• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.374-375
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• 2008

In this study, the nano-composite actuator based on Fullerene and Nafion was newly developed to improve the electro active polymer actuators. The tensile test was employed to define the mechanical stiffness and strength of the nano-composite membrane. Also, the bending displacement of the Fullerene-Nafion based nano-composite actuator was investigated under DC and AC excitations with various magnitudes and frequencies. As a result, the new nano-composite actuator based on Fullerene-Nafion shows much larger deformation than the pure Nafion based actuator and solves the straightening back Problem of the previous electro active polymer actuators.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.444-450
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• 2006

IPMC actuators have been developed with multi-walled carbon nanotubes(MWNT) and $Nafion^{\circledR}$ ionic polymers. MWNT with different diameters of $3{\sim}5,\;4{\sim}6$ and $10{\sim}15$ nm and length of $10{\sim}20{\mu}m$ were used to enhance the mechanical and electrical performances of IPMC actuators. Ultrasonic treatment and high speed mixing were used to disperse MWNT homogeneously in $Nafion^{\circledR}$ solution. The electroless plating technique is used to make electrodes on the both side of the composite membrane. SEM and TEM images were taken to characterize the surface and micro-structures of the composite actuators. In this study, improved IPMC actuators were developed and compared with respect to bending actuation performance and electrical power consumptions.

• The Journal of Korea Robotics Society
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• v.4 no.1
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• pp.34-42
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• 2009

Rodents, specially rats, can recognize distance and shape of an object and also pattern of the textures by using their whiskers. Mechanoreceptors surrounding the root of whisker in their follicle measure deflection of the whisker. Rats can move their whisker back and forth freely. This ability, called active whisking or active sensing, is one of characteristics of rat behaviours. Many researches based on the mechanism have been progressed. In this paper, we test a simple and accurate method based on deflection of the whisker: we designed biomimetic whiskers modeling after a structure of follicle using the microphone. The microphone sensor measures a mechanical vibration. Attaching an artificial whisker beam to the microphone membrane, we can detect a vibration of whisker and this can show the deflection amount of whisker indirectly.

• Transactions of Materials Processing
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• v.23 no.1
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• pp.10-15
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• 2014

Recently, micro-speakers have attracted much attention due to their increasing demand in mobile devices. Micro-speakers use polymer diaphragms, which are manufactured from thin polymer film by the thermoforming process. The diaphragm is generally designed to be a circular membrane with a cross section consisting of a double dome structure, and a number of corrugations are located in the outer region to produce better sound quality. In the current study, a finite element (FE) analysis is performed for thermoforming, and the resulting thickness reduction in the corrugation regions is estimated. The estimated thickness distribution is used in further structural and modal FE analyses, from which the effects of local thickness reduction on the stiffness and vibration characteristics are determined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.298-302
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• 2002

Equivalent volume estimation of the coupler and two coupled microphones has a key role in standard microphone pressure calibration. The equivalent volume of the microphone is determined by the dynamic characteristics of the diaphragm system and front cavity. Therefore the modal parameters of diaphragm system - natural frequency and damping fatter - should be measured explicitly for the estimation of the equivalent volume. The diaphragm system is composed of the vibrating diaphragm, back slit behind diaphragm, pressure equalization vent, and front cavity which are acoustically coupled. In the measurement, the electrostatic actuator was used to excite the system with the swept sine, and the frequency response was obtained. The close actuator in front of the diaphragm must influence the radiation impedance of the system, and then the modal parameters. From the measured frequency response, the natural frequency and the damping factor could be estimated with the Complex exponential method based on the Prony model and the zero crossing real and imaginary plot.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.9 s.114
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• pp.919-925
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• 2006

An accurate mathematical model for complex stiffness of the pneumatic spring would be necessary for an efficient design of a pneumatic spring used in vibration isolation tables for precision instruments such as optical devices or nano-scale equipments. A diaphragm, often employed for prevention of air leakage, plays a significant role of complex stiffness element as well as the pressurized air itself Therefore, effects of the diaphragm need to be included in the dynamic model for a more faithful description of dynamic behavior of pneumatic spring. But the complex stiffness of diaphragm is difficult to predict In an analytical way, since it is a rubber membrane of complicated shape in itself. Moreover, the diaphragm should be expandable in response to pressurization inside a chamber, which makes direct measurement of complex stiffness of diaphragm extremely difficult. In our earlier research, the complex stiffness of diaphragm was indirectly measured, which was just to eliminate the theoretical stiffness of pressurized air from the measured complex stiffness of the pneumatic spring. In order to reflect complex stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however. it is required to be able to predict beforehand. In this paper, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes (e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.

• Plant Journal
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• v.12 no.3
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• pp.24-31
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• 2016

Wind-induced vibration is a phenomenon that a struture is oscillated due to wind force such as buffeting, vortex shedding wake and etc., which is one of important characteristics to be considered for design in case that stack has significant slenderness ratio or low natural frequency. International design standards of stack define several criteria for evaluating the suitability of stack design, which describe the required design considerations for each range of design parameters and provide the instruction to verify the stack design against wind-induced vibration simply. However, there is a limitation that they cannot provide quantitative information in case code requirement cannot be satisfied due to constraints of plant space or economical design. In order to overcome the limiation of code, integrated numerical analysis of computational fluid dynamics, harmonic analysis and finite element analysis were proposed to investigate wind-induced vibration for multiple stacks in actual plant. Simulated results of mutual wake interference effect between adjacent stacks were evaluated and compared to the criteria in international standards.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.247-258
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• 2004

The composite shell element is developed for the solution of undamped forced vibration problem of composite curved panels. The finite element used in the current study is an 4-node enhanced assumed shell element with six degrees of freedom per node. The composite shell element is free of both shear and membrane locking phenomenon by using the enhanced assumed strain(EAS) method. A modification to the first-order shear deformation shell theory is proposed, which results in parabolic thorough-thickness distribution of the transverse shear strains and stresses. It eliminates the need for shear correction factors in the first order theory. Newmark's direct integration technique is used for carrying out the integration of the equation motion, to obtain the repones history. Parametric studies of curved composite panels are carried out for forced vibration analysis by geometrical shapes and by laminated composite; such as fiber orientation, stacking sequence.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.2284-2291
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• 2010

In this paper, we investigate the vibration analysis of plates, using an 8-node shell element that accounts for the transverse shear strains and rotary inertia. The forced vibration analysis of plates subjected to arbitrary loading is investigated. In order to overcome membrane and shear locking phenomena, the assumed natural strain method is used. To improve an 8-node shell element for forced vibration analysis, the new combination of sampling points for assumed natural strain method was applied. The refined first-order shear deformation theory based on Reissner-Mindlin theory which allows the shear deformation without shear correction factor and rotary inertia effect to be considered is adopted for development of 8-node assumed strain shell element. In order to validate the finite element numerical solutions, the reference solutions of plates are presented. Results of the present theory show good agreement with the reference solution. In addition the effect of damping is investigated on the forced vibration analysis of plates.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.279-293
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• 2004

The analysis of linear static and free vibration problems of isotropic and laminated composite plates and shells is performed by the improved 9-node shell element with the new strain displacement relationship. In that relationship, the effect of new additional terms between the bending strain and displacement has been investigated in the warping problem. Natural co ordinate based strains, stresses and constitutive equations are used. The assumed natural strain method is used to alleviate both membrane and shear locking behavior from the element. The Lanczos method is employed in the calculation of the eigenvalues of laminated composite structures and the Gauss integration rule is adopted to evaluate the mass matrix. The numerical examples are compared with the analytical solutions to validate the current formulation and the results presented could be useful for the understanding of the behaviour of laminates under free vibration conditions.