فصلنامه دریا فنون
سال دهم شماره 4 (پیاپی 34، زمستان 1402)

In this article, a metamaterial structure is proposed to reduce the mutual coupling of the elements of a microstrip array antenna. First, the metamaterial unit cell is designed for resonance at the operating frequency of 5.3 GHz, and the results of the simulation of the metamaterial unit cell show 99% absorption at the central frequency. The patch antennas are designed for the working frequency of 5.3 GHz and the mutual coupling between its elements is registered. By placing a 6x1 array of metamaterial in the upper part of the patch antenna elements, the structure is simulated again by CST software. The results of the simulation and practical measurements show that by using the metamaterial array, the mutual coupling decreases by 23 dB and reaches minus 45 dB. This amount of reduction of mutual coupling, which is done with the accurate implementation of metamaterials, has no effect on the working frequency and radiation properties of the antenna, and the results of simulation and construction are completely consistent By comparing the results of this article and similar articles, it can be concluded that only by placing 6 metamaterial unit cells in the upper part of the antennas (unlike the articles where our metamaterials are located in the antenna elements), the amount of mutual coupling has been greatly reduced.

Due to the critical role of sonar signals in identifying and tracking targets and objects in the water environment, the existence of classification systems for these targets is particularly important. There are various ways to do classification. One of these ways is using automatic systems that intelligently classify targets, which are less expensive and can perform the classification process with high accuracy.In this research, the main goal is to automatically classify targets in the water environment using passive sonar signals and through semi-supervised deep neural networks. In this research, several types of neural network architectures have been presented, which, by using new mechanisms such as the use of attention gates and jump connections, have high classification accuracy compared to existing methods and have acceptable performance in performing classification. By using only 25% of the labeled data, the proposed basic network has provided a 10.59% improvement compared to the accuracy stated in the article of the examined data, with an accuracy of 70.17% on the test data. Also, the other proposed network called Attention-Resnet-2 has exceeded by obtaining 71.92% accuracy and has achieved this improvement by 12.34%.

In this paper, a new high voltage gain DC-DC converter is proposed. The method of connecting the Z-source network to the primary side of an interleaved step-up converter achieves the advantages of both Z-source and interleaved converters, and realizes their benefits. Using the pulse width modulation (PWM) technique to control the output, zero voltage switching (ZVS) conditions at turn on times are provided for the active semiconductors and zero current switching (ZCS) conditions at the turn off times of the diodes are provided in the converter. The realization of the soft switching conditions for all power switches and diodes in the converter has reduced EMI noise and switching losses and thus increased the converter efficiency. Therefore, it is possible to design the converter to operate at high frequencies, if the appropriate devices are available, in order to reduce the size and volume of passive components of the converter, including inductors, capacitors, and filters required to increase the power density. In addition, soft switching operation helps to increase their useful life by reducing voltage and current stresses of the components. To verify the proposed converter performance, a laboratory sample of it is also designed and implemented and experimental results are given under different conditions, in addition to simulation and mathematical analysis. Here, despite changes in input voltage of 40-50 V and output power of 200-400 W, the output voltage value of 400 V is well regulated, by properly controlling the pulse width at the switching frequency of 100 kHz. In addition, maximum efficiency value of this converter is 96% in simulation results and 92.5% in the given experimental results. Considering that, the EMI noise and switching losses are effectively reduced in this converter; low conduction loss components can be used, if necessary to increase the converter efficiency, practically.

This study investigates the tensile and flexural properties of polylactic acid (PLA)-polylactic acid/aluminum multimaterial components. The aim is to characterize 3D-printed components of composite filaments produced using laboratory (desktop) extruders. The composite filament comprises a PLA polymer matrix and 40 wt.% aluminum particles as the reinforcement. The multimaterial (PLA-PLA/aluminum) tensile and flexural specimens were printed using a single nozzle fused deposition modeling 3D printer. These samples are composed of ten layers; the lower eight layers are made of PLA, and the upper two are composed of PLA/aluminum. An optimization process obtains this structure. In addition, scanning electron microscopy (SEM) was used to study the fracture section of the samples; the distribution of reinforcing particles and the fracture behavior of the samples were analyzed. Furthermore, the mechanical and structural characteristics of the samples manufactured using laboratory filament were compared to those of a commercial PLA/aluminum filament. The results showed that adding aluminum powder increases the formability of the composite filament compared to the pure PLA filament. On the other hand, pores (intra- and inter-layer) increase, and the mechanical strength diminishes.

Submerged floating tunnel (SFT) is an innovative structure to cross waterways such as straits, fjords and lakes. With the increase in width and depth of waterways, conventional structures such as cable-stayed bridges, underground tunnels or immersed tunnels become uneconomic structures. In order to properly understand the tunnel-hydrodynamic coupling behavior, this structure should be investigated under severe sea conditions and with different mooring systems and configurations. In this research, the dynamic response of SFTs with different configurations and mooring systems under regular waves has been compared. In order to obtain the dynamic responses caused by regular wave load, modeling in ABAQUS software and AQUA method has been used. The arched configuration in the SFTs reduces the range of structural responses. It has been shown that the SFT with arched configuration behaved much better than the tunnel with straight configuration. Also, from the point of view of cable mooring systems, it was found that the diagonal cables played a very effective role in controlling the change of horizontal locations; While the vertical cable bracing is also effective in the horizontal response of the structure. Also, by comparing the natural frequencies of the structure in the presented models, the probability of amplification of models with arched configuration and diagonal cable bracing is much less than other models.

Predicting the effect of waves on breakwaters is very important for port design. One of the types of breakwaters that can be installed, moved and reused in different conditions, even in deep waters, is floating breakwaters. But their complex reaction in response to the passing of the wave makes their use suitable for a certain periodicity range. One of the most important and influential issues in the efficiency of a floating breakwater is its geometric shape. In this research, numerical investigation of the effect of floating breakwater section geometry in single and double rows on the wave transmission coefficient in ANSYS-AQWA software for wave periods between 3 and 10 seconds has been investigated. For validation, the results of the present numerical model were compared with the experimental results, which are in good agreement. In the used models, the immersion depth is assumed constant and the proposed geometric sections with different masses and densities were investigated. Based on the results obtained with in the mentioned periods, a geometry with the best efficiency and lower cost has been proposed for related projects.

Today, the importance of reducing the drag force in subsurface vehicles has increased even more due to their use in the military, research and entertainment industries. In the leading research, the effect of various methods of reducing the friction drag, including the method of connecting the riblet to the body, covering the body, injecting air and heating the body, has been investigated on a subsurface vehicle. Validation of the results of the present numerical analysis was done by two solvers, Star CCM and Ansys Fluent, with experimental data. The combined shear stress transfer turbulence model was used to model the turbulent flow. The results of the study showed that the aforementioned methods in the best case reduced the drag force by 5.5%, 19.9%, 51.9% and 6.2%, respectively. All methods reduced the coefficient of friction drag. Also, the methods of coating and heating caused a slight decrease in the back pressure coefficient, while in the methods of connecting the riblet to the body and injecting air into the surrounding flow, this coefficient increased.

Nearshore is dynamic and constantly affected by the environmental conditions of the sea, on the other hand, it plays a great role in economic-social management issues. The shoreline is also a part of the nearshore that is constantly affected by tide, waves, currents and human activities. Therefore, it is expected that this section will always be accompanied by changes. The first step of any nearshore development and construction is to know the hydrodynamic conditions of the area. In this study, an attempt has been made to investigate the sensitivity of the shoreline of Bandar Lengeh County by considering the height and energy of nearshore waves. Wave height and energy data have been estimated by running the MIKE 21 spectral wave numerical model for a period of 12 months. The results have been obtained with good accuracy compared to ECMWF data. The correlation coefficient and the RMSE are equal to 0.95 and 0.239. The modeling results show that the maximum average height and energy of waves in the shoreline are 0.22 m and 0.21 kW/m, respectively, in the last months of spring and the beginning of summer. Using the fuzzy-gamma logic and considering the gamma coefficient as 0.9, shoreline sensitivity to variables has been estimated and finally divided into three classes High, moderate, and low. 20% of the shoreline is in the high class, and 23% and 57% of the shoreline are in the moderate and low class, respectively.

this paper, a Modified aperture antenna is introduced and designed using feeding by the adjacent couple method. This structure covers multi-frequency ability, improves gain and efficiency, and reduces antenna size remarkably. The proposed antenna comprises meta-material cellular units and a new fractal microstrip antenna. The indirect feeding technique in the proposed antenna increases bandwidth, design capability in the array antennae, a reduction of return losses and the unwanted radiations. The structure has an acceptable multi-band bandwidth. In addition, by increasing the frequency of the fractal antenna in smaller resonant frequencies and in a fixed frequency, the smaller antenna size and reduction of mutual promotion are covered. Finally, the results of the return loss and radiation pattern in two modes of simulation and production make a relative suitable match. The desired antenna is designed according to the logarithmic triangular patch by coupling with the adjacent feeder line. In order to reduce the number of array elements, the scale factor of K is used, while compensation is applied at the end of the feeder line, which leads to an increase in the antenna efficiency.