Process based model for riverine plastic fluxes

Hydrodynamic

Modelling particle size distribution in TELEMAC-2D with Population Balance Method

Hydrodynamic

Large-scale modeling of fine-grained sediment transport. Can we do any better?

status: publishe

Development of a new multiphase sediment transport model for free surface flows

© 2019 Elsevier Ltd Modeling of sediment transport in estuaries and coastal areas requires a lot of compromises to keep the computational costs within acceptable limits. Due to that, existing sediment transport models do not account for particle-scale physics, e.g. particle-particle interaction and turbulence modulation by sediment, which play a significant role, especially in the non-dilute regime. In the current study, a newly developed physics-based sediment transport model for free surface flows and its numerical implementation within the OpenFOAM framework is introduced. The new model is based on the multiphase mixture theory to account for interactions between sediment and water while tracking the free surface at the same time. A modified VOF equation for sediment-laden free surface flow was derived and implemented. The interphase momentum transfer is considered by solving an additional closure for the slip velocity which includes the effects of drag force, turbulent dispersion, and shear-induced diffusion. Dense granular flow rheology is used to supply the required closures for particle stresses. Additionally, suitable closures for the mixture and turbulent viscosities are introduced. The model was validated using experimental data and analytical solutions of five test cases of variable complexity. This includes pure sedimentation, laminar bedload transport, turbulent sheet flow, local scour due to a submerged jet, and wave-induced scour under a submarine pipeline.status: publishe

Evaluation of the two class population balance equation for predicting the bimodal flocculation of cohesive sediments in turbulent flow

status: publishe

Shoaling of bound infragravity waves on plane slopes for bichromatic wave conditions

status: publishe

An Approach to Modeling Biofilm Growth During the Flocculation of Suspended Cohesive Sediments

status: publishe

A tri-modal flocculation model coupled with TELEMAC for estuarine muds both in the laboratory and in the field

Estuarine and coastal regions are often characterized by a high variability of suspended sediment concentrations in their waters, which influences dredging projects, contaminant transport, aquaculture and fisheries. Although various three-dimensional open source software are available to model the hydrodynamics of coastal water with a sediment module, the prediction of the fate and transport of cohesive sediments is still far from satisfied due to the lack of an efficient and robust flocculation model to estimate the floc settling velocity and the deposition rate. Single-class and sometimes two-class flocculation models are oversimplified and fail to examine complicated floc size distributions, while quadrature-based or multi-class based flocculation models may be too complicated to be coupled with large scale estuarine or ocean models. Therefore, a three-class population balance model was developed to track the sizes and number concentrations of microflocs, macroflocs and megaflocs, respectively. With the assumption of a fixed size of microflocs and megaflocs, only four tracers are needed when coupled with the open-source TELEMAC system. It enables better settling flux estimates and better addresses the occurrence and concentration of larger megaflocs. This tri-modal flocculation model was validated with two experimental data sets: (1) 1-D settling column tests with the Ems mud and (2) in-situ measurements at the WZ Buoy station on the Belgian coast. Results show that the flocculation properties of cohesive sediments can be reasonably simulated in both environments. It is also found that the number of macroflocs created, when a larger macrofloc breaks up, is a statistical mean value and may not be an integer when applying the model in the field.status: publishe

Simulating multimodal floc size distributions of suspended cohesive sediments with lognormal subordinates: Comparison with mixing jar and settling column experiments

© 2019 Elsevier B.V. The Floc Size Distributions (FSDs) of suspended fine-grained sediment flocs play a prime role to estimate their own fate and the transport of contaminates attached to the flocs. However, developing an efficient flocculation model that is capable of simulating continuous and multimodal FSDs is still a challenge. Recently, the population balance equation solved by the Quadrature-Based Method of Moments (QBMM) with lognormal kernel density functions has been developed to investigate the aggregation and breakage processes. It coincides with some recent observations which describe a measured FSD in coastal waters with a set of constituted lognormal distributions. The newly developed lognormal QBMM was tested with several ideal flocculation kinetic kernels, none of which, however, was used for interpreting cohesive sediment dynamics. Therefore, it raised our interest to evaluate the model performance for fine-grained sediments in shear turbulence dominated environments. In this study, additional validations against two kaolinite laboratory experiments were tested in the framework of the extended QBMM. It is hypothesized that these subordinate lognormal distributions share the same value of standard deviation. Different from the previous methods, the common standard deviation is determined empirically to reduce the number of tracers and better represent the FSDs. With sediment flocculation kinetics, the predicted FSDs reasonably reproduce the FSDs observed in both the mixing chamber and the settling column experiments. Despite the lacking of explicit descriptions of microbial effects at the current stage, this model has the potential to be implemented into large-scale particle transport models and deserves a more in-depth study in the future.status: publishe