Vibration reduction with passive and active absorbers

Vibrations play a vital role regarding wind turbine fatigue. They cannot be avoided completely, therefore they have to be controlled and reduced as much as possible.

Unwanted vibrations occur in almost all industries and applications. As experts for vibrations and acoustics, we have vast experience in the field of vibration reduction and with our extensive knowledge of structural mechanics and dynamics, we have specialized in solving vibration problems.

In addition to conventional measures, such as detuning, we provide a wide range of passive and active absorber concepts, which we successfully apply to  various industries. Tuned mass dampers are mounted directly on the vibrating structure – if possible, very close to the affected area – and have a vibration-reducing effect.

If we are already involved in the product development process, we work out solutions mainly by means of FE simulation and measurements. If damping devices are considered as an option for vibration optimization in the design process, they can be conveniently integrated in the structural design. Also for existing structures with an excessively high level of vibration, damping devices are an effective option to solving the problem.

Within the wind energy sector, we offer customized solutions in the field of low-frequency structural vibrations and structure-borne sound. The reduction of structural vibrations is usually intended to reduce mechanical stress, the reduction of structure-borne sound is intended to reduce tonal sound radiations.

 

Measurement of vibrations on wind turbines

We support you with the vast experience of our highly specialized measuring engineers. Using our comprehensive equipment, we design your individual measurement campaign from planning and instrumentation up to long-term monitoring with daily or weekly reports.

Our measuring equipment includes:

  • Data acquisition system with more than 200 channels, e.g. for acceleration, sound, power, strain gauge or further physical parameters (incl. long-term recording)
  • Wide range of acceleration sensors, microphones, strain gauge technology and various meteorological masts
  • Experimental modal analysis with shakers of all performance classes
  • Laser vibrometry
  • Recording system for meteorological data
  • Proven data transfer technology between rotating (hub, blade) and stationary components (nacelle, tower)

With our electrodynamic shaker systems for universal vibration excitation, it is also possible to analyze the dynamic properties of structures.

In the field of Individual Measuring Systems, we cooperate with our partner Micromega.

Reduction of gearbox tonalities with active or passive damping devices

Vibrations in the gearbox of a wind turbine can cause tonalities (noise with a fixed frequency, e.g. whistling noise). These tonalities are particularly unpleasant for people and thus they have to be specifically considered in the evaluation of noise emissions. In accordance with legal standards, surcharges are therefore assigned to the determined sound power level of the wind turbine. With this surcharge, the authorized limits for noise emissions or the contractually agreed noise levels may be exceeded.

Therefore, tonalities have to be reduced. In the wind energy sector, Wölfel has many years of experience in the application of active and passive absorbers, which compensate the vibrations at their source before they can spread. This is achieved by precisely applied counter-vibrations.

By moving the black dots you can calculate your individual payback period with our interactive tool:

 

 

Amortisation after

12months

not possible

Noise-reduced operation of your WTG can massively reduce the yield of your wind farm. With ADD.Sound you minimize tonality and can return to the normal operation mode. This calculation includes all costs including installation.

With more than 800 systems in the market, we are proud to be the technology leader in the field of active damping devices for the reduction of gearbox tonalities.

  • ADD.Sound compensates several orders of tonal gearbox vibrations at variable speed (over the entire speed range of the wind turbine)
  • One active absorber ADD.Sound each is mounted on the torque supports (can also be retrofitted; small installation space required)
  • A compact control cabinet is installed in the nacelle
  • Due to the speed-adaptive control algorithm, ADD.Sound generates active forces which eliminate the tonal excitation forces in the gearbox
  • Tonal sound is cancelled over the entire range of speed (broadband effect, simultaneous compensation of several tonalities)

Solution for mastering tonalities with fixed frequency: Passive damper – TMD.Sound

  • Compensation of one order of tonal gearbox vibrations at one fixed speed (mostly the rated speed of the wind turbine)
  • One passive absorber TMD.Sound each is mounted on the torque supports (can also be retrofitted)
  • TMD.Sound is exactly adjusted to the tonality frequency at rated speed
  • TMD.Sound applies a force that is exactly opposite to the excitation
  • Tonal sound at rated speed is cancelled – no energy supply is required

TMD.Tower – Absorber to reduce tower vibrations

There is a variety of possible causes for vibrations affecting the entire wind turbine (WT) at its lowest natural frequencies. Some typical examples are:

  • Resonance due to rotor speeds and higher harmonics: When starting a WT, a resonance is often caused or the WT should be operated in such a way that the excitations from the rotor (1P, 2P or 3P etc.) are close to a natural frequency of the WT.
  • Excitation by periodic vortex shedding: At the tower of a wind turbine, vortices can periodically detach at certain wind speeds. Typically, this can become critical for assembled WTs (without nacelle) or for slender WTs with a low second natural tower bending frequency.
  • Wave excitation in offshore wind turbines: Wave excitation can become critical when the first natural frequency of a wind turbine is very low, since the energy of the wave excitation is particularly high at these frequencies. The trend towards ever more powerful wind turbines at greater water depths and maintaining of the monopile foundation concept reinforces this problem.

Depending on the wind turbine type and overall context, it is necessary to assess whether the expected vibrations are problematic and which solution is the most suitable for vibration reduction.

Absorbers are a very cost-effective and reliable solution for vibration problems. They are highly effective and, in particular, passive absorbers are extremely robust. Tailored to the specific application, we offer successful, individual absorber concepts to solve the respective problem.

 

Wind turbines and seismological stations – passive dampers for the reduction of seismic emissions

In Germany, there are more than 150 so-called „seismological stations“, operated by the Federal Institute of Geosciences and Natural Resources (BGR) as well as by university institutes and regional earthquake services. The high density of seismic stations in the Lower Rhine bay, the Rhine valley and the Vogtland reflect the location of seismic zones in Germany.

The seismological stations form networks that are subdivided into:

  • Emission networks to observe seismic activities,
  • Immission networks to assess the vibration impact on the earth’s surface
  • Exploration networks for the so-called reservoir-monitoring

Wind turbines as vibration generators

Wind turbines (WT) produce vibrations in the subsoil, which can spread primarily as surface waves and detrimentally affect the functional capability of adjacent seismic stations. The North Rhine-Westphalian wind power decree of November 4, 2015 (no. 8.2.12) deals with this potential conflict between wind turbines and seismic stations.

“There can be a conflict regarding the use of wind turbines and measuring stations of the Geological Service. The Geological Service NRW is responsible for the monitoring of seismic activities and seismic hazard in North Rhine-Westphalia. Moreover, North Rhine-Westphalia has installed a seismic warning system as a measure of hazard prevention and civil protection. In planning and approval processes for wind turbines, it is compulsory that the Geological Service NRW be involved for wind turbine sites within a radius of 10 km around the sites of the seismic measuring stations indicated on the website of the Geological Service.”

Vibration reduction

Vibration absorbers are a long-known and established tool for reducing vibrations in towers, buildings, bridges, machines, plants and vehicles. Taking into account the technical constraints, resonant vibrations can be reduced using vibration absorbers. For the reduction of the seismic emissions of wind turbines, passive dampers can be used. Depending on frequencies and amplitudes, which have detrimental effects, it is already possible to achieve substantial vibration reductions with small damper masses that substantial vibration reductions can be achieved.

Our range of services includes:

  • Simulations-based design (using FE-model of WT-tower, nacelle and rotor) of a vibration absorber
  • Detection of the vibration modes which are critical with respect to the seismic emissions, if necessary: supplementary comparison with vibration measurement data
  • Definition of the functional parameters of a vibration absorber and their implementation in a plant-specific design, if necessary
  • Simulation-based prognosis of the absorber’s efficacy
  • Production, delivery and commissioning

Please contact us personally

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We would be pleased to support you in solving your problem concerning "Wind turbine vibrations" and advise you on questions regarding our system and service offerings in the areas of structural health monitoring, vibration reduction, sound and noise as well as structural design.

Dr.-Ing. Georg Enß

+49 40 524715262
enss@woelfel.de
Formular

Timo Klaas
Leiter Vertrieb Systeme

+49 931 49708765
klaas@woelfel.de
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Dipl.-Ing. Bernd Wölfel