• 한국생산제조학회지
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• 제22권3호
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• pp.447-451
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• 2013

In this study, a shock absorber whose orifice area changes according to the oil pressure inside the absorber is developed. The orifice widens and narrows when the oil pressure is high and low, respectively; thus, the orifice area changes according to the oil pressure, in other words, according to the extension/compression velocity. It is well known that the damping force can be expressed as $C{\cdot}v^{\alpha}$. For fluid film damping, the force is proportional to velocity, i.e., ${\alpha}=1$, and for orifice damping, it is proportional to the square of velocity, i.e., ${\alpha}=2$. The shock absorber proposed in this paper can exhibit different relationships between the damping force and velocity because the orifice area changes according to the induced oil pressure. The motivation of this study is to develop a method for designing a shock absorber with desired values of C and ${\alpha}$ which is not just 1 or 2. Theoretical and experimental studies have been conducted to verify the damping characteristics of the shock absorber. The effect of some major design parameters on damping characteristics has been also examined to relate the design parameters to the damping characteristics.

• 대한기계학회논문집B
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• 제25권1호
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• pp.71-77
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• 2001

A flow visualization study using the oil film method and the smoke-laser light sheet arrangement is carried out to investigate the three-dimensional flow pattern around the free end surface region of a finite circular cylinder (aspect ratios of 1.25 and 4.25) mounted on a flat plate. The experiment is performed for the cases of two Reynolds numbers: 5.92${\times}$10$^3$and 1.48${\times}$10(sup)5. Various kinds of singular points on the free-end surface are disclosed from the oil surface flow visualization. The smoke-laser light sheet visualization, to aid in understanding the oil streak-line patterns, clearly demonstrates that a pair of tornado-like vortices marched along the downstream together with a pair of side tip vortices. A topological sketch to characterize the surface flow and the four vortices emanating from the top surface is included.

• 대한전자공학회논문지
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• 제20권1호
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• pp.50-54
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• 1983

민생용 전자기기에서 가장 많이 사용되고 있는 부품중의 하나인 탄소 피막 가변 저항기에서 접동자 이동시 발생하는 접촉 저항 변화의 원인을 분석하여 이에 대한 감소, 즉 접동 잡음 감소를 위한 몇 가지 방법을 착안하여 실험 검토하고 그 결과을 정리하여 본 결과 균일한 크기를 가진 탄소 분말 입자로서 고루게 배합된 저항액을 사용하고 접동자의 접촉점과 압력을 증가하면 접촉 저항 및 접촉 저항 변화. 즉 잠동 잡음을 감소시킬 수 있다.

• Tribology and Lubricants
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• 제31권5호
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• pp.205-212
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• 2015

In this research, effects of profile changes of stem section of the plunger on the lubrication characteristics of a fuel injection pump (FIP) were evaluated by hydrodynamic lubrication analysis. The clearance between plunger and barrel was divided into two regions, head and stem. The head was not involved in preventing a decrease of fuel oil pressure. So, research efforts were focused on both edges of the plunger’s stem. The two -dimensional Reynolds equation was used to evaluate lubrication characteristics with variations in viscosity, clearance and profile for a laminar, incompressible, unsteady-state flow. Moreover, the equilibrium equation of moment and forces in the vertical and horizontal directions were used to determine the motion of the plunger. The equations were discretized using the finite difference method. Lubrication characteristics of the FIP were investigated by comparing the dimensionless minimum film thickness, or film parameter, which is the ratio of minimum film thickness to surface roughness. Through numerical analyses, we showed that the profile of the lower edge of the stem had no effect on lubrication characteristics, but the profile of the upper edge had a significant influence on lubrication characteristics. In addition, changes in the profile were more effective in improving lubrication characteristics under low viscosity conditions.

• E2M - 전기 전자와 첨단 소재
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• 제11권10호
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• pp.32-39
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• 1998

Electrical breakdown strength of paper-oil and polypropylene/film-oil insulation samples was measured under dc, ac and pulsating voltages. The latter was obtained by superimposing ac upon dc volate and provides an attractive method for a simultaneous testing and assessment of the state of insulation of the various parts of HV apparatus in service. The measurements were carried out over a wide range of the pulsation ratio defined as p=Eac/Edc. The results obtained under pulsating voltages follow colsely an experssion which relates the breakdown strength to the sum of arc tangent and arc cotangent function of the parameter p. The study was carried out using dry paper as well as paper containing various degrees of moisture. The presence of moisture showed a pronounced effect upon the breakdown strength which varied with the pulsation parameter p.

• 원예과학기술지
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• 제28권3호
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• pp.492-496
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• 2010

자생허브 및 도입허브를 6종 선발하여 정유함량 분포비를 측정하였다. 또한 재배농가와 산업체에 고품질 정유생산을 위한 허브의 품질 및 등급판정 기준설정을 제시하고자 허브의 재배방법 및 수확, 건조방법에 관한 연구를 수행하였다. 대상허브는 꿀풀과 4종, 국화과 2종으로 생활형은 다년초로서 삽목이나 실생이 가능하며, 약용, 관상용, 향료 및 차 등으로 이용하였다. 허브종류별 정유함량으로 백리향 2.62%, 감국 2.0%, 라벤더 3.46%, 로즈마리 2.89% 등에서 높았다. 생육시기별 정유함량은 개화 전보다는 개화기인 7월경에 가장 높았으며, 재배유형별로는 노지재배보다 비가림재배에서 정유함량이 높았다. 또한 재배지역별로는 평야부보다 준고냉지에서의 정유함량이 높았다. 추출방법별로는 SDE(증류추출법)보다는 SFE(초임계추출법)의 정유함량이 2배 이상 높았으며, 추출부위별로는 꽃, 잎, 줄기 순으로 정유함량이 높았다. 수확 후 건조방법별 정유함량은 생체, 동결, 음건, 열풍건조 순으로 정유추출 함량이 높은 결과를 얻어 재배농가 및 가공업체에 허브 재배, 수확 및 건조방법에 대한 기준을 제시하였다.

• 대한화장품학회:학술대회논문집
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• 대한화장품학회 2003년도 IFSCC Conference Proceeding Book II
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• pp.407-416
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• 2003

In this study, we evaluate the correlation between in vitro and in vivo determination of SPF of sunscreen products containing various ingredients depending on emulsification system. For in vitro approach, we determined SPF by the method of Diffey and Robson using an TransporeTM tape(3M Health care, USA) and SPF 290-analyzer(Optometrics Co. USA). SPF values and standard deviations are calculated and displayed after completion of the run. In vivo SPF values are determined according to KFDA (the Korea Food and Drug Administration) method in panels of Fitzpatrick's skin type II or III. We investigated the difference in SPF data of sunscreen ingredient according to emulsification system. The in vivo SPF data is high in water-in oil(W/O) emulsion than in oil-in water(O/W) emulsion samples. The difference may be due to the particular behavior in each vehicles and its presence on skin surface may produce a different sunscreen film. We obtained the corrlation coefficient between in vitro and in vivo SPF data for O/W (R-squre=0.72 )and W/O emulsion(R-squre=0.77). From these results, we suggest the improvement of methodology using Transpore$^{TM}$ tape as substrate to increase the predictability of in vitro method.d.

• 한국통신학회논문지
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• 제21권12호
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• pp.3277-3285
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• 1996

In this paper, w designed an opical power distribution device for application to an optical switching and an optical subscriber loop. We fabricated PSG thin film by LPCVD. Based on the measured index of fabricted thin film, rib-type waveguide was transformed to two-dimension by the effective index method and we simulated dispersion property to find asingle-mode condition. We found that the optimum design parameters of rib-type waveguide are:cladding layer of 3.mu.m, core layer of 3.mu.m, buffer layer of 10.mu.m, and core width of 4.mu.m. Each side of the guiding region was etched down to 4.mu.m to shape the core. We used these optimum parameters of the rib-type waveguide with branching angle of 0.5.deg. and simulted the Y-branch waveguide by the BPM simulation. Numerical loss in branching area was claculated to be 0.1581dB and equal to the total loss of the Y-branch. The loss of the fabricated Y-branch waveguide on PSG film ws 1.6dB at .lambda.=1.3.mu.m before annealing but was 1.2dB after annealing at 1000.deg. C for 10 minutes. Consequently, the loss of branching area from 3000.mu.m to 6000.mu.m in the z-direction was 0.8dB, and single-mode propagation was confirmed by measuring the near field pattern. For coupling the fabricated Y-branch waveguide with an optical fiber, we fabricated V-groove which was used as the upholder of optical fiber. An etching angle was 54.deg. and the width and depth of guiding groove was 150.mu.m, 70.mu.m, respectively. The optical fiber is inserted onto V-groove. Both the Y-branch and V-groove were connected through the index matching oil. Coupling loss after connecting Y-branch and the optical fiber on V-groove was 0.34dB and that after injecting index mateching oil was 0.14dB.

• 한국화재소방학회논문지
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• 제25권6호
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• pp.146-155
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• 2011

본 연구에서는 현장방염처리(방염후처리)가 적용되고 있는 MDF 목재에 국내에서 유통되는 5개사 제품을 MDF 목재에 부착한 방염필름과 MDF 목재(무처리, 비방염필름)에 수성 유성 방염도료로 도포된 시편을 대상으로 현재 시중에서 사용되고 있는 방염처리 방법에 따라 방염성능을 비교하는 실험을 실시하였다. MDF 목재에 5개사의 방염필름을 부착하여 연소 시험한 결과 2개사 제품은 4가지 기준 내에 적합한 값을 나타냈으나 나머지 3개사 제품은 10~40 %의 불합격률을 나타냈다. 방염도료의 특성별로는 유성방염도료가 수성방염도료보다 방염성능 기준 내에서는 더 우수한 것으로 나타났지만 유성방염도료를 도포한 MDF 목재에서 수성방염도료를 도포한 MDF 목재에서 보다 독성지수의 위험등급은 상대적으로 더 높은 위험도를 나타내었다.

• Tribology and Lubricants
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• 제40권2호
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• pp.39-46
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• 2024

The Morton effect (ME) is an instability phenomenon occurring in rotating machineries supported by fluid film bearings and is induced by the thermal deformation of the overhung mass, which is a part of the rotating shaft. Herein, we describe the ME during the high-speed balancing test of a 20 MW class steam turbine. Additionally, to predict the rotating speed at which the ME occurs, we apply the sensitivity vector theory for the steam turbine. During the operation of the steam turbine, we observe a continuous increase in vibration and hysteresis near the rated speed, which is typical of the ME. Increasing the temperature of the lubricating oil supplied to the bearings from 40 to 60℃ suppresses the occurrence of the ME. The rotordynamic analysis for the steam turbine suggests the existence of a mode in which the overhung mass undergoes significant deformation near the rated speed, and we presume that such a mode will increase the occurrence of the ME. The predicted rotating speed of ME occurrence, obtained through the sensitivity vector method, correlates with the test results. Moreover, increasing the temperature of the supplied lubricating oil mitigates the occurrence of ME by reducing the sensitivity between the temperature deviation vector and unbalance mass vector.