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REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS

REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS. Dr. Christoph Heilmann 1 (Presenter), Anke Grunwald 1 , Michael Melsheimer 1 , Prof. Dr. Jochen Twele 2, 3 , Norman Pieniak 2 , Jonathan Amme 3 1: BerlinWind GmbH (heilmann@berlinwind.com)

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REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS

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  1. REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Dr. Christoph Heilmann1 (Presenter), Anke Grunwald1, Michael Melsheimer1, Prof. Dr. Jochen Twele2, 3 , Norman Pieniak2, Jonathan Amme3 1: BerlinWind GmbH (heilmann@berlinwind.com) 2: Reiner Lemoine Institut gGmbH (Jochen.Twele@rl-institut.de) 3: Hochschule für Technik und Wirtschaft – University of Applied Sciences (j.amme@htw-berlin.de)

  2. Content Investigated vertical-axis small wind turbine (SWT) and vibration measuring system Potential vibrations systems at SWT and excitation Campbell-diagram of excitation and natural frequencies Measured vibration signals during operation Evaluation of amplitudes produced by rotor speed and harmonics Conclusions

  3. Investigated vertical-axis small wind turbine (SWT) End disk Rotor blades Generator, tower connection with dampers Blade holders Accelerometers Speed sensor Minimast Long braces Steel tower Elevator house Wind vane & cup anemometer Accelerometers Measuring system box Strain gauges Clamp Short braces Balustrade NORTH Foot braces WEST Gravity foundations Accelerometers • Power: 600 W • Rotor: 1.9 x 1.9 m • Hub height: 6 m • Tower support by long and short braces • Gravity foundation: 660 kg each • Gap between tower bottom and roof • Steel framework roof, 7 floor building • Mobile vibration measuring systemwith up to 17 sensors

  4. Vibration systems… Blades + holders Rotor + dampers Top mass + minimast (MM) + tower Long braces (LB) Short braces (SB) Foot bars Gravity foundations Building • n Wake • w Mast Wind v • u Blade • v …and excitation • Blade-mast interaction producing harmonic excitation by 1*n, 3*n and 6*n

  5. SWT-Campbell-Diagram: Harmonic excitations and natural frequencies • Natural frequency (NF) from standstill tests • LB 2nd, SB 1st:47 Hz • SB 1st soft: 42 Hz • Wind • 60 n • 20 n • Natural or excitation frequency in Hz • Wind speed in m/s • Tower 2nd: 22 Hz • 6 n • Bdg high: 12.0 HzTower 1st: 10.5 HzBdg low 1st: 7.9 Hz • 3 n • 1 n • Blades+Holders: 7.5 Hz • Rotor speed in rpm • 15 Critical intersection points from harmonics with potential resonance hazard • 20 n and 60 n from generator pole pair number

  6. Measured accelerations at SWT minimast and long brace • Sensor color code: • Horizontal at minimast: blue and red (at rectangles) • Middle of long brace: green • 1500 • 1000 • 500 • 0 • -500 • -1000 • -1500 • Minimast 1 Long brace Minimast 2 • Acceleration amplitude in mg *) • SWT with long braces and removed top dampers • Measurement time: 40 min • Wind speed: 3.5 to 5.0 m/s • Rotor speed: 80 to 220 rpm • If resonance occurs amplitudes exceed gravitational constant: 1000 mg = 1.0 g = 9.81 m/s² • At long brace short-time ampli-tudes above 1500 mg = 1.5 g • Time in s • Detail • 1500 • 1000 • 500 • 0 • -500 • -1000 • -1650 • Minimast 1 Long brace Minimast 2 • Acceleration amplitude in mg *) • Time in s • *) Unit: 1 mg = milli g = 9.81 * 10-3 m/s²

  7. Sliding window vibration evaluation reveals resonances during SWT-operation • Sensor color code: • Horizontal atminimast (MM): blue and red • Middle of long brace (LB):green • MM1, 1 n • LB, 1 n • MM2, 1 n • MM1, 3 n • LB, 3 n • MM2, 3 n • MM1, 6 n • LB, 6 n • MM2, 6 n • MM1, 20 n • LB, 20 n • MM2, 20 n • MM1, 60 n • LB, 60 n • MM2, 60 n • Tower: 1st NF by 3 n • *) • Tower, 3rdNF by 20 n • LB: 1st NF by 3 n • SB: 1st NF soft by 20 n • LB: 2ndNF, SB: 1st NF by 20 n • Rotor speed: 30 to 220 rpm • Evaluation: Order analysis of sliding window ( 8 revolutions) • Blades +holders, 1st NF by 3 n • Tower, 2ndNF by 6 n • *) Unit: 1 mg = 9.81 * 10-3 m/s²NF = Natural frequency • Excitation frequency from rotor speed 1 nand harmonics 3 n, 6 n, 20 n, 60 n in Hz • Even more resonance issues from harmonics visible than expected!

  8. Conclusions Dynamics of variable-speed vertical-axis SWT very complex Harmonics produce resonance issues, despite sub-critical rotor speed Additional vibration systems formed by SWT components may amplify vibration by their resonance Total system of SWT and building relevant for resonance issues SWT design including dynamic analysis imperative, professional manufacture, siting (including dynamics) and installation as well Recommendations for the investigated SWT:- Fixing gravity foundations- Two-plane rotor balancing due to mass imbalance above limit - Removal of top dampers- Pre-tensioned guy wires instead of long braces Development of compact load measuring system and sophisticated evaluation software for SWT vibration analysis in process

  9. Thank you for your attention! say… BerlinWind GmbH (heilmann@berlinwind.com) Reiner Lemoine Institut gGmbH (Jochen.Twele@rl-institut.de) Hochschule für Technik und Wirtschaft – University of Applied Sciences (j.amme@htw-berlin.de)

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