• Wind and Structures
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• 제20권2호
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• pp.213-236
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• 2015

For high-speed railways (HSR) in wind prone regions, wind barriers are often installed on bridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the running safety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PC bridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to perform the dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by a multi-rigid-body system connected with suspension springs and dashpots. The wind excitations on the train vehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained from a wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlation with wind forces on the deck. The whole histories of a train passing over the two bridges under strong cross winds are simulated and compared, considering variations of wind velocities, train speeds and without or with wind barriers. The threshold curves of wind velocity for train running safety on the two bridges are compared, from which the windbreak effect of the wind barrier are evaluated, based on which a beam structure with better performance is recommended.

• 콘크리트학회논문집
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• 제14권6호
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• pp.900-909
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• 2002

섬유는 콘크리트의 취약점인 인장 및 균열저항성을 증가시켜 그 효용성을 크게 한다. 그러나, 섬유의 균열저항성을 합리적으로 예측하기 위해서는 균열후의 거동예측기법이 정립되어야 한다. 따라서, 본 연구의 목적은 최근 들어 개발되고 있는 구조용 합성섬유 보강콘크리트의 균열후 거동(Post-Cracking Behavior)을 예측하기 위한 해석기법을 제시하는데 있다. 이를 위하여 합성섬유 보강 콘크리트 보의 균열단면해석에 있어서, 우선적으로 균열단면을 강체운동으로 가정하고, 균열폭(crack width) 및 균열면에 대해 기울기 90$^{\circ}$ 인 단일섬유의 인발실험(pullout test)에 의한 인발 하중(pullout load)과 변위(slip)의 관계를 이용하여 개개 섬유의 균열이후 거동을 묘사하였다. 또한 실제 섬유의 매립방향과 매립길이의 다양성을 확률적으로 고려하여 균열면에서의 유효섬유개수를 산정한 뒤에 FRC 보의 휨거동해석을 수행하였고, FRC 보 실험을 시행한 결과와 비교한 결과 잘 일치하는 것으로 나타났다. 본 해석결과로부터 하중-처짐 곡선, 모멘트-곡률 곡선 등을 도출할 수 있으며, 본 연구의 모델은 일정수준의 균열 저항성 또는 인성지수(toughness performance)를 얻기 위한 섬유의 기하형상을 개발하는데 유용한 방법으로 사용될 수 있다. 또한 평균응답, 파괴모드의 운동학으로 표현된 이 모델은 FRC 보 실험 결과들을 유사하게 예측할 수 있기 때문에 앞으로 섬유보강콘크리트 부재의 합리적인 설계 및 해석에 효율적으로 활용될 수 있을 것으로 사료된다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국제학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.826-831
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• 1988

This paper presents an approach to segment an image into areas of surfaces, and to compute the surface properties from a gray-scale image in order to describe the surfaces for reconstruction of the 3-D shape of the objects. In general, an rigid body has several surfaces and many edges. But if it is not polyhedoron, it is necessary not only to describe the relation between surfaces, i.e. its line drawings but also to represent the surfaces' equations itself. In order to compute the surfaces' equation we use a probability of edge distribution. At first it is extracted edges from a gray-level image as much as possible. These are not only the points that maximize the change of an image intensuty but candidates which can be seemed to be edges. Next, other character of a surface (color, coordinates and image intensity) are extracted. In our study, we call the all feature of a surface as "texture", for example color, intensity level, orientation of an edge, shape of a surface and so on. These features of a surface on a pixel of an image plane are mapped to a point of the feature space, and segmented to each groups by cluster analysis on this space. These groups are considered to represent object surface in an image plane. Finally, the states of object surface in 3-D space are computed from distributional probability of local and overall statistical features of a surface, and from shape of a surface.a surface.

• 대한기계학회논문집A
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• 제40권5호
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• pp.497-503
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• 2016

머플러의 확장방 내부에 격벽을 최적으로 배치하기 위한 음향 위상 최적화 문제를 정식화 한다. 목표 주파수에서 삽입 손실의 하한 값을 제한하며, 격벽의 부피를 목적 함수로 선정하여 최소화한다. 기존 연구에서는 투과 손실이나 덕트 내부에서 계산된 삽입 손실을 머플러의 소음 저감 특성으로 사용하였으나, 본 연구에서는 덕트 외부에서 계산된 삽입 손실을 사용한다. 음향 해석을 위해 유한 요소 모델이 사용되고, 각 유한 요소에 입사된 음파의 투과 정도는 "0"과 "1" 사이에서 연속적으로 변화하는 설계변수의 함수에 의해 결정된다. 입사파를 모두 반사시키는 강체들이 격벽을 형성한다. 목적 주파수와 허용하는 삽입손실 값에 따른 최적 위상을 비교한다.

• 한국정밀공학회지
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• 제28권8호
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• pp.904-914
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• 2011

The volumetric errors of CNC machining centers are determined by 21 errors, including 3 linear errors, 6 straightness errors, 3 perpendicular errors, 9 angular errors and non-rigid body errors of the machine tool. It is very time consuming and hard to measure all of these errors in which laser interferometer and other parts are used directly. Hence, as many as 21 separate setups and measurements are needed for the linear, straightness, angular and perpendicular errors. In case of the 5-axis machining centers, two more rotary tables are used. It can make 35 error sources of the movement. Therefore, the measured errors of multi movements of the 5-axis tables are very complicated, even if the relative measured errors are measured. This paper describes the methods, those analyze the error sources of the machining centers. Those are based on shifted diagonal measurements method (SDM), R-test and Double ball bar. In case, the angular errors of machine are small enough comparing with others, twelve errors including three linear position errors, six straightness errors and three perpendicular errors can be calculated by using SDM. To confirm the proposed method, SDM was applied to measuring 3 axes of machine tools and compared with directly measurement of each errors. In addition, the methods for measuring relative errors of multi-axis analysis methods using R-test and Double Ball Bar are introduced in this paper.

• Archives of Plastic Surgery
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• 제36권4호
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• pp.475-480
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• 2009

Purpose: To correct the facial asymmetry and to achieve symmetry and balance, not only the soft tissue restoration of deficits but also creation and facial contour line such as mandible border and angle is important. Micro fat graft has limitation such as high resorption rate and somewhat limited ability to emphasize the rigid bony characteristics of the mandible angle due to its innate soft consistency. We have investigated the advantages of dermal fat graft over micro fat graft to correct asymmetry of the lower face in patients who had undergone mandibular reconstruction or distraction, using comparative analysis. Methods: Total of 12 patients were enrolled in our study: 6 micro fat graft and 6 dermal fat graft. Postoperative results were compared and analyzed at immediate postoperative period and more than 1 year later in each group with photographs, and analysised with image J program. Result: No complications were noted both in the micro fat type and the dermal fat type of procedures such as fat necrosis or micro calcifications. All of the patients who received micro fat graft, however had considerable amount of fat resorption after the procedure which led to two additional fat graft procedures. Although minor contour obliteration due to contracture was seen in patients who had undergone dermal fat graft procedure, no definite resorption was found even after more than one year follow-up. Results of dermal fat graft patients were satisfactory in terms of mandible angle symmetry. Secondary revision was necessary in one case due to overcorrection using dermal fat graft. Conclusion: The dermal fat graft has many advantages over the conventionally more popular micro fat graft to correct asymmetry of the lower face following mandible reconstruction owing to its lower resoption rate, more effective in emphasizing the natural curvilinear anatomical contours of the mandible angle and body and lower complication rates such as fat necrosis or micro calcifications.

• 한국강구조학회 논문집
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• 제11권2호통권39호
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• pp.153-165
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• 1999

비대칭단면을 갖는 박벽 공간뼈대구조의 횡후좌굴거동을 조사하기 위하여 기하학적 비선형 유한요소 해석법을 제시한다. 대변형효과를 고려한 연속체의 증분평형방정식으로부터, 도심에서 정의되는 딤(warping)함수를 고려하고 유한한 회전각의 2차항 효과를 포함하는 변위장을 도입하여 초기응력을 받는 박벽 공간뼈대요소의 증분평형방정식을 유도한다. 박벽 공간뼈대구조를 유한요소로 나누고 변위장을 요소변위에 관한 Hermitian 다항식으로 나타내어 이를 평형방정식에 대입함으로써 접선강도행렬을 유도한다. 또한 updated Lagrangian co-rotational formulation에 근거하여, 증분변위로부터 강체회 전변위와 순수변형성분을 분리시켜서 강체회전은 요소의 방향변화를 결정하고, 순수변형은 부재력증분을 산정하는 불평형하중 산정법을 제시한다.

• 대한기계학회논문집A
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• 제34권3호
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• pp.283-289
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• 2010

친환경기술과 신재생 에너지 자원에 대한 세계적인 관심이 증가하면서, 플라이휠 에너지 저장 장치는 화학전지나 연료전지와 같은 기존의 에너지 저장 시스템의 대안 중 하나로 부상하고 있다. 플라이휠 에너지 저장장치의 에너지 저장 용량은 극질량 관성모멘트와 회전속도의 제곱에 비례하기 때문에, 가능한 높은 회전속도와 높은 극질량 관성모멘트를 갖도록 설계하는 것이 중요하다. 하지만, 시스템의 운전안정성 확보가 최적설계의 구속조건으로 작용할 수 있다. 본 논문에서는 에너지 저장 용량을 최대화하고 운전안정성 및 외란에 대한 강인성을 확보하는 플라이휠 시스템의 최적설계를 제안한다. 그리고, 기존의 PD 제어에 비교하여 교차궤환제어법이 자이로스코프효과를 줄이고, 에너지 저장밀도를 높이는데 필수적임을 확인하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권1호
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• pp.116-131
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• 2013

The resistance performance of an icebreaking cargo vessel in pack ice conditions was investigated numerically and experimentally using a recently developed finite element (FE) model and model tests. A comparison between numerical analysis and experimental results with synthetic ice in a standard towing tank was carried out. The comparison extended to results with refrigerated ice to examine the feasibility of using synthetic ice. Two experiments using two different ice materials gave a reasonable agreement. Ship-ice interaction loads are numerically calculated based on the fluid structure interaction (FSI) method using the commercial FE package LS-DYNA. Test results from model testing with synthetic ice at the Pusan National University towing tank, and with refrigerated ice at the National Research Council's (NRC) ice tank, are used to validate and benchmark the numerical simulations. The designed ice-going cargo vessel is used as a target ship for three concentrations (90%, 80%, and 60%) of pack ice conditions. Ice was modeled as a rigid body but the ice density was the same as that in the experiments. The numerical challenge is to evaluate hydrodynamic loads on the ship's hull; this is difficult because LS-DYNA is an explicit FE solver and the FSI value is calculated using a penalty method. Comparisons between numerical and experimental results are shown, and our main conclusions are given.

• 대한치과교정학회지
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• 제49권6호
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• pp.393-403
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• 2019

Objective: Sliding mechanics using orthodontic miniscrews is widely used to stabilize the anchorage during extraction space closure. However, previous studies have reported that both posterior segment displacement and anterior segment displacement are possible, depending on the mechanical properties of the archwire. The present study aimed to investigate the effect of archwire stiffness and friction change on the displacement pattern of the maxillary posterior segment during anterior segment retraction with orthodontic miniscrews in sliding mechanics. Methods: A three-dimensional finite element model was constructed. The retraction point was set at the archwire level between the lateral incisor and canine, and the orthodontic miniscrew was located at a height of 8 mm from the archwire between the second premolar and first molar. Archwire stiffness was simulated with rectangular stainless steel wires and a rigid body was used as a control. Various friction levels were set for the surface contact model. Displacement patterns for the posterior and anterior segments were compared between the conditions. Results: Both the anterior and posterior segments exhibited backward rotation, regardless of archwire stiffness or friction. Among the conditions tested in this study, the least undesirable rotation was found with low archwire stiffness and low friction. Conclusions: Posterior segment displacement may be unavoidable but reducing the stiffness and friction of the main archwire may minimize unwanted rotations during extraction space closure.