• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.285-287
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• 2014

Equations of motion for the vibration analysis of rotating pre-twisted beams with functionally graded material properties are derived in this paper. Based on Timoshenko beam theory, the effects of shear and rotary inertia are considered. The pre-twisted beam has a rectangular cross-section and is mounted on a rotating rigid hub with a setting angle. Functionally graded material (FGM) properties are considered along the height direction of the beam. The equations of stretching and bending motion are derived by Kane's method employing hybrid deformation variables. To validate the derived equations, natural frequencies of a rotating FGM pre-twisted beam are compared to those obtained by a commercial software ANSYS. The effects of the pre-twisted angle, slenderness ratio, hub radius, volume fraction exponent, and angular speed on the modal characteristics of the system are investigated with the proposed model.

• Journal of the Korean Ceramic Society
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• v.14 no.4
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• pp.226-229
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• 1977

The infrared absorption spectrum of Synthesized magnesite is shown in the wve number region 2510 and 745cm-1. By using Wilson's GF matrices the force constants' of the Urey-Bradley force field were deterined from the infrared absorption frequencies. For magnesite the stretching force constant K=5.41, the bending force constant H=0.46, the repulsive force constant F=1.97, and the force constant for the out-of-plane vibration fθ=0.65md/Å. For calcite they are K=5.51, H=0.38, F=1.88 and fθ=0.64md/Å.

• Smart Structures and Systems
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• v.26 no.2
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• pp.213-226
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• 2020

In this manuscript, static and dynamic behaviors of geometrically imperfect carbon nanotubes (CNTs) subject to different types of end conditions are investigated. The Doublet Mechanics (DM) theory, which is length scale dependent theory, is used in the analysis. The Euler-Bernoulli kinematic and nonlinear mid-plane stretching effect are considered through analysis. The governing equation of imperfect CNTs is a sixth order nonlinear integro-partial-differential equation. The buckling problem is discretized via the differential-integral-quadrature method (DIQM) and then it is solved using Newton's method. The equation of linear vibration problem is discretized using DIQM and then solved as a linear eigenvalue problem to get natural frequencies and corresponding mode shapes. The DIQM results are compared with analytical ones available in the literature and excellent agreement is obtained. The numerical results are depicted to illustrate the influence of length scale parameter, imperfection amplitude and shear foundation constant on critical buckling load, post-buckling configuration and linear vibration behavior. The current model is effective in designing of NEMS, nano-sensor and nano-actuator manufactured by CNTs.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.126-130
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• 2008

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 ${\mu}m$ graded index multimode fiber using a short cylindrical piezoelectric transducer(PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.

• Steel and Composite Structures
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• v.45 no.6
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• pp.839-850
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• 2022

This paper presents an analytical solution to study the combined effect of non-local and stretching effect on the vibration of advanced functionally graded (FG) nanoplates. A new quasi-3D plate theory is presented; there are only five unknowns and any shear correction factor is used. A new displacement field with a new shear warping function is proposed. The equilibrium equations of the FG nanoplates are obtained using the Hamilton principle and solved numerically using the Navier technique. The material properties of functionally graded nanoplates are presumed to change according to the power-law distribution of ceramic and metal constituents. The numerical results of this work are compared with those of other published results to indicate the accuracy and convergence of this theory. Hence, a profound parameterstudy is also performed to show the influence of many parameters of the functionally graded nanoplates on the free vibration responses is investigated.

• Advances in aircraft and spacecraft science
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• v.11 no.1
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• pp.55-81
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• 2024

This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.3
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• pp.210-216
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• 2003

A nonlinear dynamic modeling method for cantilever beams undergoing axially oscillating motion is presented in this paper. Hybrid deformation variables are employed for the modeling method with which frequency response characteristics of axially oscillating cantilever beams are investigated. It is shown that the geometric nonlinear effects of stretching and curvature play important roles to accurately predict the frequency response characteristics. The effects of the amplitude and the damping constant on the frequency characteristics are also exhibited.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.11
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• pp.868-874
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• 2003

A nonlinear modeling method for an axially oscillating cantilever beam with a concentrated mass is presented in this paper. Hybrid deformation variables are employed for the modeling method with which frequency response characteristics of axially oscillating cantilever beams are investigated. The geometric nonlinear effects of stretching and curvature are considered to accurately predict the frequency response characteristics of the oscillating cantilever beam. The effects of the size and the location of the concentrated mass on the frequency characteristics are investigated. It is found that the dynamic instability is significantly influenced by the two parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.69-72
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• 2007

Cellulose is a beneficial material that has low cost, lightweight, high compatibility and biodegradability. Recently electroactive paper (EAPap) on cellulose base was discovered as a smart material and actuator through ion migration and piezoelectric effect. Furthermore cellulose has a potentiality to apply the display material, because of its high reflectivity, flexibility and high transmittance. The various shapes and height patterns of the Cellulose acetate (CA) solution, such as circle and honeycomb patterns, were fabricated and observed by field emission scanning electron microscope (FESEM, S4300 Hitachi). The resulting pattern showed uniform size in the large area without defect. After stretching the CA film with saponification process in the sodium methoxide in methanol solution, Most of the compositions become one directional ordered nanofibers below 50nm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.262-267
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• 2002

A nonlinear dynamic modeling method for cantilever beams undergoing axially oscillating motion is presented in this paper. Hybrid deformation variables are employed for the modeling method with which frequency response characteristics of a axially oscillating cantilever beams are investigated. It is shown that the geometric nonlinear effects of stretching and curvature play important roles to accurately predict the frequency response characteristics. The effects of the amplitude and the damping constant on the frequency characteristics are also exhibited.