• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1123-1129
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• 2015

A pair of two-way valves typically is used in automotive washing machines, where the water flow direction is frequently reversed and highly pressurized clean water is sprayed to remove the oil and dirt remaining on machined engine and transmission blocks. Although this valve system has been widely used because of its competitive price, its application is sometimes restricted by surging effects, such as pressure ripples occurring in rapid changes in water flow caused by inaccurate valve control. As an alternative, one three-way reversing valve can replace the valve system because it provides rapid and accurate changes to the water flow direction without any precise control device. However, a cavitation effect occurs because of the complicated bottom plug shape of the valve. In this study, the cavitation index and percent of cavitation (POC) were introduced to numerically evaluate fluid flows via computational fluid dynamics (CFD) analysis. To reduce the cavitation effect generated by the bottom plug, the optimal shape design was carried out through a parametric study, in which a simple computer-aided engineering (CAE) model was applied to avoid time-consuming CFD analysis and difficulties in achieving convergence. The optimal shape design process using full factorial design of experiments (DOEs) and an artificial neural network meta-model yielded the optimal waist and tail length of the bottom plug with a POC value of less than 30%, which meets the requirement of no cavitation occurrence. The optimal waist length, tail length and POC value were found to 6.42 mm, 6.96 mm and 27%, respectively.

• Journal of the Korean Geotechnical Society
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• v.27 no.12
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• pp.127-136
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• 2011

The laboratory tests were performed to investigate the strength characteristic of shotcrete reinforced with improved shape steel fiber developed in this study. Two different type of tests, the flexural toughness test and the bending strength test, were conducted for analyzing shotcrete strengths using three types of specimens (unreinforced shotcrete, exiting steel fiber reinforced shotcrete, and new concept steel fiber reinforced shotcrete). The results of tests represented the advancement of the strength characteristic of shotcrete reinforced with improved shape steel fiber with respect to that of shotcrete reinforced with existing steel fiber.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.5
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• pp.424-432
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• 2011

Shape parameters and design variables for a centrifugal compressor impeller were investigated for optimizing a centrifugal compressor. In order to compare the performance of an optimized impeller with the performance of the original impeller, an already tested impeller was chosen and design variables for optimization were selected. The meridional shapes at the shroud and at the hub were re-designed using the Bezier curve. The camber-lines of the impeller blade at the hub and at the tip were also expressed by the Bezier curve. The shape curves for impeller could be expressed using 6-8 control points. Among them, eight control points which have strong effect to the shape can be selected as design variables for optimization. Therefore, any impeller which is expressed by data points for its shape can be optimized using few design variables.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4381-4387
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• 2015

Ship hull is a compound curved shape and most of shipyards have been using gas heating method for the surface forming of steel plate. This traditional forming process have problems such as difficulties in heat input control and poor working conditions due to loud noise and air contamination. Recently, researches on automatic hull forming system have been conducted using high frequency induction heating method which have good control ability and favorable working environment. In this study, the induction heating simulation system for curved surface forming of steel plate was developed and induction heating experiments were performed. Based on the results of this study, efficient induction heating coil design and optimal heating conditions for the automatic hull forming system can be obtained.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.74-82
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• 2012

Proton exchange membrane fuel cell performance is changed by the complicated physical phenomenon. In this study, water discharge performance of proton exchange membrane fuel cell were performed numerically to compare serpentine channel flow fields of 5-pass 4-turn serpentine and 25 $cm^2$ reaction surface between with and without sub-channel at the rib. Through the supplement of sub channel flow field, it is shown from the results that water removal characteristic inside channel improves because the flow direction of under-rib convection is changed into the sub channel. Reacting gases supplied from entrance disperse into sub channel flow field and electrochemical reaction occurs uniformly over the reaction surface. The results obtained that total current density distributions become uniform because residence time of reacting gases traveling to sub-channel flow field is longer than to main channel.

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.269-277
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• 1998

Laboratory flume experiments to investigate the characteristics of the flows and local scour around circular bridge pier in a curved channel are performed. In this study, the effect of a circular collar device for controlling the depth of scour is examined. The scour depth with a collar is about 40% of the scour depth without collar in the straight course of the flume while it is about 44% of the scour depth without collar at the location of 150' in the curved channel. As the results of experiments using the collar of which diameter is twice of pier, the reduction of scour depth is the most effective in a straight channel when the location of collar is 0.2h( h:depth) below the channel bottom. And, the reduction of scour depth is the most effective in a curved channel when the location of collar is 0.1h below the channel bottom.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.293-293
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• 2019

최근 도심지 침수예방을 위해 구조적 비구조적인 대책 등이 수행되어 왔으나, 도심지의 국지성 호우의 발생빈도가 증가함에 따라 단시간의 도심지 침수예측의 중요성이 다시 대두되고 있다. 이에 도심지 침수 예측을 위해서는 수치모의 프로그램을 사용한 연구가 진행되어 왔으나, 국지성 호우에 의한 침수를 막을 만킁의 실시간 위험예측은 아직까지 힘든 실정이다. 한편 해양재난의 침수를 예방하기 위해서 국립재난안전연구원(2017)에서는 과학적 보간법을 적용한 침수예측 모형인 SIND(Scientific Interpolation for Natural Disaster) Model을 개발한 바 있다. 따라서 본 연구에서는 SIND Model을 도심지 침수예측에 적용하여 집중호우와 같은 단기간의 침수를 예방하고자 한다. SIND Model은 기 구축된 침수예상도를 활용하여 모든 시나리오에 대한 침수 위험도 등급을 실시간으로 평가하는 모형이다. 국토부에서 제공하는 국가홍수위험지도와 내수침수지도를 활용하였고, SIND Model은 Comsol Multyphisic를 활용하여 침수예측지도를 생성하였다. 기존에 해양재난 예측을 위해 사용하였던 Risk Grade 방정식에 시간 항(time term)과 도심지의 최초 침수 발생위치에 생성 항(source term)을 추가하여 도심지 침수특성을 반영하였다. 결과를 평가하기 위하여 CRITIC(CRiteria Importance Through Intercriteria Correlation) 방법을 활용한 형상유사도를 산출하였다. 그 결과, 기 구축된 홍수위험지도와 형상유사도는 전체 구역 중 80%의 구역이 0.8 이상의 값을 나타내었다. 20%의 구역에서는 복잡한 도심지의 건물, 구조물 등의 침수특성을 반영하지 못하여 형상유사도가 낮게 평가된 것으로 판단되며, 향후 위험도 예측을 위해 배수시스템 등의 영향인자를 고려한다면 위험도 등급 예측의 정확도를 높일 수 있을 것이라 기대된다.

• Journal of the Korea Computer Graphics Society
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• v.18 no.4
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• pp.1-8
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• 2012

We present improved deformation energy to enhance the visual quality of a shape deformation technique, where we preserve the local structure of an input planar shape. The deformation energy, in general, consists of several constraints such as Laplacian coordinate constraint to preserve the quality of deformed silhouette edges, mean value coordinates and edge length constraints to preserve the quality of deformed internal shape, and user-specified position constraints to control the shape deformation. When the positions of user-specified vertices change, shape deformation techniques compute the positions of the other vertices by means of nonlinear least squares optimization to minimize the deformation energy. When a user-specified vertex changes its position rapidly, it is frequently observed that the visual quality of the deformed shape decrease rapidly, which is mainly caused by unnecessary enlargement of the Laplacian vectors and unnecessary change of the edge directions along the boundary of the shape. In this paper, we propose improved deformation energy by prohibiting the Laplacian and edge length constraints from changing unnecessarily. The proposed deformation energy incorporated with well-known optimization technique can enhance the visual quality of shape deformation along the silhouette and within the interior of the planar shape while sacrificing only a little execution time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.703-714
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• 2010

This paper describes the design optimization of a rotating rectangular channel with staggered arrays of pin-fins by Kriging metamodeling technique. Two non-dimensional variables, the ratio of the height to the diameter of the pin-fins and the ratio of the spacing between the pin-fins to the diameter of the pin-fins are chosen as the design variables. The objective function that is a linear combination of heat transfer and friction loss related terms with a weighting factor is selected for the optimization. To construct the Kriging model, objective function values at 20 training points generated by Latin hypercube sampling are evaluated by a three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis method with the SST turbulence model. The Kriging model predicts the objective function value that agrees well with the value calculated by the RANS analysis at the optimum point. The objective function is reduced by 11% by the optimization of the channel.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.8-13
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• 2019

As increasing demand for precise machining in advanced disciplines, especially in semi-conductor, aeronautical and automotive industries, the magnetic abrasive deburring(MAD) which is able to eliminate micro-sized burr on complex surface in less time has drawn the attention in the last decades. However, the performance of MAD is subject to shape and size of a tool. Therefore, this study aim to identify deburring behavior of MAD in U-type flow channel by measuring the length rate of burr removal in radial distance of the cylindrical tool under four process factors. In order to evaluate the deburring effect of MAD on the surface, finishing regions are divided based on center of the circular cutting tool. As a results, it was defined that the amount of burr removal in a downward direction moving toward flow channel from the top surface was higher than upward direction. This is because the magnetic abrasives were detached from magnetic lines of force due to geometrical shape.