patran: msc公司提供的弹簧单元的例题

青华模具培训

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Objectives:

              Modify nodal analysis and nodal definition coordinate systems to reference a local coordinate system.

              Define bar elements connected with a spring element. (CBAR and CELAS1)

              Submit the model to MSC.Nastran.

              Apply a rigid body constraint to account for the extra DOF on a bar element. (SPC)

              Re-submit the model to MSC.Nastran.

              Compare results with a hand calculation.

MSC.Nastran 120 Exercise Workbook 20-1

WORKSHOP 20 Analysis of a Spring Element (CELAS)

Model Description:

The Figure in the title page shows a cantilever beam with a spring connection in between two elements. The spring is high-lighted for clarification. The left end is fixed into the wall, and a tensile load of 100 lbf is applied to the right end of the model.

Figure 20.1 shows two user defined coordinate systems. Nodes on the left half of the beam will reference Coordinate System 11 for displacements and location. Nodes on the right half will ref-erence Coordinate System 13.

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A spring element is attached at the midpoint of the assembly. Properties for the spring, and bar elements are shown in Table

20.1 and Table 20.2. The material properties for the model are shown in Table 20.3. Because the spring attaches the beams in the Global X direction, the model is properly connected for a hand calculation.   However, for MSC.Nastran, all DOF of the model have to be constrained against rigid body motions. When the model is first submitted for analysis, a fatal error message will be returned.

Because the right half of the bar elements also have DOF in the UY, UX, RX, RY, and RZ, an additional constraint needs to be applied. After adding the constraints and re-running the job, compare the deflection results with the hand calculation.

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Table 20.1 - Spring Properties

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Table 20.2 - Element Properties

A	1 in2
I11	10 in4
I22	10 in4
Torsional Constant	0.1

20-4 MSC.Nastran 120 Exercise Workbook

Suggested Exercise Steps:

              Open a new database.

              Define the coordinate systems.

              Create Curves to define bar elements.

              Mesh the Curves and define the nodal coordinate systems for each half of the model.

              Define the spring element.

              Define material properties.

              Define spring and bar properties.

              Apply the first constraint and load on the model.

              Submit the model to MSC.Nastran.

              Review the model for fatal messages.

              Add a constraint to account for rigid body motions.

              Re-submit the model to MSC.Nastran.

              Compare the results with a hand calculation.

MSC.Nastran 120 Exercise Workbook 20-5

WORKSHOP 20 Analysis of a Spring Element (CELAS)

Exercise Procedure:

1.     Create a new database called workshop20.db. File/New Database

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New Database Name

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workshop20

OK

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In the New Model Preferences form set the following:

Tolerance ◆ Default Analysis code:

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MSC/NASTRAN

OK

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2.   Activate the entity labels by selecting the Show Labels button on the toolbar.

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Show Labels

3. Also, activate the Node Size button.

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Node Size

4. Create coordinate frames.

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◆Geometry

Action:Object:Method:

Coord ID List:Origin:

Point on Axis 3oint on Plane 1-3:

Apply

Coord ID List:

13

20-6 MSC.Nastran 120 Exercise WorkbookMSC.Nastran 120 Exercise Workbook 20-7

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[21, 0, 0]

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Refer. Coordinate Frame:

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Coord 11

OK

Point on Plane 1-3:

Curve List:

Curve 1

Apply

5. Create parent geometry. Analysis Coordinate Frame:

◆ Geometry Refer. Coordinate Frame:

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Coord 13Coord 13

OK

Action:

Create

Curve List:

Object:

Apply

Method:

Refer. Coordinate List:

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7. Create the spring.

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Vector Coordinates List:

◆ Finite Elements

Origin Coordinates List:

Action:

Apply

Object:

Refer. Coordinate List:

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Coord 13

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Method:

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Vector Coordinates List:

Shape:

Origin Coordinates List:

Node 1 =

Apply

Node 2 =

Curve 2

6. Create the nodes (GRID) and connectivities (CBAR) by meshing

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Apply

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the curves previously created.

7a. Define spring properties.

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◆ Finite Elements

Create
Mesh
Curve
10
Bar2

◆ Properties

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Action:

Action:

Object:

Object:

Type:

Type:

Global Edge Length:

Property Set Name:

Element Topology:

Input Properties... Node Coordinate Frames...

Spring Constant

100

Analysis Coordinate Frame:

Coord 11

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20-8 MSC.Nastran 120 Exercise Workbook MSC.Nastran 120 Exercise Workbook 20-9

WORKSHOP 20 Analysis of a Spring Element (CELAS)

9. Define a material using the specified modulus of elasticity and

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DOF at Node 1

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