3D Nonlinear Hydrodynamic Analysis of Vertical Cylinder during Earthquakes. I: Rigid Motion

A finite-difference scheme was developed to solve nonlinear hydrodynamic pressures acting on a rigid vertical offshore cylinder during earthquakes. A complete three-dimensional (3D) analysis was conducted; not only were the three-dimensional equations of motion used, but the simultaneous action of three components of ground acceleration was also included in the analysis. The influence of the size factor [(defined as 2a/d0 (a= the radius of the cylinder and d0= the undisturbed water depth)] of the cylinder on hydrodynamic pressure was studied. The hydrodynamic pressure profile increases as the size factor increases. When the size factor is equal to one, the hydrodynamic pressure on the cylinder face at θ= 0° is one half of that on a vertical plate, and will approach exactly the same pressure when the size factor approaches infinity. The nonlinear effects of convective acceleration and surface wave are discussed. The principle of linear superposition of the results due to two horizontal components of ground accelerations is invalid because of the significant nonlinear effects, and the complete-three dimensional nonlinear hydrodynamic analysis should be considered for offshore cylinder analysis and design.