contact_v12_1 (2)

© 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


Contact surface

Target surface

--- Free-end Point

2D contact: Free-end point

3D contact: Free-open Edge

Contact surface

Target surface


• 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



• 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.


Application: O-ring Seal


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.


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


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


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



• 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

http://pghintranet/prod_docu/Daily_Builds_DocBr/ans_cmd/Hlp_C_CNCHECK.html



• 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


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



• 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)

http://pghintranet/prod_docu/Daily_Builds_DocBr/ans_elem/Hlp_E_TARGE170.html



• 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)




• 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– 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.

http://pghintranet/prod_docu/Daily_Builds_DocBr/ans_cmd/Hlp_C_BETAD.html

http://pghintranet/prod_docu/Daily_Builds_DocBr/ans_cmd/Hlp_C_MP.html


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.



• 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.





R11.0 Logic R12.0 Logic


Energy- and Momentum-Conserving Contact

• Contact traction– Normal Pressure

algorithmic contact gap size (based on the relative velocity constraint)

– Friction Stresses

algorithmic slip increment


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


Application: vehicle dynamics model


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


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


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


Results--qualitative comparison

• Orthotropic (fixed) and tabular friction in ANSYS vs Anisotropic and pipe-soil friction in NAFEMS

ANSYS NAFEMS


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


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


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.

http://pghintranet:8000/prod_docu/daily_builds/ans_cmd/Hlp_C_TB.html


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.


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.


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


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.


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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