Mapped Meshing–Pt Deux

Categories: Ansys

Eric Miller wrote a nice article back in February explaining the basics of using the mapped face meshing control available within ANSYS Workbench. Now…it would take a special kind of man to tell one of the directors of the company he works for that well…he just didn’t do a good enough job explaining it. Lucky for you all, I’m just that kind of man. “I have a different brain; I have a different heart; I got tiger blood, man.” – Charlie Sheen

I honestly thought my Stallone references were my best…how wrong I was

First of all, let’s start by discussing some behind-the-scenes operations being done. When you specify a side-vertex, the mesher internally concatenates the adjacent lines together to map the divisions of one block to another. So just by changing the side-vertex, you can ‘spin’ the mesh orientation around a given block. The images below show the difference as you pick different ‘side’ nodes. I had the local 3rd grade class draw lines over the map mesh source/target, divisions get mapped between same color lines.

You caught me…I never passed 3rd grade art class

So if we look at this a different way, the mapped face meshing is creating some virtual edges while still preserving the vertices for future use (e.g. applying displacements/forces). However, let’s say we really wanted to control some of the mapped divisions. We can do this using actual virtual topology to merge AND split edges (new feature in R13).

Here’s a picture of Eric’s example. It looks good enough, but for my discerning tastes I would prefer to have all of the divisions above the red dashed line match up, rather than having the divisions meander across the surface (technically speaking).

Isn’t it cute when managers try and use ANSYS?

With a little work, we can get the following:

Winning!

To get this, we just need to use some virtual topology tricks to split and combine the vertical edges. This can be done by inserting a virtual topology branch, available on the context toolbar when the ‘Model’ branch is highlighted. You then have the option of creating virtual cells or splitting edges.


To insert VT, Select the ‘Model’ level	When you have an edge selected, VT tools become available. ‘Split’ functionality available at R13

To combine two lines into one, simply select both of them and then click ‘Virtual’ Cell’. If you want to split an existing edge, highlight it and select one of the split options. If you select the ‘Split Edge at +’ it will split the line where you clicked on it:

‘+’ appears where you LMB on the edge

Once the edge is split, you can move the split location by modifying the split ratio displayed in the Details Window.

Modify ratio until you’re happy with the edge split

To get the masterpiece above, we first split the vertical lines, eyeballing the division to get the new point in-line with the bottom of the ‘notch’. Next, we combine one of the split edges with the edge above it:


Step 1: Split edges. Move ratio until it’s ~horizontal with bottom of notch	Step 2: Create virtual edge from split and neighboring edge (indicated by red arrows)

Step 3: Not shown, take long lunch and bill for 6 hours of work

The last step is just to apply a mesh edge sizing control to the proper lines:


Selected Edges	Make sure it’s a ‘Hard’ control. That way the mesher knows we mean business

Next just generate the mesh. I already know what you’re thinking…there are still some regions of the mesh that are iffy

Maybe I should leave the ‘Winning’ to the experts

We can play around with some additional settings, go back and modify the geometry, get a huge headache, and ultimately leave at the end of the day frustrated (mostly because of the curved edges that need to have divisions mapped across to a straight line). Or we can realize that maybe a free-mesh with a hex-only meshing method looks just as pretty.

Looks good to me!

Long story short….

Use new virtual topology to fine-tune the geometry to meet your mapped meshing needs
Anytime you’re dealing with curved edges, it may be worth your while to use a free mesh