In blow molding simulations, as well as for related applications, the finite-element mesh for the fluid domain may undergo large deformations. The primary type of deformation is an extension. In addition, a moderate amount of shear is also possible. Specific remeshing algorithms have been developed that allow the mesh elements to retain an acceptable shape. The objective is to keep the shape of the finite element as close as possible to a rectangle.
For 2D blow molding applications, several remeshing techniques are available in Ansys Polyflow, in order to meet the various geometrical characteristics of the computational domain. If your model includes a thin fluid parison, like the example shown in Figure 17.1: Example of Contact Detection in Blow Molding, the most appropriate technique involves the use of the thin shell method (described in Thin Shell Method) combined with a Lagrangian representation (described in Lagrangian Method) along the "master" surface.
This method is available only in 2D. In this combined method, a Lagrangian displacement (Equation 16–14) is imposed for the nodes on the surface that undergoes the contact (the master surface), whereas nodes in the thickness get remeshed with a spine rule similar to the one used for the thin shell method. This method remains robust in the presence of shear.
Note the following requirements for use of the thin shell method with Lagrangian master:
The computational domain for the fluid region must be surrounded by four boundary sides.
Topologically, the mesh must be an
regular checkerboard, as illustrated in Figure 16.9: The Effect of Tangential Remeshing in the Case of Large Deformations; in other words, the same amount of element must exist along two opposite
boundary sides. For boundary conditions, two free surfaces must be defined, along two opposite sides.