assembly modeling using ansys

© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Assembly Modeling Using ANSYS

Luc PontoireSimon Mendy

[email protected]

15/10/09

mailto:[email protected]�

© 2009 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Outline

• Overview• Connections

– CE (Constraint Equation)– CP (Coupling Equation)

• Contact• Bolt Pretension• Joints


Overview

• The CAE usage has completely changed over years. The CAE user used to realize calculations on simplified single parts.

• Today , calculations on detailed complete assemblies or subassemblies are common , thanks to the increase of computational power and code efficiency.

• It is now necessary to know the various possibilities of modeling interactions between these parts, in order to assess to best choice for the simulation


• Contact detection on motor assembly

• Contact detection allows easy setup linking of parts.• But do you do the best choice every time ?

Overview


Overview

• But do you the best choice every time ?• Let’s try to model a hinge…. ( penalty contact ?)

Pin

BaseEar

FrictionlessEar to BasePin to Base

BondedEar to Pin

1.3 hoursCPU Time


Overview

• Take a deep breath …• There is maybe something more appropriate in this

case

Pin

BaseEar

Revolute jointEar to BasePin to Base

Fixed jointEar to Pin

40CPU Time

New at R12


Outline


– Remote Point– CE (Constraint Equation)– CP (Coupling Equation)



Remote point

New Remote Point Feature

Scoping mechanism for remote BCs

Applied to face, edge, vertex of bodies

Promote remote BCs to a remote pointBenefits

Multiple boundary conditions scoped to a point

Avoid over-constraint conditionsApplications

Point mass, springs, joints, remote loads, moments

Remote Points

New at R12


Outline





Constraint Equations

• A constraint equation (CE) defines a linear relationship between nodal degrees of freedom.– If you couple two DOFs, their relationship is simply UX1 = UX2.– CE is a general form of coupling and allows you to write an

equation such as UX1 + 3.5*UX2 = 10.0.• You can define any number of CEs in a model.• Also, a CE can have any number of nodes and any combination

of DOFs. Its general form is:Coef1 * DOF1 + Coef2 * DOF2 + Coef3 * DOF3 + ... = Constant



Common applications:• Connecting dissimilar meshes• Connecting dissimilar element types• Creating rigid regions• Providing Interference fits



Connecting dissimilar meshes• If two meshed objects meet at a surface but their node patterns are

not the same, you can create CEs to connect them.• Easiest way to do this is with the CEINTF command (Preprocessor >

Coupling/Ceqn > Adjacent Regions).

– Requires nodes from one mesh (usually the finer mesh) and elements from the other mesh to be selected first.

– Automatically calculates all necessary coefficients and constants.

– For solid elements to solid elements, 2-D or 3-D.



Connecting dissimilar element types• If you need to connect element types with different DOF sets, you

may need to write CE’s to transfer loads from one to the other:– beams to solids or beams perpendicular to shells– shells to solids– etc.

• The CE command (Preprocessor > Coupling/Ceqn > Constraint Eqn) is typically used for such cases.



Creating rigid regions• CEs are often used to “lump” together portions of the model into rigid

regions.• Applying the load to one node (the prime node) will transfer appropriate

loads to all other nodes in the rigid region.• Use the CERIG command (or Preprocessor > Coupling/Ceqn > Rigid

Region).

Remark : WB doesn't CE but contact MPC to enforce rigid regions conditions

(discussed later)



Creating flexible regions• CEs are often used to “average” flexibility of portions of the model

towards a master point or node.• Applying the load to one node (the prime node) will transfer appropriate

loads to all other nodes in the “flexible” region.• Use the CERIG command (or Preprocessor > Coupling/Ceqn > Rigid

Region).


New Constraint Equation Manager Coupling of two or more remote points

Applications Use constraint equations to model

various joint/hinges

Easy idealization of complex boundaryconditions


New at R12.1


Outline





Coupling Equation

• A coupled set is a group of nodes coupled in one direction (i.e, one degree of freedom).

• A coupled equation is way of forcing degrees of freedom of a nodal group to have the same value.

• If you couple nodes 1 and 2 in the UX direction, the solver will calculate UX for node 1 and simply assign the same UX value to node 2.

DOF1 = DOF2 = DOF3 = DOF4 = DOF5 ...

• You can define any number of coupled sets in a model, but do not include the same DOF in more than one coupled set.


Common applications:• Enforcing symmetry• Frictionless interfaces• Pin joints

Coupling Equation


Enforcing Symmetry• Coupled DOF are often used to enforce translational or rotational

symmetry. This ensures that plane sections remain plane. For example:

– To model one sector of a disc (cyclic symmetry), couple the node pairs on the two symmetry edges in all DOF.

– To model a half “tooth” of a comb-type model (translational symmetry), couple the nodes on one edge in the X direction.

Symmetry BCon this edge

Couple thesenodes in UX DOF

Coupling Equation


Frictionless interfaces• A contact surface can be simulated using coupled DOF if all of the

following are true:– The surfaces are known to remain in contact– The analysis is geometrically linear (small deflections)– Friction is to be neglected– The node pattern is the same on both surfaces

• To do this, couple each pair of coincident nodes in the normal direction.

X

Y

Couple eachnode pair in UY

Coupling Equation


Cyclic Symmetry• A component or assembly is cyclically symmetric if it has a

correspondence in form or arrangement of parts (that is, repetitive patterns) centered around an axis.

• CPCYC allows modelling of cyclic symmetry• CPCYC, Lab, TOLER, KCN, DX, DY, DZ, KNONROT • By specifying a cylindrical coordinate system (KCN) and a wedge

spacing (DY) in degrees, ANSYS will find your wedge boundaries and couple them for you!

• Meshes have to match on both sides of the pattern

Coupling Equation : Cyclo-Symmetry


• Considering the following sector with a wedge spacing of 20° around Z with solid elements

CPCYC,ALL,,1,0,20,0 ! ALL allows to couple all 3 DDL : Ur, Uθ, Uz

EXEMPLE2

Coupling Equation : Cyclo-Symmetry


New Boundary Conditions Support Coupling of two or more faces

Cylindrical coordinates for displacement

Directional control for fixed rotation

Applications Use coupling to model various

joint/hinges

Apply rotation as an applied displacement

For 2D modeling, more granular control for rotations

Coupling Constraint

Fixed Rotation, Cylindrical Coordinates

New at R12

Coupling in Workbench


Outline





MPC Contact

• Limitations of existing bonded or no-separation contact ( with penalty or augmented lagrangian):

• Results depend on specified contact stiffness.• Multiple iterations are required to adjust penetration in order to

satisfy equilibrium even for small deformation problems.• Occasionally spurious natural frequencies can occur in modal

analysis.• Only translational DOFs apply

• Limitations of existing constraint tools (CERIG and RBE3)• Only suitable for small strain. • RBE3 only supports force constraints applied on the master

node, not displacements• RBE3 requires manual definition of weighing factors. MPC

surface constraints calculate weighing factors automatically


• MPC algorithm enforces compatibility at an interface using internally generated constraint equations

• Degrees of freedom of the contact nodes are eliminated– No normal or tangential stiffness required– For small deformation problem, no iteration is needed in solving system

equations– For large deformation problems, the MPC equations are updated during

each iteration– This method only applies to bonded or no-separation behaviors– Not applicable for symmetric contact pairs

• MPC is not available with node-to-node contact

MPC Contact


Outline





• You have an assembly with bolts• You want to take in consideration the prestress of

the model

Bolt Pretension


• Procedure to follow:– Model all the parts– Mesh it– Put the pretention bolt in 2 steps:

• First step: preload by load or adjustment• Second step: fix the pretension

– Put the other loads– Check the results

Bolt Pretension


Bolt Pretension

• How does ANSYS Apply bolt pretention?– Mesh bolt part– Choice of the section


• Creation of PRETS179 element:

– The goal of these elements is to create the prestress on the model by penetrate the two surfaces.

Bolt Pretension


• Check of the PRETS179 in our example:

Bolt Pretension


Input for the pretentionFirst step: loadSecond step: we lock

ResultWe can clearly see the penetration

due to the PRETS179 element

Bolt Pretension


Outline





Revolute Cylindrical

TranslationalSlot

Spherical

Planar

Universal

Joints


• The kinematic joints give the opportunity to directly impose kinematic constraints between bodies with MPC184 element.

• Example of a translational Joint:– The Constrained degrees of freedom are: UY, UZ, ROTX, ROTY, ROTZ .

Joints

Definition of a translational joint


• Setup of a kinematic joint:– Creation of two pilot nodes – Constraint equation between pilot node and Interfaces– Creation of element MPC 184

• WB automatically setup this for you

Joints

What the solver sees…..


Joints: Configure Tool

• Used to define initial position of the parts

• Can detect locking and redundancy

• Help to assemble unassembled models

• Defined with a prescribed value of angle or translational degree of freedom


• Benefits of joints– Easy to set up– Easy to model Engineer joints– Large deformations are supported– Advanced friction definition– Easy modification of bodies positions through

configure tool– Faster in most cases than penalty équivalents

Joints


Springs

• An elastic element ,used to store mechanical energy and regains original shape after force is removed

• Types:– Longitudinal – Torsional

• Inputs:– pre-load– stiffness – damping

• Can be scoped to part and/or ground

• No geometrical representation


Bushing Joint

• Has six degrees of freedom, three translations and three rotations

• Inputs:• Stiffness Coefficients • Dampening Coefficients

• Equivalent to having 6 independent springs for six DOF

• Used to introduce flexibilities to an over-constrained mechanism

© 2009 ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary

Assembly Modeling Using ANSYS

Luc PontoireSimon Mendy

[email protected]

15/10/09

Companion Samples







Companion Samples

cyclo symmetryTranslational coupling

Rigid regions versus flexible regions

Rotor/Stator and various modeling strategies

assembly modeling using ansys

Documents

large deformation

small deformation

solving system

tangential

symmetric

bolt pretension

base pin

constraint