Modal analysis of hydraulic pipelines

The laminar flow of a weakly compressible Newtonian fluid in a pipeline is treated by modal methods, aiming at a theoretical basis for the experimental modal analysis of hydraulic pipelines. For two points located at arbitrary positions along a pipeline, the frequency response function between flow rate excitation and pressure response is calculated in closed form, expanded into a modal series including transcendental modal transfer functions, and approximated by finite sums of rational fraction expressions. The preferred modal approximation is recognized as mobility function of a structurally damped mechanical multi-degrees-of-freedom system. Experimental modal analysis procedures for structurally and viscously damped mechanical systems are adapted for hydraulic pipelines and pipeline systems.