ABSTRACT

The influence of wave force linearisation methods on fatigue damage predictions for jack-up rigs is investigated, using Sesam software as the basis for comparison. The possible risk of significantly underpredicting fatigue damage is highlighted. Dynamic spectral fatigue analysis methodology is applied to a representative jack-up rig in 30 and 70 m water depth in the North Sea. Transfer functions are computed using two approaches: regular waves of constant steepness with capping of wave height at low frequencies; stochastic linearisation based on a single sea state per wave scatter diagram. It is concluded that stochastic linearisation based on a single sea state per scatter diagram is insufficient to provide an adequate characterisation of nonlinear drag forces for the dynamic spectral fatigue analysis of jack-up rigs. Superharmonic resonance effects, due to nonlinearities associated with variable submergence and drag forces, are found to be significant when computing transfer functions of structural dynamic response.

摘要

使用 Sesam 软件作为比较基础，研究了波浪力线性化方法对自升式钻井平台疲劳损伤预测的影响。强调了显着低估疲劳损伤的可能风险。动态光谱疲劳分析方法应用于北海 30 和 70 m 水深的具有代表性的自升式钻井平台。传递函数使用两种方法计算： 恒定陡度的规则波，在低频处具有波高上限；基于单个海况每波散布图的随机线性化。得出的结论是，基于每个散点图的单个海况的随机线性化不足以为自升式钻井平台的动态谱疲劳分析提供非线性阻力的充分表征。