• 한국소음진동공학회논문집
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• 제18권9호
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• pp.937-942
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• 2008

이 논문은 건설이 완료된 700MW급 발전소의 시운전 기간 중 주 급수펌프 임펠러에서 반복적으로 발생된 웨어링 이탈 및 고착, 슈라우드 손상 그리고 축 절단 등의 절손이 부분부하 조건에서 증폭되는 압력맥동과 연관이 있는 것으로 규명되었다.

• 한국재료학회지
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• 제12권10호
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• pp.820-824
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• 2002

It is of importance to know that the bonding strength and interfacial stress of SOI wafer pairs to meet with mechanical and thermal stresses during process. We fabricated Si/2000$\AA$-SiO$_2$ ∥ 2000$\AA$-SiO$_2$/Si SOI wafer pairs with electric furnace annealing, rapid thermal annealing (RTA), and fast linear annealing (FLA), respectively, by varying the annealing temperatures at a given annealing process. Bonding strength and interfacial stress were measured by a razor blade crack opening method and a laser curvature characterization method, respectively. All the annealing process induced the tensile thermal stresses. Electrical furnace annealing achieved the maximum bonding strength at $1000^{\circ}C$-2 hr anneal, while it produced constant thermal tensile stress by $1000^{\circ}C$. RTA showed very small bonding strength due to premating failure during annealing. FLA showed enough bonding strength at $500^{\circ}C$, however large thermal tensile stress were induced. We confirmed that premated wafer pairs should have appropriate compressive interfacial stress to compensate the thermal tensile stress during a given annealing process.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.178.2-178.2
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• 2010

The wind turbine gearbox is important rotating part to transmit torque from turbine blade to generator. Generally, gear shaft which rotates causes vibration by influence of stiffness and mass with gear shaft. Root cause of this vibration source is well known to gear transmission error that is decided from gear tooth property. Transmission error excites a gear, and makes excitation force that is vibrated shaft. This vibration of shaft is transmitted to gearbox housing through gearbox bearing. If the resonance about which the natural frequency of the gearbox accords with shaft exciting frequency occurs, a wind turbine can lead to failure. The gearbox for wind turbine should be considered influence of vibration as well as the fatigue life and its performance by such reason. The cause to vibration should be closely examined to reduce influence of such vibration. In this paper, the cause of the vibration which occurs by a gearbox is closely examined and the method which can reduce the vibration which occurred is shown. It is compared with vibration test outcome of a 3MW gearbox for verification of the method shown by this paper.

• 대한기계학회논문집A
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• 제32권7호
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• pp.569-575
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• 2008

In this study, disk type of thermal barrier coating system for gas turbine blade was isothermally aged in the furnace changing exposure time and temperature. For each aging condition, bond tests for three samples were conducted for evaluating degradation of adhesive or cohesive strength of thermal barrier coating system. For as-sprayed condition, the location of fracture in the bond test was in the middle of epoxy which have bond strength of 57 MPa. As specimens are degraded by thermal aging, bond strength gradually decreased and the location of failure was also changed from within top coat at the earlier stage of thermal aging to the interface between top coat and TGO at the later stage due to the delamination in the coating.

• 한국표면공학회지
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• 제37권4호
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• pp.226-233
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• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

• 동력기계공학회지
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• 제15권5호
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• pp.22-29
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• 2011

In this study, the damage mechanism of large scale steam turbine due to water induction was analyzed and recovery characteristics were reviewed. A turbine consists of the rotating rotor and the stationary casing, and the clearance between them is very small for the efficiency enhancement. If water induction, while relatively cold steam or water is introduced into turbine, occurs, the considerable humping is caused at the casing near the initial water induction point and that induces the rubbing between rotor and casing. Finally, it leads to the catastrophic failure. Bowed rotor has the different characteristics in the recovery depending on damage degree. The elastic deformation due to light rubbing is recovered by turning the rotor with 3 rpm under normal operation condition, but most plastic deformation due to rubbing deforms the local microstructure and that results in permanent deformation which could not be recovered under normal operation condition. Bowed rotor has diverse characteristics depending on the recovery method, and the method is empirical and needs the cutting edge technology. Careful recovery treatment of the rotor will eliminate the risks and secure the high quality rotor similar to new rotor. If any critical error is made during the recovery, the rotor would not be recovered permanently and it should be scrapped.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.181-184
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• 2008

오스테나이트 계열 스테인리스강의 경우 뛰어난 내열성으로 인해 가스 터빈 블레이드나 디스코 등으로 많이 사용되고 있다. 본 연구에서는 터빈 블레이드로 사용되는 316 스테인리스강의 고온 인장 및 저주기 피로 물성을 실험적으로 구하였다. 실험 결과 탄성계수와 항복강도, 최대인장강도 모두 온도 증가에 따라 감소하는 것으로 확인되었다. 소성변형률 진폭, 소성변형률 에너지 등의 인자들이 피로파괴에 미치는 영향도 조사하였다. 실험을 통해 얻어진 고온 인장 물성을 이용하여 316 스테인리스강으로 제작된 가스터빈 블레이드의 구조해석을 수행하였다.

• 한국농공학회지
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• 제17권4호
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• pp.3897-3920
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• 1975

Since the most of Korean dairy and cattle raising farms are too small to introduce western mechanized farming, it is necessary to develope small size equipments. This study has been carried to develop a rotary mower as on attachment of 8 to 10 horse powertiller which is widely spread in rural area. It will not ony be helpfull for the farmers to harvesting hay grass but also desirable to increase the power tiller utility. The protto type rotary mower designed through the fundamental investigations, has been modified and improved through the field trials, and a series of field tests has been carried to investigate its performance and economic feasibility comparing with existing vailable harvesting equipments. The results are as follows; 1. To increase the stability, two guide wheels are attached to both side of the protto type rotary mower. 2. To prevent the clinging of tall grasses, the vertical driving shafts are covered with cylindrical protectors. 3. The cutting height is adjustable in 8 steps from 2.5 to 20 centimeters by changing the length of guide wheel legs. 4. The practical Critical cutting speed were always higher than theoretical value in both case of single cutting blade and three when the cutting depth was 25 millimeter. 5. The peripheral speed of cutting blade was varied in response to the change of engine speed, mean while the peripheral speed was adequate as it was changhed from 25 to 35 meter per second when the power tiller is operated in proper working ground speed. 6. The time requirement to harvest 10 a were 88.7, 54.6 and 41.4 minutes for the first, second and third stage of ground speed respectively, and because of the difficulty of delivery, it was observed that operating with fourth stage of ground speed was not recomanendable when the grass height is taller than 90 centimeters. 7. The performance of rotary mower were 1.1-1.7, 1.4-4.0, 3.8-11.8 and 7.4-22.0 times of reciprocating mower, portable disc type cutter, hay scythe and ordinary sickle respectively. 8. When the slope exceeds, 20 degree the downward harvesting operation was impossible because of the excessive front end weight, while less than 5 degree of land slope did not effect in field operation. 9. Increased traveling spee caused higher cutting height and slight cutting failure, but seems not to effect to the gross yield, and the efficiency of cutting width were from 83 to 94 precent. 10. Tn rank of economy were rotary mower (3,2 stage operation), reciprocating mower, hay scythe, portable disc type cutter and sickle in order when the annul operation exdeeds 100 hours. From the above results, it is convinced that the protto type rotary mower is good enough to the livestock farmers as a hay harvesting equipment because of its economy, hardiness in operating and its out standing performance and hopefully it will contribute to the extension of Korean livestock farming.

• 한국항공우주학회지
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• 제45권9호
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• pp.784-793
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• 2017

관측위성에 탑재되는 2축 짐벌식 X-band 안테나는 위성의 자세 및 궤도 운동과는 무관하게 지상국을 지향하여 광학 탑재체로부터 획득한 대용량의 영상정보를 지상으로 송신하는 임무를 수행한다. 하지만, 상기 X-band 안테나는 지상 안테나로 지향을 위한 모터 구동시 미소진동을 유발하며, 이와 같은 미소진동은 고해상도 관측위성의 영상품질을 저하시키는 주된 요인으로 작용한다. 따라서 관측위성의 임무수행동안 목적하는 영상정보 획득을 위하여, 안테나의 모터 구동에 따라 수반되는 미소진동 절연이 요구된다. 본 논문에서는 상기 안테나의 미소진동 문제를 극복하기 위해 2축 짐벌식 X-band 안테나의 방위각 단에 장착되는 초탄성 SMA 블레이드 기어를 제안하였다. 본 논문에서 제안한 SMA블레이드 기어의 차세대중형위성 X-band 안테나 적용 가능성 검토를 위해 회전방향 정하중시험을 통해 기본특성을 확인하였으며, 가속수명시험 및 온도특성시험을 수행하였다. 또한 미소 진동측정시험을 수행하여 상기 SMA 기어의 미소진동 절연성능 및 기어의 설계 유효성을 입증하였다.

• 생물환경조절학회지
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• 제26권3호
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• pp.215-220
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• 2017

접수 및 대목 줄기의 회전 절단으로 인한 접목 불량 발생 가능성에 대한 문제점을 해결하기 위하여 수학적 분석 및 고속카메라를 이용하여 실측한 결과 칼날 회전반경 50mm이고 줄기직경이 5mm 일 때, 깊이는 0.11mm인 것으로 계산되어 줄기부 곡면 절단에 따른 문제는 없을 것으로 사료된다. 또한 접목시스템에서 모종 줄기를 잡는 그립퍼의 최적 형상 설계를 위하여 실시한 모종 줄기 압축시험 결과 대목의 경우 0.8mm 이상, 접수의 경우 0.6mm 이상의 범위에서 줄기부를 압축 할 경우 이전 형상으로 완전히 복원되지 않는 것으로 조사되어 그립퍼 형상 설계 시 그럼퍼 간격 결정에서 고려해야 할 것으로 사료된다. 또한 접목시기인 토마토 모종의 경우 줄기의 휨이 평균 10도 전후 인 것으로 조사되어 접목불량이 발생할 가능성이 있으므로 이를 개선하기 위한 추가 연구가 필요할 것으로 사료된다. 최적핑거 형상 시험에서는 모서리핑거 형상이 핑거간 거리 조정을 통해 정확한 중앙점을 잡을 수 있는 것으로 조사되었다. 핑거간 거리는 접수와 대목에 대해 각각 2.5mm와 3.0mm로 설정하고 신축성 있는 재질을 이용하여 1mm 두께로 코팅을 하면 대부분의 모종 줄기를 상처없이 파지 할 수 있을 것으로 조사되었다.