فصلنامه دریا فنون
سال ششم شماره 3 (پیاپی 17، پاییز 1398)

The partly unknown environment of the vast seas and the lack of prior accurate map of the workspace is one of the current challenges facing the autonomous underwater vehicle (AUV) in carrying out missions. Real-time path planning for an AUV from an initial position and velocity to a target position and velocity in a partly unknown environment by considering the pre-unknown obstacles is the main motivation of this research. For this purpose, the local rapidly-exploring random tree (L-RRT) algorithm is proposed for the AUV. This L-RRT consists of three tightly coupled components of: a path planning module (PPM), a local real-time path planning module (LRPPM) and an obstacle detection module (ODM). Each of a random vertices and related branch are generated through the PPM and then from the perspective of the kinodynamic constraints are evaluated by the low-level controller and nonlinear AUV model. If the generated vertex and related branch in the considered time satisfy the kinodynamic constraints in simultaneous manner, these and in addition the horizontal and vertical control signals are recorded through the path planner algorithm. If a pre-unknown obstacle is detected by the ODM, path is re-planed through the LRPPM based on the current position and orientation of AUV to the nearest vertex. The L-RRT is implemented on the single board computer (SBC) through the xPC-Target builder and then the ability of this algorithm is evaluated through the processor-in-the-loop (PIL) test. The results of the PIL tests indicate that the AUV through the proposed L-RRT not only plans the path by avoiding the pre-unknown obstacles in a cluttered environment, but also due to the random nature of this method the path is planned in a real-time manner.

Nowadays, one of the main challenges in the maritime is the control and monitoring of ports in different weather conditions. To achieve this, Autonomous Surface Vehicles (ASV) are used. In this research, as part of the Morvarid research project, a stereo vision system was implemented on an ASV to detect, localize, and track static and dynamic objects. In order to examine the proposed obstacle detection algorithm, two sets of experiments have been designed; first, the ASV moves toward stationary objects to localize all static and dynamic objects. Second, the ASV tracks a target boat, which equipped with an RTK-GPS and estimates relative and absolute positions and movement vector. The results showed that the proposed algorithm successfully estimated 3D size and position of the surrounding objects. The accuracy of the tracking algorithm was evaluated in the digital elevation map, with the lowest RMSE of 1.575 (m), and 0.6621 (m) using raw and EKF data, respectively.

Beamforming is one of the most important array signal processing blocks in sonar systems which due to the nature of the environment and conditions of operating, requires using of the robust and adaptive methods to provide the feasible specifications in outputs. In the present paper, the latest methods for the adaptive robust beamforming such as enhanced and modified covariance matrix methods are investigated and finally, by using of simulation in different scenarios and conditions such as steering vector error, sensors gain and phase perturbation and high power noise and strong interference, their capabilities and abilities are presented and method are evaluated. The results show that the methods of Diagonal Loading, LCMV and LCMV mod in different states are not feasible and CMR and ESB methods in the presence of error of steering vector, strong interference and high power noise and gain and phase distortion are more suitable.

Today, electrical systems, given the many advantages, have been used in propulsion and power production for typical operational vessels. In renewable electrical propulsion systems that play a significant role in reducing environmental pollutants, resources such as fuel cells, capacitors, and batteries are used. Managing the power production of these resources is one of the most important measures for proper propulsion and other loads following. In the proposed energy management strategy, with respect to the energy and power density of these resources and their response rate, the rapid changes are covered by the capacitor and the steady state energy is produced by the battery and fuel cell. For this purpose, an electrical system consisting of sources, converters, real propulsion load and hotel load is designed for a typical operational vessels, then according to the introduced energy management strategy, the system load following is evaluated. The results indicate the efficiency of the electrical system and the proposed energy management strategy. Also, in controlling the battery state of charge (SOC), the method presented in this paper is better than the two methods compared with them.

In this paper, a new design is proposed for a neural-sliding mode controller for a certain class of permanent-magnet synchronous motors to employ in unmanned submarines. Using presented specifications; first, the intended motor is designed and simulated in the Maxwell full-wave software based on the finite element method. Then, the nonlinear model is derived by the neural network using the data obtained from the simulation of the motor in the software. Since the model-based control methods are expensive and error-prone due to the high dependence on the modeling as well as the use of sensors, a sensorless controller is used, and with respect to the proposed nonlinear method, a sliding mode controller is designed for this particular motor. The proposed neural-sliding controller has obtained better results than the PID controller due to its robustness against system uncertainties and external disturbances, the overall closed-loop stability and convergence of error-trace to zero. The simulation results confirm the proper performance of the proposed model and controller.

In this research, a proper Duty Cycle Control method in Direct Torque Control (DTC) of six-phase induction machine in open phase mode is proposed. In conventional switching table DTC of six-phase induction machine, the torque and flux ripples are high and large harmonics by order (6𝑘±1) are produced. To overcome to this disadvantages a control method based on duty cycle control is used which produce less torque and flux ripples and harmonics losses. In this research, instead of using the common way to obtain new switching table in open phase mode, a new switching table is presented that can be combined to duty cycle method to achieve better results in open phase mode. In this method a simple and useful control method to calculate the duty cycle of each vector which is independent from machine parameters is used. Without considering the open phase fault, this technique has these advantages: less torque and flux ripples, independent from the load and speed changes, less current harmonics and almost sinusoidal shape, and zero power loss in (𝑧1−𝑧2) subspace. In addition, in open phase mode the results are acceptable and the machine continues to operate without speed drops. The simulation results presented in this paper show the preference of the proposed methods.

The quest for technology to build submarines equipped with an air-independent propulsion system is increasing. PEM fuel is one of the best options for a submarine power supply system. Durability is one of the main competition factor of polymer fuel cell technology with other power generation technologies. Regarding the importance of polymer fuel cell stack stability tests, for the first time in Iran, performance of polymer fuel cell stack was evaluated over a period of 200 hours. Durability test condition was determined based on universal well-known protocols and according to the intended use, in three sections: assessment of polarization curve, electrochemical impedance spectroscopy and fluoride ions (Fenton test), pH, and electrical conductivity of the anode and cathode side discharge water changes in the intervals of 25 hours. Based on the results, it was found that oxidant shortage, accumulation of water particles in the third cell, and the formation of droplets of water in needles, caused by the design of gas manifolds as well as the applied operation conditions, act as reversible factors for the performance loss of the fuel cell stack. Analyzing the electrochemical impedance spectrum, it was determined that the ohmic resistivity remained almost constant over the 200 hour test (1500mΩ/cm2). The higher charge transfer resistance in the third cell than the others can be attributed to the accumulation of water in the last cell. Investigating the fluoride ions, pH and conductivity of the outlet water from the anode and cathode side of fuel cell stack, it was revealed that performance during 200 hours does not have an effect on the membrane chemical structure, and the chemical degradation of its structure will take place at longer times.

The warming process in the Indian Ocean is a major contributor to the overall global warming trend of the global oceans and the contribution of the Arabian Sea is remarkable due to the special conditions governing it, geographically and monsoon winds. In this study, inter-and intra-annual variations of SST, SSS were studied from 2010 to 2017 using the MITgcm model in the Arabian Sea with the most accurate bathymetric data and the spatial resolution of 0.033deg and monthly temporal resolution. For this purpose, temperature, salinity, evaporation minus precipitation rate, wind, net heat flux with a spatial resolution of 1 degree and monthly temporal resolution as the initial data were first introduced to the model. In this model, Navier-Stokes equations in nonlinear, incompressible and non-hydrostatic states are solved by finite volume spatial discretization over a cubic computational grid. The results of time analysis in the mentioned period indicate that the mean sea surface temperature increased about 0.36 °C and also the mean sea surface salinity by 0.04 PSU. This is despite the fact that the highest value of temperature and surface salinity during the study period is in June 2016, the values of these variables are 30°C and 36.51 PSU respectively. The reasons can be attributed to factors such as he excess of evaporation over precipitation in the Arabian Sea, Monsoon wind stress, current inversions, net surface heat flux.

Abstract Seasonal variability of circulation and meso scale eddies in the Persian Gulf are investigated by using results from an (~3 km) Regional Ocean Modeling System (ROMS) with particular reference to the year 2009 in 16 sigma level. Circulation in the Persian Gulf is mainly due to three factors of wind stress, density (thermohaline flow) and tidal current. The main current in the Persian Gulf, which is cyclonic, is caused by a density difference. Also, oscillations in the wind stress force cause a variable flow in the Strait of Hormuz .Cyclonic circulation in the center of Persian Gulf will be stronger from April to July, so the model during August the highest clarity is observed in the formation of meso scale eddies. In this research, we selected 4 stations in various situations in Persian Gulf. We investigated the effect of eddies formation on salinity and temperature and specially the sound speed. As the method of sound wave propagation in underwater environment is very important to performance of acoustic system. So, The effect of the presence and absence of eddy on the sound velocity graphs was compared. The result is that, the presence of eddies decreases the sound speed propagation and the transmission loss .

This paper examines the total annual cost from economic view heat exchangers based on ant colony optimization algorithm and compared the using optimization algorithm in the design of economic optimization of shell and tube heat exchangers. A shell and tube heat exchanger optimization design approach is expanded based on the total annual cost measured that divided to area of surface and power consumption. The optimization and minimization of the total annual cost is considered as the objective function. There are three parameters as decision variables in optimization algorithm such as tube outer diameter, shell diameter and central baffle spacing. Two cases studies considered to demonstrate the accuracy of algorithms Results have been compared with the findings of previous studies. The total annual cost is reduced about 10% and 40% for case 1 and 2 using ant colony optimization algorithm, respectively.