Meshing is a fundamental aspect of Finite Element Analysis (FEA) in which large, complex geometries are discretized into a set of simple, interconnected elements. Put plainly, complex shapes are divided into smaller, simpler shapes using finite elements. Because mesh size, element type, and element quality all directly affect the accuracy and reliability of an FEA simulation, it is critical to learn how to generate an appropriate mesh. In this article, we’ll look at the various 3D meshing options available in Abaqus CAE, followed by a brief discussion of some common meshing best practices.
As one would expect, the Mesh module in Abaqus CAE contains the tools needed to generate a 3D mesh. Within this module, it is worth noting that the geometry becomes color-coded according to the meshing algorithm selected for a given part. As shown below, orange surfaces indicate that the part cannot be meshed automatically; this can generally be rectified by cleaning up the geometry, partitioning surfaces, or changing the type of element desired.
The other mesh-based surface colors present in Abaqus CAE are pink (Free Mesh), green, (Structured Mesh), yellow (Sweep Mesh), and Tan (Bottom-Up Mesh), which will be discussed in more detail in the following sections.
1. Free Mesh (Unstructured)
The Free Mesh algorithm, which is indicated by a pink surface color, is likely the most versatile mesh available in Abaqus CAE. This method uses an unstructured approach to fill a solid void with elements and does not require that they be regular or uniform in size. This meshing approach is sometimes the only option, especially for geometries with highly complex shapes. An example of a tetrahedral Free Mesh is shown below (note the inconsistent mesh through the cross-section).
2. Sweep Mesh
The Sweep Mesh algorithm can be identified by a yellow surface color and provides a convenient method for modeling extruded or revolved parts. This approach provides a much more consistent mesh than Free Meshing since it essentially projects a 2D mesh along a path in 3D space; this results in an evenly distributed, layered mesh across the entire part. An example of a hexahedral Sweep Mesh is shown below (note the consistent, layered mesh through the cross-section).
3. Structured Mesh
The meshing technique that typically provides the highest quality mesh is the Structured Mesh algorithm. This approach is denoted by green surfaces and can only be used on components that can be meshed with consistently sized and shaped elements. This approach is only available when the geometry is partitioned into “regular” shapes (cuboids, cylinders, etc.) and the biggest advantage to using this algorithm is that structured meshing can produce consistent, high-quality mesh. However, since structured meshing requires the elements to be arranged in a regular pattern, this option is often only available when complex geometric surfaces are manually partitioned into regular shapes (rectangles, circles, etc.).
4. Bottom-Up Mesh
In addition to the automatic meshing techniques previously discussed, Abaqus CAE offers a manual meshing option that provides users with more control over the quality of the mesh. This algorithm, referred to as Bottom-Up Meshing, can be identified by a tan surface color and offers a robust method for generating hexahedral meshes. Because this incremental meshing style uses elements that are not inherently tied to the geometry, this approach offers more versatility than the automatic meshing algorithms when it comes to modeling complex geometry.
Now that we’ve reviewed the various methods available for generating 3D mesh in Abaqus CAE, let’s take a moment to briefly discuss some other important aspects of meshing.
Selecting the appropriate element type for a given simulation is critical for obtaining accurate results. For instance, using fully-integrated hexahedral elements in bending results in shear locking (which artificially stiffens the model); similarly, using incompatible mode elements in compression can often lead to convergence difficulties.
When meshing, it is important to ensure an appropriate element size is being used. This is paramount when reviewing stress results in regions of high gradient since large elements will generally underpredict stress (since the localized force is distributed over a larger area). A mesh sensitivity study can be performed to determine whether a mesh is suitable for a given analysis.
Utilizing a high-quality mesh is required in order to obtain valid FEA results. Typically, high-quality mesh will use elements that are well-shaped, well-connected, and uniform in size. The quality of the mesh can be assessed using the element quality checks in Abaqus CAE.
Meshing is one of the most critical steps of the FEA process. A low-quality mesh will heavily impact the accuracy and reliability of your results, so be sure to use appropriate meshing techniques and follow the best practices outlined above when performing your next Finite Element simulation.
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