RENEWABLE ENERGY
installation company places this around the construction
site as a ring, before the wind turbine towers – which are up to 150m high – are driven into the seabed. Te hose ends are connected to powerful superchargers on ship decks. During the work, they pump 10 bar of oil-free compressed air into the hoses, which escapes through the holes according to a well-defined pattern. Te result is a curtain of millions of small bubbles that rise to the water surface, forming a kind of whirlpool around the construction site. Te air bubbles change the density of the water and thus break down the sound waves. Depending on the nature of the soil and water currents, hydraulic specialists also use two-ring
technology,” explains David Hoffmann, who is responsible for industrial hose solutions in the EMEA and APAC region for Continental. “Tis clever technology reduces the noise level by up to 18dB, which is a volume reduction of 95%,” Hoffmann continues. But how can the hose remain at the bottom of the sea without additional steel chains when the pressurised air provides buoyancy? To find a solution to this challenge, the development partner commissioned the hose experts from Continental. So far, installation companies are pursuing two approaches to keeping the hoses on the seabed. In the first, the hose is provided with additional weights that anchor it to the ground. Te disadvantage of this method is that it is complicated to transport it back to the water surface after the work. Te second variant consists of a pipe system. However, this is difficult to install on the seabed. “As with all construction projects,
it’s about doing the work as quickly and with as little effort as possible. Tat’s why we have developed a solution with a hose that is flexible and works without complicated anchoring with additional weights such as steel chains,” explains Hoffmann. In addition to the flexibility required to allow easy handling, the hose should also be stable. Abrasion resistance, so that rubber components are not released into the environment,
and resistance to salt water are among its other important properties.
A HEAVYWEIGHT IN THE FIELD TEST
Te technology company has solved the task with a further development of its hoses. Each hose consists of different layers of different materials, such as rubber, as well as reinforcements. Even with the hoses used as air bubble curtains, one of these layers consists of a wire mesh. Tis spring wire spiral serves as bend protection during winding and unwinding of the hose line, and keeps the shape of the hose stable in case of over or under pressure at the same time. “Te trick of our development is that we wrapped our hose with additional wire, like a spiral. Te result is a real heavyweight that can be tared very well at the desired depth. A 1m-long hose with an internal diameter of 100mm now weighs an impressive 20kg. A 1,000m hose weighing 20 metric tons is needed to wrap a ring around a construction site. Te hoses are therefore wound up on huge drums aboard ships and transported to the marine construction site. Tis may sound rather complicated at first, but it’s much easier to use than the previous solutions using steel chains or pipe systems,” reports Hoffmann. 35km northeast of the island of
A sensible measure against underwater noise from construction sites in the sea is the use of air bubbles in the water with the help of a bubble curtain
Rügen lies the construction area of the Arkona Basin Southeast wind farm. From now on, 60 wind turbines with an installed capacity of 385MW will supply 400,000 households with clean electricity. At the end of 2017, Continental tested the further developed hoses there. Te result: the gigantic hoses have passed the field test with flying colours. Several installations ran parallel at the same time. Te Big Bubble Curtain hose system worked perfectly during the construction work at a depth of 60m. It remained stable on the seabed while air bubbles reduced noise and vibrations by 95%. Te recovery after the construction work also ran smoothly without leaving any traces on the seabed. After all, the hoses should be used several times. “Overall, the handling has improved significantly with Continental’s solution compared with the use of additional weights,” says Hoffmann with satisfaction.
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