• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.291-300
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• 2000

This paper proposes the new hybrid analysis of vibration in the medium to high frequency ranges including PFA and SEA concept. The core part of this method is the applications of coupling loss factor(CLF) instead of power transmission, reflection coefficients in boundary condition. This method shows very promising compared to the classical PFA for the various damping loss factors and wide ranges of frequencies. Besides this paper presents the applicable method in Power Flow Finite Element Method by forming the joint element matrix with CLF. These hybrid concepts are expected to improve SEA and PFA methods in vibration analysis.

• Bulletin of the Korean Chemical Society
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• 제19권7호
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• pp.738-742
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• 1998

A new polyamide was prepared from 4,4'-(hexafluoroisopropylidene)di-aniline and 4-[NN-bis(2-carboxyethyl)] amino-4'-nitrostilbene. This polymer was cast into thin films by spin coating cyclohexanone solution. After being poled, the electro-optic coefficients of electrode poled polymer films were measured by the reflection measurement technique using an incident laser beam of 1.3 Jim. The film poled at the field strength of 1.2 V/μm exhibited the electro-optic coefficient (r33) of 5.9 pm/V. The relaxation behavior of the poled polymer film was compared with other reported polymers bearing the same NLO chromophores. Due to stiff and highly polar nature of the backbone and also due to formation of interchain hydrogen bonds, this polymer reveals a slower relaxation characteristics. The polymer is amorphous and soluble in various organic solvents.

• Journal of Ship and Ocean Technology
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• 제7권1호
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• pp.13-18
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• 2003

The control performances for active re-reflecting wave control suggested in the previous paper have been verified in cases of regular and irregular waves in a real two dimensional wave basin. For regular waves, the control performances are investigated in terms of reflection coefficients, expected amplitudes of propagating waves and wave absorbing capabilities after cessation of wave generation, compared with those of no-control cases. For irregular waves similar verification procedures were adopted. Though there are certain constraints due to the geometrical non-linearity of wave maker and certain nonlinear characteristics due to the near field and gravity waves these experiments show that the control logic could be useful in realizing re-reflecting wave control in conditions of real wave basin.

• Journal of the Optical Society of Korea
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• 제15권1호
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• pp.4-8
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• 2011

We have evaluated the performances of bidirectional optical amplifiers which were suited for the cost-effective implementation of amplified bidirectional passive optical networks (PONs). First, we measured the maximum gains of two simple bidirectional optical amplifiers implemented without using any optical components for the suppression of reflected signals. From the results, the maximum gains of two simple bidirectional amplifiers with a broadband light source (BLS) seeded optical source were limited to be 27 dB due to the reflection-induced in-band crosstalk, when the reflectance coefficients were measured to be -33 dB in both directions. Then, we have also implemented a bidirectional optical amplifier with two band splitters for the amplified bidirectional PON where the two different wavelength bands were allocated to the downstream and upstream signals transmission. In our measurement, we confirmed that the maximum gain of bidirectional optical amplifier with two band splitters could be increased to more than 30 dB owing to the efficient suppression of in-band crosstalk.

• 한국해양공학회지
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• 제33권1호
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• pp.61-67
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• 2019

Recently, a perforated caisson breakwater with turning wave blocks was developed to improve the water affinity and public safety of a rubble mound armored by TTP. In this study, hydraulic model tests were performed to examine the hydraulic performance of a non-porous caisson and new caisson breakwater with perforated blocks for attacking waves in a small fishery harbor near Busan. The model test results showed that the new caisson was more effective in dissipating the wave energy under normal wave conditions and in reducing the wave overtopping rates under design wave conditions than the non-porous caisson. It was found that the horizontal wave forces acting on the perforated caisson were slightly larger than those on the non-porous caisson because of the impulsive forces on the caisson with the turning wave blocks.

• 센서학회지
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• 제27권6호
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• pp.374-379
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• 2018

The piezocomposite transducer is widely used because it is highly efficient in transforming electric energy into mechanical energy, and its frequency range is broader than that of other types of ultrasound transducers. A general piezocomposite transducer is composed of an acoustic lens, impedance matching layers, piezoelectric materials, and backing layers. When an input voltage is applied to a piezoelectric material as an active material, it generates sound waves while vibrating. At that time, an impedance matching layer helps the sound waves to propagate forward while reducing the impedance mismatch that may occur at the interface between the active material and its front material. The impedance mismatch has a negative effect on the signal of an ultrasound transducer; thus, it is important to design a matching layer to overcome the issue. In this study, an optimized feature of a matching layer with gradient properties is studied. An objective function is defined to minimize both the average and the deviation of the reflection coefficients that are functions of the frequencies. As a result, an improvement in the signal characteristics with respect to the sensitivity and bandwidth is reported.

• Advances in materials Research
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• 제9권4호
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• pp.289-309
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• 2020

The aim of the present investigation is to examine the propagation of plane harmonic waves in transversely isotropic homogeneous magneto visco thermoelastic rotating medium with fractional order heat transfer and two temperature. It is found that, for two dimensional assumed model, there exist three types of coupled longitudinal waves (quasi-longitudinal, quasi-transverse and quasi-thermal) in frequency domain. phase velocities, specific loss, penetration depth, attenuation coefficients of various reflected waves are computed and depicted graphically. The effects of viscosity and fractional order parameter by varying different values are represented graphically.

• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 1997년도 정기학술강연회 발표논문 초록집 Annual Meeting of Korean Society of Coastal and Ocean Engineers
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• pp.135-138
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• 1997

The interaction of oblique monochromatic incident waves with a horizontal flexible membrane is investigated in the context of two-dimensional linear hydro-elastic theory. First, analytic diffraction and radiation solutions for a submerged impermeable horizontal membrane are obtained. Second, the theoretical prediction was compared with a series of experiments conducted in a two-dimensional wave tank at Texas A&M University. The measured reflection and transmission coefficients reasonably follow the trend of predicted values. Using the developed computer program, the performance of surface-mounted or submerged horizontal membrane wave barriers is tested with various system parameters and wave characteristics. It is found that the properly designed horizontal flexible membrane can be an effective wave barrier and its efficiency can be further improved using a porous material.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1993년도 학술논문발표회 논문집 제12권 1호
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• pp.190-194
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• 1993

In the ocean bubble layers play a significant role in the sound propagation as well as sound generation. Most of early works dealt with acoustic properties of the bubble layers with sharp flat boundaries. Bubble layers with sharp flat boundaries. Bubble layers with transition sublayers are more likely in the coean. In this paper a theory of sound propagation through plane bubble layers with transition sublayers at both borders was developed. It shows that the reflection and transmission coefficients depend on the thickness of transition sublayers. The theory with thicker transition sublayers shows weaker resonance properties of bubble layer. It gives better presentation for the peculiar behavior of the experimental data than that with sharp flat boundaries.

• 한국항만학회지
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• 제10권1호
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• pp.15-23
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• 1996

In this paper, the numerical model to analyze the wave absorbing performance of upright perforated plates is developed under the linear potential theory. If the drag force is dominent to the inertia force in passing perforated plate, the characteristics of perforated plates are determined by a nondimensionlized real-value of G or a length scaled real-value of a. The parameters (G,a), which depend on the drag coefficient, porosity and local shape of plates, can be readily obtained by simple experiments. We investigated the reflection coefficients over a wide frequency range according to the arrays of perforated plates with different values of G and a. We found that the wave absorbing system using the arrays of upright perforated plates is sufficient to install in the ocean engineering basin.