FEA software saves time in antenna design

When EMS Wireless faced the challenge of designing two of its antennas into a flagpole design, it needed to ensure each part of the structure could withstand the elements, especially excessive wind.

EMS Wireless is the largest basestation antenna manufacturer in the USA, and its antenna families include the smallest profile antennas available with improved RF performance.

In its Accellerator series, the company repackages the three-sectored triangular structure commonly seen on cell towers into a cylindrical structure that measures no more than 36 inches in diameter.

This small profile makes it possible to camouflage even a three-sector site as a flagpole, making it popular with zoning boards that require unobtrusive cell site structures.

Recently, EMS Wireless faced the challenge of designing a structure stacking two Accellerator structures in a flagpole design.

To ensure consistent, reliable performance from the antennas, the company needed to make sure each part of the structure could withstand the elements, especially excessive wind.

Anything less than accurate design analysis might produce parts that affected antenna performance adversely and require expensive and time-consuming retooling.

Specifically, the engineers had to design a structure capable of supporting winds up to a loading of 160km/h.

They created their design with Autodesk Mechanical Desktop, and optimised the parts with FEA during the design phase.

Then they performed finite element analysis (FEA) with CosmosDesignStar to determine the deflection, stress and strain of the assembly.

The Accellerator support structure consists of extruded and machined components welded together.

The main structural member is a triangular extrusion, made with an expensive extrusion die.

A similar die produces three gussets.

Retooling was too costly to consider, so EMS Wireless needed to know the structure was sound before ordering tooling.

Also, to avoid damaging the antennas in the assembly, structure's deflection had to be limited to less than two inches.

Sara Phillips, Mechanical Project Engineer, EMS Wireless, reports that she used CosmosDesignStar to prevent design errors by doing 'what if' analyses on the welded assembly.

These analyses helped Phillips optimise the profile of the triangular extrusion to improve the strength and reduce the weight.

Phillips and her team performed linear static, natural frequency and linear heat transfer analyses.

"CosmosDesignStar met our needs in each of these areas", says Phillips.

In particular, she says that the software helped the designers to optimise wall thickness as well as cross-sectional areas at the corners of the structure to make certain that the entire structure would support the wind load.

"It was especially important to do 'what if' analyses on this model", she says.

"When Cosmos results show that we have a good model, we have confidence in the design".

"And, by the time we get to real life, we're sure the piece is robust".

EMS Wireless chose CosmosDesignStar primarily because of its fast analysis time and ease of use.

"We considered other FEA packages", Phillips notes.

"We found that CosmosDesignStar provides the capabilities we need, with an intuitive interface".

"It's easy enough to use that you can pick it up after a few months and still remember how to use it".

"You don't need an FEA specialist to use it".

"Our engineers attended a DesignStar training course which provided a quick start on using the advanced features and we were able to benefit immediately".

The results of the final assembly analysis showed that the assembly design had a good safety factor against failure and the final design met all the company's specifications.

When EMS Wireless built and tested a prototype, the empirical deflection results correlated well with the FEA results.

Subsequent testing of a prototype confirmed the CosmosDesignStar displacement results.

According to Philips, EMS Wireless realised substantial savings in time and cost by using CosmosDesignStar.

Not only was she able to optimise and analyse the parts before ordering hard tooling, but she says that the analyses also helped her reduce the weight of the triangular extrusion, which also reduced the cost.

Phillips says: "The time spent on a complex analysis was two-thirds of what it would have been using a competitor's product".

"The ease of setting up problems makes it effective to use CosmosDesignStar even on a simple analysis".

CosmosDesignStar also interfaces with other CAD systems that EMS Wireless uses, such as Autodesk Inventor.

The synergy between CosmosDesignStar and Autodesk Inventor allows changes in the Inventor model to be reflected in the CosmosDesignStar model - thereby saving even more time in the design process.

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