Thomas Buhl - Academia.edu (original) (raw)
Papers by Thomas Buhl
The aeroelastic response of wind turbines is often simulated in the time domain using indicial re... more The aeroelastic response of wind turbines is often simulated in the time domain using indicial response techniques. Unsteady aerodynamics in attached flow are usually based on Jones's approximation of the flat plate indicial response, although the response for finite-thickness airfoils differs from the flat plate one. The indicial lift response of finite-thickness airfoils is simulated with a panel code, and an empirical relation is outlined connecting the airfoil indicial response to its geometric characteristics. The effects of different indicial approximations are evaluated on a 2D profile undergoing harmonic pitching motion in the attached flow region; the resulting lift forces are compared to CFD simulations. The relevance for aeroelastic simulations of a full wind turbine is also evaluated, and the effects are quantified in terms of variations of equivalent fatigue loads, ultimate loads, and stability limits. The agreement with CFD computations of a 2D profile in harmonic motion is improved by the indicial function accounting for the finite-thickness of the airfoil. Concerning the full wind turbine aeroelastic behavior, the differences between simulations based on Jones's and finite-thickness indicial response functions are rather small; Jones's flat-plate approximation results in only slightly larger fatigue and ultimate loads, and lower stability limits.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
The key objective of this paper is to investigate the frequency of normal shutdowns to be used in... more The key objective of this paper is to investigate the frequency of normal shutdowns to be used in the design stage of wind turbines, based on measurements at an offshore wind farm and thereby quantify their impact on the fatigue loads on the drivetrain and tower top. The measured shut-downs observed on a fully instrumented multi megawatt wind turbine located in an offshore wind farm are correlated with corresponding observations of shutdowns on surrounding wind turbines. The observed wind turbines have multiple shut-downs at high mean wind speeds. The normal shutdown is brought about by initiating blade pitching to feather and also sometimes using the generator torque as a brake mechanism. The shutdowns due to wind speed variation near cut-out are predicted using an Inverse First Order Reliability Model (IFORM) whereby an expected annual frequency of normal shutdowns at cut-out is put forth. A simulation model of the wind turbine is set up in the aeroelastic software HAWC2, based on...
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Wind Energy, 2010
... Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gaug... more ... Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gauge sensors Peter Bjoern Andersen, Lars Henriksen, Mac Gaunaa, Christian Bak and Thomas Buhl Wind Energy Department, Risø DTU National Laboratory for Sustainable Energy ...
All stability and simulation tools developed and used in the STABCON project are listed in the "F... more All stability and simulation tools developed and used in the STABCON project are listed in the "Final Technical Report" of the STABCON project with notes on their availability.
IEEE Transactions on Control Systems Technology, 2013
This paper presents the load reduction achieved with trailing edge flaps during a full-scale test... more This paper presents the load reduction achieved with trailing edge flaps during a full-scale test on a Vestas V27 wind turbine. The trailing edge flap controller is a frequencyweighted linear model predictive control (MPC) where the quadratic cost consists of costs on the zero-phase filtered flapwise blade root moment and trailing edge flap deflection. Frequencyweighted MPC is chosen for its ability to handle constraints on the trailing edge flaps deflection, and to target at loads with given frequencies only. The controller is first tested in servoaeroelastic simulations, before being implemented on a Vestas V27 wind turbine. Consistent load reduction is achieved during the full-scale test. An average of 13.8% flapwise blade root fatigue load reduction is measured.
Journal of Ocean and Wind Energy, 2016
This paper investigates the frequency of normal shutdowns to be used in the design stage of wind ... more This paper investigates the frequency of normal shutdowns to be used in the design stage of wind turbines based on measurements at an offshore wind farm and seeks to quantify their impact on the fatigue loads on the drivetrain and tower top. The measured shutdowns observed on an instrumented multi-megawatt wind turbine located at an offshore wind farm are correlated with corresponding observations of shutdowns on surrounding wind turbines. The observed wind turbines have multiple shutdowns at high mean wind speeds due to wind speed variations near cutout. Through the use of an Inverse First Order Reliability Model (IFORM), the expected annual frequency of normal shutdowns at cutout is put forth. A simulation model of the wind turbine is set up in the aeroelastic software HAWC2 based on which observed shutdowns are simulated along with normal operation. The simulated tower top moments are compared with the measured loads, thereby quantifying the amplification in the loads due to the shutdown action. The IFORM-determined frequency of shutdowns at cutout mean wind speed is used as an input to the fatigue load computations in the drivetrain, by which the resulting damage equivalent loads (DELs) are analyzed to quantify their coefficient of variation for varying site-specific wind conditions under both normal operation and with shutdowns.
EWEA Offshore 2015 – Copenhagen – 10-12 March 2015 The potential for structural optimization of t... more EWEA Offshore 2015 – Copenhagen – 10-12 March 2015 The potential for structural optimization of the bucket foundation’s outer stiffeners is investigated using the commercial optimization software Tosca Structure. Results show that shape optimization of the initial design can reduce stress concentrations by 38%. Additionally, topology optimization has led to a new design concept with a mass reduction of 25% when compared to the initial design. A bucket foundation design has been provided by Universal Foundation A/S and is modelled using the finite element software Abaqus. The model assumes fixed boundary conditions at the skirt (thereby neglecting soil interactions) and is loaded with an extreme static horizontal load at the top of the shaft. Both shape and topology optimization problems are then developed and solved using Tosca Structure. Shape Optimization
— Trailing Edge Flaps on wind turbine blades have been studied in order to achieve fatigue load r... more — Trailing Edge Flaps on wind turbine blades have been studied in order to achieve fatigue load reduction on the turbine components. We show in this paper how Model Predictive Control can be used to do frequency weighted control of the trailing edge flaps in order to reduce fatigue damage on the blade root. The design model is based on a modal model of the blade structure and a steady state aerodynamic model of the blade airfoils. Depending on the output filter, loads within different frequency range are decreased. A fine tuning of the Kalman filter and of the cost function allows to decrease significantly the blade root loads without damaging excessively the trailing edge flap actuators. I.
The objective of the present work is to present the latest results in effects of including large ... more The objective of the present work is to present the latest results in effects of including large blade deflections in aeroelastic calculations and to quantify the errors of the linearized approach for a modern flexible mega-watt sized turbine. In this paper three nonlinear approaches have been used to quantify the effects of large deflections. One approach is a rather simple extension of the already existing aeroelastic code HAWC, which changes the calculation basis so that small deflections are assumed around an initially large deflected blade shape. The second approach is based on a multibody formulation of the beam element used in HAWC, where nonlinear effects are included as a result of modelling the blade using several interconnected bodies. The third approach is a corotational finite element formulation where each element can be regarded as linear and the nonlinear effects are included by translation and rotation of the local element coordinate system. The results from the thr...
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This report is a collection of the measurements carried out on the TH-6R actuator from Face Inter... more This report is a collection of the measurements carried out on the TH-6R actuator from Face International Co. The work is a part of the ADAPWING project, which aims at developing a method to alleviate some of the fluctuating response of a wind turbine by using adaptive ...
The aeroelastic response of wind turbines is often simulated in the time domain using indicial re... more The aeroelastic response of wind turbines is often simulated in the time domain using indicial response techniques. Unsteady aerodynamics in attached flow are usually based on Jones's approximation of the flat plate indicial response, although the response for finite-thickness airfoils differs from the flat plate one. The indicial lift response of finite-thickness airfoils is simulated with a panel code, and an empirical relation is outlined connecting the airfoil indicial response to its geometric characteristics. The effects of different indicial approximations are evaluated on a 2D profile undergoing harmonic pitching motion in the attached flow region; the resulting lift forces are compared to CFD simulations. The relevance for aeroelastic simulations of a full wind turbine is also evaluated, and the effects are quantified in terms of variations of equivalent fatigue loads, ultimate loads, and stability limits. The agreement with CFD computations of a 2D profile in harmonic motion is improved by the indicial function accounting for the finite-thickness of the airfoil. Concerning the full wind turbine aeroelastic behavior, the differences between simulations based on Jones's and finite-thickness indicial response functions are rather small; Jones's flat-plate approximation results in only slightly larger fatigue and ultimate loads, and lower stability limits.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
The key objective of this paper is to investigate the frequency of normal shutdowns to be used in... more The key objective of this paper is to investigate the frequency of normal shutdowns to be used in the design stage of wind turbines, based on measurements at an offshore wind farm and thereby quantify their impact on the fatigue loads on the drivetrain and tower top. The measured shut-downs observed on a fully instrumented multi megawatt wind turbine located in an offshore wind farm are correlated with corresponding observations of shutdowns on surrounding wind turbines. The observed wind turbines have multiple shut-downs at high mean wind speeds. The normal shutdown is brought about by initiating blade pitching to feather and also sometimes using the generator torque as a brake mechanism. The shutdowns due to wind speed variation near cut-out are predicted using an Inverse First Order Reliability Model (IFORM) whereby an expected annual frequency of normal shutdowns at cut-out is put forth. A simulation model of the wind turbine is set up in the aeroelastic software HAWC2, based on...
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Wind Energy, 2010
... Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gaug... more ... Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gauge sensors Peter Bjoern Andersen, Lars Henriksen, Mac Gaunaa, Christian Bak and Thomas Buhl Wind Energy Department, Risø DTU National Laboratory for Sustainable Energy ...
All stability and simulation tools developed and used in the STABCON project are listed in the "F... more All stability and simulation tools developed and used in the STABCON project are listed in the "Final Technical Report" of the STABCON project with notes on their availability.
IEEE Transactions on Control Systems Technology, 2013
This paper presents the load reduction achieved with trailing edge flaps during a full-scale test... more This paper presents the load reduction achieved with trailing edge flaps during a full-scale test on a Vestas V27 wind turbine. The trailing edge flap controller is a frequencyweighted linear model predictive control (MPC) where the quadratic cost consists of costs on the zero-phase filtered flapwise blade root moment and trailing edge flap deflection. Frequencyweighted MPC is chosen for its ability to handle constraints on the trailing edge flaps deflection, and to target at loads with given frequencies only. The controller is first tested in servoaeroelastic simulations, before being implemented on a Vestas V27 wind turbine. Consistent load reduction is achieved during the full-scale test. An average of 13.8% flapwise blade root fatigue load reduction is measured.
Journal of Ocean and Wind Energy, 2016
This paper investigates the frequency of normal shutdowns to be used in the design stage of wind ... more This paper investigates the frequency of normal shutdowns to be used in the design stage of wind turbines based on measurements at an offshore wind farm and seeks to quantify their impact on the fatigue loads on the drivetrain and tower top. The measured shutdowns observed on an instrumented multi-megawatt wind turbine located at an offshore wind farm are correlated with corresponding observations of shutdowns on surrounding wind turbines. The observed wind turbines have multiple shutdowns at high mean wind speeds due to wind speed variations near cutout. Through the use of an Inverse First Order Reliability Model (IFORM), the expected annual frequency of normal shutdowns at cutout is put forth. A simulation model of the wind turbine is set up in the aeroelastic software HAWC2 based on which observed shutdowns are simulated along with normal operation. The simulated tower top moments are compared with the measured loads, thereby quantifying the amplification in the loads due to the shutdown action. The IFORM-determined frequency of shutdowns at cutout mean wind speed is used as an input to the fatigue load computations in the drivetrain, by which the resulting damage equivalent loads (DELs) are analyzed to quantify their coefficient of variation for varying site-specific wind conditions under both normal operation and with shutdowns.
EWEA Offshore 2015 – Copenhagen – 10-12 March 2015 The potential for structural optimization of t... more EWEA Offshore 2015 – Copenhagen – 10-12 March 2015 The potential for structural optimization of the bucket foundation’s outer stiffeners is investigated using the commercial optimization software Tosca Structure. Results show that shape optimization of the initial design can reduce stress concentrations by 38%. Additionally, topology optimization has led to a new design concept with a mass reduction of 25% when compared to the initial design. A bucket foundation design has been provided by Universal Foundation A/S and is modelled using the finite element software Abaqus. The model assumes fixed boundary conditions at the skirt (thereby neglecting soil interactions) and is loaded with an extreme static horizontal load at the top of the shaft. Both shape and topology optimization problems are then developed and solved using Tosca Structure. Shape Optimization
— Trailing Edge Flaps on wind turbine blades have been studied in order to achieve fatigue load r... more — Trailing Edge Flaps on wind turbine blades have been studied in order to achieve fatigue load reduction on the turbine components. We show in this paper how Model Predictive Control can be used to do frequency weighted control of the trailing edge flaps in order to reduce fatigue damage on the blade root. The design model is based on a modal model of the blade structure and a steady state aerodynamic model of the blade airfoils. Depending on the output filter, loads within different frequency range are decreased. A fine tuning of the Kalman filter and of the cost function allows to decrease significantly the blade root loads without damaging excessively the trailing edge flap actuators. I.
The objective of the present work is to present the latest results in effects of including large ... more The objective of the present work is to present the latest results in effects of including large blade deflections in aeroelastic calculations and to quantify the errors of the linearized approach for a modern flexible mega-watt sized turbine. In this paper three nonlinear approaches have been used to quantify the effects of large deflections. One approach is a rather simple extension of the already existing aeroelastic code HAWC, which changes the calculation basis so that small deflections are assumed around an initially large deflected blade shape. The second approach is based on a multibody formulation of the beam element used in HAWC, where nonlinear effects are included as a result of modelling the blade using several interconnected bodies. The third approach is a corotational finite element formulation where each element can be regarded as linear and the nonlinear effects are included by translation and rotation of the local element coordinate system. The results from the thr...
Download Resource Page. You have no right to access this resource. Try to login and try again.
This report is a collection of the measurements carried out on the TH-6R actuator from Face Inter... more This report is a collection of the measurements carried out on the TH-6R actuator from Face International Co. The work is a part of the ADAPWING project, which aims at developing a method to alleviate some of the fluctuating response of a wind turbine by using adaptive ...