INTERNATIONAL JOLRNAL FOR NUMERICAL METHODS IN ENGINEERING VOL. 36, 1717-1734 (1993) A NORMAL OFFSETTING TECHNIQUE FOR AUTOMATIC MESH GENERATION IN THREE DIMENSIONS BRUCE P. JOHNSTON* Aries zyxwvutsrqp Technology, Inc., 600 zyxwvuts Sufolk Street, Lowvll, zyxwv MA OIRj4, U.S.A. JOHN M. SULLIVAN, JR Depurtnietzt of’Mechanica1 Engineering, zyxwvutsrq 100 Institute Rd, Worcester Polytechnic Institute, Worcester, MA 01609, U.S.A. zy SUMMARY zyxwv A technique, based on a normal offsetting procedure, for the fully automatic generation of meshes suitable for finite element analysis in three dimensions is presented. The method is completely automatic, requiring no user intervention in the process and no special modelling procedures. The method is applied to three-dimensional solid geometries. The procedure positions nodes in the interior domain zyxwvu of an object by offsetting an initial set of nodes on the object boundary along vectors normal to the boundary to define a layer of new interior point locations. The offset points are processed to ensure good nodal spacing appropriate for generating well-shaped elements. Following processing, the offset points become a new boundary surrounding the remaining unmeshed region in the interior of the geometric domain. The offsetting procedure is applied again to this new boundary layer to form another offset layer farther into the domain interior. The offset-process-offset cycle is repeated until the entire region is filled with nodes. Tetrahedral elements are then formed by triangulation of the nodes. The boundary-based technique ensures good quality element shapes for analysis in critical boundary regions and facilitates applications involving integration of mesh generation with design geometry databases. Calculation of nodal locations are based on local parameters avoiding the higher-order time complexities associated with global calculations. INTRODUCTION The research presented addresses the problem of preparing a mesh of nodes and elements to form a discretized representation of a solid object domain. Such a mesh must be of the appropriate structure and quality to form the basis of a mathematical model to which numerical analysis techniques can be applied. Mesh generation is accomplished by a variety of methods including direct manual methods, specialized and application specific methods, and large-scale, general purpose methods. All these techniques have many areas of application and offer varying degrees of automation. A mesh generation technique must meet certain minimum technical requirements to be useful for numerical analysis such as contigious, non-overlapping elements. Additionally, the mesh pro- duced must reflect the geometry of the domain with sufficient resolution to model accurately the effects of geometric detail to a degree appropriate for the analysis. * Formerly graduate student at Worcester Polytechnic Institute oO29-5981/93/1017 17-18$14.00 zyxwvu 0 1993 by John Wiley & Sons, Ltd. Received 12 January 1992 Revised 14 July 1992