• 융복합기술연구소 논문집
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• 제3권2호
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• pp.17-21
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• 2013

Hot cross wedge rolling process as an incremental forming has many advantages such as the material usage, the short process time, the automatic equipment line and the low forming load. However, it occurs some defects such as the surface groove, the axis warping and the Mannesmann hole. In this paper, the defect of the Mannesmann hole was carried out. Finite element analysis was utilized to reveal the stress distribution, the rotation of the specimen and the change of section profile. Cross wedge rolling experiment was also conducted on the generation of the Mannesmann hole. It was demonstrated according to the spreading angle with respect to the various types of material. In the view point of metal flow, the smaller forming angle and the larger spreading angle increase opportunities of the defect hole generations.

• 한국통신학회논문지
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• 제19권10호
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• pp.2001-2013
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• 1994

본 논문에서는 훼손된 영상을 처리하는 방법에 대하여 연구하였다. 기존의 처리방법은 특이점이나 악 조건일 경우 수렴 속도가 늦어진다는 점과 처리시간이 많이 소요되는 단점이 있다. 이러한 단점을 보완하기 위하여 Gauss seidel 방법으로 처리하는 방법이 있으나 이러한 경우 영상을 반복해서 처리해야 하므로 처리시간이 많이 소요된다. 이러한 난점(수렴속도, 전체 처리시간)을 개선하기 위하여 본 논문에서는 기존의 신호처리(Gauss Seidel)와 제안된 알고리즘을 적용시켜 비교하여 봄으로써 특이한 혹은 악조건일 경우에도 수렴속도를 고속화하여 기존의 Gauss-Seidel 신호 처리 방법보다 처리 시간을 단축할 수 있는 영상 복원 방법을 제시하였다. 제안된 최적화 알고리즘을 영상신호에 적용시켜 가속 상수에 따른 처리 신호의 simulation과 MSE(mean-square error)의 변화를 비교하여 봄으로써 처리정도를 알아보았다. 그리고, 본 알고리즘의 유효성을 입증하기 위하여 모든 가속상수의 변화에 대한 영상복원 결과와 처리시간을 측정하여 보았다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.475-481
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• 2017

본 실험에서는 추진기관 연료의 주 성분으로 사용되는 액체 탄화수소 화합물의 초임계 분사 거동 특성을 분석하기 위해서 고속카메라 이미지를 활용한 실험을 수행하였다. 케로신의 구성성분 중 임계점의 차이가 있는 Decane과 Methylcyclohexane (MCH)를 실험 유체로 선정하였으며, 분석을 위해 Shadowgraphy 기법을 사용하였다. 제트 분사 시 임계온도 조건 하에서 각 유체의 환산압력에 따라 케이스를 나누었다. 아임계 조건의 동일한 인젝터 초기상태에서 기화가 발생하기까지 온도변화량의 차이에 따라 Decane과 MCH는 서로 다른 거동을 보였다. 하지만 초임계 조건에서는 같은 온도변화량이 필요하더라도 임계점 부근에서는 증발엔탈피가 0에 가까워져 기화과정이 아닌 초임계 유체로의 상변화가 일어나고 급격한 밀도변화가 없어 Decane과 MCH 모두 원기둥 형상의 액주가 관측되었다.

• 한국의류학회지
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• 제21권4호
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• pp.769-781
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• 1997

The purpose of this research is to show how to use the patternist's CAD system in order to make design patterns efficiantly. Using the PAD System Technologies company's PAD System Module, which is very officiant in designing patterns, the basic pattern or design pattern can be designed and applyed to the Sample Module, thus, then it could manufacture, retouch or choose a model, making it posible to go to the next level which is seam patterns for industrial use. By understanding the change of the design that is chosen through the design pattern making and Sample Module process', this study is presentated a plan on how to utilize the patternist's working adaption ability by the CAD system, and also considered the problems in using it. Ability of Design Confrontation of CAD System: 1) The result of an operation can be saved and retouched. On a saved list the patterns can be chosen and changed, thus, making it posible to complete a design very quickly. 2) When sewing every designed pattern in Sample Module, the model can be operated merely by selecting each sewing position, thus creating the same effect of a designer's muslin sample process in a much lesser time. Point at issue in the utilization CAD system: 1) When combining two darts into one place the amounts of darts that are already these have to be erasers, and then, the two darts points are moved that place, thus, containing them, which is very conplicated. 2) When making a gathering, because system can only be recognized in a opend line, the pattern should be separated in order to put a gathering inside a pattern. 3) In order to readjust the amounte of dart. The dart is erased first and then made new dart again. 4) When making tucks in a Sample Module, the form that gets narrow towards the pivot point can not be recognized so the sewing lines of the tucks is adjusted into parallel lines. 5) The Sample Module 3D operation can not attach the bodice to the shirts, instead they become fixed into each other. In the case of shoulder line tucks the amounts of pleats can not be expanded draperary naturally, thus, making it hard to showing the silhouette accurately. If these problems are solved, especially if the silhouette of a model can be created to have natural drapery in the 3D Module, models can be shown on the screen in possible to compare and examine even a change of a detail, by designing this 3D Module Production sample process will be more effective, thus, making the CAD system more useful in sewing design process.

• 설비공학논문집
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• 제3권1호
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• pp.51-60
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• 1991

The aim of this study is to investigate the heat transfer characteristics in the transient cooling process of a high temperature wall. The slow transient cooling experiment was carried out with a copper block of high thermal capacity. The results of these experiments are as follows. 1. Temperature histories measured by the thermocouple, which is 0.99, 2.00, 2.99mm from the heat transfer surface showed monotonous during the cooling process. These variation are the curves of typical temperature histories in film-boiling, transition-boiling, and nucleate-boiling regions. 2. The temperature histories were measured by thermocouple installed in the copper block. The variations of the surface heat fluxes and surface temperature were computed from the numerical solution method TDMA from the measured temperature histories for radial position one dimensional heat transfer inverse problem. The boiling curves were found by the computed temperature histories. 3. The rewetting point which starts to change from film boiling to nucleate boiling is not connected with the mass velocity and it were found that the temperature of rewetting point indicated about $100^{\circ}C$. 4. The heat flux of rewetting point was about $10^5Kcal/m^2h$, at that time, the heat transfer coeficient indicated about $1000Kcal/m^2h^{\circ}C$ irrelevent to mass velocity. 5. The wall superheat decreases as the pressure increases. But I found that rewetting point appeared under higher condition in the wall temperature.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.49-56
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• 1999

Welding is a reliable process and is mainly adopted for fabricating heavy structures. Recently, transverse cracks in the weld metal is serious problem, and they affect cost, efficiency, safety and joint reliability for various welded structures. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained are as follows; 1) The content of diffusible hydrogen in the commercial flux cored are welding wire was remarkable change by manufacturer. 2) The diffusible hydrogen content was thd main factor for weld metal transverse cracks. 3) Weld metal was immune to transverse cracking under the condition of low diffusible hydrogen content of high restraint condition. 4) The factors for weld metal transverse crack would be the content of diffusible hydrogen and restraint of weld joint.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권1호
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• pp.19-30
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• 2013

The requirements of reliability verification for new products and technology are increasing more and more in accordance with the trend change of strength for safety technology, functional skills and emotional quality. In order to conduct the purpose of robust design from the stage of product development recently, the application of reliability technology has gradually increased such as detecting the failure mode throughout the HALT technique, accelerated tests and so on. The main results are as follows; i) through the pre-test and analysis, detected the basic performance and predictable failure mode, ii) HALT technique and process has been developed that can be applied test methods for the next new products.

• Journal of the Korean Statistical Society
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• 제19권2호
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• pp.128-138
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• 1990

In this paper we study the properties of nonparametric tests for testing the null hypothesis of no changes against one sided and two sideds alternatives in scale parameter at unknown point. We first propose two types of nonparametric tests based on linear rank statistics and rank-like statistics, respectively. For these statistics, we drive the asymptotic distributions under the null and contiguous alternatives. The main theoreticla tools used for derivation are the stochastic process representation of the test staistic and the Brownian bridge approximation. We evaluate the Pitman efficiencies of the test for the contiguous alternatives, and also compute empirical power by Monte Carlo simulation.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.481-492
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• 2022

Cycloidal ball planetary transmission (CBPT) has many applications as precision reducer, such as precision machinery and automation drive systems etc. The traditional analytical model of CBPT cannot accurately describe the change of the normal force of meshing points, and thus cannot describe the precise transmission process of meshing pairs. In the paper, a method for deriving the normal force equation is put forward by using the non-linear relationship between force and deformation in elastic mechanics. The two-point contact analytical models of all the meshing pairs are established to obtain the micro-displacement analytical model of CBPT under axial pre-tightening. Then, the non-real-time two-point contact analytical models of all the meshing pairs are further constructed to obtain the normal force expression to determine the critical compression coefficients. Experimental investigations are performed to verify the analytical model using the critical compression coefficients.

• 국제학술발표논문집
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• The 1th International Conference on Construction Engineering and Project Management
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• pp.1203-1207
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• 2005

At this point of time that it is required to improve educational environment and the function of educational facilities as well as interests on educational facility business is increasing, it is actual situation that unsystematic maintenance of educational facility is not being able to cope with the change caused by introducing the 7^th curriculum. Also, in spite of enormous career in maintenance work, the function is not properly performed because of unsystematic management. In case of educational facility manager, he parallels performing general administrative work and facilities maintenance work not as a maintenance expert but as a member of administration office. So there are difficulties in performing maintenance work, and systematic maintenance work cannot be expected because of lacking maintenance manual. Therefore, in this research, I would like to investigate and analyze the status of educational facilities and to elicit the point of issue as a basic research to save maintenance expenses and to make pleasant educational environment.