Wave energy is a huge power source that can make a significant contribution to the production of renewable energy in the future. It can generate as much as 10% of the world´s present energy consumption [1]. However, Wave Energy Converters (WECs) is a relatively new field, which requires new technology development, and testing before efficient WECs can give any significant contribution to the energy production. The main difficulties lie in the harsh marine environment and the fact that wave power is delivered with high forces and low speeds. The high forces necessitates strong and durable mechanical structures and the slow speed makes efficient energy conversion challenging. Further, there is a very large variation in wave height over time, and during storms, the largest waves can be 10-25 times higher than the average wave height at the site. The maximum forces and motions can thereby be tremendous if not handled properly, and makes the development of efficient Wave Energy Converters (WEC) challenging. The dimensioning forces strongly depend on the wave power concept, the WEC implementation and the actual Power Take-Off (PTO) system. Of the many different types of WECs being researched and developed, this paper focuses on the development of a winch based point absorber wave energy converters (WBPA-WECs). This paper presents the development of a solution for a flexible chain where an elastomeric bearing is used as a means to achieve the relative motion between the links in a chain. With this solution no sliding is present and the motion is achieved as a deformation in the elastomeric bearing. A design process is formulated for determining a suitable configuration of layers of steel shims and elastomers. A test rig for bearing tests has been developed and results from these experimental tests in combination with material tests and FE analysis are presented in the paper. These are presented in the context of illustrating the proposed design process for designing these type of laminated elastomer bearings. The different steps in this design process have been illustrated for the defined test bearing and we can conclude that our findings indicate that the proposed process can be an important support method for further development of this approach with elastomer bearings.

According to the European Council, 75% of the greenhouse emissions are caused by energy production and use. In order to decarbonize the energy sector, more research is focused towards the renewable energy sources. Among the many available resources, wave energy is one of the key resources to consider. As part of the research, KTH is developing a winch based point absorber wave energy converter. The winch consists of a chain link with elastomer bearings wound around a drum. The winding and unwinding motion of chain converts wave motion into electricity. A typical winch based wave energy converter undergoes around 80 million cycles in its lifetime. This calls for a durable system design requiring minimal service and maintenance. With an elastomer bearing, the winding and unwinding of the chain over the drum is realized as deformation of the elastomer thereby eliminating sliding. While the use of elastomer enables an efficient design, it also makes it more challenging due to its highly non-linear and viscoelastic behavior. A constitutive model is necessary to determine material characteristics of an elastomer for different loading conditions. In this work, a systematic design process is outlined and an attempt is made to determine a suitable hyperelastic material model for the elastomer. The study is focused on two materials - silicone and polyurethane. The test samples are compressed and followed by shear in deformation. For material model determination, the test data is curve fit and later verified using finite element method. The material is assumed incompressible.

Wave energy has an immense potential to provide clean electricity with almost zero emission, among the many renewable energy resources. While it has a huge potential to cater 10% of the current electricity demand, there are many uncertainties involved in the development of a wave energy converter (WEC). This article discusses those challenges and benefits of a product development process to address them. A winch based point absorber (WBPA) concept being developed at KTH Royal Institute of Technology has been used as reference for all discussions. A systematic design approach provides an effective way to rationalize the project from start to end. The value analysis approach is quite useful in order to eliminate rudimentary functions thereby reducing the cost. The stage gate methods makes the systematic design approach interactive and provides an understanding if a concept must be eliminated or continued with at an early stage in the project. Elements of value analysis approach and stage gate methods have been implemented along side complementing the systematic design approach to outline a design process for the WBPA-WEC. An effort has been made to address the challenges faced in the development of a WBPA-WEC.