A new finite difference method was developed to solve the nonlinear hydrodynamic pressures on a rigid vertical offshore cylinder during earthquakes. The influence of the slenderness-ratio of the cylinder on hydrodynamic pressure is studied. The hydrodynamic pressure profile is increasing as the ratio is increasing. When the slenderness-ratio is equal to one, the hydrodynamic pressure on the cylinder face at 0 = 0° is one half of that on a vertical dam face, and will approach to exactly same when the slenderness-ratio approaching infinity.
The hydrodynamic pressures acting on accelerating struct.ures, such as dams, plates, offshore cylinders etc., has been studied extensively. The significance of the hydrodymunic pressures may be large enough to affect the safety of the structures. The first analysis of the hydrodynamic pressure on a rigid vertical wall excited by a horizontal ground motion was done by Westergaard(1933). After then, the geometry (Chwang, 1978 and Chen, 1993), and the flexibility of structures (Chopra et. al., 1981 and Hung and Chen, 1990) and the compressibility (Chopra, 1967, Hung and Wang, 1987) of water were included in the analysis by various researchers. The significant effects of the structure shape, the fluid-structure interaction and the water compressibility on hydrodynamic pressures have been reported. However, most theories of the above analyses were limited to a linear analysis. Not only the convective acceleration of the fluid flow but also the free surface wave were neglected in those analyses. Only very few nonlinear analyses were reported in the last two decades, most of them were given by Chwang (1983), and Hung and Chen (1990) for dam hydrodynamics. Recently, Wang and Chwang(1989) used a smalltime- expansion method to analyze the nonlinear hydrodynamic pressures and free surface flow around an impulsively moving cylinder.
