Journal of Fluid Mechanics

Papers

Statistical properties of mechanically generated surface gravity waves: a laboratory experiment in a three-dimensional wave basin

M. ONORATOa1, L. CAVALERIa2, S. FOUQUESa3, O. GRAMSTADa4, P. A. E. M. JANSSENa5, J. MONBALIUa6, A. R. OSBORNEa1, C. PAKOZDIa3, M. SERIOa1, C. T. STANSBERGa3, A. TOFFOLIa7 and K. TRULSENa4

a1 Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, Torino, Italy

a2 ISMAR, Castello 1364/A, Venezia, Italy

a3 Norwegian Marine Technology Research Institute A.S. (MARINTEK), PO Box 4125, Valentinlyst, Trondheim, Norway

a4 Department of Mathematics, University of Oslo, PO Box 1053, Blindern, Oslo, Norway

a5 ECMWF, Shinfield Park, Reading, UK

a6 K.U. Leuven, Kasteelpark Arenberg 40, Heverlee, Belgium

a7 Det Norske Veritas, Veritasveien 1, Høvik, Norway

Abstract

A wave basin experiment has been performed in the MARINTEK laboratories, in one of the largest existing three-dimensional wave tanks in the world. The aim of the experiment is to investigate the effects of directional energy distribution on the statistical properties of surface gravity waves. Different degrees of directionality have been considered, starting from long-crested waves up to directional distributions with a spread of ±30° at the spectral peak. Particular attention is given to the tails of the distribution function of the surface elevation, wave heights and wave crests. Comparison with a simplified model based on second-order theory is reported. The results show that for long-crested, steep and narrow-banded waves, the second-order theory underestimates the probability of occurrence of large waves. As directional effects are included, the departure from second-order theory becomes less accentuated and the surface elevation is characterized by weak deviations from Gaussian statistics.

(Received April 15 2008)

(Revised December 12 2008)

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