• 대한조선학회논문집
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• 제47권6호
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• pp.843-849
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• 2010

This paper presents definition of symmetry of a ship section where three symmetries are proposed: material, geometric, and load symmetries. Precise terminologies of centroid, moment plane, and neutral axis plane are also defined. It is suggested that force vector equilibrium as well as force equilibrium are necessary condition to determine new position of neutral axis due to translational and rotational mobility. It is also stated that new reference datum of ENMP(elastic neutral moment plane), PNMP(fully plastic moment plane), ENAP(elastic neutral axis plane), and INAP(inelastic neutral moment plane) are required to define asymmetric section properties such as second moment of area, elastic section modulus, yield moment, fully plastic moment, and ultimate moment. Since collision-induced damage and flooding-induced biaxial bending moment produce typical asymmetry of section, the section properties are calculated for a typical VLCC. Geometry asymmetry is determined from ABS and DNV rules and two moment planes of 0/30 degs are assumed for load asymmetry. It is proved that the property reduction ratios directly calculated from second moment of area are usually larger than area reduction ratio. Reduction ratio of ultimate moment capacity shows almost linearly proportional to area reduction ratio. Mobility of elastic and inelastic neutral axis planes is visually provided.

• 대한조선학회논문집
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• 제48권3호
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• pp.281-287
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• 2011

This paper explains the basic theory and a new development of for the residual strength prediction program of the asymmetrically damaged ships, being capable of searching moment-curvature relations considering neutral axis mobility. It is noted that moment plane and neutral axis plane should be separately defined for asymmetric sections. The validity of the new program is verified by comparing moment-curvature curves of 1/3 scaled frigate model where the results from new algorithm well coincide with experimental and nonlinear FEA results for intact condition and with nonlinear FEA results for damaged condition. Applicability of new algorithm is also verified by applying VLCC model to the newly developed program. It is proved that reduction of residual strengths is visually presented using the new algorithm when damage specifications of ABS, DNV and IMO are applied. It is concluded that the new algorithm shows very good performance to produce moment-curvature relations with neutral axis mobility on the asymmetrically damaged ships. It is expected that the new program based on the developed algorithm can largely reduce design period of FE modeling and increase user conveniences.

• Steel and Composite Structures
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• 제28권5호
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• pp.589-606
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• 2018

The previous studies reflected the significant effect of neutral-axis position and coupling of in-plane and out-of-plane displacements on behavior of functionally graded (FG) nanobeams. In thin FG beam, this coupling can be eliminated by a proper choice of the reference axis. In shear deformable FG nanobeam, not only this coupling can't be eliminated but also the position of neutral-axis is dependent on through-thickness distribution of shear strain. For the first time, in this paper it is avoided to guess a shear strain shape function and the exact shape function and consequently the exact position of neutral axis for arbitrary gradation of higher order nanobeam are obtained. This paper presents new methodology based on differential transform and collocation methods to solve coupled partial differential equations of motion without any simplifications. Using exact position of neutral axis and higher order beam kinematics as well as satisfying equilibrium equations and traction-free conditions without shear correction factor requirement yields to better results in comparison to the previously published results in literature. The classical rule of mixture and Mori-Tanaka homogenization scheme are considered. The Eringen's nonlocal continuum theory is applied to capture the small scale effects. For the first time, the dependency of exact position of neutral axis on length to thickness ratio is investigated. The effects of small scale, length to thickness ratio, Poisson's ratio, inhomogeneity of materials and various end conditions on vibration and buckling of local and nonlocal FG beams are investigated. Moreover, the effect of axial load on natural frequencies of the first modes is examined. After degeneration of the governing equations, the exact new formulas for homogeneous nanobeams are computed.

• Steel and Composite Structures
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• 제45권5호
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• pp.729-747
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• 2022

The critical buckling loads and buckling modes of bi-directional functionally graded porous unified higher order shear plate with elastic foundation are investigated. A mathematical model based on neutral axis rather than midplane is developed in comprehensive way for the first time in this article. The material constituents form ceramic and metal are graded through thickness and axial direction by the power function distribution. The voids and cavities inside the material are proposed by three different porosity models through the thickness of plate. The constitutive parameters and force resultants are evaluated relative to the neutral axis. Unified higher order shear plate theories are used to satisfy the zero-shear strain/stress at the top and bottom surfaces. The governing equilibrium equations of bi-directional functionally graded porous unified plate (BDFGPUP) are derived by Hamilton's principle. The equilibrium equations in the form of coupled variable coefficients partial differential equations is solved by using numerical differential integral quadrature method (DIQM). The validation of the present model is presented and compared with previous works for bucking. Deviation in buckling loads for both mid-plane and neutral plane are developed and discussed. The numerical results prove that the shear functions, distribution indices, boundary conditions, elastic foundation and porosity type have significant influence on buckling stability of BDFGPUP. The current mathematical model may be used in design and analysis of BDFGPU used in nuclear, mechanical, aerospace, and naval application.

• 대한치과교정학회지
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• 제25권3호
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• pp.273-286
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• 1995

안면골 성장유형에 따른 두개안면골의 성장양상의 차이를 조사하기 위하여 정상교합자 남자 19명 여자 14명으로 부터 8.5세에서 18.5세까지 10년 동안에 걸쳐 촬영한 연속 두부방사선규격사진을 분석 조사하였다. 이 조사에서 안면골 성장유형은 최초 8.5세에서 10년 후인 18.5세 사이의 Y-axis의 총변화량을 기준으로 Drop, Neutral, Forward군으로 구분하였다. 각 군에서 안면 각 부위의 변화를 계측 분석하여 각 유형의 10년간 성장양상의 차이를 조사한 결과는 다음과 같이 요약할 수 있었다. 본 연구에 사용된 대상에서 두개안면골 성장양상의 분포는 Neutral군이 52%, Forward군이 27%, Drop군이 21%로 나타났다. 두개저에 대한 상,하악골익 전방성장은 Forward군이 Drop군에 비해 크게 나타났으며 Neutral군과 Forward군에서 상악에 비해 하악의 전방성장이 크게 나타났다. FH plane에 대한 palaltal plane의 기울기는 연구기간 동안 Forward군이 다른 두 군에 비해 전상방으로 경사되면서 성장하였다. 또한 하악평면은 Forward군이 Drop군에 비해 반시계 방향의 회전이 크게 나타났으며 이런 경향은 남자가 여자보다 크게 나타났다. 하악체부(Go-Me)의 길이 성장은 Drop군이 Forward, Neutral군에 비해 작게 나타났다 본 연구에서 안면골의 성장에 관하여 길이 및 각도적 계측치는 각기 다양하게 나타났으나 수직적 비율의 특성은 각 군에서 비교적 일관성 있게 유지되는 경향을 나타내었다. 이상의 분석자료를 이용하여 교정진단시 개개인의 성장양상을 평가하기 위하여 8.5세에서 18.5세까지 성장유형별 Profilogram을 작성 제시하였다.

• Architectural research
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• 제13권4호
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• pp.53-60
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• 2011

Damage detection algorithms based on a one-dimensional beam model can detect damage within a beam span caused by flexure only but cannot detect damage at a joint with prescribed boundary conditions or at the middle part of a beam section where the neutral axis is located. Considering the damage at a welded joint of beam elements in steel structures and modeling the damage with twodimensional plane elements, this study presents a new approach to detecting damage in the depth direction of the joint and beam section. Three damage scenarios at the upper, middle, and lower parts of a welded joint of a rectangular symmetric section are investigated. The damage is detected by evaluating the difference in the receptance magnitude between the undamaged and damaged states. This study also investigates the effect of measurement locations and noise on the capability of the method in detecting damage. The numerical results show the validity of the proposed method in detecting damage at the beam's welded joint.

• 대한치과교정학회지
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• 제26권5호
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• pp.557-568
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• 1996

본연구는 안면성장유형에 있어서의 피개교합심도지수, 전후방부조화지수의 성장에 따른 변화 양상을 알아 보기 위하여 정상교합자 남자 19명, 여자 14명의 10년간 격년으로 촬영한 두부 X-선 규격사진을 Y-axis의 연구기간동안 총변화량에 따라 Drop, Neutral, Forward의 세군으로 나누어 분석하여 각 계측항목에 관하여 다음과 같은 결과를 얻었다. $\cdot$ 남녀 각 안면유형에서 각 연령군의 각 계측항목의 평균과 표준편차를 얻었다. $\cdot$ 안면유형에 따른 세 그룹간 비교에서 전후방부조화지수와 피개교합심도지수는 전 연령구간에서 유의차를 나타내지 않았다(p>0.05). 피개교합심도지수는 남녀 모두 전 연령구간에서 Drop, Neutral, Forward의 크기순으로 나타났다. $\cdot$ 피개교합심도지수와 전후방부조화지수는 전연구기간동안 연령증가에 따른 변화없이(p>0.05) 안정되게 유지되는 양상을 보였다. $\cdot$ Y-axis의 총변화량과 각 계측항목의 상관성 조사에서 A-B plane angle, Facial angle은 남녀 모두에서 상관성을 나타내었고(p<0.05) 전후방부조화지수는 여자에서만 상관성을 나타내었으나(p<0.001) 피개교합심도지수는 남녀 모두에서 상관성을 나타내지 않았다(p>0.05).

• Journal of Welding and Joining
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• 제31권5호
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• pp.7-14
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• 2013

The legitimacy of dominating factor in the high accuracy prediction of welding distortion was investigated for butt welding and fillet welding. When out-of-plane distortion was measured by the experiment objecting to butt welding, if tack welding was easily performed, the position of a neutral axis was variously changed by the irregularity. Then, there have been a case that out-of-plane distortion was generated in the unexpected direction. This case should be especially noted. New model for the experiment was proposed so as to solve this problem. As it was elucidated by the case of fillet welding, it was verified that the analysis should be carried out with satisfying the yield condition (especially at high temperature above 700 degree Celsius) and with closely simulating the penetration shape (heat input in weld metal) in order to solve the proposition that is the high accuracy prediction of welding distortion. It was confirmed that residual stress is highly predicted because welding distortion is highly predicted, too.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.14-26
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• 2014

This paper provides the prediction of ultimate longitudinal strengths of the hull girders of a very large crude carrier considering probabilistic damage extent due to collision and grounding accidents based on IMO Guidelines (2003). The probabilistic density functions of damage extent are expressed as a function of non-dimensional damage variables. The accumulated probabilistic levels of 10%, 30%, 50%, and 70% are taken into account for the estimation of damage extent. The ultimate strengths have been calculated using the in-house software called Ultimate Moment Analysis of Damaged Ships which is based on the progressive collapse method, with a new convergence criterion of force vector equilibrium. Damage indices are provided for several probable heeling angles from $0^{\circ}$ (sagging) to $180^{\circ}$ (hogging) due to collision- and grounding-induced structural failures and consequent flooding of compartments. This paper proves from the residual strength analyses that the second moment of area of a damage section can be a reliable index for the estimation of the residual ultimate strength. A simple polynomial formula is also proposed based on minimum residual ultimate strengths.

• Transactions on Electrical and Electronic Materials
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• 제8권5호
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• pp.191-195
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• 2007

We investigated photoluminescence characteristics of ZnO nano needle-like rods grown on a c-plane $AL_2O_3$ substrate by the hot wall epitaxy method. The nano-rods were vertically well aligned along the ZnO c-axis. The diameters of the ZnO nano-rods ranged from 20 nm to 30 nm and their lengths were between 600 and 700 nm. In the photoluminescence spectrum at 10 K, the exciton emission bound to the neutral donor dominated while defect related emission was weakly observed. With a further increase of temperature, the free exciton emission appeared and eventually became dominant at room temperature.