Parametric Excitation of Mooring Cables for Submerged Floating Tunnels

The ferry links crossing the fjords along the west coast of Norway are going to be replaced by fixed links. Among the proposed solutions is the construction of Submerged Floating Tunnels (SFT). A mooring system should be used to restrain the movements of these floating structures. Long period waves, such as swell waves, parametrically excite the system and might result in excessive vibrations in the cable. This paper presents the equations of motion of the mooring line and derives an analytical expression, which allows for a quick identification of the system’s stability. This expression is obtained through the Harmonic Balance Method (HBM) with two harmonic terms. The contribution of multiple modes of vibration is investigated for the case of small sag to span ratios. The expression is compared with the results from a numerical model, revealing the applicability of the proposed formulation.