Journal of Naval Sciences and Engineering

113-132

Authors: Ahmet YURTSEVEN

Present paper investigates the hydrodynamics of a Controllable Pitch Propeller (CPP) which is generated by geometrical modifications applied on a benchmark propeller designed as a fixed pitch propeller (FPP). The aim of the study is to examine the practical feasibility of converting a propeller model designed as a FPP to a new one operating with CPP principles. The flow around propeller models is solved via computational fluid dynamics and the results of the new generated model are presented in comparison with its parent geometry. The well-known KP505 propeller model is chosen as test case. The primary results show that the effect of the geometrical modifications on the propeller efficiency mainly depends on the propeller load and the blade pitch angle. The optimum efficiency point is determined as J=0.8, for the new design model. For the J values below this point, negative pitch angle changes improve the efficiency compared to FPP model. If the J exceeds the above mentioned value, positive pitch angle changes are needed to gain efficiency increase. The results led us to conclude that, it’s possible to convert a FPP to a CPP, but the blade pitch angle should be carefully controlled, for efficient operation.

159-173

Authors: Merve GÜVENÇ , İsmail ŞİŞMAN , A. Arif ERGİN

The structure that transforms a linear polarized signal into right-hand or left-hand circularly polarized signals is called a polarizer. In this study, a dual-band waveguide polarizer used in satellite communications is presented. The waveguide polarizer is designed using iris structures on a square waveguide. The purpose of the polarizer is to transmit the ±45° tilted linearly polarized signal at its input to the output as a right-hand or left-hand circularly polarized wave, and vice versa. At the input of the polarizer, a transition is designed between the WR42 waveguide and the square waveguide. At the output stage, a transition from square waveguide to circular waveguide is designed. In this paper, the design steps of both the polarizer and the transition sections, the optimization parameters, and simulation results are presented in full detail. The simulations are performed with a commercial electromagnetic simulation software, CST Studio Suite. The design operates within the Ka-band, specifically at 17.2 – 21.2 GHz and 27.5 – 31 GHz frequency bands. The insertion loss of the iris polarizer is <0.05 dB, the return loss is >23 dB, and the phase difference is less than 15° around 90° for both bands.

3-17

Authors: Yasemin TABAK Şeyda POLAT Ayşen KILIÇ Bayise KAVAKLI VATANSEVER

Alumina powders are utilized in many industries like electronics, metallurgy optoelectronics, and fine ceramic composites. In this study, non-aqueous-based tape casting of alumina was carried out in a non-continuous single-blade tape casting machine. A slurry of alumina powder in a solvent was cast on a stationary surface with additives like dispersants, binders, and plasticizers. After the green tapes were dried, they were sintered to obtain the final desired shape. The hydraulic pressing method was used to increase the density of the alumina tapes. Layered alumina ceramics were produced at 5 different temperatures by pressureless sintering method (1450°C, 1500°C, 1550°C, 1600°C and 1650°C) for 5 h to observe the effect of sintering temperature. Results revealed the sintering conditions for obtaining translucent alumina, with the utilized slurry composition. Translucent alumina ceramics have gained importance as parts of semiconductor devices, substrates for electric parts, as heat/corrosion materials in reaction tubes and crucibles, and are used in medical equipment.

35-51

Authors: Ahmet Yiğit ARABUL Celal Fadıl KUMRU

Submarine cables are critical assets that play an indispensable role in interconnected power systems, particularly in cross-sea energy transmission and offshore wind turbines. Their importance is further accentuated in exigent situations such as natural disasters and war, which emphasize the need for secure, reliable and uninterrupted energy supply. Furthermore, the investment and operating costs of submarine cables are relatively higher than other power system equipment, making it essential to operate them under the rated operating conditions to prevent possible faults and ensure power system stability. As thermal stress can lead to damage of cable insulation, it is an essential parameter to consider. Overloading increases thermal stress, resulting in rapid aging of the cable insulation and a shorter cable lifetime. Therefore, it is imperative to determine the maximum conductor temperatures and current carrying capacities of submarine cables under varying loading rates and ambient conditions using thermal analysis. In this study, thermal analyses are carried out for a three-phase, 220 kV HVAC, XLPE insulated submarine cable under different loading conditions. The findings demonstrate that the maximum temperature, current carrying capacity, and total losses of the cable are significantly impacted by loading rate, phase imbalance, and seawater temperature.

77-100

Authors: Alpay ACAR Murat URYAN Ali DOĞRUL Asım Sinan KARAKURT Doç. Dr. Cenk ÇELİK

HVAC system design and optimization of the ventilation and air-conditioning of indoor environments are crucial for human comfort. Especially in recent years, due to the Covid pandemic, the importance of this hot topic is noticed. This study aims to focus on the HVAC performance of a dorm compartment onboard a naval surface ship since the ship environment is a good example of indoor air ventilation problem. The HVAC performance was investigated using a RANS solver. The numerical analyses were conducted for different scenarios and the results were finally discussed in terms of HVAC system location, air temperature, air intake and outlet conditions. As a conclusion, the current HVAC system design was found insufficient and alternative solutions were proposed in order to improve indoor air quality and thermal comfort.