• 한국항공우주학회지
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• 제31권1호
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• pp.42-48
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• 2003

Lever II 헬리콥터 비행운동 방정식으로부터 주기성 트림해를 구하기 위해 DAE 해법에 근거한 PPTA(Partial Periodic Trimming Algorithm)를 제안하였다. PPTA의 반복계산으로 수정된 상태변수는 적합한 초기조건이 요구되는 DAE해법에서 수치불안정을 일으킬 수 있다. 간단하게 DAE 차수를 조절함으로써 정확한 주기성 트림을 얻을 수 있었다. 수치해법을 CBM(Common Baseline Model) 헬리콥터에 적용하여 harmonic balance 방법과 동일한 트림해를 얻었으며 시뮬레이션 초기의 과도응답을 효과적으로 제거할 수 있음을 밝혔다.

• Human Ecology Research
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• 제52권5호
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• pp.457-471
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• 2014

Family instability has a negative effect on not only an individual household but also the society. The government continues to operate family support centers as a countermeasure to family instability issues. A healthy and multicultural family support center is considered an effective support system that extends from a family unit to the local community. In this study, the satisfaction and demand levels of each center, located in Seoul and Incheon, were examined with respect to items such as operation contents, physical space, and organizational structure. The results showed that various efforts for creating a family-friendly community were implemented in healthy family support centers and multicultural family support centers. It was found that the center organizers and operators focused more on software and programs than on the physical environment. There was mostly a shortage of physical and environmental space. This space shortage limited the planned and ongoing activities in terms of the residents' self-directed participation and space formation for a family-friendly educational culture. Therefore, it was necessary to set up the space-related criteria for each center in order to solve this environmental issue. We identified the baseline data of the criteria for a center's physical and spatial design and size. In particular, it was suggested that a more strategic physical and spatial design is needed to achieve an integral and effective operation for the connection of the family with the local society.

• 한국항공우주학회지
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• 제33권1호
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• pp.48-53
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• 2005

본 연구의 목적은 기계적인 전단층 자극방법을 이용 스월제트 혼합향상의 가능성을 고찰함에 있다. 이를 위해 기계적 자극장치가 설계, 제작되었다. 주요 구성품으로는 두개의 아음속 노즐, 스월 발생기, 그리고 유동 자극기 등이다. 실험은 다음과 같은 다양한 헬리컬 모드들에서 수행되었다; m=+0, m=$\pm$1, m=$\pm$2, m=$\pm$3, m=$\pm$4. 열선유속계를 이용한 plane 파동과 헬리컬 파동 자극에 따른 제트속도 측정이 이루어 졌다. 다양한 헬리컬 모드에서의 결과 값들이 기준 값(plane-wave)과 비교되었다. 획득된 결과는 3-D mesh plot 과 2-D contour plot으로 표현되었다. 이로써 새로 고안된 장치는 헬리컬 불안정파 자극에 대한 효과를 입증하였고 또한 결과적으로 스월제트의 혼합을 증진시켰다.

• 한국전문물리치료학회지
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• 제26권4호
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• pp.1-9
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• 2019

Background: Cervical dysfunction is a common pathomechanical marker in individuals with forward head posture (FHP). To overcome the limitations of the isometric chin-tuck (ICT) exercise, dynamic neuromuscular stabilization (DNS), which emphasizes an entire spinal chain exercise, has recently shown promising clinical results. Objects: Purpose of this study was to compare the immediate effects between ICT and DNS techniques. Methods: 43 young subjects (mean age, $24.0{\pm}5.0$ years) were recruited. Group of subjects with FHP were measured under baseline, ICT, and DNS conditions. Outcome measures included sitting height, longus colli (LC) and sternocleidomastoid (SCM) muscle thickness and LC/SCM thickness ratio. One-way repeated measures ANOVA was used to compare the continuous dependent variables among FHP, ICT, and DNS conditions at p<.016. Results: Both ICT and DNS exercise conditions yielded significantly increased LC muscle thickness, LC/SCM thickness ratio and sitting height than did FHP condition (p<.0001, respectively). Sitting height was significantly greater in DNS exercise than in the ICT exercise (p<.0001). Conclusion: The present results demonstrated that sitting height was greater in the DNS exercise than in the ICT exercise, as well as both corrective postural training exercises were effective on LC/SCM muscle balance ratio when compared with the baseline FHP condition. Therefore, it is considered that DNS exercise can be the recommended exercise for people with FHP.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권5호
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• International Journal of Aeronautical and Space Sciences
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• 제7권1호
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• pp.137-147
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• 2006

In this study, shape memory alloy damper with characteristics of pseudoelastic hysteresis for helicopter rotor blades are investigated. SMAs can be available in damping augmentation of vibrating structures. SMAs show large hysteresis in the process of pseudoelastic austenite-martensite phase transformation which takes place while subjected to loading above the austenite finish temperature. Since SMAs display pseudoelastic hysteresis behavior over large strain ranges, a significant amount of energy dissipation is possible. A damper can be designed with SMA wires prestressed to a baseline level somewhere in the middle of the pseudoelastic stress range. An experimental study of the effects of pre-strain and cyclic strain amplitude as well as frequency on the damping behavior of pseudoelastic shape memory alloy wires are performed. The effects of the shape memory alloy damper on aeroelastic and ground resonance stability of helicopter are studied. In aeroelastic stability, the dynamic characteristics of blades related to pitch angle and the amplitude of lag motion for the rotor equipped with SMA damper were examined. The performance of SMA damper on ground resonance instability are presented through the frequencies and modal damping with respect to rotating speed.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1902-1912
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• 2024

This paper presents results from system-level modeling of a water-based reactor cavity cooling system using RELAP5-3D. The computational model is benchmarked with experimental data from a half-scale RCCS test facility at Argonne National Laboratory. The model prediction is first compared with a two-phase oscillatory baseline experimental case where mixed accuracy is obtained. The model shows reasonable prediction of mass flow rate, pressure, and temperature but significant overprediction of void fraction. The model prediction is then compared with a fault case where the inlet of the risers is gradually reduced using a throttling valve. As the valve is closed, the model is able to predict some major flow phenomena observed in the experiment such as the dampening of oscillations, the reintroduction of oscillations, as well as boiling, flashing, and geysering in the risers. However, the timeline of these events are not well captured by the model. The model is also used to investigate the evolution of flow regime in the chimney. This work highlights that the semi-empirical constitutive relations used in RELAP-3D could have a strong influence on the accuracy of the model in two-phase oscillatory flows.

• 자원ㆍ환경경제연구
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• 제13권2호
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• pp.271-300
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• 2004

본 연구는 최근 두 차례에 걸친 국내 온실가스 배출권 모의거래의 결과를 분석하여 그 정책적 시사점을 도출하였다. 1차 모의거래는 5개 전력사를 대상으로 baseline and credit를 기준으로 실시하였고, 2차 모의거래는 1개 전력회사를 포함 여타 에너지집약 업종의 7개 기업을 대상으로 cap and trade 방식을 택했다. 물론 모의거래 시행을 위한 여러 가정들이 채택되었으나 기본적으로 자발적인 참여를 바탕으로 각 사에 경매를 통해 인센티브를 지급하고 온라인 시스템을 활용하여 거래하는 방식을 택하였다. 본 모의거래에서 특징적인 결과를 보면 거래시장의 불안정성을 들 수 있다. 즉, 거래가격의 변화가 크고 거래시장이 수요자 중심이거나 아니면 공급자 중심으로 나타났다. 이는 본 모의거래가 자발적이고 비구속적인 상태에서 운영이 되고, 각 참여사에 돌아가는 인센티브 규모가 과도하고, 참여자간의 정보가 비대칭적이며, 참여자의 무책임한 전략적 행위, 그리고 참여자의 시스템 운영 미숙으로 인한 것이라고 할 수 있다. 본 연구는 향후 우리나라가 도입하게 될 국내배출권거래제의 기본디자인과 이를 단계적으로 도입하는 방안, 그리고 인센티브 경매방식, 인센티브 총액, 재원조달 방안 등을 언급하고 있다. 이에 대한 더 많은 후속연구가 필요하며 특히 산업계의 적응능력 향상과 더 바람직한 제도도입을 위해서 앞으로도 계속하여 모의거래를 실시 할 것을 건의하고 있다.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.290-299
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• 2017

Reconfigurable flight control using various kinds of adaptive control methods has been studied since the 1970s to enhance the survivability of aircraft in case of severe in-flight failure. Early studies were mainly focused on the failure of actuators. Recently, studies of reconfigurable flight controls that can accommodate complex damage (partial wing and tail loss) in conventional aircraft were reported. However, the partial wing loss effects on the aerodynamics of conventional type aircraft are quite different to those of BWB(blended wing body) aircraft. In this paper, a reconfigurable flight control algorithm was designed using a direct model reference adaptive method to overcome the instability caused by a complex damage of a BWB aircraft. A model reference adaptive control was incorporated into the inner loop rate control system enhancing the performance of the baseline control to cope with abrupt loss of stability. Gains of the model reference adaptive control were polled out using the Liapunov's stability theorem. Outer loop attitude autopilot was designed to manage roll and pitch of the BWB UAV as well. A 6-DOF dynamic model was built-up, where the normal flight can be made to switch to the damaged state abruptly reflecting the possible real flight situation. 22% of right wing loss as well as 25% loss for both vertical tail and rudder control surface were considered in this study. Static aerodynamic coefficients were obtained via wind tunnel test. Numerical simulations were conducted to demonstrate the performance of the reconfigurable flight control system.

• 중환자간호학회지
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• 제9권1호
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• pp.66-76
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• 2016

Purpose: This study was conducted to examine the relationship between lateral position change and sternal complications after cardiac surgery through median sternotomy. Methods: This study was a retrospective descriptive case-control study, involving 241 patients who underwent cardiac surgery through median sternotomy. Data from October 2011 to September 2014 were collected. Results: Sternal complications (i.e. dehiscence, sternal instability, mediastinitis) developed in 33 patients (13.7%). Primary symptoms of complications were discharge and erythema, and the mean time difference from surgery to appearance of symptoms was 15 days (range, 1-138 days). The factors associated with sternal complications were cancer comorbidity (${\chi}^2=5.22$, p=.039), internal mammary artery procedure (${\chi}^2=4.16$, p=.041), and duration of extra-corporeal membrane oxygenation (p=.033). Position change was not related to incidence of sternal complications (${\chi}^2=0.14$, p=.704). Pressure ulcers appeared in 63 patients (26.1%). Mean time difference from surgery until occurrence of ulcers was 6.7 hours (range, 0-323.0 hours), but position change was started from 132.4 hours (range, 27.1-503.2 hours) after intensive care unit admission. Conclusions: These results provide baseline data to create a standard position change and activity protocol for patients after median sternotomy. Furthermore, the study could help clinical practitioners establish evidence-based nursing practices.