• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.85-86
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• 2002

For rheology investigation of lubricating oils, first phase diagrams were made from determined free volume based on density measurements and the temperature-pressure relation was estimated using the expansion coefficient of free volume and the temperature-pressure relation of the viscoelastic transition point. Next, the authors proposed the density-pressure-temperature relation and the viscosity-pressure-temperature relation of the tested oils based on the free volume and the phase diagrams. Moreover, it was shown that the Ehrenfest equation or the gradient of the phase diagram is closely related to the expansion coefficient of free volume.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.2909-2915
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• 1996

Precise and accurate pressure measurements are obtained using deadweight piston gauges. Pressure distribution and elastic distortion in the piston-cylinder unit are the leading factors in determination of effective area. The distortion depends upon the pressure distribution in the clearance between piston and cylinder and those are coupled each other. Considering the viscosity pressure relation of oil and governing flow equation in the clearance, a new numerical iterative algorithm is developed. The disagreement between the monotonous and sharp pressure profiles is an indication that the pressure profile will be different for each piston and cylinder unit due to material variances.

• Advances in materials Research
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• v.3 no.2
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• pp.91-103
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• 2014

A study that demonstrates how to investigate the molded part quality and the consistency of injection process based on the rheological concept is proposed. It is important for plastic material whose melt viscosity is variable with respect to the processing condition. The formulations to couple the melt viscosity with injection pressure and fill time are derived first. Taking calculations of the measured pressure and the time by using these formulations, the melt viscosity in injection process can be determined on machine. As the relation between the injection speed and the melt viscosity is constructed, the influences of the setting parameter of injection machine on the molded part quality can be investigated through evaluating the state of the melt viscosity. In addition, a pressure sensor bushing (PSB) designed with a quick installation feature is also provided and validated. The results show that a higher injection speed improves the tensile strength of the molded part but also the consistency of the molded part quality. This work provides an alternative to evaluate the molding quality scientifically.

• Tribology and Lubricants
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• v.15 no.4
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• pp.343-353
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• 1999

The role of viscosity index improver's(Ⅶ) additives for modem engine lubrication is complex. Under the condition of atmosphere or low shear rate, the characteristics of Ⅶ added lubricant is verified and quoted frequently for mathematical model of lubricant behavior. However, recent research shows that added lubricant has the characteristics of shear thinning at high shear rate condition although it performs well enough over the whole range of working temperature. At high shear rate, they show significant decrease of apparent viscosity irrespective of temperature. Many experimental researches verify that Ⅶ added lubricant shows boundary film layer formation on the solid surface as well as shear thinning effect by its polymeric molecular characteristics. The intend of our research is to verify the effects of Ⅶ from the viewpoint of continuum mechanics, because conventional Reynolds'equation with only pressure-viscosity relation cannot fully predict the lubricant behavior under the Ⅶ added condition. In these aspects, Reynolds'equation of Newtonian fluid model lacks the reflection of real fluid behavior and there is no way to explain the non-linear characteristics of Ⅶ added lubricant. In this research, we mathematically modeled the Ⅶ added lubricant behaviors which are the characteristics of non-Newtonian fluid behavior at high shear rate and boundary film formation on the solid surface. The consideration of elastic deformation in the contact region is also included in our computation and finally the converged film pressure and the film thickness with elastic deformation are obtained. The results are compared with those of Newtonian fluid model.

• The Journal of Korean Academy of Prosthodontics
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• v.9 no.1
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• pp.79-83
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• 1969

1) 가능(可能)한한 조직(組織)이 변형(變形)되지 않아야 한다. 2) Atmospheric pressure를 이용(利用)하기 위(爲)하여 peripheral border 에 있어서의 조직변형(組織變形)이 필요(必要)한 경과(境過)는 그 정도(程度)가 eiastic force가 retentive force 보다 크지 않도록 최소한(最小限)으로 해야 한다. 3) Denture base와 조직(組織)의 원형간(原形間)에는 접촉(接觸)이 밀접(密接)해야 한다. 그래야 saliva의 film 균일(均一)하고 얇게 될 수 있다. 4) Atmospheric pressure는 denture의 retention과 중요(重要)한 연관성이 있으므로 physiologic seal area를 형성(形成)해 주는 것이 유리(有利)하다. 5) Ridge의 형태(形態)도 denture의 retention 대(對)한 하나의 중요(重要)한 인자(因子)이다. 6) Denture에 의(依)해서 피개(被蓋)되는 면적(面積)은 retention에 관계(關係)되는 한 인자(因子)로써 피개면적(被蓋面積)이 클수록 유지력(維持力)이 커진다. 7) Saliva의 viscosity도 retention의 한 인자(因子)가 된다. 8) Friction은 retention의 한 인자(因子)가 될수는 있으나 병인적(病因的)인 증상(症狀)을 유발(誘發)할수 있으므로 이용(利用)해서는 않된다.

• Journal of KSNVE
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• v.7 no.6
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• pp.959-966
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the results, the flow disturbances occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.627-635
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the reslts, the flow disturbance occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• Journal of the Korea Institute of Building Construction
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• v.14 no.2
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• pp.118-126
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• 2014

The establishment of the technology for evaluating friction resistance and pipe pressure and the relation of the fluid characteristics and pumpability of concrete is essential for concrete pumping performance for the rapid construction of super-tall buildings. In this study, a quantitative evaluation of concrete fluid characteristics and surface friction resistance was performed, applying different concrete mix proportions and pumping conditions. To achieve this, we developed a temporary horizontal pumping evaluation system to measure pipe pressure and surface friction characteristics, and performed an experiment to investigate the relations between concrete rheology characteristics and friction resistance in pipe. The experiment found that in terms of the rheology characteristics, plastic viscosity was reduced remarkably after pumping. As well, high regression between the surface friction and pressure gradient was confirmed. This means that it is possible to evaluate the friction resistance between concrete and pipe by means of a pumping system that includes a frictional resistance testing pipe. In addition, high regression between the plastic viscosity of concrete after pumping and friction resistance coefficient was confirmed. Finally, it is considered that pumping pressure can be predicted using the friction resistance coefficient derived in this study, and it has high regression.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.2
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• pp.206-212
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• 2014

Liquid silicone rubber (LSR) has been widely used in automotive, electrical, and medical components. Thus, research on the use of LSR in the injection molding process is required to obtain high-quality and high-performance products. In this study, a mold was fabricated to examine the effects of the process parameters on the molding and mechanical properties of LSR parts. A computer-aided engineering analysis was used to optimize the air vent depth and curing temperature to decrease the flash at the air vents caused by the low viscosity of LSR. Temperature and pressure sensors were mounted in the mold to determine the effects of the process parameters on the temperature and pressure in the cavity. The tensile strength of the LSR parts was also examined in relation to the process parameters.

• Journal of the Korea Institute of Building Construction
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• v.15 no.4
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• pp.375-381
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• 2015

In this study, high performance concrete of C60 and C80 were applied to a super tall building and those had satisfactory properties of fresh and hardened concrete to the requirements even changes according to time. Especially the evaluation and analysis of the relation of the rheological properties and puMPability of high performance concrete, C60-14 which was applied to the height of from 500m to 575m in the building, was carried out bymeasuring pumping pressure and pumping speed, testing concrete properties at before and after pumping. As results, themax. pumping pressure showed increase of 5% at every 25m higher pumping and the average pumping speed showed the above $25m^3$ per hour whichmeans proper productivity. Additionally it was verified that the loss of slump flow after pumping was increased according to plastic viscosity values and the increment of temperature through concrete pumping.