Effect of steady boundary-layer flow on the hydrodynamic forces on a near-wall cylinder in currents

In this work, experimental tests are carried out to investigate the effect of steady boundary layer flow (BLF) properties on the time-mean force coefficients of a cylinder laid on/above smooth/rough walls. Analysis based on boundary layer theory reveals that the force coefficients are influenced by the turbulence intensity, velocity gradient and dimensionless velocity deficit of the BLF. Testing results show that the force coefficients correlate best with the dimensionless velocity deficit among all the examined BLF properties. Empirical formula for quantifying the influence of velocity deficit on force coefficients are proposed based on the present test results and those reported in literature. Potential implications of the present findings on the stability design of subsea cables are discussed.