• Journal of the Korean Society of Safety
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• v.36 no.4
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• pp.71-79
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• 2021

In this study, a real-scale fuel-cell room of volume 1.36 m³ is constructed to confirm the explosion characteristics of hydrogen-air mixture gas in a hydrogen-powered house. A volume concentration of 40% is applied in the fuel-cell room as the worst-case scenario to examine the most severe accident possible, and two types of doors (made of plastic sheet and wood) are fabricated to observe their effects on the overpressure and impulse. The peak overpressure and impulse based on distance from the ignition source are experimentally observed and assessed. The maximum and minimum overpressures with a plastic-sheet door are about 20 and 6.7 kPa and those with a wooden door are about 46 and 13 kPa at distances of 1 and 5 m from the ignition source, respectively. The ranges of impulses for distances of 1-5 m from the ignition source are about 82-28 Pa·s with a plastic-sheet door and 101-28 Pa·s with a wooden door. The amount of damage to people, buildings, and property due to the peak overpressure and impulse is presented to determine the safe distance; accordingly, the safe distance to prevent harm to humans is about 5 m based on the 'injuries' class, but the structural damage was not serious.

• Structural Engineering and Mechanics
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• v.70 no.2
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• pp.169-178
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• 2019

The replacement of damaged components is an important task for long-span bridges. Conventional strategy for component replacement is to close the bridge to traffic, so that the influence of the surrounding environment is reduced to a minimum extent. However, complete traffic interruption would bring substantial economic losses and negative social influence nowadays. This paper investigates traffic control technologies without interruption for component replacement of long-span bridges. A numerical procedure of traffic control technologies is proposed incorporating traffic microsimulation and site-specific data, which is then implemented through a case study of cable replacement of a long-span cable-stayed bridge. Results indicate traffic load effects on the bridge are lower than the design values under current low daily traffic volume, and therefore cable replacement could be conducted without traffic control. However, considering a possible medium or high level of daily traffic volume, traffic load effects of girder bending moment and cable force nearest to the replaced cable become larger than the design level. This indicates a potential risk of failure, and traffic control should be implemented. Parametric studies show that speed control does not decrease but increase the load effects, and flow control using lane closure is not effectual. However, weight control and gap control are very effective to mitigate traffic load effects, and it is recommended to employ a weight control with gross vehicle weight no more than 65 t or/and a gap control with minimum vehicle gap no less than 40 m for the cable replacement of the case bridge.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.188-191
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• 2002

3-D orthogonal woven carbon/Al composites were fabricated using a pressure infiltration casting method. Especially, to minimize geometrical deformation of fiber pattern and $Al_4C_3$ formation, the process parameters of the minimum pressurizing force, melting temperature, delay and holding time of molten aluminum pressurizing was optimized through the PC-controlled monitoring system. Resonant ultrasound spectroscopy (RUS) was utilized to measure the effective elastic constants of 3-D orthogonal woven carbon/Al composites. The CTE measurement was conducted using strain gages in a heating oven.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.178-183
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• 2000

An efficient Newton-GMRES algorithm is presented for computing two-dimensional steady compressible viscous flows on unstructured hybrid meshes. The scheme is designed on cell-centered finite volume method which accepts general polygonal meshes. Steady-state solution is obtained with pseudo-transient continuation strategy. The preconditioned, restarted general minimum residual(GMRES) method is employed in matrix-free form to solve the linear system arising at each Newton iteration. The incomplete LU fartorization is employed for the preconditioning of linear system. The Spalart-Allmars one equation turbulence model is fully coupled with the flow equations to simulate turbulence effect. The accuracy, efficiency and robustness of the presently developed method are demonstrated on various test problems including laminar and turbulent flows over flat plate and airfoils.

• Journal of the Korean Geographical Society
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• v.41 no.2 s.113
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• pp.212-226
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• 2006

Surface data generally represent continuous distribution of geographical or social phenomena of a region in urban analysis. Instances include distribution of temperature, population of region, and various distributions related to human activities. When spatial data are given in the form of surface, surface comparison is required as a way of comprehending the surface change or the relationship between two surfaces. As for previous approaches of surface comparison, there are visualization, quantitative methods and qualitative method. All those approaches, however, show the difference between two surfaces in a limited way. Especially, they are not able to distinguish spatial difference between two surfaces. To overcome such problem, this paper proposes a method of comparing two surfaces in terms of their spatial structure. Main concept of the method comes from earth moving problem and the method is named minimum surface transformation, here. When a surface is transformed into another, total surface volume moved in the process of transformation should be the minimum. Both quantitative and spatial differences between two surfaces are evaluted by total surface volume moved and the distribution of moved surface volume of each cell respectively. The method is applied to hypothetical and actual data. From the former, it is understood that the method explains how two surfaces are quantitatively and spatially different. The result of the latter shows that moved total surface volume decreases as time goes by which fits the actual situation that population change rate gets smaller. Concerning the other measure of surface difference, the distribution of $X_{ij}$ describes detailed flow of surface volume than that of simply subtracting surface volume by indicating to what direction the population change occurs.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1392-1397
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• 2008

This study is to measure the change of the $CO_2$ and floating dust concentration depending on the volume of the ventilation and the state of on/off the ventilation for the estimation of the air pollution in classroom. The results could be summarized as follows: the test cell was the two full scaled model and the one is set up with ventilation system another was not. the volume of classroom is 170.1m3 and the number of persons are 35. 1)when the ventilation system was not installed, The experimental results of the $CO_2$ concentration showed the average of 2,150ppm and the maximum of 2,740ppm in the classroom. This was the higher than 1,000ppm, the standard value of ASHRAE and the enforcement regulations of School Sanitation Code in Ministry of Education & Human Resources Development, 1000ppm. The $CO_2$ concentration was relatively increasing during school hours. 3)In case of the volume of ventilation of $800m^3$/h, the $CO_2$ concentration of classroom showed the average of 962 ppm and the maximum of 1,380 ppm. This was higher than 1,000ppm, the standard of ASHRAE and the enforcement regulations of School Sanitation Code in Ministry of Education & Human Resources Development. 4)The floating dust(PM10) was the maximum of 0.52 mg/$m^3$, the minimum of 0.25 mg/$m^3$, and the average of 0.32 mg/$m^3$ in case of the ventilation system off. Those were higher than the standard value 0.15 mg/$m^3$. In case of the ventilation system on, the floating dust(PM10) was the maximum of 0.174 mg/$m^3$ , the minimum of 0.048 mg/$m^3$, and the average of 0.078 mg/$m^3$. These were the lower than 0.15 mg/$m^3$, the standard of the enforcement regulations of School Sanitation Code in Ministry of Education & Human Resources Development. 5)The concentrations of $CO_2$ and PM10 were largely depending on the number of students and the ventilation system, The installation of the ventilation system is necessary for the amenity environment and the management of the indoor air quality.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1038-1045
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• 2000

An experimental study was carried out to delineate the flow characteristics in a closed countescurrent two-phase thermo syphon with concentric tubes. This is to be installed in the HANARO research reactor as a part of a Cold Neutron Source(CNS). In the present investigation, experiments ata room temperature with Freon-II3 as a moderator were performed. Results show that, based on the magnitude of pressure fluctuation, the flow regimes could be divided into 4 distinct ones in the ($V_f,\;Q_i$) plane, where $V_f$ represents the volume of the charged liquid and $Q_i$ the heat load: a stable flow regime, an oscillatory flow regime, a restablized flow regime and a dryout flow regime. For $V_f$>2.5l, the flow is stable at low $Q_i$. However, as $Q_i$ increases, the flow becomes oscillatory and finally restablizes As $V_f$ increases, the oscillation amplitude decreases, reaching to the restablized flow region at low $Q_i$, and the liquid level in the moderator cell remains high. In the oscillatory flow regimes, for a fixed VI; the oscillating period of time varies with $Q_i$, having a minimum value at a certain value of $Q_i$. The heat load, where the oscillating period of time is minimum, decreases as $V_f$ increases.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.4
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• pp.293-299
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• 2016

In this paper, a projection method is introduced which is used in topology design optimization. In the projection method, each active design variable is projected onto the design domain depending on the shape and size of the projection functions, and the finite element under this projection receives a solid material. Furthermore, the size of the projection function defines the minimum length scale of the structural members. Therefore, a designer can easily apply design constraints without complicated post-processing procedure. In addition, the projection method can be combined with the homogenization theory, and applied to material design problem for composite materials. Topology design optimization for the unit-cell of the periodic structures can maximize the effective material properties, which yields the optimal material distribution with maximum bulk or shear moduli under a given volume fraction.

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.814-826
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• 2015

The most important advantage of nanoparticles is the increased thermal conductivity coefficient and convection heat transfer coefficient so that, as a result of using a 1.5% volume concentration of nanoparticles, the thermal conductivity coefficient would increase by about twice. In this paper, the effects of a nanofluid ($TiO_2$/water) on heat transfer characteristics such as the thermal conductivity coefficient, heat transfer coefficient, fuel clad, and fuel center temperatures in a VVER-1000 nuclear reactor are investigated. To this end, the cell equivalent of a fuel rod and its surrounding coolant fluid were obtained in the hexagonal fuel assembly of a VVER-1000 reactor. Then, a fuel rod was simulated in the hot channel using Computational Fluid Dynamics (CFD) simulation codes and thermohydraulic calculations (maximum fuel temperature, fluid outlet, Minimum Departure from Nucleate Boiling Ratio (MDNBR), etc.) were performed and compared with a VVER-1000 reactor without nanoparticles. One of the most important results of the analysis was that heat transfer and the thermal conductivity coefficient increased, and usage of the nanofluid reduced MDNBR.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.316-321
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• 2016

This study developed an eco-block for grass growth using the expanded vermiculites that absorb bacteria selected considering for the high pH and dry environments and plant growth. For the developed eco-block, a fundamental properties including compressive strength gain and water absorption and ecology characteristics were tested. The selected bacteria was Bacillus alcalophilus a nd Rhodoblastus acidophilus and had high concentration of $10^9cell/mL$. The expanded vermiculite that was used for shelter of bacteria was added by 7.5% and 10% replacement of the natural aggregates by volume. The developed eco-block achieved the minimum requirements specified in SPS provision and significantly effective in reducing chemical Chemical Oxygen Demand(COD) concentration and enhancing the growth of fish and plant.