An extensive model test program on the hydrodynamic forces on a submarine pipeline resting on the sea bottom and exposed to steady current, regular waves, combined steady current and regular waves, irregular waves, and combined steady current and irregular waves has been performed. The hydrodynamic forces in both the in-line and the cross-flow directions have been analyzed using three different methods, i.e., least-squares-fit analysis based on Morison-type equations, Fourier analysis, and maximum force analysis. The force coefficients associated with each method have been determined for a wide range of environmental conditions. The results of the tests are presented in terms of the calculated force coefficients and their dependence on various nondimensional parameters is discussed. Furthermore, comparisons with other test data are presented.

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Model tests were carried out in a current tank to determine the effect of the proximity of a plane boundary on the vortex-induced vibrations of a flexible pipe.The response of the center of the pipe span was measured using an optical tracking system.It was found that in the presence of a plane boundary, the maximum amplitude of vibration is limited, and the onset of vortex-induced vibrations of appreciable amplitude occurs at higher velocities than when no boundary is present.

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Model tests were carried out in a wave tank to determine the effect of combined steady and wave-induced currents and/or the proximity of a plane boundary {seabottom) on the vortex-induced vibrations of a flexible pipe. The response of the center of the pipe span was measured using a biaxial accelerometer. The results show that the proximity of the plane boundary and/or superposition of waves on the steady flow have a pronounced effect on the amplitude and frequency response in both the transverse and in-line directions.