Initial Stresses

Begin a run with an initial stress state.

Is it possible to begin a run with an initial stress state?

It is possible to define an initial stress state by using option /INISTA. This option uses an output file (Runname_0000.sty) describing the structure of the model for which a file Runname_nnnn.sty defines a stress state.

The files Runname_0000.sty and Runname_nnnn.sty can be built in a first computation (ASCII Output File (STY-File)). They can also be written using an external program, with respect to their respective formats.

As of Radioss V4.4, it is also possible to enter the initial stress values element by element in the Runname_0000.rad file, by using options /INISHE and /INISH3 for shells and 3-node shells and /INIBRI for solid elements.

As of Radioss V9.0, it is also possible to write with Radioss Engine state files Runname_nnnn.sta for shells.

Such a file will contain the geometry of selected parts (nodes coordinates and element connectivity), plus cards /INISHE and /INISH3 defining the stress, strain, and so on, of the shells and 3-node shells belonging to these parts.

If the file is included in another input deck Runname_0000.rad, the state (geometry, stress, strain, and so on) of these parts will thus be retrieved (refer to /STATE/DT in Radioss Engine Input).

Mapping initial state file to Altair Radioss model.

Is it possible with option /INISTA to begin a computation from an initial stress state given on a sub model only?

The model which is described in file Runname_0000.sty is not necessarily identical to the model which is defined in Runname_0000.rad file; but Radioss Starter will initialize the elements of the Runname_0000.rad that it will find in file Runname_0000.sty, with respect to their stress state in file Runname_nnnn.sty.

The model which is described in file Runname_0000.sty can be a submodel of the model; which is defined in Runname_0000.rad, as well as it can partially overlap or totally include the model which is defined in Runname_0000.rad.

Associating the data relative to elements and nodes standing in files Runname_0000.sty and Runname_nnnn.sty, to the elements and nodes of the Runname_0000.rad file is made according to the user identifiers of elements and nodes. The state corresponding to some element in STY-files is given to the element in file Runname_0000.rad which gets the same user ID.

Initial state file name in /INISTA.

Using OUTP files, I input the name of the file in the Runname_0000.rad file which corresponds to the state I want to begin with, but the Starter writes an error, why?

If the file Runname_0000.sty which describes the structure of the model whose Runname_nnnn.sty state file used in /INISTA is not in the working directory, the following error message is written:
.. CONTROL VARIABLES
PGFIO-F-209/OPEN/unit=14/'OLD' specified for file which does not exist.
File name = CRA2_0000.sty
In source file /radiossb/v41/start/Bug41v/lectur1/contrl.F, at line number 894
If the initial state file Runname_nnnn.sty is right justified in /INISTA, the following message is written:
** ERROR IN FILE
UNKNOWN TROUBLE WITH S0FILE: Runname_nnnn.sty

The name of this file in /INISTA must be left justified.

Check initial state file successfully used in model.

How can I check if the initial state given in ISRT_0000.sty (or ISRTY000) and ISRT_nnnn.sty (or ISRTYnnn), which are used in option /INISTA, is taken into account correctly?
  1. In order to check if the initial stress state is correctly taken into account in the new run, compare using a post-processor an Animation file; which has been written in the initial run at the same time as the Runname_nnnn.sty file, to an Animation file written at time t=0 in the new run.
  2. Also, write an Animation file at time t=0 in the new run and compare the state of some elements with the state which it is given in Runname_nnnn.sty file. When doing that, the structure of files Runname_0000.sty and Runname_nnnn.sty have to be understood
    Figure 1.


    For searching the value of some field – for instance, the plastic strain EPSP – corresponding to a shell element whose user identifier is known:

    Look for the element user identifier in column USRSHEL of block /SHELL of Runname_0000.sty file.

    The number written at the same line in column SYSSHEL gives the Index where the field value is written in file Runname_nnnn.sty.

    The same user identifier can be used to find the element in post-processors.

  3. It is also possible to write a file Runname_0000.sty for this new deck and a file Runname_0001.sty at time t=0 of this new run, and then to compare the state of some elements with their state in file Runname_nnnn.sty. But you have to watch that the internal numbers SYSSHEL of elements can differ between the two runs. The order of elements in the two Runname_0000.sty files can be different, even for the same model when the two runs are not made with the same Radioss executable.