Shhhhh! It's a Sonata

Seoul-When Hyundai decided to call its passenger sedan the Sonata, the motor company was obviously trying to evoke a feeling of peace and quiet.

But the calmness of the newest vehicle hides a great debate that happened between engineers in the design stage, says Ji Un Lee, assistant manager of the vehicle development and analysis team.

In order the reduce NVH (noise, vibration, and harshness), Lee and the other FEA analysts wanted to increase chassis stiffness-and therefore add mass-but the designer and chief engineer wanted to make the car lighter, so it would be faster and more fuel efficient.

To find a compromise, Lee used test data and FEA modeling to analyze body vibrations, and find the best frequency and resonance of noise in the chassis. He measured stiffness first by doing finite element models of point mobility. And to test those results, he would attach an accelerometer to a prototype, then tap a nearby spot with a hammer.

"That's a simple test, but very important, very useful," he says. Lee presented his work at MSC.Software's Worldwide Automotive Conference, in Dearborn, MI this October. The vehicle was designed in CATIA, with finite element analysis from MSC.Patran, and NVH analysis from MSC.Nastran.

After the stiffness tests, he ran into more tough choices-like working with the chief engineer to keep material and manufacturing costs low, and ensuring the car body was stiffer than its rubber bushings in order to damp vibrations from the suspension.

But one of the biggest challenges was minimizing the amount of compute-time needed for all those FEA analyses. Lee isolated NVH sources to small subassemblies, and just analyzed those problem areas. By calculating body stiffness at just one attachment instead of seven, Lee reduced CPU processing time from 19,000 to 300 seconds, and disk demands from 12.5 to just 0.25 GB.

In the end, Hyundai steered a compromise through the conflicting demands of vehicle design but learned an important lesson-in order to compose a peaceful Sonata, you sometimes have to scream and shout a little.