• 한국정밀공학회지
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• 제26권5호
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• pp.57-63
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• 2009

Interface friction in blanking dies, cold forging and extrusion of aluminum alloys is a major cause of inefficient process. This paper describes an investigation of femtosecond laser texturing for reduction of interface friction on sliding surfaces in forming process. Femtosecond direct writing technology was used to fabricate a laser micro-machined die and to create microgroove patterns with varying size and density on metal forming dies. A systematic approach to find the optimum parameters and computer simulation comparison of friction coefficients are provided to study the relation of friction coefficients and die profiles. In metal forming tests, the effectiveness of various laser-machined patterns for enhancing interface lubrication is determined.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.323-326
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• 1996

In a simple system, the control schemes work well provided that the characteristic of the plant or the coefficients are known and fixed. But the condition is not met in the system like satellite, for example, varying over time and the coefficients of dynamic system change due to disturbance, etc, and the better precise model is required to control the given dynamic system well. Conversely, the fixed controller make the unmodel dynamic system with a wide class of modelling error be stable within the error tolerance limits. Also, a robust model reference adaptive control scheme is designed for the plant, paying attention to the derivation of the appropriate parametric model and the design of the normalizing signal to guarantee that it has the desired properties.

• 산업기술연구
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• 제16권
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• pp.113-121
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• 1996

In the early developmental stages of robotics,hydraulics played an important role. As the power-to-weight ratio of electric motors increased, they eventually replaced hydraulic actuators in robot manipulators. Recently, however, task requirements have dictated that the manipulator payload capacity increase to accomodate greater payload, greater length, greater reaction forces, and hydraulic actusators are being studied as an effective form of robot actuation again. For efficient control of hydraulic actuators, the knowledge of its dynamic equation is essential. However, the dynamic equation of hydraulic actuators are nonlinear, and the dynamic coefficients are time varying. In this paper, an estimation algorithm of the dynamic coefficients of the hydraulic piston dynamics are formulated. Simulation results are presented to show the possibility of the parameter estimation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.678-683
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• 2000

The one-dimensional performance model of a torque converter has been widely used to analyze and predict the performance and dynamic behavior of a torque converter. But this model doesn't include the information of the operating fluid properties. Therefore, to precisely predict dynamic performance of a torque converter, the effect of operating conditions must be considered through experimental coefficients such as friction loss coefficient and shock loss coefficient. And these coefficients cannot be achieved without experiments or internal flow analysis. In this study, the effects of varying material properties of operating fluid according to various operating temperatures are clarified with flow analysis of a torque converter. And these results are verified by comparing with those of performance experiment.

• 한국유체기계학회 논문집
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• 제4권2호
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• pp.35-43
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• 2001

The flow characteristics passing a multi-point Pitot tube flow-meter of diamond shape and the characteristics of flow coefficients of the flow-meter are experimentally studied by varying combination of upstream rectangular dual elbows. The results provide the flow coefficients, which show good stability and reliability within the Reynolds number range coveted here in this study, and which can be used to measure flow-rates in practice. The variation of dual elbows upstream can change the velocity field so much that the flow pattern might thwart the precise flow measurement using the multi-point Pitot tube. The strongest swirl is detected in the case of $90^{\circ}$ dual elbow combination of all. In addition, it is observed that flow separation remains unchanged and occurs at the same point irrespective of various upstream dual elbow combinations.

• Journal of Microbiology and Biotechnology
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• 제19권11호
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• pp.1379-1384
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• 2009

Succinic acid-producing Anaerohiospirillum succinkiproducens was anaerobically grown in glucose-fed continuous cultures using glucose as a carbon source, and the metabolic flexibility of A. succiniciproducens in response to varying glucose concentrations and dilution rates was examined Both succinic acid (SA) and acetic acid (AA) formation was growth-associated, and their growth-rate-related coefficients ($K_{SA/X}$, $K_{AA/X}$) and nongrowth-rate-related coefficients ($K'_{SA/X}$, $K'_{AA/X}$) were slightly influenced by glucose concentrations. A high glucose concentration (38 g/l) and high growth rate ($0.63\;h^{-1}$) did not induce by-product formation.

• Journal of Welding and Joining
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• 제20권3호
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• pp.129-137
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• 2002

This study presents a new method to derive the constraint coefficient from the degree of angular deformation caused by welding, as measured experimentally by varying the shape of welded joints and the magnitude of constraints and from analysis results given by the elastic FEM method. The equivalent load was then calculated with this constraint coefficient. The validity of the numerical analysis involved in this new method was confirmed by its agreement with the experimental results. As for the effects of the constraints based on the shape of the welded joints in the case of Butt welding when the constraint coefficients are not considered, the deformed quantity produced by analysis is larger that produced by experiment and consequently is largely affected by the constraints. However, in the case of Fillet welding, the deformed quantity is seldom affected regardless of constraint coefficient considerations.

• 설비공학논문집
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• 제13권11호
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• pp.1141-1148
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• 2001

Experiments on the condensation heat transfer and pressure drop in the brazed type plate heat exchangers are performed with refrigerants R410A/R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different $45^{\circ},\;35^{\circ}and\;20^{\circ}$ chevron angles are used. Varying the mass flux of refrigerant (13~34 kg/$m^2$), the condensing temperatures ($20^{\circ}C\;and\;30^{\circ}C$) and the vapor quality (from 0.9 to 0.15) at the same constant heat flux ($5kW/m^2$), the condensation heat transfer coefficients and pressure drops are measured. The heat transfer coefficients decrease slightly with increasing the condensing temperature at a given mass flux in all plate heat exchangers. The pressure drop increases with increasing the mass flux and the quality and decreasing the condensing temperature and the chevron angle.

• KSBB Journal
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• 제8권3호
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• pp.266-271
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• 1993

Calcium Alginate gel에 고정화된 Aureobasidium pullulans cell을 이용한 fructo-이igosaccharides 생산 반응메카니즘에 있어서 포도당, sucrose 및 fructo-oligosaccharides의 유효확산계수를 구하고, 반응메카니즘에 대한 수학적 모벨을 제안하였다. $770g/\ell$, $860g/\ell$ 의 고농도 당용액에서 이들의 유효확산계수는 $1.2-7.6\times10^{-7}\textrm{cm}^2$/s 범위로 매우 낮은 값을 보였고, 이 결과를 모댈식에서 적용하여 기질농도, bead 크기 및 첨가비율 등을 변화시키면서 실험적으로 검증해 본 결과 실험치와 모델식이 대체로 잘 일하였다.

• Wind and Structures
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• 제4권6호
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• pp.469-480
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• 2001

The Leipzig Wind Profile is generally known as a typical neutral planetary boundary layer flow. But it became clear from the present research that it was not completely neutral but weakly stable. We examined whether we could simulate the Leipzig Wind Profile by using a ($k-{\varepsilon}$) turbulence model including the equation of potential temperature. By solving analytically the Second Moment Closure Model under the assumption of local equilibrium and under the condition of a stratified flow, we expressed the turbulent diffusion coefficients (both momentum and thermal) as functions of flux Richardson number. Our ($k-{\varepsilon}$) turbulence model which included the equation of potential temperature and the turbulent diffusion coefficients varying with flux Richardson number reproduced the Leipzig Wind Profile.