• Journal of the Institute of Convergence Signal Processing
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• v.5 no.1
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• pp.18-24
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• 2004

SPECT technology is used for the reconstructed image in the field of industry noncontact measurement system. One of the distortion problems in reconstructed image quality is a collimator characterictic. The image distortion is caused by a geometrical structure of the collimator. This paper indicated a correction method to remove the image distortion by the structure of the collimator, and compared with the existing correction method. The correction. method removed the image distortion to use deconvolution of projection data with the shift-variant blurring function in the frequency domain. In this pater, I simulated with the collimator angle and distance between the detector and the center of object. and verified with expeimental data. The validity and limitation of correction method is studied for actual industrial applications.

• Proceedings of the Korean Geotechical Society Conference
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• 1998.05a
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• pp.35-81
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• 1998

Distinct Element Method(DEM) has a great advantage to model the discontinuous behaviour of jointed rock masses such as rotation, sliding, and separation of rock blocks. Geometrical data of joints by a field monitoring is not enough to model the jointed rock mass though the results of DE analysis for the jointed rock mass is most sensitive to the distributional properties of joints. Also, it is important to use a properly joint law in evaluating the stability of a jointed rock mass because the joint is considered as the contact between blocks in DEM. In this study, a stochastic modelling technique is developed and the dilatant rock joint is numerically modelled in order to consider th geometrical and mechanical properties of joints in DE analysis. The stochastic modelling technique provides a assemblage of rock blocks by reproducing the joint distribution from insufficient joint data. Numerical Modelling of joint dilatancy in a edge-edge contact of DEM enable to consider not only mechanical properties but also various boundary conditions of joint. Preprocess Procedure for a stochastic DE model is composed of a statistical process of raw data of joints, a joint generation, and a block boundary generation. This stochastic DE model is used to analyze the effect of deviations of geometrical joint parameters on .the behaviour of jointed rock masses. This modelling method may be one tool for the consistency of DE analysis because it keeps the objectivity of the numerical model. In the joint constitutive law with a dilatancy, the normal and shear behaviour of a joint are fully coupled due to dilatation. It is easy to quantify the input Parameters used in the joint law from laboratory tests. The boundary effect on the behaviour of a joint is verified from shear tests under CNL and CNS using the numerical model of a single joint. The numerical model developed is applied to jointed rock masses to evaluate the effect of joint dilation on tunnel stability.

• Journal of Korean Society of Steel Construction
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• v.16 no.4 s.71
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• pp.407-414
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• 2004

Bridges in common use are expected to have more varieties of load in their connected members and bolts than in construction. Faults in connection members or bolts occur so often according to the time flow. One of the purposes of this study is to find out the behavior and structural features of high-tension bolted joints with faults that are very difficult and cost much to find out through experimentation with finite element analysis. Another purpose of this study is to provide sufficient data, estimated experimental results, and the scheme of the test plate for an economical experimental study in the future. Surveys of bridges with a variety of faults and statistical classifications of their faults were performed, as was a finite element analysis of the internal stress and the sliding behavior of standard and defective bridge models. The finite element analysis of the internal stress was performed according to the interval of the bolt, the thickness of the plate, the distance of the edge, the diameter of the bolt, and the expansion of the construction. Furthermore, the analysis explained the sliding behavior of high-tension bolt joints and showed the geometric non-linear against the large deformation, and the boundary non-linear against the non-linear in the contact surface, including the material non-linear, to best explain the exceeding of the yield stress by sliding. A normally bolted high-tension bolt joint and deduction of bolt tension were also analyzed with the finite element analysis of bridge-sliding behavior.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.153-153
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• 2011

현대 건축은 기능적이고 합리적이었지만 획일적이었던 박스형 건축에서 탈피해 형태와 공간에 있어서 다양한 변화를 시도하고 있다. 특별한 건축물의 실현을 위해 각 나라의 기술력은 급속한 발전을 이루었고, 보다 더 독특한 건축물에 대한 관심은 비정형 건축물에 대한 관심의 증대로 이어지고 있다. 이러한 비정형 건축물에 적합한 구조로써 프리폼(Free-Form) 구조가 있다. 프리폼 구조로 입체골조(Double Layered Structure)를 많이 사용하였으나, 최근 유리로 되어 투명하고 기하학적 모양의 건축물을 추구함에 따라 평면골조(Single Layered Structure)가 증가하고 있는 추세이다. 평면골조는 축력 지배형과 모멘트 지배형으로 분류할 수 있고 프리폼 구조의 구성 요소 중 가장 취약하고 중요한 부분은 노드이다. 본 연구에서는 프리폼 구조 중 가장 큰 관심이 고조되고 있는 평면골조 모멘트 지배형의 노드에 대한 국내외 기술 분석을 통해 향후 연구 방향성을 제시하고자 한다. 입체골조는 하나의 노드에 여러개의 부재가 3차원으로 결합되어야 하기 때문에 다른 골조 시스템에 비해 노드부가 복잡하지만, 건축물의 외관을 유리로 하여 투명하게 하고 비틀리고 구부러진 구조물에 대한 건축적 요구가 많아짐에 따라 평면골조의 인기가 높아지고 있다. 이러한 시대의 흐름에 발맞추어 건물의 구조적, 기하학적 요구를 충족시키기 위해 다양한 노드 시스템이 개발 중이며, 가해지는 하중의 특성에 따라 축력 지배형과 모멘트 지배형으로 구분하여 노드의 양상을 분류할 수 있다. 축력 지배형의 대표적인 시스템은 다이아그리드(Diagrid)이다. 축력 지배형 프리폼 구조의 노드는 전체 구조물의 하중을 축력으로 받아 모두 전달해야 하기 때문에 크기가 크고 가새가 2~4개층에 걸쳐서 설치되기 때문에 중량이다. 모멘트 지배형 노드를 갖는 프리폼 구조의 형태는 대부분 지붕 구조로써 지붕 자체의 하중만을 견디도록 설계된다. 따라서 노드부와 노드에 붙는 부재들이 가볍기 때문에 사람이 들 수 있고 노드의 크기가 작아 시공성이 좋으며 대량 생산이 가능하다는 장점이 있다. 노드의 형태는 힘의 흐름과 쓰임에 따라 다양하다. 평면골조 모멘트 지배형의 노드는 접합방식에 따라 Splice node connection과 End-Face node connection 두 가지로 분류할 수 있다. Splice node connection은 각 부재의 종축으로 노드와 구조부재 사이에 이음재를 두어 연결하고, 연결 형태에 따라 전단력을 전달할 수 있는 1~2개의 접촉면이 생긴다. 전단응력을 받는 볼트로 이음재를 이어 조립하거나 용접으로 접합할 수 있다. 대표 노드로, SBP-1, SBP-2와 POLO-1 등이 있다. End-Face node connection은 각 연결된 부재의 단부와 노드 사이의 연결면은 종축방향의 수직이고, 인장응력을 받는 볼트를 사용하거나 용접에 의해 접합할 수 있다. 대표 노드로 SBP-4, WABI-1, MERO-1(Cylinder), MERO-2(Block), MERO-4(Double Dish) 등이 있다. 본 기술 현황 분석을 통해 현재 개발된 노드를 분류하고 가장 관심이 높은 Single Layer 모멘트 지배형 노드를 비교, 분석하였다. 최근 건물의 경향을 반영한 프리폼 구조를 실현하기 위해서 필수적인 노드의 개발은 국외에서 활발히 연구되고 있지만 그 기술이 개방되어 있지 않다. 국내에서는 동대문 디자인 플라자에 새로운 노드를 적용하고 고려대학교에서 모멘트 지배형 노드를 개발하는 등 발전 가능성을 보이고 있지만 국외 사례들에 비하면 아직 초기 단계라 할 수 있다. 따라서 현장 용접을 지양하고 공장 제작하여 현장에서 조립하며, 프로젝트 별로 상이한 노드를 사용하는 것이 아닌 다양한 요구를 효과적으로 수용하는 구조 효율성을 향상시킨 노드 상세의 개발이 이루어져야 할 것이다.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.31-37
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• 2007

A $^{192}Ir$ small-focal source has been developed by using the HANARO reactor and the radioisotope production facility at the Korea Atomic Energy Research Institute (KAERI). The small-focal source with the dimension of 0.5 mm in diameter and 0.5 mm in length was fabricated as an aluminum-encapsulated form by a specially designed pressing equipment. For the estimation of the radioactivity, neutron self-shielding and ${\gamma}-ray$ self-absorption effects on the measured activity was considered. From this estimation, it is realized that $^{192}Ir$ small-focal sources over 3 Ci activities can be produced from the HANARO. Field performance tests were performed by using a conventional source and the developed source to take images of a computer CPU and a piece of a carbon steel. The small-focal source showed better penetration sensitivity and geometrical sharpness than the conventional source does. It is concluded from the tests that the focal dimension of this source is small enough to maximize geometrical sharpness in the image taking for the close proximity shots, pipeline crawler applications and contact radiography.

• Elastomers and Composites
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• v.39 no.1
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• pp.12-22
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• 2004

The plasma surface modification of natural rubber vulcanizate was carried out using chlorodifluoromethane in a radio-frequency (13.56 MHz) electrodeless bell type plasma reactor. The modification was qualitatively assessed by Fourier transform infrared spectroscopy. The frictional force of the plasma-treated surface was found to decrease with the time of plasma treatment. An increase in the surface polarity, as evidenced by the decrease in contact angle of a sessile drop of water and ethylene glycol on the natural rubber vulcanizate surface, was noted with the plasma modification. In the case of similar plasma treatment of glass surface, only a reduction in the polarity was observed. The use of geometric and harmonic mean methods was found to be useful to evaluate the London dispersive and specific components of surface free energy. Irrespective of the method used for evaluation, an increasing trend in the surface free energy was noted with increasing plasma treatment time. However, the harmonic mean method yielded comparatively higher values of surface free energy than the geometric mean method. The plasma surface modification was found to vary the frictional coefficient by influencing the interfacial, hysteresis and viscous components of friction in opposing dual manners.

• Composites Research
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• v.34 no.3
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• pp.155-160
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• 2021

Metamaterials are complexes of elements that can create properties not found in naturally occurring materials, such as changing the direction of forces, creating negative stiffness, or altering vibration and impact properties. In the case of wood pile metamaterials that are easy to manufacture and have excellent performance in reducing vibration and shock in the vertical direction, basic research on variables affecting shock transmission is needed to reduce shock. Although research on impact reduction according to geometrical factors is being conducted recently, studies on the effect of material variables on impact reduction are insufficient. In this paper, finite element analysis was carried out by variablizing the geometrical properties (lamination angle, diameter, length) and material properties (modulus of elasticity, specific gravity, Poisson's ratio) of wood pile cylinders. Through finite element analysis, the shape of the wooden pile cylinder delivering impact was confirmed, and the effect of each variable on the reduction of impact force and energy was considered through main effect diagram analysis, and frequency band analysis was performed through fast Fourier transform. proceeded In order to reduce the impact force and vibration, it was found that the variables affecting the contact area of t he cylinder have a significant effect.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.4
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• pp.9-16
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• 2014

Electrode contact resistance is a crucial factor in physiological measurements and can be an accuracy limiting factor to perform electrical impedance measurements. The electrical bio-impedance values can be calculated by the conductivity and permittivity of underlying tissue using implant electrode in human skin. In this study we focus on detecting physiological changes in the human skin layers such as the sebum layer, stratum corneum layer, epidermis layer, dermis layer, subcutaneous fat and muscle. The aim of this paper is to obtain optimal design for implantable electrode at subcutaneous fat layer through the simulation by finite element methods(FEM). This is achieved by evaluating FEM simulations geometrically for different electrodes in length(50 mm, 70 mm), in shape(rectangle, round square, sexangle column), in material(gold) and in depth(22.325 mm) based on the information coming from the subcutaneous fat layer. In bio-impedance measurement experiments, according to electrode shapes and applied voltage, we have ascertained that there was the highest difference of bio-impedance in subcutaneous fat layer. The methodology of simulation can be extended to account for different electrode designs as well as more physical phenomena that are relevant to electrical impedance measurements of skin and their interpretation.

• Economic and Environmental Geology
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• v.54 no.4
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• pp.465-473
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• 2021

This numerical study aims at analyzing the effect of flow characteristics, caused by geometrical features such as intersecting angles, on solute mixing at fracture junctions. It showed that not only Pe, the ratio of advection to diffusion, but also the intersecting angles played an important role in solute mixing at the junction. For the intersection angles less than 90°, the fluid flowed to the outlet in the same direction as the injected flow direction, which increased the contact at the junction with the streamlines coming from the different inlets. On the other hand, for the intersecting angles greater than 90°, the fluid flowed out to the outlet opposite to the flow direction in the inlet, leading to minimizing the contact at the junction. Therefore, in the former case, solute mixing occurred even at high Pe, and in the latter case, solutes transport along the streamlines even at low Pe. For Pe < 1, the complete mixing model was known to occur, but for the intersecting angle greater than 150°, no complete solute mixing occurred. Overall, the transition from the complete mixing model to the streamline-routing model occurred for Pe = 0.1 - 100, but it highly depended on the intersecting angles. Specifically, the transition occurred at Pe = 0.1 - 10 for intersecting angles ≧ 150° and at Pe = 10 - 100 for intersecting angles ≦ 30°. For Pe > 100, the streamline-routing model was dominant regardless of intersecting angles. For Pe > 1,000, the complete streamline-routing model appeared only for the intersecting angles greater than 150°. For the intersecting angles less than 150°, the streamline-routing model dominated over the complete solute mixing, but solute mixing still occurred at the fracture junction.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.2
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• pp.141-151
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• 2003

Railway bridges are subject to dynamic loads generated by the interaction between moving vehicles and the bridge structures. These dynamic loads result in response fluctuations in bridge members. To investigate the real dynamic behavior of the bridge, therefore, a number of analytical and experimental Investigations should be carried out. In this paper, a train/track/bridge interaction analysis program for evaluating the dynamic characteristics of bridges due to KTX operation in terms of structural safety, operational safety and passenger comfort is developed. To build a practical model of train/track/bridge, Hertzian spring for wheel/rail contact modeling and Winkler element for ballast are applied. This program also used torsional degree of freedom and constraint equation based on geometrical relationship in order to take into consideration three-dimensional eccentricity effect due to the operation on double track through quasi-three dimensional analysis. To verify the developed Program, comparison has been made between the measured results and those of simulation of the typical PSC box bridge(2@40m=80m) of the KHSR bridges.