ANSYS UYGULAMALARI
DOÇ. DR . NUMAN BEHLÜL
BEKTAŞ
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ANSYS Utilities An introduction to using ANSYS, including a quick ex planation of the stages of analysis, how to start ANSYS, and the use of the windows in ANSYS, and using Pro/ENGINEER with ANSYS. Introduction to Finite Element Analysis A brief introduction of the 3 stages involved in finite element analysis.
Starting up ANSYS How to start ANSYS using windows NT and Unix X-Windows.
ANSYS Environment An introduction to the windows used in ANSYS
ANSYS Interface An explanation of the Graphic User Interface (GUI) in c omparison to the command file approach.
Convergence Testing This file can help you to determine how small your meshing elements need to be before you can trust the solution.
Saving/Restoring Jobs Description of how to save your work in ANSYS and how to resume a previously saved job.
ANSYS Files Definitions of the different files created by ANSYS.
Printing Results Saving data and figures generated in ANSYS.
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Introduction ANSYS is a general purpose finite element modeling package for numerically solving a wide variety of mechanical problems. These problems include: stat ic/dynamic structural analysis (both linear and non-linear), heat transfer and fluid problems, as well as acoustic and electromagnetic problems. In general, a finite element solution may be broken into the following three stages. This is a general guideline that can be used for setting up any finite element analysis. 1. Preprocessing: defining the problem ; the major steps in preprocessing are given below: Define keypoints/lines/areas/volumes o Define element type and material/geometric properties o Mesh lines/areas/volumes as required o The amount of detail required will depend on the dimensionality of the analysis (i.e. 1D, 2D, axi-symmetric, 3D). 2. Solution: assigning loads, constraints and solving ; here we specify the loads (point or pressure), contraints (translational and rotational) and finally solve the resulting set of equations. 3. Postprocessing: further processing and viewing of the results; in this stage one may wish to see: Lists of nodal displacements o Element forces and moments o Deflection plots o Stress contour diagrams o
Starting up ANSYS
Starting up ANSYS Large File Sizes
ANSYS can create rather large files when running and saving; be sure that your local drive has space for it. Getting the Program Started
In the Mec E 3-3 lab, there are two ways that you can start up ANSYS: 1. Windows NT application 2. Unix X-Windows application
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Windows NT Start Up
Starting up ANSYS in Windows NT is simple: Start Menu Programs ANSYS 5.7 Run Interactive Now Unix X-Windows Start Up
Starting the Unix version of ANSYS involves a few more steps: in the task bar at the bottom of the screen, you should see something labeled X-Win32. If you don't see this minimized program, you can may want to reboot the computer, as it automatically starts this application when booting. right click on this menu and selection Sessions and then select Mece. you will now be prompted to login to GPU... do this. once the Xwindows emulator has started, you will see an icon at the bottom of the screen that looks like a paper and pencil; don't select this icon, but rather, click on the up arrow above it and select Terminal a terminal command window will now start up in that window, type xansys57 at the UNIX prompt and a small launcher menu will appear.
select the Run Interactive Now menu item.
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ANSYS 7.0 Environment The ANSYS Environment for ANSYS 7.0 contains 2 windows: the Main Window and an Output Window. Note that this is somewhat different from the previous version of ANSYS which made use of 6 different windows. 1. Main Window
Within the Main Window are 5 divisions: a. Utility Menu The Utility Menu contains functions that are available throughout the ANSYS session, such as file controls, selections, graphic controls and parameters. b. Input Lindow The Input Line shows program prompt messages and allows you to type in commands directly. c. Toolbar The Toolbar contains push buttons that execute commonly used ANSYS commands. More push buttons can be added if desired.
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d. Main Menu The Main Menu contains the primary ANSYS functions, organized by preprocessor, solution, general postprocessor, design optimizer. It is from this menu that the vast majority of modelling commands are issued. This is where you will note the greatest change between previous versions of ANSYS and version 7.0. However, while the versions appear different, the menu structure has not changed. e. Graphics Window The Graphic Window is where graphics are shown and graphical picking can be made. It is here where you will graphically view the model in its various stages of construction and the ensuing results from t he analysis. 2. Output Window
The Output Window shows text output from the program, such as listing of data etc. It is usually positioned behind the main window and can de put to the front if necessary.
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ANSYS Interface Graphical Interface vs. Command File Coding There are two methods to use ANSYS. The first is by means of the graphical user interface or GUI. This method follows the conventions of popular Windows and X-Windows based programs. The second is by means of command files. The command file approach has a steeper learning curve for many, but it has the advantage that an entire analysis can be described in a small text file, typically in less than 50 lines of commands. This approach enables easy model modifications and minimal file space requirements. The tutorials in this website are designed to teach both the GUI and the command file approach, however, many of you will find the command file simple and more efficient to use once you have invested a small amount of time into learning the code. For information and details on the full ANSYS command language, consult: Help > Table of Contents > Commands Manual.
FEM Convergence Testing Introduction
A fundamental premise of using the finite element procedure is that the body is sub-divided up into small discrete regions known as finite ele ments. These elements defined by nodes and interpolation functions. Governing equations are written for each element and these el ements are assembled into a global matrix. Loads and constraints are applied and t he solution is then determined. The Problem
The question that always arises is: How small do I need to make the elements before I can trust the solution? What to do about it...
In general there are no real firm answers on this. It will be necessary to conduct convergence tests! By this we mean that you begin with a mesh discretization and then observe and record the solution. Now repeat the problem with a finer mesh (i.e. more elements) and then compare the results with the previous test. If the results are nearly similar, then the first mesh is probably good enough for that particular geometry, loading and constraints. If the results differ by a large amount however, it will be neces sary to try a finer mesh yet. The Consequences
Finer meshes come with a cost however: more cal culational time and large memory requirements (both disk and RAM)! It is desired to find the minimum number of elements that give you a converged solution.
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Beam Models
For beam models, we actually only need to define a single ele ment per line unless we are applying a distributed load on a given frame member. When point loads are used, specifying more that one element per line will not change the solution, it will only slow the calculations down. For simple models it is of no concern, but for a larger model, it is desired to minimize the number of elements, and thus calculation time and still obtain the desired accuracy. General Models
In general however, it is necessary to conduct convergence tests on your finite element model to confirm that a fine enough element discretization has been used. In a solid mechanics problem, this would be done by creating several models with different mesh sizes and comparing the resulting deflections and stresses, for example. In general, the stresses will converge more slowly than the displacement, so it is not sufficient to examine the displacement convergence.
ANSYS: Saving and Restoring Jobs Saving Your Job
It is good practice to save your model at various points during its creation. Very often you will get to a point in the modeling where things have gone well and you like to save it at the point. In that way, if you make some mistakes later on, you will at least be able to come back to this point. To save your model, select Utility Menu Bar -> File -> Save As Jobname.db. Your model will be saved in a file called jobname.db, where jobname is the name that you specified in the Launcher when you first started ANSYS. It is a good idea to save your job at different times throughout the building and analysis of the model to backup your work incase of a system crash or other unforseen problems. Recalling or Resuming a Previously Saved Job
Frequently you want to start up ANSYS and recall and continue a previous job. There are two methods to do this: 1. Using the Launcher... In the ANSYS Launcher, select Interactive... and s pecify the previously o defined jobname. Then when you get ANSYS started, select Utility Menu -> File -> Resume o Jobname.db . This will restore as much of your database (geometry, loads, solution, etc) that o you previously saved. 2. Or, start ANSYS and select Utitily Menu -> File -> Resume from... and select your job from the list that appears.
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ANSYS Files Introduction A large number of files are created when you run ANSYS. If you started ANSYS without specifying a jobname, the name of all the files created will be FILE.* where the * represents various extensions described below. If you specified a jobname, say Frame, then the created files will all have the file prefix, Frame again with various extensions: frame.db Database file (binary). This file stores the geometry, boundary conditions and any solutions. frame.dbb Backup of the database file (binary). frame.err Error file (text). Listing of all error and warning messages. frame.out Output of all ANSYS operations (text). This is what normally scrolls in the output window during an ANSYS session. frame.log Logfile or listing of ANSYS commands (text). Listing of all equivalent ANSYS command line commands used during the current session. etc... Depending on the operations carried out, other files may have been written. These files may contain results, etc.
What to save? When you want to clean up your directory, or move things from the /scratch directory, what files do you need to save? If you will always be using the GUI, then you only require the .db file. This file stores the geometry, boundary conditions and any solutions. Once the ANSYS has started, and the jobname has been specified, you need only activate the resume command to proceed from where you last left off (see Saving and Restoring Jobs). If you plan on using ANSYS command files, then you need only store your command file and/or the log file. This file contains a complete listing of the ANSYS commands used to get you model to its current point. That file ma y be rerun as is, or edited and rerun as desired (Command File Creation and Execution). If you plan to use the command mode of operation, starting with an existing log file, rename it first so that it does not get over-written or added to, from another ANSYS run.
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Printing and Plotting ANSYS Results to a File Printing Text Results to a File
ANSYS produces lists and tables of many types of results that are normally displayed on the screen. However, it is often desired to save the results to a file to be later analyzed or included in a report. 1. Stresses: instead of using 'Plot Results' to plot the stresses, choose 'List Results'. Select 'Elem Table Data', and choose what you want to list from the menu. You can pick multiple items. When the list appears on the screen in its own window, Select 'File'/'Save As...' and give a file name to store the results. 2. Any other solutions can be done in the same way. For example select 'Nodal Solution' from the 'List Results' menu, to get displacements. 3. Preprocessing and Solution data can be listed and saved from the 'List' menu in the 'Utility Menu bar'. Save the resulting list in the same way described above. Plotting of Figures
There are two major routes to get hardcopies from ANSYS. The first is a quick a raster-based screen dump, while the second is a scalable vector plot. 1.0 Quick Image Save
When you want to quickly save an image of the entire screen or t he current 'Graphics window', select: 'Utility menu bar'/'PlotCtrls'/'Hard Copy ...'. In the window that appears, you will normally want to select 'Graphics window', 'Monochrome', 'Reverse Video', 'Landscape' and 'Save to:'. Then enter the file name of your choice. Press 'OK' This raster image file may now be printed on a PostScript printer or included in a document. 2.0 Better Quality Plots
The second method of saving a plot is much more flexible, but takes a lot more work to set up as you'll see... Redirection Normally all ANSYS plots are directed to the plot window on the screen. To save some plots to a file, to be later printed or included in a document or what have you, you must first 'redirect' the plots to a file by issuing: 'Utility menu bar'/'PlotCtrls'/'Redirect Plots'/'To File...'. Type in a filename (e.g.: frame.pic) in the 'Selection' Window. Now issue whatever plot commands you want within ANSYS, remembering that the plots will not be displayed to the screen, but rather they will be written to the selected file. You can
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put as many plots as you want into the plot file. When you are finished plotting what you want to the file, redirect plots back to the screen using:
'Utility menu bar'/'PlotCtrls'/'Redirect Plots'/'To Screen'.
Display and Conversion
The plot file that has been saved is stored in a proprietary file format that must be converted into a more common graphic file format like PostScript, or HPGL for example. This is performed by running a separate program called display. To do this, you have a couple of options: 1. select display from the ANSYS launcher menu (if you started ANSYS that way) 2. shut down ANSYS or open up a new terminal window and then type display at the Unix prompt. Either way, a large graphics window will appear. Decrease the size of this window, because it most likely covers the window in which you will enter the displa y plotting commands. Load your plot file with the following command:
file,frame,pic if your plot file is 'plots.pic'. Note that although the file is 'plots.pic' (with a period), Display wants 'plots,pic'(with a comma). You can display your plots to the graphics window by issuing the command like
plot,n where n is plot number. If you plotted 5 images to this file in ANSYS, then n could be any number from 1 to 5. Now that the plots have been read in, they may be saved to printer files of various formats: 1. Colour PostScript: To save the images to a colour postscript file, enter the following commands in display:
pscr,color,2 /show,pscr plot,n where n is the plot number, as above. You can plot as many images a s you want to postscript files in this manner. For subsequent plots, you only require the plot,n command as the other options have now been set. Each image is plotted to a postscript file such as pscrxx.grph, where xx is a number, starting at 00. Note: when you import a postscript file into a word processor, the postscript image will appear as blank box. The printer information is still present, but it can only be viewed when it's printed out to a postscript printer.
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Printing it out: Now that you've got your color postscript file, what are you going to do with it? Take a look here for instructions on colour postscript printing at a couple of sites on campus where you can have your beautiful stress plot plotted to paper, overheads or even posters! 2. Black & White PostScript: The above mentioned colour postscript files can get very large in size and may not even print out on the postscript printer in the lab because it takes so long to transfer the files to the printer and process them. A way around this is to print them out in a black and white postscript format instead of colour; besides the colour specifications don't do any good for the black and white lab printer anyways. To do this, you set the postscript color option to '3', i.e. and then issue t he other commands as before pscr,color,3 /show,pscr plot,n Note: when you import a postscript file into a word processor, the postscript image will appear as blank box. The printer information is still present, but it can only be viewed when it's printed out to a postscript printer. 3. HPGL: The third commonly used printer format is HPGL, which stands for Hewlett Packard Graphics Language. This is a compact vector format that has the advantage that when you import a file of this type into a word processor, you can actually see the image in the word processor! To use the HPGL format, is sue the following commands: /show,hpgl plot,n Final Steps
It is wise to rename these plot files as soon as you leave displa y, for display will overwrite the files the next time it is run. You may want to rename the postscript files with an '.eps' extension to indicate that they are encapsulated postscript images. In a similar way, the HPGL printer files could be given an '.hpgl' exte nsion. This renaming is done at the Unix commmand line (the 'mv' command). A list of all available display commands and their options may be obtained by typing:
help When complete, exit display by entering
finish
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