This Week in CFD

Applications

CFD solution for a centrifugal pump. Image from Pollution Solutions and Standard Alloys.

CFD solution for a centrifugal pump. Image from Pollution Solutions and Standard Alloys.

News in Brief

On CAD File Formats

The GrabCAD blog provides an introduction to CAD file formats which is worth reading. The article delves a bit into the issue of “precise versus tessellated” formats – in other words, analytic NURBS surfaces versus triangular facets.  I found two things to be notable.

Visual comparison of  precise (left) and tessellated (right) representations of a gear. Image from GrabCAD.

Visual comparison of precise (left) and tessellated (right) representations of a gear. Image from GrabCAD.

First, the article says that most CAD systems store the triangles used to display geometry in their native file. Pointwise does not – we generate that information as needed. We only store the geometry’s native representation in our file.

And that leads to the second notable point. It’s important to remember that there are two issues here: the native format of the geometry and how it’s displayed. In Pointwise, all geometry is displayed on screen as facets. The facets for NURBS are the result of a triangulation (based on various user-tunable parameters) but the facets for a tessellated geometry (e.g. imported from STL) are the actual triangles in the STL file. In other words, the display object for a faceted geometry format is the object itself whereas the display object for a NURBS is a distinct object that’s disposable.

The native format of the geometry also affects how it’s evaluated when it’s time to use it (i.e. to project grid points on it). A NURBS is evaluated precisely using Pointwise’s geometry kernel (see the interview on Another Fine Mesh with J.P. Abelanet) at the desired, precise parametric (u,v) coordinate. On the other hand, a faceted geometry is evaluated on its planar facets (i.e. the faceting is preserved). This is why using a faceted geometry with sufficient resolution of high curvature regions relative to your desire mesh size is so important. (See the article from The Connector about analytic versus discrete geometry.) Other folks have written tools for converting a faceted geometry to a smooth NURBS but we don’t do that – yet.

Events

Getting Youth Involved in STEM

People are flummoxed by the lack of interest shown by today’s kids in science, technology, engineering, and math (STEM) careers. Here’s a way to use the gross-out factor to get adolescents’ attention.

  • What pre-teen wouldn’t get excited about a test rig for airplane toilets?
  • Certainly bugs and their guts have a certain teenage appeal, especially when they’re blasted onto a wing’s leading edge.
  • And who can deny the appeal of the chicken gun for testing aircraft canopies? [no URL]

Bunny Bubble Bath

Bunny Bubble Bath is a funny sub-title in Miles Macklin‘s video demonstration of what he calls Position Based Fluids. He’ll be presenting this work at SIGGRAPH 2013 and the results are impressive. At the link you’ll find videos and another link to his project page where his paper and videos can be downloaded.

The Stanford Bunny takes a bath in Position Based Fluids. Screen capture from a video by Miles Macklin.

The Stanford Bunny takes a bath in Position Based Fluids. Screen capture from a video by Miles Macklin.

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One Response to This Week in CFD

  1. Rick Matus says:

    Here’s a chicken gun video, courtesy of MythBusters, another good source for getting kids interested in STEM: http://www.youtube.com/watch?v=sCQ2oZtVNpg

    Bonus, they also answer the question of whether it is better to use fresh or frozen chickens.

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