• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.150-155
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• 2001

단일 소파막에 대한 파도 반사문제와 투과. 또 이중으로 설치된 소파막에 대한 반사와 투과문제에 대한 양함수 해를 도출하였다. 단일 막에 대한 파도의 반사가 에어리 파의 해당 벽에 의해서만 입자반사로서 일어난다고 보고 이를 원거리 파도에너지와 일치시켜 반사 파고를 얻었다. 이중 막에 대해서는 각각의 파도가 독립적으로 단일 막에 의해서 반사 또는 투과가 되고 이들이 중첩되어 전체 파고가 형성되어지는 것으로 간주하여 전체 반사계수와 투과계수를 결정하였다. 단일 막에 대한 투과계수의 결과는 정성적으로 다른 계산결과와 비슷한 경향을 보이며, 실험결과보다는 높게 예측되었다. 이중 단일 막에 대한 결과는 낮은 주파수에서 실험결과와 유사한 경향을 보이고, 중간 주파수에서 완만한 감소를 보였다. 계산이 양함수 해로 얻어지므로 개념설계와 현장에서 유용하게 활용될 수 있으리라 기대된다.

• Water for future
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• v.20 no.1
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• pp.49-54
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• 1987

A numerical analysis of the characteristics of wave reflection over rippled beds (sand bars) was carried out By Boundary Element Method(B.E.M) using linear elements. It is assumed that the incident wave is normal and oblique to the rippled beds and the wave may be and the escribed by two-dimensional linear theory. The accuracy of the computational scheme is investigated by comparing the laboratory data, the analytic measured results of the other researchers. The B.E.M results for the normal incident wave is held for the mechanism of the resonant Bragg reflection at the point where the wave length of the bottom undulation is one half the wave length of the surface wave.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.193-203
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• 1996

Long period waves were measured at two stations outside and inside Chukpyon Harbor using two pressure-type wave gauges for one week that covers storm sea period. Based on the collected data the characteristics of long-period resonant oscillations were analysed: the resonant period corresponding to the peak spectral density are slightly different from one to the component wave period with the largest amplification ratio, and the latter period is suggested as that of the first resonant mode. From the analysed field data and numerical modeling, the first resonant mode of Chukpyon Harbor region appeared to be around 12 minutes with amplification ratio of 7, whose amplitude varies 10-20 cm inside of the harbour, and also the second mode appeared to be around 6 minutes. The waves of 2-3 minute periods were resonated apparently in the harbour, which is considered to be generated from group-bounded irregular waves and non-linear wave-wave interaction etc. The linearly decreasing reflection coefficients used in the numerical modeling appeared to be an alternative in calculating reflected waves in harbor.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.4
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• pp.153-165
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• 2018

In this study, the performance of irregular wave field generation of olaFlow is first verified by comparing the frequency spectrum of the generated waves by the wave-source using olaFlow and the target wave. Based on the wave performance of irregular waves of olaFlow, the characteristics of the velocity field including the average flow velocity, longshore current and turbulent kinetic energy around the three-dimensional permeable submerged breakwaters, which act as the main external forces of the salient formation, are numerically investigated. The numerical results show that as the gap width between breakwaters decreases, the wave height in the center of the gap increases and as the gap width between breakwaters increases, the longshore currents become stronger. As a result, it is possible to understand the formation of the salient formed behind the submerged breakwaters.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2101-2107
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• 2012

A current velocity measurement radar for a river or a stream estimates Doppler frequencies of return echoes to extract the corresponding surface velocity information. It is very important to maintain the reliability and accuracy of these velocity estimates for water resource management such as flooding or drought conditions. However, received Doppler spectra of water surface return echoes have very widely varying shapes according to different measurement environments and weather conditions. Therefore, serious problems may arise in maintaining the reliability and accuracy of velocity estimating algorithm in a radar sensor because of Doppler spectra which can have many different kind of shapes. Therefore, in this paper, an appropriate Doppler spectrum model is suggested to simulate many various Doppler spectra. This model can be very useful in validating the reliability and accuracy of surface velocity estimates.

• Sleep Medicine and Psychophysiology
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• v.2 no.2
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• pp.133-137
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• 1995

The author reviews current knowledge about what REM sleep is and where and how it is generated. REM sleep is the state in which our most vivid dreams occur. REM sleep is identified by the simultaneous presence of a desynchronized cortical EEG, an absence of activity in the antigravity muscles(atonia), and periodic bursts of rapid eye movements. Another characteristic phenomena of REM sleep are the highly synchronized hippocampal EEG of theta frequency and the ponto-geniculo-occipital(PGO) spike. All these phenomena can be explained in terms of changes in neuronal activity. Transection studies have determined that the pons is sufficient for generating REM sleep. Lesion studies have identified a small region in the lateral pontine tegmentum corresponding to lateral portions of the nucleus reticularis pontis oralis(RPO) and the region immediately ventral to the locus coeruleus, which is required for REM sleep. Unit recording studies have found a population of cells within this region that is selectively active in REM sleep. Cholinergic neurons of the giant cell field of pontine tegmentum(ETG), which is 'REM a sleep-on cells', has shown to be critically involved in the generation of REM sleep. Noradrenergic neurons of the locus coeruleus and serotonergic neurons of the dorsal raphe, which are called 'REM sleep-off cells', appear to act in a reciprocal manner to the cholinergic neurons. It is proposed that the periodic cessations of discharge of 'REM sleep-off cells' during REM sleep might be significant for the prevention of the desensitization of receptors of these neurons.

• The Journal of Korean society of community based occupational therapy
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• v.8 no.2
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• pp.29-37
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• 2018

Objective : Sleep disorder caused by stress or disease to elderly currently. We tried to make clear constant exercise according to exercise intensity would have effect on sleep disorder in elderly using EEG and melatonin. Methods : Thirty subjects were over 65 years old who lived a senior facility in some parts. They were able to communicate and understand the purpose of the study. They also expressed their intension to participate actively in experiment. They should have alert consciousness and orientation about time, place, and people. Sleep disorder was assessed via below 6 hr total sleep time and Pittsburge Sleep Quality Index, which was satisfied with both of criterion at the same time. Exercises composed of low intensity walking, moderate aerobic exercise, and high intensity resistance strength. We used QEEG 8-System (LAXTHA Inc. KOREA) to check wave type and Polysomnograpy (Compumedics, Australia) to test quality of sleep. and Histologic features were observed by TTC (triphenyltetrazolium chloride) staining and H & E (Hematoxylin & Eosin) staining. Results : There was a significant sleep index and change of melatonin after aerobic exercise. There was a significant SOL, S1, S2, and SWS in aerobic exercise, but there was a significant SWS in walking and resistance strength. There was a significant change of delta wave especially in frontal and temporal region between exercises. Conclusion : They had different effects according to type of exercise, when elderly who have chemical, behavioral change of circadian rhythms did exercise consistently. Aerobic exercise had more effect on sleep disorder than other exercise. Therefore, we may supply proper exercise to elderly and high quality of life.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.575-583
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• 2017

Various types of flow patterns around the stepped weir and spillway, such as the skimming flow over such structures and the wave-type flow with a standing undular hydraulic jump and roller downstream of the structures, are developed in open channels. Unsteady three-dimensional numerical simulations are carried out using a hybrid RANS-LES turbulence modeling approach and the volume of fluid method for resolving free surface fluctuations to represent the turbulent flow including the skimming flow and wave-type flow over a stepped weir installed in a rectangular channel. The comparison of numerical results with an existing experimental measurement reveals that the present numerical simulations reasonably well reproduce the turbulent flow passing the stepped weir, in terms of time-averaged velocity profiles at selected locations downstream of the weir, flow topology characterized by the wave-type and skimming flows, the maximum height and length of the standing wave and the length of reattachment of recirculating zone. The numerical result further elucidates the distinct flow behaviors of the wave-type and skimming flow by presenting instantaneous intense variations of free surface and velocity vectors, the distributions of Reynolds shear stress and turbulent kinetic energy and three-dimensional complex features of coherent structures and total pressure distribution.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.59-59
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• 2011

파랑의 전파와 변형에 대한 연구에는 수심방향으로 적분한 2차원방정식인 완경사방정식과 Boussinesq 방정식을 기반으로 한 수치모형을 이용한 연구가 최근까지 가장 활발하게 진행되어 오고 있다. 그러나 실제 구조물의 설계에는 2차원 수치모형에서 고려할 수 없는 수심방향 유속에 기인한 정확도의 문제로 인해 구조물의 형상과 재원을 설계하기 위한 정교한 수치모형실험이 어려워 주로 수리모형실험에 의존해 왔다. 수리모형실험은 실제 현상을 가장 잘 재현해낼 수 있어 신뢰성이 매우 높지만 다양한 실험을 수행하기가 어렵고 많은 시간과 비용이 소요되는 단점이 있다. 이에 따라 최근 수심방향으로 완전한 운동방정식인 Navier-Stokes 방정식을 푸는 3차원 수치모형에 대한 연구가 활발히 진행되고 있다. 이론적으로 매우 우수한 모형이긴 하나 정확도 높은 결과를 얻기 위해서는 매우 조밀한 격자를 필요로 하기 때문에 아직까지 막대한 계산시간이 필요하다는 단점이 있으나 컴퓨터 기술이 급격한 속도로 발전하고 있어 Navier-Stokes 방정식 모형의 적용 가능성은 계속 높아지고 있다. 파랑변형을 다루는 수치모형실험을 수행할 때 외부조파를 사용할 경우 구조물이나 지형에 의해 반사되어 나온 파랑이 조파지점에 도달할 때 실험영역으로 재 반사되는 문제가 발생한다. 이를 해결하기 위해 내부조파기법의 개발에 대한 연구가 필수적이었으며, 자유수면변위를 변수로 사용하는 모형의 경우 그 연구가 매우 활발하게 진행되어 왔다. 한편, Navier-Stokes 방정식 모형의 경우 자유수면변위를 변수로 사용하는 2차원 모형에 비해 상대적으로 연구가 미흡하였다. 본 연구에서는 기존의 연직 2차원 Navier-Stokes 방정식 모형에 사용된 연속방정식에 질량 원천항을 추가하는 내부조파기법을 도입하여 3차원 수치모형에서 고립파를 내부조파하고, 급경사에서의 고립파의 처오름 및 처내림 현상을 수리모형 실험결과와 비교 및 분석하였다. 수치모형은 Navier-Stokes 방정식을 엇갈림 격자체계에서 계산하는 동수압 모형으로서, Two-step projection 기법을 사용하는 유한차분모형을 사용하였다. 본 수치모형은 난류의 해석을 위해서 상대적으로 큰 에디(eddy)만을 고려하는 SANS(spatially averaged Navier-Stokes) 방정식을 계산하는 LES(large-eddy-simulation) 기반의 수치모형으로, 난류 모델링을 위해 Smagorinsky LES 모형을 사용한다. 또한, 압력장의 계산을 위해 Bi-CGSTAB 기법을 이용하여 Poisson 방정식의 해를 구하였으며, 자유수면 추적을 위하여 2차 정확도의 VOF(volume-of-fluid) 기법을 사용하였다. 수치모형실험이 전체적으로 수리모형실험에서 관측한 파랑의 처오름 및 처내림 현상을 잘 재현하고 있는 것으로 나타났으며, 정량적인 비교를 통해 수치모형의 성능을 검증하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.163-163
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• 2011

평활입자동역학법(SPH, Smoothed Particle Hydrodynamics)은 붕괴파(도수, 댐붕괴류, 쇄파) 등과 같이 수면 변동이 큰 유체 역학 문제를 해결하기 위한 무격자법 중의 하나이다. SPH를 이용한 붕괴파의 모의에서는 압력, 점성, 밀도(압축성), 척력 등 다양한 계산 인자가 필요하다. 이들 인자가 SPH 모의 결과에 미치는 영향을 도수와 댐붕괴류에 대해서 검토하였다. 그 결과 압력과 관련하여, 상태 방정식 계수로 표현되는 유체의 음속은 입자들의 흩어짐 현상과 밀접한 관계를 가지는 것을 밝혀내었다. 평활 거리는 수치해의 안정성과 밀접한 관련이 있으며, 너무 작거나 크게 설정하는 경우 해의 정확도가 떨어지는 것으로 나타났다. 일반적으로 2차원 문제의 경우 20~23개 정도의 입자가 해의 내삽에 사용되는 것이 바람직하다.