In this paper, a new design of a self-tuning bimorph PZT beam for maximum vibration energy harvesting is introduced. As is well known, a PZT beam harvester captures the most energy as it resonates with the ambient vibration. The ambient excitation frequency varies in nature so that proper tracking of the ambient frequency and adjusting the harvester’s resonance frequency accordingly would assure the most energy retrieved. The harvester introduced in the paper is composed of an elastic beam partially covered with two-sided PZT patches, the same as most others, but the method of tuning its resonance frequency is novel. A movable intermediate rigid support is attached to the beam and by adjusting the support’s position according to the sensed ambient frequency, the beam’s resonance frequency will coincide with the ambient frequency such that the harvested vibration energy is maximized. The theoretical analysis employs Hamilton’s principle, the assumed-mode method, and the receptance method. Numerical results are obtained and compared with the experimental ones. They show excellent agreement in a frequency versus support’s position chart. The most significant feature is that there can be up to ±35% of resonance frequency tunability. This achievement provides substantial advantages in power-harvesting applications. An experiment for base excitation to simulate the ambient vibration is setup as well and the results show that as little as 5% excitation frequency variation would cause more than 70% output voltage drop if there were no tuning ability. The novel design could significantly enhance the harvested energy in a short duration of time.

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The authors designed a novel type of dynamic vibration absorber, called periodic vibration absorber (PVA), for mechanical systems subjected to periodic excitation. Since the periodic rather than single harmonic excitation is themost occurring case in mechanical systems, the design of PVA is hence of engineering significance. The PVA designed in this paper is composed of a dual-beam interconnected with a discrete spring in between. By appropriately choosing the design parameters, the PVA can be of resonance frequencies in integer multiples of the base frequency such that the PVA can absorb significant amount of higher harmonics in addition to the base harmonic. The designed PVA was first experimentally verified for its resonance frequencies. The PVA implemented onto a mechanical system was then tested for its absorption ability. From both tests, satisfying agreement between experiments and numerical calculations has been obtained. The sensitivities of the design variables, such as the discrete spring’s stiffness and location, were discussed as well. The parameters’ sensitivities provided us with the PVA’s adjustable room for excitation frequency’s mismatch. Numerical results showed that within 3% of frequency mismatch, the PVA still performed better than a single DVA via adjusting the spring’s constant and location. All the results proved that the novel type of PVA could be a very effective device for vibration reduction of mechanical systems subjected to periodic excitation.

A read/write head assembly attached to a spinning disk was modeled and investigated through a different approach, in which the head assembly was represented by a suspension arm with an attached mass and an air spring (film) at its free end. The receptance method was applied to connect the spinning disk and the head assembly. The natural frequencies and mode shapes of the combined spinning disk-fixed head assembly as a whole were then interpreted. Numerical results showed that the head assembly induced extra modes from a single disk. Even for just weak coupling between disk and head, the bifurcations of mode shapes were very obvious, but the changes of natural frequencies were slight. The effects on frequency changes due to head's flexibility, air spring constant, head's location, and spinning speed were examined as well. Disk's spinning speed was found to pull the disk-head frequency loci to pass through the crossings of single disk's frequency loci and induce curve veering phenomenon.

The seismic resistance characteristics of a newly developed composite bridge pier system are examined via a series of experimental studies. In this innovative bridge pier system, the shear strength is provided by the steel tube and the concrete confined by the steel tube. No transverse shear reinforcement is used in this system. Axial and flexural strengths of the bridge pier are exerted by the longitudinal reinforcements and the concrete. A gap between the end of steel tube and the reinforced concrete foundation contributes to the steel tube providing shear resistance only without sharing the flexural moment. From the experimental results of this study, it is found that the flexural strength of the proposed composite bridge pier can be predicted accurately by the conventional method that was used in the reinforced concrete structures. Shear strength of the composite bridge pier can be obtained by summing up shear strengths of the concrete and the steel tube. Excellent deformation capacities are also found from the experimental studies. The proposed composite bridge pier system not only simplifies the construction work greatly, but also provides superior seismic resistance as compared with that of the conventional method.proposed composite bridge piers can be accurately predicted by adopting the same design method of the reinforced concrete bridge piers, whereas the shear strength of the proposed composite bridge pier is obtained from the summation of the shear strengths of the concrete and the steel tube. The proposed bridge pier system not only enhances the seismic resistance, but also simplifies the construction work greatly.