WINDLOAD sets the foundations for new WINDLASS JIP


Here we look back at the success of WINDLOAD, the predecessor of WINDLASS. Jaap de Wilde, j.dewilde@marin.nl


The remark “one man's ‘stiff breeze’ might be another's ‘soft breeze’” may have been acceptable for a naval officer in the 18th century, but today engineers seek hard numbers when working on the design of floaters. The three-year WINDLOAD JIP aimed to address this problem and improve the accuracy and reliability of wind load predictions on large floating structures, especially related to stability and mooring.


Wind tunnel benchmark study


The first task of WINDLOAD consisted of an extensive benchmark study for wind tunnel tests at three major boundary layer facilities in Europe. A ship-shaped production platform (FPSO) and a column-stabilised production platform (semi-submersible) were tested. In the boundary layer wind tunnel, the appropriate vertical velocity profile was carefully adjusted by using upstream spires and/or barriers, in addition to a long fetch of roughness elements. The wind tunnel benchmark study showed very similar results from the three facilities, but there were still more than enough improvements to be made.


CFD benchmark study WINDLOAD then led to a ‘blind’ CFD benchmark study for the same FPSO and semi-submersible (see page 26). Findings showed that modern CFD could actually predict the results of


CFD result for beam wind on an FPSO


wind tunnel tests much better than expected. The maximum differences were in the order of 10%, with the CFD having a slight tendency to under-predict results. The initial CFD was relatively expensive, however the costs came down quickly and the industry now seems to accept CFD as a valuable tool alongside wind tunnel tests.


Follow-up WINDLOAD was executed at a time when the industry was starting to overcome its understandable ‘fear’ of using the new CFD method. CFD sometimes has a negative


connotation that it is merely ‘pretty colours for directors’. Fortunately, there was a rapid decrease in the calculation costs on larger computer clusters, which meant it gained popularity. The appropriate timing of WINDLOAD is highlighted by the fact that SNAME and ITTC also started similar initiatives during this period. MARIN certainly believes the new follow-up WINDLASS JIP (see page 18) is equally well timed.


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