• Interaction and multiscale mechanics
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• 제2권3호
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• pp.223-233
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• 2009

This paper presents a new nonlocal stress variational principle approach for the transverse free vibration of an Euler-Bernoulli cantilever nanobeam with an initial axial tension at its free end. The effects of a nanoscale at molecular level unavailable in classical mechanics are investigated and discussed. A sixth-order partial differential governing equation for transverse free vibration is derived via variational principle with nonlocal elastic stress field theory. Analytical solutions for natural frequencies and transverse vibration modes are determined by applying a numerical analysis. Examples conclude that nonlocal stress effect tends to significantly increase stiffness and natural frequencies of a nanobeam. The relationship between natural frequency and nanoscale is also presented and its significance on stiffness enhancement with respect to the classical elasticity theory is discussed in detail. The effect of an initial axial tension, which also tends to enhance the nanobeam stiffness, is also concluded. The model and approach show potential extension to studies in carbon nanotube and the new result is useful for future comparison.

• Smart Structures and Systems
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• 제19권3호
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• pp.243-257
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• 2017

In this paper, free vibration of functionally graded (FG) size-dependent nanobeams is studied within the framework of nonlocal Timoshenko beam model. It is assumed that material properties of the FG nanobeam, vary continuously through the thickness according to a power-law form. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The non-classical governing differential equations of motion are derived through Hamilton's principle and they are solved utilizing both Navier-based analytical method and an efficient and semi-analytical technique called differential transformation method (DTM). Various types of boundary conditions such as simply-supported, clamped-clamped, clamped-simply and clamped-free are assumed for edge supports. The good agreement between the presented DTM and analytical results of this article and those available in the literature validated the presented approach. It is demonstrated that the DTM has high precision and computational efficiency in the vibration analysis of FG nanobeams. The obtained results show the significance of the material graduation, nonlocal effect, slenderness ratio and boundary conditions on the vibration characteristics of FG nanobeams.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.591-610
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• 2017

This paper is concerned with the static analysis of variable thickness of two directional functionally graded porous materials (FGPM) circular plate resting on a gradient hybrid foundation (Horvath-Colasanti type) with friction force and subjected to compound mechanical loads (e.g., transverse, in-plane shear traction and concentrated force at the center of the plate).The governing state equations are derived in terms of displacements based on the 3D theory of elasticity, assuming the elastic coefficients of the plate material except the Poisson's ratio varying continuously throughout the thickness and radial directions according to an exponential function. These equations are solved semi-analytically by employing the state space method (SSM) and one-dimensional differential quadrature (DQ) rule to obtain the displacements and stress components of the FGPM plate. The effect of concentrated force at the center of the plate is approximated with the shear force, uniformly distributed over the inner boundary of a FGPM annular plate. In addition to verification study and convergence analysis, numerical results are displayed to show the effect of material heterogeneity indices, foundation stiffness coefficients, foundation gradient indices, loads ratio, thickness to radius ratio, compressibility, porosity and friction coefficient of the foundation on the static behavior of the plate. Finally, the responses of FG and FG porous material circular plates to compound mechanical loads are compared.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.109-112
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• 1997

The Hydrodynamic performance of the trileaflet polymer prosthetic valves depends on the design of the leaflet and the physical properties of the leaflet membrane. In order to study the effect of leaflet membrane elasticity on the hemodynamic performance of trileaflet prosthetic valve, leaflet membranes are manufactured using two different polymers - Biospan and Tecoflex SG-93A. The hemodynamic performance parameters are measured under steady and physiological pulsatile flow, and compared with monoleaflet polymer valve(floating valve) and bileaflet mechanical valve(St. Jude Medical valve). Well designed trileaflet valve shows the lowest mean pressure drop among the tested valves. The trileaflet valves with Biospan membrane show lower pressure drop and back low comparing to those with Tecoflex membrane. More elastic membrane may provide wide opening area during systole and close membrane ree edge contact during diastole. Durability of trileaflet valves are also tested in vitro. Trileaflet valves with non-uniform membrane thickness ail within 17 days because of stress concentration. Trileaflet polymer valves with uniform membrane thickness perform well over 55 days without failure.

• Steel and Composite Structures
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• 제28권1호
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• pp.13-24
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• 2018

A size-dependent novel hyperbolic shear deformation theory of simply supported functionally graded beams is presented in the frame work of the non-local strain gradient theory, in which the stress accounts for only the nonlocal strain gradients stress field. The thickness stretching effect (${\varepsilon}_z{\neq}0$) is also considered here. Elastic coefficients and length scale parameter are assumed to vary in the thickness direction of functionally graded beams according to power-law form. The governing equations are derived using the Hamilton principle. The closed-form solutions for exact critical buckling loads of nonlocal strain gradient functionally graded beams are obtained using Navier's method. The derived results are compared with those of strain gradient theory.

• Steel and Composite Structures
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• 제42권5호
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• pp.699-710
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• 2022

This work presents a comprehensive study on the surface energy effect on the axial frequency analyses of AFGM nanorods in cylindrical coordinates. The AFGM nanorods are considered to be thin, relatively thick, and thick. In thin nanorods, effects of the inertia of lateral motions and the shear stiffness are ignored; in relatively thick nanorods, only the first one is considered; and in thick nanorods, both of them are considered in the kinetic energy and the strain energy of the nanorod, respectively. The surface elasticity theory which includes three surface parameters called surface density, surface stress, and surface Lame constants, is implemented to consider the size effect. The power-law form is considered for variation of the material properties through the axial direction. Hamilton's principle is used to derive the governing equations and boundary conditions. Due to considering the surface stress, the governing equation and boundary condition become inhomogeneous. After homogenization of them using an appropriate change of variable, axial natural frequencies are calculated implementing harmonic differential quadrature (HDQ) method. Comprehensive results including effects of geometric parameters and various material properties are presented for a wide range of boundary condition types. It is believed that this study is a comprehensive one that can help posterities for design and manufacturing of nano-electro-mechanical systems.

• 수완나부미
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• 제15권1호
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• pp.255-275
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• 2023

Trade between South Korea and Malaysia has been steadily increasing since the conclusion of the multilateral Free Trade Agreement (FTA) between the Association of Southeast Asian Nations (ASEAN) and South Korea. Bilateral FTAs such as Singapore-South Korea, Vietnam-South Korea, and Indonesia-South Korea came into effect to enhance the economic cooperation between South Korea and major ASEAN countries. However, the bilateral FTA between South Korea and Malaysia, known as Republic of Korea-Malaysia FTA, is still under negotiation. Therefore, this study aims to analyze the economic impact of a possible FTA between these two countries. To examine the economic effects of bilateral FTAs, this study analyzes the trade structure and change in the value of trade between Malaysia and South Korea using panel data analysis. Two significant findings were identified by the analysis. First, the Republic of Korea-Malaysia FTA is expected to promote trade and have a positive effect on the Gross Domestic Product (GDP) of South Korea. Second, the result of the calculated price elasticity based on substituting figures such as tariff, demand elasticity, and export value is that the value of manufacturing exports is expected to considerably get an increase. Therefore, an early FTA between South Korea and Malaysia would be beneficial for both national economies.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.793-798
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• 2002

This paper presents the analytical results on the seismic retrofit of circular bridge columns with poor lap-splice details using FRP jacket. The as-built column suffered brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. The retrofitted columns using FRP jacket showed significant improvement in seismic performance due to FRP's confinement effect. FRP's confinement effect is predicted by the classical elasticity solution for the laminated circular tube manufactural with several layers, and induces the flexural failure instead of bondslip failure.

• 환경정책연구
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• 제14권4호
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• pp.23-44
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• 2015

저탄소차협력금제도는 중대형차 위주의 국내 승용차 시장에서 소형차의 점유율을 제고하고 온실가스를 저감하기 위해 도입되었으며 2015년 시행이 예정되어 있었으나 2014년 산업부 등이 해당 제도의 온실가스 저감효과가 낮고 수입차에 상대적 혜택이 있다고 주장하였고, 관련자들의 토론을 거쳐 제도의 시행이 2020년으로 연기되었다. 2014년 집중되었던 기존의 연구는 실증분석 위주로 제도의 효과를 추정하는 데 집중되어 있었으며, 정량적 수치를 제공하지 못하는 경제모형에 입각한 구조적 논의는 별로 주목받지 못하였다. 자동차 시장 구조에 따라 보너스-부담금이 자동차 가격에 반영되는 효과가 달라질 수 있음을 경제수리모형을 통해 입증하였고 제도를 둘러싼 구조에 대한 정밀한 통찰을 제공하여 정합한 실증분석을 위한 이론적 기반을 제시하고자 한다. 자동차 공급자가 독점력을 가지고 있어 전략적 가격 설정이 가능하다면 보너스와 부담금이 자동차 가격에 반영되는 정도는 명목적으로 부여된 수준보다 작다. 보너스가 부과되는 소형차 시장만 독점력이 떨어지더라도 제도의 효과가 개선된다. 최적의 보너스와 부담금이 도입되어 있다고 가정했을 때 자동차 시장 구조가 변화한다면 최적 가격 체계를 유지하기 위한 보너스와 부담금 변화 방향은 직관과 다를 수 있다. 각 시장의 가격탄력성과 대체탄력성의 크기가 최적 보너스-부담금의 변화 방향을 결정한다. 예를 들어 대형차 수요는 탄력적이고 소형차 수요가 비탄력적이면서 대체탄력성은 낮은 경우 독점력이 강화된다면 보너스와 부담금 모두 상향 조정되어야 한다.

• Journal of the Korean Wood Science and Technology
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• 제23권2호
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• pp.70-76
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• 1995

본 연구는 왁스첨가순서(添加順序), 첨가량(添加量), 왁스종류(種類)가 Isocyanate 접착(接着) PB의 성질(性質)과 내수성(耐水性)에 미치는 영향(影響)을 구명(究明)하기 위해서 실시(實施)되었다. 왁스첨가순서(添加順序)는 PB의 기계적(機械的) 성질(性質) 및 내수성(耐水性)에 유의적(有意的)인 영향(影響)을 미치지는 않았다. 왁스에멀젼 첨가량(添加量)을 증가(增加)시킴으로써 접착력(接着力) 및 휨강도(强度) 내수(耐水) MOR은 감소(減少)되었지만 상태(常態) MOR 및 MOE는 감소(減少)되지 않았다. 상태접착력(常態接着力), 상태(常態) 및 내수(耐水) MOR과 MOE는 솔리드왁스량(量)을 증가(增加)시킴으로써 감소(減少)되지 않았지만 내수접착력(耐水接着力)은 감소(減少)되었다. 1% 및 1.5% 왁스량(量)을 첨가(添加)한 보드는 0.5% 왁스를 첨가(添加)한 보드와 비교(比較)해 보았을 때 내수성(耐水性)이 증가(增加)되지는 않았다. 솔리드왁스를 첨가(添加)한 보드의 접착력(接着力)은 왁스에멀젼을 첨가(添加)한 보드보다 더 좋은 결과(結果)를 나타내었다. 휨강도(强度)의 MOR 및 MOE, 내수성(耐水性)은 솔리드왁스와 왁스에멀젼간에 유의적(有意的)인 차이(差異)를 보이지는 않았다.