• Title/Summary/Keyword: Reflection Coefficients

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BRAGG RESONANT REFLECTION OF OBLIQUELY INCIDENT WATER WAVES

  • Cho, Yong-Sik
    • Water Engineering Research
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    • v.1 no.1
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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.

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Chartacteristics of Water-bottom Reflection Coefficients in Bransfield Strait, Antarctic Peninsula (남극 브랜스필드 해협의 해저면 반사계수 특성)

  • Jin, Yeong Geun;Hong, Jong Guk;Lee, Deok Gi
    • Journal of the Korean Geophysical Society
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    • v.2 no.4
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    • pp.241-250
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    • 1999
  • Reflection coefficients of the seafloor have been calculated from the amplitude ratio of secondary to primary water bottom reflection in seismic data obtained from Bransfield Strait, Antarctic Peninsula. Test processing for the coefficients shows that moving average is effective to reduce severe fluctuation of the coefficient measured at each point. Relationship between the coefficients and the properties of water bottom is analyzed to illuminate geological environment. In the central Bransfield Basin, the magnitude of reflection coefficients decreases as it is distant from the sedimentary sources. Reflection coefficients range from 0.12 to 0.2 near the continental slope of the basin, and from 0.1 to 0.12 in the basin floor. In the western Bransfield basin, reflection coefficients between 0.2 to 0.3 are obtained from the area eroded by glacial movement. On the volcanic structures near Deception Island, the coefficients show relatively high values more than 0.2. Paleo-geological structures uplifted by tectonic movement and outcropped by glacial erosion have relatively high coefficients.

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The Relationship between Welding Conditions and Ultrasonic Reflection Coefficients of Dissimilar Metals Friction Welded Joints (이종재 막찰용접 이음부에서의 초음파 반사계수와 용접조건과의 관계)

  • 오세규;김동조;한상덕
    • Journal of Ocean Engineering and Technology
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    • v.1 no.1
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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.

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Reflection of plane waves from the boundary of a thermo-magneto-electroelastic solid half space

  • Singh, Baljeet;Singh, Aarti
    • Coupled systems mechanics
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    • v.10 no.2
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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.

Influence of Submerged Breakwater in front of Rubble Mound Breakwater (경사식 방파제의 전면에 설치된 수중방파제의 영향에 관한 연구)

  • Min, Hyun-Seong;Cho, Yong-Sik
    • 한국방재학회:학술대회논문집
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    • 2008.02a
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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.

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Experimental Analysis of Power Transmission and Reflection In a Coupled Plate (연성평판에서의 파워투과 및 반사 특성 실험 해석)

  • Lee, Y.H.;Kil, H.G.;Lee, H.H.;Lee, K.H.;Hong, S.Y.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11b
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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.

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Numerical study on the performance of semicircular and rectangular submerged breakwaters

  • Barzegar, Mohammad;Palaniappan, D.
    • Ocean Systems Engineering
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    • v.10 no.2
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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 KR, KT, KD. The latter coefficient KD emerges due to the non-energy conserving KR and KT. 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 KR are 5-15% higher while the diffusion coefficients KD are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients KT 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.

Analysis of Reflection Coefficients of Random Waves Propagating over Multi-arrayed trenchs (다열 함몰지형을 통과하는 불규칙 파랑의 반사해석)

  • Kang, Gyu-Young;Jung, Tae-Hwa;Cho, Yong-Sik
    • 한국방재학회:학술대회논문집
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    • 2008.02a
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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.

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Reflection and Transmission of Submerged Breakwater due to Wave Groups (파군특성에 따른 잠제의 반사와 투과)

  • 이철응
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.13 no.1
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    • pp.61-72
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    • 2001
  • The effects of wave groups on reflection and transmission over a submerged breakwater are studied by using a hydrodynamic numerical model and five independent wave grouping parameters. Based on qualitative analyses of limited data, it is found that the reflection and transmission coefficients of submerged breakwater may be strongly correlated with the incident wave groups. The reflection and transmission coefficients tend to decrease as wave groups become relatively larger. In particular, the reflection and transmission coefficients due to wave groups are evaluated smaller than those of single incident waves. However, the reflection and transmission coefficients are not affected by the interval of higher wave groups. It is finally concluded that the mean of nul-length among wave grouping parameters can be an useful parameter for correlating the wave groups with the reflection and transmission coefficients of submerged breakwater.

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Design of Lossy Interstage Network for Microwave Amplifiers Considering Gain and Reflection Coefficients (이득과 반사계수를 고려한 마이크로파 증폭기용 유손실 중간단 정합회로 설계)

  • 구경헌;이충웅
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.26 no.12
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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.

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