• International Journal of Railway
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• 제5권1호
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• pp.1-9
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• 2012

Reliability means that a product maintains its initial quality and performance at a certain period of time (time, distance, cycle etc) under given condition without failure. The given conditions include both environmental condition and operating condition. Environmental condition means a common natural environment such as temperature, humidity, vibration, and working condition means an artificial environment such as voltage, current load, place for installment, and hours of use, which occurs during the life of the product. In the field of railway vehicles, it is mandatory to use a part with the proved reliability as the extension of the life of vehicle become highly necessary. But the reliable assessment method for the reliability of the part is insufficient. If the reliability of the railway vehicle parts could be assessed by using the field data, the reliability of the entire system could also be evaluated reliably. In this study, life span of micro-switch for master controller is analyzed and prediction is performed based on its field data given by an operator considering the special circumstances of railway vehicles such as the operation of a large number of trains on the same line.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.2207-2212
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• 2008

The next generation of Korean high-speed train under development will be designed for the maximum operating speed of 350km/h and maximum speed of 400km/h. This high-speed operation may cause the noise and vibration problems around tunnel exit due to the higher micro-pressure wave than present level. In this study, the nose shape optimization was conducted for the countermeasure against these problems. Axi-symmetric solver was used for numerical simulation, and response surface was used for efficiency of optimization process. Also the multi-step optimization was conducted to find out more accurate optimal shape. Through these analysis and optimization, it was found out that the optimal nose shapes for minimization of micro-pressure wave are definitely different along the nose length variation. And the mechanism of micro-pressure wave reduction was closely investigated by the analysis of generation process of compression wave in tunnel. The results are expected to be used as design guideline for performance improvement of the next generatin of Korean high-speed train.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.596-601
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• 2004

In this paper, we describe a study on the influence of the frequency variation of normal vibration using an integrated tactile display. It is necessary to consider this study because we want to find a method of displaying finer texture and know that the perception of fine textures is heavily influenced by temporal variation. Our tactile display system used in this experiment can simulate the micro shapes and roughness of surface textures by individual drives of a 6x8 pin array. Two experiments are performed. The first is a psychophysical experiment on the definition and range decision of roughness, and through the experiment, we clear up the meaning of roughness. The second is the main experiment about the frequency variation of normal vibration. We find the correlation between the vibration frequency and the texture and the condition for better display and perception of fine surfaces. The experimental results yielded two pieces of information. One is that lateral movement affects texture discrimination, and another is that normal vibration can make the perceived texture feel finer than real texture. That is, the vibrating stimulus is more effective for displaying a fine surface than static pressure, and it makes possible to display finer texture, exceeding the physical limit of the device.

• 한국정밀공학회지
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• 제25권5호
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• pp.148-154
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• 2008

Pharmacotherapy was mainly used to treat osteoporosis. However, some researches showed that pharmacotherapy could induce unexpected adverse effects. Some studies showed that whole body vibration affected beneficially osteoporosis. This paper studied the effect of whole body vibration fur osteoporosis compared with the effect of pharmacotherapy. 10 female rats were used and allocated into 4 group, CON, SHAM, DRUG, and WBV. Rats except SHAM group were ovariectomised to induce osteoporosis. Rats in WBV group were stimulated in whole body vibration at magnitude of $1mm_{peak-peak}$ and frequency 45Hz, for 8 weeks (30 min/day, 5 days/week). Rat in DRGU group was orally administered the Actonel (0.58mg/Kg), for 8 weeks (5days/week). The $4^{th}$ lumbar in rats were scanned at a resolution of $35{\mu}m$ at baseline, before stimulation, and 8 weeks after stimulation by In-vivo micro computed tomography. For detecting and tracking changes of biomechanical characteristics (morphological and mechanical characteristics) in lumbar trabecuar bone of rats, structural parameters were measured and calculated from acquiring images and finite element analysis was performed. In the results, loss of quantity and change of structure of trabecular bone in WBV group were smaller than those in both CON and SHAM groups. In addition, mechanical strength in WBV group was stronger than that in both CON and SHAM groups. In contrast, biomechanical characteristics in WBV group were similar with those in DRUG group. These results showed that reasonable whole body vibration was likely to treat osteoporosis and be substituted partly for drug treatment.

• 한국터널지하공간학회 논문집
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• 제16권2호
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• pp.249-260
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• 2014

열차가 고속으로 터널을 진입할 때 압축파가 발생하게 된다. 이 압축파가 터널 출구부에 도달하면 일부는 외부로 방출되고 일부는 팽창파의 형태로 반사되어 터널내부로 전파된다. 이러한 파는 충격파의 형태로 외부로 방출되는데, 이를 미기압(micro pressure wave)이라고 한다. 미기압파는 터널 출구부에 소음 및 진동문제를 일으키며, 이 현상이 클수록 민가 및 주변 유리창에 손상과 거주자의 불안을 일으키는 원인이 된다. 따라서 고속철도 건설을 위해서는 미기압에 대한 대책과 이에 대한 예측이 필요한 실정이다. 이에 본 연구는 운영중인 터널에서의 미기압 측정사례와 터널내 압력기울기에 대한 수치해석을 통하여, 차량의 전두부 형상 및 터널 갱구부 형상에 따른 영향을 분석하였다. 그 결과로, 본 연구에서는 미기압파의 강도를 예측하는 방법을 제시하였으며, 이를 통해서 터널 연장과 단면적에 따른 미기압 강도를 해석하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.69-72
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• 2007

Cellulose is a beneficial material that has low cost, lightweight, high compatibility and biodegradability. Recently electroactive paper (EAPap) on cellulose base was discovered as a smart material and actuator through ion migration and piezoelectric effect. Furthermore cellulose has a potentiality to apply the display material, because of its high reflectivity, flexibility and high transmittance. The various shapes and height patterns of the Cellulose acetate (CA) solution, such as circle and honeycomb patterns, were fabricated and observed by field emission scanning electron microscope (FESEM, S4300 Hitachi). The resulting pattern showed uniform size in the large area without defect. After stretching the CA film with saponification process in the sodium methoxide in methanol solution, Most of the compositions become one directional ordered nanofibers below 50nm.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.368-371
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• 2008

Cellulose based Electroactive Paper (EAPap) has been developed as a new smart material due to its advantages of piezoelectricity, large displacement, low power consumption, low cost and flexibility. EAPap can be used fur a surface acoustic wave (SAW) device using the piezoelectric property of EAPap, resulting in the cost effective and flexible SAW device. In this paper, inter digit transducer (IDT) structure using lift-off technique with a finger gap of $10{\mu}m$ was used for micro fabrication of the cellulose EAPap SAW devices. The performance of IDT patterned SAW device was characterized by a Network Analyzer. The feasibility of cellulose EAPap as a potential acoustic device was presented and explained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.444-450
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• 2006

IPMC actuators have been developed with multi-walled carbon nanotubes(MWNT) and $Nafion^{\circledR}$ ionic polymers. MWNT with different diameters of $3{\sim}5,\;4{\sim}6$ and $10{\sim}15$ nm and length of $10{\sim}20{\mu}m$ were used to enhance the mechanical and electrical performances of IPMC actuators. Ultrasonic treatment and high speed mixing were used to disperse MWNT homogeneously in $Nafion^{\circledR}$ solution. The electroless plating technique is used to make electrodes on the both side of the composite membrane. SEM and TEM images were taken to characterize the surface and micro-structures of the composite actuators. In this study, improved IPMC actuators were developed and compared with respect to bending actuation performance and electrical power consumptions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.570-575
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• 2002

Servo performance of a disk drive is greatly affected by the mechanical resonance frequencies of the head gimbal assembly (HSA). It is important factor to allow broader bandwidths for servo system in improving overall drive performance. In this paper, an optimal design for ODD suspension is attempted to increase resonance frequencies in tracking direction. Initial model was designed and the design parameter was defined to the model. The mode frequency variation for the change of design parameter was observed by modal analysis using the finite element method(FEM). The sensitivity matrix was calculated from the observed data and so through sensitivity analysis, an optimized ODD suspension was designed to have the higher resonant frequency than the initial model.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.191-196
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• 2007

With the development of micro electronic circuits and optical equipment, the demand for developing smart munitions with the ability to autonomously search for and attack targets has increased. Since the electronic components within smart munitions are affected by high temperatures, pressure, and impulsive forces upon the combustion of gunpowder, stability and reliability need to be secured for them. Securing those stability and reliability requires soft recovery system which can decelerate smart munitions. A theoretical analysis of flow is performed for the secure recovery of bullets on the basis of Navier-Stokes equation for compressible fluids. The inner pressure on a pressure tube, the speeds of bullets, and the deceleration of munitions are calculated theoretically. Theoretical results are compared with the data from the experiment with soft recovery system set up at the laboratory.