[en] The investigation of strongly transient fluid dynamic phenomena requires a consideration of flexible walls. This occurs particularly in nuclear power plant safety problems, e.g. in the field of blow-down simulations. For the solution of the problems outlined above a method is proposed which uses two separate codes, one for the structure and one for the fluid. Thus, the advantages of both methods, which may base on completely different methods, can be inserted into the calculation. On the one hand a finite element structural code is used, on the other hand a one-dimensional flow model (including pressure wave and thermodynamic non-equilibrium effects) is utilized, which is also applicable for a calculation of two- and three-dimensional fluid problems by introducing a mesh of one-dimensional fluid channels. The fluiddynamic part of the realized code consists mainly of the code DAPSY, which is a further development of the code BLAST. The setting up of the partial differential equations is performed in Eulerian coordinates and the integration is accomplished by the method of characteristics. The structure dynamics part consists of a finite element code, which has to be able to calculate time varing pressure load, momentum and wall friction forces. Up to now, only few commercial finite element codes compute time varying pressure loads, but there are no great difficulties to establish this possibility additionally. The structure codes SAPIV and ASKA were used to deliver the structure system matrices. To assure a simultaneous existence of the fluid and structure equations, it is necessary to introduce a coupling part, which organizes the data exchange