• 한국수자원학회논문집
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• 제36권3호
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• pp.447-454
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• 2003

본 연구에서는 유한요소법을 이용하여 일정 수심상에서 사각형 형상의 불투과성 수중방파제에 의한 파랑의 Bragg 반사를 수치적으로 고찰하였다. 유한요소법에 의해 계산된 반사율은 수리모형실험을 통해 얻어진 결과와 비교하였을 때 비교적 잘 일치하였으며, 고유함수전개법에 의한 결과와도 좋은 일치를 나타내었다. 그밖에 본 연구에서 개발된 모형은 불투과성 수중방파제의 폭과 길이의 변화에 따른 반사율 계산에 적용되었다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1754-1762
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• 2016

Finite difference analysis were applied to study the principle operation of monopole antenna for moisture determination in oil palm fruit at 2 GHz. The electromagnetic field interact with oil palm fruit on the interface between the antenna and oil palm fruit and cause a reflection. The reflection measurement is based on mismatch impedance or dielectric properties between two media. Reflection coefficient is used to quantify the level of reflection. The monopole antenna was made of RG405/U semi-rigid coaxial cable with an inner and outer diameter of 0.45 mm and 1.50 mm, respectively with 2.23 mm length of protruding conductor over 5.66 cm length of monopole antenna. This monopole antenna for moisture detection was compared with induced EMF method in terms of reflection coefficient at 2 GHz. The results show that the complex reflection coefficient measured using monopole antenna provides significant results to predict moisture content in oil palm fruit.

• 한국수자원학회논문집
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• 제37권9호
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• pp.729-736
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• 2004

본 연구에서는 사각형 형상 불투과성 수중방파제를 통과하는 불규칙파의 반사를 고유함수전개법을 이용하여 해석하였으며, 수리모형실험 결과와 비교하였다. 불규칙파는 다수의 규칙파의 중첩으로 구성하였으며, 각각의 규칙파의 해석결과를 합성하여 반사율을 산정하였다. 고유함수전개법에 의한 해석결과는 수리모형실험에 의한 결과와 잘 일치하였으며, 불규칙파 역시 Bragg 반사 조건에서 공명현상에 의해 반사율이 크게 증폭되었다.

• 한국수자원학회논문집
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• 제35권6호
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• pp.677-684
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• 2002

본 연구에서는 유한요소법을 이용하여 수심의 변화에 의해 발생되는 파랑의 회절에 대해 수치적 모의실험을 수행하였다. 본 모형은 정현파형 지형을 통과하는 단조파의 반사율을 계산하는데 적용되었다. 계산된 반사율은 고유 함수전개법에 의한 결과와 수리모형실험에 의한 관측결과와 비교하여 본 해석법을 검증하였으며, 이로부터 정현파형 지형의 진폭과 사련의 수의 변화에 대한 반사율의 변화에 적용하여 그의 특성을 조사하였다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.213-216
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• 2008

In this study, reflection coefficients of regular and random waves propagating over multi-arrayed trenchs are calculated respectively. When the row of trench is 3, the reflection coefficient of regular waves is more than 0.7 as maximum value. Similarly, when the row of trench is 3 and $d/L_1$ is 0.22, reflection coefficient of multi-directional random waves is more than 0.4 maximally.

• 대한기계학회논문집A
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• 제24권1호
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• pp.173-181
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• 2000

Depending upon the method of the surface generation and the quality of the boundary curves provided, the resulting surfaces may have global or local irregularities in many cases. Thus it would be necessary for the designer to evaluate the surface quality and to modify the surface. This capability is very important because the defect of the surface requires the rework of the dies that causes a big loss in cost and delivery time. To simulate the reflection line test in the actual production line, a faster generation algorithm is presented. Among., various surface interrogation methods using reflection lines, Blinn-Newell type of reflection mapping is applied to generate reflection lines on the trimmed NURBS surface. The generation of reflection lines is formulated as a surface-plane intersection problem, and solved by surface-contouring techniques. In addition, a modified reflection map is proposed to eliminate the discontinuity of reflection lines due to the configuration of the reflection map. A fast reflection line algorithm is developed utilizing an efficient traced contouring technique, and proved to be well suited for real-time quality-assessment task.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.819-827
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• 2019

Bragg reflection of water waves by three kinds of surface-piercing fixed structures with rectangular, cosinoidal and triangular shapes is studied. Boundary element method is used to analyze the wave scattering by these structures based on the linear wave theory. Results of reflection and transmission coefficients are validated by comparing with those available in literature. These structures with proper configurations are proved to be effective in attenuating waves by using Bragg reflection, and the triangular structures are found to be the best choices among the structures with same width and same area. Systematic calculations are then carried out for the triangular structures by varying the number, the draft, the width, the gap and the combination of width and gap of the structures to analyze their influences on the characteristics of Bragg reflection. The results are of reference values for design of the structures to attenuate waves based on the Bragg reflection.

• 조명전기설비학회논문지
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• 제27권12호
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• pp.38-43
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• 2013

In this paper, the location measurement method for the reliable location data using ultrasonic sensors is proposed for the dimming control of the LED flat lamp. The measurement errors depending on the reflection angle of the object have to be considered to obtain the reliable location data in the ultrasonic sensors. In the experiment, the cause of the measurement errors depending on reflection angle is analyzed and velocity change of ultrasonic wave depending on reflection angle is measured. And the location measurement method depending on velocity change of ultrasonic wave is proposed. From the results, the average absolute deviation of the x-coordinates was 1.47cm when the location measurement method was considered, and it was closer to the true values than the average absolute deviation of the x-coordinates which was 5.89cm without regard to the reflection angle.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.221-228
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• 2002

Thickness of concrete lining, voids at the back of lining or shotcrete are very important elements for inspecting the safety of tunnels. Therefore, the inspection of tunnel lining structure means to investigate the inner layer boundaries of the structure. For this purpose, seismic reflection survey is the most desirable method if it works in good conditions. However, the conventional seismic reflection method can not be properly used for investigating thin layers in the lining structure. In other words, to detect the inner boundaries, it is desirable for the wavelength of source to be less than the thickness of each layer and for the receiver to be capable of detecting high frequency(ultrasonic) signals. To this end, new appropriate source and receiver devices should be developed above all for the ultrasonic reflection survey. This paper deals primarily with the development of source and receiver devices which are essential parts of field measuring system. Interests are above all centered in both the radiation pattern, energy, frequency content of the source and the directional sensitivity of the receiver. With these newly devised ones, ultrasonic physical modeling has been performed on 3-D physical model composed of bakelite, water-proof and concrete, The measured seismograms showed a clear separation of wave arrivals reflected from each layer boundary. Furthermore, it is noteworthy that reflection events from the bottom of concrete below water-proof could be also observed. This result demonstrates the usefulness of the both devices that can be applied to benefit the ultrasonic reflection survey. Future research is being focus on dealing with at first an optimal configuration of source and receiver devices well coupled to tunnel wall, and further an efficient data control system of practical use.

• 한국해양공학회지
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• 제1권1호
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• pp.138-143
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• 1987

Friction welding has emerged as a reliable process for high-production commercial applications with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristcs of the pulse echo effects according to various change in welding conditions. This paper presents an attempt to determine the relationship between the varios welding conditions and the coefficients of reflection using the ultrasonic pulse echo method in dissibilar metals friction weld. The new approach of calculating the coefficients of reflection based on measured amplitudes of the echoes is applied in this paper. These coefficients provides a single quantitative measurement which involves both acoustic energy reflected at the welded interface as well as transmitted across the interface. As a result, it was known that the quantitave relationship between welding conditions and the coefficients of reflection using the ultrasonic pulse echo exists in dissimilar metals friction weld.