Development of a Spectral Crack Propagation Analysis Method and a Statistical Wave model for the Maintenance Planning of Ship Cracks

As the wide use of high-tensile steel in ship constructions and the significant increase of ship sizes, modern ships become more flexible. When ships cross open seas, the wave-induced loads cause relatively large deformations, which can result in fatigue problems in ship structures. Therefore, these large ship structures should be designed with enough fatigue strength. However, due to large uncertainties involved in ship fatigue design, cracks have been initiated much earlier than expected. The presence of fatigue cracks greatly affects a ship’s structural safety and serviceability. In the current study, the fracture mechanics principles are employed to predict the crack propagation in ships. It will benefit to more reliable crack inspection and maintenance planning. By taking into account the special properties of a ship’s stress response, an efficient spectral method is proposed and validated for the crack propagation analysis in ship structures. Further in order to make use of the proposed method to predict the crack growth, it is essential to know the encountered wave environments in a ship’s future operations. Therefore, a spatio-temporal statistical wave model based on measurements from both satellites and buoys is briefly introduced. It is developed to generate wave environments along any arbitrary ship routes. Combing the crack propagation method with the statistical wave model, a case study using the deck longitude stiffener of a 2800TEU containership is presented to illustrate their applications to plan the crack inspection or maintenance in ships.