فصلنامه مواد پر انرژی
سال شانزدهم شماره 2 (پیاپی 50، تابستان 1400)

The engine cooling in first stage of satellite carrier rocket via kerosene fuel leads to increase the missile range. For increasing the heat transfer coefficient of the fuel, addition of nanoparticle is a preferred method. At constant velocity of nanofuel through the fuel flow passage in combustion chamber, evaluation of the coefficient depends on assessment of the effective parameters. These parameters are: density, specific heat capacity, thermal conductivity and viscosity of the nanofuel. In this article, the kerosene nanofuel was prepared by addition of carbon nanotube with surfactant oleyl amine to the kerosene fuel. Then, effect of volume fraction of carbon nanotube on the thermophysical properties of the fuel was studied in the range of 0 to 0.08 at 30 oC. Mouromtseff number (as a thermal performance index of a liquid fuel) was obtained more than 1 for the kerosene nanofuel with respect to base fuel, indicating the increasing the heat transfer coefficient for the kerosene nanofuel.

In numerous explosive attacks, non-structural elements, including masonry walls, are severely damaged, although no serious damage is inflicted on structural elements. Besides, the structure of most buildings in military centers are made of masonry walls. Therefore, it is necessary to study the behavior of these walls subjected to blast load. In this regard, some research has focused on experimental studies. Because these experimental studies include difficulties in terms of security, safety and cost, using numerical studies as a complement can be very effective. In this paper, numerical simulation of masonry walls with mortar is described with a partial micro approach, using ANSYS AUTODYN software, and element characteristics, material models, equations of state and values of corresponding parameters are introduced step by step. By verifying the numerical analysis results with experimental data, it has been shown that this method is able to estimate the behavior and damage of masonry walls under blast loading, accurately and quickly. Moreover, the co-damage curves in terms of overpressure and impulse parameters is presented, which can be a helpful guide to the optimal design of walls based on different threat scenarios and cost. Finally, this model can be used to develop a corresponding retrofitting strategy for the existing walls in terms of possible threat scenarios.

The walls placed in structural frames can act as a loading surface against the explosion load and significantly increase the dynamic load applied to the structural members. Therefore, the durability of the walls against the blast load and how they are connected to the structural members may have a significant effect on the dynamic response of the structures to the blast load. To investigate this subject, finite element method and Abaqus software are used. Initially, to ensure the accuracy of the predictions of finite element model, verification is performed by modeling an explosive experiment on a concrete-filled steel tube column and a good agreement is observed. Then, the effect of the presence or absence of a concrete wall in the frame and how it is connected to the beam and column is investigated using dynamic explicit analysis. The results of the study showed that in the case of no wall and in the case where the wall is attached to the column only, the highest amount of plasticity has occurred in the beam. In specimens with wall-to-column connection, the maximum plastic strain is observed at the base of the column. The existence of infill wall and the attachment to a beam or column has a significant effect on the vertical displacement of the beam.

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.

Aging of a sheet explosive contain RDX explosive and HTPB binder is studied at temperatures of 50, 60 and 70 oC in times 60, 120 and 180 days. Dynamic-mechanical analysis (DMA), sol – gel analysis (SGA) and hardness measurements methods are used in this research.  The changes of tan_delta in DMA, hardness amounts and soluble fraction in SGA are measured for unaged and aged samples. The obtained results showed the samples are aged with increasing of temperature and time of aging process. The pseudo-first order kinetic equation and obtained data are used for calculation of kinetic rate constants of measured properties changes. The changes in tan_delta in DMA, hardness amounts and soluble fraction in SGA indicated kinetic rate constants, respectively, 0.9-2.3´10-3, 1.9-4.8´10-3 and 1.5-5.5´10-3 per day at temperatures of 50, 60 and 70 oC. The Arrhenius equation is used for calculation of activation energy of each changes and calculation of kinetic rate constants at temperature 25 oC. Kinetic rate constant at room temperature showed a reduction 50% in measured properties of the product after 3300 days (~9 years).

Viscosity is one of the important parameters in design and production of composite solid propellants. Propellants with low end of mix (EoM) viscosity and longer pot-life have suitable condition for casting process. Several factors control the rheology behavior of propellants. In some cases, it may be necessary to apply some additives in order to optimize the rheology of the formulation. In this research, the effect of adding 0.013 to 0.029% by weight of maleic anhydride (MA), as a pot-life extender, was investigated on rheological properties of a HTPB/DDI based composite solid propellant containing 88% solid loading. Results showed that the formulation containing 0.025% by weight of MA compared to other samples showed lower EoM viscosity. EoM viscosity enhanced by either increase or decrease in MA concentration related to this formulation. The viscosity of samples decreased due to shear stress and rotational motion of the viscometer spindle until a specific time and then will increase by progress in cure reaction in binder system. Furthermore, viscosity reached to ascendant step in relatively longer time by adding MA concentration. Furthermore, having increased amount of MA, the viscosity increases over a relatively longer period of time.