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The properties and relative stability of different structures of iron at the extreme conditions of pressure and temperature of relevance for the Earth's core were determined with ab‐initio atomistic simulations aided by a machine‐learning force‐field. We find that the body‐centered cubic (bcc) structure is mechanically stable at core temperatures, but its free energy is marginally higher than those of the hexagonal close‐packed and face‐centered cubic structures. The bcc structure is the only structure whose shear sound velocity matches seismic data. The small free‐energy difference between competing structures suggests that the role of impurities could be crucial in stabilizing the bcc structure in the inner core. Plain Language Summary: Determining the crystal structure and the elastic properties of the compound that forms the Earth's solid inner core is crucial to interpret seismic data. We know that the inner core is predominantly composed of iron, but laboratory‐based experiments and theoretical modeling haven't yet been able to constrain the crystal structure and the properties of pure Fe at the conditions of pressure and temperature found in the inner core. We have recently developed a deep‐learning‐aided atomistic simulation method that is able to determine Gibbs free energies of solids with quantum‐chemical accuracy (a few meV/atom). We find that although body‐centered cubic Fe is energetically slightly less favored than the hexagonal close‐packed form, the shear wave velocity of bcc Fe matches seismic data much better than all other crystal structures, suggesting that bcc is a strong candidate for the crystal structure of Fe in the Earth's inner core and could be stabilized by the presence of light elements in the core. Key Points: The body‐centered cubic structure of iron is mechanically stable at inner core conditionsThe hexagonal close‐packed structure is more stable, but small free energy differences could allow impurities to reverse this stabilityThe observed low shear velocity in the Earth's inner core is likely to be caused by the presence of the body‐centered cubic phase [ABSTRACT FROM AUTHOR]

Dust emission caused by wind erosion of soil is an important surface process in arid and semi-arid regions. However, existing dust emission models pay insufficient attention to the impacts of aerodynamic entrainment of particles. In addition, studies of wind erosion processes do not adequately account for the dynamics of wind erosion rates and dust emission fluxes, or for the impact of soil texture on dust emission. Our wind tunnel simulations of wind erosion and dust emission showed that the soil texture, wind erosion duration, and shear velocity are major factors that affect the dynamics of wind erosion and dust emission. Because of the limited supply of surface sand and the change in surface erosion resistance caused by surface coarsening during erosion, the wind erosion rate and the flux of particles smaller than 10 μm (PM10) caused by aerodynamic entrainment decreased rapidly with increasing erosion duration, which suggests that surface wind erosion and dust emission occur primarily during the initial stage of wind erosion. The PM10 emission efficiency decreased with increasing shear velocity following a power function, and finer textured sandy loam soils had greater PM10 emission efficiency than loamy sand soils.

Abstract The properties and relative stability of different structures of iron at the extreme conditions of pressure and temperature of relevance for the Earth's core were determined with ab‐initio atomistic simulations aided by a machine‐learning force‐field. We find that the body‐centered cubic (bcc) structure is mechanically stable at core temperatures, but its free energy is marginally higher than those of the hexagonal close‐packed and face‐centered cubic structures. The bcc structure is the only structure whose shear sound velocity matches seismic data. The small free‐energy difference between competing structures suggests that the role of impurities could be crucial in stabilizing the bcc structure in the inner core.

This study aims to elucidate the mechanism of velocity-dependent peak shear strength (PSS) for rock joints by examining the three-dimensional distribution characteristics of actual contact joint surface. Shear tests are conducted on saw-cut joints (SCJs) and natural rough rock joints under varying shear velocities (v) but a constant normal stress. The test results reveal that the PSS of SCJs decreases with increasing shear velocity, whereas the PSS of rough joints increases with v. Through analysis of the impact of v on the contact area, a PSS model is developed. The model demonstrates that for SCJs, the contact area decreases with increasing v, resulting in a reduction in the basic friction angle. Conversely, for rough joints, the contact area decreases with increasing v. However, it is observed that, considering the distribution characteristics of the apparent dip angle of asperities on the joint surface, the average roughness of joint surface increases as the contact area decreases. It is the increase in roughness that subsequently leads to an increase in the PSS of rock joints. The new model incorporates the influence of v on both the basic friction angle and peak dilation angle, and the interplay between these factors determines the PSS of rock joints. Highlights: Shear tests of rock joints are carried out under a constant normal stress with different shear velocities. A peak shear strength model considering shear velocity is obtained by analyzing the distribution of joint surface and shear velocity on the contact area. The influence of shear velocity on basic friction angle and dilation angle is taken into account in the new model. The competition between basic friction angle and dilation angle determines the increase or decrease of the peak shear strength of rock joints. [ABSTRACT FROM AUTHOR]

In fluvial sediment transport, the sediment threshold parameter Movability Number, which is the ratio of the shear velocity and the settling velocity of a sediment particle, is seen as a potential replacement for the traditional Shields parameter. Until now, the studies carried out on Movability Number have been mostly empirical or crudely analytical. In the current study, a mathematical modeling approach is attempted. Steady unidirectional flow is considered and the mode of entrainment is taken as that of rolling, with a compact sediment bed. The mathematical relationships developed here express the Movability Number as a function of either shear Reynolds number or dimensionless grain diameter. Comparisons are made with both experimental data and previous empirical formulae. The developed model is a novel approach to study the Movability Number, which bears satisfactory nearness to the previous studies. The deviation produced in terms of underestimation is due to the rolling mode of motion, which requires the least disturbing energy. The developed model can be improved by the consideration of turbulence in future studies. [ABSTRACT FROM AUTHOR]

This study assesses the accuracy of the aeolian transport model proposed by van Rijn and Strypsteen in 2020 in predicting sediment transport rates for dune growth, with a focus on the importance of grain‐related shear velocity. A 9‐month dataset of local and regional wind characteristics and dune growth from a new artificial dune with planted marram grass in an environment with minor supply limitations was analysed. The study site is located in Oosteroever, Belgium. The results revealed that utilizing local measured overall shear velocities resulted in significant overprediction of dune volume changes. Incorporating sub‐models for grain‐related bed roughness and shear velocity improved the predictions of dune growth drastically with high statistical results (r2 = 0.98 and RMSE = 0.64 m3/m). The primary driver contributing to dune growth at the study site was due to oblique onshore moderate winds of 10 m/s, as revealed from a frequency‐magnitude analysis. The model could be used with either local wind measurements or regional data transformed to local beach conditions. The study highlights the importance of considering grain‐related shear velocity in future studies to improve the prediction of sand transport rates and enhance our understanding of dune evolution. [ABSTRACT FROM AUTHOR]

Hydrological habitat associations of Amazonian macroinvertebrates remain largely unknown, especially for the beetle family Elmidae. This study provides the first insights into the association of complex hydraulic variables (shear velocity, Reynolds and Froude numbers) with the abundance and taxon richness of Elmidae in the Amazon. In a 150-m reach, a meander followed by a straight stretch, five habitats were visually identified that differed in substrate composition and water velocity. Using the Fisher-Jenks algorithm and measurements of complex hydraulic variables in this stretch, the five habitats were pooled into four hydrological classes among which we compared Elmidae genera. Greater Elmidae diversity was associated with higher hydrodynamic energy habitats and riverbed heterogeneity, with Elmidae genera being clearly associated with specific hydrological habitats. Hexacylloepus and Xenelmis were associated with meander margins and backwaters, with lower hydrodynamic energy and finer sediment. Stegoelmis, Microcylloepus, Phanoceroides, Neoelmis and Heterelmis were associated with marginal and central areas of straight stretches or the meander thalweg, with higher hydrodynamic energy, and coarser and more heterogeneous sediment. Our results may be used as a baseline for other parts of the Amazon, since we demonstrated a clear association between complex hydraulic variables and substrate diversity with the distribution, abundance and taxon richness of Elmidae. A more robust description of habitat heterogeneity using complex hydrological variables and the identification and maintenance of natural habitat heterogeneity in rivers is important for the management and conservation of Amazonian aquatic biodiversity. [Display omitted] [ABSTRACT FROM AUTHOR]

Acoustic Doppler velocimetry (ADV) is one of the most suitable devices for measuring flow characteristics. Determination of measurement frequency and duration, in a way that the results are calculated with the lowest error, is very important. The goal of this study was to determine the optimum measurement frequency and duration to save money and time. 3D instantaneous subcritical flocharacteristicsts are measured at 200, 100, 25, and 5Hz frequencies for a duration of 3 minutes, in a laboratory flume with an aspect ratio of less than 5. Then, 3D averaged velocities, shear velocity, turbulence intensity, and Reynolds shear stress are calculated. Results show that the reduction of error is independent of the number of measured data and its dependence is on the data collection duration and frequency. For measurements of 3D averaged velocity components, the appropriate measurement frequency and duration are 1Hz and 50 seconds, respectively. To determine the shear velocity, using logarithmic law, reducing the frequency and duration, results in a maximum error of 13%. For calculation of turbulence flow characteristics, like turbulence intensity and Reynolds shear stress, the measurement frequency, and duration of up to 25Hz and 50-70sec, respectively, results in an error of less than 10%.

The behavior of an ice cover on the surface of an ideal incompressible fluid of finite depth under the action of a pressure domain that moves rectilinearly at a constant velocity in the presence of a current with velocity shift is studied. Fluid flow is not potential. The ice cover is modeled by a thin elastic plate with account for uniform compression. The motion of the load can occur at an arbitrary angle to the direction of current. It is assumed that the ice deflection is steady in the coordinate system moving with the load. The Fourier transform method is used within the framework of the linear wave theory. The critical velocities and the deflection of ice cover are studied depending on the current velocity gradient, the direction of motion, and the compression ratio. [ABSTRACT FROM AUTHOR]

The study of hydraulic characteristics of water flow affected by blocked sediment is vital to assess discharge capacity in pipes with sediment sand to understand the process of pollutant and fine sand aggregation. The aim of this paper is to study the blocking effect of permeable sediments on non-full flow in circular pipe and to analyze hydraulic characteristics with backwater. Experiments and numerical simulations were performed and the porous media model is used to simulate the flow in permeable blocked sediments. To evaluate the degree of congestion, the backwater ratio β is proposed. The backwater ratio is positively proportional to blocked sediment height and inversely proportional to blocked sediment particle size and flow value. Cross-sectional velocity in the backwater zone decreases significantly and tends to be uniform as backwater ratio increases. Furthermore, the development of secondary flows and velocity distributions influenced by backwater height is discussed. The dimensionless shear velocity in backwater zone shows an exponential decrease as the backwater ratio increases, which greatly increases the possibility of further sediment deposition. HIGHLIGHTS The backwater ratio β is proposed to evaluate the effect of blocked sediment and to study the relationship between backwater height and blockage parameters.; The porous media model is used to simulate the flow in permeable blocked sediments.; The changes of flow field are observed under different backwater ratio.;

Pools are often observed in gravel-bed rivers, together with the presence of vegetation patches. In the present study, a conceptual model of a gradual varied flow with both convective deceleration and acceleration flow sections has been constructed in a flume to study turbulent flow structures. Vegetation patches with extended canopies were planted in the pool sections in order to increase the thickness of the boundary layer inside the inner zone. The effects of different flows (namely decelerating, uniform and accelerating flows) along an artificial pool on flow velocity, shear stress and bursting events have been investigated. In addition, due to the occurrence of secondary currents in shallow streams, the characteristics of turbulent shallow flow have been investigated along two axes that are parallel to the sidewall of the flume. The results showed that the application of the log law should be used with care to estimate shear velocity along a pool with a vegetated bed. The presence of a vegetation patch causes an increase in Reynolds shear stress, especially along the entrance section of the pool where the flow decelerates. The results of the quadrant analysis reveal that the sweep and ejection events have the most dominant influence over the vegetation patch in the pool; however, the contributions of outward and inward events increase near the bed, especially in the entrance section of the pool where the flow is decelerating. The distribution of stream-wise RMS of turbulence intensity along the pool generally presents a convex shape. [ABSTRACT FROM AUTHOR]

Although considerable efforts have been made in the last years to examine the physical properties of hexagonal close‐packed (hcp) iron at extreme conditions, it remains challenging to explain many geophysical observations in Earth's inner core. Here we examine the elastic and plastic behavior of hcp iron and the effects of structural defects at inner core conditions using large‐scale atomistic simulations coupled with machine learning‐based interatomic potential. Our results suggest that the seismic anisotropy pattern in the inner core can be ascribed to the elastic anisotropy (6%) of hcp iron. The observed low shear wave velocity is largely produced by viscous grain boundaries in iron polycrystal. We also found highly mobile and abundant vacancies in hcp iron yield a viscous strength (1015±1) that is consistent with the geophysical observations. Therefore, our findings highlight the role played by structural defects and lessen the demand for light elements to explain the observed seismic data. Plain Language Summary: Earth's inner core is mainly made of hexagonal close‐packed (hcp) iron. Seismic waves produced in an earthquake can explore its structure and dynamics. To interpret these seismic observations, we must understand the elastic and plastic properties of hcp iron at Earth's inner core conditions. Although considerable efforts have been made in the last years to examine hcp iron at extreme conditions, it remains challenging to explain many geophysical observations. Here we employed large‐scale molecular dynamics simulations based on the state‐of‐the‐art deep‐learning interatomic potential to investigate the physical properties of hcp iron and the effects of structural defects. Our results show that hcp iron is anisotropic enough to be compatible with the seismic anisotropy pattern in the inner core. The observed low shear wave velocity might be explained by the effects of viscous grain boundaries in polycrystalline iron. We also found that the low viscous strength of Earth's inner core is caused by highly mobile and abundant vacancies in hcp iron. Therefore, our results highlight the role played by structural defects and lessen the demand for light elements to explain the observed seismic data. Key Points: Elastic anisotropy of hexagonal close‐packed (hcp) iron is about 6% at inner core conditionsThe observed low shear wave velocity is consistent with viscous grain boundaries in iron polycrystalThe low viscosity of the inner core is caused by highly mobile and abundant vacancies in hcp iron [ABSTRACT FROM AUTHOR]

Based on field and experimental evidence, the average initial spacing (seed wavelength) of flow-transverse bedforms (ripples and dunes) appears to lie between 80 and 130 grain diameters (L = 80–130Dmm). Starting with an average initial spacing of L = 100Dmm, subsequent bedform growth proceeds by amalgamation of two successive bedforms, which results in a doubling of the spacing in each step. Geometric principles dictate that the combined volume of two smaller bedforms lacks about 40% of the volume required for a fully developed amalgamated bedform. The missing volume is gained by excavation of the troughs, i.e., by lowering the base level. Where base level lowering is prevented by the presence of a coarse-grained armor layer or hard ground pavement, the larger amalgamated bedform remains sediment starved. In its simplest form, bedform growth proceeds by continuous doubling of the spacing in response to increases in flow velocity, the process being reversible in response to flow decelerations. Bedform growth terminates when the shear velocity (u*) at the crest reaches the mean settling velocity (ws) of the sediment. At this point, 40% of the bed material is in suspension, at which point the missing volume can no longer be compensated by trough excavation. In shallow water, maximum bedform size is dictated by the water depth, whereas in deep water, bedforms can potentially grow to their ultimate size. Evaluation of bedform data from deep water settings suggests that the largest two-dimensional, flow-transverse bedforms in terms of grain size (phi) can be approximated by the equations: lnLmax = 13.72–4.03Dphi and lnHmax = 9.95–3.47Dphi for grain sizes < ~ 0.2 mm (> ~ 2.32 phi), with L and H representing bedform spacing and height in meters and D the grain size in phi. For grain sizes > ~ 0.2 mm (< ~ 3.23 phi), the corresponding relationships are lnLmax = 6.215–0.69 Dphi and lnHmax = 3.18–0.56Dphi, with notations as before, or in terms of grain diameters in mm: Lmax = 5 × 105Dmm. [ABSTRACT FROM AUTHOR]

The temperature at Earth’s core-mantle boundary (CMB) is a key parameter to understand the dynamics of our planet’s interior. However, it remains poorly known, with current estimate ranging from about 3000 K to 4500 K and more. Here, we introduce a new approach based on joint measurements of seismic shear-wave velocity, VS, and quality factor, QS, in the lowermost mantle. Lateral changes in both VS and QS above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, Tref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from VS and QS should be equal gives a constraint on Tref. Correcting Tref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, TCMB. This approach further relies on the fact that VS-anomalies are affected by the distribution of post-perovskite (pPv) phase. As a result, the inferred Tref is linked to the temperature TpPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to VS and QS measured beneath Central America and the Northern Pacific suggest that for TpPv = 3500 K, TCMB lies in the range 3,470–3880 K with a 95% likelihood. Additional measurements in various regions, together with a better knowledge of TpPv, are however needed to determine a precise value of TCMB with our method.

The corridor restoration of mountain river channels has been a considerable object over the past four decades. Among them, the friction factor of river channels can be one of the most important variables in the theory of stream corridor restoration. The Daycy friction factor is a function of the depth-to-sediment diameter (h/d) ratio for the traditional open channel flows. However, the friction factor formula is not applicable for the open channel flows on the rough steep slope mountain. The friction factor is dependent on both the h/d and energy slope S. In this study, an impervious flume with the adjustable slope was designed to investigate the river resistance of the steep slope mountain in the laboratory. The flume bottom was covered with uniform sediment in the diameter of 0.5, 1, and 1.85 mm. The flow discharge varied from 0.5 to 2.5 L/s. The h/d (divergence) was within the range of 0.84-7.27. Three slopes with the degree of 10°, 25°, and 35° were used to test the effect of the slope on the resistance factor. Experimental results show that the Darcy friction factor was larger than that for the traditional open channels, due to the roll waves on the water surface of the mountain rivers channels. The variable roll waves modified the flow resistance, leading to the stage-discharge relationship of the channel conveyance. Assume that the energy slope in a steep slope mountain channel was divided into two major components, i.e., the energy slope S1 without the roll waves, and the other S2 related to the roll waves. The energy slope S2 was caused by the roll waves that were created on the water’s surface. The rolling wave occurred on the much larger slope of open channel. The Colebrook-White formula was used to calculated the energy slope without the roll waves S1 or related friction factor f1. An indirect empirical treatment was carried out to measure the roll wave with the energy slope S2. The formula of S2 and the related friction factor f2 were derived from the energy slope S2 using present experimental data. Among them, the energy slope S2 increased with the total slope S. Finally, a semi-analytical model was developed to compute the Darcy friction factor for the steep slope open channels. The total Darcy friction factor was set as the sum of two friction components, corresponding to the traditional open channel and roll wave resistance: f=f1+f2. A total of 48 datasets of measured flume data were selected to test the validity of the present energy division formula. Each data set included the complete records of flow discharge, channel width, water depth, energy slope, median sediment size, and specific gravity of sediment. The comprehensive database covered a wide range of slopes in the mountain river channels. A comparison was made between the present formula with the measured data. Nearly all the data lay within the ±20% error band, indicating excellent consistency. Furthermore, the present formula was also developed on the basis of the mechanism of steep slope mountain river energy dissipation. The finding can provide a fundamental theory for the mountain river [ABSTRACT FROM AUTHOR]

A spur dike is a hydraulic structure, protruding in a river or channel used for several purposes like protection of river-bank erosion and deepening of the main channel. The present paper discusses pre-existing research work on flow pattern and prediction of temporal and maximum scours depth around the spur dikes placed in different locations at 90 ∘ and 180° curved channels. The equations having approximately 2.367, 4.47, 0.17, and 0.271 (average) times with their corresponding experimental data. The parameters, influencing the scour process and flow pattern, have been identified as the ratio of flow intensity to critical velocity (V/Vc ≥ 1) is below 1 and special kind of bedding material is approximately 10 % greater than under live-bed condition and many more. The numerical value of the Froude number and the geometry of the bed surface material are also discussed in this paper. Based on these parameters, the empirical formulations and experimental studies on local scours around the straight, L-shaped, T-shaped spurs, placed at 30°, 45°, 60°, 120°, and 180° azimuthal angles have been discussed. Various numerical schemes proposed in almost seventy-five literatures have been summarized. A critical review of numerical and experimental results found in different works related to temporal and maximum scour depth, flow characteristics, and bed topography around the dike shows that the data and accompanying results are insufficient for the design of spurs used as river structures in curved channels. There are needs to carry out extensive experiments, under various flow conditions, to examine the flow behavior and scouring processes around the spurs. Due to complex flow pattern and scouring processes, taking place around the spur, it becomes difficult to understand the real physics behind these phenomenon and therefore, data-driven models are suggested to arrive at more reasonable relationships required to be used for design purposes. [ABSTRACT FROM AUTHOR]

Being physical mechanical parameters of joints, normal and shear stiffnesses are indispensable components of the numerical simulation and theoretical analysis of the behavior of joints. The objective of this work is to put forward an experimental method to determine joint stiffness under constant normal load (CNL) conditions. For this purpose, joint closure and direct shear tests under CNL conditions were conducted. Normal stiffness was determined by the ratio of normal stress increment and the corresponding normal displacement; the shear stiffness was calculated by the ratio of shear stress increment to the relative shear displacement. The average and instantaneous shear stiffness were distinguished. Experimental results showed that joint normal and shear stiffness are time and spatially varying parameters during direct shearing. With increasing normal stress, average shear stiffness, maximum instantaneous shear stiffness, and normal stiffness increases. Normal stiffness was about 26–28 times higher than the average shear stiffness under one normal stress level. Average shear stiffness was little influenced by shear velocity. Instantaneous shear stiffness shows the velocity-dependent behavior. Maximum instantaneous shear stiffness decreases rapidly with increasing shear rate. At lower shear velocity, maximum instantaneous shear stiffness is higher than normal stiffness; minimum instantaneous shear stiffness can be negative and the absolute value also decreases with faster shear velocity. These findings provide a reference for selecting the appropriate value of normal and shear stiffness for evaluation of the mechanical response of interface. [ABSTRACT FROM AUTHOR]

This study was undertaken with the primary objective of modeling grain velocity based on experimental data obtained under the controlled conditions of a laboratory using a rectangular hydraulic tilting channel. Soft computing approaches, i.e., support vector machine (SVM), artificial neural network (ANN), and multiple linear regression (MLR), were applied to simulate grain velocity using four input variables; shear velocity, exposed area to base area ratio (EATBAR), relative depth, and sediment particle weight. Quantitative performance evaluation of predicted values was performed with the help of three different standard statistical indices, such as the root mean square error (RMSE), Pearson's correlation coefficient (PCC), and Wilmot index (WI). The results during the testing phase revealed that the SVM model has RMSE (m/s), PCC, and WI values obtained as 0.1195, 0.8877, and 0.7243, respectively, providing more accurate predictions than the MLR and ANN models during the testing phase. [ABSTRACT FROM AUTHOR]

Inversion of Rayleigh wave dispersion curves is challenging due to its nonlinearity and multimodality. In this paper, a Simulated Annealing (SA) algorithm is applied to the nonlinear inversion of fundamental-mode Rayleigh wave group dispersion curves for shear and compressional wave velocities. In our approach, we invert thickness, velocities and densities and their vertical gradients of four layers, sediments, upper-crust, lower-crust and lithospheric mantle.At first, to determine the efficiency and stability of the method, noise-free and noisy synthetic data sets are inverted. Results from the synthetic data demonstrate that the SA applied to the nonlinear inversion of surface wave data is interesting not only in terms of accuracy but also in terms of the convergence speed. In fact, the SA method is suitable for large-scale optimization problems, especially for those in which a desired global minimum is hidden among many local minima. In a second step, real data in SE Iran are inverted to examine the usage and robustness of the proposed approach on real surface wave data. Then, we applied 3D gravity modeling based on surface wave analysis results to obtain the density structure of each layer. The reason for using both types of data sets is that the gravity anomaly does not have a good vertical resolution and surface wave group velocities are more appropriate for placing layer limits at depth, but they are not very sensitive to density variations. Therefore, the use of gravity data increases the overall resolution of density distribution. Compared with the Shuffle Complex Evolution (SCE) method that was implemented in a previous study, we found out that the SA method is more stable and has less variability of model parameter values in successive tests. In the final step, we reapplied the SA method to invert the fundamental-mode Rayleigh wave group velocities based on the results of gravity modeling. Gravity results, such as thicknesses and densities were used to limit the search space in the SA method.Our results show that the Moho depth across the Makran subduction zone is increasing from the Oman seafloor (24–30 km) and Makran forearc setting (34–42 km) to the Taftan-Bazman volcanic arc (47–49 km). Also, the results show high shear and compressional velocities under the Gulf of Oman, decreasing to the north of the Makran region. The density image shows an average crustal density with maximum values under the Gulf of Oman, decreasing northward to the Makran region.

A series of direct shear tests on specimens with artificial joints were performed to investigate the rate-dependent characteristics of damage and roughness degradation of three-dimensional joint surfaces under different normal stresses and shear velocities. A novel method was proposed to identify and extract the damaged area of joint surfaces based on the combination of the three-dimensional scanning technology and the color image segmentation method. Based on the proposed method, two main failure modes were identified on the joint surface, including asperity wear and debris backfilling. By controlling different shear displacements and shear velocities, the rate-dependent damage evolution of the joint surface during shearing was revealed. Four damage states are defined to better understand the local damage mechanism of joints. The statistical results indicate that the damage area ratio increases with increasing normal stress and shear velocity. The damage develops more rapidly at a higher shear velocity during progressive shearing. Furthermore, the three-dimensional roughness parameter θ max ∗ / (C + 1) is measured in 36 analysis directions on the sheared joint surfaces to quantitatively describe the asperity degradation. It is observed that the average roughness parameter increases with increasing shear velocity under the same normal stress but decreases with increasing shear displacement. The results in the present study may provide some references for revealing the mechanical behavior and damage state of joints subjected to dynamic loads. Highlights: A new method is proposed to identify and extract the damage area of joint surfaces based on the three-dimensional scanning technology and the color image segmentation method. The damage area ratio increases with increasing normal stress and shear velocity. The damage develops more rapidly at a higher shear velocity during progressive shearing compared with that at a lower shear velocity. The three-dimensional roughness parameter is measured in 36 analysis directions on the sheared joint surfaces to quantitatively describe the asperity degradation. [ABSTRACT FROM AUTHOR]

Shields dimensionless stress and particle Reynolds number have been used since their introduction into sediment threshold studies. They do not separate forcing and resisting quantities so that both shear velocity and particle grain size occur in each. This study considers two different combinations of those traditional parameters to give two dimensionless variables, a dimensionless grain size independent of flow, and a dimensionless shear stress independent of the size. Considering observed data from various sources, the scatter around the new dimensionless threshold curve was found to be less than around the traditional Shields form. Simple explicit rational approximations were obtained between the new dimensionless stress and dimensionless grain size. They describe experimental results better than arbitrary formulae for the traditional Shields parameter. That, with the separation of flow and resistance, makes the solution of practical problems simpler. [ABSTRACT FROM AUTHOR]

Pools are often observed in gravel-bed rivers, together with the presence of vegetation patches. In the present study, a conceptual model of a gradual varied flow with both convective deceleration and acceleration flow sections has been constructed in a flume to study turbulent flow structures. Vegetation patches with extended canopies were planted in the pool sections in order to increase the thickness of the boundary layer inside the inner zone. The effects of different flows (namely decelerating, uniform and accelerating flows) along an artificial pool on flow velocity, shear stress and bursting events have been investigated. In addition, due to the occurrence of secondary currents in shallow streams, the characteristics of turbulent shallow flow have been investigated along two axes that are parallel to the sidewall of the flume. The results showed that the application of the log law should be used with care to estimate shear velocity along a pool with a vegetated bed. The presence of a vegetation patch causes an increase in Reynolds shear stress, especially along the entrance section of the pool where the flow decelerates. The results of the quadrant analysis reveal that the sweep and ejection events have the most dominant influence over the vegetation patch in the pool; however, the contributions of outward and inward events increase near the bed, especially in the entrance section of the pool where the flow is decelerating. The distribution of stream-wise RMS of turbulence intensity along the pool generally presents a convex shape.

Ripples made from unimodal fine sands can grow much larger on Mars than on Earth, reaching wavelengths of 1–3 m and heights exceeding 1 dm. Smaller decimeter-wavelength ripples can be superimposed on them. Classification and origins of these bedforms have been debated. They have been interpreted as analogous to subaqueous ripples on Earth, or as aeolian impact ripples with a range of grain sizes that reach large maximum sizes on Mars. This study uses a mathematical model to evaluate the formation of large Martian ripples as aeolian impact ripples to further investigate this hypothesis. The model parameters were computed using COMSALT for 100 µm grains under shear velocity of 0.65 m/s, which is a reasonable shear velocity for sand transport on Mars according to recent estimations of threshold Martian winds. The numerical experiments utilize a large grid 8 m long. Experiments also evaluate the development of secondary small ripples between the large ripples from random perturbations. The numerical simulations show the evolution of ripple wavelength and height. According to the results, the time scale for the formation of the large ripples is about 2–3 years, which is a much longer time scale compared to terrestrial impact ripples. Small secondary ripples develop only if the space between the large ripples is sufficiently large.

The current state of the art on how the circular cross-section shape of a rigid boundary channel affects the incipience of sediment entrainment is not well investigated in the literature. Moreover, the incipience of sediment entrainment studies via artificial intelligence is very limited so far. The studies for rigid boundary channels to date have yielded different incipient motion data depending on the cross-sectional shape. Also, most of the existing works were proposed for rectangular cross-sectional channels. Conversely, this study investigated the effects induced by a circular cross-sectional shape on critical dimensionless shear stress by experimental procedures under smooth flow conditions. It was found that the circular cross-sectional channel shape significantly altered the conditions in favor of reducing the critical shear stress for the incipient sediment entrainment. This implies that the circular cross-sectional channel shape exhibits the advantage of self-cleansing open channel design. For a circular cross-sectional channel and smooth flow conditions, a new critical shear stress formula is proposed based on the obtained experimental data. Ninety-seven experimental observations were performed under hydraulically transitional flow conditions with a grain shear Reynolds number (Re*) range of 5.2–41.17. Most of the experiments were performed with Re*>10. The new proposed equation is an empirical approach to express the governing equations of incipient motion in rigid boundary channels. Furthermore, a novel hybrid-geno-fuzzy inference system (GENOFIS) and the adaptive neural fuzzy inference system (ANFIS) approaches were developed using experimentally obtained data to predict the incipient motion of sediment entrainment. The performance of the quantitative results of the novel GENOFIS, ANFIS, and empirical equations were evaluated via the root mean square error (RMSE), F -test, and the coefficient of efficient (CE) model evaluation criteria. The GENOFIS is a novel attempt to revolutionize the prediction of complicated nonlinear phenomena such as incipient motion. The results show that prediction of the incipient motion of sediment via the GENOFIS approach yielded more accurate results than those of ANFIS for hydraulically transitional flow conditions. [ABSTRACT FROM AUTHOR]

Channels and surface water are ways for the transfer of pollutants to the environment and human. When any pollutant is spilled into the channel, the pollutant concentrations are decreased after the travel. Reducing the distance is an engineering expedient. To reduce the distance, mixing in water should be increased. Thus, the main goal of the present study was to investigate the effect of the triangular vane on transverse mixing used for control bank erosion. Experiments were carried out in an 80cm width flume. The vane, which was triangular, was made of Plexi-glass with a 30% width of the flume length, 15cm height and 50cm far from the tracer injection. Salt solution was used as the soluble tracer. The experiment was carried out to investigate the effect of the triangular vane for two conditions: with and without vane. The transverse mixing (ez) and complete mixing length were estimated for the two conditions of with and without vane. The results showed with installing the triangular vane, the transverse mixing was increased up to 2.5 and the length of mixing was decreased by 60%, as compared with the tests of no vane.

This study was undertaken with the primary objective of modeling grain velocity based on experimental data obtained under the controlled conditions of a laboratory using a rectangular hydraulic tilting channel. Soft computing approaches, i.e., support vector machine (SVM), artificial neural network (ANN), and multiple linear regression (MLR), were applied to simulate grain velocity using four input variables; shear velocity, exposed area to base area ratio (EATBAR), relative depth, and sediment particle weight. Quantitative performance evaluation of predicted values was performed with the help of three different standard statistical indices, such as the root mean square error (RMSE), Pearson’s correlation coefficient (PCC), and Wilmot index (WI). The results during the testing phase revealed that the SVM model has RMSE (m/s), PCC, and WI values obtained as 0.1195, 0.8877, and 0.7243, respectively, providing more accurate predictions than the MLR and ANN models during the testing phase.

Abstract The oceanic lithosphere is a primary component of the plate tectonic system, yet its evolution and its asthenospheric interaction have rarely been quantified by in situ imaging at slow spreading systems. We use Rayleigh wave tomography from noise and teleseismic surface waves to image the shear wave velocity structure of the oceanic lithosphere‐asthenosphere system from 0 to 80 My at the equatorial Mid‐Atlantic Ridge using data from the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We observe fast lithosphere (VSV > 4.4 km/s) that thickens from 20–30 km near the ridge axis to ~70 km at seafloor >60 My. We observe several punctuated slow velocity anomalies (VSV 400 km from the ridge. We observe a high velocity lithospheric downwelling drip beneath 30 My seafloor that extends to 80–130 km depth. The asthenospheric slow velocities likely require partial melt. Although melt is present off axis, the lack of off‐axis volcanism suggests the lithosphere acts as a permeability boundary for deeper melts. The punctuated and off‐axis character of the asthenospheric anomalies and lithospheric drip suggests small‐scale convection is active at a range of seafloor ages. Small‐scale convection and/or more complex mantle flow may be aided by the presence of large offset fracture zones and/or the presence of melt and its associated low‐viscosities and enhanced buoyancies.

In order to investigate the flow formation on dunes, the experimental data from a flume 12 meters long, located in Hydraulic Lab at Technical University of Graz (Austria), were collected. In this study, dunes (particle sizes of 13 and 6 mm) in a 2-D plan were developed with the wavelength of 1 meter, the lee angle of 8 degree, and the crest heights of 4 and 6 cm; these were uniformly installed across the width of flume. The analysis of the experimental flow velocity profiles measured by ADV and PIV technology and the numerical profiles modeled by SSIMM showed that in the same hydraulic conditions, there was no significant relation between drag coefficients of particles on dunes and flow discharge variation, while the water depth reduction caused a sudden increase in the drag coefficient up to 66%. Also, reducing particle size of the dune increased the drag coefficient and there was a significant relation between particle size (diameter) and dune formation, so that in smooth crested conditions, as compared with the sharp crested dune, the drag coefficient was increased up to 32%.

Extensive Mesozoic rifting along the eastern North American margin formed a series of basins, including the Hartford basin in southern New England. Nearly contemporaneously, the geographically widespread Central Atlantic Magmatic Province (CAMP) was emplaced. The Hartford basin provides an ideal place to investigate the roles of rifting and magmatism in crustal evolution, as the integration of the dense SEISConn array and other seismic networks provides excellent station coverage. Using full‐wave ambient noise tomography, we constructed a detailed crustal model, revealing a low‐velocity (Vs = 3.3–3.6 km/s) midcrust and a high‐velocity (Vs = 4.0–4.5 km/s) lower crust beneath the Hartford basin. The low‐velocity midcrust may correspond to a layer of radial anisotropy due to extension and crustal thinning during rifting. The high‐velocity crustal root likely represents the remnant of magmatic underplating resulting from the CAMP event. Our findings shed light on crustal modification associated with supercontinental breakup, rifting, extension, and magmatism. Plain Language Summary: A series of sediment‐filled rift basins exist along the passive eastern North American margin, extending from Georgia to Newfoundland. The rift basins were formed during extension leading up to the breakup of the supercontinent Pangea at approximately 200 million years ago and have preserved critical information about modification of continental crust during supercontinent breakup. The coverage of seismic stations in southern New England is excellent, benefiting from the recent deployment of the EarthScope Transportable Array in the northeastern United States and the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn). Using an advanced seismic imaging method, we constructed a detailed model of the crust beneath the Hartford basin located in central Connecticut and western Massachusetts. We discovered that the lower crust (at the depths of 18–35 km) beneath the Hartford basin is seismically much faster than its surroundings. We suggest that this high‐velocity layer may be the residual of the trapped magmas at the bottom of the crust, presumably during the formation of the Central Atlantic Magmatic Province at the time of the breakup of Pangea. Key Points: A high‐resolution crustal shear‐velocity model is constructed with full‐wave ambient noise tomographic method in southern New EnglandThe crust beneath the central Hartford basin is thinner than its surroundings with the lower crust being seismically fastThe high‐velocity crustal root results from magmatic underplating during the formation of the Central Atlantic Magmatic Province [ABSTRACT FROM AUTHOR]

A comprehensive investigation of velocity distribution is presented, and the log law is re-examined using experimental data from a smooth uniform open channel flow. It is widely reported that the coefficients of the log law in channel flows deviate from those obtained from circular pipe flows by Nikuradse (Laws of flow in rough pipes, 1933), but the mechanism is not clear and no theoretical formulae are available to express these deviations. A Laser Doppler Velocimetry system was used to measure velocity profiles at the centre of the channel. The data obtained support previous conclusions that the additive constant B of the log law in channel flows can no longer be considered to be 5.5. Interestingly, the experimental data also support Tracy and Lester's discovery that the shear velocities on both sides of the log law are different. Better agreement can be achieved if the global shear velocity (U*1) is used to normalize the measured velocity, and the local shear velocity (U*2) is used to normalize the distance from the wall. Other researchers' data in the literature also validates this new relationship. Based on this new relationship, a theoretical value of B is obtained, which agrees well with the observed B, thus a new form of log law for channel flow is suggested. The new relationship developed was verified with present experimental and past literature data suggesting its universality irrespective of wide or narrow open channels, or subcritical or super critical flow conditions. By using the developed relationship the large scatter associated with the additive constant B associated with the log law has been explained. It is found that the additive constant B in the log law is a function of channel aspect ratio. The developed relationship for B is validated from a wide range of data from the literature to confirm its universality. [ABSTRACT FROM AUTHOR]

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Time-average velocity distribution in steady and uniform channel flows is important for fundamental research and practical application as it is always three-dimensional (3D), regardless of channel geometry. However, its determination has predominantly been carried out by using complex numerical software, even for the simplest geometry such as rectangular channels. The log-law was developed initially for circular pipe flows, where a single shear velocity is used to normalize the velocity (u+) and its distance (y+). Tracy and Lester found that the performance of the log-law can be extended to express velocity profiles in rectangular channels when the global shear velocities (gRS)0.5 and (ghS)0.5 are used to normalize the measured velocity u and its distance y. This study extends this discovery from the channel central line to the corner regions, and its general form of log-law was found to be valid even in trapezoidal or triangular open channels or closed ducts. This modified log-law can produce good agreement with the measured velocity with an average error of less than 5%. Therefore, this study provides a simple and reliable tool for engineers and researchers to estimate the velocity contours in straight and smooth channel flows. [ABSTRACT FROM AUTHOR]

Estimation of reservoir parameters such as porosity, lithology and determination of elastic moduli is based on well-logging data and seismic velocity information. However, the lack of shear velocity log in many wells, and the high costs of its acquisition have led to developing different approaches for shear velocity estimation. Currently, shear velocity estimation is accomplished by common industrial methods such as empirical equations, regression analysis, intelligent methods and rock-physics models (RPMs). The current study proposes that robust, accurate and cost-effective intelligent methods coupled with suitable RPM provide reasonable estimations of the shear velocity in an optimal processing time. Hybridizing intelligent models with RPMs in the framework of a committee machine is an optimal solution for shear velocity estimation of carbonate reservoirs. The intelligent methods used in this study include neural network (NN), fuzzy logic (FL) and an adaptive-neuro fuzzy inference system (ANFIS). In this research, for each individual intelligent model and a developed RPM, the optimal weights were allocated by Metaheuristic optimization algorithms including genetic algorithm (GA), ant colony optimization routing (ACO R) and simulated annealing (SA)). To obtain the best results with the lowest mean squared error (MSE), a total of 9408, 10801 and 12288 models were created and tested in MATLAB to optimally parametrize the GA, ACO R and SA, respectively. The results showed that the combination of the applied intelligent models with the developed RPMs leads to a higher correlation coefficient with reference to the measured Shear velocity in test dataset. The use of a combination of intelligent methods in the form of committee-machine instead of individual methods has led to a reduction in error and improved the results by up to 2% Considering the high sensitivity of shear wave velocity in geomechanical and reservoir characterization studies, even small improvements in its estimation can significantly reduce error in the characterization of hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]

An experiment was carried out in an acrylic glass-sided re-circulating closed conduit with a rectangular cross section, which is similar in construction to an erosion function apparatus. An adjustable sand box, made of acrylic glass, was attached to the bottom of the conduit as the sand zone or the test section. The hydraulics of the flow in the erosion function apparatus is complicated due to the limited part of the non-smooth and erodible soil surface attached to the closed conduit. As the bed shear stress changes with the bed roughness, even though the flow velocity does not change, establishing a method to estimate the incipient motion is an important challenge for an erosion function apparatus. The present study was conducted to explore the incipient motion of sands from bed shear stress estimated by four different indirect methods on both the sand bed and the smooth bed installed in the erosion function apparatus. In the experiment, particle image velocimetry (PIV) was used to investigate flow dynamics and incipient motion in terms of dimensionless critical bed shear stress. The experimental results show that the bed shear stress estimated from the log-law profiles in the sand zone and the smooth zones are relatively higher than those of the other indirect methods. The dimensionless critical bed shear stress of threshold condition evaluated by all indirect methods was found in good agreement with those of previous results in both zones. The Manning roughness and Darcy–Weisbach friction coefficients were evaluated based on the critical shear velocity at the incipient motion. Although these coefficients were found slightly greater in the smooth zone than in the sand zone, in both zones, they showed good agreement with previous studies.

Graphical abstract Highlights • Obtaining shear wave velocity structure images of the Makran subduction zone, south-east Iran. • Constructing a new model of Moho depth in the Makran region. • Achieving density structure images of the region. Abstract In this study, we developed a method to invert jointly Rayleigh wave group velocities and gravity anomalies for velocity and density structure of the lithosphere. We applied the method to the Makran accretionary prism, SE Iran. The reason for using different data sets is that each of these data sets is sensitive to different parameters. Surface wave group velocities are sensitive mainly to shear wave velocity distribution in depth but do not well resolve density variations. Therefore, joint inversion with gravity data increases the resolution of density distribution. Our approach differs from others mainly in the model parameterization: Instead of subdividing the model into a large number of thin layers, we invert for the properties of only four layers: thickness, P- and S-wave velocities and densities and their vertical gradients in sediments, upper-crust, lower-crust and upper mantle. The method is applied first to synthetic models in order to demonstrate its usefulness. We then applied the method to real data to investigate the lithosphere structure beneath the Makran. The resulting model shows that Moho depth increases from Oman Sea (18–33 km) and Makran fore-arc (33–37 km) to the volcanic-arc (44–46 km). The crustal density is high in the Oman Sea as should be expected for the oceanic crust. We also find a high-velocity anomaly in the upper mantle under the Oman Sea corresponding to the subducting slab. The crust under the fore-arc, volcanic-arc and back-arc settings of Makran subduction zone is characterized by low-velocity zones. [ABSTRACT FROM AUTHOR]

Aeolian sand transport is a complicated process that is affected by many factors (e.g. wind velocity, sand particle size, surface microtopography). Under different experimental conditions, erosion processes will therefore produce different results. In this study, we conducted a series of wind tunnel experiments across a range of wind velocities capable of entraining sand particles (8.0, 10.0, 12.0, and 14.0 m s‐1) to study the dynamic changes of the shear velocity, aerodynamic roughness length, and sand transport. We found that the shear velocity and aerodynamic roughness length are not constant; rather, they change dynamically over time, and the rules that describe their changes depend on the free‐stream air velocity. For wind tunnel experiments without feeding sand into the airflow, the sand bed elevation decreases with increasing erosion time, and this change significantly affected the values of shear velocity and aerodynamic roughness length. A Gaussian distribution function described the relationships between the sand transport rate (qT) and the duration of wind erosion (T). It is therefore necessary for modelers to consider both deflation of the bed and the time scale used when calculating sand transport or erosion rates. © 2018 John Wiley & Sons, Ltd. The dynamic changes of various wind erosion factors and the response of soil wind erosion rate to the change of the factors was observed in a wind tunnel. Wind is the cause of sand flow, while the sand flow can affect the wind in turn. [ABSTRACT FROM AUTHOR]

To obtain the shear velocity structure across North-West of Iran and surrounding areas to a depth of 160 km, we performed a namely Hedgehog nonlinear inversion on Rayleigh wave group velocity dispersion curves in the period range from 7 to 60 s. The distributed dispersion curves are the results of our surface wave dispersion tomography using the data of 280 local and regional seismic events, recorded by the medium- and broad-band seismic stations in the region. We outline different crust and upper mantle structures for the study area based on calculated group and shear velocities. Our results reveal relatively low velocities at the shorter periods (7-10 s) in the presence of sedimentary basins (e.g., South Caspian Basin) and for eastern Anatolia and relatively high velocities along the Sanandaj-Sirjan Metamorphic zone, Alborz, Talesh, and the Lesser Caucasus Mountains. By depth inversion of group velocities, we observed 14-km-thick sediments in South Caspian Basin and Kura Depression. Based on our maps at 20 s, we outline different crustal models for the region and highlight the differences between South Caspian Basin and NW Iran, on one side, and the similarities between the South Caspian Basin and Kura Depression that extend beneath Talesh, Alborz, and Lesser Caucasus, on the other. Comparing the shear velocity of lower crust in South Caspian Basin and Kura Depression with that of NW Iran proves different origination of lower crust in the basin, probably oceanic source, because of its significant higher shear velocity rather than NW Iran. In Talesh, we observe indications of an under-thrusting of the lower crust of SCB beneath NW Iran while the middle crust is locked. The analysis of group velocities at longer periods (≥ 35 s) and obtained shear velocity models allows us to outline different lithospheric structures and crustal depth in the region. The high group velocities in Talesh, South Caspian Sea, and Lesser Caucasus on one side and Zagros Folding and Thrust Belt on the other, beside the result of shear velocity models, suggest the presence of a stable and thick mantle lid that seems to be thin or absent in the eastern Anatolia and much of NW Iran. The shallowest Moho and Lithosphere Asthenosphere boundary depths of 37 and 63 km were observed in Eastern Anatolian Accretionary Complex. The thin mantle lid in this region has affected the whole crust in such a way that we observed the lowest shear velocities inside the crust in this region. We observed a significant thickening of both crust and lithosphere in Sanandaj-Sirjan Metamorphic zone comparing to Urmieh Dokhtar Magmatic Arc and Zagros Folding and Thrust Belt on its two sides. [ABSTRACT FROM AUTHOR]

Channels and surface water are ways for the transfer of pollutants to the environment and human. When any pollutant is spilled into the channel, the pollutant concentrations are decreased after the travel. Reducing the distance is an engineering expedient. To reduce the distance, mixing in water should be increased. Thus, the main goal of the present study was to investigate the effect of the triangular vane on transverse mixing used for control bank erosion. Experiments were carried out in an 8°Cm width flume. The vane, which was triangular, was made of Plexi-glass with a 30% width of the flume length, 15cm height and 5°Cm far from the tracer injection. Salt solution was used as the soluble tracer. The experiment was carried out to investigate the effect of the triangular vane for two conditions: with and without vane. The transverse mixing (ez) and complete mixing length were estimated for the two conditions of with and without vane. The results showed with installing the triangular vane, the transverse mixing was increased up to 2.5 and the length of mixing was decreased by 60%, as compared with the tests of no vane. [ABSTRACT FROM AUTHOR]