Numerical evaluation of the tension mooring effects on the hydrodynamic response of moored ships under harbor oscillations

Abstract

Tension mooring is the main way of restraining moored ships in a port to ensure operating conditions. Harbor oscillations have been observed in many ports and adversely affected the safe operation of moored vessels. This paper analyses the influence of different line pretensions and mooring arrangements on the efficacy of tension mooring in mitigating ship motions and line forces. A hybrid Boussinesq-panel model is adopted to simulate the hydrodynamic response of a moored container ship under harbor oscillations induced by irregular waves.Results show that the moored ships near nodes and antinodes are more likely to experience larger amplitudes of horizontal motions and lead to higher loads on the shorter lines of the mooring system, which subsequently affects the lines' performance. Inceasing the pretension of mooring lines can minimize ship's horizontal motions, thus improving operational efficiency. A reasonable increase in pretension would effectively relieve line forces, while an excessive increase in pretension may accelerate the rate of fatigue and failure on the lines. The main advantage of utilizing mooring arrangements with multiple lines attached to the same bollard is reducing the uneven distribution of line forces. But this approach carries the potential risk of exerting overload pressure on the bollards.