• Steel and Composite Structures
• /
• 제44권5호
• /
• pp.707-720
• /
• 2022

In the present work, bending and free vibration analyses of multilayered functionally graded (FG) graphene platelet (GPL) and fiber-reinforced hybrid composite beams are carried out using the parabolic function based shear deformation theory. Parabolic variation of transverse shear stress across the thickness of beam and transverse shear stress-free conditions at top and bottom surfaces of the beam are considered, and the proposed formulation incorporates a transverse displacement field. The present theory works only with four unknowns and is computationally efficient. Hamilton's principle has been employed for deriving the governing equations. Analytical solutions are obtained for both the bending and free vibration problems in the present work considering different variations of GPLs and fibers distribution, namely, FG-X, FG-U, FG-Λ, and FG-O for beams having simply-supported boundary condition. First, the matrix is assumed to be strengthened using GPLs, and then the fibers are embedded. Multiscale modeling for material properties of functionally graded graphene platelet/fiber hybrid composites (FG-GPL/FHRC) is performed using Halpin-Tsai micromechanical model. The study reveals that the distributions of GPLs and fibers have significant impacts on the stresses, deflections, and natural frequencies of the beam. The number of layers and shape factors widely affect the behavior of FG-GPL-FHRC beams. The multilayered FG-GPL-FHRC beams turn out to be a good approximation to the FG beams without exhibiting the stress-channeling effects.

• 한국측량학회:학술대회논문집
• /
• 한국측량학회 2010년 춘계학술발표회 논문집
• /
• pp.197-199
• /
• 2010

A gravity survey is a base of research earth gravity field determined, perception of the vertical motion, change of Geoid, sea-level changes, climate change etc. Recently, FG-5 was adopted in NGII. NGII has completed 4 points of absolute gravity survey and 1,400 points of relative gravity survey in 2009 to aim to observe 20 points of absolute gravity survey and 6,000 points of gravity control point by 2013. Using results of gravity survey, NGII will provide citizen with data for research about renewal of geoid model and geophysics. This study aims to go over examples of utilization of absolute gravimeter & method of utilization in korea.

• 한국식품과학회지
• /
• 제54권2호
• /
• pp.179-184
• /
• 2022

본 연구에서는 열 압착 공정을 이용하여 생고분자 가식성 FG 필름과 MG 필름을 제작하였고, 제조 공정 차이에 따른 필름의 형성, 표면 미세구조, 그리고 빛 투과도를 비교하기 위해 캐스팅 방법을 이용해서도 FG 필름을 제작하였다. 열 압착을 이용하여 FG와 MG로부터 연속적이고, 균일하며, 투명하고, 그리고 매끄러운 표면을 가진 필름을 제작할 수 있었다. 열 압착된 FG 필름은 열 압착된 MG 필름보다 빛 투과도와 인장 강도가 낮았으나, 육안 관찰 및 현미경을 이용한 표면 미세구조를 관찰 시 큰 차이를 확인할 수 없었으며, 수분 투과도와 필름의 명도 및 붉은 정도에서도 유의적인 차이가 보이지 않았다. 또한, 열 압착된 FG 필름이 캐스팅된 FG 필름보다 육안으로 보았을 때 더욱 투명하고 균일한 표면을 가진 것을 확인할 수 있었고, 투명도도 캐스팅 된 FG 필름보다 높음을 알 수 있었다. 열 압착된 FG 필름이 캐스팅된 FG 필름보다 낮은 인장 강도와 높은 수분 차단 능력을 갖췄다. 열 압착된 FG 필름은 캐스팅된 FG 필름과 색도의 차이가 있었고, 캐스팅된 FG 필름보다 매끄럽고 균일한 표면 미세구조를 가진 것을 알 수 있었다. 본 연구의 결과는 열 압착 공정을 사용하는 산업적 생고분자 생산 시스템을 사용하여 우수한 수분 차단 능력을 갖춘 가식성 필름을 MG과 생선껍질로부터 얻어지는 FG을 이용해 제작할 수 있음을 보여주었다.

• Advances in nano research
• /
• 제10권5호
• /
• pp.423-435
• /
• 2021

This paper examines the thermal post-buckling behaviors of graphene-reinforced metal matrix composite (GRMMC) laminated cylindrical panels which possess in-plane negative Poisson's ratio (NPR) and rest on an elastic foundation. A panel consists of GRMMC layers of piece-wise varying graphene volume fractions to obtain functionally graded (FG) patterns. Based on the MD simulation results, the GRMMCs exhibit in-plane NPR as well as temperature-dependent material properties. The governing equations for the thermal post-buckling of panels are based on the Reddy's third order shear deformation shell theory. The von Karman nonlinear strain-displacement relationship and the elastic foundation are also included. The nonlinear partial differential equations for GRMMC laminated cylindrical panels are solved by means of a singular perturbation technique in associate with a two-step perturbation approach and in the solution process the boundary layer effect is considered. The results of numerical investigations reveal that the thermal post-buckling strength for (0/90)_5T GRMMC laminated cylindrical panels can be enhanced with an FG-X pattern. The thermal post-buckling load-deflection curve of 6-layer (0/90/0)_S and (0/90)_3T panels of FG-X pattern are higher than those of 10-layer (0/90/0/90/0)_S and (0/90)_5T panels of FG-X pattern.

• Advances in aircraft and spacecraft science
• /
• 제5권1호
• /
• pp.141-164
• /
• 2018

In this paper, the thermal effect on buckling and free vibration characteristics of functionally graded (FG) size-dependent Timoshenko nanobeams subjected to an in-plane thermal loading are investigated by presenting a Navier type solution for the first time. Material properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law form and the material properties are assumed to be temperature-dependent. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived based on Timoshenko beam theory through Hamilton's principle and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams as compared to some cases in the literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as thermal effect, material distribution profile, small scale effects, aspect ratio and mode number on the critical buckling temperature and normalized natural frequencies of the temperature-dependent FG nanobeams in detail. It is explicitly shown that the thermal buckling and vibration behaviour of a FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.

• Steel and Composite Structures
• /
• 제33권5호
• /
• pp.699-716
• /
• 2019

In this paper, wave propagations in sigmoid functionally graded (S-FG) plates are studied using new Higher Shear Deformation Theory (HSDT) based on two-dimensional (2D) elasticity theory. The current higher order theory has only four unknowns, which mean that few numbers of unknowns, compared with first shear deformations and others higher shear deformations theories and without needing shear corrector. The material properties of sigmoid functionally graded are assumed to vary through thickness according sigmoid model. The S-FG plates are supposed to be imperfect, which means that they have a porous distribution (even and uneven) through the thickness of these plates. The governing equations of S-FG plates are derived employed Hamilton's principle. Using technique of Navier, differential equations of S-FG in terms displacements are solved. Extensive results are presented to check the efficient of present methods to predict wave dispersion and velocity wave in S-FG plates.

• Advances in nano research
• /
• 제16권5호
• /
• pp.445-458
• /
• 2024

The objective of this paper is to present free vibration and static stability analyses of rotating composite beams reinforced with carbon nanotubes (CNTs) under uniform thermal loads. Beam structural equations and CNT-reinforced composite (CNTRC) beam formulations are derived based on Timoshenko beam theory (TBT). The temperature-dependent properties of the beam material, such as the elastic modulus, shear modulus, and material density, are assumed to vary over the thickness according to the rule of mixture. The beam material is modeled as a mixture of single-walled carbon nanotubes (SWCNTs) in an isotropic matrix. The SWCNTs are aligned and distributed in the isotropic matrix with different patterns of reinforcement, namely the UD (uniform), FG-O, FG-V, FG- Λ and FG-X distributions, where FG-V and FG- Λ are asymmetric patterns. Numerical examples are presented to illustrate the effects of several essential parameters, including the rotational speed, hub radius, effective material properties, slenderness ratio, boundary conditions, thermal force, and moments due to temperature variation. To the best of the authors' knowledge, this study represents the first attempt at the finite element modeling of rotating CNTRC Timoshenko beams under a thermal environment. The results are presented in tables and figures for both symmetric and asymmetric distribution patterns, and can be used as benchmarks for further validation.

• 전자통신동향분석
• /
• 제22권5호
• /
• pp.130-143
• /
• 2007

IPTV 서비스는 IP 환경에서 다양한 콘텐트를 전송하는 기술로 기존의 방송 시스템과 통신 시스템의 장점을 그대로 수용하는 기술이다. 이에 ITU-T SG13에서는 FG IPTV를 통해 요구사항 및 구조 중심의 표준화를 진행하고 있다. ITU-T FG IPTV는 6개의 WG로 구성되어 진행중에 있으며, WG3는 security aspects의 주제를 가지고 보안 기술에 대한 표준화를 진행하고 있다. 본 문서는 2007년 5월과 7월의 4차, 5차 표준화 회의를 중심으로 WG3의 표준화 동향 및 기술적 분석을 정리한다.

• 한국축산시설환경학회지
• /
• 제5권2호
• /
• pp.79-86
• /
• 1999

Recently more dairy farmers are interested in the utilization of stretch film for wrapping silage material. Most of stretch film are imported from abroad and one domestic product was developed, but its quality has not yet been tested. Therefore this study was executed to offer basic data on this material to the farmers. Measured items were tensile load, extension ratio, and tear propagation strength of stretch films. Comparisons were made among the white color of domestic product(Kw), and white(Fw), black (Fb) and green color(Fg) of foreign products. The result were summarized as follows: 1. Tensile loads of lengthwise direction in stretch films were 557.4, 377.4, 282.6 and 398.4kgf/$\textrm{cm}^2$ in Kw, Fw, Fb and Fg, respectively, and tensile loads of width direction were 415.9, 418.1, 360.2 and 433.0kgf/$\textrm{cm}^2$ in Kw, Fw, Fb and Fg, respectively. 2. Extension ratios of lengthwise direction were 650, 462.5, 512.5% and 537.5% in Kw, Fw, Fb and Fg, respectively, Extension ratios of width direction were 930, 962.5, 950 and 1,000% in Kw, Fw, Fb and Fg, respectively. 3 Tear propagation strength of lengthwise direction 187.9, 148.9, 157.3 and 142.8kgf/cm, and tear propagation strength of width direction were 141.4, 129.8, 140.4 and 106.6kgf/cm in Kw, Fw, Fb and Fg, respectively. 4. In the light transmittance, there was no difference between white and green color stretch film, but it was very low in black one. Therefore, it is thought that research on quality of roll bale silage treated with each stretch film would be needed.

• 한국균학회지
• /
• 제50권3호
• /
• pp.149-160
• /
• 2022

남해안과 금강상류 주변환경의 야생효모들의 효모 종 분포특성을 조사하고 국내 미보고된 효모들을 선별하여 이들의 균학적 특성들을 알아보고자 남해안의 해금강과 금강상류인 전북 무주의 남대천 및 금산의 금산천 주변의 물과 토양들로부터 야생효모들을 분리, 동정하였다. 해금강 주변 시료 35점에서 22종 52균주의 야생효모들을 분리, 동정하였고 무주의 남대천 주변 물과 토양 30점에서는 24 종 43균주의 야생효모들을, 금산의 금산천변 시료 60점에서 45종 79균주의 야생효모들을 분리, 동정하였다. 이들 지역에서 분리, 동정한 야생효모들중 Exobasidium rhododendri HHG10-5 (NNIBR2022633FG1), Udeniomyces pyricola NDC29-1 (NNIBR2022633FG2), Pichia scaptomyzae BAC2-3 (NNIBR2022633FG4), Diddensiella caesifluorescens GSC2-2 (NNIBR2022633FG5) 등 4균주들이 국내 미기록 야생효모들로 최종 선별되었다. 이들의 균학적 특성을 조사한 결과Udeniomyces pyricola NDC29-1 과Diddensiella caesifluorescens GSC2-2 균은 구형이었고 Exobasidium rhododendri HGG10-5 와 Pichia scaptomyzae BAC2-2 균들은 난형이었으며 Pichia scaptomyzae BAC2-3 균주만이 포자를 생성하였다. Udeniomyces pyricola NDC29-1 균주 외에는모두 vitamin-free배지에서도생육이아주양호하였고Pichia scaptomyzae BAC2-3, Diddensiella caesifluorescens GSC2-2 균주는 40% glucose 를함유한 YPD배지에서도생육하는내당성균이었다. Udeniomyces pyricola NDC29-1 균주를 제외한 나머지 균들은 Ca 등의 중금속등에 대하여 강한 내성을보였다.