جستجوی مقالات مرتبط با کلیدواژه « Level set Method » در نشریات گروه « مکانیک »

Since deterministic topology optimization (TO) does not consider the uncertainties in the structure, including materials, loading and geometric dimensions, it may provide the optimal designs with the lowest state of reliability and safety. To  solve this problem, reliability-based topology optimization (RBTO) is used, which is actually a combination of TO methods with reliability-based design methods (RBDO) based on a mathematical framework and process. In this article, by considering four TO methods including moving iso-surface threshold (MIST), SIMP, evolutionary structural optimization-extended finite element (XFEM-ESO) and level-set (LS), and considering a constraint or objective function, an optimal volume fraction (Vf) is obtained for TO by the bisection method. Then, with the aid of mean volume fraction, TO is performed and its optimized results are applied by an advanced reliability analysis method, i.e. accelerated dynamical mean value (ADMV), taking into account the uncertainties and their standard deviations to extract the most probable probability point (MPP). Having the MPP and the constraint, the bisection algorithm is used again and the optimized volume fraction for the RBTO model, and thereby the optimal layout for the RBTO solution, is achieved. Several examples are presented to validate and highlight the optimization capability of the RBTO method using a structural model and the mentioned TO methods, and the results are compared together. Based on the results, it is shown that the combination of RBDO and TO approach is able to result in powerful, stable, safe, and reliable structures completely different from the TO results.

In this research, hydrodynamic behavior of a leaky dielectric droplet under an electric field is simulated. The level set method is used for interface tracking and the ghost fluid method is used for modeling discontinuous quantities at interface. Using Taylor’s leaky dielectric model, electric field and electric force at the interface is calculated. Simulation results show the droplet deformation and induced flows inside and outside the droplet under an electric field. Droplet deformation dependent on the electric conductivity and electric permittivity ratio of droplet and surrounding fluid can be as elongation in electric field direction or perpendicular to it. The effect of electric conductivity ratio and viscosity ratio on hydrodynamic behavior of droplet is studied. According to the results, increase in these quantities increases the deformation of droplet. Also, the enhancement rate of droplet deformation is decreased by enhancement of electric conductivity ratio and viscosity ratio.

Injection of a liquid into another immiscible liquid and its breakup and formation of droplets has a basic importance in many industrial processes such as liquid-liquid extraction. In this study, liquid spraying process and drop formation in the dripping mode is simulated using a sharp interface method and effect of important parameters on this process such as Weber number, Ohnesorge number and Bond number is investigated. The level set method is used for interface tracking. Some quantities such as pressure and fluid properties are discontinuous across interface. In this research, discontinuities at the interface are imposed using the ghost fluid method. It is observed that by increasing Weber number (from 0.0027 to 0.1875), the length of the outlet liquid is increased about 7 percent and the liquid breakup time is decreased about 52 percent. Also, at higher Weber numbers, the liquid return toward nozzle after droplet detachment is less. Increasing Ohnesorge number (from 0.0002 to 0.189) increases the length of the outlet liquid about 21 percent and breakup time about 151 percent. Also, at higher Ohnesorge numbers, the liquid return toward nozzle is higher. Increasing Bond number (from 7 to 39) leads to the reduction of the length of the outlet liquid and breakup time about 26 and 91 percent, respectively. Also, at higher Bond numbers, the liquid return toward nozzle is less. Another considerable result is the reduction of the size of formed droplets by enhancement of Bond number.

The encounter between bubble pairs can be happened in the bubble flows and may result in coalescence, which is one of the most important elementary physical processes occurring in liquid columns. Sufficient knowledge of the coalescence process of two bubbles can lead to a better description of the bubbly flow’s behavior. Effects of uniform magnetic fields on the interactions and coalescence of dielectric bubbles were not studied up to now; therefore in this research, interactions and coalescence of two bubbles in a viscous stagnant liquid has been simulated numerically. Considered bubbles are spherical and fluids are stagnant, initially. Both liquid and gas phases considered being incompressible and dielectric where applied magnetic field is uniform. In the numerical simulation of the problem, the Finite Volume method was applied using the SIMPLE algorithm to discretizing the governing equations while the finite difference method was used for discretizing of the magnetic field equation. For simulating the interface of two phases, the level set method has been incorporated. The results outlined in the present study well agree with the existing experimental and numerical results. Obtained results show that applied uniform magnetic field affects shape, dynamics and also interactions and coalescence of bubble pairs. Applied magnetic field enhances coalescence between in-line rising bubbles. Therefore, the external uniform magnetic field could be used for contactless control of the coalescence process between bubbles.