According to the requirement for the dynamic design of the external pipelines of aero-engine

and for solving the wet modal characteristics of complex pipelines

the Timoshenko beam theory and the energy method were used to derive the equation of the vibration of pipeline

in consideration of the effects of mass

pressure and velocity of fluid. Based on the existing pipe element in the ANSYS

an equivalent method to consider the pressure and velocity of fluid was established by using the stiffness and damping element

and it can be used in wet modal calculation of pipelines in ANSYS. Results showed that

the lateral force difference caused by the pressure of fluid could reduce the bending stiffness of the pipeline

and the axial tension caused by pressure could increase the bending stiffness; the effect of the pressure was related to the degree of axial constraint of the supports

and the Poissons ratio. The effect of the fluid velocity on the wet modal of the pipeline was related to the boundary conditions

the modes of vibration and the axial elongation of the pipeline. At high velocity

the modal frequency was zero

that was

the buckling instability occurring.