Machine Design

FEA wizards and utilities simplify model building

The KinePak wizard in the upper left image assists creating linkage mechanisms. Of the seven available, a user has selected a four-bar linkage to test an idea. However, it cannot rotate continuously so the node at the end of the driving link appears in yellow. The final frame shows a design that can rotate continuously, so the path of the pink node shows as a circle.

With appropriate link lengths, the user has substituted proposed geometry for a paint mixing device modeled in SolidWorks. Algor's Mechanical Event Simulation software then puts the mechanism in motion and shows stresses at different times in its cycle.

The Timeline utility from Algor Inc. lets engineers define and visualize timebased event curves for the developer's Mechanical Event Simulation program. The utility lets an analyst study, for instance, a proposed bearing clevis for a transient structural analysis with linear material models, and transient thermal analysis.

There is a trend in FEA to simplify a model's construction with wizards, and to simulate its entire working environment regardless of complexity. FEA developer Algor Inc., Pittsburgh, for example, has recently released a wizard that assists with creating linkage mechanisms. A second utility manages time-based events for multiple physical phenomena, such as motion in the developer's Mechanical Event Simulation software or thermal conditions in a thermal simulation.

The linkage wizard, KinePak, simplifies the task of modeling mechanisms with linkages such as the four-bar type, and variations of it. "It's relatively easy to model falling or impacting objects," says Michael Bussler, company president. "But when models involve frequently encountered linkages, operators had to sketch designs or use CAD software to draw and redraw static models. The wizard lets engineers create linkagemechanism models based on templates from a library."

This built-in library holds seven different linkage templates and can handle the most frequently encountered mechanisms. They work this way: Select an appropriate linkage for the mechanism you're modeling and specify the size of the individual links. Each is fully parametric. Then, put the linkage in motion by grabbing it with the cursor. This checks spacing and extensions of the links. After creating a basic mechanism, operators can attach detailed CAD geometry to the mechanism.

The company's FEA software can then calculate stresses on moving parts. In the process, Mechanical Event Simulation calculates motion, dynamic loads, and stress simultaneously on the FEA model of the linkage. "You could let a motor or linear actuator drive the mechanism," says Robert Williams, development manager at Algor. "A motor element requires assigning a speed value while an actuator element would need a length value defining the extension or retraction. Engineering elements in the software provide these actions." For a more complete design of, for example, a saber saw or electric knife, the mechanism simulation software lets users apply contact and friction values between the blades and material to simulate working loads. The software would then calculate additional dynamic loads and stresses.

"Mechanical Event Simulation determines motion and resulting stresses occurring over time, which speeds up and clarifies the definition of time-based loading," says Williams.

The Timeline utility makes it easier to set up time-based loads in moving mechanisms. The software contains an editor that lets operators define load curves through mathematical equations, or import load-curve data from software such as Microsoft Excel. "An equation editor in the software can, for example, automatically generate a sine curve to describe the load carried by the mechanism," says Williams. "Typically, there is more than one time-varying load per event. There could be 10 different forces acting on the model that drive different motions and loads, and all kicking on and off at different times. A viewer in the utility shows users how all these loads interact." If the real-time motion plot is obviously incorrect, the analysis can be stopped, and user inputs checked and changed. "User-input errors are usually the reason analyses run incorrectly," he says. After making corrections, the simulation may be restarted from where it left off.

The Timeline software, especially useful in the simulation of an entire multiphysics event, examines the effects of multiple physical phenomena interacting over time. Algor software lets engineers simulate an entire part in action and run multiple, real-time analyses of the part.

"The biggest trend in our software development in the past year has been to directly link various analysis capabilities and tie them tightly together within a common user interface that is easy to use," says Williams. "With a common interface, engineers do not have to learn a different process or options for different types of analyses they need to perform. They can use the results of one analysis to carry out another analysis, all through the same interface." The company's new user interface and integrated documentation along with tools such as the linkage wizard and the timeline utility make it easier for engineers to simulate the entire working environment regardless of complexity.

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