Auto Gridder

The CEM Framework's AutoGridder application creates a fully edge-connected mesh from an underlying CSG (Constructive Solid Geometry) model. CSG is a common method of describing complex surfaces and is used extensively by BRL-CAD and other CAD programs.

CSG models are placed in an ASCII file and consist of descriptions of solids and how the solids are combined. For example, the simple jet engine model (Figure 1) consists of five solids:

  • a red outer cylinder, some of which has been eliminated by the blue inner cylinder
  • a blue inner cylinder
  • a green torus, half of which is inside the red cylinder
  • a slightly tapered yellow cylinder
  • a more tapered cyan cylinder

The AutoGridder user selects the CSG input file and the desired mesh size, and the AutoGridder does the rest. A 5 cm mesh result can be seen in Figure 2.

The AutoGridder mesh can also be formatted for a number of CEM codes, including GEMACS and NEC. Figure 3 shows the surface currents as a result of using the mesh as a surface patch model with GEMACS. Figure 4 shows the equivalent result with a NEC wire grid model.

Both these examples were submitted directly to a CEM code, as no user intervention was needed. Sometimes AutoGridder may skip a small surface region, in which case the user may have to add one or two elements to the final model. A more complex example can be seen in Figure 5, which has been meshed into a 5 cm grid as seen in Figure 6.

One distinct advantage of using the AutoGridder over gridding by other methods is that the AutoGridder is parameter based. That is, changes in the model can be made by varying one or more parameters in the CSG input file and the AutoGridder re-run on that file. A CSG model of the (now defunct) Crusader vehicle was generated from a BRL-CAD file (Figure 7). Two parameters were defined: turret rotation angle and gun elevation angle. The results of varying these parameters can be seen in Figure 8 and Figure 9.

CEM Framework version 4.111
Applied Research Associates, Computational & Applied Electromagnetics
4690 Millennium Drive, Suite 210, Belcamp, Maryland 21017
Phone: (410) 272-8862


Fig 1. Simple Jet Engine Model
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Fig 2. 5cm Mesh Result
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Fig 3. Engine Surface Currents
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Fig 4. NEC Wire Grid Model
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Fig 5. Complex Ground Vehicle
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Fig 6. 5cm Mesh Result
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Fig 7. BRL-CAD Crusader
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Fig 8. Turret Rotation
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Fig 9. Gun Elevation
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