• Journal of the Korea Fashion and Costume Design Association
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• v.14 no.1
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• pp.111-121
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• 2012

This study focused on the plane and side drape coefficients of weft knitted fabrics as a function of knit structure, stitch density, and stiffness. Fifteen weft knitted fabrics are produced with five different structures (interlock, single pique, royal interlock, cross miss interlock, and mock royal interlock) and three different gauges (7G, 10G, and 12G). Five knit structures were the application of knit, tuck, and miss stitch on the basis of interlock of the double knit fabric For this purpose, three-dimensional shapes of the draped sample were obtained by using a drapability tester which can record the contour line coordinates of a projected plane drape. Then, projected shapes of the plane and side drape were derived from those three-dimensional ones to review the relationship between plane drape coefficients and side ones. It was found that the theoretical values of plane and side drape coefficients depending on the change of deflection angles fit to their experimental ones. A5 a result of a regression analysis of the relationship between plane and side drape coefficients, the relationship could be expressed as $y=0.5838x-0.0065x^2+9.03{\times}10^{-5}x^3$. In case of mean of drape coefficient, it was increased according to the rule of that the more tuck and miss stitch overlap. A high degree of correlation was found between stiffness and drape coefficient. The regression equation of drape coefficient($y$) can be represented by $y=y=\sqrt[3]{Stiffness}-10.72$.

• Honam Mathematical Journal
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• v.27 no.2
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• pp.317-332
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• 2005

In this paper we consider the hp-version to solve non-constant coefficients elliptic equations on a bounded, convex polygonal domain ${\Omega}$ in $R^2$. A family $G_p=\{I_m\}$ of numerical quadrature rules satisfying certain properties can be used for calculating the integrals. When the numerical quadrature rules $I_m{\in}G_p$ are used for computing the integrals in the stiffness matrix of the variational form we will give its variational form and derive an error estimate of ${\parallel}u-{\widetilde{u}}^h_p{\parallel}_{1,{\Omega}$.

• International Journal of Railway
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• v.9 no.2
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• pp.46-49
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• 2016

In this study a new detection technique based on WAK is introduced that can be used for identifying unstable concrete sleeper installed in ballast by triggering activated wave on the sleeper surface. If a gap exists immediately below the concrete sleeper, static stiffness can be lower than stable case's stiffness. The concrete sleeper is assumed as a single degree of freedom system (SDOF). The static stiffness K can be obtained by iteratively calculated mass (m), stiffness (k) and damping coefficient (c) of SDOF system. Those coefficients are used to specify the ballast condition such as a gap between the sleeper and ballast. Typical test results using a small sleeper model test are summarized and explained for proof of effectiveness of the WAK test for checking unstable condition of the sleeper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1286-1291
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• 2000

A new electro-rheological squeeze film damper (ER SFD) has been sealed with slotted piston rings which have electrodes at the inside of the constant gap. The slotted ER SFD can prevent the problem of electric discharge which might be occurred in the previous configuration of an ER SFD. The current paper presents the extraction of linearized dynamic coefficients within small orbit where these coefficients are controlled by the application of electric strength. Test rig has been modified to isolate the damper section for dynamic coefficient extraction. The results show that rotordynamic coefficients, damping and inertia terms, increase with increasing supply voltages, while stiffness coefficients decrease with increasing supply voltages. Rotating speed of rigid Shaft does not affect these coefficients.

• Journal of KSNVE
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• v.10 no.6
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• pp.1029-1034
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• 2000

A new electro-rheological squeeze film damper (ER-SFD) has been sealed with slotted piston rings which have electrodes at the inside of the constant gap. The slotted ER-SFD can prevent the problem of electric discharge which might be occurred in the previous configuration of an ER-SFD. The current paper presents the extraction of linearized dynamic coefficients within small orbit where these coefficients are controlled by the application of electric strength. Test rig has been modified to isolate the damper section for dynamic coefficient extraction. The results show that rotordynamic coefficients, damping and inertia terms, increase with increasing supply voltages, while stiffness coefficients decrease with increasing supply voltages. notating speed of rigid shaft does not affect these coefficients.

• Tribology and Lubricants
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• v.23 no.3
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• pp.123-129
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• 2007

This paper presents a theoretical model for the analysis of double-bumped AFBs. The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. In the case of a lightly loaded condition where only the upper bump contributes to deformation, the double bump is in the single active region. In the case of a heavily loaded condition where both the upper and lower bumps contribute to deformation, the double bump is in the double active region. So the double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. A static and dynamic performance analysis is carried out by using the finite difference method and the perturbation technique. The results of the performance analysis for a double-bumped AFB are compared with those obtained for a single-bumped AFB. This paper successfully proves that a double bumped AFB has higher load capacity, stiffness, and damping than a single-bumped AFB in a heavily loaded condition.

• Tribology and Lubricants
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• v.30 no.1
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.379-387
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• 2002

This paper presents an analytical model on nonlinear hysteretic behavior of hybrid steel beam with reinforced concrete ends. The modeling method and appropriate coefficients with IDARC2D were proposed from the comparison with previous test results. Since the polygonal model of IDARC2D nay overestimate, new analytical model with the initial stiffness reduction coefficient was proposed. The hysteretic coefficients for the analysis of the hybrid steel beam with reinforced concrete ends were also presented. The analytical results were compared with previous experiments. The initial stiffness and the strength were predicted with less than 5% error and 10% error, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2647-2655
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• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.748-752
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• 2004

Fluid dynamic bearings (FDBs) have been replacing ball bearings of the HDD spindle motor very rapidly. But there are several demerits of HDB, such as high friction torque, variable viscosity of the fluid lubricant depending on operating temperature, low stiffness, and etc. Eccentricity is one of the major parameters which affects the static and dynamic characteristics. As the static eccentricity is larger, the stiffness and the damping coefficients become bigger. But friction torque is relatively unaffected by the static eccentricity. This research proposes a new type of journal bearing with asymmetric journal grooves which results in better dynamic characteristics. The static and dynamic characteristics of the new journal bearing are investigated by solving the Reynolds' equation with FEM, and the transient analysis is performed to predict the dynamic behavior of rotor by solving the equations of motion of a HDD spindle system with Runge-Kutta method. The result shows that the proposed Journal bearings have much bigger stiffness and damping coefficients compared with the conventional symmetric ones. And consequently, it has smaller whirl radius and tilting angle.