As more slender and more adventurous structures, such as cable-stayed bridges, are constructed, they become increasingly susceptible to large amplitude vibrations, particularly due to aerodynamic loading. Wind-induced vibrations of bridge decks, cables, towers, lamp columns and overhead electricity cables are indeed very common. This can lead to unacceptably large movements, direct structural failure, or dangerous long-term fatigue damage of structural components. Complex interactions between the wind and the structure and also between different components of the structure (e.g. cables and bridge deck) can lead to vibration problems, so for proper understanding of the behaviour, both aerodynamic and structural effects need to be considered.Whilst some of the mechanisms of wind loading of structures are reasonably well understood, others are not, and many instances of vibrations, particularly of cables, are not well explained. Recent work has developed a generalised method for analysing 'galloping' vibrations. These are caused by changes in wind forces on a structure when it starts to move, which actually tend to increase the motion. For typical bridge cables (or other similar size structures) in moderately strong winds, a particular change in the wind flow around the cable occurs, known as the drag crisis. This changes the forces on the cable and causes a special case of galloping-type vibrations, which the new method of analysis is able to predict, for the first time. Comparisons of these calculations with wind tunnel test results on inclined cylinders have confirmed that the basic method does work, but there is a need to consider additional effects, such as wind turbulence, torsional motion of the structure and more accurate account of the changes in the aerodynamic forces as the structure moves. It is proposed to develop the approach to include these effects, using further wind tunnel data, to eventually create a unified framework for wind loading analysis of any real structure for galloping, together with the other aerodynamic mechanisms buffeting (due to wind turbulence) and flutter.Meanwhile, interactions between vibrations of structural components can cause serious effects. For example, very small vibrations of a bridge deck can cause very large vibrations of the cables supporting it, through the mechanism of 'parametric excitation'. Even more surprisingly, in other instances, localised cable vibrations can lead to vibrations of the whole structure. Research under another grant is already considering these effects for very simplified structures, but it is proposed to extend the analysis to realistic full structures. Also, often cables are tied together to try to prevent vibrations of individual cables, but they can then all vibrate together as a network. This project therefore aims to analyse full cable networks, to understand how their vibrations can be limited.Finally, it is proposed to bring together the above two main areas, to include both aerodynamic and structural dynamic interactions in the analysis of slender structures. For example, because of the interactions, the wind loads on relatively small elements, such as cables, can have surprisingly large effects on the overall dynamic response of large structures. At present this is generally ignored, but the joint approach will address this issue. Also, in some instances, only a combined view of the phenomena may be able to explain the behaviour observed on full-scale structures in practice. The holistic view of the wind loading and structural behaviour should provide tools to help avoid undesirable and potentially dangerous effects of vibrations of slender structures in the future. Based on the analysis, this could be achieved by modifying the shape of the elements to change the wind loads, or introducing dampers to absorb enough vibration energy.

The ability to control the evolution of a reaction is a long-standing goal of chemistry. One approach is to use the electric field provided by a laser pulse as the guide. Recent work has focused on shaping and timing the pulse so that the field interacts with the molecules in a particular way to influence the energy flow through the molecule and thus eventually the course of a reaction. The optimal pulse shape is achieved by using a feedback loop , focusing on a signal related to the desired outcome and allowing a computer algorithm to change the pulse shape during repeated cycles of the experiment until the signal is maximised. This optimal control scheme has proved to be able to control a wide range of chemical systems, but the complicated pulse shapes provide little insight into the procedure, and the experiments have a black box nature. A different, very appealing, approach to control through a laser field is to use the field to change the shape of the potential energy surface over which the reaction proceeds. This can be acheived using a strong pulse which induces Stark shifting of the surface. By careful timing of a pulse of the appropriate strength, it has been shown that it is possible to control the products from IBr dissociation by effectively changing the barrier height to the different possible channels.The project aims to investigate theoretically this potentially general approach to laser control. The results should start to build up a picture of how the complicated potential energy surfaces of small molecules are altered by interaction with the field. This will help in the development of experiments and in our understanding of how molecules behave in a light field.

Piloting a maritime helicopter onto a ship's landing deck can be fraught with difficulties and dangers. Part of the reason is the degraded visibility and a confined landing area, as well as the ship motion and poor low-speed landing qualities. However, another source of difficulty is the unsteady airflow over the ship's superstructure, i.e. the airwake. As the helicopter rotor moves into the airwake as it separates from the top and sides of the hangar, the rotor thrust and moments vary significantly making the helicopter difficult to control. This proposal is concerned with developing an instrument that will measure the effect of this flow field on a model helicopter. The research aims to develop a new Airwake Dynamometer (AirDyn) capable of measuring aircraft loads, including pitch and roll moments. These can then be correlated with measurements of the velocity field over the landing deck, and with pilot experience in the Liverpool flight simulator. The intention is to use the AirDyn and turn our attention not just to the problem of why airwakes affect helicopter stability and pilot workload, but how the airwake can be modified to alleviate the effects, and possibly attract the helicopter to its landing spot.

The vision for this research is to develop a novel toolset for flight simulation fidelity enhancement. This represents a step-change in simulator qualification, is well-timed making a significant contribution to the UoL initiated NATO STO AVT-296-RTG activity and will have an immediate impact through engagement with Industry partners. High fidelity modelling and simulation are prerequisites for ensuring confidence in decision making during aircraft design and development, including performance and handling qualities estimation, control law development, aircraft dynamic loads analysis, and the creation of a realistic piloted simulation environment. The ability to evaluate/optimise concepts with high confidence and stimulate realistic pilot behaviour are the kernels of quality flight simulation, in which pilots can train to operate aircraft proficiently and safely and industry can design with lower risk. Regulatory standards such as CS-FSTD(H) and FAA AC120-63 describe the certification criteria and procedures for rotorcraft flight training simulators. These documents detail the component fidelity required to achieve "fitness for purpose", with criteria based on "tolerances", defined as acceptable differences between simulation and flight, typically +/- 10% for the flight model. However, these have not been updated for several decades, while on the military side, the related practices in NATO nations are not harmonised and have often been developed for specific applications. Methods to update the models for improved fidelity are mostly ad-hoc and, without a strong scientific foundation, are often not physics-based. This research will provide a framework for such harmonisation removing the barriers to adopting physics-based flight modelling and will create new, more informed, standards. In this research two aspects of fidelity will be tackled, predictive fidelity (the metrics and tolerances in the standards) and perceptual fidelity (pilot opinion). The predictive fidelity aspect of the research will use System Identification techniques to provide a systematic framework for 'enhancing' a physics-based simulation model. The perceptual fidelity research will develop a rational, novel process for task-specific motion tuning together with a robust methodology for capturing pilots' subjective assessment of the overall fidelity of a simulator. Extensive use will be made of flight simulation and real-world flight tests throughout this project in both the predictive and perceptual fidelity research.

Ultra-short and ultra-intense laser pulses provide an impressive camera into the world of electron motion. Attoseconds and sub-femtoseconds are the natural time scale of multi-electron dynamics during the ionization and break-up of atoms and molecules. The overall aim of the proposed work is to investigate attosecond phenomena, pathways of correlated electron dynamics and effects due to the magnetic field of light in three and four-electron ionization in atoms and molecules triggered by intense near-infrared and mid-infrared laser pulses. Correlated electron dynamics is of fundamental interest to attosecond technology. For instance, an electron extracted from an atom or molecule carries information for probing the spatio-temporal properties of an ionic system with angstrom resolution and attosecond precision paving the way for holography with photoelectrons. Moreover, studies of effects due to the magnetic field of light in correlated multi-electron processes are crucial for understanding a variety of chemical and biological processes, such as the response of driven chiral molecules. Chiral molecules are not superimposable to their mirror image and are of particular interest, since they are abundant in nature. The proposed research will explore highly challenging ultra-fast phenomena involving three and four-electron dynamics and effects due to the magnetic field of light in driven atoms and during the break-up of driven two and three-center molecules. We will investigate the physical mechanisms that underly these phenomena and devise schemes to probe and control them. Exploring these ultra-fast phenomena constitutes a scientific frontier due to the fast advances in attosecond technology. These fundamental processes are largely unexplored since most theoretical studies are developed in a framework that does not account for the magnetic field of light. Moreover, correlated three and four-electron escape is currently beyond the reach of quantum mechanical techniques. Hence, new theoretical tools are urgently needed to address the challenges facing attoscience. In response to this quest, we will develop novel, efficient and cutting-edge semi-classical methods that are much faster than quantum-mechanical ones, allow for significant insights into the physical mechanisms, compliment experimental results and predict novel ultra-fast phenomena. These semi-classical techniques are appropriate for ionization processes through long-range Coulomb forces. Using these techniques, we will address some of the most fundamental problems facing attoscience. Our objectives are: 1) Identify and time-resolve novel pathways of correlated three-electron dynamics in atoms driven by near-infrared and mid-infrared laser pulses. 2) Explore effects due to the magnetic field of light in correlated two and three-electron escape during ionization in atoms as well as in two and three-center molecules driven by near-infrared and mid-infrared laser pulses that are either linearly or elliptically polarized or by vector beams, i.e. "twisted" laser fields, an intriguing form of light that twists like a helical corkscrew. 3) Control correlated multi-electron ionization and the formation of highly exited Rydberg states in four-active-electron three-center molecules by employing two-color laser fields or vector beams.