• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.144-150
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• 2008

In this study, the PVDF (polyvinylidene fluoride) piero-film sensor was applied to measure the internal quality of apple. The developed sensor detected the response signal through apple after mechanical impact on the surface of apple. The acoustical parameters at time domain such as rise time (RT), ring down count (RC), energy (EN), event duration (ED) and peak amplitude (PA) and acoustical parameter at frequency domain such as spectral density (SE) were analyzed. The size of waveform decreased as storage time of apple increased. The frequency at maximum magnitude was shifted to lower frequency band according to the storage time. The acoustical parameters showed strong relationship with storage time. The multiple linear regression equation was developed to estimate storage time of apple using the acoustical parameters at time domain and its coefficient of determination was 0.97. The internal quality of apple according to storage time is predictable using developed PVDF sensor and acoustical parameters defined in this study.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.161-171
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• 1999

Impact resonance testing was carried out on small and large concrete blocks containing several types of artificial flaws respectively. Quantitative analysis of the observed peak frequencies in the impact resonance tests identifies the possible normal modes of concrete blocks containing flaws. and enables to determine the depth and size of the flaws in concrete blocks. In this study, concrete can be treated as a homogeneous and isotropic material. The flaw size and location at each section of artificial flaw series in small and large concrete blocks, determined through two-dimensional scanning of impact point and real-time fast Fourier transform, are in good agreement with real size location, respectively. Consequently, quantitative analysis method of vibration modes in the impact resonance tests, which can be applied for homogeneous and isotropic material, can be useful for the detection of flaws in any case of small and large concrete blocks in this study.

• Composites Research
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• v.28 no.4
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• pp.155-161
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• 2015

A composite structure was fabricated with embedded impact detection capabilities for applications in Structural Health Monitoring (SHM). By embedding sensor functionality in the composite, the structure can successfully perform impact localization in real time. Smart resin, composed of $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,\;Ti)O_2$ (PNN-PZT) powder and epoxy resin with 1:30 wt%, was used instead of conventional epoxy resin in order to activate the sensor function in the composite structure. The embedded impact sensor in the composite was fabricated using Hand Lay-up and Vacuum Assisted Resin Transfer Molding(VARTM) methods to inject the smart resin into the glass-fiber fabric. The electrodes were fabricated using silver paste on both the upper and bottom sides of the specimen, then poling treatment was conducted to activate the sensor function using a high voltage amplifier at 4 kV/mm for 30 min at room temperature. The composite's piezoelectric sensitivity was measured to be 35.13 mV/N by comparing the impact force signals from an impact hammer with the corresponding output voltage from the sensor. Because impact sensor functionality was successfully embedded in the composite structure, various applications of this technique in the SHM industry are anticipated. In particular, impact localization on large-scale composite structures with complex geometries is feasible using this composite embedded impact sensor.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.89-99
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• 2007

The stiffness of the asphalt concrete is represented by the complex modulus $E^*$, which is very important properties in the mechanistic design of flexible pavement system. The moduli of asphalt concrete were generally determined by dynamic modulus test. However, the dynamic modulus testing method is too complex, expensive, and time consuming to be applicable on a production basis. The IR(Impact Resonance) method has been shown to be a truly simple nondestructive testing method which produces very repetitive, consistent results. The major object of this study was to estimate of the effects on IR tests for determining modulus of asphalt concrete including impact position, specimen support condition, impact steel ball size and sampling rate. The variations of IR test results with various testing conditions are within ${\pm}2.7%$.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.2025-2026
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• 2006

충격 잡음은 전력선 통신 시스템의 성능을 열하시키는 대표적인 채널 특성 중 하나이다. 이는 배경잡음에 비해 많게는 수십 dB 이상의 레벨을 가지며, 임의 시간적으로 발생하기 때문에 추정 및 제어가 어렵다. 최근 전력선 통신 시스템이 고속화 되면서 한정된 주파수 대역상에서 한정된 신호 전력으로 대용량의 데이터를 전송하기 위해서 대역효율을 높이기 위한 변복조 기법과 오류정정 코드가 적용되고 있으나, 충격 잡음에 의해서 그 성능이 현저하게 열하된다. 일반적으로 충격잡음은 수신단에서 레벨 제한에 의해 그 영향 정도를 줄일 수 있다. 본 논문에서는 전력선 통신 시스템의 성능 향상을 위해 제안되고 있는 LDPC 부호화 OFDM 시스템에 대해 충격 잡음 수신 레벨 제한에 의한 성능 열하의 완화 정도에 대해 연구하였으며, 시뮬레이션을 통해 최적 성능을 위한 수신 레벨 제한 지표를 제시하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.481-489
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• 2000

A time-frequency analysis method was developed to analyze the dispersive waves caused by impact loads in structural members such as beams and plates. Stress waves generated by ball drop and pencil lead break were recorded by ultrasonic transducers and acoustic emission (AE) sensors. Wavelet transform (WT) using Gabor function was employed to analyze the dispersive waves in the time-frequency domain, and then to find the arrival time of the waves as a function of frequency. The measured group velocities in the beam and the plate were compared with the predictions based on the Timoshenko beam theory and Rayleigh-Lamb frequency equations, respectively. The agreements were found to be very good.

• Journal of Korean Society of Transportation
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• v.28 no.6
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• pp.75-84
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• 2010

Controlled traffic intersection is critical point in terms of transportation network performance, where the most of traffic congestion arises. One of the most important and favorable measure of effectiveness in the signal controlled intersection is approach delay. Although lots of efforts to develop traffic delay estimation models have been made throughout the years, most of them were focusing on homogeneous traffic flow. The purpose of this research is to develop a traffic delay estimation model for traffic flow mixed with bus based on the horizontal shockwave theory. Traffic simulation is performed to test the adaptation level of the model in generic environment. The result shows that the delay increases with increasing bus traffic. Overall model accuracy comparing simulation result is acceptable, that shows the error range around 10 percent.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.207-214
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• 2005

The reflected signals from the defects of a pile and the boundaries between the pile and soils are analyzed to evaluate the integrity of drilled shafts in the impact-echo test. Signals varied according to both of the stiffness ratio of the pile to defects and that of the pile to surrounding soils. Model tests using the small size pile in the laboratory and numerical analyses have limitations in finding the characteristics of the signals due to different stress wave characteristics and unreliable modelling for the interaction between the pile and soils respectively. Full scale testing piles which have artificial defects are installed by the actual construction method and they were used to investigate the characteristics of reflected signals according to defects and the stiffness ratios of the pile to soils around.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.489-491
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• 2013

In this paper, Electronic Drum based on Arduino and Processing language to communicate with a computer is implemented. First, we made a drum pad by using piezoelectric sensors. The drum pads prevent damage to the sensor and new mechanism was fabricated to mitigate the impact structure. Arduino connected to the pad, the sensor detects a signal when the shock sends it to Arduino. The received signal of Arduino sends a signal to the computer, and the signal received is stored in the computer to output sound of the drum. Through this structure, the micro-controller, the computer and communications technology can be combined and applicable to a many system.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.585-589
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• 2015

본 연구에서는 이중압축램프의 초음속 유동에서 발생하는 충격파 경계층 상호작용을 EDISON_CFD로 해석하기로 한다. 이중압축램프에선 역압력 구배로 인하여 경계층이 박리가 일어나게 되고 박리된 경계층이 다시 이중압축램프에 부착되어 생겨난 박리영역을 관찰할 수 있다. 박리영역의 앞뒤로 유동의 방향이 바뀌게 되면서 압축 팬(compression fan)과 재부착 팬(reattachment fan)이 충격파를 발생시키고 이중압축램프전방의 충격파와 만나서 복잡한 유동 구조를 가지게 됨을 확인하였다. 이와 같은 층류에서 난류, 박리와 재부착의 영역에서의 해석하기 위해선 해석자의 난류모델이 중요하다. $15^{\circ}-30^{\circ}$, $15^{\circ}-45^{\circ}$의 두 종류의 이중압축램프를 $k-{\omega}$ SST 난류 모델과 ${\gamma}-Re_{\theta}$ 천이 모델로 계산을 EDISON_CFD로 수행하였다. 난류 모델의 차이를 표면마찰계수, 압력계수, 마하수로 비교하여 차이점을 분석하였다.