Time Domain Prediction of Combined CF and IL VIV Responses Under Constant Currents

Abstract

Abstract The slender marine structure (e.g., deep water riser systems) subjected to vortex induced vibrations (VIV) can oscillate simultaneously in both cross-flow (CF) and in-line (IL) direction relative to the flow direction. The IL response is important as it may contribute to fatigue damage to the same order of magnitude as the CF responses for high mode responses. A combined CF and IL load model is also required for prediction of VIV responses in more complex flow conditions. The time domain VIV prediction load model has been extended to include an IL VIV load term. The present study aims to validate the latest combined CF and IL load model using laboratory tests and evaluate its limitations. The validation results showed that the averaged spatial and temporal energy transfer process between fluid and structure is sufficiently described by the load model. The time domain VIV load model is able to obtain reasonable prediction of key VIV responses, including curvature, frequency, fatigue damage, higher harmonic responses in both CF and IL directions as well as drag amplification in one single non-linear time domain analysis. This overcomes some of the limitations in the present frequency prediction models.