OOF: Finite Element Analysis of Microstructures
Next: Example 2: Using Data Up: Examples Previous: Examples   Contents
- . Start OOF:
- Start up the OOF graphical interface: oof.
This should create and display the main OOF menu, with
the word ``OOF'' prominently in the upper left hand corner.
(If this doesn't happen, then something is dreadfully wrong.
Make sure that the compiled version of OOF matches your
- . Initialize:
- Launch the Initialize Menu by clicking on the word initialize in the Menus subwindow. The /initialize menu should
occupy the real estate vacated by the main OOF menu.2.2
- . Uniform:
- You will see that there is currently only one type of grid -- a
uniform grid. Launch the /initialize/uniform menu by clicking
on uniform in the /initialize menu.
- . Mesh Parameters:
- Set the height of the grid by clicking on height in the
Variables list. A variable dialog box appear at the bottom right
corner of the menu, with some explanatory text. You can type in the
desired height in the dialog box; Let's make the sample taller than it
is wide by setting the height equal to 22.214.171.124 Hit the return key or click
on the Set button to tell OOF that you're done changing the
height variable. Notice that a new window pops up; this is the
message box where information is stored and reported about the current
state of OOF. Also notice that the new value of height appears
in the Variable list. The values of nx and ny specify the
number of triangular elements in the -direction (width) and the
-direction (height). nx and ny of about 20 are about
right if you want nearly instantaneous solutions, although you might
try different values to see how they affect the mesh and the
- . Function Window:
- Click once on isotropic to launch a Function Window
indicating that you want finite elements for a isotropic material to
fill the grid. (If your X-Windows manager is putting a frame around
the windows, then the words ``initialize uniform isotropic'' appear on
the window frame. This is the path to this command from the main
- . Set Material:
- The Function Window for the isotropic element provides a table
to fill out attributes for that particular type of element. The
isotropic element has three thermoelastic parameters and the table
allows you to specify the Young's modulus, the Poisson's ratio and the
thermal expansion coefficient. Note that if you hit a return in
any of the function subwindows, it causes execution of that function.
Use the mouse or the tab key to set more than one
parameter. Set the Young's modulus to 2 and the Poisson's ratio to
0.25. Let's imagine that we are doing the virtual experiment on a
thin material and set the two-dimensional stress state to be plane
stress by clicking on the false button in the planestrain
row. We won't be changing temperature in this example so the thermal
expansion coefficient alpha does not matter. The value of gray controls how the mesh will be drawn; gray takes values
between 0 and 1 inclusive, where 0 is black and 1 is white.
- . Create the Mesh:
- After all the information for the element has been entered,
initialize the mesh by executing the function by clicking on the
function name isotropic button at the top of the function
Notice that the function execution is recorded in the message window.
(Don't worry if you execute this function before you had intended,
you can always recall the function and re-execute it.)
The finite element mesh should now be ready.
- . Graphics:
- Look at the graphical representation of the mesh.
Get to the main OOF Menu by either clicking on the Home
button at the top of the /initialize/uniform submenu, or by
backtracking by clicking on the Back button.
From the main OOF Menu, open the graphics submenu.
From the /Graphics Menu, open a Drawer by executing the
open function by clicking on it twice quickly.
(Clicking on it once would open a Function Window.)
A Drawer should appear with a gray rectangle representing the
- . Drawing Control:
- Turn on the element edges so that the grid becomes apparent. The Coordinates Dashboard is currently visible. Switch to the Attributes Dashboard by clicking and holding the left mouse button on
the Dashboard Selector and selecting Attributes from the
pop-up menu. The controls visible in the Dashboard should change. Turn
on the element edges by clicking on the button next to Elements.
The mesh should be redrawn with edges turned on. The height, width
and number of elements in the mesh were determined by the values you
chose in the /initialize/uniform Menu.
- . Pick Nodes:
- Verify that the mesh has the height and width that you
Open the Node Info Dashboard on the Drawer.
Move the mouse into the image region of the Drawer and
place the hook of the ``?'' cursor over the top-right
node and click with any button.
(In this case, nodes are the vertices of the triangular elements.)
You should see information appear in the Message Window reflecting the
state of the Dashboard and the node which you queried.
If you picked correctly, the node coordinates should be
equal to width and height.
The node type should be xy meaning that the node
has an x- and a y- degree of freedom.
- . BCs:
- Set the boundary conditions. This is done by removing degrees of
freedom from nodes. Note tha this operation only affects the
behavior of the equilibration stage of the solution. We will still be
able to displace these nodes when distorting the mesh. From the main
OOF Menu, open the submenu bc. Fix the spatial degrees of
freedom by picking the fix submenu. Let's fix both the x-
and y- coordinates, by picking on the both submenu. The
/bc/fix/both submenu will have names of groups of nodes in
the Function column. We will stretch the material in the vertical
direction with fixed grips. Select top to remove the x-
and y- degrees of freedom from the top row of nodes; do the same
for the bottom nodes.
- . Set Distortion:
- Distort the mesh into the configuration for which you want a solution.
From the main OOF Menu, open the distort submenu. Open the
set submenu. There are a number of choices in the Variables
column. Prepare to stretch the material by setting a ystrain of
0.20 (a strain of 20 percent in the vertical direction.) Now you
have to specify which nodes you want to be distorted: click on
the nodegroup top. Notice that in the graphics Drawer that
nothing has happened; this is because the distortion has yet to be
- . Apply Distortion:
Move Back one menu to /distort. Keep one eye on the graphics Drawer while you click on the increment function. You will see that the top elements have been distorted. To get the entire picture back into the Drawer either click the middle mouse on the z(oom) button at the top-left corner of the image subwindow of the Drawer or open the Coordinates dashboard and click on Show Entire Image.
- . Solution:
- From the main OOF Menu, click on the equilibrate function.
Information about the solution will appear in the Message Window and
the current graphical representation will appear in the image subwindow
of the Drawer.
- . Stresses:
- Get a graphical picture of the stresses for the current solution.
On the Drawer, hold down the left button on the top (wide) selector
to bring up the list of Drawer types.
Select Stress invariant 1.
This will display the trace of the two-dimensional stress matrix:
- . Numerical Values:
- Change to the Element Info Dashboard on the Drawer. Turn on
the stress button as well as several of the components of stress
listed below it. Move the mouse onto the image and click on an
element. The numerical values of the requested stress components in
the element will appear in the message window.
- . Statistics:
Switch the Drawer back to the Mesh display and open the Attributes Dashboard. We will be selecting elements so turn on the Hot Elements option, so that the selected elements are visible. Turn on the Click to Select Elements option. In the image subwindow, drag a rectangle by holding down the mouse button as you move the mouse. The selected elements should change color. From the main OOF Menu, select the /output/stress/statistics submenu. Change the type variable to invariant (Click once on the word type in the Variables list. A pull-down menu of different statistics types appears at the bottom of the Menu. Use the left mouse button on the pull-down menu to see all the choices, or use the right or middle buttons to cycle through the choices.) Use the function selected to gather statistics on the selected elements. Output appears in the message window.
- . Play, Quit:
- You might want to play with various menus and see what's available.
When you want to quit, go back to the main OOF Menu and click on the
quit option in the Function list, or the Quit button at
the top of the window.
Next: Example 2: Using Data Up: Examples Previous: Examples   Contents /* Send mail to the OOF Team *//* Go to the OOF Home Page */