• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.9-18
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• 2016

The slender structures such as high rise building or marine riser are highly susceptible to dynamic force exerted by fluid-structure interactions among which vortex-induced vibration(VIV) is the main cause of dynamic unstability of the structural system. If VIV occurs in natural frequency regime of the structure, fatigue failure likely happens by so-called lock-in phenomenon. This study presents the numerical analysis of dynamic behavior of both structure and fluid in the lock-in regimes and investigates the subjacent phenomena to hold the resonance frequency in spite of the change of flow condition. Unsteady and laminar flow was considered for a two-dimensional circular cylinder which was assumed to move freely in 1 degree of freedom in the direction orthogonal to the uniform inflow. Fluid-structure interaction was implemented by solving both unsteady flow and dynamic motion of the structure sequentially in each time step where the fluid domain was remeshed considering the movement of the body. The results show reasonable agreements with previous studies and reveal characteristic features of the lock-in phenomena. Not only the lift force but also drag force are drastically increasing during the lock-in regime, the vertical displacement of the cylinder reaches up to 20% of the diameter of the cylinder. The correlation analysis between lift and vertical displacement clearly show the dramatic change of the phase difference from in-phase to out-of-phase when the cylinder experiences lock-in. From the results, it can be postulated that the change of phase difference and flow condition is responsible for the resonating behavior of the structure during lock-in.

• Korean Journal of Applied Biomechanics
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• v.16 no.1
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• pp.31-41
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• 2006

The primary purpose of a TKA is to restore normal knee function Therefore, ideally, a TKA should: (a) maintain the natural leverage of the knee joint muscles to ensure generating adequate knee muscle moments to accomplish daily tasks such as rising from climbing stairs; (b) provide adequate knee joint stability. A 16-channel MyoResearch XP EMG system was used to collect the differential input surface electromyography signals VM, VL, RF, BF, ST during climbing/descending stair tests. A Peak Motion Measurement System was used to collect the kinematic and kinetic data. AKIN-COM Ill isokinetic dynamometer was used for EMG of VM, VL, RF, BF and ST during maximal voluntary contraction. I Quadriceps EMG results for the VM of the passed 1year group limb demonstrated significant less RMS EMG than that of the passed 3year group limb $60^{\circ}-15^{\circ}$ of knee flexion(p<0.05). The VL of the passed 1year group limb also demonstrated significants less RMS EMG than that of the passed 3year group limb from $60^{\circ}-45^{\circ}$ of knee flexion(p<0.05). Similar to the VM and VL, the RF of the passed 1year group limb showed less RMS EMG than that of the passed 3year group limb from $60^{\circ}-30^{\circ}$ do knee flexion(p<0.05). Hamstring EMG results for the BF of the passed 1year group limb demonstrated less RMS EMG than that of the passed 3year group limb from $75^{\circ}-15^{\circ}$ of knee flexion(p<0.05). The passed 1year group limb tended to have less ADD displacement(p<0.071) than that of the passed 3year group limb. There was no significant difference of the ABD displacement between the passed 1year group and the passed 3year group limbs(p<0.73). The passed 3year group used compensatory adaptation movement strategies to compensate for the strength deficit of passed 3year group limbs. The passed 3year group limb also increased the quadriceps muscle activation level to produce more knee extension moment to compensate for the short quadriceps moment arm. The passe 3year group limb might have an unstable knee joint in the medio-Iateral direction during the climbing/descending by showing a tendency of more ADD displacement and greater hamming co-activation EMG than the passed 1year group limbs. The TKA design was not able to help the knee joint to produce adequate knee extension moment with less quadriceps muscle effort. I think that old man needs continuous exercise for muscle strength.

• Korean Journal of Applied Biomechanics
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• v.17 no.1
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• pp.165-174
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• 2007

The subject of this study was male apparatus gymnastics athlete who had scored high points doing basket with 1/2 turn on parallel bars. Then 3D motion analysis were used to calculate & analyse kinematic variables of Basket with 1/2 turn to Handstand. 1. The total average time spent for Basket with 1/2 turn took $2.16{\pm}.08sec$, at the downward upward phase took $.58{\pm}0.00sec$, $.23{\pm}.00sec$, at flight phase took $.28{\pm}.01sec$, at connected area phase took $.72{\pm}0.21sec$, at rotation area phase took $.35{\pm}.14sec$. To have a successful performance, there should be faster speed and velocity to rotate at the downward upward phase, then the upward velocity and height must be used adequately. Moreover, the speed must be faster at the flight connect phase to stabilize Center of Mass(CM) for the body, and must secure more time at the rotation area to have more stable performance. 2. After handstand on parallel bars while moving CM to right hand side, and It must be performed with big and magnificent performance with putting both hand's center to far away from the parallel bars. 3. Furthermore, CM must be moved fast from downwards to right hand side, and CM must be moved fast in vertical movement at upward and flight phase to avoid CM from moving back and forth, and left and right. 4. At downwards, the subject must rotate as bis as possible using hip-joint as wide as possible and at upwards, must put his body to vertical to have stable performance. While rotating or turning, it is better to do with bigger shoulder angle and have to make sure that trunk angle must be not scattered. To perform better and more positive in basket with 1/2 turn on parallel bars, the centrifugal force must be used big and fast at downward, and at upward and flight phase, downward movement must change to vertical movement as soon as possible while turning movement must happen at handstand position. Time spent must be shorten at connected area to stabilize CM and turning must be natural as possible while securing the necessary time of movement to well-balanced. Also, the body must be vertically closed from the ground.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.2
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• pp.23-33
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• 2011

In this study, a CFPBS (Cone-type Friction Pendulum Bearing System) was developed which controls the acceleration delivered to the structure to prevent damage and degradation of the critical communication equipment in case of an earthquake. The isolation performance of the CFPBS was evaluated by numerical analysis. The CFPBS was manufactured in the shape of a cone differenced from the existing FPS (Friction Pendulum System), and a pattern was engraved on the friction surface. The natural frequencies of the CFPBS were evaluated from a free-vibration test with the seismic isolator system consisting of four CFPBSs. In order to verify its earthquake-resistant performance, a numerical analysis program was created from the equation of the CFPBS induced from the equations of motion. A simplified theoretical equation of the CFPBS was proposed to manufacture the equipment which could demonstrate the necessary performance. Artificial seismic waves satisfying the maximum earthquake scale of the Korean Building Code-Structural (KBC-2005) were created and verified to review the earthquake-resistant performance of the CFPBS by numerical analysis. The superstructural mass of the CFPBS and skew angle of the friction surface were considered for numerical analysis with El Centro NS (1940), Kobe NS (1995) and artificial seismic waves. The CFPBS isolation performance evaluation was based on the results of numerical analysis and the executed comparative analysis between the results from numerical analysis and the simplified theoretical equation under the same conditions.

• Journal of the Korean GEO-environmental Society
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• v.21 no.1
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• pp.5-12
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• 2020

Vibration propagated from seismic sources has damping according to distance and amplification and reduction characteristic in different regions according to topography and geological structure. The vibration propagated from the seismic source to the bedrock is largely affected by the damping according to the separation distance, which can be simply estimated through the damping equation. However, it is important to grasp geological information by location because vibration estimation transmitted to the surface are affected by the natural period of the soil located above the bedrock. Geotechnical investigation data are needed to estimate the seismic intensity based on geological information. If there is no Vs profile, the standard penetration tests are mainly used to determine the soil parameters. The Integrated DB Center of National Geotechnical Information manages the geotechnical survey data performed on the domestic ground, and there is the standard penetration test information of 400,000 holes. In this study, the possibility of quantitation the amplification coefficient for each region was examined to calculated the physical interactive seismic intensity based on geotechnical information. At this time, the shear wave column diagram was generated from the SPT-N value and ground response analysis was performed in the target area. The site coefficients for each zone and the seismic intensity distribution for the seismic motion present a significant difference according to the analysis method and the regional setting.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.55-68
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• 2020

In order to investigate the hydraulic characteristics of a boundary layer streaming over the beach cusps appeared in swells prevailing mild seas, we numerically simulated the shoaling process of Edge waves over the beach cusp. Synchronous Edge waves known to sustain the beach cusps could successfully be duplicated by generating two obliquely colliding Edge waves in front of beach cusps. The amplitude A_B and length L_B of Beach Cusp were elected to be 1.25 m and 18 m, respectively based on the measured data along the Mang-Bang beach. Numerical results show that boundary layer streaming was formed at every phase of shoaling process without exception, and the maximum boundary layer streaming was observed to occur at the crest of sand bar. In RUN 1 where the shortest waves were deployed, the maximum boundary layer streaming was observed to be around 0.32 m/s, which far exceeds the amplitude of free stream by two times. It is also noted that the maximum boundary layer streaming mentioned above greatly differs from the analytical solution by Longuet-Higgins (1957) based on wave Reynolds stress. In doing so, we also identify the recovery procedure of natural beaches in swells prevailing mild seas, which can be summarized such as: as the infra-gravity waves formed in swells by the resonance wave-wave interaction arrives near the breaking line, the sediments ascending near the free surface by the Phase II waves orbital motion were carried toward the pinnacle of foreshore by the shoreward flow commenced at the steep front of breaking waves, and were deposited near the pinnacle of foreshore due to the infiltration.

• Journal of Korean Society of Steel Construction
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• v.17 no.4 s.77
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• pp.499-509
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• 2005

The excessive wind-induced motion of tall buildings most frequently result from vortex-shedding-induced across-wind oscillations. This form of excitation is most pronounced for relatively flexible, lightweight, and lightly damped high-rise buildings with constant cross-sections. This paper discusses the aerodynamic means ofmitigating the across-wind vortex shedding induced in such situations. Openings are added in both the drag and lift directions in the buildings to provide pressure equalization. Theytend to reduce the effectiveness of across-wind forces by reducing their magnitudes and disrupting their spatial correlation. The effects of buildings with several geometries of openings on aerodynamic excitations and displacement responses have been studied for high-rise buildings with square cross-sections and an aspect ratio of 8:1 in a wind tunnel. High-frequency force balance testshave been carried out at the Kumoh National University of Technology using rigid models with 24 kinds of opening shapes. The measured model's aerodynamic excitations and displacement were compared withthose of a square cylinder with no openings to estimate the effectiveness of openings for wind-induced oscillations. From these results, theopening shape, size, and location of buildings to reduce wind-induced vortex shedding and responses were pointed out.

• Journal of Navigation and Port Research
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• v.43 no.3
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• pp.143-152
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• 2019

In this paper, the towing stability of the LNG bunker barge was estimated. Currently, LNG bunkering barge is being developed for the bunkering of LNG (Liquefied Natural Gas), an eco-friendly energy source. Since the LNG bunkering barge assumes the form of a towed ship connected to the tow line, the towing stability of the LNG bunker barge is crucial f not only for the safety of the LNG bunker barge but also the neighboring sailing vessels. In the initial stages, a numerical code for towing simulation was developed to estimate the towing stability of the LNG bunkering barge. The MMG (Maneuvering Mathematical modeling Group) model was applied to the equations of motion while the empirical formula was applied to the maneuvering coefficients for use in the initial design stage. To validate the developed numerical code, it was compared with published calculation and model test results. Towing simulations were done based on the changing skeg area and the towing position of the LNG bunkering barge using the developed numerical codes. As a result, the suitability of the designed stern skeg area was confirmed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.05a
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• pp.185-188
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• 2019

In this paper, the towing stability of the LNG bunker barge is estimated. Currently, LNG bunkering barge is being developed as an infrastructure for the bunkering of LNG (Liquefied Natural Gas), an eco-friendly energy source. Since the LNG bunker barge are in the form of towed ship connected to the tow line, the towing stability of the LNG bunker barge is very important for the safety of not only the LNG bunker barge but also the surrounding sailing vessels. The numerical code for towing simulation was developed to estimate the towing stability of the LNG bunker barge at the initial design stage. The MMG(Manoeuvring Mathematical Group) model was applied to the equations of motion and the empirical formula was applied to the maneuvering coefficients so that they could be used in the initial design stage. To validity of the developed numerical code, it was compared with published calculation and model test results. Towing simulations were carried out according to with and without stern skeg of the LNG bunker barge using the developed numerical code. Through the results of the simulations, the appropriateness of the stern skeg area designed was confirmed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.1
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• pp.21-28
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• 2021

The main purpose of this study is to assess the safety of the fixed anchorages subjected to the seismic motion for an operating facilities in the actual power plant. Thus, the experimental study was conducted to investigate the load response in the event of an actual seismic to the anchorages of a nonstructural components. Since there are economic and spatial constraints to study nonstructural components that actually have various forms, alternative test specimens of steel frames with mass were built and the shaking table test was carried out. In order to evaluate the dynamic characteristics and seismic performance, the natural frequency of the target structure was identified through the shaking table test and then the load response characteristics of the anchorage were evaluated by generating an artificial seismic effect like actual seismic. Finally, the structural stiffness was reinforced by fixing the steel frame to the test specimen using bolts, thereby reducing the load transmitted to the anchorage. It will be carried out on the reliability verification of the experiments and areas that have not been carried out due to the site conditions through the analytical approach in the future.