| 1. |
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| 2. |
- Bicaku, Ani, DI, 1988-
(författare)
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Security Standard Compliance in System of Systems
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The world we live in is becoming digitalized by transforming our society and economyin an unpredicted way. Digital technologies are transforming products, manufacturingassets, and entire supply chains. These technologies revolutionize how organisations en-gage with customers, other partners, and society depending on the ability to connectpeople, technology, and processes. Distributed services through different platforms, or-ganisations, and even regions are becoming very common with the digital transformationof industrial processes. More and more systems are being constructed by interconnectingexisting and new independent systems. The transformation from traditional and isolatedsystems to connected components in a System of Systems (SoS), provides many advan-tages such as flexibility, efficiency, interoperability, and competitiveness. While it is clearthat digital technology will transform most industries, there are a number of challengesto be addressed, especially in terms of standards and security.In the past, providing a secure environment meant isolation from external access andproviding physical protection, usually based on proprietary standards. Nowadays, withthe development of state-of-the-art technologies, these systems have to meet and provideproof of fulfilling several requirements and involving many stakeholders. Thus, to assurethat organisations can move towards this multi-stakeholder cooperation, security is one ofthe challenges that need to be addressed. With the increasing number of devices, systems,and services in these complex systems and the number of standards and regulationsthey should fulfill, the need for automated standard compliance verification is of utmostimportance. Such verification will ensure that the components included in their businessprocesses comply with the imposed standards, laws and regulations.The research presented in this thesis targets the automated and continuous standardcompliance verification in SoS. Standard compliance verification provides evidence thatprocesses and their components satisfy the requirements defined by national and interna-tional standards. The thesis proposes an automated and continuous standard complianceverification framework that provides evidence if SoS components fulfill security standards’requirements based on extracted measurable indicator points. Since these systems evolveover time, the standard compliance is verified in design time and continuously monitoredand verified during run time after the SoS has been deployed.
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| 3. |
- Botella, Pablo, PhD Student, 1988-
(författare)
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Physical Properties of Ternary Metal Oxides and Carbon Nanomaterials Under Pressure
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Found in nature or synthesized, materials present amazing properties such as superconductivity, super-hardness, lightweight, or high-energy-density, among others. All these properties can be used in our benefit to improve or develop new applications. Although, many of these properties are not noticeable in the ambient conditions of pressure and temperature. Therefore, only when the materials are exposed to extreme conditions of temperature, pressure, radiation, etc., become notable. For those reasons, it is fundamental to understand their properties and how they are affected by different parameters such as the synthesis process, morphology, doping or external parameters (e.g. pressure, temperature).High-pressure studies have been shown to be an excellent tool for proving and study the robustness of material properties as well as for the synthesis of new materials. Changes as extreme and spectacular as converting oxygen gas into a superconducting metal or the well-known graphite to diamond conversion among others have been made under high-pressure conditions.Among all the materials, and due to their interesting properties, in this doctoral thesis we have studied four ternary metal oxide semiconductors (InVO4, CrVO4, InNbO4 and InTaO4) and carbon nanostructure materials (single-walled carbon nanotubes (SWCNTs)) at ambient conditions as well as under high-pressure (static or dynamic compression) using different characterization techniques such as X-ray diffraction (XRD), Raman spectroscopy (RS), optical absorption, transmission electron microscopy (TEM), photoluminescence (PL) and electrical measurements.InVO4, InNbO4 and InTaO4 are wide metal oxide semiconductors having band-gap energy of 3.62(5), 3.63(5) and 3.79(5) eV, respectively, being InVO4 a direct band-gap semiconductor and, InNbO4 and InTaO4 indirect band-gap semiconductors. These compounds undergo, under pressure, to a structural phase transition from orthorhombic, in the case of InVO4, or monoclinic, in the case of InNbO4 and InTaO4, to another monoclinic system. This structural phase transition triggers interesting phenomena due to the modification of the electronic band structure of the compounds. Phenomena observed under compression include bandgap collapse about 1-1.5 eV depending on the compound, band crossing due to the change to the local maximum on top of the valence band and colour change. Also, the electrical resistivity of the materials is affected by this change in the band structure. All these results are discussed based on our theoretical band structure calculations.On the other hand, doping these compounds below 0.2% using Tb or Yb rare-earth elements, the crystal structure is barely affected as well as their phonon structure, but the band structure does, giving rise optical excitation and emission properties in the visible and near-infrared (NIR) spectral region. From optical reflectivity measurements, the two first direct transitions are reported at 3.7/4.2 eV in InVO4, 4.7/5.3 eV in InNbO4 and 5.6/6.1 eV in InTaO4. All the compounds present self-activated photoemission signals which are discussed in terms of the distorted polyhedral coordination around V, Nb and Ta atoms. Finally, the characteristic emission of Tb atoms in the green region (5D4→7FJ) and the Yb atoms in the NIR region (2F5/2→2F7/2) are analysed and discussed based on our theoretical calculations.Even though, being a prototype structure of a family of compounds denoted as CrVO4-type materials, there is still scarce information on the behaviour under pressure of the CrVO4 compound. Here, it is also studied CrVO4 having an orthorhombic structure under pressure up to 10 GPa. Crystal structure, phonon band structure, optical and electrical properties are analysed showing a structural phase transition similar to that in InVO4 with an increase in the vanadium atoms coordination from 4 to 6. This phase transition triggers also a band-gap collapse of 1.1 eV, a change in the phonon structure and a sharp decrease in the resistivity of the material. All these results are discussed in terms of our theoretical calculations and comparison with its isostructural partner InVO4.To conclude, we study the effects of the dynamic pressure of 0.5 Mbar (50 GPa) on SWCNTs which is way beyond the limit of their structural stability in quest of new forms of carbon nanostructures. Thus, no nanotubes survived to this pressure. The recovered material is composed of two types of material which are classified in a multi-layer graphene phase (MLG) with high defect concentration and multi-phase material which dominates the sample. Even the reached conditions during the shock-compression were favourable for the diamond formation, we were unable to find traces of diamond-like carbon in the very inhomogeneous sample. The crystal size of both materials has been estimated at 13 nm for disordered carbon and 30 nm for MLG phase. The dispersion of the Raman modes was also studied using several lasers and the observations were supported by TEM analysis.
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| 4. |
- Burtseva, Evgeniya, 1988-
(författare)
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Boundedness of some linear operators in various function spaces
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis is devoted to boundedness of some classical linear operators in various function spaces. We prove boundedness of weighted Hardy type operators and the weighted Riesz potential in Morrey—Orlicz spaces. Furthermore, we consider central Morrey—Orlicz spaces and prove boundedness of the Riesz potential in these spaces. We also present results concerning boundedness of Hardy type operators in Hölder type spaces. The thesis consists of four papers (Papers A—D), two complementary appendices (A1, B1) and an introduction.The introduction is divided into three parts. In the first part we give main definitions and properties of Morrey spaces, Orlicz spaces and Morrey—Orlicz spaces. In the second part we consider boundedness of the Riesz potential and Hardy type operators in various Banach ideal spaces. These operators have lately been studied in Lebesgue spaces, Morrey spaces and Orlicz spaces by many authors. We briefly describe this development and thereafter we present how these results have been extended to Morrey—Orlicz spaces (Paper A) and central Morrey—Orlicz spaces (Paper B). Finally, in the third part, we introduce Hölder type spaces and present our main results from Paper C and Paper D, which concern boundedness of Hardy type operators in Hölder type spaces. In Paper A we prove boundedness of the Riesz fractional integral operator between distinct Morrey—Orlicz spaces, which is a generalization of the Adams type result. Moreover, we investigate boundedness of some weighted Hardy type operators and weighted Riesz fractional integral operator between distinct Morrey—Orlicz spaces. The Appendix A1 contains detailed calculations of some examples, which illustrate one of our main results presented in Paper A.In Paper B we prove strong and weak boundedness of the Riesz potential in central Morrey—Orlicz spaces. We also give some examples, which illustrate the main theorem. Detailed calculations connected to one of the examples are described in the Appendix B1. In Paper C we consider n-dimensional Hardy type operators and prove that these operators are bounded in Hölder spaces. In Paper D we develop the results from paper C and derive necessary and sufficient conditions for the boundedness of n-dimensional weighted Hardy type operators in Hölder type spaces. We also obtain necessary and sufficient conditions for the boundedness of weighted Hardy operators in Hölder spaces on compactification of Rn.
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| 5. |
- Busatto, Tatiano
(författare)
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On Waveform Distortion in Modern Low-Voltage Installations with Multiple Nonlinear Devices
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The continuing society quest for more comfort combined with the need to minimize global environmental impacts is constantly introducing new technologies into our daily lives. Among the recent developments, the advances in energy-efficient lighting and renewable energy technologies have enabled a maturity level in cleaner electricity production and efficient use of energy. Aligned with these trends, more recently we are experiencing faster progress towards the electrification of the transport system. All these developments have been largely driven by advancements in power electronic technologies which ultimately introduces a significant number of nonlinear loads in the form of power converters into the low-voltage (LV) installations and networks for electricity distribution.The overall aim of this thesis is to investigate how these nonlinear loads (individually and together) impact the current waveform distortion in modern LV installations. The work addresses several issues related to the electrical interactions between the distribution grid and different nonlinear loads, such as LED lamps, power factor correction (PFC) converters, PV inverters, and electric vehicle chargers.As a first part, the influence of the network impedance is examined. A method combining analytical impedance network modelling with a probabilistic approach for the customer side equipment was developed to address the uncertainties associated with harmonic resonances in public LV networks. It was found that the main resonance is mainly due to the transformer inductance and the total customer capacitance, while cable capacitances and customer inductances have a small impact. Additionally, it was found that increasing PV penetration shifts the harmonic resonances to lower frequencies, but also decreases the impedance magnitude.The second part includes the examination of the so-called nonlinear interaction phenomenon. A methodology has been developed and applied to quantify the extent of nonlinear interaction between devices in the same LV installation. It was observed that the interaction of different power electronic devices creates nonlinearity deviation, changing the current harmonics emission mainly for low order harmonics. The harmonic phase angle is the most affected harmonic characteristic. Additionally, linked to the first part, it was observed that changes in the network impedance and voltage source waveform have a significant impact on the nonlinear interaction.As a third part, the current zero-crossing waveform distortion has been analysed with a focus on control instabilities. Prior measurements of multiple devices fitted with power-factor controller were compared with a simulation model and instabilities were evaluated. Results from this work have confirmed that zero-crossing distortion increases proportionally with the number of devices. In addition, it was found that the network impedance plays an important role in defining the stability-criteria of these devices.Results shown in this thesis have revealed the harmonic interdependency and its consequences in different frequency ranges: harmonics and supraharmonics. Understanding the details of these new scenarios becomes of fundamental importance to mitigate future power quality issues and ensure the functioning of equipment in modern LV installations. This work presents several findings and a comprehensive discussion serving as a guideline for future work on interaction analysis and its consequences for devices in the LV network.
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| 6. |
- Chen, Yifeng
(författare)
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CO2 separation using ionic liquid-based absorbents : thermodynamics and kinetics
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ionic liquids (ILs) have shown great potential to be used as absorbents for CO2 separation owing to their unique properties such as immeasurably low vapour pressure, high thermal stability, high CO2 affinity, and tunable structure. A huge amount of researches have been carried out, and most of them focused on developing novel ILs for CO2 separation. However, high viscosity will impede the IL-based absorbents for the large-scale applications in CO2 separation.The goal of this thesis was to develop IL-based hybrid green absorbents (i.e. choline-2-pyrrolidine-carboxylic acid/polyethylene glycol/H2O ([Cho][Pro]/PEG200/H2O) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/titanium dioxide /PEG200 ([Hmim][Tf2N]/TiO2/PEG200)) for CO2 separation, in which H2O and/or PEG200 were used as co-solvents to adjust the viscosity. A systematic study was conducted from pure to multi-component systems convering experimental measurements and theoretical modeling of thermdynmaics and kinetics, and thus the effects of co-solvents on properties, phase equilibria, and kinetics were also analyzed.To provide reliable and systematic properties and study the effect of H2O, the properties of PEG200 and PEG200/H2O were surveyed, evaluated, and correlated. The density and viscosity of [Cho][Pro]/PEG200/H2O were measured and correlated, and the excess mole volume and excess Gibbs energy of activation were estimated to understand the molecular structure and interactions between [Cho][Pro]/PEG200 and H2O. The results showed that H2O and PEG200 could decrease the viscosity of the hybrid absorbent significantly, and H2O interacted strongly with [Cho][Pro]/PEG200.To obtain reliable and systematic gas solibilities and analyze the effect of H2O, the solubilities of pure CO2, CH4, and N2 in PEG200 were surveyed, measured, evaluated, and described with theoretical models. The CO2, CH4, and N2 solubilities in PEG200/H2O were measured and described with the Redlich-Kwong Nonrandom-Two-Liquid (RK-NRTL) model. The CO2 solubilities in [Cho][Pro]/PEG200 and [Cho][Pro]/H2O were also surveyed, measured, evaluated, and described using the RK-NRTL model. Furthermore, CO2 solubility in the hybrid absorbent was predicted with the model and compared with the new experimental results. The further investigation showed that the formation of carbomate dominated the entire CO2 absorption process by [Cho][Pro]/PEG200/H2O, and the presence of H2O resulted in the formation of bicarbonate.To study the kinetics systematically combined with the effect of H2O, the liquid-side mass-transfer coefficients (kL) of [Cho][Pro]/PEG200/H2O were obtained from the CO2 diffusion coefficients () and the kL values in PEG200/H2O, in which was calculated from the density and viscosity of the hybrid absorbents, while the kL values in PEG200/H2O were measured experimentally. The reaction rate constant of CO2 in the hybrid absorbents was also estimated.Based on the systematic studies from experimental measurement and modeling, it showed that 30 wt%[Cho][Pro]/H2O + PEG200 could be promising for CO2 separation with the consideration of both thermodynamic and kinetic properties. In addition, the hybrid absorbent also showed the good recyclability.To use the confinement as the other strategy for further developing IL-based technology, the CO2 solubility in [Hmim][Tf2N]/TiO2/PEG200 with different ratios of [Hmim][Tf2N]/TiO2 was measured, and the Henry’s constant and absorption enthalpy of CO2 in the hybrid absorbent were calculated. The CO2 solubility in the hybrid absorbent was described with the Henry's law, the contribution of the confinement effect on the CO2 solubility was quantified, and the relationship between the roughness of TiO2 and molecular parameters was established. The results showed that the mass ratio of [Hmim][NTf2]/TiO2 in the hybrid absorbent should be lower than 5.72 %, where the contribution of confinement occupied around 20 % of the total CO2 absorption capacity in [Hmim][NTf2]/T500/PEG200. 2.88 wt%[Hmim][NTf2]/T500 + PEG200 could be promising for CO2 separation on aspects of CO2 capacity and absorption enthplay, and further study will be conducted on the properties and CO2 absorption kinetics.
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| 7. |
- Chohan, Raeesah
(författare)
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Opportunistic Behavior in Industrial Marketing Relationships
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As humans beings, we act to our advantage. In some cases, this is done to the detriment of others; also known as opportunistic behavior. As past and current industrial marketing relationships have been impaired by opportunism, it is valuable for scholars and practitioners to gain a deeper understanding of opportunistic behavior and how to prevent it. A key driver of opportunistic behavior is information. This informs the purpose of this dissertation, which is to address its research problem: How can information facilitate and constrain opportunistic behavior in industrial marketing relationships?Agency Theory is the first theory used to address this research problem. Agency Theory focuses on governing opportunistic behavior in a principal-agent relationship. The theory has been widely applied in the marketing literature. Therefore, this dissertation’s first research question addresses: How has Agency Theory been used to constrain opportunistic behavior in industrial marketing relationships? To answer this question, an extensive literature review is conducted and future research agendas suggested.However, during the course of this dissertation it was found that Agency Theory is limited when applied to relationships where the agent is a professional. Most industrial marketing relationships comprise professional agents. Furthermore, both principals and professional agents can act opportunistically ex-ante (i.e., pre-contract) and ex-post (i.e., post-contract) at the same time. Therefore, the second research question asks: What role does information play in manifesting ex-ante and ex-post opportunistic behavior in principal and professional-agent industrial marketing relationships? This research question is answered in a purely conceptual manner, through the introduction of a new model.The remaining two papers follow a constructivist, qualitative research design. A context was needed to gain an empirical understanding on opportunism in industrial marketing relationships. The context chosen for this dissertation is the client-advertising agency relationship. The third research question therefore asks: How do clients and advertising agencies act opportunistically ex-ante and ex-post? To answer this research question, representatives from advertising agencies and clients were interviewed.Given the clear need to constrain client-advertising agency opportunism, the fourth research question asks: What role does information play in the choice of constraint mechanism for the client-advertising agency relationship? To do this, the Theory of Relationship Constraints was extended to the client-advertising agency relationship context. The theory focuses on choosing the appropriate constraint mechanism to curb opportunistic behavior. Broadly, this dissertation primarily contributes to the body of knowledge by offering a better understanding on how opportunism can manifest and be constrained in today’s industrial marketing context.The remainder of the dissertation is laid out as follows. First, the research area is introduced. Second, the key literature and theoretical perspectives are discussed. Third, the methodology employed is explained. Fourth, the findings are disclosed. Last, the theoretical contributions, managerial implications, limitations and future research agendas are presented and followed by a conclusion. The four papers that comprise this dissertation are then included. Three of these papers are published/accepted; the final paper is a working paper.
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| 8. |
- Curry, Amanda
(författare)
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Management Accounting Above and Under Ground : Field Studies of Operations Managers’ Everyday Work
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns operations managers who are required to adhere to both management accounting and operational concerns in their everyday operational work. The question addressed in this thesis is how management accounting is implicated in the everyday operational work of operations managers and their team members in production environments. The purpose is to explore management accounting practices in the everyday work of operations managers and their team members in production environments, and to theorize about their practices at the intersection of management accounting and operations. The research process drew upon ethnographic ideas and included travels back and forth between theory and practice at a mining company. This thesis shows that operations managers use management accounting in an analytical manner when they draw upon management accounting frames of reference to organize and mobilize action in their everyday operational work. An analytical use of management accounting suggests that management accounting extends beyond accounting departments and meeting rooms at operational levels and reaches out to the shop-floor and the mines. In such settings, operations managers are found doing accounting when they alternate between management accounting and operational frames of reference to interpret, construct and talk accounting in their everyday operational work. Management accounting enables operations managers to make sense of operational situations, and to gain and exert agency in their operational work. The results indicate that management accounting becomes a ‘way of doing things’ in everyday operational work via mimetic mechanisms. At times, operations managers are required to abide by management accounting in their everyday operational work via coercive mechanisms. The first conclusion is that management accounting is implicated in the everyday operational work of operations managers and their team members through its presence as a frame of reference. Operations managers do not always need to rely on accounting artefacts to mobilize action. Rather, they can rely on their developed management accounting knowledge. The second conclusion is that management accounting is implicated in the everyday work of operations managers and their team members through its presence as a practice. Management accounting influences operational routines and activities, which enables operations managers and their team members to handle the intersection between management accounting and operations by developing ways of practicing management accounting in everyday operational work. One contribution to the accounting practice literature is presenting how operations managers are shown to engage in management accounting, thereby making it a practice in their everyday work. Another contribution to the literature on the intersection between management accounting and operations is showing that operations managers gain agency via management accounting in their everyday work, which helps them navigate between management accounting and operational concerns.
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| 9. |
- Darwesh, Ali, 1966-
(författare)
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Parameters optimization of oil well drilling operation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the beginning of 2005, the ministry of natural resources in the Kurdistan region of Iraq dividedits territory into more than 50 oil blocks based on geological setting. These oil blocks were awardedlater to different international oil companies for oil investments based on Production SharingContracts (PSCs). A new oil-exporting pipe was also established from the region to the Jaihan portin Turkey at the Mediterranean Sea.This study is related to the oil well drilling operations in one of these oil blocks in northern Iraqwhich is referred as the Bazian oil block. Drilling operations in the nearby oil blocks (Taq Taq andMiran) were started earlier and the drilling data of those oil blocks were used as offset data in thedrilling program of the Bazian block. High similarities were expected between these oil blocks withrespect to lithology of the formations, oil well drilling techniques, and operation problems. By 2009over twenty oil wells were drilled in the Taq Taq oil block and it is becoming one of the mostimportant oil fields in the Kurdistan region. In the Miran oil block, exploration for oil and gas startedin early 2008, and three oil wells were completed and started to produce crude oil. By the end of2009, the geological and geophysical surveys in Bazian block were finished and the drilling operationstarted on October 1st the same year.This study (Parameter Optimization in Oil Well Drilling Operation) was recommended andsponsored by the Kurdistan Regional Governorate (KRG) aiming towards more optimized drillingin the future in the same oil block. Parameters like weight on bit, string rotation and rate ofpenetration for the future drilling operation in the Bazian oil block with more optimized valueswere predicted. This study was started by collecting detailed operational data from different sourcesduring the operations of drilling the Bazian well Bn-1. Among many sources of data, Mud LoggingUnit (MLU) data were selected for this study, as it was the most complete data set from the surfaceto the final drilled depth. This thesis contains the work of five published papers in the evaluation ofthe drilling operation at different intervals for the key well. Parameters for achieving the optimalpenetration rate were predicted for the future operations.The first paper (Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well)was on the evaluation of the drilling operation in the surface section from 9 m to 480 m. The highlyfractured Pila Spi formation was studied for its controllable parameters like Weight on Bit (WOB),drill string rotation (RPM) and the used torque. High loss of circulation and environmental effectswere studied. Optimum drilling fluid, drilling technique, and drilling parameters were proposed forthe future drilling operation.In the second paper (Kicks Controlling Techniques Efficiency in Term of Time) recorded data wereanalyzed to manage the drilling operation during the critical times in terms of controlling the BottomHole Pressure (BHP). Productive and none productive times were analyzed through the study ofthe drilling and tripping operations. Change in the drilling technique was proposed by modifyingthe drilling fluid. Drilling fluid as a first barrier to control formation pressure and well kicks werestudied for their rheological properties. During the drilling operations two techniques, circulatingtechniques and non-circulating methods, were implemented to control the BHP. Both methodshave been implemented to control kicks in the Bn-1 oil well and wells in other oil blocks in theregion. The process of drilling design and casing setting points have been studied based on theutilization of accurate values of formation pressure. Data of formation pressures were used to designsafe mud weights to overcome and prevent well kicks. The emphasis has been placed on the practicalutilization of the kicks pressure near the reservoir. The presented relationships help in betterunderstanding of the lithological columns and reduce possible hole problems during the kickappearance. Optimum casing setting point of the intermediate section was proposed for futureoperations.The third paper (Time Optimizing near the Pay Zone) was on the drilling operation inside the caprock. Time managing was studied for surface preparation facilities, subsurface expected pressurecontrol time, and the best technique to control the Bottom Hole Pressure (BHP). Well controllingtechniques in oil and gas drilling operations are used to control BHP and avoid any fluid influx fromformation to the well. Time consumed to control the formation pressure will range between a fewhours to many days. This paper also discussed the hydrostatic pressure distribution and changes nearthe pay zone for the Bazian (Bn-1) oil well. Increasing linearly drilling fluid properties such as densityand viscosity with time will help the engineer to better interpret sampling of the lithological columnsand reduce possible hole problems.Paper number four (Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods)was on the effect of wiper trips operations to control parameters during the operations in two drilledshale formations, the Tanjero and Shiranish formations. Wiper trips were evaluated based on thelifting capacity of the cutting in the drilling fluid. This paper discussed the wiper trip effects on wellinstability in shale formations. The problematic shale interval sections were studied with respect tothe time spent on the wiper trip operations. Lifting efficiency and well wall instability arecontinuously changing with time. Detailed drilling operation, formation heterogeneity, rheologicaland filtration characteristics of the proposed polymer water-based mud were discussed. The physicaland chemical properties of the drilled formation and drilling fluid were also studied.Wiper trips were analyzed based on recorded history in relationship with the controllable parameters.Two calculation models have been implemented to find the net rising cutting particle velocity inthe annular. The relation between the net rising velocity and wiper trips were analyzed with supportof results from laboratory works. Strong relationships were found between the wiper trip effects andlithology types of the penetrated shale. A modified drilling program was proposed in relationship tothe casing setting point and drilling fluid properties that make the operations more optimized.The fifth paper (Controllable drilling parameter optimization for roller cone and polycrystallinediamond bits) predicts optimized Rate of Penetration (ROP), WOB and the string rotation (RPM– rotation per minute) for the entire drilled well. The most used empirical Bourgoyne and Youngmodel (BYM) for roller cone bits were used in the optimization process. This model describes theeffect of eight parameters in one mathematical equation. The BYM was adjusted to be applicablefor other types of drilling bits like polycrystalline diamond compacts (PDC) bits. Controllableparameters like WOB, RPM and ROP were clustered based on changes in Bottom Hole Assembly(BHA) and lithology before running the model.The implemented clustering and averaging method for the collected data in short lithologicalintervals were used to eliminate the effect of noisy data and to overcome the lithology homogeneityassumption used in other previous studies. A simpler model were introduced instead to optimize thestring rotation.Multiple regression techniques were used in each cluster to determine optimized controllable drillingparameters. Optimized ROP, WOB, and RPM were predicted for future drilling operations. Aclear relationship was found between the formation lithology and the controllable parameters ineach cluster.
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| 10. |
- Decrozant-Triquenaux, Justine, 1994-
(författare)
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High Temperature Tribology of Aluminium : Effect of Lubrication and Surface Engineering on Friction and Material Transfer
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lightweight design for automotive applications has been pursued for several decades and continues to increase. The main driving forces are new and increasingly stringent emission regulations as well as the increasing popularity of electric, or hybrid, vehicles where the increased weight of the batteries need to be compensated by light weight structures. It is also critical to maintain or improve passenger safety while creating components and structures with lower weight. Materials exhibiting a high strength-to-weight ratio, such as high strength aluminium alloys, are highly interesting to realise the next generation of lightweight vehicle structures.The high strength aluminium alloys include the 5XXX, 6XXX and 7XXX series. In order to increase their formability and minimise springback induced during forming at room temperature, these alloys are preferentially formed at elevated temperatures. Different forming processes such as warm forming and hot stamping (e.g. hot forming and quenching) have been developed to enable forming of components with high geometrical complexity and mechanical properties. However, hot forming of aluminium alloys leads to a challenging tribological interface. Aluminium alloys are ductile and reactive metals, prone to severe adhesion (also termed as seizure or galling) when sliding against a harder metallic counter surface. Aluminium transfer to the forming dies affect the tool lifetime and impacts the quality of the formed component which leads to significant maintenance costs and reduced productivity. These are the main limitations that hinder the implementation of hot aluminium forming for mass production.Lubrication as well as surface engineering strategies are potential methods to control friction and wear in the hot aluminium-tool steel interface. Solid lubricants such as graphite and hexagonal boron nitride (hBN) have been studied for aluminium forming. Polymer-based lubricants are also increasingly evaluated for high-temperature applications. Surface engineering techniques includes both the control of the tool topography and the use of protective coatings. Surface roughness has been observed as a crucial parameter in the initiation of aluminium transfer to the counter surface. PVD and CVD thin coatings are increasingly studied as ways to alleviate galling. Among others, CrN and DLC coatings are known to reduce adhesion when sliding against aluminium. Despite the research efforts in this field, there is still lack of systematic studies where synergistic effects of lubrication, surface topography and coatings are explored in the context of hot aluminium forming.The aim of this research is to enhance the understanding of the tribological behaviour of aluminium sliding against tool steel at elevated temperatures. The effect of tool steel composition, surface roughness (as-received and post-polished), and PVD surface coating composition (CrTiN, CrAlN, CrN and DLC ta-C) has been evaluated under dry and lubricated conditions (hBN-based and polymer-based).High temperature tribological tests were carried out in a reciprocating sliding flat-on-flat configuration. In dry conditions, the aluminium-tool steel tribosystem is characterised by severe adhesive wear and high friction. Effective control of friction and wear was found to be highly dependent on the ability of the lubricant to remain in the contact zone. The combined use of a polymer-based lubricant with post-polished surface topography on a PVD coated tool led to the best improvements in terms of frictional stability and reduced material transfer. This was mainly attributed to prevention of direct contact between the tool material and aluminium together with minimised mechanically initiated material transfer. Post-polished uncoated tool steels resulted in the development of a protective tribolayer in the contact and together with flattening of the aluminium surface, led to friction and wear reduction. In case of post-polished PVD coatings, the lubricant entrapment in the contact zone as well as the development of mechanically mixed layers on the aluminium lowered friction and wear.
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