• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.967-974
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• 2009

Experiments were conducted to measure the heat flux and temperature over a protuberance, using an impulse hypersonic shock tunnel-coaxial thermocouples and a blowdown hypersonic wind tunnel-temperature sensitive paints(TSP). Experimental data were compared with the heat flux data using a blowdown hypersonic wind tunnel-heat flux gauges and it was confirmed data sets agreed well. The measured heat flux is large when the height of the protuberance is large. Also, the heat flux measurements at the upper positions are larger than at the lower positions. For high protuberances, a severe jump in the heat flux is observed, from about 0.6~0.7 of the height of the protuberances. However, when the protuberance is sufficiently short, a rise in the heat flux is rarely observed as the protuberance is submerged totally under the separation region.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1048-1054
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• 2012

This paper presents a Carrier phase fault detection (FD) method for GPS RTK (Global Positioning System Real Time Kinematic) in dynamic environment. There are various error sources in dynamic environment and these errors decrease the reliability of FD results. Due to the reason, Carrier phase measurements are separated into satellite induced signal, user induced signal and other remaining errors. Especially the user-induced signal is computed by user dynamic which is estimated by time-differenced Carrier phase (TDCP) and Doppler shift. TDCP makes it possible to avoid integer ambiguity resolution. Computer simulation is conducted to verify the suggested method. By applying impulse, step and ramp faults, the FD performance is analyzed.

• 대한공업교육학회지
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• v.31 no.2
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• pp.364-380
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• 2006

This paper presents a procedure for designing command to maneuver flexible structure with very little residual vibration, even in the presence of modeling errors. For the open loop maneuver, the various shaped profiles using multiple step inputs delayed in time are considered for robustness and compared with the responses of rigid body and flexible body in virtue of simulations and experiments. Input shaping generates vibration-reducing shaped commands through convolution of an impulse sequence with the desired command. A flexible model with a cylindrical hub and four symmetric appendages is considered to examine the responses to real plant, and to illustrate the effectiveness of the proposed shapers. The appendages are long and flexible, leading to low frequency vibration under any control action. It is shown by a series of simulation that a properly designed feedback controller with input shaper performs well, as compared with open loop controller with input shaper. The control objective is to achieve a fast settling time of residual vibration to flexible structure and robustness (insensitivity)to plant uncertainty, to eliminate residual vibration.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.6
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• pp.78-84
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• 2009

This paper presents measurement results of transient impedance for small-sized ground electrodes in a discharge region of soil. For a realistic analysis of ionization characteristics near the ground electrode, three types of ground rod installed outdoors and high voltage impulse generator were used for injecting test current. From the analysis of response voltage and current flowing ground electrode to earth, it is verified that the ionization near the ground electrode contributes to reduction of ground impedance and limits the ground potential rise effectively in high resistivity soil. As a threshold electric field density for ionization is small in low resistivity soil, the shape of ground electrode rarely contributes to the transient impedance. And, from the experiment result with shape of ground electrode, the rod with needles is more effective to reduce the transient impedance than the plate electrode in the voltage range including with ionization regions of soil.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.8
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• pp.1540-1546
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• 2017

Digital image processing is widely used in various fields including the military, medical, image recognition system, robot and commercial sectors. But in the process of acquiring and transmitting digital images, noise is generated by various external causes. There are various types of general noise depending on the cause and form, but AWGN and impulse noise is one of the leading methods. Removing noise during image processing is essential to the pre-treatment process such as segmentation, image recognition and characteristic extraction. As such, this paper suggests an algorithm that distinguishes the non-edge area and edge area using the Canny edge to apply different filters to different areas in order to effectively remove noise from the image. To verify the effectiveness of the suggested algorithm, it was compared against existing methods using zoom images, edge images and PSNR(peak signal to noise ratio).

• The Korean Journal of Applied Statistics
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• v.28 no.2
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• pp.201-210
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• 2015

Repeated measurements on each variables of interest often arise in bioscience or medical research. We need to account for correlations among repeated measurements to assess the correlation between two variables in the presence of replication. This paper reviews methods to estimate a correlation coefficient between two variables in repeated measurements using the variance-covariance matrix of linear mixed effect models. We analyze acoustic radiation force impulse imaging (ARFI) data to assess correlation between three shear wave velocity (SWV) measurements in liver or spleen and spleen length by ultrasonography. We present how to obtain parameter estimates for the variance-covariance matrix and correlations in mixed effects models using PROC MIXED in SAS.

• The Journal of the Korea Contents Association
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• v.9 no.6
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• pp.1-8
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• 2009

There are a lot of influences, such as location of camera, luminosity, brightness, and direction of light, which affect the performance of 2-dimensional image recognition. This paper suggests an adaptive method for face-image recognition in noisy environments using evolvable filtering and feature extraction which uses one sample image from camera. This suggested method consists of two main parts. One is the environmental-adjustment module which determines optimum sets of filters, filter parameters, and dimensions of features by using "steady state genetic algorithm". The other another part is for face recognition module which performs recognition of face-image using the previous results. In the processing, we used Gabor wavelet for extracting features in the images and k-Nearest Neighbor method for the classification. For testing of the adaptive face recognition method, we tested the adaptive method in the brightness noise, in the impulse noise and in the composite noise and verified that the adaptive method protects face recognition-rate's rapidly decrease which can be occurred generally in the noisy environments.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.11-20
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• 2016

In this paper, we propose the channel estimation scheme for Long Term Evolution-Advanced (LTE-A) downlink system. The proposed scheme uses the fast fourier transform (FFT) interpolation scheme for the user moving at a high speed. The FFT interpolation scheme converts the channel frequency response obtained from least square (LS) or minimum mean square error (MMSE) channel estimation scheme to time domain channel impulse response by taking the inverse FFT (IFFT). After windowing the channel response in the time domain, we can obtain the channel frequency response by taking the FFT. We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-A downlink system. Simulation results show that the proposed channel estimation scheme can improve signal-to-noise-plus-interference ratio (SINR), throughput, and spectral efficiency of conventional system.

• The Journal of the Acoustical Society of Korea
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• v.40 no.5
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• pp.428-438
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• 2021

For long-range communication in deep water, low carrier frequency is efficient due to a decrease in transmission loss. However, there is a limitation in that the data rate decreases due to a narrow bandwith. In order to increase the data rate in an environment with a limited bandwidth, it is necessary to design a higher-order modulation scheme. This paper analyzes the long-range communication data modulated by higher-order modulation schemes. The long-range communication experiment (23 km ~) was conducted in East Sea in October 2020. During the experiment, a vertical line array was utilized and communication sequences were modulated by Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) schemes and transmitted by a towed source. In more detail, PSK modulation consists of quadrature PSK and 8PSK, QAM modulation consists of 8QAM and 16QAM. Time reversal processing is applied to mitigate inter-symbol interference by utilizing the correlation between received signals and channel impulse responses. All modulation schemes show successful results at 23 km range, demonstrating the feasibility of higher-order modulation in long-range communication.

• Journal of the Korean Institute of Gas
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• v.25 no.5
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• pp.19-29
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• 2021

Due to the climate changing, the world's countries are tightening regulations on CO2 and air pollutants emission to solve them. In addition, eco friendly vehicles is increasing to replace automobiles in internal combustion engine. Recently, the government is supporting the expansion of hydrogen refueling infrastructure and localization of core equipment in refueling facilities according to the hydrogen economy road map. In this study, design of the Excess flow limiting device in FCEV cylinder valve using by finite element analysis and performed performance tests on prototype. Major test results as hydrostatic strength, continued operation, operation, pressure impulse, leakage showed that the excess flow limiting device meets the performance requirements according to ISO 12619-2 and ISO 12619-11.