• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.29-36
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• 2010

Ultrasonic inspection of heavy walled cast austenitic stainless steel(CASS)welds is very difficult due to complex and coarse grained structure of CASS material. The large size of anisotropic grain strongly affects the propagation of ultrasound by severe attenuation, change in velocity, and scattering of ultrasonic energy. therefore, the signal patterns originated from flaws can be difficult to distinguish from scattered signals. To improve detection and sizing capability of ID connected defect for heavy walled CASS piping welds, the low frequency segmented TRL Pulse Echo and Phased Array probe has been developed. The experimental studies have been performed using CASS pipe mock-up block containing artificial reflectors(ID connected EDM notch). The automatic pulse echo and phase array technique is applied the detection and the length sizing of the ID connected artificial reflectors and the results for detection and sizing has been compared respectively. The goal of this study is to assess a newly developed ultrasonic probe to improve the detection ability and the sizing of the crack in coarse-grained CASS components.

• Interaction and multiscale mechanics
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• v.4 no.3
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• pp.187-206
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• 2011

Accurate estimations of pre-failure deformations and post-failure responses of geostructures require that the simulation tool possesses at least three main ingredients: 1) a constitutive model that is able to describe the macroscopic stress-strain-strength behavior of soils subjected to complex stress/strain paths over a wide range of confining pressures and densities, 2) an embedded length scale that accounts for the intricate physical phenomena that occur at the grain size scale in the soil, and 3) a computational platform that allows the analysis to be carried out beyond the development of an initially "contained" failure zone in the soil. In this paper, a two-scale micropolar plasticity model will be used to incorporate all these ingredients. The model is implemented in a finite element platform that is based on the mechanics of micropolar continua. Appropriate finite elements are developed to couple displacement, micro-rotations, and pore-water pressure in form of $u_n-{\phi}_m$ and $u_n-p_m-{\phi}_m$ (n > m) elements for analysis of dry and saturated soils. Performance of the model is assessed in a biaxial compression test on a slightly heterogeneous specimen of sand. The role of micropolar component of the model on capturing the post-failure response of the soil is demonstrated.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.2
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• pp.29-35
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• 2011

The behaviors of combustion-induced internal flows of SRM equipped with fin-slot grain and submerged nozzle are very complex and diverse. Cold air-flow tests for 2D and 3D scale models of SRM have been done in order to specify the visualization method to analyze particular internal flow patterns such as roll-torque inducing flow. Swirl flow induced by asymmetric vortical tubes also has been visualized through employing various light source and recording directions.

• International Journal of Highway Engineering
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• v.6 no.3 s.21
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• pp.55-64
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• 2004

Maximum dry unit weight, ${\gamma}_{dmax}$, is the most important engineering properties for subgrade soil. Existing models to predict ${\gamma}_{dmax}$ containing many parameters, seem to be rather complex. This paper presents new simple models to predict ${\gamma}_{dmax}$. for sandy soils, A number of sieve analysis and compaction tests for 36 types of sands were conducted to develop the regression-based models. Parameters used to estimate ${\gamma}_{dmax}$ are both the geometric mean and geometric standard deviation of the soils, or the particle-size distribution curve parameters. Maximum dry unit weights predicted by the models are in good agreement with the laboratory measurements for the soil samples obtained at 16 locations within the Korea.

• Korean Journal of Health Education and Promotion
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• v.29 no.3
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• pp.63-74
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• 2012

Objectives: We aim to investigate association between health behavior, interpersonal/organizational environment and job stress among government officials. Methods: Through health examination and a survey, this cross sectional study investigated 543 government officials working at Central Government Complex in Seoul, Korea. Health behaviors included alcohol drinking, smoking, moderate exercise and food frequency. Interpersonal environment was measured by health behavior practices of significant others and social support for health promotion. And the measures of organizational environment included facilities for exercise, health related norms and health supportive organizational systems. Job stress was assessed by short version of Korean Occupational Stress Scale(KOSS). Results: The level of job stress among female officials was higher than that of male officials. Multivariate logistic model suggested that higher job stress in male officials was significantly associated with lower position(OR=0.267, p<.01) less grain intake(OR=0.642, p<.05), lower level of social support(OR=0.810, p<.01) and abdominal obesity(OR=2.407, p<.05). On the contrary, female officials' stress level was negatively associated with healthy organizational environment(OR=0.725, p<.05). Conclusions: It is suggested that addressing job stress require tailoring intervention by gender characteristics and integration of interpersonal and organizational level approaches.

• Coupled systems mechanics
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• v.5 no.4
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• pp.341-353
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• 2016

Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots, including the grain size and morphology, is highly related to the shape of the crystal-melt interface during the crystal growth process. We performed numerical simulations to analyze the thermo-fluid field and the shape of the crystal-melt interface both for steady conditions and transient processes. The steady simulations are first validated and then applied to improve the hot zone design in the furnace. The numerical results reveal that, an additional guiding plate weakens the strength of vortex and improves the desired profile of the crystal-melt interface. Based on the steady solutions at an early stage, detailed transient processes of crystal growth can be simulated. Accuracy of the results is supported by comparing the evolutions of crystal heights with the experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in simulating a practical and complex system of directional solidification system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.88-92
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• 2002

$Ba(Zn_{0.8}Co_{0.2})_{1/3}Ta_{2/3}O_3$ [BZCT(80/20)] ceramics were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of $1450{\sim}1550^{\circ}C$ for 5hr. in air. The structural properties of BZCT(80/20) ceramics were investigated as a function of sintering temperature. The BZCT(80/20) ceramics sintered at $1550^{\circ}C$ showed a polycrystalline complex perovskite structure without second phases and any unreacted materials. Increasing the sintering temperature, the bulk density and ordering were increased. The bulk density of the BZCT(80/20) ceramics sintered at $1550^{\circ}C$ was 7.50[$g/cm^2$]. Increasing the sintering temperature, the average grain size were increased and pore were decreased.

• Proceedings of the Korean Geotechical Society Conference
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• 1992.10a
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• pp.55-60
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• 1992

Hydraulically filled ground is formed by the settling of soil grains from the mixture of soil grains and water. It was generally known that the settling speed of the soil grains in governed by Stokes low. In the case of clayed dredged material, the shape of soil grains is not round, the surface of the soil grains is relatively large compared to the weight of soil grains and inter-grain ionic force is relatively large compared to the wight of soil grains. By this reason the settling and consolidation behavior of hydraulically filled quite different from that of Stokes law. This study investigated the settling and consolidation behavior of hydraulically filled materials of Yeochon industrial complex by large scale laboratory settling & consolidation container. The test results showed tat actual settling speed of soil grains in quite large compared to that of Stokes law. It was turned out that this phenomenon was due to the aggregation of soil grains. Also, it was truned out that the void ration and water content after the completion of settling process was 8.7 and 322% respectively. The consolidtion settlement of clayey hydraulic fill material was predicated better by "incremental small strain" consolidation concept than classical Terzaghj's consolidation concept (infinitesimal strain).

• Journal of Biosystems Engineering
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• v.25 no.6
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• pp.503-510
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• 2000

To improve the milling condition of brown rice a continuous type conditioning equipment was developed. To validate the performance of this machine the experimental operation was done at Sa-cheon RPC(Rice Processing Complex) using short grain rough. The initial moisture contents of brown rice were 15.0∼16.5%(w.b) and the flow rate of brown rice passing through the conditioner were 4,370kg per hour. The moisture content differences of brown rice between conditioned and non-conditioned were showed within 0.5%(w.b) This results means that the water injected to brown rice were absorbed to the surface of brown rice evenly. The moisture contents of conditioned treated milled rice were showed slightly higher than that of non-conditioned ones but it was considered that the conditioning process did not affected the weight increasing of milled rice by water supply. For initial moisture contents of 15.0∼16.5%(wb) brown rice it was found that the proper water supply rate was 0.115(cc-water)/(kg·%-brown rice) and the increments of whole rice were 2.2% compared to the non-conditioned ones. it was considered that the conditioning process did not influenced the whiteness of milled rice because the whiteness differences between conditioned and non-conditioned milled rice were negligible. About 18% of electric power which drives the abrasive type rice milling machine was saved at 0.115(cc-water)/(kg·%-brown rice) of water supply rate.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.45-51
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• 1999

The semi-solid forging is a new forging technology in which the billet is heated to the semi-solid state coexisting liquid and solid phase for making globular microstructure and subsequently formed. As the semi-solid forging is compared with conventional casting such as die casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. Simutaneously, its mechanical properties are improved by globular microstructure and the lower temperature of the slug causes the cycle time of manufacturing to be shortened and the die life to be lengthened. As it is compared with conventional cold and hot forging, it is possible to minimize the equipment of production owing to a lower forming load and reduce the number of process by a followed treatment for complex shaped product. Therefore it is needed to confirm the quality of a semi-solid forged product by defining its characteristics quantitatively under these advantages. This paper investigates the formability of a master cylinder by its forming variables. And the microstructural characteristics and mechanical property of it is also studied.