Ricardo B. Canelas

Dam-break flows over mobile beds: Experiments and benchmark tests for numerical models

In this paper, the results of a benchmark test launched within the framework of the NSF–PIRE project “Modelling of Flood Hazards and Geomorphic Impacts of Levee Breach and Dam Failure” are presented. Experiments of two-dimensional dam-break flows over a sand bed were conducted at Université catholique de Louvain, Belgium. The water level evolution at eight gauging points was measured as well as the final bed topography. Intense scour occurred close to the failed dam, while significant deposition was observed further downstream. From these experiments, a benchmark was proposed to the scientific community, consisting of blind test simulations, that is, without any prior knowledge of the measurements. Twelve different teams of modellers from eight countries participated in the study. Here, the numerical models used in this test are briefly presented. The results are commented upon, in view of evaluating the modelling capabilities and identifying the challenges that may open pathways for further research.

SPH–DCDEM model for arbitrary geometries in free surface solid–fluid flows

Abstract A unified discretization of rigid solids and fluids is introduced, allowing for resolved simulations of fluid–solid phases within a meshless framework. The numerical solution, attained by Smoothed Particle Hydrodynamics (SPH) and a variation of Discrete Element Method (DEM), the Distributed Contact Discrete Element Method (DCDEM) discretization, is achieved by directly considering solid–solid and solid–fluid interactions. The novelty of the work is centred on the generalization of the coupling of the DEM and SPH methodologies for resolved simulations, allowing for state-of-the-art contact mechanics theories to be used in arbitrary geometries, while fluid to solid and vice versa momentum transfers are accurately described. The methods are introduced, analysed and discussed. Initial validations on the DCDEM and the fluid coupling are presented, drawing from test cases in the literature. An experimental campaign serves as a validation point for complex, large scale solid–fluid flows, where a set of blocks in several configurations is subjected to a dam-break wave. Blocks are tracked and positions are then compared between experimental data and the numerical solutions. A Particle Image Velocimetry (PIV) technique allows for the quantification of the flow field and direct comparison with numerical data. The results show that the model is accurate and is capable of treating highly complex interactions, such as transport of debris or hydrodynamic actions on structures, if relevant scales are reproduced.

Two-dimensional depth-averaged modelling of dam-break flows over mobile beds

The paper is aimed at the description and validation of a novel two-dimensional depth-averaged simulation tool for highly unsteady discontinuous flows over complex time-evolving geometries. The conceptual model is developed within the shallow-flow framework and features non-equilibrium sediment transport. A fully conservative finite-volume discretization scheme is employed. The treatment of bed-slope source terms ensures that the scheme is well balanced and leads to correct energy losses in discontinuities. Existing laboratory data are used to validate the model and to discuss some of its embedded formulations. Blind-test comparison shows that the model is capable of describing the main dam-break flow and bed morphology features. The solution is shown to be sensitive to the formulations for sediment transport capacity and for adaptation length (Λ). A better functional relation of Λ with the Shields parameter is investigated. The quality of the solution is shown to be only marginally improved by the inclusion of turbulent stresses.

EXPERIMENTAL AND NUMERICAL STUDY OF SLIT-CHECK DAMS

This paper presents and discusses the results of laboratory tests and numerical simulations carried out to assess the efficiency of slit dams (open-type retention dams) and applicability as a short-term struc tural mitigation measure against debris flows in steep torrential channels. Inspired by common slit dam solutions, two different layouts of piers were tested in the experimental study – aligned and V-shaped. Some of the major experimental results about the sediment control efficiency are presented, showing that aligned layout is more appropriate to mitigate stony-type debris flows than the tested V-shaped solution. Actually, it was proved that slit-check dams mitigation efficiency is influenced by various variables and parameters, most of them previously studied by several authors, but also by pier layout in plan view. Considering aligned layout, 1.0d 95 to 1.4d 95 slit widths shall be considered to design effective slit dam solutions. Further, a numerical study was performed, providing relevant data that greatly enriched the experimental efforts and also support future slit dam design phases. The numerical results show similar quantities of retained solid material comparing with the experimental tests, indicating that the model provides reliable results, thus being able to support engineers and decision makers regarding debris flows mitigation.

Resolved Simulation of a Granular-Fluid Flow with a Coupled SPH-DCDEM Model

AbstractDebris flows represent some of the most relevant phenomena in geomorphological events. Because of the potential destructiveness of such flows, they are the subject of a vast amount of resea...

2D Simulation of Discontinuous Shallow Flows

The purpose of this work is to present a 2DH mathematical model suited for highly unsteady discontinuous geomorphic flows over complex geometries. In order to numerically simulate the flow, a finite-volume method based on the Roe Riemann solver is used, where the weak solutions are generated with a reviewed version of the solver. For simplified scenarios and fixed bed, it is shown that the 2DH model remains conservative with the careful introduction of source terms and reevaluation of the stability domain. The model is also able to find nonoscillatory solutions, is well balanced, and the correct evaluation of the discrete source terms is well made, ensuring energy dissipating solutions when necessary.