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 selectormodalNumModes
6
Number of eigenfrequencies to extractOutput
- 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 selectorharmonicFreqMin
0
Start frequency (Hz)harmonicFreqMax
1000
End frequency (Hz)harmonicFreqSteps
100
Number of frequency stepsUse 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 selectortransientDuration
1.0
Total simulation time (seconds)transientTimeSteps
100
Number of time stepsUse 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 selectorexplicitDuration
0.01
Simulation duration (seconds)explicitTimeStep
1e-6
Time step size (seconds)explicitDamping
0.05
Numerical damping factorSeismic Analysis
Evaluate structural response to earthquake loading using response spectrum or time-history methods.
Configuration
analysisType
seismic
Analysis type selectorseismicExcitationType
spectrum
spectrum or time_historyseismicPeakAcceleration
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 playbackFPS (5–60)
Adjust playback speedMode: Oscillate
Bounce back and forthMode: Forward
Play in one directionFrame stepping
Step through individual frames