• Applied Biological Chemistry
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• v.43 no.2
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• pp.116-123
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• 2000

A numerical model of three-dimensional soil water distribution for drip irrigation management under cropped conditions was developed using Richards equation in Cartesian coordinates. The model accounts for both seasonal and diurnal changes in evaporation and transpiration, and the growth of plant root and the shape of root zone. Solutions were numerically approximated using the Crank-Nicolson implicit finite difference technique on the block-centered grid system and the Gauss-Seidel elimination in tandem. The model was tested under several conditions to allow the flow rates and configurations of drip emitters vary. In general, simulation results agreed well with experimental results and were as follows. The velocity of soil-water flow decreased drastically with distance from the drip source, and the rate of expansion of the wetted zone decreased rapidly during irrigation. The wetting front of wetted zone from a surface drip emitter traveled farther in vertical direction than in horizontal direction. Under this experimental weather condition, water use efficiency of a drip-irrigated apple field was greatest for 4-drip-emitter system buried at 25 cm, resulting from 10% increase in transpiration but 20% reduction in soil evaporation compared to those for surface 1-drip emitter system. Soil moisture retention curve obtained using disk tension infiltrometer showed significant difference from the curve obtained with pressure plate extractor.

• International Journal of Highway Engineering
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• v.8 no.3 s.29
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• pp.143-153
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• 2006

The differences in the stress distribution and the critical stresses in concrete pavement systems were analyzed when the dual-wheel single-, tandem-, and tridem-axle loads were applied at the interior and the edge of the pavement. The effects of the concrete elastic modulus, slab thickness, foundation stiffness, and tire contact pressure were investigated. The stresses under the interior loads were calculated using the transformed field domain analysis and stresses under the edge loads were obtained using the finite element method. The critical stresses under the interior and the edge loads were compared with respect to various parameters and the equations to predict the ratio between the stresses under the edge and the interior loads were developed and verified. From this study, it was found that the trends of the changes in the critical concrete stresses under the interior and the edge loads were very similar and the critical stress locations under those loads were identical. The critical stress ratio, which was obtained by dividing the critical stress under the edge loads into that under the interior loads, decreased with increasing the number of axles. That ratio became larger as the concrete elastic modulus increased, the slab thickness increased, the foundation stiffness decreased, and the tire contact pressure increased.

• Journal of Korean Society of Steel Construction
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• v.21 no.6
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• pp.585-596
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• 2009

In the construction of end-plate connections, the end-plate is welded to the end of the beam in a factory and fastened by bolts in the field. This connection is widely used in advanced countries such as European countries and the U.S. Its design and connection details are prescribed in Eurocode 3, AISC LRFD, and FEMA 350. In Korea, the standards for seismic design in KBC 2005 have been reinforced based on IBC 2000 in the U.S., and it is expected that the connection details in the U.S. will be adopted for the establishment of beam-to-column design standards. In the U.S. thick end-plates are used for the connections to prevent beam rupture. The use of the connections in Korea, however, may lead toover-design. In this experimental study, the design standards for the end-plate connections provided by FEMA-350 were analyzed and structural tests for six specimens were conducted with the variables being the shim plate and the connection shape, to provide the best specifications for connections with plastic deformation in the end-plate for use in Korea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.1
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• pp.58-65
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• 2012

In this study, to reduce the motion of the vessels resulting from resonance and secondary undulation by long-period waves, numerical review on the control performance of resonator was carried out by attaching the resonator to the established harbor of real waters. In the numerical analysis, CGWAVE MODULE of commercial software SMS(Surface water Modeling System), a finite element model based on 2-dimensional elliptical mild slope equation was applied, and through comparative analysis of the existing experiments and analysis results on the rectangular model ports, the validity of the friction coefficients in which validity and effectiveness of SMS on the secondary undulation analysis is applied was verified. Based on this, the control performance of resonator was confirmed through comparative review of the secondary undulation according to whether or not to attach the resonator to rectangular harbor. In addition, to reduce long-period motion of the moored vessels and the secondary undulation which may occur in Pohang new port, the method to move the resonant period which causes abnormal motion of the vessels to long-term one was discussed through application of the resonators with various sizes, thereby identifying the availability.

• Journal of Biomedical Engineering Research
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• v.23 no.4
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• pp.269-279
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• 2002

When we inject a current into an electrically conducting subject such as a human body, voltage and current density distributions are formed inside the subject. The current density within the subject and injection current in the lead wires generate a magnetic field. This magnetic flux density within the subject distorts phase of spin-echo magnetic resonance images. In Magnetic Resonance Current Density Imaging (MRCDI) technique, we obtain internal magnetic flux density images and produce current density images from $\bigtriangledown{\times}B/\mu_\theta$. This internal information is used in Magnetic Resonance Electrical Impedance Tomography (MREIT) where we try to reconstruct a cross-sectional resistivity image of a subject. This paper describes numerical techniques of computing voltage. current density, and magnetic flux density within a subject due to an injection current. We use the Finite Element Method (FEM) and Biot-Savart law to calculate these variables from three-dimensional models with different internal resistivity distributions. The numerical analysis techniques described in this paper are used in the design of MRCDI experiments and also image reconstruction a1gorithms for MREIT.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.22-32
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• 2014

Durability is one of the most important and attractive subjects in concrete research field because not only durability of concrete is reduced by various degradation factors but also its reduction adversely influences the structural performance and service life of concrete structure. For this reason, a considerable amount of papers associated with concrete durability have been published and those researches were mainly focused on the changes of intrinsic properties of concrete due to chemicophysical degradations. However, the relationship between durability of concrete and structural behavior of concrete member has not been well established yet. In this study, calcium leaching degradation, a cause of concrete strength reduction, was dealt with. The experiments of compressive and flexural behavior of degraded concrete member were performed to evaluate the characteristics of structural behavior according to degradation level. Finally, the results from the experiments were compared with those obtained from nonlinear FEM analysis. The results from this study clearly showed that leaching degradation leads to decrease in compressive strength and compressive behavior evolves from brittle to ductile failure pattern during the degradation process. Load capacity and flexible rigidity of the degraded RC member decreased when the degradation level increased, in compressive zone. Additionally, it was found that the values from nonlinear FEM analysis, CDP model in ABAQUS, coincided well with the experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.1-9
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• 2018

The development of new technology and process in industrial Plant which builds integrated structures, facilities and systems. Has become a key element for strengthening its competitiveness. Although domestic industrial Plant has demonstrated excellence in technology with a persistent increase in order quantity and orders received, the technology gap between countries has narrowed due to global construction trend. Therefore, it is necessary to develop new technology that could help overcome constraints and limitations of the current one to follow the trend in the age of unlimited competition. This study has focused on assembly technology of Pipe-rack joint connection in an effort to strengthen technological competitiveness in industrial Plant. Through an analysis of earlier studies on Pipe-rack and a coMParative analysis of strengths and weaknesses of current assembly technology of it, a new design plan has been made to improve it efficiently. In doing this, standards for design factors of both structural and performance features have been drawn, and value of stress, strain, moment and rotation has been calculated using finite element analysis. As a result, installation technology of modular type Pipe-rack, which has not been developed in Korea and is differentiated from the current one, has been developed. It is considered that the technology reduces work time and saves cost due to simplified joint connection of steel structure, unlike the current one. Moreover, since it is installed without a welding process in the field, industrial accidents would be reduced, which is likely to have economic competitiveness and satisfy.

• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.53-64
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• 2009

MIRIS is the main payload of the STSAT-3 (Science and Technology Satellite 3) and the first infrared space telescope for astronomical observation in Korea. MIRIS space observation camera (SOC) covers the observation wavelength from $0.9{\mu}m$ to $2.0{\mu}m$ with a wide field of view $3.67^{\circ}\times3.67^{\circ}$. The PICNIC HgCdTe detector in a cold box is cooled down below 100K by a micro Stirling cooler of which cooling capacity is 220mW at 77K. MIRIS SOC adopts passive cooling technique to chill the telescope below 200 K by pointing to the deep space (3K). The cooling mechanism employs a radiator, a Winston cone baffle, a thermal shield, MLI (Multi Layer Insulation) of 30 layers, and GFRP (Glass Fiber Reinforced Plastic) pipe support in the system. Optomechanical analysis was made in order to estimate and compensate possible stresses from the thermal contraction of mounting parts at cryogenic temperatures. Finite Element Analysis (FEA) of mechanical structure was also conducted to ensure safety and stability in launching environments and in orbit. MIRIS SOC will mainly perform Galactic plane survey with narrow band filters (Pa $\alpha$ and Pa $\alpha$ continuum) and CIB (Cosmic Infrared Background) observation with wide band filters (I and H) driven by a cryogenic stepping motor.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.139-147
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• 2006

We had conducted a numerical modeling to investigate seismic properties of gas hydrate with field parameters acquired over the East sea in 1998. We used a 2-D staggered grid finite difference method to generate synthetic elastic seismograms for multi-channel seismic survey, OBC (Ocean Bottom Cable) survey and VCS (Vertical Cable Seismic) survey. The results of this study showed that the method using staggered grid yielded stable results and could be used to seismic imaging. We could find out the high amplitude anomaly and the phase reversal phenomenon of reflection wave at interface between the gas hydrate layer and free gas layer such a BSR (Bottom Simulating Reflector) which is the evidence for existence of gas hydrate in seismic reflection data. And we computed the reflection coefficients at the incident angles corresponding to offset distance with the synthetic seismograms. The reflection coefficients acquired from the numerical modeling were nearly consistent with the reflection coefficient computed by Shuey's equation.

• Advanced Composite Materials
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• v.17 no.1
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• pp.25-40
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• 2008

The research and development in soundproof materials for preventing noise have attracted great attention due to their social impact. Noise insulation materials are especially important in the field of soundproofing. Since the insulation ability of most materials follows a mass rule, the heavy weight materials like concrete, lead and steel board are mainly used in the current noise insulation materials. To overcome some weak points in these materials, fiber reinforced composite materials with lightweight and other high performance characteristics are now being used. In this paper, innovative insulation sheet materials with carbon and/or glass fabrics and nano-silica hybrid PU resin are developed. The parameters related to sound performance, such as materials and fabric texture in base fabric, hybrid method of resin, size of silica particle and so on, are investigated. At the same time, the wave analysis code (PZFlex) is used to simulate some of experimental results. As a result, it is found that both bundle density and fabric texture in the base fabrics play an important role on the soundproof performance. Compared with the effect of base fabrics, the transmission loss in sheet materials increased more than 10 dB even though the thickness of the sample was only about 0.7 mm. The results show different values of transmission loss factor when the diameters of silica particles in coating materials changed. It is understood that the effect of the soundproof performance is different due to the change of hybrid method and the size of silica particles. Fillers occupying appropriate positions and with optimum size may achieve a better effect in soundproof performance. The effect of the particle content on the soundproof performance is confirmed, but there is a limit for the addition of the fillers. The optimization of silica content for the improvement of the sound insulation effect is important. It is observed that nano-particles will have better effect on the high soundproof performance. The sound insulation effect has been understood through a comparison between the experimental and analytical results. It is confirmed that the time-domain finite wave analysis (PZFlex) is effective for the prediction and design of soundproof performance materials. Both experimental and analytical results indicate that the developed materials have advantages in lightweight, flexibility, other mechanical properties and excellent soundproof performance.