• Journal of Korean Physical Therapy Science
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• v.18 no.2
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• pp.29-40
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• 2011

Purpose: The purpose of this study was to analyze the changes of parameters of foot contact by various carrying a pack methods during walking. Method: The subjects were consisted of normal forty four persons (males 30, females 14, mean age 23). The carrying a pack methods were classified into five conditions: carrying no bag(Con 1), carrying a backpack(Con 2), carrying a shoulder bag(Con 3), carrying a cross bag(Con 4), carrying a one-hand bag(Con 5). All subjects were participated in these five condition and measured foot pressure by F-scan system during walking. Then foot contact time, foot contact area, foot contact length and width were measured and analyzed. The repeated one-way analysis of variance (ANOVA) was used to get difference between conditions and independent t-test was used to get difference between left and right foot within condition. Result: In the comparison of parameters of foot, contact time, contact area and mid foot width were significantly different between conditions(p<.05), and in both foot contact time at condition 5 showed the most significant reduction(p<.05). In the comparison of parameters of foot between left and right foot within condition, every conditions were not significantly different(p>.05). Conclusion: In this study various carrying methods changed the parameters of foot contact and showed significant difference in some articles between carrying methods. However, asymmetric load of pack by carrying methods didn't affected symmetry of parameters of foot contact between left and right foot.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.86-93
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• 2009

Elastomeric O-rings have been the most common seals due to their excellent sealing capacity, and availability in costs and sizes. One of the critical applications of O-ring seals is solid rocket motor joint seal where the operating hot gas must be sealed during the combustion. This has long been a design issue to avoid the system failure. For laterally constrained, squeezed and pressurized condition, deformed shape of O-ring was measured by computed tomography method and CCD laser sensor, compared with numerical calculations. As clearance gap changes, sealing performance had been evaluated on peak contact stresses at top, bottom and side contact surfaces. As clearance gap increases, peak contact stresses and contact widths in top and side contact surfaces increase, and the asymmetry of stress distributions is promoted due to pressure increase. It is suggested that peak stress of bottom contact surface can be approximated by simple superposition of peak ones due to squeeze and pressure. Under pressurized condition, sealing performance is dependent on not peak stresses of bottom and side contact surfaces but that of top.

• Tribology and Lubricants
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• v.16 no.6
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• pp.477-483
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• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.103-108
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• 2009

The droplet impact and merging process on a flat substrate with contact angle hysteresis is numerically studied. The droplet deformation is determined by an improved level-set method employing a sharp-interface technique for the stress condition at the liquid-gas interface and the contact angle condition at the liquid-gas-solid interline. Based on the computations, the droplet impact and merging pattern is investigated to find the optimal condition in manufacturing a micro-line. The effects of dynamic contact angles and droplet spacing on droplet motion are quantified.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1231-1237
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• 1999

Applying the conjugate contact condition, contact lines of a cylindrical worm gear has been calculated. The characteristics of tooth contact were analyzed and the pitting resistance were also assessed. It has been verified that: i) the length of contact is shortest on the 1st tooth of the front region, ii) the contact region is more narrow in the recess side than in the access side, iii) the contact region is more narrow in worm than in worm wheel. Hence, the pitting resistance is weakest in the recess side of the 1st contacting worm tooth.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.218-223
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• 2001

Many research of elastohydrodynamic lubrication (EHL) has been performed under the condition of steady state loding. However, mechanical elements undergo severe high loads that are fluctuating in general. Conventional numerical method for the circular contact of EHL study has a difficulty in converging the film pressure and thickness especially in high load of steady state. In this work, multigrid multilevel method expels the convergence problem under the condition of high load and very stable convergence is obtained under the dynamic loading condition over 1.0GPa. Several results of dynamic loading condition are shown and compared with those of steady state condition.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1732-1736
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• 2012

To increase speed up of train, in the field of catenary system, it is necessary to develop of new monitoring methods for dynamic interaction between pantograph and contact wire. Also, there is a need to develop technologies that constantly measure are from various railway structure such as uplift of contact wire, vibration of catenary, dynamic strain of contact line in tunnel. In this paper condition monitoring systems for dynamic performance of catenary systems in tunnel were proposed. An advanced method and results of field tests using high speed camera for monitoring of vertical upward movement of the grooved contact wire due to the force produced from the pantograph were presented. The proposed uplift measurement system of contact wire is expected to enhance precision of current collection quality performance assessment methods at high-speed lines.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.41-49
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• 2003

Tube oscillation behaviour is experimentally investigated for the study on the fuel rod fretting that is caused by the flow-induced vibration in nuclear reactor. The experiment was conducted in all at room temperature. The specimen of tube assembly was supported by plate springs which simulated the spacer grids and fuel rods of a fuel assembly. To investigate the influence of contact condition between the grids and rods, normal load of 10 and 5 N, gaps of 0.1 and 0.3 mm were applied. The range of the oscillation at the center of the fuel rod specimen was varied as 0.2, 0.3 and 0.4 mm to simulate the fuel rod vibration due to flow. Displacements near the contact were measured with four displacement sensors during the tube oscillation. As results, the shape of oscillation (phase) varied depending on the contact condition. The oscillation displacement increased considerably from the contact to gap condition. The displacement increased further as the gap size increased. It is regarded that the spring shape influences the tube oscillation behaviour. Simple calculation showed that the slip displacement was very small. Therefore, cumulative damage concept is necessary for the fuel rod wear. The mechanism of plowing is thought required to explain the severe wear in the case of gap existence.

• Transactions of Materials Processing
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• v.12 no.1
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• pp.34-42
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• 2003

This paper presents a rigid-plastic finite element method to handle the frictional contact problem between two deformable bodies experiencing large deformation. The variational formulation combined with incremental quasi-static model is employed for treating the contact boundary condition. The frictional behavior of the model obeys Coulomb's law of friction. The proposed contact algorithms are classified into two categories, one for searching contacting nodes and the other for calculating contact forces at the contact surface. A slave node and master contact segment are defined using the geometric condition of finite elements on the contact interface. The penalty parameter is used to limit the penetration between contacting bodies, and the finite elements are coupled with contact boundary elements.us gates and cavity thicknesses. Through this study we have observed that the jetting is related to the die swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1129-1137
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• 1990

Based on the formulation which incorporates large deformation and anisotropy, an elastic-plastic finite element code is developed with membrane element to include the contact treatment. For the analysis of the general sheet metal forming process with contact condition, the treatment of contact is considered by employing the successive skew coordinate system. Three kinds of sheet metal forming processes with contact conditions are analyzed; stretching of a square diaphragm with a hemispherical punch, deep drawing of a circular cup and deep drawing of a square cup. Then the computational results are compared with the experiment. The computed loads and the distribution of the thickness strain are in good agreement with the experiment for all cases. However, the computational results of the thickness strain show the effect of bending can not be ignored in the deep drawing process whereas the effect of bending is negligible in stretching.