Experimental and operational structural dynamics identification of the laboratory scale offshore support structure with uncertainty assessment

The paper presents an experimental campaign on the laboratory scale model of the tripod type offshore support structure. The model structure was tested in the different support and environment configurations: free-free, supported and in the large towing tank conditions. Tripod model allows to model the propagation of the circumferential crack of the cylinder. The towing tank test configuration included the wind tower with the 3 bladed rotor. Rotary support allowed to expose the tested structure to the waves coming from different angles. Test campaign accounted for the different types of sea waves. For the reference modal model of intact and damaged structure impulse modal test was performed with the stopped rotor and calm water conditions. The response of the structure to the wave were measured with 4 bi-axial underwater accelerometers located on the submerged part of the model and 4 tri-axial accelerometers located on the above-water components. Experimental and operational modal analysis were applied to identify the structural dynamics of the investigated laboratory scale model for intact and damaged state, different support and wave patterns. Numerous modal models consisting of the natural frequencies, mode shapes and corresponding damping coefficients were estimated from the measured signals. Comprehensive test matrix allowed to assess the differences in modal model parameters due to the damage, support and environmental loads.