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Stochastic Dynamic Response Analysis of Spar-Type Wind Turbines with Catenary or Taut Mooring Systems
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Floating wind turbines can be the most practical and economical way to extract the vast offshore wind energy resources at deep and intermediate water depths. The Norwegian Ministry of Petroleum and Energy is strongly committed to developing offshore wind technology that utilises available renewable energy sources. As the wind is steadier and stronger over the sea than over land, the wind industry recently moved to offshore areas. Analysis of the structural dynamic response of offshore wind turbines subjected to stochastic wave and wind loads is an important aspect of the assessment of their potential for power production and of their structural integrity.

Of the concepts that have been proposed for floating wind turbines, spar-types such as the catenary moored spar (CMS) and tension leg spar (TLS) wind turbines seem to be well-suited to the harsh environmental conditions that exist in the North Sea. Hywind and Sway are two examples of such Norwegian concepts; they are based on the CMS and TLS, respectively.

Floating wind turbines are sophisticated structures that are subjected to simultaneous wind and wave actions. The coupled nonlinear structural dynamics and motion response equations of these turbines introduce geometrical nonlinearities through the relative motions and velocities. Moreover, the hydrodynamic and aerodynamic loading of this type of structure is nonlinear. A floating wind turbine is a multibody aero-hydro-servo-elastic structural system; for such structures, the coupled nonlinear equations of motion considering nonlinear excitation and damping forces, including all wave- and wind-induced features, should be solved in the time domain. In this thesis, the motion and structural responses for operational and extreme environmental conditions were considered to investigate the performance and the structural integrity of spar-type floating wind turbines. The power production and the effects of aerodynamic and hydrodynamic damping, including wind-induced hydrodynamic and wave-induced aerodynamic damping, were investigated.

Negative damping adversely affects the power performance and structural integrity. In this thesis, the controller gains were tuned to remove servo-induced instabilities. The rotor configuration effect on the responses and power production was investigated by comparing the upwind and downwind turbines.

To develop robust design tools for offshore wind power, the competencies of the offshore technology and wind technology must be combined. Both the offshore and wind energy industries have begun to extend their existing numerical codes to account for the combined aerodynamic and hydrodynamic effects on the structure. As a result verifications of extended codes by doing experiments and code-to-code comparisons are needed. One of the aspects of the present research was to fill this gap by performing hydrodynamic and hydro-elastic comparison between commercial codes. For both CMS and TLS concepts, the comparisons were carried out prior to using the tools to study the behaviour of the CMS and TLS under wave- and wind-induced loads.

Offshore structures encounter a variety of operational and harsh environmental conditions. Limit states such as ultimate, fatigue, accidental collapse and serviceability limit states (ULS, FLS, ALS and SLS) are defined as the design criteria for offshore structures. In performing realistic ultimate limit state analysis, the extreme responses of a floating wind turbine over its life should be estimated. This estimation requires detailed analysis of the extreme response. In the present thesis, extreme value analysis for spar-type wind turbines subjected to simultaneous wave and wind actions was preformed. The structural responses and the effect of modelled forces such as turbulence on these responses were investigated. The joint distribution of the environmental characteristics of the wave and wind was applied through the contour surface method.

Stochastic wave and wind analysis showed that, while rigid body modelling was sufficient for obtaining accurate motions, consideration of the elastic behaviour of the tower/support structure was necessary to predict structural responses. The blades structural responses were found to be significantly affected by the turbulent wind. However, the mean and standard deviation of global motion and structural responses were not affected by the turbulence. Thus, to reduce the simulation time in fatigue analysis, a constant wind speed model can be applied. The CMS and TLS wind turbines are inertia-dominated structures, and the hydrodynamic viscous drag did not affect their wave-induced responses, while an increase in viscous drag could effectively reduce the resonant responses of such turbines. Under operational conditions, aerodynamic damping was found to be active in reducing both wave frequency and resonant responses. The results showed that, for a floating wind turbine, extreme response could occur in survival conditions, while for a fixed wind turbine, the extreme response occurs in operational cases related to the rated wind speed. To estimate the extreme value responses, extrapolation methods were used to reduce the sample size in Monte Carlo simulations. The accuracy of methods to estimate the extreme responses as a function of sample size and methods applied was investigated. The normalized responses for both CMS and TLS offshore wind turbines were presented to draw more generalized conclusions.

Place, publisher, year, edition, pages
NTNU, 2011.
Series
Doctoral theses at NTNU, ISSN 1503-8181 ; 2011:8
Identifiers
URN: urn:nbn:no:ntnu:diva-12458ISBN: 978-82-471-2526-7 (printed ver.)ISBN: 978-82-471-2527-4 (electronic ver.)OAI: oai:DiVA.org:ntnu-12458DiVA: diva2:409999
Public defence
2011-03-01, 00:00
Available from: 2011-04-12 Created: 2011-04-12 Last updated: 2011-04-12Bibliographically approved
List of papers
1. Dynamic Motion Analysis of Catenary Moored Spar Wind Turbine in Extreme Environmental Condition
Open this publication in new window or tab >>Dynamic Motion Analysis of Catenary Moored Spar Wind Turbine in Extreme Environmental Condition
2009 (English)In: Proceedings of the European Offshore Wind Conference, 2009Conference paper (Refereed)
Identifiers
urn:nbn:no:ntnu:diva-12420 (URN)
Conference
EOW2009
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
2. Wave and Wind Induced Dynamic Response of a Spar-Type Offshore Wind Turbine
Open this publication in new window or tab >>Wave and Wind Induced Dynamic Response of a Spar-Type Offshore Wind Turbine
2011 (English)In: Journal of waterway, port, coastal, and ocean engineering, ISSN 0733-950X, Vol. 1, no 1, 55-55 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
ASCE, 2011
Keyword
Catenary Moored Spar (CMS), Floating Wind Turbine (FWT), Stochastic Structural Dynamic Response, Operational and Survival conditions
Identifiers
urn:nbn:no:ntnu:diva-12429 (URN)10.1061/(ASCE)WW.1943-5460.0000087 (DOI)
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
3. Effect of Aerodynamic and Hydrodynamic Damping on Dynamic Response of Spar Type Floating Wind Turbine
Open this publication in new window or tab >>Effect of Aerodynamic and Hydrodynamic Damping on Dynamic Response of Spar Type Floating Wind Turbine
2010 (English)In: Proceedings of the European Wind Energy Conference EWEC2010, 2010Conference paper (Refereed)
Identifiers
urn:nbn:no:ntnu:diva-12430 (URN)
Conference
EWEC2010
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
4. Extreme Structural Dynamic Response of a Spar Type Wind Turbine
Open this publication in new window or tab >>Extreme Structural Dynamic Response of a Spar Type Wind Turbine
2010 (English)In: Proceedings of the 29th International Conference of Offshore Mechanics and Arctic Engineering / [ed] Chen, Gang, 2010Conference paper (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12431 (URN)
Conference
OMAE2010
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
5. Extreme Dynamic Structural Response Analysis of Catenary Moored Spar Wind Turbine in Harsh Environmental Conditions
Open this publication in new window or tab >>Extreme Dynamic Structural Response Analysis of Catenary Moored Spar Wind Turbine in Harsh Environmental Conditions
2011 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 133, no 4, 041103-1-041103-13 p.Article in journal, Editorial material (Refereed) Published
Identifiers
urn:nbn:no:ntnu:diva-12432 (URN)10.1115/1.4003393 (DOI)
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2012-05-15Bibliographically approved
6. Hydro-elastic Code-to-Code Comparison for a Tension Leg Spar Type Floating Wind Turbine
Open this publication in new window or tab >>Hydro-elastic Code-to-Code Comparison for a Tension Leg Spar Type Floating Wind Turbine
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12433 (URN)
Note
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Marine Structures. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in http://www.elsevier.com/wps/find/journaldescription.cws_home/405903/description#descriptionAvailable from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
7. Ameliorating the Negative Damping in the Dynamic Responses of a Tension Leg Spar-Type Support Structure with a Downwind Turbine
Open this publication in new window or tab >>Ameliorating the Negative Damping in the Dynamic Responses of a Tension Leg Spar-Type Support Structure with a Downwind Turbine
2011 (English)In: European Wind Energy Conference, 2011Conference paper (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12434 (URN)
Conference
EWEC2011
Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
8. Tension Leg Spar-Type Offshore Wind Turbine with Upwind or Downwind Rotor Configuration
Open this publication in new window or tab >>Tension Leg Spar-Type Offshore Wind Turbine with Upwind or Downwind Rotor Configuration
2011 (English)In: AWEA-WINDPOWER2011, 2011Conference paper (Refereed)
Identifiers
urn:nbn:no:ntnu:diva-12435 (URN)
Conference
AWEA-WINDPOWER2011
Available from: 2011-04-08 Created: 2011-04-07 Last updated: 2011-04-12Bibliographically approved
9. Stochastic Dynamic Response Analysis of a Tension Leg Spar-Type Offshore Wind Turbine
Open this publication in new window or tab >>Stochastic Dynamic Response Analysis of a Tension Leg Spar-Type Offshore Wind Turbine
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12438 (URN)
Note
Submitted to Wind Energy. The definitive version will be available at www3.interscience.wiley.comAvailable from: 2011-04-08 Created: 2011-04-08 Last updated: 2011-04-12Bibliographically approved

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