• 한국기계가공학회지
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• 제14권2호
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• pp.81-86
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• 2015

This study investigated electromagnetic interference (EMI) shielding effectiveness (SE) of hybrid conductive fabrics. The coaxial transmission line method was used to measure the EMI Shielding effectiveness of the conductive fabrics. We designed and constructed a measuring system, consisting of a network analyzer and a device that serves as a sample holder and at the same time as a transmission medium of incident electromagnetic waves. The measurements of SE were carried out in a frequency range from 100 MHz to 2 GHz. The results of the EMI shielding experiments showed that the maximum electromagnetic shielding effectiveness (EMSE) values of sandwich type C/A/C (carbon fiber sheet/aluminum foil tape/carbon fiber sheet) and C/Ni/C (carbon fiber sheet/magnetic shielding foil/carbon fiber sheet) samples were 55 dB and 113 dB, respectively, at a frequency of 1.9 GHz.

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.609-613
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• 2015

The onset of instability induced by impulsive spin-down of the rigid-body flow placed in the gap between two coaxial cylinders is analyzed by using the energy method. In the present stability analysis the growth rate of the kinetic energy of the base state and also that of disturbances are taken into consideration. In the present system the primary flow is a transient, laminar one. But for the Reynolds number equal or larger than a certain one, i.e. $Re{\geq}Re_G$ secondary motion sets in, starting at a certain time. For $Re{\geq}Re_G$ the dimensionless critical time to mark the onset of vortex instabilities, ${\tau}_c$, is here presented as a function of the Reynolds number Re and the radius ratio ${\eta}$. For the wide gap case of small ${\eta}$, the transient instability is possible in the range of $Re_G{\leq}Re{\leq}Re_S$. It is found that the predicted ${\tau}_c$-value is much smaller than experimental detection time of first observable secondary motion. It seems evident that small disturbances initiated at ${\tau}_c$ require some growth period until they are detected experimentally.

• 대한기계학회논문집A
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• 제21권9호
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• pp.1392-1399
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• 1997

In order to determine the Mode I stress intensity factor ($K_1$) experimentally by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a ferromagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effect of the magnetic flux on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. To remove the magnetic flux, a new measuring system was made by utilizing the characteristic of coaxial transmission line. The change in potential drop in the case without magnetic flux in the air was caused by the change in electromagnetic properties near the crack tip due to magnetization. The relationship between the change in potential drop and the change in $K_I$ was linealized by demagnetization and was found to be independent of the crack length.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.116-119
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• 2004

The existing monitoring and control systems of utility-pipe conduit (power tunnel, cable tunnel etc) have established communication lines using optical fiber, leaky coaxial cable (LCX), and several kinds of control cable. Due to the properties of the used media, the cost of equipment is considerably high and the maintenance of the system is difficult. Also, the term of carrying out is long so that the extension of the system is in difficulty. Now it is desirable to adopt Power Line Communication (hereinafter, PLC) technology in the monitoring and control systems and use the existing low-voltage power-line for lamplight as communication line. This will lead the reduction of the construction cost and the easy maintenance of the system. In this paper, we research the characteristics of PLC in conduit, design and manufacture the field test system, and analyze the performance of the system by field test. Then, we introduce the reliable monitoring and control system of utility-pipe conduit using PLC.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.167-170
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• 2005

We performed field test and analyzed results of field test in variable HFC(Hybrid Fiber Coaxial) network environments. And we investigated whether the test results is satisfied in DOCSIS(Data-over-Cable Service Interface Specification) 2.0 and OpenCable standard. Also, we propose HFC improvement problem for HFC Network quality as BcN(Broadband convergence Network) access network. We tested three sample areas. The sample areas represent various type of SO(System Operator) in korea. The field test was to measure signal level about digital channels. In results of multiple digital channels, in case of "Equalizer ON", we could be obtained very good test results. The results of field test were shown in satisfying recommended values in DOCSIS 2.0 and OpenCable. So, we could have confidence through field test that BcN will be possible to be adapted to environment of korea HFC network.

• 한국수소및신에너지학회논문집
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• 제31권1호
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• pp.96-104
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• 2020

A model combustor has been designed and fabricated for studying the combustion characteristics of oxygen (O₂)/hydrogen (H₂) flames under supercritical conditions. The combustor is designed to allow combustion experiments up to 60 bar, the supercritical pressure condition of O₂ and H₂. Injectors can be replaced to study various types of flames and the combustion chamber is designed to visualize flames by installing optical windows. Through the preliminary tests, including a high-pressure (up to 60 bar) test using air and combustion tests for coaxial jet flames of liquid oxygen (LO₂)/gaseous hydrogen (GH₂) at elevated pressure, the reliability of the combustor has been demonstrated.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1754-1762
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• 2016

Finite difference analysis were applied to study the principle operation of monopole antenna for moisture determination in oil palm fruit at 2 GHz. The electromagnetic field interact with oil palm fruit on the interface between the antenna and oil palm fruit and cause a reflection. The reflection measurement is based on mismatch impedance or dielectric properties between two media. Reflection coefficient is used to quantify the level of reflection. The monopole antenna was made of RG405/U semi-rigid coaxial cable with an inner and outer diameter of 0.45 mm and 1.50 mm, respectively with 2.23 mm length of protruding conductor over 5.66 cm length of monopole antenna. This monopole antenna for moisture detection was compared with induced EMF method in terms of reflection coefficient at 2 GHz. The results show that the complex reflection coefficient measured using monopole antenna provides significant results to predict moisture content in oil palm fruit.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.858-864
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• 2017

This study aims to restrain free conducting wire-type particles which are commonly and dangerously existing within DC gas-insulated transmission lines. A realistic platform of a coaxial cylindrical electrode was established by using a high-speed camera and a partial discharge (PD) monitor to observe the motion, PD, and breakdown of these particles. The probabilities of standing or bouncing, which can be affected by the length of the particles, were also quantitatively examined. The corona images of the particles were recorded, and particle-triggered PD signals were monitored and extracted. Breakdown images were also obtained. The air-gap breakdown with the particles was subjected to mechanism analysis on the basis of stream theory. Results reveal that the lifting voltage of the wire particles is almost irrelevant to their length but is proportional to the square root of their radius. Short particles correspond to high bouncing probability. The intensity and frequency of PD and the micro-discharge gap increase as the length of the particles increases. The breakdown voltage decreases as the length of the particles decreases.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.139-143
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• 2005

액체로켓엔진의 성능 및 냉각특성 연구를 위한 연소시험장치가 개발되었다. 본 시험장치는 액체산소와 케로신을 추진제로 사용하는 추력 1 KN 이하의 액체로켓엔진의 성능 및 냉각 특성연구가 가능하며, 일련의 연소시험을 통해 정상적인 작동을 확인할 수 있다. 또한 케로신 중심 분사 방식의 동축형 인젝터를 사용하는 엔진에 대해 물 냉각 연소시험을 수행하고 연소시험과 CEC86을 이용한 연소해석 결과를 통해 액체로켓엔진 성능 인자로서, 특성속도, 비추력 관점에서, 추진제 혼합비 및 연소실 압력의 영향을 분석한다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권6호
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• pp.271-277
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• 2003

It is important to control layer current distributions of coaxial multi-layer HTS cables, because a homogeneous layer current distribution decreases AC loss and can supply the largest operational current. We have extended the theory that treat the operational current more than the critical current by considering V-I nonlinear characteristics of HTS tapes including flux flow resistance and contacting resistance between the cable and terminals. It is important to investigate the current distribution under the condition of operational current more than the critical current of cable, because the cable has experiences of fault current. In order to verify the extended theory, we have fabricated a two layers cable with the same twisting layer pitch. It was observed that almost all the operational current less than the critical current flowed on the outer layer because of its lower inductance. In case of operational current more than critical currents of layers, the flux flow resistances affect strongly current waveform and thereby the currents of layers were determined by the flux flow resistances. And we investigated breakdown characteristics in $LN_{2}$/paper composite insulation system for the application to a HTS cable. In this experiment, we got some information out of that the electrical characteristics of the insulation materials depends on the condition of butt gap.