• 한국통신학회논문지
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• 제39A권6호
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• pp.322-332
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• 2014

본 논문에서는 굴곡진 도로를 구간 선형 모델로 근사화한 차선 검출 알고리즘을 제안한다. 기존의 차선 검출 알고리즘들은 지표면이 평면이라는 가정을 이용하기 때문에, 도로면이 굴곡진 실제 도로에서는 강건한 차선 검출이 어렵다. 제안하는 방법에서는 이 문제를 전체 차로를 구간으로 분할하고, 각 구간 내에서 차로를 가장 잘 근사하는 평면 차로를 구함으로써 해결한다. 이를 위해 각 구간 내에서 다양한 각도와 위치를 가지는 평면 형태의 구간 차로 후보들을 생성하였다. 구간 차로 후보들의 연결 조합 중 실제 차로에 가장 가까운 조합을 다이나믹프로그래밍을 이용하여 찾음으로써 굴곡진 차로를 근사한다. 평면 도로 뿐 아니라, 상하, 좌우의 굴곡이 있는 도로 영상으로 구성된 데이터세트에 대하여 제안하는 방법의 차선 검출 성능을 검증하였다. 평면 도로를 가정한 기존의 방법들이 80%에서 90% 초반의 검출률을 보이는 반면, 제안하는 방법은 90% 후반의 검출률을 보임을 통해 굴곡진 도로에서의 차선 검출의 강건성을 입증하였다.

• Steel and Composite Structures
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• 제44권2호
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• pp.155-169
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• 2022

In the present paper an analytical model was developed to study the non-linear vibrations of Functionally Graded Carbon Nanotube (FG-CNT) reinforced doubly-curved shallow shells using the Multiple Scales Method (MSM). The nonlinear partial differential equations of motion are based on the FGM shallow shell hypothesis, the non-linear geometric Von-Karman relationships, and the Galerkin method to reduce the partial differential equations associated with simply supported boundary conditions. The novelty of the present model is the simultaneous prediction of the natural frequencies and their mode shapes versus different curvatures (cylindrical, spherical, conical, and plate) and the different types of FG-CNTs. In addition to combining the vibration analysis with optimization algorithms based on the genetic algorithm, a design optimization methode was developed to maximize the natural frequencies. By considering the expression of the non-dimensional frequency as an objective optimization function, a genetic algorithm program was developed by valuing the mechanical properties, the geometric properties and the FG-CNT configuration of shallow double curvature shells. The results obtained show that the curvature, the volume fraction and the types of NTC distribution have considerable effects on the variation of the Dimensionless Fundamental Linear Frequency (DFLF). The frequency response of the shallow shells of the FG-CNTRC showed two types of nonlinear hardening and softening which are strongly influenced by the change in the fundamental vibration mode. In GA optimization, the mechanical properties and geometric properties in the transverse direction, the volume fraction, and types of distribution of CNTs have a considerable effect on the fundamental frequencies of shallow double-curvature shells. Where the difference between optimized and not optimized DFLF can reach 13.26%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2157-2161
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• 2003

In this paper, the response surface method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan, is described. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard k-e turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time

• 한국항공우주학회지
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• 제43권1호
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• pp.1-7
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• 2015

본 연구에서는 탄소섬유강화 복합재를 적층각과 적층순서에 따라 C-channel 형상에서 발생하는 스프링-인을 유한요소해석(ABAQUS)을 통해 예측하였다. 복합재 제작공정에서 냉각시의 큰 온도차 및 적층각에 따른 열팽창계수 및 화학적 수축계수의 차이로 인해 변형(스프링-인)이 발생한다. 이러한 변형은 제품의 품질과 직결되는 문제이며, 반드시 고려되어야 할 사항이다. 유한요소해석 시 CHILE모델과 화학적 수축을 고려한 서브루틴을 제작하여 적용하였으며, [0/X/Y/90]s case에 대해 X,Y를 $0{\sim}90^{\circ}$까지 변화시키며 각 case에 대한 스프링-인 발생량을 예측, 분석하였다.

• Computers and Concrete
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• 제31권5호
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• pp.371-384
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• 2023

Precast roofing systems employing prestressed elements often serve as smart structural solutions for the construction of industrial buildings. The precast concrete elements usually employed are highly engineered, and often consist in thin-walled members, characterised by a complex behaviour in fire. The present study was carried out after a fire event damaged a precast industrial building made with prestressed beam and roof elements, and non-prestressed curved barrel vault elements interposed in between the spaced roof elements. As a consequence of the exposure to the fire, the main elements were found standing, although some locally damaged and distorted, and the local collapse of few curved barrel vault elements was observed in one edge row only. In order to understand and interpret the observed structural performance of the roof system under fire, a full fire safety engineering process was carried out according to the following steps: (a) realistic temperature-time curves acting on the structural elements were simulated through computational fluid dynamics, (b) temperature distribution within the concrete elements was obtained with non-linear thermal analysis in variable regime, (c) strength and deformation of the concrete elements were checked with non-linear thermal-mechanical analysis. The analysis of the results allowed to identify the causes of the local collapses occurred, attributable to the distortion caused by temperature to the elements causing loss of support in early fire stage rather than to the material strength reduction due to the progressive exposure of the elements to fire. Finally, practical hints are provided to avoid such a phenomenon to occur when designing similar structures.

• 소성∙가공
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• 제28권6호
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• pp.335-346
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• 2019

Thick plate forming is presented to manufacture a large and curved member of steam turbine diaphragm. Due to three-dimensional asymmetry of target geometry, it is hard to consistently keep the blank position in die cavity between forming punch and die. In order to relieve the position instability of the blank during the thick plate forming, a blank support structure is proposed to be composed of guide pins and linear bearing, and blank guide arm enlarged from both longitudinal ends of the thick blank. In this study, parametric investigations with regard to the geometric position and width of the blank guide arm are carried out. As main geometric parameters, 2 positions such as maximum curvature region and minimum one on a curved cross-section profile of the target shape are selected, and 14 widths of the blank guide arm are considered. Using 28 variable combinations, three-dimensional numerical simulations are performed to predict the appropriate range of the process parameters. The compatibility and validity of the blank support structure with the blank guide arm for the thick plate forming is verified through the thick plate forming experiments.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.85-96
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• 2003

In the present investigation, the nonlinear dynamic buckling of a curved plate subjected to sinusoidal loading is examined. By the theoretical analyses, a highly nonlinear snap-through motion of a clamped-free-clamped-free plate and its effect on the overall vibration response are investigated. The problem is reduced to that of a single degree of freedom system with the Rayleigh-Ritz procedure. The resulting nonlinear governing equation is solved using Runge-Kutta (RK-4) numerical integration method. The snap-through boundaries, which vary with different damping coefficient and linear circular frequency of the flat plate are studied and given in terms of force and displacement. The relationships between static and dynamic responses at the start of a snap-through motion are also predicted. The analysis brings out various characteristic features of the phenomenon, i.e. 1) small oscillation about the buckled position-softening spring type motion, 2) chaotic motion of intermittent snap-through, and 3) large oscillation of continuous snap-through motion crossing the two buckled positions-hardening spring type. The responses of buckled plate were found to be greatly affected by the snap-through motion. Therefore, better understanding of the snap-through motion is needed to predict the full dynamic response of a curved plate.

• 한국해양공학회지
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• 제24권2호
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• pp.67-73
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• 2010

A simplified finite element analysis has been used to predict the weld-induced deformation to bead-on-plate welding of steel plates having curvatures in the welding direction. In this study, the equivalent loading method based on inherent strain was used to investigate the effect of longitudinal curvature on the weld-induced deformation of curved plates. Equivalent loads were derived from the inherent strain distribution around the weld line, and the loads were used for linear finite element analyses. These kinds of numerical simulations can, of course, be performed by using the rigorous thermalelastic-plastic analysis method. This approach is not, however, practical for use in weld-induced deformation analysis of large and complex structures, such as ship structures, in view of computing time and cost. The present equivalent load approach has been applied to several plate models having curvatures in the welding direction, and the results are compared with those obtained by thermal-elastic-plastic analysis and also with those obtained by the other simplified method found in reference. As far as the present results are concerned, the weld-induced deformation of curved plates can be accurately predicted by the method presented in this paper.

• 대한토목학회논문집
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• 제12권3호
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• pp.1-15
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• 1992

본 논문에서는 열 두가지의 가능한 지지조건을 갖는 연속 곡평면 2방향 슬래브 시스템에 대하여 실용적이고 간편한 수치해석과 최적 설계 방법을 제시하였다. 얇은 곡평판의 탄성이론에 의하여 유도된 설계모멘트 계수를 이용하여, 구조해석을 하는 수치해석 방법을 본 연구에서는 사용하였다. 최적화의 결과는 한계상태 설계법에 의해서 정의된 feasible 영역내에서 결정되도록 유도하였으며 슬래브의 주재료 경비함수를 변형시켜 유도한 목적함수는 한계상태 설계의 규정에 따라 역학적 거동의 문제와 사용성 제약조건을 모두 만족하연서 최적화에 이르도록 하였다. 형성된 최적화 문제는 고차의 비선형 문제로 유도 되었으며 이 비선형 최적화 문제를 연속 선형계획법을 이용하여 해석하므서 슬래브의 유효깊이와 중간대 및 주열대의 단위폭당 변형시킨 철근비들의 최적 설계변수들을 구하였다.

• 한국가시화정보학회지
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• 제9권2호
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• pp.34-39
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• 2011

This paper presents a novel direct fabrication method of the thin metal film RTD temperature sensor array on an arbitrary curved surface by using MEMS technology to measure a distributed temperature field up to $300^{\circ}C$ without disturbing a fluid flow. In order to overcome the difficulty in the three dimensional photography of sensor patterning, the UV pre-irradiated photosensitive dry film resist technology has been developed newly. This method was applied to the fabrication of the temperature sensor array on a glass tube, which is arranged parallel and transverse to a main flow. Gold was used as a temperature sensing material. The resistance change was measured in a thermally controlled oven by increasing the environmental temperature. The linear increase in resistance change and a constant slope were obtained. Also, the sensitivity of each RTD temperature sensor was evaluated.