Theoretical And Experimental Investigation Of Vibration Characteristics Of Fluid-filled Piping System

Pressure pulsations and vibrations of the wall in fluid-filled pipes may cause excessive noise radiation and even lead to fatigue damage of the piping systems. The excitations can be fluid or mechanical based sources. Energy due to fluid-borne and structure-borne disturbances propagating in the fluid-filled pipe can be carried by fluid and pipe wall. Energy transfer may occur between these two medias because of the coupling between wall and fluid. Accurate and clear descriptions of energy propagation processes when the system is under different forms of excitations can play a guiding role in pipeline design, vibration and noise control of such systems. From this point of view, this article concerns the detailed calculations and analysis of vibration energy transfer, transforming in the fluid-filled piping systems combining structural intensity theory.Firstly, based on Flugge shell theory and fluid pressure equation the solutions of all kinds of the wavenumbers including pure real, pure imaginary and complex numbers are obtained by combining the coupled condition. A more comprehensive discussion of each wave is made. The forced vibration of the coupled system is gotten by using residue theorem, the point and transfer motilities of the low circumferential modes are analyzed.Based on the structural intensity theory, the results of the coupled system under a circumferential line cosine harmonic force, a point force and the monopole source in the fluid excitations are obtained and compared with those in vacuo to explore the influence of the fluid. The energy exchange between shell and fluid under the first two excitations are analyzed based on the relationship between structural and acoustic intensity of the system. The results show that the energy exchange between these two medias are different in the two cases, mainly in the circumferential direction. And then the input power flow and structural intensity results when the pipe contains internal fluid flow are discussed.The free vibration characteristics of industrial pipes filled with fluid with typical boundaries are analyzed by using the wave propagation approach. The results show that the approach is still precise and can be used in the analysis of practical coupled systems. And the influence of the uniform flow contained in the system on different modes of natural frequencies is investigated.Finally, an actual piping system is built up. The excitation sources are shell and fluid based. Using the circumferential mode decomposition method, the modal accelerations in the axial, tangential and radial directions of the n=0 breathing mode and n=1 bending mode are determined from the test data, and then the energy carried by individual wave types through the fluid-filled piping system in low frequencies are obtained and compared with the theoretical results. The results show that although the theoretical results are under ideally infinite, they still have some benefits for the actual system.