فصلنامه دریا فنون
سال دهم شماره 3 (پیاپی 33، پاییز 1402)

In Non-orthogonal multiple access (NOMA), more power is allocated to a user with a weaker channel quality than to a user with a stronger channel. The strong user (SU) uses successive interference cancellation (SIC) for detecting the weak user (WU) symbols before detecting its symbols. This causes t the WU information to be intercepted at the SU. This paper uses directional modulation (DM) to create security. By using DM in a multi-input and single-output (MISO-NOMA) network, the WU data and SU data are protected from each other and eavesdroppers. This method eliminates the effect of the WU information on the location of the SU so the SU doesn’t need the SIC for detecting and eliminating the WU data. With no need for the SIC, the detection complexity is reduced for SU. Simulation confirms that this scheme creates security and a low bit error rate (BER) for transmitted information.

In this article, the design and simulation of the dual-band microstrip antenna with two circular band polarizations with a compressed structure and suitable bandwidth as well as circular polarization capability have been attempted. The proposed antenna is due to having circular polarization with suitable bandwidth and very low VSWR, which shows that the impedance matching is very good for marine applications in which the interference of sea waves with electromagnetic waves is very high, and the issues of multi-paths and reflection of waves from the sea and ocean and Even large lakes (Caspian Lake) can be very effective. In addition, to increase the bandwidth and axial ratio of the antenna as much as possible, an incomplete ground structure is used, which provides better bandwidth and axial ratio values to the user by reducing the structure. By examining the results of the proposed antenna, it can be recognized that the right-round pattern has more amplitudes than the left-round pattern in the direction of zero degrees, so the desired antenna has right-round circular polarization. Also, according to the radiation pattern, reducing the surface of the secondary petals and achieving a suitable level of radiation is one of the advantages of the proposed antenna. It is necessary to point out that the axial ratio of 0.8 and the appropriate bandwidth of the proposed antenna are helpful and helpful in overcoming fading and interference. It is multi-path. 3.5 GHz frequency which is used for weather radar, and surface ship radar, and 10 GHz working frequency which is used for communication systems for air traffic control, and sea ship traffic control. The results of the simulated antenna show that the proposed antenna has a right-handed circular polarization, which means that the proposed antenna can be practical and effective in marine communication.

Electroencephalographic signal processing of divers can reveal useful information about the brain complications caused by diving that these people suffer over the years. In this paper, an optimal method based on a convolutional neural network is presented, which extracts the optimal features from the recorded signal by the network itself. This method is suitable for recognizing the abnormalities of different brain regions in different people in different bands. The obtained results show anomalies in the alpha band and in O1, O2, T7 and T8 channels. Two groups can be separated in the alpha band with accuracy, precision and recall of 94.2%, 92.9% and 91.3%, respectively.

One of the maneuvers in marine vehicles is turning maneuver. To investigate effect of sail position in submarine turning maneuver, 6 models of Suboff with different longitudinal sail positions are performed in Star CCM+. First, the simulation method, meshing, and validation are described. Validation shows that the error of calculating the resistance is less than 10%, which indicates the accuracy of numerical solution. Then, the turning maneuvers of the submarines are performed and their results are compared. The results show that by moving the sail from the nose to the aft, drift angle of the submarine decreases and the radius of turning circle decreases then increases.

Nowadays, the need to access high speeds and durability in bad sea conditions for vessels has provided a wide and extensive field of research. Reducing Ship motions from an economic aspect leads to a reduction in the power required to move the ship and thus reducing fuel consumption and cost and increases the operational capacity of employees. One of the major problems of sea transportation is seasickness caused by Pitch motions of vessels for passengers and ship crew. When the vessels are subjected to Pitch motions by the wave, the acceleration of the heave and pitch motions will intensify. The geometric form of the underwater ship hull and the design form of its hydrofoils have a significant effect on the dynamic performance of this vessel. High-speed hydrofoil vessel has attracted the attention of ship designers and architects due to their special capabilities, and extensive research is being done on them. In this paper, the initial design of the model was done in the Rhino software. The ship hull mold and front and rear hydrofoils were made by CNC milling machine. Then model of ship was tested in the towing tank at different speeds and frequencies, and the heave and pitch motions RAO were extracted. The results showed that by increasing the frequency or decreasing the wave length, the motions of the ship are greatly reduced. At high speeds and after passing the maximum point, the ship reaches a stable state.

In this paper, interceptor appendages at heights of 2 and 3 mm with two spans of 50 and 100% vessel width were used to improve the behavior of the high-speed vessel, and the amount and effect of the mentioned appendage on the resistance components and characteristics of a vessel wake were evaluated using numerical methods. The numerical simulations were performed in a completely three-dimensional with two degrees of freedom under calm water conditions. The results of numerical simulation were validated with similar experimental results. The results show that using an interceptor with a span of 100% vessel width causes negative trim and a sharp increase in the vessel’s resistance. The trim of the vessel equipped with an interceptor with a height of 2 and 3 mm and a span of 50% of vessel width compared to the base vessel has decreased by an average of 39 and 46%, which increases wet surface area and consequently increases friction resistance.The interceptor reduces the pressure difference in the bow and stern of the vessel by increasing the pressure in the stern, and it reduces the pressure resistance of the vessel by 9 and 9.8% at the mentioned heights. The results study of the wake created behind the vessel under the influence of adding an interceptor show that by reducing trim at a constant speed, the height of the wake profile created behind the vessel decreases, and its amplitude increases.

Monopiles are the most used offshore wind turbine foundation. They are also used in oil docks and dolphin piers. Monopiles are usually 2 to 8 meters in diameter. In these piles, the ratio of free length to diameter is about 5 to 15 and the ratio of driven length to diameter is about 2 to 6. The basic concepts for monopiles in deep water are still unclear. Thus current methods lead to non-economic designs. The main purpose of this study is to investigate the mechanical behavior of a monopile under the influence of cyclic lateral loads in sandy soils. In this research, 9 Tests were designed and implemented to geotechnical centrifuge modeling at 40g acceleration. The model pile is a 5.1cm in diameter steel pipe installed in Firouzkouh-161 sand and the cumulative displacement and secant stiffness of the system were investigated by cyclic lateral loading. Based on the results of the modeling, formulas have been proposed to estimate the displacement and stiffness of these piles under the effect of different cyclic lateral loads. The results of this research show that the most important factors in the cumulative deformation of the monopile head are the type and cyclic load amplitude.

Millimeter wave channel modeling of the fifth generation (5G) cellular networks is very important in every region because of different weather parameters, especially the tropical coasts of Iran (humid climate) are very effective in the millimeter wave channel model. According to the economic importance of the Chabahar region and the development of its telecommunication networks, and also because of the extreme humidity of the region, in this article, the 5G millimeter wave channel model has been investigated in the frequency bands of 28, 38, 60, and 73 GHz. In the channel modeling the NYUSIM simulator has been used as a tool to generate parameters received power of the channel, path loss exponent (PLE), and root mean square (RMS) delay spread for omnidirectional and directional power delay profile (PDP). The selected scenario is the urban microcell with line-of-sight (LOS) and non-line-of-sight (NLOS) propagation environments and considering two types of X-Pol and Co-Pol polarization for the antenna. The results show that the received power of the channel and PLE depend on the type of polarization and propagation environment, and RMS Delay Spread depends on the type of propagation environment. NLOS environment and X-Pol polarization reduce the received power of the channel and increase the PLE. Also, the RMS delay spread decreases in the NLOS environment.

Considering the safe route, short route, less time to reach the destination leads to economic savings in fuel consumption, less depreciation of the vessel and green seafaring (less pollution). The path that meets the above conditions is called the optimal path. The purpose of this research is to evaluate the influencing factors in weather routing from the two dimensions of safety and economic savings. Influential factors in weather routing include providing weather forecast data, network generation based on the great circle route, interpolation of weather data on the network, calculation of floating speed in different routes taking into account the weather condition, considering the safety restrictions of the float and searching of the shortest route. The results showed that in order to achieve an optimal route, all the above factors must be carefully considered in the routing process.

Monitoring the concentration of heavy metals in marine sediments is very important for identifying existing and potential risks and developing prevention programs. In the present study, considering the various unloading, loading and shipping activities in Shahid Bahonar Port, the concentration of heavy metals including chromium(Cr), zinc(Zn), copper(Cu), nickel(Ni), mercury(Hg), arsenic(As), manganese(Mn), cobalt(Co), iron(Fe) and cadmium(Cd) in the eleven stations of marine area of the port was measured by atomic absorption method. The Muller's indices (Igeo), contamination factor (CF), contamination degree index (Cd), modified contamination degree index (mCd) and RI ecological risk assessment index was calculated. The average value of metal concentration was compared with NOAA and ISQGs international sediment quality standards as well.The findings showed that the highest concentration of heavy metals was related to iron > manganese > zinc > chromium > nickel > copper > cobalt > arsenic > cadmium > mercury respectively. The average value of heavy metals concentration measured in the sediments in terms of milligrams per kilogram was calculated as arsenic (3.4), cadmium (1.2), iron (22261.4), copper (61.64), zinc (116.3), manganese (333.79), mercury (0.23), cobalt (26.29), chromium (177.92) and nickel (90.96) ) respectively. The results of ecological risk indices show that heavy metals contamination is moderate or considerable in most of the studied stations and the stations inside the port basin have a higher cumulative risk than those outside the port.According to the obtained results, it can be said that the port activities, the discharge of the balance water of the ships, as well as the closure of the port basin and the low ratio of water exchange to the outside of the basin are factors that cause settlement and accumulation of heavy metals in the sediments