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Although the global market for wind energy is growing rapidly, leading-edge erosion is a critical issue hindering the development of wind power. The impact force of a droplet colliding with flat surfaces has been investigated in previous studies. However, the impact force exerted on curved surfaces, such as that experienced by eroded wind turbine blades, is not well understood. This study discusses the relationship between the impact force generated on a solid surface by a water droplet and the radius of curvature of the impacting surface. The impact force by a droplet was measured using a force sensor mounted on semi-cylindrical caps with different radii of curvature. The measurement results showed that the impact force decreased as the radius of curvature decreased. A computational fluid dynamics model solving incompressible flows showed that, unlike the case of a curved surface, the initial momentum of the droplet was mostly transferred to the flat surface. This resulted in a high impulse for an impact with a flat surface. The falling droplet was blocked by the surface, and the lateral jet was accelerated sideward. This acceleration was moderate for curved surfaces. When colliding with a flat surface, a higher impact force was generated owing to the wider area of the excited surface pressure compared with that of the curved surface. Finally, the relationship between the peak of the impact force and the surface curvature was derived, suggesting that the force peak is inversely proportional to the curvature. [ABSTRACT FROM AUTHOR]

New parameterizations for the Lennard-Jones 12/6 potential capable of reproducing the vapor pressure and surface tension with sufficient precision, but not the liquid–vapor equilibrium densities for the case of simple fluids that include Ar, Kr, Xe, Ne, and CH4 are presented in this work. These results are compared with those derived from the family of Mie(n, 6) potentials, which adequately reproduce the coexistence curve and the vapor pressure, leaving aside the surface tension. In addition, a detailed analysis is presented on different parameterizations and methodologies, which have been developed in recent decades to estimate the interfacial properties of interest here for simple fluids, such as argon, which is a molecule that is, in principle, "simple" to study but that clearly reveals the enormous discrepancy between the results reported in the literature throughout these years. These facts undoubtedly reveal one of the fundamental problems in the context of molecular thermodynamics of fluids: reproducing different thermodynamic properties with sufficient precision from a single set of free parameters for some interaction potential. In order to show the scope of the parameterizations presented for the Lennard-Jones model, they were successfully applied to the case of binary mixtures, which included Ar–Kr, Ar–CH4, and Xe–Kr. Finally, and with the aim of showing a possible solution to the problem posed in this research, results of the same interfacial properties above mentioned for argon and methane were presented in this work by using a set of molecular interactions, called ANC2s, whose flexibility allowed to reproduce the experimental evidence with just one parameterization. The results reported in this work were generated using molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

Abstract: The quasi-biennial oscillation (QBO) is thought to influence boreal winter surface conditions over Asia and around the North Atlantic. Confirming if these responses are robust is complicated by the QBO having multiple pathways to influence surface conditions as well as internal variability. The reanalysis record suggests that sudden stratospheric warmings (SSWs), breakdowns of the polar vortex that can elicit persistent surface impacts, are more frequent during easterly QBO (EQBO). Hence, this modulated frequency of SSWs may account for some of the EQBO surface responses. However, many climate models do not reproduce this QBO–SSW relationship, perhaps because it is noise or because the model QBOs are deficient. We circumvent these issues by using an ensemble of fixed boundary condition branched simulations in which a realistic EQBO is prescribed in control simulations previously devoid of a QBO, allowing us to isolate the transient atmospheric response to EQBO. Imposing EQBO accelerates the tropical upper-tropospheric wind, shifts the subtropical jet poleward, and attenuates the polar vortex. Interestingly, the latter is not entirely dependent on the statistically significant increase in SSW frequency due to EQBO. Corroborating observations, EQBO is associated with warmer surface temperatures over Asia and negative North Atlantic Oscillation (NAO) conditions. We then subsample the branched/control simulations based on which EQBO members have SSWs. The negative NAO response is primarily associated with more frequent SSWs, while the Asia warming develops irrespective of SSWs. These results have implications for wintertime predictability and clarify the pairing of particular QBO teleconnections with certain surface impacts. Significance Statement: The QBO is one of the few parts of the Earth system that is predictable months in advance and that also elicits global effects on surface temperature, circulation, and precipitation. Unfortunately, climate models and operational forecast systems do not simulate the QBO well and it is not always clear how robust the global impacts of the QBO are. Here, we impose the QBO in idealized model simulations, which modulates wintertime surface temperature and precipitation over Asia, the North Atlantic, Europe, and Africa in a manner consistent with observations. This work substantiates the importance of climate and forecast models properly simulating the QBO.

It is demonstrated that the eXtended Finite Element Method (XFEM) is of remarkable efficiency in simulating crack evolution by eliminating the need for remeshing and refinement. In this paper, it is shown how to enhance the solution efficiency through a comprehensive mathematical investigation of the solution process using XFEM. A typical example is presented to illustrate the disparities in nodal displacements along the two symmetric faces of the crack resulting from the approximation of XFEM. By analysing the structure and components of the global stiffness matrix, the underlying causes of these discrepancies are identified. Building upon these findings, two improvements of the solution are proposed to gain an acceptable accuracy in computing the nodal displacements. The first improvement consists of the subdivision of the enriched elements depending on the characteristic of the distribution of Gauss points. The second improvement is set by determining the optimal number of Gauss points in each sub-element near the crack tip. To calculate the stress intensity factor of the crack under surface pressure, such improvements are applied in conjunction with the interaction integral method, which significantly reduces computational time and eliminates the influence of surface tractions. The numerical solution is validated by comparing it with the analytical solution and the standard XFEM solution. The proposed improvements can enhance both the accuracy of the solution and the computational efficiency of XFEM. [ABSTRACT FROM AUTHOR]

Surface pressure (π)–molecular area (A) isotherms were gathered to characterize the packing of binary mixed Langmuir monolayers of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphoethanolamine (DOPE) and one of two Gemini surfactants (GS), N,N‐bis(dimethyloctadecyl)‐1,7‐nonanediammonium dibromide (18‐7‐18) or 1,9‐bis(octadecyl)‐1,1,9,9‐tetramethyl‐5‐amino‐1,9‐nonanediammonium dibromide (18‐7NH‐18) of varying molar fractions. Information about miscibility behavior was derived from the π–A curves by examining the excess free energy of mixing (ΔGexc) that was calculated through the surface area additivity rule. Surface compressibility modulus (Cs−1) was also used to characterize intermolecular interactions. Mutual interactions between GS and DOPE were analyzed in terms of excess Gibbs energy of mixing and the value of this parameter depended strongly on the composition of the mixed film. GS and DOPE are generally miscible as DOPE reduces intermolecular repulsion between highly charged GS molecules leading to the formation of more densely packed mixed monolayers. However, GS and DOPE are immiscible in equimolar mixtures due to tail group packing mismatch between saturated and unsaturated alkyl chains. The prevalence of attractive synergistic interactions in the monolayers studied differs from a previous finding of antagonistic mixing behavior in GS/DOPE micelles. These results contribute to the understanding of GS‐lipid interactions and packing that are critical to the in vitro and in vivo stability of liposomes composed of these molecules used for non‐viral gene therapy applications. [ABSTRACT FROM AUTHOR]

AbstractSustained mechanical loading on skeletal muscle tissue can lead to degeneration and cell damage over time, resulting in the development of pressure ulcers, particularly in hospital mattresses or for wheelchair-bound users. The primary risk factors for this damage are tissue ischemia caused by pressure in the contact area and tissue compressive strain. In this study, a multi-cell, multi-material foam mattress for the upper comfort layer was developed, with the aim of simultaneously minimizing soft tissue compressive strain and maximum surface pressure on the human buttocks zone. The levels of these factors were estimated using the finite element method (FEM). A multi-objective optimization (MOO) approach was employed, coupling the non-dominated sorting genetic algorithm (NSGA-II) with FEM. This algorithm helped determine the required compressive strength and the optimal cell configurations to achieve the desired outcomes. The majority of the optimal solutions exhibited contact pressures (Cpresss) below the recommended threshold to avoid local tissue ischemia. The optimized cellular material configurations resulted in soft tissue compressive strain of 12% and Cpress of 3.4 kPa, indicating longer safety times for supine support on the foam mattress without the need for repositioning. The optimization process utilized 5 softer foam materials out of the 9 firmness levels tested to achieve these results. The proposed multi-cell, multi-material foam mattress model shows promise for the prevention of pressure sores, as suggested by the optimization findings. [ABSTRACT FROM AUTHOR]

In December and January, the pressure contrast between the subtropical plains of South America (CHA) and northwestern Africa (WEM) reaches its maximum. This happens because of simultaneous and opposite surface pressure variations in these two regions. The low tropospheric winds flow from the tropical Atlantic into Amazonia and then divert southwards into the Gran Chaco region, suggesting a possible strengthening of this circulation associated with the CHA-WEM gradient. This article analyses the effect of a cross-equatorial CHA-WEM gradient intensification on the monsoon system of South America. The reinforcement of the gradient is associated with increased easterlies in the eastern equatorial Atlantic, a stronger low-level jet east of the Andes, increased moisture transport towards the CHA region, and reduced precipitation over much of Brazil. The large quasi-stationary wave in the upper troposphere, consisting of the Bolivian High and the Nordeste Low, weakens in amplitude, altering the return flow to the North Atlantic. Extratropical dynamics, such as Rossby wave trains that reach southern South America and the North Atlantic Oscillation, affect the variability in the CHA and WEM regions and modulate the CHA-WEM gradient intensity. [ABSTRACT FROM AUTHOR]

The T-bar penetrometer is currently used to characterise seabed sediments, mostly based on the full-flow mechanism around the probe in soft clays. However, open and trapped cavities may form above the T-bar during its penetration in stiffer clays, which can make the traditional interpretation method inaccurate and requires complex corrections. This paper proposes a novel T-bar test method by adding sufficient surface pressure on the soil surface to ensure the full-flow mechanism and no cavity. In this way, the current formulas based on the full-flow soil mechanism can be directly used to interpret soil strength. To verify the effectiveness of the proposed method, both laboratory tests on kaolin clay and Guangzhou offshore clay and large-deformation finite-element analyses with various surface pressures and soil strengths were conducted. The results show that, if the surface pressure is sufficient, no open cavity or trapped cavity was formed during a monotonic T-bar penetration and the first cycle of cyclic T-bar penetration tests. Without surface pressure, however, an open cavity or trapped cavity was always formed. The cavity formation contributed to a T-bar resistance 7·9–18·6% lower relative to that of a T-bar with sufficient surface pressure to maintain a full-flow mechanism. In the cyclic tests, with an additional number of T-bar loading cycles, the cavity effect diminished and the surface pressure showed minimal effect on the T-bar resistance. A critical surface pressure that ensures the full-flow mechanism was suggested for T-bar monotonic and cyclic tests in the box core sample. [ABSTRACT FROM AUTHOR]

In this paper, the friction properties of the port pair with non‐smooth surface in the pump were studied. The lubrication film was modelled and simulated to analyse dynamic pressure, velocity vector and friction coefficient. Tests were made for studying the effects of pit shape and revolution speed on friction properties of glass fibre epoxy resin (GFER) samples under seawater lubrication, with the wear of the surface and friction coefficient discussed. The results show that GFER is mainly manifested as adhesive and abrasive wear during the tests. The simulations and tests suggest that the hydrodynamic lubrication effect is improved by increasing revolution speed and using non‐smooth surfaces, with the friction coefficient being decreased. Moreover, a roughness test was conducted, and it was found that the Ra value of the 316L sample decreased, whereas the Ra value of the GFER sample increased. [ABSTRACT FROM AUTHOR]

The study addresses the critical issue of noise generation attributed to airflow around cylinders and its regulation, a subject of great significance in a range of engineering applications. This paper uses computational fluid dynamics (CFD) in conjunction with acoustic analogy to evaluate the potential of elliptical cylinder configurations to enhance aerodynamic performance and mitigate aerodynamic noise. The analysis focuses on the tandem cylinder, which is a simplified representation of aircraft landing gear, and the mechanism for noise suppression associated with elliptical cylinders. The findings demonstrate the significant influence of elliptical cylinder designs on aerodynamic performance and noise reduction. Specifically, these designs exhibit a capacity to effectively reduce the average drag coefficient and proficiently suppress fluctuations in the lift coefficient, thereby resulting in an overall reduction of noise production by the elliptical cylinder. To investigate the underlying mechanisms of noise suppression, this study assessed the process of vorticity generation around the surface of the elliptical cylinder, and found a profound decrease in the distribution of vorticity on the elliptical cylinder's surface, accompanied by a remarkable attenuation of the velocity and boundary surface pressure distribution. These changes result in a significant reduction in vorticity generation in the vicinity of the elliptical cylinder wall. These changes directly precipitate a significant contraction of the distribution of vortex structures in the wake of the elliptical cylinder, particularly impacting large-scale vortex structures. Therefore, the noise suppression mechanism proposed for the elliptical cylinder can effectively mitigate aerodynamic noise. [ABSTRACT FROM AUTHOR]

Fluidic oscillators utilize internal flow dynamics to produce oscillatory fluid jets. The Coanda surface in the mixing chamber of a fluidic oscillator plays a critical role by facilitating controlled fluid manipulation through flow attachment and redirection. The mixing chamber pressure drop, jet oscillating frequency, and deflection angles are hence dependent on the geometry of the Coanda surface. In this study, the Coanda surface is modified by using rectangular ribs of different aspect ratios. The effects of ribbed Coanda surface on oscillating jet characteristics are computed numerically through two-dimensional unsteady Favre-averaged Navier–Stokes equations. The aspect ratio (ARribs ), the ratio of rib height to rib base, is varied from 0.64 to 1.56 and air is used as a working fluid. An increase in the ARribs increases the jet oscillation frequency. The highest aspect ratio achieves an oscillation frequency of 820 Hz, contrasting with 355 Hz for the smooth case. On the other hand, the jet deflection angles are decreased as the aspect ratio increases. Interestingly the introduction of the ribs on the Coanda surface decreased the pressure drop in the oscillator. A decrease in pressure drop of 22% for an aspect ratio of 1.56 was achieved as compared to the smooth case. These results are attributed to the influence of the ribs on the formation of a separation bubble formed in the mixing chamber. The jet performance parameter, frequency-deflection-pressure ratio, was found to be 43% higher for ARribs of 1.56 as compared to the smooth case. [ABSTRACT FROM AUTHOR]

Multi-blade centrifugal fans find wide application across various fields, with their internal airflow exhibiting complex turbulent behavior in three dimensions. Historically, blade optimization relied on constant thickness airfoils, limiting the effectiveness of optimization efforts. However, marine organisms have developed airfoil structures with highly efficient drag reduction, offering a novel approach to optimizing multi-blade centrifugal fans. This study proposes an airfoil optimization design method utilizing variable-thickness airfoils to maintain consistent pressure surface leading-edge parameters. By integrating the Non-dominated Sorting Genetic Algorithm II with biomimetic optimization design, performance improvements are achieved. The study constructs an asymmetric bionic blade using a Bezier curve to fit the mean camber line of the blade. Experimental testing validates the optimized fan's performance, demonstrating the effectiveness of the proposed design approach in reducing the unsteady interaction between the impeller and the volute tongue. This reduction significantly diminishes sound pressure fluctuations on the blade surface. Notably, at the maximum volume flow rate, the optimized fan featuring the asymmetric bionic blade exhibits a remarkable enhancement, with a 10.5% increase in volume flow rate and a notable 1.7 dB reduction in noise compared to the original fan configuration. [ABSTRACT FROM AUTHOR]

Dicarboxylate metallosurfactants (AASM), synthesized by mixing N‐dodecyl aminomalonate, ‐aspartate and ‐glutamate with CaCl2, MnCl2 and CdCl2, were characterized by XRD, FTIR, and NMR spectroscopy. Layered structures, formed by metallosurfactants, were evidenced from differential scanning calorimetry and thermogravimetric analyses. Solvent‐spread monolayer of AASM in combination with soyphosphatidylcholine (SPC) and cholesterol (CHOL) were studied using Langmuir surface balance. With increasing mole fraction of AASM mean molecular area increased and passed through maxima at ~60 mol% of AASMs, indicating molecular packing reorganization. Systems with 20 and 60 mol% AASM exhibited positive deviations from ideal behavior signifying repulsive interaction between the AASM and SPC, while synergistic interactions were established from the negative deviation at other combinations. Dynamic surface elasticity increased with increasing surface pressure signifying formation of rigid monolayer. Transition of monolayer from gaseous to liquid expanded to liquid condensed state was established by Brewster angle microscopic studies. Stability of the hybrid vesicles, formed by AASM+SPC+CHOL, were established by monitoring their size, zeta potential and polydispersity index values over 100 days. Size and spherical morphology of hybrid vesicles were confirmed by transmission electron microscopic studies. Biocompatibility of the hybrid vesicles were established by cytotoxicity studies revealing their possible applications in drug delivery and imaging. [ABSTRACT FROM AUTHOR]

In the ABL wind tunnel, three inverted umbrella-shaped membrane structure groups were subjected to simultaneous pressure measurement model test. Time series of the fluctuating wind pressure were collected from 24 different wind angles. Upon examining the correlation coefficient of the fluctuating wind pressure between the upper and lower surfaces at the same pressure tap, it was discovered that the fluctuating wind pressure of the upwind roof exhibited asynchronous changes, which is a characteristic of a negative correlation area and has detrimental effects on the structure's wind resistance. The local areas with non-Gaussian properties were evaluated by analyzing the probability density function of representative pressure taps. The mechanism behind non-Gaussian wind pressure was elucidated through considerations of the central limit theorem and spatial correlation of fluctuating wind pressure. This study introduces a quantitative classification criterion for identifying the non-Gaussian distribution area of fluctuating wind pressure, setting the threshold at an 80% cumulative probability for both skewness and kurtosis. The analysis showed that the steady airflow of the structure corresponds to the Gaussian distribution area, while the non-Gaussian distribution area is primarily concentrated at the front edge of the upwind roof and the rear edge of the downwind roof. To ascertain the peak factor for the non-Gaussian distribution, the improved peak factor method was utilized, providing insights into the range of peak factor in the non-Gaussian distribution area of this particular roof configuration. This information serves as a foundation for the wind resistance design of this structure. [ABSTRACT FROM AUTHOR]

Black carbon (BC) and brown carbon (BrC) both have a versatile nature, and they have an apparent role in climate variability and changes. As anthropogenic activity is surging, BC and BrC are also reportedly increasing. So, the monitoring of BC and BrC and observations of land use land cover change (LULCC) at a regional level are necessary for the changes in various interconnected meteorological phenomena. The current study investigates BC , BrC , CO2 , BC from fossil fuels (BCff), BC from biomass burning (BCbb), and LULCC and their relationship to the corresponding meteorological conditions over Gangtok in the Sikkim Himalayan region. The concentration of BC (BrC) was found to be highest during March 2022 (April 2021) at 43.5 µgm-3 (32.0 µgm-3)​​​​​​​. Surface pressure exhibits a significant positive correlation with BC , BCff , BCbb , and BrC. Higher surface pressure results in a calmer and more stable boundary layer, which effectively retains deposited contaminants. Conversely, the wind appears to facilitate the dispersion of pollutants, showing a strong negative correlation. The fact that all pollutants and precipitation have been shown to behave similarly points to moist scavenging of the pollutants. Despite the dense cloud cover, it is clear that the area is not receiving convective precipitation, implying that orographic precipitation is occurring over the region. Most of Sikkim receives convective rain from May to September, indicating that the region has significant convective activity contributed from the Bay of Bengal during the monsoon season. Furthermore, monsoon months have the lowest concentrations of BC , BCbb , BCff , and BrC , suggesting the potential of convective rain (as rainout scavenging) to remove most of the pollutants. [ABSTRACT FROM AUTHOR]

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The concentration data of semi‐volatile n‐alkanes and PAHs in the gas phase and in PM2.5 were obtained from Nanjing and Denver. First, the gas‐particle partitioning coefficients of the target compounds were calculated and compared with the predictions based on the equilibrium absorptive partitioning theory. Although the vapor pressure (poL) estimation method was selected to improve the agreement between measured and predicted partitioning coefficients, n‐alkanes in Denver and PAHs in both cities exhibited stronger sorption to PM2.5 than predicted. By including the adsorption mechanism, the average logarithms and temporal variations of the partitioning coefficients were well simulated in both Nanjing and Denver. The partitioning of n‐alkanes in Nanjing can be primarily explained by the absorption mechanism, while the adsorption mechanism dominates that for n‐alkanes in Denver and PAHs in both cities. To obtain an optimal simulation, the poL of n‐alkanes and PAHs was estimated using the SPARC and SIMPOL—two group contribution methods, respectively, and the difference between desorption and vaporization enthalpies was set between 2 and 3 kcal mol−1 for n‐alkanes in Denver and PAHs in both cities. Therefore, the estimation of poL and surface adsorption should be carefully considered when parameterizing the gas‐particle partitioning of non‐polar organic compounds in future field and modeling studies. Plain Language Summary: The gas‐particle partitioning of semi‐volatile organic compounds is an important atmospheric process that can affect their fate and transport. The concentrations of selected n‐alkanes and PAHs significantly present in both the gas and particulate phases in Nanjing and Denver were obtained from our previous studies. When absorption in particulate organic matter (OM) was assumed as the dominant mechanism, the gas‐particle partitioning of n‐alkanes in Denver and PAHs in both cities cannot be well explained. When both absorption in the particulate OM phase and surface adsorption were considered, good agreement between measured and predicted partitioning coefficients could be obtained for all target compounds by selecting an appropriate method to estimate the vapor pressure (poL) and fixing the difference between desorption and vaporization enthalpies. In previous studies, the simulated partitioning coefficients differed by orders of magnitude from the measured values, partly due to the ignorance of poL estimation method selection and surface adsorption. Key Points: n‐Alkanes and PAHs can show stronger sorption to particulate matter (PM) than in the simulation based on the equilibrium absorptive partitioning theoryCombining absorption and adsorption mechanisms can improve the agreement between measured and predicted partitioning coefficientsThe sorption of n‐alkanes and PAHs on PM is less liquid‐like in Denver than in Nanjing [ABSTRACT FROM AUTHOR]

To study the effect of coal pressure on gas extraction under fluid‐solid coupling, the effect of gas extraction radius under different pore sizes and treatment methods was simulated by using COMSOL Multiphysics software, the time evolution law of gas pressure on coal surface was obtained, and the numerical simulation results were verified by the observation of flow rate and concentration in experimental mine combined with fluid‐solid interaction. The results show that the distance of extraction radius increases with the increase of borehole diameter, and the relation between extraction time and extraction radius is a power function, but the increase gets smaller and smaller until it becomes zero. For Φ98 mm borehole and Φ120 mm borehole, hydraulic treatment can increase the efficiency of gas extraction by 31.3% and 22.7%, respectively. For hydraulic treatment and conventional treatment, the ratio of gas drainage effect by enlarging hole size is 6.3% and 13.8% respectively. Compared with the areas without gas extraction under the four conditions, the descending speed of gas pressure from fast to slow is Φ120 mm hydraulic flushing treatment, Φ98 mm hydraulic flushing treatment, Φ120 mm conventional treatment, Φ98 mm conventional treatment. Compared with four different conditions, after 180 days of extraction the coal gas pressure decreased by 75.3% within reasonable hole spacing. At the same time, in multi‐hole pumping, the influence area of adjacent borehole is larger than that of single‐hole pumping, and the spacing of borehole should be less than twice the radius of pumping. [ABSTRACT FROM AUTHOR]

Kinetic dependences have been determined for the surface tension, dilatational dynamic surface elasticity, and ellipsometric angles of solutions of styrene copolymers with 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine. The micromorphology of the adsorbed and spread layers of these polyelectrolytes has also been studied. All kinetic dependences of the dynamic surface elasticity have turned out to be monotonic in contrast to those observed for previously studied solutions of polyelectrolytes free of polystyrene fragments. The peculiarities of the surface properties of the studied solutions may be related to the formation of microaggregates in the surface layers, because these microaggregates suppress the formation of loops and tails of polymer chains at the interfaces, and, consequently, decrease the surface elasticity after the local maximum. Atomic force microscopy data also indicate the formation of aggregates with sizes in the Z direction of 1–4 nm in the surface layers. The obtained results confirm the conclusions previously made about the formation of aggregates in the surface layers of solutions of polyelectrolytes containing fragments of sodium poly(styrene sulfonate). A 2D phase transition to a denser surface phase and the formation of aggregates with a size of 40 nm in the Z direction have been observed at surface pressures of 25–30 mN/m for the layers of the studied styrene-free polyelectrolyte spread over an aqueous substrate. [ABSTRACT FROM AUTHOR]

The flow loss caused by the fan blades in a turbofan engine with a large bypass ratio is significant, and the wake considerably affects the inlet flow of downstream components. Surfaces with bird feather-like convergent–divergent (C–D) riblets have been proven to modulate the boundary layer flow by inducing counter-rotating rolling modes; however, the effects of these surfaces on the total pressure loss and wake turbulence of transonic compressor cascades remain unexplored. In this study, the effects of C–D-riblet surfaces on the total pressure loss and wake turbulence of a transonic compressor cascade were experimentally investigated using a five-hole probe and hot-wire measurements. The flow-loss-control effects of C–D-riblet surfaces with different characteristic lengths were also analyzed. The most significant reduction in the area-averaged total pressure loss (11.23%) was achieved using a C–D-riblet surface with a characteristic length of 30 μm at a Mach number of 0.94; this total pressure loss reduction corresponded to an increase in the mean velocity and a decrease in the turbulence intensity of the wake profile. Furthermore, the effectiveness of the loss control varied significantly with the spreading position of the C–D riblets. The optimal control effect was observed in the divergence-line region, and the control was slightly less effective as the measurement position neared the convergence line. This paper demonstrates the promising potential of using C–D riblets to achieve flow loss control in transonic compressor cascades. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of rocket plume impingement on flat surfaces is critical for designing effective and sustainable landing pads. The current near vacuum study measures the surface pressures and temperature profiles arising on a flat surface due to highly underexpanded, axisymmetric plume impingement. The experiments were conducted in a dedicated, large-volume plume-regolith facility situated at the University of Glasgow. A total of eight tests were conducted, comprising of both constant and pulsed firing modes. The impingement plate is located at stand-off distances equal to 4 and 16 times the nozzle exit diameters and plate inclinations of 0 ° and 30 °. Reduced stand-off distance increases impingement pressure, with a transient peak in the early stages of impingement indicating the presence of a primary shock wave. Higher stand-off distance resulted in decreased impingement pressure without an initial peak, but with a spike at the end of impingement once the nozzle had stopped firing. For inclined plates, the centerline impingement pressure magnitude decreased by around 40% compared with the 0 ° inclination. The measured pressures at lower stand-off height are then compared with the results of both a two-way coupled direct simulation Monte Carlo/Navier–Stokes–Fourier solver and an analytical theory. The results from all methods are in good agreement with each other, with the simulation and experimental centerline pressures being within 1% of each other. As the optical thickness of the gas is very low in the experimental case, the numerical method is used to generate a Schlieren image to analyze the shock structure. [ABSTRACT FROM AUTHOR]

This study is inspired by an experimental observation for vortex-induced vibrations (VIVs) of a double-hanger cable system, in which a smaller vibration of the downwind hanger cable is re-excited over a narrow range of wind speeds beyond the "lock-in" range. This phenomenon is known as the wake vortex-induced vibrations (WVIVs), where the upstream wake flow induces downstream vibrations. To further investigate the characteristics and reasons for WVIVs, a refined wind tunnel test of double-hanger cable was conducted to consider the influence of aerodynamic interaction. The double-hanger cable was modeled by the tandem-arranged spring-mounted cylinders vibrating in two dimensions. The vibration responses of hanger cables were obtained under various wind speeds to reproduce the lock-in phenomenon. In addition, the vibration trajectory, phase relationship, damping ratio, inter-cable correlation, and the wind pressure on the surface of cables were analyzed. Finally, the Stockbridge dampers were designed to suppress the vibrations. The results show that under the aerodynamic interaction of the cables, the onset wind speed of VIVs in the double cables increases, and the downstream cable WVIVs closely follow the VIVs. During the WVIV phase, the downstream cable behavior is characterized by increased negative aerodynamic damping and an inverse displacement correlation between the cables. The phase relationships between the cables are time-varying due to the aerodynamic interaction. The first proper orthogonal decomposition mode of wind pressure dominates the cross-wind of motions and is crucial in vibrations. Stockbridge dampers can effectively reduce the amplitude of VIVs and eliminate WVIVs in cables. [ABSTRACT FROM AUTHOR]

We propose a spatiotemporal coupling deep neural network approach for time-resolved reconstruction of the velocity field around a circular cylinder. The neural network leverages two distinct data types: (1) non-time-resolved velocity field around the cylinder, consisting of fixed frequency sampling and variable frequency sampling velocity field, and (2) the time-resolved surface pressure sequence around the cylinder. The deep neural network comprises two sub-networks: a convolutional autoencoder (CAE) for nonlinear mode extraction and a Transformer for sequence-to-sequence learning. We refer to this architecture as CTNet (CAE-Transformer Network). The encoder in the CAE maps non-time-resolved velocity field to a latent vector, enabling the extraction of nonlinear modal coefficients. An appropriate time window length for the surface pressure sequence is then selected to establish a Transformer sequence learning model, using the chosen sequence as input to predict the corresponding nonlinear modal coefficients. Once the Transformer is well trained, the time-resolved nonlinear modal coefficients of velocity field can be achieved. Along with the well-trained decoder in the CAE, the time-resolved velocity field can be reconstructed from the output of the Transformer. We verify the performance of CTNet by a simulated dataset at a representative Reynolds number of 3900. The results show a relative reconstruction error of just 6.3% for the time-resolved velocity field, demonstrating high reliability in the reconstruction. We further compare the reconstructed velocity field obtained with and without the utilization of variable frequency sampling velocity field. Notably, the inclusion of variable frequency sampling velocity field significantly improves the reconstruction quality. [ABSTRACT FROM AUTHOR]

Experiments of shock wave/boundary layer interactions over a nominally two-dimensional compression ramp are conducted in a Mach 4 Ludwieg tube tunnel. Measurements of Schlieren, Rayleigh scattering, and surface pressure are performed to present the relevant flow features. The effects of two parameters, namely the Reynolds number based on the length of the flat plate and the ramp angle, on the flow stabilities are focused on. Four ramp angles of 6°, 8°, 10°, and 12° are tested under a Reynolds number of 7.22 × 105, while two other Reynolds numbers (3.66 × 105 and 9.19 × 105) are investigated with a ramp angle of 10°. Streamwise streaks are observed downstream of the reattachment point. The spanwise wavelength of the streaks remains unchanged with different ramp angles, whereas it slightly decreases as the Reynolds number increases. Power spectral density results show that the flow is transitional in the streak region and becomes turbulent where streaks break down. When increasing the ramp angle or the Reynolds number, the streamwise length of streaks shrinks. Two different patterns are distinguished at the breakdown, resembling the two unstable modes observed in the breakdown of Görtler vortices. To clarify the underlying physics of the formation of streaks, global stability analysis and resolvent analysis are carried out. Two regions of maximum optimal gain are identified, which are associated with Mack's first mode and streaks. The former can serve as an initial seed of Görtler instability via nonlinear interaction, while the latter can be associated with transient growth due to the lift-up mechanism and Görtler instability. [ABSTRACT FROM AUTHOR]

A new technology for remote measurements of marine surface pressure has been proposed, employing a V‐band differential absorption radar and a radiometric temperature sounder to calculate the total column atmospheric mass. Observing System Simulation Experiments (OSSEs) are performed to evaluate the potential impact of Spaceborne Marine Surface Pressure (SMSP) on Numerical Weather Prediction. These experiments build on prior efforts (Privé, McLinden, et al., 2023, https://doi.org/10.16993/tellusa.3254), but with an updated version of the OSSE framework and with more sophisticated simulation of the SMSP observations and a longer experiment period. Several different instrument configurations are compared, including both scanning and non‐scanning orbits. SMSP impacts are calculated for analysis quality and forecast skill, and a forecast sensitivity observation impact tool is employed to place SMSP observations in context with the global observing network. The effects of rain contamination on observation quality are explored. Different magnitudes of simulated SMSP observation error are tested in the context of data assimilation to show the range of potential behaviors. Overall, SMSP observations are found to be most beneficial in the southern hemisphere extratropics, with statistically significant forecast improvements for the first 72 hr of the forecast. A constellation of four non‐scanning SMSP satellites is found to outperform a single scanning instrument with a 250 km wide swath. Plain Language Summary: Measurements of surface pressure are very useful for weather prediction because they tell us about phenomena such as winter storms, as well as large scale atmospheric circulation patterns. Over the ocean, the only surface pressure measurements currently come from buoys and some ships, but these measurements are very far apart. Recently, some new radar technology is under development that would allow ocean surface pressures to be remotely retrieved from aircraft or satellites. In this work, these proposed new radar surface pressure measurements are simulated and tested in a weather forecast model. Several different configurations of an orbiting spaceborne radar are simulated and compared to find out how much the radar data would improve weather forecasts. The results show that a constellation of four smaller radar satellites has the most improvement on weather prediction. The effect of instrument noise was also tested, and it was found that the radar was helpful for weather forecasts for a wide range of instrument performance. Key Points: The greatest observation impacts are found in the southern hemisphere extratropics, with neutral impacts in the tropicsThe most beneficial observation impacts occur with a four‐satellite platform of non‐scanning instrumentsBeneficial impacts are found for a wide range of observation error magnitudes [ABSTRACT FROM AUTHOR]

Through data collection and field investigations of a gold mine-s goaf, a 3D digital model of the mines goaf and roadways was established using 3Dmine software. This model accurately provided information on the actual boundaries and shapes of the goaf at different levels. Based on the comprehensive analysis of goaf conditions and the mine-s production reality, a management plan was proposed. The management strategy includes the following:for goaf groups/collapse pits (above the fourth level) that have interconnected, surface waste rock filling is used; for isolated goafs on the fourth level, forced roof caving through medium-long hole blasting is employed to fill the goaf with waste rock from the surface. In addition, closed-off isolation methods are applied for joint management. For other goafs where mining has ceased and access is no longer possible, the goafs are managed by sealing off the level stone doors. For goafs under mining, filling with in-pit coarse rocks and sealed isolation methods are implemented. Through the integrated application of these various measures, the risk of large-scale ground pressure activities and surface subsidence has been thoroughly eliminated, creating favorable conditions for continued underground production operations. [ABSTRACT FROM AUTHOR]

Taking a shear wall structure in a high-intensity area of 20 floors as an example, the seismic reduction scheme of the structure was determined, and the Etabs software was used to conduct time history analysis on the seismic and non-seismic structures. The floor shear force, overturning moment, and short-term surface pressure of the isolation support were obtained. The results showed that under frequent earthquake action, the average maximum floor shear force in the direction of the isolated upper structure was only about 28 % of that of the non-isolated structure. The maximum inter story shear ratio was 0.34, and the maximum floor shear force in the direction was only about 25 % of that of the non-isolated structure. The maximum inter story shear ratio was 0.31. The average maximum overturning moment of the upper structure in the direction after isolation is about 30 % of that of the non-isolated structure. The maximum overturning moment ratio is 0.36, and the average overturning moment of the maximum floor in the direction is about 22 % of that of the non-isolated structure. The maximum overturning moment ratio is 0.26. Under rare earthquake action, the maximum inter story displacement angles in the and directions of each floor of the seismic isolation structure are 1/302 and 1/446, respectively. The maximum surface pressure value of the isolation bearing under rare earthquake is 28.9 MPa, the minimum surface pressure value is 5.58 MPa, and the maximum displacement is 579 mm, which meets the requirements of the specifications. Overall, the seismic performance of the seismic isolation structure is good, and the isolation scheme is feasible. [ABSTRACT FROM AUTHOR]

The torque-tension relationship plays a vital role in the application of bolted joints, providing essential guidance not only in controlling the preload during the tightening process but also serving as the theoretical basis for measuring the coefficient of friction on threaded surfaces. In order to develop a better understanding of the torque-tension relationship, the force and torque on the contact surface during the preload process were analyzed using a differential geometric representation of the thread surface. This representation took into account three-dimensional effects of the thread surface, particularly its non-developability. The hexahedral meshed model of the bolted joints was used in the FEA of the tightening process to obtain the pressure distribution on the contact surfaces. Based on the accurate representation of thread surface and consideration of pressure distribution forms, a novel torque-tension relationship was proposed and compared with current relationships in the literature. The error analysis showed that the proposed formulation has lower relative errors with the FEA results than those in the literature, indicating a higher level of accuracy. This proposed torque-tension relationship not only improves the safety and reliability of bolted joints, but also contributes to a better understanding of thread mechanics during tightening process. [ABSTRACT FROM AUTHOR]

When the wind turbine operates in the wind-sand environment, the sand particles will cause erosion and wear on the surface of the wind turbine blades, which will result in morphological changes and lead to changes in aerodynamic performance. In order to deeply understand the degree of wear of wind turbine blades in the wind-sand environment and its change rule with time, and to provide scientific basis for the operation and maintenance of wind turbines in the wind-sand environment, it is necessary to systematically study the dynamic evolution process of erosion and wear on the surface of the blades, as well as the change of the aerodynamic performance in this process. This study adopts the numerical model of flow-solid-erosion coupling, based on the particle concentration-time conversion method, and by simulating the erosion process of wind-sand on the wind turbine-specific airfoil S809, the dynamic evolution process of the morphology of the airfoil surface under the erosion effect of the sand particles is explored, and the depth of erosion and morphology of the airfoil surface are analyzed, and the influence law of the wind-sand particles on the morphology and its aerodynamic performance of the airfoil surface of the S809 are further investigated under different angles of attack. The influence of sand particles on the surface morphology of S809 airfoil at different angles of attack is further investigated. The study shows that, with the advancement of erosion time, the abrasion degree of sand particles on the airfoil surface increases, which makes the depth of the erosion pits deepen, and the pressure coefficient fluctuation of the airfoil surface becomes drastic. At the same time, the lift coefficient shows a trend of slight increase and then slow decrease. The particle erosion and wear were concentrated mainly in the high-pressure areas of pressure surface at the leading edge of airfoil segment. The wear area of airfoil segment was gradually enlarged with the increase of the erosion time, and the depth of wear was deepened. There was the slightly decrease rate of the maximum depth after the surface erosion of airfoil segment. The area of suction surface erosion wear was shifted to the leading edge, with the increase of angle of attack. While the area of pressure surface erosion wear was to the trailing edge. The larger the angle of attack was, the more serious the erosion wear in the region of the pressure front edge of the airfoil segment was. At the same time, the pressure coefficient of the wing section cross-section was appeared the fluctuation in the process of erosion. The more outstanding fluctuation was found with the advancement of the erosion time, especially on the more significant fluctuation of the pressure coefficient at the front edge of the suction force. Overall, the wing segment lift coefficient showed the increasing first and then decreasing in the process of particle erosion, with the advancement of erosion time. Once the angle of attack was 10° and the erosion duration was 40 h, the wing segment lift coefficient increased up to 6.3% than before. When the angle of attack was more than 12°, the coefficient of lift decreased significantly after 20 h of erosion, compared with the low angle of attack. The value of β was about 0.62 at the angle of attack from 2° to 8°, whereas, the value of β increased up to 0.82 at the angle of attack of 10°. The slow increase was observed with the increase of the angle of attack. In general, the wing segment lift-to-drag ratio was depended mainly on the incoming wind and sand at small angles of attack. There was no influence under the incoming wind and sand at large angles of attack. The findings can provide the data support and theoretical basis to maintain and repair the wind turbines in the wind-sand inflow environment. [ABSTRACT FROM AUTHOR]

The Arabian Peninsula (AP) is notable for its unique meteorological and climatic patterns and plays a pivotal role in understanding regional climate dynamics and dust emissions. The scarcity of ground-based observations makes atmospheric data essential, rendering reanalysis and satellite products invaluable for understanding weather patterns and climate variability. However, the accuracy of these products in the AP's desert environment has not been extensively evaluated. This study undertakes the first comprehensive validation of reanalysis products—the European Centre for Medium-Range Weather Forecasts' European Reanalysis version 5 (ERA5) and ERA5 Land (ERA5L), along with Clouds and Earth's Radiant Energy System (CERES) radiation fluxes—against measurements from the Liwa desert in the UAE. The data, collected during the Wind-blown Sand Experiment (WISE)–UAE field experiment from July 2022 to December 2023, includes air temperature and relative humidity at 2 m, 10 m wind speed, surface pressure, skin temperature, and net radiation fluxes. Our analysis reveals a strong agreement between ERA5/ERA5L and the observed diurnal T2m cycle, despite a warm night bias and cold day bias with a magnitude within 2 K. The wind speed analysis uncovered a bimodal distribution attributed to sea-breeze circulation and the nocturnal low-level jet, with the reanalysis overestimating the nighttime wind speeds by 2 m s−1. This is linked to biases in nighttime temperatures arising from an inaccurate representation of nocturnal boundary layer processes. The daytime cold bias contrasts with the excessive net radiation flux at the surface by about 50–100 W m−2, underscoring the challenges in the physical representation of land–atmosphere interactions. [ABSTRACT FROM AUTHOR]

Purpose: Structural design theory and method for the polyurea coating system have rarely been developed. The normally used experience-based design method may lead to unsafe, unreasonable and uneconomic results. The purpose of this paper is to investigate the deformation and failure behaviour of the polyurea coating so as to propose a rational design method. Design/methodology/approach: In this study, the fundamental theories concerning the nonlinear analysis of polyurea coating were discussed. Nonlinear Finite Element Method (FEM) models were built to investigate the mechanical behaviour, peeling behaviour and failure mode of the polyurea coating under various conditions, such as surface fracturing, surface hydraulic pressure and reverse hydraulic peeling. Findings: The main conclusions are as follows. The peeled coating at the crack location exhibits a tensile-bending stress state. Coating material damage may occur at the stress concentration point. The maximum stress increases with the increase in the hydraulic pressure and cohesive strength. The peeling length of the coating decreases with the increase in cohesive strength and increases with the increase in fracture width. The reverse hydraulic pressure-induced blister edge stress concentration is the main trigger of the polyurea coating blistering damage. The blistering height decreases with increasing coating thickness and increases with increasing blistering radius and hydraulic load. The maximum stress increases with increasing blistering radius and hydraulic load. Finally, the frame of design and simple design programme were proposed. Originality/value: Currently, a design method for polyurea anti-seepage coating can hardly be found. The reason is that the anti-seepage coating has only been recognized as a water-proofing layer, the mechanical behaviour of which has been ignored. This study focused on the mechanical behaviour of the anti-seepage coating and investigated the deformation and failure behaviour of the coating structure under various loading conditions through nonlinear FEM analysis. These research results offer a better understanding concerning the mechanical behaviour and design method of the polyurea anti-seepage coating. [ABSTRACT FROM AUTHOR]

This study examines the asymmetry in the Indian summer monsoon rainfall (ISMR) response over India and its four homogeneous regions to two distinct types of temporal evolution in La Niña. We have shown this uneven response by analysing the large‐scale dynamics over tropical Indo‐Pacific region for the period 1951–2022. We have identified two types of La Niña events during monsoon season (June–September) based on whether they evolved from El Niño or La Niña from preceding boreal winter season (December–February). India receives significantly more (less) rainfall during La Niña years, when it was preceded by El Niño (La Niña) in the preceding winter. We further observed the spatial diversity of rainfall over India with a northeast–southwest dipole pattern. When La Niña years were preceded by El Niño, positive surface pressure anomaly over west‐north Pacific, low‐level westerlies and moisture transport favoured the rainfall over south peninsula and west‐central India. Whereas moisture divergence associated with anomalous lower‐tropospheric anticyclone over west‐north Pacific suppressed the rainfall over Indo‐Gangetic plains. However, when La Niña years were preceded by La Niña in winter, the absence of westerlies and weak moisture transport subdued the rainfall over south peninsula and west‐central India. At the same time, moisture convergence and a greater number of monsoon depressions favoured rainfall over north‐west India. This study also looked at how well eight Copernicus Climate Change Service (C3S) models predicted ISMR and SST for two types of La Niña with April initial conditions during the period 1993–2016. Models were able to capture the spatial pattern of SST anomalies over Indo‐Pacific Ocean, but all models could not capture the spatial pattern of ISMR. However, in terms of intensity, six out of eight models could predict more (less) ISMR when it was preceded by El Niño (La Niña), coinciding with the observed anomaly. [ABSTRACT FROM AUTHOR]

This work has the purpose to elucidate in deeper detail the conjugated physical phenomena at the interface between two immiscible fluids in microfluidic devices. The two typical regimes—dripping and jetting—emerging in flow-focusing devices are considered for the analysis. Dynamic (time-dependent analysis of fixed or Lagrangian-tracked points) and local (lines along the interface, at a fixed time instance) analyses have been conducted from a parallel numerical simulation on a fine numerical grid. The results comprise various pressures and tangential stresses and their balance during the droplet formation process with special attention paid to the moments and locations of the droplet release. It was found that the dripping regime is characterized by the local balance of the pressure drop due to surface tension Δ p σ and the Laplace pressure Δ p Lapl across the interface. Only at the last moments before the droplet pinch-off does the former pressure dominate. In contrast, in the jetting regime, there is a clear domination of the pressure due to tension during the whole process of droplet formation. Shear stresses, presented by the von Mises criterion, are several times (jetting regime) or even an order of magnitude (dripping regime) lower than the surface tension pressure and the Laplace pressure. In both regimes, when the interface curvature κ changes locally its sign, the pressure at the centerline axis shows a clear local maximum. For the jetting regime, the downstream derivative of this centerline pressure is the first parameter that changes along the jet axis—thus indicating the onset of instabilities for this regime—and it is then followed by a wavelike change of the radius of the jet. [ABSTRACT FROM AUTHOR]

The purpose of this work is to shed light on the effect of the pivot position on the surface pressure distribution over a 3D wing in different flight conditions. The study is intended to support the design and development of aerospace vehicles where stability analysis, performance optimization, and aircraft design are of primary importance. The following parameters are considered: Mach numbers (M) of 1.3, 1.8, 2.3, 2.8, 3.3, and 3.8, angle of incidence (θ) in the range from 5° to 25°, pivot position from h = 0.2 to 1. The results of the CFD numerical simulations match available analytical data, thereby providing evidence for the reliability of the used approach. The findings provide valuable insights into the relationship between the surface pressure distribution, the Mach number and the angle of incidence. [ABSTRACT FROM AUTHOR]

Heatwaves represent a significant and growing threat to natural ecosystems and socio‐economic structures, making heatwave risk mitigation and prevention an important area of research. In exploring heatwave frequency and intensity from 1901 to 2020, the present study finds a sharp increase in both. The study also finds that the spatial distribution of heatwaves is unequal, the volatility of intensity characteristics has become more prominent over time, and the Gini coefficients of four key heatwave indictors have become larger due to increasing dryness. Although heatwaves occur more frequently in drylands, there is greater cumulative heat in humid areas, resulting in a higher heatwave risk in those areas. The global heatwave risk over the past three decades (1991–2020) has increased nearly five‐fold compared to the early 20th century (1901–1930). Furthermore, GeoDetector analysis indicates that the Palmer drought severity index (PDSI) and downward surface shortwave radiation (Srad) contributing the most in drylands and humid areas (0.29 and 0.41, respectively). The contribution of relative humidity (RH), wind speed (WS), soil moisture (SM), and the normalized difference vegetation index (NDVI) is also significant in humid areas, but is much smaller in drylands. Composite analysis shows that the years with anomalously high heatwave risk correspond to positive anomalies of 500hPa geopotential height and surface pressure. The inhibition of cloud formation due to sinking air and the resulting increase in temperature in the atmosphere may be increasing the risk of heatwave occurrence. This study emphasizes the urgent need to address worsening climate change impacts. Plain Language Summary: Heatwaves are high‐impact extreme events, and their monitoring, risk assessment, and countermeasure development are critically important. This study focuses on the evolution of heatwaves, including their risk assessment and driving mechanisms, based on Gini coefficients, GeoDetector, and composite analysis. It is found that heatwaves have become more frequent and intense over the past 120 years (1901–2020), and their occurrence rate has increased five‐fold. After 1980, heatwave characteristics (frequency, intensity, duration, and severity) increased in volatility and their spatial distribution showed an increase in inequality. Interestingly, while drylands experience more heatwaves, humid areas accumulate more heat, leading to a higher risk of heatwaves in humid areas. In fact, the intensity of heatwave risk is 7.7% higher in humid areas than in drylands, with factors such as relative humidity, wind speed, soil moisture, and the normalized difference vegetation index contributing more in humid areas than in drylands. The study also relates these changes to atmospheric circulation, which is typically characterized by higher upper atmospheric pressure and surface pressure, leading to reduced cloud formation and higher temperatures. Our study of heatwave risk highlights the increasing impacts of climate change and the need for urgent action, especially in humid areas. Key Points: Heatwaves are more frequent in drylands, but cumulative heat is greater in humid areasHeatwave risk has quintupled over one century and is higher in humid areas than in drylandsHigh heatwave risk is usually accompanied by anticyclonic anomalies [ABSTRACT FROM AUTHOR]

A spillway is a hydraulic structure of major importance in dam safety, and its current analysis usually involves a hybrid approach combining CFD modeling with experimental research, either using well-known WES design charts or conducting new model experiments in the laboratory. Flow over spillway crests involves fluid accelerations, making irrotationality an adequate simplification of the Navier–Stokes (NS) equations. However, an efficient tool using this method is currently lacking for spillway flow, particularly for ogee spillway flow. This work focuses on this aspect of the problem, and a new method for computing irrotational flow solutions over ogee spillways is proposed by developing flow net computational solutions. The proposed method entails a new iterative procedure in the complex potential plane where free surface pressures are exactly set to zero, contrary to other methods, and an automatic determination of the critical point, the unknown energy head, and the free surface profile. The model generates solutions efficiently in only a few seconds on a personal workstation, permitting a fast estimate of spillway flow operation, and is thus an effective complement to experimental and NS-CFD modeling. The solutions produced are compared with observations of a high operational head equal to five times the design head of the ogee crest, resulting in reasonable agreement. The application of the new model to investigate the limitations of analytical equations used in spillway flow, like Jaeger's theory, establishes limits for its use by relating its curvature parameter to the spillway chute slope. [ABSTRACT FROM AUTHOR]

The evaluation of the wave-induced pore pressures around the offshore piles has attracted great attentions among coastal engineers, because they have been commonly used as foundations of numerous marine infrastructures. This paper presents comparative studies of the random wave-induced transient seabed response around single and double piles in a sandy seabed through a series of wave flume experiments. The influences of relative spacing ratios, wave incidence angles, and front pile diameters under different random wave parameters on oscillatory pore pressures in the vicinity of double piles are examined. In addition, variations in wave profiles and dynamic wave pressures surrounding single and double piles are quantitatively analyzed. Based on the experimental results, the following conclusions can be drawn: (1) under the influence of random waves, the wave profiles around the double piles exhibit obvious irregularity and nonlinearity; (2) the shielding effect existing in the tandem piles results in lower dynamic wave pressures around the rear pile compared to the front pile; (3) the pore pressures on the front surface of the double piles decrease with increasing soil depth, with a decreasing attenuation rate at each layer; (4) when the relative spacing ratio G / D 2 = 3 , the group-pile effect weakens, leading to an increase in the pore pressures around the rear pile, approaching the results of a single pile under conditions of lower significant wave heights or periods; (5) the intense disturbance effect caused by large wave incidence angles exacerbates the pore pressure response around the double piles; (6) when the diameter of the front pile in the tandem piles increases, it enhances the shielding effect, thus suppressing the seabed response around the rear pile. In contrast, it causes an increase in the wave surface around the double piles, exacerbating the pore pressure response in the seabed. The latter effect becomes more pronounced when the significant wave height is larger. [ABSTRACT FROM AUTHOR]

The article explores passive systems for regulating microclimates in residential settings, with a focus on modular constructions. It investigates the use of the trombe wall system for passive ventilation to ensure comfort and hygiene. The study examines building designs that enable effective air circulation without using mechanical systems. Furthermore, the effectiveness of the passive system of using solar energy with the trombe wall as a ventilation device in modular houses has been experimentally confirmed. Although the research confirms the effectiveness of this solar system in modular homes, there is limited documentation regarding its overall efficiency, particularly concerning the impact of the surface pressure coefficient on ventilation. The study establishes the correlations governing the thermosiphon collector's effectiveness at varying air layer thicknesses. Optimal parameters, such as maximum air consumption (L = 120 m3h−1), are identified at an air layer thickness (δ) of 100 mm and outlet openings area (F) of 0.056 m2. These findings pave the way for improving passive systems aimed at maintaining optimal thermal and air conditions in modern homes. The findings suggest the potential for more efficient and sustainable housing solutions. Further research is essential to understand how factors like building design and wind speed affect ventilation system efficacy. [ABSTRACT FROM AUTHOR]

Jupiter's icy moon Ganymede has a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only atomic hydrogen and oxygen have been directly detected in this exosphere. Here, we present observations of Ganymede's CO2 exosphere obtained with the James Webb Space Telescope. CO2 gas is observed over different terrain types, mainly over those exposed to intense Jovian plasma irradiation, as well as over some bright or dark terrains. Despite warm surface temperatures, the CO2 abundance over equatorial subsolar regions is low. CO2 vapor has the highest abundance over the north polar cap of the leading hemisphere, reaching a surface pressure of 1 pbar. From modeling we show that the local enhancement observed near 12 h local time in this region can be explained by the presence of cold traps enabling CO2 adsorption. However, whether the release mechanism in this high-latitude region is sputtering or sublimation remains unclear. The north polar cap of the leading hemisphere also has unique surface-ice properties, probably linked to the presence of the large atmospheric CO2 excess over this region. These CO2 molecules might have been initially released in the atmosphere after the radiolysis of CO2 precursors, or from the sputtering of CO2 embedded in the H2O ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO2 precursors. CO2 molecules would then be redistributed via cold trapping on ice-rich terrains of the polar cap and be diurnally released and redeposited on these terrains. Ganymede's CO2 exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons. [ABSTRACT FROM AUTHOR]

In this study, a numerical model for unilateral quasi-static contact between a rigid sphere and an elastic coating has been developed. The contact problem was solved using a numerical procedure based on the FFT technique, considering various coatings with different thicknesses and mechanical properties, implemented through a Matlab code. The model calculates the contact surface deformation and pressure field through a double iteration process. The first iteration solves the contact problem for a given indenter penetration, while the second iteration refines this penetration by minimizing the difference between the fixed and calculated loads. To achieve this, influence coefficients are derived from the elasto-static equations using the Papkovich-Neuber potentials. The study discusses the influence of coating thickness and friction coefficient value on the tribological behavior of the coating. The results indicate that contact pressure increases (ranging from 1.9 to 2.5) as the coating becomes thicker or more rigid (0.02 mm to 0.2 mm). Additionally, the tribological behavior of the coated surface is affected by the coating's thickness, hardness, and friction coefficient value. Importantly, this model demonstrates versatility by being applicable to both smooth and rough surfaces. [ABSTRACT FROM AUTHOR]

AbstractRail models may be simplified at different levels in wind tunnel tests and numerical simulations. This work used delayed detached eddy simulations to analyze and compare the aerodynamic loads (drag, side force, lift, and rolling moment), surface pressure, and flow characteristics around a train model placed on subgrades with three different rail models: no-rail, simplified rail, and realistic rail. The simulations were conducted at a large yaw angle of 60°. The mean aerodynamic characteristics of the car bodies and bogies were similar with the simplified rail model and realistic rail model, while those were completely different without the rail model. The difference in aerodynamic loads between the no-rail model and the realistic rail model was as high as 53.1%, whereas the difference between the simplified and realistic rail models was only 7.7%. And for fluctuating aerodynamic characteristics of the train, there was still differences between the cases with the simplified and realistic models. Further, the rail model significantly impacted the flow (such as the velocity, turbulent kinetic energy, and vorticity) around the train, especially under the train, resulting in significant differences in the aerodynamic loads in time and frequency domains. For accurate and precise measurements of mean aerodynamic loads, incorporating a rail model (with the simplified model being sufficient) can improve accuracy by 48.0% and precision by 66.9%. When focusing on fluctuating aerodynamic loads, using a realistic rail model is essential to accurately capture amplitude-frequency characteristics. The rail model setup recommendations outlined in this work aim to enhance the accuracy and reliability of various wind tunnel tests and numerical simulations related to train aerodynamics. [ABSTRACT FROM AUTHOR]

AbstractAsymmetric gemini surfactants were synthesized by the quaternization reaction of 1-(2-hydroxypropyl)-4-ethyl piperazine with (C9, C10, C12, and C14) alkyl bromides. The surface tension of their aqueous solutions was determined by the Du Nouy ring method and the conductometric method of specific electrical conductivity. According to the concentration dependence graphs of surface tension and specific electrical conductivity, critical micelle concentration – CMC, degree of association of the counterion – β, surface area occupied by the head group of the surfactant – Amin, maximum surface excess concentration – Γmax, effectiveness or surface pressure –πCMC, adsorption efficiency – pC20 were calculated, and the change of these parameters depending on the length of the alkyl chain was determined. Simultaneously, variations in Gibbs free energies of micellization and adsorption processes were computed. The diameters of aggregates formed by asymmetric gemini surfactants in water were determined by the DLS method. Antimicrobial abilities of asymmetric gemini surfactants against gram positive and gram negative bacteria and fungi were defined by the disk diffusion method. [ABSTRACT FROM AUTHOR]

Under the assumptions of linearized water wave theory, we build a three-dimensional mathematical model that couples atmospheric pressure waves and surface ocean waves, including water compressibility and its static part, to simulate Meteotsunami propagation in the ocean. The solution uses the Laplace–Fourier double transformation technique, emphasizing axisymmetry of the mathematical problem and rigorous treatment of a fairly complicated dispersion relation while using inverse transformations. A novel derivation of the axisymmetric atmospheric pressure front is shown. The impact of water compressibility is shown through a comparative graphical representation against the incompressible case. Faster travel of free-surface waves is observed in the incompressible ocean, followed by the cases with and without static compression of the compressible ocean, respectively. The static compression shifts the phase of the acoustic-gravity modes. The locked wave is hardly influenced by the water compressibility and is entangled with the moving pressure front. The model is validated with the observational pressure data and agrees well with our computed pressure profile. Then, the locked wave profile generated from our model agrees well with the deep-ocean assessment and reporting of tsunami data. [ABSTRACT FROM AUTHOR]

The shock/boundary-layer interaction induced by a 20° compression ramp in a Mach 2 flow was investigated using fast pressure-sensitive paint with a bandwidth of about 10 kHz. The mean separated flow length-scale is about two upstream boundary layer thicknesses, which indicates the interaction is weak. The primary analysis consists of cross-correlations, coherence, and time-domain filtering. Two different frequency bands were investigated: low-frequency (f < 2000 Hz; StL < 0.1) and mid-frequency (0.1 < StL < 0.26). The low-frequency band time sequences and coherence reveal the shock-foot motion is mainly correlated with the reattachment region, which is indicative of the well-established breathing motion of the separation bubble. The breathing motion is observed to occur locally and globally (spanwise-averaged). Furthermore, in the low-frequency band, fluctuations in the upstream boundary layer are moderately correlated with the reattachment region fluctuations, but show no correlation with the intermittent region fluctuations. In the mid-frequency band, the intermittent region, separation bubble and reattachment region all exhibit significant correlation with the upstream boundary layer fluctuations, with the upstream fluctuations leading. The time-sequences in this frequency band reveal broad regions of pressure fluctuations that sweep through the interaction and affect the entire interaction. There is no known turbulent source for such large-scale fluctuations and they are believed to be due to a wind tunnel phenomenon. It is concluded that the dominant low-frequency breathing motion follows an oscillator model, but there remain significant correlations to upstream fluctuations that are not tied to the dominant breathing motion and seem to follow an amplifier model. [ABSTRACT FROM AUTHOR]

Bifurcated tunnels have many lines that significantly improve the utilization of underground space. However, the pressure waves (PWs) generated by a metro train in a tunnel may cause irreversible damage to the tunnel, particularly the more complex wave system generated by a train in a variable cross section bifurcated tunnel. Overset grid technology was adopted to simulate trains operating in tunnels; the differences between train operation in single-line and bifurcated tunnels were analyzed, and the PW characteristics of trains operating on three different lines in a bifurcated tunnel were compared. The numerical method was verified experimentally, and the pressure change trend fitted well. The results show the following: The bifurcated tunnel will increase the train surface PWs. The maximum pressure (pmax) of the surface of the train is reduced by more than 60% on average, and the minimum pressure (pmin) is basically the same. The peak-to-peak pressure (Δp) increases by more than 50% on average, but the distribution trend does not change. The influence of the bifurcated tunnel on the tunnel wall pmax, pmin, and Δp is bounded by the bifurcation area. The difference in surface pressure of trains operating on different lines in the bifurcated tunnel is mainly caused by the bifurcated area. The distribution trend of the pmax, pmin, and Δp of trains operating on different lines is the same. However, the pmax, pmin, and Δp of the wall of the train operating line are greater than those of the non-operating line. These findings can provide a reference for the design of bifurcated tunnels and route planning of metro trains. [ABSTRACT FROM AUTHOR]

This study investigates the flow behavior over roughened inline cylinders for postcritical flow, a parameter space with relatively little prior scrutiny. Two cylinders of the same relative surface roughness, k s / D = 1.9 × 10 − 3 , separated by a pitch (i.e., L, distance between the centers of two cylinders) between 1.175 ≤ L / D ≤ 10 are studied at Reynolds numbers from 3 × 10 5 to 6 × 10 5 using unsteady surface pressure measurements. As pitch ratio is increased from L / D = 1.175 , CD of the downstream cylinder increases sharply at (L / D) c = 3.25. This critical pitch ratio (L / D) c is toward the lower end of the reported range for subcritical smooth cylinders. Asymmetric mean gap flow along with alternating reattachment is found for 1.5 ≤ L / D < 2.25 (i.e., two asymmetric modes in the gap, mode 1 and mode 2, that are the reflections of each other), and symmetric gap flow with a continuous reattachment is found for 2.25 < L / D ≤ 3. The gap flow is also symmetric for the closest pitch ratio tested of L / D = 1.175. While the change in upstream cylinder drag coefficient with Reynolds number broadly follows that of an isolated cylinder, for the downstream cylinder, it is approximately independent. The critical separation is also insensitive to Reynolds number within 3 × 10 5 ≤ R e ≤ 6 × 10 5 . Transitions between the reattachment and the co-shedding flow are predominantly continuous over the spanwise planes tested. On the other hand, alternating reattachment occurs in spanwise cells, where one sectional measurement exhibits the asymmetric mode 1 while a spanwise-adjacent section exhibits the asymmetric mode 2 or even symmetric flow. Previously reported maxima in the fluctuating lift and drag coefficients of the downstream cylinder at L / D ≈ 2.4 at subcritical Reynolds numbers are absent in the current investigation. [ABSTRACT FROM AUTHOR]

The linear-time-invariance notion to the Koopman analysis is a recent advance in fluid mechanics [Li et al., "The linear-time-invariance notion to the Koopman analysis: The architecture, pedagogical rendering, and fluid–structure association," Phys. Fluids 34(12), 125136 (2022c) and Li et al., "The linear-time-invariance notion of the Koopman analysis—Part 2. Dynamic Koopman modes, physics interpretations and phenomenological analysis of the prism wake," J. Fluid Mech. 959, A15 (2023a)], targeting the long-standing issue of correlating nonlinear excitation and response phenomena in fluid–structure interactions (FSI), or, in the simplified case, flow over rigid obstacles. Continuing the serial research, this work presents a data-driven, Koopman-inspired methodology to decouple nonlinear FSI by establishing cause-and-effect correspondences between structure surface pressure and the flow field. Exploiting unique features of the Koopman operator, the new methodology renders dynamic visualizations of in-sync, fluid–structure-coupled Koopman modes possible, fostering phenomenological analysis and statistical quantifications of FSI energy transfers. Instantaneous contribution contours and densities offer new angles to evaluate pathways of energy amplification and diminution. The methodology enables better descriptions and interpretations of phenomena occurring in the flow and on the boundary (walls) of an FSI domain and readily applies to a broad spectrum of engineering problems given its data-driven nature. [ABSTRACT FROM AUTHOR]

In this paper, the flow field around a tandem arrangement of two identical oscillating NACA (National Advisory Committee for Aeronautics) 0012 airfoils was investigated using the continuous wavelet transform. Wind tunnel experiments were conducted on a test stand that provided a wide range of sinusoidal pitching motion with frequencies up to 10 Hz. This study aims to explore the flow physics of the tandem airfoils that oscillate with independent reduced frequencies. For this sake, experiments were performed at a reduced frequency of 0.15 for the front airfoil and five different reduced frequencies for the rear airfoil, ranging from 0.05 to 0.3. The chord-based Reynolds number was 6 × 104, and the horizontal distance between airfoils was equal to one chord length. The unsteady surface pressure was measured, and the wavelet transform was employed to analyze the pressure fluctuations. Findings indicate that the presence of the rear airfoil in the wake of the front airfoil prevents the formation of the laminar separation bubble. Also, the ratio of upstream/downstream airfoil reduced frequencies appears as one of the dominant frequencies of pressure fluctuations on the rear airfoil. Furthermore, when the reduced frequency ratio of the airfoils is lower than one, the normal force on the rear airfoil is often less than that experienced by an isolated single airfoil. Specifically, at equal reduced frequencies of 0.15 for both upstream/downstream airfoils, the maximum value of the normal force coefficient on the rear airfoil decreases by 30% compared to the single airfoil. [ABSTRACT FROM AUTHOR]

In contrast to other swimming modes, the motions of fins in the labriform mode can be categorized into the drag-based mode and the lift-based mode, which differ in terms of the thrust generation mechanisms. This variance in thrust generation mechanisms gives the labriform mode unique advantages in underwater propulsion. The term labriform indicates that propulsion occurs due to oscillatory movements of pectoral fins. Herein, to identify the key features of labriform locomotion, numerical simulations of a self-propelled biomimetic robotic fish with a Reynolds number (Re) of up to 3 000 000 in the labriform mode are performed. This study includes a detailed analysis of swimming performance and hydrodynamic mechanisms and their connection to three-dimensional vortex dynamics. Compared with the drag-based mode, the fish is observed to cruise faster and swim more smoothly in the lift-based mode. This study also finds that the pectoral fin can produce continuous thrust during one cycle in lift-based mode but can only generate thrust during the power stroke in the drag-based mode. By connecting vortex dynamics and surface pressure, the results show that the leading-edge vortices generated by pectoral fins are associated with most of the thrust production in both motion modes. The analysis of the vortex structure shows that the pectoral fins shed one vortex ring in one cycle of the drag-based mode and two vortex rings in one cycle of the lift-based mode. Our results provide new insights regarding the self-propelled swimming mechanism of biomimetic robotic fish with different labriform propulsion modes. [ABSTRACT FROM AUTHOR]

In this investigation, we examine individual and synergistic effects of sea surface temperature (SST) in the North Pacific and North Atlantic on precipitation interdecadal variations over eastern China using the Multi-Taper Method-Singular Value Decomposition (MTM-SVD) method and the European Center Hamburg model version 5 (ECHAM5) simulations. Results reveal that the model adequately reproduces the quasi-periodic precipitation responses corresponding to interdecadal SST forcing in the North Pacific, North Atlantic and both regions. The Pacific Decadal Oscillation (PDO) is closely related to a meridional tri-polar precipitation pattern over eastern China, which is attributed to the western Pacific subtropical high and surface pressure anomalies over northern East Asia, influenced by the joint effects of a mid-latitude wave train and SST anomalies in the central-western North Pacific. The North Atlantic basin-scale SST (NABS) correlates positively with precipitation over North China and negatively with precipitation over Southwest China. This precipitation pattern is affected by the westward shift of the atmospheric activity center over East Asia associated with the mid-latitude wave train across Eurasia. The combined SST forcing from both the North Pacific and North Atlantic results in a meridional precipitation dipole pattern, and partially explains the precipitation interdecadal variation as observed. That is, as the PDO warm phase transitions to the NABS warm phase, rainbands experience an interdecadal northward shift from South China to North China. These results are pivotal for understanding how interdecadal SST forcing in the North Pacific and North Atlantic influences the precipitation distribution over China, thereby contributing to improvements in interdecadal climate prediction. [ABSTRACT FROM AUTHOR]