• 대한기계학회논문집B
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• 제22권7호
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• pp.992-1000
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• 1998

In the present study the behavior of laminar-wavy film flowing down a vertical plate was studied analytically. The effects of film Reynolds number and interfacial shear stress on the mean film thickness, wave amplitude, wave length, and wave celerity were analysed. The anayltical results on the periodic-wave falling film showed good agreements with experimental data for Re < 100. As the film Reynolds number increased, mean film thickness, wave amplitude, and wave celerity increased, but wave length decreased. Depending on the direction of interfacial shear stress, the shape of wavy interface was disturbed significantly, especially for the intermediate-wave. As the interfacial shear stress increased, for the periodic-wave film, wave amplitude and wave celerity increased, but mean film thickness and wave length decreased.

• 비파괴검사학회지
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• 제30권6호
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• pp.578-586
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• 2010

This paper describes a theoretical model and acoustic analysis of hysteresis of contacting surfaces subject to compression pressure. Contacting surfaces known to be nonlinear and hysteretic is considered as a simple spring that has a complex stiffness connecting discontinuous displacements between two solid contact boundaries. Mathematical formulation for 1-D interfacial wave propagation between two contacting solids is developed using the complex spring model to derive the dispersion relation between the interface wave speed and the complex interfacial stiffness. Existence of the interface wave propagating along the hysteretic interface is studied in theory and discussed by investigating the solution to the dispersion equation. Unlike the linear interface without hysteresis, there can exist only one distinct mode of interface waves for the hysteretic interface, which is anti-symmetric motion. The anti-symmetric mode of interface wave propagates with the velocity faster than the Rayleigh surface wave but less than the shear wave depending on the interfacial stiffness. If the contacting surfaces are compressed so much that the linear interfacial stiffness is very high, the hysteretic stiffness does not affect the interface wave velocity. However, it has an effect on the speed of interface wave for a loosely contact surfaces with a relatively low linear stiffness. It is also found that the phase velocity of anti-symmetric wave mode converges to the shear wave velocity in despite of the linear stiffness value if the hysteretic stiffness approaches 0.5.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.115-119
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• 2009

We numerically investigated propagation of various waves in the two-phase flows such as sound wave, shock wave, rarefaction wave, and contact discontinuity in terms of pressure, void fraction, velocity and density of the two phases. The waves have been generated by a hydrodynamic shock tube, a pair of symmetric impulsive expansion, impulsive pressure and impulsive void waves. The six compressible two-fluid two-phase conservation laws with interfacial friction terms have been solved in two fractional steps. The first PDE Operator is solved by the HLL scheme and the second Source Operator by the semi-implicit stiff ODE solver. In the HLL scheme, the fastest wave speeds were estimated by the analytic eigenvalues of an approximate Jacobian matrix. We have discussed how the interfacial friction terms affect the wave structures in the numerical solution.

• 비파괴검사학회지
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• 제33권3호
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• 한국염색가공학회지
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• 제10권2호
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• pp.8-17
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• 1998

In this study we have examined electroless chemical plating on the plasma grafted poly [ethylene terephathalate］(PET) fabric in order to improve the interfacial adhesion between metal and fiber. The vapour phase of acrylic acid introduced on the PET surface and the graft polymerization was carried out by using cold plasma, resulting in the grafting yield of 0.8-1.3 wt％. The carboxyl group of the plasma grafted was identified by FT-IR-ATR spectra. The Interfacial adhesion was related to the carboxyl group. After electroless chemical plating of nickel, it showed that the more the carboxyl, the better the interfacial adhesion. Comparing to the untreated, the plasma grafted fabric showed fairly good interfacial adhesion(5B grade, ASTM D3359) . The shielding effect of electromagnetic wave showed 95dB. The shielding effect depends on the fabric structure, the surface structure, and the cross sectional shape of fibers. The dense fabric structure, the etched surface like a microcrater, and the trigonal cross sectional shape were prefered.

• 대한조선학회논문집
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• 제47권3호
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• pp.359-368
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• 2010

This paper describes the generation and propagation of internal solitary wave in a two-layer fluid system by numerical analysis. Characteristics of interfacial soliton such as wave type, wave height, wave celerity are investigated numerically with respect to an extent of initial disturbance, fluid thicknesses of the two fluids and etc. The difference between the internal wave propagation on sloping beach and flat bottom was also examined. Laboratory experiments were conducted in the wave flume and compared with the results of numerical computation for verification.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 추계학술발표회논문집(1)
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• pp.481-486
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• 1997

The interfacial shear stress is experimentally investigated for co-current air-water stratified flow in inclined rectangular channels having a length of 1854mm, width of 120mm and height of 40mm at almost atmospheric pressure. Experiments are carried out in several inclinations from $0^{\circ}\;up\;to\;10^{\circ}$. The local film thickness and the wave height are measured at three locations, i.e., L/H = 8,23, and 40. According to the inclination angle, the experimental data are categorized into two groups; nearly horizontal data group ($0^{\circ}\;{\leq}\;{\theta}\;{\leq}\;0.7^{\circ}$), and inclined channel data group ($0.7^{\circ}\;{\leq}\;{\theta}\;{\leq}\;10^{\circ}$). Experimental observations for nearly horizontal data group show that the flow is not fully developed due to the water level gradient and the hydraulic jump within the channel. For the inclined channel data group, a dimensionless wave height, $\Delta$h/h, is empirically correlated in terms of $Re_{G}$ and h/H. A modified root-mean-square wave height is proposed to consider the effects of the interfacial and wave propagation velocities. It is found that an equivalent roughness has a linear relationship with the modified root-mean-square wave height and its relationship is independent of the inclination.

• Nuclear Engineering and Technology
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• 제28권4호
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• pp.379-389
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• 1996

To experimentally investigate the several wave patterns for the horizontal countercurrent stratified air-water flow, a series of systematic experimental studies have been performed. The experiments are carried out in a horizontal pipe with 4m in length and 102mm in inner diameter. The oater and air superficial velocities vary from 0.0004 to 0.0204 and from 0 to 6m/s, respectively. The instantaneous water thickness is measured by parallel-wire conductance probes, and the wave field is recorded by high speed video camera. Also, to evaluate the wave effect on interfacial friction factor, the pressure drop is measured. Statistical data anal)sis is accomplished in order to obtain the fundamental wave parameters such as un amplitude, length and velocity, and spatial growth factor. By using these statistical parameters, the wave regime boundaries can be verified.

• 대한기계학회논문집
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• 제12권1호
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• pp.116-122
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• 1988

본 연구에서는 공기와 물을 매질로 사용하여 3차원 계면파가 존재하는 근사수평 반류성층유동에서의 계면전단응력과 마찰계수를 결정하였다. 기상과 액상의 유량조건에 따라 3차원 계면파의 특성을 needle contact법에 의하여 측정 하였으며, 기상의 압력강하와 속도분포를 구하여 계면전단응력을 구하였다. 또 공학적인 응용을 위하여 3차원과 영역에서의 계면마찰계수에 관한 실험식을 개발하였다. 그리고 거칠은 고체표면에서의 마찰계수를 표현한 Nikuradse식을 이용하여 계면의 등가조도(equivalent roughness)를 계산하였으며 이것을 계면의 파고교란강도와 비교분석하여 계면전단응력에 영향을 미치는 인자들을 규명하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2005-2011
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• 2003

Introducing the interfacial pressure jump terms based on the surface tension into the momentum equations of two-phase two-fluid model, the system of governing equations is turned mathematically into the hyperbolic system. The eigenvalues of the equation system become always real representing the void wave and the pressure wave propagation speeds as shown in the previous manuscript. To solve the interfacial pressure jump terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified as an intermediate iteration method for void fraction at fractional time step. This advanced semi-implicit method (ASIM) then becomes stable without conventional additive terms. As a consequence, including the interfacial pressure jump terms with the advanced semi-implicit method, the numerical solutions of typical two-phase problems can be more stable and sound than those calculated exclusively by using any other terms like virtual mass, or artificial viscosity.