to segment or classify the points in the cloud a priori. First, for the points associated with any component, a variant of the Levenberg-Marquardt gradient-based optimization method (ILM) is used to find the set of model parameters that minimizes the least-square errors between the model and the points. The efficiency of the ILM algorithm is greatly improved through the use of analytic geometric sensitivities and sparse matrix techniques. Second, for cases in which one does not know a priori the correspondences between points in the cloud and the geometry model\u27s components, an efficient initialization and classification algorithm is introduced. While this technique works well once the configuration is close enough, it occasionally fails when the initial parametrized configuration is too far from the cloud of points. To circumvent this problem, the objective function is modified, which has yielded good results for all cases tested. This technique is applied to a series of increasingly complex configurations. The final configuration represents a full transport aircraft configuration, with a wing, fuselage, empennage, and engines. Although only applied to aerospace applications, the technique is general enough to be applicable in any domain for which basic parametrized models are available