Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
ANDRE DR. SCHÄFER (1) F P
(1) HBM Hottinger Balwin Messtechnik GmbH, Darmstadt, Germany
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Presenter's biographyBiographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited
After being assistant lecturer and finalizing PhD, I joint HBM in 1992. In HBM I was working in different fields of sensor and measurement technique. Working in wind energy applications since 2010, I have recently presented papers in DEWEK, Wind power India and China as well as for several events in Germany and had some poster in EWEA Amsterdam and EWEA Offshore Frankfurt before. Additionally I have also been member of the review committee of EWEA Offshore Frankfurt last year. Also I had a session chair to seven international conferences so far.
Structural health monitoring (SHM) - necessity for further progress in wind turbines
Experimental stress analysis is a method to analyze structures. Structural Health Monitoring (SHM) is the logical application in wind energy. During operation you may monitor operational performance and identify statistical trends and assess the reliability & structural integrity of systems for long-term operation. Furthermore in design and test phase you may validate FE designs, learn about characteristics and fatigue behavior of prototypes by using sensors and DAQ systems to understand the structural envelope and dominant load cases by using analysis software, which allows you to predict fatigue damage in the design of key components such as shaft or composite rotor blades.
For strain measurement lifetime aspects are discussed with the choices out of electrical or optical strain gauges,or even strain transducers. Data acquisition may be even more important as the data have to be conditioned so they are there synchronized, centralized and organized to be finally qualified and classified as OK/NOK. From these data by the analysis and fatigue software “nCode DesignLife” you may identify potential weaknesses in critical components already during the design phase. This software for structural integrity certified by GL Renewables can be used for the design of cast and forged structural machinery components in wind turbines.
Main body of abstract
We see two directions for developing wind turbines: You can either try to further improve turbine reliability, or you could try to make the turbine more lightweight by keeping the present level of reliability. In any case you need reliable data on the loads, based on substantial measurement of mechanical quantities. The measurement of mechanical quantities is vital to meet the high standards required for the design of offshore wind turbines with an expected lifetime of 20 or even 25 years.
For towers and foundations this challenge can be solved by foil type strain gauge or transducers made by them such as strain meters, force washers, force transducers and other types, which allow measurement of strain everywhere, but also for very high force and torque values.
For blades made from composite material and exposed to high strain and lightning, optical strain sensors using FBG (Fibre Bragg Grating) have advantages. But also in underwater applications, using a so called coated fibre FBG technique is effortable.The paper will show different types applied, also combined strain measuring point at the foundation of an offshore turbine offers both, electrical and optical strain measurement and thus a redundancy.
In order to further optimize the design of wind turbines; manufacturers have an interest to analyse the data. According to DNV▪GL Renewables as well as German BSH it is not enough to just monitor the drive train, but also towers, offshore foundations and blades have to be monitored.
Wind turbines are getting larger and taller. Due to economic threshold this superlative is strongly related to offshore applications, their sharewill further grow. SHM can help to reduce downtime and rais availability over the whole lifetime. It can also help to extent life time. How it can be done is shown in the paper. Finally using the methods described above, major components of wind turbines such as blades, towers and offshore foundations could be operated safely, or even redesigned without any loss of reliability and a contribution to more economic wind turbines can be made as well.
The ever-growing size of WTs is needed for more profitable operation. It has brought about the demand for higher reliability. By failure analysis we found it is not enough to just monitor the drive train. Therefore we agree to the certifiers demand to monitor also towers, foundations as well as blades. Thus Structural Health Monitoring (SHM) is needed and the paper shows in detail how these measuring points should look like in practice.