Vol.22, No.3, 2022, pp. 75–83
UDC:

The article aims to establish a coupled thermo-hydraulic numerical model for calculating the first natural frequencies and the first critical velocity corresponding to the appearance of buckling in the first mode, known as static instability of a hot fluid-conveying pipe. The circulating hot fluid has flexional motion as that of pipe structure. A dynamic characteristic of a pipe conveying internal fluid undergoes mechanical load due to the inertia effect of fluid, Coriolis effect, fluid kinetic force due to fluid flow velocity, dynamic load due to inertia effect, and thermal load due to hot fluid. A numerical modal analysis is realised in the fluid-structure interaction configuration. One-dimensional beam finite element is used for investigating the dynamic behaviour of the thin pipe, where the beam type has two degrees of freedom per node. According to the approved method, different elementary matrices are extracted, which are included into Matlab^®. Results are compared with those predicted by analytical, numerical, and experimental methods. Results are presented for cases: pinned-pinned pipe conveying fluid without foundation; with elastic foundation by Winkler-model; with pressure force, for varying values of fluid velocity and thermal effect. The study shows that increase in temperature negatively affects the stability of the system, as the critical velocity of the fluid decreases regularly and corresponds to the decrease in the frequencies.

Keywords: fluid and thermal induced vibration, natural frequency, thermal loads, pressure, elastic foundation, finite element method