• 소성∙가공
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• 제24권3호
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• pp.161-166
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• 2015

The finite element method has been widely used in the analysis of ring rolling. For ring rolling it requires a high computational expense due to the non-steady state material flow characteristics of the process. The high computational expense causes the finite element analysis to be impractical for industrial applications. In the current study, we aim to develop a practical implicit finite element modeling method for ring rolling. This method uses a step-wise steady state assumption and is called the “Stepped method”. The stepped method divides the whole process time of unsteady-state flow model into a finite number of steady-state models. It then solves the process at several specific time steps until convergence is reached. In order to confirm the performance and validity of the newly proposed stepped method, the result from the stepped method were compared to the results from a Lagrangian finite element method and to results from experiments reported in the literature.

• 대한기계학회논문집
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• 제13권4호
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• pp.764-770
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• 1989

This paper analyze the steady state performance of a self-acting air lubricated slider bearing in hard disk/head system. Modified Reynolds' equation is derived from the steady state compressible Navier-Stokes equation, under slip-flow conditions. Finite difference technique and numerical procedure are described by using Newton-Raphson iteration method to slove the non-linear equations. These techniques are applied to conventional slider bearings and the effects of molecular mean free path(MMFP) for a recording surface of hard disk are shown. The calculation procedure developed here, wide applicabilities in practical head design procedures, and converges rapidly.

• 한국정밀공학회지
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• 제10권2호
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• pp.30-39
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• 1993

The study is concerned with the thermo-viscoplastic finite element analysis of nonisothermal hot container extrusion through conical dies. The problem is treated as a non-steady state incorporating the nonisothermal heat transfer analysis. The analysis of temperature distribution includes heat transfer though the boundary surface including conduction, convection and radiation. The analysis of heat transfer is decoupled with the analysis of deformation and the material interaction is considered through iteration procedure. The effect of important process parameters including die angle and extrusion ratio in the process is investigated. Due to the geometric feature for the container extrusion through conical dies, automatic remeshing is mandatory. Automatic remeshing is achieved by introducing the modular remeshing technique.

• 대한수학회논문집
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• 제22권4호
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• pp.597-608
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• 2007

We present a general uniqueness result of an endemic state for an S-I-R model with external force of infection. We reduce the problem of finding non-trivial steady state solutions to that of finding zeros of a real function of one variable so that we can easily prove the uniqueness of an endemic state. We introduce an assumption which was usually used to show stability of a non-trivial steady state. It turns out that such an assumption adopted from a stability analysis is crucial for proving the uniqueness as well, and the assumption holds for almost all cases in our model.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 제5회 압출 및 인발가공 심포지엄
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• pp.33-41
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• 2002

In case of hollow cylinder extrusion using porthole die, the effects of extrusion parameters-temperature, the speed of extrusion, the shape of the die and mandrel-on metal flow in porthole die extrusion of aluminum have been investigated. However, there have been few studies about condenser tube extruded by porthole die. This study was designed to evaluate metal flow, welding pressure, extrusion load, tendency of mandrel deflection according to variation of chamber length. in porthole die. Estimation was carried out using finite element method. Porthole die is analyzed in as non-steady state. Analytical results provide useful information the optimal design of porthole die.

• 터널과지하공간
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• 제13권5호
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• pp.389-396
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• 2003

본 연구는 정상류 Navier-Stokes 방정식에 섭동(perturbation) 이론을 적용하여 주기함수 간극에 대한 삼승법칙의 수정에 대해 논하였다. 이를 위해, 주기함수를 진폭과 파장에 대한 무차원 함수로 전환한 뒤 미소 계수에 대한 무차원 유동함수와 연속 방정식을 적용하였다. 이러한 과정을 통해 정상류 Navier-Stokes 방정식의 섭동 근사해를 구하였으며 이를 유한 차분법에 적용하였다. 단일 절리 모델에 대한유한 차분 수치해석을 통해, 수정된 삼승 법칙이 주기함수 간극의 유체 유동에 대한 정상류 Navier-Stokes 방정식의 섭동 근사해와 잘 일치하는 것으로 나타났다. 이를 통해 본 연구에서 제시된 삼승 법칙이 간극 분포에 따른 유체 유동의 평가에 있어 유용하게 적용될 수 있는 것으로 나타났다.

• 한국자동차공학회논문집
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• 제5권4호
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• pp.29-38
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• 1997

In this paper, brake steering performance of electric-driven special-purpose vehicles is investigated. A 14 DOF model is developed considering nonlinear character- istics of the suspension and tire. Based on the model, cornering performance is analyzed for brake steering, acceleration steering and pivoting, respectively. Simulation results are obtained based on the developed SIMULINK module. This analysis about the non steady state cornering performance is particularly important for armored vehicles because the projected route of the vehicle at emergency should be predicted accuracy.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권11호
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• pp.663-669
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• 1999

This paper presents new self excited DC-DC converters such as Buck-boost type, Buck type and also non-inverting Buck-boost type. The proposed converters has the following advantages: simple topology, small number of circuit components, easy control method. Therefore, these converters are suitable for the portable appliances with battery source. It is especially suited for low power DC-DC conversion applications where non isolation output power is usually required. The steady state characteristics of proposed self exciting Buck-boost DC-DC converter are analysis and the result shows good agreement with experimental value. Furthermore the experimental results for 50W class self oscillating Buck-boost DC-DC converter have been obtained, which demonstrate the high efficiency and good performance.

• 전기학회논문지
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• 제56권1호
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• pp.14-17
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• 2007

Power system restoration following a massive blackout starts with re-energizing primary restorative transmission systems at first. The comparison of the TLCC(transmission line charging capacity) and the RPC(reactive power capability) of related black-start generator should be considered in this stage because overvoltage can be caused by self-excitation at the generator when the RPC is smaller than the TLCC. The RPC can be decided by two criteria. One is stator end core heating, and the other is steady state stability. RPC in steady state stability area has been found based on a synchronous reactance Xd. This paper presents RPC limit of salient pole machine which is different from that of non-salient pole machine in steady state stability area and shows derivation process about that.

• 소성∙가공
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• 제11권2호
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• pp.138-146
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• 2002

This paper is concerned with the simulation-based process design method involved non-steady state problem of tension levelling considering the elasto-plastic hardening behavior of a metallic strip by a commercial code ABAQUS/Standard. The tension levelling process is peformed to elongate the strip plastically in combination of tensile and bending strain by a controlled manner so that all longitudinal fibers in the strip have an approximately equal amount of length and undesirable strip shapes are corrected to the flat share. Objectives of this paper are the development of a general method for the design of a tension leveller by a finite element method and parameter studies for the deisgn variables such as the applied tension, the roll intermash includes the determination of the steady state using the simple unit of the tension levelling line and the effect of the finite element mesh size on the amount and distribution of the strain calculated. The analysis provides the information about the intermesh effect on the amount and final shapes of the strip and distribution of the strain in order to determine the amount elongation for correction of the irregular share.