1. Bird Strike Analysis of the WIG Craft
2007 Winter Seminar
Bird Strike Analysis of the WIG Craft
17th. Jan. 2007
Bokwon Lee

2. OUTLINE  Introduction  Bird Impact Model Formulation
Lagrangian model
SPH(Smooth Particle Hydrodynamic) model  Preliminary Analysis  LS-DYNA Model Validation  Bird Strike Analysis of Windshield Leading Edge of WIG Craft  Conclusion and Discussion
 Introduction
 Uncertainty of Impact Analysis
 What is the Fuzzy Algorithm?
 Manipulation of Uncertain Parameter
 Discussion and Future Work

3. BIRD STRIKE MOTIVATION
From 2000~

4. BACKGROUND  Bird Strike Requirement :
 Federal Aviation Administration(FAR /575)
“Airframes for transport category aircraft requires that the aircraft be able to successfully complete a flight after impact with 4lb (1.82kg) bird”
 Something about Bird Strike
a. Since 1988, over 198 people have been killed world-wide as a result of bird strike
b. In the USA, 52,493 strikes have been reported from 1990 to 2004 (164 million $ loss)
c. Front facing components of aircraft are often most susceptible to bird strike
d. The use of computer simulation to estimate the bird impact serves as a powerful tool for development of new component by minimizing the time and cost for empirical testing

5. OBJECTIVES
Obtaining a realistic FE bird model with the help of scattered reported studies
Investigating the modeling of bird strike using different formulation : Lagrangian, SPH(Smooth Particle Hydrodynamic)
Investigate effect of the bird strike on the structure of the WIG craft (wind shield and Leading edge)
Investigate possibility of the Fuzzy algorithm to apply for dealing with uncertain parameters of the impact analysis

6. LITELATURE SURVEY
 Barber et al., : characterization of bird strike in experimental manner “pressure vs. time” > Peak pressure is independent of bird shape and size, depend on the speed2
 Cassenti, : soft body impact on rigid plate, develop the governing equation of the bird strike  Airoldi and Lagrand, : lagrangian bird model impact analysis > large deformation of FE model leads to numerical errors
 Shultz and Peters, : lagrangian bird strike simulation using LS-DYNA for impacting the inlet fan blades of jet engine
 Ubels et al, : SPH simulation bird striking on the leading edge of the wing using PAM-CRASH
 Early of 2000, High performance “Explicit Dynamic Analysis Codes“
LS-DYNA, PAM-CRASH, MSC DYTRAN etc…  Bird strike analysis are required process during design phase of the commercial aircraft

7. LAGRANGIAN MODEL and SPH MODEL
 Lagrangian method - most common technique being used currently for solid material - material moves with the mesh - Pros : easy formulation, easily track history dependant materials - Cons : suffers large deformation which could yield local errors
 SPH(Smooth Particle Hydrodynamics) method - meshless technique used to model the fluid equation of motion * initially developed to simulate astrophysical phenomenon, recently used for other physics problem - Each one particle having interpolation point and fluid properties - Pros : can solve large deformation problems with accuracy - Cons : computationally demanding

8. PRELIMINARY ANALYSIS
 Preliminary Impact Analysis: comparison of impact behavior
 Lagrangian bird model
Finite Element model
0.0sec
0.038sec
0.074sec
0.093sec
 SPH bird model
Meshless Particle model
0.0sec
0.035sec
0.064sec
0.084sec

9. Assumption or chosen value
BIRD MODELING
 Bird Modeling Parameter
No.
Parameters
Assumption or chosen value 1
Bird Mass
1.82kg 2
Bird Geometry
Cylinder with hemispherical Ends 3
Bird Density
938.5kg/m3 4
Bird Material
Viscous Hydrodynamic Fluid
* FAA standard requirement mass for bird strike : 4 lb(1.82kg)
Bird species-Sea gull (1kg~1.8kg)
Bird Material Card
* MAT_NULL : Hydrodynamic Fluid * EOS_LINEAR_POLYNOMIAL: Constitutive Response
* Semi empirical value : C1=2250 MPa, O = otherwise
Pressure to relative volume plot for bird material

10. LS-PREPOST/HYPERVIEW
BIRD MODELING
 Bird FE Modeling
TPE I : Cylinder + Hemispherical Ends
TYPE II : Cylinder (Lagrangian, SPH models)
No.
Parameters
Volume
m^3
Weight
1.82 kg
Density
938.5kg/m^3
Impact speed
Max 42m/s (34+8)
Impact angle
0 degree
114mm
152mm
SPH model
R57mm
R63mm
 Modeling Procedure
CATIA
HYPERMESH
LS-PREPOST
CAD modeling
FE modeling
DYNA code development
LS-DYNA 970
LS-PREPOST/HYPERVIEW
Explicit code solver
Post processor

11. TARGET SURFACE MODELING
 Wind Shield (Front Side)  Leading Edge (section W.S.778-W.S.1698)
> Expected material : Acrylic layer / PVB Interlayer (5mm)
> layup [(0,90)4] > Graphite/epoxy woven fabric
*Acrylic layer (Palcore)
* PVB Interlayer (DuPont)
*Graphite/Epoxy woven composite(HFG)
No.
Properties
Values 1
Mass Density
1180 kg/m3
1100 kg/m3
1.58 g/cm3 2
Young's Modulus
3.1GPa
Elastic Bulk Modulus
2 GPa
Elastic Modulus L/T
61.9 / 62 Gpa 3
Poission's ratio
0.4
Short time shear modulus
1 Gpa
Shear Modulus
3.778 GPa 4
Yield Stress
73.5MPa
Long time Shear Modulus
0.69 Mpa
Poisson's ratio
0.05 5
Tangent Modulus
Decay Constant
12.6 s-1
Thickness
0.2 mm 6
Hardening parameter
0.5
Tensile Strength L/T
965 /937.4MPa 7
Compressive Strength
581.3/513.2MPa 8
Shear Strength
127.2MPa
LS-DYNA card : * MAT_PLASTIC_KINEMATIC (ACRYLIC) * MAT_VISCOELASTIC (PVB) * MAT_COMPOSITE_DAMAGE (Composite)

12. TARGET SURFACE MODELING
*MAT_COMPOSITE_DAMAGE (LS-DYNA card 22)
Based on “Chang and Chang’s failure theory” 1987.
matrix cracking failure criteria
Compression failure criteria
Fiber breakage failure criteria
Contact-Impact Algorithm
Based on “Penalty formulation”
Lagrangian Bird Impact Model : Surface to surface contact
SPH Bird impact model : node to surface contact
When F matrix >1 then E2, G12, v1,v2 set to zero
When F comp >1 then E2, v1,v2 set to zero
When F fiber>1 then E1, E2, G12, v1,v2 set to zero

13. IMPACT MODEL VALIDATION
Experiment (Wilbeck “Impact behavior of low strength projectiles” AFML-TR-77,1977)
Leading edge shape specimen
LS-DYNA Simulation
Same geometry and material with above experimental environment (impact speed 116m/s)
Test Specification > Projectile : Gelatine (substitute for bird) * same material properties
- mass 0.033kg D=30mm, L=40mm Cylinder Type > Target : Gr/Ep [0/45]2s thick=2mm
- geometry : 200mm, 15mm tip radius
> Impact velocity : 116m/s, 142m/s, 198m/s
> US Airforce Material Laboratories
Pressure vs. Time plot
Experiment
Max 260MPa
Lagrangian bird model
SPH bird model

14. BIRD STRIKE ANALYSIS of WIG CRAFT
Windshield
Lagrangian bird impact model _ acrylic layer
Type 2 Bird model
Type 1 bird model
Impact Condition > Impact speed : 42 m/s * cruise 34m/s + gull gliding 8m/s
> Bird density : 938 kg/m3
> Bird volume : m3
> Bird mass : 1.82 kg
> Angle of Impact : 0 degree
FE model information > Windshield : 4N_shell element node, 2397 element
Bird Lagrangian : 8N_solid element, 1518 node SPH : 3751 particle, mass 1.15e-4
 Similar impact behavior(peak pressure) > Independent of size and geometry (under same mass and impact speed) > No element penetration occur

15. BIRD STRIKE ANALYSIS of WIG CRAFT
Windshield
SPH bird impact model _ acrylic layer
Lagrangian bird impact model
Type 2 Bird model
Force vs. time plot
Computational information > Termination time : sec
> Time step : 1e-5 sec
> Calculation time Lagrangian model : 5 min 35sec SPH model : 2 hour 43 min
* CPU : AMD GHz
 Post impact behavior is different > initial peak pressure is equivalent
Kinetic energy vs. time plot

16. BIRD STRIKE ANALYSIS of WIG CRAFT
Leading Edge (shell thickness 0.8mm)
Lagrangian bird impact model (0.8mm thick)
First element failure
First element failure at 2.4ms
- Leading edge support area - direct impact area
SPH Bird impact model(0.8mm thick)
First element failure at 2.3ms
- Leading edge support area - direct impact area
> Calculation time Lagrangian model : 4 min 27sec SPH model : 2 hour 8 min

17. BIRD STRIKE ANALYSIS of WIG CRAFT
Leading Edge (shell thickness 0.8mm  1.3mm)
at least 1.3mm thick leading edge can prevent damage from bird strike
Lagrangian bird impact model(4.5ms, 1.3mm thick)
SPH Bird impact model (4.5ms. 4.5ms)
First element failure
Similar impact behavior between SPH and Lagrangian model (peak pressure) > 0.8mm thick LED : element failure occur at 2.4ms > 1.3mm thick LED : no failure occur, resultant force higher than 0.8mm LED

18. CONCLUSION
The results of the bird strike analysis using LS-DYNA with two formulations are comparable to experiment in terms of pressure profile
Lagrangian and SPH bird model yields comparable numerical results Post impact behavior of the SPH model might be more close to real bird strike accident.
Different formulations of bird model can be used under different circumstances to achieve the most effective outcome.
The leading edge of the WIG craft needs to be modified to maintain structural integrity against the bird strike in according to FAA
Development of the ballistic impact model of the STF Kevlar fabric Investigate the various parameter using numerical approach - Experimental validation of the LS-DYNA model

20. BACKGROUND
Deterministic computer analysis model have many fundamental limitations.
Complex phenomena(i.e. impact) needs more realistic analysis models to comprehend the function of complex engineering system
Engineers need new tools to incorporate uncertainty into their models

21. BACKGROUND Uncertainties of the impact analysis
Bird mass
Impact velocity
peak pressure
Most real life are stochastic  Engineering quantities have to be subjected to tolerance
and can not be defined via deterministic values
Possible approach solution :
Impact angle

22. TREATMENT of UNCERTAINTY
Classical treatment
Monte Carlo simulation : Integration via Monte Carlo method : find the area under the curve, but without knowing f(x). All that must be known is if a point falls below or above f(x) * useful for obtaining numerical solutions to problems which are too complicated to solve analytically. (1964.S.Ulam)
strength distribution (controlled)
Load distribution (uncontrolled)
Degree of overlaps is failure
Strategy 1. Increase Factor of Safely
strength distribution (controlled)
Load distribution (uncontrolled)
Factor of Safely
 Result of Monte Carlo Simulation : Multi dimensional meta-model > Understanding of system is equivalent to understanding of meta-model
Strategy 2. Increase product robustness
Variability reduction
Load distribution (uncontrolled)
strength distribution (controlled)

23. STOCHASTIC SIMULATION
Definition of Stochastic Impact Problems
Input variables
Impact speed
Projectile geometry
Boundary conditions
Initial conditions
Material properties
etc
output variables
Impact pressure
Resultant stress
displacement
energy
temperature
etc
Various methods : Probability theory, Interval method Convex modeling, Monte Carlo simulation
Chaos theory, Fuzzy theory
 Why stochastic simulation?
Good reasons to do stochastic simulation - Determine the most likely performance (differs from nominal) - Determine the existence of outliers or risk - Helps understand systems better - Nature is stochastic

24. FUZZY ANALYSIS
New approach : Fuzzy Uncertainty Analysis in Bird Strikes Simulation
To incorporate the uncertainties in the simulation procedure Fuzzy algorithm is promising approach.
* stochastic approach  use of random parameters * Fuzzy approach  use of fuzzy arithmetic numbers
Comparison of deterministic set and fuzzy set
Fuzzy number and fuzzy interval

25. EXPECTED GOAL
Fuzzy parameterized LS-DYNA Modeling : The uncertain parameters are modeled by fuzzy numbers, and fuzzy parameterized impact models are evaluated by the transformation method in conjunction with LS-DYNA
Uncertainty Quantification of Bird Strike Simulation : Fuzzy uncertainty analysis allows the quantification of the individual influence of each uncertain model parameter on the overall uncertainty of bird strike output.
Development of Fuzzy Cluster Meta Model : Development of fuzzy cluster meta model in the design space with respect to the importance of preliminary identification design parameter or optimization procedures for impact resistance structure.