• 대한기계학회논문집A
• /
• 제40권2호
• /
• pp.175-183
• /
• 2016

복잡한 기계장치에 대한 내구신뢰성 평가는 단순한 응력해석을 통해 피로수명을 예측하는 것이 일반적인 방법이다. 하지만 기존 방법은 유한요소 해석 시 여러 가지 요인에 의해 일관된 응력해석 결과를 얻기 어려워 해석자에 따라 상이한 수명을 예측하는 단점을 지닌다. 하지만 구조응력을 기반으로 하는 내구신뢰성 평가 기법은 이러한 단점을 보완하여 보다 합리적인 결과를 제공해 준다. 구조응력기법은 유한요소 모델의 요소 수와 요소 형태에 무관하게 일관된 응력결과를 제공하기 때문에 신뢰성이 높은 내구도 평가 결과를 얻을 수 있다. 해석조건 및 환경에 독립적인 결과를 제공해 주는 구조응력은 최근 대형선박 설계 및 각종 기계장치의 피로수명 예측에 종종 활용되고 있어 보다 깊이 있고 체계적인 연구가 필요하다. 따라서, 본 연구에서는 (a) 유한요소모델의 형태에 상관없이 요소에 독립적인 구조응력 산출기법을 제시하고, (b) 이를 이용하여 자동차 클러치 스냅링부의 구조응력 산출하여 피로파괴를 예측하고자 한다.

• Journal of Ecology and Environment
• /
• 제44권1호
• /
• pp.41-44
• /
• 2020

The Chinese many-toothed snake (Sibynophis chinensis) is an endangered species in South Korea. To determine its reproductive activity, here we captured a gravid S. chinensis from Mulyeongari Oreum Wetland Conservation Area, Jeju Island, on May 27, 2018, and reared it at Animal Taxonomy and Morphology Laboratory, Jeju National University, South Korea. The snake oviposited a clutch of six eggs between June 12 and 20, 2018, with an average size of 24.86 ± 1.36 mm in length and 9.86 ± 0.49 mm in width, which were artificially incubated at a constant temperature of 27 ℃. After incubating for 34-41 days, five of these six eggs successfully hatched. Average snoutvent length (SVL), tail length (TL), and body weight (BW) of hatchlings were 136.5 ± 5.17 mm, 47.76 ± 2.80 mm, and 1.66 ± 0.12 g, respectively. This study observed the reproductive activity of S. chinensis and characterized its eggs and hatchlings for the first time, providing valuable information for the long-term conservation plan of S. chinensis in South Korea.

• Journal of Ecology and Environment
• /
• 제31권3호
• /
• pp.201-206
• /
• 2008

This study was conducted to determine clutch size and habitat usage of Kentish plovers (Charadrius alexandrinus) breeding on Sinja-do lslet in the Nakdong Estuary from 22 April to 12 July in 1995 and from 21 April to 20 June in 1996. The Kentish plover preferred grasslands and damp sands to dry dunes as nesting sites. The difference in hatching success among these microhabitats was attributed to high tides, which washed away many nests on damp sands, and strong winds, which frequently shifted the sand to bury eggs on dry dunes. The main mortality factor in grasslands was predation by magpies Pica pica. Each clutch contained one to four eggs, with a mode of three eggs. Hatching success was highest in two-egg clutches and lowest in one- and four-egg clutches. The mean interval for egg laying was 1.8 days between the first and second eggs and 2.1 days between the second and third eggs. The average incubation period was about 24.2 days.

• Animal cells and systems
• /
• 제4권4호
• /
• pp.329-336
• /
• 2000

Life table experiments were performed in order to examine the effects of food quality on Moina macrocopa fed with four kinds of algal foods, Botryococcus sp., Scenedesmus subspicatus, Selenastrum capricornutum, and Chlorella sp., at $20^{\circ}C$ . The temperature effects on M. macrocopa were also assessed, feeding Chlorella at $17^{\circ}C$,$20^{\circ}C$,$25^{\circ}C$, and a combination of $28^{\circ}C$ (light) and $25^{\circ}C$ (dark). The cartilaginous Botryococcs cells were Inappropriate food for Moina. Among the foods tested, Chlorella was the food of the best quality in all accounts of life history traits. Moina grown on Chlorella showed higher net reproductive rate ($R_0$), longer mean and maximum longevities, earlier mean age at maturity, longer mean carapace length at maturity, larger mean clutch size, and shorter mean time interval between clutch productions than those grown on Selenastrum and Scenedesmus. An optimal temperature for Moina was $20^{\circ}C$ . When Moina were grown on Chlorella at $20^{\circ}C$, they showed the highest r, the highest $R_0$, the shortest T, the longest mean longevity, the earliest mean age at maturity, the longest mean carapace length at maturity, and the largest mean clutch size. The results of life table experiments showed that the individual and population growth patterns were much more affected by low temperature $17^{\circ}C$, than by high temperature ($\geq 20^{\circ}C$). In the optimal condition, the r value was very high, 5.1 in $d^{-1}$. In conclusion, the food quality and the temperature are the most important factors to govern the size and continuity of Moina population, by which the individual growth rates and reproductivity of members in the population can be controlled to survive in their environment such as small and temporary water bodies in nature.

• 한국소음진동공학회논문집
• /
• 제23권3호
• /
• pp.240-248
• /
• 2013

자동차 수동변속기 내 래틀과 같은 회전체 진동은 엔진 연소폭발 주기와 연동하여 발생한다. 이러한 충격형 진동 특성은 선형 시간 불변 분석법을 적용하여 살펴볼 수 있다. 기어의 동적 특성을 이해하기 위해, 특정 형태의 앞 바퀴 굴림 방식 수동 변속기에 대한 연구를 수행하였다. 첫째, 동특성 고유값과 주파수 응답함수를 기반으로 자유도를 줄이는 방법을 제시하였는데, 이는 행렬의 크기를 줄이는 효과적인 역할을 한다. 둘째, 단일 질량 플라이휠과 이중 질량 플라이휠의 동적 특성을 비교하였다. 모빌리티 분석을 기반으로 한 이중 질량 플라이휠의 효과를 검토하였는데, 이로부터 진동에 의해 가진되는 충격을 회피하기 위한 기본 개념을 이해 할 수 있다. 마지막으로, 두 단계 클러치 댐퍼로부터 유효 강성 값을 도출하여 선형 불변형 시스템 모델을 연구하였다. 두 단계의 서로 다른 클러치 강성조합을 이용하여 클러치 댐퍼의 동적특성에 대한 관계를 예측할 수 있다.

• 로봇학회논문지
• /
• 제17권2호
• /
• pp.172-177
• /
• 2022

In general, detection robots using ultrasonic sensors are equipped with sensors to protrude outward or to contact objects. However, in the case of a screw-propelled robot that detects the inside of a reactor tendon duct, if the ultrasonic sensor protrudes to the outside, resistance due to grease is generated, and thus the propulsion efficiency is reduced. In order to increase the propulsion efficiency, the screw must be sharp, and the sharper the screw, the more difficult it is to apply a high-performance ultrasonic sensor, and the detection efficiency decreases. This paper proposes a screw shape-changing mechanism that can improve both propulsion efficiency and detection efficiency. This mechanism includes an overlapped helical ring (OHR) structure and a magnetic clutch system (MCS), and thus the shape of a screw may be changed to a compact size. As a result, the Screw-propelled robot with this mechanism can reduce the overall length by about 150 mm and change the shape of the screw faster and more accurately than a robot with a linear actuator.

• 한국환경복원기술학회지
• /
• 제15권5호
• /
• pp.155-163
• /
• 2012

This study was carried out to monitor reproductive responses of great tits in 17 urban forests in Daegu metropolitan city. The reproductive perspectives of great tits were surveyed by using 106 artificial bird nests, of which five or seven nests were set up in every urban forest. A ratio of artificial nests used by great tits for their reproduction was 27.4%. It was showing that forests, where the reproductive response was higher, was located at the edge of the city, or was known as having a good vegetation structure in the urban area. The laying date of a great tit was a little earlier in forests in the middle of the city. It might be dependent on the density of artificial land uses including a residential area and an industrial complex, which are able to increase an urban micro-temperature. Otherwise, natural forests or forest patches nearby natural forests located at the edge of the city were showing that the laying date of great tits was relatively later than the oneee in the forest in the middle of the city. There was a big difference of reproduction perspectives of great tit between the 1st and 2nd reproduction. In the 1st reproduction, a clutch size was larger, while an egg volume was so low. Otherwise, the clutch size was shown so smaller in the 2nd reproduction than in the 1st reproduction, while the egg volume was larger in the 2nd reproduction. It might be due to the survival strategy of a great tit to prepare the winter season for a juvenile. Many variables, regarding to the problem of climate changes, have been linked to the environment of urban area and the bird habitats. Finally, Monitoring a bird reproduction is a valuable work for managing an urban forest as well as for conserving a natural forest.

• 한국가금학회:학술대회논문집
• /
• 한국가금학회 2000년도 하계 학술 심포지움(한국 타조산업의 현재와 미래)
• /
• pp.39-46
• /
• 2000

타조알의 형성은 배란된 난자가 나팔관과 난백분비부, 협부, 자궁 그리고 총배설강을 통과하면서 완전한 형태의 알로 산란된다. 그리고 1 clutch size가 40$\pm$15개 정도이다. 알의 크기는 1,450g에서 200~400g의 변이가 있는 것으로 본다. 타조의 난질에는 cuticle 층이 없어서 병원균의 침입에 약하다. 그리고 알의 껍질은 2mm 정도로 두꺼우며 그주요 성분은 달걀의 껍질에서와 마찬가지로 calcium carbonate이다 타조알의수거는 수놈의 방해가 없도록 하여야 하며 bacteria나 fungi의 침입이 업도록 하여야 한다. 수거된 알은 저장하였다가 부화기의 수용능력이 되면 부화를 시작한다. 부화 전에 아를 저장할 경우 15~18$^{\circ}C$로 저장실 온도를 유지하면 7일 정도 저장이 가능하지만 7일 이상 저장할 경우 12$^{\circ}C$로 저장온도를 낮추고 이때 상대습도는 75%로 유지하는 것이 이상적이다. 부화기의 온도는 36.0~36.5$^{\circ}C$가 이상적이며 이때 이상적인 습도는 35%이하이어야 한다. 또 부화중 전란을 하여야 하는데 대개 한시간에 한번씩 74~90。로 전란 해주는 것이 바람직하다. 부화에 적당한 알은 기형적으로 크거나 작으면 부화율을 높이지 못한다.

• 한국산림과학회지
• /
• 제97권1호
• /
• pp.83-87
• /
• 2008

본 연구는 침엽수림 지역과 활엽수림 지역에서 박새류의 인공새집 이용 특성을 파악하기 위해 각각 2006년과 2007년 3월에서 6월까지의 기간 동안 실시되었다. 두 지역에 생육하고 있는 수목의 종수, 종다양도지수, 흉고단면적은 침엽수림 지역에 비해 활엽수림 지역에서 높은 것으로 나타났다. 또한 엽층의 수직분포에 있어서도 지면에서 1m 이하의 엽층을 제외한 모든 엽층의 피도량이 활엽수림 지역에서 높은 것으로 나타났다. 2년에 걸쳐 두 지역에 설치한 인공새집에서는 곤줄박이, 쇠박새, 진박새, 박새가 번식을 한 것으로 나타났다. 침엽수림 지역보다 활엽수림 지역에서 번식쌍수가 더 높았다. 진박새의 경우, 한배산란수와 한배새끼수, 번식성공률이 침엽수림 지역에서 높은 것으로 나타났다. 또한 박새는 한배새끼수와 번식성공률이 활엽수림 지역에서 더 높았다. 서식 환경 구조 및 박새류의 종간 니치(niche)에 따라 선호하는 서식지가 다른 것으로 판단된다. 다양한 서식 환경에 설치한 인공새집이 조류 군집 및 생태에 미치는 영향을 지속적으로 파악해야 할 것이며, 이를 통해 장기적으로 인공새집을 설치 및 관리해야 할 것으로 판단된다.

• 수산해양기술연구
• /
• 제47권3호
• /
• pp.194-202
• /
• 2011

Maturation and spawning of the Shotted halibut, Eopsetta grigorjewi was investigated based on the samples captured in South Korean waters from January 2008 to December 2009. Gonadosomatic index began to increase in December, and reached maximum between January to March. After spawning it began to decrease from May. Reproductive season was estimated to January-April, with peak in February. Fecundity was proportional to the size of the female, with the clutch size varying from 170,000 eggs in the smallest female (total length, 28.9cm) to 1,300,000 eggs in the largest (total length, 41.5cm). Size at 50% sexual maturity (TL50), determined from mature females, was 28.8cm. Annual reproductive cycles of this species could be divided into six successive stages; immature stage (May-October), nucleolus stage (November-January), yolk vesicle stage (January-February), vitellogenic and ripe stage (January-April) and spent stage (April-May).