• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.26-29
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• 2009

매크로 스케일(macro-scale)에서 구조재료의 거동을 보다 자세히 이해하기 위해서는 구조재료를 구성하고 있는 마이크로 스케일(micro-scale)에서의 미세구조에 대한 이해가 필요하다. 특히 다결정을 가진 다상재료는 상(phase) 분포 상태에 의해 그 특성이 다르기 때문에, 상 분포에 따른 재료의 특성을 이해하는 것이 중요하다. 본 연구에서는 미세구조의 상 분포 특성을 묘사할 수 있는 상관관계 함수를 이용하여 미세구조의 상 분포 상태를 나타내고, 이를 활용한 미세구조 재구성 방법을 사용하여 2상 미세구조에서 특정 미세구조와 유사한 상 분포를 가진 미세구조를 생성하고 그 특성을 비교하였다. 그리고 다양한 상 분포를 가진 미세구조들에 유한요소해석 기법을 적용하여 미세구조의 역학적인 거동을 분석하였다. 이를 통해, 제한된 정보를 이용하여 통계학적으로 유사한 특성을 나타내는 미세구조를 모델링 할 수 있음을 검증하였고, 이러한 미세구조들 간의 역학적 거동은 서로 거의 동일함을 확인하여 미세구조 재구성 기법이 재료의 역학적인 거동을 예측하는데 유용하게 사용될 수 있음을 확인하였다.

• Journal of The Korean Association For Science Education
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• v.30 no.8
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• pp.1097-1109
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• 2010

The purpose of this study is to analyze the ERF components patterns of observers who have different cognitive styles using magneto-encephalography (MEG). The task was developed based on the CSA (Cognitive Style Analysis) program. Eight right-handed, healthy male college students participated in voluntarily. To investigate college students' ERF components during the task, an MEG system with block design was used to measure magnetic signals in their brains. For examining the observation characteristic by cognitive style, MEG ERF components were analyzed. As a result, four ERF components (M1, M2, M3, M4) were observed. Through the results of this study, the reason for different observation characteristics by cognitive styles was verified in the neurophysiological methods. This study will have implications to establish theories on scientific observation and cognitive styles.

• Fire Science and Engineering
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• v.18 no.2
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• pp.34-40
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• 2004

The effects of external flow excitation with various frequencies and amplitudes on the flame behavior and pollution emission characteristics from a laminar jet flame are experimentally investigated. Measurements of $NO_x$ emission indices ($EINO_x$), performed in vertical lifted flame like turbulent with various exciting amplitude at a constant resonance frequency, have been conducted. It was also conducted to investigate the effects of excited frequency at a constant exciting amplitude on $NO_x$ emissions with a various frequency ranged 0 Hz to 2 KHz. From the vertical lifted turbulent flame of the excited jet with resonance frequency by strong excitation was shown that the dependence of $NO_x$ emission could be categorized into three groups Group I of long flame length with high disturbances yielding high $NO_x$ emission, Group II of intermediate flame length and relative narrow flame volume with low disturbance yielding low $NO_x$ emission and Group III of long flame length and large flame volume with high time ＆ space disturbances behaviour yielding high $NO_x$ emission.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.160-168
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• 2010

An experimental study has been conducted to investigate the effects of forcing amplitude on the tone-excited non-premixed jet flame of the resonance frequency. Visualization techniques are employed using the laser optic systems, which are RMS tomography, PLIF and PIV system. There are three lift-off histories according to the fuel flow rates and forcing amplitudes; the regime I always has the flame base feature like turbulent flame when the flame lift-off, while the flame easily lift-off in the regime II even if a slight forcing amplitude applied. The other is a transient regime and occurs between the regime I and regime II, which has the flame base like the bunsen flame of partial premixed flame. In the regime I and II, the characteristics of the mixing and velocity profile according to the forcing phase were investigated by the acetone PLIF, PIV system. Particular understanding is focused on the distinction of lift-off history in the regime I and II.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.648-651
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• 2009

Using a mode-matching technique, a waveguide structure with multiple stubs which is utilized as the component of various communication systems has frequency filtering characteristics. We define a proper fitness function to automatically design the pass and stop bands of a waveguide structure with multiple stubs for frequency filtering and the genetic algorithm can be implemented with the fitness function proposed in this paper. The frequency filtering characteristics are numerically computed and parametric sweeps are also performed.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.4
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• pp.1-9
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• 2022

In the current study, in order to understand the dynamic response characteristics of the system according to the external acoustic forcing, a numerical approach was developed by adding an sign-sweep forcing function to the existing network model. Through this model, the sensitivity of frequency and pressure amplitude changes according to system parameters such as the physical dimensions and boundary conditions of the target combustor was analyzed in a wide frequency range. Analysis results of dynamic response characteristics of the target combustor are shown that the frequency regime with high dynamic pressure response was similar to the instability frequency range measured in the same combustor, and in particular, the response of the system depends greatly on the location of the acoustic forcing source term.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.5
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• pp.482-489
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• 2010

This paper describes the test procedure, instrumentation, verification methodology and the results of the ground vibration test(GVT) and force vibration test(FVT) of the SmartUAV aircraft to estimate experimentally dynamic characteristics of the aircraft. Bungee cords are used to emulate free-free boundary conditions of the test aircraft. The SmartUAV is excited by three shakers and one-hundred frequency response functions(FRF's) is measured. The FRF's are reduced and analyzed to identify the dynamics parameters of the SmartUAV. To extract modal parameters of the SmartUAV such as, natural frequencies and damping ratios, the poly-reference least square complex exponential method is used in the time domain. The mode shape coefficients are estimated with the least squares frequency domain method to identify the vibration modes. The FVT was performed by fixed sine frequency with three shakers on the x, y and z direction and vibration characteristics of structures and detail equipments are measured.

• Journal of Korean Society of Forest Science
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• v.101 no.2
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• pp.236-243
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• 2012

The leaf growth and physiological characteristics of Forsythia saxatilis were investigated at six natural habitats under different light intensities in Bukhansan in order to figure out an appropriate growth environment for conservation and restoration of F. saxatilis that is Korean endemic plant designated as rare and endangered species. Relative light intensities (RLI) at six habitats showed from 10% to 78% of the full sun. Leaf length, leaf width, leaf area and dry leaf weight of population under highest relative light intensity (78%) were the highest. The ratio of dry leaf weight to leaf area increased with the increase of RLI. The content of photosynthetic pigments such as chlorophyll a, b and carotenoid were the highest at 78% of RLI, whereas the ratio of total chlorophyll to carotenoid content reduced according to the increase of RLI. Photosynthetic parameters, such as photosynthetic rate, also increased with the increase of RLI. The total nonstructural carbohydrate (TNC) was 1.5 times higher at 78% of RLI than that at 10% of RLI and the total soluble sugar (TSS) was the highest at 78% of RLI. In conclusion, leaf characteristics and physiological characteristics have high positive correlation with light intensity. Therefore, light condition should be primarily considered to improve growth and physiology characteristics of F. saxatilis under low light intensity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.97-100
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• 2004

물질의 진동감쇠 특성을 평가하는 대표적인 시험법은 ISO 6721, ASTM E 756 등에서 찾아 볼 수 있다. 이들 규격에서는 비접촉 가진방법으로 전자석 시스템을 사용한다. 하지만 이와 같은 방법은 강판 단독으로의 시험은 간편하나 비자성체 물질이나 도료를 도포 할 경우, 별도의 금속판이 필요하다. 또한 그에 따른 금속판의 감쇠특성을 별도로 평가해야 되며, 접착제에 대한 영향도 고려해야 된다. 이에 대한 보완으로 음압가진 방법을 이용한 비접촉 가진을 강철과 플라스틱에 적용하였다. 실험결과, 강철과 플라스틱의 공진주파수에 따른 손실계수와 탄성계수는 전자석을 이용한 실험결과와 일치하였다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.12
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• pp.943-947
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• 2014

Recently, a new method for reconstructing a forced nonlinear dynamic system has been proposed; specifically, the simultaneous reconstruction of its excitation as well as restoring characteristics of the system. The reconstruction was just theoretically shown to be possible by measuring the system's responses, based on newly introduced notions, a J-function and a zero-crossing time. However, numerically in the current paper, we are to reconstruct a linear system, i.e., we focus on numerical experiments to reconstruct both the excitation and the linear restoring characteristic of a linear forced oscillating system by using response data, based on the J-function and the zero-crossing time.