Machine -Cell Location Problems for Multiproduct Flowlines.

Jobs (parts) and machines are usually grouped into part-families and machine-cells in a flexible, cellular manufacturing system to minimize the flows of all work-in-processes (WIP). As a result of this grouping, some parts may need processing on some machines that are not in their own cells. The parts requiring machines in other cells are called \u27exceptional parts,\u27 and the corresponding machines are called \u27 bottleneck machines.\u27 Usually, there are two ways to deal with this inter-cell flow problem: using a material handling system to move the exceptional parts among the cells or duplicating the bottleneck machine(s) for the corresponding exceptional part(s). The objective of this research is to minimize the total costs of these inter-cell flows. A two-phase procedure, machine-cell location (MCL) and duplication of bottleneck machines (DBM), is presented in this research to achieve this goal. The MCL problem covers both one-dimensional layout and two-dimensional layout, especially dealing with one-dimensional equidistant (1DE), one-dimensional non-equidistant (1DNE) and two-dimensional non-equidistant (2DNE) machine-cell location problems. All versions of the MCL problem fall under the general class of quadratic assignment problem (QAP) which is NP-hard and it is difficult to solve a large problem optimally. The DBM problem, which arises as a natural extension to the MCL problem, may be classified as an integer linear programming (ILP) problem and a solution to it may provide an alternative way to reduce the total inter-cell flow costs. The 1DE problem is solved first by using a simple depth-first heuristic (SDH) which is later modified to a directional decomposition heuristic (DDH) for a better quality of solution. The directional decomposition of inter-cell flow, the core foundation of the DDH algorithm, is then extended to the one-dimensional non-equidistant (1DNE) and the two-dimensional non-equidistant (2DNE) problems. This leads to the development of the modified directional decomposition heuristic (MDDH) and the quadra-directional decomposition heuristic (QDDH), respectively. Based on the solutions to various facets of the MCL problem, a binary ILP model is proposed for solving the DBM problem optimally. Empirical tests show that heuristic DDH and its extensions, MDDH and QDDH, are more efficient than most other comparable heuristics

Multi-scale active shape description in medical imaging

Shape description in medical imaging has become an increasingly important research field in recent years. Fast and high-resolution image acquisition methods like Magnetic Resonance (MR) imaging produce very detailed cross-sectional images of the human body - shape description is then a post-processing operation which abstracts quantitative descriptions of anatomically relevant object shapes. This task is usually performed by clinicians and other experts by first segmenting the shapes of interest, and then making volumetric and other quantitative measurements. High demand on expert time and inter- and intra-observer variability impose a clinical need of automating this process. Furthermore, recent studies in clinical neurology on the correspondence between disease status and degree of shape deformations necessitate the use of more sophisticated, higher-level shape description techniques. In this work a new hierarchical tool for shape description has been developed, combining two recently developed and powerful techniques in image processing: differential invariants in scale-space, and active contour models. This tool enables quantitative and qualitative shape studies at multiple levels of image detail, exploring the extra image scale degree of freedom. Using scale-space continuity, the global object shape can be detected at a coarse level of image detail, and finer shape characteristics can be found at higher levels of detail or scales. New methods for active shape evolution and focusing have been developed for the extraction of shapes at a large set of scales using an active contour model whose energy function is regularized with respect to scale and geometric differential image invariants. The resulting set of shapes is formulated as a multiscale shape stack which is analysed and described for each scale level with a large set of shape descriptors to obtain and analyse shape changes across scales. This shape stack leads naturally to several questions in regard to variable sampling and appropriate levels of detail to investigate an image. The relationship between active contour sampling precision and scale-space is addressed. After a thorough review of modem shape description, multi-scale image processing and active contour model techniques, the novel framework for multi-scale active shape description is presented and tested on synthetic images and medical images. An interesting result is the recovery of the fractal dimension of a known fractal boundary using this framework. Medical applications addressed are grey-matter deformations occurring for patients with epilepsy, spinal cord atrophy for patients with Multiple Sclerosis, and cortical impairment for neonates. Extensions to non-linear scale-spaces, comparisons to binary curve and curvature evolution schemes as well as other hierarchical shape descriptors are discussed

Topology based global crowd control

We propose a method to determine the flow of large crowds of agents in a scene such that it is filled to its capacity with a coordinated, dynamically moving crowd. Our approach provides a focus on cooperative control across the entire crowd. This is done with a view to providing a method which animators can use to easily populate and fill a scene. We solve this global planning problem by first finding the topology of the scene using a Reeb graph, which is computed from a Harmonic field of the environment. The Maximum flow can then be calculated across this graph detailing how the agents should move through the space. This information is converted back from the topological level to the geometric using a route planner and the Harmonic field. We provide evidence of the system’s effectiveness in creating dynamic motion through comparison to a recent method. We also demonstrate how this system allows the crowd to be controlled globally with a couple of simple intuitive controls and how it can be useful for the purpose of designing buildings and providing control in team sports

National Metal Casting Research Institute final report. Volume 2, Die casting research

Four subprojects were completed: development and evaluation of die coatings, accelerated die life characterization of die materials, evaluation of fluid flow and solidification modeling programs, selection and characterization of Al-based die casting alloys, and influence of die materials and coatings on die casting quality

Evolutionary Computation Strategies applied to the UA-FLP

En la presente tesis doctoral se desarrollan dos aproximaciones distintas al problema de distribución en planta de áreas desiguales (UA-FLP). En primer lugar, se trata de incorporar el conocimiento del diseñador experto a los algoritmos clásicos de optimización, de forma que, además de buscar buenas soluciones desde el punto de vista cuantitativo, por ejemplo minimizando el flujo de materiales, se introduzca la posibilidad de que el diseñador aporte su experiencia y preferencias personales. Para facilitar la intervención humana en el proceso de búsqueda de soluciones, se ha utilizado un procedimiento de clustering, el cual permite clasificar las soluciones subyacentes en el conjunto de búsqueda, de forma que se presente al diseñador un número suficientemente representativo y, a la vez, evitándole una fatiga innecesaria. Además, en esta primera propuesta se han implementado dos técnicas de niching, denominadas Deterministic Crowding y Restricted Tournament Selection. Estas técnicas tienen la capacidad de mantener ciertas propiedades dentro de la población de soluciones, preservar múltiples nichos con soluciones cercanas a los óptimos locales, y reducir la probabilidad de quedar atrapado en ellos. De esta manera el algoritmo se enfoca simultáneamente en más de una región (nicho) en el espacio de búsqueda, lo cual es esencial para descubrir varios óptimos en una sola ejecución. Por otro lado, en la segunda aproximación al problema, se ha implementado una estrategia evolutiva paralela, muy útil para los problemas de alta complejidad en los que el tiempo de ejecución con un enfoque evolutivo secuencial es prohibitivo. La propuesta desarrollada, denominada IMGA, está basada en un algoritmo genético paralelo de grano grueso con múltiples poblaciones o islas. Este enfoque se caracteriza por evolucionar varias subpoblaciones independientemente, entre las que se intercambian individuos, haciendo posible explorar diferentes regiones del espacio de búsqueda, al mismo tiempo que se mantiene la diversidad de la población, permitiendo la obtención de buenas y diversas soluciones. Con ambas propuestas se han realizado experimentos que han arrojado resultados muy satisfactorios, encontrando buenas soluciones para un conjunto de problemas bien conocidos en la bibliografía. Estos buenos resultados han permitido la publicación de dos artículos indexados en el primer decil del ranking JCR (Journal Citation Reports).The present doctoral thesis develops two different approaches to the Unequal Area Facility Layout Problem (UA-FLP). The first approach encompasses the designer’s knowledge on classic optimization of algorithms in pursuance of good quantitative solutions (e.g. minimizing the materials flow) and also opens the possibility to include the contribution of the designer by means of his expertise and personal preferences. A clustering procedure has been used to facilitate human intervention in the process of finding solutions. This allows the underlying solutions to be classified in the search in order to present the designer with sufficiently representative solutions and, at the same time, avoiding unnecessary fatigue. In addition, two niching techniques have been implemented, called Deterministic Crowding and Restricted Tournament Selection. These techniques have the ability to maintain certain properties within the solutions space, preserve multiple niches with solutions close by local optimums, and reduce the probability of being trapped in them. In this way, the algorithm focuses simultaneously on more than one region (niche) in the search space, which is essential to discover several optimums in a single execution. The second approach to the problem comprises the implementation of a parallel evolutionary strategy. This method is useful for problems of high complexity in which the execution time using a sequential evolutionary approach is prohibitive. The proposal developed, called IMGA (Island Model Genetic Algorithm), is based on a parallel genetic algorithm of multiple-population coarse-grained. This is characterized by evolving several subpopulations independently among which individuals are exchanged. Different regions of the search space can be explored while the diversity of the population is maintained. Satisfactory and diverse solutions have been obtained as a result of this method. Experiments with both proposals have been carried out with satisfactory results, providing good solutions for a set of problems well known in the literature. These results were already published in two papers indexed in the first decile of the JCR (Journal Citation Reports) ranking

Computational fluid dynamics modelling of benzene abatement using cryogenic condensation

Eng. D. ThesisThis thesis presents a computational fluid dynamics model of aerosol nucleation and growth using a Eulerian-Lagrangian approach. The research aimed to assess the applicability of cryogenic condensation to controlling benzene emissions from an industrial process operated by the industrial research sponsors. Cryogenic condensation is an attractive option for controlling vent emissions of volatile organic compounds (VOCs). In speciality chemicals industries such as pharmaceuticals, nitrogen is often used to create an inert atmosphere in vessel headspace. Cryogenic condensation can utilise the cooling potential of existing nitrogen infrastructure, making the process energy efficient in comparison to conventional alternatives such as adsorption and thermal oxidation. However, many pollutants freeze or desublimate at the low temperatures (ca. -100°C) used in cryogenic condensation. For these high melting point VOCs, a fine particulate could form under the temperature gradients inside the condenser. Through modelling the process, the research aimed to answer two main questions: will cryogenic condensation control benzene vapour emissions down to the limits set by the environmental regulators; and will it reach this limit without generating a benzene aerosol particulate that becomes entrained in the outlet gas. The research found that the cryogenic condensation alone would not reach the strict emissions limit required by the regulation, and that particle entrainment does make a contribution to this. The model showed roughly 97% of benzene is captured (compared to 99.978% removal that would be required to meet emissions limits) with around 1% escaping as particulate. This information is useful to the industrial sponsors of the research, and other industries considering using cryogenic condensation for benzene abatement. The modelling approach used is a novel contribution to the field with wider potential applications in other areas

Visual Techniques for Geological Fieldwork Using Mobile Devices

Visual techniques in general and 3D visualisation in particular have seen considerable adoption within the last 30 years in the geosciences and geology. Techniques such as volume visualisation, for analysing subsurface processes, and photo-coloured LiDAR point-based rendering, to digitally explore rock exposures at the earth’s surface, were applied within geology as one of the first adopting branches of science. A large amount of digital, geological surface- and volume data is nowadays available to desktop-based workflows for geological applications such as hydrocarbon reservoir exploration, groundwater modelling, CO2 sequestration and, in the future, geothermal energy planning. On the other hand, the analysis and data collection during fieldwork has yet to embrace this ”digital revolution”: sedimentary logs, geological maps and stratigraphic sketches are still captured in each geologist’s individual fieldbook, and physical rocks samples are still transported to the lab for subsequent analysis. Is this still necessary, or are there extended digital means of data collection and exploration in the field ? Are modern digital interpretation techniques accurate and intuitive enough to relevantly support fieldwork in geology and other geoscience disciplines ? This dissertation aims to address these questions and, by doing so, close the technological gap between geological fieldwork and office workflows in geology. The emergence of mobile devices and their vast array of physical sensors, combined with touch-based user interfaces, high-resolution screens and digital cameras provide a possible digital platform that can be used by field geologists. Their ubiquitous availability increases the chances to adopt digital workflows in the field without additional, expensive equipment. The use of 3D data on mobile devices in the field is furthered by the availability of 3D digital outcrop models and the increasing ease of their acquisition. This dissertation assesses the prospects of adopting 3D visual techniques and mobile devices within field geology. The research of this dissertation uses previously acquired and processed digital outcrop models in the form of textured surfaces from optical remote sensing and photogrammetry. The scientific papers in this thesis present visual techniques and algorithms to map outcrop photographs in the field directly onto the surface models. Automatic mapping allows the projection of photo interpretations of stratigraphy and sedimentary facies on the 3D textured surface while providing the domain expert with simple-touse, intuitive tools for the photo interpretation itself. The developed visual approach, combining insight from all across the computer sciences dealing with visual information, merits into the mobile device Geological Registration and Interpretation Toolset (GRIT) app, which is assessed on an outcrop analogue study of the Saltwick Formation exposed at Whitby, North Yorkshire, UK. Although being applicable to a diversity of study scenarios within petroleum geology and the geosciences, the particular target application of the visual techniques is to easily provide field-based outcrop interpretations for subsequent construction of training images for multiple point statistics reservoir modelling, as envisaged within the VOM2MPS project. Despite the success and applicability of the visual approach, numerous drawbacks and probable future extensions are discussed in the thesis based on the conducted studies. Apart from elaborating on more obvious limitations originating from the use of mobile devices and their limited computing capabilities and sensor accuracies, a major contribution of this thesis is the careful analysis of conceptual drawbacks of established procedures in modelling, representing, constructing and disseminating the available surface geometry. A more mathematically-accurate geometric description of the underlying algebraic surfaces yields improvements and future applications unaddressed within the literature of geology and the computational geosciences to this date. Also, future extensions to the visual techniques proposed in this thesis allow for expanded analysis, 3D exploration and improved geological subsurface modelling in general.publishedVersio