Thermal Desktop
is a program that allows the user to quickly build, analyze, and
postprocess sophisticated thermal models taking advantage of abstract
network, finite difference and finite element modeling methods.
The
Thermal Desktop is the first package to offer the thermal engineer
full access to CAD-based geometry and CAD model building methods
without expecting the thermal engineer to be a CAD expert and without
compromising the unique aspects of thermal design analysis.
The
output of Thermal Desktop can be formatted for input into SINDA/FLUINT,
the C&R Technologies thermal analyzer, or the user may launch
SINDA/FLUINT directly from Thermal Desktop's Case Set Manager, making
the interface between the two software packages invisible. The Case
Set Manager organizes conduction generation, radiation analysis,
fluid flow network generation, SINDA execution, and post processing
under a single one-click operation. Multiple cases may be defined
and executed sequentially, automating and simplifying large analysis
jobs. The
case set manager also allows access to SINDA/FLUINT's Advance
Design modules for design optimization, test correlation and
reliability engineering.
Thermal Desktop
is designed as a parametric design tool. Input fields for surface
parameters, assembly positing, optical and material properties,
network elements, and orbital data will accept numerical values
or expressions using arbitrary user-defined variables. Parametric
trade studies and optimizations are easily executed, especially
when managed using case sets. A revolutionary new dynamic link between
SINDA/FLUINT
and Thermal Desktop allows SINDA/FLUINT to command Thermal
Desktop to recompute radks, heating rates, conduction, and capacitance
data on the fly from within a SINDA/FLUINT execution. Using the
SINDA/FLUINT Solver, optimizations may now be performed that include
optical properties and geometric sizing as design variables. Thermal
models may be automatically correlated to test data, varying all
aspects of the model including capacitance, conduction and radiation
values. Optimizations may be performed to ideally locate boxes or
electronic components, to size radiators, or minimize weight - now
including radiation dependent design variables.
Thermal Desktop
is available as a stand-alone, PC based, CAD program or as an AutoCAD®
extension
application. Powerful CAD techniques for generating geometry can
be used for generating thermal models. Custom pull-down menus, toolbars,
and dialog forms permit the construction and analysis of thermal
models directly within the AutoCAD environment. Thermal Desktop
require some knowledge of general CAD techniques.
Thermal Desktop
can analyze thermal models consisting of 3D faces, regular MxN meshes,
and arbitrary polyface meshes. These surfaces may be created directly,
or by using various mesh generation commands such as surfaces of
revolution, ruled surfaces, and edge defined patches. Thermal Desktop
is not limited to just conic surfaces like many other thermal programs.
Thermal Desktop can also import, display, and analyze existing TRASYS,
TSS, NEVADA, IDEAS FEM, FEMAP and NASTRAN models.
Thermal Desktop
contains a set of custom surface types that combine the features
of CAD with the familiarity and convenience of TSS/TRASYS/NEVADA
type surfaces. True conic surfaces can be created with multiple
nodal breakdowns. These special surfaces contain grip points that
can be selected to directly modify the surface geometry. The grip
points in conjunction with snap features enable a new level of CAD-integrated
model building.
RadCAD®,
a subset of the Thermal Desktop, is a module to calculate radiation
exchange factors and orbital heating rates. FloCAD®,
another module of Thermal Desktop, generates flow networks and calculates
convective heat transfer factors. The title “Thermal Desktop”
is commonly used to refer to Thermal Desktop and it’s integrated
modules, however, RadCAD and FloCAD may be licensed separately to
allow the user to tailor the system to optimally meet analysis needs.
RadCAD
is the
radiation analyzer module for Thermal Desktop. An ultra-fast, oct-tree
accelerated Monte-Carlo ray tracing algorithm is used by RadCAD
to compute radiation exchange factors and view factors. Innovations
by C&R Technologies to the ray tracing process have resulted
in an extremely efficient radiation analyzer. A unique progressive
radiosity algorithm has also been incorporated to compute radiation
exchange factors from view factor data. RadCAD has also incorporated
the progressive radiosity algorithm into heating rate calculations,
resulting in even faster performance. Automatic compression and
decompression of internal database files minimizes disk usage. Powerful
thermal analysis can now be performed using modest desktop computer
hardware, exceeding the performance of most UNIX based workstations.
FloCAD
is a Thermal Desktop module that allows a user to develop and integrate
both fluid and thermal systems within a CAD based environment. FloCAD
adds the capability of modeling flow circuits, including fans and
convective heat transfer, attached directly to the surfaces and
solids representing PCB boards, chips, heat fins, etc. It is specifically
targeted for electronic packaging design tasks, but since it provides
full access to the powerful and general-purpose SINDA/FLUINT thermohydraulic
analyzer, FloCAD will find use in many other applications as well.
The
Problems with Other Tools:
Why
Thermal Desktop is Different
Thermal
Desktop is not the only tool to calculate capacitance, conductance,
RADKs, heat fluxes for SINDA, but it represents a revolution in
functionality over the capabilities of other older tools. Consider
the problems associated with prior approaches:
lack
of visual interfaces
lack
of modern CAD model building methods
lack
of access to designer's geometry database
inability
to choose thermal software independent of company-standard CAD
package
lack
of access to structural engineer's FEM model
model
building methods appropriate for structural purposes, not thermal
purposes
difficult
to work with multiple cases simultaneously
slow
speeds
Thermal
Desktop solves these problems using unique and innovative user interface
concepts and algorithms that truly distinguish it from prior methods.
Problem
#1:
Lack of Access to CAD Methods and Visualization Tools
Some
older codes do not feature interactive graphical model building
and verification. Separate programs must be used to view and postprocess
models that are built "by hand" using ASCII "card image" input files
that are submitted in batch mode.
Most
other codes that do offer interactive model building do so with
no access to CAD model-building methods such as boolean operations
(e.g., removing a hole in a plate), or revolving and extruding curves.
The
Thermal Desktop Solution: Model building, viewing, verification,
RADK and heating rate solutions, and postprocessing in Thermal Desktop
are all graphical and interactive, and all are available within
a single application. The user may work exclusively with the familiar
surface-based construction methods, or may expand the range of model
building by exploiting the powerful built-in CAD-based modeling
building methods.
Problem
#2:
Lack of Concurrent Engineering - "Shoehorned" Solutions
Of the
few codes that do offer interactive model building and CAD model-building
methods, all do so by forcing a round peg into a square hole: by
making thermal engineers build thermal models using methods primarily
design for structural engineering (and with the many small structural
elements that generate untenable thermal models), or by forcing
them to use imported model data files (such as IGES or DXF files)
as thermal models, with thermal information tediously assigned to
the tiny facets. Worse, when the design changes, the thermal engineer
must start from scratch.
Thermal
engineering has long been performed outside of the concurrent engineering
realm, which is dominated by CAD and structural-oriented FEM codes.
Many thermal engineers have in fact actively resisted integrated
tool approaches, in part because of bad experiences having using
tools designed for structural applications (1).
Furthermore, these tools do not accommodate rapid configuration
changes.
The
Thermal Desktop Solution: The Thermal Desktop design recognizes
that the thermal engineer may not be the same person as the CAD
designer or the structural engineer, and that the thermal engineer
must still be able to work concurrently with designers and structural
engineers. Thermal Desktop works with all CAD packages that support
IGES, enabling the thermal engineer to directly access the design
geometry data. However, unlike other codes, Thermal Desktop does
not force thermal engineers to use such imported drawings directly,
but rather allows them to use the drawings instead as "scaffolding"
upon which a thermally appropriate model can be snapped. When the
design changes, such simplified thermal models can be stretched
to fit the new geometry with no loss of data. Design drawings may
also be linked externally to the thermal model, automatically updating
in the model when the design drawing is changed. Of course, any
portion of the design geometry that is already appropriate for thermal
modeling may be used directly.
Problem
#3:
Incompatibility with the Company-selected CAD System
Thermal
engineers rarely generate CAD drawings, and even more rarely have
any input into the selection of their organization's CAD system.
So why should the organization's selection of a particular CAD system
dictate the choice of tools available to the thermal engineer? Many
thermal engineers are left with the unpalatable choice of either
accepting a "shoehorn" approach as described above, or generating
thermal models using independent tools thereby creating configuration
management headaches along with extra work every time the design
changes.
The
Thermal Desktop Solution: The Thermal Desktop design recognizes
that the thermal engineer rarely has any say over the CAD system
(or systems) chosen by his or her organization, and yet must be
able to work concurrently with designers and structural engineers.
Thermal Desktop can therefore import model data from other CAD packages
via IGES or DXF files, and is specifically designed to avoid lost
data when changes happen and geometric data must be re-imported.
Problem
#4:
Incompatibility with the FEM World
Finite
element methods dominate the structural field, and often thermal
engineers must work hand-in-hand with structural engineers when
thermal stresses or thermal-induced deflections are a concern. This
doesn't mean a thermal engineer should have to use a structural
model. He or she must provide accurate temperatures at the nodal
points of the elements, but solving for temperatures at those points
is extremely inefficient.
Available
radiation tools are incompatible with finite element models (2),
requiring heating rates and RADKs to be based on the centroids of
the elements. Interpolation is required from a centered approach
to the finite element nodes. Worse, some tools require the generation
of a mesh more appropriate for structural analysis as the basis
of the thermal model. To require such a model again represents overkill.
For example, extra meshing around a nearly isothermal stress riser
can render a system-level thermal model unsolvable, or at least
discourages parametric sensitivity studies. Such "what-if" studies
are very important in a field like thermal engineering, which is
dominated by modeling uncertainties combined with the need to perform
system-level analyses of energy flows.
The
Thermal Desktop Solution: Thermal Desktop was designed from
the start to be directly compatible with finite element models,
avoiding the incompatibilities and interpolation problems that are
introduced when traditional thermal analysis tools are used to produce
temperatures for structural models, and avoiding the inefficiencies
of using structural models as thermal models. Thermal Desktop supports
both FD and FEM based modeling methods simultaneously, and will
contain new methods specifically designed for combined thermal conduction/convection/radiation
modeling.
Problem
#5:
Inability to Handle Variations and Cases: Poor Productivity
One
of the problems with using both older batch-style codes and even
newer graphical tools (that are not designed for thermal engineers)
is the inability to handle model variations and multiple cases within
one geometric description. Changes in material selections or optical
coatings (or uncertainties and degradations in their properties)
are difficult to address in a simple and consistent manner.
Geometric
models used for one analytic purpose are difficult to reuse for
other purposes (such as performing sizing or evaluating configuration
changes) without making a copy of the model, further confounding
efforts to stay concurrent with design changes. For example, it
is inefficient to calculate the radiation exchange factors for both
the inside and the outside of an enclosure in the same model, but
it is also unproductive to maintain separate models - one for internal
radiation analyses and another model of the same enclosure for external
analyses.
The
Thermal Desktop Solution: Thermal Desktop features several new
user interface concepts specifically intended to address the above
problems. For example, "analysis groups" can be used to let a user
turn parts of the geometry on or off, including active side information.
"Layers" can be used to store alternate geometries. "Property aliases"
allow a user to define surface optical properties indirectly using
natural names such as "anodized aluminum" or perhaps component level
names such as "battery enclosure." Changes to these aliases (or
to the user-controlled databases to which they refer) allow the
thermal engineer to quickly redefine properties in a consistent
manner, to share controlled data with other users, and to easily
perform alternate analyses (e.g., beginning of life vs. end of life).
Problem
#6:
Speed: the lack thereof
Slow
solution speeds hamper most radiation analyzers, and the need to
perform system-level analyses of large numbers of surfaces typical
of most applications ultimately either limits the useful design
information that a thermal engineer can generate, or impedes rapid
turnaround. When each run takes days and even weeks, the thermal
engineer quickly becomes the bottleneck in the design development
cycle.
The
Thermal Desktop Solution: Even discounting the significant speed
enhancements accrued by reducing inappropriate models into ones
appropriate for system-level thermal analysis, RadCAD is fast. It
is perhaps the fastest radiation analyzer available, and its solution
costs do not grow geometrically as the number of surfaces grows.
Solutions are produced in minutes on PCs instead of hours on mainframes.
In addition
to proprietary advances in Monte Carlo ray-tracing methods, RadCAD
takes advantage of recent section briefly describes various ways
to build models in RadCAD. A number of methods are available, starting
with familiar surface primitives all the way to complex solid modeling.
Any or all techniques can be combined in a single model to exploit
the unique advantages of each method.
Importing/Exporting
As an
aid to existing TRASYS users, Thermal Desktop can directly import/export
TRASYS geometry and property information (such as the model shown
here), retaining a knowledge of BCS organization on different layers,
and which can be used as selection sets to help a user better exploit
unique new Thermal Desktop features. Thermal Desktop can also import
NEVADA and TSS models.
Importing
FEM models
Thermal
Desktop allows the user to take an existing structural model from
NASTRAN, IDEAS, or FEMAP and to use it to construct a thermal model.
Using
Thermal Desktop Surfaces
Like
TRASYS, Thermal Desktop offers a list of geometric surfaces such
as cones, cylinders, disks, rectangles, spheres, and paraboloids
that can be used to generate geometric models using basic dimensions
such as length, radius, etc.
While
these surfaces can be input using specific dimensions, the user
may also stretch, shrink, rotate, etc. these surfaces directly on
the screen via the mouse-selected "grip points."
For
example, the mouse grip points of a cone are shown here.
Each
point changes a different aspect of the cone as the mouse is moved.
These
grip points are a key means by which Thermal Desktop surfaces can
be used to "snap" onto more complicated CAD drawings without using
those drawings directly as the radiation model.
Using
Existing or Imported CAD Drawings
2D or
3D CAD drawings, whether imported or native, can be used to help
develop a Thermal Desktop model. There are several ways to exploit
such a drawing. First, all or part of the drawing can be used directly
as part of the thermal model by selecting surfaces and assigning
them Thermal Desktop data such as node and property information.
Or,
the drawing can be used indirectly as scaffolding to which Thermal
Desktop surfaces can be snapped. For example, the user can select
key dimensional points on the drawing, drag an appropriate Thermal
Desktop surface over to it, and using grip points snap the Thermal
Desktop surface onto the highlighted "gravity" points on the drawing.
The underlying CAD drawing (or at least those parts not used in
the RadCAD model) can then be left as they are, discarded, or perhaps
hidden on another (temporarily) invisible layer. Thus, an appropriate
radiation model can be rapidly built without the thermal engineer
having to even know the exact underlying dimensions. If the design
changes, the drawing can be reimported and the Thermal Desktop model
can be stretched or shrunk as needed to fit the new dimensions.
Using
Native CAD Model Building Methods
If the
engineer is familiar with CAD-based drawing methods such as revolving
curves, Boolean operations, ruling, etc., they may used to generate
geometry directly in Thermal Desktop. These geometric surfaces may
be used directly in the radiation model, or these surfaces (in addition
to arbitrary construction lines, arcs, and points) may be used as
scaffolding to which RadCAD surfaces can be snapped.
Productivity-enhancing
Concepts
Analysis
Groups
One
of the most powerful new concepts in RadCAD is that of an analysis
group. Any surface, along with active side designations, can be
listed any number of times in different analysis groups. When a
radiation computation (form factors, RADKs, or fluxes) is invoked,
it operates only on the currently active analysis group.
This
provides for speed savings and convenient manipulations of the model.
For
example,
consider the simple model depicted here. The radiation on the inside
of the box could be assigned to analysis group "internal," while
the same surfaces (with different active sides) could be assigned
to the analysis group "external." This permits two faster analyses
to be performed, rather than solving the combined case or having
to maintain two separate models.
Analysis
groups have other uses as well. For example, they enable the user
to maintain alternate cases and alternate components within the
same geometric model. They are also one of the bases for creating
selection sets for model verification and for post processing.
Property
Databases and Aliases
Surface
optical properties (solar absorptivity, infrared emissivity, degree
of specularity, etc.) can be input as numbers, or indirectly as
user-defined names ("white paint," "aft canister," etc.). These
names can refer to a property identified in a user-controlled database,
or they can refer to an alias. Property aliases enable the user
to reassign coatings or materials at a high level with little work.
For example, using the alias manager as shown here, the user can
reassign the optical properties of all components designated "radiator"
to be "white paint."
Together
with an ability to quickly swap databases (i.e., to change the definition
of "white paint" with alternate white paints), aliases provide the
user with a quick means of performing what-if analyses, comparing
designs, events, and levels of degradation.
Correspondence
Trees
Another
Thermal Desktop innovation is a tree-style manager for handling
the optional correspondence (mapping) between Thermal Desktop surfaces
and SINDA nodes. (Correspondence data may be used to collect predictions
for one or more nodes together before being output for SINDA.) This
intuitive form (as shown here) provides fast visual access to this
data, which is difficult to maintain in older analyzers.
Correspondence
is also automatically maintained when postprocessing SINDA results
on the Thermal Desktop drawing (an example of which is shown on
the first page).
Cumulative
Accuracy
RadCAD
allows users to accumulate accuracy by choosing to extend a ray
tracing analysis farther after having viewed intermediate results.
Previous RADK or heating rate solutions may be continued for added
accuracy without losing prior answers. The code automatically checks
to make sure that no changes have been made that render the previous
analysis invalid as a starting point.
Performance
and Functionality
RadCAD
Functionality summary:
TRASYS
import/export, CAD drawing methods, and high-level RadCAD surfaces
including snap-on methods that use CAD drawings as "scaffolding"
Solve
for form factors, radiation exchange factors, or absorbed fluxes
Variable
degree of specularity
Choice
of solution methods: accelerated Monte Carlo ray tracing (MCRT)
or progressive radiosity
Model
verification (active sides, solids/rendering, etc.)
Variable
geometry through the use of articulators (Sun, Planet, and Star
pointing)
Example
RadCAD run times:
Imported
TRASYS model (shown earlier): 111 seconds on an Intel Pentium
200Mhz machine for calculation of solar, albedo and planet shine
orbital heating rates (per position) for a 364 node model, inclusive
of all internal operations (oct-tree set-up, database development,
etc.). Performed using RadCAD's unique progressive radiosity method,
with 5% automatic error condition.
Stacked
tetrahedra (shown here): 192 seconds on an Intel Pentium 200Mhz
machine for calculation of radiation conductors for a 256 surface
model, inclusive of all internal operation. Performed using ten
thousand rays per node with a full monte carlo ray trace solution.
Free
Evaluation Version
We understand
the hesitancy in adopting new engineering analysis tools, but we
are confident that Thermal Desktop is worth your time to install
and test. Therefore, the free evaluation version of Thermal Desktop
is quite capable. All features are enabled, except that solutions
can be performed on a maximum of 25 nodes. TRASYS model importing
and visualization is unlimited (and therefore can be used as a TRASYS
viewer). Thermal Desktop may be downloaded anonymously from C&R's
ftp site (details to be discussed shortly).
In addition,
for a limited time, C&R will supply evaluation licenses that
enable unlimited model size for all functions. All you have to do
is ask!
1.
The fact that a program can solve for temperatures does not make
it a thermal tool!
2.
SINDA/FLUINT, on the other hand, is not incompatible with FEM. Rather,
it is an equation solver that can be used to solve lumped parameter
equations, finite difference equations, finite element equations,
or simultaneous combinations of the above.
3.
Of course, TRASYS is free, but it is slow, it is not available on
most machines, it has few specular capabilities, it has no native
viewer and the few viewers that are available commercially are expensive.
(The free demonstration version of Thermal Desktop can be used for
many purposes, including as a TRASYS viewer.) Worse, TRASYS is not
supported commercially, and is no longer being enhanced by NASA.
Surface
optical properties (solar absorptivity, infrared emissivity, degree
of specularity, etc.) can be input as numbers, or indirectly as
user-defined names ("white paint," "aft canister," etc.). These
names can refer to a property identified in a user-controlled database,
or they can refer to an alias. Property aliases enable the user
to reassign coatings or materials at a high level with little work.
For example, using the alias manager as shown here, the user can
reassign the optical properties of all components designated "radiator"
to be "white paint."
