• Journal of Korean Society of Water and Wastewater
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• v.21 no.3
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• pp.287-294
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• 2007

When we use the circular pipes for wastewater and storm water, we should be known the characteristics of the flow for accurate design. To elevate the design accuracy, we want to know the profile of flow. The roughness coefficient in the Manning equation is constant, but in actuality changed with the relative depth in circular pipe. This study was conducted to calculate the relative normal depth in changing the roughness coefficient (named relative roughness coefficient) with the relative depth in the analysis of gradually varied flow in the circular pipe by Newton-Raphson method. We performed the analysis of gradually varied flow using the relative normal depth and the relative roughness coefficient. We presented the 12 flow profiles with the relative depth and the relative roughness coefficient in circular pipe. The flow classification considering relative depth in circular pipe is available to analyse gradually varied flow profiles.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.3
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• pp.228-234
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• 2012

Two-dimensional hydraulic experiments for wave overtopping under non-breaking wave condition are conducted. The wave overtopping formula for vertical structure is suggested and the results are compared with EurOtop (2007). The relative water depth coefficient (${\gamma}_{kh}$) shows that almost the same coefficient is obtained for certain range (kh > 1.55) regardless of relative water depth, that is, although the relative water depth becomes larger, the relative water depth coefficient is almost same. When the wave steepness becomes larger the wave steepness coefficient decreases. The overtopping formula are expressed by relative freeboard(R) and non-dimensional wave overtopping rate(Q) and this formula has the form of exponential function. In this formula, the effects of wave period on wave overtopping are quantitatively investigated and suggested through the relative water depth coefficient(${\gamma}_{kh}$) and wave steepness coefficient(${\gamma}_s$).

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.669-674
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• 2003

The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. The test results indicate that the diffusion coefficient increases with the increase of water-cement ratio. The diffusion coefficient decreases with the increase of relative humidity at the same water-cement ratio. The diffusion of carbon dioxide reached the steady-state within about five hours after exposure. It was found that the diffusion coefficient of cement paste is larger then that of concrete or mortar. The quantitative values of diffusivity of carbon dioxide in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Corrosion Science and Technology
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• v.4 no.2
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• pp.69-74
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• 2005

The carbonation of concrete is one of the major factors that cause durability problems in concrete structures. The rate of carbonation depends largely upon the diffusivity of carbon dioxide in concrete. The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. To this end, several series of tests have been planned and conducted. The test results indicate that the diffusion coefficient increases with the increase of water-cement ratio. The diffusion coefficient decreases with the increase of relative humidity at the same water-cement ratio. The diffusion of carbon dioxide reached the steady state within about five hours after exposure. The content of aggregates also influences the diffusivity of carbon dioxide in concrete. It was found that the diffusion coefficient of cement paste is larger then that of concrete or mortar. The quantitative values of diffusivity of carbon dioxide in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Journal of Ocean Engineering and Technology
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• v.10 no.4
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• pp.149-159
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• 1996

Multipurpose development of the coast and ocean can be considered as multifunction construction combining the functions of coastal protection, waterfront amenity and creation or rehabilitation of habitats. Multfunction development of coastal and ocean spaces can be accomplished by applying the ecosystem control structure of artificial habitats which will cultivate fishing ground with ecological harmony to the coastal protection system. To evaluate the applicability of ecosystem control structures as as fundamental coastal protection structure, wave control function of the structure is studied by numerical and physical analyses. Dimensional analysis and hydraulic experiment point out the importance of width and crest depth of ecosystem control structure, construction water depth and wave steepness. Wave control efficiency is estimated by the attenuation coefficient $(K_H)$ according to wave steepness $(H_0/L_0)$, relative constructed water depth $(h_i/H_0)$, relative berm width $(B/L_0)$ and relative crest depth $(h_B/H_0)$ of eosystem control structure. Empirical fomulas are suggested based on the results of model test by applying the multiple model based on this experimental results and numerical wave shoaling-dissipation-breaking model appears to be valid for the analysis of wave transformation around ecosystem control structure in the coastal waters.

• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1007-1015
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• 2014

This study investigates the discharge coefficient of Improved-Pneumatic-Movable (IPM) weir through the weir, a kind of movable weirs, to estimate much more accurate rating curves using laboratory flume experiments. The discharge coefficient ($C_d$) is from 0.613 to 0.634 by the stand-up angle of the weir. The upstream Froude Number ($F_{r1}$), relative crest length(${\xi}$), Headwater Ratio ($H_1/W$), the Overflow depth ratio of weir crest ($y_c/y_1$) was changed by the upstream. And the downstream Froude number ($F_{r2}$), the Overflow depth ratio of weir crest and Downstream Water depth ($y_c/y_2$) was changed by the downstream. The ratio of Downstream and Up and Downstream water Depth (${\Delta}y/y_2$) was found to be changed by both of the up and downstream flow. They considered the major influence variables and derived the Discharge coefficient Formula at this study. The Discharge coefficient of the Improved-Pneumatic-Movable (IPM) weir was settled by the height of the Movable weir, that is to say, it was settled by the flow conditions of upstream approach flow head and physical data according to the standing angle.

• Corrosion Science and Technology
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• v.16 no.3
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• pp.141-150
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• 2017

Impregnating with quality silicone water repellent on the concrete surface is an effective method of protecting concrete. Quality silicone water repellent has been widely used in the engineering profession because of its desirable properties such as hydrophobicity, keeping concrete breathable and preserving the original appearance of the concrete. The companies in China that produce silicone water repellent are listed. Test methods in the specifications or standards about silicone water repellent in China are summed. The test methods relative to durability of concrete impregnated with silicone water repellent (such as resistant to chloride ion penetration, resistant to alkali, resistance to freezing and thawing and weatherability etc.) and the constructive quality (such as water absorption rate, impregnating depth and the dry velocity coefficient etc.) are compared and analyzed. The results indicate that there are differences among test methods relative to different specifications with the same index and therefore, confusion has ensued when selecting test methods. All test methods with the exception of the method of water absorption rate by using a Karsten flask are not non-destructive methods or conducted in a laboratory. Finally, further research on silicone water repellent during application is proposed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.244-254
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• 2013

In this study, a method has been developed for estimating the change of nearshore random waves in response to sea-level rise, by extending the method proposed for regular waves by Townend in 1994. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for random waves are presented as functions of relative change in water depth. The changes in wavelength and refraction coefficient are calculated by using the significant wave period and principal wave direction in the regular-wave formulas. On the other hand, the changes in shoaling coefficient and wave height are calculated by using the formulas proposed for shoaling and transformation of random waves in the nearshore area including surf zone. The results are proposed in the form of both formulas and graphs. In particular, the relative change in wave height is compared with the result for regular waves.

• Advances in concrete construction
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• v.17 no.5
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• pp.245-255
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• 2024

The problem of carbonation-induced corrosion has become a concern in recent times, especially in the 21^st century, due to the increase in global temperatures and carbon dioxide (CO₂) concentration in the atmosphere possessing a significant threat to the durability of reinforced concrete (RC) structures worldwide, especially in inland tropical regions where carbonation is the most significant concrete degradation mechanism. Therefore, a study was conducted to predict the impact of global warming on the carbonation of RC structures in Lusaka, Zambia, and Tokyo, Japan. The Impact was estimated based on a carbonation meta-model that applies the analytic solution of Fick's 1st law using literature-based concrete mix design data and forecasted local temperature and CO₂ concentration data over a 100-year period with relative humidity assumed constant. The results showed that CO₂ diffusion increased between 17-31%, effecting a 40-45% rise in carbonation coefficient and a significant reduction in corrosion initiation time of 50-52% in the two cities. Moreover, for the same water-cement ratio, Lusaka showed almost twice higher carbonation coefficient values and one third shorter corrosion initiation time compared to Tokyo, mainly due to its higher temperature and low relative humidity. Additionally, the carbonation propagation depth at the end of 100 years was between 12-22 mm in Tokyo and 18-40 mm in Lusaka. These findings indicate that RC structures in these cities are at risk of rapid deterioration, especially in Lusaka, where they are more vulnerable.

• Tribology and Lubricants
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• v.22 no.3
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• pp.144-148
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• 2006

The experimental investigation was performed to find the associated changes in characteristics of fretting wear with various water temperatures. The fretting wear tests were carried out using the zirconium alloy tubes and the grids with increasing the water temperature. The tube materials in water of $20^{\circ}C,\;50^{\circ}C\;and\;80^{\circ}C$ were tested with the applied load of 20 N and the relative amplitude of $200{\mu}m$. The worn surfaces were observed by SEM, EDX analysis and 2D surface profiler. As the water temperature increased, the wear volume was decreased, but oxide layer was increased on the worn surface. The abrasive wear mechanism was observed at water temperature of $20^{\circ}C$ and adhesive wear mechanism occurred at water temperature of $50^{\circ}C,\;80^{\circ}C$. As the water temperature increased, surface micro-hardness was decreased, but wear depth and wear width were decreased due to increasing stick phenomenon. Stick regime occurred due to the formation of oxide layer on the worn surface with increasing water temperatures