Abstract
Abstract Safety is a key design criterion for floating structures. A high rate of mooring accidents has been reported over the past decades. Preventing mooring line failure is a key design objective for floating breakwater systems. The mooring system comprises sets of mooring lines anchored to the seabed. These components are exposed to highly cyclic nonlinear load fluctuations induced by an irregular wave climate during their service life. DNVGL-OS-E301 classifies the mooring lines for floating breakwaters as long-term elements that should be evaluated according to the fatigue limit state. Fatigue of mooring lines needs to be monitored and evaluated to warrant the station keeping and integrity of overall system. Applying an additional control device to a floating breakwater mitigates the structural response and hence mobilized tension in mooring system. The focus of present study was to examine the effect of an additional control device on fatigue life of mooring lines for floating breakwaters. To evaluate the effect of a control device on the fatigue behavior of mooring lines, a floating breakwater was simulated with a tuned liquid column damper (TLCD) attached. A time-dependent approach based on S-N curves in conjunction with the Palmgren-Miner rule was employed to evaluate the mooring line fatigue. This paper presents a further parametric study focused on the effect of TLCD on fairlead point displacement, mobilized tension, damage rate, and fatigue life of mooring lines. The results showed that TLCD increased the fatigue life of mooring line and thus dramatically decreased the likelihood of the mooring system being damaged by fatigue. This would reduce the maintenance costs and increase the lifetime and operational safety of floating breakwater. In addition, the presented case study showed that failure probability of mooring lines against fatigue damage was also reduced and was acceptable for the safety factor defined in DNVGL-OS-E301. This proposed approach of applying a TLCD is a practical tool for designing the components of a floating breakwater more efficiently.
Highlights
Growing maritime activity has led to the demand for a large amount of sheltered waters, where port facilities are protected from extreme environmental conditions
An extensive parametric study was performed to determine the effect of the tuned liquid column damper (TLCD) on a floating breakwater
A TLCD was coupled with a floating breakwater to evaluate the floating body response, fairlead displacement, mobilized tension, damage rate, and fatigue life of the mooring lines under irregular wave excitation
Summary
Growing maritime activity has led to the demand for a large amount of sheltered waters, where port facilities are protected from extreme environmental conditions. Thies et al (2014) evaluated the fatigue damage to the mooring system of a floating marine energy convertor by applying the rainflow counting method with the Palmgren–Miner rule They showed that any uncertainty in load cases would translate exponentially to the safety factor of the fatigue life. Lee and Juang (2012), Roderick (2012), Jaksic et al (2015), and Coudurier et al (2018) numerically studied the effect of a TLCD on the performance of floating structures They successfully demonstrated the benefits of the TLCD for mitigating the response of the floating part of the system, they did not consider the effect of control devices on the fatigue life of mooring lines.
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