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Hervouet, Jean-Michel, Hermans, Johan (2022): Deux nouvelles espèces du genre Cynorkis Thouars (Orchidaceae, Orchidioideae) à Madagascar, et une nouvelle combinaison pour Cynorkis tryphioides var. leandriana (H.Perrier) Bosser. Adansonia (3) 44 (9): 63-79, DOI: 10.5252/adansonia2022v44a9

SummaryThree new species: Angraecum archangelicum, A. polyphemus and A. rotundifolium are described for the first time. Pectinariella is evaluated; a case is made to keep it at subgeneric level and the necessary two new combinations are made. Angraecum dasycarpum is neotypified. Finally A. ochraceum and A. setipes are compared with the latter being reduced to a synonym of the former.

SummaryFour new species,Cynorkis kiehnii, C. marianneae, C. marmorataandC. murex,are described for the first time.Cynorkis frappieriandC. raymondianaare compared, with the latter reduced to a synonym of the former. Cynorkis gaesiformis, C. galeata, C. nutansandC. stenoglossaare compared and considered one variable species, with the nameC. nutanshaving priority. Additional information is provided aboutC. mammuthusfollowing the discovery of living material in N Madagascar.

The original version of this article unfortunately contains an error. Figure 6 on page 28 and Figure 64 on page 140 were missing from the published version of the papers.

Summary.The tribe Malaxideae (Orchidaceae, subfamily Epidendroideae) (sensuPridgeonet al. 2005: 453) in Madagascar and adjacent archipelagos is revised. In this region it comprises the four genera:Liparis, Malaxis, OberoniaandStichorkis. All of the species are described and their typification, history, identification, distribution and habitat are discussed. Conservation assessments and distribution maps are included. A checklist of the genera and species and a key to their identification are provided. Six new species:Liparis bemarahensis, L. bosseri, L. chantaliae, L. laurentii, L. magnificaandL. superclareaeare described.

Two new species of Benthamia A. Rich. (Orchidaceae) from Madagascar, B. boiteaui Hervouet, sp. nov. and B. bosseri Hervouet, sp. nov., are described. Both have been found at the summit of Ambondrombe (Haute Matsiatra region, near Ambalavao), and also, for B. boiteaui Hervouet, sp. nov. in the Ranomafana national park, and for B. bosseri Hervouet, sp. nov. in the Andringitra massif. The two species are represented in the Paris herbarium at the Museum national d'Histoire naturelle (MNHN) by specimens collected in April 1941 by Pierre Boiteau and more recently, for B. boiteaui Hervouet, sp. nov. by specimens at K, MO and TAN, and for B. bosseri Hervouet, sp. nov., by specimens collected by Jean Bosser in April 1964. With linear leaves and an elliptic dorsal sepal, B. boiteaui Hervouet, sp. nov. can easily be distinguished from other Benthamia with white flowers. The non resupinated, drooping flowers and the arching spike of B. bosseri Hervouet, sp. nov. are very distinctive too.

The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10-100km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

Bank erosion can be an important form of morphological adjustment in rivers. With the advances made in computational techniques, two-dimensional (2D) depth-averaged numerical models have become valuable tools for resolving many engineering problems dealing with sediment transport. The objective of this research work is to present a simple, new, bank-erosion operator that is integrated into a 2D Saint-Venant-Exner morphodynamic model. The numerical code is based on an unstructured grid of triangular elements and finite-element algorithms. The slope of each element in the grid is compared to the angle of repose of the bank material. Elements for which the slope is too steep are tilted to bring them to the angle of repose along a horizontal axis defined such that the volume loss above the axis is equal to the volume gain below, thus ensuring mass balance. The model performance is assessed using data from laboratory flume experiments and a scale model of the Old Rhine. For the flume experiment case with uniform bank material, relevant results are obtained for bank geometry changes. For the more challenging case (i.e. scale model of the Old Rhine with non-uniform bank material), the numerical model is capable of reproducing the main features of the bank failure, induced by the newly designed groynes, as well as the transport of the mobilized sediment material downstream. Some deviations between the computed results and measured data are, however, observed. They are ascribed to the effects of three-dimensional (3D) flow structures, pore pressure and cohesion, which are not considered in the present 2D model.

This paper investigates the use of TELEMAC (a Finite Element-based hydrodynamics suite) on massively parallel computer architectures. The performance of TELEMAC is illustrated using two separate test cases. The first considers the use of TELEMAC-2D for simulating tidal currents in the vicinity of a renewable energy marine turbine farm, in order to provide reliable estimates of the expected energy yield. The second demonstrates the use of TELEMAC-3D for assessing the effects of fresh water discharges on the salinity distribution in a coastal lagoon. The simulations have been performed with meshes ranging from 2 to 12 million elements, and good scaling performance is achieved on a variety of different computer architectures.

This paper formulates a finite volume analogue of a finite element schematization of three-dimensional shallow water equations. The resulting finite volume schematization, when applied to the continuity equation, exactly reproduces the set of matrix equations that is obtained by the application of the corresponding finite element schematization to the continuity equation. The procedure allows the consistent and mass conserving coupling of the finite element Telemac model for three-dimensional flow with the finite volume Delft3D-WAQ model for water quality. The work has been carried out as part of a joint development by LNHE and WL∣Delft Hydraulics to explore the mutual interaction of their software. Copyright © 2006 John Wiley & Sons, Ltd.

On propose dans cet article une nouvelle methode pour le traitement des fonds rigides dans les codes de calcul d'evolution morphodynamique. Les evolutions du fond sont dues a la divergence du transport solide, et la methode proposee consiste a assurer, par une limitation de ce transport solide, une valeur de sa divergence qui interdise une erosion des fonds rigides. Les details de la technique sont presentes dans le cadre de la methode des elements finis.

On propose dans cet article une methode pour resoudre les equations de Navier- Stokes a surface libre, sans hypothese de pression hydrostatique, dans le cadre de la methode des elements finis. L'al...

The application of the European Water Framework Directive and the monitoring obligation on water quality for human consumption and industrial activities create a need for water quality assessment and monitoring systems. The MIGR’Hycar research project (see: http://www.migrhycar.com), partly funded by the French National Agency for Research (ANR), was initiated to provide decisional tools and fulfil operational needs for risks connected to oil spill drifts in continental waters (river, lakes, estuaries). Within the framework of the Migr’Hycar project, a three-dimensional (3D) numerical oil spill model has been developed. A Lagrangian model describes the transport of an oil spill near the free surface. The oil slick is represented by a large set of small particles. The model enables us to simulate the main transport process that acts on the spilled oil: advection (wind, current), diffusion (turbulence) and the shoreline oiling model. In order to validate the 3D 0uary 2006, the tanker “Sigmagas” suffering technical damage collided with another tanker “Happy Bride”. 60 t of heavy fuel has been spilled in Loire estuary because of tanker collision. The oil slick drift in the estuary and the affected area location have been followed with aerial and land observations. These observations allow us to assess the quality of the numerical predictions. Promising results are found and presented in this paper.

On evoque dans cet article, a partir de l'exemple du systeme Telemac, quelques aspects du developpement des systemes hydro-informatiques par des equipes pluridisciplinaires et internationales, et l'on decrit quelques solutions techniques comme la structuration de la programmation, le couplage externe, et la generation automatique de Fortran. On mentionne enfin l'exemple de la methode SPH, progres apporte par une discipline aussi differente de l'hydraulique que l'astronomie.

The evolution of laws on dam safety in France is briefly described. Most simulation studies for such problems are currently attempted using one-dimensional models, and we investigate here the possibility of moving to two-dimensional simulations. To date, these have been constrained by lack of available computational power. Parallel processing is an obvious solution, however, to date, an efficient parallel processing method that does not require major software recoding has proved elusive. Domain-decomposition is identified as being capable of overcoming these problems, as it allows pre-existing software to be adapted to run on clusters of supercomputer processors, workstations or PCs. The development of this new parallel method is outlined and its accuracy and efficiency tested in terms of the TELEMAC-2D model applied to the Malpasset dam break accident, which occurred in 1959 in the south of France. After a discussion of the data available, a sensitivity study is performed to evaluate some physical parameters in the equations, mainly the diffusion coefficient and the bottom friction. The friction appears to be the most important. A discrepancy of 3·4% on the wave celerity is obtained between the model and field observations for a number of locations where the arrival time of the flood wave is perfectly known. The efficiency of different scalar and parallel machines is assessed. The study concludes that 2-D simulations of flood waves are already possible on domains with a length of some 10 s of kilometres. Larger domains (100 to 400 km) are also within reach with supercomputers, or with parallel architectures. Copyright © 2000 John Wiley & Sons, Ltd.

La rupture du barrage de Malpasset a eu lieu dans le sud de la France en 1959 et a cause 421 victimes. Cet exemple de rupture totale d'un barrage-voute en fait un cas exceptionnellement interessant pour tester et valider les logiciels. Dans le passe, un modele reduit et un calcul unidimensionnel ont ete realises pour reproduire l'accident. Cet article presente des calculs bidimensionnels de la ruptute du barrage de Malpasset realises avec TELEMAC-2D. Les resultats sont meilleurs que ceux du modele unidimensionnel dans les coudes serres de la riviere ainsi que lorsque l'onde debouche dans la plaine littorale. L'etude conclut que les simulations bidimensionnelles d'ondes de crues sont possibles sur des domaines de plusieurs dizaines de kilometres de longueur.

Dynamic moving–boundary problems are a common occurrence in shallow–water hydraulics, yet no generally applicable or computationally efficient framework is available for their solution. In this paper a new scheme is presented that attempts to solve the problem of representing moving–boundary shallow–water hydrodynamics on fixed numerical grids. The scheme consists of three parts: identification of partly wet elements; the development of physically appropriate treatments to deal with mass and momentum conservation discrepancies in such areas within a two–dimensional finite–element framework; and the development and testing of a proof of mass conservation for the new scheme. In particular, the algorithm is unique in distinguishing between flooding and dam–break partly wet elements in contrast to previous solutions to this problem which typically treat both types in a similar fashion. In reality, consideration of the problem physics shows that mass and momentum conservation discrepancies can only be positively identified and corrected on elements of the flooding type. Accordingly, this disaggregation of partly wet elements into flooding and dam–break types is the approach adopted. This new scheme is tested against a structured series of numerical experiments including objective tests, a newly developed analytical solution for this problem and a unique high–resolution topographic data–set recently collected for an area of tidal beach on the eastern coast of the UK. The new scheme is shown to be physically realistic, mass conservative and appears to offer a significant improvement over standard finite–element techniques.

Cet article est une description generale du systeme hydroinformatique TELEMAC. On decrit tout d'abord les pre et postprocesseurs qui sont d'une part un mailleur et d'autre part un logiciel de presentation et d'artalyse de resultats. Les modules de simulation numerique resolvent tout un ensemble d'equations dans le domaine de la mecanique des fluides a surface libre : equations de Saint-Venant, equations de Navier-Stokes a surface libre, divers modeles de houle, de qualite d'eau et de transport sedimentaire. On aborde ensuite brievement le sujet du parallelisme avec decomposition de domaines et le couplage externe de codes.

The evolution of a sand dune under the effect of a steady flow is studied with different approaches, in the framework of the Telemac system, with the morphological module Sisyphe and the hydrodynamic module Telemac-2D. First a semi-empirical formula of total transport is tested, then, in a second approach, suspension is treated apart with a depth-averaged advection-diffusion equation. The advection field is then adapted to the concentration profile on the vertical, which leads to a reduction of the suspended transport rate. Mots-clefs hydrodynamique, morphodynamique, charriage, suspension.

In the centre of the Gironde estuary, EDF exploits a power plant. A hydrodynamic model is required to prevent different risks. Indeed, accurate water levels and velocity field are needed for flood control, sediment transport and associated deposition and transport of algae or pollutant. In order to enhance the accuracy of the hydrodynamic results and to tend to a fully predictive model, two attempts have been envisaged. The first one focuses on the tide imposed at the border by a combination of different harmonic waves whose constant harmonics are extracted from a tide model. Harmonic constants from different tide models have been compared and the influence of the harmonics number have been studied. The second attempt focuses on the friction coefficient. The values of the friction coefficient have been calibrated and compared to values predicted by the equation of van Rijn 2007. With the calibrated values, the differences between the measured and computed water levels are less than 10 cm. With the predictive friction formula, limited accuracy losses have been observed, which demonstrates the feasibility of using van Rijn formula for a configuration such as the Gironde.

The purpose of this thesis is to build higher order and less diffusive schemes for pollutant transport in shallow water flows or 3D free surface flows. We want robust schemes which respect the main mathematical properties of the advection equation with relatively low numerical diffusion and apply them to environmental industrial applications. Two techniques are tested in this work: a classical finite volume method and a residual distribution technique combined with a finite element method. For both methods we propose a decoupled approach since it is the most advantageous in terms of accuracy and CPU time. Concerning the first technique, a vertex-centred finite volume method is used to solve the augmented shallow water system where the numerical flux is computed through an Harten-Lax-Van Leer-Contact Riemannsolver [135]. Starting from this solution, a decoupled approach is formulated and is preferred since it allows to compute with a larger time step the advection of a tracer. This idea was inspired by [13]. The Monotonic Upwind Scheme for Conservation Law [89], combined with the decoupled approach, is then used for the second order extension in space. The wetting and drying problem is also analysed and a possible solution is presented. In the second case, the shallow water system is entirely solved using the finite element technique and the residual distribution method is applied to the solution of the tracer equation, focusing on the case of time-dependent problems. However, for consistency reasons the resolution of the continuity equation must be considered in the numerical discretization of the tracer. In order to get second order schemes for unsteady cases a predictor-corrector scheme [112] is used in this work. A first order but less diffusive version of the predictor-corrector scheme is also introduced. Moreover, we also present a new locally semi-implicit version of the residual distribution method which, in addition to good properties in terms of accuracy and stability, has the advantage to cope with dry zones. The two methods are first validated on academical test cases with analytical solution in order to assess the order of the schemes. Then more complex cases are addressed to test the robustness of the schemes and their performance under different flow conditions. Finally a real test case for which real data are available is carried out. An extension of the predictor-corrector residual distribution schemes to the 3D case is presented as final contribution. Even in this case the RD technique is completely compatible with the finite element framework used for the Navier-Stokes equations, thus its extension to the 3D case does not present any extra theoretical problem. The method is tested on preliminary cases; Cette thèse a pour objectif la construction de schémas d’ordre élevé et peu diffusifs pour le transport d’un scalaire dans les écoulements à surface libre, en deux ou trois dimensions. On souhaite en particulier obtenir des schémas robustes, qui gardent au niveau discret les propriétés mathématiques de l’équation de transport avec une faible diffusion numérique, et les utiliser sur des cas industriels. Dans ce travail deux méthodes numériques sont envisagées : une méthode aux volumes finis (VF) et une méthode aux résidus distribués (RD). Dans les deux cas, l’équation de transport est résolue avec une approche découplée, qui est la solution la plus avantageuse en termes de précision et de coûts de calcul. Pour ce qui concerne la méthode aux volumes finis, les équations de Saint-Venant couplées à l’équation du transport sont d’abord résolues avec un schéma dit vertex-centred où le flux numérique est approximé avec un solveur de Riemann appelé Harten-Lax-Van Leer-Contact [135]. A partir de cette approche, une formulation découplée est proposée. Cette dernière permet de résoudre l’équation du transport avec un pas de temps plus grand que celui de la formulation couplée. Cette idée a été d’abord proposée pour d’autres schémas dans [13]. Pour augmenter l’ordre de précision en espace, la technique MUSCL [89] est utilisée en combinaison avec l’approche découplée. Finalement, la problématique des zones sèches est abordée. Dans le cas de la méthode aux résidus distribués, les équations de Saint-Venant sont résolues avec une méthode éléments finis, et la méthode RD est utilisée seulement pour discrétiser l’équation du transport, en focalisant l’attention sur les problèmes non stationnaires. L’équation de continuité du fluide discrétisée est employée pour garantir la conservation de la masse et le principe du maximum. Pour obtenir des schémas d’ordre deux dans les problèmes non stationnaires, un schéma prédicteur-correcteur [112] est utilisé, en l’adaptant au cas de concentration moyennée sur la verticale. Une version d’ordre 1 mais peu diffusive, est aussi présentée dans ce travail. De plus, un schéma localement implicite, complètement nouveau, est aussi formulé pour pouvoir traiter le problème des bancs découvrant. Les deux techniques sont validées d’abord sur des cas simples, pour évaluer l’ordre de précision des schémas et ensuite sur des cas plus complexes pour vérifier aussi les autres propriétés numériques. Les résultats montrent que les nouveaux schémas sont à la fois précis et conservatifs, tout en gardant la monotonie comme le prévoient les démonstrations. Un cas d’application industriel est aussi présenté en conclusion. Le schéma prédicteur-correcteur RD est adapté aussi au cas 3D, sans aucun problème théorique nouveau, par rapport au cas 2D. Les propriétés de base des schémas sont validées sur des cas test préliminaires

The application of the European Water Framework Directive on water quality for human consumption and industrial activities creates a need for water quality assessment and monitoring systems. The MIGR'HYCAR research project (http://www.migrhycar.com) was initiated to provide decisional tools for risks connected to oil spills in continental waters (rivers, lakes and estuaries), which represent more than 50% of accidental spills in France. Within the framework of this project, a new numerical oil spill model has been developed, as part of the Telemac hydro-informatics system (see: (http://www.opentelemac.org), by combining Lagrangian and Eulerian methods. The Lagrangian model describes the transport of an oil spill near the free surface. The oil spill model enables to simulate the main processes driving oil plumes: advection, diffusion, oil beaching, oil re-floating, evaporation, dissolution, spreading and volatilization. Though generally considered as a minor process, dissolution is important from the point of view of toxicity. To model dissolved oil in water, an Eulerian advection-diffusion model is used. The fraction of dissolved oil is represented by a passive tracer. This approach is able to follow dissolved hydrocarbons in the water column. Laboratory experiments were conducted to characterise the numerous kinetics of the processes listed above. In addition, meso-scale dynamic experiments in artificial channels and test cases derived from the literature are used to validate the numerical model, L'application de la Directive Cadre sur l'Eau et l'obligation de surveillance de la qualité d'eau pour la consommation humaine et les activités récréatives ou industrielles, telles que la production d'eau potable, entraînent une forte demande pour des systèmes d'évaluation et de suivi de la qualité de l'eau. Le projet de recherche MIGR'HYCAR (http://www.migrhycar.com) a donc été mis en place pour répondre à un besoin opérationnel et à un défaut d'outils d'aide à la décision adaptés face aux déversements d'hydrocarbures en eaux continentales (rivières, lacs et estuaires) qui représente plus de 50% des déversements accidentels en France. Au cours du projet de recherche MIGR'HYCAR, un modèle mathématique de dérive de nappe d'hydrocarbures, composé d'un modèle lagrangien couplé à un modèle eulérien, a été développé dans la plate-forme hydro-informatique TELEMAC (http://www.opentelemac.org). Le modèle lagrangien décrit le mouvement de la nappe en surface en considérant celle-ci comme un ensemble de particules. Ainsi le modèle développé est capable de modéliser les principaux phénomènes agissant sur une nappe d'hydrocarbures une fois celle-ci déversée : convection, diffusion, échouage, re-largage, étalement, évaporation, dissolution et volatilisation. Bien que le phénomène de dissolution ne concerne qu'un très faible volume d'hydrocarbures, ce processus peut avoir des conséquences importantes du point de vue de la toxicité. Afin de suivre l'évolution du pétrole dissous, un modèle eulérien de suivi de traceurs a été adopté. La quantité de traceur dépend directement de la masse dissoute des particules lagrangiennes. Cette approche permet le suivi des hydrocarbures dissous dans la colonne d'eau. Des cinétiques effectuées en laboratoire ont pour but la calibration du modèle numérique. En complément de cas tests issus de la littérature et de cas réels, des résultats expérimentaux issus d'expérimentations effectuées en canal d'essai doivent permettre de vérifier et valider la qualité des simulations numériques sur des situations où les conditions ne sont que partiellement contrôlées