The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Fabrice Vinatier - One of the best experts on this subject based on the ideXlab platform.
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Influence of maintenance practices on plant community properties interacting with ecosystem functions in an agricultural ditch
2020Co-Authors: Gabrielle Rudi, Jean-stéphane Bailly, Yves Caraglio, Jeanne Dollinger, Fabrice VinatierAbstract:<p><span>Maintenance practices restoring the hydraulic capacity of agricultural ditches (mowing, burning, chemical weeding or dredging) modify the plant communities in the short and medium term. However, the medium term modification of plant community composition, parameters and properties, and in turn the associated functions provided by ditches (water transport, propagules and sediment retention, biodiversity conservation) have not attracted much attention so far. Therefore, the main question raised in this study was the following : Do ditch maintenance practices affect plant community composition, parameters, and properties associated with water and particle transport processes (sediments, seeds), as well as biodiversity, in the medium term (two years)?</span></p><p><span>We designed an experiment to compare the effects of different maintenance practices in a Mediterranean agricultural ditch. We measured the plant richness, morphological parameters and properties of the plant community affecting ecosystem functions twice : before applying the maintenance practices and after two years of contrasting maintenance practices. We assessed the differences between practices using linear models and generalized linear models, followed by pairwise comparisons between means using the Tukey test.</span></p><p><span>Maintenance practices differently affected plant community composition, parameters and properties, such as richness, proportions of harmful plants, distribution of heights, densities, proportions of growth forms and total biomass. None of the maintenance strategies simultaneously improved the functions considered. After two years, mowing provided the highest alpha-diversity and had a low proportion of harmful plants. Burning was the practice that produced the highest total biomass and Blockage Factor, and therefore negatively influenced the water transport. However, this practice positively impacted seed retention and sedimentation. Our results suggest that associations of maintenance practices would preserve the trade-offs among the different functions in the medium term. </span></p><p>&#160;</p><p><br><br></p>
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Multifunctionality of agricultural channel vegetation : A review based on community functional parameters and properties to support ecosystem function modeling
Ecohydrology & Hydrobiology, 2020Co-Authors: Gabrielle Rudi, Jean-stéphane Bailly, Gilles Belaud, Cécile Dagès, Philippe Lagacherie, Fabrice VinatierAbstract:Vegetation living in agricultural channels (drainage ditches or irrigation channels) supports ecosystem functions such as water flow regulation; retention of sediments, agricultural pollutants and plant propagules; and bank strengthening. The review focuses on plant community functional parameters (aggregations of plant functional traits) and community properties that need to be considered to study the dynamics of these ecosystem functions, to support further modeling work on the functioning of these semiaquatic ecosystems. It also provides an up-to-date overview of the effects of channel management practices on vegetation, because these practices are a potential lever with which to drive plant community functional parameters and properties and, in turn, ecosystem functions. The review points out that the mean height, density, and flexibility of the plant cover, sometimes integrated in the “Blockage Factor”, mainly influence the average components of the water flow associated with the functions of water regulation, and retention of sediments and non-floating propagules. The density of plants, or area of the plant cover at the water surface, are generally used to explain floating propagule retention. The biomasses of living and dead vegetation are the properties used to assess the retention of agricultural pollutants. Root density and root length density, as well as tensile strength of the root system, are parameters generally associated with bank strengthening. Regarding the effects of channel management practices, this work highlights that research generally has focused on the resulting plant richness and diversity, but has not provided much information on associated plant community functional parameters and properties.
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From 3D grassy vegetation point cloud to hydraulic resistance: Application to close-range estimation of Manning coefficients for intermittent open channels
Ecohydrology, 2017Co-Authors: Fabrice Vinatier, Jean-stéphane Bailly, Gilles BelaudAbstract:The understanding of interrelations between biotic and abiotic processes in intermittent open-channels is currently of primary importance to better assess the services and disservices they provide. A large body of literature attempts to characterize vegetation functional traits affecting hydraulic rugosity, through the introduction of the Blockage Factor of flow by vegetation. However, this Factor has multiple definitions and is still difficult to assess in the fields with actual and diverse vegetation covers, especially for grassy plants of ditches. Our study aims at predicting flow resistance from 3D vegetation characteristics using a close-range laser scanner. Flow resistance and vegetation 3D characteristics were defined using Manning coefficient and Blockage Factors, respectively. We tested combined effects of flow discharge against plant species and densities characterizing intermittent channels in a channel flume. Our results showed a variability of Manning coefficient describing flow rugosity against species and densities, with a highest rugosity for sclerophyllous species than herbaceous ones. Different Blockage Factors were calculated on the basis of scan clouds linked to Manning coefficients using non linear equation. The best relationship (R 2 = 0.9) were found for non linear equation relating Manning coefficients to a simplified Blockage Factor figuring the mean vegetation height deduced from the projection of the scan point cloud to the channel frontal area. The introduction of a coefficient to correct underestimated values issued from herbaceous species considering their reconfiguration under hydrodynamic loading is thus discussed.
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Vegetation patch effects on flow resistance at channel scale
2015Co-Authors: Jean-stéphane Bailly, Fabrice Vinatier, Gilles Belaud, David CombemaleAbstract:Thanks to a specific experimental design in a controlled channel, this paper aimed at quantifying how patches of four different ditches plant species affect integrated flow resistance parameters, the Manning coefficient. These plants, frequently encountered in the farmland ditches and irrigation channels of the south of France, were selected according to a large range of hydrophilic requirements, flexibility and branching complexity related to the plant Blockage Factor. Eight different spatial patches (regular, random, lateral or central patches) of each plant with crescent or similar plant densities were implanted at the bottom of a controlled channel where the water levels and water velocities were measured for three different discharges in steady and unsteady flow conditions. Resistance parameters (Manning parameters) were then estimated from the total head-loss, or from flow propagation velocity in the channel thanks to inversion of an hydrodynamic model. These experiments allow us to test the significance effect of channel vegetation patches and densities on flow resistance parameters at the reach scale.
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Using a terrestrial laser scanner to characterize vegetation-induced flow resistance in a controlled channel
2015Co-Authors: Fabrice Vinatier, Jean-stéphane Bailly, Gilles Belaud, David CombemaleAbstract:Vegetation characteristics providing spatial heterogeneity at the channel reach scale can produce complex flow patterns and the relationship between plant patterns morphology and flow resistance is still an open question (Nepf 2012). Unlike experiments in laboratory, measuring the vegetation characteristics related to flow resistance on open channel in situ is difficult. Thanks to its high resolution and light weight, scanner lasers allow now to collect in situ 3D vegetation characteristics. In this study we used a 1064 nm usual Terrestrial Laser Scanner (TLS) located 5 meters at nadir above a 8 meters long equipped channel in order to both i) characterize the vegetation structure heterogeneity within the channel form a single scan (Blockage Factor, canopy height) and ii) to measure the 2D water level all over the channel during steady flow within a few seconds scan. This latter measuring system was possible thanks to an additive dispersive product sprinkled at the water surface. Vegetation characteristics and water surfaces during steady flows from 6 different plant spatial design on channel bottom for 4 plant species were thus measured. Vegetation Blockage Factors at channel scale were estimated from TLS points clouds and analyzed.
Ujjwal K Saha - One of the best experts on this subject based on the ideXlab platform.
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an adapted Blockage Factor correlation approach in wind tunnel experiments of a savonius style wind turbine
Energy Conversion and Management, 2014Co-Authors: Sukanta Roy, Ujjwal K SahaAbstract:Abstract An investigation into the Blockage correction effects in wind tunnel experiments of a small-scale wind energy conversion system in an open type test section is carried out. The energy conversion system includes a Savonius-style wind turbine (SSWT) and a power measurement assembly. As the available correlations for the closed type test sections may not be appropriate for the open test section under dynamic loading conditions, new correlations are adapted for the Blockage correction Factors with free stream wind speed, turbine rotational speed and variable load applied to the turbine to quantify the energy conversion coefficients more precisely. These are obtained for a Blockage ratio of 21.16% through a comparison of present experimental data with those of established experimental data under dynamic loading conditions. Further, the accuracy of the adapted correlations is substantiated into the experiments with smaller Blockage ratios of 16% and 12.25%. The relationships of the tip speed ratios and Blockage ratios with the Blockage correction Factor are also discussed. Using these correlations, this study provides evidence of increase of Blockage correction in the range 1–10% with the increase of both tip speed ratio and Blockage ratio. The results also indicate that for Blockage ratios approaching 10 and tip speed ratios below 0.5, the Blockage effects are almost negligible in the open type test sections.
Norbert Ulbrich - One of the best experts on this subject based on the ideXlab platform.
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the application of panel method code antares to wind tunnel wall interference problems
40th AIAA Aerospace Sciences Meeting & Exhibit, 2002Co-Authors: Norbert UlbrichAbstract:Panel method code ANTARES was developed to solve subsonic wall interference problems in a threedimensional wind tunnel with non-rectangular crosssection. The code uses a singularity representation of the test article. Volume and viscous separation wake Blockage effects of the test article are represented by chains of point doublets. Lifting effects are represented by line doublets. The closed wall, open jet, perforated wall, or slotted wall boundary condition may be assigned to each individual wall panel centroid. The code also allows the user to solve wall interference problems with a mixed set of wall boundary conditions. ANTARES may be applied to a fullspan or semispan model test. A typical panel model of the test section consists of up to 8000 panels. A LU decomposition algorithm is used to solve the corresponding large linear system of equations. Therefore, it is critical to compile the code using DOUBLE PRECISION data type in order to obtain sufficiently accurate numerical solutions of the linear system. Available classical solutions of three different wall interference correction problems show excellent agreement with numerical results obtained by using ANTARES. Nomenclature dij — matrix coefficient bi = component of right hand side vector ci» • • • , c4 = boundary condition coefficients F = upwash Factor (see Ref. [8], p.29) i = wall panel index j = wall panel index I = slot parameter (see Ref. [3]) M = Mach number n = total number of unknowns N = total number of panels R = restriction parameter * Senior Aerodynamicist; Sverdrup Technology, Inc. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. u = unit round-off error or relative machine precision for floating point operations uw = axial interference velocity UQQ = reference velocity vw = interference velocity, ^-direction ww = interference velocity, ^-direction x = x-coordinate y = t/-coordinate z — z-coordinate Aa = ww/u00; angle of attack correction e = UW/UQQ', Blockage Factor fj,j = source strength slope p = bound associated with Gaussian elimination 4> = velocity potential of wind tunnel flow field (j)m = velocity potential of test article (f)w = wall interference velocity potential of the wind tunnel flow field in combination with a set of constants ci, • • • , c4. Then, in incompressible flow, we get: n ,^ = 0 (1) where x is the streamwise coordinate, n is the outward normal vector on the test section boundary, and ci,C2,cs,C4 are coefficients that describe the wall boundary conditions. Table 2 lists values of these coefficients for six different types of boundary conditions. The total perturbation velocity potential (/> may be written as the sum of the potential c/>m caused by the test article and the potential (j)w caused by the wind tunnel walls, i.e. the wall interference potential. We get : (/> = 4>m + w (2) Combining Eqs. (1) and (2), we get : + 02 d dx / • N = ci(t)
Gilles Belaud - One of the best experts on this subject based on the ideXlab platform.
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Multifunctionality of agricultural channel vegetation : A review based on community functional parameters and properties to support ecosystem function modeling
Ecohydrology & Hydrobiology, 2020Co-Authors: Gabrielle Rudi, Jean-stéphane Bailly, Gilles Belaud, Cécile Dagès, Philippe Lagacherie, Fabrice VinatierAbstract:Vegetation living in agricultural channels (drainage ditches or irrigation channels) supports ecosystem functions such as water flow regulation; retention of sediments, agricultural pollutants and plant propagules; and bank strengthening. The review focuses on plant community functional parameters (aggregations of plant functional traits) and community properties that need to be considered to study the dynamics of these ecosystem functions, to support further modeling work on the functioning of these semiaquatic ecosystems. It also provides an up-to-date overview of the effects of channel management practices on vegetation, because these practices are a potential lever with which to drive plant community functional parameters and properties and, in turn, ecosystem functions. The review points out that the mean height, density, and flexibility of the plant cover, sometimes integrated in the “Blockage Factor”, mainly influence the average components of the water flow associated with the functions of water regulation, and retention of sediments and non-floating propagules. The density of plants, or area of the plant cover at the water surface, are generally used to explain floating propagule retention. The biomasses of living and dead vegetation are the properties used to assess the retention of agricultural pollutants. Root density and root length density, as well as tensile strength of the root system, are parameters generally associated with bank strengthening. Regarding the effects of channel management practices, this work highlights that research generally has focused on the resulting plant richness and diversity, but has not provided much information on associated plant community functional parameters and properties.
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From 3D grassy vegetation point cloud to hydraulic resistance: Application to close-range estimation of Manning coefficients for intermittent open channels
Ecohydrology, 2017Co-Authors: Fabrice Vinatier, Jean-stéphane Bailly, Gilles BelaudAbstract:The understanding of interrelations between biotic and abiotic processes in intermittent open-channels is currently of primary importance to better assess the services and disservices they provide. A large body of literature attempts to characterize vegetation functional traits affecting hydraulic rugosity, through the introduction of the Blockage Factor of flow by vegetation. However, this Factor has multiple definitions and is still difficult to assess in the fields with actual and diverse vegetation covers, especially for grassy plants of ditches. Our study aims at predicting flow resistance from 3D vegetation characteristics using a close-range laser scanner. Flow resistance and vegetation 3D characteristics were defined using Manning coefficient and Blockage Factors, respectively. We tested combined effects of flow discharge against plant species and densities characterizing intermittent channels in a channel flume. Our results showed a variability of Manning coefficient describing flow rugosity against species and densities, with a highest rugosity for sclerophyllous species than herbaceous ones. Different Blockage Factors were calculated on the basis of scan clouds linked to Manning coefficients using non linear equation. The best relationship (R 2 = 0.9) were found for non linear equation relating Manning coefficients to a simplified Blockage Factor figuring the mean vegetation height deduced from the projection of the scan point cloud to the channel frontal area. The introduction of a coefficient to correct underestimated values issued from herbaceous species considering their reconfiguration under hydrodynamic loading is thus discussed.
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Vegetation patch effects on flow resistance at channel scale
2015Co-Authors: Jean-stéphane Bailly, Fabrice Vinatier, Gilles Belaud, David CombemaleAbstract:Thanks to a specific experimental design in a controlled channel, this paper aimed at quantifying how patches of four different ditches plant species affect integrated flow resistance parameters, the Manning coefficient. These plants, frequently encountered in the farmland ditches and irrigation channels of the south of France, were selected according to a large range of hydrophilic requirements, flexibility and branching complexity related to the plant Blockage Factor. Eight different spatial patches (regular, random, lateral or central patches) of each plant with crescent or similar plant densities were implanted at the bottom of a controlled channel where the water levels and water velocities were measured for three different discharges in steady and unsteady flow conditions. Resistance parameters (Manning parameters) were then estimated from the total head-loss, or from flow propagation velocity in the channel thanks to inversion of an hydrodynamic model. These experiments allow us to test the significance effect of channel vegetation patches and densities on flow resistance parameters at the reach scale.
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Using a terrestrial laser scanner to characterize vegetation-induced flow resistance in a controlled channel
2015Co-Authors: Fabrice Vinatier, Jean-stéphane Bailly, Gilles Belaud, David CombemaleAbstract:Vegetation characteristics providing spatial heterogeneity at the channel reach scale can produce complex flow patterns and the relationship between plant patterns morphology and flow resistance is still an open question (Nepf 2012). Unlike experiments in laboratory, measuring the vegetation characteristics related to flow resistance on open channel in situ is difficult. Thanks to its high resolution and light weight, scanner lasers allow now to collect in situ 3D vegetation characteristics. In this study we used a 1064 nm usual Terrestrial Laser Scanner (TLS) located 5 meters at nadir above a 8 meters long equipped channel in order to both i) characterize the vegetation structure heterogeneity within the channel form a single scan (Blockage Factor, canopy height) and ii) to measure the 2D water level all over the channel during steady flow within a few seconds scan. This latter measuring system was possible thanks to an additive dispersive product sprinkled at the water surface. Vegetation characteristics and water surfaces during steady flows from 6 different plant spatial design on channel bottom for 4 plant species were thus measured. Vegetation Blockage Factors at channel scale were estimated from TLS points clouds and analyzed.
Wen-jei Yang - One of the best experts on this subject based on the ideXlab platform.
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Simulation of Thermal Fluid Flow Transport in a Channel Containing Slot-Perforated Flat Plates
Journal of Heat Transfer, 2008Co-Authors: Shuichi Torii, Wen-jei YangAbstract:A numerical study is performed to investigate unsteady, two-dimensional, incompressible laminar flow over both sides of a slot-perforated flat surface in a pulsating channel flow. Consideration is given to the effects of the pulsating Strouhal number fSr, the Reynolds number Re, and the Blockage Factor, i.e., the ratio of plate thickness, δ, to channel width, W, on the heat-transfer performance and the velocity and thermal fields. It is found from the study that (i) time-averaged Nusselt number at the rear plate is amplified with Re, (ii) in contrast, the corresponding performance is attenuated with an increase in the Blockage Factor, whose effect becomes larger in the lower region of the Reynolds number, i.e., Re=100, and (iii) enhancement of the Nusselt number causes an increase in fSr, whose effect becomes minor near in the region of Re=100.
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Thermal-Fluid Flow Transport Phenomenon over Slot-Perforated Flat Plates Placed in Narrow Channel
Journal of Thermophysics and Heat Transfer, 2007Co-Authors: Shuichi Torii, Wen-jei YangAbstract:A numerical and experimental study is performed to investigate unsteady, twodimensional, incompressible laminar flow over both sides of a slot-perforated flat surface, which is placed in a narrow channel. Emphasis is placed on the effect of the Blockage Factor, i.e., the ratio of plate thickness, d, to channel width, W, on the heat transfer performance and the velocity and thermal fields. It is found from the study that: (i) when the slot width is increased, the alternating change in the fluid flow disturbs the thermal boundary layer formed along the plate and induces mixing of the upper and lower streams of the plate downstream from the slot, resulting in an amplification of heat transfer performance; (ii) heat transfer performance at the rear plate is induced with an increase in slot-width and Re; and (iii) by contrast, heat transfer performance is attenuated with an increase in the Blockage Factor, whose effect becomes larger in the lower region of the Reynolds number. These results are confirmed by the flow visualization using ion-exchange resins.
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Thermal Fluid Flow Transport Phenomena in a Channel Containing Slot-Perforated Flat Plates
ASME 2007 InterPACK Conference Volume 2, 2007Co-Authors: Shuichi Torii, Wen-jei YangAbstract:A numerical study is performed to investigate unsteady, two-dimensional, incompressible laminar flow over both sides of a slot-perforated flat surface in a pulsating channel flow. Enhances is placed on the effects of the pulsating Strouhal number, the Reynolds number Re, the Blockage Factor, i.e., the ratio of plate thickness, d, to channel width, W, on the heat transfer performance and the velocity and thermal fields. It is found from the study that: (i) when the fluid stream is pulsated, the alternating change in the fluid flow disturbs the thermal boundary layer formed along the plate and induces mixing of the upper and lower streams of the plate downstream from the slot, resulting in an amplification of heat-transfer performance; (ii) heat transfer performance at the rear plate is induced with Re; (iii) by contrast, heat transfer performance is attenuated with an increase in the Blockage Factor, whose effect becomes larger in the lower region of the Reynolds number; and (iv) heat transfer performance is intensified with an increase in fSr, whose effect becomes minor in the lower region of the Reynolds number.Copyright © 2007 by ASME
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Effect of Blockage Factor on thermal-fluid flow transport phenomenon over slot-perforated flat surface in channel
Volume 2: Symposia Parts A B and C, 2003Co-Authors: Shuichi Torii, Shinzaburo Umeda, Wen-jei YangAbstract:A numerical and experimental study is performed to investigate unsteady, two-dimensional, incompressible laminar flow over both sides of a slot-perforated flat surface, which is placed in a channel. Enhances is placed on the effect of the Blockage Factor, i.e., the ratio of plate thickness, δ, to channel width, W, on the heat transfer performance and the velocity and thermal fields. It is found from the study that: (i) when the slot width is increased, the alternating change in the fluid flow disturbs the thermal boundary layer formed along the plate and induces mixing of the upper and lower streams of the plate downstream from the slot, resulting in an amplification of heat transfer performance; (ii) heat transfer performance at the rear plate is induced with an increase in d/δ and Re; and (iii) by contrast, heat transfer performance is attenuated with an increase in the Blockage Factor, whose effect becomes larger in the lower region of the Reynolds number. These results are confirmed by the flow visualization using ion-exchange resins.