• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.323-330
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• 2012

This study deals with the experiments of liquid dampers with multi cells whose vertical tubes are divided into several square columns for easily changing natural frequencies. Shaking table test is performed to verify control effectiveness of the dampers which are installed on a building structure. To design liquid dampers, a 64-story building structure is reduced to a SDOF structure with 1/20 of similitude laws based on acceleration. The structure model is made up to adjust its mass and stiffness easily, with separate mass and drive parts. Mass parts indicate real structure's weights and drive parts indicate real structure's stiffness with springs and LM guides. Manufactured liquid damper has 18 cells and its natural frequency ranges are 0.65Hz to 0.81Hz. Shaking table test is carried out with one way excitation to compare with only accelerations of a large-scale structure and a structure installed with liquid dampers. Control performance of the liquid damper is expressed by the transfer function from shaking table accelerations to the large-scale structure ones. Testing results show that the liquid damper reduced a large-scale structure's response by tuned natural frequencies.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.16-25
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• 2005

The effect of vertical riser support system on the dynamic behaviour of a classical spar platform is investigated. Spar platform generally uses buoyancy-can riser support system, but as water depth gets deeper the alternative riser support system is required due to safety and cost issues. The alternative riser support system is to hang risers off the spar platform using pneumatic cylinders rather than the buoyancy-can. The existing numerical model for hull/mooring/riser coupled dynamics analysis treats riser as an elastic rod truncated at the keel (truncated riser model), thus, in this model, the effect of riser support system can not be modeled correctly. Due to this reason, the truncated riser model tends to overestimate the spar pitch and heave motion. To evaluate more realistic global spar motion, mechanical coupling among risers, guide frames and support cylinders inside of spar moon-pool should be modeled. In the newly developed model, the risers are extended through the moon-pool by using nonlinear finite element methods with realistic boundary condition at multiple guide frames. In the simulation, the vertical tension from pneumatic cylinders is modeled by using ideal-gas equation and the vertical tension from buoyancy-cans is modeled as constant top tension. The different dynamic characteristics between buoyancy-can riser support system and pneumatic riser support system are extensively studied. The alternative riser support system tends to increase spar heave motion and needs damper system to reduce the spar heave motion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1210-1215
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• 2002

The spent fuel handling tool is used to handle the refuel bundle and treated by hoist rope on the bridge crane. The new developed handling tool of NPP(Nuclear Power Plant) should be conformed the structural stability under earthquake condition. In this study, the stress and seismic analysis of the handling tool are performed by finite element method. Using the Floor Response Spectrum(FRS) obtained through the time history analysis, the modal and seismic analysis under Operating Basis Earthquake(OBE) and Safe Shutdown Earthquake(SSE) load conditions are carried out. Total 4 cases of different locations of the trolly and the hook are investigated. With the spring-damper element, the tension analysis of hoist rope is conducted. The stability of handling tool under earthquake load condition is conformed with regulatory guide.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.979-984
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• 2003

A Dynamic vibration absorber(DVA) is developed to reduce the excessive vibration of an optical disk drive(ODD) originated from the deriving range of an wobble disk and unbalanced disk. We design the material properties and shapes of the DVA by simulating Frequency response function(FRF) such as target frequency, mass of the DVA, stiffness of damper, damping coefficient, shape and dimension, analyze dynamic characteristics and provide its design guide line for suppressing the vibration of an optical disk derive. To examine the performance of the DVA, the vibration of the feeding system with DVA and without DAA are measured by using a three-axis accelerometer, PCB derive and Pulse analyzer. The result show that the proposed DVA reduces the vibration of wide range in ODD.

• Journal of Biomedical Engineering Research
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• v.10 no.3
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• pp.269-278
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• 1989

The initial impact at foot strike is produced by a slider type mechanical model, which can be measured using a force platform to evaluate various shoes. The lower extremity and foot motion was filmed by a 16mm high speed movie camera and several points on the rear half of the shoe and those near the trochanter and the lateral epicondyle were digitized to provide the linear and angular positions and velocities during impact. With these observed kinematics, a slider type foot strike simulator composed of guide rail and sliding dummy is designed. The simulator system makes the artificial foot of the dummy with running shoe on it to follow the foot strike motion. The dummy has the relevant mass-spring-damper system modeled after McMahon's. The motion of the model is drived by the gravity force and the generated motion alone with the ground reaction forces are monitored by the same procedures afore mentioned producing the initial foot strike impact similar to the onto observed in human gait.