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Case Study

A whole lot of (virtual) shaking going on

Kevin Thomas

Femap is the preprocessor of choice for seismic analyses when models must be created from scratch

Equipment that’s hard to shake

Kevin Thomas provides engineering analysis services to manufacturers of power generation and air filtration equipment. His client list includes major companies such as Areva-TD, ABB, Belden Corporation and Flanders/CSC, along with some smaller companies. Thomas, who takes on these jobs during his “retirement,” receives this work from analysis associates familiar with his nuclear and seismic expertise, including Engineering Analytical Dynamics Corporation (Trafford, PA) and Aegis Software Corporation (Murrysville, PA).

A typical project involves large, expensive equipment that is difficult and costly to test on a shaker table. For example, a manufacturer of electrical equipment recently requested Thomas’ involvement in the design analysis of a very high voltage (500K volt) circuit breaker for use in a power transmission system. “This breaker will be used all over the world, including earthquake zones, so it has to meet strict seismic requirements,” Thomas explains.

The circuit breaker tank was approximately 3 feet in diameter and 16 feet long. The porcelain-insulated bushings extended to a height of 18 feet. As a way of minimizing the amount of physical testing the manufacturer would have to do to meet the seismic standards, the company had Thomas perform a computer simulation using finite element analysis (FEA) to predict how the breaker would respond during an earthquake. “By having me do this analysis, they can find out if the design will perform as it should without conducting a very expensive and impractical test,” says Thomas.

Building models from scratch

Thomas’ FEA solution is the Femap™ software and the NX™ Nastran® solver from Siemens PLM Software. He prefers Femap to other FEA pre- and postprocessors because he creates his finite element models from scratch, using Femap geometry creation tools, rather than importing CAD data. “The type of equipment I’m working on doesn’t lend itself to being modeled in solids so I need to be able create my own geometry,” Thomas explains. “I’ve found that other FEA packages neglect basic modeling features. Femap has the comprehensive modeling functionality I need.”

Typically Thomas creates models with plate elements, beam elements and combinations of element types. “I get drawings from my clients,” he adds. “I take the dimensions and create lines, points and so forth. In this kind of work, one needs a front end that will allow you to create geometry this way and also do it efficiently.”

Between Femap ease of use and Thomas’ familiarity with the software, he can build models quickly. This is important because, as he says, “Clients usually want results right away. They’re at a relatively late stage in the design and they need this information before they go further. I appreciate Femap because it helps me work as quickly as possible.”

Good price and support

After creating a finite element model, Thomas uses NX Nastran to subject the design to seismic input virtually. He uses Femap postprocessing functionality to display the results of the analyses (structural and thermal) and create his deliverables, which are analysis reports; typically these will feature Femap stress and displacement plots.

Thomas notes a few additional reasons why the Femap/NX Nastran solution is his preferred FEA solution. “The price is affordable for a small consultancy such as mine,” he says. “And the support from Siemens PLM Software is very good.”

Most importantly he can count on the software. “I’ve tried other FEA software and I’ve found Femap works the most reliably,” Thomas says. “I would go so far as to say it’s ‘rugged.’ You never run into situations where it doesn’t work as it should. With other programs, it’s not always that way.”

By minimizing the amount of physical testing necessary to gain seismic compliance, Thomas’ analysis work helps his clients reduce design time and costs for large equipment. With Femap and NX Nastran, Thomas is well positioned to capitalize on his expertise and continue to enjoy an interesting retirement.

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