Comparative study about the cantilever generators with different curve fixtures

Magnetic interaction and pre-stress effect are two regular ways of introducing nonlinearities for wideband energy harvesting. However, the susceptibility to the fabrication and assembling makes it a tough job to exactly tune the magnetic field distribution and the preload as desired for the purpose of avoiding large deviation from design and model, especially in the micro-electro-mechanical systems scale. The nonlinear generator by introducing a curve fixture to the cantilever beam instead of the rectangular fixture presents a feasible and simple solution with good micro-electro-mechanical system fabrication compatibility. In this article, three prototypes of with different curve fixtures with the same size requirement are fabricated for detailing the influence of the selection of the fixture curve. Experimental and numerical investigations reveal that the generator has better performance when the nonlinear stiffness introduced by the curve fixture is smooth, especially in the case of no linear stiffness segment.

Stochastic Dynamics of a Nonlinear Misaligned Rotor System Subject to Random Fluid-Induced Forces

In this paper, stochastic responses and behaviors of a nonlinear rotor system with the fault of uncertain parallel misalignment and under random fluid-induced forces are investigated. First, the equations of motion of the rotor system are derived by taking into account the nonlinear journal bearings, the unsymmetrical section of the shaft, and the displacement constraint between the two adjacent rotors. Then, the modeling on uncertainties of misalignment and random fluid-induced forces are developed based on the polynomial chaos expansion (PCE) technique, where the misalignment is modeled as a bounded random variable with parameter η distribution and the fluid-induced force as a random variable with standard white noise process. Finally, examples on the stochastic dynamic behaviors of the nonlinear generator-rotor system are studied, and the influences of the uncertainties on the effects of shaft misalignment, the stochastic behaviors near bifurcation point as well as the distribution of the system responses are well demonstrated.

UNIT COMMITMENT WITH SECURITY ASSESSMENT USING CHAOTIC PSO ALGORITHM

This paper proposes solving short-term unit commitment (UC) problems with security constraints by hybrid chaotic particle swarm optimization (CPSO). The objective of security-constrained UC (SC-UC) is to minimize the total generation cost, which is the sum of both transition cost and production cost of the scheduled combination units. The proposed CPSO method, which involves the chaotic map and the chaotic turbulence, can avoid premature convergence of PSO and escape local minima. Moreover, the proposed hybrid CPSO method has the ability of solving both the continuous and the discrete optimal programming problems. Two power systems are demonstrated for verifying the feasibility and effectiveness of the proposed method in solving SC-UC problems with constraints of a nonlinear generator and operation security assessment taken into consideration. The simulation results show that the proposed CPSO-based SC-UC method is indeed capable of obtaining efficiently high-quality UC solutions and enhancing the system security of UC operation.