• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.12
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• pp.1106-1112
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• 2005

An experimental investigation was performed to develop an empirical correlation of R-410A flowing through short tube orifices working near the critical region. Tests were executed by varying upstream pressure from 2,619 kPa to 4,551 kPa, and upstream subcooling from 2.8 and $11.1^{\circ}C$. The experimental data were represented as a function of major operating parameters and short tube diameter. As compared to mass flow trends at normal upstream pressures, flow dependency on upstream subcooling became more significant at high upstream pressures due to a higher density change. Based on the database obtained from this study and literature, an empirical correlation was developed from a power law form of dimensionless parameters generated by the Buckingham Pi theorem. The correlation yielded good agreement with the data. Approximately $92\%$ of the data were correlated within a relative deviation of $5\%$.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.133-140
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• 2019

Strain-rate and temperature have significant effects on the one-dimensional (1D) compression behavior of soils. This paper focuses on the bonding degradation effect of soil structure on the time and temperature dependent behavior of soft structured clay. The strain-rate and temperature dependency of preconsolidation pressure are investigated in double logarithm plane and a thermal viscoplastic model considering the combined effect of strain-rate and temperature is developed to describe the mechanical behavior of unstructured clay. By incorporating the bonding degradation, the model is extended that can be suitable for structured clay. The extended model is used to simulate CRS (Constant Rate of Strain) tests conducted on structural Berthierville clay with different strain-rates and temperatures. The comparisons between predicted and experimental results show that the extended model can reasonably describe the effect of bonding degradation on the stain-rate and temperature dependent behavior of soft structural clay under 1D condition. Although the model is proposed for 1D analysis, it can be a good base for developing a more general 3D model.

• The Journal of the Korea Contents Association
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• v.21 no.2
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• pp.215-226
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• 2021

The purpose of this study was to analyze the alcohol volume consumed and alcohol dependancy according to multiple rounds of drinking. Sectional data collected in 2012 as part of an International Alcohol Control Study were used, and 855 of 1,789 drinker aged 19 to 64 were conducted. The proportion of multiple rounds drinking were significantly higher in males(χ²=37.607, p<.001), students(χ²=52.466, p<.001), single(χ²=34.205, p<.001), smoking experience and stressed(χ²=40,09, p<.001; χ²=21.66, p<.001) among drinkers. In particular, the alcohol volume consumed of unmarried people, smokers, and stress groups were significantly higher than married people, non-smokers and no-stress group. The highest alcohol intake in the first, 2nd and third rounds was found in bars in the liquor trade (F=67.8g, p<0.001). The total alcohol intake increased as the number of rounds increased (F=209.993, p=0.001) and the number of drinkers who tested positive for alcohol dependency increased, using the tests RAPS4 and DSM-IV(F=129.836, p<0.001; F=94.669, p<0.001). The OR of alcohol dependancy in males was 2.3(95% CI: 1.745-3.057), unemployed was 3.2(95% CI: 1.053-9.838), smokers was 3.9(95% CI: 1.230-12.292), and stress group was 2.1(95% CI: 1.561-2.768) compared to females, employed, non-smokers, and no-stress group respectively. In conclusion, it suggests that those consuming multiple rounds drinking can become more vulnerable to alcohol harms due to its relation to smoking, stress and increased dependence on alcohol.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.304-317
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• 2009

Most crystalline rocks have much higher compressive strength than tensile strength and show brittle failure. In-situ rock mass, strong enough in general sense, often fails in brittle manner when subjected to high stress exceeding strength in due of geometrically induced stress concentration or of high initial stress. Therefore, it is necessary to verify the brittle failure characteristics of rock and rock mass for proper stability assessment of underground structures excavated in great depths. In this study, damage controlled tests were conducted on biotite-granite and granitic gneiss, which are the two major crystalline rock types in Korea, to obtain the strain dependency characteristics of the cohesion and friction angle. A Cohesion-Weakening Friction-Strengthening (CWFS hereafter) model for each rock type was constructed and a series of compression tests were carried out numerically while varying confining pressures. The same tests were also conducted assuming the rock is Mohr-Coulomb material and results were compared.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1603-1611
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• 2004

The validity of 'modified overlay model' to describe the cyclic behavior of annealed 316L stainless steel at room temperature was investigated. Material parameters(~f$_{i}$, m$_{i}$b, η, E) fur the model were obtained through constant strain amplitude test. The strain amplitude dependency of elastic limit and cyclic hardening, which were the characteristics of this model, were considered. Eight subelements were used to describe the nonlinearity of the hysteresis loops. The calculated hysteresis curve in each condition (0.5％, 0.7％, 0.9％ train amplitude test) was very close to the experimental one. Two tests, incremental step test and 5-step test, ere performed to check the validity of 'modified overlay model'. The elastic limit was saturated to the one of the highest strain amplitudes of the block in the incremental step test, so it seemed to be Masing material at the stabilized block. Cyclic hardening was successfully described in the increasing sequence of the strain amplitude in 5-step test. But, the slight cyclic softening followed by higher strain amplitude would not be able to simulate by'modified overlay model'. However, the discrepancy induced was very small between the calculated hystereses and the experimental ones. In conclusion,'Modified overlay model'was proved to be appropriate in strain range of 0.35％~ 1.0％..0％.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.134-144
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• 2011

In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.953-962
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• 1987

Domestic dissimilar structural steels, SM 45 C and SUS304 were friction welded under optimal welding condition and the micro-artificial holes were drilled at SM 45 C base metal, SM 45 C HAZ, welded zone, SUS 304 HAZ, and SUS 304 base metal for fatigue behavior tests. In this study, the fatigue limit and the behavior of micro-crack propagation, crack propagation rate, and its dependency on stress intensity factor under the low stress level and high stress level of bending stress have been investigated. The results obtained are as follows. (1) The fatgiue strength of the portion of SM45C B.M., SM45C HAZ, welded zune, SUS304 HAZ and SUS304 B.M. on notched friction welded specimens are 20 kgf/mm$^{2}$, 32 kgf/mm$^{2}$, 27kgf/mm$^{2}$, 29kgf/mm$^{2}$, and 29kgf/mm$^{2}$, respectively. (2) The fatigue strength of welded zone of unnotched and notched specimens are 32.5kgf/mm$^{2}$, and 27kgf/mm$^{2}$, respectively. (3) Micro-crack initiation in the welded zone, HAZ, and each base metals occurrs simultaneously in front and rear of micro-hole tips in the view of the rotational directions. (4) Fatigue crack propagates more slowly in the welded zone than in another protions of specimen, regardless of the magnitude of the stress level. (5) Fatigue crack propagation rates were plotted as a function of stress intensity range. The value of m in the equation da/dN=C(.DELTA.K)$^{m}$ was found to range from 2.09-2.55 in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.16-25
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• 2003

A parallel computing environment based on Windows operating system was constructed and a performance test was mode in comparison with Linux based systems. The Windows 2000 cluster was composed with servers and clients connected by Fast-ethernet, within which two sub-clusters may operates together or separately. Compaq Visual Fortran complier and two MPI libraries, MPICH.NT.1.2.2 and NT-MPICHNT.1.2 were installed as computing tools. Parallel computing performance tests were carried out using two-dimensional preconditioned Navier-Stokes code to examine the dependency on the number of processors, problem size and MPI libraries, those were compared with results from Linux clusters. Results shows that a cluster based on the user-friendly Windows operating system is also useful for the parallel computing and has good performance comparable to the previous Linux clusters.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.2
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• pp.145-154
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• 2007

In hydrothermal reaction tests, smectite-to-illite conversion was identified using a domestic bentonite which is favorably considered as a buffer material, and its dependency on various hydrothermal conditions was investigated. The analysis results of the XRD and Si concentration indicated that the smectite-to-illite conversion was a major process of bentonite alteration under the hydrothermal conditions. The temperature, potassium concentration in solution, and pH were observed to significantly affect the smectite-to illite conversion. A model of conversion reaction rate was suggested to evaluate the long-term stability of smectite composing a major constituent of bentonitic buffer. It was expected from the evaluation results that the smectite would keep its integrity for very long disposal time under a normal condition, whitens it might be converted to illite by 50 percent after over $5{\times}10^4$ year of disposal time under a conservative condition and consequently lose its swelling capacity as a buffer material of a repository.

• Journal of Computing Science and Engineering
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• v.9 no.4
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• pp.204-213
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• 2015

Under the conditional independence assumption among local features, the Naive Bayes Nearest Neighbor (NBNN) classifier has been recently proposed and performs classification without any training or quantization phases. While the original NBNN shows high classification accuracy without adopting an explicit training phase, the conditional independence among local features is against the compositionality of objects indicating that different, but related parts of an object appear together. As a result, the assumption of the conditional independence weakens the accuracy of classification techniques based on NBNN. In this work, we look into this issue, and propose a novel Bayesian network for an NBNN based classification to consider the conditional dependence among features. To achieve our goal, we extract a high-level feature and its corresponding, multiple low-level features for each image patch. We then represent them based on a simple, two-level layered Bayesian network, and design its classification function considering our Bayesian network. To achieve low memory requirement and fast query-time performance, we further optimize our representation and classification function, named relation-based Bayesian network, by considering and representing the relationship between a high-level feature and its low-level features into a compact relation vector, whose dimensionality is the same as the number of low-level features, e.g., four elements in our tests. We have demonstrated the benefits of our method over the original NBNN and its recent improvement, and local NBNN in two different benchmarks. Our method shows improved accuracy, up to 27% against the tested methods. This high accuracy is mainly due to consideration of the conditional dependences between high-level and its corresponding low-level features.