Predicting the service life of risers subjected to the VIV phenomenon is based on theoretical methods, the results of which are strongly dependent on parameters such as damping coefficients. In many cases, however, this parameter is not defined on the basis of subsidies arising from the real scale, even if indirectly. Thus, seeking to contribute to the use of values closer to reality, even if still obtained based on a subgroup of the aspects that have an impact on the dissipation of vibrations in risers, which is the relative contribution of the layers, this work aims to measure the damping coefficients in a gradually dissected riser sample, i.e. successively measured after removing each layer to identify the relative contributions. For this purpose, a riser sample with a nominal diameter of 4 inches and approximately 2 meters in length was tested for characterization in the first mode of vibration via the Impulse Excitation Technique (IET). Natural frequencies were measured from built Frequency Response Functions (FRFs), and damping coefficients were automatically determined according to the Hilbert transform (HT) to access the envelopes and linearly adjust the decrements in the logarithmic presentation. With these analyses, one can observe how the overlapping of each layer modifies the previous system. Additionally, using simplified modeling by association of effects, it was quantitatively determined that the outermost polymeric layers, namely the external high-density polyethylene (HDPE), contribute the most to total structural damping. Therefore, as a contribution to this work, we highlight the presentation of useful results for future more complex and complete theoretical models of the riser on a full scale, as well as the proposal of more effective methods of dissipation and consideration of damping in the VIV phenomenon.
As global demand for oil and gas increases, energy companies are compelled to operate in progressively deeper waters, necessitating advanced technologies and methodologies for efficient extraction and transport. In such a challenging environment, the prevalent utilization of unbounded flexible risers becomes essential for the transportation of oil and gas from the seabed to the floating platform. This is primarily attributed to the permanent dynamic loading induced by sea currents, coupled with the concurrent imposition of forces from platform motions at the riser's top.
