BEng coursework · 2025
Van frame vibration analysis in Siemens NX
Modal and harmonic FEA of a steel van frame, validated against real-world modal testing, then used to find the most weight-efficient way to stiffen it.
Key numbers
<5%
error between FE and experimental natural frequencies78.9 → 94.3 Hz
key resonance raised with corner support struts−39%
peak displacement at resonance+32%
mass, the lightest of the three fixesThe problem
Vibration in a vehicle frame drives ride comfort, noise and fatigue. The task was to predict how a steel van frame behaves dynamically, prove the model against physical tests, and find a stiffening fix that doesn't add excessive weight.
What I did
- Mesh convergence: refined the FE mesh from 17,844 to over 1.2 million elements, settling on ~217,500 elements for accuracy without wasted solve time.
- Modal analysis: identified the first three modes: torsion, lateral bending and vertical bending.
- Validation: compared against experimental modal analysis (impact hammer and accelerometers). Errors were +4.8%, +0.2% and −1.8%, inside the accepted ±10%.
- Harmonic analysis: applied a 1 N vertical force at a spring mount and found the dominant resonance at 78.93 Hz (0.454 mm peak).
Design modifications
| Design | Resonance | Peak displacement | Mass increase |
|---|---|---|---|
| Baseline (2 mm walls) | 78.93 Hz | 0.454 mm | n/a |
| Corner support struts | 94.29 Hz | 0.275 mm | +32% |
| Walls thickened to 5 mm | 94.89 Hz | 0.271 mm | +173% |
| Cross bracing | 85.77 Hz | 0.229 mm | +221% |
Corner struts gave almost the same gain as thicker walls for less than a fifth of the added mass, the best balance for a weight-sensitive vehicle.
Gallery
What I'd do next
- Swap steel for aluminium alloys or fibre-reinforced composites to cut the mass penalty.
- Use more sensors and better boundary conditions in testing to tighten validation further.
The wider coursework also covered a Simulink 3-DOF ride comfort model and experimental modal testing of a steel beam.