Design and Analysis of Wave Energy Converters

In the age of energy transition, renewable energies are playing an increasingly important role. As a result of this, hydropower, solar, and wind energy are becoming more important. In addition to these well-known examples of renewable energies, there is also the possibility of harvesting energy from ocean waves. Here, mechanical systems are positioned on the sea surface and are moving due to the incoming water waves. An internally installed electrical generator converts then this movement into electrical voltage. Since wave energy has a notably high power density compared to wind and solar energy, it has been recognized as one very promising resource of renewable energies.

In order to be able to harvest as much energy as possible, mechanical systems have to be constructed in such a way that they experience a large movement by the incoming waves. For this purpose, various questions have to be clarified, such as:

• What waves are present in the open ocean, and how can they be modeled appropriately?
• What hydrodynamic forces do water waves exert on a given mechanical system?
• How must the system parameters of the mechanical system (mass, size,...) be chosen so that it shows large movement?

This is investigated simulatively and experimentally at the Institute of Mechanics and Ocean Engineering.

There are many different methods available to describe water waves. The simplest water waves are regular waves, which can be characterized by sine functions. However, looking at the surface of an ocean reveals that real water waves are irregular. It is therefore important to clarify in which way realistic water waves can be modeled accurately, but also with little computational effort. In this way, wave energy converters can be designed and optimized in the subsequent work process to move optimally in real water waves.

The following video shows an example of an irregular water wave.

It can be seen that the system behaves differently in irregular water waves than in regular waves. The task of this research project is to adapt the system so that it exerts large movements in real irregular water waves. For this, it has to be investigated which irregular waves typically appear in the real ocean, how the associated fluid-structure interaction can be efficiently computed, and how the system has to be modified to harvest large amounts of energy.

This topic represents an interface between the fields of mechanics, electrical engineering, control engineering, numerics, and fluid dynamics and provides much space for student work. Please contact us, if you are interested to contribute to this topic within the scope of a project work or a Bachelor-/Masterthesis. Depending on your interests, you can either work on the

• modeling of water waves,
• fluid-structure interaction,
• control/optimization of system parameters, or
• the design of a more efficient electrical generator.

Prior knowledge in these areas is of course an advantage but not mandatory!

1. M. Hollm, L. Dostal, D. Yurchenko, R. Seifried: Performance increase of wave energy harvesting of a guided point absorber. In: European Physical Journal Special Topics 231(8): 1465-1473 (2022). [DOI:10.1140/epjs/s11734-022-00497-7]

2. M. Hollm, L. Dostal, J. Höhne, D. Yurchenko, R. Seifried: Investigation of the dynamics of a multibody wave energy converter excitetd by regular and irregular waves. In: Ocean Engineering 265: 112570 (2022). [DOI:10.1016/j.oceaneng.2022.112570]

3. J. Harms, M. Hollm, L. Dostal, T. A. Kern, R. Seifried: Design and optimization of a wave energy converter for drifting sensor platforms in realistic ocean waves. In: Applied Energy 321: 119393 (2022). [DOI:10.1016/j.apenergy.2022.119303]

4. L. Dostal, M. Hollm, E. Kreuzer: Study on the behavior of weakly nonlinear water waves in the presence of random wind forcing. In: Nonlinear Dynamics 3 (99): 2319-2338 (2020). [DOI:10.1007/s11071-019-05416-5] 

• Marten Hollm, M.Sc.
• Prof. Dr.-Ing. Robert Seifried