Titolo della tesi: Piezoelectric Connectors for Energy Harvesting Purposes on Wind-Excited Buildings
Recently, the concept of smart buildings has become more frequent and technologies such as Building Automation (BA) and Structural Health Monitoring (SHM) are turning into common concepts when talking about modern construction. Those systems require the installation of devices that are usually powered by cables or placed in remote places turning difficult the maintenance or the replacement of such appliances. Here, one may face two main issues which are the availability of power and sustainability when talking about the disposal of cables, for example. As a proposal for such problematics, this Ph. D. thesis presents the concept of new equipment capable of providing an infinity power supply to those referred sensors, which receive the name of PID. PIDs stand for piezoelectric dampers, and it works embed in structural members of the building. The PID device concept involves energy harvesting, which is the process of extracting energy from the environment or a system and converting it into electrical energy.
The present work goes from the conception of the device to the analysis of its operation using numerical simulation. The first general idea adopted is that besides the production of electrical energy to supply the smart devices, it also must present structural features due to the place it is installed. Later it is also considered a fact that the devices when installed in the building may produce additional damping to the structure. The PID design is a built device with a piezoelectric core material. These materials’ nature can convert mechanical energy into electrical energy or vice versa. Plus, the piezoelectric core may be able to buckle and impact the lateral walls of the device, and this impact can enhance the amount of harvested energy because the produced energy on a piezoelectric material is directed related to the frequency of vibration, which on this case increases due to the impact phenomena. In this work the analysis where all built on ANSYS® software due to its interaction on the electrical and structural area plus the specific tools that were able to be used as the contact elements.
Due to similarities in the robustness of such equipment, it was first adopted the concept of a rubber bearing to investigate its behavior. The use of those known civil engineering devices arose due to their ability to support structural loads. A specific type of rubber bearing, the lead rubber bearing (LRB), presents a geometry similar to what this work seeks which is the lead core inside it. From that, the core was first replaced by a piezoelectric material core, and with the use of the contact elements from ANSYS®, it was able to reproduce an initial prototype analysis of the PID.
After building a 3D model of the PID, some analyses were performed so the behavior of the device could be understood as well as the way it should work on the building. A called multilevel methodology was then proposed so the steps could be divided into phases to better organize the device’s functioning, where the output of one level is used as the input of the next having cascade comportment. It starts from the called global model which is a steel frame building based on the input of a Power Spectra Density of the Wind it was able to collect the data from where the PID device is located on the building. By collecting the Power Spectra Density of the Displacement of the PID ends it is generated a time-history of that data is to next be applied to the 3D model of the PIDs. From that, it can be obtained the dynamic data from the piezoelectric core to be finally applied to the last level of work of this project, which is the energy harvester model. Then, the power is evaluated.
Finally, it was concluded that the device’s performance met what was expected. This project was focused on the conceptual design of the PID device as well as its initial operation. A case study was conducted where it was possible to investigate the device and all the multilevel procedures proposed by this research. Among the PIDs distribution on the building and the evaluation of the results, it was necessary to go through some concepts and the peak acceleration and the stress strength of the piezoelectric material core, demonstrating that the PID distribution may face some limits yet to be investigated. In the end, the harvested energy value showed a great amount even with the limitation imposed.