• Korean Journal of Applied Biomechanics
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• v.31 no.1
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• pp.59-63
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• 2021

Objective: Through comparative analysis of muscle activity for whole-body vibration, walking and running movements, it is to verify the training effect of whole-body vibration exercise in terms of amount of exercise and muscle activity characteristics. Method: Flat ground walking and slope walking (10 degrees) at a speed of 5 km/h, flat ground running and slope running (10 degrees) at a speed of 11 km/h for running were performed on treadmill, and squats were maintained at 12 Hz, 20 Hz, and 29 Hz conditions on Whole body vibration exercise equipment (Galileo). Muscle activity was analyzed through EMG analysis device for one minute for each condition. Results: The Anterior Tibialis and Erector Spinae show greater exercise effect in whole-body vibration than walking and running. The Rectus Femoris, Biceps Femoris, and Gluteus Maximus have the best effect of exercise in flat running. Whole-body vibration exercise showed greater muscle activation effect as the frequency increased, and exercise effect similar to walking during the same exercise time. Conclusion: The amount of exercise through Whole-body vibration exercise was similar to that of walking exercise, and the Anterior Tibialis and Erector Spinae shows better exercise effect than walking and running.

• Journal of Wind Energy
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• v.13 no.4
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• pp.90-97
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• 2022

In this paper, a study on the vibration characteristics of the pitch gearbox of 8 MW large capacity wind turbines was conducted. The vibration analysis method of the pitch gearbox was proposed by combining the planetary gear train vibration model with the housing and carrier finite element model using the substructural synthesis method. We modeled the vibration excitation source for mass unbalance, gear mesh frequency, and bearing defect error action on the pitch gearbox, and performed a critical speed analysis. As a result of analyzing the critical speed of the pitch gearbox, the critical speed for the excitation source did not occur within the operation speed (84.87 rpm). In addition, as a result of applying 10 %, 20 %, …, 100 % of the largest load duration distribution (LDD) load, it was found that the bearing stiffness and the primary natural frequency were larger as the LDD load was larger. The primary natural frequency was 81.47 Hz for the lowest load among LDD data, which exceeded an operating speed of 84.87 rpm (5.09 Hz), so it was found that vibration caused by the change of LDD load did not occur in the operating speed range.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.26-37
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• 2018

The Korea Aerospace Research Institute has developed a 6U HiREV Nano-satellite for the observation of the earth using high resolution videos and images. Since the 6U Nano-satellite is bulky compared to the 1U/3U Nano-satellite, the first natural frequency is relatively low. Large equivalent stress and total deformation, due to structural load, can be generated. In this paper, the design of the 6U HiREV Nano-satellite is described and structure analysis, such as acceleration load analysis, modal analysis, and random vibration analysis are carried out. It is proven that the structural design of the 6U HiREV is stable. These results will be useful as reference materials for the development of additional 6U Nano-satellites, which will be applied to various future missions in KOREA.

• Journal of Energy Engineering
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• v.12 no.4
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• pp.259-266
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• 2003

Load reduction ring (LRR) was installed on the ABB-Atom sparger to reduce the oscillatory loadings due to the air bubble clouds in the water pool in case of safety relief system operations. In order to investigate the effect of LRR on the pressure field, a numerical simulation on the behavior of air bubble clouds discharging into a water pool through a ABB-Atom sparser without LRR was performed by using a commercial thermal hydraulic analysis code, FLUENT 4.5. Among the multi-phase models contained in the code, the VOF (Volume Of Fluid) model was used to simulate the interface of water, air and steam flows. By comparing the analysis results with the previous ones, the load reduction ring has an effect on reducing the oscillatory loads at the wall. It also includes the effect of air mass and inlet boundary conditions of the pipe on the pressure oscillations at the wall.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.1
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• pp.22-28
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• 2012

While a dash panel component, close to passengers, plays a very important role to protect heat and noise from a power train, it is also a main path that transfers vibration energy and eventually radiates acoustic noise into the cavity. Therefore, it is important to provide optimal design schemes incorporating sound packages such as a dash isolation pad and a floor carpet, as well as structures. The present study is the extension of the previous investigation how design variables affect sound radiation, which was carried out using the simple plate and framed system. A novel FE-SEA hybrid simulation model is used for this study. The system taken into account is a dash panel component of a sedan vehicle, which includes front pillars, front side members, a dash panel and corresponding sound packages. Design variables such as panel thicknesses and sound packages are investigated how they are related to two main NVH indexes, sound radiation power(i.e. structure-borne) and sound transmission loss(i.e. air borne). In the viewpoint of obtaining better NVH performance, it is shown that these two indexes do not always result in same tendencies of improvement, which suggests that they should be dealt with independently and are also dependent on frequency regions.

• Journal of KSNVE
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• v.5 no.4
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• pp.515-524
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• 1995

Tubes in heat exchanger of fuel rods in reactor core are supported at intemediate point by support p0lates or springs. Current practice is, in case of heat exchanger, to allow clearance between tube and support plate for design and manufacturing consideration. And in case of fuel rod the clearance in support point can be generated due to the support spring force relaxation. Flow-induced vibration of a tube can cause it to impact or rub against support plate or against adjacent tubes and can result in fretting-wear. The tube-to- support dynamic interaction is used to relate experimental wear data from single-span test rigs to real multi-span heat exchanger configurations. The dynamic interaction cna be measured during experimental wear tests. However, the dynamic interaction is difficult to measure in real heat exchangers and, therefore, analytical techniques are required to estimate this interaction. This paper describels the nonlinear impact model of DAGS(Dynamic Analysis of Gapped Structure) code which simulates the tube response to external sinusodial or step excitation and predicts tube motion and tube-to-support dynamic interaction. Three experimental measurements-two single span rods excited by sinusodial force and a two span rod impacted by a steel ball are compared from the simulation nonlinear model of DAGS code. The simulation results from DAGS code are in good agreement with measurements. Therefore, the developed model of DAGS code is good analytical tool for estimating tube-to-support dynamic interaction in real heat exchangers.

• Journal of Sensor Science and Technology
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• v.5 no.4
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• pp.71-79
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• 1996

The mechanism of electrochemical polymerization of polypyrrole was analyzed using Q.C.A. via measuring the resonant frequency and resonant resistance of AT-cut quartz crystal, whose electrodes were fabricated with indium tin oxide by sputtering method. The quantity of polymerized polypyrrole was able to be calculated from the resonant frequency and the viscoelasticity of polypyrrole film from resonant resistance. We found that the elastic film is formed at the first stage of the polymerization, but transformed to viscoelastic film later and that this transition repeated at some point. From these results, it was confirmed that the rheological characteristics of electrochemically polymerized polypyrrole thin film can be analyzed using Q.C.A.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.156-165
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• 2006

Already, vari-stem, gas-bag, power deck, air ball etc. are used by various blasting methods to take the advantage of air decking technology in abroad. Air tube product has been used continuously in domestic and air ball product was made recently. In the case study, we analyzed about the application and the effect or air deck blasting method in domestic blasting area. As results or this case study, it was shown that blasting vibration was decreased about $21{\sim}41%$ and quantities or explosives was decreased about $17{\sim}30%$. Also, in the case of using air deck blasting method, fragmentation was shown to be smaller than common blasting method.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.40.2-40.2
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• 2010

MIRIS 우주관측카메라는 과학기술위성 3호의 주탑재체로서 $0.8{\sim}2.0{\mu}m$의 근적외선영역에서 우주배경복사와 우리은하 평면의 Pa-$\alpha$ survey 관측을 목적으로 한다. 이러한 임무를 수행하기 위해 MIRIS 우주관측카메라에는 MCT(HgCdTe) IR 검출기가 사용되고 6개의 필터를 장착할 수 있는 필터휠이 설계되었으며, 열잡음을 줄이고 원하는 SNR을 얻기 위해 모두 100K 이하로 냉각이 요구된다. 효과적인 냉각 및 저온유지를 위해서 외부의 열을 1차적으로 차단하는 Cryostat 외부용기와 100K 이하로 냉각되는 내부 Cold Box의 이중구조를 가지는 Dewar가 설계 되었다. 내부 Cold Box의 냉각은 소형 stirling cooler로 이루어지고 외부의 열 유입량이 Cooler의 냉각용량을 넘지 않도록 설계하였다. Cryostat 외부용기는 radiation cooling으로 냉각되어 200K 이하의 온도를 유지하며 내부 Cold Box로의 열유입을 최소화하기 위해 GFRP(Glass Fiber Reinforced Plastic) 단열 지지대와 MLI(Multi Layer Insulation)가 사용된다. 또한 100K으로 냉각시 필터고정부와 Cold Box 구조에서 일어날 수 있는 구조적인 피로도를 줄이고 열변형에 의한 문제를 방지하기 위한 고려가 설계에 포함되었다. FM(Flight Model)은 고진공 환경의 우주공간에서 문제가 발생하지 않도록 설계되었다. 또한 EQM 진동시험결과를 토대로 발사환경에서 발생하는 강한 진동을 견딜 수 있도록 FEM(Finite Elements Method) 구조해석을 통하여 필터고정부에 flexible structure 설계와 완충제를 추가하고 필터휠 구동부와 harness 고정부 및 cooler 지지부를 비롯한 전체 구조물에서 충분히 진동을 극복할 수 있도록 설계하였다.

• Journal of the Korean Geosynthetics Society
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• v.10 no.3
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• pp.53-62
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• 2011

This paper presents the characteristics behavior of dike structure and foundation ground through the shaking table model test. The vibration loadings of design earthquake acceleration of 0.154g was applied to this laboratory model test regarding on dike structure and foundation ground under the structure. The model was formulated with 1/100 design of representative cross section for evaluating the effectiveness of vibration. Based on the test results, we can analysis the behavior of lateral displacement and settlement characteristics of structure under the earthquake loading. The pore water pressure was also monitored in the upper, middle and lower layers of ground. Finally, the actual displacements and pore water pressure of the structure can be predicted by using the results of the laboratory shaking table test.