  Representing large-scale motions and topological changes in the finite volume
(FV) framework, while at the same time preserving the accuracy of the numerical
solution, is difficult. In this paper, we present a robust, highly efficient
method designed to achieve this capability. The proposed approach conceptually
shares many of the characteristics of the cut-cell interface tracking method,
but without the need for complex cell splitting/merging operations. The heart
of the new technique is to align existing mesh facets with the geometry to be
represented. We then modify the matrix contributions from these facets such
that they are represented in an identical fashion to traditional boundary
conditions. The collection of such faces is named a Generalised Internal
Boundary (GIB). In order to introduce motion into the system, we rely on the
classical ALE (Arbitrary Lagrangian-Eulerian) approach, but with the caveat
that the non-time-dependent motion of elements instantaneously crossing the
interface is handled separately from the time dependent component. The new
methodology is validated through comparison with: a) a body-fitted grid
simulation of an oscillating two dimensional cylinder and b) experimental
results of a butterfly valve.
