Estimation of flexible cylinder displacements in wave-basin experiments

Abstract

This paper describes a method developed to estimate the three-dimensional displacement field of long, flexible cylinders subjected to wave loading. The method makes use of the relationship between curvature and displacement of a uniform beam. The technique was implemented in a large-scale experimental study to investigate the response of a pair of flexible cylinders in close proximity, with an emphasis on the collision behavior between them. The model cylinders were designed to be representative of risers or tendons of a tension-leg platform in approximately 1000 m of water. The cylinder models, approximately 17-m long and 0.03-m diameter, were instrumented to measure the cylinder curvature at discrete locations along their length. At each time step the displacement field was computed from the curvature measurements using a ‘shoot-to-fit’ numerical-integration scheme. This procedure yielded a complete description of displacement along the cylinder as a function of time. The number and location of the curvature measurements were optimized by simulating the wave-flexible cylinder interaction with a finite-element model that was also used to demonstrate the accuracy of the method. The effectiveness of the technique is demonstrated by results from the experimental program, and it appear to be feasible to adapt this approach for field experiments.