• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.464-469
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• 2003

The traditional and still most widely used, test methods for concrete structures are destructive method, such as coring, drilling or otherwise removing part of the structure to permit visual inspection of the interior. While these methods are highly reliable, they are also time consuming and expensive, and the defects they leave behind often become focal point for deterioration. In this study, tomography by theoretical inversion method in case of elastic wave using impact-echo method among concrete non-destruction test method was made. Taken model experiments are theoretical inversion method and time domain and frequency domain test on pier test model at laboratory level. Also experiment concerning frequency domain on 3 kinds of tunnel model with I-dimension form was carried out.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.255-260
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• 2003

The corrosion of steel rebars has been the major cause of the reinforced concrete deterioration. It is FRP rebar that is developed to solve problem of such steel rebar. FRP rebar in concrete structures should be used as a substitute of steel rebars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP rebar have only linearly elastic behavior; whereas, steel rebar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP rebars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse in required. The main objective of this study was to develop new type of hybrid FRP rebar. The manufacture of the hybrid FRP rebar was achieved pultrusion, braiding and filament winding techniques. Tensile and interlaminar shear test results of hybrid FRP rebar can provide its excellent tensile strength-strain behavior and interlaminar stress-strain behavior.

• Proceedings of the Korea Information Processing Society Conference
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• 한국정보처리학회 2016년도 추계학술발표대회
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• pp.603-606
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• 2016

철로를 구성하는 요소 중 하나인 선로전환기는 열차의 궤도를 변경하는 부품 중 하나로써, 열차가 주행 중에 인접한 다른 선로로 주행방향을 전환할 때 사용된다. 철로운영 지침서에 따르면 내구수명 10년 혹은 전환횟수 20만회를 선로전환기의 교체시점으로 권고하고 있으나, 실제 현장에서는 예산문제 등으로 인하여 잘 지켜지지 않는 것이 현실이다. 또한, 선로전환기에 관한 연구 문헌들에서도 선로전환기의 교체시기에 관한 학술적 실용적 차원의 연구 결과를 찾아볼 수 없다. 본 논문에서는 선로전환기의 전류 적분 값을 이용하여 선로전환기의 교체 시점을 결정하는 시스템을 제안한다. 제안된 시스템은 실제 현장에서 선로전환기의 교체시기를 판별하는 유용한 지표로 사용될 것으로 기대된다.

• Journal of the Korea Safety Management & Science
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• 제8권2호
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• pp.81-90
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• 2006

As aging society makes rapid progress, various social problems arise. The drop of productive labor and the increase of welfare cost can be taken as examples. From this point of view, a use of aged labor is a matter of great Important to national productivity improvement. But, the participation rate of the aged in economical activity amounts to 49.8 percent and their unemployment rate does 2.1 percent. The purpose of this paper is to analyze the deterioration of skill and the lowering of adaption to new working environments due to aging. Since the aging effect is closely related to worker's productivity, it should be properly measured and analyzed. The coordination tester is used to find out activity limitations. Experimental results show that the expert skill of the workers can be improved through the effective of their experience. Therefore we can say that some operation is not influenced by aging.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.95-102
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• 2002

Studies of the numerical characteristics of implicit upwind schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations ate performed. All the algorithms are expressed in approximate factorization form and Von Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min- CFL/max- VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.

• Proceedings of the Korean Society For Composite Materials Conference
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.13-17
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• 2004

In recent years, the deterioration of reinforced concrete structures has become a serious problem in civil engineering fields. This situation is mainly due to corrosion of steel reinforcing bars embedded in concrete. Recently, there has been a greatly increased demand for the use of FRP (fiber reinforced plastic) in civil engineering field due to their superior mechanical and physical properties. This paper presents an experimental study on the behavior of concrete bridge deck reinforced with FRP Box, FRP Plate, and FRP Re-bar. In tlIe study, mechanical properties of FRP Box, FRP Plate, GFRP Re-bar, and CFRP Grid have been investigated. Full scale one-way deck slab was tested under four point lateral load (equivalent to actual wheel load of DB-24 including impact). Load-deflection and load-strain data were collected through LVDT's and strain gages attached to the specimen.

• Proceedings of the KSME Conference
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.513-518
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• 2001

This research has been performed to estimate the hunting motion hysteresis of railway passenger cars. An old and a new car with almost same structure are chosen as analysis models. To solve effectively a set of simultaneous equations of motion strongly coupled with creep relations, shooting algorithm in which the nonlinear relations are regarded as a two-point boundary value problem is adopted. The bifurcation theory is applied to the dynamic analysis to distinguish differences between linear and nonlinear critical speeds by variation of parameters. It is found that there are some factors and their operation area to make nonlinear critical speed respond to them more sensitivity than linear critical speed. Full-scale roller rig tests are carried out for the validation of the numerical results. Finally, it is concluded that the wear of wheel profile and the stiffness discontinuities of wheelset suspension caused by deterioration have to be considered in the analysis to predict hysteresis of critical speed precisely.

• Proceedings of the KSME Conference
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2471-2476
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• 2008

Turbulent flow and heat transfer to water at supercritical pressure flowing in vertical pipes is investigated using direct numerical simulation (DNS). A conservative space-time discretization scheme for variable-density flows at low Mach numbers is adopted in the present study to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point. The fluid properties at these conditions are obtained using PROPATH and used in the form of tables in the simulations. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proved to play an important role in turbulent flow and heat transfer at supercritical state. Depending on the degree of buoyancy influence, turbulent heat transfer may be enhanced or significantly deteriorated, resulting in local hot spots along the heated surface.

• Proceedings of the KSR Conference
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.836-841
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• 2005

As gravel roadbed is gradually turn down by repetitive loading of train, lasting work for maintenance and management of track is necessary to reduce the settlement of roadbed and the deterioration of track. Despite of above weak point, gravel roadbed has become a basic structure of roadbed at the present time. But request for new structure of roadbed is recently presented to settle an increased transportation capacity of track, and to solve a shortage of the labor to handle maintenance work of track. Therefore, we begin to research about maintenance-free roadbed like paved track from two years ago. In this study, a series of tests were performed to clarify the characteristics of strength and permeability of concrete specimen, which is the upper part of paved track injected by cement mortar, by type of geotextile and finally to give a basic data for application of geotextile to the lower part of paved track.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제15권7호
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• pp.604-610
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• 2003

Cycle test for developed phase change material (PCM) is necessary in order to analyze the variation of latent heat, which decreases with time by deterioration. 7-history method and measurement using heat flux meter are appropriate for the cycle test in a tube filled with PCM because they do not need an extraction of sample in measuring the heat of fusion. In the present study, these methods were applied to a PCM having a melting point below a room temperature, different from the past studies for PCMs melting above a room temperature. As a result of experiment using pure water as specimen, we can obtain reason-able values for heat of fusion by both methods.