Assessment of operational limits : Effects of uncertainties in sea state description

Abstract

For operations dominated by waves, operational limits are normally expressed in terms of allowable sea state parameters, such as the significant wave height (Hs) and spectral peak period (Tp). The allowable sea states need to be assessed in the planning phase of the operations. Different sources of uncertainties (including weather forecasts, wave spectral model and numerical models) should be accounted for in the allowable sea states to provide safety margins. This study focuses on assessment of the operational limits (in terms of Hs and Tp) considering the uncertainties associated with the sea state descriptions used in the numerical analysis. The aim is to demonstrate the effects of simultaneous description of wind sea and swell sea accounting for their different directional spreading and directions of propagation. A case study using lifting operation is chosen to address these uncertainties in the allowable sea states. To illustrate the results, two types of floating crane vessels, mono-hull and semi-submersible are employed in the case study. Operability analysis by using these vessels are performed and compared using NORA10 hindcast data for a site in the Barents Sea.