Экспериментальное и теоретическое исследование высокоскоростного проникания длинных стержневых ударников в песок

Results of computations with the use of improved modified Alekseevskii-Tate theory (IMATT) are compared to experimental data on high-velocity penetration of long rod projectiles into sand in the impact velocity range of V0=0.5-3.5 km/s. Projectiles were made of three different metals: M1 copper, WNZh tungsten heavy alloy and 30KhGSA steel. The value of hardening coefficient k in the linear dependence of the projectile material yield on pressure could be determined using IMATT and experimental data on dependence of differential penetration coefficient K on the penetration velocity. At penetration in regime of the hydrodynamic erosion of projectile, differential penetration coefficient K could be approximated just by dependence on the ratio of the impact velocity of penetration to the value of the critical velocity, above which the projectile deforms plastically during penetration. The values of the critical velocity may differ for specific projectile material properties as well as the density and the humidity of sand.

Research of Operational Properties of Household Fabrics for Production of Protective Masks

Experimental studies have been conducted to determine the operational properties of fabrics used for the manufacture of protective masks. For the experimental study, 22 different fabrics were used, which are available in everyday life. Determination of the operational properties was carried out according to three indicators: the penetration coefficient of the test aerosol, paraffin oil (filtering property), breathing resistance (ergonomic property), resistance to dusting (protective action period) in accordance with the requirements of DSTU EN 149-2017 standard. According to the results of the experimental study to determine the operational properties of fabrics: breathing resistance, penetration coefficient and resistance to dust, it was found that out of the twenty-two samples tested, only eight can be used for the manufacture of protective masks, since their characteristics are able to provide a sufficient level of protection from minimal physiological impact on human (wool, two-thread cloth, velor, tricotin, jersey, frieze and satin). Theoretical calculation of the operational properties of protective masks, which can be made of these fabrics, based on experimental data allowed to make their compliance with the first class of protection according to the requirements of DSTU EN 149-2017. The scientific novelty is to clarify the relationship between the operational properties of fabrics and the operational properties of protective masks.

A mathematical model for predicting indoor PM2.5 concentration under different ventilation methods in residential buildings

Experiments and theoretical analyses are conducted in a residential building in Changzhou to study indoor PM2.5 concentrations by establishing a combined parameter model. An alternative method for predicting the particle deposition rate and penetration coefficient is proposed, and its accuracy is tested and verified by experiments using time-dependent concentrations and air exchange rate measurements. The predicted PM2.5 penetration coefficient increased from 0.70 to 0.88 when the air exchange rates were varied from 0.2 h−1 to 0.5 h−1. In addition, outdoor sources of PM2.5 dominantly contributed approximately 90% to 98% to the indoor concentrations for both mechanically and naturally ventilated structures. Finally, a mathematical model for predicting the indoor concentration is presented using a mass balance equation, which estimates the parameter values in the building. The indoor PM2.5 concentrations ranged from 40 to 46 µg/m3 by using a fresh air system with 82% filtration efficiency, while those by using open windows for natural ventilation ranged from 105 to 118 µg/m3 when the outdoor PM2.5 concentration ranged from 115 to 137 µg/m3. The results of this study can be used to estimate the indoor particle level. Practical application: By applying the ventilation criteria for acceptable indoor air quality in ASHRAE Standard 62.1, the indoor PM2.5 monitoring results show serious pollution in dwellings in 2018. More dwellings are expected to maintain a clean indoor environment in the future. Thus, it is crucial to consider the indoor PM2.5 pollution risk in the building design to prevent the possible consequences of unsafe high indoor concentrations. The use of this prediction model, as discussed in this article, will provide further information on the influence of the particle deposition rate ( K) and penetration coefficient ( P) on indoor PM2.5 concentrations.

Protective Efficiency of Filtering Respirators

In the article the dependence of protective efficiency of the respiratory protective devices on the filter penetration coefficient and leakage of the polluted air through sealing band was established. The leakage was determined by the ratio of the filter resistance and the sealing band. The relationship between increasing the filter resistance and worsening the protective effectiveness of respiratory protective device was established. Factors that worsen the respirator quality were determined: the gaps between the face and half-mask, weak tension of the head harness. Filter parameters that will ensure high efficiency for respirators of the second protection class were established.