• Geomechanics and Engineering
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• 제2권4호
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• pp.303-319
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• 2010

The effect of grain crushing on the deformation of sand in 1D compression and 1D creep at high stresses was investigated theoretically and experimentally. An approach was proposed to formulate the process of grain crushing in sand in accordance with the laws of fracture mechanics and energy conservation. With this approach, the relation between the void ratio and the amount of grains crushed in 1D compression was derived. Laboratory test data were used to verify this derived relation. In addition, it was observed that there are similarities in evolution of grain size distribution in 1D compression and 1D creep tests. This implies that the changes in microstructure in sand under 1D compression and 1D creep are comparable.

• 한국수소및신에너지학회논문집
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• 제12권3호
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• pp.169-176
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• 2001

The purpose of study is to obtain low-emission and high-efficiency in LPG engine with hydrogen enrichment. The test engine was named heavy-duty variable compression ratio single cylinder engine (VCSCE). The fuel supply system provides LPG/hydrogen mixtures based on same heating value. Various sensors such as crank shaft position sensor (CPS) and hall sensor supply spark timing data to ignition controller. Displacement of VCSCE is $1858.2cm^3$. VCSCE was runned 1400rpm with compression ratio 8. Spark timing was set MBT without knocking. Relative air-fuel ratio(${\lambda}$) of this work was varied between 0.76 and 1.5. As a result, i) Maximum thermal efficiency occurred at ${\lambda}$ value 1.0. It was shown that thermal efficiency was increased approximately 5% with hydrogen enrichment at same ${\lambda}$ value. ii) Engine-out carbon monoxide (CO) emissions were decreased at a great rate under LPG/hydrogen mixture fuelling. iii) Total hydrocarbon (THC) emission was much exhausted in rich zone, same as CO. But THC was exhausted a little bit more in lean zone. iv) Finally, engine-out oxides of nitrogen (NOx) was increased with ${\lambda}$ value 1.0 zone at a greater rate with hydrogen enrichment due to high adiabatic flame temperature.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.962-967
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• 2003

CFD data compression method based on supercompact multiwavelets is presented. High data compression can be achieved when taking advantage of the compact nature of multiwavelets. Thresholding technique is also a matter of primary concern in determining pressure ratio. In this paper, we apply thresholding for multiwavelets that considers the coefficient vector as a whole rather than thresholding individual elements. Various thresholding methods are described briefly. CFD data compression suggests that the multivariate thresholding method is suitable for supercompact multiwavelets.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.91-94
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• 2005

Experimental research was conducted to investigate the behavior of RC circular columns confined by high-strength ties. Large scale columns with concrete strength 34.1 and 65.3 MPa were tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio, tie arrangement, tie yield strength, and concrete compressive strength. The results indicate that high-strength concrete columns can be confined to achieve inelastic deformations usually predicted for normal-strength concrete columns. This can be done by providing increasing volumetric ratio and tie yield strength.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1294-1302
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• 1997

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.

• 한국정보처리학회논문지
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• 제3권5호
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• pp.1294-1306
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• 1996

본 논문에서는 한글 문서에 대해 높은 압축률을 얻기 위해 한글의 형태적 특징인 조사와 어말어미의 출현 빈도를 이용한 효율적인 한글 문서 압축 기법들을 제안하였으며 제안된 기법들의 성능 분석을 위하여 기존의 압축 기법들과 압축률을 비교 분석하였다. 한글 문서에서 조사와 어말어미가 반복적으로 출현한다는 형태적인 특성으로부터 높은 압축률을 얻기 위해 출현 빈도가 상대적으로 높은 64개의 조사 및 어말어미를 선정 하여 고정 사전을 구성하고, 이를 이용하여 한글 문서를 압축하도록 기존의 LZ77기법과 LZW기법을 수정하여 각각 HLZ77기법과 HLZW기법을 제안하였다. 또한, 본 연구에서는 수정 제안된 HLZ77기법과 HLZW기법의 성능을 분석하기 위하여 4가지 기법을 실 제 재현하여 여러 형태의 한글 문서를 대상으로 압축률을 비교하였다. 성능 결과로 부터 일반적인 한글 문서에 대해 한글의 형태적인 특성을 이용하는 HLZ77기법과 HLZW 기법이 각각 LZ77기법과 LZW기법 보다 우수한 압축률을 나타냄을 알 수 있었다.

• 한국수소및신에너지학회논문집
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• 제26권1호
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• pp.28-34
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• 2015

HCCI (Homogeneous Charged Compression Ignition) hydrogen engine has relatively narrower operation range caused by backfire occurrence due to the rapid pressure rising by using higher compression ratio and significant reaction velocity. In this study, to grasp of backfire process and characteristic in the HCCI research hydrogen engine, in-cylinder pressure, intake pressure and backfire limit range are analyzed with compression ratio and intake valve open timing, experimentally. As the result, it is observed that knock is occurred just before backfire occurrence in HCCI hydrogen engine but not spark igntion type, this phenomenon is always the same for the above variables. Also backfire limit range are expanded up to 50% for the more retarding intake valve open timing in this operating conditions.

• International Journal of Automotive Technology
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• 제7권6호
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• pp.675-680
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• 2006

In the direct injected gasoline engine, atomized spray is desired to achieve efficient mixture formation needed to good engine performance because the injection process leaves little time for the evaporation of fuels. Therefore, substantial understanding of global spray structure and quantitative characteristics of spray are decisive technology to optimize combustion system of a GDI engine. The combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition(SCCI) engine according to intake temperature and compression ratio was examined. The fuel was injected directly to the cylinder under the high temperature condition resulting from heating the intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions, which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The mixture stratification and the fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.

• Steel and Composite Structures
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• 제12권1호
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• pp.31-51
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• 2012

Local buckling can be ignored for hot-rolled ordinary strength steel equal angle compression members, because the width-to-thickness ratios of the leg don't exceed the limit value. With the development of steel structures, Q420 high strength steel angles with the nominal yield strength of 420 MPa have begun to be widely used in China. Because of the high strength, the limit value of the width-to-thickness ratio becomes smaller than that of ordinary steel strength, which causes that the width-to-thickness ratios of some hot-rolled steel angle sections exceed the limit value. Consequently, local buckling must be considered for 420 MPa steel equal angles under axial compression. The existing research on the local buckling of high strength steel members under axial compression is briefly summarized, and it shows that there is lack of study on the local buckling of high strength steel equal angles under axial compression. Aiming at the local buckling of high strength steel angles, this paper conducts an axial compression experiment of 420MPa high strength steel equal angles, including 15 stub columns. The test results are compared with the corresponding design methods in ANSI/AISC 360-05 and Eurocode 3. Then a finite element model is developed to analyze the local buckling behavior of high strength steel equal angles under axial compression, and validated by the test results. Following the validation, a finite element parametric study is conducted to study the influences of a range of parameters, and the analysis results are compared with the design strengths by ANSI/AISC 360-05 and Eurocode 3.

• 한국컴퓨터정보학회논문지
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• 제4권2호
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• pp.141-146
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• 1999

본 논문은 움직임 정보를 이용하여 기준 프레임 영상과 상관관계가 적은 프레임 영상에서는 화질을 보장하고, 기준 프레임 영상과 상관관계가 많은 프레임 영상에서는 전체 동영상의 비트율을 보장하는 픽쳐셋 필터를 제안하였다. 실험 결과, 제안한 동영상 부호화 방법은 기존의 전영역 탐색 블럭 정합 알고리즘에 비하여, 화질은 9dB이 항상되고, 압축률은 15배가 증가되었으며. 부호화시간은 70%나 단축되었다. 그리고, 차영상 알고리즘에 비하여, 화질은 25dB이 떨어졌으나, 압축률은 42배가 증가하였으며, 부호화시간은 0.9%가 단축되므로서 좋은 성능을 나타냄을 확인하였다.