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Windows: A new scheme for linking CAD and FEA

Windows: A new scheme for linking CAD and FEA

Recent conquests in the field of engineering applications have brought the specter of Microsoft Windows domination to yet another industry: go to Autofact or the National Design Engineering Show and witness the triumph of NT.

Those software vendors that have signed on cite the advantages of abandoning Unix. Intergraph Corp. (Huntsville, AL) has developed an extension to the Windows application programming interface (API) that permits a level of interoperability between different engineering applications never before seen. In effect, users will soon be able to employ Microsoft's Object Linking and Embedding (OLE) to interweave CAD, CAM, and engineering analysis programs.

That's right. The same Windows PC function people have used to plug spreadsheets and pie charts into word processing documents promises to enable engineers to plug CAD drawings into FEA programs. A loose alliance of software vendors has coalesced around Microsoft's technology in order to bring it to the engineering market.

The Design and Modeling Applications Council (DMAC) was formed early in 1995 with the purpose of expanding the role of OLE in engineering applications. Judged by its trappings, DMAC is modest, perhaps, but the organization includes some of the most influential companies in the business: Intergraph, Ansys, SolidWorks.

"Data translators, such as IGES, work adequately with straightforward geometry, but run into trouble with surfaces and edges," says Michael Payne, vice president of development, SolidWorks (Concord, MA). "Ideally, engineers want interroperability with no data translation at all, and this is the key reason to implement the DMAC API."

SolidWorks has already placed an early version of the DMAC API in its solid modeling software in an unpublished form, enabling application developers to work with it.

"The intermediate step of translating data from one application to another stifles interoperability," says Daniel Small, Microsoft's representative for the DMAC effort. "The council's objective is to develop a virtual suite of applications under Windows that cover all aspects of the design-through-manufacture process. By adopting a common interface, application vendors do not have to make changes in the APIs of their respective products."

At the Daratech CAD/CAM, CAE Strategy Workshops in Boston last winter, Small demonstrated how engineering applications could work together seamlessly.

Windows of opportunity. Byron Hanks, chairman of DMAC, is a development engineer at Ansys (Houston, PA) and a firm believer in the utility of OLE on the engineering desktop. "Ansys was invited to provide input for defining a set of interfaces for CAM and FEA," Hanks says. "These would enable DMAC to tackle the more difficult engineering tasks."

The core technology is OLE for Design & Modeling (OLE for D&M): a set of geometry and topology interface specifications that addresses specific requirements of design engineers. Through these interfaces, an application can make its native design and modeling capabilities available to compatible applications without translation. Microsoft Office 97 and other OLE-compliant software, including accounting and product data management applications, can be easily integrated into the engineering environment in a seamless manner.

According to Hanks, the OLE mechanism, as originally conceived, works well in the 2-D world for documents and in the 3-D world has been extended for assembly modelers, but it has limited use in more involved engineering applications. "An assembly problem is very much like linking Word and Excel files," Hanks says. "The individual parts are being displayed together but they are not interacting."

This similarity is what inspired OLE for D&M in the first place. Geometry constructed in different CAD packages running under Windows could be linked together in the same assembly modeling system. This capability falls short of what is needed to link CAD and FEA, however. "You need to do more than simply display data together in the same work space," Hanks says. "An FEA program needs to be able to extract solid model data from the CAD window. To do this, interfa-ces are required that enable a live connection with the geometry so the FEA program can be used to apply loads and boundary conditions and then create the mesh."

OLE for D&M specifies a standard set of interfaces for all applications. It supports embedding, display, and remote activation, as well as access and control of model geometry and topology through the native design. Although model geometry is accessible to OLE for D&M programs, changes can only be made through the original design tool. Model accuracy, precision, and scale are thereby maintained.

The existing SolidWorks API and the ACIS Geometry/Topology data-structures have been used as the starting point and the main inspiration for defining the interfaces. A meeting of the OLE for D&M council, scheduled at press time for late April, intends to present and demonstrate the completed OLE for D&M Geometry and Topology.

Integrated CAD and FEA tools for Windows do not have to wait on DMAC: many are available today. Applications developers at Structural Research and Analysis Corp. (SRAC) have used the Windows API as the basis of its partnerships with several CAD vendors, including Integraph and Solid Works. These partnerships have resulted in products based on the company's COSMOS system that permit designers to select FEA operations as if they were selecting features on a solid model.


How to do preliminary analysis

Sjchit Jain of SRAC offers these observations for designers who want to perform preliminary analyses on their models. FEA is not so intimidating, Jain notes, if you just look at it as another part of the design process.

Create the model using a solid-modeling CAD system: Just do what you have been doing.

  • Assign material properties: Many integrated packages enable users to select materials properties from a library. The designer browses the library, picks the material for his model by name--and often never has to type a number.

  • Assign loads and boundary conditions: This is the phase that most often turns people off. However, the process can be simplified by enabling loads to be assigned as if they were model features, which, for the purposes of analysis, they are. Loads are those forces, such as gravity, that the object modeled is expected to encounter in the real world. Boundary conditions define the scope of the analysis--the "givens" that are assumed. The user picks a model face and selects a load, just as if he or she were selecting a design feature, such as a hole. Boundary conditions are specified just as easily.

  • Mesh the model and run the analysis: There was a time in the not-too-distant past when meshing was a nightmare. However, FEA vendors have made great strides in auto-meshing technology--so much so that it has become a push-button process. Furthermore, some auto-meshers take care of screening unnecessary detail from the analysis, so the model geometry itself does not have to be altered.

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