An Improved Arcflow Model for the Skiving Stock Problem

Because of the sharp development of (commercial) MILP software and hardware components, pseudo-polynomial formulations have been established as a viable tool for solving cutting and packing problems in recent years. Constituting a natural (but independent) counterpart of the well-known cutting stock problem, the one-dimensional skiving stock problem (SSP) asks for the maximal number of large objects (specified by some threshold length) that can be obtained by recomposing a given inventory of smaller items. In this paper, we introduce a new arcflow formulation for the SSP applying the idea of reflected arcs. In particular, this new model is shown to possess significantly fewer variables as well as a better numerical performance compared to the standard arcflow formulation

Improved flow-based formulations for the skiving stock problem

Thanks to the rapidly advancing development of (commercial) MILP software and hardware components, pseudo-polynomial formulations have been established as a powerful tool for solving cutting and packing problems in recent years. In this paper, we focus on the one-dimensional skiving stock problem (SSP), where a given inventory of small items has to be recomposed to obtain a maximum number of larger objects, each satisfying a minimum threshold length. In the literature, different modeling approaches for the SSP have been proposed, and the standard flow-based formulation has turned out to lead to the best trade-off between efficiency and solution time. However, especially for instances of practically meaningful sizes, the resulting models involve very large numbers of variables and constraints, so that appropriate reduction techniques are required to decrease the numerical efforts. For that reason, this paper introduces two improved flow-based formulations for the skiving stock problem that are able to cope with much larger problem sizes. By means of extensive experiments, these new models are shown to possess significantly fewer variables as well as an average better computational performance compared to the standard arcflow formulation

Considering stakeholders’ preferences for scheduling slots in capacity constrained airports

Airport slot scheduling has attracted the attention of researchers as a capacity management tool at congested airports. Recent research work has employed multi-objective approaches for scheduling slots at coordinated airports. However, the central question on how to select a commonly accepted airport schedule remains. The various participating stakeholders may have multiple and sometimes conflicting objectives stemming from their decision-making needs. This complex decision environment renders the identification of a commonly accepted solution rather difficult. In this presentation, we propose a multi-criteria decision-making technique that incorporates the priorities and preferences of the stakeholders in order to determine the best compromise solution

Meso-scale FDM material layout design strategies under manufacturability constraints and fracture conditions

In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available software, were developed and refined to support the design of MPDSMs under fracture conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.U of I OnlyAuthor's request

Tarmac cowboys : an ethnographic study of the cultural world of boy racers

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Builders: The social organisation of a construction site.

This thesis is based on an ethnographic case study of a London building site. The social organisation of building work and building workers was framed by the city, and cross-cut by class, race and gender, the structures and processes of which are explored throughout. The fieldwork site was characterised by racial divides between subcontracted trade groups, which were organised around informal networks within ethnic communities. Those communities, in their turn, were bounded by patterns of gift-exchange, reciprocity and ensuing loyalties. Networked contacts, which were predominately ascribed by social, ethnic and regional origins, formed an aspect of the perpetuation of race and class structures. Strong notions of trust and loyalty fostered illegitimate activities because information concerning rule-breaking was kept within the communities and went undetected by agencies representing the formal law. Informal networks were also contrived and engineered by entrepreneurial subcontractors whose relationships with building contractors and consultants were characterised by gift-giving. This process shielded competition from rivals and closed down the competitiveness of the construction market. 'Embedded' economic relations excluded recent migrant groups and their subcontracted representatives by blocking access to jobs and contracts, despite the groups' ability to offer cheaper and harder-working labour. Contractual arrangements were informal and sometimes illicit, and this erected barriers to legal and regulatory power. Coupled with short-term and ephemeral working practices, a social order partly supported by the threat of violence was established. The masculinity expressed by builders was, in part, a consequence of this display of violence. The building industry was virtually a 'non-modern ' organisation whose social relations were marked by network morality, nepotism, reciprocity, gift relations and the threat of violence. Yet, violence underpinned forms of social power, which manufactured the imbalance of false reciprocities

Music therapy: what is it for whom? An ethnography of music therapy in a community mental health resource centre

Music therapy is widely portrayed either as a paramedical practice within which music is a technology applied as a form of treatment or as a form of psychotherapy within which the music plays a primarily symbolic role or acts as a lead in to verbal consideration of the patient’s presenting issues. Music therapy research currently focuses predominantly on demonstrating “evidence of effectiveness” in terms of symptomatic outcome, thus preserving a focus on the individual congruent with the medical model. In contrast, this thesis seeks to examine ethnographically the ways in which music therapy gets accomplished as a situated social practice within a community mental health resource centre in a UK urban area. Drawing both on the observations and experiences of the researcher (a music therapist already working within this setting) and on formal and informal interviews with the centre’s members and staff, it seeks to identify ways in which music therapy gets done and value ascribed to it. Observations are compared with the “norms” portrayed by dominant professional discourse, and reasons for discrepancies considered. Particular attention is paid to self-awareness, intimacy and conviviality as facets of what music therapy has to offer in such a setting, and to social capital theory and Goffman’s dramaturgical approach as broader conceptual frameworks for such affordances. Consideration is also given to the “fit” between the affordances of music itself, and the “craft” required of diverse actors in order that music therapy can be considered to offer an ecology which promotes health and well-being. Finally, the findings are re-addressed towards music therapy itself via the lens of what it means to be “clinical” in order that a sociological “craft” perspective maybe brought to bear within the discipline