• 한국가스학회지
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• 제12권3호
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• pp.31-37
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• 2008

본 본문에서는 유한요소법을 사용하여 여러 가지 헬멧 모델의 강도안전에 관한 응력과 변형률을 해석하였다. 차세대 헬멧은 작업자의 안전성과 작업성을 높일 수 있도록 제작되어야 하고, 오랫동안 착용해도 불편함이 없으면서 머리를 보호할 수 있어야 한다. 결국 헬멧은 안전하고, 착용성이 좋아야 하며, 헬멧의 모체 구조물을 가볍게 제작해야 한다. 따라서 헬멧은 화재나 가스폭발과 같은 가혹한 작업조건에 잘 견딜 수 있어야 한다. FEM 해석결과에 의하면, 외부의 충격력이 헬멧모체 구조물의 정상부 지역에 가해졌을 경우 최대응력과 변형률은 하중이 작용되는 지점부위에서 발생하였다. 따라서 헬멧의 모체 구조물에는 보강뼈대를 설치하고 두께를 늘려서 강도안전성을 확보하는 것이 중요하다. 반면에 헬멧의 일반적인 균일한 두게는 줄여서 헬멧의 경량화를 추구하는 것도 중요하다.

• 정보처리학회논문지B
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• 제12B권4호
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• pp.451-458
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• 2005

트랜스코딩은 한 가지 형태로 부호화된 멀티미디어 데이터를 서로 다른 재생 데이터율을 요구하는 이질적인 클라이언트에게 적응적으로 전달하기 위한 해결책이다 따라서, 트랜스코딩 기법은 입력 스트림을 복호시켜 클라이언트가 요구한 출력 스트림으로 부호화하는 것이 필요하다. 일반적으로, 계산량을 줄이기 위해서 제안된 트랜스코딩 기법들은 비디오 화질의 열화를 발생시키고 그와 반대의 경우는 많은 계산량을 초래한다. 이와 같은 계산량과 화질 사이의 문제를 해결하기 위해서 여러 가지 기법들이 연구되었다. 하지만, 대부분의 연구가 트랜스코더 내부에 한정되어 있었고, 서버 측과의 상호작용을 통한 성능 향상에 대한 연구는 적었다. 멀티미디어 데이터를 전력과 성능이 낮은 단말기 또는 낮은 대역폭의 네트워크에 속한 이질적인 클라이언트로 서비스할 때, 트랜스코더 자체의 해결 방안에 서버 측에의 특정 작업을 추가할 경우 트랜스코더에서 실제 처리해야 하는 프레임의 개수를 줄일 수 있고 이를 통해서 서비스 효율의 향상을 기대할 수 있다. 따라서 본 논문에서는 효율적인 트랜스코더와 서버 측 기반의 알고리즘을 함께 고려하여 계산 처리 과정을 줄일 수 있는 프레임 제거 트랜스코더 시스템 구조를 제안한다.

• 한국통신학회논문지
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• 제27권8A호
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• pp.836-845
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• 2002

Video Summary는 길이가 긴 Video를 고속으로 효율적으로 열람할 수 있도록 하는 도구의 하나이다. Video Summary는 대표 프레임(Key-frame)들의 집합으로 볼 수 있는데 대표 프레임은 Video의 Genre에 따라서 달리 정의 및 생성될 수 있다. 즉 모든 Genre의 Video에 대해서 획일적인 방법으로 Summary를 만드는 것은 적절하지 못한 결과를 초래할 수 있다. Video의 Genre를 구별해내는 기술은 위와 같이 효율적인 Video Summary 생성에 유용한 처리 과정이라 할 수 있다. 본 논문에서는 이와 같이 효율적 Video 관리를 위해 MPEG 부호화 영역에서 MPEG Video의 Genre를 분류하는 방법을 제안한다. 제안된 방법은 프레임을 복호하지 않고 비트스트림을 직접 처리하여 기존 방법들에 비해 계산이 비교적 단순하고 처리시간을 단축시키는 장점을 가지고 있다. 또한 제안된 방법은 대부분의 작업을 시각 정보만을 이용하여 수행하며 이 정보들의 시, 공간적 해석을 통해 Genre를 확인하게 된다. 실험은 만화(Cartoon), 광고(Commercial), Music Video, 뉴스, Sports, Talk Show의 6개 Genre Video에 대하여 실행하였다. 실험 결과, 구조가 명확한 Talk Show와 Sports의 경우 90% 이상의 결과를 얻었다.

• Earthquakes and Structures
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• 제13권2호
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• pp.165-176
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• 2017

Multi-Axial Testing System (MATS) is a 6-DOF loading system located at National Center for Research on Earthquake Engineering (NCREE) in Taiwan for advanced seismic testing of structural components or sub-assemblages. MATS was designed and constructed for a large variety of structural testing, especially for the specimens that require to be subjected to vertical and longitudinal loading simultaneously, such as reinforced concrete columns and lead rubber bearings. Functionally, MATS consists of a high strength self-reacting frame, a rigid platen, and a large number of servo-hydraulic actuators. The high strength self-reacting frame is composed of two post-tensioned A-shape reinforced concrete frames interconnected by a steel-and-concrete composite cross beam and a reinforced concrete reacting base. The specimen can be anchored between the top cross beam and the bottom rigid platen within a 5-meter high and 3.25-meter wide clear space. In addition to the longitudinal horizontal actuators that can be installed for various configurations, a total number of 13 servo-hydraulic actuators are connected to the rigid platen. Degree-of-freedom control of the rigid platen can be achieved by driving these actuators commanded by a digital controller. The specification and information of MATS in detail are described in this paper, providing the users with a technical point of view on the design, application, and limitation of MATS. Finally, future potential application employing advanced experimental technology is also presented in this paper.

• 국제초고층학회논문집
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• 제7권4호
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• pp.375-387
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• 2018

This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

• Steel and Composite Structures
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• 제31권1호
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• pp.99-112
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• 2019

Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.

• Current Photovoltaic Research
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• 제10권2호
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• pp.56-61
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• 2022

Recently, the expansion of the domestic solar market due to the promotion of eco-friendly and alternative energy-related policies is promising, and it is expected to lead the high-efficiency/high-power module market based on M10 or larger cells to reduce LCOE, 540-560W, M12 based on M10 cells Compared to the existing technology with an output of 650-700W based on cells, it is necessary to secure competitiveness through the development of modules with 600W based on M10 cells and 750W based on M12 cells. For the development of high efficiency/high-power n-type bifacial, it is necessary to secure a lightweight technology and structure due to the increase in weight of the glass to glass module according to the large area of the module. Since the mechanical strength characteristics according to the large area and high weight of the module are very important, design values such as a frame of a new structure that can withstand the mechanical load of the Mechanical Load Test and the location of the mounting hole are required. In this study, a structural analysis design model was introduced to secure mechanical reliability according to the enlargement of the module area, and the design model was verified through the mechanical load test of the actual product. It can be used as a design model to secure the mechanical reliability required for PV modules by variables such as module area, frame shape, and the location and quantity of mounting holes of the structural analysis model verified. A relationship of output drop can be obtained.

• Structural Engineering and Mechanics
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• 제9권6호
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• pp.615-636
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• 2000

Some elevated water tanks have failed due to torsional vibrations in past earthquakes. The overall axisymmetric structural geometry and mass distribution of such structures may leave only a small accidental eccentricity between centre of stiffness and centre of mass. Such a small accidental eccentricity is not expected to cause a torsional failure. This paper studies the possibility of amplified torsional behaviour of elevated water tanks due to such small accidental eccentricity in the elastic as well as inelastic range; using two simple idealized systems with two coupled lateral-torsional degrees of freedom. The systems are capable of retaining the characteristics of two extreme categories of water tanks namely, a) tanks on staging with less number of columns and panels and b) tanks on staging with large number of columns and panels. The study shows that the presence of a small eccentricity may lead to large displacement of the staging edge in the elastic range, if the torsional-to-lateral time period ratio $({\tau})$ of the elevated tanks lies within a critical range of 0.7< ${\tau}$ <1.25. Inelastic behaviour study reveals that such excessive displacement in some of the reinforced concrete staging elements may cause unsymmetric yielding. This may lead to progressive strength deterioration through successive yielding in same elements under cyclic loading during earthquakes. Such localized strength drop progressively develop large strength eccentricity resulting in large localized inelastic displacement and ductility demand, leading to failure. So, elevated water tanks should have ${\tau}$ outside the said critical range to avoid amplified torsional response. The tanks supported on staging with less number of columns and panels are found to have greater torsional vulnerability. Tanks located near faults seem to have torsional vulnerability for large ${\tau}$.

• Journal of Positioning, Navigation, and Timing
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• 제11권4호
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• pp.287-295
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• 2022

The GNSS coordinate time series is used as important data for geophysical analysis such as terrestrial reference frame establishment, crustal deformation, Earth orientation parameter estimation, etc. However, various factors may cause discontinuity in the coordinate time series, which may lead to errors in the interpretation. In this paper, we describe the discontinuity in the coordinate time series due to the equipment replacement for domestic GNSS stations and discuss the change in movement magnitude and velocity vector difference in each direction before and after discontinuity correction. To do this, we used three years (2017-2019) of data from 40 GNSS stations. The average magnitude of the velocity vector in the north-south, east-west, and vertical directions before correction is -12.9±1.5, 28.0±1.9, and 4.2±7.6 mm/yr, respectively. After correction, the average moving speed in each direction was -13.0±1.0, 28.2±0.8, and 0.7±2.1 mm/yr, respectively. The average magnitudes of the horizontal GNSS velocity vectors before and after discontinuous correction was similar, but the deviation in movement size of stations decreased after correction. After equipment replacement, the change in the vertical movement occurred more than the horizontal movement variation. Moreover, the change in the magnitude of movement in each direction may also cause a change in the velocity vector, which may lead to errors in geophysical analysis.

• 열처리공학회지
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• 제26권5호
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• pp.225-232
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• 2013

The influence of aging treatment, addition elements and rolling reduction ratio on the microstructure, mechanical, electrical and bendability properties of Cu-Ni-Si-P-x (x = Fe, Sn, Zn) alloys for connector material application was investigated. SEM/EDS analysis exhibited that Ni2-Si precipitates with a size of 20~100 nm were distributed in grains. Fe, Sn, Zn elemnets in Cu-Ni-Si-P alloy imporved the mechanical strength but it was not favor in increasing of electrical conductivity. As higher final rolling reduction ratio, the strength and electrical conductivity is increased after aging treatment, but it indicated excellent bendability. Especially, Cu-2Ni-0.4Si-0.5Sn-0.1Fe-0.03P alloy show the tensile strength value of 700MPa and the electrical conductivity was observed to reach a maximum of 40%IACS. It is optimal for lead frame and connector.