• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.552-557
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• 2015

A numerical simulation studies were performed to investigate a manoeuvring characteristics as function of stern hull form with the mathematical model. In order to consider the effect of the stern hull form and obtain the manoeuvring characteristics, a parameter($C_{wa}$) which is aft. water plane area coefficient is modified. Because modifying $C_{wa}$(${\pm}2%$) means that the stern hull form is modified to V-type or U-type, the numerical simulation was performed with this modified $C_{wa}$. A changing trend for the manoeuvring characteristics not only in deep water but also in shallow water such as directional stability, turning and zig-zag was investigated and presented as the results. Present study showed that the manoeuvrability in shallow water largely changed when the draught and water depth ratio(=d/H) become 0.5, and the stern hull form can affect to the manoeuvrability of a vessel navigating in restricted water depth. In addition, it showed that approaching the stern hull to U-type makes the advance and tactical diameter of turning motion large and the overshoot angle of zig-zag motions small. Otherwise, it showed approaching the stern hull form to V-type makes the advance and tactical diameter of turning motion small and the overshoot angle of zig-zag motions large in the present study.

• Journal of the Mineralogical Society of Korea
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• v.32 no.4
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• pp.313-321
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• 2019

Diatomite is a silicic porous sedimentary rock composed of diatom frustules, used for filtration aid, filler, absorbent, abrasive, carrier, insulator, and fertilizer. During the calcination of diatomite to improve physical properties for filtration-aid application, amorphous silica is transformed to cristobalite. X-ray diffraction and scanning electron microscopy studies were carried out for 17 diatomite samples, showing that 16 diatomite samples contain cristobalite in the range of 6~100 %. Concentration of respirable cristobalite in air is regulated as harmful substances, but the residual cristobalite in food is treated as generally safe substance. The determination procedure of cristobalite content in food was established for managing food safety. Calibration curve of cristobalite filtered on silver membrane were obtained by X-ray diffraction. The lower limit of quantification was evaluated as 2.7 mg. The cristobalite was not detected in the analyses of selected food samples using the established procedure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.3
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• pp.316-322
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• 2002

The Orthogonal Frequency Division Multiplexing(OFDM) is a special case of multicarrier transmission, where a single data stream is divided into many subcarriers and transferred in a parallel way. It reduces the necessary bandwidth using the orthogonality between the subcarriers. Therefore it requires the transmission channel which has stable characteristic. When the delay spread of the channel exceed the guard interval, then the orthogonality of the subcarriers cannot maintain and as a result the system performance degrade. In this paper, the XCP-OFDM(OFDM using cross-handed Circular Polarization) system is newly proposed. This system divides the channel in order to eliminate the overlapping of subcarrier's spectrum by using cross-handed circular polarization. Therefore, the proposed XCP-OFDM system can improve the performance without increasing the guard interval. Both theoretical analysis and simulation results are described.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.10-17
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• 2021

In this study, cold-flow test of simulant gel is conducted using a pressure swirl injector to identify spray characteristics according to gellant weight percent. Experiment results show the aircore is developed locally at the nozzle and expanded to the entire swirl chamber as the supply pressure increases. The aircore formation of simulant gel showed no significant difference compared to Newtonian fluid. The spray pattern was classified into four distinct shapes where relationship between the breakup regimes and dimensionless numbers were investigated. In the future, additional study is necessary to understand the aircore formation mechanism, stability and spray characteristics at different configuration of the swirl chamber shape.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.378-381
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• 2009

A rotating stall, an instable phenomenon of compressor, brings about reducing the pressure rise, the efficiency of compressor and a mechanical demage. In order to improve instability and extend operating range, it was performed that a stability enhancement experiment applying air injection method at the 4-stage low-speed axial compressor. The coanda nozzle was used to inject air in axial direction at rotor tip and 8 injectors were set up at regular interval at the upstream of 1st stage rotor. At 80% speed, injectors were worked before rotating stall happened. As injecting the 5.4% air of mode inception flow rate, the stability of compressor operation enhanced about 4%.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.197-203
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• 2012

In this paper, study the substantial issues which occurs upon free flight environment by performing separation assurance under multiple conflict(over 3 Aircraft), recovery en route under the terms of time constrains and fixed way point after the conflict avoidance, correlations between conflict detection distance and separation assurance by utilizing Autonomous flight algorithm. Result of this experiment demonstrates that the extension of detection distance is advantageous to solution of separation assurance and enhancing of flight efficiency, choose to maneuver by applying time constrain terms and fixed way point according to the situation of conflict prediction in case of recovery maneuver after the conflict avoidance. And separation assurance can be solved by applying 2 degrees or more of bank angle. When choosing the optimal bank angle could be drastically improved flight efficiency.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.197-197
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• 2017

본 연구에서는 입자성 오염물질을 다량 함유하고 있는 초기강우 유출수를 처리하기 위한 수처리 시설로 고속복합응집장치를 개발하였다. 고속응집복합장치의 요소기술은 마이크로 버블, 급속교반장치(인라인믹서), 전기촉매를 이용한 부상촉진장치, 볼텍스 흐름 등으로 구성되며, 기술 원리는 응집제에 의해 오염물질을 응결, 응집, 부상시켜 스컴을 제거하는 일반 응집 원리와 유사하다. 본 기술의 특징은 교반, 혼화조, 응집제를 1개의 조에 컴팩트하게 구성하여 체류시간을 10분 이내로 단축하였고, 볼텍스(voltex) 흐름을 이용한 선회류와 루버홀 형태의 스크린을 적용하여 응집효과를 극대화하였으며, 플럭에 의한 막힘이 없이 스크리닝이 이루어질 수 있도록 하였다. 또한, 부상촉진장치(전기유도)를 이용해 응집 플럭의 부상효과를 상승시켰고, 감속기와 일체화된 내통스크린이 선회류와 반대 방향으로 회전하면서 볼텍스 흐름의 가속효과에 의한 스크린 폐색 방지 및 응집부상 효율을 향상시킬 수 있도록 설계하였다. 부상슬러지는 별도의 플럭 제거 설비 없이 스크린 내통 회전에 이용되는 감속기에 부착된 스컴 제거기에 의해 동시 제거가 가능하며, 응집부상 처리수는 장치 가장 바깥 외곽에 충진된 필터층에서 최종 여과되어 방류되도록 구성함으로서 모든 처리공정이 단일 장치 내에서 이루어지도록 구성하였다. 본 고속복합응집장치는 전체 규격 ￠ $1000{\times}2,000mmH$의 시제품이 제작되어 현재 시흥소재 매화저수지에서 성능평가를 실시하고 있다.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.7
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• pp.491-498
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• 2009

We studied to develop high-efficiency removal system of odor and VOCs(Volatile Organic Compounds) from environmental infrastructure facilities and oil refineries, painting facilities and so on. It can replace RTO and RCO. We tried an removal experiment for VOCs (toluene, xylene, benzene, MEK(methyl ethyl ketone), ethanol, formalin etc. and odor compounds (hydrogen sulfide, etc.). In process, as pre-treatment we used the scrubber with vortex flow (Multi-scrone) to remove the hydrophilic VOCs and as post-treatment, used fibrous bio-filter to remove the hydrophobic VOCs. This hybrid system remove with high efficiency both the hydrophilic VOCs and hydrophobic VOCs. And we tried to make this system to be compact. In experiment using Multi-scrone, contact time is 2~3 seconds and absorption scrubbing water is diaphragm-type electrolysis water. hydrophilic VOCs like ethanol and relatively hydrophilic odor compounds like hydrogen sulfide is excellent, these substances has been removed almost completely, respectively 95~99%, 93~97%. And for MEK, formalin also Showed a high removal efficiency, respectively 78~90%, 72~85%. But in experiment using Multi-scrone, the hydrophobic VOCs like BTX showed a low removal efficiency, respectively 16~22%, 12~18%, 8~16%. In hydrophobic VOCs, toluene removal experiment using fibrous bio-filter, early efficiency was low but after 10days, adaptation period showed high efficiency 85~95%. but in the mixed phase, toluene and MEK efficiency reduced 5~10%. this show microorganism treat first MEK easy to remove. The removal efficiency for MEK using the fibrous biofilter was stable, 80~92%. This hybrid system is also high economical efficiency for RTO. This system reduce more than 50% the cost of equipment and maintenance. As a result, we expect this technology is in the limelight as high efficiency treatment of VOCs in mid-low price.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.07a
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• pp.21-23
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• 2015

해상물류는 대형 선박일수록 톤당 수송비가 절감되므로 선박의 대형화 트렌드는 불가피한 반면 기존 항구의 항로와 부두의 확장은 현실적으로 어려울 뿐만 아니라 출입항 선박의 수가 증가하여 항로와 항내 조종구역이 상대적으로 좁아지는 효과가 빠르게 진행되고 있다. 선박의 항내조종 안전을 위한 연구가 필요한 바 선박조종의 현장경험을 정리한 비교지침을 가지는 것이 합리적이다. 항행중인 전후 선박간의 합리적인 안전거리, 부두 설계기준 초과선박의 접안시 운동량의 안전범위와 감소방안, 적정예선과 예선의 효과적인 사용방안, 부두앞 조종박지에서 선회권의 축소방안, 극저속에서의 조종성 확보방안, 안전한 자연감속의 범위와 급감속 방안, 비상시의 안전대책을 정리하고 다른 현장조선의 실무에 비교지침이 되고자 함이 본 연구의 목적이다.

• The Transactions of the Korea Information Processing Society
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• v.5 no.12
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• pp.3221-3229
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• 1998

본 논문은 광역 이동컴퓨팅 환경에서 계층적인 네트워크 확장에 적합한 새로운 계층적 위치수정(Location Update)과 경로설정(Routing) 방안을 제안한다. 제안된 방안은 통신을 가장 빈번하게 요구하는 고객영역(Patron Area)의 경계에 있는 일단의 방향선회(Redirection)에이전트들로 위치수정을 제한하기 때문에 위치수정의 수를 줄이게 된다. 계층적 방향선회 개념의 적용으로 고객영역 내에서 호스트 이동에 대한 위치수정 부담이 없어진다. 가벼워진 위치수정에도 불구하고 이동호스트의 홈(Home) 네트워크의 홈 에이전트를 거치지 않고 대부분의 통신이 이루어지기 때문에 최적에 가까운 경로설정을 제공한다. 제안된 방안은 위치수정 및 경로설정의 효율성 관점에서 기존의 계층 및 비 계층 위치수정 방안과 비교 분석하였다.