• 한국안광학회지
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• 제3권1호
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• pp.129-136
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• 1998

19세에서 40세까지의 청 장년층 242안(121명)을 대상으로 Spherical Add 법과 Cross cylinder lens법을 이용하여 조절력 검사를 실시하여 다음과 같은 결과를 얻었다. Spherical Add법을 사용하여 조절력을 측정한 결과 20대의 조절력의 범위는 9~13Diopter로 나타났고, 30대의 조절력의 범위는 6~8.5Diopter로 나타났다. 20대는 왕성한 조절력을 지니고 있음을 알 수 있었고, 30대 이상은 조절력이 25세 이전과 비교해서 감소함을 알 수 있었다. Cross cylinder lens법을 이용하여 조절력을 측정한 결과 20대의 평균조절력의 범위는 6.13~10.13Diopter, 30대의 평균조력의 범위는 5.75~8.75Diopter, 40대의 평균조절력의 범위는 4.38~7.25Diopter로 나타난다. 즉 조절력은 나이가 많아짐에 따라 감소함을 알 수 있었고 남녀 모두 cross cylinder lens의 붉은점을 수평방향으로 위치시킬 때의 조절력이 cross cylinder lens의 붉은점을 수직방향으로 위치시킬 때의 조절력보다 큰 것으로 나타났다. Spherical Add법과 Cross cylinder lens 법에 의해 측정한 조절력의 분포를 살펴보면 대부분 S.A 법을 이용하여 측정한 조절력이 Cr.c 법을 이용하여 측정한 조절력보다 큰 것으로 나타났다.

• 한국안광학회지
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• 제4권2호
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• pp.39-43
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• 1999

14세에서 19세까지의 중 고등학생 1750안(875명)을 대상으로 cross cylinder lens와 적 녹 검사를 이용하여 교정후 조절력검사를 실시하여 다음과 같은 결과를 얻었다. Cross cylinder lens법을 사용하여 교정후 조절력검사를 측정한 결과 0 Dptr에서는 33%의 오차범위가 나타났고 -0.25 Dptr에서는 58%로 측정되었다. -0.75 Dptr에서는 1%의 오차 범위가 측정되었고 -1.00 Dptr에서는 오차가 측정되지 않았다. Cross cylinder lends법을 이용한 정밀구면굴절력의 오차범위는 0 Dptr에서 -0.25 Dptr까지 1%에 달하는 정밀측정 오차가 발생되었다. 적 녹검사를 이용한 교정후 조절력검사는 0 Dptr에서 -.025 Dptr에서 75%의 비율이 측정되었고 -0.50 Dptr에서는 20%가 측정되었다. 이 측정결과 Cross cylinder lens를 이용한 측정이 적 녹검사측정보다 더 세밀한 측정결과를 나타내었다.

• Wind and Structures
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• 제9권2호
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• pp.109-124
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• 2006

This paper describes the characteristics of the fluctuating lift forces when a circular cylinder vibrates in the cross-flow direction. The response characteristics on elastically supported the circular cylinder was first examined by a free-vibration test. Next, flow-induced vibrations obtained by the free-vibration test were reproduced by a forced-vibration test, and then the characteristics of the fluctuating lift forces, the work done by the fluctuating lift, the behavior of the rolling-up of the separated shear layers were investigated on the basis of the visualized flow patterns. The main findings were that (i) the fluctuating lift forces become considerably large than those of a stationary circular cylinder, (ii) negative pressure generates on the surface of the circular cylinder when the rolling-up of separated shear layer begins, (iii) the phase between the fluctuating lift force and the cylinder displacement changes abruptly as the reduced velocity $U_r$ increases, and (iv) whether the generating cross-flow vibration becomes divergent or convergent can be described based on the work done by the fluctuating lift force. Furthermore, it was found that the generation of cross-flow vibration can be perfectly suppressed when the small tripping rods are installed on the surface of the circular cylinder.

• Wind and Structures
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• 제11권3호
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• pp.221-240
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• 2008

The spanwise flow structure around a rigid smooth circular cylinder model in cross-flow has been investigated based on the experimental data obtained from a series of wind tunnel tests. Surface pressures were collected at five spanwise locations along the cylinder over a Reynolds number range of $1.14{\times}15^5$ to $5.85{\times}10^5$, which covered sub-critical, single-bubble and two-bubble regimes in the critical range. Separation angles were deduced from curve fitted to the surface pressure data. In addition, spanwise correlations and power spectra analyses were employed to study the spatial structure of flow. Results at different spanwise locations show that the transition into single-bubble and two-bubble regimes could occur at marginally different Reynolds numbers which expresses the presence of overlap regions in between the single-bubble regime and its former and later regimes. This indicates the existence of three-dimensional flow around the circular cylinder in cross-flow, which is also supported by the observed cell-like surface pressure patterns. Relatively strong spanwise correlation of the flow characteristics is observed before each transition within the critical regime, or formation of first and second separation-bubbles. It is also noted that these organized flow structures might lead to greater overall aerodynamic forces on a circular cylinder in cross-flow within the critical Reynolds number regime.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(I)
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• pp.78-81
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• 1987

The scattering characteristics are analysed for the dielectric cylinder with arbitrary cross section partially covered by thin conductors. The integro differential equations consistant with boundary conditions of conductor and dielectric boundaries are derived by the equivalence principle. They are transformed into matrix equations by moment method. The circular dielectric cylinder covered by conductors at the upper and bottom side of the cylinder is chosen for the numerical example. Current distributions on conductors and scattering cross section by the cylinder are computed for incident wave perpendicular to the conductor plane.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.582-587
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• 2001

A numerical method using FLUENT code was employed to investigate fluid drag and lift forces on a cylinder in a group of circular cylinders, subjected to a uniform cross flow. The cylinders can be arranged in tandem or in a staggered arrangements relative to the free stream flow. A vortex street behind the cylinder pairs or jets between the cylinders forms according to the arrangements. Vibration on a cylinder can occurs due to vortex shedding, fluid-elastic stiffness and wake galloping. The flow is first investigated and then the forces acting on the cylinder are calculated. The lift and drag forces on an elastically mounted cylinder in the wake of an upstream fixed cylinder arise from the mean flow plus velocity and pressure gradients in the wake. The analytical results of two staggered cylinder were compared with the existing experimental ones for validation of the present method. The analytical results of the forces were in good agreement with the experimental ones. The present method can be used for the analysis of the fluid induced vibration where the group of circular cylinders are subjected to a cross flow.

• 대한전자공학회논문지
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• 제25권2호
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• pp.125-129
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• 1988

The acattering characteristics by the TE incident wave are analysed for its dielectric cylinder with arbitrary cross section partially covered by thin conductors. The integro differential equations consistent with boundary conditions of conductors and dielectric boundaries are derived by the equivalence principle. They are transformed into matrix equations by moment method. The rectangular dielectric ctlinder partially coverd by conductors at the upper and bottom side of the cylinder is chosen for the numerical example. Current distributions on conductors and sacttring cross sections by the cylinder are computed for the TE incident perpendicular to the conductor plane.

• Structural Engineering and Mechanics
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• 제12권3호
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• pp.329-339
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• 2001

The present paper deals with the effective slenderness ratio of telescopic cylinders as a long column having different cross sections. Firstly, the slenderness ratio defined in the current standard for the telescopic cylinders is discussed to point out some difficulties which arise when the ratio is applied to the column having different cross sections. Secondly, a new effective slenderness ratio is proposed for columns having different cross sections by introducing a partial effective slenderness ratio. Finally, the proposed slenderness ratio is applied, for extending and development of discussion, to a two-staged column having piece-wise constant cross sections and a cylindrical column having linearly varying diameters.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.148-153
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• 2001

A computational investigation of the effect of the electromagnetic force(or Lorentz force) on the flow behavior around a circular cylinder, a typical model of bluff bodies, is conducted. Two-dimensional unsteady flow computation for $Re=10^2$ is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of the spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of the circular cylinder cross-flow, leading to the reduction of the drag.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.363-375
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• 2002

The effect of the electromagnetic force (or Lorentz force) on the flow behavior around a circular cylinder is investigated by computation. Two-dimensional unsteady flow computation for Re=10$^2$is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of circular cylinder cross-flow, leading to reduction of drag.