• 한국항만경제학회지
• /
• 제23권2호
• /
• pp.63-86
• /
• 2007

한국의 물류산업은 가장 빠르게 성장하고 있는 국가 기간산업이다. 이러한 물류산업의 발전을 뒷받침하기 위해 정부는 물류관련 법령의 제 개정이 빈번하게 이루어지고 있다. 그러나 물류산업의 범위가 광범위하고 관련부처가 많아 법률의 적용이 제외되는 분야도 있고, 중복 규정, 하위법령 정비 부족 등 많은 문제점을 내포하고 있다. 먼저 국회가 제정한 법률을 통해 물류와 유통의 정의 및 물류산업 및 유통산업의 범위를 정리할 필요가 있다. 국회에 계류중인 물류정책기본법에서는 광의의 물류 정의를 규정하고 있으며 향후 유통의 개념과 중복 내지 충돌할 우려도 있다. 물류산업에 대한 정의 및 범위를 명확히 하는 것도 필요한데 현재 한국표준산업분류에서 물류는 운수업으로 되어 있으며, 여행업과 장례 운영업까지 포함되어 있다. 그리고 물류시설업과 물류서비스업에 대한 구분도 명확하지 않다. 2006년 도입된 종합물류업의 인증과 발전을 위해서는 운송업, 물류시설업, 물류서비스업으로 구성되는 물류사업에 대한 정확한 통계가 필요하다. 따라서 물류관련 정부 부처는 통계청 등과 협의하여 물류산업의 범위를 명확히 하여 정확한 통계를 바탕으로 한 정부정책 수립과 물류사업의 발전이 이루어질 수 있도록 해야 할 것이다. 물류사업 발전을 위해 지속적인 규제완화와 물류서비스업에 관한 지원과 육성을 위한 법제정비가 필요할 것으로 보이며, 전체 물류관련 법규의 내용 가운데 조정이 필요한 분야는 물류관련 국가계획이다. 국가물류기본계획을 포함하여 유통, 항만, 공항 등 각 분야별 행정계획의 작성이 법에 규정되어 있으나 계획 상호간의 조정 장치는 마련되어 있지 않다. 그리고 정부부처 간에 물류표준, 물류정보의 보안 등 여러 분야도 상호 중복 규정되지 않도록 하는 노력도 필요할 것으로 보인다.

• Steel and Composite Structures
• /
• 제18권2호
• /
• pp.425-442
• /
• 2015

This paper addresses theoretically the bending and buckling behaviors of size-dependent nanobeams made of functionally graded materials (FGMs) including the thickness stretching effect. The size-dependent FGM nanobeam is investigated on the basis of the nonlocal continuum model. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a sinusoidal variation of all displacements through the thickness without using shear correction factor. The material properties of FGM nanobeams are assumed to vary through the thickness according to a power law. The governing equations and the related boundary conditions are derived using the principal of minimum total potential energy. A Navier-type solution is developed for simply-supported boundary conditions, and exact expressions are proposed for the deflections and the buckling load. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and stability responses of the FGM nanobeam are discussed in detail. The study is relevant to nanotechnology deployment in for example aircraft structures.

• Advances in nano research
• /
• 제5권4호
• /
• pp.281-301
• /
• 2017

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of magneto-electro-elastic functionally graded (MEE-FG) beams by considering porosity distribution and various boundary conditions via a four-variable shear deformation refined beam theory for the first time. Magneto-electroelastic properties of porous FG beam are supposed to vary through the thickness direction and are modeled via modified power-law rule which is formulated using the concept of even and uneven porosity distributions. Porosities possibly occurring inside functionally graded materials (FGMs) during fabrication because of technical problem that lead to creation micro-voids in FG materials. So, it is necessary to consider the effect of porosities on the vibration behavior of MEE-FG beam in the present study. The governing differential equations and related boundary conditions of porous MEE-FG beam subjected to physical field are derived by Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factor. An analytical solution procedure is used to achieve the natural frequencies of porous-FG beam supposed to magneto-electrical field which satisfies various boundary conditions. A parametric study is led to carry out the effects of material graduation exponent, porosity parameter, external magnetic potential, external electric voltage, slenderness ratio and various boundary conditions on dimensionless frequencies of porous MEE-FG beam. It is concluded that these parameters play noticeable roles on the vibration behavior of MEE-FG beam with porosities. Presented numerical results can be applied as benchmarks for future design of MEE-FG structures with porosity phases.

• Steel and Composite Structures
• /
• 제25권2호
• /
• pp.157-175
• /
• 2017

The novelty of this work is the use of a new displacement field that includes undetermined integral terms for analyzing thermal buckling response of functionally graded (FG) sandwich plates. The proposed kinematic uses only four variables, which is even less than the first shear deformation theory (FSDT) and the conventional higher shear deformation theories (HSDTs). The theory considers a trigonometric variation of transverse shear stress and verifies the traction free boundary conditions without employing the shear correction factors. Material properties of the sandwich plate faces are considered to be graded in the thickness direction according to a simple power-law variation in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear and non-linear temperature rises within the thickness direction. An energy based variational principle is employed to derive the governing equations as an eigenvalue problem. The validation of the present work is checked by comparing the obtained results the available ones in the literature. The influences of aspect and thickness ratios, material index, loading type, and sandwich plate type on the critical buckling are all discussed.

• Structural Engineering and Mechanics
• /
• 제71권2호
• /
• pp.185-196
• /
• 2019

In this investigation, study of the static and dynamic behaviors of functionally graded beams (FGB) is presented using a hyperbolic shear deformation theory (HySDT). The simply supported FG-beam is resting on the elastic foundation (Winkler-Pasternak types). The properties of the FG-beam vary according to exponential (E-FGB) and power-law (P-FGB) distributions. The governing equations are determined via Hamilton's principle and solved by using Navier's method. To show the accuracy of this model (HySDT), the current results are compared with those available in the literature. Also, various numerical results are discussed to show the influence of the variation of the volume fraction of the materials, the power index, the slenderness ratio and the effect of Winkler spring constant on the fundamental frequency, center deflection, normal and shear stress of FG-beam.

• Advances in nano research
• /
• 제7권4호
• /
• pp.249-263
• /
• 2019

In the current paper, an exact solution method is carried out for analyzing the thermo-mechanical vibration of curved FG nano-beams subjected to uniform thermal environmental conditions, by considering porosity distribution via nonlocal strain gradient beam theory for the first time. Nonlocal strain gradient elasticity theory is adopted to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field is considered. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Material properties of curved porous FG nanobeam are assumed to be temperature-dependent and are supposed to vary through the thickness direction of beam which modeled via modified power-law rule. Since variation of pores along the thickness direction influences the mechanical and physical properties, porosity play a key role in the mechanical response of curved FG nano-structures. The governing equations and related boundary condition of curved porous FG nanobeam under temperature field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved nanobeam supposed to thermal loading. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, porosity volume fractions, thermal effect, gradient index, opening angle and aspect ratio on the natural frequency of curved FG porous nanobeam are successfully discussed. It is concluded that these parameters play key roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• 한국철학논집
• /
• 제50호
• /
• pp.75-111
• /
• 2016

본 논문은 박세채의 "춘추보편"를 주요 텍스트로 삼아서, 조선조 춘추학에서 "춘추" 공부의 출발로 삼았던 표준 강령의 실체를 살펴보는 작업이다. 이 연구의 목적은 조선조 학자들이 "춘추"에 대해 가졌던 공통의 인식이나 보편적인 시각이 무엇인지 밝히는 것이다. "춘추보편"은 조선조의 성리학적 "춘추" 이해를 대변하는 책이기 때문에 이 책의 "강령(綱領)"은 조선조 학자들이 "춘추"를 공부하기 위해 반드시 알아야 할 일종의 지침이라고 할 수 있다. 본 논문에서는 "강령"의 다섯 가지 항목 중에서 <"춘추" 저술의 본질>과 <"춘추" 기록의 주제>라는 두 가지 항목을 집중적으로 살펴보았다. 첫 번째 항목은 "춘추"가 세상을 다스리는 대법이며, 그것은 현실을 추동하는 살아 있는 이치라는 것이 주요 내용이다. 두 번째 항목은 "춘추"의 구체적인 기록을 통해 "춘추" 대법의 실체를 밝히고 있다. 향후 이 논문과 함께 "강령"의 나머지 항목에 대한 추가 연구가 완료되면, 조선조 춘추학의 전반적인 성격이나 특징을 밝히는 중요한 실마리를 확보할 수 있을 것이다.

• Steel and Composite Structures
• /
• 제39권1호
• /
• pp.95-107
• /
• 2021

In this work, the dynamic response of functionally graded beams on variable elastic foundations is studied using a novel higher-order shear deformation theory (HSDT). Unlike the conventional HSDT, the present one has a new displacement field which introduces undetermined integral variables. The FG beams were assumed to be supported on Winkler-Pasternak type foundations in which the Winkler modulus is supposed to be variable in the length of the beam. The variable rigidity of the elastic foundation is assumed to be linear, parabolic and sinusoidal along the length of the beam. The material properties of the FG porous beam vary according to a power law distribution in terms of the volume fraction of the constituents. The equations of motion are determined using the virtual working principle. For the analytical solution, Navier method is used to solve the governing equations for simply supported porous FG beams. Numerical results of the present theory for the free vibration of FG beams resting on elastic foundations are presented and compared to existing solutions in the literature. A parametric study will be detailed to investigate the effects of several parameters such as gradient index, thickness ratio, porosity factor and foundation parameters on the frequency response of porous FG beams.

• Earthquakes and Structures
• /
• 제22권5호
• /
• pp.447-460
• /
• 2022

In this article, wave propagation in functional gradation plates (FG) resting on an elastic foundation with two parameters is studied using a new quasi-three-dimensional (3D) higher shear deformation theory (HSDT). The new qausi-3D HSOT has only five variables in fields displacement, which means has few numbers of unknowns compared with others quasi-3D. This higher shear deformation theory (HSDT) includes shear deformation and effect stretching with satisfying the boundary conditions of zero traction on the surfaces of the FG plate without the need for shear correction factors. The FG plates are considered to rest on the Winkler layer, which is interconnected with a Pasternak shear layer. The properties of the material graded for the plates are supposed to vary smoothly, with the power and the exponential law, in the z-direction. By based on Hamilton's principle, we derive the governing equations of FG plates resting on an elastic foundation, which are then solved analytically to obtain the dispersion relations. Numerical results are presented in the form of graphs and tables to demonstrate the effectiveness of the current quasi-3D theory and to analyze the effect of the elastic foundation on wave propagation in FG plates.

• Steel and Composite Structures
• /
• 제43권5호
• /
• pp.581-601
• /
• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.