Hydrodynamic forces acting on a bottom mounted circular cylinder

Prediction of hydrodynamic forces acting on submarine pipelines lying on the seabed is essential for on-bottom stability calculations. Classical methodology is based on Morison's equation, for which non-dimensional inertial, drag and lift coefficients must be found from the vast array in the public domain or from relevant model tests. Generally the lift force is poorly predicted. More recently a wake model has been formulated, based on field data to which empirical constants were fitted, much of this has remained proprietary information and limited in application to pipelines with diameter greater than 400 mm. An experimental programme using regular waves and currents with extensive flow visualization, has provided an insight into the physics of the problem. Traditional dimensionless force coefficients obtained using Stokes fifth order wave theory are compared to data from previous research and joint industry programmes. Analysis of flow visualization has produced correlations between the near field flow incorporating vortex motions and features in the force traces not predicted by conventional theory.