The objective of this paper is to investigate the rheological behavior of kaolinite and Hendijan mud, located at the northwest part of the Persian Gulf, and the dissipative role of this muddy bed on surface water waves. A series of laboratory rheological tests was conducted to investigate the rheological response of mud to rotary and cyclic shear rates. While a viscoplastic Bingham model can successfully be applied for continuous controlled shearstress tests, the rheology of fluid mud displays complex viscoelastic behavior in time-periodic motion. The comparisons of the behavior of natural Hendijan mud with commercial kaolinite show rheological similarities. A large number of laboratory wave-flume experiments were carried out with a focus on the dissipative role of the fluid mud. Assuming four rheological models of viscous, Kelvin-Voigt viscoelastic, Bingham viscoplastic, and viscoelastic-plastic for fluid mud layer, a numerical multi-layered model was applied to analyze the effects of different parameters of surface wave and muddy bed on wave attenuation. The predicted results based on different rheological models generally agree with the obtained wave-flume data implying that the adopted rheological model does not play an important role in the accuracy of prediction.
Results are presented from a combined experimental and numerical study aimed at comparing the flocculation behaviour of purely-cohesive (clay) and mixed (sand-clay) sediment suspensions under equivalent controlled hydrodynamic conditions. The experiments were conducted in a grid-stirred settling column and focussed on measuring the parametric influences of grid-generated shear rate and local suspended sediment concentrations on the timeevolution of the micro-and macrofloc size distributions generated in the column, as well as representative maximal and root-mean-square floc sizes. The results indicate that for kaolin clay suspensions under low-medium shear rates, initial aggregation rates and the peak or quasi-equilibrium floc sizes attained increase with the clay input concentration; this latter effect due to the larger proportion of macroflocs generated within these runs. By contrast, under high shear rates, representative floc sizes for kaolin clay suspensions remain largely unchanged over the experimental duration, with little influence from clay input or in-situ concentrations, and no macroflocs present in the resulting floc size distributions. The addition of the fine sand fraction to the kaolin clay suspensions is shown to reduce both initial aggregation rates and the representative floc sizes attained in the column for runs under low-medium shear rates, whilst having negligible effect on the flocculation behaviour for the sand-clay mixtures under high shear rates. These results suggest that the sand fraction inhibits flocculation at lower shear rates due to an additional floc break-up mechanism resulting from direct sand-clay interactions (e.g. particle-floc collisions). The importance of these inter-fractional (sandclay) interactions diminishes, in comparison to shear-induced floc break-up, under higher shear conditions. A one dimensional vertical (1DV) model incorporating a population balance equation (PBE) that includes new representation of these multi-fractional (sand-clay) collisions is applied to simulate the kaolin clay and sand-clay settling column tests. In general, the 1DV PBE model predictions provide good agreement with the measured in-situ concentrations and quasi-equilibrium floc sizes attained, but under-predict floc sizes during the initial aggregation phase due to uncertainty with the upper boundary condition in the 1DV model domain. Furthermore, the reliance of the 1DV PBE model predictions on empirical floc break-up rates associated with shear-induced floc fragmentation and multi-fractional (sand-clay) collisions warrants further attention to better define the microscale dynamics of these processes for their improved representation in the PBE model. It is anticipated that this multi-fractional approach represents an improved basis for modelling flocculation processes within natural sedimentary environments, such as estuaries and tidal inlets, where bed sediments often consist of interacting cohesive (i.e. muds) and non-cohesive (i.e. silts, sands) fractions.
The dissipation of regular and irregular waves on a muddy bed with the existence of following and opposing currents are investigated through a series of wave flume laboratory experiments. The commercial kaolinite is used as fluid mud layer. The laboratory results show the increase of both regular and irregular wave heights due to opposing currents. On the other hand, the following currents result to the decrease of the wave heights. In the numerical treatment, the deformation of wave due to current was first calculated based on the conservation equation of wave action and then the attenuation of this deformed wave due to the muddy bed is simulated by a multi-layered wave-mud interaction model. Acceptable agreements were observed between the numerical results and laboratory data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.