• Structural Engineering and Mechanics
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• 제73권2호
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• pp.191-207
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• 2020

This study aims at investigating the size-dependent free vibration of porous nanoplates when exposed to hygrothermal environment and rested on Kerr foundation. Based on the modified power-law model, material properties of porous functionally graded (FG) nanoplates are supposed to change continuously along the thickness direction. The generalized nonlocal strain gradient elasticity theory incorporating three scale factors (i.e. lower- and higher-order nonlocal parameters, strain gradient length scale parameter), is employed to expand the assumption of second shear deformation theory (SSDT) for considering the small size effect on plates. The governing equations are obtained based on Hamilton's principle and then the equations are solved using an analytical method. The elastic Kerr foundation, as a highly effected foundation type, is adopted to capture the foundation effects. Three different patterns of porosity (namely, even, uneven and logarithmic-uneven porosities) are also considered to fill some gaps of porosity impact. A comparative study is given by using various structural models to show the effect of material composition, porosity distribution, temperature and moisture differences, size dependency and elastic Kerr foundation on the size-dependent free vibration of porous nanoplates. Results show a significant change in higher-order frequencies due to small scale parameters, which could be due to the size effect mechanisms. Furthermore, Porosities inside of the material properties often present a stiffness softening effect on the vibration frequency of FG nanoplates.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.241-246
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• 1996

A new solution for the dynamic analysis of as asphalt concrete pavements under moving loads has been developed. The asphalt concrete pavement can be modeled in elastic or viscoelastic medium of multi-layered structure. The subgrade can be modeled as either a rigid base or a semi-infinite halfspace. The loads may be constant or arbitrary circular loads into one direction. The method utilizes the Complex Response Method of transient analysis with a continuum solution in the horizontal direction and a finite-element solution in the vertical direction. This proposed method incorporates such important factors as wave propagation, inertia and damping effects of the medium as well as frequency-dependent asphalt concrete properties. The proposed method has been validted with the full-scale field truck test, which was conducted on instrumented asphalt concrete section on a test track at PACCAR Technical Center in Mount Vernon, Washington. Comparison with field strain data from full-scale pavement tests has shown excellent agreement. Theoretical results have shown that the effect of vehicle speed is significant and that it is in part due to the frequency-dependent

• Steel and Composite Structures
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• 제22권6호
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• pp.1301-1336
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• 2016

In this paper, the free vibrations of a short cylindrical nanotube made of piezoelectric material are studied based on the consistent couple stress theory and using the shear deformable cylindrical theory. This new model has only one length scale parameter and can consider the size effects of nanostructures in nanoscale. To model size effects in nanoscale, and considering the nanotube material which is piezoelectric, the consistent couple stress theory is used. First, using Hamilton's principle, the equations of motion and boundary condition of the piezoelectric cylindrical nanoshell are developed. Afterwards, using Navier approach and extended Kantorovich method (EKM), the governing equations of the system with simple-simple (S-S) and clamped-clamped (C-C) supports are solved. Afterwards, the effects of size parameter, geometric parameters (nanoshell length and thickness), and mechanical and electric properties (piezoelectric effect) on nanoshell vibrations are investigated. Results demonstrate that the natural frequency on nanoshell in nanoscale is extremely dependent on nanoshell size. Increase in size parameter, thickness and flexoelectric effect of the material leads to increase in frequency of vibrations. Moreover, increased nanoshell length and diameter leads to decreased vibration frequency.

• Advances in nano research
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• 제6권4호
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• pp.377-397
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• 2018

In the present investigation, thermal buckling and free vibration characteristics of functionally graded (FG) Timoshenko nanobeams subjected to nonlinear thermal loading are carried out by presenting a Navier type solution. The thermal load is assumed to be nonlinear distribution through the thickness of FG nanobeam. Thermo-mechanical properties of FG nanobeam are supposed to vary smoothly and continuously throughout the thickness based on power-law model and the material properties are assumed to be temperature-dependent. Eringen's nonlocal elasticity theory is exploited to describe the size dependency of nanobeam. Using Hamilton's principle, the nonlocal equations of motion together with corresponding boundary conditions based on Timoshenko beam theory are obtained for the thermal buckling and vibration analysis of graded nanobeams including size effect. Moreover, in following a parametric study is accompanied to examine the effects of the several parameters such as nonlocal parameter, thermal effect, power law index and aspect ratio on the critical buckling temperatures and natural frequencies of the size-dependent FG nanobeams in detail. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams as compared some cases in the literature. Also, it is found that the small scale effects and nonlinear thermal loading have a significant effect on thermal stability and vibration characteristics of FG nanobeams.

• Steel and Composite Structures
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• 제26권4호
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• pp.513-531
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• 2018

In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.

• 대한기계학회논문집
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• 제11권3호
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• pp.444-453
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• 1987

본 연구에서는 난류구조에 대한 유선곡률의 영향을 명확히 반영하는 적절한 곡률수정 2-방정식모델을 개발하고자 한다. 이 연구에서 제안된 모델의 타당성은 다 음의 2차원 재순환유동에 대한 실험결과와 계산결과의 비교를 통해서 입증될 것이다. (1) Moss와 Bake에 의하여 맥동열선 풍속계로 측정된 두꺼운 수직벽주위의 유동` (2) 레이저 도플러 속도계로 Fraser와 Siddig에 의해 측정된 얇은 수직벽유동` (3)맥동열 선 풍속계로 Eaton이 실험한 후면벽유동` (4)맥동열선 풍속계로 Moss와 Baker가 측정 한 전면벽유동. 새로운 곡률수정 2-방정식모델은 2장에서 설명되고 있으며, 3장에서 는 경계조건과 수치계산 과정이 간단이 기술되어 있다. 그 뒤에 4장에는 계산결과와 실험치에대한 비교검토가 설명되어 있고 마지막으로 5장에서는 본 연구에 대한 결론을 맺고 있다.

• Advances in nano research
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• 제7권2호
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• pp.77-88
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• 2019

This paper infer the transient vibration of piezoelectric sandwich nanobeams, In present work, the flexoelectric effect on the mechanical properties of vibration piezoelectric sandwich nanobeam with different boundary conditions is investigated. According to the Nonlocal elasticity theory in nanostructures, the flexoelectricity is believed to be authentic for such size-dependent properties. The governing equations are derived by Hamilton's principle and boundary condition solved by Galerkin-based solution. This research develops a nonlocal flexoelectric sandwich nanobeam supported by Winkler-Pasternak foundation. The results of this work indicate that natural frequencies of a sandwich nanobeam increase by increasing the Winkler and Pasternak elastic constant. Also, increasing the nonlocal parameter at a constant length decreases the natural frequencies. By increasing the length to thickness ratio (L/h) of nanobeam, the nonlocal frequencies reduce.

• Structural Engineering and Mechanics
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• 제77권4호
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• pp.535-547
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• 2021

This paper concerns with free torsional vibration analysis of size dependent circular nanobars with von kármán type nonlinearity. Although review of the literature suggests several studies employing nonlocal elasticity theory to investigate linear torsional behavior, linear/nonlinear transverse vibration and buckling of the nanoscale structures, so far, no study on the nonlinear torsional behavior of the nanobars, considering the size effect, has been reported. This study employs nonlocal elasticity theory along with a variational approach to derive nonlinear equation of motion of the nanobar. Then, the nonlinear equation is solved using the elliptic functions to extract the natural frequencies of the structure under fixed-fixed and fixed-free end conditions. Finally, the natural frequencies of the nanobar under different nanobar lengths, diameters, nonlocal parameters, and amplitudes of vibration are reported to illustrate the effect of these parameters on the vibration characteristics of the nanobars. In addition, the phase plane diagrams of the nanobar for various cases are reported.

• 정보관리학회지
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• 제31권1호
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• pp.7-29
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• 2014

본 연구의 목적은 어린이 독서프로그램의 효과를 측정할 수 있는 성과 측정 도구를 개발하는 것이다. 먼저, 어린이 독서프로그램 효과를 고찰하고 성과측정 도구 적용 사례를 분석하여 도서관 어린이 독서프로그램의 기능 및 효과를 조사하였다. 측정 대상인 독립 변인, 종속 변인, 통제 변인에 대한 개념을 도출하고 각각의 내용을 제시하였으며 국내외 독서 성과 측정 도구의 사례를 분석하여 시사점을 도출하였다. 또한 어린이의 독서 성과 영역과 척도를 조사 분석하였으며 독립 변인과 종속 변인, 통제 변인에 관한 척도를 세분화하고 성과 측정 도구로 활용될 설문지를 개발하였다. 그리고 '2013 도서관과 함께 책읽기' 사업에 참여하고 있는 공공도서관 중 지방권역별로 10개관을 선정하여 조사 대상 도서관의 프로그램에 참여 어린이를 대상으로 프로그램 초반과 후반에 설문지로 개발된 성과 측정 도구를 적용하였다. 또한 조사대상 도서관의 프로그램 담당 사서, 기관 담당자와 강사를 대상으로 설문을 실시하였다. 이상과 같이 수집된 데이터를 모두 분석하여 독서프로그램의 성과를 측정하고 분석하였으며 측정 도구의 개선 방안을 제안하였다.

• 재활간호학회지
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• 제6권2호
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• pp.152-163
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• 2003

Purpose; This study was done to investigate the effect of foot reflexology on vital signs, general fatigue, foot fatigue, mood, and blood glucose levels in noninsulin dependent patients. Method: The Research design of this study was nonequivalent control group quasi-experimental design. 18 patients were assigned to the experimental group, 24 patients to the control group. The data were obtained diaberic patients with ambulatory endocrine outpatients clinic patients from 40 years old to 70 years old. Experimental groups received foot reflex massage for 30minutes three times/week every other days, and Control groups did not received foot reflex massage. The dependent variables were blood pressure, pulse rate, visual analogue scale for general fatigue, foot fatigue, mood, and blood sugar levels. Data were analyzed with $X^2$ test, t-test and repeated measure ANOVA at .0.05 level of significance. Results: There were significant difference in the pulse rate, general fatigue, foot fatigue and mood according to group and time between pre and post foot reflexology. But this research did not prove to decrease blood sugar levels. Conclusions : Foot reflexology can imorove pulse rate, general and foot fatigue, and mood status in diabetus patients. So further research need to explore the effect of decreasing of blood sugar levels.