abaqus-dynamic-analysis

# Abaqus Dynamic Analysis Skill This skill handles explicit and implicit dynamics for impact, crash, drop test, and transient response analysis. ## When to Use This Skill **Route here when user mentions:** - Impact, crash, collision, drop test - Transient response, time-varying response - Shock loading, blast loading, explosive loading - High-speed events, wave propagation - "What happens when it hits..." **Route elsewhere:** - Natural frequency extraction → `/abaqus-modal-analysis` - Static/constant loads → `/abaqus-static-analysis` - Harmonic/sinusoidal response → modal + steady-state dynamics - Very long transients (minutes+) → consider implicit or quasi-static ## Prerequisites Before dynamic analysis: 1. Geometry and mesh ready 2. **Material MUST have density defined** (required for mass matrix) 3. Understand event duration and loading type ## Workflow: Setting Up Dynamic Analysis ### Step 1: Gather Information from User Ask if unclear: - **What's the event duration?** Milliseconds, seconds, or longer? - **Initial velocity?** For drop tests or impact - **Is contact involved?** Parts colliding or touching - **What output needed?** Stress, velocity, acceleration, energy? ### Step 2: Choose Explicit vs Implicit | Factor | Explicit | Implicit | |--------|----------|----------| | Time scale | Short (us to ms) | Longer (ms to s) | | Step size | Automatic (very small) | User-controlled | | Nonlinearity | Handles well | May need iterations | | Memory | Lower | Higher | | Contact | Natural handling | Needs care | | Best for | Impact, crash | Vibration, long transient | **Decision rule:** - Event < 10ms with impact/contact → **Explicit** - Event > 100ms without severe nonlinearity → **Implicit** - In between → Either can work, explicit often easier ### Step 3: Set Time Period | Event Type | Typical Duration | |------------|------------------| | High-speed impact | 0.1-10 ms | | Drop test | 1-100 ms | | Blast loading | 1-50 ms | | Seismic/vibration | 1-100 s | ### Step 4: Define Initial Conditions For drop tests and impact: - Set initial velocity on the impacting part/region - Velocity is applied in the Initial step ### Step 5: Configure Output Field outputs: `S` (stress), `U` (displacement), `V` (velocity), `A` (acceleration), `PEEQ` (plastic strain) History outputs for energy balance (explicit): `ALLKE`, `ALLIE`, `ALLWK`, `ETOTAL` ### Step 6: Consider Mass Scaling (Explicit Only) | Option | Effect | When | |--------|--------|------| | None | True inertia | Very short events, accuracy critical | | At beginning | Scale once | Quasi-static explicit | | Throughout | Continuous scaling | When inertia less important | **Warning:** Mass scaling speeds up analysis but affects inertial response. ### Step 7: Run and Validate Use `/abaqus-job` to submit, then check: - Energy balance (ETOTAL approximately constant) - Stable time increment (explicit) - Results physically reasonable ## Key Parameters | Parameter | Explicit | Implicit | |-----------|----------|----------| | Time period | Event duration | Event duration | | Time increment | Automatic | Specify initial, min, max | | Element library | EXPLICIT | STANDARD | | Element type | C3D8R recommended | C3D8R or C3D8 | | Hourglass control | ENHANCED | Default | ## Validation Checklist - [ ] Density defined in material - [ ] Time period appropriate for event - [ ] Initial conditions applied (velocity, position) - [ ] Output frequency captures behavior (100+ frames typical) - [ ] Energy balance acceptable (ETOTAL constant for explicit) - [ ] Results physically reasonable ## Troubleshooting | Problem | Likely Cause | Solution | |---------|--------------|----------| | "Time increment too small" | Small/distorted elements | Use mass scaling or coarsen mesh | | Energy balance error | Hourglass or instability | Check hourglass energy, add control | | Analysis takes forever (explicit) | Long time period | Consider implicit instead | | Convergence failure (implicit) | Severe nonlinearity | Use explicit or smaller increments | ## Related Skills - `/abaqus-material` - Define density (required) - `/abaqus-amplitude` - Time-varying loads - `/abaqus-field` - Initial velocity and predefined fields - `/abaqus-interaction` - Contact for impact problems - `/abaqus-odb` - Results extraction ## Code Patterns For 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)