# Preparing Geometry Models for Meshing

Geometry modeling is the solid foundation upon which your mesh is built. With Pointwise, the geometry model from your design software can be imported accurately, made meshable (the geometry repair and clean-up process), and robustly and reliably meshed.

### Using B-Rep NURBS Geometry Models

Geometry models from contemporary Mechanical CAD (MCAD) software are comprised of non-uniform rational B-Splines (NURBS) in a Boundary Representation (B-Rep) topology. These geometry models can be imported from a variety of formats including standards such as IGES and STEP.

 ACIS CATIA Creo EGADS IGES NMB NX Parasolid PATRAN Pro/E SolidWorks STEP UG

B-Rep NURBS geometry models can exhibit a lack of watertightness. In other words, there can be gaps between surfaces and surfaces can overlap. The source of gaps and overlaps are the inexact, tolerance-based topology operations that MCAD software employs to create complex models out of relatively simple geometry. (For more information on this topic, see Why CAD Surface Geometry is Inexact on Pointwise's Another Fine Mesh blog.) Fortunately, Pointwise includes two feature suites for handling this situation.

### Preparing Geometry for Meshing: Solid Meshing

Pointwise's Solid Meshing suite of features is designed to avoid gap problems from the start. By assembling the geometry model into a watertight solid, meshing can proceed without a hitch. You can assemble solids automatically during geometry model import, which is handy for models you are very familiar with. For other geometry models, you can assemble a solid manually and interactively.

An important component of Solid Meshing is the use of virtual topology called quilts. The geometry model's original topology is the result of modeling operations in the MCAD software and not necessarily a result of design intent. A quilt is simply a region you want meshed with a single mesh. Quilts provide a mesh topology that is completely independent from the geometry model topology while still adhering to its shape. You can assemble quilts during geometry model import and quilts can be assembled manually and interactively.

### Preparing Geometry for Meshing: Fault-Tolerant Meshing

With Fault-Tolerance Meshing, the geometry model is not assembled or modified in any way. You mesh the geometry model as-is. You follow this initial mesh creation with a technique called Merging that heals the mesh across gaps in the geometry model. After the meshes have been merged, the meshing algorithms remove artifacts such as slivers and seams.

### Mastering Geometry Cleanup

In this video you will see how geometry models are prepared for mesh generation including geometry creation and editing and the strategies available to you for identifying and healing gaps.

### Tips for Handling Complex Geometries, Very Large Grids

This video demonstrates techniques that simplify working with a complex geometry model as you prepare it for meshing.

### Preparation of Geometry Models

Making geometry models suitable for CFD meshing is often a time-consuming bottleneck in CFD analysis. We discuss why this is so and some ways to alleviate the problems.

### Using Discrete Geometry Models

Geometry models for use in Pointwise can be comprised of facets formed into surfaces called Shells. These faceted or discrete geometry models can be imported from STL files and several other formats.

 NASTRAN PLOT3D STL UCD UGRID VRML XPATCH

### Preparing Geometry Models for Meshing: Feature Extraction

Relative to B-Rep NURBS geometry models, faceted models are simple because they lack topology. They are just a mesh with which we are all familiar. However, that strength is also a weakness because in order to accurately represent the geometry model with the mesh you need to respect its feature lines (also known as hard edges). Pointwise provides Feature Extraction, the ability to identify feature lines in the shells based on the relative turning angle between adjacent facets. Once identified, feature lines can be used to split the shell. Feature extraction can be performed automatically during geometry model import or interactively on any portion of the geometry model.

### Creating Geometry

There are times when you need to add to the geometry model you imported. When simulating a wind tunnel test, you will often need to create tunnel walls and model supports. Even in free air you may need to generate farfield shapes. In cases when part of the geometry model does not import properly you will need to replace it. And there are instances where you want to create a simple geometry model from scratch. Pointwise provides a variety of curve and surface creation tools to support these activities.

 Revolved Surfaces Ruled Surfaces Coons Surfaces Sweep Surfaces Fillets Planes Lines Splines Circles Offset Curves Intersections Points Notes Shapes