Actuation is the means by which forces can be applied within machine systems to give rise to controlled motion. Applications of actuation include, for example, the extrusion of material for manufacturing purposes, the manipulation of components in test machines, flight control surface adjustment in aircraft, ink jet printing, positioning in robotic systems, and active vibration/noise attenuation. There is a variety of actuator types based on different physical phenomena e.g. piezoelectric, electric, electromagnetic, pneumatic, hydraulic, and screw. The differences in performance relate to the amplitudes and frequencies of the forces that are capable of being applied, together with the motion range (stroke) and the associated precision. For example, piezoelectric actuators can deliver large forces at high frequencies, but the strokes are less than 1 mm. Alternatively, hydraulic actuators can deliver large forces over long strokes (e.g. 3 m in the opening of the Gateshead Millennium Bridge), though the frequency of the forcing is relatively low. An ideal actuator would have high performance over all metrics: force levels; frequency range or bandwidth; stroke range; and precision. At present no such actuator exists. The aim of the proposed research is to investigate the issues relating to physical characteristics, design integration and control that would enable actuation as close to the ideal to be realised. The future benefits would be widespread with the potential generation of new scientific and industrial innovations. The research will be focused on the design and integration of multi-actuation media with optimised control strategies to yield an actuator that has high performance metrics. A number of areas will be investigated. Firstly, piezoelectric actuators will be assessed for the generation of dynamic pressures within hydraulic cylinders, which would allow high frequency actuation. Additionally, piezoelectric devices will be used to deform piston and rod seals such that the friction forces provided by the seals may be used to control large stroke and high frequency motion. High frequency actuation and sub-micron control will also be achieved using a piezo-actuated valve for precise adjustment of hydraulic flows. The basic physical interactions of sliding and actuated parts will require in-depth analysis in order that the detailed design of high performance controllers can be accomplished using accurate system models. Finally, the integrated system will be realised in an experimental facility, which will be used to validate the research methodology.

The applications of hydraulics are diverse. Hydraulic actuation offers many benefits including compact and lightweight design due to high power density, fast response and good controllability. In most fluid power hydraulic systems, speed and force of the load are controlled using valves to throttle the flow and reduce the hydraulic pressure. This is a simple but extremely inefficient method as the excess energy is lost as heat, and it is common for more than 50% of the input power to be wasted in this way. An alternative method is to use a variable capacity hydraulic pump or motor. This is more efficient, but variable capacity pumps and motors are expensive.The proposed work investigates two methods of increasing the efficiency of hydraulic systems while maintaining good control of speed and force without the expense associated with variable capacity pumps. The first method is the Switched Reactance Hydraulic Transformer (SRHT), a novel device for controlling the flow and pressure of a hydraulic supply. The second method is the Electro-Hydrostatic Actuator (EHA). Both of these systems increase efficiency by removing the need for control valves. For both applications, active fluid-borne noise attenuation techniques may be necessary.Switched Reactance Hydraulic Transformer (SRHT):A new device for controlling the flow and pressure of a hydraulic supply is proposed. It consists of a high-speed switching valve and an 'inertance tube'. Acting as a transformer, the device is able to boost the pressure or flow. The device could be configured to provide the functionality of a variable capacity pump, a pressure relief valve, a pressure compensated flow control valve or a proportional valve. Each of these control modes can be achieved without an expensive variable capacity pump and without the inefficiency inherent in a control valve. Previous work highlighted problems of noise and parasitic power losses. If these problems can be overcome using more recent materials and techniques combined with careful design, it could provide a more cost-effective efficient alternative to pressure/flow control valves.Electro-hydrostatic Actuation (EHA):In EHAs, a variable speed electric motor drives a fixed displacement pump which delivers flow directly to a linear actuator. Moving from centralised power supplies to distributed multi-pump/actuator systems brings reductions in power levels for individual subsystems. Furthermore, valveless electro-hydrostatic actuation systems provide benefits of greater efficiencies compared to conventional valve-controlled hydraulic systems, further reducing the power requirements. EHA systems can suffer from noise problems because of the close coupling between pump and actuator, allowing direct transmission of pressure pulsation. The challenges are to achieve good dynamic performance while achieving higher efficiency, low noise and reduced system weight and size.Active Fluid Borne Noise Attenuation:Fluid-borne noise (FBN) is a major contributor to air-borne noise and vibration in hydraulic systems as well as leading to increased fatigue in system components. Although passive systems to reduce the noise have been shown to be effective, they require tuning to specific systems, their attenuation frequency range is limited and they may be bulky. Furthermore, attenuation devices based on expansion chambers, accumulators or hoses are likely to be unsuitable for EHA or SRHT systems as they add compliance to the system and would impair the dynamic response. Active devices, which add energy to the fluid to cancel out or destroy the pressure ripple to reduce noise levels, can be effective at a much wider range of frequencies and system designs without affecting the system's dynamic response. Both the SRHT device and EHA system may suffer from noise issues, and as such, will benefit from active noise attenuation.

Fluid dynamics underpins large areas of engineering, environmental and scientific research, and is becoming increasingly important in medical science. At Leeds, we possess research expertise across each of these domains and we have an established record of working across disciplinary boundaries. This proposal builds upon this record through the establishment of a multidisciplinary CDT in Fluid Dynamics. Research techniques that will be applied, and developed, will encompass: mathematical modelling & theory; numerical methods, CFD & high performance computing (HPC); and measurement & experimentation. Engineering application areas to be addressed include: reacting flows; carbon capture, transport & storage; flow of polymer melts; mixing problems; particulate flows; coating & deposition; lubrication; medical devices; pathogen control; heat transport; wind turbines; fluid-structure interaction; and nuclear safety. Environmental application areas will consist of: groundwater flow; river/estuary flows; tidal flows; oceanography; atmospheric pollution; weather forecasting; climate modelling; dynamics of the Earth's interior; and solar & planetary flow problems. Facilities available to undertake this research include: the University's HPC system which, combined with the N8 regional facility that is hosted at Leeds, provides ~10000 computational cores, an extensive suite of licensed software and dedicated support staff; flow measurement techniques (including Particle Imaging Velocimetry (PIV), 2-component Laser Doppler Anemometry (LDA), Phase Doppler Anemometry (PDA) and Ultrasonic Doppler Velocity Profiling (UDVP)); techniques for measuring fluid concentration (Ultrasonic High Concentration Meter (UHCM) and Optical Backscatter Probes (OBS)) and a range of optical metrology systems (e.g. pulsed and continuous wave lasers). The UK has a substantial requirement for doctoral scientists and engineers who have a deep understanding of all aspects of fluid dynamics from theory through to experimental methods and numerical simulation. In manufacturing and process engineering, for example, many processes depend critically on fluid flows (e.g. extrusion of polymer melts, deposition of coatings, spray drying, etc.) and it is essential to understand and control these processes in order to optimize production efficiency and reliability (see letter of support from P&G for example). In large-scale mechanical engineering there is a demand for expertise in reacting turbulent flows in order to optimize fuel efficiency and engine performance, and in wetting and surface flows for the design and manufacture of pumps and filters. There is also a need for a wide variety of skilled experts in environmental fluid flows to support the growing need to understand and predict local pollution and threats to safety (atmospheric, surface water, ocean and sub-surface flows), and to predict weather, climate and space weather for satellite technology. We will train a new generation of researchers who will have a broad range of skills to transfer into industry and environmental agencies, hence our approach will be multi-disciplinary throughout. All students will undertake both modelling and experimental training before embarking on their PhD project - which will be co-supervised by academics from different Schools. The MSc component of the programmee will be specifically tailored to develop expertise in the mathematical background of fluid dynamics, in CFD/HPC, and in experimental techniques. Team-based projects will be used to develop the teamwork and communication skills we believe are essential. Finally, engagement with industry will be a key feature of this CDT: all students will undertake an industrial placement, a large number of projects will be industrially sponsored, and our non-academic partners will contribute actively to our management, implementation and strategic development.

Understanding and characterising the behaviour of fluids is fundamental to numerous industrial and environmental challenges with wide-ranging societal impact. The CDT in Fluid Dynamics at Leeds will provide the next generation of highly trained graduates with the technical and professional skills and knowledge needed to tackle such problems. Fluid processes are critical to both economic productivity and the health and environmental systems that affect our daily lives. For example, at the microscale, the flow of liquid through the nozzle of an ink-jet printer controls the quality of the printed product, whilst the flow of a coolant around a microprocessor determines whether or not the components will overheat. At the large scale, the atmospheric conditions of the Earth depend upon the flow of gases in the atmosphere and their interaction with the land and oceans. Understanding these processes allows short term weather forecasting and long term climate prediction; both are crucial for industry, government and society to plan and adapt their environments. Fluid flows, and their interactions with structures, are also important to the performance of an array of processes and products that we take for granted in our everyday lives: gas and water flow to our homes, generation of electricity, fuel efficiency of vehicles, the comfort of our workplaces, the diagnosis and treatment of diseases, and the manufacture of most of the goods that we buy. Understanding, predicting and controlling Fluid Dynamics is key to reducing costs, increasing performance and enhancing the reliability of all of these processes and products. Our CDT draws on the substantial breadth and depth of our Fluid Dynamics research expertise at the University of Leeds. We will deliver an integrated MSc/PhD programme in collaboration with external partners spanning multiple sectors, including energy, transport, environment, manufacturing, consultancy, defence, computing and healthcare, who highlight their need for skilled Fluid Dynamicists. Through a combination of taught courses, team projects, professional skills training, external engagement and an in-depth PhD research project we will develop broad and deep technical expertise plus the team-working and problem-solving skills to tackle challenges in a trans-disciplinary manner. We will recruit and mentor a diverse cohort from a range of science and engineering backgrounds and provide a vibrant and cohesive training environment to facilitate peer-to-peer support. We will build strengths in mathematical modelling, computational simulation and experimental measurement, and through multi-disciplinary projects co-supervised by academics from different Schools, we will enable students to undertake a PhD project that both strengthens and moves them beyond their UG discipline. Our students will be outward facing with opportunities to undertake placements with industry partners or research organisations overseas, to participate in summer schools and study challenges and to lead outreach activities, becoming ambassadors for Fluid Dynamics. Industry and external engagement will be at the heart of the CDT: all MSc team projects will be challenges set and mentored by industry (with placements embedded); each student will have the opportunity for user engagement in their PhD project (from sponsorship, external supervision and access to facilities, to mentoring); and our partners will be actively involved in overseeing our strategic direction, management and professional training. Many components will be provided by or with our partners, including research software engineering, responsible innovation, commercial awareness and leadership.