Current and future developments of LS-DYNA I

Current and future developments of LS-DYNA I
th
4 European LS-DYNA Users Conference
Plenary Session I
Current and future developments of
LS-DYNA I
Dr. Hallquist J. O., Livermore Software Technology Corp.
4th
LS-DYNA User’s Meeting
European LS-DYNA Conference
Outline of talk
LSTC’s Perspective on the future
Version 970 status
Recent developments for crash
Arbitrary Lagrangian-Eulerian Developments
Implicit Developments
EFG (Mesh-free) Developments
MPP
Outlook
A – I - 01
th
Plenary Session I
4 European LS-DYNA Users Conference
Perspective on the future
LSTC’s major goal is to develop within
one explicit finite element program
capabilities to seamlessly solve
problems that require:
Multi-physics
Multiple stages
Multiple formulations
Multi-processing
Multi-physics
Multi-physics problems require solution
methods from more than one discipline.
Fluid-Structure interaction
A – I - 02
tire hydroplaning
airbag deployment
Thermo-mechanical problems (hot forging).
Bird strike on engine and its effect on the overall
structural dynamics of the aircraft (impact + linear
response)
th
4 European LS-DYNA Users Conference
Plenary Session I
Multiple stages
Multi-stage problems require sequential
simulations.
Manufacturing-stamping.
1.
2.
3.
Manufacturing simulation imported into
performance simulation.
1.
Binderwrap (implicit dynamics)
Sheet metal stamping (explicit with mass scaling)
Spring back (dies removed-implicit static).
Crash simulation accounts for effects of manufacturing
processing
Static initialization of dynamic simulation.
Multiple formulations
No single solution method is suitable for all
applications.
Solid mechanics:
Degree of deformation:
Nonlinear elements for large deformations.
Linear elements for eigenvalues, superelements, and linear
structural analyses.
Dynamics:
Explicit methods for short duration transient problems.
Implicit methods for static and long duration problems.
Instantaneously switch between methods
A – I - 03
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Plenary Session I
4 European LS-DYNA Users Conference
Multi-processing
Massively Parallel Processing (MPP) is here to
stay.
MPP is moving downscale: Desktop MPP under
Unix, Windows, and Linux environments
Heterogeneous processing.
Large MPP machines have many parallel jobs
running simultaneously on subsets of processors.
Processing across high speed networks.
12-32 are preferred for LS-DYNA
Stamping analysis with adaptivity is ideally suited
to MPP machines due to the simplicity of contact.
Version 970 status
Now used at many customer sites. Advantages over
version 960:
970 will become the production code at many
customer sites after the updated user’s manual is
published
A – I - 04
The implicit capabilities are greatly expanded
The ALE airbag deployment for out-of-position occupants is
nearing production level
The MPP version is more scalable and, therefore, faster
An updated theory manual is ready for release.
th
4 European LS-DYNA Users Conference
Plenary Session I
Recent crash developments
Spotwelds
Segment based contact
Mesh coarsening
Binary options for database
Model documentation in database
Element technology
Constitutive models
Rigid body related developments
MADYMO coupling
Tied contact with offsets
Slave Node
The offset distance is fixed.
Implemented with both
constraints and penalties.
Two algorithms are needed
Offset
Closest Point on Surface
Isoparametric Coordinates s,t
Structural element
formulation, includes
rotational degrees-offreedom
Continuum element
formulation, no rotational
degrees-of-freedom
MPP support
Implicit implementation for
constraint method in version
970
A – I - 05
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Plenary Session I
4 European LS-DYNA Users Conference
Tied contact with offsets
Available for contact types:
TIED_NODES_TO_SURFACE_{OPTION}
TIED_SHELL_EDGE_TO_SURFACE_{OPTION}
TIED_SURFACE_TO_SURFACE_{OPTION}
Options:
OFFSET
Normal and tangential springs, old method which may
not be orthogonal to rigid body motion
BEAM_OFFSET
Beam like penalty functions
Orthogonal to rigid body rotations
Can be numerically sensitive
CONSTRAINED_OFFSET
Exact method based on rigid body kinematics
Tied contact with offsets
Structural formulation
Slave Node s
Fm = Fs
Fi m = F m N i ( s, t ) + Fi m
M m = r × Fm
M im = M m N i ( s, t ) + M im
V m = ∑Vi m N i ( s, t )
Offset
r
Master Node i
Closest Point on Surface, m,
Isoparametric Coordinates s,t
A – I - 06
ω m = ∑ ωim N i ( s, t )
Am = ∑ Aim N i ( s, t )
ω& m = ∑ ω& im N i ( s, t )
V s =V m +ωm × r
As = Am + ω& m × r + ω m × (ω m × r )
th
4 European LS-DYNA Users Conference
Plenary Session I
Tied contact with offsets
P = M T ω = F TV
Solid formulation
Slave Node s
Virtual
Work
ω × r = Rω
z − y
0
R = − z 0
x 


 y − x 0 
Least Squares Relation Between w and V
r
( R ω − δVi m ) ⋅ ( Riω − δVi m )
2∑ i
m
m
m
Master Node i δVi = Vi − V
Offset
Closest Point on Surface, m,
Isoparametric Coordinates s,t
J=1


T
ω = ∑ Ri Ri 
 i

−1
∑R
T
j
δV jm
j
Exact for
Rigid Body
Motion
Tied contact with offsets
Solid formulation
Fi m = F s N i ( s, t )


ω =  ∑ RiT Ri  ∑ R jδV jm
 i
 j
M = r×F
~
Fi m = Ri [∑ R Tj R j ]−T M m


ω& =  ∑ RiT Ri  ∑ R jδAmj
 i
 j
m
m
δAj = A j − Am − ω × (ω × rj )
Forces on Master Segment
V s =Vm +ω ×r
m
s
j
~
Fi m
equivalent forces due to
slave force offset
As = Am + ω& × r + ω × (ω × r )
Update of Slave Node
Exact for Rigid Body
Motion
A – I - 07
Plenary Session I
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4 European LS-DYNA Users Conference
Frictional beam contact
A – I - 08
Recently improvements have been made in beam-tobeam contact
Post contact searching to reduce the number of
required global searches
Soft constraint option is added to improve
reliability
Interface friction between beams
Implicit implementation
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4 European LS-DYNA Users Conference
Plenary Session I
Spotweld modeling
Connection of shell surfaces
Spotweld models in LS-DYNA
Nodal rigid bodies
Deformable beams
Continuum elements
?
?
Spotweld modeling (bricks)
Advantages
Contact nodes on both surfaces
Axial, bending, and torsional stiffness
Size is independent of surface mesh
Real width of spotweld is modeled
Disadvantages
Mass scaling is needed
Orientation required for resultant based failure
A – I - 09
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Plenary Session I
4 European LS-DYNA Users Conference
Spotweld modeling (4-bricks)
Compared to 1 brick
Mass scaling is similar and overall problem cost increase is
insignificant.
Interface forces are realistically distributed
Spotweld modeling (mat_100)
To avoid time step size problems, the desired time
step size is defined for *MAT_SPOTWELD:
LS-DYNA prints out the added mass for ∆t.
Failure can be based on plastic strain,
strain resultants, or a
combination of plastic strain and resultants:
 N rr

N
 rrF
2
  N rt
 +
 N
  rt F
2
  M ss
 +
 M
  ssF
2
  M tt
 +
 M
  ttF
2
2
  Trr 
 +
 −1 = 0
 T 
  rrF 
The resultants are computed from the nodal point
forces.
A – I - 10
2
  N rs
 +
 N
  rsF
Currently limited to one brick per spot weld
th
4 European LS-DYNA Users Conference
Plenary Session I
New spotweld failure criterion
The stress based failure model for beam and solid spot welds,
developed at Toyota Motor Corporation, is based on the peak
axial and transverse shear stresses, fails the entire weld if the
stresses are outside of the failure surface defined by
2
 σ rr   τ 
 F  +  F  −1 = 0
 σ rr   τ 
2
The peak stresses are calculated from the resultants using
simple beam theory.
σ rr =
A
N rr
+
A
= π
M rs2 + M rt2
Z
2
τ=
d
4
M rr
+
2Z
Z
N rs2 + N rt2
A 3
= π
d
3 2
New spotweld failure criterion
Three additional failure calculations
have been implemented for beam spot
welds
Notch stress
Stress intensity factor
Structural stress
A – I - 11
th
Plenary Session I
4 European LS-DYNA Users Conference
MPP segment based contact
The name, “Segment Based Contact”
is motivated by the most fundamental difference between
segment-based contact and the standard LS-DYNA penalty
contact:
Standard Contact*
*
The name, “Segment Based
Contact”
detects penetration of
nodes into segments and
applies penalty forces to
the penetrating node
and the segment nodes.
is motivated by the most
fundamental difference
between segment-based
contact and the standard LSDYNA penalty contact:
________________________
*standard contact refers collectively to these 9 contact types: 3, a3, 10, a10, 4, 13, a13, 14, and 15
with soft=0 or soft=1.
Segment-based vs. standard
Segments hit even if nodes miss
• Because penetration of
segments by segments
is checked rather than
penetration of segments
by nodes.
A – I - 12
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4 European LS-DYNA Users Conference
Plenary Session I
Segment-based vs. standard
Sharp corners are easily handled
Because contact is
detected between
segments, individual
nodes cannot go
undetected and slip
into spaces between
segments at corners
Falling blocks-segment based
One brick element defines each block. Nodes do not
make contact with contact segments.
A – I - 13
Plenary Session I
th
4 European LS-DYNA Users Conference
Mesh coarsening for crash
The current coarsening capability in LSDYNA for
metalforming has now been extended to provide
seamless mesh coarsening for crash applications
Process Outline
Define elements to be coarsened (default=ALL)
Perform Internal Coarsening
Respect existing constraints
Establish new adaptive constraints
Initialize new mesh
Perform calculations
Applications for coarsening
A – I - 14
Process Allows Seamless Transition From OneDetailed Model to Various Impact Scenarios
Saving Multi-Model Maintenance and CPU Costs
Front Impact
Rear Impact
Side Impact
Head-Impact
Pedestrian Impact
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4 European LS-DYNA Users Conference
Plenary Session I
Binary option for ascii files
What it is not
A file format
Proprietary
What it is
I/O library developed by LSTC
Portable
Robust
Flexible
Source code is available on ftp site
Binary option for ascii files
Flexibility
Acts like a file system
Directories
Variables, Name, Type, Length
New data won’t break old applications
Easy to use
Efficiency and portability
Binary files
Library handles size/format conversions
A – I - 15
Plenary Session I
th
4 European LS-DYNA Users Conference
Binary option for ascii files
“ASCII” output files
All can be output in this format today.
Serial and MPP codes
ASCII (Default on SMP and serial machines)
Binary (Default on MPP machines)
Both ASCII and Binary possible
LS-POST is able to read and post-process the
binary database
Model documentation
ID’s with descriptor information are now
available for:
A – I - 16
Airbags
Contact
Cross-section definitions
Joints
Parts
Rigid Walls
Nodes
Elements
SPC’s
Displacement boundary conditions
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4 European LS-DYNA Users Conference
Plenary Session I
Model documentation
To keep upwards compatibility, _ID
causes ID and heading information to
be read.
This additional information is written
into the ASCII files, and their binary
counterpart, to help in post-processing
Model documentation
The ASCII files which now include model
documentation information are:
NODOUT, nodal information
ELOUT, element information
JNTFORC, joint forces
MATSUM, part statistics
SECFORC, section forces
RCFORC, contact reaction forces
ABSTAT, airbag statistics file
RWFORC, rigid wall force file
SPCFORC, single point constraint reaction forces
BNDOUT, reaction forces due to applied displacements
A – I - 17
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Plenary Session I
4 European LS-DYNA Users Conference
Abnormal termination-shells
An abnormal termination will occur if a zero or
negative Jacobian develops in a shell element.
More severe in fully integrated elements
Such terminations can be hard to debug to make
appropriate model changes.
Special checking is now available to identify “bad”
elements and either, cleanly terminate, or delete the
element and continue running.
Two flags control the checking, one for 1 point elements and
the other for fully integrated elements
Thermal shell
A single input flag activates the thermal shell.
8 fictitious nodes are created automatically to
represent the upper and lower shell surfaces.
A quadratic temperature variation is obtained
through the shell thickness.
A stiffness matrix is created for implicit solution
method used in LS-DYNA for heat transfer
A – I - 18
Element stiffness is based on 12-node brick element.
The conjugate gradient solution method is used for
speed.
Thermal contact possible through projected
surfaces
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4 European LS-DYNA Users Conference
Plenary Session I
Beam element enhancements
Offsets of the beam nodes to enable a beam to
be used as a shell stiffener
1.
Orientation vectors to position beam
1.
Added as an option for all beam formulations in
version 970 for both implicit and explicit applications
Added as an option for all beam formulations that
use the third orientation node
Cross sectional warping
Implicit applications only-being added
Introduces 1 additional degree-of-freedom per
node so scalar nodes are being added to handle
the additional DOF.
Implicit hexahedron element
48 degree-of-freedom hexahedron
element.
Accurate linear element
A – I - 19
Plenary Session I
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4 European LS-DYNA Users Conference
Implicit tetrahedron element
24 degree-of-freedom tetrahedron
element is no available for implicit
24-dof tetrahedron
A comparison of the 12 and 24 degree-offreedom tetrahedron elements is shown.
A – I - 20
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4 European LS-DYNA Users Conference
Plenary Session I
10-node tetrahedron element
Implemented for MPP and SMP
Same cost per element cycle as SRI solid
element. ∆t is small due to high frequencies
Contact treated automatically by 4 triangles
for each face
Available for both implicit and explicit
calculations
4 or 5 integration points, constant pressure
Element_direct_matrix_input
Option for reading and using superelements in
explicit computations is now extended to implicit
applications
Required input is a file in Real*8 NASTRAN format
containing:
Mass Matrix (must be positive definite)
Stiffness Matrix
Damping Matrix (optional)
The matrices share degrees of freedom with model
boundaries and also introduce additional degrees of
freedom with nodes and generalized coordinates.
A – I - 21
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Plenary Session I
4 European LS-DYNA Users Conference
Material definitions
Materials in version 970 can be defined
by a “long” name or a short name, i.e.,
*MAT_TRANSVERSLY_ANISOTROPIC_CRUSHABLE
_FOAM or simply, *MAT_142
Applies to all material models.
Orthotropic viscoplastic
Available for material models:
Viscoplasticity is optional
*MAT_SIMPLIFIED_JOHNSON_COOK
*MAT_PLASTICITY_WITH_DAMAGE
40% more costly due to iterative algorithm
Damage evolves monotonically in principle
strain directions in tension only. Orthotropic
behavior after failure.
A – I - 22
Better correlation with experimental data
Consistent results with minor input changes
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4 European LS-DYNA Users Conference
Plenary Session I
Transversely_anisotropic_
crushable_foam
For modeling low density extruded foam with
anisotropic behavior, typically with high strength in
the extruded direction
Used in energy absorbing structures to enhance automotive
safety in low and medium velocity impacts
Zero Poisson’s ratio under longitudinal loads
A smooth anisotropic yield surface produces physically
correct behavior, i.e. weaker in off-axis loading
Variable coefficients are used which depend on volumetric
strain
Accurate off-axis loading provides better results than
MAT_HONEYCOMB
Modified_crushable_foam
Rate effects are available in the extension to the
isotropic crushable foam model. (*MAT_163)
σ
1-V
A – I - 23
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Plenary Session I
4 European LS-DYNA Users Conference
Quasilinear_viscoelastic
A new model for biological tissues.
ε&1 < ε&2 < ε&3
.
NT
G (t ) = ∑ Gi exp( − β i t )
i =1
6
σ (ε ) (ε ) = ∑σ iε i
i =1
Up to 12 terms may be include in the Prony series
Built in lease squares fit optional
Implemented for solid elements-explicit only.
Hill_foam
A new hyperelastic compressible foam model, which
captures Poisson’s ratio effects. The Cauchy
stresses are defined in terms of J and the principal
stretches as:
1
ti = 
J
m
∑
j =1
C j (λ i b − J
j
−nb j

)

where i=1,2,3
A least squares fit is available for Cj and bj if
uniaxial or biaxial tension and compression test
data is available.
A – I - 24
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4 European LS-DYNA Users Conference
Plenary Session I
Viscoelastic_hill_foam
Rate effects are taken into account through linear
viscoelasticity by a convolution integral of the form:
t
σ ij = ∫0 gijkl (t − τ )
∂ε kl
dτ
∂τ
The viscoelastic stresses are added to the stress
tensor determined from the strain energy functional.
A least squares fit is available to determine the
viscoelastic constants
Low_density_synthetic_foam
For modeling rate independent
low density foams, which have
the property that the hysteresis
in the loading-unloading curve is
considerably reduced after the
first loading cycle.
After the first loading cycle the
loading-unloading curve is
identical
If orthotropic behavior develops
after the first loading cycle
where the material behavior in
the orthogonal directions are
unaffected then the _ORTHO
option should be used
Loading Curve
f or f irst cycle
σ
Loading curve f or second
and subsequent cycles
strain
A – I - 25
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Plenary Session I
4 European LS-DYNA Users Conference
Simplified_rubber
Uses uniaxial data given by a load curve which is
defined for the entire range of expected behavior
Table may be used to include strain rate effects
Force versus change in gauge length, i.e., nominal stress
versus engineering strain can be used
Models hysterisis
Engineering strain rates are optional
No fitting of material parameters means that nearly
all rubber like behavior can be approximately
simulated
1dof_generalized_spring
x’
Node 1
DOF 1
z’
Local
y’Coordinate
System 1
Node 2
z’
DOF 2
x’
y’
Local
Coordinate
System 2
A – I - 26
Couples arbitrary degrees of freedom
between nodes with springs and
dampers.
 a12
 F1 
  = −K 
 F2 
 − a1a2
.
 a12
− a1a2   q1 
 − C
2 
a2  q2 
− a1a2
− a1a2   q&1 
 
a22  q&2 
•Fi = Generalized force for node i.
•qi = Displacement for node i.
•qi = Velocity for node i.
•ai = Scale factor for node i.
•K = Stiffness.
•C = Damping.
Available in both explicit and implicit.
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4 European LS-DYNA Users Conference
Plenary Session I
Nodal rigid bodies
Two new features are implemented for
*CONSTRAINED_NODAL_RIGID_BODY
Release flags for nodal degrees-of-freedom that
allow the translation of the RBE2 constraints in
NASTRAN into the nodal rigid body option
Either local or global system
Can simulate joints between deformable bodies
Implicit implementation allows the chaining of rigid
bodies
Center of mass constraint with _SPC option
Either local or global system
Constrained_interpolation
The motion of a single independent node is
interpolated from the motion of a set in independent
nodes.
Can now be applied in either a local or a global
coordinate system.
Implicit and explicit implementations
Some applications
Tie beam or shell elements to solid elements.
Distribute mass and inertia from the dependent node to
the surrounding independent nodes
Distribute forces and moments from dependent node to
independent nodes
A – I - 27
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Plenary Session I
4 European LS-DYNA Users Conference
Joint failure
OBJECTIVE: Model mechanical failures in joints without the cost
of a finite element model of the joints.
Requested by Federal Highway Administration
Failure criteria are based on forces and moments.
Failure criteria when force and moment failure are uncoupled:
2
 max( N xx ,0)   N yy

 +

 N
N xxF

  yy F
2
  N zz
 +
 N
  zzF
2

 −1 = 0


 M xx

M
 xx F
2
  M yy
 +
 M
  yy F
2
  M zz
 +
 M
  zz F
2

 −1 = 0


Failure criteria when force and moment failure are coupled.
2
2
2
2
2
2
 max( N xx ,0)   N yy   N zz   M xx   M yy   M zz 
 −1 = 0
 +
 +
 +
 +
 +


 
 
 
 
 

N xx F
  N yy F   N zzF   M xx F   M yy F   M zzF 

If the value of a failure constant is zero, the corresponding force or
moment isn’t considering in the failure criteria.
Failure constants can be specified in either a local or the global
coordinate system.
*…_Joint_stiffness_translational
Translational stiffness has been added
to joints for joint types
Cylindrical Joint
Translational joint
Planar joint
Force
yield force
curve
elastic perfectly plastic
behavior
elastic
stiffness
negative stop
displacement
A – I - 28
Displacement
positive stop
displacement
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4 European LS-DYNA Users Conference
Plenary Session I
Madymo coupling
Extended coupling allows users to link most MADYMO
geometric entities with LS-DYNA FEM simulations.
FEM element/nodes.
FACET surfaces.
Ellipsoids/Planes.
This gives LS-DYNA Users access to the most advanced
MADYMO Dummy & Human models.
The MADYMO contact algorithm will be used to
calculate loading between the two models.
User can access elastic loading with
hysteresis/damping/friction.
MADYMO FEM Element Groups will be assigned to an LSDYNA Material, allowing these entities to be defined in
contacts with other LS-DYNA materials.
Extended MADYMO coupling
Extended coupling allows users to link most MADYMO
geometric entities with LS-DYNA FEM simulations.
FEM element/nodes.
FACET surfaces.
Ellipsoids/Planes.
This gives LS-DYNA Users access to the most advanced
MADYMO Dummy & Human models.
The MADYMO contact algorithm will be used to
calculate loading between the two models.
User can access elastic loading with
hysteresis/damping/friction.
MADYMO FEM Element Groups will be assigned to an LSDYNA Material, allowing these entities to be defined in
contacts with other LS-DYNA materials.
A – I - 29
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Plenary Session I
4 European LS-DYNA Users Conference
Example: us-sid & es2 in lincap
Vehicle/barrier/seat are LS-DYNA models.
FEM Dummies are MADYMO models.
Side Inner Panel + Side Trim Panels are the coupled
entities.
MADYMO
LS-DYNA
Vehicle Model Courtesy NHTSA.
Lincap with fem es2
•Beta release of
v6.0/v970 available
at the end of May,
2002.
A – I - 30
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4 European LS-DYNA Users Conference
Plenary Session I
Seatbelt pretensioner option
Force versus time can now be defined:
Fo r c e
Re t ract or
Out Force
Pull-
Defined Force Vs.
Time Curve
Ret ract or
Lock
Time
T ime
Nastran interface
A NASTRAN reader, developed for Superwhams by
KBS2 Inc., is now embedded in LS-DYNA version 970
to allow NASTRAN input decks to run directly in LSDYNA without translation.
Advantages:
Many production problems setup in NASTRAN format exist for
normal modes, statics, and buckling that can be used for
verification of linear capabilities and constraint equations
Nastran input can be augmented by LS-DYNA input to allow
one model for NVH and crash.
First line in the input file: *NASTRAN or, alternatively,
*INCLUDE_ NASTRAN followed by the file name
Allows change of element formulations
Mix LS-DYNA input with NASTRAN input.
A – I - 31
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Plenary Session I
4 European LS-DYNA Users Conference
Normal trimming
Normal (or 3D) trimming has been
implemented, the new features include
No vector is required
Trimming curves are projected to the element
based on its normal
Trimming curve could include several segments
Both digitized and IGES data are supported
Availability:
It is available in LS970
The Keyword is *DEFINE_CURVE_TRIM_3D
Normal trimming
A – I - 32
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4 European LS-DYNA Users Conference
Plenary Session I
Normal trimming
This method allow distorted Trimming curve
Cam trimming
One more feature available for cam trimming:
Trimming curve can be defined in global
coordinate
In *DEFINE_CURVE_TRIM, one more parameter is
added
The seventh parameter, iglobal=1, will activate this
feature
A – I - 33
th
Plenary Session I
4 European LS-DYNA Users Conference
Trimming improvements
Trimming causes
Poor aspect ratios
Large internal angles
Element size is too small
Side effect
Poor convergence for the implicit
springback prediction
Poor mesh for next forming stage
Element quality check
After trimming, elements are checked for
Size
Distortion
Aspect ratio
Internal angles
Adaptivity patterns
After checking any deficiencies are removed
Original result
A – I - 34
New trimming
Element Checking/Fixing
th
4 European LS-DYNA Users Conference
Plenary Session I
Symmetry plane with SPH
Define one or more
symmetry plane.
First symmetry plane
Ghost particles are
automatically created to
ensure local stability near
the boundary.
Set of Ghost Particles created by plane # 1
Set of Ghost Particles for plane # 2
Second symmetry plane
Symmetry Plane with SPH
A – I - 35
th
Plenary Session I
4 European LS-DYNA Users Conference
New ALE developments
MPP
Improved fluid-structure interaction
Fluid-structure interaction output
Point sources for gases
*EOS_IDEAL_GAS and *MAT_GAS_MIXTURE
*MAT_VACUUM for MMALE simulations
New mesh smoothing algorithm for high explosive simulations
*INITIAL_VOLUME_FRACTION_GEOMETRY, volume fraction
distribution for simple and complex geometries.
Mpp ALE capability
Design of airbags for out-of-position
occupants has created huge interest in ALE
capabilities in automotive design
A – I - 36
Control volume approach for airbag inflation
predicts bag pressures that are unrealistically high
and cannot be used for design purposes
1 processor requires 2 weeks per calculation.
32 processors < 12 hours
Much effort is being spent in ALE
development for airbag deployment
th
4 European LS-DYNA Users Conference
New development
in version 970
Plenary Session I
FSI
Fluid structure interaction
Keyword: *CONSTRAINED_LAGRANGE_IN_SOLID
Leakage control
Viscous damping
Alternative penalty stiffness definition for better
numerical stability
Automatic time step adjustment at high penalty
stiffness
ALE structural coupling
Prescribed motion of nodes following user defined
load curves, and rigid body translation of mesh
following mass flow
A – I - 37
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Plenary Session I
4 European LS-DYNA Users Conference
Benchmark tests
Bouncing ball
Evaluation:
check the path and the
shape of the ball
Radius 10 cm
Bulk modulus 10 GPa
Density 2000 kg/m3
40m/s
1m
Bouncing ball
Second order accurate advection with interface
reconstruction preserves shape of rubber ball.
A – I - 38
th
4 European LS-DYNA Users Conference
Plenary Session I
Flat airbag deployed with ALE
Shells – 2752
ALE Solids - 43200
Speed-up
1
8000
7000
Elapsed Time (seconds)
1.95
6000
5000
3.89
4000
3000
2000
1000
0
1
2
4
# of Processors
A – I - 39
th
Plenary Session I
4 European LS-DYNA Users Conference
New development
in version 970
FSI output
Keyword: *DATABASE_FSI
pressure
x-force
y-force
porous
leakage
mass flux
through surface
z-force
Fluid-structure interaction output
Number of surfaces: 2
id
p
fx
fy
fz
pleak
mflux
1
2
time= 0.00000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
1
2
time= 0.10200E-03
0.1632E+05
0.4091E+01
0.1947E+05 -0.4878E+01
-0.3215E+01
-0.4174E+01
0.2546E+01
0.2548E+01
0.0000E+00
0.0000E+00
-0.1284E-04
-0.7193E-05
New development
in version 97
New EOS for gases
New EOS for gases
Keyword: *EOS_IDEAL_GAS
p = ρ (γ − 1)CV T
γ = C P / CV
CV = CV 0 + C LT + C LT 2
C P = C P 0 + C LT + C LT 2
A – I - 40
th
4 European LS-DYNA Users Conference
Plenary Session I
New development
in version 970
New gas mixture model
Keyword: *MAT_GAS_MIXTURE
The model is designed for the treatment of hybrid inflators in
coupled ALE-airbag models. *MAT_GAS_MIXTURE handles the
mixing of up to eight different ideal gases.
Special action is taken to conserve the total energy in the Eulerian
advection step. Dissipated kinetic energy is automatically
transformed into heat.
up to eight different gases
p =
N
∑
i =1
ρ i (C
Pi
− C Vi ) T
density and heat capacities
of the different gas species
New development
in version 970
Point sources
Keyword: *SECTION_POINT_SOURCE_MIXTURE
The command is used to model hybrid inflators for coupled ALE-airbag simulations.
dynamic inlet temperature
section ID
inlet gas flow velocity
*SECTION_POINT_SOURCE_MIXTURE
SID
LCT
.
LCV
NIDL1
LCM1
LCM2
LCM3
LCM4
LCM5
NID1
VID1
AREA1
NID2
VID2
AREA2 n point sources
.
NIDn
VIDn
AREAn
NIDL2
LCM6
NIDL3
LCM7
LCM8
mass flow rates of the
different gas species
point source inlet areas
vectors defining the initial flow direction
nodes defining the initial location of the point sources
A – I - 41
Plenary Session I
th
4 European LS-DYNA Users Conference
Point sources-airbag inflators
Benchmark tests
Pipe
A viscous fluid flowing through a pipe
point source
shell structure
Eulerian mesh
evaluation:
check leakage in the fluid-structure
interaction and compare to an analytical
pressure distribution
A – I - 42
th
4 European LS-DYNA Users Conference
Plenary Session I
Benchmark tests
Pipe
A viscous fluid flowing through a pipe
Benchmark tests
Pipe
Pressure distribution along the pipe
analytical
LS-DYNA
x
x=0.0
x=0.8
A – I - 43
th
Plenary Session I
4 European LS-DYNA Users Conference
New development
in version 970
Airbag model
We have tested a small airbag, deployed with a hybrid inflator, in both a
uniform pressure model and in a fully coupled Eulerian model. The inflator
and the gas mixture are modeled with *SECTION_POINT_SOURCE_
MIXTURE and with *MAT_GAS_MIXTURE.
New development
in version 970
Airbag model
Airbag inside fluid mesh
A – I - 44
th
4 European LS-DYNA Users Conference
Plenary Session I
New development
in version 970
Airbag model
Gases inside bag
New development
in version 970
Airbag model
Deployment pattern, UP versus Euler
Uniform
pressure
Euler
A – I - 45
th
Plenary Session I
4 European LS-DYNA Users Conference
New development
in version 970
Airbag model
Pressure (bar)
Gas pressure inside airbag
Euler
Control volume
Time (ms)
ALE smoothing for shock fronts
A – I - 46
th
4 European LS-DYNA Users Conference
Plenary Session I
Boeing 757 pentagon impact
Courtesy of Purdue University,
Department of Civil Engineering, Prof.
M. Sozen.
Calculations and modeling: Dr. Sami
Kilic
A – I - 47
Plenary Session I
th
4 European LS-DYNA Users Conference
Initialization of volume fraction
*INITIAL_VOLUME_FRACTION_GEOMETRY
Initializing the inside of the tank with fluid
A – I - 48
th
4 European LS-DYNA Users Conference
Plenary Session I
Initialization of volume fraction
*INITIAL_VOLUME_FRACTION_GEOMETRY
Initializing the inside of the tank with fluid
Initialization of volume fraction
Sloshing tank, volume fraction of fluid inside deformable tank
A – I - 49
th
Plenary Session I
4 European LS-DYNA Users Conference
Initialization of volume fraction
Sloshing tank, stresses in deformable tank
Combined implicit-explicit
Adding an implicit solution option to an explicit code
can utilize the extremely efficient data structures,
element formulations, and contact algorithms
developed for explicit analysis.
Use latest linear direct equation solvers
Results in improved explicit algorithms
A – I - 50
Sparse matrix solver
CG iterative solvers
second order accurate formulations required for accurate
implicit calculations are automatically available for explicit
applications.
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