Numerical investigation on nonlinear wave interaction with partially submerged subsea pipe-valve structures

Abstract The dynamic behaviours of subsea pipe-valve structures—the principal components of subsea equipment—are of critical concern for the control of the lowering through the splash zone during installation. Nonlinear interactions between waves and pipe-valve combinations are challenging the investigation of the wave forces acting on large-dimension structures. This paper proposes a numerical model to study the nonlinear hydrodynamic performance of partially submerged pipe-valve structures. A two-dimensional (2D) numerical water tank (NWT) was established to efficiently generate high-accuracy incident waves, and a semi-immersed horizontal cylinder was applied to the numerical simulations of wave-structure interaction (WSI) to study the mesh and time convergence. The numerical model was validated with a comparative analysis of the modelling results with experimental data, other numerical results, and theoretical results. Numerical simulations of the interaction between Stokes-II waves and subsea pipe-valve structures were performed, and the effects of the valve height ratio, valve length ratio, and valve spacing were investigated. The subsea pipe-valve structure is a kind of multi-scale structure, the wave forces exhibited stronger nonlinearity when acting on the partially submerged valves than on the completely submerged pipe. Changes in valve structure and distribution significantly increased the overall change in the wave forces acting on the valves. The stronger nonlinearity was primarily derived from phenomena such as wave reflection, wave blockage, and wave run-up. The numerical results provide references for the structure and strength designs and offshore installations of large subsea equipment like subsea manifolds.