HexaLab.net: An online viewer for hexahedral meshes

© 2018 Elsevier Ltd We introduce HexaLab: a WebGL application for real time visualization, exploration and assessment of hexahedral meshes. HexaLab can be used by simply opening www.hexalab.net. Our visualization tool targets both users and scholars. Practitioners who employ hexmeshes for Finite Element Analysis, can readily check mesh quality and assess its usability for simulation. Researchers involved in mesh generation may use HexaLab to perform a detailed analysis of the mesh structure, isolating weak points and testing new solutions to improve on the state of the art and generate high quality images. To this end, we support a wide variety of visualization and volume inspection tools. Our system offers also immediate access to a repository containing all the publicly available meshes produced with the most recent techniques for hexmesh generation. We believe HexaLab, providing a common tool for visualizing, assessing and distributing results, will push forward the recent strive for replicability in our scientific community

BoolSurf: Boolean Operations on Surfaces

We port Boolean set operations between 2D shapes to surfaces of any genus, with any number of open boundaries. We combine shapes bounded by sets of freely intersecting loops, consisting of geodesic lines and cubic Bézier splines lying on a surface. We compute the arrangement of shapes directly on the surface and assign integer labels to the cells of such arrangement. Differently from the Euclidean case, some arrangements on a manifold may be inconsistent. We detect inconsistent arrangements and help the user to resolve them. Also, we extend to the manifold setting recent work on Boundary-Sampled Halfspaces, thus supporting operations more general than standard Booleans, which are well defined on inconsistent arrangements, too. Our implementation discretizes the input shapes into polylines at an arbitrary resolution, independent of the level of resolution of the underlying mesh. We resolve the arrangement inside each triangle of the mesh independently and combine the results to reconstruct both the boundaries and the interior of each cell in the arrangement. We reconstruct the control points of curves bounding cells, in order to free the result from discretization and provide an output in vector format. We support interactive usage, editing shapes consisting up to 100k line segments on meshes of up to 1M triangles

Iterated function systems and shape representation

We propose the use of iterated function systems as an isomorphic shape representation scheme for use in a machine vision environment. A concise description of the basic theory and salient characteristics of iterated function systems is presented and from this we develop a formal framework within which to embed a representation scheme. Concentrating on the problem of obtaining automatically generated two-dimensional encodings we describe implementations of two solutions. The first is based on a deterministic algorithm and makes simplifying assumptions which limit its range of applicability. The second employs a novel formulation of a genetic algorithm and is intended to function with general data input. Keywords: Machine Vision, Shape Representation, Iterated Function Systems, Genetic Algorithms

Control, forecasting and optimisation for wave energy conversion

This paper presents an overview of the motivation, background to and state-of- the-art in energy maximising control of wave energy devices. The underpinning mathematical modelling is described and the control fundamentals established. Two example control schemes are presented, along with some algorithms for wave forecasting, which can be a necessary requirement, due to the non-causal nature of some optimal control strategies. One of the control schemes is extended to show how cooperative control of devices in a wave farm can be beneficial. The paper also includes perspectives on the interaction between control and the broader objectives of optimal wave energy device geometry and full techno-economic optimisation of wave energy converters

Evolutionary algorithms in artificial intelligence: a comparative study through applications

For many years research in artificial intelligence followed a symbolic paradigm which required a level of knowledge described in terms of rules. More recently subsymbolic approaches have been adopted as a suitable means for studying many problems. There are many search mechanisms which can be used to manipulate subsymbolic components, and in recent years general search methods based on models of natural evolution have become increasingly popular. This thesis examines a hybrid symbolic/subsymbolic approach and the application of evolutionary algorithms to a problem from each of the fields of shape representation (finding an iterated function system for an arbitrary shape), natural language dialogue (tuning parameters so that a particular behaviour can be achieved) and speech recognition (selecting the penalties used by a dynamic programming algorithm in creating a word lattice). These problems were selected on the basis that each should have a fundamentally different interactions at the subsymbolic level. Results demonstrate that for the experiments conducted the evolutionary algorithms performed well in most cases. However, the type of subsymbolic interaction that may occur influences the relative performance of evolutionary algorithms which emphasise either top-down (evolutionary programming - EP) or bottom-up (genetic algorithm - GA) means of solution discovery. For the shape representation problem EP is seen to perform significantly better than a GA, and reasons for this disparity are discussed. Furthermore, EP appears to offer a powerful means of finding solutions to this problem, and so the background and details of the problem are discussed at length. Some novel constraints on the problem's search space are also presented which could be used in related work. For the dialogue and speech recognition problems a GA and EP produce good results with EP performing slightly better. Results achieved with EP have been used to improve the performance of a speech recognition system

Mandoline: robust cut-cell generation for arbitrary triangle meshes

Although geometry arising "in the wild" most often comes in the form of a surface representation, a plethora of geometrical and physical applications require the construction of volumetric embeddings either of the geometry itself or the domain surrounding it. Cartesian cut-cell-based mesh generation provides an attractive solution in which volumetric elements are constructed from the intersection of the input surface geometry with a uniform or adaptive hexahedral grid. This choice, especially common in computational fluid dynamics, has the potential to efficiently generate accurate, surface-conforming cells; unfortunately, current solutions are often slow, fragile, or cannot handle many common topological situations. We therefore propose a novel, robust cut-cell construction technique for triangle surface meshes that explicitly computes the precise geometry of the intersection cells, even on meshes that are open or non-manifold. Its fundamental geometric primitive is the intersection of an arbitrary segment with an axis-aligned plane. Beginning from the set of intersection points between triangle mesh edges and grid planes, our bottom-up approach robustly determines cut-edges, cut-faces, and finally cut-cells, in a manner designed to guarantee topological correctness. We demonstrate its effectiveness and speed on a wide range of input meshes and grid resolutions, and make the code available as open source.This work is graciously supported by NSERC Discovery Grants (RGPIN-04360-2014 & RGPIN-2017-05524), NSERC Accelerator Grant (RGPAS-2017-507909), Connaught Fund (503114), and the Canada Research Chairs Program

Optimising additive manufacturing for fine art sculpture and digital restoration of archaeological artefacts

Additive manufacturing (AM) has shown itself to be beneficial in many application areas, including product design and manufacture, medical models and prosthetics, architectural modelling and artistic endeavours. For some of these applications, coupling AM with reverse engineering (RE) enables the utilisation of data from existing 3D shapes. This thesis describes the application of AM and RE within sculpture manufacture, in order to optimise the process chains for sculpture reproduction and relic conservation and restoration. This area poses particular problems since the original artefacts can often be fragile and inaccessible, and the finishing required on the AM replicas is both complex and varied. Several case studies within both literature and practical projects are presented, which cover essential knowledge of producing large scale sculptures from an original models as well as a wide range of artefact shapes and downstream finishing techniques. The combination of digital technologies and traditional art requires interdisciplinary knowledge across engineering and fine art. Also, definitions and requirements (e.g. ‘accuracy’), can be applied as both engineering and artistic terms when specifications and trade-offs are being considered. The thesis discusses the feasibility for using these technologies across domains, and explores the potential for developing new market opportunities for AM. It presents and analyses a number of case study projects undertaken by the author with a view to developing cost and time models for various processes used. These models have then been used to develop a series of "process maps", which enable users of AM in this area to decide upon the optimum process route to follow, under various circumstances. The maps were validated and user feedback obtained through the execution of two further sculpture manufacturing projects. The thesis finishes with conclusions about the feasibility of the approach, its constraints, the pros and cons of adopting AM in this area and recommendations for future research

The Rationalist’s Spirituality: Campbell’s Monomyth in Single-Player Role-Playing Videogames Skyrim & Mass Effect

This thesis is an investigation of how mythographer Joseph Campbell’s monomyth narrative pattern manifests in computer and console role-playing videogames (CRPGs). It argues that this pattern is conducive to the CRPG being received as a spiritual experience, one potentially transformative in its capacity to impart and facilitate the practice of monomythic values by players, both within the game world and without. Focusing on two CRPG games, Skyrim and Mass Effect, it considers noteworthy parallels between the monomythic quest structure of these games and the ‘quest’ nature of authenticity—the modern, individual, personal search for meaning, analysing how the CRPG’s emphasis on the ‘epistemologically individualistic’ reflects aspects of alternative spirituality (as against traditional institutional religion). As such, the CRPG actively seeks to reconcile the spiritual with the material in a ‘rationalist’s spirituality’, a fact best represented in the game’s logical structuring of the monomythic hero’s journey to apotheosis as rites of passage (that is, as successive stages of narrative, but also as a numerical ‘levelling’ system for avatar development). The spiritual is exemplified by the presence of the monomythic pattern and by how the videogame draws upon themes native to fantastic fiction (ruins, deep time, dark genesis, the sublime), themes which evoke the enchanted world and ‘porous self’ of pre-modern society and represent a desire for re- enchantment and thus an enduring interest in the spiritual. These elements together operate within the rationalised framework of a rule-based game system, where the player has the freedom and agency native to the modern, rationally empowered ‘buffered self’ but is ultimately (and somewhat contrarily) answerable to these very same rules, as determined by a god-like designer. This relationship suggests a continuing albeit surreptitious belief in the transcendent, validating Victoria Nelson’s assertion that art and entertainment in the modern world serves as an ‘unconscious wellspring of religion’ (2001: viii). This thesis also explores the CRPG’s capacity to fulfil the four functions traditionally played by mythology—the mystical, cosmological, sociological and pedagogical—as described in the writings of Joseph Campbell, looking at how the sociological and pedagogical in particular are addressed by the monomythic narrative and the implicit values of this narrative (such as devotion of the self to the community). It will argue that the CRPG—in its capacity to facilitate embodied learning and action (as ritualised performance and contest)—serves as an ideal environment for the practice and possible adoption of such values by the player. Adoption, as I will illustrate, is influenced by a number of factors. Firstly, the game itself as an experience (its narrative and emotive credibility, and thus player investment in their character, or more specifically that character is an idealised construct—the ‘projective identity’). Secondly, how the player’s role is framed within the game world, and thirdly, how the player reads his/her experience. This reading can be to some degree shaped by a game’s goals and rules, and this is where procedural rhetoric—the use of game-based systems for the purposes of persuasion—may help to foreground monomythic values and lessons as well as encourage active practice of these values in day-to-day life. Herein lies the CRPG’s potential to fulfil the Romantic proposition that art can inspire moral improvement in the individual and instigate efforts to realise an idealised world. While games are ultimately shaped by the tastes of the market and the demands of the CRPG community, the question of whether a videogame should actively adopt such an approach is one that arguably falls to game designers: authors of the game-as-text. Chapter 1 provides an introduction to the thesis, while Chapter 2 explores the transition from pre-modern society to modern secularity as a default position in the West, the disappearance of the enchanted world, the emergence of alternative spiritualities as a recourse to institutional religion, and the ‘quest’ spirit that characterises the modern search for meaning (authenticity). Chapter 3 looks at the four functions previously played by mythology and how the CRPG can fulfil them, arguing for a classification of the CRPG as an alternative spirituality, and also as a continuation of a tradition of fantastic fiction representing a desire for re-enchantment, one whose origins may very well be found in modern crises of meaning. Chapter 4 details the origins of CRPG in wargaming and fantastic fiction, discussing the videogame genre’s unique emphasis on player choice, agency and autonomy, while analysing how the monomythic pattern manifests in Skyrim and Mass Effect, as well as its implied values, such as the commitment of the individual to the service of his/her society. Chapter 5 discusses how the CRPG combines fantastic fictional worlds with rational rules. The spiritual takes the form of the abovementioned aesthetic themes and the monomythic pattern, which together signal an enduring interest in re-enchantment and thus the spiritual. The rational takes the form of the videogame’s distinct emphasis on the powers of the player as a rational agent, powers that nevertheless are shaped by the rules of a transcendent, god- like game designer. This melding of the spiritual with the material, it will be asserted, represents a desire to reconcile these two disparate elements in a form of ‘rationalised’ spirituality. Chapter 6 analyses how the videogame as a form of external symbolic media can facilitate the transference of monomythic values and act as an arena for the embodied practice of these values. The transfer of such practice into the world beyond the game depends upon player investment in his/her role (via his/her idealised ‘projective identity’) and the game as a ritualised performance and contest for, if not representation of, monomythic values. Chapter 7 investigates how procedural rhetoric may help to persuade players of the significance and possible utility of monomythic values, by not only involving the player in everyday moral/ethical dilemmas within the game world but also giving him/her the freedom to address these dilemmas as s/he see fit, while discouraging actions that compromise the ‘heroic’ image of the monomythic hero. This chapter will also suggest ways for CRPGs to avoid formulaic storytelling and problematic depictions of the monomythic hero, so as to better improve the CRPG’s ability to persuade players of monomythic values and hence fulfil the pedagogical and sociological functions ascribed by this thesis. The question of whether such functions should be associated with the CRPG is one, I will argue, that game designers alone can address