M.Sc. (Computer Science) / A challenge faced when simulating the complex behaviour of cloth, especially at interactive frame rates, is maintaining an acceptable level of realism while keeping computation time to a minimum. A common method used to increase the performance is to decrease the number of nodes controlling the cloth's movement. This results in a significant decrease in the time taken to calculate each frame of the animation, but at the cost of sacrificing detail that can only be obtained using a dense discretisation of the cloth. A simple, efficient and popular method to simulate cloth is the mass-spring system, which utilises a regular grid of vertices representing discrete points along the cloth's surface. The structure of geometry images is similar, which makes them an ideal choice for representing arbitrary surface meshes in a cloth simulator whilst retaining the effciency of a mass-spring system. This dissertation presents a novel method of applying geometry images to cloth simulation in order to obtain cloth motion for surface meshes while retaining the simplicity of a massspring model. By adapting an implicit/explicit integration scheme, and utilising the regular structure of geometry images, an improvement in performance is achieved. Additionally, the cloth is able to drape over other objects, also represented as geometry images. The proposed method is efficient enough to allow fairly dense cloth meshes to be simulated in real-time.

This thesis aims to develop a design-oriented simulation approach for cloth analysis. Our approach is built on the framework of NURBS-based isogeometric analysis, which utilizes NURBS as the basis functions of analysis. NURBS is a class of parametric geometry to represent curves and surfaces in computer-aided design (CAD) programs. Recently, NURBS geometry has been used directly in analysis. The overall goal of this thesis is to develop a computation infrastructure that enables cloth analysis directly on NURBS geometry. The advantage of NURBS in the context of cloth modeling lies in the geometric smoothness. Using NURBS, it's easy to construct surfaces with C1 or higher order of continuity. Compared to C0 finite element geometry, the NURBS geometry is more effective in capturing wrinkles and folders of cloth, which are characteristics of cloth motion. The NURBS geometry enables the use of rotation-free Kirchhoff-Love shell. The rotation-free shell model not only saves freedoms, but also makes the contact/impact treatment much easier. The major contribution of this work is the development of a NURBS cloth modeling approach. The mechanical model of cloth and its implementation with NURBS geometry will be presented in detail. Proper constitutive laws are employed for fabric materials. Since NURBS geometry from CAD typically contains multiple patches and trimmed patches, a certain treatment is proposed so that geometry can be used directly in analysis. Another contribution of this work relates to a contact/impact algorithm. Contact problems in cloth simulation have been a bottleneck of continuum-based approach. Since the general contact method doesn't work well for cloth simulation, a special contact treatment is developed. The present contact model distinguishes three types of contact interactions. The first is the persistent contact force. This force in essence is the traditional penalty force, but is applied when a contact pair is within a separation tolerance instead of being penetrated. This essentially smears the abrupt contact reaction into a relatively smooth force defined only a small thickness. The second is trajectory impact, which deals with the reaction when impact occurs in a time step. The treatment ensures that a point stays on a same side of the surface it impacts on. The third is self-intersection. Intersection resorting force is introduced when the initial configuration has self-intersections, or when the trajectory impact force fails to eliminate all the collisions. We proposed a new method, the method of area minimization, to handle intersections. The contact models have been integrated into an operator-split integration algorithm. A notable feature of this integration is that the contact/impact response is singled out from the momentum equation. This work also proposes a continuum-based strain limiting scheme. Because the in-plane stiffness of cloth is much higher than the bending stiffness, numerical difficulty is encountered in either implicit or explicit time integration. The strain limiting is a numerical technique that formulates the in-plane response as a constraint problem to allow the use of lower in-plane stiffness. A number of examples are presented to show the performance of the proposed approach. In the wrinkling study, the simulated wrinkle pattern looks similar with the experimental results. In the contact study, it is found that the current method can accurately recover a constant contact pressure field (press patch test), can handle contacts of multi-layer folds and produce realistic draping effect. The intersection resolution method is illustrated to be robust to various kinds of intersections. The fast projection method can enlarge time steps while limiting the in-plane strain. The current method is also applied to the analysis of a soft armor. Beginning from CAD models the armor was put on the human body by a try-on simulation. In multi-layer models, the intersection resolution method is used to resolve the intersections between layers. Subsequently, cloth dynamics are simulated for different human motions. Mechanical indexes such as the extra torque caused by the armors, pressure force on the body, and stress in the armor are predicted. Parametric studies are performed to investigate the change in mechanical metrics under altered design parameters.

This master thesis deals with interactive cloth simulation accelerated by GPU. In the first part there is a description of all technologies used during implementation of a program. The second part discusses various simulation methods. It is mainly focused on particle systems as a most used method. These parts are followed by a design of the program, which is implemented as a part of this thesis. The program was implemented in four variants. The first variant is CPU implementation, which was then optimalized with OpenMP. CUDA implementation is based on these implementations. Last variant implemented in this thesis is optimized CUDA implementation. All these implementations are evaluated from compute complexity point of view and suitability for real time graphics.

<p>This study describes a fast approach using GPU to process self-collision in cloth animation without significant compromise in physical accuracy. The proposed fast approach is built and works effectively on a modification of Mass Spring Model which is seen in a variety of cloth simulation study. Instead of using hierarchical data structure which needs to be updated each frame, this fast approach adopts a spatial hashing technique which virtually partitions the space where the cloth object locates into small cubes and stores the information of the particles being held in the cells with an integer array. With the data of the particles and the cells holding information of the particles, self-collision detection can be processed in a very limited cost in each thread launched in GPU regardless of the increase in the amount of particles. This method is capable of visualizing self-collision detection and response in real time with limited cost in accessing memory on the GPU. </p> <p>The idea of the proposed fast approach is extremely straightforward, however, the amount of memory which is needed to be consumed by this method is its weakness. Also, this method sacrifices physical accuracy in exchange for the performance.</p>

Artists require control and predictability over physically based simulations to create their required animation. This control can lead to reduced iteration time to get the desired simulation results. Controlling cloth simulations can require manual effort to create goal keyframes for control algorithms to match. Current techniques and research utilize a keyboard and mouse to create these goal keyframes. Other research has looked at using a virtual reality (VR) head-mounted display with controllers to improve the experience of completing similar animation tasks. However, we are not aware of any research that attempts to use VR as a tool to assist artists in the process of cloth simulation. This work explores using VR to create goal keyframes of a cloth mesh for control algorithms to further artists' ability to produce and control cloth simulations. We created a system where users can produce goal keyframes using both a keyboard and mouse and using VR. A user study was conducted (n=20) utilizing this system for keyframing tasks. We found that most participants preferred to use the system in VR and found it fun and intuitive, with each input method having their own strengths in the cloth keyframe sculpting process. We also found the timing and accuracy of using VR to be comparable to using a keyboard and mouse, despite minimal VR experience among participants.

Yes / Despite great strides in past years are being made to generate motions of elastic materials such as cloth and biological skin in virtual world, unfortunately, the computational cost of realistic high-resolution simulations currently precludes their use in interactive applications. Thin elastic materials such as cloth and biological skin often exhibit complex nonlinear elastic behaviors. However, modeling elastic nonlinearity can be computationally expensive and numerically unstable, imposing significant challenges for their use in interactive applications. This paper presents a novel simulation framework for simulating realistic material behaviors with interactive frame rate. Central to the framework is the use of a constraint-based multi-resolution solver for efficient and robust modeling of the material nonlinearity. We extend a strain-limiting method to work on deformation gradients of triangulated surface models in three-dimensional space with a novel data structure. The simulation framework utilizes an iterative nonlinear Gauss–Seidel procedure and a multilevel hierarchy structure to achieve computational speedups. As material nonlinearity are generated by enforcing strain-limiting constraints at a multilevel hierarchy, our simulation system can rapidly accelerate the convergence of the large constraint system with simultaneous enforcement of boundary conditions. The simplicity and efficiency of the framework makes simulations of highly realistic thin elastic materials substantially fast and is applicable of simulations for interactive applications. / Publisher embargo ended 5th Jun 2016

This thesis presents a model of fabric bending hysteresis. The hysteresis model is designed to reproduce the fabric bending measurements taken by the Kawabata Evaluation System (KES) and the model parameters can be derived directly from these property measurements. The advantage to using this technique is that it provides the ability to simulate a continuum of property curves. Results of the model and its components are compared and constrasted with experimental results for fabrics composed of different weaves and yarn types. An attempt to incorporate the bending model as part of a fabric drape simulation is also made.

A new approach to local nonlinear image restoration is described, based on approximating functions using a regular grid of points in a many-dimensional space. Symmetry reductions and compression of the sparse grid make it feasible to work with twelve-dimensional grids as large as 22¹². Unlike polynomials and neural networks whose filtering complexity per pixel is linear in the number of filter co-efficients, grid filters have O(1) complexity per pixel. Grid filters require only a single presentation of the training samples, are numerically stable, leave unusual image features unchanged, and are a superset of order statistic filters. Results are presented for additive noise, blurring, and superresolution.

An automatic question answering system must find, within a corpus,short factual answers to questions posed in natural language. The process involves analyzing the question, retrieving information related to the question, and extracting answers from the retrieved information. This thesis presents a novel approach to answer extraction in an automated question answering (QA) system. The answer extraction approach is an extension of the MultiText QA system. This system employs a question analysis component to examine the question and to produce query terms for the retrieval component which extracts several document fragments from the corpus. The answer extraction component selects a few short answers from these fragments. This thesis describes the design and evaluation of the Redundant Inverse Term Frequency (RITF) answer extraction component. The RITF algorithm locates and evaluates words from the passages that are likely to be associated with the answer. Answers are selected by finding short fragments of text that contain the most likely words based on: the frequency of the words in the corpus, the number of fragments in which the word occurs, the rank of the passages as determined by the IR, the distance of the word from the centre of the fragment, and category information found through question analysis. RITF makes a substantial contribution in overall results, nearly doubling the Mean Reciprocal Rank (MRR), a standard measure for evaluating QA systems.

A new approach to local nonlinear image restoration is described, based on approximating functions using a regular grid of points in a many-dimensional space. Symmetry reductions and compression of the sparse grid make it feasible to work with twelve-dimensional grids as large as 22¹². Unlike polynomials and neural networks whose filtering complexity per pixel is linear in the number of filter co-efficients, grid filters have O(1) complexity per pixel. Grid filters require only a single presentation of the training samples, are numerically stable, leave unusual image features unchanged, and are a superset of order statistic filters. Results are presented for additive noise, blurring, and superresolution.