Hydrodynamic forces on a horizontal cylinder under waves and current

Graduation date: 1983By assuming the linear superposition principle to be valid, the\ud hydrodynamic forces on a horizontal cylinder under waves and current\ud are examined. In this study, towing a cylinder in waves is used to\ud simulate a cylinder under waves and current. The experimental\ud technique is proved valid through theoretical considerations and\ud experimental investigations. For large current velocity (or high tow\ud speed), the drag coefficient for waves and current approaches that\ud for steady flow. If the current is large enough, these two values\ud are nearly identical.\ud In addition, the behavior of force coefficients for a horizontal\ud cylinder in waves only with moderately large Reynolds number,\ud Keulegan-Carpenter number and frequency parameter is examined. The results show that the forces on a horizontal cylinder in waves are\ud smaller than those for planar oscillatory flow.\ud Whether the total acceleration or local acceleration should be\ud used in the inertia term is a debatable point for using the Morison\ud equation. To study this problem, the similarities and differences\ud between these two accelerations for different water depths and wave\ud heights are examined. The results show there is no evident\ud difference in force prediction if the related force coefficients are\ud used.\ud To check the suitability of this data for determining Cd and/or\ud Cm, an indicator, RR, is developed for the horizontal smooth cylinder\ud in waves and current