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Surge motion of a floating wind turbine can lead to conditions where the rotor moves backwards faster than the wind, leading to propeller-like conditions or vortex ring state (VRS). The effect of surge on the thrust of a floating turbine was investigated with OpenFOAM for conditions favourable to propeller and vortex ring state. Due to lower blade velocities and larger blade twists, a region of negative thrust is shown to extend spanwise from the blade root towards the tip signifying propeller state. Predictions that strong waves with low/moderate wind speeds leads to propeller-like conditions were confirmed for a representative surging simulation with a 9.4 m amplitude in waves with an 8.1 s period and 7 m/s wind speed. A negative thrust for the entire rotor, through the combination of an inboard region of negative and outboard region of small but still positive thrust, was observed during the expected part of the surging cycle. VRS was observed with blade tip-vortex interaction and root vortex recirculation due to the duration with a negative relative rotor velocity being similar to the blade passing period, inhibiting vortex advection downstream. This work explains and demonstrates the causes of propeller state and VRS for floating turbines.

Convection of a magnetic fluid within a perspex container was investigated experimentally and complemented by a computational Finite-Element model built according to the same physical specification. The enclosure was heated at two opposite side walls and exposed to a magnetic field provided by a Neodymium-Iron-Boron permanent magnet placed either above or below the container. The spatial temperature distribution on the front side wall of the container was recorded via infrared thermography (IR) and compared to computational results that reproduced the spatial temperature fields. The results show a significant effect on heat transfer by the location of the permanent magnet and gave evidence that the Kelvin body force can be much stronger than buoyancy. As both body forces are temperature sensitive an increase in temperature difference increased both, buoyancy and Kelvin body force, albeit with a different intensity that was explained via Curie's Law and expressed as a temperature dependent magnetisation through the pyromagnetic coefficient, K. The heat transfer was characterised by the Nusselt number and a suitable modified Rayleigh number that took the orientation of both buoyancy and Kelvin body force in account. The degree of heat transfer enhancement reported varied between a 23% reduction to a 20% enhancement.

Magnetic fluid flow and heat transfer by natural and thermomagnetic convection was studied numerically in a square enclosure. The aim was to investigate the transition from natural convection to thermomagnetic convection by exploring situations where buoyancy and the Kelvin body force would be opposing each other such that the magnetic effects would in some cases be the dominant factor throughout the domain and in other cases only in a part of the fluid. The numerical model coupled the solution of the magnetostatic field equation with the heat and fluid flow equations to simulate the fluid flow under a realistic magnetic field generated by a permanent magnet. The results suggest that the domain of influence over the flow field is largely aligned with the domain of dominance of the respective driving force. The result is that the transition from a single buoyancy-driven convection cell to a single thermomagnetically driven cell is via a two-cell structure and that the local effect on the flow field leads to a global effect on the heat transfer with a minimum of the Nusselt number in the transition region.

Renewable energy has achieved high penetration rates in many areas, leading to curtailment, especially if existing network infrastructure is insufficient and energy generated cannot be exported. In this context, Distribution Network Operators (DNOs) face a significant knowledge gap about how to implement curtailment rules that achieve desired operational objectives, but at the same time minimise disruption and economic losses for renewable generators. In this work, we study the properties of several curtailment rules widely used in UK renewable energy projects, and their effect on the viability of renewable generation investment. Moreover, we propose a new curtailment rule which guarantees fair allocation of curtailment amongst all generators with minimal disruption. Another key knowledge gap faced by DNOs is how to incentivise private network upgrades, especially in settings where several generators can use the same line against the payment of a transmission fee. In this work, we provide a solution to this problem by using tools from algorithmic game theory. Specifically, this setting can be modelled as a Stackelberg game between the private transmission line investor and local renewable generators, who are required to pay a transmission fee to access the line. We provide a method for computing the empirical equilibrium of this game, using a model that captures the stochastic nature of renewable energy generation and demand. Finally, we use the practical setting of a grid reinforcement project from the UK and a large dataset of wind speed measurements and demand to validate our model. We show that charging a transmission fee as a proportion of the feed-in tariff price between 15%-75% would allow both investors to implement their projects and achieve desirable distribution of the profit., Comment: Preprint of final submitted version

Thermomagnetic convection was investigated experimentally by infrared thermography and validated numerically by a finite-element analysis. A cavity filled with a magnetic liquid was under the influence of a permanent magnet that provided an external magnetic field and was subjected to thermal forcing by maintaining the two opposite horizontal walls at different temperatures. All configurations were chosen to explore situations where the Kelvin body force and buoyancy would either oppose each other or act perpendicular to each other. As both body forces depend on temperature, the aim was to explore the degree by which heat transfer may be enhanced by only varying the temperature difference. The results demonstrate that the Kelvin body force, which can be much stronger than buoyancy, leads to convective flow where only conduction would occur without the presence of the magnet. An effective force ratio, r , is developed which suggests that an increase in temperature difference across the cavity initially leads to a dominance of thermomagnetic forcing over buoyancy but that the overall force balance becomes more moderate at higher temperature differences. The global effect of both body forces on heat transfer was characterised by the Nusselt number and a suitable modified Rayleigh number.

Shipping is a vital industry for the global economy. Stability of ships, provided by ballast water, is a crucial factor for cargo loading and unloading processes. Ballast water treatment has practical significance in terms of environmental issues, ecosystem, and human health, because ships discharge this water into the environment before loading their cargos. This study reviews the common methods for ballast water management – exchange, heating, filtration, ultrasonic treatment, ultraviolet irradiation, chemicals, and gas supersaturation – to select the best one. This study compares water temperature, salinity, dissolved oxygen, polycyclic aromatic hydrocarbons (PAHs), and heavy metals (Co, Cr, Ni, Pb) for ballast tanks of selected ships with the recipient port environment in the Persian Gulf as a case study. The exchange of ballast water in the ocean and/or its treatment on board to prevent inadvertent effects on the environment's physicochemical conditions is related to vessel characteristics, legislation, and the environmental condition. Ecological risk study showed that the salt content in ballast water is close to that of seawater, but the values of Cr (2.1 mg/l) and Ni (0.029 mg/l) in ballast water are higher than those in seawater (1 and 0.004 mg/l, respectively).

Fluctuations in solar irradiance were varied in frequency and magnitude to investigate the performance of a directly-connected solar energy powered reverse osmosis (RO) membrane system. Typically, the system produced acceptable quality water with constant solar irradiances ranging from 400 to 1200 W m −2 . Low average motor powers were encountered during fluctuations, however, in many cases, good performance was still realised, even at solar irradiance values that were equivalent to −2 . This counter-intuitive result arises from the effect of averaging the motor power, with periods of high solar irradiance compensating for the under-performance at times when the system was off. Overall, even though the permeate flux was often low when operating under fluctuating conditions, the RO system continued to deliver satisfactory quality water and at a low specific energy consumption (SEC). Temporal studies revealed that a disruption of the concentration polarisation layer occurs via a naturally induced backwash for steps in the solar irradiance as low as 100 W m −2 . This suggests that a renewable energy powered RO filtration system could benefit from being operated from a fluctuating energy source. Furthermore, the operating conditions during the first couple of minutes after a system shutdown event is shown to be very important, with: (i) shorter off-periods resulting in good performance being achieved quicker, and (ii) short-term power availability dramatically improving system performance. These findings indicate that a renewable energy powered RO system can operate well from a fluctuating energy source, in particular when additional power – for example, via supercapacitor energy buffering – is available to boost the system after a shut-down period.

We present a new statistical wind forecasting tool based on Principal Component Analysis (PCA), which is trained on past data to predict the wind speed using an ensemble of dynamically similar past events. At the same time the method provides a prediction of the likely forecasting error. The method is applied to Meteorological Office wind speed and direction data from a site in Edinburgh. For the training period, the years 2008–2009 were used, and the wind forecasting was tested for the data from 2010 for that site. Different parameter values were also used in the PCA analysis to explore the sensitivity analysis of the results. The forecasting results demonstrated that the technique can be used to forecast the wind up to 24 h ahead with a consistent improvement over persistence for forecasting more than 10 h ahead. The comparison of the forecasting error with the uncertainty estimated from the error growth in the ensemble forecast showed that the forecasting error could be well predicted.

The effect of wind turbine wakes in large offshore wind energy arrays can be a substantial factor in affecting the performance of turbines inside the array. Turbulent mixing plays a key role in the wake recovery, having a significant effect on the length over which the wake is strong enough to affect the performance of other turbines significantly. We highlight how turbulence affects wind turbine wakes using results from LES simulations of Lillgrund offshore wind farm in the context of SCADA data selected to mirror the wind conditions simulated. The analysis here concentrated on temporal spectra of wind velocities measured by the turbine's nacelle anemometer and calculated at the turbine locations in the computational model. The effect of the wind turbine rotor on the downstream flow is quantified by analysing the change in spectral features of turbines within the wind farm compared to turbines at the side of the farm exposed to the wind.

This study investigates the potential role of electric vehicles in an electricity network with a high contribution from variable generation such as wind power. Electric vehicles are modelled to provide demand management through flexible charging requirements and energy balancing for the network. Balancing applications include both demand balancing and vehicle-to-grid discharging. This study is configured to represent the UK grid with balancing requirements derived from wind generation calculated from weather station wind speeds on the supply side and National Grid data from on the demand side. The simulation models 1000 individual vehicle entities to represent the behaviour of larger numbers of vehicles. A stochastic trip generation profile is used to generate realistic journey characteristics, whilst a market pricing model allows charging and balancing decisions to be based on realistic market price conditions. The simulation has been tested with wind generation capacities representing up to 30% of UK consumption. Results show significant improvements to load following conditions with the introduction of electric vehicles, suggesting that they could substantially facilitate the uptake of intermittent renewable generation. Electric vehicle owners would benefit from flexible charging and selling tariffs, with the majority of revenue derived from vehicle-to-grid participation in balancing markets.

A microturbine is developed for harnessing energy from an airflow, which is generated by body motion. The energy should get transformed into usable electrical energy and thus provided for powering portable electrical devices. The turbine is flown axial and rotates in the same direction independent of the incoming airflow. Different designs of the turbine are tested and opposed to figure out the best parameters. For the best turbine, the integration and the process of walking is simulated.

A magnetically held pipeless fluid transporting system is a potentially useful noncontact technique in science and technology. Keeping a stable interface between the diamagnetic liquid column and the surrounding magnetic fluid is essential. The present study gives an experimental study on the unstable interfacial wave leading to discontinuity of a liquid column maintained in a magnetic fluid by a non-uniform magnetic field. The experiments were carried out by setting two magnetic north poles in opposite position to produce the magnetic field, using water to form the diamagnetic liquid column, and a diluted kerosene-base magnetic fluid as the surrounding fluid. Unstable interfacial waves were measured. It was found that the magnetic pressure acting on the interface can stabilise the interface. The experimental results agree well with the theoretical stability condition derived from a two-fluids model.

Kelvin-Helmholtz instability is a fluid instability frequently observed in atmospheric and astrophysical situations. Previous experiments were mainly conducted in a tilting dosed tube or in open-flow experiments. We present a study of Kelvin-Helmholtz instability in a dosed annular two-layer experiment where mainly conducted in a tilting closed tube or in open-flow experiments. We present a study of Kelvin-Helmholtz instability in a closed anular two-layer experiment where the shear across the layers is maintained at a steady rate by rotating the lid in contact with the upper fluid at a constant speed. The flow can be estimated from distortions of the interface which are visible due to differences in the refractive indices of the two fluid layers. This method is applied to immiscible layers of silicone fluid and water. The initial instability of the fluid interface and the wave number of the emerging flow will be compared with linear stability calculations. The experimental results indicate that two types of instability may have been observed; one dominated by viscous effects, the other (the Kelvin-Helmholtz instability) by interfacial tension.

Two-layer fluid flow of a magnetic and a non-magnetic fluid is investigated. The present paper reports numerical results of the interface shape, velocity field, and disturbed magnetic field that are obtained by the volume-of-fluid (VOF) method of two-dimensional flow of a non-magnetic fluid over a shallow layer of a magnetic fluid.

Forces on solid objects passed through a magnetic liquid plug in a tube are measured. A simple one-dimensional model is developed based on hydrostatic and magnetic pressures. The results demonstrate its potential to be used to separate two fluids while allowing solids to pass from one fluid to the other.

A very simple lattice Boltzmann model was developed to describe the competition between surface tension and dipolar interaction in magnetic fluids. The model was used to simulate the deformation of magnetic fluid drops in a nonmagnetic fluid, as well as the deformation of a gas bubble in a magnetic fluid under the action of an external magnetic field.