• Tribology and Lubricants
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• v.35 no.1
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• pp.65-70
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• 2019

Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.

• Journal of KIISE:Information Networking
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• v.28 no.3
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• pp.406-416
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• 2001

Single path routing schemes using dynamic routing metric amy find out the dynamic network status and recompute paths to keep the traffic from the highly loaded regions of the network. This type of routing approach, however, may lead to a routing oscillation, and further, it cannot exploit multi-paths that may frequently exist in the real network. We propose a multipath routing scheme with dynamic load balancing, called MP-DLB, which is capable of reducing the overhead incurred by the multipath routing with dynamic load balancing approach while taking advantage of the high routing performance provided by the approach. According to the analysis of Internet packet traces which show that a high percentage of network traffic is destined for a small number of networks, MP-DLB applies the multipath routing with dynamic load balancing only to a limited subset of all the destinations in the network. For the rest of the destinations, it applies traditional single path routing scheme. This approach may reduce overall routing overheads by limiting the number of destinations to apply the more complicated routing scheme while it can keep the routing performance high by providing efficient routing for the most significant traffic in the routing performance. A series of simulations are done to analyze the performance of MP-DLB. The simulation results show that MP-DLB may effectively cope with the congestion and achieve high routing performance by distributing traffic streams that are generated from varying sources and heading toward a specific hot destination over multi-paths.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.17-24
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• 2011

TMED(Transmission Mounted Electric Device) parallel hybrid configuration can realize EV(Electric Vehicle) mode by disengaging the clutch between an engine and a transmission-mounted motor to improve efficiencies of low load driving and regenerative braking. In the EV mode, however, jerk can be induced since there are insufficient damping elements in the drive-train. Though the jerk gives demoralizing influence upon driving comport, adding a physical damper is not applicable due to constraints of the layout. This study suggests the jerk reduction control, composed of active damping method and torque profiling method, to suppress the jerk without hardware modification. The former method creates a virtual damper by generating absorbing torque in the opposite direction of the oscillation. The latter method reduces impulse on the mated gear teeth of the drive-train by limiting the gradient of traction torque when the direction of the torque is reversed. To validate the effectiveness of the suggested strategy, a series of vehicle tests are carried out and it is observed that the amplitude of the oscillation can be reduced by up to 83%.

• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.507-511
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• 2008

A "C-sphere" specimen geometry was used to determine the failure strength distributions of a commercially-available bearing-grade silicon nitride ($Si_3N_4$) with ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C-sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diameters indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types common to both ball diameters, that one flaw type was always associated with lower strength specimens, and that a significantly higher fraction of the 25.4-mm-diameter C-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both C-sphere geometries.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.97-103
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• 2014

To ensure durability and light weight of bridges, high-strength concrete is required for long-span deck slabs. Such a technology eventually extends the life of bridges and improves the economic efficiency. The results of this study suggests a formula for calculating the minimum thickness of long-span deck slabs built with high strength concrete. The minimum thickness is proposed based on the limit states indicated in the CEB-FIP Model Code and the Korean Highway Bridge Design Code(limit state design). The design compressive strength of concrete used for the study is 80MPa. Moreover, the required thickness for satisfying the flexural capacity and limiting deflection is estimated considering the limit state load combination. The formula for minimum thickness of deck slabs is proposed considering the ultimate limit state(ULS) and the serviceability limit state(SLS) of bridges, and by comparing the Korean Highway Bridge Design Code and similar previous studies. According to the research finding, the minimum thickness of long-span deck slab is more influenced by deflection limit than flexural capacity.

• Steel and Composite Structures
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• v.23 no.3
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• pp.285-302
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• 2017

Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1233-1238
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• 2009

This study analyzed the characterization of high temperature strength of $Si_3N_4$ composite ceramics additive based on variations in the amount of nano colloidal $SiO_2$ added. Semi-elliptical cracks about 100 ${\mu}m$ length were obtained from a Vickers indenter using a load of 24.5 N. The results showed that the heat-treated smooth specimens with $SiO_2$ nano colloidal coating exhibited the highest bending strength at 0.0 wt% $SiO_2$ nano colloidal added, which is amounted to a 187 % increase over that of smooth specimen. Limiting temperature for bending strength of crack-healed zone for bending strength was about 1273 K. However, the bending strength of SSTS-3 and SSTS-4 was considerably increased while that of SSTS-1 and SSTS-2 was decreased at a temperature of 1,573K.

• Journal of Industrial Technology
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• v.19
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• pp.245-251
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• 1999

The joint in the concrete pavement provides a control against transverse or longitudinal cracking at slab, which may be caused by temperature or moisture variation during or after hydration. Without control of cracking, random crack may cause more serious distresses and result in structural or functional failure of pavement system. Sometimes, joint itself, purposed to control crack, may cause a distresses in joint due to its inherent weakness in structural integrity. Thus, the load transfer capacity in joint is very important for serviceability and durability. The purpose of this dissertation was to develop an evaluation system at joints of jointed concrete pavement using finite element analysis was performed using ILLI-SLAB program with a selected variables which might affect fairly to on the performance of transverse joints. The most significant variables were selected from precise analysis. It was concluded that the variables which most significantly affect to pavement deflections are the modulus of subgrade reaction(K) and the modulus of dowel/concrete interaction(G), and limiting criteria on the performance of joints at JCP at 300pci, 500,000 lb/in. respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1752-1757
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• 2012

With the development in industry, power demand has increased rapidly. As consumption of power has increased, Demand for new power line and electric capacity has risen. However, in the event of fault, problems occur in extending the range of fault coverage and increasing fault current. In these reasons, protection devise is recognized as the prevention of an accident and fault current. This paper dealt with minimizing fault propagation and limiting fault current by adjusting fault current limiter (FCL) with fast interrupter. At this point, we compared and analyzed characteristics between non-inductive resistance and fault current which is limited by superconducting units. In normal state of the power system, power was supplied to the load, but when fault occurred, the interrupter was operated as CT which detected the over-current. Its operation made the limitation of fault current through a FCL. We concluded that the limiter using superconducting units was more efficient with the increase of power voltage. Superconducting fault current limiter with the fast interrupter prevented the spread of a fault, and improved reliability of power system.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.3
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• pp.312-317
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• 2014

In this paper, I propose the design technology of LLC resonant converter for the xenon flashlamp that is used to the solid state laser. Through the fabrication of 1.5kW large scale LLC resonant converter, the discharge characteristics are carried out, and introduce the new control method for limiting inrush current by the abrupt load current changes. The mathematical modeling for the lamp discharge includes the internal loss and lamp parameters. I propose the optimal method for the driving conditions of xenon flashlamp from the simulation results comparing the real measurements.