Direct measurement of aerodynamic pressure above a simple progressive gravity wave

Abstract

Measurements of the aerodynamic pressure distribution at the interface between air and simple progressive water waves are obtained with the use of a pressure sensor that follows the water surface. The theory of Miles (1957, 1959) and Benjamin (1959) on shear flows past a wavy boundary predicts a phase shift between the pressure distribution along the boundary and the boundary itself. An experimental verification of this theory is sought especially. A wind–wave facility 115 ft. long, 6 ft. high and 3 ft. wide was used. The facility is equipped with an oscil-lating-plate wave-generator which is capable of generating sinusoidal or arbitrary wave-forms, and a suction fan which can produce wind velocities up to 80 ft./sec when the water is at a nominal depth of 3 ft. The pressure sensor used for the measurements of pressure, was mounted on an oscillating device such that the sensor could be maintained at a fixed small distance (within 1/4 in.) above a propagating wavy surface at all times. The perturbation pressure over progressive waves is extracted from recorded data sensed by the moving sensor. The results compare favourably with the theoretical predictions of Miles (1959).

Growth and dissipation of wind-forced, deep-water waves

“…A pioneering development was undertaken by Shemdin & Hsu (1967) who used a disc-shaped pressure sensor and transducer mounted on a moving platform which remained approximately 6 mm above the oscillating wave surface. They found good agreement with the theoretical predictions of wind input obtained by Miles (1959).…”

“…To the best of the authors' knowledge, their recommendation of further field investigation of the spectral tail has never been pursued. Wu et al (1977Wu et al ( , 1979 completed further investigations in the same facility as Shemdin & Hsu (1967) with spectral decomposition of the input rates. These were found to be comparable with the original measurements of Shemdin & Hsu (1967).…”

“…Wu et al (1977Wu et al ( , 1979 completed further investigations in the same facility as Shemdin & Hsu (1967) with spectral decomposition of the input rates. These were found to be comparable with the original measurements of Shemdin & Hsu (1967). Donelan (1999) used a surface-following pressure probe traversing waves generated with a JONSWAP spectral distribution by a paddle in a laboratory tank.…”

“…Further, they found that the longstanding differences between measured and theoretically (or numerically) predicted growth may potentially be reconciled in terms of wave coherent tangential stresses, most importantly at low wave steepnesses. They also observed that there were few direct measurements of wind-energy input and any existing measurements have remained unreconciled with observations of net wave growth since the pioneering studies by Shemdin & Hsu (1967) and Bole & Hsu (1969).…”

Experimental study of the initial stages of wind waves' spatial evolution

“…Among the most prominent is the possibility to create stable and steady airflow at a wide range of air velocities. Positioning the sensors at accurate vertical locations is possible both in respect to the mean water surface and to the instantaneous surface elevation using wave followers (Shemdin & Hsu 1967;Papadimitrakis et al 1986;Mastenbroek et al 1996;Donelan et al 1999Donelan et al , 2005Donelan et al , 2006. To attain reasonably high airflow velocities matching the open sea values, relatively large blowers may be needed.…”