Calculation of the Natural Frequencies of a Fluid-Filled Pipe System With the Coupled Codes dyvro/rohr2: Implementation of an Alternative Coupling Concept

Abstract

The vibration of a pipe system can be caused by internal excitation, e.g., as a result of pump-induced pressure pulsations or external excitation like earthquake. For the investigation of these phenomena, the knowledge about the natural frequencies of the pipe system is essential. In this context, it is important to consider that the natural frequencies of the coupled system of fluid and structure commonly differ from the natural frequencies of the pure fluid system and of the structural pipe model in which the fluid is only taken into account as added mass. To obtain realistic natural frequencies of a pipe system filled with a fluid, the one-dimensional fluid code dyvro was coupled with the code rohr2stoss that deals with dynamic analysis of complex piping and steel structures. Two code coupling concepts were realized, the integral concept, which is also commonly used in coupling commercial pipe system software, and the alternative local coupling concept, with which the longitudinal deformation of the pipe segments can be captured. Both concepts consider a two-way fluid–structure interaction (FSI). For the integral concept, a verification was performed by comparison with an analytical solution for a simple case with a fluid column connected to a spring–mass system. Additionally, both coupling concepts were validated by comparison with experimental data from literature that revealed strong FSI during a water hammer event. The frequency content of the measured pressure fluctuations could be captured by both coupling concepts.