• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.5
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• pp.51-58
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• 2009

The total recovery ratio test on undisturbed clay soil sampling in the field and the finite element method analysis on modified static state of penetration process were conducted for the purpose of deciding the most important factor among the shape factors of thin wall tube. The adhesion between tube wall and soil did not decrease although internal clearance ratio of tube increased within the little change of tube area ratio. The most part of disturbance occurred in the tip of sampling tube during the penetration. The longitudinal displacement was larger than the lateral displacement because soil was confined laterally after being entered into tube, and also the longitudinal displacement was larger in the upper part of the sample tube than in the lower part.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.218-227
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• 1998

Present study is undertaken to optimize the lubrication reliability and frictional loss of the dynamically-loaded journal bearing in hermetic reciprocating compressor with alternative refrigerant R600a application. Thermodynamic and dynamic analysis has been conducted to investigate cylinder pressure variations by substitution alternative refrigerant R600a for R12. The modeling of the dynamics of the compressor mechanism has been performed with lumped mass method. A mathematical model is developed for analyzing the dynamics of the journal bearing system with the mobility method. It takes into account the effects of the refrigerant species, aspect ratio, clearance ratio and surface roughness. A corresponding computer program is described which enables to obtain the minimum film thickness and frictional loss. Design optimization is graphically performed by parametric studies of the aspect ratio and clearance ratio.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• Tribology and Lubricants
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• v.33 no.1
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• pp.23-30
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• 2017

The electric controlled marine diesel engine has fuel pump generating the high pressurized fuel for fuel injection to combustion chamber via a common rail. Fuel pump consists of a cam-roller system. Journal bearing installed between a roller and a cam-roller pin is subjected to fluctuating heavy and instant loads by cam lift. First, Kinematic analysis is carried out to predict bearing loads during one cycle acting on the journal bearing. Second, flexible multi-body dynamic analysis and transient elasto-hydrodynamic(EHD) lubrication analysis for journal bearing considering elastic deformation of cam-roller pin, roller and bearing are conducted using AVL EXCITE/PU software to predict lubrication performance. The clearance ratio and journal groove shape providing lubrication oil are important parameter in bearing design having good performance and can be changed easier than other design parameters such as diameter, width, oil supply pressure and bearing material grade. Generally, journal bearing performance is represented by the minimum oil film thickness(MOFT) and peak oil film pressure(POFP). As well as the traditional design parameters(MOFT, POFP), in this study, temperature rise of lubrication oil is also evaluated through the side leakage flow of supplied oil. By the evaluating MOFT, POFP and temperature rise, the optimum bearing clearance ratio is decided.

• Journal of Radiation Industry
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• v.17 no.4
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• pp.457-469
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• 2023

The clearance level by nuclide is announced by the Nuclear Safety and Security Commission. However, the clearance level of uranium existing in nature has not been announced, and research is needed. Therefore, the purpose of this study was to evaluate the clearance level of uranium nuclides appropriate to domestic conditions preliminary. For this purpose, this study selected major processes for recycling metal wastes and analyzed the exposure scenarios and major input factors by investigating the characteristics of each process. Then, the radiation dose to the general public and workers was evaluated according to the selected scenarios. Finally, the results of the radiation dose per unit radioactivity for each scenario were analyzed to derive the clearance level of uranium in metal waste. The results of the radiation dose assessment for both the general public and workers per unit radioactivity of uranium isotopes were shown to meet the allowable dose (individual dose of 10 µSv y^-1 and collective dose of 1 Man-Sv y^-1) regulated by the Nuclear Safety and Security Commission. The most conservative scenarios for volumetric and surface contamination were evaluated for the handling of the slag generated after the melting of the metal waste and the direct reuse of the contaminated metal waste into the building without further disposal. For each of these scenarios, the radioactivity concentration by uranium isotope was calculated, and the clearance level of uranium in metal waste was calculated through the radioactivity ratio by enrichment. The results of this study can be used as a basic data for defining the clearance level of uranium-contaminated radioactive waste.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.355-358
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• 2003

This paper presents characteristics of vacuum preloaded porous air bearing. Pressure distribution of a porous pad and vacuum pocket are calculated. And load capacity and stiffness of the bearing are analyzed with various vacuum parameters, that is. clearance height. tube diameter, tube length. pumping speed of vacuum pump, vacuum pocket to porous pad area ratio. From the simulation results, optimum clearance for best performance can be selected adjusting these parameters, especially tube diameter which is the most dominant source.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.217-224
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• 1997

Static characteristics of hemispherical aerodynamic bearing is studied theoretically. In this paper nonlinear equation of second order considering compressibility and slip effect of air is calculated by Newton-Raphson method. Results indicate that axial load capacity has maximum value when the inclination angle of groove is about 30$\circ$, the ratio of groove clearance to ridge clearance is two. We also present the design method of hemispherical Aerodynamic bearing based on it's load capacity taking into account manufacturing and assembling viewpoint.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.20 no.3
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• pp.153-159
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• 2017

Purpose: Acid neutralization during chemical clearance is significantly prolonged in children with cystic fibrosis, compared to symptomatic children without cystic fibrosis. The absence of available reference values impeded identification of abnormal findings within individual patients with and without cystic fibrosis. The present study aimed to test the hypothesis that significantly more children with cystic fibrosis have acid neutralization durations during chemical clearance that fall outside the physiological range. Methods: Published reference value for acid neutralization duration during chemical clearance (determined using combined impedance/pH monitoring) was used to assess esophageal acid neutralization efficiency during chemical clearance in 16 children with cystic fibrosis (3 to < 18 years) and 16 age-matched children without cystic fibrosis. Results: Duration of acid neutralization during chemical clearance exceeded the upper end of the physiological range in 9 of 16 (56.3%) children with and in 3 of 16 (18.8%) children without cystic fibrosis (p=0.0412). The likelihood ratio for duration indicated that children with cystic fibrosis are 2.1-times more likely to have abnormal acid neutralization during chemical clearance, and children with abnormal acid neutralization during chemical clearance are 1.5-times more likely to have cystic fibrosis. Conclusion: Significantly more (but not all) children with cystic fibrosis have abnormally prolonged esophageal clearance of acid. Children with cystic fibrosis are more likely to have abnormal acid neutralization during chemical clearance. Additional studies involving larger sample sizes are needed to address the importance of genotype, esophageal motility, composition and volume of saliva, and gastric acidity on acid neutralization efficiency in cystic fibrosis children.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1640-1645
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• 2004

The pumping characteristics of a single-stage disk-type drag pump ( DTDP ) are calculated,for the variation of the vertical clearance between a rotor and stator and of the radial clearance between a rotor and casing wall, by the three-dimensional direct simulation Monte Carlo (DSMC)method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on the both the upper and lower sides of a rotating disk, but the stationary disks are planar. As a consequence of results, the vertical and radial clearances have a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4 $^{\sim}$ 533 Pa. When the numerical results are compared to the experimental data, the numerical results agree well qualitatively.

• Design & Manufacturing
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• v.6 no.1
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• pp.45-51
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• 2012

The main goal of this paper is to establish an interference tolerance for determining optimal amount of clearance in the shaft-bearing system supported by radial ball bearings. The 2-D frictional contact model was employed for the FE analysis between the shaft and the inner raceway. Several examples were simulated using different material properties for the solid shaft. Efforts were focused on the deformation applied in the radial direction to select suitable bearings. The analysis results showed that the initial axial preload applied on the bearings plays a significant role to reduce bearing fatigue life. The proposed design parameters obtained by numerical simulations can approximately predict a rate of bearing life reduction as a function of shaft diameter ratio. This analysis can also be used to calculate the optimal initial radial clearance in order to obtain a shaft-bearing system design for high accuracy and long life.