• 마이크로전자및패키징학회지
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• 제10권1호
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• pp.25-29
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• 2003

이 논문은 고분자 박막이 주변으로부터 수분을 흡수하게 될 때, 탄성 기판과 점탄성 박막의 계면 모서리에서 발생하는 응력 특이성을 다루고 있다. 계면에서 발생하는 응력을 조사하기 위해서 경계 요소법이 사용되고 있다. 주어진 점탄성 모델에 대해서 특이 차수가 수치적으로 계산된다. 이 논문에서 고려하고 있는 점탄성 모델에 대해서, 응력특이계수는 시간이 경과함에 따라 이완되고 있으나 특이 차수는 증가되고 있음을 보여준다.

• 대한기계학회논문집A
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• 제24권3호
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• pp.685-690
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• 2000

This paper deals with the stress singularity induced at the interface corner between the viscoelastic thin film and the rigid substrate as the film absorbs moisture from the ambient environment. Th e time domain boundary element method is employed to investigate the behavior of interface stresses. The order of the free-edge singularity is obtained numerically for a given viscoelastic model. It is shown that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model considered.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2003년도 기술심포지움 논문집
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• pp.247-250
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• 2003

In this paper, the boundary element analysis of viscoelastic strain energy release ,ate G(t) for the cracked linear viscoelastic materials is attempted. This study proposes the G(t) equation and the calculating method of G(t) by time-domain boundary element analysis for the viscoelastic solids. The G(t) is defined as the derivative of the viscoelastic potential energy $\Pi(t)$ with respect to crack length a. Two example problems are presented to show the applicability of the proposed method to the analysis of the cracked linear viscoelastic solids. Numerical results of example problems show the accuracy and effectiveness of the proposed method.

• Steel and Composite Structures
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• 제50권4호
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• pp.429-441
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• 2024

This paper studies the free vibration behavior of trapezoidal shaped coupled double-layered graphene sheets (DLGS) system using first-order shear deformation theory (FSDT) and incorporating nonlocal elasticity theory. Two nanoplates are assumed to be bonded by an interlayer van der walls force and surrounded by an external kelvin-voight viscoelastic medium. The governing equations together with related boundary condition are discretized using a mapping-differential quadrature method (DQM) in the spatial domain. Then the natural frequency of the system is obtained by solving the eigen value matrix equation. The validity of the current study is evaluated by comparing its numerical results with those available in the literature and then a parametric study is thoroughly performed, concentrating on the series effects of angles and aspect ratio of GS, viscoelastic medium, and nonlocal parameter. The model is used to study the vibration of DLGS for two typical deformation modes, the in-phase and out-of-phase vibrations, which are investigated. Numerical results indicate that due to Increasing the damping parameter of the viscoelastic medium has reduced the frequency of both modes and this medium has been able to overdamped the oscillations and by increasing stiffness parameters both in-phase and out-of-phase vibration frequencies increased.

• Advances in nano research
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• 제14권1호
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• pp.45-65
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• 2023

This paper aimed to investigate the nonclassical size dependent free vibration behavior of regularly squared cutout viscoelastic nanobeams. The nonlocal strain gradient elasticity theory is modified and adopted to incorporate the viscoelasticity effect. The Kelvin Voigt viscoelastic model is adopted to model the linear viscoelastic constitutive response. To explore the influence of shear deformation effect due to cutout, both Euler Bernoulli and Timoshenko beams theories are considered. The Hamilton principle is utilized to derive the dynamic equations of motion incorporating viscoelasticity and size dependent effects. Closed form solutions for the resonant frequencies for both perforated Euler Bernoulli nanobeams (PEBNB) and perforated Timoshenko nanobeams (PTNB) are derived considering different boundary conditions. The developed procedure is verified by comparing the obtained results with the available results in the literature. Parametric studies are conducted to show the influence of the material damping, the perforation, the material and the geometrical parameters as well as the boundary and loading conditions on the dynamic behavior of viscoelastic perforated nanobeams. The proposed procedure and the obtained results are supportive in the analysis and design of perforated viscoelastic NEMS structures.

• 전산구조공학
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• 제8권2호
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• pp.141-145
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• 1995

이 논문은, 선형점탄성체가 과도온도상태에 있을때의 거동을 시간영역 경계요소법에 의해 해석하고 있다. 점탄성체에 대해서 '열유동단순'거동을 가정하였다. 경계요소 공식화과정을 설명한 후, 예제문제에 대한 수치해석 결과를 보여주었다.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.257-279
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• 2023

This manuscript is dedicated to deriving the closed form solutions of free vibration of viscoelastic nanobeam embedded in an elastic medium using nonlocal differential Eringen elasticity theory that not considered before. The kinematic displacements of Euler-Bernoulli and Timoshenko theories are developed to consider the thin nanobeam structure (i.e., zero shear strain/stress) and moderated thick nanobeam (with constant shear strain/stress). To consider the internal damping viscoelastic effect of the structure, Kelvin/Voigt constitutive relation is proposed. The perforation geometry is intended by uniform symmetric squared holes arranged array with equal space. The partial differential equations of motion and boundary conditions of viscoelastic perforated nonlocal nanobeam with elastic foundation are derived by Hamilton principle. Closed form solutions of damped and natural frequencies are evaluated explicitly and verified with prestigious studies. Parametric studies are performed to signify the impact of elastic foundation parameters, viscoelastic coefficients, nanoscale, supporting boundary conditions, and perforation geometry on the dynamic behavior. The closed form solutions can be implemented in the analysis of viscoelastic NEMS/MEMS with perforations and embedded in elastic medium.

• 전산구조공학
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• 제8권2호
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• pp.147-151
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• 1995

이 논문에서는 시간영역 경계요소법을 사용하여 탄성-점탄성 복합구조체의 변위와 응력을 구하는 과정을 다루고 있다. 종속영역법을 도입하여, 구조물을 탄성영역과 점탄성영역으로 나누었다. 구조물의 공유경계면에 변위연속조건과 표면력 평형조건을 적용하여, 경계요소공식을 유도하였다. 예제의 문제에 대한 수치해석 결과를 제시하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.779-782
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• 2002

We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• 대한기계학회논문집B
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• 제27권3호
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• pp.294-301
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• 2003

We examine a problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick. open-cell foam with fabric covering and a viscoelastic-painted plate of 1mm thick over an acoustic board of 4mm thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber (k$_{c}$h) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.