Vibration response of multi-span fluid-conveying pipe with multiple accessories under complex boundary conditions

Realistic multi-span fluid-conveying pipe may contain various accessories such as valves, clamps, flanges, elastic supports and vibration absorbers under complex boundary conditions in engineering applications. The dynamic response of the multi-span pipe may be affected by the presence of accessories, giving rise to complex mode shapes. Simplified and reliable methods for multi-span mode shapes calculation from eigenvector of the characteristic equation are widely applied in the pipeline engineering community. However, current methods are not valid when it comes to the amplitude of the eigenvector with a resonance frequency. Consequently, corresponding stresses cannot be further evaluated exactly. To address the above mentioned issues, a novel Frequency Response Function (FRF)-based method is proposed in this paper for the calculation of the mode shapes exactly. Furthermore, a method combining the Spectral Analysis Method (SAM) and Transfer Matrix Method (TMM) is first proposed in this paper to obtain the natural frequencies and transient response for the cascaded pipeline. The results calculated by the present method are validated by comparing them with those obtained from existing literature and conventional Finite Element Method (FEM). The effects of the accessories on the vibration characteristics of the multi-span pipes are further analyzed.