| 61. |
- Al-Madhlom, Qais
(författare)
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Potential Use of Aquifer Thermal Energy Storage System in Arid Regions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After the Oil Crises in 1973, which meant higher energy costs, the world started to look for other sources of energy. This led to the development of renewable energy techniques. Because of the intermittent nature of renewable energy, storage systems were also developed. Underground Thermal Energy Storage (UTES) systems spread and are now globally well known. In these systems, excess thermal energy (heat or cold) is stored (short term and/or long term) from the surplus period to periods of higher demand. The storage media in such systems are underground materials, e.g. rock, soil, and/or groundwater. The current study aims to examine the use of underground thermal energy storage systems in arid regions, in order to increase the efficiency of both cooling and heating systems in these regions, such that CO2 emissions and consumed electricity for these purposes are reduced. Three main parameters determine which type of Underground Thermal Energy Storage (UTES) systemis most suitable. These are site, design, and operation parameters. The site-specific parametersinclude soil properties and all geo-hydrological, environmental, geological, metrologicalconditions. Therefore, the site parameters cannot be changed after installing the storage system,since they majorly depend on the location, while the other parameters (design and operation) canbe changed after construction. The first primary goal of this study is to find how and what site parameters involved to specify the most suitable type of UTES systems in arid regions. Thus, the suitable type of UTES systems can be decided. The second primary goal is to answer how and where to select the best location to install the adopted system. To achieve the goals of the study, two arid regions within Iraq were used as case studies. They are Babylon and Karbala, where the former is characterized by its shallow aquifer, while the latter is characterized by a relatively deeper aquifer. The ArcMap-GIS software was used to prepare the relevant digital maps, e.g. maps of hydraulic conductivity, population, type of soil, aquifers, groundwater elevation, transmissivity, and slope. Then, the vulnerability (readiness for being polluted by the surface contaminants) maps of the available aquifers were determined, followed by finding the seepage velocity of the groundwater. Depending on the outputs of the vulnerability and the seepage velocity, the most suitable type of Underground Thermal Energy Storage (UTES) systems can be decided. This study, also, includes developing/inventing a general methodology that can be used to determine the best location to install Underground Thermal Energy Storage (UTES) systems, including Aquifer Thermal Energy Storage (ATES) systems. The last part of this study includes applying the suggested methodology to determine the best location to install the suitable type of Underground Thermal Energy Storage (UTES) system in the study area. The first study was in the Babylon Province. Here, groundwater table is very shallow (less than 2 m depth in some regions). The crystalline bedrock is at a depth of 9-12 km below the ground surface, overlaid by 9-12 km of sedimentary rocks on which there is a 2-50 m thick layer of alluvial silty clay sediments. The groundwater moves slowly in this aquifer (2.12*10-6 - 1.85*10-1) m/d, and it is brackish having salinity of 5000-10000 mg/l. The susceptibility (vulnerability) of the aquifer in northern part of Babylon province is low to very low having ranges from 80 to 120 on Drastic model scale, which has the overall range of 26 – 226 (i.e. 0.27- 0.47 on normalized vulnerability). The second study area was a part of Karbala Province. This area can be divided into two regions based on the geology and geo-hydrological conditions. An eastern part is located on the Mesopotamian plain, and a western part is located in Western Desert. In both parts, the groundwater table is relatively deeper than the Babylon province. In the eastern part, it is generally more than 4 mbgs (meter below ground surface). While, in the western part it is deeper and reaches to 48 mbgs in depth. The soil in the eastern part is alluvial silty clay, while the western part consists of gypcrete sandy deposits. The groundwater, which flows towards the east, has a seepage velocity range from 0 to 0.27 m/d. The salinity of the groundwater changes from slightly brackish (1000-3000) mg/l in the western parts to highly brackish (5000-10000) mg/l in the Mesopotamian parts of the province. By comparing the site parameters of each province with the different UTES systems, the type of thermal energy storage system was decided. The most important site parameters are the depth of the water table and the aquifer characteristics. For Babylon Province, the expected suitable underground thermal energy storage system is an aquifer thermal energy storage system in silty clay. For Karbala Province, two systems are suggested: for the eastern part, aquifer thermal energy storage system in silty clay is recommended, while for the western part, a deep (10-30 m depth) sandy aquifer thermal energy storage system is recommended. After that, a methodology was developed and used to determine the suitable location in which to install the Aquifer Thermal Energy Storage (ATES) system. For Babylon province, the site selection index ranges between 2.9 and 5.3 on 1 to 10 scale. About 71% of the region has a site selection index ranges between 4.71 and 5.3. Concerning Karbala study area, the site selection index ranges between 3.1 and 9.1. About 15% of the region has a site selection index between 8.1 and 9.1.The energy saving in neighboring countries to Iraq by using the Aquifer Thermal Energy Storage (ATES) system ranges from 55% to 72%. It is also expected that using a ground sink heat pump instead of a conventional air-to-air heat pump increases the COP (Coefficient Of Performance) of roughly (10) to (-17). The negative sign means that the heat is injected into the ground. More theoretical and field studies are required to cover the different aspects of the subject of potential use of Aquifer Thermal Energy Storage (ATES) system in an arid region, and to verify the improvement of COP (Coefficient Of Performance) due to using these systems.
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| 62. |
- Al-Maqdasi, Zainab, 1986-
(författare)
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Multifunctionality and Durability of Cellulosic Fiber Reinforced Polymer Composites
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall objective of this thesis is to develop and evaluate cellulose-based fiber composites with added multifunctionality for advanced applications. In the strive towards sustainable societies and industries, materials as well as production processes need to be assessed against the sustainability criteria and selected accordingly. Cellulosic fibers reinforced polymer composites are being increasingly used in applications where weight saving, and environmental friendliness is as important as structural performance. Nonetheless, these materials have their limitations regarding durability and stability of the properties, but their potential in use for advanced applications can be expanded if functionalized and considered beyond their structural performance. Such multi-functionality of composites can be achieved by the coating of fibers and/or modifying the matrix with functional reinforcement, or by both of these routes combined. Coating of fibers and modifying the matrix with nano-reinforcement are two selected approaches for imparting functionality to the cellulosic fiber composites in the current study. Conductive Regenerated Cellulose Fibers (RCFs) were produced by coating commercial RCFs with copper via electroless plating process. Electrical conductivity and mechanical performance were evaluated, and the coated fibers were transformed into an embedded strains sensor-like assembly that could be used as structural health monitoring system in composites structures. A noticeable degradation in the mechanical strength of fibers was realized and it was attributed to the influence of the chemicals of the final plating step of process on the chains of cellulose as well as the loss of crystalline order in the RCF. In order to obtain modified matrix (nanocomposites) for multifunctional wood polymer composites (WPC), the commercial masterbatches based on Graphene Nanoplatelets (GNPs) were utilized by melt extrusion process. Effect of the processing parameters in terms of change in screw configurations and the change in composition of the constituents on the structure and mechanical performance of the nanocomposites was studied. Results showed that there is insignificant effect of the change in the screw configuration in comparison with the effect of increasing the content of the GNPs. Stronger shear forces did not result in better dispersion of the nanoparticles. Addition of the compatibilizer, on the other hand, resulted in an adverse effect on the properties compared to the formulations where it is absent. The use of GNPs with larger aspect ratio resulted in much better improvement in the mechanical performance. Addition of the nanoparticles did not only improve mechanical performance but also resulted in increased thermal conductivity and diffusivity, especially when micro-scale reinforcement was added because of synergy between wood fibers and the GNPs. This synergy was reflected also in the significant 99% improved wear resistance and the >80% reduction in the creep strains of wood and graphene reinforced composites. During the design and selection of materials, quasi-static properties are often used as a selection criterion. However, in reality structures in use are often loaded during lengthy periods of time which are followed by multiple steps of unloading/reloading, depending on the service conditions. In such cases their time-dependent response becomes more crucial than instantaneous mechanical response. Typically, characterization of these properties requires a lot of time, but it may be significantly shortened if proper modeling and analysis are employed. The effect of addition of GNPs to the polymer and wood composites has been studied experimentally by short term creep tests. The materials showed highly nonlinear response even at very low loading stresses, but the addition of the nanoparticles resulted in a decrease in the nonlinearity and in the irreversible strains due to plasticity. Modelling approaches have been used to extract parameters from experimental data that could be used in predicting long term performance using Zapas model for viscoplasticity and Schapery’s model for nonlinear viscoelasticity. Overall, the results of the performed work contribute to enriching the research field with the potential the bio-based composites have to offer in the advanced application and how nano-scale reinforcement can interact synergistically with the micro-sized fibers to improve the overall performance of WPC and under different loading scenarios.
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| 63. |
- Al-Ramahi, Nawres Jabar, 1980-
(författare)
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Comprehensive numerical analysis of stress state in adhesive layer of joint including thermal residual stress and material non-linearity
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this work is to improve understanding of the stress state in the adhesive layer of bonded joints and identify key parameters which govern performance of adhesive joints. This information is crucial for the prediction of the failure initiation and propagation with the further estimation of the durability and strength of adhesively bonded structures.A systematic numerical analysis of stress state in the adhesive layer of a single-lap and double- lap joint under various loading conditions (thermal and mechanical loading) and an alternative methodology to predict the direction for crack propagation within adhesive layer are presented in this thesis. To identification of the most important parameters of joints is done based on the assessment of the peel and shear stress distributions in the adhesive layer. The thermal residual stresses arising after assembling of joints at elevated temperature are accounted for in the analysis.Initially, accurate, realistic 3D finite element model with novel boundary conditions (displacement coupling) was developed and validated. The employed boundary conditions allow to eliminate the edge effect and simulate the behavior of an infinite plate of composite laminate with off-axis layers (monoclinic materials). It is also possible to decouple the edge effects induced by the finite specimen width from the interaction with ends of the joint overlap region. Due to these advanced setting it is possible to eliminate influence of some of the parameters as well as to reduce geometry of the model without losing precision. Thus, the model is optimized with respect to the number of elements as well as element size distribution and does not require excessive computational power to obtain accurate stress distributions even near to the possible sites with stress perturbations (e.g. corners, cracks, etc). Additionally to the geometrical parameters, various material models have been employed in simulations of adhesive joints. A linear and non-linear material models (adherend and adhesive) was used for the single-lap joint, while a linear material behavior was considered for double-lap joint. The geometrical non-linearity was also included in the analysis whenever required. To make results more general and applicable to a wide range of different joints the normalized (with respect to the thickness of adhesive layer) dimensions of joints were used. Depending on the analyzed type of joint (single- or double- lap), combination of similar and dissimilar (hybrid) materials for adherends are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of the composite adherend (carbon and/or glass fibers) different laminate lay-ups were selected: uni-directional ([08]T and [908]T) and quasi-isotropic ([0/45/90/-45]S and [90/45/0/-45]S). In general, discussion and conclusions concerning the importance of various joint parameters are based on the magnitude of the peel and shear stress concentration at the ends of the overlap. In order to identify general trends with respect to the influence of mechanical properties of adherends the master curves for shear and peel stresses are constructed and analyzed. To simulate effect of the residual thermal stresses on the behavior of joints different methods for assembly of joints were considered (using dedicated adhesive or employing co-curing method). The results of this investigation lead to the conclusions that the one of the most important factors affecting the simulation results is the sequences of application of thermo-mechanical loading for different assembly methods. It is shown that simple superposition of thermal and mechanical stresses (most common approach) in the adhesive layer works properly only for linear material but it gives inaccurate results if non-linear material is considered. The thesis demonstrates the appropriate way to combine thermal and mechanical loads to obtain correct stress distributions for any material (linear and non-linear). The analysis of the influence of residual thermal stresses has shown that the peel and shear stress concentration at the ends of overlap joint and the shear stress within the over-lap region are reduced due to thermal effect. In case of composite adherend the co-curing assembly method is more favorable (in terms of reducing stress concentrations) than using adhesive for joining the materials.Finally, the simulation of the crack propagation within the adhesive layer for the bi-material (steel and composite) DCB sample with thick adhesive layer was carried out. The alternative to traditional fracture mechanics approach is proposed for the prediction of the crack path in the adhesive layer: a maximum hoop stress criterion. The hoop stress on the perimeters of a relatively large circle around the crack tip is evaluated to predict the direction of the crack extension with respect to the existing crack. The fracture mechanics is used to validate this approach and it is proved that if the Mode I is dominant for the crack propagation the hoop stress criterion be successfully used to predict crack path in the adhesive layer. This methodology is much more effective (in terms of required time and resources) than energy release based criterion or even X-FEM.The main result of this thesis is a tool to obtain accurate stress distributions in the adhesive layer of joints. This tool provided better understanding of the behavior of adhesive joints and allowed to develop new approach for prediction of crack propagation in the adhesive layer. This is definitely a development in the design of stronger, more durable adhesive joints for lighter structural components.
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| 64. |
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| 65. |
- Al-Taie, Laith
(författare)
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Performance of Clay Liners in Near-Surface Repositories in Desert Climate
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wars in Iraq (1991 and 2003) generated various types of hazardous waste (HW) in the form of soil contaminated by depleted uranium (DU). Other HW emanated from destroyed army vehicles and remnants of Iraqi nuclear facilities holding various types and amounts of chemical and radioactive material. The negative impact of the various wastes on the health conditions of the population was reported from different parts of Iraq, showing an enhanced frequency of cancer and abnormally born infants. For isolating the wastes, which represent low-level and short-lived intermediate level radioactive wastes, near-surface repositories (NSR) are proposed since they represent the least expensive way of solving future problems with sufficient safety. Internationally, the timeframe of the containment of such wastes is designated to be 300 years. Site selection affects and largely controls the selection of a suitable design the aim being to minimize or eliminate migration of hazardous elements from the waste to the environment. The formulation of siting criteria is the first vital step toward the resolution of the problem. Site selection criteria are proposed taking in account three major factors: environmental, geological and socio-economic factors. Accordingly, Iraqi deserts, which make up 60% of Iraq, represent the number one candidate for locating a safe disposal facility, primarily because of the low population, suitable topography, climatic conditions, seismic stability and availability of raw materials. Long-term performance of NSR is directly related to the function of top and bottom liner systems. They should be designed so that they are mutually compatible and combine to effectively isolate the waste. Liners are considered as the main elements of any disposal facility on the ground surface and a properly designed top liner system is of particular importance since it will minimize or eliminate water percolation into the waste body. Compacted clay liners (CCL) should preferably have with a low hydraulic conductivity, which is achievable by proper selection of raw materials, compaction density and construction methods. A further criterion is that they must not soften significantly by expansion on wetting, which puts a limit to the smectite content and density. The liners can consist of native material found near the landfill site, and be used after simple processing, primarily drying and crushing, or be mixed with fillers like silty sand. Since the hydraulic conductivity is the key property of a reliable CCL, relevant experimental determination of the hydraulic conductivity is vital. The common practice in geotechnical laboratories is to apply high hydraulic gradients for getting results quickly but this can lead to non-conservative, incorrect results. The present study involved determination of the hydraulic conductivity of a smectite-rich clay sampled at places within reasonable distance from potential NSR sites. Various hydraulic gradients were applied to samples compacted to several different densities, using two permeants and two filter types. It was concluded that the outflow filter can significantly affect the evaluated conductivity especially when applying high hydraulic gradients. This was partly explained by clogging of outflow filters of conventional fine-porous type by torn-off clay particles at such gradients. A major conclusion was that the gradient in laboratory testing should not exceed 100 m/m.In order to assess the suitability of available raw materials within the Iraqi Deserts, two smectitic soils termed as Green and Red clays were investigated for potential use in CCLs. Both clays are fairly rich in smectite, which calls for mixing them with properly graded silt/sand material from the desert for modifying the expandability. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for defining criteria for selecting suitable clay-sand ratios. The results showed that 30-50% Green clay mixed with sand and 40-60% Red clay mixed with sand were suitable for constructing top liners with a hydraulic conductivity of 1×10-9 - 1×10-10 m/s. For bottom liners, 70% Green clay mixed with sand and 80% Red clay mixed with sand would be suitable; they were found to have a hydraulic conductivity of 1×10-11 m/s.The long-term performance of CCL is controlled by a number of processes like long periods of extreme dryness and short periods of very heavy rain. The percolation of water through the top liner system of a number of design alternatives were simulated using the code HELP 3.95D and subsequently by the FE program VADOSE/W. For the assumed NSR concept the slope stability of the top liner is essential and it was determined by using FE technique considering various slope angles. The engineering properties, primarily the hydraulic conductivity, swelling pressure and shear strength of 30-50% Green clay mixed with sand were introduced in the simulations. Two initial water contents of the compacted materials were considered representing 1) optimum water content (“wet case”), and 2) air‐dry conditions (“dry case”). Application of the HELP code decided the selection of suitable CCL having a thickness of 0.5 m and inclined by 5.7ᵒ. More detailed analyses with VADOSE/W showed that a mixture at the dry case would bring 0.5 mm (0.5 litre of leaking water per square meter) through CCL in an eight year simulation period. Long-term simulations (up to 300 years) showed that CCL would undergo continuous drying without reaching saturation even in the case of periods of very heavy rain (616 mm) for the wet and dry cases. The slope stability factor for the rather steep angle 30ᵒ was found to be 1.5 for the most critical case representing complete water saturation. In conclusion, the proposed materials and design features are believed to be suitable for practical application.
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| 66. |
- Alakangas, Lena
(författare)
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Sulphide oxidation, oxygen diffusion and metal mobility in sulphide-bearing mine tailings in Northern Sweden
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large quantities of sulphide-bearing mining wastes produced from ore processing are deposited throughout the world. Sulphide oxidation in the wastes may release acidic water with high concentrations of metals to the environment. Remediation strategies are usually site specific, since the physical and chemical properties of the wastes vary. Therefore, sulphide oxidation, oxygen diffusion and metal mobility in unoxidised and oxidised, remediated and unremediated wastes have been studied in the present work. The efficiency of different cover systems on unoxidised tailings from Kristineberg, were studied in pilot-scale test cells (5*5*3 m3)under field conditions. Clayey till, sewage sludge, apatite and Trisoplast were used as sealing layers and unspecified till as a protective cover. In one cell tailings were left uncovered. Unoxidised tailings in the test-cells in the initial stage after deposition showed relatively low sulphur release (600- 800 mg/l)in leachate waters, which probably was an effect of high moisture content in the tailings prior to deposition. Near-neutral pH found in the leachates was an effect of neutralisation by carbonate minerals present and lime (Ca(OH)2) added prior to deposition. Similar sulphur concentrations were found also in the uncovered tailings. The sulphide oxidation rate increased with time in the uncovered tailings, and decreased in the covered. The lowest oxygen concentrations were observed below the cover system with sewage sludge, which was the most effective barriar against oxygen in a short-term perspective. The oxygen fluxes through the clayey till and apatite layers were within the same magnitude and varied between 0.5 and 4 mole/year,m2. The Trisoplast layer seemed to have failed as a barrier against oxygen. Tailings studied at field scale at Laver and Kristineberg had oxidised for more than 50 years. The tailings at Kristineberg have high pyrite content (c.25% and 50%) and those at Laver have low grade of pyrrhotite (2-3%). The Laver tailings are unremediated, while at Kristineberg the tailings were remediated in 1996. The transport of metals in the drainage water at Laver decreased during a study period of 8 years. The transport of dissolved sulphur indicated a declining trend of sulphide oxidation rate in the tailings, which was confirmed by oxygen measurements in the tailings and weathering rate estimations. The decline was considered to be natural as a result of the increased distance that oxygen has to travel to reach unoxidised sulphide grains. The major part of the amounts of metals released by sulphide oxidation were secondarily retained in the tailings, and to a small extent in layers cemented by jarosite and Fe-(oxy)hydroxides. Sequential extraction of these layers showed that metals such as Cu and Pb were mostly associated with crystalline Fe-(oxy)hydroxides. Most important retention mechanism was, however, sorption onto minerals surfaces below the oxidation front. The studied Impoundment 1 at Kristineberg was remediated by two different methods; on one part a dry cover consisting of a sealing layer and a protective cover were applied, and the groundwater table was raised and a single dry cover applied on the other part. When the groundwater table was raised in oxidised tailings, secondarily retained metals such as Fe, Mg, Mn, S and Zn were remobilised resulting in increased concentrations in the groundwater. The concentrations declined with time, due to dilution by inflowing uncontaminated water. Decreased concentrations of Fe, Mg, Mn, S and Zn were observed also in the groundwater below the dry cover as the amount of percolating water decreased. The concentrations of trace elements such as Cd, Co, Cr, Cu, Ni and Pb were almost depleted in the groundwater, since these metals were retained within the tailings by mechanisms such as co-precipitation, precipitation and sorption. Analysis of pyrite grains by LA-ICP-SMS showed that pyrite surfaces were important for retention of As and Cu, in particular, but also for Cd and Zn. This study shows that the physico-chemical conditions expressed by pH and redox potential have a large impact on element mobility’s. For example, As was mobilised as a result of remediation, while the concentrations of most metals decreased in the drainage waters.
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| 67. |
- Alam, Md. Minhaj
(författare)
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Laser welding and cladding : the effects of defects on fatigue behaviour
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis focuses on weld defects in laser processed materials (for laser welding, laser hybrid arc welding and laser cladding) and their effect on the fatigue life of components. Component properties were studied with particular emphasis on the macro and micro surface geometry, weld defects and clad defects. The influence of these defects on fatigue life was analyzed by; the nominal and effective notch stress method, fatigue life prediction using Linear Elastic Fracture Mechanics (LEFM), fatigue testing, metallurgical analysis, fractography, elastic and elastic-plastic Finite Element Analysis (FEA). A simplified Computational Fluid Dynamics (CFD) analysis was also carried out to better understand the formation of undercuts during the welding process. The main objective is to gain an understanding of the impact of laser weld and clad defects on the fatigue behaviour of components.In the first two papers, fatigue testing involving the bending of laser hybrid arc welded eccentric fillet joints was carried out. Based on measurements of the weld surface geometry the crack initiation location and the crack propagation path were studied, experimentally and in conjunction with FE stress analysis. The competing criteria of throat depth and stress raising by the weld toe radii and by the surface ripples are explained, showing that the topology of surface ripples can be critical to fatigue behaviour. LEFM analysis was conducted to study the effect of Lack of Fusion (LOF) on fatigue life. Cracking starts and propagates preferentially from the lower toe of the top surface for this eccentric weld, even in cases of LOF. In the third paper two-dimensional linear elastic FEA was carried out for laser welding of a high strength steel beam. The impact of the geometrical aspects of joint design and of the weld root geometry on the fatigue performance was studied. Critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the fatigue behaviour. In the fourth paper the melt pool flow behaviour during the laser hybrid arc welding process was analyzed by CFD simulation. The melt velocity behind the keyhole was measured from high speed imaging as a starting value for the simulation. It was found that a high speed flow in the thin topmost layer of the melt transferred its momentum to an underlying flow which is faster than the welding speed and this delays the lifting of the depressed melt.In the fifth and sixth papers FEA of different macro stress fields and of stress raisers produced by defects was studied in laser clad surfaces for four different fatigue load conditions. Defects were categorized into zero-, one- and two-dimensional types. Pores intersecting or just beneath the surface initiated fatigue cracking, accompanied by two circular buckling patterns. For a four-point bending load involving a surface pore on a spherical rod, the critical range of azimuthal angle was identified to be 55º. The performance of as-clad surfaces was found to be governed by the sharpness of surface notches. Planar defects like hot cracks or LOF are most critical if oriented vertically, transverse to the bar axis. A generalized theory was established, showing that the combination of the macro stress field with the defect type, position and orientation, determines whether it is the most critical stress raiser.
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| 68. |
- Alander, Sara
(författare)
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Offentliga storkök i det gröna folkhemmet : diffrakterade berättelser om hållbar utveckling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Det är nu 20 år sedan Brundtlandskommissionens rapport kom ut, och begreppet hållbar utveckling fick sin stora spridning och inter¬nationella uppmärksamhet. Nu, våren 2007, är begreppet inte omdiskuterat på samma sätt som det en gång var, idag är det i stället begrepp som ”klimathotet” som debatteras och får rubriker. Hållbar utveckling har blivit ett bärande begrepp i internationella överenskommelser och det finns också en allt mer akut medvetenhet om att hållbar utveckling fordrar omställningar och förändring av många av de förhållanden och förhållningssätt vi i västvärlden tar för givna. I de dokument som oftast pekas ut som ursprunget till aktualiseringen av hållbar utveckling, Brundtland¬rapporten och Agenda 21, framgår att hållbar utveckling vilar på tre ben; ekologiskt, ekonomiskt och socialt. I avhandlingen fokuseras offentliga sektorns storhushåll som i runda tal serverar 2 600 000 måltider varje dag, knappt 2 100 000 av dessa i grund-, gymnasie- och förskolor (Sundström 2000). Särskilt studeras den måltids¬produktion som sker i samband med skol- och förskoleverksamhet, en verksamhet som de flesta i Sverige i dag på något sätt berörs av. Hållbar måltidsproduktion förutsätter hållbara teknologier och hållbar teknologianvändning och -utveckling, med hänsyn till alla tre dimensionerna av hållbarhet. Hur hållbar utveckling kan relateras till teknologi¬användning inom offentliga sektorns måltidsproduktion har därför undersökts med hjälp av feministisk teknovetenskap. Forskningsfrågorna är: Vilka förutsättningar ger och kräver teknologianvändning i den offentliga sektorns storköks¬verksamhet? Hur rimmar dessa med socio¬kulturell, ekonomisk och ekologisk hållbarhet? För att kunna besvara dessa frågor har avhandlingen ytterligare ett syfte; att, med natur- och teknikvetenskapligt språkbruk experimentera med Donna Haraways figuration "diffraktion" som metodologi och därigenom uppmärksamma den mångfald av kunskaper och röster som är nödvändiga för att skapa hållbarhet som beaktar alla tre aspekterna av hållbar utveckling. I analyserna spelar också "situerade kunskaper" stor roll. Avhandlingens empiri består av deltagande observationer i kommunala storkök, intervjuer med kostchefer samt ledare av projekt för hållbar utveckling i offentliga sektorns måltidsproduktion och dokument. Med hjälp av feministisk teknovetenskap har jag kunnat visa på hur djupt involverad offentliga sektorns måltidsverksamhet är i teknologiska system som både fungerar småskaligt i varje enhet i verksamheten men också hur den är sammanlänkad i de storskaliga infrastrukturella systemen i vårt samhälle. Med feministisk forsknings¬metodologisk ansats har jag också visat på hur hållbar utveck¬ling kan förstås inom offentliga sektorns storköksverksamhet samt vad som kan krävas för att strävan efter hållbar utveckling ska bli lyckosam.I avhandlingsarbetet har jag rört mig mellan en fokusering på teknologiers funktioner och konsekvenser, särskilt med fokus på hållbar utveck¬ling, hanteringen av dem i förändringssammanhang och hur den teknologi¬intensiva måltids¬verk¬samheten i skolor och förskolor har betydelse för arbetet för hållbar utveckling men då inte endast som en följd av att verksamheten direkt blir föremål för resurseffektivisering. I den människotäta verksamhet som offentliga sektorns måltidsproduktion utgör är faktorer som omsorg, hälsa och välbefinnande starkt närvarande. Faktorer som är betydelsefulla för hållbar utveckling med hänsyn till alla dess dimensioner. I begreppet teknovetenskap ligger att kunskapsproduktionen och teknologi¬utvecklingen i dag äger rum i komplexa och utspridda sammanhang där universitet, företag och andra aktörer i samhället, till exempel offentliga sektorn, deltar och påverkar vägvalen, lokalt, nationellt och internationellt. Mot den bakgrunden är det väsentligt att överskrida de gränser som vi ofta drar upp mellan teknologi, vetenskap, politik och samhälle och i stället försöka visa på hur dessa länkas samman i användningen och utvecklingen av teknologi, något som är en nödvändighet för den förändringsaspekt som utmärker feministisk teknovetenskap och som feministiska vetenskapsstudier ofta syftar till. Min fokusering på hur materiella-diskursiva praktiker med en mångfald av apparaturer som teknologier, maskiner, människor, livsmedel, beräknade näringsrekommenda¬tioner etc är djupt involverade i det mer abstrakta som värderingar, skolarbete, inlärningsförmåga, sinnesintryck, förebilder… kan inspirera till ökat engagemang i de senare när förändringar och utveckling av teknologier är på gång. Avhandlingens experimenterade kan beskrivas som samtal mellan policies om hållbar utveckling, offentliga sektorns storkök som praktik, och feministisk teknovetenskap. Dessa samtal ger nya perspektiv som kan ge nya möjligheter i skapandet av hållbar utveckling.
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| 69. |
- 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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| 70. |
- Albertsson, Kim
(författare)
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Machine Learning in High-Energy Physics: Displaced Event Detection and Developments in ROOT/TMVA
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many proposed extensions to the Standard Model of particle physics predict long-lived particles, which can decay at a significant distance from the primary interaction point. Such events produce displaced vertices with distinct detector signatures when compared to standard model processes. The Large Hadron Collider (LHC) operates at a collision rate where it is not feasible to record all generated data—a problem that will be exac-erbated in the coming high-luminosity upgrade—necessitating an online trigger system to decide which events to keep based on partial information. However, the trigger is not directly sensitive to signatures with displaced vertices from Long-lived particles (LLPs). Current LLP detection approaches require a computationally expensive reconstruction step, or rely on auxiliary signatures such as energetic particles or missing energy. An improved trigger sensitivity increases the reach of searches for extensions to the standard model.This thesis explores the possibility to apply machine learning methods directly on low-level tracking features, such as detector hits and hit-pairs to identify displaced high-mass decays while avoiding a full vertex and track reconstruction step.A dataset is developed where modelled displaced signatures from novel and known physics processes are mixed in a custom simulation environment, which models the in-ner detector of a general purpose particle detector. Two machine learning models are evaluated using the dataset: a multi-layer dense Artificial Neural Network (ANN), and a Graph Neural Network (GNN). Two case studies suggest that dense ANNs have difficulty capturing relational information in low-level data, while GNNs can feasibily discriminate heavy displaced decay signatures from a Standard Model background. Furthermore it was found that GNNs can perform at a background rejection factor of 103 and a signal efficiency of 20% in collision environments with moderate levels of pile-up interactions, i.e. low-energy particle collisions simultaneous with the primary hard scatter. Further work is required to integrate the approach into a trigger environment. In particular, detector material and measurement resolution effects should be included in the simulation, which should be scaled to model the High-Luminosity Large Hadron Collider (HL-LHC) with its more complicated geometry and its high levels of pile-up.In parallel, the machine learning landscape is quickly evolving and concentrating into large software frameworks with expanding scope, while the High-Energy Physics (HEP) community maintains its own set of tools and frameworks, one example being the Toolkit for Multivariate Analysis (TMVA) which is part of the ROOT framework. This thesis discusses the long- and short-term evolution of these tools, both current trends and some relations to parallel developments in Industry 4.0.
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