Vortex-induced vibrations of moored floats in steady currents

摘要

Waters pumped up from oceans have been employed for Ocean Thermal Energy Systems since several years. Now attention is being given to the utilization of the nutrition value of the unpolluted waters from deep seas. For effective exploitation of deep waters for agricultural purposes or for industries dealing with marine products, it is important to uplift the water at minimum cost. One of the economical methods of uplifting the deep-sea water would be to use soft (flexible) pipes held in their top using either floats or buoyancy-type platforms. A basic experimental study on the behavior of a moored-float, whose prototype corresponding to a large-scale floating structure like a tension-leg-platform, under the actions of current flow has been conducted. The response characteristics due to fluid drag and lift forces are investigated. The models were placed in a circulating water channel under unidirectional current flow. The response vibrations were recorded and analyzed. The results indicate that in-line components of responses increase with flow velocity due to higher fluid drag forces. The variation in the cross-flow components is much more complex and is influenced by eddies and other forms of turbulence. Also, the vortex-induced vibration involves a feedback mechanism in which vibration of the model and the vortex formation are coupled to each other.