• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.150-155
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• 2000

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a power plant. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At the resonance, the value of vibration in this system was 595 ${\mu}m$, p-p and the sound pressure level was maximum 103 dBA. And the resonance frequency was found to be 35 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance is possible. In this system, the difference of these frequencies was 1.8%. We can evaluate the possibility of acoustic resonance by using damping parameter. We did eliminate acoustic resonance by installing baffle in tube bank. After installing baffle, the level of vibration and noise was reduced dramatically.

• 대한전기학회논문지:전력기술부문A
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• 제52권6호
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• pp.301-306
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• 2003

When a bulk power system experiences a serious disturbance or heavy load trip, the system frequency may drop and even collapse if the total generating power does not supply the system demand sufficiently. Since an isolated power system possesses a lower inertia and comes with limited reserves, the load shedding by under frequency relay becomes an important strategy to keep system natural frequency. This paper presents a scheme to determine the load shedding criteria by using the rate of change of frequency when the large disturbance happens.

• 대한조선학회논문집
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• 제42권4호
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• pp.368-378
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• 2005

The effects of rotary oscillation on the unsteady laminar flow past a circular cylinder. are numerically investigated in the present study. The numerical solutions for the 20 Wavier-Stokes equation are obtained using a finite volume method Tn the framework of an overlapping grid system. The vortex formation behind a circular cylinder and the hydrodynamics of wake flows for different rotary oscillation conditions are analyzed from the results of numerical simulation. The lock-on region is defined as the region that the natural shedding frequency due to the Karmann Vortex shedding and the forcing frequency due to the forced oscillating a cylinder are nearly same, and the quasi-periodic states are observed around that region. At the intersection between lock-on and non-lock-on region the shedding frequency is bifurcated. After the bifurcation, one frequency fellows the forcing frequency($S_f$) and the other returns to the natural shedding frequency($St_0$). in the quasi-periodic states, the variation of magnitudes and relevant phase changes of $C_L$ with forcing phase are examined.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.18-21
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• 2004

Lock-on characteristics of the flow around a circular cylinder performing a rotationally oscillation with a relatively high forcing frequency have been investigated experimentally using flow visualization and hot-wire measurements. Dominant parameters are Reynolds number (Re), amplitude of oscillation $(\theta_A)$, and frequency ratio $F_R=f_f\;/\;f_n$, where $f_f$ is the forcing frequency and if is the natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14\times10^3,\;\pi/15\leq\theta_A\leq\pi/3$, and $F_R=1.0$. The effects of this active control technique on the lock-on flow regime of the cylinder wake were evaluated through wake velocity measurements and spectral analysis of hot-wire signals. The rotary oscillation modified the flow structure of near wake significantly. The lock-on phenomenon was found to occur in the range of frequency encompassing the natural vortex shedding frequency. In addition, when the amplitude of oscillation is less than a certain value, the lock-on phenomenon was occurred only at $F_R=1.0$. The lock-on range expanded and vortex formation length decreased as the amplitude of oscillation increases. The rotary oscillation generated small-scale vortex structure just near the cylinder surface.

• Molecules and Cells
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• 제24권1호
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• pp.139-147
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• 2007

Although transforming growth factors (TGFs) are implicated in the process of endochondral ossification, which is initiated by the differentiation of mesenchymal cells into chondrocytes, it is not clear how $TGF-{\beta}3$ regulates the chondrogenic differentiation of limb bud mesenchymal cells. Here, differential display polymerase chain reaction (DD-PCR) screening and RT-PCR analysis revealed that transcripts of A Disintegrin And Metalloprotease 10 (ADAM 10) decreased during the chondro-inhibitory action of $TGF-{\beta}3$ on cultured chick leg bud mesenchymal cells. Electroporation of ADAM 10 morpholino antisense oligonucleotides inhibited the ectodomain shedding of delta-1, and cell proliferation and subsequent precartilage condensation, in a manner similar to that caused by $TGF-{\beta}3$. The suppression of mesenchymal cell proliferation induced by $TGF-{\beta}3$ and ADAM 10 morpholino antisense oligonucleotides was reversed by activation of ADAM 10 with phorbol 12-myristate 13-acetate (PMA) or knockdown of Notch-1 with siRNA. Collectively, these data indicate that, in cultured chick leg bud mesenchyme cells, $TGF-{\beta}3$ downregulates ADAM 10 and inhibits cell proliferation and subsequent precartilage condensation by inhibiting the ectodomain shedding of delta-1, and that this results in the activation of Notch signaling.

• Wind and Structures
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• 제20권3호
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• pp.405-422
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• 2015

In previous model- and full-scale studies, high-amplitude vertical vibrations of mast-arm traffic signal structures have been shown to be due to vortex shedding, a phenomenon in which alternatingly shed, low-pressure vortices induce oscillating forces onto the mast-arm causing a cross-wind response. When the frequency of vortices being shed from the mast-arm corresponds to the natural frequency of the structure, a resonant condition is created causing long-lasting, high-amplitude vibrations which may lead to the fatigue failure of these structures. Turbulence in the approach flow is known to affect the cohesiveness of vortex shedding. Results from this full-scale investigation indicate that the surrounding terrain conditions, which affect the turbulence intensity of the wind, greatly influence the likelihood of occurrence of long-lasting, high-amplitude vibrations and also impact whether reduced service life due to fatigue is likely to be of concern.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.155-156
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• 2015

Recently, electricity consumption has rapidly increased along with economic growth. The operating strategy using emergency generator is aimed, to resolve a demand response management. For strategy of peak shedding using emergency generator, it is essential to introduce the fast transfer switching device. One of the most effective solutions is to use a static transfer switch (STS) based on thyristor. However, the characteristic of natural commutated SCR thyristor should anticipate short duration voltage sag. STS system thus requires more than a quarter cycle to successfully complete transfer process. This paper proposes the operation scheme of the STS system using the forced-commutation technique to mitigate instantaneous voltage sag during peak transfer process. Proposed STS system improved turn-off characteristic thus accomplishes the peak load shedding satisfied power quality. Performance of the proposed STS system is evaluated using electromagnetic transient program (EMTP) to confirm the effectiveness.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.115-119
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• 2007

In this paper, a flow visualization analysis has been carried out on an oscillating square section cylinder, numerically, using a commercially available code CFD-ACE. In this study, the square cylinder is forced to oscillate at different frequencies of excitation, viz., fe/fo=0.5, 1.0 and 2.0 (where, fe is the excitation frequency provided to the cylinder and fo is the natural vortex shedding frequency from the stationary cylinder at a particular Reynolds number (=5200). In all the cases, the peak-to-peak amplitude of oscillation is kept at 32% of the side dimension of the square cylinder. These studies are conducted to understand the influence of frequency of oscillation on the flow field features around the cylinder, particularly the mode of vortex shedding. Results indicate that, the flow field around a square cylinder is very much influenced by the excitation frequency, in particular the vortex shedding mode. It is also found that, the vortex street parameters are significantly influence by the oscillation frequency. Comparison with earlier reported experimental studies has also been attempted in this paper. In appears that, such a numerical exercise (as performed in this paper) is first of its kind. It is believed that, these studies would enable one to understand the mechanisms underlying the flow-induced vibrations of a square section cylinder.

• Wind and Structures
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• 제20권6호
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• pp.793-810
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• 2015

Tests were conducted at the Florida International University (FIU) Wall of Wind (WOW) to investigate the susceptibility of Variable Message Signs (VMS) to wind induced vibrations due to vortex shedding and galloping instability. Large scale VMS models were tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. Data was measured for the $0^{\circ}$ and $45^{\circ}$ horizontal wind approach directions and vertical attack angles ranging from $-4.5^{\circ}$ to $+4.5^{\circ}$. Analysis of the power spectrum of the fluctuating lift indicated that vertical vortex oscillations could be significant for VMS with a large depth ratio attached to a structure with a low natural frequency. Analysis of the galloping test data indicated that VMS with large depth ratios, greater than about 0.5, and low natural frequency could also be subject to galloping instability.

• 한국동물위생학회지
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• 제35권1호
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• pp.25-31
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• 2012

This study examined the efficacy of natural ingredient formulated herbal medicine as feed additives against coccidiosis in broiler chicken. Medicinal herbs used in this study were Artemisia annua, Pulsatilla chinensis, Clematis chinensis and Scutellaria baicalensis. Two week old chicks were administered with 1% ingredient formulated herbal medicine. Observations of the efficacy were confirmed by examining the lesion score, histopathological appearance of cecum, shedding of fecal oocyst and production index in farm. S. baicalensis of the most effective substance were analyzed by UPLC. The results are as follows; among various types of Chinese medicine, the most efficacious ingredient was found to be pure bicalein. The major index substance is bicalein and $13{\mu}g/ml$ per gram was found. Feeding of chickens with S. baicalensis induced the coccidiostat effect and reduced the fecal shedding of E. tenella oocyst by 14%. Experimental results on a farm, feed conversion ratio and weight gain and production rate in the group with natural ingredient formulated additives than in control group increased. The rate of weight gain (%) in each experimental group showed 108% and 126% increase while the mortality rate was 1.4% lower than the control group. The investigation showed that the most efficacious ingredient was found to be S. baicalensis among herbal medicine products for coccidiostats. However, as it was found in the farm experiment that pure S. baicalensis alone is economically unviable. The additives with cocktailed of efficacious ingredient are suggested to be implemented for effective protection against coccidiosis.