• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.6
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• pp.490-496
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• 2001

An experimental study on the behavior of the water hold-up by condensation of a fin-and-tube heat exchanger with regard to the surface characteristics, i.e., contact angle, was conducted. The static and dynamic contact angles were measured, and condensation experiments were conducted. Flow patterns on the fins with different surface characteristics were visualized. Results showed that the static contact angle is proportional to the dynamic contact angle within the range of this study. The water hold-up of the heat exchanger increases as the static or dynamic contact angle of its surfaces increases. Existence of transition of flow patterns was found as the static or dynamic angle increase. Due to the transition in the flow patterns, changes in the gradient of the water hold-up is occurred around the static angle of 8$0^{\circ}C$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.559-560
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• 2006

Powder forging is used for heavy-loaded parts (rings of rolling-contact bearings, gears etc.) production. Rolling contact fatigue is material property values of which characterize possibility of practical utilization of such parts. Rolling contact fatigue of some steels obtained out of prealloyed powders Astaloy CrM, Atomet 4601, Atomet 4901 and powder blends iron-carbon-nickel by hot forging is studied in the present paper. Effect of various kinds of heat and thermomechanical treatment on rolling contact fatigue is determined. Thermomechanical treatment provides optimal values of rolling contact fatigue. In this case steel structure contains up to 40% of retained metastable austenite which is transformed to martensite on trials. Thus typically crack is generated on residual pores and non-metallic inclusions instead of martensite zones in wrought steels.

• Structural Engineering and Mechanics
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• v.91 no.5
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• pp.459-468
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• 2024

This study presents a frictionless receding contact problem for an orthotropic elastic layer. It is assumed that the layer is supported by two rigid quarter planes and the material of the layer is orthotropic. The layer of thickness h is indented by a rigid cylindrical punch of radius R. The problem is modeled by using the singular integral equation method with the help of the Fourier transform technique. Applying the boundary conditions of the problem the system of singular integral equations is obtained. In this system, the unknowns are the contact stresses and contact widths under the punch and between the layer and rigid quarter planes. The Gauss-Chebyshev integration method is applied to the obtained system of singular integral equations of Cauchy type. Five different orthotropic materials are considered during the analysis. Numerical results are presented to interpret the effect of the material property and the other parameters on the contact stress and the contact width.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.211-220
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• 2004

It is well known that the geometry of the articular surface has a major role in determining the position of articular contact and the lines of action for the contact forces. The contact force calculation of the knee joint under the effect of sliding and rolling is one of the most challenging issues in this field. We present a 3-D human knee joint model including sliding and rolling motions and major ligaments to calculate the lateral and medial condyle contact forces from the recovered total internal reaction force using inverse dynamic contact modeling and the Least-Square method. As results, it is believed that the patella, muscles and tendon affect a lot for the internal reaction forces at the initial heel contact stage. With increasing flexion angles during gait, the decreasing contact area is progressively shifted to the posterior direction on the tibia plateau. In addition, the medial side contact force is larger than the lateral side contact force in the knee joint during normal human walking. The total internal forces of the knee joint are reasonable compared to previous studies.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.325-336
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• 2020

In this study, the continuous and discontinuous contact problems of functionally graded (FG) layer resting on a rigid foundation were considered. The top of the FG layer was loaded by a distributed load. It was assumed that the shear modulus and the density of the layer varied according to exponential functions along the depth whereas the the Poisson ratio remained constant. The problem first was solved analytically and the results were verified with the ones obtained from finite element (FE) solution. In analytical solution, the stress and displacement components for FG layer were obtained by the help of Fourier integral transform. Critical load expression and integral equation for continuous and discontinuous contact, respectively, using corresponding boundary conditions in each case. The finite element solution of the problem was carried out using ANSYS software program. In continuous contact case, initial separation distance and contact stresses along the contact surface between the FG layer and the rigid foundation were examined. Separation distances and contact stresses were obtained in case of discontinuous contact. The effect of material properties and loading were investigated using both analytical and FE solutions. It was shown that obtained results were compatible with each other.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2989-2998
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• 2022

Line contact structures, such as the contact between graphite brick and graphite tenon, widely exist in high-temperature gas-cooled reactors. Due to the stress concentration effect, the line contact area is one of the dangerous positions prone to failure in the nuclear reactor core. In this paper, the failure mechanism of line contact structures composed of IG11 nuclear graphite column and brick were investigated by means of experiment and finite element simulation. It was found that the failure process mainly includes three stages: firstly, the damage accumulation in nuclear graphite material led to the characteristic yielding of the line contact structure, but no macroscopic failure can be observed at this stage; secondly, the stresses near the contact area met Mohr failure criterion, and a crack initiated and propagated laterally in the contact zone, that is, local macroscopic failure occurred at this stage; finally, a second crack initiated in the contact area and developed in to a Y-shape, resulting in the final failure of the structure. This study lays a foundation for the structural design and safety assessment of high-temperature gas-cooled reactors.

• KSTLE International Journal
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• v.3 no.2
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• pp.79-83
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• 2002

Sealing an oil-air mixture plays important roles to have an enhanced lubrication for high speed spindle. High speed spindle requires non-contact type of sealing mechanism. Current work emphases on the investigation of the air jet effect on the protective collar type labyrinth seal. To improve the sealing capability of conventional labyrinth seal, air jet was injected against through the leakage flow, It has a combined geometry of a protective collar type and an air jet type. Both of a numerical analysis by CFD (Computational Fluid Dynamics) and experimental measurements are carried out to verify sealing improvement The sealing effects of the leakage clearance and the air jet magnitude are studied in various parameters. The results of pressure drop in the experiment match reasonably to those of the simulation by introducing a flow coefficient Effect of sealing improvement is explained as decreasing of leakage clearance by air jetting. Thus, sealing effect is improved by amount of air jetting even though clearance becomes larger.

• The Korea Journal of Herbology
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• v.29 no.2
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• pp.55-60
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• 2014

Objectives : The aim of this study was to evaluate whether herb mixture extract (HME) would affect allergic contact dermatitis induced by 1-chloro-2,4-dinitro-chlorobenzene (DNCB) in mice. For this, the level of blood IgE was identified. To evaluate anti-inflammatory effect of HME, we tested HMC-1 cells stimulated by PMA+A231867. Methods : In order to evaluate allergic contact dermatitis effects we observed HME on contact-hypersensitive skin of Balb/cmice induced by 0.5% DNCB and measured concentration of IgE in blood of Balb/c mice. In order to evaluate anti-inflammatory effect of cytokine expression we used the method of enzyme-linked immunosorbent assay. Results : We confirmed deep wounds, erosions, progress of keratinization and drop out of dead skin cells from Balb/c mice induced by 0.5% DNCB. We also observed a remarkable decrease in symptoms of atopic dermatitis in the group that received injection of 200mg/kg HME. In addition, in the measurement outcome for IgE concentration in blood, we confirmed that IgE concentration was increased by treatment with DNCB only, while it was markedly decreased by treatment with HME. We confirmed that cytokine expression decreased through enzyme-linked immunosorbent assay and pERK, pJNK, and pp38 also decreased through western blot test Conclusions : According to the above results, HME has some effect on alleviating symptoms of allergic contact dermatitis and has anti-inflammatory effects.

• The Journal of the Korea Contents Association
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• v.13 no.1
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• pp.294-299
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• 2013

This study has investigated the effect of intentional contact through the intercom during MRI scans on the decrease of anxiety in patients. The results obtained through the test group and control group are as follows. 1. The homogeneity of the anxiety score before the scan between the two groups was not acknowledged, hence a significant result could not be deduced. 2. Intentional contact through the intercom displayed decreasing results rational discomfort (t=-2.214, p=.031). 3. Intentional contact through the intercom displayed decreasing results of (t=-3.722, p=.000), and fear (t=-2.74, p=.009). 4. Intentional contact through the intercom displayed decreasing results of heart rate (t=-4.180, p=.000). In conclusion, the attempt to perform MRI scans with intentional contact through the intercom did not display significant effect on the blood pressure of the subject after the scan, however, displayed a decrease in objective and rational discomfort, as well as the heart rate, another vital sign. Accordingly, it is judged that intentional contact through the intercom can be used as an effective substitutive treatment method in patient care and test, as it relieves psychological tension in the patient and allows the patient to feel stability.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.11
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• pp.121-126
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• 2021

In this study, the effect of thermal contact resistance between pin-channel tubes on the heat transfer characteristics was analytically examined around the channel tubes with the pins attached to two consecutive arranged channel pipes. The numerical results showed that the heat transfer coefficient decreased geometrically as the thermal contact resistance increased, and the corresponding temperature change on the contact surface increased as the thermal contact resistance increased. The thinner the pin, the more pronounced the geometric drop in the heat transfer coefficient. It was confirmed that the higher the height of the pin, the higher was the heat transfer coefficient, however, the greater the size of the thermal contact resistance, the smaller was the heat transfer coefficient. It was found that the temperature change in the inner wall of the channel tube did not significantly affect the heat transfer characteristics owing to the thermal contact resistance. Furthermore, the velocity of air at the entrance of the channel tube was proportional to the heat transfer coefficient due to a decrease in the convective heat resistance corresponding to an increase in the flow rate.