Pressure Cylinder - Educating Global Leaderschasek/ME 501/ANSYS Tutorials-Blotter/ANSYS-Basi… · Pressure Cylinder Problem: A steel pressure cylinder has an outside diameter of

Pressure Cylinder

Problem:

A steel pressure cylinder has an outside diameter of 6 inches and a 1/4 inch wall thick-ness. What pressure can this vessel carry if the maximum shear stress is not to exceed4000 psi?

Joseph Shigley and Charles Mischke. Mechanical Engineering Design5th ed. New York: McGraw Hill, May 2002.

Pressure CylinderOverview

Outcomes1) Learn how to start Ansys 8.0 2) Gain familiarity with the graphical user interface (GUI)3) Learn how to create and mesh a simple geometry4) Learn how to apply boundary constraints and solve problems

Tutorial OverviewThis tutorial is divided into six parts:

1) Tutorial Basics2) Starting Ansys3) Preprocessing4) Solution5) Post-Processing6) Hand Calculations

Anticipated time to complete this tutorial: 1 hour

AudienceThis tutorial assumes minimal knowledge of ANSYS 8.0; therefore, it goes into moderatedetail to explain each step. More advanced ANSYS 8.0 users should be able to completethis tutorial fairly quickly.

Prerequisites1) ANSYS 8.0 in house “Structural Tutorial”

Objectives1) Model the pressure cylinder in ANSYS 8.02) Analyze the pressure cylinder for maximum shear stress3) Exposure to log files

2

Pressure CylinderTutorial Basics

3

In this tutorial:Instructions appear on the left.

Visual aids corresponding to the textappear on the right.

All commands on the toolbars arelabeled. However, only operationsapplicable to the tutorial are explained.

The instructions should be used as follows:

Bold > Text in bold are buttons, options, or selections that the user needs to click on

Example: > Preprocessor > Element Type > Add/Edit/DeleteFile would mean to follow the options as shown to the right to get you to the Element Types window

Italics Text in italics are hints and notes

MB1 Click on the left mouse buttonMB2 Click on the middle mouse

buttonMB3 Click on the right mouse

button

Some Basic ANSYS functions are:

To rotate the models use Ctrl and MB3.

To zoom use Ctrl and MB2 and move themouse up and down.

To translate the models use Ctrl and MB1.

Pressure CylinderStarting Ansys

4

For this tutorial the windows version ofANSYS 8.0 will be demonstrated. The pathbelow is one example of how to accessANSYS; however, this path will not be thesame on all computers.

For Windows XP start ANSYS by eitherusing:

> Start > All Programs > ANSYS 8.0> ANSYSor the desktop icon (right) if present.

Note: The path to start ANSYS 8.0 may be different foreach computer. Check with your local network manager tofind out how to start ANSYS 8.0.


5

Once ANSYS 8.0 is loaded, two separatewindows appear: the main ANSYSAdvanced Utility Window and the ANSYSOutput Window.

The ANSYS Advanced Utility Window,also known as the Graphical User Interface(GUI), is the location where all the userinterface takes place.

The Output Window documents all actionstaken, displays errors, and solver status.

Graphical User Interface

Output Window


6

The main utility window can be broken upinto three areas. A short explanation of eachwill be given.

First is the Utility Toolbar:

From this toolbar you can use the commandline approach to ANSYS and access multiplemenus that you can’t get to from the mainmenu.

Note: It would be beneficial to take some time and explorethese pull down menus and familiarize yourself with them.

Second is the ANSYS Main Menu as shownto the right. This menu is designed to use atop down approach and contains all thesteps and options necessary to properly pre-process, solve, and postprocess a model.

Third is the Graphical Interface windowwhere all geometry, boundary conditions,and results are displayed.

The tool bar located on the right hand sidehas all the visual orientation tools that areneeded to manipulate you model.


7

With ANSYS 8.0 open select> File > Change Jobname

and enter a new job name in the blank fieldof the change jobname window.

Enter the problem title for this tutorial.> OK

In order to know where all the output filesfrom ANSYS will be placed, the workingdirectory must be set in order to avoid usingthe default folder C:\Documents andSettings.

> File > Change Directory > then select the location that you wantall of the ANSYS files to be saved.

Be sure to change the working directory atthe beginning of every problem.

With the jobname and directory set theANSYS database (.db) file can be given atitle. Following the same steps as you didto change the jobname and the directory,give the model a title.

Pressure CylinderPreprocessing

8

To begin the analysis, a preference needs tobe set. Preferences allow you to apply filter-ing to the menu choices; ANSYS willremove or gray out functions that are notneeded. A structural analysis, for example,will not need all the options available for athermal, electromagnetic, or fluid dynamicanalysis.

> Main Menu > Preferences

Place a check marknext to theStructural box.

> Ok

Look at the ANSYS Main Menu. Click onceon the “+” sign next to Preprocessor.

> Main Menu > Preprocessor

The Preprocessor options currently avail-able are displayed in the expansion of theMain Menu tree as shown to the right. Themost important preprocessing functions are:defining the element type, defining real con-straints and material properties, and model-ing and meshing the geometry.


9

Because a log file will be written toward theend of this tutorial, take particular care tofollow the tutorial exactly and avoid mis-takes. This will make the log file muchcleaner and easier to work with.

Select the “+” next to Element Type or clickon Element Type. The extension of themenu is shown to the right.

> Element Type

Select Add/Edit/Delete and the ElementType window appears. Select add and theLibrary of Element Types window appears.

> Add/Edit/Delete > Add

In this window, you can select the types ofelements to be defined and used for theproblem. For a pictorial description of whateach element can be used for, click on theHelp button.

For this model, solid10 node tetrahedronelements will be used.

> Solid > Tet 10node 187> Ok

Close the Element Types window.> Close.


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No real constants need to be defined for thiselement type.

The material properties for the pressure ves-sel need to be defined.

> Preprocessor > Material Props> Material Models

The Define Material Models Behavior win-dow should now open.

This window has many different possibili-ties for defining the materials for yourmodel. We will use isotropic linearly elasticstructural properties.

Select the following from the MaterialModels Available window:

> Structural > Linear > Elastic > Isotropic

The window titled Linear IsotropicProperties for Material Number 1 nowappears. This window is the entry point forthe material properties to be used for themodel.

Enter 30e6 (30 Mpsi) for EX (Young'sModulus) and 0.3 for PRXY (Poisson'sRatio).

> Ok

Close the Define Material Model Behaviorwindow.

> Material > Exit


11

The next step in the development of themodel is to create the geometry.

ANSYS has built in geometry functions thatcan simplify the modeling process. The par-tial cylinder will be used to model the cylin-der.

In the main menu select> Preprocessor > Modeling > Create > Volumes > Cylinder > Partial Cylinder

Once selected, the Partial Cylinder win-dow, shown to the right, should appear.This window allows the user to define thedimensions of a cylinder.

Enter the following parameters from theproblem statement into the appropriatefields:

WP X: 0WP Y: 0Rad-1: 3Theta-1: 0Rad-2: 2.75Theta-2: 90Depth: 1

WP X and WP Y represent the coordinates atwhich you want to center the circular cross-section of the cylinder. Rad-1 and Rad-2 arethe radii of the inner and outer surfacesrespectively. Theta-2 minus Theta-1 indi-cates the rotation through which to sweepthe volume. Note that we can simulate theentire vessel with a quarter of its geometry.Depth gives the cylinder the third dimen-sional geometry needed to become a cylin-der. Again, we can input 1” depth to modelthe entire length of 10” in the problem state-ment.


12

Once the values have been entered, select> Ok

The geometry should appear in the graph-ics window as shown to the right. Youmay have to rotate the object to see the 3Dshape.

Next you will mesh the volume.

You want to manually set the element sizefor this problem, to ensure that there are atleast two elements through the thickness ofthe cylinder wall. Since the wall thickness is.25”, you will set the element edge length to.125”.

> Preprocessor > Meshing> Size Cntrls > Manual Size > Global > Size

Enter .125 in the field titled Element EdgeLength.

> Ok

Mesh the volume.> Preprocessor > Meshing > Mesh> Volumes > Free

The mesh volume window opens. Select thebutton Pick All.


13

The meshed volume should appear similarto the pictures at the right.

Define a scalar parameter, P, that will repre-sent the pressure that you will apply to theinterior area of the vessel. Since you are try-ing to find a value of P that will produce acertain stress in the vessel, you will pick theinitial value of P. It is suggested that youpick P = 500.

On the Utility Menu select> Parameters > Scalar Parameters

Enter P = 500 into the selection field.

Hit Accept and then Close.

Pressure CylinderSolution

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Before applying the loads to the pressurevessel, a new analysis needs to be initial-ized. Select:

> Solution > Analysis Type> New Analysis

For the type of analysis select Static.> Ok

The next step is to apply the loads and con-straints. The vessel will have constraintsplaced on areas and have a pressure appliedto its interior area.

Rotate the model so that the bottom, left,and front surfaces are visible (see picturebelow).

On the ANSYS Main Menu select:> Solution > Define Loads > Apply> Structural > Displacement > On Areas

The Apply U, ROT on Areas windowappears. Pick the bottom face of the cylin-der and hit Ok.


15

The Apply U, ROT on Areas windowshould appear.

The bottom surface should be restrictedfrom moving in the Y direction. Select UY.

> Apply

Repeat the procedure with the left and frontsurfaces. The left surface should be con-strained from moving in X and the front sur-face should be constrained from moving inZ.

The next step is to apply the pressure to theinterior surface of the cylinder.

From the ANSYS Main Menu select:> Solution > Define Loads> Apply > Structural > Pressure> On Areas

With the Apply PRES on Areas windowopen, select the inner surface of the pressurevessel as shown to the right.

> Ok

The next window to open is the ApplyPRES on Areas Main window. Accordingto the picture to the right, apply the param-eter P to the area.

Leave all other settings as shown in the win-dow.

> Ok

The applied pressure will be represented bya red grid on the inner surface of the pres-sure vessel.


16

Your model should appear similar to the oneshown to the right.

The model is now ready to be solved.

From the ANSYS Main Menu select> Solution > Solve > Current LS

Note: Current LS means “current loadstep”; this was justdefined during preprocessing.

The Solve Current Loadstep window willappear.

> Ok

A window might appear stating that “Acheck of your model data produced 1 warn-ing. should the SOLV command be execut-ed?”

Select Yes to continue.

The computer will solve the problem.Depending on the speed of your computer,this could take a few minutes.

When the solution is complete, the Notewindow will appear.

> Close

Close the /Status Command window.> Close

Pressure CylinderPost Processing

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From the ANSYS Main Menu select:> General Postproc > Element Table> Define Table

The Element Data Table window shouldappear and should be empty. This windowshows which types of results can be plotted.

> Add

The Define Additional Element TableItems window should appear. From thiswindow the results of interest can be select-ed for analysis.

From the problem statement, the maximumshear stress is not to exceed 4000 psi. To ver-ify that the stress has not been exceeded,select Stress from the Item, Comp, Resultsdata item drag down menu. From the dragdown menu to the right of the stress selec-tion, select XY-shear SXY. Enter the nameMax Shear in the User Label for Item field.

> Ok

The picture to the right shows the line thatshould be added to the Element Data Table.

Close the Element Data Table window.> Close

With the result type selected, the results canbe plotted.


18

To view results:> General Postproc > Element Table> Plot Elem Table

This brings up a window in which the ele-ment result types can be selected.

Select MAXSHEAR to the right of Item tobe plotted. When asked if you would likethe average at common nodes select No.

> Ok

The results should be displayed in thegraphics window similar to the pictureshown to the right.

The solution returns values of SMN = -3080and SMX = -33.904 psi. These values are theshear stress minimum and maximum valuesthat occur in the elements in the XY plane.We will also check the nodes for the samemaximum stresses.

On the ANSYS Main Menu select:> General Postproc > List Results> Sorted Listing > Sort Nodes

The Sort Nodes window appears. Checkthe box to sort absolute values, enter 10 for thenumber of nodes to sort, change List sortednodes for to Results, and for Item ,Comp Sortnodes based on select Stress, XY-shear SXY.

> Ok

The nodal results do not exceed 4000 psi, soyou can still increase the value of P untileither SMN=4000 or until the maximum XYshear in any node equals 4000.


19

You will now write a log file that containsevery step that you performed in the GUI;the log file is written as text commands.

Save your model now.

To write a log file go to the Utility Menu andselect:

> File > Write DB log file...

Name the file to be saved pressurevessel.lgw. Make sure that the log file issaved to the working directory. At the bot-tom of the window there is a drop down list.Make sure that Write essential commandsonly is selected.


20

On your computer, open the folder wherethe log file was saved. Open the log file. Ifthe computer prompts you what type ofprogram to use when opening the file,choose Notepad.

The text of your log file should look similarto the text to the right. The closer you fol-lowed the steps in this tutorial, the moresimilar your log file should be.

Take a minute to read through the log fileand see what commands were written asyou went step by step through the tutorial.

You only need to make a few modificationsto the log file before you use it again. First,delete the second line of text (highlighted inred).

Next add the following lines of text to thebottom of the log file (shown in blue):

PLETAB,MAXSHEAR,NOAVPRNSOL,S,COMP

These commands will plot the element tableand show the sorted list of nodal solutionsafter the solve is completed.

The only task left is to vary the value of P sothat you can get closer to the maximumallowable value for Max Shear (4000 psi).

Find the line *SET,P,500. Change 500 to anew value of P that you choose (this will bean iterative process of choosing P and rerun-ning the solution). Save the log file afterdoing this.

/BATCH /input,menust,tmp,'',,,,,,,,,,,,,,,,1 WPSTYLE,,,,,,,,0/CWD,'J:\groups\pace\ANSYS Machine Design\Basic\Tutorial 6Basic - Pressure Vessel (Problem to be redone)\Results' /FILNAME,Pressure Vessel,0 /TITLE,Pressure Vessel /NOPR /PMETH,OFF,0KEYW,PR_SET,1 KEYW,PR_STRUC,1 KEYW,PR_THERM,0 KEYW,PR_FLUID,0 KEYW,PR_ELMAG,0 KEYW,MAGNOD,0 KEYW,MAGEDG,0 KEYW,MAGHFE,0 KEYW,MAGELC,0 KEYW,PR_MULTI,0 KEYW,PR_CFD,0 /GO /PREP7 ET,1,SOLID187 MPTEMP,,,,,,,, MPTEMP,1,0 MPDATA,EX,1,,30e6 MPDATA,PRXY,1,,.3 CYL4,0,0,3,0,2.75,90,1 ESIZE,.125,0, MSHKEY,0MSHAPE,1,3d CM,_Y,VOLU VSEL, , , , 1 CM,_Y1,VOLU CHKMSH,'VOLU' CMSEL,S,_YVMESH,_Y1 CMDELE,_YCMDELE,_Y1 CMDELE,_Y2 *SET,P,500 FINISH /SOLANTYPE,0FLST,2,1,5,ORDE,1 FITEM,2,5 /GO DA,P51X,UY, FLST,2,1,5,ORDE,1 FITEM,2,6 /GO DA,P51X,UX, FLST,2,1,5,ORDE,1 FITEM,2,2 /GO DA,P51X,UZ, FLST,2,1,5,ORDE,1 FITEM,2,4 /GO SFA,P51X,1,PRES,p SOLVE FINISH /POST1 AVPRIN,0, , ETABLE,Max Shear,S,XYPLETAB,MAXSHEAR,NOAVNSORT,S,XY,0,1,10,0 PRNSOL,S,COMP


21

Select and copy all the text of the log file tothe clipboard.

Return to ANSYS. You need to clear themodel that is currently in the GUI. To dothis, go to the Utility menu and select:

> File > Clear and Start New...

A window will open asking you whether ornot you want to Read start.ans after clear.Accept the default option and click Ok.

Another window will open, verifying thatyou want to clear the model. Select Ok.

The GUI should now be blank.

Paste the contents of the clipboard (shouldbe your modified log file) into the commandline of ANSYS.

When you hit enter, ANSYS will begin tocreate and solve the problem again, with thenew value of P that you defined. Severalmessage windows might appear during thisprocess. Ignore them until the solution isfinished (unless you get an error that pre-vents you from moving forward to the solu-tion--if this happens, check your log file forerrors).

It will take a minute or two before the solu-tion is done.

The element table is automatically definedand plotted by the log file. The sorted list isautomatically displayed. All you need to dois find the max stress (it might either appearon the sorted list or as SMN on the GUI).Adjust the value of P in the log file until youget as close to -4000 as possible.

Pressure CylinderHand Calculations

22

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