• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.159-165
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• 2001

The fundamental fluid mechanics associated with the rotation of a smooth plane disk enclosed within a cylindrical chamber have been studied experimentally. In order to acquire systematic information pertinent to this problem torque and friction loss data were obtained over a wide range of disk Reynolds numbers for axial clearance-disk radius ratio H/R from 0.025 to 0.2 and radial tip gap-disk radius ratio s/R from 0.021 to 0.105. Loss analysis of hard disk drive(HDD) is presented to describe the contribution of windage loss of a rotating disk. The minimum loss from factor of HDD can be obtained from this analysis at each operation conditions.

• Tribology and Lubricants
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• v.15 no.4
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• pp.297-303
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• 1999

O-rings in automotive engines are important components such as a coolant pipe, engine oil circulating lines and fuel injector for sealing that makes efficient performance of the engine. Life cycle of O-rings is effected in environments of the O-ring seal, like that applied pressure, working temperature, precompressed ratio and materials. It is related in extrusion, expansion and fatigue failure of O-rings. In this paper, an pressurized, compressed elastomeric O-ring inserted into a rectangular groove is analysed numerically using the nonlinear finite element method. The calculated FEM results showed that extrusion ratio and contact stress are strongly related to the gap clearance and edge radius of the groove.

• 연구논문집
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• s.30
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• pp.25-32
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• 2000

A free piston and free displacer(FPFD) Stirling cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM(Korea Institute of Machinery & Materials). A Stirling cryocooler is relatively compact, reliable, commercially available, and uses helium as a working fluid. The FPFD stirling cryocooler consists of two compressor pistons driven by linear motors which makes pressure waves and a pneumatically driven displacer piston with regenerator. The FPFD Stirling cryocooler employs 1) the Stirling cycle for refrigeration, 2) linear for driving the cryocooler, 3) spring and gas support systems, and 4) fine gap for clearance seals. It is the most suitable design for a mechanical cryocooler utilized in night vision environment. In order to get optimum operating frequency, natural frequency of piston and displacer, optimum phase angle between piston and displacer, cooling capacity, performance tests of the Stirling cryocooler by the frequency characteristics were performed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.117-122
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• 1999

An objective of this study is that when the steel sheet for automobiles would be sheared by using shearing machine, it is to design the forms of pad for obtaining the precision shearing surface to satisfy the conditions required to laser beam butt welding for processed sheared surface and to establish the appropriate condition against the size of gap between strength of pressure and location and clearance between punch and die. For doing so, we will attempt to make a precision of the most possibility of shearing machine by the shearing machine in analyzing the characteristics of the shearing working upon analyzing and clarifying the interrelation among these.

• Earthquakes and Structures
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• v.2 no.1
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• pp.1-24
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• 2011

During very strong earthquakes, seismically isolated buildings may experience large horizontal relative displacements, which may lead to poundings if an insufficiently wide clearance is provided around the building. This paper investigates, through numerical simulations, the effectiveness of using rubber bumpers, which could be attached at locations where it is likely to have impacts, in order to act as shock-absorbers. For the simulation of the dynamic behavior of such rubber bumpers during impacts, a nonlinear force-based impact model, which takes into account the finite thickness of the rubber bumpers, has been developed. Subsequently, a series of parametric analyses are performed to assess the effect of the gap size, the earthquake characteristics and the thickness, compressive capacity and damping of the bumpers. The stiffness of the moat wall is also parametrically considered during poundings of a seismically isolated building, as another potential mitigation measure for poundings of seismically isolated buildings.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.3
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• pp.447-459
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• 1993

A two dimensional finite element model was constructed to analyze the mechanical behavior of four unit fixed partial dentures (FPD) with a 2nd premolar abutment either employing a rigid or nonrigid connector and a 2nd molar abutment(Branemark implant, IMZ implants and natural tooth). Gap elements were used to model the clearance space of the nonrigid connectors and each components of implants. All FPDs with a implant abutment alter the patterns of stress distribution and displacement, but the magnitude of stress in the periodontium was not greater than that of the control. A FPD with rigid connectors induced the smaller stresses in the periodontium than a FPD with a nonrigid connector. A FPD with a Branemark implant exhibited the more desirable mechanical stress states as compared to the IMZ implants with IME or IMC.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.198-203
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• 2000

In this paper, a numerical analysis is carried out to show the effect of friction farce on the dynamic characteristics of a flow divider valve. The continuity equations and the equation of motion fur spool are numerically solved. The viscous friction force acting on the spool is considered analyzing the Reynolds equation which governs the viscous flow in the clearance gap between the spool and sleeve. Dynamic characteristics are highly affected by the viscous friction farce whose magnitude is relatively small compare with other fluid forces. Therefore present theoretical formulation and numerical scheme can be used generally in designing and performance evaluation of all the hydraulic spool valve.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.12 no.2
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• pp.53-66
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• 1999

This study has been carried out to investigate the effects of Dojuksan on the renal functions and internal secretion system, as water balance, urine volume, urinary excretion of sodium and potassium, free water clearance, urinary excretion of creatinine, plasma levels of artrial natriuretic peptide (ANP), plasma levels of aldosterone and plasma renin activity, comparing experimental group which Dojuksan water extract were administrated with control group. Sprague-Dawley rats, about 200-250 g, were used for this experiment. The results of this study were as follows: 1. Water balance decreased significantly after the administration of Dojuksan water extract. 2. Urine volume increased significantly after the administration of $100{\mu}l$ Dojuksan water extract per 100g rat. 3. Urinary excretion of sodium increased significantly but urinary excretion of potassium did not change after the administration of Dojuksan water extract. 4. Free water clearance decreased significantly after the administration of Dojuksan water extract 5. Urinary excretion of creatinine increased significantly after the administration of Dojuksan water extract 6. Plasma renin activity did not change after the administration of Dojuksan water extract 7. Plasma levels of artrial natriuretic peptide (ANP) did not change after the administration of Dojuksan water extract 8. Plasma levels of aldosterone decreased significantly after the administration of 200 ${\mu}Dojuksan water extract per l00g rat The results suggest that Dojuksan increase the urinary excretion of sodium. and thus reduce the water balance, which resulted from suppression of sodium reabsorption into renal tubule by increasing glomerular filtration rate and decreasing aldosterone.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.2
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• pp.1-6
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• 2019

With the increase in number of the athletic population and elderly demographic, the demand for orthopedic splints, which are used to support a damaged body, has rapidly increased. Current splints mainly consist of inner and outer parts, which are multiple fabrics covered with polyurethane and nonwoven fabrics, respectively. However, the laminated materials with directly applied pre-polymer coating lead to a high defect rate because of the uneven thickness on the surface. Thus, this study proposes an indirect coating method using a precise clearance controller, which enables the even application of the coating material on multiple inner parts while maintaining a constant thickness. In addition, a roll-to-roll (R2R) technique is applied instead of the sewing mechanism to bond the inner and outer materials together and enhance the productivity in the final stage. In the advanced methods, there is a storage tank that contains polyurethane, a clearance controller, and pairs of rollers in the upper and lower rows. To improve the quality of the products and optimize the equipment, three controllable factors are determined: the viscosity of polyurethane, angle of the gap controller and number of pairs of rollers in the R2R system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.736-741
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• 2017

This paper examines the design for improving the wiper system of rotorcraft. During rotorcraft operation, the wiping performance and excessive clearance can decrease. The wiper system consists of a wiper arm assembly, motor, convertor and flex drive. If there is a problem with the wiper system, the operation ability decreases because the operation is restricted in a rainy environment. There are two main causes of the problem of the wiper system: the lifting forces acting on the wiper arm in aircraft flight and the excessive gap of the components. To remedy these two problems, the wiper arm was improved. The improvements included increased contact pressure on the wiper arm (spring tension), improved gear clearance, and material and shape changes. Durability test, aircraft ground test and flight test were carried out to verify the improved shape, and it was confirmed that the wiping performance and clearance problems were solved. Currently, the rotorcraft is operated without problem by applying the improved shape, and this design improvement process will be a useful reference for future rotorcraft development.