• Nuclear Engineering and Technology
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• v.49 no.3
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• pp.632-637
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• 2017

Even though the potential for an accident in nuclear power plants is very low, multiple emergency plans are necessary because the impact of such an accident to the public is enormous. One of these emergency plans involves a robotic system for investigating accidents under conditions of high radiation and contaminated air. To develop a robot suitable for operation in a nuclear power plant, we focused on eliminating the three major obstacles that challenge robots in such conditions: the disconnection of radio communication, falling on uneven floors, and loss of localization. To solve the radio problem, a Wi-Fi extender was used in radio shadow areas. To reinforce the walking, we developed two- and four-leg convertible walking, a floor adaptive foot, a roly-poly defensive falling design, and automatic standing recovery after falling methods were developed. To allow the robot to determine its location in the containment building, a bar code landmark reading method was chosen. When a severe accident occurs, this robot will be useful for accident condition monitoring. We also anticipate the robot can serve as a workman aid in a high radiation area during normal operations.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.10
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• pp.171-180
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• 2019

In Korea, the seismic design of non-structural elements was interested by Earthquake of the 2016 Gyeong-ju and 2017 Po-hang. Among the non-structural elements, the ceiling system with steel panel used in Po-hang station showed failure examples of non-seismic design ceiling. In this study, the seismic performance of suspended ceiling with steel-panel, such as those used in Po-hang Station, was evaluated by shaking table tests. The shaking table tests were performed in accordance with the ICC-ES AC156 standard with floor acceleration being applied horizontally in one direction using a $3.3{\times}3.3m^2$ frame. The ceiling system consists of steel-panels, carrying channels, main and cross T-bars, and anti-falling clips. The anti-falling clip prevents the steel panel falling completely. The shaking table test confirmed that the damage at the previous stage had a direct impact on the damage state at the next stage. Through the shaking table test, the damage state of the T-bar type steel-panel suspended ceiling system was defined.

• Earthquakes and Structures
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• v.14 no.4
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• pp.323-336
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• 2018

Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40-50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.211-222
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• 2011

In this paper a structural analysis of the PWR(pressurized water reactor) canister with 102cm diameter is carried out to evaluate the structural safety of the canister for the impact force occurring at the moment of collision with the ground in the falling plumb down accident from the carriage vehicle which may happen during the canister handling at the spent nuclear fuel disposal repository. For this, a rigid body dynamic analysis of the canister is executed to compute the impact force using the commercial CAE system, RecurDyn, and a nonlinear structural analysis is performed to compute stresses and deformations occurring inside the canister for this computed impact force using the commercial FEM code, NISA. From these analysis results, the structural safety of the canister is evaluated for the falling plumb down accident from the carriage vehicle due to the inattention during the canister handling at the repository. The rigid body dynamic analysis performed assuming the canister as a rigid body shows that the canister falls plumb down to the ground in two types. And also it shows that early collision impact force is the biggest one and following impact forces decrease gradually. The height of the carriage vehicle in the repository is assumed as 5m in order to obtain the stable structural safety evaluation result. The nonlinear structural analysis of the canister is executed for the biggest early impact force. The structural analysis result of the canister shows that the structural safety of the PWR canister is not secured for the falling plumb down accident from the moving carriage vehicle because the maximum stresses occurring in the cast iron insert of canister are bigger than the yield stress of the cast iron.

• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.15-21
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• 2014

Many kinds of falling prevention systems with a safety block have been supplied in order to prevent falling accidents and acquire the long life and cost down for the maintenance. However, there are not the reliable and domestic the falling prevention system until now. Almost systems were imported from U.S.A, Japan, U.K and Germany. The structural safety of the imported safety block is satisfied sufficiently, but it has heavy weight due to the cover with the aluminum and thickness. Especially, the falling prevention system as the safety block is very expensive. It brings about flow the enormous money out of country. Furthermore it has a heavy weight when workers climbed the ladder with a falling prevention system and moved, many workers are not feeling themselves. Thus, the aim of this work is to develop a commercial self-escape SRL(Self Retracting Lifeline) with the safety block function that has a light weight and an advanced strength. The cost efficiency and convenience of the system and safety for workers also will be improved remarkably even though this system has a light weight. The results show that the maximum stress is obtained in each part by the lower more than yield strength and has sufficient safety in the developed new safety block.

• Physical Therapy Korea
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• v.28 no.1
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• pp.84-91
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• 2021

Background: A hip fracture may occur spontaneously prior to the hip impact, due to the muscle pulling force exceeding the strength of the femur. Objects: We conducted falling experiments with humans to measure the activity of the hip muscles, and to examine how this was affected by the fall type. Methods: Eighteen individuals fell and landed sideways on a mat, by mimicking video-captured real-life older adults' falls. Falling trials were acquired with three fall directions: forward, backward, or sideways, and with three knee positions at the time of hip impact, where the landing side knee was free of constraint, or contacted the mat or the contralateral knee. During falls, the activities of the iliopsoas (Ilio), gluteus medius (Gmed), gluteus maximus (Gmax) and adductor longus (ADDL) muscles were recorded. Outcome variables included the time to onset, activity at the time of hip impact, and timing of the peak activity with respect to the time of hip impact. Results: For Ilio, Gmed, Gmax, and ADDL, respectively, EMG onset averaged 292, 304, 350, and 248 ms after fall initiation. Timing of the peak activity averaged 106, 96, 84, and 180 ms prior to the hip impact, and activity at the time of hip impact averaged 72.3, 45.2, 64.3, and 63.4% of the peak activity. Furthermore, the outcome variables were associated with fall direction and/or knee position in all but the iliopsoas muscle. Conclusion: Our results provide insights on the hip muscle activation during a fall, which may help to understand the potential injury mechanism of the spontaneous hip fracture.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.144-150
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• 2007

In this paper, the low velocity response of four different sandwich panels with metal and laminate composite facesheets has been investigated by conducting drop-weight impact tests using an instrumented falling-weight impact tower. Square samples of 100mm sides were subjected low-velocity impact loading using an instrumented testing machine at six energy levels. Impact parameters like maximum force, time to maximum force, deflection at maximum force and absorbed energy were evaluated and compared for four different types of sandwich panels. The impact test results show that sandwich panel with composite laminate facesheet could not observe damage mode of a permanent visible indentation after impact and has a good impact damage resistance in comparison with sandwich panel with metal aluminum facesheet.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.368.2-368
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• 2002

It is increasing the interest on the comfortable dwelling environment, while sound insulation performance of materials and elements used in building is falling down as they become thicker and lighter Therefore, sound insulation performance in building has become the most important factor determining the level of housing, especially for apartment that has common wall and floor with next neighbors. (omitted)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.675-683
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• 2011

When impacts by falling objects are applied to the structures, vertical resisting member(column or column group) results in progressive collapse. By knowing clearly load-deformation relationship of a structural frame, to prevent progressive collapse by absorbing potential energy of falling objects though column groups are lost by the impact of falling object accidently. If residual strength in vertical direction exceeds vertical load, which the sum of the weight of falling objects and usual supportive vertical load as the result of absorbing released location energy, it does not result in progressive collapse. On the other hand, in case when weight of falling objects is included in usual supportive vertical load. In this paper, 1-story 4-spans model is analyzed by non-linear FEM and to examine the level of deterioration, limit analysis of 1-story 4-spans plane frame was carried out.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.149-149
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• 2018

Prediction on initial motion of sediment is crucial to evaluate sediment transport and channel stability. The condition of incipient movement of sediment is characterized by bed shear stress, which is generated from force of moving water against the bed of the channel, and by critical shear stress, which depends on force resisting motion of sediment due to the submerged weight of the grains. When the bed shear stress exceeds the critical shear stress, sediment particles begin rolling and sliding at isolated and random locations. In Mountain River, debris flow frequently occurs due to heavy rainfall and can lead some natural stones from mountain slope into the bed river. This phenomenon could add additional forces to sediment transport system in the bed of river and also affect or change direction and magnitude of sediment movement. In this paper, evaluations on incipient motion of uniform coarse gravel under falling spheres impacts using small scale flume channel were conducted. The drag force of falling spheres due to water flow and length movement of falling spheres were investigated. The experiments were carried out in flume channel made by glass wall and steel floor with 12 m long, 0.6 m wide, and 0.6 m deep. The bed slopes were selected with the range from 0.7% to 1.5%. The thickness of granular layer was at least 3 times of diameter of granular particle to meet grain placement condition. The sphere diameters were chosen to be 4cm, 6 cm, 8 cm, 10 cm. The spheres were fallen in to the bed channel for critical condition and under critical condition of motion particle. Based on the experimental results, the Shields curve of particles Reynold number and dimensionless critical shear stress were plotted. The relationship between with drag force and the length movement of spheres were plotted. The pathways of the bed material Under the impact of spheres falling were analyzed.