Prediction,measurement and comparison of fluid-structure interaction using mathematical and experimental models

Without presenting all the associated mathematics this paper considers the combined use of theoretical and experimental methods in the investigation of the fluid structure interaction of rigid and articulated structures. The structures considered are the rigid body form of the Lancaster Flexible Bag (LFB) and an articulated Cockerell raft system.In the case of the LFB the Salvesen-Tuck-Faltinsen strip theory is shown to predict vertical and horizontal bending moments which are generally consistent with measured trends (almost) irrespective of whether 2D-based or 3D-based calculated hydrodynamic active and reactive coefficients are used. The non-repeatability of some of the measured results used in the comparison caused some concern and the additional required model testing is discussed.In direct comparison application difficulties were encountered when using theoretical analyses to assist with the organization of the experiments to investigate the hydrodynamic loading of articulated systems. The finite element program PAFEC 75 was used to predict the vibration frequencies of the framework used to support the Cockerell raft model and the actuator system used to force oscillate the model. The 3D diffraction programme MATTHEW provided predictions of pressure distributions over the raft to assist with sensible positioning of the pressure transducers on the physical model. The difficulties encountered in applying these prediction tools are discussed, also the current research programme is reported.