FE update - Simulation and optimization for companies with many CAD

March 6, 2003
Most CAD systems stumble when they import models built in other software packages.

The circular cover was designed in Solid Edge and imported to 3GA.author from PlassoTech for analysis. Its part tree with features is on the left. The pane at the screen bottom shows that two and three slots are to be considered in modal and stress analyses.


After a stress analysis, users can change slot sizes by moving the slider bar from one extreme to the other. Should a value such as stress, exceed a prescribed limit, the Current Value field turns red. The software lets engineers run structural, thermal, dynamics, and behavioral modeling simulations directly on CAD parts and assemblies.


The 3GA software provides graphs for quantities of interest. In this case, its stress versus an angle on the circular pattern near the center. Even a cost analyses could be made with connections to PDM systems or Microsoft Excel which would store and run the required calculations.

At best, they strip away features and parametric underpinnings, leaving what's called dumb geometry. A solution to the problem comes in a recent FEA program from PlassoTech Inc., Encino, Calif. (www.plassotech.com). The package is based on parametric technology acquired from 3GA Corp.

"To import geometry with features and history," says Tomi Mossessian, CEO with PlassoTech and a software developer formerly with 3GA, "the software uses the Granite kernel from PTC Inc., Acis from Dassault Systemes, and Parasolid from EDS. So the system is not just translating geometry. It's a true multiCAD environment that displays geometry without the tessellations common in many viewing programs." A part tree assembled for each piece shows dimensions with tolerances, information tossed during most importations.

The software is CAD neutral and works with most CAD models. "This is the Switzerland of CAD," says Mossessian. Users can export the altered part geometry back to SolidWorks, Pro/E, or Inventor as necessary. If a Solid Edge part goes to Pro/E, Pro/E creates a new file with changed dimensions and features.

The software retains 3GA's parametric slider technology. It lets users set up simulations and assign loads, constraints, and materials with several values for each. Results come back with on-screen slider bars for each condition. Users then simply slide the bars to see how parts react to the different loads and materials. If results exceed an assigned limit, a box in the control panel turns red to alert users.

The new software includes modal and thermal analysis as well as static-linear stress. It also includes collaboration features so users can let off-site engineers open simulation-result files in a browser that includes active slider bars. Off-site users can examine the range of conditions for which the model was solved.

Similar parametric (slider-bar) capability also applies to geometry. For example, suppose the designer is asked to find the minimum number of ribs that will limit deflection at the third mode of vibration and identify that frequency. The designer can make the number of ribs a design variable and assign quantities. The system's mesher will place traditional as well as p-elements where they work best. Solvers can include MSC.Nastran or PlassoTech's. After the problem is solved, the designer examines deflection versus rib count versus vibration mode simply by adjusting the slider bars. One screen can display dozens of results. This method approaches genuine topological optimization.

A probe lets users find stresses at any points in the model. Users can also add local constraints to resolve singularities, such as high, spurious stresses that occasionally arise at sharp corners, vertices, and edges. Local constraints can include or exclude features in a study.

The software puts parts built in different CAD systems together into assemblies. To alter components for a better fit or to eliminate interferences, users identify features in question in the part tree and assign several values to them. For example, a moving arm might be tested for lengths of 15, 16, and 17 in. It takes only a few seconds to generate the different sizes. Doing this also builds the control panel or spreadsheet for what Mossessian calls on-the-fly analyses. Components that collide turn red for easy identification. Moving the slider alters the geometry of an interfering part and the collision color disappears. For markup, users can add notes (they appear in a separate window) to every feature on the part tree.

The software runs as stand-alone or as a collaboration model. Internet Explorer is embedded in the program and the software works from a server. An authoring client lets users conduct parametric studies and send results to others. A supplier could then run the software through an access client and display studies in a browser. The simulation portion of the software is available separately from the modeling features.

Mossessian says a connection to LS Dyna is coming, along with those for other types of analyses. "Most engineers have no trouble learning the system," he adds. An AVI demo is available from www.plassotech.com/Download/Info.html.


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