فصلنامه دریا فنون
سال هفتم شماره 3 (پیاپی 21، پاییز 1399)

In recent years, permanent magnet motors are used in various industrial applications due to high-performance characteristics such as reliability, efficiency, and high power and torque density. One of the newly introduced PM motors which has attracted much attention is Flux Switching Permanent Magnet (FSPM) motor. FSPM motor is a combination of regular PM motor and switched reluctance motor. One of the major problems of PM motor is the phenomenon of demagnetization which is reduced the motor performance characteristics. In this paper a perceive model for demagnetization phenomenon is presented using Time Stepping Finite Element Method (TSFEM). The results will be shown that the FSPM motor severely vulnerable to demagnetization at high temperatures. The electromagnetic torque of the motor will be declined from 132N.m to 30N.m. Also, demagnetization tolerant of FSPM motor against armature reaction, temperature, and self-demagnetization is evaluated. In addition given that until today there are no attempts in demagnetization fault detection of FSPM motor, using the electromagnetic torque spectrum at the faulty and healthy conditions of the motor, an index for demagnetization fault diagnosing will be introduced.

In the phased arrays the side lobes level (SLL) level is main problem which causes waste of energy or saturation of the receiver in the case of presence of the strong spatial blockers. In this paper, a weighting method was first used to reduce the level of SLL. However, this method increased the beam width and reduced resolution, which is not suitable for track applications. In next step hoping to increase the resolution, the distance between the antennas increased. But in this way, grating lobes appeared in the final beam. In fact, the main idea of the article is to solve this problem. It is shown that for a linear 11-element phased array system with up to 180° scan angle for simultaneously beam-forming and null-steering a resolution of 10 degrees was obtained for the amount of difference between desired beam and null points. The proposed system reduces the grating lobes to below -11.6 dB.

Today, energy efficiency in telecommunication networks is very important for the growth of users, so the presence of a wireless backup network is important for designing a heterogeneous network with energy efficiency in telecommunication networks. In this paper, the general framework for analyzing the energy efficiency of multi-layer multi-input networks, homogenous multi-output. This structure is provided in the presence of wireless backup links in both Up Link-Down Link directions in a set of telecommunication systems with the aim of optimal energy management. The studied network is designed with the assumed specifications of antenna M in each base station and user K in each cell. Spectral efficiency analysis and their complexity for Up Link-Down Link states were calculated and studied under different conditions using different methods. It has been observed that the method can be a common method, as it allows the calculation of the spectral efficiency of the spectral package in certain cases, such as non-adjacent spatial channels. Energy efficiency has also been studied in two scenarios with different powers, and it can be seen that energy efficiency using different methods is an indefinite function of operational power.

Today, the use of aluminum alloy metal sheets in the shipbuilding industry is expanded due to its high strength to weight ratio and good corrosion resistance. Due to the low formability of this alloy at room temperature, the deep hydrodynamic drawing process of AA6061 aluminum alloy double-stepped part under different heat treatment cycles has been experimentally investigated in this study. Firstly, the maximum forming depth before sheet rupture was obtained at different oil chamber pressures under the initial T6 heat treatment and 12bar was selected as the best sheet forming pressure. The results show that although by choosing the appropriate process parameters, these sheets can be formed with the least defects such as cracking and wrinkling, but the formability depth is very limited in the initial T6 state. Therefore, the effect of solution, aging and annealing heat treatments on the depth of forming, hardness and thickness distribution of hydroformed parts was investigated. Solution heat treatment at the sutiable temperature and time can improve the formability of the parts in the hydroforming process by 91.7%, while the hardness of the part is reduced by 36.2% compared to the initial T6 state. Hydroforming after the aging process reduces the formability by 16.7%, due to the increase in part hardness by 11.9% compared to the initial T6 state. With annealing heat treatment, the forming depth is improved by 116.7% compared to the initial T6, which results in a 69% reduction in the hardness of the workpiece.

During a ship’s service life, the hull is exposed to different types of loads and subjected to different damage scenarios, including corrosion deterioration that reduces the structural capacity. The most important degradation effects of ship structures are corrosion and fatigue cracks. Both of these aging effects have clear consequences of increasing stress levels and degrading the strength of ship structures for almost all relevant failure modes.Aging of ship structures may be defined as the progressive deterioration of structures as a result of normal operational use and environmental influences. The structural deterioration comes in the following forms: Coating damage, Corrosion, Cracking, Deformations and Changes in material properties. Investigation of corrosion prevention methods and their implementation in military vessels can greatly help the life of the vessel and reduce the cost of maintenance and repair. In this research, in particular, the phenomenon of corrosion in relation to the Marine Steel of military vessels has been studied. By examining the results of the experiments it was found that the vessel age is not the only criterion for assessing the strength of the sheets remaining since the results of the tensile test show that some of the lower hip specimens have less resistance to the tensile test than the higher hip specimens. In addition, maintenance management is as important as the age of the vessels.

In this research, a numerical study is conducted to simulate a separated two-phase flow of gas-liquid with the conservative two-fluid model. Also, the stability district of equations was investigated. The governing equations solved by the shock-capturing method. This technique can provide predicting the interface without using the flow field solving and the interface is obtained from the solution of the two-phase flow’s governing equations. Obtaining the well-posed criteria of the model as one of the results of this study is another novelty of this paper. Water faucet problem which is a famous and basic case study in fluid dynamics is implemented and results are compared to the analytical solution and finally, the strengths and weaknesses of the simulation are provided.

In the present study, in order to measure the functional characteristics of the diesel engine due to the mixing of the common fuel gasoline in Iran and the biodiesel fuel of the methyl ester of waste oil, various combinations of fuel with volume percentages B80, B60, B40, B20, B0 were prepared. Then, by applying different loads in a constant 1340 rpm range, the diesel engine tested (Messier Ferguson 240 tractor) was measured using an electric dynamometer of motor performance indicators. Exhaust emission temperature, thermal efficiency and air to fuel ratio up to the B40 fuel blend, and with a higher percentage of biodiesel, reduce the B40 fuel mixture. The ratio of air to fuel in the fuel mixture B40 is higher than other fuel mixtures. And the process of changing the air to fuel ratio is the same in all dynamometer loads. Particular fuel consumption and fuel consumption tune up to the B40 blend of fuel and increase the B40 fuel mix, due to the fact that the B40 fuel mixture has the lowest fuel consumption and specific fuel consumption. The use of this mixture is recommended as a superior fuel mix in terms of fuel economy in fixed-cycle diesel engines. Brake force and air flow rates are the same in all dynamometer loads and in all diesel and biodiesel fuel mixes. The reason for the stability of the braking power at a specified time is that by changing the amount of fuel, the dynamometer is kept at a constant limit of 1340 rpm. Considering the environmental requirements and the process of reducing fossil fuels, renewable energy biodiesel has been identified as one of the main alternatives to replacing diesel.

In this paper, a linear Lagrangian numerical model is used for simulating the solitary wave propagation over the sloped sea wall, as well as the regular wave propagation over an Impermeable submerged breakwater, called the relatively compact (GCM) hydrodynamic model of relatively compact particles (WCSPH). To simulate fluid turbulence, the SPS turbulence model, which was obtained by large eddy simulation (LES) approach, was used. The results of numerical simulations were compared with laboratory experiments. Also, the results of present numerical model were compared with the numerical model Shen et al. (2004). The results shown, the WCSPH computations produce better results than those of model Shen et al. (2004), with respect to the experimental data. The results of this study show that WCSPH method provides a useful tool to investigate the wave propagation over coastal structures.

When a propeller moves in the water, a strong Vortex flow generates around the Propeller Hub that reduces the performance of the propeller. Therefore, by adding rotating Fins to the back of the propeller, the flow deviates to the back of the bow cap and reduces the intensity of the vortex. In this research, Boss Cap Fins designed parametrically and added to the B-Series Propeller. The design performance points and non-design points for B-series propeller investigated and the cavitation starting point estimated. In the following, the effect of geometric changes of PBCF discussed and a geometric model proposed. In order to validate the numerical method, a Controllable Pitch Propeller has been used. The coupled Reynolds-averaged equations with cavitation mass transfer model were used to simulate flow field. The geometric changes of the Boss Cap Fins using the proposed method depict the improved efficiency in the high advanced coefficients.

The southern coast of the Caspian Sea is a very important area in the regards of economic and ecosystem activities. Results of field measurements using physical and biological sensors of a portable profiler in the southern boundary of the Caspian Sea were presented. The measurements were carried out on ten sampling stations in the study area. The observations were done during various months in warm and cold seasons by an Italian ocean seven probe. During measurements, probe was released into the water column from surface to the bottom. The collected data showed formation seasonal thermal stratification in water column. Sea surface temperature was recorded in rang of 29-26 oC in warm and 10-8 oC in cold seasons. Distribution of chlorophyll-a indicated maximum levels of 2.5 mg/m3 below the sea surface. Amounts of minimum concentrations of chlorophyll-a were recorded around 0.1 mg/m3 in across the intermediate water.