• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.508-513
• /
• 2000

An experimental investigation has been carried out for two circular cylinders having different groove configurations(U and V-shape). The results were compared with those for the smooth circular cylinder. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number $Re=8000{\sim}14,000$ based on the cylinder diameter. As a results, the U-groove circular cylinder was found to be most effective riblet shape with reducing the drag up to 21%. As the Reynolds number increases, the vortex shedding frequency of the grooved cylinders becomes a little larger, compared to the smooth cylinder. The flow visualization using the smoke-wire technique was also carried out to see the flow structure qualitatively.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2006년도 춘계학술대회 논문집
• /
• pp.165-166
• /
• 2006

Surface pattern of tribological applications is an attractive technology of engineered surface. Therefore, friction reduction is considered to be necessary for improved efficiency of machines. This study investigated the effect of friction property fur angles of micro-scale crosshatch grooved surface pattern on bearing steel flat mated with pin-on-disk. We obtain sample which can be fabricated by photolithography process. We discuss friction property depend on an angle of cross-hatch grooved pattern. We can verify the lubrication mechanism as a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter under the lubrication condition. It was found that the friction coefficient was related to angle of crosshatch on surface, even when surface pattern was the same density.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 춘계학술대회논문집
• /
• pp.530-532
• /
• 2002

This paper presents an optimum design of herringbone grooved journal bearing for spindle motor of hard disk drive (HDD) system. In addition to the conventional “rectangular” groove, various groove profiles are designed. The stiffness and damping coefficients of the oil film and frictional torque are calculated and compared for tile various groove profiles. The “circular”, “valley”, and “reversed saw tooth” grooves do not produce high direct stiffness, since they partly increase the groove depths in the direction of lubricant flow, causing to reduce the pumping action of the bearing. The maximum direct stiffness can be obtained by the “rectangular”, “saw tooth”, and “step” grooves. With the same cross sectional area of the grooves, these three grooves have the same maximum stiffness, damping coefficients, and frictional torque. Among these recommendable grooves, the saw tooth groove may keep its original profile for long, enduring metal-to-metal contact during startup and shutdown.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2003년도 학술대회지
• /
• pp.388-394
• /
• 2003

This paper deals with a premature failure mechanism of deep grooved ball bearing for automobiles. A close examination of used bearings revealed that the premature failure could be arose by dents on the ball. Universal testing machine with specially designed tools is used to simulate the practical dents on the ball and test bearings are assembled with dented balls and new hearing components. The endurance test results showed that the dents on the balls were printed on the races and these phenomena come to premature failure.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2003년도 학술대회지
• /
• pp.395-401
• /
• 2003

In this paper, the dent printing phenomena and critical dent size which lead to premature failure of deep grooved ball bearing for automobiles are presented. The results of newly assembled test bearings showed that the ball dent size strongly affect the bearing life and inner ring raceways were the major failed parts in spite of using the dented balls. The dent printing phenomena are a root cause of premature failure, which was not reported until now. And there exist the critical ball dent size for given rolling bearings and operating conditions. So, the initial condition of tribologically mating parts should be treated as important as the failed body itself.

• Tribology and Lubricants
• /
• 제18권5호
• /
• pp.364-370
• /
• 2002

In this paper, numerical analyses were undertaken to calculate the static and dynamic performances of step-pocket, inward pumping spiral grooved, outward pumping spiral grooved and herringbone grooved bearings. For each bearing, optimal values for various design parameters were obtained to maximize the load capacity and the stiffness and bearing performances were calculated. The optimized performances of these bearings were compared to conclude that the performance of step-pocket bearing is better than the other bearings.

• 한국안전학회지
• /
• 제9권4호
• /
• pp.17-28
• /
• 1994

Chip breaking is important in lathe work for maintaining good surface of the products and safety of operator. The purpose of this study is to investigate the performance of chip breaking and chip shape resulted from the carbide inserts with grooved type and obstruction type chip breaker. Experiments have been performed under the following cutting conditions, (1) constant cutting speed with variable depth of cut and feed rate, (2) constant depth of cut with variable cutting speed and feed rate. Also, the flying distance of chip and it's distribution have been investigated. As a results, good performance of chip breaking can be obtained for small radius of curvature and land width of grooved type chip breaker. And the thickness of chip increase with the increase of feed rate and decrease of cutting speed, and the chip breaking becomes easier with the increase of chip thickness due to the large deformation rate. Obstraction type chip breaker shows better performance of surface roughness than the grooved type. The flying distance of the chips over 90% are less than 1 meter, and the distance decreases as the feed rate decreases.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 춘계학술대회 논문집
• /
• pp.350-356
• /
• 2001

SG-50 steel is an important material and used for manufacturing a pressure vessel which the gas piping. In this investigation, the elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the elastic plastic fracture toughness. The side grooved specimen is very useful in estimation of the J$_{IC}$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides, it improves the accuracy of toughness values, decreases the scattering of them and tunneling and shear lip by the side groove.e.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
• /
• pp.123-126
• /
• 2007

In this study, a high luminous efficacy AC-PDP panel with long discharge gap and grooved dielectric layer has been studied. By applying this high efficacy concept and optimized driving waveform featuring negative biased sustain, ${\sim}2.6lm/W$ of luminous efficacy was achieved in 42- inch HD panel. Modified fabricating process and new discharge cell structure were investigated to obtain improved uniformity and operating characteristics.

• 설비공학논문집
• /
• 제2권1호
• /
• pp.27-36
• /
• 1990

An experimental investigation was made to study the performance characteristics of evaporator having different fin configurations and tube inner grooves. Three different types of fin such as super slitted fin, slitted fin, plain fin, and two types of tube such as inner grooved tube, and bare tube, are tested varying the air velocity, evaporation temperature and superheat of refrigerant. Results show that in the range of air side Reynolds number $3{\times}10^3\;-\;1.5{\times}10^4$ evaporator with super slitted fin and inner grooved tube shows best performance. It is 80% higher in overall heat transfer coefficient and 2.6 times higher in pressure loss compared to that with plain fin inner grooved tube. Friction factor is found to be almost independent of evaporating temperature and degree of superheat, while Colburn j factor varies with evaporating temperature.