Dr Mesh Gets You Out Of a Fix
(By Getting You Into Another One)

 

An Automatic Mesh Repair functionality was recently introduced in STAR-CCM+ V3.02 that allows users to fix poor quality triangulation, self intersection and close proximity faces at the click of a button. The one click repair may be used at any stage of the surface meshing process to provide the highest quality surface possible. We'll be looking at the Automatic Mesh Repair tool in next month's column.

In this month's column, we'll be looking at the often neglected Manual Repair Tool, which affords the experienced user node by node control. While, I'd recommend that most of you stick with automatic repair, these tools allow meshing purists (such as myself) easily identify problem regions in the imported surface, and fix them with a bit of clever stitching.

The surface repair tool can be used to find errors in your surface and then deal with them accordingly, from a simple pierced faces to re-triangulating a surface as well as tasks such as marking feature edges manually and even improving your triangle quality to get a really good volume mesh. So here is my guide to turning even the worst surface into a thing of beauty!

Fig01: Start up the repair tool and choose what you want to look for Fig02: The top of the tool will tell you how many problems you have

Turn it on!
The first step to fixing your surface is to right click on the surface representation you want to repair and hit repair you can then choose which regions you want to check and which errors you want to flag. In the case of face quality and proximity you will also be asked for a threshold value to fill in too.

Find your faults!
Once loaded the errors in your surface are shown in the top part of the tool and with the faulty faces/edges/vertices colored
differently according to what is wrong with them. You can highlight where the problems are by clicking on the colored box with the number in or you can cycle through one by one using the browse arrows. You can also choose to browse through certain types of error by un-checking the error types that you are not interested in.

Shrink ‘n’ Grow
When you browse to a surface problem a few triangles around the fault will be displayed, before you fix the problem you may need to shrink or grow what is displayed and what is selected. The display control (at the bottom of the panel) is used to control what is displayed on screen and then grow and shrink displayed faces can be used to increase and decrease the area displayed and there are also buttons for show and hide all and show and hide selected.

Once you have what you want on screen you need to select some objects, what you can select is controlled by the three boxes faces, edges and vertices, unchecking any of these will stop that object being selectable. As with the display control you can also change the selection by growing and shrinking, selecting zones and finally selecting vertices or edges connected to a triangle.

Fix it up!
There are twelve different fixing options each of which depends on what you have selected, at the bottom of the surface repair section of the panel there is also a undo and redo button so if it all goes horribly wrong you can just start again! Remember though that if you remesh the surface you have been working on, the changes will disappear and may have to be repaired all over again!

Yours,

Dr. Mesh
Dr Mesh (Ph.D. CFD)

 

Above left - Fig03: The selection and display control panels, buttons with a white triangle in the corner mean other options are available by right clicking.
Above right - Fig04: The face repair options
Below left - Fig05: The edge repair options
Below right - Fig06: Vertex repair options