definition of weight and inertia loading - msc...

APPENDIX C2

Definition of Weight and Inertia Loading

MSC.Nastran 105 Exercise Workbook C2-1

Objectives:

■ Apply boundary condition and gravity load to the model.

■ Utilize the WTMASS option to obtain the correct result.

■ Compare results.

C2-2 MSC.Nastran 105 Exercise Workbook

APPENDIX C2 Definition of Weight and Inertia Loading


Model Description:This exercise is designed to study the effect of gravity on a model. Whenmodeling a gravity load in English units, users may sometimes forget toconvert the mass density to weight density. Failure to do so will yieldresults that are incorrect.

Figure C2.1-Model Geometry

Table C2.1

Outer Diameter of Cylinder (OD) 4 in

Inner Diameter of Cylinder (ID) 3.25 in

Height (B) 16 in

Hole Diameter (h) 1.5 in

Weight Density 0.101 lbs/in3

Weight/Mass Factor 2.59E-3 sec2/in

Elastic Modulus 10.0E6 lbs/in2

Poisson’s Ratio 0.33

OD

ID

B

h


Figure C2.2-Loads and Boundary Conditions

123123123123123

123

Gravity = 7 g



Suggested Exercise Steps

■ Open the previous workshop.

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

■ Apply the fixed boundary constraints (SPC1).

First Job (Solid)

■ Apply gravity load of 7 with grav constant of 1. (GRAV).

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

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

■ Review the results.

Second Job (Solid2)

■ Apply 7g gravity with gravity constant of 386.4. (GRAV).



■ Review and compare the results.

Third Job (Solid3)

■ Apply 7g gravity with gravity constant of 386.4. (GRAV).


■ Specify the weight-mass conversion value.

■ PARAM, WTMASS, 0.00259


■ Review and compare the results.


ID SEMINAR,WORKSHOPC2______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________CEND________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________BEGIN BULK



1 2 3 4 5 6 7 8 9 10


1 2 3 4 5 6 7 8 9 10

ENDDATA



Exercise Procedure:1. Users who are not utilizing MSC.Patran for generating an input file should go

to Step 8, otherwise, proceed to step 2.

2. Open the database named Solid.db.

Change to the directory where the database is located.

3. Create a set of material properties for the plate.

4. Define the plate thickness.

File/Open...

Existing Database Name Solid.db

OK

◆ Materials

Action: Create

Object: Isotropic

Method: Manual Input

Material Name alum

Input Properties...

Elastic Modulus = 10.0E6

Poisson Ratio = .33

Density = .101

Apply

Cancel

◆ Properties

Action: Create

Dimension: 3D

Type: Solid

Property Set Name bar


5. Apply constraints to the model.

Constrain the bottom surface from displacement in all directions.

Rotate to Left side view.

Input Properties...

Material Name(Select from Material Property Sets box.)

m:alum

OK

Select Members <Select Solid Element Icon in select menu and select All the elements (Elm 1:4480)>

Add

Apply

◆ Load/BCs

Action: Create

Object: Displacement

Type: Nodal

New Set Name pinned

Input Data...

Translations <T1 T2 T3> <0, 0, 0>

OK

Select Application Region...

● FEM

Select Nodes(see Figure C2.3)

<Select all nodes at the bottom surface of the model (Left edge in the display)>

Left side view



Figure C2.3-Model Constraint

Add

OK

Apply

Select these nodes.


6. Apply gravity load to the model.

Constrain the bottom surface from displacement in all direction.

Return to the Iso 3 view.

Note: It is not necessary to specify that gravity force is negative becauseTrans Accel <A3> is defaulted to point down.

7. Now, run the analysis.

Be sure to activate the Node i.d. for Weight Generator so MSC.Nastranwill output the weight table in the .f06 file.

◆ Load/BCs

Action: Create

Object: Inertial Load

Type: Element Uniform

New Set Name gravity

Input Data...

Load/BC Set Scale Factor: 1.0

Trans Accel <A1 A2 A3> <0, 0, 7>

OK

Apply

◆ Analysis

Action: Analyze

Object: Entire Model

Method Analysis Deck

Job Name solid

Solution Type... ● LINEAR STATIC

Solution Parameters...

Iso 3 view



An MSC.Nastran input file called solid.bdf will be generated. The processof translating your model into an input file is called Forward Translation.The Forward Translation is complete when the Heartbeat turns green.MSC.Patran Users should proceed to step 9.

Node i.d. for Wt.Gener. = 0

OK

OK

Apply


Submitting the input file for analysis:

8. Submit the input file to MSC.Nastran for analysis.

8a. To submit the MSC.Patran .bdf file for analysis, find an availableUNIX shell window. At the command prompt enter: nastransolid.bdf scr=yes. Monitor the run using the UNIX ps command.

8b. To submit the MSC.Nastran .dat file for analysis, find an availableUNIX shell window. At the command prompt enter: nastran solidscr=yes. Monitor the run using the UNIX ps command.

9. When the run is completed, edit the solid.f06 file and search for the word FATAL. If no matches exist, search for the word WARNING. Determine whether existing WARNING messages indicate modeling errors.



Comparison of Results10. Compare the results obtained in the .f06 file with the results on

the following page:

C2-16

MSC

.Nastran 105 E

xercise Workbook

DIRECTION

MASS AXIS SYSTEM (S) MASS X-C.G. Y-C.G. Z-C.G.

X 6.723973E+00 0.000000E+00 1.548170E-10 8.000008E+00

Y 6.723973E+00 -6.540650E-10 0.000000E+00 8.000008E+00

Z 6.723973E+00 -6.540650E-10 1.548170E-10 0.000000E+00

0 SPCFORCE RESULTANT

0 T1 T2 T3 R1 R2 R3

0 1 -7.3691053E-14 -2.8186134E-13 -4.7067810E+01 -7.2845907E-09 -3.0786040E-08 7.6456202E-14

Verify the SPCFORCE Resultant:

Mass * gravity = Resultant

6.724 * 7 = 47.068



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

12. Proceed with the Reverse Translation process, that is importing the solid.op2 the Analysis form and proceed as follows:

To simplify the view, turn off the entity labels and reset graphics using thetoolbar.

13. Plot the results of the analysis.

To plot the results to posted FEM use the Results Application radiobutton.

◆ Analysis

Action: Read Output2

Object: Result Entities

Method Translate

Select Results File...

Select Results File solid.op2

OK

Apply

◆ Results

Action: Create

Object: Quick Plot

Select Result Case Default, Static Subcase

Select Fringe Results Stress Tensor,

Quantity: von MIses

Hide Labels

Reset graphics


Select the Fringe Attributes icon.

The results should resemble Figure C2.4.

Figure C2.4

Although the solution is correct, it was just a coincidence that thisoccurred. The weight density of aluminum is 0.101 lbs/in3. This value wasentered in the density input field for material. However, MSC.Nastran

Display: Element Edges

Label Style...

Label Format: Fixed

Significant figures 4 <use slider bar>

OK

Apply



only recognizes mass density and not weight density. Therefore, the valueof 0.101 was taken as mass density. This will yield an incorrect solution.Remember, mass desity = (weight density / gravity). Therefore, the resulthas to be divided by gravity in order to yield the correct solution.

Another mistake was the value entered for gravity (acceleration). Thevalue 7 was entered. However, the actual value is 7g. Therefore, thesolution will be off by the factor of 386.4 in/sec2.

Although both the entered mass density and gravity values were incorrect,the solution happened to be correct. The reason is because the weightdensity needs to be divided by value of gravity (386.4 in/sec2) while thegravity (acceleration) needs to be multiplied by 386.4 in/sec2. Thus, thetwo 386.4 in/sec2 canceled out each other.

Next, we will make the mistake more obvious to see. Most users, who arenot familiar with how MSC.Patran defines its density, will often make thismistake.

To reset the graphics, click on this icon:

14. Apply the correct gravity load to the model.

Apply the 7 g gravity load, where g is 386.4 in/sec2.

15. Now, run the analysis.

◆ Load/BCs

Action: Modify

Object: Inertial Load

Type: Element Uniform

Select Set to Modify gravity

Modify Data...

Trans Accel <A1 A2 A3> <0, 0, 2704.8>

OK

Apply

◆ Analysis

Action: Analyze

Reset Graphics


An MSC.Nastran input file called solid2.bdf will be generated. Theprocess of translating your model into an input file is called ForwardTranslation. The Forward Translation is complete when the Heartbeatturns green.



Job Name solid2




OK

OK

Apply





16a. To submit the MSC.Patran .bdf file for analysis, find anavailable UNIX shell window. At the command promptenter: nastran solid2.bdf scr=yes. Monitor the run usingthe UNIX ps command.

16b. To submit the MSC.Nastran .dat file for analysis, find anavailable UNIX shell window. At the command promptenter: nastran solid2 scr=yes. Monitor the run using theUNIX ps command.

17. When the run is completed, edit the solid2.f06 file and search for the word FATAL. If no matches exist, search for the word WARNING. Determine whether existing WARNING messages indicate modeling errors.



the following page:

AP

PE

ND

IX C

2 Definition of W

eight and Inertia Loading

MSC

.Nastran 105 E

xercise Workbook

C2-23

DIRECTION


X 6.723973E+00 0.000000E+00 1.548170E-10 8.000008E+00

Y 6.723973E+00 -6.540650E-10 0.000000E+00 8.000008E+00

Z 6.723973E+00 -6.540650E-10 1.548170E-10 0.000000E+00


0 T1 T2 T3 R1 R2 R3

0 1 -3.0187408E-11 -1.0866241E-10 -1.8187002E+04 -2.8147510E-06 -1.1895723E-05 2.3724134E-11


Mass * gravity = Resultant

6.724 * (386.4 * 7) = 18187.0 <= Notice that this is different from previous solution.


19. Proceed with the Reverse Translation process, that is importing the solid2.op2 the Analysis form and proceed as follows:


To plot the results to posted FEM use the Results Application radiobutton.

Select the Fringe Attributes icon.


◆ Analysis



Method Translate


Select Results File solid2.op2

OK

Apply

◆ Results

Action: Create

Object: Quick Plot

Select Result Case Default, Static Subcase_2


Apply



Figure C2.5

Most users input the correct value for gravity (acceleration). However,they may not realize the density value is incorrect. After all, most densityvalues found in references are given as weight density. Thus, it isimportant to remember that mass density is needed for calculating forcesand stresses for unit consistency.

The solution will be off by a factor of 386.4, which is the value of gravity.

Now, we will utilize the weight-mass conversion option. This option willallow the users to input weight density as density; at the same time, it willalso signal MSC.Nastran to treat that value was weight density and makethe conversion.

To reset the graphics, click on this icon:

Reset Graphics


21. Apply the correct gravity load and also include weight-mass conversionto the model.

Note: F = CMa. Where C = 1/g = 0.00259 (English weight system).

An MSC.Nastran input file called solid3.bdf will be generated. Theprocess of translating your model into an input file is called ForwardTranslation. The Forward Translation is complete when the Heartbeatturns green.

◆ Analysis

Action: Analyze



Job Name solid3



Wt.-Mass Conversion = 0.00259


OK

OK

Apply





22a. To submit the MSC.Patran .bdf file for analysis, find anavailable UNIX shell window. At the command promptenter: nastran solid3.bdf scr=yes. Monitor the run usingthe UNIX ps command.

22b. To submit the MSC.Nastran .dat file for analysis, find anavailable UNIX shell window. At the command promptenter: nastran solid3 scr=yes. Monitor the run using theUNIX ps command.

23. When the run is completed, edit the solid3.f06 file and search for the word FATAL. If no matches exist, search for the word WARNING. Determine whether existing WARNING messages indicate modeling errors.



the following page:

AP

PE

ND

IX C

2 Definition of W

eight and Inertia Loading

MSC

.Nastran 105 E

xercise Workbook

C2-29

DIRECTION


X 6.723973E+00 0.000000E+00 1.548168E-10 8.000008E+00

Y 6.723973E+00 -6.540666E-10 0.000000E+00 8.000008E+00

Z 6.723973E+00 -6.540666E-10 1.548168E-10 0.000000E+00


0 T1 T2 T3 R1 R2 R3

0 1 -7.8159701E-14 -2.8299585E-13 -4.7104336E+01 -7.2902302E-09 -3.0809911E-08 6.3584554E-14


C(weight/mass conversion) * Mass * gravity = Resultant

(1/386.4) * 6.724 * (7 * 386.4) = 47.068


25. Proceed with the Reverse Translation process, that is importing the solid2.op2 the Analysis form and proceed as follows:


To plot the results of the posted FEM, use the Results Applicationradio button.


◆ Analysis



Method Translate


Select Results File solid3.op3

OK

Apply

◆ Results

Action: Create

Object: Quick Plot

Select Result Case Default, Static Subcase_3


Apply



Figure C2.6

As shown above, the solution is the same as that of our first job (solid).This time, the correct solution is not by a coincidence.

This concludes our workshop.

Quit MSC.Patran when you are finished with this exercise.

definition of weight and inertia loading - msc...

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