Tension variations of hydro-pneumatic riser tensioner and implications for dry-tree interface in semisubmersible

In real sea environments, excessive dynamic axial tension variations can be exerted on the top-tensioned risers (TTRs) and lead to structural integrity issues. The traditional riser-tension-variation analysis, however, by using parametric formulation is only conditionally valid under certain strict limits and potentially underestimates the total magnitudes of tension variations. This phenomenon is especially important for the long stroke tensioner in dry-tree semisubmersible with larger global heave motion and longer stroke. In this paper, the hydro-pneumatic tensioner (HPT) is modeled in detailed component-level which includes a set of hydraulic and pneumatic components. The viscous fluid frictional effect in the HPT is considered. The main objectives are (i) to develop a detailed tension variation model of the HPT; (ii) to identify the deviations between the conventional parametric formulation and component-level formulation; (iii) to numerically analyze the tension variation of long stroke tensioner in a dry-tree semisubmersible (DTS). The results demonstrate the necessity of component-level formulation for long stroke tensioner in the development of DTS.