• 한국항공우주학회지
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• 제38권11호
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• pp.1130-1135
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• 2010

착륙장치는 완충장치를 이용하여 항공기 착륙 시의 충격을 흡수하는 역할을 한다. 다양한 종류의 완충장치가 존재하나, 완충효율 측면에서 가장 우수한 것은 유공압 방식이다. 착륙장치의 완충 성능은 반드시 낙하시험을 통해 입증하여야 하며, 이는 미 군사규격, 미연방 항공규정 등에서 공통적으로 요구하는 있는 사항이다. 이 논문에서는 낙하시험을 위한 설비 구성, 시험 절차 및 결과분석 방법을 실제 낙하시험 사례와 함께 제시한다.

• Biomaterials and Biomechanics in Bioengineering
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• 제2권2호
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• pp.111-125
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• 2015

For engineers, generating a mesh in porous media (PMs) sometimes represents a smaller computational load than generating realistic stent geometries with computer fluid dynamics (CFD). For this reason, PMs have recently become attractive to mimic flow-diverter stents (FDs), which are used to treat intracranial aneurysms. PMs function by introducing a hydraulic resistance using Darcy's law; therefore, the pressure drop may be computed by test sections parallel and perpendicular to the main flow direction. However, in previous studies, the pressure drop parallel to the flow may have depended on the width of the gap between the stent and the wall of the test section. Furthermore, the influence of parameters such as the test section geometry and the distance over which the pressure drops was not clear. Given these problems, computing the pressure drop parallel to the flow becomes extremely difficult. The aim of the present study is to resolve this lack of information for stent modeling using PM and to compute the pressure drop using several methods to estimate the influence of the relevant parameters. To determine the pressure drop as a function of distance, an FD was placed parallel and perpendicular to the flow in test sections with rectangular geometries. The inclined angle method was employed to extrapolate the flow patterns in the parallel direction. A similar approach was applied with a cylindrical geometry to estimate loss due to pipe friction. Additionally, the pressure drops were computed by using CFD. To determine if the balance of pressure drops (parallel vs perpendicular) affects flow patterns, we calculated the flow patterns for an ideal aneurysm using PMs with various ratios of parallel pressure drop to perpendicular pressure drop. The results show that pressure drop in the parallel direction depends on test section. The PM thickness and the ratio of parallel permeability to perpendicular permeability affect the flow pattern in an ideal aneurysm. Based on the permeability ratio and the flow patterns, the pressure drop in the parallel direction can be determined.

• 정보저장시스템학회논문집
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• 제9권2호
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• pp.56-61
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• 2013

The recent increased use of mobile phone has resulted in a technical focusing on reliability issues related to drop performance. Since mobile phone may be dropped several times during their use, it is required to survive common drop accidents. The plastic injection parts such as base stopper and carrier in the encoder type actuator can be broken easily in the actual reliability test of 1.5m free drop. So, we analyzed the shock resistance characteristics of auto focus actuator with variables in the material properties using finite element method. By applying the new resin materials, we can decrease the breakage of plastic injection parts and improve the reliability of mobile phone.

• Journal of Biosystems Engineering
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• 제26권5호
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• pp.461-468
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• 2001

Impact between fruits and other materials is a major cause of product damage in harvesting and handling systems. The oriental pears are more susceptible to bruising than other fruits such as European pears and apples, and are required more careful handling. The interest in the handling of the pears for the processing systems has raised the question of the allowable drop height to which pears can be dropped without causing objectionable damage. Drop tests on pears were conducted using an impact device developed by authors to estimate the allowable drop height without bruising. The impact device was constructed to hold in a selected orientation and to release a fruit by vacuum for dropping on to a force transducer. The drop height was adjustable for zero to 60 cm to achieve the desired distance between the bottom of the fruits and the top of the impact force transducer. The transducer was secured to 150 kg$\sub$f/ concrete block. The transducer signal was sampled every 0.17 ms with a strain gage measurement board in the micro computer where it was digitaly stored for later analysis. The selected sample fruit was Niitaka cultivar of pears which is one of the most promising fruit for export in Korea. The pears were harvested during the 1998 harvest season from an orchard in Daejeon. The sample fruit was selected from two groups which were stored for 3 months and 5 months respectively by the method of current commercial practice. The pears were allowed to stabilize at environmental condition(18$^{\circ}C$, 65% rh) of the experimental room. One hundred fifty six pears were tested from the heights of 5, 7.5. 10 and 12.5 cm while measurement were made of impact peak force, contact time, time to peak force, dwell time, pear diameter and mass. The bioyield strength and modulus of elasticity were measured using UTM immediately after each drop test. The allowable drop height was estimated on the base of bioyield strength of the pears in two ways. One was assumed the peak force during impact test increasing linearly with time, and the other was based on the actual drop test results. The computer program was developed for measuring the impact characteristics of the pears and analyzing the data obtained in the study. The peak force increased while contact times decreased with increasing drop height and contact times of the sample from the hard tissue group. The allowable drop height increased with increasing bioyield strength and contact times, and also varied with Poisson\`s ratio, mass and equilibrium radius of the pears. The allowable drop height calculated by a theoretical method was in the range from 1 to 4 cm, meanwhile, the estimated drop height considering the result of the impact test was in the range from 1 to 6 cm. Since the physical properties of fruits affected significantly the allowable drop height, the physical properties of the fruits should be considered when estimating the allowable drop height.

• 마이크로전자및패키징학회지
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• 제18권2호
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• pp.35-41
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• 2011

Recently, board level solder joint reliability performance of IC packages during drop impact becomes a great concern to semiconductor and electronic product manufacturers. The handheld electronic products are prone to being dropped during their useful service life because of their size and weight. The IC packages are susceptible to solder joint failures, induced by a combination of printed circuit board (PCB) bending and mechanical shock during impact. The board level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this paper, applying the JEDEC (JESD22-B111) standard present a finite element modeling of the FBGA. The simulation results revealed that maximum stress was located at the outermost solder ball in the PCB or IC package side, which consisted well with the location of crack initiation observed in the failure analysis after drop reliability tests.

• 한국산학기술학회논문지
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• 제18권5호
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• pp.531-542
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• 2017

강선이나 강화플라스틱선 등의 선박 재료는 선박안전법에 규정된 규격재료를 사용하는 경우로서 판두께 측정시험이나 종굽힘강도시험을 통하여 제작 선체의 구조 안전성을 쉽게 확인할 수 있다. 한편, 염가의 폴리에틸렌 등과 같은 비규격재료를 선체 전장이 짧은 플레저 보트의 선체로 사용하는 경우 역학적 특성을 파악하기 쉬워 선체 설계를 수행하기에 매우 유리하고, 대량 생산 시스템을 갖추는 경우 제작 비용이 낮아 해당 제품의 가격 경쟁력을 가질 수 있다. 그러나 폴리에틸렌 선체의 경우 비규격재료를 사용함에 따라 기존의 소형선체에 대한 종굽힘강도시험을 이용하여 선체의 구조 안전성을 평가할 수 없다. 이러한 문제점을 해결하기 위하여 본 연구에서는 플레저 보트의 낙하시험 표준절차인 플레저 보트 검사 기준과 ISO 12215-5를 기초로 폴리에틸렌 선체에 대한 낙하시험을 수행한 후 이것을 기초로 정적구조해석을 수행하여 비규격재료로 개발된 선체의 구조 안전성을 확인함으로서 플레저 보트 검사 기준과 ISO 12215-5의 낙하시험방법이 선체 구조설계에 이용될 수 있음을 보였다.

• 한국소음진동공학회논문집
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• 제20권7호
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• pp.658-664
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• 2010

A control element drive mechanism(CEDM) is a reactor regulating system, which inserts, withdraws or maintains a control rod containing a neutron absorbing material within a reactor core to control the reactivity of the core. The ball-screw type CEDM for the integral reactor has a spring-damper system to reduce the impact force due to the scram of the CEDM. This paper describes the experimental results to obtain the drop and damping characteristics of the CEDM. The drop tests are performed by using a drop test rig and a facility. A drop time and a displacement after an impact are measured using a LVDT. The influences of the rod weight, the drop height and the flow area of hydraulic damper on the drop and damping behavior are also estimated on the basis of test results. The drop time of the control element is within 4.5s to meet the design requirement, and the maximum displacement is measured as 15.6 mm. It is also found that the damping system using a spring-hydraulic damper plays a good damper role in the CEDM.

• 마이크로전자및패키징학회지
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• 제16권1호
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• pp.33-38
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• 2009

전자 기기 제품들이 소형화 및 휴대화 되면서 낙하충격 신뢰성에 대한 관심이 높아지고 있다. 본 연구에서는 대표적인 무연솔더인 Sn-3.0Ag-0.5Cu 솔더를 이용하여 ENIG (Electroless Nickel Iimmersion Gold), OSP (Organic Solderability Preservative) 표면 처리와 등온 시효 시험 (High Temperature Storage test)에 따른 보드 레벨 패키지 (board level package)의 낙하충격 신뢰성 (drop reliability) 시험을 수행하였다. 또한 충격 조건을 변화시켜 시편에 가해지는 가속도 (G:acceleration)와 충격 지속 시간 (pulse duration)에 따른 신뢰성을 평가하였다. 기판의 strain측정 결과 중앙 부위가 가장 응력이 컸으며, 충격가속도에 비례하여 응력이 증가하였다. 시효 처리 전에는 OSP처리된 기판이 다소 우수한 신뢰성을 보였지만, 시효 처리후에는 ENIG기판에서 신뢰성이 우수하였고, 반대로 OSP는 감소하는 경향을 보였다. OSP의 경우 과도한 금속간화합물 (intermetallic compound)의 성장으로 인해 접합 계면에서 취성파괴 (brittle fracture)가 일어난 것을 관찰할 수 있었다.

• 대한물리치료과학회지
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• 제26권1호
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• pp.9-14
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• 2019

Background: Pes planus, or flat foot, causes lower limb malalignment and foot pain during walking or exercise. Therefore, a highly reliable evaluation method to accurately diagnose flat feet is necessary. This study investigated the intra-and inter-rater reliability of the navicular drop test in different postures. Design: Cross sectional study. Methods: Forty healthy volunteers performed the navicular drop test in three different combinations of non-weight-bearing and weight-bearing postures (standing/standing, sitting/sitting, and sitting/standing). Two examiners alternately performed the measurements five times in each subject, and in each posture. Significant differences in measurements were obtained among the three postures, with the highest navicular drop being observed in the sitting/standing posture. Results: Inter-rater reliability was high in the sitting/standing and sitting/sitting postures. Intra-rater reliability was high in all three postures. In the sitting/sitting and sitting/standing postures, large navicular drop values and high inter- and intra-rater reliability were observed. Conclusion: Therefore, the sitting/standing and sitting/sitting postures are recommended for use in navicular drop tests to diagnose flat feet.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.855-864
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• 2017

The control rod assembly controls reactor power by adjusting its position during normal operation and shuts down chain reactions by its free drop under scram conditions. Therefore, the drop performance of the control rod assembly is important for the safety of a nuclear reactor. In this study, the drop performance of the conceptually designed control rod assembly for the prototype generation IV sodium-cooled fast reactor that is being developed at the Korea Atomic Energy Research Institute as a next-generation nuclear reactor was experimentally investigated. For the performance test, the test facility and test procedure were established first, and several free drop performance tests of the control rod assembly under different flow rate conditions were then carried out. Moreover, performance tests under several types and magnitudes of seismic loading conditions were also conducted to investigate the effects of seismic loading on the drop performance of the control rod assembly. The drop time of the conceptually designed control rod assembly for 0% of the tentatively designed flow rate was measured to be 1.527 seconds, and this agrees well with the analytically calculated drop time. It was also observed that the effect of seismic loading on the drop time was not significant.