Analysis on snap load characteristics of mooring line in slack-taut process

The mooring system may appear slack-taut alternating transformation with the motion excitation of floating structure, resulting in the dynamic tension amplitude of mooring line significantly increase. Based on the dynamic finite element analysis, a series of sinusoidal excitations with different amplitudes and frequencies are applied at the top of mooring line, and the results show that the slack-taut phenomenon would occur when the top excitation reaches a certain amplitude and frequency. The minimum value of tension is close to zero, and the maximum value can reach several times of pre-tension. The spectrum analyses show that the components of high frequency appear besides the excitation frequency, and the main factor affecting slack-taut phenomenon of mooring line is the component of excitation along axial direction of mooring line. Through improving the initial pre-tension, selecting the cable with large elastic modulus and small cross-section diameter, and making the length of mooring line as short as possible, these settings would have benefit for keeping mooring line in the taut state and avoid the occurrence of snap load. The results of this paper would have significant reference for further exploring the mechanism of snap load in the mooring system and its design and safety assessment.