Simcenter 3D Solutions Import Options for RPC-III Load Time Histories in Simcenter 3D Specialist Durability

In Specialist Durability, one common way to define a Load Event is to use a quasistatic superposition of unit load FE results and load time histories that describe the variation of these unit loads over time in the Superposition Event. In the TAB "Load Histories" of this Load Event, the user loads load time history data via the load time history interface, which identifies the format and loads the data accordingly. This also applies for RPC-III data and for this format, import options are available, which are needed due to some features of the format.

 

The RPC-III format is a common, binary load time history format. The signals stored in this format are written in blocks of given size (multiples of 2, e.g. 512, 1024 or 2048 data points). Usually the amount of data points in a signal will not match these preset block sizes, thus additional data points are added to fill the signal up to a multiple of the block size.

 

This can be done in two ways:

• by adding zeros,
• or by repeating the last data point.

 

Simcenter 3D has to deal with these two different options in a way that only the actually measured data is later on used in the simulations. 

 

 

Here is a look at these two options and the problems a wrong selection of the import option could cause.

 

Example 1: trailing zeros

X-Y graph of the signal "Record 4". 

Note that around 3s the signal drops from the range of 0.2 to 0.65 [N] to 0 [N] due to the option selected to fill up the signal.

 

List of data points in a Simcenter 3D field (Time [s]; Force [N])

The data points in the green frame are measured data, the ones in the red frame are filled up by the RPC-III format.

 

Assuming that we take this signal as input for a Specialist Durability Superposition Event this drop from 0.38N to 0N that isn't in the measured data introduces an additional cycle with approximately the same range than the biggest cycle in the complete signal and thus it should have a significant impact on the overall damage of the signal.

 

To avoid this we'd need to cut the signal at 3.010000143s. 

This can be done in the Superposition Event on TAB "Load Histories" in the option "Interval".

 

 

 

Example 2: repeating the last data point

X-Y graph of the signals "FORCE_vert", "FORCE_lat" and "FORCE_long". 

After 3.0865s the last value is repeated till the end of the signal due to the option to fill up the signal. 

 

List of data points in a Simcenter 3D field (Time [s]; Force [N]) for channel "FORCE_long"

The data points in the green frame are measured data, the ones in the red frame are filled up by the RPC-III format, repeating the last measured data point.

 

When using this signal as input for a Specialist Durability Superposition Event the additional data points added to fill up the signals to the multiple of a block length are not outside the usual range of the measured signal. This has the advantage that no additional cycle is added and thus, the fatigue damage will not be changed. There is still the disadvantage that the additional points in the quasistatic superposition will require some additional computation time, since the solver still needs to compute the superimposed stress and the local stress state for the additional time steps.

This can again be addressed by cutting the signal in the Load Event with "Interval" (see above).

 

Both methods to fill up the signal to a complete block length use repeating constant values. These constant values are either zeros added after the last measured value or this last measured value is repeated. The method used determines which constant values at the end of the signal need to be cut:

• if the repeating constant values are zeros, all of them need to be cut,
• if the repeating values are the last measured value, all except one need to be cut.

 

 

How to remove these constant values from the signal?

 

While the handling of the repeated constant values in a RPC-III signal could be dealt with in the option "Interval" after the import of the data to the Superposition Event in Simcenter 3D, there is a better option to do so.

 

The import of load time history data in the Superposition Event of Specialist Durability is done via a functionality from the load data processing tool Simcenter Tecware. This tool uses INI-files that are being read upon start of the software and that allow to define values for certain parameters influencing the operation of functionalities like the import of data from load history files. One parameter determines the "LengthRule" as import option for RPC-III data, which addresses the handling of the trailing constant values.

 

Here is an excerpt from the comment of the "RPC-III driver configuration" in the INI-file "tecware.ini":

 

The comment above explains the parameter "LengthRule". It sets the rule how to compute the channel length and it has three possible values:

• "Full" uses the product of block count and block length. This means that no constant values at the end are cut,
• "Constant" removes the trailing constant part of the signal in the last block, but keeps the data point introducing this constant part.
• "ConstantComplete" does the same than "Constant", but also removes the first data point of the constant part.

 

Thus, for a signal with trailing zeros as constant part, the "LengthRule" "ConstantComplete" should be selected to remove all zeros at the end of the signal. 

 

For a signal repeating the last data point, the preferred "LengthRule" is "Constant", because it keeps the last measured data point from the constant part.

 

 

Here is a comparison of the signal from example 2, when it's imported with a different "LengthRule":

 

LengthRule "Full"

 

Each channel has 2048 data points.

 

With "Full" each channel is filled up with a constant part, repeating the last data point. The constant part takes up almost half of the time of the signals.

 

 

LengthRule "Constant"

 

The length of the channels has shrunk to 1143 points (compared to 2048 data points for the option "Full").

 

The last data point still has the same values than the constant part in the data imported with "Full".

 

 

LengthRule "ConstantComplete"

 

The length of the channels has gone further down to 1142 points, since this "LengthRule" also removes the data point that introduced the constant part of the signals.

 

The last data points in the signals are now different, since all points of the constant section have been cut.

 

 

Where can the "LengthRule" be defined?

 

The INI-file in which this parameter is defined is somewhat hidden in the installation of Simcenter.

It can be found in a subfolder of the installation directory of Simcenter (<install_dir>/SIMULATION/tecware/data):

 

 

In theory, the Simcenter 3D user could edit the "LengthRule" in this file. In practice, being able to edit a file in the installation directory of a software is not possible for the common user and modifying files in a software installation isn't a good idea anyway. Potential mistakes in the editing of such files could lead to the software not working properly. 

 

Still, the users should be able to use the option to define their preferred values for parameters in INI-files. This is why multiple INI-files can exist at different levels and Simcenter Tecware relies on reading these INI-files from different levels in a predefined sequence. 

 

• First the "tecware.ini" at the installation level is read. 

This file contains default settings for all parameters. With these settings, the software will start and work properly. Its content serves as a template for the additional INI-files at the other levels. The individual user will not have write permission for files in the installation. 

 

• Then the "tecware.ini" from the custom-directory is read.

The custom-directory is an optional subdirectory of the installation of Simcenter Tecware where settings for a team or department of users can be shared. Any values of parameters set in the INI-file here will overwrite the ones taken from the INI-file in the installation. Since the content of the custom-directory should be managed centrally for a group of users, the individual user should not have write permission in it as well.

 

• Finally the "tecware.ini" from the private tecware-directory is read.

The private tecware-directory is a directory that contains the INI-files with the personal settings of the individual user. Any values of parameters set in this INI-file will supersede the ones from INI-files read before. These are the INI-files which the individual users are intended to customize for their own usage. Their default location is a subdirectory of the user's temp-directory, which ensures that they are permitted to edit them.

 

Here is an example of a user's private tecware-directory (C:\Users\<username>\tecware)

 

This INI-file is not only read when starting Simcenter Tecware, it's also read when Simcenter 3D is started, which means that the setting for the "LengthRule" in the INI-file is being used when importing RPC-III data in a Specialist Durability Superposition Event. Using the private "tecware.ini" for this definition sets the value for all Simcenter 3D versions that the users are running on their computer. 

 

Thus, the more convenient way to address the issues caused by the trailing constant values mentioned above, is to define the "LengthRule" in the user's "tecware.ini" in the private tecware-directory.

 

 

How to define the "LengthRule" in a private "tecware.ini"?

 

The procedure differs depending on whether the user is also a Simcenter Tecware user or not. 

 

• Users of Simcenter Tecware and Simcenter 3D will already have such a private tecware-directory with a set of INI-files.

 

• Users of Simcenter 3D that do not use Simcenter Tecware will first need to create the tecware-directory in the location given. In a second step, they need to copy the "tecware.ini" from the installation to this location.

 

With the "tecware.ini" located in the private tecware-directory, the users need to edit this file in a text editor to include the "LengthRule" parameter.

 

• Users of Simcenter Tecware and Simcenter 3D first should check if they have this parameter already in the file (e.g. via "Search - Find - "LengthRule""). If it's not present, the complete section of the "RPC-III driver configuration" should be copied from the "tecware.ini" in the installation to this file. The users can then proceed to set the value of the "LengthRule" desired.

 

• Users of Simcenter 3D that do not use Simcenter Tecware should remove all parameters from the copied "tecware.ini" that are not related to the "RPC-III driver configuration" to keep them from being modified by accident. They can then set the value of the "LengthRule" desired.

 

As indicated, these settings are read upon startup of the software. A restart is required to apply changes to the "LengthRule" done while Simcenter 3D is already open.

 

 

Extract from the "tecware.ini": the comment section of the "RPC-III driver configuration"

 

Extract from the "tecware.ini": [TSConfiguration:RPC-III] with the first parameter being the "LengthRule" set to "Full" 

 

Extract from the "tecware.ini": [TSConfiguration:RPC-III] with the first parameter being the "LengthRule" set to "Constant"

 

Extract from the "tecware.ini": [TSConfiguration:RPC-III] with the first parameter being the "LengthRule" set to "ConstantComplete"