• Wind and Structures
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• 제30권5호
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• pp.525-532
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• 2020

This work numerically investigates the effects of Reynolds number Re_D (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle α (= 0° - 90°) on the forces, Strouhal number, and wake of an elliptical cylinder, where Re_D is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and α is the angle between the cylinder major axis and the incoming flow. At Re_D = 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II)' when AR and α are varied in the ranges specified. When Re_D is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III)' materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle α_i = 32°, 37.5° and 45° are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The α_i effectively distinguishes the dependence on α and AR of force and vortex shedding frequency at either Re_D. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and α, Re_D = 150 renders higher fluctuating lift and Strouhal number than Re_D = 100.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.14-17
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• 2004

A purpose of this visual experiment is to investigate the effect of reduced frequency qualitatively by examining wake pattern change for insect flying motion. Insect is composed of two pair wing with forewing and hindwing, flying motion of insect is performed pitching and plunging so it makes a separation over the wings. The separation affects at the wake pattern and changed wake pattern has an influence on lift, drag and propulsion. This experiment is conducted by using a smoke wire technique and a camera is fixed at hindwing to take a photograph of wake. An electronic device is mounted below test section to find exact the mean positional angle of wing. The reduced frequency in experiment is 0.15, 0.3 and 0.45. We obtained the result which that reduced frequency is closely related to wake pattern that determines flight efficiency.

• 한국가시화정보학회지
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• 제2권2호
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• pp.58-65
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• 2004

The purpose of this visualization study is to investigate the effect of reduced frequency qualitatively by examining wake patterns for dragonfly flight motion. Dragonflies have two pairs of wing (a forewing and hindwing) and flight is achieved by a pitching and plunging, so it makes a separation over the wings. The separation affects the wake pattern and changed wake pattern has an influence on lift, drag, and propulsion. This experiment was conducted by using a smoke wire technique and a camera fixed above the test section used to take a photograph of the wake. An electronic device is mounted below the test section to find the exact mean positional angle of the wing. The reduced frequency in the experiment is 0.15, 0.3 and 0.45. Results show that reduced frequency is closely related to the wake pattern that determines flight efficiency.

• 동의생리병리학회지
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• 제31권2호
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• pp.83-93
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• 2017

This study covers pattern differentiation based on Korean medical references, research trend and modern clinical applications about Sleep-Wake disorders of Diagnostic and Statistical Manual of Mental Disorders(DSM-V) published by American Psychiatric Association. Insomnia disorder is mostly caused by yin deficiency of liver-kidney or liver qi depression and main patterns are heart-kidney non-interaction, deficiency-excess complex pattern containing phlegm-heat due to qi stagnation and blood stasis. Hypersomnolence disorder is more due to yang deficiency rather than yin deficiency and it's major pattern is spleen-kidney yang deficiency. Cataplexy is main feature in narcolepsy and corresponds to depressive psychosis or fainting in terms of Korean Medicine and narcolepsy is assumed to be relevant to liver wind. Breathing-related sleep disorders are related with phlegm-fluid retention brought on spleen deficiency with dampness encumbrance. Pattern of circadian rhythm sleep-wake disorders is combined with yin deficiency of liver-kidney or liver qi depression of insomnia disorder and spleen-kidney yang deficiency or dampness-phlegm of hypersomnolence disorder. Yin deficiency with effulgent fire brought on drugs or alcohol is one of main patterns of substance/medication-induced sleep disorder and combined patterns with yin deficiency of liver-kidney and blood stasis or dampness-phlegm-heat are mostly applied clinically. This study drew major and frequently applied patterns of sleep-wake disorders based on Koran medical literature and modern clinical applications. And that can be the groundwork for the task ahead like clinical practice guideline of sleep-wake disorders containing pattern differentiation, diagnosis and prescriptions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1586-1591
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• 2004

Flow visualization experiments have been performed to investigate the effects of phase lag, reduced frequency qualitatively by examining wake pattern on a dragonfly type wing. The model was built with a scaled-up, flapping wings, composed of paired wings with fore- and hindwing in tandem, that mimicked the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique, and an electronic device was mounted to find the exact positional angle of wing below the tandem wings, which amplitude is ranged from $-16.5^{\circ}$ to $+22.8^{\circ}$. Phase lag applied on the wings is $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The reduced frequency is 0.15, 0.3 and 0.45 to investigate the effect of reduced frequency. It is inferred through observed wake pattern that the phase lag clearly plays an important role in the wake structures and in the flight efficiency as changing the interaction of wings. The reduced frequency also is closely related to wake pattern and determines flight efficiency.

• 한국기계기술학회지
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• 제13권2호
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• pp.101-106
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• 2011

In this study, the velocity distribution according to upper side coner shape of underwater construction with rectangular cylinder was measured with PIV method and the wake flow characteristics was considered. According to the coner shape, the flow pattern of wake flow was also differed greatly and the step-shaped coner of cut-off ratio B/H=0.06 was similar in the slope shape in result.

• Wind and Structures
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• 제7권4호
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• pp.265-280
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• 2004

This paper presents some fundamental results on the dynamics of the periodic Karman wake behind a circular cylinder. The wake is treated like a dynamical system. External forcing is then introduced and its effect investigated. The main result obtained is the following. Perturbation of the wake, by controlled cylinder oscillations in the flow direction at a frequency equal to the Karman vortex shedding frequency, leads to instability of the Karman vortex structure. The resulting wake structure oscillates at half the original Karman vortex shedding frequency. For higher frequency excitation the primary pattern involves symmetry breaking of the initially shed symmetric vortex pairs. The Karman shedding phenomenon can be modeled by a nonlinear oscillator. The symmetrical flow perturbations resulting from the periodic cylinder excitation can also be similarly represented by a nonlinear oscillator. The oscillators represent two flow modes. By considering these two nonlinear oscillators, one having inline shedding symmetry and the other having the Karman wake spatio-temporal symmetry, the possible symmetries of subsequent flow perturbations resulting from the modal interaction are determined. A theoretical analysis based on symmetry (group) theory is presented. The analysis confirms the occurrence of a period-doubling instability, which is responsible for the frequency halving phenomenon observed in the experiments. Finally it is remarked that the present findings have important implications for vortex shedding control. Perturbations in the inflow direction introduce 'control' of the Karman wake by inducing a bifurcation which forces the transfer of energy to a lower frequency which is far from the original Karman frequency.

• 한국항공우주학회지
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• 제32권6호
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• pp.9-15
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• 2004

순간적으로 병진운동하는 2차원 원형실린더 주위의 점성유동장을 확산와류방법에 의해 계산하였다. 선두후류와 주후류의 상세한 발달 상태를 조사하였으며 Re=1200, 9500의 유선 형상, 주후류의 크기, 후방 대칭축 축방향속도 계산은 보고된 실험결과와 근접하였다. Re=1200 유동장 후류의 ${\tau}=50$까지의 장기간 동안의 발달 상태를 조사하였다. 후방후류의 와류이탈주파수는 보고된 결과와 근접하게 나왔다.

• 한국항공운항학회지
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• 제32권1호
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• pp.91-102
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• 2024

This study aimed to investigate the sleep-wake patterns, social jetlag (SJL), and daytime sleepiness (DS) among air traffic controllers (ATCs) with rotating shifts. A total of 133 shift-rotating ATCs participated by completing self-report questionnaires regarding their sleep-wake patterns and DS. SJL, indicating the mid-sleep difference between workdays (W) and free days (F), was calculated for each shift. Night-shift workdays had the shortest sleep duration (SD) (5.28 hours), whereas free days following day shifts had the longest SD (6.66 hours). SJL for day and night shifts was 2.73 and 2.71 hours, respectively. The average DS score was 7.92 out of 24, with a 28.6% prevalence of DS. There was a negative correlation between SD following day shifts and SJL for the day shifts. Given these findings, it is recommended to implement effective interventions and work schedules to maintain consistent sleep patterns and minimize social jetlag to address sleep issues for shift-working ATCs.

• Journal of Korean Biological Nursing Science
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• 제11권1호
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• pp.23-31
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• 2009

Purpose: The purpose of the present study was to investigate the prevalence and related factors of sleep-wake disturbance (SWD) in Korean post-stroke patients. This study was the first to address post-stroke SWD in Korea using a structured questionnaire. Method: We investigated the prevalence of SWD and related factors including lesion location, stroke severity, presence of depression and fatigue. We assessed sleep-wake pattern including quality of sleep, sleep latency, wake episodes, wake time after sleep onset, daytime sleep episode and sleep time at daytime. Ninety stroke patients admitted to a university affiliated hospital in Seoul between the period September 2008 and January 2009 were included in the study. Result: Thirty five patients (38.9%) complained insomnia and 32 (35.6%) complained excessive daytime sleepiness (EDS). Quality of sleep (p=.000), sleep latency (p=.000) and total sleep time (p=.001) were significantly poorer in 16 patients with both insomnia and EDS than in the others. The related factors to insomnia were level of education (p=.030), depression (p=.007) and fatigue (p=.034), though related factors to EDS were stroke onset time (p=.049), stroke severity (p=.005), motor dysfunction (p=.035), dysphasia (p=.018), fatigue (p=.001) and lesion location (p=.019). Conclusion: Sleep-wake disturbance is a common problem in Korean stroke patients. Strategies to improve quality of sleep are urgently needed in the post-stroke patients.