Ömer Civalek

Longitudinal vibration analysis for microbars based on strain gradient elasticity theory

The longitudinal free vibration problem of a micro-scaled bar is formulated using the strain gradient elasticity theory. The equation of motion together with initial conditions, classical and non-classical corresponding boundary conditions for a micro-scaled elastic bar is derived via Hamilton’s principle. The resulting higher-order equation is solved for clamped-clamped and clamped-free boundary conditions. Effects of the additional length scale parameters on the frequencies are investigated. It is observed that size effect is more significant when the ratio of the microbar diameter to the additional length scale parameter is small. It is also observed that the difference between natural frequencies predicted by current and classical models becomes more prominent for both lower values of slenderness ratio of the microbar and for higher modes.

Discrete singular convolution approach for buckling analysis of rectangular Kirchhoff plates subjected to compressive loads on two-opposite edges

Buckling analysis of rectangular plates subjected to various in-plane compressive loads using Kirchhoff plate theory is presented. The method of discrete singular convolution has adopted. Linearly varying, uniform and non-uniform distributed load conditions are considered on two-opposite edges for buckling. The results are obtained for different types of boundary conditions and aspect ratios. Comparisons are made with existing numerical and analytical solutions in the literature. The proposed method is suitable for the problem considered due to its simplicity, and potential for further development.

Mathematical modeling of vibration problem of nano-sized annular sector plates using the nonlocal continuum theory via eight-node discrete singular convolution transformation

Abstract In the present study, free vibration analysis of nano-sized annular sector plate is analyzed using the nonlocal continuum theory. The method of discrete singular convolution (DSC) is used for numerical computations. Firstly, equation of motion of thin plates is formulated via nonlocal elasticity. Then, irregular physical domain is transformed into a rectangular domain by using geometric coordinate transformation. The DSC procedures are then applied to discretization of the transformed set of governing equations and related boundary conditions. The effects of nonlocal parameter, mode numbers, sector angle and radius ratio on the vibration frequencies are investigated in detail. It is seen that the size effects are significant in vibration analysis of nano-scaled annular sector plates and need to be included in the mechanical model.

A simple mathematical model of microtubules surrounded by an elastic matrix by nonlocal finite element method

A size dependent finite element model is developed.Nonlocal elasticity theory is used.Finite element solution is presented for buckling of microtubules.The effect of elastic matrix surrounded by microtubules is modeled. A simple nonlocal beam model is proposed to study buckling response of protein microtubules. The size-effect for buckling model of microtubules is considered by using the nonlocal continuum theory. Finite element procedure is used for solution of nonlocal differential equation of microtubules for elastic stability. The influence of the small length scale on the buckling value is examined for different geometric parameters. The effect of elastic matrix surrounded of microtubules is also examined and some benchmark results are presented.

Analysis of Thick Rectangular Plates with Symmetric Cross-ply Laminates Based on First-order Shear Deformation Theory

A new numerical technique, the discrete singular convolution (DSC) method, is developed for static analysis of thick symmetric cross-ply laminated composite plates based on the first-order shear deformation theory of Whitney and Pagano [1]. Regularized Shannons delta (RSD) kernel and Lagrange delta sequence (LDS) kernel are selected as singular convolution to illustrate the present algorithm. In the proposed approach, the derivatives in both the governing equations and the boundary conditions are discretized by the method of DSC. The bending behaviors of symmetric cross-ply laminated plates for different boundary and load conditions are presented. A comparison of the results with those available in literature has been presented. The results obtained by DSC method were compared with those obtained by the other numerical and analytical methods. It is found that both types of kernels give accurate results of plate deflection, but the regularized Shannons delta (RSD) kernel give better values of stresses than the Lagrange delta sequence (LDS) kernel.

Vibration analysis of FG cylindrical shells with power-law index using discrete singular convolution technique

Abstract In the present manuscript, free vibration response of circular cylindrical shells with functionally graded material (FGM) is investigated. The method of discrete singular convolution (DSC) is used for numerical solution of the related governing equation of motion of FGM cylindrical shell. The constitutive relations are based on the Love’s first approximation shell theory. The material properties are graded in the thickness direction according to a volume fraction power law indexes. Frequency values are calculated for different types of boundary conditions, material and geometric parameters. In general, close agreement between the obtained results and those of other researchers has been found.

Discrete singular convolution method for buckling analysis of rectangular Mindlin plates

The discrete singular convolution (DSC) method is proposed for solving the elastic buckling problem of thick rectangular plates under a uniaxial compressive loading. To allow for the effect of transverse shear deformation in thick plates, the Mindlin plate theory has been adopted. The numerical results are checked against available analytical and other numerical solutions. It is found that the convergence of the DSC approach is very good and the results agree well with those obtained by other researchers.

Free vibration analysis of annular sector plates via conical shell equations

Abstract In this paper, free vibration analysis of annular sector plates has been presented via conical shell equations. By using the first-order shear deformation theory (FSDT) equation of motion of conical shell is obtained. The method of discrete singular convolution (DSC) and method differential quadrature (DQ) are used for solution of the vibration problem of annular plates for some special value of semi-vertex angle via conical shell equation. The obtained numerical results based on the two numerical approaches for annular sector plates compare well with the results available in the literature. The effects of some geometric parameters, grid numbers and types of the grid distribution have been discussed for curved plates.

Static and dynamic response of sector-shaped graphene sheets

ABSTRACT Nonlocal elasticity theory is presented for the free vibration and bending analysis of nano-scaled graphene sheets having a sector shape. An eight-node curvilinear domain is used for transformation of the governing equation of motion of sector graphene from physical region to computational region in conjunction with the Kirchhoff plate theory. The discrete singular convolution method is employed for numerical solutions of resulting nonlocal governing differential equations and related boundary conditions. Then, the effects of nonlocal parameters, mode numbers, sector angles, and radius ratios on the static and vibration results of nano-scaled sector-shaped graphene sheets are discussed.

Derivation of Nonlocal Finite Element Formulation for Nano Beams

In the present paper, a new nonlocal formulation for vibration derived for nano beam lying on elastic matrix. The formulation is based on the cubic shape polynomial functions via finite element method. The size effect on finite element matrix is investigated using nonlocal elasticity theory. Finite element formulations and matrix coefficients have been obtained for nano beams. Size-dependent stiffness and mass matrix are derived for Euler-Bernoulli beams.