• 한국소음진동공학회논문집
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• 제27권2호
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• pp.195-203
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• 2017

This paper is concerned with the active vibration control of shell structure that is subjected to internal unbalanced excitation by using active mounts and accelerometers. The unbalanced excitation is caused by a rotating unbalanced mass. The control algorithm considered in this study is the negative acceleration feedback (NAF) control. A simplified dynamic model was derived to verify the effectiveness of the NAF control. Four actuators and four accelerometers were mounted on the shell structure, so that the multiple-input and multiple-output (MIMO) NAF controller was designed by both centralized and decentralized ways. Numerical results show that both the decentralized and centralized NAF controllers are effective. Based on the numerical simulation, the proposed decentralized NAF controller was applied to the real shell structure. Experimental results show that the proposed decentralized NAF controller can effectively suppress vibrations of the shell structure.

• 한국재료학회지
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• 제16권8호
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• pp.524-528
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• 2006

On the synthesis of Au/$TiO_2$ core-shell structure nanoparticle, the effect of concentration of $Ti^{4+}$ and reaction temperature on the morphology and optical property of Au/$TiO_2$ core-shell nanoparticles is examined. A gold colloid was prepared by $HAuCl_4{\cdot}4H_2O\;and\;C_6H_5Na_3{\cdot}2H_2O$. Titanium stock solution was prepared by mixing solution of titanium(IV) isopropoxide (TTIP) and triethanolamine (TEOA). The concentrations of $Ti^{4+}$ stock solution were adjusted to $10.01{\sim}0.3$ mM, and then the gold colloid is added to the $Ti^{4+}$ stock solution. Au/$TiO_2$ core-shell structure nanoparticles could be prepared by the hydrolysis of the $Ti^{4+}$ stock solution at $80^{\circ}C$. The size of synthesized Au nanoparticles was 15 nm. The thickness of $TiO_2$ shell on the surface of gold particles was about 10 nm. The absorption peak of synthesized Au/$TiO_2$ core-shell nanoparticles shifted towards the red end of the spectrum by about 3 nm because of the formation of $TiO_2$ shell on the surface of gold particles. The good $TiO_2$ shell is produced when $Ti^{4+}$ concentration is varied between 0.01 and 0.05 mM, and reaction temperature is maintained at $80^{\circ}C$. The crystal structure of $TiO_2$ shell was amorphous.

• 한국전자통신학회논문지
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• 제18권4호
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• pp.641-648
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• 2023

최근 4차 산업 혁명 중에서 인공지능의 급성장은 반도체의 성능 향상 및 회로의 집적을 기반으로 진보하였다. 전자기기 및 장비의 내부에서 연산을 돕는 트랜지스터는 고도화 및 소형화 되어 가며 발열의 제어 및 방열의 효율 개선이 새로운 성능의 지표로 대두되었다. DUT(Device Under Test) Shell은 트랜지스터의 검수를 위하여 정격 전류를 인가한 후, 임의의 발열 지점에서 전원을 차단한 상태에서, 방열을 통하여 트랜지스터의 내구도를 평가하여 불량 트랜지스터를 검출하는 장비이다. DUT Shell은 장비 내부의 방열 구조에 따라 동시에 더 많은 트랜지스터를 테스트할 수 있기 때문에 방열 효율은 불량 트랜지스터 검출 효율과 직접적인 관계를 갖는다. 이에 본 논문에서는 DUT Shell의 방열 최적화를 위하여 배치구조의 다양한 방법을 제안하고 전산유체역학을 이용하여 최적의 DUT Shell의 다양한 변형과 열 해석을 제안하였다.

• 한국세라믹학회지
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• 제46권2호
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• pp.123-130
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• 2009

To understand the formation of core-shell structure in $BaTiO_3$ (BT) grains in multilayer ceramic capacitors, specimens were prepared with BT powders mixed with Y and Mg, and their microstructures were investigated with scanning electron microscopy, x-ray diffractometry, and transmission electron microscopy. Microstructural investigation showed that Y dissolved easily in BT lattice to a certain depth inside of the grain, whereas Mg tended to stay at grain boundaries rather than become incorporated into BT. It was considered that in case of Y and Mg addition in a proper ratio, Y could play a dominant role in the formation of shell leading to a slight dissolution of Mg in the shell. Next, the effects of ball-milling conditions on the core-shell formation were studied. As the ball-milling time increased, the milled powders did not show a significant change in size distribution but rather an increase of residual strain, which was attributed to the milling damage. The increase in milling damage facilitated the shell formation, leading to the increased shell portion in the core-shell grain.

• 한국응용과학기술학회지
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• 제27권1호
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• pp.93-97
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• 2010

Silicone dioxide absorbed polyoxyethylene alkylether sulfate (EU-S75D) surfactant was prepared. The core-shell composite of inorganic/organic were polymerized by using styrene(St) as a shell monomer and potassium persulfate(KPS) as an initiator. We studied the effect of surfactants on the core-shell structure of silicone dioxide/styrene in the presence of an anionic surfactant lauryl sulfate(SLS). The structure of core-shell polymer were investigated by measuring to the thermal decomposition of polymer composite using thermogravimetric analyzer(TGA) and morphology of latex by scanning electron microscope(SEM).

• 천문학논총
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• 제11권1호
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• pp.91-107
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• 1996

We determine analytically the onset of thin-shell formation time of fast wind bubble with power-law energy injection $E_{in}=E_0t^s$, and power-law ambient density structure, ${\rho}_0(r)={\bar{\rho}}(r/{\bar{r}})^{-{\omega}}$. Thin-shell formation time, $t_{sf}$ can be estimated by minimizing the total time elapsed before the complete cooling of shocked gas. For uniform medium (${\omega}=0$) and constant energy injection (s = 1), the onset of shell formation is found to be at $t_{sf}=5.2{\times}10^3yr$, which agrees Quite well with the results of FCT 1D numerical calculation. We solve the line transfer problem with previous result derived by numerical calculation in order to calculate line profile of [OIII] (${\lambda}=5007{\AA}$) forbidden line. In general, radiative outer shell causes the formation of double peaked line profile. Each peak corresponds to approaching and receeding shells with large velocities. Our line profiles show good agreements with observation of expanding shell structure.

• 소음진동
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• 제4권4호
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• pp.443-449
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• 1994

In the analysis of circular cylindrical shell's vibration and sound radiation, there are numerical and analytical methods. Numerical methods such as F.E.M and B.E.M, have the limit of frequency range. Analytical method can be applied to the circular cylindrical shell from low frequency to high frequency. In this paper, we use the analytical method for shell, and numerical method, F.D.M, for fluid. We also use the method using transfer matrix and eigenanalysis of transfer matrix which can therefore calculate the rotational d.o.f that is very imkportant in synthesis with inner structure. Inner structure has much effect on the submerged circular cylindrical shell vibration and sound rediation. Results for the immersed circular cylindrical shell vibration and sound radiation are compared with the analytic solutions.

• 대한기계학회논문집A
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• 제30권6호
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• pp.653-661
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• 2006

Metallic sandwich plates with various inner cores have important new features with not only ultra-light material characteristics and load bearing function but also multifunctional characteristics. Because of production possibility on the large scale and a good geometric precision, sandwich plates with inner dimpled shell structure from a single material have advantages as compared with other solid sandwich plates. Inner dimpled shell structures can be fabricated with press or roll forming process, and then bonded with two face sheets by multi-point resistance welding or adhesive bonding. Elasto-plastic bending behavior of sandwich plates have been predicted analytically and measured. The measurements have shown that elastic perfectly plastic approximation can be conveniently employed with less than 10% error in elastic stiffness, collapse load, and energy absorption. The dominant collapse modes are face buckling and bonding failure after yielding. Sandwich plates with inner dimpled shell structure can absorb more energy than other types of sandwich plates during the bending behavior.

• 한국소음진동공학회논문집
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• 제14권5호
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• pp.370-376
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• 2004

The overall aim of this paper is to determine coupling loss factor of welding point between shell and cylinder using loss factor and structural loss factor. For this purpose, two kinds of loss factor were adopted. One is loss factor of each sub structure, another is structural loss factor based on the complex welded or assembled structure. Using these two parameters, it ispossible to derive the coupling loss factor which represent characteristic condition of SEA theory. Coupling loss factor of conjunction in complex structure was expressed as power balance equation. The derived equation for a coupling loss factor has been simplified on the assumption of one way (uni-directional) power flow between multi-sub structures. Using these conditions, it is possible to find the equation of coupling loss factor expressed as above two loss factors. To check the effectiveness of above equation, this paper used two-stage application. The first approach was application between simple cylinder and shell. The next was adopted rotary compressor. Rotary compressor has three main conjunctions between shell and internal vibration part. This equation was applied to find out the optimum welding point with respect to reduce the noise propagation. It shows the effective tool to evaluate the coupling loss factor in complex structure

• 대한기계학회논문집A
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• 제29권7호
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• pp.998-1004
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• 2005

A nano-stereolithography (NSL) process has been developed for fabrication of 3D shell structures which can be applied to various nano/micro-fluidic devices. By the process, a complicated 3D shell structure on a scale of several microns can be fabricated using lamination of layers with a resolution of 150 nm in size, so it does not require the use of my sacrificial layer or any supporting structure. A layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) induced using a femtosecond laser processing. When the polymerization process is finished, unsolidified liquid state resins can be removed easily by dropping several droplets of ethanol fur developing the fabricated structure. Through this work, some 3D shell structures, which can be applied to various applications such as nano/micro-fluidic devices and MEMS system, were fabricated using the developed process.