Machine Design

A better way to diagnose mechanical problems

Analysis on a subway car door using MSC.visualNastran Desktop mechanical simulation software displays force versus time graphs and finite-element-analysis results.

The days of testing a design by traditional trial- and-error methods are gone. "What used to be the final step of using computers in designing a product is now merely the beginning," says David Baszucki from MSC.Working Knowledge. Designers can run two-dimensional CAD drawings through programs that simulate actual function. By running virtual prototypes through mechanical simulation, users can improve designs and identify the best and least expensive to build without the cost and time-constraint of a physical model.

CAD files can be imported into thesimulation software directly or throughneutral files such as STEP, IGES, and STL. Tools are included with many simulation programs for healing geometry during translation. Automatic Constraint Mapping (ACM) interprets assembly details such as mating information and relationships between parts. Rigid joints, revolute joints, and anchors between parts can be defined in the mechanical simulation program. Drive components such as motors, actuators, and springs can also be added.

The simulation runs several different analysis programs. Finite Element Analysis (FEA) determines the structural response, which includes stress, strain, and deformation. Dynamic analysis looks at gravity, interaction between the parts, inertia, and the mass of parts. Kinematic analysis examines how parts interact geometrically and the limits of their motion.

Design errors may become apparent after the software performs the analysis. Feedback from graphics and engineering data help the user redesign the system. For many CAD systems, mechanical simulation software maintains full associativity, so a change in the geometry also changes the simulation. Optimization tools let the software tell the CAD system what changes are required. For example, the program can suggest that a link needs to be a little larger, and the CAD system will make that change for the user.

This information provided by MSC.Working Knowledge, Los Angeles.

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