• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2006년도 공동학술대회 논문집
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• pp.51-59
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• 2006

서해안 조간대에서 24 channel 탐사기로 획득한 표면파 자료의 위상속도와 군속도를 구한다음, 이를 역산하여 그 결과를 비교하였다. 위상속도의 분산곡선은 tau-p stacking 방법에 의하여, 군속도의 분산곡선은 wavelet analysis와 Multiple Filtering Technique의 두가지 방법을 사용하여 구하였다. 위상속도의 오차가 군속도의 오차보다 더 큰 것을 확인하였다. 군속도의 경우, wavelet analysis가 Multiple Filtering Technique 보다 fundamental mode와 higher mode를 구분하는데 더 효과적이었다. 역산결과, 군속도의 fundamental mode와 1st higher mode 를 동시에 사용했을 때, 공간적 해상도가 가장 좋았다. 이연구는 천부 지반의 S파 속도 구조를 구하는데, 군속도의 higher mode를 포함한 군속도 분산곡선을 사용하는 것이 효과적임을 시사한다.

• 한국소음진동공학회논문집
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• 제13권1호
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• pp.26-32
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• 2003

The vibrational system of this study is consisted of a rotating cantilever pipe and the flow in the pipe. The equation of motion is derived by using Lagrange equation. The influences of the rotating angular velocity and the velocities of fluid flow in the pipe have been studied on the dynamic characteristics of a rotating cantilever pipe by numerical method. The tip-amplitude of axial vibration and maximum tip-deflection of axial direction of cantilever pipe are directly proportional to the velocity of fluid and rotating angular velocity of pipe In the steady state. respectively The bending tip-amplitude of cantilever pipe is inversely proportional to the velocity of fluid in the steady state. When the rotating angular velocity is 5 rad/s, the velocity of fluid increase with increasing the natural frequency of axial vibration at second mode and third mode, but the natural frequency axial direction of first mode is decreased. The natural frequency of lateral direction is decreased due to increase of the rotating angular velocity. It identifies that the Influence of velocity of fluid give much variation lower mode of vibration in lateral direction. And the Influence of velocity of fluid give much variation higher mode of vibration in axial direction.

• 제어로봇시스템학회논문지
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• 제12권11호
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• pp.1061-1064
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• 2006

In this study, the performance of the tracking control of a pneumatic servo motor driven position control system using sliding mode is investigated. It is usually quite difficult to obtain precise tracking control of a pneumatic servo motor driven position control system because of the nonlinear deadband and stick-slip friction of the proportional valve. Therefore, a continuous sliding mode controller with velocity feedforward gain is proposed. Experimental results show that the tracking accurracy can be remarkably improved by adding a proper velocity feedforward term to continuous sliding mode controller.

• 한국자기학회지
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• 제7권5호
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• pp.232-236
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• 1997

Mossbauer 분광계의 사인파속도 Mode에서 Fe-foil을 사용한 속도눈금매기기를 상세하게 소개하였다. 사인 파속도형 Mossbauer 분광계의 장점은 스프링의 자연진동에 의한 것으로 속도가 안정됨과 정밀함에 있다. Fe$_{3}$O$_{4}$와 U-Fe$_{3}$O$_{4}$(unbalanced Fe$_{3}$O$_{4}$)의 Mossbauer 스펙트럼을 분석하여 사인파속도 mode에서의 성능을 평가하였다.

• 한국공작기계학회논문집
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• 제12권5호
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• pp.94-100
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• 2003

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of detect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode But, in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion own. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.272-277
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• 2004

The elastic waves in the plate are dispersive waves with the characteristics of Lamb waves. However, $S_0$ symmetric mode is less dispersive in the frequency region less than first cut-off frequency. And, in anisotropic plates such as CFRP plates, the propagation velocities vary with the direction. So, the wave vector direction to be the phase velocity direction is not accord with the energy flow direction to be the group velocity direction. In this work, the group velocities of the $S_0$ symmetric mode less than the first cut-off frequency was analyzed with the group velocity dispersion curves in unidirectional CFRP plate. And, the group velocity curve obtained by the group velocity dispersion curves are compared with the measured velocities as varied the propagation direction of the Lamb wave. The measured velocities are good agreement with the corrected group velocity curve except near the fiber direction which is called the cusp region. When the propagation direction is not accorded with the principal axis, the direction of the group velocities declines to the fiber direction in the unidirectional CFRP plates. This implies that the energy propagates preferentially toward fiber direction.

• 대한의용생체공학회:의공학회지
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• 제2권2호
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• pp.141-144
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• 1981

This paper descirbes about effects of refraction of ultrasonic beam on B-mode tomogram. Both compution based on Snell's law and the experiments performed using B-mode scanner and schlieren optical method are discussed on a circular phantom immersed in water. In these results, if the discrepancy of sound velocity is more than 0. 6%, the distortion of the B-mode image becomes conspicuous and a target beyound the phantom may disappear or displayed as two targets depending on the velocity of the phantom.

• 한국농공학회지
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• 제35권4호
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• pp.38-46
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• 1993

This study is to analyze effect of exposure environment and mode of ASR on the engineering properties of synthetic lightweight aggregate concrete, such as dynamic modulus of elasticity and ultrasonic pulse velocity. The results of this study are summarized as foflows ; 1. The expansion rate of each exposure environment in 380$^{\circ}$C and NaCI 4% solution was shown higher than in 20$^{\circ}$C and normal water. The expansion rate of each exposure mode was largely shown in order of fjill immersion, wetting/drying, half immersion. 2. The dynamic modulus of elasticty and ultrasonic pulse velocity of each exposure environment in 38$^{\circ}$C and NaCl 4% solution was shown less than in 20$^{\circ}$C and normal water. The dynamic modulus of elasticity and ultrasonic pulse velocity of each exposure mode was shown smaller in order of full immersion, wetting/drying, half imersion.3. The relation between dynamic modulus of elasticity and ultrasonic pulse velocity was highly significant. The dynamic modulus of elasticity was increased with increase of ultrasonic pulse velocity. The decreasing rate of the dynamic modulus of elasticity was shown 2.1~3.4 times higher than the ultrasonic pulse velocity at each age, exposure environment and mode, respectively. 4. The expansion of each exposure environment and mode was increased with increase of curing age. The dynamic modulus of elasticity and ultrasonic pulse velocity of those concrete was increased with increase of curing age. At the curing age 28 days, the highest properties was showed at each type concrete, it was gradually decreased with increase of curing age. Specially, at the curing age 98 days of full immersion, the rate of expansion of type D was shown 3.95 times higher than the type A. But the dynamic modulus of elasticity and ultrasonic pulse velocity was decreased 17% and 8.3%.

• 지구물리와물리탐사
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• 제10권1호
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• pp.1-18
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• 2007

비선형 파동장 역산은 지하의 암석과 물성을 결정하는 물리적인 제약을 위한 탄성파 변수들을 평가하는데 강력한 방법이다. 이 논문에서는 현장자료와 2 차원 탄성파 속도 모델로부터 탄성파 속도 변화를 재구성하여 만들어낸 6 가지 탄성파 속도 모드를 제시하였다. 탄성파 반사파 자료의 정보는 종종 단파장과 장파장 성분으로 나뉘어진다. 지역검색 방법은 만약 초기모델이 실제 모델로부터 동떨어지면 장파장의 속도 변화를 측정하는데 어렵다. 그러면 송신주파수들은 낮은 대역에서 더 높은 대역들로 모델의 탄성파 변수들을 측정하기 위해 변환된다 (frequency-cascade scheme) 탄성파 변수들은 P 파와 S 파 속도가 섬도에 따라 선형으로 변화는 초기 모델 가정하에 각 역산단계에서 (simultaneous mode) 계산된다. P 파와 S 파 속도 $('V_P\;V_S\;mode')$, P 파 임피던스와 포와송 비 $('I_P\;Poisson\;mode')$, P 파와 S 파 임피던스 $('I_P\;I_S\;mode')$와 같은 세가지 모드들이 탄성파 변수들의 역산을 위해 얻어진다. 각 탄성파 역산 단계에서 밀도값들은 세가지 가정하에 개선(update)된다. 탄성파 모델을 위한 각 변수 세트들에서 역산의 정확도를 평가한 결과 $V_P\;V_S$ 모드와 $I_P$ Poisson 모드 사이에 별다른 역산 차이는 없었다. $I_P\;I_S$ 모드들에 대해서도 같은 결론이 예상된다. 이러한 결과들은 전 파장에 걸친 탄성파 파동장 역산의 견고한 기초를 제공한다.

• 지구물리
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• 제9권3호
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• pp.231-240
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• 2006

The crustal structure of the Korean Peninsula was investigated by analyzing phase velocity dispersion data of Rayleigh waves. Earthquakes recorded by three component broad-band velocity seismographs during 1999-2004 in South Korea were used in this study. The fundamental mode Rayleigh waves were extracted from vertical components of seismograms by multiple filter technique and phase match filter method. Phase velocity dispersion curves of the fundamental mode signal pairs for 14 surface wave propagation paths on the great circle in the range 10 to 80 sec were computed by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocity data of Rayleigh wave were inverted. All the result models can be explained by a rather homogeneous crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to about 33 km depth without any distinctive crustal discontinuities and an uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec. Our results turn out to agree well with recent study of Cho et al. (2006 b) based on the analysis of seismic background noises to recover short-period (0.5-20 sec) Rayleigh- and Love-wave group velocity dispersion characteristics.