Tensioned beam theory is used to calculate displacements and moments of free spanned portions of offshore pipelines. The Rayleigh method is implemented to calculate the fundamental frequency of the pipeline span under the effects of residual tension and span-Induced moments. This procedure is simple and yields a more accurate natural frequency of the pipe even with low residual tension. The effect of the residual tension and span-induced moments on the deep water pipeline was investigated. The benefit of controllable residual lay tension. In the pipe was identified. This simple analytical procedure can be applied to offshore pipelines of any size and In any water depth.
Oil and gas producers are pursuing field developments in progressively deeper water. As a result, the offshore pipeline Industry has become increasingly Interested In the design and Installation of pipelines within areas of Irregular seabed features with little or no remedial span correction. A beneficial and distinguishing feature of such deep water pipelines. Installed by conventional S-Iay, is that the pipelines acquire significant residual tension. This paper presents the analytical treatment for determining span frequency and the effects of residual tension on the vortex shedding response of pipelines. The effect of residual tension on pipelines In span is similar to the tightening of a violin strong. The natural frequency of the Violin string and the pipeline depend on the mass, length, and tension. The accurate estimation of the natural frequency of the spanned pipeline, which is the essential part of the vortex shedding analysis, is clearly affected by the residual lay tension. In this paper, tensioned beam theory is used to calculate displacements and moments of free spanned portions of a pipeline. The Rayleigh method is implemented to calculate the fundamental frequency of the pipeline span under the effects of residual tension and end moments created by the boundary conditions.
