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To optimize, analyze

To optimize, analyze

Engineers can thank the aerospace industry for developing many of the CAD/CAM/CAE applications used worldwide today. NASTRAN from NASA, Unigraphics from McDonnell Douglas, and CATIA from Dassault Aviation are some famous examples. More recently, MSC.Software (Santa Ana, CA) acquired a set of conceptual design and verification tools developed by Boeing, the EASY5 product line. So, it is with good reason these same engineers should look to the aerospace field for future trends regarding software. What will they see? Increasing use of analysis, more analysis codes, and better analysis optimization.

The graphical 'Freebody' tool now incorporated within MSC.Patran allows Boeing to visualize internal forces acting on the forward spar section in the upper portion of this vertical stablizer, with the Freebody loads exported to more detailed models of the spar section.

Certification through analysis. The aerospace industry has unique challenges that demand innovative solutions. A commercial aircraft can be in use for 30 to 40 years-and military aircraft may see duty even longer than that-so manufacturers must guarantee the structural integrity of these products for an extended period of time. Certification standards are therefore extremely rigorous and the manufacturer must maintain the design and analysis data to be able to guarantee air-worthiness of an aircraft throughout all modifications during its lifecycle.

Aerospace OEMs and suppliers that have earned JAR-21 approval (given by the Joint Aviation Authorities, or JAA) can now choose between test, analysis, or simulation for some system certification. With this trend toward certification through analysis, there has been an increase in the amount of analysis performed, and an increase in the number of specialized applications used.

For example, minimum weight and structural design criteria are essential to aircraft design. Aircraft manufacturers, consequently, perform part optimization and extensive structural analysis. However, before starting a finite element analysis for an airplane, hundreds of thousands of load cases must be applied to the aircraft structure. Most OEMs sort through all the resulting data using in-house software to find the critical load cases. But, as other industries begin to face some of the same load-sorting tasks, commercial software is now being offered to perform this data sorting, such as MSC.Explore.

In addition, improvements to the graphical user interface (GUI) for the pre- and post-processors have allowed engineers to create models, and view results graphically, rather than editing and sorting through pages of numerical data. "With more complicated simulations, you get more results," says John Chick, Airframe Structural analyst at Boeing. "The new post-processors allow me to extract the pertinent information from the simulation in a more timely manner. In the past, pre-processors supported mesh generation and simplistic loads/constraints/materials only. Today, graphical pre-processors support most of the more advanced modeling entities."

Capturing company knowledge. Given the extensive amount of analysis performed on a variety of applications, the aerospace industry has been working in partnership with the software vendors to automate certain analyses, and to optimize the entire analysis process.

Automating certain analyses can mean incorporating the analyst's knowledge into templates to allow other engineers to perform part or all of the analysis. Not only does this capture some of the company knowledge, but it also maintains a direct link between engineer and analyst, while freeing the analyst to concentrate on more difficult analyses. Airbus in Germany partnered with MSC.Software for this automated approach, and the analysis process of their wing box configuration is now 40 times faster. Airbus is now implementing "skill-tools" for designers to perform analysis throughout the company, with parametric model generation and finite element analysis using standard commercial codes that have been integrated in-house.

Volvo Aero uses MSC.Marc to simulate the welding of one vane to the outer ring, a Turbine Exhaust Case of the commercial engine V2500. The company then uses proprietary code to calculate residual deformations, jointly developed at Volvo Aero and Lulea University of Technology.

Boeing is also developing this approach with "handbook solutions" from StressCheck (ESRD). Ahsan Iqbal, manager of Structures Technology & Prototyping at Boeing Rotorcraft, explains, "Each solution is a set-up for a specific type of analysis and includes parameters that allow it to be altered to handle different model dimensions and loads." Boeing plans to develop a handbook solution to handle each family of parts, and is currently considering the possibility of implementing the handbook approach outside of the analysis group (e.g. in shop support).

Another type of automation covers specialized modules for the analyst. Many analysis codes utilize open architecture that allows analysts to create their own routines to customize commercial software. Analysts often use MSC.Patran Command Language (PCL) to streamline pre/post-processing tasks in MSC.Patran. MSC.Software application engineers also use PCL to add user-requested functionality in a quick and timely manner. These PCL routines are sometimes added to new versions of the company's software.

The graphical "Freebody" tool now incorporated within MSC.Patran is an example of this type of development. The tool allows users to visualize internal forces acting on selected portions of a structural model. The Freebody loads can also be exported to more detailed sub-structure models.

"This module has made it easier to determine how forces are distributed within the structure," observes Boeing's Chick. "Freebody analysis often uncovers modeling errors that may be missed during a traditional review of element forces and stresses."

Aircraft manufacturers are also looking to minimize the redundancy in the analysis process. One way to do this is to use a common database for a specific model drawn from the CAD data to be used to generate the necessary meshes needed for different analysis.

"The idea is to have a stress and structural repository, including design data relevant to stress," says Jean-Francois Imbert, vice president of Structural Analysis at Airbus. Airbus tailored its own solutions for this purpose using commercial PDM software, since there was no commercial solution available at the time. Since then, commercial software offering similar functionality, such as MSC.VirtualInsight (formerly from SGI, now MSC.Software) and more recently LMS Tec.Manager, have been developed.

Manufacturing included. Each OEM produces a limited number of aircraft, so there are no real manufacturing economies of scale and any error is quite costly. Manufacturing tolerances are therefore very tight, and for this reason there is a major push to include analysis of the manufacturing processes.

Volvo Aero, which supplies airplane engines and aerospace propulsion, established a manufacturing simulation department three years ago in order to improve existing manufacturing and to evaluate new manufacturing concepts for feasibility. Using MSC.MARC, Volvo Aero was able to optimize a welding sequence to reduce residual deformations and speed engineering and weld testing.

In addition to optimizing the company's manufacturing processes, Volvo can predict component behavior during production in order to track the strengths and strains that occur during manufacturing. "High stresses will lower the fatigue life of the component, so we expect this manufacturing information will eventually be incorporated into other simulations performed at the OEM," says Olsen.

These examples and others illustrate why the aerospace industry serves as a perfect weathervane for showing the next CAD/CAM/CAE trends and benefits.

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