• Journal of Welding and Joining
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• 제21권1호
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• pp.48-53
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• 2003

The object of this study is to examine the effect of short circuit time ratio (SCTR) and current rise delay time (Td) on the spatter generation at low and medium current range in $CO_2$ welding. The spatter was evaluated by the weight generated in the welding of bead-on-plate for 30 seconds (3 times). Td was varied by order of 0, 0.4, 0.8 and 1.2 msec. At each Td, the short circuit time ratio was varied by the output voltage of the welding power source. In the low current range, it was found that the optimum SCTR was 20~25%, and the minimum spatter generation weight was obtained in the case of Td=0.4msec and SCTR=22% even though the remarkable difference was not showed by the application of Td. In the medium current range, it was confirmed that the arc was stable though the SCTR was increased from 20% to 40% by the control of current wave. Spatter generation weight depended on the variation of Td, and the lowest value of spatter generation weight occurred at Td=0.8~1.2msec.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.178-181
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• 2005

The positioning accuracy of the Global Positioning System (GPS) has been improved considerably during the past two decades. The main error sources such as ionospheric refraction, orbital uncertainty, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially, if not eliminated. In this study, the GPS data collected by the GPS receivers that were established as continuously operating reference stations by International GNSS Service (IGS), Ministry of the Interior (MOl), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) Of Taiwan are utilized to investigate the impact of atmospheric water vapor on GPS positioning determination. The surface meteorological measurements that were concurrently acquired by instruments co-located with the GPS receivers include temperature, pressure and humidity data. To obtain the influence of the GPS height on the proposed impact study. A hydrodynamic ocean tide model (GOTOO.2 model) and solid earth tide were used to improve the GPS height. The surface meteorological data (pressure, temperature and humidity) were introduced to the data processing with 24 troposphere parameters. The results from the studies associated with different GPS height were compared for the cases with and without a priori knowledge of surface meteorological measurements. The finding based on the measurements in 2003 is that the surface meteorological measurements have an impact on the GPS height. The associated daily maximum of the differences is 1.07 cm for the KDNM station. The impact is reduced due to smoothing when the average of the GPS height for the whole year is considered.

• Journal of Power Electronics
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• 제18권5호
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• pp.1555-1566
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• 2018

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1891-1901
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• 2017

In this paper, optimal control of the fuel cell and design of a high-efficiency power converter is implemented to build a high-priced fuel cell system with minimum capacity. Conventional power converter devices use a non-isolated boost converter for high efficiency while the battery is charged, and reduce its conduction loss by using MOSFETs instead of diodes. However, the efficiency of the boost converter decreases, since overshoot occurs because there is a moment when the body diode of the MOSFET is conducted during the dead time and huge loss occurs when the dead time for the maximum-power-flowing state is used in the low-power-flowing state. The method proposed in this paper is to adjust the dead time of boost and rectifier switches by predicting the power flow to meet the maximum efficiency in every load condition. After analyzing parasite components, the stability and efficiency of the high-efficiency boost converter is improved by predictive compensation of the delay component of each part, and it is proven by simulation and experience. The variation in switching delay times of each switch of the full-bridge converter is compensated by falling time compensation, a control method of PWM, and it is also proven by simulation and experience.

• 한국자동차공학회논문집
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• 제2권2호
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• pp.49-58
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• 1994

A study on the performance of a Diesel engine with various intake gas compositions other than that of air are performed experimentally. In this study, the concentrations of each of oxygen, nitorgen, carbon dioxide, and argon are changed and their effects on the performance of the engine are investigated parametrically. The experiments are performed at constant engine speed condition, and main measured parameters are cylinder pressure, intake gas compositions, fuel consumption rate. Increase of oxygen concentration up to 24% improved the performance of the engine generally. The adverse effect was observed when the oxygen concentration was increased over 24%. Increase of carbon dioxide concentration degraded the performance of the engine, mainly due to the lower specific heat ratio of carbon dioxide. Adding argon gas to the intake gas improved the overall performance. Finally, it is found that two most influencing factors affecting the performance of the Diesel engine in this study of intake gas composition variation are ignition delay and specific heat ratio of the intake gas.

• 한국멀티미디어학회논문지
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• 제4권4호
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• pp.339-348
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• 2001

본 논문에서는 ATM 망이 수용하고 있는 모든 서비스 클래스에 대해 적용 가능한 다중 우선순위 기반의 셀 스케줄링 알고리 즘을 제안한다. 제안한 알고리즘은 각 서비스 클래스의 우선순위를 4 계층으로 분류하고, 각 서비스 클래스에 대한 가중치를 연결 설정시에 협정한 트래픽 변수(parameter)에 근거하여 생성한다. 제안한 알고리즘은 실시간 서비스인 CBR(Constant Bit Rate) 및 rt_VBR(Real-time Variation Bit Rate) 서비스를 우선적으로 서비스하여 지연에 민감한 트래픽의 QoS(Quality of Service)를 보장하였으며, 트래픽 전송이 지연될 경우 대역폭의 대소에 관계없이 우선적으로 전송할 수 있는 가중치를 둠으로써 작은 트래픽이라도 큐 내에서 지연되는 것을 최소화하였다. 제안한 셀 스케줄링 알고리즘의 효용성을 입증하기 위해 기존의 셀 스케줄링 알고리즘과 비교한 모의실험을 수행하였고, 그 결과를 제시한다.

• 한국연초학회지
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• 제21권1호
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• pp.77-81
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• 1999

Tobacco plants(Nicotiana tabacum cv. NC82) transformed with TMV CP cDNA were self-fertilized until 8th generation (R$_{8}$), and the transgenic plants from 6th to 8th generation were analized for their resistance to tobacco mosaic virus(TMV) and stability of the gene expression. The 6th generation of the plants(R$_{6}$) showed high resistance(81-91 %) to TMV at eight weeks after artificial inoculation with the virus. The transgenic cell line 601 was the most prominant in the expression of resistance. 98 % of the plants showed no symptom without any agronomic phynotepe variation when they were inoculated with the virus in a experimental field. However, 2% of the plants were revealed as delay type of symptom with mild mosaic on a few leaves. The viral resistance in greenhouse tests of the 7th generation (R$_{7}$) was 54-64%, and the number of delay type plants were increased than that of 6th generation plants. In the 8th generation, 81 % of the plants was complete resistant to the virus. The TMV CP cDNA of the transgenic plants of each generation was also confirmed by genomic PCR, and there was no systemic viral multiplication in the resistant plants. It suggests that the viral resistance and gene expression of the transgenic plants might be stable through the generations.ons.s.

• 대한기계학회논문집B
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• 제20권2호
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• pp.632-640
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• 1996

석탄슬러리 액적은 석유와 취급의 유사성 때문에 석유 대체에너지로서 중용하게 인식되어지고 있으며, 석유계의 연료와 비슥한 방법으로 분무연소 시키는 것이 가능하여 종래의 중유사용 연소장치를 최소한 개조하여 사용할 수 있다는 이점이 있다. 따라서 석탄슬러리 액적의 연소에 관한 연구가 활발히 진행되고 있으나 혼합되는 연료의 종류 또는 연소 및 열전달기수에 대한 해석 방법이 다양하여 아직 체계화되지 못하고 있으며 논란의 여지도 없다.

• The Journal of the Acoustical Society of Korea
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• 제22권4E호
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• pp.167-175
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• 2003

Shear wave velocity was measured and grain size analysis was conducted on two core samples obtained in unconsolidated marine sediments of the western continental margin, the East Sea. A pulse transmission technique based on the Hamilton frame was used to measure shear wave velocity. Duomorph ceramic bender transducer-receiver elements were used to generate and detect shear waves in sediment samples. Time delay was calculated by changing the sample length from the transducer-receiver element. Time delay is 43.18 μs and shear wave velocity (22.49 m/s) is calculated from the slope of regression line. Shear wave velocities of station 1 and 2 range from 8.9 to 19.0 m/s and from 8.8 to 22 mis, respectively. Shear wave velocities with depth in both cores are qualitatively in agreement with the compared model〔1〕, although the absolute value is different. The sediment type of two core samples is mud (mean grain size, 8-9Φ). Shear wave velocity generally increases with sediment depth, which is suggesting normally consolidated sediments. The complicated variation of velocity anisotropy with depth at station 2 is probably responsible for sediment disturbance by possible gas effect.

• 제어로봇시스템학회논문지
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• 제16권5호
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• pp.440-445
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• 2010

This paper proposes a single accelerometer sensor control algorithm to mobile inverted pendulum, generally called 'Segway', and evaluates the performance of this system comparing to the conventional ones. The commercialized 'Prototype Segway-PT' is initially considered as a next-generation transport vehicle. However, this robot is operated by three gyroscopes and two accelerometers to control the posture and speed, and it requires the complex signal processing for fusing the two sets of data. As the result of this, the growth rate of market size of 'Segway' is slow because of its high price mainly. In this paper, the mobile inverted pendulum is operated by a single accelerometer to simplify the control system to lower the price. Low pass filter is one of the good sensors to reducing the variation of an accelerometer, but it has time delay. This time delay disturbs real-time mobile inverted pendulum control. Like this, other various algorithms are used for this system, but each one has its own weak point. So this paper proposes a new filtering method, median filter and EKF. Median filter is used to image processing to reject impulse elements like salt and pepper noise. As the major performance evaluation parameter for the accelerometer, the high-frequency to low frequency ratio from FFT (Fast Fourier Transform) is used. Effectiveness of the proposed algorithms has been verified through the real experiments and the results are demonstrated.