| 11. |
- Byström, Alexandra
(författare)
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Compartment Fire Temperature Calculations and Measurements
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to heat transfer and fire dynamics in enclosures. It consists of a main part which summarizes and discusses the theory of heat transfer, conservation of energy, fire dynamics and specific fire scenarios that have been studied. In the second part of this thesis, the reader will find an Appendix containing seven scientific publications in this field.In particular, one- and two-zone compartment fire models have been studied. A new way of calculating fire temperatures of pre- and post-flashover compartment fires is presented. Three levels of solution techniques are presented including closed form analytical expressions, spread-sheet calculations and solutions involving general finite element temperature calculations. Validations with experiments have shown good accuracy of the calculation models and that the thermal properties of the surrounding structures have a great impact on the fire temperature development. In addition, the importance of the choice of measurement techniques in fire engineering has been studied. Based on the conclusions from these studies, the best techniques have been used in further experimental studies of different fire scenarios.
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| 12. |
- Carlsson, Oscar
(författare)
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Engineering of IoT Automation Systems
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Major societal challenges such as environmental sustainability, availability of energy and raw materials, and globalisation are creating new requirements for many actors in society. These new requirements relate to efficiency, flexibility, sustainability, and competitiveness. While these aspects have all been around for some time, and many systems have been locally optimised with regards to one or a few of these requirements, recent advances in communication and processing capabilities promise increased possibilities for connecting different parts of society, allowing optimal operation on a much larger scale.While industrial production systems have been controlled electronically for decades, the digitisation of market channels and consumer systems, together with the possibility to interconnect different production facilities, now allow for automated interaction along the whole supply chain from raw materials to end users.Simultaneously, increased demand for efficiency forces increased specialisation among actors, which with increased possibilities of interconnectivity, creates large enterprises of cooperating, specialised stakeholders.One of the major remaining obstacles for a widespread adaptation of more intelligent, more connected systems, able to deliver these envisioned results, is a coherent approach to the engineering and management of Systems-of-Systems involving very large numbers of devices and operating across several automation domains.For traditional automation systems there are established engineering procedures and numerous standards for engineering data, although most are focused on the static processes that have traditionally been the norm. For full integration with a digital society many of the existing automation systems will need significant modifications and as many automation systems are ageing and in need of replacement, a suitable solution to this may be a large scale migration to new automation solutions.The work presented in this thesis includes some new approaches and methodologies to utilise the existing engineering procedures and standards, while introducing some of the flexibility proposed by the emerging technologies. The major technical solutions presented consist of a structure way to organise connected systems and how they are related, regardless of engineering standards used to design their interactions, and an approach to allow configuration of heterogeneous systems through service interactions.Further contributions include an approach for migrating certain categories of existing industrial control systems to a service oriented architecture, as a basic outline for adaption of the next generation of automation systems in industry.Certain remaining challenges have been identified, which have to be addressed for a successful launch of widespread interconnected automation systems based on Internet of Things and associated technologies.
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| 13. |
- Chibba, Aron
(författare)
-
Supply Chain Quality Management : Exploring performance of manufacturing organizations
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses the issue of quality performance in supply chains in the manufacturers’context. Research shows that the management and performance of supply chains play a major rolein gaining competitive advantage, especially in times of decreasing international trade barriers andquickly evolving information technology. Some researchers claim that it is the supply chain itselfthat competes on a market and not merely the organisations with their specific strategies andgoals. Supply chain performance has been widely discussed in the research literature in recentyears. However, this research points out that supply chain quality management (SCQM) and itsimpact on firm performance (both inter-organisational and intra-organisational) have not beensufficiently understood. Further studies are needed to identify the direct and indirect impact ofSCQM practices on firm performance at multiple levels.A problem that many organisations face is the lack of resources and knowledge on how to managesupply chain quality performance (i.e., which performance to measure, how to controlperformance, and how to improve performance). Studies show that often even large companiesmeasure effectiveness using key performance indicators (KPI) and that these indicators often donot depict key characteristics critical to organisational performance or customer behaviour.Therefore, such indicators might be inadequate for fully capturing the performance of supplychains. As quality management standards evolve, managers need to adapt to changingrequirements. To fulfil the new version of ISO 9001, organisations are required to determinecriteria and apply methods to ensure effective operation and control of their processes (both intraorganisationaland inter-organisational performance). This includes monitoring and measuringperformance indicators. The quality performance of a supply chain is dependent on its ability toimprove and thereby enable organisations to stay competitive over time. Good measurements ofsupply chain quality performance must reflect this ability. To do so, organisations need to knowwhich measures and metrics to use and how to analyse performance of their supply chains.From the seven studies presented in this thesis we are able to draw a number of more generalconclusions that bear on the main research question: What improves quality performance of supplychains that include manufacturing? At the process level, it has been found that manufacturersshould focus on the quality and delivery performance of each process within the organisation. Atthe internal, integrated supply chain level, a manufacturing organisation should focus on quality(conformance), delivery performance (on-time delivery), and cost cutting in the internal supplychain. Collaboration using cross-functional teams seems most appropriate when working withproduct development. The use of a process-oriented mapping tool was found to facilitatedescription of information flows and physical material flows and also to identify disturbances thatcould be improved and rationalized to generate a better flow in the total supply chain. At both theupstream and downstream sides of the supply chain, one-sided measures that depict performanceover organisational boundaries were found to be the most common. At the downstream side of asupply chain, suppliers could be chosen based on cost, conformance, speed, and flexibility. At theupstream side, procedures that handle changing requirements and information about delays orincorrectness of materials were found to influence flow. The results from these seven studies arethe basis for the development of a supply chain quality improvement model. In the literature,supply chain performance is often discussed on a strategic level with measures for quality,flexibility and delivery. Managers also need metrics that can be followed up on at a detailed level(e.g., capacity load, breakdown rates, claims, cost of poor quality, and lead-times). To bridge thisgap, a Key Performance Indicators Matrix of supply chain quality performance indicators formanufacturers is proposed.
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| 14. |
- Deng, Liang, 1986-
(författare)
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Modelling of wear and galling in press hardening simulations
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Implementation of press hardened parts in automobile responses to the requirement of reduced carbon dioxide emission because the press hardened part has very high ratio of strength to weight. Furthermore, ultra high-strength steels (press hardened parts) increases the vehicle safety. The press hardening processes are prevalently applied in global automotive industries. However, the press hardening processes corresponding to heating, forming, and cooling processes result in harsh contact conditions such as cyclic pressures, high temperatures and complex reactions between coatings and tool steels. Consequently, these harsh contact conditions increase the tool maintenance due to abrasive wear and adhesive wear. In order to study tribological behaviours in the press hardening, two kinds of the tribological experiments have been developed and used. Firstly, a reciprocating test, also called SRV test, is performed at elevated temperatures to study the wear mechanisms under press hardening conditions. However, the discrepancy between the press hardening and SRV test is obvious. To overcome the disadvantage, a sliding tribometer, also called tribolgoical test, is used as the second tribological test. A unidirectional sliding process is running under the corresponding pressures, temperatures, velocities and sliding distances. These test parameters are based on press hardening simulations. According to the present study, the abrasive wear is the predominant wear mechanism in the uncoated interface of the press hardening processes. When Al-Si coated workpieces are applied in the press hardening, severe adhesive wear, also called galling, substantially occurs in the stamping tool. The modelling of the abrasive and adhesive wear is derived from the Archard wear model in which the specific coefficients for the wear are calibrated by the tribological tests. The wear predictions implemented in the press hardening simulation have been validated by a press hardening experiment, which represents a typical geometry of vehicle components.
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| 15. |
- Engström, Maria, 1974-
(författare)
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Secondary currents in groundwater
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis concerns the small vertical water movements created by thermal convection and the Coriolis force acting on groundwater flows. These small flows are of importance to vertical transports of temperature, nutrients and contaminants that would not be spread in the way they are. The first part analyzes thermally driven, seasonal groundwater convection by numerical simulation. The second part shows that the Coriolis force also induces secondary currents in groundwater flow through different vertical permeability distributions. Density driven convection occurs during the autumn in southern Sweden when the ambient air temperature cools the mean groundwater temperature from about 10ºC. When the shallow groundwater is cooled by the ambient air its increased density makes this water sink, slowly increasing in temperature, while pressing the warmer water upwards creating a convection cell. The process is ongoing as long as there is a thermal gradient between ground surface and the groundwater. Under favorable conditions convection can reach a depth of 6m. Such density-driven water movements occur most easily in more permeable soil. In northern Sweden, the situation is reversed, since the mean groundwater temperature is below 4ºC, at which water is at its density maximum. So, in springtime when the uppermost groundwater is heated to 4ºC by the warmer air the convection process starts. Here, the sinking groundwater does not reach the same depth, less than one meter. The Coriolis force has been considered too small to have any effect on groundwater flow, though its importance in meteorology and oceanography is well established. These theories have been applied using numerical simulations of groundwater flow. The numerical model has been validated by simulating some earlier studies of Coriolis forces in fluids. Furthermore the model has been extended to include porous media. It has been shown that secondary currents occur in nonlinear vertical permeability distributions. For simulations of constant and linear distributions no secondary currents have been seen. The development is more pronounced in confined aquifers. The structure of the bottom of the aquifer affects how the secondary currents arise. It was shown that both temperature gradients and the Coriolis force form secondary currents in groundwater and a general conclusion is that groundwater flow is more complex than previously assumed.
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| 16. |
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| 17. |
- Gebretsadik, Daniel Woldegebriel
(författare)
-
Tribological characteristics of some multi-layered Pb-free engine bearing materials
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lead (Pb) containing alloys such as white metals and Cu-Pb-Sn (lining) with Pb-based overlay plating have been extensively used as materials for internal combustion engine bearings during the last several decades. However, owing to environmental and health concerns, the use of Pb containing materials in automotive engine components is being restricted. In view of this, attempts are under way to develop and replace Pb-containing materials with Pb–free bearing materials.The tribological characteristics of these recently developed Pb-free bearing materials have, however, not been fully investigated and only a limited results about their tribological performance are available in open literature. This thesis therefore focuses on investigating the tribological performance of some recently developed Pb-free engine bearing materials. Although engine bearings are designed to operate in full film lubrication conditions yet they also operate in mixed and boundary lubrication regimes where the material properties do affect their tribological performance. There is thus a need to study the tribological behaviour of these new Pb-free bearing materials in mixed and boundary lubrication conditions vis a vis that of conventional Pb-containing bearing linings and overlays. This work has therefore aimed at investigating the tribological characteristics such as friction and wear, seizure behaviour, interaction with different oil formulations and embeddability behaviour of some selected Pb-free engine bearing materials.Friction and wear properties of Pb-free bearing materials Al-Sn based lining without overlay, bronze lining coated with Polyamide-Imide (PAI) based overlay containing MoS2 and graphite, bronze lining coated with Al-Sn based and PAI based overlay containing MoS2 and graphite, bronze lining coated with Sn-based overlay, and bismuth (Bi) containing bronze lining coated with Sn-based overlay have been studied using a block-on-ring test configuration under unidirectional sliding conditions in mixed and boundary lubrication regimes. The conventional Pb-containing bearing material was also studied as a reference material. Al-Sn based material showed considerably higher friction compared to the other bearing materials. The bearing material with PAI based overlay containing MoS2 and graphite showed superior friction and wear properties compared to all other materials. Sn-based overlay coated materials resulted in comparable friction and wear properties to that of Pbbased overlay. Wear mechanism in Al-Sn based material is mainly adhesive and abrasive in case of Sn based overlay.Seizure behaviour of the bearing materials were also studied using the block-on-ring test configuration in dry as well as lubricated conditions using pure base oil and a fully formulated engine oil. The PAI based overlay containing MoS2 and graphite showed no sign of seizure even at the highest test load in dry as well as lubricated conditions. Al-Sn based lining without overlay seizes at relatively lower load in dry condition compared to the other bearing materials. Adhesion or wear debris smearing onto the counter surface is the main causes of seizure in dry condition. In lubricated condition, seizure occurred at relatively higher load and the conventional Pb-containing material was found to have better seizure performance compared to the Al-Sn based and Sn-based overlay plated materials.Tribological compatibility of Pb-free bearing materials with different oil formulations was studied using a ball-on-bearing specimen test configuration in boundary lubrication under reciprocating sliding conditions. Four different bearing materials were investigated using different lubricants with and without oil additives. In general, the bearing materials lubricated with pure PAO base oil showed higher friction compared to those lubricated with oils containing additives. Lubricants containing additives improved wear properties of the bearing materials except in the case of Al-Sn based lining without overlay. It was also observed that the anti-wear additive level did not significantly influence the wear performance of bearing overlays.The embeddability behaviour of Pb-free bearing materials was studied using a fully formulated engine oil contaminated with SiC particles. Pb-free bearing materials with Snbased overlay, Bi-based overlay, PAI-based overlay containing MoS2 and composite overlay containing PAI, Al, PTFE were investigated. Tests at different rotational speeds (i.e. different oil film thickness) and a constant load were carried out using a journal bearing test rig. It was found that material removal from bearing and shaft surfaces due to abrasive wear is influenced by the lubricant film thickness. The steel counter surface showed lower wear in tests using Sn based overlay and a PAI, Al and PTFE containing composite overlay compared to Bi-based overlay and PAI-based overlay containing MoS2.
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| 18. |
- Ghosh, Rajib
(författare)
-
Assessment of rock mass quality and its effects on charge ability using drill monitoring technique
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For an efficient mining operation, it is essential to have as much information as possible aboutthe ore to be excavated and the rock masses surrounding the ore. Geological information andthe content and distribution of extractable minerals, are central concerns for long term mineplanning. However, for mine stability and production scheduling, the mechanical conditionsof ore and side rock are also very important. The underground mining process normallyconsists of a number of unit operations, such as drilling, charging, blasting, loading,transportation, hoisting etc., linked in a production chain. The quality of the initial operations(drilling, charging and blasting) normally defines the pre-conditions for the following loadingand transportation processes in the mine. The ability to fully charge holes as planned has beenidentified as one of the major obstacles for smooth fragmentation. Course or unevenfragmentation will, for example, significantly affect the loading and transportation efficiencyin the downstream production chain.Earlier studies in LKAB’s Malmberget mine have shown that the chargeability is on averagearound 90%. However, individual levels can have an average chargeability of only 70% andindividual rings, at those levels, can suffer from chargeability as low as 50%. A significantpart of these problems has its origin in geo-mechanical problems in the rock mass. Therefore,detailed knowledge of the rock mass condition surrounding the boreholes is essential toimprove the planning and execution of the charging works in a mine and to improve overallfragmentation and production efficiency.The focus of this thesis is therefore to define and evaluate geo-mechanical features in thedrilled rock mass effecting chargeability, and to evaluate drill monitoring technique for theassessment of rock mass quality and its effects on borehole’s chargeability using hydraulic In-The-Hole (ITH) percussive drilling.The research is based on literature review, drill-monitoring data, borehole filming, on-lineproduction database and monitoring of charging operation. Statistical methods are used toanalyse drill data. The data have been collected from LKAB’s underground mine inMalmberget, Sweden.Several rock mass conditions including caving, shearing, deformation, fracturing, cavities,solid rock, etc., have been identified during filming of 361 production boreholes.Measurement While Drilling (MWD) technique has been used to assess the quality of thepenetrated rock mass. In order to do so, a detailed analysis of the drilling system and thedrilling control including how monitored parameters relate to each other and to the penetratedrock mass conditions, has been performed. The results show that the MWD data containpronounced hole length dependent trends, both linear and step-wise linear, for mostparameters. By combining the borehole filming and the analyses of monitored drillparameters, the drilling responds to each geo-mechanical features in the rock mass is furtherdemonstrated. High correlation has been found between the geo-mechanical rock properties(fractures, cavities, solid rocks, etc.,), and the registered drilling system’s response. Theanalyses show that the responses from the drill monitoring system can distinguish between solid rock, fracture zone, cavity and cave-in. Based on the correlation between the registereddrilling system’s responses and the geo-mechanical features, a geo-mechanical model isdeveloped to assess the borehole chargeability. Principal Component Analysis (PCA) isperformed to model this relationship. The developed model can distinguish fans, or parts offans, with solid, non-fractured rocks where no chargeability problems can be expected, fromfans, or part of fans, with fractures, cavities or cave-in risks, where chargeability problemscan be expected. The model shows high potential for identifying charging problems in theborehole, and has been verified and validated by following an actual charging operation in thereal production environment.
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| 19. |
- Gowda, Vasantha, 1986-
(författare)
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Experimental and Computational Magnetic Resonance Studies of Selected Rare Earth and Bismuth Complexes
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rare-earth elements (REEs) and bismuth, being classified as the ‘most critical raw materials’ (European Raw Materials Initiatives, 2017), have a high economic importance to the EU combined with a high relative supply risk. REEs are highly important for the evolving technologies such as clean-energy applications, high-technology components, rechargeable batteries, permanent magnets, electric and hybrid vehicles, and phosphors monitors.This scientific research work aims at building a fundamental knowledge base concerning the electronic/molecular structure and properties of rare-earth element (REE) and bismuth complexes with dithiocarbamate (DTC) and 1,10-phenanthroline (PHEN) by employing state-of-the-art experimental techniques such as nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction (XRD) techniques together with ab initioquantum mechanical computational methods. This combination of methods has played a vital role in analysing the direct and significant effect of the heavy metal ions on the structural and magnetic resonance properties of the complexes, thereby, providing a framework of structure elucidation. This is of special importance for REEs, which are known to exhibit similar chemical and physical properties. The objectives of the work involve i) a systematic investigation of series of REE(III) as well as bismuth(III) complexes to get a profound understanding of the structure-properties relationship and ii) to find an appropriate theoretical modelling and NMR calculation methods, especially, for heavy metal systems in molecular and/or solid-state. This information can later be used in surface interaction studies of REE/bismuth minerals with DTC as well as in design and development of novel ligands for extraction/separation of metal ions.The REE(III) and bismuth(III) complexes with DTC and PHEN ligands have all provided aunique NMR fingerprint of the metal centre both in liquid and solid phase. The solid-state 13C and 15NNMR spectra of the diamagnetic REE(III) and bismuth(III) complexes were in accord with their structural data obtained by single crystal XRD. The density functional theory (DFT) methods were used to get complementary and refined structural and NMR parameters information for all diamagnetic complexes in the solid-state. The relativistic contributions due to scalar and spin-orbit correlations for the calculated 1H/13C/15N chemical shifts of REE complexes were analysed using two-component zeroth-order regular approximation (ZORA)/DFT while the ‘crystal-lattice’ effects on the NMR parameters were calculated by combining DFT calculations on molecular and periodic solid-state models. The paramagnetic REE complexes display huge differences in their 1H and 13C NMR spectral patterns. The experimental paramagnetic NMR (pNMR) chemical shifts, as well as the sizable difference of the 1H and 13C NMR shifts for these isoelectronic complexes, are well reproduced by the advanced calculations using ab initio/DFT approach. The accuracy of this approach is very promising for further applications to demanding pNMR problems involving paramagnetic f-block elements.The results presented in this thesis demonstrate that a multidisciplinary approach of combined experimental NMR and XRD techniques along with computational modelling and property calculations is highly efficient in studying molecular complexes and solids containing heavy metal systems, such as rare-earths and bismuth.
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| 20. |
- Goyal, Rahul, 1987-
(författare)
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FLOW FIELD IN A HIGH HEAD FRANCIS TURBINE DRAFT TUBE DURING TRANSIENT OPERATIONS
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydroelectricity plays an important role to balance the stability of grid network. In order to improve the stability of presently high loaded grids, hydropower plants are being operated over a wide range of operations and experiencing frequent start-stop, load rejection, and load acceptance. The turbines need to sustain sudden change in their operating condition to balance the grid frequency. Francis turbines have been widely used because of their wider operating range and higher stability in operation during rapid load variation. This has resulted in severe damage to the turbines as they are not normally designed to operate under such transient conditions.Several low and high frequency pressure fluctuations prevail during transients operating conditions. Generally, wall pressure measurements are performed which may not provide sufficient information to investigate the flow instabilities related to these fluctuations. Thus, the main objective of the present work is to simplify and perform optical measurements in a turbine during transient operating conditions to investigate the flow field. The measurements have been performed at the Water Power Laboratory using a high head model Francis turbine. The turbine is a 1:5.1 scale down model of a prototype operating at the Tokke Power Plant, Norway. The model runner diameter, net head, and discharge at the best efficiency point (BEP) were 0.349 m, 12 m, and 0.2 m3 s-1, respectively. A total ten pressure sensors were mounted at different locations namely, turbine inlet, vaneless space, and draft tube. The data were acquired at a sampling rate of 5 kHz. The instruments and sensors have been calibrated according to guidelines available in IEC standards. The determined total uncertainty in the measurement of hydraulic efficiency was ±0.15% at BEP condition. The velocity measurements in the draft tube cone were performed using a 2D PIV system and the images were sampled at a rate of 40 Hz. Steady state measurements were carried out considering the realistic design and off-design operating conditions of the prototype turbine. Therefore, the angular speed of the runner was maintained constant for all steady state conditions during the measurements. The maximum hydraulic efficiency (92.4%) was observed at nED = 0.18, QED = 0.15, and a = 9.8º, which is named BEP. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space, runner, and the draft tube. The fluctuations due to rotor-stator interaction (RSI) were observed to be most dominating at high load condition, however, fluctuations due to the rotating vortex rope (RVR) at part load (PL) condition. Two different modes (synchronous and asynchronous) modes of vortex rope are observed at PL condition of the turbine. An asymmetry in the flow leaving the runner was detected at both design and off-design conditions, with a stronger effect during off-design operating condition. Numerical simulations of the model turbine were carried out at PL operating condition. The simulations were performed using two turbulence models, standard k-ε and SST k-ω, with high-resolution advection scheme. The numerical pressure values obtained with both standard k-ε model and SST k-ω showed a small difference with the experimental values. The amplitudes of numerical pressure values were higher (~2.8%) in the vaneless space and lower (~5.0%) in the draft tube than the experimental values. The frequencies of the RSI and RVR were well captured in the turbine but the amplitudes were overestimated. During load rejection from BEP to PL, the plunging mode of the vortex rope was observed to appear first in the system than that of the rotating mode. Whereas during the load acceptance from PL to BEP, both the modes were observed to disappear simultaneously from the system. In the velocity data, the axial velocity only contributed to the development of the plunging mode and radial velocity to the rotating mode. The region of low velocity, stagnation point, flow separation, recirculation, oscillating flow and high axial velocity gradients were well captured in the system during the transients. The induced high-velocity gradients during the load acceptance from BEP to HL was observed to develop a vortex core in the draft tube.During startup and shutdown, the guide vanes angular position was moved from one to another steady state condition to achieve the minimum load condition of the turbine. At this condition, the generator of the turbine was magnetized at the synchronous speed during startup and shutdown, respectively. The frequency of wave propagation was observed to vary with the runner angular speed during startup and complete shutdown of the turbine. Comparatively high-pressure fluctuations in the draft tube were observed during the guide vane movement from the high discharge conditions. Some unsteady phenomena such as the formation of dead velocity zone, backward flow, and flow oscillations were observed during startup and shutdown of the turbine. The current work has been also used to continue a series of workshops, i.e., Francis-99. The first workshop was held on December 2014 with the cooperation of LTU and NTNU. The measurements performed in this work were used for the second workshop which was held on December 2016. The investigations presented in this thesis will be further explored in the third workshop scheduled for December 2018.
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