11,814 research outputs found

    Spatial adaptive settlement systems in archaeology. Modelling long-term settlement formation from spatial micro interactions

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    Despite research history spanning more than a century, settlement patterns still hold a promise to contribute to the theories of large-scale processes in human history. Mostly they have been presented as passive imprints of past human activities and spatial interactions they shape have not been studied as the driving force of historical processes. While archaeological knowledge has been used to construct geographical theories of evolution of settlement there still exist gaps in this knowledge. Currently no theoretical framework has been adopted to explore them as spatial systems emerging from micro-choices of small population units. The goal of this thesis is to propose a conceptual model of adaptive settlement systems based on complex adaptive systems framework. The model frames settlement system formation processes as an adaptive system containing spatial features, information flows, decision making population units (agents) and forming cross scale feedback loops between location choices of individuals and space modified by their aggregated choices. The goal of the model is to find new ways of interpretation of archaeological locational data as well as closer theoretical integration of micro-level choices and meso-level settlement structures. The thesis is divided into five chapters, the first chapter is dedicated to conceptualisation of the general model based on existing literature and shows that settlement systems are inherently complex adaptive systems and therefore require tools of complexity science for causal explanations. The following chapters explore both empirical and theoretical simulated settlement patterns based dedicated to studying selected information flows and feedbacks in the context of the whole system. Second and third chapters explore the case study of the Stone Age settlement in Estonia comparing residential location choice principles of different periods. In chapter 2 the relation between environmental conditions and residential choice is explored statistically. The results confirm that the relation is significant but varies between different archaeological phenomena. In the third chapter hunter-fisher-gatherer and early agrarian Corded Ware settlement systems were compared spatially using inductive models. The results indicated a large difference in their perception of landscape regarding suitability for habitation. It led to conclusions that early agrarian land use significantly extended land use potential and provided a competitive spatial benefit. In addition to spatial differences, model performance was compared and the difference was discussed in the context of proposed adaptive settlement system model. Last two chapters present theoretical agent-based simulation experiments intended to study effects discussed in relation to environmental model performance and environmental determinism in general. In the fourth chapter the central place foragingmodel was embedded in the proposed model and resource depletion, as an environmental modification mechanism, was explored. The study excluded the possibility that mobility itself would lead to modelling effects discussed in the previous chapter. The purpose of the last chapter is the disentanglement of the complex relations between social versus human-environment interactions. The study exposed non-linear spatial effects expected population density can have on the system and the general robustness of environmental inductive models in archaeology to randomness and social effect. The model indicates that social interactions between individuals lead to formation of a group agency which is determined by the environment even if individual cognitions consider the environment insignificant. It also indicates that spatial configuration of the environment has a certain influence towards population clustering therefore providing a potential pathway to population aggregation. Those empirical and theoretical results showed the new insights provided by the complex adaptive systems framework. Some of the results, including the explanation of empirical results, required the conceptual model to provide a framework of interpretation

    Revealing the co-action of viscous and multistability hysteresis in an adhesive, nominally flat punch: A combined numerical and experimental study

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    Viscoelasticity is well known to cause significant hysteresis of crack closure and opening when an elastomer is brought in and out of contact with a flat, rigid, adhesive counterface. A separate origin of adhesive hysteresis is small-scale, elastic multistability. Here, we study a system in which both mechanisms act concurrently. Specifically, we compare the simulated and experimentally measured time evolution of the interfacial force and the real contact area between a soft elastomer and a rigid, flat punch, to which small-scale, single-sinusoidal roughness is added. To this end, we further the Green's function molecular dynamics method and extend recently developed imaging techniques to elucidate the rate- and preload-dependence of the pull-off process. Our results reveal that hysteresis is much enhanced when the saddle points of the topography come into contact, which, however, is impeded by viscoelastic forces and may require sufficiently large preloads. A similar coaction of viscous- and multistability effects is expected to occur in macroscopic polymer contacts and to be relevant, e.g., for pressure-sensitive adhesives and modern adhesive gripping devices.Comment: 24 pages, 12 figures. Published in the Journal of the Mechanics and Physics of Solids. Conceptualization: All authors. Writing original draft: CM, MHM, MS. Experimental methodology and investigation: MS, supervision experiments: RH+EA. Numerical methodology: CM, MHM, simulations and data analysis: CM, supervision simulations: MH

    Study of the behavior of a thermoplastic injection mold and prediction of fatigue failure with numerical simulation

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    Tese de doutoramento em Engenharia MecânicaO objetivo deste trabalho é a criação de uma metodologia de análise da resistência à fadiga de moldes de injeção de termoplásticos. Uma metodologia capaz de satisfazer o mercado atual que exige a diminuição do tempo de entrega e custos de moldes de injeção, sem comprometer a sua fiabilidade. Para o desenvolvimento desta metodologia, foram utilizados modelos digitais. Com estes modelos é possível executar-se várias iterações sem os custos de um modelo físico. Além do menor custo dos modelos digitais, também é possível compreender o comportamento de cada molde no decorrer da fase de projeto. Com o aumento da complexidade dos componentes injetados, o estudo da resistência à fadiga tende a ser cada vez mais importante. Neste trabalho serão apresentados cuidados a ter na preparação dos modelos digitais, de forma a obter-se resultados fiáveis. No desenvolvimento desta metodologia, usaram-se dois softwares de simulação numérica para gerar os modelos digitais. Um deles dedica-se ao estudo reológico de peças termoplásticas e outro ao comportamento estrutural dos moldes de injeção. A execução de simulações numéricas requer uma boa caracterização dos materiais usados. No caso dos termoplásticos, os fabricantes têm uma grande base de dados com a informação necessária para as simulações numéricas. No entanto, para as simulações estruturais, os fabricantes tendem apenas a fornecer os dados das curvas monotónicas, os quais não fornecem qualquer informação sobre o comportamento à fadiga. Portanto, neste trabalho foram estudados modelos empíricos que se adaptam aos aços usados em moldes de injeção, a partir dos quais é possível gerar as curvas S-N e e-N. De modo a avaliar qual o modelo empírico que se adaptaria melhor a esta área, foram realizados ensaios experimentais com provetes feitos em EN 1.2311. A partir destes ensaios, escolheu-se o modelo empírico mais conservador. Com base no modelo empírico escolhido, foi desenvolvida uma aplicação capaz de gerar as curvas S-N e e-N, a partir das informações fornecidas pela aciaria. Além da caracterização dos materiais, também é importante que as condições de carregamento do modelo numérico estrutural sejam o mais aproximadas possível do que irá ocorrer no modelo físico. Como as cargas deste modelo numérico podem ser previstas a partir do modelo numérico reológico, a criação de uma ponte entre estes dois modelos numéricos é imprescindível. Logo, neste trabalho foi construída uma aplicação capaz de converter os dados gerados pelo software comercial Moldflow em ficheiros capazes de serem lidos por softwares comerciais de simulação numérica estrutural. Usando esta aplicação para a conversão dos dados, foram realizadas simulações e comparadas com os respetivos modelos físicos. Verificou-se que é possível replicar o comportamento do molde em modelos digitais. No entanto, os modelos digitais dos moldes de injeção estudados tenderam a apresentar resultados conservadores quando comparados com os modelos físicos. Por fim, foi desenvolvida uma aplicação capaz de usar dados calculados a partir de softwares comerciais de cálculo numérico estrutural para a determinação da resistência dos moldes à fadiga. Aqui foi tido em conta o modelo para geração das curvas de fadiga dos materiais validado. Os modelos de cálculo à fadiga na aplicação baseiam-se na regra de Palmgren – Miner para a determinação dos ciclos até à nucleação da fissura. O cálculo das tensões alternadas foi realizado a partir de dois métodos, o critério da tensão de corte octaédrica e o método de Sines. Para testar a aplicação foram escolhidos cinco moldes que apresentaram falhas por fadiga. Em seguida, foi aplicada a metodologia proposta neste trabalho para a determinação da resistência dos mesmos à fadiga. A partir da aplicação desta metodologia e das ferramentas desenvolvidas para o seu emprego, foi possível verificar que esta é capaz de prever as zonas onde ocorreram as falhas, bem como outras com probabilidade de nucleação de fissuras. Portanto, no decorrer deste trabalho foi possível criar uma metodologia e ferramentas de apoio para o cálculo de moldes à fadiga. Assim, projetistas de moldes podem ter uma boa perspetiva da resistência à fadiga de moldes de injeção ainda em projeto, tendo por base métodos científicos.The objective of this work is to create a methodology to analyze the fatigue resistance of thermoplastic injection molds. A methodology capable of satisfying the current market that demands a decrease in the delivery time and costs of injection molds, without compromising their reliability. To develop this methodology, digital models were used. With these models it is possible to execute several iterations without the costs of a physical model. Besides the lower cost of digital models, it is also possible to understand the behavior of each mold during the design phase. With the increasing complexity of injected components, the study of fatigue resistance tends to be more and more important. In this work, care will be presented in the preparation of the digital models, in order to obtain reliable results. In the development of this methodology, two numerical simulation software’s were used to generate the digital models. One of them is dedicated to the rheological study of thermoplastic parts and the other to the structural behavior of injection molds. The execution of numerical simulations requires a good characterization of the materials used. In the case of thermoplastics, manufacturers have a large database with the information needed for numerical simulations. However, for structural simulations, manufacturers tend to provide only monotonic curve data, which do not provide any information about fatigue behavior. Therefore, in this work, empirical models that fit the steels used in injection molds were studied, from which it is possible to generate the S-N and e-N curves. In order to evaluate which empirical model would best fit this area, experimental tests were performed with specimens made in EN 1.2311. From these tests, the most conservative empirical model was chosen. Based on the chosen empirical model, an application capable of generating the S-N and e-N curves from the information provided by the steel mill was developed. Besides the characterization of the materials, it is also important that the loading conditions of the numerical structural model are as close as possible to what will occur in the physical model. Since the loads of this numerical model can be predicted from the rheological numerical model, the creation of a bridge between these two numerical models is essential. Therefore, in this work was built an application capable of converting the data generated by the commercial software Moldflow into files capable of being read by commercial structural numerical simulation software. Using this application for data conversion, simulations were performed and compared with the respective physical models. It was found that it is possible to replicate the mold behavior in digital models. However, the digital models of the injection molds studied tended to present conservative results when compared to the physical models. Finally, an application capable of using data calculated from commercial numerical structural calculation software was developed for determining the fatigue resistance of molds. Here the validated model for generating the fatigue curves of the materials was taken into account. The fatigue calculation models in the application are based on the Palmgren - Miner rule for the determination of the cycles until crack nucleation. The alternating stresses calculation was performed from two methods, the octahedral shear stress criterion and the Sines method. To test the application, five molds that presented fatigue failures were chosen. Then, the methodology proposed in this work was applied to determine their fatigue resistance. From the application of this methodology and the tools developed for its use, it was possible to verify that it is able to predict the areas where the failures occurred, as well as others with a probability of crack nucleation. Therefore, during this work it was possible to create a methodology and support tools for the calculation of fatigue molds. Thus, mold designers can have a good perspective of the fatigue resistance of injection molds still in project, based on scientific methods

    Outdoor Insulation and Gas Insulated Switchgears

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    This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

    Wind-assisted ship propulsion of a series 60 ship using a static kite sail

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    Following the International Maritime Organization’s goal to reduce greenhouse gas emissions, the interest in the application of wind-assisted ship propulsion (WASP) in maritime transportation is on the rise. Although a variety of WASP systems exist, the application in maritime shipping is still limited, especially in the case of kite sails. This paper presents a numerical model to carry out a theoretical assessment of the influence of the kite planform area and wind speed on the aerodynamic performance of a kite sail providing propulsive assistance to a 75 m long ship having a Series 60 hull. A static kite sail is assumed, on which a tail wind generates a thrust force to pull the vessel via a tether. While the mass of the kite is neglected, that of the tether is accounted for. A model is implemented for the tensioned tether having a catenary profile. The results generally show a positive correlation between the aerodynamic forces and the kite parameters. As expected, the output parameter values corresponding to the optimal angle of attack for a range of vessel speeds are also found to increase with an increasing relative wind speed. It is concluded that a static 320 m2 kite sail would be sufficient to meet the entire propulsion requirements of the vessel under consideration under appropriate wind conditions.peer-reviewe

    Computational and Experimental Investigation of Conventional and Cryogenic Cooling in Milling Operations

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    In machining, high thermo-mechanical loads which limit tool life and efficiency are often managed using coolants. Appropriate coolant selection and well targeted application can transport significant thermal loads away from the cutting region, along with providing lubrication and aiding in chip evacuation. In this work, numerical and experimental studies of coolant applications contribute to both increasing fundamental understanding of coolant behaviours and supporting the design of improved cutting tools. A multiphase conjugate heat transfer computational fluid dynamics (CFD) model is developed in OpenFOAM to study both the coolant coverage and tool temperatures during the application of an oil-water emulsion coolant in milling processes via through-tool channels. Utilising this model to investigate a standard tool design has shown the coolant jet is targeted near to the cutting edge, with coolant spreading out to cover the tool and workpiece surfaces to provide good coverage along the cutting edge. To support the development of improved tool designs, the CFD model has been further utilised in an exploration of the coolant channel design space and optimisation study. As well as providing new tool designs with minimised tool temperatures and maximised coolant coverage in this study of the design space, key physical features such as a shift in coolant spreading behaviour and the presence of designs with significant levels of splashing have been identified for the first time. Cryogenic coolants provide a cleaner alternative to oil-water emulsion coolants in cutting operations. Liquid CO2 is one such coolant which has shown promise in experimental machining tests. To build towards the development of a CO2 CFD model which can support innovation of tool designs to maximise the benefits of this new coolant, fundamental experimental and modelling work is presented in this thesis. An experimental rig design has been developed to analyse heat transfer when using CO2 coolants in a simplified setting and this has been used to successfully validate a CFD model capturing the conjugate heat transfer when using liquid CO2 coolant

    Coupled point neutron kinetics and thermal-hydraulics models of transient nuclear criticality excursions in wetted fissile uranium dioxide (UO2) powders

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    This thesis describes a phenomenologically based mathematical and computational methodology for the simulation of a postulated transient nuclear criticality excursion initiated by the incursion of water, from a fire-sprinkler system, into a bed of dry UO2 powder. These potentially hazardous multi-phase dispersed particulate systems may form as a result of a fire or explosion in a nuclear fuel fabrication facility. The models proposed in this thesis aim to support nuclear criticality safety analysis and assessment. In addition, the development of these models aims to support emergency planning and preparedness. The point neutron kinetics equations are coupled to phenomenological models of water infiltration, sedimentation, fluidisation, nuclear thermal hydraulics, radiolysis and boiling, through the use of multivariate reactivity feedback components. The spatial and temporal solution of this set of equations enables the modelling of postulated transient nuclear criticality excursions in highly dispersed three-phase particulate systems of UO2 powder. The results indicate that there is the potential for large positive reactivities to be added to a UO2 powder system as pores become filled with water. Generally, thermal expansion and Doppler broadening are insufficient to control the transient, leading to significant radiolysis and boiling on the surface of the UO2 powder particles. Radiolytic gas and steam bubble induced fluidisation and sedimentation significantly alters the characteristics of a transient nuclear criticality excursion and should be carefully considered. Research has also been undertaken examining transient nuclear criticality excursions in weak intrinsic neutron source UO2 powder systems by solving the forward probability balance equation and using a Gamma probability distribution function to estimate mean wait-time probability distributions. Significant variations in the potential initial peak power are predicted for highly enriched, wetted, UO2 powders as a function of the stochastic behaviour associated with criticality excursions in low neutron population systems.Open Acces

    Applications of machine learning approaches in aerodynamic aspects of axial flow compressors: A review

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    A compressor is one of the key components of a gas turbine engine and its performance and characteristics significantly affect the overall performance of the engine. Axial flow compressors are one of the most conventional types of compressors and are widely used in turbine engines for large-scale power generation. Intelligent techniques are useful for numerical simulation, characterization of axial compressors, and predicting their performance. The present work reviews studies applying different intelligent methods for performance forecasting and modeling different aerodynamic aspects of axial compressors. Corresponding to the outcomes of the considered research works, it can be expressed that by using these methods, axial compressors can be characterized properly with acceptable exactness. In addition, these techniques are useful for performance prediction of the compressors. The accuracy and performance of these methods is impacted by several elements, specifically the employed method and applied input variables. Finally, some suggestions are made for future studies in the field
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