Three-dimensional dynamic response analysis of a vertical L-shaped suspended pipeline in shallow sea

A submarine pipeline will not only be suspended in the straight section, but also in the expansion bend. In this case, the horizontal suspension section and the vertical riser section are L-shaped and under the excitation of wave currents. The dynamic response and fatigue damage caused by wave currents cannot be ignored. Based on the vector form intrinsic finite element (VFIFE) method and considering the three-dimensional pipe-soil contact effect, the dynamic response of a vertical L-shaped submarine suspended pipeline in Chengdao waters under the combined action of wave and current was simulated by using the fifth-order non-linear STOKES wave. The resistance displacement model of lateral soil considering reciprocating motion was established. The dynamic response under the special circumstances of combined action of wave and current and the loosening of bottom pipe clamp was analyzed, and its effect on fatigue life was evaluated. The results show that for the vertical L-shaped submarine suspended pipeline with fixed ends, the most disadvantageous point is the pipe clamp, followed by the pipe-soil separation point, elbow, and mid-span. There are four potential dangerous points, of which the peak stress in mid-span is smaller. There is a significant difference between considering wave-current interaction and not considering wave-current interaction. Only the transversely restrained pipe clamp is superior to the fixed pipe clamp in the minimum fatigue life of the pipe. Considering the lateral reciprocating soil action theory, the stress and fatigue of the whole pipeline are less affected, but the displacement at the mid-span and the separation point of the pipeline and soil is more affected. © 2020, Editorial Office of Journal of Vibration and Shock. All right reserved.