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