Fenders are a key element of float-over topsides installations protecting the vessel and jacket legs by absorbing impact energy. Fender capacity is defined in accordance with expected vessel motions, vessel hull strength, and anticipated impact energy. Translating those dependencies from full-scale float-over scenarios to model-scale experiments provides added challenges when devising experimental approaches.
This paper describes the design and development of model-scale fenders and their application in float-over topsides installation experiments. Current model fenders use multi-stage cantilevered leaf springs to develop the required non-linear stiffness curve which is calculated from full-scale fender data. Spring material and geometry, relative position, and loading location are key variables used to match the target fender stiffness as changes in these parameters directly affect the force-deflection characteristics of the model-scale fenders.
The force-deflection characteristics (stiffness) of the model-scale fenders were checked before, during, and after wave experiments, using both isolated bench tests and in situ verifications. Multiple iterations of stiffness checks were completed during the stiffness curve matching process prior to the experimentation. The achieved load-deflection characteristics of the fender units were within 2% of the target stiffness curve. The damping characteristics of the fenders were not specifically modeled, but were measured for each of the stiffness stages. The model fenders have successfully been used in multiple float-over experimental campaigns.