STATIC NONLINEAR ANALYSIS OF VESSELS BERTHED AT DOLPHINS

Resumo

Vessel mooring systems consist of mooring lines, fenders and a fixed (harborage) structure.
Their role is to ensure the operational safety of port terminals by restraining the vessel movements at
berth during loading and unloading operations. This work presents partial results of an on-going research
on the dynamic behavior of a vessel berthed at dolphins subjected to environmental oscillatory loadings.
It is a case study of a VLCC (Very Large Crude Carrier) berthed at the Porto Central/ES, Brazil,
subjected to wind and current forces. At first, a simplified static analysis, used in structural design’s
current practice, is made to estimate the maximum loads in the mooring lines. Then, a nonlinear static
analysis with geometrical nonlinearities, caused by the slacking of the mooring lines and loss of contact
between the vessel and the fenders, as well as physical nonlinearity due to the fenders ́ stiffness and
buckling-column-type behavior, is performed. The analysis consists of balancing the resultant forces
and moments applied to vessel by the environment against the reaction forces exerted by the mooring
lines’ stretching and the fenders’ compression. As a result, we arrive at a system of nonlinear equations
as a function of the vessel ́s displacements, which are then solved by a fully consistent Newton's
numerical method. At last, the behavior of the mooring system with respect to the vessel’s displacements
is investigated in order to better understand the effects of the considered nonlinearities.