نشریه مهندسی برق دریایی
سال دوم شماره 1 (پیاپی 2، بهار 1401)

The line of welds in welding may contain defects that cause irreparable damage to the entire project. Therefore, it is necessary to check the quality and strength of the welding line. There are several ways to evaluate this quality. Among the non-destructive testing methods, or NDT for short, that do not change the properties of the object under inspection and include X-ray, visual method and use of ultrasonic method. These images should be reviewed by weld line inspectors. Sometimes these x-ray images are of low quality due to the problems that arise in the process of imaging or digitizing and transferring them. In this article, we will try to improve the quality and clarity of the defects of these images. In this proposed method, after scanning and digitizing the images, an attempt has been made to remove the noise and increase the quality of their resolution with image processing methods, which include textural equalization, stretching the difference in color brightness, sharpening the edges and reducing noise, as well as morphological operations. Finally, the amount of quality improvement has been evaluated quantitatively using methods such as mean square error and peak signal-to-noise ratio. The results of using this method, which are in the quality determination section, clearly show that the images are of better quality than other methods.

In this paper, an electrostatic comb drive resonator structure in the frequency range below 3 kHz with the ability to resonate at several frequencies is designed, simulated and analyzed for use in active sonar. With the studies performed on the research background, one of the challenges of designing the comb drive resonator structure of electrostatic comb drive is to increase the frequency adjustment percentage, increase the frequency adjustment range and decrease the initial resonant frequency and voltage applied to the resonator structure; Here, to solve these challenges, the method of fingers with different non-uniform lengths, the method of changing the lengths of fingers non-uniformly and increasing the number of folded beams are suggested, respectively. In the following, the relationships related to the proposed structure, beams, comb drives and resonance frequency are researched and studied. The initial resonant frequency of this micro resonator was evaluated using two different software that are very close to each other (2549 Hz and 2384 Hz). This proximity to software results and analysis confirms the reliability of this structure. By increasing the voltage from 0 to 65 volts, this frequency can be adjusted from 2549 Hz to 280 Hz, which increases the frequency tuning range; Therefore, here we will have 88% change of resonant frequency, which in comparison with the work done, the range of resonant frequency adjustment has increased by 31%.

Frequency selective surface or FSS are widely used in the microwave and are used as 3D filters in many microwave appliances. This technology is used in marine radio systems and other microwave systems for use in radios, reflectors, frequency isolators, radar cross-section reduction, etc.In this paper, metamaterials and their applications are briefly introduced. Due to the importance of designing structures functioning in some discrete frequency ranges, some common methods for achieving multi-resonance metamaterials are investigated. The multi-resonance metamaterials are applicable for designing multiband structures such as filters, absorbers, FSS structures, etc. in microwave region. Two different multi-band metamaterial FSS structures, operating at 0.8 GHz, 1.6 GHz, and 2.4 GHz are proposed and simulated. Since the first proposed FSS is designed on one FR-4 substrate, it can be said that a more compact structure has been achieved as previous designs have been proposed in two-layer structure. In the second proposed design, the parameters used in the first structure have been taken into consideration. The number of structural parameters in the second design has been reduced in order to increase the speed of optimization, as well as its reconfigurability.

In military systems in order to Concealment naval vessels of weapons (missiles and torpedoes), be sure to check their audio frequency spectrum noises. Sources of noise, in the general case for marine vessels divided into three categories: hydrodynamic hull noise, machinery noise and noise from Propeller. Propeller noise impact is higher. cavitation and non_cavitation noise are different. Frequency spectrum analysis of global standards through octave filters are calculated. In this paper, received the noise of propeller at different speeds (200 to 2000 cycles Per minute) and constant pressure, with the high-sensitivity hydrophone and stored in the computer then with passes of octave filters is analyzed. Analysis of one-third octave band noise in three different tests. According to hydrophone distance to the propeller, propeller noise frequency spectrum in different periods have been mapped and compared. This analysis shows that periods of high-intensity noise in the bands 30 and 40 (frequency between 1000 and 10000) are more distributed.Based on the analyzes performed, the noise power spectrum in octave bands 40 to 42 are about 25 percent more than other bands, and increases as impeller speed increases. On the other bands these noise band are the musf effective bands on detection of torpedoes.

Control of the router's underwater remotely Operated Vehicles (ROVs) is challenging due to its highly nonlinear nature, strong coupling among variables, and unknown environment of the underwater in terms of underwater currents.The classic sliding mode controller is a popular control method in nonlinear dynamic tracking systems. The most obvious feature of the sliding mode controller is its high robustness. However, one of the problems with this control method is chattering in its control signal. this causes the use of high-frequency actuators. Eventually, it can reduce life duration and damage.Therefore, in this study, to reduce the chattering and High frequency fluctuations of the control signal applied to the trusters, a Model-Free High Order- sliding mode control is proposed. Finally, the performance of the proposed controller has simulated on a router underwater remotely Operated Vehicle. And the performance of the proposed system is compared with a standard mode sliding controller.

ower loss in multilevel converters has an essential role in many applications, especially in renewable energy systems. In this paper, a new topology with a reduced number of semiconductor power switches for the three phase multilevel inverter (MLI) has been proposed. This topology includes only equivalent power supplies which are connected in series to produce the output levels. Without using more than two series-connected power switches in each leg of the proposed MLI, the output levels are extended and therefore the conduction loss is reduced. The basic structure of the proposed topology is constructed of a five-level inverter which is connected in three legs configuration for three-phase applications. Furthermore, the modular configuration of the proposed MLI is constructed by adding the basic cells to the proposed five-level inverter and the output can be extended to more levels with the simple modular connection. The proposed modular multilevel inverter (MMLI) is simulated with sinusoidal pulse width modulation (SPWM) and its main features such as the number of power devices, switching and also conduction losses are investigated carefully and compared with reported ones. Moreover, the performance of this inverter has been verified by a three-phase five-level laboratory (1KVA/400v) prototype.