Singing Risers - National competence building initiative on turbulent flow for optimum flow control of gas in export risers and flowlines.

Floating production platforms in the North Sea and Arctic Frontier have experienced severe vibration and noise problems due to high frequency vibrations in flexible risers. This problem, related to large-diameter, composite flexible pipes used for gas ex port and gas injection, has been experienced both at Åsgard, Troll, Norne, Visund and Sciehallion. Vibrations are induced in gas export and gas injection risers at normal design flow rates, causing vibrations in attachments and secondary piping both subs ea and topside, of such an intensity that the vibrations over time constitute real security hazards for un-controlled release of hydrocarbons. At present, the vibration problems are controlled by imposing restrictions on gas export volumes or by boosting the gas export pressures. Several industry projects have been carried out to control the problems, but even today there is no unified understanding of the physical mechanism behind. The problem is characterized by complex interaction between fluid flow , acoustic response and structural dynamics in the composite pipe wall. Finally, the geometric scale of the basic mechanisms is such that the problem cannot be solved by existing numerical models or tools. In order to establish the knowledge and underst anding required to analyse, mitigate and control the "singing riser" phenomenon, the following tasks will be performed: * Fundamental theoretical investigations of turbulent flow of natural gas under high pressure along rough surfaces. * Experimental in vestigations to identify the parameters governing the fluid flow field, interaction with acoustic response and structural vibration * Integration of the scientific disciplines that are necessary to bring forth efficient solutions to the problem (fluid mec hanics/multiphase flow, acoustics, structural mechanics). * Cooperation with oil companies and offshore supplier industries to develop solutions that are feasible and cost effective.