NONLINEAR WAVE FORCES ON A RUBBLE COVERED PIPELINE

William G. McDougal, Norimi Mizutani, Ayman M. Mostafa

Abstract


A nonlinear numerical model is developed for the interaction of waves with a pipeline covered with rubble. The wave field utilizes a fully nonlinear potential formulation while the porous medium is governed by modified Navier-Stokes equations. The model employs the BEM in the water column and the FEM in the rubble layer. Wave forces on the pipeline are calculated by integrating pressure around the pipeline perimeter. The numerical and experimental results for the wave kinematics in the pipeline vicinity are found to be in reasonable agreement. Numerical analyse indicate that the horizontal wave force is larger than the vertical force for all tested wave and rubble conditions. Forces increase with increasing wave height and decreasing depth. However, for the cases examined there is an intemediate water depth at ML « 1/6 for which the forces are largest. The armor stone size and rubble layer pososity have little influence on the magnitudes of the forces. The horizontal force is nearly independent of the depth of rubble cover over the pipeline. However, the vertical force increases significantly as the depth of cover decreases. Also, for partial pipeline cover, the maximum horizontal and vertical forces are more in phase, which combined with the larger vertical force, results in a substantially less stable condition.

Keywords


pipeline; wave force; nonlinear waves; rubble covered pipeline

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