• Steel and Composite Structures
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• 제16권5호
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• pp.521-531
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• 2014

In this paper we consider a periodic solution for nonlinear free vibration of conservative systems for thick circular sector slabs. In Energy Balance Method (EBM) contrary to the conventional methods, only one iteration leads to high accuracy of the solutions. The excellent agreement of the approximate frequencies and periodic solutions with the exact ones could be established. Some patterns are given to illustrate the effectiveness and convenience of the methodology. Comparing with numerical solutions shows that the energy balance method can converge to the numerical solutions very rapidly which are valid for a wide range of vibration amplitudes as indicated in this paper.

• 한국의학물리학회지:의학물리
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• 제8권1호
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• pp.37-45
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• 1997

차폐된 질 원주기구를 이용한 강내치료시 Co-60 선원에 대한 정확한 흡수선량을 결정 하고자 선원을 교정하고, 질 원주기구에 의한 선량분포변화를 조사하였다. 선량분포의 변화량은 직경 2.5 cm 차폐된 질 원주기구를 폴리스틸렌 팬톰에 설치하여 전리함으로 측정하였으며, 부채꼴 모양인 0.55cm 두께의 9$0^{\circ}C$ 연으로 차폐된 면과 차폐되지 않은 면의 선량분포에 대한 영향을 상대선량 감소율로 측정하였다. 측정된 선량분포의 변화량을 제작사의 선량분포도 및 다점 분할방식으로 구한 선량율표와 비교하였다. 질 원주기구를 이용한 선량 감소율은 차폐되지 않은 변의 경우 원주기구 표면 1cm 거리에서 4.4%를 보였고, 차폐된 면에서는 원주기구 표면에서 20.4% 를 나타냈다. 9$0^{\circ}C$연 차폐된 질 원주기구의 선량감쇄효율은 Co-60 선원에서 평균 0.2가 되었다. Co-60 이동형 선원의 선량분포는 다 점분할방식의 선량율표와 4.1% 이내로 일치하였다.

• Steel and Composite Structures
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• 제27권3호
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• pp.255-271
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• 2018

This paper deals with the transient dynamic analysis and elastic wave propagation in a functionally graded graphene platelets (FGGPLs)-reinforced composite thick hollow cylinder, which is subjected to shock loading. A micromechanical model based on the Halpin-Tsai model and rule of mixture is modified for nonlinear functionally graded distributions of graphene platelets (GPLs) in polymer matrix of composites. The governing equations are derived for an axisymmetric FGGPLs-reinforced composite cylinder with a finite length and then solved using a hybrid meshless method based on the generalized finite difference (GFD) and Newmark finite difference methods. A numerical time discretization is performed for the dynamic problem using the Newmark method. The dynamic behaviors of the displacements and stresses are obtained and discussed in detail using the modified micromechanical model and meshless GFD method. The effects of the reinforcement of the composite cylinder by GPLs on the elastic wave propagations in both displacement and stress fields are obtained for various parameters. It is concluded that the proposed micromechanical model and also the meshless GFD method have a high capability to simulate the composite structures under shock loadings, which are reinforced by FGGPLs. It is shown that the modified micromechanical model and solution technique based on the meshless GFD method are accurate. Also, the time histories of the field variables are shown for various parameters.

• Steel and Composite Structures
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• 제28권3호
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• pp.331-347
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• 2018

In this paper history of stresses, strains, radial and circumferential displacements of a functionally graded thick-walled hollow cylinder due to creep phenomenon is investigated. The cylinder is subjected to an arbitrary non-axisymmetric two dimensional thermo-mechanical loading and uniform magnetic field along axial direction. Using equilibrium, strain-displacements and stress-strain relations, the governing differential equations of the problem containing creep strains are derived in terms of radial and circumferential displacements. Since the displacements are varying with time due to creep phenomenon, an analytical solution is not available for these equations. Thus, a semi-analytical procedure based on separation of variables and Fourier series together with a numerical procedure is employed. The numerical results indicate that the non-axisymmetric loading and the material grading index have significant effect on stress redistributions. Moreover, by proper selection of material for any combination of non-axisymmetric loading, one can arrive suitable response for the cylinder to achieve optimal design. With some simplifications, the results are validated with the existing literature.

• 대한기계학회논문집A
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• 제39권12호
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• pp.1265-1273
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• 2015

석탄하역기는 화력발전소의 주 원료인 석탄을 체인 버킷을 구동하여 선박으로부터 컨베이어 벨트로 하역하는 장비이다. 그러나 국내에서는 석탄하역기의 하역위치에 따라 붐 각도를 제어하는 유압시스템인 붐 호이스팅 실린더에 대한 연구가 이루어지지 않아, 전량 수입하고 있는 실정이다. 이에 본 연구에서는 두꺼운 실린더에서 접촉면압의 이론 값을 FEM 을 수행하여 얻은 결과 값과 비교하여 접촉면압 해석기법의 타당성을 확립하였고, 이를 통하여 브이 실을 갖는 붐 호이스팅 실린더에서 작동유의 누설 여부 판단과 접촉면압을 최대로 갖는 브이 실 형상을 설계하였다. 또한, 실린더의 스트로크에 따른 구동시뮬레이션을 수행하였고, 최대 출력 상태에서의 붐 호이스팅 실런더의 구조 안전성을 검증하였다.

• 한국의류산업학회지
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• 제7권2호
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• pp.247-251
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• 2005

In this the study, the effects of the manufacturing process conditions on the properties Thick and Thin Diameter yarns(TTD yarns) prepared with hot plate device in the draw winder were determined. Physical properties including wet shrinkage, tenacity and elongation of the samples were measured and thick and thin effect was analysed with the evenness tester. The results were as the follows: There was little change the wet shrinkage of the TTD yarns in the range of $70^{\circ}C{\sim}80^{\circ}C$ of $R_1$ temperature(lower hot cylinder) with the same Hot Plate(H/P) temperature, but the wet shrinkage of the TTD yarns decreased 5-10% when $R_1$ temperature was $90^{\circ}C$. The wet shrinkage of the TTD yarns decreased with the H/P temperature at the same temperature of $R_1$. There was little effect of $R_1$ and H/P temperature on the tenacity of TTD yarns. The elongation of TTD yarns increased with $R_1$ temperature at the same H/P temperature. The elongation of TTD yarns increased little bit for the first time and then decreased above that temperature with increasing H/P temperature at the same $R_1$ temperature. The thick and thin effect on the TTD yarns was obvious in $110^{\circ}C$ of H/P temperature regardless of $R_1$ temperature, while there was no thick and thin effect on the TTD yarns in $140^{\circ}C$ of H/P temperature.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.41-64
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• 2014

The main objective of this article is the exploitation of a stochastic hybrid mesh-free method based on stochastic generalized finite difference (SGFD), Newmark finite difference (NFD) methods and Monte Carlo simulation for thermoelastic wave propagation and coupled thermoelasticity analysis based on GN theory (without energy dissipation). A thick hollow cylinder with Gaussian uncertainty in mechanical properties is considered as an analyzed domain for the problem. The effects of uncertainty in mechanical properties with various coefficients of variations on thermo-elastic wave propagation are studied in details. Also, the time histories and distribution on thickness of cylinder of maximum, mean and variance values of temperature and radial displacement are studied for various coefficients of variations (COVs).

• Structural Engineering and Mechanics
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• 제53권4호
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• pp.703-723
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• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.137-140
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• 2005

Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

• 한국자기학회지
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• 제17권2호
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• pp.103-107
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• 2007

본 연구에서는 고체 안에 둘러쌓인 감마선 원천핵 $^{133}Cs$를 금판(gold plate)으로 된 실린더 안에 놓았을 때 첫 여기상태인 81 keV 에너지 준위폭이 더 좁아짐을 볼 수 있었다. 이러한 결과는 에너지 준위의 수명이 연장된 것을 의미한다. 두께 0.5 mm, 길이 5 cm, 반경 1 mm의 실린더를 사용했을 때 4.2 K에서 에너지 준위폭은 6.1 %정도 좁아지는 결과를 얻었다.