• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1257-1264
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• 2011

This paper presents 3D simulation by STAR-CCM+ for lean premixed combustion in a stationary gas turbine combustor with separate pilot and main nozzles. The constant for the source term in the flame area density transport equation was modified to account for a low global equivalence ratio and validated against measurement data. A Partially-premixed Coherent Flame Model(PCFM) involves propagation of a laminar premixed flame with the predicted flame surface density and equilibrium assumption in the burned gas with spatial inhomogeneity. The conditions for cooling by radiation and convection are considered for accurate determination of the heat flux on the wall. A parametric study is of the pilot-fuel-to-total-fuel-ratio is carried out. A chemical reactor network (CRN) was constructed on the basis of the 3D simulation results and compared against measurements of NOx.

• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.487-493
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• 2016

The moment analysis of lysozyme was implemented using chromatograms that were obtained from weak cation exchange column in high performance liquid chromatography system. Three elution sodium phosphate buffers containing 1.0, 0.75, 0.5M sodium chloride were used. Experiments were conducted by varying flow rate, elution sodium chloride concentration, and lysozyme solute concentration. The general rate (GR) model was employed to calculate the first moment and the second moment. By plotting $L/u_0$ vs. $({\mu}_1-t_0)/(1-{\varepsilon}_e)(1-{\varepsilon}_i)$] equilibrium constants (K) were obtained from first moment analysis. Intra-particle diffusivity was obtained from theoretical plate number data. Based on the results of moment analysis, van Deemter plots were drawn in order to investigate the contributions of $H_{ax}$, $H_f$, and $H_d$ to total Height Equivalent to a Theoretical Plate (HETP, $H_{total}$). The effect of intra-particle diffusion ($H_d$) was the most dominant factor contributing to HETP while external mass transfer ($H_f$) was negligible factor.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.8
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• pp.730-740
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• 2000

The software rejuvenation method for highly available multiplex systems uses a pro-active fault-tolerant approach to handle system failures. The software rejuvenation prevents failures from occurring, while the previous methods recover from failures after happening. Especially, since the software aging proceeds fast in the software used for the multimedia mobile computing due to the loss of communications or data, the preventive method from failures using software rejuvenation can be used for the multimedia mobile computing. In this paper, according to the operational parameters such as rejuvenation period, rejuvenation time, failure rate and repair rate of the servers, number of running servers, duration of running time, and type of running modes, we calculate steady-state probabilities, downtime, availability, and cost of the multiplex systems using software rejuvenation method. We validate the closed-form solutions of the mathematical model by experiments based on various operational parameters and find that the software rejuvenation method can be adopted as preventive fault-tolerant technique. The failure rate and unstable rate of the servers are essential factors for the decision making of the rejuvenation policies.

• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.461-468
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• 1991

The cationic polymerizations of substituted oxiranes which have pendant energetic groups such as azido, and nitrato, are investigated theoretically using the semiempirical MNDO, and $AM_1$ methods. The nucleophilicity and basicity of substituted oxiranes can be explained by the negative charge on oxygen atom of oxiranes. The reactivity of propagation in the polymerization of oxiranes can be represented by the positive charge on carbon atom and the low LUMO energy of active species of oxiranes. Ring opening of the complexed cyclic oxonium ion to the open chain carbenium ion is expected computational stability of the oxonium and carbenium ion by 30∼40 kcal/mol favoring the carbenium ion. The relative equilibrium concentration of cyclic oxonium and open carbenium ions will be a major determinant of mechanism. The chain growth $SN_1$, mechanism will be at least as fast as that for $SN_2$ mechanism.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.429-435
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• 2012

An abrasion due to continuous friction between a work roll and strip causes the mass of the work roll to be unbalanced in the rolling process. We developed a mathematical model for the rolling mill considering the unbalanced mass and verified the model experimentally. The work roll was approximated as a rigid rotor with eccentricity, and the effect of the unbalanced mass on chatter vibration was investigated. The joint forces computed by quasistatic analysis were applied to the work roll in the rolling mill. Transient responses were obtained, and frequency analysis was performed by solving equations of motion using a direct integration method. Horizontal vibrations were more strongly affected by eccentricity than vertical vibrations. In the horizontal direction, a small eccentricity of 1% of the work roll radius considerably increased the amplitude of the chatter frequency.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.671-682
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• 2004

This study investigated the effects of a shear slip on the deflection of steel-concretecomposite beams with partial shear interaction. Under the guidance of various current design codes, this deflection was related to the strength of shear connectors in the composite beams. In this paper, a shear connector stiffness based on exact solutions, regardless of loading conditions, was developed. The equivalent rigidity of composite beams that considered three different loading types was first derived, based on equilibrium and curvature compatibility, from which a general formula accounting for slips was developed. To validate this approach, the predicted maximum deflection under the proposed method was compared against currently used equations to calculate beam effective stiffness (AISC)Nie's equations, which have recently been proposed. For typical beams that were used in practice, shear slips might result in stiffness reduction of up to 18% for short-span beams. For full composite sections, the effective section modulus with the AISC specifications was larger than that of the present study, which meant that the specifications were not conservative. For partial composite sections, the AISC predictions were more conservative than those in the present study.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.509-518
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• 2002

In order to perform the spatial buckling and static analysis of the nonsymmetric thin-walled beam-column element, improved exact static stiffness matrices were evaluated using equilibrium equation and force-deformation relationships. This numerical technique was obtained using a generalized linear eigenvalue problem, by introducing 14 displacement parameters and system of linear algebraic equations with complex matrices. Unlike the evaluation of dynamic stiffness matrices, some zero eigenvalues were included. Thus, displacement parameters related to these zero eigenvalues were assumed as polynomials, with their exact distributions determined using the identity condition. The exact displacement functions corresponding to three loadingcases for initial stress-resultants were then derived, by consistently combining zero and nonzero eigenvalues and corresponding eigenvectors. Finally, exact static stiffness matrices were determined by applying member force-displacement relationships to these displacement functions. The buckling loads and displacement of thin-walled beam were evaluated and compared with analytic solutions and results using ABAQUS' shell element or straight beam element.

• Journal of Korea Water Resources Association
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• v.38 no.2
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• pp.133-142
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• 2005

The settling concentration of fine suspended solid particles(alumina(Al$_2$O$_3$) and quartz(SiO$_2$)) is investigated with the physico-chemical effects(initial concentration, pH and NaCl). Laboratory tests have confirmed the significant influence of increasing initial concentration and salinity which can lead to flocculation due to the intermolecular attraction. Furthermore, the influence of the pH value on the concentration-time corves of alumina has been on firmed. Besides a numerical model to predict the behaviour of cohesive deposit under still water is analyzed by solving the unsteady one-dimensional diffusion-advection equation with a explicit, implicit, Crank-Nicolson and finite difference scheme. The model predicts the existence of an equilibrium concentration. Application of the model with implicit centered difference to data from settling experiments shows a similar distribution.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.5
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• pp.474-480
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• 2011

Space Imaging Sensor operated on LEO is affected from the Earth IR and Albedo as well as the Sun Radiation. The Imaging Sensor exposed to extreme environment needs thermal control subsystem to be maintained in operating/non-operating allowable temperature. Generally, units are periodically dissipated on spacecraft panel, which is designed as radiator. Because thermal design of the imaging sensor inside a spacecraft is isolated, heat pipes connected to radiators on the panel efficiently transfer dissipation of the units. First of all, preliminary thermal design of radiating area and heater power is performed through steady energy balance equation. Based on preliminary thermal design, on-orbit thermal analysis is calculated by SINDA, so calculation for thermal design could be easy and rapid. Radiators are designed to rib-type in order to maintain radiating performance and reduce mass. After on-orbit thermal analysis, thermal requirements for Space Imaging Sensor are verified.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.84-89
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• 2007

Direct decomposition of hydrocarbon (methane, propane) was studied using a thermal plasma to produce high purity hydrogen and carbon black. Thermodynamic equilibrium compositions were calculated based on the minimization of Gibb's free energy, and decomposition experiments were performed on the basis of calculation results. The purity of hydrogen was found to be depended strongly on the flow rate of hydrocarbon. The decomposition conditions for high purity hydrogen were investigated. The purity of hydrogen produced from methane decomposition was higher than that from propane. In the case of propane, it was investigated that by products such as methane, acetylene, and ethane etc., by radical recombination under thermal plasma were produced more than that of methane. Produced carbon blacks were characterized by material analyses, such as XRD, Raman spectroscopy, SEM, and particle size analysis. In both methane and propane decompositions, well-crystallized carbon blacks were produced and showed uniform and sphere-like morphologies. The size of carbon black synthesized from methane was observed to be smaller than that from propane.