A Prediction of Dynamic Stresses for Long, Large-Diameter Horizontal Pipes at or Near the Ocean Free Surface

Abstract

A straight-beam approximation is applied to a long, stiff pipeline located at or near the ocean free surface. The analytical model determines vertical and horizontal transverse motions in a linear frequency-domain framework. Longitudinal dependence is expressed through a modal expansion, with the hydrodynamic loads calculated through slender-body theory. This method is validated by comparing predicted bending stresses for a 9.1-m-(30-ft-) dia pipe with corresponding model basin data. Maximum stresses occur when the wave angle allows a simultaneous matching of frequencies and projected wavelengths. Results also show peak stresses near the aft end of the pipe. Finally, it is confirmed that in deep water, bending stresses in the horizontal plane are in general smaller than those in the vertical plane.