• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2012.04a
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• pp.290-293
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• 2012

화재는 콘크리트 구조물의 역학적 특성에 치명적 손상을 일으켜 건축물의 안전성을 급격하게 감소시킬 수 있다. 특히 고강도콘크리트는 폭렬이 발생하여 심각한 단면 손실과 노출된 철근으로 인하여 건축물의 안전성에 치명적인 영향을 미친다. 이러한 폭렬에 대하여 다양한 연구가 진행되고 있지만, 폭렬의 발생원인은 명백하게 밝혀지진 않았다. 이에 본 연구는 콘크리트의 함수율과 열응력이 폭렬에 미치는 영향을 분석하여 폭렬로부터 구조물의 안전성을 확보하기 위한 기초 자료를 제시하였다.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.703-710
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• 2011

As the spacer in the membrane module provide the channel space to flow the feed solution smoothly and induce the flow turbulence, it could help to reduce both the concentration polarization and to take the long-term operation of membrane modules with high permeate flux by mixing the accumulated contaminants on the membrane surface into the bulk solution. In this study, the concentration distribution in membrane module with respect to the spacers which have the cross-sectional shapes of circle, cross, diamond and hexagon, the angles of spacer configuration, solute rejection and permeate flux were interpreted and optimized numerically using the "COMSOL Multiphysics" software. The concentration on the membrane surface was kept the lowest level for the cross-shape among the above four types of spacers. Also the 30 degree spacer configuration was showed as the most efficient case. The concentrations on the membrane surface at the module outlet for without spacer and the cross shape with the 30 degree spacer configuration were 2.09 and 1.29 times higher than those at inlet, respectively. The reduction effect of concentration polarization increased rapidly as the permeate flux increased.

• Korean Journal of Food Science and Technology
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• v.42 no.4
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• pp.459-467
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• 2010

The substitution effects of broccoli powder for flour in the preparation of sponge cake were determined by physicochemical and sensory analysis. The specific gravity and viscosity of the cake batter and cooking loss of the cake increased with an increasing amount of broccoli powder, whereas specific loaf volume and moisture content of the cake decreased. Lightness, redness, and yellowness of crust and crumb decreased with increasing broccoli powder content. A texture analyses revealed that the hardness, chewiness, gumminess, adhesiveness, and fracturability of the cake tended to increase in proportion to the amount of broccoli powder in the formula. In the sensory evaluation, cake prepared with 5% broccoli powder was similar to the control in moistness, softness, chewiness, and springiness. These results suggest that adding 5% broccoli powder is the best substitution ratio for sponge cake.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.2
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• pp.115-131
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• 2011

Recently, considering the aspects of disaster prevention and environmental damage, the construction of a twin tunnel is increasing. When constructing a twin tunnel, the stresses are concentrated at the pillar so that stability of the tunnel is decreased. Since the previous studies on the behavior of a twin tunnel pillar are mainly restricted to the estimation of the tunnel behavior and the analysis of surface settlement, there is a limit to a quantitative stability estimation of the pillar. Therefore, it was quantitatively investigated how the pillar width of a twin tunnel affects its stability. To ensure this end, global tunnel safety factors obtained numerically using shear strength reduction technique, local safety factors of a pillar using the equation that Matsuda et al. suggested, and strength/stress ratios of the pillar were estimated and their results were analyzed for two sections with different rock covers. For a reasonable design of a twin tunnel pillar, it was turned out that strength/stress ratio, the local pillar safety factor, and global tunnel safety factor should be used interrelatedly rather than independently.

• Journal of the Korean Wood Science and Technology
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• v.15 no.4
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• pp.45-58
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• 1987

This study was carried out to improve the physical and mechanical properties of Pupulus alba $\times$ glandulosa treated by the heat and compression. The results obtained were as follows. 1. The specific gravity of the wood was conspicuously increased by the lincreasing of pressing level. 2. The shrinkage of the wood was increased. by the increasing of pressing level. The radial shrinkage was 6.41-8.81%, the tangential shrinkage was 8.98-19.81 %, and the longitudinal shrinkage was 1.46-1.91 %. Comparing to the untreated stock, the rate of increase was 48.7-104.4% in radial direction. 1.7-124.4% in tangential direction and 60.4-109.9% in longitudinal direction, respectively. 3. The rate absorption of 30% compressed stock was Similar to that of untreated stock. but the rate of absorption of 40 % or more compressed stock was increased highly. 4. The thickness swelling of the wood was not changed in radial direction at pressing level, but was conspicuously increased in tangential direction under the pressing level of 40% and 50%. 5. The heat and compression treatment affected on the mechanical properties of the wood. The longitudinal compressive strength was increased under the pressing level of up to 40%, but was decreased under the pressing level of 50%. The bending strength was not changed under the compression percentage of up to 30%, but was decreased under the pressing level of 30% or more. And, the absorbed energy in impact bending was increased to 128% under the pressing level of up to 30%, but was decreased under the pressing level of 30% or more. Conclusionly, the mechanical properties of the wood was improved by the heat and compression treatment, but the strength of the wood was decreased under the pressing level of a certain level or more(in this study, pressing level of 30% or more). This was because of the wood deterioration due to the deformation(shrinkage, crack, failure) of wood tissues induced by the heat and compression treatment, the heat analysis of wood components induced by the heating, and the drop of the degree of polymerization.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.1-12
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• 1990

The study is concerned with the analysis of combined forging of non-axisymmetric shapes with inclined protrusions by UBET technique. Work hardening is considered for the given range of strain rate during the forging process. A complex shape with inclined cavities is analyzed by subdividing the workpiece into finite UBET elements for which simple velocity fields are applicable. An experimental set-up was designed and manufactured for the experiment, and experiments are carried out with lead billets. The devised set-up can be used for closed-die forging of complex shapes with protrusions in which the dies can be separated automatically for easy removal of the forged products. Based on the derived kinematically admissible velocity fields for corresponding UBET elements, general computer programs have been developed. Since the energy dissipation rate for each elemental region is provided by subprograms (Subroutine or Function), the developed program can be applied to the forging problems of various shapes. The present study has shown that the method developed can be effectively applied to forging of non-axisymmetric shapes with complicated protrusions.

• Water for future
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• v.27 no.3
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• pp.123-134
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• 1994

The reattachment of buoyant effluent to shore in a crossflow is investigated experimentally. The effluent is produced by discharging warm water through projecting side channel into a confined cross-flow of the same depth. In the projecting effluent, the size of recirculating region, which is formed by defleted thermal plume on the lee of the effluent, tends to increase, but the maximum temperature decreases in the direction of the crossflow and it has more even transverse spreading compared to non-projecting type. The heat flux across the crossflow is found to be independant of the projected length of the side channel under relatively low buoyancy flux on the contrary to high buoyancy flux. The reattachment of the effluent can be specified by both velocity ratio and densimetric Froude number, whereas only the velocity ratio is governing factor to the reattachment of the effluent in the case of non-projecting type.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.517-534
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• 2021

Hydrogen fuel is emerging as an new energy source to replace fossil fuels in that it can solve environmental pollution problems and reduce energy imbalance and cost. Since hydrogen is eco-friendly but highly explosive, there is a high concern about fire and explosion accidents of hydrogen fueled vehicles. In particular, in semi-enclosed spaces such as tunnels, the risk is predicted to increase. Therefore, this study was conducted on the applicability of the equivalent TNT model and the numerical analysis method to evaluate the hydrogen explosion pressure in the tunnel. In comparison and review of the explosion pressure of 6 equivalent TNT models and Weyandt's experimental results, the Henrych equation was found to be the closest with a deviation of 13.6%. As a result of examining the effect of hydrogen tank capacity (52, 72, 156 L) and tunnel cross-section (40.5, 54, 72, 95 m²) on the explosion pressure using numerical analysis, the explosion pressure wave in the tunnel initially it propagates in a hemispherical shape as in open space. Furthermore, when it passes the certain distance it is transformed a plane wave and propagates at a very gradual decay rate. The Henrych equation agrees well with the numerical analysis results in the section where the explosion pressure is rapidly decreasing, but it is significantly underestimated after the explosion pressure wave is transformed into a plane wave. In case of same hydrogen tank capacity, an explosion pressure decreases as the tunnel cross-sectional area increases, and in case of the same cross-sectional area, the explosion pressure increases by about 2.5 times if the hydrogen tank capacity increases from 52 L to 156 L. As a result of the evaluation of the limiting distance affecting the human body, when a 52 L hydrogen tank explodes, the limiting distance to death was estimated to be about 3 m, and the limiting distance to serious injury was estimated to be 28.5~35.8 m.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.1
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• pp.27-48
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• 1984

This study is conserned with the optimization of reinforced concrete frames using limit state design theory. Formulations of the optimal design for reinforced concrete frame based on the limit state theory turn out to be the nonlinear programming problems which have to deal with the required steel area, the width and effective height of the beam and column section and the moment reduction factor as the design variables. The objective function is formulated as the total construction cost which considers the costs of steel, concrete and forming for the reinforced concrete frames, and the basic constraints are imposed upon both ultimate and serviciability limit state concepts. Also, the stress blocks assumpted in CP110 and Hognestad et al. theory are applied to analysis an ultimate resistant section force for the ultimate limit state and only the criteria of CP110 are used for serviciability limit state. The optimized technique which is applied to solve the nonlinear programming problems for the optimization of reinforced concrete frames is SUMT utilizing the modified Newton-Raphson method. This algorithm is used to test for the two reinforced concrete frames, and then is compared and analysized with the numerical results of reference(10) to examine its convergence, applicability and stability under the same conditions. The results of this study are discussed about the economy comparision of the optimal values for CP110 and Hognestad et al., and the applicability, stability, convergence and validity of this algorithm used herein through the numerical analyses.

• Journal of the Society of Disaster Information
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• v.19 no.1
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• pp.60-68
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• 2023

Purpose: In order to find out stability condition which governs design of drystone masonry retaining walls and changing patterns of installed width of blocks of the wall for each stability conditions, typical wall was assumed and designed. Method: For the purpose of this study, 10 m high drystone masonry retaining wall with general block size and soil properties were considered and dimensions of the wall were determined by applying stability conditions of sliding and overturning and the design results were compared with each other. Result: According to the design results, installed width of blocks determined by considering stability of sliding were greatly less than those determined by considering stability of overturning and these differences were not decreased noticeably even though same values of factors of safety for sliding and overturning were applied. Between the two methods of determining the installed width of blocks, it could be seen that the method of considering failure wedge of lower part of overturning parts of the wall governed the design instead of considering horizontal base of overturning parts of the wall. Conclusion: In case of considering failure wedge of lower part of overturning parts of the wall, it could be seen that the installed width of blocks increased as the inclination angle of failure wedge increased. In case of considering overturning at the lower part of the wall with certain assumed inclination angle of failure wedge, it could be seen that installed width of blocks decreased as the inclination angle of failure wedge decreased by geometric restrictions of the wall.