Under certain conditions time varying parameters of dynamical systems cause parametric resonance which leads to an exponential increase in oscillation amplitude. Parametric res- onance has been widely observed in floating bodies. Depending on application objectives parametric resonance can be both desired and undesired. In both avoiding parametric resonance or triggering it, a robust control of the system is necessary. This thesis considers the application of Tuned-Mass-Dampers (TMDs) and Nonlinear Energy Sinks (NESs) to passively suppress parametric pitch and roll motions from heaving floating bodies, with the objectives of vertical stability in ships, marine based sensors and spar platforms, and maximizing power output from heaving motion in wave energy converters. We present a numerical investigation considering a case study of a simplified two degrees of freedom system, comprising a heaving and pitching cylinder representing the floating bodies. The performance of the NES and TMD, in mitigating the parametric pitch motion of the cylinder is analyzed. Read
The wave energy conversion is a clean and inexhaustible energy source. However, under the current power performance level, the technology has to undergo some changes in order to be competitive. The conventional model of wave energy converter (WEC) is designed to resonate with the frequency of incoming waves. At resonance, the velocity of the system is in phase with the dynamic pressure and force of the wave, so that the amplitude of oscillations linearly increases, generating a massive amount of energy. As an alternative, the model can be oscillated by the periodic parameter with frequency twice its natural frequency. This practice stimulates an exponential increase in the amplitude of oscillations and explained by the phenomenon called parametric resonance. Parametric resonance could increase the amount of generated energy, and hence improve the performance of WEC. In this work, the phenomenon of parametric resonance is utilized on the single degree of freedom model mimicking a simpli ed WEC device. The model incorporates a mass modulation as a periodic parameter and exploits its eect on power performance. The parameters describing the model, such as damping and mass modulation coe cients have to be de ned and optimized. Also, the long-term solution as stability diagram and Floquet theory is suggested to simplify the complexity of the non-linear model. Read
Vortex induced vibration (VIV) is one of the most concerning phenomenon when comes to the interaction between fluid and solid. It is especially most practical for those that have a geometrically low aspect ratio, for example skyscrapers and bridges. The study regarding VIV has a history well over fifty years, but even till this day, the behavior of this phenomenon is not yet fully defined. This thesis focus on investigating the behavior of this phenomenon with OpenFOAM with controlled velocity, shape, mass, fluid property, and natural frequency. With the numerical results obtained, frequency ratio, amplitude ratio, settling time, and critical value are investigated with a variable mass. Read
As the composition of the energy mix shifts thoughout the years towards sustainable energy generation, the interest in various renewable energy sources has skyrocketed. This includes the Wave Energy Converters (WEC), which have been considered one of the most promising sources. Wave Energy is a distinguished opportunity for coastal countries. The Oscillating Water Column (OWC) is the most researched WEC, because of its simplicity and capability of long-term operation. The greatest tool in the development and optimisation of OWC technology is Computational Fluid Dynamics (CFD). Using CFD simulations various geometries and approaches can be studied and compared cost-effectively, as no real-life model is needed for these experiments. The biggest drawback in CFD simulations is the need to compromise between accuracy and computational time. Finer meshes can lengthen the computational time exponentially with only slightly more accurate results. Therefore the main goal in setting up these CFD models is to find a balance between accuracy and time. In the present work the various developments in OWC technology are summarized, mainly in CFD applications. This is followed by a examination and comparison of various mesh approaches of the OWC chamber, highlighting the shortcomings of each and making suggestions for further improvements. The numerical simulations were conducted using commercial CFD-based ANSYS Fluent 19.1 software. The output of the CFD modeling effort performed by our team is to be submitted to the International Energy Agency's Ocean Energy Systems "Task 10 - Wave Energy Converter (WEC) modelling verification and validation project”. The project investigates the possibility to include simulations that will support the development of standards under the International Electrotechnical Commission (IEC). The particular oscillating water column (OWC) test case represents model scale testing performed by Korea Research Institute of Ship & Ocean Engineering (KRISO). Read
Wireless computers and mobile devices have shrunk in size and power consumption over the previous decade. Originally, these devices had high power consumption, necessitating the use of batteries as an energy source. The decrease in size and power requirements of electronics is leading to numerous new opportunities for wireless sensor networks. Sensor networks will be able to function for considerably longer periods of time at a lower cost by harvesting energy from the environment. Thermal energy harvesting is one of the options to meet these needs. A part of the energy ow can be transformed into usable power. This is accomplished by incorporating a device that harvests thermal energy into the sensor node. The temperature dierence between the top collector, used as a heat source, and the cool sink, is the requirement for thermal energy harvesting. The thermoelectric device sandwiched between them used to convert the heat ow across it into electrical power. This thesis will discuss the thermal energy harvesting for wireless sensor networks, focusing on the design of the device that can harvest the energy. Read
In today’s life, the public is starting to be aware of the importance of renewable energy. However, fossil energy still plays a massive role in global energy production. The use of natural gas, fuel, and coal to generate electricity is harmful to humans and contributes to air pollution and global warming. These days, the development of technology has really skyrocketed, the efficiency of devices has increased a lot during the past years. Some of the things that we could only dream of had become the facts. Hydropower, thermal power, wind power, tidal power, and many other resources that come from nature have become more and more grown methods to generate energy. Over the last decade, the size and the power consumption for wireless sensors have significantly decreased, which brings the topic to this report. This report investigates the method to provide a robust power supply for autonomous wireless sensor networks in the environment. This project will involve the optimization of a thermal energy harvesting device. The technologies discussed in this report are thermoelectric devices known as thermal generators. Simulations of thermal generators are going to be done in different situations. Read