Study of the Factors Influencing Circumferential Wavenumber Coupling in Filled Pipes

Mining pipeline transportation systems often operate under partially filled conditions. Filling level variations induce circumferential asymmetry, modifying the pipe mass distribution and dynamic characteristics and invalidating conventional axisymmetric vibration models. In particular, the mechanism of circumferential modal wavenumber coupling under partially filled conditions remains unclear. To investigate the vibration behavior of partially filled pipes, a bidirectional acoustic-structural coupled dynamic model for partially filled pipes was developed. We introduce an acoustic-pressure integral work formulation accounting for filling volume variations to quantify the fluid-structure coupling. Based on this framework, wavenumber-frequency, harmonic response, and modal shape analyses are combined to investigate the effects of filling level on circumferential modal wavenumber coupling and frequency response characteristics. The model was validated through impact hammer experiments on water- and coal-slime-filled pipes. The results demonstrate that asymmetric mass distribution induced by partial filling is the primary mechanism responsible for circumferential modal wavenumber coupling. Under empty and fully filled conditions, the system remains approximately axisymmetric, and the vibration response is dominated by a single circumferential wavenumber. At intermediate filling levels, circumferential symmetry is broken, leading to multimodal wavenumber participation, splitting of degenerate modes, additional resonance peaks, and an upward shift in modal frequencies.