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Decision support method for ship energy systems synthesis with environmental and economic sustainability objectives
Get PDFShipping industry's significant economic and environmental impact along with the enforcement of stringent environmental regulations led to growing interest in enhancing shipping operations sustainability. In recent years, various technologies and alternative fuels were introduced to address the ship energy systems contribution to energy consumption and air pollution during the ship lifetime. The abundance of the available technologies and potential combinations renders ship energy systems selection process very challenging during the early design phase. The novelty of this research lies in the decision support method developed to optimise the ship energy systems synthesis at the early stage design with respect to environmental and economic objectives, as well as considerations of the ship lifetime operating requirements.Mathematical models of established and emerging technologies were developed to estimate the ship energy systems performance. The integrated ship energy systems synthesis was formulated as a multi-objective combinatorial optimisation problem, with the objectives of life cycle cost and exhaust gas emissions minimisation, whilst considering the environmental regulations as constraints. NSGA-II was employed to solve the ship energy systems synthesis problem.;The developed method was evaluated with two case studies, an Aframax oil tanker and a cruise ship. The visualisation of the optimal configurations on the Pareto front allows decision makers understanding and managing trade-offs between the environmental and economic objectives. The comparison of the optimal solutions estimated carbon emissions with the EEDI values indicated that the index does not capture the real carbon impact of the configurations. An uncertainty analysis assessed the robustness of the solutions. The sensitivity analysis of the two case studies indicated that changes in the fuel prices and emerging technologies have different implications on the two ships. The optimal configurations for different operating profiles were identified and insights were gained on the most promising future configurations under derived carbon pricing scenarios.Shipping industry's significant economic and environmental impact along with the enforcement of stringent environmental regulations led to growing interest in enhancing shipping operations sustainability. In recent years, various technologies and alternative fuels were introduced to address the ship energy systems contribution to energy consumption and air pollution during the ship lifetime. The abundance of the available technologies and potential combinations renders ship energy systems selection process very challenging during the early design phase. The novelty of this research lies in the decision support method developed to optimise the ship energy systems synthesis at the early stage design with respect to environmental and economic objectives, as well as considerations of the ship lifetime operating requirements.Mathematical models of established and emerging technologies were developed to estimate the ship energy systems performance. The integrated ship energy systems synthesis was formulated as a multi-objective combinatorial optimisation problem, with the objectives of life cycle cost and exhaust gas emissions minimisation, whilst considering the environmental regulations as constraints. NSGA-II was employed to solve the ship energy systems synthesis problem.;The developed method was evaluated with two case studies, an Aframax oil tanker and a cruise ship. The visualisation of the optimal configurations on the Pareto front allows decision makers understanding and managing trade-offs between the environmental and economic objectives. The comparison of the optimal solutions estimated carbon emissions with the EEDI values indicated that the index does not capture the real carbon impact of the configurations. An uncertainty analysis assessed the robustness of the solutions. The sensitivity analysis of the two case studies indicated that changes in the fuel prices and emerging technologies have different implications on the two ships. The optimal configurations for different operating profiles were identified and insights were gained on the most promising future configurations under derived carbon pricing scenarios
Understanding tourists' holiday destination choices through the construct of perceived value
Get PDFMarketing scholars are increasingly getting interested in the concept of perceived value as a major driving force behind consumer purchase behaviour. However, the existing studies on perceived value have primarily focused on consumer goods and service markets with a very limited number of scholars exploring the impact of value on consumer purchase behaviour in the context of holiday destination choice and travel. This study aims to fill this gap.The overarching aim of the study was to get a comprehensive understanding of the value formation process and its relationships with other important marketing constructs. Four objectives were set in order to achieve the above-mentioned aim.;The first objective of the research focused on the development of a valid and reliable way of measuring the perceived value construct. The study adopted a multidimensional approach where the perceived value is understood as a trade-off between its two sub-constructs: a) perceived benefits and b) perceived sacrifices. Based on this understanding of the construct, the scale development process focused on three key areas: 1) dimensionality of the perceived benefits, 2) dimensionality of the perceived sacrifices, and 3) conceptualisation and operationalisation of a trade-off between the perceived benefits and sacrifices. The scale development process strictly followed the works of Churchill's (1979), Malhotra and Birks (2003), and DeVellis (2012) who provided a thorough step-by-step guide on how to develop a multi-item measurement scale. The process consisted of a number of qualitative and quantitative stages. The scale was pilot tested as well as cross-validated.;The outcome of the process was a valid and reliable perceived value measurement scale developed specifically for the context of the international holiday destination choice.The second objective of the study explored the relationships of the perceived value with its key antecedents using moderator variables. The study confirmed that the travel motivation, attitude towards the destination (utilitarian and hedonic) and information sources (traditional, personal and digital) have a strong positive direct impact on tourists' perception of value. However, the moderated linear regression analysis showed that some of the direct effects of antecedents are not as strong, and their direct impact to a large degree is moderated through the interaction terms of other moderator variables. Furthermore, the conducted Subgroup Analysis revealed that tourists are not a homogeneous group and there are significant differences in the way they perceive value of a holiday destination.;The third objective of the study focused on the possibility of using the perceived value construct as a predictor of tourists' travel behaviour. The analysis confirmed that the perceived value is a significant, positive predictor of the tourists' actual travel/purchase behaviour.The final objective of the study focused on applying the Theory of Planned Behaviour (TPB) in the context of tourism and international holiday destination travel. The analysis of the TPB model confirmed that the attitude towards behaviour and the perceived behavioural control are positive and significant predictors of the behavioural intention. However, the social norm failed to have a significant direct impact on behavioural intention. Additionally, unlike theorised by the TPB, the empirical evidence did not support the hypothesis that the behavioural intention and perceived behavioural control have a significant direct impact on tourists' actual travel/purchase behaviour.;Furthermore, within the scope of this objective, the comparative analysis of predictive abilities of the TPB and perceived value was conducted, as well as, an attempt was made to enhance the predictive ability of the TPB by integrating the perceived value construct within its framework. The outcome of the analysis suggests that, firstly, the perceived value is a better predictor of the actual travel/purchase behaviour than the TPB and, secondly, the integration of the perceived value has considerably improved the predictive ability of the TPB.Marketing scholars are increasingly getting interested in the concept of perceived value as a major driving force behind consumer purchase behaviour. However, the existing studies on perceived value have primarily focused on consumer goods and service markets with a very limited number of scholars exploring the impact of value on consumer purchase behaviour in the context of holiday destination choice and travel. This study aims to fill this gap.The overarching aim of the study was to get a comprehensive understanding of the value formation process and its relationships with other important marketing constructs. Four objectives were set in order to achieve the above-mentioned aim.;The first objective of the research focused on the development of a valid and reliable way of measuring the perceived value construct. The study adopted a multidimensional approach where the perceived value is understood as a trade-off between its two sub-constructs: a) perceived benefits and b) perceived sacrifices. Based on this understanding of the construct, the scale development process focused on three key areas: 1) dimensionality of the perceived benefits, 2) dimensionality of the perceived sacrifices, and 3) conceptualisation and operationalisation of a trade-off between the perceived benefits and sacrifices. The scale development process strictly followed the works of Churchill's (1979), Malhotra and Birks (2003), and DeVellis (2012) who provided a thorough step-by-step guide on how to develop a multi-item measurement scale. The process consisted of a number of qualitative and quantitative stages. The scale was pilot tested as well as cross-validated.;The outcome of the process was a valid and reliable perceived value measurement scale developed specifically for the context of the international holiday destination choice.The second objective of the study explored the relationships of the perceived value with its key antecedents using moderator variables. The study confirmed that the travel motivation, attitude towards the destination (utilitarian and hedonic) and information sources (traditional, personal and digital) have a strong positive direct impact on tourists' perception of value. However, the moderated linear regression analysis showed that some of the direct effects of antecedents are not as strong, and their direct impact to a large degree is moderated through the interaction terms of other moderator variables. Furthermore, the conducted Subgroup Analysis revealed that tourists are not a homogeneous group and there are significant differences in the way they perceive value of a holiday destination.;The third objective of the study focused on the possibility of using the perceived value construct as a predictor of tourists' travel behaviour. The analysis confirmed that the perceived value is a significant, positive predictor of the tourists' actual travel/purchase behaviour.The final objective of the study focused on applying the Theory of Planned Behaviour (TPB) in the context of tourism and international holiday destination travel. The analysis of the TPB model confirmed that the attitude towards behaviour and the perceived behavioural control are positive and significant predictors of the behavioural intention. However, the social norm failed to have a significant direct impact on behavioural intention. Additionally, unlike theorised by the TPB, the empirical evidence did not support the hypothesis that the behavioural intention and perceived behavioural control have a significant direct impact on tourists' actual travel/purchase behaviour.;Furthermore, within the scope of this objective, the comparative analysis of predictive abilities of the TPB and perceived value was conducted, as well as, an attempt was made to enhance the predictive ability of the TPB by integrating the perceived value construct within its framework. The outcome of the analysis suggests that, firstly, the perceived value is a better predictor of the actual travel/purchase behaviour than the TPB and, secondly, the integration of the perceived value has considerably improved the predictive ability of the TPB
Robust lot sizing with remanufacturing, theory and practice
Get PDFWith the increasing importance of means of recovering items, practices such as reuse, recycling and remanufacturing have been gaining increasing importance in production systems. In this thesis, we aim to explore methods to obtain cost-efficient production plans for manufacturing systems that employ remanufacturing. A crucial challenge here is regarding parameter uncertainty. Commonly, decision makers have to tackle uncertainties on aspects such as operational costs, demands and in the case of production recoveries, the number of items returned by customers. Our work aims to address these challenges through the framework of robust optimization, where we impose uncertainty on demands and/or returns. In Chapter 1, we provide an introduction outlining the methods and formulations related to our study. In Chapter and 2, we review the literature on lot sizing problems, and the implications of remanufacturing. Following this, we introduce a robust lot sizing problem with remanufacturing in Chapter 3, where we consider uncertainties in both customer demand and return and implement a min-max decomposition approach for this problem. In Chapter 4, we propose a novel approach which employs extended reformulations for the master problem, while addressing computational challenges. In Chapter 5, we consider a different setting for the lot sizing problem with remanufacturing, where a two-level multi-component variation is considered. We consider the case where fixed costs are imposed on components and only variable costs are considered for the end-item. This is then followed by a robust formulation for and a min-max decomposition approach. We show that certain optimality properties have to be enforced to derive costs correctly. In Chapter 6, we consider the two-level multi-component problem with fixed costs on the end-item level. We show certain optimality conditions for this problem, and show how these properties can be exploited in the dynamic programming setting introduced in Teunter et al. [2006]. Throughout Chapters 4 and 5, we provide extensive computational experiments. Finally, in Chapter 7, we provide future research directions and conclusions, where potential advantages and limitations are discussed. Keywords: Integer Programming, Lot-Sizing, Remanufacturing, Robust Optimization, DecompositionWith the increasing importance of means of recovering items, practices such as reuse, recycling and remanufacturing have been gaining increasing importance in production systems. In this thesis, we aim to explore methods to obtain cost-efficient production plans for manufacturing systems that employ remanufacturing. A crucial challenge here is regarding parameter uncertainty. Commonly, decision makers have to tackle uncertainties on aspects such as operational costs, demands and in the case of production recoveries, the number of items returned by customers. Our work aims to address these challenges through the framework of robust optimization, where we impose uncertainty on demands and/or returns. In Chapter 1, we provide an introduction outlining the methods and formulations related to our study. In Chapter and 2, we review the literature on lot sizing problems, and the implications of remanufacturing. Following this, we introduce a robust lot sizing problem with remanufacturing in Chapter 3, where we consider uncertainties in both customer demand and return and implement a min-max decomposition approach for this problem. In Chapter 4, we propose a novel approach which employs extended reformulations for the master problem, while addressing computational challenges. In Chapter 5, we consider a different setting for the lot sizing problem with remanufacturing, where a two-level multi-component variation is considered. We consider the case where fixed costs are imposed on components and only variable costs are considered for the end-item. This is then followed by a robust formulation for and a min-max decomposition approach. We show that certain optimality properties have to be enforced to derive costs correctly. In Chapter 6, we consider the two-level multi-component problem with fixed costs on the end-item level. We show certain optimality conditions for this problem, and show how these properties can be exploited in the dynamic programming setting introduced in Teunter et al. [2006]. Throughout Chapters 4 and 5, we provide extensive computational experiments. Finally, in Chapter 7, we provide future research directions and conclusions, where potential advantages and limitations are discussed. Keywords: Integer Programming, Lot-Sizing, Remanufacturing, Robust Optimization, Decompositio
ActiveChat, the feasibility of a classroom-based physical activity and sedentary behaviour programme in Scottish secondary schools
Get PDFIntroduction: Self- report data suggest 82% of Scottish adolescents are insufficiently active. Schools play a pivotal role in the promotion of physical activity (PA) and reduction in sedentary behaviour (SB). The purpose of this thesis was to develop and trial the ActiveChat programme: a classroom-based PA and SB programme implemented into Scottish secondary schools. This PhD consisted of three studies: i) a systematic review and meta-analysis of classroom-room based PA and SB programmes in adolescents; ii) an evaluative case study to explore teachers' and teacher educators' perceptions of the ActiveChat programme ; iii) a feasibility trial of the ActiveChat programme.;Methods: The feasibility trial of the ActiveChat programme was implemented within a secondary school over eight weeks. Motivation, psychological needs, attitudes, and habitual PA and SB were assessed pre- and post-programme using subjective methods. In-class PA and SB were assessed objectively. Evaluation of the ActiveChat programme was conducted through focus groups/interviews with teachers and pupils, teacher evaluation, and observation.;Results: The meta-analysis demonstrated non-significant results on PA and SB based on limited studies (PA, p = 0.55, d = 0.05; SB, p = 0.16, d = -0.11). Results of the case study suggested the ActiveChat programme met learning outcomes from the areas of health and wellbeing, literacy, and numeracy of the Curriculum for Excellence, and emphasised the programmes place in Personal and Social Education.;Results of the feasibility study demonstrated significantly positive effects of ActiveChat on internalised forms of motivation, competence, relatedness, and attitudes towards SB. In-class PA was significantly higher in the ActiveChat class compared to control (11%). The evaluation demonstrated that pupils and teachers were positively receptive to ActiveChat, and the programme was delivered with good levels of fidelity (63%). Overall, this PhD research determined the feasibility of a teacher-led classroom-based PA and SB programme within secondary schools.Introduction: Self- report data suggest 82% of Scottish adolescents are insufficiently active. Schools play a pivotal role in the promotion of physical activity (PA) and reduction in sedentary behaviour (SB). The purpose of this thesis was to develop and trial the ActiveChat programme: a classroom-based PA and SB programme implemented into Scottish secondary schools. This PhD consisted of three studies: i) a systematic review and meta-analysis of classroom-room based PA and SB programmes in adolescents; ii) an evaluative case study to explore teachers' and teacher educators' perceptions of the ActiveChat programme ; iii) a feasibility trial of the ActiveChat programme.;Methods: The feasibility trial of the ActiveChat programme was implemented within a secondary school over eight weeks. Motivation, psychological needs, attitudes, and habitual PA and SB were assessed pre- and post-programme using subjective methods. In-class PA and SB were assessed objectively. Evaluation of the ActiveChat programme was conducted through focus groups/interviews with teachers and pupils, teacher evaluation, and observation.;Results: The meta-analysis demonstrated non-significant results on PA and SB based on limited studies (PA, p = 0.55, d = 0.05; SB, p = 0.16, d = -0.11). Results of the case study suggested the ActiveChat programme met learning outcomes from the areas of health and wellbeing, literacy, and numeracy of the Curriculum for Excellence, and emphasised the programmes place in Personal and Social Education.;Results of the feasibility study demonstrated significantly positive effects of ActiveChat on internalised forms of motivation, competence, relatedness, and attitudes towards SB. In-class PA was significantly higher in the ActiveChat class compared to control (11%). The evaluation demonstrated that pupils and teachers were positively receptive to ActiveChat, and the programme was delivered with good levels of fidelity (63%). Overall, this PhD research determined the feasibility of a teacher-led classroom-based PA and SB programme within secondary schools
How does cement influence the mechanical properties of sands and sandstones?
Get PDFDeformation bands can act as barriers and baffles in sandstone reservoirs. An increasing number of deformation bands have been studied in poorly cemented sandstones, yet there are questions about how grains can break (rather than slide past one another) in such loose sediments/rocks. The strength and distribution of cement may provide an answer. Detailed 3D observations are required to understand the cement and porosity variability that may control the formation of deformation bands.;Integrating x-ray microtomography (X-CT) with microscopic observations, the first part of this thesis analyses cement and porosity distribution across deformation band samples from Utah, Hungary and Arran by comparing 2D slice to 3D sub-volume analysis methods.;Characterisation of cement in outcrops of sand(stone)s is complex due to variable mineralogy and multiple periods of cementation. The second half of this thesis strips back the compositional complexities of sand(stone)s to recreate poorly cemented synthetic sandstones in the laboratory. Here gypsum and calcite were used as cementing phases with percentage of cement in the synthetic samples ranging from 3.5 - 26.7%. X-CT analysis shows that gypsum cement forms a network of needles encasing the sand grains meanwhile the calcite (formed by microbially induced calcite precipitation) forms at point contacts between the sand grains.;In order to quantify the strength of each of the synthetic sandstones a series of shear box, uniaxial compression testing (UCS) and triaxial experiments were carried out. The results from these experiments show that as the percentage of cement increased the shear and compressive strengths of these samples also increased. The maximum shear strengths of the synthetic samples produced ranged from 103 to 458 kPa.Meanwhile, maximum UCS results ranged from 139 to 2408 kPa. In addition, the mineralogy of these poorly cemented synthetic sandstones was shown to impact the mechanics and hydraulics of the synthetic sandstones.Deformation bands can act as barriers and baffles in sandstone reservoirs. An increasing number of deformation bands have been studied in poorly cemented sandstones, yet there are questions about how grains can break (rather than slide past one another) in such loose sediments/rocks. The strength and distribution of cement may provide an answer. Detailed 3D observations are required to understand the cement and porosity variability that may control the formation of deformation bands.;Integrating x-ray microtomography (X-CT) with microscopic observations, the first part of this thesis analyses cement and porosity distribution across deformation band samples from Utah, Hungary and Arran by comparing 2D slice to 3D sub-volume analysis methods.;Characterisation of cement in outcrops of sand(stone)s is complex due to variable mineralogy and multiple periods of cementation. The second half of this thesis strips back the compositional complexities of sand(stone)s to recreate poorly cemented synthetic sandstones in the laboratory. Here gypsum and calcite were used as cementing phases with percentage of cement in the synthetic samples ranging from 3.5 - 26.7%. X-CT analysis shows that gypsum cement forms a network of needles encasing the sand grains meanwhile the calcite (formed by microbially induced calcite precipitation) forms at point contacts between the sand grains.;In order to quantify the strength of each of the synthetic sandstones a series of shear box, uniaxial compression testing (UCS) and triaxial experiments were carried out. The results from these experiments show that as the percentage of cement increased the shear and compressive strengths of these samples also increased. The maximum shear strengths of the synthetic samples produced ranged from 103 to 458 kPa.Meanwhile, maximum UCS results ranged from 139 to 2408 kPa. In addition, the mineralogy of these poorly cemented synthetic sandstones was shown to impact the mechanics and hydraulics of the synthetic sandstones
Long term extreme analysis of moored FPSO with emphasis on the effect of hydrodynamic drag coefficient
Get PDFOne of the key coupling mechanisms between the FPSO and the mooring/riser, which remains to be a challenging topic, is the damping contribution from the mooring lines. The mooring line damping especially from hydrodynamic drag forces is of vital importance to FPSO's low frequency motion in deep water and its associated maximum mooring line tension and the maximum offset. The coupled analysis can take the mooring line damping into account automatically, but it suffers from the extremely high computational cost. Some methods use a linear damping coefficient to represent the damping effect but that estimate may not be accurate due to the line damping depending on several factors such as the wave frequencies, the response and offset position. An efficient and accurate analysis method is required to balance accuracy and efficiency. Morison's equation with a drag coefficient is often employed to calculate the hydrodynamic drag loads of mooring lines. The drag coefficient is not easily determined, particularly for chain, with its complex shape. The variation of hydrodynamic drag coefficient would alter the level of line damping. That means the drag coefficient is important to the damping and the ensuing extreme offset and maximum line tension. Therefore, it is worthwhile to investigate the effects of the hydrodynamic drag coefficient on the damping contribution to the extreme low frequency FPSO motion and the maximum mooring line tension. To begin with, a hybrid time and frequency domain method is developed for dynamic analysis of moored FPSO. The time domain simulation with a large time step is performed for low frequency motion of the FPSO, whilst the wave frequency response of the mooring lines at a given mean offset position will be conducted in the frequency domain.;The frequency domain analysis will be based upon a specific linearization approach where the damping to the low frequency FPSO motion from the wave frequency response of the mooring line can be accounted for in the form of an increased mean tension. Comparison is made of the tension/motion results with that of the dynamically coupled time-domain analysis, as well as the computational efficiency. Next, the methodologies for the long term extreme analysis are validated. The all sea state method for the long term extreme analysis is performed by use of Kriging metamodel (Simpson et al., 1998; Wang and Shan, 2006). The Monte Carlo simulation is applied for the long term probability integral based on the Kriging metamodel.;The improved method based on the environmental contour method and accurate distribution tail extrapolation method is proposed. The contour line method assumes that the short term variability could be accounted for separately. This method evaluates the extreme response based on limited sea states along a well-defined environmental contour line with a given return period. Then the short term variability is considered by selecting a high fractile. The distribution of the response is evaluated by the average conditional exceedance rates (ACER) method. The ACER method, which can accurately capture the effect of statistical dependence for the extreme value prediction problem, is less restrictive and more flexible than the one based on asymptotic theory. Finally, the reliability analysis for the extreme response considering the uncertainty influence of the drag coefficient is performed. The conditional distribution for the long term extreme response with given the drag coefficient is estimated by contour line method and ACER method. The perturbation method based on 4th-order expansion is developed. The asymptotic approximation method based on the Laplace's method is also employed for the approximation of probability integral . The asymptotic evaluation is based on the assertion that the greatest contribution to an integral derives from the locations where the integrand is a maximum point.One of the key coupling mechanisms between the FPSO and the mooring/riser, which remains to be a challenging topic, is the damping contribution from the mooring lines. The mooring line damping especially from hydrodynamic drag forces is of vital importance to FPSO's low frequency motion in deep water and its associated maximum mooring line tension and the maximum offset. The coupled analysis can take the mooring line damping into account automatically, but it suffers from the extremely high computational cost. Some methods use a linear damping coefficient to represent the damping effect but that estimate may not be accurate due to the line damping depending on several factors such as the wave frequencies, the response and offset position. An efficient and accurate analysis method is required to balance accuracy and efficiency. Morison's equation with a drag coefficient is often employed to calculate the hydrodynamic drag loads of mooring lines. The drag coefficient is not easily determined, particularly for chain, with its complex shape. The variation of hydrodynamic drag coefficient would alter the level of line damping. That means the drag coefficient is important to the damping and the ensuing extreme offset and maximum line tension. Therefore, it is worthwhile to investigate the effects of the hydrodynamic drag coefficient on the damping contribution to the extreme low frequency FPSO motion and the maximum mooring line tension. To begin with, a hybrid time and frequency domain method is developed for dynamic analysis of moored FPSO. The time domain simulation with a large time step is performed for low frequency motion of the FPSO, whilst the wave frequency response of the mooring lines at a given mean offset position will be conducted in the frequency domain.;The frequency domain analysis will be based upon a specific linearization approach where the damping to the low frequency FPSO motion from the wave frequency response of the mooring line can be accounted for in the form of an increased mean tension. Comparison is made of the tension/motion results with that of the dynamically coupled time-domain analysis, as well as the computational efficiency. Next, the methodologies for the long term extreme analysis are validated. The all sea state method for the long term extreme analysis is performed by use of Kriging metamodel (Simpson et al., 1998; Wang and Shan, 2006). The Monte Carlo simulation is applied for the long term probability integral based on the Kriging metamodel.;The improved method based on the environmental contour method and accurate distribution tail extrapolation method is proposed. The contour line method assumes that the short term variability could be accounted for separately. This method evaluates the extreme response based on limited sea states along a well-defined environmental contour line with a given return period. Then the short term variability is considered by selecting a high fractile. The distribution of the response is evaluated by the average conditional exceedance rates (ACER) method. The ACER method, which can accurately capture the effect of statistical dependence for the extreme value prediction problem, is less restrictive and more flexible than the one based on asymptotic theory. Finally, the reliability analysis for the extreme response considering the uncertainty influence of the drag coefficient is performed. The conditional distribution for the long term extreme response with given the drag coefficient is estimated by contour line method and ACER method. The perturbation method based on 4th-order expansion is developed. The asymptotic approximation method based on the Laplace's method is also employed for the approximation of probability integral . The asymptotic evaluation is based on the assertion that the greatest contribution to an integral derives from the locations where the integrand is a maximum point
Understanding colloidal interactions at oil/rock/brine interfaces
Get PDFThis thesis was previously held under moratorium from 22/08/19 to 22/08/21Carbonate rock reservoirs comprise approximately 60% of the world’s oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate.The main aim of this work is to gain fundamental understanding of physicochemical mechanisms involved in wettability modification of carbonate minerals in the presence of diluted brines. This work utilises a combination of experimental and theoretical approaches examined carbonate surface characteristics using different surface analytical techniques to investigate the effect of ionic type and ionic strength by examining the same systems from different perspectives. Thereby, this work investigates the influence of different types of salts (NaCl, CaCl2, MgCl2, NaHCO3, and Na2SO4), and their concentration (0–100 mM) on the surface characteristics, such as surface charge, surface wettability, and surface forces of unconditioned and model oil (stearic acid and/or asphaltene) conditioned carbonate (calcite and/or dolomite) surfaces, by zeta potential, static contact angle, and atomic force microscopy measurements. Additionally, this work utilises theoretical calculations to validate experimental results, including the minerals surface energy using the Van Oss Chaudhury Good (VOCG) theory and and colloidal forces at oil-rock brine interfaces using the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory.Our results indicate that the adsorption of potential determining cations (Ca2+ and Mg2+) driven by coulombic interactions results in increased electrostatic attraction, and charge reversal of carbonate surfaces from negative to positive. While adsorption of potential determining anions (HCO−3 and SO24−) increased electrostatic repulsion, it maintained negative zeta potential of carbonate surfaces and increased its magnitude up to 10 mM, before decreasing at higher salt concentration and, therefore, enhanced water-wet conditions. Additionally, the adsorption of model oil components alters the zeta potential of the carbonate surfaces to more negative values, reduces total the surface energy of carbonates, due to reduction in the polar acid-base contribution and, consequently, results in more oil-wet surfaces. Evidence of ion-bridging forces in the presence of Mg2+ cations, and unbinding and stretching of the adsorbed stearic acid layer on calcite surfaces in the presence of SO24− anions, were observed.The suggested mechanism in this study for LSW is surface charge modification of carbonates, due to adsorption of ions, which alters the diffuse layer structure by expansion of the electric double layer (EDL), which may result in wettability alteration toward a more water-wet condition to improve oil recovery, by having a positive contribution to the disjoining pressure and facilitating the formation of a thicker and more stable water film. Therefore, this work utilises experimental and theoretical processes to extend the current knowledge base for dynamic water injection design by determining the effect of ionic composition and ionic strength on surface characteristics of carbonate formation.Carbonate rock reservoirs comprise approximately 60% of the world’s oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate.The main aim of this work is to gain fundamental understanding of physicochemical mechanisms involved in wettability modification of carbonate minerals in the presence of diluted brines. This work utilises a combination of experimental and theoretical approaches examined carbonate surface characteristics using different surface analytical techniques to investigate the effect of ionic type and ionic strength by examining the same systems from different perspectives. Thereby, this work investigates the influence of different types of salts (NaCl, CaCl2, MgCl2, NaHCO3, and Na2SO4), and their concentration (0–100 mM) on the surface characteristics, such as surface charge, surface wettability, and surface forces of unconditioned and model oil (stearic acid and/or asphaltene) conditioned carbonate (calcite and/or dolomite) surfaces, by zeta potential, static contact angle, and atomic force microscopy measurements. Additionally, this work utilises theoretical calculations to validate experimental results, including the minerals surface energy using the Van Oss Chaudhury Good (VOCG) theory and and colloidal forces at oil-rock brine interfaces using the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory.Our results indicate that the adsorption of potential determining cations (Ca2+ and Mg2+) driven by coulombic interactions results in increased electrostatic attraction, and charge reversal of carbonate surfaces from negative to positive. While adsorption of potential determining anions (HCO−3 and SO24−) increased electrostatic repulsion, it maintained negative zeta potential of carbonate surfaces and increased its magnitude up to 10 mM, before decreasing at higher salt concentration and, therefore, enhanced water-wet conditions. Additionally, the adsorption of model oil components alters the zeta potential of the carbonate surfaces to more negative values, reduces total the surface energy of carbonates, due to reduction in the polar acid-base contribution and, consequently, results in more oil-wet surfaces. Evidence of ion-bridging forces in the presence of Mg2+ cations, and unbinding and stretching of the adsorbed stearic acid layer on calcite surfaces in the presence of SO24− anions, were observed.The suggested mechanism in this study for LSW is surface charge modification of carbonates, due to adsorption of ions, which alters the diffuse layer structure by expansion of the electric double layer (EDL), which may result in wettability alteration toward a more water-wet condition to improve oil recovery, by having a positive contribution to the disjoining pressure and facilitating the formation of a thicker and more stable water film. Therefore, this work utilises experimental and theoretical processes to extend the current knowledge base for dynamic water injection design by determining the effect of ionic composition and ionic strength on surface characteristics of carbonate formation
Combined wet milling crystallisation methods for particle engineering
Get PDFRecent advances in pharmaceutical manufacturing for consistent supply of medicines with the required physical properties has emphasised the need for robust crystallisation processes which is a critical separation and purification technique. Mechanical milling is employed post crystallisation as an offline unit operation usually in a separate dry solids processing facility for adjusting the particle size and shape attributes of crystalline products for downstream processing. An emerging and increasingly applied technology is high shear wet milling in crystalline slurries for inline size and shape modification during particle formation. This potentially avoids the need for multiple crystallisation trials and offline milling saving time, costs and powder handling. Similarly, sonication is a powerful particle engineering tool through immersing ultrasound probes directly in solution. This PhD project is focused on the investigation and process integration of wet milling and indirect ultrasound for enhancing crystallisation processes and engineering particle attributes. The experimental study combined a cooling and isothermal crystallisation (seeded & unseeded) process with wet milling and indirect sonication. Results from the combined method provides the ability to modify and selectively achieve a range of product outcomes including particle sizes with tight spans, equant shapes and low surface energies as well as increased nucleation rates.;High shear from wet milling is also implemented as a seeding protocol configured to a mixed-suspension mixed-product removal continuous crystalliser which proved to be an adequate seed generation strategy.Deploying accurate quantitative analysis of size and shape attributes for solid particles is further explored. A multi-sensor measurement approach was employed using inline sensors, computational tools and offline techniques. The performance of these tools were vigorously tested for strengths and limitations which was proven to be beneficial for characterising the breakage of crystalline materials as well as overall process understanding and opportunities for process control.Recent advances in pharmaceutical manufacturing for consistent supply of medicines with the required physical properties has emphasised the need for robust crystallisation processes which is a critical separation and purification technique. Mechanical milling is employed post crystallisation as an offline unit operation usually in a separate dry solids processing facility for adjusting the particle size and shape attributes of crystalline products for downstream processing. An emerging and increasingly applied technology is high shear wet milling in crystalline slurries for inline size and shape modification during particle formation. This potentially avoids the need for multiple crystallisation trials and offline milling saving time, costs and powder handling. Similarly, sonication is a powerful particle engineering tool through immersing ultrasound probes directly in solution. This PhD project is focused on the investigation and process integration of wet milling and indirect ultrasound for enhancing crystallisation processes and engineering particle attributes. The experimental study combined a cooling and isothermal crystallisation (seeded & unseeded) process with wet milling and indirect sonication. Results from the combined method provides the ability to modify and selectively achieve a range of product outcomes including particle sizes with tight spans, equant shapes and low surface energies as well as increased nucleation rates.;High shear from wet milling is also implemented as a seeding protocol configured to a mixed-suspension mixed-product removal continuous crystalliser which proved to be an adequate seed generation strategy.Deploying accurate quantitative analysis of size and shape attributes for solid particles is further explored. A multi-sensor measurement approach was employed using inline sensors, computational tools and offline techniques. The performance of these tools were vigorously tested for strengths and limitations which was proven to be beneficial for characterising the breakage of crystalline materials as well as overall process understanding and opportunities for process control
Monitoring of incremental rotary forming
Get PDFAs manufacturing processes move toward full automation, reliable instrumentation is vital for improved process control. This work examines new applications of nondisruptive monitoring techniques for incremental rotary forming (IRF) processes. IRF processes such as flow forming (FF) and spinning make rotationally symmetric components. These cold, incremental processes produce parts to near net shape with improved mechanical properties and high material utilisation. The design and operation of these processes is limited by an incomplete understanding of forming mechanics and process design.Monitoring is used in many industries to improve process understanding, control and operation. The relevance of existing monitoring technologies to IRF was assessed and three were selected. Acoustic and vibration monitoring were both investigated fordetecting fracture during FF. An ultrasonic (US) monitoring system was developed toscan the contact area between the tool and the material during FF and spinning.;The results showed that acoustic monitoring can detect major fracture events in FF. Vibration monitoring did not show useful results. Testing of the US system showed that it is possible to record changes in the tool-workpiece contact area, detect internal fractures in the part, and measure the thickness of parts spun in free air. Fracture,contact area and thickness have never before been measured in-process.This work demonstrates for the first time the ability to monitor IRF contact properties, thickness and fracture in real time. Monitoring of these could be used in industry to refine the design of tooling and processes, validate modelling, and avoid unexpected failures. In the medium term, improved monitoring will allow improved process control and automation with reduced risk.As manufacturing processes move toward full automation, reliable instrumentation is vital for improved process control. This work examines new applications of nondisruptive monitoring techniques for incremental rotary forming (IRF) processes. IRF processes such as flow forming (FF) and spinning make rotationally symmetric components. These cold, incremental processes produce parts to near net shape with improved mechanical properties and high material utilisation. The design and operation of these processes is limited by an incomplete understanding of forming mechanics and process design.Monitoring is used in many industries to improve process understanding, control and operation. The relevance of existing monitoring technologies to IRF was assessed and three were selected. Acoustic and vibration monitoring were both investigated fordetecting fracture during FF. An ultrasonic (US) monitoring system was developed toscan the contact area between the tool and the material during FF and spinning.;The results showed that acoustic monitoring can detect major fracture events in FF. Vibration monitoring did not show useful results. Testing of the US system showed that it is possible to record changes in the tool-workpiece contact area, detect internal fractures in the part, and measure the thickness of parts spun in free air. Fracture,contact area and thickness have never before been measured in-process.This work demonstrates for the first time the ability to monitor IRF contact properties, thickness and fracture in real time. Monitoring of these could be used in industry to refine the design of tooling and processes, validate modelling, and avoid unexpected failures. In the medium term, improved monitoring will allow improved process control and automation with reduced risk
A new apparatus for experiments with Caesium Bose-Einstein Condensates
Get PDFThis thesis reports on the design and construction of an experimental apparatus capable of generating Bose-Einstein condensates (BECs) of spin-polarised caesium-133 atoms. Caesium condensates offer excellent control over interatomic interactions due to the rich landscape of low-field magnetic Feshbach resonances, which enables the study of quantum gases in attractive and repulsive interaction regimes. An ultra-high vacuum system, laser systems and magnetic field coils were assembled to trap and cool the atoms from room temperature to temperatures on the order of 1 nK. Absorption imaging was implemented as a means to detect the number and density distribution of the atoms. Laser cooling and trapping methods are introduced, and the effects of each cooling stage on the gas are demonstrated. The final cooling stage, evaporative cooling, is presented by way of examining the gas after it has undergone each evaporation phase so we observe the onset of Bose-Einstein condensation. Evaporative cooling produces BECs containing on the order of 2×105 atoms, with a condensate fraction of 0.48. We demonstrate that the atom number can be fine-tuned by removal of the most thermal atoms in the trap. We also exhibit our ability to observe expanding condensates in a guiding beam for durations of up to 1 s, and our ability to cause the condensate to implode, by tuning interactions. Measuring the temperature of the gas in sub-nK regimes is currently a challenge when using traditional time-of-flight thermometry. Some modifications to the apparatus have been described, that would permit thermometry using dilute caesium atoms in a different spin state to probe the main gas.This thesis reports on the design and construction of an experimental apparatus capable of generating Bose-Einstein condensates (BECs) of spin-polarised caesium-133 atoms. Caesium condensates offer excellent control over interatomic interactions due to the rich landscape of low-field magnetic Feshbach resonances, which enables the study of quantum gases in attractive and repulsive interaction regimes. An ultra-high vacuum system, laser systems and magnetic field coils were assembled to trap and cool the atoms from room temperature to temperatures on the order of 1 nK. Absorption imaging was implemented as a means to detect the number and density distribution of the atoms. Laser cooling and trapping methods are introduced, and the effects of each cooling stage on the gas are demonstrated. The final cooling stage, evaporative cooling, is presented by way of examining the gas after it has undergone each evaporation phase so we observe the onset of Bose-Einstein condensation. Evaporative cooling produces BECs containing on the order of 2×105 atoms, with a condensate fraction of 0.48. We demonstrate that the atom number can be fine-tuned by removal of the most thermal atoms in the trap. We also exhibit our ability to observe expanding condensates in a guiding beam for durations of up to 1 s, and our ability to cause the condensate to implode, by tuning interactions. Measuring the temperature of the gas in sub-nK regimes is currently a challenge when using traditional time-of-flight thermometry. Some modifications to the apparatus have been described, that would permit thermometry using dilute caesium atoms in a different spin state to probe the main gas
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