Métodos simplificadores para análise de fadiga em risers

Abstract

With the increasing demand for floating production units to explore of oil reservoirs in deep waters, the environmental conditions are even more challenging when designing subsea production systems. The oceanic waves induce oscillatory motion to the floating unit, causing cyclic loading on risers which can be damaged due to fatigue failure mechanism. During design phases, it is required to evaluate fatigue damage induced by environmental loads to avoid eventual failure for the whole exploration system life. The research presented herein studies numerical methods which can provide fatigue damage estimates with reduced computational costs by simplifying the environmental loading matrix. Two different classes of methods were evaluated: the equivalent blocks methods, and the response surface methods. Both were tested with an example of a steel catenary riser (SCR) connected to a semisubmersible vessel. Fatigue analysis was performed using finite element models in time domain, considering irregular waves formulation and de-coupled vessel motions. Obtained results were compared to conventional methods and showed that it is possible to obtain acceptable damage estimates for annual fatigue damage with up to 90% reduction in the design environmental load cases.