• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.47-55
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• 2009

In this study, a robot foot having toes for firm stepping on uneven surface is proposed. The toes are connected to the lower leg by parallel links so that the lower leg can rotate in the rolling and pitching directions during stance phase without ankle joint. The landing performance of the foot on uneven surface was evaluated by relative comparison with that of the most common foot making point contact with the walking surface, since the test conditions considering real uneven surface could be hardly defined for its objective evaluation. Anti-slip margin(ASM) was defined in this study to express the slip resistance of a robot foot when it lands on a projection with half circular-, triangular- or rectangular cross section, assuming that uneven surface consists of projections having these kind of cross sections in different sizes. Based on the ASM analysis, the slip conditions for the two feet were experimentally confirmed. The results showed that the slip resistance of the new foot is not only higher than that of the conventional point contact type foot but also less sensitive to the surface friction coefficient.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.565-569
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• 1999

In these days, the silicone insulators have been increasingly studied and applied for outdoor insulators because it has superior characteristics than porcelain and glass insulators, which have been used for outdoor insulators. First of all, The excellent performance of the silicone rubber in polluted and wet conditions is attributed to the ability of the material to maintain the hydrophobicity of the surface in the presence of severe contamination and wet conditions. This is because of the presence of low molecular weight mobile fluid in the silicone rubber which diffuses to the surface and to above the contamination layer. But, the leakage current and some surface discharge occurs on surface of the composite polymeric insulation materials when the insulator is used for a long time with severe contaminative condition and it can lead the contamination flashover. So the leakage current and the discharge current are important to estimate the condition of the silicone rubber surface. In this paper, the average leakage current, the relation of surface discharge current and phase angle were study to investigate electrical conduction of silicone rubber surface with the salt fog condition.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.153-164
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• 2020

Tunnel excavation in shallow soft ground conditions of urban areas experiences inevitable surface settlements that threaten the stability of nearby infrastructures. Surface settlements during shield TBM tunneling are related to a number of factors including geotechnical conditions, tunnel geometry and excavation methods. In this paper, a database collected from a construction section of Hong Kong subway was used to analyze the correlation of settlement-inducing factors and surface settlements monitored at different locations of a transverse trough. The Pearson correlation analysis result revealed a correlation between the factors in consideration. Factors such as the face pressure, advance speed, thrust force, cutter torque, twin tunnel distance and ground water level presented a modest correlation with the surface settlement, while no significant trends between the other factors and the surface settlements were observed. It can be concluded that an integrated effect of the settlement-inducing factors should be related to the magnitude of surface settlements.

• Journal of the Korean institute of surface engineering
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• v.48 no.3
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• pp.93-99
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• 2015

This test focuses on the correlations between joining axial force at non-room temperature and at room temperature according to the surface treatment (Geomet, Dacro, Green Kote, Armore Galv.). The quality characteristics of the fastening axial force required by the KSB 2819 and EN14399-10 standards were discussed. Surface treatment was implemented to S10T and 10.9HRC sets of bolts under the same environmental factors. Development for the stabilization of the fastening axial force required by each standard should continually be enforced, and the fastening and storage in the field should be maintained at room temperature. Managing stabilization of torque enumerated data is required after application of surface treatment. It is concluded that, by conducting the test of applying surface treatment to effectively manage, each lot-specific rate of axial force at room temperature conditions should be maintained below the maximum 4.47%. The decline rate of axial force should be maintained under 2.15% maximum, and the standard deviation of the room temperature condition should be maintained below 0.5.

• Korean Journal of Remote Sensing
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• v.22 no.1
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• pp.11-24
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• 2006

Coastal sea surface temperature (CSST) and meteorological data from January through December 1995 are used to estimate the net surface heat flux and heat content for Sendai Bay. The average annual surface heat flux in the area north of the bay is estimated to be $+35Wm^{-2}$, whereas the southwestern area is estimated to be $+56Wm^{-2}$. Therefore, the net surface heat flux shows a net gain of heat over the whole bay. The largest heat gain occurs near Matsukawaura, where the strong Kuroshio/Oyashio interaction produces anomalously cold SST and wind is more moderate than in other regions of Sendai Bay over most of the year. The lowest heat gain occurs around Tashiro Island, where the temperature difference between air and sea surface is lower and wind is stronger. The heat budget shows that both surface forcing and horizontal advection are potentially important contributors to the seasonal evolution of CSST in the bay. From the A VHRR and SeaWiFS data, it is found that offshore conditions between the bay and Eno Island are different due to the presence of the Ojika Peninsula. It is also shown that the temporal behaviors of SSTs in the bay are closely connected with the air-sea heat flux and offshore conditions.

• Advances in nano research
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• v.11 no.6
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• pp.607-620
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• 2021

In this paper, the vibrations of boron nitride nanotubes (BNNTs) are investigated by considering the electric field. To consider the size effect at nanoscale dimensions, the surface elasticity theory is exploited. The equations of motion of the BNNTs are obtained by applying Hamilton's principle, and the clamped-guided boundary conditions are also considered. The governing equations and boundary conditions are discretized using the differential quadrature method (DQM), and the natural frequency is obtained by using the eigenvalue problem solution. The results are compared with the molecular dynamic simulation in order to validate the accurate values of the surface effects. In the molecular dynamics (MD) simulation, the potential between boron and nitride atoms is considered as the Tersoff type. The Timoshenko beam model is adopted to model BNNT. The vibrations of two types of zigzag and armchair BNNTs are considered. In the result section, the effects of chirality, surface elasticity modulus, surface residual tension, surface density, electric field, length, and thickness of BNNT on natural frequency are investigated. According to the results, it should be noted that, as an efficient non-classical continuum mechanic approach, the surface elasticity theory can be used in scrutinizing the dynamic behavior of BNNTs.

• Current Optics and Photonics
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• v.3 no.5
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• pp.423-428
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• 2019

Visibility of road-surface markings is one of the critical issues that should be secured for self-driving cars as well as human drivers. Glass beads are taking on the role of retroreflectors, and therefore are considered a necessity in modern pavements. In this context, retroreflectance is sensitively dependent not only on the refractive index of glass beads but also on that of the surrounding medium. This implies that the optimum refractive index of glass beads immersed in water, i.e. under wet conditions, is different from that of glass beads surrounded by air, i.e. under dry conditions. A refractive index of approximately 1.9, which is known to maximize retroreflectance under dry conditions, actually exhibits much poorer retroreflectance under wet conditions. This suggests that glass beads with optimal refractive index for wet conditions need to be installed together with those for dry conditions. We propose a facile but practical model capable of calculating retroreflectance of glass beads surrounded by an arbitrary medium, here water in particular, and experimentally verify its capability of assessing the refractive index of commercial glass beads. Changes in retroreflectance according to the mixing ratio of glass beads with different refractive indices are also discussed, in an effort to propose the proper use of glass beads produced for dry and wet conditions.

• Journal of the Korean institute of surface engineering
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• v.53 no.5
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• pp.241-248
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• 2020

The change of the deposition behavior of diamond through a pretreatment process of the base metal prior to diamond deposition using HFCVD was investigated. To improve the specific surface area of the base material, sanding was performed using sandblasting first, and chemical etching treatment was performed to further improve the uniform specific surface area. Chemical etching was performed by immersing the base material in HCl solutions with various etching time. Thereafter, seeding was performed by immersing the sanded and etched base material in a diamond seeding solution. Diamond deposition according to all pretreatment conditions was performed under the same conditions. Methane was used as the carbon source and hydrogen was used as the reaction gas. The most optimal conditions were found by analyzing the improvement of the specific surface area and uniformity, and the optimal diamond seeding solution concentration and immersion time were also obtained for the diamond particle seeding method. As a result, the sandblasted base material was immersed in 20% HCl for 60 minutes at 100 ℃ and chemically etched, and then immersed in a diamond seeding solution of 5 g/L and seeded using ultrasonic waves for 30 minutes. It was possible to obtain optimized economical diamond film growth rates.

• Tribology and Lubricants
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• v.34 no.6
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• pp.254-261
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• 2018

In order to reduce resistance torque and energy loss, minimizing friction between race surface and rolling elements of a bearing is necessary. Recently, to reduce friction in bearing element, solid lubricant coating for the bearing raceway surface has been receiving much attention. Considering the operating conditions of real bearings, verifying the effect of solid lubricant coatings under extreme conditions of high load that is more than 1 GPa is necessary. In this study, we evaluated the friction and wear characteristics of SUJ2 bearing steels deposited by carbon-based coatings (Si-DLC, ta-C), $MoS_2$ and graphite. In case of $MoS_2$ and graphite coatings, different surface treatments were applied to the coatings to verify the effect of surface treatment. A pin-on-disc type tribotester was used to evaluate the tribological characteristics of the coatings. It was possible to quantitatively estimate the friction and wear characteristics of solid lubricant under dry and lubrication conditions. The carbon-based coatings improved the friction and wear properties of SUJ2 bearing steels under the high load condition, but $MoS_2$ and graphite coatings were not suitable for high load conditions due to its low hardness. Different friction and wear behaviors were found for different substrate surface treatment method. Also, it was confirmed that solid lubricant coatings had a more positive effect than just applying the lubricant for improving the tribological characteristics.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1233-1243
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• 2023

Shell-and-tube heat exchanger (STHX) is widely used by virtue of its simple structure and high reliability, especially in a space-constrained surface ship. For the STHX of the surface ship, roll, pitch and other motion of the ship will affect the heat transfer performance, resistance characteristics and structural strength of the heat exchanger. Therefore, it is urgent to carry out numerical simulation research on three-dimensional thermal hydraulic characteristics of surface ship STHX under the marine conditions. In this paper, the numerical simulation of marine shell and tube heat exchanger of surface ship was carried out using the porous media model. Firstly, the mathematical physical model and numerical method are validated based on the experimental data of a marine engine cooling water shell and tube heat exchanger. The simulation results are in good agreement with the experimental results. The prediction errors of pressure drop and heat transfer are less than 10% and 1% respectively. The effect of marine conditions on the heat transfer characteristics of the heat exchanger is investigated by introducing the additional force model of marine condition to evaluate the effect of different motion parameters on the heat transfer performance of the heat exchanger. This study could provide a reference for the optimization of marine heat exchanger design.