• Geomechanics and Engineering
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• v.16 no.6
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• pp.569-575
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• 2018

The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.381-386
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• 1999

The member with external unbonded tendon has two remarkable characteristics, i.e., eccentricity variation and slip by friction force at deviators, compared with internal bonded or unbonded member. An efficient numerical procedure for the nonlinear analysis of prestressed concrete beam with external unbonded tendon considering two remarkable characteristics is formulated and corresponding computer code is developed. On the basis of statistical process of parametric study results, strain compatibility method, eccentricity variation predictor and tendon stress predictor at ultimate state are proposed and verified with test results and existing Codes, which can evaluate flexural behavior at ultimate state. Finally, the proposed procedure and predictors can be efficiently used for the realistic and accurate analysis of prestressed concrete members with external unbonded tendons.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1630-1632
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• 1996

The static charges are generated by streaming electrification phenomena when insulating oil flowing by force for the purpose of cooling at the internal of Ultra-high power transformer. In this thesis, their elimination method was studied. In this paper the effect of Additive on the electric conductivity of Insulating oil is studied. The variation of electric conductivity disappear when Additive is molten in insulating oil, the variation of Additive is not enough to decrease streaming electrification of insulating oil(${\sigma}>10^{-12}$[S/cm]).

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.5
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• pp.96-103
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• 2005

One of the major problems limiting the accuracy of piezoelectric transducers fur cylinder pressure measurements in an internal combustion (IC) engine is the thermal shock. Thermal shock is generated from the temperature variation during the cycle. This temperature variation results in contraction and expansion of the diaphragm and consequently changes the force acting on the quartz in the pressure transducer An empirical equation for compensation of the thermal shock error was derived from consideration of the diaphragm thermal deformation and actual pressure data. The result indicate that the thermal shock equation provides reliable correction based on known surface temperature swing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.252-261
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• 1988

Through the careful interpretation of the results of the cutting tests carried out in this study, it is found that under the cutting conditions when the internal shear of the chips take place the cutting can be treated essentially as a steady state problem. A new shear angle equation has been developed employing the conditions of force and moment equilibrium about the tool edge and the stress distribution model suggested by Zorev.The equation contains the chip-tool contact length C and stress distribution index n as important parameters.

• Tribology and Lubricants
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• v.13 no.2
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• pp.89-95
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• 1997

This paper considers two dimensional analysis for lubrication between the single piston ring and the cylinder liner. The piston ring is treated as a reciprocating, hydrodynamic bearing with combined sliding and squeeze motion. Reynolds' equation is used, to model lubrication with Reynolds' cavitation boundary condition. This analysis is developed to get the cyclic variation of minimum film thickness and viscous frictional force. Two types of piston ring face shape are considered. This result can be used to study the influence of ring shape design parameter to improve the characteristics of sealing and lubrication.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.53-53
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• 2015

Basin-scale motions in a stratified lake rely on interactions of spatially and temporally varying wind force, bathymetry, density variation, and earth's rotation. These motions provide a major driving force for vertical and horizontal mixing of inorganic and organic materials, dissolved oxygen, storm water and floating debris in stratified lakes. In Lake Tahoe, located between California and Nevada, USA, basin-scale circulations are obviously important because they are directly associated with the fate of the suspended particulate materials that degrade the clarity of the lake. A three-dimensional hydrodynamic model, ELCOM, was applied to Lake Tahoe to investigate the underlying mechanisms that determine the characteristics of basin-scale circulations. Numerical experiments were designed to examine the relative effects of various mechanisms responsible for the horizontal circulations for two different seasons, summer and winter. The unique double gyre, a cyclonic northern gyre and an anti-cyclonic southern gyre, occurred during the winter cooling season when wind stress curl, stratification, and Coriolis effect were all incorporated. The horizontal structure of the upwelling and downwelling formed due to basin-scale internal waves found to be closely related to the rotating direction of each gyre. In the summer, the spatially varying wind field and the Coriolis effect caused a dominant anti-cyclonic gyre to develop in the center of the lake. In the winter, a significant wind event excited internal waves, and a persistent (2 week long) cyclonic gyre formed near the upwelling zone. Mechanism of the persistent cyclonic gyre is explained as a geostrophic circulation ensued by balancing of the baroclinc pressure gradient (or baroclinic instability) and Coriolis effect. Topographic effect, examined by simulating a flat bathymetry with constant depth of 300m, was found to be significant during the winter cooling season but not as significant as the wind curl and baroclinic effects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.103-111
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• 2014

In this study, the probabilistic internal pressure fragility analysis was performed by using the non-linear finite element analysis method. The target structure is one of the containment buildings of typical domestic pressurized water reactors(PWRs). The 3-dimensional finite element model of the containment building was developed with considering the large equipment hatches. To consider uncertainties in the material properties and structural capacities, we performed the sensitivity analysis of the ultimate pressure capacity with respect to the variation of four important uncertain parameters. The results of the sensitivity analysis were used to the selection of the probabilistic variables and the determination of their probabilistic parameters. To reflect the present condition of the tendon pre-stressing force, the data of the pre-stressing force acquired from the in-service inspections of tendon forces were used for the determination of the median value. Two failure modes(leak, rupture) were considered and their limit states were defined to assess the internal pressure fragility of target containment building. The internal pressure fragilities for each failure mode were evaluated in terms of median internal pressure capacity, high confidence low probability of failure(HCLPF) capacity, and fragility curves with respect to the confidence levels. The HCLPF capacity was 115.9 psig for leak failure mode, and 125.0 psig for rupture failure mode.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.3
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• pp.83-88
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• 2010

This study aimed to enhance the durability by distributing the stress concentration at the contact and increasing the mechanical characteristics, as well as by changing the surface shape for LIP in the low-pressure seal among oil seals installed to the power steering of automotive. Accordingly, results were derived from comparisons and reviews with oil seals under the existing mass production by carrying out the performance tests after designs and productions are done with the addition of embo shapes on the surface of LIP in the low-pressure seal. As a result of this study, it has been identified that the durability of oil seals with the addition of embo shapes was enhanced with higher radial force and less variation in the internal diameter for the LIP. In addition, it was seen that the sealing ability for those oil seals is superior to the existing oil seals as their rotational torque values are less than those of the existing oil seals.

• Journal of the korean Society of Automotive Engineers
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• v.5 no.1
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• pp.45-53
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• 1983

There exist many kinds of frictions in internal combustion engine such as piston ring and skirt, cam and tappet, bearing friction etc. Among them, the frictions between piston ring, skirt and cylinder are particular. These frictions for motoring test are differ from that of firing test even though the temperature of cooling water and lubricating oil keep identically. The frictions for firing test are increased due to combustion pressure and products. The precise calculation of the friction is difficult. But we can assume that the friction is governed by the viscosity of lubricating oil and gas pressure of cylinder. And the viscosity of lubricating oil is dependant on gas temperature of cylinder, so the piston friction may be governed by gas pressure and temperature of cylinder. In this treatise, we propose the method of evaluating piston friction under the condition of constant engine speed, and we analyzed the behaviours and influence of factors concerned with the piston friction for output correction when the inlet pressure and temperature were varied. The main results are as follows: 1) The behaviours on the inlet conditions for the contact force of the piston rings and the viscosity of the lubricating oil concerned with piston friction are found. 2) The essential point the these behaviours is dependant on the cyclic variation following to the inlet conditions. 3) According to our analysis, It was observed that the viscosity of lubricating oil is more effective than the contact force to the piston rings.