• Journal of Mechanical Science and Technology
• /
• v.18 no.8
• /
• pp.1470-1478
• /
• 2004

In this paper, a new 'presumed' Probability Density Function (PDF) approach coupled with a Lagrangian tracking method is proposed for turbulent combustion modeling. The test and the investigation of the model are conducted by comparing the model results with DNS data for a premixed flame subjected in a decaying turbulent field. The newly constructed PDF, which incorporates the instantaneous chemical reaction term, demonstrates consistent improvement over conventional assumed PDF models. It has been found that the time evolution of the mean scalar, the variance and the mean reaction rate are strongly influenced by a parameter deduced by a Lagrangian equation which takes into account explicitly the local reaction rate. Tests have been performed for a moderate Damkohler number, and it is expected the model may cover a broader range of Damkohler number. The comparison with the DNS data demonstrates that the proposed model may be promising and affordable for implementation in a moment-equation solver.

• Journal of the Korea Concrete Institute
• /
• v.12 no.3
• /
• pp.77-85
• /
• 2000

Various concretes are used for construction works depending on the types of structure, building element and method of construction. An internal vibration work is one of the important processes for adequately pouring various concrete into a certain form. This study was undertaken to find out the effects of internal vibration on flowability of fresh concrete by concrete flow test under eight conditions of vibration. Presumable equation models also were created to show all vibration effects without regard to kinds of concrete. As the results of this study, the degree of vibration effects were varied according to the properties of concrete. Acceleration amplitude of vibration that applied to fresh concrete was effective value of the properties of vibration in a viewpoint of flowability. Moreover, This research presents the presumed equation models including variables created by acceleration amplitude and measuring value of vibrated concrete flow test. These models are presumable methods of vibration effects regardless of kinds of concrete.

• Journal of the Korean Society of Combustion
• /
• v.15 no.4
• /
• pp.22-28
• /
• 2010

The Direct Quadrature Method of Moments (DQMOM) has been presented for the solution of population balance equation in the wide range of the multi-phase flows. This method has the inherently interesting features which can be easily applied to the multi-inner variable equation. In addition, DQMOM is capable of easily coupling the gas phase with the discrete phases while it requires the relatively low computational cost. Soot inception, subsequent aggregation, surface growth and oxidation are described through a population balance model solved with the DQMOM for soot formation. This approach is also able to represent the evolution of the soot particle size distribution. The turbulence-chemistry interaction is represented by the laminar flamelet model together with the presumed PDF approach and the spherical harmonic P-1 approximation is adopted to account for the radiative heat transfer.

• Journal of Mechanical Science and Technology
• /
• v.14 no.8
• /
• pp.879-890
• /
• 2000

This study investigates the nonpremixed $H_2/CO$-air turbulent flames numerically. The turbulent combustion process is represented by a reaction progress variable model coupled with the presumed joint probability function. In the present study, the turbulent combustion model is applied to analyze the nonadiabatic flames by introducing additional variable in the transport equation of enthalpy and the radiative heat loss is calculated using a local, geometry independent model. Calculations are compared with experimental data in terms of temperature, and mass fraction of major species, radical, and NO. Numerical results indicate that the lower and higher fuel-jet velocity flames have the distinctly different flame structures and NO formation characteristics in the proximity of the outer core vortex zone. The present model correctly predicts the essential features of flame structure and the characteristics of NO formation in the bluff-body stabilized flames. The effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.5 no.4
• /
• pp.19-30
• /
• 2002

The stability of slope using root-pile like to the reinforcements is affected by the interaction behavior mechanism of soil-reinforcements. Through the studying on the interaction in joint of its, therefore, the control roles can be find out in installed slope. In study, the stress level ratio based on the insert angle of installed reinforcements in soil used to numerical analysis, which was results from the duty direct shear test in Lab. The maximum shear strain variation on the reinforcements was observed at insert angle, which was approximately similar to the calculated angle based on the equation proposed by the Jewell. The elasto-plastic joint model on the contact area of soil-reinforcements was presumed, the reinforced soil assumed non-linear elastic model and the reinforcements supposed elastic model, respectively. The finite element analysis of assumed models was performed. The shear strain variation of non-reinforced state obtained by the FEM analysis including elasto-plastic joint elements were shown the rationality of general limit equilibrium analysis for the slope failure mode on driving zone and resistance zone, which based on the stress level step according to failure ratio. Through the variation of shear strain for the variation of inserting angle of reinforcements, the different mechanism on the bending and the shear resistance of reinforcements was shown fair possibility.

• Bulletin of the Korean Chemical Society
• /
• v.3 no.4
• /
• pp.133-139
• /
• 1982

It has been presumed that the molten sulfur above $159^{\circ}C$ consists of an equilibrium mixture of $S_8$ rings and $S_x$ polymers where the number average degree of polymerization, P, is large. But it is known that admixture of halogens with liquid sulfur greatly reduce the viscosity. Constructing a new equilibrium equation, it is possible to evaluate the viscosity when halogens are added to liquid sulfur. Calculated viscosity is in good agreement with experimental values. Using the proposed model, the thermodynamic properties of liquid sulfur are also calculated over a wide range of temperature which the sulfur exists as the polymer.

• Korean Journal of Soil Science and Fertilizer
• /
• v.36 no.4
• /
• pp.181-192
• /
• 2003

We developed a mathematical simulation model to portray the vertical distribution of soil water from the measured weather data and the known soil hydraulic properties, and then compared simulation results with the periodically measured soil water profiles obtained on Jungdong sandy loam to verify the model, In this model, we solved potential-based Richards' equation by the implicit finite difference method superimposed on the predictor-corrector scheme. We presumed that: soil hydraulic properties are homogeneous; soil water flows isothermally; hysteresis is not considered; no vapor flows; no heat transfers into the soil profiles; and water added to soil surface is distributed along the soil profile following partial displacement principle. The input data were broadly classified into two groups: (1) daily weather data such as rainfall, maximum and minimum air temperatures, relative humidity and solar radiation and (2) soil hydraulic data to approximate unsaturated hydraulic conductivity and water retention. Each hydraulic polynomial function approximated using the Chebyshev polynomial and least square difference technique in tandem showed a fairly good fit of the given set of data. Vertical distribution of soil water as approximations to the Richards' equation subject to changing surface and phreatic boundaries was solved numerically during 53 days with a comparatively large time increment, and this pattern agreed well with field neutron scattering data, except for the surface 0.1 m slab.

• The Journal of the Korea Contents Association
• /
• v.13 no.12
• /
• pp.389-401
• /
• 2013

The objective of this study is to devise and empirically validate a model in which information characteristics influence the success of SCM system as assessed by the Information Capabilities method. The four factors examined in this study include Information Quality, Operational Information Sharing, Strategic Information Sharing, Information Capabilities. The research model was analyzed by the structural equation modeling(SEM) technique, supported by SPSS 21 and SMART-PLS 2.0. The results of this study can be summarized as follows. The study confirmed the presence of positive influence of information quality on operational information sharing, strategic information sharing and IO. And, information sharing, as expected, had a significant impact on SCM performance as assessed by the IO method. A major contribution of the study is that it provides empirical evidence of the relationships that have been presumed to exist between information characteristics and information performance of SCM system. Also, the study provides both researchers and practitioners a solid foundation for future studies and practice for more successful implementation of SCM system.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.22 no.1
• /
• pp.114-123
• /
• 2014

Due to the recent aircraft accidents both in Ethiopian airline and Malaysian airline, almost all the media are focusing the importance of the airline safety. Especially, media's eyes and ears are interested in the reasons why Malaysia airline's missing presumed as by either terrorist attack or pilot's mistake. Safety Behaviors of pilot are viewed as the most important human factor issues among researchers. This is because, if it were the case of a commercial airline, pilot's safety behavior would be directly related to the lives of couple of hundreds passengers. This paper considers the antecedents of this safety behaviors as pilot's leadership, pilot's leadership and self-efficacy. This paper has tried to find out which human factors of a pilot would have significant impact on their safety behaviors. According to the empirical research result from SEM (Structural Equation Model), it was found out both the leadership and self-efficacy of a pilot had direct impact on their safety behaviors through safety motivation. Thus it could be concluded that flight crew must follow the instruction of a pilot who had the authority of the flight operation. The managerial implication are discussed in the conclusion part of this paper. As an implication, this paper concluded that it would be necessary to do further research on pilot's leadership and self-efficacy.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.12 no.4
• /
• pp.168-180
• /
• 2000

In the Part I, the three dimensional model testing with NNW deep water wave direction gave the results such that the occurrence of breaking waves over the peak of Ear-Do caused very small wave height at the structure position. But the measured wave forces were rather greater than the calculated forces based on deep water wave height. Furthermore, It was also perceived that the time series of the forces looked like corresponding to the case that waves were superimposed by an unidirectional current. In the present Part II, the current is presumed to be a flow secondly induced by breaking waves, and an extensive study to clarify the current in a quantitative sense is performed through numerical analysis and hydraulic experiment. The results showed that a strong circulation can surely occur in the vicinity of the structure due to radiation stress differentials given by the breaking waves. It was also recognized that the velocity of the induced current varied with the magnitude of energy dissipation rate introduced in the numerical analysis. The numerical analysis was tuned adjusting the dissipation rate so that the calculated wave field could closely match with the experimental results of Part I. The fluid force (in prototype) for the optimal match showed approximately 2.2% increased over the calculated value based on the deep water wave height (24.6m) whereas the force corresponding to the average of the experimental values showed the increase of about 13.0%.