Pictures of the Future    Spring 2007

The Color of Quiet

One day people will have to battle noise as bitterly as they did cholera and the plague in the past," predicted Robert Koch, who was awarded the Nobel Prize for Medicine just under a century ago. The fact that he was right is proven by the existence of professional noise-reduction experts like Holger Ennes, a member of a six-person team at Siemens Power Generation in Erlangen, Germany. Sitting at a large monitor, Ennes uses special software to simulate techniques for toning down the noise generated by a combined-cycle power plant that has an output of several hundred megawatts.

Some of the disturbing sounds are created in the cooling tower by huge fans that condense the steam from the turbine back into water. Others come from a gas turbine that screeches like a jet taking off. But despite all this activity, acoustic experts have succeeded in turning the roar from such plants into a whisper. "We could place such a facility in a city and people around it wouldn’t know it was a power plant," says Ennes. "They would hardly hear what was going on inside." Ennes and his colleagues consider not only nearby residents, but also the people who work in power plants. Using a building block approach, they put together new power plants piece by piece on computer screens, modeling the cooling towers, boilers, gas turbines, transformers, pumps and fans three-dimensionally. Each component has a precisely measured and calculated noise output level. "For the simulation, we also need other data, such as the plant’s distance from the nearest private residences," says Ennes.

Red Means Loud. Regulations in Germany stipulate that the noise level of a new power plant—measured from the nearest residence—must be 10 dB lower than the level of ambient noise measured before the facility was built. This means that if around 43 dB(A) (comparable to light radio music) is measured outside someone’s bedroom at night due to street noise, the noise from a power plant built in the vicinity may not exceed 33 dB(A) at that location. A 10-dB reduction is perceived as a roughly 50-% decrease in noise volume.

Experts in acoustics can achieve this in a variety of ways. For example, simulations will show them how well the hall facade should dampen noise, how powerful the gas turbines’ noise dampeners should be, whether the pumps will require noise-dampening hoods, whether low-noise transformers and machines should be used, and whether heat recovery steam generators need to be insulated. Such measures can cost five percent of a power plant’s contract volume, which often totals hundreds of millions of euros.

A computer simulation program adds up all noise sources and calculates the plant’s total sound propagation. "The calculation can take up to two days, depending on the size and complexity of the plant," says Ennes. But in the end, it produces a "noise map" in which color-coded sound contours form a ring around the facility and individual buildings.

Areas with the same acoustic pressure are the same color. The colors range from dark red for very loud to light green for very quiet. Parameters are then adjusted until residential areas are in the green zone, which means that people in nearby residential areas will be able to enjoy a good night’s sleep.

According to Germany’s Fraunhofer Institute for Structural Durability (LBF), over 100 million people in Europe are affected by noise. Road traffic is the biggest culprit, followed by noisy neighbors, airplanes, trains and noise from industry and businesses. To help find a remedy, Prof. Holger Hanselka from the LBF launched a noise reduction project in 2004 in cooperation with the Technical University of Darmstadt. With a budget of 34 mill. €, the project develops new materials that will make machines, cars, planes and trains quieter. A total of 42 partners, including Siemens Transportation Systems (TS), from 13 European countries are involved. Specialists in rail systems technology, for instance, are examining new materials for rail vehicle fans. Especially in diesel locomotives, cabinet-sized fans transfer engine heat to the outside, creating loud vibrations. By stiffening under pressure, the new materials will reduce vibrations.

"We’ve been working on making trains quieter for a long time," says TS innovation expert Friedrich Moninger. One example is the low-noise Eurorunner locomotive that hit the rails in 2002. Today, around 180 of the units are in operation. The 80-t, 2-MW diesel locomotive is significantly quieter than the legal maximum for rail vehicles. This decrease is due to sidewalls made of an aluminum honeycomb sandwich structure instead of thin, stiffened sheet steel; large fans with lower speeds; wheel disk brakes instead of loud shoe brakes; and an encapsulated engine compartment with sound insulation.

Europe’s newest and fastest series-produced passenger railcar, the electric-powered Velaro will soon be covering the new 625-km stretch from Madrid to Barcelona at a speed of 350 km/h. It will make the trip, which took four hours in its predecessor, in two and a half hours. Noise emissions—especially those related to wind resistance from—have also been reduced by TS developers.

Normally, at high speeds, every crevice and edge generates whistling sounds. That’s why the Velaro’s roof, including its pantograph, have been streamlined. What’s more, aprons installed between the undercarriage and track also reduce wind noise, as do wheel coverings on the chassis. The train’s suspension was modified as well. Dampers now minimize the oscillations of the railcar body in the low-frequency range between five and 400 Hz, thereby ensuring maximum comfort in the railcar interior.

Moninger believes the dampers offer particular potential. "The trend is toward intelligent systems," he says. So-called "yaw" dampers improve a train’s performance in curves by mechanically suppressing the oscillations arising in the curves. Active yaw dampers that use data from sensors and electronic systems to autonomously adjust to oscillations in curves and so suppress noise are being developed. These devices will make it possible to better control the forces in curves—particularly when heavy locomotives are involved—and thus optimally transfer the motor power to the rails.

Compact and Quiet. TS’ latest contribution to rail noise reduction is its Syntegra system, which for the first time combines the chassis, drive system and brakes into one unit that is smaller, more compact and lighter than a conventional chassis (see Rail Propulsion Systems in Pictures of the Future, Spring 2006). Syntegra trains will make their commercial debut in the Munich subway system in summer 2007. The new design has made it possible to eliminate the transmission, as the wheels are driven directly by a synchronous motor. The traction motor fan has also been eliminated, further reducing noise levels.

Siemens VDO automotive is embarking on a similar noise reduction path by planning the development of a new type of drive system. Specialists working on a project called "eCorner" have combined the engine, brakes and steering system into a "hub motor" (see  Transportation)—a complete, purely electrical powertrain. Although the system remains a dream for the future, one part of it—the electronic wedge brake—should be ready for mass production by 2010. Electric cars based on eCorner technology will produce no combustion noises, making them much quieter than today’s vehicles, even when accelerating rapidly.

The combustion engine itself has also been significantly improved in recent years. For example, the typical diesel knocking noise can now be heard only in older vehicles. The reason: high-pressure piezo injection systems. With this piezo technology, more fuel injections can be used. As a result, the pressure in the cylinder rises very gradually during combustion, thereby reducing noise levels. In the past, combustion was essentially explosive. "For us, the next step will be to use combustion management systems to select up to seven individual injections that can be precisely positioned from a total of 11 possible injections," says Dr. Klaus Wenzlawski from Siemens VDO. In this way, it will be possible to reduce irritating noises step by step and decibel by decibel—thus making life a little quieter for everyone.
                                                                                                                    Rolf Sterbak