Abstract:

A methodology is proposed to enhance the buckling and parametric excitation stability of fluid-conveying pipes by designing their natural frequencies. As a direct indicator of structural stiffness with respect to deformation, which is intrinsically related to the overall structural stability, the natural frequency is adopted as the primary design criterion for enhancing system stability. Based on the generalized Hamilton’s principle, the governing equation for a multi-restrained pipe system is derived. The analysis reveals that, the natural frequencies can be maximized by appropriately selecting the constraint locations, which induces the best buckling stability. Although increasing the flow velocity generally reduces the natural frequency, the optimal constraint location remains relatively unchanged, eventually approaching the location of the maximal critical flow speed, beyond which the pipe loses its static stability. Furthermore, the proposed method introduces additional nodes into the natural mode shape, indicating that a higher energy threshold is required to trigger the resonance. Consequently, the parametric resonance under pulsating flow conditions becomes more difficult to initiate. Meanwhile, with the frequency design, the pipe can prevent the occurrence of parametric resonance with smaller critical damping. Compared with other approaches aimed at enhancing the stability of fluid-conveying pipe systems, the proposed method offers greater practicality for engineering applications, as it only requires adjusting the constraint locations and the optimal location is insensitive to the flow speed.

Key words: fluid-conveying pipe, frequency design, static bifurcation, stability of parametric resonance, optimal stability