Simulering av olika underhållsstrategier inom processindustri

Syftet med detta examensarbete är att utvärdera om simulering av flöden på en emballeringsavdelning kan vara till hjälp för att kunna planera in stopp av packmaskiner så att förebyggande underhåll kan utföras. Med hjälp av simulering har kölängder, kötider och beläggningsgrader hos emballeringsavdelningen kunnat predikteras. Genom att skapa olika hypotesgrundade scenarion i simuleringsmodellen har ett antal resultat genererats.Resultaten av simuleringarna har gett värdefull information till underhållsavdelningens planerare. Informationen bör kunna vara ett viktigt beslutsunderlag för att kunna avgöra vid vilka tillfällen som de planerade stoppen kommer att ge upphov till minst störning av driften. Arbetet har visat att simulering av flöden är ett bra hjälpmedel för att kunna planera in stopp för förebyggande underhåll.För att kunna uppfylla syftet har en simuleringsmodell skapats över emballeringsavdelningen. Genom studier av processer och genom informationshämtning från kunnig personal har en användbar modell kunnat skapas. Även studier av underhållsteorier och simuleringslitteratur har varit till hjälp för att kunna uppfylla syftet med detta examensarbete.De utförda analyserna bygger till stor del på rekommendationer hämtade från den simuleringslitteratur som studerats men även på tips och stöd från författarnas handledare som har lång erfarenhet inom området.

Conceptual and statistical modelling of environmental effects in population dynamics

Population dynamics are generally viewed as the result of intrinsic (purely density dependent) and extrinsic (environmental) processes. Both components, and potential interactions between those two, have to be modelled in order to understand and predict dynamics of natural populations; a topic that is of great importance in population management and conservation. This thesis focuses on modelling environmental effects in population dynamics and how effects of potentially relevant environmental variables can be statistically identified and quantified from time series data. Chapter I presents some useful models of multiplicative environmental effects for unstructured density dependent populations. The presented models can be written as standard multiple regression models that are easy to fit to data. Chapters II IV constitute empirical studies that statistically model environmental effects on population dynamics of several migratory bird species with different life history characteristics and migration strategies. In Chapter II, spruce cone crops are found to have a strong positive effect on the population growth of the great spotted woodpecker (Dendrocopos major), while cone crops of pine another important food resource for the species do not effectively explain population growth. The study compares rate- and ratio-dependent effects of cone availability, using state-space models that distinguish between process and observation error in the time series data. Chapter III shows how drought, in combination with settling behaviour during migration, produces asymmetric spatially synchronous patterns of population dynamics in North American ducks (genus Anas). Chapter IV investigates the dynamics of a Finnish population of skylark (Alauda arvensis), and point out effects of rainfall and habitat quality on population growth. Because the skylark time series and some of the environmental variables included show strong positive autocorrelation, the statistical significances are calculated using a Monte Carlo method, where random autocorrelated time series are generated. Chapter V is a simulation-based study, showing that ignoring observation error in analyses of population time series data can bias the estimated effects and measures of uncertainty, if the environmental variables are autocorrelated. It is concluded that the use of state-space models is an effective way to reach more accurate results. In summary, there are several biological assumptions and methodological issues that can affect the inferential outcome when estimating environmental effects from time series data, and that therefore need special attention. The functional form of the environmental effects and potential interactions between environment and population density are important to deal with. Other issues that should be considered are assumptions about density dependent regulation, modelling potential observation error, and when needed, accounting for spatial and/or temporal autocorrelation.

Interatomic potentials for fusion reactor material simulations

Fusion energy is a clean and safe solution for the intricate question of how to produce non-polluting and sustainable energy for the constantly growing population. The fusion process does not result in any harmful waste or green-house gases, since small amounts of helium is the only bi-product that is produced when using the hydrogen isotopes deuterium and tritium as fuel. Moreover, deuterium is abundant in seawater and tritium can be bred from lithium, a common metal in the Earth's crust, rendering the fuel reservoirs practically bottomless. Due to its enormous mass, the Sun has been able to utilize fusion as its main energy source ever since it was born. But here on Earth, we must find other means to achieve the same. Inertial fusion involving powerful lasers and thermonuclear fusion employing extreme temperatures are examples of successful methods. However, these have yet to produce more energy than they consume. In thermonuclear fusion, the fuel is held inside a tokamak, which is a doughnut-shaped chamber with strong magnets wrapped around it. Once the fuel is heated up, it is controlled with the help of these magnets, since the required temperatures (over 100 million degrees C) will separate the electrons from the nuclei, forming a plasma. Once the fusion reactions occur, excess binding energy is released as energetic neutrons, which are absorbed in water in order to produce steam that runs turbines. Keeping the power losses from the plasma low, thus allowing for a high number of reactions, is a challenge. Another challenge is related to the reactor materials, since the confinement of the plasma particles is not perfect, resulting in particle bombardment of the reactor walls and structures. Material erosion and activation as well as plasma contamination are expected. Adding to this, the high energy neutrons will cause radiation damage in the materials, causing, for instance, swelling and embrittlement. In this thesis, the behaviour of a material situated in a fusion reactor was studied using molecular dynamics simulations. Simulations of processes in the next generation fusion reactor ITER include the reactor materials beryllium, carbon and tungsten as well as the plasma hydrogen isotopes. This means that interaction models, {\it i.e. interatomic potentials}, for this complicated quaternary system are needed. The task of finding such potentials is nonetheless nearly at its end, since models for the beryllium-carbon-hydrogen interactions were constructed in this thesis and as a continuation of that work, a beryllium-tungsten model is under development. These potentials are combinable with the earlier tungsten-carbon-hydrogen ones. The potentials were used to explain the chemical sputtering of beryllium due to deuterium plasma exposure. During experiments, a large fraction of the sputtered beryllium atoms were observed to be released as BeD molecules, and the simulations identified the swift chemical sputtering mechanism, previously not believed to be important in metals, as the underlying mechanism. Radiation damage in the reactor structural materials vanadium, iron and iron chromium, as well as in the wall material tungsten and the mixed alloy tungsten carbide, was also studied in this thesis. Interatomic potentials for vanadium, tungsten and iron were modified to be better suited for simulating collision cascades that are formed during particle irradiation, and the potential features affecting the resulting primary damage were identified. Including the often neglected electronic effects in the simulations was also shown to have an impact on the damage. With proper tuning of the electron-phonon interaction strength, experimentally measured quantities related to ion-beam mixing in iron could be reproduced. The damage in tungsten carbide alloys showed elemental asymmetry, as the major part of the damage consisted of carbon defects. On the other hand, modelling the damage in the iron chromium alloy, essentially representing steel, showed that small additions of chromium do not noticeably affect the primary damage in iron. Since a complete assessment of the response of a material in a future full-scale fusion reactor is not achievable using only experimental techniques, molecular dynamics simulations are of vital help. This thesis has not only provided insight into complicated reactor processes and improved current methods, but also offered tools for further simulations. It is therefore an important step towards making fusion energy more than a future goal.

Trust and Collectives

"Trust and Collectives" is a compilation of articles: (I) "On Rational Trust" (in Meggle, G. (ed.) Social Facts & Collective Intentionality, Dr. Hänsel-Hohenhausen AG (currently Ontos), 2002), (II) "Simulating Rational Social Normative Trust, Predictive Trust, and Predictive Reliance Between Agents" (M.Tuomela and S. Hofmann, Ethics and Information Technology 5, 2003), (III) "A Collective's Trust in a Collective's action" (Protosociology, 18-19, 2003), and (IV) "Cooperation and Trust in Group Contexts" (R. Tuomela and M.Tuomela, Mind and Society 4/1, 2005 ). The articles are tied together by an introduction that dwells deeply on the topic of trust. (I) presents a somewhat general version of (RSNTR) and some basic arguments. (II) offers an application of (RSNTR) for a computer simulation of trust.(III) applies (RSNTR) to Raimo Tuomela's "we-mode"collectives (i.e. The Philosophy of Social Practices, Cambridge University Press, 2002). (IV) analyzes cooperation and trust in the context of acting as a member of a collective. Thus, (IV) elaborates on the topic of collective agency in (III) and puts the trust account (RSNTR) to work in a framework of cooperation. The central aim of this work is to construct a well-argued conceptual and theoretical account of rational trust, viz. a person's subjectively rational trust in another person vis-à-vis his performance of an action, seen from a first-person point of view. The main method is conceptual and theoretical analysis understood along the lines of reflective equilibrium. The account of rational social normative trust (RSNTR), which is argued and defended against other views, is the result of the quest. The introduction stands on its own legs as an argued presentation of an analysis of the concept of rational trust and an analysis of trust itself (RSNTR). It is claimed that (RSNTR) is "genuine" trust and embedded in a relationship of mutual respect for the rights of the other party. This relationship is the growing site for trust, a causal and conceptual ground, but it is not taken as a reason for trusting (viz. predictive "trust"). Relevant themes such as risk, decision, rationality, control, and cooperation are discussed and the topics of the articles are briefly presented. In this work it is argued that genuine trust is to be kept apart from predictive "trust." When we trust a person vis-à-vis his future action that concerns ourselves on the basis of his personal traits and/or features of the specific situation we have a prediction-like attitude. Genuine trust develops in a relationship of mutual respect for the mutual rights of the other party. Such a relationship is formed through interaction where the parties gradually find harmony concerning "the rules of the game." The trust account stands as a contribution to philosophical research on central social notions and it could be used as a theoretical model in social psychology, economical and political science where interaction between persons and groups are in focus. The analysis could also serve as a model for a trust component in computer simulation of human action. In the context of everyday life the account clarifies the difference between predictive "trust" and genuine trust. There are no fast shortcuts to trust. Experiences of mutual respect for mutual rights cannot be had unless there is respect.

Optimering av hålltidstabeller vid Normaliseringsugnen

Analyserna av hålltiderna i Normaliseringsugnen visar att i de flesta fall kan hålltiderna förkortas, beroende på om man väljer att godkänna värmebehandlingen vid en temperatur15C° eller 5C° under börvärdet. Om 5C° väljas kan det krävas att vissa ugnstider förlängs. Det finns ingen anledning att hålla övertid på plåtarna i ugnen, vilket kan leda till korntillväxt och ett sprött material. Undersökningen visar att övertiden ökar med plåttjockleken. Temperaturavvikelsediagrammet för värmebehandlingen visar att inom tjockleksintervallet 30mm - 50mm är temperaturdifferensen vid hålltidens slut störst gentemot börvärdet. Man bör dock komma ihåg att pyrometern endast mäter yttemperaturen. Kärntemperaturen är förmodligen något lägre och då krävs en viss övertid för att säkerställa en homogen temperatur genom hela plåten. Vid ett lyckat experiment med att plana en plåt, efter att ha värmt upp den till 650°C, gjordes en simulering i dataprogrammet Steeltemp 2D. Simuleringen visar svalningskurvor för en given analyskod från 600°C för olika plåttjocklekar. Temperaturen på experimentplåten vid inträdet i planmaskinen var 350°C. Resultatet som redovisas i Steeltempdiagrammet visar att det inte finns risk att plåttemperaturen sjunker under 350°C.

Utveckling och prov av en 50 kJ elektrisk pulsgenerator

Detta arbete beskriver en elektrisk pulsgenerator, dess konstruktion och ingående komponenter.Särskild uppmärksamhet ägnas åt det triggade gnistgapet och triggpulsgeneratorn. Gnistgapetskonstruktion beskrivs. En SPICE-modell utvecklas för gnistgapets urladdningskanal.Urladdningskanalens egenskaper simuleras. Simulerad och fotograferad kanalradie jämförs.Några genomförda försök beskrivs kort, däribland det katastrofala och avslutande försöket. Detavslutande försöket analyseras. Avslutningsvis avhandlas några tänkbara utbyggnader ochförbättringar.

Luftsolfångares termiska prestanda

Luftuppvärmning är ett utbrett sätt att använda solenergi,bl a i husuppvärmning, luftkonditionering och torkning av jordbruksprodukter.I denna rapport framläggs ett nytt sätt att beräkna värmeprocessen i en luftsolfångare, vilket ger möjlighet till riktigare simulering av icke symmetrisk luftuppvärmning i luftsolfångarens kanaler.En bearbetad analytisk-numerisk metod av tvådimensionell icke stationär temperaturfältsberäkning presenteras, vilket ger möjlighet att göra kompletteringar till simuleringsprogrammet TRNSYS, speciellt avpassat för det sätt som luftsolfångare uppvärmer luften.Vid sidan om den teoretiska analysen av luftsolfångare, framläggs i denna rapport, medodik för experimentella undersökningar av luftsolfångare. Vidare diskuteras krav på mätutrustning vid experimentella mätningar av luftsolfångares termiska prestanda.

Multi-objective optimization of material model parameters of an adhesive layer by using SPEA2

The usage of multi material structures in industry, especially in the automotive industry are increasing. To overcome the difficulties in joining these structures, adhesives have several benefits over traditional joining methods. Therefore, accurate simulations of the entire process of fracture including the adhesive layer is crucial. In this paper, material parameters of a previously developed meso mechanical finite element (FE) model of a thin adhesive layer are optimized using the Strength Pareto Evolutionary Algorithm (SPEA2). Objective functions are defined as the error between experimental data and simulation data. The experimental data is provided by previously performed experiments where an adhesive layer was loaded in monotonically increasing peel and shear. Two objective functions are dependent on 9 model parameters (decision variables) in total and are evaluated by running two FEsimulations, one is loading the adhesive layer in peel and the other in shear. The original study converted the two objective functions into one function that resulted in one optimal solution. In this study, however, a Pareto frontis obtained by employing the SPEA2 algorithm. Thus, more insight into the material model, objective functions, optimal solutions and decision space is acquired using the Pareto front. We compare the results and show good agreement with the experimental data.

Modelling and simulations of ductile iron solidification-induced variations in mechanical behaviour on component and microstructural level

The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.

Analys av ett mikronät vid Ihushi Development Center i Tanzania

Denna studie omfattar en undersökning om hur ett hybridnät har fungerat, i detta fall Ihushi Development Center som ligger I Tanzania. De mätningar som har gjorts, har följt en standard för att kunna universellt användas vid en fortsatt studie eller direkt kunna användas för att jämföras med andra hybridnät med liknande uppsättning och förutsättningar. Under arbetets gång så har en ny modell tagits fram för att smidigt kunna analysera rådata och uträkning av de nödvändiga parametrarna. Detta underlättar även kommande arbeten kring detta hybridnät. Det har också blivit en typ av simulering då det har funnits många olika typer av utspridda och kontinuerliga fel som har behövts hanteras. Dessa värden har då behövts uppskattats utifrån olika källor och metoder, för att sedan användas. Det har sedan räknats ut effektiviteter och prestanda på olika delar i systemet som sedan kommenteras och kan direkt användas för en utvärdering i en framtida studie. Dessa resultat har bitvis jämförts med tidigare utvärdering men då det saknats information från föregående rapport så har en fullständig jämförelse och slutsats inte varit möjlig.