Eine Numerische Analyse eines Kranschiffes mit Bezug auf Windsee und Schwell
David Albert, Technische Universität Berlin
A numerical analysis of the workability of a large offshore crane vessel with respect to wind sea and swell waves
David Albert, Technische Universität Berlin
This thesis presents a workability calculation splitting wind sea and swell, aiming to
provide safe operational limits. The investigated scenario involves a new floating crane
vessel of DEME Offshore during heavy lifting operations on its starboard side. Moored
next to the crane vessel is a North Sea barge, acting as a feeder.
The first part of the thesis focuses on setting up a model in frequency domain with six
degrees of freedom for each vessel and an additional three translatory degrees of freedom
for the crane load. The resulting equations of motion, a system of 15 coupled linear
equations have been solved to produce response amplitude operators (RAOs), describing
the motions of the involved vessels and crane load. The necessary hydrodynamic
components, added mass, potential damping and excitation force have been calculated
with the boundary element method code NEMOH and validated with ANSYS Aqwa.
In the second part split hindcast weather data of various locations has been used to
apply separate sea spectra for wind sea and swell, representing the double peak of the
sum sea state. The spectra in combination with the RAOs made the calculation of
the motion envelope of the hoisted cargo, pitch and roll motions of the crane vessel,
the dynamic amplification factor (DAF) of the lifting operation and the load rehit risk possible. It has been shown how setting the vessel heading angle in reference to swell
has the largest impact on workability. The optimum heading angle to this reference has
been established. Using this heading area specific monthly workability values have been
calculated. Finally results have been evaluated independent of their time and location
to show separate general operability limits for windsea and swell.
