The Influence of Rainflow Filtering on the Distributions of Characteristic Wave Parameters

Jesper Rydén

Centre for Mathematical Sciences
Mathematical Statistics
Lund Institute of Technology,
Lund University,

ISSN 1403-9338
Calculation of the exact distributions for characteristic wave parameters by means of the regression-approximation method requires as input a spectral density. The high-frequency cut-off in the spectrum plays an important role for such computations. We use the rainflow filter as an alternative to the band-pass filters traditionally used. The rainflow filter is a non-linear filter which can be used to eliminate small-amplitude oscillations in a signal. For a spectrum of JONSWAP type, the joint distribution of crest height and crest period is calculated, and the filtering approaches are compared. The rainflow filter yields results which are closer to the distributions obtained
from a spectrum with high-frequency content.
Key words:
wavelength, wave period, rainflow cycle, filtering, spectrum