Wave-induced sand ripples

1982 ◽  
Vol 9 (2) ◽  
pp. 285-295 ◽  
Author(s):  
Michael C. Quick
Keyword(s):  
Velocity Field ◽  
Fluid Velocity ◽  
Sand Transport ◽  
Sediment Characteristics ◽  
Sand Ripples ◽  
Sand Ripple ◽  
Wave Orbital Velocity ◽  
Wave Induced ◽  
Flat Sand

Development of sand ripples from a flat sand bed subjected to shallow water wave action is explained in terms of the unsteady kinematics of the sand particles that form the sand ripple. The steady kinematic requirements for a fully developed sand ripple are also specified, and are shown to be consistent with an idealized solution of the fluid velocity field near the sand bed. This idealized velocity field is a result of the interaction between the surface wave velocity field and the sand ripple shape. The velocity field is related to the sand transport rate by using an adaptation of Bagnold's transport equation for steady flow. Expressions are derived that define the maximum ripple height and wavelength in terms of the wave orbital velocity and sediment characteristics. Theoretical estimates are made of the vortex strength shed from the ripple crest and the role of this crest vortex is considered. Keywords: Sedimentation, sediment transport, waves, ripples, coastal engineering, hydrodynamics.

Correlated continuous-time random walk in the velocity field: the role of velocity and weak asymptotics

Soft Matter ◽  
2021 ◽  
Author(s):  
Jian Liu ◽  
Caiyun Zhang ◽  
Jing-Dong Bao ◽  
Xiaosong Chen
Keyword(s):  
Random Walk ◽  
Velocity Field ◽  
Waiting Time ◽  
Continuous Time ◽  
Fluid Velocity ◽  
Time Correlation ◽  
Space Time ◽  
Continuous Time Random Walk ◽  
Weak Asymptotics

Within the framework of space-time correlated continuous-time random walk model, anomalous diffusion of particle moving in the velocity field is studied in this paper. The weak asymptotic form ω(t) ∼ t−(1+α); 1 < α < 2 for large t, is considered to be the waiting time distribution. Analytical results reveal that the diffusion in the velocity field, i.e., the mean squared displacement, can display a multi-fractional form caused by dispersive bias and space-time correlation. Numerical results indicate that the multi-fractional diffusion leads to a crossover phenomenon in-between the process at intermediate timescale, followed by a steady state which is always determined by the largest diffusion exponent term. In addition, the role of velocity and weak asymptotics is discussed. The extremely small fluid velocity can make the diffusion to be characterized by diffusion coefficient instead of diffusion exponent, which is distinctly different from the former definition. Especially, for the waiting time displaying weak asymptotic property, if the anomalous part is suppressed by the normal part, a second crossover phenomenon appears at intermediate timescale, followed by a steady normal diffusion, which implies that the anomalies underlying the process are smoothed out at large timescale. Moreover, we discuss that the consideration of bias and correlation could help to avoid a possible not readily noticeable mistake in studying the topic concerned in this paper, which may be helpful for the relevant experimental research.

scholarly journals SAND RIPPLE GEOMETRY AND SAND TRANSPORT MECHANISM DUE TO IRREGULAR OSCILLATORY FLOWS

1988 ◽  
Vol 1 (21) ◽  
pp. 129 ◽  
Author(s):  
Shinji Sato ◽  
Kiyoshi Horikawa
Keyword(s):  
Transport Mechanism ◽  
Field Data ◽  
Sand Transport ◽  
Laboratory Measurements ◽  
Oscillatory Flows ◽  
Sand Ripples ◽  
Irregular Wave ◽  
Sand Ripple ◽  
Empirical Relations ◽  
Flow Transport

This paper describes characteristics of sand ripples and sand transport mechanism in regular and irregular oscillatory flows on the basis of detailed laboratory measurements. A set of empirical relations were proposed to evaluate the sand ripple geometry as well as the onset of the sheet flow transport. The applicability of the proposed relationships to the irregular wave conditions with prototype scales was confirmed with existing field data.

Wave-induced circulation in submerged sands

1972 ◽  
Vol 52 (4) ◽  
pp. 903-914 ◽  
Author(s):  
J. E. Webb ◽  
J. L. Theodor
Keyword(s):  
Physical Properties ◽  
Organic Material ◽  
Weather Conditions ◽  
Organic Component ◽  
Sand Ripples ◽  
Unconsolidated Sand ◽  
Harpacticoid Copepods ◽  
Branchiostoma Lanceolatum ◽  
Wave Induced

Pressure waves moving across the sand beds at 3 m depth at Le Racou caused circulation of water in the unconsolidated sand layer. The pattern of circulation apparently depended on the depth of the unconsolidated layer and the form of the sand ripples. The rate of flow was determined by the height of the surface waves and the permeability of the deposit. The physical properties of the sands at the crests and in the troughs of the ripples were in part determined by the organic component which in turn would have been governed largely by the patterns and flow rates of the interstitial currents supplying organic material and nutrients to the sand. Differences in the physical properties of the sediment at the crest and in the trough of a ripple due to the organic component were such as would have affected substantially the prevalence of Branchiostoma lanceolatum and harpacticoid copepods. Sand properties dependent on the organic component would clearly be subject to change in accordance with the prevailing weather conditions and hence the supply of organic material. The role of irrigated sands in the removal of organic material from shallow seas is discussed.

Numerical study of the flow of a mixture of reacting gases in an inhomogeneous catalyst layer

2003 ◽  
Vol 3 ◽  
pp. 246-254
Author(s):  
C.I. Mikhaylenko ◽  
S.F. Urmancheev
Keyword(s):  
Velocity Field ◽  
Chemical Reactions ◽  
Porous Layer ◽  
Computational Experiment ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Catalyst Layer ◽  
Granular Catalyst ◽  
Fluid Velocity Field

The behavior of a liquid flowing through a fixed bulk porous layer of a granular catalyst is considered. The effects of the nonuniformity of the fluid velocity field, which arise when the surface of the layer is curved, and the effect of the resulting inhomogeneity on the speed and nature of the course of chemical reactions are investigated by the methods of a computational experiment.

Wave Motion of a Compressible Viscous Fluid Contained in a Cylindrical Shell

1993 ◽  
Vol 115 (3) ◽  
pp. 302-312 ◽  
Author(s):  
J. H. Terhune ◽  
K. Karim-Panahi
Keyword(s):  
Velocity Field ◽  
Viscous Fluid ◽  
Imaginary Part ◽  
Fluid Velocity ◽  
Wave Number ◽  
Mode Shapes ◽  
Infinite Length ◽  
Complex Frequency ◽  
Compressible Viscous Fluid ◽  
Fluid Velocity Field

The free vibration of cylindrical shells filled with a compressible viscous fluid has been studied by numerous workers using the linearized Navier-Stokes equations, the fluid continuity equation, and Flu¨gge ’s equations of motion for thin shells. It happens that solutions can be obtained for which the interface conditions at the shell surface are satisfied. Formally, a characteristic equation for the system eigenvalues can be written down, and solutions are usually obtained numerically providing some insight into the physical mechanisms. In this paper, we modify the usual approach to this problem, use a more rigorous mathematical solution and limit the discussion to a single thin shell of infinite length and finite radius, totally filled with a viscous, compressible fluid. It is shown that separable solutions are obtained only in a particular gage, defined by the divergence of the fluid velocity vector potential, and the solutions are unique to that gage. The complex frequency dependence for the transverse component of the fluid velocity field is shown to be a result of surface interaction between the compressional and vortex motions in the fluid and that this motion is confined to the boundary layer near the surface. Numerical results are obtained for the first few wave modes of a large shell, which illustrate the general approach to the solution. The axial wave number is complex for wave propagation, the imaginary part being the spatial attenuation coefficient. The frequency is also complex, the imaginary part of which is the temporal damping coefficient. The wave phase velocity is related to the real part of the axial wave number and turns out to be independent of frequency, with numerical value lying between the sonic velocities in the fluid and the shell. The frequency dependencies of these parameters and fluid velocity field mode shapes are computed for a typical case and displayed in non-dimensional graphs.

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