Porous materials are effective for the isolation of sound with medium to high frequencies, while periodic structures are promising for low to medium frequencies. In the present work, we study the sound insulation of a periodically rib-stiffened double-panel with porous lining to reveal the effect of combining the two characters above. The theoretical development of the periodic composite structure, which is based on the space harmonic series and Biot theory, is included. The system equations are subsequently solved numerically by employing a precondition method with a truncation procedure. This theoretical and numerical framework is validated with results from both theoretical and finite element methods. The parameter study indicates that the presence of ribs can lower the overall sound insulation, although a direct transfer path is absent. Despite the unexpected model results, the method proposed here, which combines poroelastic modeling and periodic structures semi-analytically, can be promising in broadband sound modulation. IntroductionOwing to their high stiffness-to-weight ratio, multipanel structures are widely used in engineering applications, such as aircrafts, underwater, and architectural structures. Their acoustic performance has been studied for a long time [1,2,3]. Composite multipanel structures without any attachments or fillings are always the simplest to operate. Both theoretical, and experimental and numerical methods are developed with regard to their sound transmission loss (STL); for example, the theoretical models by Xin [4], Sakagami [5] (with experiments) and the semi-empirical models by Sharp [1], Gu [6], Davy [7]. These prediction models were reviewed and compared by Hongisto [3] and Legault [8] contemporarily.However, none of them are appropriate for the case studied herein.Composite multipanel structures with attachments or absorption fillings are emphasized more. However, their absorption fillings are complicated; in most cases, they are or can be considered as porous materials. Therefore, two widely used models for porous media can be used, i.e., the Biot theory [9] and the equivalent fluid model (EFM) [10]. In these absorption filling (cavity) problems, the EFM, owing to its simplicity, is widely used together with numerical [11] or semi-analytical methods [8,12,13]. For elastic frame porous problems, the Biot theory should be used [14,15] as the EFM is invalid. Using the Biot theory, together with the simplifications of Deresiewicz [16] and Allard [17], Bolton [18] studied a two-dimensional (2D) multipanel structure with elastic porous materials, where the closed form expressions for 2D poroelastic field are obtained. The three-dimensional (3D) counterpart, with closed-form poroelastic field expressions, has been revealed by Zhou [19]. The effect of flow on these structures was subsequently studied by Liu [20]. The numerical methods [14] for these structures, based on the Biot theory, were also developed.Meanwhile, multipanel structures with attachments were prominent as well.The ...

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Electromagnetic railguns have an advantage over traditional chemical propulsion weapons, in that the projectile can be accelerated to extremely high speeds and effective damage can be achieved. However, during the launch from an electromagnetic railgun, the ammunition will be subject to a harsh environment, including very strong and violently changing electromagnetic fields, high-g acceleration impact, high temperatures, and so on; and thus, the reliability of the fuze is threatened, and the safety and damage effectiveness of the ammunition will be seriously degraded. In this paper, the harsh environment during the launch process is first reviewed, including the experimental data, the modeling, and simulation of the multiphysics fields. In particular, the coupling effect of these multiphysics fields are revealed, which aggravates the extreme environment. Furthermore, this paper reviews the protection of fuzes against strong magnetic fields and high-g impacts from three aspects, namely, materials, devices, and systems, and presents prospects for future research. This review will guide studies on the protection of fuzes and the stability of ammunition, as well as promote the effectiveness of electromagnetic railguns.INDEX TERMS Electromagnetic launching, fuze, reliability, harsh environment of multiphysics fields, electromagnetic shielding, anti-high-g impact technology.

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Many single-tower reinforced concrete core wall-steel frame (RCC-SF) buildings have been built in China, but there are no buildings of different-height multi-tower hybrid system. A multi-tower RCC-SF tall building was thus studied because of its structural complexity and irregularity. First, a 1/15 scaled model structure was designed and tested on the shake table under minor, moderate, and major earthquake levels. Then, the dynamic responses of the model structure were interpreted to those of the prototype structure according to the similitude theory. Experimental results demonstrate that, despite the complexity of the structure, the lateral deformation bends as the "bending type" and the RC core walls contribute more than the steel frames to resist seismic loads. The maximum inter-story drift of the complex building under minor earthquakes is slightly beyond the elastic limitation specifi ed in the Chinese code, and meets code requirements under major earthquakes. From the test results some suggestions are provided that could contribute favorable effect on the seismic behavior and the displacement of the building.