A Novel Semi-Empirical Non-Linear Time-Domain Formulation of Wave Elevation Diffracted by a Vertical Column

Abstract

A novel semi-empirical non-linear formulation for fast and efficient computation of the disturbed elevation time series under large-volume platform in steep irregular waves is described and validated against model test data with a single fixed circular column. The method makes use of a linear diffraction model as a basis, which is then subject to non-linear amplification derived from a previous established crest amplification formula. The validation test data includes a large test matrix of regular waves with systematic variations in the wave period and steepness, some tests were also run in a steep irregular wave as well as various bi-chromatic waves. The simulations show a good agreement with model test time series. Initial simulations in the irregular waves disclosed some steep wave events for which the model predicted too strong non-linear amplification due to high local steepness close to or beyond breaking. A threshold criterion were introduced. Leeward (shadow) effects are also addressed, and a practical model for this is proposed.