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This work presents an investigation of the aeroelastic effects occurring on the IEA 15-MW reference wind turbine in a turbulent atmospheric boundary layer. Large Eddy simulation is carried out using an actuator line method coupled to the finite element beam solver BeamDyn. The results show that the blades experience significant displacements, leading to an important variation of the loads along the blade span. The turbulence also interacts with the blades natural frequencies, resulting in a variation of the spectra of the various loads. The impact of the flexibility is also evaluated on the wake by comparing the undeformed configuration with a statically and dynamically deformed rotor. It appears that the mean deformation plays an important role in the wake development due to changes in the load distribution, but that the dynamic effects have minimal impact on the wake behavior.

The current trend of wind turbine upscaling has led to the use of long and slender blades prone to large structural deformations. In the present study, the impact of the aeroelastic effects is assessed for the NREL-5MW wind turbine in a turbulent wind. To this end, an actuator curve method coupled to a one-dimensional finite-element structural solver is implemented in a fourth-order finite difference code that can perform large eddy simulation (LES) of realistic winds. The approach is computationally affordable compared to blade-resolved simulations and hence long time series can be computed. This, combined to the ability of the LES to capture the relevant scales of the unsteadiness wind, leads to a better estimation of the fluctuating loads and power of the turbine. The results are here shown for one and two wind turbines operating in a neutrally stable atmospheric boundary layer. It appears that the blade mostly deforms according to its first bending mode. The rotation of the blade in the sheared atmospheric flow is responsible for large amplitude deformations, but the turbulence also plays a role in causing deformations at higher frequencies with a smaller amplitude. The azimuthal distributions of loads and of power are significantly affected when the aeroelasticity is considered.

Summary Background The global health community is devoting considerable attention to adolescents and young people, but risk of death in this population is poorly measured. We aimed to reconstruct global, regional, and national mortality trends for youths aged 15–24 years between 1990 and 2019. Methods In this systematic analysis, we used all publicly available data on mortality in the age group 15–24 years for 195 countries, as compiled by the UN Inter-agency Group for Child Mortality Estimation. We used nationally representative vital registration data, estimated the completeness of death registration, and extracted mortality rates from surveys with sibling histories, household deaths reported in censuses, and sample registration systems. We used a Bayesian B-spline bias-reduction model to generate trends in 10q15, the probability that an adolescent aged 15 years would die before reaching age 25 years. This model treats observations of the 10q15 probability as the product of the actual risk of death and an error multiplier that varies depending on the data source. The main outcome that we assessed was the levels of and trends in youth mortality and the global and regional mortality rates from 1990 to 2019. Findings Globally, the probability of an individual dying between age 15 years and 24 years was 11·2 deaths (90% uncertainty interval [UI] 10·7–12·5) per 1000 youths aged 15 in 2019, which is about 2·5 times less than infant mortality (28·2 deaths [27·2–30·0] by age 1 year per 1000 live births) but is higher than the risk of dying from age 1 to 5 (9·7 deaths [9·1–11·1] per 1000 children aged 1 year). The probability of dying between age 15 years and 24 years declined by 1·4% per year (90% UI 1·1–1·8) between 1990 and 2019, from 17·1 deaths (16·5–18·9) per 1000 in 1990; by contrast with this total decrease of 34% (27–41), under-5 mortality declined by 59% (56–61) in this period. The annual number of deaths declined from 1·7 million (90% UI 1·7–1·9) in 1990 to 1·4 million (1·3–1·5) in 2019. In sub-Saharan Africa, the number of deaths increased by 20·8% from 1990 to 2019. Although 18·3% of the population aged 15–24 years were living in sub-Saharan Africa in 2019, the region accounted for 37·9% (90% UI 34·8–41·9) of all worldwide deaths in youth. Interpretation It is urgent to accelerate progress in reducing youth mortality. Efforts are particularly needed in sub-Saharan Africa, where the burden of mortality is increasingly concentrated. In the future, a growing number of countries will see youth mortality exceeding under-5 mortality if current trends continue. Funding UN Children's Fund, Bill & Melinda Gates Foundation, United States Agency for International Development.

International audience; Sibling survival histories are a major source of adult mortality estimates in countries with incomplete death registration. We evaluate age and date reporting errors in sibling histories collected during a validation study in the Niakhar Health and Demographic Surveillance System (Senegal). Participants were randomly assigned to either the Demographic and Health Survey questionnaire or a questionnaire incorporating an event history calendar, recall cues, and increased probing strategies. We linked 60–62 per cent of survey reports of siblings to the reference database using manual and probabilistic approaches. Both questionnaires showed high sensitivity (>96 per cent) and specificity (>97 per cent) in recording siblings’ vital status. Respondents underestimated the age of living siblings, and age at and time since death of deceased siblings. These reporting errors introduced downward biases in mortality estimates. The revised questionnaire improved reporting of age of living siblings but not of age at or timing of deaths.

To meet the SDG requirement of spatial disaggregation of indicators, several methods have been developed to generate estimates of under-five mortality at the sub-national level. The reliability of sub-national mortality estimates in children aged 5-14 with the available survey data has not been evaluated so far. We generate Admin-1 sub-national estimates of the risk of dying in children aged less than five (5q0) and those aged 5 to 14 years old (10q5). We use 96 Demographic and Health Surveys (DHS) in 20 Sub-Saharan countries having at least 3 surveys designed to be representative at a sub-national level. The estimates account for the complex sample design of DHS and HIV-related biases in young children. A Bayesian space-time model previously developed for under-five mortality is used to smooth estimates across space and time in both age groups to reduce problems associated with data sparsity. The posterior distributions of the probability10q5are used to compute coefficients of variation and assess precision. Sufficiently precise estimates are retained to study the sub-national relationship between age-specific mortality rates (5q0and10q5), accounting for uncertainty in sub-national levels. Out of 1,132 space-time estimates, 62.3% are considered sufficiently precise with high heterogeneity across countries. Across all periods, sub-national estimates of mortality in children aged 0-4 are highly correlated with those in older children and young adolescents but this correlation is largely driven by the mortality decline. Within specific periods of time, it is often impossible to assess the relationship between mortality rates in the two age groups at the sub-national level, except in Nigeria, Ethiopia, Cameroon, Senegal and Zambia. As increased attention is devoted to survival after age 5, more research is needed to ensure that sub-national areas with specific interventions required for older children can be correctly identified.

The atmospheric mechanisms responsible for the loess grain‐size variations in central Asia are less clear, and an increasing number of studies have found that the coarse‐grained component is likely supplied by the surface circulation rather than by the westerlies (westerlies circulation). In this study, we attempt to determine the atmospheric dynamics patterns in the Afghan‐Tajik Basin during the past 800 kyr, based on the coarse grain‐size fraction of loess, combined with a study of modern dust transport processes. We suggest that the coarse grain‐size fraction can be used to indicate the intensity of near‐surface winds, while on glacial‐interglacial time scales, the variations of loess grain size in Tajikistan are dominated by Northern Hemisphere ice volume via its effect on the strength of the Siberian High. In addition, we suggest that atmospheric greenhouse gases concentration affected the loess grain size during interglacials via their influence on the temperature of southern high latitudes.

The advance in wind turbine technology has led to a tendency to gather the turbines into wind farms to benefit from economies of scale. However, the farm configuration often leads to a drastic power loss due to the interactions between the turbines. To mitigate this issue, the turbines are typically misaligned with the dominant wind direction to deviate their wake. In this paper, a tilt-induced wake deviation strategy is studied in a farm configuration using large eddy simulation of an atmospheric boundary layer and an actuator line model for the blade. The results show an effective wake deviation and a significant increase of the total power production of the farm. The evolution of the time-averaged and unsteady loads is also assessed in the wind farm, and the resulting damage equivalent load is shown to be reasonably modified when the turbines are tilted. The tilted configuration is also compared with a wind farm with yawed turbines and is found to lead to a larger power output for a reduced damage equivalent load.

Wind turbine wake physics is by nature unsteady and highly sensitive to the local wind characteristics. While modern Computational Fluid Dynamic methods (eg: Large Eddy Simulation) allow to accurately capture the flow at the wind farm scale, they still come at a prohibitive computational cost preventing their use for online control or Machine Learning schemes. This work pursues the recent efforts undertaken by Marichal et al. (2017) to develop a computationally affordable yet accurate unsteady Wake Model. Marichal et al. (2017) introduced and successfully tested a vorticity-based skeleton Wake Model (WM). This vorticity-based skeleton essentially consists of a regularized Vortex Sheet Tube (VST) in the near wake which then transitions into a Vortex Dipole Line (VDL) in the far wake. The rotor operation itself is modelled using the Blade Element theory. The present study further assesses the performances of the WM: it extends the validation procedure to various wind turbine settings (ie: different Tip Speed Ratios) and inflow conditions. The data recovered from the wake model is compared to that extracted from high fidelity numerical simulations performed on the NREL 5MW wind turbine using an Immersed Lifting Line-enabled Vortex Particle-Mesh (VPM) flow solver. Online model update strategies are then discussed. Indeed, the existing WM still requires the knowledge of the upstream wind conditions in order to provide an accurate downstream wind field estimate. Following Bottasso et al. (2018), an Extended Kalman Filter (EKF) estimating the Rotor-Effective Wind Speed by a Blade-Load- based Estimator is implemented. This EKF allows to estimate the wind profile upstream the wind turbine and eventually to feed it to the vorticity-based skeleton wake model as an input parameter. We finally plan to extend the tools developed to a two-turbines system. The downstream wind profile provided by the Kalman estimator will be compared to that given by the wake model computed by the upstream turbine. Data assimilation techniques will then be used to correct the wake model online.

The water cycle is the central component of most environmental systems. A sustainable water management can only be achieved by developing system-wide approaches that encompass the different components of the water cycle. A numerical model is an ideal tool to achieve this goal. In this work, we have developed a suite of numerical models for surface and subsurface water flows. These models solve the 3D Richards equation (RE) and couple it with a 2D surface runoff model based on the non-inertia approximation of the shallow water equations. Unlike classical models of RE, we first consider an explicit time integration scheme to achieve both mass conservation and perfect scaling on High Performance Computers. This saturated/unsaturated subsurface model is then coupled to a surface runoff model, using a coupling method naturally derived from the RE model. In a second step, we consider another formulation that is better suited for water-saturated areas. By slightly degrading the model scalability, we can then handle complex infiltration and evaporation test cases with almost no constraints on the time step and very good numerical efficiency. These models have been thoroughly parameterized and validated on a range of test cases of increasing complexity. They form the building blocks of more complex models that will simulate the water cycle from the raindrop to the ocean. (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2019

Wind turbine wake physics is by nature unsteady and highly sensitive to the local wind characteristics. While modern Computational Fluid Dynamic methods (eg: Large Eddy Simulation) allow to accurately capture the flow at the wind farm scale, they still come at a prohibitive computational cost, preventing their use for online control or Machine Learning schemes. This work aims at developing a computationally affordable yet robust wake meandering model. The latter is based on the commonly used passive tracer hypothesis which states that the wake is advected by the downstream background flow. Providing a robust wake characterization requires the knowledge of the upstream wind conditions, i.e. velocity and turbulence intensity. Following previous work of Bottasso et al.(2017), an Extended Kalman Filter was developed to estimate the wind profile upstream the wind turbine based on the blade loads. The flow characteristics as estimated by the filter are then fed to the wake model as input parameters. The present study assesses the performances of both the wind estimator and the wake model on the NREL 5MW wind turbine thanks to data recovered from high fidelity numerical simulations. An Immersed Lifting Line-enabled Vortex Particle-Mesh method is used for simulations at the scale of a single wind turbine, while windfarm simulations are performed by a fourth-order finite difference Large Eddy Simulation code.

Wind turbine wake physics is by nature unsteady and highly sensitive to the local wind characteristics. While Large Eddy Simulations (LES) allow to accurately capture the flow at the wind farm scale for a wide range of atmospheric conditions, they still come at a prohibitive computational cost when it comes to online control. Based on the Dynamic Wake Meandering model (Larsen, 2007), the presented model couples a meandering model and a wake speed deficit model in order to estimate the velocity field downstream the wind turbine. Focus is laid on limiting the number of input parameters by building on recent advances in flow sensing to feed the wake model with estimated inflow conditions. The remaining parameters are fine-tuned through online data assimilation techniques, thus adapting to inflow conditions. The performances of the resulting wake model are assessed using data recovered from high fidelity LES simulations.

The tidal response of Titan′s two largest northern seas, Ligeia Mare and Kraken Mare, is studied by means of a two-dimensional, depth-averaged, shallow water model, SLIM (http://www.climate.be/slim). Kraken Mare is formed of two basins, the northern one being assumed to be linked by a single strait, Trevize Fretum, to Ligeia Mare. The tidal motions tend to be independent of each other in each basin (i.e., Ligeia Mare, Kraken 1 and Kraken 2) which results in sharp transitions in the straits. Our results are overall rather similar to those of Tokano et al. (2014), suggesting that a 2D model such as SLIM is adequate for modelling Titan′s tides and, since it is (presumably) less computationally demanding, may be better for sensitivity studies. For instance, the maximum tidal range in Kraken and Ligeia Maria respectively are 0.29 m and 0.14 m, which is within the range predicted by Lorenz et al. (2014) although smaller by 0.07 m and larger by 0.04 m than the estimates of Tokano et al. (2014) (but it occurs at the same location). The tidal currents are faster (by about one order of magnitude) in the straits linking those Maria than in the basins themselves (with a maximum of 0.36 m/s in the strait linking Kraken 1 and Kraken 2, Seldon Fretum). A decomposition of the tidal history into different harmonic components is carried out. Except in specific areas such as the straits and the amphidromic point(s), the main tidal component has a period of 1 Titan Day. We also briefly studied the eigenmodes of the northern seas whose period is close to the tidal period: such modes are very local. Indeed, their magnitude is significant (with respect to the magnitude of the modes elsewhere in the seas) in small bay(s) or near the islands of Kraken 2 and Ligeia Mare. They are not excited by the tides as they do not appear in the tidal motion. A sensitivity analysis to poorly constrained parameters (bottom friction coefficient, depth of Trevize Fretum and attenuation factor – the latter is briefly discussed with respect to the values of the Love numbers found in the literature) is also conducted. The model parameters are seen to have a significant impact on the liquid exchanges between the basins and, consequently, on the tidal range and phase, fluid velocity and location of amphidromic point(s).

Cette recherche a pour principal objectif d’évaluer l’utilité de prendre en compte des mesures totale- ment automatiques de la compétence phraséologique pour estimer la qualité de textes d’apprenants de l’anglais langue étrangère. Les analyses, menées sur plus de 1000 copies d’examen du First Certificate in English, librement mises à disposition par Yannakoudakis et coll., confirment que l’approche qui consiste à assigner aux bigrammes et aux trigrammes de mots présents dans un texte des scores d’association collocationnelle calculés sur la base d’un grand corpus de référence natif est particulièrement efficace. Si les indices extraits des trigrammes sont moins efficaces que ceux extraits des bigrammes, ils apportent une contribution utile à ces derniers. Les analyses soulignent aussi les bénéfices apportés par un emploi simultané de plusieurs mesures d’association collocationnelle.

Sea ice cover and thickness have substantially decreased in the Arctic Ocean since the beginning of the satellite era. As a result, sea ice strength has been reduced, allowing more deformation and fracturing and leading to increased sea ice drift speed. We use the version 3.6 of the global ocean–sea ice NEMO-LIM model (Nucleus for European Modelling of the Ocean coupled to the Louvain-la-Neuve sea Ice Model), satellite, buoy and submarine observations, as well as reanalysis data over the period from 1979 to 2013 to study these relationships. Overall, the model agrees well with observations in terms of sea ice extent, concentration and thickness. The seasonal cycle of sea ice drift speed is reasonably well reproduced by the model. NEMO-LIM3.6 is able to capture the relationships between the seasonal cycles of sea ice drift speed, concentration and thickness, with higher drift speed for both lower concentration and lower thickness, in agreement with observations. Model experiments are carried out to test the sensitivity of Arctic sea ice drift speed, thickness and concentration to changes in sea ice strength parameter P*. These show that higher values of P* generally lead to lower sea ice deformation and lower sea ice thickness, and that no single value of P* is the best option for reproducing the observed drift speed and thickness. The methodology proposed in this analysis provides a benchmark for a further model intercomparison related to the relationships between sea ice drift speed and strength, which is especially relevant in the context of the upcoming Coupled Model Intercomparison Project 6 (CMIP6). David Docquier and Antoine Barthélemy work on the PRIMAVERA project (PRocess-based climate sIMulation: AdVances in high-resolution modelling and European climate Risk Assessment), which is funded by the European Commission’s Horizon 2020 programme, grant agreement no. 641727. François Massonnet is funded by the Belgian Fonds National de la Recherche Scientifique (FNRS) and was funded by the Ministerio de Economía, Industria y Competitividad (MINECO). Neil F. Tandon is supported by the Canadian Sea Ice and Snow Evolution (CanSISE) Network. Olivier Lecomte is a research assistant within the Belgian FNRS. The present research benefited from computational resources made available on the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement no. 1117545. Computational resources have also been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11. We would like to thank Hugues Goosse, Martin Vancoppenolle, Jonathan Raulier and Véronique Dansereau for their very helpful comments regarding this study. We also acknowledge Pierre-Yves Barriat for his help in using computing resources at UCL and Damien François for his advice in improving Python scripts. Finally, we thank the editor Dirk Notz and the two anonymous reviewers for helping to improve the original paper.

Pour déterminer si certaines mesures d’association lexicale fréquemment employées en TAL attribuent des scores élevés à des n-grammes que le hasard aurait pu produire aussi souvent qu’observé, nous avons utilisé une extension du test exact de Fisher à des séquences de plus de deux mots. Les analyses ont porté sur un corpus de quatre millions de mots d’anglais conversationnel extrait du BNC. Les résultats, basés sur la courbe précision-rappel et sur la précision moyenne, montrent que le LL-simple est extrêmement efficace. IM3 est plus efficace que les autres mesures basées sur les tests d’hypothèse et atteint même un niveau de performance presque égal à LL-simple pour les trigrammes.

This paper describes the system developed by the Centre for English Corpus Linguis- tics (CECL) to discriminating similar lan- guages, language varieties and dialects. Based on a SVM with character and POStag n-grams as features and the BM25 weighting scheme, it achieved 92.7% ac- curacy in the Discriminating between Sim- ilar Languages (DSL) task, ranking first among eleven systems but with a lead over the next three teams of only 0.2%. A sim- pler version of the system ranked second in the German Dialect Identification (GDI) task thanks to several ad hoc postprocess- ing steps. Complementary analyses car- ried out by a cross-validation procedure suggest that the BM25 weighting scheme could be competitive in this type of tasks, at least in comparison with the sublinear TF-IDF. POStag n-grams also improved the system performance.

Short-term and decadal sea-ice prediction systems need a realistic initial state, generally obtained using ice-ocean model simulations with data assimilation. However, only sea-ice concentration and velocity data are currently assimilated. In this work, an Ensemble Kalman Filter system is used to assimilate observed ice concentration and freeboard (i.e. thickness of emerged sea ice) data into a global coupled ocean–sea-ice model. The impact and effectiveness of our data assimilation system is assessed in two steps: firstly, through the assimilation of synthetic data (i.e., model-generated data) and, secondly, through the assimilation of satellite data. While ice concentrations are available daily, freeboard data used in this study are only available during six one-month periods spread over 2005–2007. Our results show that the simulated Arctic and Antarctic sea-ice extents are improved by the assimilation of synthetic ice concentration data. Assimilation of synthetic ice freeboard data improves the simulated sea-ice thickness field. Using real ice concentration data enhances the model realism in both hemispheres. Assimilation of ice concentration data significantly improves the total hemispheric sea-ice extent all year long, especially in summer. Combining the assimilation of ice freeboard and concentration data leads to better ice thickness, but does not further improve the ice extent. Moreover, the improvements in sea-ice thickness due to the assimilation of ice freeboard remain visible well beyond the assimilation periods.

In the context of the emergence of extraterrestrial oceanography, we adapted an existing oceanographic model, SLIM (www.climate.be/slim), to the conditions of Titan, a moon of Saturn. The tidal response of the largest southern lake at Titan’s surface, namely Ontario Lacus, is simulated. SLIM solves the 2D, depth-averaged shallow water equations on an unstructured mesh using the discontinuous Galerkin finite element method, which allows for high spatial resolution wherever needed. The impact of the wind forcing, the bathymetry, and the bottom friction is also discussed. The predicted maximum tidal range is about 0.56 m in the southern part of the lake, which is more than twice as large as the previous estimates (see Tokano, Ocean Dyn 60:(4) 803–817doi:10.1007/s10236-010-0285-3 2010). The patterns and magnitude of the current are also markedly different from those of previous studies: the tidal motion is not aligned with the major axis of the lake and the speed is largernearshore. Indeed, the main tidal component rotates clockwise in an exact period of one Titan day and the tidal currents can reach 0.046 ms−1 close to the shores depending on the geometry and the bathymetry. Except for thesespecific nearshore regions, the current speed is less than 0.02 ms−1. Circular patterns can be observed offshore, their rotational direction and size varying along the day.

This work focuses on the investigation of various wall modeling strategies for the large-eddy simulation (LES) of high Reynolds number wall-bounded turbu- lent flows with mild pressure gradients. A half channel flow setup at Reτ = 2000 is considered. A periodic blowing and suction at the upper boundary is added to obtain a fluctuating pressure gradient. A wall-resolved LES is first performed to provide a reference solution and insight into the flow topology. Wall-modeled LES is then considered. Two strategies are investigated and compared. First, algebraic models are considered, without and with pressure gradient correction to the law of the wall used by the model. We also investigate various spatial and temporal averaging techniques when using the model. Second, RANS sub-layer models are considered, without and with pressure gradient corrections to the turbulent eddy viscosity model.

This study belongs to the field of automatic scoring of texts written in a foreign language. It aims to evaluate in depth the utility to take into account automatic measures of the phraseological competence. The phraseological features were obtained by assigning to each bigram in a text several association scores computed on the basis of a large native corpus. The analyzes performed on three datasets indicate that the phraseological features are useful for estimating text quality and that they are complementary to simpler lexical measures. External validation, carried out by learning and testing the predictive model on very different sets of texts, shows that these indices have a high degree of generalizability.

We examine the recent (1979–2010) and future (2011–2100) characteristics of the summer Arctic sea ice cover as simulated by 29 Earth system and general circulation models from the Coupled Model Intercomparison Project, phase 5 (CMIP5). As was the case with CMIP3, a large inter-model spread persists in the simulated summer sea ice losses over the 21st century for a given forcing scenario. The initial 1979–2010 sea ice properties (including the sea ice extent, thickness distribution and volume characteristics) of each CMIP5 model are discussed as potential constraints on the September sea ice extent (SSIE) projections. Our results suggest first that the SSIE anomalies (compared to the 1979–2010 model SSIE) are related in a complicated manner to the initial 1979–2010 sea ice model characteristics, due to the large diversity of the CMIP5 population (at a given time, some models are in an ice-free state while others are still on the track of ice loss). In a new diagram (that does not consider the time as an independent variable) we show that the transition towards ice-free conditions is actually occuring in a very similar manner for all models. For these reasons, some quantities that do not explicitly depend on time, such as the year at which SSIE drops below a certain threshold, are likely to be constrained. In a second step, using several adequate 1979–2010 sea ice metrics, we effectively reduce the uncertainty as to when the Arctic could become nearly ice-free in summertime (between 2041 and 2060 for a high climate forcing scenario).

Detecting communities in large networks has drawn much attention over the years. While modularity remains one of the more popular methods of community detection, the so-called resolution limit remains a significant drawback. To overcome this issue, it was recently suggested that instead of comparing the network to a random null model, as is done in modularity, it should be compared to a constant factor. However, it is unclear what is meant exactly by "resolution-limit-free," that is, not suffering from the resolution limit. Furthermore, the question remains what other methods could be classified as resolution-limit-free. In this paper we suggest a rigorous definition and derive some basic properties of resolution-limit-free methods. More importantly, we are able to prove exactly which class of community detection methods are resolution-limit-free. Furthermore, we analyze which methods are not resolution-limit-free, suggesting there is only a limited scope for resolution-limit-free community detection methods. Finally, we provide such a natural formulation, and show it performs superbly.