scholarly journals Superhydrophobic frictions

2019 ◽  
Vol 116 (17) ◽  
pp. 8220-8223 ◽  
Author(s):  
Timothée Mouterde ◽  
Pascal S. Raux ◽  
Christophe Clanet ◽  
David Quéré
Keyword(s):  
Terminal Velocity ◽  
Water Repellent ◽  
Viscous Liquids ◽  
The Relationship

Contrasting with its sluggish behavior on standard solids, water is extremely mobile on superhydrophobic materials, as shown, for instance, by the continuous acceleration of drops on tilted water-repellent leaves. For much longer substrates, however, drops reach a terminal velocity that results from a balance between weight and friction, allowing us to question the nature of this friction. We report that the relationship between force and terminal velocity is nonlinear. This is interpreted by showing that classical sources of friction are minimized, so that the aerodynamical resistance to motion becomes dominant, which eventually explains the matchless mobility of water. Our results are finally extended to viscous liquids, also known to be unusually quick on these materials.

Statistics for, Death and Injury on the Roads: What Do They Tell Us about Risk and Safety Engineering?

2002 ◽  
Vol 75 (3) ◽  
pp. 223-227
Author(s):  
A. H. Reinhardt-Rutland
Keyword(s):  
Present Article ◽  
Water Repellent ◽  
Safety Engineering ◽  
Seat Belts ◽  
Crucial Issue ◽  
Road Surfaces ◽  
The Relationship

A reasonable strategy for reducing road casualties should reside in safety engineering: seat-belts; airbags; ABS brakes; water-repellent road-surfaces; and the like. Yet, for some time there have been rumblings about whether engineering initiatives are ever effective over the long term. One crucial issue that has emerged concerns the interpretation of trends in casualty rates; the present article is directed primarily to this issue and, specifically, to what appears to be a paradox in the relationship between death and injury statistics.

Research on the Flight Status of Badminton Based on the Method of Mechanics Analysis

2012 ◽  
Vol 507 ◽  
pp. 246-251
Author(s):  
Xiao Liang Xie ◽  
Kun Jiang
Keyword(s):  
Research Method ◽  
Terminal Velocity ◽  
Measured Data ◽  
Motion Equation ◽  
Movement Trajectory ◽  
Flight Trajectory ◽  
Motion Equations ◽  
Air Resistance ◽  
Mechanics Analysis ◽  
The Relationship

The main purpose of this research is to establish and validate the flight movement equation of a badminton, and found the relationship between the velocity of badminton and the air resistance. The research method is based on the motion laws of aerodynamics,which establish a motion equation of flight trajectory under the influence of the gravity and air resistance by applying the theory of aerodynamics. The results show that the motion equations of flight trajectory of a badminton can be determined through the structure of terminal velocity,and the measured data is quite good fitting with the prediction of badminton movement trajectory. Findings also show, the resistance is proportional to the square of the badminton's speed. In addition, the angle and intensity of the wind may affect the trajectory.

scholarly journals Wing loading, not terminal velocity, is the best parameter to predict capacity of diaspores for secondary wind dispersal

2020 ◽  
Vol 71 (14) ◽  
pp. 4298-4307 ◽  
Author(s):  
Wei Liang ◽  
Zhimin Liu ◽  
Minghu Liu ◽  
Xuanping Qin ◽  
Carol C Baskin ◽  
...  
Keyword(s):  
Shape Index ◽  
Terminal Velocity ◽  
Wind Dispersal ◽  
Wing Loading ◽  
Dispersal Capacity ◽  
Secondary Dispersal ◽  
Lift Off ◽  
Best Parameter ◽  
The Relationship ◽  
Primary Dispersal

Abstract Lift-off velocity may be the most useful surrogate to measure the secondary dispersal capacity of diaspores. However, the most important diaspore attribute determining diaspore lift-off velocity is unclear. Furthermore, it is not known whether terminal velocity used to characterize the primary dispersal capacity of diaspores can also be used to predict their secondary wind dispersal capacity. Here, we investigate how diaspore attributes are related to lift-off velocity. Thirty-six species with diaspores differing in mass, shape index, projected area, wing loading, and terminal velocity were used in a wind tunnel to determine the relationship between diaspore attributes and lift-off velocity. We found that diaspore attributes largely explained the variation in lift-off velocity, and wing loading, not terminal velocity, was the best parameter for predicting lift-off velocity of diaspores during secondary wind dispersal. The relative importance of diaspore attributes in determining lift-off velocity was modified by both upwind and downwind slope directions and type of diaspore appendage. These findings allow us to predict diaspore dispersal behaviors using readily available diaspore functional attributes, and they indicate that wing loading is the best proxy for estimating the capacity for secondary dispersal by wind.

scholarly journals Effect of Vertical Air Motion on Disdrometer Derived Z-R Coefficients

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 77
Author(s):  
Silas Michaelides ◽  
John Lane ◽  
Takis Kasparis
Keyword(s):  
Vertical Velocity ◽  
Terminal Velocity ◽  
Radiosonde Data ◽  
Radiosonde Station ◽  
Data Points ◽  
Similar Appearance ◽  
Air Speed ◽  
Drop Size Distributions ◽  
The Relationship ◽  
Air Effect

For synoptic-scale motions the vertical velocity component is typically of the order of a few centimeters per second. In general, the vertical velocity is not measured directly but must be inferred from other meteorological fields that are measured directly. In the present study, a Joss–Waldvogel disdrometer was used in order to establish the drop size distributions (DSD) at Athalassa, Cyprus. Data from a radiosonde station co-located with the disdrometer were also collected which were subsequently used to derive estimates of vertical velocities. Meteorological fields, including vertical velocities, were extracted from an atmospheric reanalysis, for an area centered over the disdrometer and radiosonde station instrumentation. The disdrometer data were used to determine the Z-R disdrometer derived coefficients, A and b, where Z = A Rb. To model the vertical air effect on the Z-R disdrometer derived coefficients an idealistic notion of flux conservation of the DSD is adopted. This adjusted DSD (FCM-DSD) is based on the exponential DSD and is modified by the relationship between drop terminal velocity (D) and vertical air speed w . The FCM-DSD has a similar appearance to the popular gamma DSD for w < 0. A clear segregation is seen in the A-w plane for both data and model. The data points are also clearly segregated in the b- w plane, but the model points are on opposite sides of the w = 0 line. It is also demonstrated that vertical velocities can be extracted from radiosonde data if initial balloon volume is accurately measured, along with an accurate measurement of the mass of the complete radiosonde-balloon system. To accomplish this, vertical velocities from radiosonde data were compared to reanalysis vertical velocity fields. The resulting values of initial balloon volume are found to be within the range of measured values.

scholarly journals Refinements in the Treatment of Ice Particle Terminal Velocities, Highlighting Aggregates

2005 ◽  
Vol 62 (5) ◽  
pp. 1637-1644 ◽  
Author(s):  
David L. Mitchell ◽  
Andrew J. Heymsfield
Keyword(s):  
Doppler Radar ◽  
Terminal Velocity ◽  
Current Theory ◽  
Cloud Base ◽  
Ice Crystal ◽  
Rigid Spheres ◽  
Liquid Drops ◽  
Accurate Treatment ◽  
Radar Measurements ◽  
The Relationship

Abstract Recent work on the terminal velocity of ice crystal aggregates suggests that their “Re–X” relationship may not be well predicted by current theory. This study examines possible reasons for this departure from theory, and develops a new Re–X relationship appropriate for ice crystal aggregates. The methodology of Khvorostyanov and Curry was applied to this new relationship to formulate power-law expressions for all ice particle types. Fall speed differences between the Khvorostyanov and Curry approach and the approach described here were as large as 50% for aggregates and 30% for single crystals. This was primarily due to the following: 1) surface roughness coefficients used in the former were appropriate for rigid spheres and liquid drops but not for ice crystals and 2) the relationship between Reynolds number Re and Best number X at high Re is better described for aggregates by adding a second term to the Re–X governing equation, as done in this work. The corrections and improvements described here may be critical to the calculation of snowfall rates, to the modeling of the aggregation process, and for interpreting Doppler radar measurements during snowfall events. Since most of the size distribution mass is generally associated with aggregates below cloud base, an accurate treatment of aggregate fall speeds is needed for determining snowfall rates.

scholarly journals Mass Exchange of Water and Soil on the Soil Surface in the Rainfall Splash Erosion

2021 ◽  
Vol 9 ◽  
Author(s):  
Sun Sanxiang ◽  
Zhang Yunxia ◽  
Lei Pengshui
Keyword(s):  
Kinetic Energy ◽  
Mass Exchange ◽  
Soil Surface ◽  
Terminal Velocity ◽  
Erosion Process ◽  
Liquid Drops ◽  
Splash Erosion ◽  
The Impact ◽  
The Relationship ◽  
Soil Interface

This research aims to unfold the mass exchange mechanism of water and soil on the soil surface in the rainfall splash erosion process. We regard the rainfall splash erosion process as a collision process between the raindrop and the soil particle on the soil interface. This recognition allows us to incorporate research approaches from the spring vibrator model, which has been developed for simulating the impact of liquid drops on solid surface. We further argue that because a same set of factors determine the splash amount and infiltration amount and it is relatively simpler to observe the infiltration amount, an investigation into the relationship between the splash amount and infiltration amount would be able to provide a new channel for quantifying the splash erosion. This recognition leads us to examining the relationship between single raindrop, rainfall kinetic energy and splash erosion from both theoretical and empirical angles, with an emphasis on the relationship between the infiltration amount and the splash erosion. Such an investigation would add value to the collective effort to establish mass exchange law in water-soil interface during rainfall splash erosion. It is found that during the rainfall splash process, the splash erosion is proportional to the rainfall kinetic energy; and has a linear relation to the infiltration amount, with the rainfall intensity as one of important parameters and the slope depending on the unit conversation of the infiltration amount and the splash erosion. If the units of two items are same, the slope is the ratio of the soil and water density, and the splash erosion velocity of the rainfall is half of the rainfall terminal velocity. The single raindrop kinetic energy and the splash erosion have a quadratic parabola relation, and the splash velocity is about 1/3 of single raindrop terminal velocity.

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