CAD
Translator ™
CAD Interface to the Agile Engineering Design System®
The AGILE™ Engineering Design System is a suite of software tools that allow a mechanical engineer to design and analyze rotating fluid machinery. The end result of the system is a set of geometry for the primary flow path of the machine (inlet, impeller, stationary vanes, volute, etc.). If STRESSPREP™ or AXISTRESS™ is included, the full geometry of the rotating impeller (disk, backface, bore, shroud, etc.) is also generated.
Exporting the geometrical output from the AGILE™ system into a general purpose CAD system is frequently necessary in order to prepare the machine for analysis or manufacturing. Likewise it is often necessary to take a design from a CAD system and move the geometry into the AGILE™ system for analysis or optimization. In addition, a company’s vaulted product definition may reside in a CAD model requiring moving the data back and forth between the AGILE™ system and CAD system as new designs are generated.
This document will provide information on the approaches that can be used to move geometry between the AGILE™ system and CAD packages. There are over 100 different organizations that currently use the AGILE™ system to design products. These companies use a diverse set of CAD tools such as CATIA®, Pro/ENGINEER®, Unigraphics®, SolidWorks®, AutoCAD®, Solid Edge® and many others. Moving data between various CAD systems can be a time-consuming and possibly error-prone process; however, we have customers that have successfully created interfaces in both directions to all of the major CAD systems, and we are confident that any organization can create seamless processes to move geometry. Most of this document will present information that is independent of the CAD system; however, we have built specific interfaces to Pro/ENGINEER and Unigraphics that may facilitate the transfer of data with these systems.
CAD integration is a very complex problem and we welcome suggestions from customers on ways to improve our capabilities in this area. This document does not contain detailed instructions for importing and exporting data, it is simply an overview of our capabilities which can be used during an evaluation of our software or to facilitate discussions between Concepts NREC and our customers on the best approach for integrating the AGILE™ system with the customer’s CAD tools. Detailed documentation for each of the import/export methods described here is available from Concepts NREC.
Exporting Geometry to CAD from the AGILE™ Engineering
Design System
There are five primary geometrical output methods from the AGILE™
system:
- Flat (text) files containing coordinates
- IGES files
- Pro/ENGINEER ibl files
- Unigraphics Parasolid ® 3D solid model files
- FEA hexahedral meshes
Flat (text) Files Containing Coordinates
Text files containing coordinates are the most common format
that our customers use to move geometry from the AGILE™ system
to their CAD systems. CCAD® and AXCAD™ both produce
several different text file formats. These files can be generated
as points along the blade centerline with a thickness value at
each point, or coordinates of the surface of the blade. In addition,
r and z coordinates of any axisymmetric flow path can be added
to the file. The number of points in the streamwise and spanwise
direction can be specified so the density can be high enough to
match the desired tolerance for geometrical data. Typically, customers
write an importing routine for their specific CAD system to take
these files and produce a CAD representation. Concepts NREC can
assist with the development of the importing routines or be contracted
to develop these routines. An example of a blade surface file
is contained in Table 1.
IGES Files
IGES is a standard data interchange format for CAD programs. Any
CAD program that understands the IGES format can read the IGES
file that AXCAD, CCAD, STRESSPREP and AXISTRESS create. There
are many different ways to represent geometry in an IGES file.
An IGES file consists of a number of geometrical entities. Each
CAD system will handle each type of IGES entity differently and
many CAD systems provide algorithms which ‘heal’ the IGES entities
into a solid or surface model native to the CAD system. The fidelity
with which these healing algorithms work and the amount of manual
effort required for the healing vary with the CAD system and the
type of entities used in the IGES file. For this reason, the AGILE™
system provides great flexibility in choosing how the IGES file
will be constructed.
Figure 1 shows a screen capture of the IGES file output dialog from CCAD. Notice the drop-down entity choices which include
- Solid
- Surfaces (default)
- Wireframe
- Guide curves - a minimal set of curves outlining the blade.
- Cross-sections - a set of surfaces that are lengthwise cross-sections of the blade.
- Cross-section contours - the edges of the cross-section surfaces.
Pro/ENGINEER ibl Files
Pro/ENGINEER ibl files are text files of geometrical coordinates
in a format that can be processed by user-developed macros inside
Pro/ENGINEER to accurately build solid models. Figure 2 shows
a screen capture of the Pro/ENGINEER file output dialog from CCAD.
Unigraphics Parasolid 3D Solid Model
Files
Parasolid (.x_t) is the format of the Parasolid CAD kernel. A
Parasolid file contains a 3D solid representation of a part in
the native format for the Parasolid kernel. Since Parasolid is
the 3D kernel used by Unigraphics, SolidWorks, Solid Edge, and
dozens of other CAD systems, the transition into these systems
is seamless with no programming or tedious manual steps. Currently
the Parasolid file is generated by the Concepts NREC CAD translator
which takes data generated by CCAD and AXCAD and converts them
to Parasolid. Figure 3 is a screen capture showing the Concepts
NREC CAD translator.
FEA Hexahedral Meshes
STRESSPREP produces a structured grid model of a cyclically symmetric
sector of the rotor. This includes nodes and elements for main
and splitter blades plus fillets, backface, shroud, bore, balance
rings, etc. This file is output for structural analysis in NASTRAN,
COSMOS, ABAQUS, or ANSYS and is in the native format for each
particular FEA system. Most FEA packages include an interface
to CAD, and this link can be used to capture the analytical geometry
in CAD format. Typically the customer will write a short routine
as a macro inside of the FEA system, to select particular surfaces
or boundaries of the mesh and then produce a CAD representation.
Concepts NREC can assist with the development of these routines
on behalf of the customer.
Importing Geometry from CAD to the AGILE™ Engineering
Design System
There are currently three primary geometrical output methods from
the design system.
Text Files Containing Coordinates
The use of text files containing coordinates is the most common
format that our customers use to move geometry from CAD systems
to the AGILE™ system. Both CCAD and AXCAD process several different
file formats through tools called CADFIT and AXCADFIT respectively.
These files can be generated as points along the blade centerline
with a thickness value at each point, or coordinates of the surface
of the blade. In addition, r and z coordinates of any axisymmetric
flow path can be added to the file. The number of points in the
streamwise and spanwise direction can be specified so that the density
can be high enough to match the desired tolerance for geometrical
data. Typically customers write exporting routines in the CAD system
to produce these files. We can assist with the development of the
exporting routines or be contracted to develop these routines. An
example of a blade surface file is contained in Table 1.
Once the data file containing points is produced, it must be converted to the native format of CCAD and AXCAD which both build 3D solids from 2D Bezier and NURBS curves. The conversion process is handled in the CADFIT or AXCADFIT feature which selects parameters for the native CCAD and AXCAD models to achieve the desired data fidelity. Both CADFIT and AXCADFIT are interactive tools where the user can see the quality of the curve fits and adjust the fitting parameters if necessary. A screen capture of a typical CADFIT session is shown in Figure 4.
IGES and Parasolid Files
The CAD translator tool is used to import data from IGES and Parasolid
files into the AGILE™ system. Using the CAD translator, a user
can open an IGES file and see the part displayed on the screen
along with a list of entities that make up the part. The user
must then map the entities to the appropriate turbomachinery nomenclature
(e.g. hub surface, pressure surface, suction surface, etc.) so
that the CAD translator can convert the IGES file into an appropriate
format for use in the CADFIT and AXCADFIT algorithms described
in the above section. A screen capture of the CAD translator is
shown in Figure 5.
Future Plans
The current capabilities of the AGILE™ design system are sufficient
to move data back and forth to any CAD system with a level of
integrity to match the requirements of our customers. We at Concepts
NREC are constantly seeking ways to make the interfaces to CAD
easier and more cost-effective for our customers. Our plans to
improve our interface to CAD are as follows:
- Make the CAD translator bi-directional: This means that it will be used not only to import CAD data to the AGILE™ System but also to take the final design configuration and provide CAD files in various formats. With the Parasolid geometry kernel used for both import and export, we will leverage over 300 man-years of development in CAD geometry and file formats.
- Expand the geometric capability of the CAD translator: Currently only the blades and stationary vanes are handled by the CAD translator, other geometric entities are worked with the methods described above. Our goal is to be able to work seamlessly to import and export CAD geometry at any level of the analysis (meanline, blading, CFD, stress and vibration, rotordynamics, manufacturing, etc.) and to appropriately handle all of the needed geometry at each step.
- Expand the list of CAD formats: The Parasolid kernel provides import capability for Unigraphics, IGES, SolidWorks, and Solid Edge. Export capability includes these formats plus STL. We would like to expand this list by licensing additional modules from Unigraphics to work with native files from other systems, such as CATIA.
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