The Snap Tension Analysis of Taut-Slack Mooring Line with tanh Method

Su-Xia Zhang,Xi-Jun Liu,Shengli Chen,Rui-Zhi Shi

doi:10.1155/2017/8519523

Abstract

The continuous model is introduced, and the nonlinear partial differential equations of taut-slack mooring line system are transferred to nonlinear algebraic equations through tanh method, and four solitary solutions are obtained further. At the same time, to express the results clearly, the curve surfaces of strains, displacements, and tension are plotted. The results show that there are four different solutions in the system. With the pretension increasing, the tension changes from one solitary solution to snap tension, and when the pretension is increased further, the curve converts to continuous line, until straight line, which is corresponding to the taut mooring line. In the process of increasing of pretension, the mooring line transfers from slack to taut, accompanied with tension skipping, which is reduced by the system parameters, and different combination of parameters may introduce different tension in line, and the uncertainty may cause the breakage of mooring system. The results have an agreement with experiment, which shows that the calculating method in this paper may be believable and feasible. This work may provide reference for design of mooring system.

Highlights

With the development of exploitation of deep-water resources, TLP and SPAR platforms are designed and used in some areas and are considered as the excellent platforms in deep water, in which mooring line is one of the most important parts of platforms.Mooring lines are flexible structures and have unidirectional stiffness; that is, they can only bear tension and cannot bear compressive loading
The tension changes from one solitary solution to snap tension, and when the pretension is increased further, the curve converts to continuous line, until straight line, which is corresponding to the taut mooring line
In the process of increasing of pretension, the mooring line transfers from slack to taut, accompanied with tension skipping, which is reduced by the system parameters, and different combination of parameters may introduce different tension in line, and the uncertainty may cause the breakage of mooring system

Summary

Introduction

With the development of exploitation of deep-water resources, TLP and SPAR platforms are designed and used in some areas and are considered as the excellent platforms in deep water, in which mooring line is one of the most important parts of platforms. Huang and Vassalos studied the impulse loads under alternative taut-slack conditions by using the model of bilinear string [3, 4] They neglected the effect of floating structure, the cable was simplified into the model subjected to periodic sinusoidal excitation at the top end of cable, and the snap tension of the mooring cable was calculated [5]. Zhang et al studied the analytical solution of taut-slack mooring line with tanh method and obtained snap tension curves in four cases [8]. The snap tension is obtained, which may be the reason causing the breakage of mooring line

The tanh Method

Equations of Motion

Results and Discussions

Conclusions