NX Nastran TUTORIAL Using a DMAP Alter to Create MPC ...NX Nastran TUTORIALUsing a DMAP Alter to...

NX Nastran TUTORIAL

Using a DMAP Alter to Create MPC Equations to Sum Interface Forces

NX Nastran

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MPC Equations Tutorial in NX Nastran

Content subject to change without notice. © 2018 ATA Engineering, Inc. NX Nastran is a trademark of Siemens PLM Software, Inc.

Overview

This document shows the process of using a DMAP alter to create MPC equations that can be used to sum interface forces. It uses an example model consisting of two plates connected at four locations.

Software:NX NastranFemapIMATMATLAB

Difficulty Level:Intermediate

Preceding Tutorial:None

Input Files Required:flat_plates.datflat_plates_mpc.mpcflat_plates_chk_mpc.datcutloads.dmapconvert2mpc.m

Output Files Created:flat_plates_mpc.datflat_plates_chk_mpc.pch

This tutorial is part of a series of free Siemens PLM Software training resources provided by ATA. For more tutorials, whitepapers, videos, and macros, visit ATA’s PLM Software website: http://www.ata-plmsoftware.com/resources.

http://www.ata-plmsoftware.com/resources



Content subject to change without notice. © 2018 ATA Engineering, Inc. NX Nastran is a trademark of Siemens PLM Software, Inc.

Concepts• Generating inputs for the alter (this example uses Femap)

• Converting the DMIG results into a format for MPC cards (this example uses IMAT and MATLAB)

• Checking the MPC equations using unit loads



1 Content subject to change without notice. © 2018 ATA Engineering, Inc. NX Nastran is a trademark of Siemens PLM Software, Inc.

ContentsTutorial 21. Generate Inputs and Run the Input File 2

1.1. Import the Model to Femap 21.2. Create a Group of the Interface Elements 21.3. Add All Related Entities to the Group 31.4. Create a New Node at the Center of the Interface Elements 31.5. Create a Constraint Set on the Nodes on One Side of the

Interface 41.6. Create a New Analysis Set and Activate the ASET 41.7. Write Out the Nastran Input File 41.8. Edit the .dat File to Do a DMAP Run 41.9. Run the Job to Generate a Punch File 5

2. Convert the Punch File into MPC Format 62.1. Run the IMAT Script 6

3. Check the MPC Equations Using Unit Loads 73.1. Run the Job to Check MPC Equations 73.2. Check the Punch File 7




Tutorial

1. Generate Inputs and Run the Input FileThis DMAP alter creates DMIG matrices that relate the loads through a section of a structure to the displacement of nodes on the section. The DMIG matrices can be converted to MPC equations to put section cut outputs back in the model.

The bulk data file should contain all the elements on one side of the cut, along with all related nodes, coordinate systems, properties, etc. The nodes on one side of the cut are identified on ASET cards.

Forces and moments will be resolved around a node that is not connected to any element and which is placed in the S-set and also on the PARAM,GRDPNT card. The resultant loads will be recovered in the displacement coordinate system of this node.

1.1. Import the Model to Femap

1. Import the model flat_plates.dat to Femap using File → Import → Analysis Model. Adjust view preferences as desired.

Tip: Try importing the model using this free API from the ATA PLM Software website to automatically set some common view preferences.

1.2. Create a Group of the Interface Elements1. Create a new group by following Group → Create/Manage and

selecting New Group. Name the group “Interface_Springs.”

2. Add elements to the group using Group → Element → ID. Add elements 10001–10004, the four springs connecting the top and bottom plates. The associated nodes are 10001–10004 and 10011–10014.

Figure 1-1: ▶Model includes two plates connected at four locations.

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1.3. Add All Related Entities to the Group1. In the Model Info pane under Groups, right-click Interface_Springs

and select Add Related Entities. The group will include eight nodes, four elements, and one property.

1.4. Create a New Node at the Center of the Interface ElementsThe node will be used for the MPC Equations.

1. Find the coordinates of the interface elements using List → Model → Node and selecting the Interface_Springs group in the Entity Selection window.

2. Press OK to accept the defaults of the Listing Options.

3. Copy the list results to Excel, using the Text Import Wizard to split the data into multiple columns.

4. Find the average X1, X2, and X3 coordinates.

5. Use Model → Node (or Ctrl+N) to create a new node at the average coordinates from the previous step. Set the Node ID to 10000.

Figure 1-2: ▶Entity Selection window to list nodes.

Figure 1-3: ▶Average coordinates are found in Excel.

Figure 1-4: ▶Enter coordinates and ID for the new node.




6. Add the node to the Interface_Springs group by following Group → Node → ID and adding Node 10000.

1.5. Create a Constraint Set on the Nodes on One Side of the Interface

1. Create the constraints using Model → Constraint → Nodal and naming the constraint set

2. Select nodes on one side of the interface. In this case, apply the constraints to nodes 10001–10004.

3. Select the Fixed button to check each DOF box, then click OK to apply the constraints.

1.6. Create a New Analysis Set and Activate the ASET1. Open the Analysis Set Manger at Model → Analysis.

2. Select New… in the Analysis Set Manager and set the title to Flat_Plates_MPC.

3. Click Next… until you reach the Nastran Bulk Data Options window.

4. Use the dropdown next to Portion of Model to Write to select the Interface_Springs group.

5. Click Next… until you reach the Boundary Conditions window.

6. Use the dropdown next to Master (ASET) to select the interface constraint set.

7. Click OK.

1.7. Write Out the Nastran Input File1. From the Analysis Set Manager window, click Export.

2. Name the file flat_plates_mpc.dat.

1.8. Edit the .dat File to Do a DMAP Run1. In the Executive Control Section:

a. Remove the lines that begin with NASTRAN, ID, and SOL.

b. Add the DMAP as an include file with the line

INCLUDE ‘cutloads.dmap’

2. In the Case Control Section:

a. Remove the output request lines, which begin with DISPLACEMENT, SPCFORCE, OLOAD, FORCE, and STRESS.

b. Set the SPC line to

SPC = 10000




3. In the Bulk Data Section:

a. Update the PARAM,GRDPNT line to

PARAM,GRDPNT,10000

b. Add a line to put an SPC on the free node

SPC1,10000,123456,10000

1.9. Run the Job to Generate a Punch FileUse Nastran to solve the input file. A punch file will be created with DMIG matrices that can be converted into MPC equations.

Figure 1-5: ▶Input file to run DMAP.




2. Convert the Punch File into MPC FormatThe punch file created by the DMAP alter contains DMIG cards that define six columns of a matrix. Each column gives the corresponding resultant force or moment about the node placed in the S-set transformed to the displacement coordinate system of that node. The DMIG cards can be reformatted as MPC cards to recover resultant loads from the model.

This tutorial uses a simple IMAT command to convert the DMIG cards into MPC cards for use in a Nastran input file. IMAT (Interface between MATLAB, Analysis, Test) is a suite of utilities offered by ATA Engineering, Inc. which facilitates data sharing between MATLAB, analysis tools, and test software. More information on IMAT can be found here.

This tutorial does not cover other methods to convert the DMIG matrices into MPC cards.

A file with the converted MPC cards has been provided if you cannot immediately complete this step.

2.1. Run the IMAT Script1. Place convert2mpc.m in the same folder as the punch file to convert

2. Ensure the units and file names are correct

3. Run the script to generate an .mpc file with the MPC equations.

Figure 2-1: ▶First MPC card.

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3. Check the MPC Equations Using Unit LoadsThe MPC equations should always be checked by applying unit loads to the model and reporting the displacements of the resultant nodes, which should match the resultant forces and moments through the cut.

An input file to check the MPCs has been provided. The MPC has been identified in the Case Control section, and the .mpc file with the MPC cards are added with an Include file in the Bulk Data section. The Output Requests send the displacements of the MPC node to a punch file. These displacements correspond to the forces across the interface. Six subcases apply unit loads in each DOF individually to a node on the top plate, while the four corners of the bottom plate are constrained.

3.1. Run the Job to Check MPC Equations1. Run flat_plates_chk_mpc.dat after checking that file titles and node

and element IDs are consistent with your local copy of the model.

3.2. Check the Punch File1. Check the punch file to make sure that section cut loads are as

expected.

2. Although the punch file reports nodal displacements, the MPC was constructed so that the displacements are equal to the forces that are transmitted across the interface. The text below shows the punch file from the unit load check. Note that for the Unit Fx results, the displacement in the X direction is 1.0, which means there was 1.0 N transmitted across the interface in that direction as expected. The other displacements and rotations are small or negligible, indicating there are no loads or moments in those directions.

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Tutorial1.Generate Inputs and Run the Input File1.1.Import the Model to Femap1.2.Create a Group of the Interface Elements1.3.Add All Related Entities to the Group1.4.Create a New Node at the Center of the Interface Elements1.5.Create a Constraint Set on the Nodes on One Side of the Interface1.6.Create a New Analysis Set and Activate the ASET1.7.Write Out the Nastran Input File1.8.Edit the .dat File to Do a DMAP Run1.9.Run the Job to Generate a Punch File

2.Convert the Punch File into MPC Format2.1.Run the IMAT Script

3.Check the MPC Equations Using Unit Loads3.1.Run the Job to Check MPC Equations3.2.Check the Punch File

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