• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.597-601
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• 1997

The technology of Semi-Solid Forging(SSF) has been actively developed to fabricate near-net shape products using light and hardly formable materials. Generally, the SSF process is composed of slug heating,forming,compression holding and ejecting step. After forming step in SSF, the slug is comperssed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. This paper presents the analysis of temperature,solid fraction and shrinkage at compression holding step for a cylindrical slug,then predicts the solidification time to obtain the final shaped part. Enthalpy-based finite element analysis is performed to solve the heat transfer problem considering phase change in solidification.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.102-108
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• 1997

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials. Generally, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. This paper presents the analysis of temperature, solid fraction and shrinkage at compression holding step for a cylindrical slug, then predicts the solidification time to obtain the final shaped part. Enthalpy-based finite element analysis is performed to solve the heat transfer problem considering phase change in solidification.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.199-203
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• 1995

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. The compression holding time that can affect mechanical properties and shape of products is important to make decision, where it is necessary to find overall hert transfer coefficeient properly which has large effect on heat transfer between slug and die. This paper presents the procedure to predict compression holding time of octaining the final shaped part with information of temperature and solid fraction for a cylindrical slug at compression hoiding step in closed-die compression process using heat transfer analysis considering latent heat by means of finite element method. The influence of the predicted compression hoiding time on mechanical properties of products is finally investigated by experiment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.3
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• pp.258-263
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• 2012

In this paper the Chemical Propulsion Subsystem of COMS is briefly explained and some telemetries acquired by a series operations of CPS during the Launch and Early Operation Phase of COMS are presented. The pressure and temperature of pressurant tank telemetries are compared with the results of the developed computer program. The changes in pressure are due to the two major phases. The first one is the initialization phases of CPS composed of the venting phase to vent the helium gas in the pipe network from the downstream of the propellant tanks to the thrusters for safety, the priming phase to fill the vented pipe network with oxidizer and fuel respectively and then the pressurization phase to pressurize the ullage of propellant tank to regulated pressure. And the other is the apogee engine firings in which COMS CPS is in the orbit raising phase to use helium as a pressurant to keep the pressure of propellant tank as the liquid apogee engine get fired until COMS reached to the target orbit. This program can be applicable to prepare basis design data of the next Geostationary Satellite CPS.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.89-89
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• 2003

로켓엔진의 연소에 필요한 추진제를 안정적으로 공급하기 위한 추진제 공급시스템의 주요 구성과 설계 주요 인자를 정리하였다 공급시스템은 추진제 주입/배출 장치, 추진제탱크 가압 및 배기 장치, 추진제 공급 주/분기 배관, 극저온 산화제 온도 유지 장치 등으로 구성되어 있다. 주요 설계 제한 조건으로는 터보 펌프 입구에서의 추진제 압력 및 온도, 필요 추진제 공급 유량 및 온도 그리고 추진제 충진 및 비상 배출 허용 시간 등이며 이는 각 로켓의 해당 임무에 따라 적절히 결정된다. 발사체로부터 할당된 중량값 이내에서 고신뢰도의 작동성, 안정성이 보장되는 시스템을 설계하여야 하며 초기 설계 단계에서 개발 및 수급 가능성을 동시에 고려하여야 할 것이다. 또한 고추력 생성을 위해 엔진 클러스터링이 수행되어야 할 경우 각 엔진으로의 균등한 추진제 배분 공급이 설계의 중요한 요구 조건이 된다. 이러한 공급시스템의 개념은 액체산소와 케로신 조합의 액체 로켓인 100kg급 소형 위성 발사체(KSLV-Ⅰ)에 적용될 예정이다.

• Korean Journal of Food Science and Technology
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• v.29 no.6
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• pp.1202-1207
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• 1997

Inactivation of Leuconostoc sp. isolated from kimchi using carbon dioxide under pressure was investigated in terms of operating parameters in order to evaluate its feasibility as a novel nonthermal process. Inactivation rates increased with increasing pressure, temperature and exposure time, but with decreasing working volume. Microbial reduction of 3 log cycles was achieved within 150 min under a $CO_2$ pressure of $60\;kg/cm^2$ at 30^{\circ}C$. It was confirmed that microbial inactivation by the high pressure $CO_2$ was governed essentially by the characteristic of $CO_2$ mass transfer and thus penetration of $CO_2$, into cells was a rate limiting step to determine efficiency of the inactivation process. The experimental results suggested that the high pressure $CO_2$ treatment could be used as one of the effective nonthermal methods for preserving foods.

• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.1-11
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• 1989

Numerous losses of decay heat removal capability have occurred at U during stutodwn while its significance to safety is needless to say. A study is carried out as an attempt to assess what could be done to lower the frequency of these events and to mitigate their consequences in the unlikely event that one occurs. The shutdown risk model is developed and analyzed using Event/Fault Tree for the typical pressurized water reactor. The human cognitive reliability (HCR) model, two-stage bayesian approach and staircase function model are used to estimate human reliability, initiating event frequency and offsite power non-recovery probability given loss of offsite power, respectively. The results of this study indicate that the risk of a Pm at shutdown is not much lower than the risk when the plant is operating. By examining the dominant accident sequences obtained, several design deficiencies are identified and it is found that some proposed changes lead to significant reduction in core damage frequency due to loss of cooling events.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.70-77
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• 2010

Microcement grouting and micro pile are frequently used for ground modification during tunnel construction. The influence of grouting pressure of microcement grouting and micro pile to the existing bridge which is directly over the constructing tunnel is investigated. Three dimensional seepage flow-structure interactive analysis considering firm water pressure with full stages of construction including the construction of upper bridge, microcement grouting, micro pile and tunnel is performed. The settlement and tilting of the pier of existing bridge violate the design code and the reaction of the bridge are highly increased after grouting. The stress of tunnel bracings such as rockbolt and shotcrete also exceed the limit of the code. The pressure of microcement grouting is confined by bedrock and transmit to the surrounded soil and the upper bridge. Microcement grouting needs mid-high pressure to penetrate through weak fault plane and the pressure greatly influence the safety of the upper structure. It is important to decide and care the grouting pressure to improve weak fault plane directly under the existing structures and the pressure of microcement grouting should be considered in underground analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.274-274
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• 2010

한국은 국제핵융합실험로 (ITER) 사업에 참여하고 있으며, 삼중수소 증식을 시험하기 위한 시험 모듈(TBM, Test Blanket Module)로서 HCML (Helium Cooled Molten Lithium) TBM을 설계, 개발하고 있다. 헬륨 및 액체 리튬을 냉각재와 증식재로 사용하는 개념으로, 구조재로서 Ferritic Martensitic (FM) 강이 사용될 예정이다. 특히, HCML TBM의 일차벽은 중성자 및 플라즈마로부터 입사되는 입자들을 차폐하기 위한 Be 차폐체와 FM강으로 구성되어 있으며, 일차벽 제작법 개발을 위해서는 Be과 FM강 간의 접합과 FM강 간의 접합 방법이 개발되어야 한다. FM강 간의 접합은 기존의 연구를 통해 접합 조건이 이미 도출되었고, 고열부하 시험을 통해 검증 완료한 상태이다. 그러나, Be과 FM강 간의 접합은 현재 개발단계에 있다. 본 논문에서는 고려 중인 구조재와 Be 차폐체 사이의 접합법 개발을 위해, 고온등방가압(HIP, Hot Isostatic Pressing) 조건을 도출하고, 운전조건과 유사 혹은 가혹한 조건에서 고열부하를 인가하여, 그 건전성을 평가하는 일련의 과정을 기술하였다. 본 연구에서는 Be과 FM강 간의 접합법 개발 및 검증을 위해 제작된 $80{\times}80{\times}1$ Be/FM강 mock-up을 국내에서 구축된 고열부하 시험 장비인 KoHLT를 활용하여 수행한 고열부하 시험에 대한 것이다. 본 mock-up은 $80{\times}80{\times}10mm(t)$의 Be tile 3개를 동일 크기에 두께가 각각 25mm와 50 mm인 FM강과 스테인레스강에 접합된 것으로, 고열부하 장비에 설치하여 고열부하 시험을 수행하였다. 냉각수의 온도 및 속도는 25 C, 0.15 kg/sec로 유지되었고, 열부하는 $0.5\;MW/m^2$로 유지하였다. 시험 조건에 대한 예비해석을 통해, 가열시의 온도 및 stress, strain 분포를 얻었고, 이를 통해, cycle to failure 값을 도출하였다. 1000 사이클의 가열 실험을 마친후 초음파를 활용한 접합 계면의 결함확인 및 파괴검사를 통한 접합 건전성을 확인하였다. 3가지 접합법 모두 일부 접합면이 이탈되었으며, 향후 보다 건전한 접합방법 개발이 진행되어야 할 것으로 보인다.

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.393-402
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• 1995

The structural analysis of the reactor coolant system mainly consist of too fields. The one is the static analysis considering the impact of pressure and temperature built up during normal operation. The other is the dynamic analysis to estimate the impact of postulated events such as the seismic loads or postulated branch line pipe breaks event. Since the most important goal of the RCS structural analysis is to prove the safety of the RCS during normal operation or postulated events, a widely proven theory having enough conservatism is adopted. The load occurring on the RCS during normal operation is considered as the basic design loading condition throughout whole plant life time. The most typical characteristic of the RCS during normal operation is the thermal expansion of the RCS caused by reactor coolant with high temperature and pressure. Therefore, the exact estimation on the thermal movement of the RCS is needed to get more clear understanding on the thermal movement behavior of the RCS. In this study, the general structural analysis concept and modeling method to evaluate the thermal movement of the RCS under the normal plant operation condition are presented. To discuss the validation of the suggested analysis, analysis results are compared with the measured data which ore referred from the standardized 1000 MWe PWR plant under construction.