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Overview

Geometry cleanup is one of the most time-consuming stages of any simulation workflow. CAD models built for manufacturing are dense with features that are irrelevant to simulation — small fillets, logo embossments, thin slivers, fastener detail — and imported geometry from suppliers often arrives with translation artefacts: gaps, duplicate faces, non-manifold edges, and missing surfaces. Nexus can carry out geometry cleanup directly inside your simulation pre-processor, working through an inspection-and-repair loop that mirrors what an experienced analyst would do manually — but faster and without the repetitive overhead. Nexus is particularly effective in Ansys Discovery and Ansys SpaceClaim, both of which expose a rich set of programmatic geometry operations that the agent can drive precisely and repeatably.

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What Nexus is good at

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Rules-based defeaturing

Many cleanup tasks follow a clear rule: “remove all fillets below 2mm”, “suppress all holes smaller than M4”, “delete cosmetic features on exterior faces”. Nexus excels at this class of task because the rule can be stated once and applied systematically across the entire model — including assemblies with dozens of bodies — without the analyst touching each feature individually. This is the highest-value use of Nexus in cleanup: tasks that are conceptually simple but manually expensive due to repetition.

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Geometry healing

Imported STEP, IGES, and Parasolid files frequently carry translation defects. Nexus can run a structured inspection, categorise the issues it finds, and apply targeted fixes:
  • Gap closure — stitch open edges where faces don’t meet within tolerance
  • Missing face repair — reconstruct faces that failed to translate
  • Duplicate geometry removal — collapse coincident faces or bodies that cause solver errors
  • Normal consistency — flip reversed face normals on surface models

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Small face and sliver removal

Short edges, needle-shaped triangular faces, and sliver surfaces cause poor mesh quality and often force the mesher to generate extremely small elements at localised regions — degrading solve time and solution accuracy. Nexus can identify these features by size threshold and remove or merge them automatically.

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Idealisations

For thin-walled structures, Nexus can extract mid-surfaces and replace the solid geometry with shell representations suitable for structural or thermal analysis. It can also create beam idealisations from cylindrical features such as pipes or struts.

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Repair validation

After cleanup, Nexus will confirm that the geometry is watertight, manifold, and free of the issues it targeted — giving you a structured report to review before handing off to the mesher.

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Supported environments

Geometry cleanup with Nexus runs natively inside:
PlatformNotes
Ansys DiscoveryFull geometry kernel access; rules-based cleanup, healing, mid-surface extraction
Ansys SpaceClaimSame geometry kernel as Discovery; also used as the geometry stage in Ansys Mechanical workflows
Ansys Mechanical (SpaceClaim geometry stage)Cleanup applied to the geometry component before meshing

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Example prompts

In the current Discovery model, remove all fillets and rounds with a radius smaller than 1.5mm. Also suppress all threaded hole features — replace them with simple cylindrical holes at the nominal diameter. Report how many features were removed.

The file at C:/Projects/Supplier/housing_v2.step was imported and likely has translation issues. Run a full geometry check: identify gaps, non-manifold edges, missing faces, and duplicate bodies. List each issue with its location, then apply automatic healing where possible and confirm whether the resulting body is a valid closed solid.

Find all faces with an area smaller than 0.25mm² and all edges shorter than 0.1mm on the current body. Merge or collapse them to improve mesh quality. Do not change any face that forms part of a bolt hole, fillet, or external boundary.

This sheet metal bracket has a uniform wall thickness of 1.5mm. Extract the mid-surface from all bodies and replace the solid geometry with a surface model. Set the shell thickness to 1.5mm. Confirm that the resulting surface model is continuous and has no free edges at internal connections.

Before I mesh this assembly, run a geometry health check and give me a summary report covering:
1. Any bodies that are not closed solids
2. Faces or edges below my minimum mesh size of 0.5mm
3. Non-manifold topology
4. Shared faces between bodies that may require contact definition
Do not make any changes — I want the report only.

Open C:/Projects/Pump/pump_assembly.scdoc. For each body in the assembly:
1. Remove all fillets below 0.8mm radius
2. Suppress all cosmetic holes smaller than 3mm diameter
3. Merge small faces below 0.1mm²
When done, list each body, how many features were removed from it, and whether it passes a solid body check.

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Cleanup before meshing: a typical workflow

A structured cleanup sequence that works well as a Nexus prompt chain:
1

Import and inspect

Start with a full geometry report before making any changes. This gives you a baseline and prevents unnecessary operations.
Import C:/Projects/Part/bracket_supplier.step into a new Discovery session. Run a geometry health check and list all issues: gaps, short edges, small faces, non-manifold topology, and any bodies that are not closed solids.
2

Heal translation defects

Fix structural issues first — these are blockers that can prevent defeaturing tools from working correctly.
Heal all gaps with a tolerance of 0.05mm. Close any open shells where the missing face can be reconstructed from adjacent edges. Report what was repaired.
3

Defeature for simulation

Apply simulation-specific simplification rules.
Remove all fillets below 1mm radius, all holes below 4mm diameter, and all embossed text or logo features. Do not touch any face that is part of the load application region or the fixed support region.
4

Validate

Confirm the model is ready to mesh.
Run a final geometry check. Confirm: (1) all bodies are closed solids, (2) no edges shorter than 0.2mm remain, (3) no faces smaller than 0.05mm² remain. List any remaining issues.

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Tips for geometry cleanup prompts

  • Set size thresholds explicitly — “remove fillets below 1mm” is actionable; “remove small fillets” is ambiguous. Give Nexus a number to work to.
  • Protect important faces — Tell Nexus which faces must not change: load application surfaces, mounting interfaces, datum references. This avoids unintended simplification at critical regions.
  • Separate inspection from repair — Ask for a report first, review it, then instruct cleanup. This gives you control over what gets changed and prevents unwanted modifications.
  • State the target mesh size — Cleanup thresholds are relative to mesh size. Telling Nexus “my target mesh size is 2mm” lets it calibrate what counts as a problematic small feature.
  • Use rules for assemblies — Rules-based prompts scale much better than feature-by-feature instructions on assemblies with many bodies. “Remove all features below X” across the whole assembly is more reliable than targeting each body individually.
  • Validate before handing off — Always ask Nexus to run a final health check before passing geometry to the mesher. A watertight, manifold solid is the minimum bar.