February 16, 2007 In an interesting development, the same technology that is used in noise-cancelling headphones (roughly speaking) is to be applied to heavy marine engines to reduce their noise and vibrations. The vibrations from marine diesels spreads through the entire hull, but researchers have now found a way of blocking the sound immediately below the engine with the help of computer-controlled counter-vibrations from an active damper between the engine and the bearing by which the engine is attached to the hull. This active bearing is made primarily from piezo-ceramics, materials that can change their shape when electrically stimulated. If they are stimulated very quickly, they generate high-frequency vibrations – which are exactly what marine engines need. Using sophisticated sensors, the scientists measure the engine’s vibrations and trigger the piezo-ceramics such that they precisely counteract this motion.
Marine engines are attached to the ship’s hull via bearings, either directly or on an engine mount. Their vibrations can thus easily spread through the entire hull of the ship. The only way to dampen these vibrations is by absorbing them directly at the bearing. The solution devised by the researchers is to install an active damper between the engine and the bearing. This active bearing is made primarily from piezo-ceramics, materials that can change their shape when electrically stimulated. If they are stimulated very quickly, they generate high-frequency vibrations – which are exactly what marine engines need. Using sophisticated sensors, the scientists measure the engine’s vibrations and trigger the piezo-ceramics such that they precisely counteract this motion. Because the active bearings carry the weight of the engine directly, they are able to perform to maximum effect. Conventional approaches involve dampers that either vibrate against the base of the engine from the side or are located in a hollow space inside the bearing. As today’s engines do not rest directly on these vibrating parts, the vibrations can only be offset indirectly. As a result, such systems require far more power to achieve a satisfactory damping effect.
Meanwhile, the researchers have tested their method on an engine larger than that of a truck in the institute’s laboratories in Darmstadt. This year, the new vibration damping system will be tried out for the first time on board a ship. The work will be done in cooperation with the Friedrich Lürssen shipyard in Bremen. “Our partners’ ship-building expertise enabled us to specify the exact details of the ship, for example the rigidity and resonance of its metal,” says LBF engineer and project manager Michael Matthias. In addition, the shipyard will provide a ship for test runs in the coming year. “Following the tests recently carried out in the laboratory, we are confident that the method will also work under real conditions,” says Matthias. “The test scheduled to be carried out in the summer will show just how much better it is than conventional damping systems.”
