• Journal of Biosystems Engineering
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• 제23권1호
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• pp.67-74
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• 1998

A nondestructive quality inspection technique using acoustic impulse response method was developed for eggshell inspection. An experimental system was built to generate the impact force, to measure the response signal and to analyze the frequency spectrum. This system includes an impulse generating unit, an egg holding seal a microphone with preamplifier, and a DSP board installed on Personal Computer. A simple algorithm .was developed for crack detection. Using the developed system with algorithm, crack detection ability was evaluated and the error rate to estimate the normal egg as cracked was found to be 4% and the error rate to estimate the cracked egg as normal was also found to be 4%. This system could be adopted in industry with some modification.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1802-1812
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• 2001

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure Loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The results are verified by comparison with FEM results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 하계종합학술대회 논문집
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• pp.69-72
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• 1999

In this paper, an efficient time domain equalization algorithm for discrete wavelet multitone(DWMT) data transmission is developed. In this algorithm, the time domain equalizer(TEQ) consists of two stages, i.e., the channel impulse response shortening equalizer(TEQ-S) in the first stage and the channel frequency flattening equalizer(TEQ-F) in the second stage. TEQ-S reduces the length of transmission channel impulse response to decrease intersymbol interference(ISI) followed by TEQ-F that enhances the channel frequency response characteristics to the level of an ideal channel, hence diminishes the bit error rate. TEQ-S is implemented using the least-squares(LS) method, while TEQ-F is designed by using the least mean-square(LMS) algorithm. Since DWMT system also requires of the frequency domain equalizer in order to further reduce ICI and ISI the hardware complexity is an another concern. However, by adopting an well designed and trained TEQ, the hardware complexity of the whole DWMT system can be greatly reduced.

• 대한의용생체공학회:의공학회지
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• 제27권5호
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• pp.229-236
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• 2006

The acoustic field analysis method is the superior calibration method for rectifying the ultrasonic probe sensitivity. This method also can be applied to evaluate the probe performance in clinical fields without numerical analysis and precise measurements. In this paper, we propose the method of acoustic field pattern analysis with probe channel division for the evaluation of diagnostic ultrasound probe characterization. In order to verify our purpose, we performed a set of experiments. We measured the acoustic-field pattern of the three inferiority probes by channel division to evaluate an acoustic field distribution and impulse response characteristics. By comparing the results of acoustic field measurement method with that of conventional method such as impulse response and live image test for linear array probes, it is demonstrated that the ultrasound field measurement method is more effective then conventional method in detection of defective elements.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.955-960
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• 2008

In this paper, an impulse of an industrial chop Saw is identified by experimental method and the impulse is reduced by structural modification. For the impulse identification, vibration signals are measured by an accelerometer when the chop saw is operating. From some experiments, it is found that the impulse occurs when there is slip between spindle and the wheelwasher and contact area is small between the wheelwasher and cutting discs. The design of the wheelwasher for optimization is performed by the FEM and experiments and the prototype is manufactured. It is verified that considerable amount of impulses are reduced by the structural modification.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.168-169
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• 2005

• Smart Structures and Systems
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• 제20권4호
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• pp.473-481
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• 2017

This study suggests a simple, convenient and non-destructive method for investigation of the Young's modulus detection in stepped shafts which only utilizes the first-order resonant frequency in flexural mode and dimensions of structures. The method is based on the impulse excitation technique (IET) to pick up the fundamental resonant frequencies. The standard Young's modulus detection formulas for rectangular and circular cross-sections are well investigated in literatures. However, the Young's modulus of stepped shafts can not be directly detected using the formula for a beam with rectangular or circular cross-section. A response surface method (RSM) is introduced to design numerical simulation experiments to build up experimental formula to detect Young's modulus of stepped shafts. The numerical simulation performed by finite element method (FEM) to obtain enough simulation data for RSM analysis. After analysis and calculation, the relationship of flexural resonant frequencies, dimensions of stepped shafts and Young's modulus is obtained. Numerical simulations and experimental investigations show that the IET method can be used to investigate Young's modulus in stepped shafts, and the FEM simulation and RSM based IET formula proposed in this paper is applicable to calculate the Young's modulus in stepped shaft. The method can be further developed to detect mechanical parameters of more complicated structures using the combination of FEM simulation and RSM.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.53-64
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• 2011

The present study considers multi-level approach for the analysis of parametric roll phenomena. Three kinds of computation method, GM variation, impulse response function (IRF), and Rankine panel method, are applied for the multi-level approach. IRF and Rankine panel method are based on the weakly nonlinear formulation which includes nonlinear Froude-Krylov and restoring forces. In the computation result of parametric roll occurrence test in regular waves, IRF and Rankine panel method show similar tendency. Although the GM variation approach predicts the occurrence of parametric roll at twice roll natural frequency, its frequency criteria shows a little difference. Nonlinear roll motion in bichromatic wave is also considered in this study. To prove the unstable roll motion in bichromatic waves, theoretical and numerical approaches are applied. The occurrence of parametric roll is theoretically examined by introducing the quasi-periodic Mathieu equation. Instability criteria are well predicted from stability analysis in theoretical approach. From the Fourier analysis, it has been verified that difference-frequency effects create the unstable roll motion. The occurrence of unstable roll motion in bichromatic wave is also observed in the experiment.

• 한국정보통신학회논문지
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• 제10권6호
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• pp.1025-1031
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• 2006

본 논문에서는 FIR 근사를 기반으로한 전역통과 시스템에 대한 deconvolution 필터링 기법을 제안한다. 제안한 기법은 안정한 non-causal deconvolution 필터를 FIR 근사에 의해 안정한 causal deconvolution 필터로 변환시키는 것이다. 본 논문에서 보인바와 같이 전역통과시스템에 대한 deconvolution 필터의 임펄스 응답은 전역통과 시스템 자체의 임펄스 응답의 거울 영상(mirror image) 임을 알 수 있다. 이와 같이 전역통과 시스템에 대한 임펄스 응답과 그 시스템의 deconvolution 필터에 대한 임펄스 응답의 대칭성 때문에, 제안한 기법은 전역 통과 필터의 차수에 상관없이 동일하게 적용할 수 있다. 제안한 기법의 성능을 보이기 위하여 1차, 2차 및 400차의 전역통과 시스템에 대한 컴퓨터 시뮬레이션 결과를 포함한다.

• 한국음향학회지
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• 제7권2호
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• pp.26-38
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• 1988

이 논문은 긴 잔향을 갖는 실내의 음향전달계의 임펄스 레스폰스를 DFT(Discrete Fourier Transform)의 알고리즘으로 크로스 스펙트럼 (cross spectrum method)에 의해 구하는 3가지 방법에 대해 기술한다. 첫째의 방법은 종래부터 사용되어온 방법으로 음원신호로서 백색잡음(white noise)을 사용한다. 따라서, 임펄스 레스폰스 추정시 매우 긴 시간창의 데이터와 다수회의 DFT를 행하여야 한다. 두번째 방법은 음원신호로써 짧은 지속시간의 랜덤노이즈(random noise)를 사용하여 첫번째 방법에서 DFT수행시 데이타의 시간창의 길이를 짧게 하기 위하여 개발된 방법이다. 세번째 방법은 본 논문에서 제안한 방법으로 음원신호로써 짧은 지속시간의 두 종류의 확정산호를 교차하여 발생하는 방법이다. 이 방법은 DFT수행시 시간창의 길이는 두번째 방법과 같고 FFT 계산횟수는 5번으로 행할 수 있다. 이들 음원신호에 대해 잔향이 긴 음향전달계의 임펄스 레스폰스 측정은 전자계산기의연산처리능력과 임펄스 레스폰스 측정정도의 관점에서 비교 시험한 결과는 마지막 방법이 가장 유리하다는 결론을 얻었다.