فصلنامه دریا فنون
سال نهم شماره 3 (پیاپی 29، پاییز 1401)

Due to the widespread usage of three-phase induction motors in various industries, including power plants, refineries, petrochemicals, mining, transportation, shipping, etc., requirements for monitoring their conditions to detect various incipient defects are increasingly growing. It is necessary to detect the induction motor faults, which may cause the motor to stop unintentionally, in the shortest time with the highest accuracy in order to eliminate the problem with prior planning before spreading it. Some effective indices for detecting different types of the rolling-element bearing localized faults are derived from the motor vibration signal. In this paper, the mentioned indices are measured and analyzed in different scenarios to evaluate their reliability using laboratory test results. The results show that the influence of the motor temperature in the range from 30 to 75oC on the magnitudes of the indices is between 1 to 3 dbs; considering the magnitudes of the indices, such influence is rather negligible. Similarly, increasing the motor load from no-load up to full-load can influence the magnitude of the best selected indices by up to 2 dbs. In addition, increasing the localized defect severity (the hole diameter) from 2 to 5 mm usually affects the indices magnitudes by an oscillating manner with a maximum oscillation amplitude of 20 dbs.

One of the consequences of the wave disturbances for a surface vessel is the creation of roll motion. This, disrupts the operation of weapons, navigation equipment, personnel and missions, especially on a frigates. Therefore, roll motion and control of ship motion, especially, frigates using appropriate controllers, is very important.The nonlinear model of roll motion has a high computational complexity, so most researchers have used its linearized model. On the other hand, in many researches, for the simplicity, has not been considered, the fin actuator model and its effect on the roll model. In this paper, the fin stabilizer is used to stabilize the roll motion of a frigate and the model used in this research is a nonlinear roll motion model combined with the fin actuator model. In order to reduce of the roll motion, has been used of a robust adaptive sliding mode controller, due to the lack of sensitivity to external factors as well as estimating the disturbance band and reducing the angle of the desired roll motion. The closed-loop stability of the system has also been proved using Lyapunov theory. Then the simulation results of the closed loop system with the proposed controller are compared with the conventional PID controller and the superiority of the proposed controller performance is shown.

Underwater image retrieval has been considered an essential part of modern navigation, spatial positioning, and marine exploration. Image retrieval systems extract the visual content in feature vector information and similar image evaluations. In this work, two neural networks are combined for image feature extraction. The proposed system extracts image features using the VGG-16 neural network. Reinforcement of the features from the previous step with the discovery of the relationships between the features and the dynamics of the image has been done using the LSTM recursive network. Combining the two categories of image features has made it possible to describe images more closely. The proposed method was evaluated on the underwater visible image dataset. The results show that the accuracy of the proposed method in retrieving similar images based on the structural similarity index (SSIM) method and Feature similarity index matrix (FSIM) is 42.6% and 76%, respectively.

In recent years, multi-hull vessels due to their special features such as good seakeeping, high hydrostatic stability, low hydrodynamic resistance and large deck area have been considered by architects and designers and a lot of research is under taken on their. One of these vessel is a SWATH that consists of two or more submerged under water hulls and a cross deck that bodies connected together by cross deck. In these ship, wave loading on the cross deck is of particular importance that in the preliminary design phase the forces and moments on this part of the structure should be determined. In this paper, the modified body of a swath, called semi-swath has been produced and determined wave induced forces at zero speed and at different forward speeds in regular waves with the installation of multi-axis load cells on cross structure. The results show that the maximum force is related to the force Fz (force in the direction of the model transverse axis) and the lowest force in Fy (force along the longitudinal axis) is observed. In the case of moments, the moment is also about the longitudinal axis (maximum) and the lowest moment with a large difference is Mz (torque about the transverse axis). The existnce of Kinks and the creation of maximum and minimum points on the diagrams indicates the coupling of the heave and pitch motion with the forces and moments of thc cross deck of vessel.

This study has been conducted for three levels of impact energy (three Drop weight elevations). Sheets are made of st12, with dimensions of 230 * 220 mm and with thicknesses of 1 mm, 2 mm in length connected by bolts. The sheets are placed in a completely free manner on the fixture. The screws are made of a type of bolt Standard din933. In the experimental method, the picker acceleration has been measured by the accelerometer sensor and the permanent deformation of the sheet is measured at the end of the impact. The parameters to be evaluated include the impact acceleration on the sheet, the degree of permanent deformation and the energy absorption for the sheets. ABAQS finite element software has been used for numerical modeling. Comparing the results of experimental and numerical methods shows that these two research methods have close results. The results also show that energy absorption in sheets of one layer is greater than double-layered sheets, as well as acceleration in double-layered sheets more than sheets of one layer.

This study investigated the performance of a labyrinth weir with a trapezoidal cross-section at different heights. For this purpose, the geometry of the weirs was designed in Inventor software, and simulation was performed in Flow3D software. Validated the model with laboratory data, and the results of the model were in good agreement with the results of laboratory data. Examined the numerical model at three heights of 10, 14 and 18 cm and three different angles and two apex widths; Analysis of the results showed that with decreasing the weir height (P), the discharge coefficient (Cd) increases. Reducing the weir height by 44% increased the average discharge coefficient by 2 to 3%. In all simulated models, with decreasing relative water head, the decreasing trend of discharge coefficient was also reduced. During the constant crest length, with a 100% increase in the weir angle, the discharge coefficient of all three weir heights increased by 20 to 25%. A 40% increase in crest length at a fixed angle increased the average discharge coefficients of all three heights by 12 to 15%. As a result, at a constant angle, the increase in crest length is greater than the second case (constant crest length and increase in weir angle) on the flow rate; This is important in designing labyrinth weirs to have a maximum discharge coefficient and should be considered.

In this paper, a linear Lagrangian numerical model is used for simulating the wave propagation due to dam breaks on a dry bed with a hump, as well as the regular wave propagation on impermeable sloped sea wall, called the relatively compact (GCM) hydrodynamic model of relatively compact particles (WCSPH). This model is two-dimensional and considers the fluid to be weakly compressible. In addition to solving the viscous fluid governing equations for velocity and density field uses the state equation for obtaining the pressure. This reduces the computational volume compared to the base method of the particle hydrodynamic model. To simulate fluid turbulence in the wave propagation process due to dam break on a dry bed with a hump and regular wave propagation on impermeable sloped sea wall 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 other numerical model. The results shown, the WCSPH computations produce better results than those of other numerical model, with respect to the experimental data. The modeling results show that many complex phenomena that occur in wave propagation over a hump, such as hydraulic jump, wave breaking and partial reflections can be well modeled using the WCSPH method. The results of this study show that WCSPH method provides a useful tool to investigate the wave propagation due to dam break and regular wave over impermeable hump.

In this research, the microstructural study of geopolymer concrete based on mechanical tests and durability of concrete has been done. In this regard, one design of ordinary concrete and three designs of geopolymer (in two categories) were made. The first group of geopolymer concrete in three designs contained 0, 4 and 8% nanosilica and after selecting the optimal design (in terms of superiority of results in tests) from these three designs, the second category includes two other designs and adding 1 and 2% of polyolefin fibers were made to the optimal design (a total of 6 mixing designs). Scanning electron microscopy (SEM) imaging tests, compressive strength, modulus of elasticity and capillary water absorption at 90 days of processing age were performed on concrete samples. The results of this study indicate that the mechanical properties and durability of geopolymer concrete are superior to ordinary concrete. In the design, geopolymer concrete contained 8% nanosilica compared to the design without nanosilica). Addition of up to 2% of fibers to the geopolymer concrete composition resulted in a 7% and 23% improvement in modulus of elasticity and water permeability in concrete. SEM results indicate the production of a large volume of hydrated gels in the microstructure of geopolymer concrete compared to conventional concrete, which is due to the abundance of aluminosilicate particles in slag and nanosilica used in the composition of geopolymer concrete.

The aim of this study is analyzing the sequential pattern of monthly river flow wet and dry spells in some hydrometric stations (a 20-year period), West-Azarbaijan Province. The wet-dry spells of river flow were determined using Runs theory and the Power Laws Analysis method was used to determine the long-term pattern of low and high flow periods. Then, the drought severity and duration value of wet and dry periods were represented on double-logarithmic plots. Also, the sequence counts of dry and wet periods were determined through 1 to 47-month periods. The results showed that there is an inverse relationship between the severity and persistence of dry periods. The maximum severity of drought was observed in Ghasemlou and Dashbnd stations (0.55 slope of fitted line), and the highest intensity of wet period was related to Pei-Qaleh station (slope of fitted line is 0.6). In other words, the Ghasemlou and Dashbnd stations had the persistent dry periods and Pei-Qaleh station had the highest stability in occurrence of wet periods. The maximum duration of dry and wet periods was observed in Pole-Bahramlou and Sariqmysh stations, respectively having 11 and 15-month average maximum duration occurrence through the studied stations. Also, the results showed that the occurred dry spells over the South parts of the study area had the highest duration and intensity with respect to central and Northest parts of the study area. The results can be used to determine the susceptible area with high drought duration and intense drought periods in planning of surface water resources. The use of power analysis method allows the study of dry and wet periods and also the determination of changes in the behavior of time series of hydrological data due to climate change or human intervention.

Automated Guided Vehicles (AGVs) have been widely used in industrial factories and seaport due to their high efficiency and ability to move in recent years. Nevertheless, controlling AGVs to keep moving in the predefined (correct) direction is one of their most important challenges. In this paper, an automated guided control system is designed using the direct current of servomotor. In order to guide the automatic control robot in the predefined and rotational paths, the Proportional-Integral-Derivative (PID) control system with proportional, integral, and derivative parts is used. Adaptive adjustment of PID controller coefficients is difficult due to the nature of the used control system location. Hence in this study, an optimally set up of the coefficients of PID controller is used in control system of AGV by applying adaptive Radial Basis Function Neural Network (RBFNN). The simulation results indicate that the proposed controlling scheme can optimally increase the accuracy rather than traditional PID-based method. In addition, the proposed scheme is practically implemented as a prototype robot leading to provide an experimental validation to be used as an applicable solution in AGV control systems due to the low cost of design and optimal performance.