m.r maheri - Assistant Professor, Shiraz University, Shiraz, Iran
m.r khodaei-nassaj - Graduate Student, Shiraz University, Shiraz, Iran

For effective solution of arch dam-reservoir dynamic interaction and other structure-fluid systems, new, ۲۱-noded and ۲۷-noded, ۳-D, Lagrangian curvilinear fluid elements are formulated and incorporated into an existing general purpose PC-run structural analysis program. The effect of surface waves is readily included in the formulation. To model the true behaviour of water at the dam interface, an effective ۱۸-noded compatible interface element is also formulated and added to the program. The program is uniquely capable of carrying out a modal superposition seismic analysis in which the user is able to select the appropriate modes required for the analysis. To eliminate the problem of zero-energy modes, in addition to the introduction of rotational constraints and low frequency surface modes as used before, a new "shift" method is also introduced. The method is applied to the dynamic and seismic analysis of a number of dams and the accuracy of the results is checked against other solutions.