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When Physical Prototypes Fail, Simulation Provides the Answers

Tue, 04/15/2014 - 9:45am
Alexandra Foley, COMSOL Inc.

Figure 1: TOMS mounting options—on the rim for traditional sensors that require batteries, or in the inner lining of the tire for Siemens’ new design. Images: COMSOLIn today’s fast-paced markets, engineers are continuously challenged to deliver products that meet market demand, improve operational efficiency and exceed customer expectations. Multiphysics simulation is an essential component of the product design workflow for creating innovative designs, especially when building prototypes becomes impractical or when taking actual measurements is not possible. A key advantage of multiphysics simulation is that it allows accurate virtual experiments to be conducted that explore the boundaries of different physical mechanisms—experiments that would be difficult, time consuming and expensive to test in the real world. This is essential for applications ranging from microelectromechanical systems (MEMS) and microfluidic devices—where size leads to expensive testing of physical prototypes—to the prediction of device performance over a span of time, such as determining corrosion in large-scale applications.

Simulation ensures safety, economy
In an example, researchers at TRB, a steel manufacturer located in France, used multiphysics simulation to gain information about a blast furnace’s performance when accurate measurements were nearly impossible to obtain. Inside a blast furnace, molten metal can reach temperatures of 1,500 C, necessitating that every precaution be taken to keep workers and production equipment safe. A potential hazard arises when molten metal leaves the furnace and enters a runner where slag is removed.

To prevent splashing molten metal from leaving the runner, a roof made of cast iron with a concrete lining covers the runner’s length. Typical roof runners are relined with concrete about once a month due to thermal shock, corrosion and erosion. Because TRB has hundreds of blast furnaces and runners, it’s advantageous to design runners economically while still maintaining overall safety. Previously, runners were designed using trial-and-error testing.

Using COMSOL Multiphysics, the R&D team at TRB simulated the operation of the runner over a week-long period. The simulation took into account heat transfer by convection and conduction, as well as the airflow within the runner. To verify their results, thermal images of the exterior of the runner were taken to compare with the simulated values.

Surprisingly, the team found that the temperature inside the runner is between 400 and 500 C, much lower than expected.

Figure 2: Fluid-structure interaction simulation shows the resulting velocity field caused by feeding the mechanical cantilever energy into the disordered kinetic energy of the surrounding gas.Modeling optimizes energy harvester
When it comes to testing physical prototypes, MEMS researchers have to overcome a battery of constraints—MEMS prototypes are notoriously expensive to build and their small scale makes accurate analyses difficult to obtain. To reduce testing costs and efficiently optimize their design, researchers at Siemens AG, Munich, Germany, used multiphysics simulation to explore the design of an innovative energy-harvesting MEMS device. The device in question was a microgenerator for a Tire Pressure Monitoring System (TPMS) driven by the motion of a rotating wheel. Because the device wouldn’t need batteries, it could be placed within the tire as opposed to on the rim (Figure 1), where it can monitor temperature, friction, wear and torque, and assist with optimal tracking and engine control in addition to measuring tire pressure. However, the sensor would need to withstand gravitational acceleration up to 2,500 g, be very light so as to prevent tire imbalance and last the full life of the tire, a minimum of eight years.

The team needed to optimize the cantilever in order to minimize damping, compensate for the high dynamic forces and ensure that the mechanical oscillations of the device transferred as much energy as possible to the electrical domain. The transfer of mechanical energy to the surrounding air within the tire was critical to the device’s design, as was measuring the deflection of the cantilever as the tire rotated (Figure 2).

According to Siemens, it would take three designers over four months and more than $100,000 to test just a few prototypes.

“Without the option of numerical modeling, we would have had to make numerous physical structures, which would have been time consuming and expensive. Instead, we were able to get on with the process of optimizing the MEMS design,” says Dr. Ingo Kuehne, simulation engineer at Siemens AG. Simulation results from COMSOL Multiphysics were used to determine how to numerically describe the behavior of the structure for use in physical prototypes. Siemens is looking to develop innovative technologies that will be used in the future, rather than specific products. The TPMS is just one device that Siemens is developing that demonstrates how multiphysics simulation can empower the designs of the future.

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