Abstract
The mechanisms governing the evolution of the wind-wave field in time and in space are not yet fully understood. Various theoretical approaches have been offered to model wind-wave generation. To examine their validity, detailed and accurate experiments under controlled conditions have to be carried out. Since it is next to impossible to get the required control of the governing parameters and to accumulate detailed data in field experiments, laboratory studies are needed. Extensive previously unavailable results on the spatial and temporal variation of wind waves accumulated in our laboratory under a variety of wind-forcing conditions and using diverse measuring techniques are reviewed. The spatial characteristics of the wind-wave field were determined using stereo video imaging. The turbulent airflow above wind waves was investigated using an X-hot film. The wave field under steady wind forcing as well as evolving from rest under impulsive loading was studied. An extensive discussion of the various aspects of wind waves is presented from a single consistent viewpoint. The advantages of the stochastic approach suggested by Phillips over the deterministic theory of wind-wave generation introduced by Miles are demonstrated. Essential differences between the spatial and the temporal analyses of wind waves’ evolution are discussed, leading to examination of the applicability of possible approaches to wind-wave modeling.
Highlights
The process of the generation of sea waves by wind has fascinated the human mind since ancient times, attempts to understand the processes leading to the excitation of waves by wind started only about 100 years ago
For unsteady wind forcing, the situation is more complicated, since the statistical characteristics of waves in this case depend on time as well as on space
Only limited experimental data on waves under time-dependent wind under controlled conditions are currently available; these works were briefly reviewed in the Introduction
Summary
The process of the generation of sea waves by wind has fascinated the human mind since ancient times, attempts to understand the processes leading to the excitation of waves by wind started only about 100 years ago. Our understanding of physics governing the interaction of atmosphere and ocean in general, and, of mechanisms leading to the excitation of waves on the water surface and their evolution and growth due to the action of wind remains incomplete. Unsteady and unpredictable environmental and wind-forcing conditions are just two of the many formidable difficulties that accompany field experiments and complicate obtaining reliable information. Even when the requirement of steadiness of wind forcing can be seen as effectively satisfied, field measurements are often performed at a single location, preventing studies of wave evolution with fetch and limiting the possibilities for direct estimates of wind-wave growth rates. To mitigate some of the difficulties, Donelan et al [8,9] carried out wind-wave measurements in relatively small lakes, while the Atmosphere 2019, 10, 562; doi:10.3390/atmos10090562 www.mdpi.com/journal/atmosphere
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