• Tribology and Lubricants
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• v.29 no.6
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• pp.366-371
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• 2013

Various heat treatment and surface coating methods have been applied to machine parts. Nowadays, diamond-like carbon (DLC) coatings are widely used because of their excellent tribological characteristics. Despite the numerous studies on DLC-coated engineering surfaces, the exact wear mechanisms related to the coating thickness and elastic modulus have not been fully examined. In this study, a sliding contact problem between a small spherical hard particle and a DLC-coated steel surface is analyzed using a nonlinear finite element code, MARC. The maximum principal stress distributions and deformed surfaces are compared for different coating thicknesses and Young's modulus values. Plastically deformed surface shapes such as a groove and torus indicate that the most dominant wear mechanism for a DLC-coated surface is abrasive wear. Fatigue wear can also play a role in a case where the coating thickness is relatively large and the elastic modulus is high.

• Journal of Korean Association for Spatial Structures
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• v.16 no.1
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• pp.53-64
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• 2016

Solar power is being spotlighted recently as a new energy source due to environmental problems and applications of solar power to curved structures are increasing. Solar panels installed on curved surfaces have different efficiencies depending on its position and the efficient positioning of solar panels plays a critical role in the design of solar power generation systems. In this study, the changing characteristics of solar irradiance were analyzed for hemispherical dome with a large curvature and the positioning of solar panels that can efficiently utilize solar energy was investigated. With an icosahedron-based hemispherical dome consisting of triangular elements as target model, a program for calculating solar irradiance using a normal vector of the solar module on each face was developed. Furthermore, the change of solar irradiance according to the sun's path was analyzed by time and season, and its effects on shades were also examined. From the analysis results, the effective positioning could be determined on the basis of the efficiency of the solar panels installed on the dome surfaces on solar irradiance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3686-3694
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• 1996

A numerical investigation of natural convection flow along irregular vertical surfaces is reported. A transformation method is applied to the problem of natural convection under the assumption of a large Grashof number. A vertical wavy surface is used as an example to demonstrate the advantages of the transformation method, and to show the heat transfer mechanism near such surfaces. Surface non-uniformities on the boundary layer flow induced by a constant was temperature, semi-infinite surface are investigated. Also the effects of Prandtl number, flow index, and surface amplitude in Non-Newtonian fluids are discussed. When possible, the comparison of the numerical results shows a good agreement. The amplitude is proportional to the amplitude of a wavy surface. The results demonstrate that the local heat flux along a wavy surface is smaller than that of a flat surface. The frequency of the wavy surface is half that of the local heat transfer rate. The amplitude of the local Nusselt number gradually decreases downstream where the natural convection boundary layer grows thick.

• Wind and Structures
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• v.31 no.4
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• pp.335-350
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• 2020

In coastal residential communities, especially along the coastline, flooding is a frequent natural hazard that impacts the area. To reduce the adverse effects of flooding, it is recommended to elevate coastal buildings to a certain safe level. However, post storm damage assessment has revealed severe damages sustained by elevated buildings' components such as roofs, walls, and floors. By elevating a structure and creating air gap underneath the floor, the wind velocity increases and the aerodynamics change. This results in varying wind loading and pressure distribution that are different from their slab on grade counterparts. To fill the current knowledge gap, a large-scale aerodynamic wind testing was conducted at the Wall of Wind experimental facility to evaluate the wind pressure distribution over the surfaces of a low-rise gable roof single-story elevated house. The study considered three different stilt heights. This paper presents the observed changes in local and area averaged peak pressure coefficients for the building surfaces of the studied cases. The aerodynamics of the elevated structures are explained. Comparisons are done with ASCE 7-16 and AS/NZS 1170.2 wind loading standards. For the floor surface, the study suggests a wind pressure zoning and pressure coefficients for each stilt height.

• Journal of Advanced Navigation Technology
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• v.12 no.6
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• pp.653-658
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• 2008

The automotive environment is particularly demanding on connector performance, and is characterized by large temperature changes, high humidity and corrosive atmospheres. Fretting is a contact damage process that occurs between two contact surfaces. Fretting corrosion refers to corrosion damage at the asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration. This paper critically reviews the works published previously on fretting corrosion of electrical connectors. Various experimental approaches such as testing machines, material selection, testing environments, acceleration testing techniques and preventing methods are addressed. Future research prospects arc suggested.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1418-1425
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• 2003

In CAD systems, a surface to be machined is expressed by a series of curves, such as B-spline, Bezier and NURBS curves, which compose the surface and then in CAM systems the curves are divided into a large number of line or arc segments. These divided movement commands, however, cause many problems including their excessive size of NC data that makes almost impossible local adjustment or modification of the surface. To cope with those problems, the necessity of real-time curve or surface interpolators was embossed. This paper presents an efficient real-time tool-path generation method fur interpolation of NURBS surfaces in CNC machining. The proposed tool-path generation method is based on an improved iso-scallop strategy and can provide better precision than the existing methods. The proposed method is designed such that tool-path planning is easily managed in real-time. It proposed a new algorithm for regulation of a scallop height, which can efficiently generate tool-paths and can save machining time compared with the existing method. Through computer simulations, the performance of the proposed method is analyzed and compared with the existing method in terms of federate, total machining time and a degree of constraint on the scallop height.

• Journal of the Korean Solar Energy Society
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• v.34 no.5
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• pp.11-22
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• 2014

It is usual to determine silver-town location by people's experienced knowledge or intuition considering many different type of thematic variables simultaneously. This paper is primarily intended to locate sunny silver-town according to catchment-wide solar radiation as single key variable. GIS based solar simulation realistically identified catchment-wide solar radiation in the study area using large scale spatial precision. More than 90% over the worst catchment were identified shadow surfaces while the optimal catchment was heavily covered by sunny radiation surfaces. It is confirmed that standard GIS technology can offers the viable method of measuring and comparing the catchment-wide solar radiation. Guidelines for a replicable methodology are presented to provide a strong theoretical basis for the standardization of factors involved in locating the sunny silver-town; delineation of catchment boundary, solar simulation, catchment-wide comparison etc. They could be used as an evidence to determine sunny catchment in comparison with other catchment, based solar simulation. It is anticipated that this research output could be used as a valuable reference to confirm the potential of introducing the new concept of "catchment specific solar radiation" to support more scientific and objective decision-making in the process of locating silver town.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.505-510
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• 2002

We have focused on the development of a fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system in order to measure temperature distributed on large structures. Also, we present a feasibility study of the fiber optic sensor to monitor the distributed temperature on a building construction. A fiber optic BOTDA sensor system, which has a capability of measuring the temperature distribution, attempted over several kilometers of long fiber paths. This simple fiber optic sensor system employs a laser diode and two electro-optic modulators. The optical fiber of the length of 1400 m was installed on the surfaces of the building. The change of the distributed temperature on the building construction was well measured by this fiber optic sensor. The temperature changed normally up to 4℃ through one day.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.509-515
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• 2011

The radar cross section (RCS) of warships is a crucial design factor to improve the survivability in terms of not only low observablity of the platform but also efficiency of on-board sensors and jamming devices against enemy threat. In design stage, numerical models are generated in order to quantitatively assess RCS, of which hull surfaces are modeled with the finite number of the flat plate. However, in practice, hull surfaces are permanently deformed by various kinds of loads such as winds and ocean waves faced during operations. In this paper, the effect of these shell plate deformation to RCS is numerically investigated. For this purpose, RCS calculations are carried out for various kinds of numerical models, such as single plates, dihedrals, large-sized undulate plates, and virtual warships, with some extent of permanent deformation. The results are compared with those of corresponding models without permanent deformation. It is concluded that the permanent deformation of hull surface highly influences RCS characteristics of warships, therefore they should be considered in the RCS analysis.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1218-1223
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• 2004

Porous silicon materials have been shown to have bright prospects for applications in light emitting, solar cell, as well as light- and chemical-sensing devices. In this report, structures of porous silicon prepared by anodic etching in HF-based solution with various etching times were studied in detail by Atomic Force Microscopy and Small Angle X -ray Scattering technique using the high energy beam line at Pohang Light Source in Korea. The results showed the coexistence of the various pores with nanometer and submicrometer scales. For nanameter size pores, the mixed ones with two different shapes were identified: the larger ones in cylindrical shape and the smaller ones in spherical shape. Volume fractions of the cylindrical and the spherical pores were about equal and remained unchanged at all etching times investigated. On the whole uniform values of the specific surface area and of the size parameters of the pores were observed except for the larger specific surface area for the sample with the short etching time. The results implies that etching process causes the inner surfaces to become smoother while new pores are being generated. In all SAXS data at large Q vectors, Porod slope of -4 was observed, which supports the fact that the pores have smooth surfaces.