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The parametrizations of meteorological variables provided by the Monin–Obukhov similarity theory (MOST) is of major importance for pollutant dispersion assessment. However, the complex flow pattern that characterizes the urban areas limits the applicability of the MOST. In this work, the performance of different existing parametrizations of the standard deviation of vertical wind velocity were tested in the city of Rome. Results were compared with experimental data acquired by a sonic detection and ranging (SODAR) and a sonic anemometer. Different scaling variables estimated from the anemometer data by considering two coordinate systems—one aligned with the geodetic reference frame and the other following the flow streamlines—were used to evaluate the effects of flow distortion due to the presence of buildings. Results suggest that the MOST parametrizations perform better if the scaling variables obtained using the coordinate system following the flow streamlines are used. This estimation of the scaling variables would make it possible to overcome the difficulties in conducting measurements of turbulent fluxes, either at different altitudes or even in the constant flux layer.

This study presents an experimental dataset documenting the evolution of a turbulent boundary layer downstream of a rough-to-smooth surface transition. To investigate the effect of upstream flow conditions, two groups of experiments are conducted. For the Group-Re cases, a nominally constant viscous-scaled equivalent sand grain roughness , respectively. The energy distribution in near-wall small scales is mostly unaffected by the presence of the outer flow with rough-wall characteristics, which can be used as a surrogate measure to extract the local friction velocity.

Velocity time series of hydrodynamic and magnetohydrodynamic (MHD) turbulent flow are analyzed by means of complex network analysis in order to understand the mechanism of fluid patterns modification due to the external magnetic field. Direct numerical simulations of two cases are used, one for the plane hydrodynamic turbulent channel flow at the low Reynolds number of 180, based on the friction velocity, and the corresponding MHD flow with an external streamwise magnetic field with a magnetic interaction number of 0.1. By applying the visibility graph algorithm, we first transformed the time series into networks and then we evaluated the network topological properties. Results show that the proposed network analysis is not only able to identify and detect dynamical transitions in the system's behavior that identifies three distinct fluid areas in accordance with turbulent flow theory but also can quantify the effect of the magnetic field on the time series transitions. Moreover, we find that the topological measures of networks without a magnetic field and as compared to the one with a magnetic field are statistically different within a 95% confidence interval. These results provide a way to discriminate and characterize the influence of the magnetic field on the turbulent flows.

The possibility of reconstructing the dynamic parameters (surface wind speed, friction velocity and roughness height) of the atmospheric boundary layer in a hurricane based on wind speed profiling by GPS dropwindsondes and collocated data of the Stepped Frequency Microwave Radiometer (SFMR) is discussed. The parameters of the atmospheric boundary layer were obtained from the data of GPS dropwindsondes with the use of the self-similarity of the velocity profile in the atmospheric boundary layer, previously proposed and successfully tested in laboratory conditions. The preliminary results of data processing showed that at surface wind speeds exceeding 35 m/s, the friction velocity saturates and the surface drag coefficient decreases accordingly. Based on the comparison of the measured dynamic parameters and the surface emissivity, empirical equations are proposed, which take into account the discovered properties of the dynamic parameters of the atmospheric boundary layer and potentially can be used for remote diagnostics of the boundary layer parameters.

Hydrogen sulfide (H2S) is commonly used as an indicator for odorous gas emission monitoring in wastewater treatment plants. The H2S emission estimations can be performed using algebraic mathematical models or carrying out measurements at the source, with the dynamic flux chamber, for example. This work brings together these two methodologies in a computational fluid dynamics analysis. Fifteen liquid-phase mass transfer coefficient ( $${k}_{L}$$ ) models were initially evaluated in establishing, at the liquid–gas interface in a flux chamber, an H2S emission flux based on the friction velocity field from three different inlet flows (2, 5, and 10 L min−1). Ten $${k}_{L}$$ models were fully simulated, and the numerical results were compared with available experimental data. The higher the inlet flow, the higher the friction velocity at the interface, and the higher the H2S emission. The H2S emission was also strongly dependent on the constant coefficients of the existing $${k}_{L}$$ models. Small variability on those coefficients generates considerable changes in emissions at the interface. Few and different models performed well in describing the available concentration data at the outlet sampling probe for different inlet flows, which shows there is still no single model capable of representing all simulated friction velocity ranges (0.005 to 0.017 m s−1).

The present experimental study investigates the frictional properties of gelatin based soft lubricants between two smooth glass surfaces. Slide-hold-slide (SHS) experiments in direct shear mode show that the frictional behaviour of the thin layer of the lubricant is very similar to the soft solids. It is observed that static, dynamic and residual stresses increase with both shear velocity and concentration of gelatin in the lubricant. Coulomb’s law of friction is used for determining adhesive stress and coefficient of friction of the sliding interface. Both components of friction increase with gelatin concentrations. The scaling laws, in terms of lubricant concentration, reveal that their exponent follows the trend as static>dynamic>residual stress. Further, although exponent of the adhesive stress is larger than the coefficient of friction in the case of static friction, the same is opposite in the case of dynamic and residual stresses. These observations are explained in view of the relative competition between normal stress and molecular chains controlled friction mechanisms at the sliding interface of the gelatin based soft lubricants.

So far, few studies have focused on the concept of critical flow velocity rather than bed shear stress for incipient sediment motion. Moreover, few studies have focused on sediment mixtures (graded sediment) and shape rather than uniform sediment for incipient motion condition. Different experiments were conducted at a hydraulic laboratory at the University of Guilan in 2015 to determine hydraulic parameters on the incipient motion condition. The aim of this study is to conduct a comparison between uniform and graded sediments, and a comparison between round and angular sediments. Experiments included rounded uniform bed sediments of 5.17, 10.35, 14 and 20.7 mm, angular uniform sediment of 10.35 mm, and graded sediment. Results demonstrated that angular sediment has a higher critical shear velocity than rounded sediment for incipient motion. Results also showed that for a given bed sediment, although critical shield stress and relative roughness increased with the bed slope, the particle Froude number (based on critical velocity) decreased. In terms of the sediment mixture, the critical shear stress (Vc*) was higher for the graded sediment than for the three finer uniform sediment sizes. The finer fractions of the mixture have a higher particle Froude number than their corresponding uniform sediment value, while the coarser fractions of the mixture showed a lower stability than their corresponding uniform sediment value. Results demonstrated that the reduction in the particle Froude number was more evident in lower relative roughness conditions. The current study provides a clearer insight into the interaction between initial sediment transport and flow characteristic, especially particle Froude number for incipient motion in natural rivers where stream beds have different gravel size distribution.

We investigate the effects of wind–wave interactions on the surface sea-spray-generation flux. To this end, the Marine Aerosol Tunnel Experiment (MATE2019) was conducted at the Pytheas Institute large wave–wind facility in Luminy (Marseille, France) over the period June–July 2019. A unique range of air–sea boundary conditions was generated by configuring the laboratory with four types of wave forcing and five wind speeds spanning 8–20 m s $$^{-1}$$ . Young and developed waves were included, with wave ages between 1.3 and 9.5 (defined in terms of phase speed and friction velocity). Vertical sea-spray-concentration profiles measured over the 0.1–47.5 $$\upmu $$ m radius range and a flux–profile method allowed estimation of the sea-spray-generation flux. Results show that the flux increases for increased wind-induced wave breaking, and is highest for steep and heavily-breaking waves. Scaling analysis shows that the sea-spray generation is best correlated with the wave-slope variance for larger droplets (20 $$\upmu $$ m and above, assumed predominantly spume droplets generated by surface tearing). For smaller droplets (7–20 $$\upmu $$ m, presumed predominantly jet droplets generated by bubble bursting), the highest correlation is found with a non-dimensional number combining the wave-slope variance with the friction velocity cubed. This is reflected in the formulation of two wave-state-dependent sea-spray-generation functions, each valid for wind speeds 12–20 m s $$^{-1}$$ and droplet radii 3–35 $$\upmu $$ m, thereby covering jet and spume droplet production.

According to the Makishema–Mackenzie model assumption, the dissociation energy and packing density for a quaternary TeO2-As2O3-B2O3-Li2O glass system were evaluated. The dissociation energy rose from 67.07 to 71.85 kJ/cm3, whereas the packing factor decreased from 16.55 to 15.21 cm3/mol associated with the replacement of TeO2 by LiO2 compounds. Thus, as a result, the elastic moduli (longitudinal, shear, Young, and bulk) were enhanced by increasing the LiO2 insertion. Based on the estimated elastic moduli, mechanical properties such as the Poisson ratio, microhardness, longitudinal velocity, shear velocity, and softening temperature were evaluated for the investigated glass samples. In order to evaluate the studied glasses’ gamma-ray shield capacity, the MCNP-5 code, as well as a theoretical Phy-X/PSD program, were applied. The best shielding capacity was achieved for the glass system containing 25 mol% of TeO2, while the lowest ability was obtained for the glass sample with a TeO2 concentration of 5 mol%. Furthermore, a correlation between the studied glasses’ microhardness and linear attenuation coefficient was performed versus the LiO2 concentration to select the glass sample which possesses a suitable mechanical and shielding capacity.

Using the discrete element method, we investigate the force chain characteristics of dense particles in a parallel-plate particle flow friction system, and considering the influence of pressure load as well as shear velocity. Simulation results show that the shear dilatancy process of this particle friction system can be divided into three typical stages: plastic expansion stage, whole flow stage, and plastic compression stage. The distribution of force chain generally decreases with the increase of dimensionless contact force f. The distribution and bearing rates of force chains depend on the pressure load as well as the shear velocity. The direction of force chain gradually changes closer to the y-axis with the increase of the pressure load, and shifts from y-axis to x-axis with the increase of shear velocity. The magnitude of the total force chain decreases with shear velocity. Moreover, the total force chain fluctuates significantly at lower shear velocity and start-up stage.

The shear velocity and friction coefficient for representing the resistance of flow are key factors to determine the flow characteristics of the open-channel flow. Various studies have been conducted in the open-channel flow, but many controversies remain over the form of equation and estimation methods. This is because the equations developed based on theory have not fully interpreted the friction characteristics in an open-channel flow. In this paper, a friction coefficient equation is proposed by using the entropy concept. The proposed equation is determined under the rectangular, the trapezoid, the parabolic round-bottomed triangle, and the parabolic-bottomed triangle open-channel flow conditions. To evaluate the proposed equation, the estimated results are compared with measured data in both the smooth and rough flow conditions. The evaluation results showed that R (correlation coefficient) is found to be above 0.96 in most cases, and the discrepancy ratio analysis results are very close to zero. The advantage of the developed equation is that the energy slope terms are not included, because the determination of the exact value is the most difficult in the open-channel flow. The developed equation uses only the mean velocity and entropy M to estimate the friction loss coefficient, which can be used for maximizing the design efficiency.

We model the nonlinear response of a lubricated contact composed of a two-dimensional lipid membrane immersed in a simple fluid between two parallel flat and porous walls under shear. The nonlinear dynamics of the membrane gives rise to a rich dynamical behavior depending on the shear velocity. In quiescent conditions (i.e., absence of shear), the membrane freezes into a disordered labyrinthine wrinkle pattern. In the presence of shear, we find four different regimes depending on the shear rate. Regime I. For small shear, the labyrinthine pattern is still frozen, but exhibits a small drift which is mainly along the shear direction. In this regime, the tangential forces on the walls due to the presence of the membrane increase linearly with the shear rate. Regime II. When the shear rate is increased above a critical value, the membrane rearranges, and wrinkles start to align along the shear direction. This regime is accompanied by a sharp drop of the tangential forces on the wall. Regime III. For larger shear rates, the wrinkles align strongly along the shear direction, with a set of dislocation defects which assemble in pairs. The tangential forces are then controlled by the number of dislocations, and by the number of wrinkles between the two dislocations within each dislocation pairs. In this dislocation-dominated regime, the tangential forces in the transverse direction most often exceed those in the shear direction. Regime IV. For even larger shear, the membrane organizes into a perfect array of parallel stripes with no defects. The wavelength of the wrinkles is still identical to the wavelength in the absence of shear. In this final regime, the tangential forces due to the membrane vanish. These behaviors give rise to a non-linear rheological behavior of lubricated contacts containing membranes., Soft Matter (2021)

An extensive investigation on the effect of linear friction welding parameters on the microstructure, texture distribution and mechanical properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joints was performed. Results indicate that a critical shear velocity is necessary to be reached to obtain a sound joint. The width of the thermomechanically-affected zone (TMAZ) was reduced with friction pressure or/and shear velocity, while the width of the weld center zone (WCZ) remained constant. In WCZ, a microstructure of recrystallized β grains with acicular α laths was formed, and the grain size became smaller with friction pressure. Electron back scattered diffraction was carried out to analyze the texture development with welding parameters. With the increase in friction pressure, the intensity of {112} β texture increased; in the case of α texture, the intensity of T texture increased while decreased for the rest. By examining mechanical properties, strong relationships between maximum hardness and β grain size, as well as between joint elongation and PAZ width, were identified.

Simultaneous two-phase particle image/tracking velocimetry (PIV/PTV) measurements are conducted on a particle-laden turbulent boundary layer (TBL) over a horizontal smooth-flat plate under net sedimentation conditions. Dilute desert sand grains with a median diameter of 203 μm and bulk volume fraction of O(10−5) are used as the discrete phase, and the characteristic Reynolds number of the TBL is relatively high (Reτ = 5500 based on the friction velocity uτ and boundary layer thickness δ). The two-dimensional velocity filed in the streamwise/wall-normal plane is measured by four CCD cameras aligned along the streamwise direction, which resolves a wide spectrum of the scales, ranging from small-scale energetic eddies to large-scale motions (LSMs) in the TBL. An improved phase separation algorithm and discrete particle matching method are developed for two-phase measurements. The results presented here provide new information concerning the effect of high-inertia particles with a dilute concentration on wall-bounded turbulence, especially at high Re. Analysis of the velocity spectrum of the gas phase reveals, for the first time, that the presence of sand grains with a size on the order of the Kolmogorov length scale attenuates turbulence fluctuation by suppressing small-scale sweep-ejection cycles in the near-wall region. A critical layer (y/δ = 0.12 or y+ = 670) is found to partition the streamwise evolution of both the local concentration and the streamwise mean velocity of the sand grains into a non-equilibrium near-wall region and a quasi-parallel outer region. In addition, a balance between the strength and probability between the sweep and ejection events of sand grains is reached at this layer. Such a critical layer might be a good indicator of the upper bound of the particle saltation process, in which LSMs are believed to play a significant role.

Motivated by the need for accurate determination of wall shear stress from profile measurements in turbulent boundary layer flows, the total shear stress balance is analysed and reformulated using several well-established semi-empirical relations. The analysis highlights the significant effect that small pressure gradients can have on parameters deduced from data even in nominally zero pressure gradient boundary layers. Using the comprehensive shear stress balance together with the log-law equation, it is shown that friction velocity, roughness length and zero-plane displacement can be determined with only velocity and turbulent shear stress profile measurements at a single streamwise location for nominally zero pressure gradient turbulent boundary layers. Application of the proposed analysis to turbulent smooth- and rough-wall experimental data shows that the friction velocity is determined with accuracy comparable to force balances (approximately 1 %–4 %). Additionally, application to boundary layer data from previous studies provides clear evidence that the often cited discrepancy between directly measured friction velocities (e.g. using force balances) and those derived from traditional total shear stress methods is likely due to the small favourable pressure gradient imposed by a fixed cross-section facility. The proposed comprehensive shear stress analysis can account for these small pressure gradients and allows more accurate boundary layer wall shear stress or friction velocity determination using commonly available mean velocity and shear stress profile data from a single streamwise location.

The aerodynamic roughness length (Z0) plays an important role in the land–air exchange. At present, the atmospheric numerical models cannot accurately describe the Z0 in different underlying surfaces, which affects the simulation performance and the description of the momentum and heat exchange and atmospheric environment. In this study, the regional air quality model WRF/Chem with updated Z0 of the various underlying surface categories is used to study the impacts of Z0 on the boundary layer meteorological conditions and atmospheric environment over the Pearl River Delta (PRD) region. Two numerical experiments are conducted, including default Z0 (Base experiment) and updated Z0 (Case experiment). By comparing the simulations with the observations from 9 meteorological stations and 30 national air quality monitoring stations, the updated Z0 improves the model simulation performance of 10 m wind speed in PRD. The impacts of updated Z0 on 2 m temperature and relative humidity are relatively small, while the influences of updated Z0 on surface skin temperature (TSK), ground heat flux (GRDFLX), sensible heat flux (HFX), friction velocity (U*), 10 m wind speed (WS) and planetary boundary layer height (PBLH) are evident. The impacts of updated Z0 in the urban are greater than that in the evergreen broadleaf forest. In the urban, the updated Z0 reduces TSK, lowers GRDFLX, increases HFX during the daytime, and increases U*, causing the reduction of WS, while the vertical velocity also increases, which is conducive to the elevation of PBLH. With the updated Z0, the surface carbon monoxide (CO) concentrations generally increase, especially in the central urban areas, due to the impact of wind speed, turbulent motion and planetary boundary layer height. The updated Z0 has a little impact on CO concentration profile during the daytime, which is affected by horizontal wind speed and turbulent motion; while at night, the updated Z0 produces an increase of CO concentration below 300 m, which is affected by the horizontal wind speed.

In a steady, spatially homogeneous neutral stability flow dominated by mechanical turbulence, the friction velocity ($$ u_{*} $$) and the roughness length (z0) can be estimated by applying linear regression to measurements of wind speed (u) at several heights (z). Surface-layer wind profile plots in the scientific literature normally have ln(z) on the vertical axis and u on the abscissa, which might suggest a linear regression, such as the ordinary least-squares method, which minimizes the vertical residuals, i.e., the ln(z) deviations, from the fitted line. Here, we show that ordinary least-squares fitting of the profile data is sensitive to the choice of the variable whose residuals are being minimized, and that the linear regression should be computed as u versus ln(z), i.e., minimizing the u deviations. This is equivalent to ln(z) being the independent variable and u the dependent variable. The differences in the estimated values of $$ u_{*} $$ and z0 compared to those resulting from the ln(z) versus u linear regression can be expressed as a function of the coefficient of determination (r2) of the wind-profile data. Applying the ordinary least-squares method while minimizing the deviations of ln(z) leads to systematic overestimation of the $$ u_{*} $$ and z0 values. Using these values as input into the atmospheric dispersion model AERMOD leads to increased shear-induced turbulence and consequently enhanced dilution of the plume.

Tower-based measurements from within and above the urban canopy in two cities are used to evaluate several existing approaches that parametrize the vertical profiles of wind speed and temperature within the urban roughness sublayer (RSL). It is shown that current use of Monin–Obukhov similarity theory (MOST) in numerical weather prediction models can be improved upon by using RSL corrections when modelling the vertical profiles of wind speed and friction velocity in the urban RSL using MOST. Using anisotropic building morphological information improves the agreement between observed and parametrized profiles of wind speed and momentum fluxes for selected methods. The largest improvement is found when using dynamically-varying aerodynamic roughness length and displacement height. Adding a RSL correction to MOST, however, does not improve the parametrization of the vertical profiles of temperature and heat fluxes. This is expected since sources and sinks of heat are assumed uniformly distributed through a simple flux boundary condition in all RSL formulations, yet are highly patchy and anisotropic in a real urban context. Our results can be used to inform the choice of surface-layer representations for air quality, dispersion, and numerical weather prediction applications in the urban environment.

The potential exists to use ultrasonic shear velocity for real-time microstructure assessment of the quenching step in the heat treatment of L80 steel pipe. L80 steel samples were austenitised and ...

Determination of the threshold shear velocity is essential for predicting sand transport, dust release and desertification. In this study, a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand. Saline sand samples (mean particle size of 164.50–186.08 µm and the total silt, clay and salt content of 0.80%–8.25%) were collected from three saline sand dunes (one barchan dune and two linear dunes) in the Qarhan Desert, Qaidam Basin of China. Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation, respectively. Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment. The motion of sand particles was determined by the observers with a solid laser. The laser sheet (0.80 cm thick), which was emitted by the solid laser, horizontally covered the sand surface and was bound to the sand. Results show that the cohesion of saline sand results from a combination of salt and water. The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes. There is a positive linear correlation between the original moisture content and relative threshold shear velocity. The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content. Our results will provide valuable information about the sand transport of highly saline soil in the desert.

The aim of this work is to obtain estimates and parameterization of the dissipation rate of the turbulence kinetic energy (TKE dissipation), e, induced in the upper water layer by the presence of wind waves at the surface. For this purpose, data from the laboratory measurements of the wind waves and three components of currents at six horizons in the upper water layer and four different winds are used. The measurements are performed in the wind-wave channel of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS) [1, 2]. It is established that, for most horizons, Kolmogorov-type ranges with the property $${{S}_{{Uz}}}(f) \propto {{f}^{{ - 5/3}}}$$ are clearly seen in the frequency spectra $${{S}_{{Uz}}}(f)$$ for the vertical velocity component Uz of the flow induced by wind and waves. Using the algorithms described in [3, 4], this fact allows us to obtain estimates of the TKE dissipation at the corresponding horizons and then establish the dependence of e on the friction velocity $${{u}_{*}}$$ , the height of waves at the surface a0, the peak frequency of the spectrum ωp, and the depth of the horizon z. An analysis of the results (according to the available data) makes it possible to propose a parameterization of the form e ≈ 0.00025 $$u_{*}^{3}{{a}_{0}}/{{z}^{2}}$$ for which a physical interpretation is proposed.

Flux chambers are commonly used to measure emission rates of odorous compounds at passive liquid surfaces in wastewater treatment plants. Different flux chambers configurations are found in the literature and the main concern regards to the mixing inside the chamber, which is linked to impact on the overall mass transfer between emitting surface and headspace, and the sampling recovery efficiency. However, aspects related to the airflow and mass transfer inside the chambers influence the measured emission rates. The mass transfer coefficients in the liquid and gas phases are functions of the friction velocity on the liquid surface. This work investigates the airflow and odorous compounds transport (with different Henry’s law constants) inside a flux chamber using Computational Fluid Dynamics, to determine the influence of inlet airflow rate (2, 5 and 10 L min−1), inlet configurations (4, 6 and 8 inlet holes) and the inclusion of internal fans on the surface friction velocity and emission rate. The results showed a complex flow inside the chambers and a concentration field that reaches steady state after 6 residence times. The use of an internal fan promoting downward flow increased turbulence and produced values of friction velocity at the liquid interface closer to those found in the near surface flow in the boundary layer, whereas all other configurations tested showed much lower values of friction velocity. Therefore, the use of a fan is recommended.

Macroscopic yielding is essentially important in structural application. In this study, a wisdom semi-empirical model, based on the rule of mixture (RoM), has been proposed to predict the yielding strength in in-situ metallic glass matrix composites (MGMCs). The present model not only successfully predicts the yielding strength of a variety of dendrite-reinforced MGMCs, but also can be verified in bimetal alloys or composites with different systems. A quantitative relationship between the specific strength and shear velocity in metallic materials was established, which provides a guidance for the development of light-weight and high-strength MGMCs.

The inclusion of local site effects into seismic hazard analysis is an important issue and has been attempted previously in both deterministic and probabilistic manner. The present study is an attempt to combine the local site response with the standard probabilistic seismic hazard analysis. The site response was computed by performing an equivalent linear analysis in the frequency domain. The input soil profiles for the analysis were taken from the borehole data of the North Kerala region (one of the Southerly states in India). The uncertainty in estimating the shear velocity profile (VS) has been addressed by applying multiple VS–N correlations. The variability in the choice of input motions has been reduced by selecting multiple ground motions representing distinct hazard levels (return period of 50–2000 years). The uniform hazard spectrum developed for the host reference site conditions has been adjusted to the target region and the input motions are scaled accordingly. The analyzed soil profiles were categorized into three distinct soil types namely ‘Sand’, ‘Clay’ and ‘All soil’ based on the predominant soil content. The empirical amplification equation as a function of input rock spectral acceleration (Sar) was developed for each soil type. ‘Sand’ exhibits nonlinear behavior for Sar > 0.1 g whereas ‘clay’ demonstrates sustained amplification at longer periods. The average spectral amplification observed is 3 for ‘All soil’, 5 for ‘clay’ and 3.5 for ‘sand’ in the study region. The regionally developed amplification function aids in transforming a Ground Motion Prediction Equation (GMPE) from generic to site-specific. The modified GMPE is integrated with the regional seismic source model to estimate site-specific probabilistic seismic hazard. The study produces site-specific spectrum and surface hazard maps which can be of direct use to planners and designers in creating a seismic resilient built environment.

The surface energy imbalance or non-closure problem, where the sum of turbulent heat fluxes measured by the eddy covariance method is systematically lower than the available energy, is one of the greatest challenges in micrometeorology. We examine the energy balance closure ratio (EBR) and its relationship with related variables over a wide variety of ecosystems including alpine meadow, desert, shrub, and crops in the Heihe River Basin (HRB), China, which is representative of endorheic river basins. The results show that half-hour EBR values over different ecosystems range from 0.53 to 0.99, with a mean of 0.84. In different HRB ecosystems, the trends of EBR values with friction velocity (u*), thermally induced turbulence (TT), atmospheric stability (z/L), correlation coefficients for vertical velocity and water vapor (Rwq) and potential temperature (Rwθ), and relative vertical turbulent intensity (RI) are consistent with previous results obtained from other ecosystems. A significant negative linear relationship exists between the EBR and variation values of surface temperatures at landscape and local scales. Additionally, the field data confirm our previous findings from large eddy simulations that there is a positive linear relationship between the turbulent kinetic energy (TKE) and EBR values. Because the TKE diurnal variations explain a larger fraction (71%) of EBR diurnal variations than other variables (u*, TT, z/L, RI, Rwθ and Rwq), we argue that TKE is mainly responsible for EBR diurnal variations and explains the different EBR diurnal variations observed here and in previous studies. The possible reason for this better performance of TKE than other variables is that the TKE includes comprehensive effects of shear, buoyancy, turbulent transport and dissipation from the TKE budget equation. Thus, TKE may be a promising indicator for potential energy balance closure correction. Our findings contribute to a better understanding of the surface energy imbalance problem.

An accurate quantification of the frictional behaviour of joints under cyclic normal load conditions during the cyclic shear process is important to characterize the joint and fault interactions during earthquakes and rock bursts. We conducted experimental studies and numerical simulations to investigate the cyclic frictional responses of planar joints subjected to cyclic changes of normal loads. Experiments were conducted on artificial rock-like planar joints using a large shear box device (GS-1000), with different vertical and horizontal impact frequencies, vertical impact load amplitudes, horizontal shear displacement amplitudes, and normal load levels. The average normal displacement of the upper block increased with decreasing normal load and decreased with increasing normal load during each cycle. The normal displacement decreased gradually with increasing number of shear cycles due to damage to the micro-asperities at the contact surface. Shear force and the apparent coefficient of friction (k = FShear/FNormal) changed cyclically with a change in shear direction, where k followed a square wave curve with the same peak value at the stable shear stage. The cyclic normal load amplitudes, horizontal shear displacement amplitudes, cyclic normal load frequencies, cyclic horizontal shear frequencies, and static normal force levels had little influence on the peak values of k. Numerical simulations proved that the spatial movement pattern of the loading plate and upper block of the specimen rotated clockwise or anti-clockwise at different shear displacements. Due to the rotation of the upper block, shear and normal stresses distributed at the contact surface were inhomogeneous, which generated a stress gradient along the interface. Consequently, the samples were damaged at the two edges due to the high local stresses. Finally, a mathematical equation is proposed, which can be used for predicting the shear strength of planar joints under cyclic changes of shear velocity and normal load.

Background The mechanical properties of Mn-Cr ferrite of different compositions are important for industrial applications in everyday life. Ferrites are used in electric choke coils, electric transformers, and many other electronic and optical devices. The elastic properties can be understood by studying the longitudinal sound velocity (V l) and shear velocity (V s). Results The longitudinal sound velocity (V l) and shear velocity (V s) are measured at room temperature by pulse transmission technique at the frequency of 1659 Hz, which is ideally representing the mechanical properties of the ferrite crystal. The shear sound velocity was found to be around 4 × 103 m∕s while the longitudinal sound velocity was ranging according to the doping concentration from 6 × 103 to 1 × 104 m∕s. The behavior of Young’s modulus (E), rigidity modulus (n), mean sound velocity (V m), and Debye temperature (θ D) is quite similar, where a change in the slope was noticed at Cr concentration higher than 0.7 in the spinel lattice. Conclusion We have characterized the elastic properties of the spinel structure Mn-Cr ferrite with different Cr ion concentration at a fixed sound frequency using the pulse transmission technique. The longitudinal sound velocity showed an increase with increasing Cr ion concentration, the rigidity constant as well as Debye temperature, Isotropic compressibility, and the acoustic impedance showed behavioral change at Cr ion concentration x = 0.7 which is correlated to the intra-ionic distances change due to the replacement of Fe ions with smaller size Cr ions.

The evolution and utilization of estuarine and coastal regions are largely restricted by sediment issues. Waves and currents are the main dynamic driving forces of sediment transport in estuary and coastal areas. The study of wave-current movement and sediment transport is of great significance in both academic research and engineering practice, which has received much attention from many scholars and engineers. The northwestern head of Bohai Bay belongs to a transitional area from silty coast to muddy coast, where the sediment movement is complex. Firstly, based on the field observation data measured with a tripod system and the hydrological data in the northwestern head of Bohai Bay, the characteristics of tidal currents, waves, and suspended sediment concentration (SSC) changes under different hydrological conditions were analyzed. Sediment density distribution was detected by a γ-ray densitometer. Results show that the SSC is mainly influenced by wave-induced sediment suspension: Under light wind conditions the SSC was very low, with the peak value generally less than 0.1 kg/m3; the SSC increased continuously under the gales over 6−7 in Beaufort scale, with sustained wind action. The measured peak SSC at 0.4 m above the seabed was 0.15−0.32 kg/m3, with the average value of 0.08−0.18 kg/m3, which is about 3−6 times the value under light wind conditions. The density at the bed bottom was about 1.4− 1.6 g/cm3, and decreased to 1.02−1.03 g/cm3 at 0.1−0.2 m above the bed; there was rarely little fluid mud in the study area. Secondly, the mechanism of wave-induced SSC was studied from the view of flow structure, shear stress in the bottom boundary layer. The friction velocity was calculated by fitting the datasets of the measured logarithmic velocity profile. Comparison shows that the wave shear stresses (calculated from the bottom velocity profile) is higher than the current shear stress (calculated from the upper velocity profile). Following the Reynolds’ decomposition method, expressions of wave-induced and current-induced shear stress were derived by splitting the variables into a fluctuating component, an averaged component and an oscillatory component. Compared with uniform flow, an additional item of wave streaming leads to a higher wave-induced shear stress. Finally, by analytically solving the sediment diffusion equation, a numerical procedure was proposed for sediment concentration under combined action of waves and currents. Some key approaches for fine sediment simulation were presented, including stratification effects, hindered settling, moving bed roughness, reference concentration and critical shear stress. Under combined wave-current conditions, the combined sediment diffusivity is given by the square sum of the wave-related and current-related diffusivities, and a toe-type distribution of wave-related eddy viscosity was employed. The stratification effects are considered by introducing the turbulence damping coefficient. The approaches of hindered settling for silt were employed. The enhanced roughness due to mobile bed effects was included. Comparison shows that, these approaches can properly simulate the measured wave-induced sediment concentration. This study provides basic data for coastal protection and utilization as well as for scientific study of silty-muddy coast, which is of great significance in practice and theory.

The lowermost mantle beneath the central Atlantic is bounded by the western edge of African Large Low Shear Wave Province (LLSVP) and a high-velocity region beneath the eastern Americas, which is attributed to the accumulated subducted slab material at the core-mantle boundary (CMB). Data recorded at broadband seismic arrays in western Europe and Morocco allow us to investigate the detailed structure beneath the Central Atlantic, which provides an important constraint on how remnant slab material and LLSVP interact and reshape the D″ layer. Here, we exploit lower mantle triplicated S waveform data from deep earthquakes beneath South America. Our modelling results show that the D″ discontinuity is constantly observed from north to south beneath the Central Atlantic but at varied depths and with varied shear velocities. In the lowermost mantle beneath east of Caribbean, our results indicate a sharp 2.1% shear velocity increase at 340 km above the CMB, representing a possible bridgmanite dominant normal mantle D″ layer. Whereas, the models of northern and southern portions of Central Atlantic indicate a gradual velocity increase of 4.2% across 200 km starting from 360 km above the CMB downwards. We also find a distinct low velocity zone on top of the velocity jump, which can be interpreted as an upwelling produced by the dynamic response of ancient slab material reaching the CMB.

Although gobi is a major source of dust storms in northern China, few studies have investigated the effect of roughness density (λ) of gobi beds on aeolian sediment entrainment. This wind tunnel study quantitatively evaluated the effect of λ on aeolian entrainment from gobi beds with λ of 0.05–0.51 using Rt and RQ. Rt referred to the ratio of the entrainment threshold for a bare sand bed to those of gobi beds; RQ was the entrainment rate ratio, whose calculation was just reversed with Rt. The results indicated that a two-to five-fold increase in entrainment threshold and 41.4–100% of entrainment rate was attenuated within an experimental friction velocity (u*) range of 0.40–0.63 m s−1. Moreover, the variation of RQ with λ was almost negligible, as λ reached 0.176, 0.203, 0.313, and 0.375 for u* values of 0.40, 0.49, 0.54, and 0.63 m s−1, respectively, which were specific for the Gobi Desert with their typical gravel beds. This study also indicated that for higher u* of 0.54 and 0.63 m s−1, aerodynamic entrainment plays a significant role in aeolian entrainment, whereas at lower u* of 0.40 and 0.49 m s−1, splash entrainment exerts a greater impact.

The present study experimentally investigated variations in the mechanical behaviours of natural rough rock joints during shearing under cyclic loading and constant normal stiffness conditions, using a servo-controlled shear testing apparatus. The influences of initial normal stress (σn0), normal stiffness (kn) and shear velocity (v) on the shear behaviours are estimated and analysed. The results show that the shear stress (τ), normal stress (σn) and normal displacement (δv) for both unfilled and infilled rock joints decrease with the increase in the number of cycles (N), especially in the N range of 1–2. This is because some asperities on the joint surface are sheared during the first shear process, and the subsequent shear tests for N > 2 were subjected to the frictional process. The σn0 and kn both contribute significantly to the variations in the shear behaviour of rock joints. For unfilled rock joints, increasing σn0 from 2 to 4 MPa increases the shear stress and normal stress by 128.5% and 106.5%, respectively, when shear displacement (δh) = 2 mm and N = 1. Increasing kn from 3 to 5 GPa/m enhances the shear stress and normal stress by 19.4% and 10.4%, respectively, when δh = 2 mm and N = 1. For infilled rock joints, the shear stress and normal stress increase with increasing σn0 when N 0.78. Using the proposed models, the fillings decrease the τ and σn by approximately 24.96–65.52% and 9.38–57.95%, respectively, while increasing the normal displacement (δv) by 0.5 mm on average during the entire shear process.

The effects of directional riblets surfaces on the turbulent/non-turbulent (T/NT) interface in turbulent boundary layers are experimentally investigated using two-dimensional time-resolved particle image velocimetry (PIV). The velocity field of streamwise—wall-normal plane for the smooth surface, converging and diverging riblets surfaces are measured. The interface is detected using the criterion of local kinetic energy. The statistical properties of interface height and conditional averaged velocity for different surfaces are analyzed. It is shown that, the converging and diverging riblets surfaces have little effect on the fractal dimension of the T/NT interface, but they cause the intermittency profile deviate from error function and the probability distribution of interface height deviate from Gaussian function. To be specific, the distribution of interface height for the converging riblets surface shows a positive skewness while it shows a negative skewness for the diverging riblets surface. Moreover, the conditional averaged streamwise velocity and spanwise vorticity across the interface are analyzed, and it is found that their self-similarities are preserved for different surfaces when normalized with respective friction velocity. The correlation analysis reveals that near-wall streamwise velocity fluctuation and interface height show a negative correlation.