فصلنامه دریا فنون
سال ششم شماره 4 (پیاپی 18، زمستان 1398)

iIn this article, the consideration of design and manufacturing method of laser base under water digital communication system for transformation of every kind of data (video, image, sound, text) is presented. By studying the effects of transmission channel (water) on the propagation properties of laser, 532 nm has been chosen as laser source wavelength. Then, the transmitter and receiver systems are discussed. Each of these systems includes two main parts: software and hardware. In software parts, to control transmission, receiption and processing of the every kind of data, essential codes have been written in MATLAB software for serial port. In hardware parts, computer and laser TTL modulation circuit in transmitter and detector circuit and computer in receiver are related by USB to serial converter FTDI chip. Finally, the field test shows that this system is able to best communicate (every kind of data) in 100 m link length by 3 Mb/s rate.

In this paper, design and mathematical simulation of a multifunctional piezoelectric capacitive-resistive Nano accelerometer sensor has been investigated using Comsol multiphisics finite element software. The governing equation of motion in thetransverse direction for a cantilever Euler-Bernoulli beam is derived considering electrostatic and van der Waals-Casimir forces. The effect of existence of piezoelectric layer, piezoresistive and capacitive patches in the bending behavior of the sensor is considered applying the physical properties of piezopatches and then simulated and solved using mathematical modules of the Comsol software. For four simulated modes of Nano sensors the obtained results are included to the values of ∆R/R,∆V/V and ∆C/C for piezo patches with respect to the variation of applied acceleration of the sensor, stress distribution along the length of the beam and maximum value of von Mises stress to compare with the yield stress of the sensor, deflection of the beam with respect to the variation of applied acceleration of the sensor, fatigue analysis for the sensor and the sensor’s mode shapes and natural frequencies to determine the performance of the sensor.

In this paper, an anti jammer GPS antenna is designed for blind null steering in direction of jammers without calibration requirement by using particle swarm optimization (PSO) method. For this purpose, the received power form the antennas is minimized by proper weighting of them. The PSO method is used to minimize the array output power, efficiently. The proposed antenna dosn't need any calibration approach as well as knowing jammers direction of arrival. High efficiency, Low cost and low complexity of this proposed method compared with the sate of the arts literature review prove its ability for using in the marine systems.

In this paper, a numerical study was conducted to study the effect of the liquid phase compressibility variability in the two-fluid single-pressure model. The two-fluid model is solved by a class of conservative shock-capturing method.The two-fluid model is solved once with the assumption that the density of the liquid phase and one is assumed, assuming that the liquid phase density is varied. In order to examine the compressibility effect, the liquid phase density of the three sample problems was used with different pressure conditions. The results show that, under atmospheric conditions, variations in the density of the liquid phase can be neglected and have no effect on the accuracy of the results of the two-fluid single-pressure model. In the case of extreme pressure gradients, the variability of the liquid phase density in a two-fluid single-pressure model causes deviation of numerical results. Therefore, in the case of extreme pressure gradients, two-fluid single-pressure model is a more accurate model assuming that the liquid phase density is constant.

In this paper, optimization of fuel consumption and NOx and soot emissions in a direct diesel engine is done using neural network and ant algorithm by applying the parameters of inlet air temperature, rate of fuel injection mass and engine speed. Complexity of the behavior of internal combustion engines was first determined by using experimental experiments to establish the relationship between the input and output parameters by the neural network. The artificial neural network with the Levenberg-Marguerite training algorithm is used to model and train the existing relationship between the above parameters and is used as a subroutine for predicting optimal values in the ant colony algorithm. Results show the engine optimized parameters are drawn to lower temperatures due to lower NOx and soot emissions by lowering the inlet air temperature. Also the results of modeling and prediction performed by neural network show 98% and 94% concordance with the experimental data in emissions and fuel consumption, respectively. On the other hand, improving the quality of NOx values, because of its high weight in the objective function, affects the overall optimization result and the behavior of the objective function in convergence is very similar to NOx behavior. Also, combination of neural network-Ant algorithm approach due to its fast convergence and consequently short response time can be used as an effective method of diesel engine intelligent control systems to reduce emissions and fuel consumption.

In this paper we investigate the seakeeping effects (especially vertical acceleration) in an reversed ship bow form. Reversed or inverted bow form for ships have special features that discriminate them from conventional bow form. Slight technical data has been released on the seakeeping performance and acceleration effects of inverted bows ship. Earlier studies have stated in relation to vertical motions and accelerations,water spray (deck wetness) ,slamming criteria,retained that we can anticipated many deviations in ship responses. For analysis about acceleration, we restructured a NA8-14 fishing vessel model from British ship research association series in solid works and Rhinoceros soft wares and finally three scale models (60degree bow form , 45degree bow form and conventional bow form) were contrived and tested in regular waves from head seas at towing tank. The variances between acceleration results of three models experimental tests are categorized in terms time.

In order to control seagliders dynamic motion, the full recognition of the hydrodynamic forces affecting their motion is very important. In this paper, the dynamic motion of a seaglider with a spherical nose has been studied and evaluated by using a developed computer code to obtain the hydrodynamics forces. Based on this algorithm, the time when the seaglider dives into the water until it returns to the water surface, as well as the parameters affecting the seaglider motion were investigated. Also, using a meta-heuristic optimization algorithm, the parameters affecting the optimal performance of the glider were determined. The investigated parameters include diving speed, diving angle, wing angle, distance and position of the seaglider center of mass relative to the center of buoyancy (center of the coordinate system). The speed varies from 0.5 to 5 m/s, the diving angle includes 15, 30, 45 and 60 degree, the wing angle includes 0, 5, 10, 15 and 20 degree and the distance between the center of mass and the center of buoyancy is assumed to be 0, 1, 3 and 5 cm. According to the results, the diving angle of 30°, the wing angle of 5° and the center of mass and the center of buoyancy distance of zero and 1 cm at the diving speed of 5 m/s were selected as optimal values.

In This paper aims to design an underwater remotely operated vehicle (ROV) for deep sea search and inspection, using the ABAQUS software, stress and natural frequencies of ROV, onshore and underwater are extracted. High strength and low weight materials have been used to make the ROV float under different conditions. Using natural frequency analysis underwater, considering the acoustic properties of water fluid, the natural frequencies of ROV have been extracted. For this purpose, acoustic analysis has been used in ABAQUS software and the effects of added mass on different modes of vibration of the ROV have been investigated. the stress analysis results show the robustness of the underwater robot at critical boundary conditions due to hydrostatic forces and drag. Natural frequency analysis with has shown that in higher frequency modes, the effect of the surrounding fluid is reduced the effect of added mass at high frequencies. For fluid analysis around the structure, the fluid dimensions are raised until the increase in dimensions no longer changes the structural frequencies. This is about 5 times the size of the device underwater. The study showed that due to the effects of water mass, the device's natural frequencies will decrease up to 40%.

The sensitivity analysis is conducted on fix marine structure responses, including maximum displacement, base shear and overturning moment to the main wave force parameters of drag coefficient, inertial coefficient and wave height. For this purpose, two simple structures namely mono-pile and four-leg truss are considered. The kinematics of waves are extracted through the New Wave theory and applied in the Morrison equation to calculate time series of wave force. ANSYS APDL15 software is applied for dynamic analysis and structural responses are obtained. The sensitivity analysis shows that, in comparison to the drag coefficient and inertia, structural responses are more sensitive to wave height variations. The results also show that, despite the nonlinear relationships between structural responses and wave force parameters, the nonlinear deviation is less than 3% and can be neglected.

In this research, the effects of pitting corrosion different patterns on the Static strength of the tubular T joints under out-plane bending were investigated. Using the finite element method, simulation of the behavior of the joint was performed. The validity of the numerical results was investigated by the results of a test, then two parameters of the dispersion pattern and depth of the pitting were considered in 90 numerical models. The results showed that the corrosion dispersion in the intersection area of the joints, especially on the chord, reduced the static strength of the other patterns, as well as increasing the depth of the pitting in the range of distribution of stress concentration and reduction of joint strength.