• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1995.11a
• /
• pp.87-96
• /
• 1995

인공위성의 궤도진입에 사용되는 액체추진제 로켓엔진의 개발에서 분사기 설계를 적절히 수정, 보완 할 목적으로 수행된 핵심부품별 유동해석의 내용이 기술되었다. 단일 격자계를 구성하기 어려운 복잡한 형상의 분사기 유동장에 대한 격자계 구성을 용이하게 하고, 3차원의 점성 유동해석을 컴퓨터 기억 용량에 제한없이 수행하기 위한 다중블럭 격자기법이 사용되었다. 분사기의 내부유동은 3차원 비압축성 Navier-Stokes 방정식으로 pseudocompressibility 방법을 이용하여 수치모사되었다. 정상상태의 해는 근사 인자분해에 의한 ADI 기법으로 계산되고, 공간미분항에 대해 nonstaggered 격자계에서 2차 중앙차분을 사용하며 수치해의 안정성을 위해 인공점성항을 추가하였다. 난류계산을 위해 Baldwin- Lomax의 대수적 난류모델에 다수의 벽면효과를 고려하였다. 해석결과는 분사기의 성능에 영향을 미칠 수 있는 유동조건에 따라 분석되었다.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.3
• /
• pp.337-344
• /
• 2006

Characteristics of flocculent aggregates have great effects on membrane fouling. Floc from kaolin particles gave higher permeate throughputs than floc from natural particles at the same conditions. Therefore, the objectives of this study are to thoroughly analyze characteristics of flocculated aggregates and to investigate effects of flocculated aggregates on membrane fouling. Image analysis, specific rake resistance and cake compressibility were used for characterization of flocs. Different flocculent aggregates formed with natural and kaolin particles were employed in this study. The fractal dimensions from the image analysis were $D_2=1.79{\pm}0.07$ for floc from natural particles and $D_2=1.84{\pm}0.06$ for floc from kaolin particles. The lower fractal dimension($D_2$) of floc from natural particles indicated that the aggregates were more porous and less compact than floe from kaolin particles. In addition, both the specific cake resistances and compressible degrees of flocs from natural particles showed greater values than those of flocs from kaolin particles. The results implied that the porous and loose flocs from natural particles were more easily compressed on membrane surface than the dense and compact flocs from kaolin particles. The compressed flocs yielded the great hydraulic resistances by hindering the water flow through the cake layer.

• Tunnel and Underground Space
• /
• v.28 no.2
• /
• pp.156-169
• /
• 2018

The relationship between the mechanical and textural properties of sedimentary rocks has been studied for decades. However, inconsistencies in the results have arisen from both the inhomogeneity of natural rocks and the difficulties encountered in controlling just one textural factor of interest in each experiment. This work produced artificial sedimentary rocks to enable control of every independent parameter at all times. Their homogeneity lowered the deviation of the results, and thus they produced clearer correlations than for natural rocks. The samples were made by mixing bassanite powder with water and silica sand, which produced rocks consisting of sand and gypsum cement. The effect of grain content and size on mechanical properties such as uniaxial compressive strength, Young's modulus, and seismic velocity was estimated. Increasing grain content lowered the compressive strength but raised Young's modulus and seismic velocity. Overall, grain size did not linearly affect the mechanical properties of the samples, but affected them in some way. In future, these results can be compared and integrated with similar experiments using different cement or grain types. This should allow comparison of the effects of the rock constituents themselves and their interactions, with applicability to all kinds of sedimentary rocks.

• Journal of the Korean GEO-environmental Society
• /
• v.21 no.11
• /
• pp.11-20
• /
• 2020

For water barrier and reinforcing grout in soft ground, the verification of durability was conducted over the initial and long-term ages under various curing conditions. The grout was made of water glass system, fast-hardening mineral (FHM) system, and acrylic polymer system. There were three types of curing conditions that were tab water curing, artificial seawater curing, and atmospheric curing. And the various tests were performed for each sample by age, uniaxial compressive strength, length change, and weight change. As artificial seawater, MgCl₂ and MgSO₄ aqueous solutions were prepared and used, respectively. As the test results, the fast-hardening mineral system and acrylic polymer system were cured stably without significant change in durability in tap water and artificial sea water, whereas water glass system showed a very rapid drop in durability under artificial sea water conditions compared to tap water. In atmospheric curing conditions, durability is lowered compared to water curing in all cases, and in particular, the weight loss in the FHM system and water glass system is about 62% and 60%, respectively, resulting in a significant decrease in durability.

• Korean Journal of Agricultural Science
• /
• v.18 no.1
• /
• pp.33-40
• /
• 1991

This study was performed to obtain the basic data applied to use of synthetic lightweight aggregate concrete affected by alkali silica reaction. The results obtained were summarized as follows; 1. The compressive strength of type A concrete was increased with increase of curing age. At the curing age 28 days, the highest compressive strength was showed at type Band C concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete. 2. The flexural strength of type A concrete was increased with increase of curing age. At the curing age 14 days, the highest flexural strength was showed at type Band C concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete. 3. The correlation between compressive and flexural strength of the sample was shown highly significant only at type A concrete. 4. It was shown that the water absorptions of the type Band C were 7.0-7.8 times higher than the type A concrete. It was significantly higher at the early stage of immersed time at all sample. 5. The correlation between compressive strength and water absorption of the sample was significant only at the type A concrete.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.23-29
• /
• 2003

In this paper, effects of the acidification of ground and the chemical additive materials-ferric oxide, calcium chloride and calcium sulphate on the compressibility characteristics of the marine clay treated with quick lime were investigated. The rapid inflection point method was carried out. Results showed that the compression index of the untreated marine clay increased as the pH of pore water decreased. Also, the preconsolidation pressure, the coefficient of consolidation and the coefficient of permeability of the untreated marine clay decreased with pH of pore water. In the case of the marine clay treated with the quick lime-calcium chloride, the compression index decreased and the coefficient of consolidation and the coefficient of permeability increased. Specially, the preconsolidation pressure of sample treated with the quick lime-ferric oxide was higher than that of another samples.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.425-428
• /
• 2008

To use lightweight aggregate concrete with the structural material, it was need to evaluate property of mechanic and drying shrinkage and creep of the lightweight aggregate concrete, but these weren't. So the purpose of this study which it sees follows the mechanical property of the eco lightweight aggregate concrete according to the water binder ration in the high strength concrete. Eco lightweight aggregate was made with clay and crushed rock in this study. To make experiment, water binder ratio was divided 35% and 39%. And the fresh concrete properties were that slump flow was 500${\pm}$50mm, air contents was 2.0${\pm}$1.0%. It evaluated the hold a drying shrinkage and the creep the effect, it analyzed quality and reliability of the eco lightweight aggregate concrete.

• Korean Journal of Agricultural Science
• /
• v.24 no.2
• /
• pp.218-225
• /
• 1997

This study was performed to evaluate the physical and mechanical properties of surlightweight polymer concrete using synthetic lightweight aggregate. The following conclusions were drawn; 1. Unit weight was in the range of $810~970kgf/m^3$, the unit weights of those concrete were decreased 58~65% than that of the normal cement concrete. 2. The highest strength was achieved by $P_1$, it was increased 112% by compressive strength, 378% by bending strength and 290% by tensile strength than that of the normal cement concrete, respectively. 3. Ultrasonic pulse velocity was in the range of 2,206~2,595m/s, which was low showed compared to that of the normal cement concrete. 4. Durability of surlightweight polymer concrete was superior to that of the normal cement concrete. 5. Compressive, tensile and bending strength were largely showed with the increase of unit weight. But, ultrasonic pulse velocity was low showed with the increase of unit weight.

• Journal of Bio-Environment Control
• /
• v.9 no.1
• /
• pp.47-59
• /
• 2000

In order to investigate the physical and chemical properties of artificial culture media, the specimens were substituted with 5~20％ clay, 10~30％(w) quick lime, 5~l5％(w) burnt plaster and 10％(w) sawdust. Fly ash-clay bodies were sintered at 1,050~1,20$0^{\circ}C$ and then their properties were determined. It was found that 90FA10JC(fly ash ＋clay(90：10, ％(w)) specimen sintered at 1,15$0^{\circ}C$ for 10 min. had good physical and chemical properties. When this composition was supplement with 10％(w) sawdust, bulk density water absorption, apparent porosity, compressive strength and pH after 240 hrs curing time were 1.14, 54.4％, 39.5％, 54 kgf.cm$^{-2}$ and 7.1 respectively. The physical properties of fly ash-quick lime-burnt plaster system specimens were superior to FAJC systems. However, this composition we not suitable as a artificial culture media because of its high pH. In this study, it was shown that 90FA10JC10SD(90FA10JC ＋10％(w) sawdust) system exhibited the best physical properties.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.287-298
• /
• 2003

The feasibility of using neural networks to model the complex relationship between piezocone measurements and the undrained shear strength of clays has been investigated. A three layered back propagation neural network model was developed based on actual undrained shear strengths, which were obtained from the isotrpoically and anisotrpoically consolidated triaxial compression test(CIUC and CAUC), and piezocone measurements compiled from various locations around the world. It was validated by comparing model predictions with measured values about new piezocone data, which were not previously employed during development of model. Performance of the neural network model was compared with conventional empirical method, direct correlation method, and theoretical method. It was found that the neural network model is not only capable of inferring a complex relationship between piezocone measurements and the undrained shear strength of clays but also gives a more precise and reliable undrained shear strength than theoretical and empirical approaches. Furthermore, neural network model has a possibility to be a generalized relationship between piezocone measurements and undrained shear strength over the various places and countries, while the present empirical correlations present the site specific relationship.