A Combined Numerical and Experimental Investigation on the Effect of Dynamics Characteristics of Metal Expansion Bellows

Purpose Metal expansion bellows is an important flexible element used to absorb extension or shrinkage and vibrations of the piping system used in various process applications. Failure of the bellows occurs due to the unpredictable behavior in its convolutions due to severe working conditions. Hence, determination of its dynamic characteristics is of prime importance. Objective To find and analyse dynamic characteristics like axial natural frequencies, modal frequency responses and mode shapes of U-shaped convolution bellows as well as the effect of increase in number of convolutions on the dynamic characteristics. Methods In this paper, analytical, numerical simulation and experimental investigations are performed to find the axial natural frequencies of bellows. Numerical simulation is performed using the mathematical model in MATLAB and modal analysis is performed using ANSYS 15. The deformation and axial natural frequency response of bellows with eight, nine and ten convolutions are obtained by FE analysis for various modes when bellows are subjected to different end conditions. Results As per the simulation and experimental modal analysis, it is seen that the range of axial natural frequencies with less number of convolutions shows maximum deformation and larger number of convolutions shows minimum deformation. Conclusion To decrease the axial natural frequency for the given flow rate and to avoid resonance, the number of convolutions of the bellows should be increased for designing the new configuration.