• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.4
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• pp.743-754
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• 2019

The erosive potential of precipitation can be evaluated by the kinetic energy transferred to the soil by the impact of the rain drop. A kinetic energy rate of the rain drops was estimated by the disdrometer classifying impact signals. This equation in the form of power presented an adjustment measure between the rain rate and rainfall quantity of 97% and 95% for continental and maritime rains, respectively. The exponent of the power equation, initially, shows no dependence on the type of rainfall. However, the multiplicative factor presented variation, which can be adjusted according to rainfall events. This equation was validated by the coefficient of determination, the average absolute error and the confidence error. The kinetic energy of precipitation, associated to certain types of soil, will allow the determination of the potential of the erosion caused by the rains.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.2
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• pp.8-15
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• 2001

In the continuing quest for increased turbomachinery efficiency, the part played by blade profile shape remains crucial. The application of a heated thin metallic film with CTA(constant temperature anemometer) to the measurements of the laminar and turbulent boundary layer behavior(shock-boundary layer-interaction) in a transonic wind tunnel. Results of measurements with hot-film sensors on transonic compressor blades are extremely difficult to interpret because of ambiguous probe signals due to the complexity of the local flow pattern. In order to get the explicit information and give the designer to interpret characteristic signals from hot-film probes, a method was developed by comparing the results with other measuring technic results.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.3
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• pp.106-115
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• 1999

본 연구에서는 충격잡음이 부가되는 비정상 신호 및 잡음 환경하에서 실시간 시지연 추정이 가능한 SLMPTDE와 ZFLMSTDE의 새로운 적응 시지연 추정 방법을 제안하였다. 본 연구에서 제안한 방법은 중간직교 척도를 바탕으로 임의의 SαS 확률과정에 강건하게 적용할 수 있도록 유도된 확률적 경사형적응 추정 알고리즘으로 구성되었으며, SαS 분포를 갖는 다양한 충격잡음을 대상으로 모의 실험하여 알고리즘의 통계적 수렴특성 및 우정 오차에 대해 분석하였으며, 기존의 LMSTDE 방법과 일정시지연의 경우와 시변시지연의 경우에 대해 실시간 시지연 추정능력을 비교, 분석하였다. 실험결과로부터, LMSTDE 방법은 α≥1.9인 가우시안 잡음에 대해서만 시지연 추정이 가능하였고 P=1로 설정한 SLMPTDE 방법은 1〈α≤2인 경우의 SαS 잡음에 대해 정확한 시지연 추정능력을 보였으며, ZFLMSTDE 방법은 0〈α≤2인 모든 경우의 잡음 환경에 대해 그 능력이 입증되었다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.3
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• pp.247-255
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• 2010

Bonding strength of shotcrete is a significant influential factor which plays the role of collapse prevention of tunnel crown and of debonding prevention of shotcrete induced by the blasting vibration. Thus, the evaluation of the shotcrete bonding state is one of the core components for shotcrete quality control. In this study, the peak particle velocities induced by blasting were measured on the shotcrete in a tunnel construction site and its effect on the bonding state of shotcrete is investigated. Drilling and blasting technique was used for the excavation of intersection tunnel connecting the main tunnel with the service tunnel. Blast-induced vibrations were monitored at some points of the main tunnel and the service tunnel. The shotcrete bonding state was evaluated by using impact-echo test coupled with the time-frequency domain analysis which is called short-time Fourier transformation. Analysis results of blast-induced vibrations and the time-frequency domain impact-echo signals showed that the blasting condition applied to the excavation of intersection tunnel hardly affects on the tunnel shotcrete bonding state. The general blasting practice in Korea was evaluated to have a minor negative impact on shotcrete quality.

• Journal of the Institute of Convergence Signal Processing
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• v.13 no.2
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• pp.91-98
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• 2012

Power Quality (PQ) signal such as sag, swell, harmonics, and impulsive transients are the major issues in the operations of the power electronics based devices and microprocessor based equipments. The effectiveness of wavelet based denoising techniques and recognizing different power quality events with noise has been presented in this paper. The algorithms involved in the noisy PQ recognition system are the wavelet based denoising and the back propagation neural networks. Also, in order to verify the real-time performances of the noisy PQ recognition systems under the noisy environments, SIL(Software In the Loop) and PIL(Processor In the Loop) were carried out, resulting in the excellent recognition performances.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.43-50
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• 2004

For the simultaneous measurement of strain and damage signal a fiber Bragg grating sensor system with a dual demodulator was proposed. The dual demodulator is composed of a demodulator using a tunable Fabry-Perot filter measuring the low-frequency signal with large magnitude such as strain and the other using a passive Mach-Zehnder interferometer detecting the high-frequency signal with small amplitude such as impact or damage signal. Using the proposed fiber Bragg grating sensor system, both the strain and damage signals of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundreds of kilohertz at the instant of matrix crack propagation in the 90 degree layer in composite beam.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.3
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• pp.45-51
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• 2016

Existing real-time signal control system was brought up typical problems which are supersaturated condition, point detection system and loop detection system. For that reason, the next generation signal control system of advanced form is required. Following thesis aimed at calculating queue length for the next generation signal control system to utilize basic parameter of signal control in crossing queue instead of the volume of real-time through traffic. Overflow saturated condition which was appeared as limit of existing system was focused to set-up range. Real-time location information of individual vehicle which is collected by GPS data. It converted into the coordinate to apply shock wave model with an linear equation that is extracted by regression model applied by a least square. Through the calculated queue length and link length by contrast, If queue length exceed the link, queue of downstream intersection is included as queue length that upstream queue vehicle is judeged as affecting downstream intersection. In result of operating correlation analysis among link travel time to judge confidence of extracted queue length, Both of links were shown over 0.9 values. It is appeared that both of links are highly correlated. Following research is significant using real-time data to calculate queue length and contributing to signal control system.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.831-837
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• 2010

Optimal conditions of 40 Gbps RZ format for implementation of optical time division multiplexing/wavelength division multiplexing (OTDM/WDM) transmission system are induced by analyzing and comparing performance depending on duty cycle and extinction ratio (ER). Optical phase conjugator (OPC) and inline dispersion management (DM) are applied into optical transmission links for compensating signal distortion due to chromatic dispersion and nonlinearity of fiber. It is confirmed that RZ format of 0.25 duty cycle is less effected by system performance change depending on ER and it is suitable for multiplexing to 160 Gbps signal through OTDM. Also, it is shown that performance improvement of RZ format determined by same net residual dispersion (NRD) is more increased as residual dispersion per span (RDPS) becomes large.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1192-1198
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• 2008

In this paper, the vibration and shock of an HDD car-holder are reduced through vibration analysis and a structural modification. In order to identify the exciting frequency components of vibration and shock, vibration signals are measured and analyzed from the wind shield or dashboard. In addition, the modal test for the current HDD car-holder is performed to investigate the dynamic characteristics of the car-holder. From these experiments, it is found that the exciting frequencies coincide to the natural frequencies of the car-holder. For the purpose of avoiding resonance, some FEM simulations are carried out and then structural modifications are made for the car-holder. Based on the results of simulations, a prototype of new car-holder are manufactured and tested to demonstrate the reduction of vibration and shock. It is verified by the test that a considerable amount of vibration and shock are reduced.