• International Journal of Highway Engineering
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• v.13 no.4
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• pp.19-28
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• 2011

This study developed a solar radiation reflection pavement, so called a cool pavement, to lessen the urban heat island effect by coating a pavement surface with acrylic resins mixed with light-colored pigments. From a laboratory test, simulating solar heating process in pavements, the cool pavement reduced more than $12^{\circ}C$ of pavement temperature at $60^{\circ}C$ compared to a control porous pavement. With the increase of the mixing ratio of the pigments to acrylic resins, the temperature reduction effect increased, but its workability became worse due to higher viscosity. As a result, an appropriate mixing ratio was determined as 15%. The cool pavement had better durability than the control pavement: One quarter of Catabro loss and twofold dynamic stability. Its adhesion was also higher enough not to be debonded under traffic loading. In-situ noise and friction tests conducted in two field sites showed that the cool pavement reduced its noise level by 3.7dB in average and increased its friction level by 30% compared to the control pavement. The permeability of the cool pavement was little lower than the control pavement, but higher enough to satisfy the minimum requirement for porous pavements.

• Atmosphere
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• v.26 no.1
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• pp.111-126
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• 2016

In the numerical weather model, surface properties can be defined by various parameters such as terrain height, landuse, surface albedo, soil moisture, surface emissivity, roughness length and so on. And these parameters need to be improved in the Seoul metropolitan area that established high-rise and complex buildings by urbanization at a recent time. The surface roughness length map is developed from digital elevation model (DEM) and it is implemented to the high-resolution numerical weather (WISE-WRF) model. Simulated results from WISE-WRF model are analyzed the relationship between meteorological variables to changes in the surface roughness length. Friction speed and wind speed are improved with various surface roughness in urban, these variables affected to temperature and relative humidity and hence the surface roughness length will affect to the precipitation and Planetary Boundary Layer (PBL) height. When surface variables by the WISE-WRF model are validated with Automatic Weather System (AWS) observations, NEW experiment is able to simulate more accurate than ORG experiment in temperature and wind speed. Especially, wind speed is overestimated over $2.5m\;s^{-1}$ on some AWS stations in Seoul and surrounding area but it improved with positive correlation and Root Mean Square Error (RMSE) below $2.5m\;s^{-1}$ in whole area. There are close relationship between surface roughness length and wind speed, and the change of surface variables lead to the change of location and duration of precipitation. As a result, the accuracy of WISE-WRF model is improved with the new surface roughness length retrieved from DEM, and its surface roughness length is important role in the high-resolution WISE-WRF model. By the way, the result in this study need various validation from retrieved the surface roughness length to numerical weather model simulations with observation data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1131-1136
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• 2015

In a diesel engine, the wear of the cylinder liner occurs because of the continuous reciprocating motion of the piston ring. This wear reduces the performance of the diesel engine and shortens its service life. This study evaluated the wear characteristics of GT metal and a conventional metal used for cylinder liners using a ship's diesel engine. Wear tests were performed at temperatures of $25^{\circ}C$, $175^{\circ}C$, and $325^{\circ}C$, and under loads of 10 N, 30 N, and 50 N. The amount of wear, specific wear rate, and friction coefficient were evaluated for each condition. To analyze the wear mechanism, observations were made on an SEM. In the case of both metals, abrasive and adhesion wear occurred on the wear surfaces at room temperature, and corrosion wear was observed at high temperatures. The amount of wear and the specific wear rate of the GT metal were lower than those of the conventional metal at all temperatures, and hence it can be concluded that the wear characteristics of the GT metal are much better.

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.351-356
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• 2008

Thermally sprayed tungsten carbide-based powder coatings are being widely used for a variety of wear resistance applications. The coating deposited by high velocity processes such as high velocity oxy-fuel (HVOF) thermal spraying is known to provide improved wear resistant property. In this study, optimal coating process (OCP) is obtained by the study of coating properties such as surface hardness, porosity, surface roughness and microstructure of 9 coatings prepared by Taguchi program for 3 levels of four spray parameters. The Friction and wear behaviors of HVOF WC-CoCr coating prepared by OCP, electrolytic hard chrome (EHC) plating and Inconel718 (In718) are investigated by reciprocating sliding wear test at $25^{\circ}C$, $450^{\circ}C$. Friction coefficients (FC) of all of the 3 samples are decreased as increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. FC of WC-CoCr decreases as increasing the surface temperature from $0.33{\pm}0.02$ at $25^{\circ}C$ to $0.26{\pm}0.02$ at $450^{\circ}C$, showing the lowest FC among the 3 samples. Wear trace (WT) and wear depth (WD) of WC-CoCr are smaller than those of EHC and In718 both at $25^{\circ}C$ and $450^{\circ}C$. These show that WC-CoCr is highly recommendable for protective coating on In718 and other metal components.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.67-76
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• 2011

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. Adfreeze bond strength is considered to be the most important design parameter for foundations in cold region. Many studies in last 50 years have been conducted to analyze characteristics of adfreeze bond strength. However, most studies have been performed under constant temperature and normal stress conditions in order to analyze affecting factors like soil type, pile material, loading speed, etc. In this study, both freezing temperature and normal stress acting on pile surface were considered to be primary factors affecting adfreeze bond strength, while other factors such as soil type, pile material and loading speed were predefined. Direct shear box was used to measure adfreeze bond strength between Joomoonjin sand and aluminium because it is easy to work for various roughness. Test was performed with temperatures of > $0^{\circ}C$, $-1^{\circ}C$, $-2^{\circ}C$, $-5^{\circ}C$, and $-10^{\circ}C$ and vertical confining pressures of 1atm, 2atm, and 3atm. Based on the test results, the effects of temperature and vertical stress on adfreeze bond strength were analyzed. The test results showed that adfreeze bond strength increases with decreased temperature and increased vertical stress. It was also noted that two types of distinct sections exist, owing to the rate of increase of adfreeze bond strength along the change of freezing temperature: 1)rapidly increasing section and 2)gradually decreasing section. In addition, the results showed that a main factor affecting adfreeze bond strength switches from friction angle to adhesion as freezing temperature decreases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.1-7
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• 2020

Although the temperature load is an important load among the various loads affecting the behaviors of general rahmen-type temporary bridges (GRTB), no study of the thermal load has been carried out. In the case of GRTB, horizontal displacement should be free, and the generated internal force should be minimized to reduce stress due to a temperature load. Sliding girder type bridge (SGTB) allows the axial deformation due to thermal load, and decreases the axial stress and delivers bending stress. This study examined the temperature behavior of an SGTB. Structural analysis was carried out for four types of spans (eq, 10, 20, 30, and 40m) and three types of pier heights (eq, 2, 4, and 6m) along with the GRTB. The applied loads were a fixed vertical load and an axial temperature load. The friction coefficient was 0.4, which is a representative value of a steel girder. Consequently, the stress of the SGTB increased with increasing span length, regardless of the temperature load. The stress of the GRTB increased with increasing temperature and span length. Compared to the GRTB, the stress of the SGTB decreased by 20% to 50% at the center of the girder and by 50% to 90% at the bottom of the pier. This could secure the structural efficiency compared to the GRTB with the same specifications.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.533-540
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• 2012

Rubber laminated bearings with lead core are highly affected by changes in temperature because key materials which are rubber and lead have temperature dependencies. In this study, two full scale LRB(D800, S=5) are manufactured and temperature dependency tests on shear properties are accomplished. The shear properties at the 3rd cycle are used at $-10^{\circ}C$, $0^{\circ}C$, $10^{\circ}C$, $20^{\circ}C$, $30^{\circ}C$, $40^{\circ}C$ respectively. The double shear configuration, simultaneously testing two pieces, is applied for compression shear test in order to minimize the friction effects due to the test machine, described in ISO 22762-1:2010. Characteristic strength, post-yield stiffness, effective stiffness, equivalent damping ratio are estimated and presented coefficient due to the temperature changes.

• Journal of the Korean Solar Energy Society
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• v.36 no.6
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• pp.25-35
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• 2016

In this study, the evaluation of the dynamic behavior and thermal performance of the "Façade integrated Natural circulation Solar Water Heating System" installed in the residential house was carried out. Experimental tests were performed during the all year around in the rural houses of $166m^2$ in size. Facade integrated solar collector of $5m^2$ were installed on the south-facing. Electrical heater of 1 kW capacity as an auxiliary heater was installed at the upper part of the heat storage tank. The analyzing results are as follows. (1) Monthly average solar fraction was 51 to 87% and yearly average value is 64%. (2) Hot water supply temperature in December which has the lowest solar altitude is 37 to $76^{\circ}C$. The highest working fluid temperature of solar collector in this period was below $84^{\circ}C$. The temperature difference of working fluid between the collector inlet and outlet has been shown to be around 9 to $26^{\circ}C$. (3) Overheating which is one of the biggest problems during summer did not appear at all, but rather had hot water supply temperature is rather low as $30{\sim}47^{\circ}C$ in summer than winter, which is supplied by a small solar load. The solar collecting temperature has been shown to maintain below $55^{\circ}C$. (5) The thermal performance of Facade integrated solar collector can be increase due to the reduction of heat loss to the back of the collector wall integration of the collector is reduced. As a conclusion, Facade integrated natural circulation type Solar Water Heating System is a well-functioning without any pumps or controllers, and it was found that the disadvantages of conventional solar water heaters, hot water or hot water system can be greatly improved.

• Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.349-362
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• 2016

The numerical solutions of unsteady hydromagnetic natural convection Couette flow of a viscous, incompressible and electrically conducting fluid between the two vertical parallel plates in the presence of thermal radiation, thermal diffusion and diffusion thermo are obtained here. The fundamental dimensionless governing coupled linear partial differential equations for impulsive movement and uniformly accelerated movement of the plate were solved by an efficient Finite Element Method. Computations were performed for a wide range of the governing flow parameters, viz., Thermal diffusion (Soret) and Diffusion thermo (Dufour) parameters, Magnetic field parameter, Prandtl number, Thermal radiation and Schmidt number. The effects of these flow parameters on the velocity (u), temperature (${\theta}$) and Concentration (${\phi}$) are shown graphically. Also the effects of these pertinent parameters on the skin-friction, the rate of heat and mass transfer are obtained and discussed numerically through tabular forms. These are in good agreement with earlier reported studies. Analysis indicates that the fluid velocity is an increasing function of Grashof numbers for heat and mass transfer, Soret and Dufour numbers whereas the Magnetic parameter, Thermal radiation parameter, Prandtl number and Schmidt number lead to reduction of the velocity profiles. Also, it is noticed that the rate of heat transfer coefficient and temperature profiles increase with decrease in the thermal radiation parameter and Prandtl number, whereas the reverse effect is observed with increase of Dufour number. Further, the concentration profiles increase with increase in the Soret number whereas reverse effect is seen by increasing the values of the Schmidt number.

• Tunnel and Underground Space
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• v.26 no.2
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• pp.68-86
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• 2016

Understanding the frictional properties of rock discontinuities is crucial to ensure the stability of underground structures. In particular, the frictional behavior at depth depends on the complex interaction among mechanical, hydraulic, thermal and chemical characteristics and their coupled effects. In this study, a series of shear tests were carried out in a triaxial compression chamber to investigate the shearing behavior of saw-cut granite surface and rough shear surface of synthetic rocks. The test results were analyzed using Coulomb's shear strength criterion. The frictional behavior of saw-cut granite surface showed little variation at different confining, water pressures and temperature conditions, however in case of synthetic rocks, the frictional behavior showed different trend depending on normal stress level. In addition, the variation of stiffness and dilation at different testing conditions were analyzed, and the stiffness and dilation showed little variation at different water pressures and temperature conditions.