Abaqus Amplitude Skill
This skill defines time-varying load and boundary condition profiles in Abaqus. Amplitudes act as multipliers that scale loads/BCs over time.
When to Use This Skill
Route here when user mentions:
- "Gradually increase the load", "ramp up the force"
- "Cyclic loading", "sinusoidal excitation"
- "Pulse load", "impulse", "impact loading"
- "Time-varying boundary condition", "loading history"
- "Smooth transition", "avoid sudden load application"
- "Earthquake input", "harmonic excitation"
Route elsewhere:
- Constant static loads (no amplitude needed) →
/abaqus-load - Initial conditions, predefined fields →
/abaqus-field - Dynamic analysis setup →
/abaqus-dynamic-analysis
Workflow: Defining Amplitudes
Step 1: Understand User's Load Profile
Ask if unclear:
- What shape? Ramp, sinusoidal, pulse, decay, custom?
- What timing? Duration, frequency, peak time?
- What magnitude? Amplitude is a multiplier (0.0-1.0 typical)
Step 2: Choose Amplitude Type
| User Describes | Amplitude Type | Key Parameters |
|---|---|---|
| Linear increase/decrease | TabularAmplitude | Time-value pairs |
| Smooth transition (no shock) | SmoothStepAmplitude | Time-value pairs |
| Sinusoidal/harmonic | PeriodicAmplitude | Frequency, coefficients |
| Exponential decay | DecayAmplitude | Initial, decayTime |
| Custom time history | TabularAmplitude | User-provided data |
| Sudden on/off | TabularAmplitude | Step-like data points |
Most common: TabularAmplitude with linear ramp (0,0) to (1,1)
Step 3: Determine Time Reference
| Setting | When to Use |
|---|---|
timeSpan=STEP | Time relative to current step start (most common) |
timeSpan=TOTAL | Time from analysis beginning (multi-step analyses) |
Step 4: Define Data Points
For TabularAmplitude and SmoothStepAmplitude:
- Data is (time, amplitude_factor) pairs
- Time values must be strictly increasing
- Factor typically ranges 0.0 to 1.0 (can exceed if needed)
- Factor multiplies the load/BC magnitude
Step 5: Apply to Load or BC
Amplitudes are referenced by name when creating:
- Loads: ConcentratedForce, Pressure, Gravity, etc.
- BCs: DisplacementBC, VelocityBC, etc.
Key Decisions
Common Load Profiles
| Profile | Data Pattern | Use Case |
|---|---|---|
| Linear ramp | (0,0), (1,1) | Quasi-static loading |
| Ramp up/down | (0,0), (0.5,1), (1,0) | Load cycle |
| Hold at peak | (0,0), (0.1,1), (1,1) | Ramp then sustain |
| Triangular pulse | (0,0), (0.001,1), (0.002,0) | Impact/impulse |
| Step function | (0,0), (0,1), (1,1) | Sudden application |
Smooth vs. Tabular
| Use SmoothStepAmplitude when | Use TabularAmplitude when |
|---|---|
| Dynamic analysis (avoid shocks) | Static analysis |
| Convergence issues from sudden loads | Exact load profile needed |
| Continuous derivatives required | Step functions needed |
What to Ask User
| Input | Required | How to Get |
|---|---|---|
| Load profile shape | YES | Ask: "How should the load vary over time?" |
| Peak time | YES | Ask: "When should the load reach its maximum?" |
| Duration | YES | Typically matches step time |
| Frequency (if cyclic) | If periodic | Ask: "What frequency in Hz?" |
| Smooth or sudden | Recommended | Ask if dynamic analysis |
Validation Checklist
After defining amplitude:
- Time values are strictly increasing
- Factor range is appropriate (usually 0.0-1.0)
- timeSpan matches analysis intent (STEP vs TOTAL)
- Amplitude name matches what load/BC references
- For dynamic: smooth transitions to avoid numerical shocks
- For periodic: frequency and coefficients are correct
Troubleshooting
| Problem | Likely Cause | Solution |
|---|---|---|
| "Amplitude not monotonic in time" | Time values not increasing | Fix time sequence |
| Convergence issues with sudden load | Discontinuity in profile | Use SmoothStepAmplitude |
| Load too high/low | Misunderstanding multiplier | Amplitude is factor; adjust load magnitude |
| Wrong timing in multi-step | STEP vs TOTAL confusion | Check timeSpan setting |
Code Patterns
For API syntax and code examples, see:
- API Quick Reference - Full parameter details
- Common Patterns - Ready-to-use snippets
- Troubleshooting Guide - Error solutions
