This paper aims to discuss mainly the vertical wave forces acting on a submerged sphere located near the bottom and free surface boundaries. The time variations and maximum values of the wave forces are investigated in relation to the appropriate dimensionless physical quantities. The bottom and free surface boundaries are shown to affect significantly the vertical wave force acting on the sphere. On the other hand, the boundary proximities affect little the horizontal wave force. The lift force caused by the asymmetric pressure distribution and the flow separation dominate over the vertical inertia and drag forces in the case that the sphere is located near the bottom boundary. The lift force enlarges the maximum vertical force. This paper proposes new equations which estimate well the wave force acting on the sphere located near the boundaries. Good agreement between the measured and calculated wave forces is confirmed.
Exact estimation of the wave force acting on coastal and offshore structure is one of the most important problems subjected to the field engineer. The Morison equation (Morison et al., 1950) which is originally proposed for estimation of the wave force on the circular cylinder is useful to evaluate the wave force on the structure whose size is small compared with the incident wavelength. Iwata and Mizutani (1989a, 1989b) have di scussed the characteristics of the wave force acting on the submerged sphere and the Morison equation is revealed to be applicable to estimate accurately the horizontal wave force acting on the sphere. On the other hand, since the second or more higher order harmonic components are included in the vertical wave forces on the sphere located near the bottom and free surface boundaries, the Morison equation cannot be always applied to estimate the vertical wave force.
