Calculation Of Cylinder Added Mass And Damping Coefficient In Forced Motion By CFD

For ship in waves, it will generate a motion of six degree of freedom, which is usually predicted by the potential theory. For vertical motion, hull suffers less viscous effect, the value calculated by potential theory meet the engineering requirements in common. However, for roll, in particular, the hull is often accompanied by more viscous composition, it will produce flow separation and vortex escape and so on, which can't be solved well by potential theory. To forecast the ship roll in waves accurately, the most difficulty is determination of roll damping.Currently, the most effective method to get the damping coefficient is still physical test. However, the test is costly and loaded down with trivial details, the result often impact by equipment and personnel measurement error, there is also a problem of scale on model and real ship. With the development of computer technology, numerical simulation based on CFD is becoming a trend,which offer a new accomplishing means of complex issues as roll.Based on CFD RANS method, included in viscous and free surface effects, this paper simulates the single-degree-of-freedom forced motion of a ship section and computes added mass and damping coefficient of sway,heave and roll mode. For numerical calculation, gird quality have a tremendous impact on results. In order to research adaptability mesh of this motion type, it used two different types of gird, and compared results between them. In the form of exercise known under the premise of the hull, the overall computational domain is superior to the local grid update redraw the grid, the former in terms of stability and computer, have a greater advantage.For roll, use the section that installed on bilge keel, calculate the roll damping with large angle, get the rull of change between keel size and roll damping, describe the velocity distribution and vortex motion feature before and after bilge keel installation.