• Validation of the 1D+ "ISM" model in transient regime.
• Inter-comparison of different 1D, 1D+, and 2D methods.
• Addressing methodological questions: handling of confluences and diffluences, boundary conditions, and structures with ISM.

Abstract

The objective of this thesis is to make operational an improved unidimensional modelisation method (1D+) for overflowing rivers, named Independent Sub-section Method (ISM) [Proust et al., 2009]. Whereas the classical 1D models solve the Saint-Venant or Bernoulli equation in the total cross-section, ISM solves the momentum equation in each subsection. Besides, ISM models explicitly the mass transfer between subsections, as well as the lateral momentum transfer. Before this thesis, this model has been validated with experimental data collected from different laboratories in steady uniform and non-uniform flows [Proust et al., 2009, 2010; Bousmar et al., 2016 ; Proust et al., 2016]. Firstly, ISM's performance has been assessed in unsteady flow. To this end, an unsteady experiment has been conducted. Data treatment methodology has been detailed. This experience has been simulated with ISM and with a 1D classical model in order to compare 1D+ and 1D approaches. We concluded that ISM reproduced better water depths than the 1D because (i) ISM accounts for the discharge distribution between subsections in the upstream boundary condition, (ii) ISM models explicitly the lateral discharge along the channel, (iii) the momentum transfer due to coherent structures and (iv) the momentum transfer due to lateral discharge exchange. Besides, at the interface MC/FP, the lateral velocity and the lateral discharge are well reproduced by the 1D+ simulations. Secondly, two methodological questions were treated, in order to apply ISM in operational conditions. The first question concerns the upstream boundary condition : how to construct the ISM upstream boundary condition (one discharge per subsection) from the available data (one unique discharge in the total cross-section). We proposed to compute the total discharge distribution in a steady uniform flow using ISM equations. This distribution of the total discharge at the upstream boundary condition is compared to the distributions computed using existing method. The second question concerns confluence modelisation, since ISM didn't model confluences before this thesis. We needed to find a solution to distribute the discharges in each subsection of the inflowing branches in a confluence over the 3 subsections of the outflowing branch. We proposed an approach that consists of conserving the discharges of the exterior FPs of the inflowing branches in the FPs of the outflowing branch, and summing the rest of subsection discharges of the inflowing branches in the MC of the outflowing branch. Then, a real river has been chosen to apply ISM in an operational conditions. Two situations has been studied : a simple model with one branch and a model with a confluence. Simulations has been realized with the 1D+ model ISM as well as with the 1D DCM method FudaaCrue and the 1D method DEBORD [Nicollet and Uan, 1979]. In the current ISM implementation, simulations showed the necessity to have an overflow over all the river FPs to be able to simulate. For the moment, we suggested to force the overflow, waiting for a more satisfactory solution. In this river case, after calibrating the turbulent exchange coefficient [Bousmar and Zech, 1999], ISM reproduces better the water levels than other 1D models with a maximal absolute errors lower than those obtained with the models Debord and FudaaCrue. In confluence simulation, the maximum absolute errors of Mage ISM were more important but still in the order of magnitures generally accepted. A suggestion has been done in order to enhance the ISM simulation. Furthermore, ISM enables to find more informations, unreachable to the classical 1D models as the filling and evacuation of FPs. Besides, ISM enables to analyze the discharge distribution between subsections, as well as the lateral discharge exchange and the shear stress between subsections.

Publications and communications

• Publication d’un article intitulé « Unsteady compound open-channel flows: a laboratory experiment and a 1D+ model» pour la conférence IAHR World (38th IAHR World Congress, September 1-6, 2019, Panama City, Panama); Auteurs : Yassine Kaddi, Sébastien Proust, Jean-Baptiste Faure, François-Xavier Cierco
• Article en préparation, intitulé «Unsteady flows in compound open-channels: laboratory and 1D+ numerical investigations» en préparation pour Journal of Hydraulic Research; Auteurs : Yassine Kaddi, Sébastien Proust, Jean-Baptiste Faure, François-Xavier Cierco

Cite the thesis

Yassine Kaddi. Modélisation 1D par lit (ISM) d’un réseau hydraulique ramifié maillé : application au contexte opérationnel de la prévision des fortes crues et des crues de dimensionnement d’ouvrages. Mécanique des fluides [physics.class-ph]. Université de Lyon, 2021. Français. ⟨NNT : 2021LYSE1200⟩. ⟨tel-03637028⟩

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