• 한국운동역학회지
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• 제12권2호
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• pp.91-107
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• 2002

이 연구는 배드민턴 경기기술 중 클리어에 대한 연구 대부분 경기분석 및 타법사용에 대한 연구에 국한되어 있어 여자중학생 배드민턴 선수를 대상으로 하이클리어 동작을 운동학적 변인으로 측정 분석하였다. 이 연구의 대상자는 충청북도에 위치한 C여자중학교 배드민턴 선수 4명이었으며, 동작의 분석 범위는 준비자세에서 동작의 시작순간, 라켓이 최대로 백 스윙 된 순간, 라켓과 셔틀콕이 임팩트 되는 순간, 임팩트 이후의 마무리 스윙동작까지로 단계별 동작을 설정하였다. 여자중학생 하이클리어 동작을 운동학적으로 분석한 결과 다음과 같은 결론을 얻었다. 피험자 대부분 백 스윙 단계에서 어깨 및 팔꿈치 관절을 충분히 회전하지 못한 것으로 나타났고, 특정 관절 부분에만 좋은 동작을 나타내 관절의 협용동작이 떨어지는 것으로 보였다. 피험자 S1과 S2가 임팩트 단계에서 어깨 및 팔꿈치 관절은 크게 천천히 스윙하다가 오른 손목관절 및 라켓헤드의 속도는 빠르게 나타나 다른 피험자 보다 관절의 협웅동작이 잘 이루어진 것으로 나타났다. 피험자 모두 성장기에 있는 학생으로서 관절의 유연성에 기인하여 오른 어깨각도 변화는 큰 각도를 보였고 각속도는 피험자 S3이 다른 피험자 보다 기술적 차이를 보여 개선될 점으로 나타났다. 피험자 모두 오른 팔꿈치 각도 변화는 비슷한 양상을 보였고 각속도에서 피험자 S2는 백 스윙단계부터 임팩트 시 심한 굴곡의 형태를 보여 힘을 효과적으로 사용하지 못한 것으로 나타났다. 피험자 모두 오른 손목각도의 변화는 백 스윙 직후 큰 각도를 이루지 못하고 임팩트 직후 손목의 빠른 굴곡이 형성되지 못하여 셔틀콕의 속도가 감속될 것으로 나타났다. 그러나 각속도는 피험자 S1과 S4는 임팩트 시 음(-)의 각속도 값을 보여 강한 스냅을 이용하고 빠르게 움직이고 있다고 볼 수 있다. 피험자 모두 임팩트 시 무릎각도의 크기는 큰 각도를 이룬 반면 고관절 각도는 작은 각도를 보여 무릎관절과 고관절과의 합성동작인 강한 허리힘을 이용하지 못한 것으로 나타났다.

• 대한기계학회논문집A
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• 제26권5호
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• pp.939-951
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• 2002

We propose a new multiscale Galerkin method based on interpolation wavelets for two-dimensional Poisson's and plane elasticity problems. The major contributions of the present work are: 1) full multiresolution numerical analysis is carried out, 2) general boundaries are handled by a fictitious domain method without using a penalty term or the Lagrange multiplier, 3) no special integration rule is necessary unlike in the (bi-)orthogonal wavelet-based methods, and 4) an efficient adaptive scheme is easy to incorporate. Several benchmark-type problems are considered to show the effectiveness and the potentials of the present approach. is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.

• Structural Engineering and Mechanics
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• 제13권5호
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• pp.543-556
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• 2002

A dynamic elastic local buckling analysis is presented for a pile subjected to an axial impact load. The pile is assumed to be geometrically perfect. The interactions between the pile and the surrounding soil are taken into account. The interactions include the normal pressure and skin friction on the surface of the pile due to the resistance of the soil. The analysis also includes the influence of the propagation of stress waves through the length of the pile to the distance at which buckling is initiated and the mass of the pile. A perturbation technique is used to determine the critical buckling length and the associated critical time. As a special case, the explicit expression for the buckling length of a pile is obtained without considering soil resistance and compared with the one obtained for a column by means of an alternative method. Numerical results obtained show good agreement with the experimental results. The effects of the normal pressure and the skin friction due to the surrounding soil, self-weight, stiffness and geometric dimension of the cross section on the critical buckling length are discussed. The sudden change of buckling modes is further considered to show the 'snap-through' phenomenon occurring as a result of stress wave propagation.

• 한국운동역학회지
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• 제13권3호
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• pp.217-229
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• 2003

The purpose of this study was to present the basic data on improving the skills for 3 junior high school national badminton players in clear and drop motion through the 3-dimensional image analysis. Therefore, the results of this study are as follows: 1. In the duration times per phase, subject C relatively showed a similar time between clear and drop motion. Accordingly, C took a more effective motion than A and B. 2. In the velocities of racket head, subject A and C showed similar changes relatively. However, in case of subject B, the velocity was decreased before back swing(E2) and increased until impact(E3). 3. Regardless of clear and drop motion, the changing phases of joint angle for wrist and elbow showed similar changes comparatively. 4. In the angles of upper body, clear motion was average 85.0 degree and drop one was average 80.7 degree during the impact(E3). Hence, it showed that drop motion hit the ball bowing the upper body more than clear one. 5. In the angles of racket head, clear motion was average 87.7 degree and drop one was average 85.6 degree during the impact(E3). Consequently, drop motion was impacted forward more than clear one.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.60-67
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• 2001

As a method of variable valve train(VVT), Electro-Mechanical Valve(EMV) has been studied. Compared with conventional VVT system, the EMV system has a relatively simple structure. The system has two electromagnets, springs and an armature. The system can be operated by reciprocal action between armature and two electromagnets. And, the operating event can be controlled by electrical signal from controller. Therefore, reduction of emission and fuel consumption can be achieved through valve event control at each engine operating condition. In this study, characteristics of EMV system were investigated by simulations and experiments. The results of simulation and experiment show that the core shape and material characteristics are dominant parameters on magnetic force and delay time. In order to apply the system to commercial engine, it has a compact size and high stiffness springs(50N/mm) to increase the valve speed. Because of high valve seating velocity, loud noise and high impact force generated, which can lead to reduction of actuator durability. Therefore, further research is required to reduce valve seating velocity.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.846-855
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• 2020

A loose part monitoring system is used to detect unexpected loose parts in a reactor coolant system in a nuclear power plant. It is still necessary to develop a new methodology for the localization and mass estimation of loose parts owing to the high estimation error of conventional methods. In addition, model-based diagnostics recently emphasized the importance of a model describing the behavior of a mechanical system or component. The purpose of this study is to propose a new localization and mass-estimation method based on finite element analysis (FEA) and optimization technique. First, an FEA model to simulate the propagation behavior of the bending wave generated by a metal sphere impact is validated by performing an impact test and a corresponding FEA and optimization for a downsized steam-generator structure. Second, a novel methodology based on FEA and optimization technique was proposed to estimate the impact location and mass of a loose part at the same time. The usefulness of the methodology was then validated through a series of FEAs and some blind tests. A new feature vector, the cross-correlation function, was also proposed to predict the impact location and mass of a loose part, and its usefulness was then validated. It is expected that the proposed methodology can be utilized in model-based diagnostics for the estimation of impact parameters such as the mass, velocity, and impact location of a loose part. In addition, the FEA-based model can be used to optimize the sensor position to improve the collected data quality in the site of nuclear power plants.

• Journal of Mechanical Science and Technology
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• 제15권2호
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• pp.180-191
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• 2001

The widely used spot welded sections of automobiles(hat and double hat shaped section members) absorb most of the energy in a front-end collision. The sections were tested with respect to axial static(10mm/min) and quasi-static(1000mm/min) loads. Based on these test results, specimens with various thicknesses, width ratios and spot weld pitches on the flange were tested at high impact velocity(7.19m/sec and 7.94m/sec) which simulates an actual car crash. Characteristics of collapse have been reviewed and structures for optimal energy absorbing capacity is suggested.

• 한국자동차공학회논문집
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• 제13권4호
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• pp.160-166
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• 2005

In recent, recreational vehicles, which efficiently provide wide inner space for various utilities, are highly preferred in automobile market. Though those vehicles enable to load much luggage in space behind the last seat, in case of frontal impact with high velocity the luggage strongly collides into the seat back and the passengers in. the last seat could be severely injured. Therefore, high strength against luggage intrusion is required for the last seat, and it is regulated by law of ECE R17. In this study, for a recreational vehicle under developing, an analysis technique for simulating seat crash in accordance with luggage intrusion test of ECE R17 was investigated. The results exhibited good correlation with the test ones.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1412-1419
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• 2002

Dynamic shear tests for the tough-pitch copper at high strain and high strain rate was performed. The Split Hopkinson Pressure Bar (SHPB) compression test system was modified to yield a shear deformation in the specimen. Hat-shaped specimens for the tough-pitch copper were adopted to generate high strain of γ=3～4 and high strain-rate of γ= 10$^4$/s. The dynamic analysis by ABAQUS 5.5/EXPLICIT code verified that shear zone can be localized in hat-shaped specimens. A proper impact velocity and the axial length of the shear localization region wert determined through the elastic wave analysis. The displacement in a hat-shaped specimen is limited by a spacer ring which was installed between the specimen and the incident bar. The shear bands were obtained by measuring the direction of shear deformation and the width of deformed grain in the shear zone. The decrease of specimen length has been measured on the optical displacement transducer. Dynamic shear stress-strain relations in the tough-pitch copper were obtained at two strain-rates.

• Earthquakes and Structures
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• 제23권2호
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• pp.129-138
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• 2022

One of the objectives to prevent building pounding between two adjacentstructures is to considerseparation distance or decrease relative displacement during seismic excitation. Although the majority of building codes around the world have basically suggested some equations or approximately recommended various distances between structuresto avoid pounding hazard, but a lot of reportsin zone of pounding have obviously shown thatsafety situation or economic consideration are not always provided due to the collisions between buildings and the cost of land, respectively. For this purpose, a dynamic MDOF model by having base isolation system is numerically considered and using various earthquake records, relative displacements are mathematically investigated. Different equations to determine the value of damping ratio are collected and the results of evaluations are listed for comparison among them to present a new equation for determination of impact damping ratio. Presented equation is depends significantly on impact velocity before and after impact based on artificial neural network, which the accuracy of them is investigated and also confirmed. In order to select the optimum equation, hysteresisloop of impact between base of building and rubber bumper is considered and compared with the hysteresis loop of each impact, calculated by different equations. Finally, using representative equation, the effect of thickness, number and stiffness of rubber bumpers are numerically investigated. The results of analysis indicate that stiffness and number of bumpers have significantly affected in zone of impact force while the thickness of bumpers have not shown significant influence to calculate impact force during earthquake. For instance, increasing the number of bumpers, gap size between structures and also the value of stiffness is caused to decrease impact force between models. The final evaluation demonstrates that bumpers are able to decrease peak lateral displacement of top story during impact.