فصلنامه دریا فنون
سال پنجم شماره 3 (پیاپی 13، پاییز 1397)

Abstract: The Inertia Navigation Systems (INS) error, which today's basic navigation system for many uses, including military applications increases in time. Therefore, in order to achieve greater accuracy and reliability, especially in long-time navigation, such as in marine applications, an assistance system alongside the inertial navigation system should be used. In this case, the Global Positioning System (GPS) is the best navigational assistance system due to its complementary features. In an integrated navigation system consisting of a basic navigation system, along with a navigation assistance system, the Extended Kalman Filter (EKF) is a very common tool for integrating GPS and INS data. However, measurement and process noise covariance matrices are two important parameters in the Kalman filter, whose correct adjustment during navigation estimation process is very important in reducing the estimation error. In addition, since the governing equations of the inertial system are inherently nonlinear, the process of linearization in the Kalman filter adds an error due to linear approximation. Hence, researchers are looking for alternative algorithms for the Kalman filter, and so far a lot of research has been done. In this paper, an estimator based on particle optimization algorithm (PSO) is used as a substitute for Kalman filter based estimator. In this way, as soon as GPS observations are received, the estimation error of the navigation system based on the PSO algorithm is minimized to estimate the best output for the system. The simulation results and their application to several practical databases show that the proposed method significantly improved the accuracy of the estimation of navigational states by the integrated navigation system compared with conventional integration methods, such as the extended Kalman filter.

Detection and classification of Marine vessels based on their acoustic radiated noise is an important part of sonar systems. I this paper passive sonar targets classification algorithms is reviewed and a new algorithm is proposed. LDA feature extraction algorithm and Fusion of short time Fourier and timbre features is used in proposed algorithm which is called STFTLDA-Timb. Extracted features of proposed algorithm, are highly discriminant and classification accuracy of proposed algorithm is 8.45% better than STFT based classification algorithm. Obtained results of real data passive sonar classification show that classification accuracy of proposed algorithm is better than some common classification algorithms like statistical classifiers, neural networks and Ensemble Learning algorithms.

Abstract: Detection of small moving targets is of utmost importance in defense systems. For this purpose, using Infrared (IR) images is preferred to visible images for the reason that in circumstances such as marine navigation in fog and dust conditions, visible images are coming with false alarms that render the detection of small target difficult. So far different methods presented for IR small targets detection and false alarm reduction. In this study, first of all the image was enhanced with a morphological operation called Top-Hat. Then, the IR small target detection problem was considered as a tow-class pattern recognition problem and Fuzzy Cognitive Map (FCM) was applied for the classification. FCM is a simple, but also powerful intelligent method which is used for modeling and analysis of information. This paper is the first attempt to present FCM for IR small target detection. The obtained results indicate that FCM can detect the IR small targets with higher accuracy than any other pattern recognition methods.

SFCLs in normal operating conditions hasn’t any effect on power system, but in fault condiotion they bring a relatively large impedance in fault current path and limit it to a certain level. Faults in ships are usually due to fire, water penetration into the float and human factors. The failure of the electrical system and the sudden rise of the current are the main reasons for the fauls of the electronic equipment on ship, Considering the type of equipment used in the float, the cost and difficulty of replacing or repairing them, the issue of floating protection has particular importance. The magnetic shield SFCL is one of the most reliable categories of superconducting fault current limiting. In this paper, with the focus on these types of fault current limiters, simulations are needed to examine behavioral characteristics and the amount of fault limitation and it is proved that the proposed limiting mechanism has a good effect in reducing the short circuit current. It is also shown by measuring the amount of materials used in the structure of the core and windingsthat the proposed design is more economical than the similar ones.

Security is one of the most important problems facing the wider use of hydrogen and the increased risk of release into the closed environments. The existence of hydrogen gas in submarine's battery well is also accidental. One way to reduce this risk is to identify the behavior of hydrogen in different situations. For this reason, In this paper, transient behavior of the hydrogen gas in leakage and diffusion in a closed cylinder chamber is simulated numerically. Hydrogen Volume Fraction (HVF) extracted during 60 s leakage and up to 100 minutes after stopping the leak and compared with experimental data of the Shebeko work , in 2 , 50 and 100 minutes after stopping the leak. Moreover, location of the leakage parameter, investigated numerically. Studies have shown that high-risk regions of flammability are formed in top of the room, quickly and with an increase in height of release hole, hazard regions has become broader and becomes more lasting.

One of the most effective methods for reducing the drag force on planning hulls is the use of steps at the bottom of the ship. A step reduces the wetted surface area and consequently decreases the drag. In this article, the effect of using two transverse steps on the hydrodynamic performance of a hard-chined planning craft is considered with finite element based finite volume method. Navier stokes average time equations are solved with standard k-ɛ turbulence model coupled with volume of fluid equations for simulation of free surface turbulent flow around the hull using the Ansys-CFX software. In order to validate the proposed numerical model in this article, the obtained numerical results are compared against experimental results of Taunton et al. Subsequently, the results pertinent to the drag force, pressure distribution on the hull, the wetted surface, the water spray from the chine and wave pattern around the considered hull are presented and analyzed. Double-stepped planing hulls are found to have smaller drag, since flow separates from the steps and lead to reduction of the wetted surface which itself leads to significant reduction of frictional resistance. Meanwhile, they indicate some negative effects in their hydrodynamic performance in calm water like larger free water elevation behind the transom and larger hydrodynamic pressure in their bow section. It should be mentioned that two-stepped planing hulls have a small variable trim angle in comparison with one-stepped and non-stepped hulls and also improve the control of longitudinal running attitude.

In order to estimate the distance between the transmitter and receiver placement of transmitting audio (at a frequency of 50 kHz) in a stratified environment (three layers of different densities) used in laboratory conditions. Experiments in a glass tank with a length of 300 cm and a width of 50 cm and depth of 100 cm is conducted. is water, we recorded the noises contained in data Batrvs removed using a filter. Receivers, sound passing through each layer due to the speed of sound changes due to the density difference between layers with a time lag receives. By comparing this Akhtlafzmany there when passing through an environment resulting from changes in the speed of sound layering, and a homogeneous environment (tank full of water) and changes in peak-to-peak signal, received signal power and strength to help in moments of sound transmission techniques. compressed pulse we calculate the distance between the sensors.

Waves from deep water entering the shallow water, influenced by bottom topography, undergo changes such as wave breaking. Wave breaking causes parallel and vertical currents on the shore creating near shore currents. Its property of being parallel is called Long shore current. This research aims at studying these currents in Nayband bay. First, considering the height and the direction of the waves in the area in different seasons and years, the related wave roses, using the software WRlot, for the year 1992 and also the 11-year wave roses from 1992 to 2002 are drawn. The predominant wave direction in the area is found. Then, using the hydrographic map of the area, the shore’s slope is measured and after that, using the data gathered for the wave including height, period, direction in May, June, July and August (1992), the velocity of long shore currents is measured. The results show that the average velocity for the Long shore current in Nayband bay is 0.3 m/s the North eastern current is the predominant direction. The Width of surf zone in Nayband bay is 65 m.

Study of the northern Indian ocean climate from trade, economical and military aspect is important for Iran. In this study, by using data obtained from the sea surface temperature, wind stress and the empirical orthogonal functions analysis and spectral analysis the dominant modes of sea surface temperatures and wind stress are calculated and the contours have been drawn also have been analyzed. Then by calculating the cross correlation between dominant modes of the sea surface temperature and wind stress, mutual connection between these two quantities is analyzed separately. So that the interaction between these two quantities is synonymous more strongly than their interactions with the delay of time. The results show that sea surface temperature and wind stress have about high and inverse correlation. By comparing the first mode of changes in temperature and wind stress can be result that extreme irregularity of surface temperatures that are The main cause of dipole in the Indian ocean was affected displacement atmospheric and local and remote winds. also the change of wind stresses which are fluctuating with the cycle of the year through the monsoons cause the change in ocean surface temperature. In other words, Sea surface temperatures and wind stress are coupling system of ocean- atmosphere that interaction of these two physical quantity appears on climate change of area.

Noshahr port is one of the most important commercial ports of Iran in the Caspian Sea. The normal operation of the Noshahr port has been affected by sedimentation problems during the recent years. In this research, a numerical modoel (Mike 21) validated by field measured data has been applied to study the hydrodynamic and sediment condition around port for a year (2013). The results have been shown that the model is capable.to simulate the hydrodynamic condition such as: water level, wave height, current speed and sedimentation correctly. Also, The numerical results have been shown that different factors have effective role in sedimentation of Noshahr port.