• 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.

• Computers and Concrete
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• 제25권5호
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• pp.411-425
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• 2020

In this paper, the shell material has been taken as functionally graded material and their material quantity is located by the exponential volume fraction law. Moreover, the impact of ring supports around the shell circumference has been examined for their various positions along the shell axial length. These rings support restraints the radial displacement in the transverse direction. While the axial modal deformation functions have been estimated by characteristic beam functions and nature of materials used for construction of cylindrical shells. The fundamental natural frequency of cylindrical shell of parameter versus ratios of length- and height-to-radius for a wide range has been reported and investigated through the study. In addition, by increasing height-to-radius ratio resulting frequencies also increase and frequencies decrease on ratio of length-to-radius. Though the trends of frequency values of both ratios are converse to each other with three different boundary conditions. Also it is examined the position of ring supports with length-to radius ratio, height-to-radius ratio and varying the exponent of volume fraction. MATLAB software package has been utilized for extracting shell frequency spectra. The obtained results are confirmed by comparing with available literature.

• 대한기계학회논문집B
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• 제32권11호
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• pp.817-823
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• 2008

A pin fin with variable fin base thickness is optimized based on the ratio of heat loss to the maximum heat loss using a two-dimensional analytic method. The temperature profile along the normalized radius position in the fin is presented. For fixed fin outer radius, the optimum heat loss, fin length and efficiency as a function of fin base thickness, outer radius, convection characteristic numbers ratio and ambient convection characteristic number are presented. One of the results shows that the effect of fin outer radius and ambient convection characteristic number on the optimum fin length is remarkable.

• 대한기계학회논문집B
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• 제20권2호
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• pp.689-696
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• 1996

A comparison is made of the heat loss from a hollow cylinder, computed using an one-dimensional analytic method and a two-dimensional separation of variables scheme. For a two-dimensional analysis, the temperature of the inner surface as a boundary condition can be varied along the length of the cylinder by varing the temperature variation factor, b. Comparisons of the heat loss from the hollow cylinder using these two methods are given as a function of non-dimensional cylinder length, the ratio of the outer radius to the inner radius, temperature variation factor and Biot number. The result shows that the value of the heat loss from the hollow cylinder obtained using the one-dimensional analytic method becomes close to the value given by the two-dimensional separation of variables scheme as the value of Biot number and the non-dimensional hollow cylinder length increase and as the ratio of the outer radius to the inner radius decreases.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.127-133
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• 2007

This paper represents the numerical study on Taylor flow according to the radius ratio and the angular velocity for flow between tow cylinder. The numerical model is consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8 mm, the numerical parameters are angular velocity and radius ratio. The numerical method is compared with the experimental results by Wereley, and the results are very good agreement. The critical Taylor number is calculated by theoretical and numerical analysis, and the results is showed the difference about ${\pm}10\;%$. As $Re/Re_c$ is increased, Taylor vortex is changed to wavy vortex, and then the wave number for azimuthal direction is increased. Azimuthal wave according to the radius ratio is showed high amplitude and low frequence in case of small radius ratio, and is showed low amplitude and high frequence in case of large radius ratio.

• 산업기술연구
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• 제28권B호
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• pp.3-7
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• 2008

A cylindrical pin fin with variable fin base thickness is optimized based on fixed outer radius by using the one dimensional analytic method. Heat loss from the pin fin with fixed outer radius is presented as a function of the fin length. The ratio of in length for optimum heat loss to that for the maximum heat loss is listed. The maximum heat loss and effectiveness and the fin length for the optimum heat loss are presented as a function of fin base thickness and outer radius. One of the results presents the maximum effectiveness decreases rapidly first and then decreases slowly as the fin outer radius increases.

• 한국공작기계학회논문집
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• 제12권5호
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• pp.88-93
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• 2003

Buckling behavior of stiffened laminated composite cylindrical panel was studied using linear and nonlinear deformation theory. Various buckling load factors are obtained for stiffened laminated composite cylindrical panels with rectangular type longitudinal stiffeners and various longitudinal length to radius ratio, which made from Carbon/Epoxy USN150 prepreg and are simply-supported on four edges under uniaxial compression. Buckling behavior design analyses are carried out by the nonlinear search optimizer, ADS.

• 대한기계학회논문집B
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• 제24권7호
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• pp.957-966
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• 2000

The effect of rotation on the discharge coefficient of orifices with various length-to-diameter ratios and two different inlet corner radii was studied. Length-to-diameter ratios of the orifices range from 0.2 to 10, while the inlet shapes are square edged, or round edges of radius-to-diameter ratio of 0.5. From the experiment, we found that rotational discharge coefficient and Rotation number, when based on ideal exit velocity of the orifice considering momentum transfer from the rotor, describe the effect of rotation very well. In this study, the discharge coefficients of rotating orifices are shown to behave similar to those of the well-known non-rotating orifices. For both rotating and non-rotating orifices, the discharge coefficients increase with the length-to-diameter ratio until a maximum is reached. The flow reattachments in the relatively short orifices are responsible for the increase. The coefficient then decreases with the length-to-diameter ratio due to the friction loss along the orifice bore. The length-to-diameter ratio that yields maximum discharge coefficient, however, increases with the Rotation number because the increased flow-approaching angle requires larger length-to-diameter ratio for complete reattachment. The length-to-diameter ratio for complete reattachment is shorter for round edged orifices than that of square edged orifices by about a unit length-to-diameter ratio.

• Advances in nano research
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• 제8권3호
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• pp.215-228
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• 2020

In this paper, a new method based on the Sander theory is developed for SWCNTs to predict the vibrational behavior of length and ratio of thickness-to-radius according to various end conditions. The motion equation for this system is developed using Rayleigh-Ritz's method. The proposed model shows the vibration frequencies of armchair (5, 5), (7, 7), (9, 9), zigzag (12, 0), (14, 0), (19, 0) and chiral (8, 3), (10, 2), (14, 5) under different support conditions namely; SS-SS, C-F, C-C, and C-SS. The solutions of frequency equations have been given for different boundary condition, which have been given in several graphs. Several parameters of nanotubes with characteristic frequencies are given and vary continuously in length and ratio of thickness-to-radius. It has been illustrated that an enhancing the length of SWCNTs results in decreasing of the frequency range. It was demonstrated by increasing of the height-to-radius ratio of CNTs, the fundamental natural frequency would increase. Moreover, effects of length and ratio of height-to-radius with different boundary conditions have been investigated in detail. It was found that the fundamental frequencies of C-F are always lower than that of other conditions, respectively. In addition, the existence of boundary conditions has a significant impact on the vibration of SWCNTs. To generate the fundamental natural frequencies of SWCNTs, computer software MATLAB engaged. The numerical results are validated with existing open text. Since the percentage of error is negligible, the model has been concluded as valid.

• Advances in nano research
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• 제10권2호
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• pp.129-138
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• 2021

In present article, utilizing the Love shell theory with volume fraction laws for the cylindrical shells vibrations provides a governing equation for the distribution of material composition of material. Isotopic materials are the constituents of these rings. The position of a ring support has been taken along the radial direction. The Rayleigh-Ritz method with three different fraction laws gives birth to the shell frequency equation. Moreover, the effect of height- and length-to-radius ratio and angular speed is investigated. The results are depicted for circumferential wave number, length- and height-radius ratios with three laws. It is found that the backward and forward frequencies of exponential fraction law are sandwich between polynomial and trigonometric laws. It is examined that the backward and forward frequencies increase and decrease on increasing the ratio of height- and length-to-radius ratio. As the position of ring is enhanced for clamped simply supported and simply supported-simply supported boundary conditions, the frequencies go up. At mid-point, all the frequencies are higher and after that the frequencies decreases. The frequencies are same at initial and final stage and rust itself a bell shape. The shell is stabilized by ring supports to increase the stiffness and strength. Comparison is made for non-rotating and rotating cylindrical shell for the efficiency of the model. The results generated by computer software MATLAB.