Thermal Analysis of Wave Energy Converter : Developing a Compact CHT Model for Operational Insights

Abstract: Climate change is a critical global issue that continues to shape the way we understand and interact with the world around us. It is discussed more than ever before, especially in politics. To slow down the temperature rise of our planet, decreasing the amount of green house gas emissions produced by our way of living, industries, and the production of energy is necessary. Ocean Harvesting Technologies (OHT), a company from Sweden based in Blekinge, is currently developing a new iteration of renewable, wave energy converters (WEC) that they claim to be ecient from both an energy and cost perspective. A new prototype is in development where thermal and fluid characteristics inside the WEC during operation, are important aspects that need to be evaluated. This project is aimed to develop a computational simulation model of the WEC and perform simulations in order to evaluate the cooling and heating performance of the current model that is under development. The methodology used for this project was divided into three stages to streamline the work: steady-state stationary conjugate heat transfer(CHT) simulations, and transient airflow simulations with motion and compressible air, that are combined into a full-system transient CHT model for operational conditions. CAD models and delimi- tations were provided by OHT and the model was broken down, simplified and assessed to begin the work. The computational software used for the simulations in this project was STAR-CCM+ and the complete process of pre-processing, simulation setup/run and post-processing was executed using the same software. To simulate the fluid and the oper- ational motion of the WEC, the Overset mesh methodology was used, and to resolve the turbulent flow, URANS k! SST was used in the solver. The thermodynamic simulations were initially set up and simulated in two sub-models in order to speed up the method development and to get an early indication of the performance of the WEC. The first sub-simulation handled the compressible air together with the Overset mesh motion while the second simulation aimed to model the thermodynamics of the generator components, ball screw, and other solids. Since OHT is in a relatively early development phase, no experimental data could be used for validation, however, data sheets for generator com- ponents and simple handbook calculations were used to validate the simulation models performance. The sub-simulations resulted in an ecient simulation strategy and a lot of knowledge and understanding of the system performance was gained to implement in the full-system model The final outcome of this thesis work was a complete CHT model that showed the ca- pability of running several hundreds of seconds of operational time while producing a significant amount of performance data such as temperature profiles of critical parts, air pressure/temperature fluctuations, and drag losses of the complete WEC. Furthermore, the sub-simulation models can be used individually as stand-alone models in order to op- timize the system on a component level, e.g., drag losses from the generator components during motion.