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In this paper, for the purpose of investigating horizontal sound propagation, based on the results obtained from practical measurements in the Strait of Hormoz and available data on sound speed variations at different depths, a comprehensive model for shallow water multipath underwater acoustic channel is presented. Mathematical modeling of multipath effect is based on ray theory and the image method. In channel modeling, attenuation due to wave scatterings at the surface and bottom reflections is considered. In addition, we also consider attenuations due to the absorption of sound by different materials and the presence of ambient noises such as the sea state noise, shipping noise, thermal noise and turbulence noise. Then, complete underwater communication system consisting transmitter, channel and receiver was simulated. We use QPSK modulation. Data is transmitted at a rate of 5 kbit/sec with a carrier frequency of 27 kHz, for a maximum range of 1km. The channel estimation is based on a training sequence which occupies about 10% of the signal bit rate.

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Friction stir welding as a joining process in solid state welding various alloys widely used metal, particularly aluminum alloys. Although the low heat generated during the process does not melt the base metal, but the thermal cycle applied to the sample, which reduces the mechanical properties of the junction. Recently, this method of welding process is used in the cooling methods. In this study the microstructure and mechanical properties of 5050 aluminum alloy weld in two conditions: with friction stir welding in the air and on underwater friction stir welding was studied. The results of underwater friction stir welding were compared with samples of friction stir welding in the air. Results showed that the structure of the underwater welding was 36% more finely than welded structures in air and its tensile strength was improved about 6%. Also, the SZ zone in underwater friction stir welding has a higher hardness than friction stir welding in air.

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Abstract- The aim of this paper is to develop a numerical procedure for simulating underwater explosion phenomena with a simplified mathematical and two fluid model. The two fluid Kapila five equation model is selected as the governing equations and the ideal gas and Stiffened gas equations of state (SG-EOS) are used to obtain pressure in the gas bubble and the surrounding water zone, respectively. The modified Schmidt EOS is used to simulate the cavitation regions with low pressure. A Godunov numerical method and HLLC Reiman solver is extended for Kapila two fluid model. The numerical results of the present method and comparing them with available experimental results, verify that the proposed method has good capablity of predicting complex physics involved in a spherical underwater explosion and its interaction with free surface. The method also shows a very good performance with no spurious oscillation in cavitation zone simulation in two-dimensional problems

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In this study a safe and smooth path planning containing the slightest risk is considered for an Unmanned Underwater Vehicle (UUV). To do so, three smooth and continues functions resembling the three dimensional path are introduced and then their parameters are optimized using the particle swarm optimization method to find the safest possible path. For each point in space a numeric value is considered as vulnerability and the objective function is the integral of the vulnerability over the path produced. This path forms controlling signals which through a TSK fuzzy controller, the UUV is guided. The new arrangement of the propulsion vehicle subsurface was modeled. Since for the design of the controller, the parameters of the Under Water Vehicle dynamic system not used, so the control system is robust with respect to parameter Uncertainties. In the last section three environments with different complexities are considered to illustrate the creating process’s performance of the path and it is concluded that this method demonstrates desired performance in the development of a safe and smooth path through a harmful environment and the design of an adequate controller.

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In this paper the effect of horizontal control surfaces (stern fins) angle on the drag force of the Subsea R&D Autonomous Underwater Vehicle (AUV) is investigated using both experimental fluids dynamic and numerical fluids dynamic methods. The experiments were conducted in the Subsea R&D towing tank using a 1:1 scale model of the AUV, at various stern angles and in a speed range of 1 to 3 m/s. A pair of Naca shaped struts was used to connect the AUV to the carriage dynamometer. The stern drag force was experimentally calculated at various stern angles and towing speeds. The results obtained by experimental method compared with those obtained numerically by commercial computational fluid dynamics CFX code. Both experimental and numerical results showed that as the stern angle increases, the total AUV drag force increases, and the drag force coefficient can be estimated by a second order polynomial. The results showed that, at a speed of 1.5m/s, as the stern angle increases to 45 degree, the drag coefficient increases up to 174 percent It was also observed that at a specific stern angle, the drag force due to stern fin increases with the AUV speed. Variation of axial force as a function of stern angle was determined by using both experimental and numerical methods. The results obtained by both methods showed that the expensive experiments conducted in towing tanks can be replaced by numerical simulations.

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In recent years, Underwater Acoustic Communications (UAC) has been a great matter of consideration because of its importance in different areas such as commercial and military applications. Underwater acoustic communications channel is known as a time-varying and doubly selective channel in both time and frequency domains. The orthogonal frequency division multiplexing (OFDM) modulation is an effective technique to communicate over challenging acoustic channels. In addition, using multiple-input multiple-output (MIMO) systems increases channel capacity which results in high data rate communications. Recently, basis expansion models (BEMs) have been widely used to estimate an underwater acoustic channel. In particular, when the channel is time-varying, the BEM model can effectively estimates the channel with a reduced number of coefficients and low computational complexity. To improve the performance of a MIMO communication channel, various beamforming techniques have been proposed in different areas. Inspired by the basis expansion modeling of an underwater acoustic channel, in this paper we develop a BEM based adaptive space-time beamforming for both the transmitter and receiver of an UAC. The Laguerre basis expansion model is employed in the linearly constrained minimum variance (LCMV) beamformer to obtain an adaptive scheme for updating the beamforming weights at the transmitter and receiver and to optimize the system performance in real-time.  Our Simulation results show that the proposed BEM based beamformer method improves the Bit-Error-Rate (BER) and Minimum-Square-Error (MSE) performance substantially for a Rayleigh fading underwater acoustic channel. In particular, our method improves the BER and MSE about 10dB and 4dB compared to the discrete prolate spheroidal sequence (DPSS) method.

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Inertial navigation system has drift error in underwater applications. Use of DVL with Kalman filter for position and attitude correction is common. Using velocity data decreases drift error in position estimation but this error exists and increases linearity with time. In this article the navigation system consists of inertial measurement unit (IMU) and a Doppler velocity log (DVL) along with depth sensor. With use of magnetic field measurement and earth magnetic field map a new measurement is generated. Discrete extended Kalman filter with indirect feedback is used for tightly coupled integrated navigation algorithm. This algorithm is based on inertial navigation error dynamics. This paper demonstrates the effectiveness of algorithm through simulation. The procedure of simulation is done by sensor data generation. Arbitrary trajectory with specific kinematic characteristic (linear and angular velocity and acceleration) is generated. Sensor data by adding noise and bias to kinematic characteristic of trajectory is produced. Simulation results reveal that the new algorithm with use of magnetic data and earth magnetic field map decreases the drift error with comparison to conventional INS-DVL integrated navigation algorithm.

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A nonlinear model for Autonomous Underwater Vehicles is proposed. In order to describe a more precise dynamic behavior, the nonlinear model for both Lateral and Longitudinal subsystems is derived based on all applied forces and moments. The proposed model can be explained as an extended linear model for AUV in depth and azimuth motions where some nonlinearities are taken into account. Due to some practical issues as well as the form of proposed model, the identification problem based on Least Square method is formulated to achieve the system parameters. By considering unstable dynamic of system, the open loop system cannot be excited. In this case, the PID regulators with simple tuning parameters are proposed in both Lateral and Longitudinal subsystems and the identification problem by utilizing sinusoidal inputs is followed within a feedback loop. Based on measurable variables i.e. linear moments, angular velocities and Euler angles, and utilizing some dynamic filters, the Least Square method is then applied to estimate the model parameters. The effectiveness of proposed nonlinear model as well as the parameter identification approach are finally demonstrated through some numerical simulations.

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Guidance of an underwater vehicle in the wake of target due to the complexity of guidance in water and also sensor limitations, is still the most important homing guidance method. Disadvantages of wake guidance can be mentioned as zigzag motion for rediscovering the wake in its path which according to the decreasing linear speed of approaching the target, sometime it doesn't reach the target and collision fails. Therefore various ideas, with both positive and negative aspects, have been introduced to improve movement in the wake path. According to complexity of the wake model and also its instability in order to extract its parameters, makes it a very nonlinear phenomenon and guidance in it is a problematic in underwater vehicle. Since the wake detection area by the sensor is not enough widespread, wake is just discovered in the near of itself. Hence the real wake path is not detectable and therefore advanced guidance method is not available. For this reason, it is suggested to use a method of unknown path tracking for the wake guidance. This guidance law consists of two parts of path estimation and nonlinear guidance. The estimation method is performed using particle filter that has the ability to estimate nonlinear paths. The stability proof of nonlinear guidance method is done by Lyapunov.

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Currently, hovering type autonomous underwater vehicles (HAUV’s) are very noteworthy, due to theirs unique capabilities and features. Appropriate maneuverability and controllability is the most important feature for a HAUV that, make it better than other AUV’s. In order to increase stability and controllability of robot, the ballast tank is applied for a HAUV. Using of ballast tank in HAUV was not common before. In this paper a new underwater vehicle is presented, including three ballast tanks and three thrusters. In this underwater vehicle, the number of thrusters is less than original robot. In this paper, dynamics modeling and tracking control of this new underwater vehicle is investigated. The results show that the heave and pitch DOF’s can be reachable by using of the ballast tanks and we don’t need to use extra thrusters for these degrees of freedoms.

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In this paper, a new controller is presented based on robust feedback linearization controller in combination with integral-exponential error dynamics and potential functions for tracking control of an underwater robot in an obstacle-rich environment. Underwater robots are considered as nonlinear, underactuated systems with indefinite, uncertain dynamics. In this research, by assuming a boundary for external disturbances and uncertainties a proposed robust control method has been put to use. Along with the robust feedback linearization algorithm which has been developed based on the dynamics of the nonlinear error defined for the underwater robot, and in order to avoid the obstacles, the control laws are combined with the virtual potential functions. The considered virtual potential functions make a repulsive force between the robot and the obstacles which intersect the desired path and then they bring about a safe move of the robot in obstacle-rich environments. Finally, the performance of the proposed new control algorithm is compared with the results of the implementation of classical sliding mode control laws. The results show the effectiveness of potentially directed proposed controller through obstacle-rich paths which operate far better facing obstacles.

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In this paper, a constrained predictive controller is designed using Laguerre functions to control the depth and steering of an autonomous underwater vehicle considering underwater disturbances. Due to under-actuated nonlinear coupled dynamics, parameters uncertainty, external underwater disturbances autonomous underwater vehicles are complicated. Moreover, the underwater autonomous vehicle investigated in this study includes constraints on actuators leading a more complex problem. In this study, first, the nonlinear dynamics of the autonomous underwater vehicle utilized for the controller design has been modeled. Then, Laguerre orthogonal functions were used in the constrained predictive controller design for reducing computational time and accelerating optimization process. Optimized, online, high precision, implementation capability, consider constraints purposefully and robust properties against disturbances can be mentioned as the most important advantages of designed controller. In addition, predictive control method is robust against disturbances. To monitor the methods’ performance, the autonomous underwater vehicle was modeled and then a comparison between the controller's calculation time with and without the Laguerre functions was also represented. At the end, the simulation results obtained from this controller, using Laguerre functions, showed the efficiency and effectiveness of the proposed solution.

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Today, the use of underwater robots to explorer underwater conditions has significant grown. Underwater gliders (UG) are robot of the favorite of researchers for long-time operations due to their low energy consumption. Exact the identification of dimensional parameters is critical to evaluate the hydrodynamic performance of underwater gliders, which properly can rising the efficiency of robots. In this research, an attempt has been made to first extract a nonlinear dynamic model from UG. The dynamic model has been verified with the results of related other research. After checking the accuracy of the model, dimensional parametric investigation in robot hydrodynamic performance has been performed. Parameters such as buoyancy tank volume, Pitch angle and wing geometry have been target this research. In the study of each parameter, other parameters are considered constant so that the effect of target parameter can be measured. The results indicate that parameters have a significant impact on efficiency and hydrodynamic performance of the robot. Properly designed glider can be more flexible in the face of external disturbances, and causes higher speeds can be achieved when efficiency is not very important.