• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.55-60
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• 2011

In the present work, isogeometric analysis in linear elasticity problem is conducted using the basis functions from NURBS. The objectives of isogeometric analysis introduced is to integrate both geometric modeling(CAD) and computational analysis(CAE), and this can be accomplished from direct usage of geometric modeling by NURBS as the computational mesh. The merit of the isogeometry analysis is that NURBS surface are able to represent exact geometry from the control points and knot vectors, and also subsequent refinement is relatively simple relatively. In order to verify the computer codes developed in this study, it has been applied to two structural models of which geometry are simple ; 1) circular cylinder subjected to the constant internal pressure loading, 2) square plate with circular hole at center subjected to uniform tension. The exact solutions of these two models are available. Convergence of the approximate solutions by the present code for the isogeometry analysis are investigated by mesh refinement with inserting knots (h-refinement) and by mesh refinement with order elevation of the basis functions (p-refinement).

• The Journal of Engineering Geology
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• v.2 no.1
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• pp.19-35
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• 1992

aThe elastic properties of the fault zone (width; 3~12m), the shattered zone (width; over 40m) and the fresh rock zone distributed under the core foundation of fill dam in granitic gneiss have widely different range. The deformation moduli of the fresh rock zone, the fault zone and the shattered zone obtained from in situ rock tests - Plate Load Test and Bore Hole Deformation Test - show a range of $42,000~168,000kg/\textrm{cm}^2,{\;}963~2,204kg/\textrm{cm}^2{\;}and{\;}1,238~2,098kg/\textrm{cm}^2$, respectively. The differential settlements hetween the fault zone and the fresh rock zone are expected after the dam construction. Therefore, the displacement of foundation and concrete fill are evaluated using FEADAM 84 program of finite element analysis. The geometric distribution of discontinuifies obtained from the site mapping and drilling is considered in the finite element analysis. The analysis shows that the differential settlements between the fault zone and the fresh rock zone is about 6cm, while that of concrete fill is within 0.5cm.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.4
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• pp.271-277
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• 1998

Nondestructive method can include both testing itself and analysis or evaluation of the testing results. Although vast amount of testing can be accomplished in a fairly short amount of time due to the advancement of electronic technology. it is really difficult matter to identify whether the indication found during testing corresponds to be a real defect. Thus, in ultrasonic testing, advanced digital signal processing techniques have been widely studied in order to identify the shape of the defect during testing, and one of the signal processing techniques, synthetic aperture focusing technique(SAFT) was tried for holes machined in carbon steel plate in this study. Result showed that signal to noise ratio has been improved considerably compared to the result from original RF signals.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.1-12
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• 2015

Well-designed bolted connections can exhibit excellent ductile behavior through bearing mechanism until the occurrence of bolt shear rupture. The ultimate strength analysis of eccentric bolted connections is an economical and mechanistic approach which uses such ductility. However, the bolt load-deformation relationship, which forms basis of the current practice, is based on very limited combinations of bolt and steel materials. The primary objective of this study was to establish the general bolt force-deformation relationship based on systematic single-bolt bearing connection tests. The test results showed that the projected area of the bolt hole and the strength and thickness of the plate to be connected are the main factors affecting the force-deformation relationship. The results of this study can be used for the instantaneous center of rotation method (ICRM) to achieve more accurate analysis and economical design of a variety of group-bolted connections subjected to eccentric shear.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.450-467
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• 1998

The characteristics of the unstable impinging circular jet is investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes S1 and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed. At low speed the S2 mode is dominant and switched by the S1 mode as the speed increases. When the jet speed is high the S1 mode is very active over the impinging distance from half the nozzle diameter to its ten times, while the S2 mode occurs at shorter distance corresponding to stage 2 and 3. The helical mode H seems unstable, likely to be influenced much by the experimental environment, and occurs at relatively high speed with almost the same frequency characteristics as the S2 mode. By estimating the convection speed of the unstable jet, it is found that the ratio of the convection speed to the jet speed decreases with both Strouhal number and Reynolds number and the speed of S2 mode is faster than the Si mode. When the present experimental results are compared with the previous investigations performed for the hole tone and the impinging tone with a small plate, the S1 mode is found to be associated with the ring vortex of large diameter with low speed, but the S2 mode with the vortex of small diameter with high speed. In addition, the frequency is found to be influenced by the nozzle configuration but the characteristics is almost the same. From the impinging distance and frequency range, it can be deduced that S1 mode is related with the jet column mode and S2 mode with the shear mode.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3516-3524
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• 1996

Service conditions for structures at elevated temperatures in nuclear power plant involve transient thermal and mechanical load levels that are severe enough to caeuse inelastic deformations due to creep and plasticity. Therefore, a systematic mehtod of inelastic analysis is needed for the design of structural components in nuclear poser plants subjected to such loading conditions. In the present investigation, the Chabodhe model, one of the unified viscoplastic constitutive equations, was selected for systematic inelastic analysis. The material response was integrated based on GMR ( generallized mid-point rule) time integral scheme and provided to ABAQUS as a material subroutine, UMAT program. By comparing results obtaned from uniaxial analysis using the developed UMAT program with those from Runge-Kutta solutions and experimentaiton, the validity of the adopted Chaboche model and the numerical stability and accuracy of the developed UMAT program were verified. In addition, the developed material subroutine was applied for uniaxial creep and tension analyses for the plate with a hole in the center. The application further demonstrates usefulness of the developed program.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.48-57
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• 2007

The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by usiag the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location.

• Journal of the Korean Society of Safety
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• v.5 no.1
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• pp.19-29
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• 1990

The objective of this paper is to investigate the effect of residual stresses on the $\Delta$K$\sub$th/ and fatigue crack growth behavior of butt weldments. For this purpose, transverse butt sutmerged arc welding was performed on SM50A steel plate and CT(compact tension) specimens which loading direction is perpendicular to weld bead were selected. Welding residual stresses distribution on the specimen was determined by hole drilling method. The case of crack located parallel to weld bead, the states of as weld and PWHT, $\Delta$K$\sub$th/ of specimens(HAZ, weld zone) was higher than that of the base metal probably because of the compressive residual stresses of crack tip. In low $\Delta$K region, it is estimated that the effects of residual stresses for da/dN are great. In region II, the da/dN of weldments in as weld state was lower than that of the base metal. Though da/dN of Weldments in PWHT state was similar to that of the base metal. The constant of power law, m in two states consisted with the base metal. Therefore , it is estimated that the value of m is not affected by residual stresses. Fatigue crack growth behavior of weldments consisted with the base metal considering the effective stress intensity factor range($\Delta$K$\sub$eff/) included the effect of initial residual stress(Kres). Thus, we can predict the fatigue crack growth behavior of weldment by knowing the distribution of initial residual stress at the crack tip.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.4
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• pp.283-289
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• 2008

An experimental investigation was conducted to investigate the heat/mass transfer for impingement/effusion cooling system with inclined jet. Jets with inclined angle of 60 are applied to impingement/effusion cooling. At the jet Reynolds number of 10,000, the experiments were carried out for blowing ratios ranging from 0.0 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result indicates that the inclined jet causes the non-uniform and low heat/mass transfer compared to the vertical jet. At stagnation region, the peak position is shifted from the geometrical center of injection hole due to Coanda effect and its level is higher than that of vertical jet due to increase in turbulence intensity by steep velocity gradient near the stagnation region. Further, the secondary peak region disappears because the interaction between adjacent wall jets weakens. When the initial crossflow occurs, the distorted heat/mass transfer pattern appears. As the blowing ratio (crossflow rate) increases, the heat/mass transfer distributions become similar to those of the vertical jet. This is because the effect of crossflow is dominant compared to that of inclined jet under high blowing ratio $(M{\geq}1.0)$. At low blowing ratio $(M{\leq}0.5)$, averaged Sh value is 10% lower than that of vertical jet, whereas its value at high blowing ratio $(M{\geq}1.0)$ is similar to that of vertical jet.

• Journal of Microbiology and Biotechnology
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• v.15 no.1
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• pp.155-160
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• 2005

Abstract A direct approach was used to retrieve active lipases from Paenibacillus polymyxa genome databases. Twelve putative lipase genes were tested using a typical lipase sequence rule built on the basis of a consensus sequence of a catalytic triad and oxyanion hole. Among them, six genes satisfied the sequence rule and had similarity (about 25%) with known bacterial lipases. To obtain the six lipase proteins, lipase genes were expressed in E. coli cells and lipolytic activities were measured by using tributyrin plate and pnitrophenyl caproate. One of them, contig 160-26, was expressed as a soluble and active form in E. coli cell. After purifying on Ni-NTA column, its detailed biochemical properties were characterized. It had a maximum hydrolytic activity at $30^{\circ}C$ and pH 7- 8, and was stable up to $40^{\circ}C$ and in the range of pH 5- 8. It most rapidly hydrolyzed pNPC$_6$ among various PNPesters. The other contigs were expressed more or less as soluble forms, although no lipolytic activities were detected. As they have many conserved regions with lipase 160-26 as well as other bacterial lipases throughout their equence, they are suggested as true lipase genes.