Geometry Modeling and Mesh Generation – Part 1

NASA’s CFD Vision 2030 Study stated that “most standard CFD analysis processes for the simulation of geometrically complex configurations are onerous.” A major factor contributing to this perception is the preparation of geometry models for mesh generation, a task deemed a “significant bottleneck” in CFD workflows.

Why this should be so is often unclear. Many CFD practitioners know it to be true while also not fully appreciating the underlying reasons. That’s why we wrote Preparing Geometry Models for Mesh Generation and CFD, a 20-page paper that’s freely available on our website.

A computational geometry model is an idealized mathematical representation of an object’s shape. It is a model used for generating a mesh in precisely the same sense that a turbulence model is used for solving the Reynolds-Averaged Navier-Stokes equations. Both models are useful approximations of reality. Not all geometry models are the same, even those purportedly of the same object.

That’s how the Geometry Modeling Fundamentals section of the paper begins. The parallel drawn between geometry models and turbulence models is more than just hyperbole. Geometry models are as vexing to mesh generation as turbulence models are to CFD.

Geometry model suitability is not just a process-oriented efficiency issue. Geometry should be considered a first-order effect on the CFD solution’s accuracy. If the shape of the object is not modeled accurately, the usefulness of the simulation result is unclear at best and completely misleading at worst.

This geometry model exhibits typical challenges for meshing; in particular, several surfaces didn’t import properly. (This is the geometry model of a UAV from the meshing contest at the 22nd International Meshing Roundtable. For more details on meshing this particular geometry model see the article on our website.

Here’s the paper’s table of contents so you know what the paper includes.

  • Geometry Model Suitability for CFD
  • Geometry Modeling Fundamentals
    • Boundary Representation
      • Analytic Geometry
        • B-Splines and NURBS
        • T-Splines and U-Splines
        • Subdivision Surfaces
      • Discrete Geometry
        • Meshes
        • 3D Scans
      • Boundary Topology
    • Volumetric Representation
      • Constructive Solid Geometry
      • Spatial Occupancy
      • Implicit Modeling
    • Originating Intent & Software
    • Sources of Geometry Model Unsuitability
      • Interoperability & Translation
        • Interoperability by File Exchange
          • Standards and Specifications
          • Translation & Representation
        • Interoperability by Direct Interface
        • Interoperability by CAD Embedding
      • Intersections, Trimming, and Tolerances
      • Details – Too Many, Too Few
        • Excessive Detail
        • Insufficient Detail
  • Summary
  • References
  • Notes and Acknowledgements
  • Appendix: Geometry Modeling in the CFD Vision 2030 Study

Twenty pages and 43 references provide the reader with a solid background in all the relevant topics and issues. Head on over to our website and download your copy today.

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