Advanced Defense Science and Technology
Year:2017 | Volume:8 | Issue:2 |Papers Count:8

Multi supply in sensitive areas - as an inverter based Microgrid - is necessary for improving reliability and stabilizing the network in case of losing one or some of the electricity generation units. In addition, islanded mode of Microgrids is a guarantee of continuing operation during black out or failing stiff power system. In order to utilize variety types of distributed generations and renewable energies in Microgrid structure, usage of Power Electronic Interfaces (PEI) is inevitable. As a result, Frequency Tracking (FT) method with decentralized control in order to stabilizing inverter-based Microgrid is introduced. In the proposed novel method, all generation units follow the frequency of one generation unit as a Master and provide required power in network after deployment of Droop Control. The simulation results of proposed control system on two distinct networks in PSCAD confirm its proper functioning.

Designing a suitable camouflage pattern for a building is one of the fundamental challenges in the field of passive defence. In this study, to design visible camouflage patterns, an automatic method based on high resolution satellite images processing is proposed. In the proposed method, the area around the target building on the image is first removed. Then, using the surrounding of the removed part, an artificial image is reconstructed by a texture extraction method. In the next step, the main colors of the image are extracted from reproduced image using K-means clustering algorithm, and then, the camouflage pattern is created by assigning the color of center of each cluster to all pixels of that cluster. The obtained camouflage pattern is evaluated on two different dataset in both visual assessment and computation the saliency value. Successful visual assessment and the 27 percent decrease in obtained saliency value using the second dataset indicate the high ability of the proposed method to camouflage buildings.

Steganalysis is one of the challenging and attractive subjects for the scientists interested in the development of steganography methods. Steganalysis is the procedure to detect the hidden information from the stego created by known steganography algorithms. Different kinds of extraction methods have been proposed for steganalysis, each have their own advantages when attacking different kinds of steganography methods. Making a combination of different feature sets will improve the performance of the steganalysis system. Most modern steganalysis algorithms train a supervised classifier on the feature vectors. One of the most popular and most accurate classifier is support vector machine (svm). In this paper, based on experiences and study different ways, an efficient steganalysis method using windowing on high-frequency coefficients of wavelet transform is proposed. In the proposed method, the final decision on the entire images is announced by majority voting technique using extracted convenient features of each window. Experimental and simulation results show that the proposed method for the detection message embedded in images, especially in low rates compared to existing steganalysis methods has more carefully hidden by about 99 percent.

Underground structures have entered into the passive defensce discussions as the secure structures in the past five decades. The resistance of tunnel concrete lining subjected to the loads generated by an external explosion is investigated in this study. For this purpose, investigation of tunnel lining subjected to blast waves has been performed using ABAQUS software. Effects of intensive impact loads caused by surface blasts on the underground tunnel concrete lining with compressive strength of 30 MPa and also with ultra high strength concrete, both reinforced with steel fibers, with and without steel bars, have been studied. The comparison of the results based on the variation of elastic stresses and strains in tunnel lining has been performed. Explosion of explosive materials induce two types of shock and induction waves at the ground level, both considered simultaneously in this study.The results indicates that the addition of steel fibers to the regular and ultra high strength concrete, with and without steel bars, in comparison to regular reinforced concrete with compressive strength of 30 MPa, under similar loading conditions, can lead to increase in compressive strength of the lining when subjected to explosion.

A new method for solving single-objective and multi-objective two-person zero-sum game problems with fuzzy payoffs is proposed in this paper. The single-objective game problem with fuzzy payoffs is converted to a singleobjective game problem with interval payoffs by considering the concept of nearest interval approximation of fuzzy numbers, and a pair of linear programming problems is obtained to compute the optimistic and pessimistic solutions for each of the players. By the strong duality theorem of linear programming, it is proved that the optimistic value of Player I is equal to the pessimistic value of Player II and also, the pessimistic value of Player I is equal to the optimistic value of Player II in interval-valued matrix game. Then, two multiobjective linear programming problems are introduced to compute the optimistic and pessimistic values of interval-valued multiobjective game and their corresponding Pareto optimal strategies for each of the players. As an application, the battle between U.S. and Germany forces in Avranches Gap in World War II is discussed by game theory and is concluded that the obtained optimal strategies of model by the mentioned method for commanders is identical with the analysis of the U.S. military doctrine. Finally, an example of a military battle is considered in which each of the commanders has two objectives.

Although existing Planning methods can plan under uncertainty and decentralize situation, most of them malfunction in some complicated conditions of command and control scenarios such as real time decision making, needing more accurate planning, bounded communication between agents, dynamic worlds and partially observable environments. Among suitable models for these situations, extended models of DEC-POMDPs such as MAOP-COMM can be considered for handing these conditions. It is possible to improve MAOP-COMM model to do planning for agents with double precision. In this paper, the algorithm of MAOP-COMM model has been improved by upgrading value function heuristic and using "two steps look ahead" in the strategy of finding best policy and making correct decision. In the next step, the improved method was implemented in a web service frame work. The web service gets the desired bounded scenario from the architect and performs online planning to generate plans and sequence of actions regarding to environment dynamicity. The obtained results, show preference of the improved algorithm, So that the designed service with improved algorithm can perform online planning for agents in a decentralized multi-agent system in uncertain condition with better performance and high percent of correct decision making.

An accurate and safer analysis for structure is possible if we can identify factors in the analysis more accurately.One of the important factors in the analysis is the identification the kind and intensity of structural loading. Among the types of loading, especially dynamic loads and impact loads resulting from the explosion, is far more complicated and difficult to determine. According to lab explosion modeling problems, using numerical modeling to analyze these phenomena can be reasonable. Uses grid methods like Finite element method caused a numerical error due to intense deformation and high velocity of blast. In this paper, underwater explosion was modeled and programmed with numerical mesh-less method, Smooth Particle Hydrodynamics (SPH), using Fortran programming language and explosion pressure and water level changes in the blast were studied. Finally the solving problem is compared with empirical relation. The results of this model are very similar to empirical relationship. This program can be used for underwater explosions modeling and the results can be used to determine pressures and impacts on marine structures.

Safety and secutity of reactor containment building and its resistance against external forces is particularly important. Paying attention to this subject has been increased due to the incident plane hit the twin towers on September 11, 2001. One of the factors in the vulnerability of a building against the external collision is its geometry. The purpose of this study is to select the optimal geometry of a concrete containment building with the lowest vulnerability against an aircraft crash. Thus, two different geometric forms, one with cubic body and a flat roof and the other with a cylindrical body and domed roof were modeled numerically. Numerical modeling was performed using ABAQUS 6.12-1 software. Considering the impact of building form and in order to reduce the solution time and considering physical symplicity, homogeneous concrete without reinforced bars were chosen.Strike of Phantom F4 to the roof and body of the containment building was simulated at various angles and responses were compared in the whole structure and in the contact location. Results of this study indicate that the cylindrical form is less vurnable in comparison with cubic form exept in the intersection of wall and dome.