This paper establishes the model basis regarding the ultimate limit state consisting of structural, loading, and probabilistic models of the support structure of offshore wind energy converters together with a sensitivity study. The model basis is part of a risk based assessment and monitoring framework and will be applied for establishing the “as designed and constructed” reliability as prior information for the assessment and as a basis for designing a monitoring system. The model basis is derived considering the constitutive physical equations and the methodology of solving these which then in combination with the ultimate limit state requirements leads to the specific constitutive relations. As a result finite element models based on shell elements incorporating a structural and a loading model are introduced and described in detail. Applying these models the ultimate capacity of the support structure and the tripod structure are determined with a geometrically and materially nonlinear finite element analysis. The observed failure mechanisms are the basis for the definition of the ultimate limit state responses. A probabilistic model accounting for the uncertainties involved is derived on the basis of literature review and measurement data from a prototype Multibrid M5000 support structure. In combination with the developed structural and loading models, sensitivity analyses in regard to the responses are performed to enhance the understanding and to refine the developed models. To this end, as the developed models necessitate substantial numerical efforts for the probabilistic response analysis predetermined designs of numerical experiments are applied for the calculation of the sensitivities using the Spearman rank correlation coefficient. With this quantification of the sensitivity of the random variables on the responses including nonlinearity the refinement of the model is performed on a quantitative basis.

References

References
1.
Thöns
,
S.
,
Faber
,
M. H.
,
Rücker
,
W.
, and
Rohrmann
,
R. G.
, 2008,
“Assessment and Monitoring of Reliability and Robustness of Offshore Wind Energy Converters,”
ESREL 2008 and 17th SRA-Europe Conference
.
Valencia, Spain
. Proceedings, pp. 1567-1575.
2.
Faber
,
M. H.
,
Maes
,
M. A.
,
Baker
,
J. W.
,
Vrouwenvelder
,
T.
, and
Takada
,
T.
, 2007,
“Principles of Risk Assessment of Engineered Systems,”
10th International Conference on Applications of Statistics and Probability in Civil Engineering
,
The University of Tokyo
,
Kashiwa Campus, Japan.
3.
Kühn
,
M. J.
, 2001,
“Dynamics and Design Optimisation of Offshore Wind Energy Conversion Systems,”
Ph.D. thesis
,
Technical University of Delft, Delft
,
The Netherlands.
4.
Ansys Inc., 2006, Release 11.0 Documentation for ANSYS, Canonsburg, USA.
5.
Schaumann
,
P.
Böker
,
C.
Rutkowski
,
T.
, and
Wilke
,
F.
, 2007,
Stahlbaukalender 2007, Prof. Dr.-Ing. Ulrike Kuhlmann, Tragstrukturen für Windenergieanlagen
in German.
6.
DIBt, 2004, “Guideline for the Certification of Wind Turbines,” A publication of the German Institute for Building Technology (DIBt) in German, Berlin, Germany.
7.
DIN EN 1993-1-6, 2007, “Eurocode 3 - Design of Steel Structures. Strength and Stability of Shell Structures,” Beuth-Verlag, Berlin, Germany.
8.
Sørensen
,
J. D.
and
Tarp-Johansen
,
N. J.
, 2005,
“Optimal Structural Reliability of Offshore Wind Turbines,”
ICOSSAR Rome, Millpress Science Publishers, Rotterdam (CD only)
, Netherlands.
9.
JCSS, 2006, “Probabilistic Model Code,” A publication of the Joint Committee on Structural Safety (JCSS), http://www.jcss.byg.dtu.dk.
10.
DIN EN 10025, 2005, “Hot Rolled Products of Structural Steels, Part 2: Technical Delivery Conditions for Non-Alloy Structural Steels,” Beuth-Verlag, Berlin, Germany.
You do not currently have access to this content.