This thesis investigates the damping effects of a metamaterial, on structural vibration, by inducing periodic voids in the base damping material as opposed to infusing the damping material with other material. Metamaterials have been used previously to improve the damping of vibrational waves and acoustic waves through wave scattering and wave reflection at periodic impedance changes. Impedance changes can occur at both material boundaries and geometric changes of the medium. Impedance changes cause wave scattering, wave reflection, and changing of wave speed. The low frequency region of the vibration spectrum is generally harder to dampen due to the longer wavelengths. By slowing the waves down, the wavelength can be shortened and the viscoelastic material will be more effective at damping the waves. The metamaterial in the thesis has one, two, three, and four periodically located voids in the viscoelastic damping material to determine the effectiveness of the damping compared to the same beam with no damping material applied and the beam covered completely with the standard viscoelastic damping material. This research will include both finite element models of the beam and concept testing to explore the damping effects of the metamaterial. / Master of Science / In the field of mechanical engineering vibrations are one of the main causes of failure of machinery components. Reducing vibrations greatly effects the longevity and effectiveness of a machine. The research in this thesis focuses on how to reduce the vibration in a beam by using a metamaterial. Standard damping materials provide damping, reduction of vibration, at various quantities depending on the frequency and wavelength of the vibrational wave. Metamaterials are particular materials designed to reduce vibration by influencing the physical phenomena of a wave as it travels through the material usually by periodic wave scatters. The metamaterial in this research is designed to slow the flexural waves down, therefore shortening the wavelength, making it easier to dampen the vibration compared to a standard damping material. The damping effectiveness of the metamaterials explored in this research will be quantified via finite element modeling and testing in a laboratory.

Wave energy is one of the possible solutions for meeting the future energy demand in a clean and sustainable way. Extracting large amounts of energy, a wave energy device would be subjected to extreme and fatigue loads from the waves. Designing such a device, a trade off needs to be done between making a device that is strong enough to withstand the loads and on the same time not too heavy making it inefficient and too costly. Having good estimations of extreme and fatigue loads are therefore critical when designing an efficient wave energy device. This thesis has aimed to create a tool that can be used between the already existing hydrodynamic and solid mechanic models available at CorPower Oceean. The goal has been that the tool shall extract the extreme and fatigue loads from the hydrodynamic model and format them in a way so that they can be used in the solid mechanical model. Four different tools have been created and compared for calculating fatigue using amplitude and spectral methods, where the amplitude methods also are able to estimate extreme loads. The fatigue tools have been evaluated against each other in a simple example showing that the estimated accumulated fatigue damage can be decreased by using several variables. An application of the tools has been done on a critical sub system of the wave energy device developed by CorPower Ocean. Where in this application critical points against extreme loading and fatigue have been localized. A new design has been suggested based on the strength analysis from the first one. Increasing the number of variables and using the tools developed in this thesis can significantly improve the fatigue damage estimations of the system. What fatigue method to use depends on the details for each case.