Ripple Spacing Research Articles

New experimental evidence of surface ripples on gallium arsenide in laser annealing

This letter presents new experimental evidence of periodic structure or ripples which occur on the surface of crystalline or ion-implanted gallium arsenide in laser annealing. A new kind of ripple, whose direction does not depend on the electric field vector of the laser beam, appears for the larger angle of incidence between the laser beam direction and the surface normal. The variation in this ripple spacing with the incident angle of the laser beam to the surface normal is different from that for previously reported ripples, whose direction is always found to be almost perpendicular to the electric field vector for the linearly polarized laser beam. We suggest that the spacing for the new ripples can be interpreted from the reinforcement of the initially induced weak and straggling surface disturbances caused by the interference between the incident laser beam and succesively scattered waves.

Ripple marks in intertidal Lower Bhander Sandstone (late Proterozoic), Central India: A morphological analysis

The late Proterozoic, intertidal Lower Bhander Sandstone (Bhander Group, Vindhyan Supergroup) developed around Maihar, central India, is characterized by alternations of sandstone and shale in different scales and shows profuse ripple marks of widely varying morphology. Visual examination of their external morphology led to the identification of wave ripple, current ripple and others of intermediate character. Standard deviation and average of ripple spacing and height of symmetrical and assymmetrical ripples show genetically significant differences analogous to those obtained by Harms (1969) for wave- and current-generated ripples. Different dimensionless parameters, e.g., R.I., R.S.I., S.I., etc., processed separately for the two types of ripples, show a wide variation in their range which encompasses the total spectrum of values stipulated for wave and current ripples. However, the frequency of any particular genetic type of ripple differs widely when analysed in terms of different dimensionless parameters. Several scatter plots, prepared after Tanner (1967) also indicate the presence of various genetic types of ripples, but there are ripples for which results remain inconclusive. Furthermore, scatter plots involving the vertical form index (ripple length/ripple height) and median grain size of a few asymmetrical ripples, following Reineck and Wunderlich (1968a), led to the discrimination between current ripple and wave ripple and the distinction is grossly consistent with the results obtained by other means. Ripple spacing, ripple index and grain-size data of a few representative samples of ripples of possible wave origin, analysed after Tanner (1971) and Allen (1979) indicate that they were generated in a shallow basin with restricted fetch. Internally, the ripples, irrespective of their symmetry, are often characterized by unidirectional bundles of foresets consisting of rhythmically alternating sand and mud laminae. The sets of cross-laminae may be complexly organized with planar or curved erosional boundaries separating them. In many instances internal structures typical of wave ripples are also noted. Inconsistencies, however, exist between the results obtained by application of different criteria in interpretation of these ripple marks. The limitations in applicability of

Wave‐generated structures in the Devonian lacustrine sediments of south‐east Shetland and ancient wave conditions

ABSTRACTThe most common wave‐generated structures in the nearshore lacustrine sediments of the south‐east Shetland basin are cosets of undulatory and unidirectional ripple cross‐lamination. The undulatory lamination was produced at relatively high oscillatory flow strengths by accretion of rolling grain (post‐vortex) ripples, and the unidirectional cross‐sets were formed by the migration of vortex (orbital) ripples at lower strengths.Unidirectional solitary lenses were generated under moderate but discontinuous wave activity on a partly sand‐starved substrate. Some lenses were reworked during periods of more prolonged wave activity.The Inman‐Komar plot of near‐bottom orbital diameter versus ripple spacing (λ= 0.80d0 for small d0, or λ= 0.65d0 as modified by Miller & Komar) may only be used in estimating ancient wave conditions for vortex ripples with low Vertical Form Indices and small wavelengths. This laboratory based relationship (minimum d0 conditions) is utilized in this study since wave periods in lakes are small.The estimation of ancient wave conditions suggests that the ripples were produced in water depths of up to 10 m and in most cases less than 5 m. The formative waves possessed periods of up to 3.4 sec and suggest that the lake was relatively small, perhaps of the order of 20 km wide.

Some guidelines in reconstructing ancient sea conditions from wave ripplemarks

The collection of substantial field data on wave ripple mark spacing (wavelength), steepness, grain size and symmetry index from the Miocene Burdigalian sandstones of western Switzerland has allowed apparently close reconstruction of sea conditions. Results indicate, however, that ancient wave reconstructions must be restricted at present to data from relatively steep ripple marks (VFI less than 7.5, i.e. vortex ripples). Data from the flatter ripple marks (post-vortex types) formed at high oscillatory shear stresses, do not provide “reasonable” estimates of wave conditions. Penecontemporaneous overwashing and/or post-depositional compaction, ripple formation near the destruction condition rather than the threshold of sediment movement, orbital diameters far exceeding ripple spacing and superimposed unidirectional currents are all factors which seriously affect wave reconstructions. Evaluation of ancient wave conditions provides insight into geologically important phenomena such as local water depth and basin size.

A field investigation of the relationship between oscillation ripple spacinng and the near-bottom water orbital motions

ABSTRACT Measurements of oscillation ripples have been obtained in the high-energy wave environment off the Oregon coast, and in the relatively mild summer-wave environment near Fisher's Island, New York. Scuba-equipped divers measured ripple characteristics while the simultaneous causative near-bottom orbital motions were determined from a wave pressure transducer and electromagnetic current meter mounted near the bottom. The data collected in this study, together with previously published field measurements of oscillation ripples, are compared with empirical relationships for ripple geometry based on laboratory data. As expected, the field data are more scattered than the laboratory data. Reasons for this scatter include several wave spectral effects, ocean waves in the study areas having wi e spectra in contrast to the simple harmonic motions of the laboratory devices. Any selected trend that relates the ripple spacing to the wave orbital motions must take into consideration this spectrum and the manner in which the orbital parameters are defined. Orbital parameters calculated from a significant wave height were found to give the best comparison with the laboratory results.

Oscillation Sand Ripples Generated by Laboratory Apparatus

ABSTRACT Laboratory data on the geometry of oscillation ripples, collected by a number of investigators using a variety of experimental devices, have been compared to determine differences among oscillating bed, wave flume and water tunnel devices. Additional data have been obtained employing a wave flume that generates large waves. It was found that ripples formed in oscillating-bed devices do not correspond well with those developed under progressive waves in flumes and in water tunnels. The remaining vortex ripple data, the class of ripples primarily formed under ocean waves, are found to correspond to the linear relationship, = 0.65do, where is the ripple spacing and do is the near-bottom orbital diameter. The data depart from this relationship as the orbital diameter increases, the departure occurring at higher orbital diameters as the grain size increases. A tentative diagram is developed relating the maximum possible tipple spacing to the median sand diameter.

Test of scale modelling of sediment transport in steady unidirectional flow

AbstractIn two steady uniform flows at different physical scales in a small open channel, with variables characterizing flow, sediment, and fluid adjusted for dynamic similitude by means of four dimensionless modelling parameters (a Reynolds number, a Froude number, a density ratio, and a length ratio), measured frequency distributions of height, spacing, and migration rate of current ripples were almost identical when scaled, thus verifying that exact Reynolds‐Froude modelling of loose‐sediment transport is valid and workable. Modelling should be valid as well for a wide range of other transport conditions in the same kind of flow, because no additional kinds of forces or effects would be present in transport of loose grains in modes other than as ripples. In scaled‐down modelling, a scale ratio of 2.5 is attainable without recourse to exotic fluids by use of water at 85°C to model natural flows at 10°C.

Optimal Fin-Side Design of Compact Tube-in-Fin Heat Exchangers with Rippled Fins

The optimal design of rippled fins found in the common compact heat exchanger is addressed to maximize the heat transferred per unit pressure drop (pumping power). Ripples are common for structural integrity and to facilitate handling and manufacture. Typical designs operate at Reynolds numbers below about 1200. Because a complex flow with heat transfer-process is involved, the optimal design synthesis approach—modeling, objective function definition and optimization—coupled with the desire to efficiently verify the results leads to a highly effective hybrid design technique and substantially less experimentation than might be expected. The model uses a finite difference marching procedure and variable fluid properties. General results for ripple designs and spacings are obtained and corroborated experimentally. In general a short ripple of about 25 deg and height/fin spacing of 0.25 are optimum. Distance between ripples is shown to be a simple function of Reynolds numbers. The final discussion addresses aspects of this approach, its strengths and limitations.

Sedimentological and fluid-dynamic implications of the turbulent bursting phenomenon in geophysical flows

The bursting process in turbulent boundary layers provides new insight on turbulence phenomena, mechanics of sedimentation, and genesis of bedforms in natural geophysical flows. Recent visualization experiments suggest that the turbulent boundary layer can be divided into an inner zone, whose essential characteristics scale with inner (wall) variables, and an outer zone, whose properties scale with the fluid-dynamic variables of the entire flow. The inner zone is distinguished by (i) a viscous sublayer displaying spanwise alternations of high-and low-speed streaks and (ii) episodic disruption by lift-ups of low-speed streaks. Oscillatory growth and breakup stages of the Stanford model of bursting characterize the turbulent structure of the outer zone. The burst cycle exists in turbulent boundary layers of all natural flows except perhaps (i) open-channel flows in the upper part of the upper flow regime and (ii) wind-generated surface waves.Fluid motions described as kolks and boils in incompressible open-channel flows correspond to the oscillatory growth stage andthe late oscillatory growthand breakup stages, respectively, of the Stanford model of bursting. Supporting evidence includes (i) close similarity of gross fluid motions, (ii) equivalent scaling of boils and bursts, and (iii) intensification of boils and bursts in adverse pressure gradients and over rough beds. McQuivey's (1973) turbulence measurements show that the Eulerian integral time scaleTEscales with the same outer variables asboilperiodicity and burst periodicity. It is hypothesized thatTEequals the mean duration of bursts at a point in the flow.Bedforms governed by the turbulent structure of the inner zone (microforms) cannot form if the sublayer is disrupted by bed roughness. The conditions for the existence of two common microforms and their spacings scale with the inner variables. Grain roughness increases the vertical intensity of the turbulence (by enhancing lift-ups) within the inner zone, thereby explaining textural differences between the coarse ripple and fine ripple bed stages of Moss (1972).Mesoforms respond to the fluid-dynamical regime in the outer zone and scale with the outer variables. The mean spacing of dunelike large-scale ripples in equilibrium open-channel flows is proportional to the boundary-layer thickness and equals the length scale formed by the product of the free-stream velocity and the boil period.Strong upward flow in a burst provides the vertical anisotropy in the turbulence which is needed to suspend sediment. Bursting promotes the entrain-ment of more and coarser sediment than tractive forces alone can accomplish.

Some Effects of Environment and Frequency on the Fatigue Properties of an Age-Hardening Aluminium Alloy

AbstractAn Al-Cu-Mg alloy has been fatigued in various environments at high (20 kHz) and low (96 Hz) frequency. A frequency effect was observed and is discussed in relation to the influence of environment and the inhibition of the nucleation and early crack-growth mechanisms at high frequency. Metallographic and fracto graphic examination of the high- and low- frequency specimens revealed similar fatigue features, except that at high frequency the ripple spacing tended to be smaller, persistent slip-bands were more localized and, in certain environments, multiple cracking occurred.

Propagation of Sound in Plate-Shaped Solid Delay Lines

Acoustic propagation in plate-shaped solid delay lines is analyzed using diffraction theory. The analysis yields the dependence of group velocity (time delay), phase velocity, pulse shape, pulse rise time, output amplitude ripple spacing, and ripple amplitude on the parameters of frequency, delay line length, free-medium sound velocity, and plate thickness. Data are presented corroborating the theory quantitatively for time delay dependence on frequency and plate thickness, ripple spacing dependence on frequency and mode, and pulse rise-time dependence on frequency. The diffraction theory is compared to the wave equation plane-wave solutions for infinite plates. The results of the diffraction analysis are more appropriate for the description of sound propagation in plate-shaped delay lines.

DummyCross-shore ripple variations under laboratory partially standing waves : a possible clue to paleo-wavelength

Setting the experimental condition under partially standing wave, which little attention has been given to in spite of being found in nature, a series of wave-flume experiments of development of ripples were performed, using four kinds of sand with different diameters (0.15 mm≤D≤1.23 mm). Ripples developed under partially standing waves showed the cross-shore variations in ripple spacing, asymmetry and crest-line pattern, depending on the positions to ‘nodes’ and ‘anti-nodes’, and on grain size. Ripple spacing was the largest under nodes and the smallest under anti-nodes and was associated with the variation in the orbital diameter. Ripples with rounded crests and bifurcated crest-lines tended to form under anti-nodes.