Traditional analysis of aquifer tests uses the observed hydrograph at one well caused by pumping at another well for estimating transmissivity and storage coefficient of an aquifer. The analysis relies on Theis' or Jacob's approximate solution, which assumes aquifer homogeneity. Aquifers are inherently heterogeneous at different scales. If the observation well taps into a low permeability zone while the pumping well is located in a high permeable zone, the resulting situation contradicts the homogeneity assumption embedded in the traditional analysis. As a result, a practical but important question we ask: What do we derive from the traditional analysis? Using numerical experiments in synthetic aquifers, we answer this question. Results of the experiments indicate that the effective transmissivity, Teff , and storage coefficient, Seff , values vary with time, as well as the principal directions of the transmissivity, but both values approach their geometric means of the aquifer at large times. Analysis of the estimated transmissivity (T) and storage coefficient (S ) using well hydrographs from a single observation well shows that at early times, both the estimated T and S values vary with time. At late times, both estimates approach local averages near the observation well. The T value approaches but does not equal Teff , representing an average value over a broad area in the vicinity of the observation well while the S value converges to the value dominated by the storage coefficient near the observation wells (i.e., its average area is much smaller than that of the t value).

A combination of climate change, due to anthropogenic CO2 emissions and concerns over energy security, due to fluctuating fuel prices, has led to the UK pushing to increase its renewable energy production. Harnessing tidal stream energy is an infant sector in the UK’s renewable energy portfolio, despite the UK’s large tidal stream resource, and is harnessed through deploying tidal stream energy converters. This thesis focuses on the design of a novel vertical axis tidal turbine (VATT) called CarBine which is driven by drag force and therefore has several unique advantages, including slow rotational speed, omni-directionality and a simple design. This research focused on the optimisation of the CarBine design and was split into two areas: physical testing and numerical modelling. A conventional Savonius was also analysed in both of these respects and this enabled a direct comparison of CarBine to a competing drag force driven VATT. Physical testing measured the power of the turbines and was conducted in hydraulic flumes at both Cardiff University (CU) and IFREMER in Northern France for a range of flow conditions. Testing at IFREMER enabled the quantification of the blockage effect in the CU experiments. Physical testing resulted in the optimised design of CarBine being one with a four arm configuration. From physical testing at CU, CarBine showed inferior efficiency performance to that of the conventional Savonius, a Cp of 0.117 compared to 0.225 at U∞=0.72 m/s. As a result a hybrid of both the Savonius and CarBine was tested, namely a Savonius with flaps. However, results from physical testing showed the Savonius with flaps to have inferior performance to both CarBine and the conventional Savonius, with a Cp of 0.103 at U∞=0.72 m/s at CU. Numerical modelling was conducted using the commercial CFD software package, Ansys CFX. Both transient and steady state simulations along with 2D and 3D models were used to model both CarBine and the Savonius. Both the k-ε and SST turbulence models were used for comparison. The two degrees of rotational freedom present in the CarBine design resulted in CarBine being difficult to model precisely. The numerical modelling results were validated against the physical testing results and where available, 3D results showed closer validation than the 2D results.

Based on the concepts of water exchange timescales, a three-dimensional model has been refined to predict the age of water (AW). The model has been applied to two estuaries with very different characteristics. One estuary is a partially stratified micro-tidal estuary, i.e., the Pearl River Estuary (PRE), China and the other one is a well-mixed macro-tidal estuary, i.e., the Severn Estuary and Bristol Channel, UK (SEBC). The focus of this study is to investigate the influence of density-induced circulation on the estuarine water exchange process. A comparison between the predictions made using the barotropic mode and the baroclinic mode has been undertaken in the above two estuaries. The results indicate that due to the partially stratified phenomenon, in the PRE lower AW values are observed at the water surface, with higher AW values occurring near the bed. In the wet season, a more obvious AW stratification can be observed. The density-induced circulation causes an increase in the water mixing rate and a decrease in the timescales by a ratio greater than 50%. The stratification of the AW distribution is also enhanced. However, in the homogenous phenomenon of the SEBC, the baroclinic forcing’s impact on the water exchange process is very small. A model investigation is then carried out to predict the spatio-temporal variation of AW distribution in response to other dynamic factors. A regression analysis reveals that the age of freshwater exponentially decreases with the growth of discharge. Scenario analyses show that the tidal influence becomes more pronounced when the discharge is relatively small, and the varying tidal range mainly impacts on the fluctuation range of the AW, instead of its depth-averaged value. Moreover, the iv vertical variation in the AW is enhanced during neap tides due to less mixing. The age of seawater in the estuary is lowest near the estuary mouth and it increases further upstream. In the SEBC, the impacts of proposed tidal stream turbines with two different array arrangements on the water exchange process are analysed to investigate changes in the water level, current speed and AW distributions. A physical model investigation into the water exchange processes in a small scale model of the SEBC is then undertaken to estimate the travel time between different locations, and the water and tracer fluxes through two selected cross sections.

In this study, a hydro-environmental numerical model is utilised to further demonstrate the applicability of computer models to predict tidal flow in coastal waters. In particular, high resolution model simulations are performed at two selected sites: the Ogeechee Estuary, USA to assess the hydro-kinetic energy potential near Rose Dhu Island, a small island in the estuary; and at Swansea Bay, UK to assess faecal coliform pollution levels in the bay. Model results from the Ogeechee Estuary simulations revealed that better representation of branching smaller creeks located inshore enhanced the magnitude of tidal currents by approximately 30% near Rose Dhu Island. Evaluation of spatial and temporal distribution of currents revealed that local hot-spots of hydro-kinetic energy exist within the estuary and a maximum annual power of 4.75MW is available from the tidal streams surrounding the island. Investigation of the sensitivity of model parameters related to intertidal storage and bottom friction showed that ebb tide dominance in the estuary is reduced by lowering wetland elevation and by increasing bottom friction in the channel. Increasing the marsh friction to represent the resistance offered by marsh vegetation decreased the influence of intertidal storage on tidal distortion as ebb-dominance is reduced. Model results from the Swansea Bay simulations showed that three distinct flow patterns exist in the bay including re-circulating eddy like patterns, due to the presence of a headland located towards to the south-west end of the bay. The model-predicted distribution of Faecal Indicator Organisms (FIO) helped identify major pollution sources that negatively influence the rating of the Swansea Bay bathing water site. Investigation of the spatial distribution of FIO concentrations at the Designated Sampling Point (DSP) revealed that that the samples collected at DSP for compliance monitoring would correctly represent the pollution levels in the surrounding areas, however, at locations further off-shore significant spatial variability by up to five times was observed. As expected, intermittent peaks in FIO concentrations were noticeable following rainfall events, however, a strong temporal variability within a day was also observed at the DSP with concentration values varying by up to ten times in magnitude.

Main purpose of the paper is to present high-response hydraulic linear drive, which is controlled with new digital piezo valve and where the new position transducer is integrated as a part of hydraulic cylinder. Hydraulic digital piezo valve with main static and dynamic characteristics as well as its functionality is presented in detail. The main static and dynamic characteristics of dygital piezo valve which influence directly on the linear drive performance are high resolution of the volume flow rate and high resposne of the valve. Beside valve characteristics the new integrated position transducer, the digital controller and control method, presented in the paper, have major impact on linear drive preformance. At the end of the paper the step response and position resolution of the hydraulic linear drive controlled with the new digital valve is compared with the results of reference hydraulic drive controlled with high response proportional valve.

The dynamic of cavitation in hydraulic components cannot be computed accurately yet and therefore cavitation is hard to predict. The cavitation phenomenon can be divided in three sub-phenomenona: Pseudo-cavitation, Gas-cavitation and Vapour-cavitation. Pseudo-cavitation discribes the enlargement of an air bubble due to a pressure drop. Gas-cavitation refers to bubble growth which is driven by diffusion of dissolved air from the surrounding fluid into the bubble, when the solubility of air in the fluid is lowered by a pressure drop. Vapor-cavitation is the evaporation of the liquid phase on the bubble surface. Usually all three sub-phenomenona occur simultaneously when the pressure decreases and are summarised as cavitation in general. To implement the physics of gas-cavitation in a dynamic mathematical model it is necessary to know the diffusion coefficient of air in the hydraulic liquid and the maximum amount of air which can be dissolved in the liquid. The calculation can be accomplished by using the Bunsen coefficient. In this paper both coefficients for three different hydraulic oils are calculated based on experimental results.

Fuel cost represents a significant operating expense for owners and fleet managers of hydraulic off-highway vehicles. Further, the upcoming Tier IV compliance for off-highway applications will create further expense for after-treatment and cooling. Solutions that help address these factors motivate fleet operators to consider and pursue more fuelefficient hydraulic energy recovery systems. Electrical hybridization schemes are typically complex, expensive, and often do not satisfy customer payback expectations. This paper presents a hydraulic energy recovery architecture to realize energy recovery and utilization through a hydraulic hydro-mechanical transformer. The proposed system can significantly reduce hydraulic metering losses and recover energy from multiple services. The transformer enables recovered energy to be stored in a high-pressure accumulator, maximizing energy density. It can also provide system power management, potentially allowing for engine downsizing. A hydraulic test stand is used in the development of the transformer system. The test stand is easily adaptable to simulate transformer operations on an excavator by enabling selected mode valves. The transformer’s basic operations include shaft speed control, pressure transformation control, and output flow control. This paper presents the test results of the transformer’s basic operations on the test stand, which will enable a transformer’s full function on an excavator.

Besides the braking system the steering system is one of the most important systems on vehicles. The reliability and the performance of a steering system decides on the controllability of the vehicle under normal conditions as well as emergency situations. In everyday use the characteristics, the connectivity to assistance systems and the energy efficiency of the steering system become more and more important to fulfill the increasing demands regarding fuel consumption, carbon dioxide emissions and comfort. To meet these demands, new steering systems must be implemented and new technologies have to be developed. This contribution compares different approaches regarding functionality and energy efficiency to give an indication which system is the most promising solution for future front axle steering systems as well as rear steered axles (tag- or pusher axle) on trucks.

The implementation of an energy recovery system for retreiving otherways wasted energy is an effective method for reducing the overall energy consumption of a mobile machine. In a fork lift, there are two subsystems that can be effectively modified for recovering energy. These are the driveline and the lift/lower function of the mast. This study focuses on the latter by studying a recovery system whose main component is a hydraulic transformer consisting of a hydraulic motor, a variable displacement pump and an induction motor. Since the flow rate/pressure - ratio can be modified, the utilization of the hydraulic transformer enables downsizing of the accumulator volume. However, the decrease of the gas volume leads to an increase in the compression ratio of the accumulator, which in terms leads to higher gas temperatures after charging and consequently to higher thermal losses during holding phase. In order to reduce these losses, a thermally regenerative unit was implemented to the gas volume of an accumulator to reduce the temperature build up during charging. In this study, the effect of improving the thermal characteristics of the accumulator to the efficiency of the whole energy recovery system is investigated by means of measurements.

Dirt ingress in hydraulic cylinders is one of the sources that leads to pollution of hydraulic systems. There are already several test rigs to investigate external contamination mechanisms. However, until now only the behavior of the whole sealing system was analyzed. A new testing method to understand the dirt particle transport between a reciprocating motioned rod and a wiper is presented. The new approach aims to avoid known issues such as limited reproducibility and long duration. The paper describes the test rig design and operating principle. First measurement results are shown.