Experimental Methods of Investigating Airborne Indoor Virus-Transmissions Adapted to Several Ventilation Measures

This study introduces a principle, which unifies two experimental methods for airborne indoor virus-transmissions adapted to several ventilation measures. A first-time comparison of mechanical/natural ventilation and air purifiers with regard to infection risks is achieved. Effortful computational fluid dynamics demand detailed boundary conditions for accurate calculations of indoor airflows, which are often unknown. Hence a suitable, simple and generalized experimental set up for identifying the spatial and temporal infection risk for different ventilation measures is required. A trace gas method is suitable for mechanical and natural ventilation with outdoor air exchange. For an accurate assessment of air purifiers based on filtration a surrogate particle method is appropriate. The release of a controlled rate of either trace gas or particles simulates an infectious person releasing virus material. Surrounding substance concentration measurements identify the neighborhood exposure. One key aspect of the study is to prove that the requirement of concordant results of both methods is fulfilled. This is the only way to ensure that the comparison of different ventilation measures described above is reliable. Two examples (a two person office, several classrooms) show how practical both methods are and how the principle is applicable for different types and sizes of rooms.

On modelling of thermodynamic interaction of particles suspended in two-dimensional medium

Analytical description of temperature distribution in a medium with foreign inclusions is difficult due to the complicated geometry of the problem, so asymptotic and numerical methods are usually used to model thermodynamic processes in heterogeneous media. To be convinced in convergence of these methods the authors consider model problem about two identical round particles in infinite planar medium with temperature gradient which is constant at infinity. Authors refine multipole expansion of the solution obtained earlier by continuing it up to higher powers of small parameter, that is nondimensional radius of thermodynamically interacting particles. Numerical approach to the problem using ANSYS software is described; in particular, appropriate choice of approximate boundary conditions is discussed. Authors ascertain that replacement of infinite medium by finite-sized domain is important source of error in FEM. To find domain boundaries in multiple inclusions’ problem the authors develop “fictituous particle” method; according to it the cloud of particles far from the center of the cloud acts approximately as a single equivalent particle of greater size and so may be replaced by it. Basing on particular quantitative data the dependence of domain size that provides acceptable accuracy on thermal conductivities of medium and of particles is explored. Authors establish series of numerical experiments confirming convergence of multipole expansions method and FEM as well; proximity of their results is illustrated, too.

Investigation of the microstructure and thermo-mechanical properties of functionally graded materials fabricated by the vibrating centrifugal solid particle method

In this research, SiC/Al A413.1 functionally graded materials (FGMs) were fabricated by the vibrating centrifugal solid particle method (VCSPM), and the effects of the SiC particles on the microstructure and thermo-mechanical properties of an A413.1 aluminium alloy were investigated. The benefits of a vibration during centrifugal casting of FGMs are illustrated. After designing and fabricating the centrifugal casting machine, cylindrical FGM specimens were produced using the centrifugal solid particle method (CSPM) and VCSPM. This study used SiC particles with an average particle size from 50 to 62 μm as reinforcements to fabricate A413.1-10 wt% SiC functionally gradient composites at three annular mould speeds (900–1500 and 2100 rpm) and with or without a vibration of the mould. The Brinell hardness was measured; the yield strength (YS), ultimate tensile strength (UTS) and Young’s modulus (E) were determined by tensile testing; the density was determined by the Archimedes method; and the thermal expansion coefficients were measured with a dilatometer. A comparison of the samples produced by the conventional method and VCSPM shows a significant reduction in the porosity and an increase in the distribution gradient of the reinforcing particles for the VCSPM case. It can be concluded that in both processes, the mechanical and thermal properties improved in most cases by moving from the inner radius to the outer radius because of the movement of particles towards the outer radius from the centrifugal force. The results also show that the use of a vibration dramatically increased the rate and speed of migration of gas bubbles towards the inner radius, and the mechanical properties (hardness, YS, UTS and E) improved by moving from the inner to outer radius due to an increase in the percentage of silicon carbide particles. Upon increasing the velocity and using the VCSPM, the slope of these changes becomes steeper than those for the vibration-free mode and at low rotation speeds.

Particle dynamics in drying colloidal solution using discrete particle method

We study particle dynamics in drying colloidal solutions using the numerical simulation with discrete particle method (DPM). Simulations of two different systems were conducted; the drying dynamics of monodispersed and binary mixture of colloidal solution, and compared with those from the previous studies. In the monodispersed colloidal solution, the time evolution of particle concentration profile for varying Péclet number was simulated with the same initial particle concentration. In the binary colloidal solution, when the particle size ratio α is 3, three different stratification modes were observed varying Péclet number and initial particle concentration. By comparison, our method was in a good agreement with the existing methods. Additionally, because of the mesh-based Eulerian approach in our model, other various multi-physical phenomena, such as effect of thermal Marangoni or chemical reaction, can be included in an easy way. From the results, we expect that this work can provide a physical insight for predicting the quality of colloidal drying in a complicated situation.

Modeling of the impact of a shock wave on port infrastructure facilities

Факты возникновения аварийных и катастрофических состояний портовой инфраструктуры при погрузке (выгрузке) взрывчатых веществ свидетельствуют о наличии проблемы связанной с построением системы обеспечения безопасности при грузовых операциях и мест их складирования. Неправильно выбранные: место, техническое сопровождение и организация погрузки взрывчатых веществ, в определенных условиях становятся причинами возникновения катастрофических ситуаций разного уровня опасности. При моделировании ситуаций рассматривается использование метода крупных частиц и теории точечного взрыва при воздействии ударной волны на объекты портовой инфраструктуры. Математическая модель метода заключается в разделении по физическим процессам исходной нестационарной системы уравнений Эйлера, записанной в форме законов сохранения. Процесс вычислений состоит из многократных итераций, каждая из которых содержит три этапа. Основанием для разработки программы является необходимость компьютерного моделирования процесса возникновения и развития ударной волны в условиях сложного рельефа местности, вызванной подрывом заряда конденсированного взрывчатого вещества. Автор считает, что такой подход существенно улучшит скорость и качество оценки безопасности выбранной системы погрузки (выгрузки) взрывоопасных и взрывчатых веществ, потенциальных рисков возникновения различных катастрофических состояний, и прогноза сценария их развития. The facts of the occurrence of emergency and catastrophic conditions of the port infrastructure during the loading (unloading) of explosives indicate the existence of a problem associated with the construction of a security system for cargo operations and their storage locations. Incorrectly chosen: location, technical support and organization of loading of explosives, under certain conditions, become the causes of catastrophic situations of different levels of danger. When modeling situations, the use of the large particle method and the theory of a point explosion under the impact of a shock wave on port infrastructure facilities is considered. The mathematical model of the method consists in the separation by physical processes of the initial non-stationary system of Euler equations, written in the form of conservation laws. The calculation process consists of multiple iterations, each of which contains three stages. The basis for the development of the program is the need for computer modeling of the process of the occurrence and development of a shock wave in a complex terrain caused by the detonation of a charge of a condensed explosive. The author believes that such an approach will significantly improve the speed and quality of the safety assessment of the selected system of loading (unloading) of explosive and explosive substances, the potential risks of various catastrophic conditions, and the forecast of their development scenario.