• Journal of Korean Society of Steel Construction
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• v.23 no.5
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• pp.535-546
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• 2011

In this paper, semi-rigid elasto-plastic post-buckling analysis of a space frame was performed using various explicit arc-length methods. Various explicit arc-length methodsand a large-deformation and small-strain elasto-plastic 3D space frame element with semi-rigid connections and plastic hinges were developed. This element can be appliedto both explicit and implicit numerical algorithms. In this study, the Dynamic Relaxation method was adopted in the predictor and corrector processesto formulate an explicit arc-length algorithm. The developed "explicit-predictor" or "explicit-corrector" were used in the elasto-plastic post-buckling analysis. The Eulerian equations for a beam-column with finite rotation, which considers the bowing effects, were adopted for the elastic system and extended to theinelastic system with a plastic hinge concept. The derived tangent stiffness matrix was asymmetrical due to the finite rotation. The joint connection elements were introduced for semi-rigidity using a static condensation technique. Semi-rigid elasto-plastic post-buckling analyses were carried out to demonstrate the potential of the developed explicit arc-length method and advanced space frame element in terms of accuracy and efficiency.

• Korea-Australia Rheology Journal
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• v.17 no.3
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• pp.131-140
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• 2005

In this work we show the results of our most recent Direct Numerical Simulations (DNS) of turbulent viscoelastic channel flow using spectral spatial approximations and a stabilizing artificial diffusion in the viscoelastic constitutive model. The Finite-Elasticity Non-Linear Elastic Dumbbell model with the Peterlin approximation (FENE-P) is used to represent the effect of polymer molecules in solution, The corresponding rheological parameters are chosen so that to get closer to the conditions corresponding to maximum drag reduction: A high extensibility parameter (60) and a moderate solvent viscosity ratio (0.8) are used with two different friction Weissenberg numbers (50 and 100). We then first find that the corresponding achieved drag reduction, in the range of friction Reynolds numbers used in this work (180-590), is insensitive to the Reynolds number (in accordance to previous work). The obtained drag reduction is at the level of $49\%\;and\;63\%$, for the friction Weissenberg numbers 50 and 100, respectively. The largest value is substantially higher than any of our previous simulations, performed at more moderate levels of viscoelasticity (i.e. higher viscosity ratio and smaller extensibility parameter values). Therefore, the maximum extensional viscosity exhibited by the modeled system and the friction Weissenberg number can still be considered as the dominant factors determining the levels of drag reduction. These can reach high values, even for of dilute polymer solution (the system modeled by the FENE-P model), provided the flow viscoelasticity is high, corresponding to a high polymer molecular weight (which translates to a high extensibility parameter) and a high friction Weissenberg number. Based on that and the changes observed in the turbulent structure and in the most prevalent statistics, as presented in this work, we can still rationalize for an increasing extensional resistance-based drag reduction mechanism as the most prevalent mechanism for drag reduction, the same one evidenced in our previous work: As the polymer elasticity increases, so does the resistance offered to extensional deformation. That, in turn, changes the structure of the most energy-containing turbulent eddies (they become wider, more well correlated, and weaker in intensity) so that they become less efficient in transferring momentum, thus leading to drag reduction. Such a continuum, rheology-based, mechanism has first been proposed in the early 70s independently by Metzner and Lamley and is to be contrasted against any molecularly based explanations.

• Structural Engineering and Mechanics
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• v.57 no.1
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• pp.1-20
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• 2016

On the basis of the geological conditions of high and steep mountainous slope on which an exit portal of an express railway tunnel with a bridge-tunnel combination is to be built, the composite structure of the exit portal with a bridge abutment of the bridge-tunnel combination is presented and the stability of the slope on which the express railway portal is to be built is analyzed using three dimensional (3D) numerical simulation in the paper. Comparison of the practicability for the reinforcement of slope with in-situ bored piles and diaphragm walls are performed so as to enhance the stability of the high and steep slope. The safety factor of the slope due to rockmass excavation both inside the exit portal and beneath the bridge abutment of the bridge-tunnel combination has been also derived using strength reduction technique. The obtained results show that post tunnel portal is a preferred structure to fit high and steep slope, and the surrounding rock around the exit portal of the tunnel on the high and steep mountainous slope remains stable when rockmass is excavated both from the inside of the exit portal and underneath the bridge abutment after the slope is reinforced with both bored piles and diaphragm walls. The stability of the high and steep slope is principally dominated by the shear stress state of the rockmass at the toe of the slope; the procedure of excavating rockmass in the foundation pit of the bridge abutment does not obviously affect the slope stability. In-situ bored piles are more effective in controlling the deformation of the abutment foundation pit in comparison with diaphragm walls and are used as a preferred retaining structure to uphold the stability of slope in respect of the lesser time, easier procedure and lower cost in the construction of the exit portal with bridge-tunnel combination on the high and steep mountainous slope. The results obtained from the numerical analysis in the paper can be used to guide the structural design and construction of express railway tunnel portal with bridge-tunnel combination on high and abrupt mountainous slope under similar situations.

• Korean Journal of Food Science and Technology
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• v.37 no.2
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• pp.233-240
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• 2005

To discover new functional materials using edible plants, antioxidant activities of methanol extracts from various parts of seven wild vegetables were investigated in vitro. Total polyphenol contents, determined by Folin-Denis method, varied from 16.74 to $130.22{\mu}g/mg$. Radical-scavenging activities of methanol extracts were examined using ${\alpha},\;{\alpha}-diphenyl-{\beta}-pirrylhydrazyl$ (DPPH) radicals and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) assay. Inhibition effects on peroxidation of linoleic acid determined by ferric thiocyanate (FTC) method and on oxidative degradation of 2-deoxy-D-ribose in Fenton-type reaction system were dose-dependent. Athyrium acutipinulum Kodama (leaf and rood), Achyranthes japonica (Miq.) Nakai (seed), and Solidago virga-aurea var. gigantea Nakai (root) showed relatively high antioxidant activities in various systems.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.125-135
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• 2009

Statement of problem: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. Purpose: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. Material and methods: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques(10, 20, 30 and 40 Ncm) and the external loading(250 N, $30^{\circ}$) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. Results: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. Conclusion: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.6
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• pp.307-317
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• 2002

In this paper we propose a new mesh reconstruction scheme that produces a displaced subdivision surface directly from unorganized points. The displaced subdivision surface is a new mesh representation that defines a detailed mesh with a displacement map over a smooth domain surface, but original displaced subdivision surface algorithm needs an explicit polygonal mesh since it is not a mesh reconstruction algorithm but a mesh conversion (remeshing) algorithm. The main idea of our approach is that we sample surface detail from unorganized points without any topological information. For this, we predict a virtual triangular face from unorganized points for each sampling ray from a parameteric domain surface. Direct displaced subdivision surface reconstruction from unorganized points has much importance since the output of this algorithm has several important properties: It has compact mesh representation since most vertices can be represented by only a scalar value. Underlying structure of it is piecewise regular so it ran be easily transformed into a multiresolution mesh. Smoothness after mesh deformation is automatically preserved. We avoid time-consuming global energy optimization by employing the input data dependant mesh smoothing, so we can get a good quality displaced subdivision surface quickly.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.515-527
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• 2014

This study conducted experiment for understanding engineering characteristics of domestic sands by examining standard sand and sand from Yokji Island and Nakdong River in terms of confining pressure, $K_0$, over consolidation and relative density factors through triaxial compression test. The test showed that deviator stress by strain positively changed as confining pressure and relative density grow while $K_0$ and over consolidation factors do not directly correlated with it. Angle of internal friction decreases as confining pressure increases which strengthens contact force between particles, and declines as relative density drops, whereas $K_0$ and over consolidation factors hardly affect the results. When it comes to volumetric strain, volume expansion decreases as confining pressure increase due to crushability and rearrangement of particles while $K_0$ and over consolidation shows same movement unconditionally, and relative density appears compressed as it grows at the beginning however it expands as axial strain increases. Modulus of elasticity ($E_{sec}$) by strain has tendency into convergence resulting in initial secant modulus of elasticity ($E_{ini}$) > secant modulus of elasticity($E_{sec}$) > tangent modulus of elasticity ($E_{tan}$). On the other hand, it grows as confining pressure and relative density increase while indicating similar modulus of elasticity ($E_{sec}$) regarding on $K_0$ and over consolidation. Slope of critical line (M) tended to decrease as confining pressure increases, follow same line according to $K_0$, confining pressure and relative density, and increase as relative density grows.