What auto can learn from aero: simulating without prototypes

Automotive Design & Production, Oct, 2003 by Lawrence Gould

SOFTWARE AS PROTOTYPES Back about 40 years ago, according to Richard Smith, director of CAD/CAM products and services for The Boeing Commercial Airplanes, whatever software Boeing had for aircraft design and simulation was all internally developed. Comments John Givens, director of engineering math process for General Motors Pwertrain (Pontiac, MI), "Because of the expense to develop aircraft, [the aircraft manufacturers] have developed computer-aided tools for a lot longer time than we have in automotive."

Boeing developed FlyThru, a high-performance CAD visualization system. This program was first used to "preassemble" the Boeing 777, thereby helping engineers determine the geometric relationships and mechanical interferences between parts. This program was the basis of the digital mockup. Boeing also developed Easy5 (now owned by MSC software; Bellevue, WA), a set of engineering analysis software tools used to model, simulate, and analyze dynamic systems containing hydraulic, pneumatic, mechanical, thermal, electrical, and digital subsystems. Other Boeing software performed noise protection modeling. Hydraulics analysis was done using commercially available software.

The company's Voxmap PoinShell evaluates part proximity and part interferences. This software program detected over 10,000 part interferences in the initial computer modeling. Boeing also had two programs for ergonimic analysis, which helped determine whether assemblers had enough space when building an aircraft. The same software helped assess the ability of people to perform aircraft maintenance.

Over time, commercial software products have reached and exceeded the capability of the software Boeing had developed. The result is that, one by one, internally developed software programs have been taken out of service. For instance, Boeing's structural analysis programs have been replaced by Elfini (finite element analysis system from Dassault Systemes) and Nastran. Moreover, estimates Smith, nearly two-thirds of the software used for airplane design is Catia 5 from Dassault Systemes. Boeing enhanced Carla with other applications, such as BCSLIB-EXT, a utility for solving very large problems that cannot fit in the central memory of a computer. This let engineers view up to 500 parts at a time and electronically assemble major airplane sections. Boeing's EPIC (electronic preassembly integration on CATIA) tests the fit of components.

The company currently simulates the manufacturing process "to varying degrees," according to Smith. For instance, it simulates the placement of airplanes in the factory so that aircraft don't bump into each other during production. Some internally developed software exists for simulating assembly.

Boeing's migration from internally developed design and simulation software to commercially available software is based on a simple, basic criterion: When the features in the externally created software meet or exceed the internally developed software, when the accuracy from the externally developed software provides the answers Boeing demands, then it's time to switch. When the two types of software have reached parity, there's an assessment and, adds Smith, "probably quite a bit of turmoil to make a decision. It's hard to turn the tide. People get attached to [software] for one reason or another."

Souring computer-aided tools is similar to automotive engineering/design. GM's Givens guesses that 30% of GM's current software tools are internal developments; the rest are commercially available. Internally developed software, he continues, is "another source of structural cost--the cost to maintain internally developed tools." For that reason, GM's engineering departments are trying to use commercial software more; however, as with Boeing, continual internal software development is basically driven by the lack of commercial software availability. There is also an "awkward" situation in the move toward commercial software, explains Givens. "Sometimes the proponents of the internally developed stuff are the authors."

S0ME PROTOTYPING REQUIRED

In the past, new aircraft models required a long series of experiments to quantify and validate all the elements of a new design. Typically, the experiments began with wind tunnel tests on several models of varying size and complexity. These were followed by a flight test program involving building a lull-scale air-craft--and flying it.

Nowadays, aerodynamics analysis at Boeing is almost all done from internally developed programs. Virtually all of the company's aerodynamic modeling is done without a wind tunnel. "Physical models have gone down in significance," continues Smith. "We produce a number of aerodynamic test cycles digitally, and one cycle physically. The physical model ]measuring three to lout feet in wingspan] validates the simulation, to see if the simulation is giving us the right answers." That's a huge difference compared to 30 years ago. Back then, Boeing engineers used the wind tunnel model to create new and working designs.