German Engineering Firm Designs for High Safety, Lower Weight

ALGOR SOFTWARE HELPS GERMAN ENGINEERING FIRM DESIGN FOR HIGH SAFETY, LOWER WEIGHT

Jochen Pötter of the engineering firm Ingenieurbüro Pötter is shown here at the company's headquarters in Hamburg, Germany.

The optimization of vacuum chamber designs is a popular application of finite element analysis. However, some challenges are much harder than others. Mr. Jochen Pötter of Ingenieurbüro Pötter was presented with such a challenge recently when a German National Airline called upon his firm to design an unusual vacuum chamber. Mr. Pötter's engineering firm, headquartered in Hamburg, Germany, provides structural design and analysis services for the machine building and aviation industries.

Safety a Must

In this particular case, the need for safety was obvious, since the vacuum chamber is used for the maintenance of aircraft devices. What made it unusual was that the customer had two unique design requirements: First, the upper and lower sections of the unit had to separate asymmetrically to allow for easy loading of parts; Second, it was important that the weight of the device be reduced as compared to past vacuum chamber designs.

"This is a very unusual design for a pressure-applied structure," said Mr. Pötter. "While the sealing characteristics of the vacuum chamber were critical, the split design resulted in the deflections of the lower part of the chamber being quite different from those of the upper section. That is one reason we decided that an Algor analysis would be vital."

This light-shaded view of the vacuum chamber clearly shows the "off-center" design of the pressure vessel's top-opening lid. This type of design is very unusual for pressure-applied structures.

Modeling with Multiple Element Types

"To accurately model the geometry of the pressure vessel it was necessary to combine different types of elements," continued Mr. Pötter. "The vessel shell consists of plate elements, and bricks are used to model the frame reinforcements and sealing flanges. The Algor software was used to combine the elements into a single model. A negative pressure of 0.8 bar was applied to both the upper and lower sections of the pressure vessel. At that point we were ready to begin the optimization process."

Several Analyses in a Short Time

Mr. Pötter analyzed a variety of different designs before arriving at the final version. In each case, the displacement of the upper and lower sections of the pressure vessel were carefully checked to ensure a safe and consistent seal.

Here we see a stress analysis of the lower part of the vacuum chamber. The stress contours are shown on a deflected model.

Weight Down 30%

"Through stepwise reduction of the thickness of the plates and variations of the reinforcement designs, a weight reduction of 30 percent was achieved when compared to the former vacuum chamber design," said Mr. Pötter. "By using this process, we were able to analyze a very large number of potential designs in a relatively short period of time."

Algor is the Primary Design Tool

"In the aviation industry, and the construction of pressure-applied structures, problems often present themselves as instabilities. In these situations, Algor is our primary design tool for combining the sometimes contradictory requirements of high safety and reduced weight," said Mr. Pötter. "We chose Algor because of its ease-of-use, its cost effectiveness, the data exchange capabilities via IGES and DXF, and last but not least, the company's customer-oriented philosophy."