• Composites Research
• /
• v.26 no.6
• /
• pp.380-385
• /
• 2013

Characteristics of delamination factor and surface roughness by drilling condition for glass fiber reinforced plastic (GFRP) composites were investigated in this paper. An expression to quantify the delamination factor was induced by using image pixels of the entry and the experimental drilling was accomplished by fabricating several GFRP specimens in condition of minimizing the effect of vibration and heat. A method for measuring 6 points average surface roughness was applied to acquire the more reliable roughness values. The experimental results showed that the delamination factor was decreased as the feed rate was increased and it was also slightly decreased as the cutting speed was increased. Also, it was investigated that the surface roughness at inner surface of drilled holes was increased as the feed rate was increased, whereas the roughness values were not affected by the cutting speed variation.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.8
• /
• pp.75-84
• /
• 2013

Soil freezing is a phenomenon arising due to temperature difference between atmosphere and ground, and physical properties of soils vary upon the phase change of soil void from liquid to solid (ice). A heat-transfer mechanism for this case can be explained by the conduction in soil layers and the convection on ground surface. Accordingly, the evaluation of proper thermal properties of soils and the convective condition of ground surface is an important task for understanding freezing phenomenon. To describe convection on ground surface, simplified coefficient methods can be applied to deal with various conditions, such as atmospheric temperature, surface vegetation conditions, and soil constituents. In this study, two methods such as n-factor and convection coefficient for the convective ground surface boundary were applied within a commercial numerical program (TEMP/W) for modeling soil freezing phenomenon. Furthermore, the numerical results were compared to laboratory testing results. In the series of the comparison results, the convection coefficient is more appropriate than n-factor method to model the convective boundary condition.

• New & Renewable Energy
• /
• v.7 no.1
• /
• pp.22-28
• /
• 2011

The surface solar radiations were calculated and analyzed with spatial resolutions (4 km and 1 km) using by GWNU (Gangneung-Wonju National University) solar radiation model. The GWNU solar radiation model is used various data such as aerosol optical thickness, ozone amount, total precipitable water and cloud factor are retrieved from Moderate Resolution Imaging Spectrometer (MODIS), Ozone Monitoring Instrument (OMI), MTSAT-1R satellite data and output of the Regional Data Assimilation Prediction System(RDAPS) model by Korea Meteorological Administration (KMA), respectively. The differences of spatial resolutions were analyzed with input data (especially, cloud factor from MTSAT-1R satellite). And the Maximum solar radiation by GWNU model were found in Andong, Daegu and Jinju regions and these results were corresponded with the MTSAT-1R cloud factor.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2003.11a
• /
• pp.201-209
• /
• 2003

In the mixed lubrication regime, the roughness effects are very important due to the presence of interacting asperities. An average Reynolds equation using flow factors is very useful to determine effects of surface roughness on mixed lubrication. In this paper, the pressure flow factors and shear stress factor for Gaussian and non-Gaussian surfaces are evaluated in terms of kurtosis and skewness. particularly, the elastic deformation of the surface is considered.

• Structural Engineering and Mechanics
• /
• v.37 no.3
• /
• pp.285-296
• /
• 2011

The plane crack-contact problem for an infinite elastic layer with two symmetric rectangular rigid stamps on its upper and lower surfaces is considered. The elastic layer having an internal crack parallel to its surfaces is subjected to two concentrated loads p on its upper and lower surfaces trough the rigid rectangular stamps and a pair of uniform compressive stress $p_0$ along the crack surface. It is assumed that the contact between the elastic layer and the rigid stamps is frictionless and the effect of the gravity force is neglected. The problem is reduced to a system of singular integral equations in which the derivative of the crack surface displacement and the contact pressures are unknown functions. The system of singular integral equations is solved numerically by making use of an appropriate Gauss-Chebyshev integration formula. Numerical results for stress-intensity factor, critical load factor, $\mathcal{Q}_c$, causing initial closure of the crack tip, the crack surface displacements and the contact stress distribution are presented and shown graphically for various dimensionless quantities.

• Progress in Superconductivity and Cryogenics
• /
• v.21 no.3
• /
• pp.22-26
• /
• 2019

With an increasing potential to realize quantum computer, it has recently been an important issue to extend the capabilities of RF cavities to maintain longer coherent quantum system. Using superconductors instead of normal metals allows the quantum system to have a substantially enhanced quality factor. In this paper, surface impedances of superconducting cavities are calculated by the Mattis-Bardeen theory with Python & MATLAB programs. With a simulation of electromagnetic field distribution, the sensitivity to dielectric and surface losses of the superconducting cavities are determined. Then calculations of the resonance frequency and quality factor of three-dimensional superconducting resonators made of Al or Nb are discussed.

• Smart Structures and Systems
• /
• v.28 no.6
• /
• pp.791-798
• /
• 2021

Current investigation aims to analyze the characteristics of magnetohydrodynamic boundary layer flow of bioconvection Casson fluid in the presence of nano-size particles over a permeable and non-linear stretchable surface. Fluid passes through the Darcy-Forchheimer permeable medium. Effect of different parameter such as Darcy-Forchheimer, porosity parameter, magnetic parameter and Brownian factor are investigated. Increasing Brownian factor leads to the rapid random movement of nanosize particles in fluid flows which shows an expansion in thermal boundary layer and enhances the nanofluid temperature more rapidly. For large values of Darcy-Forchheimer, magnetic parameter and porosity factor the velocity profile decreases. Higher values of velocity slip parameter cause decreasing trend in momentum layer with velocity profile.

• Geomechanics and Engineering
• /
• v.22 no.4
• /
• pp.319-328
• /
• 2020

This paper investigates the effect of the width of failure and tension crack (TC) on the stability of cohesive-frictional soil slopes in three dimensions. Working analytically, the slip surface and the tension crack are considered to have spheroid and cylindrical shape respectively, although the case of tension crack having planar, vertical surface is also discussed; the latter was found to return higher safety factor values. Because at the initiation of a purely rotational slide along a spheroid surface no shear forces develop inside the failure mass, the rigid body concept is conveniently used; in this respect, the validity of the rigid body concept is discussed, whilst it is supported by comparison examples. Stability tables are given for fully drained and fully saturated slopes without TC, with non-filled TC as well as with fully-filled TC. Among the main findings is that, the width of failure corresponding to the minimum safety factor value is not always infinite, but it is affected by the triggering factor for failure (e.g., water acting as pore pressures and/or as hydrostatic force in the TC). More specifically, it was found that, when a slope is near its limit equilibrium and under the influence of a triggering factor, the minimum safety factor value corresponds to a near spherical failure mechanism, even if the triggering factor (e.g., pore-water pressures) acts uniformly along the third dimension. Moreover, it was found that, the effect of tension crack is much greater when the stability of slopes is studied in three dimensions; indeed, safety factor values comparable to the 2D case are obtained.

• Carbon letters
• /
• v.14 no.1
• /
• pp.14-21
• /
• 2013

Physically and chemically activated carbons (ACs) exhibited high adsorption capacities for organic and inorganic pollutants compared with other adsorbents due to their expanded surface areas and wide pore volume distribution. In this work, seven steam-ACs with different burn-off have been prepared from cotton stalks. The textural properties of these sorbents were determined using nitrogen adsorption at $-196^{\circ}C$. The chemistry of the surface of the present sorbents was characterized by determining the surface functional C-O groups using Fourier transform infrared spectroscopy, surface pH, $pH_{pzc}$, and Boehm's acid-base neutralization method. The textural properties and the morphology of the sorbent surface depend on the percentage of burn-off. The surface acidity and surface basicity are related to the burn-off percentage. A theoretical model was developed to find a mathematical expression that relates the % burn-off to ash content, surface area, and mean pore radius. Also, the chemistry of the carbon surface is related to the % burn-off. A mathematical expression was proposed where % burn-off was taken as an independent factor and the other variable as a dependent factor. This expression allows the choice of the value of % burn-off with required steam-AC properties.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.30 no.3
• /
• pp.114-120
• /
• 1988

A water surface profile computation model using a standard step procedure was developed for gradually varied flow at an irrigation channel network. Flow characteristics ab Banweol district near Suweon were field monitored during irrigation periol of 1987. The model was applied to the main system at the district and the simulation results were compared to the field data. The results are sumrnarized as follows ; 1. The simulated water surface profiles from the model were in good agreement with the measured water surface profiles at different flow rates. 2. The model applicability for defining a stage-discharge relationship at a channel reach was demonstrated with reasonable accuracy when water stage and friction factor were given. 3. The roughness coefficient was found to be a major factor sigrificantly affecting computed water surface profile among a few physical input parameters for the model.