• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.3
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• pp.67-73
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• 2005

An accuracy of theodolite system may be affected by a measurement environment and a measurement distance change from theodolite to scale bar and/or targets. This study was performed for measuring an accuracy when the distance from thodolite system to scale bar was changed $2\~6m$ on the distance 4m between two theodolites. The results showed that an accuracy was ${\pm}0.025mm$ or better when the distance from theodolite system to targets was 3, 4 and 5m. According to the results, it was found that the best distance from theodolite system to scale bar was $3\~4m$ when the collimation distance was $3\~4m$.

• International Journal of Highway Engineering
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• v.15 no.1
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• pp.23-36
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• 2013

PURPOSES: The problem under this circumstance is that the erosion not only drops strength of the steel dowel bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem, alternative dowers bars are developed. METHODS: In this study, the bearing stresses between the FRP tube dowel bar and concrete slab are calculated and compared with its allowable bearing stress to check its structural stability in the concrete pavement. These comparisons are conducted with several cross-sections of FRP tube dowel bars. Comprehensive laboratory tests including the shear load-deflection test on a full-scale specimen and the full-scale accelerated joint concrete pavement test are conducted and the results were compared with those from the steel dowel bar. RESULTS: In all cross-sections of FRP tube dowel bars, computed bearing stresses between the FRP tube dowel bar and concrete slab are less than their allowable stress levels. The pultrusion FRP-tube dowel bar show better performance on direct shear tests on full-scale specimen and static compression tests at full-scale concrete pavement joints than prepreg and filament-winding FRP-tube dowel bar. CONCLUSIONS: The FRP tube dowel bars as alternative dowel bar are invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Also, the pultrusion FRP-tube dowel bar performed very well on the laboratory evaluation.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.37-43
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• 2004

A measurement accuracy of theodolite system may be affected by a measurement environment, a measurement distance change and so on. This study was performed for measuring an accuracy when the height of scale bar is changed 0.05m, 0.5m, 1m and 1.5m under the distance 3m between two theodolites, the distance 4m from the theodolite system to scale bar and the distance 5m from the thodolite system to the horizontal target bar. And we could know that the best height is 0.05m and 1m.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.48-54
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• 2005

The theodolite system consists of two theodolites, a scale bar and a target bu. A measurement accuracy of theodolite system is affected by a measurement distance of each equipment. This study was performed fir measuring an accuracy when the distance from theodolite to scale bar was changed 2~ 6 m on two theodolites distance 3 a The results showed thai the measurement accuracy could be $\pm$0.021 mm when the distance from theodolite to target was 2,3 and 6 n Specially, it was found that the maximum measurement accuracy was 10.017mm on theodolite collimation distance 3m and the distance 4 m of the theodolite and scale bar.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.13-21
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• 2005

The affected factors for an accuracy of theodolite system are not only the measurement environment of temperature, illumination, etc. but also the measurement processes of the distance between two theodolites, the distance from theodolite system to scale bar and the distance from theodolite system to targets. We have known that the best collimation distance between two theodolites and the best distance from theodolite system to scale bar is $3{\sim}4m$. This study was performed for searching the best distance from theodolite system to targets on above measurement configuration. And, we could know that the best distance from theodolite system to targets is $2{\sim}6m$ and the system accuracy could be within ${\pm}0.025mm$.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.47.3-48
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• 2021

We studied the large scale dynamo process in a system forced by helical magnetic field. The dynamo process is basically nonlinear, but can be linearized with 𝛼&𝛽 coefficients and large scale magnetic field $\bar{B}$. This is very useful to the investigation of solar (stellar) dynamo. A coupled semi-analytic equations based on statistical mechanics are used to investigate the exact evolution of 𝛼&𝛽. This equation set needs only magnetic helicity ${\bar{H}}_M({\equiv}{\langle}{\bar{A}}{\cdot}{\bar{B}}{\rangle},\;{\bar{B}}={\nabla}{\times}{\bar{A}})$ and magnetic energy ${\bar{E}}_M({\equiv}{\langle}{\bar{B}}^2{\rangle}/2)$. They are fundamental physics quantities that can be obtained from the dynamo simulation or observation without any artificial modification or assumption. 𝛼 effect is thought to be related to magnetic field amplification. However, in reality the averaged 𝛼 effect decreases very quickly without a significant contribution to ${\bar{B}}$ field amplification. Conversely, 𝛽 effect contributing to the magnetic diffusion maintains a negative value, which plays a key role in the amplification with Laplacian ∇²(= - k²) for the large scale regime. In addition, negative magnetic diffusion accounts for the attenuation of plasma kinetic energy E_V(= 〈 U² 〉/2) (U: plasma velocity) when the system is saturated. The negative magnetic diffusion is from the interaction of advective term - U • ∇ B from magnetic induction equation and the helical velocity field. In more detail, when 'U' is divided into the poloidal component U_pol and toroidal one U_tor in the absence of reflection symmetry, they interact with - B • ∇ U and - U • ∇ B from ∇ × 〈 U × B 〉 leading to 𝛼 effect and (negative) 𝛽 effect, respectively. We discussed this process using the theoretical method and intuitive field structure model supported by the simulation result.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.199-205
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• 2001

This paper describes the design methodology, manufacturing process, rebar tensile and bending properties. Braidtrusion is a direct Composite fabrication technique utilizing an in-line braiding and pultrusion process. The produced Composite rebar exhibits ductile stress-strain behavior similar to that of conventional steel bar. Various rebar diameters ranging from modeling scale(3m) to full-scale prototype of 9.5mm have been produced Glass Fiber Reinforced Plastics(GFRP) rebar were successfully fabricated at $\phi$8.5mm and $\phi$9.5mm nominal diameters of soild and hollow type using a braidtrusion process. Tensile and bending specimens were tested and compared with behavior of stress-strain of GFRP rebar and steel bar.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.6
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• pp.712-723
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• 2015

This study was conducted to develop the SWCC estimation equation using scaling technique, and to investigate relative sensitivity of the SWCC according to the soil water tension, for the four kinds of soil texture such as Sand [S], Sandy Loam [SL], Loam [L] and Clay Loam [CL]. The SWCC estimation equation of scale factor [${\Theta}sc$] (Eq. 1) was developed based on the log function (Eq. 2) and exponential function (Eq. 3). ${\Theta}sc=[({\Theta}-{\Theta}r)/({\Theta}s-{\Theta}r)]$ (Eq. 1) ${\Theta}sc=-0.196ln(H)+0.4888$ (Eq. 2) ${\Theta}sc=0.3804(H)^{(-0.448)}$ (Eq. 3) where, ${\Theta}$: water content (g/g %), ${\Theta}s$: water content at 0.1bar, ${\Theta}r$: water content at 15bar, H: soil water tension (matric potential) (bar) Relative sensitivity of soil water content was decreased as increase soil water tension, those according to soil water tension were 0.952~0.620 compared to 0.1bar case. Relative sensitivity of scale factor was also decreased as increase soil water tension, those according to soil water tension were 0.890~0.577 compared to 0.2bar case.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.5-9
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• 2010

In the paper, the dynamic characteristics obtained from hot-firing tests of 1/2.5-scale thrust chamber for 75 tonf-class liquid rocket engine were described. To investigate the dynamic characteristics by engine start transient period and chamber pressure variation, hot-firing tests were performed in the chamber pressures of 30 bar and 60 bar. According to these variations, combustion stability in the combustion chamber was examined.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.4
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• pp.36-42
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• 2003

Theodolite measurement system is non-contacted 3-dimensional measurement system. The system accuracy is ${\pm}0.5mm$or better for distance 0~100m. And the system is used for the measurement of a product of middle and large scale. This study is performed for the measurement error factors of the system. We could know that the main measurement error factors are temperature, illumination and skill. Also, we performed the study for the effect according to the height difference of scale bar.