Sep. 1 2018

When designing offshore units against structural failure modes, such as yielding and buckling, the popular technique today is to review a limited number of load cases.

These are defined to maximize a design load, such as vertical bending moment, horizontal bending moment, acceleration, pitch, and roll angle. Questions arise, however, when dealing with unconventional units, such as those with large breadth/length ratio, unusual structural arrangement or a round hull. Are those design load cases still relevant? And how, among the 100 million waves encountered during the unit life, do we choose the few ones that are dimensioning for the structure?

The solution lies in combining HOMER, the powerful Bureau Veritas hydro-structure software, with an iterative methodology that defines the design waves to directly maximize the stress levels in some selected structural elements.

By comparison with spectral analysis, it is verified that a dozen different Design Waves can maximize stress in all structural elements. Yielding and buckling checks can then be applied to verify the structure. This approach is a very good example of how R&D tools and methods can be used to improve efficiency and accuracy in offshore unit design.