Mesh defeaturing for CAE

Preparing models, particularly models in mesh form, for CAE simulation, can be a very time-consuming process. You can see the scars of battle, and the pride, in those that have to do it regularly. Often it can be the most time-consuming and labour-intensive part of the CAE process.

There are several challenges, which include

• Creating a topologically correct, watertight mesh free from strictly defined mesh errors such as self-intersections and non-manifold geometry
• Removing small mesh artefacts that can cause the CAE remesher and solver problems
• Removing small features that lead to the CAE remesher creating unnecessarily dense meshes, leading to longer runtimes, without improving the accuracy or reliability of the overall result.

This blog covers how Polygonica can be used to more efficiently resolve and remove some of these problems.

Example Code

The demonstration videos associated with this blog were all created using example code that is available to Polygonica customers or evaluees on request.

Automatic Mesh Healing

Polygonica is rightly well-known for the power and quality of its automatic mesh-healing. It regularly wins extensive benchmarks against well-known systems, with the determinant of success being ‘with Polygonica we can process X% more models than we can process without it’. 

Polygonica’s automatic healing will address, with a high degree of reliability:

• Watertightness
• Inconsistent orientation
• Self-intersections
• Tiny noise/void shells
• Non-manifold geometry
• Foldovers – polygons that fold back on each other, or overlap, without causing self-intersections
• Precision – safely converting from one precision to another e.g. double precision to single precision float

But this blog is not really intended to be about healing …

Removing and mitigating small features

Polygonica has range of tools that facilitate user-guided feature removal on ‘dumb’ polygon meshes i.e. where there is no known BREP structure e.g. this is a cylinder, this is a cone, this is a NURBS surface etc. 

The workflow used in the videos associated with this blog is as follows:

• Augmented selection – use a range of tools to facilitate easier selection
• Deletion of selected faces/triangles from the mesh
• Advanced hole filling – use Polygonica’s advanced curvature sensitive hole filling to close the gaps created by the deletion of the selected faces
• Optional remeshing – use Polgonica’s remesher to improve the aspect ratio of triangles in the selected region, or across the entire mesh

Augmented Selection

Polygonica has a range of techniques to augment user selection of triangles and faces, including:

• Feature detection – identify entire features such as holes, pockets, islands, filets, chamfers and labels
• Surface detection – identify portions of surfaces such as planes, spheres, cylinders, cones and toruses
• Region selection followed by feature or surface detection – on large models surface and feature detection can be constrained to a region of interest, improving performance and interactivity
• Selection of a region based on various parameters – number of rings, bounding edges, spherical/cylindrical/geodesic distance etc
• Growing a selected region
• Merge and split selected regions
• Offset region boundaries (curves) across the surface to grow or shrink regions
• Selections of chains of edges, for example sharp edges or boundaries between faces with different property values e.g. colour
• Geodesic curve selection across the surface
• Curve imprinting to create new edges in mesh surface

Advanced Hole Filling

Polygonica provides a number of standard and advanced hole filling algorithms.

Standard:

• Planar: a planar fill intended for planar and nearly planar regions
• Min Area: Minimises the total area of new surface added to fill the hole
• Smooth: Attempts to create a smooth match with surrounding geometry

Advanced:

• Features: Attempts to connect features across holes. Useful for restoring edges, chamfers and single curved blends 
• Features Smooth: The surface is reconstructed by considering all surrounding curvature. Additionally gaps within pockets or deep holes will be joined
• Ruled Surface: Useful for connecting surfaces or joining adjacent open edges of a hole

These are demonstrated in the videos accompanying this blog.

Quality-based Remeshing

Polygonica includes an advanced quality-based surface remesher. This is not a full CAE-remeshing solution – it does not support quads or volume remeshing. It is useful for producing even, good aspect ratio triangles across the mesh surface, either for the entire part or for selected regions (local remeshing).  

Thickening thin flaps

Thin regions that taper to a point can cause excessive volume elements to be generated during CAE remesh process. There are a number of ways Polygonica can be used to remove, or more accurately, thicken them. A simple way is to identify the sharp edge chain then subtract geometry e.g. a series of overlapping cubes, centred along the edge.

An alternative way, demonstrated in the videos, is to use Polygonica's curve offsetting across a suface to create a selection region a uniform distance from the end of the flap. This imprint curve can then be used to trim the flap, and the open edges are then closed using hole filling.

YouTube Playlist

You can view a series of videos demonstrating some of the techniques described in this blog in our YouTube defeaturing playlist. The playlist is split into a series of shorter videos, which can be explored more easily on YouTube itself.