The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking is employed in order to represent a supply vessel equipped with a mooring line system, and the real-time loading during the full-scale measurement is recorded. The second vessel Tor Viking served as an ice breaker to maintain the physical ice management activities with different ice-breaking schemes i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns are investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Both deterministic and probabilistic fatigue assessments are investigated. For the probabilistic approach, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress range with application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the deterministic approach. Among the difference scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.

Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.