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Keywords: offshore wind turbines, finite element modelling, static analysis, dynamic analysis, environmental loads, structural decomposition.

Summary

Offshore wind turbines are relatively complex structural and mechanical systems located in a highly demanding environment. In the first part of this study, a systemic decomposition of the relevant elements, both physical related and due to the external conditions, is performed.

The offshore wind turbine structure is organized hierarchically, considering the structural parts categorized in three levels:

MACROSCOPIC (macro-level), related to geometric dimensions comparable with the whole construction; the parts so considered are called structural systems;
MESOSCOPIC (meso-level), related to geometric dimensions still relevant if compared to the whole construction but connected with specialized role in the structural system; the parts so considered are called structures or substructures;
MICROSCOPIC (micro-level), related to smaller geometric dimensions and specialized structural role: these are components or elements.

Following the performed systemic decomposition, numerical modelling is established taking into account many of the critical aspects, and allowing for the parametric exploration of different structural configurations. The attention has been focused on three different types of support structures commonly adopted for a water depth less than 50m, specifically monopile, tripod and jacket. Reliability and robustness requirements have been accounted for in order to ensure that the components are designed for the extreme loads.

During the design procedure different model types are adopted, at an appropriate scale and level of detail in accordance to the specific performance or structural behaviour under inquiry. In general four steps of structural analysis are defined, each one with a different model scale and level of detail:

systemic-level: the model scale comprises the whole wind farm and can be adopted for evaluating the robustness of the overall plant;
macro-level or global modelling (G): in these models the scale is reduced to the single turbine neglecting the connections between different structural parts and their shape; beam elements are adopted and aeroelastic and hydroelastic phenomena are accounted for;
meso-level or extended modelling (E): these models are characterized by the same scale of the previous level but with a higher degree of detail;
micro-level or detail modelling (D): these models are characterized by the highest degree of detail and are used for simulating the structural behaviour of specific individual components, including joints.

The dynamic behaviour has been investigated by means of modal analysis, while at this stage, stationary load cases are considered. The analytical results obtained by the analysis indicate that the maximum shear stress at the mud line is reached for the load case characterized by maximum wave height and reduced wind speed; whereas the combination giving the maximum bending moment at the mud line corresponds to extreme wind and reduced wave height.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 88 PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and M. Papadrakakis Paper 275 Offshore wind turbines: Basis of Structural Design K. Gkoumas, F. Petrini, S. Manenti and F. Bontempi School of Engineering, University of Rome "La Sapienza", Italy doi:10.4203/ccp.88.275 purchase the full-text of this paper Full Bibliographic Reference for this paper K. Gkoumas, F. Petrini, S. Manenti, F. Bontempi, "Offshore wind turbines: Basis of Structural Design", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 275, 2008. doi:10.4203/ccp.88.275 Keywords: offshore wind turbines, finite element modelling, static analysis, dynamic analysis, environmental loads, structural decomposition. Summary Offshore wind turbines are relatively complex structural and mechanical systems located in a highly demanding environment. In the first part of this study, a systemic decomposition of the relevant elements, both physical related and due to the external conditions, is performed. The offshore wind turbine structure is organized hierarchically, considering the structural parts categorized in three levels: MACROSCOPIC (macro-level), related to geometric dimensions comparable with the whole construction; the parts so considered are called structural systems; MESOSCOPIC (meso-level), related to geometric dimensions still relevant if compared to the whole construction but connected with specialized role in the structural system; the parts so considered are called structures or substructures; MICROSCOPIC (micro-level), related to smaller geometric dimensions and specialized structural role: these are components or elements. Following the performed systemic decomposition, numerical modelling is established taking into account many of the critical aspects, and allowing for the parametric exploration of different structural configurations. The attention has been focused on three different types of support structures commonly adopted for a water depth less than 50m, specifically monopile, tripod and jacket. Reliability and robustness requirements have been accounted for in order to ensure that the components are designed for the extreme loads. During the design procedure different model types are adopted, at an appropriate scale and level of detail in accordance to the specific performance or structural behaviour under inquiry. In general four steps of structural analysis are defined, each one with a different model scale and level of detail: systemic-level: the model scale comprises the whole wind farm and can be adopted for evaluating the robustness of the overall plant; macro-level or global modelling (G): in these models the scale is reduced to the single turbine neglecting the connections between different structural parts and their shape; beam elements are adopted and aeroelastic and hydroelastic phenomena are accounted for; meso-level or extended modelling (E): these models are characterized by the same scale of the previous level but with a higher degree of detail; micro-level or detail modelling (D): these models are characterized by the highest degree of detail and are used for simulating the structural behaviour of specific individual components, including joints. The dynamic behaviour has been investigated by means of modal analysis, while at this stage, stationary load cases are considered. The analytical results obtained by the analysis indicate that the maximum shear stress at the mud line is reached for the load case characterized by maximum wave height and reduced wind speed; whereas the combination giving the maximum bending moment at the mud line corresponds to extreme wind and reduced wave height. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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