FEM Dynamic Analysis
Vibrations, impacts, and frequency response
Overview
Dynamic analysis studies how structures respond to time-varying loads, vibrations, and impacts. confBuild supports five dynamic analysis types from eigenfrequency extraction to full explicit crash simulation.
Modal
Natural frequencies & mode shapes
Harmonic
Frequency response (swept sine)
Transient
Time-dependent dynamic response
Explicit & Seismic
Crash, blast & earthquake
Modal Analysis
Extracts natural frequencies (eigenfrequencies) and vibration mode shapes of your structure. Essential for understanding resonance behavior.
When to Use
- Determine natural frequencies to avoid resonance
- Characterize vibration behavior of components
- Prerequisite for harmonic and seismic analysis
- Verify structural stiffness and mass distribution
Configuration
analysisType
modal
Analysis type selector
modalNumModes
6
Number of eigenfrequencies to extract
Output
- Eigenfrequencies — Natural frequencies in Hz for each mode
- Mode shapes — Displacement patterns visualized with deformation scale
- Use the time series animation to cycle through mode shapes
Harmonic Analysis
Calculates the steady-state response to sinusoidal loading across a frequency range. Use this to find resonance peaks and evaluate vibration amplitudes.
Configuration
analysisType
harmonic
Analysis type selector
harmonicFreqMin
0
Start frequency (Hz)
harmonicFreqMax
1000
End frequency (Hz)
harmonicFreqSteps
100
Number of frequency steps
Use Cases
- Vibration isolation design — evaluate transmissibility
- Resonance identification in rotating machinery
- Acoustic response of enclosures
- Fatigue assessment under cyclic loading
Transient Analysis
Solves the time-dependent dynamic response to arbitrary loading histories using implicit time integration.
Configuration
analysisType
transient
Analysis type selector
transientDuration
1.0
Total simulation time (seconds)
transientTimeSteps
100
Number of time steps
Use Cases
- Impact loads (drop tests, hammer impacts)
- Sudden load application or removal
- Machine start-up and shutdown transients
- Response to arbitrary force-time histories
Explicit Dynamics
For very fast events like crashes, blasts, and ballistic impacts where implicit methods are too slow or fail to converge.
Configuration
analysisType
explicit_dynamics
Analysis type selector
explicitDuration
0.01
Simulation duration (seconds)
explicitTimeStep
1e-6
Time step size (seconds)
explicitDamping
0.05
Numerical damping factor
Seismic Analysis
Evaluate structural response to earthquake loading using response spectrum or time-history methods.
Configuration
analysisType
seismic
Analysis type selector
seismicExcitationType
spectrum
spectrum or time_history
seismicPeakAcceleration
3.0
Peak ground acceleration (m/s²)
seismicDuration
10
Earthquake duration (seconds)
Use Cases
- Building and bridge design to seismic codes
- Equipment anchorage verification
- Piping stress analysis under seismic loads
- Nuclear safety assessments
Time Series Animation
Dynamic results can be animated to visualize mode shapes and time responses.
Animation Controls
Play / Pause / Stop
Control animation playback
FPS (5–60)
Adjust playback speed
Mode: Oscillate
Bounce back and forth
Mode: Forward
Play in one direction
Frame stepping
Step through individual frames