LOAD CALCULATION ON WIND TURBINES: VALIDATION OF FLEX5, ALASKA/WIND, MSC.ADAMS AND SIMPACK BY MEANS OF FIELD TESTS

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1 Proceedings of the ASME 214 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 214 August 17-August 2, 214, Buffalo, New York, USA DETC LOAD CALCULATION ON WIND TURBINES: VALIDATION OF FLEX5, ALASKA/WIND, MSC.ADAMS AND BY MEANS OF FIELD TESTS János Zierath W2e Wind to Energy GmbH 1855 Rostock Germany Roman Rachholz Christoph Woernle Chair of Technical Dynamics University of Rostock 1859 Rostock Germany {rachholz, Andreas Müller University of Michigan- Shanghai Jiao Tong University Joint Institute Shanghai China ABSTRACT Load calculations on wind turbines are an essential part of its development. In the preliminary design phase simplified multibody models are used for the estimation of the interface loads. The interface loads are used within an iterative development loop to design the components of the wind turbine such as gearbox, blades, tower and so on. Due to the early application of load calculations within the development process, the quality of the simulation results has a great influence on the wind turbine design. In this contribution the simulation results of the multibody codes, and are compared with measurements obtained from a prototype of a 2.5 MW wind turbine developed by W2e Wind to Energy. Furthermore, simulation results of the special wind turbine design code, developed at the Technical University of Denmark Copenhagen, are taken into account. A statistical and dynamical evaluation of the simulation and measurement results has been done. Due to the use of the same controller procedures as used on the physical wind turbine, the wind turbine models show almost the same behaviour (electrical power, pitch angle, rotor speed) as the wind turbine in the field. Differences occur during the evaluation of the interface loads due to the different kinds of wind turbine modelling. Address all correspondence to this author. INTRODUCTION Load calculations on wind turbines are an essential part of its development. In the preliminary design phase simplified multibody models are used for the estimation of the interface loads. The interface loads are used within an iterative development loop to design the components of the wind turbine such as gearbox, blades, tower and so on. Due to the early application of load calculations within the development process, the quality of the simulation results has a great influence on the wind turbine design. This contribution describes the development of a state-ofthe-art multibody model of a 2.5 MW wind turbine designed by W2e Wind to Energy. The prototype of the wind turbine erected in Tarnow, Mecklenburg-Western Pomerania, Germany, is shown in Fig. 1. As it can be seen, the wind turbine is a typical horizontal axis design with three blades. It has a double-fed asynchronous generator. The prototype has a tubular tower and a nominal hub height of 1 m. The nominal rotor diameter of the turbine is 93 m. A special drive train concept was developed for the wind turbine, see Fig. 1b. Instead of the typical three-point mounting of the drive train which is industrial standard, the rotor is mounted by a moment bearing well known from tunnel construction machinery. The gearbox is fixed at the position of its centre of gravity by a ring mounting consisting of elastic bushings. In addition the gearbox is also coupled to the rotor by elastic bush- 1 Copyright c 214 by ASME

2 multibody model with the aerodynamic code and the controller is presented. Then, a general description of the different simulation models follows. Interaction Scheme of the Multibody Program with the Aerodynamic Code and the Controller The simplified interaction scheme of the multibody simulation with the aerodynamic code and the controller of the wind turbine is shown in Fig. 2. a position and velocity of blade elements generator speed, pitch angle Aerodynamic Code Multibody Code Controller b FIGURE 1. PROTOTYPE OF THE 2.5 MW WIND TURBINE ERECTED IN TARNOW, MECKLENBURG-WESTERN Pomerania, GERMANY. a PROTOTYPE. b CAD-MODEL OF THE DRIVE TRAIN ings. Both elastic mountings behave like an universal joint. As result of the moment bearing and the elastic bushings, no bending moments and shear forces act on the gearbox expanding its durability. For validiation, different programs are chosen to build up a wind turbine model. Beside the special purpose program the general purpose 212 x64 [1], alaska/wind 8.3 x64 [2] and 9.3 x64 [3] were chosen to build up the wind turbine model. The aerodynamic forces are applied within and using the AeroDyn source code v13.1 developed by NREL [4, 5], whereas and use their own aerodynamic modules. In contrast to [6], the aim of this contribution is not to propose one program as a reference but to compare all programs with measurements on the prototype. THE MULTIBODY MODEL AND ITS INTERACTION WITH THE AERODYNAMIC CODE AND THE CONTROLLER The aim of this section is to describe the multibody model and its interaction to other codes which are necessary to simulate an overall wind turbine model. First, the interaction of the aerodynamic forces and torques on blade generator torque, pitch velocity FIGURE 2. SIMPLIFIED INTERACTION SCHEME OF THE WIND TURBINE MODEL A discrete interface was developed for the interaction of the controller with the multibody program. The aim of this interface is to integrate the same controller software into the multibody simulation as implemented on the physical wind turbine. The interaction scheme represents a software-in-the-loop principle and was developed in analogy to the hardware-in-the-loop principle described in [7]. The multibody program contacts the controller at discrete time steps and waits until the controller provides the corresponding output data. Due to the fact that the integrator of the multibody program generally has a variable step size, the interface has to be realised in such a way that the controller is contacted only at prescribed constant time steps. The controller on the physical wind turbine operates with a cycle time of 1 ms, which is also chosen as prescribed time step for the interface. Between the discrete cycle time the output values of the previous time steps are used and kept constant. This interface scheme does not present any real-time capabilities which is, however, not necessary and not realisable for large simulation models. The multibody model also interacts with the aerodynamic code. The aerodynamic code used in was developed at Danish Technical University and is integrated directly into the multibody code. Within the aerodynamic code is also integrated into the multibody code and was developed at the Institute of Mechatronics in Chemnitz, Germany. The aerodynamic code used in and Adams is based on Aero- 2 Copyright c 214 by ASME

3 Dyn provided by the National Renewable Energy Laboratories (NREL). The aerodynamic codes include a calculation based on the blade element momentum theory. For this purpose, the blade is divided into separate aerodynamic elements. As shown in Fig. 2, the multibody code provides the position and velocity of the blade elements. The aerodynamic code provides the aerodynamic forces and moments. In addition, the aerodynamic code from NREL is extended by the general dynamic wake theory which is based on the acceleration potential theory, see [8]. Furthermore, provides an interface to the aerodynamic code from ECN based on the lifting line theory, see [9]. For comparison of the results of the multibody codes used, the blade element momentum theory is applied within this research work only. Simple Multibody Model of the Wind Turbine in The model has a fixed topology comprising overall 28 degrees of freedom as shown in Fig. 3. Parametric Multibody Model of the Wind Turbine in The multibody model in is parametrically built up. That means, instead of defining the model within the Adams/View preprocessing environment, the model is created within the MATLAB environment. The Matlab code generates an Adams command file in the ASCII format, which can be imported by Adams/View. The same principles were also applied for model generation of the high-lift mechanisms of a modern transport aircraft, see [1]. discrete beam blade model detailed drive train model y h Mode 1 x Mode 2 z Mode Description 1-6 Tower Foundation 7-8 Tower bending thrust direction 9-1 Tower bending side-side 11 Tower top yaw 12 Tower top tilt 13 Rotation of main shaft 14 Bending of main shaft x-axis Bending of main shaft y-axis 16 1st flapwise mode of blade nd flapwise mode of blade st edgewise mode of blade nd edgewise mode of blade 1 2 1st flapwise mode of blade nd flapwise mode of blade st edgewise mode of blade nd edgewise mode of blade st flapwise mode of blade nd flapwise mode of blade st edgewise mode of blade nd edgewise mode of blade 3 28 Torsion of main shaft FIGURE 3. DEGREES OF FREEDOM OF THE FLEX5 WIND TURBINE MODEL Within this given topology, the model of a specific wind turbine is defined by a fixed set of parameters. A general parameter file contains, above all, the geometric parameters, the load case parameters, a tower parameter file, and two parameter files for the blade containing the mechanical and aerodynamic properties. An implementation of another topology of the model is possible by a modification of the computer code only. The elasticity of the blade and the tower is represented by a superposition of the first two modes in the two independent directions, respectively. The degrees of freedom can be switched off independently within the general parameter file. Due to the small number of degrees of freedom, the calculation time is very short. A typical run of a ten minute time series with turbulent wind conditions on an Intel Core i7-26 takes about one minute. modal based tower model FIGURE 4. THE MULTIBODY MODEL OF THE WIND TURBINE USING MSC.ADAMS The Adams model comprises a flexible tower model based on a finite element model, blades built up of discrete beams and a detailed drive train model, see [11]. The discrete beams consist of lumped mass elements and EULER-BERNOULLI beams. Compared to a blade model consisting of flexible bodies, a higher numerical stability of discrete beams in during startup of the wind turbine could be achieved. Furthermore, effects like centrifugal stiffness are taken into account, and the interface loads along the blade can be obtained easily. As a result, a multibody model with approximately 6 degrees of freedom is obtained, see Fig. 4. The higher model depth of the simulation leads to larger CPU times compared to. The simulation of a ten minute time series with turbulent wind conditions on an Intel Core i7-26 takes about 2 minutes. Structured Multibody Model of the Wind Turbine in The multibody model within is structured into submodels. A typical model comprises submodels of the foundation, the tower, the nacelle, the yaw drive, the pitch drive, the rotor (hub and blades), the drive train, the generator and the controller. Due to a source-target-concept, the submodels can be exchanged easily. This is an appropriate way, for example, to integrate a detailed drive train model. The model is shown in Fig Copyright c 214 by ASME

4 modal based blade model time. As a result, the wind turbine model consists of 44 degrees of freedom, see Fig. 6. detailed drive train model detailed drive train model modal based tower model modal based blade model FIGURE 5. THE MULTIBODY MODEL OF THE WIND TURBINE USING ALASKA/WIND The blades and the tower are generated using the input filter of the Workbench, resulting in a modal representation of the flexible components. The model comprises different types of drive trains. The most simple drive train model consists of two masses only coupled via a torsional spring damper element. The spring damper element is parametrised according to the first eigenfrequency of the drive train. Also a detailed drive train model similar to the Adams and Simpack model, see [11], was implemented. The model with the simple drive train has 21 degrees of freedom, the detailed drive train model has 44 degrees of freedom. The simulation of a ten minute time series with turbulent wind conditions on an Intel Core i7-26 with the simple drive train model takes about 6 minutes, with the detailed drive train model about 13 minutes. Flexible Multibody Model of the Wind Turbine in SIM- PACK The detailed multibody model of the 2.5 MW wind turbine developed in 8.93b is described in [11]. For the results shown in this contribution, a revised model built up in 9.3 is used. For comparison with the and alaska/wind models, the tower and the blades are modelled elastically. A detailed drive train model including two planetary gear stages and a spur gear stage is integrated, comprising torsional stiffness of shafts and the contact-stiffness of interacting gears. Blades, tower, and drive train are substructures within the main model. By this, they can be easily exchanged in order to simulate different wind turbine designs. In order to gain comparable results in accordance to measurements at the wind turbine in the field, the original controller from the real wind turbine is implemented using an interface. The flexible bodies are based on a finite element formulation. The tower consists of solids and TIMOSHENKO beam elements. Additionally lumped masses are used. The blades are modelled by TIMOSHENKO beam elements. Modal superposition techniques are used to reduce the number of degrees of freedom of the finite element models and to speed up simulation modal based tower model FIGURE 6. THE MULTIBODY MODEL OF THE WIND TURBINE USING For simulating different load cases time efficiently, an open source code script developed by and refined for the 2.5 MW wind turbine is used. A ten minute time series with turbulent wind conditions takes approximately minutes on an Intel Core i COMPARISON OF SIMULATIONS AND MEASURE- MENTS A very important aspect is the experimental validation of the simulations which are also needed for type certification of the wind turbine. Therefore, the prototype of the wind turbine is equipped with numerous measurement sensors, e.g. strain gages at the blade root, in the tower or at the low speed shaft, see Fig. 7a. In addition, a measurement mast equipped with wind vanes and cup anemometers is built up in front of the wind turbine, see Fig. 7b. The aim of this research work is not to establish one of the simulation environments as a reference but to compare equivalent models developed by means of the simulation packages with the measurement results. The objective is to evaluate the different modelling concepts used in the packages for wind turbine simulation. In contrast to this method, other research projects validate their program development for wind turbine simulation by comparison to generally accepted design codes, see [6]. The differences in model generation and build-up of the equations of motion lead to difficulties in the direct comparison of the design codes. In the author s opinion, it is more meaningful to evaluate each program by comparing the numerical results with real measurements. Hence, the scatter plots in the next sections compare the simulations of,, and SIM- PACK with measurements from the prototype of the wind turbine. 4 Copyright c 214 by ASME

5 a encapsulated Strain Gage a comparison of the dynamic loads using rainflow counting procedures, see [12]. The load cycles are estimated for the product life cycle with respect to the wind distribution in the wind class GL IIa according to the GL guideline [13]. Electrical Power (Power Curve) The power curve is important for the economics of a wind turbine. High earnings especially in the part-load operational range leads to a fast return of invest which is requested by the operators of wind farms. The maximum, minimum and mean electrical power of the,, and simulations compared to the measurement results are shown in Fig. 8. The diagrams show a very good agreement of simulations with,, and compared measurements. The use of the same controller on the prototype and within the simulations contributes to this result. b Measurement Mast Wind Turbine FIGURE 7. MEASUREMENT SETUP OF THE WIND TURBINE. a STRAIN GAGE AT THE BLADE ROOT. b PROTOTYPE OF THE 2.5 MW WIND TURBINE AND MEASUREMENT MAST The continuous time series obtained from the measurements are split up into ten minute time series in analogy to the simulated time series. The resulting time series are classified with respect to mean wind speed and the turbulence intensity of the wind. To compare simulations and measurements, statistical evaluations of the calculated and measured results are done, as it is difficult to transfer the wind conditions from the measurement to the simulations. The statistical values used for comparison are the minimum, maximum, mean value and standard deviation. All calculations and measurements are done with a turbulence intensity of 1 %. For statistical confidence, the calculations are done with different wind seeds. A comparison of all measured interface loads and operating values is not possible within this paper. For comparison of the wind turbine behaviour, the measured and calculated electrical power, pitch angle and rotor speed are chosen. To evaluate the simulated loads the bending moments at blade root and the tilt bending moment at tower base are compared. The vertical green line within the statistical diagrams denotes the rated wind speeds. Because the predominant loads are applied on the blades, the bending moments at the blade root are chosen for Pitch Angle The pitch angle shows the functionality of the controller, especially of the pitch controller above rated wind speed. In Fig. 9, the maximum, minimum and mean pitch angle of blade 1 of the,, and simulations are shown in comparison to the measurement results. The diagrams show a very good agreement of simulations with compared to measurements. The simulation results (maximum and mean value) using, and lie above the measured curves. It can be noticed that the slope of the simulated mean values is slightly steeper compared to the measurements. The use of the same controller on the prototype and within the simulations contributes to the good agreement of simulation and measurements. Rotor Speed Another method to check the working principle of the controller is the comparison of the rotor speed n Rotor = 3ω Rotor /π. The maximum, minimum and mean rotor speed of the,, and simulations compared to the measurement results are shown in Fig. 1. As it can be seen in Fig. 1, the mean values of simulation and measurement agree very well around rated wind speed. The maximum values around rated wind speed lie above the measured values using, and. For the rotor speed the best agreement between simulation and measurement is obtained using the code. 5 Copyright c 214 by ASME

6 P - [kw] 1 Theta - [ ] P - [kw] Theta - [ ] P - [kw] Theta - [ ] P - [kw] Theta - [ ] FIGURE 8. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE ELECTRICAL POWER FIGURE 9. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE PITCH ANGLE ϑ 1 6 Copyright c 214 by ASME

7 n Rotor - [rpm] Flapwise Bending Moment at the Blade Root The flapwise bending moment at the blade root, see Fig. 11, is caused by the lift of the aerodynamic profile of the blade. The maximum, minimum, and mean flapwise bending moment at the blade root as well as the corresponding standard deviation of the,, and simulations compared to the measurement results are shown in Fig M flap wind direction n Rotor - [rpm] n Rotor - [rpm] n Rotor - [rpm] FIGURE 1. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE ROTOR SPEED FIGURE 11. DEFINITION OF THE FLAPWISE BENDING MO- MENT AT THE BLADE ROOT The direction of the moment M flap acting on the cut free blade and the wind direction in Fig. 11 indicate that the values of the bending moment are negative. The mean values obtained from the simulations with und with the measurements show a better agreement compared to the and simulations. Especially, this is seen at rated wind speed, that means around 1-11 m/s. However, the absolute values from the and simulations exceed those from the measurements, indicating that the simulations lead to conservative load estimations. Beside the statistical evaluation of flapwise bending moment at the blade root, a dynamic evaluation has been done. Therefore, the rainflow matrix is estimated from the time series of the flapwise bending moment. The flapwise bending moment is strongly influenced by the turbulence of the wind. The rainflow matrices from the simulations are shown in Fig. 13. The rainflow matrices show a large number of load cycles at a small load range fora broad range of mean values. The corresponding rainflow matrix of the measurements is presented in Fig. 14. Due to the stochastic behaviour of the wind during measurements and the use of different wind simulators during the simulations, a qualitative comparison of the rainflow matrices is difficult. Also a quantitative comparison is not appropriate because of the discrete classification during the rainflow counting procedure. To circumvent these problems, the load cycles are summed over each load range class neglecting their mean values. Subsequently, the load cycles are accumulated in that way that load cycles with a large load range comprises all load cycles with smaller load ranges. The corresponding diagrams of the load range vs. accumulated load cycles are shown in Fig.. As it can be seen from Fig., the simulations using show a non-conservative behaviour for large load ranges com- 7 Copyright c 214 by ASME

8 MBBl1 flap MBBl1 flap MBBl1 flap MBBl1 flap FIGURE 12. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE FLAPWISE BENDING MOMENT AT THE BLADE ROOT FIGURE 13. SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COMPARISON OF THE DY- NAMIC VALUES (RAINFLOW MATRIX) OF THE FLAPWISE BENDING MOMENT AT THE BLADE ROOT 8 Copyright c 214 by ASME

9 Edgewise Bending Moment at the Blade Root The edgewise bending moment at the blade root, see Fig. 16, is mainly caused by the dead weight of the blade. Furthermore, the loads of the dead weight of the blade are superposed by dynamical mass effects and aerodynamic loads due to the lift of the blade. The maximum, minimum, and mean edgewise bending moment at the blade root of the,, and simulations compared to measurement results are shown in Fig. 17. M edge wind direction FIGURE 14. RAINFLOW MATRIX OF MEASUREMENT OF THE FLAPWISE BENDING MOMENT AT THE BLADE ROOT FIGURE 16. DEFINITION OF THE EDGEWISE BENDING MO- MENT AT THE BLADE ROOT Load Range - MBBl1 flap Load Ranges vs. accumulated Load Cycles for Comparison Measurement Adams Number of accumulated Cycles FIGURE. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE DYNAMIC VALUES (LOAD RANGE VS. ACCU- MULATED LOAD CYCLES) OF THE FLAPWISE BENDING MO- MENT AT THE BLADE ROOT The comparison of simulations and measurement show some differences in the statistical values. A possible uncertainty is the calibration of the strain gages at the blade root. The sensors are calibrated by the dead weight and a slow revolution of the wind turbine. Typically, the wind turbine coasts freely during calibration. Due to the strong influence of the dead weight, the rainflow matrix has a typical characteristic. The rainflow matrices of the simulations in Fig. 18 and the rainflow matrix of the measurement in Fig. 19 show three peaks within all diagrams. The single peak in the higher load range is caused by the first order static moment of the blade and the revolutions of the wind turbine during its life cycle. However, the comparison of the load range vs. the accumulated load cycles in Fig. 2 show a conservative behaviour of all simulations for the edgewise bending moment compared to measurements. It can be seen that large loads act on the wind turbine with more than load cycles during its product life cycle. pared to measurements. In contrast the comparison of simulations using, and and measurements show a good agreement or conservative behaviour for dynamic loads over the whole accumulated load cycle range. The results obtained using are the most conservative ones compared to the other simulation packages. 9 Copyright c 214 by ASME

10 MBBl1 edge MBBl1 edge MBBl1 edge MBBl1 edge FIGURE 17. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE EDGEWISE BENDING MOMENT AT THE BLADE ROOT FIGURE 18. SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COMPARISON OF THE DY- NAMIC VALUES (RAINFLOW MATRIX) OF THE EDGEWISE BENDING MOMENT AT THE BLADE ROOT 1 Copyright c 214 by ASME

11 M tilt wind direction FIGURE 21. DEFINITION OF THE TILT BENDING MOMENT AT THE TOWER BASE packages provide a very good agreement compared to the measurements. The large influence of the rotor thrust results in same characteristics of flapwise bending moment and tilt bending moment at tower base. The best agreement between measurement and simulation regarding maximum, minimum and mean values are achieved using. FIGURE 19. RAINFLOW MATRIX OF MEASUREMENT OF THE EDGEWISE BENDING MOMENT AT THE BLADE ROOT Load Range - MBBl1 edge Load Ranges vs. accumulated Load Cycles for Comparison Measurement Adams Number of accumulated Cycles FIGURE 2. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE DYNAMIC VALUES (LOAD RANGE VS. ACCU- MULATED LOAD CYCLES) OF THE EDGEWISE BENDING MO- MENT AT THE BLADE ROOT Tilt Bending Moment at the Tower Base The tilt bending moment at the tower base, see Fig. 21, is mainly caused by the thrust of the rotor. Also some dynamic effects of the mass of the nacelle and the rotor affects the tilt bending moment at the tower base. The maximum, minimum, and mean tilt bending moment at the tower base of the,, and simulations compared to measurement results are shown in Fig. 22. Due to the fact that the wind turbine almost behaves like a cantilever beam with a single mass at its end, all simulation CONCLUSION The present contribution compares the multibody codes,, alaska/wind and with measurements done on a prototype of 2.5 MW wind turbine developed by W2e Wind to Energy. The comparisons show in general a good agreement for all simulation packages. Hereby, the simulations use the same controller software as implemented on the physical wind turbine. The loads at blade root and tower base show some differences between simulation and measurements. The main loads act on the rotor of the wind turbine and thus on the blade root. The best agreements are obtained using the discrete beam model within, which includes nonlinear effects like large deformations and centrifugal stiffness effects. The -like blade models in and produces conservative results compared to the measurements. The behaviour of the model are the basis of ongoing investigations within a cooperation of W2e Wind to Energy and the Institute of Mechatronics in Chemnitz, Germany. An important aspect beyond the results is the usability of the general purpose multibody programs. Within a fixed topology model like the user parametrises a wind turbine model only. General purpose multibody programs provide a lot of modelling features but need an extensive knowledge in multibody modelling. The number of model errors and uncertainties may also increase by the number of degrees of freedom of the model. A guided model buildup could support the user. A very good example is the Workbench. provides an example model of the generic NREL wind turbine which can be adapted to a specific wind turbine model. The ADWIMO module for provided by MSC.Software has not been tested so far. Instead, the model buildup and load case generation for the Adams wind turbine model has been done by a user-written MATLAB script. 11 Copyright c 214 by ASME

12 MBTwr tilt MBTwr tilt The most important aspect in the simulation of mechatronic systems is the integration of the controller. The integration of the same controller software as on the physical wind turbine increases the quality of the simulation results and helps to avoid possible errors in the controller design. Among the programs tested within this study, is the only program which provides a free programmable discrete controller interface in C++. and also provide extension capabilities using FORTRAN, but a discrete controller interface has to be created by the user. This possibly requires the need of extensive technical support. All general purpose multibody programs tested have their pros and cons. But nevertheless, a transition from specific wind turbine calculation tools such as and BLADED to general multibody programs is an appropriate way to develop the wind turbine of the future. It enables a closer look into the dynamical behaviour of the wind turbine leading to an extensive understanding and an advanced design of wind turbines. ACKNOWLEDGMENT The authors would like to thank the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety for supporting this research. MBTwr tilt MBTwr tilt FIGURE 22. MEASUREMENT AND SIMULATIONS WITH FLEX5, MSC.ADAMS, ALASKA/WIND AND : COM- PARISON OF THE STATISTICAL VALUES (MAXIMUM, MINI- MUM, MEAN VALUE) OF THE TILT BENDING MOMENT AT THE TOWER BASE REFERENCES [1] MSC.SOFTWARE, 212. Adams 212.2: Adams 212 Online Help. Tech. rep., MSC Software Corporation, Santa Ana, California. [2] INSTITUTE OF MECHATRONICS, 213. alaska 8: Modelling and Simulation of mechatronic Systems - Users Guide. Tech. rep., Institute of Mechatronics, Chemnitz, Germany. [3], 213. Simpack v9.3: Documentation to Simpack. Tech. rep., Simpack AG, Gilching, Germany. [4] LAINO, D. J., and HANSEN, A. C., 22. AeroDyn v12.5: User s Guide. Tech. rep., Windward Engineering (Prepared for the National Renewable Energy Laboratory), Salt Lake City. [5] JONKMAN, B. J., and JONKMAN, J. M., 213. Addendum to the User s Guides for FAST, A2AD, and AeroDyn Released March 21 - February 213. Tech. rep., National Renewable Energy Laboratory, Golden, Colorado. [6] TAUBERT, M., CLAUSS, S., FREUDENBERG, H., KEIL, A., MÄRZ, M., MOSER, W., and WULF, H. O., 211. Wind Turbine Design Codes: Eine Validierung von mit BLADED, FAST und FLEX5. Tech. rep., Institut für Mechatronik, Chemnitz. [7] WOERNLE, C., KAEHLER, M., RACHHOLZ, R., HER- RMANN, S., ZIERATH, J., SOUFFRANT, R., and BADER, R., 21. Robot-Based HiL Test of Joint Endoprosthe- 12 Copyright c 214 by ASME

13 ses. In Lenarcic, J. (Eds.): Advances in Robot Kinematics: Analysis and Control, Springer. [8] SUZUKI, A., 2. Application of Dynamic Inflow Theory to Wind Turbine Rotors. PhD thesis, Department of Mechanical Engineering, University of Utah, Salt Lake City. [9] VAN GARREL, A., 23. Development of a Wind Turbine Aerodynamics Simulation Module. Tech. rep., ECN Wind Energy, Petten, The Netherlands. [1] ZIERATH, J., WOERNLE, C., and HEYDEN, T., 29. Elastic multibody models of transport aircraft high-lift mechanisms. AIAA Journal of Aircraft, 46(5), pp [11] RACHHOLZ, R., WOERNLE, C., and ZIERATH, J., 212. Dynamics of a Controlled Flexible Multi-body Model of a 2 MW Wind Turbine. In Proceedings of the 2nd Joint International Conference on Multibody System Dynamics - IMSD, Stuttgart. [12] KÖHLER, M., JENNE, S., PÖTTER, K., and ZENNER, H., 212. Zählverfahren und Lastannahme in der Betriebsfestigkeit (German Edition). Springer, Berlin. [13] GERMANISCHER LLOYD, 21. Guideline for the Certification of Wind Turbines, Edition 21. Germanischer Lloyd, Hamburg. 13 Copyright c 214 by ASME