• Water Engineering Research
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• 제1권1호
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• pp.75-81
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• 2000

The bragg reflection of obliquely incident monochromatic water waves propagating over a sinusoidally varying topography is theoretically investigated in this study. The eigenfunction expansion method is first employed to calculate reflection coefficients of water waves due to depth changes. A reasonable agreement is observed. Obtained reflection coefficients of normally incident waves are compared with laboratory measurements. Reflection coefficients of obliquely incident waves are then calculated. The wavenumber providing the Bragg reflection agrees well with analytical predictions.

• 지구물리
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• 제2권4호
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• pp.241-250
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• 1999

남극 브랜스필드 해협에서 획득한 탄성파 자료로부터 다중반사파와 해저면 반사파의 진폭비를 이용하여 해저면 반사계수를 구하였다. 시험 자료처리 결과에 의하면 측점에 따른 심한 변동오차를 감소시키기 위하여 이동평균이 효과적임을 보여준다. 계산된 해저면 반사계수와 해저면 물성에 반영된 지질환경과의 관련성을 분석하였다. 중부 브랜스필드분지 지역에서는 퇴적물의 공급원으로부터의 거리가 멀수록 반사계수가 감소하는 변화양상이 우세하여, 사면 근처에서는 0.12∼0.2 사이, 분지의 중심에서는 0.1∼0.12 사이의 반사계수를 나타낸다. 서부 브랜스필드분지에서 지역적으로 나타나는 빙하침식 지형에서는 반사계수가 0.2∼0.3의 범위 내에서 변하였으며, 확장중심의 화산분출물이 노출된 지역은 0.2 이상의 큰 반사계수를 나타냈다. 또한 지체구조운동에 의해 상승작용을 받은 고지층들이 후기의 빙하침식작용에 의해 해저면에 드러난 지역에서는 해저면 반사계수가 비교적 크게 나타났다.

• 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.

• Coupled systems mechanics
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• 제10권2호
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• pp.143-159
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• 2021

The theory of generalized thermo-magneto-electroelasticity is employed to obtain the plane wave solutions in an unbounded, homogeneous and transversely isotropic medium. Reflection phenomena of plane waves is considered at a stress free and thermally insulated surface. For incidence of a plane wave, the expressions of reflection coefficients and energy ratios for reflected waves are derived. To explore the characteristics of reflection coefficients and energy ratios, a quantitative example is set up. The half-space of the thermo-magneto-electroelastic medium is assumed to be made out of lithium niobate. The dependence of reflection coefficients and energy ratios on the angle of incidence is illustrated graphically for different values of electric, magnetic and thermal parameters.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.217-220
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• 2008

The reflection coefficients and the run-up heights affected by submerged structures are studied by using the numerical and the laboratory experimental methods. The three-point method is chosen to calculate the reflection coefficients in both the experimental and the numerical methods. The results of numerical simulations are shown a good agreement with laboratory measurements. The reflection coefficients increase and the run-up heights decrease when the rubble mound breakwater is defended by low-crested structures.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
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• pp.170-173
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• 2005

The objective of this paper is to perform measurements of power transmission and reflection coefficients in a coupled plate. The coupled plate has been divided into 2 subsystems. The out-of-plane vibration has been only considered with assumption of relatively small in-plane vibration. The coupling loss factors have been measured with consideration of the power balance condition. The power transmission and reflection coefficients has been estimated from the measured values of the coupling loss factors. The measured power transmission and reflection coefficients have been compared with the corresponding theoretical coefficients in a semi-infinite coupled plate.

• Ocean Systems Engineering
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• 제10권2호
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• pp.201-226
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• 2020

A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. un the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.

• 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.

• 한국해안해양공학회지
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• 제13권1호
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• pp.61-72
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• 2001

천해영역에서 적용 가능한 동수역학적 수치모형을 이용하여 규칙 입사파군이 수직으로 입사할 때 잠제에 의하여 발생되는 반사와 투과의 거동 특성을 해석하였다. 여러 입사파군 조건에서 계산된 잠제의 반사율과 투과율이 파군의 발달정도를 해석하기 위하여 제시된 변수들의 함수로 표시되었다. 입사파군과 잠제의 반사율 및 투과율의 관계를 정성적으로 해석한 결과, 고파군이 발달될수록 잠제에 의하여 발생되는 입사파랑의 반사율과 투과율의 크기가 감소하는 것으로 나타났다. 특히 파군으로 입사하는 경우의 반사율과 투과율이 단일 파랑으로 입사하는 경우의 반사율과 투과율에 비하여 상대적으로 작게 나타났다. 그러나 고파군과 고파군의 간격에 따른 반사율과 투과율의 차이는 크지 않은 것으로 나타났다. 비록 제한적이지만 본 연구에서 해석된 결과에 의하면 파랑 연이음의 평균을 이용할 때 입사파군과 잠제의 반사율 및 투과율의 관계가 가장 잘 해석될 수 있다.

• 대한전자공학회논문지
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• 제26권12호
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• pp.1940-1946
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• 1989

A design method of lossy interstage networks for broadband microwave amplifiers is presented. A lossy interstage network is assumed as the combination of two lossless networks between which a lossy serial impedance or a lossy parallel admittance is inserted. For the circuit with two transistors and a lossy element, realizable ranges of gain and reflection coefficients are derived. And the relationships between gain and reflection coefficients are derived. Illustrative examples are presented by using the proposed method.