Print Email Facebook Twitter Ill-posedness in modeling mixed sediment river morphodynamics Title Ill-posedness in modeling mixed sediment river morphodynamics Author Chavarrias Borras, V. (TU Delft Rivers, Ports, Waterways and Dredging Engineering) Stecca, G. (National Institute of Water and Atmospheric Research (NIWA); Università di Trento) Blom, A. (TU Delft Rivers, Ports, Waterways and Dredging Engineering) Date 2018-04-01 Abstract In this paper we analyze the Hirano active layer model used in mixed sediment river morphodynamics concerning its ill-posedness. Ill-posedness causes the solution to be unstable to short-wave perturbations. This implies that the solution presents spurious oscillations, the amplitude of which depends on the domain discretization. Ill-posedness not only produces physically unrealistic results but may also cause failure of numerical simulations. By considering a two-fraction sediment mixture we obtain analytical expressions for the mathematical characterization of the model. Using these we show that the ill-posed domain is larger than what was found in previous analyses, not only comprising cases of bed degradation into a substrate finer than the active layer but also in aggradational cases. Furthermore, by analyzing a three-fraction model we observe ill-posedness under conditions of bed degradation into a coarse substrate. We observe that oscillations in the numerical solution of ill-posed simulations grow until the model becomes well-posed, as the spurious mixing of the active layer sediment and substrate sediment acts as a regularization mechanism. Finally we conduct an eigenstructure analysis of a simplified vertically continuous model for mixed sediment for which we show that ill-posedness occurs in a wider range of conditions than the active layer model. Subject Ill-posednessMixed sedimentRiver morphodynamics To reference this document use: http://resolver.tudelft.nl/uuid:030c1056-2128-4bbf-a57b-0cf0fc3f6b30 DOI https://doi.org/10.1016/j.advwatres.2018.02.011 ISSN 0309-1708 Source Advances in Water Resources, 114, 219-235 Part of collection Institutional Repository Document type journal article Rights © 2018 V. Chavarrias Borras, G. Stecca, A. Blom Files PDF 1_s2.0_S0309170817302658_main.pdf 1.5 MB Close viewer /islandora/object/uuid:030c1056-2128-4bbf-a57b-0cf0fc3f6b30/datastream/OBJ/view