• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.3
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• pp.375-384
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• 2009

The GRACE satellite, Launched in March 2002, is applied to research on glacial melt of polar regions, glacial isostatic adjustment(GIA), sea level change, terrestrial water storage(TWS) variation of river basin and large-scale earthquake etc. In this research, the TWS variation of Yangtze river basin from August, 2002 to January, 2009 is analyzed using Level-2 GRACE monthly gravity field model. Particularly, gravity changes of the Three Gorges Dam during the impoundment process in 2003, 2006 and 2008 is observed by estimating equivalent water thickness(EWT). The research results show the distinct annual and seasonal changes of Yangtze river basin, and its amplitude of annual variation is 2.3cm. In addition, we compare the results with water resource statistics and hydrologic observation data to confirm the possibility of research of TWS variation of river basin using GRACE observation data, and also the satellite gravity data is of great help for the research on the movement and periodic changes of river basin.

• Structural Engineering and Mechanics
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• v.62 no.5
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• pp.587-593
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• 2017

The objective of this analytical study is to calculate the elasto-plastic stresses of Functionally Graded (FG) hyperbolic disc subjected to uniform temperature. The material properties (elastic modulus, thermal expansion coefficient and yield strength) and the geometry (thickness) of the disc are assumed to vary radially with a power law function, but Poisson's ratio does not vary. FG disc material is assumed to be non-work hardening. Radial and tangential stresses are obtained for various thickness profile, temperature and material properties. The results indicate that thickness profile and volume fractions of constituent materials play very important role on the thermal stresses of the FG hyperbolic discs. It is seen that thermal stresses in a disc with variable thickness are lower than those with constant thickness at the same temperature. As a result of this, variations in the thickness profile increase the operation temperature. Moreover, thickness variation in the discs provides a significant weight reduction. A disc with lower rigidity at the inner surface according to the outer surface should be selected to obtain almost homogenous stress distribution and to increase resistance to temperature. So, discs, which have more rigid region at the outer surface, are more useful in terms of resistance to temperature.

• Structural Engineering and Mechanics
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• v.70 no.5
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• pp.551-562
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• 2019

In the present study, a suitable mathematical model considering parabolic transverse shear strains for dynamic analysis of laminated composite skew plates under different types of impulse and spatial loads was presented for the first time. The proposed mathematical model satisfies zero transverse shear strain at the top and bottom of the plate. On the basis of the cubic variation of thickness coordinate in in-plane displacement fields of the present mathematical model, a 2D finite element (FE) model was developed including skew transformations in the mathematical model. No shear correction factor is required in the present formulation and damping effect was also incorporated. This is the first FE implementation considering a cubic variation of thickness coordinate in in-plane displacement fields including skew transformations to solve the forced vibration problem of composite skew plates. The effect of transverse shear and rotary inertia was incorporated in the present model. The Newmark-${\beta}$ scheme was adapted to perform time integration from step to step. The $C^0$ FE formulation was implemented to overcome the problem of $C^1$ continuity associated with the cubic variation of thickness coordinate in in-plane displacement fields. The numerical studies showed that the present 2D FE model predicts the result close to the analytical results. Many new results varying different parameter such as skew angles, boundary conditions, etc. were presented.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.1-7
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• 2014

For the resistance spot welds of CR1180 and GA1180 TRIP steels, the weld quality evaluation method using the digitalized X-ray transmission imaging apparatus was investigated in comparison with the crosssectional examination method. In the case of the resistance spot welding of CR1180, three circular regions, such as WZ(white zone), GZ(grey zone) and DZ(dark zone), appeared on X-ray image and they corresponded to the diameters of indentation mark, nugget and corona bond, respectively. The variation of X-ray transmission thickness due to the thickness variation of the weld seemed to be mainly responsible for the formation of those contrasts. The X-ray image contrast formed from the variation of transmission thickness at the outer border line of DZ could also enable the inspections of the notch shape, nonuniformity of the welding pressure and spatter from its sharpness, concentricity and the normal straight line, respectively. The X-ray image of the resistance spot weld of galvannealed GA1180 TRIP steel was very similar to that of CR1180 TRIP steel except the crown shaped outer border line of DZ which was considered to be due to the melting behavior of zinc having the boiling temperature even lower than the melting temperature of steel.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1539-1544
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• 2005

The gauge control of the fishing mill is very important because more and more accurately sized hot rolled coils are demanded by customers recently. Because the mill constant and the plasticity coefficient vary with the specifications of the mill, the classification of steel, the strip width, the strip thickness and the slab temperature, the variation of these parameters should be considered in the automatic gauge control system(AGC). Generally, the AGC gain is used to minimize the effect of the uncertain parameters. In a practical field, operators set the AGC gain as a constant value calculated by FSU (Finishing-mill Set-Up model) and it is not changed during the operating time. In this paper, the thickness data signals that occupy different frequency bands are respectively extracted by adaptive filters and then the main cause of the thickness variation is analyzed. Additionally, the AGC gain is adaptively tuned to reduce this variation using the online tuning model. Especially ANFIS(Adaptive-Neuro-based Fuzzy Interface System) which unifies both fuzzy logics and neural networks, is used for this gain adjustment system because fuzzy logics use the professionals' experiences about the uncertainty and the nonlinearity of the system. Simulation is performed by using POSCO's data and the results show that proposed on-line gain adjustment algorithm has a good performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.218-225
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• 2008

When the heat release and acoustic pressure fluctuations are generated in the combustor by irregular combustion, these fluctuations affect the mass flow rate of the propellants injected through the injectors. Also, the variations of the mass flow rate by these fluctuations again bring about irregular combustion and furthermore that is related with combustion instability. Therefore, it is very important to identify the mass variation for the pressure fluctuation on the injector and to investigate its transfer function. So, we first have studied quantifying the variation of mass flow rate generated in simplex swirl injector by injection pressure fluctuation. To acquire the transient mass flow rate in orifice with time, we have tried to measure of the flow axial velocity and liquid film thickness in orifice. The axial velocity is acquired through theoretical approach after measuring the pressure in orifice and the flow area in the orifice is measured by electric conductance method. As results, mass flow rate calculated by axial velocity and liquid film thickness measuring in orifice accorded with mass flow rate acquired by direct measuring method in the small error range within 1 percents in steady state and within 6 percents as average mass flow rate in pulsated state. Hence this method can be used to measure the mass flow rate not only in steady state but also in unsteady state because the mass flow rate in the orifice can acquire with time and this method shows very high accuracy based on the experimental results.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.93-96
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• 2017

The structural, electrical and optical properties of Ti thin films fabricated by dual magnetron sputtering were investigated under various film thicknesses. The fabricated Ti thin films exhibited uniform surfaces, crystallinity, various grain sizes, and with various film thicknesses. Also, the crystallinity and grain size of the Ti thin films increased with the increase of film thickness. The electrical properties of Ti thin films improved with the increase of film thickness. The results showed that the performance of TCO-less DSSC critically depended on the film thickness of the Ti working electrodes, due to the conductivity of Ti thin film. However, the maximum conversion efficiency of TCO-less DSSC was exhibited at the condition of 100 nm thickness due to the surface scattering of photons caused by the variation of grain size.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1068-1071
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• 2004

We report the techniques to obtain the high uniformity of the phosphor film thickness in the cold cathode fluorescent lamps, which are widely used as a back-light for the liquid crystal display. The thickness variation of the phosphor layer was sensitive to blowing conditions. The optimum conditions were obtained at flow rate of 15 sccm for 30 min at 40 $^{\circ}C$. The optimum and uniform thickness of a phosphor layer gives good luminous output.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.91-92
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• 2002

Most studies of elsatohydrodynamic lubrication are oriented only to the measurement of film thickness itself with optical interferometer. In order to exactly investigate the characteristics of a certain lubricant under the condition of additives. especially for traction performance. it is also important to get the information of traction force as well. In this work. we developed the device for measuring friction force of EHL contact condition, which can trace the film thickness over the contact area with optical interferometer. To verify the validity of the measuring system, the friction force and film thickness under EHL condition are measured with the variation of additive ratios of viscosity Index improvers.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.267-271
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• 2002

Most studies of elsatohydrodynamic lubrication are oriented only to the measurement of film thickness itself with optical interferometer. In order to exactly investigate the characteristics of a certain lubricant, it is also important to get the information of traction force as well. In this work, we developed the device for measuring friction force of ehl contact condition together with the film thickness. To verify the validity of the measuring system, the friction force and film thickness under ehl condition are measured with the variation of additive ratios of viscosity index Improvers.