The use of wave spectra in offshore engineering is a key ingredient of the design process. Empirical formulations of wave spectra are used extensively in offshore engineering. These spectra describe a smooth spectral density that represents the wave energy density for a given wave frequency and direction. Two of the most commonly used spectral formulations are forms of the Pierson Moskowitz (PM) and JONSWAP formulations, which describe fully develop and fetch-limited seas, respectively. An interesting result of the JONSWAP study is that a wave spectrum continues to evolve with increasing fetch or duration without actually becoming fully developed.
The JONSWAP spectrum, which was derived from fetch-limited measurements made in the North Sea, has a mean shape represented with a peak enhancement factor, [[Unsupported Character - Symbol Font ]], equal to 3.3, which in engineering applications is often adopted on the assumption that this spectral shape is valid for all locations. This is primarily because historically there has been insufficient measured raw wave data to enable the characterization of basin specific wave spectra. In reality, the wind field is rarely sufficiently steady or spatially homogeneous for sea states to be fetch-limited, and as a result the mean JONSWAP formulation may not be suitable to describe wave energy densities for design purposes.
This paper presents the results of a study of measured wave spectra offshore Sabah and Sarawak, Malaysia. The study is the first systematic analysis of raw wave data to determine the shape of the wave spectrum offshore NW Borneo. The characteristics of these measured spectra are discussed here together with a comparison to the JONSWAP formulation.