Analysis of fluid-structure interaction vibration and fatigue life of fluid-filled pipelines in underwater vehicles

This study investigates vibration characteristics and fatigue damage mechanisms in underwater vehicles subjected to complex coupled loading (external random excitation and internal fluid pulsation). Focusing on fluid-filled straight and bent pipes, this research complements existing analyses of multi-type pipelines and coupled vibration fatigue. A bidirectional fluid-structure interaction time-domain analysis framework is established based on a three-dimensional finite element model to quantify dynamic responses and predict fatigue life. Key findings demonstrate that: (1) Fluid pulsation dominates stress distribution, with fluid-filled pipes exhibiting 40 % lower modal frequencies than empty pipes, indicating that the incompressibility of the fluid suppresses pipe deformation; (2) Straight pipe configurations show a 42 % reduced equivalent stress compared to bent counterparts, which highlights bend-induced vibration amplification; (3) Vortex-induced pressure fluctuations at pipe bends accelerate fatigue damage progression. These findings provide practical significance for analyzing the dynamic behavior and damage resistance of piping systems, as well as enhancing the safety and reliability of engineered pipelines.