Wave-induced Oscillatory Flow Research Articles

Efficient numerical model for sediment transport on vortex ripple bed in wave-induced oscillatory flow

Sediment motion on rippled bed under wave action plays an important role in coastal landforms, but the application of traditional numerical model is limited by large computational work or bottom sediment condition due to unsteady effects. A single-phase model is proposed to maintain low computation and high accuracy for the vortex structure development and suspended sediment motion on vortex rippled bed in wave-induced oscillatory flow. The 2D bottom sediment condition takes into account the acceleration effect and asymmetric boundary layer development under nonlinear waves as well as the sediment phase-lag. The particle inertia and wake flow around sediment particle are considered in sediment turbulence, and the SST k-ω turbulence model which is suitable for inverse pressure gradient flow on rippled bed is selected to close the Reynolds stress. The single-phase model well predicts the velocity on vortex ripples, periodic concentration at fixed points and vertical distribution of averaged sediment concentration. The results show qualitative formation, development and ejection of vortex, and demonstrate quantitative development of vortex center, radius and strength in symmetric and asymmetric flows. In addition, the model well performs the development of sediment cloud referring to vortex structure.

Modified logarithmic distribution of wind-driven flow velocity in remote foreshore of the non-tidal sea

The paper presents the results of the novel modelling of the wind-driven current in the southern Baltic Sea. The steady current is accompanied by wave-induced orbital velocities. The bed boundary layer related to wave-induced oscillatory flow gives rise to the appearance of additional shear stresses affecting the wind-driven current. This impact included in the wind-driven current model yields a modified logarithmic velocity distribution. Theoretical velocity profiles are compared with the field data. The measurement database includes wind, wave and current parameters. The velocities and directions of the wind were collected from the anemometer installed at the Coastal Research Station (CRS) in Lubiatowo. Wave-current parameters at a depth of about 17 m were obtained from a location of approx. 1.5 Nm from the shoreline in the vicinity of CRS Lubiatowo. The study site hydrodynamics is typical of the south Baltic coast. The analysis shows good agreement between the measured flow velocities and the theoretical vertical distributions in the form of the modified logarithmic profile.

Wave-Induced Oscillatory Flow Over a Sloping 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.

A New Phase Diagram for Combined-Flow Bedforms

Abstract Combined-flows, which involve a combination of unidirectional and wave-induced oscillatory flow, are omnipresent in coastal and lacustrine environments. Despite the extensive progress made in understanding the bedforms generated by such flows in past studies, there still remains a wide range of unexplored flow conditions where the bedform geometry, and hence consequent sedimentary structures, have not been explored, especially for strong unidirectional flows (greater than 0.30 m s−1) and intermediate oscillation periods (between 2 and 8 seconds). To address this gap in our knowledge, the stability of bedforms in a 0.25 mm diameter sand bed was studied under pure unidirectional, pure-oscillatory, and combined-flow conditions with oscillation periods of 4, 5, and 6 s. The maximum orbital velocity (Uo) was varied from 0.00 to 1.00 m s−1 while the unidirectional component (Uu) was varied from 0 to 0.50 m s−1. The experimental data collected under unidirectional flows stronger than 0.30 m s−1 allows expansion of current understanding of the bed configurations for current-dominated combined-flows, where the phase boundary between combined-flow bedforms and current ripples was uncertain. Under these flow conditions, ten distinctive bedform states can be recognized: no motion (NM), 2D symmetric ripples (2D SR), 3D symmetric ripples (3D SR), 3D symmetric dunes (3D SR), 3D asymmetric ripples (3D AR), 3D quasi-asymmetric ripples (3D QAR), 3D asymmetric dunes (3D AD), 3D current ripples (3D CR), 3D current dunes (3D CD), and upper-stage plane bed (USPB). Each of these bedform stages is described, quantified, and characterized in dimensional phase diagrams. A complete re-evaluation of the nomenclature for combined-flow bedforms is proposed, which includes their planform and cross-sectional geometry, in order to better represent the bed morphologies. This new nomenclature also unifies past research on bedforms in both unidirectional and oscillatory flows and thus presents a new synopsis of bedforms developed under such flows. One of the main changes proposed that allows integration with the nomenclature used in unidirectional flows is the reclassification of large ripples as dunes. Furthermore, the introduction of the planform and cross-sectional geometries as properties by which to classify bedforms leads to the definition of a stable phase space for two-dimensional symmetrical ripples and three-dimensional quasi-asymmetrical ripples. These new data and analysis allow proposition of a new unified phase diagram for combined-flows.

Transient three‐dimensional‐patterned ripples appear during deformation of a two‐dimensional ripple field under wave‐induced oscillatory flow

AbstractWave‐flume experiments on the process of deformation of pre‐existing two‐dimensional ripples revealed that one of two distinct types of three‐dimensional patterned ripple, the rhombic or the barrel type, emerged in the early stages of the experimental runs. Rhombic‐type ripples were characterized by a staggered pattern of similar‐sized mounds, whereas the barrel‐type ripples had a barrel‐like plan shape arranged in echelons. The former ripples were formed under strongly asymmetrical flow conditions with large excursion distances of water particle motion near the pre‐existing rippled bed, whereas the latter were formed under relatively symmetrical flow conditions with small excursion distances. The emergence of both types of ripples was also highly dependent on sediment grain size. Copyright © 2009 John Wiley & Sons, Ltd.

Predicted and Field-Measured Resuspension of Flooded Mine Tailings

Shallow water covers are often implemented over sulphide-bearing mine tailings to reduce oxygen uptake by the tailings and, consequently, acid generation. At some sites, however, wind-induced waves could resuspend the tailings and possibly impact the quality of the overlying water cover. Wind-induced resuspension was investigated for a base metal mine site using published semiempirical preditive methods, measured tailings properties, and field measurements. The results of the predictions were compared with field measurements. Tailings erosion occurred when the bed shear stress due to the wave-induced oscillatory flow and countercurrent flow exceeded the measured critical shear stress, 0.12<τ\dc<0.17 Nm\u-2, of the tailings. For this site and for the maximum hourly average wind speed of 10 m/s observed during the study, the critical depth for tailings resuspension was predicted to be 1.18-1.34 m. Field Data suggested that tailings resuspension occurred primarily in parts of the tailings pond where the water cover depth was 1 m or less. Following erosion and resuspension, tailings were carried by surface drift current and bottom return currents to deeper locations.

Dynamics of sand ripples and burial/scouring of cobbles in oscillatory flow

The purpose of this paper is to present the results of a series of laboratory experiments aimed at better understanding (i) the dynamics of sand ripples formed in a wave-induced oscillatory flow and (ii) the influence of sand ripples on the behavior of solid objects (which are free to move) in steady oscillatory flow. This problem is closely related to the migration and burial/scouring of isolated cobbles/mines on a sandy floor by an oscillatory flow such as that occurs in coastal waters beyond the region of wave breaking. The aims of the study were (i) to mimic this process in laboratory experiments and (ii) to develop a physical understanding of the processes involved in the water motion and cobble and sandy surface interaction. The oscillatory flow was created in a long tank of rectangular cross-section using standing waves (first mode) of large amplitudes. Model cobbles (mostly disks) were placed on the sandy bottom and their subsequent behavior, the temporal evolution of the sandy bottom profile and the velocity field in water were observed. The main findings include (i) the demonstration that long-time changes of the bottom topography occur and this may lead to the periodic burial/unburial of cobbles and (ii) the scouring of the bedform surrounding the cobbles is relatively unimportant in the burial/unburial process.

The motion of large bottom particles (cobbles) in a wave-induced oscillatory flow

The purpose of this paper is to present the results of a series of experiments aimed at better understanding the dynamics of the motion of large bottom particles (cobbles) in a wave-induced oscillatory flow. This problem is closely related to the motion of cobbles along the bottom in an oscillatory flow such as occurs in coastal waters beyond the region of wave breaking. The aims of the study were (i) to mimic this process in laboratory experiments and (ii) to develop a physical model to predict cobble movements. The oscillatory flow was created in a long tank of rectangular cross-section using standing waves of large amplitude. Objects of different shapes (spheres and disks) were placed in the flow and their subsequent motion along the tank floor was studied. The results of the observations were compared with the predictions of a theoretical model. For the range of parameters used in the experiments (shape, size, aspect ratio and density of cobbles, amplitude and frequency of the oscillatory flow and bottom friction), reasonable agreement between the measured and calculated values of the cobble displacements as a function of time was obtained.

Effect of wave-induced oscillatory flow on grazing by a subtidal sea urchin Strongylocentrotus nudus (A. Agassiz)

Oscillating-flow-tank experiments were conducted to evaluate the effect of wave-induced oscillatory flow on feeding by subtidal sea urchins Strongylocentrotus nudus (A. Agassiz). Feeding rates by two size groups (mean test diameter=53 and 80 mm) were measured for rehydrated dried blades and fresh live thalli of kelp Laminaria spp. Feeding rate of the larger sea urchins was markedly reduced at the peak velocity of 0.3 m/s and virtually ceased beyond ≈0.40 m/s. The peak velocities at which feeding rate began to decrease and reached almost nil were somewhat lower for the smaller sea urchins than for the larger ones. The velocity limit for feeding does not appear to be a function of temperature. Movement by sea urchins was reduced to half the rate in still water at the peak velocity of 0.30–0.40 m/s. Sea urchins could hardly move beyond 0.70 m/s. The depth variation in the mean of the wave-induced significant peak bottom water velocity, predicted from 6-yr offshore wave data available on the northeastern Pacific coast of Honshu, Japan, was consistent with depth distributions of S. nudus and kelp. The predicted frequency of the significant peak velocity <0.40 m/s, in which sea urchin grazing might be possible, was as high as 70% at 12 m depth but was only 3% at 2 m depth. Mirroring this, sea urchins were almost absent at 2 m depth and increased in density with increasing depth while the kelp decreased in density with increasing depth and were almost absent at 12 m depth.

Predicting suspended sediment concentration on continental shelves

Field observations of the near-bottom suspended sediment concentration, current and wave at a depth of 90 m on the Washington Shelf and at a depth of 1.5 m on the coastal Beaufort Sea show that wave-induced oscillatory flow plays a dominant role in resuspending bottom sediment. The suspended sediment concentration can be reasonably predicted from the measured flow data by applying a diffusion model. Good agreement between the predicted and observed concentrations is obtained by using a reference concentration proportional to the square root of the excess boundary shear stress. For a sediment bed consisting of multiple grain sizes, the differential rate at which material is eroded leads to a significant change in the surfacial grain-size composition. The fraction of the fine-grain sediment in the surface layer decreases sharply with increasing boundary shear stress. A procedure is presented to model this change of the grain-size distribution in the surface layer. The analysis indicates that neglecting the change of the surfacial grain-size distribution with flow may overestimate the erosion depth by a factor of 10 at bottom orbital velocities exceeding 70 cm s −1.

Some Unusual Ripple Marks from the Triassic of Utah

Previous articleNext article No AccessGeological NotesSome Unusual Ripple Marks from the Triassic of UtahWm. Lee StokesWm. Lee Stokes Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 58, Number 2Mar., 1950 Article DOIhttps://doi.org/10.1086/625714 Citations: 2Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:T. Sekiguchi Transient three-dimensional-patterned ripples appear during deformation of a two-dimensional ripple field under wave-induced oscillatory flow, Earth Surface Processes and Landforms 34, no.66 (May 2009): 839–847.https://doi.org/10.1002/esp.1774 References, (Jan 1982): 515–593.https://doi.org/10.1016/S0070-4571(08)71007-0