Bredmose, Henrik

Larsen, Torben J.

Verelst, David Robert

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 20, 2017Experiences with the Poseidon measurement campaign and moreLarsen, Torben J.; Verelst, David Robert; Bredmose, HenrikPublication date:2012Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Larsen, T. J., Verelst, D. R., & Bredmose, H. (2012). Experiences with the Poseidon measurement campaignand more [Sound/Visual production (digital)]. Experts Meeting on Computer Code Validation for Offshore WindSystem Modeling, Boulder, CO, United States, 15/05/2012Experiences with the Poseidon measurement campaign and more Torben J. Larsen,  David Verelst, Henrik Bredmose  DTU Wind Energy tjul@dtu.dk    Experts Meeting on Computer Code Validation for Offshore Wind System Modeling Millennium Harvest House Hotel Boulder, Colorado May 15-16, 2012 DTU Wind Energy, Technical University of Denmark Poseidon, by  • Wave energy platform (demo project), 37m wide • Three Gaia 11kW turbines mounted • A turret mooring system with three lines are applied DTU Wind Energy, Technical University of Denmark The Gaia 11kW turbine • 2 Bladed stall regulated wind turbine • Asynchronous generator • Down wind configuration • Passive yaw (stick-slip) • Teeter mechanism in hub to alleviate loads (non-linear spring) DTU Wind Energy, Technical University of Denmark Overview of measurement campaigns 4 4 June 2012 DTU Wind Energy, Technical University of Denmark Show movie Title of the 5 DTU Wind Energy, Technical University of Denmark Location of the Poseidon demonstration platform (discussion) Title of the • The wave energy device needs to be scaled according to the specific wave climate (constant ratio of wave and platform length) • The scale of the demonstration platform fits the waves in the confined Danish water    DTU Wind Energy, Technical University of Denmark Wind and Wave characteristic • Site provides cases with: – Small waves and high wind – Large waves and low wind – Large waves and high wind – Small waves and low wind • Allow for analysis of platform motion and turbine loads in all different operational conditions 21-aug-2008 Title of the 7 Wind Waves  DTU Wind Energy, Technical University of Denmark Experimental setup • Sea state as 20 min statistics (5 min) – Wave height, period and direction – Current speed and direction • Wind characteristic (35 Hz) – Wind speed and direction at hub height (12m) • Platform motion – Inclinometers measuring platform DC pitch and roll (35 Hz) – One 3-axis accelerometers at each of the three turbine foundations (35 Hz) – Platform direction (1 min) • Turbine loads (35 Hz) – Tower bottom and top bending in two directions – Shaft rotating bending and driving torque – Blade root bending in two directions – Yaw, rotor and teeter position – Rotor speed Title of the DTU Wind Energy, Technical University of Denmark Result of second measurement campaign with turbines • Four months of continues operation • Accounting for periods with signal outage and special test campaigns a total of 6799 10 minutes time series are available for analysis  Title of the DTU Wind Energy, Technical University of Denmark Tilt and roll motion of platform DTU Wind Energy, Technical University of Denmark Power spectrum – no turbines Frequencies from DHI: Tilt:  0.146 Hz Roll: 0.203 Hz DTU Wind Energy, Technical University of Denmark Mean Platform pitch and roll Title of the • 10 minutes mean pitch and roll • Very constant in roll • Stepwise behavior of pitch => can be reduced by changed ballast control strategy  DTU Wind Energy, Technical University of Denmark Platform pitch and roll amplitudes Title of the • Absolute value of min and max excursion around mean position for each 10 minutes time series • Pitch in general below 4deg, but up to 8deg are seen • Roll is approx. 2 times lower than pitch  DTU Wind Energy, Technical University of Denmark Effect of wind turbines on platform motion Title of the • Collect periods with no turbines running and periods where at least two turbines are running   DTU Wind Energy, Technical University of Denmark Effect of wind turbines on platform motion Title of the • Collect periods with no turbines running and periods where at least two turbines are running • Fit trend line to data points • Increased pitch activity for small waves • Decreased pitch activity for large waves • Increased roll activity for small waves • No effect at large waves   DTU Wind Energy, Technical University of Denmark Turbine tower fatigue Title of the • Use standard deviation as fatigue indicator • Standard deviation of tower bottom bending versus standard deviation of platform pitch • Wind speeds between 9 and 10 m/s => constant aerodynamic loading • Linear increased tower “fatigue” with increased platform motion  DTU Wind Energy, Technical University of Denmark Turbine blade fatigue Title of the • Standard deviation of blade root bending versus standard deviation of platform pitch • Wind speeds between 9 and 10 m/s => constant aerodynamic loading • Blade loads not affected by platform motion DTU Wind Energy, Technical University of Denmark Comparison at stand still with simulations performed with coupled HAWC2-WAMSIM approach -Floaters not active, turbines at standstill -Hs=0.66m, Tp=3.5s, V=2.5m/s -Incoming wave direction 0deg. -A good agreement is seen, but high frequencies only present in measurements DTU Wind Energy, Technical University of Denmark Comparison during wind turbine operation -Floaters not active, turbines are operating -Hs=0.51m, Tp=3.44s, V=6.4m/s, Vdir=12deg, tint=9% -Incoming wave direction 0deg. -Agreement is not very good, but high frequencies only present in measurements, however 4P signal only present in simulations. DTU Wind Energy, Technical University of Denmark Platform alignment to wind and waves • Yaw errors have been mapped • Operating turbine increases wind alignment • In only one front turbine is present, large misalignment occurs. • A halfwake situation occurs at 24deg. DTU Wind Energy, Technical University of Denmark Model test of a flexible monopile.  New tests at DHI with a rigid and a flexible structure  DTU: Henrik Bredmose Torben J. Larsen Signe Schløer Bo Terp Paulsen    DHI: Flemming Schlütter Jacob T. Sørensen Anders W. Nielsen Zang & Taylor (2010) Experiments at DHI with focused wave groups DTU Wind Energy, Technical University of Denmark Results and brief analysis Irregular JONSWAP waves, unidirectional  Tp=14s Hs=11m  Free surface elevation 0.15m from pile  Measured inline force on pile Acceleration of top point Displacement of top point DTU Wind Energy, Technical University of Denmark Results and brief analysis DTU Wind Energy, Technical University of Denmark Results and brief analysis ‘conti uous’ forci g of 1st n tural mode  from wave-nonlinearity Impulsive load from breaking/          (presumably the force load ce        DTU Wind Energy, Technical University of Denmark Model test of a 3bladed, downwind, passive yaw turbine in the Delft Open-jet wind tunnel  Part of an EU-funded Marie-Curie project WINDFLOWER (3E, DTU-WIN, TUDelft)  Goal is a robust, servicefree medium sized wind turbine for 3rd world countries (100kW range)  Wind tunnel tests at the TU Delft Open Jet Facility (OJF):  Comparing different degrees of blade flexibility, different cone angles  Free yawing, downwind turbine  Comparison HAWC2 simulations with wind tunnel tests 25 DTU Wind Energy, Technical University of Denmark Overview of the OJF test setup   OJF properties: – Nozzle exit section 2x2m – Wind speeds: 3 – 25 m/s  The wind turbine: – Free yawing (tower base), control with wire – Blades made from injected PVC foam, internal glass fiber stiffener – No active RPM control  Measurements: – Rotor speed – Tower base strain FA, SS – Blade strain (flapwise) – Yaw angle – Tip deflection (HS camera) – Electrical power, load side 26 DTU Wind Energy, Technical University of Denmark Rotor design considerations  Full scale starting point (only existing on paper) – 100kW – 24m rotor diameter – Optimal tip speed ratio (TSR): ~ 6 – Typical Reynolds numbers at optimal TSR: •0.50e6 - 1.30e6  Scaled down model: – Rotor diameter < 1.8m (wind tunnel size restriction) – Maintain TSR, consequently optimal RPM's / wind speeds are: •300 RPM @ 4 m/s, 750 RPM @ 10 m/s – Typical Reynolds number similarity is not maintained: •0.10e6 – 0.15e6 – Selected airfoil profiles for which 2D wind tunnel data exists at given Reynolds numbers: NREL S822 and S823 – Maximize blade tip deflection (see next slides) 27 DTU Wind Energy, Technical University of Denmark More details on the rotor  4 sets of blades: – PVC foam injection into negative mold – Stiff, less stiff, flexible, swept+flexible – Stiff and less stiff have glass fiber sandwich  inner beam and PVC foam around – Stiff and less stiff fitted with strain gauges – Flexible: pure foam  The stiff blades where additionally tested for a coning angle of 10 degrees  Verify blade pitch angle, estimate tip deflection with a high speed camera.  Operational inflow conditions: – Fixed yaw at zero yaw error – Free yawing – Impose yaw error and release 28 May 9, 2012 DTU Wind Energy, Technical University of Denmark Early results: tower shadow passage introduced blade vibrations   Some early results 29 The damping is clearly higher for the high rpm operation. Centrifugal forces affect the strain level DTU Wind Energy, Technical University of Denmark Early results: free yaw stability  30 At low rpm (in stall), a large yaw misalignment is seen. At high rpm the yaw misalignment is ~1deg. The decay is fast without overshoot. DTU Wind Energy, Technical University of Denmark Discussion • Model tests in windtunnels, wave basin and open air/water are essential. Can supplement the knowdledge at early stage, but not replace the final full scale measurements. • General performance of sub components (eg. Airfoils) and stability related matters can be clarified with known environmental conditions. • Even though the wind and wave input are well defined, it does not necessarily represent ambient complexs loading. Especially atmospheric turbulence is allways missing. • It is not possible to downscale a turbine with all correct properties. Reynolds numbers too low, structure easily becomes too stiff, centrifugal forces much more dominent. Choices have to be done. • Since the data for the model does not really reflect a fully correct scaling of all parameters it might be easier to distribute data. • From a simulation and measurement point of view it requires just as much work as for a full scale comparison… • As with all other comparisons, start out simple and gradually increase the loading complexity. 31 DTU Wind Energy, Technical University of Denmark Example of a consequence study: - Influence of non-linear waves impact DTU Wind Energy, Technical University of Denmark Wave load methods • Classic linear irregular Airy theory with wheeler stretchning • Stream function theory – regular waves • Full non-linear solution of the 3D Laplace equation for the velocity potential with nonlinear boundary conditions at the free surface and an impermeability condition on a variable depth [1]  [1] Engsig-Karup, A.P., Bingham, H.B., Lindberg, O. An efficient flexible-order model for 3D nonlinear water waves. Journal of computational physics 228 (2009) 2100-2118  DTU Wind Energy, Technical University of Denmark Time series – an example Tower bottom bending and wave elevation for Hs=9m The single large waves may cause ringing 2% log. decr. 10% log. decr. 

Experiences with the Poseidon measurement campaign and more

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Experiences with the Poseidon measurement campaign and more

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