Dec 19 2006
As energy prices continue to climb, the wind power sector is experiencing a global boom. Because wind blows more steadily and much more strongly at sea than on land, more and more countries around the globe are planning and constructing sea-based wind energy plants. The first German offshore testbed – comprising 12 wind turbines of the five-megawatt class – is now being built off the North Sea coast. In a joint project carried out with WeserWind GmbH Offshore Construction Georgsmarienhütte and Technologiekontor Bremerhaven GmbH, Fraunhofer researchers from the Institute for Manufacturing Engineering and Applied Materials Research IFAM and the Center for Wind Energy and Maritime Technologies CWMT accompanied the planning process for the construction of a three-legged foundation, also known as a tripod. This was not an easy task, as the bulky components of the 30-meter-high tripod, weighing a total of over 600 metric tons, had to be assembled in the perfect order as quickly and precisely as possible. “Otherwise it would have taken two cranes a whole working day to, say, reposition a large strut,” explains Holger Fricke of the IFAM. “Ensuring the best possible fit therefore constitutes a considerable cost and quality factor in constructing a tripod. Welding must be kept to a minimum and the most suitable position needs to be established for each part.”
The best-fit method determines the best join partners available for each designated assembly position. For this purpose, the IFAM researchers developed an algorithm that enables the workload to be calculated in advance. The parts are measured at the manufacturing plant, and the data are then imported into the best-fit system and matched against the components that have already been installed. On the basis of these measurement data, the best-fit analysis calculates the ideal allocation of each strut to its respective join partner, and determines their precise position. Unlike conventional measurement techniques, this method not only verifies the best fit for each strut, but also rationalizes all welding work by means of combinatorial analysis. Therefore, when a new component is delivered, the engineers already know how and where to install it. Owing to the best-fit system’s clear graphic representation, any potential problems regarding production can be identified and resolved at an early stage. To ensure that everything goes to plan at sea, the researchers have first been testing the system on land, during the manufacture of the tripod prototype. This will provide them with valuable experience when it goes into series production.