abaqus-step

# Abaqus Step Skill This skill defines analysis steps and procedures in Abaqus. Steps control what physics are solved and how the solution proceeds. ## When to Use This Skill **Route here when user mentions:** - "static analysis", "dynamic step", "frequency analysis" - "heat transfer step", "thermal step", "transient analysis" - "analysis type", "time increments", "nlgeom" - "convergence issues", "increment size", "time step" - "multi-step analysis", "sequential loading" - "buckling analysis", "modal analysis" - "impact simulation", "crash analysis" **Route elsewhere:** - Applying boundary conditions → `/abaqus-bc` - Applying loads → `/abaqus-load` - Setting up optimization → `/abaqus-optimization` - Configuring output requests → `/abaqus-output` ## Workflow: Creating Analysis Steps ### Step 1: Understand User's Physics Ask if unclear: - **What physics?** Stress, vibration, heat transfer, coupled? - **Static or dynamic?** Constant load vs time-varying? - **Linear or nonlinear?** Small or large deformations? ### Step 2: Choose Step Type | Analysis Goal | Step Type | Key Parameter | |---------------|-----------|---------------| | Stress under constant load | StaticStep | nlgeom=OFF/ON | | Natural frequencies | FrequencyStep | numEigen | | Buckling modes | BuckleStep | numEigen | | Transient dynamics (smooth) | ImplicitDynamicsStep | timePeriod | | Impact/crash | ExplicitDynamicsStep | timePeriod | | Heat conduction | HeatTransferStep | response | | Thermal + structural | CoupledTempDisplacementStep | timePeriod | | Harmonic response | SteadyStateDynamicsStep | frequencyRange | **Most common:** StaticStep with nlgeom=OFF for linear stress analysis. ### Step 3: Determine Linearity | Condition | nlgeom Setting | When | |-----------|----------------|------| | Small deformation, linear material | OFF | Default, fastest | | Large rotation/displacement | ON | Thin structures, cables | | Plasticity | ON | Material yields | | Contact | ON | Parts touching | | Buckling | ON | Post-buckling behavior | ### Step 4: Configure Increment Control | Convergence Difficulty | initialInc | minInc | maxInc | |------------------------|------------|--------|--------| | Easy (linear) | 1.0 | 1e-6 | 1.0 | | Moderate | 0.1 | 1e-8 | 0.2 | | Difficult (contact, plasticity) | 0.01 | 1e-12 | 0.05 | ### Step 5: Chain Multiple Steps (if needed) For sequential loading: 1. First step uses `previous='Initial'` 2. Subsequent steps chain from previous step name 3. Each step can have different physics or settings ## Key Parameters | Parameter | Purpose | Typical Value | |-----------|---------|---------------| | timePeriod | Duration of step | 1.0 for static | | initialInc | Starting increment size | 0.1 for nonlinear | | maxNumInc | Maximum iterations | 100 | | minInc | Smallest allowed increment | 1e-8 | | maxInc | Largest allowed increment | 0.1-1.0 | | numEigen | Modes to extract | 10 | | deltmx | Max temp change per increment | 5.0-10.0 | ## Special Considerations ### Frequency/Modal Analysis - Always from Initial step (no preload needed for basic modal) - Use LANCZOS eigensolver for large models - Extract 10-20 modes typically ### Buckling Analysis - Usually follows a load step (to apply reference load) - Eigenvalues are load multipliers - First positive eigenvalue is critical ### Explicit Dynamics - Time period should be very short (milliseconds) - Increment size determined automatically - Mass scaling may be needed for quasi-static problems ### Heat Transfer - STEADY_STATE for equilibrium temperature - TRANSIENT for time-varying temperature - deltmx controls accuracy vs speed ## Troubleshooting | Problem | Likely Cause | Solution | |---------|--------------|----------| | "Too many increments" | Convergence difficulty | Reduce maxInc, increase maxNumInc | | "Negative eigenvalues" | Unconstrained or unstable | Check BCs, add stabilization | | "Time increment too small" | Severe nonlinearity | Add stabilization, check material | | "Explicit time increment" | Very small elements | Use mass scaling or coarsen mesh | ## Validation Checklist After step creation, verify: - [ ] Step type matches analysis physics - [ ] nlgeom setting appropriate for deformation level - [ ] Increment control parameters reasonable - [ ] Step chains correctly from previous - [ ] Time period appropriate for transient analysis ## Code Patterns For actual API syntax and code examples, see: - [API Quick Reference](references/api-quick-ref.md) - [Common Patterns](references/common-patterns.md) - [Troubleshooting Guide](references/troubleshooting.md)