• Proceedings of the KSR Conference
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• 2004.06a
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• pp.804-810
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• 2004

Tilting train can pass curve at higher speed without affecting passenger comfort by tilting Carbody. But the centrifugal force proportional to square of velocity increases the track lateral force. This is the one of the problems to be solved when applying tilting train. The one countermeasure we selected the light weight design by applying distributed traction EMU system and light weight materials such as FRP. The other countermeasure was to adopt steering bogie concept in order to reduce the guiding force on Curve track. This paper describes the design study of self steering mechanism applied to the Bogie for 180 km/h Korean Tilting Train(TTX), which was done as a part of the Korean National R&D project.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.22-23
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• 2006

High velocity compaction (HVC) is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. Investigated here are green body data such as density, tensile strength, radial springback, ejection force and surface flatness. Comparisons are performed with conventional compaction using the same pressing conditions. Cylindrical samples of a pre-alloyed water atomized iron powder are used in this experimental investigation. The HVC process in this study resulted in a better compressibility curve and lower ejection force compared to conventional quasi static pressing. Vertical scanning interferometry measurements show that the HVC process gives flatter sample surfaces.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.151-154
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• 2005

Tilting train improves a traveling velocity through giving a tilt the car-body without ride comfort deterioration In curve. Dynamic behavior in deceleration will show quite another feature in constant velocity, In this study, we see through the dynamic behavior due to a variation of braking force in Korean Tilting Train. Hence we compose of 3D dynamic model, as well as we check upon the property in service braking condition and unique braking condition with a fault system. This study has the meaning with reference data of developing Korean Tilting Train test traveling.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.751-752
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• 2012

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.17-25
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• 2016

Revetments help protect levee slopes from erosion. If the design of the revetment is not appropriate, the levee may collapse as a result of scouring due to the strong flow velocity and tractive force. Therefore, when designing a revetment, it is very important to calculate the representative velocity. However, the average velocity and depth calculated by 1-D varied flow analysis are generally applied to the design, which do not reflect the increase in velocity caused by the free and force vortex. Therefore, it is necessary to correct the representative velocity in order to ensure the stability of the revetment in a meandering channel. In this study, the applicability of the method of calculating the representative velocity considering the curve and scour was studied (by comparing it with) the average and maximum velocities determined by numerical simulation. The representative velocity corrected for the effect of the curve and scour and the maximum velocity calculated by the numerical simulation were found to match quite well. In addition, the riprap size of the gabion in the meandering and straight channels were compared by applying them to the conventional design formulas. In the future, it is necessary to perform additional numerical simulations for various rivers with different characteristics, in order to propose a method of designing a suitable revetment for Korean characteristics. At this time, the results of this study are expected to be able to be used as basic data.

• Earthquakes and Structures
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• v.22 no.3
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• pp.219-230
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• 2022

Knowing that the variability of soil properties is an important source of uncertainty in geotechnical analyses, we will study in this paper the effect of this variability on the seismic response of a structure within the framework of Soil Structure Interaction (SSI). We use the proposed and developed model (N2-ISS, Mekki et al., 2014). This approach is based on an extension of the N2 method by determining the capacity curve of the fixed base system oscillating mainly in the first mode, then modified to obtain the capacity curve of the system on a flexible basis using the concept of the equivalent nonlinear oscillator. The properties of the soil that we are interested in this paper will be the shear wave velocity and the soil damping. These parameters will be modeled at first, as independent random fields, then, the two parameters will be correlated. The results obtained showed the importance of the use of random field in the study of SSI systems. The variability of soil damping and shear wave velocity introduces significant uncertainty not only in the evaluation of the damping of the soil-structure system but also in the estimation of the displacement of the structure and the base-shear force.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.4
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• pp.313-320
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• 2005

Stick-slip friction is one of the material removal mechanisms in tribology. It occurs when the static friction force is larger than the dynamic friction force, and make the friction curve fluctuated. In the friction monitoring of chemical mechanical polishing(CMP), the friction force also vibrates just as stick-slip friction. In this paper, an attempt to show the similarity between stick-slip friction and the friction of CMP was conducted. The prepared hard pa(IC1000/Suba400 stacked/sup TM/) and soft pad(Suba400/sup TM/) were tested with SiO₂ slurry. The friction force was measured by piezoelectric sensor. According to this experiment, it was shown that as the head and table velocity became faster, the stick-slip time shortened because of the change of real contact area. And, the gradient of stick-slip period as a function of head and table speed in soft pad was more precipitous than that of hard one. From these results, it seems that the fluctuating friction force in CMP is stick-slip friction caused by viscoelastic behavior of the pad and the change of real contact area.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.10
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• pp.813-820
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• 2021

In this study, a low-velocity impact test was performed to obtain the dynamic properties of solid propellants. The dynamic behavior of the solid propellant was examined by measuring the force and displacement of the impactor during the low-velocity impact test. The bending displacement was calculated by compensating for the local displacement caused by the low-velocity impact test in the form of three point bending and the shear displacement caused by using a short and thick solid propellant specimen. Stress and strain were calculated using compensated displacements and measured force, and dynamic properties of solid propellants were obtained from the stress-strain curve and compared with static bending test. The dynamic properties of solid propellant under the low-velocity impact loading at various operating temperature conditions such as room temperature(20 ℃), high temperature(63 ℃), and low temperature(-32 ℃) were compared and investigated.

• Tribology and Lubricants
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• v.13 no.2
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• pp.52-59
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• 1997

An experimental study is presented for the characteristics of the high temperature superconductor as an application of the repulsive type magnetic bearing. A ring shaped YBCO type superconductor and Neodium permanent magnets are employed for the experiment. For the case of field cooling, superconductor shows strong repulsive force, which is due to the Meissner effect, as the gap between the superconductor and the magnet gets closer. The repulsive force variation with respect to the gap change shows hysterisis characteristics. The area of the loop of the hysterisis curve represents the dissipation of energy, which reveals that the magnetic bearing with superconductor has large damping. The effect of the initial gap and the magnetic flux density on the repulsive force is analyzed experimentally and the static stiffness variation is calculated from the measured repulsive force variation. The relative sliding velocity between the superconductor and the magnet has little effect on the repulsive force which is quite different from the usual sliding element bearing. As the initial gap for the field cooling becomes larger, the maximum repulsive force at the minimum gap increases and approaches to the value for the case of zero field cooling.

• Geomechanics and Engineering
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• v.8 no.5
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• pp.741-756
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• 2015

The prediction of impending collapse of deep tunnel is one of the most difficult problems. Collapse mechanism of deep tunnel in layered soils is derived using a new curved failure mechanism within the framework of upper bound theorem, and effects of seepage forces are considered. Nonlinear failure criterion is adopted in the present analysis, and the possible collapse shape of deep tunnel in the layered soils is discussed in this paper. In the layered soils, the internal energy dissipations along velocity discontinuity are calculated, and the external work rates are produced by weight, seepage forces and supporting pressure. With upper bound theorem of limit analysis, two different curve functions are proposed for the two different soil stratums. The specific shape of collapse surface is discussed, using the proposed curve functions. Effects of nonlinear coefficient, initial cohesion, pore water pressure and unit weight on potential collapse are analyzed. According to the numerical results, with the nonlinear coefficient increase, the shape of collapse block will increase. With initial cohesion of the upper soil increase, the shape of failure block will be flat, and with the lower soil improving, the size of collapsing will be large. Furthermore, the shape of collapsing will decrease with the unit weight decrease.