Optimizing inlet channels of small hydropower plants with TELEMAC-3D

Hydrodynamic

Flow structure in a compound channel: benchmarking 2D and 3D numerical models

The benchmarking test of 2D and 3D numerical models on a compound channel flow with a rectangular-shaped main channel and a rectangular-shaped floodplain was carried out by the IAHR Working Group on Compound Channels. The selected test case is the flume experiment by Nezu and Tominaga (1991). Nine depth-averaged 2D models and four 3D models participated in the benchmark. In the 2D models, the depth-averaged streamwise velocity profiles in the lateral direction were compared. In the 3D models, velocity components in three directions as well as the distribution of the turbulence kinetic energy in a cross-section were compared. Through the comparison, the applicability and limitations of each model are highlighted and discussed with regard to the model characteristics.Konferencija je održana na daljinu (on-line), bez fizičkog prisustva i sav materijal se nalazi na web-stranici organizatora skupa

Modélisation numérique bidimensionnelle du transport solide et de la dynamique fluviale. Validation sur deux sites en Loire et sur l Arc

La modélisation à une échelle fine des évolutions morphologiques à court terme (quelques années au maximum) en rivière est rendue possible par des outils numériques qui résolvent les équations de Saint-Venant bidimensionnelles et calculent le transport solide et l évolution du lit résultante sur un maillage représentant la topographie du site. Ces outils sont encore peu utilisés en ingénierie car il existe de fortes incertitudes sur les processus physiques à prendre en compte et les formulations à utiliser pour les représenter (charriage/suspension, formes de fond, granulométrie étendue, effet de la pente ). Le but de la thèse est de tester les possibilités de ce type d outils et de définir une méthodologie pour leur application. L outil utilisé est un code industriel (système TELEMAC) qui dispose de la plupart des fonctionnalités nécessaires dont le couplage entre calculs hydrauliques et sédimentaires, la prise en compte des fonds non-érodables et la granulométrie étendue. La démarche suivie consiste à appliquer ce code à deux cas pour lesquels des campagnes de mesures détaillées sont disponibles. L un des sites choisis se trouve sur la Loire près du Fresne-sur-Loire et d Ingrandes, l autre sur l Arc en Savoie près de La Chambre. Dans les deux cas le processus de transport dominant est le charriage. Les périodes simulées sont des crues pour lesquelles l évolution bathymétrique du lit a été mesurée ; dans le cas de la Loire des simulations à plus long terme (quelques années) sont aussi présentées. Les évolutions mesurées sont reproduites de manière satisfaisante. Les formulations utilisées sont cohérentes entre les deux cas, mais les processus pris en compte sont différents : dans le cas de la Loire qui est une rivière de sable il est nécessaire de tenir compte des dunes, alors que dans le cas de l Arc qui est une rivière de gravier les processus prépondérants sont le tri granulométrique et les effets de pente. L intérêt de l outil a donc été démontré, et des enseignements précieux pour son utilisation ont été dégagés. Ils concernent en particulier le choix des formulations pour représenter les processus physiques, la définition de la complexité minimale nécessaire de ces formulations selon les sites et les objectifs de la modélisation, et la méthodologie de calage de ces formulations à partir des données disponibles.Numerical modelling of morphological evolutions in rivers at a fine spatial scale can be undertaken with models solving the two-dimensional shallow water equations and computing bed load transport and the resulting bed evolution on a mesh representing the topography of the site. These tools are not widely used in engineering applications yet because there remain large uncertainties on the physical processes to take into account and the corresponding formulations (bed load/suspension, bed forms, graded sediment, bed slope effects ). The goal of this work is to assess the possibilities of this kind of tools and to define a methodology for their use. The tool we will use is a commercial modelling package (TELEMAC system) that has most of the necessary functionalities (dry bed, coupling between hydrodynamic and sediment computations, rigid bed, graded sediment ) already implemented. We will apply this tool on two sites where detailed data are available. One of them is on the Loire river near Fresne-sur-Loire and Ingrandes, the other on the river Arc in Savoie near La Chambre. In both cases, bed load is the main transport process. The periods simulated are floods for which computed bed evolutions are compared to measurements. Longer term simulations (a few years) are also presented in the case of the Loire river. The measured evolutions are well reproduced by the model. The formulations used are coherent between the two cases, but the physical features and processes taken into account are different: dunes in the case of the Loire which is a sand-bed river, graded sediment and bed slope effects in the case of the Arc which is a gravel bed river. The pertinence of the numerical tool tested is demonstrated, and many advises are presented about the way it should be used. They concern in particular the choice of formulations to represent physical processes depending on the site studied, and the way these formulations should be calibrated with the available data.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Coupling Surface Grain-Size and Friction for Realistic 2D Modelling of Channel Dynamics on Massive Bedload Deposition

International audienceThe paper compares observations from a small-scale model of a planned debris basin trapping a massive bedload deposition with results of a 2D depth-averaged hydraulic and morphologic numerical model. It is used as a validation case of its capability to reproduce flow and bed changes in this steep and laterally unconfined case with coarse sediment. The numerical model used a fractional transport approach enabling to compute grain size sorting and segregation processes. The fractional transport rates were computed with Meyer-Peter Muller equation. Water depth was computed with the “variable power equation” developed by Ferguson to account for both low, intermediate and high submergence (depth/grain size). Comparison of the numerical and physical models was done qualitatively (based on animations of the numerical results compared to videos of the physical model) and quantitatively computing an indicator of ratio of active channels (i.e., transporting sediment) measured using the large scale image velocimetry technique applied to time-lapse videos. The results show that fractional transport in itself does not bring significant improvement. However, dramatic improvements of the modelled channelization pattern and dynamics, both qualitatively and quantitatively, emerged when coupling the fractional transport with the friction law (through the active layer D84). In essence, when computing local grain size, it should be taken into account in the hydraulics too. This approach is a step forward to achieve better predictions of flow and channel dynamics on unconfined active morphologies and depositional systems

Coupler granulométrie de surface et loi de frottement pour une modélisation 2D réaliste de la dynamique des chenaux des zones de dépôts massifs de charriage

International audienceThe paper compares observations from a small-scale model of a planned debris basin trapping a massive bedload deposition with results of a 2D depth-averaged hydraulic and morphologic numerical model. It is used as a validation case of its capability to reproduce flow and bed changes in this steep and laterally unconfined case with coarse sediment. The numerical model used a fractional transport approach enabling to compute grain size sorting and segregation processes. The fractional transport rates were computed with Meyer-Peter Muller equation. Water depth was computed with the “variable power equation” developed by Ferguson to account for both low, intermediate and high submergence (depth/grain size). Comparison of the numerical and physical models was done qualitatively (based on animations of the numerical results compared to videos of the physical model) and quantitatively computing an indicator of ratio of active channels (i.e., transporting sediment) measured using the large scale image velocimetry technique applied to time-lapse videos. The results show that fractional transport in itself does not bring significant improvement. However, dramatic improvements of the modelled channelization pattern and dynamics, both qualitatively and quantitatively, emerged when coupling the fractional transport with the friction law (through the active layer D84). In essence, when computing local grain size, it should be taken into account in the hydraulics too. This approach is a step forward to achieve better predictions of flow and channel dynamics on unconfined active morphologies and depositional systems

Global economic burden of unmet surgical need for appendicitis

Background There is a substantial gap in provision of adequate surgical care in many low- and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially

Global economic burden of unmet surgical need for appendicitis

Background There is a substantial gap in provision of adequate surgical care in many low- and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially