• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.36-42
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• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• Journal of the Korean Solar Energy Society
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• v.35 no.3
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• pp.17-25
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• 2015

The main objective of this study is to predict the wind power generation at the wind farm using various wake models. Modeling of wind farm is a prerequisite for prediction of annual energy production at the wind farm. In this study, we modeled 20 MW class Seongsan wind farm which has 10 wind turbines located at the eastern part of Jeju Island. WindSim based on the computational fluid dynamics was adopted for the estimation of power generation. The power curve and thrust coefficient with meteorology file were prepared for wind farm modelling. The meteorology file was produced based on the measured data of the Korea Wind Atlas provided by Korea Institute of Energy Research. Three types of wake models such as Jensen, Larsen, and Ishihara et al. wake models were applied to investigate the wake effects. From the result, Jensen and Ishihara wake models show nearly the same value of power generation whereas the Larsen wake model shows the largest value. New positions of wind turbines are proposed to reduce the wake loss, and to increase the annual energy production of the wind farm.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.59.2-59.2
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• 2011

Although there are many activities on the construction of wind farm to produce amount of power from the wind, in practice power productions are not as much as its expected capabilities. This is because a lack of both the prediction of wind resources and the aerodynamic analysis on turbines with far wake effects. In far wake region, there are velocity deficits and increases of the turbulence intensity which lead to the power losses of the next turbine and the increases of dynamic loadings which could reduce system's life. The analysis on power losses and the increases of fatigue loadings in the wind farm is needed to prevent these unwanted consequences. Therefore, in this study velocity deficits have been predicted and aerodynamic analysis on turbines in the far wake is carried out from these velocity profiles. Ainslie's eddy viscosity wake model is adopted to determine a wake velocity and aerodynamic analysis on wind turbines is predicted by the numerical methods such as blade element momentum theory(BEMT) and vortex lattice method(VLM). The results show that velocity recovery is more rapid in the wake region with higher turbulence intensity. Since the velocity deficit is larger when the turbine has higher thrust coefficient, there is a huge aerodynamic power loss at the downstream turbine.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.980-985
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• 2003

The present study addresses a computational work to investigate the influence of a turbulent wake flow on the pressure recovery of a subsonic diffuser. The turbulent wake is generated by a cylinder with a small diameter, which is installed at the inlet of a 2-dimensional diffuser. Computation are applied to three-dimensional steady Navier-Stokes equations. The fully implicit finite volume scheme is used to discretize the governing equations. The computational results are qualitatively well compared to the experimental results. The results show that the pressure recovery of the subsonic diffuser is dependent on the diameter and location of cylinder. It is found that a certain diameter and location of the cylinder to generate the turbulent wake give a better pressure recovery, compared with no cylinder flow.

• Journal of KSNVE
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• v.6 no.5
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• pp.661-669
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• 1996

Proposed is an aero-acoustic performance prediction method of axial fan. The fan aerodynamic performance is predicted by combining pitch-averaged quasi 3-D flow analysis with pressure loss models for blade boundary layer and wake, secondary flow, endwall boundary layer and tip leakage flows. Fan noise is assumed to be radiated as dipole distribution type, and its generation is assumed to be mainly due to the vortex street shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex stree shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex street model with thin airfoil theory. The aero-acoustic performance prediction results by the present method are in good agreement with the measured results of several axial fans. With the present prediction method, parametric studies are carried out to investigate the effects of blade chord length and spacing on the efficiency and the noise level of fan. In the case of lightly loaded fan, both efficiency improvement and noise reduction can be achieved by decreasing chord length or by increasing blade specing. However, when fan is designed at highly loaded condition, the noise reduction by increasing blade spacing penalizes the attaninable efficiency of fan.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.468-475
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• 2020

A good acoustic word embedding that can well express the characteristics of word plays an important role in wake-up word detection (WWD). However, the representation ability of acoustic word embedding may be weakened due to various types of environmental noise occurred in the place where WWD works, causing performance degradation. In this paper, we proposed triplet loss based Domain Adversarial Training (tDAT) mitigating environmental factors that can affect acoustic word embedding. Through experiments in noisy environments, we verified that the proposed method effectively improves the conventional DAT approach, and checked its scalability by combining with other method proposed for robust WWD.

• Journal of Wind Energy
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• v.13 no.1
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• pp.5-14
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• 2022

Currently, the Korean government is driving the construction of large-scale floating offshore wind farms to increase domestic renewable energy generation and decrease carbon emissions. In offshore wind farms, maintenance approaches can be limited more often than onshore wind farms by marine weather conditions (wave height, etc.). Therefore, maintenance planning optimization is more important to minimize maintenance costs and power generation loss by downtime. Additionally, the power generation of a wind farm is affected by wind speed as well as wind direction because of the wake effect, so it is possible that power generation loss by downtime is also dependent on combinations of weather conditions (wind speed and direction) and the location of wind turbines for maintenance. In this study, the effects of the wind conditions and the locations of tripped wind turbines on power generation loss were explored for a hypothetical floating offshore wind farm. In order to calculate the power generation of a wind farm, a wake effect calculator was developed based on Jensen's formula. Then, a simple methodology of determining maintenance priorities that minimize power generation loss was proposed.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.661-667
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• 2001

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7. According to a wake-passing through the cascade, two velocity deficits appear near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit is caused by a periodic wake and the second one appears after some delayed time. The second velocity deficit may be interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreases the duration time of separation appearance and the lesser loss of aerofoil is resulted.

• Sleep Medicine and Psychophysiology
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• v.19 no.1
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• pp.5-10
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• 2012

The release of hormones and the metabolism of human body are controlled by the circadian rhythm related to sleep-wake cycle. Growth hormone, prolactin, thyroid stimulating hormone, cortisol, glucose, and insulin-secretion rates fluctuate according to the sleep-wake cycle. In addition, sleep is related to the appetite regulation and carbohydrate and other energy metabolism. Hypocretin (orexin), an excitatory neuropeptide, regulates waking and diet intake, and the poor sleep increases diet intake. The short sleep duration increases one's body mass index and impairs the function of the endocrine and metabolism, causing increases in the risk of glucose intolerance and diabetes. The poor sleep quality and sleep disorders have similar impact on the metabolic function. In short, the sleep loss and the poor quality of sleep have a detrimental effect on the endocrine and energy metabolism. The improvement of sleep quality by the future research and appropriate clinical treatment would contribute to the decrease of the metabolic diseases such as diabetes.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.453-459
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• 2009

The DSME guide plate(GP) has been developed with the target to improve the cavitation and vibration performance when used with discharging cooling water around the outlet of LNG carrier. It was proven that it could as well be applied as a powerful wake control device on its own, even without discharging cooling water. However, it has to be taken into account that it inevitably results in speed loss. This study shows the possibility to design a GP which simultaneously improves both vibration and speed performance. The study intends to outline how to design the preliminary GP configurations from both the vibration and the speed performance points of view. Further, the study offers design guidance for the hull form and the propeller when adapting GP as a wake control device.