Ripple Wavelength Research Articles

Granule Ripples in the Kumtagh Desert, China: Morphological and Sedimentary Characteristics, and Development Processes

AbstractGranule ripples are widespread on Earth and are a fundamental component of dryland sedimentary systems, but the relationship between their wavelength and surface particle size is unclear; in addition, their sedimentary bedding and granule ripple development are incompletely understood. In this study, we examined the relationship between granule ripple development, morphology, and the surface grain‐size distribution. We measured the morphology and particle‐size distribution of granule ripples in China's Kumtagh Desert, and found an exponential relationship between ripple wavelength and average crest particle size, which contradicts previous results. We hypothesize the ripples resulted from creep of coarse particles caused by saltation impacts, accompanied by decreasing bed elevation, leading to crest migration and increased crest height. The size composition and wind regime determined the movement mode of particles, which controlled ripple development and size, but dry–wet and freeze–thaw cycles also contributed. We established a new conceptual model for the development of large granule ripples. Sand ripples and small granule ripples develop similarly, but large ripples did not form from merger of smaller ripples. We report for the first time that particles between 2.3 and 4.7 mm in diameter were missing in the ripple crests (confirmed in wind tunnel experiments). This gap affects the particle movement mode. Since the threshold wind speed for particle saltation at 4.7 mm approaches the regional maximum wind speed, quantifying the missing particles may permit prediction of regional maximum wind speeds, and has practical significance for identifying wind conditions elsewhere, including the surface of Mars.

A mathematical conjecture associates Martian TARs with sand ripples

Abstract Considering that aeolian sand ripples are formed primarily by creeping particles caused by wind-driven saltation sand particles, we obtain a formulation for determining the height of saturated aeolian sand ripples by incorporating the reptation fluxes with previous experimental results on migration velocities of sand ripples. Based on existing observational results of terrestrial sand ripples on Earth's surface, it estimates that the wavelength of aeolian sand ripples on Mars is generally up to several meters. This implies a possibility that there is another sand ripple on Mars similar in scale to Transverse Aeolian Ridges (TARs) at some time when surface saltation was prevalent. Moreover, perhaps part of the widely observed TARs is the degradation of saltation sand ripples, whose formation is intimately related to saltation and reptation of sand particles. While the other two types of ripple-like morphologies (plain ripples and crater ripples) found by Opportunity Rover are essentially not. Further, we propose that the main factor controlling the scale feature of Martian sand ripples is the intense particle-bed collision process.

Edge rippling and petal shape of lilies

Ripples arise along flower petal edges of the species, Lilium casablanca, likely due to differential growth rates at the edges. Torn plastic sheets also exhibit edge ripples analogous to lily ripples. In both cases, the ripples are a consequence of excess edge length. Using both time-lapse videos of blooming lilies and still images of torn plastic sheets, we find that ripples in both systems are well-described by a scaling relationship where ripple amplitude is proportional to an expression dependent on ripple wavelength and arc length.

Travertine crystal growth ripples record the hydraulic history of ancient Rome\u2019s Anio Novus aqueduct

Travertine crystal growth ripples are used to reconstruct the early hydraulic history of the Anio Novus aqueduct of ancient Rome. These crystalline morphologies deposited within the aqueduct channel record the hydraulic history of gravity-driven turbulent flow at the time of Roman operation. The wavelength, amplitude, and steepness of these travertine crystal growth ripples indicate that large-scale sustained aqueduct flows scaled directly with the thickness of the aqueous viscous sublayer. Resulting critical shear Reynolds numbers are comparable with those reconstructed from heat/mass transfer crystalline ripples formed in other natural and engineered environments. This includes sediment transport in rivers, lakes, and oceans, chemical precipitation and dissolution in caves, and melting and freezing in ice. Where flow depth and perimeter could be reconstructed from the distribution and stratigraphy of the travertine within the Anio Novus aqueduct, flow velocity and rate have been quantified by deriving roughness-flow relationships that are independent of water temperature. More generally, under conditions of near-constant water temperature and kinematic viscosity within the Anio Novus aqueduct channel, the travertine crystal growth ripple wavelengths increased with decreasing flow velocity, indicating that systematic changes took place in flow rate during travertine deposition. This study establishes that travertine crystal growth ripples such as those preserved in the Anio Novus provide a sensitive record of past hydraulic conditions, which can be similarly reconstructed from travertine deposited in other ancient water conveyance and storage systems around the world.

Mathematical modeling and stability analysis for laser cutting via asymptotic expansion

A new model for laser cutting is presented. It is derived by an asymptotic expansion of a free boundary problem for the arising melt and describes the coupled movements of the melt boundaries by a system of two nonlinear partial differential equations. The paper extends former models by presenting a complete first-order expansion allowing to include arbitrary higher-order terms. A stationary solution is derived and investigated for stability since damped perturbations do not disturb the solidification process whereas growing perturbations lead to unwanted ripple structures at the cutting front. New higher order terms in the model are identified with physical phenomena which are shown to provide stabilization of the process. The stability analysis is evaluated in a parameter study with varying cutting velocities for 1µm fiber laser cuttings and validated with published experimental and simulated data for the same study. Increasing the cutting speed provides larger stability areas leading to smoother cutting fronts. As a novelty, published ripple depth tendencies are shown to be met qualitatively by our model and typical ripple wavelengths are predicted in the order of magnitude. Hence, our model provides a purely analytical method to investigate the cutting quality.

RANSE Modeling of the Oscillatory Flow Over Two‐Dimensional Rigid Ripples

AbstractThe oscillatory turbulent flow over two‐dimensional ripples is numerically simulated. Both the profile of the ripples and the values of the parameters used in the present study are typical of vortex ripples at the bottom of sea waves. The flow is computed numerically by using a RANSE approach. The results show that, as the ratio between the fluid excursion and the ripple wavelength is increased, the vortex shed on one side of the ripple crest is no longer the mirror image of the vortex shed on the other side and the dynamics of the vortex structures becomes quite complex. Moreover, the formation of steady recirculating cells, which might distort the profile of ripples in an erodible bed, is observed. A horizontal steady streaming is also generated, whose positive/negative direction depends on the values of the parameters.

Surface force-mediated dynamics of droplets spreading over wetting films

Despite tremendous interest in the wetting dynamics at the microscale, attention to nanodroplets has started rising only over the last two decades. In the current work, we examine the dynamics of droplets of size comparable with the range of the surface force action spreading over wetting (adsorbed) films. We show that wetting exponents are strongly affected by the ratio between the droplet height and the film thickness dictated by the surface forces, and that Cox–Voinov law is not applicable anymore for such droplets. We pay particular attention to the shape of the advancing droplet menisci and bridge our results with the Landau–Levich problem. We show both numerically and analytically that depending on the strength of the surface forces, capillary ripples of different depths can emerge in the vicinity of the advancing front. The dependence of the ripple wavelength as well the ripple amplitude on capillary number is non-monotonic. We derive the conditions at which the capillary ripples can be fully suppressed by the surface force action.

Projectile’s mass-dependent nanopatterning of Si (1 0 0) for different incidence angles

Control over the dimensions of nanoscale patterns on macroscopic areas of solid surfaces by varying ion beam parameters has been useful in electronic, optic and optoelectronic applications. This work presents a comparative study on projectile’s (Ar and Kr) mass-dependent growth of ripples as a function of the incidence angle. Oblique implantation produces ripples between 50°-70° with highest ordering at ∼ 60°. Heavy mass implantation (Kr+) produces higher amplitude of ripples with shorter wavelength as compared to lighter Ar+ ion, and vice versa. Compositional study shows that the broader near surface damage for Ar+ under higher penetration range produces longer ripple wavelength as compared to Kr+.

Fabrication of three-dimensional sin-shaped ripples using a multi-tip diamond tool based on the force modulation approach

A novel cutting strategy of machining microstructure surface with the multi-tip diamond tool based on the force modulation approach is proposed in this paper. The multi-tip diamond tool with periodic sinusoidal microstructures was prepared by focused ion beam technique. The influence of applied cutting forces on the depths of cut and material removal states was investigated experimentally. MD simulations revealed a significant phenomenon of no material side flow when using the multi-tip diamond tool cutting on single crystal copper substrate. The movement of stacking faults, Lomer-Cottrell locks and Hirth locks jointly governed the formation mechanism of machined surface. To demonstrate the feasibility and effectiveness of this proposed cutting strategy, the fabrication of periodic sinusoidal microstructures under constant forces was successfully realized on the microsphere surface. Furthermore, three-dimensional sin-shaped ripples required variable forces controlling were achieved with high-precision surface quality. The cross-sectional topography of obtained ripples matched the geometry of used MTD tool quite well. In particular, the processing parameters, including the time period of loading forces and cutting speeds, determine the expected wavelength of ripples and play a central role in the surface machining accuracy.

Ripple patterns over oblique Ar+ sputtered SiC/Si(1 1 1) surfaces: Role of preferential sputtering

Controlled surface structuring of amorphous silicon carbide (a-SiC) thin films as grown on silicon substrates Si(111) by Radio Frequency (RF) sputtering and irradiation of obliquely incident 80 keV Ar+ ion beam has been investigated. Sub-wavelength ripple patterns with wave-vector parallel to the ion beam projection are found to evolve on argon sputtered surfaces. Studies reveal that the temporal parameters such as ripple wavelength and amplitude, ordering and homogeneity of these patterns vary non-linearly with argon ion fluence. The formation of such surface structures is attributed to the preferential sputtering of silicon in comparison to carbon. Our results reveal that ion irradiation can be exploited to fabricate controlled surface nanostructures by optimizing the irradiation parameters.

Shallow water transmission loss inversion for seafloor characterization

A Bayesian inference algorithm has been developed for seafloor geoacoustic parameter determination through analysis of transmission loss measurements taken in shallow water environments. It uses a parallel tempering scheme for improved parameter space sampling and bias reduction, and evaluates ray acoustic forward models in Bellhop. The algorithm is verified by application to synthetic data generated using finite element and ray acoustic propagation models for frequencies from 0.5 to 5 kHz. Verification is assessed through the ability to recover inversion parameter values prescribed within the synthetic data, and inspection of ambiguous inversion situations. Initial inversion parameters include bulk sediment density, sound speed, and attenuation, as well as ripple height and wavelength for some seafloors. The inversion yields posterior probability distributions for each inversion parameter, which inform parameter resolvability and covariance. Algorithm accuracy, efficiency, and applicability to data from different ocean environments will be discussed. [This work has been supported by the Office of Naval Research, Task Force Ocean.]

Surface Gravity Wave Interaction With a Submerged Composite Wavy Porous Plate Attached to a Vertical Wall

Abstract The hydrodynamic performance of composite wavy submerged porous plate attached to a wall is investigated using numerical method multi-domain boundary element method in the linearized water wave theory in which wave past the porous barriers are modeled using Darcy’s law. Effect of the presence of wall on the hydrodynamic parameters like reflection coefficient, dimensionless wave height, wave force and moment acting on the composite wavy porous structure, and horizontal force on the vertical rigid wall is analyzed for various physical parameters like the number of ripple wavelength, structural porosity, submergence depth, and relative amplitude of composite wavy porous plate. The study demonstrates that the efficiency of hydrodynamic characteristics of the composite wavy porous plate attached to the wall is better compared to a horizontal porous plate attached to the wall of the same applicability conditions (around 27% reduction in wave reflection). Moreover, optimum performance of this kind of breakwater system is increased by considering the lower submergence, higher relative ripple amplitude, appropriate relative amplitude, and suitable moderate porosity of the structure in the range of wavenumber 1 < k0h < 5. Dimensionless wave height, horizontal load on the impermeable wall are reduced to zero, while substantial minimization of vertical load on the structure with suitable consideration of the other influencing parameters of porosity Gp = 0.3, relative amplitude Ds/h = 0.1, relative ripple wavelength m > 3, and submergence depth h1/h = 0.3. The present structural arrangement will be useful for attenuating wave effects on the sea wall.

The Occurrences and Formation of Ladderback Ripples on Barchans Dunes of Najaf Dunes Field, Iraq, in Aeolian Environments

This paper concerns the study of ripples that occur on the windward of Barchan dunes from the dunes field of Najaf governorate, Iraq. These dunes consist mainly of sand sediments with variable sizes, including medium, fine, and very fine sands. Quartz represents the major light mineral in the Najaf Dunes sand. The prevailing wind direction in the study area is NW-SE. The major ripple crest series of every pattern are oriented perpendicular to the NW-SE wind direction, whereas imbricated ripple groups within the troughs of the preexisting ripples are created by the WSW-ENE wind trend. These ripples tend to be formed by shortened ripples that occupy the troughs of the prolonged series. All crests of the ladderback ripples are oriented at right angles to asymmetry ripples. The ladderback ripples were noticed from fine to very fine- grained sediments, which consist mainly of quartz. The wavelength of the ladderback ripples ranges from 2 – 4 cm, while they are 0.1 – 0.2 cm in height. The occurrence of ladderback ripples within an aeolian environment indicates a variety of wind directions, which influenced the arrangements of the crest ripples.

Nanoscale dynamics during self-organized ion beam patterning of Si. I. Ar+ bombardment

Coherent grazing-incidence small-angle X-ray scattering is used to investigate the average kinetics and the fluctuation dynamics during self-organized nanopatterning of silicon by Ar$^+$ bombardment at 65$^{\circ}$ polar angle. At early times, the surface behavior can be understood within the framework of linear theory. The transition away from the linear theory behavior is observed in the dynamics through the intensity correlation function. It quickly evolves to exhibit stretched exponential decay on short length scales and compressed exponential decay on length scales corresponding the dominant structural length scale - the ripple wavelength. The correlation times also peak strongly at the ripple length scale. This behavior has notable similarities but also significant differences with the phenomenon of de Gennes narrowing. Overall, this dynamics behavior is found to be consistent with simulations of a nonlinear growth model.

Characterisation of magnetisation ripple using Lorentz microscopy: Effect of ultra-thin Ni79Fe21 seed layers on magnetic properties of Ni45Fe55

Ni45Fe55 has long been a high moment alternative for Ni80Fe20, which is commonly used in hard disk drive (HDD) read-write head design. In this paper we investigate the effect of ultra thin Ni79Fe21 seed layers on controlling the physical and magnetic behaviour of Ni45Fe55. Transmission electron microscopy (TEM) was used to observe grain size variation. Introducing a seed layer of 0.5 nm thickness reduced the average grain size diameter by over 80% to 2 nm. Diffraction analysis shows texture exists along the [010] direction for the unseeded and 0.25 nm seed layer films. The addition of the Ni79Fe21 seed layer reduces film texture. Bulk magnetic measurements showed seed layers improved uniaxial anisotropy, with decreasing easy axis coercivity HC, and an increase in the anisotropy field HK. The Fresnel mode of Lorentz microscopy was used to image micromagnetic behaviour during in situ magnetising experiments. The nano-scale visualisation of the magnetic structure allows for not only the mapping of hysteresis behaviour, but quantitative characterisation of the material in the form of magnetisation ripple. This was characterised in two ways; the ripple dispersion and wavelength. The addition of Ni79Fe21 seed layers acted to significantly reduce ripple wavelength and dispersion angle. The dramatic effect of seed layer addition suggests that the ultra-thin film is a good candidate for controlling both the physical and magnetic properties of Ni45Fe55 films, whilst maintaining a high magnetic moment density.

Theory of nanoscale surface ripple formation during oblique-incidence thin film deposition

We develop a theory of surface ripples that can emerge spontaneously when an amorphous thin film is grown by oblique-incidence sputter deposition. For simplicity, we consider the case in which two diametrically opposed, broad atomic beams are simultaneously incident on the substrate and focus on the angles of incidence just above the threshold angle for ripple formation. At early times, the ripples are roughly sinusoidal in form, but as time passes, they become increasingly faceted as their wavelength and amplitude grow. The facet slopes and the form of the ripple crests and troughs are found analytically at long times, and these predictions are in good agreement with our simulations. Ultimately, the ripples become highly ordered in the transverse direction and few dislocations remain. However, because the ripple wavelength and the amplitude vary in the longitudinal direction, the ripples are not perfectly ordered, even at long times.

Large Eddy Simulation of three‐dimensional flow structures over wave‐generated ripples

AbstractWe performed a three‐dimensional high‐resolution Large Eddy Simulation using a sinusoidal ripple‐like bedform geometry with spacing and amplitude consistent with equilibrium conditions under the prescribed oscillatory forcing. The simulation results are validated qualitatively and quantitatively with previous laboratory experiments and numerical simulations. Our numerical simulations allow to analyze the presence of “ribs”, strong flow rotational features in the spanwise direction developing perpendicular to the ripple crest. We show that ribs tend to appear on the upslope and crest of ripples and display a dominant spacing, ranging from 0.5λ to λ, during wave phases associated to flow acceleration. When the vortex is transported over the downstream ripple during the flow deceleration, ribs appear for the second time over the upslope of the downstream ripple, with the dominant spacing about 1/8 ripple wavelength. The presence of flow three‐dimensionality corresponds to a large variability of the shear stress over ripples in the spanwise direction, which could ultimately favor the development of three‐dimensional geometry. The three‐dimensional vortex dynamics are evaluated using the concept of vortex strength. Peak vortex strength is observed at the maximum free stream velocity, but the largest variation of the vortex strength and vortex size in the spanwise direction occurs prior to the flow reversal. The variability of the vortex structures might provide a favorable setting for the development of ribs and might relate to the spacing of ribs.

Sediment transport and deposition in flood-tidal deltas: Insight from the Texas Coast

While tidal environments are ubiquitous around the planet, limited work on these systems, particularly those that are in microtidal settings, hinders our understanding of tidal paleo-environments. In this study, we analyze the modern sediment dynamics of the San Luis Pass area, a microtidal system located on the Texas Gulf Coast. The focus of this work is to characterize sediment distribution and establish a quantitative relationship between sedimentary structure geometry, water depth, sediment grain size, and current velocities. A total of 160 seafloor sediment samples were collected in the modern San Luis Pass tidal delta between July 2017 and August 2018; this time span coincided with the landfall of Hurricane Harvey in the area in August 2017. Ripple geometry was measured in 46 locations along the flood-tidal delta. There is a rapid transition in grain size, from proximal (fine sand) to distal (silt and very fine sand) sediments at about 4.3 km from the mouth of the tidal inlet. This change is likely due to a decrease in current velocities away from the inlet entrance, resulting in a change in sediment transport from a combined bedload/suspension to suspension. Post Hurricane Harvey sediments are finer grained compared to those collected before the hurricane landfall, most likely due to high runoff during the storm event. In addition, increased water depths were measured after the hurricane landfall, indicating a significant erosion in the San Luis Pass area. Current ripples were only present in the proximal (sandier) area. We found a positive correlation between ripple height/ripple wavelength and water depth. However, the correlation is much stronger for ripple wavelength, even when compared to other published ripple measurements. We, therefore, propose to use ripple wavelength as a more reliable means to estimate paleo-water depths instead of ripple height. Nevertheless, more measurements from modern environments are necessary to establish a more robust geometric relation from ripples in a variety of paleoenvironments.

Observation of ordered arrays of endotaxially grown nanostructures from size-selected Cu-nanoclusters deposited on patterned substrates of Si.

We report the first time observation of endotaxial growth during thermal treatment of size-selected nanoclusters on a patterned substrate, when we fabricate highly ordered and partially embedded 3D crystalline Cu nanostructure arrays of controlled size in Si-substrates. For this purpose, we combine low energy cluster deposition on the ripple-patterned substrate with controlled annealing. We have investigated, in detail, the effect of the substrate pattern on the deposited size-selected clusters upon heat treatment. At the annealing temperature of 400 °C, nanosized islands are found to be organized into regular arrays, following the alignment of the substrate pattern exactly. The formed islands are trapped at the specific sites of the substrate where surface curvature is maximum and concave. It is also observed that the size of the produced nanoislands (or particles) in the direction of the ripple wave vector, i.e., across the ripples, are in congruence with the ripple wavelength. All the formed islands are partially buried in the substrate and the growth inside the substrate exhibits endotaxial growth. Such an embedded size-controlled nanoscale system can be very promising as sinter-resistant heterogenous catalyst with strong potential in clean energy technology and industrial chemical synthesis.

SERS based detection of Dichlorvos pesticide using silver nanoparticles arrays: Influence of array wavelength/amplitude

Ion beam irradiation produced ripple nanopatterns on Si surface was used to produce a highly dense and sensitive SERS substrate for detecting Dichlorvos pesticide below the permissible limit. The wavelength of the ripple varied from 22 nm to 35 nm by changing ion beam energy from 200 eV to 500 eV. Highly regular nanoparticles arrays were produced down to 22 nm wavelength choosing the proper ion beam parameter and ripple orientation during deposition. The shape of deposited nanoparticles on ripple nanostructures changed from elongated to spherical upon increasing wavelength and amplitude of ripples at different ion energies. The optimization of SERS intensity was carried out using crystal violet dye which revealed that the maximum enhancement (enhancement factor ~107) occurred for the 300 eV irradiated substrate. The optimized substrate was used for detecting Dichlorvos up to 1 ppm level without using any binder molecule.