فصلنامه دریا فنون
سال هشتم شماره 1 (پیاپی 23، بهار 1400)

Multilevel inverters have great applications nowadays as one of preferred solutions for medium and high power applications. As one of the most popular hybrid multilevel inverter topologies, the five-level active-neutral-point-clamped inverter combines the features of the conventional flying-capacitor type and Neutral-Point-Clamped (NPC) type inverter and was commercially used for industrial applications. In order to further decrease the number of active switches, this paper proposes a five-level five-switch NPC topology, which employs only five active switches and four discrete diodes. The modulation strategy for five-level five-switch NPC inverter is discussed. A 4.5KVA single phase prototype is simulated using the PSPICE software to verify the validity and flexibility of the proposed topology and control method.

In this paper a interference-resistant ultra-wide-band low noise amplifier is presented in frequency range of 3.1-10.6 GHz for high data rate wireless communication and radio receiver. Second and third order input intercept point (IIP2 and IIP3) are enhanced in the novel circuit by new circuit structure and by adopting the Improved Complementary Derivative Superposition (ICDS), Forward Body Bias (FBB)and resistive feedback. The proposed LNA uses low pass filter and common source topology as wide-band input matching. Utilizing FBB technique reduce the threshold voltage and hence lower power consumption is achieved. The post-layout simulation of the proposed LNA in a 180 nm RF CMOS process show S11 less than - 10 dB in the entire band. Minimum of noise figure is 2.6 dB, power gain is about 11 dB, maximum of IIP3 and of IIP2 are 3.61 dB and 31.11 dB, respectively. The chip area is 734 mm ×870 mm. The DC power consumption is only 7.4 mW with 1.2V DC supply.

Today there are generally two types of forming methods used in the manufacture of body and metal components for ships and vessels, each of which has its own advantages and disadvantages. In this paper, the use of pulsating pressure hydroforming method has increased the formability of metal sheets and it has been shown that steel plate can be formed with higher height than conventional methods. For this purpose, a sheet hydroforming die was made in which cylindrical workpieces of different heights were formed. The cylindrical workpiece was chosen as a standard shape for forming. To apply the oil pressure with different modes, a device was developed that was capable of generating pulsating pressure paths such as sinusoidal, triangular, stepped and trapezoidal states. The results showed that if the oil was applied at a constant pressure of 180 bar, the formation depth increased by 56.25% compared to the oil-free state. Also, increasing the oil pressure under the sheet increases the height of the rupture. Using pulsating pressure in the range of 180 to 220 bar with a frequency of 20Hz, the rupture height was increased more than 4 times and 47.82%, respectively, without oil and with 220 bar constant pressure. It was observed that as the pressure increased, the deviation from the thickness distribution increased. However, if the pulsating pressure is used, the deviation from the standard thickness of the workpeice is less than 220 bar. However, the forming depth of the workpiece with pulsating pressure is approximately 50% greater than the constant pressure state of 220 bar.

To develop environmentally friendly ships, an integrated system with the ability to generate electricity and fresh water has been proposed to restore the heat dissipation of a marine engine.The system includes a marine diesel engine, an organic Rankin cycle and a multi-impact desalination unit. The results of the modeling show that the proposed cycle is capable of producing 387.97 kW of electricity and 7.04 cubic meters per hour of fresh water. The organic Rankin cycle has a 67% share of total energy depletion, while it is 33% for the desalination plant. Also, the effect of the main design parameters, which are heat transfer oil temperature, turbine inlet pressure and pinpoint temperature difference in the evaporator on the performance of the system has been evaluated and shown.

Interaction of the propeller-rudder system is important in design of propulsion system as well as maneuvering for all types of ships. This paper is presented to analyze the propeller-rudder system using ANSYS-Fluent commercial software. The results of calculating the hydrodynamic dimensionless coefficients, streamlines and pressure distribution on the propeller-rudder are presented and compared in different advance coefficients. Also, hydrodynamic coefficients of the propeller-rudder have been studied and compared at various rudder angles of 0, 10, 20 and 30 degrees. In all cases, the efficiency increases with increasing the advance coefficient, however the torque and thrust coefficients decreases. So, in high advance coefficient, the existence of the rudder the efficiency increases by 3% and with increasing the angle of the rudder, this effect is double (6%). The existence of the rudder in the low advance coefficients, torque and thrust coefficients increases by 5% and 9% respectively. In high advance coefficients, the angle of the rudder is causes the torque coefficient and trusted coefficient to increase 17% and 9% respectively. In the existence of the rudder-propeller to angle of 10 [deg.] and without propeller to an angle of 20, the increasing of advance coefficient does not have significant effect on the lift and drag coefficients.

The existence of a hull body against progressive waves could change the profile of the wave hitting the structure depending on the dimensions of the hull compared to the wavelength. The diffraction wave applies the first and second order forces on the body behind the first body. In this paper, the results obtained from numerical simulations of a cylindrical platform were compared with experimental data. Then, to examine the interaction between two floating structures, by placing two fixed and floating cylinders in front of the second-order Stokes wave, the effect of changing the distance between these cylinders is addressed to obtain the forces applied on the floating cylinder. Numerical analysis in the frequency domain is performed using the boundary element software in ANSYS-AQWA based on the 3D diffraction/radiation theory. According to the results achieved from AQWA, it can be concluded that by increasing the distance between the floating cylinder and the fixed cylinder, the diffraction force decreases and the maximum of this force occurs at higher frequencies. Moreover, at lower frequencies, less drift force is applied to the floating cylinder. Eventually, the drift force increase with the increasing wave frequency. By examining the effect of increasing the radius of the floating cylinder, it can be seen that as the cylinder radius increases, the amount of drainage force and the dispersion of the floating cylinder increases with a higher rate.

Due to the presence of too many parameters in the problem of the marine propeller design such as the existence of several conflicting objectives, unstable and very complex environmental conditions, marine propellers design has been one of the challenging subjects for designers and researchers in this field. Nowadays, meta-heuristic algorithms are used as one of the highly efficient solutions to solve complex engineering problems. In this paper, for the first time, SMA algorithm is used to design the marine propellers. For this purpose, two targets viz. maximize the efficiency and minimize the cavitation, which are in conflict with each other, as the fitness function is considered. To do this, during several trials, the effect of two important parameters on the fitness function, i.e. chord and thickness of the propeller, is calculated and the most optimal mode is selected by the SMA algorithm. In order to compare the results, the benchmark algorithms such as GWO، ALO، MFO و BBO are used. The results show that the propeller with 5 or 6 blades with rotation speeds between 180 to 190 RPM will have the best performance in the tradeoff between efficiency and cavitation. Results indicate the improvement of 2.4 percent in efficiency and 21dB reduction in cavitation level.

In this paper, the effects of the presence or initiation of damage in the core of sandwich beams of a ship hull are investigated in terms of variations in mechanical behavior.This type of damages is difficult to detect due to the presence in depth of the laminate and is essential to predict their mechanical effects.As one of the measures of mechanical behavior, the effect of damage characteristics on Hotspots of the structure of longitudinal stiffeners of sandwich beam is determined by the buckling response changes.Firstly, the beam model is simulated through ABAQUS 6-14 finite element software and the Hotspots and their stress states are determined by static analyses. By evaluating the measures of mechanical criteria parameters of the beam structure in Hotspots, initial core damage effects are described as a result of analyses and determination of critical buckling loads.The accuracy and validation of the simulation and analyses results from ABAQUS finite element software has been confirmed by comparing the results of buckling analyses from the software in different modes with the experimental and analytical theory(formula) results.Therefore, by knowing the sensitivity of the structure response to the damage properties, the design of beams and stiffeners in the hull of ships based on damage tolerant philosophy has been possible.

There are different soil-pile-structure interaction models that can affect on the response of offshore wind turbine structures. In this research, we tried to estimate the response of wind turbine offshore structures under tree different soil-pile-structure models which includes fixity level length with 2, 4, 6 and 8 times of pile diameter, stiffness matrix and independent springs and compared with more advanced and complete model of non-linear Winkler beam model. Results show the model of fixity level length with 8 times of diameter gives the best result among other models for axial loads in structural bracing elements and can be used as simplified pile-soil-structure interaction for wind turbine offshore structures.

The Global Positioning System (GPS) receiver is vulnerable to variety of interferences, inclusive of intentional and unintentional ones. This accordingly decreases the navigation accuracy of receiver, and thus causes the receiver cannot work correctly in presence of interference. Consequently, a research effort has begun to study detection and mitigation of GPS spoofing approaches as a serious interference. For the question of GPS spoofing detection, the guidelines are usually raw-based and hard to mathematically model. This make the use of a fuzzy design for the GPS data ideal. A fuzzy logic system is introduced in this paper to analyze and examine the vulnerability of civil GPS receivers towards different kinds of spoofing attacks. This system improves decision-making capability of the receiver from inexact data. The proposed method utilizes the fuzzy set and then the theory of statistical test to recognize fake signals. The studied parameters as input variables are selected from tracking and navigation stage of the GPS receiver.