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2586 |
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Tuesday, September 27, 2011, Saal E 2:50 PM Windenergie |
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Launching of a floating met mast project |
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Kay-Uwe Fruhner* / Germanischer Lloyd, Deutschland Dr. Ing. Bernhard Richter / DVS, Germany Marian Lopez/ IDERMAR / APIA XXI, Spain |
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During July 2009 the first of twelve offshore wind turbines has been erected within the German territorial waters. In the meantime all wind turbines of the first German offshore wind farm alpha ventus are installed and the commissioning has been finalized. However before an installation and commissioning can be realized, detailed information regarding wind conditions are required. Therefore the Germanischer Lloyd (GL) was responsible for the erection of the first research platform Fino 1 and also operates this platform in the Northern Sea. The second platform Fino 2 is located in the Baltic Sea and is also under operation by GL. In the meantime the third research platform Fino 3 in front of the island Sylt has been commissioned. This structure has been certified by GL. However for the installation of offshore wind turbines in the deep water zone less information related to wind loads and boundary conditions are available. Thus additional research work is required in this field of wind engineering. This means not only additional research work for the construction, but rather more for the boundary conditions. Within these boundary conditions the load assumptions, wind speed and wave height are determining the behaviour of the structure. On the other hand, in North Spain a new product called Meteorological Floating Mast is developing from January 2009 for acquisition of wind loads and other meteorological values at ocean environments. These structures are not fixed to the seabed but are floating anchoring to three mooring lines. From June 2009 the first prototype is anchored in the Cantabrian Sea at approximately 2 miles from the coast and in a marine area of 50 m depth; 60 m emerged above the sea level and, almost 40 m remains under it. This first prototype has been submitted to waves of 13 m and winds of more than 100 km/h. In the same way, from May 2010 a second prototype is anchored, also in the Cantabrian Sea, at approximately 8 miles from the coast and in an area of 200 m depth; it is emerged 80 m above the sea level and, almost 40 m remains submerged. At present, a new develop of this Floating Mast, now commercial, is manufactured and ready for anchoring also in the Cantabrian Sea at almost 2 miles from the coast and in a marine area of 50 m depth. This mast shall be emerged 90 m above the sea level and other 40 m remains submerged. This mast is been certified by GL. Based on the results of these research projects the load case definition, rules development and safety values have been defined respectively developed. Besides of this the additional influence regarding wave loads has to be considered at offshore wind turbines. Thus not only fatigue loads can be mandatory for the design, even ultimate loads due to wave loads can be mandatory. However a floating structure has to be calculated not only for the worse operation conditions but for the most critical phases: launching, marine transport and anchoring. During these phases of erection, the structure is continuously subjected to a lot of constant external and internal strengths: waves, submerged currents, tides, winds, expansion-contraction cycles, etc. These strengths create inside the molecular structure of the material a lot of small stresses. So, manufacturing must be extensively controlled and fabrication techniques have to be continuously checked in order to guarantee the adequate technical characteristics of material at final structure. Even, new fabrication processes shall be designed for avoiding the addition of un-necessary stresses to the material. In the context of manufacturing surveillance for a floating met mast the foundation and lattice tower have been inspected. This inspection can be evaluated as a part of type certification if applicable. Within this topic the characteristics according to calculation and construction will be compared with respect to the welding requirements of a floating structure. |