• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.39-62
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• 2020

In this study, Barcelona Basic Model (BBM) was implemented into TOUGH2-MP/FLAC3D for the numerical analysis of coupled thermo-hydro-mechanical (THM) behavior of unsaturated soils and the prediction of long-term behaviors. Similar to the methodology described in a previous study for the implementation of BBM into TOUGH-FLAC, the User Defined Model (UDM) of FLAC based on the Modified Cam Clay Model (MCCM) and the FISH function of FLAC3D were used to extend the existing MCCM module in FLAC3D for the implementation of BBM into TOUGH2-MP/FLAC3D. In the developed BBM module in TOUGH2-MP/FLAC3D, the plastic strains due to change in suction increase (SI) in addition to mean effective stress are calculated. In addition to loading-collapse (LC) yield surface, suction increase (SI) yield surface is changed by hardening rules in the developed BBM module. Several numerical simulations were conducted to verify and validate the implementation of BBM: using an example presented in the FLAC3D manual for the standard MCCM, simulation results using COMSOL, and experimental data presented in SKB Reports. In addition, the developed BBM analysis module was validated by simultaneously performing a series of modeling tests that were performed for the validation of the Quick tools developed for the purpose of effectively deriving BBM parameters, and by comparing the Quick tools and Code_Bright results reported in a previous study.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.60-68
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• 2010

In this study, the conventional plane tip, double squealer tip, and various groove tip blades were tested in a linear cascade in order to measure the effect of the tip shapes on tip surface heat transfer coefficient distributions. Detailed heat transfer coefficient distributions were measured using a hue-detection based transient liquid crystals technique. Two tip gap clearances of 1.5% and 2.3% of blade span were investigated and the Reynolds number based on cascade exit velocity and chord length was $2.48{\times}10^5$. Results showed that the overall heat transfer coefficients on the tip surface with various grooved tips were lower than those with plane tip blade. The overall heat transfer coefficient on grooved along suction side tip was lower than that on the squealer tip.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.422-430
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• 2006

The horn and movable parts around the gap of the conventional semi-spade rudder are visualized by high speed CCD camera with the frame rate of 4000 fps (frame per second) to study the unsteady cavity pattern on the rudder surface and gap. In addition, the pressure measurements are conducted on the rudder surface and inside the gap to find out the characteristics of the flow behavior. The rudder without propeller wake is tested at the range of $1.0{\leq}{\sigma}_v\;1.6$ and at the rudder deflection angle of $-8{\leq}{\theta}{\leq}10^{\circ}$. The time resolved cavity images are captured and show strong cavitation around the rudder gap in all deflection angles. As the deflection angle gets larger, the flow separated from the horn surface increases the strength of cavitation. The accelerated flow along the horn decreases its pressure and the separated flow from the horn increases the pressure abruptly. The pressure distribution inside the gap reveals the flow moving from the pressure to suction side. In the negative deflection angle, the turning area on the movable part initiates the flow separation and cavitation on it.

• Tribology and Lubricants
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• v.30 no.5
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• pp.295-302
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• 2014

The tribological behavior of an Fe-based bulk amorphous alloy while sliding against a AISI 304 disc is investigated using a unidirectional pin-on-disc type tribometer in dry and distilled water environments. The rod-shaped bulk pins are fabricated by suction casting. The crystallinities of the bulk amorphous alloys before and after the friction tests are determined by X-ray diffraction. The friction coefficient and specific wear rate of the amorphous pin in the water environment are found to be twice and thrice as much as in the dry environment at a low applied pressure, respectively. However, at a higher pressure, the friction coefficient and specific wear rate are 0.4 and 1.02 mg/(Nm/s), respectively, in the water environment. A microstructure analysis shows that the worn surface of the alloy is characterized by delamination from the smooth friction surface, and thus delamination is the main wear mechanism during the friction test in dry sliding environment. In contrast, brittle fracture morphologies are apparent on the friction surface formed in distilled water environment. For the sample tested at a lower sliding speed, the XPS data from the oxide layer are similar to those of the pure element with weak suboxide peaks. For higher sliding speeds, all the main sharp peaks representing the core level binding energies are shifted to the oxide region.

• Wind and Structures
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• v.20 no.1
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• pp.37-58
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• 2015

As wind flows around a sharp-edged body, the resulting separated flow becomes complicated, with multiple separations and reattachments as well as vortex recirculation. This widespread and unpredictable phenomenon has long been studied academically as well as in engineering applications. In this study, the flow characteristics around rectangular prisms with five different aspect ratios were determined through wind tunnel experiments and a detached eddy simulation, that placed the objects in a simulated deep turbulent boundary layer at $Re=4.6{\times}10^4$. A series of rectangular prisms with the same height (h = 80 mm), different longitudinal lengths (l = 0.5h, h, and 2h), or different transverse widths (w = 0.5h, h, and 2h) were employed to observe the effects of the aspect ratio. Furthermore, five wind directions ($0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $45^{\circ}$) were selected to observe the effects of the wind direction. The simulated results of the surface pressure were compared to the wind tunnel experiment results and the existing results of previous papers. The vortex and spectrum were also analyzed to determine the detailed flow structure around the body. The paper also highlights the pressure distribution around the rectangular prisms with respect to the different aspect ratios. With an increasing transverse width, the surface suction pressure on the top and side surfaces becomes stronger. In addition, depending on the wind direction, the pressure coefficient experiences a large variation and can even change from a negative to a positive value on the side surface of the cube model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.311-318
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• 2010

In this study, the conventional plane tip, double squealer tip, and various groove tip blades were tested in a linear cascade in order to measure the effect of the tip shapes on tip surface heat transfer coefficient distributions. Detailed heat transfer coefficient distributions were measured using a hue-detection based transient liquid crystals technique. Two tip gap clearances of 1.5% and 2.3% of blade span were investigated and the Reynolds number based on cascade exit velocity and chord length was $2.48{\times}10^5$. Results showed that the overall heat transfer coefficients on the tip surface with various grooved tips were lower than those with plane tip blade. The overall heat transfer coefficient on grooved along suction side tip was lower than that on the squealer tip.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.521-529
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• 2017

Three-dimensional flow characteristics within a high-acceleration first-stage turbine vane passage has been investigated in a newly-built vane cascade for propulsion. The result shows that there is a strong favorable pressure gradient on the vane pressure surface. On its suction surface, however, there exists not only a much stronger favorable pressure gradient than that on the pressure surface upstream of the mid-chord but also a subsequent adverse pressure gradient downstream of it. By employing two different oil-film methods with upstream coating and full-coverage coating, a four-vortex model horseshoe vortex system can be identified ahead of each leading edge in the cascade, and the separation line of inlet boundary layer flow as well as the separation line of re-attached flow is provided as well. In addition, basic flow data such as secondary flow, aerodynamic loss, and flow turning angle downstream of the cascade are obtained.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.77-86
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• 2007

The repair technique utilizing surface impregnant is widely used due to its simple construction procedures and economical benefit. Surface protection through this reparing technique cannot increase the bearing capacity of concrete members much but increase the durability performance and service life efficiently. In this study, fundamental tests such as water suction and permeation are performed for concrete specimens with several organic/inorgarnic impregnant and suitable impregnant is selected on the basis of the results. Finally, durability tests such as carbonation, freezing and thawing, and chloride attack are carried out for the concrete specimens with selected impregnant and it is experimentally verified that they have good resistance to deteriorations.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.91-103
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• 2009

Slope failure depends upon the climatic features related to related rainfall, structural geology and geomorphological features as well as the variation of the mechanical behaviors of soil constituting a slope. In this paper, among many variables, effects of soil layer thickness on the slope failure process, and variations of matric suction and volumetric water content were observed. When the soil layer is relatively thick, the descending wetting front decreases matric suction and the observed matric suction reaches to "0" value. When the wetting front reaches to the impermeable boundary, the bottom surface of steel soil box, ascending wetting front was observed. This observation can be postulated to be the effects of various sizes of pores. When macro size pores exist, the capillary effects can be reduced and infilling of pore will be limited. The partially filled pores would be filled with water during the ascending of the wetting front, which bounces from the impermeable boundary. This assumption has been assured from the observation of variation of the volumetric water contents at different depth. When the soil layer is thick (thickness = 20 cm), for granular material, erosion is a cause triggering the slope failure. It has been found that the initiation of erosion occurs when the top soil is fully saturated. Meanwhile, when the soil layer is shallow (thickness = 10 cm), slope slides as en mass. The slope failure for this condition occurs when the wetting front reaches to the interface between the soil layer and steel soil box. As the wetting front approaches to the bottom of soil layer, reduction of shear resistance along the boundary and increase of the unit weight due to the infiltration occur and these produce complex effects on the slope failure processes.