Thermoacoustic systems can either generate acoustic work (i.e., p-v work) from thermal energy, or consume acoustic work to transfer heat from low to high temperature sources. They are the so-called thermoacoustic prime movers or heat pumps, essentially acting as the acoustical equivalents of Stirling engines or coolers. If a travelling sound wave propagates through a regenerator with a positive temperature gradient along the direction of sound wave propagation, the gas parcels experience a Stirling-like thermodynamic cycle. As such, thermal energy can be converted to acoustic power. Similar to Stirling engines and thermo-fluidic oscillators, thermoacoustic engines can be externally heated with various heat sources and are capable of utilising low-grade thermal energy such as industrial waste heat and solar thermal energy. Both the simplicity, and even the absence of moving parts of thermoacoustic engines demonstrate that they have the potential for developing low-cost power generators therefore, they have attracted significant research effort for developing coolers or electric generators. The target design principle of a thermoacoustic engine is to maximise acoustic power production within the thermoacoustic core whilst minimising the acoustic losses in the resonator. One of the main issues with current thermoacoustic systems is low efficiency, which is largely attributed to acoustic losses in the resonator and the regenerator. There would be a significant impact on the thermoacoustic field if a suitable travelling wave resonator were developed with the least losses. Despite the different engine configurations for developing these engines, they all work on the same thermodynamic principle, i.e., the Stirling cycle. In this study, the first issue is resolved by employing a by-pass configuration, and the second is addressed by using a side-branched volume technique. The current study focuses on the investigation of looped-tube travelling-wave thermoacoustic engines with a by-pass pipe. The novelty of such a by-pass configuration is that the by-pass and feedback pipes actually create a pure travelling wave resonator. The engine unit extracts a small amount of acoustic work from the resonator, amplifies it and sends it back to it. As the pure travelling wave resonator has very low losses, it requires very little acoustic power to sustain an acoustic resonance. This idea is analogous to children playing on swings, where a small push could sustain the swinging for a long time. The present research demonstrates that travelling wave thermoacoustic engines with such a by-pass configuration can achieve comparable performances with other types of travelling wave thermoacoustic engines which have been intensively researched. According to the results, this type of engine essentially operates on the same thermodynamic principle as other travelling wave thermoacoustic engines, differing only in the design of the acoustic resonator. The looped-tube travelling-wave thermoacoustic engine with a by-pass pipe was then implemented in the design of an engine with a much longer regenerator and higher mean pressure to increase its power density. A thermoacoustic cooler was also coupled to the engine to utilise its acoustic power, allowing evaluation of thermal efficiency. A linear alternator has also been coupled to the tested engine to develop an electric generator. This research additionally addresses the effect of a side-branched Helmholtz resonator to tune the phase in looped- tube travelling wave thermoacoustic engine. This action is performed in order to obtain the correct time-phasing between the acoustic velocity and pressure oscillations within the regenerator, to force gas parcels to execute a Stirling-like thermodynamic cycle, so that thermal energy can be converted to mechanical work (i.e., high-intensity pressure waves). By changing its volume one can change the acoustic impedance at the opening of the Helmholtz resonator, and thus adjust the acoustic field within the loop-tubed engine. It can essentially shunt away part of the volumetric velocity at the low impedance region of the engine, so that the acoustic loss can be reduced within the engine. Both the simulations and the experimental results have demonstrated that the proposed side-branched volume can effectively adjust the acoustic field within the looped-tube engine and affect its performance. There is an optimal acoustic compliance corresponding to the best performance in terms of acoustic power output and energy efficiency when the heating power input is fixed.

As the need for smaller, more compact and integrated products has evolved, it is no surprise that manufacturing technologies have significantly evolved in order to make miniaturisation to smaller scales possible. More specifically non-conventional machining technologies, relative newcomers in the field of machining, have proven well suited to the task at hand. Among those technologies is micro-EDM (short for Electrical Discharge Machining) that has been the subject of numerous developments. A certain number of variants of micro-EDM exists among which are wire micro-EDM, die-sinking micro-EDM, micro-EDM milling and micro-EDM drilling. While die-sinking macro-EDM is quite common, its micro counterpart isn’t due to problematic tool wear. In order to optimise the die-sinking micro-EDM process in terms of time and cost and make its use more interesting and viable, the present work aims at optimizing the initial tool shape so that it compensates for future wear. The first step was to design a simulation tool effectively able to predict the location and magnitude of wear during the simulation process. An iterative geometrical method was developed, first using NURBS as support geometries then voxels embedded in an octree data structure in order to improve speed and accuracy.

China currently occupies the world’s leading Electric bicycle (e-bike) market. However, the popularity of e-bikes is accompanied by massive numbers of injuries and deaths due to accidents involving e-bikes. As a result, the safety of e-bikes has recently received much attention from the public and the government and researchers have concentrated on improving the safety features of e-bikes with innovative technologies. It has been shown that well-designed protective shells can protect a driver involved in an e-bike accident. However, there is a lack of criteria on which to base the design of an effective protective shell for e-bikes. Therefore, this research focuses on the development of a design criterion based on the specific case of Roly-Poly stability. This stability criterion can be formulated for one curved surface as r > h, which is in a stable stability configuration - one of a number of static stability configurations. In this study, static stabilities are configured based on knowledge of potential energy (PE). In order to verify the design criteria, three types of protective shells are designed with different stability conditions. The first type follows the design criterion (r > h), while the remaining two do not (r = h and r < h). A finite element model of an e-bike is constructed with key components, such as the main frame, CoM (the position of which is obtained by a plumb line experiment), and the designed protective shells. The meshed models are produced and employed to determine the contact parameters using the frictionless penalty method. The corresponding results of sideways falling simulation successfully demonstrate the validity of the design criterion.

Compared to conventional rigid robotic manipulators and unlike traditional industrial robotic manipulators, flexible manipulator can be more efficient and safer to operate due to their low power consumption and lightness. Moreover, the next generation of robots will require compliance to be able to perform safe and close interactions with human beings. However, due to the flexibility in arms and joints, flexible manipulator control and operation suffers from severe structural vibration, leading to the inaccuracy in end-effector trajectory tracking and visual servoing. This research work aims to address the problem by developing a systematic motion estimation methodology for flexible robotic manipulators by using vibration and visual sensing. The aim was achieved by addressing several research objectives that include the investigation of the dynamics characteristics of a flexible robotic manipulator for the end-effector’s motion estimation, the study of decentralized vibration control of a multi-link flexible manipulator with piezoelectric sensor, the development of motion estimation framework experimentally through a single-link flexible manipulator test-rig and also the development the computer vision based motion estimation method for a flexible robotic manipulator with an eye-in-hand configuration. The dynamic characteristics of the flexible manipulator were investigated for development of the end-effector’s motion estimation. This was obtained by incorporating the modelling of flexible manipulator with embedded smart piezoelectric transducer based on co-rotational finite element method. This modelling method allows the simulation of non-linear dynamic motion of a flexible multi-link manipulator undergoing not only large rotations and translations of the manipulator, but also potentially large non-linear structural deformations of flexible links. Numerical simulations were performed on single-link and two-links flexible manipulator embedded with smart piezoelectric transducers. The results have demonstrated that this model could be effectively used to study the motion of end-effector for a multi-link flexible robotic manipulator undergoing complex large motions, while allowing the use of embedded piezoelectric transducers for measuring its structural vibration. In order to suppress the structural vibration of flexible manipulator, a decentralized control scheme based on the voltage rate feedback using pairs of collocated piezoelectric actuator/sensor has been utilized. The numerical case studies of single-link and two-links manipulator have been performed respectively. A special consideration is given for finding the best location for piezoelectric transducers over the multi-link flexible system. Generally speaking, motor encoder measures rigid body motion of the manipulator while vibration signals measure the flexible body motion of flexible manipulator. Thus a Kalman filter is developed as to estimate the motion of end-effector of flexible manipulator with the signals of piezoelectric sensor and motor encoder. The effectiveness of the proposed estimation method is evaluated and demonstrated by the developed co-rotational finite element model. The benefit of this method is that although the motion of flexible manipulator can be highly non-linear due to large rotations, the use of a linear Kalman filter, combined with the encoder information, may be sufficient for the estimation purpose for determining the motion of end-effector. On the other hand, robotics vision sensing has been intensively studied from various aspects in the last decade due to the increasing computational power available for processing images. This work proposes a visual-based motion estimation method for flexible robotic manipulator with an eye-in-hand configuration. The object tracking is proposed based on the autocorrelation method that measures the similarity of features between consecutive frames thus the estimation of corresponding apparent motion. The apparent motion is then combined with the geometry of the calibrated camera allowing deriving the angular position of the flexible arm at high frequency with high accuracy. This kind of method requires minimum computation and suitable for fast vision computation applications. Experimental results performed on the single-link flexible manipulator test rig demonstrated the feasibility of its application in flexible manipulator with eye-in-hand system. The developed vision sensing method obtains more precise information of the end-effector location and it is easy to extend to multiple flexible-link problems. The benefit of using this vision sensing method is that it can provide a direct measurement method without the need of any complex transformation procedures and also can be easily extended to multiple-link flexible manipulator cases without additional measurement devices or sensors.

Numerous concepts, national and commercial design standards developed and proved for metallic gears, now are being migrated over to polymer gears. However, it is uncertain whether the same procedures should apply and there is only limited data available to attempt a validation. Since wide mechanical and thermal properties’ discrepancies exist between metals and polymers, it is essential to develop and establish their individual investigation methods and science of design. The work presented in this thesis endeavours to bridge this gap between practical application and theory, through exploring advances in fundamental experimental investigation approaches and providing effective test data. New studies on wear and failure mechanisms, in addition to adopting the prevailing methods (i.e. SEM examining worn tooth surfaces), and inspecting wear debris are proposed and employed. Schemes are proposed for measuring the temperatures and velocities in the airflow surrounding the operating gears and gear bulk temperatures. Their use adds to the work for predicting surface temperatures of polymer gears. Deliberate misalignment is introduced to investigate. Wear and failure mechanisms of polyacetal gears at various loads and a speed of 1000 rpm are studied. Various regimes of wear debris and topographies of worn tooth surfaces are presented. The dynamic evolutions of wear, wear rate and the temperatures of airflow and the tooth body (bulk) are presented. It is found that transition temperatures are more reliable for assessing the gear wear compared to transition torques. Gross misalignment effects on the performance of polyacetal gears are investigated. Strikingly distinct topographies of worn tooth surfaces and regimes of wear debris are presented. It is indicated that polyacetal gears are most sensitive to pitch misalignment. Micro-cracks are noted near pitch points and tooth roots. Aerodynamic characteristics of operating gears are studied and an improved model is proposed. On the basis of it, methods for improving the durability of polyacetal gears are proposed. Further investigations on aerodynamics, thermal-mechanism and misalignment are recommended to gain a better temperature and wear prediction, and understanding of misalignment.

Several control strategies are proposed to improve overall performances of conventional (geared equipped) and hydrostatic offshore wind turbines. Firstly, to maximise energy capture of a conventional turbine, an adaptive torque control technique is proposed through simplifying the conventional extremum seeking control algorithm. Simulations are conducted on the popular National Renewable Energy Laboratory (NREL) monopile 5-MW baseline turbine. The results demonstrate that the simplified ESC algorithms are quite effective in maximising power generation. Secondly, a TMD (tuned mass damper) system is configured to mitigate loads on a monopile turbine tower whose vibrations are typically dominated by its first mode. TMD parameters are obtained via H2 optimisation based on a spatially discretised tower-TMD model. The optimal TMDs are assessed through simulations using the NREL monopile 5-MW baseline model and achieve substantial tower load reductions. In some cases it is necessary to damp tower vibrations induced by multiple modes and it is well-known that a single TMD is lack of robustness. Thus a control strategy is developed to suppress wind turbine’s vibrations (due to multiple modes) using multiple groups of TMDs. The simulation studies demonstrate the superiority of the proposed methods over traditional ones. Thirdly, the NREL 5-MW baseline turbine model is transformed into a hydrostatic wind turbine (HWT). An H∞ loop-shaping torque controller and a light detection and ranging-based linear-parameter-varying anti-windup pitch controller are designed for the HWT. The tests on a monopile HWT model indicate good tracking behaviours of the torque controller and much improved performances of the linear-parameter-varying pitch controller over a gain-scheduled PI pitch controller. Finally, the hydraulic reservoir of a barge HWT is made into a bidirectional-tuned- liquid-column-damper (BTLCD) to suppress barge pitch and roll motions. The simulation results validate the effectiveness of the optimal BTLCD reservoir in reducing the tower loads and power fluctuations.

Interest in using polymer gears has been growing dramatically in the last decade. Increasing understanding of their working behaviour has improved appreciation of their advantages compared to their limitations when selecting appropriate applications. However, restricted knowledge still leaves many unfulfilled areas that might benefit from their valuable advantages and control of their limitations, for example, in replacing. their metallic counterparts in more applications. Given their very different materials properties, it is important to develop bespoke design and rating methods for polymer gears, with properly validated rules, that are not mere modifications to metallic gearing rating methods. A major aim of this thesis is to provide a new deeper understanding for use when designing and rating some technologically important types of polymer gears for wider applications. Having identified an important research gap in polymer gearing theory and practice, this thesis covers mostly experimental studies involving continuously monitored wear and wear rate and microscopic evaluation of underlying tribologies. It examines the behaviour of polymer gears made of acetal, nylon (moulded and machine-cut) and polycarbonate, all common gearing materials, during and after running under different physically realistic conditions. Some modifications to test rigs uniquely designed to operate at a continually constant load enable study of surface thermal behaviour under dry and lubricated conditions and with simulations of moderate gear misalignments. In dry-running cases, gear load capacity and wear behaviour of different polymers and variations in underlying tribology all presented important relations between the gear tooth wear rate, the applied load and the tooth surface temperature. Quite similar patterns were seen under oil lubricated conditions. Typically, though, there was a nearly three-fold improvement in gear load capacity, the wear rate and gear tooth surface temperature were decreased, and SEM showed some changes in surface tribology. Finally, deliberately introduced angular misalignments between gear pairs indicated a reasonable tolerance of small but practical levels, with different tribological behaviours between the left and right sides of the tooth surfaces. A severe increase in wear rate and tooth failure arose from misalignments above 0.8ο yaw angle and 0.4ο pitch angle. After a unifying discussion, conclusions are drawn and further work is proposed for extended studies over different parameter ranges.

Direct numerical simulations (DNS) have been performed for turbulent pipe flows using a high-order spectral element method code Nek5000. This is one of the first DNS studies of spatially developing turbulent pipe ow with a 90° bend. A turbulent inflow condition was implemented using a recycling technique. To study the unsteady oscillations of the Dean vortices, i.e., swirl switching phenomenon, the pressure force acting on the pipe wall around the bend is analysed. The lateral pressure force exhibits spatio-temporal oscillations. Conditional averaging is performed for large (positive/negative) force oscillation events to find the flow structure responsible for the force oscillation. It is found that the quasi-periodic force oscillation is closely associated with the swirl switching phenomenon. It is also observed that the mass flow rate oscillates with the swirl switching, and the frequency of this oscillation is found to be about St 0:5. 3D conditional averaging analysis reveals that the travelling wave-like three-dimensional ow structures are responsible for the spatio-temporal oscillations of the pressure force. Effects of the bend curvature ratio and Reynolds number on the flow recovery downstream of the bend and the swirl switching phenomenon are investigated. Both mild and sharp pipe bends were considered. Clear dependence on the curvature ratio are observed for various key flow properties, including pressure drop, friction factor, mean velocity profile, velocity fluctuations, etc. It is found that turbulence recovers faster downstream of a sharper bend. Conditional averaging for different curvature ratios shows that 90° bend pipe flow features an underlying travelling wave-like characteristic. The swirl switching frequency is observed to be higher when flow separation is present, whereas it appears to be not affected by the Reynolds number. The first DNS has been performed for a temporally accelerating turbulent pipe flow. Transient behaviour of turbulence statistics is analysed through ensemble averaging. The effect of acceleration rate on the response of turbulence is also investigated. The wall shear stress exhibits a distinctive four-stage development in the transient pipe flow. The pipe core region is found to be frozen during the initial transient stages. Turbulence starts to respond in the near-wall region first, and then propagates radially towards the pipe centre. The propagation speed is observed to be very similar among the three velocity components, and it is largely independent of the acceleration rate. During acceleration, the streamwise velocity component always responds first, followed by the other two components with a longer delay.

Methods of describing hyperelastic material behaviour by constitutive equations have been investigated to determine the most appropriate modelling method to use for elastomeric components. The two main mathematical formulations, the phenomenological and statistical mechanics methods were compared by consideration of examples of each. The models studied were the Mooney-Rivlin and Ogden phenomenological models, along with the 8-Chain statistical mechanics model. The types of material to be modelled were characterised by a series of deformation tests. Tensile, compressive and both static and dynamic shear tests were used to determine material stress-strain characteristics, including variations due to temperature and strain rate (loading frequency in dynamic tests). Finite Element Analysis was used to model the tensile and compressive tests, applying the constitutive equations considered previously. The results were used to assess the applicability of each model to the task. It was concluded that although the Ogden model could give the greatest accuracy by using a large range of test data, the 8-Chain model provided the most accurate results from a minimum of testing. The 8-Chain method was then used to model a commercial application, a torsional drive coupling. The modelling results were compared with empirical results, showing a close correlation.

The current work, sponsored by the SKF Engineering and Research Centre in the Netherlands, is focused on studying aspects of lubrication relevant to rolling element bearings using electrical capacitance. This includes comparative film thickness measurements in glass-on-steel and steel-on-steel contacts, interaction of polar components with surfaces, as well as grease lubrication. It has been proven that the capacitive method can be successfully applied to very thin films, even down to around 10 nm thickness. The main part of the experimental work has been conducted on a test rig that simulates a contact between a ball and a raceway in a ball bearing. In this apparatus an EHD contact is formed between a steel ball and either a glass, or steel disc. For the first time it has been possible to perform parallel measurements of film thickness with an optical method, and electrical capacitance of an EHD contact, which allowed establishing an alternative approach to extracting quantitative film thickness values from the measured capacitance. This procedure has been further applied to a modified rolling element bearing in which all but one of the steel balls were replaced with non-conductive ceramic balls. By simplifying the experimental setup and focusing on a contact between a single ball and raceways it was possible to eliminate some of the system variables, such as unloaded region capacitance, thus giving a much clearer picture of the film thickness in a rolling bearing. The current study shows a high potential of the method giving further insight into the behaviour of lubricants in high-pressure contacts. The information obtained from measured capacitance can be treated as complementary to the output of other available techniques (optical interferometry, surface force apparatus, resistance, and ultrasound) providing a better understanding of the phenomena observed.