• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1660-1663
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• 2005

Unwanted vibrations are inevitably induced in other directions when pure unidirectional vibration motion is desired for the vertical scratching mechanism. Pure vertical vibration motion of the scratching machine can be obtained by driving identical two motors with symmetrically positioned eccentric unbalance masses. The desired optimal condition for driving pure vertical vibration for the scratching machine is assumed to be the resonance condition in that direction. Imposing the flexibility of the scratching machine in the horizontal direction, we can find out the amount of horizontal vibration component while maintaining the resonance in vertical direction. The desired stiffness in horizontal direction which produces the minimum vibration in horizontal direction are defined which can be used as a guide line to design the supporting structure of the scratching machine.

• Journal of Ocean Engineering and Technology
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• v.38 no.1
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• pp.1-9
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• 2024

The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude's method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.272-277
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• 2007

Generally railway vehicle runs on the rail with endless interaction between wheel and rail. Irregularity of rail causes the periodic motion of the vehicle. In association with this motion, the design of vehicle would be carried out in order to avoid the resonance between car-body and bogie. It may be seen that the first vertical bending mode of car-body contributes considerably to the vertical ride comfort level. In this paper to know the effect of the car-body first vertical bending mode on vertical ride comfort, the mode has been considered with dynamic model. I-DEAS program was used to get the car-body first vertical bending mode and VAMPIRE program was used to analyze ride comfort index(Wz) with FE interface file.

• Wind and Structures
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• v.9 no.1
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• pp.59-74
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• 2006

Vertical stabilizer plates have been found to be an effective aerodynamic measure to improve the aerodynamic stability of bridges either with an open cross section or with a streamlined box cross section in wind tunnel testings and have been adopted in some long span bridges. By taking an open deck II-shaped section and a closed box section as examples, the mechanism of vertical stabilizer plates for improving aerodynamic stability are investigated by using numerical simulation based on Random Vortex Method. It is found that vertical stabilizer plates can increase the amplitude of the heaving motion, and decrease that of the rotational motion of the bridge decks.

• Wind and Structures
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• v.19 no.1
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• pp.89-111
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• 2014

The dynamics of a tornado-like vortex with touching down is investigated by using the LES turbulence model. The detailed information of the turbulent flow fields is provided and the force balances in radial and vertical directions are evaluated by using the time-averaged axisymmetric Navier-Stokes equations. The turbulence has slightly influence on the mean flow fields in the radial direction whereas it shows strong impacts in the vertical direction. In addition, the instantaneous flow fields are investigated to clarify and understand the dynamics of the vortex. An organized swirl motion is observed, which is the main source of the turbulence for the radial and tangential components, but not for the vertical component. Power spectrum analysis is conducted to quantify the organized swirl motion of the tornado-like vortex. The gust speeds are also examined and it is found to be very large near the center of vortex.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.6
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• pp.413-424
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• 2016

The vertical design spectrum for Korea, which is known to belong to an intra-plate region, is developed from the ground motion records of the earthquakes occurred in Korea and overseas intra-plate regions. From the statistical analysis of the vertical response spectra, a mean plus one standard deviation spectrum in lognormal distribution is obtained. Regression analysis is performed on this curve to determine the shape of spectrum including transition periods. The developed design spectrum is valid for the estimation both spectral acceleration and displacement. The ratio of vertical to horizontal response spectrum for each record is calculated. Statistical analysis of the ratios rendered the vertical to horizontal ratio (V/H ratio). Subsequently the ratio between the peak vertical ground acceleration to the horizontal one is obtained.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.5
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• pp.401-406
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• 2020

Continuously monitoring of Horizontal and Vertical movements in vulnerable areas due to earthquakes and volcanic activities is vital. These geohazard activities are the result of a slow deformation rate at the tectonic plate boundaries. The recent development of GPS (Global Positioning System) technology has made it possible to attain a millimeter level changes in the Earth's crust. This study used continuously observed GPS data at the flank of Ol Doinyo Lengai volcanic Mountain to determine crustal motion caused by impinging volcano from mantle convention. We analyzed 8 GPS observed from June 2016 to Dec 2019 using a well-documented Global Kalman Filter GAMIT/GLOBK software. The resulting velocity from GAMIT/GLOBK analysis was then used to compute the relative motion of our study area with respect to Nubia plate. Our analysis discovered a minor motion of less than 5mm/year in both horizontal and vertical components.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.189-196
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• 1996

Vibration of a beam translating over supports in vertical motion is investigated in this paper. Equations of motion are formulated using the virtual work principle by regarding the supports as kinematical constraints imposed on an unrestrained beam and by discretizing the beam via the assumed mode method. Differential-algebraic equations of motion are derived and reduced to differential equations in independent generalized coordinates by the generalized coordinate partitioning method. Geometric stiffness of the beam due to translating motion is considered and how the geometric stiffness of beam affects dynamic stability is also investigated. Instability of the beam. in various conditions is also investigated using Floquet theory and then the results are verified through the dynamic response analysis. Results of numerical simulation are presented for various prescribed motions of the beam.

• Journal of Navigation and Port Research
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• v.38 no.2
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• pp.97-103
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• 2014

In these days, the world has been increasing navy forces such as aircraft carriers and high-tech destroyers etc. and the importance of submarines is being emphasized. Therefore, accurate values of the derivatives in equations of motion are required to control motion of the submarines. Hydrodynamic derivatives were measured by the vertical planar motion mechanism(VPMM) model test. VPMM equipment gave pure heave and pitch motion respectively to the submarine model and the forces and moments were acquired by load cells. As a result, the hydrodynamic derivatives of the submarine are provided through the Fourier analysis of the forces and moments in this paper.

• Journal of the Korea Society of Computer and Information
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• v.27 no.1
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• pp.97-105
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• 2022

The purpose of this study was to analyze the effects of flossing band exercise on the range of motion and vertical jump for taekwondo demonstration athletes with ankle functional instability. The subjects of this study were 21 male Taekwondo Demonstration Team athletes enrolled at D University. They were divided into functional ankle instability group(FAIG, n=7), mild ankle instability group(MAIG, n=7), and ankle stability group(ASG, n=7). All groups performed a acute flossing band exercise program. The results of this study are as follows; dorsi flexion(p<.01), inversion(p<.01), eversion(p<.05) and vertical jump(p<.01) were significantly increased in the FAIG. Flossing band exercise of Taekwondo demonstration team with FAI increased joint range of motion and vertical jump. Therefore, it was confirmed that it could be an intervention that can improve performance and reduce the risk of ankle injury.