Studies on the ecology & behaviour of British shrews

PhDAll five species of British shrews (Sorex araneus, S. minut, Neomys fodiens, Crocidura suaveolens and C. russula were studied with the emphasis being placed on the commoner species. The population dynamics and seasonal fluctuations in numbers of S. araneus and S. ininutus were investigated. A seasonal cycle of captures of S. araneus was demonstrated, with peaks of occurrence in summer, low numbers in winter and a re-emergence of high numbers in spring. Closer study indicated a great mortality of old adults and. juveniles in autumn which commenced before the onset of harsh weather conditions, but overwintering survival of remaining shrews was high. Home ranges and activity of S. araneus appeared to be reduced in winttc. A study of food availability aid diet of S. araneus, S. ininutus and N. fodiens showed major prey items to include adult coleopterans, insect larvae, araneids, isopods and lumbrlcids which occurred In large numbers throughout the year; no decrease in numbers or biomass of prey was found to account for the decrease in body weight of shrews in autumn and winter aid their apparent decline in numbers. Food consumption of shrews ranged from 4 of the body weight daily for C. suaveolens to i6 for S. minutus, but was not directly related to body weight within a species. Conaurnption by S. araneus was reduced at low temperatures. Studies of fat storage by wild. shrews showed no great seasonal differences, although captive shrews ac.cumirulated fat in warm conditions. Studies on the foraging and burrowing behaviour of S. araneu3 showed that they are generally poor burrowers but that they are able to recover insect pupae buried up to 120mm deep in soil. It is sugges ted. that overwintering shrews adopt a more subterranean existence, spending longer periods in the nest to conserve body heat aid less time foraging. Mortality due to increased. predation in autumn, aid reduced activity on the ground surface probably account for low numbers of captures in winter.Mary Scharlib Awar

Evaluation of different wind fields for the investigation of the dynamic response of offshore wind turbines

As the size of offshore wind turbines increases, a realistic representation of the spatiotemporal distribution of the incident wind field becomes crucial for modeling the dynamic response of the turbine. The International Electrotechnical Commission (IEC) standard for wind turbine design recommends two turbulence models for simulations of the incident wind field, the Mann spectral tensor model, and the Kaimal spectral and exponential coherence model. In particular, for floating wind turbines, these standard models are challenged by more sophisticated ones. The characteristics of the wind field depend on the stability conditions of the atmosphere, which neither of the standard turbulence models account for. The spatial and temporal distribution of the turbulence, represented by coherence, is not modeled consistently by the two standard models. In this study, the Mann spectral tensor model and the Kaimal spectral and exponential coherence model are compared with wind fields constructed from offshore measurements and obtained from large‐eddy simulations. Cross sections and durations relevant for offshore wind turbine design are considered. Coherent structures from the different simulators are studied across various stability conditions and wind speeds through coherence and proper orthogonal decomposition mode plots. As expected, the standard models represent neutral stratification better than they do stable and unstable. Depending upon the method used for generating the wind field, significant differences in the spatial and temporal distribution of coherence are found. Consequently, the computed structural design loads on a wind turbine are expected to vary significantly depending upon the employed turbulence model. The knowledge gained in this study will be used in future studies to quantify the effect of various turbulence models on the dynamic response of large offshore wind turbines.publishedVersio

Airfoil data sensitivity analysis for actuator disc simulations used in wind turbine applications

To analyse the sensitivity of blade geometry and airfoil characteristics on the prediction of performance characteristics of wind farms, large-eddy simulations using an actuator disc (ACD) method are performed for three different blade/airfoil configurations. The aim of the study is to determine how the mean characteristics of wake flow, mean power production and thrust depend on the choice of airfoil data and blade geometry. In order to simulate realistic conditions, pre-generated turbulence and wind shear are imposed in the computational domain. Using three different turbulence intensities and varying the spacing between the turbines, the flow around 4-8 aligned turbines is simulated. The analysis is based on normalized mean streamwise velocity, turbulence intensity, relative mean power production and thrust. From the computations it can be concluded that the actual airfoil characteristics and blade geometry only are of importance at very low inflow turbulence. At realistic turbulence conditions for an atmospheric boundary layer the specific blade characteristics play an minor role on power performance and the resulting wake characteristics. The results therefore give a hint that the choice of airfoil data in ACD simulations is not crucial if the intention of the simulations is to compute mean wake characteristics using a turbulent inflow

Floating Platform Effects on Power Generation in Spar and Semisubmersible Wind Turbines

The design and financing of commercial-scale floating offshore wind projects require a better understanding of how power generation differs between newer floating turbines and well-established fixed-bottom turbines. In floating turbines, platform mobility causes additional rotor motion that can change the time-averaged power generation. In this work, OpenFAST simulations examine the power generated by the National Renewable Energy Laboratory\u27s 5-MW reference turbine mounted on the OC3-UMaine spar and OC4-DeepCWind semisubmersible floating platforms, subjected to extreme irregular waves and below-rated turbulent inflow wind from large-eddy simulations of a neutral atmospheric boundary layer. For these below-rated conditions, average power generation in floating turbines is most affected by two types of turbine displacements: an average rotor pitch angle that reduces power, caused by platform pitch; and rotor motion upwind-downwind that increases power, caused by platform surge and pitch. The relative balance between these two effects determines whether a floating platform causes power gains or losses compared to a fixed-bottom turbine; for example, the spar creates modest (3.1%-4.5%) power gains, whereas the semisubmersible creates insignificant (0.1%-0.2%) power gains for the simulated conditions. Furthermore, platform surge and pitch motions must be analyzed concurrently to fully capture power generation in floating turbines, which is not yet universal practice. Finally, a simple analytical model for predicting average power in floating turbines under below-rated wind speeds is proposed, incorporating effects from both the time-averaged pitch displacement and the dynamic upwind-downwind displacements