ABAQUS Workshop

Workshop 1

Importing and Editing an Orphan Mesh: Pump Model

Copyright 2003 ABAQUS, Inc 科研中国 http://www.SciEi.com 收集

这个实例中要用到的 cad 模型文件和脚本文件都可以在 abaqus 的

sample 文件夹（或者那个*.zip 文件）里找到。这个实例涉及到了用

abaqus 进行分析的整个流程中的各个细节，是入门的好帮手。像我这

样的新手一定会喜欢的：）

部件：泵体+垫片+底盖+螺栓

荷载条件：螺栓预紧+内压

Introduction The structural response of the pump assembly shown in Figure W3–1 will be determined. The assembly components include the pump housing (imported as an orphan mesh), a gasket, a cover, and eight bolts (all imported as CAD geometry). The analysis involves application of pre-tensioning loads in the bolts followed by internal pressure.

pump housing

gasket

cover

bolts

Figure W3–1. Pump assembly

In this workshop, you will create the parts of the model. Use the Part module of ABAQUS/CAE to import the mesh of a pump housing. Some modifications of its geometric features follow. The other components of the pump assembly (cover, gasket, and bolts) will be imported as CAD geometry. All of the parts will be halved to take advantage of symmetry.

Copyright 2003 ABAQUS, Inc.

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Note: The parts created in this workshop will be used in subsequent workshops to build the complete model and to perform the analysis. It is important that you use the dimensions stated and not deviate from the workshop instructions; otherwise, you may find it difficult to complete the subsequent workshops.

Orphan mesh import Follow the steps below to import the mesh of the pump housing model.

1. Start a new session of ABAQUS/CAE from workshops/pump directory. ABAQUS/CAE automatically loads the Part module. 2. From the main menu bar, select File Import Model. From the list of

available models, select pump_ribs.inp. 3. ABAQUS/CAE takes a few seconds to import the model. Once the model is

imported, you will be in the Assembly module. Switch back to the Part module. Notice that a new model (named pump_ribs) which contains the imported part (named PUMP–1) has been created. The model appears as shown in Figure W3–2.

Figure W3–2. Orphan mesh of pump housing

Editing nodal coordinates Your first task will be to change the inner diameter of the hole that goes through the top of the pump. The coordinates of the nodes along the inner diameter need to be changed. Since these nodes lie on a circular surface, it will be advantageous to define a cylindrical coordinate system and simply change the radial coordinate of the nodes. Follow the steps below to achieve this task.

1. From the main menu bar, select View Views Toolbox. In the Views dialog box, select the 1–2 view. Turn off the perspective view by clicking the Turn Perspective Off tool ( ), and zoom into the component so that the hole is clearly visible (see Figure W3–3).


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Figure W3–3. Top view of pump housing 2. From the main menu bar, select Tools Datum. The Create Datum dialog box

appears (see Figure W3–4). Select CSYS as the datum type. Select the 3 points method, and click OK. When prompted for the type of coordinate system, choose Cylindrical. Place the coordinate system at the origin (0.0, 0.0, 0.0) and click Create Datum. A cylindrical datum coordinate system is created. The origin of the coordinate system coincides with the position of the center of the hole.

Figure W3–4. Create Datum dialog box

3. You will now modify the inner diameter of the hole. From the main menu bar, select Tools Edit Mesh. In the Edit Mesh dialog box, select Node as the category and Edit as the method, as shown in Figure W3–5. Click OK to close the dialog box and proceed.


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Figure W3–5. Edit Mesh dialog box 4. You will be prompted to select the nodes to be modified. Begin by setting the

selection filters as shown in Figure W3–6 by clicking the Show/Hide Selection

Options tool, in the prompt area.

Select entities inside the drag shape

Circular drag shape

Toggle off the selection of entities closest to the screen

Figure W3–6. Selection filters

5. The nodes can be selected in one of two ways: • Try selecting the nodes individually (the default selection technique) using a

Circular Drag Shape. The center of the drag shape should be the center of the cylindrical coordinate system defined earlier (see step 2). Select a perimeter point for the drag shape such that you include all the nodes on the inside surface of the hole. The selected nodes will be highlighted in red after the selection, as shown in Figure W3–7. You may wish to rotate your model to check whether all the nodes have been selected properly.

• You may also select the nodes using the face angle method (i.e., by specifying the maximum deviation in the angle between adjacent element faces). This technique is generally more efficient than selecting the nodes individually: all nodes that pertain to the element faces that satisfy the face angle criterion are automatically selected. In the prompt area, choose by face angle as the method by which the nodes will be selected. Then, click on any element face located on the inner surface of the hole. The nodes on the inner surface are


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highlighted in red after the selection. As before, rotate your model to make sure all the nodes have been selected properly.

Once you are satisfied with the selection (using either method), click Done in the prompt area.

Figure W3–7. Modified nodes 6. The Edit Nodes dialog box appears, as shown in Figure W3–8. This dialog box

will be used to change the diameter of the hole. Click Select in the upper right corner of the dialog box, and choose the cylindrical coordinate system defined in step 2 by clicking on it in the viewport when prompted to choose a local coordinate system.

7. Using the Coordinates specification method, change the 1–coordinate (i.e., the radial coordinate) by selecting Specify from the pull down list and entering 0.65. Click OK to close the dialog box and then Done in the prompt area to complete the operation.

Figure W3–8. Edit Nodes dialog box

Deleting elements You will now remove the ribs on the pump housing and then you will remove half of the part. Begin by removing some of the elements in the rib located near the front of the housing, as shown in Figure W3–9. Use the 1–3 view from the Views Toolbox, and rotate the pump to view one of the front ribs, as shown in Figure W3–9.


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Figure W3–9. Rib elements 1. From the main menu bar, select Tools Edit Mesh. In the Edit Mesh dialog

box, select Element as the category and Delete as the method. Click OK. 2. When prompted to select the elements to be deleted, use the Show/Hide

Selection Options tool to change the drag shape to a Polygon. Select some of the elements located near the 90° bend of the rib, as shown in Figure W3–9.

3. In the prompt area, toggle on Delete associated unreferenced nodes. 4. Zoom out and rotate the view to confirm that only elements pertaining to the ribs

have been selected. If any other elements are highlighted, deselect them using [Control]+Click. When you are satisfied with the selection, click Done to delete the elements and their associated nodes.

5. The remaining ribs on the pump housing can be removed by carefully selecting them in a similar fashion. This can be a tedious and time-consuming process for large, complicated models. To facilitate such tasks, elements may also be deleted using sets. A. From the main menu bar, select Tools Edit Mesh. In the Edit Mesh

dialog box, click OK to continue deleting elements. B. In the prompt area toggle on Delete associated unreferenced nodes. C. In the prompt area, click Sets to open the Region Selection dialog box. In

this dialog box, select the set RIBS and toggle on Highlight selections in viewport to highlight the elements belonging to this set.

D. Click Continue to delete the remaining rib elements. E. Click Cancel to close the dialog box. You will now halve the pump housing. Use the 1–2 view from the Views Toolbox to facilitate element selection.

6. From the main menu bar, select Tools Edit Mesh. In the Edit Mesh dialog box, click OK to continue deleting elements.

7. In the prompt area, toggle on Delete associated unreferenced nodes.


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Tip: If the Region Selection dialog box appears, click Select in Viewport on the right side of the prompt area so you can select elements in the viewport.

8. Select the upper half of the pump housing for deletion, as shown in W3–10. When you are satisfied with the selection, click Done to delete the elements and their associated nodes. The half pump housing without the ribs is shown in Figure W3–11.

9. Save the model database. Name the model database file PumpAssy.cae.


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rectangular drag shape

selected elements

Figure W3–10. Select half of the pump housing.

Figure W3–11. Halved pump housing without ribs

Importing CAD geometry You will now import the remaining components of the assembly into ABAQUS/CAE.

1. From the main menu bar, select File Import Part to open the Import Part dialog box.

2. In this dialog box, set the file type to ACIS SAT. From the list of available files, select cover.sat. Click OK in the dialog box to proceed.

3. In the Create Part from Acis File dialog box, select the Name-Repair tab and toggle on all the available repair options. Click OK to close the dialog box and continue. The imported part is shown in Figure W3–12a.

4. After the part is imported, use the Geometry diagnostics part query tools (Tools Query) to check for any invalid or imprecise entities.

5. Repeat steps 2 through 4 to import the part defined in file gasket.sat. The imported part is shown in Figure W3–12b.

6. Import the part defined in file n_bolts.sat without any repair options turned on. The imported part is shown in Figure W3–12c.

7. Review the different parts of your model. Query the important dimensions using the Query tools and note them for future reference.


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8. Save your model database as PumpAssy.cae.

(a) cover

(b) gasket

(c) bolts

Figure W3–12. Components of pump assembly

Halving the imported geometry You will now remove half of each of the imported parts. Begin with the cover.

1. From the Part list located under the tool bar, select cover to access the cover geometry.

2. From the main menu bar, select View Specify. Using the Viewpoint method, enter the coordinates of the viewpoint as 0,0,-1 and the coordinates of the up vector as 0,-1,0. Click OK to apply the view and close the dialog box. Next, create a datum axis using the steps outlined below. This axis will be used to orient the part in the sketch plane when creating the cut profile.

3. From the main menu bar, select Tools Datum. 4. In the Create Datum dialog box, choose Axis as the type and Principal axis

as the method. Click OK. 5. Choose the principal Y-Axis as the datum axis. 6. From the main menu bar, select Shape Cut Extrude. 7. Select the top surface of the cover, indicated in Figure W3–13, as the plane on

which to sketch.


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sketch plane datum axis

Figure W3–13. Sketch plane and datum axis

8. Select the datum axis as the edge that will appear vertical and on the right of the

sketch. 9. From the main menu bar, select Add Line Rectangle. Sketch a rectangle

enclosing the upper half of the cover, as shown in Figure W3–14.

cut rectangle

Figure W3–14. Cut profile

10. Click mouse button 2 to continue, and click Done in the prompt area. 11. In the Edit Cut Extrusion dialog box, choose the end condition Through All.

The direction of extrusion is into the cover. Click OK. The final cover geometry is shown in Figure W3–15.

Figure W3–15. Cover


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Similarly, halve the gasket and bolt parts.

12. From the Part list located under the tool bar, select gasket to access the gasket geometry. Use the 1–2 view from the Views Toolbox.

13. As before, define the datum axis to orient the part. From the main menu bar, select Tools Datum.

14. In the Create Datum dialog box, click OK to create another Axis using the Principal axis method. Choose the principal Y-Axis as the datum axis.

15. From the main menu bar, select Shape Cut Extrude. 16. Select the top surface of the gasket as the plane on which to sketch, as shown in

Figure W3–16. Select the datum axis as the edge that will appear vertical and on the right of the sketch.

17. From the main menu bar, select Add Line Rectangle. Sketch a rectangle enclosing the upper half of the gasket, as shown in Figure W3–16.

surfaces selected as sketch planes

Figure W3–16. Cut profiles

18. Click mouse button 2 to continue, and click Done in the prompt area. 19. In the Edit Cut Extrusion dialog box, choose the end condition Through All.

The direction of extrusion is into the gasket. Click OK. 20. Repeat steps 12 through 19 to remove four of the bolts from the part named

n_bolts. Note that the top surface of any of the bolts to the left of the datum axis may be used as the sketch plane for the extruded cut. The final gasket and bolt parts are shown in Figure W3–17.

21. Save the model database as PumpAssy.cae.

cut rectangle (a) gasket (b) bolts


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Figure W3–17. Gasket and bolts

(a) gasket (b) bolts

Workshop 2

Material and Section Properties: Pump Model

Copyright 2003 ABAQUS, Inc. 科研中国 http://www.SciEi.com 收集

Introduction In this workshop you will use the ABAQUS/CAE Property module to define the material and section properties of the components in the pump assembly. The gasket will be defined using gasket material properties. All other components (pump housing, cover, and bolts) are assumed to possess the properties of steel.

Defining a linear elastic material and solid section properties Follow the steps outlined below to complete the steel property and section assignments for the pump components. Note that the units used in this model are in, lb, and psi.

1. Start a new session of ABAQUS/CAE from the directory containing the pump assembly model.

2. From the main menu bar, select File Open to open the model database file PumpAssy.cae.

3. Switch to the Property module. 4. From the Model list located under the toolbar, select pump_ribs to access the

pump_ribs model. 5. From the main menu bar, select Material Create to create a linear elastic

material named Steel. Specify a Young’s modulus of 30.E6 psi and a Poisson’s ratio of 0.3.

6. From the main menu bar, select Section Create to create a homogeneous solid section named steelSection that refers to the material named Steel.

7. From the main menu bar, select Assign Section to assign the section named steelSection to the parts named cover, n_bolts, and PUMP-1. Tip: You will need to make the section assignments individually; select the different parts by choosing them from the Part pull-down list.

Defining the gasket material and section properties The typical specification of gasket material properties in ABAQUS involves a tabular representation of the pressure versus closure relationship in the thickness direction of the gasket. The pressure versus closure models available in ABAQUS allow the modeling of very complex gasket behaviors, including nonlinear elasticity, permanent plastic deformation, and loading/unloading along different paths. These behaviors are usually calibrated from test data. A detailed discussion of gasket material behavior, however, is beyond the scope of this course. For your convenience (and to make the analysis realistic) the gasket properties are defined in a script that you will read directly into ABAQUS/CAE.

1. From the main menu bar, select File Run Script.


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The Run Script dialog box appears. 2. Select the file named gasket_material.py. Click OK in the dialog box. 3. From the main menu bar, select Material Manager to open the Material

Manager. Notice that the material named Gasket has been added to the model database.

4. Select Gasket, and click Edit. 5. Review the gasket material properties. Note the gasket has membrane elasticity of

12155 psi, shear stiffness of 6435 psi, and a coefficient of thermal expansion of 1.67 E−5 /°F.

6. Select Gasket Thickness Behavior from the list of available Material Options in the dialog box, and notice the tabular specification of the loading and unloading curves for the gasket (see Figure W5–1).

Figure W5–1. Edit Material dialog box

You can use the plotting capabilities within ABAQUS/CAE to plot the loading and unloading curves. This may help you obtain a better understanding of the material behavior.

7. Open the Loading tabbed page. Right-click your mouse over the column headings of the table, and select Create XY Data from the list of options that appears. Name the curve loading when prompted for a name in the Create XY


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Data dialog box. Repeat the same operation for the unloading curve to create a curve named unloading.

8. Switch to the Visualization module. 9. From the main menu bar, select Tools XY Data Manager.

The XY Data Manager appears. 10. Select both the curves (using the shift key), and click Plot. You should see a

similar plot in the viewport as that shown in Figure W5–2.

Figure W5–2. Loading and unloading gasket behavior

11. Click Dismiss in the XY Data Manager, and switch back to the Property

module to continue with the gasket section property specification. 12. From the main menu bar, select Section Create to create a gasket section. 13. In the Create Section dialog box, select Other as the category and Gasket as

the type. Name the section gasketSection (see Figure W5–3) and click Continue.


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Figure W5–3. Create Section and Edit Section dialog boxes

14. In the Edit Section dialog box (see Figure W5–3), select Gasket as the material and accept all other defaults.

15. Assign the section named gasketSection to the part named gasket. 16. Save your model database as PumpAssy.cae.

Workshop 3

Pump Model Assembly

Copyright 2003 ABAQUS, Inc. 科研中国http://www.SciEi.com

Introduction In this workshop you will create a single part instance of each component of the pump model and use the different positioning techniques available in ABAQUS/CAE to position the part instances relative to each other in a global coordinate system.

Instancing and positioning the pump housing 1. From the main menu bar, select File Open and open the model database file

PumpAssy.cae. 2. Switch to the Assembly module, and select pump_ribs from the list of available

models. Note that since you imported the pump housing as a model, an instance of the part PUMP-1 has already been created. No further positioning of this part instance is required.

Instancing and positioning the gasket 1. From the main menu bar, select Instance Create to create an instance of the

part named gasket. You must position the gasket such that its top surface touches the bottom surface of the pump housing. The most convenient way to do this is to use the Face to Face positioning constraint.

2. From the main menu bar, select Constraint Face to Face. Select any element face on the bottom of the pump housing as the face on the movable part instance. To facilitate the selection of a planar face on the fixed part instance (i.e., the gasket), you will suppress the visibility of the pump housing.

3. From the main menu bar, select View Assembly Display Options and suppress the visibility of instance PUMP-1 in the Instance tabbed page.

4. Select the top face of the gasket as the face on the fixed part instance. You should now see two arrows pointing in opposite directions in the viewport, as shown in Figure W6–1. (You may need to select View Auto-Fit from the main menu bar to see this.)

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gasket

pump housing

Figure W6–1. Housing and gasket arrows initially point in opposite directions

The pump housing will be moved so that its arrow points in the same direction as that of the gasket.

5. Click Flip in the prompt area to reverse the direction of the arrow on the pump housing so that both arrows point in the same direction. When both arrows point in the same direction, click OK in the prompt area.

6. Accept 0.0 as the default distance from the fixed plane along its normal. 7. Use the assembly display options to restore the visibility of the pump housing. 8. Verify that the pump housing is now exactly on top of the gasket.

Tip: Use the Query tools to calculate the distance between a point on the lower surface of the pump housing and a point on the top surface of the gasket. If the pump is exactly on top of the gasket, the third component of the distance vector should be zero.

Instancing and positioning the cover 1. Instance the part named cover.

The cover must be rotated such that the rounded side of the cover is inside the pump. This requires rotating the cover about the global 1-axis.

2. From the main menu bar, select Instance Rotate. Select the cover when prompted for the instance to be rotated. Tip: Click Instance List in the prompt area to select the cover from a feature list. This is often easier than selecting instances from the viewport.

3. Enter the coordinates of the origin (0.0, 0.0, 0.0) as the start point for the axis of rotation.

4. Enter (1.0, 0.0, 0.0) as the coordinates of the end point for the axis of rotation.

5. Enter 180.0 as the angle of rotation. See Figure W6–2 for the configuration after the rotation operation (note the visibility of the pump housing has been suppressed in this figure).


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Figure W6–2. Gasket and cover

6. The cover also needs to be positioned so that its top touches the bottom of the

gasket. Use the Contact constraint to position the top of the cover with respect to the bottom of the gasket. Alternatively, you could also use the Face to Face constraint.

7. From the main menu bar, select Constraint Contact. 8. Select the top face of the cover (shown in Figure W6–3) when prompted for the

face of the movable part instance.

face of movable part instance (cover)

face of fixed part instance (gasket)

Figure W6–3. Positioning of cover relative to the gasket

9. Select the bottom face of the gasket (shown in Figure W6–3) when prompted for the face of the fixed part instance.

10. Pick a point on the top surface of the cover as a start point for the direction of contact, as shown in Figure W6–4


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end point

start point

Figure W6–4. Contact positioning constraint

11. Select a point on the bottom surface of the gasket as the end point for the direction of contact, as shown in Figure W6–4.

12. When prompted for a clearance between the surfaces, enter a value of 0.0. 13. Verify that the gasket is now just in contact with the cover.

Instancing and positioning the bolts 1. Instance the part n_bolts. 2. The bolts will be in position when their ends are aligned with the bottom of the

cover. Use the Face to Face constraint to accomplish this task. The pump assembly with the bolts in their final positions should look similar to that shown in FigureW6–5.

Figure W6–5. Final positions of the bolts


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The complete assembly is shown in Figure W6–6.

Figure W6–6. Complete pump assembly

3. Save your model as PumpAssy.cae.

Workshop 9

Free and Swept Meshing: Pump Model


Introduction In this workshop you will use the Mesh module of ABAQUS/CAE to generate the finite element meshes for the pump assembly model. The required tasks include assigning mesh attributes to each part instance, assigning mesh seeds, and generating the meshes.

Modifying the pump housing element type 1. Open the model database file PumpAssy.cae. Switch to the Mesh module; and,

from the context bar, select pump_ribs from the list of available models. 2. Use the assembly display options (View Assembly Display Options) to

suppress the visibility of all part instances save for the pump housing. In addition, suppress the visibility of all datum planes and axes.

3. Next, create a set that includes all the elements comprising the pump housing. From the main menu bar, select Tools Set Create.

4. In the Create Set dialog box, select Element as the set type. Name the set pump-mesh and click Continue.

5. Select all the elements in pump housing using a rectangular drag window. Use the selection filters if necessary. Click Done when the selection is complete. Use the Query tools to determine the type of element currently assigned to the mesh.

6. From the main menu bar, select Tools Query. The Query dialog box appears.

7. From the list of available General Queries, select Element and click Apply. Click on any element and note that the element’s label, type, and nodal connectivity are listed in the message area, as shown in Figure W9–1. Repeat this for other elements in the mesh.

Figure W9–1. Selected element attributes

8. Click Cancel in the Query dialog box to close it. 9. The element type for the pump housing is the linear tetrahedron (C3D4), which is

not suited for an analysis involving contact. Thus, change the element type assigned to the pump housing to modified second order tetrahedrons (C3D10M).

10. From the main menu bar, select Mesh Element Type. 11. When prompted for the type of region, click Sets on the right side of the prompt

area.

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12. The Region Selection dialog box appears. Select the set pump-mesh and click Continue.

13. The Element Type dialog box appears. Review the current settings. Toggle on Quadratic under Geometric Order. Notice that the element type message changes to C3D10M. Click OK.

14. Use the Query tools to confirm that the element type associated with the mesh has been updated.

Generating the bolt mesh Use the assembly display options to restore the visibility of the bolts and suppress the visibility of the pump housing. The bolts are colored yellow, indicating they can be readily meshed with hexahedral elements using a swept mesh technique. Mesh the bolts with a local edge seed of 8 using first-order incompatible mode hexahedral elements (C3D8I).

1. From the main menu bar, select Seed Edge by Number. 2. Select all the edges of the bolts using a rectangular drag window. 3. When prompted for the number of elements along the edges, enter 8. 4. From the main menu bar, select Mesh Element Type to change the element

type associated with the bolts. Tip: Click Select in Viewport on the right side of the prompt area to select the bolts directly in the viewport.

5. In the prompt area, select Geometry as the region type. Using a rectangular drag shape, select all the bolts.

6. In the Element Type dialog box, choose Incompatible modes under Element Controls. Click OK.

7. From the main menu bar, select Mesh Instance to mesh the bolts. Click one of the bolts when prompted for the instance to be meshed.

8. Review the mesh when the operation is complete. The mesh of one of the bolts is shown in Figure W9–2.

Generating the cover and gasket meshes

The Cover Use the assembly display options to restore the visibility of the cover and suppress the visibility of the bolts. The cover is colored orange, indicating that it cannot be meshed with hexahedral elements without the aid of partitioning. For the purpose of this exercise, mesh the cover using the free tetrahedral mesh technique. Use a global seed size of 0.35 and element type C3D10M.

1. From the main menu bar, select Mesh Controls. Select the cover as the region to which mesh controls will be assigned; and, in the Mesh Controls dialog box, select Tet as the element shape. Click OK to continue.


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The part is now colored pink, indicating it can be meshed with the free mesh technique.

2. Assign a global mesh seed size (Seed Instance) of 0.35 and local edge seeds (Seed Edge By Number) of 8 to the edges comprising the bolt holes.

3. From the main menu bar, select Mesh Element type. Select the cover geometry as the region to which the element type will be assigned and choose the modified quadratic tetrahedron element type (C3D10M).

4. Generate the cover mesh. The mesh on the cover plate is shown in Figure W9–2.

The Gasket Use the assembly display options to restore the visibility of the gasket and suppress the visibility of the cover. The gasket is colored yellow, indicating it can be readily meshed with hexahedral elements using a swept mesh technique.

1. Assign a global mesh seed size (Seed Instance) of 0.25. 2. Assign the linear hexahedral gasket element type (GK3D8) to the gasket

geometry (Mesh Element type). 3. Generate the gasket mesh. The mesh on the gasket is shown in Figure W9–3.

Figure W9–2. Bolt and cover meshes

Figure W9–3 Gasket mesh

4. Save the model database as PumpAssy.cae, and exit the ABAQUS/CAE

session.

Workshop 13

Nonlinear Static Analysis of a Pump Assembly


Introduction In this workshop you will use ABAQUS/CAE to complete the pump assembly model and to submit it for analysis. You will begin by defining the analysis steps and the output requests associated with these steps. Next, you will define the interactions between the different components of the model. You will also apply bolt and pressure loads and boundary conditions to the model. Finally, you will create and submit a job for analysis and evaluate the analysis results.

Defining the analysis steps The analysis history of the pump assembly consists of two steps: a step that simulates the pre-tensioning in the bolts, followed by a step that simulates the pressurization of the bolted assembly.

1. Open the model database file PumpAssy.cae. Switch to the Step module, and in the context bar select pump_ribs from the list of available models.

2. Create a general static step named PreloadBolts. Activate geometric nonlinearity (toggle on Nlgeom), and specify an initial time increment of 0.05 and a total time period of 1.0.

3. Create a second general static step named Pressure. Insert this step after the step named PreloadBolts. Specify an initial time increment of 0.1 and a total time period of 1.0.

4. Activate the contact diagnostic printout for both the steps. From the main menu bar, select Output Diagnostic Print. In the Diagnostic Print dialog box, click in the blank area under the Contact column for both steps so that tick marks appear, thus activating contact diagnostic output for these steps.

5. Click OK to close the dialog box.

Defining contact and constraints The mere proximity of the model components does not indicate that the part instances will interact during the analysis. Thus, unless explicitly specified, the individual components of an assembly will not interact with one another. For any loads to be properly transmitted between the components, you must define interactions between the components. In structural analysis problems the most common method of transferring loads between unconnected regions of a model assembly is through contact interactions. To define a contact interaction between any two bodies, however, you must first identify the regions of each body that will be involved in contact (e.g., define surfaces). Your next task in this workshop, therefore, will be to define surfaces on each component that will be involved in contact.

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Defining the surfaces In ABAQUS/CAE a surface can be created either on a part that has underlying geometry (such a surface is known as a geometry-based surface) or on a part that does not have underlying geometry (e.g., an orphan mesh; such a surface is known as a mesh-based surface). Since this assembly consists of both imported geometry and an orphan mesh, you will create both types of surfaces.

1. Switch to the Interaction module. 2. Make only the pump housing visible using the Assembly Display Options

dialog box (View Assembly Display Options). 3. Create a surface named PumpBot by following the steps given below:

A. From the main menu bar, select Tools Surface Manager. B. In the Surface Manager, click Create. C. The Create Surface dialog box appears. Select Mesh as the surface type.

Name the surface PumpBot, and click Continue. D. You will be prompted for the regions to define the surface. For a mesh-based

surface, you can either select the elements individually or select a group of elements by specifying the maximum deviation in the face angle between adjacent elements. The face angle method is in general a more efficient way of choosing elements to define a surface. Hence, in the prompt area select by angle as the selection method and enter a face angle of 5 degrees.

E. Click any element face on the bottom of the pump. All the element faces on the bottom of the pump will then be highlighted in red, as shown in Figure W13–1. Click Done in the prompt area when you are finished.

Figure W13–1. Surface PumpBot

4. Similarly, create a surface named PumpBolts that defines a surface in the region of the pump that will come into contact with the heads of the bolts. Select the surface using a face angle of 5 degrees, as shown in Figure W13–2.

5. Next, define a surface in the region where the internal pressure will be applied to the pump. Name the surface PumpInside. Using the face angle method with a


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maximum deviation of 24.1 degrees, select the element faces shown in Figure W13–3. Tip: Use [Shift]+Click to select more than one item at a time. Select as many regions as possible using the face angle technique; then select any remaining regions individually. Zoom in as necessary to facilitate your selections. To deselect any unintentionally selected regions, use [Ctrl]+Click.

Figure W13–2. Surface PumpBolts

Figure W13–3. Surface PumpInside

6. Use the Assembly Display Options dialog box to restore the visibility of the cover and to suppress the visibility of the pump housing.

7. Define a geometry-based surface named CoverTop on the region of the cover where it contacts the gasket.

8. Define a surface named CoverInside that defines the region where the pressure load will be applied as shown in Figure W13–4.

9. Create a surface for each of the four holes in the cover as shown in Figure W13–5. Name these surfaces BoltHole-1 through BoltHole-4.


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Note: Keep track of the order in which you define the bolt hole surfaces since later you will have to create corresponding surfaces on the bolt shanks. You should save your current view (View Save User 1) to make it easier when defining the bolts surfaces later.

10. Restore the visibility of the gasket and suppress the visibility of the cover using the Assembly Display Options dialog box. Define surfaces on the top and bottom regions of the gasket. Name these surfaces GasketTop and GasketBot, respectively.

11. Suppress the visibility of the gasket, and restore the visibility of the bolts. Set the view to the user-defined view (View Views Toolbox and click 1 in the Views dialog box).

12. Create a surface for each bolt thread corresponding to each bolt hole surface in the cover, as shown in Figure W13–5. Name the surfaces BoltThread-1 through BoltThread-4.

13. Create a single surface that includes the regions directly under the heads of all the bolts as shown in Figure W13–5. Name this surface BoltHeads.


surface CoverInside

Figure W13–4. Surface CoverInside

surface BoltHeads

surface BoltThread surface BoltHole

Figure W13–5 Bolt-related surfaces

Defining the contact interaction Now that you have defined the surfaces that will be involved in contact, you can define the contact interactions between the different components. Defining contact interactions in ABAQUS/CAE involves choosing the surfaces involved contact and defining contact


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properties (friction, etc.) for each interaction. Follow the steps given below to define the contact interactions for this model.

1. From the main menu bar, select Interaction Property Create to create a contact property named Friction.

2. In the Edit Contact Property dialog box, select Mechanical Tangential Behavior. Choose the Penalty friction formulation, and define a coefficient of friction of 0.2. Click OK to close the dialog box.

3. From the main menu bar, select Interaction Create to create an ABAQUS/Standard surface-to-surface contact interaction in the Initial step. Name the interaction Pump-Bolts.

4. Click Surfaces in the prompt area to select the regions involved in contact using the surfaces defined earlier. In the Region Selection dialog box, choose the surface PumpBolts as the master surface (since it is continuous) and the surface BoltHeads as the slave surface (since it has a relatively finer mesh and is discontinuous). Use the Small sliding formulation, adjust slave nodes within 1.e-5 in. of the master surface to ensure that the surfaces are initially in contact, and accept Friction as the contact property.

5. Create another ABAQUS/Standard surface-to-surface contact interaction in the Initial step between the bottom of the gasket and the top of the cover. Name the interaction named Cover-Gasket. Choose the surface CoverTop as the master surface (since the underlying elements are much stiffer) and GasketBot as the slave surface. Use the Small sliding formulation, adjust slave nodes within 1.e-5 in. of the master surface to ensure that the surfaces are initially in contact, and accept Friction as the contact property.

Defining tie constraints Tie constraints will be used to tie the gasket to the pump. You will also define tie constraints to simulate the effect of the bolt threads when fastened to the bolt holes.

1. From the main menu bar, select Constraint Create. Name the constraint PumpGasket. Select Tie as the constraint type and click Continue.

2. The list of previously defined surfaces appears in the Region Selection dialog box; select the surface PumpBot as the master surface and the surface GasketTop as the slave surface. Accept all the default settings in the Edit Constraint dialog box, and click OK to close the dialog box.

3. In a similar fashion, define tie constraints between each bolt thread and its corresponding bolt hole. In each case, select the bolt hole to be the master surface and the bolt thread to be the slave surface. Name the constraints Tie-1 through Tie-4. In the Edit Constraint dialog box, specify a distance of 0.07 as the position tolerance and toggle off Adjust slave node initial position for each constraint. Tip: After creating the first tie constraint between the bolt and the bolt holes, copy the constraint and edit the region selections.


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Defining loads and boundary conditions Your next task will be to define the loads and boundary conditions that will act on the structure.

Applying bolt loads In ABAQUS/CAE assembly or bolt loads are applied across user-defined pre-tension sections in the bolt. When modeling the bolt with solid elements, the pre-tension section is defined as a surface in the bolt shank that effectively partitions the bolt into two regions. Follow the steps given below to create the pre-tension sections in the bolts.

1. Switch to the Load module. 2. Using the Assembly Display Options dialog box, suppress the visibility of all

part instances except for the bolts. Define a datum plane for the purpose of partitioning the bolts at the location where the pre-tension sections will be defined.

3. From the main menu bar, select Tools Datum. In the Create Datum dialog box, select Plane as the datum type.

4. Select Offset from plane as the method, and click OK. Offset the datum plane from the bottom of the bolts (select the bottom face of any bolt). Click Enter Value in the prompt area. Flip the arrow indicating the offset direction if necessary so that it points from the bottom of the bolt toward the bolt head. Enter an offset distance of 0.5.

5. Partition the bolts using this datum plane. From the main menu bar, select Tools Partition. Create a Cell partition using the Use datum plane method. Select all the bolts as the cells to be partitioned. Note: The bolt meshes will have to be regenerated as a result of this partition. Switch to the mesh module after creating the partition. Respecify the edge seeds for the bolts with 8 elements along the edges and recreate the bolt meshes.

6. To view the partitions, switch the rendering style to wireframe . 7. To define the direction along which the bolt load will be applied, create a datum

axis along the principal Z-axis. From the main menu bar, select Tools Datum. Select Axis as the type and Principal axis as the method. Click Z-axis in the prompt area.

8. From the main menu bar, select Load Create to define the bolt load. The Create Load dialog box appears. Select the step named PreloadBolts as the step in which the load will be applied. Select Bolt load as the load type as shown in Figure W13–6. Click Continue.


W13.7

Figure W13–6. Create Load dialog box

9. In the prompt area, click Geometry as the region type. 10. Select the internal surface of any bolt (e.g., as shown in Figure W13–7). This

surface defines the pre-tension section.

Figure W13–7. Bolt internal surface

11. Select the datum axis defined earlier when prompted for a datum axis parallel to

the bolt centerline. 12. Enter a bolt load of 500 lb in the Edit Load dialog box. Accept all other default

settings in the dialog box. 13. Repeat steps 8 through 12 for the other bolts.

Tip: After creating the first bolt load, copy the load and edit the region selections. 14. Typically, you want to tighten the bolts to a predefined load level (pre-tensioning)

and then “freeze” the deformation in the subsequent load steps (pressure loading, heating up, etc). To do this, proceed as follows:


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A. From the main menu, select Load Manager. The load manager appears in the viewport.

B. Select any bolt load in the Pressure step by clicking Propagated and click Edit in the dialog box.

C. In the Edit Bolt Load dialog box, select Fix at current length as the method and click OK in the dialog box.

D. Repeat steps B and C for the other bolt loads.

Applying the pressure load and boundary conditions 1. Display the pump housing using the assembly display options. Switch the render

style to shaded . 2. From the main menu bar, select Load Create to define a pressure load named

PumpLoad in the step named Pressure. Apply the load to surface PumpInside. Specify a load magnitude of 1000 psi.

3. Similarly, apply a pressure of 1000 psi to the surface CoverInside. Name the load CoverLoad.

4. Assume that the bottom of the cover is welded against a rigid plate. From the main menu bar, select BC Create.

5. In the Create Boundary Condition dialog box, select Symmetry/ Antisymmetry/Encastre as the boundary condition type and the Initial step as the step in which to apply the boundary condition and click Continue.

6. In the prompt area, click Select in Viewport to permit direct selection of the affected region in the viewport. Select the bottom region of the cover and click Done in the prompt area. In the Edit Boundary Condition dialog box, select Encastre as the boundary condition type and click OK to close the dialog box.

7. Apply symmetry boundary conditions to the cover and gasket as follows: A. From the main menu bar, select BC Create. B. In the Create Boundary Condition dialog box, accept Symmetry/

Antisymmetry/Encastre as the boundary condition type and the Initial step as the step in which to apply the boundary condition. Click Continue.

C. In the prompt area, select Geometry as the region type. Select the faces on the symmetry planes of the cover and gasket using [Shift]+Click and click Done in the prompt area. In the Edit Boundary Condition dialog box, select YSYMM as the boundary condition type and click OK to close the dialog box.

8. Similarly, apply symmetry boundary conditions to the nodes on the symmetry plane of the pump housing. For this part the region type is Mesh.

9. Save your model database.


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Creating and submitting a job for analysis Now you are ready to create and submit the model for analysis. You will use the Job module to create an analysis job and submit it for analysis.

1. Switch to the Job module. 2. Create a job named PumpAnalysis. Enter any suitable job description. Accept

all other default job settings. 3. Submit the job for analysis.

Note: This analysis job takes about 30 minutes to complete on a Windows 2000 machine with a 1700 MHz processor. Monitor the job for several minutes to ensure it is running properly. Then proceed with the next lecture before continuing with this workshop.

Visualizing the analysis results After the analysis is complete, you will review the results in the Visualization module. For the kind of analysis you just performed, some of the interesting results would be the distribution of the sealing pressure in the gasket at different stages of operation, the history of the bolt force in the bolts, the deformed shape and stresses in the bolts, etc.

1. Switch to the Visualization module, and open the PumpAnalysis output database file.

2. Look at the undeformed and deformed plot of the model. You will notice that the pump housing does not undergo large deformations because of its stiffness. Most of the deformation takes place in the gaskets and the bolts. Use the Create Display Group dialog box to look at the deformed shape in the bolts and gaskets only.

3. Plot the Mises stresses in the model. Use the Create Display Group dialog box to plot the Mises stresses in the bolts only.

4. Plot a contour of the sealing pressure in the gasket. First use the Create Display Group dialog box to view the gasket only. The sealing pressure in the gasket is the S11 component of the stress tensor. From the main menu bar, select Result Field Output. In the Field Output dialog box select the S11 component and click OK.

5. Plot an animation of the sealing pressure in the gasket. Specify a minimum value of 0.0 and a maximum value of 325 in the Limits tabbed page of the Contour Options dialog box. From the main menu bar, select Animate Time History to animate the results.

6. Create a path plot of the sealing pressure along a critical location in the gasket. Follow the steps given below: A. From the main menu bar, select Tools Path Create. The Create Path

dialog box appears in the viewport.


W13.10

B. The Node list type is selected by default. Click Continue in the dialog box. C. In the Edit Node List Path dialog box, click Add After. D. You will be prompted to select the nodes from the viewport to be inserted into

the path. Pick the nodes as shown in Figure W13–8. Click Done in the prompt area when the selection is complete. Click OK in the Edit Node List Path dialog box.

beginning of path

end of path

Figure W13–8. Node path

E. From the main menu bar, select Tools XY Data Create. Select Path in

the Create XY data dialog box and click Continue. F. Browse the settings in the XY Data from Path dialog box. In the Y-values

frame, click Step/Frame. G. In the Step/frame dialog box, select the last frame of the step named

Pressure. Click OK. H. Make sure that Field output variable is set to S11 in the XY Data from

Path dialog box. Click Plot in the dialog box to view the path plot. I. Save the plot as Step-2. J. Similarly, create a path plot of the sealing pressure for the same set of nodes

for the PreloadBolts step. Save the plot as Step-1. K. View the saved plots. From the main menu bar, select Tools XY

Data Manager. In the XY Data Manager dialog box, select both the saved plots using [Shift] +Click and click Plot in the dialog box. The plot should look similar to the one shown in Figure W13–9.


W13.11

Figure W13–9. Sealing pressure along the path

From this figure it is clear the gasket unloads during the pressurization step. In this exercise, however, nominal bolt and pressure loads were applied. At these load levels, the maximum pressure in the gasket after the bolt load step is approximately 330 psi, which is less than the largest pressure specified in the loading data (6835.4 psi). Thus, during the pressurization step, the gasket unloads elastically; i.e., along the loading curve.

Optional analysis To observe the distinct loading and unloading behaviors of the gasket, make the following modifications to the model:

1. Apply a load of 12000 lb to each bolt. 2. Apply a pressure load of 10000 psi.

Rerun the analysis and postprocess the results. You will notice that in this case the peak pressure in the gasket after the bolt load step is approximately 8000 psi, which is greater than the largest pressure value specified in the loading data. In the pressurization step, then, the gasket unloads along the unloading curve. To see this, create a pressure vs. closure curve as described below:

1. Using field data, create and save X–Y curves of S11 (i.e., pressure) and E11 (i.e., closure) versus time at the integration points of the element indicated in Figure W13–10. Since the element has four integration points, eight curves are created.


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Choose this element

Figure W13–10. Element used for pressure-closure curve

2. Create a new curve by combining the pressure and closure curves of a given integration point (say integration point 1) into a single curve. The resulting curve is shown in Figure W13–11 and clearly illustrates the distinct loading and unloading behaviors of the gasket. The response predicted by ABAQUS follows the material data very closely.

largest pressure specified in data

Figure W13–11. Pressure-closure predicted by ABAQUS at higher load levels

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