The downstream wake response of marine current energy converters operating in shallow tidal flows

This paper presents findings from an experimental study investigating the downstream wake response from marine current energy convertors operating in various degrees of vertical flow constraint. The paper investigates deep vertically unconstrained sites, mid-depth sites and there is a particular emphasis on shallow tidal stream sites. Shallow tidal resources could be utilised for the deployment of first generation farms. The nature of the downstream wake flow will be a critical factor when determining the farm layout and the wake length is heavily influenced by the flow depth or ratio of rotor diameter to flow depth. A porous actuator disk is used to model the marine current energy convertor and an Acoustic Doppler Velocimeter is used to map the downstream wake. Linear scaling of length ratios suggests mid depth sites of 30-50m will produce the shortest wake lengths and for deeper and shallower sites the wake length increases. It is hoped that these relationships between vertical flow constraint and wake length will help with the layout design of tidal stream farm

Turbulence and its effects on the thrust and wake of a porous disc rotor simulator

Marine current turbines are still in their infancy with many devices at the development stage. Studies are often carried out using small scale laboratory experiments in flumes, towing tanks and numerical simulations to investigate the wakes and performance of scale marine current turbines. However, the characteristics of the inflow turbulence used in such studies is often not fully considered. Tidal flows are highly turbulent with a broad range of eddy sizes and intensities. So differences are expected when predictions of array energy yields are made from towing tanks studies with zero turbulence. This work considers the effects of turbulent eddy size on the thrust and wake behind a porous disc rotor simulator commonly used to represent marine current turbines in small scale experiments. The results show an increase in thrust coefficient with increasing length scale and a corresponding reduction in velocity deficit in the wake. These findings have implications to array special planning and hence energy yields

Student project allocation using integer programming

The allocation of projects to students is a generic problem in many universities within the U.K. and elsewhere, not only in engineering but also in various other disciplines. This paper defines the student project allocation problem explicitly by an objective function and a number of constraints. Two integer program models are presented, the first of which is a dynamic program. A general purpose solver is used to solve the models, and the input files are included in the Appendix. The models are computationally efficient and easily solved on a PC. Important issues in interpreting the model outputs are highlighted. As with any optimization problem it is possible for constraints to be too tight to permit any feasible solution. Application of the models is demonstrated by using data from the Department of Civil and Environmental Engineering, University of Southampton, for the academic year 2001-2002. The model has been used successfully to allocate Individual Project and Group Project to students and is likely to become the defacto method of allocation of projects in the future. This paper demonstrates how operations research techniques used widely in optimizing use of resources can be applied in education

The sensitivity of actuator-disc RANS simulations to turbulence length scale assumptions

It has previously been shown that ambient turbulence affects the results from computational fluid dynamics (CFD) models when using an actuator disc to simulate marine current turbines. The turbulence parameters are often estimated using an empirical equation that is dependent on a turbulence length scale. In most literature this length scale is commonly highlighted as the authors ‘best guess’ with little scientific reasoning. The work presented here investigates the effects of using different length scales on the development of a flow in a circulating water channel. The results showed that the best agreement is achieved with a length scale of one third the channel depth. The obtained turbulence parameters were then used with an actuator disc model. Agreement with experimental data was initially poor as the velocity deficit was severely under predicted. The addition of a turbulence source at the disc improved the agreement with experimental data significantly. It was found that the length scale of the disc turbulence should be the diameter of the holes used on the porous discs for experiments. However, there were still discrepancies between the experimental and model turbulence intensities. A possible cause of this may be that the turbulence intensity added at the disc was under predicted. Further work is needed to establish if better agreement can be achieved by increasing the turbulence at the disc

Field study on thermal comfort in a UK primary school

This paper presents findings from a field survey in a naturally ventilated primary school building in Southampton, UK. The study included thermal comfort surveys and simultaneous measurements of indoor environmental variables. Approximately 230 pupils aged 7-11 in all 8 classrooms of the school were surveyed in repeated survey runs outside the heating season, from April to July 2011. In total 1314 responses were gathered. The survey involved questions on the thermal sensation and preference of the pupils. This paper investigates the children’s thermal sensation trends, their perception of overall comfort and tiredness. Furthermore, it compares the survey results to predictions achieved with current adult-based comfort standards, namely ISO 7730 and EN 15251. The results suggest that children have a different thermal perception than adults. Possible explanations are discussed in relation to the particularities and specific character of school environments

Location, location, location: domestic small-scale wind field trial report

The Energy Saving Trust’s work in small-scale domestic wind dates back to 2005. A report compiled for the DTI1 concluded that ‘with the appropriate support, small wind could supply four per cent of the UK electricity requirement and reduce domestic CO2 emissions by six per cent’. Subsequently, our reports ‘Microwind Electricity Generation in the UK Residential Sector’ and ‘Generating the Future’, both completed in 2007, provided further predictions of the potential market for small wind turbines in the UK by 2050. These projections were based on modelled data and were produced before actual performance data from small-scale wind turbines was widely available. As such, it was difficult at the time to determine the accuracy of such future projections. Since these reports were published, the UK market for domestic small-scale wind has developed rapidly