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 . : 3D modeling of fractional sediment transport

A 180° channel bend, Yen & Lee (1995)

ABSTRACT A fully three-dimensional non-hydrostatic model was applied to compute the flow and morphodynamic processes in a laboratory flume. The laboratory experiments provided data for bed deformation and grain sorting processes in a 180° channel bend. The data were used for validating the numerical model applying three different sediment transport approaches. A formula for uniform sediments was compared with two advanced non-uniform sediment transport formulas that considered the interaction between individual grain sizes by defining hiding-exposure approaches. Figure 2 shows an example of a three-dimensional view of the calculated bed deformation in the 180° channel bend. Results showed that the three-dimensional model is able to predict bed deformations and sorting processes in the laboratory bend with the correct magnitude and trend when using the default configuration. However, the computed results considerably overestimated the bar evolution. Computed results improved significantly when applying any of the two non-uniform sediment transport approaches. The best results were obtained when the absolute values of the hiding-exposure exponents were reduced for both approaches. The results of the non- uniform approaches showed less sorting intensity and smaller bar heights, both giving a better fit to the measured data. The computed results of the non-uniform approaches in comparison with the default configuration represent the physical mechanisms of the hiding-exposure effect well. The superior agreement with compared to the default approach shows that these mechanisms ocour in nature and that they significantly influence the bed deformation and sorting processes. Both non-uniform approaches predicted the total sediment transport with satisfactory agreement.

Picture 1: Measured bed changes in the planview


Picture 2: Calculated bed changes with using the v.Rijn formlua depicted in four different cross-sections

Picture 3: Distribution of d50 over the width in cross section 90°

Click [here] for an animation of the depth over time (8.0 MB)

Click [here] for an animation of cross section 173 over time (0.9 MB)

 : . 3D modeling of fractional sediment transport
 © by NR  Last Update 13.11.2006