The equations were discretised by finite element methods: Displacement based finite elements were used to discretise the wall equations which were formulated in Lagrangian coordinates; the discretisation of the Navier-Stokes equations (formulated in spatially fixed, Eulerian coordinates) was achieved by utilising a moving mesh which adapted itself in response to the wall deformation. The method of spines was used for the automatic mesh update. The figure below shows the structure of the mesh (the symmetry of the configuration was exploited by only discretising one half of the domain) -- the actual computations were carried out with a much finer resolution.