A study has been conducted to investigate the effect of nonlinear wave forces on a marine pipeline. A hydraulic model of a marine pipeline buried in a sand seabed has been constructed and tested in a twodimensional wave. The pipeline model has been exposed to various wave conditions ranging from stokes 2nd-order to Stokes 3rd-order waves as well as broken waves. Measurements have been made for the porewater pressure on the pipeline and water surface elevation around the pipeline location. A coupled BEM-FEM model has been modified and employed to simulate the nonlinear interactions among waves, seabed and the pipeline. Comparisons have been conducted between numerical results and experimental records. The validity of the BEMFEM model and the reliability of the experimental results have been confirmed. It has been found that the pore pressure on the pipe surface is considerably influenced by higher order wave components. Also found is that the normalized wave force increases for higher waves in intermediate water depths, but the force decreases for higher long waves in shallow water depths. Moreover, it has been found that the vertical force is generally higher than the horizontal one when nonlinear wave effects are minor. However, the nonlinear wave effects become more significant in shallow water and the wave front is sharper. High pressure gradient and forces act on the pipeline in the horizontal direction, and the horizontal force may exceed the vertical one.
Pipelines are sometimes installed over or in the seabed away from the shoreline. They are used to transport fluids, e.g., crude oil or natural gas or sewage water, to/from offshore sites from/to the shore or on a short cut across a bay. Vertical forces acting on the pipeline may cause pipe flotation or ultimately breakage in the pipeline and environmental catastrophes.
