• Advanced Composite Materials
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• 제18권3호
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• pp.233-249
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• 2009

Safe installation and operation of high-pressure composite cylinders for hydrogen storage are of primary concern. It is unavoidable for the cylinders to experience temperature variation and significant thermal input during service. The maximum failure pressure that the cylinder can sustain is affected due to the dependence of composite material properties on temperature and complexity of cylinder design. Most of the analysis reported for high-pressure composite cylinders is based on simplifying assumptions and does not account for complexities like thermo-mechanical behavior and temperature dependent material properties. In the present work, a comprehensive finite element simulation tool for the design of hydrogen storage cylinder system is developed. The structural response of the cylinder is analyzed using laminated shell theory accounting for transverse shear deformation and geometric nonlinearity. A composite failure model is used to evaluate the failure pressure under various thermo-mechanical loadings. A back-propagation neural network (NNk) model is developed to predict the maximum failure pressure using the analysis results. The failure pressures predicted from NNk model are compared with those from test cases. The developed NNk model is capable of predicting the failure pressure for any given loading condition.

• Tribology and Lubricants
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• 제28권5호
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• pp.233-239
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• 2012

The engine of a large ship operates under wet conditions using a fuel such as bunker C oil, which includes sulfur and many impurities. A cylinder liner made of cast iron is very susceptible to damage such as scuffing on the surface. This scuffing can reliably be attributed to the destruction of the oil film and the corrosion wear caused by water and sulfur included in the fuel, along with abrasion impurities and poor lubricants. In this study, a reciprocating friction and wear test was carried out with a cast iron specimen, which was used to simulate an engine cylinder in a corrosive environment. Base-oil and stirred oil containing distilled water, NaCl solution, and dilute sulfuric acid were used as lubricants. The friction surface was analyzed using a microscope and EDAX, and the friction coefficient was measured using a load-cell under each experimental condition. We then attempted to investigate the damage to the cylinder liner using the results.

• 한국안광학회지
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• 제20권3호
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• pp.349-354
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• 2015

목적: 크로스실린더를 이용한 난시정밀검사에서 망막 상의 최소착란원 위치가 난시교정값에 미치는 영향을 알아보고자 하였다. 방법: 평균나이 $22.24{\pm}2.48$세의 62명(115안)을 대상으로 검사하였다. 방사선시표를 이용한 난시검사 후 최대교정시력이 얻어진 구면굴절력(MPMVA) 상태에서 크로스실린더를 이용한 정밀검사를 실시하였다. 그런 다음 S+0.75 D, S+0.50 D, S+0.25 D, S-0.25 D, S-0.50 D, 그리고 S-0.75 D의 렌즈를 각각 더한 상태(최소착락원의 위치이동)에서 동일한 정밀검사를 실시하고, 얻어진 검사값을 MPMVA 상태에서 얻어진 검사값과 비교하였다. 결과: MPMVA 상태의 검사값과 비교하여 더해준 (+)구면렌즈와 (-)구면렌즈가 증가할수록 축 변화량은 증가하였다. 동일한 검사상태에서 난시굴절력이 높을수록 축 변화량은 감소하였다(p<0.05). MPMVA 상태의 검사값과 비교하여 더해준 (+)구면렌즈가 증가할수록 난시굴절력은 낮게 나타났고(p<0.05), (-)구면렌즈가 증가할수록 높게 나타났다. (+)구면렌즈를 더해준 경우, 동일한 검사상태에서 난시굴절력이 높을수록 검사값의 차이는 더 크게 나타났다. 결론: 올바른 난시교정값을 얻기 위해서 크로스실린더를 이용한 난시정밀검사 전 최소착락원 위치를 정확히 조정하여야 한다.

• 한국지반공학회논문집
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• 제31권3호
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• pp.5-16
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• 2015

본 연구에서는 토사 또는 암반 틈새에 주입하는 그라우팅(시멘트 페이스트)에 섬유를 혼합할 경우 발생하는 인장강도의 특성을 연구하였다. 이와 같이 시멘트로 고결된 토목재료의 인장강도 평가에는 간접적인 방법으로 인장강도를 평가하는 쪼갬인장시험을 주로 사용하고 있다. 하지만, 본 연구에서는 강섬유 또는 PVA 섬유를 중량비로 0%, 0.5%, 또는 1% 혼합한 시멘트 페이스트 내에 유압 실린더를 내장한 직경 15cm, 높이 30cm의 공시체를 제작한 다음 공시체 내부에서 직접 인장력을 가하는 직접인장시험법을 개발하였다. 또한 동일한 재료로 직경 5cm, 높이 10cm 공시체를 만들어 쪼갬인장시험을 실시하여 인장강도 시험방법에 따른 시멘트 페이스트의 인장강도를 비교, 평가하였다. 각각의 공시체는 대기 중에서 7일 또는 28일 양생한 다음 인장시험을 실시하였다. 시험방법에 따른 인장강도는 내장형 실린더를 이용한 직접인장시험법이 쪼갬인장시험법 보다 96%-290% 정도 높은 값을 보였다. 한편 두 종류의 인장시험법에 대한 3차원 유한요소해석을 실시하였으며, 실험 결과와 유사하게 내장형 실린더 인장시험법이 3배 정도 높은 인장강도를 보였다. 섬유 혼합량이 1%까지 증가함에 따라 인장강도는 시험방법에 관계없이 7일 양생한 공시체는 119%-190%, 28일 양생한 공시체는 23%-131%까지 증가하였으며, 양생일수가 7일에서 28일로 증가함에 따라 인장강도는 대부분 감소하는 경향을 보였다. 대부분의 경우 강섬유가 포함된 경우보다 PVA 섬유가 포함된 경우에 약 14%-38% 정도 높은 인장강도를 보였다.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2429-2435
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• 2002

The aim of this paper is to investigate the problem of strip down method, which is usually used to evaluate the engine friction level. The validity of strip down method was investigated by theoretical analysis of friction in crank and piston assembly. The friction of cylinder and piston assembly was analyzed under the various test conditions. The measured cylinder pressure was used as boundary conditions of friction torque and loss calculation. The friction loss of crank and piston assembly was influenced by test conditions that resulted from the variation of load condition. From the results, we have known that the strip down method could be possible to distort the friction loss of engine moving components.

• 한국안전학회지
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• 제23권6호
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• pp.122-130
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• 2008

The cracking behavior of prestressed concrete members is important for the rational evaluation of PCC pipes. However, the test data on the cracking behavior of PCC pipes are very limited. The purpose of the present study is to investigate the cracking behavior of PCC pipes under different settlement conditions. In this paper, experimental test on the full scale model of PCC pipe was conducted and observed in order to study cracking load in PCC pipes. Based test and FEM analysis results, this paper also presents the cracking load prediction in PCC pipe. Based on the numerical analysis results performed in this research, the cracking behaviors of PCC pipe with the variation of the settlement conditions were evaluated.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.146-149
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• 1998

In this study, the chloride ion penetration test and the compressive strength test should be done simultaneously on the standard cylinder specimen. And from analyzing the data from those tests, a strength estimation equation with high credibility is to be developed.

• 대한기계학회논문집A
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• 제26권3호
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• pp.479-486
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• 2002

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature structures of liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The thermal ratchet deformation at the reactor baffle cylinder of the liquid metal reactor can occur due to the moving temperature distribution along the axial direction as the sodium free surface moves up and down under the cyclic heat-up and cool-down transients. The ratchet deformation was measured with the laser displacement sensor and LVDTs after cooling the structural specimen which is heated up to 55$0^{\circ}C$ with steep temperature gradients along the axial direction. The temperature distribution of the test cylinder along the axial direction was measured with 28 channels of thermocouples and was used for the ratchet analysis. The thermal ratchet deformation was analyzed with the constitutive equation of nonlinear combined hardening model which was implemented as ABAQUS user subroutine and the analysis results were compared with those of the test. Thermal ratchet load was applied 9 times and the residual displacement after 9 cycles of thermal load was measured to be 1.79mm. The ratcheting deformation shapes obtained by the analysis with the combined hardening model were in reasonable agreement with those of the structural tests.

• 대한기계학회논문집B
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• 제38권10호
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• pp.859-864
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• 2014

본 연구는 상류 쪽에 설치된 물체의 직경 변화에 따른 후류에 존재하는 하류 쪽 물체의 영향에 대해 조사한 실험적 연구이다. 풍동의 측정부에서 상류 쪽에는 알파벳 V자 형태의 물체를 삽입하고, 하류 쪽에는 로드셀을 장착한 원기둥을 설치하여 상류 쪽 물체의 직경 변화에 따라 후류의 유속분포가 어떻게 변화하는지를 조사하였다. 그리고 후류에 존재하는 원기둥의 위치를 변화시키면서 원기둥의 변동양력과 카르만 와류 방출 주파수를 조사하므로서 다음과 같은 결론을 얻었다. i) 후류의 유속은 주유속보다 작다. ii) 상류 쪽 물체의 직경이 하류 쪽 물체의 직경보다 클 때 록크-인 현상이 일어난다. iii) 후류에 있는 원기둥의 변동양력이 최대가 되는 위치는 상류 쪽 물체의 직경의 변화에 따라 위치도 함께 변해야 한다.

• 동력기계공학회지
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• 제6권1호
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• pp.20-26
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• 2002

The purpose of this study is preventing the stick, scuffing, scratch between piston and cylinder in advance, and obtaining data for duration test in actual engine operation. The temperature gradient in cylinder bore according to coolant temperature were measured using $1.5{\ell}$ class diesel engine. 20 thermocouples were installed 2mm deep inside from cylinder wall near top ring of piston in cylinder block, at which points major thermal loads exist. It is suggested as proper measurement points for engine design by industrial engineers. Under full load and $70^{\circ}$, $80^{\circ}C$ and $90^{\circ}C$ coolant temperature conditions, the temperature in cylinder block and engine oil increased gradually according to the increase of coolant temperature, the siamese side temperature of top dead center is $142^{\circ}C$ in peripheral distribution, that is about $20^{\circ}C$ higher than that at thrust, anti-thrust, and rear side temperature, respectively. The maximum pressure of combustion gas in $70^{\circ}C$ coolant temperature is about 2 bar lower than those of $80^{\circ}C$ and $90^{\circ}C$ coolant temperature. The engine torque in $80^{\circ}C$, $90^{\circ}C$ coolant temperature condition is about 4.9Nm higher than that of $70^{\circ}C$ coolant temperature.