NONLINEAR HYDRODYNAMIC PRESSURES GENERATED BY A MOVING HIGHRISE OFFSHORE CYLINDER

Both analytical (small time expansion) and numerical (finite-differenc e) approaches have been used to solve the earthquake-induced nonlinear hydrodynamic pressure acting on a rigid high rise offshore cylinder. For the high rise offshore cylinder, the most part of the flow field i s independent of z and a three dimensional hydrodynamic analysis can b e reduced to a two dimensional analysis. At onset, the dimensionless g round displacement epsilon(2) = 0, for the two dimensional analysis, t he normalized hydrodynamic pressures across cylinder face is a constan t and is independent of the radius of the cylinder. The normalized hor izontal force coefficient C-fx is independent of intensity of ground a cceleration and is approximately linear and proportional to epsilon(2) and its onset value is equal to pi. For a linear analysis, i.e. negle cting nonlinear convective acceleration, the normalized hydrodynamic p ressure coefficient is also independent of the radius of cylinder. The analytical method was good for ground motion in a single direction, t he results of simultaneous action of two components of ground accelera tion can be obtained by the superposition of the results due to separa te excitation. But the superposition method is only valid in the linea r analysis. For highly nonlinear problem, the present finite differenc e approach is recommended. Copyright (C) 1996 Elsevier Science