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 representations of the absorber, were developed earlier to solve the problem. In both methods the rod displacements are described by a Taylor expansion, such that the boundary condition needs only be considered at the surface of a static rod. Only one of the methods is applicable in two dimensions. In this paper an alternative method is developed and used for the solution of the problem. 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 agreement with those of the previous methods.