Comparing multi-fidelity modelling approaches for Articulated Tug Barge motions and pin loads in wave conditions

An Articulated Tug Barge (ATB) was designed for Carbon Collectors to operate for carbon capture and storage (CCS) in
depleted gas reservoirs in the Southern North Sea. MARIN was commissioned to perform a calm water resistance assessment. Changes to the barge bow and stern and tug details decreased resistance. Major changes to the tug would have allowed for a larger reduction, but could not be committed due to the maturity of the design. This underlines the added value of early stage design support. Furthermore model tests to verify motion and pin loads was performed. For ATBs typical coupled out-of-phase pitch motion was observed. Multiple pitch excitation mechanisms cause the motion range to be wide-banded between 0.5 and 1.2 rad/s. The model tests proved to Carbon Collectors that the concept is viable, minor improvements to mitigate green water and excessive pitch motions were done. Test results were replicated in frequency and time domain simulations, the availability of model test data is valuable to obtain high quality models. Linearization assumptions in wave loads and hydrostatic stiffness cause some inaccuracy in the roll and
pitch amplitudes, general motion behaviour and pin loads are captured well. Improvements of time domain simulations may be found in non-linear stiffness and wave excitation in diffracted wave fields.