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.

Analysis the dynamics formation of a vapor supersonic jet under outflow from thin nozzle

The dynamics formation of a vapor jet with near-critical state parameters outflowing from a high-pressure vessel through a thin nozzle is studied. The numerical modeling of this process, by using a system of model equations for gas-vapor-liquid mixture, which include conservation laws of mass, momentum, and energy of phases in accordance with one-pressure, one-velocity and two-temperature approximations, was conducted, taking into account heat and mass transfer processes of evaporation and condensation under conditions of equilibrium state with modified reactingTwoPhaseEulerFoam solver of open package OpenFOAM. The process of barrel shock formation in supersonic boiling jet with shaping Mach disk is shown. It was found that the process of boiling fluid outflow is accompanied by formation of vortex zones near axis of symmetry and leads to generation of acoustic wave pulses series preceding the main jet flow, which are the source of pulsations, observed in experiments. The justification of applied numerical method reliability is shown by comparing the computational and analytical solutions for Sedov’s problem of a point explosion in gas-water mixture at the plane case.

Supercomputer model of dynamical dusty gas with intense momentum transfer between phases based on OpenFPM library

The paper considers the solution of model gas-dynamic problems (propagation of plane sound wave, one-dimensional shock tube problem, three-dimensional problem of a point explosion in a continuous medium) in the case of a gas-dust medium. The interaction of dust and gas was taken into account using the IDIC method within the SPH method used to solve gas-dynamic equations. An important feature of the work is the use of the open computational package OpenFPM, which makes it easy to carry out parallel computations. The main advantage of this package is the ready-made (implemented by the authors of the package) and intuitive, automatically parallelizable vector data structures, the use of which is identical both in the case of calculations on a personal computer and in the case of using supercomputer resources. The paper analyzes the efficiency of parallelization of numerical solutions of the considered problems.

Does one heavy load back squat set lead to postactivation performance enhancement of three-point explosion and sprint in third division American football players?

Background American football players need the ability to provide maximal muscular power in a modicum of time. Postactivation performance enhancement (PAPE), which is characterized by an acute improvement of a performance measure following conditioning contractions, could be of value for American football players. The aim of the present study was to determine the effect of a heavy load back squat PAPE protocol on three-point explosion (TPE; an essential blocking technique and drill) and 40-yard dash (40YD) performance compared to a traditional warm-up in American football players. Methods In a crossover study design, eighteen male competitive regional league American football players (mean ± SD: body mass 93.9 ± 15.5 kg, height 181.4 ± 6.8 cm, age 24.8 ± 3.9 years) performed a TPE on a double blocking sled (weight: 150 kg) and a 40YD (36.6 m with a 5 and 10 m split) 8 min after two different warm-up conditions. One condition was a traditional, football specific warm-up (TWU) consisting of game related movements (e.g. backward lunges, lateral power steps), whereas the other condition (PAPE) consisted of three explosive back squats with a load of 91 % one-repetition maximum. Results There was no significant difference in TPE between TWU and PAPE. For the 40YD, we found significantly shorter sprint times in the PAPE condition with medium effect sizes for the 5 m (p = 0.007; r = 0.45) and 10 m (p = 0.020; r = 0.39) but not for the whole 36.6 m distance (p = 0.084; r = 0.29) compared to the TWU condition. Conclusions The used heavy load back squat PAPE protocol improved sprint performance over short distances (≤ 10 m) but not complex movements like the three-point explosion.

Comparison of the numerical and self-similar solutions of Sedov’s problem on a point explosion in gas

Comparative analysis of solutions of Sedov’s problem of a point explosion in gas for the plane case, obtained by the analytical method and using the open software package of computational fluid dynamics OpenFOAM, is carried out. A brief analysis of methods of dimensionality and similarity theory used for the analytical self-similar solution of point explosion problem in a perfect gas (nitrogen) which determined by the density of uncompressed gas, magnitude of released energy, ratio of specific heat capacities and by the index of geometry of the explosion is given. The system of one-dimensional gas dynamics equations for a perfect gas includes the laws of conservation of mass, momentum, and energy is used. It is assumed that at the initial moment of time there is a point explosion with instantaneous release of energy. Analytical self-similar solutions for the Euler and Lagrangian coordinates, mass velocity, pressure, temperature, and density in the case of plane geometry are given. The numerical simulation of considered process in sonicFoam solver of OpenFOAM package built on the PISO algorithm was performed. For numerical modeling the system of differential equations of gas dynamics is used, including the equations of continuity, Navier-Stokes motion for a compressible medium and conservation of internal energy. Initial and boundary conditions were selected in accordance with the obtained analytical solution using the setFieldsDict, blockMeshDict, and uniformFixedValue utilities. The obtained analytical and numerical solutions have a satisfactory agreement.

MODELING OF BLAST EFFECTS ON UNDERGROUND STRUCTURE

Modeling of the impact of a point explosion shock wave on a soil mass and an underground structure at different locations of the explosion epicenter from the ground surface was performed. The study of the stress- strain state of soils was carried out usi ng a nonlinear dynamic method and a fully coupled numerical model, in­cluding various models of materials. The result of numerical modeling showed the adequacy of the adopted nu­merical calculation methods. The findings showed that solving the problem in a nonlinear dynamic formulation allows obtaining the parameters of the shock wave at different depths from the explosion center, as well as ob­taining a complete picture of the interaction of the shock wave with the underground structure in surface and un­derground explosions.

Air Bubble Entrainment, Breakup, and Interplay in Vertical Plunging Jets

The entrainment, breakup, and interplay of air bubbles were observed in a vertical, two-dimensional supported jet at low impact velocities. Ultra-high-speed movies were analyzed both qualitatively and quantitatively. The onset velocity of bubble entrainment was between 0.9 and 1.1 m/s. Most bubbles were entrained as detached bubbles from elongated air cavities at the impingement point. Explosion, stretching, and dejection mechanisms were observed for individual bubble breakup, and the bubble interaction behaviors encompassed bubble rebound, “kiss-and-go,” coalescence and breakup induced by approaching bubble(s). The effects of jet impact velocity on the bubble behaviors were investigated for impact velocities from 1.0 to 1.36 m/s, in the presence of a shear flow environment.

Vibration of a Cylindrical Tunnel under a Centric Point-Source Explosion

Underground tunnels are vulnerable to terrorists’ bombing attacks, which calls for studies on tunnel’s response to internal explosive loading. In this paper, the dynamic response of a cylindrical tunnel to an ideal centric point explosion was treated as an axisymmetric 2-dimensional problem, in which the tunnel was modeled with a continuous anisotropic shell, while the ground medium’s effect was accounted for with linear elastic Winkler springs and the explosive loading described by a temporal and spatial function. The governing equation of the motion is a fourth-order partial differential equation, for which a numerical method combining finite difference with the implicit Newmark-β method was adopted. This method avoided complicated integral transform and numerical inverse transformation, thus allowing efficient parameter study. The maximum radial displacement was found on the cricle of the center of explosive, where hoop stress is the maximum principal stress. The anisotropy showed little influence on maximum hoop stress. Within the range of ground medium’s modulus, minor influence on maximum hoop stress was incurred. This research may be helpful to hazard assessment and protective design for some critical subway tunnels.