• 대한전자공학회논문지SP
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• 제48권3호
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• pp.112-118
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• 2011

선박은 위급상황에 노출될 경우 육상의 교통수단에 비해 해양 환경이라는 제약성 때문에 그 위험성이 더 크다. 따라서 위험 요소를 사전에 발견하고 먼저 조치를 취하는 것이 매우 중요하다. 이 논문에서는 선박에 가해지는 위험 요소를 지속적으로 감시하고 상태를 파악할 수 있는 상태감시시스템을 제안하였으며 이를 위해 선박 내에 화재 센서 모듈, 기울기 센서와 비틀림 센서를 설치하여 선박의 안전 상황을 판가름하는 기초가 되는 센서 데이터를 수집하였다. 획득한 센서 데이터는 역전파 신경망을 설계하여 분석하였으며 분석된 데이터를 토대로 판단한 선박 상태 정보는 승무원의 개인 단말기로 송신되어 이동 상황에서도 선박의 상태를 실시간으로 점검할 수 있다. 상황인식 실험 결과 연출된 화재 상황에서 약 95%의 정확도를 보였고 선체의 충격 위험 요소에 대해서 약 89%의 정확도를 보였다.

• 한국지반공학회논문집
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• 제16권1호
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• pp.107-116
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• 2000

4개 현장에 실물크기의 강관말뚝과 PC 및 PHC 말뚝의 축방향에 대한 지지거동을 알아보기 위하여, 강관말뚝에 스트레인게이지를 부착하고 항타시 계측기 손상여부를 조사하면서 동재하시험을 수행하였다. 아울러 동일한 말뚝에 대하여 2일과 7일 경과후에 정재하시험을 실시하여 하중-침하량 거동과 주면 및 선단지지력을 분리 측정하였다. 그 결과, CAPWAP 해석에 Davisson방법을 적용하여 구한 강관말뚝의 허용지지력은 정재하시험에서 구한 허용지지력 보다 약 2~33%정도 크게 나타났다. 그리고 정재하시험 결과에서 구한 산술평균한 허용지지력은 CAPWAP해석에서 Davisson's offset방법으로 구한 허용지지력보다 극한지지력에 FS=2.5를 적용하여 구한 허용지지력에 더 근접하는 경향을 보였다. 또한, 단위면적당 주면지지력은 깊이가 증가함에 따라 증가하였고, 말뚝선단부 1~2m 이내에서 발휘되는 비율이 상당히 큰 것으로 나타났다.

• 한국방재학회 논문집
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• 제6권3호
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• pp.9-16
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• 2006

기존 대부분의 구조물 건전도 모니터링 시스템에서는 제한적인 위치와 범위에서의 변형률 계측이 가능한 국부 변형률 센서를 이용하여 구조물 또는 구조 부재의 부재력을 계측하고 이에 기반하여 구조 안전성을 평가하고 있다. 그러나 실 구조물의 부재력 계측을 통한 안전성 평가는 하중의 크기 및 분포에 대한 불확실성 등의 다양한 이유로 부재 내 최대응력 작용점을 정확하게 파악하기 어렵다. 이러한 경우 구조물의 사이즈에 비하여 센서의 길이가 미소한 국부 변형률 센서를 이용한 안전성 평가의 적절성은 센서의 위치 및 개수에 좌우되는 한계를 가지게 된다. 이러한 한계를 극복하기 위하여 센서의 수를 증가시키면 처리해야하는 데이터의 양과 비용이 증가하게 되므로 현실적인 적용성에 문제점을 가지게 된다. 그러므로 본 연구에서는 이러한 한계와 문제점을 극복할 수 있는 대안으로 장대광변형센서에 의한 평균변형률을 이용한 보-기둥의 부재력 계측 기법을 제시하였다.

• 디지털융복합연구
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• 제15권7호
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• pp.223-229
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• 2017

유럽, 미국을 비롯한 일본 등 선진 업계에서는 오랜 기간의 시험을 거쳐 충격계수의 시험결과를 보유하고 있으며, 장비를 설계할 때 이를 적용하여 구조물의 안정성을 확보하고 있다. 그러나 국내 산업체의 실정으로는 실제 구조물이 받는 여러 가지 동적인 외력에 의한 영향을 시험을 통해 충격계수를 확보하기에는 많은 비용과 시간이 소요되기 때문에 선진업체에서 제공하는 충격계수를 활용하여 장비를 설계하고 있다. 본 논문에서는 유한요소해석 프로그램인 NX/NASTRAN을 이용하여 반도체 검사 장비인 PCB Handler의 정하중해석과 충격하중에 대한 과도응답 해석을 진행하고, 변위 결과를 비교하는 방법으로 충격계수를 산출하였다. 충격계수 산출 방법은 일본 구조 구격에서 사용하고 있는 방법을 적용하였으며, PCB Handler가 검사를 위해 급출발 또는 급정지 시 충격계수는 1.27로 산출되었다. 해석으로 얻어낸 충격계수는 향후 장비의 구조개선과 기존장비를 기반으로 제품 개발 시 사용할 수 있어 업계에 도움이 될 것으로 판단된다.

• KCI Concrete Journal
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• 제12권1호
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• pp.57-68
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• 2000

The effect of structure size on the nominal strength of unidirectional fiber-polymer composites, failing by propagation of a kink band with fiber microbuckling, is analyzed experimentally and theoretically. Tests of novel geometrically similar carbon-PEEK specimens, with notches slanted so as to lead to a pure kink band (without shear or splitting cracks), are conducted. The specimens are rectangular strips of widths 15.875, 31.75. and 63.5 mm (0.625, 1.25 and 2.5 in and gage lengths 39.7, 79.375 and 158.75 mm (1.563, 3.125 and 6.25 in.). They reveal the existence of a strong (deterministic. non-statistical) size effect. The doubly logarithmic plot of the nominal strength (load divided by size and thickness) versus the characteristic size agrees with the approximate size effect law proposed for quasibrittle failures in 1983 by Bazant This law represents a gradual transition from a horizontal asymptote, representing the case of no size effect (characteristic of plasticity or strength criteria), to an asymptote of slope -1/2 (characteristic of linear elastic fracture mechanics. LEFM) . The size effect law for notched specimens permits easy identification of the fracture energy of the kink bandand the length of the fracture process zone at the front of the band solely from the measurements of maximum loads. Optimum fits of the test results by the size effect law are obtained, and the size effect law parameters are then used to identify the material fracture characteristics, Particularly the fracture energy and the effective length of the fracture process zone. The results suggest that composite size effect must be considered in strengthening existing concrete structural members such as bridge columns and beams using a composite retrofitting technique.

• Nano
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• 제13권11호
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• pp.1850126.1-1850126.10
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• 2018

Flexible strain sensors, as the core member of the family of smart electronic devices, along with reasonable sensing range and sensitivity plus low cost, have rose a huge consumer market and also immense interests in fundamental studies and technological applications, especially in the field of biomimetic robots movement detection and human health condition monitoring. In this paper, we propose a new flexible strain sensor based on thick CVD graphene film and its low-cost fabrication strategy by using the commercial adhesive tape as flexible substrate. The tensile tests in a strain range of ~30% were implemented, and a gage factor of 30 was achieved under high strain condition. The optical microscopic observation with different strains showed the evolution of cracks in graphene film. Together with commonly used platelet overlap theory and percolation network theory for sensor resistance modeling, we established an overlap destructive resistance model to analyze the sensing mechanism of our devices, which fitted the experimental data very well. The finding of difference of fitting parameters in small and large strain ranges revealed the multiple stage feature of graphene crack evolution. The resistance fallback phenomenon due to the viscoelasticity of flexible substrate was analyzed. Our flexible strain sensor with low cost and simple fabrication process exhibits great potential for commercial applications.

• 한국지반공학회논문집
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• 제25권10호
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• pp.31-40
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• 2009

전기저항식 변형율계를 이용한 콘 관입시험기는 온도 변화에 의해 선단저항력이 달라진다-본 연구에서는 FBG센서를 이용하여 직경 0.5mm의 온도센서와 직경 7mm의 마이크로콘을 제작하여 온도의 변화가 콘 선단저항력에 미치는 영향을 평가하고 이를 효과적으로 보상하고자 하였다-광섬유 마이크로콘과 온도센서는 콘의 구조, 센서 부착 위치 및 광섬유를 이용한 온도보상법 등을 고려하여 제작하였다-온도영향 시험결과, 전기저항식 변형율계의 콘 선단저항력은 온도에 의해 영향을 받으며 온도 차이가 클수록 오차도 증가하는 것으로 나타났다. 반면, FBG센서에서 측정된 콘 선단저항력은 FBG 온도센서를 이용하여 효과적으로 온도의 영향을 보상할 수 있었다. 또한 온도 보상을 실시한 전기저항식 변형율계의 콘 선단저항력은 심도에 따라 일정한 분포를 보였으며 관입과 동시에 온도의 영향이 보상되는 FBG센서의 결과와도 매우 유사한 것으로 나타났다. 본 연구를 통해 온도 변화가 선단저항력에 미치는 영향을 평가하였으며, FBG센서를 이용하여 효과적으로 온도 영향을 보상할 수 있음을 확인하였다.

• Journal of Biosystems Engineering
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• 제1권1호
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• pp.15-15
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• 1976

In analyzing the operational characteristics of a rice whitening machine, the internal radial pressure of the machine was measured using strain gage equipment. Changes in cylinder and feed screw configurations, screen type, cylinder speed and counter-pressure levels were examined to determine their impact on the quality and quantity of milled rice and the performance of the machine. The results are summarized as follows: 1. The internal radial pressure in the whitening chamber varied with the surface condition of the grain being processed. During the first or second pass through the machine, pressure was relatively low, reached a maximum after two to three passes with combinations I and II, three to six with combination III and then began to fall. 2. The pitch of the feed screw and the size of the feed gate opening which determine the rate of entry of grain into the whitening chamber, appeared to be the most important factor aff-::cting the degree of radial pressure, quality and quantity of milled rice and the efficiency of the machine. Using a feed screw with a wide pitch (4.8cm), radial pressure was relatively high and head rice recovery ratio \vere quite low. In this case capacity and machine effic?iency were much higher than obtained when using a feed screw with a narrow pitch (2.3cm). Very significant responses in radial pressure, head rice recovery rates and machine capacity were observed with changes in cylinder speed and counter-pressure levels when using the wide pitch feed screw. 3. The characteristics of the screen which surrounds the whitening chamber had an important effect on whitening efficiency. The existence of small protuberances on the original screen resulted in significant increases in both machine capacity and efficiency but without a significant decrease in head rice recovery or development of excessive radial pressure. Further work is required to determine the effects of screen surface conditions and the shape of the cylinderical steel roller on the rate of bran removal, machine efficiency and recovery rates. The size of the slotted perforations 0:1 the screen affects total milled rice recovery. The opening size on the original screen was fabricated to accommodate the round shape of Japonica rice varieties but was not suitable for the more slender Indica type. Milling Indica varieties with this screen resulted in a reduction in total milled rice recovery. 4. An increase in cylinder speed from 380 to 820 rpm produced a positive effect on head rice recovery for all machine combinations at every level of counter-pressure used in the tests. Head rice recovery was considerably lower at 380rpm using a wide screw pitch when compared to the results obtained at speeds from 600 to 820 r.p.m. The effects of cylinder speed On radial pressure, capacity and machine efficiency showed contrasting results, depending on the width of the feed screw pitch. With a narrow feed screw pitch (2.3cm), a direct proportional relationship was observed bet?ween cylinder speed and both radial pressure and machine efficiency. In contrast, using a 4.8 centimeter pitch feed roller produced a series of inverse relationships between the above variables. Based on the results of this study it is recommended when milling Indica type long grain rice varieties that the cylinder speed of the original machine be increased from 500-600 rmp up to a minimum of 800 rpm to obtain a greater abrasive effect between the grain and the screen. The pitch of the feed screw should be also reduced to decr?ease the level of internal radial pressure and to obtain higher machine efficiency and increased quality of milled rice with increased cylinder speeds. Further study on the interaction between cylinder speed and feed screw pitch is recommended. 5. An increase in the counter pressure level produced a negative effect On the head rice recovery with an increase in radial pressure, capacity, and machine efficiency over all combinations and at every level of cylinder speed. 6. Head rice recovery rates were conditioned primarily by the pressure inside the whitening chamber. According to the empirical cha racteristics curve developed in this study, the relationships of head rice recovery ($Y_h$) and machine capacity ($Y_c$/TEX>) to internal radial pressure ($X_p$) followed an inverse quadratic function and a linear function respectively: $$Y_h^\Delta=\frac{1}{{1.4383-0.2951X_p^\ast+0.1425X_p^{\ast\ast}}^2} , (R^2=0.98)$$$$Y_c^\Delta=-305.83+374.37X_p^{\ast\ast}, (R^2=0.88)$$The correlation between capacity and power consumption per unit of brown rice expressed in the following exponential function: $$Y_c^\Delta=1.63Y_c^{-0.7786^\{\ast\ast}, (R^2=0.94)$$These relationships indicate that when radial pressure increases above a certain range (1. 6 to 2.0 kg/$cm^2$ based On the results of the experiment) head ricerecovery decrea?ses in a quadratic relation with a inear increase in capacity but without any decrease in power consump tion per unit of brown rice. On the other hand, if radial pressure is below the range shown above, power consumption increases dramatically with a lin?ear decrease in capacity but without significant increases in head rice recovery. During the operation of a given whitening machine, the optimum radial pressure range or the correct capacity range should be selected by controlling the feed rate and/or counter-pressure keeping in mind the condition of the grain, particulary the hardness. It was observed that the total number of passes is related to radial pessure level, feed rate and counter-pressure level. The higher theradial pressure the fewer num?ber of pass required but with decreased head rice recovery. In particular, when using high feed rates, the total number of passes should be increased to more than three by reducing the counter-pressure level to avoid decreaseases in head rice recovery (less than 65 percent head rice recovery on the basis of brown rice) at every cylinder speed. 7. A rapid rise in grain temperature seemed to have a close relationship with the pressure generated inside the whitening chamber and, subsequently with head rice reco?very rates. The higher the rate of increase, the lower were the resulting head rice recoveries.

• Journal of Biosystems Engineering
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• 제1권1호
• /
• pp.17-48
• /
• 1976

In analyzing the operational characteristics of a rice whitening machine, the internal radial pressure of the machine was measured using strain gage equipment. Changes in cylinder and feed screw configurations, screen type, cylinder speed and counter-pressure levels were examined to determine their impact on the quality and quantity of milled rice and the performance of the machine. The results are summarized as follows: 1. The internal radial pressure in the whitening chamber varied with the surface condition of the grain being processed. During the first or second pass through the machine, pressure was relatively low, reached a maximum after two to three passes with combinations I and II, three to six with combination III and then began to fall. 2. The pitch of the feed screw and the size of the feed gate opening which determine the rate of entry of grain into the whitening chamber, appeared to be the most important factor aff-::cting the degree of radial pressure, quality and quantity of milled rice and the efficiency of the machine. Using a feed screw with a wide pitch (4.8cm), radial pressure was relatively high and head rice recovery ratio \vere quite low. In this case capacity and machine effic\ulcorneriency were much higher than obtained when using a feed screw with a narrow pitch (2.3cm). Very significant responses in radial pressure, head rice recovery rates and machine capacity were observed with changes in cylinder speed and counter-pressure levels when using the wide pitch feed screw. 3. The characteristics of the screen which surrounds the whitening chamber had an important effect on whitening efficiency. The existence of small protuberances on the original screen resulted in significant increases in both machine capacity and efficiency but without a significant decrease in head rice recovery or development of excessive radial pressure. Further work is required to determine the effects of screen surface conditions and the shape of the cylinderical steel roller on the rate of bran removal, machine efficiency and recovery rates. The size of the slotted perforations 0:1 the screen affects total milled rice recovery. The opening size on the original screen was fabricated to accommodate the round shape of Japonica rice varieties but was not suitable for the more slender Indica type. Milling Indica varieties with this screen resulted in a reduction in total milled rice recovery. 4. An increase in cylinder speed from 380 to 820 rpm produced a positive effect on head rice recovery for all machine combinations at every level of counter-pressure used in the tests. Head rice recovery was considerably lower at 380rpm using a wide screw pitch when compared to the results obtained at speeds from 600 to 820 r.p.m. The effects of cylinder speed On radial pressure, capacity and machine efficiency showed contrasting results, depending on the width of the feed screw pitch. With a narrow feed screw pitch (2.3cm), a direct proportional relationship was observed bet\ulcornerween cylinder speed and both radial pressure and machine efficiency. In contrast, using a 4.8 centimeter pitch feed roller produced a series of inverse relationships between the above variables. Based on the results of this study it is recommended when milling Indica type long grain rice varieties that the cylinder speed of the original machine be increased from 500-600 rmp up to a minimum of 800 rpm to obtain a greater abrasive effect between the grain and the screen. The pitch of the feed screw should be also reduced to decr\ulcornerease the level of internal radial pressure and to obtain higher machine efficiency and increased quality of milled rice with increased cylinder speeds. Further study on the interaction between cylinder speed and feed screw pitch is recommended. 5. An increase in the counter pressure level produced a negative effect On the head rice recovery with an increase in radial pressure, capacity, and machine efficiency over all combinations and at every level of cylinder speed. 6. Head rice recovery rates were conditioned primarily by the pressure inside the whitening chamber. According to the empirical cha racteristics curve developed in this study, the relationships of head rice recovery ($Y_h$) and machine capacity ($Y_c$/TEX>) to internal radial pressure ($X_p$) followed an inverse quadratic function and a linear function respectively: $$Y_h^\Delta=\frac{1}{{1.4383-0.2951X_p^\ast+0.1425X_p^{\ast\ast}}^2} , (R^2=0.98)$$ $$Y_c^\Delta=-305.83+374.37X_p^{\ast\ast}, (R^2=0.88)$$ The correlation between capacity and power consumption per unit of brown rice expressed in the following exponential function: $$Y_c^\Delta=1.63Y_c^{-0.7786^\{\ast\ast}, (R^2=0.94)$$ These relationships indicate that when radial pressure increases above a certain range (1. 6 to 2.0 kg/$cm^2$ based On the results of the experiment) head ricerecovery decrea\ulcornerses in a quadratic relation with a inear increase in capacity but without any decrease in power consump tion per unit of brown rice. On the other hand, if radial pressure is below the range shown above, power consumption increases dramatically with a lin\ulcornerear decrease in capacity but without significant increases in head rice recovery. During the operation of a given whitening machine, the optimum radial pressure range or the correct capacity range should be selected by controlling the feed rate and/or counter-pressure keeping in mind the condition of the grain, particulary the hardness. It was observed that the total number of passes is related to radial pessure level, feed rate and counter-pressure level. The higher theradial pressure the fewer num\ulcornerber of pass required but with decreased head rice recovery. In particular, when using high feed rates, the total number of passes should be increased to more than three by reducing the counter-pressure level to avoid decreaseases in head rice recovery (less than 65 percent head rice recovery on the basis of brown rice) at every cylinder speed. 7. A rapid rise in grain temperature seemed to have a close relationship with the pressure generated inside the whitening chamber and, subsequently with head rice reco\ulcornervery rates. The higher the rate of increase, the lower were the resulting head rice recoveries.