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Analysis of Nonlinear Energy Harvesting Systems under Random Excitations and Providing Solutions for Increasing the Harvested Energy

Makarem, Hadi | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52399 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Vossoughi, Gholamreza; Nejat Pishkenari, Hossein
  7. Abstract:
  8. Providing energy for small but out-of-access devices has led industries to harvest energy from the environment, especially environmental vibrations. The problem of vibrational energy harvesters with linear behavior, is their small bandwidth and consequently, their high sensitivity to frequency content and excitation spectra. Particularly in random excitations with vibrational energy spreading over a frequency range, linear harvesters do not seem appropriate. Under these conditions, harvesters with nonlinear stiffness are possible substitutes for linear systems. However, prediction and estimation of the behavior of systems with nonlinear stiffness under random excitation has been complicated, which makes it difficult to evaluate the performance of these systems. Particularly when the stiffness of the system exhibits bistability, conventional analytical methods lose their accuracy. In this thesis, depending on the model of the excitation spectrum, some analytical methods have been proposed to estimate the behavior of harvesters with nonlinear stiffness under random excitation, giving better accuracies than conventional methods. Monte-Carlo simulations have been the criterion for assessing the accuracy of the analytical methods, and in order to verify the simulation results, a laboratory test has been defined and implemented. Next, finding optimal nonlinear stiffness for the maximum harvested energy is considered. It has been shown in various methods that for a constant excitation spectrum, linear stiffness with optimal design, results in the highest harvested power; but in terms of resistance to changes in the excitation center frequency, a nonlinear system with a bistable stiffness is a more appropriate choice
  9. Keywords:
  10. Vibrational Energy Harvesting ; Nonlinear Stochastic Differential Equations ; Fokker-Planck-Kolmogrov Equation ; Moment Closure ; Duffing Differential Equation ; Bistability ; Monte Carlo Simulation

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