Nonlinearity Research Of Free Spanning Pipelines Considering Fluid-Structure Coupling

The vortex-induced vibration of submarine free spanning pipelines is a multiple field coupling problem.At present,a lot of basic theories about that are not that clear yet.There are three purposes for this paper:(1)In order to get a reasonable value about the interaction length between pipe and soil at both ends of pipeline when some finite element simulations or experimental studies are done;(2)To make a assessment about ultimate spanning length to guarantee the safety when the submarine pipelines are designed;(3)To make up the lack of research achievements about the vibration characteristics of multi-spanning pipelines.In this paper,some finite element models,which is based on fluid-structure coupling,are built by using the ABAQUS and ANSYS software to make some researches about the effective interaction length of pipe and soil,ultimate spanning length and the vibration characteristics of multi-spanning pipelines.It is found that the effective interaction length between pipe and soil should be just about 0.5 times of spanning length if there is no compressive stress when people do simulations or experiments.The ultimate spanning length is easily affected by current velocity,residual stress,and it also would be affected by the boundary condition which is selected.For multi-spanning pipelines,because of the middle supporting soil,there exists a restriction between the adjacent two spans.The multi-spanning pipeline should be studied as a single spanning pipeline while the length of middle supporting soil reaches to a certain value.The vibration of multi-spanning pipelines will be dominated by higher order modes as the current speed increasing.