• International Journal of CAD/CAM
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• 제8권1호
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• pp.11-20
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• 2009

The conventional methods of boundary-conformed 2D surfaces generation usually yield some problems. This paper deals with two boundary-conformed 2D surface generation methods, one conventional approach, the linear Coons method, and a new method, boundary-conformed interpolation. In this new method, unidirectional 2D surface has been generated using some of the geometric properties of the given boundary curves. A method of simultaneous displacement of the interpolated curves from the opposite boundaries has been adopted. The geometric properties considered for displacements include weighted combination of angle bisector and linear displacement vectors at all the data-points of the two opposite generating curves. The algorithm has one adjustable parameter that controls the characteristics of transformation of one set of curves from its parents. This unidirectional process has been extended to bi-directional parameterization by superimposing two sets of unidirectional curves generated from both boundary pairs. Case studies show that this algorithm gives reasonably smooth transformation of the boundaries. This algorithm is more robust than the linear Coons method and capable of resolving the 2D boundary-conformed parameterization problems.

• Applied Microscopy
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• 제47권3호
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• pp.110-120
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• 2017

Non-isothermal thermogravimetry (TG) measurements on melt-quenched $Bi_xSe_{100-x}$ specimens (x=0, 2.5, 7.5 at%) were made at a heating rate ${\beta}=10^{\circ}C/min$ in the range $T=35^{\circ}C{\sim}950^{\circ}C$. The as-measured TG curves confirm that $Bi_xSe_{100-x}$ samples were thermally stable with minor loss at $T{\leq}400^{\circ}C$ and mass loss starts to decrease up to $600^{\circ}C$, beyond which trivial mass loss was observed. These TG curves were used to estimate molar (Se/Bi)-ratios of $Bi_xSe_{100-x}$ samples, which were not in accordance with initial composition. Shaping features of conversion curves ${\alpha}(T)-T$ of $Bi_xSe_{100-x}$ samples combined with a reliable flow chart were used to reduce kinetic mechanisms that would have caused their thermal mass loss to few nth-order reaction models of the form $f[{\alpha}(T)]{\propto}[1-{\alpha}(T)]^n$ (n=1/2, 2/3, and 1). The constructed ${\alpha}(T)-T$ and $(d{\alpha}(T)/dT)-T$ curves were analyzed using Coats-Redfern (CR) and Achar-Brindley-Sharp (ABS) kinetic formulas on basis of these model functions, but the linearity of attained plots were good in a limited ${\alpha}(T)-region$. The applicability of CR and ABS methods, with model function of kinetic reaction mechanism R0 (n=0), was notable as they gave best linear fits over much broader ${\alpha}(T)-range$.

• 대한수학회지
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• 제32권1호
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• pp.103-108
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• 1995

It is a well-known classical result of Mazur and Ulam that an isometry T from a real Banach space X onto a real Banach space Y with T(0) = 0 is automatically linear[5].

• 한국재료학회지
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• 제22권12호
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• pp.689-695
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• 2012

We have examined the co-doping effects of 1/2 mol% NiO and 1/4 mol% $Cr_2O_3$ (Ni:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Ni,Cr-doped ZBS, ZBS(NiCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ were detected for all of compositions. For the sample with Sb/Bi = 1.0, the Pyrochlore was decomposed and promoted densification at lower temperature by Ni rather than by Cr. A homogeneous microstructure was obtained for all of the samples affected by ${\alpha}$-spinel. The varistor characteristics were not dramatically improved (non-linear coefficient, ${\alpha}$ = 5~24), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.17 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to have been divided into two types, i.e., one is tentatively assigned to ZnO/$Bi_2O_3$ (Ni,Cr)/ZnO (0.98 eV) and the other is assigned to a ZnO/ZnO (~1.5 eV) homojunction.

• 콘크리트학회논문집
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• 제26권1호
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• pp.79-86
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• 2014

이 연구는 표면매입 보강된 FRP 판과 콘크리트사이의 응력전달기구를 이론적으로 연구한 것으로서 이선형 부착모델을 이용하여 부착거동을 묘사하고 이를 실험 결과와 비교하여 신뢰성있는 해석방법을 제시하였다. 연구로부터, 표면매입된 FRP 판과 콘크리트사이의 계면특성을 고려한 미분방정식에 이선형 부착-미끄러짐 관계곡선을 사용하여 해석할 경우, 모델의 임계값인 최대전단강도와 미끄러짐 변위, 그리고 박락에 의한 연화거동이 시작될 때의 변위값 선정과정이 제시되었다. 또한 제안된 모델을 사용하여 부착길이가 다르게 보강된 표면매입 FRP 판의 미끄러짐 거동을 해석한 결과 실제 거동을 매우 근사하게 묘사할 수 있는 것으로 나타났다.

• 한국전산유체공학회지
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• 제17권1호
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• pp.44-53
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• 2012

Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.

• Tribology and Lubricants
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• 제21권4호
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• pp.171-176
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• 2005

O-ring seal is an essential component in various mechanical apparatuses for a sealing of oil container and pressure vessels. This paper presents the sealing pressure and compressive contact behaviors of hi-polymer O-rings, which is made by an outer shell of FFKM material and an inner solid ring of FKM one. The contact normal pressure and its ratios are measured by experimental method with an automatic control system of the working temperature and analyzed numerically by using the non-linear Marc FEM program. The results show reasonably good agreements between the computed FEM results and measured ones when the operating temperature is kom normal temperature of $18^{\circ}C$ and a high temperature of $300^{\circ}C$ But the compared values between the computed and tested results show a little difference because of the increased temperature, which is related to the non-linear parameter of the O-ring material. Bi-polymer 0-ring shows a good contact normal stress and compression behavior for a given operation temperature and compression ratio.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권4호
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• pp.443-450
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• 2016

The linearization technique for low noise amplifier (LNA) has been implemented in standard $0.18-{\mu}m$ BiCMOS process. The MOS-BJT derivative superposition (MBDS) technique exploits a parallel LC tank in the emitter of bipolar transistor to reduce the second-order non-linear coefficient ($g_{m2}$) which limits the enhancement of linearity performance. Two feedback capacitances are used in parallel with the base-collector and gate-drain capacitances to adjust the phase of third-order non-linear coefficients of bipolar and MOS transistors to improve the linearity characteristics. The MBDS technique is also employed cascode configuration to further reduce the second-order nonlinear coefficient. The proposed LNA exhibits gain of 9.3 dB and noise figure (NF) of 2.3 dB at 2 GHz. The excellent IIP3 of 20 dBm and low-power power consumption of 5.14 mW at the power supply of 1 V are achieved. The input return loss ($S_{11}$) and output return loss ($S_{22}$) are kept below - 10 dB and -15 dB, respectively. The reverse isolation ($S_{12}$) is better than -50 dB.

• Steel and Composite Structures
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• 제4권2호
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• pp.149-167
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• 2004

Offshore platforms have to serve in harsh environments and hence are likely to be damaged due to wave induced fatigue and environmental corrosion. Welded tubular joints in offshore platforms are most vulnerable to fatigue damage. Such damages endanger the integrity of the structure. Therefore it is all the more essential to assess the capacity of damaged structure from the point of view of its safety. Eight internally ring stiffened fatigue damaged tubular joints with nominal chord and brace diameter of 324 mm and 219 mm respectively and thickness 12 mm and 8 mm respectively were tested under axial brace compression loading to evaluate the reserve capacity of the joints. These joints had earlier been tested under fatigue loading under corrosive environments of synthetic sea water and hence they have been cracked. The extent of the damage varied from 35 to 50 per cent. One stiffened joint was also tested under axial brace tension loading. The residual strength of fatigue damaged stiffened joint tested under tension loading was observed to be less than one fourth of that tested under compression loading. It was observed in this experimental investigation that in the damaged condition, the joints possessed an in-built load-transfer mechanism. A bi-linear stress-strain model was developed in this investigation to predict the reserve capacity of the joint. This model considered the strain hardening effect. Close agreement was observed between the experimental and predicted results. The paper presents in detail the experimental investigation and the development of the analytical model to predict the reserve capacity of internally ring stiffened joints.

• 한국재료학회지
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• 제22권12호
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• pp.682-688
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• 2012

In this study we aimed to examine the co-doping effects of 1/6 mol% $Co_3O_4$ and 1/4 mol% $Cr_2O_3$ (Co:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Co,Cr-doped ZBS, ZBS(CoCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ were formed in all systems. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 by Cr rather than Co. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(CoCr), the varistor characteristics were improved (non-linear coefficient, ${\alpha}$ = 20~63), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.20 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to be composed of an electrically single barrier (0.94~1.1 eV) that is, however, somewhat sensitive to ambient oxygen with temperature. The phase development, densification, and microstructure were controlled by Cr rather than by Co but the electrical and grain boundary properties were controlled by Co rather than by Cr.