CoA. PhD, EngD, MPhil & MSc by research theses
Permanent URI for this collection
Browse
Browsing CoA. PhD, EngD, MPhil & MSc by research theses by Publisher "Cranfield University"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Open Access Development of a Port-Hamiltonian Model for use in oscillating water column control scheme investigations.(Cranfield University, 2014-12) Farman, Judith; Amaral Teixeira, JoaoWith global energy demand estimated to rise considerably and global warming accepted by the majority of scientists, the pressure to reduce fossil fuel usage is increasing. To this end, the UK government has set a target of generating 50% of electricity from renewable energy sources by 2050. It can therefore be deduced that decreasing the cost of renewable energy by increasing the energy capture is critical. Oscillating Water Columns (OWCs) employing bidirectional turbines coupled with generators can be used to capture energy from oceanic waves and convert it to electrical energy. This thesis includes a study to quantify the potential power smoothing that can be achieved from a wave farm of ideal OWC devices and from auxiliary hardware such as flywheel energy storage systems. Also detailed are the upgrades to the OWC test facility at Cranfield University, including the world-first capability to simulate polychromatic waves. This test facility has been employed to validate turbine characteristics derived from Computational Fluid Dynamic (CFD) numerical results. This thesis contains a literature review of the existing control strategies for OWCs that concludes that the optimization of power capture from individual components in the energy chain forces system-level compromises. This conclusion drove the development of an unique energy-based model of the complete wave-to-wire system utilizing port-Hamiltonian mechanics which mandated two modifications to the port-Hamiltonian framework. The first modification to the port-Hamiltonian framework resulted in a new generalized means of modeling systems where the potential energy is dependent on the momentum variables. The second modification expands the port-Hamiltonian framework to allow the modeling of ow source systems in addition to effort source systems. The port-Hamiltonian wave-to-wire OWC model enables the future development of a control approach that optimizes power capture at a system level. As a first step to achieving this goal an Injection Damping Assignment (IDA) Passivity Based Control (PBC) strategy was successfully applied to an OWC system and an energy storage flywheel system. These strategies pave the way for future developments utilizing optimization techniques, such as the use of cost functions to identify the peak efficiency operating condition.Item Open Access Error control in finite elements for fluid modelling.(Cranfield University, 1997-10) Onomor, E.M.; Morris, Alan J.The main objective of this thesis was to ascertain and to catalogue the possible sources of errors in the finite element method when used for fluid modelling. Some of these errors are inherent in the finite element method whilst others are introduced by the user when performing a fluid mechanical analysis. This thesis distinguishes from the two and provides where possible, ways of preventing or controlling them. The form is based on the SAFESA Technical manual, which is an equivalent for structural analyses. Focus is then made, as an example, on a real world problem; "The Backward Facing Step" where, based on experimental data an element sensitivity analysis is performed within ANSYS/FLOTRAN. This analysis attempts to determine the magnitude of errors associated with prescribed element distortions in relation to aspect ratio, skew angle and taper ratio. The results contained within are in the form of graphical velocity profile plots, contour plots and tables at the varying distortions. The results show a strong deviation from the control mesh as the distortion is increased.Item Open Access Experimental investigation of lubricant film thickness in an automotive final drive unit.(Cranfield University, 2013-11) Fusco, Lucia; Sherwood, GlennSociety has been aware of the environmental impact of vehicles for some time now, with governments trying to control and reduce this impact by introducing emissions standards to control pollutants as well as CO₂ emissions. One way in which total emissions can be reduced is by increasing the efficiency of vehicles as a whole, resulting in greater fuel economy. Related to increased transmission efficiency, lubricant flow within a final drive unit (FDU) was researched, enabling a better understanding of the system through visualisation and laser induced fluorescence (LIF) measurements. A LIF measurement technique has been developed, along with a quantitative wedge calibration method, to measure lubricant thicknesses within a Jaguar Land Rover X150 FDU. The measurements and data recorded in this thesis are taken from an original clear-cased replica FDU, which proved to be suitable for visualisation and LIF measurements. The results show lubricant thickness trends are dependent on the fill volume and rotational speed of the gear. The measured peak lubricant thickness on the carrier- and cover-side of the crown wheel increased with fill volume. As the fill volume increased, the amount of lubricant entrained by the crown wheel increased, resulting in the increased lubricant thickness. As the equivalent vehicle road speed increased to approximately 8mph, the measured lubricant thickness increased to its maximum value of 1.75mm for a fill volume of 900ml. From 8mph onwards, the lubricant thickness was found to decrease again to less than 0.1mm at around 10mph. Up to 8mph, gravity appeared to be the overriding influence, pulling the lubricant from the crown wheel. At 8mph, these forces seemed to be in balance, resulting in the greatest measured lubricant thickness. Above 8mph, the force from the gear rotation ejected lubricant from the crown wheel. Gathered data and relationships provide new quantitative metrics for measurement and enhanced understanding of lubricant movement within the FDU. The methodology and equipment developed here for studying the FDU are suitable for wider use in any geared or lubricated system.Item Open Access An investigation into heat dissipation from a stationary commercial vehicle disc brake in parked conditions.(Cranfield University, 2013-11) Stevens, Kevin; Tirovic, Marko; Skipworth, HeatherDetailed understanding of heat dissipation from a stationary disc brake is of considerable importance for vehicle safety. This is essential for both park braking on inclines and for preventing brake fluid boiling in hydraulic brakes. Despite the experience proving the significance of such conditions, there is very little published data dealing with this phenomenon, and even ECE Regulation 13 does not specify hot parking braking performance. The problem of heat dissipation from stationary brake may appear simplistic but it is actually more complex than from a rotating disc, due to the lack of symmetry through or a dominant mode of heat transfer as natural convection is the only driving force behind the airflow. All three heat transfer modes exist in a transient process, with complex heat transfer paths within and between brake components. This Thesis investigates the cooling performance of a Commercial Vehicle (CV) brake whilst in stationary conditions. The research is predominantly orientated towards the thermal aspects of Electric Parking Brake (EPB) application in CVs. Contraction of large brake components after hot parking may lead to vehicle rollaway on inclines, with tragic consequences. An extensive theoretical and experimental study was conducted. An analytical model of a disc brake in free air was developed, enabling good prediction of disc temperatures and average surface convective heat transfer coefficients (hcₒnv) over the entire cooling range. A comprehensive CFD modelling of the 3-dimensional flowfield around the disc brake was also conducted, as well as predicting the surface convection coefficient distribution. Shear Stress Turbulence model was found to be most suitable for such studies. FE models were created to predict temperatures in all components of the brake assembly. A special Thermal Rig was developed for experimental validations, which uses an induction heater for heating the disc brake, and numerous surface mounted and embedded thermocouples for measuring component temperatures, as well as ‘free standing’ for determining air temperatures in specific points. IR cameras provided further temperature field information. The results clearly show little influence of the conductive heat dissipation mode. The study also showed, for the experimental arrangement used, a constant value of surface emissivity (ɛ = 0.92). With well-defined conductive and radiative heat dissipation modes, the emphasis was placed on investigating convective heat dissipation from a stationary disc brake. It has been demonstrated that the anti-coning straight vane design of brake disc does not cool effectively in stationary conditions. Expected ‘chimney effects’ in disc vent channels do not materialise due to large scale recirculation regions preventing airflow from entering the channels, which drastically reduces the convective cooling. Complex thermal interactions between the large assembly components are explained, with typical cooling time being just over an hour for disc brake cooling from 400°C to 100°C. Extracted heat transfer coefficients were used for establishing a complex FE assembly model, which enables accurate prediction of temperatures of individual components over the entire cooling period. The developed approach is used for predicting temperature of the existing brake assembly but is equally suited for generating new designs with more favourable characteristics. In addition to being a powerful design tool for assisting in EPB design and validation process, the methodology developed offers wide applications, such as thermal optimisation of the caliper housing for the installation of continuous wear monitoring sensors, smart slack adjusters (for low friction drag brakes), etc. EPBs in passenger cars have been successfully used for over 10 years now. They use a relatively simple approach for ensuring safe parking from hot by over-clamping (applying approximately twice the required actuating force) and re-clamping (repeated application after the vehicle has been parked). Large CV actuating forces prevent the use of over-clamping as this could damage the disc, whilst re-clamping would need to be repeated several times over a much longer period of time, requiring the vehicle battery to power the electronic systems for a longer period of time without recharging. Neither approach is acceptable, requiring a more in- depth thermal study of the CV brake in stationary conditions, as investigated in this Thesis. In addition to technical, there are marketing and financial aspects which make EPB introduction and acceptance in commercial vehicles very different to passenger car applications. Such an investigation was conducted, exploring the market the CV EPB will be sold in and whether it would accept the new technology. Two questionnaire analyses were carried out, with the second giving the respondent detailed information about the EPB. It was found that using an informed, knowledge based approach yielded more positive feedback to the proposed product. The outcome may be even considered more contrary than expected, rather than instigating mistrust, the new CV EPB technology created interest. Furthermore, reports of pneumatic malfunction indicated that independence from the pneumatic system should be used as the key selling point for the EPB, for all beneficiary segments.Item Open Access Optimal time and handling methods for motorsport differentials.(Cranfield University, 2014-12) Tremlett, Anthony; Assadian, Francis; Vaughan, Nicholas D.In the motorsport environment, where traction at one wheel is often compromised due to high cornering accelerations, Limited Slip Differentials (LSD) offer significant improvements in traction and vehicle stability. LSDs achieve these performance benefits through the transfer of torque from the faster to slower rotating driving wheel. In the majority of racing formulae, modern devices have evolved to become highly adjustable, allowing this torque bias to alter both ultimate vehicle performance and handling balance through specific corner entry, apex and corner exit phases. This work investigates methods to optimise LSD setup parameters, both for minimum lap time and desirable handling characteristics. The first stage of addressing this objective involved the creation of a range of contemporary motorsport LSD models. These included a plate or Salisbury type, a Viscous Coupling (VC) and a Viscous Combined Plate (VCP). A differential test rig was developed to validate these models. The parameter optimisation is addressed in two main parts. Firstly, a Quasi Steady State (QSS) time optimal method is used to maximise the vehicle's GG acceleration envelope using a direct, nonlinear program (NLP). A limitation of this approach however, is that system transients are neglected. This is addressed through the development of an alternative indirect, nonlinear optimal control (NOC) method. Both methods were able to find LSD setup parameters which minimised lap time, providing significant improvements over traditional open and locked devices. The NOC method however, was able to give greater insight into how a locked device ultimately limits the vehicle yaw response during quick direction changes. The time optimal analysis was extended to investigate aspects of vehicle stability and agility. These factors are known to have a major influence on driveability and thus, how much of the theoretical performance limit the driver can extract. A more unified GG diagram framework was implemented, to characterise both the vehicle's acceleration limits, and how its stability and agility changes leading up to this limit. The work has generated a number of novel contributions in this research field. Firstly, the creation and validation of a range of state-of-the-art motorsport LSD models. Secondly, the methodologies used to optimise LSD setup parameters, the results from which, have themselves provided the basis of a novel, vehicle speed dependent LSD device. Finally, a more practical and intuitive way to evaluate vehicle stability and agility at different cornering phases. This has laid the foundations of a procedure which not only maximises the vehicle's acceleration limits, but also allows its response to be tailored to suit individual driver preferences.Item Open Access A physics-based maintenance cost methodology for commercial aircraft engines(Cranfield University, 2014-08) Stitt, Alice C.; Laskaridis, Panagiotis; Singh, RitiA need has been established in industry and academic publications to link an engine’s maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the “virtual-workshop” workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic / steady state).