The acoustic black hole (ABH) phenomenon in thin-walled structures with a tailored power-law-profiled thickness allows for a gradual change of the phase velocity of flexural waves and energy focalization. However, ideal ABH structures are difficult to realize and suffer from potential structural problems for practical applications. It is therefore important to explore alternative configurations that can eventually alleviate the structural deficiency of the ideal ABH structures, while maintaining similar ability for wave manipulation. In this study, the so-called imperfect two-dimensional ABH indentation with different tailored power-law-profiled is proposed and investigated. It is shown that the new indentation profile also enables a drastic increase in the energy density around the tapered area. However, the energy focalization phenomena and the process are shown to be different from those of conventional ABH structure. With the new indentation profile, the stringent power-law thickness variation in ideal ABH structures can be relaxed, resulting in energy focalization similar to a lens. Different from an ideal ABH structure, the energy focalization point is offset from, and downstream of indentation center, depending on the structural geometry. Additional insight on energy focalization in the indentation is quantitatively analyzed by numerical simulations using structural power flow. Finally, the phenomenon of flexural wave focalization is verified by experiments using laser ultrasonic scanning technique.

Due to the heterogeneous nature and electric anisotropy, it is challenging to establish a numerical model to analyze the electromagnetic properties of multilayer carbon fiber-reinforced polymer (CFRP) laminate. In this study, we focus on the exploration of an effective electromagnetic modeling approach for calculation of eddy currents in CFRP laminate composite, as well as eddy current testing signals due to surface cracks. In order to prove the feasibility of modeling CFRP laminate with homogeneous anisotropic layers, the electrical parameters in the three directions are measured, and eddy current path in CFRP is investigated according to the measurement results. A finite element solver based on reduced magnetic vector potential ( A _r) formulation and edge elements is developed to enable the eddy current simulation of anisotropic CFRP material, which avoids matching the discretization of source coils with the rest of conductor mesh, and can easily solve the field continuity problem in the interface between two adjacent fiber layers of CFRP laminate. The A _r formulation and way to calculate the eddy current testing signals are described. To validate of the developed simulation code, a comparison is conducted between the calculated signals and experimental results of thin-opening cracks in a CFRP test piece, which indicates the simulation code can predict eddy current testing signals with good precision.

Frequency up-converting vibration energy harvester can bridge the gap between high-frequency response and low-frequency input, greatly increasing the efficiency of energy conversion. This article proposed a novel frequency up-converting energy harvester based on 1:3 internal resonance in 2 degree-of-freedom cubic nonlinear systems. The harvester consists of two asymmetric cantilevers corresponding to two vibration degrees-of-freedom. The ratio of cantilevers’ first-order resonances is (or close to) 1:3. When excited frequency matches the resonant frequency of the first assisting cantilever, 1:3 internal resonance of the harvester system occurs, leading to drastic vibration of the second generating cantilever at its resonance. The generated voltage frequency is then three times increased. Finally, simulated and experimental results clearly proved this frequency up-converting principle. In addition, the resonant frequency tuning and wideband behaviors of the harvester were also investigated, which increased the viability of the proposed harvester under the practical environment vibrations.

A previously proposed planar axisymmetric dynamic vibration absorber (DVA), with embedded acoustic black hole (ABH) features, has been shown to suffer from the very selective coupling with the host structure, thus compromising its vibration reduction performance. To tackle the problem, an eccentric ABH-based circular DVA whose thickness profile is tailored according to a circumferential gradient variation is proposed. This new configuration preserves the ABH profile in the radial direction and breaks the axisymmetric of the original DVA design at the same time. While the former permits the ABH features to fully play out in a continuous manner, the later entails a more effective coupling with the host structure. These salient properties have been demonstrated and confirmed both numerically and experimentally by examining a benchmark plate structure. For analyses, a coupling model embracing the host structure and the add-on DVAs is established which allows the calculation of the coupling coefficient, a vital quantity to guide the DVA design. Studies demonstrate the advantages of the proposed DVA over existing designs for the same given mass. The enriched structural coupling and the enhanced modal damping, arising from the eccentric and circumferentially graded ABH design, are shown to be the origin of such improvement. All in all, the physical process underpinning the dynamic absorber principle and waveguide absorber from the host structures is simultaneously consolidated, thus leading to superior broadband structural vibration suppression.