• 제목/요약/키워드: Friction sector

검색결과 10건 처리시간 0.028초

농용 무인헬리콥터의 원심클러치 설계 - 동력 전달의 이론분석 - (Centrifugal Clutch Design for an Unmanned Helicopter - Theoretical Analysis of Power Transfer -)

  • 이재홍;구영모;신시균
    • Journal of Biosystems Engineering
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    • 제33권1호
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    • pp.14-20
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    • 2008
  • An agricultural unmanned helicopter was suggested for an alternative to current pesticide application methods to solve such problems as high cost, low efficiency, shirking task and unsafe work. To pursuit this trend, researches on the development of unmanned helicopters have been accelerated in Korea as well. In this research, a guide type centrifugal clutch that plays an important role in the unmanned helicopter was studied. Theoretical analyses and experimental tests were conducted for designing an optimal clutches. Main design factors of the guide type centrifugal clutch were found to be spring constant, free length of spring, mass of friction sector, contact area, allowable pressure, number of friction sector, friction coefficient, radius of drum, and clutch arrangement. And these design factors could be the functions of engaging engine speed and desired power transfer capacity. The result of the single clutch test showed the power transfer capacity of 14.1 PS at 5,800 rpm and the result of the dual clutch test showed that the capacity of 17.7 PS at 5,600 rpm. These experimental results agreed well the theoretical simulations.

농용 무인헬리콥터의 원심클러치 설계 - 최적 설계치의 시뮬레이션 - (Centrifugal Clutch Design for Unmanned Helicopter - Simulation of Optimal Factors -)

  • 이재홍;구영모
    • Journal of Biosystems Engineering
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    • 제34권2호
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    • pp.89-94
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    • 2009
  • Aerial application using an agricultural unmanned helicopter was suggested for an alternative against current pesticide application methods. Centrifugal clutches play important roles in the performance and safety of the helicopter operation. A previous study analyzed and verified the power transfer theory of the guide type centrifugal clutch. Based on the clutch theory, optimal designs of the clutch became possible and feasible using a simulation method. Design criteria of the clutch were the power transfer capacity of 24.66 kW(33.5 PS) at the rated engine speed and the engaging range speed of 3,000${\sim}$3,500 rpm. Various designs were accomplished using the simulation. An optimal clutch was simulated by determining the values of spring constant and mass of friction sector, which were 94,700 N/m and 123.7 g, respectively. The design performed the power capacity of 24.86 kW(33.8 PS) and engagement speed of 3,069 rpm, meeting the design criteria. Using the designed clutch, an efficient transfer of the power would be possible for the unmanned agricultural helicopter.

Determination of Urban Surface Aerodynamic Characteristics Using Marquardt Method

  • Zhang, Ning;Jiang, Weimei;Gao, Zhiqiu;Hu, Fei;Peng, Zhen
    • Wind and Structures
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    • 제12권3호
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    • pp.281-283
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    • 2009
  • Marquardt method is used to estimate the aerodynamic parameters in urban area of Beijing City, China, including displacement length (d), roughness length ($z_0$) and friction velocity (u*) and drag coefficient. The surface drag coefficient defined as the ratio between friction velocity and mean wind speed is 0.125 in our research, which is close to typical urban area value. The averaged d and $z_0$ are 1.2 m and 7.6 m. d and $z_0$ change with direction because of the surface heterogeneity over urban surface and reach their maximum values at S-SW sector, this tendency agrees with the surface rough element distribution around the observation tower.

PI-LEAD 알고리즘을 이용한 2축 안정화 짐벌 시스템 제어 (The Control for the 2-Axis Stabilized Gimbal using the PI-LEAD Algorithm)

  • 이진복;최한고
    • 융합신호처리학회논문지
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    • 제14권2호
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    • pp.117-123
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    • 2013
  • 서보 시스템에서 마찰과 같은 비선형 요소는 측정이 어려우며, 또한 정확한 예측이 어려워 보상하기가 쉽지 않다. 특히, 2축 안정화 짐벌 시스템에서 마찰은 큰 오차를 발생시켜 최종적으로 제어 성능을 만족시키지 못한다. 이와 같은 문제점을 해결하기 위해 관측기 등을 적용한 마찰 보상 연구가 많이 진행되어 왔으나 특정 조건에서만 적용되어 군수 분야에서 정밀도를 요하는 2축 안정화 짐벌 시스템에 적용하는데 제한적이다. 본 논문에서는 가장 일반적이면서 강인성이 입증된 PID 알고리즘을 변형시킨 PI-LEAD 알고리즘을 사용하여 모델링 및 시뮬레이션을 통해 마찰 보상 효과를 입증하고, 실제 2축 안정화 짐벌 시스템에 적용하여 효과를 검증한다. 성능시험을 통해 PI-LEAD 알고리즘이 마찰에 의한 오차를 최소화하여 정밀 서보 시스템에서 요구하는 성능을 만족하는 것을 검증하였다.

도시철도 곡선구간 콘크리트궤도 진동특성에 관한 연구 (A study on urban transit vibration characteristics for curved concrete track)

  • 김경민;김진호;이광도
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2011년도 춘계학술대회 논문집
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    • pp.442-445
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    • 2011
  • Concrete track on the new railway lines of the existing roads are built on high ground, or less than 400m radius of the sharp curve sectors will occur. sharp curve sectors the rail and wheel friction, stick-slip due to the band of 1,000Hz or squeal noise occurs from the increase in civil complaints about noise is a real situation. In this study, discussed in previous studies, noise measurements for each radius of concrete track and frequency analysis, followed by the radius of the curve in order to investigate vibration characteristics of urban railway sector sharp curve radius less than 400m and 400m ~ 1,000 m further to the point selected track components(rails, sleepers, ballast) according to the vibration measurements and analysis of the frequency characteristics and the results were derived.

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우리나라 자동차산업의 미국투자 입지동기 분석 - 현대자동차 미 앨라배마 투자 사례를 중심으로 - (An Analysis of the Locational Motives for the Korean Auto Industry′s Investment in the U.S. - Case Study of Hyundai Motor Manufacturing Alabama -)

  • 서정욱
    • 한국경제지리학회지
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    • 제7권1호
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    • pp.65-81
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    • 2004
  • 해외직접투자는 기업의 장기적인 성장전략 차원에서 여러 가지 동기를 가진다. 본 연구는 현대자동차의 미국 앨라배마주 현지투자에 대한 사례연구를 통해 우리나라 자동차산업의 관점에서 미국에 대한 직접투자의 동기와 입지선택시의 고려요인을 분석한다. 이 논문은 미국에 대한 수출이 최근 호조세를 지속하고 있는 상황에서 생산원가 면에서 유리하지 않은 미국내 투자가 이루어진 동기는 무엇인가에 대한 문제 제기에서 출발한다. 조사결과 미국투자의 가장 강력한 동기는 대미통상마찰 완화였다. 즉, 수출의 상당부분을 미국시장에 의존하고 있는 상황에서 현지생산을 통하여 자동차부문의 심각한 한ㆍ미간 무역수지 불균형현상을 완화하여 미국과의 통상마찰을 회피하고 무역분쟁의 소지를 줄이고자 하는 방어적 차원의 전략적 동기가 현대자동차 미국 현지투자의 가장 큰 이유였다. 소비자에의 접근성 향상 등 기타 요인은 부수적인 중요성에 머물렀다. 그러나, 국가 단위의 선택이 이루어진 후 local 단위의 선택에 있어서는 여러 가지 입지적 요인들이 종합적으로 고려되었으며, 특히 지방정부의 적절한 인센티브 제공이 중요한 역할을 하는 것으로 나타났다. 이러한 연구결과는 우리나라 제조업의 선진국에 대한 해외투자는 전통적인 해외직접투자 이론으로써는 설명할 수 없는 방어적 차원의 전략적 동기가 중요하게 작용한다는 것을 시사한다. 아울러, 각급 정부단위의 적절한 유인구조 설계가 해외직접투자 유치에 중요하다는 것을 확인한다.

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시판 태권도복의 기능성 증진을 위한 키토산 처리 효과 (Effect of Chitosan Treatment for Improving Physical Properties of Taegwondo Uniform)

  • 김선희;전미선;김혜수
    • 복식문화연구
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    • 제17권3호
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    • pp.424-430
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    • 2009
  • Taegwondo uniforms need powerful durability in fabrics against friction and shock because of higher exercising power. Therefore, in this study we developed more comfortable Taegwondo uniform for functional fabrics(deodorization rate, antibacterial activity and static charge). Chitosan is a deacetylated product of chitin, has widely been used in the biomedical sector, food industry, and textile industry. For the purpose of this study, we used the chitosan, which was congenial to the human body. Then, we compared the differences between the chitosan treated fabrics and non treated fabrics of Taegwondo uniform(100% polyester, 65% polyester/35% cotton). Chitosan was dissolved in 1% acetic acid. Also, the fabrics were washed using distilled water. Afterward, its treatment with chitosan was completed by padding the sample to its wet pick-up at $80{\pm}5%$ and by heating $150^{\circ}$ for 3 minutes. The chitosan treated Taegwondo uniform was improved on deodorization rate than non treated uniform. And the chitosan treated Taegwondo uniform was improved remarkably the antibacterial activity in all samples. In the further researches, the static charge was reduced in chitosan treatment uniform.

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패드의 선단압력을 고려한 부채꼴 모양의 피봇식 추력베어링의 성능해석 (An analysis of the performance of sector shaped, pivoted pad thrust bearings in consideraation of the inlet pressure)

  • 김종수;김경웅
    • 대한기계학회논문집
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    • 제12권5호
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    • pp.1063-1070
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    • 1988
  • 본 연구에서는 부채꼴형 유한폭 패드베어링에서의 선단압력을 구하기 위하여 3차원 유동모델을 제시하였으며, 이 유동모델을 기초로 하여 구해진 선단압력을 패드 선단에서의 압력경계조건으로 사용하여 유막내의 압력을 구하고 베어링의 하중지지능 력, 마찰토오크 및 윤활유량등을 계산함으로써 베어링의 성능을 해석하였다. 그 결 과 선단 압력이 크게 발생하는 운전조건일수록 선단압력을 무시한 종래의 베어링 성능 해석결과와는 상당한 차이가 있었으며, 특히 관성계수가 큰 운전조건에서 사용되는 피 봇식 추력베어링에서는 선단압력의 영향으로 인하여 하중지지능력을 최대로하는 피봇 점의 위치가 패드 선단부쪽으로 크게 이동되었다.

한국에 영향을 미치는 약해진 열대저기압 활동과 태평양 10년 주기 진동과의 관계 (A Possible Relation of Pacific Decadal Oscillation with Weakened Tropical Cyclone Activity over South Korea)

  • 장민희;박두선;김다솔;박태원
    • 한국지구과학회지
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    • 제43권1호
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    • pp.23-29
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    • 2022
  • 열대저기압이 한반도로 접근할 때 중심최대풍속이 34 knot보다 약해졌더라도(weak tropical cyclone; WTC) 수도권 지역으로 상륙하면 상당한 피해를 일으키지만 WTC만 독립적으로 조사한 학술연구는 거의 없다. 본 연구에 따르면 WTC 활동은 Pacific Decadal Oscillation (PDO)와 관련되어 있는 것으로 보인다. PDO가 음의 위상일 때는 양의 위상일 때보다 95% 신뢰구간에서 유의하게 더 많은 WTC가 한반도에 영향을 미치는 것으로 나타났다. PDO 양의 위상에 비해 음의 위상 시기에는 북서태평양 북부에서 양의 상대소용돌이 아노말리가 나타난 반면, 북서태평양 남부에서는 강한 연직바람시어와 음의 상대소용돌이 아노말리가 나타났다. 이런 조건 하에서 열대저기압의 발생위치가 보다 북쪽으로, 즉 동아시아 대륙에 더욱 근접할 수 있었던 것으로 보이며 이에 따라 열대저기압의 전체 생애가 짧아졌을 것이다. 게다가 PDO 음의 위상 시기에 일본열도 상공에 자리한 고기압성 아노말리는 열대저기압의 진로를 좀 더 서쪽으로 밀어내어 육지에 의한 마찰과 황해 저층 냉수대의 영향도 증가하였을 것이다. 이에 따라 열대저기압의 생애최대강도와 상륙 시 강도가 약해져 PDO 음의 위상 때 WTC 활동이 한반도에서 증가한 것으로 분석된다.

한미간(韓美間) 정보통신분야(情報通信分野) 통상마찰예방(通商摩擦豫防)과 해소방안(解消方案)에 관한 연구(硏究) (A study on The U.S.-Korean Trade Friction Prevention and Settlement in the Fields of Information and Telecommunication Industries)

  • 정재영
    • 무역상무연구
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    • 제13권
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    • pp.869-895
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    • 2000
  • The US supports the Information and Communication (IC) industry as a strategic one to wield a complete power over the World Market. However, several other countries are also eager to have the support for the IC industry because the industry produces a high added value and has a significant effect on other industries. Korea is not an exception. Korea recently succeeded in the commercialization of CDMA for the first time in the world, after the successful development of TDX. Hence, it is highly likely to get tracked by the US. Although the IC industry is a specific sector of IT, there is a concern that there might be a trade friction between the US and Korea due to a possible competition. It will be very important to prepare a solution in advance so that Korea could prevent the friction and at the same time increase its share domestically and globally. It will be our important task to solve the problem with the minimum cost if the conflict arises unfortunately in the IT area. The parties that have a strong influence on the US trade policy are the think tank group and the IT-related interest group. Therefore, it would be important to have a close relationship with them. We found some implications by analyzing the case of Japan, which has experienced trade frictions with the US over the long period of time in the high tech industry. In order to get rid of those conflicts with the US, the Japanese did the following things : (1) The Japanese government developed supporting theories and also resorted to international support so that the world could support the Japanese theories. (2) Through continual dialogue with the US business people, the Japanese business people sought after solutions to share profits among the Japanese and the US both in the domestic and in the worldwide markets. They focused on lobbying activities to influence the US public opinion to support the Japanese. The specific implementation plan was first to open culture lobby toward opinion leaders who were leaders about the US opinion. The institution, Japan Society, were formed to deliver a high quality lobbying activities. The second plan is economic lobby. They have established Japanese Economic Institute at Washington. They provide information about Japan regularly or irregularly to the US government, research institution, universities, etc., that are interested in Japan. The main objective behind these activities though is to advertise the validity of Japanese policy. Japanese top executives, practical interest groups on international trade, are trying to justify their position by direct contact with the US policy makers. The third one is political lobby. Japan is very careful about this political lobby. It is doing its best not to give impression that Japan is trying to shape the US policy making. It is collecting a vast amount of information to make a correct judgment on situation. It is not tilted toward one political party or the other, and is rather developing a long-term network of people who understand and support the Japanese policy. The following implications were drawn from the experience of Japan. First, the Korean government should develop a long-term plan and execute it to improve the Korean image perceived by American people. Second, the Korean government should begin public relation activities toward the US elite group. It is inevitable to make an effort to advertise Korea to this elite group because this group leads public opinion in the USA. Third, the Korean government needs the development of a relevant policy to elevate the positive atmosphere for advertising toward the US. For example, we need information about to whom and how to about lobbying activities, personnel network who immediately respond to wrong articles about Korea in the US press, and lastly the most recent data bank of Korean support group inside the USA. Fourth, the Korean government should create an atmosphere to facilitate the advertising toward the US. Examples include provision of incentives in tax on the expenses for the advertising toward the US and provision of rewards to those who significantly contribute to the advertising activities. Fifth, the Korean government should perform the role of a bridge between Korean and the US business people. Sixth, the government should promptly analyze the policy of IT industry, a strategic area, and timely distribute information to industries in Korea. Since the Korean government is the only institution that has formal contact with the US government, it is highly likely to provide information of a high quality. The followings are some implications for business institutions. First, Korean business organization should carefully analyze and observe the business policy and managerial conditions of US companies. It is very important to do so because all the trade frictions arise at the business level. Second, it is also very important that the top management of Korean firms contact the opinion leaders of the US. Third, it is critically needed that Korean business people sent to the USA do their part for PR activities. Fourth, it is very important to advertise to American employees in Korean companies. If we cannot convince our American employees, it would be a lot harder to convince regular American. Therefore, it is very important to make the American employees the support group for Korean ways. Fifth, it should try to get much information as early as possible about the US firms policy in the IT area. It should give an enormous effort on early collection of information because by doing so it has more time to respond. Sixth, it should research on the PR cases of foreign enterprise or non-American companies inside the USA. The research needs to identify the success factors and the failure factors. Finally, the business firm will get more valuable information if it analyzes and responds to, according to each medium.

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