One of the key endeavors in mitigating climate change is making the energy mix more sustainable. Photovoltaic (PV) systems are well known as an almost CO2 neutral means to provide electrical energy. One drawback is that they need a lot of space, a commercially available solar panels won’t generate much more than 180 W/m² . Therefore a lot of interest goes out to offshore floating photovoltaics (OFPV), using the available area on the sea surface (see Figure 1).
Figure 1: Offshore floating photovoltaics.
Currently, several layouts are investigated to optimize the performance of the floating foundation. The most common schemes consist of either one single “island” or of inter-connected subunits. These systems should survive all kinds of weather conditions (including storms which can bring along very large waves). Therefore the interactions between the water surface and the platform of panels should be well understood, since the waves could result in rather large motions as shown in Figure 2.
Figure 2: Interaction between panel and waves.
Numerical methods are for this case often cheaper and more insightful than experiments, which is especially beneficial for early design stages. A fluid-structure interaction (FSI) simulation couples a Computational Fluid Dynamics (CFD) solver to a Computational Structure Mechanics (CSM) solver, and is a good means of investigating this interaction between a platform and water waves. Different FSI methods will be used and compared in this thesis, for different wave conditions. This will produce valuable results for research towards floating photovoltaics, that are potentially also useful for other offshore floating structures.
Two different CFD methods can be used for the modelling of the flow: Finite Volumes and Smoothed Particle Hydrodynamics (SPH). In Finite Volumes the conservation laws are expressed on a discretized grid (also called mesh), such that they are respected on the level of a single cell. This is the most used method in CFD simulations. In SPH the fluid is modelled as a (large) collection of particles and the behavior of the flow emerges from the modelling of the mutual interaction between all particles. The latter is an example of a mesh-free method.
Figure 3: (left) Finite volume mesh and pressure contour. (right) Smoothed Particle Hydrodynamics.
Both methods have proven to work very well for many cases and the results often compare very well. FSI simulations are usually coupled by communicating forces and displacements at the interface between fluid and structure. The differences between the flow solvers at that location will be of determining importance. This thesis is a collaboration between the research group of Coastal Engineering and the research group of Sustainable Thermo-Fluid Energy Systems (STFES). The Coastal Engineering group is very experienced with SPH method and uses those in FSI simulations with an own coupling code. The STFES team has an in-house FSI code which is actively maintained and improved, coupling different Finite Volume CFD programs to Finite Elements CSM programs.
The goal of this thesis is twofold. First FSI simulations will be done on a benchmark case, both using the SPH and finite volume method as flow solver. The results will be compared and the pros and cons of both methods in the specific case of floating photovoltaics will be evaluated. Secondly, different wave conditions will be investigated for the method of choice. The effect of the waves on the behavior of the device will be a valuable scientific contribution to the design of these kind of systems.
In short you will: