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ADAMS Methodology

Contact Modeling(Webex Walter Daniel, MSC.Software)

Benelux ADAMS User Meeting

Chris Verheul, SayField International

ADAMS Methodology

Contact Modeling(Webex Walter Daniel, MSC.Software)

Benelux ADAMS User Meeting

Chris Verheul, SayField International

ADAMS Contacts Topics

•Overview

•Theory and Parameters

•Geometry and Contacts

•Contacts Outputs

•Best Practices and Tips

•Contact Examples

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Contacts Overview

� Objectives:� Show the source and development of ADAMS

contacts

� Deeper understanding of ADAMS contacts

capabilities and settings

� IMPACT function description

� Analytical & ADAMS geometry vs. 3D

CAD geometry

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IMPACT Function

� Has been in ADAMS/Solver for many years

� IMPACT(dist, veloc, d_trig, k, e, c, d)

� Stiffening spring (e >1.0) that limits penetration

� User includes distance, velocity and trigger distance

� Basis for later contact development

� Still useful today

� BISTOP: for two sided contact

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General Solid Geometry Contact

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Robust and Accurate Polygon Interference Detection

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Contacts Theory and Parameters

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Contact Friction parameters

� Contacts: Velocity only based friction step-step function)

� Joints: Stick-slip friction law with max deforma-tion (brush model type)

� Note: low Vstiction � stiff damper

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Contacts and Geometry

� ADAMS analytical shapes

� ADAMS CSG solids

� Imported CAD solids

� Imported CAD shells

� Converted ADAMS geometries

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ADAMS CSG solids

� Full parametrisation is maintained !!

� Loss of analytical functionality � tricking

is OK� Set part inertia to

User Defined

� Add fake geometry

for contacts

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Converted ADAMS geometries

� Use RAPID + ADAMS/Solver to Export *.shl file from any geometry

� Advantages:

� Freeze accuracy of mesh used by

RAPID

� Visualise RAPID contacts mesh

� Speed up Solver start for multiple

runs

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Analytical Geometry + RAPID

� Since ADAMS 2010: more use of analytical geometry in contact with 3D solids

� Analytical solids are automatically detected

� Only pure sphere / cylinder / torus / box frustum allowed (no CSGs)

� Vast improvement of speed and accuracy

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Contact Outputs

� Pre-defined object measures for

Last_Run

� Function Measures

� Contact Tracks

� User Routines: cffsub + cnfsub

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Contact User Routines

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� CNFSub: Contact Normal

Force Sub.

� CFFSub: Contact Friction

Force Sub.

� Modification of Normal Force

& Contact Friction laws

� Additional Contact Data

Output: Pen, Vel, …

Best Practices and Tips

� Integrator & contact settings

� Geometry penetration

� Contact patch size

� Static equilibrium

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Integrator & contact settings

� Default GSTIFF integrator works

well

� Using Hmax may help

� Change to SI2 Formulation better

handles

speed changes

� Many contacts: consider HHT

integrator

� Test & tweak Mesh tolerance

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� Challenges in contact penetration

� Extremely thin objects in contact

� � additional contact geometry

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Static Equilibrium with Contacts

� Static Eq. can work with contacts

� Defaults parameters usually not OK

� Use small TLimit (transl. limit per

iteration)

� Likely increase Maxit (Max. iterations)

� Move parts to start with engaged

contacts !!

� Remember: speed based friction

only (i.e. on slopes)

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Example: Friction tester

� Solid geometry � analytical contact

� Plane – Sphere - Plane

� Completely contact balanced part: SI2 faster

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Example: Friction tester

Example: Magic Spin

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