NX Nastran Advanced Non-linear Demonstration / Tutorial Vernon McKenzie EnDuraSim Pty Ltd Sydney Australia
• Two examples: “static” and transient. Impact of steel coil against safety barrier.
Bowing of rolled sheet steel at the mill
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• Create a new NX model (called strip_bow). • Dimensions are mm.
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• File | Import | Parasolid -> Strip_Bow.x_t • Request files from
[email protected]
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• Start | Advanced Simulation • In the Simulation Navigator, right click strip_bow.prt and choose New FEM and Simulation • Press OK to the first dialog box • Modify second (next page)
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• Modify Solution Type to ADVNL 601,106 = Adv Non-lin static. • Other aspect of this solution setup will be changed later. • Press OK.
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• Any plate contact modelling is assisted by “backface culling” to easily identify the top/bottom of surfaces.
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• Insert | Simulation Region (or pick icon from toolbar).
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• Repeat for the 3 surfaces of steel strip.
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• Apply a fixed constraint to the 2 surfaces of the roll.
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• From the Advanced Simulation Toolbar, choose Surface to Surface Contact from the Simulation Object Type dropdown.
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• Create the Contact manually, and because the roll is rigid (via its constraints) it should be the target. • Create AdvNL BCTPARA (details follow)…
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• Change OFFTYPE to Half Shell Thickness (accounts for plate thickness). • Change SEGNORM to Used (smooths out mesh faceting). • Press OK x 2 to complete this and the Contact dialog. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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Loads and Constraints… • One of the loads will be a time dependent displacement which will be ramped up with an initial slow start to assist with convergence – and to demonstrate the method. • Select “Fields” in the Simulation Navigator and right-click to choose New Field -> Table. • Independent variable is Time. • Dependent variable is Length. • Use “Edit Table in Spreadsheet” where we will paste from an existing spreadsheet. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• • • • •
Title Time Length Use Excel See next page for details
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• Paste cells from “real” spreadsheet. • Then in Add-Ins tab… • Press “Update Table” • Must close this temp worksheet to return to NX. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
Paste from real sheet
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• Create a new enforced displacement from the toolbar icon.
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• Create a new force from the toolbar. It applies 25kN tension to the steel strip using the edge of the strip to define the direction of the force.
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• In the Simulation Navigator, double click on the .fem • Also, it is useful to expand the Simulation File View, as this makes it easy to switch between .fem and .sim
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• We will create a new material and use a table field to create its stress-strain curve, in a similar way to the creation of the ramp load. • Tools | Materials | Manage Materials. • We could copy and modify a Library Material, but in this case we will create a material from scratch. • Press the “Create Material” icon at the bottom right of the form.
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• • • • •
Fill in as shown… Name Elastic Constants Yield Stress Strain via function dropdown: Table Constructor • Table Domain is 1D general. Paste curve from Excel as before. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• 1D General • Use Excel to get data pairs.
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• Can display graph of Stress-Strain function. • Press OK to create the material. • Then press Close on the Manage Materials dialog.
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• Press “Return to Model” icon to switch from the graph back to the FE model.
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• Choose Insert | Physical Property from the menu, or press the icon. • Give it a name and press Create. • Fill in the PSHELL info. • Press OK. • Create another for the roll (.01mm, as the roll is fully constrained). • Close after creating both. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Create 2 x Mesh Collectors (Insert | Mesh Collector from the menu, or press the icon. • One should reference the 2mm strip property, the other should reference the Roll property. • Give it a name that makes it identifiable. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Insert | Mesh | Mesh Control (16 elements) to all of the strip curves running in the width direction (not on the roll). Switch off the roll display to make selection easier. • Good practice is to stitch the bodies. If not, then remember to select the two pairs of duplicate curves.
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• Insert | Mesh | 2D Mesh or choose from dropdown icon. • Fill in as indicated: PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Repeat for highlighted curved section of strip using a size of 30mm. • Smaller size helps convergence when initially curved (but unstrained) strip springs past the roll.
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• Repeat mesh step for roll (but 40mm mesh size, and choose roll mesh collector). • Meshed model…
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• In the Simulation File View, double click on the Sim file to return to the Simulation Model. • We now create User Defined Constraints on two nodes to guide the strip as it moves. • It is critical to ensure the coordinate systems and degrees of freedom selected are correct to produce the guiding effect. • The objective is to prevent the strip moving out of plane and transversely.
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• One end of strip.
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• Repeat for a centreline node at the other end of the strip.
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• The expanded Simulation Navigator looks approx like… • Right click on the Nonlinear Implicit Subcase and choose “edit”
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• Defaults are not best. Should change! • Displ, Stress, Strain (recommend CORNER for EVERY NX NASTRAN ANALYSIS!). • OK x 2 to complete dialogs.
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• Right click on Solution 1 and choose Edit. • In Case Control tab, select same set of output requests just created. • Create Time Step Interval and Strategy Parameters (see next page).
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• 400 time steps of 0.02 secs, results every 4 steps. • Press OK to this. • NUMEROUS strategy parameters to change. Multiple dialog boxes on following pages.
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• .
1
• OK to the Strategy Parameters once finished.
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• Back on the Solution dialog, choose the Parameters tab, and MAKE SURE Large Displacements (or Large Strains) is checked. Many AdvNL solutions will be wrong or effectively linear unless one of these is checked. • Press OK to complete. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Recommend going to the run directory and saving a text file called tmpadvnlin.rto which contains the single line: STOP=1 • This stops the analysis cleanly and saves results to that point to check. • View results by creating an animation of the results increments. • This completes the activities for this example.
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Example 2: Steel coil impact with safety barrier post.
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• • • • •
Back in NX modelling… File | New -> Model (mm). Name= Roll_ramp. File | Import | Parasolid -> roll_ramp.x_t Request files from
[email protected] Unite the two halves of the roll.
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• Start | Advanced Simulation. • In the Simulation Navigator, right click on the Roll_ramp.prt and choose New FEM and SIM. • OK to 1st dialog. • On 2nd dialog (Solution), change Solution Type to SOL601,129 (Advanced Non-linear transient), then OK. • In the Simulation File View, double click on the fem1_i (part) and then promote all the bodies. This example could be completed without the idealised part. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Use the Simulation File View again to double click on the Sim. • Create a Gravity Load of 9810mm/sec2 in the Negative Y direction. • Create a fixed constraint on the entire ramp (2 surfaces), and at the base of the post. • Backface culling ON.
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• Create 3 Regions (right click in Sim Navigator): 1. Surface of Roll 2. Ramp (both surfaces) 3. Face of post (note via the backface culling that the contact face of the post is the BOTTOM face (2 surfaces).
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• Right Click the Simulation Object Container in the Simulation Navigator, and choose New… Surface to Surface Contact. • Type = Manual • 1. Source = Roll, Target = Ramp (this order is important because the Ramp is fully constrained = rigid). Friction = 0.6 Change BCTPARA as per next page. • 2. Source = Post, Target = Roll (this order is preferred, because the source will have a finer mesh). Refer to same BCTPARA. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• SEGNORM is USED (smooths the element faceted representation of the contact.) • Account for plate half thickness. • OK to the Contact Parameters and “Post_to_Roll” Contact dialog.
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• Use the Simulation File View to switch across to the FEM. • Create a material (for simplicity, use same as the strip bow example, except density MUST be added (transient solution). Density is 7.8e-6 kg/mm3.
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• Create 3 Physical Properties… • 1. 10mm plate (PSHELL) for the post • 2. 0.01mm plate (PSHELL) for the ramp (very thin is OK because it is rigid). • 3. Solid property (PSOLID) for the roll. • Create 3 corresponding Mesh Collectors for the 2 plate properties and the solid property. • Remember to select the material for each property, enter the plate thickness for each plate property, and choose the right property for each collector. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Mesh the Ramp surfaces with 400mm elements. • Mesh the Post surfaces with 30mm elements • Mesh the Roll with 250mm elements. • Remember to choose the correct Mesh Collectors.
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• Return to the Sim. • Apply a “dummy” load to the top of the post (say 100N). We have anecdotal evidence that unloaded structures can have trouble with convergence due to error norms being ratios of very small numbers. • Right Click on the Subcase to edit. Change the Output Requests to “Structural Output Requests 1” and edit to recover corner stresses, and strains and SORT1. PLM Connection 2012. NX Nastran Advanced Non-linear. www.endurasim.com.au
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• Right click Solution 1 to edit. • On the Parameters tab select Large Strain. • On the Case Control Tab, create a Time Step interval: 700 steps of 0.002, Skip Factor = 5. • Also create a Strategy Parameters setup and do the same as for the Strip Bow problem, except for the revised exceptions (next page).
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• .
1
1e-5
• OK to the Strategy Parameters once finished.
1e-3
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Run and animate! Thank you. Q&A...
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