The isothermal evolution of a shock-filament interaction

ABSTRACT Studies of filamentary structures that are prevalent throughout the interstellar medium are of great significance to a number of astrophysical fields. Here, we present 3D hydrodynamic simulations of shock-filament interactions where the equation of state has been softened to become almost isothermal. We investigate the effect of such an isothermal regime on the interaction (where both the shock and filament are isothermal), and we examine how the nature of the interaction changes when the orientation of the filament, the shock Mach number, and the filament density contrast are varied. We find that only sideways-oriented filaments with a density contrast of 102 form a three-rolled structure, dissimilar to the results of a previous study. Moreover, the angle of orientation of the filament plays a large role in the evolution of the filament morphology: the greater the angle of orientation, the longer and less turbulent the wake. Turbulent stripping of filament material leading to fragmentation of the core occurs in most filaments; however, filaments orientated at an angle of 85° to the shock front do not fragment and are longer lived. In addition, values of the drag time are influenced by the filament length, with longer filaments being accelerated faster than shorter ones. Furthermore, filaments in an isothermal regime exhibit faster acceleration than those struck by an adiabatic shock. Finally, we find that the drag and mixing times of the filament increase as the angle of orientation of the filament is increased.

МОДЕЛЮВАННЯ ІЗОТЕРМІЧНОГО РЕАКТОРА ДЛЯ НАСИЧЕННЯ САХАРОЗОЮ ЦУКАТІВ З ГАРБУЗА

Універсальна моделююча програма ChemCad дозволяє провести моделювання процесу насичення плодів гарбуза цукром. Результати моделювання дають можливість здійснення технологічного процесу з мінімальними енергозатратами та максимальним збереженням поживних речовин в готовому продукті, в якому єдиним консервантом буде цукор.За допомогою універсальної моделюючої програми ChemСad був змодельований ізотермічний реактор насичення частинок гарбуза цукром, який працює за умов постійної концентрації сахарози в сиропі і одночасним збільшенням концентрації сахарози в цукатах. Такий процес був змодельований стаціонарним з інтенсивним перемішуванням, працює в ізотермічному режимі і в якому кількість випаруваної води компенсує кількість виділеної води з цукату.Для моделювання необхідно було попередньо шляхом аналізу математичного опису знайти умови реалізації ізотермічного режиму, розробити математичне забезпечення для проектування реактора.Отримані числові значення результату моделювання, розрахункові та графічні залежності насичення цукатів сахарозою та проаналізовані отримані результати. Доведено, що проводити процес насичення цукатів цукром в стаціонарному режимі доцільно, з точки зору збереження органолептичних властивостей, оптимального насичення цукату, який буде довго зберігати свої властивості і не пліснявіти. ChemCad's universal simulator allows you to simulate the process of saturation of pumpkin fruit with sugar. The simulation results allow the implementation of a technological process with minimal energy consumption and maximum preservation of nutrients in the finished product, in which the only preservative is sugar. With the help of the universal simulation program ChemСad, an isothermal saturation reactor for sugar pumpkin particles was modeled, which operates under the constant concentration of sucrose in syrup and simultaneously increases the concentration of sucrose in candied fruits.Such a process was modeled by stationary with intense mixing, operating in isothermal mode and in which amount of evaporated water compensates for the amount of water extracted from candied fruit. For simulation, it was necessary to pre-analyze the mathematical description of the conditions for the implementation of the isothermal regime, to develop a mathematical support for the design of the reactor.For simulation, it was necessary to pre-analyze the mathematical description of the conditions for the implementation of the isothermal regime, to develop a mathematical support for the design of the reactor to include:- determination of the constant concentration of sugar in vaporized syrup at the end of the process, the flow of solution and vapor;- duration of sucrose saturation under stationary conditions;- definition of reactor design characteristics, diameter height and height of the liquid;Numerical simulation values, graphical and computational relationships are obtained, the result is analyzed.It is proved that the process of saturation of succulents with sugar in the steady state is advisable, in terms of preservation of organoleptic properties, optimum saturation of candied fruit, which will retain its properties and molds for a long time.

A model of isotropic damage with strain-gradient effects: existence and uniqueness of weak solutions for progressive damage processes

We propose a linearized model for isotropic damage with strain-gradient effects in the small-strain isothermal regime. We account for pressure-confinement effects induced by spatial variations of volume changes, which might locally determine a self-healing-type behavior. We prove the existence and uniqueness of weak solutions under conditions of progressive damage.

The history effect in bubble growth and dissolution. Part 1. Theory

The term ‘history effect’ refers to the contribution of any past mass transfer events between a gas bubble and its liquid surroundings towards the current diffusion-driven growth or dissolution dynamics of that same bubble. The history effect arises from the (non-instantaneous) development of the dissolved gas concentration boundary layer in the liquid in response to changes in the concentration at the bubble interface caused, for instance, by variations of the ambient pressure in time. Essentially, the history effect amounts to the acknowledgement that at any given time the mass flux across the bubble is conditioned by the preceding time history of the concentration at the bubble boundary. Considering the canonical problem of an isolated spherical bubble at rest, we show that the contribution of the history effect in the current interfacial concentration gradient is fully contained within a memory integral of the interface concentration. Retaining this integral term, we formulate a governing differential equation for the bubble dynamics, analogous to the well-known Epstein–Plesset solution. Our equation does not make use of the quasi-static radius approximation. An analytical solution is presented for the case of multiple step-like jumps in pressure. The nature and relevance of the history effect is then assessed through illustrative examples. Finally, we investigate the role of the history effect in rectified diffusion for a bubble that pulsates under harmonic pressure forcing in the non-inertial, isothermal regime.

Influence of Limited Efficiency and Competition of Vacancy Sinks/Sources on the Diffusion-Controlled Intermediate Phase Growth

Kinetics and structural evolution of the intermediate phase layer formation during reactive diffusion is revisited. Main new input is an account of limited efficiency of vacancy sinks/sources at the moving interfaces and in the bulk, leading to nonequilibrium vacancy concentration gradients. Competition of the two types of vacancy sinks/sources is studied – K-sinks (providing Kirkendall lattice shift) and F-sinks (Frenkel-Kirkendall voids formation). Reactive diffusion with limited vacancy sources/sinks power in isothermal regime as well as in adiabatic SHS-regime is considered.

Preparation and Crystallization Kinetics of FeSiB Amorphous Ribbons under Non-Isothermal Regime

The aim of the present work was the preparation and characterization of FeSiB amorphous magnetic ribbons with the following chemical composition: Fe80SixB20-x, x=5,6,8 and Fe75Si15B10. Differential Scanning Calorimetry was employed in order to study the thermal stability and structural changes during the transformations that took place. Much emphasis is placed on the analysis of the crystallization kinetics.

Investigation of sintering in electroceramics by thermodilatometry

Solid-state sintering was investigated in electroceramic samples using thermodilatometric measurements. The samples were studied in the isothermal regime at the temperatures 500, 600, 700, 800, 900, 1000 and 1050?C. The relative expansion was measured for a period of 8 h. At a given temperature a dominant diffusion mechanism for the sintering process was determined, and the corresponding porosity together with the pore size distribution was also measured.