Ling Hai

Modelling a point absorbing wave energy converter by the equivalent electric circuit theory : A feasibility study

There is a need to have a reliable tool to quickly assess wave energy converters (WECs). This paper explores whether it is possible to apply the equivalent electric circuit theory as an evaluation tool for point absorbing WEC system modelling. The circuits were developed starting from the force analysis, in which the hydrodynamic, mechanical, and electrical parameters were expressed by electrical components. A methodology on how to determine the parameters for electrical components has been explained. It is found that by using a multimeter, forces in the connection line and the absorbed electric power can be simulated and read directly from the electric circuit model. Finally, the circuit model has been validated against the full scale offshore experiment. The results indicated that the captured power could be predicted rather accurately and the line force could be estimated accurately near the designed working condition of the WEC.

Force in the Connection Line for a Wave Energy Converter: Simulation and Measurement Experimental Setup

In order to capture ocean wave energy and transform it into electric energy, Uppsala University has developed a point absorber wave energy converter (WEC) for electricity production. For a better understanding of a torus shaped buoy’s performance, this paper conducts a force analysis under linear conditions, to investigate the hydrodynamic characteristic and line force differences between the torus buoy that is going to be deployed, and two similar cylindrical buoys. The result reveals the line force from this torus buoy is roughly 5% larger than from cylindrical buoys for the most energy dense wave climate in Lysekil test site, and negative added mass phenomena won’t have a significant impact for the line force.To measure the line force, a force measurement system has been designed. A detailed description is given on the design of the 500 kN force measurement system, and the major differences compared with former force measurement systems. Onshore test result has also been presented. With the force measurement experiment, hydrodynamic analysis for torus buoy can be validated when the system performs linearly, and extreme force for storm weather can be monitored to provide information for future WEC structure’s mechanical design.Copyright

A Methodology of Modelling a Wave Power System via an Equivalent RLC Circuit

The equivalent circuit method can be an effective modelling technique for system studies of point absorbing wave energy converters (WECs). For the continuously evolving design and study of WEC systems, an instruction on how to draw the corresponding equivalent RLC circuit model is needed. It is not only vital to make sure the model is correct, but to allow the model to be easily adapted for different cases and implemented by different researchers. This paper presents a force analysis-oriented methodology based on a typical WEC unit composed of a heaving buoy and a linear generator. Three cases are studied in order to demonstrate the procedures: the generator with a retracting spring, the connection line with a rubber damper, and buoy motion in both heave and surge directions. The presented methodology serves as a guide to produce nonlinear circuit models that give a reliable description of the dynamics of real wave energy systems.