Hydrodynamic pressures on axisymmetric offshore structures considering seabed flexibility

A special boundary method for earthquake-induced hydrodynamic pressures on rigid axisymmetric offshore structures of arbitrary shape is presented, including both the water compressibility and seabed flexibility. This method makes use of a complete set of Trefftz functions, which satisfy all boundary conditions except that at the structural surface. An azimuthal decomposition of the solution allows us to reduce the three-dimensional problem to a two-dimensional one. The pressure distribution is expressed as a linear combination of natural modes of water and participation factors. Such coefficients are determined by using the Mikhlin approach, with which the remaining boundary condition is satisfied in the least-squares sense. Numerical results are computed for different geometries of the structural surface. The effects of water compressibility and seabed flexibility are examined over wide ranges of practical interest. The efficiency of this technique is validated by comparison with analytical and numerical solutions.