HYBRID 3-DIMENSIONAL FINITE-DIFFERENCE AND FINITE-ELEMENT ANALYSIS OFSEISMIC-WAVE INDUCED FLUID-STRUCTURE INTERACTION OF A VERTICAL CYLINDER

The two-dimensional finite-difference scheme has been extended to thre e dimensions to solve nonlinear hydrodynamic pressures and structural responses of a deformable, vertical and circular surface-piercing offs hore cylinder during earthquakes. A complete three-dimensional analysi s has been made with both the three-dimensional equations of motion an d the simultaneous action of three components of ground acceleration i ncluded in the analysis. Not only the magnitude but also the direction of the acting ground motion can be varied with time. The dynamic resp onse of a cylinder is approximated by the displacements in the fundame ntal modes of vibration. A comparison of the dynamic displacement of t he cylinder with and without surrounding sea water has been made. The flexibility of the offshore cylinder can significantly increase the hy drodynamic pressures acting on cylinder faces, that is, the fluid-stru cture interaction is necessary in offshore cylinder analysis. Although the hydrodynamic pressure induced by the vertical ground acceleration of the El Centro 1979 earthquake is significant, the calculated struc tural dynamic response of a cylinder is very small and the correspondi ng resultant hydrodynamic force is almost nil. The hydrodynamic force induced by two-horizontal ground acceleration is about the same as tha t by three simultaneous components of ground acceleration. For a solid and stubbier circular cylinder, the vertical component of ground acce leration may be neglected. (C) 1998 Elsevier Science Ltd. All rights r eserved.