6.2.1. Effect of the sill on the dimensionless added mass and damping coefficient
Figs. 4–6 illustrate the hydrodynamic effects of the sill height ratio which is defined
here as the ratio of the sill height to the still water depth, on the dimensionless added
masses and damping coefficients of the structure. It can be seen that for fixed h1/a and
d1/h1, the effects of the sill are different for different radiated motions of the structure. The
following aspects deserve one’s attention. (1) The effect of the sill height ratio h4/h1on the
damping coefficient of heave is very small and can be neglected in the whole water region
(from very shallow water to very deep water), while the added mass of heave becomes
large with the increase of the sill height ratio in the whole water region. (2) The effects of
the sill on the hydrodynamic coefficients of sway and roll motions can be divied into three
regions. The first region is 0!h1/L!hc1, the second hc1!h1/L!hc2 and the third region is
hc2!h1/L!N, where hc1 and hc2 are the two critical depth ratios shown in Figs. 4–6. In
region 1, the larger the sill height ratio, the larger the added masses and damping
coefficients of sway and roll. In region 2, the larger the sill height ratio, the smaller the
added masses and damping coefficients of sway and roll, and In region 3, the effect of sill
height ratio is very small and can be neglected. It should be noted that hc1 and hc2 have
different values for different cases. For example in Fig. 4, hc1z0.13 and hc2z0.65 are for