نشریه مهندسی شناورهای تندرو
پیاپی 58 (بهار و تابستان 1400)

One of the most important factors in using military vessels is the ability to maneuvering. Determining the distance between the impellers and the body of the boats and the angle of the flow into the butterflies are very complex issues that ship designers particularly look at. In This article investigated the hydrodynamic modeling and analysis of a military vessel by taking two anti-rotating propeller using computational fluid dynamics. Fluent 5.14 software is used to simulate this process. The stern of the vessel is one of the components that it’s shape is effective on the resistance forces acting on the body of the vessel. The target vessel in this article was Frigate DTMB5415. First by altering the angle of the stern and displacement of the curvature of the stern, the best stern chosen from hydrodynamic point of view. Then two anti-rotating propeller was placed at the back of the chosen stern and analysis was performed for the shaft angles equal to zero and two degree respectively. Simulation of turbulent flow was performed by using k- ɛ RNG model with two equation. Two phase flow were considered for the analysis and modeling of two phase flow was carried out by volume of fluid method.

The negative effects of climate change in the future due to the rapid development of industry, technology and less attention to the environment, this will be a very serious issue as it is a serious threat to the future of humanity as Earth's climate is essential. Intergovernmental Panel on Climate Change IPCC with the primary objective of recognizing the aspects of climate change and in particular how human activities affect it, the Board has published a collection of evaluation and expert reports that are the most authoritative sources of information on climate change are well known have documented and the results announced them in first, second, third and fourth assessment reports. The Intergovernmental Panel on Climate Change has used the new RCP scenarios as representatives of trajectories of different concentrations of greenhouse gases in compiling its fifth evaluation report. According to the study of climate change in different parts of the world, this study has studied the changes in the Persian Gulf region of Iran. The result of the study is obtaining long-term forecast charts and observing the trend of temperature for this region in the long term from 1950 to 2100, from different models of IPCC Intergovernmental Panel on Climate Change scenarios, CNRM-CM5 and MIROC-CHEM prediction models were selected for prediction simulation and maximum temperature and minimum temperature prediction and the model was drawn and studied for three regions of Qeshm, Abu Musa and Bushehr located in the Persian Gulf

Any electrical transmission line that includes power transmission or electrical signal requires the matching of electrical parameters between different classes such as driver, source, cable, transmitter and receiver electronics, and transmitter and receiver elements such as antenna or signal converter; Because the transmission of maximum power and maintenance of the transmission signal in terms of amplitude and waveform, is a basic goal among the classes. In designing an electrical impedance matching circuit or network (EIMN) for piezoelectric sensors, actuators and converters requires careful consideration of operating frequencies, transmitter or receiver impedance, power supply or driver impedance, and receiver electronic impedance, as well as analysis of parameters affecting them. In this article, the latest and most widely used methods and effective factors for matching the impedance of sensors and piezoelectric converters under study in the world, based on which executive work has been done and with special attention to articles written based on practical results, are presented and studied. Has been analyzed. Also, the most widely used and well-known piezoelectric equivalent circuits, the selection of each, the types of impedance matching methods, the introduction of some of the software used in this topic are introduced between the sections and effective and more studied working and environmental factors will be explained and presented.

Internal combustion engines have a special importance and place in the transportation industry as generators of propulsion and the beating heart of vehicles. In recent years, according to global conditions and laws on environmental requirements and energy efficiency, is one of the priorities of manufacturing companies and optimization of these engines, Maximum use of the capacity of a product with high productivity and optimal fuel consumption; Therefore, the issues of power, torque and fuel consumption are more important than other engine components. To maximize the capacity of an internal combustion engine produced or upgraded, two proposed solutions are considered. The first solution is to study and study the geometric parameters of the engine and redesign it in terms of dimensions. The second solution is to study the technical components (main parameters) of the engine and calculate the solution to optimize them, which is possible with minor changes in some non-main parts of the engine. In this article, by reviewing and reviewing articles, books and resources related to specialized workshops and conferences presented in this field, These two solutions are discussed theoretically from two perspectives of increasing engine power and engine output efficiencies and after reviewing each, solutions and suggestions to increase the power of these engines are provided.

A three-dimensional hydrodynamic model was implemented to study water circulation in the Persian Gulf using the FVCOM model. This model included accurate depth measurements of the Persian Gulf, long-term wind regime, evaporation, precipitation, surface temperature and also water inflow from Arvand River. Boundary data included changes in water tidal level as well as changes in temperature and salinity of water entering the model. Modeling was performed over a long period of 16 years. The results of the model were compared with field data on water level and flow velocities using the statistical parameters of root mean square estimation errors (RMSE) and correlation coefficient. Changes in water level and horizontal water velocity components had a high correlation with field data and showed a very low error rate. Also, the pattern of wind currents at the surface and depth in the Persian Gulf were completely consistent with the results of previous valid studies. The results of the model show the ability of the model to use it in marine research.

One of the undesirable phenomena in the achievement of planing vessels at high speeds is the phenomenon of longitudinal instability. This phenomenon, which is in fact an unstable coupling between heave and pitch, causes damage to the vessel, equipment and crew. In order to evaluate and accurately calculate the speed of occurrence of this phenomenon in the design stages, it is necessary to perform numerical analysis or model testing. Therefore, the existence of a valid data set to validate these analyzes, especially numerical analysis is essential.In this paper, by setting the dynamic trim as a criterion for the occurrence of porpoising in a planing boat, the amount of this trim at different speeds is measured on a sample of a cougar boat without steps in the sea. These results show that the dynamic trim has an increasing trend with increasing speed and after the float is in planing mode, it gradually decreases and tends to an almost constant value at high speeds.

High speed craft is one of the most sophisticated marine vehicles. Stability and speed are two important factors in the construction of planing hulls. The attractiveness and complexity of this type of vessel has led many researchers to work in this field. In the current paper, the effect of wedge on the stability and resistance of a mono-hull high speed craft is experimentally investigated. The studied vessel has a constant deadrise angle and the length to width ratio is 4.8. The tests were conducted at transverse Froude numbers of 0.1 - 4.26 at the National Iranian Marine Laboratory. The measured parameters are trim, rise up, resistance and the wetted length of chine and keel. The vessel at the speed of 8 m/s was unstable. To stabilize the vessel, a wedge with a height of 5 mm and a length of 92 mm has been used. In this case, in addition to the absence of porpoing, the resistance of the vessel, decreases.

Nowadays, maritime transport is increasing significantly, and the probability of collisions between ships in densely populated region has increased. In this regard, improving the ship maneuvering performance has a significant impact directly on the economy and safety of navigation. Therefore, the study of maneuver parameters is considered as a mandatory issue in the process of designing a ship. In this study, first the validation of the results has been done for the KCS. The benchmark ship at froud number 0.201 was simulated in three degrees of freedom including: surge, heave and pitch and calm water conditions, then the results were compared by computational fluid dynamics. Validation was performed according to the ITTC Recommendation by three levels of gridding, and the value of numerical uncertainty was also estimated. Uncertainty less than 12% and numerical error respect to experimental less than 6% were extracted. A good match was presented between the numerical and laboratory results. A good match was presented between the numerical and laboratory results. The two-phase flow the Volume Of Fluid (VOF) method and the DES turbulence model were used to model the flow around the hull. The effect of propeller was induced by actuator disk method and based on flowchart in ship stern.