Influence of Excitation on Junction Coupling at Water Hammer in Piping Systems

A comprehensive study on junction coupling in two piping system configurations in dependency of the excitation’s condition were performed. The source of the hydraulic excitation is characterized by water hammer produced at various initial mean flow velocities. The resulting forces on the piping system caused bend oscillations. For each system configuration and initial mean flow velocity the support position of the bend was varied. Thus the structural frequency was altered. The pressure inside the pipe, the displacement of the bend, the acceleration at the anchorage and the supports were recorded. Additionally, optical measurement equipment was utilized in order to characterize the structural oscillation more detailed. For both system configurations fluid-structure interaction effects were identified, but two-way effects at the base frequency of water hammer only occurred in one system. The amplitude of excitation had influence on the amplitudes of the pressure, displacement and acceleration and on the number of modes which built up. The results of the measurements pointed out that not only the bend oscillated but also the anchorage and pipe sections behind the bend. In both systems, an energy transfer from the fluid to the anchorage could be observed. Due to the bending of the anchorage, the bends oscillated in multiple directions.