Mech UCO Lect 06 Using APDL 1

Chapter 6Chapter 6

Using APDL in Mechanical 1

ANSYS Mechanical Advanced (Using Command Objects)

6-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

June 2009Inventory #002669

( g j )


Training ManualOverview• Using an understanding of Mechanical APDL acquired from the

previous chapters, this section will demonstrate how to use APDLcommands to access advanced functionality within Mechanical.

• Consider the APDL commands as a scripting language to:– Manipulate the mesh directly– Access advanced solver functionality– Access advanced postprocessing capabilities

• In this chapter, using “Commands” objects in the Geometry, RemoteIn this chapter, using Commands objects in the Geometry, RemotePoints, and Connections branches will be explored.




Training ManualA. Preliminaries• Before diving into the details of using “Commands” objects in

Mechanical, some general topics will be reviewed:– Solver unit system– Saving the Mechanical APDL database– Creating/deleting elements and other entities– Branches in the Outline Tree applicable to “Commands” objects




Training Manual… Unit System• APDL commands may involve the input of values that are unit-

dependent, such as piezoelectric coefficients. Because “Commands” objects are general, there is no mechanism to convert entered

f farguments of APDL commands if a user decides to change the active unit system from the “Units” menu.

• Consequently, it is strongly recommended to manually specify the l i i h D il i f h “A l i S i ”solver unit system in the Details view of the “Analysis Settings”

branch. “Solver Units: Manual” allows the user to specify the unit system for the Mechanical APDL solver

B tti “S l U it M l” ith “S l– By setting “Solver Units: Manual” with “SolverUnit System” set appropriately, the user-specifiedunit system will always by used by theMechanical APDL solver, regardless of what, gthe active unit system is in Mechanical

– This ensures that, if another user obtains theWorkbench project, their solution will be in the

i



correct unit system


Training Manual… Saving the Mechanical APDL database• Mechanical uses the file.rst result file for postprocessing. Most

postprocessing operations can be done in Mechanical using User Results, dicussed later. However, there may be unforeseen circumstances where a user may wish to postprocess results in Mechanical APDL– Postprocessing in Mechanical APDL was covered in an earlier chapter

• Because of this reason, it is highly recommended to save the Mechanical APDL database (file.db).– In the Details view of the “Analysis Settings”

b h t “S ANSYS db Y ”branch, set “Save ANSYS db: Yes”– The default is not to save file.db, so this must

be specified by the user




Training Manual… Creating/Deleting Elements• When elements or nodes are created or deleting using APDL

commands, please note that Mechanical will not be aware of these changes to the mesh.– If elements/nodes need to be created using APDL commands in a

“Commands” branch, postprocessing of these elements must be done inside of Mechanical APDLIf possible avoid deleting elements via APDL commands Consider– If possible, avoid deleting elements via APDL commands. Consider modifying the geometry/mesh to omit regions that are not of interest




Training Manual… Inserting Commands Objects• The following branches in the Outline tree allow

users to insert “Commands” objects:– Any Body under a “Geometry” branch– Any Remote Point under a “Remote Points” branch– Any Contact Region under “Connections” branch– Any Spot Weld under “Connections” branch– Any Joint under “Connections” branch– Any Spring under “Connections” branch– Any Beam under “Connections” branch– Directly under any analysis branch– Directly under the “Solution” branch

• The details of each of these options will be covered in this chapter




Training Manual… Supplementary Branches• Two branches that do not use “Commands” objects

directly but are quite helpful are the “Coordinate Systems” and the “Named Selections” branches– As will be discussed later, a Coordinate System can be

assigned a manual coordinate system ID number, which can be used in APDL commands. For example, this is useful for selecting a node near a coordinatethis is useful for selecting a node near a coordinate system or transforming results in a particular coordinate system in Mechanical APDL.

– Named Selections will appear as nodal or elementppcomponents in Mechanical APDL, where a “component” is a “group” of nodes or elements. This allows users to conveniently reference entities without having to worry about geometry node/element IDhaving to worry about geometry, node/element ID number, etc., and this method can be used for updated geometry as well.




Training Manual… Other Branches• Other branches, such as “Construction Geometry”,

“Virtual Topology”, “Symmetry”, “Mesh”, and “Solution Combination” branches, are not applicable

Cto APDL commands, so “Commands” objects are not inserted under those branches.




Training ManualB. Geometry Branch• A “Commands” object may be inserted under a

Body under the “Geometry” branch– Note that a “Commands” object cannot be inserted

directly under the “Geometry” branch or directly under a multibody part. It can only be inserted under a particular bodyPoint Masses are also not applicable for “Commands”– Point Masses are also not applicable for Commands objects

• The below lists some reasons to use a “Commands”• The below lists some reasons to use a Commands object associated with a Body:– Definition of composite materials

Solving other types of physics not native to– Solving other types of physics not native to Mechanical

– Adding nonlinear material models, such as creep or viscoelasticity or anisotropic hyperelasticity



y p yp y


Training Manual… Geometry Branch• Once a “Commands” object is inserted, APDL commands can be

pasted or typed into the text area.• The “Commands” object inserted under a Body can be used to

change the following element attributes for that Body:– Element type– Material Properties– Real Constants/Section Properties– Element Coordinate System

• Use the APDL parameter MATID to reference the element type, p ypmaterial property, real constant, or section property ID number.– The Element Coordinate System ID will typically be “0” (default) unless a

Coordinate System has been associated with that body




Training Manual… Geometry Branch: Element Type• As discussed in a previous chapter, changing element types is done

via the following two commands:– ET,MATID,…– KEYOPT,MATID,…

• Changing the element type allows a user to solve different physics or use a specialized element. However, the nodal connectivity must be the same between the original and target element type– The “Mesh” branch controls whether the element will be higher- or lower-

order. The Mesh Method also dictates what the element shape will be ( h h d l t t h d l)(e.g., hexahedral, tetrahedral)

• If any element-specific options (“keyoptions”) need to be set, use the KEYOPT command




Training Manual… Geometry Branch: Element Type• Caution concerning pyramid elements:– Note that while most higher-order elements have a pyramid shape, not all

lower-order elements have a pyramid shape. Hence, check the Elements R f t th t th l t d l t t t idReference to ensure that the selected element type supports pyramids.

For example, the structural 8-node pbrick element SOLID185 does not show a pyramid form, so a user should not attempt to use this element if pyramids are present

• Pyramids appear when a Mesh Method of “Hex-Dominant Meshing” or “MultiZone” (with Free Mesh Type set) is used

element if pyramids are present

“MultiZone” (with Free Mesh Type set) is used. • When pyramids are present, this also typically means that tetrahedrons are

present as well. Mechanical will generate tetrahedrons as a 10-node tet while pyramids and wedges are degenerate 20-node hex elements. Hence, in these

ill t th 10 d t t l t hil 1 ill f t



case, MATID will represent the 10-node tet elements while MATID+1 will refer to the 20-node hex element type ID.


Training Manual… Geometry Branch: Element Type• Note about Element Control:– In the Details view of the “Geometry” branch,

the user can change “Element Control”• By default, this is set to “Program Controlled,”

where the Mechanical APDL solver may changekeyoptions automatically prior to solution

• Currently applicable to structural elementsy pp• APDL Command is ETCONTROL• See the Commands Reference for ETCONTROL

for additional details




Training Manual… Geometry Branch: Element Type• Note about Element Control (continued):– During solution, the following will be printed in the “Solution Information”

branch:• If automatic resetting of keyoptions is not desired, be sure to set “Element

Control: Manual” in the Details view of the “Geometry” branch

Notice that certain keyoptions have been automatically reset by Mechanical APDL.

Alth h th t ti tti fAlthough the automatic setting of options is meant to aid the user in selecting appropriate element formulations, etc., the k l d bl t tknowledgeable user may not want keyoptions automatically overridden. In this case, set “Element Control: Manual” prior t l ti



to solution.


Training Manual… Geometry Branch: Material Properties• Deleting all existing material properties for the particular body is

done via the following commands:– MPDELE,Label,MATID– TBDELE,Label,MATID

• As a review, defining linear elastic material properties:– MP,Label,MATID,… (constant materials)– MPTEMP,… and MPDATA,Label,MATID,… (temperature-dependent)

• To define nonlinear material properties, use:– TB,Label,MATID,… to activate a particular material table, , , p– TBTEMP,… and TBDATA,… or TBPT,… to define the parameters

• In all of the above cases Label refers to the material property name• In all of the above cases, Label refers to the material property name. See the MP or TB help in the Commands Reference for details.




Training Manual… Geometry Branch: Material Properties• Material Properties are the only element attribute which allows

superimposing multiple definitions.• For example, to define density and elastic modulus, one would repeat

the MP command as follows:– MP,EX,MATID,10e6– MP,DENS,MATID,0.1/386.1

• To define bilinear isotropic plasticity and creep, one would do the following:– MP,EX,MATID,200e3

Defines linear elastic properties– MP,NUXY,MATID,0.3– TB,BISO,MATID,1– TBDATA,1,300,2e3

Defines linear elastic properties

Defines bilinear plasticity constants

– TB,CREEP,MATID,1,3,10– TBDATA,1,3.125E-14,5,0

• For nonlinear structural material combinations, see “Section 2.6

Defines creep law and its coefficients



o o ea st uctu a ate a co b at o s, see Sect o 6Material Model Combinations” in the Elements Reference for details


Training Manual… Geometry Branch: Material Properties• Points to keep in mind:– When adding creep material properties via TB,CREEP,MATID, note that

Mechanical, by default, will not request creep strains to be saved. By ddi O S C i “C d ” bj t d th l iadding OUTRES,EPCR,ALL in a “Commands” object under the analysis

branch (discussed later), one can ensure that creep strains are stored for postprocessing. (Note that, in the specific case of creep, RATE,ON must also be added in the “Commands” object under the analysis branch.)j y )

– For user-defined materials with TB,USER,MATID or user-defined creep with TB,CREEP,MATID,,,100, state variables are often defined via TB,STATE,MATID. As with the above case, the user should add

i “C d ” bj t d th l i b h tOUTRES,SVAR,ALL in a “Commands” object under the analysis branch to ensure that state variables are stored in the result file for postprocessing.




Training Manual… Geometry Branch: Section Properties• The Elements Reference in the Mechanical APDL help system

describes whether a particular element uses real constants or section properties– In either case, the APDL scalar parameter MATID can be used to reference

the real constant and section property ID number of that particular Body.• Deleting existing real constants or section properties:– RDELE,MATID– SDELETE,MATID

• Recall the definition of a new real constant or section property:– R,ID,…– SECTYPE,ID,… and SECDATA,…

• Modification of a real constant:– RMODIF,ID,…

– (No equivalent functionality is present for sections. One must delete an existing section and define a new section instead.)




Training Manual… Geometry Branch: Section Properties• Tip for composite (layered) elements:– Composite elements define the material properties for each layer via real

constants or section properties. There is no need to redefine or modify th t i l ID b i t d ith th B dthe material ID number associated with the Body.

• Note, however, that structural damping (MP,DAMP) and reference temperature for thermal strains (MP,REFT) are defined via the material ID number, not per layer.y

– For composite elements, one must define the material ID numbers used in each layer within the Commands object

• Use material ID numbers that are larger than the number of parts present when d fi i th t i l ID b f h ldefining the material ID number for each layer

• The actual material property definition used in layers only needs to be performed once in the event that multiple bodies have composite definition

– From the Workbench Project Schematic, link the “Model” to aFrom the Workbench Project Schematic, link the Model to a “Mechanical APDL” system. Then, verify the composite definition inside of Mechanical APDL using /ESHAPE,1 to visualize the 3D cross-section, including layeres.




Training ManualC. Remote Points• Remote Points are an integral part of many features

in Mechanical:– Point Mass– Joints– Springs– Moment– Remote Force– Remote Displacement

• Each Remote Point has an (x, y, z) location and is ( y )scoped to a geometric entity. One can think of Remote Points as “tying” nodes on a geometric entity to the remote point location, either with a ‘deformable’ or ‘rigid’ behavior.

• Understanding how Remote Points work allows users to take advantage of them with “Commands”



objects


Training Manual… Uses for Remote Points• The below are some reasons why one may wish to use “Commands”

objects with Remote Points:– Reduce the interface nodes for creation of CMS superelements for more

efficient system-level analyses– Define monitor locations, such as the average deformation of a given

surfaceC t MNF fil f ith Ad /Fl †– Create an MNF file for use with Adams/Flex†



† Adams is developed by and is a registered trademark of MSC Software


Training Manual… Remote Point Representation• A Remote Point consists of contact and target elements– The target element is a 1-node element, representing the remote point

location– The contact elements are associated with the vertex, edge, or surface that

is scoped in the Remote Point Definition – This is an example of surface-based constraints using contact elements.

For details see Chapter 9 of the Contact Technology GuideFor details, see Chapter 9 of the Contact Technology Guide.

TARGE170 Element (circled)



CONTA174 Elements (purple)


Training Manual… Remote Point Behavior• To better understand the “deformable” and “rigid” behavior, consider

the simple 2D plate with a remote force (via remote point) applied to the center hole: Deformable behavior: circle does not retain shapep



Rigid behavior: circle maintains shape


Training Manual… Remote Points• Insert a “Commands” object under a Remote Point:– The parameter _npilot reflects the node ID number. One can define a

new parameter to keep track of this node ID number for later use, such as d fi i t DOFdefining master DOF:

MY_INTERFACE_NODE = _npilotm,MY_INTERFACE_NODE,all

The parameter TID is the target element’s element type ID number For– The parameter TID is the target element s element type ID number. For example, if one may wish to constrain only UX and UY DOF rather than all 6 (or all 3, if 2D), one can use the following command:

keyopt,TID,4,11




Training Manual… Remote Points• Tips on using APDL with Remote Points:– Keep in mind that APDL parameters are persistent throughout the

Mechanical APDL run. Hence, per the previous slide, the parameter C O ill h th l f th d ID b dMY_INTERFACE_NODE will have the value of the node ID number and can

be used in postprocessing as well.– Most functionality with regards to Remote Points, such as load

application postprocessing displacements or reaction forcesapplication, postprocessing displacements or reaction forces, spring/joint definition, are already built into the Mechanical GUI. Hence, prior to using “Commands” objects with Remote Points, consider whether or not the sought capability already exists within Mechanical.




Training ManualD. Contact Regions• “Commands” objects may also be inserted

under any Contact Region• There are many situations where APDL

commands can access advanced controls:– Definition of debonding/delamination with CZM– Use of fluid pressure-penetration loading– Near-field contact radiation and convection– Definition of multiphysics contact (coupled

thermal-electric-structural) with frictional heat tigeneration

– Inclusion of orthotropic friction or dynamic coefficient of friction, along with cohesionChanging contact detection locations– Changing contact detection locations…other options available as well!




Training Manual… Contact Regions• Most of the commonly-used contact options are present in the

Mechanical GUI.

• However, ANSYS contact elements have a plethora of options to allow users to simulate many different scenarios

• To understand the various contact capabilities that are available, p ,refer to the following sections in the Help documentation:– Contact Technology Guide > Chapter 3: Surface-to-Surface Contact– Contact Technology Guide > Chapter 7: Multiphysics Contactgy p p y– Contact Technology Guide > Chapter 12: Debonding




Training Manual… Contact Regions• Insert a “Commands” object of the Contact Region of interest:– The parameters CID and TID are used to refer to the contact and target

element type IDs, respectively.– To apply fluid pressure-penetration loading where pressure loading

occurs when a contact status opens, use the following:esel,s,type,,CIDsfe all 1 pres 120sfe,all,1,pres,,120allsel,all

– To change the contact detection type to “normal from target”, usekeyopt,CID,4,2keyopt,CID,4,2




Training Manual… Contact Regions• Tips on Contact Regions and APDL:– Because Contact Regions are not included in Named Selections, to

reference a contact region for later use, use either of the following:• Define a parameter(s) with the CID (and TID) values• Create an element component (group) for later use via ESEL and CM commands

– Understand the situations where symmetric and asymmetric contact pairs exist If “Behavior: Symmetric” is set for “Pure Penalty” orpairs exist. If Behavior: Symmetric is set for Pure Penalty or “Augmented Lagrange” algorithms, ensure that any change real constants or material properties are reflected for both CID and TID.




Training ManualE. Joints• Typical uses of “Commands” objects inserted

for Joints include the following:– Definition of Screw Joints and other joints not

available in the Mechanical GUI– Incorporation of nonlinear stiffness, nonlinear

damping, and/or Coulomb friction1

Obt i i d t il d t l j i t– Obtaining more detailed control over joint behavior, such as applying rotational stops and locks on a General Joint



1 Note that, at release 12.0, the hysteretic friction capability of Joints (MPC184) has been removed in favor of the Coulomb friction model.


Training Manual… Joints• Many sophisticated joint functionality are present in Mechanical:– Torsional stiffness and damping for Cylindrical and Revolute Joints– Bushing Joint, which can be thought of as a General Joint where a user

may input stiffness and damping relationships between all 6 relative DOF– Joint stops and locks for many joint types

• Prior to implementing “Commands” objects for Joints, review the Help system to ensure that the capability is not already present:– “Mechanical (formerly Simulation) > Using the Mechanical Application

Features > Geometry in the Mechanical Application > Joints”




Training Manual… Joints• If it is deemed necessary to include a “Commands” object to access

functionality via APDL commands, review the following Help manual:– “Multibody Analysis Guide > Chapter 2. Modeling in a Multibody

Simulation > Section 2.3 Connecting Multibody Components with Joint Elements”

– “Elements Reference > Element Library > MPC184”

• The element type used for joints is MPC184. Note that the joint (MPC184 element) is connected to the solid model via Remote Points.– If the connection between the joint and solid part needs to be modified,

define a Remote Point with a “Commands” object, as discussed in an earlier section of this chapter.Only insert a “Commands” object under a “Joint” branch if the joint– Only insert a Commands object under a Joint branch if the joint property will be modified. This includes constraining relative DOF, adding stops/locks, or defining joint “material properties”




Training Manual… Joints• The APDL parameter “_jid” refers to the element type, material, real

constant, and section ID number of the MPC184 element:– To define nonlinear stiffness for a Translational Joint:

tb,join,_JID,1,4,jnsatbpt,,U1,F1

• …repeat (Each TBPT command defines pair of displacements Ui and forces Fi)T dd t ti l t f l ti Z t ti f G l J i t b t– To add a rotational stop for relative Z-rotation for a General Joint between -45° and 45°:

secstop,6,-acos(-1)/2,acos(-1)/2

• (Notice input is in radians, and “6” refers to relative DOF 6 or ROTZ)(Notice input is in radians, and 6 refers to relative DOF 6 or ROTZ)




Training Manual… Joints• Tips on using APDL commands with Joints:– The SECTYPE command is required to define the joint behavior and is

typically defined by Mechanical. Hence, to add stops/locks, one should t th S C d if it l d d fi d b M h i l b tnot use the SECTYPE command if it already defined by Mechanical, but

one can just add SECLOCK and SECSTOP commands, as the particular joint ID will already be “active”.

– Not all Joints support stops locks and joint “material” definition– Not all Joints support stops, locks, and joint material definition (friction, stiffness, damping) – for example, the Spherical Joint supports neither. Consult the Elements Reference for details on each Joint type prior to using APDL commands to ensure that the feature is available for that joint type

– Modifying the local coordinate system which defines the orientation of the relative joint DOF is highly discouraged since Mechanical will incorrectly report results for that jointincorrectly report results for that joint.

– The DJ command applies joint constraints while the FJ command applies loading to the joints. However, when possible, use of “Joint Loads” in Mechanical is recommended over using APDL commands, as the former



g ,is much easier to implement.


Training ManualF. Springs and Beams• In addition to Contact Regions and Joints, the

“Connections” branch allows use of Springs and Beams– Springs are longitudinal springs and/or

dampers with preload capabilities– Beams have circular cross-sections and are

meant to represent structural connections thatmeant to represent structural connections that carry bending loads

• As with Joints, Springs and Beams are connected to 2D or 3D bodies via Remoteconnected to 2D or 3D bodies via Remote Points– If a Remote Point is not explicitly used, the

underlying finite element representation is stillunderlying finite element representation is still using surface-based constraints of contact and target elements, as elaborated in the Remote Points section of this chapter




Training Manual… Springs and Beams• A Spring is represented with a COMBIN14 element, and a Beam is

modeled with a single BEAM188 element.– Line Bodies are also represented with BEAM188 elements, and the two

should not be confused with each other.• When modeling beam structures, use line bodies (number of beam elements

per line body is controlled via Mesh Sizing).• To model a connection that can carry bending loads a Beam connection mayTo model a connection that can carry bending loads, a Beam connection may

be applicable.

• Using “Commands” objects for Springs and Beams is not as common as its usage in other branches, although a few reasons for g , gdoing so are listed below:– Changing the longitudinal Spring to a torsional one via keyoption– Replacing the Beam with a rigid beam (MPC184)– Replacing the Spring with nonlinear or other types of spring elements




Training Manual… Springs and Beams• For Springs, after inserting a “Commands” object, use the parameter _sid to reference the spring’s element type, material, and real constant ID number– Example of changing to a torsional spring:keyopt,_SID,3,1

– Note that ‘stiffness’ and ‘force’ will refer to ‘torsional stiffness’ and ‘moment’

– Springs do not use a section ID, so the section ID number will be “1”• For Beams, the parameter _bid refers to the beam’s element type,

material, real constant, and section ID number– To replace the deformable beam with a rigid one, use the following:mpdele,all,_BIDet,_BID,184,1,0

– Note that the Beam has material properties, so density and thermal expansion may be used, if present. To prevent these materials from being used MPDELE is included in the above example to delete the



being used, MPDELE is included in the above example to delete the material definition for _BID (beam’s material ID).


Training Manual… Springs and Beams• 1D springs may be required for an analysis, where the stiffness in a

particular direction is known beforehand.– 1D springs should be modeled with COMBIN14 and KEYOPT(2)=1 through

6. The best practice is to model 1D springs with coincident nodes.– Because Springs in Mechanical are longitudinal springs, they must have

finite length. Hence, Springs should not be converted to 1D springs.T t 1D i b t b di d fi 2 R t P i t t th– To create 1D springs between bodies, define 2 Remote Points at the same location but scoped to the 2 bodies’ geometric entities. Add “Commands” objects under both Remote Points to record the pilot node ID number as parameters. Using “Commands” object in the analysis p g j ybranch (described shortly), 1D spring(s) can be defined using the two pilot node locations.

– Springs operate in the nodal coordinate system. Hence, if Remote Points d th t th f d di t t thare used, ensure that the referenced coordinate systems are the same.



Date post:	28-Dec-2015
Category:	Documents
Upload:	percy-romero-murillo
View:	131 times
Download:	3 times

Mech UCO Lect 06 Using APDL 1

Documents