A Simple Empirical Model for Tube–Support Normal Impact Interaction

Flow-induced vibration in a steam generator may cause tube–support interaction. This long term interaction is a challenging problem as it may lead to tube fretting-wear and possibly tube failure. An estimation of the normal impact force during tube–support interaction is important to precisely quantify material removal. A precise study of the interaction presents several challenges as a result of the many parameters involved during the interaction, including fluid forces, number and type of supports, and geometry of contact. The present study investigates tube–support interaction using a simple experimental rig, consisting of a tube interacting with a flat support positioned at the tube midspan. The work investigates the normal force–displacement relationship and arrives at an estimation of empirical parameters, associated with the nonlinearity in this relationship. The resulting empirical model is used to simulate tube–support interaction for various gap sizes and excitation forces. Comparison with experiments indicates that using the nonlinear spring–damper model significantly reduces the predicted impact force error, to less than 20%, when compared to experimental tests. Various energy dissipation mechanisms during tube–support interaction, including impact and structural damping are also studied. The effect of impact damping on the tube response is investigated, using the Hunt and Crossley model. Investigation on structural damping suggests that using a higher effective structural damping during tube–support contact, depending upon tube–support gap size, improves the accuracy of the estimation of the tube response, at least for moderate gap sizes.