MODEL THE COMPLEXITY
The future of mass transit?
skyTran, a NASA Space Act company, brings us closer to the dream of fast, convenient travel around cities without congestion or noise.
By Anna Wood
skyTran is using Simcenter™ MAGNET™ software to develop a revolutionary transport system. The technology is in its infancy but confidence in the modeling is speeding up its development.
skyTran’s design for city transport
Maglev trains have already set world speed records; a Japanese bullet train achieved a record 375 mph in 2015.
Although they are hugely expensive to design and build, the benefits are enormous. Maglev-based transport is attractive because it achieves speeds comparable to aircrafts but does not use any fossil fuel. skyTran’s design has an added benefit in that its vehicles hang from an overhead rail that rests on pylons, removing the need to acquire large continuous strips of urban real-estate. Numerous Maglevs exist globally but they tend to focus on hub-to-hub travel, such as city-to-city or airport-to-city. skyTran’s lower-cost infrastructure and unique switching technology could change this and the way we travel in cities.
The new design could free our cities from cars, pollution and congested streets with a personal rapid transit system that glides above the urban landscape. Passengers would travel directly to their destinations at speeds of up to 100 mph in pod-shaped vehicles suspended from an overhead rail. skyTran is a NASA Space Act company that received a grant from the Research and Innovation Technology Institution of the US Department of Transportation.
skyTran’s vehicles will operate autonomously with proprietary switching technology that enables each one to navigate to its destination. The prototype for this utopian transport system brings us closer to the dream of fast, convenient travel around our cities without any congestion or noise.
A breakthrough in maglev technology
skyTran uses a particular variant of Maglev technology called electrodynamic suspension that works by magnetic levitation combined with a propulsion system. The propulsion system comprises a drive motor with a magnetic rotor and an aluminum stator. This operates together with the levitation system which is driven by the interaction between the steel guideways and the electromagnets in the vehicle.
There is a need to understand how the high transit speeds of the vehicles will affect the magnetic forces. This part of the project is pushing the limits of current modeling techniques.
A full-scale rig is used to test the concept but each test takes a lot of time to set up and is expensive in terms of materials and resources. It is particularly costly to test how the vehicles will operate at full speed, so simulation is playing an important role. It is speeding up the development work and reducing the number of physical prototypes by around 90%.
skyTran recruited Iana Volvach, a specialist in Finite Element Analysis and expert in the modeling of electromagnetic devices and spintronics, the physics of nano-magnetic materials. Volvach set to work to build simulation models for the levitation and propulsion systems and soon made progress. “When we use Simcenter MAGNET we quadruple the rate at which we develop, test and manufacture new parts”, she explains.
Volvach imported CAD models of the hardware into Simcenter MAGNET and built a model of the electromagnetic devices in the maglev mass transit system. She used this to tackle one of the most fundamental aspects of skyTran’s maglev system – the phenomenon of eddy currents.
The disadvantage of eddy currents
Eddy currents are initiated by a magnet passing a steel rail. In maglev vehicles, eddy currents induce electromagnetic drag and reduce the attraction force between the magnet and the rail. As a result, an increase in speed decreases the attraction force and increases the drag force. Both effects are undesirable and are a key focus of skyTran’s research and development.
Volvach knew that if the cores of the steel rail were formed from laminated steel layers it would increase the resistance of the steel rail to the circulating eddy currents. This is because the stacking of steel layers and insulation makes each lamination become a separate electrical conductor but allows the magnetic flux to pass through. Therefore, the design of the laminations for the steel rails would become a pivotal area of research for the new system. skyTran needed to know how to design the lamination, which materials to use and how to model the motion to see if the design was correct.
Volvach created Simcenter models to measure the eddy currents, first with solid steel and then with laminated steel to determine the best design to limit the eddy currents that occur at high speeds. She added a rigorous validation process to be sure that she could have confidence in her models.
It took a lot of work to optimize the design for the laminated steel and it was particularly difficult to determine how many layers would be required. Volvach needed to determine the smallest number of steel plates that would suppress the eddy currents within the company’s specification.
Strange results and a pleasant surprise
Volvach could model the laminated steel rails with layers of insulation between the steel plates, so she assumed she had an exact representation of her physical tests, however the simulations were revealing an anomaly. The results did not match her physical tests. It was not clear if this was due to an unknown property of the lamination or an error.
At this point Siemens Digital Industries Software provided some help. They have a knowledge base article on anisotropy and the Simcenter MAGNET perfect electric insulator (PEI) boundary condition to approximate the thin layers of insulation between steel laminations and a Siemens support engineer suggested a few adjustments to the simulations.
Volvach had been modeling steel plates of 10, 20, and 30 mm thickness with thin areas between the layers. She did not know that the mesh is stretched in the spaces between the layers, and that this adds inaccuracy.
Volvach measured the lift and drag forces in relation to travel speed and different air gaps, coil currents and steel material parameters. The results confirmed that the lift force and drag force are both related to these variables and revealed the optimum number of layers to use. The results were a little surprising. She says:
“The particularly interesting thing we found is that we didn’t need nearly as many laminations as we expected, which made our final design much simpler.”
Volvach is confident that her model accurately predicts the behavior of the maglev system. The simulation results correspond closely to the results from the physical tests with the difference between Simcenter MAGNET and the real-world experiments ranging between 5% and 10%. Volvach is pleased with the outcome:
“Given that the materials always vary and that there are errors due to physical measurements, and that the model is simplified to make modeling easier, we were very happy to have a difference averaging 7% between the physical test and the simulation.”