فهرست مطالب saeed tavangar roosta

Numerical methods as one of the subcategories of theoretical models can predict the behavior of energetic materials with appropriate accuracy and away of experimental tests limitations. In this investigation, computational fluid dynamics tool has been used to predict the blast wave propagation with Consideration of geometrical obstacles. Two solvers (extendedSonicFoam and blastFoam) from the open source technology module, OpenFOAM  have been used for simulations and To enhance confirmation with reality, large eddy simulation method was employed for turbulence modeling. In addition to the ideal gas equation of state (EOS), the BKW EOS, which is a complete EOS with an explicit temperature dependence, have been used to correlate the various thermodynamic parameters. Several gauges were positioned to record the pressure-time signals and the experimental data reported in the resources were used for validation. It should be noted that the maximum error of simulations was 12.29% for different blast wave parameters. deviation from standard for ideal gas numerical results was greater than that of real gas assumption and blastFoam solver has been predicted maximum positive phase overpressure, arrival time and positive phase impulse, which are the important parameters of blast wave, with less error in comparison to extendedSonicFoam solver.

The high-expensive empirical analysis of blast waves motivates the researchers to investigate the explosion using numerical simulations. The literature shows that the computational fluid dynamics predicts the blast wave behavior accurately. Meanwhile, many methods such as the turbulence method, and the method of applying the explosion energy to the equations were presented to increase the accuracy of the numerical analysis. However, one of the most important factors in the results’ accuracy is the equation of state that describes the physical behavior of the explosion productions. The ideal-gas equation of state as the simplest equation of state was used in most of the previous researches. In this research the effect of using JWL and BKW, the real gas equations of state, on the results’ accuracy in comparison with the ideal-gas equation of state is investigated. To do this investigation, the problem of explosion close to a canopy is simulated. The numerical simulation of explosion phenomenon is done using the blastfoam solver of the openFoam open source code, and the results are compared with the previous studies. Finally, the constants of the BKW and JWL equations of state are calibrated using the empirical data.

Blast walls are implemented in order to attenuate the explosion blast wave and protect the important objects. These obstacles decrease the blast wave intensity by reflecting a portion of the wave to the explosion source and producing turbulence in the blast wave flow. The geometrical shape of the blast wall, as an influential factor, decrease the intensity and increase the protective effect of these obstacles. In this thesis, the angle of curvature of the canopy blast walls was studied to find the optimum angle with the most attenuation effect. To simulate the interaction of the blast wave with the blast wall, computational fluid dynamic with finite volume method and OpenFOAM software (an open source software) was used. The results of the simulation with LES turbulence model, was presented the more exact description for the attenuation of the blast wave interacted with the canopy blast wall. The comparison of the overpressure peak and the created vortexes behind the canopy and oblique wall, shows that the canopy wall was increased the attenuation of the blast wave up to 14%. On the other hand, by increasing the angle of curvature of the canopy wall from 0° to 67.5°, the attenuation of the interacted blast wave with the obstacle was increased step by step up to 4%.

The purpose of this paper is to review the effect of polymer additives on the final viscosity of PBX slurry and viscosity reduction mechanism. Variables related to the formulation and manufacturing process affects PBX viscosity. PBX viscosity directly affects the process of mixing and charging of these materials and hence it is necessary that the viscosity values to be low in order to facilitate the mixing and casting these materials. In this study, a summary of the performance of polymer additives to reduce viscosity is studied. So the effect of additives on the experimental values of viscosity is investigated. Additives are divided into two groups: The first group contain materials such as lecithin and silane by reducing surface tension binder leading to complete wetting of solid particles and the viscosity decreases. The second group is compounds such as phosphate oxides, aziridines and blocking agents of curing reaction leading to increase pot life and decrease viscosity.

As the computation power developing, the simulation of the explosion blast wave becomes more accurate and much more codes and softwares designed for this purpose. Besides the numerical methods, there are some other effectives like: turbulence model, equation of state and the explosion models which affect the accuracy of the blast wave simulation results. This paper reviewed the numerical methods and also other effectives in the simulation of the dense explosives explosions and gas explosions blast waves. Also the summery of the past simulations characteristics have been placed in some tables to help the researchers of this field.

In this article, microgel rheological properties has been studied at different Carbopol 940 concentrations in water using the rotational and capillary rheometer. The results obtained at shear rates less than 1000 1/s showed that the gels follow the Herschel-Bulkley rheological model. Investigation of the rheological properties’ temperature variation indicated the stability of the gels up to 50 °C. The effect of time on the rheological properties of the gels showed their appropriate stability in a period of 40 days at 25 °C. With respect to the effectiveness of pH of the medium on the gels’ behavior, the effect of pH was studied by addition of caustic soda and it was indicated that in a neutral medium, the gels have the maximum viscosity. The capillary tube rheometer was used to investigate the fluid behavior at high shear rates (shear rate range of 190000-600000 1/s). The results of the application of oscillatory rheometer showed a nonlinear and weak viscoelastic behavior of this kind of gels up to a Carbopol concentration of 0.5% compared to other viscoelastic fluids such as water-methyl cellulose solutions.