Numerical simulation of cracking using embedded surfaces in a three dimensional constitutive model for concrete

This thesis presents three new three-dimensional constitutive models for cementitious materials. All three models use embedded damage planes and adopt the theory of contact mechanics to describe the characteristic behaviour of cracks formed in concrete and other cementitious materials. The first of these is a smooth frictional contact model which incorporates a simplified Mohr-Coulomb yield surface to capture plastic slip planes in concrete. The aim of the model is to accurately represent the behaviour of smooth construction joints in large concrete structures. The second proposed model is the dual-surface contact model. The model employs two contact surfaces, each of which nominally represents a different component of concrete composite, i.e. coarse aggregate particles and mortar. The third model is the 'embedded planes with local plasticity contact' model (EPLPC). The model adopts a yield surface, which is similar to the damage surface in strain space, to capture plastic embedment on crack surfaces. This model, as with the dual-surface contact model, is developed to simulate crack opening-closing, as well as the behaviour of aggregate interlock. The models are integrated with a hardening/softening frictional plasticity component that uses a smoothed triaxial plastic yield surface developed from that used by Lubliner et al. (1989). Each of the proposed models is implemented with a consistent tangent stiffness operator and return mapping algorithm, similar to that of the Closest Point Projection algorithm. The models are coded in Fortran77 and implemented in a constitutive driver program, and also a finite element software package LUSAS. The models are assessed using a series of stress/strain paths at the constitutive level, and also validated against a range of experimental data. These include data from uniaxial and multiaxial compressive tests, uniaxial tensile tests with and without unloading-reloading cycles, and also tests in which shear load is applied on open cracks

MIGRATION, EDUCATION & ECONOMIC DEVELOPMENT

Migration and education have long been issues of major interest in regional science, economics and geography. The interest is quite understandable because they can have substantial consequences for society, individuals, regions and families. Exactly how migration and education affect economic development and inequality (positively and negatively) is not fully resolved. Recognising this, we look at the positive and normative roles that migration and education can play in determining economic prosperity. To serve this purpose, the thesis builds frameworks using dynamic general equilibrium theory to provide some analytical solutions and applies these empirically with panel data to determine the impacts of migration in a market economy. Overall, empirically we find that disparities among individuals and regions still exist despite the migration process. However, migration and education are both susceptible to market failure due to fixed costs and liquidity constraints. The thesis moves on to examine the role and incentives for facilitating education and migration in non-market environments. In particular, we examine these processes within intergenerational family settings. Intra-family intergenerational transfers motivated by altruism are studied but we show that public intervention is also generally necessary to achieve Pareto optimality. Finally we consider the empirical evidence on intergenerational mobility in education and occupation for migrants

Human factors aspects of control room design: Guidelines and annotated bibliography

A human factors analysis of the workstation design for the Earth Radiation Budget Satellite mission operation room is discussed. The relevance of anthropometry, design rules, environmental design goals, and the social-psychological environment are discussed

In-plane shear behaviour of composite walling with profiled steel sheeting

This thesis introduces a novel form of double skin composite walling with profiled steel sheeting and an infill of concrete. This is a logical extension of research on composite slabs with profiled steel sheeting currently known as popular "Fastrack" construction. The composite walling is thought to be specially applicable as shear or core walls in steel frame buildings. The profiled steel sheeting will act as a temporary shear bracing to stabilise the frame against wind and destablising forces during construction and also act as a form work for infill of concrete. In the service stage, they will act as a reinforcement to carry axial, lateral and in-plane forces. This thesis investigates the behaviour of composite walls under in-plane shear so that they can be used as shear elements in buildings. The investigation includes analytical, numerical and small scale model tests. Design recommendations for the composite walls are the final aim of the research. The investigation is based on the concept that the in-plane shear strength and stiffness of the composite wall will be derived from the individual sheeting, concrete core and from the interaction between the two. Based on above, individual behaviour of the sheeting and concrete core was studied before considering the composite wall as a whole. A shear rig has been designed and fabricated to carry out the model tests of approximately 1/6 th scale using very thin sheeting (profiled in house) and microconcrete. Analytical equations for the shear strength and stiffness of the sheeting, profiled concrete and composite wall are derived. These equations are validated by model tests and finite element analysis. Finite element analysis included modelling of composite walling with full composite action and some parametric studies using interface elements. The stiffness of the composite wall is found to be greater than the individual summation of stiffness of the sheeting and concrete core. The profiled steel sheeting will provide sufficient shear bracing to the frame during construction. The composite wall is capable of taking high in-plane shear loads which is greater than the summation of individual capacity of the sheeting and concrete and confirms its potential to be used as shear elements in buildings. Simple equations for the calculation of shear strength and stiffness of the composite wall are derived which can safely be used for design purposes. Further research directions are also outlined.This thesis introduces a novel form of double skin composite walling with profiled steel sheeting and an infill of concrete. This is a logical extension of research on composite slabs with profiled steel sheeting currently known as popular "Fastrack" construction. The composite walling is thought to be specially applicable as shear or core walls in steel frame buildings. The profiled steel sheeting will act as a temporary shear bracing to stabilise the frame against wind and destablising forces during construction and also act as a form work for infill of concrete. In the service stage, they will act as a reinforcement to carry axial, lateral and in-plane forces. This thesis investigates the behaviour of composite walls under in-plane shear so that they can be used as shear elements in buildings. The investigation includes analytical, numerical and small scale model tests. Design recommendations for the composite walls are the final aim of the research. The investigation is based on the concept that the in-plane shear strength and stiffness of the composite wall will be derived from the individual sheeting, concrete core and from the interaction between the two. Based on above, individual behaviour of the sheeting and concrete core was studied before considering the composite wall as a whole. A shear rig has been designed and fabricated to carry out the model tests of approximately 1/6 th scale using very thin sheeting (profiled in house) and microconcrete. Analytical equations for the shear strength and stiffness of the sheeting, profiled concrete and composite wall are derived. These equations are validated by model tests and finite element analysis. Finite element analysis included modelling of composite walling with full composite action and some parametric studies using interface elements. The stiffness of the composite wall is found to be greater than the individual summation of stiffness of the sheeting and concrete core. The profiled steel sheeting will provide sufficient shear bracing to the frame during construction. The composite wall is capable of taking high in-plane shear loads which is greater than the summation of individual capacity of the sheeting and concrete and confirms its potential to be used as shear elements in buildings. Simple equations for the calculation of shear strength and stiffness of the composite wall are derived which can safely be used for design purposes. Further research directions are also outlined

Model-based development of thermoelectric energy harvesting systems

The motivation of this work is the study of thermoelectric energy harvesting systems (EHS). The main research focus in the scientific community is on the development of new, more efficient, cheaper and environmentally friendly thermoelectric materials. But besides the material research, the complete development, build-up and optimization of thermoelectric EHSs are also necessary points to be studied. For this reason, this work deals with the model-based development of thermoelectric EHSs. The first objective is the modeling and simulation as well as design and controlling of these systems. For this purpose, a library should be developed and published to provide end-users with an easy tool to configure and build-up these systems in a simulation environment (Modelica/Dymola). The second objective is the elaboration and presentation of a development process to support the setup of a thermoelectric EHS. Finally, to show the usefulness of the developed scheme and library, three real application examples will be presented. These are an EHS at a radiator to supply an electronic thermostat valve in an office, the green barbecue and an EHS at a heating mockup of an oil-fired heater.Diese Arbeit befasst sich mit thermoelektrischen Energy Harvesting Systemen (EHS). Der aktuelle Forschungsschwerpunkt in der Wissenschaft liegt vor allem in der Entwicklung neuer thermoelektrischer Materialien. Diese sollen effizienter, kostengünstiger und umweltfreundlicher sein. Neben der Materialforschung sind jedoch auch die komplette Entwicklung, der Aufbau sowie die Optimierung der thermoelektrischen Gesamtsysteme von hoher Bedeutung. Aus diesem Grund beschäftigt sich diese Arbeit mit der modellbasierten Entwicklung thermoelektrischer EHS. Eine erste Zielsetzung dabei ist die Modellierung und Simulation sowie Auslegung und Regelung solcher Systeme. Zu diesem Zweck soll eine Modellbibliothek entwickelt und veröffentlicht werden. Diese soll einem Endnutzer als einfaches Werkzeug dienen um die Systeme in einer Simulationsumgebung (hier: Modelica/Dymola) zusammenzusetzen und konfigurieren zu können. Die zweite Zielsetzung besteht in der Ausarbeitung und Präsentation eines Entwicklungsprozesses zur Unterstützung des Aufbaus eines thermoelektrischen EHS. Zur Demonstration des entworfenen Entwicklungsprozesses sowie der entwickelten Modellbibliothek, werden abschließend drei reale Anwendungsbeispiele vorgestellt. Dabei handelt es sich um ein EHS, welches an einem Heizkörper in einem Büro angebracht wurde um ein elektronisches Thermostatventil zu versorgen, den „grünen Schwenker“ sowie ein EHS an einem Heizungsnachbau einer ölbefeuerten Heizungsanlage

Generating CT-TH-PM surfaces using EPT-based aggregate modelling

Cycle Time-Throughput-Product mix (CT-TH-PM) surfaces give the mean cycle time as a function of throughput and product mix for manufacturing workstations. To generate the CT-TH-PM surface, detailed simulation models may be used. However, detailed models require much development time, and it may not be possible to estimate all model parameters. Instead, we proposean aggregate simulation model to generate a workstations CT-TH-PM surface. In the aggregate model, the various workstation details are lumped into an Effective Process Time (EPT) distribution. The EPT distribution in the aggregate simulation modelis estimated from arrival and departure data measured at the workstation in operation. We validate the proposed method using a simulation example representing a semiconductor workstation. We find that the method can accurately predict the mean cycletime in a region around the workstations operational product mix. We also present an industry test case; the applicability of the method is demonstrated for a workstation in the Crolles2 wafer factory

Modelling shallow landslides: the importance of hydrological controls and lateral reinforcement

Shallow landslides are important as geomorphic agents of erosion, sources of catchment sediment and potential hazards to life and infrastructure. The importance of these mass movements is difficult to define using solely field- based approaches because these are often too limited in both duration and resolution to fully determine the magnitude and frequency of these processes. Modelling is a powerful alternative tool for providing insight into underlying processes governing shallow landslides and for testing new hypotheses regarding environmental and land-use change impacts. The explanatory power of models is a function of their process representation and predictive ability. Current models suitable for catchment-scale application provide valuable probabilistic information on failure, but not detailed deterministic predictions. Using the English Lake District as a study area, this thesis addresses three issues necessary to provide the process-basis of these probabilistic analyses. First, poorly constrained or spatially variable input parameters such as soil depth, root reinforcement or material properties are often used to explain the locations of failure within a larger area that has a high, sometimes equal, probability of failure. The thesis develops rigorous new methods to quantify and minimise error in these parameters, representing them as distributions to capture both their natural variability and the error in their measurement. Results suggest that lateral root reinforcement even for grasses and shrubs may provide important additional strength (as much as 6 kPa) in the top 0.5 m of the soil. Second, infinite slope stability analysis neglects important additional lateral friction and root reinforcement effects at the margins of an unstable block. More sophisticated three-dimensional stability analyses can represent this process but are limited in their applicability by computational and data resolution requirements. This thesis derives from first principles a set of analytical governing equations for three-dimensional analysis; tests these against benchmark geotechnical methods; and applies them to establish key landslide scaling relationships. Third, shallow landslides in the UK are almost exclusively hydrologically triggered, resulting from local high pore water pressures. In line with the current paradigm existing stability models assume that the topography plays a dominant role in defining the spatial pattern of soil moisture and therefore pore water pressures in the landscape. This hypothesis is tested: first at the hillslope scale (10(^1) km(^2)) with a network of ֊100 wells; then the catchment scale (10(^2) km(^2)) using high resolution orthorectified aerial photographs to identify vegetation indicative of wet habitats and applying these as a proxy for soil moisture. These studies indicate that, for the case-study, wet areas are controlled at the landscape scale by a set of broad topographic limits in terms of slope and contributing area. Within these there is considerable scatter, resulting from the interplay of local factors such as: bedrock topography, preferential flow and soil stratification. Lateral root cohesion represents an important source of additional strength which can be included within analytical stability equations to create a threshold dependence on landslide size. Patterns of instability will then depend on the spatial pattern of other influencing factors (e.g. soil strength and pore pressure). At present the limits to available data and our understanding of hillslope hydrology constrain our ability to predict slope instability in environments like the Lake District. Future research might usefully identify landscape scale controls on this predictability