Influence of surface roughness on vibration response characteristics of flexible structures on offshore floating platforms

Abstract

The expanding interest in floating offshore renewable energy technologies, including floating wind turbines and solar platforms, is attributed to their multifarious benefits. One pivotal factor influencing the power generation efficiency of these technologies is the vibration response of the flexible structures connected to the platforms, such as mooring systems, dynamic power cables, and flexible pipelines. In this research, a numerical investigation is conducted on the response characteristics of vortex-induced vibration (VIV) of cylinders with varying surface roughness in oscillatory flow. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and dynamic equation are used for fluid-structure interaction. The results reveal that for rough cylinders, multiple frequencies are involved in the vibration. For most simulated cases, the vibration frequency in the cross-flow (CF) direction is an integer multiple of the frequency of the oscillatory flow and associated with the quantity of shedding vortex pairs during a single period of the oscillatory flow. For rough cylinders, the CF vibration frequency differs by one from the number of shedding vortex pairs within one period of the oscillatory flow. With the increase of surface roughness, the maximum vibration amplitude shows an increasing trend (12%), then a decreasing trend (21%). Furthermore, the vortex shedding flow pattern presents C + S mode or S mode. This study offers valuable insights for analyzing the vibration response characteristics of authentic flexible structures.