Direct observation via in situ heated stage EBSD analysis of recrystallization of phosphorous deoxidised copper in unstrained and strained conditions

Recrystallization of phosphorous deoxidised copper used for strength critical applications at elevated temperatures was investigated by means of in situ heated stage EBSD analysis using a Gatan Murano heated stage mounted within a Carl Zeiss Sigma FEGSEM electron microscope. The influence of applied strain as the result of deformation within a Nakajima test as an analogue for industrial forming on the recrystallization temperature was investigated, the impact of increased heating rates on microstructural evolution was also investigated. Inverse pole figure plots combined with regions of reduction in local misorientations and variations in geometrically necessary dislocations were used to establish the point of recrystallization and the recrystallized fraction of the material. Recrystallization was observed to occur at temperatures as low as 130 °C in highly strained samples compared to around 300 °C within the annealed samples dependent upon heating rate. Increased heating rates were observed to produce a finer final grain structure but had little effect on presence of 60° grain twins, which was influenced more by initial material condition

The cumulative impact of tidal stream turbine arrays on sediment transport in the Pentland Firth

This contribution investigates the impact of the deployment of tidal stream turbine arrays on sediment dynamics and seabed morphology in the Pentland Firth, Scotland. The Pentland Firth is arguably the premier tidal stream site in the world and engineering developments are progressing rapidly. Therefore understanding and minimising impacts is vital to ensure the successful development of this nascent industry. Here a 3 dimensional coupled hydrodynamic and sediment transport numerical model is used to investigate the impact on sediment transport and morphodynamics of tidal stream arrays. The aim of the work presented here is twofold: firstly to provide prediction of the changes caused by multiple tidal stream turbine array developments to some of the unique sandy seabed environments in the Pentland Firth and secondly as a case study to determine the relationship between impacts of individual tidal stream farms and cumulative impacts of multiple farms. Due to connectivity in tidal flow it has been hypothesized that the cumulative impact of multiple arrays on sediment dynamics might be non-linear. This work suggests that, for the Pentland Firth, this is not the case: the cumulative impact of the 4 currently proposed arrays in the area is equal to the sum of the impacts of the individual arrays. Additionally, array implementation only has minimal effect on the baseline morphodynamics of the large sandbanks in the region, smaller more local sandbanks were not considered. These two results are extremely positive for tidal stream developers in the region since it removes the burden of assessing cumulative impact from individual developers and suggests that impacts to sub-sea morphodynamics is insignificant and hence is unlikely to be an impediment to development in the Pentland Firth with the currently proposed levels of extraction

Wave-turbulence separation at a tidal energy site with empirical orthogonal function analysis

Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at tidal stream energy sites; they are used to estimate several parameters, including turbulent kinetic energy (TKE). However, estimates of TKE from ADCPs are often swamped by wave action. We surmise that this bias can be detected as a data mode: to test this, we present an empirical orthogonal function (EOF) analysis of two months of TKE estimates from ADCP measurements at a tidal energy site with significant wave activity. The results of the analysis were compared with linear wave theory, using data from a wave buoy. The first data mode identified from EOF analysis agrees well with the wave bias predicted by linear theory, and the resulting decomposition of the data set into wave and turbulent components appears realistic. This decomposition is possible from ADCP data alone, and therefore offers a novel and widely applicable analysis technique for simultaneous assessment of turbulence and waves at highly-energetic tidal sites. The method can also be applied retrospectively to historical data sets. We also show that the decomposition can be improved by including higher EOF modes, but this requires an independent measurement of waves to determine the optimum number of modes

Comparison of dense optical flow and PIV techniques for mapping surface current flow in tidal stream energy sites

Marine renewable energy site and resource characterisation, in particular tidal stream energy, require detailed flow measurements which often rely on high-cost in situ instrumentation which is limited in spatial extent. We hypothesise uncrewed aerial vehicles (UAV) offer a low-cost and low-risk data collection method for tidal stream environments, as recently techniques have been developed to derive flow from optical videography. This may benefit tidal and floating renewable energy developments, providing additional insight into flow conditions and complement traditional instrumentation. Benefits to existing data collection methods include capturing flow over a large spatial extent synchronously, which could be used to analyse flow around structures or for site characterisation; however, uncertainty and method application to tidal energy sites is unclear. Here, two algorithms are tested: large-scale particle image velocimetry using PIVlab and dense optical flow. The methods are applied on video data collected at two tidal stream energy sites (Pentland Firth, Scotland, and Ramsey Sound, Wales) for a range of flow and environmental conditions. Although average validation measures were similar (~ 20–30% error), we recommend PIVlab processed velocity data at tidal energy sites because we find bias (underprediction) in optical flow for higher velocities (> 1 m/s)

Characterizing the Marine Energy Test Area (META) in Wales, UK

With lack of convergence on any single wave or tidal technology, test centres have a unique role in the marine renewable energy industry. Test centres facilitate real testing at sea for devices and components at various TRLs (Technology Readiness Level), reducing the time, cost, and risks faced by marine energy developers. META (Marine Energy Test Area) is a £2.7M project managed by Marine Energy Wales (MEW), consisting of eight test areas in the Milford Haven Waterway and surrounding waters (Pembrokeshire, Wales). Although various datasets have been collected from the META test areas over the last decade, and some aspects of these data have been published in various reports, the data has not been gathered together, systematically analysed and critically assessed – the aim of this study. Here, we describe and interpret the various META datasets, including multibeam, ADCP (acoustic Doppler current profiler), and wave buoy data. We report the key parameters of relevance to testing at META, including bathymetry, the nature and magnitude of the tidal currents, turbulence, and wave climates. We make recommendations on future priorities for data collection at META, and discuss the future of the test areas, including expansion into floating wind and other evolving marine energy technologies

Intercomparison of surface velocimetry techniques for drone-based marine current characterization

Mapping tidal currents is important for a variety of coastal and marine applications. Deriving current maps from in-situ measurements is difficult due to spatio-temporal separation of measurement points. Therefore, low-cost remote sensing tools such as drone-based surface velocimetry are attractive. Previous application of particle image velocimetry to tidal current measurements demonstrated that accuracy depends on site and environmental conditions. This study compares surface velocimetry techniques across a range of these conditions. Various open-source tools and image pre-processing methods were applied to six sets of videos and validation data that cover a variety of site and weather conditions. When wind-driven ripples are present in imagery, it was found a short-wave celerity inversion performed best, with mean absolute percentage error (MAPE) of 5–6% compared to surface drifters. During lower wind speeds, current-advected surface features are visible and techniques which track these work best, of which the most appropriate technique depends on specifics of the collected imagery; MAPEs of 9–21% were obtained. This work has quantified accuracy and demonstrated that surface current maps can be obtained from drones under both high and low wind speeds and at a variety of sites. By following these suggested approaches, practitioners can use drones as a current mapping tool at coastal and offshore sites with confidence in the outputs

Comparison of tab-to-busbar ultrasonic joints for electric vehicle li-ion battery applications

Recent uptake in the use of lithium-ion battery packs within electric vehicles has drawn significant attention to the selection of busbar material and corresponding thickness, which are usually based on mechanical, electrical and thermal characteristics of the welded joints, material availability and cost. To determine joint behaviour corresponding to critical-to-quality criteria, this study uses one of the widely used joining technologies, ultrasonic metal welding (UMW), to produce tab-to-busbar joints using copper and aluminium busbars of varying thicknesses. Joints for electrical and thermal characterisation were selected based on the satisfactory mechanical strength determined from the T-peel tests. Electrical contact resistance and corresponding temperature rise at the joints were compared for different tab-to-busbar joints by passing current through the joints. The average resistance or temperature increase from the 0.3 mm Al tab was 0.6 times higher than the 0.3 mm Cu[Ni] tab, irrespective of busbar selection

Electro-thermo-mechanical behaviours of laser joints for electric vehicle battery interconnects

An automotive battery pack used in electric vehicle (EV) comprises several hundred to a few thousand of individual Lithium-ion (Li-ion) cells when cylindrical cells are used to build the battery pack. These cells are connected in series and/or parallel to deliver the required power and capacity to achieve the designed vehicle driving range. This triggers the need for suitable joining methods capable of providing mechanical strength together with the required electrical and thermal performances. A range of joining techniques are currently employed to connect large numbers of cells, and of these, laser welding is estimated to be the one of most efficient methods. Typically, the cylindrical cell casing is made of electrical grade steel which is electrically connected to copper tabs representing the cylindrical cell terminal to tab interconnect within the battery pack assembly. This study focuses on identifying the effect of laser welding process parameters on the mechanical, electrical and thermal responses of the laser welded joints produced using a 150 W Quasi-CW IR laser. Mechanical strength is assessed by evaluating the lap shear strength of the joint whereas the electrical and thermal responses are captured using voltage sensors and a thermal imaging camera respectively. It was observed that mechanical strength of the joint is highly correlated with electrical resistance and corresponding temperature raise at the joint. Furthermore, the optical micrographs reveal the microstructural characteristics of the joint

Evaluation of key geometrical and mechanical properties for remote laser welded AC-170PX aluminium joints

Use of lightweight materials to produce automotive body structures is one of the key trends adopted by automotive manufacturers to minimise emission of greenhouse gases, and subsequently, reduction of fuel consumption. Aluminium alloys are one of the promising lightweight materials which are increasingly used for automotive body-in-white structures. Such applications demand both efficient and effective joining/welding methods to produce repeatable, durable and strong joints without significant alteration of material properties. Remote laser welding (RLW) is an emerging joining technology and increasingly being used to produce lightweight joints as it satisfies the demand for high production throughput at low cost. This paper investigates the effects of process parameters when seam tracking remote laser welding is used to create an autogenous fillet edge weld of automotive grade aluminum alloy (AC-170PX) in lap configuration without shielding gas. The effects of laser power and welding speed on the key geometric features are reported together with details of the weld microstructure. Joint strength is evaluated by performing a lap shear test. It is found that the laser power and welding speed have dominant influence on key geometric features and subsequently on the lap shear strength. Relatively larger grain size in the fusion zone reduces the microhardness by up to 20% in comparison with the base material