- In this paper, analytic diffraction (Linton and Evans, 1990) and radiation (Kim, 1992) solutions for arrays of bottom-mounted vertical circular cylinders are used to compute hydrodynamic forces on deep-draft-column-based offshore platforms, such as tension-leg platforms (TLPs). In order to account for the cylinder bottom and pontoon effects, rational bottom and pontoon corrections are also developed. The numerical results are validated through the comparison with those obtained from a three-dimensional panel program. The present method is especially powerful when the number of legs is large, for which existing panel programs cannot be used. The present method not only quickly produces reasonably accurate solutions but also precludes the laborious grid generation and convergence test, which are unavoidable in any numerical methods based on boundary discretization. Due to the minimal CPU or memory requirements, this program can be routinely run on ordinary personal computers (PCs) and workstations, hence is the most suitable for the parametric study in preliminary design stage.