Lifespan assessment of flexible risers involves the evaluation of fatigue parameters, requiring accurate predictions of stresses and their variation in pipe components. For predicting the effect of complex three-dimensional nonlinear dynamics on component stress histories, multi-scale methods can combine generality of application with computational efficiency. In this paper, we describe the development of a two-scale computational homogenisation procedure linking a coarse-scale analysis model using specialised beam elements, and a detailed stress prediction model consisting of a pipe section with components modelled with shell elements and frictional contact interactions.
To use the procedure, the detailed model first functions as a virtual test rig, by which parameters of the global model may be determined. For detailed stress prediction, the global model is tested under the operating conditions of interest providing a set of generalised strains which are applied to the detailed model. The models are implemented in the general-purpose finite-element package Abaqus. As key aspects of the procedure, we show how generalised stresses and strains can be imposed on the detailed model uniformly without introducing spurious boundary effects and demonstrate how local stresses can be determined using strain data from the global model.