scholarly journals Numerical Analysis of Modified Seabed Topography Due to the Presence of Breakwaters of Varying Reflection Characteristics using Physics-based Morphology Model [SeoulFoam]

2021 ◽  
Vol 33 (4) ◽  
pp. 168-178
Author(s):  
Yong Jun Cho
Keyword(s):  
Boundary Layer ◽  
Numerical Model ◽  
Reflection Coefficient ◽  
Wave Amplitude ◽  
Standing Waves ◽  
Sand Wave ◽  
Sand Waves ◽  
Seabed Topography ◽  
Morphology Model ◽  
Reflection Characteristics

Numerical simulations were implemented to look into the modified seabed topography due to the presence of breakwaters of varying reflection characteristics. The numerical model was composed of OlaFlow, an OpenFoam-based tool box, and a physics-based morphology model [Seoul Foam]. In doing so, the interaction between the seabed, which undergoes deformation due to siltation and scouring, and the incoming waves was described using Dynamic Mesh. The rubble-mound, vertical, and curved slit caisson breakwaters with varying reflection characteristics resulted in standing waves that differ from each other, shown to have a significant influence on the seabed topography. These results are in line with Nielsen’s study (1993) that sands saltated under the surface nodes of standing waves, where the near-bed velocities are most substantial, convected toward the surface antinodes by boundary-layer drift. Moreover, the crest of sand waves was formed under the surface antinodes of standing waves, and the trough of sand waves was formed under the surface antinodes. In addition, sand wave amplitude reaches its peak in the curved slit caisson with a significant reflection coefficient, and the saltation of many grains of sand would cause this phenomenon due to the increased near-bed velocity under the nodes when the reflection coefficient is getting large.

scholarly journals Numerical Analysis of Modified Bed-profiles due to the Presence of a Rubble Mound Breakwater using Physics-Based Morphology Model[SeoulFoam]

2021 ◽  
Vol 8 (3) ◽  
pp. 151-163
Author(s):  
Yong Jun Cho
Keyword(s):  
Numerical Simulations ◽  
Wave Length ◽  
Standing Waves ◽  
Sea Waves ◽  
Incoming Wave ◽  
Sand Waves ◽  
Morphology Model ◽  
Scouring Depth ◽  
Rubble Mound ◽  
The Many

Among the many scouring-protection works near a rubble mound breakwater, stacking armoring rocks in multiple or single layers are most popular. The rationale of these scouring-protection works is based on the Equilibrium regime or the maximum scouring depth. However, considering natural beaches, which constantly change their shape according to sea waves conditions, the equilibrium regime or the maximum scouring depth mentioned above seems to foot on the fragile physical background. In this study, in order to test the above hypothesis, numerical simulations were carried out on the partial reflection from the slopes of rubble mound breakwater, and its ensuing standing waves formed in the front seas of a breakwater, the change in the bed profiles due to the formation of standing waves, and scouring depth at the base of a rubble mound breakwater. In doing so, numerical simulations were implemented using OlaFoam, an OpenFoam-based toolbox, and SeoulFoam (Cho, 2020), a physics-based morphology model. Numerical results show that the wave length of sand waves is closely linked with the incoming wave period, while amplitudes of sand waves are determined by incoming wave height. Moreover, the seabed profiles underwent significant changes due to the presence of a rubble mound breakwater. It was shown that the size of sand waves increased when compared before the installation, and the shape of sand waves is getting skewed toward the shore direction. It was also shown that as exposure time to standing waves increased, the amplitude of sand waves also increased, and the scouring depth near the base of a breakwater increased. These results are contrary to the Equilibrium regime, and the scouring prevention works based on the stacking of armoring rocks should be re-evaluated.

Pipeline plough performance in sand waves. Part 2: kinematic calculation method

2010 ◽  
Vol 47 (1) ◽  
pp. 65-77 ◽  
Author(s):  
Mark Fraser Bransby ◽  
Michael John Brown ◽  
Keith Lauder ◽  
Andrew Hatherley
Keyword(s):  
Calculation Method ◽  
Wave Amplitude ◽  
Scale Model ◽  
Sand Wave ◽  
Small Scale ◽  
Offshore Pipelines ◽  
Sand Waves ◽  
Calculation Methodology ◽  
Small Scale Model ◽  
Good Agreement

Offshore pipelines can be buried in the seabed by ploughing a trench, placing the pipe at its base, and then backfilling. The presence of sand waves or megaripples on the seabed surface can affect the progress of the plough and prevent the plough from generating a level trench with a uniform trench depth. A calculation method has been presented that makes assumptions about the motion of the plough to predict the kinematics of ploughs through regions of nonuniform seabeds. Results from the calculation methodology are compared with those from small-scale model tests with good agreement, and the detailed kinematics of ploughs are then examined. The calculation method suggests that as a plough moves through a sand-wave field, the oscillation of the plough about the skids results in the trench base being formed alternately by the share tip and heel. The new method allows prediction of likely offshore plough performance given known plough geometry, sand wavelength, and wave amplitude and may be used as a tool for assessing the feasibility of pipeline ploughing in zones of sand waves or megaripples.

Study of sand wave migration over five years as observed in two windfarm development areas, and the implications for building on moving substrates in the North Sea

2014 ◽  
Vol 105 (4) ◽  
pp. 241-249 ◽  
Author(s):  
Ken P. Games ◽  
David I. Gordon
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
Oil And Gas ◽  
Sand Wave ◽  
Sand Waves ◽  
Migration Rates ◽  
The North ◽  
The North Sea ◽  
Wave Migration ◽  
The Impact

ABSTRACTSand waves are well known indicators of a mobile seabed. What do we expect of these features in terms of migration rates and seabed scour? We discuss these effects on seabed structures, both for the Oil and Gas and the Windfarm Industries, and consider how these impact on turbines and buried cables. Two case studies are presented. The first concerns a windfarm with a five-year gap between the planning survey and a subsequent cable route and environmental assessment survey. This revealed large-scale movements of sand waves, with the displacement of an isolated feature of 155 m in five years. Secondly, another windfarm development involved a re-survey, again over a five-year period, but after the turbines had been installed. This showed movements of sand waves of ∼50 m in five years. Observations of the scour effects on the turbines are discussed. Both sites revealed the presence of barchans. Whilst these have been extensively studied on land, there are few examples of how they behave in the marine environment. The two case studies presented show that mass transport is potentially much greater than expected and that this has implications for choosing turbine locations, the effect of scour, and the impact these sediment movements are likely to have on power cables.

scholarly journals Study on hydraulic resistance of erodible bed at the Chiyoda experimental flume

2014 ◽  
Vol 39 ◽  
pp. 81-87
Author(s):  
T. Kakinuma ◽  
T. Inoue ◽  
R. Akahori ◽  
A. Takeda
Keyword(s):  
Large Scale ◽  
Flow Distribution ◽  
Longitudinal Survey ◽  
Sand Wave ◽  
Vertical Flow ◽  
Sand Waves ◽  
Wave Development ◽  
Logarithmic Distribution ◽  
Steady Flow Condition ◽  
Experimental Flume

Abstract. The authors made erodible bed experiments under steady flow condition at the Chiyoda Experimental Flume, a large-scale facility constructed on the floodplain of the Tokachi River, and observed sand waves on the bed of the flume. In this study, the characteristics of the sand waves are examined along the longitudinal survey lines and confirmed to be dunes. Next, the authors estimated Manning's roughness coefficients from the observed hydraulic values and assumed that the rise of the coefficients attributed to the sand wave development. Finally, vertical flow distribution on the sand waves are examined, and observed velocity distribution on the crest of waves found to be explained by the logarithmic distribution theory.

scholarly journals NUMERICAL MODEL OF BREAKWATER WAVE FLOWS

1988 ◽  
Vol 1 (21) ◽  
pp. 149 ◽  
Author(s):  
Alex C. Thompson
Keyword(s):  
Mathematical Model ◽  
Numerical Model ◽  
Reflection Coefficient ◽  
Water Wave ◽  
Wave Equations ◽  
Seepage Flow ◽  
Experimental Results ◽  
Simplified Model ◽  
Flow Equations ◽  
Shallow Water Wave Equations

A mathematical model of flow on a sloping breakwater face is described and results of calculations compared with some experimental results to show how the model can be calibrated. Flow above the surface of the slope is represented by the shallow water wave equations solved by a finite difference method. Flow within the breakwater is calculated by one of two methods. A solution of the linear seepage flow equations, again using finite differences or a simplified model of inflow can be used. Experimental results for runup and reflection coefficient are from tests performed at HRL Wallingford.

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