• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.2
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• pp.61-67
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• 2001

Development of a barrier system for floating debris at river is introduced. The system is to prevent pollution of coastal water caused by marine debris which originates from land. The system consists of harrier boom, mooring system and boom winder. The harrier boom, which is self-inflatable with circular band spring, guides floating debris to a collecting conveyer system. Design parameters of the harrier system were reviewed and its design criteria were established. Based on the established design criteria, a pilot harrier system was built and tested at Tanchon branch of the Han river. It is proved that the suggested system is very efficient to collect floating debris at river.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.4
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• pp.404-408
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• 2003

This paper discusses the physical properties of permeable high quality concrete using blast furnace slag or steel slag as a part of aggregate. In the case of steel slag, aging treatment was adopted to prevent the volume expansion. With high range water reducing agent, the concrete using slag aggregate showed compressive strength up to 24MPa at the age of 28 days and the water permeability of the concrete was over the level of 0.1 m/s in this experiment. Also, there was no expansion problem in the concrete substituted with aged slag as a part of aggregate.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.41-47
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• 2011

Turbopump, which is a part of 75 ton open cycle liquid rocket engine has a super sonic impulse turbine. This paper investigated the leading edge thickness effect on the turbine performance experimently. Two rotors were tested with the different leading edge thickness. The ratios (rotor thickness to Pitch) are 1.9 and 1.4 times to 30 ton turbine rotor. As a result, a rotor with 1.4 times ratio had a 1.5% higher efficiency gain than a rotor with 1.9 times ratio. The pressure ratio with the maximum efficiency on the same rotational speed was increased to the full expansion ratio of nozzle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.3
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• pp.107-115
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• 2018

A design combining the use of a compressor and expander was introduced in order to improve the cycle performance of a $CO_2$ automotive air conditioning system. Both the compressor and expander used were of rotary vane type and were designed to share a common shaft in a housing. Numerical simulation was carried out to evaluate the merit of the combined unit. In a typical automotive air conditioning operating conditions, the COP of the system was improved by 8.7% by the application of the combined unit. The compressor input was reduced by 5.2% through use of the expander output. In addition, about 3.06% increase in the cooling capacity was obtained through isentropic expansion in the expander. Our study noted that, as the pressure difference between the gas cooler and the evaporator becomes larger, the COP of the system improved increases unless the mass flow rate in the expander exceeds that in the compressor.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.397-400
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• 2008

MgO powder-mixed concrete, expanded at the lower temperature around $850{\sim}1000$ degree celcius, might have long-term expansibility, which could remunerate for the contraction of concrete with delayed expansion, and through the process, the crack resistance of mass concrete might be improved. Currently used expandable concrete additive has three different types : CSA, CaO and MgO. In this study, therefore, such tests as carbonation, chloride diffusivity, freezing-thawing resistance and sulfate resistance after 56 days' curing were implemented and compared the results with the concrete with no MgO mixed to evaluate the durability of 5% MgO-mixed concrete after longer period of time. The degree of hydration for the MgO-mixed cement paste was analyzed after 1 day, 3 days, 7 days, 28 days, and 56 days using SEM, XRD, DSC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.101-110
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• 2014

Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.34-40
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• 2014

High-performance fiber-reinforced cement composite (HPFRCC) shows very high autogenous shrinkage, because it contains a low water-to-binder ratio (W/B) of 0.2 and high fineness admixture without coarse aggregate. Thus, it needs a method to decrease the cracking potential. Accordingly, in this study, to effectively reduce the shrinkage of HPFRCC, a total of five different ratios of SRA (1% and 2%), EA (5% and 7.5%), and a combination of SRA and EA (1% and 7.5%) were considered. According to the test results of ring-test, a combination of SRA and EA (1% and 7.5%) showed best performance regarding restrained shrinkage behavior without significant deterioration of compressive and tensile strengths. This was also verified by performing modified drying shrinkage crack test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.8
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• pp.3366-3373
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• 2011

In this study, performance characteristics of a water source heat pump system using $CO_2$ as a refrigerant are investigated experimentally. Cooling and heating capacities and COP of the system are analyzed for various system performance variables such as refrigerant charge, expansion valve opening, compressor frequency and internal heat exchanger. Results show that optimum amount of refrigerant charge and expansion valve opening exists at maximum point of COP curve, and cooling capacity increases but COP decreases with the increase of compressor frequency. When the internal heat exchanger is installed, cooling capacity increases about 4.0% whereas heating capacity decreases about 0.89% compared to the case without internal heat exchanger.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.94-100
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• 2002

This paper is concerned with the development, and performance test of LIPCA (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuators. LIPCA is composed of top fiber composite layers with a high modulus and low CTE (Coefficient of Thermal Expansion), a middle PZT cermaic wafer, and base layers with a high modulus and high CTE. The performance of each actuator was evaluated using an actuator test system consisting of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. The simply supported condition actuator was excited by the power supplier with 1.0Hz cycle and up to $100\sim400V_{pp}$. The displacement at the center point of actuator was measured with non-contact laser displacement measuring system, It has been shown that the LIPCA-C2 can 34% decrease in mass and 13% increase in displacement compared to THUNDER.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.18-25
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• 2001

The results of systematic numerical experiments of secondary gas injection thrust vector control are presented. The effects of secondary injection system such as injection location and nozzle divergent cone angle onto the overall performance parameters such as thrust ratio, specific impulse ratio and axial thrust augmentation, are investigated. Complex nozzle exhaust flows induced by the secondary jet penetration is numerically analyzed by solving unsteady three-dimensional Reynolds-averaged Navier-Stokes equations with Baldwin-Lomax turbulence model for closure. Numerical simulations compared with the experiments of secondary air injection into the rocket nozzle of $9.6^{\cire}$ divergent half angle showed good agreement. The results obtained in terms of overall performance parameters showed that locating the secondary injection orifice further downstream of primary nozzle ensures the prevention of occurrence of reflected shock wave, therefore is suitable for efficient and stable thrust vectoring over a wide range of use.