• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.299-307
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• 1991

A unified correlation of the interfacial friction factor for air-water and steam-water flows in inclined rectangular channels has been developed. The correlation was expressed in the form of a power law of the liquid and the gas Reynolds number, and the liquid-to-gas viscosity ratio. In addition, a relation between the equivalent roughness and the intensity of wave height fluctuation of the interface has been investigated. A new dimensionless intensity of fluctuation including a liquid film Reynolds number is proposed. It has been shown that the dimensionless equivalent roughness, which is calculated from the Nikuradse equation, can be uniquely related to this dimensionless intensity of fluctuation for both air-water and steam-water flows.

• Journal of Navigation and Port Research
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• v.28 no.7
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• pp.619-627
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• 2004

Introduction of wave model, considered the effect of shoaling, refraction, diffraction, partial reflection, bottom friction, breaking at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster prevention problems. As waves move from deeper waters to shallow coastal waters, the fundamental wave parameters will change and the wave energy is redistributed along wave crests due to the depth variation, the presence of islands, coastal protection structures, irregularities of the enclosing shore boundaries, and other geological features. Moreover, waves undergo severe change inside the surf zone where wave breaking occurs and in the regions where reflected waves from coastline and structural boundaries interact with the incident waves. Therefore, the application of mild-slope equation model in this field would help for understanding of wave transformation mechanism where many other models could not deal with up to now. The purpose of this study is to form a extended mild-slope equation wave model and make comparison and analysis on variation of harbor responses in the vicinities of Ulsan Harbor and Ulsan New Port, etc. due to construction of New Port in Ulsan Bay. We also considered the increase of water depth at the entrance channel by dredging work up to 15 meters depth in order to see the dredging effect. Among several model analyses, the nonlinear and breaking wave conditions are showed the most applicable results. This type of trial might be a milestone for port development in macro scale, where the induced impact analysis in the existing port due to the development could be easily neglected.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.08a
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• pp.217-225
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• 2004

Introduction of wave model, considered the effect of shoaling, refraction, diffraction, partial reflection, bottom friction, breaking at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster prevention problems. As waves move from deeper waters to shallow coastal waters, the fundamental wave parameters will change and the wave energy is redistributed along wave crests due to the depth variation, the presence of islands, coastal protection structures, irregularities of the enclosing shore boundaries, and other geological features. Moreover, waves undergo severe change inside the surf zone where wave breaking occurs and in the regions where reflected waves from coastline and structural boundaries interact with the incident waves. Therefore, the application of mild-slope equation model in this field would help for understanding of wave transformation mechanism where many other models could not deal with up to now. The purpose of this study is to form a extended mild-slope equation wave model and make comparison and analysis on variation of harbor responses in the vicinities of Ulsan Harbor and Ulsan New Port, etc. due to construction of New Port in Ulsan Bay. This type of trial might be a milestone for port development in macro scale, where the induced impact analysis in the existing port due to the development could be easily neglected.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.5
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• pp.383-392
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• 2011

The basic research of the estuarine circulation at Gyeong-Gi bay has not been well studied up to now, although coastal development pressures have been continuously increased. To understand the oceanographic phenomena at the Han River estuary, it's essential to understand the propagation characteristic of tidal wave which is the strongest external forcing in this region. In this study, we investigate the tidal wave propagation characteristics along the 3 major channels using observation data and numerical model. It is found that 3 channels are all hyper-synchronous and the most important physical factor controlling the tidal wave propagation is topographical convergence of estuary shape and friction. The result of analytic solution at ideal channel considering the topographical convergence and friction show that the contribution of physical role of convergence and friction varies at 3 different channel. And the ratio of convergence and friction at Yeomha channel is four times larger than Seokmo channel. Because of this effect, the location of maximum amplitude at Yeomha channel is showed up downward than Seokmo channel. The ratio of decreasing amplitude and increasing phase per unit distance between stations is bigger than Seokmo channel. Although 3 major channel show a hyper-synchronous pattern, Yeomha shows more frictionally dominant channel and Seokmo channel is more dominantly affected by convergence effect.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.177-188
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• 2001

The paper presents the method to estimate the bottom shear stress driven by waves and current on rough turbulent flow. Parameter adjusting technique is suggested for the computation of bed shear stress driven by uni-directional flow, and the value ofpararneter is determined by comparing the computational results against Bijker's laboratory data. For the computation of combined flow bottom shear stress, two methods are presented; one is the modified Bijker approach (BYO Model) and the other is the modified Fredsoe approach (FY Model), both of which are refined by the present writers. BYO model is again refined in the computation of maximum shear stress, and the final version is tested against Bijkcr's laboratory data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.212-220
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• 1993

A numerical model for the transformation of irregular waves in a coastal area is developed, which takes account of shoaling, refraction, diffraction, bottom friction and wave breaking. The governing equations are the usual energy conservation equation and kinematic conservation equations, but to consider the diffraction effects additional terms are included in the usual kinematic conservation or wave number equations. A linear superposition technique is used to represent the spectral formation. and an explicit formula is developed for the estimation of friction factor of irregular waves. A breaking criterion of component waves, which is the modified form of the Kitaigorodskii saturation relation, is employed to restrict the growth of shoaling waves in very shallow waters. The model was applied to a laboratory test and satisfactory agreement was obtained between the computation and measurement.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.3
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• pp.100-107
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• 2008

The heat transfer and friction characteristics of heat exchangers having convex louver fins are experimentally investigated, and the results are compared with those of wave fin counterparts. Eighteen samples (nine convex louver fin samples and nine wave fin samples) which had different fm pitches (1.81 mm to 2.54 mm) and tube rows (one to four) were tested. The convex angle was $11.7^{\circ}$. The j factors are insensitive to fin pitch, while f factors increase as fin pitch increases. The effect of fin pitch on f factor is more significant for the wave fin compared with the convex louver fin. It appears that the complex fin pattern of the convex louver fin induces intense mixing of the flow, and thus reduces the effect of fin pitch. Both the j and f factors decrease as the number of tube row increases. However, as the Reynolds number increases, the effect of tube row diminishes. Comparison of the convex louver fin j factors with those of wave fin reveals that convex louver fin j factors are 18% to 29% higher than those of wave fin. The f factors are 16% to 34% higher for the convex louver fin. The difference increases as fin pitch decreases. Existing correlation fails to adequately predict the present data. More data is needed for a general correlation of the convex louver fin geometry.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.186-195
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• 2001

The purpose of this study is to develop the time-dependent, one-dimensional numerical model on the interaction between irregular waves and two-layer permeable coastal structures, by extending and modifying the numerical model PBREAK(Wurjanto and Kobayashi, 1992) which is applicable only to one-layer permeable coastal structures. The two-layer permeable coastal structure consists of two permeable underlayers with different permeable media resting on an impermeable slope and an armor layer covering the permeable underlayer. The numerical model of this study simulates the wave over rough permeable underlayer of arbitrary geometry as well as the waves inside two-permeable underlayers of arbitrary thickness for specified normally-incident irregular waves. The utility of the numerical model is founded from comparing with PBREAK and the four hydraulic model tests under irregular waves. The sensitivities of computed results according to typical parameters(porosity, stone diameter, horizontal width of the permeable underlayer) and major factors(friction factor of primary armor layer etc.) discussed.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.141-147
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• 2011

A two-phase numerical model for plate-fin heat exchangers with plain fins and wave fins is studied incorporating the thermodynamic properties and the characteristics of fluid flow. The numerical simulations for the two fins in cryogenic conditions are earned out by employing a homogenous two-phase flow model with the CFD code ANSYS CFX. The heat transfer coefficients and the friction factor for nitrogen saturated vapor condensation process inside two types of plate fin heat exchanger are evaluated including the effects of saturation temperature (pressure), mass flow rate and inlet vapor quantity. The convective heat transfer coefficients and friction factors will be used for design of plate-fin type heat exchangers operating under cryogenic conditions.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.2
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• pp.29-38
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• 2000

Air side heat transfer and pressure drop for f 9.52 fin-tube heat exchanger with various types of slit and louver fins were measured, and compared with wave-slit fin. Longitudinal and transverse tube spacings of the heat exchangers are 21.65 mm and 25mm respectively. Actual heat exchanger was tested using water, and the tests were performed for 2 row heat exchangers with 3 different fin spacings, 1.3, 1.5 and 1.7 mm. The overall performance of the enhanced fins was evaluated by comparing heat transfer coefficient with respect to fan power