• 한국가시화정보학회지
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• 제14권3호
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• pp.28-31
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• 2016

In this study, we investigate the wake characteristics in two cases which are laminar inflow and turbulent inflow. To solve the flow with wind turbines and its wake, we use large eddy simulation (LES) technique with actuator line method (ALM) and turbulent inflow of Turbsim. Turbulent inflow which contains the characteristic of the stable atmospheric boundary layer is used. We perform the quantitative analysis of velocity deficit and turbulence intensity in two cases. Time series of velocity deficit at the first, the second column in two cases are compared to observe the performance of wind turbine. The performance in the first column in laminar inflow is overestimated compared to that in turbulent inflow. And we observe that wake in the case with turbulent inflow drive to the span-wise direction and wake recovery in turbulent inflow is more effective. In quadrant analysis of Reynolds stress, the ejection and the sweep motion in turbulent inflow case are bigger than those in laminar inflow case.

• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.899-906
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• 2005

It is known that an oscillating airfoil can Produce a driving force through the generation of a reversed $K\'{a}rm\'{a}n$ vortex street, and this can be expected to be a new highly effective propulsion system. The wake formation behind the heaving airfoil was visualized and was measured using PIV systems We have been examined various conditions such as frequency number, amplitude in NACA 0010. As Strouhal number is greater than 0.08. wake profile with velocity deficit can be transformed into the wake with velocity excess After evaluating vortex center flow patterns in the wake investigated using tracking trajectories in temporal evaluation of the shedding vortices. We also Presented the experimental results on the unsteady vortices structure of the heaving airfoil at various parameters.

• Ocean Systems Engineering
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• 제10권3호
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• pp.289-316
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• 2020

In the present paper, the effect of the location of stern planes on the flow entering the submarine propeller is studied numerically. These planes are mounted on three longitudinal positions on the submarine stern. The results are presented considering the flow field characteristics such as non-dimensional pressure coefficient, effective drag and lift forces on the stern plane, and the wake flow formed at the rear of the submarine where the propeller is located. In the present study, the submarine is studied at fully immersed condition without considering the free surface effects. The numerical results are verified with the experimental data. It is concluded that as the number of planes installed at the end of the stern section along the submarine model increases, the average velocity, width of the wake flow and its turbulence intensity formed at the end of the submarine enhance. This leads to a reduction in the non-uniformity of the inlet flow to the propulsion system.

• Journal of Ship and Ocean Technology
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• 제4권3호
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• pp.1-12
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• 2000

A number of numerical methods like Computational Fluid Dynamics(CFD) have been developed to predict the flow fields of a vessel but the present study is developed to infer the wake fields on propeller plane by Statistical Fluid Dynamics(SFD) approach which is emerging as a new technique over a wide range of industrial fields nowadays. Neural network is well known as one prospective representative of the SFD tool and is widely applied even in the engineering fields. Further to its stable and effective system structure, generalization of input training patterns into different classification or categorization in training can offer more systematic treatments of input part and more reliable result. Because neural network has an ability to learn the knowledge through the external information, it is not necessary to use logical programming and it can flexibly handle the incomplete information which is not easy to make a definition clear. Three dimensional stern hull forms and nominal wake values from a model test are structured as processing elements of input and output layer respectively and a neural network is trained by the back-propagation method. The inferred results show similar figures to the experimental wake distribution.

• 대한전자공학회논문지SD
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• 제41권10호
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• pp.77-83
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• 2004

VLSI 시스템에서 전력 소모를 줄이기 위해서는 메가블록이 동작하지 않는 동안 전원을 차단하여 누설 전류를 억제하는 방법이 효과적이다. 최근 들어 다중 문턱 전압 CMOS를 사용하여 전원을 차단하는 방법이 널리 연구되고 있으나, 동작 주파수가 증가함에 파라 전원 복귀에 필요한 시간이 짧아지게 되고, 짧은 시간에 전원이 복귀되면서 전원선에 대량의 전류가 순간적으로 흐르게 된다. 이에 따라 매우 큰 전원 잡음이 생겨서 전원 전압이 안정적이지 못하고 흔들리게 되며 이는 많은 경우 시스템의 오동작을 초래하게 된다. 본 논문에서는 이러한 문제점을 해결하기 위하여 새로운 전원 복귀 기법을 제안한다. 제안하는 기법은 메가블록의 전원이 차단되었다가 다시 복귀할 때 한꺼번에 전원을 켜는 것이 아니라 파이프라인 방식으로 몇 단계로 나누어 전원을 켬으로서 전원선에 흐르는 최대 전류 및 이에 따른 전원 잡음을 크게 억제한다. 제안하는 파이프라인 전원 복귀 기법을 검증하기 위해서 컴팩트 플래시 메모리 제어기 칩에 본 기법을 적용하여 곱셈기 블록의 전원을 차단하고 복귀할 때의 전원 잡음을 모의실험하고 분석하였다. 모의실험 결과, 제안하는 기법은 기존의 전원 차단 기법에 비해 전원 잡음을 매우크게 줄일 수 있음을 확인하였다.

• 대한조선학회논문집
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• 제40권5호
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• pp.26-35
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• 2003

Propellers operating in a given nonuniform ship wake generate unsteady loads leading to undesirable stern vibration problems. The skew is known to be the most proper and effective geometric parameter to control or reduce the fluctuating forces on the shaft. This paper assumes the skew profile as either a quadratic or a cubic function of the radius and determines the coefficients of the polynomial function by applying the simplex method. The method uses the converted unconstrained algorithm to solve the constrained minimization problem of 6-component shaft excitation forces. The propeller excitation was computed either by applying the two-dimensional gust theory for quick estimation or by the fully three-dimensional unsteady lifting surface theory in time domain for an accurate solution. A sample result demonstrates that the shaft forces can be further reduced through optimization from the original design.

• 한국가시화정보학회지
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• 제19권3호
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• pp.46-53
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• 2021

In the present study, wind tunnel experiments were performed to reduce the drag of a paragliding helmet in the range of Reynolds numbers from 46,000 to 155,000. The drag force of the helmet model with dimples and deflectors installed was measured by varying the dimple depth and the slant angle of the deflector. The dimples were effective in reducing the drag at low Reynolds numbers, but no significant drag reduction was found in the Reynolds number range in which an actual paraglider flight takes place. On the other hand, the deflector installed tangentially to the side outline of the helmet showed an average drag reduction of 7% in the flight Reynolds number range of real paragliding. This was because the deflector shrunk the size of the wake region and moved the wake region downstream of the deflector.

• 한국강구조학회 논문집
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• 제23권6호
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• pp.763-775
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• 2011

경사진 평행 병렬 사장재 케이블의 웨이크 갤로핑 발현 특성을 2차원 부분모형을 통하여 규명하였다. 경사진 병렬 사장재를 모사하기 위하여 두 실린더를 나란히 경사배치 하였으며 중심간격 변화에 따른 풍상측 및 풍하측 실린더의 진동을 관찰하였다. 실린더 지름의 여섯 배까지 케이블강교량설계지침의 허용값을 초과하는 진동이 관할되었다. 이는 설계 시 관용적으로 사용되는 검토기준이 비교적 적정함을 의미하는 것이다. 반면, 감쇠의 증가는 웨이크 갤로핑의 발현을 억재하는 데 효과적이지 않음을 확인할 수 있었다.

• Journal of Veterinary Science
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• 제25권5호
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• pp.60.1-60.6
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• 2024

Importance: Alzheimer's disease (AD) is the most common cause of dementia in the elderly with the incidence rising exponentially after the age of 65 years. Unfortunately, effective treatments are extremely limited and definite diagnosis can only be made at autopsy. This is in part due to our limited understanding of the complex pathophysiology, including the various genetic, environmental, and metabolic contributing factors. In an effort to better understand this complex disease, researchers have employed nonhuman primates as translational models. Case Presentation: This report aims to describe the AD-like neuropathology in the brain of a 37-year-old female baboon (Papio hamadryas), which at the time of her death made her the oldest hamadryas baboon at any member institution of the Association of Zoos and Aquariums. A diagnostic necropsy was performed, and the brain was evaluated for neurodegenerative disease. Frequent amyloid-β deposits were identified, consistent with what has been described in other geriatric nonhuman primates. Phospho-tau pathology, including neurofibrillary tangles, a feature not well-described in other primate models, was also abundant. Conclusions and Relevance: Our results suggest that more detailed, prospective, longitudinal studies are warranted utilizing this particular species to see if they represent a viable model for human brain aging.

• 한국자동차공학회논문집
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• 제22권3호
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• pp.136-142
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• 2014

Distinct features in heart rate signals during the driver's wake and sleep states could provide an initiative for the development of a safe driving systems such as drowsiness detecting sensor in a smart wheel. We measured ECG from health subjects ($23.5{\pm}2.5$ in age) during the wake and drowsiness states. The proposed method is able to detect R waves and R-R interval calculation in the ECG even when the signal includes in abnormal signals. Heart rate variability(HRV) was investigated for the time domain and frequency domains. The STD HR(0.029), NN50(0.044) and VLF power(0.0018) of the RR interval series of the subjects were significantly different from those of the control group (p < 0.05). In conclusion, there are changes in heart rate from wake to drowsiness that are potentially to be detected. The results in our study could be useful for the development of drowsiness detection sensors for effective real-time monitoring.