The dynamics of a floating vessel restrained by cables is analysed and an optimum parametric analysis of the mooring lines is developed. A frequency domain approach to the linearized problem is adopted. Namely the hydrodynamic boundary value problem is recast in integral form by using the proper Green function and the relevant integral equations are numerically solved. A variational formulation for the cable dynamics is then proposed and its frequency response matrix is obtained in a closed analytical form by a Rayleigh-Ritz approach. The procedure is applied in the frame of an optimization technique and the sensitivity of the moored vessel response to some mooring line design parameters is investigated. Two basic advantages of the proposed procedure are enlightened. First the frequency approach avoids heavy numerical computations in the time domain. Moreover the impedance matrices formulation allows to update only the cable dynamic response during the iterative optimization. Numerical simulations are presented to show the effectiveness of the method.
In this paper an optimum parametric analysis of the mooring lines of a floating vessel in waves is developed. This problem is of paramount importance at the design stage of moored ships, offshore structures and floating production storage and offloading systems. The theoretical prediction of the dynamic response of such vessels to waves action requires the coupled solution of the hydrodynamic and structural problems. In principle, this is a non-linear partial differential problem to be solved (numerically) in time-domain. This complex approach is not suitable for dealing with optimum analysis where two basic obstacles are encountered. First, the nondeterministic behaviour of the wave exciting force compells to consider long time-simulation to obtain significant statistical information on the vessel response. Second, the search of an optimal configuration implies the analysis of several designs that makes the procedure unfeasible in practice.
