Wave Energy Transfer Mechanisms in Wind-Wave Tunnels

Theoretical and experimental results are reviewed for five exponential mechanisms that operate on small-amplitude deepwater gravity waves in wind-wave tunnels. Energy source term mechanisms are those due to: (1) tangential shear stress a₁; (2) phase-shifted normal stress a₂; and (3) airflow-pressure-gradient normal stress a₃. Energy sink term mechanisms include only those due to viscous dissipation in the far field, a₄, and in the wall boundary layers, a₅. The results of experiments by Liang are shown to compare favorably with the theoretical a₃ and to confirm its importance. On the basis of this result, a₂ is recalculated for the laboratory wave growth data of Bole and Hsu and is found to be an average of only 1.7 times the theoretical results of the Miles inviscid shear-flow model. This finding is in substantial agreement with the recent field measurements of Elliot but is in disagreement with earlier field investigations. Graphs are presented to illustrate the relative importance of the five energy transfer mechanisms for laboratory experimental conditions.