This paper carries out the static bending analysis of symmetric three-layer functionally graded sandwich beams, in which each layer is made from different functionally graded materials, and they are connected by shear connectors due to sliding movement. The finite element formulations are based on Timoshenko’s first-order shear deformation beam theory (FSDT) and the finite element method to establish the equilibrium equation of beams. The calculation program is coded in the MATLAB environment, and then verification examples are given out to compare the numerical data of present work with those of exact open sources. The impact of several geometrical and material parameters on the mechanical response of the structure, such as the height-to-length ratio, boundary conditions, volume fraction index, and especially the shear coefficient of connectors, is being explored. When designing and using these types of structures in engineering practice, the computed results can be utilized as a valid reference.

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This work is the first exploration of the static bending and dynamic response analyses of piezoelectric bidirectional functionally graded plates by combining the third-order shear deformation theory of Reddy and the finite element approach, which can numerically model mechanical relations of the structure. The present approach and mechanical model are confirmed through the verification examples. The geometrical and material study is conducted to evaluate the effects of the feedback coefficients, volume fraction parameter, and constraint conditions on the static and dynamic behaviors of piezoelectric bidirectional functionally graded structures, and this work presents a wide variety of static and dynamic behaviors of the plate with many interesting results. There are many meanings that have not been mentioned by any work, especially the working performance of the structure is better than that when the feedback parameter of the piezoelectric component is added, that is, the piezoelectric layer increases the working efficiency. Numerical investigations are the important basis for calculating and designing related materials and structures in technical practice.

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The knowledge of velocities of a remotely operated underwater vehicle (ROV) is crucial for the study of the ROV motion. The ROV motion equations are complemented by hydrodynamic parameters and forces acting upon the ROV. The matrices of hydrodynamic damping coefficients and external forces acting upon the ROV are considered in this study as well. The computational results obtained by the Runge-Kutta method are compared with the experiment. It appears that the presented model can be useful for the design and investigation of remotely operated underwater vehicles.

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The paper presents a method of determining the dynamic parameters of multiple-rocket-launcher system mounted on the wheeled vehicle based on Newton's law of motion. The dynamic simulation was conducted and then the results were compared with the corre-sponding experimental data to verify the reliability of the model. The model was ap-plied in calculation and tested out on multiple-rocket-launcher system B?-21 (of Rus-sia). The theoretical model calculation results are relatively consistent with the meas-ured experimental data. The dependence of the launcher oscillation on the rate of fire was investigated, which determined the optimal rate of fire for each launcher. These results are used to evaluate the firing stability of the launcher when firing individual shots and firing bursts. This is an important theoretical basis which can be a reference for designers in the design process of improvement, manufacture, exploitation and use of a launcher mounted on the wheeled vehicle.

A new fern species, Polystichum quangbinhense, a member of P. subg. Haplopolystichum (Dryopteridaceae), is described and illustrated from Quang Binh Province in central Vietnam. It is the southernmost cave species of the genus discovered so far. Polystichum quangbinhense is most similar to P. obliquum in having oblong pinnae, but the two can be distinguished from each other by the morphology of pinna margins. Polystichum quangbinhense was found inside a karst cave at an elevation of 120 m with humid and shady conditions and is currently known from two populations occurring at two sides of the Doi Cave (So Dua Cave), Quang Binh Province, central Vietnam, and is classified as Critically Endangered (CR) following IUCN Red List criteria.