• Smart Structures and Systems
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• v.34 no.1
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• pp.17-23
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• 2024

Non-destructive methods are extensively utilized for assessing the integrity of rock bolts, with longitudinal wave speed being a crucial property for evaluating rock bolt quality. This research aims to propose a method for predicting reliable longitudinal wave velocities by leveraging various properties of the rock surrounding the rock bolt. The prediction algorithm employed is the Multilayer Neural Network (MNN), and the input properties includes elastic modulus, shear wave speed, compressive strength, compressional wave speed, mass density, porosity, and Poisson's ratio, totaling seven. The implementation of the MNN demonstrates high reliability, achieving a coefficient of determination of 0.996. To assess the impact of each input property on longitudinal wave speed, an importance score is derived using the random forest algorithm, with the elastic modulus identified as having the most significant influence. When the elastic modulus is the sole input parameter, the coefficient of determination for predicting the longitudinal wave speed is observed to be 0.967. The findings of this study underscore the reliability of selecting specific properties for predicting longitudinal wave speed and suggest that these insights can assist in identifying relevant input properties for rock bolt integrity assessments in future construction site experiments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.448-453
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• 2016

Erosion and abrasion caused by cavitation damage occur in fluid equipment, such as ships or impellers. Similarly, the equipment damage from noise and vibration can shorten its life. This study analyzed the importance of the parameter characteristics of the process optimization of HVOF (High Velocity Oxygen Fuel spraying), which is generally used in a variety of industries for enhancing the resistibility from the cavitation phenomenon. The surface of the ALBC3 substrate was coated with an amorphous powder as a filler metal according to the experimental design using the Taguchi method, and then the characteristics with each parameter were analyzed using a porosity measurement test. The optimal process conditions was a combustion pressure of 80psi, coating distance of 270mm, gun speed of 200mm/s, and powder feed rate of 25g/min as a result of the HVOF coating by applying the experimental design. The combustion pressure, coating distance and powder feed rate were more than 25% and indicated a similar contribution rate, but the contribution rate of the gun speed was 19%, which was slightly less than the others. The contribution rate with each parameter was only slightly significant. On the other hand, all four parameters were found to be important in the contribution rate aspects of the HVOF coating process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.10-16
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• 2020

Computational simulations of adsorption columns were carried out to investigate the removal characteristics of VOCs from a laundry shop. n-Decane was selected as the representative component among the VOCs emitted, and the activity of the adsorbents, such as activated carbon, was evaluated using commercial CFD code. The mathematical framework was composed of continuity and Navier-stokes equations, and the simulation was performed using the Matlab program. The adsorption isotherms of LDF, Freundlich, and Langmuir were evaluated, and the adsorption amount of the adsorption isotherms with the adsorption parameter was compared. The simulation was carried out using a particle porosity, dispersion coefficient, particle density, bed diameter, and bed length of 0.79, 42.4 ㎠/min, 485 g/L, 2.0 cm, and 2.5 cm, respectively. The effect of the gas velocity, dispersion coefficient, and voidage on the adsorption amount was compared in the Langmuir adsorption isotherm. The simulation was carried out in the velocity range of 50 to 200 cm/min, dispersion coefficient range of 100 to 400 ㎠/min, and particle porosity range of 0.66 to 0.79. The simulation results of activated carbon with benzene coincided with the Langmuir isotherm. Three types of adsorption isotherm were compared under similar conditions, and the simulation results showed the efficient adsorption condition for hydrocarbons.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.187-197
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• 2021

Clay mineral content of weathered zone is a key parameter for landslide studies. Electrical resistivity tomography is usually performed to delineate the geometry of complex landslides and to identify the sliding surface. In clay-bearing weathered zone, parallel resistivity Archie equation is employed to investigate the effect of conductivity added (resistivity reduced) by clay minerals of kaolinite and montmorillonite, which is dependent on their specific surface area and cation exchange capacities (CEC). A decrease of overall resistivity and apparent formation factor is observed with increasing pore-water resistivity, significantly in montmorillonite. Formation factor is found decreased with increasing porosity and decreasing cementation factor. Parallel Archie equation was applied to the electrical resistivity data from the test area (Sinjindo-ri, Taean-gun, Chungcheongnam-do, Korea) which experienced land creeping in the year of 2014. A panel test with varying clay-mineral contents provides the best fit section when the theoretical section constructed with the assumed contents approaches the field section, from which the clay-mineral content of the weathered zone is estimated to be approximately 10%. Resistivity interpretation schemes including the clay mineral contents for land creeping studies explored in this paper can be challenged more when porosity, saturation, and pore-water resistivity are provided and they are included in the numerical resistivity modeling.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.255-264
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• 2009

Permeability coefficient of concrete is a substaintial key parameter for understanding the durability performance of concrete and its microstructural densification. Many researches for the issue have been accomplished, however, it is very rare to deal with the theoretical study on permeability coefficient in connection with carbonation of concrete and the the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. The purpose of this study is to establish a fundamental approach to compute the permeability coefficeint of (non)carbonated concrete. When simulating a microstructural characteristics as a starting point for deriving a model for the permeability coefficient by the numerical simulation program for cementitious materials, HYMOSTRUC, a more realistic formulation can be achieved. For several compositions of cement pastes, the permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. Emphasis was on the microstructural changes and its effective change of the permeability coefficient of carbonated concrete. For carbonated concrete, reduced porosity was calculated and this was used for calculating the permeability coefficeint. The computational result was compared with experimental outcome.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.442-449
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• 2015

The effects of coating parameters were investigated in wear resistance coatings of Diamalloy-406 on Inconel 718 to obtain an optimum coating condition by high velocity oxy-fuel spraying. The coating parameters, the flow rates of source gases (hydrogen and oxygen), the powder feed rate, and the spray distance, were designed by the Taguchi method. The optimal conditions were determined: oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min, and spray distance 7 inch. Friction coefficients of the coating and the substrate decreased with an increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. The friction coefficient of Diamalloy-4006 coating decreased as the sliding surface temperature increased from $0.43{\pm}0.01$ at $25^{\circ}C$ to $0.29{\pm}0.01$ at $450^{\circ}C$. The wear trace and wear depth of the coating were smaller than the substrate at all temperatures tested. The relationship between spray parameters and wear resistance was discussed extensively, based on the measured roughness, hardness, and porosity in each coating.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.790-799
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• 2010

The Upper Devonian Grossmont Formation in Alberta, Canada reserves an estimated 50 billion cubic meters of bitumen and possess about 1/6 of the total bitumen resources in northern Alberta. However, unlike the overlying Athabasca oil sands, non conventional bitumen resources has not been developed as yet. The carbonate rocks of Grosmont Formation have been subject to various stages of diagenesis, including dolomatization and karstification with a strong effect on the distribution of porosity and permeability, which resulted in highly heterogeneous reservoirs. An extensive fracture logging and mapping was performed on total of six boreholes located in the study area to explore the characteristics of fracture geometry system and the subsurface structures of carbonates reservoir that holds bitumen. Fractal dimension was used as a measure of the statistical homogeneity of the fractured rock masses. The applicability of random Cantor dust, Dc, as a fractal parameter was examined systematically. The statistical homogeneity of fractured carbonates rock masses was investigated in the study area. The structural domains of the rock masses were delineated depthwise according to estimated Dc. The major fracture orientation was dominated by horizontal beddings having dip of $0-20^{\circ}$. Also, fractures having high dip angles existed with relatively low frequency. Three dimensional fracture network modeling for each structural domain has been performed based on fracture orientation and intensity, and some representative conceptual models for carbonates reservoir in the study area has been proposed. The developed subsurface conceptual models will be used to capture the geomechanical characteristics of the carbonates reservoir.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.41-47
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• 2007

Geotechnical Phenomena such as landslide, groundwater recharge and groundwater fluctuation due to rainfall can be explain to use a dielectric response and infiltration variation by the movement of a wetting front in the subsurface. The infiltration of a wetting front is infiltrating to the connected pores which are distributed in unsaturated soil. In this study we carried out to laboratory experiment of a vertical infiltration column test using ethanol mix-ing tracer which has same the specific gravity of water. All physical values are detected to use a variation of dielectric constant and calculated to use a dielectric mixing model and tracer test model. This dielectric method measured by each dielectric constant of geological soil porous materials should be of for the geotechnical information and useful a field monitoring technique for detecting the variations of the volumetric water content and the wetting front, which are insignificant the key parameter to understanding the landslide by rainfall.

• Journal of Powder Materials
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• v.24 no.3
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• pp.210-215
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• 2017

In this study, STS316L powders prepared by gas atomization are used to manufacture bulk structures with dimensions of $10{\times}10{\times}10mm^3$ using selective laser melting (SLM). The microstructures and hardness of the fabricated 316L stainless steel has been investigated with the laser beam overlap varied from 10% to 70%. The microstructures of the fabricated STS316L samples show a decrease in the balling and satellite of powders introducing defect in the bulk samples and the porosity caused by the gap between the molten metal pools disappearing as the overlap ratio increases, whereas a low overlap ratio results in significant balling and a large amount of isolated powders due to the increased gap between the melt pools. Furthermore, the highest value in Vickers hardness is obtained for the sample fabricated by 30% overlapped laser beams. These results show that the overlap ratio of laser beams in the SLM process should be considered as an important process parameter.

• Polymer(Korea)
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• v.25 no.3
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• pp.318-326
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• 2001

PLLA scaffold loaded with gentamicin sulfate (GS) was prepared by emulsion freeze-drying method for the prevention of infection and the improvement of wettability. i.e., the cell- and tissue-compatibility. GS-loaded PLLA scaffolds were characterized by scanning electron microscopy (SEM), mercury porosimetry and blue dye intrusion, and the GS release pattern was analyzed by high performance liquid chromatography (HPLC). GS-loaded PLLA scaffolds with porosity above 50%, medium pore size ranging from 30 to 57 ${\mu}{\textrm}{m}$ (with larger pore diameters greater than 150 ${\mu}{\textrm}{m}$), and specific pore area in the range of 35 to 75($m^2$ /g )were manufactured by varying processing parameter as GS concentration. It was observed that GS-loaded PLLA scaffolds were highly porous with good interconnections between pores for allowing cell adhesion and growth. These scaffolds may be applicable for scaffold as structures that facilitate either tissue regeneration or repair during reconstructive operations.