ANALYTICAL STUDY ON THE VERTICAL HYDRODYNAMICS OF A TRUNCATED CYLINDER WITH UPPER POROUS WALL AND INNER COLUMN

Based on the linear potential flow theory, an analytical model for the diffraction and radiation problem of a truncated cylinder with upper porous wall and inner columns has been built by using the eigenfunction expansion method and the linear relationship between the pressure difference on the two sides of the porous wall and the fluid velocity inside it. Then, the formulae for the heave RAO (Response Amplitude Operator) was deduced. The model was verified by comparing the present results with the published results for the vertical porous cylinder and that for the impermeable truncated cylinder. The effect of porous coefficient, the radius ratio (ratio of the radius of the inner column to that of the outer cylinder), and the draft ratio (ratio of the draft of the inner column to that of the outer cylinder) on the vertical hydrodynamics (response amplitude, added mass, radiation damping and the exciting force) of the cylinder in a heave mode were investigated. The analytical results showed that:the added mass and the radiation damping increase with the increasing of the porous coefficient, and the opposite is true for peak value of heave RAO, also the considerable reduction of a vertical exciting force was found in the lower frequency region, those may improve the stability of the structure; the radius ratio and the draft ratio affect the vertical hydrodynamics of the cylinder significantly.