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Application of transformation theory to underwater acoustics has been a challenging task because highly anisotropic density is unachievable in water. A possible strategy is to exploit anisotropic modulus rather than density, while has not been experimentally demonstrated. We present an annular underwater acoustic cloak designed from particular graded solid microstructures. The geometry tailored microstructures mimics meta-fluid with highly anisotropic modulus through substantially suppressed shear wave. Transient wave experiments are conducted with the cloak in a designed 2D underwater waveguide system and proved excellent cloaking performance for enclosed target over broadband frequency 9-15 kHz. This finding paves the way for controlling underwater acoustics using the structured anisotropic modulus meta-fluid.

Base-isolated structures are vulnerable to long-period ground motions due to resonances. The hybrid control strategy combining traditional tuned mass dampers (TMDs) with base-isolation systems has been proved by some researchers to be effective in preventing the resonant behaviors. However, large space for TMDs is required because of large stroke lengths of TMDs, which may be difficult to realize in practical applications. In this paper, a non-traditional TMD that is directly connected to the ground by a dashpot is adopted to mitigate the resonant behavior of a structure. It is found that the conventional design method of traditional TMDs based on the quasifixed points theory cannot provide the global minimum value of the objective function for non-traditional TMD systems. An optimum design method for obtaining a wide suppression bandwidth is proposed. Seismic-induced vibration control for a three degree-of-freedom base-isolated structural system with a non-traditional TMD is studied. The control effect of the optimally designed non-traditional TMD is significantly improved, and the stroke length of the non-traditional TMD is greatly reduced, compared with the traditional TMD during near-field long-period earthquakes. In these regards, non-traditional TMDs may provide a better solution for retrofitting or constructing base-isolated structures. = 0.119): (a) absolute acceleration of primary structure; (b) stroke length of tuned mass damper (TMD). OPTIMUM DESIGN FOR MORE EFFECTIVE TMD

Summary: A novel method was developed to prepare an exfoliated styrene butadiene rubber (SBR)/clay nanocomposite with a strong interface between the clay layers and the rubber. An exfoliation mechanism was proposed and verified based on X‐ray diffraction (XRD)/transmission electron microscopy (TEM) analyses of the intercalation/exfoliation phenomena after each step of the process. The significant improvements of mechanical properties may give the first evidence that both exfoliation and a strong interface play critical roles in nanoreinforcement.TEM image of a SBR/AA‐clay nanocomposite.imageTEM image of a SBR/AA‐clay nanocomposite.

SUMMARY Floor isolation system (FIS) achieving very small floor accelerations has been used to ensure human comfortability or protect important equipments in buildings. Tuned mass damper (TMD) with large mass ratios has been demonstrated to be robust with respect to the changes in structural properties. This paper presents the concept of a TMD floor vibration control system, which takes advantages of both the FIS and TMD. Such a system is called ‘TMD floor system’ herein. The TMD floor system (TMDFS) in which building floors serve as TMDs can achieve large mass ratio without additional masses. Furthermore, multiple TMD floors installed in a building can control multimode vibrations. Then, an optimal design process, where the objective function is set as the maximum magnitude of the frequency response functions of inter‐storey drifts, is proposed to determine the TMD floor parameters. Additionally, the multimode approach is applied to determine the optimal locations of TMD floors if not all of the floors in a building can serve as TMDs. In addition to the numerical simulations, a scaled model shaking table experiment is also conducted. Both the numerical and experimental results show that the absolute accelerations of the TMD floors are smaller than those of the main structural storeys, which indicates the TMDFS maintains the merit of FIS while greatly reducing seismic responses of main structures. Copyright © 2013 John Wiley & Sons, Ltd.