• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.537-542
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• 2012

Rolling stocks are often subjected to the effects of natural strong wind or wind pressure caused by the crossing train. These wind pressure cause the falling-off in running stability and overturn safety. It is sometimes reported that trains are blown over by a gust of wind. So, many countries enact regulations to secure the overturn safety for wind speed. In this study, theoretical equations of overturn safety based on multi-body model are derived and analyzed the difference between the result of the solid model and that of multi-body model. In case of multi-body model, it is assumed that the degrees of freedom for carbody and bogie are assigned an independent values respectively. The results show that the latter approach based on multi-body model can access the overturn safety of train and replace the conventional method by using commercial software which is accessing with decrement of wheel load.

• New & Renewable Energy
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• v.16 no.3
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• pp.35-41
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• 2020

In this study, a floating LiDAR system (FLS) is investigated through a field test involving two steps. First, correlations among wind speeds, measured using the met mast and two LiDARs, are computed to analyze the acceptance criteria of LiDAR for measuring wind speed. The results of the analysis show that the slopes of single variant regression between mean wind speeds are below 1.03 and the coefficient of determination is above 0.97. Next, correlations among wind speeds measured using the FLS and a fixed LiDAR are determined through a field test carried out in Doomi-doo, Tong-young, Gyeongsangnam-do. The FLS is installed 300 m away from the fixed LiDAR on the ground. The results show that the slope of single variant regression is approximately 1.0275 and the coefficient of determination is above 0.971. According to the IEA/wind 18 recommendation, it is found that the developed FLS measures valid wind speeds to assess wind resources for the development of offshore wind farms.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1078-1085
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• 2011

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor's "2.5D" model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44mm depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.6
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• pp.635-642
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• 2004

In electric motor coaches. the rolling stocks move by the adhesive effort between rail and driving wheel. Generally, the adhesive effort is defined by the function of both the weight of electric motor coach and the adhesive effort between rails and driving wheel. The characteristics of adhesive effort is strongly affected by the conditions between rails and driving wheel. When the adhesive effort decreases suddenly, the electric motor coach has slip phenomena. This paper proposes a re-adhesion control based on disturbance observer and sensor-less vector control. The numerical simulation and experimental results point out that the proposed readhesion control system has the desired driving wheel torque response for the tested bogie system of electric coach. Based on this estimated adhesive effort, the re-adhesion control is performed to obtain the maximum transfer of the tractive effort.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.369-374
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• 2007

Unsteady aerodynamic characteristics of the wing with flaperon flying over nonplanar ground surface are investigated using a boundary-element method. The time-stepping method is used to simulate the wake shape according to the motion of the wing and flaperon over the surface or in the channel. The aerodynamic coefficient according to the periodic motion of the flaperon is shown as the shape of loop. The rolling moment coefficient of the wing flying in the channel is same as that of the wing flying over the ground surface. The variation range of pitching moment is wider when the wing flies in the channel than over the ground surface. The present method can provide various aerodynamic derivatives to secure the stability of superhigh speed vehicle flying over nonplanar ground surface using the present method.

• Fire Science and Engineering
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• v.30 no.6
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• pp.9-13
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• 2016

Anti-oxidation and flame resistant polyurethane nanofibers were prepared by electrospinning and aluminum hydroxide addition. Electrospinning was carried out under the following procedure conditions; applied voltage, 20 kV; polymer solution feeding rate, 1.2 ml/h; collector rolling speed, 120 rpm; and tip to collector distance, 15 cm. Aluminum hydroxide was added to the prepared polymer solution for electrospinning to enhance the oxidation and flame resistant properties. The thermal properties were investigated by thermogravimetric analysis to determine the polymer decomposition temperature, integral procedure decomposition temperature, final decomposition temperature, and remaining amount after thermal decomposition. The activated energy for polymer degradation was also investigated using the Horowitz-Metzger equation. The activation energy increased to more than 50%. The thermal properties of the polyurethane nanofibers were improved by a hydration reaction during the thermal decomposition of aluminum hydroxide around $300{\sim}500^{\circ}C$.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.537-542
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• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• Progress in Superconductivity
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• v.7 no.2
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• pp.145-151
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• 2006

Nickel and nickel-tungsten alloy were electroplated on a cold rolled and heat treated copper(Cu) substrate. 4 mm-thick high purity commercial grade Cu was rolled to various thicknesses of 50, 70, 100 and 150 micron. High reduction ratio of 30% was applied down to 150 micron. Rolled texture was converted into cube texture via high temperature heat treatment at $400-800^{\circ}C$. Grain size of Cu was about 50 micron which is much smaller compared to >300 micron for the Cu prepared using smaller reduction pass of 5%. 1.5 km-long 150 micron Cu was fabricated with a rolling speed of 33 m/min and texture of Cu was uniform along length. Abnormal grain growth and non-cube texture appeared for the specimen anneal above $900^{\circ}C$. 1-10 micron thick Ni and Ni-W film was electroplated onto an annealed cube-textured Cu or directly on a cold rolled Cu. Both specimens were annealed and the degree of texture was measured. For electroplating of Ni on annealed Cu, Ni layer duplicated the cube-texture of Cu substrate and the FWHM of in plane XRD measurement for annealed Cu layer and electroplated layer was $9.9^{\circ}\;and\;13.4^{\irc}$, respectively. But the FWHM of in plane XRD measurement of the specimen which electroplated Ni directly on cold rolled Cu was $8.6^{\circ}$, which is better texture than that of nickel electroplated on annealed Cu and it might be caused by the suppression of secondary recrystallization and abnormal grain growth of Cu at high temperature above $900^{\circ}C$ by electroplated nickel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.224-231
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• 2015

An experimental study on aerodynamic coefficients of a lambda wing configuration was performed at the low speed wind tunnel of Agency for Defense Development. The main purpose of this study was to investigate the effects of sideslip angle on various aerodynamic coefficients. In the case of $0^{\circ}C$ sideslip angle, nose-up pitching moment rapidly increases at a specific angle of attack. This unstable pitching moment characteristic is referred to as pitch break or pitch up. As the sideslip angle increases, the pitch break is found to be generated at a higher angle of attack. Rolling moment is found to show similar behavior pattern to 'pitch break' style with angle of attack at non-zero sideslip angles. This trend gets severer at greater sideslip angles. Yawing moment also shows substantial variation of the slope and the unstable directional stability with sideslip angles at higher angles of attack. These characteristics of the three moments clearly implies the difficulty of the flight control which requires efficient control augmentation system.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.1
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• pp.88-97
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• 1998

Large aluminium extrusions can be used in rolling stocks and high speed vessels to reduce weight and labor cost. As sandwich plates with corrugated core have enough strength in transverse and longitudinal direction, welding lines to connect members are reduced and transverse members to strength longitudinal members are not required. However, for proper design of aluminium extrusion plates, understanding of structural behaviors of the exclusions are necessary. In this paper, at first, detailed finite element analysis is carried out to understand structural behavior. And then, simple theoretical formulas for design purpose are proposed using the orthotropic plate theory. Shear stresses resulting from end twisting which is characteristics of deep aluminium extrusion plates can also be calculated by the simple theoretical formula. Comparison with the results by detailed finite element analysis shows good accuracy of the proposed simple formulas. The simple formulas can be useful in repetitive analysis in the initial design stage.