A co-ordinate transformation technique for studying flux perturbations induced by strong vibrating absorbers

Calculation of the neutron noise, induced by small amplitude vibrations of a strong absorber is a difficult task because the traditional linearisation technique cannot be applied. Two methods, based on two different represent ations of the absorber, were developed earlier to solve the problem. In bot h methods the rod displacements are described by a Taylor expansion, such t hat the boundary condition needs only be considered at the surface of a sta tic rod. Only one of the methods is applicable in two dimensions. In this p aper an alternative method is developed and used for the solution of the pr oblem. The essence of the method is a variable transformation by which the moving boundary is transformed into a static one without Taylor expansion. The corresponding equations are solved in a linear manner and the solution is transformed back to the original parameter space. The method is equally applicable in one-and two dimensions. The solutions are in complete agreeme nt with those of the previous methods. (C) 1999 Elsevier Science Ltd. All r ights reserved.