| 21. |
- Alberg, Henrik
(författare)
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Simulation of welding and heat treatment : modelling and validation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many aerospace components with complex geometry are fabricated from smaller parts using joining techniques such as welding. Welding and the heat treatment which usually follows, can result in unwanted deformation and stresses. Expensive materials, tight geometrical tolerances and the need to decrease product and manufacturing development time, cost and associated risks have motivated the development of models and methods for the simulation of manufacturing processes. The work presented concerns methodologies and modelling techniques for the simulation of welding and heat treatment of fabricated aircraft-engine components. The aim of the work was to develop modelling practices to enable the use of finite element analysis for the prediction of deformation, residual stresses and material properties such as microstructure during and after welding and heat treatment. Achieving this aim has required investigation of geometrical discretisation, modelling of boundary conditions and material behaviour for these processes. The case study components were made of a martensitic stainless steel, Greek Ascoloy. Phase evolutions models and models for rate-independent, rate-dependent, and creep were used as the material models in the welding and heat treatment simulations. The work also includes discussion of numerical considerations in material modelling. A toolbox for evaluation of constitutive models and to obtain material parameters for the plasticity models was developed. The heat transfer coefficient is an important parameter for describing energy transfer between the component and a gas. Due to the complexity of the gas flow in the heat treatment furnace during cooling, a method using computational fluid dynamics was developed to obtain an approximate distribution of the heat transfer coefficient. Due to the impact that modelling and simulation predictions can have, the creditability of the computational results are of great concern to engineering designers, managers and other affected by decisions based on these predictions. In this work, a validation methodology for welding and post weld heat treatment models was developed. The model used for welding simulations gives results with the accuracy required for predicting deformation and residual stresses at all stages of the product and manufacturing development process. The heat treatment model predicts deformations and residual stresses resulting from stress relief heat treatment of sufficient accuracy to be used in the concept and preliminary stages of product and manufacturing development. The models and methodology have been implemented, tested and are in use at Volvo Aero.
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| 22. |
- Albing, Malin
(författare)
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Contributions to process capability indices and plots
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents contributions within the field of process capability analysis. Process capability analysis deals with how to assess the capability of processes. Based on process capability analysis one can determine how the process performs relative to its product requirements or specifications. An important part within process capability analysis is the use of process capability indices. This thesis focuses on process capability indices and process capability plots. The thesis consists of six papers and a summary. The summary gives a background to the research area, a short overview of the six papers, and some suggestions for future research. The thesis summary also consists of some new results, not presented in any of the appended papers. In paper I, the frequency and use of process capability analysis, together with statistical process control and design of experiments, within Swedish companies hiring alumni students are investigated. We also investigate what motivates organisations to implement or not implement these statistical methods, and what is needed to increase the use. In papers II-III we generalize the ideas with process capability plots and propose two graphical methods, for deeming a process capable at a given significance level, when the studied quality characteristic is assumed to be normally distributed. In paper II we derive estimated process capability plots for the case when the specification interval is one-sided. In paper III we derive elliptical safety region plots for the process capability index Cpk and its one-sided correspondences. The proposed graphical methods are helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. In papers IV-VI we propose a new class of process capability indices designed for the situation with an upper specification limit, a target value zero, and where the studied quality characteristic has a skewed, zero- bound distribution with a long tail towards large values. The proposed class of indices is simple and possesses properties desirable for process capability indices. The results in papers IV-VI are also valid for the situation with a target value, not equal to zero but equal to a natural lower limit of the quality characteristic. Three estimators of the proposed class of indices are studied and the asymptotic distributions of these estimators are derived. We also consider decision procedures, based on the estimated indices, suitable for deeming the process capability at a given significance level. The new results in the summary combines the ideas from paper II with the results in papers IV-VI and a graphical method for the class of indices proposed in IV-VI are derived.
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| 23. |
- Allard, Christina
(författare)
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Two sides of the coin - rights and duties : the interface between environmental law and Saami law based on a comparison with Aoteoaroa/New Zealand and Canada
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The needs of indigenous peoples are related to land, water and other natural resources for sustaining a more or less traditional livelihood. Such needs typically compete with other societal interests. There are, on the one hand, specific interests in exploiting natural resources within traditional indigenous areas, while, on the other hand, concerns regarding conservation and preservation measures of valuable nature areas. This thesis contains two perspectives: an environmental protection perspective and a customary rights perspective. The thesis also contains a comparison of certain aspects of the law in Aotearoa/New Zealand, Canada and Sweden. Although the examination has a comparative approach, Swedish law is in prime focus. The objective is twofold. On the one hand, it includes an analysis of the interface between Saami customary rights, foremost the reindeer herding right, and environmental protection and natural resources legislation. On the other, it analyses and discusses ways in which the legislation may contribute to a sustainable use of land and natural resources within the reindeer herding area in Sweden. In this way, the second part of the objective is a succession of the former. It includes, above all, discussions de lege ferenda with the focus on Swedish environmental law. Evidently, it is the reindeer herding area per se that is in prime focus. Inherent in the examination as a whole, there are, hence, sustainability aspects. A correct comprehension of Saami customary rights is also important to the promotion of a sustainable use of the reindeer herding area. The interrelation of the two legal areas, environmental/natural resources law and aspects of the indigenous law, is, however, more evident with respect to the New Zealand and Canadian laws. Nevertheless, the connection also exists in a Swedish legal context, even though not as emphasised. Hence, there may be a call for a greater interrelation of these two legal areas. While general environmental requirements on the reindeer husbandry are abundant, specific requirements relating to regional or local circumstances are scarce. Such specific provisions may be designed to promote sustainability objectives better and, at the same time, to take into account specific Saami interests. Given the many conflicting land uses in the reindeer herding area, a stricter order of preferences taken on a strategic level generally provides advantages. Now, decisions are commonly left to be solved on a case by case basis with little guidance. Despite many shortcomings in specific legislation, above all, a regional and comprehensive environmental planning would greatly support the goal of sustainable uses of the land and resources in the area.
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| 24. |
- Almqvist, Andreas
(författare)
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On the effects of surface roughness in lubrication
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tribology is a multidisciplinary field defined as the science and technology of interacting surfaces in relative motion, and embraces the study of friction, wear and lubrication. A typical tribological application is the rolling element bearing. Tribological contacts may also be found in other types of bearings, cam-mechanisms, gearboxes and hydraulic systems. Examples of bearings inside the human body are the operation of the human hip joint and the contact between teeth during chewing. To fully understand the operation of this type of application one has to understand the couplings between the lubricant fluid dynamics, the structural dynamics of the bearing material, the thermodynamical aspects and the resulting chemical reactions. This makes modeling tribological applications an extremely delicate task. Because of the multidisciplinary nature, such theoretical models lead to mathematical descriptions generally in the form of non-linear integro-differential systems of equations. Some of these systems of equations are sufficiently well posed to allow numerical solutions to be carried out, resulting in accurate predictions on performance. In this work, the influence on performance of a surface microscopical nature, the surface roughness, in contact interfaces between different types of machine element components is the subject of study. An example is the non-conformal lubricated contact between one of the rollers and the inner ring in a rolling element bearing. The tribological contact controlling the operation of the human hip joint is also very similar to this. Another example of a non-conformal contact occurs when driving on rainy roads, where the hydrodynamic action of the water separates the tire. To enable investigations of these types of problems, different theoretical models were studied; for the selected model, a numerical solution technique was developed within this project. This model is based on the Reynolds equation coupled with the film thickness equation. The numerical solution technique involves a multilevel technique to facilitate the solution process. Results presented in this thesis, utilizing this approach, study elementary surface features such as ridges and indentations passing each other inside the lubricated conjunction. The Reynolds equation is derived under the assumptions of thin fluid film and creeping flow, and considers in its most general form shear thinning of the lubricant. This type of equation describes the hydrodynamic action of the lubricant flow and may be used when the interfaces consist of either conformal or non-conformal conjunctions. Examples of applications having conformal interfaces are thrust- and journal- bearings or the contact between the eye and a (optical) contact lens. In such types of applications the load carried by the interface is distributed over a fairly large area that under certain circumstances helps to prevent mechanical deformation of the contacting surfaces. Such applications are said to operate in the hydrodynamic lubrication (HL) regime. Lubricant compressibility and cavitation are important aspects and have received some attention. However, the main objective when modeling HL has been to investigate and develop methods that enable the influence of surface roughness to be to be studied efficiently. Homogenization is a rigorous mathematical concept that when applied to a certain problem may be regarded as an averaging technique as well as it provides information about the induced effects of local surface roughness. Homogenization inflicts no restrictions on the surface roughness representation other than the representative part of the chosen surface roughness being assumed periodically distributed and of course the assumptions of thin film flow made through the Reynolds equation. The homogenization process leads to a two sets of equations one for the local scale describing surface roughness, scale and one for the global scale describing application geometry. The unequivocally determined coefficients of the global problem, which may be regarded as flow factors, are obtained through the solution of local problems. This makes homogenization an eminent approach to be used investigating the influence of surface roughness on hydrodynamic performance. In the present work, homogenization has been used to derive computationally feasible forms of problems originating from incompressible and compressible Reynolds type equations that describe stationary and unstationary flows in both cartezian and cylindrical co-ordinates. This technique enables simulations of surface roughness induced effects when considering surface roughness descriptions originating from measurements. Moreover, the application of homogenization facilitates the interpretation of results. Numerical investigations following the homogenization process have been carried out to verify the applicability of homogenization in hydrodynamic lubrication. Homogenization has also been shown here to enable efficient analysis of rough hydrodynamically lubricated problems. Also of note, in connection to the scientific contribution within tribology, collaboration with a group in applied mathematics has lead to the development of novel techniques in that area. These ideas have also been successfully applied, with some results presented in this thesis. At start-ups, the contact in a rolling element bearing could be both starved and drained from lubricant. In this case the hydrodynamic action becomes negligible in terms of load carrying capacity. The load is carried exclusively by surface asperities, the tribo film, or both. This is hereby modeled as the unlubricated frictionless contact between rough surfaces, i.e. a contact mechanical approach. A variational principle was used in which the real area of contact and the contact pressure distribution minimize the total complementary potential energy. The material model is linear elastic-perfectly plastic and the energy dissipation due to plastic deformation is accounted for. The numerics of this contact mechanical approach involve the fast Fourier transformation (FFT) technique in order to facilitate the solution process. Investigation results of the contact mechanics of realistic surfaces are presented in this thesis. In this investigation the variation in the real area of contact, the plasticity index and some surface roughness parameters due to applied load were studied.
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| 25. |
- Amer, Eynas
(författare)
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Pulsed laser ablation studied using digital holography
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pulsed digital holographic interferometry has been used to study the plume and the shock wave generated in the laser ablation process on different targets under atmospheric air pressure. A pulsed Nd-YAG laser system (pulse duration 12 ns) has been used both for ablating the material (wavelength 1064 nm) and for measurement (wavelength 532 nm). Digital holograms were recorded for different time delays using collimated laser light passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. The Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Intensity maps have been calculated from the recorded digital holograms and used to calculate the attenuation of the probing laser beam by the ablated plume. Qualitative and quantitative information have been extracted from both the phase map and the intensity map to help describing the laser ablation process. Also 3D information about the induced plume has been obtained by numerical reconstruction of the digital holograms at different planes along the plume. The amount of released energy due to laser impact on a PCBM target has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and the target has been calculated and it seems to be constant around 80 %. The 3D refractive index fields have been used to calculate the shock wave front density and the electron number density distribution within the induced plasma. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3x1015 electrons/cm3ns. The effect of the laser spot diameter on the shock wave generated in the ablation process of a Zn target has been studied. The induced shock wave has an ellipsoidal shape that approaches a sphere for decreasing spot diameter. A model was developed that approaches the density distribution that facilitates the derivation of the particle velocity field. The method provides quantitative results that are discussed; in particular a comparison with the point explosion theory. The effect of the physical properties of the target on the laser ablation process has been studied. The comparison of the laser ablation of Zn and Ti shows that different laser ablation mechanisms are observed for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism. The results show that pulsed digital holographic interferometry is a promising technique to give a physical picture and increase the understanding of the laser ablation process in a time resolved manner.
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| 26. |
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| 27. |
- Andersson, Christian
(författare)
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Biobased production of succinic acid by Escherichia coli fermentation
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prospects of peak oil, climate change and the dependency of fossil carbon have urged research and development of production methods for the manufacture of fuels and chemicals from renewable resources (biomass). The present thesis illustrates different aspects of biobased succinic acid production by a metabolically engineered E. coli strain. The main areas of the thesis are sugar utilisation and feedstock flexibility, and fermentation inhibition, both due to toxic compound derived from the raw material and the fermentation products themselves.The first part of this thesis aimed to investigate the fermentation characteristics of AFP184 in a medium consisting of corn steep liquor, inorganic salts and different sugar sources without supplementation with high-cost nutrients such as yeast extract and peptone. The effects of different sugars, sucrose, glucose, fructose, xylose, equal mixtures of glucose-fructose and glucose-xylose, on succinic acid production kinetics and yields in an industrially relevant medium were investigated. AFP184 was able to utilise all sugars and sugar combinations except sucrose for biomass generation and succinate production. Using glucose resulted in the highest yield, 0.83 (g succinic acid per g sugar consumed anaerobically). Using a high initial sugar concentration resulted in volumetric productivities of almost 3 g L-1 h-1, which is above estimated values for economically feasible production. However, succinic acid production ceased at final concentrations greater than 40 g L-1. To further increase succinic acid concentrations, fermentations using NH4OH, NaOH, KOH, K2CO3, and Na2CO3 as neutralising agents were performed and compared. It was shown that substantial improvements could be made by using alkali bases to neutralise the fermentations. The highest concentrations and productivities were achieved when Na2CO3 was used, 77 g L-1 and 3 g L-1 h-1 respectively. A gradual decrease in succinate productivity was observed during the fermentations, which was shown to be due to succinate accumulation in the broth and not as a result of the addition of neutralising agent or the subsequent increase in osmolarity.To maintain high succinate productivity by keeping a low extracellular succinic acid concentration fermentations were interrupted and cells recovered and resuspended in fresh media. By removing the succinate it was possible to maintain high succinic acid productivity for a prolonged time. Cells subjected to high concentrations of succinate were also able to regain high productivity once transferred into a succinate-free medium.In the last part of the thesis succinic acid production from softwood dilute acid hydrolysates was demonstrated. This study involved establishing the degree of detoxification necessary for growth and fermentation using industrial hydrolysates. Detoxification by treatment with lime and/or activated carbon was investigated and the results show that it was possible to produce succinate from softwood hydrolysates in yields comparable to those for synthetic sugars.The work done in this thesis increases the understanding of succinic acid production with AFP184, illustrate its limitations, and suggests improvements in the current technology with the long term aim of increasing the economical feasibility of biochemical succinic acid production.
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| 28. |
- Andersson, Charlotte
(författare)
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Factors affecting MFI membrane quality
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are crystalline aluminosilicates with molecular sieving properties and are widely used in industrial applications such as catalysis, sorption and ion-exchange. Zeolite membranes are highly interesting due to their capability to continuously separate molecules under severe conditions. The MFI zeolite structure has suitable pore diameter for many applications, and its thermal and chemical stability is high. In order to obtain high performance MFI membranes, a thin and defect free film is needed for high flux and high selectivity. In this thesis, parameters affecting quality of zeolite membranes have been investigated. Different MFI-zeolite membranes were prepared using seed crystals and hydrothermal synthesis. Thereafter, membranes were characterized using scanning electron microscopy, single gas permeation measurements, porosimetry and separation experiments. The effect of grain boundaries was investigated by preparing membranes with small crystal size. It was found that a high amount of grain boundaries reduced the quality of the membranes. In another study, the effect of exposure to aqueous solutions was found to increase the amount of non-zeolitic pores in the membrane, and thus it decreased the quality of the membrane. However, no such effect was found for ethanol that was identified as a safe rinsing media. Membranes with different Si/Al ratio were also prepared and evaluated. It was observed that the Si/Al ratio of a MFI membrane influences the performance of the membrane. It was found that an increase of aluminium makes the membrane more polar which leads to an improved adsorption of, and selectivity for polar molecules. The effect of support invasion was also evaluated and the regularity and extension of the support invasion was observed to affect membrane quality. The effect of heating rate during calcination was investigated and no correlation between heating rate and membrane quality was observed. Calcination of membranes was studied in-situ by high temperature synchrotron radiation and a model for crack formation was postulated. In summary, this work has shown that in order to obtain high quality membranes, the amount of grain boundaries, the film thickness and support invasion should be controlled. To obtain the best performance of the membranes the Si/Al ratio should be chosen with respect to the application. Finally, water exposure affects the lifetime of the MFI membranes in certain applications.
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| 29. |
- Andersson-Chan, Anneli
(författare)
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Biofiltration of odorous gas emissions
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biofiltration has shown its potential as an interesting treatment alternative for contaminated gas streams. Unlike conventional technologies, such as adsorption, scrubbers, and incineration, biofiltration offers effective pollution control at relatively low capital and operating costs, and without the generation of secondary pollution that may require subsequent treatment. The disadvantages of biofiltration have been the large space requirements and frequent media replacements as a result of deterioration or ageing. Extensive biofilter research and development have taken place over the past 20 years internationally, in particular laboratory experiments that address the removal of single pollutants at fairly high concentrations under constant operating conditions. In field applications, such conditions are highly unusual and the feasibility of treating complex mixtures at very low concentrations relevant to many odorous gas emissions has not received much attention. The overall objective of this thesis was to reduce the knowledge gap between laboratory studies and field conditions on the topic of biofiltration for odorous gas emissions. Various operational and process related problems, such as fluctuating flows, temperatures, and pollutant concentrations, that affected the biofilter performance by creating suboptimal living conditions for the microbes were identified. A newly designed compact pilot-scale biofilter was used in three different applications with odour problems, namely restaurant, pulp mill and wastewater pumping station. The gas streams were complex mixtures with chemically diverse contaminants whose concentrations varied significantly with time. Aldehydes were the dominant compounds in restaurant emissions, while reduced sulphur compounds, primarily dimethyl sulphide, dominated the pulp mill and wastewater emissions. Overall, very low concentrations of individual compounds were found (ppb-level), and very low or no removal of the targeted compounds was achieved in the biofilter. Limitations of the biomass density in the filter media is a plausible explanation since pollutant concentrations at the ppb-level may have been too low to build up and support the bacteria. Due to the low solubility of many identified compounds, a mass transfer limitation may also have occurred due to the prevailing short residence times. Drying of the filter medium was partly a problem, pointing to the need for an improved humidification system or using a trickling filter design. In a case study at a wastewater treatment plant, a method to evaluate odour problems was developed involving local observers in an odour panel together with operational data and weather observations. Working with an odour panel proved useful in several ways; they took an active interest in and increased their knowledge of the complexity of odour problems. However, relating the panel reports to specific events at the treatment plant proved difficult, and the reports were not always consistent with current wind directions.
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| 30. |
- Andersson, Mikael
(författare)
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Hur kan akademi organisera samverkan för tillväxt? : Deliberativ Organiserad Samverkan, DOS, en ny styrningsmodell
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within research and education policies of later decades, a clear trend can be seen in expanded attempts to stimulate growth-concentrated cooperation between government, academia and industry. With economic financing, channelled to academia through different kinds of research and development councils, follows a responsibility to operationally organize the actors' cooperation. This task is rather complex. The cooperative process is expected to be equal, provided that the participating actors have different professional identities, belong to different organizations, have different values and ideas of norms, and satisfy different interests. With present research and education policies, follows the idea of academia acting as a potential growth engine that should be directly used to develop society's innovation system, production system and markets. In connection with this, discussions regarding academic capitalism, commercialisation of research results, incubation processes, etc., are being conducted. The traditional role of academia as a research university has also been complemented by the roles of organizer for growth-concentrated cooperation and entrepreneur.Pursuing independent research, being an organizer for similar cooperation, and satisfying their personal interests all at the same time is contradictory. A way for academia to prevent their own interests from getting out of hand during cooperation is to avoid all forms of external management, and instead focus on stimulating the participating actors to evaluate, develop and manage their cooperation themselves. Conventional education, research and project models are developed for purposes other than this. Desipte this, their usage with the cooperative task is rather widespred. For cooperative actors to understand and handle their activities in an aware, collective and flexible manner, they need to use some form of management model that allows for communicative coordination, evaluation and development of organizational action. As an alternative to those conventional models, a new management model has been developed in this thesis, called Deliberative Organized Cooperation, DOC. The model is developed with inspiration from deliberative theory. Simply put, the actors' cooperation is expected to occur through repeated dialectic movements between deliberative phases (management process), where actors produce valid action alternatives and legitimate interpersonal and systematic relations, and systematic phases (operational activities), where the actors transform the gained validity and legitimacy in systematic action and resulting factuality. While the deliberative phase corresponds to evaluation and development orientated logic with open rationality conditions, the systematic phase corresponds to production orientated logic with closed rationality conditions.The primary empirical results of the thesis are collected from activities that have been driven or are driven within or closely connected to two competence centres located at Luleå Univeristy of Technology. The first competence centre, the Polhem Laboratory, is presently being phased out and replaced by the Faste Laboratory. Both operations can be described with help from the Triple Helix model. Simply stated, the government contributes with direct economic funding for R&D as well as the overall rules of the game regarding the actors' cooperation, the industry with supplementary economic funding and direct turnover of the developed knowledge. The economic funding also goes to academia with an organizing of the cooperation process, knowledge development and commercialisation of interesting spin-off knowledge. An essential element in the operations of the Polhem and Faste Laboratories constitutes the so-called Sirius Project, an industrially oriented product development project conducted by fourth year students in the mechanical engineering program. This project is primarily conducted in cooperation between academia and large companies. Closely connected to this activity, Arena innovative technology and business, organizes multi-science undergraduate studies. An important part of this education is to cooperate in so-called greenhouse projects. Here, students from various study years and majors, meets researchers/teachers from different subject fields, and actors from different companies and development firms. The over-all aim of the projects is to stimulate entrepreneurship and starting of new robust companies. DOC comprises an attempt to solve management problem identified in connection to the above activities.The activities have been investigated through participating observations. Individual events have been worked upon and weaved together into a cohesive and anonymous scenario that is told by giving voices to a variety of the participating actors. In the theoretically oriented chapter of the thesis, events are problematised from the scenario through analytical and pragmatic reflections. With help of these reflections, the DOC model is successively built up.
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