Laboratory Study of Low-Frequency Wave Dissipation Due to an Opposing Wind

摘要

Estimates of wave dissipation due to an opposing wind based on correlating pressures above the waves with the surface slope were first undertaken by Snyder et al., 1981. These indicated that decay rates due to an opposing wind were roughly an order of magnitude smaller than wind generated wave growth rates. Other field measurements (Hasselman and Bosenberg, 1991) and laboratory measurements (Young and Sobey, 1985) using this technique have also indicated that dissipation rates are very small. However, wave dissipation rates can also be derived from measurements of the decline in surface variance with fetch. The measurement of surface variance has been used by Misuyasu and Honda, 1982 to estimate the growth rates of laboratory paddle waves due to a concurrent wind. Such measurements are more direct and have consistently yielded higher growth rates than pressure correlation techniques in the air (Bole and Hsu, 1969). Recent theoretical estimates (Mastenbroek, 1996 and Cohen, 1997) using second order turbulence closure models anticipate that dissipation rates should be substantially higher than indicated by previous studies. In this report, we, present the results of recent laboratory experiments that provide alternative estimates of wave dissipation due to an opposing wind obtained from measurements of the surface wave field. These show that the reported levels of dissipation obtained by the technique of measurements in the air are far too low. Furthermore, they show, that theoretical estimates also underestimate the dissipation rates by a factor of at least 3. Further work is required to improve the accuracy of the measurements and to extend the range of wind speeds and wave frequencies investigated.