Presentations

Abstract

The Vole au Vent jack-up has successfully installed hundreds of wind turbine generators (WTGs) through its years at Jan De Nul. Before each wind turbine installation, the vessel has to be carefully positioned and jacked up. The phase where the jack-up changes from being a free-floating vessel to a bottom founded platform is called going-on-location. The relatively short impact phase is typically most onerous, determines the workability and therefore has a significant influence upon WTG installation scheduling. Calypso has developed a simulation model for the impact phase to accurately determine the effect of wave action on the vessel and the resulting allowable sea state. This allowable sea state can be expressed in terms of 1) total sea state, 2) sea state components wind sea and swell, and 3) a 2D wave spectrum stating wave energy distribution over frequency and direction. Implementing 1) in on-board decision making is straightforward and typically used, but this paper shows this is inaccurate to -50% to + 100%, so only ballpark. Implementing 2) is more elaborate and is aided by an analog, physical tool to help crew on board take into account multiple sea state components. Mocean Forecast has developed the MO4 on-board decision making support unit which obtains forecasted 2D wave spectra and determines workability based upon those. This system is shown to be capable for implementing 3), the most accurate decision-making method. It is shown that decision making based upon total sea state only should not be done if the actual sea state consists of more than one wave system, e.g. a wind sea and a swell component. Taking these into account using an analog aid improves insight and is shown to be sufficiently accurate. Using a dedicated on-board console is the most accurate method for determination of workability.