• 대한기계학회논문집A
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• 제22권4호
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• pp.826-833
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• 1998

The energy-absorbing characteristic of impact limiters affects the cask design so significantly that it should be evaluated as accurate as possible. The objective of this study is to find the influence of the impact limiter's steel case and gusset plates which enclose the shock absorbing cellular material on the impact energy absorption. The influence of impact limiter's steel case and gusset plate stiffeners on the impact energy absorption behavior under horizontal drop impact was evaluated for a radioactive isotope transport cask. Though the impact limiters mitigate the impact damage of the cask, the impact limiter's steel case and gusset plate stiffeners increase the impact force so significantly that should be designed as soft as possible. The impact analysis without considering impact limiter's steel case and gusset plates stiffener gives non-conservative results, so the stiffness of the steel case and gusset plates should be considered in impact analysis.

• Advanced Composite Materials
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• 제16권1호
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• pp.45-61
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• 2007

This paper describes a damage accumulation mechanism in cross-ply CFRP laminates $[0_2/90_2]_{2S}$ subjected to out-of-plane loading. Drop-weight impact and static indentation tests were carried out, and induced damage was observed by ultrasonic C-scan and an optical microscope. Both tests gave essentially the same results for damage modes, sizes, and load-deformation history. First, a crack occurred in the bottom $0^{\circ}$ layer accompanying some delamination along the crack caused by bending stress. Then, transverse cracks occurred in the middle $90^{\circ}$ layer with decreasing contact force between the specimen and the indenter. Measured local strains near the impact point showed that the stress state changed from a bending dominant state to an in-plane tensile dominant state. A cohesive interface element was used to simulate the propagation of multiple delaminations and transverse cracks under static indentation. Two types of analytical models are considered, one with multiple delaminations and the other with both multiple delaminations and transverse cracks. The damage obtained for the model with only multiple delaminations was quite different from that obtained from the experiment. However, the results obtained from the model with both delaminations and transverse cracks well explain the characteristics of the damage obtained in the experiment. The existence of the transverse cracks is essential to form the characteristic impact damage.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1859-1863
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• 2007

A new type of a fretting wear tester has been designed and developed in order to simulate the actual vibration behavior of a nuclear fuel rod for springs/dimples in room temperature. When considering the actual contact condition between fuel rod and spring/dimple, if fretting wear progress due to the flow-induced vibration (FIV) under a specific normal load exerted on the fuel rod by the elastic deformation of the spring, the contacting force between the fuel rod and dimple that were located in the opposite side should be decreased. Consequently, the evaluation of developed spacer grids against fretting wear damage should be performed with the results of a cell unit experiments because the contacting force is one of the most important variables that influence to the fretting wear mechanism. Therefore, it is necessary to develop a new type of fretting test rig in order to simulate the actual contact condition. In this paper, the development procedure of a new fretting wear tester and its performance were discussed in detail.

• Structural Engineering and Mechanics
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• 제63권4호
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• pp.509-519
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• 2017

Wind field in mountainous regions demonstrates unique distribution characteristic as compared with the wind field of the flat area, wind load and wind effect are the key considerations in structural design of television towers situated in mountainous regions. The television tower to be constructed is located at the top of Xiushan Mountain in Nanjing, China. In order to investigate the impact of terrain factors of hilltops on wind loads, firstly a wind tunnel test was performed for the mountainous area within 800m from the television tower. Then the tower basal forces such as bending moments and shear strength were obtained based on high frequency force balance (HFFB) test. Based on the experiments, the improved method for determining the load combinations was applied to extract the response distribution patterns of foundation internal force and peak acceleration of the tower top, then the equivalent static wind loads were computed under different wind angles, load conditions and equivalent goals. The impact of terrain factors, damping ratio and equivalent goals on the wind load distribution of a television tower was discussed. Finally the equivalent static wind loads of the television tower under the 5 most adverse wind angles and 5 most adverse load conditions were computed. The experimental method, computations and research findings provide important references for the anti-wind design of high-rise structure built on hilltops.

• 한국음향학회지
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• 제30권2호
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• pp.92-99
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• 2011

본 연구의 목적은 일본의 표준 중량충격원인 임팩트 볼을 국내의 표준중량충격원으로 도입시 바닥충격음 실험에 있어서 정확성에 대해 실험을 통해 알아보고자 했다. 이를 위하여 임팩트 볼을 이용하여 낙하 높이별, 가진위치를 바꾸어서, 수음점 높이에 대한 논의를 진행하였고, 임팩트 볼을 이용한 바닥충격음을 측정하고 이를 실제 충격원인 뛰는 충격음과 비교하여 실제 충격음과 가장 유사한 낙하 높이에 대한 검토를 실시하였다. 또한 일본 주택에서 주로 사용되고 있는 목구조와 국내 공동주택의 기본 구조인 콘크리트 구조에서의 바닥충격음 특성차이를 알아보기 위해 실험동에서 같은 조건으로 시험을 실시하여 시공재료 및 구법에 따른 차이를 알아보고자 하였다. 이에 대한 결과는 목구조에서는 낙하 높이가 10 cm에서 30 cm사이의 충격음이 실제 충격음과 비슷한 음압레벨을 갖는 것으로 나타났고 콘크리트 구조에서는 유사한 음압의 높이는 없었다. 또한 사람이 임팩트 볼을 운용하면서 표준낙하높이를 기준으로 상 하 10 cm 높이차로 생기는 오차는 역 A특성 값에서 약 1 dB이하 정도로 작은 오차를 나타내긴 하지만 우리나라에 표준 중량충격원으로 도입할 때에는 다양한 콘크리트 바닥구법에 따른 바닥충격음의 특성에 따른 적합한 임팩트 볼의 낙하 높이 및 측정 마이크로폰의 높이에 대한 고려는 신중히 하여야 한다.

• 유공압시스템학회논문집
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• 제2권2호
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• pp.14-20
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• 2005

This study developed and evaluated a shoe cushioning system to reduce impact force patterns during running. The shoe cushioning system is composed with a poly urethane pocket, which contains water and porous grains to absorb the force against the weight inside the pocket. Load-displacement curves for the shoe cushioning system were obtained from an instrumented testing machine and the results were compared with various pockets that have air, water or grains. Mechanical testings showed that the pocket with 5 g particles was the best for the shoe cushioning system. This founding will be helpful to designing the shoe.

• 천문학회지
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• 제38권2호
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• pp.283-287
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• 2005

The slow evolution of global magnetic fields and other dynamical processes in atmospheres of CP magnetic stars lead to the development of induced electric currents in all conductive atmospheric layers. The Lorentz force, which results from the interaction between a magnetic field and the induced currents, may modify the atmospheric structure and provide insight into the formation and evolution of stellar magnetic fields. This modification of the pressure-temperature structure influences the formation of absorption spectral features producing characteristic rotational variability of some spectral lines, especially the Balmer lines (Valyavin et al., 2004 and references therein). In order to study these theoretical predictions we began systematic spectroscopic survey of Balmer line variability in spectra of brightest CP magnetic stars. Here we present the first results of the program. A0p star $\Theta$ Aur revealed significant variability of the Balmer profiles during the star's rotation. Character of this variablity corresponds to that classified by Kroll (1989) as a result of an impact of significant Lorentz force. From the obtained data we estimate that amplitudes of the variation at H$\alpha$, H$\beta$, H$\gamma$ and H$\delta$ profiles reach up to $2.4\%$during full rotation cycle of the star. Using computation of our model atmospheres (Valyavin et al., 2004) we interpret these data within the framework of the simplest model of the evolution of global magnetic fields in chemically peculiar stars. Assuming that the field is represented by a dipole, we estimate the characteristic e.m.f. induced by the field decay electric current (and the Lorentz force as the result) on the order of $E {\~} 10^{-11}$ cgs units, which may indicate very fast (< < $10^{10}$ years) evolution rate of the field. This result strongly contradicts the theoretical point of view that global stellar magnetic fields of CP stars are fossil and their the characteristic decay time of about $10^{10}$ yr. Alternatively, we briefly discuss concurring effects (like the ambipolar diffusion) which may also lead to significant atmospheric currents producing the observable Lorentz force.

• 대한토목학회논문집
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• 제31권4B호
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• pp.323-332
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• 2011

하천에서 수목의 관리를 위해서는 수목이 홍수에 미치는 영향이나 생태적 특성을 고려하여 대책을 수립하여야 한다. 수목에 의한 수리학적 영향은 통수능 감소와 유수력에 의한 전도로 인한 하류 하천시설물의 기능 저해이다. 현장 인발시험은 수목이 전도될 때의 최대 저항력을 측정하여, 하천 내의 수목이 외력에 저항하는 정도를 파악하기 위해 시행하였다. 수목의 전도모멘트를 파악하기 위한 인자는 수목의 외형적 특성인 수종, 흉고직경, 수고 등이며, 본 연구에서는 전도모멘트와 흉고 직경의 상관관계를 이용하였다. 수목의 한계 전도모멘트는 흉고직경 4.9-32.8 cm의 관목과 교목 100주를 바탕으로 검토되었다. 교목과 관목을 함께 고려할 경우에는 흉고직경과 한계 전도모멘트의 상관관계를 도출하기 어려웠다. 그러나 교목만을 고려할 경우에는 흉고직경과 한계 전도모멘트 사이에 일정한 상관관계가 있음을 확인하였다.

• 한국기계가공학회지
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• 제17권1호
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• pp.130-137
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• 2018

In long freight trains, there is a brake time delay in the neighboring freight cars that causes damage and fractures of couplers, especially the knuckle of them. If there is a problem for couplers in the cars, this could cause a derailment and lead to damage of human life and property damage. In this study, maximum forces on the couplers are studied when a long freight car brakes, with brake delay time and coupler gap. We have made a dynamic model of 50 freight cars and couplers, applying contact between couplers and a characteristic curve for expressing force and displacement of buffers with SIMPACK, a multi-body dynamics program. We use EN 14531-2 from the British Standards Institution, a standard of freight car brakes for the verification of the dynamic model. We also use a simplified method to analyze the dynamic model of 50 freight cars. With changing coupler gap and brake delay time, we do comparative analysis with AAR M-201 from the Association of American Railroads, a standard of AAR couplers. From this result, we find that the standard on fatigue limit is satisfied, such that the brake delay time is within 0.06 second if the coupler gap of the AAR coupler is within 20 millimeters.

• 소성∙가공
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• 제23권6호
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• pp.363-368
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• 2014

Electromagnetic forming(EMF) is one of the high-speed forming methods, and has been used to deform metal sheets. The advantages of electromagnetic forming are reduced wrinkling due to non-contact characteristic and fine formability because of the high speed impact. In the current study, we suggest the application of electromagnetic forming to emboss pattern shapes using electromagnetic forces with only one forming coil and one punch. The high impact of the sheet at speeds of 100~300m/s produces significant coining pressure. In the current paper, electromagnetic forming was applied to Al 1100-O sheets; with thickness of 1.27mm and an area of $40mm{\times}40mm$. Using a single spiral coil, totally different types of patterns were created. Four different patterns were successfully produced on the aluminum sheet. The length and depth of the patterns were measured by three-dimensional scanning. Comparisons to the die shape showed good agreement. The test results confirm that emboss pattern forming by EMF using a single die can be used to replace the costly conventional method.