Coherence Function of Wind and Waves ofMetocean Data

In this paper, a research regarding analysis of metocean data is done that includes two main
parameters; wind and waves. The objective of this project is mainly to apply Coherence
Function as the mechanism tool for frequency domain analysis of a linear system between
wind and wave from the full scale metocean data of three platforms located in different
operating field. From here we are able to determine the correlation of these environmental
forces to estimate the significance frequency where these forces acts in linear functions in the
system, thus identify the response of the platform structural members as we assume the inputs
to be stationary. It is very crucial to determine the response of the structural members so that
we can improve the platform design standards and also as approaches to standard
maintenance procedures. This project will focus on the metocean data collected from each
platform for different field operation; Dulang-B platform from Peninsular Malaysia
Operation (PMO), Tukau platform form Sarawak Operation (SWO) and Samarang platform
from Sabah Operation (SBO). This is to ensure that we are able to distinguish the
environmental condition for each set of metocean data as well as the seasonal pattern. The
measured data is analyzed using the assistance of mathematical software, PASW 18 in order
to compute the complex algorithm involved. The results obtained show that the wind is not
actually the major factor to generate the wave at specific platforms. It is estimated up to 30%
only while other factors that contribute to generate wave are possibly the tidal effect, gravity
pull or other parts of the sea. The coherency differs for platform at different operation field
region, as well as for seasonal pattern. The highest coherency recorded is the interaction of
wind and waves at Tukau during non monsoon season, where the interaction of both forces
optimum at frequency O.lHz, while other platforms show a true non linear relationship of
wind and waves. However during monsoon season shows the other way around where
Dulang-B platform and Samarang shows a quite similar seasonal pattern, but slightly differs
in the coherency range.