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Freak waves are unique phenomena that appear unexpectedly on the ocean surface. These waves are not only a danger to fishermen and yachtsmen, but are also capable of damaging large vessels and offshore and coastal structures. The available field measurements that provide insight into the origin and physics of freak waves are very limited. The main objective of the present study was to analyze a unique set of wave data comprising 19,025 wind-wave records from the southern Baltic Sea to provide information on the occurrence, parameters, and prevailing conditions of the formation of freak waves. The complex nature of freak waves was investigated by obtaining spectral and statistical parameters of freak-wave-prone sea states using a wide set of tools. The study revealed a large number of freak-type waves, including waves over 12 m high. The study indicates that these hazardous waves may even exceed 20 m during severe storms in the Baltic Sea. Multi-point wind-wave measurements are needed to provide more information about the physics of freak waves and to eventually develop a prediction or warning system to avoid casualties. [ABSTRACT FROM AUTHOR]

Theoretical investigations supported by a series of original laboratory experiments are conducted to study a wave-induced vertical mixing process. The derived semi-analytical solution is very efficient and is applied to predict the effects of water waves on the temperature changes and the evolution of temperature profiles. The results indicate that waves increase a mixing process. The rate of change of the temperature is higher when waves contributed to mixing process and this process increases with increasing the wavelength to water depth ratio. The analysis indicates that for typical ocean waves the contribution of water waves to mixing may be several orders of magnitude higher than a corresponding contribution arising from the classical diffusion process. This implies a need to conduct more theoretical studies and experimental investigation on the effect of water waves on mixing processes. A series of original laboratory experiments were conducted in the insulated wave flume to verify the derived model. The comparisons show a reasonable agreement between predicted and measured temperature profiles. A reasonable agreement between theoretical results and experimental data is observed for the whole considered range of initial temperature distributions. The comparisons indicate that the model is applicable even to cases when gradients in temperature distributions over water depth are fairly high. [ABSTRACT FROM AUTHOR]