Vibration and Stability Analyses of Submarine Fluid-Conveying Pipelines with Local Stiffness Variation Under External Flow Fields

This study analyzes the vibration and stability characteristics of a submarine fluid-conveying pipeline with local variation in stiffness under the influence of external flow fields. Utilizing the absolute nodal coordinate formulation (ANCF), the dynamic equation for the submarine pipeline with local stiffness variation under arbitrary boundary conditions is derived. Through numerical solutions, curves depicting complex frequency variations as a function of the internal flow velocity of the pipeline system are obtained. Additionally, the effects of external flow velocity, geometrical parameters, and local stiffness variation on the vibration and stability characteristics of the submarine pipeline under three different boundary conditions are investigated. Results indicate that the stability of the pipeline system decreases across the three boundary conditions under the influence of the external flow field. Increased external flow velocities lead to further reductions in system stability. Furthermore, as the length-to-diameter ratio increases and the thickness-to-diameter ratio decreases, the first three orders of frequencies of the pipeline gradually diminish. Enhancing local stiffness contributes to improving the stability of the system, whereas reducing local stiffness has the opposite effect.