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© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
Release 12.0 enhancements for contact analysis
Release 12.0 enhancements for contact analysis
© 2009 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
Pressure Penetration Loading
• Modeling of fluid penetrating into the interface between two contacting bodies.
• It supports:– 2D/3D surface-to-surface contact pair– Small and large sliding contact– Rigid-flexible and flexible-flexible contact
• Path-dependent loading
Fluid pressure is applied
Fluid pressure is not applied
© 2009 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary
Contact surface
Target surface
--- Free-end Point
2D contact: Free-end point
3D contact: Free-open Edge
Contact surface
Target surface
Pressure Penetration Loading
• Fluid pressure applied to contact and target elements– SFE,elem,1,PRES,,val1,val2,val3,val4– Apply the pressure to contact elements only, if rigid-flexible
contact, symmetric contact pair• Fluid penetration starting points:
– Points are exposed to the fluid pressure– ANSYS picks default points
Free-open edge
© 2009 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary
Pressure Penetration Loading
• User defined fluid penetration starting points:– SFE, elem, 2, PRES,,STA1, STA2, STA3, STA4– STAi = 0 (default) --- ANSYS determines whether the ith node is
a starting point based on the contact status. The ith node can be a default starting point if it is a node of a 2D free points or on a node of 3D free edges.
– STAi = 1 --- the ith node is the starting point which initially exposed to the fluid. It can be a penetrating point if initial contact status is "open". The node may no-longer be the start point when contact status changes during deformation process.
– STAi = 2 --- the ith node is a penetrating point. The node is always subjected to the fluid pressure in spilt of the contact status change.
– STAi = -1 --- the ith node will no longer be a default starting point.
© 2009 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
Application: O-ring Seal
© 2009 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary
Performance & Efficiency
• Contact performance improvements– A new searching algorithm has been implemented
which speeds up contact searching by 20X-200X, depending on the nature of the contact model.
– Only limited internal MPCs for rigid surface constraint are built which greatly reduce solver time.
– The computation time for contact element assembly and contact results is reduced by at least 50%.
– Contact results related to “far field” contact are no longer computed and stored, which greatly reduces the size of the results file.
© 2009 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary
Contact Speed-up Example
BOOTSEAL 3D
Elem: 11090
Nodes: 5040
Dofs: 30240Rigid-Deformable +Self
Contact
11.0 12.0 speedup
Contact database 11.72 0.216 54.26
Contact Search 3465.04 75.64 45.80
Contact Elements 505.64 188.95 2.67
Other Elements 4907.18 2301.7 2.13
Eq. Solver 276.77 211.35 1.30
Total CPU 9154.65 2777.64 3.29
Elapsed Time 9207 2788 3.30
No. of Iterations 246 240 1.02
No. of Substeps 42 43 0.97
Boot Seal
© 2009 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary
Contact Performance:Nonlinear Customer Model
CPU V110 V120
Contact Searching
148372s 60.6s
Contact Elements
1488s 791s
Wall time 167455s 12141s
Elems:49701 Nodes:67582 Dofs: 405492
© 2009 ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary
BenchMark results by ARTERSON
R12.0
CONTACT DATABASE 6661.095CONTACT SEARCH 10159.940CONTACT ELEMENTS 6872.640OTHER ELEMENTS 2391.016EQUATION SOLVER 25744.922TOTAL SYSTEM 45170.309
R11.0
CONTACT DATABASE 72482.973CONTACT SEARCH 717404.719CONTACT ELEMENTS 676.445OTHER ELEMENTS 3242.742EQUATION SOLVER 101088.141TOTAL SYSTEM 822412.047
From 9.5 days in R11.0 to half day in R12.0
© 2009 ANSYS, Inc. All rights reserved. 10 ANSYS, Inc. Proprietary
Performance & Efficiency
• New contact pair trimming logic– The CNCHECK command has new options for
removing (TRIM) or unselecting (UNSE) contact and target elements which are initially in far field. The new capabilities improve solution efficiency for small sliding contact or assembly contact, especially in Distributed ANSYS runs.
Before trimming After trimming
© 2009 ANSYS, Inc. All rights reserved. 11 ANSYS, Inc. Proprietary
Performance & Efficiency
• New contact pair trimming logic
No TRIM
With TRIM
2CPU 17922 15756
4CPU 10920 10493
8CPU 9521 7439
A benchmark test from John Deere
8CPU NoTRIM
With TRIM
Elements 193390 72913
Wall time 15758 <6000
A benchmark test from a German user
Before trimmingAfter trimming
© 2009 ANSYS, Inc. All rights reserved. 12 ANSYS, Inc. Proprietary
Robustness & Accuracy
• Improve “Force distributed surface constraint” (RBE3) under large rotation– It is key component to link joints and flexible bodies.– It is critical for modeling flexible bodied dynamics
R11.0 solution R12.0 solution
© 2009 ANSYS, Inc. All rights reserved. 13 ANSYS, Inc. Proprietary
Robustness & Accuracy
• Shell-shell, Shell-solid assembly– A new option for shell-solid assemblies (target element
TARGE170 with KEYOPT(5) = 5) improves the stress distribution at the shell-solid interface.
Keyopt(5)=3 (shell-solid constraint type)
Keyopt(5)=5 (solid-shell constraint type)
© 2009 ANSYS, Inc. All rights reserved. 14 ANSYS, Inc. Proprietary
Robustness & Accuracy
• Shell-shell, Shell-solid assembly– Auto constraint type-detection for shell-shell
assemblies (target element TARGE170 with KEYOPT(5) = 0) has been improved so that the program chooses the constraint type that is most efficient for the given contact situation.
R11.0 default Keyopt(5)=0(use shell-shell constraint typeDecouple rotational DOFs & translational DOFs)
R12.0 default Keyopt(5)=0(use shell-solid constraint typeCouple rotational DOFs & translational DOFs)
© 2009 ANSYS, Inc. All rights reserved. 15 ANSYS, Inc. Proprietary
Robustness & Accuracy
• Overconstraint detection and elimination– When a degree of freedom is subjected to multiple
constraints, overconstraint occurs, a condition which often results in solver-failure convergence difficulties or inaccurate solutions. The program now automatically eliminates a limited set of overconstraints detected during solution and issues appropriate warning messages. For troubleshooting purposes, you can display certain eliminated constraints in the POST1 postprocessor
© 2009 ANSYS, Inc. All rights reserved. 16 ANSYS, Inc. Proprietary16
The assembly is connected with MPC contacts
In these regions Parts are not correctly connected
Contact status
Solution in R12:2 elements in sweep direction
Contact status
Robustness & Accuracy
© 2009 ANSYS, Inc. All rights reserved. 17 ANSYS, Inc. Proprietary
Robustness & Accuracy
• Robustness & Accuracy– Stiffness multiplier damping (BETAD or MP
,DAMP) is no longer applied to contact elements in a full transient analysis, resulting in more accurate simulations, especially in the contact force calculations.
© 2009 ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary
Rigid Target Surface and Rigid Body
• Boundary Conditions on Rigid Target Surfaces – In previous releases, only the pilot node of a
rigid target could accept boundary conditions, and only the pilot node could connect to other elements for an entire rigid target surface. These restrictions have been removed. Now, any rigid target nodes can have boundary conditions and can connect to other elements. The enhancement allows rigid target surfaces to represent rigid bodies.
© 2009 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary
Rigid Target Surface and Rigid Body
• Modeling Rigid Bodies with Rigid Target Surfaces– You now define a rigid target surface (a set of target element
nodes and a single pilot node) to represent the rigid body.– Only one target element type is necessary.– Over-constraints can be easily detection and eliminated.– The size of DB, ESAVE and RST files are greatly reduced. The
storage for processing target elements is limited.– Improve robustness for rigid-rigid contact with large rotation.– In addition, a new POINT target segment has been added to the
existing segment sets of target elements TARGE169 and TARGE170. You can apply boundary conditions (point loads, displacement constraints, etc.) at any location for a rigid body.
© 2009 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary
Rigid Target Surface and Rigid Body
R11.0 Logic R12.0 Logic
© 2009 ANSYS, Inc. All rights reserved. 21 ANSYS, Inc. Proprietary
Energy- and Momentum-Conserving Contact
• Contact traction– Normal Pressure
algorithmic contact gap size (based on the relative velocity constraint)
– Friction Stresses
algorithmic slip increment
© 2009 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary
Energy- and Momentum-Conserving Contact
– It satisfies momentum and energy balance for the contact/target interface.
– It imposes additional constraints on relative velocities between contact and target surfaces.
– It predicts the duration of contact and the rebound velocities after separation more accurately
– It is compatible with both Newmark as well as HHT time integration methods
– It is be activated by setting KEYOPT(7)=4 for any 2D/3D contact element—CONTA171-178
– It activates Automatic time predictor• Auto,on & SOLCN,on,on
© 2009 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary
Application: vehicle dynamics model
© 2009 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary
http://images.pennnet.com/articles/os/thm/th_0510offpipe3.gif
Coulomb Friction Definition:Fixed/Tabular spec & UPF
• Tabular data for μ with up to two field dependencies TIME,TEMP,NPRE,SLDI,SLRVTB,FRIC,1,2,,ISO TBFIELD,TEMP,100.0
TBFIELD,SLDI,0.1 TBDATA,1,0.8 TBFIELD,SLDI,0.5 TBDATA,1,0.6
TBFIELD,TEMP,200.0 TBFIELD,SLDI,0.2 TBDATA,1,0.6TBFIELD,SLDI,0.7 TBDATA,1,0.5
• User programmable subroutine: – USERFRIC
• Use with 2D and 3D contact elements: – CONTA171 through CONTA178
• Use TB,FRIC with TBOPT=USER to invoke USERFRIC
• Interface to compute friction forces, contact tangent matrix and update history variables
• Example for isotropic Coulomb friction in 2D and 3D is included with ANSYS
© 2009 ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary
Thermal buckling of a pipeline
• A pipeline that is laid on the seabed will tend to expand because of the thermal expansion. If this motion is restrained (for example, by the friction of the seabed) then an axial compressive forces may cause column buckling. Imperfections in pipelines are a result of an uneven seabed, the laying process, or wave and current action.
• Various loads need to be considered:– Gravity load– Coulomb friction– Internal and external pressure– Temperature load
• ANSYS provides all necessary tools for such buckling analysis. In this example, transient analysis is done to simulate buckling
http://images.pennnet.com/articles/os/thm/th_0510offpipe2.gif
© 2009 ANSYS, Inc. All rights reserved. 26 ANSYS, Inc. Proprietary
Analysis load steps
• Load Step 1—Laying pipeline on ground– Apply gravity load
• Load Step 2—Geometric imperfections– Apply lateral displacements
• Load Step 3—Geometric imperfections– Release lateral displacement
• Load Step 4—Hydrostatic loads– Apply internal and external pressure
• Load Step 5—Buckling under thermal load– Apply temperature load--ramped with transient analysis
• Load Step 6—Steady state– Continue transient analysis
© 2009 ANSYS, Inc. All rights reserved. 27 ANSYS, Inc. Proprietary
Results--qualitative comparison
• Orthotropic (fixed) and tabular friction in ANSYS vs Anisotropic and pipe-soil friction in NAFEMS
ANSYS NAFEMS
© 2009 ANSYS, Inc. All rights reserved. 28 ANSYS, Inc. Proprietary
Brake Squeal Analysis
• Full nonlinear prestressed modal analysis– More accuracy, it includes prestress effect.– Expensive, It may encounter convergence
difficulties.– It can not model rigid body modes
• Partial prestresses modal analysis– It includes prestress effect.– Rigid body modes can be included in partial
solution phase.– Fast way to get unsymmetric matrix due to sliding.
• Linear non-presstresses modal analysis– Quick & fast method– Newton-Raphson iterations are not required.
Brake Assembly
© 2009 ANSYS, Inc. All rights reserved. 29 ANSYS, Inc. Proprietary
Comparing results obtained from all three methods
Linear non pre-stressed modal solve
Partial pre-stressed modal solve
Full nonlinear pre-stressed modal solve
Mode Real Imaginary Mode RealImagina
ry Mode Real Imaginary
18 0 4668.8 18 0 4667.6 18 0 4667.6
19 0 4769.6 19 0 4767 19 0 4767
20 0 5241.7 20 0 5241.4 20 0 5241.4
21 21.607 6474.3 21 21.902 6470.2 21 21.902 6470.2
22 -21.607 6474.3 22 -21.902 6470.2 22 -21.902 6470.2
23 0 6763.4 23 0 6763.2 23 0 6763.2
24 0 6765.6 24 0 6765.5 24 0 6765.5
25 0 6920.7 25 0 6919.6 25 0 6919.6
© 2009 ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary
FKN –Normal Contact stiffness
• V110: The default contact normal stiffness is affected by defined material properties, regardless of the material property status. If any material with any TB plasticity is defined in the database, the default contact normal stiffness is reduced by a factor of 100, even if the defined material property is not used.
• V120: The default contact normal stiffness is independent of TB plasticity.
© 2009 ANSYS, Inc. All rights reserved. 31 ANSYS, Inc. Proprietary
FKN –Normal Contact stiffness
• The change will affect many existing models ↓– We need to clearly document the change.– Users may need to modify the FKN to achieve better
convergence. – When KEYOPT(10)=0 is set, FKN/100 in V120 is equivalent to
FKN in V110– If KEYP(10)=1 is set, this change most likely with affect the
contact stiffness in first sub-step.– If KEYP(10)=2 is set, this change will affect the initial contact
stiffness in 1st iteration. – V110 logic can be recalled by issuing CNTR,REVISION,110.
© 2009 ANSYS, Inc. All rights reserved. 32 ANSYS, Inc. Proprietary
Auto Contact settings
• Command: CNCH,AUTO,RID1,RID2,RINC– No change in the meaning of individual keyop values.– Replaces only defaults values with recommended
settings.– Does not change the pre-defined settings (if KEYO
and real constants were pre-defined to a none zero values) except a few special cases.
– The recommended (optimal) settings should be based on the overall pair behaviors and pre-defined settings.
– Should be issued before the first solve and after contact pairs have been generated.
© 2009 ANSYS, Inc. All rights reserved. 33 ANSYS, Inc. Proprietary
Auto Key Option settings
KEYO Description Default Auto Setting
1 Selects DOF* Manual Auto set based on DOFs of underlying elements
2 Contact Algorithm Aug. Lagr. MPC for bonded or no-separation contact
Aug. Lagr. for rigid contact or debonding
4 Location of contactdetection point
Gauss Nodal point for MPC or Lagrange contact
5 CNOF/ICONT adjustment
No adjustment Auto CNOF if tiny gap exists
9 Effect of initialpenetration or gap
Include all Exclude all for MPC contact
10 Contact stiffnessupdate
Betweeniterations
No update for initial interference ramping option
© 2009 ANSYS, Inc. All rights reserved. 34 ANSYS, Inc. Proprietary
Auto Key Option settings
Real Cnst Description Default Auto Setting
FKN Normal penalty stiffness factor
1 Set to 5 if KEYOPT(9) = 2 (ramp initial penetration) and KEYOPT(10) > 0.
PINB Pinball Region Cut in half if spurious contact is detected or contact searching is slow.
TCC Thermal contact conductance
0 Highest conductivity of underlying element and overall model size.
ECC Electric contact conductance
0 Highest permitivity or lowest resistivity of underlying element and overall model size.
MCC Magnetic contact permeance
0 Highest emissivity of underlying element and overall model size.
© 2009 ANSYS, Inc. All rights reserved. 35 ANSYS, Inc. Proprietary
PADT bolted plate model
Dual core laptop, 4 GB ram, Sparse Solver
Default CNCH,auto
#iterations 142 55Max Eqv Stress 297877 297877
WALL 3158 1434
6 /GE /
March 19, 2009ETCoE Stress &Life
PADT Sliding Bolted J oint, Abaqus vs Ansys
Scale Factor 1.67
Scale Factor 1.5
Abaqus provides a means of providing contact stabilization which allows for convergence in fewer iterations (79 in Abaqus vs. 142 in Ansys)
The number of iterations required in Ansys is affected by the number of processors (this is not the case in Abaqus).
There is almost a 1% difference in peak Mises Stresses between the Ansys 1 & 2 cpusolution (this is not true in Abaqus)
Abaqus provides slightly better scalability than Ansys
3XCNCHECK,AUTOcommand Setskeyopt(10)=2
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