جستجوی مقالات مرتبط با کلیدواژه "free vibrations" در نشریات گروه "مواد و متالورژی"

In this paper, the free vibrations of multi-layered composite cylindrical shells with rectangular cutout are analyzed analytically. Cylindrical shell equilibrium equations are derived based on classical shell theory (CST) and using Newton's method. Boundary conditions of the two-headed shell are considered simply supported. According to the boundary conditions, the displacement components are written as double Fourier series expansions. Relationships of the strain-displacement and curvature displacement are considered based on Love’s approximation theory. Modeling of the cutout by distribution function (Heaviside) is considered based on the equilibrium equations of the composite cylindrical shell. In order to obtain the natural frequency of the rectangular cutout composite cylindrical shell, the equations of motion have been solved using the Galerkin method. For validation, firstly, the results of the composite cylindrical shell have been compared with the Abaqus finite element software and the Previous literature in this field, that there is a good match between them. Finally, the effect of the geometrical parameters of the composite cylindrical shell with cutout, such as the length, radius, thickness and layering of the cylindrical shell, as well as the dimensions, direction and location of the cutout, on the natural frequency of the structure was investigated, that the results show that with increasing The dimensions of the cutout increase the reduction of the natural frequency of the structure.

In this study, an analytical model was presented for investigating the free vibrations of sandwich conical shells with lattice cores. A novel smeared method was employed to determine the stiffness contribution of the stiffeners. In this approach, the lattice core was approximated with an equivalent composite conical shell. The stiffeners were considered as a beam which support the shear loads and bending moments in addition to the axial loads. For this purpose, the stiffness contribution due to the stiffeners was firstly determined through the forces and moments analysis of a unit cell and then superimposed with those of the inner and outer skins in order to obtain the stiffness parameters of the whole structure. The governing equations were deduced using the classical shell theory of Donnell type and Galerkin method. In order to validate the analytical results, a 3-D finite element model was also created using ABAQUS software. Comparison of the results, revealed good agreements between the two approaches and demonstrated that the proposed analytical model is qualified enough to investigate the free vibrational behavior of sandwich conical shells with lattice cores. Results given are novel and can be used as a benchmark for future studies.

This article for the first time is concerned with effects of parameters as local smart stiffness and smart attached mass dimensions of dynamic behavior of thick laminated plates with attached mass. In deriving governing equations, Gark-Kant’s higher order theory is used and effects of SMA and attached mass`s stiffness taken into account and finally vibration equations of thick plate carrying attached mass contain SMA is reached by using Hamilton`s principal. Then by means of Galerkin method, mass and stiffness matrices are extracted for achieving to a standard eigenvalue vibration problem. In this problem simply supported boundary condition is used for each four edges. Some important parameters such as ratio of local stiffness to stiffness of host structure and smart attached mass dimension on main frequencies of laminated thick plate is studied. A Comparative result with those in published references is presented. These numerical results show that local stiffness due to smart attached mass has a great role on dynamic behavior of thick laminated plates that if SMA didn`t active properly or ignore the effect of attached mass`s stiffness the dynamic response of system will have a lot of changes.

Laminated composite conical shells are used as components of aerospace, marine industries and civil engineering structures. In this research free vibration of grid stiffened composite conical shell with simply support boundary condition is studied. No study has yet been done on vibration analysis of these structures. Smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole structure. The stiffeners are considered as a beam and support shear loads and bending moments in addition to the axial loads. Geodesic path is applied to the stiffeners. Equations were derived using classical shell theory of Donnell type and were solved using energy functional with the Rayleigh-Ritz method. A 3D finite element model was built using ABAQUS software. Results were compared and validated for grid stiffened structure with ABAQUS software. Comparisons and validations revealed good agreements. The effects of shell geometrical parameters and variations in the cross stiffeners angle on the natural frequencies were investigated.Results given are novel and can be used as a benchmark for further studies.