• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.45-55
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• 1999

Wave-induced response, liquefaction and stability of unsaturated seabed are studied. The unsaturated seabed is modeled as a fluid-filled polo-elastic medium. The coupled process of fluid flow and the deformation of soil skeleton is formulated in the framework of Biot's theory. The resulting governing equations are solved using a semi-analytical method to evaluate the stresses and pore water pressure of unsaturated and multi-layered seabed. The semi-analytical method can be applied to calculate a pore pressure and the stresses of in anisotropic inhomogeneous seabed. The results indicate that the degree of saturation influences mostly on the magnitudes of a pore pressure and the stresses of unsaturated and multi-layed seabed. Based on the pore pressure and stresses in seabed, the analysis on the possibilities of liquefaction and shear failure was performed. The results show that the maximum depth of shear failure occurrence is deeper than the maximum liquefaction depth.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.405-412
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• 2015

This paper represents a filter design to estimate the airspeed of a spin-stabilized, trajectory-correctible artillery ammunition. Due to the limited power and space in operational point of view, the airspeed sensor is not installed, and thus the airspeed need to be estimated using limited sensor measurements. The only IMU measurements(three-axis specific forces and angular rates) are used in this application. The extended Kalman filter algorithm is applied since a linear filter can not cover the its wide operational range in airspeed and altitude. In the implementation of the EKF, the state and measurement equations are transformed into the no-roll frame for simple form of Jacobian matrix. The simulation study is conducted to evaluate the performance of the filter under various environment conditions of sensor noise and wind turbulence. In addition, the effect of the choice in filter design parameters, i.e. process error covariance matrices is analyzed on the performance of the estimation of airspeed and angular rates.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1165-1173
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• 1997

The steady state close-contact melting phenomenon occurring between a phase change material and an isothermally heated flat plate with relative motion is investigated analytically, in which the effects of vertical convection in the liquid film and solid-liquid density difference are incorporated simultaneously. Not only the scale analysis is conducted to estimate a priori qualitative dependence of system variables on characteristic parameters, but also an analytical solution to a set of simplified model equations is obtained to specify the effects under consideration. These two results are consistent with each other, in that the vertical convection affects both the solid descending velocity and the film thickness, and that the density difference alters only the solid descending velocity. While the effect of vertical convection can be characterized conveniently by a newly introduced temperature gradient factor which asymptotically approaches the unity/zero with decreasing/increasing the Stefan number, that of density difference is represented by the liquid-to-solid density ratio. It is shown that the solid descending velocity depends linearly on the density ratio, and that the ratios of solid descending velocity, film thickness and friction coefficient to the conduction solution are proportional to 3/4, 1/4 and -1/4 powers of the temperature gradient factor, respectively. Also, established is the fact that the effect of convection can be legitimately neglected in the analysis for the range of the Stefan number less than 0.1.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.251-258
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• 2005

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings (HDB) in an HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Reynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigen value problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.572-578
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• 2003

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings in a HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Raynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigenvalue problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• 한국해양학회지
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• v.17 no.2
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• pp.41-50
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• 1982

We present theoretical models for the unstedy transports driven by the time-varying wind stress in horizontally unbounded shallow seas of an uniform depth. We derive linearized transport equations that inchude the acceleration, the Coriolis firce, the wind stress and the bottom friction. The steady transport in a shallow sea is different from the classical Ekman transport because of a presence of non-negligible bottom fricttttion. The transient reansport and an inertial oscillation of which frequency of rotation is the same as the frequency of the wind stress forcing. The transprt associated with a wind stress of which direction changes linearlywith time is decribed by a superpoeition so a free inertial oscillation with a pweiod of one inertial day, The theoretical models of the transports are useful in understanding the time-varying currents and the transports of nutrients in shallow seas.

• Journal of the Korean Geotechnical Society
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• v.33 no.6
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• pp.27-36
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• 2017

Gravel compaction pile method has been widely used to improve the soft ground on the land or sea as one of the soft ground improvement technique. The ultimate bearing capacity of the ground reinforced by gravel compaction piles is affected by the soil strength, the replacement ratio of pile, construction conditions, and so on, and various prediction equations have been proposed to predict this. However, the prediction of the ultimate bearing capacity using the existing models has a very large error and variation, and it is not suitable for practical design. In this study, multiple regression analysis was performed using field loading test results to predict the ultimate bearing capacity of ground reinforced by gravel compaction pile, and the most efficient input variables are selected through evaluation of error by leave one out cross validation, and a multiple regression equation for the prediction of ultimate bearing capacity was proposed. In addition, the prediction error was evaluated by applying artificial neural network using the selected input variables, and the results were compared with those of the existing model.

• Journal of the Korean Chemical Society
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• v.48 no.3
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• pp.236-242
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• 2004

The critical micelle concentration (CMC) and the counterion binding constant (B) in a mixed micellar state of the Dodecylpyridinium chloride (DPC) with the Cetyldimethylethylammonium bromide (CDEAB) at 25$^{\circ}C$ in aqueous solutions of n-butanol were determined as a function of ${\alpha}_1$ (the overall mole fraction of DPC) by the use of electric conductivity method. Various thermodynamic parameters (($X_i,\;{\gamma}_i,\;C_i,\;a^M_i,\;{\beta},\;and {\Delta}H_{mix})$were calculated by means of the equations derived from the nonideal mixed micellar model. The effect of n-butanol on the mixed micellization of the DPC/CDEAB mixtures has been also studied by analyzing the measured and calculated thermodynamic parameters (CMC, B 및 $;{\Delta}G_o\;^m$).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.729-732
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• 2010

The present study has been motivated by the development of a reliable numerical methodology for simulation of kerosene/LOx coaxial swirl injectors. To deal with thermodynamic non-ideality and anomalies of transport properties pronounced at supercritical pressures, a set of subroutine libraries has been constructed based on the cubic equations of state, and applied to an existing flamelet analysis code. For computational efficiency, two-dimensional axisymmetric RANS formulation with swirl was adopted and validated successfully against an isothermal coaxial swirling jet. For the actual problem with high pressure combustion, however, numerical results show that the RANS models yield excessive production of turbulence probably due to high density gradient magnitude in the vicinity of mixing layer of swirling film flow, and imply strongly further improvement of the turbulence models.

• Journal of the Korean Institute of Gas
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• v.22 no.1
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• pp.1-8
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• 2018

FCV is installed with a automatic valve attached in an high pressure cylinder to control the hydrogen flow. The supply of hydrogen from the cylinder into the fuel cell stack is controlled via the on/off operation of a solenoid attached to the automatic valve. The solenoid needs to provide the necessary attraction force even at any saturation temperature caused by drive of the vehicle. In this study, the simplified prediction equations for the saturation temperature are suggested. The finite element analysis was performed by steady state technique, according to the boundary condition in order to predict the saturation temperature and attraction force. Finally, the saturation temperature was validated through comparison between the analysis results and measurement results. From the results, the measured saturation temperature $5.9^{\circ}C$ lower with respect to the analysis results. And the error of attraction force ranged from 1.0 to 2.1 N at testing conditions.