• Fire Science and Engineering
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• v.29 no.1
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• pp.1-6
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• 2015

In this study, the damages of high strength concrete exposed to high temperature have been evaluated by the impact echo method. Elastic wave velocity and dynamic modulus of elasticity were measured by the impact echo method, and the compressive strength and the static modulus of elasticity were measured by the compression testing method after exposure to high temperature. The results showed that elastic wave velocity has a linear correlation with the compressive strength and dynamic modulus of elasticity has a linear correlation with static modulus of elasticity. Based on results, it is concluded that the impact echo method can be effectively applied to evaluate the mechanical properties of fire damaged high strength concrete.

• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.843-850
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• 2010

The dynamic modulus of elasticity of concrete can be determined nondestructively using impact echo test as prescribed in KS F 2437. The fundamental longitudinal frequency of the concrete cylinders with free-free boundary condition was estimated by the wavelet transform theory. The advantage of the wavelet transform over either a pure spectral or temporal decomposition of the signal is that the features of the pertinent signals can be characterized in the time-frequency plane. For the concrete mix design utilized in this study, no significant difference between the dynamic and the static moduli of elasticity was observed. This was contrary to the perceived general notion of having the dynamic modulus considerably higher than the static modulus. It has been shown that the modulus from static and dynamic by impact echo test are comparable to each other fairly well, when the effect of strain level was properly taken into account. In this experimental test, it was shown that the dynamic modulus is approximately equal to the tangent modulus at $1{\times}10^{-4}$ strain level.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.6
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• pp.628-633
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• 2014

This paper proposes a performance improvement method of the conventional double talk detection method which can operate before convergence of the echo canceller. The proposed method estimates the coefficients of the linear predictive coding(LPC) filter by using the primary input signal. The time-varying threshold for double talk detection is determined based on the LPC filter gain of the primary input signal level. The proposed method can reduce not only false detection rate which means wrong detection of single talk as double talk but also double talk detection delay. Computer simulation was performed using a long-term real speech signals. It is shown that the proposed method improves the conventional method in terms of lowering the false detection rate and shortening the detection delay.

• 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.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.5
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• pp.538-542
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• 2018

Echo generated in digital hearing aid vent give rise to user's discomfort. For cancelling feedback echo in vent, it is required to estimate vent impulse response exactly. The vent impulse response has time varying and sparse characteristics. The IPNLMS has been known a useful adaptive algorithm to estimate vent impulse response with these characteristics. In this paper, subband sparse adaptive filter which applying IPNLMS to subband hearing aid structure is proposed to cancel echo of vent by estimating sparse vent impulse response. In the propose method, the decomposition of input signal to subband can pre-whiten each subband signal, so adaptive filter convergence speed can be improved. And the poly phase component decomposition of adaptive filter increases sparsity of each components, and the better echo cancellation can be possible without additional computation. To derive coefficients update equation of the adaptive filter, by defining the cost function based weight NLMS is defined, and the coefficient update equation of each subband is derived. For verifying performances of the adaptive filter, convergence speed, and steady state error by white signal input, and echo cancelling results by real speech input are evaluated by comparing conventional adaptive filters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.550-551
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• 2012

• Journal of Biomedical Engineering Research
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• v.21 no.6
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• pp.575-581
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• 2000

본 논문에서는 척추침생검 시뮬레이터에서 사용의 햅틱 디바이스인 PHANToM(sup)TM을 이용하여 사실적인 힘을 구현하는 방법을 보여준다. PHANToM(sup)TM은 툴의 끝부분에서 좌표축 방향으로만 힘을 낼 수 있는 단점이 있으며, 시스템의 구동장치의한계로 인하여 딱딱한 물체에 닿을 때 불안정한 특성을 보인다. 또한 좁은 영역 안에서 복잡한 조직들로 인한 급격한 강도 변화도 시스템의 불안정을 초래한다. 모사되는 힘은 두가지 성분으로 나뉜다. 하나는 바늘이 삽입될 때 바늘의 길이 방향으로 느껴지는 힘으로 생체 조직의 모델을 통해 값이 구해진다. 다른 하나는 바늘이 피부를 뚫고 지나간 이후에 바늘이 초기 삽입 방양을 유지 시켜주는 회전방향 힘으로 피봇을 이용하여 구현하였다. 불안정성 문제와 바늘이 튀어나오는 문제는 램핑 필터와 시간변수를 이용하여 제거하였다. 침생검 과정은 생체조직의 탄성 변형뿐 아니라 파괴가 일어나는 변형이므로 사실적인 힘을 구현하기 위해서 실험 데이터를 이용하여 삽입 깊이에 따라 탄성 계수와 마찰 상수가 변하는 모델을 제안하였다.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.1
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• pp.86-96
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• 1999

Laboratory experiment was performed for the TDR to measure the soil moisture, and the results, were compared with the design water content and the one measured by oven-try method. Sand and kaolinite were used . Varaiables for the experiment were water content (10-50%), void ration (0.7 -1.3), mixture rate of kaolinite (10-30%), and measurement methods (TDR and oven-dry). In all cases , TDR method showed very accurage and reliable results , and average error and error range were far lews than the oven-dry method which is widely used. Considerable error was noticed when water contnet was 50% where saturation was achieved for both methods. Therefore, TDR was thought to be applicable to the field moisture measurement if it is unsaturated. For field scale application of TDR, more research and verification of the accuracy with diverse soil conditions including physical ,chemical and mineral properties are recommended.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.731-739
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• 2002

recently out door stadiums have been built as multi purpose stadium for athletic sports It hold but also various events and huge concerts. in the past, out-door stadium usually was built, but recently the out-door stadium which of the 50 ％ of roof covered by doom have been built increasingly. as the result, the sound obstacle is becoming very important. but a design of sound has become unplaned except some of the stadium, also rarely been built by sound-absorption material. as the result, the purpose of this study is investigating, analyzing the theory for plan of electric acoustic sound, a drawing of acoustic design and measurement a result value, comparison, evaluating a main sound factor with criteria of the Seoul City design. and reservation time, clearness, sound pressure level suitable for using purpose, so the necessary quantities will be added to financial budget of building acoustic design. and For verification, this contains acoustic analyser measurement and computer simulation and this study will find the solution of helping method.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.163-169
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• 2020

The asynchronous bistatic sonar needs to estimate direct blast arrival time at a receiver to localize targets, and therefore the direct blast arrival time estimation error could be added to target localization error in comparison with synchronous system. Direct blast especially appears as several peaks at the matched filter output by multipath, thus we compared the first peak detection technique and the maximum peak detection technique of those peaks for direct blast arrival time estimation through sea trial data. The test was performed in a shallow sea with bistatic sonar made up of spatially separated source and line array sensors. Line array sensors obtained the target signal which is generated from the echo repeater. As a result, the first peak detection technique is superior to maximum peak detection technique in direct blast arrival time estimation error. The result of this analysis will be used for further research of target tracking in the asynchronous bistatic sonar.