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Periodic Report Summary 2 - OFFSHORE FSI (Fluid-structure interactions in offshore engineering)

Inside the fluid-structure interaction field in which this project can be classified, one of the goals of this Marie Curie International Outgoing Fellowship (IOF) project is to study the water slamming of marine structures. There is a need for data collection regarding deformation of bow like models for different wave heights, length, steepness, and the geometry and immersion of the impacted structure. Surface vessels, floating production systems, and new offshore energy generation devices are mainly the applications. The project aimed to produce new results on the loading produced by water slamming on offshore structures. The fellow designed the slingshot impact testing system (SITS) which allows simulating water impact on different types of structures. The 2 000 kg machine produced very nice experimental data and it provides a new facility for future investigations at Caltech. Publications relating these experiments are now accepted in one of the best international journals in the field: ocean engineering.

Another important objective of the project was the study of the flow-induced or vortex-induced vibrations (VIV) of flexible structures which are extremely common in marine engineering and offshore facilities. There are still major concerns about the effect of sheared flows, the effect of surface waves and motions on the structural response, array configurations and the effect of developed wakes on downstream structures. Those are problems that definitely need further study. The knowledge acquired when approaching those problems, can be later on applied to other engineering applications in the future. During the first period of the fellowship a large amount of new data was produced in the free surface tunnel at Caltech.

During the outgoing stage of the fellowship, the focus was given to the use advanced optical measurement techniques, combined with classical strain gauge and other instrumentation measurements, to investigate these two problems: the dynamic response of different structures and shapes under the effect of vortex-induced vibrations and the wave loading of several offshore devices. Gharib's group at Caltech developed a three-dimensional (3D) imaging technique, the defocusing digital particle image velocimetry (DDPIV), which was used to look at the time evolution of the deformation of flexible bodies. The characterisation of the wake will be accomplished qualitatively by using flow-visualisation techniques and quantitatively by using digital particle image velocimetry (DPIV). The fellow has learned, used and applied the DDPIV technique in very innovative experiments at Caltech. He has also had the chance to participate in experiments carried out in the Large Cavitation Channel (LCC) of the United States Navy in Memphis, Tennessee. This is the largest facility of its kind in the world, and experiments were performed using DDPIV in order to measure the dynamic response of marine propellers under different operating conditions. This was the first time anyone measured optically and with the level of precision we did, the motion of the different blades of the propeller in normal operation. Publications are being prepared now and we believe the technique can have important impact in propeller design and validation.

The return phase was focused on finishing the analysis of the work done during the outgoing phase, writing and publishing papers with that work, the creation of a new research group, writing proposals and applying for new sources of funding to continue this Marie Curie project and designing and constructing new facilities and instrumentation such as DDPIV for future research at URV.