IRANIAN JOURNAL OF MARINE TECHNOLOGY
Year:2023 | Volume:10 | Issue:1|Papers Count:10

In this paper, a comprehensive study is performed on the realization of inhomogeneous materials, the extraction of the electromagnetic parameters, and the applications in microwave engineering. First, the concepts and definitions of inhomogeneous materials are presented as one of the main categories of electromagnetic complex media. Then, the applications of these materials in microwave engineering are introduced, namely gradient refractive index lenses, radar absorbing materials and radomes. In the next step, the realization methods of these materials are presented. Designing devices and achieving various applications requires intimate knowledge of the electromagnetic parameters. In the last part, the methods for retrieving and measuring the electromagnetic properties of inhomogeneous materials in the microwave frequency range are explained. Numerous articles which deal with the subject of inhomogeneous materials in microwave engineering, confirm the importance of this topic. According to the applications mentioned for inhomogeneous materials, these can be used in military and naval systems to increase the country's defense and military capabilities. Therefore, it is important to perform a comprehensive review of inhomogeneous materials in microwave engineering and to make researchers more familiar with this field and facilitate the future researches. In this research, in the form of a review article, this issue has been addressed.

Each software Global Positioning System (GPS) receiver consists of three sections called acquisition, tracking, and navigation. The acquisition section is known as the first part of the receiver that has some serious problems to increase the speed of acquiring the GPS signals. In some cases, the Doppler Effect (DE) that causes the relative motion between satellite and receiver leads to transforming the carrier frequency of the GPS receiver. In this study, we propose new method to achieve fast acquisition in GPS receivers. In our presented method, the Doppler frequency band has a deviation of ; so that it has been considered in the worst case. In the proposed method, we limit the frequency band by using a smaller filter and then completely cover the space of by shifting the filter. In each shift, the satellites in Line of Sight (LOS) are detected and separated from the collection list of satellites. In this method, the best filter that reduces the acquisition time is selected. To validate proposed method, we utilize five real datasets that two of them were collected from around Iran University of Science and Technology. The experimental results represent that our suggested method outperforms the conventional band-fixed method in terms of the execution time and computational complexity by approximately 22% and 19%, respectively.

Slamming is usually a combination of different loads on the vessel hull and is one of the main causes of failure and failure in the structure of vessels. The influence of slamming compared to other loads from the sea waves is so significant that in some cases the vessels are severely damaged locally by structural damages. Failure to accurately estimate the influence of slamming will result in improper design of the ship's structure, thereby weakening the ship's safety. In trimaran vessels, the fluid force applied to the side hulls is transmitted to the main hull by a transverse deck. As a result, one of the most important parts of the structure of this vessel is the transverse deck structure, the design of which requires the calculation of the incoming wave forces. In this paper, the phenomenon of slamming on the side hull and the transverse deck of the trimaran has been examined experimentally by measuring the pressure created by the collision of the model of trimaran vessel with the water surface. The results showed that in bottom regions of trimaran vessels, the pressure on bottom is increased going from stem towards stern. Also, the pressure on the transverse deck increases from the main hull to the side hulls. In the position of the shaft axis and the shaft post at the main hull, owing to the earlier impact of the stern of the main hull with the water surface compared to the side hulls, the pressure is higher than the other positions.

In recent decades, the use of aerated concrete in offshore structures has been considered by researchers due to its superior properties of mechanical properties and thermal resistance compared to ordinary concrete. In this laboratory research, a mixing plan was made of ordinary concrete with a cement grade of 450 kg/m3. A mixing design was also made of fermented concrete based on composite kiln slag to compare and evaluate the compressive strength of concrete under ambient temperature and temperature of 500 °C, at a 90-day curing age. Following X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM) images at 90 days of processing age at ambient temperature and 500 °C to evaluate the microstructure and verification of compressive strength test results on samples Concrete was done. The results show that the compressive strength at ambient temperature is 62.43 MPa for ordinary concrete and 68.03 MPa for mild concrete, which have a difference of about 9%. By applying heat to concrete samples, the rate of compressive strength drop in conventional concrete was 37.7% and in quilted concrete was 16.4%. The results of XRD and SEM tests were coordinated with each other and overlapped with the results of compressive strength test at ambient temperature and high temperature.

Baron Dam is located 12 km south of Makou city, on the Zangmar River near the village of Baron. In this study, using two-dimensional models of HEC-RAS and CCHE2D, modeling of dam failure and flood flow routing due to failure of Baron Makou embankment dam performed and so on the depth and speed of the flow presented. According to the depth range and speed flow, the risk index map obtained and Flood risk management is prepared and presented according to the time of flooding to different downstream points. Comparing the two software, it can be said that in HEC-RAS software, the number of points considered in one section is limited and the software can detect only 300 dots in a period, but in CCHE2D software there is no such limitation in terms of mesh network and the cross section can be extended up to several kilometers. The biggest time difference in the arrival of the wave front is related to the last period, the end of Mako city, and the reason is that the mesh size is greater. At the end of Makou city, due to the low manning coefficient and also the smoothness of the area route, the water depth decreases and extension more in the cross section. The most areas that are likely to be submerged are Qaleh Juq village and Valiasr town. According to the risk index, the risk of flooding is 100 in most parts of the region, which indicates that in the event of a dam failure, the loss of life and property will be very high.

The first step in studying wind energy potential in an area is providing suitable wind. The typical method to gather wind data is installing wind masts. This method entails huge costs that can be irreversible when that area has not good wind potential. An alternative method for collecting appropriate data, very common today, is using numerical models. In this study, the WRF model and its various physical parameterizations are investigated to evaluate wind energy in Kish Island. In the first step, five different boundary layer parameterizations were evaluated in order to obtain optimal settings for simulating wind flow. Then, the best parameterization was obtained by comparing the schemes with data measured by the wind mast of the Renewable Energy Organization of Iran. Finally, the model was run for one year with the optimal settings obtained, and the results were compared with the available data. For comparison, Weibull distribution, daily and monthly average wind speed diagrams, vertical wind shear and wind direction diagrams were used. The results showed that MYNN2.5 parameterization has the best performance among the five schemas used. In addition, the shape and scale parameters of the model and the measured data differed slightly, and the wind direction showed slight counterclockwise deviation. In general, it can be said that the WRF model has good ability in simulating wind field in Kish area.

In recent decades, different methods of wave prediction model have been used. Experimental methods, numerical methods, soft computing algorithms are among such methods. In this study, the height of the waves in the Gulf of Mexico is predicted in two different sections. In the first part, the ALM algorithm and GIDS model and in the second part, the experimental methods of SPM and CEM are investigated. For this purpose, first, the collected data and wind stress factor in SPM model were pre-processed using ALM and GIDS models. After investigations, it was determined that the wind stress factor should be corrected with a dimensionless correction factor p⁄((1⁄2 ρ〖〖 u〗_10〗^2 ) ). In the next step, the most suitable input of the GIDS model was selected and in order to reduce the time of this modeling, different combinations of modified wind stress factor Ua with wavelength were considered, which resulted in the parameter U_a (gX)^(-0.02) The most appropriate input for the GIDS model is in predicting the height of the waves. In the second part of the paper, each of the SPM and CEM models was implemented and compared with the optimized GIDS model. The results showed that the GIDS model was more accurate in predicting the wave height of the Gulf of Mexico. Then the wind speed correction coefficient was modified using a genetic algorithm and with this operation the SPM model was modified and presented as the most appropriate prediction model.

In this study, the seasonal variations of the sound speed in the water column and consequently the temperature and salinity in Babolsar area were investigated based on the field measurements. Data used in this study were carried out in two hot (summer) and cold (winter) seasons of 2019, from inshore to far offshore. The mixed layer depth was calculated using the seasonal combination threshold value of 1.25 (C°) for summer data and 0.1 (C°) for winter data. The results show that in the summer, due to the hot weather and increased stratification, the mixed layer depth is shallower than what is observed in winter. In winter, vertical convection increased due to the decrease in air temperature which leads to the deep mixed layer depth and in most of the stations whole water column is completely mixed. Consequently, whole column water surrounded with the sonic layer channel during the winter while in summer any sonic channel was observed. The surface temperature in summer is significantly higher than winter. Also, the thermocline slope is very strong in summer and very weak in winter.

Ports are important hubs that connect maritime transport to other modes. For this reason, ports are considered important infrastructures for freight transportation, trade, and the global economy. Therefore, optimizing port plans and operations will play a significant role in port costs and revenues. Berth planning is part of port operations that includes two problems; Berth Allocation Problem (BAP) and Quay Crane Assignment Problem (QCAP). The optimal solution to these two problems can affect the freight transportation speed and cost. This paper integrated modeling two problems BAP and QCAP, and solved them using four metaheuristic algorithms (GA, ICA, TS, ACO). Whereas berth planning is in a disrupted environment and unforeseen events may occur during the program's execution, incurring additional costs for the port, or even stopping the initial plan execution, rescheduling the original berth plan is necessary. This paper uses two methods (global and local rescheduling) with metaheuristic algorithms to find the optimal method for berth rescheduling. Numerical analysis shows the proper performance of GA and ICA algorithms in solving the initial berth planning model and the global rescheduling method. In contrast, for local rescheduling, the ACO algorithm has better performance. Evaluation and validation of models and methods of solving this paper are done using the data of ships' arrival and departure in Shahid Rajaei port.

In this paper, a new high step-up current-fed LLC resonant DC-DC converter with a center-tapped transformer is proposed. By selecting the switching frequency to be lower than, but near to, the series resonant frequency of the LLC resonant tank, soft-switching operation of all semiconductors, i.e., zero voltage switching (ZVS) turn-on of power MOSFETs and zero current switching (ZCS) turn-off of diodes is achieved. This leads to lower electromagnetic interference (EMI) and lower switching losses and improves the converter efficiency. An interleaved structure is used at the primary side. Thus, input current ripple is smaller, and its frequency is twice the switching frequency. Consequently, a smaller input filter is necessary in practice. The converter with 1.2 kW output power and 760 V regulated output voltage with 80-200 V input voltage variations is simulated. The output voltage is regulated by using asymmetric pulse width modulation (APWM) at 200 kHz switching frequency. Finally, a 700-W prototype has been implemented and experimental results are also presented to verify the simulation results.