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Analysis of diesel combustion in four-stroke marine engines : an integrated CFD and reduced chemical kinetics approach
Get PDFThe present thesis aims at characterising and understanding flow and combustion processes in four-stroke marine engines by means of detailed Computational Fluid Dynamics (CFD) modelling. In particular, two dual-fuel engines operating in the diesel mode are considered: Lister LV1 and Wärtilä 50DF. A systematic approach is followed, consisting in: (a) Characterising the spray dynamics in a constant volume chamber, and adapting the Cascade Atomisation Breakup (CAB) spray model, for conditions relevant to operation of the engines considered in the present study. (b) Adapting a tool developed by means of coupling the chemical kinetics CHEMKIN-II code with the KIVA-3vr2 CFD code, thus enabling CFD simulations with reliable chemistry. (c) Performing CFD simulations of flow and combustion in the two engines for operation in the 80% load for Lister LV1, and in the full load range for Wärtilä 50DF, and comparing results against one-step chemistry simulations, as well as against respective experimental data. Thus, to author’s knowledge, the present thesis reports the first CFD studies in marine engines operating in the diesel mode, including realistic combustion chemistry. The computational results demonstrate that the spray breakup corresponds to the catastrophic regime. Adaptation of the CAB model has yielded values of model constants in a range that does not considerably deviate from relevant literature studies. Two validated reduced-order chemical kinetic mechanisms of n-heptane combustion have been implemented in the course of the present CFD studies: (i) Patel et al. (2004), with 29 species and 52 elementary reactions, and (ii) Ra and Reitz (2008), with 45 species and 142 elementary reactions. The two mechanisms have been supplemented with a NOx sub mechanism. The main findings of the present study can be summarised as follows: - Ignition delay times are in good agreement with chemical kinetics simulations using realistic chemistry. - For simulations with reduced order chemistry, fuel disintegration nearly terminates at the end of injection, in contrast to results of the one-step approach. On the other hand, similarities in Rate of Heat Release Rates are attained for the two approaches. - The evolution of important species can differ considerably between the two reduced mechanisms. - The distribution of main pollutants bears similarities between the two reduced mechanisms, and may differ significantly from the one-step approach. While the present study demonstrates that using reduced order chemistry is essential for characterising engine aerothermochemistry albeit at a significant increase in computational cost, the one-step approach is shown to still be valid as an engineering tool, providing a basic characterisation of flow and combustion, which can be useful in the frame of marine engine development.The present thesis aims at characterising and understanding flow and combustion processes in four-stroke marine engines by means of detailed Computational Fluid Dynamics (CFD) modelling. In particular, two dual-fuel engines operating in the diesel mode are considered: Lister LV1 and Wärtilä 50DF. A systematic approach is followed, consisting in: (a) Characterising the spray dynamics in a constant volume chamber, and adapting the Cascade Atomisation Breakup (CAB) spray model, for conditions relevant to operation of the engines considered in the present study. (b) Adapting a tool developed by means of coupling the chemical kinetics CHEMKIN-II code with the KIVA-3vr2 CFD code, thus enabling CFD simulations with reliable chemistry. (c) Performing CFD simulations of flow and combustion in the two engines for operation in the 80% load for Lister LV1, and in the full load range for Wärtilä 50DF, and comparing results against one-step chemistry simulations, as well as against respective experimental data. Thus, to author’s knowledge, the present thesis reports the first CFD studies in marine engines operating in the diesel mode, including realistic combustion chemistry. The computational results demonstrate that the spray breakup corresponds to the catastrophic regime. Adaptation of the CAB model has yielded values of model constants in a range that does not considerably deviate from relevant literature studies. Two validated reduced-order chemical kinetic mechanisms of n-heptane combustion have been implemented in the course of the present CFD studies: (i) Patel et al. (2004), with 29 species and 52 elementary reactions, and (ii) Ra and Reitz (2008), with 45 species and 142 elementary reactions. The two mechanisms have been supplemented with a NOx sub mechanism. The main findings of the present study can be summarised as follows: - Ignition delay times are in good agreement with chemical kinetics simulations using realistic chemistry. - For simulations with reduced order chemistry, fuel disintegration nearly terminates at the end of injection, in contrast to results of the one-step approach. On the other hand, similarities in Rate of Heat Release Rates are attained for the two approaches. - The evolution of important species can differ considerably between the two reduced mechanisms. - The distribution of main pollutants bears similarities between the two reduced mechanisms, and may differ significantly from the one-step approach. While the present study demonstrates that using reduced order chemistry is essential for characterising engine aerothermochemistry albeit at a significant increase in computational cost, the one-step approach is shown to still be valid as an engineering tool, providing a basic characterisation of flow and combustion, which can be useful in the frame of marine engine development
Ecological studies of Clostridioides difficile and COVID-19 infection with the application of space-time risk models
Get PDFInfectious diseases continue to pose major global health threats. With the recent devastation from the COVID-19 pandemic and growing concerns of healthcare-associated infections (HAIs), there is a worldwide requirement for stringent techniques to monitor and understand the key drivers for infections. Infectious diseases have an inherent spatial dimension due to the contagious nature of viruses and bacteria. This thesis aims to explore the use of spatial and spatio-temporal techniques applied to infections, specifically Clostridiodies difficile infection (CDI) and COVID-19, to identify risk factors at an ecological population-based level. A mixture of open-sourced and routinely collected data, at different spatial scales, were used to understand the surveillance capacities of observational public health data. Antimicrobial prescribing and stewardship have been a global focus in the last decade as concerns have grown with emergent novel antibiotic-resistant infections. CDI has been shown to have a well-defined association with certain broad-spectrum antibiotic classes and other environmental factors, however, there is a gap in the literature aiming to understand these relationships ecologically and spatially. The main focus of this thesis was to use spatio-temporal models to investigate spatial risk factors of CDI incidence, such as GP antimicrobial prescribing, in Scotland and Wales. Similar spatial techniques were then applied to investigate the spatial distribution of COVID-19 testing during the first wave of the 2020 epidemic in Scotland. The relevant spatial and spatio-temporal models applied throughout this thesis were initially discussed in Chapter 2. The spatial distribution of Scottish GP antibiotic prescribing rates, from 2016 to 2018, was investigated in Chapter 3 using spatial point-location correlation methods. Risk factors of increased GP antibiotic prescribing were explored, showing GP practice demographic information as key drivers of increased antibiotic prescribing. These analyses were followed by an exploration of Scottish CDI incidence data, from 2014 to 2018, at a small areal level (intermediate zones (IZ)), to understand spatial auto-correlation and temporal trends of CDI incidence in Chapter 4. Population demographic risk factors, as highlighted in the literature, were obtained at the same spatial scale and assessed as ecological risk factors of CDI incidence using conditional autoregressive (CAR) models. The next phase of this thesis then combined the previous two analyses, introducing a multi-level spatial problem, which aimed to explore central risk factors of CDI that were not available at the same spatial scale in Chapter 5. Spatial interpolation methods were applied to manipulate GP antibiotic prescribing point-location data and areal-unit cattle density data to match the CDI incidence at an IZ spatial scale. These data could then be explored as ecological risk factors of CDI incidence, carrying forward the previously defined CAR model from Chapter 4 and adjusting for demographic confounders. Welsh CDI incidence and primary care antibiotic prescribing data offered the opportunity to compare between two countries in the UK. The retrospective ecological study in Chapter 6 used aggregated disease surveillance data to understand the impact of total and high-risk Welsh GP antibiotic prescribing on total and stratified inpatient/noninpatient CDI incidence. Location and health board information were anonymised preventing a formal spatial analysis, however, the results were comparable to previous chapter findings and supported the hypothesis of an increased risk of CDI incidence reflected in GP antibiotic prescribing rates, particularly high-risk antibiotics, and population demographics. Finally, at the beginning of the COVID-19 pandemic, it became evident that the methodologies applied in this thesis could support the investigation of the spread of COVID-19 infections. The work presented in Chapter 7 aimed to explore how best to capture spatial patterns of community COVID-19 infection by conducting a spatiotemporal analysis on three data streams { positive test rates, relevant NHS24 calls and COVID Symptom Study (CSS) predicted cases, to assess which was best for early disease surveillance. Results showed both sources to identify similar trends of COVID-19 and gold-standard testing data, particularly when used in parallel. This thesis has provided new insights into the associated risks between CDI incidence and GP antibiotic prescribing in Scotland and Wales, demonstrating the capabilities of open-source and routinely collected public health data when applied in a spatial framework. These results support the requirement of stringent measures to reduce antibiotic prescribing in the community. It also highlights the beneficial use and suitability of analysing infectious disease data with spatial techniques to address gaps in the literature to understand population-based risk factors of disease. There is a strong argument for future research into methods of analysing multi-level spatial data, particularly in the application of observational public health data.Infectious diseases continue to pose major global health threats. With the recent devastation from the COVID-19 pandemic and growing concerns of healthcare-associated infections (HAIs), there is a worldwide requirement for stringent techniques to monitor and understand the key drivers for infections. Infectious diseases have an inherent spatial dimension due to the contagious nature of viruses and bacteria. This thesis aims to explore the use of spatial and spatio-temporal techniques applied to infections, specifically Clostridiodies difficile infection (CDI) and COVID-19, to identify risk factors at an ecological population-based level. A mixture of open-sourced and routinely collected data, at different spatial scales, were used to understand the surveillance capacities of observational public health data. Antimicrobial prescribing and stewardship have been a global focus in the last decade as concerns have grown with emergent novel antibiotic-resistant infections. CDI has been shown to have a well-defined association with certain broad-spectrum antibiotic classes and other environmental factors, however, there is a gap in the literature aiming to understand these relationships ecologically and spatially. The main focus of this thesis was to use spatio-temporal models to investigate spatial risk factors of CDI incidence, such as GP antimicrobial prescribing, in Scotland and Wales. Similar spatial techniques were then applied to investigate the spatial distribution of COVID-19 testing during the first wave of the 2020 epidemic in Scotland. The relevant spatial and spatio-temporal models applied throughout this thesis were initially discussed in Chapter 2. The spatial distribution of Scottish GP antibiotic prescribing rates, from 2016 to 2018, was investigated in Chapter 3 using spatial point-location correlation methods. Risk factors of increased GP antibiotic prescribing were explored, showing GP practice demographic information as key drivers of increased antibiotic prescribing. These analyses were followed by an exploration of Scottish CDI incidence data, from 2014 to 2018, at a small areal level (intermediate zones (IZ)), to understand spatial auto-correlation and temporal trends of CDI incidence in Chapter 4. Population demographic risk factors, as highlighted in the literature, were obtained at the same spatial scale and assessed as ecological risk factors of CDI incidence using conditional autoregressive (CAR) models. The next phase of this thesis then combined the previous two analyses, introducing a multi-level spatial problem, which aimed to explore central risk factors of CDI that were not available at the same spatial scale in Chapter 5. Spatial interpolation methods were applied to manipulate GP antibiotic prescribing point-location data and areal-unit cattle density data to match the CDI incidence at an IZ spatial scale. These data could then be explored as ecological risk factors of CDI incidence, carrying forward the previously defined CAR model from Chapter 4 and adjusting for demographic confounders. Welsh CDI incidence and primary care antibiotic prescribing data offered the opportunity to compare between two countries in the UK. The retrospective ecological study in Chapter 6 used aggregated disease surveillance data to understand the impact of total and high-risk Welsh GP antibiotic prescribing on total and stratified inpatient/noninpatient CDI incidence. Location and health board information were anonymised preventing a formal spatial analysis, however, the results were comparable to previous chapter findings and supported the hypothesis of an increased risk of CDI incidence reflected in GP antibiotic prescribing rates, particularly high-risk antibiotics, and population demographics. Finally, at the beginning of the COVID-19 pandemic, it became evident that the methodologies applied in this thesis could support the investigation of the spread of COVID-19 infections. The work presented in Chapter 7 aimed to explore how best to capture spatial patterns of community COVID-19 infection by conducting a spatiotemporal analysis on three data streams { positive test rates, relevant NHS24 calls and COVID Symptom Study (CSS) predicted cases, to assess which was best for early disease surveillance. Results showed both sources to identify similar trends of COVID-19 and gold-standard testing data, particularly when used in parallel. This thesis has provided new insights into the associated risks between CDI incidence and GP antibiotic prescribing in Scotland and Wales, demonstrating the capabilities of open-source and routinely collected public health data when applied in a spatial framework. These results support the requirement of stringent measures to reduce antibiotic prescribing in the community. It also highlights the beneficial use and suitability of analysing infectious disease data with spatial techniques to address gaps in the literature to understand population-based risk factors of disease. There is a strong argument for future research into methods of analysing multi-level spatial data, particularly in the application of observational public health data
Design and analysis of an LVDC offshore microgrid for improving the electrical infrastructure of the multi-use platform
No full textHybrid and interconnected energy sources are becoming the norm for the low carbon energy sector. This implies parallel connection of different sources to a common platform, as it is seen in wind farm connection, self-contained microgrids, offshore Multi-Use Platforms (MUPs), etc. MUPs and their associated marine activities draw the attention of many countries worldwide to exploit resources of the oceans which cover over 68% of the surface of the earth. This helps to cut greenhouse gas emissions and also facilitate provision of food in a sustainable way. There are many challenges relating to developing the microgrid of the MUPs. These include space limitation, high costs of system components, installations related issues, unavailability of backup options, critical loads concerns such as aquaculture or isolated communities, power quality issues and turbine failure. To tackle the aforementioned problems, this research focuses on improving the electric infrastructure of MUPs by considering Direct Current (DC) systems for the offshore microgrid of these platforms. Integrating various energy resources, such as wind, tidal and solar, in a floating structure is proposed under this research. A new graphical concept for the optimal sizing of the MUPs’ microgrid is proposed which is verified by the Matlab/Linprog tool. In addition, a new methodology is proposed to determine the optimal number of parallel DC-DC converters connected to wind/tidal turbines for conversion efficiency maximization, and for increasing turbines’ reliability and availability. A case study for an MUP at the North Sea is discussed to demonstrate the validity of the proposed optimal sizing concept and the proposed methodology forefficiency maximisation. A new adaptive Instantaneous Average Current Sharing (IACS) controller is proposed for minimizing the circulating current among parallel DC-DC converters. A generalized model of n-parallel-connected DC-DC converterswith the improved IACS controller is derived for stability analysis purposes. A New coordinated controller is proposed for the Low Voltage Direct Current (LVDC) microgrid of the MUPs with n-parallel floating structures. A Model of a floating structure is derived which comprises wind and tidal turbines, solar array and energy storage, with boost and bidirectional converters.The outcomes of this research show that wind/tidal turbine failures could be reduced while increasing the turbines’ efficiency and availability by determining the optimal number of parallel DC-DC converters connected to the turbine. Based on the newdeveloped technique of determining optimal number of parallel converters instead of a single rated converter, the annual average efficiency of a wind turbine would be increased from 57 to 75 % under the case study considered in this research. Also, the novel adaptive IACS controller reduced the circulating current among parallel-connected DC-DC converters faster than the conventional controller. In addition, the load voltage is accurately regulated to the nominal value with applying this novel controller, while a steady error is recorded for the load voltage with applying the conventional IACS controller. Modeling and stability analysis were conducted for the DC wind/tidal turbines, which has never been done in the literature, showed that the turbine-based surface-mounted permanent magnet synchronous generator is stable, but two conditions should be fulfilled for a turbine-based interior-mounted permanent magnet synchronous generator to ensure turbine stability. Lastly, based on the modelling and stability analysis held for the LVDC microgrid of the MUPs, the new idea of considering DC system for MUPs is a viable solution that ensures stable and more efficient operation.Hybrid and interconnected energy sources are becoming the norm for the low carbon energy sector. This implies parallel connection of different sources to a common platform, as it is seen in wind farm connection, self-contained microgrids, offshore Multi-Use Platforms (MUPs), etc. MUPs and their associated marine activities draw the attention of many countries worldwide to exploit resources of the oceans which cover over 68% of the surface of the earth. This helps to cut greenhouse gas emissions and also facilitate provision of food in a sustainable way. There are many challenges relating to developing the microgrid of the MUPs. These include space limitation, high costs of system components, installations related issues, unavailability of backup options, critical loads concerns such as aquaculture or isolated communities, power quality issues and turbine failure. To tackle the aforementioned problems, this research focuses on improving the electric infrastructure of MUPs by considering Direct Current (DC) systems for the offshore microgrid of these platforms. Integrating various energy resources, such as wind, tidal and solar, in a floating structure is proposed under this research. A new graphical concept for the optimal sizing of the MUPs’ microgrid is proposed which is verified by the Matlab/Linprog tool. In addition, a new methodology is proposed to determine the optimal number of parallel DC-DC converters connected to wind/tidal turbines for conversion efficiency maximization, and for increasing turbines’ reliability and availability. A case study for an MUP at the North Sea is discussed to demonstrate the validity of the proposed optimal sizing concept and the proposed methodology forefficiency maximisation. A new adaptive Instantaneous Average Current Sharing (IACS) controller is proposed for minimizing the circulating current among parallel DC-DC converters. A generalized model of n-parallel-connected DC-DC converterswith the improved IACS controller is derived for stability analysis purposes. A New coordinated controller is proposed for the Low Voltage Direct Current (LVDC) microgrid of the MUPs with n-parallel floating structures. A Model of a floating structure is derived which comprises wind and tidal turbines, solar array and energy storage, with boost and bidirectional converters.The outcomes of this research show that wind/tidal turbine failures could be reduced while increasing the turbines’ efficiency and availability by determining the optimal number of parallel DC-DC converters connected to the turbine. Based on the newdeveloped technique of determining optimal number of parallel converters instead of a single rated converter, the annual average efficiency of a wind turbine would be increased from 57 to 75 % under the case study considered in this research. Also, the novel adaptive IACS controller reduced the circulating current among parallel-connected DC-DC converters faster than the conventional controller. In addition, the load voltage is accurately regulated to the nominal value with applying this novel controller, while a steady error is recorded for the load voltage with applying the conventional IACS controller. Modeling and stability analysis were conducted for the DC wind/tidal turbines, which has never been done in the literature, showed that the turbine-based surface-mounted permanent magnet synchronous generator is stable, but two conditions should be fulfilled for a turbine-based interior-mounted permanent magnet synchronous generator to ensure turbine stability. Lastly, based on the modelling and stability analysis held for the LVDC microgrid of the MUPs, the new idea of considering DC system for MUPs is a viable solution that ensures stable and more efficient operation
Integrated energy efficiency of shipping
Get PDFEnergy is a strength and one of the most indispensable resources for maritime transport activities. There is still a research need on the ship-port interface regarding energy efficiency. These complex logistic chains should comprise port performance to reduce shipping delays to create a better energy-efficient system. Therefore, this research is addressing the following question: How can we produce an integrated analysis for the energy efficiency of the port and ship?;The objective of this PhD thesis is to improve our understanding of port and ship operation with a focus on energy efficiency by implementing Bayesian Belief Networks (BBN) and ARENA Discrete Event Simulation (DES) based modelling. A modelling framework is developed to investigate how ports and ships could work together to reduce energy consumption and maximise efficient operation time. This PhD study investigates integrated energy-efficient shipping in a holistic way by focusing on ship-port interface and interoperability to increase energy efficiency. BBN focused on more comprehensive ship port integration, and DES analysed more micro-sized parts of this complex integrated port-ship system for a container port.;This study improved the energy efficiency of integrated shipping elements by increasing the interoperability between interdependent shipping system elements. The research is addressing dependability by deploying a BBN technique. ARENA application on a case study showed that considering the integrated system's energy efficiency instead of only port energy efficiency, the whole system's energy consumption and CO2 pollution have around 6% improvement in the port area. The case study also clearly demonstrates that ship operation is the main contributor and has a more significant effect on the integrated system. Results also prove that port operation and ship operation can be more energy-efficient and need more appropriate analyses. As a result, this thesis creates a solution to analyse the energy efficiency of the ship and port integration which is a gap in the literature.Energy is a strength and one of the most indispensable resources for maritime transport activities. There is still a research need on the ship-port interface regarding energy efficiency. These complex logistic chains should comprise port performance to reduce shipping delays to create a better energy-efficient system. Therefore, this research is addressing the following question: How can we produce an integrated analysis for the energy efficiency of the port and ship?;The objective of this PhD thesis is to improve our understanding of port and ship operation with a focus on energy efficiency by implementing Bayesian Belief Networks (BBN) and ARENA Discrete Event Simulation (DES) based modelling. A modelling framework is developed to investigate how ports and ships could work together to reduce energy consumption and maximise efficient operation time. This PhD study investigates integrated energy-efficient shipping in a holistic way by focusing on ship-port interface and interoperability to increase energy efficiency. BBN focused on more comprehensive ship port integration, and DES analysed more micro-sized parts of this complex integrated port-ship system for a container port.;This study improved the energy efficiency of integrated shipping elements by increasing the interoperability between interdependent shipping system elements. The research is addressing dependability by deploying a BBN technique. ARENA application on a case study showed that considering the integrated system's energy efficiency instead of only port energy efficiency, the whole system's energy consumption and CO2 pollution have around 6% improvement in the port area. The case study also clearly demonstrates that ship operation is the main contributor and has a more significant effect on the integrated system. Results also prove that port operation and ship operation can be more energy-efficient and need more appropriate analyses. As a result, this thesis creates a solution to analyse the energy efficiency of the ship and port integration which is a gap in the literature
Investigation of trim influence on resistance, seakeeping and propulsive performance
Get PDFThere has been a lot of interest in recent years in trim and ballast optimisation in which the ballast of a vessel is varied to reduce fuel consumption and greenhouse gas emissions. Trim optimisation is one of the easiest and cheapest methods among many fuel-saving measures recommended by IMO as it does not require any hull shape modification or engine upgrade. Many existing ships are designed for a single operational condition with the aim of producing low resistance at their design speed and draft with an even keel. Given that a ship will often sail outside this condition over its operational life, the effect of trim on ships resistance and powering will be significant. However, limited research has been performed to investigate trim influence on ship performance. In many cases, the work has concentrated on minimisation of resistance; often focussing on calm-water resistance in model scale. The impact of trim on added resistance and propulsive performance of ships is less well understood.In this context, the main aim of this PhD study is to gain an improved understanding of the impact of trim on the resistance, seakeeping and propulsive performance of vessels by using Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) methods. This study covers model tests in towing tank, model scale and full scale CFD analyses for various operating points in calm water and waves.This study consists of three main parts. In the first part, trim influence on the calm water resistance of the KRISO Container Ship (KCS) was investigated. A series of resistance tests for various trim angles and speeds were conducted at 1:75 scale at design draft. CFD computations were carried out for the same conditions and also for ballast draft with the hull both fixed and free to sink and trim. Trim influence on individual resistance components was discussed. Full-scale numerical simulations are also carried out and differences between model scale and full-scale findings are discussed to investigate scale effects on optimum trim.In the second part of this study, the effects of trim angles on added resistance and motion responses of KCS were evaluated experimentally and numerically in six different trim angles. Effects of trim angles on added resistance were analysed and results concerning the performance of the vessel at different trim angles were plotted. Experimental and numerical results for the heave and pitch motions and the added resistance were compared. Furthermore, the range of trim and wave conditions were identified for the application of the rapid linear potential flow method.The study is then extended to include a model of the propeller to investigate the trim influence on the propulsive performance of the KCS. Self-propulsion simulations were performed using two different methods, namely, sliding mesh with 3-D propeller geometry and body force method based actuator disk approach. Effects of trim angles on propulsive characteristics were analysed and results concerning the performance of the vessel at different trim angles were plotted. The differences in optimum trim based on pure resistance simulations and self-propulsion simulations were investigated. As trim optimisation studies require the analysis of large number of different operating conditions, the applicability and accuracy of a quicker simplified actuator disk approach was tested.This author believes that methods and findings presented in this study contribute towards better understanding of the trim influence on resistance and powering performance of ships. Additionally, these findings may be used to further develop accurate and efficient trim optimisation tools for minimizing fuel consumption and emissions accordingly.There has been a lot of interest in recent years in trim and ballast optimisation in which the ballast of a vessel is varied to reduce fuel consumption and greenhouse gas emissions. Trim optimisation is one of the easiest and cheapest methods among many fuel-saving measures recommended by IMO as it does not require any hull shape modification or engine upgrade. Many existing ships are designed for a single operational condition with the aim of producing low resistance at their design speed and draft with an even keel. Given that a ship will often sail outside this condition over its operational life, the effect of trim on ships resistance and powering will be significant. However, limited research has been performed to investigate trim influence on ship performance. In many cases, the work has concentrated on minimisation of resistance; often focussing on calm-water resistance in model scale. The impact of trim on added resistance and propulsive performance of ships is less well understood.In this context, the main aim of this PhD study is to gain an improved understanding of the impact of trim on the resistance, seakeeping and propulsive performance of vessels by using Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) methods. This study covers model tests in towing tank, model scale and full scale CFD analyses for various operating points in calm water and waves.This study consists of three main parts. In the first part, trim influence on the calm water resistance of the KRISO Container Ship (KCS) was investigated. A series of resistance tests for various trim angles and speeds were conducted at 1:75 scale at design draft. CFD computations were carried out for the same conditions and also for ballast draft with the hull both fixed and free to sink and trim. Trim influence on individual resistance components was discussed. Full-scale numerical simulations are also carried out and differences between model scale and full-scale findings are discussed to investigate scale effects on optimum trim.In the second part of this study, the effects of trim angles on added resistance and motion responses of KCS were evaluated experimentally and numerically in six different trim angles. Effects of trim angles on added resistance were analysed and results concerning the performance of the vessel at different trim angles were plotted. Experimental and numerical results for the heave and pitch motions and the added resistance were compared. Furthermore, the range of trim and wave conditions were identified for the application of the rapid linear potential flow method.The study is then extended to include a model of the propeller to investigate the trim influence on the propulsive performance of the KCS. Self-propulsion simulations were performed using two different methods, namely, sliding mesh with 3-D propeller geometry and body force method based actuator disk approach. Effects of trim angles on propulsive characteristics were analysed and results concerning the performance of the vessel at different trim angles were plotted. The differences in optimum trim based on pure resistance simulations and self-propulsion simulations were investigated. As trim optimisation studies require the analysis of large number of different operating conditions, the applicability and accuracy of a quicker simplified actuator disk approach was tested.This author believes that methods and findings presented in this study contribute towards better understanding of the trim influence on resistance and powering performance of ships. Additionally, these findings may be used to further develop accurate and efficient trim optimisation tools for minimizing fuel consumption and emissions accordingly
Investigation of laser-solid interaction physics with tightly focused, ultra-intense laser pulses
Get PDFPreviously held under moratorium from 12th April 2022 until 12th April 2023.This thesis reports on experimental investigations of laser-solid interactions forintensities at the frontier of what is possible using current laser technology. Peaklaser intensities of up to 5 × 1021 Wcm−2 were achieved through the focusing ofpicosecond laser pulses to near-wavelength sized focal spots with a novel, elliptical focusing plasma mirror. The influence of these high intensities and smallfocal spot sizes on proton acceleration in the relativistic transparency regime andon the temperature scaling and dynamics of fast electrons is explored. These twoaspects of laser-solid interactions are of critical importance to the realisation ofmany envisioned applications, in addition to providing insight into the fundamental underpinning physics. The work reported here is structured into two mainsections.The first study reports on an investigation of the influence of ultra-high intensity and near-wavelength sized focal spot, achieved through the use of F/1focusing plasma optics, on proton acceleration from ultra-thin foil targets, forwhich the highest proton energies to date are achieved. In this regime, acceleration occurs via a transparency-enhanced, TNSA-RPA hybrid mechanism. Whencomparing the spectral properties of protons accelerated using F/1 focusing toa F/3 focusing geometry, significant reductions in both maximum proton energyand laser-to-proton energy conversion efficiency were observed, despite the highernominal laser intensity. Furthermore, the measured holeboring velocity was alsofound to be reduced for F/1 focusing, when compared with the F/3 case. Thesefindings are explained in terms of transparency-induced self-focusing, which occurs very strongly in the F/3 case, but to a negligible extent for F/1 focusing,and is shown by 2D particle-in-cell simulations. This results in an enhancementin the peak intensity achieved by the F/3 following the onset of transparency,boosting the intensity beyond the nominal peak intensity of the F/1 focusinggeometry. This increased intensity subsequently results in enhanced proton energies, with both the peak intensity and proton energy maximised for an optimalfocal spot size (ϕL = 5 µm) and target thickness (ℓ = 100 nm). Limited enhancement occurs for F/1 focusing to close to the laser wavelength or when the targetremains opaque for the duration of the interaction, as self-focusing cannot takeplace. This result will help guide the design of future experiments, by showingthat optimal proton energies in the transparency regime are obtained for moreconventional focusing conditions, significantly reducing the technical challengesand financial expense involved.The second study presents findings related to the scaling of fast electron temperature within thin foil targets, and the effect of this on electron refluxing andproton acceleration via the TNSA mechanism. Using measurements of copper Kαphotons from 25 µm thick copper targets and protons accelerated via the TNSAmechanism from 6 µm thick aluminium targets, the fast electron temperaturescaling with intensity was determined. This was found to scale more slowly withincreasing intensity than would be expected from existing models, resulting inreduced electron temperatures. Analytical modelling shows that this slower scaling is likely due to the inhibition of electron heating as a result of the relativisticskin-depth, which becomes on the order of ∼ 10 nm for intensities > 1021 Wcm−2.The decreasing skin-depth alone is however not suffice to fully explain the slowingof the temperature scaling. Modifications to the plasma density within the skindepth, based on relativistic effects or radiation pressure induced compression arediscussed, supported by analytical modelling and 2D particle-in-cell simulations,are shown to produce better agreement with the results measured experimentally.The electron temperatures measured are also shown to result in significantly increased electron refluxing within the target, whilst the effect of the slower scalingwith intensity is shown to adversely affect the scaling of maximum proton energiesgenerated via the TNSA mechanism. This result highlights that, when movingto higher intensities, the gains in electron temperature may not be as significantas previously predicted, which has a significant impact on the generation of highenergy particles and ionising radiation.This thesis reports on experimental investigations of laser-solid interactions forintensities at the frontier of what is possible using current laser technology. Peaklaser intensities of up to 5 × 1021 Wcm−2 were achieved through the focusing ofpicosecond laser pulses to near-wavelength sized focal spots with a novel, elliptical focusing plasma mirror. The influence of these high intensities and smallfocal spot sizes on proton acceleration in the relativistic transparency regime andon the temperature scaling and dynamics of fast electrons is explored. These twoaspects of laser-solid interactions are of critical importance to the realisation ofmany envisioned applications, in addition to providing insight into the fundamental underpinning physics. The work reported here is structured into two mainsections.The first study reports on an investigation of the influence of ultra-high intensity and near-wavelength sized focal spot, achieved through the use of F/1focusing plasma optics, on proton acceleration from ultra-thin foil targets, forwhich the highest proton energies to date are achieved. In this regime, acceleration occurs via a transparency-enhanced, TNSA-RPA hybrid mechanism. Whencomparing the spectral properties of protons accelerated using F/1 focusing toa F/3 focusing geometry, significant reductions in both maximum proton energyand laser-to-proton energy conversion efficiency were observed, despite the highernominal laser intensity. Furthermore, the measured holeboring velocity was alsofound to be reduced for F/1 focusing, when compared with the F/3 case. Thesefindings are explained in terms of transparency-induced self-focusing, which occurs very strongly in the F/3 case, but to a negligible extent for F/1 focusing,and is shown by 2D particle-in-cell simulations. This results in an enhancementin the peak intensity achieved by the F/3 following the onset of transparency,boosting the intensity beyond the nominal peak intensity of the F/1 focusinggeometry. This increased intensity subsequently results in enhanced proton energies, with both the peak intensity and proton energy maximised for an optimalfocal spot size (ϕL = 5 µm) and target thickness (ℓ = 100 nm). Limited enhancement occurs for F/1 focusing to close to the laser wavelength or when the targetremains opaque for the duration of the interaction, as self-focusing cannot takeplace. This result will help guide the design of future experiments, by showingthat optimal proton energies in the transparency regime are obtained for moreconventional focusing conditions, significantly reducing the technical challengesand financial expense involved.The second study presents findings related to the scaling of fast electron temperature within thin foil targets, and the effect of this on electron refluxing andproton acceleration via the TNSA mechanism. Using measurements of copper Kαphotons from 25 µm thick copper targets and protons accelerated via the TNSAmechanism from 6 µm thick aluminium targets, the fast electron temperaturescaling with intensity was determined. This was found to scale more slowly withincreasing intensity than would be expected from existing models, resulting inreduced electron temperatures. Analytical modelling shows that this slower scaling is likely due to the inhibition of electron heating as a result of the relativisticskin-depth, which becomes on the order of ∼ 10 nm for intensities > 1021 Wcm−2.The decreasing skin-depth alone is however not suffice to fully explain the slowingof the temperature scaling. Modifications to the plasma density within the skindepth, based on relativistic effects or radiation pressure induced compression arediscussed, supported by analytical modelling and 2D particle-in-cell simulations,are shown to produce better agreement with the results measured experimentally.The electron temperatures measured are also shown to result in significantly increased electron refluxing within the target, whilst the effect of the slower scalingwith intensity is shown to adversely affect the scaling of maximum proton energiesgenerated via the TNSA mechanism. This result highlights that, when movingto higher intensities, the gains in electron temperature may not be as significantas previously predicted, which has a significant impact on the generation of highenergy particles and ionising radiation
Engineered silk hydrogels for the delivery of mesenchymal stem cells to the stroked brain
No full textGiants of the Clyde, memory and post-industrial archaeology on Clydeside
Get PDFThis thesis seeks to explore the material culture of one remaining and one removed giant crane along the River Clyde. It approaches the cranes as individual sites of both remembering and forgetting. The many giant cantilever cranes that have stood along the River Clyde in Glasgow can be seen as totems of both the excellence of Clyde engineering and the dynamism of industrial Scotland. For the people and communities living and working around the river, the cranes symbolise the pride of being part of industrial Scotland, often being beacons of cultural identity locally and helping to define and reinforce community identity. Around 50 giant cranes were built, with ten left, four of which are in Scotland. This project considers Scotland’s remaining and removed giant cranes through the memories and interactions of the people and communities that have existed around them. This thesis does not intend to make a case for their preservation, though aims to highlight the various ways in which these fragments of industrial archaeology have been perceived, reused and re-animated in a way that that can seek to inform the conservation processes of these structures, and of post-industrial archaeological sites in general. This thesis takes an interdisciplinary approach, combining history and archaeology to explore the connections people have with industrial fragments. The thesis combines new oral history testimony, documentary source analysis and material culture studies to account for the post-industrial phases of these cranes. This thesis asserts that the cranes have, over time, transitioned from working objects to cultural artefacts, and that in studying them, a better understanding of the relationship that people have with deindustrialisation and post-industrialism on Clydeside can be found. The original contribution to knowledge comes via considering, for the first time, the post-industrial archaeology on Clydeside, and the wider materiality of industrial change, in a global context, adding to the emergent field of deindustrialisation studies.This thesis seeks to explore the material culture of one remaining and one removed giant crane along the River Clyde. It approaches the cranes as individual sites of both remembering and forgetting. The many giant cantilever cranes that have stood along the River Clyde in Glasgow can be seen as totems of both the excellence of Clyde engineering and the dynamism of industrial Scotland. For the people and communities living and working around the river, the cranes symbolise the pride of being part of industrial Scotland, often being beacons of cultural identity locally and helping to define and reinforce community identity. Around 50 giant cranes were built, with ten left, four of which are in Scotland. This project considers Scotland’s remaining and removed giant cranes through the memories and interactions of the people and communities that have existed around them. This thesis does not intend to make a case for their preservation, though aims to highlight the various ways in which these fragments of industrial archaeology have been perceived, reused and re-animated in a way that that can seek to inform the conservation processes of these structures, and of post-industrial archaeological sites in general. This thesis takes an interdisciplinary approach, combining history and archaeology to explore the connections people have with industrial fragments. The thesis combines new oral history testimony, documentary source analysis and material culture studies to account for the post-industrial phases of these cranes. This thesis asserts that the cranes have, over time, transitioned from working objects to cultural artefacts, and that in studying them, a better understanding of the relationship that people have with deindustrialisation and post-industrialism on Clydeside can be found. The original contribution to knowledge comes via considering, for the first time, the post-industrial archaeology on Clydeside, and the wider materiality of industrial change, in a global context, adding to the emergent field of deindustrialisation studies
Text mining and natural language processing for the early stages of space mission design
Get PDFA considerable amount of data related to space mission design has been accumulatedsince artificial satellites started to venture into space in the 1950s. This data has todaybecome an overwhelming volume of information, triggering a significant knowledgereuse bottleneck at the early stages of space mission design. Meanwhile, virtual assistants,text mining and Natural Language Processing techniques have become pervasiveto our daily life.The work presented in this thesis is one of the first attempts to bridge the gapbetween the worlds of space systems engineering and text mining. Several novel modelsare thus developed and implemented here, targeting the structuring of accumulateddata through an ontology, but also tasks commonly performed by systems engineerssuch as requirement management and heritage analysis. A first collection of documentsrelated to space systems is gathered for the training of these methods. Eventually, thiswork aims to pave the way towards the development of a Design Engineering Assistant(DEA) for the early stages of space mission design. It is also hoped that this work willactively contribute to the integration of text mining and Natural Language Processingmethods in the field of space mission design, enhancing current design processes.A considerable amount of data related to space mission design has been accumulatedsince artificial satellites started to venture into space in the 1950s. This data has todaybecome an overwhelming volume of information, triggering a significant knowledgereuse bottleneck at the early stages of space mission design. Meanwhile, virtual assistants,text mining and Natural Language Processing techniques have become pervasiveto our daily life.The work presented in this thesis is one of the first attempts to bridge the gapbetween the worlds of space systems engineering and text mining. Several novel modelsare thus developed and implemented here, targeting the structuring of accumulateddata through an ontology, but also tasks commonly performed by systems engineerssuch as requirement management and heritage analysis. A first collection of documentsrelated to space systems is gathered for the training of these methods. Eventually, thiswork aims to pave the way towards the development of a Design Engineering Assistant(DEA) for the early stages of space mission design. It is also hoped that this work willactively contribute to the integration of text mining and Natural Language Processingmethods in the field of space mission design, enhancing current design processes
Nonlinear hydrodynamic interaction analysis of multi-platform system
Get PDFAlong with the technological development of ocean engineering, offshore platforms are gradually becoming larger and more complex. The recent development in the deep water region often involves multiple floating platforms adjacent to each other to perform more complex functions. Several aspects should be concerned due to the larger and more complex offshore structures in the offshore area, like water surface elevation and wave run-up around structures, motion characteristics of platforms in the multi-platform system and wave loads on platforms in multi-platform system. 3D potential flow method is applied in the present study. The perturbation theory is employed to divide the velocity potential into first-order and second order potential. The boundary value problem at each order is solved by boundary element method. This research describes the investigation carried out on the surface elevation around single column and multiple columns structures since the peak surface elevation often impacts the offshore structures with nonlinear wave loads and potentially causes slamming to platforms. The near-trapping frequency mode for circular columns is extended and applied for the rounded corner square columns and validated. The characteristics of different mechanism (superposition and near-trapping) for peak surface elevation are identified in the present thesis. The peak value of the second-order surface component caused by superposition decreases with higher corner ratio of column. However, for the peak surface elevation caused by near-trapping, the second order surface component decreases with lower corner ratio of column. Additionally, the peak surface elevation caused by near-trapping is located at the area enclosed by columns. These characteristics are applied to distinguish the mechanism of peak surface elevation.This thesis also contains the study on dynamic responses of a two platforms system containing a Tension Leg Platform (TLP) and a tender assisted drilling (TAD) with a flexible connection between the two platforms. The mooring lines and tendons are taken into consideration in the coupled analysis of the multi-body platform's system. The numerical model is validated by the published experimental result. Both frequency domain analysis and time domain coupled analysis are conducted. The motion responses and wave load characteristics on the two platforms in the multi-platform coupled model are investigated in the numerical simulation. Itis found that the nonlinear wave force on TLP (Sum-frequency wave force) and TAD (Drift force) are changed significantly due to the existence of adjacent platform. The impact of hydrodynamic interaction on each platform is primarily determined by the incident wavedirection and the arrangement direction of the platforms. The multi-platform system is not only applied in the oil and gas area but also in the renewable energy area. Research of interaction between an offshore wind turbine and support vessel is contained in the present study. The relative distance and the force along the connecting lines between the wind turbine and support vessel are investigated under different wind-wave misalignment conditions during the operation period. The maximum relative distance and tension in the connecting lines are significantly influenced by the wind-wave misalignment under the low environmental condition (LC) and medium condition (MC). However, there is little impact of misalignment under high condition (HC). For floating wind turbine, the impact of wind-wave misalignment for the floating wind turbine is rather small when the environmental condition is medium and high condition. There is also an interesting discovery that increasing wind speed and wind-wave misalignment evidently leads to a jump of maximum relative distance and maximum tension in the connecting lines.Along with the technological development of ocean engineering, offshore platforms are gradually becoming larger and more complex. The recent development in the deep water region often involves multiple floating platforms adjacent to each other to perform more complex functions. Several aspects should be concerned due to the larger and more complex offshore structures in the offshore area, like water surface elevation and wave run-up around structures, motion characteristics of platforms in the multi-platform system and wave loads on platforms in multi-platform system. 3D potential flow method is applied in the present study. The perturbation theory is employed to divide the velocity potential into first-order and second order potential. The boundary value problem at each order is solved by boundary element method. This research describes the investigation carried out on the surface elevation around single column and multiple columns structures since the peak surface elevation often impacts the offshore structures with nonlinear wave loads and potentially causes slamming to platforms. The near-trapping frequency mode for circular columns is extended and applied for the rounded corner square columns and validated. The characteristics of different mechanism (superposition and near-trapping) for peak surface elevation are identified in the present thesis. The peak value of the second-order surface component caused by superposition decreases with higher corner ratio of column. However, for the peak surface elevation caused by near-trapping, the second order surface component decreases with lower corner ratio of column. Additionally, the peak surface elevation caused by near-trapping is located at the area enclosed by columns. These characteristics are applied to distinguish the mechanism of peak surface elevation.This thesis also contains the study on dynamic responses of a two platforms system containing a Tension Leg Platform (TLP) and a tender assisted drilling (TAD) with a flexible connection between the two platforms. The mooring lines and tendons are taken into consideration in the coupled analysis of the multi-body platform's system. The numerical model is validated by the published experimental result. Both frequency domain analysis and time domain coupled analysis are conducted. The motion responses and wave load characteristics on the two platforms in the multi-platform coupled model are investigated in the numerical simulation. Itis found that the nonlinear wave force on TLP (Sum-frequency wave force) and TAD (Drift force) are changed significantly due to the existence of adjacent platform. The impact of hydrodynamic interaction on each platform is primarily determined by the incident wavedirection and the arrangement direction of the platforms. The multi-platform system is not only applied in the oil and gas area but also in the renewable energy area. Research of interaction between an offshore wind turbine and support vessel is contained in the present study. The relative distance and the force along the connecting lines between the wind turbine and support vessel are investigated under different wind-wave misalignment conditions during the operation period. The maximum relative distance and tension in the connecting lines are significantly influenced by the wind-wave misalignment under the low environmental condition (LC) and medium condition (MC). However, there is little impact of misalignment under high condition (HC). For floating wind turbine, the impact of wind-wave misalignment for the floating wind turbine is rather small when the environmental condition is medium and high condition. There is also an interesting discovery that increasing wind speed and wind-wave misalignment evidently leads to a jump of maximum relative distance and maximum tension in the connecting lines
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