Effects of the wall shear stress on the energy dissipation in the fluid-filled riser subjected to heave motion

Abstract

For deep-sea mining risers subjected to heave motion, longitudinal vibration induces unsteady internal flow primarily governed by wall shear stress effects. This study proposes both the extended and partitioned shell-based water hammer models to analyze the axisymmetric dynamic response of fluid-filled risers under heave excitation. Three wall shear stress formulations, quasi-steady, Brunone, and weighting function-based models, are implemented to assess their impact on system energy dissipation. The numerical models are validated against experimental data from a reservoir-pipe-valve system, demonstrating good agreement with measured pressure histories. Analysis of numerical dissipation reveals that non-unity Courant numbers introduce significant artificial energy loss, whereas structural damping and wall shear stress represent the primary physical mechanisms for energy dissipations. For deep-sea mining risers under heave motion, results indicate that the choice of wall shear stress expression has negligible influence on dynamic amplification factors and energy dissipation rates. The system exhibits resonance at frequencies corresponding to both structural natural frequencies and fluid-structure interaction modes, with energy dissipation rates generally increasing with heave frequency and local maxima observed at pressure wave oscillation frequencies. These findings provide important insights of energy dissipation patterns under varying operational conditions of the deep-sea mining riser subjected to heave motion.