<p>We consider network modelling and numerical simulation of a simple CO₂ heat pump consisting of a compressor, a valve and two heat exchangers. In a first step we investigate analytical and numerical properties of the heat exchanger model. The heat exchanger model is derived from the Euler equations under the assumption that the velocity of the refridgerant flow is small compared to the local speed of sound. While the Euler equations form a hyperbolic system, the character of the new system, called The zero Mach number limit of the Euler equations, is unclear. The lack of a time derivative in the momentum equation makes the heat exchanger model by itself a PDAE system.</p><p>We analyse a frozen-coefficient linearisation of the heat exchanger model by transformation to a canonical form. The canonical form reveales that the system is equivalent to a hyperbolic equation and a parabolic block. The parabolic block is equivalent to a parabolic equation and an algebraic-differential relation, similar to the system that results when the heat equation <i>ut = uxx + f </i>is written as a first order system. We prove a stability estimate suggesting that the solution is more sensitive to perturbations, especially in time-dependent boundary conditions, than is indicated by previous results.</p><p>Furthermore, we consider semidiscretisation of the linearised heat exchanger model. In a method of lines approach using collocation at the gridpoints, we suggest that it is possible to use a simple first order difference scheme taking into account the direction of the flow and the boundary conditions. We show that using this difference scheme, the solution to the semidiscrete equations satisfies a discrete analogue to the stability estimate in the continuous case.</p><p>The results of the linear analysis is verified in numerical experiments with the nonlinear heat exchanger model.</p>

<p>Work in control rooms, or so-called Centers of coordination, places demands both on humans and technology. The people working there have to be able to make quick decisions as well as be alert during less busy times. The work has to be coordinated within the group, since the operators are much depending on each other's work. This places special demands on the technology; it should be fast, trustworthy and easy to manipulate so that the complexity of the work is reduced. This type of work has been a source of interest in the research area of Computer Supported Cooperative Work, especially so since the needs for real-time coordination is great in these settings.</p><p>SOS Alarm is a company that is responsible for managing the telephone calls made to the emergency number 112 in Sweden. They have 20 centers covering Sweden. This thesis present an overview of the SOS operators work; how they coordinate the information and tasks between them; how the technology supports that work. This study presents a fully computerized setting, compared to many other studies of centers of coordination that are not.</p><p>This ethnographic workplace study has been inspired by ethnomethodological perspectives as well as earlier field studies of work and technology use. Its main results are a description of the work practice and technology at two centers, implications for design of a new computer aided dispatch system that is currently developed at SOS Alarm and general design ideas for control rooms.</p>

Diss. (sammanfattning) Uppsala : Univ., 2007. / Härtill 5 uppsatser.

Diss. Umeå : Umeå universitet, 2006.

No description available.

This thesis concerns the approximation of optimally controlled partial differential equations for inverse problems in optimal design. Important examples of such problems are optimal material design and parameter reconstruction. In optimal material design the goal is to construct a material that meets some optimality criterion, e.g. to design a beam, with fixed weight, that is as stiff as possible. Parameter reconstrucion concerns, for example, the problem to find the interior structure of a material from surface displacement measurements resulting from applied external forces. Optimal control problems, particularly for partial differential equations, are often ill-posed and need to be regularized to obtain good approximations. We here use the theory of the corresponding Hamilton-Jacobi-Bellman equations to construct regularizations and derive error estimates for optimal design problems. The constructed Pontryagin method is a simple and general method where the first, analytical, step is to regularize the Hamiltonian. Next its Hamiltonian system is computed efficiently with the Newton method using a sparse Jacobian. An error estimate for the difference between exact and approximate objective functions is derived, depending only on the difference of the Hamiltonian and its finite dimensional regularization along the solution path and its L² projection, i.e. not on the difference of the exact and approximate solutions to the Hamiltonian systems. Another treated issue is the relevance of input data for parameter reconstruction problems, where the goal is to determine a spacially distributed coefficient of a partial differential equation from partial observations of the solution. It is here shown that the choice of input data, that generates the partial observations, affects the reconstruction, and that it is possible to formulate meaningful optimality criteria for the input data that enhances the quality of the reconstructed coefficient. In the thesis we present solutions to various applications in optimal material design and reconstruction. / Denna avhandling handlar om approximation av optimalt styrda partiella differentialekvationer för inversa problem inom optimal design. Viktiga exempel på sådana problem är optimal materialdesign och parameterskattning. Inom materialdesign är målet att konstruera ett material som uppfyller vissa optimalitetsvillkor, t.ex. att konstruera en så styv balk som möjligt under en given vikt, medan ett exempel på parameterskattning är att hitta den inre strukturen hos ett material genom att applicera ytkrafter och mäta de resulterande förskjutningarna. Problem inom optimal styrning, speciellt för styrning av partiella differentialekvationer,är ofta illa ställa och måste regulariseras för att kunna lösas numeriskt. Teorin för Hamilton-Jacobi-Bellmans ekvationer används här för att konstruera regulariseringar och ge feluppskattningar till problem inom optimaldesign. Den konstruerade Pontryaginmetoden är en enkel och generell metod där det första analytiska steget är att regularisera Hamiltonianen. I nästa steg löses det Hamiltonska systemet effektivt med Newtons metod och en gles Jacobian. Vi härleder även en feluppskattning för skillnaden mellan den exakta och den approximerade målfunktionen. Denna uppskattning beror endast på skillnaden mellan den sanna och den regulariserade, ändligt dimensionella, Hamiltonianen, båda utvärderade längst lösningsbanan och dessL²-projektion. Felet beror alltså ej på skillnaden mellan den exakta och denapproximativa lösningen till det Hamiltonska systemet. Ett annat fall som behandlas är frågan hur indata ska väljas för parameterskattningsproblem. För sådana problem är målet vanligen att bestämma en rumsligt beroende koefficient till en partiell differentialekvation, givet ofullständiga mätningar av lösningen. Här visas att valet av indata, som genererarde ofullständiga mätningarna, påverkar parameterskattningen, och att det är möjligt att formulera meningsfulla optimalitetsvillkor för indata som ökar kvaliteten på parameterskattningen. I avhandlingen presenteras lösningar för diverse tillämpningar inom optimal materialdesign och parameterskattning. / QC 20100712

No description available.

<p>This thesis focuses on the numerical and theoretical studies of gas quenching in industrial furnaces. Gas quenching is the rapid cooling of metal pieces, aiming at forcing a phase transformation of the metal structure to improve its mechanical properties. The numerical methodology has been evaluated with respect to the desired accuracy and different aspects of the flow with importance for achieving an optimized process have been investigated. Initially, attention was paid to the flow and heat transfer fields both in an empty furnace and in a furnace loaded with different charges with the objective to study the influence of the charge configuration on the flow and heat transfer uniformity. This study led to the identification of several possible improvements, which are currently being implemented by the industrial partners of this project. As earlier studies had shown the importance of flow uniformity on the quality of the heat treatment, the subsequent work focused substantially on the flow uniformity upstream of the quenching zone resulting in design recommendations for the particular type of furnace under consideration. The dependence of the performance of the coolant medium on its composition was investigated theoretically and an analysis of most important parameters was carried out. Improved knowledge of the effect of gas mixture composition on heat transfer was added to the body of knowledge already available.</p>

This thesis focuses on the numerical and theoretical studies of gas quenching in industrial furnaces. Gas quenching is the rapid cooling of metal pieces, aiming at forcing a phase transformation of the metal structure to improve its mechanical properties. The numerical methodology has been evaluated with respect to the desired accuracy and different aspects of the flow with importance for achieving an optimized process have been investigated. Initially, attention was paid to the flow and heat transfer fields both in an empty furnace and in a furnace loaded with different charges with the objective to study the influence of the charge configuration on the flow and heat transfer uniformity. This study led to the identification of several possible improvements, which are currently being implemented by the industrial partners of this project. As earlier studies had shown the importance of flow uniformity on the quality of the heat treatment, the subsequent work focused substantially on the flow uniformity upstream of the quenching zone resulting in design recommendations for the particular type of furnace under consideration. The dependence of the performance of the coolant medium on its composition was investigated theoretically and an analysis of most important parameters was carried out. Improved knowledge of the effect of gas mixture composition on heat transfer was added to the body of knowledge already available. / QC 20101019

<p>In this thesis, we present algorithms for local and global minimization of some <i>Procrustes</i> type problems. Typically, these problems are about rotating and scaling a known set of data to fit another set with applications related to determination of rigid body movements, factor analysis and multidimensional scaling. The known sets of data are usually represented as matrices, and the rotation to be determined is commonly a matrix <i>Q</i> with orthonormal columns.</p><p>The algorithms presented use Newton and Gauss-Newton search directions with optimal step lengths, which in most cases result in a fast computation of a solution.</p><p>Some of these problems are known to have several minima, e.g., the weighted orthogonal Procrustes problem (WOPP). A study on the maximal amount of minima has been done for this problem. Theoretical results and empirical observations gives strong indications that there are not more than 2ⁿ minimizers, where <i>n</i> is the number of columns in <i>Q</i>. A global optimization method to compute all 2ⁿ minima is presented.</p><p>Also considered in this thesis is a cubically convergent iteration method for solving nonlinear equations. The iteration method presented uses second order information (derivatives) when computing a search direction. Normally this is a computational heavy task, but if the second order derivatives are constant, which is the case for quadratic equations, a performance gain can be obtained. This is confirmed by a small numerical study.</p><p>Finally, regularization of ill-posed nonlinear least squares problems is considered. The quite well known L-curve for linear least squares problems is put in context for nonlinear problems.</p>