• 한국수소및신에너지학회논문집
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• 제18권4호
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• pp.374-381
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• 2007

In order to verify the feasibility of expansion of back-fire limit equivalence ratio in the hydrogen-fueled engine with external mixture, the characteristics of performance and combustion are experimentally analyzed with change of intake/exhaust valve timings under the fixed valve overlap period of $0^{\circ}$ CA(non-valve overlap period). These characteristics are also tested for the change of exhaust valve closing timing while intake valve opening timing is fixed to clear the main cause of back-fire occurrence. As the results, the less valve overlap period center is retarded, the more back-fire limit equivalence ratio increases and back-fire does not occurred after TDC. In addition, it was shown that the control of back-fire is dependent on intake valve opening timing than valve overlap period.

• 한국분무공학회지
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• 제14권4호
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• pp.171-177
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• 2009

This study proposes a new stratified charge system for low emission and ultra lean burn. In order to examine combustion characteristics of the new system, sparkplug with a hole at positive pole and a common CNG injector for injecting fuel were used in this study as injector-type spark plug. The new stratified charge system injects fuel of extremely small quantities and ignites mixture around sparkplug gap. Also, the system was fitted in a visualized constant volume chamber. Then, for analysis of the combustion characteristics, we examined combustion pressure, lean inflammable limit, and visualized combustion flame according to equivalence ratio by comparison with homogeneous charge (HC) method and the new stratified charge (SC) method. As results of this study, in the case of using this system, the propagation speed of initial flame was increased and total combustion period was reduced in the ultra lean burn in the same equivalence ratio. These phenomena occurred clearly under the conditions of lean equivalence ratio. Furthermore, the lean inflammable limit of mixture was extended by using the injector-type spark plug.

• Geomechanics and Engineering
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• 제37권4호
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• pp.371-382
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• 2024

Measurement or prediction of compression index (C_c) of soils is essential for assessment of total and differential settlement of structures. It is a well-known fact that this parameter is controlled by several index identifiers of soil including initial void ratio, Atterberg limits, overconsolidation ratio, specific gravity, etc. Many studies in the past proposed relationships for prediction of C_c based on different index properties. Therefore, this study aims to present a comparison of previously proposed equations for estimation of C_c. Data from literature was compiled, and a total of 90 and 623 test results on remolded and undisturbed specimens were used to question the validity of previously proposed equations. Nevertheless, the modeling ability of 7 and 12 equations for estimation of C_c of remolded and undisturbed soils were questioned by use of compiled data. Moreover, new empirical relationships based on initial void ratio and toughness limit for prediction of C_c was proposed by use of nonlinear multivariable regression and evolutionary based regression analyses. The results are promising-the performances of models established are quite acceptable, which are verified by statistical analyses.

• 한국안전학회지
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• 제27권5호
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• pp.42-48
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• 2012

Peel-tension fatigue experiments were conducted for investigating on fatigue strength of mechanical press joints of SPCC steel sheet used in the field of the automobile industry. In addition, finite element method analysis on the peel-tension specimen was conducted using HyperMesh and ABAQUS softwares. The cold rolled mild steel was used to join the T-shaped peel-tension specimen with a button diameter of 5.4 mm and a punch diameter of 8.3 mm. The fatigue limit load amplitude was found to be 112.4 N at the number of cycles 106, indicating that the ratio of fatigue limit load to static peel-tension strength was about 8%. This value suggests that the mechanical press joint is highly vulnerable to peel-tension load rather than to tensile-shear load, considering that the ratio of fatigue limit load to static tensile-shear strength was about 43%. Fatigue failure mode was found to be interface-failure mode.

• 대한예방의학회:학술대회논문집
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• 대한예방의학회 1994년도 교수 연수회(역학)
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• pp.164-168
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• 1994

Single serologic tests may occasionally influence clinicians in making diagnoses. The antistreptolysin O (ASO) test is a frequently used tool for detecting recent Streptococcus pyogenes infection and is helpful in the diagnosis of diseases like rheumatic fever. Using data from a 1989 prospective study of 600 healthy male military recruits, in which 43% experienced S. pyogenes upper respiratory tract infection (2-dilution rise in ASO), this report compared two methods of interpreting a single ASO titer. Using the 'upper limit of normal' (80 percentile) method, recruits with an ASO titer of greater than 400 showed evidence of recent S. pyogenes infection. This method had a sensitivity and specificity of only 65.9 and 81.9% respectively. In contrast to the 'yes-no'. dichotomy of the 'upper limit of normal' method. the likelihood ratio method statistics were ASO value specific, more consistent with clinical judgment, and better emphasized the caution clinicians must use in interpreting a single ASO test.

• 한국지진공학회논문집
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• 제28권4호
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• pp.223-231
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• 2024

For the OPR1000, a standard power plant in Korea, an analytical model of the containment building considering voids and deterioration was built with multilayer shell elements. Voids were placed in the vulnerable parts of the analysis model, and the deterioration effects of concrete and rebar were reflected in the material model. To check the impact of voids and deterioration on the seismic performance of the containment building, iterative push-over analysis was performed on four cases of the analytical model with and without voids and deterioration. It was found that the effect of voids with a volume ratio of 0.6% on the seismic performance of the containment building was insignificant. The effect of strength reduction and cross-sectional area loss of reinforcement due to deterioration and the impact of strength increase of concrete due to long-term hardening offset each other, resulting in a slight increase in the lateral resistance of the containment building. To determine the limit state that adequately represents the seismic performance of the containment building considering voids and deterioration, the Ogaki shear strength equation, ASCE 43-05 low shear wall allowable lateral displacement ratio, and JEAC 4601 shear strain limit were compared and examined with the analytically derived failure point (ultimate point) in this study.

• 한국철도학회논문집
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• 제15권2호
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• pp.154-161
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• 2012

철도교량 동적 설계 및 동적 안전성을 해석적으로 평가하기 위해서는 교량의 감쇠비를 산정하는 것이 매우 중요하다. 본 연구에서는 국내 고속 및 일반철도에서 일반적으로 사용되고 있는 소수주형강합성교, PSC Box, Steel Box, PSC, IPC, Precom, Preflex에 대하여 실내 모형실험 및 운행 중 현장계측을 하였다. 이러한 고속 및 일반철도의 대표적 교량형식에 대한 실내외 시험을 통해 대수감소율을 적용하여 감쇠비를 분석하였다. 따라서 철도교량의 감쇠비는 하중크기, 가진주파수, 진폭에 영향을 받지 않는 것으로 분석되었다. 또한, 기존 철도설계기준에 제시된 감쇠비 하한치와 비교하여 PSC구조 및 강합성구조 철도교량의 경우 감쇠비 하한값을 1.0%로 적용하는 것이 합리적이라 판단되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1830-1835
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• 2007

In the present work, the effect of strength mismatch on plastic limit loads is quantified for strength-mismatched plates with constant-depth surface cracks under tension, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate and crack geometries are systematically varied, in addition to the weld width. An important finding is that a parameter related to the weld width-to-ligament ratio is proposed, based on which limit loads can be uniquely quantified. The proposed limit load solutions is a valuable input to estimate nonlinear fracture mechanics parameters based on the reference stress approach.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.466-472
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• 1988

Pneumatic transportation systems are operated most economically, if the transportation velocity is somewhat greater than the limit velocity. Therefore it is very important to find out this limit velocity. That is well known for coarse and fine particles, but not yet for long ribbon type material. In this study a formula for the mass ratio of transported material to air in limit load point is derived for ribbon type material from the pneumatic transportation theory and the model theory. A relationship for estimating the limit velocity is also found out through experiments. The possibility of the generalization of this formula, which is obtained from a given pneumatic transportation system, should be estimated through further systematic studies.

• 한국추진공학회지
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• 제15권4호
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• pp.11-17
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• 2011

가스터빈 연소기의 화염 특성을 알기 위하여 분할 연소기 시험을 수행하였다. 점화시험은 여러 가지 연소기 유입 공기속도와 공기과잉율에 따라 토치 점화장치를 이용하여 수행되었다. 또한, 연료를 충분히 공급한 상태에서 점화를 수행한 후 점차 연료량을 감소시켜가며 희박연소한계를 측정하였다. 실험결과, 공기과잉율 6에서 안정한 점화를 보였고 이 값은 연소기 공기 유입속도에 따라 점점 증가함을 보였다. 최소 실화한계는 연소기 공기 유입속도 40 m/s 에서 약 4였고, 이 값은 연소기 공기유입속도에 따라 약 10까지 증가함을 보였다. 화염특성 시험결과, 화염안정성은 연소기 유입속도가 커질수록 희박화염소실한계는 넓어짐을 알 수 있었고, 연소기 유입 공기속도가 약 65 m/s 에서 가장 큰 화염소실 한계를 보였다.