• Korean Institute of Interior Design Journal
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• v.26 no.3
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• pp.45-54
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• 2017

A social phenomenon that occurs in a physical space is said to be a complex system. However, space syntax, which is commonly employed by researchers to identify such social phenomena, has various limitations in interpreting their complexity. On the other hand, agent-based modeling considers a variety of factors including the personality of the agent, objective-oriented work flows, estimation according to time flows and better prediction of space use through diverse parameters depending the situation, as well as the characteristics of the space. The agent-based method thus has the potentials to be developed as an alternative to space syntax techniques. In particular, discrete event driven simulation(DEVS), which is part of the agent-based modeling method, embraces the concept of networks just like space syntax, which allows a possible theoretical linkage in the future. This study suggests a procedural model of agent-based DEVS reflecting two different connection methods, i.e. connections between adjacent areas and those of the entire space, and attempts to identify the relationship between the local and regional indices of space syntax. A number of spaces were selected as examples-one for a preliminary experiment and eight modified for the main experiment-and space syntax and DEVS were applied to each of them. The comparative analysis of the results led to the conclusions as follows: 1) Adjacent connections were closely related to local indices, while the whole-space approach to regional indices. Local integration shows both characteristics. 2) Observation of the time flow model indicated a faster convergence with the range of 1 to 3-fold of the total time of one lap, with the error of less than 10%. 3) The heat map analysis showed more obvious characteristics of using the space for the entire space rather than adjacent connections. 4) Space syntax shows higher eligibility than ABM.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1518-1528
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• 1995

The deformation and departure processes of a bubble attached to the wall are studied experimentally and numerically to understand the phenomena of the nucleate boiling heat transfer enhancement under DC electric field. An air-bubble is injected in a dielectric liquid with different electric fields generated by changing three types of electrode system (Type 1,2 and 3) in the bubble generator. Experimental variables are the electric field strength and the distance and the shape of the electrodes under DC electric field. From experimental results, it is observed that the bubble under Dc electric field is elongated in the same direction as the electric field and the contact angle increases. For the parallel plate electrode which generates a uniform electric field, bubble departure volume doesn't seem to decrease within our experimental range. However, when a needle is raised a few millimeters from the lower electrode to make a nonuniform electric field around the needle, bubble departure volume decreases continuously with the increase of an applied voltage. The reduction effect of bubble departure volume is the most effective under a strong nonuniform electric field generated with Type 3. As the nonuniformity of the electric field due to the shape of a electrode increases, the terminal velocity and the acceleration of a bubble increase largely. For the comparison with visualization results, the deformation of a bubble attached to the electrode is carried out by a numerical method. Numerical results show good agreement qualitatively with experimental results.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.3
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• pp.37-43
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• 2004

Water-jet trajectory visualization and velocity deficits from a high pressurized steam-generator nozzles were experimentally observed. In order to find an optimal nozzle configuration. several parameters affecting plugging and erosion onto the steam generator tube were quantitatively analyzed. For the experiments, a high-pressurized pump (pressure in use: 200 kg/$\textrm{cm}^2$, 15 HP, 11 kW, output flow Q : 301/min) was utilized. Visualization, velocity distribution, and spray growth rate with different nozzle configurations have been mainly focused using a 2-D PDPA system. The results indicated that trajectories along the centerline regardless of their configurations has its potential core region. However, the phenomena from the peripheral part need to be meticulously considered. Accordingly, it is evident that quantitative velocity deficits at the outer region are outstanding due to the aerodynamical drag and entrainment.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.1
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• pp.51-57
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• 2009

In this study, a new topology optimization method is developed to design heat-dissipating structure with forced convection. To cool down electrical devices or mechanical machines, two types of convection models have been widely used: the natural convection model with a large Archimedes number and the forced convection with a small Archimedes number. In these days, lots of engineering application areas such as electrochemical conversion devices (Fuel cell) or rocket propulsion engines adopt the forced convection to dissipate the generated heat. Therefore, to our knowledge, it becomes an important issue to design flow channels inside which the generated heat dissipate. Thus, this paper studies optimal topological designs considering fluid-heat interactions. To consider the effect of the advection in the heat transfer problem, the incompressible Navier-stokes equation is solved. This paper numerically studies the coupling phenomena and presents optimal channel design considering forced convection.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.121-128
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• 2009

During a hypothetical high-pressure accident in a nuclear power plant (NPP), molten corium can be ejected through a breach of a reactor pressure vessel (RPV) and dispersed by a following jet of a high-pressure steam in the RPV. The dispersed corium is fragmented into smaller droplets in a reactor cavity of the NPP by the steam jet and released into other compartments of the NPP by a overpressure in the cavity. The fragments of the corium transfer thermal energy to the ambient air in the containment or interact chemically with steam and generate hydrogen which may be burnt in the containment. The thermal loads from the ejected molten corium on the containment which is called direct containment heating (DCH) can threaten the integrity of the containment. DCH in a NPP containment is related to many physical phenomena such as multi-phase hydrodynamics, thermodynamics and chemical process. In the evaluation of the DCH load, the melt dispersion rates depending on the RPV pressure are the most important parameter. Mostly, DCH was evaluated by using lumped-analysis codes with some correlations obtained from experiments for the dispersion rates. In this study, MC3D code was used to evaluate the dispersion rates in the APR1400 NPP during the high-pressure accidents. MC3D is a two-phase analysis code based on Eulerian four-fields for melt jet, melt droplets, gas and water. The dispersion rates of the corium melt depending on the RPV pressure were obtained from the MC3D analyses and the values specific to the APR1400 cavity geometry were compared to a currently available correlation.

• Journal of Korea Water Resources Association
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• v.37 no.4
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• pp.293-304
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• 2004

Sedimentation basin plays an important role in urban water treatment, and there are many complicated phenomena which need to be understood for efficient design and control of it. Especially, the study on the improvement of settling efficiency is required. In this study, commercial CFD (Computational Fluid Dynamics) program, FLUENT, and particle tracking method were used to simulate the flow in sedimentation basin, and to predict the settling efficiency. Computational domain of real scale was made, and detail factors such as porous wall, and outlet trough were considered instead of being simplified. The simulation results were compared with the experimental data to calibrate the parameters of particle tracking method. Sensitivity analysis showed that the particle diameter had more significant effects on settling efficiency than the particle density. The computation results gave the best agreements with the experimental data, when the value of particle diameter was 26.5 ${\mu}{\textrm}{m}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1172-1182
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• 2002

In the present study a general criterion for local thermal equilibrium is presented in terms of parameters of engineering importance which include the Darcy number, the effective Prandtl number of fluid, and the Reynolds number. For this, an order of magnitude analysis is performed for the case when the effect of convection heat transfer is dominant in a porous structure. The criterion proposed in this study is more general than the previous criterion suggested by Carbonell and Whitaker, because the latter is applicable only when conduction is the dominant heat transfer mode in a porous medium while the former can be applied even when convection heat transfer prevails. In order to check the validity of the proposed criterion for local thermal equilibrium, the forced convection phenomena in a porous medium with a microchanneled structure subject to an impinging jet are studied using a similarity transformation. The proposed criterion is also validated with the existing experimental and numerical results for convection heat transfer in various porous materials that include some of the parameters used in the criterion such as a microchannel heat sink with a parallel flow, a packed bed, a cellular ceramic, and a sintered metal. It is shown that the criterion presented in this work well-predicts the validity of the assumption of local thermal equilibrium in a porous medium.

• Journal of Sensor Science and Technology
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• v.3 no.2
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• pp.16-23
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• 1994

Developed fiber-optic biosensor for the detection of organophosphorus compounds in a contaminated water needs the analysis of an enzyme kinetics and the transport phenomena in the reaction part to analyze the sensor signal and to design the sensor. The enzyme inhibition kinetics was investigated and the reactor model was proposed to design the reaction part in the proposed sensor. Since the acetylcholinesterase was inhibited by the organophosphorus compounds, experiments for enzyme inhibition reaction were performed from 0 to 2 ppm to be detected by the developed sensor, and irreversible enzyme inhibition kinetics was proposed. The reactor parts were divided into the two phases, i.e. bulk phase and immobilized enzyme layer, to analyze the flow and diffusion. Sensor signal was able to be analyzed based on the total reactor model established by linking the enzyme reaction kinetics. Based on the proposed model, the effects of loading enzyme amount and enzyme layer thickness on the magnitude of readout signal were simulated.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.1
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• pp.95-105
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• 2012

The selective catalytic reduction (SCR) system is a highly-effective aftertreatment device for NOx reduction of diesel engines. Generally, the ammonia ($NH_3$) was generated from reaction mechanism of SCR in the SCR system using the liquid urea as the reluctant. Therefore, the precise urea dosing control is a very important key for NOx and $NH_3$ slip reduction in the SCR system. This paper investigated NOx and $NH_3$ emission characteristics of urea-SCR dosing system based on model-based control algorithm in order to reduce NOx. In the map-based control algorithm, target amount of urea solution was determined by mass flow rate of exhaust gas obtained from engine rpm, torque and $O_2$ for feed-back control NOx concentration should be measured by NOx sensor. Moreover, this algorithm can not estimate $NH_3$ absorbed on the catalyst. Hence, the urea injection can be too rich or too lean. In this study, the model-based control algorithm was developed and evaluated on the numerical model describing physical and chemical phenomena in SCR system. One channel thermo-fluid model coupled with finely tuned chemical reaction model was applied to this control algorithm. The vehicle test was carried out by using map-based and model-based control algorithms in the NEDC mode in order to evaluate the performance of the model based control algorithm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.77-83
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• 2002

A computational study on the performance prediction of a two-stage axial compressor has been performed. A quasi-steady mixing-plane method is used on the rotor/stator interface to simulate the unsteady interaction phenomena. Detail flow mechanisms, for example, choke, stall, shock/boundary interaction, etc., have been observed and discussed in conjunction with performance characteristics. Calculational data agree reasonably well with the experimental data in terms of the performance characteristics showing the applicability of computational methods to the design validation of multistage axial compressors instead of experimental methods. But it is found that the stall margin of the original compressor was rather small, thus the design modification adopting a simple 1D/2D method has been conducted and its corresponding computations are also carried out. As a result of the redesign process, the stall margin becomes wide enough, but the overall performance is unsatisfactory, therefore, it seems that the redesign of the blades using 3-D methods is needed in the future work.