102 - understanding static analyses.pdf

8/14/2019 102 - Understanding Static Analyses.pdf

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StructuralAnalysisIUnderstandingStaticAnalysesLecture

UnderstandingStaticAnalyses.mp3

Understanding Static Analyses

Static Analyses are used to calculate deformations, stresses, and

strains in a model in response to specified loads and constraints.

Input: Loads

Steady state only; no time varying Loads Can be Structural, Thermal, or Prescribed Displacement Multiple Load sets permitted

Input: Constraints

Structural constraints applied to geometry Inertia relief

Output: Values

Stresses StrainsDeformations (linear and angular)

Force reactions

Output: Formats

Max/Min values Fringe Plots Graphs ASCII, MS-Excel, Tabulated text


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Model for Static Analysis

Results of Static AnalysisLectureNotes

Static Analyses


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Static Analyses can be used to calculate deformations, stresses, and strains in aPro/ENGINEER part or assembly model in response to specified steady loads andconstraints. This type of structural analysis does not account for any structural

damping effects or time-varying loads.

The Static Analysis can also be used to check for large deformations or stresses due to

contact between structural components.

Static Analysis Input

In general, an analysis is the calculation of a models response to loading andboundary conditions. Structural analyses are performed on a product in order to findthe stress and displacement distribution over the entire structure. Mechanicas StaticAnalysis is a structural analysis enabling the evaluation of these quantities in differentforms, either fringe plots or graphs. The input for a Static Analysis can be acombination of loading conditions (and/or enforced displacement constraints) andconstraints:

Loads can be either structural (geometry or steady-state inertia forces) and/orthermal (Global Temperature or Mechanica Thermal). An enforced or prescribeddisplacement can also act as a loading condition. The loads can varygeometrically in 3D space, but they cannot be varied with respect to time. Theloads can be combined in multiple load sets and their structural effects can beexamined individually or cumulatively.

Constraints can be any structural constraints applied directly to the geometry(surfaces, edge/curves, or points). If no boundary conditions are specified, themodel can be analyzed structurally by imposing inertia relief. This optionenables Mechanica to analyze the model as if it was floating freely in space but

with the loads applied.

Static Analysis Output

The results from a Static Analysis are stresses, strains and deformations (includingrotations). You can also evaluate force reactions. These results can be singlenumerical values (if youre looking for maximum/minimum values) or can be valuescomputed at any location in the model (fringe plots or graphs). You can also createprobes at certain locations in the model (also known as Mechanicas Measures) andmake readings of the quantities of interest at those locations.

All these values can be found either in the Static Analysis summary report or bycreating result windows. By default, all these quantities are evaluated in binary formatbut can be exported to ASCII format as well. Graphs can be easily exported to MS-Excel or in tabulated text forms as well.

Best Practices

Your model's loading condition determines the type of analysis you should use. For a Static Analysis with inertia relief, ensure that the model does not contain

unconnected bodies. If multiple bodies exist in your model and they are not


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connected to one another, the analysis will fail with an under-constrained error.To run an inertia relief analysis with multiple bodies, ensure that all the bodiesare connected in such a way that there is no relative motion between thebodies.

You can combine more than one constraint set into a new single set, orcalculate results for any one constraint set.

UnderstandingStaticAnalysesDemonstrationUnderstandingStaticAnalyses_demo.mp4

UnderstandingStaticAnalysesProcedureProcedure: Creating Static Analyses

ScenarioIn this procedure, you will define a Static Analysis in a Pro/ENGINEER assembly model for

which loads and constraints were already created and defined.

CreateStatic flanges.asm

Task 1.Open the Mechanica Application, investigate the model and existingMechanica Simulation Features, and define a Static Analysis.

1. Click Applications > Mechanica.

2. Explore and examine the model. From the top of the model tree, click Show >Expand All.


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Note the existing Mechanica simulation features including:

Internal and External Pressure Loads Cyclic and Mirror Symmetry Constraints A Translation Constraint A Fastener and its associated Measures

3. Click Mechanica Analyses/Studies from the main toolbar.

4. Click File > New Static...

5. In the Name field type FLANGES_STATIC.

Providing a short description of the analysis is not a required step, but it can

be beneficial for other users who would access this data in order tounderstand your analysis.

6. Select the Combine Constraint Setscheck box and click each of the constraint

sets defined in the model.

7. If necessary, select the Pressureload from the Loads section of the dialog box.


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This is an educational example in which we have defined a constraint set for

each of the constraints in the model. In everyday examples, these

constraints could be added to single or multiple constraint sets.

8. Select the Outputtab and verify that the Stresses, Rotations, and Reactions

check boxes are selected, and that Plotting Grid is set to 4as shown in the figure.

The value you specify for Plotting Grid determines the number of intervalsalong each edge of each element that Mechanica uses to create plotting

grids. Mechanica calculates quantity values at the intersections of grid lines

and reports precise results for each grid intersection point and interpolates

these values to show results elsewhere.

9. Select the Convergencetab and select Single-Pass Adaptivefrom the Method

drop-down menu, if necessary.

Note the existence (but do not select) the check boxes for NonlinearandInertia Relief.

10. The dialog box should now appear as shown in the figure. Click OKto completethe Static Analysis Definition and close the dialog box.

11. Close any open dialog boxes.


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Task 2.Save the model and erase it from memory.

1. Return to the Standard Pro/ENGINEER mode by clicking Applications > Standard.

2. Click Save from the main toolbar and click OKto save the model.

3. Click File > Erase > Current > Select All > OKto erase the models from

memory.

This completes the procedure.

UnderstandingStaticAnalysesExerciseExercise: Static Analysis


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Objectives

After successfully completing this exercise, you will be able to:

Configure and Run Mechanica Static Analyses. Examine and set up the proper Mechanica Model Type based on the input and

material properties. Compare the results from 3D, 2D Axisymmetric, and 3D with Cyclic Symmetry

model types and identify the benefits of using each of these model types.

ScenarioIn this exercise, you will use Mechanica to evaluate the stresses and deformations in a

supporting component made out of Brass. The loads exerted on this component are

internal pressure and external loads. The model is fully constrained and you will evaluateand compare the stresses and deformations for this component using the following model

types:

3D (the default model type) 2D Axisymmetric 3D with Cyclic Symmetry

3D 2D Axisymmetric 3D with Cyclic Symmetry


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3D

2D Axisymmetric


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3D with Cyclic Symmetry

The model is a revolved feature with stiffeners placed transversely along the length of thecylinder. There are two loads in the model: an external surface load of 50 N and an

internal pressure of 30 MPa. The model is held fully constrained at the bottom of the

support housing.

The material is isotropic (BRASS) with Youngs Modulus (E) of 103 GPa. The material is a

rather soft, ductile material with a Yield Strength of about 190 MPa. Since the material isisotropic, the model has the same properties in all three directions.

You will start by running an analysis for this geometry using the 3D (default) Model Type.That is, were going to apply the load and constraints in the model in its current

geometrical configuration.

However, you may wish to reduce the number of finite elements by using the advantage

that the model exhibits the same properties in the 3D domain. There are two possible

solutions:

Imagine youre slicing a sheet of paper-like sliver surface from this 3D model. Next,revolve this sliver surface 360 around its axis of revolution. The outcome is thesame, geometry-wise, as the full 3D model. But, by using this idealization

approach, we can reduce the number of elements (since we are now working in 2D)and be able to provide the same results as a 3D model. This model type is called in

Mechanica: 2D Axisymmetric.

Another possibility is to cut the model (like a slice of pie) and use a special type ofconstraints (Cyclic Symmetry) to simulate the fact that the remaining model is still

there. Its still going to be a 3D model type, but the finite element count willdramatically drop.


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Although each one of these design and analysis approaches are interesting to examine,

we will concentrate our attention to the 2D Axisymmetric model type. In the end, we willexamine the results from all these three model types and discuss the benefits of using any

of these idealizations.

StaticHousing housing_support.prt

Task 1.Resume the Cut Feature in the Pro/ENGINEER 3D Model and open theMechanica application.

You need to create a 3D cut in the original model in order for you to select

the surface(s) for the 2D Axisymmetric model.

1. From the main menu, click Edit > Resume > Resume All.

Note that the AXISYMMETRY_CUTand AXIS_CSYSwere resumed.

For a 2D Axisymmetric model, the angle of the pie-like cut is not of critical

importance (it can be 2, 45, or 359). However, you must be able to

select the surface of that cut which is revolved about the axis to give us the

same final 3D shape.


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2. Click Applications > Mechanica.

3. From the main menu, click Edit > Mechanica Model Setup... > Advanced.

4. Select the 2D Axisymmetricradio button.

Before proceeding, note that the AXIS_CSYScoordinate system is oriented

such that the X and Y axes lie in the plane of the geometry you are going toselect (shown in red) for the 2D axisymmetric model. If this were not the

case, you would need to create a coordinate system that was oriented in this

way before continuing.

5. Select AXIS_CSYSfrom the model tree as the Coordinate System reference.

6. Select the surface shown under the mouse cursor in the figure as the GeometryReference.

7. Click OKto complete the Mechanica Model Setup and close the dialog box. Click

Confirmto acknowledge the deletion of all simulation modeling entities.

Note: Once you enter Mechanica with the 2D Axisymmetric model type,

Mechanica will add a blue color line to the perimeter of the surfaces you

have selected for the model. This is a visual aid used in order to differentiate

between a 2D Axisymmetric and a 3D model type.

Task 2.Define Loads, Constraints, Materials and a Static Analysis for the 2DAxisymmetric Model.


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1. Click Force/ Moment Load and select the top edge of the 2D geometry asshown in the figure.

2. Type -50in the Y field in the Force area of the dialog box and verify that the unitsfor the Force are set to Nas shown in the dialog box.

Note: This load application is equivalent to applying the load on the entire

top surface when in the original 3D model, but because you are in a 2D

Axisymmetric model now, you select an edge.

Note: Notice that due to being in a 2D Axisymmetric model you are

constrained in the XY plane. No forces can be applied in the Z direction and

moments can be only applied about the Z-axis.


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3. Click OKto complete the Force/Moment Load definition and close the dialog box.The load should now display as shown in the figure.


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4. Click Pressure Load and select the inside vertical edge shown in the figure.

5. Type 30in the Value field and verify that the units field is set to MPaas shown inthe figure.

Note: This load application is equivalent to applying pressure load on the

entire inner wall surface of the original 3D model.


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6. Click OKto complete the Pressure Load definition and close the dialog box. The

pressure load should now show on the model as shown in the figure.

7. Click Displacement Constraint and select the outside short vertical edge asshown in the figure.


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8. Verify that both translational degrees of freedom are set to Fixed Translation

and the single rotational degree of freedom is set to Fixed Rotation as shown inthe figure.

Note: This constraint is equivalent to constraining the entire outside surface

that this edge is coincident within the original 3D model.


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9. Click OKto complete the Constraint definition and close the dialog box. Theconstraint should now show on the model as shown in the figure.


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10. Click Material Assignment to open the Material Assignment dialog box. ClickMore...next to the Material field.

11. In the Materials dialog box that appears, select brass.mtlfrom the list of

materials and click Add Material to add it to the Materials in Model list. Click OKto close the Materials dialog box.

12. For the References, select the 2D surface you selected as part of the 2DAxisymmetric Model Type definition as shown in the figure.

13. Verify that the Material field is set to BRASSand click OKto assign BRASS to the2D Section.


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14. From the Main toolbar, click Mechanica Analyses/Studies .

15. Select File > New Static...

16. In the Name field, type STATIC_AXISYMMETRIC.

17. Verify that the constraint set and load set you created are selected in the Static

Analysis Definition dialog box.

18. From the Method drop-down menu, on the Convergence tab, select Multi-PassAdaptive.

19. Type 9in the Maximum field.

20. Type 5in the Percent Convergence field.

21. Verify that the Local Displacement, Local Strain Energy and Global RMS

Stressradio button is selected.

22. The dialog box should now appear as shown in the figure. Click OKto completethe Static Analysis Definition and close the dialog box.


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23. Verify that STATIC_AXISYMMETRICis selected in the Analyses and Design

Studies dialog box and click Start Run > Yesto start the design study.

24. Click Display Study Status once the analysis is started.

The analysis should take about 1530 seconds to complete. AutoGEM has

generated around 80 finite elements (2D Solids) for this model.

Task 3.Review the STATIC_AXISYMMETRICresults.

1. When the analysis is complete, click Closeto close the Run Status window, and

click Closeto close the Diagnostics dialog box.

2. Verify that STATIC_AXISYMMETRICis still selected in the Analyses and DesignStudies dialog box and click Results to enter Results mode.


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2D

Axisymmetric290 1.396 80 12

3D with CyclicSymmetry

291 1.389 396 35

3D 295 1.394 1531 61

Although this example is not intended as a verification model in Mechanica,

we can easily identify that the results for each model type are close for both

Von Mises stress and displacement.

The conclusion is more from productivity point of view: it takes less time and

elements to mesh and solve the 2D Axisymmetric model versus the 3D

Mechanica default model type. The 2D Axisymmetric model type can be

applied for all cases where the loads, constraints, materials are symmetrical

about an axis of revolution.

3. Click File > Exit Results > Noto exit the Result Window without saving any

results.

Task 5.Save the open models and erase them from memory.

1. Close all open Diagnostics dialog boxes.

2. Close all open Run Status dialog boxes.

3. Click Save from the main toolbar and click OKto save the model.

4. Click File > Close Window.

5. Repeat steps 3 and 4 for all open models

6. Click File > Erase > Not Displayed > OKto erase the models from memory.

This completes the exercise.

102 - understanding static analyses.pdf

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