• Tribology and Lubricants
• /
• v.13 no.3
• /
• pp.48-55
• /
• 1997

The ball bearing with thin-section raceways which is much lighter than other conventional bearings used in most modem passenger cars and small tracks. The important design parameters of this bearing is the groove radius of raceways, the diametral clearance, the free contact angle and so on. The optimal value of these parameters were determined by considering the dynamic load capacity, the contact angle and the calculated fatigue life. The contact angle between a ball and raceways was calculated by considering the local contact deformation and the structural deformation of thin-section raceways which was estimated by FEM. The raceways were made by means of the press-forming process. The fatigue life tester was designed and manufactured. The fatigue life test was executed and the reliability of this bearing was confirmed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.4
• /
• pp.357-366
• /
• 2007

The present study investigated local heat/mass transfer characteristics on the surface of the rotating turbine blade with various incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with the mean tip clearance of 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. At design condition, the inlet Reynolds number is $Re_c=1.5{\times}10^5$ which results in the blade rotation speed of 255.8 rpm. Also, the effect of off-design condition is examined with various incidence angles between $-15^{\circ}$ and $+7{\circ}$. The results indicated that the incidence angle has significant effects on the blade surface heat transfer. In mid-span region, the laminar separation region on the pressure side is reduced and the laminar flow region on the suction side shrinks with increasing incidence angle. Near the tip, the effect of tip leakage flow increases in span wise and axial directions as the incidence angle decreases because the tip leakage flow is formed near the suction side surface. However, the effect of tip leakage flow is reduced with positive incidence angle.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3357-3368
• /
• 1994

Total pressure losses required to calculate the total-to-total efficiency are estimated by integrating empirical loss coefficients of four loss mechanisms along the mean-line of blades as follows; blade profile loss, secondary flow loss, end wall loss and tip clearance loss. The off-design points are obtained on the basis of Howell's off-design performance of a compressor cascade. Also, inlet-outlet air angles and camber angle are obtained from semi-empirical relations of transonic airfoils' minimum loss incidence and deviation angles. And nominal point is replaced by the design point. It is concluded that relatively simple loss models and Howell's off-design data permit us to calculate the off-design performance with satisfactory accuracy. And this method can be easily extended for off-design performance prediction of multi-stage compressors.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1446-1454
• /
• 1990

A systematic method of design modification to reduce the influence of impact from multiple clearances in a planar four bar mechanism is developed. For this purpose, an optimization method is used with the objective function which is the linear sum of the Earles and Wu criteria for every joints with clearances. One coil spring is attached to a joint of limited range of revolution to reduce the undesirable dynamic effects due to clearances at joints. The stiffness of the coil spring and its pre-loading angle are chosen as design variables. A numerical example is taken for a four bar mechanism. The initial and modified mechanisms are compared using a clearance mechanism analysis technic to see the difference in dynamic effects due to contact loss. It is found that the modified mechanism produces much more smooth joint contact forces than the original design.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.982-986
• /
• 2000

Perpendicular guideway mechanism has a different behavior with horizontal guideway mechanism due to the slider weight. So, to decrease its weight effect, counter balances such as weight type and hydraulic cylinder type are used. But it can also make another motion behavior by weight rate of slider and counter balance, its connected position. Therefore, it is necessary to find design parameters and analyze their effect. This paper dealt with the optimal design of perpendicular guideway mechanism. For analysis, the theoretic model as same as real machine tool and sib plate to adjust the clearance was used. Rotational angle and displacement of slider, pressure distribution, friction distribution were calculated. Stick slip, intermittent motion of slider according to friction change was adapted to the perpendicular guideway mechanism.

• Journal of the Korean housing association
• /
• v.14 no.5
• /
• pp.105-116
• /
• 2003

The purpose of this study is to suggest the method of prevention of staircase accidents, and to make housing environment better through researching the dimension of a housing staircase for Korean. The scope and method of this thesis is to investigate the dimension limits of a staircase (slope, minimum width of tread, maximum height of riser), and to analyze the characteristics of foot condition (jutting rate, foot angle, ball joint, nosing clearance, clearance distance) using the experiment which takes a photograph of foot motion during walking stairs. The results of this thesis are as follows. The slope of a staircase in house is $32.3^{\circ}$$^{\circ}$-$42.1^{\circ}$$^{\circ}$. The riser should be less than 190 mm. The minimum size of tread is 210 mm and proper size is 270 mm.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1996.11a
• /
• pp.921-927
• /
• 1996

The purpose of this study is to compute the stress intensity factors of various conditions in the cracked p! ate. The stress intensity factor of pin-loaded cracked plate is investigated using the finite element method. This paper is divided into the two parts. The first part is the contact analysis, and the second is to compute the stress intensity factors. In the contact analysis, the iterative method is used, and convergence of this method is presented. In the computation of the stress intensity factors of plate, the length of crack, clearance, and angle are considered

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.1
• /
• pp.127-134
• /
• 2002

This study present a direct steering system using rack and pinion for ultra-small vehicles. The traditional small vehicles for special use had the limitation of space by reason of short wheel tread. These vehicles has adopted a indirect steering system or a center arm system for steering. The disadvantages of these system were deterioration of gear efficiency and increase of parts. For direct-linkage to both knuckles, steering system is made up of out-side tie rods, tie-rod ends, and gear box. Thus, the proposed system has a minimum number of parts. The experimental results show a maximum efficiency at minimum steering angle and a minimum clearance circle. These effects were accomplished by adopting a Ackerman-Jantaud theory.

• Proceedings of the KIEE Conference
• /
• 2001.07a
• /
• pp.449-451
• /
• 2001

This paper described the switching overvoltage analysis on the 345kV and 154kV transmission system by EMTP(Electromagnetic transient Program) for the enactment of current insulation design standards of KEPCO. The air clearance design of current transmission tower was reviewed and revised by the calculated result, considering swing angle for the each type of insulator string by the wind velocity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.4-4
• /
• 1998

이 연구에서는 100인승 항공기 급의 저익-주익장착나셀(wing mounted nacelle)의 추진기관 장착설계 방법을 제시하였다. 장착설계 방법을 구체적으로 설명하기 위해 세부적인 설계제한조건(design constraint)과 설계요구조건(design requirement and objectives)을 정의하고, 그러나 기준을 근거로 실례의 항공기(K100)를 사용하여 주익장착방식의 장착설계를 수행하였다. 장착설계는 간접항력(interference drag), roll clearance, ground clearance, nose gear collapse margin, rotor burst, 연료탱크용량 등의 설계제한 사항들을 고려하여 엔진성능을 만족시킬 수 있는 최적의 나셀 장착위치(spanwise, FS, WL)와 장착각도(toe-in, incidence, droop angle), wing day의 위치와 크기를 결정하여 향후에 개발될 주익장착방식의 추진기관 장착설계에 활용될 수 있는 설계절차를 구축하였다.