Machine Design

Simulation digs into large excavator models

A new approach to rigid-body simulation lets engineers with Hitachi Construction Machinery (HCM), Tokyo, model motions of off-highway vehicles that typically don't have shock-absorbing suspension systems.

Dynamic simulation refined the design of this tracked excavator to minimize shock and vibration.
Tracked excavators have about 200 rigid-body parts such as sprockets and track links. The frame of the elastic model has about 16,000 nodes.
A simulation of an excavator moving over rough terrain shows the body rocking from vibrations.
Dynamic stress distribution on the main frame stems from structural analysis based on RecurDyn output load data.

Instead, impact and vibrations are absorbed by the equipment's flexible steel frame. RecurDyn dynamic analysis software from FunctionBay Inc., Ypsilanti, Mich. ( uses a recursive approach to generate equations of motion and relative coordinates that represent the construction equipment.

Complex rigid bodies would seem ideal for multibody simulation software. But conventional multibody programs typically have a difficult time contending with the large number of rollers, joints, linkages, and other parts touching one another in track assemblies. The process of modeling many parts and defining interconnections separately is tedious and time consuming with conventional software. In addition, conventional simulations tend to behave erratically during the lengthy simulation runs.

The mathematical approach in RecurDyn simplifies the simulation, minimizes analysis time, and still preserves model detail. The software even handles intermittent contact from the vehicle's bending and twisting. Toolkits for special-purpose analyses, as for tracked vehicles, let users quickly build and solve complex models.

According to HCM engineer Akio Hoshi, "Design engineers as well as expert analysts can build models for dynamic analysis using toolkits in the software. Even relatively untrained engineers can complete sophisticated models in a week or so."

-- Paul Dvorak

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