• 대한기계학회논문집A
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• 제26권6호
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• pp.1203-1208
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• 2002

LNG demand has been rapidly increasing in Korea for a variety of reasons including stable supply, non-polluting, and high combustion efficiency characteristics. As a result the construction and expansion of LNG storage facilities have been continuing at a vigorous pace. Korea Gas Corp. (KOGAS) has developed the design technology of the LNG storage tank. One of the most important structural core element of the LNG storage tank is the membrane, made by stainless steel. The membrane to be applied inside of LNG storage tank is provided with corrugations to absorb thermal contraction and expansion caused by LNG temperature. Analytical results have been performed to investigate the strength of the membrane and the reaction farce at the anchor point. Experimental studies are performed to investigate the deformation and strength of the membrane which is designed by Kogas. All experiments are conducted on the basis of RPIS, and we found the results are fully satisfied with the RPIS.

• 한국가스학회지
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• 제7권3호
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• pp.13-17
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• 2003

LNG 저장탱크의 주요 구조인 멤브레인은 LNG 누설을 방지하기 위하여 설계되었다. 멤브레인 유닛은 $-162^{\circ}C$의 액화시킨 LNG의 접촉에 따라 발생하는 가스압, 액압, 그리고 열하중을 지지하도록 설계되므로 멤브레인 구조의 강도를 실험적 방법을 이용하여 측정하는 것이 매우 중요하다. 본 논문에서는 상용 전기저항식 스트레인 게이지와 자체적으로 제작한 기계적 열 변형 측정 장치를 이용한 변형 측정 시스템을 제안하였다.

• 한국기계가공학회지
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• 제16권2호
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• pp.81-87
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• 2017

The pipe connection process using a clamping ring is used for joining small pipes in the refrigerator and air-conditioner industries instead of the brazing process, which induces inevitable thermal deformation in the pipes. However, few studies have been carried out on the process to select optimal parameters in joining pipes, and studies on the relation between the process parameters of the connection and connecting force of the joint have not been conducted. In this study, the connection process of pipes with the clamping ring was modeled using the finite element method (FEM) and analyzed to obtain the contact stress distribution between the pipes with which the connecting force of the joint was estimated. Considering the characteristics of pipe connection, the process was modeled and simulated in a two-dimensional axisymmetric solution domain. With the numerical model, the effect of ring shape on the connection was studied by adding a projection to the end of a ring or changing the length of a ring. The results of the analyses revealed that the contact stress distribution could be predicted with the suggested model. The effect of the ring shape was also presented. The effect of any combination of process parameters could be easily estimated through the related analyses.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1589-1597
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• 1997

The high-velocity impact forging process with eccentric loading condition is analyzed using the explicit time integration finite element method. In order to consider the strain hardening, strain rate hardening and thermal softening effects, which are frequently observed in high-velocity deformation phenomena, the Johnson-Cook constitutive model is applied to model the workpiece. It is assumed that the material response of the dies is elastic in the study. As a result of the eccentric loading simulation, it is found that the increase of the eccentric ratio and the allowable tilting angle cause the decrease of the maximum forging load and the blow efficiency, and it is also found that the forging load and the blow efficiency generated in the high-velocity impact forging process with three-dimensional geometry can be obtained efficiently.

• 한국주조공학회지
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• 제29권5호
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• pp.187-191
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• 2009

Microstructures and shape memory characteristics of $Ti_{50}Ni_{20}Cu_{30}$ alloy strips fabricated by arc melt overflow have been investigated by means of XRD, optical microscopy and DSC. The microstructure of as-cast strips exhibited columnar grains normal to the strip surface. X-ray diffraction analysis showed that one-step martensitic transformation of B2-B19 occurred in the alloy strips. According to the DSC analysis, it was known that the martensitic transformation temperature ($M_s$) of B2 $\rightarrow$ B19 in $Ti_{50}Ni_{20}Cu_{30}$ strip is $57^{\circ}C$. During thermal cyclic deformation with the applied stress of 60 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be $3.7^{\circ}C$ and 1.6%, respectively. The as-cast strip of $Ti_{50}Ni_{20}Cu_{30}$ alloy also showed a superelasticity and its stress hysteresis was as small as 14 MPa. These mechanical properties and shape memory characteristics of the alloy strips were ascribed to B2-B19 transformation and the controlled microstructures produced by rapid solidification of the arc melt overflow process.

• 한국세라믹학회지
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• 제20권1호
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• pp.43-48
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• 1983

The formation of strontium titanate from several molar $SrCO_3$ and $TiO_2$ mixtures was studied in air and $CO_2$ gas Mixtures of $SrCO_3$ and $TiO_2$ were heated in air at 400-$600^{\circ}C$ DTA-TG was used to obtain thermal histories of simples heated in air and $CO_2$ gas. X-ray diffraction analysis was used to determine both the phase composition and the amounts of each phase present. The phase relationship of various compounds $SrTiO_3$, $Sr_2TiO_4$, $Sr_2Ti_3O_7$ and $Sr_4Ti_3O_{10}$ formed by the sintering in each composition was shown by the calibration curves. High temperature X-ray analysis was used to determine both the formation process and deformation process of each products. Small amount of SrTiO3 is formed first at the surface af contact SrTiO3 reacts with $SrCO_3$ to form Sr2TiO4 this is affected on the $CO_2$ pressure.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1453-1458
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• 2009

본 논문은 중공을 가진 판재 두 매를 결합하기 위하여 중공 주위를 따라 기존 레이저 용접법 대신 기계적 프레스 결합법을 적용하는 것에 관한 연구이다. 이를 통해 레이저 용접을 적용했을 때 불가피하게 발생하는 열 변형을 효과적으로 없앨 수 있다. 유한요소해석을 통하여 중공형 판재를 기계적으로 결합시킬 수 있는 금형 설계 방법을 제안하였다. 기계적 결합력을 최대화시키는 데 관련 있는 다섯 가지 설계인자를 선택하여 다꾸치 실험법을 적용한 결과 성형 깊이와 펀치모서리 반경이 가장 크게 영향을 미치는 인자로 나타났다.

• Nuclear Engineering and Technology
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• 제20권2호
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• pp.88-104
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• 1988

이차원의 유한요소법을 이용하여 axisymmetric R-$\theta$system으로 나누어서 정상과 부하추종 운전시에 핵연료 페렛트와 피복관의 열역학적 거동을 분석하기 위해서 FURA전산코드를 개발하였다. 온도분포와 내부압력을 정확히 계산하기 위해서 페렛트와 피복관의 변형과 핵분열의 기체방출을 전체 핵연료봉 길이로 고려하였다. 열역학적 평 형방정식을 얻기 위해서 Galerkin's Technique과 가상일의 원리를 사용하였고 역학적 해석을 위해서 탄성-소성, 크리프뿐만아니라 스엘링, 재배열, 고밀화 현상등을 고려하였다. 기하학적 모델에서는 4-결점 요소라 페레트 길이의 1/2만을 택하였다. 비선형식을 안정하게 해석하기 위해서 음해법을 도입하여 뉴튼-랩손 반복법을 적용하였다 이 코드의 검증은 해석해와 실험데이타로 비교하였다. 핵연료봉의 일반적인 거동은 axisymmetry system으로 계산하였고 균열된 페레트에 접촉하는 피복관의 거동은 R-$\theta$system을 사용하였다. 부하추종에 의한 피복관의 변형시효의 민감도는 출력율, 진동수, 진폭등으로 비교하였다.

• Steel and Composite Structures
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• 제10권3호
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• pp.207-222
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• 2010

Fire incident in buildings is common, so the fire safety design of the framed structure is imperative, especially for the unprotected or partly protected bare steel frames. However, software for structural fire analysis is not widely available. As a result, the performance-based structural fire design is urged on the basis of using user-friendly and conventional nonlinear computer analysis programs so that engineers do not need to acquire new structural analysis software for structural fire analysis and design. The tool is desired to have the capacity of simulating the different fire scenarios and associated detrimental effects efficiently, which includes second-order P-D and P-d effects and material yielding. Also the nonlinear behaviour of large-scale structure becomes complicated when under fire, and thus its simulation relies on an efficient and effective numerical analysis to cope with intricate nonlinear effects due to fire. To this end, the present fire study utilizes a second-order elastic/plastic analysis software NIDA to predict structural behaviour of bare steel framed structures at elevated temperatures. This fire study considers thermal expansion and material degradation due to heating. Degradation of material strength with increasing temperature is included by a set of temperature-stress-strain curves according to BS5950 Part 8 mainly, which implicitly allows for creep deformation. This finite element stiffness formulation of beam-column elements is derived from the fifth-order PEP element which facilitates the computer modeling by one member per element. The Newton-Raphson method is used in the nonlinear solution procedure in order to trace the nonlinear equilibrium path at specified elevated temperatures. Several numerical and experimental verifications of framed structures are presented and compared against solutions in literature. The proposed method permits engineers to adopt the performance-based structural fire analysis and design using typical second-order nonlinear structural analysis software.

• 터널과지하공간
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• 제8권3호
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• pp.184-193
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• 1998

방사성 폐기물의 안전한 처분을 위해서는 암반의 역학적, 열적, 유체 거동 뿐 아니라 암반과 물 사이의 물리 화학적 상호작용을 이해할 필요가 있다. 또한 지질구조, 지하현지응력, 습곡, 열수작용, 마그마의 관입, 판구조 등과 같은 많은 조건을 모델링하고 예측하기 위해서는 암석의 역학적, 수리적 특성을 알아야 한다. 이 연구는 심부 암반에 폐기물 처분과 관련된 암석역학적인 사항들에 대해 연구들에 기초하고 있다. 이 논문은 변하는 온도 상태에서 암반의 역학적 수리적 거동, 암반의 열-수리-역학적 상호작용 해석과 불연속 암석의 거동 특성 등을 포함한다. 역학적 특성은 Interaken 암석역학 시험 시스템으로 측정되었으며, 수리적 특성에는 순간 증압 투수계수 측정 시스템이 사용되었다. 모든 결과에서 암석 특성은 온도 변화에 민감함을 보였다.