• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.18-25
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• 2013

Recently the requirement of long-term mobile energy source for mobile robot or small-sized unmanned vehicle is highly increased, and the micro turbine generator(MTG) which is known to have high energy and power density is under development. MTG is designed to have air foil bearing and high speed rotor of which operating speed is 400,000rpm. In the development stage of high speed rotor and bearing, stability analysis for the full operational speed range is essential and the dynamic coefficients such as stiffness and damping coefficients of bearing depending on the rotational speed are required for that. Although perturbation method is usually used to identify the dynamic coefficients, it's not easy to give the perturbation to the high speed rotating rotor. In this study, we present the dynamic coefficients measurement system for air foil bearing which consists of electromagnets, gap sensors, high speed motor and controller. This measurement system can exert the sine sweep force to the rotor-bearing, measure the displacement of rotor and get FRF(Frequency response function) of rotor-bearing. The least square estimation method is applied to identify the dynamic coefficients of bearing from the measured frequency response at the different rpm and the identified dynamic coefficients for the wide rotational speed range are presented.

• Computational Structural Engineering
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• v.5 no.3
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• pp.105-112
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• 1992

The design of reactor internals requires the accurate vibration characteristics of each component for subsequent dynamic structural response analysis. For Korean standard nuclear power plant some modifications on the Control Element Assembly shroud from the reference design have been made. Since the shroud is complex in geometry having an array of vertical round tubes and webs in a square grid pattern, and being tied down by preloaded tie rods into position, it is planned to perform a vibration measurement program consisting of both experimental and analytical modal studies upon that component. To determine the proper test conditions, the pre-test analysis has been performed using the general purpose structural analysis program ANSYS. Also the effects of the number of master degrees of freedom, holes in the web and tie-rod preload on the natural frequencies are examined prior to the pre-test analysis. After decision of appropriate finite element model, frequency analysis and harmonic analysis are performed and ideas for the test conditions such as the number of measurement points, their locations, measurement frequency range and the excitation force level are determined.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1732-1734
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• 2001

The purpose of this experiment was to develope Triggered Vacuum Switch(TVS) and to improve understanding of the high current vacuum arc phenomena in the TVS. The TVS has an array of rods of alternate polarity in which a fixed gap spacing is maintained between the rods. The cross section of each rod has trapezoidal shape. Breakdown of the TVS produced high current vacuum arc plasma. A spectroscopic measurement was performed over 20 kA peak current in the center of electrodes, in the vicinity of cathode, and outside electrodes. The electrode material tested was Fe. Measured Fe spectrum range was from 200 nm to 900 nm. Measurement result showed that over 90 percent of the charge states were FeII and the others were FeI and FeIII. The electron temperature was determined from the relative line intensity ratio methode of FeII system by assuming the local thermal equilibrium(LTE). The electron temperature at the center of electrodes was measured as 1.5 eV at 26 kA peak current. The electron temperature varied with its peak current. Intensity of spectrums is the highest in the vicinity of the cathode. Further we will also present study result of the diode phenomena in the TVS.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.5
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• pp.9-15
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• 2001

This paper describes measurement method of dielectric properties of dielectric materials using cylindrical cavity resonator's. Dielectric properties of concern here are relative permittivity, loss- tangent, quality factor and so on. An analysis of $TE_{011}$mode in dielectric properties of concentric dielectric-rod inserted cylindrical cavity resonator is presented. The frequency variation by the air gap at $TE_{011}$ mode turns out to be the least sensitive. A technique using a $TE_{011}$ mode of concentric dielectric-rod inserted cylindrical cavity resonator and an exact field representation of neo non-decaying mode are introduced for measurement of dielectric properties.

• Journal of Ecology and Environment
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• v.34 no.4
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• pp.411-423
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• 2011

This study was conducted to quantify soil $CO_2$ efflux using the continuous measurement method and to examine the applicability of an automatic continuous measurement system in a Korean deciduous broad-leaved forest. Soil respiration rate (Rs) was assessed through continuous measurements during the 2004-2005 full growing seasons using an automatic opening/closing chamber system in sections of a Gwangneung temperate deciduous forest, Korea. The study site was an old-growth natural mixed deciduous forest approximately 80 years old. For each full growth season, the annual Rs, which had a gap that was filled with data using an exponential function derived from soil temperature (Ts) at 5-cm depth, and Rs values collected in each season were 2,738.1 g $CO_2$ $m^{-2}y^{-1}$ in 2004 and 3,355.1 g $CO_2$ $m^{-2}y^{-1}$ in 2005. However, the diurnal variation in Rs showed stronger correlations with Ts (r = 0.91, P < 0.001 in 2004, r = 0.87, P < 0.001 in 2005) and air temperature (Ta) (r = 0.84, P < 0.001 in 2004, r = 0.79, P < 0.001 in 2005) than with deep Ts during the spring season. However, the temperature functions derived from the Ts at various depths of 0, -2, -5, -10, and -20 cm revealed that the correlation coefficient decreased with increasing soil depth in the spring season, whereas it increased in the summer. Rs showed a weak correlation with precipitation (r = 0.25, P < 0.01) and soil water content (r = 0.28, P < 0.05). Additionally, the diurnal change in Rs revealed a higher correlation with Ta than that of Ts. The $Q_{10}$ values from spring to winter were calculated from each season's dataset and were 3.2, 1.5, 7.4, and 2.7 in 2004 and 6.0, 3.1, 3.0, and 2.6 in 2005; thus, showing high fluctuation within each season. The applicability of an automatic continuous system was demonstrated for collecting a high resolution soil $CO_2$ efflux dataset under various environmental conditions.

• Transactions on Electrical and Electronic Materials
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• v.7 no.6
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• pp.313-318
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• 2006

This paper introduces a partial discharge (PD) severity metric, S, based on the evaluation of time-sequence PD data capture and resulting Time-Sequence-Analysis Discharge (TSAD) level distributions. Basically based on an IEC60270 measurement technique, each PD event is time stamped and the discharge level noted. By evaluating the time differences between a previous and subsequent discharge, a 3D plot of time-sequence activity and discharge levels can be produced. From these parameters a measurement of severity, which takes into account dynamic or instantaneous variations in both the time of occurrence and the level of discharge, rather than using standard repetition rate techniques, can be formulated. The idea is to provide a measure of the severity of PD activity for potentially measuring the state of insulation within an item of plant. This severity measure is evaluated for a simple point-plane geometry in $SF_{6}$ as a function of gap distance and applied high voltage. The results show that as the partial discharge activity increases, the severity measure also increases. The importance of future investigations, quantifications and evaluations of the robustness, sensitivity and importance of such a severity measurement, as well as comparing it with typical repetition rate assessment techniques, and other monitoring techniques, are also very briefly discussed.

• Journal of Fashion Business
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• v.19 no.5
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• pp.139-156
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• 2015

The purpose of this study is to investigate various information relating to research on the dimensions of clothing used in the sale of products via the internet that used to target global SPA((Specialty Store Retailer of Private Label Apparel) brands sold in Korea. A total of 12 SPA brands including seven global SPA brands and five national. SPA brands were surveyed in this study. Brands were chosen net sales and consumer preferences the last three years. In all SPA brands, literal size designation such as S, M, L and numeric size designation such as 0, 2, 4 or 32, 34, 36 etc. were mixed, but in case of Jean, the size codes mark waist circumference were dominant. European size codes were more common in case of European brands while literal codes were more dominantly used for American size codes with in the US brands. By reviewing the measurement information of the body and product size, the product measurement methods of UNIQLO, FOREVER 21 and TOPTEN were much more accountable and excellent than other brands. However, most of the others didn't offer proper information such as pictograms or figures about measurement methods relating body sizes and product sizes. In addition, most of global SPA brands offered size conversion chart which consumers could reference, however of none of the national SPA brands offered a conversion size chart on their website. Regardless of the type of clothing, the coverage of clothing size was higher than in global SPA brands such as H&M GAP compared to national SPA brands. In particular, 8seconds did not present apparel size ranges that fit consumers' individual clothes sizes.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• Korean Journal of Applied Biomechanics
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• v.31 no.2
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• pp.104-112
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• 2021

Objective: This study aimed to analyze the effects of consecutive whole body vibration through heel raise posture on the center of pressure and electromyography of anterior tibial muscle, lateral gastrocnemius and soleus muscles during single-leg stance. Method: The subjects of this study included 30 healthy males in their 20's, with the following inclusion criteria: no history of orthopaedic medical history, no participation in regular exercises, no history of whole body vibration exercise, and right leg being the dominant leg. The experimental procedure involved pretreatment measurement of eye open single-leg stance, application of whole body vibration for 30 seconds, post-treatment measurement (3 measurements in total). Static and dynamic movements have been measured over 2 separate experiments, with 72 hours gap between the experiments. Static movement involved maintaining single-leg heel raise posture for 30 seconds while applying whole body vibration, and dynamic movement involved heel raise (15 repetitions over 30 seconds) while applying whole body vibration. The strength of applied whole body vibration was 35 Hz frequency and 2~4 mm amplitude. Results: As the single-leg posture after static heel raise posture, mediolateral velocity of the center of pressure at post 2 and post 3 were significantly reduced compared to the pre-treatment measurement. In addition, the percentage for reference voluntary contraction in anterior tibial muscle and soleus and median frequency at anterior tibial muscle and lateral gastrocnemius muscle at post 3 were significantly decreased compared to the pre-treatment value. As the single-leg posture after dynamic heel raise posture, the mediolateral 95% edge frequency of the center of pressure and median frequency at anterior tibial muscle, lateral gastrocnemius muscle, and soleus muscle at post 3 were significantly reduced compared to the pre-treatment value. Conclusion: Acute whole body vibration via static and dynamic heel raise posture have positive effect on mediolateral posture control during single-leg stance.

• Korean Journal of Agricultural Science
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• v.49 no.4
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• pp.937-948
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• 2022

Agricultural operations are performed in uneven environments by attaching an implement on the 3-point hitch of a tractor. A high load is thus placed on the 3-point hitch, and fatigue and failure of the hitch may occur during agricultural operations. In this study, a dynamic simulation model was developed to predict the load occurring on the eyebolt of a 3-point hitch, which is the main damaged component. The simulation model was developed and validated using agricultural data as simulation input and validation data. The dynamics model was developed using the specifications of a 78 kW class tractor. A measurement system was constructed to measure the simulation input and validation data. The simulation model was validated using a traction load on an eye bolt, which was measured during plow tillage operation. The measurement results showed that the average traction load on the left and right lower link and the top link were 8,099.97, 4,943.06, and 636.11 N, respectively. The simulation results and the measured traction load on the left eyebolt were respectively 610.30 and 597.15 N. The simulation results and measured traction load on the left eyebolt were respectively 1,179.78, and 1,145.06 N. The error between the simulation and measurement data was roughly 2% on the left eyebolt and 3% on the right eyebolt.