• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.5
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• pp.1-11
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• 2004

In order to recognize thermal efficiency and power improvement in case that diesel cycle is turned into diesel-atkinson cycle, the fuel-air diesel-atkinson cycle considered gas exchange process is analyzed non-dimensionally and thermodynamically. As a result, in case of diesel-atkinson cycle, as expansion ratio is increased, thermal efficiency and mean effective pressure is increased and it has maximum value at Rec=1. When diesel cycle is turned into diesel-atkinson cycle by late intake valve closing timing, thermal efficiency and power is decreased because of the decline of effective compression ratio and intake airflow, but it could be compensated by increase of compression ratio or super-charged. In case compression ratio is compensated, Rec appears 1 around 100$^{\circ}$ ABDC, and it is expected that thermal efficiency is enhanced by 14.3% compared with conventional diesel cycle. In case compression ratio and intake airflow are compensated simultaneously, super-charged pressure is demanded 2.06bar at Rec=1 and it is more efficient when only compression ratio is compensated in the view point of thermal efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.13-21
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• 2000

The advantages of the SITVC (Secondary Injection for Thrust Vector Control) technique over mechanical thrust vectoring systems include a reduction in both the nozzle weight and complexity due to the elimination of the mechanical actuators that are used in conventional vectoring. The optimal operating conditions of SITVC were investigated using in-house developed compressible flow analysis codes. Numerical experiments were used to examine the impact of the thrust vector direction with a variety of injection positions, mass flow rates, and injection angles on the two-dimensional expansion cone of a supersonic nozzle. The computational results showed that the optimal position of the secondary injection, with the maximum deviation angle and side thrust, was where the oblique shock generated by the secondary injection reached the end of the nozzle exit.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.765-770
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• 2020

The turbochargers used widely in diesel and gasoline engines are effective devices to reduce fuel consumption and emissions. In this study, the isentropic turbine efficiency of the steady flow in a twin-scroll turbocharger for the passenger vehicle gasoline engine was analyzed. The cold gas test bench was designed and made. The pressure and temperature of the inlet and exit of the turbine were measured at 60,000, 70,000, 90,000, and 100,000rpm under the steady-state flow. The isentropic turbine efficiency was calculated. The efficiency was the range of 0.53 to 0.57. The BSR and expansion ratio were changed from 0.71 to 0.84 and from 1.24 to 1.72, respectively. The isentropic turbine efficiency decreased with increasing BSR and expansion ratio. The operation of only scroll A or B was compared with that of the twin-scroll turbine. The isentropic efficiency of using only scroll B was higher than those of only scroll A at 60,000rpm. The isentropic efficiency of using only scroll A was higher than those of only scroll B at 100,000rpm. Therefore, the twin-scroll turbine used in this study is operating effectively in the wide speed range.

• Journal of the Korean GEO-environmental Society
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• v.19 no.2
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• pp.5-12
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• 2018

Underground cavities could induce road subsidence, which have been frequently observed in urban areas. Therefore, adequate backfilling materials and the restoring methods of the cavities are required to prevent the road subsidence. The objective of this paper is to evaluate the suitability of backfilling methods using foaming lightweight grouting materials considering the flow values, unit weights, and air contents at slurry and expanded states, and unconfined compressive strengths. The grouting materials consist of water, cement, and foaming agent whose proportions of water, cement, and foaming agent are 25: 25: 1.0 and 25: 25: 1.2. The flow values of the two materials are greater than 200 mm, and their unconfined compressive strengths at 28 days age are smaller than 1.3 MPa. From the results, the two proportions of materials are expected to be effectively used as a backfilling material. However, the material components should be carefully mixed because poor mix of these materials could induce non-homogeneous distribution of air bubbles. The unexpectedly non-homogeneous distribution of air bubbles may induce significant cracks or additional cavities.

• Geotechnical Engineering
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• v.10 no.3
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• pp.55-78
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• 1994

Decomposed granite soil is a Granitic Gneiss, and it is a c Korean peninsula. It is known a changed significantly when it is aim of this study is to evaluat utility of the constitutive laws. Firstly, triaxial tests were pe sites prepared by the laborato scrutinized the characteristics results were analysed and the p evaluated. Finally, the predicted Even though the origins of slight difference in the angle of pression line( A) : both soils show In the effective mean normal uniqueness of the Normal Compr The relationships between the the decomposed granite soil tier OCR is larger than 2, the stress stress(MDS) or. even thous moved below the theoretical Ros was found to coincide with the (NC) soils, the pore pressure parameter, A,, increased up to 1.3. This phenomenon might be mainly due to the effect of the particle crushing during shearing, When the OCR value approaches 7, the negative pore pressure is developed in undrained tests and the dilatancy is observed in drained tests. The predicted and the observed behavior of drained tests showed relatively good fitting with the Cam-Clay model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.515-527
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• 2014

This study conducted experiment for understanding engineering characteristics of domestic sands by examining standard sand and sand from Yokji Island and Nakdong River in terms of confining pressure, $K_0$, over consolidation and relative density factors through triaxial compression test. The test showed that deviator stress by strain positively changed as confining pressure and relative density grow while $K_0$ and over consolidation factors do not directly correlated with it. Angle of internal friction decreases as confining pressure increases which strengthens contact force between particles, and declines as relative density drops, whereas $K_0$ and over consolidation factors hardly affect the results. When it comes to volumetric strain, volume expansion decreases as confining pressure increase due to crushability and rearrangement of particles while $K_0$ and over consolidation shows same movement unconditionally, and relative density appears compressed as it grows at the beginning however it expands as axial strain increases. Modulus of elasticity ($E_{sec}$) by strain has tendency into convergence resulting in initial secant modulus of elasticity ($E_{ini}$) > secant modulus of elasticity($E_{sec}$) > tangent modulus of elasticity ($E_{tan}$). On the other hand, it grows as confining pressure and relative density increase while indicating similar modulus of elasticity ($E_{sec}$) regarding on $K_0$ and over consolidation. Slope of critical line (M) tended to decrease as confining pressure increases, follow same line according to $K_0$, confining pressure and relative density, and increase as relative density grows.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.463-469
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• 2016

In this paper, compressive strength and water permeability performance for two types of crack self-healing materials such as SH-PO-0 composed of mineral admixtures(expansive agent, swelling material and crystal growth agent) and SH-PO-(5, 15, 30) blended with SH-PO-0 and phosphate additive(PO) dissolving easily calcium ion, were evaluated. The test results show that the water flow of SH-PO-0 decreased steeply at the early age although compressive strength decreased about 9% at 28 days compared with OPC. The higher PO replacement ratio is, the lower compressive strength and more improved water permeability performance is, and thus, based on such results, adequate PO replacement ratio is 15%. It is also found that the self-healing performance of SH-PO-15 was quite improved at the early ages and however, the performance of SH-PO-15 is similar to one of SH-PO-0 at long-term ages, and 28 days compressive strength of SH-PO-15 decreased about 8% compared with SH-PO-0. In addition, it is confirmed from the analysis of SEM-EDS that calcium ions of SH-PO-15 were crystallized more than those of SH-PO-0.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.1
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• pp.19-29
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• 2002

The purpose of this study was to compare the polymerization shrinkage and the compressive strength of composite and compomer cured with two different light sources ; conventional halogen-light curing unit and recently-developed plasma arc curing unit. The 'strain gauge method' was used for determination of polymerization shrinkage and the compressive strength was measured by universal testing machine. The results of the present study can be summarized as follows: 1. Filling materials in polyethylene molds showed the initial expansion in the early phase of polymerization. This was followed by the rapid contraction in volume during the first 60 seconds and gradually diminished as curing process continued. 2. The polymerization shrinkage in tooth samples was generally lower than in the mold samples. 3. The generally lower amount of linear polymerization shrinkage was observed in compomer and plasma arc curing unit group when compared to composite and conventional curing unit. 4. The higher compressive strength values was found in composite groups regardless curing methods. The results of this study strongly support the application of plasma arc system and fluoride-containing compomer in the field of clinical pediatric dentistry claiming its effectiveness in curing the esthetic dental materials and the anticariogenic capacity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.3
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• pp.15-29
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• 2001

For the pertinent use of NMT method, both characteristics of joints (JRC, JCS and ${\phi}_r$) and characteristics of rock mass (Q-Value) must be investigated carefully. The main objective of the study presented is to investigate how sensitive the predicted behaviour of an underground excavation is to various realistic assumptions about some input parameter for the jointed rock mass. Joint pattern in the tunnel is predicted by statistical approach (chi-square test). In this paper, sensitivity studies involving in joint characteristics were carried out. The parametric studies involving change in Barton-Bandis joint model have shown that JCS is relatively insensitive to JRC and ${\phi}_r$. An increase in JRC value may not, according to the Barton-Bandis model, necessarily lead to a decrease in displacement. The importance of dilation in predicting the behaviour of a rock mass around an excavation is emphasized from a comparison of the Barton-Bandis joint behaviour model with the Mohr-Coulomb model. The Barton-Bandis model predicted higher stress, which allow for the build-up of stress caused by dilatant behaviour.

• Polymer(Korea)
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• v.29 no.6
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• pp.605-612
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• 2005

This study investigates the isothermal crystallization behaviors of polypropylene-polyethylene-(1-butene) terpolymer and the adiabatically expanded polyolefin structured foams. For this purpose, butane gas was used as a physical blowing agent. Avrami equation has been used to interpret theoretically the experimental results obtained by either DSC or polarized optical microscope. It is believed that elongation induced crystallization occurring during the adiabatic expansion process has resulted in an increase in crystallization rate, eventually leading to a faster growth rate of spherulites and an increase in the nucleation density. An analysis of the foam by SEM images showed that the structure of foam is uniform (below diameter 30 $\mu$m closed cell) In addition, the thermal conductivity and the compressive strength of the polyolefin structured foams was measured. The thermal conductivity of foamed resin with excellent insulation characteristics is reduced compared with unfoamed resin. The compressive strength is decreased with increase in the expansion ratio.