• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.1-14
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• 2006

Present study examines the numerical issues of cell structure simulation for various regimes of detonation phenomena ranging from weakly unstable to highly unstable detonations. Inviscid fluid dynamics equations with $variable-{\gamma} $ formulation and one-step Arrhenius reaction model are solved by a MUSCL-type TVD scheme and 4th order accurate Runge-Kutta time integration scheme. A series of numerical studies are carried out for the different regimes of the detonation phenomena to investigate the computational requirements for the simulation of the detonation wave cell structure by varying the reaction constants and grid resolutions. The computational results are investigated by comparing the solution of steady ZND structure to draw out the minimum grid resolutions and the size of the computational domain for the capturing cell structures of the different regimes of the detonation phenomena.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.58-63
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• 2005

As fuel cells approach commercialization, hydrogen production becomes a critical step in the overall energy conversion pathway. Reforming is a process that produces a hydrogen-rich gas from hydrocarbon fuels. Hydrogen production via autothermal reforming (ATR) is particularly attractive for applications that demand a quick start-up and response time in a compact size. However, further research is required to optimize the performance of autothermal reformers and accurate models of reactor performance must be developed and validated. The design includes the requirement of accommodating a wide range of experimental set ups. Factors considered in the design of the reformer are capability to use multiple fuels, ability to vary stoichiometry, precise temperature and pressure control, implementation of enhancement methods, capability to implement variable catalyst positions and catalyst arrangement, ability to monitor and change reactant mixing, and proper implementation of data acquisition. A model of the system was first developed in order to calculate flowrates, heating, space velocity, and other important parameters needed to select the hardware that comprises the reformer. Predicted performance will be compared to actual data once the reformer construction is completed. This comparison will quantify the accuracy of the model and should point to areas where further model development is required. The end result will be a research tool that allows engineers to optimize hydrogen production via autothermal reformation.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.1
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• pp.78-88
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• 2007

In the present study a detailed examination of various porous media models for predicting filtration efficiency and pressure drop of diesel particulate filter (DPF), such as sphere-in-cell and constricted tube models, are attempted. In order for demonstrating their validities of correct estimation on permeability, geometry of property configurations common in commercial cordierite DPFs are correlated to the porous media flow models, and validations of predicted filtration efficiencies due to the use of different unit collectors are made with experiments. The result shows that the porosity, pore size and permeability of cordierite DPF can be successfully correlated by Kuwabara flow field with correction factor of 0.6. The unit collector efficiency predicted by sphere-in-cell model agrees very well with measurements in accumulation mode, whereas that by constricted tube model with significant prediction error.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.864-873
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• 2006

As fuel cells approach commercialization, hydrogen production becomes a critical step in the overall energy conversion pathway. Reforming is a process that produces a hydrogen-rich gas from hydrocarbon fuels. Hydrogen production via autothermal reforming (ATR) is particularly attractive for applications that demand a quick start-up and response time in a compact size. However, further research is required to optimize the performance of autothermal reformers and accurate models of reactor performance must be developed and validated. The design includes the requirement of accommodating a wide range of experimental set ups. Factors considered in the design of the reformer are capability to use multiple fuels, ability to vary stoichiometry, precise temperature and pressure control, implementation of enhancement methods, capability to implement variable catalyst positions and catalyst arrangement, ability to monitor and change reactant mixing, and proper implementation of data acquisition. A model of the system was first developed in order to calculate flowrates, heating, space velocity, and other important parameters needed to select the hardware that comprises the reformer. Predicted performance will be compared to actual data once the reformer construction is completed. This comparison will quantify the accuracy of the model and should point to areas where further model development is required. The end result will be a research tool that allows engineers to optimize hydrogen production via autothermal reformation.

• Journal of Animal Reproduction and Biotechnology
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• v.39 no.1
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• pp.19-30
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• 2024

Background: Although an understanding of the proliferation and differentiation of fish female germline stem cells (GSCs) is very important, an appropriate threedimensional (3D) research model to study them is not well established. As a part of the development of stable 3D culture system for fish female GSCs, we conducted this study to establish a 3D aggregate culture system of ovarian cells in marine medaka, Oryzias dancena. Methods: Ovarian cells were separated by Percoll density gradient centrifugation and two different cell populations were cultured in suspension to form ovarian cell aggregates to find suitable cell populations for its formation. Ovarian cell aggregates formed from different cell populations were evaluated by histology and gene expression analyses. To evaluate the media supplements, ovarian cell aggregate culture was performed under different media conditions, and the morphology, viability, size, gene expression, histology, and E2 secretion of ovarian cell aggregates were analyzed. Results: Ovarian cell aggregates were able to be formed well under specific culture conditions that used ultra-low attachment 96 well plate, complete mESM2, and the cell populations from top to 50% layers after separation of ovarian cells. Moreover, they were able to maintain minimal ovarian function such as germ cell maintenance and E2 synthesis for a short period. Conclusions: We established basic conditions for the culture of O. dancena ovarian cell aggregates. Additional efforts will be required to further optimize the culture conditions so that the ovarian cell aggregates can retain the improved ovarian functions for a longer period of time.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.91-100
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• 2008

Numerical implementation with a Cartesian cut-cell method is conducted in this study. A Cartesian cut-cell method is an easy and efficient mesh generation methodology for complex geometries. In this method, a background Cartesian grid is employed for most of computational domain and a cut-cell grid is applied for the peculiar grids where the flow characteristics are changed such as solid boundary to enhance the accuracy, applicability and efficiency. Accurate representation of complex geometries can be obtained by using the cut-cell method. The cut-cell grids are constructed with irregular meshes which have various shape and size. Therefore, the finite volume method is applied to numerical discretization on a irregular domain. The HLLC approximate Riemann solver, a Godunov-type finite volume method, is employed to discretize the advection terms in the governing equations. The weighted average flux method applied on the Cartesian cut cell grid for stabilization of the numerical results. To validate the numerical model using the Cartesian cut-cell grids, the model is applied to the rectangular tank problem of which the exact solutions exist. As a comparison of numerical results with the analytical solutions, the numerical scheme well represents flow characteristics such as free surface elevation and velocities in x-and y-directions in a rectangular tank with the Cartesian and cut-cell grids.

• Journal of the Korea Convergence Society
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• v.7 no.4
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• pp.181-190
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• 2016

The objective of this study is to find the effective stiffness and compressive strengths of a unit-cell pinwheel truss and double pinwheel truss model designed following a double helical geometry similar to that of the DNA (deoxyribonucleic acid) structure in biology. The ideal solution for their derived relative density is correlated with a ratio of the truss thickness and length. To validate the relative stiffness or relative strength, ABAQUS software is used for the computational model analysis on five models having a different size of truss diameter from 1mm to 5mm. Applied material properties are stainless steel type 304. The boundary conditions applied were fixed bottom and 5 mm downward displacement. It was assumed that the width, length, and height are all equal. Consequently, it is found that the truss model has a lower effective stiffness and a lower effective yielding strength.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.19 no.38
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• pp.9-15
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• 1996

The purpose of this research is to develop a method for part-machine grouping subject to production and management constraints. In the proposed integer programming model, minimization of operating and material-handling costs are considered as an objective function. The model allows one to recognize the existing parts and machines into disaggregated cells. New constraints are introduced in the model to resolve unbalancing capacity and bottleneck problems. It is found that this approach could have a better flexibility on cell size design for mote alternatives than conventional methods. Experimental grouping and comparison studies with ROC algorithm are given for evaluation purposes.

• Proceedings of KOSOMES biannual meeting
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• 2001.10a
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• pp.137-144
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• 2001

A Plankton ecosystem model was developed to investigate effects of hydrodynamic processes including advection and diffusion on size-structured phytoplankton dynamics in the mesohaline zone of the York River estuarine system, Virginia, USA. The model included 12 state variables representing the distribution of carbon and nutrients in the surface mixed layer. Groupings of autotrophs and heterotrophs were based on cell site and ecological hierarchy Forcing functions included incident radiation, temperature, wind stress, mean How and tide which includes advective transport and turbulent mixing. The ecosystem model was developed in FORTRAN using differential equations that were solved using the 4th order Runge-Kutta technique. The model showed that microphytoplankton blooms during winter-spring resulted from a combination of vertical advection and diffusion of phytoplankton cells rather than in-situ production in the lower York River estuary.

• KSBB Journal
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• v.10 no.4
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• pp.358-369
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• 1995

A mathematical model using local thermodynamic equilibrium isotherms for adsorption in encapsulated adsorbent is proposed in order to optimize the design parameters in situ bioproduct separation process. The model accurately follows the experimental data on the adsorption of berberine, secondary metabolite produced in Thaictrum rugosum plant cell culture. The adsorption rate on encapsulated adsorbent is compared with that on alginate-entrapped adsorbent. The result shows that the higher loading capacity in encapsulated adsorbent is mainly due to the increase in the maximum solid phase concentration. Based on the adsorption rate and loading capacity, the encapsulated adsorbent would be more useful than the entrapped adsorbent when used in situ bioproduct separation process. Design parameters in situ bioproduct separation process, such as the size of the capsule, membrane thickness, the ratio of capsule volume to bulk volume, the ratio of single capsule volume to total capsule volume and the adsorbent content in the capsule, are evaluated by using the model. The ratio of single capsule volume to total capsule volume is the most effective parameter for adsorption of berberine on encapsulated adsorbent.