• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.84-88
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• 2003

In this paper, The optimum design of a die shape has been carried out the FEM analysis of a pilger mill process considering various factors. The pilger mill forming process consists of a pair of rotating die which has appropriate surface shape. The important design parameters of the pilger mill are the feed rate and the profile of grooved die. Optimum design procedure was performed in order to investigated effects on the forming load and the deformed shape of material depending on the die radius profile. Profile of the die surface for the optimum design were suggested with the linear, the cosine and the quadratic curve considering a physical forming process. The surface of each die was modeled using the 3DAutoCAD and the analysis of pilger forming process was performed using the LS-DYNA3D. The optimum profile of the die shape for the pilger mill was determined to the quadratic profile. Since the analysis results provide that the model of the quadratic profile gives the lowest forming load and a proper deformed shape.

• 오토저널
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• 제2권1호
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• pp.21-31
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• 1980

Two phase boundary layer equations of laminar filmwise condensation are solved by an approximate integral method under the following condition; saturated vapour flows vertically downward over a cooled surface of uniform temperature, the condensate film is so thin that the inertia and convection terms are neglected. The following conclusions are drawn under the above assumptions. 1. free convection In case of the linear temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$=4/3,(G $r_{l}$ /4.H)$^{1}$4/ and in case of the quadratic profile, numerical results may be expressed as N $u_{m}$=2/1.682,(G $r_{l}$ /H)$^{1}$4/. 2. Forced convection When the temperature profile is assumed to be linear in a liquid film, numerical results fir the average heat transfer coefficients may be expressed as N $u_{m}$=(A, R $e_{l}$ /H)$^{1}$2/. This expression is compared with the experimental results hitherto reported; For theoretical Nusselt number (N $u_{m}$)$_{th}$<2*10$^{4}$, the experimental Nusselt number (N $u_{m}$)$_{exp}$ is on the average larger than theoretical Nusselt number (N $u_{m}$)$_{th}$ by 30%. For (N $u_{m}$)$_{th}$>2*10$^{4}$, experimental Nusselt number (N $u_{m}$)$_{exp}$ is about 1.6 times as large as theoretical Nusselt number (N $u_{m}$)$_{th}$. These large deviation may be caused by the presence of turbulence in the liquid film. In case of the quadratic temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$'=(2,A,Re/H)$^{1}$2/. This formular shows that theoretical Nusselt number (N $u_{m}$)$_{th}$ is larger than experimental Nusselt number (N $u_{m}$)$_{exp}$ by 60%. It is speculated that when the temperature difference between cooled surface and saturated vapour is small, temperature profile in a liquid film is quadratic.quadratic.. quadratic.quadratic..atic..

• 한국농공학회지
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• 제29권3호
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• pp.153-162
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• 1987

A numerical procedure for the analysis of slender arch buckling problems for uniform dead weight is presented in this paper. Such loading changes in the arch profile. The problem is nonlinear. The numerical procedure is limited to an inextensible analysis and to elastic behavior. Based upon a numerical integration technique developed by Newmark for straight beams, a large deflection bending analysis is combined with small deflection buckling routines to formulate the numerical procedure. The numerical procedure is composed of a combination of the numerical integration and successive approximations procedure. The results obtained in this study are as follows : 1.The critical loads obtained in this study coincide with the results by Austin so that the algorithm developed in this study is verified. 2.The numerical results are converged with good precision when the half arch is divided into 10 segments in both Prime and Quadratic section. 3.The critical loads are decreased as the ratios of rise versus span are increased. 4.The critical loads are increased as the moments of inertia at the ends are increased. 5.The critical loads of Prime section are larger than that of Quadratic section under the same profile conditions.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2000년도 학술발표회 발표논문집
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• pp.346-351
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• 2000

The study was carried out to investigate the characteristics of vertical velocity distribution measured by current meter at Kangkyung station in Keum river during the period of 1995 to 1997. It suggests the quadratic parabola equation to estimate the vertical velocity profile only from the measurement data of surface velocity. The equation was found to be statistically very stable and showed high significance to express the surface velocity and bottom velocity. The vertical velocity profile was determined by the relationships to the surface velocity, and a coefficient of the quadratic parabola equation. The vertical velocity profile can be applied to calculating the mean velocity and discharge, and to and to analyse the dispersion of pollutant materials in the streamflow.

• 한국수자원학회논문집
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• 제33권2호
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• pp.169-179
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• 2000

이 연구에서는 1995년부터 1997년까지 금강수계 강경지점에서 유속계로 측정한 유속자료를 분석하여 자연하천의 연직방향 유속분포특성을 규명하였다. 또한, 현장유속 측정조건이 불량하여 다점법으로 유속분포를 측정하기 곤란한 경우, 간단하게 표면유속만을 측정하여 상대깊이별 유속을 추정할 수 있는 연직 유속분포식을 유도하였다. 2차 포물선의 유속분포식은 통계적으로 매우 안정적이고, 표면유속과 바닥유속 등과 고도의 유의성을 보였다. 2차 포물선식의 상수 및 계수와 표면유속과의 상관관계를 구하였으며, 실측 검정자료에 적용한 결과, 유속분포특성을 잘 반영하는 것을 확인할 수 있었다. 연직 유속분포식으로 추정된 유속은 실제수심을 적용하여 평균유속과 유량을 결정할 수 있으며, 이는 또한 하천의 오염물질이동 등 수질해석에 적용할 수 있을 것이다.

• 한국기계가공학회지
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• 제16권3호
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• pp.30-37
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• 2017

When a wheel profile of a train-tram is designed, both train and tram tracks should be considered. This study designed a wheel profile that enables high-speed driving(200km/h) on the train track and low speed driving on the tram track with multiple sharp curves. The study used the approximation optimization method to reduce cost and time, used the sequential quadratic programming method as the optimized algorithm, and the central composite design and response surface method as an approximate model. The optimized wheel shape based on this approximation optimization method reduced wear of the initial wheel showed a better performance in terms of derailment and lateral force.

• 한국컴퓨터정보학회논문지
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• 제22권10호
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• pp.27-34
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• 2017

In this paper, we propose a novel radiometric calibration method which can effectively compensate the nonlinearity of the detector for hyper-spectral camera. In general, the detector of hyper-spectral camera can produce nonlinear output depending on radiance and integral time. The conventional radiometric calibration methods extract the imprecise radiance profile from the spectral profile of the target due to this nonlinearity. In our proposed method, we use a quadratic equation instead of a linear equation to describe the relation between output of detector and radiance. Then, we use a fractional function to compensate variation of integration time. Thus, our proposed method can extract more precise spectral profile of radiance than conventional radiometric calibration method.

• 한국정밀공학회지
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• 제29권6호
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• pp.607-612
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• 2012

The wear problem of wheel flange occurs at sharp curves of rail. This paper proposes a procedure for optimum design of a wheel profile wherein flange wear is reduced by improving an interaction between wheel and rail. Application of optimization method to design problem mainly depends on characteristics of design space. This paper compared local optimization method with global optimization according to sensitivity value of objective function for design variables to find out which optimization method is appropriable to minimize wear of wheel flange. Wheel profile is created by a piecewise cubic Hermite interpolating polynomial and dynamic performances are analyzed by a railway dynamic analysis program, VAMPIRE. From the optimization results, it is verified that the global optimization method such as genetic algorithm is more suitable to wheel profile optimization than the local optimization of SQP (Sequential Quadratic Programming) in case of considering the lack of empirical knowledge for initial design value.

• Advances in Computational Design
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• 제5권4호
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• pp.397-416
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• 2020

Functionally graded material (FGM) illustrates a novel class of composites that consists of a graded pattern of material composition. FGM is engineered to have a continuously varying spatial composition profile. Current work focused on buckling analysis of beam made of stepwise linear and quadratic graded material in axial direction subjected to axial span-load with piecewise function and rested on shear layer based on classical beam theory. The various boundary and natural conditions including simply supported (S-S), pinned - clamped (P-C), axial hinge - pinned (AH-P), axial hinge - clamped (AH-C), pinned - shear hinge (P-SHH), pinned - shear force released (P-SHR), axial hinge - shear force released (AH-SHR) and axial hinge - shear hinge (AH-SHH) are considered. To the best of the author's knowledge, buckling behavior of this kind of Euler-Bernoulli beams has not been studied yet. The equilibrium differential equation is derived by minimizing total potential energy via variational calculus and solved analytically. The boundary conditions, natural conditions and deformation continuity at concentrated load insertion point are expressed in matrix form and nontrivial solution is employed to calculate first buckling loads and corresponding mode shapes. By increasing truncation order, the relative error reduction and convergence of solution are observed. Fast convergence and good compatibility with various conditions are advantages of the proposed method. A MATLAB code is provided in appendix to employ the numerical procedure based on proposed method.

• 제어로봇시스템학회논문지
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• 제20권8호
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• pp.828-834
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• 2014

This paper presents a comparison among three types of approaches to an ARC (Active Roll Control) with an AARB(Active Anti-Roll Bar) for a vehicle system. Lateral acceleration and road profile are considered as disturbance. The ARC is designed with an LQ SOF (Linear Quadratic Static Output Feedback) control, $H_{\infty}$ control and SMC (Sliding Mode Control). These approaches are compared in terms of rollover prevention and ride comfort. For comparison, Bode plot analysis based on linear model and frequency response analysis based on CarSim simulation are performed.