INNOVATIVE MASS TRANSIT TECHNOLOGY TO BECOME LIGHTER AND SAFER WITH AID OF ALGOR SOFTWARE

As city centers worldwide become more crowded, transportation engineers seek the best way to get people from here to there. From New York City’s subway to the Bay Area Rapid Transit system to Japan’s bullet train and the emergence of magnetic levitation, mass transit technology evolves in search of more comfortable, faster, environmentally compatible and less-expensive methods.

California-based Aeromovel USA (http://www.aeromovel.com/) has developed a unique technology that uses air produced by electric blowers to propel vehicles along elevated guideways. Aeromovel trains are running in Porto Alegre, Brazil, and Jakarta, Indonesia.

Brazilian company PCE Ltda. (http://www.pce.com.br/) used software from Algor, Inc., (www.algor.com) to perform a linear static stress analysis on Aeromovel’s truck design. PCE engineers wanted to know whether the truck assembly would withstand required loading conditions, which include passenger weight, wind, centrifugal forces and emergency stops.

This illustration shows the CAD solid model of the vehicle's truck assembly. Severo imported the model into Algor and used Superdraw to create a finite element model for analysis.

Dagoberto Schubert Severo, director of PCE and a mechanical engineer, used Algor’s linear static stress analysis capability to determine fatigue and load limits on the vehicle’s truck assembly.

"Algor offers the most extensive range of capabilities at the best price," Severo said, explaining why he chose Algor. "That, coupled with the luxury of being able to purchase only those modules that you need, makes Algor our FEA tool of choice."

Aeromovel provided Severo with a CAD drawing of the truck, created in Autodesk’s Mechanical Desktop.

From that start, Severo used Superdraw, Algor’s precision finite element model-building tool, to create three finite element models of the truck for analysis. He used bricks to model the wheels and axes, plate elements to model the metal plates making up the top and bottom parts of the housing and bricks to model connecting rods attaching the top and bottom parts.

"Unlike other FEA software that I used in the past, with Algor you can easily create and directly edit the mesh," Severo said. "Supersurf is another powerful tool to construct plates, because after I created the surface and the mesh, I could easily generate different mesh densities."

Severo then assigned material properties to the parts – most being assigned steel properties. Severo said he used the ASM Metals Handbook to determine the properties of the steel. He used rubber in the areas where the connecting rods joined the top and bottom housing parts and where the housing meets the wheel axes. The rubber properties were determined through experimentation, he said. Because of the rubber material’s nonlinear properties, Severo also could have used Algor’s Accupak/NLM or Accupak/VE analysis packages. Accupak/NLM performs linear and nonlinear static stress analysis using linear or nonlinear material models. Even more versatile is Accupak/VE, which provides the ability to analyze models at each moment in time while they are in motion.

Severo defined boundary conditions for his analysis at the point where the wheels contacted the rails and the point on top of the truck assembly where it was attached to the vehicle.

Among the three models, he spread 11 different loads: vehicle weight, passenger weight, increased force of vertical acceleration in vertical curves, increased vertical force due to lateral acceleration of the centrifugal acceleration in horizontal curves, reaction from vehicle retention force, wind action, increased lateral force due to centrifugal acceleration in horizontal curves, friction braking, deceleration by emergency brakes, torsion loads, superelevation in horizontal transition curves and suspension failure.

After each analysis, Severo viewed the von Mises stress results with Superview, Algor’s postprocessing and presentation package that allows engineers to quickly evaluate and present their work. The latest Superview version offers such features as dynamic viewing, Windows-based pull-down menus and floating toolbars.

Based on the results, he changed the thickness or shape of his elements until he ultimately came up with a truck that was 30 percent (344 kg) lighter than the original design. The new design also features fewer welds, meaning fewer areas for structural fatigue, and is fully compliant with National Fire Protection Association, Americans with Disabilities Act and other U.S. codes and standards.

Creating a vehicle as light as possible is critical to the success of the Aeromovel vehicle, Severo said.

"In the Aeromovel vehicle, unlike most transit systems, there are no onboard motors or traction devices," he said. "So the vehicle is very light and simple, carrying two to three times more people per ton of deadweight than most alternatives. The lighter the vehicle and the truck, the less energy needed to move the vehicle."

When he was through with analysis of the original design, Severo took his results to the laboratory for validation. Using strain-gages and load cells, he set up physical tests of the original and altered designs to determine the correlation between the simulated and measured analysis. The physical tests proved Algor’s linear static stress analysis to be accurate within 7.4 percent with regard to the connection rods and 3.6 percent with the main axle. Severo said Aeromovel was comfortable with that margin of error because of the complicated nature of the analysis.

This illustration shows the results of Severo's linear static stress analysis. Severo examined the stresses on the main axles and the pin in the center that connects to the Aeromovel vehicle. None of the stresses were significant enough to initiate yielding.

"I am very satisfied with the results of the tests," Severo said. "Because of the complexity of the model - an assembly with rubber - I was not anticipating an exact match between the FEA and physical test results."

Severo said a prototype of the truck assembly – designed according to the Algor analysis - is under development and should be available for testing later this year. He also has more plans to work with Algor software.

"I am involved in several analyses for smelting companies that produce aluminum, with which I have to perform electric, thermal and fluid flow analyses," he said. "These are multiphysics analyses and we are developing programs to interface with Algor using Microsoft's Visual C++ in order to automate the design process."