• Journal of Aerospace System Engineering
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• v.14 no.3
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• pp.24-31
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• 2020

A study on the H2O2 based low toxic hypergolic propellant was conducted. The fuel candidates were chosen as a mixture of Amine solvent and reactive additive. The analytical performance was calculated via the NASA CEA code and 96% Isp of the NTO/UDMH was confirmed. The ignition delay measurement with drop test was performed and all candidates showed less than 10 ms in the best performance cases. Based on these results, the feasibility of high response H2O2 based low toxic hypergolic propellant was confirmed.

• Journal of Advanced Navigation Technology
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• v.25 no.5
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• pp.390-396
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• 2021

In this research, design and fabrication of marine repeater capable to extend communication coverage in monitoring system of fishing gear automatic identification, which is one of implementation method of the real-name electric fishing gear system declared by Ministry of Oceans and Fisheries in 2016, is reported. The proposed marine repeater is fabricated in a form of RF repeater with interference cancellation system (ICS), which can cancel the oscillation due to feedback signal between service antenna and link antenna. In design process, we secure the isolation of 30 dB between service antenna and link antenna. It is confirmed that when the level of feedback signal into repeater input be lower of 15 dB than repeater gain, error vector magnitude due to oscillation can be lower than the performance criterion of 6%, from the test verification. It is expected that the service coverage will be extended by applying the developed marine ICS RF repeater into marine IoT network including monitoring system of fishing gear automatic identification.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.151-160
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• 2019

EPC companies to continue operating overseas, it is increasingly becoming apparent that risk is no longer something to be avoided but a subject to be managed. During the bidding stage, the requirements, specifications and project line items within the bid package must be studied in details to analyze the various risk factors in order to avoid cost overruns. However, reviewing vast quantities of bidding documents is time consuming and labor intensive and is not an easy task and this is where automated information technology can help. For this study, I have constructed an ITB analysis model based on Watson AI that can analyze and apply vast amount of documents more effectively in a short time. Configuration of the Watson Explorer AI architecture for AI-based ITB risk management model research, the selection of learning procedures and analysis subjects, and the performance evaluation criteria were defined, and a test bed was constructed to conduct a pilot research. Consequently, I verified the effectiveness of the analytical time reduction and the quality of its results and VOC operations by professionals.

• Journal of Advanced Navigation Technology
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• v.23 no.1
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• pp.61-68
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• 2019

Underwater wireless light communication system is quite necessary to retrieve recorded data from underwater devices or the black box without taking back it body. In this paper, a research on the light sensor technology in underwater wireless light communication under turbid sea was studied. A noise source under turbid sea for light communication was analysed, and a sensor system for light sensing using the reference light signal to remove the noises and to improve the output swing power wasstudied. Also, an underwater communication system was manufactured to validate the good performance of the development system, and using the system, the good performance of the developed system was validated through the light communication test in the tank containing the turbid sea water was presented.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.65-72
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• 2021

700 W class laboratory model Hall thruster, which can be used for the orbit control or station keeping of small satellites, was developed. The size of the discharge channel was determined using a scaling law, and the magnetic field was designed to be symmetric with respect to the midline of the discharge channel and to be maximized outside the discharge channel. Base pressure of a vacuum chamber was maintained below 2.0×10^-5 Torr during experiments, and the thrust was measured by a thrust stand. The anode flow rate and coil current were varied with the fixed anode voltage at 300 V. Under the operation condition at 2.36 mg/s anode flow rate and 2.4 A coil current, performance was optimized as 38 mN thrust, 1,540 s total specific impulse, and 50 % anode efficiency at 620 W anode power.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.335-342
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• 2022

In this study, self-healing hybrid capsules were prepared by mixing self-healing solid capsules and self-healing microcapsules using inorganic materials as core materials. Self-healing hybrid capsules were mixed with 3 % according to the composition ratio of 3:7, 5:5, and 7:3 based on the mass of the cement to prepare a self-healing cement composite material. The healing properties of crack self-healing hybrid capsules were evaluated through hydrostatic water permeability test and surface crack monitoring. It was found that the self-healing hybrid capsules prepared by mixing the composition ratio of the self-healing solid capsules and the self-healing microcapsules at 7:3 has a great effect on improving the crack self-healing performance.

• Journal of the Korean Geosynthetics Society
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• v.21 no.3
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• pp.29-39
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• 2022

The engineering characteristics of synthetic polymer-silica sol, which has the effect of reducing leakage, was evaluate and compared with typical grouting material, the water glass-based SGR injection material in this study. The result of the laboratory tests on strength and durability about the synthetic polymer-silica sol showed more than twice as high as LW-based injection materials in uniaxial compressive strength, significantly lower values in shrinkage rate and permeability. The result of pH was less than 8.5 (the drinking water quality standard). As a result of the leaching test, the Na₂O elution amount of the synthetic polymer-silica sol was measured to be 3 to 4 times smaller than that of the water glass grout. These results be assumed that the synthetic polymer-silica sol has better durability and permeability than those of the typical water glass-based grout.

• Journal of IKEEE
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• v.26 no.4
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• pp.537-544
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• 2022

This paper analyzes the occurrence and cause of bond wires fusing used in the manufacture of pulsed high power amplifiers. Recently GaN HEMT has been spotlight in the fields of electronic warfare, radar, base station and satellite communication. In order to produce the maximum output power, which is the main performance of the high-power amplifier, optimal impedance matching is required. And the material, diameter and number of bond wires must be determined in consideration of not only the rated current but also the heat generated by the transient current. In particular, it was confirmed that compound semiconductor with a wide energy band gap such as GaN trigger fusing of the bond wire due to an increase in thermal resistance when the design efficiency is low or the heat dissipation is insufficient. This data has been simulated for exothermic conditions, and it is expected to be used as a reference for applications using GaN devices as verified through IR microscope.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6A
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• pp.809-817
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• 2008

Recently, the external prestressing method is being much frequently used in strengthening reinforced concrete structures because of it's excellent load resistance and serviceability increases comparing to other strengthening methods. However, it is true that the research on fatigue performance of concrete structures strengthened by the external prestressing using FRP tendons is rare. Therefore, the purpose of this study is to evaluate the safety and feasibility of the external prestressing method by analyzing the characteristics of the reinforced concrete beam strengthening using FRP tendons under repeated loads. Test variables adopted in this experimental study are the types of external prestressing material (steel or FRP tendon) and the repeated load ranges. The repeated load range have the minimum 50% of yield load of reinforced concrete beam and the maximum 70-85%. The test beams are loaded by 4 point loadings with 3 Hz sine wave. From this experimental study, it is confirmed that the reinforced concrete beams strengthened using FRP tendons have sufficient safety against fatigue, especially in FRP tendon itself, tendon at deviators and tendon at anchorages.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.501-508
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• 2023

Addressing urban noise problems, this study develops eco-friendly, inorganic sound-absorbing panels, overcoming the limitations of traditional PMMA and cement-based panels. These conventional panels pose safety risks due to flammability and environmental concerns due to carbon emissions. Utilizing industrial waste, the research comprises two phases: initial tests for physical and performance characteristics (fluidity, density, compressive strength, sound absorption) and subsequent development of optimized panel mixtures. This approach aims to replace existing panels with sustainable, effective alternatives, significantly contributing to safer, environmentally responsible urban infrastructure. The findings of this study have implications for the sound panel market, offering novel solutions for noise control while aligning with environmental and safety standards.