Geometry Validation: Ensuring Accuracy in Finite Element Mesh Generation

Geometry validation is a critical step in Finite Element Analysis (FEA), ensuring that the model is error-free, meshing-friendly, and structurally sound. Poor geometry leads to meshing errors, and therefore solver errors afterwards, poor mesh quality, and computational inefficiencies. This article outlines key validation techniques to prepare geometries for mesh generation efficiently.

Why is Geometry Validation Essential?

Before meshing, geometry must be prepared and checked to prevent:

• Mesh Distortions: Poor geometry leads to irregular elements and poor mesh quality. When the geometry is not properly validated, the resulting mesh can have distorted elements that do not accurately represent the physical structure. This can lead to incorrect results, potentially causing the analysis to predict failure where none would occur or miss critical stress concentrations.
• Solver Failures: Unconnected nodes due to unconnected surface edges, duplicate nodes, or overlapping surfaces cause numerical issues. These issues can cause the solver to fail to converge or lead to incorrect stiffness and stress distribution. Learning how FEM is used in structural analysis provides important context for understanding these failure modes.
• Excessive Computation: Overcomplicated geometry results in an unnecessarily dense mesh. Complex geometries with too many small features can trigger an excessive number of elements. This not only slows the simulation but also does not guarantee improved results. Knowing why mesh quality matters is crucial to balance complexity and performance.

Common Geometry Issues and Fixes

For example: A CAD-to-FEA model may contain tiny fillets or holes that complicate meshing. These small features can create very small elements in the mesh, which result in numerical issues and inefficiencies. Simplifying these geometries is vital to achieving a quality mesh. You can explore more about these challenges in mesh generation for FEA.

Solution: Remove non-essential features while retaining structural integrity. This can be done by using defeaturing tools in the CAD software or manually editing the geometry to remove these small features.

Effective Geometry Validation Techniques

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Automated Repair Tools

Modern structural analysis software, like SDC Verifier, provide:

• Auto-gap closing to merge discontinuities: This feature automatically detects and closes small gaps in the geometry, ensuring the mesh can be generated without issues. It’s especially useful for complex assemblies where small gaps between parts are hard to detect manually.

Tools like non-manifold add help create a single solid from overlapping surfaces, while geometry and feature editing tools provide additional commands to assist in repairing and preparing the model.

• Coincident node detection and merging: SDC Verifier ensures that all coincident nodes are properly merged, preventing errors during meshing and analysis due to disconnected or overlapping geometry.
• Coincident element detection: The software identifies and removes duplicated elements that may result from overlapping surfaces or faulty imports, improving model integrity.
• Free edge detection tool: This tool highlights all free edges (disconnected or unconnected nodes), helping engineers spot and fix unintended discontinuities in the model.
• Feature simplification to remove unnecessary details: Automated FEA tools can identify and remove small features that do not significantly affect the overall structural behavior, in example holes, fillets, etc. This helps in reducing the complexity of the mesh and improving computational efficiency.
• Mesh diagnostics to highlight distorted elements: SDC Verifier can analyze the generated mesh and identify elements that are overly distorted or have poor quality. This allows the engineer to make necessary adjustments to the geometry or meshing parameters to improve the mesh quality.

Manual Inspection and Fixing

For complex models:

• Use section views and the Free Edge Tool from SDC Verifier to detect internal voids: Section views allow engineers to look inside the geometry and identify any internal voids or gaps that may not be visible from the outside. These voids can cause issues during meshing and need to be addressed.
• Merge narrow or irregular to prevent distorted mesh regions: Very thin or irregularly shaped surfaces can create very thin elements in the mesh, which can lead to numerical issues. Merging these surfaces or removing them can help in generating a better-quality mesh.
• Adjust geometry tolerance settings for proper edge connections: Ensuring that the edges of different parts of the geometry are properly connected is crucial for generating a good quality mesh. Adjusting the tolerance settings can help in achieving this.

Pre-Meshing Quality Checks

• Mesh Transition Check: Prevents sudden element size changes. Sudden changes in element size can lead to inaccuracies. Ensuring a smooth transition in element size can help in generating a better-quality result.

After–Meshing Quality Check

• Aspect Ratio Analysis: Ensures elements are not overly stretched. Elements with a high aspect ratio can lead to numerical inaccuracies. Analyzing the aspect ratio of the elements and making necessary adjustments to the geometry or meshing parameters can help in improving the mesh quality.
• Load Path Verification: Confirms mesh aligns with expected stress flow. Ensuring that the mesh aligns with the expected load paths can help in accurately capturing the stress and strain distribution in the structure.

Best Practices for Geometry Validation

Achieving reliable FEA results requires adopting effective geometry validation practices. Below are some recommendations:

• Think upfront: Simplify before you even start modeling
  Before creating or importing geometry, consider what is truly necessary for the analysis. Ask yourself what features can be safely ignored to reduce complexity. For instance, decide whether to use beam or plate elements for a part, or whether you can model just a quarter of the geometry and apply symmetrical constraints. Consider how different parts will be connected and whether certain features can be neglected.

Even when importing a STEP file, assess whether you need the entire model or just specific parts.

• Start Early: Validate geometry before meshing to avoid rework. Starting the validation process early in the design phase can help in identifying and addressing issues before they become more difficult to fix.
• Balance Detail & Simplicity: Remove unnecessary features while keeping critical design elements. Striking a balance between detail and simplicity can help in generating a good quality mesh without unnecessarily increasing the computational cost.

Conclusion

Geometry validation is an indispensable part of the FEA process, ensuring that the model is ready for accurate and efficient mesh generation. By addressing common geometry issues and employing effective validation techniques, engineers can significantly improve the quality of their simulations, leading to more reliable and insightful results.

Proper geometry validation not only helps in preventing solver errors and computational inefficiencies but also ensures that the analysis results are accurate and reliable. This, in turn, leads to better decision-making and improved product designs.