Preserving the order and format of bulk data through the round-trip process

The term round trip refers to the process of data conversion that occurs when you import a solver data file and then export the same file. The software contains commands and options that you can use to help preserve the order and format of the bulk data entries in your Nastran files during the round-trip process.

Currently, these round trip capabilities are limited to:

• ASCII format files only.

• Selected entries within the bulk data section of the Nastran input file.

Specifying your intent to round trip data when you import a file

When you import an ASCII format Nastran file, you can use the Create Round Trip Parameters modeling object option in the Import Simulation dialog box to indicate that you want to preserve the format of your data as much as possible for future export. If you select the option, the software then creates a Round Trip Parameters modeling object in the associated FEM file.

Note:

For large models, if you select this option, there may be a performance impact.

There is a customer default that you can use to set the default state of the Create Round Trip Parameters modeling object option in the Import Simulation dialog box.

1. Choose File→Utilities→Customer Defaults.

2. In the Customer Defaults dialog box, select Simulation→Pre/Post→General.

3. On the Environment tab, select or clear the Create Round Trip Parameters Modeling Object on Import check box.

Round Trip Parameters modeling object

The software primarily uses the Round Trip Parameters modeling object to store data about the input file. You cannot edit the content of a Round Trip Parameters modeling object or create a new one.

You can use the Round Trip Parameters dialog box to specify a limited number of options that control how the software processes the data. You can specify, for example:

• Whether you want to preserve the order of the bulk data entries.

• Whether you want to preserve the field format of the bulk data entries.

The software associates the Round Trip Parameters modeling object with the related solution. On the general Tab of the Solution dialog box, the Round Trip Parameters option lists the associated modeling object. If you subsequently decide that you do not want to use this capability, you can remove the reference to the Round Trip Parameters modeling object from your solution.

When you export the model, the Export Simulation dialog box lists the related Round Trip Parameters modeling object in the Formatting Options section.

Bulk data entries supported for the round-trip process

Currently, not all bulk data entries can be preserved exactly through the data round trip process. In general, this release supports the round trip of the following types of bulk data entries:

• GRID entries

• Element entries

• Material entries

• Physical property entries

• Degree-of-freedom (DOF) set entries

• Load and constraint entries

• Coordinate system entries

• BSURF, BSURFS, and BLSEG entries

Other types of bulk data entries are partially supported for the round-trip process.

Support for cards that are processed as user defined text

The software imports bulk data entries in an input file as a User Defined Text modeling object when:

• You use the By card name option in the Selective Import group (Import Simulation dialog box) to import selected entries as a User Defined Text modeling object.

• You use the Import unsupported cards option in the Advanced Options group (Import Simulation dialog box) to import cards that are not currently supported as either a commented or uncommented User Defined Text modeling object.

Round trip support for include files

Include files are supported for the data round-trip process. If the imported file contained include files, on export, the software:

• Inserts the content of the include file at the location of the INCLUDE statement.

• Inserts comment cards before and after the included file to indicate the beginning and end of the included file.

Preservation of load and boundary condition naming

The software tries to preserve the names of loads, boundary conditions, and Simulation objects when you export a Nastran input file and subsequently re-import the same file. Currently, the labels (IDs) for loads, boundary conditions, and Simulation objects are not preserved. Names are preserved when you use either the Import Simulation dialog box or the Solver Deck Append dialog box to import the input file data.

The software also preserves the first 80 characters of the names of the Load Container, Constraint Container, and Simulation Object Container from the Simulation Navigator. However, the order of the loads, constraints, and Simulation objects within those containers are not preserved during the data round-trip process.

Note that:

• You can use this capability with a Nastran .dat file or with a Nastran OP2 file that contains the IBULK datablock. The IBULK data block is an unsorted copy of the original bulk data, including comments. Use the PARAM,OIBULK,YES parameter to include the IBULK datablock in your input file.Note: If you import your data from a Nastran OP2 file, the software capitalizes lowercase letters.

• If the software imports multiple instances of a load or boundary condition, it appends a numerical extension to the root name of the load or boundary condition to make the names unique.

• The software may be unable to preserve load and boundary condition names if the original Nastran input file that you export contains a Round Trip Parameters modeling object that is referenced in a solution.

When the Import selective loads as field data option is selected in the Import Simulation dialog box:

• Any TEMP(LOAD) commands that are referenced by an Axisymmetric Structural solution are imported as a node ID table.

• Any ACCEL1 bulk data entries that are referenced by a Structural solution are imported as a node ID table.

Exporting a file

When you export a file, you can:

• Decide not to round-trip the data by removing the Round Trip Parameters modeling object from the solution.

• Modify the options in the associated Round Trip Parameters modeling object.

When you export the file, the software places any bulk data entries that could not be matched with items in the original input file in a separate section immediately following the BEGIN BULK entry up to the following commented text:

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*$* ROUND TRIP CARDS$*$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Note:

With the round-trip process, the software always exports the same Nastran bulk data entries regardless of whether your solution references a Round Trip Parameters modeling object. The Round Trip Parameters modeling object simply rearranges the order of the entries in the bulk data section of the exported file.

Known limitations

The Nastran round-trip capabilities currently have some known limitations. The following items are not currently supported by the round-trip process.

• The SID fields for most load and boundary condition bulk data entries.

• Bulk data entries associated with dynamic loading, such as RLOADx or TABLEDx.

• Scale factors and other multipliers, such as the F and Nx fields on the FORCE entry.

• Bulk data entries, such as SPC, SPOINT, and TEMPD which can have data for multiple entries on a single entry. The software only preserves the data for the first entry through the round-trip process. For example, given SPC, SID, G1, C1, G2, C2 in the input file, the software only preserves SPC, SIG, G1, C1

• The format of card fields that have real data. For example:0.0000 may be truncated to 0.0.100.E2 may be changed to 100.E4.1.+2 may be changed to 100.0.

• The content of continuation fields.

• Blank values for the CP and CD fields on the GRID entry.

• Contact sets (BCTSET) and their associated parameters (BCPARAM, BCTPARA).

• Glue sets (BGSET) and their associated parameters (BGPARM).

• Field data in the form of the TABLED, TABLES, TABLEST, and TABLEM entries.

• CORD1x entries.

• Real values specified on the CORD2x entry. Equivalent values are used, but the data that is exported may not exactly match the original input data.

• The BAROR and BEAMOR entries.

• The DESVAR and DOPTPRM entries.

• Entries, such as TEMP, FORCE, and PLOAD4, when they are used to key off the node or element ID but are repeated for different subcases, such as TEMP, 200,604,20 and TEMP, 201,604,20

• Comments that appear on the same line as other entries or commands. Only comments on separate lines are preserved during the round-trip process.

Where do I find it?

Application	Pre/Post
Prerequisite	An active FEM or Simulation file with Simcenter Nastran or MSC Nastran as the specified solver
Command Finder	Modeling Objects →Type list→Round Trip Parameters
Menu	Insert→Modeling Objects→Type list→Round Trip Parameters

Learn more

Nastran import and export support

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Preserving the order and format of bulk data through the round-trip process, Simcenter 3D 2021.1 Series

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