• Journal of Electrical Engineering and Technology
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• v.1 no.2
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• pp.161-169
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• 2006

Load representation has a significant impact on power system analysis and control results. In this paper, composite load models are developed based on on-line measurement data from a practical power system. Three types of static-dynamic load models are derived: general ZIP-induction motor model, Exponential-induction motor model and Z-induction motor model. For the dynamic induction motor model, two different third-order induction motor models are studied. The performances in modeling real and reactive power behaviors by composite load models are compared with other dynamic load models in terms of relative mismatch error. In addition, numerical consideration of ill-conditioned parameters is addressed based on trajectory sensitivity. Numerical studies indicate that the developed composite load models can accurately capture the dynamic behaviors of loads during disturbance.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.119-119
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• 1998

The purpose of this study is to investigate the effects of operation factors of a typical main spindle system on the efficiency of machine tool. In this study. both static and dynamic analysis of typical main spindle system of the machine tool are performed using a finite element method. These finite element results are then used to predict the bearing stiffness. the amount of heat generation as well as the bearing life in the spindle system. Effects of material type of ball-bearing. bearing-lubricant type and main spindle bearing preload are examined.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11a
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• pp.1-26
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• 2002

This study addresses preliminary design and construction specification for micropiles. Especially several design methods for micropiles in sands, clays or mixed soil layers are described. The bearing capacity of micropiles are mainly depended upon the shaft resistance. Therefore, the pressure of grouting is one of the most important design parameters for the bearing capacity evaluation of micropile. There is no theoretical way to evaluate the shaft resistance of micropile up to now because grouting method is another key parameter for micropile design approach. Because of above reasons, the present design approaches of the micropile are based on the collected field data The bearing capacities of designed micropiles should be verified by static load tests before and after construction at the planned site.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.156-161
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• 1999

new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under a13 bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number)0.01, we can not ignore the effect of slip for journal bearing.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.162-169
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• 1999

Herringbone groove journal bearing (HGJB) is developed to improve the static and dynamic performances of hydrodynamic journal bearing. Conventional studies on HGJB were based on the Narrow Groove theory assuming that the number of grooves approaches infinity. In this study, an oil lubricated HGJB is analyzed using Finite Element Method. Load carrying capacity, attitude angle, stiffness and damping coefficients are obtained numerically for various bearing configurations especially for the inclined width ratio and asymmetric ratio and compared with the results obtained using Finite Volume Method. The bearing load and stability characteristics are dependent on geometric parameters such as inclined width ratio, asymmetric ratio, groove depth ratio, groove width ratio, groove angle.

• Tribology and Lubricants
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• v.19 no.3
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• pp.139-145
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• 2003

In this paper, static characteristics of a cryogenic hydrostatic journal bearing which has 2-rows staggered recesses are numerically analyzed. The regime of operation of this bearing is fully turbulent with large fluid inertia effects. The turbulent lubrication equation is solved under the assumption that turbulence parameters are decided by the Reynolds numbers. Pressure drop caused by inertia effect at the recess edge is considered in this analysis. Also density and viscosity of working fluid are considered as function of only pressure. Numerical results for a cryogenic Hydrostatic journal bearing show pressure distribution, load capacity, flow rate, and recess pressure. The effects of turbulent flow, pressure drop and variable liquid properties are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.421-426
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• 2010

With hydraulic noise test facility, a variety of tests were performed to investigate the pulsation pressure generation mechanism and its transmission characteristics and to derive the noise control methodology. Many experiments were carried out by changing average pressure, flow rate, pump speed, hose length and MCV spool condition. From the test results, the correlations between pulsation pressure and other design parameters, such as static pressure, flow rate and MCV spool opening area and length of hose, were found out. And also each contribution factors were evaluated from the regression analysis. By changing hose length, the pulsation pressure resonance phenomenon was investigated. In order to find out the pulsation pressure reduction measures pulsation pressure analysis, such as pulsation pressure of hydraulic pump itself and pulsation pressure of hydraulic system, by using AMESim were studied. In addition hydraulic silencer was developed based on the Helmholtz resonator. And its performance was evaluated by installing the silencer at the excavator.

• Earthquakes and Structures
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• v.1 no.1
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• pp.129-146
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• 2010

This paper proposes an approximate procedure to estimate seismic displacement capacity - defined as yield displacement times the displacement ductility - of piles in marine oil terminals. It is shown that the displacement ductility of piles is relatively insensitive to most of the pile parameters within ranges typically applicable to most piles in marine oil terminals. Based on parametric studies, lower bound values of the displacement ductility of two types of piles commonly used in marine oil terminals - reinforced-concrete and hollow-steel - with either pin connection or full-moment-connection to the deck for two seismic design levels - Level 1 or Level 2 - and for two locations of the hinging in the pile - near the deck or below the ground - are proposed. The lower bound values of the displacement ductility are determined such that the material strain limits specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) are satisfied at each design level. The simplified procedure presented in this paper is intended to be used for preliminary design of piles or as a check on the results from the detailed nonlinear static pushover analysis procedure, with material strain control, specified in the MOTEMS.

• Structural Engineering and Mechanics
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• v.14 no.6
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• pp.661-677
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• 2002

The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

• Structural Engineering and Mechanics
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• v.20 no.6
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• pp.713-726
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• 2005

Based on the improved first order Taylor interval expansion, a new interval analysis method for the static or dynamic response of the structures with interval parameters is presented. In the improved first order Taylor interval expansion, the first order derivative terms of the function are also considered to be intervals. Combining the improved first order Taylor series expansion and the interval extension of function, the new interval analysis method is derived. The present method is implemented for a continuous beam and a frame structure. The numerical results show that the method is more accurate than the one based on the conventional first order Taylor expansion.