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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Advanced rotor technologies' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Soo-Hyun Kim Korea Institute of Energy Research, Korea, Republic of
Co-authors:
Hyung-joon Bang (1) F P SooHyung Kim (1) Hyungki Shin (1) Kangsu Lee (2) Jongdeuk Ahn (3)
(1) Korea Institute of Energy Research, Daejeon, Korea, Republic of (2) KIOST, Daejeon, Korea, Republic of (3) KETEP, Seoul, Korea, Republic of

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Dr. Kim is currently a senior researcher at the Korea Institute of Energy Research in Daejeon, Rep. of Korea, and he has been involved in various wind turbines design and blade development projects.
He studied structural analysis and optimal design of composite structure at the Korea Advanced Institute of Science and Technology, and was granted a Ph. D. degree in 2008. After his studies he worked at the wind turbine division of Samsung Heavy Industries until 2011.
His research is focused on the WT system design and design load analysis, and optimal design and FE analysis of composite wind blade.

Abstract

Three-dimensional deflection estimation of a composite blade using a modal approach based shape estimation algorithm with embedded sensor array

Introduction

As wind turbines become large, the blades are designed to be more flexible to reduce fatigue loads. Accordingly, the importance of the dynamic stability of the wind turbine blade structure has been emphasized, and therefore many structural condition monitoring technologies have been developed as a method of securing the reliability of the structures during operation. In this study, a shape estimation technique using embedded optical fiber sensor array was developed and applied for the measurement of bending deflection of a composite wind turbine blade.

Approach

In this study, a FBG interrogator capable of multiplexed strain sensing was developed and applied for the measurement of bending deflection of a composite structure. For the estimation of the composite blade deflection on the basis of the modal approach, the displacement-strain transformation (DST) matrix was obtained from the finite element model.
Finally, the strain based deflection monitoring test was performed by using embedded 9 FBG sensors in the real wind turbine blade. In this study, the deflection-monitoring test of the 11m span composite blade was conducted to verify the applicability of the FBG sensors in shape estimation under dynamic loading.

Main body of abstract

Real-time deflection monitoring of a composite wind turbine blade was accomplished using the shape estimation algorithm with modal approach and strain data from embedded fiber Bragg grating (FBG) sensors. The finite element model of the composite wind turbine blade was created and the displacement-strain transformation (DST) matrix on the basis of the modal approach was obtained. The locations of the nine FBG strain sensors were optimized by minimizing the condition number of the displacement-strain transformation matrix. The deflection-monitoring test of the 11m span composite blade was conducted to verify the shape reconstruction algorithm and applicability of the FBG sensors in structural condition monitoring. The estimated shapes measured by embedded Bragg grating sensors are compared with the directly captured deflection shapes measured by stereo pattern recognition (SPR) cameras. The results confirm very close agreement showing the potentials of the proposed shape estimation technique using arrayed Bragg grating sensors. On the blade surface, 33 reflecting markers for stereo pattern recognition (SPR) were bonded and 8 high-speed cameras for SPR system were installed for the comparison of the measured deformation. On the dynamic loading test, snapback load with initial 100mm deflection was applied to the flap-wise direction on the 95% blade span location.

Conclusion

In this study, a high-speed FBG interrogator was used for the strain-based deflection shape estimation of composite wind turbine blade. FEM based strain-displacement transformation process was proposed for the deflection shape estimation of the composite blade using arrayed FBG sensors. For the shape estimation using modal approach, FE analysis of composite blade was done to formulate the DST matrix. To verify the applicability of the FBG sensors in shape estimation under dynamic loading, the flap-back deflection loading test was conducted and the results were compared with the SPR measured deflections.


Learning objectives
From the series of experiments, it is clear that out-of-plane deflections can be nicely estimated by the arrayed FBG sensors and the possibilities of optical fiber sensors in structural shape monitoring was confirmed.