**Importing Geometry into Thermal Desktop From Different Formats**

[Pulling in IGES](#pulling-in-iges)

[Pulling in STEP](#pulling-in-step)

[To break surfaces up](#to-break-surfaces-up)

[To make Thermal Desktop surfaces](#to-make-thermal-desktop-surfaces)

[General notes on working with imported
geometry](#general-notes-on-working-with-imported-geometry)

[Importing from NASTRAN](#importing-from-nastran)

[Importing Pro/Mechanica (NASTRAN) mesh of a Pro/E
part](#importing-promechanica-nastran-mesh-of-a-proe-part)

[Importing Nastran Bulk Data into Thermal Desktop: Lessons
Learned](#importing-nastran-bulk-data-into-thermal-desktop-lessons-learned)

General geometry import from Pro/E gives you only surfaces that you
cannot then re-mesh -- you have to snap native Thermal Desktop surfaces
on to them to re-mesh. If you want a fine mesh, the method described
under the section "Importing from NASTRAN" may be preferred.

### Pulling in IGES

#### This pulls in boxes and flat surfaces nicely but doesn't handle surface orientation. That has to be changed manually.

-   **Set model to correct units for imported geometry (e.g. mm)**

![](media/image1.png){width="3.879861111111111in"
height="3.0930555555555554in"}

Type igesin (Import geometry)

![](media/image2.png){width="4.458333333333333in"
height="3.7916666666666665in"}

Set options as desired (for surfaces, default options work fine)

Select desired file

This is too detailed on a curved surface....

![](media/image3.png){width="6.0in" height="4.55625in"}

Set model back to desired units (e.g. m) (uncheck "Do not rescale model
to new units")

This works well on flat simple surfaces (*capes_assy_asm.igs*):

![](media/image4.png){width="6.0in" height="4.55625in"}

After bringing in the geometry, you have to go through the below process
under "**To make Thermal Desktop surfaces"** to make them into Thermal
Desktop surfaces.

However, the surface normals will not necessarily all point the same
way, so if you are setting properties by side, or having surfaces active
on one side only, this requires hand-work to change:

![](media/image5.png){width="6.0in" height="4.55625in"}

Another method is to bring in mid-plane IGES surfaces as created by the
structural analyst in PATRAN:

![](media/image6.png){width="6.0in" height="4.55625in"}

After bringing in the geometry, you have to go through the below process
under "**To break surfaces up"** and "**To make Thermal Desktop
surfaces"** to make them into Thermal Desktop surfaces.

Try ACIS in future -- when Pro set up for that

### Pulling in STEP

#### This pulls in curved surfaces but makes them all triangle surfaces. Triangles cannot be meshed more finely. Active surfaces appear to be all in same direction on the outside of a solid.

Set model to correct units for imported geometry (e.g. mm)

Type stepin (Import geo) -- pull in STEP 203 file from Pro (no
difference between 214 to 203 setting in Pro):

![](media/image7.png){width="4.458333333333333in"
height="3.7916666666666665in"}

*mech_to_thermal_solid_203.stp*

![](media/image8.png){width="6.0in" height="4.55625in"}

Set model back to desired units (e.g. m) (uncheck "Do not rescale model
to new units")

After bringing in the geometry, you have to go through the below process
under "**To break surfaces up"** and "**To make Thermal Desktop
surfaces"** to make them into Thermal Desktop surfaces.

after three explode iterations:

![](media/image9.png){width="6.0in" height="4.55625in"}

### To break surfaces up

Select everything

Modify... Explode (until I have surfaces)

If original model is not in desired units, easiest way will usually be
to change unit sets at this point:

> Set model back to desired units (e.g. m): Thermal...Preferences, set
> length to "m" (uncheck "Do not rescale model to new units")

Export... to 3DS (3ds out)

![](media/image10.png){width="5.995833333333334in"
height="4.3180555555555555in"}

Select all (or type "all" at prompt)

ACI, chg Auto-smoothing if necessary

Close drawing

Open new drawing

(Change unit preferences if necessary -- or change unit preferences
before making the 3ds file)

Insert...3DStudio file

Add All

![](media/image11.png){width="6.0in" height="4.55625in"}

**Modify...Explode (all) before making TD surface**

Then follow below under "To make Thermal Desktop surfaces"

![](media/image12.png){width="6.0in" height="4.55625in"}

### To make Thermal Desktop surfaces

Thermal...Surfaces/Solids...From AutoCAD surface

Select all

For single-sided, check "Use same Ids both sides", then have active
Top/Out

Give it thickness, material, optical material

Re-sequence Node Ids -- make sure you have all elements posted so that
all actually get selected

### General notes on working with imported geometry

Convert surfaces/boxes in groups:

-   Grab everything you want to be 2-sided surfaces with the same
    thickness, and convert them together to TD surfaces.

-   Grab everything you want to be 1-sided surfaces with the same
    thickness, and convert them together to TD surfaces.

If you need to grab several surfaces and change a variable on them that
is not already the same (e.g., you want to change them all to be single
nodes, i.e. use the same node number for both sides), then grab them
all, do Thermal...Edit, and uncheck the box, then grab them all again
and then check the box.

### Importing from NASTRAN

A preferred method in many cases will be to take the meshed geometry
from the structural station. This avoids all the manual steps of
re-orienting surface normals, exploding grouped geometry, creating
Thermal Desktop surfaces, and meshing.

#### Importing from NASTRAN: Steps

Set model to correct units for imported geometry (e.g. mm)

Thermal...Import...NASTRAN

Check "Import FE Model as a thermal model" (default)

![](media/image13.png){width="4.458333333333333in"
height="3.0416666666666665in"}

Find desired NASTRAN .bdf file (may have to chg file extension)

![](media/image14.png){width="6.0in" height="4.8in"}

Set model back to desired units (uncheck "Do not rescale model to new
units")

If surface normals are oriented correctly in NASTRAN, and only one side
is desired in Thermal Desktop, this leaves all the active surfaces in
the same direction. The model, however, can now not be remeshed by the
thermal analyst (which is true anyway for most imported geometry).
Thicknesses of surfaces come in correctly.

Calculations can be run on this imported model directly:

![](media/image15.png){width="6.0in" height="4.55625in"}

It will be the easiest to work with the components if they are brought
in separate files from NASTRAN (Structural person can save as groups
from PATRAN). To do this, make a new layer for each part and make it
current before the file is brought in (remember new items will only go
on the layer that is current). Then that entire part mesh will be on a
single layer, which will make display and selection by part much easier.

A similar method to this is to import an ANSYS mesh.

These meshes can be created by pulling the geometry into Patran and
meshing for NASTRAN or ANSYS, or via another tool such as FEMAP.

### Importing Pro/Mechanica (NASTRAN) mesh of a Pro/E part

Open Pro/E Wildfire

Open part (or assy) file

Do Applications...Mechanica (you must have Mechanica installed)

Check on "FEM Mode"

Go to Thermal (can also do in Structural)

Select Mesh, Create, Solid, Start

It will create the mesh (check it or change it if you want to) \-- it
only does tet for solids

Select Run, under SOLVER pick NASTRAN

Under Analysis leave it on Structural

Leave it on Output to File

Hit OK -- it will export the NASTRAN mesh file

Close Pro/E

Edit the NASTRAN file to have each of the following lines not carry over
to a second line:

> \$ Global Coordinate System of the model
>
> CORD2R,1,0,0.,0.,0.,0.,0.,1.,
>
> ,1.,0.,0.
>
> \$ Coordinate System for grid coordinates
>
> CORD2R,2,1,0.,0.,0.,0.,0.,1.,
>
> ,1.,0.,0.
>
> \$ Coordinate System for default grid displacement
>
> CORD2R,3,2,0.,0.,0.,0.,0.,1.,
>
> ,1.,0.,0.

Open a Thermal Desktop file

Go to Thermal...Import...NASTRAN (make sure you set units first)

Select file by changing to \*.nas files -- pick your desired file

You have a meshed model!

Right now display of a complex model is pretty slow, but I think it will
be better in Mechanical Desktop or AutoCAD 2005.

### Importing Nastran Bulk Data into Thermal Desktop: Lessons Learned 

This section is courtesy of <deborah.m.lemons@nasa.gov> at NASA JSC.

Integrated structural/thermal analysis is facilitated by model sharing
between disciplines, particularly FEMs. Thermal Desktop is one of
several thermal analysis programs that are capable of importing finite
element networks and converting them into thermal networks. (Other such
programs include SINDA/ATM, FEMAP TMG, and IDEAS TMG.) MSC.Nastran is a
widely used stress analyzer whose FEMs, compiled in "bulk data" format,
are recognized by the Thermal Desktop translator. (Other recognized, but
less-widely used, formats include FEMAP neutral, IDEAS universal, and
STEP-209.) Following a successful thermal analysis in Thermal Desktop,
temperature results for FEMs that are also used for mechanical stress
analysis can be fed back into the Nastran solver, thus closing the loop
on an integrated structural/thermal stress analysis.

During translation, network grid locations and many Nastran element
types are retained. However, due to inherent differences between thermal
and structural analysis methods, discontinuities are likely to occur
when translating an FEM that was specifically created for modeling
mechanical stress. (In other words, certain modeling practices suited to
mechanical analysis do not appropriately treat thermal phenomena).
Furthermore, because model translators must struggle to support
ever-changing technology, they suffer from a perpetual need to become
increasingly robust, seamless, and user-friendly. This report, based on
user experience, contains helpful information for addressing these kinds
of difficulties encountered upon importing Nastran bulk data into
Thermal Desktop. The intent is to promote correct and efficient
translation and, ultimately, a better final product.

#### Getting Started

Analysts can increase the odds of a successful translation by becoming
familiar with common Nastran element types and bulk data entry
formatting (see Reference 1). (Examples of Nastran element types that
are relevant to thermal modelers include CTRIA3, CQUAD, CTETRA, CPENTA,
CHEXA, CBAR, CROD, PSHELL, PBAR, PROD, PCOMP, PSOLID, RBE2/RBE3,
MAT\[n\].) Users should also refer to the Thermal Desktop User's Manual
(Reference 2) regarding which Nastran element types are recognized, and
which types are deliberately altered during translation.

Armed with basic knowledge of both programs, analysts are advised to
conduct a review of the Nastran bulk data set prior to translation in
order to learn which specific element types are used and to identify
potential translation problems. As will be discussed in this report,
many of these problems are more easily resolved up front---by editing
the bulk data file---rather than by editing the translated geometry
within Thermal Desktop.

Analysts may also benefit from considering whether symmetry of geometry
and environment permit adequate thermal characterization based on a
section (e.g. half) of the original FEM, thus reducing labor and model
size. Such decisions should be based on informed consultations with
designers and other structural or thermal analysts. Ideally, the
original model is truncated *before* translation via changes to the bulk
data file; a modular organizational scheme facilitates this process.
(Owners of the Nastran model are best equipped to perform the actual
truncation at this point in the process.) Otherwise, unneeded sections
can be deleted from the translated geometry within Thermal Desktop,
although this method might be tedious and error-prone if the mesh is
very fine.

Throughout this preliminary stage, analysts are encouraged to take
advantage of ongoing consultations with mechanical designers and the
stress analysts who developed the original model.

#### Element Translation

-   Several of the Nastran element types that are recognized by Thermal
    Desktop represent elongated shapes (CBAR, CROD, and CONROD). Thermal
    Desktop automatically converts each of these "beam" elements into a
    linear SINDA conductor with one SINDA node on each end. The analyst
    should carefully consider whether the new configuration is
    significant and/or appropriate for a specific thermal model, then
    modify conductor and node definitions accordingly. In many cases, it
    is acceptable to delete all instances of reconfigured beam elements.
    However, the possibility exists that a beam represents a significant
    energy path, and thus should be represented with a user conductor or
    some alternate configuration within the thermal model.

-   Thermal Desktop does *not* recognize several potentially significant
    Nastran element types. Because their omission may compromise the
    thermal model, analysts should carefully consider whether and how to
    represent their thermal effects.

    -   CBEAM is an unrecognized element type, but has the same physical
        configuration as CBAR, CROD, and CONROD; indeed, all of the beam
        elements are *thermally* equivalent. If missing CBEAMs are
        needed for thermal reasons, they can be retained by changing
        them into CBARs in the bulk data file according to the
        formatting guidelines in the MSC.Nastran Quick Reference Guide
        (Reference 1).

    -   So-called "Multi-Point Constraint" (MPC) elements---RBE1, RBE2,
        RBE3, RBAR, RSPLINE---and "spring"
        elements---CELAS1/CELAS2---are also unrecognized by Thermal
        Desktop. These "connective" elements impose *mechanical*
        constraints between planar elements, but their loss during
        translation results in a lack of *thermal* coupling. Such breaks
        between adjacent planar elements in the thermal network may not
        be readily visible; elements may appear to be thermally coupled
        when they are not, with obvious thermal implications. The *Show
        Free Edges* command in Thermal Desktop can be used to locate
        disconnected areas, and the *Merge Coincident Nodes* option is
        one way to reconnect them.

    -   A CONM2 element, which is used in Nastran to represent a point
        mass with zero mechanical load, is *not* recognized by Thermal
        Desktop but may contribute thermally significant mass and/or
        surface area. Analysts should assess and, if necessary,
        compensate for the thermal effects of CONM2 elements.

-   The Thermal Desktop translator does not recognize any Nastran bulk
    data entries in "large-field" format. A large-field entry occupies
    multiple text lines in the Nastran bulk data file; it is denoted by
    an asterisk appended to the end of the element type (e.g. CQUAD4\*)
    on the first line, then another asterisk at the beginning of the
    second line. If access to Patran is available, the analyst select
    the small-field format option and re-output the bulk data file.
    Alternatively, the analyst can examine the bulk data file for any
    large-field entries and manually convert them to "small field"
    format according to guidelines in Reference 1.

-   Experience has demonstrated the possibility of unpredictable
    behavior by isolated planar elements after translation. (Evidence
    suggests that this phenomenon may occur after the thermal analyst
    has modified the original mesh within MSC.Patran.) For example, a
    bad element may indicate an ambiguous *Active Side* definition for
    purposes of radiation modeling in Thermal Desktop: the active
    side(s) as indicated by the *Display Active Sides* tool does not
    agree with the element's thermal model definition. Discoloration of
    the element's surface in comparison to other elements may also
    indicate a bad element. The impact of bad elements on analysis
    results is unpredictable, so analysts are encouraged to visually
    inspect the model and use the *Display Active Sides* tool to
    identify bad elements that may need to be redefined and/or
    re-imported in order to function properly.

#### Materials and Properties

-   Generally, the translation of property values (e.g. density) from
    Nastran to Thermal Desktop is not reliable. Depending on how the
    material element is referenced by the Nastran model (e.g. via
    property elements PSHELL, PBAR, or PCOMP), newly created Thermal
    Desktop materials may take on zero or default property values after
    translation. The *Color by Property Value* function is useful for
    visually detecting incorrect values such as density and conductivity
    (of planar and solid elements only). The best way to solve
    discrepancies is to determine the correct material compositions by
    referring to mechanical design documentation and/or Nastran bulk
    data, and then create and assign the correct materials in Thermal
    Desktop.

-   Thermal Desktop *does* recognize use of the Nastran property element
    PCOMP for composite planar elements; the translator creates and
    assigns the material name P#, where \# is the Nastran PCOMP
    identifier (PID). However, thickness values of PCOMP elements are
    *not* correctly retained, and property values of the newly created
    materials are erroneous. The *Color by Property Value* function is
    useful for visually detecting incorrect thicknesses and property
    values, after which the analyst may need to calculate thermally
    effective thicknesses and/or properties and assign them accordingly.

#### Geometry

-   Experience has shown that planar elements may unpredictably, and
    incorrectly, translate with *zero* thickness. The *Color by Property
    Value* function is useful for visually detecting incorrect surface
    thicknesses. Thermal analysts can consult with designers and/or
    stress analysts to identify correct element thicknesses, then edit
    the model accordingly.

-   Due to the nature of Nastran modeling, translated geometry may
    contain areas where multiple planar elements are coincident in the
    same plane. This phenomenon is a product of techniques that are
    valid for mechanical stress analysis, but that might compromise a
    thermal model. Elements located in that same plane, but whose edges
    are offset, are detectable within the AutoCAD interface by
    relatively close inspection. However, *precisely* overlapping
    elements, whose edges line up perfectly, are virtually invisible;
    their coincidence is apparent when the user selects what looks like
    one planar element, but the AutoCAD Text Window reports the
    selection of two (or more) objects. [Analysts should exercise great
    caution when deciding whether to retain coincident elements, because
    their inclusion in a single Radiation Analysis Group causes
    unpredictable and erroneous results during the ray tracing
    process.]{.underline}

-   In order to achieve the desired orientation and location for the
    imported geometry in Thermal Desktop, it may be necessary to first
    re-orient and/or re-locate the meshed model within MSC.Patran.
    However, the process of creating new coordinate systems and/or
    translating between multiple coordinate systems within Patran may
    introduce confusion as to which system(s) will be referenced by the
    resulting bulk data set and by Thermal Desktop. (For example, the
    inclusion of a CORD\[n\] element within the bulk data file may have
    the effect of re-orienting or moving geometry upon importation into
    Thermal Desktop, so that the imported grid locations may not match
    the grid locations as printed in the bulk data file.) Analysts are
    encouraged to verify location and orientation after importing
    geometry Thermal Desktop, consulting References 1 and 3 as
    necessary.

\[References:

> 1\. MSC.Nastran 2001 Quick Reference Guide, MSC.Software Corporation.

2\. Thermal Desktop User's Manual Version 4.4, C&R Technologies, August
2001.

3\. MSC.Patran 2001 Reference Guide, MSC.Software Corporation.\]