Numerical Investigations of a Two-Way Coupled Fluid–Structure Interaction Approach for Fast Transients in Fluid-Filled Flexible Piping Systems

Fluid–structure interaction in fluid-filled flexible pipelines is modeled here with a time explicit nonlinear 1-D coupled approach. The internal steam–water fluid is modeled using a homogeneous equilibrium model where kinematic, mechanical, thermal, and thermodynamic equilibrium between liquid and steam water is assumed. As a consequence, the nonlinear convective effects are taken into account as well as the temperature variations in the fluid model. The mechanical behavior of the pipelines is obtained following the Euler–Bernoulli beam theory. This leads to structural equations taking into account axial, flexural, lateral, and torsional pipe motion. In addition, plasticity is also considered in the structural behavior. Thus, the overall model corresponds to the nonlinear extension of the so-called seven degree-of-freedom fluid–structure interaction model. Furthermore, radial expansion of the pipe cross section due to the internal fluid pressure loading is also taken into account, while the pipe radial motion is neglected. Both junction and friction coupling mechanisms are considered in the present model, whereas the Poisson coupling is ignored in this study. An explicit finite-volume method is used for approximating the fluid equations and is coupled with an explicit finite-element approach used for the structural beam equations. This leads to an explicit two-way coupling approach for fluid–structure interactions which is assessed on a selection of several experiments involving non-isothermal steam–water behavior or significant FSI effects during fast-transient events. Comparisons are given with the experimental data on all considered experiments, which clearly demonstrates the ability of the present approach to be efficient and representative.