Drilling risers are key equipment to connect drilling platform and subsea blowout-preventer in deep-water drilling. Vortexes are formed beside the drilling risers when the flowing ocean currents over the risers. Drilling risers vibrate both in in-line (IL) and cross-flow (CF) directions for the effect of vortex-induced forces. This phenomenon is called vortex-induced vibration (VIV). When the vortex shedding frequencies are close to the natural frequencies of the risers, vortex shedding lock-in occurs. This condition causes significant fatigue of the risers, thereby affecting safety of drilling platform and crews. A considerable number of experiment studies and numerical simulations for VIV have been performed so far. However, currents are not uniform. Marine structures like drilling risers are under the effect of irregular flow currents. Therefore, investigating VIV mechanism under irregular flow is necessary.
This project aims to investigate the mechanism of the vortex induced vibration under the irregular flow. First, an experiment for VIV under the irregular flow was conducted in a deep-water offshore basin at Shanghai Jiao Tong University. But, the experimental data have not been analyzed. We'll go on analyzing the experimental data by modal analysis method to investigate the vortex induced vibration mechanism under the irregular flow.Second,to establish a coupled fluid-structure for drilling riser based on wake-oscillator model and potential flow theory. The model will be solved by finite element method and dynamic analysis procedure well be developed by Fortran, and the VIV mechanism of the drilling riser under irregular flow will be simulated and compared with experimental results.The results of this project will provide insight into how to control VIV for drilling engineers, product wuppliers and manufacturers iin related industry.