Increased Surface Friction Research Articles

On the Influences of Urbanization on the Extreme Rainfall over Zhengzhou on 20 July 2021: A Convection-Permitting Ensemble Modeling Study

This study investigates the influences of urban land cover on the extreme rainfall event over the Zhengzhou city in central China on 20 July 2021 using the Weather Research and Forecasting model at a convection-permitting scale [1-km resolution in the innermost domain (d3)]. Two ensembles of simulation (CTRL, NURB), each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes, were conducted using different land cover scenarios: (i) the real urban land cover, (ii) all cities in d3 being replaced with natural land cover. The results suggest that CTRL reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region, although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members. The ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%, and the maximum hourly rainfall simulated by each member is reduced by 15–70 mm in CTRL relative to NURB. The reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south, southeast, and east of Zhengzhou. Their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer (PBL), which exaggerates the PBL drying effect due to reduced evapotranspiration and also enhances the wind stilling effect due to increased surface friction in urban areas. As a result, the lateral inflows of moisture and high-θe (equivalent potential temperature) air from south and east to Zhengzhou are reduced.

Improvement in the physical and mechanical properties of the cement-based composite with the addition of nanostructured BN\u2013Fe3O4 reinforcement

In this work, the performance of modified cement by nanostructures consisting of boron nitride (BN) and iron oxide inorganic nanoparticles (Fe3O4) was analyzed. The mechanical strength, electrical resistivity, and the degree of cement hydration as well as the microstructure were investigated in detail. A hybrid filler boron nitride-iron oxide (BN–F) composed of Fe3O4 and BN was successfully synthesized using a chemical reaction. Transmission electron microscope (TEM) results showed proper binding of BN–F nanostructures. Addition of the hybrid nanostructured BN–F5 (containing 0.5 wt.% Fe3O4 and 0.5 wt.% BN) into the cement matrix increased the compressive strength and flexural strength by 65%, and 74%, respectively, after 28 days of curing. The improvement in mechanical strength is attributed to the increased surface friction induced by the Fe3O4 nanoparticles on the BN surfaces, resulting in increased interaction with the matrix. Microstructural studies, such as scanning electron microscope (SEM), showed the formation of a dense structure due to improved dispersion in the cement environment and hybrid performance in preventing crack growth, which is the main reason for the overall improvement in mechanical properties. The concrete resistance gauge (RCON, Giatec) and simultaneous thermal analysis (STA) tests revealed a significant increase in thermal and electrical conductivity in composite reinforced with nanostructured BN–F.

Design and Investigation of a 3D-Printed Micro-Fluidized Bed

Micro-fluidized bed has aroused much attention due to its low-cost, intensified-process and fast-screening properties. In this paper, a micro-fluidized bed (15 × 15 mm in cross-section) was designed and fabricated with the use of the stereolithography printing technique, for the investigation of bubbles’ hydrodynamics and comparison of the solids (3D-printed particles VS fungal pellets) fluidization characteristics. In a liquid–gas system, bubble flow regime started from mono-dispersed homogeneous regime, followed by poly-dispersed homogeneous regime, transition bubble regime and heterogeneous bubble regime with increasing gas flowrates from 3.7 mL/min to 32.7 mL/min. The impacts from operating parameters such as gas flowrate, superficial liquid velocity and gas sparger size on bubble size, velocity and volume fraction have been summarized. In liquid–solid fluidization, different solid fluidization regimes for both particles bed and pellets bed were identified. From the bed expansion results, much higher Umf of 7.8 mm/s from pellets fluidization was observed compared that of 2.3 mm/s in particles fluidization, because the hyphal structures of fungal pellets increased surface friction but also tended to agglomerate. The similar R–Z exponent n (5.7 and 5.5 for pellets and particles, respectively) between pellets and particles was explained by the same solid diameter, but much higher Ut of 436 µm/s in particles bed than that of 196 µm/s in pellets bed is a consequence of the higher density of solid particles. This paper gives insights on the development of MFB and its potential in solid processing.

Gyro-Sensor-Based Vibration Control for Dynamic Humanoid-Robot Walking on Inclined Surfaces.

An efficient motor-control system for stable walking of the lightweight humanoid robot KONDO KHR-3HV on inclined surfaces is investigated. The motor-control system is based on the angular velocity of the pitch motion of the robot, which is detected by a gyro sensor attached to the robot torso and referred to as the angular-pitch velocity. The robot gait is analyzed for different downslopes with and without the motor-feedback control. A novel method of frequency-domain analysis of the angular-pitch velocity is proposed for explaining the reasons behind the instabilities of dynamic humanoid-robot walking on inclined surfaces. The results show, that a nonlinear nature of the motor torque, due to a force induced by the slope, gives rise to harmonics of the fundamental walking frequency of 1.73 Hz. These harmonics are the origin of the unstable robot walking. Additionally, the feedback-gain parameters KA and KH affect the amplitudes of the harmonics, which give rise to vibrations at a higher surface inclination. Increased surface friction allows a reduction of the feedback gain, which reduces this specific contribution to the harmonics and thus stabilizes the robot. To improve the walking stability on inclined surfaces, it is found that the damped natural frequency of the motor-control system must be kept lower than the fundamental walking frequency.

A Numerical Study of Typhoon Megi (2010). Part II: Eyewall Evolution Crossing the Luzon Island

AbstractTyphoon Megi (2010) experienced drastic eyewall structure changes when it crossed the Luzon Island and entered the South China Sea (SCS), including the contraction and breakdown of the eyewall after landfall over the Luzon Island, the formation of a new large outer eyewall accompanied by reintensification of the storm after it entered the SCS, and the appearance of a short-lived small inner eyewall. These features were reproduced reasonably well in a control simulation using the Advanced Weather Research and Forecasting (ARW-WRF) Model. In this study, the eyewall processes of the simulated Megi during and after landfall have been analyzed. Results show that the presence of the landmass of the Luzon Island increased surface friction and reduced surface enthalpy flux, causing the original eyewall to contract and break down and the storm to weaken. The formation of the new large eyewall results mainly from the axisymmetrization of outer spiral rainbands after the storm core moved across the Luzon Island and entered the SCS. The appearance of the small inner eyewall over the SCS was due to the increased surface enthalpy flux and the revival of convection in the central region of the storm core. In a sensitivity experiment with the mesoscale mountain replaced by flat surface over the Luzon Island, a new large outer eyewall formed over the western Luzon Island with its size about one-third smaller after the storm entered the SCS than that in the control experiment with the terrain over the Luzon Island unchanged.

Increase in Surface Friction Dominates the Observed Surface Wind Speed Decline during 1973–2014 in the Northern Hemisphere Lands

AbstractDuring 1973–2014, a reduction trend in the observed surface wind speed (10 m) in the Northern Hemisphere lands has been widely reported; this reduction is referred to as “global stilling.” The primary determining factors of global stilling include atmospheric circulation, turbulent friction, and surface friction when ignoring the vertical influencing factors. Most of the existing studies on the attribution of global stilling do not take changing surface friction into account. In addition, there are other changes in the climate system, such as aerosol loading, which could have an impact on atmospheric circulation, but are not included in the majority of current models either. Here, we developed a novel approach based on modeled winds calculated from sea level pressure observations and applied the method to approximately 4000 weather stations in the Northern Hemisphere lands from 1973 to 2014 to attribute the stilling in the three factors. In our methods, we neglected the vertical influencing factors on surface wind speed but took the aerosols’ changes on atmospheric circulation and gradual urbanization effect on surface wind speed into account. We found that atmospheric circulation has dictated the monthly variation in surface wind speed during the past four decades. However, the increased surface friction dominates the long-term declining trend of wind stilling. Our studies had uncertainties while neglecting the influence of vertical factors on surface wind stilling, despite most of the existing studies showing their effect was minor compared to the three factors explored in our study.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Effect of Functionalized MWCNTs on the Tribological Properties of Polyimide Film

Multi-walled carbon nanotubes (MWCNTs) are incorporated into Polyimide (PI) film in both pristine and functionalized forms through in-situ polymerization. MWCNTs and NH2-MWCNTs lead to improved mechanical properties such as better tensile strength and elongation at break, as well as increased surface friction coefficient. The NH2-MWCNTs can reduce the total wear weight loss of the composite to a larger extent compared with MWCNTs. 1.0 wt% NH2-MWCNTs/PI has the lowest weight loss of 20.6 % of pure PI. Mechanism of two-stage wear procedure is discussed. We found that PI composite films with lower friction coefficient tend to lose less weight in the first stage, and the ones with better mechanical properties show better wear resistance in the whole wear procedure. Owing to the low surface energy, Natural mica is employed as the substrate for PI film.

A numerical investigation of supercells in landfalling tropical cyclones

[1] Supercell thunderstorms are known to occur in the outer rainbands of tropical cyclones (TCs), and these cells are of interest because they are occasionally tornadic. A series of multi-scale quasi-idealized TC simulations are used to study the development of outer rainband supercells. Within the environment of landfalling TCs, the sea-to-land transition of the rainbands is found to locally benefit supercell development onshore due in part to (1) enhanced surface-based destabilization during the day and (2) increased surface friction slowing and backing the low-level winds. Landfall time of day is shown to have a substantial impact on the average number, strength, and lifetime of the ensemble of simulated supercells. These idealized simulations represent a first attempt at controlled hypothesis tests for supercell and tornado ingredients within the context of a highly resolved parent TC.

The effect of etching on low-stress mechanical properties of polypropylene fabrics under helium/oxygen atmospheric pressure plasma

Polypropylene nonwoven fabrics were exposed to He/O2 atmospheric pressure glow discharge plasma. Surface chemical analysis and contact angle measurement revealed the surface oxidation by formation of new functional groups after plasma treatment. Weight loss (%) measurement and scanning electron microscopy analysis showed a significant plasma etching effect. It was investigated in low-stress mechanical properties of the fabrics using Kawabata Evaluation System (KES-FB). The surface morphology change by plasma treatment increased surface friction due to an enhancement of fiber-to-fiber friction, resulting in change of other low-stress mechanical properties of fabric.

The influence of surface padding properties on head and neck injury risk.

A validated computational head-neck model was used to understand the mechanical relationships between surface padding characteristics and injury risk during impacts near the head vertex. The study demonstrated that injury risk can be decreased by maximizing the energy-dissipating ability of the pad, choosing a pad stiffness that maximizes pad deformation without bottoming out, maximizing pad thickness, and minimizing surface friction. That increasing pad thickness protected the head without increasing neck loads suggests that the increased cervical spine injury incidence previously observed in cadaveric impacts to padded surfaces relative to lubricated rigid surfaces was due to increased surface friction rather than pocketing of the head in the pad.

The Propagation of Mountain Waves into the Stratosphere: Quantitative Evaluation of Three-Dimensional Simulations

On 6 January 1992 measurements of a mountain wave with significant amplitude were taken over the southern tip of Greenland during an ER-2 flight at an altitude of about 20 km. This work focuses on 3D numerical simulations of the wave generation and its propagation into the stratosphere during this event. The sensitivity of the simulated mountain wave to surface friction and horizontal resolution is explored. A nonhydrostatic model is used for experiments with horizontal resolutions of 12, 4, and 1.3 km. In all simulations the flow over the southern tip of Greenland generates a mountain wave, which propagates into the stratosphere. Changes of surface friction and horizontal resolution affect mostly the amplitude of the mountain wave. Increasing surface friction on the slopes reduces the amplitude of the excited orographic gravity wave. Horizontal diffusion required for numerical stability attenuates gravity waves during their propagation into the stratosphere. Increasing the horizontal resolution permits a smaller diffusion and thereby results in larger stratospheric wave amplitudes. The experiment with increased surface friction at 1.3-km horizontal resolution shows the best agreement with the observational data of the wave in the stratosphere. The differences between the simulated and measured amplitudes of vertical displacement and temperature anomaly are less than about 20%. The disparity in vertical velocity is larger ; downward velocities were observed up to 4.8 m s21 and simulated up to 2.7 m s21. In the experiments with lower surface friction at 4-km resolution, the accuracy regarding the amplitude of vertical displacement and temperature anomalies is similar, but the simulated maximum downdraft is even weaker. The other experiments with increased surface friction at 4-km resolution and normal friction at 12-km resolution significantly underestimate the wave amplitude. The results of the experiments suggest that the generation of orographic gravity waves and their propagation into the stratosphere can be simulated in three dimensions in a realistic manner provided that the magnitude of the parameterized surface friction is in a realistic range and the horizontal resolution is sufficient.