nastran-lesson007

WORKSHOP 7

Linear Static Analysis of a Simply-Supported Truss

MSC.Nastran 120 Exercise Workbook 7-1

Objectives:■ Create a finite element model by explicitly defining node

locations and element connectivities.

■ Define a MSC.Nastran analysis model comprised of CROD elements.

■ Prepare a MSC.Nastran input file for a linear static analysis.

■ Visualize analysis results.

7-2 MSC.Nastran 120 Exercise Workbook

WORKSHOP 7 Simply-Supported Truss (Sol 101)


Model Description:Figure 7.1 is a finite element representation of the truss structureshown on Page 7-1. The nodal coordinates provided are defined inthe global cartesian coordinate system (MSC.Nastran Basic system).

The structure is comprised of truss segments connected by smoothpins such that each segment is either in tension or compression. Thestructure is pinned at Node 1 and supported by a roller at Node 7.Point forces are applied at Nodes 2, 4, and 6.

Figure 7.1

Figure 7.2 - Loads and Boundary Conditions

Table 7.1 - Model Properties

Cross-Sectional Area: 5.25 in2

Elastic Modulus: 1.76E+06 psi

Tension Stress Limit: 1900 psi

Compression Stress Limit: 1900 psi

1

2

3

4

5

6

7

1

2 3

456 7

8

9 10 11

X

Y

Z

[0,0,0]

[140,72,0]

[288,144,0]

[192,0,0] [384,0,0]

[432,72,0]

[576,0,0]

Y

12 3456

1500.

3456

3456

1500.

3456 3456

1500.

2

XZ

1300.

1300.

1300.


Suggested Exercise Steps:

■ Open a new database.

■ Explicitly generate a finite element representation of the truss structure without defining any geometry, i.e., the nodes (GRID) and element connectivities (CROD) should be defined manually.

■ Define material (MAT1) and element (PROD) properties.

■ Apply simply-supported boundary constraints (SPC1) and point forces (FORCE).

■ Use the load and boundary condition sets to define a load case (SUBCASE).

■ Prepare the model for a linear static analysis (SOL 101 and PARAMs).

■ Generate an input file and submit it to the MSC.Nastran solver.

■ Post-process results.

■ Quit MSC.Patran.



Exercise Procedure:

1. Create a new database called workshop7.db.

In the New Model Preferences form set the following:

Activate the entity labels by selecting the Show Labels button on thetoolbar.

NOTE:Whenever possible, toggle off the ❑ Auto Execute option byleft clicking the check box.

2. Create the nodes by manually defining their respective coordinates:

File/New...

New Database Name: workshop7

OK

Tolerance: ◆ Default

Analysis Code: MSC/NASTRAN

Analysis Type: Structural

OK

◆ Finite Elements

Action: Create

Object: Node

Method: Edit

❑ Associate with Geometry

Node Location List: [0, 0, 0]

Apply

Show Labels


Repeat the previous operation to create the remaining nodes. Referto the Figure 7.1 for the nodal coordinates.

Next, manually define the truss segment connectivities with BAR2elements using our newly created nodes. Again, refer to Figure 7.1for connectivity information.


Apply


Apply


Apply


Apply


Apply


Apply

◆ Finite Elements

Action: Create

Object: Element

Method: Edit

Shape: Bar

Topology: Bar2

Node 1 = Node 1

Node 2 = Node 2

Apply



Repeat the previous operation until all the truss segments have beencreated.

Node 1 = Node 1

Node 2 = Node 2

Apply

Node 1 = Node 2

Node 2 = Node 4

Apply

Node 1 = Node 4

Node 2 = Node 6

Apply

Node 1 = Node 6

Node 2 = Node 7

Apply

Node 1 = Node 2

Node 2 = Node 3

Apply

Node 1 = Node 3

Node 2 = Node 4

Apply

Node 1 = Node 4

Node 2 = Node 5

Apply

Node 1 = Node 5


The completed model resemble Figure 7.3.

Figure 7.3

3. Define a material using the specified modulus of elasticity andallowable stresses.

Node 2 = Node 6

Apply

Node 1 = Node 1

Node 2 = Node 3

Apply

Node 1 = Node 3

Node 2 = Node 5

Apply

Node 1 = Node 5

Node 2 = Node 7

Apply

◆ Materials

Action: Create

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11

X



4. Reference the material that was created in the previous step. Definethe properties of the truss segments using the specified cross-sectional data.

Object: Isotropic

Method: Manual Input

Material Name: mat_1

Input Properties...

Constitutive Model: Linear Elastic

Elastic Modulus = 1.76E6

OK

Apply

Constitutive Model: Failure

Tension Stress Limit =??? (Enter material limit)

Compression Stress Limit =??? (Enter material limit)

OK

◆ Properties

Action: Create

Object: 1 D

Method: Rod

Property Set Name: rod

Input Properties...

Material Name: m:mat_1

Area:???

(Enter cross-sectional area)

OK

Select Members: Elm 1:11


5. Visually verify element connectivities. To make this process easier,scale down the elements by 10%. Use the Display/FiniteElements... option.

6. Create two constraints and apply them to the analysis model. Theseboundary conditions represent the simply-supported ends of thetruss.

6a. The left-hand support is defined as follows:

Add

Apply

Display/Finite Elements...

FEM Shrink: 0.10

Apply

Cancel

◆ Loads/BCs

Action: Create

Object: Displacement

Method: Nodal

New Set Name: pin

Input Data...

Translation < T1 T2 T3 > < 0, 0, >

OK

Select Application Region...

Geometry Filter: ◆ FEM

Select Nodes: Node 1

Add

OK

Apply



6b. The right-hand constraint is located at the opposite end of the truss.

The displacement constraints are shown in Figure 7.4.

Figure 7.4

7. Apply forces to the upper joints of the truss as shown in Figure 7.2.Vertical forces of 1500 lbs and horizontal forces of 1300 lbs shouldbe applied at the proper nodes.

◆ Loads/BCs

Action: Create

Object: Displacement

Method: Nodal

New Set Name: roller

Input Data...

Translation < T1 T2 T3 > <, 0, >

OK



Select Nodes: Node 7

Add

OK

Apply

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11 12 2

X


7a. First, define the vertical forces.

The vertical forces should resemble Figure 7.5.

Figure 7.5

7b. Define the horizontal loads.

◆ Loads/BCs

Action: Create

Object: Force

Method: Nodal

New Set Name: force_1

Input Data...

Force < F1 F2 F3 > <, -1500, >

OK



Select Nodes: Node 2:6:2

Add

OK

Apply

◆ Loads/BCs

Action: Create

1500.

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11

1500. 1500.

X



The forces should resemble Figure 7.6.

Figure 7.6

Object: Force

Method: Nodal

New Set Name: force_2

Input Data...

Force < F1 F2 F3 > < -1300,, >

OK



Select Nodes: Node 2:6:2

Add

OK

Apply

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11

1985.

1985.

1985.

X


7c. Reset the display by selecting the Reset Graphics icon on the TopMenu Bar.

To display only the horizontal forces, change the Action on theLoad/BCs form to Plot Markers.

Select the Force_force_2 set in the Assigned Load/BC Sets box byhighlighting it. Also apply the markers to the current groupdefault_group.

The display should appear as follows:

Figure 7.7

8. Create a load case that references the forces and boundaryconditions that have already been defined.

◆ Loads/BCs

Action: Plot Markers

Assigned Load/BC Sets:

Select Groups:

Apply

◆ Load Cases

Reset Graphics

Force_force_2

default_group

1300.

1300.

1300.

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11

X



* NOTE: Do not to enter any load more than one time into thespreadsheet. Doing so will result in increasing the loadby a factor equal to the number of times the load isentered into the spreadsheet. The increase in factor canbe shown in two different manners. First, the LBC ScaleFactor may show a value greater than one, or second, thespreadsheet may contain repeated entries of the sameload. Either condition will result in erroneous loadingconditions.

Reset the display by selecting the Reset Graphics icon on the TopMenu Bar.

Plot the Load/BCs markers and post them to the current group.

Select all the Load/BC sets in the Assigned Load/BC Sets box byhighlighting all of them. Post the markers to the current group.

Action: Create

Load Case Name: truss_lbcs

Load Case Type: Static

Assign/Prioritize Loads/BCs

Select Individual Loads/BCs (Select from Menu)

OK

Apply

◆ Loads/BCs

Action: Plot Markers

Assigned Load/BCs Sets:

Select Groups:

Displ_pinDispl_rollerForce_force_1Force_force_2

Reset Graphics

Displ_pinDispl_rollerForce_force_1Force_force_2

default_group


The display should appear similar to the figure below:

Figure 7.8

9. Deactivate the entity labels by using the Display/Entity Color/Label/Render... option.

Reset the display by selecting the Reset Graphics icon on the TopMenu Bar.

Display the model in its unscaled state using the Display/Finite El-ements... option.

Apply

Display/Entity Color/Label/Render...

Hide All Entity Labels

Apply

Cancel

Display/Finite Elements...

FEM Shrink: 0.0

Y

Z

1

2

3

4

5

6

7

1

2 3

45

6 7

8

9 10 11

12

1985.

1985.

1985.

2

X

Reset Graphics



10. Generate an input file for analysis.

Click on the Analysis radio button on the Top Menu Bar and com-plete the entries as shown here.

Apply

Cancel

◆ Analysis

Action: Analyze

Object: Entire Model

Method: Analysis Deck

Job Name: truss

Solution Type...

Solution Type: ◆ Linear Static

Solution Parameters...

■ Database Run

■ Automatic Constraints

Data Deck Echo: Sorted

Wt.- Mass Conversion =0.00259 (For English units)

OK

OK

Subcase Select...

Subcases For Solution Sequence: truss_lbcs

Subcases Selected:Default (Click on this to deselect)

OK

Apply


An MSC.Nastran input file called truss.bdf will be generated. Thisprocess of translating the model into an input file is called the For-ward Translation. The Forward Translation is complete when theHeartbeat turns green.



Submitting the Input File for Analysis:11. Submit the input file to MSC.Nastran for analysis.

11a. To submit the MSC.Patran.bdf file for analysis, find anavailable UNIX shell window. At the command promptenter: nastran truss.bdf scr=yes. Monitor the run usingthe UNIX ps command.

11b. When the run is completed, edit the truss.f06 file andsearch for the word FATAL. If no matches exist, searchfor the word WARNING. Determine whether existingWARNING messages indicate modeling errors.

11c. While still editing truss.f06, search for the word:

D I S P L A C E (spaces are necessary).

What are the components of the displacement vector for GRID 7(translation only)?

Search for the word:

S I N G L E (spaces are necessary).

What are the components of the reaction force at GRID 1?

Disp. X =

Disp. Y =

Disp. Z =

Force X =

Force Y =

Force Z =


Search for the word:

S T R E S S (spaces are necessary).

What is the margin of safety for CROD 2?

What is the Axial Stress for CROD 7?

M.S. =

Axial Stress =



12. MSC.Nastran Users have finished this exercise. MSC.Patran Users should proceed to the next step.

13. Proceed with the Reverse Translation process, that is, attaching thetruss.xdb results file into MSC.Patran. To do this, return to theAnalysis form and proceed as follows:

When the translation is complete and the Heartbeat turns green, bringup the Results form.

Choose the desired result case in the Select Result Cases list and se-lect the result(s) in the Select Fringe Result list and/or in the SelectDeformation Result list. And hit Apply to view the result(s) in theviewport.

To reset the display graphics to the state it was in before post-pro-cessing the model, remember to select the Reset Graphics icon.

Quit MSC.Patran after completing this exercise.

◆ Analysis

Action: Attach XDB

Object: Result Entities

Method: Local

Select Results File...

Filter

Selected Results File truss.xdb

OK

Apply

◆ Results

Action: Create

Object: Quick Plot

Reset Graphics

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