• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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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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• 제15권4호
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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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• 통권30호
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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.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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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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• 제2권1호
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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.

• 대한치과보철학회지
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• 제31권3호
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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.

• 한국정밀공학회지
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• 제17권1호
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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.

• 한방안이비인후피부과학회지
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• 제12권2호
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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.

• 한국기계가공학회지
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• 제18권2호
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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.

• 한국산학기술학회논문지
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• 제18권6호
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• pp.736-741
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• 2017

본 논문은 회전익 항공기의 와이퍼 시스템의 설계 개선에 관한 연구이다. 국내 회전익 항공기의 우천환경 운용 시, 와이퍼 닦임 성능 저하 및 떨림 현상이 발생하였다. 와이퍼 시스템은 크게 와이퍼 암 조립체, 전동기, 와이퍼 변환기 조립체, 플랙스 드라이브로 구성되며, 와이퍼 시스템에 문제가 발생하면 우천환경의 작전에 제한사항이 발생하여 작전능력이 감소한다. 이러한 와이퍼 시스템의 문제를 야기한 원인은 크게 2가지로 검토되었으며, 첫번째 사유는 항공기 기동조건에서 와이퍼 암에 작용하는 부상력 때문이며, 두번째는 구성품들의 과다한 유격 때문이다. 이 2가지 문제를 개선하기 위해서 본 연구가 수행되었으며, 4가지의 와이퍼 구성품 중 와이퍼 암을 개선하였다. 개선 내용으로는 와이퍼 암의 누름압(스프링 장력) 증가, 기어 공차 개선, 재질 및 형상 변경이 수행되었다. 개선형상의 검증은 구성품 단위 내구성 시험, 항공기 지상 시험, 비행 시험이 수행되었으며, 설계 개선된 와이퍼 암을 장착하였을 시 닦임 성능 및 유격문제가 해소된 것을 확인 할 수 있었다. 닦임성능은 육안으로 확인하였으며, 유격문제는 와이퍼 작동거리를 측정하여 확인하였다. 현재 국내 회전익 항공기는 개선 형상을 적용하여 문제없이 운용하고 있으며, 이러한 설계 개선 과정은 향후 회전익 항공기 개발 시 유용한 참고자료가 될 것이다.