• Geomechanics and Engineering
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• 제36권2호
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• pp.99-109
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• 2024

Studying the dynamic behavior of axially moving cylindrical shells in hygro-thermal environments has important theoretical and engineering value for aircraft design. Therefore, in this paper, considering hygro-thermal effect, the nonlinear forced vibration of an axially moving cylindrical shell made of functionally graded materials (FGM) is studied. It is assumed that the material properties vary continuously along the thickness and contain pores. The Donnell thin shell theory is used to derive the motion equations of FGM cylindrical shells with hygro-thermal loads. Under the four sides clamped (CCCC) boundary conditions, the Gallekin method and multi-scale method are used for nonlinear analysis. The effects of power law index, porosity coefficient, temperature rise, moisture concentration, axial velocity, prestress, damping and external excitation amplitude on nonlinear forced vibration are explored through parametric research. It can be found that, the changes in temperature and humidity have a significant effect. Increasing in temperature and humidity will cause the resonance position to shift to the left and increase the resonance amplitude.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.165-171
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• 2011

A Consider the dead man's switch installed in each and every locomotive cab, which support operational safety on railways around the world. The concept is very simple - every 150 to 180 seconds an illuminated push-button demands to be acknowledged so as to know that the Train Driver is alive and active. In the absence of a response over a period of minutes, the vigilance control will automatically apply the train brakes and bring the train to a stand. If we multiply the resetting of the vigilance control 60 times per hour by a 10-hour shift it equals 600 presses of the button during the shift that a Train Driver must pay attention to and acknowledge. This adds a fair bit of pressure on the train driver's job, particularly when he/she is driving through stations, with passengers moving about on platforms in an environment of complex signaling arrangements - all the while looking out for restricting signals. From this perspective, the Vigilance System's demand to be acknowledged every 150/180 seconds is disturbing and can unnecessarily take a driver's attention away from what is happening outside the confines of the cab. A much more dramatic situation can happen when a train driver is driving hour after hour at night when, by Mother's Nature request - people need to sleep. Experience and research shows that the the dead man's switch can be pressed by train driver in a state of deep relaxation and 'micro-sleep'. The vigilance control system which is applied to reduce the drive load considering bio-response multiple unit train is proposed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권3호
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• pp.239-245
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• 2017

As a new technical approach, wave energy converter by using vertical motion of water in the multiple water chambers were developed to realize actual wave power generation as eco-environmental renewable energy. And practical use of wave energy converter was actually to require the following conditions: (1) setting up of the relevant device and its application to wave power generation in case that severe wave loading is avoided; (2) workability in installation and maintenance operations; (3) high energy conversion potential; and (4) low cost. In this system, neither the wall(s) of the chambers nor the energy conversion device(s) are exposed to the impulsive load due to water wave. Also since this system is profitable when set along the jetty or along a long floating body, installation and maintenance are done without difficulty and the cost is reduced. In this paper, we describe the system which consists of a float, a shaft connected with another shaft, a rack and pinion arrangement, a ratchet mechanism, and rotary type generator(s). Then, we present the dynamics model for evaluating the output electric power, and the results of numerical calculation including the effect of the phase shift of up/down motion of the water in the array of water chambers aligned along the direction of wave propagation.

• 마이크로전자및패키징학회지
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• 제24권1호
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• pp.57-65
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• 2017

모바일 기기 내부에 있는 전자부품들은 반도체 칩이나 그 밖의 여러 가지 재료로 구성되어 있다. 이러한 전자부품들은 매우 얇고, 구성된 재료들은 다양한 열팽창 계수를 가지고 있으므로 온도 변화나 외부 하중에 의해서 쉽게 굽힘이 일어난다. 그림자 무아레 방법은 비접촉으로 전체 영역에 걸친 면외변위를 측정하는 광학적 방법이지만 측정 감도를 $50{\mu}m/fringe$ 이내로 하기 어려워서 반도체 패키지의 굽힘변형을 측정하기에는 적당하지 않은 면이 있었다. 본 논문에서는 그림자 무아레 기법의 여러 실험조건들을 최적화하여 $25{\mu}m/fringe$의 향상된 감도를 갖는 측정 방법을 구현하였다. 또한 이로부터 위상이동에 의해 기록되는 4장의 그림자 무늬를 영상 처리하여 감도가 4배 향상된 그림자 무늬를 얻어내고 이를 스마트폰의 소형 전자부품들에 적용하여 온도변화에 따라 발생하는 굽힘 변위를 $5{\mu}m/fringe$의 고감도로 측정하였다.

• 조명전기설비학회논문지
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• 제23권5호
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• pp.88-95
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• 2009

본 논문은 연료전지용 전력변환기 개발에 관한 연구로 높은 승압비를 갖는 DC/DC 컨버터를 구성함에 있어서 기존 방식과 달리 변압기의 2차측 출력을 직렬로 연결하여 다이오드와 콘덴서 및 리액터를 줄일 수 있는 구조의 새로운 멀티 DC/DC 컨버터의 구조를 제안한다. 이러한 구조는 직렬 연결된 변압기의 2차측의 정류부분과 필터부분이 하나의 모듈로 구성되는 장점을 가지며 레벨수의 증가가 용이하다. 또한 제안된 구조에서 출력전압 리플을 줄일 수 있는 새로운 가변 위상 변위형 스위칭 방식을 제안한다. 이러한 모든 사항을 시뮬레이션과 실험을 통하여 검증 하였으며, 제안된 컨버터는 넓은 영역의 출력이 요구되는 부하에 매우 유용할 것으로 사료된다.

• 한국해양환경ㆍ에너지학회지
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• 제6권3호
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• pp.16-25
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• 2003

본 논문에서는 RORO선을 이용한 연안운송에 따른 CO₂가스 배출량과 NOx가스 배출량의 삭감 효과에 대하여 고찰한다. 먼저 국내 CO₂가스 배출량과 수출입 컨테이너화물의 물동량에 대하여 고찰한다. 다음에 RORO선의 특성, CO₂가스 배출량 기준과 NOx가스 배출량 기준에 대하여 고찰한다. 또한 경인지역과 부산항 사이의 수출입 컨테이너 화물의 운송에 있어서 도로운송을 연안운송으로 전환한 경우의 CO₂가스 배출량과 NOx가스 배출량 삭감 효과에 대하여 계산한다. 마지막으로 RORO선의 적재율과 연안운송 분담율 변화에 따른 CO₂가스 배출량과 NOx가스 배출량 변화에 대하여 조사한다. 본 논문의 결과를 통하여 수출입컨테이너 화물의 운송을 도로운송으로부터 RORO선을 이용한 연안운송으로 전환하는 것이 CO₂가스 배출량 삭감에는 효과적이나 NOx가스 배출량 삭감에는 큰 효과가 없는 것을 확인하였다.

• 대한인간공학회지
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• 제26권2호
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• pp.157-165
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• 2007

The Work-Related Musculoskeletal Disorders (WMSDs) can be occurred by various factors such as repetition, forceful exertions and awkward postures. Especially, occurrences of the WMSDs on the waist and lower limb are reported in workplaces, demanded standing postures for a long time, in service and manufacturing industry. The static and standing postures without movement for a long time increase work loads to the lower limb and the waist. Accordingly, anti-fatigue mat or anti-fatigue insole is used as a preventing device of the WMSDs. However anti-fatigue mats are limited in space and movement. In this study, multi-elastic insoles are designed and shown the effects of the workload reduction for a long time under the standing work. The foot pressures and EMG (Electromyography) are measured at 0 hour and after 2 hours by 6 health students in their twenties. The 6 prototype insoles are designed with three elastic (Low, Medium and High). These insoles are compared with no insole (insole type 7) as control group. The EMG measurement was conducted to waist (erector spinae muscle), thigh (vastus lateralis muscle) and calf (gastrocnemius muscle). The foot pressure is analyzed by mean pressure value and the EMG analysis is investigated through MF (Median Frequency), MPF (Mean Power Frequency) and ZCR (Zero Crossing Rate). The results of the foot pressure show that the multi-elastic insoles had smaller foot pressure value than that of no-insole. Moreover, Insole 2 and Insole 3 have the smallest increasing rate in foot pressure. The EMG results show that the multi-elastic insoles had smaller EMG shift value than that of no-insole in 2 hour, and then shift value shows the smallest value in Insole 2. Therefore, this study presents that the multi-elastic insoles have reducing effects of the work load for a long time standing work in both side of foot pressure and EMG.

• 한국군사과학기술학회지
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• 제20권4호
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• pp.528-535
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• 2017

Fuel cells have been spotlighted in the world for being highly efficient and environmentally friendly. A hydrogen which is the fuel of fuel cell can be obtained from a number of sources. Hydrogen source for operating the polymer electrolyte membrane fuel cell(PEMFC) in the current underwater environment, such as a submarine and unmanned underwater vehicles are currently from the metal hydride cylinder. However, metal hydride has many limitations for using hydrogen carrier, such as large volume, long charging time, limited storage capacity. To solve these problems, we suggest diesel reformer for hydrogen supply source. Diesel fuel has many advantages, such as high hydrogen storage density, easy to transport and also well-infra structure. However, conventional diesel reforming system for PEMFC requires a large volume and complex CO removal system for lowering the CO level to less than 10 ppm. In addition, because the preferential oxidation(PROX) reaction is the strong exothermic reaction, cooling load is required. By changing this PROX reactor to hydrogen separation membrane, the problem from PROX reactor can be solved. This is because hydrogen separation membranes are small and permeable to pure hydrogen. In this study, we conducted the pressurized diesel reforming and water-gas shift reaction experiment for the hydrogen separation membrane application. Then, the hydrogen permeation experiments were performed using a Pd alloy membrane for the reformate gas.

• 한국운동역학회지
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• 제23권3호
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• pp.209-218
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• 2013

This study was to perform the kinetic analysis of forward $1\frac{1}{2}$ somersault on the platform diving. Six men's diving players of the Korea national reserve athletes participated in this study. The variables were analyzed response time, velocity, center of mass (COM), angle, center of pressure (COP) and ground reaction force (GRF) of motion. For measure and analysis of this study, used to synchronized to 4 camcorder and 1 force plate, used to the Kwon3D XP (Ver. 4.0, Visol, Korea) and Kwon GRF (Ver. 2.0, Visol, Korea) for analyzed of variables. The results were as follows; Time factor were observed in maximum knee flexion depending on the extent of use at phase 1 of take-off to execute the somersault. This enabled the subject to secure the highest possible body position in space at the moment of jumping to execute the somersault and prepare for the entry into the water with more ease. Regarding the displacement of COM, all subjects showed rightward movement in the lateral displacement during technical execution. Changes in forward and downward movements were observed in the horizontal and vertical displacements, respectively. In terms of angular shift, the shoulder joint angle tended to decrease on average, and the elbow joints showed gradually increasing angles. This finding can be explained by the shift of the coordinate points of body segments around the rotational axis in order to execute the half-bending movement that can be implemented by pulling the lower limb segments toward the trunk using the upper limb segments. The hip joint angles gradually decreased; this accelerated the rotational movement by narrowing the distance to the trunk. Movement-specific shifts in the COP occurred in the front of and vertical directions. Regarding the changes in GRF, which is influenced by the strong compressive load exerted by the supporting feet, efficient aerial movements were executed through a vertical jump, with no energy lost to the lateral GRF.

• Safety and Health at Work
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• 제13권1호
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• pp.9-16
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• 2022

Background: The global shift toward greener societies demands new technologies and work operations in the waste-management sector. However, progressive industrial methods do not necessarily consider workers' health. This study characterized workers' exposure to bioaerosols and investigated the bioaerosols' potential to engage the immune system in vitro. Methods: Full shift personal aerosol sampling was conducted over three consecutive days. Dust load was analyzed by gravimetry, fungal and actinobacterial spores were analyzed by scanning electron microscopy, and endotoxin by limulus amebocyte lysate (LAL) assay. In vitro exposure of HEK cells to airborne dust samples was used to investigate the potential of inducing an inflammatory reaction. Results: The total dust exposure level exceeded the recommended occupational exposure limit (OEL) of 5.0 mg/m³ in 3 out of 15 samples. The inhalable endotoxin level exceeded the recommended exposure level by a 7-fold, whereas the fungal spore level exceeded the recommended exposure level by an 11-fold. Actinobacterial spores were identified in 8 out of 14 samples. In vitro experiments revealed significant TLR2 activation in 9 out of 14 samples vs. significant TLR4 activation in all samples. Conclusion: The present study showed that the dust samples contained potentially health-impairing endotoxin, fungi, and actinobacterial levels. Furthermore, the sampled dust contained microbial components capable of inducing TLR activation and thus have the potential to evoke an inflammatory response in exposed individuals.