• Journal of computational fluids engineering
• /
• v.14 no.3
• /
• pp.123-130
• /
• 2009

Hydromagnetic flow in a confined enclosure under a uniform magnetic field is studied numerically. The thermally active side walls of the enclosure are kept at hot and cold temperatures specified, while the top and bottom walls are insulated. The coupled momentum and energy equations associating with the electromagnetic retarding force as well as the buoyancy force terms are solved by an iterative procedure using the SIMPLER algorithm based on control volume approach. The changes in the flow and thermal field based on the orientation of an external magnetic field, which varies from 0 to $2{\pi}$ radians, are investigated. Resulting heat transfer characteristics are examined too.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08a
• /
• pp.644-647
• /
• 2007

We have fabricated vertical type organic thin film transistor using tris-8-hydroxyquinoline aluminum $(Alq_3)$. The effects of the growth control of $Alq_3$ thin layer on the grain structure and the flatness of film surface have been investigated. In addition, we have fabricated light emitting transistor and then investigated electroluminescent properties.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.43 no.4
• /
• pp.601-606
• /
• 1994

This paper describes the effect of elongation on electrical properties and molecular structrue of high density polyethylene. Thin polyethylene films films obtained dy roll elongation after extruded at 220$^{\circ}C$ and elongated to draw rations of 16. Crystallinity of polyethylene films was measured by X-Ray diffraction and electrical properties were estimated by conductivity and TSC(Thermal Simulated Current). It was foung that the crystallinity increases and the electrical conductivity decreases as the elongation increases. The elongation dependence of electrical conductivity may be explained by the trap density. Thus, the control of polymer structure and crystallinity makes its properties better and can be applicated in order to get more active properties.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.251-252
• /
• 2020

화석연료 사용으로 발생하는 환경문제 대처방안으로 풍력 등 신재생 에너지원 사용의 필요성이 강조되고 있으며, 이러한 사회적 요구에 따라 신재생 에너지 발전 시스템의 대용량화 추세에 있다. 시스템 대용량화에 있어 안정적인 에너지 발전과 공급을 위해 전력변환장치의 신뢰성 향상이 필요하다. 특히, 풍력발전시스템의 경우 돌풍 등 일정하지 않은 풍속으로 인하여 전력변환장치의 잦은 고장이 발생하고, 이는 전체 시스템의 신뢰성 결정에 주된 영향을 미친다. 본 논문에서는 병렬형 전력변환장치에서 높은 고장률을 보이는 스위칭 소자의 열적 스트레스를 줄이기 위한 무효전력순환 기반 능동 열 제어기법을 제안한다. 제안한 기법의 동작특성을 이론적으로 분석하고, 열 회로망 시뮬레이션을 통해 그 영향을 검증한다.

• Fire Science and Engineering
• /
• v.18 no.3
• /
• pp.1-8
• /
• 2004

As a predominant active fire suppression method, closed-type sprinkler systems are used for the purpose of fire control and suppression at the nuclear power plants as well as the industrial facilities. It goes without saying that the proper selection of the system guarantees the adequate actuation of the thermal device. Consequently, the appropriate evaluation should be executed for the thermal behavior with the theoretical and empirical approach. For this purpose, the comparison of activation time for the fusible-link type sprinkler head with the simplified fire case and t-square fire growth case was evaluated. At this paper, the comparison output was presented with the tendency of thermal behavior. In addition, we issued some technical comments for the most appropriate equation in case of the estimation of the sprinkler head activation time. We also raised some idea that should be incorporated for the usage of the t-square equation for the realistic application in the field of the performance-base fire protection approach.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2540-2543
• /
• 2008

Liquid crystal displays (LCD's) are continuously coated with some chemicals in the clean room of a factory. Spreading of these chemicals is causing serious problems both in controlling clean room quality as well as to the workers inside the factory. It is required to alleviate or properly control the offensive odor which is mainly composed of propylene glycol mono ethyl acetate, novolak resin and photo active compound. The control strategy employed is to bleed the offensive odor gas out the clean room. A full scale 3D CFD model was created with anisotropic porous media, chemical species transport with no volumetric reaction, and thermal diffusion with propane gas (tracer gas) to simulate the odor spreading. A segregated implicit solver with standard k-$\varepsilon$ model is employed. The detailed CFD analysis made it possible to develop an effective method of ventilating the coater room and optimizing their capacities.

• Journal of Applied Reliability
• /
• v.17 no.3
• /
• pp.224-235
• /
• 2017

Purpose: Reliability is the most important factor to detect defects as wind turbines are deployed in large blades. The methods of detecting defects are various, such as non-destructive inspection and thermal imaging inspection. We propose the phased array ultrasonic testing method of non-destructive testing. Methods: We propose the active pressure mechanism for wind power blade. The phase array ultrasonic inspection method is used for fault detection inner blade surface. Controlled pressure of mechanism with respect to z-axis is important for guarantee the result of phase array ultrasonic inspection. The model based control and proposed mechanism are utilized for overall system stability and effectiveness of system. Result: The result of proposed pressure mechanism B is more stable than A. Convergence speed is also faster than A. Conclusion: We confirmed the performance of the proposed constant pressure mechanism through experiments. Non-destructive testing was applied to the specimen to confirm the reliability of detecting defects.

• Smart Structures and Systems
• /
• v.24 no.3
• /
• pp.361-377
• /
• 2019

The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

• Journal of Microbiology and Biotechnology
• /
• v.22 no.2
• /
• pp.256-263
• /
• 2012

A strain of bacterium producing antifungal antibiotic was isolated and identification of the strain was attempted. We could identify the bacterium as being a Bacillus sp., based on morphological observation, physiological characteristics, and 16S rDNA sequence analysis, thus leading us to designate the strain as Bacillus sp. AH-E-1. The strain showed potent antibiotic activity against phytopathogenic and human pathogenic fungi by inducing mycelial distortion and swelling and inhibiting spore germination. The antibiotic metabolite produced by the strain demonstrated excellent thermal and pH (2-11) stability, but was labile to autoclaving. From these results, we could find a broader antifungal activity of Bacillus genus. Isolation and characterization of the active agent produced by the strain are under progress.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.3
• /
• pp.227-247
• /
• 2015

An X-band $8{\times}16$ dual-polarized active phased array antenna system has been implemented based on the substrate integrated waveguide(SIW) technology having low propagation loss, complete EM shielding, and high power handling characteristics. Compared with the microstrip case, 1 dB less is the measured insertion loss(0.65 dB) of the 16-way SIW power distribution network and doubled(3 dB improved) is the measured radiation efficiency(73 %) of the SIW sub-array($1{\times}16$) antenna element. These significant improvements of the power division loss and the radiation efficiency using the SIW, save more than 30 % of the total power consumption, in the active phased array antenna systems, through substantial reduction of the maximum output power(P1 dB) of the high power amplifiers. Using the X-band $8{\times}16$ dual-polarized active phased array antenna system fabricated by the SIW technology, the main radiation beam has been steered by 0, 5, 9, and 18 degrees in the accuracy of 2 degree maximum deviation by simply generating the theoretical control vectors. Performing thermal cycle and vacuum tests, we have found that the SIW array antenna system be eligible for the space environment qualification. We expect that the high efficiency SIW array antenna system be very effective for high performance radar systems, massive MIMO for 5G mobile systems, and various millimeter-wave systems(60 GHz WPAN, 77 GHz automotive radars, high speed digital transmission systems).