Bird Strike Analysis
Bird Strike: Theoretical Foundations
What is Bird Strike?
Professor, is bird strike analysis about aircraft colliding with birds?
Yes. FAR 25.631 / CS 25.631 mandates aircraft bird impact resistance. The main evaluation targets are engine ingestion, impact on the windshield, and impact on the wing leading edge.
Bird Modeling
Birds deform fluidly upon impact (behavior closer to fluid than solid). In FEM:
| Model | Characteristics | Application |
|---|---|---|
| SPH Particles | Mesh-free. Strong against large deformations | Most common |
| ALE | Treats bird as Eulerian fluid | High accuracy |
| Lagrangian Solid | Standard solid elements | Low-speed impact |
Modeling the bird with SPH particles!
SPH particles have no connections between nodes, so they can naturally represent the bird's "splattering" behavior upon impact. LS-DYNA's SPH + Lagrangian (aircraft structure) coupling is standard.
Impact Conditions
Typical conditions per FAR 25.631:
- Bird Mass: 1.8 kg (4 lb) — Medium-sized bird
- Impact Velocity: Equivalent to V_c (cruise speed). 180–250 m/s
- Impact Energy: $E = mv^2/2$ ≈ 30–60 kJ
Impact at 180 m/s... that's an incredible amount of energy.
60 kJ is less than a car crash (180 kJ at 56 km/h), but because the impact area is extremely small, localized penetration occurs. The structural integrity of the windshield and engine intake is tested.
Summary
Key Points:
- Mandated by FAR/CS 25.631 — Bird impact resistance performance
- Model bird with SPH particles — Represents fluid-like deformation
- LS-DYNA SPH + Lagrangian coupling — Industry standard
- High-speed impact at 180–250 m/s — Pay attention to localized penetration
Bird Strike Impact Force Exceeds Imagination
When a 1.8kg bird collides with an aircraft at 800 km/h, the impact load reaches about 150 kN at its peak. FAR 25.571 mandates testing with a 1.8kg bird at flight speed, and for CFRP windshield certification tests, SPH method simulations using Abaqus became standardized among major Western manufacturers after the 2000s.
Computational Methods for Bird Strike
Bird Model Using SPH
SPH bird model in LS-DYNA:
```
*SECTION_SPH
1, 1.0, 0.0, 0.0, 0, 0
*MAT_NULL
1, 950. $ Density 950 kg/m3 (bird ≈ close to water)
*EOS_GRUNEISEN
1, 1480., ... $ Equation of state for water
*INITIAL_VELOCITY_SET
bird, 200000., 0., 0. $ 200 m/s (mm/ms)
```
Bird density is 950 kg/m³, close to water?
A bird's body is mostly water (70–80%). During high-speed deformation upon impact, the bird behaves as a fluid. The equation of state for water (EOS_GRUNEISEN) describes the pressure-density relationship.
Structure Side Modeling
Summary
SPH Method Changed Bird Strike Analysis
Traditional Lagrangian FEM had the problem of computational failure due to excessive deformation of the bird body mesh, but the situation changed completely after SPH (particle method) was implemented in LS-DYNA in the late 1990s. The bird body is modeled with an equation of state equivalent to water (Mie-Grüneisen model), and realistic pressure waveforms can be reproduced with about 5000 particles of particle diameter 0.003–0.005 m.
Bird Strike in Practice
Bird Strike Practice
Bird strike testing is mandatory for aircraft Type Certification (TC). Validate beforehand with FEM.
Practical Checklist
Is it a pass if there's no penetration?
For windshields, the criterion is "no penetration" (crew safety). For wing leading edges, the criterion is "ability to continue safe flight". Even without penetration, failure can occur if large deformation damages hydraulic lines, etc.
Engine Fan Testing is Common Worldwide
For bird strike certification based on EASA CS-E 800 standards, a 1.8kg bird is projected at high speed into the first-stage fan of a turbofan engine to confirm the engine can safely shut down. For the Boeing 787 GEnx-1B engine certification, parametric analysis covering over 200 incidence angle and velocity conditions was performed using ANSYS LS-DYNA before actual firing tests.
Bird Strike: Software & Solver Comparison
Bird Strike Tools
Which solver is most commonly used in the aerospace industry?
LS-DYNA dominates. The reason: excellent SPH implementation, mature bird strike models, and strong integration with CAD/CAM in the aircraft industry. However, Abaqus Explicit is gaining ground, especially in composite windshield analysis.
Bird Strike Simulation Data: Public Benchmark
The FAA and EASA have published reference test data for bird strike impact on aircraft structures. Academic institutions often use LS-DYNA with published material parameters (bird density 950 kg/m³, equation of state coefficients) to create reproducible benchmark models. This standardization is critical for regulatory acceptance of FEM-based certification.