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Recent studies show that near-bed turbulence may be better scaled using a mixed velocity scale u*U , where u* is the shear velocity and U denotes the characteristic bulk flow velocity. This implies that the classical scaling consideration for sediment transport rates could be improved by redefining the Shields number based on the mixed velocity scale. To investigate this potential improvement, a series of analyses was performed with laboratory data from 25 sources of sediment discharge studies. The data were carefully selected by minimizing effects of some factors including sidewall, particle gradation, particle density, and fluid viscosity. The findings indicate that the relationship between sediment discharges and flow conditions can be enhanced significantly when the analysis is carried out based on the redefined Shields number. The new relationship does not depend on the type of bedforms, and therefore facilitates the prediction of sediment discharge. Finally, by comparing with previous studies, it shows that the proposed formula markedly improves the prediction of bed-material sediment discharges. [ABSTRACT FROM AUTHOR]

In this paper, we leverage the direct numerical simulation (DNS) data for closed-channel flow for a range of friction Reynolds number (Reτ∼180–5,000) to develop a new one-point friction velocity method (OPFVM) to calculate friction velocity U* in terms of free-surface velocity Um , flow depth h , and kinematic viscosity ν. In contrast to prevalent methods that require several cumbersome near boundary measurements to obtain friction velocity, the OPFVM relies on a single easy-to-measure free-surface velocity measurement. The formulation is used to obtain friction velocity for a closed-channel flow (CCF) DNS regime with Reτ=10,049 and on four open-channel flow (OCF) DNS regimes with Reτ∼180–2,000. The same formulation was then experimentally verified in our laboratory. To avoid being prescriptive, a sensitivity analysis was performed to determine the permissible variation in Um to restrict the error in estimated U* to 2%. The relationship between the depth-averaged velocity Ub and the maximum free-stream velocity Um is also explored using the DNS data sets and an approximate relationship between Ub and Um is proposed. With advances in remote-sensing technology that enables free-stream velocity measurements, this method extends the potential to measure even the friction velocity remotely. Practical Applications: Measuring friction velocity U* is difficult in both laboratory and field settings for engineers and scientists. The proposed new method overcomes this challenge to estimate the friction velocity U* by measuring the velocity Um close to the free surface, flow depth h, and temperature (for viscosity). Because near-surface measurement of velocity is not difficult, this method greatly simplifies the measurement of U* with better accuracy than other prevalent methods in practice. In addition, direct numerical simulation (DNS) data has been used to estimate the average velocity Ub using the measured free-stream velocity Um , which further enables measurement of discharge using a single-point measurement of velocity near the free surface in smooth channels. [ABSTRACT FROM AUTHOR]

A robust assessment of tunnels due to uncertainties present in soil and ground motion properties can affect the dynamic response of these structures. In this paper, a stochastic analysis considering an aleatory variability in shear velocity Vs by performing Monte Carlo simulations and assessing its influence on underground tunnels. To numerically assess the response of the soil‐tunnel system to near‐fault earthquake ground motion, the required computational domain usually spans multiple kilometers including both earthquake fault and the structure. Thus, these simulations are computationally expensive. An efficient alternative method, that is, the Domain Reduction Method (DRM), in which a modular two‐step methodology for reducing the computational costs in the large domain analysis is employed. A 3‐D soil‐tunnel structure interaction is modeled to simulate the response of tunnel subjected to an inclined earthquake fault. The numerical simulation of the soil‐tunnel‐fault system is conducted in an open‐source FE package called Multi‐hazard Analysis for STOchastic time DOmaiN phenomena (MASTODON) based on MOOSE framework. The interactive analyses are carried out for three distinct types of soils based on National Earthquake Hazards Reduction Program (NEHRP) provision, that is, soft, medium, and hard, by generating 130 realizations. The results provide many insights into the influence of local site effects, that is, frequency shift for the peak response and the importance of input ground motion characteristics that govern the response of underground structures. The dynamic response of the structure is very sensitive to the uncertainty in rock material properties, especially, the stiffness of the rock sample and the shear wave velocity. [ABSTRACT FROM AUTHOR]

This paper presents a discrete element method (DEM) study of confined shear flow to explore its nonlinear behavior. As a supplement to the analog experiments, the DEM simulation facilitates to capture of the behavior of confined shear flow and allows a detailed analysis of the microscopic mechanisms of granular matter. Using DEM, we perform a series of simulations with different boundary conditions applied during the shear processes. We first extend our understanding of the side friction effect in the confined shear flow, and the physical friction parameter of the sidewall is also evaluated to ensure the efficiency of simulation and its viability in subsequent studies. We then demonstrate how the velocity profile of the particle assemblage depends on the level of the overlying pressure and applied shear velocity. It is found that the linearized velocity profile is mainly generated by the enhancement of uniformity of the normal stress network in the spatial distribution. We specifically investigate the dilation within the particle assemblage and two distinct mechanisms emerged, which depend on the overlying pressure and the applied shear velocity, that is, the rate-dependent dilation and the rolling-induced densification. As a consequence, strong links have been built to demonstrate the underlying microscopic mechanisms that trigger the macroscopic nonlinear behaviors, including the velocity profile and the dilation. [ABSTRACT FROM AUTHOR]

Laumontite is a common and potentially frictionally unstable hydrothermal alteration product present in deep faults of the Gonghe EGS reservoir. We characterize the friction‐stability characteristics of synthetic laumontite gouge under in situ reservoir conditions. The pure laumontite gouge is frictionally strong (μ = 0.73–0.98) and the quartz/laumontite mixture (1:1) is generally less strong (μ = 0.73–0.78) under experimental conditions (Pc = 95 MPa, T = 90–250°C, Pf = 0–90 MPa). The shear velocity was stepped between 6.1, 0.61, then 0.061 μm/s for our experiments. For both gouges, the friction coefficient is independent of temperature and increases with elevated pore pressures. The pure gouge and mixture are strongly velocity‐weakening over a broad range in temperatures (∼90–220°C) and excess pore pressures (0–90 MPa) relevant to the Gonghe stimulation. Microearthquakes (MEQs) observed during stimulation are confined to within the broad depth range of inferred frictional instability—although fluid overpressures are also limited to this region. The observation that laumontite mixtures are frictionally unstable over a broad range of pressures and especially temperatures representative of EGS reservoirs and insensitive to the presence of the coexisting mineral phase (quartz) suggests its presence is a strong indicator of potential seismic hazard. Plain Language Summary: Laumontite is a very low‐grade altered mineral that can easily occur in fractures or faults in granite, basalt, or sandstone. Laumontite is widely developed in the Gonghe geothermal reservoir of Western China. Fluid injection into deep geothermal rock mass may reactivate subsurface faults containing altered minerals and cause earthquakes. Hence, we conducted laboratory experimental analysis on the frictional characteristics of simulated laumontite gouge to further understand the impact of fluid injection on the triggering of deep fault earthquakes. These experiments were performed at conditions reflecting the temperature and pressure of the water injection depth of the Gonghe geothermal reservoir. The results showed that the fault's strength and friction stability strongly depend on pore pressure and temperature. Our study emphasizes the significant role of the altered mineral laumontite in controlling fault strength and stability, as well as its potential for inducing earthquakes. A possible implication of this work is that when selecting geothermal resource targets that require fluid‐injection operations, it is best to avoid laumontite‐rich sites or reservoir sections. Key Points: We report the first evaluations of frictional stability properties for laumontite gouge and mixtures under hydrothermal conditionsGouges are strongly velocity‐weakening over a broad range of temperatures and insensitive to pressures and relative proportionsThis instability field is coincident with P‐T conditions typical for EGS and hence an indicator of ubiquitous seismic hazard [ABSTRACT FROM AUTHOR]

We performed in situ X‐ray diffraction and ultrasonic sound velocity measurements on hcp‐Fe up to 15 GPa, 873 K in a multi‐anvil apparatus. The elastic moduli and their pressure and temperature derivatives were determined by fitting the velocity and density data to the third‐order finite strain equations, yielding KS0 = 169.0(57) GPa, KS0′ = 5.4(6), (∂KS/∂T)P = −0.031(3) GPa/K, G0 = 104.5(27) GPa, G0′ = 1.7(2), (∂G/∂T)P = −0.060(2) GPa/K. Within the experimental P‐T range, we find significant temperature effect on the density‐velocity (ρ − VPor S) relations and caution the use of the temperature‐independent Birch's law for extrapolation to core conditions. Furthermore, temperature‐induced velocity decrease is more significant in VS than in VP, offering a possible explanation for the high Poisson's ratio in the core. Extrapolations based on our results together with previous experimental data suggest that VP of hcp‐Fe aligns with PREM at Earth's core conditions, while Vs and density are approximately 10% and 2.7% higher than PREM, respectively. Plain Language Summary: Iron is believed to be the predominant constituent of the Earth's core. Comparing the physical properties of Fe at high P‐T conditions with the seismological observations provides a strong constraint on the composition of Earth's core and thus aids our understanding of the dynamics and evolution of the Earth. In this study, we measured the density, compressional and shear velocities of iron simultaneously at high pressure and high temperature conditions. We found that temperature plays a significant role in decreasing the velocity of iron, especially for the shear wave velocities. We modeled the velocity profiles of Earth's inner core based on elasticity data from this study and previous studies. Our results suggest that while the compressional velocity of hcp‐Fe demonstrates a good match, the density is slightly heavier, and the shear velocity is faster than the seismic observations. A comprehensive explanation of the seismic observations necessitates considering other light elements in the core. Key Points: Direct measurements of sound velocities of hcp‐Fe at simultaneous high P‐TLarge temperature‐induced shear softening in hcp‐Fe help explain the high Poisson ratio in the Earth's inner coreVelocity profiles of hcp‐Fe at Earth's inner core are faster than PREM [ABSTRACT FROM AUTHOR]

Miniature vortex generators (MVGs) have the potential to control turbulent boundary layers (TBLs). Analyzing the scaled turbulent structure of MVG TBLs in experiments typically requires indirect methods for accurate friction velocity U τ determination. The established methods for U τ determination need to be verified for non-generic TBLs, such as MVG TBLs, especially at near-wake stations. This study compares the performance of the five most common U τ -determination methods when applied to MVG TBLs. The methods are tuned in terms of their free parameters and fitting ranges using direct measurements of U τ from large eddy simulation data, and applied to a corresponding experiment to assess their accuracy. Based on the findings, an "inner" method, which is the Musker function with a drifting buffer layer incorporating a bump function, is recommended for MVG TBLs of the form investigated, as it provides a good estimation of U τ with uncertainty < 3 % for all streamwise stations. The method is applied to three further experimental tests with different flow conditions to study trends in U τ . The error of the drag variation is < 6 % , which indicates the method is reliable for MVG TBLs at high Reynolds numbers. [ABSTRACT FROM AUTHOR]

The double-scroll wrap can effectively increase the volume flow rate compared with the commonly used single-scroll structure, but its built-in volume ratio is extensively reduced. With the aim of improving its built-in volume ratio, this study presented a fully meshed double-scroll profile, or called modified double-scroll, and proposed a generation method for it; its profile equations as well as relationships between its geometric parameters were obtained, and effects of the geometric parameters on the compressor performance were analyzed. Moreover, thermodynamic characteristic and working process of the double-scroll compressor were numerically simulated and verified with its performance experiment. It is found that the proposed fully meshed double-scroll significantly increases the built-in volume ratio by 33.8 %; meanwhile, it increases the volume flow rate, reduces the friction velocity between the orbiting and fixed scrolls, and decreases scroll dimensions. The proposed fully meshed double-scroll can be applied to the design and manufacture of scroll compressors. [ABSTRACT FROM AUTHOR]

Ferromagnesian silicates are the dominant constituents of the Earth's mantle, which comprise more than 80% of our planet by volume. To interpret the low shear-velocity anomalies in the lower mantle, we need to construct a reliable transformation diagram of ferromagnesian silicates over a wide pressure-temperature (P-T) range. While MgSiO3 in the perovskite structure has been extensively studied due to its dominance on Earth, phase transformations of iron silicates under the lower mantle conditions remain unresolved. In this study, we have obtained an iron silicate phase in the perovskite (Pv) structure using synthetic fayalite (Fe2SiO4) as the starting material under P-T conditions of the lower mantle. Chemical analyses revealed an unexpectedly high Fe/Si ratio of 1.72(3) for the Pv phase in coexistence with metallic iron particles, indicating incorporation of about 25 mol% Fe2O3 in the Pv phase with an approximate chemical formula (Fe2+ 0.75Fe3+ 0.25)(Fe3+ 0.25Si0.75)O3. We further obtained an iron silicate phase in the postperovskite (PPv) structure above 95 GPa. The calculated curves of compressional (VP) and shear velocity (VS) of iron silicate Pv and PPv as a function of pressure are nearly parallel to those of MgSiO3, respectively. To the best of our knowledge, the iron silicate Pv and PPv are the densest phases among all the reported silicates stable at P-T conditions of the lower mantle. The high ferric iron content in the silicate phase and the spin-crossover of ferric iron at the Si-site above ~55 GPa should be taken into account in order to interpret the seismic observations. Our results would provide crucial information for constraining the geophysical and geochemical models of the lower mantle. [ABSTRACT FROM AUTHOR]

There is a general consensus that the characteristic velocity and length scales for a plane wall jet exhibit power law with distance downstream of the jet nozzle/slot, x; however, no definitive values are given for the power-law exponents. In view of this, plane wall jet self-similarity is reappraised using a compilation of experimental and direct numerical data of plane wall jets. The plots of compensated distributions of the maximum velocity Umax and length y 1 / 2 , the location where the velocity is equal to U max / 2 in the outer part of the flow, reveal that these variables follow the power laws U max ∼ y 1 / 2 n and y 1 / 2 ∼ x m , where n ∼ − 1 / 2 and m ∼ 1 , which comply with self-similarity solutions. While n ∼ − 1 / 2 is in agreement with the existing results, the linear growth of y 1 / 2 contrasts with the common belief that m should be less than 1. It is argued that the limited ranges of x and Reynolds numbers (Re) used in the previous studies prevent this latter behavior to be observed. This behavior emerges when these data are compiled into a single set, allowing a reasonable range of x and Re. It is further observed that only one velocity scale, either Umax or u τ , the friction velocity, is needed for the outer region, which complies with a requirement imposed by self-similarity under a linear growth y 1 / 2 . In the inner region, either ν / u τ or y 1 / 2 , i n (the location where the velocity is equal to U max / 2 in the inner part) can be used as a scaling velocity, while u τ should be the adequate scaling velocity. The present analysis provides some support to the argument that scaling could be universal, at least when the Reynolds number is large enough and the flow is allowed to evolve over a very long distance. [ABSTRACT FROM AUTHOR]

In addressing snowdrift disasters in high-speed railway cutting areas, this study utilized the improved delayed detached eddy simulation turbulence model, synthetic eddy method, and Eulerian two-phase flow model (Euler–Euler). Coupled with grid dynamic deformation techniques, the investigation facilitated extracting temporal variations in snow particle accumulation profiles within the cutting areas. The predicting accuracy of the numerical method was validated through the wind tunnel and wind–snow experimental data. Building upon this foundation, the study investigated how uniform and turbulent flow conditions impact snow distribution in the high-speed railway cutting areas. The analysis examined the turbulent flow structures, friction velocity distribution, and snow accretion contours within the cutting area. Findings indicate that the snow mass on the windward slope in the cutting area remains consistent under both flow conditions. However, there are significant differences in the rate of snow mass growth and the characteristics of snow accretion distribution. The disappearance of vortex structures at the base of the leeward slope is crucial for indicating the transition in the accumulation states of the surrounding snow particles. Under turbulent incoming flow conditions, the transition from large-scale vortex systems to vortex pairs on the leeward slope of the cutting is delayed, resulting in a postponed stable growth period for snow accretion. Additionally, strong erosion between the track bed and the leeward slope results in reduced snow accretion mass in these areas. In particular, at the simulation time of t = 150 min, under turbulent incoming flow conditions, the overall snow accumulation in the cutting decreased by 20.8% compared to the uniform incoming flow conditions. The snow mass in the leeward slope area decreased by 38.3%, and the track bed area experienced a 23.3% reduction in snow accumulation. In contrast, the snow quantity on the windward slope remained relatively consistent. [ABSTRACT FROM AUTHOR]

Understanding scour at bridge piers is crucial for safeguarding public safety, ensuring infrastructure resilience, and planning effective maintenance. Despite over six decades of extensive studies aiming to develop predictive formulas for the equilibrium scour depth at bridge piers, more than 20 000 highway bridges in the United States have been spotted "scour critical." The traditional reliance on existing empirical formulas has posed a severe challenge for researchers, hindering to achieve a unified relation for the equilibrium scour depth from a fundamental scientific tenet. This perspective article presents a breakthrough—a universal law governing the equilibrium scour depth at a circular pier embedded in a sediment bed, specifically in clear-water scour condition. Derived from a phenomenological model, the universal law reveals that the equilibrium scour depth to pier diameter ratio obeys a consistent two-fifths scaling law with the introduction of a newly coined pier-scour number. This number accounts for all the key parameters involved in a local scour phenomenon, including the approach mean flow velocity, threshold shear velocity for sediment grain motion, approach flow depth, pier diameter, and sediment grain size. Importantly, the scaling law contains an additional term involving the drag coefficient raised to the power of 2/5, addressing the impact of the pier shape on the equilibrium scour depth. The derived universal law undergoes the validation through an extensive dataset of experimental measurements on circular pier scour. [ABSTRACT FROM AUTHOR]

Cultivation under screens and in screenhouses protects the crops from insects and extreme climate conditions and allows water saving. Previous studies considered the aerodynamic properties of boundary layers along two types of screens: a small shading thermal screen covering a hedgerow citrus orchard and a large 50-mesh, insect-proof screen covering a pepper plantation. To extend the previous results, a third type of screen was analysed in this study, a large flat-roof 17-mesh white woven shading screen covering a banana plantation. Vertical profiles of wind speed, air temperature, relative humidity, and friction velocity were measured by a lifting tower, and wind profiles were analysed under near-neutral atmospheric stability. Results show that normalised friction velocity, normalised roughness length, normalised zero plane displacement height and aerodynamic resistance are closer to the previous results of the large insect-proof screenhouse than those of the small shade net. • Boundary layer properties were analysed along a large banana screenhouse. • Results are presented under near-neutral atmospheric stability conditions. • Quantitative differences between the large screenhouses and the small shade net. [ABSTRACT FROM AUTHOR]

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]

Exploring the mechanical response of rock joint subjected to dynamic shear load is essential for revealing the mechanism of dynamic disasters in jointed rock masses. Using an impact-induced direct-shear method, a series of dynamic shear experiments were conducted on artificial granite joints with regularly undulating interface. The dynamic friction coefficient of joint was first obtained from planar jointed granite specimens before the dynamic shear strength and shear displacement of the regularly undulating joints were tested. During the test, the effects of normal stress and shear rate were both considered. The results show that when the shear velocity ranges from 1 to 9 m/s, the dynamic friction coefficient of the planar joint is negatively correlated with shear velocity, and decreases by at least 50% compared with that under quasi-static condition. The rate dependence of shear strength appears opposite for granite joints with undulating angles of 11.3° and 26.6°, respectively. A shear strength model for rock joint with an undulating angle of 11.3° is then suggested based on the test results. During impact shear sliding, the maximum shear displacement of the joint is linearly negatively related to the initial normal stress. While, non-driven sliding may occur under low normal stress and high impact velocity, which leads to a large magnitude of shear slip. Highlights: The shear strength and shear displacement of rock joints are tested with shear rate ranging from 1 to 9 m/s. The rate dependence of shear strength appears opposite for rock joints with sharp and gentle undulation and a shear strength model is suggested. Besides impact-driven sliding, the non-driven sliding may also occur in the joint under low normal stress and high impact velocity. [ABSTRACT FROM AUTHOR]

We introduce an analytical model that describes the vertical structure of Ekman boundary layer flows coupled to the Monin-Obukhov Similarity Theory (MOST) surface layer representation, which is valid for conventionally neutral (CNBL) and stable (SBL) atmospheric conditions. The model is based on a self-similar profile of horizontal stress for both CNBL and SBL flows that merges the classic 3/2 power law profile with a MOST-consistent stress profile in the surface layer. The velocity profiles are then obtained from the Ekman momentum balance equation. The same stress model is used to derive a new self-consistent Geostrophic Drag Law (GDL). We determine the ABL height (h) using an equilibrium boundary layer height model and parameterize the surface heat flux for quasi-steady SBL flows as a function of a prescribed surface temperature cooling rate. The ABL height and GDL equations can then be solved together to obtain the friction velocity (u ∗) and the cross-isobaric angle ( α 0 ) as a function of known input parameters such as the Geostrophic wind speed and surface roughness (z 0) . We show that the model predictions agree well with simulation data from the literature and newly generated Large Eddy Simulations (LES). These results indicate that the proposed model provides an efficient and relatively accurate self-consistent approach for predicting the mean wind velocity distribution in CNBL and SBL flows. [ABSTRACT FROM AUTHOR]

This study probes the lithosphere‐asthenosphere system beneath 155 Ma Pacific seafloor using teleseismic S‐to‐p receiver functions at the Pacific Lithosphere Anisotropy and Thickness Experiment project ocean‐bottom‐seismometers. Within the lithosphere, a significant velocity decrease at 33–50 km depth is observed. This mid‐lithospheric discontinuity is consistent with the velocity contrast between the background mantle and thin, trapped layers of crystallized partial melt, in the form of either dolomite or garnet granulite. These melts possibly originated from deeper asthenospheric melting beneath the flanks of spreading centers, and were transported within the cooling lithosphere. A positive velocity increase of 3%–6% is observed at 130–155 km depth and is consistent with the base of a layer with partial melt in the asthenosphere. A shear velocity decrease associated with the lithosphere‐asthenosphere boundary at 95–115 km depth is permitted by the data, but is not required. Plain Language Summary: Using seismic waves from distant earthquakes recorded by seismometers deployed on the seafloor, we investigated the seismic velocity structure beneath old Pacific seafloor. Within the lithosphere, we see a decrease in velocity at depths of roughly 40 km, which can be modeled as crystallized layers of partial melt that were emplaced in the lithosphere when it was young. The data indicate the presence of a velocity increase at depths of 130–155 km, and are consistent with (but do not require) a velocity decrease at depths of 95–115 km. These boundaries could mark the lower and upper boundaries of a layer in the asthenosphere that contains higher fractions of partially molten rock. Key Points: Lithosphere and asthenosphere beneath 155 Ma western Pacific crust are measured by S‐to‐p receiver functions using the Pacific Lithosphere Anisotropy and Thickness Experiment ocean‐bottom seismometers dataA mid‐lithospheric discontinuity at ∼40 km depth is observed and can be explained by layers of crystallized partial meltA partial melt‐bearing layer from 95 to 155 km depth is consistent with the receiver function observations [ABSTRACT FROM AUTHOR]

Numerical simulations of dust emission processes are essential for dust cycle modeling and dust‐atmosphere interactions. Models have coarse spatial resolutions which, without tackling sub‐grid scale heterogeneity, bias finely resolved dust emission. Soil surface wind friction velocity (us*) drives dust emission non‐linearly with increasing model resolution, due mainly to thresholds of sediment entrainment. Albedo is area‐integrated, scales linearly with resolution, is related to us* and hence represents its sub‐grid scale heterogeneity. Calibrated albedo‐based global dust emission estimates decreased by only 2 Tg y−1 (10.5%) upscaled from 0.5 to 111 km, largely independent of resolution. Without adjusting wind fields, this scaling uncertainty is within recent estimates of global dust emission model uncertainty (±14.9 Tg y−1). This intrinsic scaling capability of the albedo‐based approach offers considerable potential to reduce resolution dependency of dust cycle modeling and improve the representation of local dust emission in Earth system models and operational air quality forecasting. Plain Language Summary: Global computer models for atmospheric dust were developed to understand the global dust cycle. However, these coarse resolution global dust models cannot accurately represent small‐scale dust emission processes and partly cause different dust emission estimations between the models. Using our new approach based on satellite products, we show that global dust emission estimation is largely independent of model resolution. Key Points: Wind friction velocity calibrated to linearly upscaled albedo was largely independent of model resolution between 0.5 and 111 kmWithout modifying wind fields, global dust emissions decreased by only 10.5% (within model uncertainty) from 0.5 to 111 km model resolutionSub‐grid scale heterogeneity is necessary to accurately represent grain‐scale sediment supply and entrainment in large scale modeling [ABSTRACT FROM AUTHOR]

The thermodynamic non-equilibrium (TNE) effects and the relationships between various TNE effects and entropy production rate, morphology, kinematics, and dynamics during two initially static droplet coalescences are studied in detail via the discrete Boltzmann method. Temporal evolutions of the total TNE strength D ¯ * and the total entropy production rate can both provide concise, effective, and consistent physical criteria to distinguish different stages of droplet coalescence. Specifically, when the total TNE strength D ¯ * and the total entropy production rate reach their maxima, it corresponds to the time when the liquid–vapor interface length changes the fastest; when the total TNE strength D ¯ * and the total entropy production rate reach their valleys, it corresponds to the moment of the droplet being the longest elliptical shape. Throughout the merging process, the force contributed by surface tension in the coalescence direction acts as the primary driving force for droplet coalescence and reaches its maximum simultaneously with coalescent acceleration. In contrast, the force arising from non-organized momentum fluxes (NOMFs) in the coalescing direction inhibits the merging process and reaches its maximum at the same time as the total TNE strength D ¯ * . In the coalescence of two unequal-sized droplets, contrary to the larger droplet, the smaller droplet exhibits higher values for total TNE strength D ¯ * , merging velocity, driving force contributed by surface tension, and resistance contributed by the NOMFs. Moreover, these values gradually increase with the initial radius ratio of the large and small droplets due to the stronger non-equilibrium driving forces stemming from larger curvature. However, non-equilibrium components and forces related to shear velocity in the small droplet are consistently smaller than those in the larger droplet and diminish with the radius ratio. This study offers kinetic insights into the complexity of thermodynamic non-equilibrium effects during the process of droplet coalescence, advancing our comprehension of the underlying physical processes in both engineering applications and the natural world. [ABSTRACT FROM AUTHOR]

The seismological data recorded at our four semi-permanent broadband seismographs installed by the CSIR-NGRI, Hyderabad, Telangana in the Aravalli mobile belt (AMB) and Rajasthan craton in the northwest Indian shield during the period 2014–2016 are used in the study. The 16 selected regional Indian earthquakes of Mw 5.5–7.8 that occurred in the North India region recorded at the four seismic stations are used to compute the surface wave (both Rayleigh and Love waves) group velocity dispersion characteristics and average 1-D regional shear wave velocity (Vs) structure beneath the North India which covers the northern part of India between the whole Himalayan region and Rajasthan craton including AMB. First, we compute Rayleigh waves (at 7–87 s) dispersion curves and Love waves (at 7–82 s) group velocity dispersion curves by utilizing the standard frequency time analysis (FTAN) of 3-component broadband data recorded at these four 3-component broadband seismic stations. After that, using the logarithmic stacking technique, we compute the final average stacked fundamental mode dispersion curves of surface waves (both Love and Rayleigh waves) for our study area. Then, we finally invert the final average dispersion curves of surface waves (both Love and Rayleigh waves) to compute the average one-dimensional regional shear velocity structure beneath North India. Our modelling result in North India suggests a two-layered crustal structure with a crustal thickness of 39 km. The thickness of the first crustal layer (upper crust) is 20 km with a shear wave velocity (Vs) of 3.30 km/s. On the other hand, the second crustal layer (lower crust) marks a 19-km thickness with a Vs of 3.70 km/s. Our modelling result suggests that the Vs of the upper mantle is found to be 4.35 km/s below the study region. Research highlights: Modelled average one-dimensional regional Vs structure below northern part of India. A 2-layered crustal velocity model below North India. Upper crust at 20 km thick with Vs of 3.30 km/s. And, lower crust at 19 km thick with Vs of 3.70 km/s. The Moho depth is 39 km and Vs below the Moho depth is found to be 4.35 km. [ABSTRACT FROM AUTHOR]

Drifting and blowing snow are important features in polar and high mountain regions. They control the surface mass balance in windy conditions and influence sublimation of snow and ice surfaces. Despite their importance, model representations in weather and climate assessments have high uncertainties because the associated physical processes are complex and highly variable in space and time. This contribution investigates the saltation system, which is the lower boundary condition for drifting and blowing snow models. Using a combination of (previous) measurements and new physics-based modeling with large-eddy simulation (LES), we show that the prevailing parameterizations that describe the saltation system in atmospheric models are based on contradictory assumptions: while some scaling laws are typical of a saltation system dominated by aerodynamic entrainment, others represent a saltation system controlled by splash. We show that both regimes can exist, depending on the friction velocity. Contrary to sand saltation, aerodynamic entrainment of surface particles is not negligible. It is important at low wind speeds, leading to a saltation height and near-surface particle velocity which increase with the friction velocity. In a splash-dominated saltation regime at higher friction velocities, the saltation height and near-surface particle velocity become invariant with the friction velocity and closer to what is observed with sand. These findings are accompanied by a detailed description of the theoretical, experimental and numerical arguments behind snow saltation parameterizations. This work offers a comprehensive understanding of the snow saltation system and its scaling laws, useful for both modelers and experimentalists. [ABSTRACT FROM AUTHOR]

We develop a 3‐D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land‐based seismographs to investigate along‐strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land‐based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high‐velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from VS reduction and VP/VS are larger than those determined using VP reduction in prior studies, likely due to water in cracks affecting VS more than VP. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments. Plain Language Summary: This study uses seismic data from the 2018–2019 Alaska Amphibious Community Seismic Experiment and other land stations to image the 3‐D seismic velocity structure of the Alaska subduction zone. The analysis combines constraints from both Rayleigh waves and converted body waves. The results provide insight into the distinct lateral variations observed for many properties of the subduction zone. Thick, low‐velocity forearc crust is found beneath the Kodiak and Semidi segments, which may be related to the higher seismic coupling in these regions. The Bristol Bay Basin has a thin crust with a high velocity lower layer, suggesting a dense mafic lower crust emplaced by the extensional processes that formed the basin. Low velocities in the incoming plate near the trench in the Shumagin segment indicate pronounced mantle hydration, extending to about 18 km below the Moho. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments. Key Points: Crustal thickness of the inner forearc (35–42 km) generally exceeds that of the volcanic arc, but becomes variable in the Shumagin segmentThe Shumagin segment has more incoming plate mantle hydration than the Semidi segment, aligning with abundant plate bending normal faultsHydration extends to depths of 18 km below the Moho, indicating more water subducts than most previous estimates [ABSTRACT FROM AUTHOR]

The observation-reanalysis difference method (OMR) and wind profile fitting method were used to analyze the influence urbanization has on the near-surface wind speed in Shanghai during tropical cyclone events. The data used include daily wind speed data from the Shanghai Meteorological Observatory Station collected from 1991 to 2020, hourly wind speed data from 100 m high wind towers from 2017 to 2019, and reanalysis data that covered the same period. The results indicated that during tropical cyclone occurrence, the wind speed of the OMR in the central urban region was significantly lower than that in the suburban area, and the OMR declined more obviously over the year, down to -8 m/s in 2020. Urbanization leads to the increase of average wind weakening rate to be higher than the maximum wind weakening rate, causing the maximum weakening rate of the central urban region to the average wind over 80%, while maximum wind speed was less than 80%. The weakening rate of both the average and maximum wind speeds during tropical cyclone impacts is greater than the rate that the annual average wind speed was reduced. A logarithmic variation was visible in the wind profile of the island station during tropical cyclone occurrence, with an average friction velocity U* of 0.9389 m/s and an average rough length Z0 of 0.4915 m. The wind speed during tropical cyclone events was higher than the three-year average wind speed within each layer. The suburban stations show a linear variation, and every hundred meters of height results in an increase of 5-6 m/s in the wind speed change rate. At 100 m of altitude, the wind speed in the suburban region is reduced by approximately 40%. [ABSTRACT FROM AUTHOR]

Buoyancy fluxes and submarine melt rates at vertical ice‐ocean interfaces are commonly parameterized using theories derived for unbounded free plumes. A Large Eddy Simulation is used to analyze the disparate dynamics of free plumes and wall‐bounded plumes; the distinctions between the two are supported by recent theoretical and experimental results. Modifications to parameterizations consistent with these simulations are tested and compared to results from numerical and laboratory experiments of meltwater plumes. These modifications include 50% weaker entrainment and a distinct plume‐driven friction velocity in the shear boundary layer up to 8 times greater than the externally‐driven friction velocity. Using these updated plume parameter modifications leads to 40 times the ambient melt rate predicted by commonly used parameterizations at vertical glacier faces, which is consistent with observed melt rates at LeConte Glacier, Alaska. Plain Language Summary: Over the past two decades, the outward flow of tidewater glaciers has accelerated, which has contributed to sea level rise. There is growing evidence that this acceleration has been triggered by melting at ice‐ocean interfaces, where the ocean comes into contact with and drives the melting of glaciers. In particular, commonly used models and theories describing the ocean turbulence and melt dynamics at vertical ice‐ocean interfaces underestimate observed melt rates by an order of magnitude. This study tests proposed changes to existing theories and uses a turbulence‐resolving ocean model to validate this alternative (plume with a wall) theory instead of commonly used (plume without a wall) theories; the first type is more appropriate and better takes into account how ocean turbulence drives the melting of a vertical ice wall. We show that these proposed changes are consistent with existing melt observations and are an important step toward understanding a critical process that may help us improve sea level rise predictions. Key Points: A modified wall‐bounded plume parameterization motivated by recent numerical/lab work is proposed as an alternative to free plume theorySubglacial discharge plume simulations at a vertical ice face are consistent with entrainment/plume dynamics from wall‐bounded plume theoryMelt rate estimates using updated parameters are consistent with observations at LeConte Glacier (40 times greater than standard estimates) [ABSTRACT FROM AUTHOR]

In this study, the amplitude modulation effect in a turbulent boundary layer over anisotropic porous walls is investigated experimentally at the Reynolds number based on friction velocity of Reτ = 236–319. The streamwise and wall-normal velocity fields were measured using time-resolved particle image velocimetry. To clarify the coherent structures related to the amplitude modulation over the porous wall with skin friction reduction effect, the large-scale structures are extracted from the low-pass filtered streamwise velocity fluctuations. The small-scale events related to high fluctuation energy are detected by the variable-interval space-averaging technique. Over the porous wall, the induced upwash and downwash motion leads to a notable suppression of large-scale structures. The small-scale motions in the near-wall region are mainly caused by the ejection events, while the sweep events are significantly suppressed. The amplitude modulation effects indicate that the positive and negative large-scale velocity streaks produce suppression and enhancement effects to the near-wall small-scale turbulence, respectively, which is contrary to the conventional phenomenon over the smooth wall case. The interaction between outer large-scale and inner small-scale structures is significantly weakened by the porous wall, contributing to the overall skin friction reduction. [ABSTRACT FROM AUTHOR]

It is necessary to find food additives that can reduce the food friction coefficient, in order to make it easier for the elderly and people with dysphagia to swallow. The sesame paste and rice paste are two typical foods eaten by the elderly. In this research, the tribological and rheological properties of 2 paste with 12 hydrocolloids were investigated. The results showed that three hydrocolloids (xanthan gum, gellan gum, and pectin) could reduce the friction coefficients of sesame paste and rice paste within a certain range of oral friction velocity. The friction coefficients of two kinds of original paste are in the order of 10−1. The addition of three hydrocolloids can reduce them to about 10−2, effectively improving lubrication. After adding hydrocolloids, the particles cross‐link to form a network structure, which improves the viscosity and lubrication of food to a certain extent. This has potential application value for designing food that is more conducive to swallowing. [ABSTRACT FROM AUTHOR]

The mechanical properties of granular materials at a low shear rate are frequently viewed as rate-independent, and a rate-independent constitutive relation is used to describe the mechanical behaviors of the granular material. However, time-dependent behaviors (or creeping behaviors) become significant in the long run. In this paper, we conduct triaxial experiments to observe the creep of granular materials under both dynamic and static loading conditions. Three typical creeping behaviors, aging, transitional, and fluidic, have been observed. To describe the time-dependent behaviors, an internal state variable characterizing the fluidity of the granular system is introduced to propose a rate-dependent constitutive relation which we call in this paper, a state evolution model. A characteristic strain is also introduced into the model to account for the influences of historic strain on the current state. The experiments are analyzed using the proposed model and it has been found that our model can well discern the observed three creeping behaviors. A criterion to identify the stability of a granular system is also given out based on the proposed model. Two key factors dominating the stability of the granular system are recognized – shear wave velocity and critical velocity. Our laboratory experiments in combination with the proposed criterion offer a physical explanation of the intrinsic triggering mechanism of system evolution from a stable to fluidic state: decrease in wave velocity or/and critical velocity. [ABSTRACT FROM AUTHOR]

Understanding the motion of particles in very dense granular flows is crucial for comprehending the dynamics of many geological phenomena, and advancing our knowledge of granular material physics. We conduct transparent ring shear experiments to directly observe the granular motion under relatively high‐pressure conditions, and find that the granular velocity non‐linearly decays, forming an approximately 7‐particle‐diameter‐thick localized shear band. A fitting curve underlying non‐local physics can be used to well predict velocity profile geometries that are almost independent of normal stress and shear velocity. Moreover, experimental results show monotonically decreasing granular kinetic temperature, which may be caused by energy dissipation due to more inelastic contacts under high confining pressures. The variation of granular temperature will significantly influence the local yield stress and rheological properties, which may lead to inhomogeneous fluidity of the material and thus to shear localization in very dense granular flows. Plain Language Summary: Understanding how particles move under high pressure is essential for studying various geological phenomena and advancing our understanding of granular material physics. In this study, transparent ring shear experiments are conducted to observe the motion of granular particles in very dense granular flows under high normal stress. It is found that the velocity distribution progressively decays and forms a shear band with a width of approximately 7 particle diameters. We suggest an equation that can well predict the velocity profile both of the quasi‐linear velocity in the fast‐moving shear zone and the exponential velocity curve in the slow‐motion region. Furthermore, we analyze the distribution of particle velocity fluctuation and particle density across the sample. Near the moving plate, the particle velocity fluctuation is more intense and the particle density is lower, gradually decreasing far from the moving plate. This phenomenon may be caused by energy dissipation due to inelastic contact between particles. The mechanical properties of the granular material are influenced by these variations in velocity fluctuation and particle density. Thus, this leads to an inhomogeneous shear strain rate and promotes the formation of shear zones under relatively high‐pressure conditions. Key Points: A nonlinearly decayed velocity profile and spontaneous shear localization are observed in plane shear granular flows under high normal stressThe monotonically decayed granular temperature may lead to inhomogeneities in very dense granular flows and thus to shear localizationThe length scale of the non‐local model in very dense granular flows is estimated based on experimental observation [ABSTRACT FROM AUTHOR]

In this paper, the spatiotemporal evolution of wind turbine (WT) wake characteristics is studied based on lattice Boltzmann method-large eddy simulations (LBM-LES) and grid adaptive encryption at different incoming flow velocities. It is clearly captured that secondary flow occurs in the vortex ring under shear force in the incoming flow direction, the S-wave and the Kelvin–Helmholtz instability occur in the major vortex ring mainly due to the unstable vortex ring interface with small disturbance of shear velocity along the direction of flow velocity. The S-wave and Kelvin–Helmholtz instability are increasingly enhanced in the main vortex ring, and three-dimensional disturbances are inevitable along the mainstream direction when it evolves along the flow direction. With increasing incoming flow, the S-wave and Kelvin–Helmholtz instability are gradually enhanced due to the increasing shear force in the flow direction. This is related to the nonlinear growth mechanism of the disturbance. The analysis of the velocity signal, as well as the pressure signal with a fast Fourier transform, indicates that the interaction between the vortices effectively accelerates the turbulence generation. In the near-field region of the wake, the dissipation mainly occurs at the vortex at the blade tip, and the velocity distribution appears asymmetric around the turbine centerline under shear and the mixing of fluids with different velocities in the wake zone also leads to asymmetric distributions. [ABSTRACT FROM AUTHOR]

Direct numerical simulation combined with a one-way coupled Lagrangian particle tracking technique is employed to investigate dilute particle-laden turbulent flows in open square ducts with a free surface. The focus is on examining the influence of the mean cross-stream secondary flow on particle transport near the wall, free surface, and across the duct cross section. Based on the duct half-width and mean friction velocity, a shear Reynolds number of Reτ = 300 is considered, with the corresponding particle Stokes numbers ranging from St+ = 0.31 to 260. The results reveal that particle concentration near the sidewalls is lower than that near the bottom wall, and the minimum particle concentration is observed at the free surface. Along the bottom wall centerline orientated upward, particle concentration gradually decreases. An exception to this is in the vicinity of the free surface where a slight increase is observed for the heavier particles (St+ ≥ 25), and the amplitude of this increase gradually declines as the Stokes number increases. In the streamwise direction near the free surface, heavier particles tend to preferentially concentrate in regions where the instantaneous transverse secondary flow velocity is negative. As the Stokes number increases, the position of the maximum streamwise velocity for heavier particles is closer to the free surface, and the rotation centers of inner and outer secondary particle motions gradually disappear. The streamwise root mean square velocity for the lightest St+ = 0.31 particles is higher than that for particles with higher inertia in the middle region of the free surface. [ABSTRACT FROM AUTHOR]

Surface hotspot motions are approximately a factor of two faster in the Pacific than the Indo‐Atlantic, and the Indo‐Atlantic large low shear velocity province (LLSVP) appears to be significantly taller than the Pacific LLSVP. Hypothesizing that surface hotspot motions are correlated with the motion of plume sources on the upper surface of chemically distinct, intrinsically dense LLSVPs, we use 3D spherical mantle convection models to compute the velocity of plume sources and compare with observed surface hotspot motions. No contrast in the mean speed of Pacific and Indo‐Atlantic hotspots is predicted if the LLSVPs are treated as purely thermal anomalies and plume sources move laterally across the core‐mantle boundary. However, when LLSVP topography is included in the model, the predicted hotspot speeds are, on average, faster in the Pacific than the Indo‐Atlantic, even when modest topography is assigned to both LLSVPs (e.g., 100–300 km). The difference in mean hotspot speed increases to a factor of two for larger and laterally variable LLSVP topography estimated from seismic tomographic model S40RTS (up to 1,100–1,500 km for the Indo‐Atlantic region vs. 700–1,400 km for the Pacific region) and our results also broadly reproduce the convergence of Pacific hotspots toward the center of the Pacific LLSVP. These largescale features of global hotspot motions are only reproduced when ambient mantle material flows over large, relatively stable topographical features, suggesting that LLSVPs are chemically distinct and intrinsically dense relative to ambient mantle material. Plain Language Summary: Seismic observations reveal two continent‐sized anomalies at the base of the Earth's mantle, referred to as Large Low‐Shear‐Velocity Provinces (LLSVPs), through which seismic waves travel slowly. Slow seismic velocity is generally interpreted as increased temperature. However, buoyant plumes of hot material rise from the LLSVPs and produce hotspot volcanoes on the Earth's surface, and the geochemistry of these lavas suggest that LLSVPs are primordial, which suggests the LLSVPs cannot be purely thermal anomalies. To explain why the LLSVPs have remained at the base of the mantle for billions of years, they must have higher intrinsic density that the ambient mantle in addition to being hot, but this is still debated. To contribute to understanding whether LLSVPs are intrinsically dense, chemically distinct piles versus purely thermal, we compare the velocity of ambient mantle flow, which may advect plume sources over LLSVPs, with surface hotspot motions. Results show that the largescale differences in surface hotspot motions are reproduced only when LLSVPs behave like topography that deflects ambient mantle flow. Because LLSVPs would only behave like topography that deflects ambient mantle flow if they are denser than ambient mantle material, our results provide additional evidence in support of LLSVPs as dense thermochemical piles. Key Points: Pacific hotspot motions are on average two times faster than Indo‐Atlantic hotspots in commonly used reference framesThe contrast in mean hotspot speed is reproduced in the models only if Large Low‐Shear‐Velocity Provinces (LLSVPs) behave like topography that plume sources are advected overLLSVPs would behave like topography that plume sources are advected over only if they are denser than ambient mantle material [ABSTRACT FROM AUTHOR]

A few studies on ozone deposition over lake water are available and so far only one using the eddy covariance technique (Wesely et al., 1981, https://doi.org/10.1007/BF00122295). A 23‐day field campaign was held in August‐September 2012 at the Lake Kuivajärvi in Hyytiälä, Finland. The results showed a mean flux of −30 ± 1 ng m−2 s−1 and deposition velocity of 0.86 ± 0.05 mm s−1. Deposition velocity showed a weak diurnal cycle over the lake with elevated values during the nighttime. The daytime and nighttime portions of the data set differed statistically. Analysis showed that waterside convective mixing enhanced deposition and such conditions pre‐dominantly occurred during nighttime. We compared the measured deposition velocities with the dry deposition model of air‐sea exchange, adjusted for the chemical sinks relevant for the lake. We suggest that the buoyant mixing and unaccounted chemistry can be responsible for the difference between the model results and observations. Plain Language Summary: Ozone deposition was studied over lake in Southern Finland. Deposition velocity showed elevated values during the nighttime. Higher ozone deposition at night was related to enhanced convective mixing in uppermost water layers. Key Points: Ozone deposition over the lake is enhanced by waterside buoyancy velocityWind speed and friction velocity had minor or no impact on ozone deposition, instead waterside convective mixing enhanced depositionIn late summer, over diurnal course higher deposition velocities occurred at night [ABSTRACT FROM AUTHOR]

The vertical structure of downslope velocity within sub-aqueous gravity-driven flows of (smoother) glass beads and (rougher) natural sand is investigated for both fixed roughness and erodible beds using high-resolution, MHz-frequency acoustics. The observed velocity profiles within the O(1) cm thick, O(10) cm/s flows exhibit a negative shear layer extending downward from the sediment–water interface to a velocity maximum at ∼ 9 grain diameters depth within the layer, below which the velocities decrease to near-zero values at the pre-flow bed location for fixed roughness beds and to non-zero values for mobile beds. The attenuation of sound transmitted through the moving layer is used to constrain the depth-averaged solids concentration to a value of ∼ 0.52. The observed negative shear at the interface indicates that, unlike the sub-aerial case, interfacial friction is dynamically important in gravity-driven sub-aqueous granular flows. It is shown that the observed vertical structure of velocity within the layer can be well represented by continuum viscous flow models. Solids concentration and effective viscosity are estimated from the best-fit model parameters using the Zarraga–Hill–Leighton (2000) empirical relation for suspensions of negatively buoyant particles, yielding vertically averaged values ∼ 0.57. While the sub-millimeter vertical resolution of the measurements is too coarse to provide precise estimates of the friction velocity at the interface, the model-data comparisons nevertheless indicate that the vertical structure of the downslope flow consists of a weakly stratified dense layer and a thin, dilute transition layer between the dense flow and the overlying water. [ABSTRACT FROM AUTHOR]

One of the last remaining floating tongues of the Greenland ice sheet (GrIS), the Petermann Glacier ice shelf (PGIS), is seasonally shielded from warm Atlantic water (AW) by the formation of sea ice arches in the Nares Strait. However, continued decline of the Arctic sea ice extent and thickness suggests that arch formation is likely to become anomalous, necessitating an investigation into the response of PGIS to a year-round mobile and thin sea ice cover. We use a high-resolution unstructured grid 3-D ocean–sea ice–ice shelf setup, featuring an improved sub-ice-shelf bathymetry and a realistic PGIS geometry, to investigate in unprecedented detail the implications of transitions in the Nares Strait sea ice regime, that is, from a thick and landfast sea ice regime to a mobile, and further, a thin and mobile sea ice regime, with regard to PGIS basal melt. In all three sea ice regimes, basal melt near the grounding line (GL) presents a seasonal increase during summer, driven by a higher thermal driving. The stronger melt overturning increases the friction velocity slightly downstream, where enhanced friction-driven turbulent mixing further increases the thermal driving, substantially increasing the local melt. As the sea ice cover becomes mobile and thin, wind and (additionally in winter) convectively upwelled AW from the Nares Strait enter the PGIS cavity. While its effect on basal melting is largely limited to the shallower (<200 m) drafts during winter, in summer it extends to the GL (ca. 600 m) depth. In the absence of an increase in thermal driving, increased melting under the deeper (>200 m) drafts in winter is solely driven by the increased vertical shear of a more energetic boundary layer current. A similar behaviour is noted when transitioning from a mobile to a thin mobile sea ice cover in summer, when increases in thermal driving are negligible and increases in melt are congruent with increases in friction velocity. These results suggest that the projected continuation of the warming of the Arctic Ocean until the end of the 21st century and the accompanying decline in the Arctic sea ice extent and thickness will amplify the basal melt of PGIS, impacting the long-term stability of the Petermann Glacier and its contribution to the future GrIS mass loss and sea level rise. [ABSTRACT FROM AUTHOR]

The crustal structure in south‐central Alaska has been influenced by terrane accretion, flat slab subduction, and a modern strike‐slip fault system. Within the active subduction system, the presence of the Denali Volcanic Gap (DVG), a ∼400 km region separating the active volcanism of the Aleutian Arc to the west and the Wrangell volcanoes to the east, remains enigmatic. To better understand the regional tectonics and the nature of the volcanic gap, we deployed a month‐long north‐south linear geophone array of 306 stations with an interstation distance of 1 km across the Alaska Range. By calculating multi‐component noise cross‐correlation and jointly inverting Rayleigh wave phase velocity and ellipticity across the array, we construct a 2‐D shear wave velocity model along the transect down to ∼16 km depth. In the shallow crust, we observe low‐velocity structures associated with sedimentary basins and image the Denali fault as a narrow localized low‐velocity anomaly extending to at least 12 km depth. About 12 km, below the fold and thrust fault system in the northern flank of the Alaska Range, we observe a prominent low‐velocity zone with more than 15% velocity reduction. Our velocity model is consistent with known geological features and reveals a previously unknown low‐velocity zone that we interpret as a magmatic feature. Based on this feature's spatial relationship to the Buzzard Creek and Jumbo Dome volcanoes and the location above the subducting Pacific Plate, we interpret the low‐velocity zone as a previously unknown subduction‐related crustal magma reservoir located beneath the DVG. Plain Language Summary: The Alaska Range in south‐central Alaska has been shaped by different geological processes. One puzzling aspect is the Denali Volcanic Gap, a region of about 400 km between the Aleutian Arc and the Wrangell volcanoes. To understand this volcanic gap and regional tectonics better, we obtained a 2‐D model of shear wave velocity down to a depth of about 16 km, using a month‐long linear geophone array with over 300 stations placed at 1 km intervals across the Alaska Range. In the shallow crust, we found areas with low‐velocity associated with sedimentary basins. We observe a narrow anomaly related to the Denali fault with low‐velocity extending to at least 12 km depth. About 12 km below the northern flank of the Alaska Range, we discovered a significant zone with low seismic velocities. This zone is believed to be related to magma and is located above the subducting Pacific Plate. We interpreted the anomaly as a magma reservoir beneath the volcanic gap, based on its tectonic and spatial relationship with nearby volcanoes. Key Points: We present a 2‐D shear velocity model of the top 16 km of the crust in south‐central Alaska across the Alaska rangeThe Denali fault was identified as a narrow localized low‐velocity anomaly extending to at least 12 km depthWe observe a low‐velocity zone ∼12 km beneath the volcanic gap. We interpret the anomaly as a subduction‐related magma reservoir [ABSTRACT FROM AUTHOR]

In the equilibrium range of the wave spectrum's high-frequency tail, energy levels are proportional to the wind friction velocity. As a consequence of this intrinsic coupling, spectral tail energy levels can be used as proxy observations of surface stress and wind speed when direct observations are unavailable. Proxy observations from drifting wave-buoy networks can therefore augment existing remote sensing capabilities by providing long dwell observations of surface winds. Here we consider the skill of proxy wind estimates obtained from observations recorded by the globally distributed Sofar Spotter network (observations from 2021 to 2022) when compared with collocated observations derived from satellites (yielding over 20 000 collocations) and reanalysis data. We consider physics-motivated parameterizations (based on frequency−4 universal tail assumption), inverse modeling (estimate wind speed from spectral energy balance), and a data-driven approach (artificial neural network) as potential methods. Evaluation of trained/calibrated models on unseen test data reveals comparable performance across methods with generally of order 1 m s−1 root-mean-square difference with satellite observations. [ABSTRACT FROM AUTHOR]

We present a new data set of nearly 100 earthquakes which show clear evidence of the Hawaiian ultra-low velocity zone (ULVZ) in the S   core-diffracted phase (Sdiff), representing the most comprehensive Sdiff data set of a ULVZ to date. Using a Bayesian inversion approach, as outlined in Martin et al., and a subset of the data set, we characterise the 2-D morphology and velocity of the Hawaiian ULVZ. The results suggest that the ULVZ is smaller than previously estimated, with an elliptical shape, and oriented along the direction of the large low-shear velocity province boundary. Using forward modelling, we infer that the ULVZ has a height of 25 km and shear velocity reduction of 25 %. [ABSTRACT FROM AUTHOR]

Between 2017 and 2019, the CSIR-NGRI, Hyderabad, Telangana, established a broad-band seismic-network with fifty-five 3-component broadband seismometers in the Himalayan region of Uttarakhand, India. Out of 55 three component broadband seismic (BBS) networks, we chose 17 for the present study. Using digital waveform data from twenty-one (21) regional Indian earthquakes of Mw 5.0–6.2 that were recorded in the 17 broadband seismometer, we compute fundamental mode group-velocity dispersion (FMGVD) characteristics of surface waves (Love and Rayleigh waves) and the average one-dimensional regional shear-wave velocity (Vs) structure of the Uttarakhand Himalayan region. First, we compute FMGVD curves for Love waves (6–73 s) and Rayleigh waves (at 6.55–73 s) period, and then, we finally invert these dispersion curves to compute the final average one-dimensional regional crustal & sub-crustal shear-wave velocity (Vs) structure below the Uttarakhand Himalaya. Our best model in Uttarakhand Himalayan region, India, reveals the 8-layered crust with a mid-crustal low velocity layer (MC-LVL) (approximately a drop of 1.5–2.3% in Vs) between 8 and 20 km depth in the proximity of MCT (Main Central Thrust). In the upper crustal part (0–20 km depths), our modelling suggests shear velocities (Vs) varies from 3.1 to 3.9 km/sec while shear velocities (Vs) in the lower crustal part (20–45 km depth) are modelled to be varying from 3.7 to 4.69 km per sec. The Moho-depth is calculated to be 45 km deep below the K-G Himalaya, and the shear-velocity (Vs) in the sub-crustal sector is 4.69 km/sec. Our estimated mid-crustal low-velocity layer (MC-LVL) could be linked to the presence of metamorphic fluids in the fractured Main Himalayan Thrust (MHT), resulting from the weakening of the crustal material at the interface between the overriding Eurasian plate and upper part of the underthrusting Indian plate. [ABSTRACT FROM AUTHOR]

Transverse bulk phonons in a multimode integrated quantum acoustic device are excited and characterized via their free-space coupling to a three-dimensional (3D) microwave cavity. These bulk acoustic modes are defined by the geometry of the Y-cut lithium niobate substrate in which they reside and couple to the cavity electric field via a large dipole antenna, with an interaction strength on the order of the cavity linewidth. Using finite element modeling, we determine that the bulk phonons excited by the cavity field have a transverse polarization with a shear velocity matching previously reported values. We demonstrate how the coupling between these transverse acoustic modes and the electric field of the 3D cavity depends on the relative orientation of the device dipole, with a coupling persisting to room temperature. Our study demonstrates the versatility of 3D microwave cavities for mediating contact-less coupling to quantum, and classical, piezoacoustic devices. [ABSTRACT FROM AUTHOR]

We develop an asymptotic theory of the compressible turbulent boundary layer on a flat plate, in which the mean velocity and temperature profiles can be obtained as exact asymptotic solutions of the boundary-layer equations, which are closed using functional relations of a general form connecting the turbulent shear stress and turbulent enthalpy flux to mean velocity and enthalpy gradients. In this part of the study, we consider the near-wall region that consists of viscous and logarithmic sublayers. The solution is constructed in the form of expansions in a small parameter ε that is proportional to the Mach number formed with the friction velocity and the speed of sound on the wall. Three characteristic flow regimes are possible in the viscous sublayer, which occur at small (including zero), moderate, and large negative wall heat flux. For the first two regimes, the flow is incompressible to the first approximation, while the compressibility is significant in the viscous sublayer on a strongly cooled plate. The Crocco integral in the logarithmic region is obtained, which in the zeroth-order approximation in ε gives the Waltz equation, but in contrast to it, the new relation describes well the dependence of temperature on velocity for any heat flux on the wall. Along with the constants known for incompressible flow, the theory contains two new universal constants, which are determined from a comparison with direct numerical simulation data for velocity and temperature. [ABSTRACT FROM AUTHOR]

The investigation on dynamic shear fracture behaviour of rocks subjected to the simulated geo-stress is of great importance for deep rock engineering. Four groups of dynamic mode II fracture tests with different axial pre-forces were conducted on the granite short core in compression (SCC) specimens using a coupled static–dynamic loading system. It can be found that dynamic mode II fracture toughness rises with increasing loading rate at a given pre-force ratio and decreases with increasing pre-force ratio at a given loading rate. Total fracture toughness exhibits evident rate dependence and it is almost independent of the pre-forces. An empirical model was established to describe the influence of the pre-force and loading rate on the Mode II fracture toughness. Deformation, damage and fracture characteristics of rock were elaborated based on surface deformation field. The results indicate that (1) The original damage caused by pre-force increases with the pre-force ratio; (2) The fracture path is independent of pre-force ratio and the loading rate in the studied range; (3) At a given pre-force ratio, the loading rate has a significant effect on the final failure pattern of the SCC specimen. In addition, a novel relative shear velocity (RSV), defined as the ratio of relative shear displacement and time spent from deformation onset to the generation of complete shear fracture, is proposed to depict the dynamic shear crack propagation. The results indicate that the RSV increases with loading rate irrespective of the pre-force, showing a power function relationship with loading rate. Highlights: Dynamic mode II fracture tests were conducted on the granite short core in compression specimens using a coupled static–dynamic loading system. The relationship between dynamic mode II fracture toughness with axial pre-force and loading rate is analysed qualitatively and quantitatively. Deformation, damage and fracture features of granite were elaborated using three-dimensional high-speed digital image correlation technique. A novel index, relative shear velocity, based on surface displacement field, is proposed to depict the dynamic shear crack propagation. [ABSTRACT FROM AUTHOR]

Surface-layer parameterizations for heat, mass, momentum, and turbulence exchange are a critical component of the land surface models (LSMs) used in weather prediction and climate models. Although formulations derived from Monin–Obukhov similarity theory (MOST) have long been used, bulk Richardson (Rib) parameterizations have recently been suggested as a MOST alternative but have been evaluated over a limited number of land-cover and climate types. Examining the parameterizations' applicability over other regions, particularly drylands that cover approximately 41% of terrestrial land surfaces, is a critical step toward implementing the parameterizations into LSMs. One year (1 January–31 December 2018) of eddy covariance measurements from a 10-m tower in southeastern Arizona and a 200-m tower in western Texas were used to determine how well the Rib parameterizations for friction velocity ( u * ), sensible heat flux (H), and turbulent kinetic energy (TKE) compare against MOST-derived parameterizations of these quantities. Independent of stability, wind speed regime, and season, the Rib u * and TKE parameterizations performed better than the MOST parameterizations, whereas MOST better represented H. Observations from the 200-m tower indicated that the parameterizations' performance degraded as a function of height above ground. Overall, the Rib parameterizations revealed promising results, confirming better performance than traditional MOST relationships for kinematic (i.e., u * ) and turbulence (i.e., TKE) quantities, although caution is needed when applying the RibH parameterizations to drylands. These findings represent an important milestone for the applicability of Rib parameterizations, given the large fraction of Earth's surface covered by drylands. Significance Statement: Weather forecasting models rely upon complex mathematical relationships to predict temperature, wind, and moisture. Monin–Obukhov similarity theory (MOST) has long been used to forecast these quantities near the land surface, even though MOST's limitations are well known in the scientific community. Researchers have suggested an alternative to MOST called the bulk Richardson (Rib) approach. To allow for the Rib approach to be used in weather forecasting models, the approach needs to be tested over different land-cover and climate types. In this study, we applied the Rib approach to dry areas of the United States and found that the approach better represented turbulence variables than MOST relationships. These findings are an important step toward using Rib relationships in weather forecasting models. [ABSTRACT FROM AUTHOR]

Accurate and reliable river discharge evaluation at a river station is an essential piece of information to obtain. This work modifies a power-law (PL)-based model and a single point velocity measurement (SPM) method for calculating channel discharge. Specifically, modifications are proposed for the constant shear velocity assumption, water surface effects, the underlying velocity distribution, and the number of measurements. A coefficient of water surface (cw) is proposed to consider the impact of water surface on distribution of velocity. Additionally, a power-wake-law (PWL) method is proposed to cope with the velocity dip phenomenon, where the maximum velocity occurs below the water surface. A critical assessment of the performance of the modifications using laboratory and field data is introduced. A trial-and-error procedure is applied to the laboratory data to obtain the value of the proposed coefficient cw and the parameters of PWL velocity distribution, α and β. It is found that cw=0.3 , α=1.5/m , and β=0.6 are the most appropriate values that produce minimum errors in most cases. A combination approach is applied to the field data to demonstrate the performance of the modifications and the impact of increasing the number of measurements. It is found that considering a water surface effect has significantly improved the accuracy. Also, it is found that the modified PL- and PWL-based models can estimate discharge with a reasonable accuracy using five measured velocimetry points in most tested cross-sections. In most studied rivers, the five-point combinations reduce the mean absolute percentage error (MAPE) value to less than 5%. [ABSTRACT FROM AUTHOR]

The photoelectric factor (PEF) is an important well-logging tool to distinguish between different types of reservoir rocks because PEF measurement is sensitive to elements with high atomic numbers. Furthermore, the ratio of rock minerals could be determined by combining PEF log with other well logs. However, PEF logs could be missing in some cases such as in old well logs and wells drilled with barite-based mud. Therefore, developing models for estimating missing PEF logs is essential in those circumstances. In this work, we developed various machine learning models to predict PEF values using the following well logs as inputs: bulk density (RHOB), neutron porosity (NPHI), gamma ray (GR), compressional and shear velocity. The predictions of PEF values using adaptive-network-fuzzy inference system (ANFIS) and artificial neural network (ANN) models have errors of about 16% and 14% average absolute percentage error (AAPE) in the testing dataset, respectively. Thus, a different approach was proposed that is based on the concept of automated machine learning. It works by automatically searching for the optimal model type and optimizes its hyperparameters for the dataset under investigation. This approach selected a Gaussian process regression (GPR) model for the accurate estimation of PEF values. The developed GPR model decreases the AAPE of the predicted PEF values in the testing dataset to about 10% AAPE. This error could be further decreased to about 2% by modeling the potential noise in the measurements using the GPR model. [ABSTRACT FROM AUTHOR]

The artificial joint is one of the most effective methods to treat joint injuries. The service performance of artificial joints is gradually weakened because of the wear of artificial joints in actual service. In order to obtain the potential failure mechanism of the artificial joint in actual service, the study was carried out with the multiple factors that affect the service performance of the artificial joint. The experimental study was carried out on the change rule of mechanical behavior of the contact interface between the artificial joint of titanium alloy and cortical bone. The multi-factor is compression load, contact load, friction velocity, and lubrication environment, respectively. The results indicate that the friction coefficient, wear mass, and wear coefficient of Ti-6A1-4V titanium alloy decreased with the increasing of the compression load. The friction rate and the friction coefficient of Ti-6A1-4V titanium alloy decreased with the increasing of the contact load. The wear mass and friction coefficient of Ti-6A1-4V titanium alloy increased with the increasing of contact load. The lubrication effect is better with the increasing of lubricant concentration. Based on the observation of the SEM, the wear type influenced by compression load and friction rate is mainly abrasive wear and oxidation wear. The wear type influenced by contact load is mainly abrasive wear and adhesive wear. The wear type influenced by lubricants is mainly oxidation wear. When wear mass and wear coefficient are used as the criteria for evaluating friction and wear, the order of influential factors to friction and wear of Ti-6Al-4V titanium alloy plate is friction rate, compression load, contact load, and lubricant concentration. This research can provide a theoretical reference for the optimal manufacture of the artificial joint of titanium alloy and optimal rules of safe service conditions. [ABSTRACT FROM AUTHOR]

The shear strength and stiffness of granular materials are crucial parameters for evaluating both stability and sustainability in geoenvironmental engineering. Two types of shear loading, static and cyclic, may directly influence the mechanical properties of granular materials; however, the investigation of stiffness improvement of granular materials has not yet been sufficiently investigated using a loading method. The one-way repeated loading method described in this study may overcome the drawbacks of classical testing approaches. One-way repeated direct shear (DS) and direct simple shear (DSS) tests were conducted on a series of poorly graded bead gradations to investigate the shear strength and stiffness of granular materials under a drained and strain-controlled condition with a shear velocity of 0.1 mm/min. All samples in the two tests were prepared using the same method and initial geometry. Three types of samples referring to different curvature coefficient (Cu) values of 1.8, 3.3, and 5.8 and normal stresses (σn) of 50, 100, and 150 kPa were applied. The test results show that an increase in Cu results in an increase in the shear stress of the granular materials at the peak and ultimate states for both the DS and DSS tests. The peak shear stress ratios between the two tests (τDSS/τDS) ranged from 0.75 to 0.95 when Cu and σn were increased. The angles of shearing resistance from the DS test were in a wide range of 25.7°–33.7° at the peak state and 24.9°–31.3° at the ultimate state, whereas those found in the DSS test were in narrow ranges of 26.0°–28.4° and 23.6°–27.9° at the peak and ultimate states, respectively. It should be noted that an increase in Cu led to the increase in the stiffness ratio in both test methods. The difference in stiffness ratios determined from the DS and DSS tests was approximately 14%. Under one-way repeated shear loading, the DS test is recommended to determine the residual shear strength generated along the shear plane, whereas the DSS test is recommended to determine the maximum shear stress at the weakest shear zone developed horizontally owing to repeated shearing. [ABSTRACT FROM AUTHOR]

We consider the evolution of a passive scalar advected by a parallel shear flow in an infinite cylinder with bounded cross section, in arbitrary space dimension. The essential parameters of the problem are the molecular diffusivity ν$\nu$, which is assumed to be small, and the wave number k$k$ in the streamwise direction, which can take arbitrary values. Under generic assumptions on the shear velocity v$v$, we obtain optimal decay estimates for large times, both in the enhanced dissipation regime ν≪|k|$\nu \ll |k|$ and in the Taylor dispersion regime |k|≪ν$|k| \ll \nu$. Our results can be deduced from resolvent estimates using a quantitative version of the Gearhart–Prüss theorem, or can be established more directly via the hypocoercivity method. Both approaches are explored in the present example, and their relative efficiency is compared. [ABSTRACT FROM AUTHOR]

In this paper, a general power form of head-loss (pressure-drop) equation and the concept of shear velocity were used to study non-Darcy filtration through coarse granular materials. Using new laboratory data, the validity of four widely-used power form pressure-drop equations were evaluated. The results indicated that for the lower size of grain diameter (d ≤ 8.7 mm) the Wilkins (in: Proceedings of the 2nd Australia-New Zealand Conference on Soil Mechanics and Foundation Engineering, Christchurch, 1956) method has predicted satisfactorily the hydraulic gradient, while for the higher size of grain diameter (d ≥ 15.6 mm), the Stephenson (Rockfill in Hydraulic Engineering, Elsevier Science Publishers B.V., Amsterdam, 1979) method predicted acceptably the pressure gradient. The results also indicated that the best estimation for the Izbash coefficient a is the Wilkins method. Finally, new correlations for friction factor, shear velocity and Reynolds number as well as new threshold limits for Darcy, partially-turbulent, and fully-turbulent flow regimes are presented and discussed. [ABSTRACT FROM AUTHOR]

• Factors affecting Bevameter soil characterization investigated with a newly developed Bevameter using partially saturated sandy soil. • Soil preparation influences both the pressure-sinkage and shear stress relationships significantly. • Rotational and translational shear mechanism investigated, resulting in a difference of up to 17.6% • Shear contact area influenced shear stress relationship by up to 20% • Shear rate had a limited influence on the shear stress relationship. The Bekker-Wong soil-wheel interaction model has been widely adopted in the terramechanics field. This model requires the soil to be characterised using a Bevameter, which entails performing in situ plate sinkage and shear stress tests. Bevameter soil characterisation is not a standardised test procedure, and the test setup may influence the identified soil model parameters. This study investigates the influence of the following five factors for partially saturated sandy soil: I) soil preparation method on pressure-sinkage, II) soil preparation method on shear stress, III) torsional vs. translational shear mechanism, IV) shear contact area, and V) the influence of shear velocity. The results indicate that the influence of soil preparation on pressure-sinkage response is substantial, exhibiting an order-of-magnitude difference. The influence of soil preparation on shear tests is notable, but less significant. The shear mechanism, shear contact area and shear velocity exhibited a maximum absolute shear stress difference of 18%, 20% and 10%, respectively. Moreover, depending on the test setup configuration and data processing decisions, the estimated internal soil friction angles ranged from 16.5 to 37.5° for the same soil. The findings are expected to have significant implications for the prediction of vehicle drawbar pull using the Bekker-Wong model. [ABSTRACT FROM AUTHOR]

In this study, the static and kinetic friction coefficients and their effect on the noise generation were investigated by preparing the coating agent using polyurethane resin, polysiloxane, ethylene and propylene oxide (EO/PO)-modified polysiloxane, PP wax, carbon black, and SiO2. The difference between the static and kinetic friction coefficients decreased with the fraction of (EO/PO)-modified polysiloxane while sharply increasing with the friction velocity. The differences in these friction characteristics reduced the magnitude of noise generation, and the matting property was also increased by the addition of PP wax. [ABSTRACT FROM AUTHOR]