• Journal of the Korean Society for Railway
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• v.8 no.5
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• pp.405-410
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• 2005

In this paper, the train resistances for HSR-350x(Korean High Speed Train project), which has been obtained by the coast-down test, have been proposed in cases of the open field and tunnel. They are approximated as quadratic functions suggested by the Davis equation. The coast-down simulations for HSR-350x using the estimated train resistances have performed and the results have been compared with those of the same conditions of the coast-down tests. It is concluded that the proposed train resistances can be considered to provide good estimations for HSR-350x. Also, the effects of the infrastructure conditions, such as tracks, curves and tunnels have been reviewed. These results show that the tunnel plays an important role in determining the train resistance but others does not.

• Tribology and Lubricants
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• v.33 no.4
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• pp.153-167
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• 2017

The aim of this study is to find the change in trend in the eccentricities of two journal bearings supporting the crankshaft of a single cylinder engine and the degree of misalignment of the shaft. We analyze the change in oil film thickness considering the wear scar under mixed-elasto-hydrodynamic lubrication regime at potential wear regions. For this, we first calculate the central eccentricities of the two journal bearings by using the mobility method. Then we calculate the outer end eccentricity by using the geometry of the bearings. Further, the tilting angle and degree of misalignment of the shaft are calculated by using the eccentricities of the two bearings. We show that the eccentricity of bearing #1, on which higher load is applied, increases at the beginning of the start-up cycle and during the coast-down cycle. However, the eccentricity of bearing #2, on which lower load is applied, decreases at the beginning of the start-up cycle and increases during the coast-down cycle. From the results of the analysis of oil film thickness, we show that the mixed-elasto-hydrodynamic lubrication regime for a misaligned shaft is at the initial stages of the start-up cycle for both bearing #1 and #2 and at the final stage of the coast-down cycle for only bearing #1.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.3
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• pp.18-24
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• 2017

Appropriate selection of the starter is essential for successful starting of the gas-turbine engine. Thus, aerodynamic drag during starting phase should be analyzed to assess the feasibility of the starter. In this paper, aerodynamic drag is modeled based on the speed profile from the engine coast down test, and it is scaled with respect to the target engine by comparing the compressor load. Afterward, the govern equation of the starting phase is developed with the torque model of the starter, and the design scheme to select the feasible starter will be finally suggested. The proposed model of starting phase will be useful to perform a preliminary design of the starting system of the gas-turbine engine.

• Tribology and Lubricants
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• v.33 no.4
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• pp.168-186
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• 2017

This paper presents a wear analysis procedure for calculating the wear of journal bearings during the start-up and coast-down cycles of a motoring stripped-down single cylinder engine operating with a tilted shaft. In order to decide whether the lubrication state of a journal bearing is in the mixed-elasto-hydrodynamic lubrication regime, we utilize lift-off speed and MOFT (most oil film thickness) under mixed-elasto-hydrodynamic lubrication regime at the corresponding aligned shaft. We formulate an equation for the modified film thickness in a misaligned journal bearing considering the additional wear volume described in Part I of this study. For this, we use the calculation results of the degree of misalignment and tilting angle obtained after finding the eccentricities of the two bearings supporting the crankshaft of a single cylinder engine. In this Part II, we calculate the wear of journal bearings using the fractional film defect coefficient, the asperity load sharing factor, and the modified specific wear rate for the application of mixed-elasto-hydrodynamic lubrication regime. We show that the accumulated wear volume after turning the ignition switch on and off once, increases to ${\sigma}=39{\mu}m$ and then decreases from ${\sigma}=39{\mu}m$ with increasing in surface roughness.

• Journal of Auto-vehicle Safety Association
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• v.10 no.1
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• pp.45-51
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• 2018

There are some ambiguities of the information on the fuel economy provided to the consumers because the standard and the detailed regulations for the fuel economy of the two-wheeled vehicle have not been established in Korea. Since Korea has been a signatory of World Forum for Harmonization of Vehicle Regulations since 1998, it is possible to remove the ambiguities by adopting the WMTC (Worldwide-harmonized Motorcycle Test Cycle) measurement method for the fuel economy of the two-wheel vehicle. As a preliminary study on the WMTC mode fuel economy, road loads measured by coast down method and table method were compared for the two types of two-wheeled motorcycles on sales in domestic market. In the same model, it was confirmed that the deviation of WMTC mode fuel efficiency was below -5% between products. On the other hand, the difference of WMTC fuel economy exceeded 5% between the coast down method and table method.

• Tribology and Lubricants
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• v.31 no.3
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• pp.125-140
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• 2015

In this paper, we present the results of the wear analysis of journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. We calculate journal bearing wear by using a modified specific wear rate considering the fractional film defect coefficient and load-sharing ratio for the asperity portion of a mixed elastohydrodynamic lubrication (EHL) regime coupled with previously presented graphical data of experimental lifetime linear wear in radial journal bearings. Based on the calculated wear depth, we obtain a new oil film thickness for every crank angle. By examination of the oil film thickness, we determine whether the oil film thickness at the wear scar region is in a mixed lubrication regime by comparing dimensionless oil film thickness, h/σ, to 3.0 at every crank angle. We present the lift-off speed and the crank angles involved with the wear calculation for bearings #1 and #2. The dimensionless oil film thickness, h/σ, illustrates whether the lubrication region between the two surfaces is still within the bounds of the mixed lubrication regime after scarring of the surface by wear. In addition, we present in tables the asperity contact pressure, the real minimum film thickness at the wear scar region, the modified specific wear rate, and the wear angle, α, for bearings #1 & #2. To show the real shape of the oil film at wear scar region, we depict the actual oil film thickness in graphs. We also tabulated the ranges of bearing angles related with wear scar. We present the wear volume for bearings #1 and #2 after one turn-on and turn-off of the engine ignition switch for five kinds of equivalent surface roughness. We show that the accumulated wear volume after a single turn-on and turn-off of an ignition switch normally increases with increasing surface roughness, with a few exceptions.

• Tribology and Lubricants
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• v.31 no.3
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• pp.109-124
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• 2015

This paper presents a wear analysis procedure for the journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. A journal bearing is in the mixed elastohydrodynamic (EHL) lubrication region when the shaft speed is less than the corresponding lift-off speed. Below the lift-off speed, a wear scar can form on bearing surfaces. In part 1 of this paper, we develop the appropriate formulations and the calculation procedure for the analysis. Specifically, we formulate an equation for modified film thickness in a journal bearing considering the additional wear volume. In order to obtain the modified specific wear rate induced by the modified Archard’s wear coefficient, we utilized the extended non-dimensional diagram for the specific wear rate, k, the fractional film defect coefficient, Ψ and the asperity load sharing factor, γ₂. This asperity load sharing factor is newly calculated by setting the Zhao-Maietta-Chang (ZMC) asperity contact pressure equation coupled with the central film thickness equation derived by using the ZMC asperity contact model equal to the modified central contact pressure derived by using the central (or maximum) contact pressure at the dry rough line-contact configuration. We can use the procedure introduced in this paper to determine the lifetime (or longterm) linear wear in radial journal bearings that is a result of repeated stop-start cycles.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.2
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• pp.51-61
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• 1995

A coast down test mothod has been used to determine the resistance forces on running vehicle due to the aerodynamic drag, rolling resistance and driveline resistance. Most of the tests, however, are based on the Velocity-Time measurements, which require a sophisticated velocity measuring device and contain much error by nature. In the present study a coast down test method based on Distance-Time measurements is introduced, which contains the original idea of Russian scientist Prof. Petrushov along with the suggestions for improvement of the accuracy.

• Journal of Environmental Science International
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• v.14 no.1
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• pp.41-51
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• 2005

Using three-dimensional non-hydrostatical numerical model with one way double nesting technique, atmo­spheric circulation in the mountainous coastal region in summer was investigated from August 13 through 15, 1995. During the day, synoptic westerly wind blows over Mt. Mishrung in the west of a coastal city, Sokcho toward the East Sea, while simultaneously, easterly upslope wind combined with both valley wind from plain (coast) toward mountain and sea-breeze from sea toward inland coast blows toward the top of the mountain. Two different directional wind systems confront each other in the mid of eastern slope of the mountain and the upslope wind goes up to the height over 2 km, becoming an easterly return flow in the upper level over the sea and making sea-breeze front with two kinds of sea-breeze circulations of a small one in the coast and a large one in the open sea. Convective boundary layer is developed with a thickness of about 1km over the ground in the upwind side of the mountain in the west and a thickness of thermal internal boundary layer from the coast along the eastern slope of the mountain is only confined to less than 200 m. On the other hand, after sunset, no prohibition of upslope wind generated during the day and downward wind combined with mountain wind from mountain towardplain and land-breeze from land toward under nocturnal radiative cooling of the ground surfaces should intensify westerly downslope wind, resulting in the formation of wind storm. As the wind storm moving down along the eastern slop causes the development of internal gravity waves with hydraulic jump motion in the coast, bounding up toward the upper level of the coastal sea, atmospheric circulation with both onshore and offshore winds like sea-breeze circulation forms in the coastal sea within 70 km until midnight and after that, westerly wind prevails in the coast and open seas.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.496-497
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• 2005