scholarly journals Wave-Induced Oscillatory Flow Over a Sloping Rippled Bed

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1618 ◽  
Author(s):  
Carla Faraci ◽  
Pietro Scandura ◽  
Carmelo Petrotta ◽  
Enrico Foti
Keyword(s):  
Oscillatory Flow ◽  
Thin Layers ◽  
Steady Streaming ◽  
Wave Flume ◽  
Flow Asymmetry ◽  
Horizontal Part ◽  
Cohesive Bed ◽  
Sloping Beach ◽  
Wave Induced ◽  
Rippled Bed

In this paper, the findings of an experimental analysis aimed at investigating the flow generated by waves propagating over a fixed rippled bed within a wave flume are reported. The bottom of the wave flume was constituted by horizontal part followed by a 1:10 sloping beach. Bedforms were generated in a previous campaign performed with loose sand, and then hardened by means of thin layers of concrete. The flow was acquired through a Vectrino Profiler along two different ripples, one located in the horizontal part of the bed and the second over the sloping beach. It was observed that, on the horizontal bed, near the bottom, ripple lee side triggered the appearance of an onshore directed steady streaming, whereas ripple stoss side gave rise to an offshore directed steady streaming. On the sloping bed, a strong return current appears at all positions, interacting with the rippled bottom. The turbulence is non-negligible within the investigated water depth, particularly when velocities were onshore directed, due to flow asymmetry. Turbulence caused a considerable flow stirring which, above a non-cohesive bed, could lift the sediment up in the water column and give rise to a strong sediment transport.

scholarly journals WAVE INDUCED VELOCITIES CLOSE TO A RIPPLED BED

1982 ◽  
Vol 1 (18) ◽  
pp. 21
Author(s):  
C.G. Du Toit
Keyword(s):  
Flow Field ◽  
Oscillatory Flow ◽  
Flow Fields ◽  
Flow Reversal ◽  
Velocity Measurements ◽  
Rippled Beds ◽  
Wave Induced ◽  
Rippled Bed

The results are reported of velocity measurements in oscillatory flow over rippled beds. Velocities were measured with a laserdoppler anemometer in both an oscillating tray rig and an oscillatory flow U-tube. Both self-formed and artificial ripples were examined. The results obtained in the two test rigs were compared and it was concluded that the flow fields obtained in the two cases were dynamically similar. Measurements of the flow field clearly showed the formation, growth and ejection of vortices, as well as a strong surge of fluid over the ripples during and after flow reversal.

scholarly journals COMPARATIVE ANALYSIS OF SUSPENDED SAND CONCENTRATION RECORDED WITH DIFFERENT TECHNIQUES IN A RIPPLED BED REGIME

2011 ◽  
Vol 1 (32) ◽  
pp. 9
Author(s):  
Alireza Ahmari ◽  
Hocine Oumeraci ◽  
Joachim Gruene
Keyword(s):  
Oscillatory Flow ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Large Wave ◽  
Wave Flume ◽  
Sea Bed ◽  
Load Regime ◽  
Coherent Vortex ◽  
Sediment Entrainment ◽  
Rippled Bed

Sediment entrainment processes due to the oscillatory flow above rippled and plane sea beds are fundamentally different. Whereas above plane beds the sheet flow or bed load regime dominates and the momentum transfer is primarily caused by turbulent diffusion, above a sea bed covered with long crested vortex ripples the well organised coherent vortex mechanisms induce sediment-laden lee vortices at the ripple crest, which will be detached from the bed ejected into the water column and finally shed when the flow reverses. To investigate the sediment entrainment processes above vortex ripples, a study was carried out in the Large Wave Flume (GWK) aiming firstly to find out the most appropriate measuring technique to determine the suspended sediment concentration both temporarily and spatially. and secondly to analyse the intra-wave sediment entrainment processes around a steep ripple.

scholarly journals Wave-Induced Distribution of Microplastic in the Surf Zone

2020 ◽  
Vol 7 ◽  
Author(s):  
Nils B. Kerpen ◽  
Torsten Schlurmann ◽  
Alexander Schendel ◽  
Jannek Gundlach ◽  
Daniel Marquard ◽  
...  
Keyword(s):  
Surf Zone ◽  
Vertical Direction ◽  
Accumulation Point ◽  
Shallow Waters ◽  
Regular Waves ◽  
Wave Flume ◽  
Particle Parameter ◽  
Run Up ◽  
Sloping Beach ◽  
Wave Induced

In this study, the wave-induced distribution of 13 microplastic (MP) samples of different size, shape, and density was investigated in a wave flume with a sandy mobile beach bed profile. The particle parameter were chosen based on an occurrence probability investigated from the field. MP abundances were analyzed in cross-shore and vertical direction of the test area after over 40,000 regular waves. It was found, that MP particles accumulated in more shallow waters with increasing size and density. Particles with high density (ρs>1.25 g/cm3) have been partly confined into deeper layers of the sloping beach during the formation of the bed profile. Particles with a density lower than that of water used in the experiments floated constantly in the surf zone or deposited on the beach caused by wave run-up. A correlation was found between the settling velocity of the MP particles and the flow velocity at the accumulation point and a power function equation developed. The obtained results were critically discussed with findings from the field and further laboratory studies.

Three-dimensional numerical simulation of wave-induced scour around a pile on a sloping beach

2021 ◽  
Vol 233 ◽  
pp. 109174
Author(s):  
Jinzhao Li ◽  
David R. Fuhrman ◽  
Xuan Kong ◽  
Mingxiao Xie ◽  
Yilin Yang
Keyword(s):  
Numerical Simulation ◽  
Three Dimensional ◽  
Sloping Beach ◽  
Wave Induced

A numerical study of the wave-induced solute transport above a rippled bed

1995 ◽  
Vol 299 ◽  
pp. 267-288 ◽  
Author(s):  
K. T. Shum
Keyword(s):  
Flow Field ◽  
Solute Transport ◽  
Concentration Profile ◽  
Vortical Flow ◽  
Sediment Surface ◽  
Normal Velocity ◽  
Advective Transport ◽  
Fluid Particles ◽  
Wave Induced ◽  
Rippled Bed

The role of wave-induced separated flow in solute transport above a rippled bed is studied from numerical solutions to the two-dimensional Navier–Strokes equations and the advection-diffusion equation. A horizontal ambient flow that varies sinusoidally in time is imposed far above the bed, and a constant concentration difference between the upper and lower boundaries of computation is assumed. The computed flow field is the sum of an oscillatory rectilinear flow and a vortical flow which is periodic both in time and in the horizontal. Poincaré sections of this flow suggest chaotic mixing. Vertical lines of fluid particles above the crest and above the trough deform into whorls and tendrils, respectively, in just one wave period. Horizontal lines near the bottom deform into Smale horseshoe patterns. The combination of high shear and vortex-induced normal velocity close to the sediment surface results in large net displacements of fluid particles in a period. The resulting advective transport normal to the bed can be higher than molecular diffusion from well within the viscous boundary layer up to a few ripple heights above the bed. When this flow field is applied to the transport equation of a passive scalar, two distinct features – regular temporal oscillations in concentration and a linear time-averaged vertical concentration profile – are found immediately above the bed. These features have also been observed previously in field measurements on oxygen concentration. Advective transport is shown to be dominant even in the region where the time-averaged concentration profile is linear, a region where vertical solute transport has often been estimated using diffusion-type models in many field studies.

scholarly journals WAVE LOADS ON HORIZONTAL CYLINDERS

1978 ◽  
Vol 1 (16) ◽  
pp. 147
Author(s):  
P. Holmes ◽  
J.R. Chaplin
Keyword(s):  
Oscillatory Flow ◽  
Vertical Plane ◽  
Vertical Cylinder ◽  
Irregular Waves ◽  
Wave Loads ◽  
Incident Flow ◽  
Cylinder Axis ◽  
Straight Line ◽  
Horizontal Cylinders ◽  
Wave Induced

The problem of predicting wave induced loads on cylinders is an enormously complex one. It is clear from the scatter present in most experimental determinations of force coefficients that there are many individual factors which influence the mechanisms of flow induced loading. Among these are some, for instance Reynolds number, separation and periodic vortex shedding, which are inter-related and whose influences cannot be studied in isolation. Others, such as shear flow, irregular waves and free surface effects, can at least be eliminated in the laboratory, in order to approach an understanding of the more fundamental characteristics of the flow. A vertical cylinder in uniform waves experiences an incident flow field which can be described in terms of rotating velocity and acceleration vectors, always in the same vertical plane, containing also the cylinder axis, whose magnitudes are functions of time and of position along the length of the cylinder. Some of the essential features of this flow can be studied under two-dimensional oscillatory conditions, in which either the cylinder or the fluid is oscillated relative to the other along a straight line (planar oscillatory flow). The incident velocity and acceleration vectors are then always concurrent, normal to the cylinder axis, and oscillating in magnitude with time.

Calculation of Wave-Induced Shallow Stratum Seabed Slides in the Subaqueous Yellow River Delta

2009 ◽  
Author(s):  
Guohui Xu ◽  
Xin Wang ◽  
Congcong Wei ◽  
Zibu Fu ◽  
Qingpeng Zhao
Keyword(s):  
Slip Surface ◽  
Yellow River ◽  
Limit Equilibrium ◽  
Yellow River Delta ◽  
Friction Angle ◽  
Calculation Model ◽  
Safety Coefficient ◽  
Wave Flume ◽  
Calculation Results ◽  
Wave Induced

Wave-induced seabed slide could happen even at very gently sloping silty seabed. Based on the wave-seabed interaction, the safety coefficient calculation model of wave-induced gentle seabed slides in the seabed instability was carried out using limit equilibrium method, Bishop Method, in this paper. The calculated results shows that the effective internal cohesion c′ and the effective internal friction angle φ′ affect the location of slip surface and the magnitude of the safety coefficient significantly. The safety coefficient rises linearly with the increases of c′ and φ′ at a fixed depth. The results fit reasonable well with the slide calculation results from a wave flume experiment in laboratory. Additionally, it was concluded that the silty seabed tended to slide under wave actions at the depth less than 5 meters in the Yellow River Subaqueous Delta.

Numerical Modeling of Turbulent Wall-Bounded Oscillatory Flow and its Effect on Small-Diameter Pipelines

2020 ◽  
Author(s):  
Hongyi Jiang ◽  
Liang Cheng
Keyword(s):  
Boundary Layer ◽  
Oscillatory Flow ◽  
Small Diameter ◽  
Viscous Sublayer ◽  
Theoretical Estimation ◽  
Wall Boundary Condition ◽  
Mesh Resolution ◽  
Turbulent Wall ◽  
Wave Induced ◽  
Wave Boundary

Abstract This study investigates the effect of wave-induced boundary layer on the on-bottom stability of small-diameter pipelines laid on the seabed. An ω-based wall boundary condition is adopted, owing to its high mesh resolution down to the viscous sublayer to resolve the flow around the pipeline. By taking into account the wave boundary layer, the present numerical simulations predict required specific gravity for small-diameter pipelines close to the theoretical estimation by Cheng et al. (2016) and, as expected, much smaller than those recommended by DNV-RP-F109.

Unsteady flow about a sphere at low to moderate Reynolds number. Part 1. Oscillatory motion

1994 ◽  
Vol 277 ◽  
pp. 347-379 ◽  
Author(s):  
Eugene J. Chang ◽  
Martin R. Maxey
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Steady Flow ◽  
Oscillatory Flow ◽  
Reynolds Numbers ◽  
Oscillatory Motion ◽  
Rigid Sphere ◽  
Flow Conditions ◽  
Steady Streaming ◽  
Moderate Reynolds Number

A direct numerical simulation, based on spectral methods, has been used to compute the time-dependent, axisymmetric viscous flow past a rigid sphere. An investigation has been made for oscillatory flow about a zero mean for different Reynolds numbers and frequencies. The simulation has been verified for steady flow conditions, and for unsteady flow there is excellent agreement with Stokes flow theory at very low Reynolds numbers. At moderate Reynolds numbers, around 20, there is good general agreement with available experimental data for oscillatory motion. Under steady flow conditions no separation occurs at Reynolds number below 20; however in an oscillatory flow a separation bubble forms on the decelerating portion of each cycle at Reynolds numbers well below this. As the flow accelerates again the bubble detaches and decays, while the formation of a new bubble is inhibited till the flow again decelerates. Steady streaming, observed for high frequencies, is also observed at low frequencies due to the flow separation. The contribution of the pressure to the resultant force on the sphere includes a component that is well described by the usual added-mass term even when there is separation. In a companion paper the flow characteristics for constant acceleration or deceleration are reported.

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