• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.321-329
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• 1998

To ensure the structural integrity of the autofrettaged thick-walled cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation lives of the cylinder based on the fracture mechanics concepts were predicted and compared to the experimental fatigue lives evaluated from the C-shaped simulation specimens. There were good correlations between the predicted and experimental fatigue lives within a factor of 3 for the single and double grooved C-shaped simulation specimens. Predicted fatigue crack propagation lives of the double grooved cylinders were about 1.5-5 times longer than those of the single grooved cylinders depending on the levels of autofrettage.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.508-513
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• 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.

• Tribology and Lubricants
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• v.16 no.2
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• pp.114-120
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• 2000

This paper reports on the theoretical analysis on the lubrication characteristics between the piston ring and the grooved cylinder liner. The circular shape piston ring and two types grooves are consider, and the minimum oil film thickness during the full engine cycle are obtained by using iterative technique. The comparative results of minimum oil film thickness and viscous friction force between the smooth and grooved liner are presented. And various design parameter of piston ring and liner groove are tested. The groove in the liner generally reduces the minimum value of minimum oil film thickness, but the maximum viscous friction force is increased at the minimum film position.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.260-268
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• 2001

Wake structures behind two circular cylinders with different groove configurations(U and V-shape) have been investigated experimentally. The results were compared with those for the smooth cylinder having the same diameter D. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number in the range of Re(sub)D=8,000∼14,000. As a result, the U-shaped groove was found to reduce the drag up to 18.6%, but the V-shaped groove reduced drag force only 2.5% compared with the smooth cylinder. As the Reynolds number increases, the vortex shedding frequency becomes a little larger than that of the smooth cylinder. The visualized flow using the smoke-wire and particle tracing methods shows the flow structure qualitatively.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.622-627
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• 2003

A numerical study is made of a flow in a cylinder with a rotating grooved endwall disk. The aim is to describe differences in the flow fields when there is concentrically-grooved obstacle characterized by amplitude(a) and wave number(N). The Reynolds number(Re) is varied from $10^{3}$ to $10^{4}$ and the aspect ratio(Ar) fixed to 1.0 for the most part of the simulation. For the various cases of amplitude(a) and wave number(N), numerical results are acquired. As the endwall groove roughness increases until certain limit, the interior azimuthal velocity component(v) increases drastically. But over the limit, the swirl motion chararcterized by velocity v decreases and finally it approaches much alike Ar=1.0-a case. The reason of activating swirl motion is based on increasing of torque transported by endwall disk. Torque coefficients($C_{T}$) are aquired for the various (a,N,Re) combinations and the limiting phenomena of swirl motion activation is explained.

• Tribology and Lubricants
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• v.8 no.2
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• pp.44-49
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• 1992

Hydrodynamic lateral forces acting on circumferentially grooved and tapered pistons in hydraulic piston pumps are analyzed for the case where the axis of piston and cylinder are tilted with each other. The effects of grooves and tilting on lateral force and leakage flowrate are discussed from the analytical solution of one-dimensional Reynolds equation. The analytical solution is in accordance with the numerical solution of two-dimensional Reynolds equation as the number of grooves increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.325-333
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• 2015

This study was devoted to elucidating the change in the flow characteristics of a laminar flow past a circular cylinder by modifying the cylinder shape with O-grooves. A numerical analysis was performed in a two-dimensional framework. The cylinder was represented using an immersed boundary method and marker particles on a Cartesian grid system. The number and locations of the O-grooves were the key parameters. An analysis of the flow pattern and flow-induced forces was performed at Re = 40 and 50. In addition, we calculated the critical Reynolds number depending on the number of O-grooves and their locations.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.4
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• pp.35-46
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• 1990

The instantaneous friction in main bearings of a single cylinder diesel engine was determined by measuring the instantaneous angular velocity, calculating the resulting forces acting on the bearings, and solving the unsteady Reynolds equation in combination with the mobility method. The considered system consists of only the crankshaft with flywheel and oil pump. The thermal effects were not considered because of the short testing time. The tests were conducted using an electric start motor. The results indicated that when the bearing is not near equilibrium for very small speeds, simple film lubrication theories are not accurate. The details of grooves and unsteady terms in the Reynolds equation cannot be ignored for increasing efficiency of instantaneous friction calculation of the engine bearings. The effects of speed on instantaneous friction and energy lost in friction were determined.

• Transactions of Materials Processing
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• v.14 no.3 s.75
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• pp.245-250
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• 2005

Recently, micro machining technology for high precision mold becomes more interested for mass production of high performance optical parts micro-grooved on the surface, which is under very active development due to its effectiveness in the view point of optical performance. Mechanical micro machining technology now has more competitiveness on lithography, MEMS or LIGA processes which have some problems to fabricate especially cylinder type of groove in such as lenticular lens for illumination angle modulation system. In this study. a lenticular lens mold with U-type micro groove is fabricated making utilizing of the benefit of the mechanical micro machining technology. A shaping machining process is adapted using 3 axis degree of freedom micro machining system and single crystal natural diamond tool. A brass and a electroless nickel materials are used for mold fabrication. Machining force, chip shape and machined surface are investigated from the experiment and an optimal machining condition is found based on the examined problems from the micro cutting process.