The goal of wind-waves research is to predict the waves field and its effect on the environment. That environment could be natural or imposed by human endeavour. The mechanism of wind generated waves is described in the present work as a wind-bulk flow interaction rather than as a mechanical process which only transfers the wind energy to the wave. In the light of this description, the generation and growth of surface waves are functions of the physical properties of the interface, density of the bulk flow perturbations and wind shear stress. While the present models for the prediction of surface growth and evolution show some consistence - in some cases - with observations that were conducted in laboratories and in real fields, the work presented in this thesis justifies and explains the inconsistency or contradictions in other cases between the observations and the predictions. Also, physical interpretations for observations, for example wave growth with fetch, are suggested in the present work. To illustrate the physical mechanism responsible for wave generation and growth under the effect of wind action, two approaches are used. The first involves studying the effect of the physical properties of the water surface on atmospheric input into the bulk and thus the effect on the formation and growth of capillary waves. The second involves studying the correlation between the wave formation and growth and the density of the bulk perturbations. Wide ranges of previous data are used to analyse the effect of the physical properties of the water surface on wave generation and growth mechanism for the first approach. Also, a group of experiments using the PIV system (Particle Image Velocimetry) were conducted to study the correlation between the wind speed, bulk flow evolution and wind-waves‟ generation and growth for the second approach. The main physical parameters which are responsible for the generation and growth of capillary waves are determined. The Ohnesorge number is modified to predict the generation and growth of surface waves. In the second part, additional physical parameters of the bulk flow are introduced to illustrate the correlation between the wind generated waves and bulk flow evolution. A new parameter is used to scale the transition of the bulk flow from laminar flow to turbulent flow or the transition of the water surface from an undisturbed surface to a fully disturbed surface. The history of wind-wave research is relatively short. Although there were basic developments in the 18th century, a concentrated effort really began as a result of the military imperative of the Second World War. These developments were however, largely empirical. A theoretical frame work began to develop with the studies of wind-wave generation in the last century. The present work is conducted to fill some gaps in wind generated surface waves research and to introduce new approaches to simplify understanding wind-waves field and its effect on the environment.

A quantitative description of wind-wave and wind-current momentum transfer in high wind conditions is currently unresolved, mainly due to the severe character of the problem. It is, however, necessary for accurate wave models, storm and hurricane forecasting, and atmosphere-ocean model coupling. In this research, strongly forced wind-wave conditions were simulated in a laboratory tank. On the air side, a static pressure probe mounted on a vertical wave follower measured wave-induced airflow pressure fluctuations in close proximity to the surface. Vertical profiles of wave-induced pressure fluctuations were resolved and wave phase dependent features, such as airflow separation, identified. Based on the pressure measurements, wind-wave momentum fluxes were obtained. The dependence of the spectral wave growth function on wind forcing, wave steepness, and wave crest sharpness was also investigated. The bulk air-sea momentum fluxes were estimated using the "total budget" experimental technique. It provided information on the contribution of a wind-wave flux induced by a single wave to the total air-sea momentum flux. The percentile contribution of wind-wave momentum flux into one wave was found to be dependent on the wave's steepness. An arbitrary change in steepness, however, was found to modify the wave field in such a way that it had little effect on the total wind stress. To complement wind stress measurements velocity profiles in the water were measured using Particle Image Velocimetry technique. Mean current, turbulent stress, turbulent kinetic energy and turbulent dissipation rate vertical profiles were studied as a function of wind speed. Together with wave spectrum evolution measurements they form a complete empirical description of momentum fluxes in the laboratory tank. The results provide a detailed empirical view on airflow pressure fluctuations over a wavy surface, on total wind stress, and on the velocity response in the water. A new wave growth parameterization with wind forcing range extended into storm conditions is the most significant stand alone result of this work. Combined with the near surface vertical profiles, these empirical data also serve as a test bed for coupled air-sea numerical models.