An adaptive Lagrangian boundary element approach for three-dimensional transient free-surface Stokes flow as applied to extrusion, thermoforming, andrheometry

An adaptive (Lagrangian) boundary element approach is proposed for the gene ral three-dimensional simulation of confined free-surface Stokes flow. The method is stable as it includes remeshing capabilities of the deforming fre e surface and thus can handle large deformations. A simple algorithm is dev eloped for mesh refinement of the deforming free-surface mesh. Smooth trans ition between large and small elements is achieved without significant degr adation of the aspect ratio of the elements in the mesh. Several flow probl ems are presented to illustrate the utility of the approach, particularly a s encountered in polymer processing and theology. These problems illustrate the transient nature of the flow during the processes of extrusion and the rmoforming, the elongation of a fluid sample in an extensional rheometer, a nd the coating of a sphere. Surface tension effects are also explored. Copy right (C) 2001 John Wiley & Sons, Ltd.