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Dimensionering av monopåle för grundläggning av vindkraftverk till havs: Baserat på finita elementanalyser
2014 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Wind power is a renewable and non emission natural resource and a global development is expected. The key benefits with offshore wind power are better wind conditions and lower demands on account for landscape and to local residents. This implies that bigger wind turbines can be built, which use the wind more effective. For offshore wind parks a method for foundation that is rational and flexible is essential. When designing an offshore construction is it important to take into account the cyclic loads from wind and waves the construction is exposed to. Traditionally the recommendations published by American Petroleum Institute, API, are used. However, the API recommendations for piles are based on some few laboratory and field tests of piles that are slender and longer than conventional monopiles. Therefore the method is questioned whether it is appropriate for design of monopiles. Norwegian Geotechnical Institute, NGI, has developed a constitutive material model for analyzing constructions exposed to combined static and cyclic loading. The model is called PDCAM and is a result of decades of research within the topic. PDCAM account for soil degradation under cyclic loading and model effects as accumulated strains, accumulated pore pressure, reduced stiffness and reduced undrained shear strength.The capacity of a conventional monopile in saturated and very dense sand is calculated. The calculations refer to ultimate load state. The monopile in the study has a diameter of 6 meters and is drilled 25 meters below seabed. The calculations are performed with PDCAM implemented in the finite element program PLAXIS 3D Foundation. The results are compared with calculations based on the API recommendation, called the p-y method.In order to validate the mesh, the results and save time the calculations with PDCAM are complemented with more simple calculations with the material model Hardening soil.PDCAM gives a safety factor for at least two. The horizontal deformation indicates an additional capacity. The calculations are very time consuming and a better precision of the result has not been established due to lack of time. The calculations based on the API recommendation and with Hardening soil gives a safety factor of 3.2 respectively 4.5. The results show a significant degradation of capacity due to cyclic loading. PDCAM is a very advanced material model that requires indata which are time and resource consuming to produce. If no indata for PDCAM are accessible the p-y method can provide results to be used as guidelines. A further development of PDCAM is needed to improve the usability. In order to develop commercial models for cyclic loading PDCAM can be a good base for further research.

Place, publisher, year, edition, pages
2014. , 64 p.
Keyword [en]
Keyword [sv]
Teknik, PDCAM, PLAXIS, Monopile, 3D Foundation, cyklisk belastning
URN: urn:nbn:se:ltu:diva-48751Local ID: 62ed71f8-ac8b-44d3-bde3-f3d30be37ff1OAI: diva2:1022095
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20140203 (global_studentproject_submitter)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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