• Journal of the Korean Society for Precision Engineering
• /
• v.30 no.10
• /
• pp.1069-1077
• /
• 2013

These days, the interest of high speed robotic system is increasing because it is very important to get the cost-competitiveness. The parallel kinematic mechanism is more useful than the serial kinematic mechanism. For the reason, the researches on the parallel robot system as a high speed robotic one are have been done by many researchers. In this paper, the research on the design and analysis of the high speed parallel robot has been done by the authors. First, Basic robot structure is designed and modal analysis is studied to get the basic characteristics of the vibrational motion. Second, the harmonic analysis is studied to get the information of the natural frequency in some different designs of the outer-arm of the parallel robot. Finally, actual robot system is designed and implemented and it is confirmed that the analysis results coincide with the experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.928-933
• /
• 2004

The vibration characteristic is a primary design factor. The cylindrical shells are used as a primary components of complex structure. also, The cylindrical shells have oblique angle. In this study, The vibrational characteristics of steel and plain wave GFRP cylindrical shell with an oblique end are given by experimental and finite element method. To be find characteristic of the oblique end, the mass of the cylindrical shell is maintained. Natural frequency and mode shapes of isotropic and plain weave composite shells are obtained by modal test. The results are compared with those of the finite element method. The simply supported boundary conditions with bolts along the circumferential direction of the GFRP shell are well achieved. Also, The clamped boundary conditions is applied to the steel specimen. Those are shown to agree well with the analytical results and finite element analysis results.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.6
• /
• pp.430-437
• /
• 2003

A conveying fluid cantilever pipe subjected to a uniformly distributed tangential follower force and three moving masses upon it constitute this vibrational system. The influences of the velocities of moving masses, the distance between two moving masses, and the uniformly distributed tangential follower force have been studied on the dynamic behavior of a cantilever pipe system by numerical method. The uniformly distributed tangential follower force is considered within its critical value of a cantilever pipe without moving masses, and three constant velocities and three constant distances between two moving masses are also chosen. When the moving masses exist on pipe, as the velocity of the moving mass and the distributed tangential follower force Increases. the deflection of cantilever pipe conveying fluid is decreased, respectively Increasing of the velocity of fluid flow makes the amplitude of a cantilever pipe conveying fluid decrease. After the moving mass passed upon the pipe, the tip- displacement of a pipe is influenced by the coupling effect between interval and velocity of moving mass and the potential energy change of a cantilever pipe. Increasing of the moving mass make the frequency of the cantilever pipe conveying fluid decrease.

• Steel and Composite Structures
• /
• v.24 no.6
• /
• pp.711-726
• /
• 2017

In the present work, by considering the agglomeration effect of single-walled carbon nanotubes, free vibration characteristics of functionally graded (FG) nanocomposite sandwich plates resting on Pasternak foundation are presented. The volume fractions of randomly oriented agglomerated single-walled carbon nanotubes (SWCNTs) are assumed to be graded in the thickness direction. To determine the effect of CNT agglomeration on the elastic properties of CNT-reinforced composites, a two-parameter micromechanical model of agglomeration is employed. In this research work, an equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented straight CNTs. The 2-D generalized differential quadrature method (GDQM) as an efficient and accurate numerical tool is used to discretize the equations of motion and to implement the various boundary conditions. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The benefit of using the considered power-law distribution is to illustrate and present useful results arising from symmetric and asymmetric profiles. The effects of two-parameter elastic foundation modulus, geometrical and material parameters together with the boundary conditions on the frequency parameters of the laminated FG nanocomposite plates are investigated. It is shown that the natural frequencies of structure are seriously affected by the influence of CNTs agglomeration. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated plates.

• Advances in nano research
• /
• v.7 no.6
• /
• pp.431-442
• /
• 2019

Vibration analysis of carbon nanotubes (CNTs) is very essential field owing to their many promising applications in tiny instruments. In current study, the Eringen's nonlocal elasticity theory with clamped-clamped and clamped-free end conditions is utilized for the vibration analysis of armchair and zigzag SWCNTs. The Fourier method is utilized to solve the ordinary differential equation. The motion equation for this system is developed using a novel wave propagation method. Complex exponential functions have been used and the axial model depends on BCs that has been described at the edges of CNTs. The behavior of different nonlocal parameters is considered to find the vibrational frequency of SWCNTs. It is exhibited that the effect of frequencies against aspect ratio by varying the bending rigidity. It has been investigated that by increasing the nonlocal parameter decreases the frequencies and on increasing the aspect ratio increases the frequencies for both the tubes. To generate the fundamental natural frequencies of SWCNTs, computer software MATLAB engaged. The numerical results are validated with existing open text. Since the percentage of error is negligible, the model has been concluded as valid.

• Advances in aircraft and spacecraft science
• /
• v.3 no.1
• /
• pp.1-14
• /
• 2016

The Carrera Unified Formulation (CUF) is here extended to perform free-vibrational analyses of rotating structures. CUF is a hierarchical formulation, which enables one to obtain refined structural theories by writing the unknown displacement variables using generic functions of the cross-section coordinates (x, z). In this work, Taylor-like expansions are used. The increase of the theory order leads to three-dimensional solutions while, the classical beam models can be obtained as particular cases of the linear theory. The Finite Element technique is used to solve the weak form of the three-dimensional differential equations of motion in terms of "fundamental nuclei", whose forms do not depend on the adopted approximation. Including both gyroscopic and stiffening contributions, structures rotating about either transversal or longitudinal axis can be considered. In particular, the dynamic characteristics of thin-walled cylinders and composite blades are investigated to predict the frequency variations with the rotational speed. The results reveal that the present one-dimensional approach combines a significant accuracy with a very low computational cost compared with 2D and 3D solutions. The advantages are especially evident when deformable and composite structures are analyzed.

• Journal of the Korean Chemical Society
• /
• v.67 no.1
• /
• pp.13-18
• /
• 2023

We evaluate electron density functional theories for the computation of 0-1 and 1-2 transition energies of local OH stretching motion of water molecules in condensed phases. By examining thirteen density functionals and nine sets of basis functions, it was found that the optimal combination that predicts the transition energies highly correlated with those calculated by the coupled cluster theory, CCSD(T), is the hybrid density functional theory developed by Head-Gordon group, ωB97X(D)/6-31+G^*.

• Steel and Composite Structures
• /
• v.48 no.2
• /
• pp.191-206
• /
• 2023

The present research investigates how micromechanical models affect the behavior of Functionally Graded (FG) plates under different boundary conditions. The study employs diverse micromechanical models to assess the effective material properties of a two-phase particle composite featuring a volume fraction of particles that continuously varies throughout the thickness of the plate. Specifically, the research examines the vibrational response of the plate on a Winkler-Pasternak elastic foundation, considering different boundary conditions. To achieve this, the governing differential equations and boundary conditions are derived using Hamilton's principle, which is based on a four-variable shear deformation refined plate theory. Additionally, the Galerkin method is utilized to compute the plate's natural frequencies. The study explores how the plate's natural frequencies are influenced by various micromechanical models, such as Voigt, Reuss, Hashin-Shtrikman bounds, and Tamura, as well as factors such as boundary conditions, elastic foundation parameters, length-to-thickness ratio, and aspect ratio. The research results can provide valuable insights for future analyses of FG plates with different boundaries, utilizing different micromechanical models.

• Steel and Composite Structures
• /
• v.46 no.1
• /
• pp.15-31
• /
• 2023

Organic solar cells utilized natural polymers to convert solar energy to electricity. The demands for green energy production and less disposal of toxic materials make them one of the interesting candidates for replacing conventional solar cells. However, the different aspects of their properties including mechanical strength and stability are not well recognized. Therefore, in the present study, we aim to explore the chaotic responses of these organic solar cells. In doing so, a specific type of organic solar cell constructed from layers of material with different thicknesses is considered to obtain vibrational and chaotic responses under different boundaries and initial conditions. A square plate structure is examined with first-order shear deformation theory to acquire the displacement field in the laminated structure. The bounding between different layers is considered to be perfect with no sliding and separation. On the other hand, nonlocal elasticity theory is engaged in incorporating the structural effects of the organic material into calculations. Hamilton's principle is adopted to obtain governing equations with regard to boundary conditions and mechanical loadings. The extracted equations of motion were solved using the perturbation method and differential quadrature approach. The results demonstrated the significant effect of relative glass layer thickness on the chaotic behavior of the structure with higher relative thickness leading to less chaotic responses. Moreover, a comprehensive parameter study is presented to examine the effects of nonlocality and relative thicknesses on the natural frequency of square organic solar cell structure.

• Korean Journal of Materials Research
• /
• v.2 no.4
• /
• pp.279-284
• /
• 1992

Oxygen adsorption on the single crystal NbC(111) surface was studied by high-resolution electron energy loss and ultraviolet photoelectron spectroscopy. On the NbC(111) surface, oxygen molecules as well as oxygen atoms were adsorbed. Oxygen atoms were located at the 3-fold hollow site of the NbC(111) surface with the frequency of 548c$m^{-1}$. It was found that oxygen molecules had vibrational frequency of 968c$m^{-1}$which was much lower than that of the free oxygen molecule. Also the work function of the NbC(111) surface has increased by adsorption of oxygen molecule. These suggest electron tranfer from the NbC(111) substrate to the 2p${pi}_g$ substrate of the oxygen molecule.