• Journal of the Korean Society for Precision Engineering
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• v.25 no.5
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• pp.77-81
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• 2008

Structural components subjected to high frequency vibrations, such as those used in vibrating parts of gas turbine engines, are usually required to avoid resonance frequencies. Generally, the operating frequency is designed at more than resonance frequencies. When a vibrating structure starts or stops, the structure has to pass through a resonance frequency, which results in large stress concentration. This paper presents the transient thermoelastic stress analysis of vibrating cantilever beam using infrared thermography and finite element method (FEM). In FEM, stress concentration factor at the 2nd resonance vibration mode is calculated by the mode superposition method of ANSYS. In experiment, stress distributions are investigated with infrared thermography and dynamic stress concentration factor is estimated. Experimental result is agreed with FEM result within 10.6%. The advantage of this technique is a better immunity to contact problem and geometric limitation in stress analysis of small or micro structures.

• International Journal of Ocean System Engineering
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• v.1 no.2
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• pp.95-101
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• 2011

Perforated plates with cutouts (or holes) are widely used in structural members. These cutouts provide stress concentration in plates. Extensive studies have been carried out on stress concentration in perforated plates, which consider cutout shapes, boundary conditions, bluntness of cutouts, and more. This study presents stress concentration analyses of perforated plates with not only various cutouts and bluntness but also different cutout orientations. Especially, the effect of cutout orientation on stress concentration is emphasized since structural members have become more complicated recently. To obtain stress concentration patterns, a finite element program, ANSYS, is used. For the designated goal, three parameters are considered as follows: the shapes of polygonal cutouts (circle, triangle, and square), bluntness (a counter measure of radius ratio, r/R), and rotation of cutouts (${\theta}$). From the analyses, it is shown that, in general, as bluntness increases, the stress concentration increases, regardless of the shape and rotation. A more important finding is that the stress concentration increases as the cutouts become more oriented from the baseline, which is the positive horizontal axis (+x). This fact demonstrates that the orientation is also a relatively significant design factor to reduce stress concentration. In detail, in the case of the triangle cutout, orienting one side of the triangle cutout to be perpendicular to the applied tensile forces is preferable. Similarly, in the case of the square cutout, it is more advantageous to orient two sides of square cutout to be perpendicular to the applied tensile force. Therefore, at the design stage, determining the direction of a major tensile force is required. Then, by aligning those polygon cutouts properly, we can reduce stress concentration.

• Journal of the Korean GEO-environmental Society
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• v.21 no.9
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• pp.15-24
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• 2020

In this study, the stress concentration ratio for the improved material of the low slump mortar grouting was evaluated through the composite ground method, the ground arching theory, the plastic angle method, the 2D and 3D numerical analysis and the 3D model experiment. The stress concentration ratio calculated by the composite ground method was 89.3, 3.75~59.0 when the three-dimensional ground arching theory was applied, and 82.8 for the three-dimensional plastic angle method. As a result of the 2D numerical analysis, the stress concentration ratio was 63.0~77.0, which was found to increase as the improvement ratio increased. The results of 3D numerical analysis were predicted to be 50.0~56.0 smaller than the results of 2D analysis. In the case of a special model experiment using a large triaxial compression cell, the stress concentration ratio for each load step was 53.0~60.0, and the stress concentration ratio evaluated by the experiment was measured within 2D and 3D numerical analysis predictions. In this study, a predictive equation for the stress concentration ratio according to the improvement ratio is proposed based on the analysis and experimental values for the improved ratio of the low slump mortar grouting.

• KSBB Journal
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• v.15 no.4
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• pp.393-397
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• 2000

The cometaboic biodegradation conditionso f trichloroethylene(TCE) by Burkholderia cepacia G4 were optimized using response surface analysis. The experimental sets of phenol concentration temperature and pH were designed using central composite experimental design. The optimal conditions of phenol concentration temperature and pH were determined to be 0.91 ppm 21.5$^{\circ}C$ and 7.65 respectively by the Ridge analysis of the contour plot for TCE biodegradation rates. The TCE biodegradation rate could be enhanced up to 2.43 nmol.mg protein$.$min by response surface methodology.

• Journal of the Ergonomics Society of Korea
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• v.18 no.2
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• pp.25-34
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• 1999

The objective of this study is to evaluate the emotional change of a driver according to the change of temperature, humidity, $CO_2$ gas concentration and $C_4H_{10}$ gas concentration in the automobile by electroencephalogram(EEG) spectrum analysis. The experiment was performed in an automobile simulated shielding room with healthy volunteers(age : 18-31, male : 14, female : 7). The subject's emotion at every different condition was indexed 11-point scale(+5 : most pleasant, -5 : least pleasant). The emotion index at each condition resulted in as follows; in temperature $1.00(23.5^{\circ}C)$, $-2.33(30.5^{\circ}C)$, in humidity 1.50(45%), -1.50(65%), in $CO_2$ gas concentration 0.67(500ppm), -0.57(6,000ppm), in $C_4H_{10}$ gas concentration -0.25(0ppm), -2.75(1,200ppm). From EEG spectrum analysis, the average mean power frequency(MPF) value at each different condition was shown as follows; in temperature $5.48(23.5^{\circ}C)$, $4.06(30.5^{\circ}C)$, in humidity 11.03(45%), 3.03(65%), in $CO_2$ gas concentration 7.16(500ppm), 6.38(6,000ppm), in $C_4H_{10}$ gas concentration 10.21(0ppm), 2.87(1,200ppm). When the environment became unpleasant to the subject, all of the obtained MPF values were decreased. It was found that there is close agreement between subjective evaluation by subject's scaling and objective evaluation by EEG spectrum analysis at different environment. These results indicated that the EEG spectrum analysis is a proper method to assess emotional response of a driver in the changing automobile environment.

• Journal of Environmental Health Sciences
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• v.46 no.3
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• pp.276-284
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• 2020

Objectives: This study was conducted to identify the effects of PM₁₀ and PM_2.5 on hospital visits in the Incheon area over the period of 2016-2018. Methods: We applied correlation analysis and Poisson regression to perform the analysis using cardiovascular disease and respiratory disease data from the National Health Insurance Service and the daily average PM₁₀ and PM_2.5 from the Korea Environment Corporation adjusting for time lag. Results: When the daily average PM₁₀ concentration increased by 10 ㎍/㎥, the number of cardiovascular disease patients were 1.002 times higher (95% CI [Confidence Interval]; 1.000-1004) in Ganghwa County. As the daily average PM_2.5 concentration increased by 10 ㎍/㎥, the number of cardiovascular disease patients were 1.012 times higher (95% CI; 1.008-1.016) in Ganghwa County. As the daily average PM₁₀ concentration increased by 10 ㎍/㎥, the respiratory disease patients were 1.003 times (95% CI; 1.002-1.004) higher in Gyeyang and Michuhol Counties. As the PM_2.5 concentration increased by 10 ㎍/㎥, the respiratory disease patients were 1.003 times higher (95% CI; 1.002-1.005) in Bupyeong County. Conclusions: In some parts of the Incheon area there was a correlation between the number of patients with respiratory and cardiovascular conditions and the concentration of PM₁₀ and PM_2.5.

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.6
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• pp.593-604
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• 2017

The suspended particulate matter(PM) was measured in subway tunnel of Seoul Line 1 to 9 in order to evaluate the pollution degree and characteristics of the PM in the subway tunnel. Also, to analyze the effect of outdoor aerosol concentration on the PM concentration of subway tunnels, the ambient PM concentration around the subway station was extracted by spatial analysis using $PM_{10}$ data of Seoul air pollution monitoring network. Finally, in order to understand pollution pattern in the Seoul subway tunnels, cluster analysis was performed based on input data set such as PM levels in tunnel, tunnel depth, length, curvature radius, outdoor ambient air pollution levels and so on. The average concentration of $PM_{10}$, $PM_{2.5}$, and $PM_1$ on subway tunnels were $98.0{\pm}37.4$, $78.4{\pm}28.7$, and $56.9{\pm}19.2{\mu}g/m^3$, respectively. As a result of the cluster analysis, tunnels from Seoul subway Line-1 to Line-9 were classified into five classes, and the concentrations and physical properties of the tunnels were compared. This study can provide a method to reduce PM concentration in tunnel for each pollution pattern and provide basic information about air quality control in Seoul subway tunnel.

• Proceeding of KASS Symposium
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• 2005.05a
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• pp.89-98
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• 2005

Membrane structures, a kind of lightweight soft structural system, are used for spatial structures. The material property of the membrane has strong axial stiffness, but little bending stiffness. Therefore membrane structures arc unstable structures initially. These soft structures need to be introduced initial stresses first because of its initial unstable state, and it happens large deformation phenomenon. To find the structural shape after large deformation caused by initial stiffness introduced, we need the shape analysis considering geometric nonlinearity in structural design procedure. In this study, we investigate into the stress concentration at crack of membrane structures. Therefore, using the nonlinear analysis program that NASS (Nonlinear Analysis for Spatial Structures) perform nonlinear analysis, and stress distribution for creak length investigate for using linear elastic fracture mechanics.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.525-530
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• 2000

The loss of soil and nutrients from land surfaces to surface water supplies continues to be an important source of nonpoint source pollution. This study was initiate to develop an empirical relationship among the contaminants. SS, COD, T-N, and T-P were collected from agricultural surface water quality studies carried out in Hwasung-Gun, Kyonggi-Do. Correlation analysis, regression analysis, and reliability analysis were conducted. The regression equations were developed between SS and COD, SS and T-P, COD and T-P, and the resulting r$\^$2/ value was over 0.78. The regression equation enables a reasonable prediction of phosphorus concentration and COD concentration for known suspended solid concentration.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.5
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• pp.98-109
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• 1994

This paper is studied on the junction stress of the large tank and the cylindrical outlet such as a pressure vessel attached to a pope or nozzle theoretically. It is assumed that the diameter of tank is much larger than that of the nozzle cylinder, so it can be approximated that nozzle cylinder is attached to plate. As the current nozzle shape is manufactured as "Through Type" to reduce the stress concentration around the nozzle junction part of pressure vessel, a theoretical analysis on the cylinder with finite length should be performed to accomodate this fact. Each theoretical optimal values were obtained through the analysis of stress concentration caused by the variation of cylinder length and thickness, and these results were estimated by performing FEM Analysis. Analysis.