Surface Fluctuations Research Articles

Relaunching the TY tracksite: tridactyl dinosaur footprints from the Lower Jurassic of southern Africa

ABSTRACT Comprising more than 350 dinosaur footprints and at least 38 trackways, the TY tracksite described herein is located close to the border of NW Lesotho, near Teyateyaneng (TY), and is probably identical to the site originally mentioned by Dornan in 1908. The tridactyl footprints are exposed as natural casts on a cliff overhang and a fallen block at the base of the cliff in the uppermost Elliot Formation (Sinemurian, Lower Jurassic). High-resolution photogrammetry and zoom lenses facilitated the detailed ichnological documentation of the otherwise inaccessible overhang. The tracks vary greatly in morphology, likely due to moisture fluctuations in the tracking surface during their formation. Repeated wetting and drying of the track-bearing sediment is indicated by the cross-cutting relationship of the several generations of desiccation cracks and tracks. Two footprint size classes can be distinguished, with the smaller class being Grallator-like and the larger class being assignable to Eubrontes. All tracks are likely attributable to bipedal, small to moderately large theropod dinosaurs that roamed the drylands of the region c. 190 million years ago. Our ichnological account turns this aesthetic TY footprint site into an apt geoheritage destination with scientific and educational value for all.

Experimental study on the effect of fracture surface morphology on plugging zone strength based on 3D printing

In this paper, laser scanning combined with stereo-lithography appearance (SLA) is used to study the influence of fracture surface morphology on the plugging effect of laboratory fracture plugs, in order to incorporate the fracture surface fluctuation into the design of plugging formula for fractured formations. To our knowledge, this is the first study on the maximum plugging pressure considering the real fracture surface fluctuation using 3D printing technology. The experimental results show a significant positive correlation between the maximum plugging pressure of the average bulge height, the average inclination angle of fracture surface, and the JRC coefficient. With the increase of these characteristic parameters of fracture surfaces, the maximum plugging pressure also increases. Observation of the fracture plugging zone after the experiment indicates that the front edge of the fracture plugging zone is the same as the violent local fluctuations in the height of the fracture surface. The present research suggests that the fluctuation of fracture surface provides many inclined supporting surfaces and strengthens the supporting effect of fracture surface on loss control materials (LCM). The dislocation of the “step-like” flow channel caused by the sudden change of the fracture can induce local single-particle straining and local multi-particle bridging in the flow channel, which significantly improves the maximum plugging pressure of the fracture plugging zone. According to the fracture surface fluctuation difference, the plugging effect of the same formula for fractures with the same opening is different, so it is necessary to improve the plugging formula design in combination with a geological engineering background. This understanding is of great significance for the analysis of fracture plugging mechanisms and optimized design of plugging formulas for fractured reservoirs. It will contribute to the high-efficiency and environment-friendly exploitation of energy and resources.

Using Noncontact Measurement of Water Surface Dynamics to Estimate River Discharge

AbstractEstimating river discharge requires simultaneous measurement of velocity and flow depth. While surface velocities are relatively easy to measure using noncontact techniques, depth measurement usually requires physically intrusive instrumentation. This limits our capability to remotely monitor discharge in natural rivers subject to bed level variations. This work tests the potential to estimate the surface velocity, the water depth, the depth average velocity, and then discharge of a river using only a sequence of images of the dynamic water surface. The method is based on a comparison between the spatiotemporal Fourier spectra of the pixel intensities of these images and the theoretical dispersion relations of turbulence‐generated surface fluctuations and gravity‐capillary waves. The method is validated through the analysis of water surface videos obtained with fixed cameras from two river sections equipped with conventional discharge gauging. The applicability of the approach is demonstrated and the measurement uncertainties are quantified. The method is affected by two main sources of uncertainty: one derives from the estimation of the velocity index and the other from the obtainable resolution of the Fourier analysis. This resolution strongly controls the observation of depth and/or velocity variations in space and in time. The technique has advantages over current approaches: it has clear physical foundations; the equipment is low cost and is highly mobile; it does not need artificial tracers or physical equipment to measure depth; and it can directly provide estimates of the key flow parameters just from time series of images of the water surface.

Hydrodynamic interactions between charged and uncharged Brownian colloids at a fluid-fluid interface

HypothesisThe cluster formation and self-assembly of floating colloids at a fluid/fluid interface is a delicate force balance involving deterministic lateral interaction forces, viscous resistance to relative colloid motion along the surface and thermal (Brownian) fluctuations. As the colloid dimensions get smaller, thermal forces and associated drag forces become important and can affect the self assembly into ordered patterns and crystal structures that are the starting point for various materials applications. NumericsLangevin dynamic simulations for particle pairs straddling a liquid–liquid interface with a high viscosity contrast are presented to describe the lateral interfacial assembly of particles in Brownian and non-Brownian dominated regimes. These simulations incorporate capillary attraction, electrostatic repulsion, thermal fluctuations and hydrodynamic interactions (HI) between particles (including the effect of the particle immersion depth). Simulation results are presented for neutrally wetted particles which form a contact angle θ=900 at the interface. FindingsThe simulation results suggest that clustering, fractal growth and particle ordering become favorable outcomes at critically large values of the Pe numbers, while smaller Pe numbers exhibit higher probabilities of final configurations where particle motion remains uncorrelated in space and particle pairs are found to be more widely separated especially upon the introduction of HI.

Flow field characteristics of a two-dimensional moonpool under uniform flow conditions

ABSTRACT Moonpools are holes in the middle of a ship's hull and through its deck. In this study, the flow mechanisms in moonpools in calm water were investigated. Star-CCM+ software was used to calculate the flow within a two-dimensional (2D) moonpool under uniform flow conditions. A 2D moonpool numerical calculation model was constructed, and the convergence analysis results and experimental data were used to verify the accuracy of the calculated results. Flow field and free surface fluctuations are the main factors that cause the drag force of the moonpool. The drag force increases with the flow velocity, and the drag coefficient presents different trends at different stages. With an increase in the Froude number, Fr, the 2D moonpool enters the frequency lock-in state of the piston and sloshing natural frequency. Additionally, increasing the moonpool length results in a nonlinear change in the flow state.

Thermal properties and application of a novel CaCl2·6H2O/expanded graphite shape-stabilized composite phase change material for electric radiant heating

In recent years, electric heating has been popularized and applied as a heating form of clean energy. In order to realize the peak shifting and valley filling of heating electricity to reduce heating cost and improve energy efficiency, phase-change heat storage electric heating system has become a hot topic of research and application. In this paper, using CaCl2·6H2O as phase change material (PCM), SrCl2·6H2O as nucleating agent and expanded graphite (EG) as porous supporting carrier, a novel shape-stabilized composite PCM was prepared by melt blending method. The thermal physical properties of shape-stabilized composite PCM with different prepared proportions were studied through experiments. The experimental results showed that 88%CaCl2·6H2O + 2%SrCl2·6H2O + 10%EG (50 mesh to 100 mesh) is the optimal prepared proportion of the shape-stabilized composite PCM. The composite PCM with a latent heat of 172.92 kJ/kg, a thermal conductivity of 3.85 W/m·K and a super-cooling degree less than 2 °C, has good shape stability and thermal reliability. A kind of novel electric heating module was fabricated with prepared composite PCM and carbon fiber heating wire. The heat storage and release characteristics of the module were studied through experiments, and the effects of different electric heating power, EG particle size and module size on its thermal performance were also studied. The experimental results showed that the internal temperature of the module was uniform and the module can maintain stable heat dissipation for a long time. The temperature fluctuation of the module surface is relatively small. In summary, the module can meet the heating requirements of buildings when applied to electric radiant heating in the building, and the CaCl2·6H2O/EG shape-stabilized composite PCM shows great promise in building energy saving.

Hydraulic characteristics of the Parshall flume entrance wingwall: Numerical simulation and test

AbstractThe Parshall flume is a common open channel water‐measuring facility that is widely used in hydrological monitoring, agricultural irrigation and municipal water supply. In engineering applications, there is no clear requirement for the form of the wingwalls connecting the channel and Parshall flume. Therefore, it has different effects on flow measurement accuracy, flow velocity distribution and hydraulic characteristics. To standardize its construction requirements, a wingwall form with high flow measurement accuracy is evaluated. Computational fluid dynamics (CFD) numerical simulations and hydraulic experiments have shown the influence of different wingwalls on hydraulic characteristics. The governing test parameters include wingwall forms, incoming flow and degree of submergence. By measuring water surface fluctuation, streamline distribution and flow measurement error, the effects of different wingwall forms on flow measurement accuracy and hydraulic characteristics were evaluated. The results showed that the fluctuation of the water surface is affected by the boundary conditions. Layout I has the highest flow measurement accuracy and has an arc‐shaped wingwall with a radius of 1.5 m. By comparing the results of the tests and simulations, the average error is 3%. The results showed that the hydrodynamic model of the Parshall flume can provide a theoretical basis for the design and development of the measurement structure in the future.

Flow aeration and surface fluctuations in moderate-slope stepped chute: from aeration inception to fully developed aerated flow

ABSTRACT Although stepped chute flows have been studied for a variety of chute geometries and flow conditions, reports on air–water flow development in the fully developed aerated region are not as comprehensive as those in the nonaerated and developing aerated regions. In this paper, skimming air–water flows in a large stepped chute (1V:2.5H) were studied comparatively for two step heights, showing different stages for velocity and aeration development downstream the inception point. The mean air concentration reached a constant level while the bubble frequency kept increasing slowly in the fully developed region. The developed mean air concentration was related to the sloping angle, step height and flow discharge. The results provided possible prediction of maximum bubble frequency and its longitudinal evolution, and a glance at the scale effect on it. The free-surface fluctuations and splash height were presented, with particular attention to the effects of step height on the turbulence and aeration modification.

Study the Effect of SEN Depth on Jet Flow and Level Fluctuation under Permanent Magnet Controlling in Continuous Casting Mould by Numerical Simulation

In this paper, a new method named permanent magnet controlling mould to get majorization flow pattern and suppress fluctuation of free surface was proposed. The effect of permanent magnet controlling on the molten steel in the continuous casting process is simulated by using k-ε turbulence model. The features of permanent magnetic field and flow field inside a 1450 mm × 230 mm mould with combined permanent magnets have been calculated. The calculated results showed that the magnetic field generated by combined permanent magnets could take over both meniscus region and jet flow impingement region. Additionally, Lorentz force generated by the combined permanent magnets can effectively control the upper vortex and suppress the level fluctuation. With the SEN depth increasing, the fluctuation of free surface becomes more stable. However, the lower vortex core gets into the deeper of the slab.

Bisphenol A exposure induces multiple effects in DOPC membrane models

• BPA affects the DOPC π-A isotherms without altering the lipid fluidity. • BPA surface activity has an important role in the morphology of lipid monolayers. • The interaction with lipid occurs by phosphate groups and promotes a disorder in the lipid tail. • BPA induces multiple morphology changes on giant unilamellar vesicles. • The effect of BPA on vesicles showed a size dependence. Due to its now well-known endocrine-disrupting behavior, Bisphenol A (BPA) has focused on many interactions, detection, and removal studies in the last few years. The application of simple membrane models to identify specific interactions in some regions of the cells, such as the membrane, is essential to help understand the aspects of the mechanisms of action. This work evaluated the effects of the BPA exposure over membrane models of a fluid phospholipid, the 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC). The BPA interaction with the DOPC monolayers was performed using Langmuir films, evaluating changes in π-A isotherms, lipid fluidity, and interaction at the molecular level by PM-IRRAS spectroscopy. Giant unilamellar vesicles (GUVs) were used to reveal alteration in the shape and morphology of the lipid bilayers promoted by BPA. Multiple effects were observed in the GUVs, including surface fluctuations, an endocytosis-like effect, the formations of budding, and scissions. These alterations could be related to changes observed in the phosphate groups of DOPC in the PM-IRRAS analysis and the lipophilic properties of BPA. Furthermore, the changes observed indicate that BPA has an affinity to the membrane, which could lead to different implications or effects in cells not yet understood, which requires further investigations.

Structure, Thermodynamics, and Dynamics of Thiocyanate Ion Adsorption and Transfer across the Water/Toluene Interface

Molecular dynamics simulations are used to examine in detail the structure, thermodynamics, and dynamics involve in the adsorption and transfer of the thiocyanate ion (SCN-) across the water/toluene interface. Free energy, hydration structure, and several dynamical properties as a function of the ion location along the interface normal are calculated and contrasted with recent experiments. The free energy profile exhibits a local minimum near the interface corresponding to adsorption free energy relative to bulk water of -6 kJ/mol, in reasonable agreement with experiments. The simulations provide insight into the water surface fluctuations that are coupled to the ion transfer, demonstrating formation of water finger-like structures assisting the transfer process.

Secrecy Performance Analysis for Water-to-Air Visible Light Communication

This paper investigates the physical-layer security for water-to-air (W2A) visible light communication (VLC). The impacts of surface fluctuation and underwater scattering on the channel gain are theoretically analyzed, which is verified in a laboratory W2A-VLC link. The statistical properties of wave slope under experimental conditions are measured by image processing and the probability density function of the slope can be approximated by a logistic distribution. We observe that dynamic waves can cause information leakage and experimental results indicate that the probability of secure communication increases from 90.39% to 96.18% as the eavesdropper’s elevation increases from 1.15 m to 1.42 m, which are approximately consistent with the numerical results. To investigate the parameters affecting the secrecy performance, several secrecy performance metrics are numerically calculated under different wave intensities, eavesdropper’s locations, divergence angles of LED, underwater scattering coefficients and wavelengths of transmitted beam. It is seen that the secrecy performance is degraded as the wave intensity increases, while random scattering can mitigate the water surface fluctuations and reduce the probability of information leakage.

Spatiotemporal Change Assessment of Lake Beseka, Ethiopia Using Time Series Landsat Images

Changes in lake surface area and fluctuations in water levels are common especially in the Ethiopian Rift Valley region. The aim of this study was to present the spatiotemporal changes of lake Beseka from 1985 to 2020 using multi-temporal Landsat images. Four spectral water indices, namely Normalized Differential Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI) and Automated Water Extraction Index (AWEI) were used for the extraction of the lake water. The results of the study show that lake Beseka has tended to expand significantly and strongly over the past 35 years. During 1985, the lake surface area was around 30.9km2 and within the next 35 years, the lake surface area increased by 18.18 km2and in 2020, its surface area is about 49.1 km2. lake Beseka shows 0.2412km2 area change from 2015 to 2020. This indicates lake Beseka has a decreasing trend of expansion compared to its history. However, the topography of Lake Beseka is lower in elevation a small water level rise in the lake can cover a large area and lead to significant impacts on the surrounding environment. Therefore, the monitoring of lake surface changes by multi-temporal satellite images is very necessary and of decisive importance.

Creation of promising technologies for producing holes in parts of a high-frequency ion engine

The article considers application areas of various machining methods for perforating holes in parts with unpredictable surface fluctuations. The most effective methods of obtaining holes in parts of a high-frequency ion engine are shown. Studies of perforation technologies using various machining methods have been carried out. Qualitative relations between the geometric dimensions of a spherical billet perforated using a mechanical method, and the quality of the product surface layer are considered. An analysis of modern machining methods is carried out; promising technologies for obtaining holes in parts with a variable profile are presented. The necessity of using high-tech technologies for perforation in high-frequency ion engine parts is justified. The results obtained allow us to significantly expand the production technological capabilities, as well as significantly improve the technical characteristics of special equipment products in mechanical engineering.

Hydromechanical characterization of tide-induced head fluctuations in coastal aquifers: The role of delayed yield and minor permeable layers

Tidal analysis is an aquifer scale testing that is a low-cost alternative to pumping tests for evaluating aquifer hydraulic parameters without groundwater extraction. Many analytical solutions may be used to assess aquifer head fluctuations in response to tidal fluctuations. Nonetheless, they are rarely used in practice. Aside from that, most analytical solutions are based on a conceptual model that typically consists of an unconfined aquifer and a confined aquifer separated by an aquitard, where hydraulic head fluctuations in the unconfined aquifer part are commonly neglected. Additionally, the frequent confined aquifer short response time to sea-level fluctuations cannot rely on hydraulic connection of the confined aquifer to the sea through the aquitard. As a consequence, when analytical solutions are applied to real-world cases, the hydraulic diffusivity is overestimated. In this study, we investigate through different numerical simulations the fluctuations of the phreatic surface by considering the delayed yield. Numerical results demonstrate that the mechanical effect generated by the load over the sea bottom exerted by sea-level fluctuations is a key factor when determining aquifer parameters. We further show that in multilayer systems, head fluctuations in various aquifer layers can cause interferences and, consequently, increased attenuation of the tidal signal, resulting in an overestimation of the inferred hydraulic diffusivity. Our results provide guidance on how to properly reproduce tidal responses in coastal aquifers.

Accurate determination of viscosity and surface tension by surface light scattering in the presence of a contribution from the rotational flow in the bulk of the fluid

HypothesisNear the critical damping of surface fluctuations, surface light scattering (SLS) signals are affected by the rotational flow in the bulk of the fluid. The adequate consideration of this bulk shear mode is essential for a reliable determination of viscosity and surface tension, yet not fully resolved so far. ExperimentsTo elucidate the influence of the bulk shear mode on the recorded correlation functions related to surface fluctuations with an oscillatory behavior, different evaluation procedures are compared. A new evaluation approach is suggested, which makes use of the entire signal information and represents the contribution of the bulk shear mode to the signal in a convenient and physically meaningful way. This allows to unambiguously access the dynamics of the probed surface fluctuations, i.e. their mean lifetime and frequency as well as their response to the rotational flow in the bulk of the fluid. FindingsBy applying the evaluation approach to SLS signals for eight different vapor–liquid systems corresponding to reduced capillary numbers between about 0.4 and 15, it is demonstrated that the developed strategy allows for an accurate determination of viscosity and surface tension. This strategy facilitates the thermophysical property research on fluids by SLS experiments performed close to the critical damping.

Emergent nematicity and intrinsic versus extrinsic electronic scattering processes in the kagome metal CsV3Sb5

Fermi surface fluctuations and lattice instabilities in the 2D metallic kagome superconductor CsV$_3$Sb$_5$ are elucidated via polarization-resolved Raman spectroscopy. The presence of a weak electronic continuum in high-quality samples marks the cross-over into the charge-density-wave (CDW) ordered phase, while impurity-rich samples promote strong defect-induced electronic scattering processes that affect the coherence of the CDW phase. CDW-induced phonon anomalies appear below $T_{\mathrm{CDW}}$, with emergent $C2$ symmetry for one of the CDW amplitude modes, alluding to nematicity. In conjunction with symmetry-breaking lattice distortions, a kink-like hardening of the A$_{1g}$ phonon energy at $T_{\mathrm{CDW}}$ signifies a concerted interplay of electronic correlations and electron-phonon coupling in the exotic CDW order.

Numerical and Analytical Study of Fluid Flow and Thermal Transfer in a Rough Fracture

The surface morphology of rough fractures significantly affects the fluid flow and heat transfer characteristics in the fractures. A thermal-flow coupling model with specific geometric fractures was established to investigate the influence of surface morphology on the heat transfer characteristics of a single fracture. The effect of temperature on the physical properties of rocks and fluids was included in the study to reflect the actual situation more realistically. The research results show that the temperature of the fluid in the rough fracture is nonlinearly distributed along the flow direction and the higher the flow velocity, the higher the heat transfer efficiency. The fracture surface morphology has a significant impact on the heat transfer characteristics, and the surface fluctuation will greatly affect the flow velocity, causing the fluid temperature to change abruptly at the fracture surface. Under the same flow rate, with the increase of the fluctuation degree of the fracture surface and the fluctuation frequency, the larger the heat exchange area of the fracture surface, the stronger the heat exchange performance. The heat transfer efficiency of the fracture is directly related to the heat transfer area of the fracture, so even with the same permeability, the heat transfer performance of fractures with different surface topography is different.

Influence of Sea Surface Fluctuation on Internal Waves’ Vertical Structures in a Two-Layer Model

Influence of Sea Surface Fluctuation on Internal Waves’ Vertical Structures in a Two-Layer Model

Mechanics and Strategies for Wrinkling Suppression: A Review

Wrinkling is a well-known phenomenon observed at various length scales for diverse materials. Despite a variety of research studies focusing on investigating wrinkling mechanisms and utilizing them to create surface patterns recently, wrinkling also brings about the loss of specific functional properties that were initially endowed to the thin films. For instance, wrinkling may result in the degradation of electrical and optical properties of the film; and the wrinkled films are easily delaminated. Therefore, it is still meaningful to find ways for the suppression of wrinkling on the thin film, although the relevant works are far less than those that utilize the surface instability to achieve certain structures. In this review, the approaches to restrain the emergence of wrinkles will be introduced. Following the introduction part, numerical analysis for wrinkle generation will be first discussed, by which the key parameters determining wrinkle initiation and morphology will be provided. Then, wrinkle suppression strategies by tailoring these parameters will be introduced in the following sections. This review aims to provide useful guidance for future research on alleviating surface fluctuations and achieving desired device functionality.