• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.99.2-99.2
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• 2007

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.554-558
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• 2002

A magnetostrictive sensor is used to measure stress waves propagating in a ferromagnetic cylinder without physical contact. The performance of a magnetostrictive sensor is affected most significantly by the bias magnetic field applied around the measurement location. The goal of this paper is to carry out the topology optimization of the bias magnet and yoke assembly to maximize the sensor output for traveling bending waves. We will use the multi-resolution topology optimization strategy to find the assembly of the bias magnet and the yoke that is easy to realize. The effectiveness of the present design is confirmed by an actual measurement of the sensor signal with the proposed bias magnet and yoke configuration.

• 대한의용생체공학회:의공학회지
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• 제22권4호
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• pp.321-330
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• 2001

In this paper, we propose a new synthetic aperture focusing scheme for improving the lateral resolution which is one of the most important factors determining the quality of ultrasound imaging. The proposed scheme enables full round-trip dynamic focusing with approximately limited property. This properties are obtained through transmitting plane waves of which the traveling angle varies with the receive subaperture position, as opposed to stepping the spherical wave source across an array in other synthetic aperture focusing schemes, and employing dynamic focusing in receive. In this paper, the properties of the proposed scheme is analyzed in which a hypothetical infinite line source is used to transmit the plane waves and verified through computer simulation results. Also, we show that the proposed scheme is realizable with an array transducer with a finite aperture size. In summary, it is shown through comparison between the field contours of the proposed scheme and the conventional scheme that the proposed scheme can improve greatly the lateral resolution of ultrasound imaging.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.107-111
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• 2005

It has been reviewed whether it would be suitable that the application of the time-frequency signal analysis techniques to estimate the location of the impact source in plate structure. The STFT(Short Time Fourier Transform), WVD(Wigner-Ville distribution) and CWT(Continuous Wavelet Transform) methods are introduced and the advantages and disadvantages of those methods are described by using a simulated signal component. The essential of the above proposed techniques is to separate the traveling waves in both time and frequency domains using the dispersion characteristics of the structural waves. These time-frequency methods are expected to be more useful than the conventional time domain analyses fer the impact localization problem on a plate type structure. Also it has been concluded that the smoothed WVD can give more reliable means than the other methodologies for the location estimation in a noisy environment.

• 대한원격탐사학회지
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• 제27권3호
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• pp.213-223
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• 2011

The purpose of this study is to estimate the spherical wave parameters that appears in synthetic aperture radar (SAR) image acquired over the coast of Chukk, Micronesia. The retrieval of ocean wave parameters consists of two main stages: the first is to determine the dominant wavelengths by Fast Fourier Transform (FFT) over 16 sub-image areas and the second is to estimate wave slopes and heights using dispersion relationship under various water wave conditions. It is assumed that the spherical waves are linear and progressive. These type of waves have the range and azimuth components traveling in radial directions. The azimuth travelling waves are more affected by the velocity bunching mechanism and it is difficult to estimate the wave parameters for these affected areas in SAR imagery. In order to compensate these effects, the velocity bunching ratio (VBR) based on modulation transfer function (MTF) was compared with the intensity ratio for neighbor area in the radial direction in order to assign the spherical wave properties for azimuthally travelling waves. Dispersion relation provides the good estimates for the wave heights for all the selected sub-image areas in the range of 1m to 2m. VBR based on MTF was found to be 0.78 at wave height of 1.36m, while the intensity-based VBR was 0.69 which corresponds to the height of 1.75m. It can be said that the velocity bunching accounts for azimuthally travelling spherical waves and the difference results from the sea-bottom effects.

• 한국해안·해양공학회논문집
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• 제28권6호
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• pp.397-407
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• 2016

이안제 좌 우측으로 각각 분기되어 진행하는 파랑은 회절에 의해 이안제 배후 안쪽으로 휘어져 위상간 간섭을 일으키며 중첩되면서 전파된다. 지형적인 여건으로 진행방향이 같아지게 되고 항 입구부로 향한다면 파랑의 에너지 중첩에 의한 영향이 항내로 나타날 수 있다. 본 연구에서는 항 입구부에 이안제가 설치되는 경우, 이안제 길이에 따라 발생하는 좌 우측 회절 파랑의 위상차가 항내 파고에 미치는 영향을 수치실험을 통해 검토하였다. 이로부터 항내에서의 파고는 이안제의 길이에 따른 좌 우측 회절파랑의 위상차에 의한 중첩의 영향으로 증폭 혹은 상쇄되어 나타남을 확인하였다.

• 한국해안해양공학회지
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• 제19권1호
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• pp.16-28
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• 2007

이 연구에서는 심해 풍파 아래에서의 응집구조(coherent structures)에 대한 실험실 실험 결과를 제시하였다. 풍속과 취송거리가 서로 다른 실험 조건에서 입자화상유속계를 이용하여 취득된 심해 풍파의 속도장으로부터 와도장을 가시화하고 응집구조가 시 공간적으로 변천하는 양상 및 그에 따른 와도의 연직 분포 변화를 정성적으로 분석하였다. 파봉 아래에서는 파와 같은 위상으로 함께 진행하는 응집구조가 존재함을 확인하였다. 이 응집구조의 회전 방향은 바람이 10 m/s 이하인 실험 조건에서는 파 내부의 입자 궤도 운동과 반대 방향인 반면, 바람의 세기가 약 13 m/s이고 파봉 근처에서 쇄파가 발생하는 경우에는 같은 방향이었다. 수면 근처에서는 응집구조의 진행에 따른 복잡한 소용돌이 상호 작용이 나타나는 반면, 수면으로부터 깊은 수심에서는 파 궤도 운동의 영향이 미미하여 응집구조의 시 공간적 변화가 거의 없었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.185-185
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• 2009

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. Using the flexural vibration mode of PZT bar, a piezopump is successfully made. The PZT bar is polarized with thickness direction. The proposed structure for the piezo-pump consists of an input and an output port, piezoelectric ceramic actuator, actuator support, diaphragm. The traveling flexural wave along the bar is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. Fluid is drawn into a forming chamber, eventually the forming chamber closes trapping the fluid therein. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump the highest pressure level of 83.4kHz.

• Journal of Astronomy and Space Sciences
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• 제9권1호
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• pp.69-88
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• 1992

전파 전파에 있어서 전리층의 영향은 산란, 감쇄, 각오차, 위치오차, 및 시간 지연등이다. 적당한 전리층 조건 아래서 하전입자는 전파로 부터 에너지르 뺏어 전파 감쇄의 원인이 되게 한다. 또한 전자밀도가 균일하지 않은 경로를 따라 전파가 전파되는 경우, 전파 방향, 위치, 전파 시간등에 변화가 생기게 된다. 본 논문에서는 1985년 1월 부터 1989년 10월까지 전파연구소에서 관측된 국내 전리층 관측자료를 토대로 Chapman법칙에 따른 전리층 모델을 정립 하였으며, 이로부터 전파 전파에 있어서 각 오차, 위치 오차, 시간 지연, 및 감쇄등을 주파수와 위성의 고도에 따라 고찰하여 보았다.

• 한국해양공학회지
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• 제21권1호
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• pp.1-6
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• 2007

While a typhoon is traveling, characteristics of its wind fields are continuously changing, producing severe changes in local water level and wave conditions, especially, when a typhoon comes into shallow water. However, there have not been many studies related to local typhoon effects, especially, considering real time changes of wind direction related to the coastal topography. In the study, the characteristics of the wind field by typhoon and topographical characteristics in shallow water are considered, as well as conditions of wave climate estimation. These are performed by the SWAN (Simulating waves nearshore) model, in order to estimate the growth of wave energy due to the wind field. It can be strongly suggested that the wave energy of theof an inner bay should be estimated when the direction of the bay entrance and the wind direction of the typhoon are identical. The result of the numerical calculations is in better agreement with the observed data than the result of the conventional estimation techniques.