Abstract
Synthetic fibre mooring lines are used as an alternative to traditional steel wire ropes due to their higher strength to weight ratio. Benefits are also found in relative ease of handling, and therefore the marine industry has largely accepted this type of mooring line. By rules and regulations, the design of mooring lines should be based on a coupled dynamic analysis of a particular mooring system and moored vessel. This approach incorporates damping and inertial forces (i.e., hydrodynamic reactions) acting directly on the mooring lines due to their motion through the seawater. On the basis of the outer diameter of the synthetic fibre rope, the Morison equation gives estimations of the mooring line hydrodynamic reactions. In comparison to the traditional steel wire ropes, the synthetic mooring lines usually have relatively larger elongations and consequently larger reductions of the outer diameter. Furthermore, the lower diameter certainly leads to reduced values of damping and added mass (of mooring lines) that should be considered in the coupled model. Therefore, the aim of this study was to develop a new numerical model that includes diameter changes and axial deformations when estimating the hydrodynamic reactions. The development of the model is carried out with a nonlinear finite element method for mooring lines with the assumption of large three-dimensional motions. The obtained results show the effectiveness of the newly developed model as a more accurate approach in calculation of hydrodynamic reactions.
Highlights
Synthetic fibre mooring lines are used as an alternative to traditional steel wire ropes and chains due to their lower submerged mass, lower cost, the potential to reduce peak loadings, and the reduced footprint of the floating systems [1]
This study presents a new finite element intended for modelling of mooring lines made of synthetic fibre ropes
The specifics of the kind of rope was considered in the calculation of damping and added mass
Summary
Synthetic fibre mooring lines are used as an alternative to traditional steel wire ropes and chains due to their lower submerged mass, lower cost, the potential to reduce peak loadings, and the reduced footprint of the floating systems [1]. The usual dynamic mooring analysis only considers hydrodynamic forces over the mooring line induced by the relative motion of the line through the still seawater. With such an approach, the direct wave loads acting on a mooring line are disregarded. The Morison equation is used to calculate the hydrodynamic forces This model is very versatile, and recently is used for some studies found in practical problems as an investigation of the interaction between ship generated waves and slender structures [38] or for the position keeping of a crane barge during use [39]. In detail, the analytical expressions were used as an independent numerical validation of the proposed model and to present the improvement over the current practice
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