BREAKING WAVE DESIGN: A CASE HISTORY

An approach is described which was used to estimate the wave loading on a small offshore gas platform located at a shallow water site in the southern North Sea. Extreme kinematics were predicted to be due to spilling breakers and the resulting forces drag dominated. The design wave was modelled in a laboratory flume at Edinburgh University to a scale of 1:120, and the velocities and accelerations were measured using a novel laser Doppler system. These values were compared with numerical predictions obtained using the Dean's stream function theory, taking into account the appropriate Froude scaling. Measured velocities and accelerations were in general agreement with the computed values but were slightly higher in the crest region. On this basis, the grid of velocities derived from Dean's method was modified before being input to the design programme. The calculated loadings resulted in minimal structural changes for the particular design configuration.