• 전기학회논문지
• /
• 제58권3호
• /
• pp.566-572
• /
• 2009

This paper has studied breakage possibility of glass insulators by resonance and accelerated deterioration through the comparison of the natural vibration and on site vibration. The natural frequencies of the strut tube glass insulator was measured within a range of less than 1kHz. In the on site vibration, the largest frequency that was imposed on strut tube glass insulators was 80Hz with 1.13g of vertical vibration in the viaduct section, the largest vertical vibration (0.38g) was detected at 103Hz in the open route section. When site vibration and natural vibration of strut tube glass insulators were compared in terms of characteristics, the resonance frequency was not the same. In both the viaduct and open route sections, it seems that the impact by vertical vibration in strut tube glass insulators is large. It's very unlikely that glass insulators were damaged by fatigue accumulation of vibration since the possibility of damage by resonance was very low in consideration of the characteristics of natural vibration and site vibration of glass insulators. In addition, no damage was detected in the accelerated deterioration test.

• 한국자기공명학회논문지
• /
• 제24권2호
• /
• pp.53-58
• /
• 2020

Free radicals including reactive oxygen species (ROS) are important chemicals in the research area of biology, pharmaceutical, medical, and environmental science as well as human health risk assessment as they are highly involved in diverse metabolism and toxicity mechanisms through chemical reactions with various components of living bodies. Electron spin resonance (ESR) spectroscopy is a powerful tool for detecting and quantifying those radicals in biological environments. In this work we observed the ESR signal of 2,2,6,6-Tetra-methyl piperidine 1-oxyl (TEMPO) in aqueous solution at various concentrations to estimate the uncertainty factors arising from the experimental conditions and signal treatment methods. As the sample position highly influences the signal intensity, dual ESR tube geometry (consists of a detachable sample tube and a position fixed external tube) was adopted. This type of measurement geometry allowed to get the relative uncertainty of signal intensity lower than 1% when triple measurements are averaged. Linear dependence of signal intensity on the TEMPO concentration, which is required for the quantification of unknown sample, could be obtained over a concentration range of ~10³ by optimizing the signal treatment method depending on the concentration range.

• 한국소음진동공학회논문집
• /
• 제17권6호
• /
• pp.498-506
• /
• 2007

Using wind tunnel, experimental approaches were employed to investigate fluidelastic instability of tube bundles, subjected to uniform cross flow. There are several flow-induced vibration excitation mechanisms, such as fluidelastic instability, periodic wake shedding resonance, turbulence-induced excitation and acoustic resonance, which could cause excessive vibration in shell-and tube heat exchanges. Fluidelastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to cross flow. The system comprised of cantilevered flexible cylinder(s) and rigid cylinders of normal square array, In order to see the characteristics of flow in tube bundles, particle image velocimetry was used. From a practical design point of view, Fluidelastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping. The threshold flow velocity for dynamic instability of cylinder rows is evaluated and the data for design guideline is proposed for the tube bundles of normal square array.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2011년도 추계학술대회 논문집
• /
• pp.101-106
• /
• 2011

In the present paper, the phenomena of abnormal noise and vibration due to acoustic resonance of CFBC(Circulating Fluidized Bed Combustion) boiler was presented. The acoustic resonance which occurred in the gas path of CFBC boiler system was caused by coincidence of vortex shedding frequency of tube bank and acoustic natural frequency of duct and hopper. And, the phenomena of beating arose from the interference of two closed resonant waves at 66.4Hz and 70.8Hz. There are two control methods for acoustic resonance in this system. The first method is to change the vortex shedding frequency from the structural alterations on the tube bank. And the second method is to change the acoustic natural frequency of the gas path with the installation of anti-noise baffles. The second one which is relatively easy to apply, was adapted in this study. As a result, the noise and vibration level have been decreased by 41dB and 94% at 66.4Hz, respectively. And the improvement of noise and vibration at 70.8Hz was identified by sensory evaluation.

• 조명전기설비학회논문지
• /
• 제15권6호
• /
• pp.8-14
• /
• 2001

메탈핼라이드램프는 고효율, 고연색성이며 집광능력이 좋다. 그러나 메탈핼라이드 램프의 단점은 아크튜브내에서 음향공명현상이 발생되는 것으로 알려져 있다. 이러한 음향공명은 점등상태의 불안정과 기체의 심한 파동을 일으킨다. 심한 파동과 불안정한 점등으로 아크가 소멸되는 부위는 전압이 상승되고, 방전관내벽에 근접된 아크는 국부의 과열로 튜브를 금가게한다. 이 연구의 목적은 펄스스타트 메탈핼라이드램프 MH200[W]의 아크튜브내에서 음향공명을 감소시키는 것이다. 음향공명현상을 감소시키기 위하여 전자식안정기가 84.6[kHz]에서 94.2[kHz] 대역내에 있는 89[kHz]의 단독주파수인 정현고주파를 램프에 공급하기 위하여 설계되었다. 실험결과 고효율 펄스스타트 MH200[W] 램프의 방전관내에 음향공명 현상이 없었다.

• 한국항공우주학회지
• /
• 제32권10호
• /
• pp.112-117
• /
• 2004

본 연구는 공기역학적 운동에너지를 이용하여 점화장치를 구성하는데 따른 해석과 실험에 관한 연구로써 공기역학 점화기는 크게 노즐과 공명관으로 구성되어 있다. 압축가스가 노즐을 통과하여 공명관으로 유입되며, 이때 노즐과 공명관사이에 압력맥동이 발생한다. 이러한 압력맥동에 의한 운동에너지는 일정한 조건하에 공명관 내부에서 열에너지로 변화하게 된다. 본 연구에서는 음속노즐과 초음속 노즐을 두개의 각기 다른 공명관에서 실험과 수치해석을 실시하였으며, 노즐표면의 마찰손실과 공기역학 손실을 최소화하는 초음속 노즐의 최적형상을 제시하였다.

• Journal of Magnetics
• /
• 제19권4호
• /
• pp.372-377
• /
• 2014

The purpose of the study is to investigate how uptake counts of $^{201}Tl$ of radioisotopes in the human body could change, when taking computed tomography and magnetic resonance imaging right after injecting contrast media. $^{201}Tl$ radioisotope substances of iodine contrast medium, which is a computed tomography contrast medium, and paramagnetic contrast medium, which is an magnetic resonance imaging contrast medium, were used as study materials. First, $^{201}Tl$ was put into 4 cc of normal saline in test tube, and then a computed tomography contrast medium of Iopamidol$^{(R)}$ or Dotarem$^{(R)}$, was put into 2 cc of normal saline in test tube. An magnetic resonance imaging contrast medium of Primovist$^{(R)}$ or Gadovist$^{(R)}$ was also put into 2 cc of normal saline in test tube. Each contrast medium was distributed to make $^{201}Tl$ as 3 mCi, with a total of 4 cc. Gamma camera, low energy high resolution collimator, and pinhole collimator were used to obtain images. The uptake count of $^{201}Tl$ was measured with 1000 frames of images, and obtained after 10 times of repetition. This study revealed that the use of Gadovist$^{(R)}$, which is an magnetic resonance imaging contrast medium, showed the smallest number of uptake count, after measuring $^{201}Tl$ uptake count by low energy high resolution collimator. On the other hand, the use of Iopamidol$^{(R)}$, which is a computed tomography contrast medium, showed the biggest difference in uptake count, when measuring $^{99m}Tc$ uptake count by Pinhole collimator. When examining with gamma camera, using contrast medium and $^{201}Tl$, identifying the changes of uptake count is very important for improving the value of diagnosis.

• 수산해양교육연구
• /
• 제28권3호
• /
• pp.645-652
• /
• 2016

At the initial stage of propulsion shaft design, in line with shaft alignment, an intensified consideration of lateral vibration is needed to verify its operational safety. Recently the alignment problem affecting the lateral vibration has been becoming issues. However, the theoretical method of forced lateral vibration analysis is not cleary established so far and it is about to simply limited among the classification societies and international standards to avoid the blade natural frequency resonance cpm outside of ${\pm}20%$ of engine rpm at MCR. On the other hand, longer center distance between each support bearing shows an affirmative result normally in shaft alignment analysis whereas the blade order resonance speed may cause lowering near the limitation in the aspect of lateral vibration. Therefore, it is required careful attention to engineers as described above. As a method to solve the problem, it is mainly considered that remove forward stern tube bearing. In this paper, based on a medium size container ship case, theoretical study was carried out in the context of the forward stern tube bearing. The various effects and functions of forward stern tube bearing are reviewed and evaluated. Then an guidance note to lead the conclusion is proposed.

• 한국태양에너지학회 논문집
• /
• 제32권2호
• /
• pp.105-112
• /
• 2012

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100 mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200 mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm,20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

• 한국태양에너지학회:학술대회논문집
• /
• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
• /
• pp.516-521
• /
• 2012

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm, 20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.