• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.2963-2971
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• 2000

In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1240-1245
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• 2003

Reduced activation ferritic steel (JLF-1) is considered as a promising candidate material for blanket or first-wall structure of D-T fusion reactors. The fracture tests of fracture resistance curve (J-R curve) and $J_{IC}$ are desirable to investigate the exact fracture toughness of JLF-1 steel, since it has a high ductility. The fracture toughness of JLF-1 steel is affected by the configuration of test specimen such side groove, specimen thickness or specimen size. In this study, the fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The test results showed the standard specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen.

• Journal of Korea Foundry Society
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• v.33 no.1
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• pp.13-21
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• 2013

The effects of rare earth element (R.E.) and cooling rate on the eutectic reaction of flake graphite cast irons were studied by combined analysis of macro/micro-structure and cooling curve data. The correlation between eutectic reaction parameter and macro/micro-structure was systematically investigated. Two sets of chemical compositions with the different addition of R.E. were designed to cast. Three types of molds for cylindrical specimens with the different diameters were prepared to analyze cooling rate effect. The difference between undercooling temperature and cementite eutectic temperature (${\Delta}T_1=T_{U}-T_{E,C}$), which is increased by adding R.E. and decreased by increasing cooling rate, is considered to be a suitable eutectic reaction parameter for predicting graphite morphology. According to the criterion, A-type graphite is mainly suggested to form for ${\Delta}T_1$ over $20^{\circ}C$. Eutectic reaction time (${\Delta}t$), which is decreased by adding R.E. or increasing cooling rate, is a suitable eutectic reaction parameter for predicting eutectic cell size. Eutectic cell size is found to decrease in a proportion to the decrease of ${\Delta}t$.

• Journal of Magnetics
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• v.20 no.4
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• pp.421-426
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• 2015

This paper presents a practical method for estimation of average temperature in the permanent magnet (PM) of electric machine by using finite element analysis (FEA) and dynamo load experiment. First of all, the temperature effect of PM to the torque has been employed by FEA in order to evaluate the Temperature-Torque characteristic curve. The 1st order polynomial equation which is torque attenuation coefficient is derived by the FEA result of the Temperature-Torque curve. Next, torque saturation test with constant current condition is performed by dynamo load experiment. Then, the temperature trend can be estimated by adding the initial starting temperature using the torque attenuation coefficient and torque saturation curve. Lastly, estimated temperature is validated by infrared thermometer which measures temperature of PM surface. The comparison between the estimated result and experimental result gives a good agreement within a deviation of maximum $8^{\circ}C$.

• Journal of applied mathematics & informatics
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• v.23 no.1_2
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• pp.73-86
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• 2007

The general stereographic projection which maps a point on a sphere with arbitrary radius to a point on a plane stereographically and its inverse projection have the pythagorean-hodograph (PH) preserving property in the sense that they map a PH curve to another PH curve. Upon this fact, for given spatial $C^1$ Hermite data, we construct a spatial PH curve on a sphere that is a $C^1$ Hermite interpolant of the given data as follows: First, we solve $C^1$ Hermite interpolation problem for the stereographically projected planar data of the given data in $\mathbb{R}^3$ with planar PH curves expressed in the complex representation. Second, we construct spherical PH curves which are interpolants for the given data in $\mathbb{R}^3$ using the inverse general stereographic projection.

• Communications of the Korean Mathematical Society
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• v.15 no.1
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• pp.103-109
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• 2000

In this paper, we present the proof of generalized Fenchel's theorem by estimating the Gauss-Kronecker curvature of the tube of a nondegenerate closed curve in R$^{n}$ .

• The Mathematical Education
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• v.25 no.3
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• pp.77-100
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• 1987

Let G : R$^n$${\times}$R\longrightarrowR$^n$ be defined by a Homotopy solving a system F($\chi$)=0 of nonlinear equations. For the vector v$\^$k/ with G'(u$\sub$k/)v$\^$k/=0, ∥v$\^$k/∥=1 where uk is one point in Zero Curve let u$\sub$0/$\^$k/=v$\^$k/＋$\tau$v$\^$k/ be the first prediction for the next point u$\^$k+1/, $\tau$$\in$(0, 1). When u$\sub$0/$\^$k/ approaching too losely to some unwanted point. to follow the Zero Curve may occur the returning or cycling. One lion for it is discussed and tile parametrizied Homotopy algorithm for solving F($\chi$)=0 with it been established. Also some theorems by means of the regular value have been discussed for Zero Curves of G(u)=0 and some theorems for algorithm have been obtained.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.3-46
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• 1999

A new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D founded in clay. The steps involved are ; 1. taking samples at the bridge pier site, 2. testing them in an Erosion Function Apparatus called the EFA to obtain the scour rate z versus the hydraulic shear stress applied $\tau$, 3. predicting the maximum shear stress r max which will be induced around the pier by the water flowing at ν Ο before the scour hole starts to develop, 4. using the measured z versus r curve to obtain the initial scour rate zi corresponding to r max , 5. predicting the maximum depth of scour zmax for the pier, 6. using zi and zmarx to develop the hyperbolic function describing the scour depth z versus time t curve, and 7. reading the z vs. t curve at a time corresponding to the duration of the flood to find the scour depth which will develop around the pier. A new apparatus is developed to measure the z vs t curve of step 2, a series of advanced numerical simulations are performed to develop an equation for the $\tau$ max value of step 3, and a series of flume tests are performed to develop an equation for the zmax value of step 5. The method is evaluated by comparing predictions and measurements in 42 flume experiments.

• Communications of the Korean Mathematical Society
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• v.33 no.1
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• pp.293-303
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• 2018

In this paper, we consider biharmonic slant curves in S-space forms. We obtain a main theorem, which gives us four different cases to find curvature conditions for these curves. We also give examples of slant curves in ${\mathbb{R}}^{2n+s}(-3s)$.

• Bulletin of the Korean Mathematical Society
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• v.53 no.6
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• pp.1707-1714
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• 2016

Let $C{\subset}{\mathbb{P}}^r$ be a nondegenerate projective curve of degree d > r + 1 and of maximal regularity. Such curves are always contained in the threefold scroll S(0, 0, r - 2). Also some of such curves are even contained in a rational normal surface scroll. In this paper we study the minimal free resolution of the homogeneous coordinate ring of C in the case where $d{\leq}2r-2$ and C is contained in a rational normal surface scroll. Our main result provides all the graded Betti numbers of C explicitly.