• KSCE Journal of Civil and Environmental Engineering Research
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• 제28권5D호
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• pp.649-654
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• 2008

In the definition of non additive path, the sum of travel costs of links making up the path is not equal to the path cost. There are a variety of cases that non-additivity assumption does not hold in transportation fields. Nonetheless, traffic equilibrium models are generally built up on the fundamental hypothesis of additivity assumption. In this case traffic equilibrium models are only applicable within restrictive conditions of the path cost being linear functions of link cost. Area-wide road pricing is known as an example of realistic transportation situations, which violates such additivity assumption. Because travel fare is charged at the moment of driver's passing by exit gate while identified at entry gate, it may not be added linearly proportional to link costs. This research proposes a novel Wordrop type of traffic equilibrium model in terms of area-wide road pricing schemes. It introduces binary indicator variable for the sake of transforming non-additive path cost to additive. Since conventional shortest path and Frank-Wolfe algorithm can be applied without route enumeration and network representation is not required, it can be recognized more generalized model compared to the pre-proposed approaches. Theoretical proofs and case studies are demonstrated.

• Proceedings of the KSME Conference
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.56.2-56.2
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• 2005

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.52-53
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• 2003

• Proceedings of the KSME Conference
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2684-2689
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• 2007

Non-equilibrium first order extrapolation boundary condition proposed by Guo et $al.^{(9)}$ proposed has a good application for complex geometries, a second order accuracy and a treatment on non-slip wall boundary condition easily. However it has a lack of the numerical stability from high Reynolds number. Guo et $al.^{(9)}$ substituted the density value of adjacent nodes for the density of boundary nodes. This procedure causes the numerical instability on the boundary. In this paper, we derived a procedure of density extrapolation and compared to previous results.

• Journal of Korean Society of Environmental Engineers
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• 제27권10호
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• pp.1043-1051
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• 2005

In this stduy, adsorption and transport characteristics of Fe in the soil were investigated using convection-dispersion local equilibrium sorption model and two-site non-equilibrium sorption model. In batch experiments with different Fe concentration, characteristics of Fe adsorption was investigated using Freundlich and linear isotherm. Column experiments with different flow rate, organic matter content md Fe concentration were also carried out. We measured Fe concentrations in injection-liquid and in effluent, and then applied them to CXTFIT program. As a result of column experiments, some parameters(D, R, ${\beta}$, ${\omega}$) used in two-site non-equilibrium adsorption model were obtained. Characteristics of Fe transport were analyzed using the parameters(D, R, ${\beta}$, ${\omega}$) obtained from the CXTFIT program, Consequently, characteristics of Fe transport in the soil were predicted through two-site non-equilibrium adsorption model.

• Journal of applied mathematics & informatics
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• 제30권3_4호
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• pp.365-380
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• 2012

Non-negative matrix factorization (NMF) is a very efficient method to explain the relationship between functions for finding basis information of multivariate nonnegative data. The multiplicative update (MU) algorithm is a popular approach to solve the NMF problem, but it fails to approach a stationary point and has inner iteration and zero divisor. So the elementwisely alternating projected gradient (eAPG) algorithm was proposed to overcome the defects. In this paper, we use the fact that the equilibrium point is stable to prove the convergence of the eAPG algorithm. By using a classic model, the equilibrium point is obtained and the invariant sets are constructed to guarantee the integrity of the stability. Finally, the convergence conditions of the eAPG algorithm are obtained, which can accelerate the convergence. In addition, the conditions, which satisfy that the non-zero equilibrium point exists and is stable, can cause that the algorithm converges to different values. Both of them are confirmed in the experiments. And we give the mathematical proof that the eAPG algorithm can reach the appointed precision at the least iterations compared to the MU algorithm. Thus, we theoretically illustrate the advantages of the eAPG algorithm.

• Journal of computational fluids engineering
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• 제20권3호
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• pp.1-7
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• 2015

When the steam is used as working fluid in fluid machinery, different from other gases as air, phase transition (steam condensation) can occur and it affects not only the flow fields, but also machine performance & efficiency. Therefore, considering phase transition phenomena in CFD calculation is required to achieve accurate prediction of steam flow and non-equilibrium wet-steam model is needed to simulate realistic steam condensing flow. In this research, non-equilibrium wet-steam model is implemented on in-house code(T-Flow), the flow fields including phase transition phenomena in convergent-divergent nozzle are studied and compared to results of advance researches.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제31권7호
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• pp.620-627
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• 2007

In this paper, we adapt a modified internal energy non-equilibrium first-order extrapolation thermal boundary condition to the thermal lattice Boltzmann model (TLBM). This model is the double populations approach to simulate hydrodynamic and thermal fields. The bounce-back boundary condition which is a traditional boundary condition of lattice Boltzmann method has only a first order in numerical accuracy at the boundary and numerical instability. A non-equilibrium first-order extrapolation boundary condition has been verified to be of better numerical stability than the bounce-back boundary condition and this boundary condition is proved to be of second-order accuracy for the flat boundaries. The two-dimensional natural convection flow in a square cavity with Pr=0.71 and various Rayleigh numbers are simulated. The results are found to be in good agreement with those of previous studies.

• The Bulletin of The Korean Astronomical Society
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• 제36권2호
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• pp.114.1-114.1
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• 2011

We present the near-infrared spectra (2.5-5.0 um) of shocked $H_2$ gas, observed with the InfraRed Camera onboard the satellite AKARI. Two supernova remnants, IC 443 and HB 21, were observed, and they all showed the ortho-to-para ratios (OPRs) of less than 3.0: 2.1-2.2 for IC 443 and 1.6-1.8 for HB 21. These non-equilibrium OPRs are first reported at E(v,J) > 7000 K, as far as we are aware of. Based on our previous study, we try to interpret that the non-equilibrium OPRs originate from dissociative J-shocks. Dissociative J-shocks mainly generate infrared H2 emissions from their $H_2$ reformation zone, and the OPR of 3.0 are expected for the reformed $H_2$ from the theoretical study. This is contradictory to our observational results. We propose other possible origins of the non-equilibrium OPRs, such as, abnormal $H_2$ reformation, partially dissociative J-shocks, etc.

• Advances in aircraft and spacecraft science
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• 제8권1호
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• pp.1-15
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• 2021

Mars exploration demands aerodynamic computations for a proper design of missions of spacecraft carrying instruments and astronauts to Mars. Both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) method play a key role for this purpose. To the author's knowledge, the altitude separating the fields of applicability of CFD and DSMC in Mars atmosphere entry is not yet clearly defined. The limitations in using DSMC at low altitudes are due to technical limitations of the computer. The limitations in using CFD at high altitudes are due to thermodynamic non-equilibrium. Here, this problem is studied in Mars atmosphere entry, considering the Mars Pathfinder capsule in the altitude interval 40-80 km, by means of a DSMC code. Non-equilibrium is quantified by the relative differences between translational temperature and: rotational (θt-r), vibrational (θt-v), overall (θt-ov) temperatures, anisotropy is quantified by the relative difference between the translational temperature component along x and those along y (θx-y) and along z (θx-z). The results showed that θt-r, θt-v, θx-y, θx-z are almost equivalent. The altitude of 45 km should be the limit altitude for a proper use of a CFD code and the altitude of 40 km should be the limit altitude for a reasonable use of a DSMC code.