• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.121-127
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• 2017

From the perspective of commercializing rotating machines equipped with magnetic bearings, maintaining the error between the mechanical center and the magnetic center within an acceptable level is crucial. The existing method of measuring the center error is to adjust the position references that minimize the current imbalance present in levitation control outputs. However, this method can be applied only after all the components of the system are operational. In this paper, we present a new method of estimating the center error by using only the position sensors and a current source. A force model that relates the position of the rotor with the coil currents is set up. Using this model, the center error is estimated by minimizing the difference between the force angles and the contact angles measured in a pull test. The feasibility of the method is numerically and experimentally validated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.10
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• pp.823-832
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• 2014

Displaced non-Keplerian orbit, center of mass is displaced from orbit plane, enables special spacecraft missions. It requires continuous thrust to maintain the orbit, and solar sail is useful for this purpose. Equations for feasible region and stability analysis are derived for non-Keplerian orbit for general continuous thrust. Differences for solar sail spacecraft are discussed. Non-keplerian orbits are classified into four types. Location-specific required accelerations for orbit maintenance are calculated. Orbit stabilities of each orbit type are analyzed and verified by numerical simulations. In order to control non-Keplerian orbit in unstable region, a control algorithm using the real-time LQR control is developed and evaluated by numerical simulations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.94-100
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• 2002

This paper is concerned with the development, and performance test of LIPCA (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuators. LIPCA is composed of top fiber composite layers with a high modulus and low CTE (Coefficient of Thermal Expansion), a middle PZT cermaic wafer, and base layers with a high modulus and high CTE. The performance of each actuator was evaluated using an actuator test system consisting of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. The simply supported condition actuator was excited by the power supplier with 1.0Hz cycle and up to $100\sim400V_{pp}$. The displacement at the center point of actuator was measured with non-contact laser displacement measuring system, It has been shown that the LIPCA-C2 can 34% decrease in mass and 13% increase in displacement compared to THUNDER.

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.133-149
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• 2000

The study area which contains the coastal terrace of the southeastern part of Korean peninsula, well developed the lineaments which are NNE, NE and WNW directions. The area crops out Cretaceous sedimentary rocks and granite porphyry, Tertiary conglomerate, tuffite and basalt and Quarternary deposits. Coastal terraces are subdivided into low, middle and upper terraces(LT, MT, UT) based on the topographic levels. Terrace gravels are deposited on these wave-cut erosional surface during the initial lowering stage of sea level fluctuation. Terrace gravels are typified by granule to pebble layers with slightly inclined beddings. These gravels are interpreted as beach gravels belonging to berm or swash zone based on the present distribution of beach gravels. The Suryum fault is characterized by the thrust which is gradationally changing the strike from ENE to NNE. The extension of the fault is about 200m and Maximum displacement is about 1.5m.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.6
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• pp.67-74
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• 2010

Because of the difference between the actual and computed eccentricity of buildings, symmetrical buildings will be affected by torsion. In provisions, accidental eccentricity is intended to cover the effect of several factors, such as unfavorable distributions of dead- and live-load masses and the rotational component of ground motion about a vertical axis. The torsional amplification factor is introduced to reduce the vulnerability of torsionally imbalanced buildings. The effect of the torsional amplification factor is observed for a symmetric rectangular building with various aspect ratios, where the seismic-force-resisting elements are positioned at a variable distance from the geometrical center in each direction. For verifying the torsional amplification factor in provisions, nonlinear reinforced concrete models with various eccentricities and aspect ratios are used in rock. The difference between the maximum displacements of the flexible edge obtained between using nonlinear static and time-history analysis is very small but the difference between the maximum torsional angles is large.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.27-37
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• 2011

A series of centrifuge model tests to investigate the suction pile pullout loading capacity in sand have been performed. The main parameters that affect the pullout loading capacity of a suction pile include the mooring line inclination angle and the padeye position of the suction pile. With respect to the padeye position, the maximum pullout loading capacity is obtained when the padeye position is near 75% of the pile length from the top. The direction of the pile rotation changes when the padeye position reaches somewhere near 50~75% for all mooring line inclination angles. The translation displacement of suction pile to develop the time of maximum pullout loading capacity decreased as the mooring line inclination angle increased. In addition, the vertical displacements of the center of a suction piles for all cases appeared to develop toward the ground surface.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.259-267
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• 1997

Wind tunnel test results and their interpretations focused on the behavior of girder, which were performed to study the aerodynamic stability of a self-anchored suspension bridge with lateral sag of main cable, are presented in this paper The shape of the girder which has the best aerodynamic stability was selected based on the section model test under uniform and turbulent flow conditions. Good performance of the selected section was confirmed in the full bridge model test. Measured flutter derivatives are presented for further study. Buffeting response was investigated to check the fatigue problem and serviceability of the bridge but it was found to be acceptable from the engineering point of view. Even though the drag coefficient of the girder had high value, the amplitude of the lateral vibration was found to be very low. This may be due to the restraint provided by the lateral sag of the cables.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.193-203
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• 2004

Arching effects in backfill materials generate a nonlinear active earth pressure distribution on a rigid retaining wall with rough face, and arching effects on the shape of the nonlinear earth pressure distribution depends on the mode of wall movement. Therefore, the practical shape of failure surface and arching effect in the backfill changed with the mode of wall movement must be considered to calculate accurate magnitude and distribution of active earth pressure on the rigid wall. In this study, a new formulation for calculating the active earth pressure on a rough rigid retaining wall rotating about the base is proposed by considering the shape of nonlinear failure surface and arching effects in the backfill. In order to avoid mathematical complexities in the calculation of active earth pressure, the imaginary failure surface composed of four linear surfaces is used instead of the nonlinear failure surface as failure surface of backfills. The comparisons between predictions from the proposed equations and existing model test results show that the proposed equations produce satisfactory predictions.

• Korean Journal of Applied Biomechanics
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• v.19 no.3
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• pp.425-433
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• 2009

The purpose of this study was to investigate relation between fastball motion and longtoss motion, and the kinematical analysis using APAS(Ariel Performance Analysis System). Eight people(age: $21.2{\pm}3.6years$, height: $177.1{\pm}3.1cm$, weight $68.6{\pm}2.5kg$) participated in the experiment. Followings are the conclusion. In displacement of fore-aft on COG(Center of Gravity), fastball motion moved more forward than longtoss motion. In displacement of vertical on COG(Center of Gravity), fastball motion was lower than longtoss motion In velocity of right hand, greater release velocity was measured for fastball motion than for longtoss motion. In displacement of elbow and shoulder joint, more extended displacement was exhibited in fastball motion than longtoss motion. In displacement of trunk tilt, fastball motion showed foreward tilt, longtoss motion showed backward tilt. In stride, fastball showed longer than longtoss.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.481-487
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• 2020

In this study, finite element analysis was performed to evaluate the track irregularity of the existing track system on urban transit according to the large-scale excavation work that is constructed adjacent to the serviced line. Based on the numerical analysis, the effect of track irregularity generated during the step-by-step construction process was analytically derived, and the stability in terms of track deformation was evaluated through comparison with related standards. As the results, in the case of track irregularity items evaluated based on the relative displacement difference at a certain distance, such as alignment and vertical irregularity, it occurred most clearly at the location where deformation of the existing structure begins, such as the end point of adjacent excavation work. On the other hand, the overall vertical and horizontal displacement of the track was the largest deformation at the center of the construction section. The vulnerable position of the deformed side of the existing structure due to adjacent excavation is analytically proven that the both of the end point section and the center of the construction can be a vulnerable position in terms of track irregularity.