مجله علوم و فناوری های پدافند نوین
سال سیزدهم شماره 4 (پیاپی 50، زمستان 1401)

Since providing and increasing security in special and public places has always been the focus of everyone in various fields, many measures such as installing surveillance cameras and placing officers on the spot have been taken to provide and increase security in public places such as schools, universities, offices, and so on. Because these cameras detect suspicious activity by human operators, factors such as distraction, lack of awareness, fatigue, and a variety of other factors can affect the quality of surveillance; however, the firearms detection system detects and identifies defined weapons automatically. They can send special messages to military and security officials in a timely manner. In this paper, the Yolo version 5 algorithm is used to detect and track firearms (pistols) and cold weapons (knives), and the Deepsort algorithm is used for tracking. The article investigates the system's performance. Finally, after training with a special data set of firearms and cold steel, the proposed system performs firearms and cold steel detection operations with 99.50 percent accuracy. Furthermore, the proposed system has provided adequate accuracy in terms of scale, rotation, and obstruction.

Use of microwave absorbers and radar-absorbing materials is one of the growing needs in military and civilian applications. Weight reduction, improvement of absorbing characteristics, high microwave absorption and wide operating bandwidths are important issues in absorbing materials. One of the most suitable compounds is nanocomposite of carbon nanotubes/magnetic metals. In this work, nanocomposites of carbonyl iron (CI) and multi-walls carbon nanotubes (MWCNT) with different %Wt via homogeneously mixing with paraffin were prepared and their microwave absorbing properties were investigated in the frequency range of 8-18 GHz. SEM and XRD images of nanocomposites showed uniform dispersion of MWCNT and CI particles in the matrix. Also, the results of wave absorption showed that by increasing of iron carbonyl respect to carbon nanotubes and the formation of carbon nanotube-based nanocomposite absorbers, the absorption and absorption bandwidth increase. For the nanocomposite containing 70% by weight of carbonyl iron, the highest amount of reflection loss was 11.33 dB at the frequency of 18 GHz. Also, in the bandwidth of 10.1 GHz to 18 GHz, the amount of reflection loss was obtained more than 4 dB.

Conventional Analysis of Reinforced Concrete Slabs under blast load requires a long process. This process, in addition to being time consuming, does not determine the extent to which the geometric parameters of the slab are loaded. To overcome this problem, in this study, by Analyzing 351 different concrete slabs under blast load by LS-DYNA software, the maximum Deflection, its corresponding arrival time and Slab Stiffness were recorded. Then, by using the genetic algorithm method, by processing the data related to the maximum Deflection and its time, a direct relationship between the calculation of these parameters was extracted. Considering the nature of the relationship extracted from the Response Surface Method, the coefficients of the relationship variables presented for stiffness determined the importance of each variable in the stiffness of the slab. Finally, the cosine amplitude method has been used to determine the maximum sensitivity of the slab to geometric parameters and loading. The results of this study show that the explosive distance parameter (R) has the most effect and the cross-sectional variable of steel (AS) has the least effect on the maximum slab deflection. It has the maximum effect at the time of reaching the maximum deflection.

Scientists and researchers have more attention plasma actuators, especially corona plasma actuators as propulsion system, due to their low power consumption, no moving part, silent, high efficiency and infrared waves. An example of corona discharge applications is lifters. In this research, triangular, square and three sides’ with a common vertex models with a common vertex were designed and built. Then, the parameters of electric power, effectiveness coefficient and thrust in the discharge of positive and negative coronas were investigated in the experimental study. The results of the research show that in all three models, the relationship between voltage changes and thrust in positive and negative coronas is almost linear, and increasing the amount of voltage causes an increase thrust. But the relationship between voltage and electric power in all three models in positive and negative coronas is parabolic. The highest amount of thrust in both positive and negative coronas was related to the square model and then the three sides’ model with a common vertex. Finally, the highest effectiveness coefficient in the positive corona is related to the square model and then the three sides’ model with a common vertex, and in the negative corona, it is related to the square model and the triangular model, respectively

Cellulose nanocrystal is a functional material because of its properties like high specific surface ratio, high crystallinity, and good mechanical and optical properties. It has emerged as a new material class for advanced military products such as bulletproof vests, fire-resistant materials, propellants, and electronic products. In this study, high purity cellulose was extracted from sugar beet pulp by soda-anthraquinone pulping method and bleached to remove maximum hemicellulose and lignin. Then cellulose nanocrystal was produced from extracted cellulose with 64% sulfuric acid. The resulting crystalline nanocellulose was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). Transmission electron microscopy analysis confirmed the presence of cellulose nanocrystal. Hydrolysis with concentrated sulfuric acid increased the crystallization of bleached cellulose and reduced its size to the nanoscale. The diameter of cellulose nanocrystal was less than 20 nm, the length was in the 200-400 nm range, and the production yield was 53%, which is comparable to cellulose nanocrystal from wood and other biomass sources. This product can be used in various military applications, including durable and lightweight composites, surfaces with anti-corrosion properties, and bandages.

Ribbon parachutes are used for speed reduction and stabilization of high-speed payloads and aircrafts. In the present research, a ribbon parachute is designed for air-dropped payload recovery and simulated by using multiple engineering softwares to analyze aerodynamic loads and structural stresses. The canopy is made from nylon 66; its deployed diameter is equal to 1.2 m and consists of 8 gores. The aerodynamic loads, pressure, and structural stress distributions are computed in four different free stream velocities of 40, 80, 100, and 120 (m/s). Based on these results, the most critical point on canopy structure is designated. The results show that the location where the suspension lines are attached to the fabric has the highest amount of tension and displacement due to the aerodynamic loads.