Using the controllable pitch propeller (CPP) in marine propulsion system makes it possible to have maximum ship speed and low fuel consumption at different engine rpm. Good maneuverability is another advantage of such propeller. This feature has persuaded designers to use CPP in ships with various mission profiles like tugs or ferries. The hub boss is of great importance in CP Propellers because it provides housing for blade actuation mechanism. On the other hand, hub boss geometry should be selected as small as possible since it has negative effect on hydrodynamic performance of propeller, specially its thrust and efficiency. In this article, a 3D potential flow-based solver is developed to predict the hydrodynamic characteristic of marine propellers for preliminary and basic design purposes. Through applying the time stepping scheme, it is possible to generate the rollup wake pattern at each time step. As a result, the interaction of vortex wake-lifting/ non-lifting bodies are correctly taken into consideration. Validation of the proposed numerical model is carried out with two standard marine propellers (DTMB4119 and KP505) and a high skewed B-series Controllable Pitch Propeller (CPP). Subsequently, Mehdi Pourmostafa

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Interaction of an oscillating foil in uniform flow would produce a forwarding thrust. The efficiency of this phenomenon is very dependent on the heave and pitch frequencies, and especially different phase angles. It is also well known that in the case of two foils in tandem arrangement, the frequency of heave and pitch motion of forward foil affects the lift/drag force of aft ward foil and thus the shape of emanating vortex sheet. In this paper, the thrust coefficient and efficiency of two oscillating foils in tandem arrangement are investigated. The interference of airfoils frequencies is investigated. A threedimensional unsteady code is developed, based on boundary element method, and applied to simulate all the targeted cases. The trailing edge vortex sheet is also modeled using vortex filament and time stepping method. This approach is adopted due to its powerful ability for estimating the hydrodynamic forces on the lifting bodies. In order to model the heave/pitch motion, it is imperative to solve the 2-DOF equations for each foil in conjunction with BEM solver. For validation purpose, the developed program is applied to a single stationary and flapping foil and the thrust coefficient is compared against existing experimental data. Subsequently, the developed code is used to analyze tandem flapping foils. The induced wake shape behind foils is compared with the single flapping foil. Based on the obtained results, the effects of forward flapping foil are clearly observed on the aft ward foil wake shape. It is also demonstrated that for better efficiency, the optimum angle of attack for the aft ward foil is zero.

A 3D unsteady computer solver is presented to compute incompressible Navier-Stokes equations combined with the volume of fraction (VOF) method on an arbitrary unstructured domain. This is done to simulate fluid flows in various applications, especially around a marine vessel. The Navier-Stokes solver is based on the fractional steps method coupled with a finite volume scheme and collocated grids by which velocity components and pressure fields are defined at the center of the control volume. However, the fluxes are defined at the midpoint on their corresponding cell faces. On the other hand, the CICSAM (Compressive Interface Capturing Scheme for Arbitrary Meshes) scheme is applied to capture the free surface. In the presented fractional step method, the pressure Poisson equation suffers from poor convergence rate by simple iterative methods like Successive Overrelaxation (SOR), especially in simulating complex geometrics like a ship with appendages. Therefore, to accelerate the convergence rate, an agglomeration multigrid method is applied on arbitrary moving mesh for solving pressure Poisson equation with two well-known cycles, V and W. In order to maintain accuracy, the geometry details should not change in grid coarsening procedure. Therefore, the boundary faces are assumed to be fixed in all grids level. This assumption requires nonstandard cells in coarsening procedures. To investigate the performance of the applied algorithm, various flows including one and two-phase flows are studied in two and three dimensions. It is found that the multigrid method can speed up the convergence rate of fractional step twofold. In most cases (not all), W cycle displays better performance. It is also concluded that the efficiency of the cycle depends on the number of meshes and complexity of the problem and this is mainly due to the data transferring between grids. Therefore, the type of cycle should be selected judiciously and carefully, while considering the mesh size and flow properties.