Figure 4: Activation of the erg-reader module through the TASverter GUI
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The ESARAD erg-reader module of TASverter is activated from the command line using the option:
--from_erg=ergFile.erg
When the TASverter GUI is used, the "Model Type" of the "From"-file must be set to "ESARAD erg" (see figure below):
Figure 4: Activation of the erg-reader module through the TASverter GUI
When this option is activated, TASverter expects an ESARAD erg formatted file as input. The contents of this file are read and stored in memory in the internal STEP-TAS format (the so-called Part 21).
The development of the erg-reader module was based on the information found in the ESARAD Reference Manual. If any construct in the input file does not comply with the format specified in the manual, TASverter will stop and provide an error message to the user (this error message will be displayed in the output box when the TASverter GUI is used).
The ESARAD erg language does not provide a means to specify the length unit to be used by the model. Therefore, the ESARAD erg-reader module has to assume a unit. The chosen default unit is metre.
This default can be overridden by selecting a different unit using the command line option --source_length_unit.
Cutting or boolean operations are supported by the erg-reader module, but with the following limitations:
c = a1 + a2 - b;but the erg-reader module will only accept it once it has been re-written in the form:
a = a1 + a2;
c = a - b;
The erg-reader module stores the cutting operations in the STEP-TAS dataset but does not evaluate them.
Note that any subsequent conversion of these cutting operations will only be "successful" if the destination tool format also supports cutting operations. If the destination tool does not support cutting operations the policy is to write out the "uncut" surface and comments that provide the definition of the surface that was supposed to be used as the cutting tool. The purpose of the comment is to supply as much information as possible so that the user can reconstruct the intended geometry in the destination tool using some other route if possible.
It is therefore recommended that users of tools that support cutting operations (such as ESARAD) should avoid the use of cutting operations if they know in advance that the model will need to be converted to a tool format that does not support cutting operations (such as THERMICA and TRASYS).
The ESARAD colours specified for ESARAD SHELLs are converted to the STEP-TAS colour definitions using RGB-values.
TASverter has been updated along with the STEP-TAS protocol and libraries to support the Space Kinematic Model (SKM) module. The Esarad geometry reader and writer modules can now convert ASSEMBLY variables to and from the SKM representation. However, until the Space Mission Aspects (SMA) module has been implemented, the erg_writer can only generate simple ASSEMBLY variables without mission-related orientation and pointing. TASverter does not handle any redefinition of the position and orientation of the ASSEMBLY components that may take place as a result of executing the ESARAD kernel after the ESARAD erg file was loaded.
In other words, the model that is created by TASverter will reflect the initial position and orientation of the ESARAD model when the ESARAD erg file is newly loaded into ESARAD, but before the analysis has been defined or run using the ESARAD kernel.
Note that converting an ESARAD model that contains an ASSEMBLY into a different output format will result in an non-kinematic model that will be equivalent to using a SHELL union to represent the ASSEMBLY.
The only comments which are stored in the STEP-TAS dataset are those which precede the BEGIN_MODEL statement. These comments are stored as an information attribute of the STEP-TAS geometrical model. All other comments are skipped.
The "label" attributes of the primitive SHELLs are the only descriptive elements that are transferred to the STEP-TAS dataset.
The erg-writer module of TASverter can be activated from the command line using the option:
--to_erg=ergFile.erg
When the TASverter GUI is used the "Model Type" of the "To" file must be set to "ESARAD erg" (see figure below):
Figure 5: Activation of erg-writer module through the TASverter GUI
The generated ESARAD erg-file starts with comments that describe:
When there is any descriptive information stored with the geometrical model, the erg-writer module writes out this description just before the BEGIN_MODEL statement.
The ESARAD erg language does not provide a means of specifying the length unit to be used by the model. TASverter assumes a default length unit of the metre for the length values in the generated ESARAD erg model. This default can be overridden using the --destination_length_unit command line option to select a different unit.
If length unit conversion is applied, information about the conversion is included at the beginning of the generated model file in the form of a comment.
The ESARAD modelling language uses variables. Examples of variable types are SHELL and OPTICAL. The erg-writer obtains the variable names from the from the identifiers of the corresponding entities in the STEP-TAS dataset. These STEP-TAS identifiers may start with a digit, but ESARAD does not allow variable names which begin with a digit. If the STEP-TAS identifier corresponding to an ESARAD OPTICAL variable starts with a digit or underscore, the erg-writer prefixes the identifier with 'o_'. Similarly STEP-TAS identifiers corresponding to ESARAD SHELL variables are prefixed with 's_'. If necessary, sequence numbers are appended to the generated variable names to avoid problems with duplicated names.
The STEP-TAS dataset contains information about optical properties using STEP-TAS materials and material environments. If the STEP-TAS dataset contains a single material environment, the erg-writer converts the optical properties information into a set of ESARAD OPTICAL variables. If the STEP-TAS dataset contains more than one material environments, the erg-writer generates a series of IF-THEN-ELSE constructs, with each branch representing one of the material environments and containing a different definition of the ESARAD OPTICAL variables.
The user can select which material environment to use during the ESARAD radiative analysis by entering a string variable in the Material Environment input field in the TASverterGUI. If no value is provided, the first material environment will be used by default.
Setting the Material Environment input field in the TASverterGUI is equivalent to specifying the TASverter option:
--material_environment=MATERIAL_ENVIRONMENT
Note that once TASverter has created the ESARAD erg file, the user is free to edit the file to change the selected environment.
ESARAD allows most geometrical primitives to be specified in two ways: by using points, or by using parameters (the so-called SCS method).
The erg-writer module generates primitives using the method that is closest to the STEP-TAS representation of that primitive. This means that the following SHELL definition procedure calls are used for defining primitives in the target ESARAD erg file:
The positions and orientations of quadrilaterals, rectangles and triangles are defined by points using the SHELL_QUADRILATERAL, SHELL_RECTANGLE and SHELL_TRIANGLE primitives. The other primitives are defined by parameters and are then moved to the correct position and orientation using TRANSLATE and ROTATE calls.
In principle, ESARAD supports an infinite number of levels in the model hierarchy. This means that the complete hierarchy of the model in STEP-TAS can be represented in the ESARAD geometry model.
All boolean cutting operations that are stored in the STEP-TAS dataset are converted to the ESARAD erg language, except for cutting with an infinite cylinder. Currently no mapping is implemented for this cutting tool shape.
ESARAD supports colour specification on both sides of a SHELL. Each ESARAD colour that the erg-writer assigns is the one with the RGB-values that most closely match the RGB-values of the STEP-TAS colour.
ESARAD SHELLs have associated parametric directions that are used when defining the thermal node mesh dimensions and the order in which the mesh elements are numbered. How these parametric directions are defined depends on the ESARAD SHELL types. The thermal node numbers for each side of a SHELL are defined using these parametric directions and mesh element order in combination with a thermal node number specification that defines the base node number and the node number increment.
It is possible that the thermal node mesh associated with a STEP-TAS representation of a SHELL is incompatible with the ESARAD representation using base node number and node increment. In this case, the erg-writer generates an equivalent set of single node sub-SHELLs.
STEP-TAS supports surfaces that act as pure radiation blockers. ESARAD does not have this kind of SHELL, and indeed ESARAD considers a SHELL where both sides are inactive to be "invisible" as far as the radiative analysis is concerned. In order to emulate the pure radiation blocking surfaces of STEP-TAS, the erg-writer converts them to SHELLs where both sides are active and have solar absorptance and infra-red emissivity values equal to 1.0 so that they absorb all incident radiation. The thermal node number of the nodes meshed on the SHELL is set to the inactive node number.
The inactive node number can be specified using the Inactive Node input field in the TASverterGUI. This corresponds to the TASverter option:
--inactive_node=INACTIVE_NODE
The user must take care that this node is also declared as inactive, i.e. an X-node, in the $NODES block of any ESATAN input file produced after the ESARAD radiative analysis of the generated erg file.
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