Abstract
Critical events in random wave trains that can lead to impact on offshore structures are addressed. Experience from model testing has shown that impact is correlated with steep and energetic waves, characterized by high crests, wave heights, orbital velocities, slope, or a combination of all. A new impact alert parameter derived directly from a wave record, unifying these properties in a physically consistent way, is proposed. Hilbert transform analysis is applied. The analysis is demonstrated through application on numerical and laboratory wave records. Impact responses from model tests with floating offshore structures in steep storm sea states are compared to predictions made by the new simple alert parameter derived from the calibrated wave records. It is found that a large majority of events identified by the new parameter turn out to be real critical events also in the response records.