ANSYS® Explicit Dynamics and AUTODYN® Applications

57 Pages·2011·8.49 MB·English

ANSYS® Explicit Dynamics and
AUTODYN® Applications
Ashish Jaiswal
ANSYS Inc.
1 © 2011 ANSYS, Inc. 8/29/11
Explicit Dynamics and AUTODYN
Applications
Street Blast
Marine Blast Can Crush
Mine Blast
Drop Tests
Missile Impact
Aircraft Impact
Blast In a Building Portable Explosive Devices
Explosive Mining
2 © 2011 ANSYS, Inc. 8/29/11
Why Use Explicit Dynamics?
Impact Response of Materials
Solution Impact Strain Rate Effect
Velocity (m/s) (/s)
Implicit <10-5 Static / Creep
< 50 10-5 - 10-1 Elastic
Elastic-Plastic (material
50 -1000 10-1 - 101
strength significant)
Primarily Plastic (pressure
1000 - 3000 105 - 106 equals or exceeds
material strength)
Hydrodynamic (pressure
3000 - 12000 106 - 108 many times material
strength)
Vaporization of colliding
Explicit > 12000 > 108
solids
3 © 2011 ANSYS, Inc. 8/29/11
Why Use Explicit Dynamics?
Impacts at Low and High Velocity
VELOCITY LOW HIGH
Deformation Global Local
Response Time ms - s µs - ms
Strain <10% >50%
Strain Rate < 10 s -1 > 10000 s -1
10-100 x
Pressure < Yield Stress
Yield Stress
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Wave Propagation
Average Velocity
Computes wave propagation
Velocity at Gauge 1
Rarefaction
Shock
Constant pressure applied to left surface for 1 ms
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Stability Time Step
To ensure stability and accuracy of the
Ø ø
h
solution, the size of the time step used in D £ *
t f
Œ œ
Explicit time integration is limited by the
º c ß
CFL (Courant-Friedrichs-Levy[1])
min
condition. This condition implies that the
time step be limited such that a
disturbance (stress wave) cannot travel
further than the smallest characteristic
element dimension in the mesh, in a
single time step.
The time steps used for explicit time
integration will generally be much
h
smaller than those used for implicit time
integration

•
e.g. for a mesh with a
characteristic dimension of 1
mm and a material sound
speed of 5000 m/s. The
resulting stability time step
would be 0.18 µ-seconds. To
solve this simulation to a
6 © 2011 ANSYS, Inc. 8/29/11
termination time of 0.1
seconds will require 555,556
time steps
®
ANSYS Explicit Dynamics and
®
AUTODYN
Non-linear dynamics programs
§
§ Components of ANSYS® Workbench
™
Model the non-linear response of
§
solids, fluids and gases and their
interactions
Can be used to study a wide range of
§
events involving impact and
blast loadings
Provide a detailed understanding of
§
the transient dynamics involved
Determine the expected deformation
§
and damage
Provide insight into ways damage
§
could be mitigated
o Design
o Protection
7 © 2011 ANSYS, Inc. 8/29/11
® ®
ANSYS AUTODYN Solutions
Coupling
Euler (CFD) Solvers
Lagrange (FE) Solvers
(Multi-material, Blast)
(Solids, shells &
beams)
Interactions Solid / Gas / Fluid Flow
Structural Response
Blast Waves
Complex Materials Solid Impact
FSI (Deforming
Bonding /
Coupling
Structures)
Contact
Combined Blast &
Mesh Free Solver
Impact Loading
ALE Solver
Hypervelocity Impact
Fluid-Structure Interaction
Brittle Material Fracture / with Strong Structures
Fragmentation
Bonding / Contact
8 © 2011 ANSYS, Inc. 8/29/11
Lagrange Solvers
Use meshes that are
imbedded in material and
move and distort with the
material
Three element types
– Solid
– Shell
– Beam
Provide the most efficient
and accurate method for
computing structural
9 © 2r01e1 AsNSpYS,o Incn. se8/29/11
Lagrange Solvers
Erosion
If excessive material movement
occurs, the mesh may become
highly distorted
Inaccurate and inefficient
solutions
Mesh tangling (terminates
solution)
This problem can usually be avoided by
application of an erosion algorithm
•
Extremely distorted cells are
removed from the problem
•
Element strain over 200% when
10 © 2011 ANSYS, Inc. 8/29/11
eroded
•
Inertia of eroded elements is
maintained as free mass points
that continues to interact with
the mesh