Prediction of two dimensional separated flows about a circular cylinder in the presence of boundaries

Abstract

The behaviour of the hydrodynamic loading experienced by a circular cylinder in the presence of boundaries has been the subject of investigation by various investigators in recent years. Amongst other things it is relevant to the design of offshore structures and subsea pipelines. It is important to be able to assess the behaviour of such components of an offshore structure because it has to be designed to withstand loading due to flow interactions which are complicated in nature and not yet fully understood. To gain a clearer insight into the effects of anodes on the overall loading of an offshore structure, for example, the local flow around a cylindrical member in the presence of boundaries must be understood. In the present study, a numerical model based on the Discrete Vortex Method has been developed as a means of analysis of such flows since, in comparison to experimental methods, it is a less expensive and less time consuming approach in gaining that knowledge. The algorithm is developed in such a way as to enable application to a range of cylinder / cylinder, cylinder / anode, and cylinder / wall configurations subject to a variety of steady and time dependent flows. The technique has been applied in a number of case studies which include the investigation of the flow interactions occuring when two cylinders are in close proximity and also when a cylinder is close to a plane boundary. The engineering applications are the interference of structurel members, the loading on structural elements due to the presence of anodes, and the loading on free spanning subsea pipelines. The in-line and transvese force coefficients arising from the case studies and also the flow patterns obtained are presented in order to provide a more detail description of the flow phenomena and interactions involved. The comparison of the results with both experimental and numerical evidence is also presented and the range within which the algorithm produces good results is identified.