• 한국가스학회지
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• 제17권1호
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• pp.7-12
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• 2013

자동차 배기가스 규제가 강화됨에 따라 천연가스에 수소를 첨가하는 수소-천연가스 혼합연료(HCNG)를 기존의 압축천연가스(CNG) 엔진에 적용하려는 많은 연구들이 진행되고 있다. 그러나 수소의 높은 연소 속도로 인한 역화, 조기착화, 노킹(knocking) 등의 이상연소 발생 가능성은 엔진의 가열 또는 열효율 및 출력의 저하를 야기하는 문제점이 발생할 수 있다. 본 연구에서는 CNG 연료에 수소를 일정 부분 혼합한 HCNG 연료를 기존의 CNG 엔진에 적용하여 희박연소 한계 확장을 통해 연소 성능 개선을 확인하고, CNG와 HCNG 연료의 노킹 특성을 파악하고자 하였다. 공기과잉율의 변화에 따른 노킹 발생 조건을 관찰함으로써 HCNG 연료의 적용성 및 노킹마진을 평가하고자 하였다. HCNG 연료 사용 시 최적운전조건에서 노킹 문제없이 엔진을 운전할 수 있었으나 노킹이 일어날 수 있는 가능성이 높아져 이에 대한 대비가 필요할 것으로 판단된다.

• 폴리머
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• 제37권2호
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• pp.204-210
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• 2013

첨가제(윤활제 및 산화방지제)와 용융혼합 조건(온도, 시간 및 로터 속도)이 폴리프로필렌(PP) 기반 WPC(wood polymer composite)의 기계적 특성에 미치는 영향을 조사하였다. WPC는 용융혼합 후 압축성형하여 제조하였다. 용융혼합 과정을 이해하기 위해 WPC 용융혼합물의 토크 변화를 측정하였다. 말레산무수물로 개질된 폴리프로필렌을 상용화제로, 나노점토를 보강재로 각각 사용하였다. WPC의 기계적 특성을 측정하기 위해 UTM과 충격시험기를 이용하였고 색차계를 이용하여 WPC의 용융혼합 조건에 따른 변색을 측정하였다. 기계적 특성 분석에 따른 최적용융혼합 조건은 $170^{\circ}C$, 15분, 60 rpm인 것으로 나타났다. 윤활제와 산화방지제의 함량이 증가할수록 WPC의 기계적 특성이 하락함을 확인하였다. 용융혼합 과정에서 목분만을 별도로 나중에 투입하는 이단계 방법이 전형적인 일단계 방법보다 WPC의 기계적 특성 향상에 더 효과적이었다.

• 한국정보통신학회논문지
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• 제21권9호
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• pp.1808-1817
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• 2017

대잠, 대함, 보급 등, 함정에 요구되는 임무가 다양해지면서 함정의 추진체계 또한 임무를 효과적으로 수행하기 위해 ECS(Engineering Control System)를 필요로 한다. ECS는 추진체계를 모니터링하고 제어함으로써 함정이 임무를 수행할 수 있도록 한다. 최근 ECS 국산화 개발이 진행되면서 ECS에 대한 시험 검증을 위한 시스템이 요구되었고, CODOG 기반의 함정 추진체계 시뮬레이터를 개발하였다. CODOG 기반의 함정 추진체계 시뮬레이터는 가스터빈 모델, 디젤엔진 모델, 감속기어 모델, 가변추진기 모델로 나누어 제어 명령에 대한 피드백을 모의한다. 실험 결과, ECS 추진 모드에 따른 가스터빈, 디젤엔진 및 축의 속도, 토크, 출력 등을 확인할 수 있었다.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.44-48
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• 2007

In recent years, the size of plane substrates and semiconductor wafers has increased. As conventional contact transportation systems composed of, for example, carrier rollers, belt conveyers, and robot hands carry these longer and wider substrates, the increased weight results in increased potential for fracture. A noncontact transportation system is required to solve this problem. We propose a new noncontact transportation system combining acoustic viscous and aerostatic forces to provide damage-free transport. In this system, substrates are supported by aerostatic force and transported by acoustic viscous streaming induced by traveling wave deformation of a disk-type stator. A ring-type piezoelectric transducer bonded on the stator excites vibration. A stator with a high Q piezoelectric transducer can generate traveling vibrations with amplitude of $3.2{\mu}m$. Prior to constructing a carrying road for substrates, we clarified the basic properties of this technique and stator vibration characteristics experimentally. We constructed the experimental equipment using a rotational disk with a 95-mm diameter. Electric power was 70 W at an input voltage of 200 Vpp. A rotational torque of $8.5\times10^{-5}Nm$ was obtained when clearance between the stator and disk was $120{\mu}m$. Finally, we constructed a noncontact transport apparatus for polycrystalline silicon wafers $(150(W)\times150(L)\times0.3(t))$, producing a carrying speed of 59.2 mm/s at a clearance of 0.3 mm between the stator and wafer. The carrying force when four stators acted on the wafer was $2\times10^{-3}N$. Thus, the new noncontact transportation system was demonstrated to be effective.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.655-662
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• 2022

Recently, with the increase in the use of UAV(unmanned aerial vehicles), research on horizontal maintenance stations that can take off and land in various environments has been actively conducted. These stations can safely land UAV through multiple DOF(degrees of freedom) or at least 2-DOF-based actuator actuation. Among them, many researchers are dealing with the multi-DOF stewart platform due to its high safety. However, the stewart platform requires high-precision control technology because it requires a lot of torque to actuate according to the load action. Therefore, in this paper, to solve the mentioned problem, a bevel gear-based 2-DOF horizontal maintenance station system is proposed. The proposed system is configured to prevent damage due to air resistance when maintaining ships and to install it in a small space. Also, in terms of system configuration, the bevel gear-based horizontal maintenance system has the main advantage of being able to take off and land UAVs of various sizes through the replacement of station pads. The driving of the system consists of a simple form that can control the motor by adjusting the rotation speed of the motor according to the sea waveform.

• 대한물리치료과학회지
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• 제29권4호
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• pp.27-42
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• 2022

Background: Although children with cerebral palsy (CP) are able to walk independently, gait imbalance occurs due to abnormal muscle tone, musculoskeletal deformity, loss of balance, and selective motor control impairment. Gait restriction in the community and school is a major problem of rehabilitation in CP. Home-based therapy (HBT) provides a variety of interventions in which the therapist and the parent work together to resolve the activities and problems caused by the child's body structure. Therefore, we investigate the effectiveness of home-centered therapy on gross motor function in CP and try to present the possibility of clinical application. Design: A Systematic Review Methods: Research papers were published from Jan, 2012 to Jan, 2022 and were searched using Medline and PubMed. The search terms are 'family-centered' OR 'home-based' AND 'cerebral palsy'. A total of nine papers were analyzed in this study. The paper presented the quality level based on Physiotherapy Evidence Database (PEDro) scores to assess the quality of randomized clinical trials studies. Results: The results showed that HBT for strengthening exercise in lower extremity has a positive effect on the isokinetic torque and gross motor function. home-based treadmill therapy in CP is effective to perform at least 12 sessions of treadmill HBP in which the therapist determines the treadmill speed every week and the child's own gait pattern is modified. Conclusion: These results suggest that it will be important data for founding evidence on the effectiveness of home-centered therapy on gross motor function in children with cerebral palsy to advance clinical protocols.

• Tribology and Lubricants
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• 제28권4호
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• pp.167-172
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• 2012

The turbo pump of a liquid rocket engine is composed of three main parts: the oxidizer pump, fuel pump, and turbine. Liquid oxygen ($LO_X$) is the working fluid in the cryogenic environment in the oxidizer pump, but tests are usually performed using liquid nitrogen ($LN_2$), which has a boiling point similar to that of $LO_X$ but is comparatively safer and easier to use for the test. In this study, a bearing test rig is developed and its performance is evaluated using a cryogenic ball bearing with $LN_2$ as the working fluid. Verifying the performance of the bearing test rig is crucial for ensuring correct working of the turbo pump unit in the liquid rocket engine. A stable test rig for the bearing in a cryogenic environment makes the bearing technology enhance its reliability. The test results show that the system operates stably and the requirement of performance time of 500 s is met. The test results of temperature, motor speed, and torque are discussed. The developed cryogenic bearing test rig is expected to help in widening knowledge and expanding research on ball bearings in the future.

• 한국전문물리치료학회지
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• 제19권3호
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• pp.20-30
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• 2012

The purpose of this study was to determine the effect of ankle joint mobilization with movement (MWM) on the range of motion (ROM) in the ankle, on the muscle strength of lower extremities, and on spatiotemporal gait parameters in chronic hemiplegic patients. Fifteen subjects with chronic stroke were divided into two groups: an experimental group (8 subjects) and a control group (7 subjects). Both groups attended two or three sessions of physical therapy each week. The experimental group also attended additional MWM training sessions three times a week for five weeks. For both groups, the ROM of the ankle, the muscle strength of the lower extremities, and the spatiotemporal gait parameters in paretic limbs were evaluated before and after the training period. The results showed that the experimental group experienced more significant increases than did the control group in terms of passive (6.10%) and active (21.96%) ROM of the ankle, gait velocity (12.96%), and peak torque, of the knee flexor (81.39%), the knee extensor (24.88%), and the ankle plantar flexor (41.75%)(p<.05). These results suggest that MWM training in patients with chronic stroke may be beneficial in increasing ROM in the ankle, muscle strength in the lower extremities, and gait speed.

• Journal of Advanced Marine Engineering and Technology
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• 제36권1호
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• pp.172-178
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• 2012

이동식 발전설비는 이송이나 설치의 편리성과 산간지역이나 도서지역 등의 전력 공급이 어려운 지역에서도 사용할 수 있는 장점을 갖고 있다. 하지만 기존의 이동식 발전설비는 공기식 시동시스템에 의해 기동 되므로 공기 압축기 및 탱크시스템 등이 필요하다. 이러한 장치의 추가로 공기시동시스템은 비용 및 용적률 측면에서 손실이 발생하고 에너지 효율이 감소하게 된다. 본 연구에서는 공기식 시동시스템의 단점을 개선하기 위해서 에너지 효율의 증가, 부피와 용적률 및 비용의 절감, 안전사고의 위험성 감소, 시동의 정확성 증가 및 시동시간의 감소 효과를 기대할 수 있는 전기시동전동기인 직류직권전동기를 개발하였다.

• 동력기계공학회지
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• 제18권2호
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• pp.5-11
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• 2014

The purpose of this study is to investigate the specific characteristics of combustion and exhaust emissions on a 4-cylinder common rail diesel engine as EGR rate and the rate of blended bio-diesel was altered. Bio-diesel fuel which is a sort of alternative fuels can be adapted to diesel engine directly without modifying. This study was performed to 2000rpm of engine speed with torque 30Nm while EGR rate and the rate of blended bio-diesel was changed. Decreasing combustion pressure and increasing the rate of heat were occurred when we had changed the EGR rate on the 20% of bio-diesel blended diesel fuel. The maximum pressure of combustion and the IMEP became higher as the EGR rate and the rate of blended bio-diesel were changed. Exhaust gas temperature was increased the higher rate of the blended bio-diesel under the fixed EGR rate. However, it went down as the EGR rate increased. The amounts of CO and Soot were reduced with increasing the rate of the blended bio-diesel without changing EGR rate and raised with increasing of the EGR rate. On the fixed EGR rate, NOx was increased along with growing the rate of the bio-diesel. On the other hand, it was decreased while EGR rate were going up.