مجله علوم و فناوری های پدافند نوین
سال هشتم شماره 1 (پیاپی 27، بهار 1396)

In battlefield, the soldiers are equipped with an array of communication systems. The size and weight of these tools will create problems for user. In this paper, a new technique to reduce size of soldiers worn smart espar antenna is suggested. In addition to reducing the size and weight, the proposed antenna will improve radiation characteristics of soldier’s conventional espar. The new technique is based on the use of a metal disc above monopole in conventional espar antenna. The proposed antenna with maximum dimension of 15 cm and height of 2.03 cm has a gain over 5 dB and a bandwidth of 18% (1.6-1.92 GHz). Moreover the antenna has a directional pattern so that the H plane pattern will cover different direction with different position of switch. Directional pattern increase coverage and reduce power consumption and most importantly will enhance the security of communication nodes in ad hoc network.

It is not so easy to do evaluation tests for countermeasures against real threats that are flying in a real speed and altitude. The causes of the threats are not always accesible and if we want to make a test, it will be costly. Moreover, it is very dangerous to destroy and explode a target in the field tests. Thus, countermeasures proceedings, design and manufacturing of infrared seeker testers have been considered as a serious topic. One of the main countermeasures activities against infrared missiles is usually throw a flare (false target) by aerial targets being tracked. In this paper, laboratorial simulation of flare deception countermeasures has been accompolished on current tester and design and manufacturing of a complementary tester for infrared seekers has been proposed. A comparison is also made between the current tester and the proposed tester based on their conceptual designs. The proposed tester presents a more accurate and perfect simulation for deception countermeasures and provide a performance evaluation for infrared seekers in various conditions. Study and analysis of the simulation results can not only promote deception countermeasures but also will improve the performance of infrared seekers.

A probability based assessment procedure has been proposed in this study aiming to take into account the stochastic nature of explosive loading and different blast scenarios. It is first necessary to identify the structure behavior against the explosions and probabilistic assessment of responses considering the structural and loading uncertainties. A reinforced concrete building has been considered to evaluate the efficiency of proposed approach in this study. The ANSYS Autodyn Ver.14 software has been utilized for modeling and analysis under blast loading and the damage level of structure has been specified using the pressure-impulse diagrams and the structural fragility curves dependent on the explosive weight and scaled distance have been utilized to evaluate the structural reliability. The sensitivity of the probability of structural failure respect to the uncertainty parameters of blast loading indicates that the uncertainty parameters related to the blast loading are more important in comparison with the uncertainties in structural characteristics. In general, the reliability analysis of the existing buildings can be an appropriate way to decide for repairing or renovating of the structure.

Graphite bombs are modern and non-destructive weapons causing wide area blackouts in power systems by applying short circuit faults. In this paper, a special protection scheme is presented to deal with graphite bombs and prevent blackouts. In this method, substations are categorized according to the system response to their outage event. In next stage, special protection scheme for each group is designed according to the available communication infrastructure. Load shedding, islanding, generation trip are the methods utilized along each other to tackle blackouts. The proposed methods are tested on IEEE 39 bus test system in different operation scenarios. Simulation results prove the validity of the proposed method in dealing with graphite attacks.

Underground tunnels, play an important role in protecting important installations from various forces including explosions. Surface and penetrating blasts could deteriorate tunnel surcharge, enveloping space and exerting a lot of load on the tunnel lining. Therefore, to withstand the blast, blast load should be taken into account in tunnel design, in such a way that the tunnel could bear the loading caused by devastation of surrounding soil and rock. One of the widely used criteria for assessing failure of tunnel and underground structures due to blast loads is “Peak Particle Velocity”. In the present paper, this criterion is employed in order to investigate the behavior of underground tunnels under blast load using of explicit dynamic nonlinear finite element software LSDYNA. Then, the effect of cross-section on tunnel under blast load is investigated by comparing the peak participle velocity parameter, displacement of center of roof and Von-Mises stress on the rectangular and horseshoe cross-section. It has been shown that, with equal dimension, the environment enveloping the rectangular cross-section possesses higher resistance than horseshoe cross section.

The use of Loran system is a strong defense for navigation due to its immunity against jamming and ability to penetrate indoor locations. This system can be used as a navigation aid system especially in times of crisis and GPS disconnection. One of the most important error sources in Loran navigation system is the Cross Rate Interference (CRI). If such interference is not eliminated, the accuracy of the navigation will considerably be decreased. The aim of this study was to eliminate the CRI in Loran systems using a hybrid filter and loran signal analysis in frequency domain. The results demonstrated that the hybrid filter could eliminate the interference of the irritating chain completely and, therefore, there was not any destructive effect on the desired spectrum signal. However, the spectral lines located in the frequencies which are equal to reverse of the greatest common divisor between the Phase Code Interval (PCI) of desirable chain and adjacent irritating ones could not be eliminated with the proposed phase coding approach. Spectral lines that could not be eliminated, are few and do not have significant effects on the system performance. In practice, it is feasible to completely eliminate the remaining spectral lines using two or three of very narrow-band notch filters without causing significant effects on the standard Loran spectrum. Furthermore, Loran system has been analyzed in frequency domain, using the proposed filter in order to discuss the design of the new PCI in eliminating CRI effects caused by Loran irritating chains.

The main signaling protocol of next generation networks especially in multimedia applications (e.g. video conference, IPTV and VoIP) is session initiation protocol (SIP). Different types of Denial of Service (DoS) attacks are applicable to SIP entities because of the stateful functionality and text based nature of SIP. More than 98 percent of these attacks against SIP entities are caused by misconfiguration and implementation shortcomings. In this paper, a feature set for using in anomaly detection systems by feature engineering approach is generated. The knowledge of SIP packets, SIP internal state machine and normal behavior of this protocol were employed to create features that make machine learning algorithms work. The performance of the engineered feature set is evaluated with two different classifiers by applying three different data sets. The experimental results show the performance of proposed feature set in terms of detection and false alarm rate.

xPlanes, helicopters and other military aircrafts are one of the important features of a country's military power. Therefore, maintenance of this equipment from potential threats and vulnerabilities in the domain of passive defense appear to be necessary. Results of previous studies on aircraft hangars had been predominantly in the range of static loads and little research has been done in the field of special loads such as explosion. . Whit due attention to the spread of terrorist attacks, necessity of appropriate operation of these structures under blast loads is become clarified. Therefore in this research, behavior of semi cylindrical concrete hangar under blast loading of 1 tone TNT at near, intermediate and far from hangar has investigated. The location of explosives substance was considered in three state of perpendicular to the hangar axis in mid-length, along the axis in front of the hangar door and in front of hangar entrance with a deviation of 45 degrees. Modeling had been done with ABAQUS software. Study parameters included: the stresses created in the body of the hangar, horizontal and vertical displacement of the crown and the air pressure in the tunnel. The failure modes of the hangar also discussed in the different cases and safe scaled distance is obtained. Using the results of this study, safe distance for arbitrary values of explosives substance could be estimated. It is expected during this distance, no failure occurs in the body of hangar.