Articulated pipes conveying fluid pulsating with high frequency

Stability and nonlinear dynamics of two articulated pipes conveying fluid w ith a high-frequency pulsating component is investigated. The non-autonomou s model equations are converted into autonomous equations by approximating the fast excitation terms with slowly varying terms. The downward hanging p ipe position will lose stability if the mean flow speed exceeds a certain c ritical value. Adding a pulsating component to the fluid flow is shown to s tabilize the hanging position for high values of the ratio between fluid an d pipe-mass, and to marginally destabilize this position for low ratios. An approximate nonlinear solution for small-amplitude flutter oscillations is obtained using a fifth-order multiple scales perturbation method, and larg e-amplitude oscillations are examined by numerical integration of the auton omous model equations, using a path-following algorithm. The pulsating flui d component is shown to affect the nonlinear behavior of the system, e.g. b ifurcation types can change from supercritical to subcritical, creating sev eral coexisting stable solutions and also anti-symmetrical flutter may appe ar.