tutorial 1

FEMAP Tutorial 1: Uniaxial Rod

E:\whit\Classes\CRCD\tutorial_1.doc p. 2

FEMAP Tutorial 1: Simple Structures

In this tutorial, we will construct FEMAP finite element models of the above simple structures, perform the analysis of the model, view the results, and compare those results to the strength of materials calculations for each structure. We will first construct the uniaxial rod, and then we will adapt this structure to represent a simple beam. In order to accomplish this task, we have to describe four types of information about the configuration using FEMAP:

Constitutive What the model is comprised of (materials, properties)

Geometry The shape of the model

Boundary conditions Loads and constraints acting on the model

Compatibility How the elements fit together

Explanation of Notation:

Navigating menus can be troublesome. I will give the correct path using a shorthand notation, which is best described with an example. Consider the phrase

Create.load.nodal

This indicates that one should click the Create menu item, followed by the load submenu item, and then finally the nodal sub-submenu item.

When a dialog box is to be filled in, the label for each field will be given with the required input in parenthesis. For example,

Youngs Modulus, E(30000000)

Indicates that you should put 30000000 in the field labeled Youngs Modulus, E

Many times in FEMAP it is easiest to select a feature of the model on the screen with the mouse rather than typing in its ID number. This will be indicated by underlining the action you should perform. For example,

Geometry.Curve Line.Points

Create Line from Points. Select the points X(-3) Y(1) and X(-3) Y(0)

Means that when the Create Line from Points box comes up, you should select the points X(-3) Y(1) and X(-3) Y(0) with your mouse.

Sometimes you must select a checkbox. This will be indicated by label(check), where label is the label for the checkbox.

Ctrl-Z is undo if you get into trouble and need to back up. There is no redo command

Ctrl-D is redraw, which will clear away deleted features and redraw the model.

The screen may be zoomed in or out by using the scroll button on your mouse

A way to avoid getting in to trouble is to save the model under different filenames as you complete major sections. When you are finished you should have seven or eight files of the model at the different stages of its construction to avoid having to start from a clean slate in order to change one aspect of it.

File.New

File.Save As(FemapTut1)

Define the workplane

Defining the workplane is like creating a sheet of paper that you will draw on. This will specify the location, size, and orientation of the space in which we will create the model. It will give us a frame of reference for our model by creating a grid and visible coordinate axes.

Tools.Workplane(or Press Ctrl-W) to bring up Workplane Management

Snap Options

Grid And Ruler Spacing.Uniform(check)

Grid And Ruler Spacing.X Grid(0.5)

Grid Style.Dots(check)

Snap To.Snap Grid(check)

Workplane Size.X from (-5) To (15)

Workplane Size.Y from (-10) To (10)

Adjust to Model Size(Uncheck)

OK

Define Material Group

As we create our model, we will want groups of materials that we will use to build our structure. To create materials in FEMAP, you simply assign specific material characteristics (i.e. Youngs Modulus, Poissons Ratio, etc.) to a material ID number. For example, Material ID # 1 might have the material characteristics of carbon steel, and Material ID # 2 might have the material characteristics of 2024 aluminum. Then as we create our model we can specify elements that will be carbon steel and others that will be aluminum. You may define materials by manually entering in the values of those characteristics or by loading a saved material from the material library, as we will do in this exercise.

Model.Material

Load

AISI 4130 Steel (Select from list)

OK

OK

Cancel

Define Property Set

We need to define element property groups that will determine what type of elements will be used to build our model. We will complete this task in the same way that we defined the groups of materials. Property data defines the elements geometry (thickness, areas, radii, etc.), specifies mass, and inertia, and it selects a material for the element from the groups you have previously determined. There are many different property types to choose from: line elements (rods and beams), plane elements ( membranes and laminates), and 3-dimensional solid elements. Although we will be modeling a rod and a beam in this exercise, we will be doing so using membrane elements to view the internal stresses in the structure.

Model.Property

Title(1/4 Steel)

Material(select AISI 4130 Steel)

Elem/Property Type

Membrane(check)

OK

Thicknesses,Tavg or T1(0.25)

OK

Cancel

Model Geometry

Geometry provides the framework for most finite element models. Think about it as if you were drawing a picture of an object. First, you would draw the outline of its shape, and then you would color in the outline to better describe it. Here we will use FEMAPs geometry commands to create the outline, and then later we will color it in with elements. Thus, we will have created our model.

Part 1: The Rod/Beam

Geometry.Point

X(0) Y(0) Z(0) OK

X(5) Y(0) Z(0) OK

X(10) Y(0) Z(0) OK

X(0) Y(1) Z(0) OK

X(5) Y(1) Z(0) OK

X(10) Y(1) Z(0) OK

Cancel

View.Autoscale.All (or Press Ctrl A )

There are many ways to create rectangles in FEMAP. We will cover two of those ways: drawing them from points and using the Rectangle commanding in the Geometry menu. Regardless of the technique used, you are really just defining some lines. These lines will be used later to define the regions to be meshed.


Create Line From Points.Select the points X(0) Y(0) Z(0) and X(5) Y(0) Z(0)

Select the points X(5) Y(0) Z(0) and X(10) Y(0) Z(0)

Repeat this command until seven lines have been drawn using the six points created, as is shown below.

OK

Cancel

Part 2: The Base

Now well use another method for creating rectangles. Please note that this command creates a quadrilateral out of four curves that intersect at right angles.

Geometry.Curve Line.Rectangle

First Corner X(-3) Y(-3) Z(0)

Diagonally Opposite Corner X(0) Y(0) Z(0)

OK

Geometry.Curve Line.Rectangle

First Corner X(-3) Y(1) Z(0)

Diagonally Opposite Corner X(0) Y(4) Z(0)

OK


Create Line from Points.Select the points X(-3) Y(1) and X(-3) Y(0)

OK

Cancel

Autoscale the screen to fit the model. It should look similar to the picture below, without the numbers 1-5.

View.Autoscale.All (or Press Ctrl A ) The five rectangles will be the five superelement members of our mesh. In FEMAP, however, they are only the geometric framework where we will create our mesh. For convenience, theyll be referred to as rectangles 1, 2, 3, 4, and 5 as labeled above.

Creating the Mesh

Now that the shape of the model has been created, we can subdivide the superelements to create our mesh. We will use the Mesh.Between command, which subdivides a four-sided element by making divisions along the first and second directions defined. The directions referred to are determined by the first and second node specified (direction 1) and the second and third (direction 2) node specified. This is demonstrated in the figure below:

As you create these meshes, it is also important to make sure that the nodes along sides of abutting superelements line up. Here are two examples, one that will work and one that will return an error message:

Now use this command to mesh our 5 superelements

Mesh.Between (or Control B)

Node And Element Options.Property(1..1/4 Steel)

Mesh Size.#Nodes.Dir1(10)


OK

X(-3) Y(1) Z(0) OK

X(-3) Y(4) Z(0) OK

X(0) Y(4) Z(0) OK

X(0) Y(1) Z(0) OK

Note: If the snap option is not set to Snap to Point, right click anywhere on the screen, and select Snap to Point off the pop-up menu that appears. Now, instead of manually entering in the coordinates in the meshing sequence below, you may easily and accurately select them with your mouse.





OK

X(-3) Y(0) Z(0) OK

X(0) Y(0) Z(0) OK

X(0) Y(1) Z(0) OK

X(-3) Y(1) Z(0) OK





OK

X(-3) Y(0) Z(0) OK

X(-3) Y(-3) Z(0) OK

X(0) Y(-3) Z(0) OK

X(0) Y(0) Z(0) OK





OK

X(0) Y(0) Z(0) OK

X(5) Y(0) Z(0) OK

X(5) Y(1) Z(0) OK

X(0) Y(1) Z(0) OK





OK

X(5) Y(0) Z(0) OK

X(10) Y(0) Z(0) OK

X(10) Y(1) Z(0) OK

X(5) Y(1) Z(0) OK

Compatibility

Now these superelements must be combined into one structure to satisfy our compatibility requirement. To accomplish this task, we use the Check Coincident Nodes command, which combines nodes that occupy the same location (coinciding in the same place). By combining these nodes, the superelements are then connected by these shared nodes. If you neglect to combine the nodes, it will be easy to notice that in the analysis results, the model will be disjointed along those boundaries.

Tools.Check.Coincident Nodes

Entity Selection.Select All

OK

OK to specify additional range of nodes to merge? Yes

Entity Selection.Select All

OK

Options.Merge Coincident Entities(check)

OK

Loads and Constraints

Loads and constraints are applied similarly in FEMAP as they are applied when we do finite element analysis by hand calculations. To apply a load or a constraint to a model, you first must create a set in which the load or constraint will exist. This allows you to change the loading or the constraints on your model very easily and quickly by simply defining a new set and only applying that set in the analysis. Once the load and constraint sets have been defined, you may apply either in a variety of ways. In this exercise, we will constrain and load individual nodes.

Create a constraint set

Model.Constraint.Set (or Shift-F2)

Title(ConstraintSet1)

OK

Specify the constraints

For this model we will constrain the nodes along the left side of the base of the rod, fixing them so they may not move in either the x or y direction.

Model.Constraint.Nodal

Entity Selection.Hold the shift key and drag a box over the nodes on the left boundary of the model (A schematic is shown below.)

OK

DOF.TX(check)

DOF.TY(check)

OK

Cancel

Create a load set

Model.Load.Set (or Control-F2)

Title(LoadSet1)

OK

Specify the loading

For this model, we will place a single point load at the center of the right end of the rod. The load will be axially applied to demonstrate the internal stresses inside a rod. At a later point in the exercise, we will change this load to a transverse load. This will allow us to model a beam and examine its internal stress state.

Model.Load.Nodal

Entity Selection.Select the center node of the rods right side

OK

Load.FX.Value(1000)

OK

Cancel

Model Analysis

CAEFEM analysis using FEMAP generated models

File.Export.Analysis Model (or Press Ctrl T)

Export To.CAEFEM(check)

OK

OK to save model? Yes

The CAEFEM analysis window will now automatically open. The following section refers to commands in this window.

Analysis Options

Constraint Set(Select ConstraintSet1)

LoadSet(Select LoadSet1)

Run

Results Generation.Linear Static(check)

OK

CAEFEM will automatically import the results back into FEMAPMI/NASTRAN analysis using FEMAP generated models. You may now go directly to the post-processing section of this tutorial.

Exporting Models from FEMAP to MI/NASTRAN... skip in 306Once you have created a valid model in FEMAP, you must export that model in order to perform the analysis so it can be used in the MI/Tools application. To do this, perform the following commands:

File.Export

Analysis Model

Type(1..Static)

NASTRAN(check)

Select ME/NASTRAN off the pulldown menu

OK

The program will now create a NASTRAN Input Deck (or .NID file). It will allow you to name the file and place it in an appropriate directory. If possible, place the file in a new subdirectory of the MITOOLS folder. It will then begin to write the Input Deck.

NASTRAN Executive and Solution Control

OK

NASTRAN Case Control

Select 2..Print and PostProcess on the pull-down menu

Title (Describe the model)

OK

COSMIC NASTRAN Bulk Data

OK

The .NID file will now be ready to run in NASTRAN

MI/NASTRAN Analysis

Open the MI/Tools Application. Using the folder explorer open the folder the .NID file has been placed in. Highlight the .NID file and click the MI/NASTRAN button. This will run the job deck. A subdirectory to the current directory with the same name as the .NID file will be created containing the results of the analysis. To see if the analysis was completed successfully, open the results directory and open the .F06 file using the File Editor button of the MI/Tools Application. If the analysis was completed successfully, then there should be no major error messages and displacement vectors should be printed.

Importing Data to FEMAP for Post-Processing

The displacement and stress data may now be imported back into FEMAP for post-processing. To do this perform the following steps from FEMAP:

File.Import

Analysis Results

NASTRAN(check)

Select ME/NASTRAN off the pulldown menu

OK

Find the output directory created in the directory in which your .NID file is located, and having the same name.

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