The trade-off between tidal-turbine array yield and impact on flow: A multi-objective optimisation problem

Abstract This paper introduces a new approach for investigating trade-offs between different societal objectives in the design of tidal-turbine arrays. This method is demonstrated through the trade-off between the yield of an array, and the extent to which that array alters the flow. This is posed as a multi-objective optimisation problem, and the problem is investigated using the array layout optimisation tool OpenTidalFarm. Motivated by environmental concerns, OpenTidalFarm is adapted to not only maximise array yield but also to minimise the effect of the array upon the hydrodynamics of the region, specifically the flow velocity. A linear scalarisation of the multi-objective optimisation problem is solved for a series of different weightings of the two conflicting objectives. Two idealised test scenarios are evaluated and in each case a set of Pareto solutions is found. These arrays are assessed for the power they generate and the severity of change they cause in the flow velocity. These analyses allow for the identification of trade-offs between these two objectives, while the methods proposed can similarly be applied to the two key societal objectives of energy production and conservation, thus providing information that could be valuable to stakeholders and policymakers when making decisions on array design

The application of multi-scale and adaptive simulation methods to tidal energy systems

Generating energy from clean renewable sources is clearly attractive for a number reasons. In stark contrast to other further developed and exploited resources such as wind, tidal-based energy conversion has the crucial benefit of being entirely predictable. However, a new tidal-energy-based industry will only flourish if the development of large installations, such as turbine arrays comprising 100s of individual devices, can be shown to be both economically viable and to have a minimal impact on the environment. This new industry is currently in its early stages where no major projects have yet been developed, although many have been approved and are in various stages of planning. Sophisticated numerical simulation methods are vitally important to support resource analysis, array design, and the optimisation of financial profits while minimising environmental impacts. Since the installation of large numbers of energy converters can fundamentally change the nature of the resource, fully-coupled simulations of the large-scale resource including the presence of arrays of turbines is required. In addition, individual turbines need to be either resolved or parameterised in order to accurately represent the turbulent turbine-wake-turbine interactions which are crucial for the purpose of individual turbine micro-siting as a component of array design analysis and optimisation. This results in the requirement for simulations that resolve spatial scales in the horizontal greater than 100 km to represent the tidal resource, and down to sub-metre scale to resolve turbines and their turbulent wakes: i.e. scales varying by at least five orders of magnitude. Also, depth-averaged dynamics can be considered in the far-field, whilst fully three-dimensional dynamics should be considered at the smallest scales. This is therefore a truly multi-scale, timely and challenging engineering problem which requires the design of highly efficient numerical techniques, especially given that multiple flow calculations will be required as part of array optimisation strategies. In this presentation we will describe the approaches we have taken to tackle this multi-scale problem, including the use of unstructured mesh generation, anisotropic mesh adaptivity, and gradient-based optimisation algorithms. Applications of the developed technology to idealised as well as real-world case studies will be presented. Future topics such as the inclusion of uncertainty, and multi-rate time-stepping may also be discussed

Nurses' attitudes, behaviours and perceived barriers towards pressure ulcer prevention

Background. Pressure ulcers are not a plague of modern man; they have been known to exist since ancient Egyptian times. However, despite the increasing expenditure on pressure ulcer prevention, pressure ulcers remain a major health care problem. Although nurses do not have the sole responsibility for pressure ulcer prevention, nurses have a unique opportunity to have a significant impact on this problem. Aims and objectives. The specific aims of the study were to identify: • Staff nurses’ attitudes towards pressure ulcer prevention. • The behaviour of staff nurses’ in relation to pressure ulcer prevention. • Staff nurses’ perceived barriers towards pressure ulcer prevention. Design. A cross-sectional survey method was used. Methods. A randomly selected sample of staff nurses (n = 300) working in an acute care setting in an urban location was invited to participate. Data were collected using a prepiloted questionnaire. Data analysis was carried out using SPSS version 10 and SPSS Text Smart version 1.1. Results. The nurses surveyed demonstrated a positive attitude towards pressure ulcer prevention. However, prevention practices were demonstrated to be haphazard and erratic and were negatively affected by lack of time and staff. These barriers prevented the nurses’ positive attitude from being reflected into effective clinical practice. Education, although poorly accessed, or made available, was rarely cited as impeding practice in this area. Conclusion. This study suggests that positive attitudes are not enough to ensure that practice change takes place, reinforcing the complex nature of behavioural change. Implementation strategies should introduce ways in which key staff can be empowered to overcome barriers to change. Relevance to clinical practice. This study provides a unique exploration of Irish nurses’ attitudes, behaviours and perceived barriers towards pressure ulcer prevention, thereby contributing to the body of knowledge on this subject. As tissue viability is a new and emerging speciality, this information will contribute to evidence based practice in this area of patient care and will form the basis for the development of an educational strategy for pressure ulcer prevention and management