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Abstract
Experimental and numerical modeling of settlement and consolidation of cohesive sediment bed as well as fluidisation of cohesive sediment bed subject to surface water waves has been conducted in this research. Radioactive density gauge is utilized for determining density not only for the first experiment but extended for the second experiment, where measurement of density in the similar experiment was conducted by sampling method. It is a non intrusive measurement, therefore the accuracy increase.
Result of the experiment on settlement and consolidation is compared with numerical simulation by assuming the settling rate depends only on density. The comparison shows good agreement where the higher the initial density, the smaller the discrepancy between the numerical result and the experiment. The discrepancies of the samples range 0.7% - 5.0%. Settling rate of particles at a particular concentration is higher when the initial density of the mixing mud-water is denser.
During the fluidisation process, slight changes of density do occur in the upper part of the sediment layer about 2 – 10 mm below the interface. Prediction of the depth of fluidisation was conducted by estimating the total depth which the wave acts, by a trial and error method. The average discrepancy between measured and predicted depth is 7.4 mm. Results of the experiment are also compared with the viscous model and viscoelastic model. The viscous fluid model has a better agreement for low density of mud, and the viscoelastic fluid model depict more precise for high density of mud (ρ>1271.04 g/L).
The volume of fluid model in the computational fluid dynamic software package FLUENT was used for numerical simulation of the fluidisation process by assuming the model domain consist of a stratified density fluid. The wave motion was transferred to the fluid flow by applying a moving frame of reference to the model domain. Comparison to the experimental data indicates that the CFD model was appropriate to simulate the fluidisation phenomenon, and the performance of the CFD model was better than the viscous model and the viscoelastic model.