فهرست مطالب سعید توانگر روستا

In addition to the inherent characteristics of explosives, the power of the detonation is affected by arrangement of the explosive train. Therefore, the correct design of the explosive train, especially for insensitive explosive charges containing aluminum, play a fundamental role in order to be more effective. In the current research work, by changing the dimensions of the booster pellet and its position relative to the main charge; the detonation behavior of the main charge has been investigated. In this study, the booster pellet (COMP-A3) is modeled with JWL equation of state and the main charge (PBXN-111) is modeled with ignition and growth equation of state. The simulations has been done using AUTODYN software. The coefficient used in the equation of state (ignition and growth) has been evaluated with experimental results. The simulation results show that by reducing the diameter of the booster pellet from 5cm to 3cm, for a certain length of the booster pellet, reaching to the steady detonation increases due to the greater divergence of pressure wave into the charge. In the case where the booster is inside the charge, the peak pressure values increase in the corners of the charge and adjust the pressure drop due to the divergence. The simulation shows that for the case where the booster and the main charge are placed on top of each other, the booster with a diameter of two centimeters with any length of the booster pellet is not able to create stable detonation in the main charge. For a submerged condition of the same diameter, the booster can produce stable detonation in the main charge. This study showed that a booster pellet with a diameter of 5 cm and a length of 4 cm can cause a complete detonation in PBXN-111. The length of the region to reach stable detonation with this booster is 15 cm.

The presence of high combustion temperatures requires effective cooling methods in the combustion chamber. Most chambers in liquid propellant engines have regenerative cooling. A new way to improve heat transfer performance in the regenerative cooling process is to add nanoparticles to the cooling fluid. In this study, the regenerative cooling in a liquid propellant engine was simulated numerically by fluent software. The engine is designed to work on a mixture of kerosene as fuel and liquid oxygen as an oxidizer with a thrust of 300 kN. In the following, carbon nanotubes and alumina nanoparticles were used in 2% and 5% volume fraction to be added to kerosene for nanofluid production. In this study, the fluid flow in the three-dimensional cooling channel is assumed to be steady-state, turbulent and the k-ε turbulence model is used for turbulent flow, and the nanofluids are modeled as single-phase. Addition of nanoparticles alumina and carbon nanotube to kerosene as cooling fluid increased the heat transfer coefficient by 8% and 15%, respectively. According to the results, carbon nanotubes have a higher ability to increase heat transfer coefficient and improve regenerative cooling than alumina nanoparticle.

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.

Co-crystallization is an attractive molecular engineering approach for realizing improved energetic materials (explosives, propellants, and pyrotechnics). When two or more neutral species are combined to form a new structure, co-crystals are created with distinct solid-state properties. The performance criteria of energetic materials (explosive power, thermal stability, and physical sensitivity) are critically depended on some properties such as density and melting point. So, using co-crystallization could improve existing materials and even energetic compounds which were previously abandoned, due to having several disadvantages such as low density or high sensitivity. In this article, several most important efforts of scientists in the novel energetic molecular design field through co-crystallization technic are introduced. Also, reasons of the formation of a co-crystal are investigated from molecular structure point of view.

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.

In the current research work, a zero-dimensional code for the internal ballistic of gun analysis has been developed with a deterrent layer propellant. Today, the driving of the deterrent layer is widely used in small and medium-caliber weapons. The deterrent layer is in the form of a thin coating on the surface of a single base or double base gun propellants. The main purpose of this type of propellants is to increase the muzzle velocity by observing the maximum allowable pressure for the weapon. It has been developed for internal ballistic analysis of the thermodynamic model or the next zero-based on Badr software relations. In order to validate the analysis results, experimental results and results of other valid codes related to 20 mm weapon and 30 mm laboratory weapons were used. The code is able to analyze the combustion of two-layers propellants with a variety of conventional geometries for a grain. The effect of the engraving force on the accuracy of the examined results and the impact of deterrent layer on internal ballistic of gun performance has been discussed. The results show that in case of using the deterrent layer with increasing the load density can be reach to higher muzzle velocities with maintaining maximum allowable pressure. The investigation on M55A2 ammunition demonstrated 9.5% increasing in muzzle velocity by using of deterred propellants rather than undeterred propellants.

When dealing with research and development of the gun propellants, a less expensive, quicker and safer process of the closed vessel evaluation adopted can be used rather than the gun firing test. In the current research work, a computer program (BRCBADR) has been developed for in order to obtain the burning rate reduction coefficients from the closed vessel test data. Correct The correct determination of the thermo-chemical properties of the propellants provides accurate results of interior ballistics analysis. The BRCBADR code has been developed based on a zero dimensional model for evaluating pressure history of burning propellants in a the closed chamber. A new curve fitting method based on the shooting Shooting algorithm is used to calculate burning rate coefficients. In this program, the experimental values of impetus and co-volume have determined from the Noble-Able equation of state. The results of present code are in well agreed agreement with the results of other validated codes. Using of burning rate calculation method has resulted in accurate muzzle velocity prediction (less than one percent error) from 122 mm gun firing. The results of This this research showed that,exhibited the regardless of slivering effects during the burning of seven perforated cylindrical grains, while resulted tothe additional unreal impulse is applied to the projectile.

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.