فصلنامه علوم و فناوری دریا
سال بیست و هفتم شماره 107 (پاییز 1402)

It is a big challenge for a ELINT system to distinguish between some same type radars pulses that received from one direction and a frequency hopping radar. The aim of this paper is to classifying same type radar with frequency hopping that work in a near frequency band in the most complicated state. In existing methods, a unit's information is collected in peacetime and distinguished from same type radars in wartime by classification. In this research, the received signals from same type radars without prior knowledge are separated. This method is based on radar signature that parameters extracted from the pulse envelope, are used for pulse separation and determining the accurate number of radars. Due to the uncertainty of the number of radars, clustering is made in some iteration from 1 to k clusters resulting from frequency separation. Validation Criteria are then used to determine the correct number of clusters. The proposed method was tested by randomly generating 100 radar pulses from 5 classmate radar samples and the result shows and its results show the higher accuracy of Davis Boldin and Silhouette criteria than Gap and Kalinsky criteria in different SNRs. Also, Skewness and kurtosis properties have been shown to be relatively more stable at low SNRs.

As the use of underwater wireless networks is developed by introducing the Internet of Underwater Things (IoUT) idea, underwater communications attract considerable attention. One of the challenges in the new generation of networks is the high request of a large number of users to access the shared network resources simultaneously. Thus, applying a proper multiple access scheme is a serious requirement of these networks. Up to recently, using orthogonal multiple access (OMA) schemes was conventional. However, due to the limited network resources, conventional schemes cannot afford high users’ requests for utilizing shared resources and efficiently divide resources among different users as well. Non-orthogonal multiple access (NOMA) has emerged as a helpful solution for this problem as it allows users to share network resources simultaneously. On the other hand, in underwater environments acoustic and optical waves are used for communications, thus, this paper examines NOMA schemes in underwater wireless acoustic and optical communications. For that, first, the advantages, challenges, and limitations of underwater acoustic, and optical channels are examined. Then, after a brief description of NOMA, NOMA-based underwater investigations are reviewed and compared.

The behavior prediction of two-phase stratified flow considering the effect of surface tension is one of the great challenges in the two-phase flow problems. In the presented study, a spectral method has been used to solve this perplexity. In modeling, two moving fluids, in different phases, are moving parallel to each other along a channel. To increase accuracy of simulation; the two-pressure model and the surface tension model are considered. After imposing an initial small perturbation to the interface of two phases, behavior of wave length is analyzed both numerically and analytically. For the numerical simulation, spectral technique with a basic trigonometric function is used to solve governing equations. For linearization of non-linear parameters in spectral method, Newtonian linearization procedure is chosen. In order to evaluate the accuracy of spectral method in solving equations adapted for analyses, equations are solved with the finite difference scheme either. Results obtained from spectral and finite difference methods are compared with analytical solution. It is concluded that the spectral method is the most precise one to predict flow instability limit. This superiority demonstrates the capability of the spectral method in solving two-phase flow problems.

Proper design of ducting in the air conditioning system in ships is one of the most important parameters affecting the comfort of personnel. Currently, ducting on ships is designed based on the maximum transferable discharge in living spaces, while in practice the discharge required by living spaces varies at different time intervals. Therefore, duct design should be designed based on variable air volume. Among the three methods introduced for the design of ductwork for air conditioning systems in the 1997 ASHRAE Standard for ships, the only method based on optimization is the T method. In this method, the goal is to determine the size of the channels to reduce the cost of the life cycle. For variable volume air systems, a method based on the equations of the T-method and using the evolutionary algorithm of colonial competition has been performed in this paper. The conditions of the sample for design based on the proposed optimization method include changes in the inlet air flow rate to the ducts and changes in the rate of energy consumption calculation parameters. The colonial competition algorithm showed that it has the ability to show a more appropriate performance in achieving the optimal answer than the previous algorithms.

Choosing the right propulsion system is one of the important priorities of the vessel design process. Waterjet is actually a pump that is installed at the end of the vessel and its axis is rotated by the motor. This pump takes the water from under the vessel and ejects it from the back as a water jet. This action causes a reaction which is the same as the driving force or thrust. Due to its high propulsion efficiency, good maneuverability and less vibration, the waterjet propulsion system is widely used to propel marine vessels at high speed, so that the waterjet propulsion system can be a big step in the development and improvement of various vessels, especially in the field of fast vessels and be military. In this research card, the change in the form of the vessel body of the waterjet has been done in the software, and then by building the model, the behavior of the roll movement has been evaluated with the conditions of different regular waves in the traction pool. With the increase of the speed of the model, the amount of changes in the roll movement rate was also analyzed graphically. The results show that at relatively higher speeds, the rate of roll motion has a relatively high impact rate at the same encounter frequencies.

In this study, in order to investigate the concentration of heavy metals in Sefidrud river sediments and environmental effects, 15 sediment samples collected and concentrations of heavy metals (iron, arsenic, cobalt, chromium, nickel, lead, copper and zinc) by ICP- OES method were determined. Concentration of heavy metals in sediments for arsenic (0.25-26.24 ppm), cobalt (10.28-2.2ppm), chromium (50.2-126.2 ppm), nickel (26.50-50.25 ppm) copper (19.5- 49.3 ppm), lead (15-45 ppm) and zinc (60-74 ppm) were obtained. Based on the degree of pollution (Cd), Sefidrud sediments are classified in the moderate pollution range. Also, based on the modified degree of contamination index (mCd), all samples except 5 stations are classified in the range of low to medium degree of pollution and pollution load index (PLI) in most stations showed in the range of more than 1 (slightly polluted to polluted), but ecological risk (RI) were still in the low risk range. Evaluation of enrichment factor (EF) also showed chromium, lead and zinc are enriched.

As profitability is an efficiency indicator expressed fractionally, in this paper a fractional linear programming model for solving the container shipping problem along a specific route is presented. Due to the existing uncertainty in the parameters such as travel time and container weights, the fuzzy set theory is used to select a number of containers with different weights that contain different goods from among all the containers available at the port so that, in addition to the maximum transportation profitability, the maximum cargo capacity is also transported by the ship. Finally, this model is implemented and analyzed on a real example.

After the industrial and technological revolutions ،the dependence of military forces on new technologies increased to the extent that the revolution in military technology has caused a revolution in military strategies as well. For this reason most countries are developing and planning extensively to achieve new and emerging technologies. In the meantime the Republic of Iran has also achieved significant progress in the field of new and emerging sciences and technologies, so that it can be placed among the pioneering countries in this field. Among the new and emerging technologies, marine technologies are of special importance, so that the growth of marine technologies is noticeable for the activists of this field, both in the military and civilian fields. The Islamic Republic of Iran is a country with long sea borders, and this maritime situation of Iran requires a very efficient navy to be able to defend the national interests of the Republic of Iran at sea. Due to its continuous presence in the high seas on the one hand and being equipment-oriented on the other hand, the Iranian Navy should improve and develop its capabilities by monitoring the emerging marine technologies. For this reason, researchers seek to identify emerging technologies effective on the combat readiness of naval vessels of the Islamic Republic of Iran in anti-submarine warfare, which is one of the decisive operations in naval warfare. The present research was carried out in a descriptive and mixed approach and in two independent qualitative and quantitative stages. The statistical population used in this research is 100 people and the sample size is 80 people using Morgan's table. The results of the research show that the emerging technologies in the anti-submarine warfare of the naval ships of the Islamic Republic of Iran include artificial intelligence, acoustics, quantum and electromagnetics, which have a great impact on the discovery, identification, interception and destruction of subsurface targets.