2-intro_truss_1lt+2th

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Practical Introduction to FEM-Software 1

Dipl.-Ing. U. Navrath

Autumn 2006

Introduction and truss systems

Hohenzollern Bridge, Cologne, by Frank Puettbach, Solingen


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FEM-Lab I, Autumn 2006 2

1 Introduction

ANSYS is a large and complex program with many different capabilities. Learning the pro-gram and documentation of the various features can be a significant challenge for the user.This handout is intended to assist the new ANSYS user get started. There are a number ofsites on the web where you can get information on ANSYS (do a search with www.google.com).A few tutorials are listed below.

University of Alberta : http://www.mece.ualberta.ca/tutorials/ansys/

University of Kentucky: http://www.engr.uky.edu/jrbake01/ansystutor.html

Cornell University: http://instruct1.cit.cornell.edu/courses/ansys/

University of Washington: http://www.aa.washington.edu/courses/aa430/gradystutorials/toc.html

University of Darmstadt: http://www.tu-darmstadt.de/hrz/software/fem/ansys.tud

ANSYS Corp.: http://www.ansys.com

CADFEM: http://www.cadfem.de

This section describes the general work with ANSYS. ANSYS finite element analysissoftware enables engineers to perform the following tasks:

Build computer models or transfer CAD models of structures, products, components,or systems.

Apply operating loads or other design performance conditions.

Study physical responses, such as stress levels, temperature distributions, or electro-magnetic fields.

Optimise a design early in the development process to reduce production costs.

Do prototype testing in environments where otherwise it would be undesirable or im-possible (for example, biomedical applications).

1.1 Graphical User Interface

The ANSYS program has a comprehensivegraphical user interface(GUI) that gives users easy,interactive access to program functions, commands, documentation, and reference material.An intuitive menu system helps users navigate through the ANSYS program. Users can inputdata using a mouse, a keyboard, or a combination of both.

You start ANSYS on Windows System usually overSTART>Programme>ANSYSxx>ANSYS Product Launcher

Double click left mouse button on ANSYS Product Launcher. Chose a product (the amount ofproducts depends on the available licenses), for the lab we will work with the product ANSYSUniversity Advanced. Switch to File Management Card and enter the Working directory:C:/fem (local drive!!!) and the Initial jobname. Now you can start ANSYS by pressing therun botton.


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Fig. 1: Configure ANSYS 9.0 Window (Product Launcher)

In the Release 9.0 the Ansys GUI consist of a main frame with five main regions:

Utility Menu

Comand Line or Input Window

Toolbar

Main Menu

Graphics Window

Additional a separate output window will be opened by the program. The output windowlists text output from the program in response to every function or comand executed. It isusually positioned behind the main frameand can be raised to the front when necessary.

1.2 Direct Command input and input files

As an alternative to the graphical user interface described above, the ANSYS commands canbe input directly. This can be done either directly with the command input window or bycreating an input file using notepad or some other text editor and reading it into ANSYS.Also, as mentioned above, these commands are recorded in the filename.logfile. This file canbe edited to correct errors, and used to restart the run without repeating the operations thatproduced the filename.log file. Thus it is useful to be familiar with direct input commands.

An overview of a general input file format is as follows. The ANSYS commands are on theleft, and the comments following the ! are for your information and are not entered. (note:ANSYS uses a ! for comments. If you have a comment you would like to include within an


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Fig. 2: Ansys 9.0 Main-Frame, with the five main regions

input file, precede it with an exclamation point. The comment will then extend to the end ofthe line).

/clear ! clear RAM database from ANSYS

/prep7 ! The prep7 module (the preprocessor is for problem definition! (just like clicking PREPROCESSOR in the menu)

/input,[filename] ! execute the file that you have created

/pbc, [option], [option] ! show boundary conditions

/psf, [option], [option] ! show loading

/et,[option], [option] ... ! define a element type

/mp,[option], [option] ... ! define a material

.

.

.

eplot ! plot elements (mesh)

aplot ! plot areas

lplot ! plot lines


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nplot ! plot nodes

finish ! exit the prep7 preprocessor.

/solu ! enter the solution processor

! (just like clicking SOLUTION in the menu)

d, [option], [option] ... ! define BCs

.

.

.

solve ! initiate the solution

finish ! exit the solution processor

/post1 ! enter the post-processor, used to look at the results

plnsol,[option], [option] ! a number of commands! are used here to view the results

finish ! exits the post processor

/eof ! end of file stops the reading from the file at this position

This example is meant only to convey the form most of your input files will have. Itshould not actually be entered, as it wouldnt do anything useful (it doesnt supply ANSYSwith any model geometry or constraints). An input file is always read from beginning toend, and the three stages of solving an ANSYS model must be adhered to at some point inthe solution process. These are: 1) PREPROCESSOR (PREP7) 2) SOLUTION (SOLU) 3)POSTPROCESSOR (POST1)

As can be seen from the input file listing above, each module is entered, module spe-cific commands are executed, and then each module is exited. This is important becauseeach module only recognises certain commands. For example, attempting to use the plnsolcommand while in the PREPROCESSOR module will produce an error (not a recognisedPREP7 command) whereas the same command would produce no error when used withinthe appropriate POSTPROCESSOR module. Learning which commands are appropriate forwhich ANSYS module is a matter of experience. By working the examples below you will gaininsight as to how to use these commands. Another thing to note about this general input fileis that all three modes are entered, whereas in an actual input file this is not usually the case.You will often find it easiest to define only model geometry, characteristics and constraintswith the input file (these are all PREPROCESSOR commands). Then run the solution and

review the results manually using the command input window. The reason for this is thatANSYS will attempt to continue with an input file even if errors are found. This can wastetime if you realise that you made a mistake in the model definition. The best approach is toalways make sure that you have the model properly defined and constrained before proceedingto the solution. Much of the ANSYS documentation can be obtained on-line. To get help onany command, typehelp,{command}, example: help, ameshAnother option to get help is to select HELP on the menu bar at the top of the screen. Hereyou can read about the commands, theory, and element types used by ANSYS.

The ANSYS commands below are some of the most widely and commonly used ANSYScommands. These and other commands will be used in the examples given below.

k ! define a keypoint


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l ! define a line

a ! define an area

n ! define a node

e ! define elements

nplot ! plot nodes

kplot ! plot keypoints

aplot ! plot areas

eplot ! plot elements

lplot ! plot lines

nlist ! list nodes

klist ! list keypoints

alist ! list areas

elist ! list elements

llist ! list lines

prdisp ! list displacements

pldisp ! plot displacements

prnsol ! list nodal solution

plnsol ! plot nodal solution

lmesh ! mesh lines (PREP7 command)

emesh ! mesh elements (PREP7 command)

amesh ! mesh areas (PREP7 command)

etable ! generate element table (POST1 command)

pretab ! print a list of etable results (POST1)

pletab ! plot etable results (POST1)

/pbc ! show boundary conditions

/psf ! show applied loads

/pnum ! apply nodal numbering

/show ! direct output to a device

/zoom ! zoom in or out

1.3 Element Library

This chapter gives an overview of elements, in numerical order. Descriptions common to

several elements appear in separate sections of General Element Features and are referencedwhere applicable.

For more details use the help command, for example: help, plane42The details of the element should also be reviewed in the ANSYS, Inc. Theory Reference,

which explains how the element input items (such as the real constants, material properties,KEYOPT switches, etc.) are used to produce the element output.


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Element Library

LINK1 2-D Spar (or Truss)PLANE2 2-D 6-Node Triangular Structural SolidBEAM3 2-D Elastic BeamBEAM4 3-D Elastic BeamSOLID5 3-D Coupled-Field SolidCOMBIN7 Revolute JointLINK8 3-D Spar (or Truss)INFIN9 2-D Infinite BoundaryLINK10 Tension- or Compression-only SparLINK11 Linear ActuatorCONTAC12 2-D Point-to-Point Contact

PLANE13 2-D Coupled-Field SolidCOMBIN14 Spring-DamperPIPE16 Elastic Straight PipePIPE17 Elastic Pipe TeePIPE18 Elastic Curved Pipe (Elbow)PIPE20 Plastic Straight PipeMASS21 Structural MassBEAM23 2-D Plastic BeamBEAM24 3-D Thin-walled BeamPLANE25 Axisymmetric-Harmonic 4-Node Structural SolidCONTAC26 2-D Point-to-Ground Contact

MATRIX27 Stiffness, Damping, or Mass MatrixSHELL28 Shear/Twist PanelFLUID29 2-D Acoustic FluidFLUID30 3-D Acoustic FluidLINK31 Radiation LinkLINK32 2-D Conduction BarLINK33 3-D Conduction BarLINK34 Convection LinkPLANE35 2-D 6-Node Triangular Thermal SolidSOURC36 Current SourceCOMBIN37 Control

FLUID38 Dynamic Fluid CouplingCOMBIN39 Nonlinear SpringCOMBIN40 CombinationSHELL41 Membrane ShellPLANE42 2-D Structural SolidSHELL43 4-Node Plastic Large Strain ShellBEAM44 3-D Elastic Tapered Unsymmetric BeamSOLID45 3-D Structural SolidSOLID46 3-D 8-Node Layered Structural SolidINFIN47 3-D Infinite BoundaryCONTAC48 2-D Point-to-Surface Contact

continued on next page


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Element Library

CONTAC49 3-D Point-to-Surface ContactMATRIX50 Superelement (or Substructure)SHELL51 Axisymmetric Structural ShellCONTAC52 3-D Point-to-Point ContactPLANE53 2-D 8-Node Magnetic SolidBEAM54 2-D Elastic Tapered Unsymmetric BeamPLANE55 2-D Thermal SolidHYPER56 2-D 4-Node Mixed u-P Hyperelastic SolidSHELL57 Thermal ShellHYPER58 3-D 8-Node Mixed u-P Hyperelastic SolidPIPE59 Immersed Pipe or Cable

PIPE60 Plastic Curved Pipe (Elbow)SHELL61 Axisymmetric-Harmonic Structural ShellSOLID62 3-D Magneto-Structural SolidSHELL63 Elastic ShellSOLID64 3-D Anisotropic Structural SolidSOLID65 3-D Reinforced Concrete SolidPLANE67 2-D Thermal-Electric SolidLINK68 Thermal-Electric LineSOLID69 3-D Thermal-Electric SolidSOLID70 3-D Thermal SolidMASS71 Thermal Mass

HYPER74 2-D 8-Node Mixed u-P Hyperelastic SolidPLANE75 Axisymmetric-Harmonic 4-Node Thermal SolidPLANE77 2-D 8-Node Thermal SolidPLANE78 Axisymmetric-Harmonic 8-Node Thermal SolidFLUID79 2-D Contained FluidFLUID80 3-D Contained FluidFLUID81 Axisymmetric-Harmonic Contained FluidPLANE82 2-D 8-Node Structural SolidPLANE83 Axisymmetric-Harmonic 8-Node Structural SolidHYPER84 2-D Hyperelastic SolidHYPER86 3-D Hyperelastic Solid

SOLID87 3-D 10-Node Tetrahedral Thermal SolidVISCO88 2-D 8-Node Viscoelastic SolidVISCO89 3-D 20-Node Viscoelastic SolidSOLID90 3-D 20-Node Thermal SolidSHELL91 Nonlinear Layered Structural ShellSOLID92 3-D 10-Node Tetrahedral Structural SolidSHELL93 8-Node Structural ShellCIRCU94 Piezoelectric CircuitSOLID95 3-D 20-Node Structural SolidSOLID96 3-D Magnetic Scalar SolidSOLID97 3-D Magnetic Solid



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Element Library

SOLID98 Tetrahedral Coupled-Field SolidSHELL99 Linear Layered Structural ShellVISCO106 2-D 4-Node Large Strain SolidVISCO107 3-D 8-Node Large Strain SolidVISCO108 2-D 8-Node Large Strain SolidTRANS109 2-D Electromechanical SolidINFIN110 2-D Infinite SolidINFIN111 3-D Infinite SolidINTER115 3-D Magnetic InterfaceFLUID116 Thermal-Fluid PipeSOLID117 3-D 20-Node Magnetic Solid

HF118 2-D High-Frequency Quadrilateral SolidHF119 3-D High-Frequency Tetrahedral SolidHF120 3-D High-Frequency Brick SolidPLANE121 2-D 8-Node Electrostatic SolidSOLID122 3-D 20-Node Electrostatic SolidSOLID123 3-D 10-Node Tetrahedral Electrostatic SolidCIRCU124 General CircuitCIRCU125 Common or Zener DiodeTRANS126 Electro-mechanical TransducerSOLID127 3-D Tetrahedral Electrostatic Solid p-ElementSOLID128 3-D Brick Electrostatic Solid p-Element

FLUID129 2-D Infinite AcousticFLUID130 3-D Infinite AcousticSHELL131 4 Node Layered Thermal ShellSHELL132 8 Node Layered Thermal ShellFLUID141 2-D Fluid-ThermalFLUID142 3-D Fluid-ThermalSHELL143 4-Node Plastic Small Strain ShellROM144 Electrostatic-Structural ROMPLANE145 2-D Quadrilateral Structural Solid p-ElementPLANE146 2-D Triangular Structural Solid p-ElementSOLID147 3-D Brick Structural Solid p-Element

SOLID148 3-D Tetrahedral Structural Solid p-ElementSHELL150 8-Node Structural Shell p-ElementSURF151 2-D Thermal Surface EffectSURF152 3-D Thermal Surface EffectSURF153 2-D Structural Surface EffectSURF154 3-D Structural Surface EffectSHELL157 Thermal-Electric ShellHYPER158 3-D 10-Node Tetrahedral Mixed u-P Hyperelastic SolidLINK160 Explicit 3-D Spar (or Truss)BEAM161 Explicit 3-D BeamPLANE162 Explicit 2-D Structural Solid



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Element Library

SHELL163 Explicit Thin Structural ShellSOLID164 Explicit 3-D Structural SolidCOMBI165 Explicit Spring-DamperMASS166 Explicit 3-D Structural MassLINK167 Explicit Tension-Only SparTARGE169 2-D Target SegmentTARGE170 3-D Target SegmentCONTA171 2-D 2-Node Surface-to-Surface ContactCONTA172 2-D 3-Node Surface-to-Surface ContactCONTA173 3-D 4-Node Surface-to-Surface ContactCONTA174 3-D 8-Node Surface-to-Surface Contact

CONTA175 2-D/3-D Point-to-Surface and Edge-to-Surface ContactCONTA178 3-D Node-to-Node ContactPRETS179 2D/3D Pre-tensionLINK180 3-D Finite Strain Spar (or Truss)SHELL181 Finite Strain Layered ShellPLANE182 2-D 4-Node Structural SolidPLANE183 2-D 8-Node Structural SolidMPC184 Multi-Point Constraint Rigid Link and Rigid BeamSOLID185 3-D 8-Node Structural SolidSOLID186 3-D 20-Node Structural SolidSOLID187 3-D 10-Node Tetrahedral Structural Solid

BEAM188 3-D Linear Finite Strain BeamBEAM189 3-D Quadratic Finite Strain BeamSOLID191 3-D 20-Node Layered Structural SolidINTER192 2-D 4-Node Linear InterfaceINTER193 2-D 6-Node Quadratic InterfaceINTER194 3-D 16-Node Quadratic InterfaceINTER195 3-D 8-Node Linear InterfaceMESH200 Meshing Facet


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2 Truss Systems

(1000,0,0) (2000,0,0)

F

F_x=1000

(1000,1000,0)

F_y=1500

(0,0,0) x

y

Fig.3: Framework

Analyse how the given framework deforms under the force F. Therefor create the frame-work as shown in the figure and calculate the resulting stress in each truss. Then calculatethe new length of each truss.

2.1 Listing

FINISH

/clear

/TITLE, Simple Truss

/FILNAM,Problem_1a

/PREP7 ! start Pre-processor

ET, 1, link1 ! define Element type

MP,ex,1,210000 ! E-Modul 210 000 N/mm2

R,1,2000 ! Cross-section Area 2000 mm2

N,1,0,0,0 ! define the nodesN,2,1000,0,0

N,3,2000,0,0

N,4,1000,1000,0

NPLOT,1 ! plot the nodes with numbers

E, 1, 4 ! define elements between nodes

E, 2, 4

E, 3, 4

FINISH ! finish Pre-processor

SAVE,Problem_1a, db ! save the Problem

/SOLU ! start solution processor

D,1,all,0 ! define boundary conditions on nodes


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D,2,all,0 0

D,3,all,0

F,4,fx,1000 ! define forces on nodes

F,4,fy,1500

SOLVE ! solve the problem

FINISH ! finish solver

/POST1 ! start Post-processor

PLDISP,1 ! Plot displacements

PRNS,U,COMP ! list displacements

!******************************************************************

ETABLE,SAXL_I,LS, 1 ! write results in a table

ETABLE,SAXL_J,LS, 1

PLLS,SAXL_I,SAXL_J,1,0 ! plot data

Lx=Nx(4)+Ux(4) ! calculate the new length of the spars

Ly=Ny(4)+Uy(4)

L1=sqrt(Lx*Lx+Ly*Ly)

L2=sqrt(Ux(4)*Ux(4)+Ly*Ly)

L3=sqrt((Nx(3)-Lx)*(Nx(3)-Lx)+Ly*Ly)

*status all ! list all variables to the output window

FINI ! finish Post-processing

2.2 Results

Fig.4: Visualisation of the result

rod 1 rod 2 rod 3

Length of undeformed truss 1414,21356 1000,00000 1414,21356

Length of deformed truss 1414,21742 1000,00209 1414,21266


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2.3 Exercise

Calculate the displacement of the nodes for the following simple truss system. For the case

a) a displacement ofuy =4mm in the y-direction is applied. Instead of the displacementapply in case b) a force offy = 100Nin the y-direction.

1

5

432

l

3 4

l

a)

uy=4mm

b)

y

x

21

diameter of a rod: 10mm

l: 500mm

= /3

fy=100N

cross section area: 78.5mm^2

Youngs Modulus: 210 000 N/mm^2

433.0127

433.0127

Make a note of the results, because in the exerciseFoundations of Finite Element Methodswe will calculate the same truss system by hand.

Results:

case a)node ux uy

1

2

3

4

case b)

node ux uy

1

23

4

Another example of a 2D truss system you will find on the internet side of the Universityof Alberta.

http://www.mece.ualberta.ca/tutorials/ansys/BT/Truss/Truss.html

2-intro_truss_1lt+2th

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