مجله علوم و فناوری های پدافند نوین
سال یازدهم شماره 2 (پیاپی 40، تابستان 1399)

In this paper, a quasi-optical millimeter wave imaging antenna at central frequency of 94 GHz in W-band is designed. The designed imaging system requires resolution less than 30 mm at distance of 5 meters to recognize metal objects. This passive system consists of a combination of a dielectric lens (primary optics) to focus the radiation and a pyramidal horn (secondary optics) with open metal walls to properly direct and couple the focal radiation to the detector. The general parameters of this system are calculated using the geometrical optics method. Then the combination of Gaussian beam method and ABCD ray transfer matrix is used to analyze the lens antenna to find the location and size of the feeding horn. The powerful optical design software ZEMAX was used to design the lens and to verify the design results based on ray tracing. The designed dielectric lens is made of High Density Polyethylene (HDPE) with a diameter of 650 mm. Then, an optimized pyramidal horn with gain of 18.9 dB at center frequency of 94 GHz is designed. The simulation of the horn and investigation of its results performed using the FEKO and CST commercial softwares. The simulation results of the pyramid horn antenna indicate that its combination with dielectric lens is appropriate and the hybrid method (geometrical optics, Gaussian beam and ABCD matrix) to design the quasi-optical system, including the lens and the horn antenna for imaging with considered requirements, is accurate, simple and efficient.

The aim of optimal planning of renewable system is to maximize achieved benefits from this investment. Modelling the problem with more details will cause to achieve the results with more reality and practicality. One of the most important off-grid areas are border garrisons. Although, these spots are disconnected from each other electically, but, their energy usages are interconnected because of the presence of unique fuel transportation system. In this paper, the reduction of energy provision’s cost from a overhead organization’s aspect has been considered as objective function. To model the problem with elboration, the fuel transportation system has been considered as the one of cost source of problem. In addition, the constraints of economical evaluation have been written to guarantee the economic condition of carried out investment. The results of simulation using the test system including 4 garrisons, show that with an economical investment, the total cost of energy provision can be decreased up to 78%.

Human manipulation is one of the reasons which causes a fault in distribution networks and power outage is occurred. For such matter, a prompt procedure of locating the fault and identifying subversive factors is consequential. In this paper, an improved impedance-based fault location method is proposed in smart distribution networks. Data loggers record load data with a specified time constant. Therefore, the load of each node is estimated by utilizing the pre-recorded load data. Furthermore, by employing line parameters and estimated loads, the equivalent impedance at the end of each section is calculated. Fault location is conducted through solving a fifth order algebraic equation with regard to fault distance using distributed parameters line model.  To evaluate the accuracy of the proposed method, a modified 11 node test Feeder is simulated in MATLAB software (R2018b). The results are presented in different fault conditions such as fault distances, fault types, fault resistances and fault inception angles. The results indicate the high accuracy of this method.

The present work studies a model predictive controlled two- and three-level active front-end rectifier system for supplying LORAN transmitter system. Up to now, the LORAN transmitters have been supplied by only diode rectifiers, which inject sever harmonics into the AC network and induce a very low input power factor when supplying pulsed loads. Therefore, an MPC-controlled active rectifier system with three level neutral point clamped topology is proposed to attenuate the input current harmonics and improve the input power factor. Compared with the conventional methods (e.g. voltage oriented control (VOC), direct power control (DPC)), the proposed control method provides such advantages as improved power quality indices, reduced switching frequency, and simplicity for controlling different indices just by changing the weighting factors of the relevant cost function. The results of comparing these thee methods demonstrate that the MPC method could not only give a power factor close to unity and negligible harmonic distortion, but also very lower switching frequency, as compared to the two other methods. Using the MPC, VOC, and DPC control methods, the switching frequencies for a typical load were found to be 11.3, 74.5, and 60 kHz, respectively. Moreover, the intuitive logic and easy implementation of the MPC method, compared to the two other ones, besides achieving an improved operating point with a lower cost, represent the other important advantages of the MPC method.

Weapon target allocation (WTA) is a command and control main components.In this process, the critical          time-based decisions often is made under uncertainty.In this paper attempt has been made to propose a realistic approach to WTA problem. We consider a multi-stage weapon target allocation with multiple criteria including: Minimizing the expected total value of surviving targets, minimizing the military resource costs and minimizing the allocation risks. In the following study to develop a more realistic weapon target allocation model, we have tried to bring almost all ignored constraints such scarcity of weapons, technological, atmospheric/geographical (e.g. terrain) and structural limitations into account. Finally Non-dominated Sorting Genetic Algorithm-II (NSGA-II) has been used for solving multi-objective WTA problem and a Pareto optimal front for the model is depicted. Comparison of the calculated solutions (from the point of quality and speed of calculation) with those provided with expert commanders, suggests that the modelling and solving method have been successfully designed and match the application greatly.

Absorbents are used in RCS reduction to prevent reflection of the wave and not interfere with the test wave.By reducing the amount of reflection in a wave using materials used in adsorbents, they reduce the reflection.The things that are to be considered in relation to these reflections are the effects of these waves, which are termed ”pure environmental reflections“, the error caused by not considering the pure reflections of the environment and other problems caused by weaknesses. The main wave of the note is noteworthy. In this research, the optimum thickness of adsorbent material has been determined using genetic and Particle Swarm Optimization (PSO) algorithms with the aim of determining the minimum amount of electromagnetic wave reflection. The genetic algorithm is used to adjust the plate resistance values as well as the PSO algorithm to determine the optimal screen thickness. The results show that determination of microwave absorption coating parameters has a significant effect on the absorption rate of the wave. The applied method provides the conditions for achieving optimal coverage.

Signal bandwidth (BW) is one of the most important factors in transmitting and receiving rate of information in portable radio receiver systems in advanced defense science .Therefore, it is desire to design different parts of these systems with a larger bandwidth and less power consumption. In this paper, self-coupling method is applied to the quadrature modulator in order increase its bandwidth. In this approach, without the addition of active blocks, modulator’s order is increased and its bandwidth is also improved which results in power saving. Utilizing this method increases the number of zeros in quadrature modulator transfer function and results in a higher order modulator performance. The proposed method is applied to a three-order quadrature modulator, and it is significantly increased the bandwidth. The purposed method results in a 0.05fs bandwidth and a signal-to-noise ratio (SNR) of 91.25 dB which is improved by 25% compare to the results obtained in a modulator without the self-coupling( BW=0.04fs and SNR= 92.86dB).

Considering the importance of identifying and determining the nature of the sonar targets in marine battles, the purpose of this paper is to design a system with the ability to classify active and passive sonar targets using multi-layer perceptron neural networks (MLP NNs). Considering the defects of MLP NNs in dealing with real-world data, as well as low classification accuracy and low convergence rate, this paper proposes a new meta-parasitic algorithm called Chaotic Groups Particles Swarm Optimizer (CGPSO) to train an MLP NN. This algorithm explores the search space faster and better than normal particle swarm Optimizer (PSO) using chaotic and independent groups. To evaluate the designed system, a benchmark sonar dataset, a passive laboratory data set and an active dataset were developed. In order to have a comprehensive comparison, the designed system was compared with PSO, biogeography-based Optimizer (BBO) and Gray Wolf Optimizer (GWO) in terms of convergence rate, classification accuracy, and reliability. Results show that the designed system was more accurate than the best available classifier, by average 2.33%.

The occurrence of the explosion in the saturated sandy soils can cause the shear resistance of the soil to tend to zero and show the fluidal behavior.In this case, in fact, stress is removed from solid soil particles and exerted on the pore water pressure.Nowadays, considering the multiplicity of construction on the soils prone to the liquefaction and the terrorist and military attacks, the recognition of the behavior of these soils is important.In this research, the liquefaction of sandy soils under the explosion loading has been investigated.For this purpose, a 3D finite element model was employed in the LS-Dyna software, in which the explosive is located at the depth of 5 meters in the sandy soil. In this regard, the stresses induced by the explosion in the soil and the soil liquefaction range were investigated. The results show that by increasing the weight of the H6 explosive from 7.5kg to 75kg, the Yang Li soil liquefaction range, increased from 4.5m to 16m, also by modifying the explosive from H6 to TNT the soil liquefaction range was reduced.

The use of buckling-restrained braces began in Japan at 1980s and was then followed by other countries all over the world. Many behavioral problems associated with the conventional steel braces might be neglected when this type of bracing system is used, due to the difference between their tension and compression strength capacity. In this paper, the effect of mega buckling-restrained braces on the response of tall structures subjected to the blast load is investigated. For this purpose, a 30-story structure is retrofitted by mega buckling-restrained braces in twelve different modes. Then, the best positioning of this control system is introduced based on the maximum response of the structure. In this regard, the structure is subjected to four states of blast loads produced by 1000 and 1200 kilograms of TNT at a distance of 5 and 10 meters from the structure. The results showed that by decreasing the amount of blast material and also increasing the distance of TNF from the structure, the damaging effects and also the maximum response of the structure reduced; and therefore, the structure went to the safe level (IO). The results also indicated that the A1 state is the best positioning for the controlled system, in which the maximum displacement of the roof, the maximum rotation of the structure is less than these values for the original structure (the structure with the conventional braces system). Also, the A1 state can be chosen as the best candidate for placement of the controlled system since it reduces the weight of the bracing system more than 16% rather than this value for the original structure.