فصلنامه دریا فنون
سال چهارم شماره 2 (پیاپی 8، تابستان 1396)

Nowadays, Variable Reluctance (VR) resolvers, due to their simple structure, compact design and thermal stability, are widely used in marine navigation systems for detecting the angular position. However, they suffer from some disadvantages such as winding complexity and being highly influenced by eccentricity fault. In this paper, after studying the challenges, a new structure with simple winding is studied to overcome the challenges. To show the preference of the new design, its performance is analyzed using 3-D time stepping finite element method and then compared with conventional variable reluctance resolver. The comparison shows peak to peak position error of the new resolver under 35μm static eccentricity (based on ABEC492 standard) is improved more than 13 Arc Min. with respect to the conventional resolver. Finally, the prototype of the new resolver is built and tested. Experimental results confirm the success of the new resolver.

Three-dimensional simulations are presented on the motion of a deformable bubble in a combined coquette and poiseuille flow at finite Reynolds number. The full Navier-Stokes equation are solved by a finite volume method on a regular, fixed and staggered grid. Interface is tracked by marker points on an irregular, triangle and moving grid. The effect of surface tension is included. The effects of capillary number and Reynolds number on the lateral migration of a bubble are studied. It is found that a bubble migration to an equilibrium position about halfway between the wall and the centerline regardless of its original position. Simulations also show that the bubble shape is strongly dependent on the capillary number. As the Reynolds number increases, the effect of viscosity decreases and the equilibrium position moves closer to the wall. The effect of the radius of a bubble is also examined. With increasing the radius of the bubble, the centroid of the bubble moves to the centerline. The bubbles are more deformed with negative pressure gradient and migrate to the centerline.

composite sandwich plate widely used in manufacturing of the hull of advanced fast boat. sandwich plate of the boat hull that is contact with water in one side supply the Flexural stiffness and dissipate the vibrational energy cused by internal and external factors. In this paper, composite sandwich plate consider with two external laminate face consists of two type fiber Grphite and Glass in the epoxy resin with Polyisobutylene foam core. laminates of face have orthotropic elastic manner and core have isotropic viscoelastic manner that viscoelastic mechanical property of the core received from reference. In this paper for mechanical manner of the visoelastic core, relaxation Master Curve extract with used isothermal curves. Natural frequencies and mode shapes of the composite sandwich plate are determined with clamped boundary conditions in the finite element software. results of natural frequencies and mode shapes of the composite sandwich plate are compared in air and contact with water.

Helideck design is one of the main objects in the naval vessel design process. Despite structural constraints that affect the flight deck of the helicopter takeoff and landing performance is on board these vessels. There's hanger or any other structure in front of the flight deck will cause turbulent flow through to flight deck then the floating topside ship design should be designed that at least there is turbulence on the flight deck. Today, Trimaran for use in military industry with unusual attention Pavements have been. The most complex matters, which is angled topside addition to complying with the requirements of stealth, must create the best one on the flight deck. First, to select the correct flow forecasting model in turbulent flow, flow modeling was evaluated on a staircase. Six basic geometry was changed in the geometry in order to reduce the separation zone and helicopter landing zone were analyzed together finally, the best geometry on the deck of one flow-based product.

Implementation of bottom step in high speed planing hulls can lead to resistance reduction. Moreover, by using step, rough water performance of planing hulls will improve because the lift force is distributed over the hull bottom which can lead to porpoising stability in waves. In this paper, three dimensional fluid flows around a stepped hull is simulated. The governing equations is solved by finite volume method in conjunction with volume of fluid. Free surface flow and the complexity related to the flow separation from step have been thoroughly investigated. Moreover, in the presented simulation, hull has two degrees of freedom in sinkage and dynamic trim. Therefore, dynamic fluid-body interaction (DFBI) solver based on the mesh morphing approach is utilized. In process of numerical solution, computational domain is fixed and the mesh around the hull is moved. The obtained results for the resistance, dynamic trim and sinkage, Chine wetted length and keel wetted length of stepped hull, at different velocities, have been compared and validated against available experimental data. Also, dry length after step and stagnation line variations in various velocities is discussed. The obtained results indicate that the proposed numerical model can be used for optimal design of stepped hulls.

Stability of the rubble mound breakwater is a very important issue in coastal and ocean engineering. It can be determined by stability number which depends on sea state and structural parameters. However, there are a lot of uncertainly in determining stability number. These uncertainties suggest that reliability analysis should be carried out for armour stones stability to ensure a desirable level of safety for breakwater. In the present study, a probabilistic framework was developed for estimating the stable armour weight placed on a rubble mound breakwater. By using this method, with a particular reliability level or expected risk, armour weight can be calculated. It is therefore, possible for design engineers to decide on the armour weight based on economical and/or construction restrictions. Application of this method was illustrated in Noshar port’s breakwater as a typical case study. The analysis yielded an almost Lognormal distribution for the armour weight. Consequently, armour weight can be assessed by analyzing the distribution based on the required reliability level. Results showed that, to get about 95% reliability, 13000 Kg weight stones must be placed at the breakwater.

In this study, the manner of performance acoustic equipment using active sonar equations, for both the northern and southern areas of the Caspian Sea were studied in the spring. In this study, acoustic wave equation was solved through a ray theory in 40 KHz frequency, then environment transmission losses were calculated. Then a hypothetical object with the strength 12 dB in distance 9km from the acoustic source at a depth of 5 meters was installed, The transmission loss the return signal at the receiver at the location of the acoustic source were installed at depths of 50.5 and 300 meters, were calculated, The results showed that at North Station, when the receiver at a depth of 5 meters at the site of transmission, is installed, The return signal from the body in about -50 dB show transmission losses compared to South Station, but in the lower depths of 50 meters, about -15 db was observed.