• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.320-321
• /
• 2020

본 논문은 AC 계통 불평형 발생 시 출력전력의 동요를 저감시키기 위한 POD 전략을 수행하는 MMC-HVDC 시스템의 내부 동적상태를 분석하였다. POD 전략을 통해서 MMC 출력전류의 역상분을 제어하여 계통에 주입되는 유효 전력의 발진을 제거함으로써, MMC-HVDC 시스템이 연계된 인근 계통에 공급 신뢰도를 향상시킬 수 있다. POD 전략에서 유효 전력만 출력할 경우, MMC의 각 상에는 동일한 전력이 흐른다. 반면, 계통 전압 보상을 위해서 무효 전력을 동시에 공급할 경우, 각 상에 흐르는 전력은 불균형해지기 때문에 MMC의 암전류 불평형이 발생하여 스위치 소자의 정격 용량 및 열 스트레스를 증가 시켜 MMC의 안정성을 저해시킨다. 본 논문은 POD 전략을 수행하기 위해서 무효 전력이 MMC 암 전류에 미치는 영향을 분석하였으며, 200 MW MMC-HVDC 모델을 바탕으로 PSCAD/EMTDC 시뮬레이션 툴을 이용하여 분석 결과를 검증하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.04a
• /
• pp.686-687
• /
• 2013

• Journal of Korean Neurosurgical Society
• /
• v.43 no.3
• /
• pp.143-148
• /
• 2008

Objective: Postoperative delirium (POD) is characterized by an acute change in cognitive function and can result in longer hospital stays, higher morbidity rates, and more frequent discharges to long-term care facilities. In this study, we investigated the incidence and risk factors of POD in 224 patients older than 70 years of age, who had undergone a neurosurgical operation in the last two years. Methods: Data related to preoperative factors (male gender, >70 years, previous dementia or delirium, alcohol abuse, serum levels of sodium, potassium and glucose, and co-morbidities), perioperative factors (type of surgery and anesthesia, and duration of surgery) and postoperative data (length of stay in recovery room, severity of pain and use of opioid analgesics) were retrospectively collected and statistically analyzed. Results: POD appeared in 48 patients (21.4%) by postoperative day 3. When we excluded 26 patients with previous dementia or delirium, 17 spontaneously recovered by postoperative day 14, while 5 patients recovered by postoperative 2 months with medication, among 22 patients with newly developed POD. The univariate risk factors for POD included previously dementic or delirious patients, abnormal preoperative serum glucose level, pre-existent diabetes, the use of local anesthesia for the operation, longer operation time (>3.2 hr) or recovery room stay (>90 mini, and severe pain (VAS>6.8) requiring opioid treatment (p<0.05). Backward regression analysis revealed that previously dementic patients with diabetes, the operation being performed under local anesthesia, and severe postoperative pain treated with opioids were independent risk factors for POD. Conclusion: Our study shows that control of blood glucose levels and management of pain during local anesthesia and in the immediate postoperative period can reduce unexpected POD and help preventing unexpected medicolegal problems and economic burdens.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.6
• /
• pp.751-759
• /
• 2008

In this study, the effect of an unsteady flow field around a body of aerostatic/aerodynamic forces were investigated using rectangular cylinders (B/D = 2, 3, 4, 5). Proper orthogonal decomposition (POD) was introduced to the analysis of the fluctuating pressure field that was measured on the stationary/oscillatory B/D=4 rectangular cylinder, and the characteristics of the proper functions with flow patterns were identified. In addition, the physical decoupling and interactions in the different co-existing flow patterns were investigated through POD. The comparison with the identified proper function associated with a particular flow pattern revealed that the Karman vortex is almost not affected by the separation bubble, but that the Karman vortex considerably interferes in the development of the separation bubble around the trailing edge. It can be considered that the Karman vortex induces the increment of the curvature of the substantial separated flow.

• Mycobiology
• /
• v.45 no.4
• /
• pp.392-400
• /
• 2017

Peanut yield and quality are seriously affected by pod rot pathogens worldwide, especially in China in recent years. The goals of this study are to analyze the structure of fungal communities of peanut pod rot in soil in three peanut cultivars and the correlation of pod rot with environmental variables using 454 pyrosequencing. A total of 46,723 internal transcribed spacer high-quality sequences were obtained and grouped into 1,706 operational taxonomic units at the 97% similarity cut-off level. The coverage, rank abundance, and the Chao 1 and Shannon diversity indices of the operational taxonomic units were analyzed. Members of the phylum Ascomycota were dominant, such as Fusarium, Chaetomium, Alternaria, and Sordariomycetes, followed by Basidiomycota. The results of the heatmap and redundancy analysis revealed significant variation in the composition of the fungal community among the three cultivar samples. The environmental conditions in different peanut cultivars may also influence on the structure of the fungal community. The results of this study suggest that the causal agent of peanut pod rot may be more complex, and cultivars and environmental conditions are both important contributors to the community structure of peanut pod rot fungi.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.918-927
• /
• 2020

Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-u turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

• Wind and Structures
• /
• v.34 no.1
• /
• pp.29-42
• /
• 2022

Following the BARC initiative, wind tunnel measurements have been performed on a 5:1 rectangular cylinder. Pressure distribution has been measured in several sections, checking the two-dimensionality of the flow around the model. Mean values compare well with previous data. These measurements have been processed using the standard Proper Orthogonal Decomposition (POD) and the snapshot POD to obtain phase-resolved cycles. This decomposition has been used to analyze the characteristics of the flow around the cylinder, in particular, the behavior of the recirculation bubble in the upper/lower surfaces. The effect of the angle of attack, the turbulence intensity and the Reynolds number has been studied. First and second modes extracted from POD have been found to be related to the reattachment of the flow in the upper surface. Increasing the angle of attack is related to a delay in the reattachment position, while an increase in turbulence intensity makes the reattachment point to move towards the windward face.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1773-1777
• /
• 2008

The proper orthogonal decomposition(POD) is used to the modal analysis of microcantilever of dynamic mode atomic force microscopy(AFM). The proper orthogonal modes(POM) are extracted from vibrating signals of microcantilever when it resonates and taps the sample. We present recent ideas based on POD and detailed experiments that yield new perspectives into the microscale structures. The linearized modeling technique based on POD is very useful to show the principal characteristics of the complex dynamic responses.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.12
• /
• pp.1679-1689
• /
• 1997

In this paper, a precise description is given to the basic theory as well as the detailed algorithms for the numerical treatment of the method of POD (proper orthogonal decomposition). This method is then applied to analysing the numerical solutions of one-dimensional shallow-water equations to show how the method is affected by various parameters such as the sampling time, sampling numbers, and the spatial resolution for the autocorrelation function. A few curious features associated with this flow model found through the analysis are further explained and discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.4
• /
• pp.414-421
• /
• 2010

The proper orthogonal decomposition(POD) is used to the vibration analysis of microcantilever in tapping mode atomic force microscopy(AFM). The proper orthogonal modes (POM) are extracted from vibrating signals of microcantilever when it resonates and taps the sample. We present recent ideas based on POD and detailed experiments that yield new perspectives into the microscale structures such as the tapping cantilever. The linearized modeling technique based on POD is very useful to show the principal characteristics of the complex dynamic responses of the AFM microcantilever.