Applications of oscillators in energy conversion

Abstract

The scope of this dissertation concerns environmental excitations such as sea waves and sound. Two individual aspects are examined, the first deals with the harvesting of ocean wave energy, while the second deals with the reduction of noise pollution in air and ground transportation vehicles by means of acoustic treatment for the comfort of the passengers. The gradual exhaustion of fossil fuel deposits has been a crucial issue for the scientific community. Along with the environmental effects that accompanies their use and the detrimental effects to human health, a turn to "green", renewable energy sources consists a top priority. The increasing exploitation of solar and wind energy does not reflect equally on the utilization of sea wave energy, which in fact has higher energy density compared to the aforementioned energy sources. Consequently, sea wave energy consists an area of great interest and great, untapped potential. Regarding noise pollution in means of transportation, the main issue concerns the treatment of low frequency noise -where conventional means of passive treatment have limited capabilities- which is the range of noise generated mainly from the rotating engines, motors etc. of these vehicles. Solutions such as acoustic "sandwich" type panels, deal poorly with low frequency noise as most often coincides with the eigenfrequencies of these structures. Moreover, the performance of solutions like local dampers, is associated with increase in mass of the total structure. This fact conflicts with the ever-increasing demands for weight reduction in transportation vehicles to minimize fuel consumption and satisfy power requirements. Conclusively, two different implementations of oscillators for energy conversion and utilization of sea wave energy are examined, while in the field of noise control, a segregation is made between passive and active means of acoustic treatment. In one hand, a passive solution for acoustic treatment of low frequency noise is proposed based on the incorporation of the KDamper oscillator, in the design of acoustic panels and later, on meta-materials for the generation of bandgaps in noise propagation, at selected low frequency ranges. On the other hand, the design of an acoustic transducer (loudspeaker) using dielectric elastomer (DE) actuators is presented. The purpose of this electro-active polymer (EAP) loudspeaker is to be used in automatic, active noise control systems in the compartments of the passengers.