Coupled Simulation of Oscillatory Flow, Sediment Transport and Morphology Evolution of Ripples Based on the Immersed Boundary Method

2014 ◽  
Author(s):  
Georgios A. Leftheriotis ◽  
Athanassios A. Dimas
Keyword(s):  
Sediment Transport ◽  
Numerical Solution ◽  
Suspended Sediment ◽  
Immersed Boundary Method ◽  
Oscillatory Flow ◽  
Orbital Motion ◽  
Immersed Boundary ◽  
Morphology Evolution ◽  
Boundary Method ◽  
Motion Amplitude

In the present study, numerical simulations of oscillatory flow over a rippled bottom, coupled with bed and suspended sediment transport, as well as the resulting morphology evolution, are performed. The simulations are based on the numerical solution of the Navier-Stokes equations and the advection-diffusion equation for the suspended load, while empirical formulas are used for the bed load. The bed morphological evolution is obtained by the numerical solution of the conservation of sediment mass equation. A fractional time-step scheme is used for the temporal discretization, while finite differences are used for the spatial discretization on a Cartesian grid. The Immersed Boundary method is implemented for the imposition of fluid and sediment boundary conditions on the ripple surface. Two types of ripples are examined, i.e., ripples of parabolic shape with sharp crests and sinusoidal ripples, and cases of ripple length to orbital motion amplitude ratio of 1.6 and ripple height to orbital motion amplitude ratios of 0.16, 0.20 and 0.24, at Reynolds number equal to 5×103. The effect of ripple steepness and ripple shape on suspended sediment and ripple migration is discussed.

scholarly journals Numerical Prediction of Hydrodynamic Loading on Circular Cylinder Array in Oscillatory Flow Using Direct-Forcing Immersed Boundary Method

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Ming-Jyh Chern ◽  
Wei-Cheng Hsu ◽  
Tzyy-Leng Horng
Keyword(s):  
Immersed Boundary Method ◽  
Oscillatory Flow ◽  
Immersed Boundary ◽  
Cylindrical Structures ◽  
Hydrodynamic Loading ◽  
Cylinder Array ◽  
Boundary Method ◽  
Marine Structure ◽  
Virtual Forces ◽  
Direct Forcing

Cylindrical structures are commonly used in offshore engineering, for example, a tension-leg platform (TLP). Prediction of hydrodynamic loadings on those cylindrical structures is one of important issues in design of those marine structures. This study aims to provide a numerical model to simulate fluid-structure interaction around the cylindrical structures and to estimate those loadings using the direct-forcing immersed boundary method. Oscillatory flows are considered to simulate the flow caused by progressive waves in shallow water. Virtual forces due to the existence of those cylindrical structures are distributed in the fluid domain in the established immersed boundary model. As a results, influence of the marine structure on the fluid flow is included in the model. Furthermore, hydrodynamic loadings exerted on the marine structure are determined by the integral of virtual forces according to Newton’s third law. A square array of four cylinders is considered as the marine structure in this study. Time histories of inline and lift coefficients are provided in the numerical study. The proposed approach can be useful for scientists and engineers who would like to understand the interaction of the oscillatory flow with the cylinder array or to estimate hydrodynamic loading on the array of cylinders.

Immersed Boundary Method for Simulation of Oscillatory Flow Past a Submerged Cylinder Near Above a Horizontal Bed

2014 ◽  
Author(s):  
Efstratios N. Fonias ◽  
Athanassios A. Dimas
Keyword(s):  
Reynolds Number ◽  
Immersed Boundary Method ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Immersed Boundary ◽  
Critical Range ◽  
Flow Past ◽  
Boundary Method ◽  
Flow Past A Cylinder ◽  
Submerged Cylinder

In the present work, the oscillatory flow past a submerged cylinder near above a horizontal bed is simulated by a Navier-Stokes equations solver. The boundary conditions, i.e., the no-slip condition on solid boundaries are imposed with the immersed boundary method. A Cartesian grid with variable size is used for the spatial discretization, and a time-splitting scheme is used for the temporal discretization. The numerical method was validated simulating the unidirectional flow past a cylinder at Reynolds number ReD = 300. For the oscillatory flow past a cylinder of diameter D at a distance G above a horizontal bed, all variables were rendered dimensionless using the maximum velocity, Uo, and the amplitude of the orbital motion, αo, of the oscillatory flow. Several tests with differing values of αo/D and G/D were considered, for Reynolds number Reα = 5,000 and Keulegan–Carpenter numbers in the range from 6.28 to 62.8. Results show that the critical range for the suppression of vortex shedding at the lower side of the cylinder is G/αo<0.01, while the critical range for the generation of vorticity uplift from the bed boundary layer is G/αo<1.0. Also, as G/D decreases, both the amplitude of the drag force and the bias towards positive values of the lift force increase.

scholarly journals INTERACTION BETWEEN WAVES AND HANGING HIGHLY FLEXIBLE KELP BLADES

2018 ◽  
pp. 31 ◽  
Author(s):  
Long-Huan Zhu ◽  
Kimberly Huguenard ◽  
David Fredriksson
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Immersed Boundary Method ◽  
Aquatic Vegetation ◽  
Wave Model ◽  
Immersed Boundary ◽  
Cable Model ◽  
Nutrient Distribution ◽  
Boundary Method ◽  
Recent Attention

The interaction between waves and flexible blades has drawn recent attention because of the capacity of nature-based infrastructure, such as aquatic vegetation and kelp, to attenuate waves. In this study, a new numerical model was developed to study the wave-blade interaction for both bottom-fixed and suspended blades. The dynamics of the blades simulated by a cable model were coupled with OpenFOAM®-based wave model IHFoam with the immersed boundary method. The results showed that the distribution of the blade-induced vortices was asymmetric with more vortices upstream for the single bottom-fixed blade while more vortices downstream for the single suspended blade. For both submerged and suspended canopies, the vortex distribution is also asymmetric. More vortices concentrate upstream for the submerged canopy. For a suspended canopy, more vortices concentrate upstream and below the bottom of the suspended canopy. Yet near the surface above the suspended canopy, more vortices concentrate downstream. Understanding the distribution of vortices is important for predicting the sediment transport and nutrient distribution.

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