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Long-term exposure to high concentrations of fine particulate matter (PM2.5) in the atmosphere has negative impact on the long-term health effect of human beings. Traditional air filtration materials are difficult to take into account the high-efficiency and low-resistance protection, and are non-degradable, which not only aggravates global plastic pollution, but also tends to cause stronger microplastics hazards. To solve the problems above-mentioned, self-powered and biodegradable nanofibrous membranes with air slip effect are developed to achieve a long-term and low-resistance respiratory protection. A two-step hydrothermal method is proposed to prepare the easily dispersed BTO dielectric with an average particle size of 49.6 nm, then the BTO nanoparticles (BTO NPs) are embedded into the PLA nanofibrous membranes by a combined “electrospinning‒electrospray” strategy. The frictional electricity effect and size effect of BTO NPs are utilized to simultaneously regulate the filtration efficiency and resistance of nanofibrous membranes. By controlling the concentration of BTO NPs in spraying suspension, the relationship between it and electroactivity, filtration properties and mechanical properties of PLA/BTO nanofibrous membranes is investigated. Microstructure characterization and performance testing show that the PLA/BTO nanofibrous membranes have excellent electroactivity, filtration properties and mechanical properties. The surface potential of PLA/BTO nanofibrous membranes is up to 5.9 kV, the dielectric constant is up to 1.20 F/m, and the average output voltage is up to 12.4 V. Benefiting from the enhanced slip effect and increased electroactivity, the electrospun-electrosprayed PLA/BTO10 nanofibrous membrane could significantly reduce air resistance (as low as 20 Pa), while improving the filtration efficiency of PM0.3 by 7.78%−9.05% and the filtration efficiency of PM2.5 by 2.90%−13.19%. Even at the high airflow velocity of 85 L/min, the filtration efficiency of PM2.5 still achieves as high as 97.25%. At the same time, the increase of tensile strength of PLA/BTO nanofibrous membranes is up to 60% (22.5 MPa), the increase of elongation at break is up to 68% (25%), and the fracture toughness increases by 1.3 times (3.6 MJ/m3). Therefore, the proposed degradable PLA/BTO nanofibrous membrane filters with long-term and low-resistance filtration properties have some broad application prospects in the field of respiratory protection, and also provide a new approach to alleviate the plastic pollution exacerbated by discarded masks.

The results of the analysis of the influence of the aerodynamic characteristics of the road train on its fuel efficiency are presented. Based on the analysis of known studies, the power balance equation and the known equation of road fuel consumption, it is shown that air resistance has a significant effect on fuel economy indicators. Through the analysis of the air resistance equation and taking into account known studies, it was concluded that one of the key parameters that affect the aerodynamics of the road train is the distance between the cab and the semi-trailer. The results of computer modeling of the aerodynamics of a two-track road train are presented. Based on the proposed model, it is shown that the distance between the cabin and the semi-trailer has a non-linear effect on the total air resistance expressed through the reduced pressure. On the basis of this, an assumption was made about the possibility of optimizing the specified distance according to the criterion of minimum air resistance. It has been established that the use of such technologies as aerodynamic panels can significantly improve the aerodynamic characteristics of a road train, which, in turn, will have a positive effect on fuel economy and other operational characteristics of the road train. A real example of how a decrease in the coefficient of ease of movement, which also takes into account air resistance, affects fuel consumption. It is shown that a decrease in the coefficient of ease of movement by only 0.04 units leads to a decrease in fuel consumption by 11%. It was concluded that the influence of the geometry of the road train, namely the distance between the cab and the semi-trailer, on the indicators of aerodynamics and fuel efficiency requires further research both by computer modeling and by researching physical models of road trains in a wind tunnel.

The present study was designed to determine the contribution of the cross-sectional area of the ski poles (Sp) to the total aerodynamic drag during alpine skiing. At three different wind speeds in a wind tunnel, 10 skiers assumed typical alpine skiing postures (high, middle, and tuck), and their frontal aerodynamic drag was assessed with a force plate and their cross-sectional area, along with that of their ski poles, determined by interactive image segmentation. The data collected were utilized to examine intra-subject variation in Sp, the effects of Sp on the coefficient of aerodynamic drag (Cd), and the product of Cd and total cross-sectional area (Cd∙S. The major findings were as follows: (i) Sp ranged from 0.0067 (tuck position) to 0.0262 m2 (middle position), contributing 2.2–4.8% of the total cross-sectional area, respectively; (ii) Sp was dependent on wind speed in the high and middle positions; (iii) intra-subject variations ranged from 0.0018 m2 (27.6%) in the tuck position to 0.0072 m2 (30.5%) in the high position; (iv) Sp exerted a likely effect on Cd and Cd∙S. The extensive intra- and inter-skier variability in Sp can account for as much as ~5% of the total frontal cross-sectional area and future investigations on how elite skiers optimize their positioning of the poles in a manner that reduces aerodynamic drag are warranted.

When the planing hull is sailing at high speed, the proportion of air resistance to the total resistance increases significantly. Therefore, by studying the aerodynamic characteristics of the planing hull shape, we can analyze the influence of the hull shape on the aerodynamic performance of the planing hull, and find a method to reduce the proportion of air resistance. The research took the planing trimaran as the research object, completed the wind tunnel test, and established the numerical simulation method by solving the RANS equation and combining the k-ε turbulence model. Combined with the wind tunnel test data, the calculation accuracy of the computational fluid dynamics (CFD) method was judged. Then, four superstructure shapes and two tail shapes were simulated by the CFD method, and the characteristics of the air resistance and airflow field of several drag reduction schemes with a volume Froude number between 7.00–17.51 were analyzed. The research focuses on the aerodynamic force of the planing hull. The results show that the circular arc stern has a more obvious drag reduction effect than the square stern, and the streamlined mid-arched superstructure has certain advantages in the drag reduction effect.

In terms of speed lost and fuel consumed, wind loads are considered one of the main factors for large ship design, especially for container ships. Alongside water resistance, air resistance in strong wind conditions has a significant impact on the fuel efficiency and performance of container ships with large box-type bodies. This paper reports the effects of wind loads acting on a 20,000 TEU container ship carrying large numbers of deck containers using a commercial CFD software program (ANSYS Fluent V14.5 with RANS equation). A 1/255.3 scale model was used in this study to reveal the air resistance on the container ship configuration. The aerodynamic formations of the complex vortices, pressure, velocity contours, and streamlines, as well as the air forces acting on the container ship, are presented and discussed. The pressure distributions show that the gap air flows increase the stagnation pressure at the face side and decrease the pressure on the backside of each container gap through separate eddies. The difference in pressures created in the gaps contribute to the air resistance acting on the ship. It is confirmed that the use of side covers of deck containers to close the gap flows between container blocks can significantly reduce the air resistance for wind directions in the range of 30 to 60 degrees.

Food packaging manufacturers often resort to lamination, typically with materials which are neither non-biodegradable nor biobased polymers, to confer barrier properties to paper and cardboard. The present work considers a greener solution: enhancing paper’s resistance to moisture, grease, and air by aqueous coating suspensions. For hydrophobization, a combined approach between nanocellulose and common esterifying agents was considered, but the water vapor transmission rate (WVTR) remained excessively high for the goal of wrapping moisture-sensitive products (>600 g m−2 d−1). Nonetheless, oil-repellant surfaces were effectively obtained with nanocellulose, illite, sodium alginate, and/or poly(vinyl alcohol) (PVA), reaching Kit ratings up to 11. Regarding air resistance, mineral-rich coatings attained values above 1000 Gurley s. In light of these results, nanocellulose, minerals, PVA, pullulan, alginate, and a non-ionic surfactant were combined for multi-purpose coating formulations. It is hypothesized that these materials decrease porosity while complementing each other’s flaws, e.g., PVA succeeds at decreasing porosity but has low dimensional stability. As an example, a suspension mostly constituted by nanocellulose, sizing agents, minerals and PVA yielded a WVTR of roughly 100 g m−2 d−1, a Kit rating of 12, and an air resistance above 300 s/100 mL. This indicates that multi-purpose coatings can be satisfactorily incorporated into paper structures for food packaging applications, although not as the food contact layer.

The definition of air resistance is nonuniform when analyzing the bearing capacity, stiffness, and stability of an orifice throttling aerostatic restrictor. In this study, a capillary tube similar to the inlet section of an aerostatic restrictor is used as the research object, and the Bernoulli equation under adiabatic conditions is established. Through an experiment, the pressure and temperature of the capillary tube inlet and outlet and the flow through the capillary tube are measured. Based on the air resistance definition, the empirical formula of the coefficient k is obtained, and the theoretical air resistance of the capillary path is calculated. The relative error between the theoretical air resistance and experimental air resistance is kept within 10%. The comparison results verify the accuracy of the air resistance theory and provide a basis for the subsequent establishment of a universal definition of air resistance. Subsequently, air resistance can be used to design aerostatic bearings and help improve their characteristics.

Currently, the emission generation protocol of electronic cigarettes has only one standardized vaping regimen that is consistent with mouth-to-lungs inhalation. Recent works show the significant increase in performance of the device with the use of a direct lung vaping regimen (167 mL s−1, consistent with direct lung inhalation). However, requirements are needed for its use in a laboratory. This work aims at identifying mechanical characteristics of a device and providing a classification based on recommended power range, electrical resistance, heating surface, and air resistance of twenty-six tested devices. The electrical resistivity relation allows the estimation of the wire surface using its diameter and its length. The air resistance is obtained by measuring the pressure drop of the tested device with airflow rates ranging from 1–10 L min−1. Through the wide panel of tested devices, results allow separating them in two categories: classical and sub-ohm electronic cigarettes consistent with the two inhalation behaviours. Differences up to 71 mm2 for the wire surface and up to 4.8 Pa 0.5 min L−1 for the air resistance are observed between them. This limit seems to correspond to a required power of 25 W and an electrical resistance of 1.1 Ω.

The aim of the study was the application of high-tech wind tunnel device to identify the changes in the biokinetic parameters of running performed on the specially designed treadmill. The research was carried out in the “Planica Nordic Centre—PNC” in the wind tunnel system, where the AirRunner Assault treadmill, which was equipped with four sensors measuring the vertical and horizontal ground reaction forces, was installed. To obtain biokinetic data, the runners performed the treadmill’s run under conditions of airflow directed at each participant’s back (backwind speeds +3 m/s and +5 m/s) and the chest (headwind speeds −5 m/s and −7 m/s). The runner’s speed was measured via image analysis using a DSLR camera and markers on the belt of the treadmill. Additionally, a high-speed camera synchronised to the force acquisition system was used to analyse the contact phase via comparison of foot placement and time series of the ground reaction forces. The contact phases of the running step were found to be longer than the flight phases, with their duration ranging from 0.15 to 0.20 s and the maximum forces at take-off were found to be greater than when running with the backwind. It should be noted that the application of high-tech devices wind tunnel and treadmill were found to be sufficiently accurate to perform kinetic measurements of running parameters in changing conditions, such as resistance and assistance (facilitating).

This paper presents the impact of air resistance (air resistance) on fuel consumption of the particular vehicle under real traffic conditions. In the introductory and subsequent part of the paper, the individual resistances influencing the moving vehicle are characterized. In the following chapter, the specific factors such as air resistance, driving speed, air temperature and air resistance coefficient in the context of their impact on fuel consumption of the particular vehicle are identified and described; as well as the comparisons of fuel consumption when the vehicle is moving on the highway with closed and open windows under different conditions of road traffic are performed.

Recently, the construction of external ventilated walls has become popular for public and office buildings. These blocks are used without internal rendering because of their good interior surface, stable dimensions and various filling of masonry joints, which provide an attractive architectural appearance. However, problems with the airtightness of such walls often occur. Currently, there are no standard methods to predict the airtightness of such wall. In practice, samples of particular walls are produced, and their air permeability is measured at laboratories. For the broader use of the results of laboratory air permeability measurements, a methodology has been developed to predict the air permeability of block masonry walls using experimentally determined air flow resistances of the individual layers. The masonry from various blocks were used for the research; mineral wool boards of various air permeability were used for thermal insulation and the wind protection layer. After measuring the air resistance of the samples, the air flow resistances of walls of different construction were calculated. This study compared the calculated and measured air permeability values of different wall masonry samples and evaluated the suitability of created calculation method for prediction of the airtightness of insulated block masonry wall.

This study investigated the resistance performance of ships, using the air resistance correction method. In general, air resistance is calculated using an empirical formula rather than a direct calculation, as the effect of air resistance on the total resistance of ships is relatively smaller than that of water. However, for ships with large superstructures, such as container ships, LNG (liquefied natural gas) carriers, and car-ferries, the wind-induced effects might influence the air resistance acting on the superstructure, as well as cause attitude (trim and sinkage) changes of the ship. Therefore, this study performed numerical simulations to compare the total resistance, trim, and sinkage of an 8000 TEU-class container, ship with and without superstructures. The numerical simulation conditions were verified by comparing them with the study results of the KCS (KRISO Container Ship) hull form. In addition, the differences in the above values between the two cases were compared using the coefficients calculated by the empirical formula to identify the effects on the air resistance coefficient.

В статтье проводится выбор и обоснование аналитических функций, которые используются для описания силы сопротивления воздуха. Рассматриваются характерные участки и особенности изменения функций сопротивления воздуха в зависимосты от скорости полета снаряда, обосновывается набор аппроксимирующих функций, которые с достаточной точностю воспроизводили бы характер их изменений. Предложено в качестве аппроксимирующих функций использовать функцию ошибок и функцию Гауса. Показано, что изменение определенных характеристик аппроксимирующих функций позволяет на заданом отрезке приблизить значения их кривых к заданому значению силы сопротивления воздуха.

Planing crafts were specifically designed to achieve relatively high speeds on the water. When a planing craft is running at high speed, dynamic pressure on the bottom makes the boat rise on the surface of the water. This reduces the area of the sinking surface of the boat to increase air resistance. Air resistance means the resistance that occurs when the hull and deck house over the surface of the water come in contact with the air current. In this paper, we carried out a CFD numerical analysis to find optimal deck houses that decreased air-resistance on the water when planing crafts are running at high speed. We finally developed the deck house shape of high-speed planing crafts that optimally decreased air resistance.

A molecular kinetic model is developed for the gas-dynamic flow around a flat plate moving through the air at positive and negative angles of attack. It is shown that, at low velocities of the plate motion, the lift and the drag are determined by the gas-dynamics of the air flow in the rear region while at high velocities close to the speed of sound velocity the impact interaction between the plate and the molecules of the surrounding medium in the front region is of critical importance. No separated flow occurs behind the plate at low velocities. The conditions under which the drag and the lift of the plate reverse their directions are determined.

Wind-tunnel experiments are the most effective approaches both to elucidate the flows around runners in track-and-field athletics, and to evaluate their air resistances. In the present study, we develop a moving-belt system, and show its basic performance, such as the distributions of time-mean flow velocity and turbulent intensity above the moving-belt using a hot-wire anemometer. As a result, we have confirmed the effective improvement of the velocity distributions in terms of flow uniformity and turbulence reduction, especially near the moving-belt surface. Following, using this the developed moving-belt system, we investigate the air resistance on a runner in solo running and in duet running. For solo running, we reveal an increase in air resistance of more than 10% in comparison with the conventional result with no moving-belt system. For duet running, we reveal the optimum duet-running formation where a following runner behind a pacemaker experiences small air resistances or strong drafts.

Concerning most of track-and-field athletics such as the marathon, it is important to clarify the flow around track runners and to evaluate their air resistances (or wind resistances, drags). In wind-tunnel experiments which are the most effective approaches to such a problem as well as field observasions and numerical analyses the moving-belt system is indispensable for precise aerodynamic measurements, if the so-called “ground effect” is negligible. In the present study, we develop a moving-belt system, and show its basic performance such as the distributions of time-mean velocity and turbulent intensity above the moving-belt system using a hot-wire anemometer. Then, the authors investigate the air resistance of a runner in solo running and of a runner in duet running in various duet-running formations. Especially for duet-running formations, the authors reveal the optimum one.

The paper describes the car motion when the contact between its wheels and the road surface is lost. A simulation of such car motion was carried out using a mathematical package "Maple 6" for the two cases: 1) The car flies off a horizontal surface; 2) The car runs over a springboard. The dependencies of the main parameters of motion (velocity and distance) upon the height of the horizontal road step or upon the springboard height and its inclination angle (in the second case) were found. The work presents the graphs of these motion parameters and evaluates the influence of air resistance in both cases.

Scooters are manufactured with speed limiters. If these speed limiters are removed, the motor-scooter will exceed speed limits and break traffic rules. To determine whether the scooter exceeds the speed limit, the mobile stand for scooter’s speed metering is designed and manufactured. The loads of the scooter are calculated for various driving speeds. The testing of the stand is performed using an electric engine and the scooter. A relative speed measurement error is determined as 1.2%. The conclusion is made that the stand for scooter’s speed check can accurately determine the actual speed of the scooter. Article in Lithuanian. Motorolerio greičio patikros stendo konstravimas ir galimybių tyrimas Santrauka. Motoroleriai yra gaminami su greičio ribotuvais. Jei šie greičio ribotuvai pašalinami, motoroleris viršija leidžiamąjį greitį ir yra pažeidžiamos Kelių eismo taisyklės. Siekiant nustatyti, ar motoroleriai viršija leidžiamąjį greitį, suprojektuotas ir pagamintas mobilus motorolerio greičio patikros stendas. Buvo apskaičiuota, kokios apkrovos turi veikti motorolerį esant įvairiems važiavimo greičiams. Stendo bandymai buvo atliekami su elektros varikliu ir su motoroleriais. Santykinė motorolerio maksimalaus greičio matavimo klaida buvo nustatyta – 1,2 %. Išvada – šiuo motorolerio greičio patikrinimo stendu galima tiksliai nustatyti faktinį motorolerio greitį. Reikšminiai žodžiai: motoroleris; greičio ribotuvas; maksimalus greitis; oro priešprieša; riedėjimo priešprieša.

The paper describes the car motion when the contact between its wheels and the road surface is lost. A simulation of such car motion was carried out using a mathematical package “Maple 6†for the two cases: • The car flies off a horizontal surface; The car runs over a springboard. The dependencies of the main parameters of motion (velocity Va and distance S) upon the height H of the horizontal road step or upon the springboard height and its inclination angle (in the second case) a were found. The work presents the graphs of these motion parameters and evaluates the influence of air resistance in both cases. First Published Online: 27 Oct 2010

Resumo Os tiros de comemoração referem-se aos tiros dados para o alto por ocasião de celebrações festivas. Este é um hábito em países como o Afeganistão, Paquistão e algumas regiões da América Latina. Neste artigo, resolvemos o problema de projéteis com velocidade subsônica atirados para alto, considerando a resistência do ar. Com fins didáticos, traçamos um paralelo entre esse caso e aquele em que a resistência do ar é desprezada. Concluímos que mesmo projéteis de pequeno calibre podem ser letais na queda, apesar da diminuição da velocidade e da energia cinética.