In prepositioning and fine positioning, the soft tissues are very simplified which can lead to interpolation artefacts.
A possibility to improve the results is to add custom affine functions to refine locally the deformation. To do that:
- define groups in your favorite pre-processor with node numbers corresponding to the locations where you want the affines. Name the groups
custom_affine__adding after the name of the PIPER entity. For example:
custom_affine__Skin_of_body_proper. Here is an example for the Child pedestrian model in Ls-Dyna:
*SET_NODE_LIST_TITLE custom_affine__Skin_of_left_free_lower_limb $# sid da1 da2 da3 da4 solver 9920070 0.0 0.0 0.0 0.0MECH $# nid1 nid2 nid3 nid4 nid5 nid6 nid7 nid8 20000955 20000563 20000557 20001160 20000770 20000750 20000840 20000894 20001237 20001207 20000810 0 0 0 0 0 *SET_NODE_LIST_TITLE custom_affine__Skin_of_body_proper $# sid da1 da2 da3 da4 solver 9920071 0.0 0.0 0.0 0.0MECH $# nid1 nid2 nid3 nid4 nid5 nid6 nid7 nid8 30000137 30000132 30000001 30000497 30000624 30000382 30000489 30000632 30006548 30000252 30006239 30000237 30006839 0 0 0
- Add the groups in an include file that PIPER reads (e.g. groups in affines_namedmetadata.k, and modify main file as in Child_model_affine.dyn to include it.
- change the PIPER metadata file (.pmr) to list these groups as generic metadata (i.e. whose function will be based on the name of the groups. Hence, it is very important to name the groups correctly). (example file here: Child_model_custom_affines.pmr)
<genericmetadata name="Auto"> <keyword kw="*SET_NODE_LIST_TITLE"> <id>9920070 9920071</id> <!-- custom affines --> </keyword> </genericmetadata>
check the box to enable the custom affines in the parameters before starting the positioning modules (settings_affine)
start a positioning module. You can check if the affines were interpreted correctly by enabling them in the display box (show_affines)
When you position, then affines are used to interpolate the soft tissues, which can help mitigating some of the artefacts. Below is an example of the Child pedestrian model (from left to right) raising a leg without the affines in the pre and fine positioning, and after adding custom affines. Surface artefacts are reduced.
If you want to use affines, you should experiment on how many to use and where to place them (the example above is just to show the feature and should not be used as a guideline).