The paper considers the problem of simultaneous modeling of structure and flow in a piping system. It takes a middle road between full coupled analysis on the one hand, and the simplified case of treating the liquid as a rigid mass. The suggested method allows the use of standard beam and rod elements for the analysis. Two approaches to the problem of dynamic interaction between pipe and medium are compared in the given paper: 1) The first one treats medium as mass rigidly connected to the pipe finite-element model’s nodes. 2) In the second one medium is modeled by the finite-element system of rod-elements. In this case the basic fluid-structure interaction (FSI) effects are taken into account. The main techniques for FE modeling of some pipeline elements are presented in the paper. The second approach can be implemented by the use of general purpose FE programs. A model of a feed water pipeline of VVER-440 type NPP has been developed to study how the FSI affects on pipeline response. The results of the analysis which allow estimation of inaccuracy arising from medium dynamics neglecting are as follows: • calculation of eigen frequency and mode shapes; • seismic analysis using the response-spectrum method; • accidental blast impact assessment with the use of time history analysis; • operating vibration assessment on the basis of harmonic analysis. It has become apparent that the way of medium modeling has an essential influence on the dynamic behavior of pipelines.

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