Modal Analysis of Pipe Line Under Fluid-Structure Interaction by Simulation and Experiment

Abstract

In this paper, modal analysis of a test loop filled with and without water was studied experimentally and numerically. For experimental modal analysis, a section of a test loop is considered and the considered piping system is divided in to fourteen elements with fifteen nodal points. At each nodal point, response was measured in two mutually perpendicular directions using vibration sensors. For excitation, Impact hammer with a force transducer is used. Hammer input force and response from the accelerometers are taken to an LMS PIMENTO vibration analyzer. Frequency Response Function between the response and force are plotted and further analyzed. First four mode shapes in each two mutually perpendicular directions and a radial mode shape are plotted. Amplitude ratio between the pipe with water and without water are studied and compared. For numerical analysis, the commercially available Finite Element Package ANSYS is used. The pipe is modeled using the geometry creation option available in WORKBENCH. For meshing, three dimensional solid elements was used and analyzed using the standard model analysis solver available with FEM package. Fluid loading is simulated using the special element available in ANSYS. Analysis was performed in both conditions. The reduction in frequency, due to fluid loading is studied and observed. Natural frequencies obtained by both FEM and experimental modal analysis (EMA) are studied and compared. Scope for further study is discussed.