Author(s): Richard Silvester; Suphat Vongvissessomjai

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Abstract: The PIERON-MOSKOWITZ (PM) ocean wave spectrum, derived from analyses of many ocean wave records, contains two constants α and β for fully arisen sea (FAS) conditions. This frequency spectrum can be converted to a period base, termed an energy distribution curve (EDC) that contains the same contants. The EDC is almost triangular in shape, with the period Tmax at the apex increasing with the steady wind velocity. A unique relationship result between the ignificant wave height H⅓ and Tmax. A new dimensionless form of the PM spectrum and EDC is presented which incorporates wave age (C/U). The triangular form of the latter permits the definition of working upper (TU) and lower (TL) period limit of the many wave trains present. Using a recently derived growth relationship for wave in a developing sea, the variations of α and β in the spectral equation of the FAS are determined. Knowing the fetch of the FAS, value of α and β have been related to the ratio F/FFAS for fetch controlled conditions. Substitution of these values back into the pectrum or EDC equations exhibits the growth pattern of the developing sea. This also displays “over hoot effect”, or the excess energy state in the smaller period waves part-way along the fetch to the equilibrium values at the FAS state. The minimum fetch (FFAS) for the FAS has been related to the steady wind velocity. It has also been connected to the minimum duration (tFAS), by using a mean group velocity of the progessively enlarging Tmax trains, to any pecified point in the fetch. In this way values of t/tFAS have been related to ratio of F/FFAS, and hence, to corresponding value of α and β.

DOI: https://doi.org/10.1080/00221687009500328

Year: 1970