To investigate the characteristics of wave induced lift force on a horizontal pipeline near plane boundary, a series of measurements had been carried out in" an Utube. High velocity in U-tube had extended the Keulegen-Carpenter number range up to about 100 and forms a better bases for discussing the lift force on pipeline. The results show that the frequency of the lift force increases from 1 to 10 times of the frequency of oscillating flow with increasing KC number. Spectrum analysis shows that the main energy of the lift force distributes on low frequency zone even by high frequency oscillating force. Within one diameter from plane boundary, the magnitude of the lift force increases obviously as the gap ratio decreases. Outside one diameter, the boundary effect is negligible. Potential theory fails to express the lift force characteristics.
In recent years the submarine pipeline design enact an important role in highly developed ocean engineering such as for ocean outfalls, fuel, oil and water transport etc. The most important part of the pipeline design is the estimation of waves and currents induced forces. The hydrodynamic forces on a horizontal pipeline can be divided into t\., o parts: the inline force which is on the same progressive direction with wave and current, and the transverse (lift) force which is perpendicular to the in line force and the pipeline. From the many previous studies, it has been shown that the lift force is essential to the pipeline design. e.g. the experimental results of Bidde (1971), Sarpkaya (197S) and Kao (1984), etc. showed that the magnitude of lift force can reach a high considerable portion of inline force. Neglecting the lift force may cause the underestimation of the total force. Another notable point of lift force is the character of high frequency.