فصلنامه دریا فنون
سال هشتم شماره 2 (پیاپی 24، تابستان 1400)

Nowadays, numerous economic benefits can be obtained from oceans and seas. It is obvious that to realize these benefits, the areas should be monitored in a real-time manner. One of the technologies that can be used in this regard is the Underwater Wireless Sensor Network (UWSN). Due to the extent of the areas targeted to cover by UWSNs and the performance goals such as high reliability and low latency, designing a communication network to collect underwater sensors data is optimally complex. This study aims to provide a way to design an overlay network of relays to achieve acceptable reliability in acceptable time. To reduce the complexity, the idea of the current work is to divide the problem into two sub-problems and solve them iteratively. In the first dub-problem, using a formulation based on linear programming, a network of routers will be built to cover all the sensors. In the second sub-problem, more routers are iteratively added to the communication network to ensure the required reliability threshold. In this sub-problem, while balancing the degree of routers in the network graph, it is aimed to maximize the number of network links. Simulations results show that the proposed method can significantly improve network reliability in acceptable time.

In this paper, the fracture of V- notches with end holes (VO- notch) in tungsten-copper functionally graded material (W-Cu FGM) under the prevalent mode II loading is studied experimentally and theoretically. W-Cu FGM specimens are made by powder metallurgy technique in the experimental part. Several fracture tests are done on VO- notched W-Cu FGM specimens under prevalent mode loading for different notch tip radii and notch depths. To predict the fracture loads of VO- notched FGM specimens under prevalent mode loading, the Averaged Strain Energy Density (ASED) over a well-defined control volume is applied in the theoretical section. Moreover, the effect of notch tip radius, notch depth and notch opening angle on the fracture loads is investigated. In addition to good agreement between the numerical and experimental results, this study shows that Strain Energy Density (SED) theory works well on VO- notched FGM specimens under prevalent mode loading.

A significant amount of the produced energy in marine vehicles is used in the air conditioning sectors. Therefore it is necessary to reduce this amount by using efficient methods. . One of the new efficient methods is liquid desicants. Using of liquid desicants can be a good solution to reduce energy consumption, especially in hot and humid areas. The use of membrane contactors is one of the suitable methods for making contact between liquid desicant and humid air. In the present study polysulfone membranes were synthesized by phase separation method using two different types of solvents. The structure and performance of the membranes were examined thorough dehumidification process. The best dehumidification efficiency was 45.14%, which was related to the PSU-DMF-3 sample. The weather conditions in Bushehr port and the 1800-ton landing craft ship (designed by the shipbuilding and offshore industries company) as an example were used in simulation process. The results of simulation showed that by using a membrane contactor with a channel height of 10 mm and a membrane length of 8.644 m and a PSU - DMF-3 membrane in the air conditioning system of ships, the energy saving can reach to 34.4%

In this study, the use of exhaust heat from, flow gas of the engine of an oil tanker in the single and double absorption system, thermodynamically and economically, has been analyzed for air conditioning of its residential space. The input parameters of the models are placed in the equations according to the tropical climate of the ship and the minimum recoverable heat of the engine exhaust gas, and the output of the models is calculated using EES software. The Lithium Bromide Single Effect Cycle does not meet the ship's needs for tropical conditions, but the double effect cycle with high reliability is suitable for all weather conditions. If the absorption cycle is affected, the amount of heat dissipation of fuel energy is 206.92 GJ/year, while this value is 47762 GJ/year for the compression cycle. Exergy analysis shows that the highest irreversibility rate in the double-effect absorption system is related to the high-temperature generator (at the rate of 76.94 kW). The recovery time of the initial cost of the double effect cycle compared to the compression cycle is calculated to be 3.78 years.

Daily increase in fuel cost and also marine environment pollution tends designers and engineers to design and optimizebased on reducing losses and energy consumption. Reduction of fuel consumption and marine environment pollutionare categorized in high priority problems in design of new vessels and optimization of current ones. Using hydrofoilbetween two hulls is one of the best strategies in optimization cycle of fuel consumption of catamarans. HYSUCATcomes from ‘‘Hydrofoil Supported Catamarans’’ and stands for a vessel which is composed of a catamaran hull andhydrofoils mounted between two hulls. These hydrofoils tolerate part of hull weight in high speed and decrease wettedsurface of vessel. This element reduces drag of vessel and consequently fuel consumption by decreasing the wetted surface. This research deals with determination of a suitable hydrofoil section to reduce drag and increase stability of a catamaran vessel using experimental data. Full-scale foils were constructed and mounted on a vessel in continue, and itsperformance was examined in sea tests. Determining the best section and also the most suitable position for mountingthe foil is a novel study in the field of hydrodynamics of catamaran vessels.

Solar Autonomous Underwater Vehicles uses solar panels for providing energy. As limitation of energy and power in solar AUVs is strict and vital, the exact estimation of hydrodynamic resistance and power is important. In this paper, numerical hydrodynamic calculation for an AUV with 50 watts solar panels is performed. Hydrodynamic resistance in several speeds is calculated by CFD method in ANSYS FLUENT18, based on solving RANS equation and using K-ω SST turbulent method. For validation of CFD results, experimental results the Myring AUV is used and compared to numerical results. It shows a good agreement between numerical and experimental results and clears that K-ω SST turbulent method is an ideal method for simulating the low speed AUV problems

One of the important issues in evaluating the numerical analysis of ship resistance by the computational fluid dynamics method is to investigate its uncertainty, which includes verification and validation studies. In this study, the KCS container Ship in calm water was simulated numerically at the design speed, equivalent of Froude number 0.26. The finite volume method was used to discretize the Navier Stokes equations and the turbulence model of shear stress transfer. The free surface was modeled by the fluid volume and inertia of the ship motions using the coupled rigid-body coupling equations with fluid. Uncertainty values were assessed for verification and validation studies. The verification study was investigated by three simulation solutions with different mesh resolution . The numerical method uncertainty was less than 5.76% after the study and in the validation study, considering the uncertainty of the model test, the uncertainty was 5.84%. The results showed good accuracy of the method used and gridding.

Determination of the breach parameters and resulting hydrograph of the embankment dam failure due to overtopping and piping erosion has great importance because of the significant injuries and environmental impacts. In this research, by investigations on the erosion mechanisms, the affecting processes on the embankment dam failure are examined, and empirical relationships are presented to determine the peak outflow discharge (Qp), time, and breach characteristics in the overtopping and piping failure cases. Physical models with different heights and technical specifications were constructed and failed in the experimental flume to study the breach expansion rates. In the other part of the research, new empirical relations have been developed to predict the eroded volume (Ver) based on the breach characteristics and the contribution of various resources including historical, experimental, and hypothetical failures of the real embankments. The BREACH mathematical model has been used to obtain the failure parameters related to the hypothetical breach of the recent dams. According to observations, the failure time (tf) is highly dependent on hydraulic and breach characteristics. Therefore, the tf is considered as a function of these characteristics in the proposed formulas. Based on the performance indices, the values of the determination coefficient (R^2) for the newly proposed Qp relations are equal to 0.94 and 0.91, respectively, in the overtopping and piping failures. This coefficient for the development of the Ver relationship is equal to 0.98, and for the development of tf equations are equal to 0.85 and 0.87, respectively. Since the outflow hydrograph of a breached embankment dam is largely depended on the geometry and evolution time of the breach, the failure hydrographs of real embankments are simulated using a combination of regression analysis and evolutionary algorithms as a case study.

For design and construction of coastal structures, including breakwaters, after preliminary design based on experimental relationships, it is necessary to perform physical modeling to select the optimal design. In this research, the design wave effects on the protection seawall of Chabahar’s Shahid Beheshti Port were evaluated through physical modeling in the wave flume. The results of the test were monitored by several sensors in different stages of modeling. It was revealed that the project is over-designed, since the structure underwent no changes after being exposed to the designed waves. Since the sections of this breakwater were designed in the form of reshaping berm breakwater, it was expected that it changes to S shape profile, however, it did not occur and the sections remained stable like conventional rubble mound breakwater. Thus, considering value engineering and in order to reduce the project cost, the project was re-designed, modeled, and tested several times to find the most optimized condition for the design.

In this paper, an improved phase-shifted full-bridge (PSFB) dc-dc converter with coupled inductors and a current doubler rectifier (CDR) for battery charger applications in electric vehicles (EVs) is proposed. By using two coupled inductors as opposed to traditional output filter inductors, the RMS currents, the circulating current, and the voltage stresses on the secondary side are decreased. Besides, the zero-voltage-switching (ZVS) operation range is lengthened. Therefore, higher efficiencies are achieved. The two recursive inductors in the primary side have small and negligible values compared to the output inductors and, consequently, neither complex control systems nor extra components (like auxiliary circuits and active clamps) are needed. Thus, by using the proposed topology a simple structure with a simple control system will be obtained. Utilizing the proposed converter leads to reduce the RMS currents, the circulating current, and the voltage stresses on the secondary side. Besides, the cost and size of the system are not changed compared to the traditional one, as well. Moreover, the required energy for ZVS operation of power MOSFETs will be decreased which leads to higher efficiencies over a more extended operation range. Finally, the proposed and traditional converters have been simulated under the following conditions: the input voltage (150-250 V), switching frequency (200 kHz), the output voltage (75-85 V), and the output current (1.85-18.5 A). The simulation results validate the major benefits of the proposed phase-shifted full-bridge dc-dc converter over the traditional one.