Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

Long term nitrogen budget modelling in a small agricultural watershed: hydrological control assessment of nitrogen losses with semi-distributed (SWAT) and distributed (TNT2) models

Nitrogen exports in catchments are known to be greatly variable because nitrogen cycle in watershed is controlled by different factors such as landuse, farm management practices, climate, soil type and hydrological setting. Our aim is to study the relative importance of the processes controlling nitrogen losses at catchment scale in the long term using a modelling approach constrained by a long term record of observations. The study area is a catchment of 330 ha with 95 % of intensive agriculture in a hilly shallow soil context, in the south west of France. Historical field rotation and nitrogen river load data have been collected for a 20 year period. Two process-based and spatially distributed models have been chosen to simulate nitrogen transfer and transformation in the whole catchment. The first one is the fully distributed TNT2 model, developed and validated in a different context (farming systems in north-western France). The second one is the widely used, semi-distributed SWAT model, used and recognizedto be realistic in many studies on nitrogen transfer in river. This comparative modelling approach was used to evaluate the effect of different modelling approaches on the identification of controlling factors, and the ability of both models to simulate alternative scenarios. The discharge, especially during storm flow, is well simulated by the curve number approach and the semi-distributed hydrological parameter description used SWAT, while the Topmodel-derived approach used in TNT2 tends to underestimate some peak discharges. Nitrogen dynamic simulations are considered to be acceptable for both models for a long time period but the use of both models allows to exhibit their respective capacity and limits. TNT2 has higher potentiality to test the impact of complex agricultural scenarios because the description of management practices and the simulation of crops to management options is more detailed. It permits the assessment of spatial interactions and focussed spatial management, like the set up of grass or tree strips. SWAT can then be used to scale up change scenarios from TNT2 small catchment results to large catchments

Dynamics of Nitrogen loads in surface water of an agricultural watershed by modelling approach, the Save, Southwest France.

Agriculture is known to have a great impact of nutrients enrichment on continental water resources. In south-West of France (Gascogne region), water resource are essentially surface water and shallow aquifer. Nitrogen dynamic in river is complex and highly variable throughout season and year, depending on hydrology, landuse, removal in stream. In this context, agricultural impacts on nitrogen concentration are a matter of concern for agricultural decision-maker. In order to introduce sustainable land use concepts in this hilly, clayey and agricultural shallow soil context, the hydrological simulation model SWAT2005 has been tested as a valuable tool to evaluate the consequences of such land use changes on water and nutrient balance components. This semi-distributed hydrological model coupled with agronomical model EPIC is able to simulate the impact of each agricultural landuse at the outlet of the Save catchment (1100 km2). Hydrological parameters model are calibrated based on 14-year historical record (1994–2008). Nitrogen losses have been measured during 2 years (2006-2008) at the outlet and are used to validate the model calibration. Agricultural data at communal scale coupled with Spot image analyses have been used to evaluate agricultural distribution and pressure in SWAT. The aim of this modelling exercise is to simulate nitrogen cycle in whole agricultural Hydrological Response Units (HRU), depending on plant growth and culture rotation, to simulate accurately nitrate load in river. The ability of SWAT to reproduce nitrogen transfert and transformation at this scale and in this agricultural context will be evaluated by a discussion of importance of each nitrogen cycle process in nitrogen losses. SWAT could be a useful tool to test agricultural scenario to improve the nitrogen management in river

The leaves of Mediterranean mandarin could be used as an important source of hesperidin, nobiletin and tangeretin. : S20P04

Citrus are rich in flavonoids such as flavones and flavanones. Recent studies have shown that these phytonutrients play a beneficial role for human health. Citrus plants can contain high levels of hesperidin, a flavanone which is effective in the treatment of chronic venous insufficiency. Nobiletin and tangeretin are two polymethoxylated flavones. Nobiletin has been shown to increase hepatic insulin sensitivity and decrease atherosclerosis. Tangeretin may have antiproliferative and anticarcinogenic effects by blocking MAPKs activation and ROS generation. Studies on flavonoids from citrus are generally focussed on ripe fruits and on one group of metabolites. The aim of this study is to quantify accurately all groups of flavonoid from leaves of mandarin (Citrus deliciosa). Flavones and flavanones analysis was carried out by liquid chromatography and mass spectrometry (LC-MS) using a new generation column. Moreover, a specific gradient was designed to evaluate both flavanones and methoxylated flavones. This method was applied to leaves from mandarin tree. All leaves were fully-expanded, and were about one-year-old from the spring flush of the previous season. They were of similar height above the ground, had the same east orientation and experienced similar exposure to light. Comparison of metabolite levels revealed that mandarin leaves were rich in hesperidin, nobiletin and tangeretin. Interestingly, nobiletin and tangeretin also accumulated in high level. (Texte integral

Simulating the long term impact of nitrate mitigation scenarios in apilot study basin

The agro-hydrological model TNT2 was used to explore for a period of 14 years (1987–2001) the likelyconsequences of mitigation scenarios on nitrate contamination of the stream water in a small agriculturalcatchment. The Best Management Practices (BMPs) historically designed and implemented in 1992 andtwo devised agricultural scenarios (catch crop (CC) implementation and a global reduction of N fertilizer)are evaluated in term of nitrate contamination in the environment. Two of the BMPs consist in imple-menting natural strips of Poplar and rye-grass strips (5 meters large) along stream and ditches and thethird is a delay in the burial of wheat straws (from August to October). Simulations indicated that naturalstrips implementation would lead to a slight decrease of Nitrate Fluxes (NF) in river by respectively 3.3%and 6.6% for rye-grass and poplar strips: a benefit associated to the non fertilization of strips area. Denitri-fication has not been particularly disrupted in such areas. The delay in the burial of wheat straw in autumndecreases annual mineralization rate and annual plant uptake (by respectively 9 and 13 kg N ha−1y−1)but increases denitrification fluxes by 6 kg N ha−1y−1. This would lead to a slight decrease by 6% of NFin stream (equivalent to 3.3 mg NO3−l−1) and an average decrease of the following sunflower yield by27%. The global reduction of fertilization by 10% would decreased NF in stream by 13.8% (equivalent to8 mg NO3−l−1), with a global decrease by 8 kg N ha−1y−1of plant uptake. The cumulative effect of BMPsand CC would have together lead to a decrease of nitrate concentration from 57.5 to 46.6 mg NO3−l−1reaching the UE environmental quality objectives (below 50 mg NO3−l−1). Spring crops yield followingCC would have been penalized and the decrease of NF is balanced by an increase of denitrification fluxesin the environment contributing to release of N2O, a greenhouse gas, into the atmosphere

Segmentation-based approaches for characterising plant architecture and assessing its plasticity at different scales

International audiencePlants are modular organisms that develop by the repetition of elementary botanical entities or constructional units through the three main and fundamental morphogenetic processes of growth, branching and reiteration (Barthélémy and Caraglio, 2007). Repetition of these entities induces gradual or abrupt changes in their characteristics. These characteristics are quantified through several variables, called the entity attributes. On the one hand, differences between entities reflect different stages of differentiation in the meristems (Nicolini and Chanson, 1999), which are ordered in time and correspond to the notion of physiological age of meristems (Barthélémy and Caraglio, 2007). The changes of one attribute through the plant structure are referred to as morphogenetic gradient. On the other hand, part of the entity differences can be imputed to environmental factors. Based on this botanical model of plant functioning, our approach jointly relies on categories of entities with similar characteristics, a description of those within-category characteristics and the category topological organisation within the plant. This constitutes a useful summary of the plant architecture, which is the basis for 1) highlighting hidden regularities in plant structures, for a better understanding of the gradients and organisation rules; 2) proposing and validating ecophysiological hypotheses, and new sampling protocols; 3) adopting a powerful paradigm for modelling plant development. In this work, the entity categories are identified using a hidden Markov tree (HMT) model, in which local dependencies only ( i.e. interactions between connected entities) are accounted for. This is not sufficient to accurately describe the topological distribution of the entities within the plant, and the changes of the plant topology. This is why various complementary methods and models (among which edit distance algorithms and sequence analysis using Markovian models), performed at different scales, are used in our approach to provide a more detailed description of the architecture, and to assess how various controlled factors affect architecture plasticity

Continuous measurement of nitrate concentration in a highly event-responsive agricultural catchment in south-west of France: is the gain of information useful?

A nitrate sensor has been set up to measure every 10 min the nitrate signal in a stream draining a small agricultural catchment dominated by fertilized crops during a 2-year study period (2006–2008) in the south-west of France. An in situ sampling protocol using automatic sampler to monitor flood events have been used to assume a point-to-point calibration of the sensor values. The nitrate concentration exhibits nonsystematic concentration and dilution effects during flood events. We demonstrate that the calibrated nitrate sensor signal gathered from the outlet is considered to be a continuous signal using the Nyquist–Shannon sampling theorem. The objectives of this study are to quantify the errors generated by a typical infrequent sampling protocol and to design appropriate sampling strategy according to the sampling objectives. Nitrate concentration signal and flow data are numerically sampled to simulate common sampling frequencies. The total fluxes calculated from the simulated samples are compared with the reference value computed on the continuous signal. Uncertainties are increasing as sampling intervals increase; the method that is not using continuous discharge to compute nitrate fluxes bring larger uncertainty. The dispersion and bias computed for each sampling interval are used to evaluate the uncertainty during each hydrological period. High underestimation is made during flood periods when high-concentration period is overlooked. On the contrary, high sampling frequencies (from 3 h to 1 day) lead to a systematic overestimation (bias around 3%): highest concentrations are overweighted by the interpolation of the concentration in such case. The in situ sampling protocol generates less than 1% of load estimation error and sample highest concentration peaks. We consider useful such newly emerging field technologies to assess short-term variations of water quality parameters, to minimize the number of samples to be analysed and to assess the quality state of the stream at any time

Existence de la cowdriose (heartwater) à Cowdria ruminantium chez les ruminants des Antilles françaises (La Guadeloupe) et des Mascareignes (La Réunion et Ile Maurice)

La cowdriose (heartwater) à Cowdria ruminantium a été récemment identifiée aux Antilles françaises (La Guadeloupe) et aux Mascareignes (La Réunion et Ile Maurice