• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.875-882
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• 2002

The modeling for turbulent flow through a porous media has not been confirmed because of a undetermined constant which appears in the governing equations. In present study, the turbulent porous modeling based on the local thermal equilibrium has been extended to the turbulent clear flow. A undetermined constant is also suggested by microscopic analysis. The microscopic analysis is performed in the flat tube with micro-channels, and it confirms that the undetermined constant is 0.99. It is shown that the results of the macroscopic analysis using confirmed constant agree well with those of the microscopic analysis with a maximum error of 3.5%.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.441-450
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• 2004

The velocity distribution of gas molecules from the experimental results was confirmed as the same with the Maxwell-Boltzmann's theoretical results within the experimental error. This study is on the realization of the Maxwell-Boltzmann's velocity distribution of gas molecules by the molecular dynamics(MD) method. The Maxwell-Boltzmann's velocity distribution of gas molecules is extremely important to confirm the equilibrium state because the properties of a thermodynamic system shall be obtained from the system's equilibrium configuration in the MD method. This study is the first trial in the successive researches to calculate the properties of a thermodynamic system by the computer simulations. We confirmed that the maxwell-boltzmann's velocity distribution is developed in some transient time after starting a simulation and dependent on the size of a system. Also it is found that the velocity distribution has no relation with an initial configuration of gas molecules.

• Journal of KSNVE
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• v.9 no.3
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• pp.621-628
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• 1999

The fundamental dynamic properties of the planar electric charged particle are investigated experimentally. The experiment is conducted using electric charged spheres(4 table tennis balls with conductive surfaces) suspended by insulating strings to cancel the gravitational force. The measurements of the equilibrium angles and the natural frequencies of oscillation agree well with the analytical predictions with some error, respectively.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.395-402
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• 1999

This paper discusses the theoretical researches subject to elastic buckling problems of the structures. The purpose is to ensure the characteristic of buckling be true by arc-length method and the finite element method. The difficulties in processes calculating the equilibrium curve after buckling is to get the equilibrium owe near singular point at which the determinant of stiffness matrix is zero. The purpose of the load-displacement curve is to determine the buckling load of the structure, and further to get the information about the characteristic after buckling. Here, this paper expresses the incremental solution at particular point by the linear combination of both homogeneous mode and particular mode, then uses the method which gets the unknown parameter including this function, through trial-and-error method including modified N-R convergence process. Finally, this paper describes the multiple bifurcation of truss dome as the numerical examples according to this algorithm.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.8
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• pp.482-491
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• 2003

In this paper are presented kinematic and dynamic modeling and path-tracking of four-wheeled mobile robots with 2 d.o.f haying the limited drive-torques. Controllability of wheeled-mobile robots is revealed by the kinematic model. Instantaneously coincident coordinate system, force/torque propagation and Newton's equilibrium law are used to drive the dynamic model. When drive-torques generated by inverse dynamics exceed the limitation, we make wheeled-mobile robots follow the reference path by modifying the planned reference trajectory with time-scaling. The controller is introduced to compensate for error owing to modeling uncertainty and measurement noise. And simulation results prove that method proposed by this paper is efficient.

• Analytical Science and Technology
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• v.22 no.2
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• pp.159-165
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• 2009

The thermochromism of fluoran has been examined. The DCF exists as a colorless lactone in aprotic solvents. However, the DCF exists in the form of an equilibrium mixture of a colored zwitter-ion and a colorless lactone in protic solvents. When an acid is added to the solution, the DCF exists an equilibrium mixture as a colorless lactone and a colored cation even in aprotic solvents. In order to understand the interaction between the DCF and the solvent, absorption spectra of the DCF in various solvents were measured. The thermodynamic parameters of the DCF have also been investigated. From the variation of absorbance with temperature, the standard enthalpy changes ${\Delta}H^0$ of the equilibrium between the lactone and the zwitter-ion in various solvents have been determined. The standard enthalpy change ${\Delta}H^0$ is approximately -2.0 kJ/mol in protic solvents. In acidic solution, the standard enthalpy change is measured to be to zero in protic solvents within the experimental error. When the carboxylic group is protonated in acidic solution, a poor interaction between the dye and the solvent is expected.

• Korea Trade Review
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• v.43 no.5
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• pp.159-177
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• 2018

The container shipping sector is an important international logistics operation that connects open economies. Freight rates rapidly change as the market fluctuates, and staff related to the shipping market are interested in factors that determine freight rates in the container market. This study uses the Vector Error Correction Model(VECM) to estimate the impact of factors affecting container freight rates. This study uses data published by Clarksons. The analysis results show a 4.2% increase in freight rates when world container traffic increases at 1.0%, a 4.0% decrease in freight rates when volume of container carriers increases by 1.0%, a 0.07% increase in freight rates when bunker price increases by 1.0%, and a 0.04% increase in freight rates accompanying 1.0% increase in libor interests rates. In addition, if the current freight rate is 1.0% higher than the long-term equilibrium rate, the freight rate will be reduced by 3.2% in the subsequent term. In addition, if the current freight rate is 1.0% lower than the long-term equilibrium rate, the freight rate will decrease by 0.12% in the following term. However, the adjusting power in a period of recession is not statistically significant which means that the pressure of freight rate increase in this case is neglectable. This research is expected to contribute to the utilization of scientific methods in forecasting container freight rates.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.692-695
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• 2000

This paper is concerned with Accuracy Design of LM Guide System in Machine Tools. Elastic deformation of bearing is calculated by Hertz contact theory and motion error of LM block is analyzed. A new algorithm using block stiffness is proposed fur the analysis of motion accuracy of the table. The best advantage of this algorithm is fast analysis speed because it isn't necessary iteration processes for satisfying equilibrium equation of the table. Motion errors of the table analyzed under artificial form error of rail theoretically and experimentally. Only one of two rails is bent by putting a thickness gauge into horizontal direction. This form error of rail is measured by gap sensor against the other rail. Then, motion errors of the table are predicted by proposed new algorithm theoretically and measured by laser interferometer. Measurements are carried out by changing the preload and thickness. The results show that the table motion errors are reduced from 1/2 to 1/60 times than form error of rail according to its height and width. And the effect of preloading is almost negligible.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.3
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• pp.285-291
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• 2011

The error motion of a machine tool spindle directly affects the surface errors of machined parts. The error motions of the spindle are not desired errors in the three linear direction motions and two rotating motions. Those are usually due to the imperfect of bearings, stiffness of spindle, assembly errors, external force or unbalance of rotors. The error motions of the spindle have been needed to be decreased to desired goal of spindle's performance. The level of error motion is needed to be estimated during the design and assembly process of the spindle. In this paper, the estimation method for the five degree of freedom (5 D.O.F) error motions of the spindle is suggested. To estimate the error motions of the spindle, waviness of shaft and bearings, external force model was used as input data. And, the estimation models are considering geometric relationship and force equilibrium of the five degree of the freedom. To calculate error motions of the spindle, not only imperfection of the shaft, bearings, such as rolling element bearing, hydrostatic bearing, and aerostatic bearing, but also driving elements such as worm, pulley, and direct driving motor systems, were considered.

• The Korean Journal of Financial Management
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• v.12 no.2
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• pp.207-219
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• 1995

This paper develops an equilibrium asset pricing model with taxation in the economy. The expected excess rate of return on a risky asset is shown to be an increasing function of the covariance of asset return with aggregate consumption rate changes and the covariance of asset return with the tax rates as well. Thus, the expected execss rate of return can be decomposed as the consumption risk premium and the tax premium. The capital asset pricing model derived in the absence of taxes is shown to understate the expected excess rate of return and to have a misspecification error in the economy with taxation.