The proposed method allows the efficient computation of natural frequency mode shape and harmonic response of submerged rotationally periodic structures, such as turbine or centrifugal pump wheels. The geometry of such structures is complex and the influence of the surrounding fluid has to be taken into account. The fluid is assumed to be incompressible and at rest. Both fluid and structure domains are modelled using the finite element method. The size of the problem is appreciably reduced using the properties of wave propagation in periodic systems combined with modal techniques. The efficiency of the method is shown by an application to a submerged centrifugal pump wheel where the numerical results are compared to experimental results. Copyright (C) 1996 Elsevier Science Ltd