فصلنامه دریا فنون
سال دوم شماره 2 (پیاپی 4، پاییز و زمستان 1394)

Propeller propagated noise is very important for surface and submarine vessel. This phenomenon is non favorite for commercial and military ships. Originally, there are three sources for vessel noise, hydrodynamic hull, machinery and propeller noise. The propeller noise is higher than other two sources. In cavitation and non_cavitations, the propeller noise is different. In the article, Propeller Model B, the tunnel cavitation at different speeds (200 to 2000 RPM) and constant pressure to spin and propeller noise without the cavitation and the cavitation by Hydrvfn 8103 high sensitivity at a computer store and analyze its .
According to the analysis carried out, increasing the impeller and flow water in the tunnel, increase the intensity of the propeller noise. The effective frequency band acoustic noise impeller in band audio systems and high intensity is a strong noise. The propeller noise SPL in octave band NO.15 is 72dB and in octave band No.18 is 75dB. In cavitation state the propeller noise in octave band NO.15 is 70dB and in octave band No.18 is 75dB

Today, many navigation systems come into contest with Global Positioning System (GPS). Some of these systems are GLONASS, Galileo and Beidou.The best way for incresing the number of satellites in user view is to combine these systems. Likewise, since it is possible for GPS or GLONASS satellites to be blocked by intentional or unintentional interventions, combining becomes more efficacious way against this kind of happening. In this paper, in addition to discussing about GPS and GLONASS combination effects on positioning accuracy improvement, we will propose a method against GPS satellites blocking using GLONASS integration. Though high accuracy of proposed method, it has real-time positioning ability and low implementation complexity. It also has abitity to deal with intentional blocking. As Kalman filter is one of the cheapest and applicable tool that can be be implemented on chip precessors. The real data used for implementation in this paper is collected by a GPS and GLONASS receiver and simulation results has been successfully shown accurcy improvement in proposed method.

In this paper, a new method for estimating distance and speed Warship or Helicopter of enemy in sea battle, with using a camera which installed under the Submarine, is objected to study. It is assumed that no additional tool is available to locate the distance and speed between of target and Submarine and just a part of target size and camera information are available. By accessing the camera information, the incoming image is processed ,by using simple mathematical operation, processed to estimate of the parameters of distance parameters and target speed. The proposed method in the project has higher processing speed and it has lower error about 0.6 percentage compared with other existing methods. This project has been practically implemented in Mashhad Samen Stadium to estimate the 3D position of the cable. for estimating the distance and speed of warship with using of camera that installed under the submarine, the movie has been prepared and with using of image processing techniques that will be explain in the future, the speed and positional warship will be estimate.

In this paper, the sliding mode control is designed for ship roll-fin dynamic to decrease the effects of the disturbance and uncertainties. For design of sliding mode control in the first The nonlinear model of the system is considered and then uncertainties are added to the model. The sliding mode control is designed to overcome on the uncertainties and disturbances. The stability of the closed loop system is proved by using lyapunov method. To evaluate the performance of the proposed method, some simulation is done and result is compared with the PID controller. The results shows the proposed method have preference performance respect to PID method. smaller variations in roll of the ship when the sliding mode control is used.

Today, more than 80% of the produced energy in the world comes from fossil fuels. Therefore, the search of new methods is considered in order to use of new source energy. Sea is one of the most important sources of energy. The waves are the main sources of energy that by using technology and modern equipment, it can be converted into needed energy for different purposes. In this paper, according to this fact, the modeling of device is considered that can be used to model the energy of ocean waves into electrical energy for different goals. This device has a cylindrical buoy which uses heave motion in order to produce energy. The simulation of mathematic equations of the device has been done in Matlab Simulink and the results of modeling and analysis, including displacement, velocity, force and power has been considered.

With increasing demand for rapidly sea transport, it is needed to overcome the constraints related to vessel low speeds. This demand appears mainly in the Millitary and passengers-carrying fields, which necessitates the need to high speed mono-hull or multi-hull vessels. With increase in the size and speed of the vessels, the need to develop an understanding of the structural dynamic loads and structural flexible responses is felt. The most important issues that the designers are interested in them are extraction of the bending moments and shear forces and also the forces induced by slamming effect. Among the different methods available for prediction of the affecting forces and structural responses full scale model test, numerical methods and scaled model test can be mentioned.
Hydroelastic method, rigid backbone method and flexible backbone method are used in testing the scaled models. In the backbone method, a continuous beam is attached to the model. The methods to implement the measuring equipments on the rigid and flexible beams are different from each other. In this study, dimensional characteristics of the applied elastic hinges in the flexible beams in the scaled test models are extracted and the way to implement them in order to perform the tests is described.

Perforated breakwaters are newer generation of vertical breakwaters in which some how the problems of high wave reflection and forces exerted to the structure have been solved. In this paper the effect of hole shapes of vertical perforated breakwaters on reflection of solitary waves was investigated using numerical method. A single and double walls vertical breakwater with four different hole shapes and four different front wall porosity were considered. The breakwater was modeled in 3D using FVM method of FLOW-3D software. The free surface was modeled using VOF method while RNG-k-ε was used to model turbulent effect. The results show that in single wall breakwater as porosity increases the wave reflection increases as well so that a 40% porous wall reflects 90% of incident waves. Furthermore the reflection coefficient has a fluctuating nature as non- dimensional ratio of B/L increases (B is width of caisson and L is incident wave length). Moreover double wall breakwater is able to damp wave energy up to 20 to 25% greater than that of the single wall.

The combined high-order panel method and boundary layer theory applied for the calculation of the aerodynamic characteristicsof 2D airfoils moving above the free surface. The body is divided into 2nd order panels, which are approximated by the quadratic Bezier curve form. Each panel is associated with a vortex distribution of unknown strength which varies linearly.The collocation approach was employed to satisfy the Neumann boundary condition. The flow past a lifting body cannot be uniquely determined unless some additional condition (i.e. Kutta Condition) is specified. In addition, the free surface is modeled by point source singularity. Having solved for the unknown strengths, 2nd Green’s theorem can be used in order to find the potential at any point inside the fluid domain.
This method is then extended to determine the viscous effect by utilizing the semi-empirical formula, which is implemented in different boundary layer regimes.
Results show when the wing is close to the ground, the lift force increases while the drag decreases. In addition, the result shows the lowest point of the lower surface of the foil has to be located at the nearest possible position to the trailing edge.

Jacket platforms are constantly exposed to harsh environmental conditions, so it seems necessary to assessment of existing platforms for various conditions and environmental factors. One of the most important factors is corrosion of steel elements of platforms at sea. In this research, effect of applying corrosion on members’ natural frequency changes is investigated. For this part of the study, some members with details of SPD1 members are assumed, and influence of corrosion on natural frequency changes, in two different conditions, under and out of water, with four support conditions, has been investigated.

In this paper, the distribution of the frequencies 200 kHz sound inside the perimeter of the turbulent plume stratification in the middle (influx) will be studied in the laboratory. This physical phenomenon is usually "in where the rivers run into the sea or small areas such as the Persian Gulf, Arabian Sea can be seen out and cause internal waves in the environment(1). In this study the acoustic signal processing time output, peak to peak signal changes, changes in the signal, the received signal strength at different moments of the arrival of the Stratified plume has been studied and compared with each other. The compressed pulses through signal processing technology, the influence of the times, the thickness of the signal is affected is investigated.