PREDICTION OF DEVELOPMENT OF SAND SPITS AND CUSPATE FORELANDS WITH RHYTHMIC SHAPES CAUSED BY SHORELINE INSTABILITY USING BG MODEL

The BG model (a three-dimensional model for predicting beach changes based on Bagnold’s concept) was used to simulate the shoreline evolution caused by the high-angle wave instability discussed by Ashton et al. Three calculations were carried out: the wave direction was assumed to be obliquely incident from 60˚ counterclockwise (Case 1) or from the directions of ±60˚ with probabilities of 0.5:0.5 (Case 2) and 0.65:0.35 (Case 3), while determining the incident wave direction from the probability distribution at each step. The three-dimensional development of multiple sand spits and cuspate forelands with rhythmic shapes was successfully explained using the BG model. The results of the previous study conducted by Ashton et al. were reconfirmed and reinforced.

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Flow dynamics and enhanced mixing in a converging–diverging channel

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.621 ◽

2016 ◽

Vol 807 ◽

pp. 167-204 ◽

Cited By ~ 10

Author(s):

S. W. Gepner ◽

J. M. Floryan

Keyword(s):

Three Dimensional ◽

Travelling Wave ◽

Flow Dynamics ◽

Streamwise Vortices ◽

Dimensional Model ◽

Three Dimensional Model ◽

Wave Instability ◽

Unsteady Separation ◽

Flow Stabilization ◽

Diverging Channel

An analysis of flows in converging–diverging channels has been carried out with the primary goal of identifying geometries which result in increased mixing. The model geometry consists of a channel whose walls are fitted with spanwise grooves of moderate amplitudes (up to 10 % of the mean channel opening) and of sinusoidal shape. The groove systems on each wall are shifted by half of a wavelength with respect to each other, resulting in the formation of a converging–diverging conduit. The analysis is carried out up to Reynolds numbers resulting in the formation of secondary states. The first part of the analysis is based on a two-dimensional model and demonstrates that increasing the corrugation wavelength results in the appearance of an unsteady separation whose onset correlates with the onset of the travelling wave instability. The second part of the analysis is based on a three-dimensional model and demonstrates that the flow dynamics is dominated by the centrifugal instability over a large range of geometric parameters, resulting in the formation of streamwise vortices. It is shown that the onset of the vortices may lead to the elimination of the unsteady separation. The critical Reynolds number for the vortex onset initially decreases as the corrugation amplitude increases but an excessive increase leads to the stream lift up, reduction of the centrifugal forces and flow stabilization. The flow dynamics under such conditions is again dominated by the travelling wave instability. Conditions leading to the formation of streamwise vortices without interference from the travelling wave instability have been identified. The structure and the mixing properties of the saturated states are discussed.

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NUMERICAL SIMULATION OF THREE-DIMENSIONAL SEGMENTATION OF ELONGATED WATER BODY USING BG MODEL

Coastal Engineering Proceedings ◽

10.9753/icce.v33.sediment.65 ◽

2012 ◽

Vol 1 (33) ◽

pp. 65 ◽

Cited By ~ 2

Author(s):

Takaaki Uda ◽

Masumi Serizawa ◽

Shiho Miyahara

Keyword(s):

Numerical Simulation ◽

Aspect Ratio ◽

Water Body ◽

Principal Axis ◽

Three Dimensional ◽

Large Aspect Ratio ◽

Dimensional Model ◽

Wave Direction ◽

Three Dimensional Model ◽

Three Dimensional Segmentation

In a slender water body with a large aspect ratio, the angle between the direction normal to the shoreline and the wave direction exceeds 45°, resulting in the emergence of cuspate forelands and the subdivision of a lake, because wind fetch along the principal axis becomes long. In this study, the BG model (a three-dimensional model for predicting beach changes based on Bagnold’s concept) was applied to this problem. The 3-D subdivision process of a long slender water body was predicted.

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