By assuming the linear superposition principle to be valid, the
hydrodynamic forces on a horizontal cylinder under waves and current
are examined. In this study, towing a cylinder in waves is used to
simulate a cylinder under waves and current. The experimental
technique is proved valid through theoretical considerations and
experimental investigations. For large current velocity (or high tow
speed), the drag coefficient for waves and current approaches that
for steady flow. If the current is large enough, these two values
are nearly identical.
In addition, the behavior of force coefficients for a horizontal
cylinder in waves only with moderately large Reynolds number,
Keulegan-Carpenter number and frequency parameter is examined. The results show that the forces on a horizontal cylinder in waves are
smaller than those for planar oscillatory flow.
Whether the total acceleration or local acceleration should be
used in the inertia term is a debatable point for using the Morison
equation. To study this problem, the similarities and differences
between these two accelerations for different water depths and wave
heights are examined. The results show there is no evident
difference in force prediction if the related force coefficients are
used.
To check the suitability of this data for determining Cd and/or
Cm, an indicator, RR, is developed for the horizontal smooth cylinder
in waves and current