• Steel and Composite Structures
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• 제30권5호
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• pp.483-492
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• 2019

In the current study, the influence of the initial lateral (sweep) shape and the cross-sectional twist imperfection on the lateral torsional buckling (LTB) response of doubly-symmetric steel I-beams was investigated. The material imperfection (residual stress) was not considered. For this objective, standard European IPN 300 beam with different unbraced span was numerically analyzed for three imperfection cases: (i) no sweep and no twist (perfect); (ii) three different shapes of global sweep (half-sine, full-sine and full-parabola between the end supports); and (iii) the combination of three different sweeps with initial sinusoidal twist along the beam. The first comparison was done between the results of numerical analyses (FEM) and both a theoretical solution and the code lateral torsional buckling formulations (EC3 and AISC-LRFD). These results with no imperfection effects were then separately compared with three different shapes of global sweep and the presence of initial twist in these sweep shapes. Besides, the effects of the shapes of initial global sweep and the inclusion of sinusoidal twist on the critical buckling load of the beams were investigated to unveil which parameter was considerably effective on LTB response. The most compatible outcomes for the perfect beams was obtained from the AISC-LRFD formulation; however, the EC-3 formulation estimated the $P_{cr}$ load conservatively. The high difference from the EC-3 formulation was predicted to directly originate from the initial imperfection reduction factor and high safety factor in its formulation. Due to no consideration of geometric imperfection in the AISC-LFRD code solution and the theoretical formulation, the need to develop a practical imperfection reduction factor for AISC-LRFD and theoretical formulation was underlined. Initial imperfections were obtained to be more influential on the buckling load, as the unbraced length of a beam approached to the elastic limit unbraced length ($L_r$). Mode-compatible initial imperfection shapes should be taken into account in the design and analysis stages of the I-beam to properly estimate the geometric imperfection influence on the $P_{cr}$ load. Sweep and sweep-twist imperfections led to 10% and 15% decrease in the $P_{cr}$ load, respectively, thus; well-estimated sweep and twist imperfections should considered in the LTB of doubly-symmetric steel I-beams.

• 비파괴검사학회지
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• 제30권3호
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• pp.225-235
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• 2010

There are many types of the geometric transitions such as dent, bulge, protrusion, expansion, etc, on the inner and outer surfaces of heat exchanger tubes, steam generator tubes, and condenser tubes of nuclear power plants. Such geometric transition causes a local residual stress in heat exchanger tubes and acts as a structural factor accelerating the evolution of defects, in particular stress corrosion cracks. In the conventional eddy current test methods, the bobbin coil profilometry can provide 2-dimensional geometric information on the variation of the average inner diameter along the tube length, but the 3-dimensional distribution and the quantitative size of a local geometric transition existing in the tube cannot be measured. In this paper, a new eddy current probe, developed for the 3-dimensional profile measurement, is introduced and its superior performance is compared with that from the conventional bobbin coil profilometry for the various types of geometric transition. Also, the accuracy of the probe for the quantitative profile measurement is verified by comparing the results with that from the laser profilometry. It is expected that the new eddy current probe and techniques can be effectively used for an optimization of the tube expansion process, and the management of tubes with geometric transitions in service.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.92-92
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• 2008

The surface flatness of heteroepitaxially grown 3C-SiC thin films is a key factor affecting electronic and mechanical device applications. This paper describes the surface flatness of polycrystalline 3C-SiC thin films by the gas flow control according to the location change of geometric structure. The polycrystalline 3C-SiC thin film was deposited by APCVD(Atmospheric pressure chemical vapor deposition) at $1200^{\circ}C$ using HMDS(Hexamethyildisilane : $Si_2(CH_3)_6)$ as single precursor, and 5 slm Ar as the main flow gas. According to the location of geometric structure, surface fringes and flatness changed. It shows the distribution of thickness is formed uniformly in the specific location of the geometric structure.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송∙미디어공학회 2018년도 추계학술대회
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• pp.87-89
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• 2018

We proposed an improved reliable SVD-based watermarking scheme resistant to geometric attacks while having high fidelity with no false-positive problem. Principal components of a watermark image are embedded into singular values of LL, LH, HL, and HH sub-bands of a transformed cover image by RDWT(redundant discrete wavelet transform) with optimal scale factors. Each scale factor is generated by trading-off fidelity and robustness using Differential Evolution (DE) algorithm. Zernike Moment (ZM) is used to estimate the geometric distortion and to correct the watermarked image before extracting watermark. The proposed scheme improves fidelity and robustness of existing reliable SVD based watermarking schemes while resisting to geometric attacks.

• 대한방사선기술학회지:방사선기술과학
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• 제23권1호
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• pp.13-19
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• 2000

We have presented with the "A study on overexposure rate according to over-density in chest X-ray radiography(I)" last year. In this report, We could calculate the entrance skin dose from chest X-ray film density the formula $I_0=Ix/e^{-{\mu}x}{\times}mG$, (mG is Bucky factor) was used to deliver the skin dose. At that time, There was two problems that the Bucky factor from maker was not equal to field experience and the field size influenced on the Attenuation Rate. The experiment of Bucky factor was done from film method and retried the Attenuation Rate of Acryle phantom according to Good & Poor geometry. As the results, The Bucky factor from maker higher than in this experiments $30{\sim}40%$. The Attenuation Rate in good geometric condition brings about a little alteration compare with poor geometric condition. In the field experiment, we could get the chest image with very low entrance skin radiation dose $29.3{\mu}Sv$, especially with air gap methode, the entrance skin dose was detected $10{\mu}Sv$.

• 디지털융복합연구
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• 제12권8호
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• pp.475-480
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• 2014

대상을 상징하는 기호로서의 의미를 포함하고 있는 기하학적 패턴은 조형표현에 있어서 20세기 이후 예술가들의 작품을 통해 재구성되어 현대적인 이미지를 나타내는 중요한 모티브가 되고 있으며 패턴의 단순하고 간결한 형태는 외형뿐만 아니라 문양 장식을 통하여 새로운 아름다움을 창출하고 있다. 기하학적 패턴의 문양장식은 단순화되고, 이성적이며 현대적인 세련미와 잘 어울린다. 이렇듯 기하학적 패턴을 활용한 문양은 팔각형, 반원, 삼각형, 사각형 등의 기하학적 도형들을 이용하여 단순한 미로 현대인에게 만족감을 준다. 또한, 기하학적 패턴은 규칙적이고 단순명료하여 시각적으로 강렬한 효과를 유도하며 운동감과 속도감이 주는 역동성으로 3차원적 공간감으로 확장되기도 한다. 이로 인해 주목성이라는 특성이 나타나는데 테이블웨어에서도 이러한 기학학적 패턴을 이용한 디자인은 강한 주목성으로 시각적인 즐거움을 준다. 또한 이는 우연성의 요소에 근거해서 만들어지는 형태가 아니기 때문에 객관화될 수 있으며 반복적인 재현이 가능하다. 이러한 반복구성은 테이블웨어를 만드는 많은 디자이너에게 영향을 줄 수 있으며 테이블웨어 디자인을 더욱 더 고급화하여 도자 산업에 고부가가치를 창출할 수 있는 새로운 가능성을 제시할 것으로 생각된다.

• 한국학교수학회논문집
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• 제13권4호
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• pp.655-678
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• 2010

초등수학에서 기하교육은 공간에 대한 직관의 계발을 통해 도형에 대한 이해와 공간 감각을 이끌어내는데 초점을 맞추어야 한다. 이와 함께 시각화는 기하에서의 문제해결 을 결정짓는 중요한 요소 가운데 하나이다. 지금까지 시각화에 대한 분석은 주로 중등 기하교육에서 다루어진 반면, 초등수학에서 평면도형과 공간도형에서의 문제해결과 관련해서 학생들의 시각화에 대한 논의는 부족했다. 본 연구는 초등수학에서 시각화가 기하문제해결에 미치는 영향을 분석한 것으로, 기하문제해결에서 나타나는 시각화 방법과 시각화에 영향을 미치는 요소, 그리고 이 과정에서 나타나는 어려움을 살펴본 것이다. 먼저 평면도형과 입체도형의 문제해결에서 시각화 방법을 구분하여 살펴보고, 이러한 방법에 따라 도형에 대한 이해와 시각화 과정이 어떻게 진행되는지를 도식화하여 살펴본다. 또한 시각화에 영향을 미치는 요소를 구분하고, 시각화 과정의 어려움으로 인해 어떤 오류가 나타나는가를 살펴보고, 이를 통해 초등기하문제해결에서 시각화에 대한 논의를 이끌어낸다.

• 한국안전학회지
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• 제11권2호
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• pp.79-88
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• 1996

A hypothetical accident in the containment vessel of liquid metal reactor could cause a pressure, temperature rise, and a strong aerosol release. The computer codes relating to the modelization of these accident make it necessary to use various input parameter, among which is the dynamic shape factor of aerosols produced. Combustion experiments of sodium spray fire carried out in a closed vessel, which was vertical cylinder made of 1.2m in diameter and 1.8m hight with a volume of 1.7$m^3$. The results of theoretical analysis presented here was compared to data obtained from experiments. The experimental results were summarized as follows. 1) The aerodynamic diameter and geometric diameter of aerosols are decreasing with increasing of injection pressure and injection temperature of sodium 2) The dynamic shape factor of aerosol is proportional to the aerodynamic diameter for a given particle. 3) The correspondence between the aerodynamic diameter and geometric diameter can be as $D_{ae}=0.70 D_{ge}$. 4) Peak pressure rose with increase in pressure and temperature of injection sodium, being more sensitive to the injection pressure than the injection temperature.

• Steel and Composite Structures
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• 제30권4호
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• pp.305-313
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• 2019

Creating different cutout shapes in order to make doors and windows, reduce the structural weight or implement various mechanisms increases the likelihood of buckling in thin-walled structures. In this study, the effect of cutout shape and geometric imperfection (GI) is simultaneously investigated on the critical buckling load and knock-down factor (KDF) of composite cylindrical shells. The GI is modeled using single perturbation load approach (SPLA). First, in order to assess the finite element model, the critical buckling load of a composite shell without cutout obtained by SPLA is compared with the experimental results available in the literature. Then, the effect of different shapes of cutout such as circular, elliptic and square, and perturbation load imperfection (PLI) is investigated on the buckling behavior of cylindrical shells. Results show that the critical buckling load of a shell without cutout decreases by increasing the PLI, whereas increasing the PLI does not have a great impact on the critical buckling load in the presence of cutout imperfection. Increasing the cutout area reduces the effect of the PLI, which results in an increase in the KDF.

• Communications for Statistical Applications and Methods
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• 제7권2호
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• pp.549-562
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• 2000

Default Bayes factors are computed to test the equality of one Poisson population mean and the equality of two independent Possion population means. As default priors are assumed Jeffreys priors, noninformative improper priors, and default Bayes factors such as three intrinsic Bayes factors of Berger and Pericchi(1996, 1998), the arithmetic, the median, and the geometric intrinsic Bayes factor, and the factional Bayes factor of O'Hagan(1995) are computed. The testing results by each default Bayes factor are compared with those by the classical method in the simulation study.