scholarly journals 3D Modeling and Mechanism Analysis of Breaking Wave-Induced Seabed Scour around Monopile

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Xiaojian Liu ◽  
Cheng Liu ◽  
Xiaowei Zhu ◽  
Yong He ◽  
Qisong Wang ◽  
...  
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Laboratory Data ◽  
Suspended Load ◽  
Breaking Wave ◽  
Offshore Structure ◽  
Nearshore Sediment Transport ◽  
Wave Induced

Breaking wave-induced scour is recognized as one of the major causes of coastal erosion and offshore structure failure, which involves in the full 3D water-air-sand interaction, raising a great challenge for the numerical simulation. To better understand this process, a nonlinear 3D numerical model based on the open-source CFD platform OpenFOAM® was self-developed in this study. The Navier–Stokes equations were used to compute the two-phase incompressible flow, combining with the finite volume method (FVM) to discretize calculation domain, a modified VOF method to track the free surface, and a k−ε model to closure the turbulence. The nearshore sediment transport process is reproduced in view of shear stress, suspended load, and bed load, in which the terms of shear stress and suspended load were updated by introducing volume fraction. The seabed morphology is updated based on Exner equation and implemented by dynamic mesh technique. The mass conservative sand slide algorithm was employed to avoid the incredible vary of the bed mesh. Importantly, a two-way coupling method connecting the hydrodynamic module with the beach morphodynamic module is implemented at each computation step to ensure the fluid-sediment interaction. The capabilities of this model were calibrated by laboratory data from some published references, and the advantages/disadvantages, as well as proper recommendations, were introduced. Finally, nonbreaking- and breaking wave-induced scour around the monopile, as well as breaking wave-induced beach evolution, were reproduced and discussed. This study would be significantly helpful to understand and evaluate the nearshore sediment transport.

scholarly journals Numerical investigation of flow and scour around a vertical circular cylinder

2015 ◽  
Vol 373 (2033) ◽  
pp. 20140104 ◽  
Author(s):  
C. Baykal ◽  
B. M. Sumer ◽  
D. R. Fuhrman ◽  
N. G. Jacobsen ◽  
J. Fredsøe
Keyword(s):  
Sediment Transport ◽  
Vortex Shedding ◽  
Large Scale ◽  
Stokes Equations ◽  
Early Stage ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Suspended Load ◽  
Frequency Variation ◽  
Suspended Sediment Transport

Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynolds-averaged Navier–Stokes equations. The model incorporates (i) k - ω turbulence closure, (ii) vortex-shedding processes, (iii) sediment transport (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment transport is not accounted for. Alternatively, the effects of vortex shedding are found to be limited to the very early stage of the scour process. Flow features such as the horseshoe vortex, as well as lee-wake vortices, including their vertical frequency variation, are discussed. Large-scale counter-rotating streamwise phase-averaged vortices in the lee wake are likewise demonstrated via numerical flow visualization. These features are linked to scour around a vertical pile in a steady current.

Modelled nearshore sediment transport in open-water conditions, central north shore of Prince Edward Island, Canada

2016 ◽  
Vol 53 (1) ◽  
pp. 101-118 ◽  
Author(s):  
Gavin K. Manson ◽  
Robin G.D. Davidson-Arnott ◽  
Donald L. Forbes
Keyword(s):  
Sediment Transport ◽  
Prince Edward Island ◽  
Open Water ◽  
Suspended Load ◽  
Bedload Transport ◽  
Water Levels ◽  
Bed Load ◽  
Wave Direction ◽  
North Shore ◽  
Nearshore Sediment Transport

The central north shore of Prince Edward Island comprises embayments separated by subtle headlands that may constrain nearshore sediment transport. The study area includes two such embayments informally known as Brackley and Tracadie bights, both of which are sand-rich onshore and sand-starved between 20 and 50 m water depth. Storm winds and waves from the northwest and northeast are common in autumn and winter. The hydrodynamic model Delft3D is used to simulate waves, currents, water levels, and sediment transport in Brackley and Tracadie bights during 23 autumn seasons between 1955 and 2005. When compared with wave and current measurements from a field experiment in the autumn of 1999, the model successfully simulates conditions during storms and fair-weather periods. Results from the simulations show that, in autumn, the weighted mean direction of transport is to the southeast (133°). Bedload transport is directed onshore to the south (170°), and suspended load is directed offshore to the northeast (67°). When aggregated over the 23 seasons, transport magnitudes and directions differ between Brackley and Tracadie bights. Rates of transport are higher in Tracadie Bight and directed more to the east. During individual storms, transport is dependent on the storm wind and wave direction. Most transport occurs in bed load, and deposition occurs at the shoreline, with erosion offshore. The patterns of bed load and suspended load suggest a mechanism for the landward migration of this shoreline during transgression, and may explain the existence of the sand-starved zone offshore.

A 3D Wave-Structure-Seabed Interaction Analysis of a Gravity-Based Wind Turbine Foundation

2017 ◽  
Author(s):  
Yuzhu Li ◽  
Tian Tang ◽  
Muk Chen Ong
Keyword(s):  
Shear Stress ◽  
Wind Turbine ◽  
Pore Pressure ◽  
Stokes Equations ◽  
Wave Structure ◽  
Numerical Code ◽  
Seabed Interaction ◽  
Wave Induced ◽  
Seabed Soil ◽  
Dynamic Wave

In order to prevent the future risk of soil and structural failures, it is essential to evaluate the dynamic seabed soil behaviors in the vicinity of the offshore foundations under dynamic wave loadings. Three-dimensional (3D) numerical analysis is conducted on the interaction between waves, seabed soil and a gravity-based wind turbine foundation. An OpenFOAM based numerical code developed by Tang [1]for wave-structure-seabed interaction is applied. The nonlinear waves are modeled by solving the Navier-Stokes equations for incompressible flow. The dynamic structural response of the foundation is computed using a linear elasticity solver. The transient responses of the seabed are solved by an anisotropic poro-elastic soil solver. The dynamic interaction between different physical domains is implemented by boundary condition coupling and updating in the integrated FVM based framework. The dynamic wave pressure on the structure and the seabed, the elastic responses of the structure and the changes of the pore pressure, shear stress and seepage flow structure in the seabed are investigated. Highest wave-induced shear stress along the foundation is predicted by solving the deformable structure model. For the seabed soil in the vicinity of the foundation, it is found that the presence of the foundation affects the soil responses by amplifying the wave induced shearing effect on the underlying seabed. Vertical distributions of the pore pressure in the seabed beneath the foundation are investigated with different angles relative to the wave propagation direction. A parametric study of isotropic and anisotropic soil permeability is performed and demonstrates that for the simulated soil in this work, the consideration of the anisotropic permeability is suggested.

Numerical Investigation of Sediment Transport of Sandy Beaches by a Tsunami-Like Solitary Wave Based on Navier–Stokes Equations

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Cheng Liu ◽  
Xiaojian Liu ◽  
Changbo Jiang ◽  
Yong He ◽  
Bin Deng ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Solitary Wave ◽  
Stokes Equations ◽  
Laboratory Data ◽  
Sandy Beaches ◽  
Transport Processes ◽  
Navier Stokes ◽  
Wave Runup ◽  
Navier Stokes Equations

To improve our current understanding of tsunami-like solitary waves interacting with sandy beach, a nonlinear three-dimensional numerical model based on the computational fluid dynamics (CFD) tool OpenFOAM® is first self-developed to better describe the wave propagation, sediment transport, and the morphological responses of seabed during wave runup and drawdown. The finite volume method (FVM) is employed to discretize the governing equations of Navier–Stokes equations, combining with an improved volume of fluid (VOF) method to track the free surface and a k–ε model to resolve the turbulence. The computational capability of the hydrodynamics and the sediment transport module is well calibrated by laboratory data from different published references. The results verify that the present numerical model can satisfactorily reproduce the flow characteristics, and sediment transport processes under a tsunami-like solitary wave. The water-sediment transport module is then applied to investigate the effects of prominent factors, such as wave height, water depth, and beach slope, in affecting the beach profile change. Finally, a dimensionless empirical equation is proposed to describe the transport volume of onshore sediment based on simulation results, and some proper parameters are recommended through the regression. The results can be significantly helpful to evaluate the process of transported sediment by a tsunami event.

scholarly journals SEDIMENT TRANSPORT AND RIPPLES DUB TO WAVES AND CURRENTS

1978 ◽  
Vol 1 (16) ◽  
pp. 98
Author(s):  
Zbigniew Pruszak ◽  
Ryszard B. Zeidler
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Sediment Transport ◽  
Boundary Layer Equation ◽  
Laboratory Data ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Flat Bottom ◽  
Rippled Bed ◽  
Bed Friction

Water velocities and shear stresses have been determined for a laminar boundary layer of a progressive wave travelling over a regular series of ripples. The Lavrentiev variational method was used to transform conformally the water area with ripples into a strip with flat bottom, while the Lin approach permitted solution of the boundary layer equation. The theoretical prediction of the bed friction was verified experimentally with a new mechanical apparatus. By coupling the theoretical shear stress at the rippled bed with laboratory data for ripple parameters one can expose the friction conditions that control the growth and decay of ripples. If waves develop higher values of shear stress, the rippled bed becomes gradually washed out. Eor known shear stresses, basing on the Erijlink-Bijker formula one can compute sediment transport rates. In the respective diagram, a curve of s.t. rate versus bottom friction consists of two branches. The stages of the growth and decay of ripples are reflected in the lower and upper branches of the curve. For identical ripple height there are two values of s.t. rate , for two different wave intensities, likely to differ by as much as 25 per cent. Three-dimensional ripples have been analyzed with regard to bed friction and compared with two-dimensional conditions.

scholarly journals A MULTIPLE-SIZED TRANSPORT FORMULA FOR NONUNIFORM SEDIMENTS UNDER CURRENT AND WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 34 ◽  
Author(s):  
Weiming Wu ◽  
Qianru Lin
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Size Composition ◽  
Suspended Load ◽  
Transport Rate ◽  
Bed Load ◽  
Nonuniform Sediment ◽  
Load Transport ◽  
Bed Load Transport ◽  
Bed Material

Nonuniform sediment transport exhibits difference from uniform sediment, even when the mean grain size is the same for both cases. The hiding, exposure, and armoring among different size fractions in the nonuniform bed material may significantly affect sediment transport, morphological change, bed roughness, wave dissipation, etc. It is necessary to develop multiple-sized sediment transport capacity formula to improve the accuracy and reliability of coastal analysis tools. The Wu et al. (2000) formula, which was developed for river sedimentation, is herein extended to calculate multiple-sized sediment transport under current and waves for coastal applications. This formula relates bed-load transport to the grain shear stress and suspended-load transport to the energy of the flow system. It considers the effect of bed material size composition in the hiding and exposure correction factor, which is omitted in many other existing formulas. Methods have been developed in this study to determine the bed shear stress due to waves only and combined current and waves, and in turn to compute the bed-load and suspended-load transport rates using the Wu et al. (2000) formula without changing its original formulation. The enhanced bed-load formula considers the effect of wave asymmetry on sediment transport, calculates the onshore and offshore bed-load transport rates separately and then derives the net transport rate, whereas the enhanced suspended-load formula calculates only the net transport rate due to the limit of available data. The formula has been tested using the single-sized and multiple-sized sediment transport data sets. The formula provides reliable predictions in both fractional and total transport rates. More than half of the test cases are predicted within a factor of 2 of the measured values, and more than 90% of the cases are within a factor of 5. This accuracy is generally reasonable for sediment transport under current and waves, which is very complex and little understood.

scholarly journals Characteristics of Breaking Wave Forces on Piles over a Permeable Seabed

2021 ◽  
Vol 9 (5) ◽  
pp. 520
Author(s):  
Zhenyu Liu ◽  
Zhen Guo ◽  
Yuzhe Dou ◽  
Fanyu Zeng
Keyword(s):  
Wave Breaking ◽  
Stokes Equations ◽  
Slope Angle ◽  
Wave Force ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Secondary Wave ◽  
Wave Forces ◽  
Breaking Wave ◽  
Breaking Wave Forces

Most offshore wind turbines are installed in shallow water and exposed to breaking waves. Previous numerical studies focusing on breaking wave forces generally ignored the seabed permeability. In this paper, a numerical model based on Volume-Averaged Reynolds Averaged Navier–Stokes equations (VARANS) is employed to reveal the process of a solitary wave interacting with a rigid pile over a permeable slope. Through applying the Forchheimer saturated drag equation, effects of seabed permeability on fluid motions are simulated. The reliability of the present model is verified by comparisons between experimentally obtained data and the numerical results. Further, 190 cases are simulated and the effects of different parameters on breaking wave forces on the pile are studied systematically. Results indicate that over a permeable seabed, the maximum breaking wave forces can occur not only when waves break just before the pile, but also when a “secondary wave wall” slams against the pile, after wave breaking. With the initial wave height increasing, breaking wave forces will increase, but the growth can decrease as the slope angle and permeability increase. For inclined piles around the wave breaking point, the maximum breaking wave force usually occurs with an inclination angle of α = −22.5° or 0°.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

Shear stress and sediment transport calculations for sheet flow under waves

2003 ◽  
Vol 47 (3) ◽  
pp. 347-354 ◽  
Author(s):  
Peter Nielsen ◽  
David P. Callaghan
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Sheet Flow
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