• International Journal of Railway
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• 제3권2호
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• pp.46-53
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• 2010

Electric railroad systems consist of rolling stock, track, signal and catenary system. In the catenary system, one of the most important factors is the impedance according to the design and characteristic. Before the catenary system is designed, the impedance should be precedently researched. The railroad catenary system is complex system which is composed by five conductors. The five conductors classify up and down feeders, up and down contact wire group, rail group. Therefore, we should compose the catenary system of the equivalent five-conductors model. In this paper, we suggest a geometrical model and a equivalent conductor model by using geometric mean radius of five conductors in the catenary system. Also, we calculate demanded parameter values in the model. By using those, line constants of five conductors are analyzed by applying the equivalent method called as the condensed joint matrix.

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.743-750
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• 2003

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and nay include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. Typical ESM modeling uses two groups of equivalent source positions. One group includes the first order images of the source inside the enclosure. The Positions of the other group are usually on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal far field sources positions when using the equivalent source method. In general, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study. optimal far field source locations are searched using simulated annealing method for various radii of spheres where far field sources are located. Simulation results showed that optimally located sources with adequate distance away from the enclosure center gave better result than sources with even distribution even with a smaller number of far field sources.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.216-221
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• 2001

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. In the ESM modelling, some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal equivalent source positions, the far field sources. Typically, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study, optimal far field source locations are searched using simulated annealing method and simulation results showed that optimally located sources gave better accuracy even with a smaller number of far field sources.

• 한국안광학회지
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• 제4권2호
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• pp.23-31
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• 1999

본 연구에서는 안과적 질환이 없는 한국인 성인 남녀의 안광학적요소를 측정하여, 안축의 길이를 각막 양주경선의 평균곡률반경으로 나눈 값(Al/CR비)과 눈의 굴절이상과의 상관성을 분석하였다. 눈의 굴절이상과 안축의 길이, 각막곡률반경과는 각각 -0.77(0.001>p), 0.29(0.01>p)의 상관관계가 있었으나, AL/CR비와는 이것들보다 훨씬 높은 -0.89(0.001>p)의 상관성을 보였다. 그러므로 눈의 굴절이상의 대부분은 AL/CR비에 의해서 결정된다고 할 수 있다. 또한 Al/CR비에 기여하는 안광학 요소를 알아보기 위해 AL/CR비와 안광학요소와의 상관성을 분석한 결과, 안축의 길이와는 0.82(0.001>p), 유리체의 깊이와는 0.80(0.001>p), 전방의 깊이와는 0.57(0.001>p), 각막굴절력과는 0.40(0.001>p), 각막골률반경과는 0.39(0.001>p), 수정체의 굴절력과는 -0.35(0.01>p) 등의 순서로 나타났다. 그러므로 눈의 굴절이상은 안광학요소 중 안축의 길이와 각막곡률반경의 비에 의해서 가장 많은 영향을 받으며, 이 AL/CR비는 안축의 길이, 초자처의 깊이, 전방의 깊이 등이 밀접한 관련성이 있으나, 수정체의 두께는 유의할 만한 상관성이 없음을 알았다.

• Structural Engineering and Mechanics
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• 제89권4호
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• pp.411-420
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• 2024

The purpose of this research was to investigate the cyclic behavior of the D-shaped dampers (DSD). Similarly, at first, the numerical model was calibrated using the experimental sample. Then, parametric studies were conducted in order to investigate the effect of the radius and thickness of the damper on energy dissipation, effective and elastic stiffness, ultimate strength, and equivalent viscous damping ratio (EVDR). An analytical equation for the elastic stiffness of the DSD was also proposed, which showed good agreement with experimental results. Additionally, approximate equations were introduced to calculate the elastic and effective stiffness, ultimate strength, and energy dissipation. These equations were presented according to the curve fitting technique and based on numerical results. The results indicated that reducing the radius and increasing the thickness led to increased energy dissipation, effective stiffness, and ultimate strength of the damper. On the other hand, increasing the radius and thickness resulted in an increase in EVDR. Moreover, the ratio of effective stiffness to elastic stiffness also played a crucial role in increasing the EVDR. The thickness and radius of the damper were evaluated as the most effective dimensions for reducing energy dissipation and EVDR.

• 대한기계학회논문집
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• 제15권1호
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• pp.139-144
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• 1991

본 연구에서는 절삭가공시 생성되는 칩의 형상해석의 일환으로 2차원 절삭시 칩은 절삭날에 수직한 방향으로 공구경사면을 흘러간다는 기본적인 전제조건과 Kluft 등의 칩흐름각 예측에 대한 제안중 노으즈반경(nose radius) 및 기울임각의 영향을 중 첩시키고, 또한 절삭날에 연하여 미변형 칩두께(undeformed chip thickness)가 달라지 는 경우 칩흐름의 세기는 이에 비례한다는 Baart등의 가정을 도입하여 칩흐름각에 대 한 새로운 해석을 시도하였다.

• 전기학회논문지
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• 제65권12호
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• pp.1971-1978
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• 2016

In this paper, electrical and physical characteristics associated with the ionization growth of soil under impulse voltages in a coaxial cylindrical electrode system to simulate a horizontally-buried ground electrode were experimentally investigated. The results were summarized as follows: Transient ground resistances decreased significantly by soil ionization. The voltage-current (V-I) curves for non-ionization in soil lined up in a straight line with the nearly same slope that is the ground resistance, but they showed a 'cross-closed loop' of ${\infty}$-shape under ionization. The conventional ground resistance and equivalent soil resistivity were inversely proportional to the peak value of injected impulse currents. On the other hand, the equivalent ionization radius and time-lag to the maximum value of ionization radius were increased with increasing the incident impulse voltages. An analysis method for the transient ground resistances of the ground electrode based on the ionization phenomena was proposed. The proposed method can be applied to analyze the transient performances of grounding systems for lightning protection in power system installations.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.51-56
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• 2003

It is important to evaluate the fracture initiation behaviors of steel structure. It has been well known that the ductile cracking of steel would be accelerated by triaxial stress state. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameters, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of notch radius, which can elevate plastic constraint due to heterogeneous plastic straining on critical condition to initiate ductile crack using two-parameters. Hense, the crack initiation testing were conducted under static loading using round bar specimens with circumferential notch. To evaluate the stress/strain state in the specimens was used thermal elastic-plastic FE-analysis. The result showed that equivalent plastic strain to initiate ductile crack expressed as a function of stress triaxiality obtained from the homogeneous specimens with circumferential notched under static loading. And it was evaluated that by using this two-parameters criterion, the critical crack initiation of homogeneous specimens under static loading.

• 소성∙가공
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• 제11권6호
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• pp.503-512
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• 2002

The drawbead is used to control material flow into the die during the binder wrap process and the stamping process in the sheet metal forming process. Since the dimension of drawbead is relatively small in comparison with the typical dimensions, it is difficult to include drawbeads in finite element analysis of the sheet metal forming process. It is because the mesh system has to be fine enough to describe the drawbead and the computation time is drastically increased. In this paper, simulation of drawbead forming has been carried out to obtain the equivalent boundary conditions in the binder wrap process and the stamping process. In order to investigate the effect of various die geometries, parameter studies are performed with the variation of parameters such as the blank length, the drawbead depth, the drawbead radius, the inclination of die and the friction coefficient.

• 디지털융복합연구
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• 제14권11호
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• pp.435-440
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• 2016

양안 굴절이상 차이에 의한 안광학상수 변화도 분석을 통한 양안 굴절이상 차이의 특성을 이해 할 수 있는 기초자료를 제공하고자 하였다. 20-59세의 건강한 성인 100명을 대상으로 KR-8800을 이용하여 등가구면 굴절력과 각막곡률 반경을, IOL Master를 사용하여 안축장길이와 전방깊이를 측정하였으며, 측정값의 차이는 우안 측정값-좌안 측정값의 차이값에 절대 값을 구하여 사용하였다. 전체 대상자의 등가구면 굴절력은 $-1.83{\pm}2.17D$이고, 안축장길이는 23.00~24.99mm, 각막곡률반경은 7.50~7.89mm, 전방깊이는 3.60~4.09mm의 범위에서 가장 많았다. 양안 등가구면 굴절력 차이에 따른 양안 안축장길이 차이와 양안 전방깊이의 차이가 유의한 상관관계가 있었다. 또한, 양안 굴절력 차이에 의한 양안 안축장 길이 차이가 가장 크고, 가장 높은 상관성이 있었다. 양안 굴절력 차이는 안광학 상수와 밀접한 관계가 있고, 양안 굴절력 차이에 의하여 여러 가지 시기능 문제가 발생 할 수 있으므로, 양안 굴절이상 차이에 따른 요인별 분류를 통한 융복합 연구가 필요하다.