numerical simulation

In this paper, the ballistic behavior of sandwich panels with aluminum-polyurea face sheets and aluminum cores in the form of semi-cylindrical waves or with hemispherical cavities (single or multi-layer) has been investigated. To increase the ballistic resistance of sandwich panels, the effects of core geometry, core layout, polyurea plates, number of core layers, and projectile impact location at high velocities (50 to 400 m/s) have been simulated. A number of 12 different modes were examined in terms of the placement of the face sheets and core layers. The results of the investigation showed that in single-layer cores, by changing the geometry of the core from semi-cylindrical to hemispherical, the ballistic limit velocity increased by 16%. In two-layer cores, by shifting the layers with different waves (from semi-cylindrical -hemispherical to hemispherical- semi-cylindrical), the ballistic limit velocity increased by 4%. The use of polyurea in the sandwich panel increased the ballistic limit velocity by 15%. By increasing the number of semi-cylindrical and hemispherical core layers, the ballistic limit velocity increased by 32 and 29%, respectively. Among the investigated sandwich panels, the values of the ballistic limit and the ratio of expended energy per unit of mass are the best for SP2 panel (sandwich panel with aluminum and polyurea face sheets with a thickness of 1 mm and a semi-cylindrical core (double layer) with a thickness of 0.5 mm and radius arc 10 mm) compared to the weakest ones SP5 panel (sandwich panel with aluminum and polyurea face sheets with a thickness of 1 mm and a hemispherical core with a thickness of 0.5 mm and an arc radius of 20 mm); 92.3% and 254.4% respectively.

The increasing demand for highly pure crystalline materials with narrow Crystal Size Distribution (NCSD) leads related industries to utilize the Draft Tube Baffle (DTB) Crystallizers. The product Crystal Size Distribution (CSD) significantly alters by enhancing the mixing characteristics inside crystallizer, therefore acquiring a precise vision of hydrodynamics will help in designing and scaling up the DTB crystallizer. There are numerous studies on the flow field in the DTB crystallizers, but none of them investigates the interactions and effects of the internal arrangement of DTB crystallizers. In this study, the optimal configuration of three geometrical parameters (tube diameter, the ratio of tube diameter to baffle diameter, and the width of the annular settlement zone) was obtained by numerical simulation of the flow field in 18 DTB crystallizers. The interaction of parameters was studied by employing the general factorial method. Each crystallizer was divided into five compartments where various results such as the distribution of axial velocity, the turbulent kinetic energy, and streamlines were considered for data analysis. The results demonstrate that the hydrodynamics requirements in each compartment will be satisfied in crystallizer with 17.5 cm tube diameter, the ratio of tube diameter/baffle diameter=0.5, and the width of the annular settlement zone equal to the tube diameter.

The most important objective in the drop weight tear test (DWTT) is obtaining the fracture energy. DWTT use in the military, steel and pipeline industries. By installing the proper equipment, the dynamic impact load can be measured in terms of the hammer displacement of the DWTT machine and it can calculate many parameters such as initiation energy, propagation and total fracture energy. For this purpose, numerical analysis by ABAQUS software was used to determine the proper location of the strain gauge on the hammer. Then, the strain gauge circuit (load-cell) was installed and calibrated using analytical and experimental methods. In order to use the circuit, the voltage must be converted to the load values. The analytical and experimental methods were used to obtain the desired coefficient. The two coefficient had an acceptable difference. In addition, in order to increase the accuracy and repeatability, other equipment such as guide and micro-swich were used in the DWTT machine. Experiments with the DWTT machine showed the repeatability of the results.

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 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.

The electric initiator is an important component of the explosive train which provides requiered energy to initiate a chemical reaction by converting the electric current to the heat via a bridgewire. This initiator is widely used in the field of aerospace industry in the solid rocket propellant motors, separation systems and etc due to its low weight and high reliability. In this research, a mathematical model has been introduced to investigate the effective parameters on the electric initiator performance. Comparison of numerical simulation results by finite difference method and experimental data showed that this model has the ability of the prediction of the ignition time and determine the transient temperature profile in axial and radial direction. The model showed that the reduction of the contact heat transfer coefficient between the bridgewire and the primer compared to its increase has a greater effect on the heat transfer rate. It was also found that with increasing the current, the temperature changes decreased along the axial direction and increased in radial direction.