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Crack growth modelling from stress concentrations under cyclic loading histories
Get PDFStructural integrity is a vitally important field of engineering with fracture and fatigue causing the vast majority of mechanical failures. This is of particular importance within the power industry where the consequences of failure can be severe. Power plant components may contain complex geometries and critical features which can introduce stress concentrations, and are often subject to complex cyclic loading histories. Consequently,fatigue is a dominant failure mechanism which can limit the component life.This research is targeted towards industrial gas turbines, with a specific application to nozzle guide vanes, in which, the extreme temperatures involved induce great thermal loading, compromising their integrity. To this end, extensive development is continually performed to carefully balance their thermal and structural requirements. However,there is still a need to improve understanding of these complex stress distributions.Conventional fatigue life assessment methods can be overly simplistic and tend to offer a one-size-fits-all approach, potentially providing overly conservative values of fatigue life. More realistic methods with improved levels of accuracy are therefore needed. This highlights the requirement for more bespoke techniques that can offer a greater understanding of the stress distributions in these complex components and high specification materials. During the development of such bespoke methods, it is important that they are readily accessible for routine use within engineering, by providing a user-friendly step-by-step approach. This industrial sponsored research aims to address these issues and provide a turn-key solution.Included in this procedure, are two novel methodologies which have been developed during the course of this work. These are the Reversed Plasticity Domain Method for the determination of the critical loads to cause low cycle fatigue failure, and the Modified Monotonic Loading Concept for the calculation of the cyclic J-integral.Structural integrity is a vitally important field of engineering with fracture and fatigue causing the vast majority of mechanical failures. This is of particular importance within the power industry where the consequences of failure can be severe. Power plant components may contain complex geometries and critical features which can introduce stress concentrations, and are often subject to complex cyclic loading histories. Consequently,fatigue is a dominant failure mechanism which can limit the component life.This research is targeted towards industrial gas turbines, with a specific application to nozzle guide vanes, in which, the extreme temperatures involved induce great thermal loading, compromising their integrity. To this end, extensive development is continually performed to carefully balance their thermal and structural requirements. However,there is still a need to improve understanding of these complex stress distributions.Conventional fatigue life assessment methods can be overly simplistic and tend to offer a one-size-fits-all approach, potentially providing overly conservative values of fatigue life. More realistic methods with improved levels of accuracy are therefore needed. This highlights the requirement for more bespoke techniques that can offer a greater understanding of the stress distributions in these complex components and high specification materials. During the development of such bespoke methods, it is important that they are readily accessible for routine use within engineering, by providing a user-friendly step-by-step approach. This industrial sponsored research aims to address these issues and provide a turn-key solution.Included in this procedure, are two novel methodologies which have been developed during the course of this work. These are the Reversed Plasticity Domain Method for the determination of the critical loads to cause low cycle fatigue failure, and the Modified Monotonic Loading Concept for the calculation of the cyclic J-integral
Numerical investigation of freak wave effects on offshore structures
Get PDFThe freak wave is extremely dangerous to offshore structures due to its unexpected high wave height and strong nonlinearity. Although increasingly more attention is paid to the investigations of freak wave, the principle of its generation mechanism and the factors that contribute to its occurrence remain unclear. Also, few efforts were exerted to investigate the interactions between offshore structures and a freak wave such as wave run-up and slamming force. In this present work, both the two dimensional (2D) and three dimensional (3D) numerical wave tanks are established based on Navier-Stokes equations for viscous, incompressible fluid by CFD commercial software FLUENT.;At first, the regular waves are generated numerically. Two different wave generation methods, paddle wave making method and the source function wave making method, are introduced. The paddle wave-making method is a physical wave generation technology which is to imitate the wave makers in the laboratory. The source function wave-making method is discussed later and the empirical formulas of the source size and source intensity are introduced. The numerical wave elevations are compared with the linear analytical results.;Second, the freak waves are generated numerically. According to Longuet-Higgins wave model theory, the wave free surface can be represented by the linear sum of the individual wave components with different frequencies and random phases. Improving this wave model, the wave components have their phase adjusted, so that a large amount of energy is located at the focus position at a given time. Then two more efficient and realistic freak wave models are presented, combining wave models and phase modulation wave models, respectively. Finally, the numerical results of the shift of freak wave train focusing position and focusing time are analysed, and the time history of wave elevations are compared with the analytical results.;Third, a 3-D numerical wave tank is established to perform the interactions between a freak wave train and a single cylinder or a pair of two cylinders. How the focused wave parameters, including wave steepness, frequency bandwidth, focused position and the distance between the two cylinders, affect the freak wave run-up and total slamming forces on the cylinders are investigated.;Finally, the hydrodynamic behaviour of a rectangular body in roll motions under both freak wave excitation and internal flow sloshing is investigated in a CFD numerical wave tank. In this study, three different freak wave conditions are considered, and two different water levels are investigated.;The comparisons of numerical regular wave elevations and first order analytical results show that the current CFD numerical wave tank based on computational fluid dynamic commercial software FLUENT has a good capacity in sea water waves simulation. The focused wave parameters, such as frequency bandwidth and input wave steepness, have an obvious effect on the nonlinear behaviour of a focused wave group.;This nonlinear behaviour will not only downstream shift the focused position and focused time, but also change the wave elevation at the focused position largely. The increased nonlinear behaviour of a focused wave group will increase the wave run-up along a fixed vertical cylinder at the incident wave facing direction largely. The bigger nonlinear behaviour of a focused wave group can result in larger rolling motion amplitude for a floating rectangular body, however the anti-rolling behaviour is obvious for the low filling case.The freak wave is extremely dangerous to offshore structures due to its unexpected high wave height and strong nonlinearity. Although increasingly more attention is paid to the investigations of freak wave, the principle of its generation mechanism and the factors that contribute to its occurrence remain unclear. Also, few efforts were exerted to investigate the interactions between offshore structures and a freak wave such as wave run-up and slamming force. In this present work, both the two dimensional (2D) and three dimensional (3D) numerical wave tanks are established based on Navier-Stokes equations for viscous, incompressible fluid by CFD commercial software FLUENT.;At first, the regular waves are generated numerically. Two different wave generation methods, paddle wave making method and the source function wave making method, are introduced. The paddle wave-making method is a physical wave generation technology which is to imitate the wave makers in the laboratory. The source function wave-making method is discussed later and the empirical formulas of the source size and source intensity are introduced. The numerical wave elevations are compared with the linear analytical results.;Second, the freak waves are generated numerically. According to Longuet-Higgins wave model theory, the wave free surface can be represented by the linear sum of the individual wave components with different frequencies and random phases. Improving this wave model, the wave components have their phase adjusted, so that a large amount of energy is located at the focus position at a given time. Then two more efficient and realistic freak wave models are presented, combining wave models and phase modulation wave models, respectively. Finally, the numerical results of the shift of freak wave train focusing position and focusing time are analysed, and the time history of wave elevations are compared with the analytical results.;Third, a 3-D numerical wave tank is established to perform the interactions between a freak wave train and a single cylinder or a pair of two cylinders. How the focused wave parameters, including wave steepness, frequency bandwidth, focused position and the distance between the two cylinders, affect the freak wave run-up and total slamming forces on the cylinders are investigated.;Finally, the hydrodynamic behaviour of a rectangular body in roll motions under both freak wave excitation and internal flow sloshing is investigated in a CFD numerical wave tank. In this study, three different freak wave conditions are considered, and two different water levels are investigated.;The comparisons of numerical regular wave elevations and first order analytical results show that the current CFD numerical wave tank based on computational fluid dynamic commercial software FLUENT has a good capacity in sea water waves simulation. The focused wave parameters, such as frequency bandwidth and input wave steepness, have an obvious effect on the nonlinear behaviour of a focused wave group.;This nonlinear behaviour will not only downstream shift the focused position and focused time, but also change the wave elevation at the focused position largely. The increased nonlinear behaviour of a focused wave group will increase the wave run-up along a fixed vertical cylinder at the incident wave facing direction largely. The bigger nonlinear behaviour of a focused wave group can result in larger rolling motion amplitude for a floating rectangular body, however the anti-rolling behaviour is obvious for the low filling case
Drama convention approaches and primary-secondary transition : pupils' and teachers' views
Get PDFThis study was undertaken in the west coast of Scotland and contributes to literature in the fields of Drama (with particular focus on Drama Convention approaches), and primary-secondary transition. The research questions were: 1. How do young people understand and respond to the Drama Convention approaches used in this study to explore primary-secondary transition? 2. How do primary teachers understand and respond to the Drama Convention approaches used in this study to explore primary-secondary transition? 3. How does the evidence from the thesis correlate with literature?The investigator devised three Drama structures that addressed a fictional Primary seven pupil's transition to secondary school. Data was gathered through a research diary, pupil focus groups, pupil questionnaire and exit cards, teacher observations of pupils' interactions with the Drama structure, a teacher semi-structured interview. Data was analysed using an interpretivist stance, within a case study approach, through iterative thematic coding. The participants indicated that Drama Convention pedagogy is child-centred, motivational and engages young people in transitional learning; the majority of pupils expressed their positivity about transferring to secondary school. Drama Convention approaches developed themes of: citizenship, solidarity, empathy, meta-awareness, multiple perspectives, understanding of bullying at transition, and real-world learning. The thesis contributes to Drama literature by providing an analysis of pupil and teacher voice on thirteen specified Drama Convention approaches (Neelands and Goode, 2016). In addition, the thesis contributes to the transitional literature by indicating that Drama Convention approaches provide an engaging pedagogical approach that empowers young people to discuss their transitional thoughts and opinions in a safe and purposeful learning environment. The implications and recommendations of this study are that further research should be implemented in using Drama Convention approaches as a pedagogical method for primary-secondary transitional learning and that greater support should be given to teachers in developing their understanding of Drama pedagogy.This study was undertaken in the west coast of Scotland and contributes to literature in the fields of Drama (with particular focus on Drama Convention approaches), and primary-secondary transition. The research questions were: 1. How do young people understand and respond to the Drama Convention approaches used in this study to explore primary-secondary transition? 2. How do primary teachers understand and respond to the Drama Convention approaches used in this study to explore primary-secondary transition? 3. How does the evidence from the thesis correlate with literature?The investigator devised three Drama structures that addressed a fictional Primary seven pupil's transition to secondary school. Data was gathered through a research diary, pupil focus groups, pupil questionnaire and exit cards, teacher observations of pupils' interactions with the Drama structure, a teacher semi-structured interview. Data was analysed using an interpretivist stance, within a case study approach, through iterative thematic coding. The participants indicated that Drama Convention pedagogy is child-centred, motivational and engages young people in transitional learning; the majority of pupils expressed their positivity about transferring to secondary school. Drama Convention approaches developed themes of: citizenship, solidarity, empathy, meta-awareness, multiple perspectives, understanding of bullying at transition, and real-world learning. The thesis contributes to Drama literature by providing an analysis of pupil and teacher voice on thirteen specified Drama Convention approaches (Neelands and Goode, 2016). In addition, the thesis contributes to the transitional literature by indicating that Drama Convention approaches provide an engaging pedagogical approach that empowers young people to discuss their transitional thoughts and opinions in a safe and purposeful learning environment. The implications and recommendations of this study are that further research should be implemented in using Drama Convention approaches as a pedagogical method for primary-secondary transitional learning and that greater support should be given to teachers in developing their understanding of Drama pedagogy
Increasing the reliability of wind turbine condition monitoring systems
Get PDFWind turbines are leading the way in helping to reduce the dependency on fossil fuel energy sources. However to compete with other energy sources there is a need to reduce the cost of energy from wind turbines. It has been shown in the literature that as wind turbines increase in size their reliability decreases. As wind turbines move further offshore and into deeper water this becomes more of an issue as carrying out maintenance becomes more challenging and costly. One way of improving the reliability of wind turbines is through the use of condition monitoring systems (CMS) which can continually monitor the health of the machine and allow more optimised maintenance and repair scheduling. Although the benefits of using a CMS may seem evident, operators have been slow in the uptake of such systems. One reason for this is due to issues with the reliability of CMS themselves. As stated in the literature, CMS must accurately detect 60-80% of faults to be economically justifiable. Not detecting faults or the occurrence of false alarms is detrimental to the effectiveness of CMS. The work presented in this thesis aims to address the issue of CMS reliability. Through the installation of two CMS in operational wind turbines the author of this thesis has gained valuable insight into the design, build and installation of CMS which has facilitated the novel contributions from this work. The first contribution comes from the formulation of an engineering design process which incorporates five categories of robustness which were identified by the author through Failure-Mode Effects Analysis on a wind turbine CMS that was installed in an operational wind turbine. The engineering design process incorporating the robustness categories will allow wind turbine CMS to be designed which are capable of operating reliably in the harsh environment they are subjected to. The second contribution comes from the development of three techniques which will increase CMS reliability by reducing false alarms and introducing the ability to detect erroneous data.Wind turbines are leading the way in helping to reduce the dependency on fossil fuel energy sources. However to compete with other energy sources there is a need to reduce the cost of energy from wind turbines. It has been shown in the literature that as wind turbines increase in size their reliability decreases. As wind turbines move further offshore and into deeper water this becomes more of an issue as carrying out maintenance becomes more challenging and costly. One way of improving the reliability of wind turbines is through the use of condition monitoring systems (CMS) which can continually monitor the health of the machine and allow more optimised maintenance and repair scheduling. Although the benefits of using a CMS may seem evident, operators have been slow in the uptake of such systems. One reason for this is due to issues with the reliability of CMS themselves. As stated in the literature, CMS must accurately detect 60-80% of faults to be economically justifiable. Not detecting faults or the occurrence of false alarms is detrimental to the effectiveness of CMS. The work presented in this thesis aims to address the issue of CMS reliability. Through the installation of two CMS in operational wind turbines the author of this thesis has gained valuable insight into the design, build and installation of CMS which has facilitated the novel contributions from this work. The first contribution comes from the formulation of an engineering design process which incorporates five categories of robustness which were identified by the author through Failure-Mode Effects Analysis on a wind turbine CMS that was installed in an operational wind turbine. The engineering design process incorporating the robustness categories will allow wind turbine CMS to be designed which are capable of operating reliably in the harsh environment they are subjected to. The second contribution comes from the development of three techniques which will increase CMS reliability by reducing false alarms and introducing the ability to detect erroneous data
Characterisation and modification of residual stress in brazed dissimilar material joints for a future fusion divertor
Get PDFIn a future nuclear fusion reactor, the critical divertor component will require dissimilar material joining of an armour and a structural material. Tungsten (armour) and copper or steel alloy (structural) have been identified as suitable candidates. A review of existing divertor designs and material combinations highlighted a requirement for further development of tungsten based dissimilar material joints and the associated residual stresses. An improvement in the residual stress state at the interface is seen as a way to improve the performance of the divertor under cyclic loading. A method of beneficially modifying the residual stress state of vacuum brazed, fusion relevant, tungsten dissimilar material joints is presented in this thesis. Tungsten-copper and tungsten-316L stainless steel parts were successfully brazed using a eutectic gold-copper brazing alloy. A total of 30 dissimilar material brazed joints were successfully manufactured and analysed. The brazed parts have been characterised using a range of metallurgical and residual stress measurement techniques. The residual stress state has been predicted using finite element analysis. Temperature dependent thermo-mechanical material properties were experimentally determined for the gold-copper alloy to facilitate accurate finite element modelling. Good agreement between predicted and X-ray diffraction and Contour Method measured residual stresses for brazed tungsten-316L parts was obtained. The need for further research into the complex interfacial region, and translation of this region into a predictive model, was identified to improve correlation of predicted and measured residual stresses in brazed tungsten-copper parts. Damaging tensile residual stresses in the brittle tungsten material were beneficially reduced in a brazed tungsten-316L part using thermal autofrettage. Reduction of high brazing induced tensile stresses was achieved both analytically and experimentally. This improvement in the residual stress distribution has promising applications in beneficially modifying real divertor dissimilar material tiles.In a future nuclear fusion reactor, the critical divertor component will require dissimilar material joining of an armour and a structural material. Tungsten (armour) and copper or steel alloy (structural) have been identified as suitable candidates. A review of existing divertor designs and material combinations highlighted a requirement for further development of tungsten based dissimilar material joints and the associated residual stresses. An improvement in the residual stress state at the interface is seen as a way to improve the performance of the divertor under cyclic loading. A method of beneficially modifying the residual stress state of vacuum brazed, fusion relevant, tungsten dissimilar material joints is presented in this thesis. Tungsten-copper and tungsten-316L stainless steel parts were successfully brazed using a eutectic gold-copper brazing alloy. A total of 30 dissimilar material brazed joints were successfully manufactured and analysed. The brazed parts have been characterised using a range of metallurgical and residual stress measurement techniques. The residual stress state has been predicted using finite element analysis. Temperature dependent thermo-mechanical material properties were experimentally determined for the gold-copper alloy to facilitate accurate finite element modelling. Good agreement between predicted and X-ray diffraction and Contour Method measured residual stresses for brazed tungsten-316L parts was obtained. The need for further research into the complex interfacial region, and translation of this region into a predictive model, was identified to improve correlation of predicted and measured residual stresses in brazed tungsten-copper parts. Damaging tensile residual stresses in the brittle tungsten material were beneficially reduced in a brazed tungsten-316L part using thermal autofrettage. Reduction of high brazing induced tensile stresses was achieved both analytically and experimentally. This improvement in the residual stress distribution has promising applications in beneficially modifying real divertor dissimilar material tiles
Characterisation of grating properties for MOTs at multiple wavelengths and laser cooling Rb on the 5S1/2 - 6P3/2 transition at 420nm
No full textThis thesis presents progress towards making a blue magnetic-optical trap (MOT) utilizing a reflective diffraction grating, a 780nm and a 420nm laser. Taking advantage of the narrower line width of the 6P3/2 state, 420nm lasers can theoretically make a factor of 10 colder MOT than those using 780nm ones based on the Doppler limit. However, considering the low capture rate caused by this narrower linewidth, 87Rb atoms are planned to be captured using a MOT on the 5S1/2 - 5P3/2 transition at 780nm for pre-cooling and then transferred to a MOT on the 5S1/2 - 6P3/2 transition at 420nm. As the very first group intending to make a 420nm grating-MOT, we studied the behaviour (diffraction efficiency, polarisation efficiency) of diffraction gratings with different etch depth, coating material, duty cycle to find suitable gratings which work for both 780nm and 420 nm. To investigate other potential laser sources, 423nm laser diode samples were tested to explore the possibility of reaching the desired wavelength (420.297 nm) for cooling.This thesis presents progress towards making a blue magnetic-optical trap (MOT) utilizing a reflective diffraction grating, a 780nm and a 420nm laser. Taking advantage of the narrower line width of the 6P3/2 state, 420nm lasers can theoretically make a factor of 10 colder MOT than those using 780nm ones based on the Doppler limit. However, considering the low capture rate caused by this narrower linewidth, 87Rb atoms are planned to be captured using a MOT on the 5S1/2 - 5P3/2 transition at 780nm for pre-cooling and then transferred to a MOT on the 5S1/2 - 6P3/2 transition at 420nm. As the very first group intending to make a 420nm grating-MOT, we studied the behaviour (diffraction efficiency, polarisation efficiency) of diffraction gratings with different etch depth, coating material, duty cycle to find suitable gratings which work for both 780nm and 420 nm. To investigate other potential laser sources, 423nm laser diode samples were tested to explore the possibility of reaching the desired wavelength (420.297 nm) for cooling
High pressure as a tool for polymorph screening in small organic molecules
Get PDFApplication of high pressure is a well-known tool used to induce. Presented in this thesis are the studies of three small organic molecules under high pressure,investigating the importance of particle size, the choice of pressure-transmitting medium (PTM) and the solvent from which the material is recrystallised on the high-pressure behaviour of the material.Chapters 3 describes the characterisation of a metastable polymorph of glycolide,formed at high pressure and recovered to ambient conditions. Chapter 4 describes a neutron diffraction study of glycolide under high pressure, characterising the behaviour of each of the two known forms as well as seeking to characterise a third polymorph which had been observed during earlier work.Chapter 5 presents a neutron diffraction study of acrylamide under high pressure inthree different pressure-transmitting media - a 1:1 (v/v) mixture of pentane and isopentane,a 4:1 (v/v) mixture of methanol and ethanol, and iso-propyl alcohol (IPA).A different high pressure phase was identified in each of the three media, with the crystal structures of those in the pentanes and methanol/ethanol environments being fully solved.Chapter 6 describes a study of caprolactam under high pressure, through a combination of single crystal X-ray diffraction and powder neutron diffraction. In this study, it was observed that a caprolactam sample recrystallised from ethylacetate underwent a polymorph transition to one high pressure phase, while a sample recrystallised from alcohol (either ethanol or 1-butanol) underwent a polymorph transition to a different high pressure form despite the fact that both samples were in the same polymorphic form at the beginning of the experiment.The high pressure form observed from the sample recrystallised from ethanol (or 1-butanol) was fully structurally solved. Recent progress made by the group beyond the scope of this PhD have permitted unit cell parameters to be fitted to the neutron diffraction data, although associated discussion of this form is limited due to time constraints.Application of high pressure is a well-known tool used to induce. Presented in this thesis are the studies of three small organic molecules under high pressure,investigating the importance of particle size, the choice of pressure-transmitting medium (PTM) and the solvent from which the material is recrystallised on the high-pressure behaviour of the material.Chapters 3 describes the characterisation of a metastable polymorph of glycolide,formed at high pressure and recovered to ambient conditions. Chapter 4 describes a neutron diffraction study of glycolide under high pressure, characterising the behaviour of each of the two known forms as well as seeking to characterise a third polymorph which had been observed during earlier work.Chapter 5 presents a neutron diffraction study of acrylamide under high pressure inthree different pressure-transmitting media - a 1:1 (v/v) mixture of pentane and isopentane,a 4:1 (v/v) mixture of methanol and ethanol, and iso-propyl alcohol (IPA).A different high pressure phase was identified in each of the three media, with the crystal structures of those in the pentanes and methanol/ethanol environments being fully solved.Chapter 6 describes a study of caprolactam under high pressure, through a combination of single crystal X-ray diffraction and powder neutron diffraction. In this study, it was observed that a caprolactam sample recrystallised from ethylacetate underwent a polymorph transition to one high pressure phase, while a sample recrystallised from alcohol (either ethanol or 1-butanol) underwent a polymorph transition to a different high pressure form despite the fact that both samples were in the same polymorphic form at the beginning of the experiment.The high pressure form observed from the sample recrystallised from ethanol (or 1-butanol) was fully structurally solved. Recent progress made by the group beyond the scope of this PhD have permitted unit cell parameters to be fitted to the neutron diffraction data, although associated discussion of this form is limited due to time constraints
Studies and improvement of molecular docking methods in rigid and flexible receptors
Get PDFPreviously held under moratorium in Chemistry Department (GSK) from 24th May 2017 to 24th May 2019.Computational chemistry is a field of chemistry that uses computers to model chemical structures and properties and as such has been used in drug discovery since the eighties.1 Computational chemistry within the field of Drug Design can be sub-divided into a number of different areas, including target identification, high-throughput screening analysis, de novo design, molecular docking, activity predictions, etc. These methods aim to predict the properties of molecular systems, such as the energy, the activity profile or the physico-chemical properties. The main objective of computational chemistry in the pharmaceutical industry context is to help decision making by guiding research scientists as to which molecules to synthesise or test.2 In the case of structure-based drug design, computational chemistry relies on structural biology to provide structural data, for instance crystal structures of protein-ligand complexes. These crystal structures give information about the interaction of the ligand and the protein binding site and can be used in the design of subsequent and more optimised molecules. The use of rigid receptor molecular docking is exemplified in this work through the investigation of the LTA4H system. A number of analogue compounds of 5 were docked in LTA4H successfully and it was shown that molecular docking could be used as a tool for stereochemistry assignment for the closely related LTA4H ligands 10a-d. In this work, molecular docking predicted the isomers associated with measured potencies and these predictions were confirmed by subsequent experimental data. One drawback of rigid receptor docking is that it does not account for the flexibility of the target. The investigation of protein flexibility in molecular docking, therefore, followed. Standard protocols from the Schrödinger modelling suite were investigated first and the results were benchmarked for the fXa and CDK2 dockings, which were compared to the published Schrödinger results. The Induced Fit Docking (IFD) protocol was tested with default settings, and with automated and manual truncations of amino acids. These experiments concluded that the selection of amino acids could be improved as was also the case for the scoring function, IFDScore. Therefore, in this work a new approach for the automatic selection of amino acids for flexible exploration of the binding site was introduced. In addition, a modified scoring function was investigated and applied to fXa, CDK2 and UPPS systems. The new selection and scoring protocols showed some advantages over the standard Schrödinger IFD protocol.Computational chemistry is a field of chemistry that uses computers to model chemical structures and properties and as such has been used in drug discovery since the eighties.1 Computational chemistry within the field of Drug Design can be sub-divided into a number of different areas, including target identification, high-throughput screening analysis, de novo design, molecular docking, activity predictions, etc. These methods aim to predict the properties of molecular systems, such as the energy, the activity profile or the physico-chemical properties. The main objective of computational chemistry in the pharmaceutical industry context is to help decision making by guiding research scientists as to which molecules to synthesise or test.2 In the case of structure-based drug design, computational chemistry relies on structural biology to provide structural data, for instance crystal structures of protein-ligand complexes. These crystal structures give information about the interaction of the ligand and the protein binding site and can be used in the design of subsequent and more optimised molecules. The use of rigid receptor molecular docking is exemplified in this work through the investigation of the LTA4H system. A number of analogue compounds of 5 were docked in LTA4H successfully and it was shown that molecular docking could be used as a tool for stereochemistry assignment for the closely related LTA4H ligands 10a-d. In this work, molecular docking predicted the isomers associated with measured potencies and these predictions were confirmed by subsequent experimental data. One drawback of rigid receptor docking is that it does not account for the flexibility of the target. The investigation of protein flexibility in molecular docking, therefore, followed. Standard protocols from the Schrödinger modelling suite were investigated first and the results were benchmarked for the fXa and CDK2 dockings, which were compared to the published Schrödinger results. The Induced Fit Docking (IFD) protocol was tested with default settings, and with automated and manual truncations of amino acids. These experiments concluded that the selection of amino acids could be improved as was also the case for the scoring function, IFDScore. Therefore, in this work a new approach for the automatic selection of amino acids for flexible exploration of the binding site was introduced. In addition, a modified scoring function was investigated and applied to fXa, CDK2 and UPPS systems. The new selection and scoring protocols showed some advantages over the standard Schrödinger IFD protocol
The role of materials engineering to mitigate corrosive wear in oil field pumping applications
Get PDFThis thesis was previously held under moratorium from 25/04/2018 to 01/05/2023Hydraulic fracturing is a technique used to stimulate the flow of oil/gas from tight formations of subterranean rock. The pumping equipment used operates under harsh environments; hence, has a short life expectancy. This research focuses on an investigation of corrosive wear issues associated with hydraulic fracturing pump components with a view of finding cost-effective solutions to combat these problems.A recirculating slurry impingement rig was used to test the materials under corrosive wear conditions. To comprehend the various wear mechanisms occurring during testing a recently-developed, in-house volumetric analysis technique was employed, which combined electrochemical monitoring tests and 3D surface profiling. A novel repetitive impact slurry rig was developed to mimic the repetitive impact metal-metal wear occurring on valves and seats used in the hydraulic fracturing pump.The enhanced volumetric analysis technique and information from segmented specimens provided a means of unravelling the complex deterioration processes that occur in the different regions of a submerged jet specimen. Post-test examinations of specimens using light-optical and scanning electron microscopy was also undertaken to yield information on mechanisms of degradation.As hydraulic fracturing equipment is likely to have to operate in a range of water salinities, the effect of salinity on the currently used fluid end (i.e. pump casing) material (UNS G43400) as well as alternative material options was investigated. Increasing salinity from 0.05%NaCl to 10%NaCl was found to have a marginal increase in material loss for the stainless steel alloys, whereas, there was a significant increase for the low alloy steel. Sacrificial anode cathodic protection was also observed to be beneficial in reducing the material loss for the low alloy steel in the corrosive wear conditions. The effect of nitriding Stellite 6 weld claddings was assessed as a hardfacing and/or repair option for hydraulic fracturing pump components. The nitriding process was found to be detrimental to the corrosion resistance of the Stellite 6 weld claddings; however, the volumetric analysis technique demonstrated that the nitriding process was capable of improving their mechanical erosion resistance. Additively manufactured alloys were also assessed as alternative materials and/or a repair technique for hydraulic fracturing pump components. The additive manufactured alloys were compared to equivalent alloys which were conventionally manufactured. The additively manufactured alloys were observed to have significantly better corrosion resistance than the wrought alloys in static and flowing conditions. Under solid-liquid erosion-corrosion testing, the additive manufactured alloys and equivalent wrought alloys performed similarly. A wide range of materials (soft/ductile to hard/brittle) were assessed under repetitive impact with slurry conditions. The results from the novel testing apparatus indicated that there was an optimum material hardness for repetitive impact wear resistance. Hence, suggesting that hardness is required to resist plastic deformation and toughness is required to resist brittle failures.Hydraulic fracturing is a technique used to stimulate the flow of oil/gas from tight formations of subterranean rock. The pumping equipment used operates under harsh environments; hence, has a short life expectancy. This research focuses on an investigation of corrosive wear issues associated with hydraulic fracturing pump components with a view of finding cost-effective solutions to combat these problems.A recirculating slurry impingement rig was used to test the materials under corrosive wear conditions. To comprehend the various wear mechanisms occurring during testing a recently-developed, in-house volumetric analysis technique was employed, which combined electrochemical monitoring tests and 3D surface profiling. A novel repetitive impact slurry rig was developed to mimic the repetitive impact metal-metal wear occurring on valves and seats used in the hydraulic fracturing pump.The enhanced volumetric analysis technique and information from segmented specimens provided a means of unravelling the complex deterioration processes that occur in the different regions of a submerged jet specimen. Post-test examinations of specimens using light-optical and scanning electron microscopy was also undertaken to yield information on mechanisms of degradation.As hydraulic fracturing equipment is likely to have to operate in a range of water salinities, the effect of salinity on the currently used fluid end (i.e. pump casing) material (UNS G43400) as well as alternative material options was investigated. Increasing salinity from 0.05%NaCl to 10%NaCl was found to have a marginal increase in material loss for the stainless steel alloys, whereas, there was a significant increase for the low alloy steel. Sacrificial anode cathodic protection was also observed to be beneficial in reducing the material loss for the low alloy steel in the corrosive wear conditions. The effect of nitriding Stellite 6 weld claddings was assessed as a hardfacing and/or repair option for hydraulic fracturing pump components. The nitriding process was found to be detrimental to the corrosion resistance of the Stellite 6 weld claddings; however, the volumetric analysis technique demonstrated that the nitriding process was capable of improving their mechanical erosion resistance. Additively manufactured alloys were also assessed as alternative materials and/or a repair technique for hydraulic fracturing pump components. The additive manufactured alloys were compared to equivalent alloys which were conventionally manufactured. The additively manufactured alloys were observed to have significantly better corrosion resistance than the wrought alloys in static and flowing conditions. Under solid-liquid erosion-corrosion testing, the additive manufactured alloys and equivalent wrought alloys performed similarly. A wide range of materials (soft/ductile to hard/brittle) were assessed under repetitive impact with slurry conditions. The results from the novel testing apparatus indicated that there was an optimum material hardness for repetitive impact wear resistance. Hence, suggesting that hardness is required to resist plastic deformation and toughness is required to resist brittle failures
Development and deployment of dynamic reconfiguration capabilities in the telecommunications sector
Get PDFThe telecommunications sector faces rapid technology changes, which require huge capital investment, changes in rules and regulations, changes in customer behaviour and increasing customer demand. This rapid development directs how the telecommunication service operators deploy their strategies and network infrastructure and continue to evolve their business models. A unique requirement of the telecom industry is the need to manage and deploy planned, unplanned and emergency resources concurrently. The 'dynamic capabilities' (DC) approach can be used as a framework to respond to this critical requirement for both managers and researchers. This study has a particular focus on dynamic reconfiguration capabilities (DRC), as these play a critical role in the deployment of strategy. The current literature shows clear limitations regarding how DRC emerge and how they can be used to manage concurrent strategy approaches, which are relevant to the telecommunications sector. Five case studies from a telecommunication service provider are used in this research. Three types of data were collected, namely: 23 interviews, 10 direct observations and over 120 documents. A two-stage coding process is conducted for each case, and causal network diagrams are used to extract findings. A cross-case analysis enabled the identification of the empirical practices relating to the research questions. Findings from the case studies confirm the relevance of several practices previously highlighted in the literature. They also revealed additional practices that support the DRC lifecycle. The case studies are performing most of the practices outlined in the theory of the DRC lifecycle framework, with different degrees of emphasis, especially in the deployment phase. This research extends the current theory by identifying the role of DRC in deploying concurrent strategic approaches. It extends the resource-based view (RBV) and agility theories, which fail to adequately address long-term plans, and collapse when the market is very dynamic. Furthermore, it contributes to the DC literature by identifying the organisational practices that support development, deployment and improvement in the telecommunication industry. Also, it addresses an important gap in the literature by providing organisational practices and evidence of the DRC role to support the concurrent approaches to strategy deployment in the telecommunication industry.The telecommunications sector faces rapid technology changes, which require huge capital investment, changes in rules and regulations, changes in customer behaviour and increasing customer demand. This rapid development directs how the telecommunication service operators deploy their strategies and network infrastructure and continue to evolve their business models. A unique requirement of the telecom industry is the need to manage and deploy planned, unplanned and emergency resources concurrently. The 'dynamic capabilities' (DC) approach can be used as a framework to respond to this critical requirement for both managers and researchers. This study has a particular focus on dynamic reconfiguration capabilities (DRC), as these play a critical role in the deployment of strategy. The current literature shows clear limitations regarding how DRC emerge and how they can be used to manage concurrent strategy approaches, which are relevant to the telecommunications sector. Five case studies from a telecommunication service provider are used in this research. Three types of data were collected, namely: 23 interviews, 10 direct observations and over 120 documents. A two-stage coding process is conducted for each case, and causal network diagrams are used to extract findings. A cross-case analysis enabled the identification of the empirical practices relating to the research questions. Findings from the case studies confirm the relevance of several practices previously highlighted in the literature. They also revealed additional practices that support the DRC lifecycle. The case studies are performing most of the practices outlined in the theory of the DRC lifecycle framework, with different degrees of emphasis, especially in the deployment phase. This research extends the current theory by identifying the role of DRC in deploying concurrent strategic approaches. It extends the resource-based view (RBV) and agility theories, which fail to adequately address long-term plans, and collapse when the market is very dynamic. Furthermore, it contributes to the DC literature by identifying the organisational practices that support development, deployment and improvement in the telecommunication industry. Also, it addresses an important gap in the literature by providing organisational practices and evidence of the DRC role to support the concurrent approaches to strategy deployment in the telecommunication industry
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