Digital Hydraulic Power Take Off for Wave Energy

Project Details


The technical challenge in designing a lasting structure and PTO is the key issue for any wave energy concept. The project aims at solving this main hindrance for wave energy converters. The intention with the project is to further develop a digital hydraulic PTO system with focus on the mechanical implementation.

It is also the intention of the project to broaden the knowledge to more than just a single absorber system. In reality, a WEC most often consists of several moving parts in the water, such as several floats which strongly interact hydrodynamically and possibly also mechanically. The focus in the project is, therefore, also on array effects.

The purpose of the project is to:

Perform numerical and small-scale laboratory array interaction tests with several
absorbers in an array consisting of multiple closely spaced point absorbers. Experimental tests will be performed at small scale in a wave basin on 5 existing experimental set-ups which are available at the Department of Civil Engineering, Aalborg University.

Further develop full-scale digital hydraulic PTO system. The use of better and
cheaper components, and including further measurements of forces and accelerations. This is achieved by upgrading, improving and further developing the digital hydraulic PTO-system, which is tested at the Department of Energy Technology, Aalborg University. Development will have a strong focus on the valve control strategies to reduce and minimize the loads on the structure by more intelligent switching of the valves, while maintaining a high power output.

Apply existing methods and do further development on fatigue analysis, reliability and risk assessment strategies for a digital hydraulic PTO. Tools like Fault Three Analysis (FTA)/Failure Mode and Effects Analysis (FMEA) will be used to define critical failure modes of the PTO system and their influence on the structural loads. The fatigue analysis of the structural parts is performed using existing probabilistic reliability methods.

Measure in reality prototype performance of the digital hydraulic PTO which
Wavestar plans on implementing at their demonstrator test machine at Hanstholm. Sensors for measuring forces, pressures and accelerations will be implemented in the demonstrator, thereby enabling real investigations on the behaviour of the system and making further development possible.

Investigate new control strategies to maximize the power output of a highly
efficient PTO while the minimization of structural loads is taken into account. Relevant parameters such as PTO efficiency, motion and force constraints are included in the design. The strategies are to be implemented in the wave basin and ultimately in Wavestar test machine at Hanstholm.
Effective start/end date01/01/201431/12/2018

Collaborative partners

  • Wave Star A/S (Project partner)


  • Energinet SOV: DKK8,767,000.00


  • Wave energy
  • Wave energy converter
  • Power take off
  • PTO
  • Digital PTO
  • Numerical model tests
  • Small-scale model tests
  • Tests
  • WEC


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