pinecone/core-2020-05-10-deduplication huggingface dataset:
Cost performance and risk in the construction of offshore and onshore wind farms

This article investigates the risk of cost overruns and underruns occurring in the construction of 51 onshore and offshore wind farms commissioned between 2000 and 2015 in 13 countries. In total, these projects required about $39 billion in investment and reached about 11 GW of installed capacity. We use this original dataset to test six hypotheses about construction cost overruns related to (i) technological learning, (ii) fiscal control, (iii) economies of scale, (iv) configuration, (v) regulation and markets and (vi) manufacturing experience. We find that across the entire dataset, the mean cost escalation per project is 6.5% or about $63 million per windfarm, although 20 projects within the sample (39%) did not exhibit cost overruns. The majority of onshore wind farms exhibit cost underruns while for offshore wind farms the results have a larger spread. Interestingly, no significant relationship exists between the size (in total MWor per individual turbine capacity) of a windfarm and the severity of a cost overrun. Nonetheless, there is an indication that the risk increases for larger wind farms at greater distances offshore using new types of turbines and foundations. Overall, the mean cost escalation for onshore projects is 1.7% and 9.6% for offshore projects, amounts much lower than those for other energy infrastructure
Reliability based design of fluid power pitch systems for wind turbines

This paper presents a qualitative design tool for evaluation of the risk for fluid power pitch systems. The design tool is developed with special attention to industry standard failure analysis methods and is aimed at the early phase of system design. Firstly, the concept of Fault Tree Analysis is used for systematic description of fault propagation linking failure modes to system effects. The methodology is conducted solely on a circuit diagram and functional behavior. The Failure Mode and Effects Criticality Analysis is subsequently employed to determine the failure mode risk via the Risk Priority Number. The Failure Mode and Effect Criticality Analysis is based on past research concerning failure analysis of wind turbine drive trains. Guidelines are given to select the severity, occurrence and detection score that make up the risk priority number. The usability of the method is shown in a case study of a fluid power pitch system applied to wind turbines. The results show a good agreement to recent field failure data for offshore turbines where the dominating failure modes are related to valves, accumulators and leakage. The results are further used for making design improvements to lower the overall risk of the pitch system
Statistical learning for wind power : a modeling and stability study
  towards forecasting

We focus on wind power modeling using machine learning techniques. We show on
real data provided by the wind energy company Ma{\"i}a Eolis, that parametric
models, even following closely the physical equation relating wind production
to wind speed are outperformed by intelligent learning algorithms. In
particular, the CART-Bagging algorithm gives very stable and promising results.
Besides, as a step towards forecast, we quantify the impact of using
deteriorated wind measures on the performances. We show also on this
application that the default methodology to select a subset of predictors
provided in the standard random forest package can be refined, especially when
there exists among the predictors one variable which has a major impact
Modeling space-time correlations of velocity fluctuations in wind farms

An analytical model for the streamwise velocity space-time correlations in
turbulent flows is derived and applied to the special case of velocity
fluctuations in large wind farms. The model is based on the Kraichnan-Tennekes
random sweeping hypothesis, capturing the decorrelation in time while including
a mean wind velocity in the streamwise direction. In the resulting model, the
streamwise velocity space-time correlation is expressed as a convolution of the
pure space correlation with an analytical temporal decorrelation kernel. Hence,
the spatio-temporal structure of velocity fluctuations in wind farms can be
derived from the spatial correlations only. We then explore the applicability
of the model to predict spatio-temporal correlations in turbulent flows in wind
farms. Comparisons of the model with data from a large eddy simulation of flow
in a large, spatially periodic wind farm are performed, where needed model
parameters such as spatial and temporal integral scales and spatial
correlations are determined from the large eddy simulation. Good agreement is
obtained between the model and large eddy simulation data showing that spatial
data may be used to model the full temporal structure of fluctuations in wind
farms.Comment: Submitted to Wind Energ
Improved Very-short-term Wind Forecasting using Atmospheric
  Classification

We present a regime-switching vector-autoregressive method for
very-short-term wind speed forecasting at multiple locations with regimes based
on large-scale meteorological phenomena. Statistical methods short-term wind
forecasting out-perform numerical weather prediction for forecast horizons up
to a few hours, and the spatio-temporal interdependency between geographically
dispersed locations may be exploited to improve forecast skill. Here we show
that conditioning spatio-temporal interdependency on `atmospheric modes' can
further improve forecast performance. The modes are defined from the
atmospheric classification of wind and pressure fields at the surface level,
and the geopotential height field at the 500hPa level. The data fields are
extracted from the MERRA-2 reanalysis dataset with an hourly temporal
resolution over the UK, atmospheric patterns are classified using
self-organising maps and then clustered to optimise forecast performance. In a
case study based on 6 years of measurements from 23 weather stations in the UK,
a set of three atmospheric modes are found to be optimal for forecast
performance. The skill in the one- to six-hour-ahead forecasts is improved at
all sites compared to persistence and competitive benchmarks. Across the 23
test sites, one-hour-ahead root mean squared error is reduced by between 0.3%
and 4.1% compared to the best performing benchmark, and by and average of 1.6%
over all sites; the six-hour-ahead accuracy is improved by an average of 3.1%
Estimating the potential yield of small building-mounted wind turbines

This is the peer reviewed version of the following article: HEATH, M.A., WALSHE, J.D. and WATSON, S.J., 2007. Estimating the potential yield of small building-mounted wind turbines. Wind Energy, 10 (3), pp. 271 - 287, which has been published in final form at http://dx.doi.org/10.1002/we.222. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The wind profile in the urban boundary layer is described as following a logarithmic curve above the mean building height and an exponential curve below it. By considering the urban landscape to be an array of cubes, a method is described for calculating the surface roughness length and displacement height of this profile. Firstly, a computational fluid dynamics (CFD) model employing a k-ϵ turbulence model is used to simulate the flow around a cube. The results of this simulation are compared with wind tunnel measurements in order to validate the code. Then, the CFD model is used to simulate the wind flow around a simple pitched-roof building, using a semi-logarithmic inflow profile. An array of similar pitched-roof houses is modelled using CFD to determine the flow characteristics within an urban area. Mean wind speeds at potential turbine mounting points are studied, and optimum mounting points are identified for different prevailing wind directions. A methodology is proposed for estimating the energy yield of a building-mounted turbine from simple information such as wind atlas wind speed and building density. The energy yield of a small turbine on a hypothetical house in west London is estimated. The energy yield is shown to be very low, particularly if the turbine is mounted below rooftop height. It should be stressed that the complexity of modelling such urban environments using such a computational model has limitations and results can only be considered approximate, but nonetheless, gives an indication of expected yields within the built environment
Mesh-adaptive simulations of horizontal-axis turbine arrays using the
  actuator line method

Numerical models of the flow and wakes due to turbines operating within a
real-scale offshore wind farm can lead to a prohibitively large computational
cost, particularly when considering blade-resolved simulations. With the
introduction of turbine parametrizations such as the actuator disk (AD) or the
actuator line (AL) models, this problem has been partially addressed, yet the
computational cost associated with these simulations remains high. In this
work, we present an implementation and validation of an AL model within the
mesh-adaptive three-dimensional fluid dynamics solver, Fluidity, under a
unsteady Reynolds-averaged Navier-Stokes based turbulence modelling approach. A
key feature of this implementation is the use of mesh optimization techniques,
which allow for the automatic refinement or coarsening of the mesh locally
according to the resolution needed by the fluid flow solver. The model is first
validated against experimental data from wind tunnel tests. Finally, we
demonstrate the benefits of mesh-adaptivity by considering flow past the
Lillgrund offshore wind farm
HAWT near-wake aerodynamics, part I : axial flow conditions

An improved physical understanding of the rotor aerodynamics of a horizontal axis wind\ud
\ud
turbine (HAWT) is required to reduce the uncertainties associated with today’s design\ud
\ud
codes. Wind tunnel experiments contribute to increased knowledge and enable valida-\ud
tion and construction of models. The present study focuses on the near-wake of a model\ud
\ud
HAWT in both axial and yawed flow conditions. At three downstream planes parallel to the\ud
\ud
rotor plane, single-sensor hot-film traverses are made. The phase-locked unsteady three-\ud
dimensional flow velocity vector is determined by a novel data reduction method. A series\ud
\ud
of two papers discusses the near-wake aerodynamics of a model HAWT. The main goals\ud
\ud
are to obtain a detailed understanding of the near-wake development and to arrive at\ud
\ud
a base for model construction and validation. The first paper presents the experimental\ud
\ud
setup, data reduction and the results for the baseline case (axial flow conditions). In the\ud
\ud
second paper, the results for the yawed flow cases are presented and the effect of yaw\ud
\ud
misalignment on the near-wake development is discussed. Copyrightpeer-reviewe
Estimating the angle of attack from blade pressure measurements on the National Renewable Energy Laboratory phase VI rotor using a free wake vortex model : yawed conditions

Wind turbine design codes for calculating blade loads are usually based on a blade element momentum (BEM) approach. Since wind turbine rotors often operate in off-design conditions, such as yawed flow, several engineering methods have been developed to take into account such conditions. An essential feature of a BEM code is the coupling of local blade element loads with an external (induced) velocity field determined with momentum theory through the angle of attack. Local blade loads follow directly from blade pressure measurements as performed in the National Renewable Energy Laboratory (NREL) phase IV campaign, but corresponding angles of attack cannot (on principle) be measured. By developing a free wake vortex method using measured local blade loads, time-dependent angle of attack and induced velocity distributions are reconstructed. In a previous paper, a method was described for deriving such distributions in conjunction with blade pressure measurements for the NREL phase VI wind turbine in axial (non-yawed) conditions. In this paper, the same method is applied to investigate yawed conditions on the same turbine. The study considered different operating conditions in yaw in both attached and separated flows over the blades. The derived free wake geometry solutions are used to determine induced velocity distributions at the rotor blade. These are then used to determine the local (azimuth time dependent) angle of attack, as well as the corresponding lift and drag for each blade section. The derived results are helpful to develop better engineering models for wind turbine design codes.peer-reviewe
Simulation of wind turbine wake interaction using the vorticity transport model

The aerodynamic interactions that can occur within a wind farm can result in the constituent turbines generating a lower power output than would be possible if each of the turbines were operated in isolation. Tightening of the constraints on the siting of wind farms is likely to increase the scale of the problem in the future. The aerodynamic performance of turbine rotors and the mechanisms that couple the fluid dynamics of multiple rotors can be most readily understood by simplifying the problem and considering the interaction between only two rotors. The aerodynamic interaction between two rotors in both co-axial and offset configurations has been simulated using the Vorticity Transport Model. The aerodynamic interaction is a function of the tip speed ratio, and both the streamwise and crosswind separation between the rotors. The simulations show that the momentum deficit at a turbine operating within the wake developed by the rotor of a second turbine is governed by the development of instabilities within the wake of the upwind rotor, and the ensuing structure of the wake as it impinges on the downwind rotor. If the wind farm configuration or wind conditions are such that a turbine rotor is subject to partial impingement by the wake produced by an upstream turbine, then significant unsteadiness in the aerodynamic loading on the rotor blades of the downwind turbine can result, and this unsteadiness can have considerable implications for the fatigue life of the blade structure and rotor hub
Simulating the aerodynamic performance and wake dynamics of a vertical-axis wind turbine

The accurate prediction of the aerodynamics and performance of vertical-axis wind turbines is essential if their design is to be improved but poses a signifi cant challenge to numerical simulation tools. The cyclic motion of the blades induces large variations in the angle of attack of the blades that can manifest as dynamic stall. In addition, predicting the interaction between the blades and the wake developed by the rotor requires a high-fi delity representation of the vortical structures within the fl ow fi eld in which the turbine operates. The aerodynamic performance and wake dynamics of a Darrieus-type vertical-axis wind turbine consisting of two straight blades is simulated using Brown’s Vorticity Transport Model. The predicted variation with azimuth of the normal and tangential force on the turbine blades compares well with experimental measurements. The interaction between the blades and the vortices that are shed and trailed in previous revolutions of the turbine is shown to have a signifi cant effect on the distribution of aerodynamic loading on the blades. Furthermore, it is suggested that the disagreement between experimental and numerical data that has been presented in previous studies arises because the blade–vortex interactions on the rotor were not modelled with sufficient fidelity
Modelling the aerodynamics of vertical-axis wind turbines in unsteady wind conditions

Most numerical and experimental studies of the performance of vertical-axis wind turbines have been conducted with the rotors in steady, and thus somewhat artificial, wind conditions - with the result that turbine aerodynamics, under varying wind conditions, are still poorly understood. The Vorticity Transport Model has been used to investigate the aerodynamic performance and wake dynamics, both in steady and unsteady wind conditions, of three different vertical-axis wind turbines: one with a straight-bladed configuration, another with a curved-bladed configuration and another with a helically twisted configuration. The turbines with non-twisted blades are shown to be somewhat less efficient than the turbine with helically twisted blades when the rotors are operated at constant rotational speed in unsteady wind conditions. In steady wind conditions, the power coefficients that are produced by both the straight- and the curved-bladed turbines vary considerably within one rotor revolution because of the continuously varying angle of attack on the blades and, thus, the inherent unsteadiness in the blade aerodynamic loading. These variations are much larger, and thus far more significant, than those that are induced by the unsteadiness in the wind conditions
A low-cost experiment for determining raindrop size distribution

Precipitation is usually classified as convec-\ud
tive or stratiform. Convective precipitation\ud
is normally associated with cumulus and\ud
cumulonimbus clouds within which a sig-\ud
nificant vertical velocity keeps the cloud\ud
droplets inside the cloud, enhancing their\ud
growth until the vertical currents are not\ud
able to counteract the force of gravity any\ud
longer and precipitation is produced.\ud
Stratiform precipitation is produced mainly\ud
by nimbostratus and sometimes by strato-\ud
cumulus/altocumulus. In these clouds the\ud
vertical velocity is lower than inside the con-\ud
vective clouds, and it cannot prevent cloud\ud
droplets from falling earlier. The result is a\ud
smaller raindrop in these clouds (Houze,\ud
1993).Peer ReviewedPostprint (published version
Geomagnetic observatories: monitoring the Earth’s magnetic and space weather environment

Geomagnetism research provides insight into the Earth’s properties and processes, from the core out to space. For this reason continuous geomagnetic field observations have been carried out in the UK for more than 170 years. Geomagnetism also has diverse applications, in navigation, maps, even smart phone apps, and in the monitoring and prediction of space weather impacts on technology. Modern instruments, together with digital sampling, real-time data processing and product dissemination, support global space weather monitoring and modelling activities. In this review we describe the role of the UK geomagnetic observatory network in Earth and space weather science and applications
The influence of ocean variations on the climate of Ireland

\ud
\ud
The influence of the ocean circulation on the climate of Ireland is more subtle than it first appears. Temperatures in Ireland are warmer than similar Pacific maritime climates. It is heat - carried primarily in the Atlantic overturning circulation - released over the Atlantic that provides this additional warmth. We investigate variations in Irish climate using long-term station-based time series. The Atlantic multidecadal oscillation (AMO) explains over 90% of the pronounced decadal temperature and summer precipitation variation. Understanding the impact of these ocean variations when interpreting long climate records, particularly in the context of a changing climate, is crucial
Long-term observations of increasing snow cover in the western Cairngorms

As part of the UK Environmental Change Network (ECN) long-term monitoring, an automatic repeat-photography camera was installed to record changes in landscape phenology in the Allt a'Mharcaidh catchment, Cairngorms National Park, Scotland. For 13 consecutive winters between 2002 and 2015, the date for the onset of continuous winter snow cover, and subsequent melt, was recorded on slopes of north and north-easterly aspect at altitudes between 450m and 1111m amsl. Results show that the period of time during which snow is continuously present in the catchment has increased significantly by 81 (±21.01) days over the 13-year period, and that this is largely driven by a significantly later melt date, rather than earlier onset of winter snow cover
Meteorological effects of the 20 March 2015 solar eclipse over the United Kingdom

On 20 March 2015 a deep partial eclipse of the Sun, the most significant since the 11 August 1999 total solar eclipse, occurred over the UK. No comparably deep UK solar eclipse will occur until 2026 (e.g. Williams 1996, Espenak 1987). It is well known that solar eclipses cause transient meteorological effects, the most obvious of which is a drop in temperature, but – because total or major partial solar eclipses are fairly rare from any one point on the Earth’s surface and many areas are not well instrumented - there are relatively few systematic studies covering a wide region. The UK has one of the densest networks of weather stations compared with many other parts of the world. This applies to both amateur and professional station networks. Therefore the 2015 event was a unique opportunity to gather and analyse meteorological data. This has already been done for the main Met Office network of Meteorological Monitoring System sites (Hanna et al. 2016, Clark 2016), so here I present the results of a similar exercise based on amateur weather stations. I compare the meteorological effects of the 2015 eclipse over the UK with the 11 August 1999 eclipse for which I carried out a previous study (Hanna 2000)
The winter 2015/2016 floods in the UK: a hydrological appraisal

The flooding in winter 2015/2016 was one of the most extraordinary hydrological episodes witnessed in the UK in recent decades. The winter was defined by a succession of severe storms, bringing extreme rainfall and associated widespread flooding across northern and western regions. For the UK, December 2015 was the wettest month (for any calendar month) and it was the second wettest winter (December–February) in a series from 1910, while a number of new records were established for rainfall accumulations over shorter timescales. The hydrological response was remarkable; period of record maximum peak flows were established across northern areas of the UK, and the high flow response was notable in terms of its spatial extent, duration and frequency. The flooding had severe impacts on properties, infrastructure and livelihoods. Inevitably, the flooding was at the forefront of public, political and media attention through much of the winter and, occurring only two years after the major flooding of 2013/2014, led to a significant debate around flood management in a warming world
Fog at Abu Dhabi International Airport

Fog that reduces visibility to the point
 where aircraft have to divert to another airport
 is not uncommon at Abu Dhabi
 International Airport (ADIA) in the United
 Arab Emirates (UAE). Over the
 period 1982 to 2003, the average annual
 frequency of fog at ADIA was 38 nights a
 year, the highest being 56 in 2000 and the
 lowest 23 in 1992. Fog is defined as
 occurring when water vapour in the
 atmosphere condenses into minute water
 droplets and the horizontal visibility falls
 below 1000 m (UK Meteorological Office
 (UKMO), 1991).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1477-8696hb2016Geography, Geoinformatics and Meteorolog