In this paper, the free vibration and buckling analyses of the cylindrical sandwich panel with magneto-rheological fluid layer for simply supported boundary conditions was performed based on an improved higher order sandwich panel theory. This paper deals with investigation of the effects of magnetic field, geometrical parameters such as the core thickness to the panel thickness ratio, MR layer thickness to the panel thickness ratio and the fiber angle on the natural frequencies, loss factors and buckling loads corresponding to the first four mode shapes. In order to validate the results obtained from the present study, the cylindrical sandwich panel was simulated and analyzed in finite element software ABAQUS. A good agreement was observed between the results of present method and those extracted from simulation.

This paper dealt with free vibration analysis of thick double curved composite sandwich panels with simply supported or fully clamped boundary conditions based on a new improved higher order sandwich panel theory. The formulation used the first order shear deformation theory for composite face sheets and polynomial description for the displacement field in the core layer which was based on the displacement field of Frostig's second model. The fully dynamic effects of the core layer and face sheets were also considered in this study. Using the Hamilton's principle, the governing equations were derived. Moreover, effects of some important parameters like that of boundary conditions, thickness ratio of the core to panel, radii curvatures and composite lay-up sequences were investigated on free vibration response of the panel. The results were validated by those published in the literature and with the FE results obtained by ABAQUS software. It was shown that thicker panels with a thicker core provided greater resistance to resonant vibrations. Also, effect of increasing the core thickness in general was significant decreased fundamental natural frequency values. KeywordsFree vibration, Double curved sandwich panel, Boundary conditions, Improved higher order sandwich panel theory.Improved high order free vibration analysis of thick double curved sandwich panels with transversely flexible cores INTRODUCTIONStructural efficiency is an important attribute for aircraft structures. A higher order theory approach, used by Kant and Patil (1991), replaced sandwich structure with an equivalent higher order shear deformable structure, which lacked the ability to determine local buckling modes and imperfection effects on the overall behavior. Using the three-dimensional elasticity equations, Bhimaraddi (1993) studied the static response of orthotropic doubly curved shallow shells. He assumed that the ratio of the shell thickness to its middle surface radius is negligible as compared to unity. The high- er order sandwich panel theory was developed by Frostig et al. (1994Frostig et al. ( , 2004, who considered two types of computational models in order to express governing equations of the core layer. The second model assumed a polynomial description of the displacement fields in the core that was based on displacement fields of the first model. Their theory did not impose any restrictions on distribution of the deformation through thickness of the core. Singh (1999) studied free vibration of the open deep sandwich shells made of thin layers and a moderately thick core. Rayleigh-Ritz method was also used to obtain natural frequencies. The improved higher order sandwich plate theory (IHSAPT), applying the first-order shear deformation theory for the face sheets, was introduced by Malekzadeh et al. (2005Malekzadeh et al. ( , 2006.

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For the first time, the bending analysis of a double curved sandwich panel was presented which was subjected to point load, uniform distributed load on a patch, and harmonic distributed loads and was based on a new improved higher order sandwich panel theory. Since the cross-sectional warping was accurately modeled by this theory, it did not require any shear correction factor. Also, the present analysis incorporated trapezoidal shape factor (the 1+z/R terms) of a curved panel element. Geometry was used for the consideration of different radii curvatures of the face sheets, while the core was unique. Unlike most of other reference works, the core can have non-uniform thickness. The governing equations were derived by the principle of minimum potential energy. The effects of types of boundary conditions, types of applied loads, core to panel, and radii curvatures ratios on the bending response were also studied.

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Based on a new improved higher-order sandwich panel theory, the buckling analysis of a truncated conical composite sandwich panel with simply supported and fully clamped boundary conditions was performed for the first time. This panel was subjected to axial compression and external pressures. The governing equations were derived by using the principle of minimum potential energy. The first-order shear deformation theory was used for the composite face sheets, and for the core, a polynomial description of the displacement fields was assumed. Geometry was used for the consideration of different radii curvatures of the face sheets and the core was unique. The effects of types of boundary conditions, conical angles, length to smaller radius of core ratio, core to panel thickness ratio, and smaller radius of core to panel thickness ratio on the buckling response of truncated conical composite sandwich panels were also studied. The results were validated by the results published in the literature and the presented FE results were obtained by ABAQUS software.