• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.1 s.106
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• pp.12-18
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• 2006

This research investigates the electromechanical characteristics of a spindle motor in a free-falling mobile hard disk drive before unexpected shock. Electromechanical simulation includes a time-stepping finite element analysis of the magnetic field in a speed controlled brushless DC motor and dynamic analysis of the stationary and rotating part linked by the fluid dynamic bearing under the free-falling condition. Analysis results show that the dynamic characteristics of the rotating spindle system during free-falling state have an effect on the relative motion between the stationary and rotating part of HDD. It results from the variation of reaction force in the bearing area due to the gravity force exerted on the rotating part of HDD, and the free-falling condition can be detected by observing the signal of the spindle motor and disk-head interface without using an accelerometer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.324-329
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• 2005

This research investigates the electromechanical characteristics of a spindle motor in a free-falling mobile hard disk drive before unexpected shock. Electromechanical simulation includes a time-stepping finite element analysis of the magnetic field in a speed controlled brushless DC motor and dynamic analysis of the stationary and rotating part linked by fluid dynamic bearing under the free-failing condition. Analysis results show that the dynamic characteristics of the rotating spindle system during free-falling state have an effect on the relative motion between the stationary and rotating part of HDD. It results from the variation of reaction force in the bearing area due to the gravely force exerted on the rotating part of HDD, and the free-failing condition can be detected by observing the signal of the spindle motor and disk-head interface without using the accelerometer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.197-204
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• 2021

If a failure or an abnormal maneuver occurs during the flight test of a missile, the missile is deliberately self-destructed so as not to continue the flight. At this time, debris are produced and it is important to estimate the impact area in real-time whether it is out of the safety area. In this paper, we propose a method to estimate the debris dispersion area and falling time in real-time using a Fully-Connected Neural Network (FCNN). We applied the Unscented Transform (UT) to generate a large amount of training data. UT parameters were selected by comparing with Monte-Carlo (MC) simulation to secure reliability. Also, we analyzed the performance of the proposed method by comparing the estimation result of MC.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.25-25
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• 1998

진동시험기를 사용한 충격시험은 자유 낙하식 충격시험기를 이용하는 것 보다 여러 가지 장점이 있으며, 충격반응 스펙트럼 시험의 요구가 점점 증가하고 있다. 진동시험기를 이용하여 충격반응 스펙트럼 시험을 실시하는데 진동시험기에서 허용하는 최대 힘, 속도, 변위에 의하여 제약을 받게 된다. 충격반응 스펙트럼을 만족하는 충격파형은 무수히 많으나 최대 가속도, 속도, 변위 등이 작으면 작을수록 그 충격파형의 품질이 우수하다고 말할 수 있다. 충격 지속시간이 짧고 충격가속도의 최대치가 큰 충격파형을 인가할 수 없지만, 충격 지속시간이 보다 길고 충격가속도의 최대치가 작은 파형이 동일한 충격반응 스펙트럼 규격을 만족할 수 있다. 진동시험기를 사용하여 충격반응 스펙트럼 시험을 수행하기 위한 충격파형이 웨이브레트를 이용하여 시험규격의 충격반응 스펙트럼을 만족하도록 합성된다. 웨이브레트의 매개변수는 주파수, 반파의 개수, 지연시간, 극성이다. 각 웨이브레트의 진폭은 시험규격의 충격반응 스펙트럼을 만족하도록·반복적으로 조절된다. 이렇게 합성된 충격파형은 진동시험기를 사용한 충격반응 스펙트럼 시험의 참조 가속도 파형으로 간주된다.

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.41-45
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• 2007

The shutoff unit was designed to provide rapid insertion of neutron absorbing material into the reactor core to shutdown the reactor quickly and also to withdraw the absorber slowly to avoid a log-rate trip. Four shutoff units were installed on the HANARO reactor but the half-core test facility was equipped with one shutoff unit. The reactor trip or shutdown is accomplished by four shutoff units by insertion of the shutoff rods. The shutoff rod(SOR) is actuated by a directly linked hydraulic cylinder on the reactor chimney, which is pressurized by a hydraulic pump. The rod is released to drop by gravity, when triplicate solenoid valves are de-energized to vent the cylinder. The hydraulic pump, pipe and air supply system are provided to be similar with the HANARO reactor. The shutoff rod drops for 647mm stroke within 1.13 seconds to shut down the reactor and it is slowly inserted to the full down position, 700mm, with a damping. We have conducted the drop test of the shutoff rod in order to show the performance and the structural integrity of operating system of the shutoff unit. The present paper deals with the 647mm drop time and the withdrawal time according to variation of the pool water temperature, the water level and the core flow.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.450-457
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• 2020

In this study, engineering characteristics such as flowability, segregation and compressive strength by age to derive fast hardening material mixing proportion using excavated soil. And based on optimal mixing proportion, field simulation experiment conducted in laboratory to examine the effectiveness of the method such as kelly ball drop test and soil penetration test for reviewing the following process. As as a result of evaluation, in case of kelly ball drop test and soil penetration test were securing the following process initiation time 3 hours after place CLSM. As results of these assessments, kelly ball drop test and soil penetration test were applicable for revewing following process in construction field besides unconfined compressive strength method.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.109-110
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• 2023

Domestic ultra-hard road repair materials require a lot of time before the road can be opened to traffic. Therefore, in this study, Methyl Methacrylate (MMA) based road repair material was used to improve the above problems. Furthermore, the basic physical properties of MMA-based pavement repair materials are examined to confirm their suitability in concrete pavements. For this study, two types of MMA road repair materials (A type and B type) were selected. Then, the curing of the test specimens prepared for painting was carried out under three conditions. The experimental items were viscosity (drop time) and drying time (set to touch, dry-hard). As a result of the experiment, viscosity (drop time) was faster in type A than in type B. The drying time results were as follows. In the case of set ti touch, both type A and type B dried in about 10 minutes regardless of the curing conditions. In the case of dry-hard, regardless of the curing conditions, A type dried longer than B type, but it dried faster than conventional road repair materials. Therefore, within the scope of this study, it is considered that A type has a high potential for utilization as a road repair material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.751-758
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• 2015

Mathematical models are actively used to reduce the experimental expenses required to understand physical phenomena. However, they are different from real phenomena because of assumptions or uncertain parameters. In this study, we present a calibration and validation method using a paper helicopter and statistical methods to quantify the uncertainty. The data from the experiment using three nominally identical paper helicopters consist of different groups, and are used to calibrate the drag coefficient, which is an unknown input parameter in both analytical models. We predict the predicted fall time data using probability distributions. We validate the analysis models by comparing the predicted distribution and the experimental data distribution. Moreover, we quantify the uncertainty using the Markov Chain Monte Carlo method. In addition, we compare the manufacturing error and experimental error obtained from the fall-time data using Analysis of Variance. As a result, all of the paper helicopters are treated as one identical model.

• Journal of the Korean GEO-environmental Society
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• v.19 no.11
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• pp.5-14
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• 2018

Worldwide, soil compaction work is one of the most important activities that are carried out on civil engineering works sites. Compaction work, particularly in the area of road construction, is considered to be important, as poor compaction work is closely related with poor construction even after a construction is complete. Currently, the plate bearing test or the sand cone method relative to the unit weight of soil test are commonly used to measure the degree of compaction, but as these require a great deal of time, equipment and manpower, it is difficult to secure economic efficiency. The method that is used to measure the degree of compaction according to the penetration depth achieved by free fall objects through gravity is the Free-Fall Penetration Test (FFPT), which uses a so-called "portable compaction measuring meter (PCMM)." In this study, the degree of compaction was measured and a penetration depth graph was developed after the field test using the portable compaction measuring meter. The coefficient of determination was 0.963 at a drop height of 10 cm, showing the highest level of accuracy. Both horizontal axis and longitudinal axis were developed in a decimal form of graph, and the range of allowable error was ${\pm}1.28mm$ based on the penetration depth. The portable compaction measuring meter makes it possible to measure the degree of compaction simply, quickly and accurately in the field, which will ensure economic efficiency and facilitate the process management.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.75-86
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• 2019

The biggest obstacle in the nuclear power generation is the high level radioactive waste such as the spent nuclear fuel. High level radioactivities and generated heat make the safe treatment of the spent nuclear fuel very difficult. Nowadays, the only treatment method is a deep geological disposal technology. This paper treats the structural safe design problem of the spent nuclear fuel disposal canister which is one of the core technologies of the deep geological disposal technology. Especially, this paper executed the nonlinear structural analysis for the stresses and deformations occurring in the canister due to the impulsive force applied to the spent nuclear fuel disposal canister in the case of an accidental drop and ground impact event from the transportation vehicle in the repository. The main content of the analysis is about that the impulsive force is obtained using the commercial rigid body dynamic analysis computer code, RecurDyn, and the stress and deformation caused by this impulsive force are obtained using the commercial finite element static structural analysis computer code, NISA. The analysis results show that large stresses and deformations may occur in the canister, especially in the rid or the bottom of the canister, due to the impulsive force occurring during the collision impact period.