Among the many new features introduced in Pointwise V18.1, alignment sources may be the most subtle yet the most powerful. You can use them to align the cells in a surface mesh to any curve without increasing the cell count by increasing clustering density.
Mesh clustering sources were introduced in Pointwise Version 18. Sources are user-defined shapes within the mesh (boxes, cylinders, spheres) on which you specify a target edge length. Sources are perfect for refining a mesh away from its boundaries such as wakes or vortices.
For surface meshing in particular, there are times when you need to enforce alignment of the mesh without influencing cell size. Pointwise Version 18.1 introduced alignment sources for surface meshes. You can draw a curve on a surface to which the mesh should be aligned. But unlike a clustering source, you won’t specify a target edge length.
Here’s an illustrative example for a rocket fairing. The geometry model was imported as a B-Rep solid from a CATIA file. Meshable regions within the model were created by segregating the model into quilts along feature lines where the turning angle between adjacent surfaces exceeded a user-defined limit (30 degrees in this case).
If you apply Pointwise’s quad-dominant surface meshing technique to the single quilt shown above, the result is the mesh shown below. You’ll notice that the mesh spacing around the perimeter is a constant value and the edge lengths were set to grow on the mesh’s interior. Every point in this mesh is constrained to the geometry model.
For the purpose of demonstration, let’s assume that there are two lines along the fairing to which I’d like the mesh to be aligned. If this fairing was a wind tunnel or flight test article, those lines may represent rows of pressure taps. I do not want to cluster to those lines, just align to them.
Using Pointwise’s curve drawing tools, I draw two lines on the fairing surface as shown below. These are my alignment sources.
Now when I re-initialize the mesh with the quad-dominant algorithm, it interprets the lines as alignment sources and aligns the mesh with those shapes as shown below.
Alignment sources don’t have to be lines. For example, something we have all had a problem with at one time or another is resolving fillets or blends or other regions of local curvature using a coarse mesh. The sheet metal part shown below typifies this type of problem.
When meshed relatively coarsely with triangles (using the Delanuay mesher) the rounded edges become quite jagged as shown below. Keep in mind that because this geometry model has been assembled into a single quilt, a single surface mesh will result and flow over the intra-surface boundaries.
I drew two curves on the geometry model for use as alignment sources: one around the squarish bump on the top left and one along the upper ridge that runs from front to back on the left. The regenerated mesh more closely approximates the shape of the object despite not being any more refined than the original.
Hopefully you can see that although the effects of an alignment source can be fairly subtle, they provide a level of control over the mesh that can be quite beneficial in certain cases. When used with clustering sources and the attributes within the meshing technique, you have a broad arsenal of tools to generate exactly the mesh you need.
If you’re ready to try alignment sources yourself, request your free trial license of Pointwise today.