The Model initialization file performs the following basic functions:
Thus, the Model Initialization File can be divided into the following five sections:
| Section | Purpose |
|---|---|
| [File Management] | File Management directives allow the user to specify the names and locations of input, output, and database files. |
| [Output Control] | Output Control directives allow the user to control what output files are generated and what they have in them. |
| [Memory Management] | Memory Management directives allow the user to control what type of memory (virtual or physical) and how much will be used for memory intensive tasks such as matrix assembly and decomposition. By optimizing memory usage the user can optimize performance. |
| [Program Control] | Program Control directives allow the user to customize program execution by controlling how and what tasks are to be performed. |
| [Parameters] | Parameter statements that are specified using the PARAMETER command or entry can be specified in this section using the directive format. See Section 5, Parameters. |
Each section has associated with it a group of related directives and each directive has a default setting (see down below the Model Initialization Directive Descriptions section, for directive syntax and default settings).
For most configurations, the default settings in the nastran.ini file will provide optimal performance. There are a few directives you may want to change depending on your configuration. Changes can be made either using a standard text editor or through the Autodesk Nastran Editor Options menu.
The easiest way to modify the Nastran Model Initialization File (nastran.ini) is to open the Autodesk Nastran Editor, which is located in the installed product’s folder. For example, for Autodesk Simulation Mechanical 2016, it will be under Start, All Programs, Autodesk, Autodesk Simulation Mechanical 2016, Autodesk Nastran, Editor. Then select Setup, Default Analysis Options and click on the desired section and option. To set model specific options, open the Model Input File and use the options menu displayed to the left.
The first directive you may want to modify is the scratch file folder. Double-click on File Management, then on the FILESPEC directive to change the folder. You will want to select a folder on a disk with a large amount of available space. If you specified a scratch folder during installation, it will be displayed here.
The next setting you may want to modify is under Memory Management, RAM. This setting can greatly affect performance and may not be initially optimized for your particular computer. On ia-32 systems with 2 GB or more of memory, set RAM equal to 1800. For systems with less than 2 GB, set RAM equal to the system memory in MB. On x64 systems set RAM equal to the installed system memory in MB minus 1000 MB (which will be used for the operating system). For example, if you have 8 GB of physical memory, set RAM equal to 7000. If you specified a RAM available value during installation, it will be displayed here.
Another directive you may want to modify is under Geometry Processor Parameters, SHELLRNODE. Turning SHELLRNODE to ON converts all CQUAD4 and TRIA3 elements to CQUADR and CTRIAR. The CQUADR and CTRIAR elements are complete 6 DOF/node elements, which typically give more accurate results.
One last directive you may want to modify is under Solution Processor Parameters, SOLUTIONERROR. You can avoid getting a fatal error when a non-positive definite caused by a modeling error is encountered by setting SOLUTIONERROR to ON and FACTDIAG to 0.0. You can also avoid getting a fatal error when a singularity is encountered by setting SOLUTIONERROR to ON and FACTDIAG to 1.0E-10. Note that while these options are useful for detecting modeling errors, they may lead to solutions of poor quality or fatal messages later in the run. It is recommended that SOLUTIONERROR be set to OFF for production runs.
The Model Initialization directives are described in two different formats:
A single sentence Description is given, which states the function of the directive.
The directive syntax is defined under Format.
A typical example is given under Example.
Additional information about the directive is given under Remarks.
A complete description is given under Description, which states the function of the directive along with usage guidelines, any notes, and other pertinent information.
Option keyword syntax or allowable data range is given under Option. Character keywords are separated by a “/”. Only one keyword can be specified.
The default option is given under Default.