In this study, theoretical analyses are performed to investigate the characteristics of the static and dynamic stiffness of a nonlinear vibration isolator system. The vibration isolator system is modeled as an equivalent nonlinear oscillator. Based on the model, the static equilibrium and frequency response solutions are obtained with the variations of external static load and/or system parameters. It is shown that the static stiffness of the nonlinear vibration isolator tends to be hardened with the increase of external static load, which prevents the occurrence of excessively large deflection. This static stiffness-hardening effect is more remarkable with a larger spring constant ratio. The dynamic stiffness is also strengthened when the spring constant ratio increases, which enlarges the force transmissibility and reduces the isolation frequency bandwidth. Thus, the static stiffness- hardening improves the robustness of the nonlinear vibration isolator, whereas the dynamic stiffness-hardening rather degrades its performance. Thus, the opposite tendency of the static and dynamic stiffness-hardening effects should be considered in the design process of the nonlinear vibration isolator.

This study compared and analyzed the difference in performance between the existing soot probe and the improved one that was applied to the actual inspection vehicle at the actual inspection site, which has been developed under the specific conditions based on the excellent results through the performance evaluation. As the results, probe(b) involves a structure designed close to the center of the circumference of the exhaust pipe, and the suction efficiency was improved by adding a center unit. The improved probe(b) can enhance the effectiveness of the inspection when applied to total and regular tests inspections, and the possibility of contributing to the reduction of carbon dioxide emissions generated in the transportation sector has been confirmed.

In this study, the frequency response analysis of a bistable electromagnetic vibration energy harvester is performed, based on an electromagnetic oscillator model, to investigate its nonlinear dynamic behaviors. The displacement and current responses are obtained, by the direct integration of the model, with the variations of mechanical and electromagnetic parameters. It is shown that the operating frequency band of the system can be broadened by the increase in mechanical parameters(inertial mass and Q-factor), but it does not depend significantly on any electromagnetic parameters(an external load resistance and the internal resistance of a coil). On the other hand, the output current of the energy harvester is affected only by the electromagnetic parameters (specifically, the sum of two resistances). Thus, the mechanical and electromagnetic parameters of the electromagnetic energy harvester must be designed properly, respectively, for broader and more efficient performance.

In this study, a bistable energy harvester (BEH) with a piecewise potential function is proposed to improve its energy harvesting performance. A mathematical model of the piecewise BEH (PWBEH) system is established first and a series of numerical simulation are performed, based on the developed model, in order to investigate the nonlinear dynamic behaviors and energy-harvesting performance of the system. The analysis results for the proposed PWBEH system are compared with a conventional BEH (CBEH). The frequency response results show the stiffness-softening interwell motion of the PWBEH, due to the piecewise potential energy function, which is contrary to the stiffness-hardening behavior of the CBEH. Such softening behavior of interwell motion tends to reduce the operating frequency of the BEH, while significantly increasing the output power. This observation indicate that the introduction of the piecewise potential function to a BEH would be beneficial to the system design for enhancing enegy-harvesting performance at the cost of redundant frequency band, which depends on the characteristics of environmental vibration sources.