Session: 06-05-04 Marine Hydrodynamics IV

Paper Number: 126665

126665 - Experimental Study on Hydrodynamic Damping of an Oscillating Cylinder Under Small Keulegan-Carpenter Numbers 

This paper presents an experimental study on the hydrodynamic drag and inertia coefficients of an oscillating cylinder in quiescent water under small Keulegan-Carpenter number (KC) conditions. The objective is to address a discrepancy demonstrated by Ren et al. (2021) where experimentally determined drag coefficient under small KC conditions deviated significantly from the analytical solutions and the results from direct numerical simulations (DNS). It was found that under small KC (<1) conditions the drag coefficient, which was decomposed from the total measured force through Morison equation, was extremely sensitive to the experimental conditions, such as the test setup and the synchronization of sensors for measuring the forces (recorded by the load cells) and cylinder motion (recorded by the accelerometer). In one case, a phase lag (or lead) of 0.1% oscillation period in cylinder motion and force signals lead up to 200% difference on calculated drag coefficient. This is because the drag force accounts for a small proportion (~ 4%) of the total force under small KC. As a results, even a tiny mismatch on the force and motion signals affects the drag estimation. A post-processing strategy is proposed to reduce the phase lag. After implementing this strategy, the calculated drag coefficients agree well with those obtained from the analytical solutions and DNS. Hence, the proposed strategy improves the estimation of drag coefficient at small KC. The suitability of the proposed analysis method for other applications is discussed in the paper.

Presenting Author: Guanning Dong South China University of Technology

Presenting Author Biography: Guanning Dong (1997-), Ph.D student of South China University of Technology, majoring in marine engineering, main research direction: hydrodynamics of cylindrial structures under wave and steady current conditions.

Authors:

Guanning Dong South China University of Technology
Liang Cheng South China University of Technology
Chengjiao Ren The University of Western Australia
Feifei Tong The University of Western Australia