Experimental Study on Vortex-Induced Vibration of Marine Riser Model with Coupling Interference Effect Under Combined Internal and External Flow

A partition model of interference efficiency was constructed to study the coupling interference effect under combined internal and external flow. The concept of “internal flow efficiency”, “velocity ratio” and “interference efficiency” were introduced to quantify the effect of internal flow and interference, and reveal the coupling mechanism among internal flow, external flow and interference effect. The results showed that the dynamic response of risers under variable angles was significantly different after considering the effect of internal flow. When the external flow velocity was smaller than 0.25 m/s, the vibration of risers was promoted by the internal flow. With the increase of external flow velocity, the effect of internal flow was weakened and the dynamic response of riser mainly depended on the external flow and interference effect. Under the effect of different internal flow, the interference efficiency had similar change trend. The interference effect amplified the complex secondary flow effect inside the riser, making the dynamic response of riser complex and random. In this paper, the overlap area and subdivision criterion of interference effect were constructed within the range of experimental velocity ratio, and the change curve of interference efficiency was obtained with an average meaning, which may have important practical meaning.