Crash Simulations Using LSDYNA

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Crash Simulations Using LS-DYNA
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By Levaughn Denton
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Outline

• Background
• Ls-Dyna
• Front Rail Testing
• Project Design/Methods
• Front rail example
• Dodge Neon example
• Specific Aims
• Quadtree hierarchical structure

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LS DYNA Software (Livermore Software Technology
Corp.)

• Solve multi-physics problems
• Thermal stress
• Load
• Use LS DYNA to determine the deformation of a
  frontal rail (or bar) after impact
• Using a single processor
• 2 processor implementation is possible

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LS DYNA Options

• Several versions of LS DYNA
• Windows
• Parallel (memory can be allocated differently)
• Serial
• Unix
• Parallel
• Serial
• Linux
• Parallel
• Serial
• Each has its own set of keywords

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Frontal Crash Simulation

• Frontal rails play an integral role in crash
  tests
• Responsible for absorbing energy during an impact
• Amount of energy absorbed is directly
  proportional to a vehicles deformation

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Crash Test Methodologies

• Quasi-Static Testing
• Frontal rail will experience deformation as a
  result of a constant force

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Crash Test Methodologies Contd

• Impact Testing
• Frontal rail will experience deformation as a
  result of an initial impact speed that decreases
  with time

Velocity at Time 2 lt Velocity at Time 1
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Simulate a Frontal Rail

• Finite Element Model
• Split into planes of symmetry in bar
• Model only a portion of the bar
• Crash into a rigid wall

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LS-DYNA Input Parameters

• Given the material parameters, a grid of nodes
  will be generated
• 1369 nodes
• Each node has an initial velocity in the z
  direction

Material Model 1 Density (g/cm3) 8.98 Elastic
Modulus (g/microsec.2 cm) 1.1 Tangent Modulus
(g/microsec2 cm) 1.0x10-3 Yield Strength
g/microsec2 cm) 4.0x10-3 Harding Parameter 1.0
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LS-DYNA Input File

• First block of code defines output parameters
• Units gm, cm, microsec, 1e07 N, Mbar, 1e07
  N-cm
• 
  
• Control Ouput
• 
  
• ...gt....1....gt....2....gt....3....gt....4....gt....5
  ....gt....6....gt....7....gt....8
• CONTROL_TERMINATION
• endtim endcyc dtmin endneg
  endmas
• 82.10
• CONTROL_ENERGY
• hgen rwen slnten rylen
• 2

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LS-DYNA Input File Contd

• Second block of code defines Mesh and Material
  Parameters
• Define Parts and Materials
• 
  
• ...gt....1....gt....2....gt....3....gt....4....gt....5
  ....gt....6....gt....7....gt....8
• PART
• pid sid mid eosid
  hgid adpopt
• Bar
• 1 1 1
• MAT_PLASTIC_KINEMATIC
• mid ro e pr
  sigy etan beta
• 1 8.930 1.17 0.350
  0.004 0.001 1.0
• src srp fs
• 0.0 0.0 0.0

Material Model 1 Density (g/cm3) 8.93 Elastic
Modulus (g/microsec.2 cm) 1.1 Tangent Modulus
(g/microsec2 cm) 1.0x10-3 Yield Strength
g/microsec2 cm) 4.0x10-3 Harding Parameter 1.0
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LS-DYNA Input Parameters Contd
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Third block of code defines boundary definitions
Initial Conditions ...gt....1....gt....2....
gt....3....gt....4....gt....5....gt....6....gt....7....
gt....8 Nodes within box 2 are given an
initial velocity in the neg z-direction.
These are all the nodes except for those on the
bottom of the bar. INITIAL_VELOCITY nsid
nsidex boxid 0 0
2 vx vy vz vxe
vye vze 0.0 0.0 -0.0227
0.0 0.0 0.0
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LS-DYNA Input Parameters Contd
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Third block of code defines boundary definitions

Define
Nodes and Elements

Many nodes have boundary conditions to
simulate symmetry. NODE node
x y
z tc rc 1
0.000000E00 0.000000E00 0.000000E00
7 7 2 5.330000E-02
0.000000E00 0.000000E00 5 7
3 1.067000E-01 0.000000E00
0.000000E00 5 7 4
1.600000E-01 0.000000E00 0.000000E00
5 7 5 2.133000E-01
0.000000E00 0.000000E00 5 7
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Results After Impact
HP Pavilion dv2700 3GB RAM w/ (2 CPUs) Time
278 secs 1 CPU
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Neon Crashed Into a Rigid Wall
http//www.topcrunch.org/benchmark_results.sfe
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Improving the Performance(software approach)

• The mesh storage structure has a direct impact on
  the
• the amount of memory used
• the CPU time necessary for assembly
• the complexity of the programming
• Suggest the quadtree hierarchical structure is
  used to store information

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Quadtree Structure Contd

• Locate part of the frontal rail that experienced
  deformation using the boundary coordinates of a
  node

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Quadtree Structure
LULEÅ UNIVERSITY OF TECHNOLOGY  Department of
Computer Science and Electrical Engineering
With a depth, d, a neighboring node can be found
in O(d 1) time.
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Thank You