Rogue/Freak Waves

Abstract

Rogue/freak waves are surface gravity waves whose wave heights are much larger than expected for the sea state. The most common operational definition requires a rogue wave to be at least twice as large as the significant wave height. Wave refraction by water depth and currents may cause difficult wave conditions in certain local areas, but otherwise, the probability of occurrence of rogue waves appears to be consistent with linear and high-order random wave theory. There are exceptions, however, though it is unclear whether these represent measurement errors, statistical outliers, or are caused by additional nonlinear physics. A clear deviation from linear theory is found in 2-D numerical simulations and wave flume experiments, where a higher frequency of occurrence of rogue waves is found due to a high-order nonlinearities. Recent theoretical, numerical, and experimental results indicate that such deviations are suppressed by wave directionality.