Chapter 13: Combining and Archiving
Models
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13.1 Combining Models
You may need to combine two or more separate models if you are working on a
portion of a model while another person works on a different portion of the same
model. Or perhaps you have subdivided a large modeling task into smaller
separate tasks, which created several separate models. One way to combine
these models would be to merge all the input (commands) together, if you have
kept copies of the input files. Conflicts may result with this method, however,
because entities on different files may share the same number, material properties
may overlap, etc.
One alternative method is to use the CDWRITE command to write out ASCII files
that you can combine with the CDREAD
command:
- To write data to an ASCII file, use one of these methods:
Command(s):
GUI:
Main Menu>Preprocessor>Archive Model>Write
- To read the data back in, use one of these methods:
Command(s):
GUI:
Main Menu>Preprocessor>Archive Model>Read
The advantage of this method is that the combination of the write and read
operations takes care of conflicting data by automatically writing appropriate NUMOFF commands to each file that is
produced. When these files are read in, the NUMOFF commands prevent conflicts in
data numbers by offsetting existing data numbers. The data that is being read in
retains its original numbering. You can use the NUMCMP command (Main
Menu>Preprocessor>Numbering Ctrls> Compress Numbers) to remove gaps
in numbering that can result from these NUMOFF operations.
On large models, you can save time by writing out only the portion of the models
that you wish to combine. For instance, with the CDWRITE operation, you have the
capability of writing out only the solid model information or only the database
information. The database information consists of the finite element model
without any solid model or solid model loading information. If you are planning on
combining two unmeshed solid models, consider saving only the solid model
information with the CDWRITE
operation. You can then use the CDREAD operation to read in the solid
model files.
13.2 Archiving Models
What is the best way to keep, or archive the models that you have made or the
analyses you have performed? You can save your model , a single load case,
and a set of solution option settings by saving the log file, the database file, or the
file(s) produced by the write operation [CDWRITE]. Multiple solutions and
postprocessing steps can be archived by saving the log file. There are
advantages and disadvantages to each type of file; they are described below.
13.2.1 Log File (File.LOG)
This file is probably the best file to save in terms of compactness. Also, this file is
a record of the commands you used to create your model, so you will probably
recognize the steps that you used, and why you did operations in a particular
order. Also, since the file is saved in text file format (normally ASCII), you can
transfer it from one machine to another through such methods as E-mail, etc. In
addition, since you can modify these files with any text editor, you can change
your model by changing this file, and you can add /COM commands (comment lines) to describe
your input. This will help you understand the input at a later date. Parametric
models (and thus models used in optimization analyses) can be archived using
the log file. Finally, this is the best file to give to other people (perhaps your ASD)
who are helping you with questions or problems.
Note-File.LOG is automatically created during an ANSYS session. If this file is
lost or corrupted, you can write a command log file for the current ANSYS
database using the LGWRITE command
(Utility Menu>File>Write DB Log File). See the ANSYS Operations Guide for more information on
using LGWRITE.
You will have to rerun the input in this file in order to get a database. Because
such things as entity numbering, meshes, etc. can change between different
hardware systems or between releases of ANSYS, you'll probably need to rerun
the input at the same release of the program that you originally used to create the
model. Also, if you created your model interactively, you may have difficulty
running the input on this file in batch mode to recreate the model. If there are any
errors in the input, they can terminate a batch run, which means that your model
will not be built completely. If you encounter this problem, run your input
interactively with the /INPUT command
(Utility Menu>File>Read Input from).
13.2.2 Database File (File.DB)
The database file can be resumed [RESUME] within the ANSYS version that the
file was created in. As long as you are resuming the file into the same ANSYS
version that it was created in, you do not need to manipulate or modify the file in
any way.
Note-Although not guaranteed, you can also usually resume a database file
created in the previous version of ANSYS into the current version. For example,
you can probably resume an ANSYS 5.2 database file into ANSYS 5.3 without
encountering problems. However, ANSYS is not expected to resume an ANSYS
5.2 database file into ANSYS 5.4 or later.
Large models can produce large database files, which can soon cause you to run
out of disk space. Also, because this file is saved in binary format (IEEE), transfer
from one machine to another is sometimes more difficult than with a text file.
13.2.3 CDWRITE File(s)
Relatively compact text file(s) (with the .cdb extension) are produced by the CDWRITE operation. Since CDWRITE saves the current model in
terms of geometric and finite element entities(rather than the commands used to
create the model), nearly all hardware platforms and or program release
dependencies are eliminated. CDWRITE files can typically be used to
re-create a model on any hardware platform and in any upward compatible
release of the program. Also, because these files can be modified with a text
editor, you can put descriptive comments in these files to help you identify and
understand them at a later date. Imported files used to create the model need not
be saved.
If you are writing data to a new file, select the BLOCKED format to allow faster
reading of the file. If you have been using data from files previously created in
ANSYS for another application, select the UNBLOCKED option when writing to
.cdb files intended for use in that application, or modify the application accordingly
to accommodate the BLOCKED format.
Files produced by CDWRITE are
essentially a text file format dump of the database. While ANSYS commands
(and possibly IGES information) are contained in the files, they may not be the
same commands that you used to create your model, and they will not be in the
same order as the commands that you used. For this reason, it is difficult (and
not recommended) to modify these files when you are trying to change a model.
Parametric model information is not saved, so changing the model by modifying
parameter values is not possible. For this reason, it is also not possible to save a
model to be used for an optimization analysis using CDWRITE. Also, to re-create your model,
you must read these files in with the CDREAD command, which can take a
moderate amount of time for large models.
If you have been using data from files previously created in ANSYS for another
application, you must use the UNBLOCKED format when writing to .cdb files
intended for use in that application, or change the application accordingly to
accommodate the BLOCKED format.
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