Compaction equipment manufacturer Bomag GmbH & Co. in Germany used FEA software to analyze and optimize the polygonal rollers on the company's recently developed earth compactors. Their unusually shaped rollers are said to be more efficient and able to compact soil to greater depths than can conventional, smooth, circular rollers for applications including postcompacting subsoil, compacting layers that are thicker than usual, and preparing landfills. MSC.Marc from MSC.Software Corp., Santa Ana, Calif., provided the nonlinear FEA software.
Bomag Engineer Peter Erdmann says the idea for a polygonal roller came from the company's experience with soil compaction. "We thought polygonal drums might work well, but it's not easy to tell just by looking at soil. So in addition to real-world testing, we used MSC.Marc to model the dynamic behavior and interaction of the soil with the rollers to visualize and explain why the drums are so effective."
The unusual design consists of three side-by-side octagonal drums mounted on the same axis. A self-adjusting vibrator in the drum calculates the energy needed for compaction by measuring interactions of the drum and soil stiffness using acceleration values measured from the drum. The system optimizes compaction energy so rollers never bounce.
Polygonal drums continuously roll from plate to wedge segments. Plate segments work by applying a concentrated vertical pressure. Wedge segments deform the soil with shearing forces that locally displace the soil. These actions knead the soil so as to avoid compacting only the crust. Forces from circular drums, however, remain constant during rolling. Engineers first tested both circular and polygonal drums for effectiveness by measuring compaction states of test soil using standard penetration tests, density measurements, and by evaluating the stiffness of the compacted soil.
Erdmann says he then developed a soil model for use in MSC.Marc to find the soil's dynamic behavior with the rollers. "The FEA model provides a good tool to explain why real-world testing shows that the polygonal drum produces better compaction at greater depths. Continued testing lets us fine-tune the model, which can then be used in future designs."
MSC.Software Corp., mscsoftware.com